Abstract

Exploration for gas at shallow depths and subsequent development of previously discovered gas by Atlantic Richfield Indonesia Inc. (ARII) in the Northwest Java Sea has recenty become more important. This is primarily due to increased industry demand and the desire for Indonesia to be less reliant on fuel oil for power generation. Historically, the Parigi and Pre-Parigi carbonate buildups are known to contain large quantities of gas and thus offer the best opportunity for obtaining new reserves at reasonable cost.

Reservoir development in the Parigi and Pre-Parigi arises through the presence of vugular, mouldic and intragranular porosity uniformly distributed throughout the carbonate section. The reservoired gas is dry and interpreted to be thermogenic with insignificant amounts of C₂+ and CO₂. The hydrocarbons were sourced from deeper Talang Akar shales and coals just before, or during, the early phase of oil generation. The migration of gas has been interpreted to occur through vertical fault migration from the Talang Akar into the higher sections. Absence of oil in the Parigi and Pre-Parigi reservoirs implies that the heavier hydrocarbon fractions were either stripped during migration or were prevented from accumulating in the buildups owing to the presence of the earlier migrated gas.

Parigi and Pre-Parigi buildups of varied thicknesses have been drilled. Although direct hydrocarbon indications from seismic are useful in high-grading some prospects, most pre-drill seismic predictions have been inconclusive.