Biogenic gas generation effects on anthracite molecular structure and pore structure

This study carries out a simulated experiment of biogenic gas generation and studies the effects of gas generation on the pore structure and molecular structure of anthracite by mercury intrusion porosimetry, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results show that methanogenic bacteria can produce biogenic gas from anthracite. CO2 and CH4 are the main components of the generated biogas. After generation, some micropores (<10 nm) and transitional pores (10–100 nm) in the coal samples transform into large pores. In the high-pressure stage (pressure>100 MPa) of the mercury intrusion test, the specific surface area decreases by 19.79% compared with that of raw coal, and the pore volume increases by 7.25% in total. Microbial action on the molecular structure causes changes in the pore reconstruction. The FT-IR data show that the side chains and hydroxyl groups of the coal molecular structure in coal are easily metabolized by methanogenic bacteria and partially oxidized to form carboxylic acids. In addition, based on the XRD data, the aromatic lamellar structure in the coal is changed by microorganisms; it decreases in lateral size (La) and stacking thickness (Lc). This study enriches the theory of biogenic coalbed gas generation and provides a pathway for enhancing the permeability of high-rank coal reservoirs.