Evaluation of the Inhibition Performance of a Hybrid Depth Eutectic Solvent Used as an Inhibitor for Water-Based Drilling Fluids and Its Mechanistic Analysis

Drilling instability in oil and gas drilling has long challenged drilling safety and economics. Conventional oil-based drilling fluids offer high-temperature resistance and good inhibition. However, oil-based drilling fluids have significant problems in terms of environmental impact, cost, and waste fluid disposal. This has led to the widespread use of water-based drilling fluids. This study aims to investigate the synthesis of a new water-based drilling fluid inhibitor, a hybrid low eutectic solvent ChCl-Gly-Urea (CGU-DES), and its performance evaluation. While conventional eutectic solvents (DES) usually consist of a single type of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD), CGU-DES extends its performance characteristics by introducing a combination of one HBA and two HBDs. The study confirmed the successful synthesis of CGU-DES using FT-IR spectroscopy. The following advantages of CGU-DES over CU-DES and CU-DES consisting of a single type of HBA and HBD were verified. Below 175 °C, the temperature resistance of CGU-DES is better, and the mass loss rate is less than 5%. The first and second rolling recoveries of CGU-DES aqueous solution with low concentration (<0.5 wt %) were greater than 95% and 85%, respectively, higher than the rolling recoveries of CG-DES and CU-DES.CGU-DES has a good ability to reduce water activity. When the dosage is 10%, the activity of DES aqueous solution is less than 0.950, and the efficiency of reducing water activity is nearly twice that of CG-DES and CU-DES. CGU-DES is compatible with sodium slurry and drilling fluids with polymer-sulfonated materials because it has little influence on rheology and fluid loss. At 180 °C, 0.7% CGU-DES was added to the polysulfonate drilling fluid system, and the fluid loss reduction rate reached 30.59%. Experiments show that CGU-DES can inhibit the hydration and dispersion of shale by inserting into the crystal spacing of montmorillonite , adsorbing onto the surface, reducing the surface tension of drilling fluid, reducing the contact angle between drilling fluid and shale, and reducing the water activity of drilling fluid. In summary, CGU-DES, a new type of green solvent, has potential application prospects in water-based drilling fluids and provides new technical support for solving the borehole instability problem during drilling.