Sammendrag
In recent years, drilling fluids have become more complex in nature to satisfy diverse requirements in drilling operations. Accurate prediction of the frictional pressure losses while drilling is complex because of a combination of various drilling parameters. In the present study, a computational-fluid-dynamics (CFD) analysis is performed to investigate the hydraulics of solids-free non-Newtonian drilling fluids with an eccentric annulus coupled with a rotating drillstring. The Herschel-Bulkley fluid model is used to describe the non-Newtonian fluid behavior of the drilling fluid. Annular inlet fluid velocities are varied from 0.5 to 1.2 m/s (laminar flow). Simulation results are compared with the experimental data from the in-house flow-loop results. The flow loop has a 10-m-long annulus section with a 100-mm-inner-diameter (ID) wellbore and 50-mm-outer-diameter (OD) fully eccentric drillstring. Pressure-drop results from the flow-loop experiments at various flow velocities with and without drillstring rotation are reported. Experimental results show that the pressure drop increases with the drillstring rotation in an eccentric annulus. Pressure-drop predictions from CFD analysis are in close agreement with the experimental results. Also, it has been observed that drilling fluids with similar viscosity profiles measured according to API RP 13D (2017) can have significantly different hydraulic and cuttings-transport behavior. As observed from experimental results, drilling fluids with similar viscosity profiles and density have different pressure drops. This study will contribute to a better understanding of the hydraulic behavior of drilling fluids.