Stress sensitivity of ultra-deep tight sandstone gas reservoirs based on microscopic fluid-solid coupling
Ultra-deep tight sandstone gas reservoirs exhibit strong stress sensitivity.At present,the commonly used stress sensitivity research methods include pressure pulse experiment method and real-time online CT scanning method.The former fails to reveal the microscopic mechanisms underlying stress sensitivity,and the latter is unable to simulate the high-pressure and and high-stress conditions in deep reservoirs.To address the shortcomings in stress sensitivity experiments,this paper develops a microscopic fluid-solid coupling algorithm based on the discrete element method and the pipeline network model.In addition,a simulator is worked out,and the correctness of its mechanical calculation and fluid-solid coupling module is verified.Then,the influences of stress value,stress loading direction and pore pressure on core permeability are analyzed.Finally,the stress sensitivity mechanism of deep tight sandstone gas reservoir is revealed microscopically.And the following research results are obtained.First,stress increases the normal pressure on both sides of the throat perpendicular to it,so as to reduce the hydraulic radius of the throat,thereby reducing reservoir permeability.Second,high pore pressure impedes particle movement under stress,so as to alleviate the deformation of pores and throats,thereby maintaining high model permeability.Third,the permeability of tight sandstone gas reservoirs is under the joint control of stress and formation pressure,and exhibits anisotropy with dominant channels for greater permeability in the direction of minimum principal stress.Fourth,abnormal pressure hinders the compaction of in-situ stress,which is favorable for the protection of reservoir pores,contributing to better reservoir performance and higher permeability.In conclusion,the fluid-solid coupling algorithm established based on the discrete element method and the pore network model can provide a theoretical reference for understanding the stress sensitivity in deep tight sandstone,and guide the scientific and efficient development of deep tight sandstone gas reservoirs.
Ultra-deep strataTight sandstone gas reservoirDiscrete element methodFluid-solid couplingPermeabilityStress sensitivityNumerical simulation
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