Research on Wellbore Instability of Shale Formation in Extremely Complex Geo-Mechanical Environment

Borehole instability problems are commonly encountered while drilling highly deviated and horizontal shale gas wells within the formations associated with high-dip bedding planes. An integrated rock mechanical study is described in this paper to evaluate risk of borehole area. First, a set uniaxial compressive tests carried out measure strength shales on cores different angles between load direction A critical criterion then proposed based test results. Next, stress state arbitrary inclination azimuth determined through coordinate transformations. Finally, combining borehole, investigated for dips (0–90°) dip directions (45° 90° minimum σh). The results show dependence orientation planes formation as well well. most desirable trajectory from viewpoint stability at normal For specifically, if perpendicular σh, relatively high except along However, there moderate acute angle (e.g., 45°) low unless σh.