Experimental Studies on the Effect of Mechanical Cleaning Devices on Annular-Cuttings Concentration
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 134269, ’Experimental Studies on the Effect of Mechanical Cleaning Devices on Annular Cuttings Concentration and Applications for Optimizing ERD Systems,’ by Ramadan Ahmed, SPE (currently with the University of Oklahoma), Munawar Sagheer, SPE, Nicholas Takach, SPE, Reza Majidi, SPE, Mengjiao Yu, SPE, and Stefan Miska, SPE, University of Tulsa, and, Christophe Rohart, SPE, and Jean Boulet, SPE, VAM Drilling, originally prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed.

In horizontal and highly deviated portions of an extended-reach-drilling (ERD) well, cuttings beds form on the low side of the annulus. The cuttings bed partially blocks the annulus, resulting in excessive pressure loss and a higher equivalent circulating density (ECD). Recently, the use of downhole mechanical cleaning devices (MCDs) has been introduced to mitigate the problem without inducing excessive ECD. The full-length paper presents results of an experimental study that was conducted to evaluate cuttings-removal efficiency of MCDs. Results indicate that the tools significantly reduce the amount of cuttings in the annulus. 

Introduction

Efficient cuttings transport is an important issue in drilling highly deviated and horizontal wells. In directional wells, drilled cuttings tend to accumulate on the low side of the annulus and form a thick cuttings bed when the flow velocity becomes insufficient to suspend the cuttings-bed particles. Particularly in high-angle and horizontal boreholes, the formation of a thick cuttings bed can give rise to numerous difficulties such as lost circulation, differential sticking, and high torque and drag.  Recently, hydromechanical hole-cleaning devices (HHCDs) have been developed to enhance cuttings-transport efficiency in directional wells. These tools are introduced in the drillstring with different spacing arrangements.

These tools have helical grooves or blades on their surface to assist cuttings-bed removal. A negative angle also is designed on each blade to improve the scooping effect on the cuttings bed. While rotating the drillpipe, the blades scoop the cuttings bed and help to bring the cuttings into suspension. At the same time, the circulation of the drilling fluid allows the suspended cuttings particles to be carried away, thus leading to better hole cleaning. Because of hydrodynamic and hydromechanical effects, the tools help to reduce the cuttings accumulation in highly deviated and horizontal sections of the wellbore where the buildup of a cuttings bed cannot be avoided. Thus, several of these tools are used in a typical drilling application to reduce the in-situ cuttings concentration and, hence, reduce the occurrence of hole-cleaning-related problems.

HHCDs improve hole cleaning by creating more turbulence, bringing cuttings into suspension, and scooping the cuttings bed. The interaction between the tools and the slurry that contains cuttings particles and drilling fluid is a complex fluid-mechanics problem for which an analytical solution would be difficult to develop. Therefore, an experimental approach is the best option to provide practical solutions, perform sensitivity analysis, and obtain a better understanding of the use of these tools.