Abstract
Abstract Recent advances in the calculation of circulating pressure drop produced by drillpipe rotation have led to questions regarding the way the drilling industry traditionally calculates pressure drop in a circulating annulus. Because few publications discuss the hydraulics of rotation of an inner pipe in an annulus where the outer wall is stationary, there is still not a large volume of work on the subject. This paper reviews the published literature on fluids in laminar flow and discusses what is missing from the equations and the way forward. Common equations in the literature use multiple factors to calculate pressure drop in annuli without including the effects of drillpipe rotation. The most frequently used equations include shear rate at the wall (various methods), shear stress at the wall, numerous coefficients used as patches to power-law (PL) and Bingham plastic (BP) hydraulic models, shear rate and hole geometry correction factors, drillpipe roughness factors, and drillpipe eccentricity (ε). All of the equations are missing a general, straightforward method for calculating pressure drop, both with and without rotation of an inner pipe. Because the current API Recommended Practice 13D "Rheology and Hydraulics of Oil-well Fluids" (2010) recommends the Herschel-Bulkley (HB) rheological model for hydraulics calculations, special mention is made in this paper regarding use of the pertinent equations employing the HB model. In short, there should be a fairly straightforward method for calculating laminar flow pressure drop for axial flow with no drillpipe rotation and for helical flow that is produced by drillpipe rotation in a circulating annulus. The proposed method for calculation of fluids in laminar flow includes: A grid across the narrowest annular gap as defined by the input drillpipe eccentricity (ε).A single velocity equation that predicts point velocities across the annular gap.Average shear rates calculated for each pair of predicted velocities in adjacent cells.Average local shear stresses calculated for each average annular shear rate.Cumulative shear stresses necessary to move the entire annular cross-sectional area.Pressure drops calculated from the cumulative shear stresses. With this fairly straightforward method, hydraulic calculations are simplified because special coefficients or correction factors are not used. Drilling engineers should find that the outlined methods help to clarify traditional pressure drop calculations for fluids in laminar flow.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call