Geomechanical modelling of fault reactivation in the Cooper Basin, Australia

Geophysical Prospecting

Amrouch

Cooke

et al. 2017

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.

Section: G E O L O G I C a L S E T T I N Gmentioning

confidence: 99%

Section: G E O L O G I C a L S E T T I N Gmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

Geophysical Prospecting

Amrouch

Cooke

et al. 2017

“…To predict whether low relief structural traps exist within the province, geophysicists must select a depth conversion method that provides minimum error. However, as a detailed study had not been performed, many researchers adopt the most basic methods (Kulikowski et al, 2015;Kulikowski et al, 2016b), or choose to retain seismic data in the time domain (Kuang 1985;Apak et al, 1997;Hillis et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

A Statistical Approach to Assessing Depth Conversion Uncertainty on a Regional Dataset: Cooper-Eromanga Basin, Australia

ASEG Extended Abstracts

Hochwald²,

Cooke

et al. 2016

SUMMARYDeciding on the most accurate grid based depth conversion method can often be an arbitrary choice made by geophysicists, particularly if previous research is limited. The importance of accurate depth conversion is particularly crucial in the CooperEromanga Basin, where the presence of oil rich, low relief structural traps are questionable depending on the method used. Previous depth conversion studies are limited to local scales, limited well control and a focus on select horizons. To investigate the depth conversion uncertainty on a regional scale, this research performs a comprehensive and regionally extensive depth conversion analysis utilising 13 3D seismic surveys with 73 interpreted TWT grids and 657 wells. Depth conversions were performed using the 4 most commonly used methods; average (pseudo) velocity, time-depth trend, kriging with external drift using TWT, and kriging with external drift to tie stacking velocities to average well velocities.To manage the large volume of data, a looping script was written to automate the depth conversion process and utilise the crossvalidation, or blind-well method (use n wells to predict the n th +1 well). Statistics on several variables were captured after each loop, with cluster analysis performed on the final data set to test variable significance on depth conversion accuracy. A database of approximately 10000 error calculations found that although the average velocity method is the most accurate at a high level (average absolute error ~24.9 feet), the best method and the expected error changes significantly (tens of feet) depending on the combination and value of the most significant variables. The variables which impacted uncertainty the most were; location (3d survey), formation, distance to the nearest well, and the spatial location of the predicted well relative to the existing well data envelope.

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

Amrouch

2017

Tectonics

The use of core samples, borehole image logs, and seismic data is common practice for obtaining valuable structural data; however, these data are often obtained in isolation from other methods and not usually used for paleostress inversion processes. Therefore, for the first time, we present a new approach for constraining paleoprincipal stress orientations and regimes by integrating geophysical data (seismic and well data) with calcite twin principal stress orientation inversion analysis to refine the evolution of entirely subsurface or offshore basins; a case study on the subsurface Cooper‐Eromanga Basin, Australia. Calcite samples were collected from oriented core, natural fracture data collected from borehole image logs, and fault data interpreted from three‐dimensional seismic surveys. The analysis of microscale, mesoscale and macroscale data constrained the paleoprincipal stress orientations and regimes of six successive tectonic events: (1) NNW‐SSE oriented strike‐slip Carboniferous Alice Springs event; (2) SE‐NW oriented compressional Mid‐Permian event; (3) NE‐SW oriented strike‐slip Late Permian Daralingie event; (4) E‐W compressional Late Triassic Hunter‐Bowen event; (5) E‐W compressional Late Cretaceous event; and (6) N‐S compressional Paleogene event. This study shows the applicability of integrating geophysics with calcite twin stress inversion to decipher the tectonic evolution of entirely subsurface and offshore provinces.