Enhancement of Static and Dynamic Sag Performance of Water-Based Mud Using a Synthetic Clay.

Fluid homogeneity and stability are of high importance as they greatly affect the fluid performance in drilling operations. Solid settlement or solid sag is a severe issue that occurs in weighted drilling muds, especially at elevated temperatures, where the weight material tends to settle down causing well control problems. This study evaluates the effectiveness of a synthetic clay (laponite) to prevent the static and dynamic sag tendency of barite-weighted drilling fluid for elevated-temperature drilling applications. Several high-density mud samples were prepared by varying the concentration of the synthetic clay. The sag tendency of the fluid samples was evaluated in the lab using dynamic and static sag tests, and the optimal concentration was determined. The impact of synthetic clay on the density, pH, and rheological properties was also studied. Moreover, the filtration properties of the developed formulation were measured using high-pressure high-temperature filtration experiments. The synthetic clay was found to be effective in reducing the static and dynamic sag tendency of barite-weighted water-based drilling fluids. 0.75 lb/bbl of laponite was adequate to eliminate solid sag at a temperature up to 250 F. This amount of laponite slightly increased the plastic viscosity by 8%, while an increase of 42% and 43-115% in the yield point and gel strength, respectively, was observed. A significant enhancement in the filtration performance was observed; the filter cake thickness and the filtrate volume were decreased by 15-20%. Additionally, the synthetic clay had an insignificant effect on the fluid density and pH.