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ABSTRACT: New play in a mature basin: Prospecting for gas

Zeliff, C. W. and Dixie Bastian , Gulf Indonesia Resources Ltd, Jakarta, Indonesia

Drilling for traditional oil reservoirs in a remote 1991 wildcat well set the stage for a large-scale gas development in the South Sumatra Basin and opened a prolific new exploration play for fractured basement reservoirs. Dayung-1 found oil targets in the Talang Akar sandstones shaled out, but encountered deeper gas pay in fractured preTertiary granite wash and granite. Despite major uncertainties in the quality and storage capacity of these fractured reservoirs, the reserve potential of this large (45 sq. km) basement uplift initiated a highly successful deep drilling campaign and inspired a billion dollar gas project. There were significant obstacles along the way: resolution of deeply buried structures was hampered by poor seismic data quality, drilling hazards included severe lost circulation and hostile, high temperature environments, the unique reservoir challenged conventional petrophysical analysis and well testing encountered hazardous CO2 and H2S bearing gas.

Since Dayung, Gulf has discovered 8 gas fields where basement metasediments and igneous rocks represent the primary reservoir. To date the success rate has been 80% for prospects with basement originally identified as the primary target.

The success of this new play has not only provided gas reserves for the Caltex Duri steamflood and power generation in the Republic of Singapore, but has also resulted in the creation of a pipeline infrastructure in Sumatra which will encourage the ongoing search for new gas resources by all contractors in the basin.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia