Investigation of the inhibition mechanism of polymer/nano-silica composite as shale inhibitor in water-based drilling fluids

Wellbore instability caused by shale hydration and swelling is the critical issue in the drilling process of oil and gas wells. In this study, the nano-silica/cationic polymer composite (NS-DD) was synthesized and evaluated as novel shale inhibitor in water-based drilling fluids (WDFs). The inhibition performance of NS-DD was carried out and compared with the conventional inhibitor potassium chloride (KCl) and the extensively utilized inhibitor polyether diamine (PDA), where the inhibition performance tests consisted of bentonite inhibition tests, linear swelling tests, and shale cuttings rolling recovery tests. The results revealed that NS-DD exhibited outstanding inhibition performance compared to KCl and PDA even in high temperature environment. Specifically, in the presence of KCl and PDA, the third roll recoveries of shale cuttings after hot rolling at 150 °C for 16 h were 28.62% and 42.15%, respectively, however, the recovery of shale cuttings was as high as 70.06% when NS-DD was attended. Additionally, we proposed that the excellent inhibition ability of NS-DD may be attributed to its strong adsorption with clay through hydrogen and ionic bonding and plugging of nano-pores in WDFs filter cake and shale, preventing water penetration into the reservoir causing shale hydration and swelling based on the results of scanning electron microscopy, zeta potential, thermogravimetric and X-ray diffraction analysis. This study revealed the potential application of NS-DD as the shale inhibitor in WDFs.