Effect of anisotropy on wellbore stability based on transversely isotropic strength criteria in shale formation

• DOI: 10.1190/geo2024-0487.1
• Publication Date: 2025-04-03T15:39:09Z
• Authors: Xiangsen Gao; Min Wang; Xian Shi; Peng Dai; Mingming Zhang; Ahmad Ramezanzadeh
• Keywords: Transverse isotropy; Wellbore

The shale reservoir serves as the primary driver of global oil and gas production growth. However, during exploitation these reservoirs, frequent instability in formations often leads to complex situations significant non-productive time. underlying mechanisms formation are not yet fully understood. Shale's distinctive transverse isotropy, resulting from its depositional processes, differentiates it other lithologies. To explore instability, this study performed triaxial compression experiments on samples under varying bedding dip angles confining pressures. revealed shale's strength anisotropy properties, an anisotropic criterion was established using least squares method. Based this, a wellbore collapse pressure prediction model incorporating both elastic developed. used effects modulus Poisson’s ratio stress distribution around wellbore. Additionally, differences predictions three criteria were analyzed. results show that SPW Pariseau exhibit errors for layered rock strength, whereas PPW provides more accurate strength. has minimal effect tangential compared anisotropy. is highly sensitive variations This, combined with Poisson's anisotropy, amplifies concentrations Among evaluated criteria, tends overestimate pressure, while underestimates it. In contrast, fall between two extremes, considered most reasonable overall. These findings enhance accuracy safety determination optimal drilling fluid density formations, aiding mitigation subsurface challenges improving operational efficiency.