ABSTRACT: Kaji-Semoga, Indonesia's largest onshore oil discovery in the decade of 1990-2000

Hutapea, Oskar M., Surarso Hardjono, and Dindot Soebandrio , P.T. Exspan Sumatera, Jakarta, Indonesia

Kaji-Semoga, a structural-stratigraphic controlled oil accumulation with current estimated ultimate recoverable oil exceeding 150 MMBO, is one of the largest onshore oil discoveries in Indonesia during the last decade of the twentieth century. The field, located within the mature exploration province on the southern part of the Sumatera island, Indonesia, was discovered in 1996 by P.T. Exspan Sumatera.

The field comprises two separate pools, with the Semoga pool oil-water contact being 220 feet higher than in Kaji. The production is mainly from reefal carbonates of the Early Miocene Baturaja Formation. Further, fluvio-nearshore clastics of the Oligo-Early Miocene Talang Akar Formation and nearshore sands of the Early-Mid Miocene Telisa Formaton also productive locally. The production units in each pool share a common oil-water contact. The Baturaja carbonates have good reservoir quality except at the reef edge where tight facies occurs and which provides a permeability barrier and stratigraphic entrapment exceeding the simple four way structural closures. In contrast, the Talang Akar and Telisa reservoirs are rather tight.

Accurate seismic depth mapping of the producing horizons at Kaji-Semoga is complicated by velocity variations. Velocity data from new downdip well controls have frequently increased the areal extent of the oil accumulation in the known reservoirs that necessitate a revision of the reserve estimations. Similar changes can still be expected in the future. The reserve additions may also be indicated when plans to optimally produce the Talang Akar and Telisa sandstones reservoirs are materialized.

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