Investigation of collapse pressure in layered formations based on a continuous anisotropic rock strength criterion

Abstract Wellbore instability severely constrains the exploration and development of shale gas. In order to evaluate impacts anisotropy water on wellbore instability, three different types criteria are fitted strength data LMX shales with moisture contents. A new model transversely isotropic borehole stability considering compliance incremental tensor induced by natural fractures is proposed, then a more preferred drilling direction performed model. Results indicated that, Pariseau’s attractive in predicting strength, including difference between vertical bedding parallel bedding. Based model, prediction accuracy improved 33.04%. The Pariseau’ gives disparate collapse pressure from Jæger’s weak plane criterion, most unstable area shifts northeast southwest central corresponding relatively lower inclination. only decreased 0.55 MPa elastic parameters, but have distinct influence. Compared results predicted weakness, increased 8.55 using Besides, invasion will aggravate especially late period, for 6.35 MPa. Shale depends not hydrostatic orientation angle, also content, which should be considered mud weight design well trajectory optimum.