Effects of solids loading on drag reduction in polymeric drilling fluids through straight and coiled tubing

An experimental study has been conducted to evaluate the effects of solids on the drag reduction characteristics of polymeric drilling fluids, loaded with solids, through straight and coiled tubing. The polymers investigated were PHPA and XCD. These polymers were dissolved in brines which were prepared by mixing potassium, chloride (KCl) and sodium formate (Na-formate) in water. Various concentrations of polysaccharide gum (XCD) and partially hydrolyzed polyacrylamide (PHPA) polymers were dissolved in the KCl and Na-formate solutions. These fluids were pumped through straight pipes. Based on the results, it was established that the PHPA/KCl solution exhibited better drag reduction than PHPA/Na-formate, XCD/KCl, and XCD/Na-formate solutions in straight pipes. Thus, the PHPA/KCl solution was selected for further study. This polymer solution was then loaded with barite and bentonite to simulate solid cuttings. The fluid system was pumped through different sized coiled tubing and straight pipes. A correlation in terms of Fanning friction factor and generalized Reynolds number was developed, and percentage drag reduction was calculated. It was observed that, when clear polymeric solutions were loaded with solids, drag reduction decreases drastically. Finally, the effect of curvature on the flow of solid-laden was studied. It was observed that frictional losses in coiled tubing were almost twice those of frictional losses in straight tubing for the solid-laded polymeric fluids under investigation.