Study on the evolution model of coal porosity based on pyrolysis reaction kinetics

In situ thermal injection modification is an effective approach to address issues such as low production efficiency and poor safety in deep coal mining. During pyrolysis, the pore structure of coal significantly changes, which in turn alters the permeability of pyrolyzed coal seams. Research on porosity evolution models during pyrolysis is crucial for evaluating oil and gas production efficiency and assessing groundwater environmental impacts in mining areas. To address the current limitations of experimental methods that cannot achieve real-time continuous measurement and quantitative description, a universal porosity evolution model for coal during pyrolysis is established in this study. The model is based on the mechanism of organic matter decomposition and is combined with pyrolysis reaction kinetics. Taking the No.2 coal seam of Cixi Mine in Fengfeng Mining Area and the No.12 coal seam of Zhaogezhuang Mine in Kailuan Mining Area, both with a burial depth of over 1000 m, as the research objects, the calculated values were compared with the measured data. The error was relatively small, and the simulated curve of coal porosity variation during pyrolysis was highly consistent with the measured curve, which proves that the established model can accurately and quantify the porosity evolution process of pyrolyzed coal.