Study on 4D Geomechanical Modelling for Fault Critical Re-Active Stress Evaluation in Underground Gas Storage

Abstract During the high-speed injection and extraction cycle of an underground gas storage reservoir, the pool's pore pressure, effective stress, and faults change periodically, which may cause formation damage and natural gas leakage, thus affecting the sealing of the entire reservoir. At the same time, the non-homogeneity easily causes local pressure accumulation, which makes the pore pressure and effective stress distribution extremely unbalanced, and the local pressure accumulation in the formation is a potential threat to the operation of the gas storage reservoir. At the same time, clarifying the fault stress field evolution can provide theoretical support for raising the upper limit pressure at a later stage. Therefore, the study of four-dimensional stress field evolution characteristics of the gas storage reservoir geologic body is directly related to the safe operation and efficient use of the gas storage reservoir. This paper investigates the evolution characteristics of fault stress fields in light of the characteristics of multi-cycle high-flow injection and extraction cycles in gas storage reservoirs. In this paper, numerical simulation is used to analyze the factors affecting the integrity of the fault. At the same time, gas-water two-phase seepage and flow-solid coupling principles are used to analyze the seepage mechanics and geomechanics of the conceptual model by combining with the integrated software of geoengineering. According to the simulation results, the pressure and stress fields with time and space changes and distribution characteristics were carried out, and the destructive prediction was carried out to find the submerged destabilized parts. A large-scale seepage-stress coupling field model was established based on the field data, and the model's accuracy was verified by simulation. Finally, seepage mechanics and geomechanical analysis were carried out for the actual model, and the results can provide theoretical support for the construction of the project and the adjustment of the injection and mining program in the later stage to improve the upper limit pressure.