GEOLOGY OF THE DELLA FIELD, A PERSPECTIVE ON THE HISTORY OF THE COOPER BASIN

Abstract

The Della Field produces dry gas from stacked fluvial sandstone reservoirs in the Early Permian Patchawarra Formation and Late Permian Toolachee Formation. Localised but severe fault activity and erosion in the late Early Permian have resulted in structural and stratigraphic complexities, particularly on the western flank of the field.

A detailed study of lithofacies associations from cores has enabled constraints on the resolution of petrophysical logs to be appreciated. Within these constraints major facies associations are mappable across the field. Active channel migration in the Patchawarra Formation resulted in erosion and hence incomplete preservation of the fluvial sequence, which hinders mapping across the field. In contrast, the successive fluvial cycles of the Toolachee Formation are more completely preserved, enabling intrafield and some interfield correlation and mapping. The contrast is due to changing responses of the fluvial regime to prevailing tectonic conditions.

A preliminary fluvial facies model, proposed after the first six Della wells, was upgraded during development drilling, with the result that productive reservoirs were successfully predicted. Integration of all available data provides one perspective on the evolution of the Cooper Basin in South Australia.