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Biogenic or microbial methane (CH₄) emissions, believed to be the main driver of the recent surge in global atmospheric CH₄ emissions, have altered monitoring, measurement, and mitigation of fossil-fuel emissions. As of 1981, over 20% of the world’s natural gas reserves were biogenic in origin. Additional biogenic CH₄ reserves from coal have been discovered since 1981 mixed (40–80%) with thermogenic CH₄. Biogenic CH₄ accumulates up to 100% in coal reservoirs in the Powder River Basin (PRB), USA. Biogenic CH₄ is generated by microbial breakdown of fossil organic matter as an early-stage (primary) type during burial over geologic time and is rarely preserved. Also, biogenic CH₄ is generated as a late-stage (secondary) type from recent geologic to present times and is commonly preserved. Late-stage biogenic CH₄ is sustained by nutrients and microbes in meteoric/surface waters discharged into coal aquifers. Groundwater is pumped from wells in coal aquifers to desorb and produce CH₄ and dewater coal mines. The co-produced water with dissolved CH₄ is discharged into diverse surface aquatic systems. The emission factors (EFs) of co-produced water are 2.0522 × 10⁻⁹ Gg CH₄/gal of water in the PRB and 2.0694 × 10⁻³ Gg CH₄/well in the Black Warrior Basin, U.S. Accurate data on biogenic CH₄ emissions from coal sources is a major gap in the accounting of current global groundwater-driven CH₄ whose average flux is estimated to be 3.9 ± 6.2 mmol/m²/day or accounting for up to 70% of CH₄ emissions from surface aquatic systems. Biogenic CH₄ emissions from coal mining and coalbed gas extractions and related infrastructures are overlooked because the focus has been on coalmine methane (CMM) emissions. CMM data from ground-based measurements is highly variable and used by the Intergovernmental Panel on Climate Change three-tier system to estimate EFs for national inventories. However, 90% of CMM emissions are attributable to a small group of the most coal-consuming-and-producing countries but fails to capture other coal sources worldwide. This created gaps and “blind spots” in “unstructured” low-concentration, diffused biogenic CH₄ emission data. These key “blind spots” include sources from flooded, abandoned coal mines; coalbed methane (CBM) co-produced water with dissolved CH₄ and infrastructures/facilities; and groundwater drawdown from water withdrawals during coal mining and CBM extraction. Also, a critical “blind spot” is the mixing of biogenic CH₄ emissions from subsurface coals with biogenic CH₄ generated at the surface from wetlands, agriculture, and landfills/wastes, which grew 85% from 2008 to 2020. Limited understanding of the mixing of biogenic CH₄ from diverse sources and their contributions to global methane requires accurate attribution of overlapping isotopic signatures (δ¹³C_CH4 and δD). This paper addresses knowledge gaps in coalbed biogenic CH₄ emissions by a systematic review of the literature and specific study cases, which provided insights on key “blind spots” in their mitigation. Full article

The coal industry is the largest global emitter of carbon dioxide (CO₂). However, recent data suggests that coal mine methane (CH₄) emissions worldwide are higher than those of the oil and gas industry. Furthermore, the coal industry is less active in reducing methane emissions than the oil and gas sectors due to lower profitability. Although uncertainties remain in quantifying methane emissions from mines, the use of satellite observations is revolutionizing the process of monitoring and improving the accuracy of emission accounting. The methodology presented here allows us to determine background CH₄ concentrations and improve our ability to detect emission events using Sentinel-5P data. Knowing the background concentrations for the area of interest provides us the opportunity to track seasonal and annual variations and trends, as well as quickly detect periodic or accidental emissions from unregulated sources, etc. The methodology and systematic research applied in this paper for the period of May 2018 to the end of 2022 enables us to detect hundreds of large-scale emissions of CH₄, NO₂, and CO from the coal mines in the Kuznetsk Basin (the Kemerovo region), the largest coal mining area in Russia. We estimated that the amount of these emissions is significantly higher than the emissions reported by various authors for other coal mining regions such as Poland and Australia. We found that in cases of high methane quantity there is a positive correlation between NO₂ and CO emissions in time and location. The source of emissions in the study area is homogeneous, which allows it to be used as a benchmark for building models to estimate and track emissions in heterogeneous areas. Full article

Deep coalbed methane (CBM) is widely distributed in China and is mainly commercially exploited in the Qinshui basin. The in situ stress and moisture content are key factors affecting the permeability of CH₄-containing coal samples. Therefore, considering the coupled effects of compressing and infiltrating on the gas permeability of coal could be more accurate to reveal the CH₄ gas seepage characteristics in CBM reservoirs. In this study, coal samples sourced from Tunlan coalmine were employed to conduct the triaxial loading and gas seepage tests. Several findings were concluded: (1) In this triaxial test, the effect of confining stress on the permeability of gas-containing coal samples is greater than that of axial stress. (2) The permeability versus gas pressure curve of coal presents a ‘V’ shape evolution trend, in which the minimum gas permeability was obtained at a gas pressure of 1.1MPa. (3) The gas permeability of coal samples decreased exponentially with increasing moisture content. Specifically, as the moisture content increasing from 0.18% to 3.15%, the gas permeability decreased by about 70%. These results are expected to provide a foundation for the efficient exploitation of CBM in Qinshui basin. Full article