Achieving the hydrophobic alteration by functionalized nano-silica for improving shale hydration inhibition

Abstract

Shale hydration is the primary cause of wellbore instability during drilling processes. In this study, two non-fluorinated silane-coupling agents, octyltriethoxysilane (OTES) and (3-Aminopropyl) triethoxysilane (APTES), were grafted onto the nano-silica surface to develop a hydrophobic material (SHM). Various performance characterizations, including infrared spectroscopy, thermogravimetric analysis, surface tension, wetting alteration, capillary self-suction height, bentonite expansion, and shale dispersion, were employed to investigate the shale inhibition properties of SHM comprehensively. Experimental results revealed that SHM could significantly improve shale hydration inhibition. For instance, in a 2 % SHM liquids, the shale hot rolling recovery rate increased from 25.39 % to 83.78 %, and the bentonite expansion height decreased from 7.65 mm to 2.80 mm. The inhibition performance was notably superior to potassium chloride (KCl) and polyether amine (PEA). Inhibition mechanisms analysis unveiled that the outstanding inhibitory effect of SHM was achieved through electrostatic adsorption, wettability alteration, and surface tension reduction. Firstly, SHM contained numerous amine groups that could demonstrate strong adsorption on the clay surface through electrostatic and hydrogen bonding interactions. Secondly, with long hydrophobic alkyl chains, it formed a highly hydrophobic film enveloping the shale surface, effectively preventing water from invading. Thirdly, it reduced liquid surface tension, further minimizing the water infiltration. As a result, the use of SHM significantly enhanced shale hydration inhibition during the shale drilling process.