Influence of CMC Molecular Weight and Degree of Substitution on Clay Swelling Inhibition in Water‐Based Drilling Fluids

Abstract

SummaryIn this paper, the clay hydration inhibitive properties of carboxymethylcellulose (CMC) in drilling fluids systems were studied. The clay swelling degree was evaluated as a function of time in presence of different aqueous solutions containing sodium chloride, potassium chloride, CMC A (9 × 104 g/mol − DS 0.7), CMC B (2.5 × 105 g/mol − DS 0.7), CMC C (2.5 × 105 g/mol − DS 1.2) and a commercial clay inhibitor based in quaternary amine, that was used as reference pattern. According to results obtained, the low molecular weight CMC showed slightly lower clay swelling degree compared to the high molecular weight along 180 minutes. In parallel, it was confirmed the higher efficiency of quaternary amine‐based commercial inhibitor (QABCI) to control the clay swelling mechanism. Basically, this inhibition effect was attributed to the ability of cationic quaternary ammonium groups to form electrostatic interactions with negatively charged surfaces of the clay, enhancing associative interaction between their particles. Besides, it was visualized by microscopy that the highest molecular weight of CMC provided a reduction in formation and pores size compared to CMC of lower molecular weight after 1,000 minutes in aqueous medium. This behavior could be attributed to the dynamic of interactions between clay and high molecular weight CMC along the time, which is a result of strong contribution of electrostatic interactions between carboxylate groups located along the polymer backbone and positively charged clay layers edges as well as hydrogen bonds.