MIXED MODE FRACTURE FOR LINEAR ELASTIC MATERIALS BASED ON STRAIN THEORY USED IN LOW PERMEABILITY RESERVOIRS

The commonly used MTS criterion is independent of the material Poisson's ratio, and can't distinguish the difference between plane stress and plane strain. Furthermore, the classical fracture criteria ignores coefficient of higher order term at the crack tip, which resultings in significantlarge errors between mixed mode fracture predicted by the classical criteria and their experiments. Therefore, based on the consideration of the T-stress at the crack tip and the defects of the MTS criterion, the purpose of this paper is to establish the maximal circumferential strain criterion for the brittle fracture to predict fracture of mixed mode conditions. Then using this criterion, the influence of T stress and Poisson's ratio on rock crack propagation are investigated. The Rresults show that when the crack inclination angle is the same, the crack initiation angle decreases with the increase of Poisson's ratio. The brittle fracture is controlled by a combination of singular stresses (characterized by K) or non-singular stress (T stress). The results predicted by the maximum circumferential strain criterion considering the T stress are more consistent with the experimental data, and brittle fracture is controlled by a combination of singular stresses (characterized by K) or non-singular stress (T stress). The T stress and Poisson's ratio are also shown to have an influence on brittle fracture, which is useful for the design and construction of fracturing in low permeability reservoirs.