Core-based sedimentological and sequence stratigraphic analysis of shale-dominated gas plays: An example of the early to middle permian Roseneath-Epsilon-Murteree strata in the Cooper basin, Australia

Abstract

The early to middle Permian Roseneath-Epsilon-Murteree (REM) strata of the Cooper Basin are considered the most feasible shale gas play in Australia. The sedimentary evolution of the fluvial-lacustrine REM strata is complex and previous studies on the facies architecture have been very few and rough in nature. A systematic, core-based sedimentological and sequence stratigraphic analysis from this study reveals a range of complex features and sheds new light on the depositional process. More than 1400-m cores from nine wells penetrating the REM strata have been described in detail to study the lithofacies, facies associations, and associated stacking patterns. Twelve lithofacies are identified and further categorized into eight facies associations: (1) open lacustrine, (2) lacustrine shoreface, (3) flood plain/interdistributary bay/channel fill, (4) distributary channel/fluvial channel, (5) crevasse channel/splay/natural levee, (6) distributary mouth bar, (7) prodelta, and (8) mire/swamp. The Roseneath and Murteree Shales were deposited in a widespread lake with dominant rhythmites and claystones whereas the Epsilon Formation was formed in a transitional environment with a mixture of fluvial, deltaic, shoreface and mire deposits. Sequence stratigraphic analysis of cores and wireline logs reveals that the REM strata were deposited within two 1st-order Transgressive-Regressive (T-R) cycles and can be further separated into four sequence units. Lower-order T-R cycles are also observed among these 1st-order cycles. This study provides a good analogue and/or a case for comparison with other shale-dominated gas plays around the world and a similar approach should help clarify their depositional process.