Abstract

The Kutei (Indonesia) and Sarawak (Malaysia) basins are two important petroleum producing provinces in Borneo where deepwater exploration efforts require an integrated technical approach to reducing pre-drill reservoir risk. In Southeast Asia, additional risk pertains to increased distance from Type III coaly source rocks formed in updip coastal-plain paleoenvironments. In Sarawak (northern Borneo), successful pre-drill prediction of reservoir type and content in deepwater blocks was based on regional sequence stratigraphic correlation and seismic facies calibration. Sequence stratigraphic analysis resulted in interpretation of a NE-SW trending fluvial-dominated delta in the deepwater prospect area. As predicted, abundant, thick marine sandstone reservoirs were penetrated in wells drilled in the deepwater. Less success was experienced with predicting hydrocarbon charge which post-drill studies indicate are related to maturity and the distance (>20 km) from coeval coastal-plain coals. In the Mahakam delta (southeast Borneo), regional mapping of Miocene and Pliocene shelf sequences proved critical to identifying sand-prone fairways for deepwater lowstand reservoirs. Maps constructed from seismic, cores, and logs pointed to key canyon system entryways and adjacent sand-prone highstand deltas. Defining the location of lowstand depocenters also reduced risk regarding source rock, as these provide the major kitchens for hydrocarbon migration. Recent discoveries of oil, gas, and condensate in thick Upper Miocene and Pliocene deepwater sandstone reservoirs have validated the pre-drill predictions in reservoir and source rocks.