On the mechanical stability of inclined wellbores

Abstract

Consideration of the stress field around an arbitrarily oriented borehole shows that in an extensional stress regime (σv > σH > σh), well-bores parallel to the direction of minimum horizontal principal stress are the least prone to compressive shear failure (breakout). The most stable deviation angle (from the vertical) depends on the ratio of the horizontal principal stresses to the vertical stresses, and the higher the ratio σH/σv, the higher the deviation angle for minimizing breakout. In a strike-slip stress regime (σH > σv > σh), horizontal wells are the least prone to breakout, and the higher the ratio σH/σv, the closer the drilling direction should be to the azimuth of σH. A new compr..