Stimulation effect of Fe₃O₄ nanozyme-ammonium persulfate fracturing fluid in coalbed methane development

The efficient development of coalbed methane (CBM) calls for innovative technologies capable of simultaneously enhancing gas desorption, diffusion, and reservoir permeability, going beyond conventional fracturing methods that mainly focus on permeability improvement through physical cracking. Nanozymes, which combine nanomaterial properties with enzyme-like catalytic activity, have attracted wide attention due to their high catalytic efficiency, stability, and scalability. Among them, peroxidase-like nanozymes represent one of the most applied categories. For instance, the strong oxidizing sulfate radical (SO₄⁻·) can be generated via the Fe₃O₄ nanozyme–ammonium persulfate system. However, whether such radicals can effectively modify coal reservoirs and thereby enhance CBM production remains insufficiently investigated. long-flame coal is used as the substrate to examine the degradation process induced by Fe₃O₄ nanozyme–ammonium persulfate fracturing fluid. The coal samples, before and after degradation, are analyzed using FTIR, XPS, Raman spectroscopy, ¹³C-NMR, and isothermal adsorption experiments to qualitatively and quantitatively evaluate changes in functional groups, molecular weight, and methane adsorption affinity. Mercury intrusion porosimetry is employed to characterize alterations in the coal pore structure, while permeability measurements are conducted to assess the effect of the nanozyme system on reservoir flow capacity. The results show that after treatment with the Fe₃O₄ nanozyme–persulfate system, the content of oxygen-containing functional groups, methyl groups, and other saturated functional groups on the coal surface is reduced, leading to decreased methane adsorption capacity and thus promoting CBM desorption. Moreover, partial degradation of coal macromolecules into small soluble molecules increases matrix porosity and total pore volume, while reducing tortuosity and breakthrough pressure—favorable for improving CBM diffusion. Furthermore, nanozyme-mediated degradation contributes to enhanced coal reservoir permeability. This study confirms that the proposed fracturing fluid not only performs conventional fracture creation but also integrates functions for enhancing desorption, diffusion, and permeability, thereby strengthening the “upstream” output of CBM. The Fe₃O₄ nanozyme–persulfate system extends the application scope of nanozyme materials and offers a multi-functional approach for coal reservoir stimulation.