FRACTURE INITIATION FROM INCLINED WELLBORES IN ANISOTROPIC FORMATIONS

This paper presents a wellbore-stability ''design code'' that can be u sed to drill, complete, and stimulate inclined wells optimally. The de sign code was developed for the most general case, where the borehole, in-situ-stress, and rock-property coordinate frames are totally indep endent of each other, It essentially consists of a 3D linear-elastic-s tress analysis in anisotropic formations, Although this particular pap er is limited to tensile failure, on the basis of the minimum-normal-s tress theory, the numerical model is also able to consider shear failu re by involving a generalized 3D anisotropic yield criterion. The desi gn code allows selection of the optimum borehole orientation and wellb ore-fluid gradient to avoid fracture initiation. It is also useful in conducting sensitivity studies, particularly when data are scanty. Exe rcising such a code led to the remarkable finding that fracture initia tion is strongly dependent on the formation anisotropy, contradicting current industry thinking.