Fluid phase behavior during multi-cycle injection and production of underground gas storage based on gas-condensate reservoirs with oil rim

Underground gas storage (UGS) plays an important role in energy supply and peak shaving of urban natural gas. Fluid phase behavior and mass transfer are complicated during multi-cycle injection and production of UGS especially based on gas-condensate reservoirs with oil rim, which will impact the fluid properties, gas-oil recovery factor and stability of UGS. This work innovatively develops an experimental approach to investigate the phase behavior during multi-cycle gas injection and production in a UGS based on gas-condensate reservoir with oil rim in Bohaiwan basin, China. The produced fluid composition, residual fluid properties and oil recovery factor are analyzed. Results indicated that the condensate oil recovery factor is only 24.12% and the oil rim influences condensate oil recovery factor during primary depletion. The oil recovery factors of individual cycles are 8.33%, 5.79%, 3.83%, 1.92% and 0.88%, respectively. The total condensate oil recovery is 20.75% after five cycles, indicating multi-cycle gas injection and production can effectively extract and evaporate oil phase especially in the first and second cycles. As the cycles increase, the composition difference between injected gas and oil rim becomes larger and the evaporation of oil rim by gas injection is weakened. The GOR of oil rim under the 24 MPa decrease from 190.5 to 162.5 m3/m3, indicating gas dissolving ability of oil rim decrease. The remaining oil saturation is 1.7% after five cycles, lower than the primary depletion (3.8%), indicating part of oil rim is also produced and the gas storage capacity is enhanced after multi-cycle injection and production. This work provides an approach to understand the phase behavior of UGS in condensate gas reservoirs with oil rim and is beneficial for the efficient operation of UGS.