EXPERIMENTAL STUDY ON THE EFFECT OF STRESS ON THE PERMEABILITY OF TIGHT SANDSTONE RESERVOIRS UNDER SATURATED FORMATION WATER CONDITIONS.

Tight reservoirs have complex rock mineral composition and pore structure, which lead to extremely complex reservoir permeability stress sensitivity in the process of developing oil and gas resources. Quantitative evaluation of the effect of stress on reservoir permeability has important reference value for formulating reasonable development strategies. In this paper, taking the deep tight sandstone in L Oilfield as an example, the variation law of stress sensitivity of tight sandstone under saturated formation water condition was measured by overburden pressure porosimeter. The research shows that the acoustic and dynamic mechanical parameters of the samples after water saturation tend to increase, and the increments are: Vp, 12.3%; Vs, 1.5%; Young's modulus, 9.9%; Poisson's ratio, 40%. The values of mechanical parameters were increased in triaxial conditions compared with those in uniaxial conditions. When the core contains a certain number of micro-fractures, the fracture permeability accounts for most of the core permeability; when the stress increases, the fractures close, resulting in a significant decrease in permeability. When the fracture is basically closed and the effective stress continues to increase, the fracture permeability will not change much; however, it will cause deformation of the matrix pores of the rock skeleton, and the matrix permeability will decrease. Therefore, when the effective stress reaches a certain level, the change of rock permeability tends to be stable. The flow pressure decreases during the elastic-plastic deformation process, and the permeability of the sample is difficult to return to the initial state during the pressure recovery process, resulting in irreversible core damage. The change of the stress sensitivity coefficient with the initial value of permeability conforms to the linear function distribution. In low-permeability reservoirs, the better the development of rock fractures, the greater the porosity and permeability of the reservoir, but in contrast, fractures are easier to seal than matrix pores, so fractures play a leading role in the stress sensitivity of rock. [ABSTRACT FROM AUTHOR]