The Effects of Coarsening Phenomenon on Foam Flow Behavior in Fractured Reservoirs

Gas is very efficient for displacing oil in enhanced-oil-recovery projects because of its high microscopic-displacement efficiency. However, the process at the reservoir scale suffers from poor sweep efficiency due to lower density and lower viscosity compared to in-situ fluids. Foam substantially reduces the mobility of injected gas and hence improves the sweep. Foam rheology in 3D geological porous media has been characterized both theoretically and experimentally. In contrast, the knowledge of foam flow in fractured porous media is far less complete. Due to the gas diffusion between bubbles, foam structure will be evolved over time. There is a good understanding of coarsening behavior in a bulk foam; however, coarsening in confined geometries such as porous media is not well defined. Based on the previous studies, coarsening will cause foam lamellae to move to low energy configurations in the pore throats, leading to increased capillary resistance when the flow is restarted. In this study, the impact of coarsening phenomena on the static foam behavior has been studied. Two different fracture geometries , including an irregular model with a mean pore diameter of 80 µm, and a regular model with a mean pore diameter of 60 µm, have been employed to conduct this study. Besides, the coarsening effects at two different foam qualities have been investigated using image analysis by ImageJ software. The results depict that the gas diffusion significantly depends on fracture geometry. The gas diffusion was ended after 5 hrs in the regular model, and the foam reached the equilibrium condition. In contrast, although after 18 hours, the coarsening rate became very slow in the irregular model, it cannot be confirmed that the coarsening rate has been stopped. Moreover, the results show that the variation in the foam quality can alter coarsening behavior. The amount of water present can effect on coarsening rate. When there is more water, capillary pressure is expected to be lower, Plateau borders are swollen, and there is less lamella area for diffusion. Hence, the coarsening rate in the dry foam was much quicker than the wet foam. In the final step, in order to estimate the capillary pressure, the fracture models have been profiled, and these estimations have been compared for both regular and irregular models. The results indicate that the capillary pressure ranges in the regular model were almost two times larger than the irregular model.