An Experimental Study of Drag Reduction of Polymer Solutions in Coiled Tubing

Abstract

The drag-reduction (DR) behavior of xanthan gum, partially hydrolyzed polyacrylamide, guar gum, and hydroxyethyl cellulose at various polymer solutions has been experimentally investigated with a full-scale coiled-tubing (CT) test facility that consists of 1-, 1 1 ⁄2-, and 2 3 ⁄8-in. CT reels. Data analysis revealed that the tubing diameter, curvature ratio, and polymer concentration are important factors affecting the DR in CT. The modified DR envelope is a useful tool for evaluating the DR performance of polymer solutions in CT. IntroductionCT has found many applications in the petroleum industry, including drilling, cementing, wellbore cleanout, and hydraulic fracturing. 1 However, the excessive friction-pressure loss because of the relatively small tubing diameter and because of the tubing curvature often limits the maximum obtainable fluid-injection rates. A recent experimental investigation 2 indicates that the frictional loss in CT is significantly higher than in straight tubing.One way to increase the injection rate and reduce pumping costs is to use drag-reducing additives (or drag reducers). Typical drilling and completion fluids, usually polymer solutions, have been found to exhibit some drag-reducing property. Therefore, it is of practical importance to investigate the DR properties of these solutions in CT.Frictional pressure in turbulent pipe flow can be drastically reduced by adding small quantities of certain long-chain polymers to the solvent, such as water. This phenomenon is called DR. Credit is generally given to Toms 3 for being the first to observe the phenomenon; therefore, DR is also called the Toms effect.Several references 4-10 from petroleum literature indicate the importance and potential applications of DR to this industry. Savins 4 reported pipe flow tests using a number of synthetic and natural polymeric materials and three tubing sizes, and factors affecting the drag ratios were studied. He also compared the test data with Dodge-Metzner 11 friction-factor correlation and observed the "diameter effect."There have been several extensive reviews on DR, such as Lumley, 12 Hoyt, 13,14 Virk, 15 and Berman. 16 The paper by Virk 15 addresses the DR fundamentals of dilute solutions of linear, random-coiling macromolecules in turbulent pipe flow. It covers broad areas of DR studies, including gross flow, mean velocity profile, turbulence structure, and mechanisms. Virk 15 proposed the concept of a maximum DR asymptote and the DR envelope, which has proven to be a useful tool for evaluating the DR performance of polymer solutions.The additional difficulty in studying DR behavior in CT is caused by the different flow fields in CT flow. Because of the effect of centrifugal forces, a secondary flow of vortical form occurs in the CT cross section. Dean 17,18 pioneered the theoretical study of Newtonian fluid flow in curved pipes. A similarity parameter, later called the Dean number [defined as N DN ‫ס‬N Re (a/ R) 0.5 ] was introduced to characterize flow in curved pipes. In 1929, White 19 conduct...

An Experimental Study of Flow Behavior of Coiled Tubing Drilling System

“…CT, the solvent is Xanthan with concentration of 40 lb/Mgal and the experimental conditions of which are similar to that of our experiment. When the maximum flow rate and Reynolds number are achieved in Xanthan experiment, the maximum value of DRR is about 60%, which is very close to the results of Shah and Zhou [5]. When the circulation flow rate is small, namely, under the low Reynolds number, the effect of polymers does not afford to drag reduction but increases the pressure losses of experimental fluid.…”

“…For Xanthan, we adopt concentration of 4 g/L, the rheological parameters of which are within the recommended range of Shah and Zhou [18]; its experimental data can be compared with the data in the literature.…”

“…Among three kinds of polymer experimental fluid, the drag reduction effect of PF is the best. In Shah and Zhou's [5] experiment with 1-in. CT, the solvent is Xanthan with concentration of 40 lb/Mgal and the experimental conditions of which are similar to that of our experiment.…”

“…Shah et al [4] and Shah and Zhou [5] studied influence on drag reduction effect through the polymer concentration, the curvature of CT, and velocity of flow and found that the drag reduction effect is closely relative to turbulent intensity. Willingham and Shah [6] studied the law of frictional pressure losses of four kinds of polymer with different concentration and a kind of drilling mud and arrived at frictional pressure losses correlations which are applicable to the above fluid by fitting the experimental data according to the least squares method.…”

Drag reduction characteristics in straight and coiled tubing — An experimental study

“…In recent years, the rapid increase in use of coiled tubing has created increased interest in research activities on coiled tubing hydraulics using full-scale experiment (McCann and Islas, 1996;Azouz et al, 1998;Shah and Zhou, 2003;Zhou et al, 2006). Therefore, this investigation is an attempt to study the characteristics of one of the most widely used drag reducing polymers, i.e.…”