Mechanical Stability of Horizontal Wellbore Implementing Mogi-Coulomb Law

In this paper, a linear elastic constitutive model is described. The model consists of a three dimensional analyses of stress concentration around an arbitrarily oriented borehole, due to anisotropic in situ stress combined with internal wellbore pressure. Studying the principal stresses around a borehole require the consideration of three possible permutations for the principal stresses: (1) σz ≥ σq ≥ σr, (2) σq ≥ σz ≥ sr, and (3) σq ≥ σr ≥ σz. Considering the practical field conditions, in normal faulting stress regime and reverse faulting stress regime, wellbore stability analysis can be simplified by only assuming case 2 (σθ ≥ σz ≥ σr) for the principal stresses around horizontal borehole. In strike-slip stress regime, however, all the three possible permutations for the principal stresses should be considered in wellbore stability analysis. The constitutive model in conjunction with Mogi-Coulomb law has been used to introduce a new wellbore stability model for horizontal boreholes. The developed model has improved wellbore stability analysis compared to adopting the classical Mohr-Coulomb criterion that is commonly applied. This has been verified by several typical field case studies. Key words: Wellbore stability; Borehole failure; Collapse pressure; Mogi-coulomb criterion; Horizontal drilling