ANALYSIS OF BOREHOLE STABILITY FOR INCLINED WELLS IN FRACTURED CARBONATE FORMATION

Typically, the required mud weight is determined by a wellbore stability analysis in which the rock material is assumed to be linear elastic, homogeneous, and isotropic in mechanics and strength behaviors. This traditional stability analysis, however, may lead to erroneous results particularly for a well drilled into fractured carbonate formation, and ignoring the strength anisotropy associated with planes of weakness such as foliations, or schistosity presented in carbonated rocks. Therefore, based on the porous elastic mechanics model of borehole stability and the single weak-plane strength theory, borehole stability model for inclined wells in fractured carbonate formations is established. Based on those, this paper quantitatively analyzed the effects of attitude of fissures and system researched the hole collapse pressure under different well track along with the change of weak plane occurrence characteristics. The basis for wellbore stability during drilling and production was provided. The results showed that collapse pressure is controlled by weak plane occurrence characteristics. Compared with traditional hole stability analysis model, the method of this article can provide a scientific calculated means and methods for solving the carbonate borehole instability.