Prediction Model for Critical Gas Injection Rate of Gas-Liquid Two-Phase Coupling in Reservoir Underground Gas Storage

Aiming at the expansion mechanism of the gas-drive oil-water mixed liquid phase during the gas injection process of the gas storage reconstructed from a flooded reservoir, this study breaks through the traditional prediction method of the critical gas injection rate for single-phase displacement, and solves the difficult problems such as large prediction error, instability of the gas-liquid contact and loss of gas storage space. Based on the gas-liquid flow law and the geometric relationship of the Dietz model, the saturation function of the oil-water two-phase and the correction of the relative permeability are introduced in the liquid phase region, and a dynamic coupling prediction model of the critical gas injection rate for gas-drive liquid and oil-water co-flow is constructed, and the conditions and main factors for stable gas injection drive in the secondary gas cap of the reservoir gas storage are clarified. The research shows that the accuracy of this model is on average 11.6% higher than that of the traditional single-phase drive model; the oil-water permeability, density, viscosity, and the formation dip angle are the main factors affecting the critical rate, and the greater the oil-water permeability, density and formation dip angle are, the greater the critical gas injection rate is, which is more favorable for the stable formation of the secondary gas cap and the utilization of the underground space. The case analysis shows that this model takes into account the oil-water co-flow mechanism in the liquid phase region, which is more scientific and reasonable. The research results provide a basis for the optimization of the gas injection parameters during the construction of the reservoir gas storage, and are of great significance for the stable formation of the secondary gas cap and the improvement of space utilization.