Abstract

The DOE Class 2 Demonstration Project operated by OXY USA Inc. in the West Welch Unit was designed to enhance economics in IOR projects in lower quality shallow shelf carbonate reservoirs. Accurate reservoir description is critical to the effective evaluation and efficient design of IOR projects in heterogeneous reservoirs. Therefore, the majority of the pre-injection effort was devoted to developing a geologic model that would allow a flow simulator to accurately match and predict reservoir performance. A base geologic model was constructed utilizing standard correlation and extrapolation methods to distribute the wellbore data across the interwell area. With the base geologic model, the flow simulator could only obtain a history match by making changes in porosity, net pay, and permeability of grid cells in the model. The changes were made using conventional history matching techniques, and the revised geologic model may not have been representative of the formation although a history match was obtained.

The base geologic model was then enhanced by incorporating seismic-guided porosity and pore volume map data to define the interwell properties. Since the seismic traces were on approximately the same spacing as the model grids, reservoir properties of porosity and thickness were available at each grid block. With the enhanced geologic model, the simulator was able to match the historical total fluid rates without the use of porosity or permeability multipliers. The simulator's water/oil ratio was too low with this model. Net pay and pay continuity were identified by other methods as the controlling parameters in the waterflood history match. The revisions resulted in higher oil saturation at the start of CO flood and an increase in forecasted oil production during tertiary recovery than when not using the seismic data. The predicted injection for the first three months is matching the actual field rates indicating these were valid changes to the simulator.

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