Experimental and Numerical Pore Scale Study of Residual Gas Saturation in Water/Gas Imbibition Phenomena

Residual gas saturation is one of the most important parameter in determining recovery factor of water-drive gas reservoir. Visual observation of processes occurring at the pore level in micromodels can give an insight to fluid displacements at the larger scale and also help the interpretation of production performance at reservoir scale. In this study experimental tests in a glass micromodel were used to determine the influence of the capillary number and pore morphology on the residual gas saturation in gas–liquid two-phase flow. The saturation of the phases was determined through recorded images in the micromodel. 2D modeling and simulation of this process is presented in this study and simulation results are verified by comparing to experimental results where sufficient agreement was confirmed.  The simulation results indicate that pore morphology and capillary number have significant influence on the competition between frontal displacement and snap-off.  Frontal displacement leads to high recovery and snap off causes gas entrapment. It is concluded that increasing the pore and throat sizes, increasing the coordination number and increasing angularity (decreasing half angle) result in reducing the residual gas amount. The results also indicate that residual gas saturation is not only a function of petrophysical property and pore morphology, but also it depends on flow rate and the experimental procedure. Residual gas saturation does not change significantly when Nc is less than 10-7.