Study on Coal Chemical Structure Changes During the Migration Path After Coalbed CH₄ Replacement by Natural CO₂

Based on displacing coalbed methane by the natural CO₂ injection in Yaojie coalfield, coal samples and gas samples are taken continuously at different distances away from CO₂ injection points. Infrared spectroscopy analysis is done for series of coal samples; the results show that the absorption peaks change significantly in the spectra wavenumbers of 2 800～3 000 cm^-1, 2 270～2 413 cm^-1, and 1 000～1200 cm^-1. Then, the coal samples before and after supercritical CO₂ treatment are analyzed from another coal mines, The above-mentioned wavenumbers of the absorption peak intensity also change, and treated coal sample absorption peak intensity is lower. These experiments demonstrate that injection of supercritical CO₂ can extract the aliphatic aromatic hydrocarbons and part of the minerals from the coal matrix during the migration path.