Area Summary L12-14 - Department of Mines and Petroleum

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GSWA Table 1. Petroleum wells up to 35 km south of State Acreage Release Area L12-14 and within the Bunbury Trough TD age Year Operator Status1 Status2 Gas show Oil show Total depth (m) Rig elevation (KB m, ASL) Name Class Latitude (S) Longitude(E) Chapman Hill 1 NFW 33°46'15.9" 115°18'54" 36.45 1 350 Jurassic 1992 Discovery Dry P&A Nil Nil Sabina River 1 NFW 33°39'53.3" 115°24'40.3" 13.24 4 309.3 Permian 1982 BP Dry P&A Poor Nil Whicher Range 1 NFW 33°50'07.9” 115°22'28.0" 153.16 4 653.08 Permian 1968 Union Gas P&A G Good Nil Whicher Range 2 EXT 33°50'26.3” 115°23'02.0" 159.19 4 330 Permian 1980 Mesa Gas P&A G Good Nil Whicher Range 3 EXT 33°52'15.0” 115°23'39.2" 137.58 4 496 Permian 1982 BP Gas P&A G Excellent Nil Whicher Range 4 EXT 33°50'22.3” 115°22'06.4" 140.12 4 575 Permian 1997 Pennzoil Gas SUSP G Excellent Nil Whicher Range 5 EXT 33°50'54.3” 115°21'36.8" 134.3 4 307 Permian 2003 Amity Gas P&A G Good – Wonnerup 1 NFW 33°50'54.3” 115°21'36.8" 24.38 4 727.45 Permian 1972 Union Dry P&A Fair Nil Amity Southern Amity Inc. BP BP Petroleum Development Australia Ltd Discovery Discovery Petroleum NL Mesa Mesa Australia Ltd Pennzoil Pennzoil Exploration Australia Inc. Union Union Oil Development Corp. P&A Plug and abandoned G Gas SUSP Suspended – No data NOTES: ASL Above sealevel TD Total depth NFW New field wildcat EXT Extension (as of December 2007) Wells in bold font are the most relevant and are discussed in detail. 6 1995). The corresponding rate for the Bunbury Trough is 1.9°C/100 m, despite the Early Cretaceous thermotectonic event, which resulted in widespread injection (and flows) of doleritic rocks in the Bunbury Trough (Iasky and Lockwood, 2004), including the Release Area (Commander, 1982; Iasky and Lockwood, 2004). Thus, a burial depth of more than 3 km is required for source rock maturity in the Bunbury Trough, as modelled for Wonnerup 1 and Sabina 1 (Iasky, 1993, figs. 38–41), although with increasing depth, reservoir quality is also likely to deteriorate (Crostella and Backhouse, 2000, fig. 30). It is also likely that contact metamorphism may have some local detrimental effect on reservoir quality (Sharif, 2007). Igneous intrusives are known from the Willespie Formation in Wonnerup 1, and the Lesueur Sandstone and the Yarragadee Formation in Whicher Range 2 (Crostella and Backhouse, 2000). Stratigraphy Geophysical studies suggest that the northern part of the Bunbury Trough is likely to contain a Permian section that is more than 6 km thick (Crostella and Backhouse, 2000, fig. 12). The section consists of the Stockton Group, directly overlain with the coal-bearing Sue Group (Fig. 4). The latter group includes thermally mature source rocks, and potential sandstone reservoirs. The Permian section has an overburden up to 4 km thick, mainly consisting of Triassic and Jurassic continental clastic facies. These are likely to be overlain with up to about 400 m of the Lower Cretaceous Leederville Formation in the central-northern and eastern parts of the Release Area. A veneer of late Cenozoic sediments not more than 30 m thick may cover the Swan Coastal Plain, mainly along the Whicher Scarp. The Upper Jurassic Yarragadee Formation and the Lower Cretaceous Bunbury Basalt and the Leederville Formation may be exposed along, and to the east of, the axis of the Capel Anticline, in the central to northwestern parts of the Release Area (Commander, 1982). Since the southern part of the Perth Basin was probably emergent during most of the Permian and Mesozoic (Norvick, 2004), regional or effective marine seal and source rocks — such as the Lower Triassic Kockatea Shale or the Middle Jurassic Cadda Formation — are unlikely to be present in the Bunbury Trough (Fig. 4). Thus, blanketing of the Permian synrift reservoirs by a thick post-rift and shale-rich Lower Triassic succession did not extend to the south. For the same reason, good quality shallow marine reservoirs may be missing from the Permian section in the south (Crostella and Backhouse, 2000, fig. 26). Permian Deposition in the southern Perth Basin began in the Early Permian with the Stockton Group, consisting of fluviolacustrine argillaceous sandstone and siltstone of the Mosswood Formation and a basal diamictite unit (Fig. 4). This formation grades up to the Sue Group, consisting
of poorly sorted feldspathic sandstone with subordinate intervals of conglomerate, siltstone, shale, and sporadic thin or lenticular sub-bituminous to bituminous coal. The Sue Group consists of two intervals of coal measures and three sandstone-rich units in the Vasse Shelf area (Crostella and Backhouse, 2000). However, none of the wells in the Bunbury Trough has completely penetrated this succession. Wonnerup 1 penetrated 623 m of the Willespie Formation at the top of the Sue Group (depth of 4104–4727 m, Crostella and Backhouse, 2000, appendix 3), including two doleritic sills 2 m and 13 m thick. Analyses of wireline logs show that porosity ranges between 29% and 43% and permeability between 32 mD and 650 mD, whereas water saturation varies between 38% and 74% in this formation (Crostella and Backhouse, 2000, table 6). These values are well above those normally given for a tight sand reservoir (0.1 mD; WA:ERA, 2012). Sabina River 1 also penetrated 469 m of the Willespie Formation, showing porosity of 9.5% to 16%. This well may have failed to test a valid trap, and it is likely that subseismic faulting has compromised trap integrity in Wonnerup 1 (Crostella and Backhouse, 2000). Triassic The Triassic section consists of the fluvial Sabina Sandstone and the Lesueur Sandstone (Fig. 4). The Sabina Sandstone consists of moderately sorted, poorly consolidated and micaceous green-grey sandstone with disconformable contact with the Willespie Formation, and grading up to the Lesueur Sandstone. The Sabina Sandstone is 226 m thick in Sabina River 1 and 461 m thick in Wonnerup 1. This unit may become over 500 m thick in the northeastern part of the Bunbury Trough (Crostella and Backhouse, 2000, fig. 13), containing thicker or more frequent layers of shale, claystone, and siltstone with increasing distance from the Vasse Shelf. The Lesueur Sandstone is likely to be more than 1700 m in the Release Area (Crostella and Backhouse, 2000, fig. 14). It is divided into two informal members, the Wonnerup and the Yalgorup (formerly the Myalup), in ascending order. The Wonnerup Member is 1004 m thick at its type section in Wonnerup 1, consisting of homogenous, poorly sorted, coarse to very coarse-gained and feldspathic, lightgrey sandstone. The Yalgorup Member is 1158 m thick in Wonnerup 1, consisting of dark-grey sandstone, probably grading up to the Eneabba Formation rather than the Cattamarra Coal Measures. The boundary between the two members of the Lesueur Sandstone is a regional seismic marker, although they were both probably deposited as channel deposits in fluviatile environments. Jurassic The Jurassic section consists of predominantly continental deposits in the Perth Basin, except for the relatively thin marine Cadda Formation, which is restricted to the northern part of the basin (Fig. 4). The Lower Jurassic Geology and petroleum prospectivity of State Acreage Release Area L12-14, Southern Perth Basin 7 Cattamarra Coal Measures may be over 1200 m thick in the Release Area (Crostella and Backhouse, 2000, fig. 15), given that it is 1271 m thick in Wonnerup 1 and thins out to 850 m in Sabina River 1 (Crostella and Backhouse, 2000). Thickness of the coal measures may increase from 429 m in bore 1 of the Boyanup Line near the coast to as much as 635 m in bore 1 of the Picton Line, east of Bunbury (Fig. 3). The upper contact with the Yarragadee Formation appears to generally deepen from the west to the east across the Release Area (Smith, 1984). As noted above, the distinction between the Cattamarra Coal Measures and the Eneabba Formation is not clear in the Bunbury Trough. The Cattamarra Coal Measures contain coarse-grained quartz sandstone, interbedded with dark and carbonaceous fine-grained clastic rocks and coal seams. The coal seams are good seismic markers, although they cannot be correlated over a large distance because of the lenticular nature of the seams (Crostella and Backhouse, 2000). The sandstone units are interpreted to have been deposited in distributory channels within a fluvial braided and paludal complex. Coaly intervals indicate deposition in a marshy embayment, showing a conformable contact with the overlying Middle–Upper Yarragadee Formation. The Yarragadee Formation is about 800 m thick in the Sabina River 1 and Wonnerup 1, becoming up to about 850 m thick in Picton Line bore number 4 (PL 4) near the Darling Fault (Fig. 3; Wharton, 1980). This unit has a comparable thickness of 700 m to 800 m in bores BL 2, BL 3, and BL 4 along the Boyanup Line, although its thickness is reduced to about 500 m near the coast in bore BL 1 (Smith, 1984). The formation consists of fine to coarse-grained, poorly sorted feldspathic sandstone, showing a conformable contact with the overlying Parmelia Group. Thin beds of shale, siltstone and coal may be also present with the formation, which is predominantly of fluvial origin, with minor overbank or swamp deposits. Along the Quindalup Line (Fig. 3), the Mesozoic section is dissected by the Darradup Fault between bores QL 5 and QL 6 (Wharton, 1981, fig. 3). The top of the Cattamarra Coal Measures deepens eastward between QL 4 and QL 9, and the overlying Yarragadee Formation thickens in the same direction, becoming over 1200 m near the Darling Fault. These trends are in general agreement with those of seismic interpretation (Iasky, 1993), confirming that the thickness of the Mesozoic section increases from west to east across the Release Area. Cretaceous The Cretaceous sedimentary section is divided into a number of units within the Bunbury Trough (Crostella and Backhouse, 2000). The Bunbury Basalt and the Leederville Formation are most widely intersected in hydrogeological bores, covered by no more than a few tens of metres of Cenozoic sediments, mainly near the coast and the Whicher Range. The Leederville Formation and the basalt may crop out in the northwestern part of the area (Commander, 1982).
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Area Summary L12-14 - Department of Mines and Petroleum

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