Numerical simulation of UGS facilities rebuilt from oil reservoirs based on the coupling of seepage and temperature fields

Peak shaving and supply guarantee are the functions of Underground Gas Storage（UGS）. The accurate prediction of the UGS construction index is related to the number of new wells and investments. When a complex fault block reservoir is transformed into UGS, it encounters three-phase flow（oil, gas, and water） during multi-cycle and high-velocity operations. The petrophysical properties of oil and gas are greatly affected by temperature. Without considering the temperature disturbance after cold gas injection and the additional pressure loss of high-velocity turbulence, the index prediction accuracy of the existing numerical simulation methods for UGS is low. To improve the accuracy of index prediction for a UGS rebuilt from a complex fault block oil reservoir, combined with fluid viscosity-temperature and high-velocity turbulence experiments, a coupled mathematical model of seepage and temperature is established. The model is solved discretely using the Finite Volume Method（FVM）, with a Two-Point Flux Approximation（TPFA） scheme for spatial discretization and a backward （implicit） Euler scheme for temporal discretization. The material balance and pressure of the reservoir and single well in the depletion development stage are matched with high precision. The sensitivity analysis of the UGS operation index is carried out in an example. The results show that the disturbance of the cold gas injection temperature field and high-velocity non-Darcy effect is the main controlling factors of accumulative oil production and gas volume error respectively. The well control temperature range increases logarithmically with the gas injection rate and the water-phase seepage capacity increases when the oil-phase and gas-phase seepage capacity decreases significantly, resulting in the increase of the produced liquid volume and the decrease of formation pressure. The additional pressure drop caused by high-velocity turbulent flow results in some injected natural gas not being produced, leading to an increase in natural gas reserves and pressure over successive cycles.