f Chasing Subtle Plays in a Mature Carbonate Province

The Central Luconia Province is a stable Late Tertiary platform, flanked by two area’s of active deltaic sedimentation, located offshore Sarawak. It is characterised by widespread carbonate deposition, which started in the Early Miocene, and during Middle to Late Miocene high-relief carbonate build-ups developed with some reaching a thickness of more than 1500m. This carbonate depositional phase ended with a series of regressive events, and the build-ups became subsequently covered by marine shales derived from prograding deltas. These high relief carbonates formed the historic exploration objective since the mid- 1960’s, with some 40 Tscf reserves discovered to date. This play, which was evaluated on 2D data, is well understood and very mature. The success rate of this play has been decreasing, culminating in a 5 well drilling campaign in 2000, without a commercial success. The play appeared creamed with limited volume potential left. The advent of larger production-oriented 3D surveys provided new insights into the early phases of carbonate growth and allowed the identification of subtle traps adjacent to the prolific discoveries. Making use of constrained sparse spike inversion a porosity sweetspot, encased in a potential low permeable facies, was identified near the large Eli Field. This was subsequently drilled as a secondary objective of a deeper test. The result of this well proved that a sealing tight carbonate facies is present as the GWC extends 250 ft below the structural closure, making this discovery a true stratigraphic trap. This discovery has resulted in a different way of looking at carbonates, moving away from high relief 2D structural evaluation towards subtle, 3D based, facies mapping. Several other low relief build-ups have been identified since on 2D and <br>late 2003 the first exploration 3D has been acquired to mature this play further.