Publications

It has been well documented that seismic compressional velocities exhibit a gas effect “slow down” with relatively low gas saturations. Consequently shallow seismic amplitude anomalies are commonly associated with low gas saturation. In 1979 the Bawal-1 exploration well in Block B, Natuna Sea discovered stacked gas pay sands in the Miocene Arang formation associated with anomalous seismic amplitudes. The shallowest seismic amplitude objective penetrated a reservoir termed “Zone 0” exhibiting high gamma ray values with serrated log patterns indicating a silty reservoir. Conventional petrophysical analysis using standard shaly sand log analysis methods indicated Zone 0 to be water bearing or a low saturated gas reservoir. However, the Zone 0 amplitude expression exhibits strong conformance to structure, indicating buoyant gas trapped on this structure. This is hard to reconcile with low gas saturations which would typically be associated with a dynamic state of charge and imperfect top seal, and not buoyantly trapped hydrocarbons. In 2012 the Bawal 01 development well was drilled and 7 reservoir zones completed using IWS completion technology. The IWS well technology enabled individual completions to be remotely turned on or off and presented an opportunity to isolate and evaluate Zone 0. As a result Zone 0 flowed gas during a short period well test demonstrating that the reservoir was gas saturated. New petrophysical analysis on Zone 0 was consequently run using modified Indonesian equation. This analysis calculated a consistently low water saturation that matched with mud logs data and well test results. This integrated study has * ConocoPhillips Indonesia Inc. Ltd. proven gas production from a low resistivity reservoir previously considered to be water wet. It leads to further potential for economic development of similar prospects in Block B and elsewhere.