Investigation of Critical Capillary Number for Gas-Water System Through Experiment and Reservoir Simulation

ABSTRACT

Residual gas saturation is important in determining recovery from a gas reservoir with water influx. This research addressed residual gas saturation and other variables resulting from spontaneous and forced imbibition tests in porous media.

A new Critical Capillary Number for gas-liquid system was investigated through experimental procedures and numerical reservoir simulations. Capillary pressure curves and relative permeability curves were extracted from the spontaneous experimental data and were further applied to 1D and 3D numerical simulations to simulate the experimental data from co-current and counter-current spontaneous imbibition tests. Relative permeability curves were also calculated from forced co-current imbibition, which followed primary spontaneous imbibition. Different 1D numerical simulation
models were then used to simulate the data from forced imbibition experiments. The simulations showed the important role of gas compressibility and verified the residual gas saturation. Under the effect of gas compressibility, the Critical Capillary Number for gas-liquid systems is significantly decreased compared to the conventional number for oil-water systems. Sensitivity studies for different variables were also addressed in the simulation and it was found that the capillary pressure curve is the crucial parameter in the spontaneous imbibition tests but it is no longer important in the forced imbibition tests.

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