HIGH RESOLUTION SEQUENCE STRATIGRAPHY, RESERVOIR ANALOGUES, AND 3D SEISMIC INTERPRETATION—APPLICATION TO EXPLORATION AND RESERVOIR DEVELOPMENT IN THE BARYULAH COMPLEX, COOPER BASIN, SOUTHWEST QUEENSLAND

Abstract

Gas exploration and reservoir development in the Baryulah area, Cooper Basin, southwest Queensland has focussed on the fluvial-lacustrine, Permian coal-bearing Patchawarra Formation, Murteree Shale, Epsilon and Toolachee Formations. Geological interpretation of drilling and 3D seismic data has benefitted from integration of sequence stratigraphic concepts with the judicious use of reservoir analogues and seismic attribute mapping. Initially, a coherent regional chronostratigraphic framework was established, based on broad palynological zonations, and correlating extensive lacustrine flooding surfaces and unconformities, tied to 3D seismic reflectors. This framework was subdivided by using local key surfaces identified on wireline logs (usually high-gamma shaly intervals overlying coals), resulting in recognition of numerous high-resolution genetic units. Wireline log character, calibrated by cores from analogous fields around the Cooper Basin and supported by analogue studies, forms the basis for a logfacies scheme that recognises meandering fluvial channels, crevasse splays, floodplain/basin, and peat swamps/mires. Fluvial stacking patterns (aggradational, retrogradational or progradational), produced by the ratio of sediment supply to accommodation within each genetic unit, were used to help determine depositional systems tracts (alluvial lowstand, transgressive, or highstand) and likely reservoir connectivity. Log signature maps for genetic intervals form the basis of palaeogeographic mapping. Modern and ancient depositional analogues were used to constrain likely facies distribution and fluvial channel belt widths. Syndepositional structural features, net-to-gross trends, and seismic attribute mapping are used to guide the scale, distribution and orientation of potential reservoir trends. When used in conjunction with structural and production data, the palaeogeographic maps help develop stratigraphic trap play concepts, providing a predictive tool for locating exploration or appraisal drilling opportunities.