Quaternary ammonium gemini surfactants having different spacer length as clay swelling inhibitors: Mechanism and performance evaluation

The swelling of shale formation upon exposure to water-based drilling fluids leads to several problems. Common shale (clay) inhibitors used in the industry have several shortcomings which adversely affect the drilling mud properties. This study involves the development, application, and mechanism of new quaternary ammonium gemini cationic surfactants as clay swelling inhibitors. These gemini surfactants are structurally similar but different in terms of the spacer lengths. The inhibition characteristics of gemini surfactants were evaluated using a linear swell tester, capillary suction timer, scanning electron microscope (SEM), rheology, filtration, wettability, and zeta potential analysis. It was observed that the new gemini cationic surfactants with various lengths of spacers reduced the clay swelling. The GS12 surfactant, containing flexible large spacer C12 proved to be a beneficial swelling inhibitor as compared to GS8 and GS10 due to increased hydrophobicity. It also showed acceptable performance compared to the common shale inhibitor used in the industry. SEM images revealed that water caused significant damage to clay structures showing irregular and sharp edges. However, the surfactant-treated clay showed a fine, dense, and smooth surface. An inhibition mechanism using synthesized surfactants was also proposed. Experimental tests showed the synthesized surfactants adsorb and intercalate between layers of clay through hydrogen bonding and attractive electrostatic forces. The orientation of lipophilic tails inhibits the water adsorption in the clay which results in reduced clay swelling. The synthesized surfactants reduced the clay swelling without affecting the other mud properties such as rheology, stability, and filtration properties.