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

Saturation in the vadose zone is known to reduce the ground penetrating radar (GPR) electromagnetic wave velocities. We examine the impact of increased water content in highly-permeable beach and dune systems on GPR velocities along coastal margin of Perth, Western Australia. We acquire repeat GPR transects in May and August before and after annual high rainfall periods. The assumption of exceedingly flat water table reflector permits us to estimated change in GPR velocity at successive dates. This change in velocity can be translated to an estimated change in water saturation via the Topp relationship which is an imperial mapping of water saturation to dielectric permittivity.

The presence of Neogene fault systems can have a significant impact on hydraulic connectivity of aquifers, juxtaposing otherwise disconnected aquifers, enhancing recharge and/or discharge or acting as barriers to flow and consequently compartmentalising groundwater resources. Previously, regional airborne electromagnetics (AEM) transects allied with groundwater investigations have pointed to the potential for localised compartmentalisation of the Daly River Basin groundwater systems. However, existing data is sparse, and equivocal.

In this context, the main aim of the Daly River Basin Project is to determine if compartmentalisation of the aquifers is a significant factor and thus should be explicitly considered in groundwater modelling and water allocation planning. The objectives of the project main goals of the project are to: (1) map Neogene faults through the use of airborne electromagnetic (AEM) and morphotectonic mapping, and (2) assess the permeability and transmissivity of mapped fault zones and their role in potential groundwater system compartmentalisation. Data acquisition includes 3325 line-kilometres of new AEM and airborne magnetics, ground (ground magnetic resonance (GMR)), and borehole geophysics, drilling, groundwater sampling and hydrochemical analysis, geomorphic and morphotectonics mapping. Hydrogeophysical, geomorphic and hydrogeological data will also be used to better understand groundwater-surface water connectivity and the potential for managed aquifer recharge schemes to replenish extracted groundwater resources. The outcomes of this project will inform decisions on water allocations and underpin effective and efficient groundwater use. This paper specifically reports on the ability of AEM and morphotectonics mapping to identify Neogene fault systems in the Daly River Basin.

Development of hydraulic conductive zones in crystalline rock can result from a wide range of geological conditions which include primary structures, post crystalline tectonics, fluid solution and movement within a developing and eroding regolith.

Crystalline rock areas mostly have low water resource potential due to inherent extremely low storage and water conductive properties. Therefore, fracture zones of high hydraulic conductivity have an important role in developing groundwater resources that may be distant or where it may be difficult to obtain alternative sources in these areas.

Mechanisms for development of open tension or pull-apart fractures in brittle rocks are similar to those involving development of mineralised veins. The same structural analytical techniques can be applied for water bearing structures.

Crystalline rock fracture zones can be amenable to rapid recharge through rainfall runoff. They are also significant in that they provide a mechanism for underdrainage through ‘delayed yield’ of surrounding or enclosing low conductive rocks such as saprock/saprolite, pelite and phyllite.

In addition to brittle rocks, open tension fracture zones of enhanced hydraulic conductivity may also occur in more fissile pelitic rocks such as slate and phyllite. These conductive zones are often associated with crestal zones of folds, strike deviations produced by conjugate shears and fracture zones discordant with layering and foliation. The development of conjugate joint sets in a region frequently provide a significant basis for this type of fracture analyses.

This presentation provides examples of water supplies developed from crystalline rock structures in a range of geological and earth environments.

A prominent TE and TM mode split is observed in magnetotelluric (MT) data below 0.5 Hz collected in the Perth Basin over the Harvey Ridge, Western Australia. We investigate the causes of mode splitting and consider implications on inversion of the MT data to subsurface electrical conductivity distribution. Twenty-five broad-band MT stations were acquired and remote reference processing was completed to arrive at a data set located midway between the Darling Fault and the Indian Ocean. We used forward modelling to test our strong suspicion that the Indian Ocean, Darling fault and architecture of the Granitic Basement were indeed the major contributors to mode splitting that we observed. Forward modelling of synthetic data was completed for comparison with the Harvey MT data. We were surprised at the match between synthetic and field data given the simplicity of the forward model and the considerable lateral distance between the MT soundings and the Indian Ocean or Darling fault. We were then able to make significant improvements to the MT inversion outcome by introducing a large scale geo-electrical architecture as the seed model for inversion. Our work demonstrates that large scale geo-electrical contrasts at considerable lateral distance from an MT transect, or the target zone need to be systematically introduced to the inversion if a quality outcome is to be achieved.

In the Fitzroy Basin of Western Australia, both ground and borehole Nuclear Magnetic Resonance (NMR) techniques have been applied during a groundwater prospectivity assessment of the Cenozoic sediments, and the Palaeozoic and Mesozoic sandstone aquifers. Ground magnetic resonance (GMR) data was acquired at ten sites from the within the basin and the data was inverted to obtain estimates of the one-dimensional water content for the top 100m. Where these sites were co-located with boreholes, the results were consistent with inverted borehole NMR data and other litho-stratigraphic information although with a reduced horizontal resolution.

Both the GMR and borehole data suggest that the Palaeozoic Grant Group and Poole Sandstone have high water content and have the potential to be highly productive aquifers. Furthermore GMR can be used estimate the depth to water table for unconfined aquifer, using 5 volume % as the threshold for saturated zone.

Neogene fault systems are increasingly recognised as an important control on hydraulic connectivity in some of Australia’s energy rich basins. However, accurate delineation of these faults systems is challenging and expensive. In this context, the main objective of the Exploring for the Future (EFTF) Surat-Galilee Basin (Phase 1) Project is to test novel methods for more cost-effective mapping of Neogene fault systems in the Coal Seam Gas (CSG) basins of eastern Australia. Methods assessed in this project include morphotectonic mapping using temporal remote sensing data and high-resolution terrain mapping techniques, airborne electromagnetics (AEM), and the use of earthquake databases to inform active tectonic and geomechanical analysis.

The project is funded by Geoscience Australia (GA) as part of its EFTF Programme, and is focussed on exemplar areas in the Surat and Galilee Basins where Neogene fault activity has been interpreted on high-resolution 2D and 3D seismic reflection surveys. This paper reports on the use of airborne electromagnetics (AEM) for detecting near-surface (<50-150m) Neogene faults in both basins. Approximately 4,500 line km of AEM data were acquired in a number of smaller acquisition blocks where Neogene faults had previously been identified. The AEM inversion results are compared with interpretation of seismic reflection data, morphotectonic mapping, and other hydrogeological and tectonic/geomechanical data. The utility of AEM to map the broader hydrogeological system in these basins, including groundwater-surface water connectivity (springs and rivers), is also assessed.

Following the 2016 publication of volume 1 of the Onshore Basin Inventory: the McArthur, South Nicholson, Georgina, Wiso, Amadeus, Warburton, Cooper and Galilee basins, central Australia (Carr et al, 2016); Geoscience Australia is continuing to provide a concise inventory of available data and geological knowledge of Australia’s onshore basins. Three new basins, the Canning, Officer and Perth basins expand on this work (Hashimoto et al., in press).

Seismic integration has been a successful accessory in every data interpretation project. For shale gas exploration design, development and implementation, high-resolution seismic data are necessitated. In this context, every exploration project needs multi-disciplinary datasets and their integration that can minimize the ambiguity of the interpretative outcomes. What are the integrated solutions for imaging and interpreting shale gas and how do they impact our shale prospect business? How do we organize and standardize our integrated workflows to address issues of exploration, field development, including drilling campaigns of the unconventional reservoirs? So far, the conventional reservoirs of many worldwide basins did produce even without integrated workflows. With the increase in intricacy in structural and stratigraphic settings, in particular with the fractured shale environments, exploration and field development plans have become multifaceted, complicating the field operations. How do we take on the exploration, development and drilling campaign decisions using the integrated seismic solutions? How do we suggest the “integrated solutions” to our valued operators and service providers? Why are the conventional technologies failures and setbacks? How can we guide and recommend the petroleum companies on appropriate technologies and the reserve computations in shale environments? We come up with an “Integrated Seismic” (IS) strategy, addressing the issues and challenges. The applicability and feasibility of IS in various exploration projects including their execution and implementation in worldwide shale gas basins are discussed. IS has been playing a vital role, making huge impacts on the integrated interpretation projects, especially during prospect identification and risk evaluation stages.

The eigenvalues of the gravity gradient tensor can be expressed as functions of two parameters: a magnitude and a phase. The decomposition gives physical meaning to the eigenvalues: the magnitude measures the amount of curvature and the phase is related to the type of source. Their understanding allows to propose new quantities to interpret. As an example, a modified phase eigenvalue offers the interpreter an enhanced version of the vertical gravity gradient which is demonstrated with model data and applied to FALCON airborne gravity gradiometer data from the Perth Basin, Australia

In the application of electroprospecting for mineral exploration, there are few clearly observed trends based on the development of electroprospecting technologies, hardware, software and computer technologies aimed at: a) the increase of electroprospecting application in comparison with other EM methods; b) application of electroprospecting at all stages of the exploration cycle; c) the increase of application of induction electroprospecting methods and, first of all, these which are based on the study of the natural EM field of the Earth (NEMFE). A special role here is played by the method of Broadband Magnetovariational Profiling (BMVP).

Three stages in the application of electroprospecting are quite clearly distinguished: a) exploration for new mining provinces according to the distribution of resistivity in the Earth’s crust and upper mantle (the AusLAMP project, a revolutionary idea proposed by Australian scientists; deep MT, scale 1 : 5,000 000 - 1 : 1,000 000); b) exploration for large conductive ore bodies, areas with a prospecting survey square area of more than 100 km² by airborne geophysics, for areas with smaller size - 5-component AMT on a scale of 1 : 200,000 - 1 : 50,000; c) detailization and support of drilling operations, mapping of veins and dikes - 5-component AMT on the scale 1 : 20,000 - 1 : 5,000 in complex areas with induction and geometric soundings using control source if Induced Polarization is an exploration factor.

Buried valley aquifers, consisting of permeable sand and gravel deposits in eroded bedrock valleys, are important sources of groundwater supply in many regions of the United States and Canada.

Investigations of the Spiritwood aquifer in southern Manitoba by the Geological Survey of Canada and other workers, have demonstrated the value of helicopter time domain electromagnetic (HTEM) surveys in aquifer mapping and characterization using the contrasts between Quaternary glacio-lacustrine sand-gravels (high resistivity) that are relatively permeable and clay-tills (low resistivity) that are relatively impermeable, as well as the deeper, much less resistive Cretaceous Pierre Formation Shale basement rocks. This success provided the impetus for the North Dakota State Water Commission to fly a VTEM helicopter EM survey in the Jamestown, ND region in October, 2016.

The VTEM data collected over the Spiritwood-JT block allowed for geological mapping from near surface to depth, in spite of relatively weak resistivity contrasts (<10X). These data were inverted with a layered-earth algorithm to produce resistivity-depth models. These models were able to resolve the location and depths to the top and bottom of the Spiritwood aquifer throughout the central portion of the block providing more detailed pictures of the aquifer’s geometry. In addition to resolving the main aquifer as well as its deeper channels, the VTEM data and models highlighted several smaller, previously undiscovered aquifers that cross-cut/branch-off from the main Spiritwood channel. These are interpreted as probable transverse low-K barriers that were apparent from the existing test drilling and aquifer testing.

Mesozoic and Tertiary clastic and carbonate reservoirs are prolific producers of high quality liquid-rich gas onshore PNG. LNG projects are among the lowest cost and most profitable globally. Accordingly there has been a recent resurgence of petroleum exploration in PNG.

In 2015 Oil Search undertook a country-wide petroleum Common Risk Segment analysis that highlighted potential for giant new oil and gas fields of sufficient scale to support future LNG projects. It also concluded that 40 trillion cubic feet of gas plus 550 million barrels of oil resources remain to be found (representing approximately 60% of PNG’s total petroleum resource).

In 2016 Oil Search completed an ambitious integrated structural, stratigraphic, burial, maturation, migration, uplift and erosion model of PNG’s total petroleum system to quantify the locations for highly prospective under-explored regions.

Tectonic events at plate and basin scales were re-assessed and correlated within a new country-wide PNG Chrono-stratigraphy of regionally mappable sequences and flooding events, some of Global extent.

A Base Tertiary Mega-Sequence Boundary is mappable over the entire onshore to deepwater regions. 130 1D burial models combined with restored 2D structural and stratigraphic cross sections, have contributed to a new regional petroleum charge model of the Foldbelts, Foreland and Offshore regions.

It is concluded that petroleum was generated pre- foldbelt during Late Cretaceous times in interior PNG while petroleum is currently being generated at the present day mountain front.

A holistic 4D charge model explains why very young foldbelt traps are petroleum charged.

This study records 315 paleo-pockmarks with associated focused fluid flow pipes within the Jurassic and Triassic sediments over three study areas on the Exmouth Plateau, offshore Northwest Australia. Paleo-pockmarks are identified along a surface that represents the top of Jurassic sediments, while the fluid flow pipes extend into Triassic sediments from the base of these pockmarks. The pockmarks and pipes form in linear trends that are parallel to and laterally offset from the tops of extensional faults intersecting an interval from the top of Jurassic sediments into Triassic sediments, where they are seen to terminate. Bases of the fluid flow pipes are observed to intersect and terminate along these extensional faults within the Triassic sediments. The pockmarks and associated fluid flow pipes are interpreted to have formed when extensional faults developed that intersected an overpressured unit within Triassic sediments. This caused a localized reduction of lithostatic pressure along the overpressured sequence at the intersection which then acted as a focal point for fluid escape and vertical migration. The source of the fluid overpressure could not be confirmed in this study. The Triassic sequence is a known hydrocarbon source and 1D modelling shows that at the time of fluid flow and pockmark formation, these Triassic sediments were entering the hydrocarbon generation window. However, no evidence of hydrocarbons associated with the pockmarks has been observed. Our findings identify fluid migration pathways that are seal risks for hydrocarbon reservoirs, but could also potentially be fluid migration pathways that were previously untested.

Productivity of a well in an unconventional reservoir is governed by various static and dynamic reservoir characteristics. Many of these characteristics have proxies among pre and post stack seismic attributes that can be derived from Multiazimuth 3D Seismic Data. The task of a geoscientist in this kind of reservoir is to understand these proxies to predict production behaviour. Natural fracture density and azimuth, as well as horizontal stress azimuth are the key attributes that seismic can help predict. Seismic Velocity and Amplitude variations with azimuth can be used to predict fracture strike, relative fracture density and define potential structural sweet spots. Azimuthal data from a Multiazimuth 3D seismic survey in the Nappamerri Trough of Cooper Basin has been interpreted to estimate fracture intensity and orientation. Co-rendered structural maps are used to create stress maps for different interval of interest. Stress maps help to identify areas of higher anisotropy and areas of lower minimum horizontal stress and so facilitate optimised well placement. To test the geological significance of these maps, correlation of stress vectors against well Image log and cross dipole sonic data was completed. This ground truth validates the prediction of direction and distribution of reservoir fractures based on full azimuth seismic data in this area.

The FDEMS method was introduced in the former USSR at the turn of the 50s and 60s of the last century as an integral part of the triad of induction EM methods (MT, FDEMS, TDEM), which were actively developed in the 50s after the grand discoveries by A.N. Tikhonov and L. Cagniard. The method was not widely used, primarily due to lack of suitable hardware and software for data processing and interpretation. Nevertheless, FDEMS was actively developed in certain regions of Russia and Ukraine until the present days. Interest in the method is supported by the potentially high accuracy of mapping high-resistivity boundaries, since in the FDEMS method there is a direct relationship between the ratio (R / H) of the sounding spacing (R) to the depth (H) to the high-resistivity reference horizon pronounced by significant points of amplitude and phase frequency characteristics (curves). A number of successful FDEMS surveys were completed on the Ukrainian Shield and its slopes, Dnipro-Donetsk basin (Ukraine) and different parts of Russia and Uzbekistan which achieved positive results (1977-2000). To date, the capabilities of modern multifunction and multichannel equipment, software for processing and interpreting field data allows to realize to a large extent the prospective capabilities of the FDEMS method for high-precision mapping of boundaries in the geoelectric section and mapping of low-contrast objects.

The Pilgangoora Lithium-tantalum pegmatite deposit with a total resource of 156.3 Mt grading 1.25% Li2O and 128ppm Ta2O5, is a globally significant hard-rock lithium-tantalum deposit. The deposit is located in the East Pilbara Terrane of the northwest Pilbara Craton in Western Australia. The Northwest Pilbara Craton is one of the world’s major lithium-tanatlum provinces with large scale lithium-caesium-tantlum bearing pegmatites located at Mt Francisco, Wodgina, Pilgangoora and Strelley.

Pegmatites bearing columbite-tantalite at Mt. York were first described in government geological surveys in 1906. Subsequent interest in the pegmatites focussed on their tin and tantalum mineral potential, with small scale hardrock, eluvial and alluvial mining, chiefly in the period 1947-1978. Larger scale alluvial and eluvial mining of tin-tantalum was carried out over 1978-1982 and 1992-1996 by a number of junior companies. In May 2014, Pilbara Minerals acquired the Pilgangoora Project for its lithium potential and has since drilled over 1450 holes for approximately 120,000 metres.

The Pilgangoora pegmatite intrusions crop out in a well exposed greenstone belt, with little weathering at surface. Exploration drilling programs along with detailed geological mapping of the Pilgangoora tenement group has provided a better understanding of the geological setting of the fractionated pegmatite intrusions within the East Strelley greenstone belt. This work has led to the recognition of some valuable exploration criteria that may be applied locally to locate additional resources and, longer term, may be used more strategically to review other pegmatite fields across the Pilbara region.

Lightning strikes generate electromagnetic (EM) waves, known as sferics, which are used in passive Audio-Frequency Magnetotelluric (AMT) and Geomagnetic depth soundings (GDS). Global lightning networks detect sferics and catalogue the time and location of up to four million lightning strikes per day. In this research, we use lightning network data and model earth-ionosphere waveguide propagation to predict time of arrival, azimuth, and amplitude for each known sferic in our time series EM data.

Since conductors effectively rotate electromagnetic fields, we can in principle infer the location and geometry of local and regional structures by calculating the rotation of measured data from their predicted arrival azimuths.

Geological, geophysical and remote sensing data have been used in the northweast Capricorn Orogen to map crustal scale structures beneath Paleoproterozoic Basins that may have focused mineralising fluids. The interpretations were largely based on upwardly continued bouguer gravity and magnetic data, then tested using petrophysically constrained forward modelling techniques. The most likely interpretation for deep crustal component of the region was found to be the Bandee Seismic Provence modelled with a mafic petrophysical character. A small portion of the study area in the northern part of the study area was modelled as an extension of the Pilbara Craton with overlying Hamersley-Fortescue Groups. Various gravity lows observed in the data were tested to determine if they represented a sub-basin, granitoid intrusion or shallow batholith. The gravity lows were found to be most likely related to granitoid intrusions. One significant deep-crustal scale structure in the central-southern part of the study area can be related to a fault mapped at surface and from Landsat 8 data. The structure has had limited exploration along its extent. The integrated approached of mapping, including surface geological mapping, indicates potential carbonaceous sediments in the hangingwall of the southern major fault zone could be prospective for uranium and gold-silver mineralisation. The friable nature of the coarse grained sandstone of the Bresnahan Group, that un-conformably overlies the carbonaceous mudstone, indicates fluid flow interaction with the unconformity could have occurred which enhances the prospectivity for uranium.

The Bureau of Meteorology (BoM) to meet the role of compiling and delivering Australia’s water information under the conditions set out in the Federal Water Act 2007 developed the Australian Water Resource Information System (AWRIS) and the National Groundwater Information System (NGIS) to support AWRIS. Functionality of the NGIS relied on compiling state and territory groundwater databases.Completeness of the data contained in these databases was critical in facilitating data migration to the NGIS and groundwater bores in the Galilee Basin were identified as a priority target for addressing data gaps.

Published wire-line log interpretation information was used to create and map structure surfaces for the Galilee Basin. These structure surfaces were used to create a 3D stratigraphic framework to visualise the basin architecture. Assessment of the 3D stratigraphic framework, structure surfaces and wire-line log interpretations identified numerous inconsistencies with the established basin stratigraphy. This is partially attributed to the large number of interpretation sources, exploration relevance and an incomplete understanding of facies variability. Additional areas of concern that were also identified included inconsistent surface geology mapping and a poor understanding of regional lineaments.

To address these inconsistencies systematic reinterpretation of the published wire-line log data was undertaken to validate or reassign inconsistent existing stratigraphic interpretations in the Galilee Basin. The highest percentage of inconsistent interpretations was concentrated in the eastern Galilee Basin and this area was chosen as the priority focus area. Reinterpretation relied on utilising a suite of wire-line log data from multiple data sources that included stratigraphic drill holes, coal seam gas (CSG), oil and gas exploration drill holes and groundwater bores. The availability of gamma wire-line log data was the minimum data requirement.

Reinterpretation of the wireline log data has resulted in producing revised stratigraphic formation data for the tops of the Moolayember Formation/Base Eromanga Basin, Rewan Group, Dunda beds, Clematis Group, Bandanna Formation/Betts Creek beds, Colinlea Sandstone and Joe Joe Group. This revision has shifted some of these formation tops vertically by up to 300m in some instances leading to significant modification of some structure contour surfaces and the lateral extents of some formations. The Clematis Group, Dunda beds and Rewan Group have undergone the greatest level of modification.

Uncertainty over the internal architecture of the Galilee Basin has significant implications for understanding the hydrogeology of aquifer systems and springs in the basin. Reinterpretation by a single operator has assisted in removing some of this uncertainty and provided a consistent dataset of interpretations.