Onshore Energy Security Program Research Articles

Fractal scaling of Airborne EM data: an indicator of lithology and fluid connection?

Electrically conducting fluids within the subsurface account for a large portion of the Earth?s electrical response and therefore mapping of groundwater and regions of high salinity can be undertaken using Airborne Electromagnetic (AEM) methods. While the majority of nearsurface conduction is generally due to fluids in porous or fractured media, there is always an ambiguity in determining the cause of the electrical response. For example, clay layers and mineralization may also significantly enhance conduction. Analysis of how the Earth?s resistivity varies with spatial-wavelength through determining the associated fractal dimension is proposed as an additional tool that can assist in differentiating anomalies of similar magnitude but dissimilar sources. AEM, using the TEMPEST and VTEM systems, has recently been collected by Geoscience Australia through the Onshore Energy Security Program over the Pine Creek region in Northern Territory. Approximately 21,000 line-km of TEMPEST and 9000 line-km of VTEM were collected. A moving window is passed across each line of data creating small overlapping subsets on which the fractal dimension is calculated. These values are then gridded to create a map of the fractal dimension of the Pine Creek AEM survey data. Such maps are compared with existing geological and hydrological information allowing for inferences to be made on the differing sources of anomalism.

Acquisition and processing of seismic reflection, refraction and magnetotelluric data, northern Eyre Peninsula, Gawler Craton

SUMMARY In 2008 Geoscience Australia acquired regional seismic reflection, wide-angle refraction/reflection, gravity, and magnetotelluric (MT) data along a 253km east-west transect across northern Eyre Peninsula, Gawler Craton in South Australia as part of the Australian Government’s Onshore Energy Security Program (OESP). These datasets provide complementary information on the crustal architecture and evolution of this part of the Gawler Craton. Twenty three Earth Data recorders were deployed along the reflection transect as a fixed, wide-angle recording array, with 5 and 10 km interval spacing, using threecomponent seismometers. The high quality data of up to 60-70 km offsets were collected using vibroseis sources. MT data were acquired at 40 broadband and 12 long period sites along the reflection transect. This paper presents acquisition parameters and processing steps for these datasets, to highlight their advantages and limitations, and improve the quality of the geological interpretation over the Gawler Craton.

Understanding the architecture and petroleum potential of Australia?s onshore sedimentary basins with deep seismic reflection data

The Onshore Energy Security Program, funded by the Australian Government and conducted by Geoscience Australia, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Interpretation of the new seismic data from these onshore basins, focusing on overall basin geometry, internal sequence stratigraphy and petroleum potential, will be presented here. This will provide the basis for ongoing work which will aim to assess the petroleum potential of these basins.

A new automated method to determine depth to magnetic basement ? the Gawler Craton depth to basement map

A new method has been developed to determine the depth to magnetic basement. This method uses an efficient automated approach that produces depth estimates via inverse modelling the azimuthally averaged log of the power spectra of gridded airborne magnetic data. The model consists of a horizontal slab possessing band limited fractal magnetisation. The sensitivity and uncertainty of the depth estimates were analysed based on the magnetic slab?s fractal property using Bayesian analysis via Markov chain Monte Carlo and Jeffery?s prior. A sliding window technique with an appropriate amount of overlap to the adjacent data window has been applied to a magnetic grid of the Gawler Craton region. The window size selected was optimised to produce depth estimates for relatively shallow magnetic sources due to the relatively thin cover material in the region The resulting depth estimates were combined with drill-hole data and seismic data and then gridded using the minimum curvature technique to produce a depth to basement map of the region. The new automated depth method was developed within Geoscience Australia?s Geodynamic Framework Project, part of the Onshore Energy Security Program.

The conductivity structure of the Georgina-Arunta region from magnetotelluric data

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 Ωm). In contrast, the Aileron Province, which underlies and surrounds the Irindina Province, is predominantly conductive (resistivities <50 Ωm). 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.

From Surface to Mantle; An Overview of Downloadable MT Data from South Australia

Magnetotelluric (MT) techniques measure natural time variations of the Earth?s magnetic and electric fields to infer subsurface electrical conductivity structure. Data are collected over a range of frequencies, providing insights into how this structure varies with depth. Depending on the Earth conductivity and frequencies used, information can be obtained from the near surface to depths of hundreds of kilometres. MT surveying has been used in a wide variety of geological scenarios, from investigations of continental-scale structures to mineral and geothermal exploration, and in the search for ground-water, and many such surveys have now been undertaken in South Australia. Recently, surveys have been conducted by Geoscience Australia (GA) under the Australian Government?s Onshore Energy Security Program (OESP) along deep crustal seismic reflection transects, in part in collaboration with the University of Adelaide (UA), the Geological Survey of South Australia, Primary Industry and Resources South Australia (GSSA, PIRSA) and the Australian National Seismic Imaging Resource (ANSIR) across the Gawler Craton and Curnamona Province. Given the wide range of applications for MT data, it is proposed to deliver these data online as industry-standard electrical data interchange (EDI) files, starting with the most modern datasets. This paper presents an overview of the MT data and reports presently available for South Australia. All MT data are available for download online from the South Australian Resources Information Geoserver (SARIG), and both seismic and MT data acquired by GA and collaborators under the OESP are available for download from the GA web site.

Magnetotelluric investigation complement multi-disciplinary geophysical data

As part of the Australian Government?s Onshore Energy Security Program, Geoscience Australia has acquired magnetotelluric data along 12 deep crustal seismic reflection transects in Australia. The magnetotelluric projects, which total more than 640 stations over 3700 km in distance, have been undertaken by Geoscience Australia in collaboration with state and territory geoscience agencies. Broadband and long period MT data have been acquired for investigating geological structures from the shallow surface to upper mantle. These data, along with the deep seismic reflection, magnetic, gravity and geological data form the basis for multi-disciplinary investigations of crustal architecture, and energy and mineral potential, providing precompetitive information to industry and researchers.

New government geophysics from the Onshore Energy Security Program

SUMMARY As part of the recently completed Onshore Energy Security Program, Geoscience Australia has delivered new types of pre-competitive data to as well as the more familiar government pre-competitive data types such as aeromagnetics. These new data provide industry with additional information for assessing the geological prospectivity of a region and making targeting decisions. The visionary AWAGS continental airborne magnetic and radiometric survey enabled the first ever national merging of all radiometric surveys to produce the Radiometric Map of Australia. The rigorously calibrated data supports quantitative normalisation of uranium anomalies against rock-type, and hence identification of zones of uranium enrichment, at either a prospect or regional scale. Geoscience Australia also undertook three large AEM surveys (>50,000km2) to map regional scale geological structures important for uranium deposition. These surveys were effective in imaging depth of regolith, geological unconformities, shale units and fault zones. Often these features are not apparent in regional magnetic or gravity data. MT data are now acquired along all deep crustal seismic transects to image the deep conductivity structure. These data are highly complementary to the structural information interpreted from the seismic sections. MT can also detect conductivity features in the non-reflective crust below the Moho.

The Frome airborne electromagnetic survey, South Australia

The Frome airborne electromagnetic (AEM) survey is the largest of three regional AEM surveys flown under the 5-year Onshore Energy Security Program (OESP) by Geoscience Australia (GA). The aim of the survey is to reduce risk and stimulate exploration investment for uranium by providing reliable pre-competitive data. The Frome AEM survey was flown between 22 May and 2 November 2010, is approximately 95 450 km2 in area and collected 32 317 line km of new data at an average flying height of 100 m. The Frome AEM survey covers the Marree (pt), Callabonna (pt), Copley (pt), Frome (pt), Parachilna (pt), Curnamona, Olary and Chowilla (pt) 1:250 000 standard map sheets in South Australia and was flown largely at 2.5 km line spacing, with the northern portion flown at 5 km line spacing. GA partnered with, the Department of Primary Industries and Resources South Australia and an industry consortium. The survey results indicate a depth of investigation (DOI - depth of reliable signal penetration) of up to 400 m in areas of thin cover and resistive basement (e.g., Adelaidean rocks in the Olary Ranges). In Cenozoic ? Mesozoic sediments in the Frome Embayment and the Murray Basin the DOI is up to 100-150 m. A range of under-cover features are revealed, including (but not limited to): extensions to known palaeovalley networks in the Frome Embayment; the under-cover extent of the Benagerie Ridge; regional faults in the Frome Embayment and Murray Basin; folded and faulted Neoproterozoic rocks in the Adelaide Fold Belt; Cenozoic ? Mesozoic stratigraphy in the Frome Embayment; neotectonic offsets in the Lake Eyre Basin; conductive Neoproterozoic rocks associated with copper-gold mineralisation; and, coal-bearing structures in the Leigh Creek area, as well as groundwater features.

Key features of new deep seismic reflection lines across frontier sedimentary basins in central Australia: the Arckaringa, Officer, Amadeus and Georgina Basins

The Onshore Energy Security Program, funded by the Australian Government and conducted by Geoscience Australia, in conjunction with State and Territory geological surveys, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Here, we present the key aspects of the stratigraphy and structural architecture identified using seismic data from the Arckaringa, Officer, Amadeus and Georgina basins on seismic lines 09GA-GA1 and 08GAOM1.

The Frome Airborne Electromagnetic Survey: Uncovering 10% of South Australia

The Frome airborne electromagnetic (AEM) survey was acquired by Geoscience Australia (GA) under the Australian Government’s Onshore Energy Security Program (OESP). This area is considered to have great potential for uranium mineralisation and includes Australia’s only two producing in situ leach uranium mines, Beverley and Honeymoon. In contrast to deposit-scale investigations carried out by industry, the Frome AEM survey was designed to reveal new geological information at a regional scale, reducing exploration risk, stimulating exploration investment and enhancing the prospectivity within the region primarily for uranium, but also for other commodities including copper, gold, silver, lead, zinc, iron ore, coal and groundwater. The Frome AEM survey (Figure 1) was flown by Fugro Airborne Surveys for GA, using the TEMPESTTM time-domain AEM system.

Structural and stratigraphic architecture of Australia's frontier onshore sedimentary basins: the Western Officer and Southern Carnarvon basins, Western Australia

During the past five years, the Onshore Energy Security Program, funded by the Australian Government and conducted by Geoscience Australia, in conjunction with state and territory geological surveys, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. This extended abstract presents data from two seismic lines collected in Western Australia in 2011. The 487 km long Yilgarn-Officer-Musgrave (YOM) seismic line crossed the western Officer Basin in Western Australia, and the 259 km long, Southern Carnarvon Seismic line crossed the Byro Sub-basin of the Southern Carnarvon Basin. The YOM survey imaged the Neoproterozoic to Devonian western Officer Basin, one of Australia's underexplored sedimentary basins with hydrocarbon potential. The survey data will also provide geoscientific knowledge on the architecture of Australia's crust and the relationship between the eastern Yilgarn Craton and the Musgrave Province. The Southern Carnarvon survey imaged the onshore section of the Ordovician to Permian Carnarvon Basin, which offshore is one of Australia's premier petroleum-producing provinces. The Byro Sub-basin is an underexplored depocentre with the potential for both hydrocarbon and geothermal energy. Where the seismic traverse crossed the Byro Sub-basin it imaged two relatively thick half graben, on west dipping bounding faults. Structural and sequence stratigraphic interpretations of the two seismic lines are presented in this extended abstract.

Kombolgie AEM Survey Images to 2 km

Airborne electromagnetic (AEM) data are being acquired by Geoscience Australia (GA) under the Australian Government’s Onshore Energy Security Program (OESP) in areas considered to have potential for uranium or thorium mineralisation. The surveys are managed and interpreted by members of GA’s AEM Acquisition and Interpretation Project. In contrast to deposit-scale investigations carried out by industry these surveys are designed to reveal new geological information at a regional scale. The Pine Creek AEM survey shown in Figure 1 is comprised of three survey areas: Woolner Granite, Rum Jungle and Kombolgie. The TEMPESTTM AEM system was used for the Woolner Granite and Rum Jungle surveys and the VTEMTM system was used for the Kombolgie survey.

Structural and stratigraphic architecture of Australia's frontier onshore sedimentary basins: the Arckaringa, Officer, Amadeus, and Georgina basins

The Onshore Energy Security Program—funded by the Australian Government and conducted by Geoscience Australia—has acquired deep seismic reflection data in conjunction with state and territory geological surveys, across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Here, we present data from two seismic lines collected in SA and NT. Seismic line 08GA-OM1 crossed the Arckaringa and Officer basins in SA and the southern-most Amadeus Basin in NT. Seismic line 09GA-GA1 crossed the northeastern part of the Amadeus Basin and the complete width of the southern Georgina Basin in NT. Structural and sequence stratigraphic interpretations of the seismic lines will be presented here, followed by an assessment of the petroleum potential of the basins. Seismic line 08GA-OM1 also crosses the Neoproterozoic to Devonian eastern Officer Basin. The basin is structurally complex in this area, being dominated by south-directed thrust faults and fault-related folds—providing potential for underthrust petroleum plays. The northern margin of the basin is overthrust to the south by the Mesoproterozoic Musgrave Province. To the north, the Moorilyanna Trough of the Officer Basin is a major depocentre of up to 7,000 m deep. Both seismic lines cross parts of the eastern Amadeus Basin. Seismic line 08GA-OM1 shows that the southern margin of the basin is overthrust to the north by the Musgrave Province with the main movement during the Petermann Orogeny. In the northeast, seismic line 09GA-GA1 crosses two parts of the basin separated by the Paleoproteroozic to Mesoproterozoic Casey Inlier (part of the Arunta Region). The northern margin of the basin is imaged seismically as a southward-verging, thinned-skinned thrust belt, showing considerable structural thickening of the stratigraphic succession. Seismic line 09GA-GA1 was positioned to cross that part of the southern Georgina Basin that was considered previously to be in the oil window. Here, the basin has a complex southern margin, with Neoproterozoic stratigraphy being thrust interleaved with basement rocks of the Arunta Region. The main part of the basin, containing a Neoproterozoic to Devonian succession, is asymmetric, thinning to the north where it overlies the Paleoproterozoic Davenport Province. The well, Phillip–2, drilled adjacent to the seismic line, intersected basement at a depth of 1,489 m, and has been used to map the stratigraphic sequences across the basin.

Fractal scaling of Airborne EM data: an indicator of lithology and fluid connection?

Electrically conducting fluids within the subsurface account for a large portion of the Earth’s electrical response and therefore mapping of groundwater and regions of high salinity can be undertaken using Airborne Electromagnetic (AEM) methods. While the majority of nearsurface conduction is generally due to fluids in porous or fractured media, there is always an ambiguity in determining the cause of the electrical response. For example, clay layers and mineralization may also significantly enhance conduction. Analysis of how the Earth’s resistivity varies with spatial-wavelength through determining the associated fractal dimension is proposed as an additional tool that can assist in differentiating anomalies of similar magnitude but dissimilar sources.AEM, using the TEMPEST and VTEM systems, has recently been collected by Geoscience Australia through the Onshore Energy Security Program over the Pine Creek region in Northern Territory. Approximately 21,000 line-km of TEMPEST and 9000 line-km of VTEM were collected. A moving window is passed across each line of data creating small overlapping subsets on which the fractal dimension is calculated. These values are then gridded to create a map of the fractal dimension of the Pine Creek AEM survey data. Such maps are compared with existing geological and hydrological information allowing for inferences to be made on the differing sources of anomalism.

The role of deep seismic reflection data in understanding the architecture and petroleum potential of Australia's onshore sedimentary basins

The onshore energy security program, funded by the Australian Government and conducted by Geoscience Australia, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Detailed interpretation of deep seismic reflection profiles from four onshore basins, focussing on overall basin geometry and internal sequence stratigraphy, will be presented here, with the aim of assessing the petroleum potential of the basins. At the southern end of the exposed part of the Mt Isa Province, northwest Queensland, a deep seismic line (06GA–M6) crosses the Burke River structural zone of the Georgina Basin. The basin here is &gt;50 km wide, with a half graben geometry, and bounded in the west by a rift border fault. Given the overall architecture, this basin will be of interest for petroleum exploration. The Millungera Basin in northwest Queensland is completely covered by the thin Eromanga Basin and was unknown prior to being detected on two seismic lines (06GA–M4 and 06GA–M5) acquired in 2006. Following this, seismic line 07GA–IG1 imaged a 65 km wide section of the basin. The geometry of internal stratigraphic sequences and a post-depositional thrust margin indicate that the original succession was much thicker than preserved today and may have potential for a petroleum system. The Yathong Trough, in the southeast part of the Darling Basin in NSW, has been imaged in seismic line 08GA–RS2 and interpreted in detail using sequence stratigraphic principles, with several sequences being mapped. Previous studies indicate that the upper part of this basin consists of Devonian sedimentary rocks, with potential source rocks at depth. In eastern South Australia, seismic line 08GA–A1 crossed the Cambrian Arrowie Basin, which is underlain by a Neoproterozoic succession of the Adelaide Rift System. Stratigraphic sequences have been mapped and can be tied to recent drilling for mineral and geothermal exploration. Shallow drill holes from past petroleum exploration have aided the assessment of the petroleum potential of the Cambrian Hawker Group, which contains bitumen in the core, indicating the presence of source rocks in the basin system.

The Radiometric Map of Australia

Geoscience Australia and the Australian State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma-ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth’s surface. However, the individual surveys that comprise the national gamma-ray spectrometric radioelement database are not all registered to the same datum. This limits the usefulness of the database as it is not possible to easily combine surveys into regional compilations or make accurate comparisons between radiometric signatures in different survey areas. To solve these problems, Geoscience Australia has undertaken an Australia-Wide Airborne Geophysical Survey (AWAGS), funded under the Australian Government’s Onshore Energy Security Program, to serve as a radioelement baseline for all current and future airborne gamma-ray spectrometric surveys in Australia.The AWAGS survey has been back-calibrated to the International Atomic Energy Agency’s (IAEA) radioelement datum. We have used the AWAGS data to level the national radioelement database by estimating survey correction factors that, once applied, minimise both the differences in radioelement estimates between surveys (where these surveys overlap) and the differences between the surveys and the AWAGS traverses. The database is thus effectively levelled to the IAEA datum. The levelled database has been used to produce the first ‘Radiometric Map of Australia’ – levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100 m resolution.Interpreters can use the map to reliably compare the radiometric signatures observed over different parts of Australia. This enables the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions with contrasting landscape histories.

Airborne electromagnetic survey results from the Paterson Province, WA

Geoscience Australia (GA) is acquiring regional airborne electromagnetic (AEM) data in areas of Australia considered prospective for energy commodities as part of the Onshore Energy Security Program (OESP) and to encourage industry exploration activity. The aim of the AEM surveys under the OESP is to release pre-competitive regional data and conductivity-depth information to the public. As part of this initiative, private exploration companies have collaborated with GA by subscribing to infill selected areas at closer line spacings. In return, for favourable financial conditions and management of the survey process, companies will allow GA to release the infill data to the public at the end of a twelve month moratorium period. The large volumes of data acquired under the OESP will be publicly available from GA once internal QA-QC procedures are completed. The Paterson Region in Western Australia (WA) is the first area surveyed under the AEM acquisition program of the OESP. The main aim of this survey is to promote exploration for unconformity-related uranium deposits in previously under-explored and predominantly undercover areas. The uranium systems in this area are believed to be related to the unconformity between the Coolbro Sandstone and the underlying Rudall Complex (McKay and Miezitis, 2001). They may also be related to the contact between the Broadhurst Formation and the Coolbro Sandstone, and are also likely to be controlled by the location of basement faults. Other types of uranium mineralisation that may be prospective in the survey area are surficial calcrete-style uranium systems and sandstone-hosted uranium systems that may be active within buried palaeovalleys.

What can deep seismic reflection data tell us about hydrocarbon prospectivity in onshore

Now in its third year, Geoscience Australia’s Onshore Energy Security Program has acquired several suites of regional geological and geophysical data. The data includes several deep seismic reflection surveys that have been designed to image: basement provinces with high geothermal gradients that may contain uranium enrichments and are potential candidates for geothermal energy; geological terrane boundaries; and, sedimentary basins that are known to host petroleum system elements but are under-explored. Seismic signals are recorded down to 20 seconds two-way-time (TWT) which corresponds to 25–35 km depth depending on dominant lithologies. Basinal sections normally extend down to 6–8 sec TWT and the data is of such high quality that any section of the seismic profile can be enlarged without significant loss of resolution. Deep reflection surveys are able to image the relationship between crystalline basement and overlying basin sequences very clearly and also allow interpretations of structural styles as well as impacts of deformational processes on the basin-fill. A new basinal section was discovered beneath the Eromanga Basin suite of sediments. Named the Mullangera Basin,its structural style and basement relationship seem to indicate some affinity with the Georgina Basin, located further west. The succession is clearly composed of several sequences that contain both fine and coarse-grained sediments. If a geological relationship with the Georgina Basin can be ascertained, a new hydrocarbon prospective area could be delineated. Another new section was discovered beneath the Devonian section of the Darling Basin. Judging by the fast acoustic velocities, the entire basin-fill sequence appears to be very dense and therefore largely non-porous and of low permeability. While low poro-perm characteristics would normally be translated to low prospectivity for oil and gas, the potential for unconventional hydrocarbons such a tight-gas and shale-gas warrants further attention.

The Australia-wide airborne geophysical survey - accurate continental magnetic coverage

Continental-scale merges of Australian airborne magnetic data are only accurate for wavelengths less than about 100 km, due to limitations of survey size and data processing. Wavelengths greater than about 400 km are available from satellite data; thus, there is a ?gap? in the spectrum for intermediate wavelengths between 100 and 400 km (Milligan and Franklin, 2004; Milligan et al., 2004). Geoscience Australia has filled this gap by acquiring new airborne magnetic data as part of the Australian Government?s Onshore Energy Security Program. Intermediate wavelengths are important, for example, for better definition of sedimentary basins for petroleum prospectivity evaluation, for interpreted depths to bottom of magnetic sources in attempts to define the Curie Point isotherm, and for long wavelength regional removal in magnetic modelling.