Deep Eutectic Solvents with Different Alkyl Chain Lengths as Inhibitors for Shale in Water-Based Drilling Fluids

Traditional drilling operations have relied on water-based drilling fluids, but shale's sensitivity to water poses several challenges, such as wellbore instability. To address this issue, four kinds of deep eutectic solvents (DESs) were prepared with varying alkyl chain lengths to prevent shale hydration expansion. FT-IR and proton NMR were used to analyze the structure of these DESs. To evaluate the inhibitory properties of the DESs, a series of tests were conducted, including the linear expansion test, the shale rolling recovery experiment, and the rheological properties test. The results showed that DESs were effective in preventing shale expansion due to hydration, and the results were compared to the properties of potassium chloride. Various analysis methods were adopted to understand the interaction mechanism between the clay particles and DESs, including the zeta potential test, particle size analysis, and X-ray diffraction determination. The analysis revealed that DESs can adsorb on the clay surface through electrostatic attraction and hydrogen bonding, compress the clay's electric double layer, and prevent surface hydration. Moreover, DESs can reduce the osmotic hydration as they can enter the clay layer and lower the clay layer spacing. The results indicated that DESs have the potential to be a promising shale inhibitor.