Abstract: Based on the Reference [1], the reason of higher measured rock compressibility is due to the skin effect of cores. This paper believes that this kind of effect does exist in lab experiment, but it is not the main reason of it. The main reason is that equation for porosity compressibility is sensible to porosity volume in low porosity sample. On the basis of comprehensive analysis of rock stress, this paper proposes a new regulation equation, which gets over the fault of equation from the Reference [1] and provides right relationship of compressibility vs porosity. These results are significant to correct understanding of the reason of higher measured rock compressibility in lab experiment, proper correction and computation of it in reservoir engineering.

Key words: porosity, compressibility coefficient, stress, sensitivity