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Abstract Faults are weak areas in rocks; however, faults have a very important impact on the construction and operation of underground gas storage. When gas is injected or produced into the gas storage, the increase or decrease in pore pressure in the surrounding rock mass may cause fault slip. A three-dimensional geomechanics model is established to study the evaluation methods and indicators of fault slip activation under alternating working conditions of gas storage. To accurately evaluate the stability of faults under alternating stresses and quantify their bearing capacity, this study established a three-dimensional dynamic rock mechanics model based on a fine three-dimensional geological model, combining one-dimensional rock mechanics modeling data and reservoir simulation results. This model uses a reservoir simulator and a rock mechanics simulator to calculate in synergy to reflect how the periodic pressure fluctuations inside the formation affect the local underground stress field and cause elastic and plastic deformation of the formation rock. Then, based on the relevant rock mechanics principles, the stability of the fault within the designed operating range can be quantitatively evaluated to optimize the operating pressure range of the gas storage in the best way. Set the fault to be open or closed for numerical simulation, observe the changes in the pressure monitoring curve of the monitoring well near the fault, and compare the observed curve with the pressure curve of the injection and production operation cycle to determine the closure of the fault. The calculation results show that one of the three faults is open. Drilling accidents are identified and analyzed to provide calibration data for formation stress and rock mechanics models, and a reliable three-dimensional geomechanics model is established. The grids through which the fault passes are marked as fault units, and their mechanical properties are obtained by distributing the equivalent rock mechanics parameters according to the different weights of the fault and the intact rock, and quantitatively describe the shear force, normal stress, pore pressure and friction coefficient acting on the fault plane. Based on the analysis of the maximum pressure rise in the geomechanics state and weak faults, the minimum limit formation pressure of the three faults is 42.5 MPa. Based on the analysis results of the gas storage fault, the ultimate bearing pressure of the gas storage is about 42MPa. Safety is always the top priority for gas storage. In addition to deploying monitoring wells, numerical simulation and rock mechanics research were also conducted to determine the evaluation method and calculate the safety index parameters for the safe operation of gas storage during the alternation of injection and production conditions, setting a benchmark and example for the operation of similar gas storages in this oilfield.