Experimental Investigation of Frictional Pressure Losses in Coiled Tubing

This paper presents an experimental investigation of tubular frictional pressure loss in coiled tubing (CT) and straight sections of seamed and seamless tubing. Fluids investigated include water, linear guar gum and hydroxypropyl guar (HPG), and borate-crosslinked guar gum and HPG, under conditions typically encountered in many CT field applications. The equipment used includes a system of one 1000-ft and two 2000-ft CT reels that can be arranged to provide total CT lengths of 1,000, 2,000, 3,000, 4,000, and 5,000 ft. The system also includes straight sections of seamed and seamless tubing with the same nominal diameter (1-1/2 in.) and wall thickness (0.156 in.) as that of the CT. The investigation focuses mainly on the effects of CT curvature, tubing seam, fluid pH, and shear history on frictional pressure loss. Results obtained with water indicate that curvature, as well as the seam inside the CT, significantly affect the frictional pressure losses. Results obtained with various polymer solutions and gels, however, suggest that tubing curvature has a more significant effect on the frictional pressure losses than the tubing seam. Moreover, it is observed that, for borate-crosslinked HPG, the pressure gradient is dependent on both the fluid pH and the length of CT across which it is measured. However, for borate-crosslinked guar gum, the pressure gradient is a function of pH and is not very sensitive to the length of tubing along which it is measured.