Injection–production mechanisms and key evaluation technologies for underground gas storages rebuilt from gas reservoirs

Abstract

Underground gas storages (UGSs) rebuilt from gas reservoirs is the most popular UGS type in the world. It accounts for 75% of the total active gas of all gas storages. In order to design more scientific and reliable geological schemes for constructing the underground gas storages rebuilt from gas reservoirs and optimize the UGS operation parameters, we analyzed the UGS basic characteristics of multi-cycle high-rate injection and production. Then, the dynamic sealing capacity of traps and the water–gas high-speed interactive flow mechanism of UGSs rebuilt from gas reservoirs with complex geological conditions were investigated by both physical simulation and numerical simulation. Finally, the key technologies for evaluating the dynamic sealing capacity of caprocks and faults and the storage capacity parameters were developed. Some results were obtained. First, the alternating stress in the process of UGS injection and production weakens the original static capillary sealing capacity and mechanical integrity of caprocks to different extents, and the trap sealing capacity can be quantified and evaluated comprehensively by using dynamic breakthrough pressures, shear safety indexes and other indicators. Second, a UGS capacity design method based on effective gas-bearing pores was developed according to the local pore-based recovery mechanism revealed in the high-speed gas–water mutual flooding test. Field application in the multi-layer UGS of H shows that these technologies provide an effective guidance for the design of geologic schemes. After five cycles of injection and production, its ramp-up ratio reached 91.8% and the peak shaving capacity increased quickly to 36.3 × 108 m3 from 2.7 × 108 m3 in the early stage of production. Moreover, the operation indicators matched well with the design. Keywords: Underground gas storage rebuilt from gas reservoir, Production mode, Operation law, Dynamic sealing capacity of trap, Evaluation index, Injection–production mechanism, Injector–producer flow, Storage capacity parameter