Enhancing the shale inhibition performance of low-melting mixture solvents utilizing DTAB in water-based drilling fluids

Wellbore instability issue is a common occurrence in the development of clean energy sources such as shale gas. Low-melting mixture solvents (LoMMSs), as a novel and environmentally friendly liquids material, are anticipated to be utilized to address this issue. In this work, a novel shale inhibitor (LoMMSs-2) was formulated through introducing a cationic surfactant with a long hydrophobic chain, dodecyl trimethyl ammonium bromide (DTAB), into a commonly used choline chloride/glycerol LoMMSs. Inhibition assessment results indicated that the swelling height of bentonite in LoMMSs-2 solutions decreased by 53.46 %, and shale recovery rate reached as high as 89.51 %, demonstrating superior hydration inhibition compared to commercial inhibitors. The mechanism for inhibiting hydration in LoMMSs-2 was explored through tests involving zeta potential, particle size, interlayer spacing, shale wettability, and surface tension, etc. The findings revealed that choline cations and quaternary ammonium cations in LoMMSs-2 could tightly adsorb to the clay surface. The exposed long alkyl chains made the rock more hydrophobic, increasing the water contact angle from 22.49 degrees to 65.26 degrees. Subsequently, more interlayers water in the clay was expelled, leading to a significant reduction in adsorbed water. Additionally, the lower surface tension and stronger hydrophobicity corresponded to a smaller capillary force, further minimizing water infiltration into shale. Therefore, introducing hydrophobic groups into LoMMSs was a promising approach for developing efficient shale inhibitors to address wellbore instability issue in shale gas drilling.