Publications

Four wells drilled near the edge of isolated carbonate platforms in Cepu Block, East Java basin, have found low porosity with average ~8% compared to 20-35% in the Platform Interior in the majority of the fields. Understanding the width, porosity and variability of the tight zone is a key step to estimating the oil and gas volume and to forming a development plan. The only way to model these factors with only a few well penetrations is to study the core evidence of the deposition and diagenetic differences between the tight edge and the high porosity Platform Interior and then describe a geologic process that predicts the width and distribution. Thin section analysis of both core and cuttings data from Cepu block indicate that the tight zones average 400’ wide, occur on both the oceanward and landward edges and are caused by a combination of depositional and diagenetic processes, primarily a lack of leaching that makes the Platform Interior such a good reservoir. This study examines available data describing tight carbonate buildup edges for other SE Asia fields to understand the robustness of the occurrence. The study of the ExxonMobil database and the literature reveals few other wells drilled on the flanks of carbonate buildups. Malampaya is possibly the best example and has wells with tight zones on both edges. The geometry of Malampaya is highly asymmetric similar to the geometry in Cepu suggesting a variation in wave energy is he probable cause of the tight edges. The high relief buildup edges have access to high wave energy from the deep ocean. The energy is not as strong on the buildup interior allowing the meteoric lens to develop better there and leach the primary depositional facies. Several SE Asian buildups have asymmetric profiles and we correlate the steepest * Mobil Cepu Ltd. sides with the direction of the most ocean energy on the paleo-reconstructions rather than the more commonly described correlation to the windward direction.