Abstract:

During the exploitation of oilfield, the formation pressure depletes gradually, but the effective stress to the rock grain increases. The effective stress may cause rock to deform, resulting in the elastic or plastic deformation; and the rock permeability is quite sensitive to effective stress due to the deformation. Therefore, it is necessary to know the property of stress sensitivity for the low permeability tight reservoir. The permeability of sand rock core samples of Daqing oilfield under different effective stresses is tested, and the reduction property of permeability is obtained. Considering the microscopic characteristics of pore structure and occurrence states of clay, new capillary-tube model is proposed; and the deformation law of single capillary is studied. The research shows that the stress sensitivity of rock increases with the decrease of rock permeability; and there is exponent relation between initial permeability and the loss rate of permeability. The new capillary-tube model can explain the difference of stress sensitivity between low-permeability and medium-high permeability reservoirs based on the microscopic mechanism.

Key words: tight reservoir, effective stress, stress sensitivity, pore structure, capillary model