The Officer Basin is a Neoproterozoic (Adelaidean) - middle Palaeozoic (Devonian) basin.
Officer Basin represents one of the last remaining onshore frontier exploration areas where large petroleum discoveries may still be made.
|Age||Neoproterozoic (Adelaidean) - middle Palaeozoic (Devonian)|
|Area in South Australia||176 000 km2 (67 935 sq miles)|
|Exploration Well Density||1 well per 8,800 km2 (1 well per 3396 sq. miles)|
|Success ratio||No discoveries|
|Depth to target zone||200-2000m|
|Thickness||Up to 10 000m|
|Hydrocarbon shows||Found in 4 formations, the majority in a lay carbonate in the Marla Overthrust Zone.|
|First commercial discovery||None|
|Undiscovered resources (50%)||400x106 kL (2516 mmbl) recoverable oil (DEM estimate 1997, Monte Carlo method)|
|Depositional setting||Marine shelf - epeiric sea, sabkha - alkaline playa|
|Regional structure||Foreland basin, thrust complexes (Adelaidean, Late Cambrian, Devonian); salt walls, salt pillows.|
|Seals||Shale, Siltstone, evaporites|
|Source rocks||Siltstone, carbonate|
|Number of wells||20 petroleum exploration, 32 Stratigraphic/deep mineral (>400m)|
Seismic line km
|13528 2D onshore, 509 2D offshore|
The Officer Basin represents one of the last remaining onshore frontier exploration areas where large petroleum discoveries may still be made. It has close geological affinities with the productive Amadeus Basin in the Northern Territory, and with basins in the former USSR and Oman, both of which host giant oil and gas fields and have proven oil reserves in the order of billions of barrels.
Numerous oil shows are known in the Officer Basin from mineral and stratigraphic drillholes, although there has been little on-structure drilling for petroleum targets. Excellent reservoir quality and source are proven. Evaporites and salt tectonics are evident and may provide viable trapping and preservation mechanisms.
The two major depocentres in South Australia, the Birksgate Sub-basin and Munyarai Trough, are separated by a structural rise, and contain 5–10 km of sediment respectively. Subsidence began in the Neoproterozoic (~820 Ma). A single drillhole in each depocentre indicates similar Neoproterozoic sections. A thin Devonian section overlies the Ordovician in the Munyarai Trough, but much of this has been removed elsewhere by Carboniferous erosion following the Alice Springs Orogeny.
Northeast-trending thrust faults separate the Munyarai Trough from the Manya and Tallaringa troughs which contain mainly Early Cambrian sediments. Thin, mainly Neoproterozoic strata extend across the Murnaroo Platform.
During the early Neoproterozoic, the Officer was a component of the giant Centralian Superbasin. The two main episodes of structuring occurred during the Late Devonian to Early Carboniferous (Alice Springs Orogeny) and the terminal Proterozoic (Petermann Ranges Orogeny). Uplift and erosion also affected the NE part of the basin during the Late Cambrian Delamerian Orogeny.
(See figures 1 and 2)
Comalco exploration significantly improved understanding of the geology and petroleum potential of the NE Officer Basin. Amoco briefly explored an adjacent area in the mid 1980s, acquiring 235 km of 2D Vibroseis data and tying Munyarai 1 to Ungoolya 1. In 1993 AGSO recorded a 550 km transect (explosive source) across the Murnaroo Platform and Birksgate Sub-basin. In the same year, the Mines and Energy department recorded 378 km of Vibroseis in the Marla area.
Hemley Exploration, operator of PELs 61 and 63 in the Marla Overthrust Zone, carried out a detailed aeromagnetic investigation in 1998. This new aeromagnetic data was meshed in with previous aeromagnetic and seismic data and interpreted by Leigh Rankin.
Canadian explorer Rodinia Oil Corp, through an affiliate, Officer Basin Energy Pty Ltd, was granted two PELs in the Officer Basin in July 2007 after successfully concluding a conjunctive access agreement with the traditional Aboriginal owners of Maralinga Tjarutja Lands (Officer Basin Energy became Rodinia Oil Corp. in 2008). The company recorded 985 line-km of seismic in late 2007 and early 2008 (Phase I seismic program), then followed up with 526 line-km of exploration seismic in early 2009 (Phase II). Between November 2010 and June 2011 Rodinia acquired an additional 41 lines of seismic data totalling 2536 line km in PELs 81 and 253.
In June 2011 Rodinia spudded its first oil exploration well in PEL 253 (near the SA-WA border) and drilled to a depth of ~2700m intersecting five prospective formations. Rodinia has stated that the well, Mulyawara 1, confirmed the presence of excellent reservoir quality rocks in the Neoproterozoic succession and provided evidence of a petroleum system. A second well, Kutjara 1, was also drilled in Q4 2011. Rodinia Oil Corp. currently holds two PELs (PELs 81 and 253) and three PELAs (303, 351 and 445) in the Officer Basin. Rodinia Oil is now in liquidation and the licence assets may be sold in the near future.
PELA 139 (now PELs 499 and 500) was granted in April 2007 to Dawnpark Holdings Pty Ltd and Standard Oil Pty Ltd. The companies were then operators of seven PELAs in the Officer Basin, and planned to negotiate access with the traditional Aboriginal owners of Anangu Pitjantjatjara Yankunytjatjara and Maralinga Tjarutja lands in 2007–08. Ahava Energy Pty Ltd (Ahava) farmed in to the Standard–Dawnpark licences in 2008 and commenced exploration in the Officer Basin with a 1300 line-km seismic program in early 2009. Ahava acquired an additional 362 line-km of seismic data in late 2009 and drilled three petroleum exploration wells (Welbourn Alpha 1 – PEL 499, Trainor Echo 1 – PEL 138 and Trainor Alpha 1 – PEL 138) in 2010. In 2011 Ahava acquired a small seismic survey comprising 7 lines for a total 85 line km in PEL 499 and in 2012 drilled a petroleum exploration well (Adi 1) near the southern boundary of PEL 143.
PELAs 147 and 148 were granted to Ahava in July 2011. Ahava (and subsidiary companies) now holds six PELs (138, 143, 147, 148, 499, 500) and 13 PELAs in the Officer Basin. Ahava are now actively seeking farm-in partners to progress exploration of these permits.
(See figure 1)
Stratigraphy of the eastern Officer Basin and a rock-relation diagram linking the Birksgate Sub-basin, Munyarai Trough and Murnaroo Platform Details of each unit are available in reports cited below. The sediment packages of immediate interest are the Neoproterozoic (Willouran, Marinoan) and Cambro-Ordovician.
The oldest rocks in the cover sequence, the ~800 million year old Pindyin Sandstone and Alinya Formation were deposited in the (present day) southern reaches of a saline supergiant basin that might have been up to 2 000 000 km2 in area. The section ranges from 200 m to at least 600 m thick. Outcrops are sparse; but the formations are widespread on seismic evidence. Giles 1 and Watson Siding 1 were the only well intersections until Rodinia Oil Corp drilled the Mulyawara 1 and Kutjara 1 wells in 2011.
Correlated units in Western Australia are the Townsend Quartzite, Browne and Lefroy beds; in the Amadeus Basin, Northern Territory, the Heavitree Quartzite and Bitter Springs Formation are equivalents. Salt in the Alinya sabkha facies formed a major decollement for the propagation of thrust faults; salt structures (swells, pillows and salt walls) occur on the NW margin of the Murnaroo Platform. The aeolian–fluvial Pindyin Sandstone has excellent reservoir potential and the sabkha facies of the Alinya Formation contains gas-prone source rocks and seal potential.
Ordovician and Devonian
Ordovician and Devonian rocks locally exceed 1 km in thickness and were once probably up to 3 km thick. The Ordovician is sandstone dominated while the Devonian, intersected only in Munyarai 1, is characterised by freshwater lacustrine deposits (with fossil fish fragments) and evaporative redbeds. These rocks are important indicators of a northward thickening sediment wedge which buried Cambrian strata to petroleum generative depths. The Ordovician and Devonian are structurally concordant with the underlying rocks and were deformed with them by the advancing thrust sheets that signalled the Alice Springs Orogeny. Excellent potential reservoirs exist in the Ordovician Mt Chandler Sandstone, but unless structurally sealed beneath hanging wall rocks, they are at risk from Permian erosion.
(See figures 2, 4, 5 and 6)
A quite distinct oil family occurs in the non-marine, alkaline playa lake sediments of the Observatory Hill Formation. There are nine recorded occurrences of oil bleeds and oil stains in vugs and fractures from depths as shallow as 200 m below surface. TOC values range from 0.5 to 1.4%, calculated vitrinite reflectance (VRcalc) places the Byilkaoora 1 intersection in the oil window (VRcalc = 0.9–1.0). The playa lake facies (Parakeelya Alkali Member) extends for 200 km along the Manya Trough, reaching the surface at Observatory Hill. (See figure 3)
The Munyarai and Manya Troughs and the Marla Overthrust Zone are prospective for conventional oil and gas and unconventional tight gas.
Burial history modelling (Gravestock and Hill, 1997) of the Manya Trough (based on Manya 6 well) suggests the entire sequence below ~175m lies in the gas window with wet gas down to ~944 m. Significantly, source rocks of the Ouldburra Fm have remained in the wet gas window just after the Alice Springs Orogeny (~360 Ma) and have remained in the wet gas window to present day. It is expected that structures that were in place as a result of the Petermann and Delamerian Orogenies could be charged.
The Ordovician Mt Chandler Sandstone (porosity 12.7–19.7%, permeability 0.26–238 mD) is a clean quartzose sandstone. Reservoir potential is good but due to its stratigraphic position the Mt Chandler risks lack of seal resulting from Permian erosion. However, it presents an excellent footwall target in overthrust zones.
Evaporites, which may act as very good seals, have been recorded at many horizons below the Middle Cambrian including the Observatory Hill Formation, Ouldburra Formation, Mena Mudstone Member, Tanana Formation, Dey Dey Mudstone, Meramangye Formation, Coominaree Dolomite and the Alinya Formation. Evaporites of the Alinya Formation have been deformed diapirically across much of the NE of the basin. However, to the SW of the Birksgate – Coober Pedy Corridor there is evidence of stable evaporites overlying sediments of high reflectivity.
(See figure 2)
Although no commercial discoveries have been made in the Officer Basin, hydrocarbon shows have been found in 4 formations (the majority in a playa carbonate in the Marla Overthrust Zone) including significant oil bleeds in the Observatory Hill Formation in Byilkaoora 1 stratigraphic well.
Traps range from simple domes and faulted anticlines to salt swells, pillows and salt walls and drape over basement horst blocks (movie: 3D model of the Manya and Wintinna Trough areas. Stratigraphic traps are expected in the carbonates. Neoproterozoic thrust zones were reactivated in the Late Devonian and provide trap opportunities close to the Musgrave Block and on the northern margin of the Manya Trough. The largest fault complex strikes NE–SW almost 140 km, with vertical displacements up to 2 km. Hanging wall anticlines are the principal targets. (See figure 7)
TIGHT GAS PLAY
Burial history modelling of the Marla Overthrust Zone (Gravestock and Hill, 1997), based on Byilkaoora 1, suggests that the Dey Dey Mudstone – Karlaya Limestone source rock package entered the wet gas window at ~550 Ma during the Delamerian Orogeny and passed into the dry gas window between ~490 and 475 Ma. In this region, thick sandstone sequences of the Tarlina Sandstone and Murnaroo Formation and interbedded sandstone, siltstone and conglomerates of the Narana Formation represent viable tight gas targets.
The average estimate of the potential plays is ~400 x 106 kL (~2516 mmbbl) of recoverable oil. These estimates may appear to be large in comparison to other, geologically younger, Australian petroleum basins, but are comparable to Proterozoic–Cambrian analogues elsewhere in the world. The Lena–Tunguska province in the Siberian Platform has a predicted potential of 318 x 106 kL (2000 mmbbl) of oil and gas liquids and 2417 x 106 m3 (85.8 bcf) of gas; the Moscow Basin has a potential of 2353 x 106 kL (14 800 mmbbl) of gas liquids. Proterozoic sediments are a very significant source for the prolific oil and gas fields of the Persian Gulf area; the proven oil reserves in Oman alone are 795 x 106 kL (5000 mmbbl).
Table 1- Undiscovered recoverable oil resources of the Officer Basin (South Australia)
|UNDISCOVERED POTENTIAL 106 kL (mmbbl)|
|PLAY||Probability that the ultimate potential will exceed the stated value:|
There are no current projects in the
The Officer Basin underlies Maralinga Tjarutja and Anangu Pitjantjatjara Yankunytjatjara (APY) lands and Yalata Aboriginal Reserve. Access to these areas is discussed under Aboriginal issues. Traditional Aboriginal owners of both APY and Maralinga Tjarutja lands have expressed willingness to allow further petroleum exploration on their lands.
Entry to the Woomera Prohibited Area, main roads excepted, must be cleared with the Director, Woomera Test Facility, located at the RAAF Base in Edinburgh, South Australia. Operators proposing to conduct activities within the prohibited area are required to liaise with the Director, Woomera Test Facility, and the Defence Legal Service to determine appropriate levels of insurance and indemnities to the Commonwealth. Some areas of the Woomera Prohibited Area (WPA) may be subject to access restrictions. Further important information regarding access to the WPA is available in the ‘Land Access’ section of the website.
A petroleum exploration or production licence could be acquired over the Mintabie Precious Stones Field. However, the number of open cut mines could make access for petroleum exploration hazardous.
(See figure 9)
Recent studies by Cuneen, Crowe and Peters (2014) in the Western Australian portion of the basin has shown that reactivation of salt in the Cenozoic has occurred and the degree of reactivation needs to be assessed for the risk of trap breaching.
The recent round of drilling by Ahava and Rodinia (2010-2012) did not locate commercial hydrocarbons but numerous oil and gas shows were recorded throughout the Officer Basin sequence.
Licence activity in the previous year is discussed in the ‘Exploration and development’ section of the website, and Figure 10 shows the licence status at the time of publication. Use this link for further information on holders of petroleum tenements in South Australia.
Boult PJ and Rankin L, 2004. Eastern Officer Basin — new play — sleeping giant? In: Boult, PJ, Johns DR and Lang SC eds, PESA’s Eastern Australasian Basin Symposium II, Adelaide 2004. Petroleum Exploration Society of Australia. Special Publication, pp. 231-242.
Brewer AM, Dunster JN, Gatehouse CG, Henry RL and Weste G, 1987. A revision of the stratigraphy of the eastern Officer Basin. South Australia. Geological Survey. Quarterly Geological Notes, 102.
Cunneen, J.P., Crowe, W. and Peters, G. 2014 Cenozoic salt tectonics in the Officer Basin, Western Australia: implications for hydrocarbon exploration APPEA Journal, 54:167-180
Gravestock DI and Hibburt JE, 1991. Sequence stratigraphy of the eastern Officer and Arrowie basins: a framework for Cambrian oil search. APEA Journal, 31:177-190.
Hoskins D and Lemon NM, 1995. Tectonic development of the eastern Officer Basin, central Australia. Exploration Geophysics, 26:395-402.
Kamali MR, 1995. Sedimentology and petroleum geochemistry of the Ouldburra Formation, eastern Officer Basin, Australia. University of Adelaide. National Centre for Petroleum Geology and Geophysics. PhD thesis. South Australia. Department of Primary Industries and Resources. Open file Envelope, 8591 (unpublished).
Kamali MR, Apak SN and Lemon NM, 1995. Porosity generation and reservoir potential of the Ouldburra Formation in the Officer Basin, South Australia. APEA Journal, 35:106-120.
Lindsay JF ed, 1995. Geological atlas of the Officer Basin, South Australia. Australian Geological Survey Organisation and Department of Mines and Energy, South Australia.
McKirdy DM, 1993. Oil shows and source rocks of the eastern Officer Basin — a review. In: Alexander EM and Gravestock DI eds, Central Australian Basins Workshop, Alice Springs, 13–14 September 1993. Program and Abstracts, pp. 68-70.
Michaelsen BH, Kamali MR and McKirdy DM, 1995. Unexpected molecular fossils from Early Cambrian carbonates. Proceedings of the 1995 Organic Geochemistry Conference. The University of Adelaide, p. 46.
Morton JGG and Drexel JF eds, 1997. The petroleum geology of South Australia. Vol. 3: Officer Basin. South Australia. Department of Primary Industries and Resources. Petroleum Geology of South Australia Series, Vol. 3.
Payenberg T.H.D., Lang, S., Deller, K., Ceglar, N. Reilly, M.R.W., Cotton, T and Krapf, C.B.E, 2005. Reducing critical uncertainties for deepwater stratigraphic architecture in the Officer Basin – the significance of outcrop analogues in the Flinders Ranges. University of Adelaide. Australian School of Petroleum. Reservoir Analogues Research Group. Unpublished Report, ASP-RARG-2005-01.
Rankin, L., 2003. Eastern Officer Basin: Structural framework from geophysical data. South Australia. Department of Primary Industries and Resources. Report Book, 2003/00032.
Sukanta, U., Thomas, B., von der Borch, C.C. and Gatehouse, C.G., 1991. Sequence stratigraphic studies and canyon formation, South Australia. PESA Journal, 19:68-73.
Thomas B, 1990. Summary of seismic interpretation in the eastern Officer Basin. South Australia. Department of Mines and Energy. Report Book, 90/00058.
Tingate PR and McKirdy DM, 2003. Exploration opportunities in the Officer Basin, South Australia. Revised edn. South Australia. Department of Primary Industries and Resources. Report Book, 2003/00001.
Zang W, 1995. Early Neoproterozoic sequence stratigraphy and acritarch biostratigraphy, eastern Officer Basin, South Australia. Precambrian Research, 74:119-175.
Zang W and McKirdy DM, 1994. Microfossils and molecular fossils from the Neoproterozoic Alinya Formation — a possible new source rock in the eastern Officer Basin. PESA Journal, 22:89-90.
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