Scheme Design of Rebuilding Gas-Cap Sandstone Reservoirs into Underground Gas Storage

At present, the main types of underground gas storage (UGS) are depleted gas reservoir, aquifer and salt cavern, and the technology of gas-cap sandstone reservoir reconstruction is not fully mature. NP-N UGS is rebuilding from gas-cap sandstone reservoir. With complex geological structure and fluid distribution, the design and construction of NP-N UGS is complex and difficult. In this paper, we design the construction scheme from the aspects of trap dynamic and static sealing evaluation, storage capacity parameter design, and operation mode of construction. It is found that the geological body of NP-N UGS has a good sealing property, and the maximum formation pressure that the geological body can bear to maintain dynamic sealing is 27.2 MPa, which is 1.2 times of the original formation pressure. The design storage parameters are 1.2 times of the original formation pressure, the gas reservoir operating pressure is 9.6–27.0 MPa, the oil reservoir operating pressure is 10.6–27.0 MPa, the overall effective storage capacity is 18.14 × 108m3, the working gas volume is 10.52 × 108m3, the working gas is 2.68 × 108m3 more than the original formation pressure design. The gas reservoir is restored by efficient gas injection, and the reservoir is transformed from injection and production controlled by single gas drive to area interactive flooding, and pressure and liquid drainage are gradually expanded. NP-N UGS is the first overpressure designed gas-cap sandstone reservoir in China, and this scheme design will provide a reference for the scheme design of similar reservoirs.