Synthesis of a hydrophobic quaternary ammonium salt as a shale inhibitor for water-based drilling fluids and determination of the inhibition mechanism

Abstract

During the drilling process, when the drill encounters easily hydrated shale formations, the problems generated by the shale hydration are often very serious, and developing a method of effectively inhibiting the shale hydration is a major difficulty. In order to further enhance the ability of small-molecule quaternary ammonium salts to inhibit shale hydration, in this study, a hydrophobic quaternary ammonium salt inhibitor (SJAY) was synthesized via a nucleophilic substitution reaction. The performance of SJAY in inhibiting shale hydration was investigated through mudball immersion, linear swelling, shale recovery, water absorption, and bentonite inhibition experiments. The mechanism by which SJAY inhibits shale hydration was investigated through zeta potential, particle size distribution, contact angle, surface tension, thermogravimetric analysis, and X-ray diffraction analyses. The experimental results revealed that with the addition of 1 wt% SJAY, the shale recovery of easily hydrated shale reached 92.5% (the recovery in deionized water was 11.3%), the 4-h water absorption of modified montmorillonite was only 4.69%, and the water contact angle of the shale slice reached 118.2°. The analysis of the inhibition mechanism revealed that the SJAY was adsorbed onto the clay through electrostatic attraction and hydrogen bonding. First, the SJAY formed a hydrophobic barrier on the surface of the clay, blocking the adsorption of water molecules. Then, the SJAY entered the clay interlayer and expelled the interlayer water molecules. Moreover, the SJAY reduced the capillary force effect by decreasing the surface tension and increasing the contact angle. The results of this study demonstrate that SJAY can be used as an effective inhibitor in water-based drilling fluids.