SummaryThis study is part of the groundwater investigations of the Ord Bonaparte plains in the East Kimberley region of Western Australia. A key project aim is to establish a spatial hydrostratigraphic framework to better understand the hydrogeology.To achieve this, AEM data, inverted using 1D SELMA model, were produced as conductivity sections and elevation grids. Interpretation of the AEM data, in conjunction with lithostratigraphic information from three petroleum wells and seven project bores, aided the mapping of hydrostratigraphic units of the Devonian to Permian sequence of the Bonaparte Basin. Mapping results show that the Carboniferous Weaber and Kushill Groups are dipping to the east-northeast and contain laterally continuous stacked aquifers. Within the strata, resistive signatures are associated with sandstone aquifers, slight to moderate conductors are mapped as fine textured aquitard, or as interbedded fine to coarse textured sediment forming semi-confining layers.A water table elevation map was constructed using surface NMR water content profile and machine learning approach to extrapolate across the study area. Using Archie’s Law, groundwater conductivity was predicted from AEM conductivity and porosity derived from borehole NMR measurements.
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.
A new approach for developing a 3D temperature map of the Australian continent is currently being developed that relies on combining available proxy data using high-performance computing and large continental-scale datasets. The new modelling approach brings together the current national-scale knowledge contained in datasets collected by Geoscience Australia and others, including AusMoho, OZTemp, OzSeebase, OZCHEM, surface temperature, the Surface Geology of Australia, sedimentary basins’ thermal conductivity and the National Gravity Map of Australia. Bringing together such a range of datasets provides a geoscientific basis by which to estimate temperature in regions where direct observations are not available. Furthermore, the performance of computing facilities, such as the National Computational Infrastructure, is enabling insights into the nature of Australia’s geothermal resources which had not been previously available. This should include developing an understanding of the errors involved in such a study through the quantification of uncertainties. Currently the new approach is being run as a pilot study however, initial results are encouraging. The pilot study has been able to reproduce many observed temperature trends without using direct bore-hole temperature observations as an input into the modelling process. Furthermore, a number of regional areas have now been identified which may warrant further study.
SummaryThe development of Northern Australia has been identified as a national priority, with water availability being fundamental to economic development. Surface water options are limited hence identification of new groundwater resources and water banking options is essential. Over the past four years, Geoscience Australia, in concert with State and Territory partners, has been involved in focussed groundwater investigations in 10 geographic areas as well as broader regional investigations (Figure 1). New data acquisition has included airborne electromagnetics (AEM); drilling (sonic, rotary mud, air core and diamond); slug and bore testing; ground geophysics (surface nuclear magnetic resonance, microgravity, passive seismic, seismic reflection and ground penetrating radar); borehole geophysics (induction, spectral gamma, nuclear magnetic resonance); hydrochemical and hydrodynamic analysis; age dating of water and landscape materials; and mapping (geomorphic, morphotectonic, regolith, geological and hydrological). These investigations inform hydrogeological assessments and water allocation planning.Overall, this multi-physics, inter-disciplinary approach has been critical in enabling the rapid identification and assessment of significant new potential fresh groundwater resources within tectonically inverted Palaeozoic sedimentary basins in the Fitzroy Basin (WA), Bonaparte Basin (WA-NT), Wiso Basin (NT), and Southern Georgina Basin (NT), and helped define the extents of a new groundwater resource for the town of Alice Springs (NT). Potential brackish and saline groundwater resources have also been identified in Cenozoic paleovalleys and Tertiary and Paleozoic Basins.
The Australian Government has recently provided Aus$100.5M to Geoscience Australia over 4 years (2016-2020) to manage the Exploring for the Future (EFTF) programme designed to increase investment in minerals, energy and groundwater resources, primarily in Northern Australia. The programme includes Aus$30.8M for groundwater-specific investigations, recognizing that there are major gaps in our knowledge of Northern Australia’s groundwater systems and resources. The groundwater component of the EFTF programme is focused on addressing these knowledge gaps, with the aim of underpinning future opportunities for irrigated agriculture, mineral and energy development, and community water supply. The groundwater programme will include identification and assessment of potential groundwater resources and water banking options in priority regional areas, while also analyzing the salinity risk (including seawater intrusion).To rapidly map, characterise and assess regional groundwater systems and resources in the data-poor ‘frontier’ areas of Northern Australia, a multi-physics, inter-disciplinary approach has been developed. The programme involves the initial use of temporal remote sensing ‘data cube’ technologies for surface hydrology and landscape mapping, and acquisition of airborne electromagnetic (AEM) and Ground Magnetic Resonance (GMR) datasets. This provides a framework for targeted investigations including passive seismic, microgravity and GPR; borehole geophysics (Induction, gamma and Nuclear Magnetic Resonance (NMR)); drilling and pump testing; hydrochemistry and geochronology (water, landscapes and geology); as well as soils, regolith and basin/bedrock geological, hydrogeological and structural mapping and modelling.This methodology has enabled rapid identification and assessment of potential groundwater resources, salinity and seawater intrusion hazards, and groundwater dependent ecosystems in several priority regions.
The delineation of near-surface (0-300m) hydrostratigraphy and tectonic features is essential for successful characterisation of groundwater systems and subsequent hydrogeological modeling. While most remote sensing of such systems is commonly achieved using high-resolution airborne electromagnetic data, validated by drilling data, and complemented by the use of terrain and multispectral data, it is shown that there is also a useful role for high-resolution magnetic survey data. Various filtering of gridded magnetic data, when image-enhanced and interrogated with other datasets, reveal features such as faults, dykes and other structures which may influence the distribution and movement of groundwater. One of the most useful enhancements of magnetic data is tilt, in which the range of data from ±90° acts as an automatic gain control to highlight both strong and weak source responses. While it is difficult to obtain accurate depth information from magnetic data, useful relative depth estimates can be obtained by using, for example, the Tilt-depth method, in which half the width between the ±45° contours of the tilt grid is a measure of the depth to source. These depth estimates can be calibrated, where possible, by comparison with other data. Dip directions of source contacts can be estimated by using the attitudes of multiscale edges, derived from the maxima of total horizontal derivative data. Examples of the utility of high-resolution magnetic data, in its complementary role, are presented for two groundwater assessment project areas - the Menindee Lakes region in western NSW and the Keep River catchment in the Northern Territory.
Summary Airborne electromagnetics (AEM) has successfully mapped and characterised groundwater systems in a range of landscapes and geological settings in the East Kimberley Region of north-western Australia. The AEM data enabled rapid imaging of key elements of hydrogeological systems in near-surface Cenozoic paleovalley, alluvial fan and colluvial sediments, and in underlying tectonically-inverted sedimentary basins. Rapid mapping and assessment of groundwater systems, MAR targets and salinity hazards involved the integration of AEM data with Ground Magnetic Resonance (GMR), seismic reflection, drilling and pump tests, borehole geophysics, soils, regolith, geological and structural mapping, and hydrogeological and hydrochemical investigations. AEM survey design was aided by the use of spatio-temporal analysis of Landsat data to identify areas of potential surface-groundwater interaction. A suite of equivalent 1D AEM inversion models produced comparable images of the sub-surface hydrostratigraphy and faults. However, 2.5D inversions produced different solutions in key locations. 3D inversions were subsequently performed, and drilling and tectonic analysis was used to assess all AEM inversion models. Recognising zones of structural complexity was important in the successful development of appropriate AEM inversion strategies and models. Overall, the success of groundwater system mapping has been due to the use of AEM within a broader, inter-disciplinary, multi-physics project framework.
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