Numerical Simulation Of Geologic Body Stress Field In Gas Storage Traps

As an important energy storage facility,the evaluation of trap integrity is an important subject of structural storage and environmental safety,which is of great significance to the research on reservoir,caprock and fault integrity of underground gas storage.According to the British Geological Survey,26 % of the more than 100 safety accidents of underground gas storage are related to the integrity failure of caprock and fault.Therefore,in the reconstruction of underground gas storage project,how to correctly and reasonably evaluate the integrity of traps can effectively prevent the failure of underground gas storage in the operation process and prevent the safety accidents of underground gas storage.In order to better guarantee the safe and efficient operation of underground gas storage,this paper evaluates the integrity of trap geological body of gas storage by using numerical simulation method.Firstly,referring to the published literature,the dynamic coupling model of trap ground stress and reservoir seepage was established to simulate the dynamic stress field.And the simulation results were compared with the published literature results to verify that the model established met the engineering requirements.Based on the verification model,the sensitivity analysis of each parameter was carried out to clarify the main controlling factors affecting the deformation of underground gas storage.Then the triaxial compression test and fault friction strength test were carried out based on existing or artificial cores,and Poisson’s ratio,elastic modulus,fault friction strength and other parameters were obtained.On the basis of these parameters and logging data,the stress state of a single well was calculated.Finally,taking Q depleted gas reservoir of high-pressure as the research object,considering the characteristics of stress field changes under alternating stress,combined with geological,logging and laboratory rock mechanics experimental results,the dynamic coupling model of ground stress and reservoir seepage of large-scale traps in Q gas storage area was established.And the stability of reservoir,caprock and fault under alternating stress was comprehensively evaluated after the development and reconstruction of Q gas storage.The results show that:(1)The most sensitive parameter to reservoir deformation is reservoir porosity,followed by elastic modulus of surrounding rock,reservoir thickness,reservoir permeability and mesh fineness,and Poisson’s ratio of surrounding rock is negligible.(2)Reservoir porosity is the most sensitive parameter to surface deformation also,followed by reservoir permeability,elastic modulus of surrounding rock and reservoir thickness.The influence of Poisson’s ratio of surrounding rock and mesh fineness on surface deformation can be ignored.(3)The minimum horizontal principal stress of Q gas storage is consistent with the trend of formation pressure,and the stress in the gas-bearing areas has obvious influence,while the influence range is small in the area of low reservoir permeability and poor connectivity.(4)High-speed reciprocating injection-production results in about 0.0269 m subsidence of reservoir and 0.0041 m subsidence of surface;(5)During the early development and later injection-production cycle of Q gas storage,the stress-Mohr circle of reservoir and caprock is always located below the rock failure envelope,that is,no shear failure occurs in the whole life cycle of reservoir and caprock.(6)The sliding stability value,sliding trend index and plastic shear strain value of fault are all within the critical indexs,that is,the fault has good stability during the entire life cycle.