Pipe-Rotation Effect on Hole Cleaning for Water-Based Drilling Fluids in Horizontal and Deviated Wells
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 114965, "Effect of Pipe Rotation on Hole Cleaning for Water- Based Drilling Fluids in Horizontal and Deviated Wells," by M.E. Ozbayoglu, Middle East Technical University; A. Saasen, StatoilHydro; M. Sorgun, Middle East Technical University; and K. Svanes, StatoilHydro, prepared for the 2008 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Jakarta, 25-27 August. The paper has not been peer reviewed.
A major concern while drilling horizontal and directional wells is proper hole cleaning. For a stationary bed of drilling cuttings in the annulus, generally, an increase in the fluid velocity will erode the bed significantly. However, depending on the drilling conditions, very-high fluid velocities are needed for bed removal, which may not be possible because of hydraulic and physical limitations. In such cases, pipe rotation may enhance cuttings transport mechanically, and effective hole cleaning may be achieved even at fluid velocities lower than the critical annular fluid velocities required to prevent stationary-bed development. The effect of pipe rotation on hole cleaning was investigated.

Introduction
Increasing the fluid viscosity or flow rates for vertical wells can improve the cuttings-transport performance. However, as hole inclination progresses from vertical to horizontal, additional challenges arise, such as cuttings-bed development. At inclinations between 40 and 60°, hole cleaning is most difficult because of back sliding of the cuttings inside the wellbore. Such cases require higher flow rates. Also, for inclined wellbores, fluids with high viscosities do not clean the hole as observed in vertical cases. Also, during drilling operations, the drillstring usually is rotating, which increases the complexity of the drilling-fluid behavior and cuttings transport inside the wellbore.
Although many studies on the relationship between the pipe rotation and cuttings-transport performance are available in the literature, there is a lack of understanding about the contribution of pipe rotation to hole cleaning. This study provides detailed information on the effects of pipe rotation on hole cleaning. The basis of the information was experimental work conducted by varying major drilling parameters.

Theory
Many drilling variables influence hole cleaning. For realistic modeling, all variables that affect cuttings transport should be taken into consideration. From the point of view of hole cleaning, pipe rotation will affect not only the cuttings-distribution scheme inside the wellbore but also the fluid properties and pipe alignment, especially in eccentric cases. Use of all data will increase the difficulty of predicting the contribution that pipe rotation makes in cuttings transport and hydraulics. For example, in an eccentric annulus, frictional pressure loss will decrease as the pipe eccentricity increases, if all other parameters are kept constant. However, when the pipe is rotated, frictional pressure loss increases, most probably because of the orbital motion. It is more difficult to predict the behavior of pressure loss with the presence of cuttings in the system. However, the volume of stationary bed decreases with increased pipe rotation, which leads to an increased fluid-flow area. Thus, frictional pressure losses might decrease as pipe rotation is increased.