Precise prediction of Equivalent Circulating Density (ECD) is one of the most important challenges during drilling operations. This becomes more vital in deep-water offshore wells in which formation pressure is very close to the fracture pressure. In addition, techniques such as Managed Pressure Drilling (MPD) rely on the precise estimation of frictional pressure losses.
Although many theoretical and experimental studies have been conducted on fluid flow through pipes and annuli to predict the pressure losses, majority of them undermine or simply ignore the effect of tool joints. A few studies that take the effect of tool joints into account indicate that it can have significant effect on pressure loss. Therefore, there is a strong need to determine the amount of additional pressure loss caused by the tool joints.
This paper presents a Computational Fluid Dynamics (CFD) approach to investigate the effect of tool joint on annular pressure losses. The utilized software package in this simulation study uses Finite Volume methods to solve the problem. The effects of important parameters such as flow rate, mud type, mud weight and mesh size are investigated. The pressure loss in the annuli, with and without tool joint, is obtained and additional pressure loss due to presence of tool joint is calculated accordingly.
Simulation results show that the ratio of annular pressure loss with tool joints to the pressure loss without tool joints (α) strongly depends on the flow regime. In Laminar flow, this ratio remains relatively constant, regardless of the type of the drilling fluid. In turbulent flow, it increases rapidly with increasing Reynolds number and can be precisely estimated by the proposed correlation. It has been found that in deep offshore wells and high range of operational flow rate, the additional pressure loss due to tool joints can be as high as 30% of the total frictional pressure loss and must be taken into consideration during ECD calculations.