A simple segregated flow model was developed to describe an alternate water and gas (WAG) injection process in a linear reservoir system. The model was developed based on the geometries of segregated fluid interfaces and on a volume balance of the injectants and the initial reservoir fluids. Results obtained from the model showed good agreement with published experimental and field data.

Assumptions in the model development includes immiscible water and gas phases, incompressible fluid flow, no trapped oil volumes and a uniform initial water saturation. Segregated flow interfaces depict the injected gas channeling to the top and the injected water channeling to the bottom of the oil zone. It assumes a pistonlike displacement and a fully segregated flow process.

The model tracks the progress of the respective interfaces and estimates the cumulative injection required to gas and water breakthrough. The model considers the fillup of initial free gas volume. The model can be easily extended to a five spot pattern by utilizing a streamtube approach, or by using an independently determined areal sweep efficiency.

A comparison of published experimental production data for different gas/water injection ratios with that predicted from the model showed excellent agreement. The model was satisfactorily used to predict the production performance of a field WAG process.

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