GEOMETRY OF RESERVOIR TRENDS IN THE EPSILON FORMATION SANDS, SOUTHERN COOPER BASIN, SOUTH AUSTRALIA

Abstract

Sandstone reservoirs within the Lower Permian Epsilon Formation, despite being gas productive in several fields in the Cooper Basin of South Australia, in particular Big Lake and Moomba, have proved to be elusive targets for exploration. This is mainly due to the distribution pattern of these sands, which differs markedly from that of the thicker and laterally extensive fluvial sands which are prevalent in the Toolachee and Patchawarra formations. As a consequence, there has been some acceptance that the distribution of Epsilon Formation reservoirs are unpredictable.

Log correlation studies of the Epsilon Formation, in conjunction with sand trend mapping, have identified sands which are either laterally continuous ('sheet' sands) or laterally discontinuous ('ribbon' sands).

Core facies analysis supports the interpretation that the 'sheet' sands are lake shore strandline deposits whereas the 'ribbon' sands are distributary channel deposits of prograding delta systems.

Based on the inferred depositional models, and with the aid of detailed isopach maps, it has been possible to project reservoir trends of the channel sands and prepare sand maps, at varying gamma-ray cutoffs, of the shoreface sands.

An understanding of the geometry of the various sand bodies has clarified the prospectivity of the Epsilon Formation and facilitated the selection of development well locations throughout the Southern Cooper Bas