The Effect of Equivalent Diameter Definitions on Frictional Pressure Loss Estimation in an Annulus with Pipe Rotation

Abstract

Annular flow of non-Newtonian fluids remains a ubiquitous phenomenon in drilling operations but accurately estimating the frictional pressure loss with drill pipe rotation still poses a great challenge. Since annular frictional pressure losses increases the equivalent circulating density (ECD), it becomes imperative to accurately estimate the annular pressure loss in order to keep the ECD above the pore pressure and below the fracture gradient especially in deep offshore drilling where the pore pressure and fracture pressure are so close together. When annular flows are encountered, a common practice is to calculate an effective diameter such that the flow behavior in a circular pipe would be roughly equivalent to the flow behavior in the annulus. This equivalent diameter definition replaces the diameter term in the friction factor, effective Reynolds number and Taylors number equations used for pipe flow thus resulting in different frictional pressure loss estimation. As a result, the selection of appropriate correlation for the respective fluids, flow regimes and putting into consideration pipe rotation has become important but has received very little attention. In this study, the seven different equivalent diameter definitions used for estimating frictional pressure losses in an annulus were reviewed and theoretical analysis were performed on experimental data obtained from literatures to determine the effect of these definitions on wellbore hydraulics. Pressure loss ratios (PLR) which relates pressure loss with pipe rotation to pressure loss without pipe rotation weredevelopedfor each equivalent diameter definitionusing dimensional analysis techniques. These hydraulic models combined with conventional frictional pressure loss estimation were tested with experimental measurements to determine the model with an equivalent diameter definition that best predicts frictional pressure losses for power law fluids.

Annular Frictional Pressure Losses During Drilling—Predicting the Effect of Drillstring Rotation

“…Escudier and Gouldson [35] demonstrated experimen tally how such Taylor vortices alter the velocity profile in the annulus. Anifowoshe and Osisanya [36] found a variation of pres sure drop prediction when using different equivalent diameter definitions. The examples shown in Figs.…”

CFD Analysis of Pressure Losses and Deposition Velocities in Horizontal Annuli

“…However, it is difficult to select a definition for a field application as those were developed and/or applied empirically. A comparison of multiple definitions in predicting pressure losses is presented by Anifowoshe and Osisanya [3]. Other issues that make the estimation of pressure losses in drilling holes difficult are the eccentricity and the rotational speed of inner drill pipe.…”

“…Other issues that make the estimation of pressure losses in drilling holes difficult are the eccentricity and the rotational speed of inner drill pipe. Many studies have been done on the flow of non-Newtonian fluids in annuli to introduce empirical/ analytical models which allow to take these effects into account [1,[3][4][5][6][7][8][9][10]. e results of the previous studies show that the annular pressure losses for non-Newtonian (power law) fluids flowing in a drill hole depend on drill pipe rotation speed, fluid properties, flow regimes (laminar/ transitional/turbulent), diameter ratio, eccentricity, and equivalent hydrodynamic roughness.…”

Simulation of Drilling Pressure Profile in Directional Drilling and User Program Development

“…To transform annular flow to pipe flow, the effective diameter needs to be replaced the diameter parameter. Anifowoshe et al [3] found that the definition of hydraulic diameter as expressed in (3) is the appropriate estimation of pressure loss for power law fluid. Hence frictional pressure loss inside an annulus using slot equation is defined as (4)…”