Study On Stress Sensitivity Of Tight Sandstone Based On Digital Rock

In this paper,tight sandstone is taken as the research object.Based on the gray image,a set of effective methods for microscopic pore structure characteristics analysis and core-scale seepage simulation is established,which provides a theoretical guidance for the development of tight sandstone gas reservoirs..Through the CT gray image and the pore network equivalent model from maximum spherical algorithm,the pore structure characteristics are analyzed.The results show that the pore type in the tight sandstone is the residual intergranular pore,the throat type is the curved throat and both of them are very small.The connectivity between pores is analyzed and the result shows the connectivity poor.Based on the pore surface model and the Navier-Stokes equations,the flow simulation in pore scale is performed,and then the absolute permeability is calculated through the Darcy's law.The calculation proves that the absolute permeability of the tight sandstone in the X direction is 0.114×10^-3?m²,the Y direction is 0.162×10^-3?m²,and the Z direction is 0.09×10^-3?m²,the core permeability is anisotropic.The Knudsen number of CH₄ gas under different conditions is calculated and the results show that micro-scale effect in tight gas reservoir is dominated by slip flow.The micro-scale effect flow simulation results of the two-dimensional plate model and the pore structure model show that the permeability is increased because of the micro-scale effect,and the increment is affected by the pore structure characteristics.The uniaxial medium deformation simulation shows that the core pore shrinkage is not uniform due to the influence of the pore structure,and the core equivalent elastic modulus is 24.56GPa.The results of stress-sensitive simulations show that the permeability loss rate of core permeability is 42%,permeability damage degree is moderately weak,and the porosity loss can be neglected.The influence of elastic modulus on permeability can be divided into two stages.When the elastic modulus of tight sandstone is less than 20GPa,the permeability is greatly affected by elastic modulus,and when the elastic modulus is more than 20GPa,the permeability is changes slowly.