Novel Deep Eutectic Solvents for Stabilizing Clay and Inhibiting Shale Hydration

Abstract

The hydration and swelling of shale caused by water in water-based drilling fluids is one of the most important problems that causes wellbore instability. The development of high-performance shale inhibitors is an important prerequisite for ensuring the drilling of shale formations. In this study, four deep eutectic solvents (DESs) based on choline chloride (urea-DES, Gly-DES, Oxa-DES, and Cit-DES) were synthesized and introduced as promising shale inhibitors. Fourier transform infrared spectroscopy (FT-IR) and hydrogen nuclear magnetic resonance spectroscopy (1H NMR) were used to characterize the structural information on DESs. The inhibition ability of DESs was evaluated by a bentonite inhibition test, a linear swelling test, and a settlement test. Compared with the traditional inhibitors, such as potassium chloride (KCl) and polyether amine, the four DESs can effectively inhibit the hydration and swelling of shale. Five wt % DESs can maintain low rheological parameters when the content of sodium bentonite (Na-bent) was as high as 40 wt %. Among them, Gly-DES not only exhibited the most efficient inhibition capability but also had the advantage of not affecting the basic performance of the drilling fluid. Inhibitory mechanism analysis showed that the electrostatic interaction and hydrogen bonding between DESs and sodium bentonite (Na-bent) are the most important factors to inhibit clay hydration. Besides, the reduction of the surface tension of the liquid by DESs effectively weakened the driving force for water to penetrate the Na-bent layer. Finally, it is important to note that, although DESs exhibited strong inhibitory capabilities, some DESs, such as Oxa-DES and Cit-DES, are prone to adversely affect the basic performance of drilling fluids. Therefore, a careful selection is required.

Recent Advances in Deep Eutectic Solvents as Shale Swelling Inhibitors: A Comprehensive Review

“…With similar concentrations, DESs such as urea-DES, gly-DES, oxa-Des, and cit-DES reduced the swelling rate of the Na-bent sample by 29.38%, 21.57%, 37.31%, and 39.66%, respectively. 216 …”

“…DESs are adsorbed on the surface and interlayers of Na-bent, compressing the diffuse electric double layer and restricting Na-bent dispersion, attributable to choline cations, OH, COOH, NH 2 , and other functional groups. 214 , 216 , 224 …”

“…Ma et al (2021) analyzed the rheological properties of Na-bent suspension with and without adding inhibitors. 216 The experiment showed that the suspension of Na-bent with increasing concentration quickly became too viscous to measure the AV value without any inhibitor. However, after adding inhibitors, the value of AV increased sharply, indicating the degree of inhibition.…”

“…Ma et al (2021) conducted the linear swelling test for Na-bent shale samples with six different types of inhibitors with the same concentration of 5 wt %. 216 Among the six inhibitors, KCl and polyether amino are the conventional swelling inhibitors, but the other four are new types of chemicals having a good antiswelling ability. At the beginning of the linear swelling test, the sample was powdered and seized through the mesh.…”

Improvement of Emulsion Stability and Plugging Performance of Nanopores Using Modified Polystyrene Nanoparticles in Invert Emulsion Drilling Fluids

“…Currently, research on wellbore instability in shale oil and gas formations has mainly focused on shale hydration inhibition mechanisms ( Huang et al, 2018a , 2018b ; Du et al, 2020 ; Ma et al, 2021 ). Due to the increased usage of OBFs, research into the controls of shale wellbore collapse has been extended to studies of the micro-structures of shale and other formations ( Arif et al, 2021 ; Tian et al, 2021 ).…”