This work evaluates the influence of chemical additives, namely, starch, high-viscosity carboxymethylcellulose (HV-CMC), and calcite on rheological and filtration properties of inhibited drilling fluids composed by potassium citrate. A total of 11 experiments were conducted using a 2 3 -factorial design, three of which were in the central point. The concentration of starch varied from 0 to 0.0343 kg/L, the concentration of HV-CMC ranged between 0 and 0.0043 kg/L, and the concentration of calcite from 0 to 0.071 kg/L. Rheological and filtration properties were determined for the studied fluids. According to the results, starch and HV-CMC influence statistically the rheological properties of the studied fluids. The filtration properties, on the other hand, are statistically affected by these additives. The best results for fluid loss were obtained with fluids comprising starch and calcite in high concentrations, or with starch, HV-CMC, and calcite in high concentrations.

This work aims to evaluate the influence of the clay swelling inhibitor in the filtration properties of water-based drilling fluids. Drilling fluids were prepared with and without adding potassium citrate clay inhibitor. The following additives were used in the composition of the fluid: viscosity agent (xanthan gum), filtrate reducer (starch and low viscosity carboxymethylcellulose (CMC LV)), antifoam, bactericide, sealant (calcite), lubricant and pH controller. The concentration of inhibitor was used of 15, 20, 25 and 30 g/ 350 mL of water. We determined the filtration properties (filtrate volume (FV), spurt loss (SL), cake thickness (CT) and permeability (K)) of drilling fluids. According to the results, it was concluded that: (i) adding the inhibitor to the fluid promoted reduction of FV and K of fluids containing starch in the composition and (ii) the inhibitor promoted satisfactory reductions in the CT and increased of SL for all the studied fluids. Finally, the inhibited fluids prepared with higher concentrations of starch, CMC LV, calcite and potassium citrate than 25 g/ 350 mL of water showed the best performance compared to FV and SL.