STRESSES AROUND HORIZONTAL BOREHOLES DRILLED IN SEDIMENTARY ROCKS

Aadnoy, B.S., 1989. Stresses around horizontal boreholes drilled in sedimentary rocks. J. Pet. Sci. Eng., 2: 349-360. The main purpose of this paper is to present the anisotropic stress equations that can be used to analyze fracturing or collapse problems for horizontal boreholes, and to show how anisotropy in the elastic properties of the rock affects the stress field around a horizontal borehole. This paper gives the complete equations to determine stresses around boreholes in transverse isotropic, but linear elastic sedimentary rocks. The equations to determine the effective stresses are also given. It is shown that the stress fields and their direction is affected by the anisotropic material properties of the rock. Also shown is the deformation pattern of the borehole, which for anisotropic rocks is elliptical rather than cylindrical. Finally, a hydraulic fracturing example is given to show the effect of elastic anisotropy on the fracturing pressure.