A chemo-poro-elastic wellbore stability model considering the shale transverse isotropic effect is developed. In poroelastic theory, the pore fluid motion and solid structure deformation are coupled. Lubinski’s one-way coupling scheme is adopted in this study which assumed a rock has strong structure and the effect of solid skeleton deformation on fluid flow is negligible.
It is found that normal stress along the cylindrical axis is affected by Young’s modulus on both the symmetrical plane and the axial direction.
A Taguchi orthogonal simulation design strategy is adopted to reduce the number of simulations while still achieving meaningful results. Analysis of variance (ANOVA) is conducted and parameter contributions to the mud weight window have been investigated. It can be found that among the 11 parameters of interest, wellbore inclination angle, hydraulic conductivity and water activity of drilling fluid play the most important roles in determining the mud weight window.
Knowledge of percentage contributions of the parameters in this chemo-poro-elastic wellbore stability model greatly helps drilling engineers identify the critical factors for wellbore stability control. This study also helps well trajectory design and drilling fluid optimization.