Shale Bedding Impact on Wellbore Stability and Drilling Optimization

Abstract It is well known that shale can be a problematic lithology that is capable of creating issues such as tight hole and pipe stuck during a drilling operation. Shale bedding is recognized as one of the key factors that directly contributes to drilling problems. This paper focuses on shale bedding's impact on wellbore stability, which is investigated with the comparison of wellbore stability results of the shale formation with shale bedding and without shale bedding. The geomechanical simulation results show that: (1) the characteristics of wellbore stability polar plot for all well trajectories can be dramatically changed by shale bedding; (2) both well azimuth and well inclination have significant impact on wellbore stability; (3) stress dominated and shale bedding dominated wellbore breakouts can be evaluated; (4) formation strength control and shale bedding strength control wellbore stability are indentified. Based on those simulated wellbore stability characteristics, optimizations for well azimuth, well inclination, well trajectory, and mud weights can be designed for drilling operation to mitigate the potential drilling hazards.