Development and mechanistic study of hydrophobic shale inhibitors for water-based drilling fluids

Maintaining wellbore stability is a constant and hot issue in the drilling industry. The hydrophilic nature of rocks makes them susceptible to destabilization by physicochemical reactions with water-based drilling fluids. Amine-based inhibitors have been widely studied because of their effectiveness in inhibiting rock hydration. On the basis of maintaining the original inhibition mechanism of amine-based inhibitors, a hydrophobic amine-based inhibitor [(named hydrophobic organic amine (HOA)] was prepared by hydrophobically modifying the amine-based inhibitor. It has the ability to change the hydrophilicity of rocks, which is expected to further enhance the inhibition performance of amine-based inhibitors. The inhibition performance of the HOA was evaluated through experiments measuring the relative inhibition ratio, rolling recovery ratio, linear expansion rate, and water absorption rate. The performance of HOA in conventional drilling fluid systems was also systematically evaluated. HOA exhibited exceptional temperature resistance and the ability to suppress clay swelling. At an HOA dosage of 1.0%, bentonite exhibited relative inhibition ratios of 92.9% and 87.5% before and after aging at 150 degrees C, respectively, along with a rock fragment rolling recovery ratio of 75.1% (compared to 11.4% in pure water). The inhibition mechanism of HOA was investigated through contact angle, zeta potential, particle size distribution, and surface tension experiments. HOA had the inhibition mechanism of traditional amine-based inhibitors, that is, it could neutralize the negative charge on the surface of the clay, reduce the hydration repulsion between the clay layers, and effectively inhibit the clay hydration. Furthermore, HOA could also electrostatically adsorb onto the shale surface to form a hydrophobic layer, thereby reversing the wetting of hydrophilic rocks and reducing their water intake capacity. In addition, HOA could significantly reduce the surface tension of aqueous solutions. HOA, which can change the hydrophilicity of rocks, has better inhibition performance on rock hydration and is expected to become the next generation of amine-based inhibitors. [Graphical Abstract]