INCORPORATING TOOL JOINT INFLUENCE ON MODEL FOR EQUIVALENT CIRCULATION DENSITY ESTIMATION IN HORIZONTAL WELL DRILLING

Abstract

Modern drilling techniques involving horizontal well (HW) drilling for production of petroleum verify that the well is adequately planned prior to commencement of drilling or completion, especially in drilling of deep and ultra-deep water wells. Because of more rigorous and complex well geometries, planning ensures that drilling or/and completion engineers reach target depths in their respective operations. Equivalent circulation density (ECD) is one of the parameters that is monitored and controlled during well planning and drilling of wells. ECD, when properly managed, leads to successful drilling especially when working in areas of narrow mud-weight window. Poor management of ECD could result in severe problems during drilling such as loss of circulation and kicks. Mud column hydrostatic head and annular frictional pressure loss (AFPL) govern ECD. As such, several factors influence ECD viz: drill string (DS), well geometry, rheology of drilling fluid, and flow rates. Several literature studies have focused on fluid flow through annuli and pipes for AFPL computations. However, tool joint (TJ) effect in the estimation of pressure loss (PL) in annulus is either ignored or underestimated in several cases. The overall contribution of TJs effect on ECD is of great importance. In this paper, TJ effect on AFPL has been evaluated. Dimensional analysis and theoretical methods were utilized for model development that incorporates TJs effect for AFPL computation and, consequently, ECD prediction. AKUBU X12 well, a HW with measured depth (MD) of 11070ft from Niger delta was utilized as a case study. Mud of 8.6 ppg was utilized for the study with model simulation carried out using Matlab software (by Mathworks Inc.-version R2014B). Results show that as the rate of flow increases, TJs presence creates strong hydraulic resistance, which increases localized AFPL and ECD. Also, as the depth and rate of flow increases, the AFPL also increases, leading to an increase in ECD. Pipe rotation affects PL. Such increase in pipe rotation causes PL to either decrease or increase depending on shear thinning as well as inertial effect. Thus, for accurate prediction of ECD and wellbore pressure, TJ effects should be considered.