New 2D seismic data acquired by Geoscience Australia in the northern Houtman Sub-basin of the Perth Basin provides important information on the prospectivity of this frontier area. To date, lack of quality seismic data and limited geological understanding have led to the perception that the hydrocarbon potential of the area is very low. However, interpretation of newly collected data suggests that the northern Houtman depocentre contains up to 15 km of pre-breakup sediments comprised of Permian, Triassic and Jurassic successions, which potentially contain multiple source rock, reservoir and seal intervals. The Permian syn-rift succession is confined to a series of large half-graben that are controlled by basement-involved faults separating the Houtman depocentre from the Bernier Platform. This succession is up to 10 km thick and is mapped throughout the inboard part of the new seismic grid. A prominent unconformity at the top of the Permian syn-rift sequence is overlain by a thick (up to 1800 m) and regionally extensive seismic sequence interpreted as the Lower Triassic Kockatea Shale. The thickness of the overlying Triassic succession ranges from approximately 1 km in the inboard part of the basin to up to 5 km further outboard. The Jurassic succession is thickest (up to 4 km) in the outboard part of the basin and is interpreted to contain sequences corresponding to the Cattamarra, Cadda and Yarragadee formations. Our study integrates new results from regional mapping, geophysical modelling and petroleum systems analysis, which enables a more accurate prospectivity assessment of this frontier basin.
SUMMARYThe northern Houtman Sub-basin is an under-explored region of Australia's western continental margin. It is located at the transition between the non-volcanic margin of the northern Perth Basin and the volcanic province of the Wallaby Plateau and lies adjacent to the Wallaby-Zenith Transform Margin. In 2014, Geoscience Australia acquired new 2D seismic data (GA-349, 3455 km) across the northern Houtman Sub-basin to assess its hydrocarbon prospectivity. Previous studies of the Houtman Sub-basin indicated that en-echelon basin bounding N-NW trending faults are associated with the Permian half graben complex, however, it was not known if this structural style continued into the northern area of the Houtman Sub-basin. This study integrated interpretation of the recently acquired survey, with regional interpretation of the Houtman Sub-basin. This was further supported by well data and geophysical modelling and a regional 2D structural and stratigraphic interpretation developed. Structural mapping was done for the basement, Early Triassic (Woodada Formation) and Early Jurassic (Eneabba Formation). The basement structure of the northern Houtman Sub-basin is controlled by a series of large en-echelon NW-SE trending SW dipping faults, some of which have a throw of more than 10 km. These basement-involved faults control a series of Permian half graben separated by transfer zones and fault ramps. This basement architecture is similar to the inboard part of the southern Houtman Sub-basin, however the structures are larger. The Early Triassic and Early Jurassic faults trend NW-SE similar to the basement-involved faults, however major faults within the Jurassic succession lie about 50 km to the west of the Permian faults. Interpretation of the northern Houtman Sub-basin reveals a structurally complex basin containing a wide range of structural and stratigraphic traps at several stratigraphic levels. Potential plays have been identified in the upper Permian, Triassic and Jurassic successions. They include large stratigraphic plays in the Upper Permian/Lower Triassic, rollover anticlines within the Lower Triassic and Jurassic, and fault propagation folds and fault block plays in the Jurassic.
The Geological and Bioregional Assessment Program is a series of independent scientific studies undertaken by Geoscience Australia and the CSIRO, supported by the Bureau of Meteorology, and managed by the Department of Agriculture, Water and the Environment. The program consists of three stages across three regions with potential to deliver gas to the East Coast Gas Market. Stage 1 was a rapid regional prioritisation conducted by Geoscience Australia, to identify those sedimentary basins with the greatest potential to deliver shale and/or tight gas to the East Coast Gas Market within the next 5–10 years. This prioritisation process assessed 27 onshore eastern and northern Australian basins with shale and/or tight gas potential. Further screening reduced this to a shortlist of nine basins where exploration was underway. The shortlisted basins were ranked on a number of criteria. The Cooper Basin, the Beetaloo Subbasin and the Isa Superbasin were selected for more detailed assessment. Stage 2 of the program involved establishing a baseline understanding of the identified regions. Geoscience Australia produced regional geological evaluations and conceptualisations that informed the assessment of shale and/or tight gas prospectivity, ground- and surface-water impacts and hydraulic fracturing models. Geoscience Australia’s relative prospectivity assessments provide an indication of where viable petroleum plays are most likely to be present. These data indicate areal and stratigraphic constraints that support the program’s further work in Stage 3, on understanding likely development scenarios, impact assessments and causal pathways.
The northern Houtman Sub-basin is an under-explored region of Australia's western continental margin. It is located at the transition between the non-volcanic margin of the northern Perth Basin and the volcanic province of the Wallaby Plateau, and lies adjacent to the Wallaby-Zenith Transform Margin. In 2014-15, Geoscience Australia acquired new 2D seismic data (GA-349) across the northern Houtman Sub-basin to assess its hydrocarbon prospectivity. This study integrated interpretation of the recently acquired GA-349 survey, with Geoscience Australia's existing regional interpretation of the Houtman and Abrolhos sub-basins, to develop a 2D structural and stratigraphic interpretation for the study area. As there are no wells in the northern Houtman sub-basin, the age and lithologies of the mapped sequences were derived from regional mapping, stratal relationships and seismic facies. The new data clearly images a large depocentre, including a much thicker Paleozoic section (up to 13 km) than previously recognised. Extending the length of the inboard part of northern sub-basin are a series of large half-graben (7-10 km thick), interpreted to have formed as a result of Permian rifting. Overlying these half-graben, and separated by an unconformity, is a thick succession (up to 6 km) interpreted to represent a subsequent late Permian to Early Jurassic phase of the thermal subsidence. A second phase of rifting started in the Early Jurassic and culminated in Early Cretaceous breakup. The sedimentary succession deposited during this phase of rifting is highly faulted and heavily intruded in the outboard part of the basin, adjacent to the Wallaby Saddle, where intrusive and extrusive complexes are clearly imaged on the seismic. In contrast to the southern part of the Houtman Subbasin, which experienced rapid passive margin subsidence and regional tilting after the Valanginian breakup, the northern sub-basin remained mostly exposed sub-aerially until the Aptian while the Wallaby Zenith Fracture Zone continued to develop.
Poster G10 The upper Permian to lower Triassic sedimentary succession in the southern Bonaparte Basin represents an extensive marginal marine depositional system that hosts several gas accumulations, including the Blacktip gas field that has been in production since 2009. Development of additional identified gas resources has been hampered by reservoir heterogeneity, as highlighted by preliminary results from a post drill analysis of wells in the study area that identify reservoir effectiveness as a key exploration risk. The sedimentary succession that extends across the Permian–Triassic stratigraphic boundary was deposited during a prolonged marine transgression and shows a transition in lithofacies from the carbonate-dominated Dombey Formation to the siliciclastic-dominated Tern and Penguin formations. Recent improvements in chronostratigraphic calibration of Australian biostratigraphic schemes, spanning the late Permian and early Triassic, inform our review of available palynological data, and re-interpretation and infill sampling of well data. The results provide a better-resolved, consistent and up-to-date stratigraphic scheme, allowing an improved understanding of the timing, duration and distribution of depositional environments of the upper Permian to lower Triassic sediments across the Petrel Sub-basin and Londonderry High. To access the poster click the link on the right. To read the full paper click here
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