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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper explores the difficulties in modeling an oil rim with a large gas-cap using black-oil and compositional formulations. The example is from the Poleng field located in the Poleng Block, East Java Basin, Indonesia. This reservoir is a reefal carbonate system with a limited aquifer within the Kujung-I interval.Production from the field commenced in 1975, was suspended in 1978 and re-activated by Kodeco in 1998. In 2002-03, a full-field study was conducted to re-evaluate the OOIP and OGIP and investigate future development options such as booster compression, gas and/or water injection, workovers, and infill wells. For this study, a new reservoir simulation model was developed based upon new/updated data. Two fluid PVT models (modified black oil and compositional) were also developed. At the start of the study, the operator felt that compositional formulation might be needed for modeling the gas injection processes. However, most of the work was performed using the modified black oil model because of computational speed consideration. The history match process showed that many simulation layers (grid blocks) were required to match the wells near the fluid contacts. Grouping some components in the compositional model was helpful to reduce run time, but the resulting equations of state (EOS) were generally not reliable for both the gas-cap and oil zones.Simulation results indicated that an OOIP of 98.5 MMSTB was required to obtain a good history match. The original free gas-in-place was estimated to be 210.1 BSCF. The best future development option was a booster compression project.For a 10-year prediction period, additional oil and gas recoveries for the booster compressor were predicted to be about 1.7% OOIP and 19.0% OGIP compared to the base case. Gas injection was less favorable because it would defer some volume of the gas sales, while water injection, workover and infill wells resulted in very small incremental oil and gas recoveries. The main reasons for the low oil recovery are high residual oil saturations estimated from core analyses, reservoir heterogeneity, and gas fingering from the large gas-cap.

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