The excessive friction pressure loss due to the small tubing diameter and the curvature (which believed to cause secondary flow) of coiled tubing (CT) often limits the maximum obtainable flow rate in CT operations. This paper presents an experimental study of drag reduction performance of several polymer solutions in coiled tubing using a sophisticated full-scale coiled tubing test facility for an industry-university joint research project. The facility includes of seven reels of coiled tubing with diameters of 1", 1-1/2", and 2-3/8", fluid mixing and pumping equipment, and data acquisition system. Fluids investigated include water and solutions of polymers currently used in the well drilling and completion industry – Xanthan gum, partially hydrolyzed polyacrylamide (PHPA), guar gum, and hydroxyethylcellulose (HEC). Experimental results showed that the amount of friction drag reduction differs significantly among the different types of polymers at various concentrations. Data interpretation and analysis revealed that the CT diameter and the CT-to-reel drum diameter ratio are important geometrical parameters affecting drag reduction. The flow data indicate that the onset of turbulent flow in CT is suppressed in the polymer solutions. This paper introduces the concept of the modified drag reduction envelope for flow of polymer solutions in coiled tubing.

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