Experimental study on the inlet behavior of CO2 foam three phase displacement processes in porous media

In relation with the potential applications of CO2 foam technology on Enhanced Oil Recovery and CO2 geological storage, the foam assisted CO2 displacement process in a surfactant solution and oil pre-saturated porous medium is experimentally investigated with special attention on the dynamic foam propagation behavior in the entrance region of porous media. Computational Tomography (CT) imaging is employed to visualize the transient CO2 foam sweep process and the dual-energy CT measurement is performed to obtain the dynamic three phase saturation distributions along the sample core. Studying parameters include the comparison with N2 foam, system backpressure and the porous medium permeability. It is found foam could push most of the liquid phase in the latter part of the porous media but leaves the forepart of the sample less flooded, showing a clear entrance effect of foam flooding process. Compared to CO2 foam, N2 foam displacement process shows higher liquid phase saturation in the entrance section and presents less oil recovery rate. Elevating system backpressure to 1.0 MPa leads to less pressure drop for CO2 foam flooding process without compromising the oil phase sweep efficiency. The CO2 foam flooding process in lower permeable medium shows higher pressure drop and higher oil recovery rate. The mechanisms for the inlet behavior of the foam displacement processes have been scrutinized based on good qualitative and quantitative agreement of the experimental and numerical results with the stochastic bubble population balance model.