Consideration of Tool-joint Effects for Annular Pressure Loss Calculation.

Managed pressure drilling (MPD) is an innovative approach which can be used to solve the drilling problems caused by narrow safety pressure window. The precise wellbore flow model is not only premising to realize accurate wellbore pressure control, but also the key for safe and efficient drilling. In order to improve the prediction accuracy of wellbore pressure, annular pressure loss needs to be calculated accurately. Using dimensional analysis in conjunction with theoretical methods, the influence of tool joint and drill pipe rotation on annular pressure loss is studied in this paper. New annular pressure loss model has been developed to account for the contribution of tool-joints and pipe rotation to the total annular pressure loss, which enhanced wellbore pressure prediction accuracy. Model predictions show strong hydraulic resistance created by the tool-joint that increases the local annular pressure loss significantly as the flow rates increases. As well depth and flow rate increase, cumulative pressure loss of tool-joint increases. As pipe rotation increases, pressure loss may increase or decrease depending on the result of inertial effect and shear thinning. The new models are very useful to predict ECD and wellbore pressure accurately which is very important in hydraulic calculation for managed pressure drilling. [ABSTRACT FROM AUTHOR]