A model to calculate the pressure loss of Newtonian and non-Newtonian fluids flow in coiled tubing operations

The coiled tubing is a system consisting of a long, continuous and flexible steel pipe used in many processes, especially in the oil industry. As the fluid flow in curved pipes generates significant energy dissipation compared to a straight pipe, it is essential to predict the pressure drop to obtain the pumping pressure to be used in the operation and optimize process control. In this work, the pressure drop in the flow of Newtonian and non-Newtonian fluids was evaluated in a pilot unit and a mathematical model was developed to simulate the pressure drop along the coiled tube. Water and an aqueous solution of xanthan gum, with rheological power-law parameters similar to those observed in cement slurries, were used in experimental tests. The experimental unit is 375 m long divided into 8 layers with pressure measurements in each layer where fluids were pumped at different volumetric flow rates and curvature ratios. A mathematical model was proposed to calculate the pressure drop assuming the existence of a sequential pumping of different fluids along the coiled tubing, with different curvature ratios and internal tube diameters. The mathematical modeling could predict the pilot experiments for Newtonian fluids and, based on the results obtained in the laboratory, the parameters of a friction factor correlation for non-Newtonian fluids present in the literature were re-estimated. A case study of a real well abandonment operation with a coiled tubing system was used to validate the proposed modeling. The developed software was used to simulate the real conditions, where a good approximation to the field data was observed, with a percentage error between the experimental and calculated values below 7%.