Study on Gas Adsorption-Desorption and Diffusion Behaviour in Coal Pores Modified by Nano Fracturing Fluid

Nanoparticles are added to clean fracturing fluids to formulate nanoparticle-modified clean fracturing fluids, compared with ordinary clean fracturing fluid, it has the advantages of good temperature resistance, low loss of filtration, and so forth, and has good application prospects in coal-bed methane. However, the current research on nanoparticle-modified clean fracturing fluids is mostly focused on the study of their rheological properties. The mechanism of nano-fracking fluid influence on methane adsorption-desorption characteristics is not clear. Therefore, this study chooses Jiulishan anthracite coal (high-rank coal), Pingdingshan coal (medium-rank coal), and Geng village mine long bituminous coal (low-rank coal) of the three rank coal samples. Using indoor experiments and molecular simulation methods, a study on the influence of methane adsorption and desorption capacity and diffusion ability of coal samples provides a modified fracturing fluid formulation of 0.8% CATB + 0.2% NaSal + 1% KCl + SiO₂. The experimental results show that nanofracturing fluid-treated coal samples compared to clean fracturing fluid treated coal samples, both methane adsorption and desorption capacities, were increased to some extent. Construction of methane adsorption systems with different apertures and calculation of isosteric heat of adsorption, indicating that the interaction force between methane and coal molecules is smaller after nanofracturing fluid treatment, which facilitated methane desorption. A simulation study of methane diffusion in coal samples treated with two systems of fracturing fluids at different aperture was carried out using molecular dynamics methods, indicating that nanoparticle-modified clean fracturing fluids can reduce the damage of clean fracturing fluids to the desorption-diffusion ability of coal reservoirs. Comparison of 6 MPa as the most suitable pressure for nanofracturing fluids to function provides a basis for the future development of nanofracturing fluids and their popularization.