Abstract:

The capillary hysteresis effect in porous media has been studied extensively over many years, leading to a relatively unified conclusion. Due to the influence of capillary hysteresis, the morphology of capillary pressure-saturation curves and various parameters such as the saturation of trapped phases during gas-water alternating injection cycles are influenced by the saturation path and history. In petroleum engineering applications involving multiphase flow under alternating conditions, the capillary hysteresis phenomenon cannot be ignored. Current numerical simulation studies of CO2-water alternating processes often fail to fully consider the hysteresis effect, resulting in discrepancies between simulated and actual values for key parameters such as CO2 storage and oil recovery rates during development. Therefore, based on the Larsen & Skauge three-phase hysteresis model, this study designed and conducted multi-cycle CO2-water miscible and immiscible flooding experiments under high-temperature and high-pressure conditions using oil-bearing cores. The changes in capillary pressure curves during gas-water alternating cycles, with different initial injection phases under both miscible and immiscible conditions, were systematically analyzed. Numerical simulations were performed by fitting core experimental results using the Larsen & Skauge three-phase hysteresis model, and the fitting results of the experimentally measured hysteresis parameters were compared with those obtained from the corrected hysteresis parameter fitting. The results show that hysteresis is more pronounced in immiscible experiments compared to miscible ones. Additionally, the core’s initial saturation state also influences the gas-water alternating displacement effect. The hysteresis parameters measured by experiments are only applicable as initial fitting values, and separate experimental fittings should be conducted for different operational conditions. The findings of this study provide a reference for evaluating the capillary hysteresis effect in CO2-water alternating processes, reveal the changes in capillary pressure curves during multi-cycle gas-water alternating displacement, and improve the accuracy of numerical simulation studies on oil recovery and CO2 storage in relation to capillary hysteresis effects.

Key words: capillary hysteresis, CO2-water alternating, high temperature and pressure, numerical simulation, Larsen & Skauge model