ASEG Extended Abstracts - ASEG2013 - 23rd Geophysical Conference, 2013

We present a multi-objective optimization approach to the subsurface geomodel updating problem using stochastic search techniques. This is a new approach to the geomodeling process for which a variety of direct and indirect measurements can simultaneously constrain the geomeodel. Due to the inherent uncertainties and noise in real data measurements, geological and geophysical datasets acquired in the same area may be in conflict with each other and a realistic subsurface model can only be obtained by simultaneously integrating the combined datasets in a reasonable manner. One approach to this problem is to perform joint inversion of multiple geological and/or geophysical datasets, where an optimal model is achieved by optimization of a linear combination of several objective functions measuring the match of the simulated datasets with the observed datasets. In this paper, we consider joint inversion of multiple datasets for geomodel updating, as a Multi- Objective Optimization Problem (MOOP), where separate objective functions for each subset of the observed data are defined. Then, a stochastic optimization technique is employed to find the set of best-compromise model solutions that fit the defined objectives along the Pareto front. We demonstrate that a customized initialization of the algorithm can speed up the convergence and result in a set of improved model solutions. We apply the proposed approach on a 3D reservoir litho-facies model that must honour a set of geological and geophysical attributes (e.g. log data and inverted seismic P- and S-wave impedances).

Towed transient electromagnetic (TEM) survey, coupled with resistivity modelling software is an effective method of detailing small scale groundwater conceptual models and assisting with near surface geological investigations. Practical investigation depth ranges from 1 m to 100 m or more given the restrictions of today’s electronics and practical trailer dimensions.

Towed TEM survey using loops on trailers behind land vehicles or boats may be conducted using various loop configurations. Due to the loop area and separation requirements of loops from each other and from towing vehicles, design of trailers and/or sleds must be tightly integrated with design of loop configurations. Although separated loops (slingram configuration) are good for avoiding mutual inductance problems and may permit exploration to maximum possible depth, they are difficult to tow, especially around corners. Alternative arrangements with overlapping loops or bucking coils, all on a single platform, permit design of more practical platforms. On such platforms, not only must mutual inductance of coils be minimized but practical means of minimization are limited by achievable dimensional accuracy and stability of towed platform designs. Design is further restricted by the need to avoid use of metallic materials in most places and the need to separate and/or de-couple the metal survey vehicle from the loops.

Case studies showing results of survey conducted with various platforms will be presented.

Estimating subsurface temperature and assessing the thermal structure in numerical models requires a vast database of measured values, a detailed geological model and the ability to identify, incorporate and constrain uncertainty in the parameters to provide a reliable and robust result. Sparse datasets with limited results required additional observables to be gathered. Using groundwater bores temperature in the shallow crust can be measured over a widely distributed area and in depth profiles. Calibration of the Sydney Basin thermal model has shown that using shallow groundwater bores strong constraints on parameters can be made, thus reducing overall model uncertainty. Deep measurements are limited therefore shallow groundwater bores are a good data substitute. The largest sources of uncertainty are the parameters governing temperature dependent thermal conductivity of the basement and Permian Coal Measures, as well as the basal temperature condition and unconstrained heterogeneities in the basement rocks. Variance in these parameters may significantly influence the resulting estimate of subsurface temperature. However through calibration the possible variance is limited due to the large number of available calibration points.

The Gippsland Basin is a potential site for CO2 storage which is dependent on the regional top seal in providing a secure subsurface containment. We present here some geological parameters derived with the aid of seismic attributes and inversion from 2D and 3D reflection seismic surveys predominantly along the southern flank of the basin. These parameters are potentially influential on the top seal efficiency and CO2 containment security in the basin.

An important factor in top seal efficiency is the spatial variation of its shale content (Vsh). The empirical relationship between acoustic impedance and shale content was used to estimate Vsh. Composite seismic amplitude and acoustic impedance traces were constructed to establish a tie with the well-derived reference Vsh. Using a multi-attribute regression analysis, a transformation was established from seismic attributes and impedance to Vsh and used to define Vsh pseudotraces. Eight vertical profiles were produced in the Southern flank of the basin and the Vsh data were interpolated to reveal the first order variation in shale content for the top seal.

Equally important in the assessment of containment risk is the distribution and density of faults in top seal. Seismic spectral blueing and attributes were used to increase the resolution of the 2D seismic data and a meta- attribute that sharpens the faults and suppresses non-fault discontinuities was coupled with similarity attributes to ensure a better imaging of low-displacement faults (<20 m). Automated mapping of the faults provided fracture density maps which depict the intensely deformed areas with potentially decreased seal efficiency on the southern flank of the basin.

A method of joint inversion of Magnetotelluric, seismic refraction and seismic reflection (JIMRR) is developed especially for typical hydrocarbon or hard-rock mineral exploration. JIMRR includes two parts: jointed seismic refraction and seismic reflection; and its combination with Magnetotelluric (MT) method. The objective of the research is to enhance spatial resolution of the three model parameters: electrical resistivity, seismic velocity and reflector depth. Since horizontal coordinates of reflector are not treated as model parameters in existing travel time inversion algorithm, seismic forward modelling may loss the true reflection point locations at the side edges of reflector with limited extension. We developed the technology of extensible reflector to overcome this problem. JIMRR is completed by employing the cross-gradient function as constraints which enforces the structural similarity between the resistivity and the seismic velocities, so as to reduce velocity-depth ambiguity. The cross-gradient constraints are incorporated into the solution through least squares and Lagrange multiplier method. This method results in integrated symmetric square linear matrix that is solved by bi-conjugate gradient method (BiCG). Two example synthetic models show that our joint inversion can significantly enhance the spatial resolution of inversion; and also the velocity-depth ambiguity caused by reflection travel time inversion can be notably reduced by constraints from shallow lithologies.

Under high in situ stresses, the excavation of underground openings generally causes the creation of a disturbed (EdZ: Excavation disturbed Zone) and/or damaged (EDZ: Excavation Damaged Zone) zone, resulting from the initiation and growth of cracks and fractures and from the pre-existing stress redistribution. The EdZ or EDZ changes the mechanical and hydromechanical properties which in return, constitute a potential risk for the performance of the geologic and/or engineered structures in the context of waste underground storage. Ultrasonic experiments have been implemented to characterize the EDZ extension around drifts and its evolution in time according to the structural support type (soft or rigid) and the environmental conditions. Those studies consist of two experimental components: (1) the prior auscultation of the floor and sidewalls of the gallery by ultrasonic transmission tomography, (2) the monitoring of the time-dependant evolution of EDZ and the analysis of measurable changes in the propagation of ultrasonic waves in the medium term. A code for computing these continuous in situ velocity measurements into the elastic has been developed. Then, the five dynamic elastic constants for the assumed transverse isotropic character of the rock are derived as a function of time and the distance from the drift wall. Performed a few months after the excavation of the galleries, the tomography shows that ultrasonic velocities are higher in the orthoradial direction (both in the concrete support and rock). This velocity field highlights clearly the damaged zone and induced stress shift.

A shallow high-resolution seismic reflection test survey was conducted in the Maryborough Basin in an area near Gundiah, Queensland. The purpose of the seismic reflection test survey was to evaluate the application of using high resolution seismic data acquisition methods to detect thin coal seams at between 30 m to 150 m depth for open-cut coal exploration.

The seismic test survey tested three seismic sources which included a 50 kg weight-drop from 2 m height, a 7 kg sledgehammer, and a 12 g (blank cartridge) in-hole shotgun. Seismic forward modelling indicated that thin coal seams (1 to 2 m thickness) should provide seismic reflections at shallow depths of 30 m, using 72 channel recording with 2 m geophone intervals. The seismic source tests showed that the 12 g in-hole shotgun produced the strongest seismic signal at the furthest geophone offsets. The seismic recording spread consisted of 96 seismic channels with single spiked 30 Hz geophones spaced at 2 m geophone intervals. Based on the seismic source tests, the 12 g in-hole shotgun was used to record a seismic test line with shot-points recorded from one end of the 96 channel spread through to the other end of the spread.

The recording arrangements provided seismic data to both test data quality with shot to receiver offset, and examine the optimum common depth point (CDP) fold coverage to use for a larger seismic survey.

Based on the seismic data processing results, a larger seismic survey could be conducted using a 72 channel recording spread with 4 m geophone and shot-point intervals and achieve production rates of 400 m per day with a 3-man crew.

We extend our previous work on 2D internal multiple attenuation without subsurface information to a 3D operation. We describe our implementation that involves selecting traces that honour the azimuth of acquisition for constructing multiple contribution gathers and then segmenting the chosen traces in a layer stripping fashion to predict internal multiple model without identifying the multiple-generating interfaces. We demonstrate through synthetic and field data examples that, by including crossline apertures in the prediction process and selecting traces with correct azimuths in the convolution and correlation processes, substantial improvement in image quality can be obtained for those data that exhibit the internal multiple problem.

Adjoint-state methods (ASMs) have proven successful for calculating the gradients of the functionals commonly found in geophysical inverse problems. The 3D ASM image-domain tomography (IDT) formulation of the seismic velocity estimation problem highlights imperfections in migrated image volumes and, using appropriate penalty functions (e.g., differential semblance), forms an objective function that can be minimized using standard optimization approaches. For time-lapse (4D) seismic scenarios, we show that the 3D ASM-IDT approach can be extended to multiple (e.g. baseline and monitor) datasets and offers high-quality estimates of subsurface velocity change. We discuss two different penalty operators that lead to absolute and relative 4D inversion strategies. The absolute approach uses the difference of two independent 3D inversions to estimate a 4D model perturbation (i.e. slowness squared). The relative approach inverts for the model perturbation that optimally matches the monitor image to the baseline image - even if migrated energy is imperfectly focused. Both approaches yield good 4D slowness estimates; however, we assert that the relative approach is more robust given the ubiquitous presence of non-repeatable 4D acquisition noise and imperfect model estimates.

In this paper we present a case history of multi-azimuth 3D PSDM processing. The datasets show strong HTI as well as VTI anisotropy. We show the processing workflow with emphasis on the construction of an imaging velocity model that correctly represents the orthorhombic anisotropy and short-wavelength velocity variations. The PSDM image is improved over earlier processings.

A 3D geological model for King Sound, in the offshore Canning Basin, Western Australia, was produced by interpretation of FALCON® high resolution airborne gravity gradiometry and magnetic data, aided by 2D gravity models, 2D seismic data and well logs. Pseudo- depth slices of the vertical gravity gradient (GDD) and magnetic data and interpreted seismic horizons were used to constrain the vertical distribution of sedimentary sequences, intrasedimentary intrusives and basement rocks. Basement depth was determined from the magnetic data using traditional profile-based automated magnetic depth estimation techniques with well control.

The 3D model indicates an elevated, fault-bounded platform of Archaean to Proterozoic basement in the north. The platform is rimmed by Late Devonian and Early Carboniferous carbonate reefs and carbonate breccias and in the south, contemporaneous siliciclastic submarine fans and turbidite deposits occur in a deep marine environment.

Density values derived from published literature and measured in wells at King Sound were assigned to units in the geological model. A forward model was calculated and compared to the observed GDD data. The assigned density values were then modified, within the expected range for each rock type, using property inversions until a good fit between the modelled and observed data was obtained.

Models derived from potential field data can be beneficial for petroleum exploration in frontier basins worldwide, where only limited well and seismic data are available. The 3D geological model provides a good framework for use in designing future exploration programs in the area and it aids data visualisation and interpretation.

Each layer of rock or sediment has its own velocity, that is, there are different velocities along the subsurface layers of the earth. Moreover, each layer has various values for different types of velocity. Therefore, the suggestion raised was to study the effects of vertical velocity heterogeneity on stacking velocity and depth conversion with different spread lengths, i.e. a small spread with a maximum offset of 2000 m and a large spread with a maximum offset of 4000 m. This study focused on the variation between stacking velocity and average velocity. In addition, the traveltime equation of Taner and Koehler (1969) for two terms and three terms was examined in order to find out which one provided better results.

Understanding the variations between the different types of velocities was crucial to this approach, which was carried out using data from the Tirrawarra-29 well in the Cooper Basin, South Australia. Well log data are used to calculate different types of velocities such as average velocity, root-mean-square velocity (for both short offset and three terms) and stacking velocity.

The results for both the T − X plots and the T² − X² plots for small (2000 m) and large spreads (4000 m) proved that the variation between average velocity and stacking velocity increases with offset. Furthermore, using the traveltime equation for three terms on the residual moveout plots for small and large offsets provided better results than using only two terms.

We show how refraction tomography (also called first arrival travel time tomography) helps to produce more accurate and detailed depth velocity models below a shallow seafloor. We do not use refractions by themselves to build a complete shallow velocity model. In our proposed workflow, refraction tomography complements standard reflection tomography and the priority remains with the reflections to guarantee stability of the solution and to avoid uncertainties associated with refracted or diving waves in complex media.

We use wave equation modelling to calculate synthetic gathers and estimate the travel time mismatch between real and synthetic first arrivals. It leads to a robust workflow which can be easily introduced into production depth-velocity processing.

We show how this joint reflection/refraction velocity inversion works using a real 1000sq.km 3D marine seismic dataset acquired in an area where the water depth varies from 20 m to 1100 m.

Over recent years, seismic methods have emerged as a potential imaging technique for delineation of ore-bodies and for mine planning. The application of surface seismic methods in hard rock environments is however challenging due to various effects such as energy attenuation and scattering. Borehole seismic methods can be used to reduce these effects. The methods offer higher resolution at target depths, thus allowing better delineation and understanding of reflections from ore deposits.

We present a synthetic study to understand the ability of the cross-hole seismic method to delineate ore bodies. Three variations of a simple scenario typical of nickel deposits found in the Yilgarn Craton were considered. Of the three models, two consist of volcanics overlying a granite body and a thin sulphide mineralized zone along the contact but at different locations relative to the source and receiver boreholes. The third consists of only the rock units with no sulphide mineralized zone along the contact. Synthetic shot records were produced and wavefield separated. Up-going wavefields were then used to create depth migrated images. The resulting images correlate well with the volcanic-granite contact and massive sulphide lens, showing the potential of using the cross-hole seismic method to delineate ore bodies.

Airborne TEMPEST electromagnetic (EM) and magnetic data was acquired over the Bulman project area in the McArthur Basin to identify the geological environment of stratabound carbonate-hosted Pb-Zn mineralisation. The Late Palaeoproterozoic to Early Mesoproterozoic sedimentary fill of the McArthur Basin in the Bulman area is intruded by Early Mesoproterozoic dolerite dykes and sills. The location of the dykes and sills was mapped using magnetic data. The depth of the intrusives was estimated by mapping resistive basement on Conductivity Depth Transforms (CDTs) generated from the TEMPEST B-field Z-component data. Additionally, a 3D conductivity voxel model was constructed from the CDTs to show the conductivity distribution in rocks.

There is no marked conductivity contrast between intrusives and sediments making up the resistive basement. Instead, the resistive basement horizon is interpreted to represent the base of the Cenozoic unconsolidated deposits or part of the Proterozoic sedimentary rocks. In places, the base of a sub-surface conductive zone is interpreted to be the top of the intrusives. The thickness of sediments above the resistive basement is variable, reaching up to 170 metres in the central - eastern part of the study area.

3D geological model was constructed to assist in visualising the distribution of interpreted geological units and the tectonic pattern

This study was carried out in Harat Rahat (south of Almadinah Almonwarah) using seismic reflection and resistivity methods. The main objectives of this study are to determine the extent of the basaltic layer and to define the subsurface faults and fractures that could affect and control the groundwater movement in the study area. A 2D seismic profile was acquired and the result shows that the subsurface in the study area has a major fault. We obtained a well match when the seismic result was compared with drilled wells. As a complementary tool, the resistivity method was applied in order to detect the groundwater level. The results of the resistivity method showed that six distinct layers have been identified. The interpretation of these six layers show that the first three layers, the fourth layer, the fifth layer and the bottom of the section indicated various subsurface structures and lithologies; various basaltic layers, fractured basalt, weathered basement and fresh basaltic layers, respectively. It is obvious that the eventual success of geophysical surveys depends on the combination with other subsurface data sources in order to produce accurate maps.

This study was carried out in Wadi Nisah to the south- west of Riyadh, Saudi Arabia, at latitude of 24° 14′ 28 N and longitude of 46° 29′ 59 E. The main purpose of this study is to investigate the depth of the shallow groundwater aquifer and the geological structures that could affect the ground water bearing layer in the area. For this purpose, the high-resolution seismic reflection technique was performed along Six 2D seismic lines and geophone spacing of one meter. The constructed seismic sections revealed that the depth of the water bearing formation lies in the range of 100 m to about 240 m and normal faulting affect the surface of this formation. The interpreted water-bearing formation is correlated with Biyadh Formation as confirmed by the drilled near water wells. The output of this research proved that the high resolution seismic reflection technique can be an effective method for determining water bearing layer depth in such arid area.

The purpose of this study is to evaluate the efficacy of using multichannel analysis of surface wave (MASW) to detect the near-surface cavities. The methods used in this study include interpreting dispersion curves and amplitude mapping of the multichannel analysis of surface wave technique and interpreting the delay in first arrivals of compressional waves. To test these methods, a seismic survey was conducted above a known near surface cavity in Al-Suman Area, Saudi Arabia. The cause of the cavity is carbonization in the area; there are many cavities similar to this one. The seismic data were collected using a seismograph system with 48 vertical geophones. Both techniques show a tangible result for detecting the cavity. The 2D section of shear wave velocity, which was obtained by inverting the dispersion curves from the MASW technique, leads us to determine the shape of the cavity, as described by a low-velocity zone. Frequency against relative offset is plotted and shows a significant frequency drop in the presence of the cavity, which also provides an indication to the presence of cavity underneath. This interpretation is matched by the interpretation of observed delays in first arrivals of compressional waves. The integration of both P-wave seismic refraction and MASW gives confidence in the result and matches observations of the existing cavity closely.

The 3DVSP technique becomes more popular with the emergence of multilevel 3 component borehole tools.

The value of the information derived from VSP is not always well understood.

In this paper we will present a case history of a joint surface and borehole seismic acquisition, with the goal to de-risk a shaft sinking location on a platinum mine.

TD was about 650 m and the VSP tool was 110 m long. On surface a dense grid of receivers and vibrator source points were laid out in a 1.2 km radius circle centred on the well head. A12 level 3C VSP digital tool was lowered in the borehole, in three successive depth positions.

The surface 3D cube was processed and interpreted independently from the 3D VSP data. On a near target reflector, the surface data structural interpretation showed mainly a clear E/W fault, and additional sub-seismic lineaments of differing azimuths, difficult to identify in terms of fault. The 3D VSP image limited to a short radius around the borehole confirmed the fault/dyke nature of these lineaments, separating monocline compartments.

As a consequence, the surface data was carefully re- interpreted and on the second structural images derived from two surface seismic reflectors and the near surface fault footprint from 3DVSP residual statics, a series of subtle faults were clearly assessed. Last, the few faults intersecting the borehole can be clearly recognized on the logs and the borehole radar logs.

This case study demonstrates the added value of a joint interpretation of surface and borehole data in a decision making process for shaft sinking.

Seismic-While-Drilling (SWD) utilises drill bit vibrations as a seismic source and receivers at the surface or in a borehole to acquire reverse VSP data. The basic processing technique is based on cross correlation to generate active shot-gather-like profiles. The successful implementation of SWD will yield time-depth information and image around the drill bit, which can aid drilling and geological understanding of the area.

To study the feasibility of using diamond impregnated drill bits for seismic-while-drilling, we conducted a small pseudo 3D SWD experiment at Brukunga, South Australia. It has been used to investigate the signals generated from diamond drilling, and study the potential to use a drill bit as a seismic source.

The drill bit energy for seismic imaging is influenced by the rig power setting, and the state of the drill bit (new or worn bit). The experiment shows that normally the diamond drilling frequency band is wide with strong discrete peaks, however sometimes due to changes in the drilling mode, e.g. increase or decrease the drilling power, the frequency spectrum can be smoothed. The strong peaks in the spectrum mean strong periodicity of the signal and as such, the signals do not lend themselves to standard cross correlation. Thus, we use a generalised cross correlation that produces results similar to an active shot gather-like profile.

Scintrex GRAVILOG borehole gravity meters are now successfully deployed by Abitibi Geophysics crews in boreholes for mining exploration in Canada and USA, and by Scintrex and Micro-g LaCoste crews in wells used for CO2 injection, sequestration and leaching in Canada, USA and Europe. In 2013, GRAVILOG systems and crews will be available in Europe, Russia, Brazil and Australia. Scintrex has developed and will be testing a dual sensor GRAVILOG probe in early 2013.

A brief review of the GRAVILOG development and specifications is presented, followed by several recent case histories. The result from Donner Metals / Xstrata Zinc’s Bracemac KT Zone in the Matagami region of Quebec is the first documented use in mining exploration of borehole gravity to measure excess mass coincident with a borehole EM conductor. Forward modeling and inversion of GRAVILOG data from multiple holes has proven effective in outlining the mineralization and estimating the tonnage of the Virginia Mines’ Lens 44 on the Coulon property in Quebec. Apparent bulk density measurements from multiple holes at the Labrador Iron Mines’ James South Extension iron ore deposit near Schefferville, Quebec reduce drilling costs and time needed to obtain this information.

A major source of error in bulk density measurements of thin beds is minimized by the dual sensor GRAVILOG system. In addition to eliminating the error in the depth interval between the sensors, common mode noise rejection improves the gravity difference data.

Assuming without evidence that magnetic sources are magnetised parallel to the geomagnetic field can seriously mislead interpretation and can result in drill holes missing their targets. I present two new methods for providing information about magnetisation of anomaly sources, independent of the geometry of the causative bodies. The first method is based on analysis of magnetic gradient tensor data. Integral moments of tensor invariants locate the horizontal and vertical centres of magnetisation and estimate the magnetisation direction. The depth estimate allows correction of the integral moments for the finite range of integration, which can accordingly be restricted to the main part of the anomaly. This reduces interference from neighbouring sources. This method provides information on location, total magnetic moment (magnetisation × volume), and magnetisation direction of a compact source, without making any assumptions about its shape.

The second method employs a single combined gradiometer/magnetometer, operating in base station mode within a magnetic anomaly of interest. The response to geomagnetic time variations allows the contributions of induced magnetisation and remanence to the anomaly to be separated. This method allows remote estimation, prior to drilling of (i) the total magnetisation direction of the source, which is a key to accurate modelling (ii) the remanence direction, which can provide geological information such as age of intrusion or alteration, (iii) the Koenigsberger ratio Q, which is indicative of the magnetic mineralogy of the source. If the source is compact, the method also provides a direct indication of the direction to its centroid.

Recent noise reductions in airborne electromagnetic (AEM) systems have allowed detection of conductors at great depths, but systems now have also become sensitive to superparamagnetic (SPM) effects. We distinguish SPM effects in airborne electromagnetic survey data from the response of good conductors. In electromagnetic data processing, off-time data can be accurately represented as amplitudes of a set of basis functions that are comprised of decays that decrease exponentially as a function of time. The SPM impulse response can be approximated by a decay that is proportional to time to the inverse power, a time dependence associated with magnetic viscosity. We identify the presence of SPM effects, as distinct from the decay of good conductors, by using inverse power- law decays as additional basis functions in constrained least-squares fitting. Application of the method to airborne time-domain electromagnetic (TEM) surveys shows that the method allows correction of SPM and hence aids significantly in conductive target identification.

The 11GA-YO1 deep seismic reflection survey reveals information on the crust down to ~66 km depth, imaging the crust-mantle boundary and the upper mantle. The seismic survey traverses the Yilgarn Craton, Officer Basin and Musgrave Province yielding information on their key structures and boundaries.

Interpretation of the seismic reflection data was complemented with forward modelling and 3D inversion of gravity and magnetic data. This allowed the geological structures interpreted in the seismic data to be investigated and extended into 3D space.

The 3D gravity and magnetic inversions reveal information on the geology and structure of the crust in the Yilgarn-Officer-Musgrave (YOM) region. In particular, information on the nature of dipping bodies beneath the Officer Basin and the boundary between the Yilgarn Craton and Musgrave Province.

One of the first usages of spectral methods in EM was by Peter Annan in development of the algorithm for EM modelling program “PLATE”, popular in the days of mainframe VAX computers. Using recent developments in spectral methodology and parallel computing on GPU boards, it is predicted to be possible on a desktop to run geologically plausible AEM forward models in microseconds, and inversions in milliseconds. In practice, the limitations of noise, imperfectly known waveforms, coupled with the effects of dielectric permittivity, viscous magnetism (superparamagnetism) and induced polarization conspire to limit the accuracy and speed of the process.

In electromagnetic exploration using broadband sensors and systems, joint recording of B and dB/dt data derived from the same physical sensor allows for a greater number of “signal” bits that lie above sensor noise. Optimum choice of a crossover frequency where the gains of B and dB/dt data match may double the number of useable bits. Field data confirms general expectations that B mode of operation is good at low frequencies, dB/dt operation good for high frequencies, but that both can be collected from the same ARMIT sensor.

The critically important steps to get best value from your gravity gradiometry data, assuming your contractor has done his job well in designing and acquiring the data, is the preparation of the representation of the potential field gradients. The ~200 m resolving power of existing gradiometer systems approaches what is necessary for minerals applications. In particular, beyond the aircraft, the topographic surface represents the largest and most proximal density contrast encountered in an airborne survey. Hence terrain effects can have significant impact on AGG data. The critical steps are:

• Terrain correction and determining ‘best’ terrain density
• Gridding, using all the measured gradients to constrain the interpolation
• Smoothing/de-noising by using the 3 rd order tensor constraints
• Anti-alias filtering of the gradient signals so that wave lengths are properly represented in all directions
• Transformation of the gradients by integration to estimate the gravity or magnetic field

Terrain corrections are a necessary step in the processing of observed AGG data in rugged terrain, in order to highlight subsurface density variations with a minimal overprint from the terrain. We propose a simple and rapid AGG tensor-based method to estimate an optimum bulk terrain density for subsequent terrain-correction. Each of the currently deployed systems for acquiring gradiometry is evolving driven by competition and the users’ needs. Mining applications of the technology to directly detect ore-bodies that show up as anomalies can now be successful provided the dimensions are of the order of 200 m or more. High resolution 3D geology models of operating mines can be used to calibrate gradiometry surveys

A synthetic rock analogue with simple microstructure was used to advance our understanding of the influence of cracks and pore fluids on seismic properties. The glass beads with ~ 300 μm diameter were sintered near the glass transition with average 1~2% porosity and subsequently quenched from high temperature into water at room temperature to introduce cracks with uniformly low aspect ratio α ~ 0.0007. Jackson-Paterson attenuation apparatus, with independently controlled confining and pore-fluid pressure systems, was used for both torsional and flexural mode forced oscillations at seismic frequencies to extract shear and Young’s modulus respectively, with or without the presence of pore fluids (e.g. argon, water) of varying viscosities. By perturbing the pore pressure at either end of the cracked specimen by ~5 MPa, permeability was obtained by analysing the evolution curve for pore fluid re- equilibration. Shear modulus is found lower with longer oscillation periods for the cracked and argon pore fluid saturated material possibly indicating the transition from the saturated isolated to saturated isobaric regime, with minimal strain-energy dissipation 1/Q < 0.003. The averaged elastic moduli for different oscillation periods and permeability are discovered to be extremely sensitive to variation of effective pressure. The crack closure effects can be observed easily at the effective pressure level at ~ Eα, consistent with the theoretical prediction.

Australia wide maps have recently been generated and released by CSIRO and Geoscience Australia using the 14 band satellite-borne ASTER sensors. Seventeen map products related to surface composition have been developed, based on spectral absorption features representing either abundance of mineral groups, specific minerals and their chemistry, vegetation cover or regolith related characteristics. This study aims to test the geoscience mapping capabilities of these products, individually, and integrated with airborne geophysics and DEMs over the semi-arid Mt Fitton area, South Australia, and within the agricultural Wagga Wagga region, New South Wales. The robustness of these techniques is evaluated by comparing the results from these two areas with different geological exposure and cultivation.

Various image processing, statistical and principal component analytical (PCA) techniques were utilised. ASTER map products including Ferric Oxide Content, Ferrous Iron Index, AlOH Group Content, MgOH Group Content, MgOH Group Composition, Ferrous Iron Content in MgOH, and Silica Index products proved useful discriminating previously mapped host or altered units of Mt Fitton. PCA correlation statistics proved helpful in devising potentially useful RGB composite imagery incorporating ASTER and geophysics. 2 D scatterplots between different products also proved useful for classifying surface composition. However ASTER map products within the Wagga area proved strongly affected by agricultural and floodplain cover. Slope per cent products generated from Wagga DEMs were useful in focussing ASTER products in areas of hilly and piedmont outcrop or eroded exposures.

In order to evaluate the use of shallow seismic technique to map the bedrock up to the depth of 20-25 meters, three high resolution seismic reflection profiles were carried out. The data were acquired using a Strata Visor with 48- channel, 40 Hz geophones and a weight drop system as seismic source. Seismic reflection data were recorded using a CMP (common mid-point) acquisition method. The results show that the bedrock lies at about 18-25 meters depth. The bedrock related horizon observed here is of low frequency, its depth is almost similar in all three seismic lines and thus giving us the enough confidence in results and also following the subsurface structure. Reflection line 3 is been crossed by reflection line 1 and reflection line 2. To confirm the structure and same statics, I did tie these lines to confirm and the reflectors are exactly matching, hence no need to give any shifting. There is high frequency loss due to high attenuation in near surface. A good structural image of subsurface is visible from the seismic sections and for interpreter it’s easy to mark structure and integrate it with other methods. With the proper equipment, field parameters and particularly great care in data collection and processing, we can image reflections from layers as shallow as 25 meters.

Eureka: (def.) “An interjection used to celebrate discovery.” Literally: “I have found it!” Reaching a ‘eureka moment’ is the result of much thought, effort, success, failure, perseverance, patience, and fortune. It usually occurs as the result of a team effort - although one person may lead the way. With regard to gravity gradiometry - and its ‘coming of age’ - the “eureka moment” comes when an explorationist realizes that something that couldn’t be done before can now be accomplished.

Gravity gradiometry surveys have been commercially available since 1999. Over the past 14 years, the capability has grown to a point of what could be called “adolescence.” Adolescence (from Latin: adolescere meaning “to grow up”) is a transitional stage of physical and capability development occurring during the period from youth to adulthood The period of adolescence is most closely associated with the teenage years. While gravity gradiometry doesn’t retain human qualities and characteristics, the analogy is used here to review and discuss the advances and maturity of the capability. Improvements and growth in system performance, operational readiness, survey volume, and value of information will be addressed in this review.

Airborne time-domain electromagnetic (EM) surveys are effective tools for mineral exploration, geologic mapping and environmental applications. 3D inversion of airborne electromagnetic data is a challenging computational problem. The size of the surveys and the spatial resolution required to adequately discretize the transmitters and receivers results in very large meshes. Solving the forward problem repeatedly on such a mesh can quickly become impractical. Fortunately, using a single mesh for both the forward and inverse problem for all of the transmitters is not necessary. The forward problem for a single source or a small group of sources can be solved on different meshes, each of which need only be locally refined with fine cells close to the selected transmitters and receivers. Away from the selected transmitters and receivers, the mesh can be coarsened. The forward problem can then be broken into a number of highly parallel problems. Each forward modelling mesh is optimized specific to the selected transmitters and receivers and has far fewer cells than the fine inversion mesh. In this abstract, we present an implementation of this idea using a finite volume discretization on OcTree meshes. We demonstrate our approach on a VTEM data set over a porphyry deposit in Canada.

Reservoir simulation is a key component for reservoir monitoring and flow prediction. Unfortunately such simulations and further flow predictions can fail due to the lack of knowledge of reservoir parameters such as porosity and hydraulic conductivity. To alleviate this difficulty we develop a new technique that combines reservoir simulation and electromagnetic imaging. We show how to use flow simulation in order to better invert borehole electromagnetic data and how in turn, the inversion results can improve flow simulation and prediction.

The equivalent source is usually calculated by an iterative method, designed to converge on the observed potential field, magnetic or gravitational. Each iteration involves two Fourier transforms, one forward and one inverse. As the number of grid point increases the time penalty may become prohibitive. However, the number of transforms can be dramatically reduced by the a priori transformation of the observed potential field to the frequency domain. We describe this method which reduces the number of Fourier transforms from n to two, and demonstrate its use on a simple magnetic anomaly. An extension of this equivalent source technique is also given for the case of a draped magnetic survey that requires leveling correction. The observed data is separated into layers according to the height changes, and the equivalent source is iteratively calculated via comparisons of the upward continued data. Whilst this process is computationally intensive, it is designed to scale with the complexity, and hence the discretisation, of the topographical changes. This gives the method a speed advantage compared with similar Taylor series approaches. A synthetic example containing multiple dipole sources is used to test the method, and to illustrate the advantages and differences of draped surveys and the need to reduce the data to a common datum.

Easily recognized bright events on seismic data can infer a host of phenomena, ranging from lithology interplay to indicating lucrative prospects in relatively greenfield settings. The availability of seismic angle stacks integrated to a geological model afford the petroleum explorationist more options to reduce obviously incorrect conclusions and help to identify the more likely cause(s) of these bright events within the seismic data.

A combination of simultaneous seismic inversion, and far and near angle stack comparisons gave more confident deductions on certain recognized seismic features as well as identifying potential interesting prospects to pursue and study in the context of petroleum exploration in offshore Myanmar. In the Bay of Bengal Rakhine Outer Fold Belt, exploration 3D seismic acquisition was carried out in 2010 and a significant gas discovery made in 2012. We present some examples of features that were identified on seismic data and how the range of geological hypotheses could be narrowed by seismic inversion.

Aeromagnetic data over eastern Australia reveal a pattern of domains defined by systematic regional highs and lows, emphasised by low-pass filtering, over which are superimposed shorter (<20 km) wavelength anomalies related to mappable geology and its inferred subsurface continuation. Long-baseline levelling by Geoscience Australia has clarified the definition of these magnetic domains, and confirmed that they are not an artefact of grid merging. Geothermal and teleseismic data indicate that neither variation in Curie depth nor upper mantle magnetisation can produce the long-wavelength pattern. Hence, domain-wide variations in magnetisation at the middle to lower crustal level are presumably the cause of these long-wavelength features. Although reversed polarity remanence could contribute to deeply sourced negative magnetic anomalies, the correspondence of magnetic low domains with the Proterozoic Curnamona Craton and the Ordovician Macquarie Arc, and of a high domain with the western Lachlan Orogen floored by Cambrian ocean crust, suggests that the control may be simply stark contrasts in lower to middle crustal susceptibility. Moho thickness determined by the AusMoho model mimics the pattern of susceptibility domains, suggesting a relationship between tectonic history and mid to lower crustal composition. Implicit in this analysis is a division of the domains into continental and oceanic basement, with implications for the tectonic evolution of the Tasmanides and the distribution of mineral systems in eastern Australia. The mid to lower crust below the Macquarie Arc appears to be continental, and the Thomson Orogen is a compound feature, comprising both attenuated continental/arc crust and accreted oceanic crust.

We present a Gauss-Newton-based 3D inversion method for airborne ZTEM (Z-axis Tipper Electromagnetic) data to define resistivity structure relating to uranium deposits in the Athabasca Basin of Saskatchewan, Canada. The geophysical targets in this region can be represented by conductive plunging dykes in a resistive basement beneath a thick, more resistive overburden. We demonstrate using synthetic examples the effectiveness of the inversion method for detecting and delineating the target dykes and discuss how the inversion results are affected by various factors. It is shown that the dykes can be well imaged to depths more than 2 km even for the data from 200-m receiver height, provided the flight line is oriented perpendicular to the strike, and that the inversion results are relatively robust to the choice of the starting model. It is also shown that topographic effects are not serious for detecting the dykes at depth, because topographic effects are more significant at higher frequencies, while the sensitivity to the dykes increases with decreasing frequencies. One important finding is that if the flight line is oblique to the strike, the dependence of the starting model increases and the overall resolution decreases, compared to the 2D case, due to 3D effects.

Vibrators are the preferred sources for onshore vertical seismic profile (VSP) surveys. Truck-mounted units are especially useful as they are more road mobile than buggy-based units. In particular, they can be driven directly to the wellsite, resulting in improved response times, simplified logistics with fewer vehicles and personnel at the wellsite and improved transport safety.

Acquiring broad-bandwidth, high-quality VSP data, using state-of-the art vibrator equipment, however, has generally required the use of the latest buggy-mounted vibrators, compromising well-site logistics and transportation safety for VSP operations. To deliver optimum performance, two new truck vibrator models specifically designed to take advantage of all of the most recent developments in vibrator technology while retaining the logistical advantages of truck-mounted units have been developed.

These new truck-mounted vibrators offer greatly improved data quality with tests showing that they can transmit a signal with a frequency bandwidth of 6.6 octaves compared to previous models which can only transmit 2.5 octaves. Being mounted on modern truck chassis these vehicles retain all the mobility and HSE advantages of truck vibrators.

The vertical resolution of conventional seismic data limits the illumination and definition of thin sand reservoirs offshore North West Australia. With the availability of more wells within a field it is justified to use a well-centric stochastic seismic inversion approach to characterize the reservoirs. The stochastic AVO seismic inversion yields multiple triplet realizations of acoustic impedance, Poisson’s ratio and density at the fine enough vertical sampling for a more relevant reservoir modelling procedure. The paper will discuss the stochastic seismic inversion approach, followed by a structured analysis workflow which condenses the generated multiple realizations to more interpretable data volumes.

New Liquefied Natural Gas (LNG) processing plants are being developed and constructed along the eastern and western seaboards of Australia. In support of tendering processes for engineering design and construction, geotechnical site investigations are required over these large construction site foot print areas. The foot print areas often span across remote and inaccessible onshore and nearshore marine environments. Previously the domain of the resource exploration industry, geophysical expertise is now being increasing used to support traditional site investigation techniques in order to provide complete and accurate geotechnical characterisation of large LNG construction sites. High resolution and near-surface geophysical techniques, when integrated with intrusive sampling and testing, are proving to be a cost effective and reliable way to image and test large volumes of onshore and nearshore footprint areas. Geophysical techniques are particularly helpful where borings and intrusive testing are limited or restricted for reasons that may include investigation budget limitations, permitting, inaccessibility and environmental disturbance constraints. Integration of geophysics with geotechnical investigative techniques offers the potential to improve management of project risks and costs, as well as enhance understanding of site conditions. This article describes some proven geophysical techniques in geotechnical investigations of large footprint LNG plant construction sites.

Phase equilibrium of CO2-brine fluids is important to studies related to CO2 sequestration in deep saline aquifers and CO2 enhanced oil recovery. Furthermore, the study of the seismic properties of CO2 saturated and not saturated brines as pore fluids helps to understand their influence on the 4D seismic properties of rocks.

In this work we reported results of measurements of the acoustic velocities in brines with dissolved CO2. We investigate the effects of pressure (from 2 MPa to 38 MPa), temperature (from 30 °C to 70 °C), and salinity (0, 10,000 ppm, 20,000 ppm, 40,000 ppm, 100,000 ppm) of KCl-NaCl brines on ultrasonic velocities. We also study the time lapse effect of CO2 dissolution into the brine.

It has been found that CO2 dissolution in brine has significantly changed acoustic properties of brine.

Quantitative knowledge of the acoustic response of rock from an injection site on supercritical CO2 saturation is crucial for understanding the feasibility of time-lapse seismic monitoring of CO2 plume migration. A suite of sandstones with similar composition but different petrophysical properties has been tested to reveal the effects on acoustic responses of supercritical CO2 injection into brine saturated sandstones. CO2 is first injected into dry samples, flushed out with brine and then injected again into brine saturated samples. Such experimental protocol allows us to obtain acoustic velocities of the samples for the wide range of CO2 saturations from 0 to 100%. On injection of supercritical CO2 (scCO2) into brine-saturated samples, some of samples exhibit observable perturbation of ~10% of compressional velocities with the increase of CO2 saturation form 0% to maximum (~50%). However for some sample effect of scCO2 injection on acoustic properties is negligible.

The results of the first low frequency experiments conducted on a sandstone sample (Donnybrook, Western Australia) flooded with supercritical CO2 (scCO2) are presented. The aim of the experiments was to investigate the effects of scCO2 injection on the elastic and anelastic properties of the rock. The sandstone sample (porosity - 11.4%, permeability - 0.28 mD) was cut in the drection ortogonal to a formation bedding plane and tested in a Hoek’s triaxial pressure cell equipped with the means for independent control of pore and confining pressures. The pore and confining pressures were set up at 10 and 31 MPa correspondingly. The low-frequency system and the pump comprising scCO2 were held at a temperature of 42°C. Supercritical CO2 was injected into the sample preliminary saturated with distilled water. The elastic parameters obtained for the sample with scCO2 at frequencies from 0.1 to 100 Hz are very close to those for the dry sample. Some discrepancy in calculated acoustic velocities can result from the difference in water and scCO2 densities. The increase of the extensional attenuation after scCO2 injection into water saturated sandstone was insignificant. The applicability of Gassmann’s fluid substitution theory for the interpretation of obtained results was also tested during the experiments.

Relatively poor performance of full pre-stack migration in hard rock seismic exploration is related to our inability to produce accurate velocity field which, is caused by complicated structures, highly variable reflectivity, and low signal to noise ratio. That is why the estimation of velocities becomes a significant problem in hard-rock environment. Consequently we wish to use imaging approaches which are loosely dependent or completely independent of the knowledge of rock velocities. To get there, we review and analyse different velocity- independent imaging techniques developed over nearly past three decades.

However, seismic imaging in complicated geological conditions often requires more than just one parameter such as accurate velocity field. Improvements of signal to noise ratio and data regularisation are typically necessary to enable construction of high resolution, high quality images. In such data, pre-conditioning should enable enhanced performance of velocity-less imaging techniques since their performance is critically dependent on input S/N ratio. The final approach, then, involves merging several techniques such are denoising, wave- field reconstruction/interpolation and velocity- independent tools together to improve image quality in hard-rock environment.

The search and recovery for base and precious metals in recent years has led to surveys in more challenging areas over complex deposits and in extreme terrains. Such deposits frequently have accessory minerals that can be detected by induced polarization (I.P.) surveys. Due to their complex shapes and host terrains, 3-D surveys and inversion models are necessary to accurately resolve them. However, in some cases, the survey lines are not arranged rectilinearly. To accommodate an arbitrary arrangement of the electrodes, a model discretisation that is independent of the electrode positions is used. The rugged terrain can be accurately modelled by the use of the finite-element method where the surface of the mesh matches the topography. Innovative arrays such as the offset pole-dipole array have been used to rapidly survey large areas at a lower cost compared to traditional dipole- dipole arrays. Such arrays frequently have large geometric factors that make it difficult to accurately calculate the I.P. anomalies with the conventional linear perturbation approach that uses the difference of two resistivity calculations. The complex resistivity method, where the I.P. component becomes the imaginary component of the resistivity model, avoids this problem as it effectively decouples the resistivity and I.P. calculations. Furthermore, time-lapse 3-D surveys using surface and borehole electrodes have been conducted to monitor the flow of sodium cyanide solution directly injected in steep-sided ore rock piles for secondary recovery of gold. A 4-D resistivity inversion method is used to map the flow of the solution during the injection process.

Brain computer interface (BCI) systems emerging as a breakthrough technology of the 21st century. As is the case with other developing technologies, proof of concept must be demonstrated before advanced methods are pursued. This article presents the first published case study of a brain controlled geophysical software package. We show how brain computer interface systems can facilitate accelerated learning in the geoscience community. Our results show that processed brainwaves from the NeuroSky MindWave electroencephalography (EEG) device can be used to control various geophysical survey parameters with an acceptable degree of accuracy and to model the corresponding data in real-time.

We summarise and extend the concept of Gaussian, or normal, distributions into multivariate statistics over many dimensions. We demonstrate how multivariate statistics can be applied to probability distributions. Through assumptions in the linearisation of the inverse problem, we show that the best-fit inverse model parameters are normally distributed with mean values and associated variance and covariance values that obey Gaussian statistics. Variance and covariance values describe how the model parameters interact with each other. By changing one value in the model parameter vector, other parameters are changed through the covariance that links them. We apply Gaussian statistics over many dimensions to query our models for statistically meaningful questions that can only be answered by taking the integral of the multivariate distribution over the multidimensional space that contains the model parameter values. We illustrate this with an example of aquifer detection, using resistivity limits, for an electromagnetic transect adjacent to the Gascoyne River near Carnarvon, Western Australia.

The temporal and metallogenic relationships between BIFs and IOCGs in the Mt Isa Block are controversial and difficult to assess quantitatively. In this study we examine new magnetic data, anisotropy of magnetic susceptibility (AMS) and remanent magnetisation to define potential structural controls on mineralisation, and try to determine temporal relationships between a barren hematite-magnetite BIF and a carbonate-hosted IOCG, Monakoff. The results showed that the BIF was magnetically isotropic, but that it had a high remanent component (Q=13). The remanent magnetisation has Dec= 238.4° and Inc= -38.6°, which is offset from the present field and previous data from Cloncurry, so it likely formed during deposition, or early in the deformation history e.g. D1, D2. Conversely, the ore has very low remanent magnetisation (Q<0.2) but significant AMS, oriented Azimuth=225°, Plunge=75°, which is consistent with NE-SW (D3) shortening. 3-D magnetic modelling, constrained by magnetic property data and geophysical enhancements, showed that the BIF horizon formed a tight synform. However, modelling of the ore body showed it to be sub vertical. Based on the recognition that the ore body formed during D3 shortening, we infer that the ore formed in a zone of dilation sub-perpendicular to the shortening direction, rather than in a layer sub-parallel jog. The results suggest that the intersection of NW-oriented, sub-vertical faults with stratiform BIF horizons, adjacent to mafic volcanics are prospective for Monakoff-style IOCGs.

The accessibility of high-powered computers, plus readily available and detailed topography, allows the explorer to account for the effect of terrain in gravity and gravity gradiometry surveys applied to highlight subterranean density variations.

Similarly, accounting for other known density contrasts can further enhance the geological understanding of a survey area. The bedrock/overburden interface, lake depth and snow thickness can be mapped to provide 3D geometric surface models. The gravity gradient responses of these surfaces are presented.

Overburden and lakes are shown to have significant influence on the survey data. The effect of snow cover on survey data was found to be negligible. However, it may be important for the next generation of airborne gravity gradiometer instruments.

Seismic reflection method has been successfully used in the petroleum industry for the last few decades. Until recently, the mining industry has been reluctant to use seismic methods for mineral exploration because of its high cost, uncertain performance, and potentially ambiguous interpretation results. However, shallow mineral reserves are depleted and exploration is moving towards deeper targets in order to extend existing and to find new mineral reserves. In that space it is perceptible that seismic method will become an important if not primary exploration tool to delineate subsurface structures hosting ore bodies. One of the outstanding issues along the application of seismic methods for mineral exploration is our ability to grasp and then interpret excessively complex seismic images.

Volumetric interpretation is performed in 3D, in real- time by applying opacity and transparency filters to grasp the global structures and by rotating and viewing the seismic volume from different angles which allows in- depth understanding of the volume analysed. This, initial stage of volumetric interpretation is followed by more specific tasks aimed towards mapping the interfaces and associated structures of exploration interest. The ore shoots or occurrences are predicted by numerical modelling based on the priori knowledge. The targeting strategy is constructed according to the numerical response and map of the main interfaces and structures. This, for hard rock, novel interpretation methodology is aimed towards direct targeting and estimates of the ore reserves. The implementation is demonstrated on the field data from Kambalda, WA.

The aim of extremal inversion is to construct models with maximal or minimal characteristics, but which nonetheless fit the observed data acceptably well. Given one model which fits the data, extremal inversion enables the user to explore the permissible range of model parameters, hence determine parameter uncertainty. A 1D extremal inversion algorithm has been developed for horizontal loop TEM. Extremal inversion is effected via linear programming. The objective is maximisation or minimisation of a particular layer conductivity or depth. Bounds (on conductivity or depth) can be imposed explicitly as inequality constraints. Extremal models can differ markedly from the first model which fits the data. Extremal inversion is non-linear and is not confined to a neighbourhood which is “linearly close” to the first model. As an example of the application of this method, 1D extremal inversion is applied to airborne TEM data acquired over shallow seawater to determine upper and lower bounds on depths of seawater and bedrock and on conductivities of seawater and marine sediment. The results compare favourably with available ground truth data. Estimates of parameter uncertainty derived from extremal inversion are as follows: ±0.6 S/m for seawater conductivity, ±0.2 S/m for sediment conductivity, ±0.7 m for seawater depth, and ±8 m for bedrock depth.

Much of the highly prospective Paterson Province of Western Australia lies under sand cover, which has previously inhibited mineral exploration in much of the region. The Yeneena Project, held by WA - based company Encounter Resources, lies in this region and is actively being explored using geophysics to identify undercover targets. AEM has proved a particularly effective geophysical technique in mapping unexposed regional structures and geological units. Surveys generated by both Geoscience Australia and Encounter has directly led to the identification of new targets and significant investment in detailed ground geophysics and drilling. Crucially, these activities have led to the discovery of copper sulphides and prospective mineral systems within the Yeneena Project, demonstrating the significant impact that regional geophysical datasets can have on the exploration potential of an area.

Anomalous horizontal stress conditions within reservoir rock can result in azimuthally anisotropic elastic properties, the effects of which can be observed in borehole and 3D seismic data. The amount of stress- induced anisotropy can vary depending on sedimentary rock type and on subsurface stress conditions. There is currently no methodology we are aware of to quantify the relationship between azimuthal anisotropy and sand-shale content in unconsolidated sediments. We use data from the Stybarrow Field, located offshore NW Australia in the Carnarvon Sedimentary Basin, which is an area where strong anomalous horizontal stress conditions are present and have induced azimuthal anisotropy. We model azimuthally anisotropic gathers from logs and spatially correlate azimuthal AVO variations with sand-shale content. We derive a relationship that predicts the Thomsen parameter gamma as a function of the shale volume (for volume ratios greater than 0.3), and use this relationship to predict spatial variations in the azimuthal anisotropic AVO observed in the seismic data at Stybarrow. Implications from this work are that azimuthal anisotropy can be a strong function of sand- shale content, and that spatial variations in the sand-shale ratio can be estimated from azimuthal AVO.

In 2011, a large offshore borehole seismic program was acquired in the highly deviated GOR-3B well. It consisted of a Vertical Incidence (Walkabove) VSP and a total of four Walkaway VSP lines, out of which two deep walkaway lines were acquired for anisotropy and two shallow walkaway lines were acquired for imaging. The entire operation took 30 hours. An array of eight Versatile Seismic Imager (VSI) receivers was used as downhole sensors while a three 250 cc airgun cluster was deployed along the side of the UOS Discovery vessel at a safe distance during the entire job thus saving considerable time of changing source locations between different survey types. TRISOR was used as source controller while SWINGS was used as navigation system. Five good shots were stacked within a target circle for each Walkabove VSP station while single shot data was acquired for all four walkaway lines. Real time acquisition support was provided remotely and at the well site to monitor and guide the acquisition. The data quality was good for obtaining high quality time-depth information and for further advanced processing. Quick look processing results were produced within 48 hours followed by advanced processing of the full datasets. Based on the operational and technical success of this project, several advanced borehole seismic projects have been done on successive wells.

In this paper, we propose an adaptive implementation for separating multiples from primary events in seismic data and subsequently removing the embedded multiples from noisy seismic data using the curvelet transform. Because of the sparseness of the curvelet coefficients of seismic data, the optimization problem is formularized by incorporating L1- and L2-norms, based on the framework of Bayesian Probability Maximization. Iterative soft- thresholding can be used for solving the above optimization problem. By making use of least-square matching filtering, we precondition the multiple models to match the actual multiples in the seismic data prior to the separation step.

Moreover, in order to meet the challenges faced by various types of data complications, we develop a frequency regularized adaptive curvelet domain separation approach. This flexibility overcomes the varying effectiveness of separation methods for different frequency bands in responding to the noise and model inaccuracy control. Accordingly, the high adaptability of this extension leads to its higher separation fidelity than existing curvelet domain separation implementations. We demonstrate the applications of our approach on synthetic and field data examples by comparing them with the results from the conventional least-square separation method.

Understanding of seismic attenuation plays an important role in successful application of seismic imaging and subsurface characterisation techniques based on amplitude analysis. Zero-offset vertical seismic profiling (VSP) is one of the principal tools which can be used to study seismic attenuation.

Apparent attenuation estimated from seismic data analyses comprises of scattering and intrinsic components. Scattering mechanism can play significant role in hard rock environments in areas associated with fracture zones or other complex structures. As such seismic attenuation can be an important seismic exploration attribute.

Meanwhile attenuation analyses from VSP data are almost routinely done in oil and gas industry they are still uncommon in mineral exploration.

In this study we analyse zero-offset VSP data acquired in Western Australia on one of DET CRC test sites using both hydrophones and 3C geophones as receivers. We compare several methods for apparent attenuation estimation and evaluate their applicability to VSP data acquired in crystalline rocks. Extensive wire line log coverage for the well allows us to investigate relative contribution of different attenuation mechanisms.

A study of the low frequency dispersion and attenuation in sedimentary rocks is important for interpreting seismic data obtained during fluid extraction in producing fields or during injection of carbon dioxide for storage purposes. We present the results of the laboratory measurements of elastic and anelastic parameters of dry and distilled water/brine saturated sandstones with low (~7.8 and 9.6 mD) and high (~590 mD) permeability conducted at seismic (1-100 Hz) and teleseismic (0.1-1 Hz) frequencies. The experiments were performed with a laboratory apparatus utilizing stress-strain relationship which was developed to measure the complex Young’s moduli of rocks at seismic frequencies. The measurements carried out in saturated sandstones with low permeability at effective pressures from 2.5 to 23 MPa revealed prominent peaks of attenuation in the seismic and teleseismic bands. A significant dispersion of the Young’s moduli was also observed. The change in the salinity of the fluid from 0 to 45,000 ppm NaCl did not affect any of the measured parameters. The dispersion of the elastic moduli of the dry sandstones was within the accuracy of our measurements.

A geological complex near-surface traditionally yields poor quality first arrival picks in land sesmic surveys making use of vibroseis sources. Uphole surveys can reduce the uncertainty, but are costly to undertake. Simultaneous joint inversion used as a static solver in combination with non-seismic data can reduce the number of uphole shots and improve the computed near- surface static solution.

A comprehensive magnetic analysis of the Lachlan Orocline and Macquarie Arc, both located in the Lachlan Orogen, eastern Australia has been undertaken to test the potential relative rotation of this block to the surrounding units. These results are compared with palaeomagnetic data from the region and a series of geologically constrained crustal-scale forward models of lithospheric magnetisation for the area, with focus on the large-scale structural components of the Lachlan Orocline.

The forward model method treats each geological unit present in both the Macquarie Arc itself and the surrounding areas as independent parameterised stratigraphic units. Using a Geographical Information System (GIS) approach, known geological, structural and physical properties are used to produce a series of vertically integrated value grids. These grids are then used as input to model the regional magnetisation in the global scale magnetic field forward model.

Interbed (or internal) multiples, caused by ringing between strong reflectors, can play havoc with the interpretation of primary reflections deeper within a seismic section, and have been historically difficult to suppress. True wide-azimuth, relatively sparsely acquired 3D data (like OBC) add to the complexity of this problem.

For this case study, we present our testing and on-going developments on interbed multiple suppression. Two methods are shown. The first is an interpretive pattern- recognition technique applied after migration. The second, applied to unmigrated data, is a new version of wavefield modelling that attempts to predict interbed multiples without any knowledge of the actual multiple generators. A well-constrained adaptive subtraction methodology is required, and the testing and development of a new 3D subtraction algorithm is reviewed. Both methods have been shown to perform well.

Gravity gradiometry offers multiple single components and possible combinations of components to be used in interpretation. Knowledge of the information content of components and their combinations is therefore crucial to their effectiveness and so a quantitative rating of information level is needed to guide the choice. To this end we use linear inverse theory to examine the relationship between the different tensor components and combinations thereof and the model parameters to be determined. The model used is a simple prism, characterized by seven parameters: the prism location, xc, yc, its width w and breadth b, the density ρ, the depth to top z, and thickness t. Varying these values allows a wide variety of body shapes, e.g. blocks, plates, dykes, rods, to be considered. The Jacobian matrix, which relates parameters and their associated gravity response, clarifies the importance and stability of model parameters in the presence of data errors. In general, for single tensor components and combinations, the progression from well- to poorly-determined parameters follows the trend of ρ, xc, yc, w, b, z to t. Ranking the estimated model errors from a range of models shows that data sets consisting of concatenated components produce the smallest parameter errors. For data sets comprising combined tensor components, the invariants I1 and I2 produce the smallest model errors. Of the single tensor components, Tzz gives the best performance overall, but those single components with strong directional sensitivity can produce some individual parameters with smaller estimated errors (e.g., w and xc estimated from Txz).

A special challenge of hard rock exploration is to identify targets of interest within complex geological settings. Interpretation of the geology can be made from direct geological observations and knowledge of the area, and from 2D or 3D seismic surveys. These interpretations can be developed into 3D geological models that provide the basis for predictions as to likely targets for drilling and/or mining. To verify these predictions we need to simulate 3D seismic wave propagation in the proposed geological models and compare the simulation results to seismic survey data. To achieve this we convert geological surfaces created in an interpretation software package into discretised block models representing the different lithostratigraphic units, and segment these into discrete volumes to which appropriate density and seismic velocity values are assigned. This approach allows us to scale models appropriately for desired wave propagation parameters and to go from local to global geological models and vice versa. Then we use these digital models with forward modelling codes to undertake numerous 3D acoustic wave simulations. Simulations are performed with single shot and with exploding reflector (located on extracted geological surface) configurations.

As the search for mineral deposits moves to greater depths, seismic methods, with its penetration ability and unmatched resolution power, are becoming more important tool for exploration of mineral resources underneath the deep cover. However the performance of seismic appears to be still inconsistent which prevents it from becoming the primary exploration method in the mineral sector, similar to its role in oil exploration. The performance of seismic methods is affected by complex geology, excessive ambient noise, access restriction, weak reflectivity and/or low signal to noise ratio, limited acquisition program due to cost restriction, etc. Two other factors are emerging recently as important: a) lack of correlation of seismic images and b) miss-match between survey design and target characteristics. The first one is the greatest threat to the affirmation of seismic in the mineral sector as it prevents seismic images to be utilised in any constructive way. The second one translates to the use of simplified 2D geometries to delineate complex 3D structures which may cause seismic to underperform. On the positive side there are clearly favourable cases for the application of reflection seismic. Those can be primarily related to the massive, concentrated mineralisation such are massive sulphides.

The less favourable geological settings require much more elaborate analysis to allow seismic method to perform. It appears that the lack of understanding of the complexity and the variability of seismic responses in different geological settings is what still prevents the widespread use of this method for mineral exploration. In general seismic could be useful in different ways, from regional to deposit scale and from exploration to production stage.

Magnetotelluric data was collected across the Habanero geothermal site in the Cooper Basin, South Australia, in view of delineating the crustal structure underneath the geothermal area and to monitor fluid injection of the Habanero 3 borehole. Two surveys were carried out. Initially, two perpendicular profiles have been stablished, each about 20 km long, to obtain 2D profiles across the Habanero site. The aim is to estimate the sediment thickness to allow for constrained 3D forward modelling for fluid injection scenarios. Furthermore, the broadband data with periods up to 1000s allows a view into the crust. Geochemical data from the Mound Springs shows that the seeping water contains a minor component of mantle CO2. MT can be used to image the fluid pathways if such a connection exists. The results will be compared to recent findings from fluid pathways in the Lake From embayment a few hundred km south of the Cooper Basin. Additionally, initial results from the fluid injection monitoring experiment of the Habanero 3 borehole will be shown. In November 2012, fluids were pumped at depth of around 4 km for a period of two weeks. The fluids exceed the amount introduced into the Paralana EGS in July 2011, however a pre-existing fluid reservoir from a prior fluid injection exists. We report on surface MT response changes due to the fluid reservoir at depth.

Tendaho is one of the high temperature geothermal areas in Afar depression in north east Ethiopia. A total of 129 MT sites were acquired from Tendaho high temperature field. The 2D inversion of MT data from Tendaho high temperature field revealed three main resistivity structures down to a depth of 10 km: low resistivity surface layer underlain by a resistive layer followed by good conducting structure. The low resistivity surface layer show areas with either sediments, lateral flow of geothermal fluids or zeolite-clay alteration zone. Below the conductive layer, is a high resistivity zone that can be correlated to Afar stratoid basalts or epidote alteration zone .The high resistivity structure has been associated with the deep reservoir of the geothermal system. The deep good conductive body is probable heat source of the geothermal system.

The application of equipotential surface curvatures and Poisson’s relation to airborne gravity gradient data is presented. The mean and differential curvature of the equipotential surface, the curvature of the gravity field line, the AGG Geometry Map, the zero contour of the Gaussian curvature of the equipotential surface and the zero contour of the determinant of the gravity gradient tensor should improve the understanding and geological interpretation of gravity gradient data.

Seismic vibrators are the preferred sources for land vertical seismic profile (VSP) surveys as they are relatively repeatable, controllable, have high energy, have a low environmental impact, and are cost-effective. Unfortunately, due to the mechanical and hydraulic constraints of the vehicles, the typical swept bandwidth has been quite limited, typically of the order of 3 octaves. In this paper we show that dramatic improvements in seismic data quality can be achieved by extending the bandwidth used for Vibroseis VSPs. These increases are dependent, however, on the use of modern vibrators, specialised low-frequency enhancing sweeps, and downhole sensors with an extended frequency response range.

Seafloor canyons and complex seafloor topography pose significant challenges when analysing seismic data from the North West shelf off the Western Australian coast. Several prolific gas fields in this area lie beneath the continental shelf break, which contains large canyons that cause significant seismic amplitude distortion and complex wavefield behaviour (e.g. scattering and wavefield multi-pathing), and lead to irregular and poor illumination, unreliable AVO analysis, and difficulties in velocity model building. To illustrate these issues we present 3D elastic finite-difference simulation results from a model of a region of the North West Shelf in Western Australia. Using a high-performance computing cluster we model elastic wavefields through complex seabottom topography. We simulate plane-wave propagation through a bathymetric model to generate a pseudo stack. We observe many expected complex effects including wavefield (de)focusing, diffractions and triplications. We also measure wavefield amplitude variations of a factor of four over scale lengths of a few hundred metres; this is sufficient to cause significant imaging issues. By accurately modelling full 3D wavefield effects we can now generate data to benchmark existing algorithms and develop new techniques/algorithms for handling complex bathymetry.

Consistent and successful mineral exploration requires substantial experience and a broad knowledge base that traditionally takes years of resources to develop through hands-on experience in multiple and varied exploration projects. This creates a critical industry issue that implies many exploration decisions are sub-optimal prior to attaining an appropriate level of experience.

To address this issue, we present the unique and novel e- learning environment, exSim, which simulates exploration scenarios where users can develop and test their strategies and assess the consequences of their choices. This simulator provides an engaging platform for self-learning and experimentation in exploration strategies, providing a means to build experience more effectively.

We present an initial prototype of exSim, displaying features to facilitate decisions in ground selection, geophysical surveys, drill testing, and interpretation.

With increasing demands on groundwater resources, concerns about the impacts of groundwater abstraction on groundwater dependent ecosystems and the new paradigm of large scale managed aquifer recharge, there comes a requirement for more robust definition for water resources. Seismic reflection surveying may offer this higher level of definition. Resolution at depth and the ability to map detailed structures cannot be matched with any other method. Seismic reflection is able to recover information that may contribute to revealing aquifer geometry and system fluxes. It also increases the value of existing borehole information. Take up of seismic reflection by the groundwater industry has been slow but is certainly gathering momentum with several high resolution basin scale surveys now providing clear examples of the value of seismic reflection. Seismic reflection surveying is expensive, so the key to success is strategic location of lines and selection of suitable acquisition parameters with sufficient resolution to answer key questions regarding the targeted hydrogeological system. We present several examples from the West Australian aquifer systems, compare the acquisition parameters selected and then clearly identify hydrogeological value of the outcome for each setting.

In October 2012 a series of known oil & gas fields in the North Sea were surveyed with the newly developed towed streamer EM system. This is the first commercial Controlled Source EM (CSEM) system where both source and receivers are towed in a similar fashion as 2D seismic, and the technology is also combinable with 2D seismic facilitating simultaneous acquisition from one vessel. One of the selected targets was an average size oil & gas field located 2,100 m below mudline, where approximately half of the recoverable oil has been produced, but with the gas cap still intact. The source was towed at 10 m and the 8,700 m long EM streamer was towed at a depth of 50 m. The resulting electric field was measured at 23 offsets ranging from 0 to 7,700 m. The towing speed was 4 kn, and the water depth was 110 - 125 m in the survey area. The rich sampling makes the towed streamer EM acquisition technology ideal for the recently introduced synthetic aperture processing. The accuracy in the frequency responses enabled the detection of the depocenter of the reservoir with a signal strength only 7-8% above background with an uncertainty of 5% in a non-optimized synthetic aperture processing. The improved sensitivity provided by optimized synthetic aperture processing increased the signal above background to 200%. Further, by focusing the energy on the target it will also de-emphasize the strength of the anomalies of no interest located in proximity to the reservoir under evaluation.

Simultaneous AVO inversion of seismic data is an integral part of oil and gas exploration. Traditionally this technique is applied to surface seismic data, relying on availability of various angle stacks as well as on presence of offset wells for low frequency models. This paper investigates how a Walkaway Vertical Seismic Profile (WVSP) can be utilized for localized AVO inversion. Traditionally WVSP are designed for one of the following three purposes: imaging, anisotropy and AVO/AVA analysis. This paper shows a set of conditions that allow for WVSP data to be inverted following a commonly utilized simultaneous seismic inversion technique. The advantage of performing a localized WVSP AVO inversion is that low frequency models are measured during WVSP acquisition. This significantly reduces the ambiguity of the background models for inversion. Another advantage is that the inversion input derived during WVSP migration comes from measured vertical velocities, thus allowing more accurate angle stacks, thus improving the quality of the inversion. Lastly, WVSP images are generally of higher frequency content, thus producing high frequency density, Acoustic Impedance and VpVs images in the vicinity of the wellbore. The results can assist in calibrating the surface seismic inversion once more well data are available as well as making quick drilling decisions for deepening or side tracking wells.

Subsurface resistivity is a key component of many mineralization models including unconformity-related uranium, palaeochannel hosted uranium and nickel sulphides. Other key applications of subsurface resistivity involve environmental aspects of the subsurface such as groundwater detection, and civil engineering applications including detection of buried pipes and cables. Measuring subsurface resistivity is the aim of electromagnetic (EM) geophysical techniques. It involves transmitting an electromagnetic field into the Earth, and then recording this field - and the Earth response - on a receiver. The transmitted field signal can be removed from the received field to determine the Earth response.

Airborne EM (AEM) is a geophysical technique that allows this process to be undertaken from an airborne (aeroplane or helicopter) platform. AEM exploration first commenced in South Australia with AFMAG (Audio- Frequency Magnetic technique) surveys in the 1960s, and VLF (Very Low Frequency) surveys from 1971. Numerous platforms including RepTEM, GeoTEM, Input, QUESTEM, HoistEM, TEMPEST and VTEM are now routinely used within South Australia. Each technique provides a different view of the subsurface dependant on the system parameters and the processing undertaken on the data.

Given the increase in AEM surveying within South Australia and the wide applications available for this data a review of this technique within the State has been undertaken. This poster presents a summary of AEM within South Australia, focussing on a number of significant surveys and their outcomes. Surveys in the Cariewerloo Basin and Fowler Domain in particular have been used to model uranium prospectivity and help define nickel deposits. All data reviewed is now downloadable online via SARIG.

Current models for regional mineral exploration targeting for nickel and gold mineralisation emphasize the significance of deep penetrating geological structures and the margins of cratonic blocks as areas of greatest prospectivity. As part of a study on regional prospectivity, magnetotelluric (MT) surveys have been completed in several prospective Proterozoic and Archean terrains in Western Australia. These data, which have been interpreted in associated with potential field, seismic, geological and geochemical data, demonstrate that MT surveys can be used to identify such prospective features based on variations in the electrical conductivity of the crust and upper mantle. For example, a survey in the southern Yilgarn Craton has identified lateral changes in deep crust and upper mantle conductivity structure consistent with palaeo-cratonic boundaries inferred from studies using isotope geochemistry. The MT data allow the boundaries to be accurately located; the isotopic results being limited by the spatial distribution of outcrops of suitable lithotypes.

The areas of interest in Western Australia are geographically remote and often environmentally and culturally significant. MT surveys represent a comparatively cheap means of evaluating regional prospectivity, whilst causing minimal cultural and environmental disturbance.

A modified one-way equation pre-stack depth migration of up-going and down-going pressure wavefields was applied to two datasets derived from 3D towed dual- sensor streamer data in offshore Australia and Malaysia. The primary objective was to mitigate the well-known cross-line acquisition footprint effects upon shallow data quality and interpretability.

The new methodology introduced here exploits the illumination corresponding to surface multiple energy and thus exploits what has historically been treated by the seismic industry as unwanted noise. Whereas a strong cross-line acquisition footprint affected the very shallow 3D data using conventional processing and imaging, the new results yield spectacular continuous high resolution seismic images, even up to, and including the water bottom. One implication of these results is that very wide-tow survey efficiency can be achieved without compromising shallow data quality if dual-sensor streamer acquisition and processing is used, even in very shallow water areas such as that discussed here. The imaging methodology can account for all degrees of lateral variability in the velocity model, full anisotropy, and angle gathers can be created to assist with velocity model building.

An innovative 3D towed streamer project in offshore Gabon used a dual-vessel continuous long offset streamer configuration to acquire 0-12 km offsets with ten dual- sensor streamers. Streamer control for the 6 km streamers was robust and avoided operational complications or logistical penalties. Simultaneous shooting maximized inline shot density for long record lengths, thus capturing unaliased deep target reflections from rugose base-salt and sub-salt horizons. Survey design benefited from prior 2D survey experiences with a variety of broadband source and streamer technologies, and the use of 2D streamers as long as 12 km. 3D illumination modelling further suggested that offsets as long as 16 km could be expected to yield useful base-salt and sub-salt reflections.

Wavefield separation processing yielded full receiver- side deghosting onboard, followed by an inversion-based separation of simultaneous shots onshore. The ultra-long 12 km offsets combined with strong amplitudes of deghosted low frequencies have yielded encouraging sub- salt and pre-salt imaging.

To interpret magnetic responses of different mineral settings in Papua New Guinea, field campaigns were conducted by the Geological Survey Division in two mineral fields in the Rigo District, Central Province.

In December 2011, geological mapping accompanied by a ground magnetic survey was conducted over iron-rich gossan within a volcanic sequence at Kore. In March 2012, an analogous program was undertaken in a sedimentary-hosted manganese field near Kemaea village.

Ground magnetic surveys in both areas comprised a series of north-south magnetic profiles, up to 1 km in length separated by 100 m.

The results of the magnetic survey show significantly different responses that are apparently related to the style of mineralisation.

The total magnetic response of a gossan within a volcanic rock unit is characterised by high frequency signals that require extensive filtering to outline the trend of distinct magnetic source. In contrast, the limestone-hosted strata- bound manganese deposit has a well-defined north- westerly structural trend that is easily distinguished by the response in the total magnetic field.

Applying a reduced to magnetic equator algorithm and generating an upward continuation of the magnetic field enhances these structural trends.

The results of the survey demonstrate that background knowledge of mineral systems, including major mineral composition and style of deposit is essential to interpret imagery from ground magnetic surveys of mineral deposits and that different styles of mineralisation generate unique magnetic responses.

Enhancement of potential field datasets using operators based on one or more of the spatial derivatives is common practice. The performance of these methods in the presence of noise is poorly understood; other than a general acceptance that they can be significantly affected, especially when higher order derivatives are used. Most published descriptions which involve noise tests use random noise and a dense and uniform sampling of the test region. More realistic tests of the effects of noise should account for the incomplete and anisotropic sampling within most datasets and also correlated noise such as due to incorrect levelling. An understanding of the effects of noise on the different methods of enhancement is particularly important when working with lower quality (older) and lower resolution datasets.

Interpretation of geophysical data from West Africa, as part of a major project on the prospectivity of the region, is being undertaken. Much of the data available is of relatively low quality and resolution. An important component of the work will involve determining how best to enhance the gravity and magnetic datasets. Initial results working on gridded data show that the “generalized derivative operator” is the most robust derivative based enhanced product for low resolution data.

Beam Migration has specific advantages, in its speed and high signal-to-noise levels, which make it suitable for both depth velocity modelling and final imaging. One property of Beam Migration is that wavelets can, based upon a combination of criteria, be weighted down or excluded from reconstruction. It is possible to reject wavelets that match a multi-dimensional multiple model. This model is based upon a combination of interpretation, normal moveout and spatial & temporal location.

Data examples from the North West Shelf, Australia, illustrate the flexibility of this approach and demonstrate its effectiveness in the complex inter-bed multiple area of Browse Basin.

Advances in the acquisition and processing of 3D seismic data have led to significant improvements in our ability to image subsurface reservoirs. The limitations of conventional 3D seismic measurements for reservoir characterization include its band-limited vertical resolution as well as the non-uniqueness of inverting seismic amplitudes for reservoir properties. These limitations have an impact on our ability to accurately model thin reservoirs for volumetric computations. Stochastic seismic inversion addresses these concerns by producing multiple, equally likely realizations, consistent with the available well and seismic data, at the fine-scale vertical resolution required for such reservoirs. The nature of the algorithm results in a large number of realizations (typically in excess of 200). We, therefore, require a methodology to rank the realizations in a way that is meaningful for the problem at hand and identify models corresponding to the P10th, P50th, and P90th percentiles.

In the example presented here a feature recognized on a 3D deterministic seismic inversion result was interpreted as a mitten-shaped tidal bar using well-log data. The stochastic seismic inversion process generated realizations that showed a wide variation in the extent and geometry of the tidal bar. In this work we present an innovative ranking method used to classify the broad range of stochastic inversion results targeted at approximating this tidal bar geomorphological feature. From these results we were successful in identifying the various percentile models required for further analysis including input to reservoir simulation modeling.

Geological interpretations of aeromagnetic and gravity images are highly subjective but are rarely accompanied by a quantitative confidence assessment, which is a key limitation on the usefulness of the results. This paper outlines a method with which the relative level of data richness can be assessed quantitatively, leading to an improved understanding of spatial variations in interpretational confidence. Simple rules were used to quantify the likely influence of several major sources of uncertainty. These were: 1) the level of geological constraint, using the local abundance of outcropping rock and the scale of geological mapping; 2) the interpretability of the data, considering the strength of edge-like features and the degree of directionality of these features; 3) data collection and processing errors, including gridding errors, and the influence of anisotropic line data collection on the detection of gradients. From these individual sources of uncertainty an overall data richness map was generated through a weighted summation of these grids. Weightings were assigned so as to best match the result to the interpreter’s perception of interpretational confidence. This method produced a map of data richness, which reflects the opportunity that the data provided to the interpreter to make a correct interpretation. An example from central Australia indicated that the data influences were preserved over a moderate range of weighting factors, and that strong bias was required to override these. In addition to providing a confidence assessment, this method also provides a way to test the potential benefits of additional data collection.

Magnetic and gravity data have great potential to inform us about regional-scale features. Major fault zones, basin geometries, basement character, Moho, intra-crustal boundaries etc can all be imaged. However, modelling results are inherently non-unique and often highly uncertain. This feeds into the reliability of the method and its usefulness in resource exploration. Following Occam’s razor, traditional methods have usually sought to find the simplest model possible, through use of maximum smoothness regularization (e.g. UBC-GIF), or through simplifying the model to an analytically unique problem (e.g. Parker-Oldenburg). More recent software packages allow the process to be constrained by lithology and the explicit incorporation of geological knowledge into the process. This increased degree of freedom leads to greater flexibility, but also greater ambiguity in results. A single result is clearly not adequate in these cases. Here we present some examples at regional and continental scales where the inclusion of variability measures has greatly increased the usefulness of the inversion process to understand 1) the features of interest and 2) the robustness of the solution.

Australia, via the efforts of the Government geological surveys, has a program of releasing ever bigger, higher- resolution, continental-scale datasets. The recently released isostatically corrected gravity data images many deep and large-scale crustal features. This is a key dataset for understanding the primary structure of the deep crust across thousands of kilometres. Direct “inversion” of this dataset to a consistent 3D fault surfaces network explains more than 50% of the primary information.

The method of choice relies on multi-scale edge detection or “worming”. This continues to prove effective in the regional mapping domain. Large-scale minerals and oil exploration mapping often make use of this technique. With the current shift to 3D geology modelling, issues arise to improve/generalise the worming technology to produce 3D contacts that can be interpreted, particularly the sub-set that indicates a primary fault network.

The new method allows the gathering of related worms to rapidly compute a consistent 3D fault network for the entire Australian continent by linking the dominant 30 km deep features back to the surface. If measured gravity curvature gradients are available, an improved and more detailed use of the method is now available at the prospect scale.

Potential field geophysical modelling techniques can be applied to better understand the subsurface morphology of volcanoes, and when linked with observations of surface geology can be used to develop a more complete understanding of the volcanic centres eruptive history.

High resolution ground gravity and magnetic data were acquired across several maar volcanoes located within the Newer Volcanics Province (NVP) of Western Victoria. The maar volcanoes surveyed represent a range of the different sizes and styles of eruptions observed within maar volcanoes of the NVP.

Gravity and magnetic data were subject to 2D forward and 3D inverse modelling in order to reveal details on the depth, geometry and petrophysical property distributions within subsurface volcanic structures. Gravity lows with corresponding magnetic highs are observed across the maar craters and were reproduced during modelling with the presence of a diatreme. Smaller wavelength gravity and magnetic anomalies detected in the centre of the more complex volcanic craters can be explained by the presence of intrusive dykes or vents filled with a higher proportion of denser volcanic debris.

Modelling suggests that multiple coalescing diatreme structures exist below the volcanic edifices, some containing intrusive dykes or a denser central vent filled in with volcanic debris. Multiple diatreme structures suggest a complex eruption history involving vent migration, while preserved dykes within the diatreme suggest short-lived fluctuations between phreatomagmatic and magmatic eruption styles.

The global demand for clean energy alternatives is constantly increasing, creating significant interest for more sustainable energy resources such as uranium and geothermal. Australia is host to over 25% of the world’s known uranium resources as well as having significant geothermal potential.

The Mount Painter Domain, in the Northern Flinders Ranges in South Australia, is in a region of anomalously high heat flow generated by radiogenic decay of uranium and thorium rich granites. Two distinct uranium deposits have formed from dissolved uranium carried from the ranges by fluids, being deposited where reduction in sediment pH causes uranium precipitation.

In May 2012 a magnetotelluric profile was collected, extending from the Northern Flinders Ranges to the Lake Frome embayment to help constrain existing resistivity models. Precipitation of uranium at the Beverley Mine site is anomalous as no surface water flow is present, suggesting the presence of subsurface processes. A conductive pathway extending to the surface at Beverley is linked to a 50 Ω m conductive body at the brittle- ductile boundary of the mid-crust, directly under the Paralana geothermal prospect.

To better characterise the eruptive histories and subsurface structures of several maar volcanoes from the Newer Volcanics Province, forward and inverse geophysical modelling is combined with a study on the geology of the volcanic centres. The maar volcanoes under investigation include the Red Rock Volcanic Complex (RRVC), Ecklin maar, the Mount Leura Volcanic Complex (MLVC).

High resolution gravity and magnetic data were acquired across each of the maars and the data was modelled in two and three dimensions to understand the subsurface morphology of the volcanoes vents.

Varied geophysical responses are observed across each of the maars surveyed, indicating the complex and variable nature of the subsurface volcanic vent, even when they present similar surface morphology. Where corresponding gravity and magnetic lows are detected across a maar crater, it is suggested that all the available magma was erupted and the maar diatreme (subsurface collapse structure) was not intruded by any dykes. The gravity low arises because of lower density lake sediments and pyroclastic debris infilling the crater. The lack of any intrusive dykes or remnant vents within the diatreme suggest that groundwater was available for phreatomagmatic explosions.

Maars with corresponding gravity and magnetic highs indicate a large volume of subsurface basalt, resulting from the ponding of magma at the surface of the vent. This results from a lack of groundwater for magma to interact with during the eruption, which facilitates magma rising upwards through the diatreme where it is fragmented at shallower levels.

As a part of the Airport Tunnel project in Brisbane, an MASW survey was carried out to investigate the nature of the fill site of an old rock quarry. The main target of the survey is the depth of the landfill after the quarrying operation to avoid the tunnelling penetrate the fill material. The site is currently used as a shopping centre car park in an inner suburb of Brisbane along one of the main roads. To avoid excessive noise, the survey took place at night.

Some part of the seismic data presented an unusual but consistent noise pattern. External sources of this unusual noise, such as buried electric cables and drainage were considered, but no source could account for it. Therefore the noise was determined to be due to composition of the materials underground.

The analysis of the seismic data outlined the depth and shape of the quarry. The noisy area was identified as a shallow hard rock left in the quarry, perhaps as an access ramp. This was verified a historic photography of the old quarry.

The depth of the quarry was found shallower than the proposed depth of the tunnel to ensure the safety of boring.

This paper is inspired by an image of a time slice from the prolific hydrocarbon state of Texas showing a stacked channel system. Similar channel systems also exist in Australia’s Cooper Basin but are often difficult to see with legacy sparse seismic acquisition geometries. Due to reasons of cost and environmental and cultural heritage protection, relatively wide (‘sparse’) line intervals have been used, though these also allow coverage of larger areas than would otherwise be achieved. These sparse designs can combine low environmental impact with reasonable images at target. Lack of traces at medium and near offset ranges may result in strong amplitude artefacts in the final image - “acquisition footprint”. This case study is from the 2012 acquisition where, to reduce these artefacts, we deployed sources in a smooth “wavy” sinusoidal pattern, modified as necessary to follow natural features in the terrain. This methodology results in acquisition with a minimal visual and environmental impact and provides significant benefits in reducing the acquisition footprint. Innovative survey design and data processing techniques which accommodate non-uniform sampling resulted in the dataset where channel features are now clearly visible on the migrated volumes. The acquisition technique also features broadband point- source vibroseis using a non-linear Maximum Displacement sweep of 2 to 100 Hz, broadband digital point-receivers and dense sampling along both the source and receiver lines. Using the described technologies the acquired survey not only met, but by far exceeded, the initial expectations, and within the specified time frame. This survey has shown that exploration seismic surveys can be tailored to minimize environmental and acquisition foot print, and provide a high quality seismic dataset suitable for seismic attributes extraction.

Interpreting magnetotelluric (MT) models requires solid modelling of the data as well as good knowledge from other geophysical data and geological constraint in the particular tectonic setting of the survey area. MT measurements, relating the natural variations of electric and magnetic field to obtain the electrical resistivity distribution of the crust and mantle appear to show that enhanced electrical conductivity zones are more abundant at certain depths. Models show that frequently enhanced conductivity zones are topping out in the upper crust at depths of about 10-15 km. These features are discrete and extend usually over a few km to tens of km laterally, and can be found across the Delamerian Orogeny, in zones of high heat flow east of the Northern Flinders Ranges and also in the central Eyre Peninsula. We interpret this to be related to recent findings on dynamic interactions between brittle and ductile layers leading to mid- to upper crustal detachment faults. A second zone of higher conductivity occasionally appears in the lower crust, as imaged east of the Flinders Ranges at depths of around 25-35 km. Thirdly, at 80 km depth mantle conductors appear in stable Archean and Proterozoic terranes around the world, such as in the Slave Craton, Kaapvaal Craton and the Gawler Craton. In summary, information from geodynamic modelling helps to understand the processes in the earth in regards to fluid movement and potential mapping of heat flow and corresponding shift in depth of brittle-ductile boundaries.

We have investigated techniques for the efficient early detection of landslides using time series analysis incorporating synthetic aperture radar (SAR) images. The study area, in the Miyazaki, Nagasaki, and Saga prefectures in Kyushu, was determined based on interference fringes detected during interference SAR (InSAR) analysis. We used ALOS/PALSAR data acquired from 2006-2011 to detect early warning signs of landslides that were poorly expressed geomorphologically by conducting time series analysis of InSAR data acquired periodically. Moreover, in order to remove the noise caused by geographical feature stripes or phase retardation, we applied median filtering, histogram extraction processing, and clearisation of the displacement with a Laplacian filter. We evaluated the validity of each filter separately and in combination with other filters and assigned a gradient vector to each pixel value of the SAR picture using altitude data. In order to confirm the assumption that surface-of-the-earth displacement proceeds in the dip direction, we conducted direction analysis and a technique and confirmed the results of InSAR analysis by field survey. Our results prove the effectiveness of InSAR analysis in hazard monitoring over a wide area through the detection of local landslides.

Geoscientific data interpretation is a highly subjective and complex task as human intuition and biases play a significant role. Based on these interpretations, however, mining and petroleum industries make decisions with paramount of financial implications. As a first step towards understanding and improving the interpretation process, we carried out two experiments to monitor the human-data interactions during the process of identifying ‘targets’ (porphyry-style intrusive systems) within the aeromagnetic imagery. This is achieved by capturing the eye gaze position using an eye tracker system and the brain responses using electroencephalography (EEG).

The first experiment was intended to analyse the target spotting performance and the data observation patterns. For this experiment participants performed exercises, where the same magnetic image was presented in different orientations. Some key findings include: inconsistencies in target spotting performance within and between the interpreters; an improvement performance when the data were viewed in multiple orientations; and a strong correlation between the target spotting performance and efficient (systematic) data observation pattern. There was no correlation between success in identifying targets and the participants’ perception of their expertise.

The second experiment was designed to identify the characteristics of the targets that are easier to detect using EEG. For this experiment images with targets and without targets were presented in a rapid visual display. The analysis on the image characteristics based on the human visual attention model show a strong correlation between target spotting difficulty and dispersion of the visual attention.

Accurate and efficient identification and mapping of geological structures has broad application across the minerals industry. Recent advances in data acquisition technologies using Unmanned Aerial Vehicles (UAV), have led to a growing interest in capturing high- resolution rock surface images and analysing those datasets remotely. However due to the large volumes of data that can be captured in a short flight, efficient analyses of these data brings new challenges.

We propose a semi-automated method that allows efficient mapping of geological structures using photogrammetry of rock surface data collected by UAV. Our method harnesses advanced automated image analysis techniques and human data interactions to identify structures and calculate dip and dip angles of structures. Geological features were detected in two dimensional (2D) images and the corresponding three dimensional (3D) features were automatically identified from 3D surface models. The location, dip and dip angle of geological features were then calculated.

A feature map generated by our semi-automated method correlates well with a fault map resulting from visual interpretation by an expert. Some advantages of our semi-automatic method include the following: Firstly; it generates results in few minutes whilst manual interpretation took around an hour, thus contributing significantly in time saving. Secondly; unlike manual interpretation, our software technology provides objective and consistent results that can be reproduced.

We evaluate the use of airborne electromagnetic data from the SPECTREM2000 system flown for ore body detection, regolith mapping and assessment of aquifers. Since the position and orientation of the receiver bird are not measured, the primary field at the bird cannot be known and removed precisely. In order to successfully invert the AEM data, and produce conductivity-depth models, we first reinstate the removed primary field estimate and convert the data from ppm units to Teslas. We then simultaneously inverte the X and Z component data, to solve for a 1D layered conductivity model and receiver position.

The SPECTREM system has flown many line kilometres in other parts of the world but substantially less in Australia. Through further processing and inversions we have resolved conductivity-depth structures very similar to those previously obtained from other well-established AEM systems flown under Australian conditions. We also present a section of AEM data with logged drilling core data as a means of assessment of our inversion models against an independent data set.

This paper demonstrates recent advances in grid-based reflection tomography model building in conjunction with anisotropic pre-stack depth migration. These advances significantly benefit the imaging and resolution of 3D seismic data in a number of structurally complex basins.

Using 3D seismic imaging examples from Petroleum Exploration Permit PEP 51558 in New Zealand’s Taranaki Basin, this paper demonstrate how reflection tomography techniques can utilize implicit geological constraints to resolve complex velocity variations and, thereby, reduce structural and imaging uncertainty.

One challenge associated with velocity modelling in the Taranaki Basin is to adequately resolve the large lateral velocity contrasts across major faults. This work shows how the use of steering filters during the reflection tomography process significantly improves the resolution and delineation of these fault-constrained velocity contrasts. This approach is compared with the conventional gridded tomography approach of velocity model building.

Using a detailed velocity model from the Taranaki Basin, comparisons were made between time and depth migration, as well as alternate depth migration techniques.

Geophysical data interpretation is largely an anomaly detection task which involves recognising and synthesising anomalous patterns within single or multiple datasets. The accuracy and efficiency of these interpretations heavily relies on the skills and practices of interpreters, thus the greatest challenge is to minimise personal biases to produce objective and consistent interpretation outcomes. We present an innovative data visualisation method which can empower interpreters to effectively delineate anomalies of varying frequency scales within aeromagentic data using a single image display. This is achieved by harnessing the power of image enhancement and visualisation techniques to assist interpretation.

We adapted and extended the use of colour composite techniques to present different frequencies presented in potential field data. Aeromagnetic data from an area in Kirkland Lake, Ontario, Canada is used for our experiment. long wavelength and short wavelength anomalies are identified from the data using low pass- and high pass filters respectively. These two different frequency enhanced images and the original image are represented as separate colour channels which are then combined to generate a composite image. The luminance of the composite image is scaled to highlight high frequency signals as they hold the key for detailed structure interpretation. We use a technique called dynamic range compression, which preserves the integrity of the phase component of the signal while performing high pass filtering. The resulting display is compared to the geological map of the area to validate the effectiveness of the method. The proposed technique is widely adaptable for different types of datasets.

In 2011 a review of an historical TEMPEST airborne electromagnetic survey in the Murchison Region of Western Australia identified a number of discrete bedrock conductor anomalies potentially associated with base metal mineralisation. One of the anomalies identified was in close proximity to a known gossan at Hollandaire, within rocks of the Archaean Mt Eelya Complex. The Hollandaire gossan had been previously investigated during the mid-late 1970’s using a variety of geological, geochemical and geophysical methods, including ground magnetics, induced polarisation, magnetic induced polarisation and time-domain electromagnetics.

A single line of time-domain in-loop transient electromagnetic data was collected at Hollandaire during 2011, in order to follow up the TEMPEST bedrock conductor. A strong time-domain EM anomaly was identified, with a very high time-constant of 107 ms. Plate modelling of the in-loop data resulted in a target at depth-to-top 100 m, dipping at 45 degrees to the west- northwest, and with conductance 5000 S. The nine initial holes drilled to test the electromagnetic target all intersected sulphide mineralisation. The inferred resource now totals 2.8 million tonnes at 1.6% Cu, 0.4 g/t Au and 5 g/t Ag, with the supergene zone averaging 4.7% Cu. Subsequent downhole electromagnetic (DHEM) surveys have identified an off-hole electromagnetic conductor to the south of the known mineralisation, which has not yet been tested by drilling.

Seismic methods can be utilized in unconventional resources characterization studies to achieve an improved understanding of the entire reservoir heterogeneity, structure and stress orientation. This assists in an identification of production “sweet spots” and more efficient well placement. To enable this type of study with surface seismic, we need to analyse and invert the data not only against offset but also azimuth. This requirement places greater demands on the seismic than would be the case for a purely structural image.

In this paper we will describe the use of a potential “best-practice” solution based on experience in Australia and elsewhere for the design and implementation of the high specification “Winnie 3D” seismic survey. This survey featured broad-band point-sources and point-receivers using a non-linear maximum displacement sweep of 1.5 to 110 Hz. The omni-directional symmetrical dense sampling, in combination with long offsets, resulted in uniform azimuthal coverage and extremely high trace density. This design combined with a broad-band acquisition enables azimuthal analysis, inversion and seismic attributes extraction.

We will demonstrate how this 3D design, tailored for unconventional targets, allowed extraction of seismic attributes even in the early stages of data processing, enabling detection of anomalies that could be related to shallow igneous intrusions.

Over the last two decades 3D reflection seismic has been applied for mine planning in South Africa. For coal exploration, the mining targets are at shallower depths of less than 400 m. The challenge set by the mining companies is to obtain high-resolution seismic data with maximum vertical resolution at this depth of investigation. The cost of geophysics must also be more attractive than that of the ‘total drilling’ alternative. Seismic source trials were therefore conducted at one mine site. The ICIS (Internal Combustion Impulse Source) has been developed by CGG to provide a solution for shallow target surveys and for in-fills where access for conventional sources is restricted. The ICIS and Mini-vibrator performance were tested in shallow coal prospects, where existing 2D data have been acquired by Nomad 65 heavy vibrator. The tests demonstrated that ICIS is well suited to image target depths less than 500 m with frequencies up to 100 Hz. The comparison with the vibroseis sources showed that ICIS I) Delivered very good near offset data (> 50 m) and for up-hole/low velocity layer survey ii) Required more shots per shot point in the medium offset range (1000 m) due to its low energy iii) Not designed for far offset data (3000 m). ICIS was found to be a viable geophysical and logistic solution for certain high-resolution mineral surveys.

Full Tensor Gradient (FTG) gravity data measures the derivatives of the Earth’s gravitational field. Such variations in the gravitational field may be due to the presence of bodies of higher or lower density relative to the surrounding rock.

As the gravity tensor contains 5 independent components, effective visualisation of this high-dimensional dataset is advantageous for efficient processing of the FTG data. We present two aspects of visualising mass anomalies in FTG gravity datasets. First, we create a textured image where the orientations of the resulting texture reflect local lateral orientations encoded in the FTG data. It uses a colour map to highlight geologically significant structures such as linear features and radially symmetric points by identifying different geological features and using colour components to represent different feature types. This visualisation method is shown to be robust to significant levels of modelled noise, and we demonstrate its applicability to a field FTG survey.

Second, we present an algorithm for estimating the depths of mass anomalies in FTG data. A voxel representation of the subsurface is created and voxels are voted for according to gravitational curvature properties encoded in the FTG tensor. A visualisation of the volume at successive depths highlights 3D locations of mass anomalies at local maxima of the volume. The algorithm is evaluated on a forward-modelled FTG dataset where the depths of mass anomalies are known. The depths of mass anomalies are shown to be accurately located in the presence of noise.