Abstract: In the quantitative research on fracture, some principles for rock fracture are usually adopted to confirm when and in which direction the rock fractures occur under stress. Usually, tectonic fracture appears in several forms such as tension fracture, conjugate shear fracture and tension-shear fracture. It is necessary to comprehensively apply the tension fracture principle and the shear fracture principle in case studies. On the basis of Coulumb-Mohr and Griffith fracture principles, this paper puts forward rock-cracking examination principle for low-permeability sand reservoir in combination with the results of rock mechanical test, in which Griffith principle is applied to tension fracture examination, while Coulumb-Mohr principle to shear fracture examination.

Key words: fracture, low permeability, cracking, Coulumb-Mohr principle, Griffith principle