ABSTRACT During the drilling process of shale reservoirs, problems such as wellbore instability and reservoir damage, which are caused by clay hydration and swelling as well as the water locking effect due to liquid phase invasion, have not been properly solved. In this study, a hydrophobic nano‐emulsion (PMBA) with a median particle size of 330 nm was prepared through emulsion polymerization. The results showed that PMBA could increase the shale surface roughness from 0.86 nm to 7.17 nm and raise the water contact angle from 27.4° to 128.7°, thereby achieving wettability reversal of the shale surface. Meanwhile, the surface tension of the aqueous solution could be reduced to 26.43 mN/m, and the spontaneous water absorption of shale rock was decreased by 69.1%, which significantly reduced the spontaneous water absorption of the aqueous phase in shale. Therefore, PMBA could effectively reduce the hydration swelling rate of shale samples and alleviate the reservoir water locking effect. In conclusion, PMBA could not only realize the wettability reversal of the shale surface but also reduce the surface tension of the aqueous solution, thus providing effective support for wellbore stability and reservoir protection during the shale oil and gas drilling process.
Zhang et al. (Thu,) studied this question.