Basement structural architecture and hydrocarbon conduit potential of polygonal faults in the Cooper‐Eromanga Basin, Australia

Abstract

A thorough and complete understanding of the structural geology and evolution of the Cooper‐Eromanga Basin has been hampered by low‐resolution seismic data that becomes particularly difficult to interpret below the thick Permian coal measures. As a result, researchers are tentative to interpret the basement fault architecture within the basin, which is largely undefined. To provide a better understanding of the basement fault geometry, all available two‐dimensional seismic lines together with 12 three‐dimensional seismic surveys were structurally interpreted with assistance from seismic attribute analysis. The Upper Cretaceous Cadna‐owie Formation and top Permian reflectors were analysed using a common seismic attribute technique (incoherency) that was used to infer the presence of faults that may have otherwise been overlooked. Detailed basement fault maps for each seismic survey were constructed and used in conjunction with two‐dimensional seismic data interpretation to produce a regional basement fault map. Large north‐northeast–south‐southwest‐striking sinistral strike–slip faults were identified within the Patchawarra Trough appearing to splay from the main northeast–southwest‐striking ridge. These sinistral north‐northeast–south‐southwest‐striking faults, together with field‐scale southeast–northwest‐striking dextral strike–slip faults, are optimally oriented to have potentially developed as a conjugated fault set under a south‐southeast–north‐northwest‐oriented strike–slip stress regime. Geomechanical modelling for a regionally extensive system of Cretaceous polygonal faults was performed to calculate the Leakage Factor and Dilation Tendency of individual faults. Faults that extend into Lower Cretaceous oil‐rich reservoirs with strikes of between 060°N and 140°N and a high to near‐vertical dip angle were identified to most likely be acting as conduits for the tertiary migration of hydrocarbons from known Lower Cretaceous hydrocarbon reservoirs into shallow Cretaceous sediments. This research provides valuable information on the regional basement fault architecture and a more detailed exploration target for the Cooper‐Eromanga Basin, which were previously not available in literature.

Combining geophysical data and calcite twin stress inversion to refine the tectonic history of subsurface and offshore provinces: A case study on the Cooper-Eromanga Basin, Australia

“…It is well known that inverted high‐angle extensional faults and vertical strike‐slip faults are extensive within this basin (Figure ); however, there is little mention of low‐angle reverse faults in literature [ Kuang , ; Apak et al ., ; Gravestock and Jensen‐Schmidt , ; Grant‐Woolley et al ., ; Kulikowski et al ., , ]. Recent works utilizing depth‐converted 3‐D seismic data have acknowledged the presence of vertical strike‐slip faults [ Grant‐Woolley et al ., ; Kulikowski et al ., , ], low‐angle reverse faults [ Kulikowski et al ., , ], and inverted high‐angle extensional faults [ Grant‐Woolley et al ., ; Kulikowski et al ., , ] with no mention of non‐Andersonian faults.…”

“…It is well known that inverted high‐angle extensional faults and vertical strike‐slip faults are extensive within this basin (Figure ); however, there is little mention of low‐angle reverse faults in literature [ Kuang , ; Apak et al ., ; Gravestock and Jensen‐Schmidt , ; Grant‐Woolley et al ., ; Kulikowski et al ., , ]. Recent works utilizing depth‐converted 3‐D seismic data have acknowledged the presence of vertical strike‐slip faults [ Grant‐Woolley et al ., ; Kulikowski et al ., , ], low‐angle reverse faults [ Kulikowski et al ., , ], and inverted high‐angle extensional faults [ Grant‐Woolley et al ., ; Kulikowski et al ., , ] with no mention of non‐Andersonian faults. The analysis of macroscale fault data therefore follows a more elementary methodology than mesoscale natural fracture analysis but remains in line with the fundamental rock failure principles [ Anderson , ]: low angle (~30°) faults develop under a compressional stress regime parallel to the dip direction; high‐angle faults (~60°) develop under an extensional stress regime with the minimum horizontal stress oriented parallel to the dip direction; and near‐vertical faults formed under a strike‐slip stress regime 30° from the maximum principal stress direction [ Anderson , ; Zoback et al ., ].…”

“…Examples of inverted basement normal faults and the distribution of Cretaceous polygonal faults in Merrimelia 3‐D [after Kulikowski et al ., ]. See Figure for location.…”

“…These major ridges isolate the NE‐SW elongate Patchawarra (PT), Nappamerri (NT), and Tenappera (TT) troughs (Figure ). Much of the original research explored the evolution of the basin using sparse poor‐resolution 2‐D seismic data, with only very recent works utilizing new 3‐D seismic data [ Grant‐Woolley et al ., ; Kulikowski et al ., , , ]. There does remain some uncertainty regarding the maximum principal stress orientation of paleotectonic events, which can be attributed to limited high resolution 3‐D seismic data at depths and poor exposure at surface.…”

An automated cross‐validation method to assess seismic time‐to‐depth conversion accuracy: a case study on the Cooper and Eromanga basins, Australia

“…; Kulikowski ; Kulikowski et al . ,b). In addition to these NE‐SW striking lineaments, SE‐NW strike‐slip faults are also present across the basin and can significantly complicate hydrocarbon production (Grant‐Wooley et al .…”