“…Despite these efforts to modify the wellbore stability models, numerous accidents associated with wellbore instability in shale gas reservoirs have been reported (Yan et al, 2013Ma and Chen, 2014a,b,c). Zoback (2012) and Lee et al (2012Lee et al ( , 2013 found that the shapes and orientations of failure regions are significantly affected by anisotropic strength, and a few researchers have also studied the influence of anisotropic strength on instability regions around the borehole (Lee et al, 2012(Lee et al, , 2013Ma and Chen, 2014b). In addition, a few researchers have investigated the influence of multiple weak planes Chen et al, 2014a).…”