Study on Expansion Mechanism and Displacement Efficiency of Reservoir Gas Storage

At present, the technical research and construction of underground gas storage for reservoir reconstruction are carried out. It is necessary to deeply study the mechanism of storage capacity expansion and the efficiency of gas injection and oil drive for reservoir reconstruction, and to understand the law of capacity expansion, so as to facilitate the scientific design of storage capacity parameters for reservoir type gas storage. Guided by the theory of percolation mechanics and molecular dynamics of oil and gas reservoirs, this paper expounds 10 mechanisms of oil and gas flooding and oil expansion in reservoir gas storage, and defines that the injection pressure difference driving is the main mechanism of oil flooding and oil expansion, accounting for more than 70% of the total expansion capacity. Through innovative experimental research on gas injection and production of full simulation gas storage, it is concluded that gas displacement efficiency of conventional reservoir is positively correlated with injection and production cycles, but when injection and production are 8–10 cycles, the gas displacement efficiency of single cycle approaches 0, and the total gas displacement efficiency reaches the maximum value. The total gas displacement efficiency of high, medium and low permeability reservoirs is about 45%, 40% and 30%. The corresponding storage capacity is about 45%-30% of the volume of crude oil according to the storage height, medium and low permeability conditions. This result has a guiding significance for the design of reservoir storage parameters.