Analytical investigation of failure criteria in determination of the optimum direction of drilling

Estimation of mud weight is one of the important steps in preventing instability in oil wells. Analytical and numerical methods are commonly used to obtain this estimation. Several failure criteria have been evaluated by researchers, but so far there is no certain failure criterion that can be applied in any field. Moreover, many assessments have been carried out using hypothetical data, thus, the results are not reliable in real fields. In this study, using analytical methods in normal fault stress regime, the number of failure criteria have been studied using field data. Using analytical methods, nine failure criteria have been investigated by MATLAB software. The results show that in normal fault stress regime, the optimum drilling azimuth is in the direction of minimum horizontal stress. Angular deviation function to optimize mud weight is less dependent on the ratio of maximum to minimum horizontal stresses. As the ratio of maximum to minimum horizontal stresses increases, the optimum deviation angle goes away from 90°.

Keywords:

Mud weight , Analytical and numerical methods , Failure criterion , Normal fault stress regime , Optimum drilling direction