EVALUATION OF WATER SATURATION IN A LOW RESISTIVITY ZONE: ARANG ZONE 0, BAWAL FIELD

摘要

The Bawal Field was discovered in 1979 in the South Natuna Sea Basin, by the Bawal-1 exploration well. The well targeted the crest of a simple anticline with DHI amplitude conformance in the Miocene Middle/Upper Arang clastics.rnThe Bawal reservoirs consist of sub angular to rounded, well sorted, silt to very-fine quartz sandstones typical of this region. The Arang clastic reservoirs are interpreted to have been deposited in a fluvio-deltaic environment. The Bawal Field is comprised of 8 stacked Arang reservoirs namely Arang Zone 0-8. Uniquely, Zone 0 displayed extremely low resistivity, while paradoxically showing high total mud gas readings, low gamma ray log and conforming bright seismic amplitude response. At that time Zone 0 was considered to be a low saturation, water-wet zone with low saturation gas amplitude effects seen on seismic. Recent re-evaluation encouraged a trial production test which was successful for gas in Zone 0.rnThis paper discusses the standard shaley sand log analysis methods which gave pessimistic values of water saturation when applied to Bawal-01 well Zone 0. Comparison of water saturation calculations between the modified Indonesian and Simandoux equations are discussed to find which one is more consistent with the mud gas data and production test result.rnApplying the properly calibrated equation will lead to improved saturation calculations for similar zones across the low resistivity zones in the Arang and potential shallow gas pays in the West Natuna Basin.