Generation Processes and Geochemical Analysis of Simulated Biogenic Coalbed Methane from Lignite

Abstract

Under laboratory conditions, biogenic CBM generation process from lignites simulated to study the geochemical producing process, as well as the possible generation pathways and mechanisms. Research results indicate that the generation process of biogenic CBM from lignite has at least two gas-generation peaks, and the gas-generation field in the first peak is higher than that in the second peak. During the first gas-generation peak, huminite is considered to be easily degraded by microorganism, while during the second gas-generation peak, liptinite and inertiniteare degraded by methanogens. The compositions of carbon (δ¹³C₁) and hydrogen (δD) isotope in methane show that the simulated bio-methane mainly generates from the pathway of acetic acid fermentation. The concentrations of CH₄ and CO₂ are mutually increasing and decreasing with the passage of experiment time, and produced CH₄ enriched less ¹³C in the later period, both of which indicates that some CH₄ may be from way of carbon dioxide reduction, especially in the end process. When lignite vitrinite reflectance (R_o) value increased, the gas-generation quantities decrease and CH₄ concentrations decrease linearly, and there was a trend of decreasing δ¹³C₁ value linearly at the same time. Identify the generation process and geochemical property of biogenic CBM from lignite is crucial to understanding and improving biogenic CBM production.