Abstract:

The effective stress will vary with pore pressure in reservoir rocks, which then will induce the change of permeability and the stress sensitivity to permeability. Laboratory study of the stress sensitivity to permeability has been carried out. Experiments include aging treatment and four cycles. Each cycle is run under constant-confining-stress through decreasing and increasing pore pressure. Experimental data are collected with steady-state method. The results show that permeability varies with pore pressure. At low confining stress, the variation range of permeability is larger, while at high confining stress, it is smaller. For equivalent net stress in different cycles, permeability is different. The change of permeability, with the change of pore pressure at some cycles, belongs to a typical step change. Meanwhile, the effective stress coefficients for permeability are calculated by Bernabe’ model. The calculated results，according to Benabe’s viewpoint, show that the step change of permeability is resulted from the change of microcrack deformation with stress change. The stress sensitivity evaluation to permeability has done; and the results show that the tight sandstone reservoir studied puts up the moderate stress sensitivity.

Key words: tight sandstone, net stress, effective stress, effective stress coefficient for permeability, stress sensitivity to permeability