Generalized Hydraulic Calculation Method for Axial Flow of Non-Newtonian Fluids in Eccentric Annuli

Abstract

Summary The flow of non-Newtonian fluids through eccentric annuii is prevalent during drilling and cementing operations of directional and horizontal wells. The flow pattern in an eccentric annulus can differ greatly from that in a concentric annulus, and this difference affects both the pressure drop and the flow rate at which the laminar-turbulent transition occurs. Errors resulting from ignoring the effect of eccentricity on frictional pressure drop and equivalent circulating density can lead to formation fracture or well-control problems in some situations. In this paper, a new method is presented for calculating pressure losses in eccentric annuli. The method is based on an effective diameter that accounts for the effects of both conduit geometry and fluid rheology. Predictions of the method are compared with an extensive set of data for drilling fluids obtained from a large-scale flow loop. The results demonstrate that the new method is capable of reliably predicting the pressure drop of most drilling fluids in both laminar and turbulent flow regimes for eccentric annular geometries of practical interest.