Investigation of Parameters Controlling Equivalent Circulating Density ECD in Managed Pressure Drilling MPD

Abstract

In Managed Pressure Drilling (MPD), it is possible to drill holes that simultaneously expose formations with narrow safe mud windows and with pore pressures close to the fracture pressures of other exposed formations with minimal formation influx or mud losses, and also minimal future formation damage during production. In Continuous Circulation Systems (CCS), as a sub-class of MPD, the dynamic or circulating pressure is adjusted to control formation pressures. Therefore, the key factor in success of CCS and prevention of unprecedented formation damage is Equivalent Circulating Density (ECD). This is because a small error in calculation of the ECD can cause a kick influx or drilling fluid loss. Therefore, there is a strong need to investigate the effects of various parameters affecting ECD, which is the objective of this work. In this study, a section of a vertical annulus was simulated using Computational Fluid Dynamics (CFD) in 3-D and 2D to determine the effects of different affecting parameters on ECD. The seven investigated parameters in this section consist of DP rotational speed, eccentricity, rate of penetration (ROP), cuttings size, drilling fluid density, rheological parameters, and radius ratio (of drill-pipe OD to wellbore diameter). The CFD simulation results show that the ECD of MPD may be significantly affected by the aforementioned parameters. The ECD shows to change due to unprecedented change of the aforementioned affecting parameters. This can potentially jeopardize the MPD drilling operation success. Among the parameters, in laminar flow, radius ratio Yield Point and ROP showed the greatest effect on ECD whereas in turbulent flow radius ratio, PV and mud density showed to have the greatest effect with the other parameters to have minimal effects.