Numerical Characterization of the Annular Flow Behavior and Pressure Loss in Deepwater Drilling Riser

Abstract

In drilling a deepwater well, the mud density window is narrow, which needs a precise pressure control to drill the well to its designed depth. Therefore, an accurate characterization of annular flow between the drilling riser and drilling string is critical in well control and drilling safety. Many other factors influencing the change of drilling pressure that should be but have not been studied suffi- ciently. We used numerical method to simulate the process of drill string rotation and vibration in the riser to show that the rotation and transverse vibration of drill string can increase the axial velocity in the annulus, which results in the improvement of the flow field in the annulus, and the effect on pressure loss and its fluctuation amplitude. In addition, there are also multiple secondary flow vortices in the riser annulus under certain eccentricity conditions, which is different from the phenomenon in an ordinary wellbore. The findings of this research are critical in safely controlling well drilling operation in the deepwater environment.