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ABSTRACT: AVO application in the Geragai Deep and Betara Complex Jabung Block, South Sumatera, Indonesia

Budihardjo, Santoso, and Farid Saifuddin , Santa Fe Energy Resources Jabung Ltd, Jakarta, Indonesia

Amplitude versus Offset analysis has played an important role in the 100% drilling success rate for delineation wells at North Geragai Field and the subsequent exploration and development success at Makmur in the Geragai Deep area. In this area, a strong positive AVO response correlates well with the presence of hydrocarbons (gas and its associated high GOR oil leg) in reservoir sands. While successfully applied in the Geragai Deep, we have been unable to fully utilize AVO in the Betara Complex area (Northeast Betara, North Betara, and Gemah fields).

Our studies suggest that there seems to be a threshold of thickness for gas-filled reservoir sands to generate a recognizable AVO anomaly (e.g., positive P*G attribute) to distinguish it from thinner gas or non-gas sand reservoirs. In an ideal case (no noise), synthetic modeling of well logs suggests that we should be able to detect positive an AVO response for an individual gas sand as thin as 15 ft. However, due to the presence of noise in the currently available seismic data, this threshold is estimated to be in the order of 25 ft. Therefore, the presence of an AVO anomaly is indicative of presence of relatively thick (25 ft or greater) gas-charged reservoir. Also, based on these results, absence of an AVO anomaly does not necessarily imply absence of hydrocarbons.

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