GEOLOGY AND PETROLEUM PROSPECTIVITY OF STATE ACREAGE RELEASE AREAS L13-4 AND L13-5, OFFICER BASIN, WESTERN AUSTRALIA

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1 Government of Western Australia Department of State Development GEOLOGY AND PETROLEUM PROSPECTIVITY OF STATE ACREAGE RELEASE AREAS L13-4 AND L13-5, OFFICER, WESTERN AUSTRALIA by Geological Survey of Western Australia Perth 2013

2 MINISTER FOR MINES AND PETROLEUM Hon. Bill Marmion MLA DIRECTOR GENERAL, DEPARTMENT OF MINES AND PETROLEUM Richard Sellers EXECUTIVE DIRECTOR, GEOLOGICAL SURVEY OF WESTERN AUSTRALIA Rick Rogerson REFERENCE The recommended reference for this publication is: Geological Survey of Western Australia 2013, Geology and petroleum prospectivity of State Acreage Release Areas L13-4 and L13-5, Officer Basin, Western Australia: Geological Survey of Western Australia, 10p. National Library of Australia Card Number and ISBN PDF Published 2013 by Geological Survey of Western Australia This publication is released in digital format (PDF) as part of a digital package, and is available online at < Further details of geological products and maps produced by the Geological Survey of Western Australia are available from: Information Centre Department of Mines and Petroleum 100 Plain Street EAST PERTH WESTERN AUSTRALIA 6004 Telephone: Facsimile:

3 Contents Abstract...1 Introduction...1 Location and infrastructure...5 Seismic and well coverage...5 Exploration history...5 Regional structure and stratigraphy...6 Petroleum prospectivity of L13-4 and L Conclusions...9 References...9 Figures 1. Location of State Acreage Release Areas L13-4 and L13-5 in the Yowalga area and simplified geology of the western Officer Basin region Seismic coverage and well locations within and around Release Areas L13-4 and L Interpreted upper part of a crustal seismic line across the Yowalga area Generalized time and seismic stratigraphy, tectonic events, source, reservoir, and seal rocks of the Yowalga area Modelled maturity profile across the northern Yowalga area...8 Tables 1. Wells inside or close to State Acreage Release Areas L13-4 and L iii

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5 Geology and petroleum prospectivity of State Acreage Release Areas L13-4 and L13-5, Officer Basin, Western Australia Abstract State Acreage Release Areas L13-4 and L13-5 are contiguous and cover km 2 of the northern Yowalga area of the western Officer Basin. There have been several hydrocarbon shows in Western and South Australian parts of the basin, indicating that significant resources may be present. Results of recent drilling in South Australia have also been encouraging. Despite its remoteness, access to the area is reasonable, allowing a crustal seismic line to be acquired in Seismic coverage and well control are fair. Yowalga 3 is the deepest well in the basin and it is located in L13-5. The well intersected a thick section of the prospective early Neoproterozoic Buldya Group, which includes significant intervals of halite, shale, and mudstone. Structural leads have been mapped around this well and elsewhere in the area and other elements of a petroleum system appear to be present. There may also be subsalt and unconventional hydrocarbon resources, such as shale-gas and oil or tight sand reservoirs. KEYWORDS: petroleum prospects, gas exploration, petroleum exploration Introduction State Acreage Release Areas L13-4 ( km 2 ) and L13-5 ( km 2 ) lie in the northern Yowalga area (former sub-basin) of the western Officer Basin (Fig. 1; Hocking et al., 1994). This is the most explored part of the basin (Fig. 2), and there have been several studies on its structural and stratigraphic development, and petroleum potential (Apak and Moors, 2000a,b; Ghori, 2002; Apak et al., 2002; Grey et al., 2005; Simeonova and Iasky, 2005; Carr et al., 2012). There are seven wells in the Release Areas and their seismic coverage is fair, except for the northeastern part of L13-5 over the Warri Arch (Fig. 2; Table 1). This is a basement high that unconformably underlies the northeastern margin of the western Officer Basin (Apak et al., 2002, fig. 5; Carlsen et al., 2003, fig. 2). The northwestern flank and crest of the arch are covered by the Phanerozoic Canning Basin. To the east and southeast, the Warri Arch joins the Mesoproterozoic crystalline Musgrave Province. Gravity and magnetic signatures of the arch and the province continue northwest toward the Rudall Province in the northwestern Paterson Orogen (Perincek, 1996; Blundell, 1999). The Musgrave Province separates the Officer Basin from the closely related Amadeus Basin, both of which are components of the Centralian Superbasin (Walter et al., 1995). The Officer Basin is one of the largest under-explored onshore basins of Australia, covering approximately km 2 (Grey et al., 2005; Boult and Rankin, 2004). It is sparsely exposed for over 1500 km from the southeastern flanks of the Pilbara and Yilgarn Cratons in central Western Australia (WA) to central western South Australia (SA), and between the Musgrave Province and the Gawler Craton. Its remoteness and extensive Phanerozoic cover have discouraged exploration, although evidence of potentially significant hydrocarbon resources has been found throughout the basin (Apak et al. 2002; Ghori, 2002; Carlsen et al., 2003; Boult and Rankin, 2004). Nearly one-third of the basin (approximately km 2 ) lies in WA and may show significant differences from the eastern part of the basin in SA in its structure and stratigraphy (Jackson and van de Graaff, 1981). The thickest Neoproterozoic succession has been found in WA (Grey et al., 2005; Haines et al., 2008). However, the succession is extensively buried under the Phanerozoic Gunbarrel Basin, which becomes up to 1.5 km thick in the southwestern Yowalga area (Hocking et al., 1994). The Gunbarrel Basin is not prospective, although its thickness influences thermal maturity of the Neoproterozoic succession. The latter overlies older Precambrian rocks of unknown petroleum potential. The Neoproterozoic succession extends through the basin in South Australia. It has been recently intersected in two wells near the border that prove the presence of an 1

6 GSWA PILBARA CRATON ' ' ' ' GREAT ' Throssell Range SANDY Group Marble Bar Lamil Group DESERT Nullagine Telfer Route MURRABA Newman COLLIER HAMERSLEY LITTLE SANDY DESERT Ward Inlier SALVATION NW P a Canning SCORPION t e rs on OFFICER O Oldham Inlier EARAHEEDY ro Rudall Complex gen GSWA Trainor 1 Stock GSWA Lancer 1 Gunbarrel Highway Gary CANNING L13-4 L13-5 Clutterbuck Inlier GIBSON DESERT Highway Warburton 22 00' 24 00' AMADEUS Giles Musgrave Province Arunta Province 26 00' Wiluna Leinster Sandstone Goldfields Gas YILGARN CRATON Leonora Great Central Laverton BMR Throssell 1 Road Yowalga area GSWA Empress 1/1A WMC NJD 1 11GA Highway -YO1 Anne Beadell GSWA Vines 1 OFFICER Highway 28 00' Menzies Transmission Edjudina GUNBARREL over basement Sue NTOra Banda QLD Broad Arrow WA SA Coolgardie NSW Southern Officer Cross Marvel Basin Loch VIC. TAS. Pipeline Kalgoorlie Kambalda Albany raser Orogen Connie EUCLA Trans-Australian Railway To Adelaide 30 00' SNA km Centralian Superbasin Gunbarrel Basin over Officer Basin Eucla Basin over Officer Basin Younger basins Meso- and Paleoproterozoic basins Orogens Petroleum exploration and stratigraphic well Mineral exploration drillholes 11GA-YO1 seismic line Seismic line Road Railway Cratons Petroleum pipeline Locality Figure 1. Location of State Acreage Release Areas L13-4 and L13-5 in the Yowalga area and simplified geology of the western Officer Basin region 2

7 Geology and petroleum prospectivity of state acreage release areas L13-4 and L Locality Map L13-4 Gunbarrel BMR Browne 1 Warri Arch L ( km ) 2 ( km ) WA Highway 26 Tjirrkarli Lungkarta 1 Browne 1 Browne 2 MUSGRAVE COMPLEX Yowalga 3 Yowalga 1,2 WARBURTON BMR Talbot 1,2,3,4,5 Westwood Shelf BMR Westwood 1 Kanpa 1/1A Great Central Road BMR Yowalga 4 Yowalga area BMR Westwood 2 GSWA Empress 1/1A Lennis 1 Neale Arch ARG246a km Centralian Superbasin Gunbarrel Basin over Officer Basin Younger basins Orogens Petroleum exploration well Stratigraphic test drillhole Mineral exploration drillholes Oil show Gas show Oil and gas show Aboriginal communities Seismic line Road Approximate position of the profile shown in Figure 5 Figure 2. Seismic coverage and well locations within and around Release Areas L13-4 and L13-5 3

8 GSWA Table 1. Wells inside (bold) or close to State Acreage Release Areas L13-4 and L13-5 Name Class (a) Latitude (S) Longitude (E) Rig elevation Total depth (KB m) ASL (a) (m) TD Formation Year Operator (b) Status1 Status2 (a) Gas show Oil show BMR Browne 1 STR 25 31' 59.04" '34.89" Paterson 1972 BMR Dry P&A Nil Nil BMR Talbot 1 STR 26 09' 06.89" '35.01" Townsend Quartzite 1972 BMR Dry P&A Nil Nil BMR Talbot 2 STR 26 09' 19.12" '24.93" Cenozoic 1972 BMR Dry P&A Nil Nil BMR Talbot 3 STR 26 09' 33.16" '13.05" Lefroy 1972 BMR Dry P&A Nil Nil BMR Talbot 4 STR 26 09' 45.05" '59.01" Lefroy 1972 BMR Dry P&A Nil Nil BMR Talbot 5 STR 26 09' 55.01" '04.90" Wahlgu 1972 BMR Dry P&A Nil Nil BMR Yowalga 4 STR 26 49' 58.89" '37.82" Paterson 1972 BMR Dry P&A Nil Nil Browne 1 STR 25 51' 10.03" '02.89" Browne 1965 Hunt Dry P&A Poor Poor Browne 2 STR 25 55' 55.03" '49.90" Browne 1965 Hunt Dry P&A Poor Poor Kanpa 1A NFW 26 31' 36.72" '56.58" ?Mesoproterozoic Shell Dry P&A Nil Poor Lungkarta 1 NFW 26 04'38.38" '50.86" Hussar 1984 Shell Dry P&A Nil Nil Yowalga 1 STR 26 10'12.00" '00.12" Lennis sandstone 1965 Hunt Dry P&A Nil Nil Yowalga 2 NFW 26 10'12.00" '00.00" Kanpa 1966 Hunt Dry P&A Nil Nil Yowalga 3 NFW 26 08'58.16" '00.99" Browne Shell Dry P&A Poor Poor SOURCE: WAPIMS NOTES: (a)nfw: new field wildcat, STR: stratigraphic, TD: total depth, P&A: plugged and abandoned, ASL: above sea level, KB: Kelly Bushing. (b)bmr: Bureau of Mineral Resources (now Geoscience Australia), Hunt: Hunt Oil Company Pty. Ltd., Shell: Shell Company of Australia Pty. Ltd. 4

9 Geology and petroleum prospectivity of state acreage release areas L13-4 and L13-5 active petroleum system (Boult et al., 2012). Scattered hydrocarbon shows across the western Officer Basin indicate that at least small volumes of hydrocarbons were generated and migrated through the system, and there is more than one petroleum system (Apak et al., 2002). Maturity modelling suggests that the most significant hydrocarbon traps formed before most of the potential source rocks entered the oil window. The mature interval becomes thicker in the Yowalga area, where it remains in the oil window (Ghori, 1998, 2002). Nevertheless, the western Officer Basin remains largely a frontier area with only 34 exploration and stratigraphic wells in total, and mostly shallow stratigraphic tests (Simeonova and Iasky, 2005, appendix 2). The Officer Basin is comparable with petroliferous basins of the same age in Oman and Russia (Ghori et al., 2009). As a part of the Centralian Superbasin, it shows greater similarity to the Amadeus Basin (Fig. 1), which has recorded some significant Neoproterozoic hydrocarbon occurrences, such as the subeconomic Dingo gasfield. A preliminary study of source rocks suggests that the Amadeus Basin may contain shale-gas resources (Tiem et al., 2011). However, there has been no assessment of the unconventional or subsalt hydrocarbon resources of the western Officer Basin. Location and infrastructure The Yowalga area is located about 1250 km northeast of Perth. It is largely flat and reasonably accessible. The sealed Kalgoorlie to Laverton road links to the wellmaintained and unsealed Great Central Road, which leads to Warburton and carries heavy transport for most of the year. A deep crustal seismic survey line was shot along the road in 2011 (Figs 1, 3; Carr et al., 2012). Warburton is the most significant settlement in the area and it is linked to the Trans-Australian Railway about 500 km to the south (Fig. 1). The Gunbarrel Highway also passes through northern parts of both Release Areas, although this is only a four-wheel drive track for much of its length. A well-maintained gravel road links Warburton to other communities in SA and Alice Springs in the Northern Territory (NT). Side roads and four-wheel drive tracks extend to other parts of the Release Areas and can be used in dry weather. The Goldfields Gas Transmission Pipeline extends from the North West Shelf to Esperance on the south coast, at a distance of about 300 km to the west of the Release Areas (Fig. 1). Potential markets or delivery points for commercial discoveries could include mining centres along the pipeline, Alice Springs, and southern ports. Seismic and well coverage Seismic coverage is fair and all seismic lines have been reprocessed (Fig. 2; Simeonova, 2003, pl. 1). Of a total of 19 wells drilled in the Yowalga area, two are located in L13-4 and five in L13-5 (Table 1). Yowalga 3 is the deepest well in the western Officer Basin and Kanpa 1A has penetrated the entire evaporitic section of the Browne Formation. The latter is located about 12.5 km south of the Release Areas. Oil and gas shows have been encountered in this well and Browne 1 and 2 (Carlsen et al., 2003, table 1). Simeonova and Iasky (2005) carried out postmortems of the important wells. Well completion and post-completion specialist reports, well logs, and details of seismic and other geophysical surveys can be downloaded from the Western Australian Petroleum and Geothermal Information Management System (WAPIMS) database via the Department of Mines and Petroleum (DMP) website at < dmp.wa.gov.au>. The acreage release data package also includes key publications and relevant unpublished material. Exploration history Petroleum exploration commenced in the 1960s with drilling of five shallow (<1000-m deep) wells in the Yowalga area (Phillips et al., 1985). There were minor oil and gas shows in Browne 1 and 2 from the Browne Formation (Carlsen et al., 2003, table 1). Subsequently, the former Bureau of Mineral Resources (BMR, now Geoscience Australia) drilled a series of shallow stratigraphic boreholes in the Yowalga area during 1972 (Jackson and van de Graaff, 1981). A second phase of exploration followed in the 1980s when Shell Company of Australia acquired 4682 line-km of seismic data and drilled three deep wells in the area, including Yowalga 3 and Kanpa 1/1A (Townson, 1985). The latter well encountered a minor oil show in the Steptoe Formation and revealed three potential source intervals in the Browne Formation. The well proved the presence of a reservoir and seal pair, respectively, in the Hussar Formation sandstone and Kanpa Formation mudstone. The most recent phase of exploration began in 1995 when Japan National Oil Corporation (JNOC) reprocessed 50 key seismic lines (2165 line-km) and conducted a high-resolution aeromagnetic survey ( km total length). JNOC (1997) also conducted source rock characterization and thermal maturation studies using drill cuttings from wells in the Yowalga area. The Geological Survey of Western Australia (GSWA) reprocessed further seismic data and conducted seismic stratigraphic and additional geochemical studies, including basin modelling in key areas (Ghori, 1998, 2002; Ghori et al., 2009). GSWA has also drilled three stratigraphic wells in the central and western part of the basin. Empress 1/1A is the closest stratigraphic well to the area (Fig. 1; Stevens and Apak, 1999), providing a complete cored stratigraphic section through the basin succession, terminating in a late Mesoproterozoic basin. Finally, Geoscience Australia and GSWA sponsored the acquisition of a crustal seismic survey line about 20 km away from Yowalga 3 and Kanpa 1A in 2011 (Figs 1 and 3; Carr et al., 2012). Sparse mineral exploration holes through the area provide additional data of relevance to hydrocarbon prospectivity. The most noteworthy is WMC NJD 1 (Fig. 1; Hocking, 2003). Core from the bottom of this hole, possibly Neoproterozoic in age, displayed oil 5

10 Interpreted upper part of a crustal seismic line across the Yowalga area. See Figure 1 for location (from Carr et al., 2011). SNA66 V:E = 1:4 4 2 CDP The Neoproterozoic succession comprises mixed carbonate, siliciclastic, and evaporitic lithologies including shallow marine, glacial, and non-marine facies. The succession is divided into four supersequences (Fig. 4; Grey et al., 2005). The Buldya Group (Supersequence 1) Two-way time (s) SW Salt Most of the structural leads mapped in two northwesttrending zones in the Yowalga area are attributed to salt-tectonics (JNOC, 1997; Apak et al., 2002, fig. 10; Simeonova and Iasky, 2005). There are also positive topographic features associated with some salt diapirs in the area (Fig. 3). However, vintage quality seismic profiles may not image the base of thick autochthonous evaporitic successions, as found in the Browne Formation. Thus, the subsalt geology of the basin remains poorly understood, particularly in the northern trough. Carr et al. (2012) and Preiss et al. (2010) also questioned the cause of some acoustically opaque zones that rise vertically through the basin fill on newly acquired seismic profiles in the western and eastern parts of Officer Basin (Fig. 3). Base Cenozoic Base Lennis Sandstone Base Table Hill Volcanics GSWA Empress 1/1A Base Wahlgu Formation Base Steptoe Formation Base Kanpa Formation 50 km Kanpa Base Hussar Formation Intra Browne Formation 2 Intra Browne Formation 1 Yowalga The western Officer Basin has undergone asymmetric subsidence, resulting in the development of a deep trough along its northeastern margin that rises gradually toward a broad shallow shelf to the southwest (Fig. 3). Total thickness of sediments is locally up to 8 km in the trough (Townson, 1985; D Ercole et al. 2005). Carlsen et al. (1999), Apak and Moors (2000a), and D Ercole et al. (2005) regarded the trough as a foredeep. Thrust faults typically dip towards the rigid, upthrust Musgrave Province (Blundell, 1999, fig. 11; Carlsen et al., 2003, fig. 4; D Ercole et al., 2005, fig. 19; Preiss et al., 2010). The complex may have also served as the main source of sediment to the basin, having undergone several kilometres of uplift (Lambeck, 1986). A similar pattern of subsidence and basin architecture has also been found in the eastern Officer Basin (Haddad et al., 2001). By comparison, Carr et al. (2012) suggested extension and steep normal faulting as the cause of subsidence accompanied with more intense syntectonic sedimentation in the trough. This is in agreement with the general view that the Officer Basin originated in an intracratonic extensional setting during the early Neoproterozoic (c. 830 Ma; Carlsen et al., 1999). It is also widely known that the basin has undergone contraction, uplift, and erosion from mid-neoproterozoic time onward (Fig. 4). Carr et al. (2012) also attributed salt mobilization to compressional tectonics during the Petermann Range and younger orogenies. Some of the old normal faults have also been reactivated as reverse faults (Carlsen et al., 1999; Preiss et al., 2010). Uplift and erosion caused a hiatus of up to 100 my in the stratigraphic record after the deposition of the Buldya Group (Grey et al., 2005). Thus, the Centralian Superbasin progressively fragmented through several phases of tectonic upheavals (Fig. 4; Walter et al., 1995). Figure Base Officer Basin Base Mesoproterozoic metasedimentary rocks Regional structure and stratigraphy Fault NE staining. In addition, excellent source rock potential was identified in a thin interval of shaly siltstone near the base of the Neoproterozoic succession GSWA

11 Geology and petroleum prospectivity of state acreage release areas L13-4 and L13-5 Age Ma Stratigraphy and tectonic events Super seq. Sequence Para seq. sets Basin Tectonic events Source Reservoir Seal PALEOZOIC P C D Ord. S 300 Paterson Formation Wanna Formation Lennis Sandstone GUNBARREL Alice Springs Orogeny Rodingan Movement Cambrian v Punkerri Ss Table Hill Volcanics v Vines Fm Lungkarta Formation v Wirridar beds SS4 Delamerian Orogeny 580 Petermann Ranges Orogeny NEOPROTEROZOIC Buldya Group Wahlgu Formation Lupton and Pirrilyungka Fms. Steptoe Formation Kanpa Formation Hussar Formation Browne Formation SS3 SS2 Buldya Group ( SS1 ) S K H B S2 S1 K2 K1 H5 H4 H3 H2 H1 B6 B5 B4 B3 B2 OFFICER Areyonga Movement B1 Lefroy Formation 840 Townsend Quartzite Miles Orogeny PRE-OFFICER RMH Sandstone Dolomite v v Volcanic rock Unconformity Evaporite/halite Shale/mudstone Diamictite Figure 4. Generalized time and seismic stratigraphy, tectonic events, source, reservoir, and seal rocks of the Yowalga area (from Ghori et al., 2009) 7

12 GSWA includes basal sandy and coarser siliciclastic units (Townsend Quartzite) overlain by mixed siltstone, shale, carbonate, and evaporites that are divided into Lefroy, Browne, Hussar, Kanpa, and Steptoe Formations in ascending order. The Browne Formation contains one or more salt intervals, which have been mobilized in the deeper parts of the basin (Simeonova and Iasky, 2005). Evaporitic diapirs bring the Browne Formation to the surface in some places. Supersequence 2, including the older (Sturt) glacial succession, is probably present in the Yowalga area, although is mismapped as Permian rocks and the Lupton Formation (Hocking, R, 2012, written comm.). Supersequence 3 is represented by the glacial Wahlgu Formation, inferred to be the local representative of the widespread Elatina Glaciation (Grey et al., 2005). Supersequence 4 includes the non-marine Lungkarta Formation deposited synchronously with the latest Neoproterozoic early Cambrian Petermann Range and Paterson Orogenies. Post-Supersequence 4 rocks that are collectively included in the Gunbarrel Basin include the Cambrian basaltic Table Hill Volcanic rocks and overlying Lennis and Wanna Formations of uncertain Paleozoic age. Mesozoic strata is excluded from the Officer Basin and belong to the Gunbarrel Basin. Petroleum prospectivity of L13-4 and L13-5 Prospectivity of the Release Areas is inferred to be restricted to the Buldya Group (c Ma), although it is possible that hydrocarbons sourced in the group may migrate to traps higher in the succession. Evidence of oil migration has been recorded from several wells in the area and elsewhere in the basin (Apak and Moors, 2000a, appendix 1; Carlsen et al., 2003, table 1; Simeonova and Iasky, 2005, table 2). There is also the possibility that hydrocarbons are sourced from underlying (probably Mesoproterozoic) basins, although the geology of such basins is very poorly known. If the richest source rocks identified in mineral corehole WMC NJD 1 (Fig. 1; Hocking, 2003) thicken and extend into deeper and more mature locations within the Release Areas, then there is potential to source significant volumes of hydrocarbons. Geochemical studies and thermal modelling suggest that relatively thin, but organic-rich and mature source intervals are present in the Buldya Group, and that hydrocarbon expulsion has taken place after the formation of traps, from the late Neoproterozoic onward (Carlsen and Grey, 1998; Ghori, 1998, 2002). Based on analyses of data from ditch cuttings of wells in the areas, including Yowalga 3 and Kanpa 1/1A, mature source intervals with good oil and gas generating potential (mainly type II kerogen) occur within the Browne, Kanpa, and Hussar Formations (Fig. 5). Sandstone reservoirs with porosities greater than 20% and permeabilities ranging from hundreds of millidarcys to more than one darcy are present at several levels, particularly in the Hussar Formation. Halite in the Browne Formation, intraformational shales at higher levels in the Buldya Group, and glacial diamictite overlying the Buldya Group offer potential seals. The presence of salt is particularly significant as halotectonic Depth (km) SW SP 100 SP 4725 SP 500 Empress 1 and 1A (T1-21-AB) Kanpa 1A (T82-42) (80-07) Lupton Fm. McFadden Fm. Steptoe S2 Steptoe S1 Hussar H3 Hussar H2 Townsend Qtz. Maturity (%Ro) Immature Early mature <0.5%Ro %Ro Mid-mature %Ro Late mature %Ro Mainly gas >1.3%Ro Well Pseudowell Table Hill Volc. Kanpa K2 Kanpa K1 Hussar H5 Hussar H4 Hussar H1 Browne B6 Browne B5 Browne B4 Browne B3 Browne B2 Browne B1 Yowalga 3 Samuel Fm. Paterson Fm. Lennis Ss. SP 2030 (T80-11) Distance (km) ARG136c Figure 5. Modelled maturity profile across the northern Yowalga area, from Empress 1/1A in the south to SP 2030 on seismic line T80-11 in the north. See Figure 2 for location (from Ghori, 2002). (%Ro = vitrinite reflectance) activity has resulted in a range of possible trapping configurations. Thus, a structural lead has been mapped around Yowalga 1, 2, and 3 within L13-5 (Apak et al., 2002, fig. 10), and various play types have been proposed, although none has been tested (Simeonova and Iasky, 2005, fig. 31). The oil window is deeper in the Yowalga area (Fig. 5). Movement of salt during the Neoproterozoic produced two laterally persistent structural domains: the salt-ruptured and thrusted zones, both of which cross the Release Areas (Simeonova and Iasky, 2005, fig. 17). JNOC (1997) also initially mapped structural leads within these zones (Simeonova and Iasky, 2005, fig. 31). Thus, all elements of a petroleum system appear to be in place. Apak and Moors (2000b) also subdivided the Buldya Group into many parasequence and correlated them across the area. These include thick shale-rich intervals, which may hold potential shale-gas and liquid resources, given the presence of source rock intervals with mature type II kerogen within some of the shaly intervals. NE 8

13 Geology and petroleum prospectivity of state acreage release areas L13-4 and L13-5 Conclusions Acreage Release Areas L13-4 and L13-5 lie in the most explored part of the Yowalga area with reasonable access for exploration. Seismic coverage is fair to good. A crustal seismic line has also been acquired and interpreted from the area. There are seven wells within both Release Areas, three of which have penetrated the prospective Buldya Group. Good source beds and proven reservoirs capped by thick sections of halite or shale have been intersected. A major structural lead has been mapped in L13-5 around Yowalga 3, and Kanpa 1/1A is another key well close to the Release Areas. The present oil window is deeper in the area, and it appears that all elements of a petroleum system are present. There may also be subsalt and unconventional hydrocarbon resources, as indicated by the existence of good source rock near the base of the Neoproterozoic succession in a mineral corehole in the southern Yowalga area. References Apak, SN, Ghori, KAR, Carlsen, GM and Stevens, MK 2002, Basin development with implications for petroleum trap styles of the Neoproterozoic Officer Basin, Western Australia, in The Sedimentary Basins of Western Australia 3 edited by M Keep and SJ Moss: Proceedings of Petroleum Exploration Society of Australia Symposium, Perth, Western Australia, 2002, p Apak, SN and Moors, HT 2000a, Basin development and petroleum exploration potential of the Yowalga area, Officer Basin, Western Australia: Geological Survey of Western Australia, Report 76, 61p. Apak, SN and Moors, HT 2000b, A sequence stratigraphic depositional model of Neoproterozoic strata, Yowalga area, Officer Basin, Western Australia: APPEA Journal, v. 40, p Boult, P, Bennet, PJ and Freeman, A 2012, Structure, stratigraphy and petroleum potential of the central Officer Basin, South Australia: AAPG International Conference and Exhibition, Singapore, September 2012, Abstract Boult, PJ and Rankin, L 2004, Eastern Officer Basin new play sleeping giant?, in Eastern Australasian Basin Symposium II edited by PJ Boult, DR Johns, and SC Lang: Petroleum Exploration Society of Australia, Special Publication, p Blundell, KA 1999, Waigen gravity survey the contribution of semidetailed gravity data to the stratigraphic and structural interpretation of the Waigen Sub-basin, Officer Basin, Geological Survey of Western Australia, Record 1999/8, 33p. Carlsen, GM, Apak, SN, Ghori, KAR, Grey, K and Stevens, MK 1999, Petroleum potential of the Neoproterozoic Western Officer Basin, Western Australia, based on a source-rock model from Empress-1A: APPEA Journal, v. 39, p Carlsen, GM and Grey, K 1998, GSWA Empress 1A and petroleum evaluation of the western Officer Basin, in Geological Survey of Western Australia Annual Review : Geological Survey of Western Australia, Perth, Western Australia, p Carlsen, GM, Simeonova, AN and Apak, SN 2003, Petroleum systems and exploration potential in the Officer Basin, Western Australia: APPEA Journal, v. 43, p Carr, LK, Korsch, RJ, Mory, AJ, Hocking, RM, Marshall, SK, Costelloe, RD, Holzschuh, J and Maher, JL 2012, Structural and stratigraphic architecture of Australia s frontier onshore sedimentary basins: the western Officer and southern Carnarvon Basins, Western Australia: External (web) publication, Catalogue No < DETAILS&catno=72705>. D Ercole, C, Irimies, F, Lockwood, AM and Hocking, RM 2005, Geology, geophysics, and hydrocarbon potential of the Waigen area, Officer Basin, Western Australia: Geological Survey of Western Australia, Report 100, 51p. Ghori, KAR 1998, Petroleum source rock potential and thermal history of the Officer Basin, Western Australia: Geological Survey of Western Australia, Record 1998/3, 52p. Ghori, KAR 2002, Modelling the hydrocarbon generative history of the Officer Basin, Western Australia: PESA Journal, v. 29, p Ghori, KAR, Craig, J, Thusu, B, Lüning, S and Geiger, M 2009, Global Infracambrian petroleum systems: a review, in Global Neoproterozoic Petroleum Systems: the emerging potential in North Africa edited by J Craig, J Thurow, B Thusu, A Whitham and Y Abutarruma: The Geological Society, London, Special Publications, v. 326, p Grey, K, Hocking, RM, Stevens, MK, Bagas, L, Carlsen, GM, Irimies, F, Pirajno, F, Haines, PW and Apak, SN 2005, Lithostratigraphic nomenclature of the Officer Basin and correlative parts of the Paterson Orogen, Western Australia: Geological Survey of Western Australia, Report 93, 89p. Jackson, MJ and van de Graaff, WJE 1981, Geology of the Officer Basin, Western Australia: Australia Bureau of Mineral Resources, Bulletin 206, 102p. Japan National Oil Corporation (JNOC) 1997, Geological and geophysical surveys in the western Officer Basin integrated geological interpretation study: Geological Survey of Western Australia, Statutory petroleum exploration report, S10275 (unpublished). Haddad, D, Watts, AB and Lindsay, J 2001, Evolution of the intracratonic Officer Basin, central Australia: implications from subsidence analysis and gravity modelling: Basin Research, v. 13, p Haines, PW, Hocking, RM, Grey, K and Stevens, MK 2008, Vines 1 revisited: are older Neoproterozoic glacial deposits preserved in Western Australia?: Australian Journal of Earth Sciences, v. 55, p Hocking, RM, 2003, Drillhole WMC NJD 1, western Officer Basin, Western Australia: Stratigraphy and petroleum geology: Geological Survey of Western Australia, Record 2002/18, 26p. Hocking, RM, Mory, AJ and Williams, IR 1994, An atlas of Neoproterozoic and Phanerozoic basins of Western Australia, in The Sedimentary Basins of Western Australia edited by PC Purcell and RR Purcell: Petroleum Exploration Society of Australia, Western Australian Branch, Perth, Western Australia, p Jackson, MJ and van de Graaff, WJE, 1981, Geology of the Officer Basin: BMR Bulletin 206, 102p. Lambeck, K 1986, Crustal structure and evolution of the central Australian basins, in The Nature of the Lower Continental Crust edited by JB Dawson, DA Carswell, J Hall, and KH Wedepohl: The Geological Society, London, Special Publication No. 24, p Perincek, D 1996, The age of Neoproterozoic Paleozoic sediments within the Officer Basin of the Centralian Super-basin can be constrained by major sequence-bounding unconformities: APPEA Journal, v. 36, p Perincek, D 1998, A compilation and review of data pertaining to the hydrocarbon prospectivity of the Officer Basin: Geological Survey of Western Australia, Record 1997/6, 209p. 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