This paper describes the procedures of a simulation study to design an optimum CO2 flood process for the Texaco operated Roberts Unit located in the Wasson Field, Yoakum County, Texas. The designing process includes geological study to define flow units, CO2 target area selection, model area determination, fluid characterization, model calibration by history matching waterflood performance, compositional simulation forecasting for tertiary recovery, and economic analyses.

An equation-of-state (EOS) compositional simulator was used for both waterflood history matching and CO2 flood predictions.

Phase behavior of the CO2/Hydrocarbon system was calibrated by matching laboratory PVT test results. Tertiary forecasts were run for various continuous, water-alternating-gas (WAG) and hybrid modes of operation. Simulation results were scaled to represent the entire Roberts Unit CO2 target area. An economic indicator was then used to determine the optimum method of CO2 injection.

Study results revealed that hybrid mode of injection consisting of a 10% hydrocarbon pore volume (HCPV) initial slug followed by 1:1 WAG for a total CO2 injection of 40% HCPV yields optimum economics. The ultimate tertiary oil recovery in the target area is estimated at 14.1%- original oil-in-place.

The majority of the simulation study was performed on the RISC 6000 model 320 workstation. This study provides an insight to compositional simulation on a workstation platform.

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