Evaluation of selenium-doped nanocomposites (Se@Ag/AgO-ZnO) for enhanced clay swelling inhibition

The instability of reactive shale formations remains a critical challenge in drilling operations, leading to borehole collapse and significant non-productive time, particularly when using environmentally friendly water-based drilling fluids (WBDFs). This study aims to develop a high-performance, eco-friendly shale inhibitor by synthesizing a Se@Ag/AgO-ZnO nanocomposite using a green chemistry approach mediated by Pinus nigra pollen extract. The synthesized nanocomposite was characterized using XRD, SEM/EDS, XPS, and UV-Vis spectroscopy. The results revealed a hexagonal wurtzite structure with an average crystallite size of 15.14 nm. The inhibition performance was evaluated through rheological measurements, zeta potential analysis, and hot-rolling dispersion tests using bentonite-based drilling fluids. The results indicated that the nanocomposite effectively mitigates clay hydration through a dual mechanism involving electrostatic neutralization and physical pore plugging. Zeta potential measurements showed a significant shift from - 49 mV for the base mud to approximately - 1 mV at a nanocomposite concentration of 5000 ppm, confirming effective surface charge screening. Rheological tests demonstrated that the addition of 5000 ppm nanocomposite reduced the Yield Point of highly contaminated mud containing 10 wt% bentonite from 58 to 33 lb/100 ft², significantly outperforming the conventional 3 wt% KCl inhibitor. Furthermore, hot-rolling dispersion tests showed a cutting recovery of 88% for the nanocomposite-treated fluid, compared with only 7.4% for the KCl-based system. These findings demonstrate that the Se@Ag/AgO-ZnO nanocomposite is a highly effective, thermally stable, and non-toxic alternative to conventional halide salts for stabilizing water-sensitive shale formations in drilling applications.