ASEG Extended Abstracts - 1st Australasian Exploration Geoscience Conference – Exploration Innovation Integration, 2018

800-2400 km long transcontinental paleovalleys straddle the modern landscape of Western Australia (WA). These valleys formed following emergence of the Canning Basin at the end of the Lower Cretaceous, and reached their greatest development during Eocene time. They owe their preservation to limited erosion/burial and to an overall drying climate since the Upper Cretaceous. They represent the largest network of inactive valleys visible at the Earth’s surface.

These valleys debouch at their downstream ends into well-dated depocentres and paleo-shorelines, which provide age constraints and firm milestones of their temporal and spatial evolution. Drainage network evolution and valley long profiles constrain the timing of long (~1000 km) to intermediate wavelength (~200 km) variations in uplift and subsidence rates over the continental interior. We use these data to decipher the respective contributions of regional tectonics and dynamic topography to the evolution of the Northwest Shelf. Upon emergence uplift determined the shape of the initial drainage that started to drain the emerging landmass. Later, a changing field of surface uplift triggered drainage rearrangements in the early Cenozoic. Rearrangement resulted in piecemeal rerouting of water and sediments towards the North West Shelf.

Increasing aridity during the Neogene contributed to the tectonic defeat of some of these rivers. We use the Badlands surface model developed by the Basin Genesis Hub to quantify sediment and water delivery to the North West Shelf during the lifespan of the drainage. Further, there is some debate regarding the chronology of aridification in the continental interior. We use the modelling to derive the first quantitative estimates of the water balance to see if numeric water balance assessments can reconcile discrepant sets of paleoclimatic proxies.

The Ohi nuclear power station is located at the northern Oshima Peninsula in the Wakasa Bay on the coast of Japan Sea, central Japan. The geology of the site of the power station is composed mainly of shales, diabases, gabbros and ultramafic rocks of the Palaeozoic Yakuno Ophiolite. Ultramafic rock is a key geology since fracture zones in the study area can be found only in the ultramafic bodies.

To map the distribution of ultramafic bodies, we conducted magnetic surveys on ground and at sea around Daibahama beach. A ground magnetic survey was carried out on a grid and along specified lines on a small peninsula and some reefs by using a proton magnetometer. A seaborne magnetic survey was also conducted by a small rubber boat on which a Cesium magnetometer was mounted. Both measured data were merged and IGRF residual magnetic anomalies were reduced onto a smoothed surface at an altitude of 2.5 m above ground and above sea level at sea assuming equivalent anomalies below the observation surface. 3D magnetic imaging has been applied to the magnetic anomalies and the resultant magnetic structure is generally associated with a dipping-dike by a previous 2D modelling. A reversely magnetized body was imaged with a seaward dip below the surface along the 2D profile but has a horizontal limitation. This means the magnetic imaging is helpful to reveal the three-dimensional subsurface structure of the area.

In the Howards East Aquifer (HEA) in Darwin’s Rural District, groundwater resources in a dolomitic and karstic aquifer system provide important water security for Darwin and a large horticultural industry. Previously (2011), a widely-spaced (550m) regional airborne electromagnetics (AEM) survey in this area mapped conductivity anomalies that were interpreted as potential zones of seawater intrusion (SWI) coincident with major fault zones. Subsequent drilling confirmed elevated groundwater salinities in some bores marginal to the main aquifer. It was recommended that more detailed investigations be undertaken to better define the SWI risk.

The Howards East Project is an inter-disciplinary study which focussed on delineating and characterising the present SWI interface and potential future hazards from sea water intrusion. The Project is funded by Geoscience Australia (GA) as part of the Exploring for the Future (EFTF) Programme. New data acquisition includes 2,096 line-kilometres of 100 m line-spaced AEM and airborne magnetics data, ground magnetic resonance (GMR), and borehole nuclear magnetic resonance (NMR) data, drilling and pump testing; and hydrochemistry. The main aims of this study are to: (1) delineate potential SWI zones; (2) quantify the porosity, permeability and transmissivity of the Koolpinyah-Coomalie Dolomite aquifer along potential fault zones (coincident with magnetic anomalies) and (3) identify other structural and/or sedimentological preferential flow paths or barriers to ingress.

This paper reports on: (1) initial AEM inversion results and spatio-temporal changes in groundwater quality arising since acquisition of previous AEM in 2011, and (2) the interplay between the sea water intrusion interface and structural/sedimentological flow paths/barriers.

The Middle Ordovician Stairway Sandstone consists of a succession of siliciclastic shallow marine sediments, stratigraphically positioned between the dark organic-rich siltstones of the Horn Valley Siltstone, and the regressive siltstones and shales of the overlying Stokes Siltstone, in the Amadeus Basin. The Stairway Sandstone is notable for containing early arandaspid fish fossils, and is a prospective reservoir for Larapinta Petroleum System hydrocarbons. The unit has not been directly dated, but a field sample from the uppermost Stairway Sandstone has yielded an abundant and well-preserved fauna, including micro-vertebrate and conodont fossils that enable correlation to high resolution international conodont biozonation schemes. Vertebrate microfossils represent three agnathan genera, Arandaspis, Porophoraspis and Sacabambaspis. Conodont species include Microzarkodina ozarkodella and Baltoniodus medius; index fossils that allow correlation to the upper subzone of the Eoplacognathus pseudoplanus Zone of the Middle Darriwillian. The conodont fauna also includes stratigraphically wide-ranging larapintine species, as well as endemic forms and new species. The abundance of the fauna, and the presence of Erraticodon, indicates sea-level rise at the time of the latest Stairway Sandstone deposition. The global Stein Lowstand event, represented by a hiatus at the top of the Horn Valley Siltstone and the subsequent shallow or aeolian influence over the lower and middle parts of the Stairway Sandstone, occurs at 463.71 ma, and the top of the E. pseudoplanus zone occurs at 462.52 ma (GTS2016). The intervening time constrains the end depositional age of potential reservoir sands of the Stairway Sandstone, and age of the earliest Gondwana fish fauna.

We present an updated resistivity model from inversion of the 09GA-GA1 deep magnetotelluric survey, also known as the Georgina-Arunta survey. The data were originally collected in 2009 under Geoscience Australia’s Onshore Energy Security Program, together with deep seismic reflection data along the same line. The magnetotelluric data comprise broadband and long-period data. The broadband data were originally processed to a bandwidth of 0.04 s to 100 s, but have been reprocessed yielding an extended bandwidth of 0.04 s to 1000 s, which improves the resolution of deeper (>20 km depth) structures. Inversions have been carried out using the ModEM 3D inversion code given that the data indicate the presence of 3D geoelectric structure. The updated resistivity model reveals that the Casey Inlier and Irindina Province are associated with high resistivities (>2000 Dm). In contrast, the Aileron Province, which underlies and surrounds the Irindina Province, is predominantly conductive (resistivities <50 Dm). The Georgina Basin is associated with low resistivities, as would be expected for a sedimentary basin, while the Amadeus Basin is associated with low resistivities in the southern part of the line (where it overlies the Casey Inlier), and higher resistivities further north.

Production or flow-back water from shale gas stimulation has been reported in the USA to contain high salinity, TDS and variable concentrations of potentially toxic metals such as uranium, barium, or lead. The shales of the Cooper Basin REM sequence have a high prospectively for unconventional gas. Water reactions of shale core samples were performed in mildly oxic conditions and at elevated temperature and pressure to investigate potential for metal mobilisation. A relatively higher concentration of lead, vanadium, chromium, zinc and copper, was measured in the Roseneath shale core, which on water reaction mobilized a higher concentration of dissolved uranium, cadmium, cobalt, chromium, zinc, copper and nickel. Mobilized metal concentrations were however generally <10% of the amount available in the core. Relatively higher concentrations of calcium, magnesium and sodium were mobilized from the Murteree shale. Mobilised uranium and barium however remained low. SEM-EDS indicated that the carbonates were most reactive, with dissolution creating porosity in the Roseneath shale. Fe-rich precipitates were also formed in both cases. We found the presence and type of carbonate and sulphide minerals have a strong control on water chemistry and generated acidity. When reacted with HCl, the Epsilon Formation sample showed strong corrosion of carbonates leaving pits, with no Fe-rich precipitates formed. Experimental fluid-rock interactions can give understanding and insights to the potential chemistry of flow back water which may be different from different shale formations.

Geomechanics helps us understand the life-cycle of a hydrocarbon reservoir and, in turn, impacts geophysical monitoring programs. A common geomechanical problem is to predict reservoir compaction or zones of abnormal pore pressure. These predictions mostly use simple empirical relations, but recently, the use of rock deformation models based on static poroelasticity are becoming the norm. These models require accurate values for the poroelastic parameters. We present a digital rock workflow to determine these poroelastic parameters which are difficult to extract from well-log or laboratory measurements. The drained pore modulus is determinant in the compaction problem. This modulus represents the ratio of pore volume change to confining pressure when the fluid pressure is constant. In laboratory experiments, bulk volume changes are accurately measured by sensors attached to the outer surface of the rock sample. In contrast, pore volume changes are notoriously difficult to measure because these changes need to quantify the pore boundary deformation. Hence, accurate measures of the drained pore modulus are challenging. We simulate static deformation experiments at the pore-scale utilizing digital rock images. We model an Ottawa F-42 sand pack obtained from X-ray micro-tomographic images. We stack two-dimensional micro-CT images to generate a three-dimensional F-42 sand pack sample. We extract a sub-volume from this sample for numerical simulation. We first segment the cropped sample consists of grains and pore spaces and then use the segmentation to generate a volumetric mesh. We compute the elastic, linear momentum balance in the structural domain (grains) and solve the system using the commercial software package ABAQUS. The network of grains (solid phase) is assumed elastic, isotropic, and homogeneous. We calculate the change in pore volume using a new post-processing algorithm, which allows us to compute the local changes in pore volume due to the applied load. This process yields an accurate drained pore modulus. We then use an alternative estimate of the drained pore modulus. We exploit its relation to the drained bulk modulus and the solid phase bulk modulus (i.e., Biot’s coefficient) using the digital rock workflow. Finally, we compare the drained pore modulus values obtained from these two independent analyses and find reasonable agreement.

Resolution plays a fundamental role in any quantitative image analysis. Higher resolution images contain more details for further analysis but trade-off encounters when resultant smaller sample size raised question on representativeness of the whole sample. Image acquisition time and cost are also major issues that high resolution images have to face. To identify maximum image resolution that can avoid these issues as well as can provide accurate results in calculating shape factors, we study images of quartz sand grains acquired with four different resolutions. We present a comprehensive processing technique that can effectively extract individual grains from a 3D micro-CT image. Then we calculate equivalent diameter, volume and surface area of the grains at different resolutions. For all four resolutions, volume of grains shows very little change in lower two resolutions and almost no change through higher three resolutions, minimum of which can be considered as optimum. On the other hand, surface area for all the grains shows increasing trend with increasing resolution, but different in gradient. This different increasing trend can be explained by the surface rugosities and whether the image resolution can be able to resolve those. The higher two resolutions can effectively resolve surface irregularities of most of the grains, which is evident by their similar values of calculated surface areas. Therefore, minimum of these two resolutions can be considered as optimum image resolution in calculating shape factors for the studied grains.

Understanding of compaction trends of elastic and hydraulic properties in anisotropic shales is crucial for exploration of energy resources, ecological disposal of nuclear waste, and hydrogeological applications. However, complexity of the natural shale mineralogy and lack of quality data available for analysis results in poor knowledge of these compaction trends.

Careful control over the shale mineralogy, pore fluid composition and applied stresses allows us to simulate the natural environments and acquire quality data on the properties of artificial shales. Here for the first time we present methodology and describe a setup that allows simultaneous acquisition of all five independent elastic constants and extremely low hydraulic permeability values of transversely isotropic artificial shale samples during mechanical compaction experiments (porosity decrease from 40% to 10%).

Hydraulic permeabilities of artificially compacted samples are comparable to the ones of natural shales. Permeability drops exponentially with compaction. Silt fraction and clay mineralogy are the two key parameters that are responsible for broad variations of permeability in shales with the same porosity. We provide analytical equations that allow calculating permeability if porosity and silt fraction are known.

Elastic constants of clay matrix exhibit positive linear trends with the porosity decrease. Small variations in clay mineralogy have a minor effect on absolute values of elastic coefficients or anisotropy but lead to noticeable increase of the compressional (VP) to shear (VS) velocities ratio at the same porosity. Finally, strong correlations (R² above 0.95) of the hydraulic permeability with acoustic impedance and VP/V S ratio are observed for all the prepared samples.

Distributed Acoustic Sensing (DAS) uses standard telecommunication fibre optic cables to detect acoustic and seismic signals. The technique utilises optical time-domain reflectometry; a “light-box” measures the light backscattered from a series of laser pulses emitted into the fibre. As seismic waves impinge on the cable, the fibre is strained, causing variations in the time taken for the backscattered light to travel back up the fibre. The acoustic signal can then be reconstructed by analysing phase differences in the backscattered light. DAS is especially suited for VSP applications, as it offers significant efficiency advantages when compared to conventional borehole acoustic sensors. Conventional VSP surveys usually take an extended period to acquire as the tools need to be placed in multiple positions in the well to record data. With DAS, the complete fibre is a sensor, and thus all levels are acquired simultaneously, reducing the cost considerably.

In this work, we compare the results of acquiring a VSP survey using a conventional 3-component geophone tool, a cemented fibre-optic cable, and a suspended fibre-optic cable deployed loosely in the well. The VSP data was acquired at both near and far offset points. Results show that the cemented DAS approached the quality of a conventional geophone VSP survey. The suspended DAS data had smaller SNR, while still clearly acquiring up-going and down-going PP-wave reflections.

Carbon isotope fingerprinting has been widely used to study gas origin, maturity and gas-source correlations. However, natural gas accumulation in gas reservoirs can be affected by secondary alteration processes. In contrast, palaeo gases trapped in fluid inclusions (FIs) are free of any secondary alterations that may have occurred in the reservoir. FIs are normally less than 10 um in diameter, hence the gases trapped are at trace level amounts. An online crushing-trapping system has been developed in this study which enabled carbon isotope analyses of hydrocarbon gases which are normally in low concentrations. The crushing-trapping system mainly comprises of a gas-tight crusher and a gas concentrator interface module. The micro-trap is a critical part of the gas concentrator as it collects and concentrates all the released FI gases which results in sharp chromatographic peaks. This novel design is very sensitive, making it an increased challenge to obtain an acceptable blank before running samples. A clean blank is very important for such trace-level gas analysis. System blank results show that there are no hydrocarbon gases but trace amounts of CO2 (20 mV) detected in the blank. These trace amounts of CO2 in the blank have no influence on the carbon isotope calculation. It was found that no isotope fractionation was attributable to the cryo-trapping and subsequent thermal release from the trap but there is fractionation due to re-absorption onto the freshly crushed rock matrix (quartz or calcite) powder.Compound specific carbon isotope analysis of hydrocarbon gases (C1-C5 except M-C4) and CO2 released from a FI sample from the Cooper-Eromanga Basin was achieved for the first time as a proof of concept of the technique. Preliminary research on FI gases has been carried out in the Browse Basin, Australia.

The interior of Australia plays host to a series of vast sedimentary basins spanning c. 2.5 billion years of the island continents geological history. Many of these basins contain significant reserves of both conventional and unconventional hydrocarbons. In addition to being active offshore, Santos Ltd has a long history of hydrocarbon exploration (generally as Operator) in several of the onshore basins, which notably include the Bowen, Gunnedah, Cooper, Amadeus and McArthur Basins. Frontier exploration involves various regional geological studies, these being geared towards deriving an early assessment of hydrocarbon potential and directing the geographical focus of future exploration work. Due to the general lack of data in the early exploration phase, much effort is expended in maximising the interrogation and understanding of all available open source and proprietary datasets. These typically include surface geology, surface elevation, surface vegetation, Landsat, gravity, magnetics, radiometry, existing seismic and existing boreholes (including water bores). The key to extracting every ounce of useful geological information from these data is through data integration and co-visualisation. To this end, Santos has developed a tried-and-tested regional exploration workflow, which often involves some novel visualisation techniques (e.g. use of 3D anaglyphs). This presentation will include discussion of basic workflows, the various data types and principles of data integration and interpretation, illustrated with numerous real-world examples from Santos’ extensive exploration experience in several of the aforementioned basins.

Conventionally, there has been an entrenched aversion to explore oil and gas in regions with volcanic geology. In other words, petroleum systems affected by igneous geology have not been considered with substantial oil and gas discoveries. However, the presence of volcanics is well known in many petroleum basins although not published in great details (including the North West Shelf of Australia), and there has been an increase in the number of hydrocarbon discoveries in volcanic basins worldwide.

On the other hand, there has been volcanics geology factor associated with unsuccessful exploration wells. In the NWS of Australia, explorers care about the evidences as several unsuccessful wells, widely distributed in the area, have penetrated volcanics within the Triassic-Jurassic succession, which indicates a significant exploration risk.

A primary purpose in writing this article was to illustrate that the presence of volcanics and their impacts on sedimentary rocks may lead to complex overprints for oil and gas exploration. Several 2D and 3D seismic datasets in addition to well information, from Barcoo Sub-basin of the NWS of Australia, were analysed and interpreted to demonstrate the fact that features we sometimes get with volcanics can be very misleading for hydrocarbon exploration.

Volcanic rocks within the Triassic-Jurassic succession at the NWS of Australia are not considered favourable conditions for hydrocarbon accumulation. It is therefore important to develop an approach to better understand their impact on petroleum system and derisk prospects for exploration.

We obtain the basic parameters of the rocks of Qingshankou formation by performing the rock uniaxial and triaxial compression mechanics experiments. Different brittleness indexes are computed and we select the best brittleness index of B2 (E/u, Young’s modulus / Poisson’s ratio) to evaluate rock brittleness characteristics. The coefficient of brittle stress drop is introduced to evaluate rock brittleness characteristics which coincide with the selected brittleness index. The relationships between brittleness indexes and rock parameters such as elastic parameters, mineral components and reservoir physical properties (porosity, and density) are analyzed. Results show that E and u are the good indicators of rock brittleness, while shale content has no obviously influence on the elastic parameters. Quartz and carbonate minerals are considered as brittle components for evaluating rock brittleness. There is a good correlation between the brittleness index B2 and reservoir porosity, which is important for analyzing rock brittleness characteristics in the study area.

Geoscience data including seismic, well log, sensor and core measurements are fundamental for Petroleum exploration. Due to recent advancements in sensor and computer technologies, the volume of this data is constantly increasing. Having a unified repository of this data of various types, structure and complexity (Big Data) is crucial for maintaining data integrity.

This study addresses petroleum exploration data integrity issues. Current trends in data management technologies and current data practices in Petroleum Geoscience are explored and a practical data management solution to facilitate data access, storage and sharing is recommended. A prototype of a well log database was developed to demonstrate the advantage of having a unified repository of downloaded and sanitized data for multiple users. In comparison with current practices, such a database will prevent duplicate downloads from public websites by petro physicists and make data use more efficient within a particular organisation. The prototype was developed using cloud-based technology and the PAWSEY supercomputing facility (a joint venture of CSIRO with Western Australian universities) for storing both the raw (.las and .DLIS files.) and the sanitized well log datasets from Bonaparte Basin. PostgreSQL database was used to store the sanitized well log data, metadata and links to raw data. PostgreSQL architecture was selected for its ability to support advanced data types (arrays, JSON etc.), plug in to languages like Python, and link to PostGIS, a spatial database extender. A web-based graphical user interface was developed to view, upload and download well log data. In addition meaningful metadata standards were established in collaboration with expert petro physicists.

Understanding of shales elastic properties behaviour with saturation changes is important for geological storage of nuclear waste, CO2 sequestration as well as for development of conventional and unconventional shale oil and gas reservoirs. Existing data describing effects of saturation on elastic properties of shales are sparse and contradictory. To improve understanding of the effects of changing water content on elastic properties in shales, we conduct an experimental study on Opalinus shale samples. We measure vertical and horizontal ultrasonic P- and S-wave velocities of the same set of samples with controlled water content. The measured velocities are used to calculate components of elastic stiffness tensor in the shale at different saturations assuming its vertical transverse isotropy. Obtained results show increasing C11 and decreasing C33 with drying of the samples. Moreover, we observe 80% and 60% increase of shear moduli C44 and C66, respectively, with reduction of the water content from 5.5% weight in the preserved state to 0.3%. Conventional rock physics models are not designed to explain the observed dynamics. Here we perform a theoretical investigation of the influence on the shale moduli of following factors: (1) mechanical softening of the rock with the decrease of water saturation; (2) shrinkage of clay leading to reduction of porosity; (3) chemical hardening of clay particles; and (4) enhancing stiffness of contacts due to removing of water between clay particles.

Stage 2C of the Otway project aims to detect a small injection of CCh-rich mixture into a saline aquifer, verify stabilisation of the injection and evaluate the detectability threshold of CO2 achievable by surface seismic. Over the past three years, we have produced five vintages of high-quality 4D seismic data showing the evolution of the 15,000 tonnes of injected scCO2/CH4 gas mixture into the saline aquifer at 1500 m depth. The time-lapse seismic processing workflow was built based on the findings from a synthetic feasibility study and processing of the baseline dataset. Through this workflow we processed the time-lapse data which allowed monitoring of small incremental injections (about 5 000 tonnes each). Here we elaborate on effect of various processing routines on the quality of 4D image, namely, amplitude restoration, prestack cross-equalization and imaging. We aim at preservation and restoration of time-lapse signal and suppression of time-lapse noise. We evaluate the results of the processing efforts in post-stack domain through estimates of 4D signal-to-noise ratio in vicinity of the injection interval. The usefulness of individual processing routines for improvement of time-lapse signal cannot be established independently from other routines in the same workflow. Surprisingly, images with pre-stack AGC applied have consistently higher time-lapse signal-to-noise ratio compared to images produced without it. Improvement of the resolution and appearance of 3D images does not guarantee increase of time-lapse signal-to-noise ratio.

Rain has long been a problem for land seismic surveys. I measured the seismic signature of rainfall using both water dripped from height using a pipette, and natural rain in Winchester, England, over a three month period. My results showed that rain noise is concentrated at frequencies above 80 Hz with a detectable range of less than 1 m. Drops of water landing directly on a geophone result in events with amplitudes nearly 30 times larger than those landing next to the geophone. Items placed on the surface of the ground, such as cables, absorb the energy of the impact and reduce the level of the resulting seismic noise. Burying geophones results in attenuation of rain noise by between 7.7 and 8.6 dB/0.1 m. But, given the effort required to bury geophones, it is likely that data processing algorithms, or the placement of vibration absorbent matting, are likely to be the preferred strategies for dealing with noise.

Land seismic surveys are most often acquired in remote areas, thus the predominant noise source is often the wind. In urban areas, however, noise sources abound, including electrical cables, mechanical equipment, aircraft, and traffic. We recorded seismic data continuously over three days at a test site located in suburban Perth, Western Australia (32° 0’ 40”S, 115° 53’ 22”E). and found that the highest amplitude noise was mechanical (centred on 75 Hz), but the most consistent noise was traffic related (10-25 Hz). Electrical noise was identified but given its moderate amplitude and relatively consistent frequency it should be easily removed in processing. Aircraft flying over the test site resulted in moderately high level of noise with a wide bandwidth (30-200 Hz) but the noise generally lasted only a minute.

Based on these results we recommend that: acquisition should be carried out during the late night/early morning; receiver locations should be chosen with care to avoid sources of noise; analogue cabling should be as short as possible to avoid electrical noise; real-time QC should be in place to identify short-duration high-amplitude noise periods during which acquisition should cease.