THE STOKES GAS FIELD, SOUTHWEST QUEENSLAND

Abstract

The Stokes gas field is located in South West Queensland permit ATP 259P, close to the South Australia/Queensland state border. It was discovered and successfully appraised by the Stokes-1,-2 and -3 wells drilled during 1993 and early 1994. Productive zones, with DST flow rates of up to 237 x 103m3/d, are present in the Early Permian Epsilon and Patchawarra formations with moderate gas liquids contents present in the higher reservoirs. A total net pay thickness of 63 m occurs in Stokes-2. Generally, reservoir quality is moderate to good with core permeabilities occasionally exceeding one darcy. Some low deliverability Patchawarra Formation reservoirs are present which contain greater than 20 per cent kaolin. These microporous reservoirs are characterised by low resistivity responses similar to that of water saturated reservoirs.

The field's discovery coincided with the onset of renewed South West Queensland gas exploration. Seismic data were recorded in 1990 and 1992 to mature the Stokes prospect to drillable status. The structure had been recognised as being highly prospective due to its regional setting. Proved and probable gas-in-place exceeds 5.7 x 109 m3 which approximates the highside case estimated from pre-drill probabilistic reserves distributions.

Comprehensive reservoir pressure data were obtained from each well and were instrumental in locating appraisal wells and demonstrating that reservoirs are filled to the structural spill point. The Stokes-3 results indicate that some fault compartmentalisation may occur suggesting a more complex structure than originally mapped. Isolation of other reservoirs may also occur between Stokes-1 and -2.