Abstract

The Middle Miocene Mid-Main Carbonate (MMC) build-ups are the primary producing reservoirs in the Seribu Shelf area, north-northeast of Jakarta. One of the reservoirs, the MB MMC build-up, with cummulative production of 29 MMBO and 23 BCFG, is still producing more than 2,000 BOPD. It was estimated that a water flood could yield 5 MMBO additional reserve. As a water flood candidate, it was important to determine the depositional model as well as the reservoir flow units.

The MB MMC build-up was deposited on a well-oxygenated, open marine carbonate shelf. This build-up is a north-south elongated patch reef complex, composed of interbedded limestones and shales. These interbedded rocks were formed during several build-up development stages. The limestones are typically wackestone and grainstone, consist mainly of foraminifera bioclasts, bivalves, and echinoderm fragments, together with corals and reef algae. The shales are mainly terrigenous non-carbonate sediments deposited after each carbonate development stage. Based on RFT analysis, these shale breaks could act as baffles or permeability barriers to fluid movement during reservoir production.

High resolution wireline logs and cores show several transgressive-regressive cycles in an overal transgressive succession during MMC deposition. Karst breccia facies has also been recognized as evidence of sub-aerial exposure. Between the carbonate build-ups, some low-stand or inter-reef clastic sediments can be recognized in the log correlations. They were deposited as onlap to the build-ups and could be hydrocarbon carrier beds for the MMC reservoirs.

The result of this study is a retrograding carbonate build-up model, along with the determination of its flow units within the reservoir.