Most of oil fields managed by PT PERTAMINA (PERSERO) are considered as brownfields and the oil produced only from primary recovery stage. To get better recovery of oil in those brown fields, it is necessary to have a long term project such as Enhanced Oil Recovery (EOR). Some screening criteria had been completed to select appropriate method which could be applied in certain field. In this study, we present gas injection program in West Java to obtain better recovery of the mature field/brownfield. The gas injection program include natural gas such as ethane, propane and CO2 flooding.

The viability relates mainly to the availability of CO2, the structure complexity, and finally the achievement of the Minimum Miscible Pressure (MMP). In the Jatibarang Field, it is not an issue of gas and CO2 availability since gas and CO2 sources are available in the field itself, and near by fields.

The Jatibarang Field primary recovery is only 16.2%, and the current reservoir pressure is as low as 500 psia. The reservoir performance shows the driving mechanism in this zone is very weak water influx. Therefore a Waterflood and/or EOR Program need to be evaluated to increase oil recovery.

Based on the screening criteria for oil fields in West Java, there are several possible CO2 flood candidates, one of which is the Jatibarang Field. A fluid compatibility test was conducted using Jatibarang Field fluids, from current to initial conditions. The fluid properties of current and initial conditions were compared and analyzed using numerical simulation. Then an appropriate fluid model was selected to represent the reservoir conditions. Regression and fine-tuning of the equation of state resulted in the fluid characterization for this study. Tuning of the EOS should give a fluid model that closely matches the lab test results.

Reservoir pressure is very important when it comes to designing gas and CO2 floods, as it is usually far below the MMP, as was the case in the Jatibarang Field. Based on the fine tuned fluid model, several gas and CO2 processes (immiscible and miscible flooding) were evaluated for the Jatibarang Field. These also included evaluation of different compositions of the natural gas and CO2 gas.

The best tuning of EOS will give the fluid model that closely matches the lab test results. and then the fluid is applied to the compositional reservoir simulation. More than 25 alternatives of gas injection is studied using the compositional simulation. The best recovery is combination of water injection, CO2, ethane and propane flooding (% incremental oil recovery).

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