Design of experiments to evaluate clay swelling inhibition by different combinations of organic compounds and inorganic salts for application in water base drilling fluids

• The inhibition of swelling clays by organic and inorganic salts was successful.
• Design of experiments allowed optimizing water-based drilling fluid formulations.
• KCl-poly quaternary ammonium blends do not alter the rheological properties of fluids.

In this study the synergistic behavior that occurs when three different cationic inhibitors for clay swelling were associated with brines containing NaCl and KCl was evaluated. These commercial inhibitors are based on a cationic quaternary polyamine chloride with quaternary ammonium group (INIB 1), on a cationic polyacrylamide chloride with quaternary ammonium group (INIB 2) and on a quaternary ammonium chloride salt (INIB 3). Each inhibitor was characterized considering the amount of chlorides and content of active matter. The tests were performed with a commercial bentonite. Capillary suction timer (CST) and linear swell meter (LSM) were used for the evaluation of clay–water interaction in the presence of various fluids. For a better interpretation of the experimental results statistical analysis (DOE — design of experiments) via response surface methodology (RSM) was used, taking into account the type and concentration of inhibitors, the type and concentration of brines as well as the contact time of the inhibitor solutions with clay. The results showed different efficiencies, in other words, inhibitors mixed with brines were more effective than the inhibitors alone. The best results were obtained for cationic polyacrylamide chloride with quaternary ammonium group at 7 lb/bbl (pounds per barrel) in KCl brine at 18.74 lb/bbl with contact time of brine and clay of 7.6 h. Solutions containing these combinations presented greater inhibition of clay swelling. However, for field operations, other parameters should be considered as operating cost, environmental requirements and the application time of each product.

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