Turbulent Frictional Drag of Weighted Fracturing Fluids in Pipes: Experiments and Large-Eddy Simulations

As the development of deep oil and gas resources advances continuously, the role of weighted fracturing fluids in reducing wellhead operating pressure becomes increasingly important. However, the turbulent frictional drag behaviors of weighted fracturing fluids in pipes have not been understood systematically. The frictional drag characteristics and flow behaviors of non-weighted and weighted fracturing fluids in pipes are investigated at different flow rates, densities, pipe diameters, and rheological parameters via steady-state rheological tests and pipe flow friction experiments, together with large-eddy simulation and a power-law constitutive model for generalized Newtonian fluids. Main findings are as follows. The drag reduction rates of non-weighted polyacrylamide solutions basically increase with flow rate, and the optimal molecular weight of 600–700×104 corresponds to the highest drag reduction rate of 62%, while excessively large molecular weights weaken drag reduction effectiveness due to enhanced chain entanglement. The types of weighting salts have a significant effect on drag reduction performance. The 20% KCl system obtains the highest drag reduction rate of 64.8%, while the high-density CaBr2 system gets the lowest of 42.3% because high salinity suppresses the stretching of polymers. Parameter sensitivity analysis indicates that the power-law index n is the most sensitive parameter controlling frictional drag, followed by pipe diameter D. The novelty of this study lies in integrating experimental investigation, LES, and parameter sensitivity analysis to provide a theoretical basis for deep fracturing working conditions and fracturing fluids design.