Numerical Simulation of Gas-Water Two-Phase Microflow Mechanism in Carbonate Gas Reservoir

Abstract

AbstractCarbonate gas reservoir is characterized by strong heterogeneity, complex pore structure, and complex two-phase flow mechanism. It is difficult to accurately describe the pore structure and flow characteristics by traditional methods. To enhance the understanding of pore structure and flow mechanism of the carbonate gas reservoir, this paper reconstructed a digital core and a 2D pore network of a carbonate gas reservoir based on CT images, intuitively shown the microstructure of the carbonate reservoir, and made quantitative analysis. Based on the 2D pore network, the gas-water two-phase flow was simulated based on the phase-field method, and the change of the two-phase interface could be described in real-time by tracking the two-phase interface. The simulation results were compared with the analytical solutions to verify the reliability of the numerical simulation. Based on the two-phase flow method of the micro pore network, this paper analyzed the key factors affecting the two-phase flow, and intuitively shown the gas-water distribution. The results show that the medium wettability and the injection rate have great influences on the gas-water flow. By observing the flow process, the residual gas can be summarized into three types: the trapped gas at the blind end or corner, the trapped gas formed by circumfluence, and the stuck gas caused by throat contraction. This work provides a theoretical basis for further improving the development efficiency of carbonate gas reservoirs.KeywordsCarbonate gas reservoirDigital corePhase-field methodTwo-phase flowTrapped gas