Novel approach to improve shale stability using super-amphiphobic nanoscale materials in water-based drilling fluids and its field application

In this study, super-amphiphobic nano-silica nanoparticles (SA-NPs) were used to enhance the shale stabilization performance of water-based drilling fluids (WBDFs) by altering the surface wettability, preventing the capillary self-priming effect, and plugging the nano-micro pores of shale. The results of transmission electron microscopy, particle size distribution, and scanning electron microscopy characterization revealed that SA-NPs exhibited a nanoscale "coalesce" structure, which is composed of spherical particles joined together, and could form a nano-papillary structure on the shale surface. Due to the presence of nano-micro scale rough structures and ultra-low surface energy components, the shale treated by SA-NPS exhibited super-amphiphobic surface property in the contact angle test. Contact angles of water and hexadecane on the shale surface reached up to 154.13 degrees and 151.34 degrees after being treated with SA-NPs, respectively. Furthermore, the addition of 1% SA-NPs in WBDFs could reduce the linear swelling rate from 40.5 to 6.0%, increase the shale cuttings recovery percentages from 82.5 to 95.6%, increase the plugging rate of low permeability shale core from 81.25 to 94.00%, and raise the high-temperature and high-pressure uniaxial compressive strength from 3.45 to 4.87 MPa. Compared with the polyether amine and fumed nano-silica, the addition of SA-NPs produced the best performance. Based on the excellent shale stabilization performance of SA-NPs, a high-performance WBDF was developed and applied in Dagang Oilfield. During the drilling operation? no wellbore instability, sticking, and other complex situations occurred. The results indicate that SA-NPs could better address the issue of wellbore instability in shale formations and have a great application prospect in shale well drilling.