Study on the mechanism of anisotropic wellbore instability in continental shale in Songliao Basin

Abstract Wellbore instability is frequently encountered in the process of shale oil drilling. Due to anisotropic strength characteristics shale, most conventional models are not suitable for wellbore stability analysis layered formation. In this paper, taking continental north Songliao Basin as research object, elasticity and parameters measured experimentally. Based on pore elastic mechanics, an model established, variation collapse pressure under different formation conditions analyzed. The results show that considering anisotropy, largest, influence anisotropy significantly greater than anisotropy. horizontal wells drilled along maximum principal stress optimal, followed by vertical small angle directional wells. actual drilling G101 well basically consistent with prediction results, which confirms accuracy model. According traditional model, equivalent density section 1.58 ~ 1.76 g/cm 3 . It much lower 1.86 calculated study. findings study can help better understanding mechanism formations. be used guide engineering design reduce losses caused wellbore.