Study On Effective Stress Of Low Permeability Sandstone Permeability In Daniudi Gas Field

The common effect of deformation of microcracks and pores will result in non-linear characteristics of effective stress in the exploitation process of low-permeability gas reservoirs. The linear effective stress theory doesn’t accord with the variation law of permeability with pore pressure in the exploitation process, so the influence of stress sensitivity on exploitation of low-permeability gas reservoirs can’t be evaluated accurately. In this study, based on the previous theoretical and experimental study about the effective pressure, the law change rule of effective pressure for permeability and stress sensitivity for permeability is researched by the effective pressure for permeability experiment of low permeability sandstones. Besides, the influence of stress sensitivity on exploitation of low permeability gas reservoirs is analyzed with numerical simulation. Major outcomes and conclusions achieved are following:(1) Conventional testing for porosity and permeability, Mercury Penetration, Scanning Electron Micrograph and Rock Slice Micrograph are carried out to analyze the microstructures of rock samples;(2) A new method for determining the effective pressure coefficient for permeability is designed based on the definition of effective pressure and the analytical method of experimental date;(3) The experimental program of effective pressure for permeability is designed. Conventional stress sensitivity test and experiments of the effective stress for permeability of ten low-permeability sandstones are finished respectively;(4) The effective stress coefficients for permeability are gained on the basis of experimental date. The change rule of the effective stress coefficient for permeability with pore pressure and confining pressure is analyzed;(5) The change rule between effective stress coefficient for permeability and Terzaghi’s effective stress is analyzed. And the functions between permeability and Terzaghi’s effective stress are built;(6) The relationship between effective stress and permeability is analyzed. The functions between permeability and effective stress are built. And the applicability of function is analyzed;(7) The stress sensitivity for permeability of low-permeability sandstones is evaluated by different effective stress theories and different evaluation methods;(8) The influence of permeability-stress-sensitivity on exploitation of low-permeability gas reservoirs is analyzed by numerical simulator and the productivity of fractured horizontal well are evaluated.In this study, a new method for determining the effective stress coefficient for permeability is designed. Effective pressure experiment research deepens our knowledge to the variation rule of effective pressure law, evaluates the influence of stress sensitivity on exploitation of low permeability gas reservoirs accurately, and provides theoretical base to evaluate stress sensitivity of low-permeability reservoir rocks and develop reservoirs rationally:...