RESERVOIR CHARACTERISATION OF THE MOORARI/WOOLKINA FIELD COMPLEX, COOPER BASIN

Abstract

The Tirrawarra Sandstone oil accumulation at the Moorari/Woolkina Field complex in the Cooper Basin, Central Australia has been under miscible gas flood EOR since 1984. A facies-based reservoir characterisation study of the field was undertaken to help explain unpredicted field performance and to provide a reliable model on which to base any future field development and necessary engineering studies prior to blow down.

The reservoir is dominated by the interaction of fluvial braid-plain and glacio-lacustrine shoreface processes in a braid-delta setting. It comprises five basic facies from which eleven sub-facies are identified, eight containing oil bearing reservoir. An extensive field wide lacustrine mudstone acts as a vertical barrier and divides the reservoir into two gross sand units. The individual sub-facies were petrographically and petrophysically characterised and mapped in detail to provide a model of the field architecture, within which the residency of the original and remaining oil-in-place was determined.

A substantial increase in OOIP explained the better than predicted performance from the EOR pattern and highlighted the field flanks for assessment for incremental development. This was confirmed by the engineering data review which also revealed that the poor structurally low wells were affected by relative permeability effects. As a result of this study, plans for incremental field development are in progress with the goal of increasing reserves and production.