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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]

Zwitterionic gemini surfactants, which have the advantages of both zwitterionic and gemini surfactants, have been widely used in various disciplines. Sulfobetaine-type zwitterionic gemini surfactants consisting of 1,2-bis[N-methyl-N-(3-sulfopropyl)-alkylammonium]ethane (2CnSb with 6, 8 and 10 carbon atoms) were evaluated for their interfacial activities at the water/crude oil interface. The 2C10Sb molecules showed a remarkable ability to decrease the interface tension (IFT) of water/crude oil, and the degree of decrease was much greater than those in either zwitterionic or gemini surfactant systems by at least two orders of magnitude. Furthermore, the effects of salts (NaCl, CaCl2, and MgCl2) on the IFT of the 2C10Sb system were thoroughly investigated. Interestingly, the delicate balance between the effects of additional cations and the intramolecular interactions of 2C10Sb molecules played crucial roles in the interfacial arrangements of 2C10Sb molecules, which were mainly dependent on the bonding abilities of the cations. Moreover, a zwitterionic surfactant and a cationic gemini surfactant were employed in control experiments to verify the proposed mechanisms. [ABSTRACT FROM AUTHOR]