Geochemistry Analysis for Reoptimizing Gas well to be Developed – Case Study Asri Basin, Offshore Sotheast Sumatra

 ABSTRACT

Asri Basin is one of the prolific basins in Indonesia, with cumulative oil production up to 549 MMBO. For many years exploration and development, focus on chasing oil from TalangAkar Formation (TAF), the proven productive reservoir. During the exploration stage, Susana-01 was drilled to the multiple targets; primary target is Gita member – TAF, and the secondary target is Air Benakat anomaly which is indicated by Direct Hydrocarbon Indicator (DHI) and confirmed also by the result of geochemistry laboratory test in Field “C” well.A large number of methane (98.85 mol percent) is showed by the gas analysis result, with gas wetness 0.50 %, calculated gas gravity 0.561, and calculated gross heating value 1007.2 BTU/ft3 dry gas (@ 14.730 PSIA and 60o F). Gas stable isotope composition data is used to identify genetic gas characterization; and based on the Schoell‟s diagram result, it showed unlikely to be a biogenic gas without generated hydrocarbons. During the exploration and development stages, this feature is considered as a suspect of drilling risk. Therefore, only limited data to be identified and evaluated as shallow gas potential. Based on Susana-01 drilling report, gas was founded in sandstone reservoir – Air Benakat Formation. This gas also exists in “C” development field. Thus, the distribution of gas reservoir needs to be mapped.Gas supply is one of main concerns for oil production support in this area. Existing turbine is fueled by gas and still relied from another gas field in other basin. If the gas supply can deliver within Asri Basin, it would be beneficiary for the field performance in forward. The subsurface preliminary review conducted to evaluate whether this shallow gas potential or only keep as a drilling hazard.

Keywords: Air Benakat reservoir, isotope, methane, shallow gas