Abstract: There are different conclusions about the stress-sensitivity reservoir permeability. Some researchers think that the variation degree of permeability via effective stress is not related to the initial permeability, while others hold the contrast viewpoint. By means of stress-sensitive experiment, capillary model and starting pressure gradient theory, the reason that causes researchers hold different opinions is found: it is because the permeability values of cores which they studied are great different. By carefully analyzing, we draw the conclusion: because of starting pressure gradient, low-permeability reservoir is more stress sensitive than medium-high permeability, and when initial permeability is lower than a critical value, the lower the permeability is, the more stress-sensitive the reservoir is, and when permeability is greater than this value, regardless of the initial permeability, the reduction in permeability is a function of effective stress only. For tight reservoirs, reservoir deformation has great effect on oil and gas production, which increase the exploitation difficulties of this kind of reservoirs.

Key words: permeability, stress-sensitivity, starting pressure gradient, tight reservoir