Abstract:According to the theory of computing stress intensity factor by straight-notched Brazilian disc(SNBD) specimens,a set of experimental equipment is designed and constructed to test fracture toughness of rock mode-II. 20 rock specimens are prepared from pay zone and barrier layer between 1 500 and 2 000 m in WG oil field,China,and the tests are conducted successfully. Based on the experimental results,the relationship among fracture toughness of mode II,confining pressure and tensile strength is analyzed with the least square method,and the prediction model of fracture toughness of mode II is established by the geophysical logging data. Finally,the fracture toughness mode II is predicted,which is verified in field application by combining the KIIc prediction mode with the horizontal in-situ stress and tensile strength prediction based on acoustic logging,density logging and GR logging data from Well H341. The method is beneficial for solving the lack of continuous fracture toughness mode II along the well bore in field hydraulic fracturing operation.