Experimental investigation and molecular dynamics simulation for the effect of a novel Gemini cationic surfactant on gas coal wettability

Water-injected fracturing fluids can wet the coal body and reduce the amount of dust produced during coal mining. In order to enhance the wetting performance of fracturing fluids, a Gemini cationic surfactant named Gemini-TOH was innovatively synthesized in this paper using a three-step process. On this basis, a Gemini-TOH/KCl composite fracturing fluid system was developed by adding KCl. The wetting behavior of this composite system on gas coal was systematically analyzed through macro and micro experiments, and the wetting mechanism was deeply investigated. The results showed that the Gemini-TOH/KCl composite system was able to significantly improve the wettability of the coal samples, with the contact angle reduced to 22.3° and the surface tension reduced to 32.64 mN/m. The composite system not only exhibited a faster wetting rate and significant flocculation capacity, but also positively affected the compositional content of the coal body. According to the simulated results, the water molecule diffusion coefficient (D) had reached 10.29 × 10⁻⁹m²/s after the introduction of the Gemini-TOH/KCl composite system. It further revealed that the composite system had modified the molecular structure of the surface of the coal dust, thus demonstrating its excellent wettability properties.