Pressure transfer characteristics during the process of gas injection in tight reservoir

The pressure-transfer has a significant effect on energy supplement and enhancing oil recovery during the process of gas injection in tight reservoirs. Based on the one-dimensional core pressure monitoring and nuclear magnetic resonance technology, the dynamic pressure transfer characteristics and coefficient are investigated, and the effects of permeability, viscosity, and pressure difference on pressure transfer rate are analyzed. Different from the traditional view that the pressure transmission coefficient is a constant value, the pressure transmission coefficient during the gas injection process can be divided into three stages. When the oil saturation is higher than 79%, it is in the gradual change stage of the low pressure-transfer coefficient, and the pressure transfer coefficient decreases slowly with the decreasing of oil saturation (2.1 × 10−6 → 0.9 × 10−6 m2/s). However, it is in the mutation stage of pressure transfer coefficient when the oil saturation is between 79% and 68%, and the pressure transfer coefficient jumps from the order of 10−6 to 10−4 m2/s with a further decrease in oil saturation. When the oil saturation is lower than 68%, it is in the gradual change stage of the high pressure-transfer coefficient, and the pressure transfer coefficient increases slowly with the decreasing of oil saturation (1.3 × 10−4 → 4.4 × 10−4 m2/s). There is a significant positive correlation between pressure transfer coefficient and reservoir permeability as well as reservoir pressure and pressure difference, while the fluid viscosity has a significant negative correlation with the pressure transfer coefficient. The proposed method offers technical support for upcoming tight reservoir exploit and gas injection projects.