Optimizing Wellbore Inclination and Azimuth to Minimize Instability Problems

Wellbore stability is of critical importance in the success of drilling operations. One of the main goals of any drilling mission is to drill the well as cost-effective as possible. Wellbore instability can be detrimental to this goal. Therefore, wellbore stability analysis has been included in well planning stage of many companies.Wellbore stability is a function of several factors such as inclination and azimuth, in-situ stresses, mud weight, rock strength parameters, etc. Some of these factors are controllable and some are not. Among the controllable factors are inclination, azimuth and mud weight. By changing these parameters, one can reduce stability problems significantly. Theoretically, it is possible to design the well trajectory in a way to face least stability problems.In this paper linear elastic constitutive model along with Mohr-Coulomb failure criterion have been utilized to perform stability calculation for different inclinations and azimuths. It is shown that drilling wells parallel to minimum in-situ horizontal stress causes less stability problems. Also the effect of in-situ stress field on wellbore stability has been investigated and it has been demonstrated that in the case of high difference between the in-situ stresses, the optimum path for a well is a low inclination and an intermediate azimuth.

Keywords:

Optimization , Inclination , Azimuth , In-situ stress , wellbore Instability