PRESSURE STUDY OF THE FLACOURT FORMATION AQUIFER IN THE THEVENARD ISLAND AREA OF THE BARROW SUB-BASIN

Abstract

Thevenard Island area lies in the offshore Carnarvon Basin off the northwest coast of Western Australia. The Flacourt Formation of the Cretaceous Barrow Group sequence is the primary oil-producing reservoir. West Australian Petroleum Pty Limited (WAPET) as operator on behalf of its participants (Chevron, Texaco, Shell and Mobil) has been producing from this reservoir since 1989. It has widely been held that in this area the relatively thick, multi-darcy Barrow Group oil accumulations have had infinite aquifer pressure support with no regional draw-down effect.

After the commencement of oil production from the Flacourt Formation, wireline pressure surveys in exploration and development wells have indicated anomalous pressure trends in the reservoir. Initially, the accuracy of pressure gauges and elevation measuring devices were questioned.

Recent studies based on WAPET's production history in the region and re-analysis of wireline pressure data have shown that the Flacourt Formation does experience regional draw-down in aquifer pressure due to production. This paper demonstrates the existence of draw-down and how this information has aided in the evaluation of the Flacourt Formation and the overlying Mardie Greensand reservoirs.