Abstract: During the exploitation of low permeability reservoir, the formation pressure depletes slowly and the effective stress to the rock grain increases. The effective stress may cause rock grain to deform, resulting in the primary or structural deformation; and this deformation makes the rock physical property parameters such as porosity and permeability become quite sensitive to effective stress. Therefore，it is necessary to know the function mechanism and property of stress sensitivity for low permeability reservoir. Based on the particle accumulation model, a capillary module, considering the arrangement of particles and the deformation of particles, has been established to express the stress sensitivity of capillary and porous media. The elastic deformation amount of the capillary has been calculated by Hertz contact deformation principle. And the quantitative characterization of stress sensitivity for capillary and porous media has been studied. The function mechanism on stress sensitivity of low permeability reservoirs is discussed by using the effective percentage of capillary and capillary deformation law. The research results show that the stress sensitivity for permeability is much more important than that for porosity in low permeability reservoirs. The effect of stress variation on porosity is small; but its influence on permeability is very large. The permeability stress sensitivity of three-grain contact deformed rock is greater than that of four-grain primary deformed rock. Compared with the primary deformed rock, the structural deformed rock has stronger permeability stress sensitivity. The stress sensitivity of low permeability reservoirs depends on some distinct factors such as the arrangement of particles, the deformation of particles, microscopic pore structure, solid-fluid interfacial force and threshold pressure gradient. The stronger the heterogeneity of low permeability reservoir is, the greater the stress sensitivity is; and thus the effect on oil production is larger. The quantitative module of stress sensitivity considering the effective percentage of capillary and the elastic deformation amount can explain the stress sensitivity of low permeability reservoirs based on the microscopic mechanism. These results offer a very important base and guide for researching and designing the production performance of the low permeability reservoir.

Key words: low permeability reservoir, stress sensitivity, quantitative module, arrangement of particles, effective percentage of capillary