Application of a Natural Deep Eutectic Solvent Prepared from Choline Chloride and Tannic Acid as a Shale Inhibitor for Wellbore Stabilization.

To address wellbore instability issues associated with water-based drilling fluids during drilling operations and ensure the sustainable development of oil and gas resources, a deep eutectic solvent (DES-TA) is prepared by stirring and heating choline chloride with tannic acid, and its potential as a shale inhibitor is investigated. The inhibition performance of DES-TA was evaluated through hot-rolled recovery, clay linear swelling, and bentonite inhibition tests. The results revealed that DES-TA increased shale cutting recovery from 8.9 to 84.2% (a 75.3% increase) at 180 °C, inhibited the hydration swelling of 35 wt % bentonite at 90 °C, and reduced the swelling height of bentonite by 50.4% at 25 °C. In addition, the mechanism of action of DES-TA was analyzed through a series of analytical studies. DES-TA adsorbed onto the surface and interlayers of bentonite via electrostatic neutralization and hydrogen bonding, reduced the electrostatic repulsion between bentonite particles, and altered the hydrophilicity of the bentonite surface, thereby inhibiting the hydration and swelling of bentonite. DES-TA has excellent inhibition performance, but it has a serious adverse effect on the rheological properties and fluid loss of WBDF. When DES-TA is used, its compatibility with WBDF must be considered.