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

After more than a decade of research and development our Eureka Moment is presented discussing a new differential geometry solution applied to the problem of digital surface analysis. The solution applies a completely different approach in mathematics without the use of existing techniques or algorithms. The process entails the calculation of a complete set of morphometric properties for the surface as it is defined by Differential Geometry. All processing of the data is automated, fast and accurately locates objects within the surface without the introduction of high frequency artefacts commonly associated with existing approaches. A number of objective evaluation methods are demonstrated offering comparative analysis with other published technologies on known mathematical models (with noise). Real data examples are provided showing the application of this technology on the analysis of data surfaces from seismic and potential fields surveys The queryable database of accurate and high quality elements becomes and essential aspect to highly simplify and speed up the data mining process. While this new approach and philosophy is demonstrated here on specific types of surface data, it has application to problems related to the analysis of any digital signals, images, surfaces and volumes.

Electrical anisotropy, defined as the directional dependence of electrical conductivity within a medium, is an important property to consider when interpreting magnetotelluric (MT) data. We propose the use of anisotropic forward modelling to model fluid flow within a geothermal setting.

Forward models provide synthetic MT responses for hypothetical structures which are compared with measured data to obtain knowledge about the subsurface geology of a region.

Comparisons between synthetic and measured data shows anisotropic fluid volumes are acceptable approximations of fluid injected into the crust. As a result, we support the use of anisotropic forward modelling as a means of modelling fluid motion at depth within a fractured geothermal system.

Energy spectral analysis techniques have been applied to magnetic and gravity data acquired over the Olympic Dam area of South Australia. Analysis has been conducted along two deep seismic lines previously acquired. There is a strong correlation between interfaces found in this analysis and structures interpreted from the seismic data. Lateral interpretation of the magnetic and gravity data allows for a valuable extension of the seismic interpretation. A bland zone apparent in the seismic data has been associated with the Olympic Dam ore-body by various authors. The top of this bland zone is strongly associated with a density interface found from the gravity data, and this may be a significant correlation. Further deep crustal structures are evident, including the Moho, and indications of the Curie isotherm.

The results obtained from energy spectral analysis over this area suggest that a much wider application of this approach across the Australian continent could be highly valuable.

Spatio-temporal information on the distribution of salt in floodplain soils and groundwater is integral to effective floodplain management strategies along the Great Darling Anabranch in NSW. Geophysical technologies have the potential to provide detailed spatial information on the variability of salt stored in the near surface and for monitoring surface water -groundwater interactions across the floodplains, and in particular looking at the spatial controls on those processes. The research sought to examine the role of hydrogeophysical methods in monitoring changes in floodplain sediment condition, linked to ecological investigations.

A two stage investigation, to examine the role of a low cost, near surface, geophysical method for monitoring changes across several sites located adjacent to the Anabranch. It represented a short term spatio-temporal investigation of inundation on salt in the floodplain.

Our results clearly show changes in the near-surface conductivity distribution at the sites surveyed. These changes are attributed to variations in the flows over the year, pumping of groundwater and changes in vegetation.

The survey shows that EM techniques are a useful tool in aiding our understanding of floodplain processes resulting from changes in flows along the Anabranch and can be applied in other floodplain environments as a low- cost survey to observe changes in conductivity in the near surface.

It is an effective method to monitor variations in conductivity in the floodplains due to changes in environmental flows and can aid in understanding changes in sediment conditions and be used to validate floodplain processes, contributing to ecological investigations of river floodplains.

Many geophysical models are created without satisfactory uncertainty analysis. Most geophysicists are aware of their model’s limitations, but if the model is passed on to a third party, this information is lost and the risk of misinterpretation arises.

This project develops multi-solution inversion techniques to improve inversion and joint inversion modelling of geophysical data in mineral exploration. The main focus is the advancement of the probability and uncertainty analysis of inversion models to increase their reliability. To create solution ensembles, a bootstrapping resampling approach is taken, which produces reduced data sets from a base data set by random omission of data points. Each of these new data sets is run through a conventional inversion process to produce a variety of solutions with minor variations.

In the appraisal stage the solution ensemble is statistically analysed to infer model uncertainties, which are then visualised to allow easy communication of the results. The process yields a clear and easy to interpret uncertainty map for the connected model and we demonstrate its effectiveness with several case studies.

Furthermore, we are currently investigating swarm intelligence based global search algorithms as a second approach to solution ensemble creation.

This paper utilises modern reflection seismic data, surface geology and well information, including petrophysical/lithological characteristics and biostratigraphy. The aim is to construct a new chronostratigraphic framework for the Onshore Otway Basin, while answering unresolved questions about the basin’s early rift history. These include the order in which individual depocentres were formed, the corresponding timing of deposition of laterally varying stratigraphic packages, and which units were confined to individual rift depocentres. The integration of stratigraphic correlations, petrophysical interpretation, drill-core descriptions, petrological/lithological analysis and biostratigraphy with interpreted seismic data resulted in the identification of at least two extra chronostratigraphic sequences. This study focused on high-resolution volumetric modelling of all stratigraphic sequences within the Otway rift system. Particular attention was paid to the Early Cretaceous stratigraphy following the identification and mapping of the two previously undocumented sedimentary sequences within the Victorian section of the basin. This led to a revised chronostratigraphic framework for the Onshore Otway Basin, which, in-turn, served to explain the relationship between fluvio-lacustrine sedimentation and tectonism during the early history of intercontinental rift systems.

Time-lapse seismic monitoring of reservoir fluid flow and other time-variant subsurface phenomena can be achieved with active and/or passive source seismology. We present new concepts that demonstrate the benefits of using the full time-lapse wavefields more accurately, for example via 4D prestack depth migration, 4D wave- equation migration velocity analysis, and 4D full waveform inversion. These new concepts provide an opportunity for more accurate imaging of complex scattered 4D wavefields, and the possibility to monitor very weak signals using 4D coda waves, useful for monitoring reservoir gas depletion or injection-induced seismicity.

We are developing a seismic technology for CCS, CO2- EOR and permanent reservoir monitoring using ultra- stable and long duration seismic source. We use seismic- ACROSS (Accurately controlled and Rousingly Operated Signal System) developed in Japan and multi- seismometers for the above purpose. We carried out synthetic evaluations of reservoir change imaging assuming single seismic sources and field experiment of time-lapse related to underground air injection in Japan in 2011.

We are applying a seismic ACROSS in the context of carbonate rocks in Saudi Arabia. The Al Wasee water pumping site approximately 120 km east of Riyadh has been selected as a test-site. The intention is to observe the changes in aquifers induced by pumping operations. One ACROSS unit was installed at the Al Wasee site this December 2011. The instrument has been operated from 10 to 50 Hz with 40 ton-f at 50 Hz. We use a device with a horizontal rotational axis. Using alternatively clockwise and counter clockwise rotations we can synthesize vertical and horizontal forces, respectively. 31 three-components and 8 nearby geophones have been used to monitor the seismic changes from pumping the water.

Comparing the data during one and half month, we identified waveform changes and clear daily variations. These waveform changes might be caused by the change of water table. In this report, we will show the preliminary results obtained in this field. This experiment is conducted in the cooperation by Japan and KACST funded by JCCP (Japan Cooperation Center, Petroleum) and KACST.

The ability to integrate data from a range of different images is often a crucial requirement for successful interpretation. Interactive multi-image blending is presented as a tool for facilitating the interpretation of complex information from multiple data sources. Traditionally, image blending has only been considered for cross-dissolving effects between two images. However, it is common for there to be more than just two images of interest in an interpretation task. We have developed a family of different multi-image blending tools to fill this need. These have been designed to support a number of different interpretation tasks and image types. For image blending to be a useful tool for multiple image interpretation it is important that the association between features and individual input images remain identifiable and distinct within the blend. We argue that interactivity of the blend is an important component for achieving this. Blending can also be usefully employed to interactively explore parameter variations for enhancement techniques. Often the best parameter values to use cannot be known beforehand, and it is common for different regions of an image to require different parameter values for best enhancement. By preparing a set of images processed over a sequence of scales and parameter values, and then interactively blending between these images, the interpretation of a data set can be greatly facilitated.

The most important factors in an earthquake are the casualties and financial losses; therefore it can help city managers to be ready before the events by a good simulation of what can happen in such disaster and recognizing vulnerable regions and consequently estimation of the amount of casualties and damages. Accordingly, one of the most important steps in developing Gorgan’s earthquake scenario was estimation the amount of destruction after the earthquake. Beside the site study, site effects study performs an important role in determining the amount of destruction after earthquakes. Our data for site study condition in Gorgan were: log data available in the offices, field study and geological reports, and soil geotechnical tests done by some special housing projects and urban development organization, used as important information in the Gorgan’s earthquake scenario process. Fortunately, bores that we used have an appropriate distribution in the city, in a manner that we could study site conditions in Gorgan by relying on their information. After that we modelled the bore loges information in Pro-Shake, and then we selected and applied a referenced accelerogram which used to calculate shear wave velocity, displacement and acceleration on Earth’s surface for output. In comparison of input accelerogram and output accelerogram we can find site amplification factor in a given point. By calculating this ratio in the center of squares with 250*250 meters dimensions, site amplification zoning map in the Gorgan region was provided, which was one of the information layers in developing of Gorgan earthquake scenario.

The polar oceans’ sea ice cover is a challenging geophysical target to map. Current state of practice helicopter-electromagnetic (HEM) ice thickness mapping is limited to 1D interpretation due to common procedures and systems that are mainly sensitive to layered structures. We present a new generation Multi-sensor, Airborne Sea Ice Explorer (MAiSIE) to overcome these limitations. As the actual sea ice structure is 3D and in parts heterogeneous, errors up to 50% are observed due to the common 1D approximation. With MAiSIE we present a new EM concept based on one multi frequency transmitter loop and a three component receiver coil triplet without bucking The small weight frees additional payload to include a line scanner (lidar) and high accuracy INS/dGPS. The 3D surface topography from the scanner with the EM data at from 500 Hz to 8 kHz, in x, y, and z direction, will increase the accuracy of HEM derived pressure ridge geometry significantly. Experience from two field campaigns shows the proof-of-concept with acceptable sensor drift and receiver sensitivity. The preliminary 20 ppm noise level @ 4.1 kHz is sufficient to map level ice thickness with 10 cm precision for sensor altitudes below 13 m.

The seismic method is able to produce highly accurate images of the Earth’s subsurface. Having such detail is not only an important factor in mining, but also in civil engineering. Bauxite exploration attracts both government and industrialists to invest in it because of the high percentage of aluminum present. The economic importance of extracting aluminum from bauxite encouraged us to take this challenge; to image bauxite layers by using a high-resolution seismic reflection method at Al Qassim, Saudi Arabia. Since the subsurface structure of the area is complex, this high-resolution reflection method was carried out along a 2D line with geophone and source interval, with settings at 5 m. The result for the seismic section shows that the depth and thickness of the bauxite layer varied between 20 to 34 m, and 3 to 7 m respectively. In addition, the bauxite layer was sandwiched between clay layers. In order to achieve an even more precise depth than presented by seismic section alone, we tied the drilled wells to the seismic data and we accomplished a well match with an approximation error of 1-2 m, which may have been caused by the upper clay layer or by very shallow loose subsurface material. The seismic method thus applied shows the ability to detect significant details within the near surface of the earth, and is considered more cost- effective than only drilled wells.

We investigate an active rock slide in Western Norway with ground- and airborne resistivity mapping to ultimately find weakness zones & sliding planes embedded in crystalline bedrock. The study area comprises phyllite, a low grade metamorphic rock type that tends to be reworked to clay in disturbed zones. Mapping these electrically conductive clay zones was the aim of the survey. GPS measurements over the last 5 years indicate that precipitation drives rock slide movements. The role of ground water is thus a crucial factor to investigate for risk assessment in the area.

Based on a successful airborne electromagnetic (AEM) demonstration survey, we conducted a total of 1.600 profile meters of ground resistivity (ERT) measurements to confirm AEM anomalies, to gain precise 2D geometries and to link conductivity anomalies with geology.

All resistivity results confirm AEM anomalies and refine their lateral extent. In the East we find consistency between a strong conductor, dipping sub horizontal SW with an outcropping thrust fault, separating phyllite and gneiss. In the West a conductor dipping steeply NNW seems to be fed by surface water and may represent a formerly unknown sliding plane. While ERT and AEM anomaly shapes generally agree within their mutual resolution limitations, the resistivity values significantly deviate. It remains unclear whether anisotropy or strong 3D artefacts cause this disagreement.

Comparing AEM data from different systems is always an interesting exercise. Differences, some minor, some major, are almost always observed. Some are caused by system characteristics while others arise in the interpretation, including by settings employed in inversion. In this paper differences resulting from varying regularization parameters, specifically those associated with vertical constraints, when inverting are examined with respect to the detail resolved in transported sediments. These sediments are host to sedimentary uranium mineralisation in the Frome Embayment of South Australia. Subtle changes in ground conductivity linked to changes in the character of cover has significance for a variety of reasons, including the definition of layers or boundaries that could be employed in geochemical sampling as part of an exploration programme, or for defining aquifers, their character, and groundwater they contain. Hence an understanding of approaches to better resolve subsurface conductivity variation is important.

Coincident lines of TEMPEST and SkyTEM data along with induction conductivity logs have made it possible to make direct comparisons of inversion results. Individual soundings of AEM data have been inverted and the re- sults compared against borehole conductivity logs to esta- blish appropriate inversion settings. This has also been extended to a flight line of data. Borehole lithological logs have been used to verify that the optimisation of the vertical constraints resulted in improved conductivity- depth sections for TEMPEST AEM data acquired for both fine and regional-scale studies. This study confirms the importance of carefully considering the optimisation of inversion parameters for a particular survey.

Reversible fluid flow within low aspect ratio cracks is expected to cause seismic velocities in hard rock to be strongly frequency dependent. Experimental measurements are necessary to constrain theoretical velocity dispersion models in order to allow comparisons between laboratory measurements at megahertz frequencies, sonic logging at kilohertz frequencies and in-situ exploration seismic at typically 10-300 Hz frequencies, but are rare due to the complexity of low frequency measurements on core samples. Quartzite samples from Cape Sorell, Australia and Alberta, Canada are thermally cracked to induce ~2% crack porosity with aspect ratio <0.01. The shear and Young’s moduli of the samples are measured at frequencies of 0.01-1 Hz and 1 MHz while the samples are dry, saturated with argon and saturated with water over effective pressures of 10-150 MPa. As anticipated, no dispersion is exhibited while the samples are dry. Similarly, no dispersion is observed while the samples are argon saturated as a result of the low viscosity and high compressibility of argon. Water saturation, however, causes significant dispersion in both the shear and Young’s moduli of the samples between the low and high frequency measurements.

ZTEM helicopter AFMAG electromagnetic and aeromagnetic surveys over the Ad Duwayhi IRGD gold deposit were designed to characterize the deposit signatures. Field data and 2D EM inversion results indicate the Ad Duwayhi intrusive centre features low magnetic susceptibilities and high resistivities that are consistent with the iron-depleted, quartz-sericite- carbonate alteration. Closer inspection of the ZTEM resistivity image suggests that the mineralized breccia zones represent weak resistivity lows within the larger resistive intrusion. The Ad Duwayhi gold porphyry lacks a visible low resistivity alteration halo that distinguishes IRGD’s from porphyry copper deposits. The combined aeromagnetic low and ZTEM resistivity high signatures might allow discrimination of other buried IRGD gold deposits regionally.

Helicopter AeroTEM, VTEM and ZTEM surveys were flown over the 501 zone in the McFauld’s Lake area, northern Ontario. The 501 zone is a relatively small VMS deposit that appears to respond well to all three active and passive airborne EM systems that have surveyed the property. Comparisons between these data sets and the geology are showcased using 1D-2D-3D EM inversion modeling.

Helicopter VTEM active source, ZTEM AFMAG passive source EM and aeromagnetic survey results are compared over the Nuqrah Sedex massive sulphide deposit in Western Arabian Shield of KSA. Field data and 1D-2D- inversions are used to show that all surveys map major controlling structures that host the Nuqrah deposits. VTEM directly detects more massive sulphide mineralized vent portions of Sedex orebodies; whereas ZTEM likely defining larger, less conductive and weakly mineralized distal portions of Sedex system. ZTEM also maps possible conductive down-dip extension of Nuqrah South Sedex below 750 m depths.

A continuous reservoir monitoring system has been installed for Shell, on a medium heavy-oil onshore field situated in the northeast of the Netherlands, to re-develop oil production by Gravity- Assisted Steam Drive. The challenge was to continuously monitor using seismic reflection the lateral and vertical expansion of the steam chest injected in the reservoir during production over more than a year.

The main problems for onshore time-lapse seismic are caused by near-surface variations between base and monitor surveys which affect the seismic signal coming from the reservoir. In our system, a set of permanent shallow buried sources and sensors has been installed below the weathering layer to both mitigate the near- surface variations and minimize the environmental footprint.

The very high sensitivity of our buried acquisition system allows us to track very small variations of the reservoir physical properties in both the spatial and calendar domains. The 4D reservoir attributes obtained from seismic monitoring fit the measurements made at observation, production, and injector wells (pressure, temperature, and oil/water production).

A daily 4D movie of the reservoir property changes allows us to propose a scenario that explains the unexpected behaviour of the production and confirms that the steam does not follow the expected path to the producer wells but rather a more complicated 3D path within the reservoir.