Investigation for the novel use of a typical deep eutectic solvent as a potential shale inhibitor.

The hydration and swelling of shale cause borehole instability and seriously threaten the drilling safety, especially for the use of water-based drilling fluids. In this paper, the potential application of a typical deep eutectic solvent CU-DES comprised of choline chloride and urea (molar ratio 1:2) as a novel shale inhibitor was investigated for the first time. The inhibitive properties of CU-DES were evaluated by experiments such as bentonite inhibition test, linear swelling test, and shale cuttings hot-rolling dispersion test. Compared with traditional inhibitors KCl and polyether diamine (PDA), CU-DES with a lower concentration exhibited the much higher inhibitive capacity. Furthermore, CU-DES maintained excellent performance even at high temperature (160°C), which made it possible to utilize in high-temperature well drilling. To explain the inhibition mechanism of CU-DES, a series of analytical methods, including particle size distribution measurement, Zeta potential measurement, SEM, FTIR, and XRD were conducted. The results demonstrated that the great inhibitive properties of CU-DES were mainly dependent on both the electrostatic attraction and the hydrogen bond between CU-DES and clay. [ABSTRACT FROM AUTHOR]