First-Order Assessment of the Fault Seal Risk in the Gippsland Basin, Australia

Ciftci, Bozkurt N.¹; Langhi, Laurent¹; Strand, Julian¹; Goldie Divko, Louise²
¹Earth Science and Resource Engineering, CSIRO-Australia, Bentley, WA, Australia.
²Victorian Department of Primary Industries, Melbourne, SA, Australia.

The Gippsland Basin is one of the most prolific hydrocarbon basins in Australia and has substantial brown coal resources which provide fuel for low-cost electricity for the state of Victoria. Geological carbon storage is a key mitigation strategy in the basin for reduced green house gas emission and long-term utilization of coal resources. Containment of CO2 in the basin is contingent upon the regional top seal, the Lakes Entrance Formation, providing an effective seal. Although the formation generally possesses high seal capacity across the basin, a number of hydrocarbon leakage and seepage indicators were previously reported. Common co-location of these indicators with fault zones emphasizes the critical role of fracture systems on the integrity and containment potential of the regional top seal.

Deformation of the top seal was modelled using multiple parameters including strain and curvature of the bounding horizons; and displacement, shale gouge ratio, slip tendency and dilation tendency of the cross cutting faults. These parameters were correlated to known leakage and seepage indicators in the basin to rank each parameter's performance in predicting areas of top seal bypass. Several parameters with good predictive performance were identified and integrated into multi-parameter leakage assessment factors (FLAF and OLAF). FLAF models the relative risk associated with seismic scale faults and OLAF captures the risk due to sub-seismic scale deformation separated from the main fault zones. These parameters were mapped across the study area showing consistent distribution with known leakage and seepage indicators and predicting additional areas with potential risk of top seal bypass. The risk maps provide useful input to CO2 storage and hydrocarbon exploration efforts at a regional scale.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012