Assessment of swelling inhibitive effect of CTAB adsorption on montmorillonite in aqueous phase

Abstract

Physicochemical aspect of wellbore stability during drilling shale formations is linked to the interaction between montmorillonite (Mt) and aqueous phase. This study conducts for the first time a comprehensive study to assess swelling inhibitive effect of cetyltrimethylammonium bromide (CTAB), a celebrated cationic surfactant in petroleum industry, adsorption on Mt in the aqueous phase. Initially, the adsorption behavior of CTAB on Mt below and above the critical micelle concentration (CMC) was assessed by batch equilibrium experiments and then the adsorption data were examined using four famous adsorption equilibrium models. It was found that Mt has a great tendency to adsorb CTAB. Furthermore, the equilibrium data for monomeric and micellar adsorptions suited very well to Langmuir and Linear isotherms, respectively. The swelling inhibitive feature of CTAB was explored through extensive experiments comprising mud making, settlement, filtration, zeta potential, particle size, water adsorption, scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). In contrast to deionized water, CTAB aqueous solution exhibited fairly low rheological profile with larger amount of Mt loading (225g/L). The dispersion of pre-hydrated Mt was fully unstable after being exposed to CTAB. Mt lost completely its ability to control fluid loss in aqueous solution of CTAB. The addition of CTAB to Mt dispersion extremely changed the magnitude of zeta potential from negative to positive, specifically before micelles formation. Compared to deionized water, Mt particles gave larger particle sizes in aqueous solution of CTAB, indicating the low degree of particle delamination. The affinity of Mt to water decreased by about 70% after modification via CTAB. Unlike deionized water, modification of Mt in aqueous solution of CTAB led to the larger size of aggregates, according to SEM analysis. TGA demonstrated that modified Mt in aqueous solution of CTAB has 4.68% water content less than that of modified in deionized water. The findings convey the message that CTAB can act as a far superior clay stabilizer at concentration much higher than CMC. Finally, Fourier transform infrared spectroscopy (FT-IR) analysis was carried out to prove the adsorption of CTAB on Mt. It was concluded that the intercalation of CTAB (molecules and CTA+) into the interlayer space of Mt through cation exchange and hydrophobic interaction is probably the main inhibition mechanism.