Reservoir Simulation Challenges for Modeling a Thin Volatile Oil Rim With Large GasCap in the Poleng Field, Kujung-I Oil Reservoir, East Java Basin, Indonesia

摘要

This paper explores the difficulties in modeling an oil rim witha large gas-cap using black-oil and compositionalformulations. The example is from the Poleng field located inthe Poleng Block, East Java Basin, Indonesia. This reservoiris a reefal carbonate system with a limited aquifer within theKujung-I interval.Production from the field commenced in 1975, wassuspended in 1978 and re-activated by Kodeco in 1998. In2002-03, a full-field study was conducted to re-evaluate theOOIP and OGIP and investigate future development optionssuch as booster compression, gas and/or water injection,workovers, and infill wells. For this study, a new reservoirsimulation model was developed based upon new/updateddata. Two fluid PVT models (modified black oil andcompositional) were also developed. At the start of the study,the operator felt that compositional formulation might beneeded for modeling the gas injection processes. However,most of the work was performed using the modified black oilmodel because of computational speed consideration. Thehistory match process showed that many simulation layers(grid blocks) were required to match the wells near the fluidcontacts. Grouping some components in the compositionalmodel was helpful to reduce run time, but the resultingequations of state (EOS) were generally not reliable for boththe gas-cap and oil zones.Simulation results indicated that an OOIP of 98.5MMSTB was required to obtain a good history match. Theoriginal free gas-in-place was estimated to be 210.1 BSCF.The best future development option was a boostercompression project. For a 10-year prediction period,additional oil and gas recoveries for the booster compressorwere predicted to be about 1.7% OOIP and 19.0% OGIPcompared to the base case. Gas injection was less favorablebecause it would defer some volume of the gas sales, whilewater injection, workover and infill wells resulted in verysmall incremental oil and gas recoveries. The main reasonsfor the low oil recovery are high residual oil saturationsestimated from core analyses, reservoir heterogeneity, and gasfingering from the large gas-cap.