Influence of solids concentration and solid/polymer interaction on the apparent viscosity of drilling fluids

Drilling fluids perform several functions such as lubrication and cooling of the drill bit, carrying the cuttings to the surface and also maintaining the stability of the well. The physicochemical characteristics of solid particles affect the drilling fluid properties, such as density, chemical composition, and surface charge. In this research, the effects of concentration, surface charge, and adsorption of different solid additives (Barite, Calcite, and Glass spheres) in carboxymethylcellulose (CMC) aqueous solutions were evaluated to quantify its influence on the apparent viscosity of drilling fluids. A study of the polymer hydration time was also carried out. The suspensions were characterized and analyzed by the rheological parameters, the morphology, the surface charge, and the chemical composition. The results showed that suspensions with solids concentration higher than 25% (m/v) presented an increase of the frictional effect of solids, leading to a significant increase in the apparent viscosity of the suspensions. The morphology of the glass spheres facilitated the fluid flow, leading to the lowest apparent viscosity among the suspensions. Ca2+ ions from calcite solids reduced the energy barrier against flocculation, making the apparent viscosity of calcite suspensions the highest. The barite suspensions showed the highest zeta potential value (in modulus) among all suspensions. The appearance of two bands related to the carbonyl in the FTIR spectrum of barite suspensions proves chemical adsorption with the CMC polymer, justifying its lower apparent viscosity compared to calcite suspensions.