EXPERIMENTAL INVESTIGATION OF FRICTIONAL PRESSURE LOSSES IN COILED TUBING

This paper presents an experimental investigation of tubular frictiona l pressure loss in coiled tubing (CT) and straight sections of seamed and seamless tubing. Fluids investigated include water, linear guar gu m and hydroxypropyl guar (HPG), and borate-crosslinked guar gum and HP G, under conditions typically encountered in many CT field application s. 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 se ctions 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 invest igation focuses mainly on the effects of CT curvature, tubing seam, fl uid pH, and shear history on frictional pressure loss. Results obtaine d with water indicate that curvature, as well as the seam inside the C T, significantly affect the frictional pressure losses. Results obtain ed with various polymer solutions and gels, however, suggest that tubi ng 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 bor ate-crosslinked guar gum, the pressure gradient is a function of pH an d is not very sensitive to the length of tubing along which it is meas ured.