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This study was carried out to document the source and stable isotopic characteristics of coal bed gas and associated coal bed water samples of the Raniganj Basin, West Bengal, India. The Raniganj Basin is one of the largest coal bed gas-producing sites in India. However, the gas isotopic composition of this basin was not well investigated until now. The exploration has been focused on mature coals with a high content of assumed thermogenic methane. Interestingly, the present study has revealed that although the gas is thermogenic, there is a significant effect of microbial activities in gas generation. The gas explored from this Basin contains almost 98–99% methane (CH 4 ) in general with very little portions of other hydrocarbons and thus, this gas can be considered as “dry gas”. It is consistent also with late-stage microbial alteration of thermogenic gases. The δ 13 C and δD values of CH 4 range from −47.4 to −49.7‰ and −207 to −211‰ respectively across the three wells as well as from −48.8 to −50.1‰ and −209 to −211‰ respectively in the gas samples collected from gas gathering station. The Whiticar style cross plot of these two parameters reveals that the gas samples have mixed thermogenic and biogenic sources and the microbial gas was generated through the CO 2 reduction pathway rather than the acetate fermentation pathway. The difference in δD values of water and methane samples [δD (H 2 O-CH 4 )], that varies from 173 to 175‰, may also exhibit that the biogenic methane was produced through reduction of CO 2 . The stable hydrogen and oxygen isotopic signatures of formation water samples (δD and δ 18 O-H 2 O) stand with the mixed origin of the gas. The cross-plot of these two parameters reveals that the water samples lie almost along the Global Meteoric Water Line (GMWL), which may suggest the combined effect of methanogenesis due to mixing of coal seam formation water with modern meteoric water. In summary, the produced coal bed gas from the Raniganj Basin, although being largely thermogenic in origin, has been influenced by secondary microbial alteration. [ABSTRACT FROM AUTHOR]

Carbon and hydrogen isotope compositions of CH 4 generated via methanogenesis in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation waters grown on coal, acetate and H 2 + CO 2 were investigated. CH 4 production and molecular analysis confirmed the presence of active microbial communities that are able to convert coal into CH 4 using both acetoclastic and hydrogenotrophic pathways. The representative bacterial sequences were dominated by Bacteroidetes , Firmicutes and Deltaproteobacteria , while Methanosaeta and Methanosarcina were the most prevalent archaeal methanogens present in the cultures. CH 4 produced in this study's culturing experiments has δ 13 C values in the range of − 50 ‰ to − 20 ‰, with most values falling outside the current understanding of the carbon isotopic boundaries for biogenic CH 4 (− 110 ‰ to − 30 ‰). However, the corresponding apparent carbon isotopic α factor ( α c = 1.02 ± 0.006), and isotopic effect ( ε c = − 20.1 ‰ ± 15.3) showed that CH 4 in SSB cultures was predominantly produced by acetoclastic methanogenesis, which is consistent with the results of molecular DNA analysis. In addition, the calculated contribution of CO 2 reduction from the δ 13 C values of coal-treated cultures was overall < 50 %, further confirming the high contribution of the acetoclastic pathway to CH 4 production in the SSB cultures. The outcome of this experimental study also suggests that δ 2 H-CH 4 values may not provide a reliable basis for distinguishing methanogenic pathways, while apparent carbon isotopic fractionation factor ( α c ) and isotope effect ( ε c ) are considered more useful indicators of the methanogenic pathway. The high δ 13 C-CH 4 values (≥ 30 ‰) and the dominance of Methanosaeta over Methanosarcina indicate that methanogens within the SSB cultures were operating at low substrate concentrations. An unusually positive δ 13 C-CH 4 suggests a substrate depletion effect, which is thought to be related to a decrease in the relative abundance of key bacterial coal degraders with formation water inoculum storage time. Closer observation of δ 13 C-CH 4 values during the growth of cultures within a single experiment also showed a 13 C-enrichment trend over time. At log phase of growth, the CH 4 produced was 13 C-depleted when compared to the stationary phase that also indicates substrate depletion effects. Finally, the δ 13 C-CH 4 values encountered in this study (as high as − 20 ‰) highlight the possible positive extension of δ 13 C-CH 4 values of acetoclastic methanogenesis from those currently reported in the literature for natural and experimental samples (as high as − 30 ‰). [ABSTRACT FROM AUTHOR]

In numerous global coal–bearing basins, methane, possessing a biogenic stable isotope composition, is spatially and temporally associated with groundwater recharge. However, beyond groundwater inoculating the subsurface with microorganisms, the biological mechanisms that control the distribution of biogenic methane are poorly understood. In this study, we examined the interactions between bituminous coal and a) methanogenic microbial communities sourced from the goaf of a Bowen Basin underground coal mine and b) pure cultures of methanogens. When coal mine microbial consortium was amended with acetate and a low concentration of coal (1 g in 25 mL medium), methane production was stimulated compared to the addition of acetate alone, though the presence of coal did not affect the methane production from H 2 /CO 2 . To test whether methanogens benefited directly from the addition of coal, 1 g of either quartz sand or bituminous coal was added to a pure culture of Methanococcus maripaludis , a hydrogenotrophic methanogen isolated from the coal mine and grown on H 2 /CO 2 , and to a pure culture of Methanosarcina barkeri , an acetoclastic methanogen grown on acetate. In this experiment coal was not included as an energy source for microbial growth but to test interactions between coal and methanogens. The presence of coal in the medium did not affect methane production by Ms. barkeri but slightly inhibited methane production by M. maripaludis at the start of the growth phase. Scanning electron microscopy revealed that M. maripaludis cells were attached to both sand grains and coal particles, with preferential attachment to rough surfaces, such as cracks within broken coal pieces and clay-rich areas of coal. When the experiment with M. maripaludis and Ms. barkeri was repeated with a 1:1 volumetric ratio of bituminous coal to medium, which more accurately reflects the environmental conditions of a coal seam, methane production by M. maripaludis and Ms. barkeri was completely inhibited. In addition, M. maripaludis cell numbers declined after inoculation. This suggests that at a high coal: fluid ratio, methanogenesis is inhibited by some component of the coal, e.g. , bitumens in the coal or coal-sourced hydrocarbons dissolved into the medium. Based on these laboratory results, we propose that in coal seams, the dilution of inhibitory compounds may be one mechanism by which groundwater recharge promotes biogenic methane production. [ABSTRACT FROM AUTHOR]

Coal bed methane (CBM) has recently been produced from sub-bituminous to high volatile bituminous low rank coals (vitrinite reflectance 0.39 to 0.53%) from the Paleocene Cuervos Formation in the Cesar Sub-basin, Colombia. Understanding CBM gas origin is vital for designing exploration and production strategies, in order to target either shallow economic accumulations of microbial gas or deeper and thermally mature coal seams. In this context, this study aims to determine whether thermogenic gas, biogenic gas, or a mixture of both gas types have contributed to gas yield in the Cesar Sub-basin; it also discusses the relationship between gas origin and tectonics. For the first time, co-produced waters and gas samples from CBM multi-seam production wells and shallow aquifer water-wells were collected in the Boqueron compartment (Cesar Sub-basin) and were analysed via stable isotope composition and molecular geochemistry. Structural compartmentalisation in the Sub-basin as a result of interplate shortening during the Mid-Paleogene has resulted in slightly different coal ranks, saturation, and gas contents between compartments of the Paleocene Cuervos Formation. This event could have interrupted early thermogenesis and allowed the introduction of meteoric waters carrying bacteria consortia responsible for biogenesis. The produced waters from the CBM wells were HCO 3 > Na+ > Cl− type, and ranged in TDS (Total dissolved solids) from 2268 to 6602 mg/L (avg. 3887 mg/L). Recently revised genetic diagrams of δ13C-CH 4 versus δ2H-CH 4 and additional parameters, such as gas dryness ratio and water chemistry, corroborated biogenesis as the main gas origin. Carbon isotopic differences between carbon dioxide and methane (Δ13C H2O–CH4), as well as those of hydrogen isotopes in water and methane (Δ2H H2O–CH4), also indicated a typical microbial CO 2 reduction pathway. The positive carbon isotope composition of dissolved inorganic carbon (δ13C-DIC) not only showed a clear differentiation between waters from CBM wells and those from shallow aquifers, but also confirmed the occurrence of methanogenesis when paired with high alkalinity. In addition, the water quality analysis showed increasing sodium and bicarbonate concentrations with depth, which is typical of CBM production basins. Although biogenic gas was identified, tectonic settings do not seem to explain gas origin occurrence, since secondary biogenesis was expected in an uplifted basin such as Cesar Rancheria. Isotopic data was not decisive in differentiating primary versus secondary biogenesis, since the gas isotope compositions plot close to the boundary between the primary and secondary biogenic gas fields. Further studies on isotopic chemistry are required to refine this interpretation and confirm gas generation in the other two compartments. [ABSTRACT FROM AUTHOR]

Abstract: Late Permian coals and coal measures in the Bowen Basin, Australia, are extensively mineralised with carbonates as cleat fillings and veins. The calcites in coal samples exhibit large variations in rare-earth element (REE) patterns and Sm–Nd ratios with some superchondritic values. Samples enriched in heavy REE (HREE) relative to light REE (LREE) define an Sm–Nd isochron corresponding to an age of 235±15 Ma, which is consistent with the timing of final contractional phase of the Hunter–Bowen orogeny. The corresponding initial εNd is +1.2 combined with HREE-enriched patterns suggests significant fluid interaction with primitive source rocks, which are consistent with arc-related volcanogenic sediments in the basin. Calcites characterised by HREE depletion relative to LREE are not in Sm–Nd isotopic equilibrium with the former samples that is interpreted to be due to the effect of a later hydrothermal event during the Late Triassic–Early Jurassic. Vein calcites in mudrocks from the coal measures display more pronounced HREE depletion and significant positive EuCN anomalies, which is related to the later hydrothermal event. REE distributions, together with the basin burial history, suggest that physico-chemical environments of fluid-flow events during the two separate major tectonic regimes were significantly different. This study shows that a combined application of Sm–Nd dating and REE geochemical tracing of authigenic carbonate minerals is very useful to constrain the evolution of multiple fluid-flow events in a sedimentary basin with a complex history. [Copyright &y& Elsevier]

Temporal changes in microbial community structures during methanogenesis were investigated in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation water (SSB5) grown on three coals of different rank (Burung sub bituminous Rv 0.39%, Mangus sub bituminous Rv 0.5%, Mangus anthracite Rv 2.2%). Methane production accelerated from day 6, peaked around day 17 and then levelled off around day 20. The initial bacterial community from the SSB formation water was predominantly Acetobacterium , Acidaminobacter , Bacteroides and Pelobacter species, while the archaeal community consisted of Methanosaeta , Methanosarcina and Methanobacterium members. A general pattern was observed in all cultures with the three coals. Over time the bacterial members decreased in proportion whereas the archaeal component increased. The increase in the proportion of archaeal methanogens corresponded with an increase in methane production yield. Enrichment cultures produced similar communities when grown on coals from the same seam (Mangus sub bituminous and Mangus anthracite), rather than from different seams of similar type (Burung sub bituminous and Mangus sub bituminous). Methanosaeta was the dominant methanogen species in the sub bituminous Burung coal culture, but was a lesser proportion in cultures of both Mangus sub bituminous and anthracite coals where Methanosarcina species were a greater proportion. Interestingly, obligate hydrogenotrophic methanogens from the genera of Methanobacterium , which were present at low levels in culture enrichment of all coal substrates, increased in proportion only in the absence of coal in the no-coal control enrichment cultures. These results suggest that the low rank Burung sub bituminous coal favours methane production by the obligate acetoclastic Methanosaeta members while both Mangus coals also favour metabolically versatile Methanosarcina members, and the absence of coal favours hydrogenotrophic methanogens. Despite the similarity of communities grown on coals from the same seam, greater quantities of methane were generated from the lower rank coals when compared to higher rank coals. [ABSTRACT FROM AUTHOR]

Highlights: [•] Indonesia CSG resources are in part of biogenic origin. [•] Viable methanogen consortia are present in Indonesia CSG reservoirs. [•] The consortia are capable of producing methane from Indonesian and Australian coal. [•] The CO2 reduction pathway dominates the production of biogenic methane in the study area. [Copyright &y& Elsevier]

Apatite may be a common accessory mineral in coal seams, but interpretation of its origins can vary from syndepositional mineral detritus, early precipitation during diagenesis, and post coalification precipitation and replacement from hydrothermal or other fluids. It is hypothesised that paragenesis is reflected in the modes of occurrence in different stratigraphic units of the Late Permian in the Bowen Basin. From samples analysed in this study, apatite in the youngest unit, the Rangal Coal Measures, most commonly occurs as pore-apatites (i.e. apatites infilling preserved plant cell cavities of fusinite and semifusinite macerals and commonly associated with kaolinite) and less commonly as fracture-apatites (i.e. apatites infilling micro-fractures) and detrital-apatites intermixed with the organic coal layers (Detrital-B). In the tuffaceous Fort Cooper Coal Measures and equivalents, apatite occurs more commonly as detrital-apatites intermixed with the lithic layers (Detrital-A) (Detrital. Within the basal unit, the Moranbah Coal Measures and its equivalents, the mode is commonly encrusting-apatites (i.e. small apatite crystallites encrusting silicate minerals). Almost all apatites in the coal samples tested by electron microprobe microanalysis (EPMA), regardless of stratigraphic location and mode, are fluorapatite. Although there are some locality-driven enrichments, the minor and trace-element chemistry vary more so by mode of occurrence. For comparison, apatites from dykes intersecting the coal measures and from tuffs were also added to the study. These had lower fluorine (F) but measurable chlorine (Cl) contents and are enriched in light rare earth elements (LREE), similar to the Durango apatite that is of magmatic origins. Most of the detrital-A apatites are also enriched in LREE similar to the tuff-apatites, but with variable enrichment in the rare earth and yttrium elements. Detrital-B apatites have minimal Cl but also show the magmatic LREE trend. The pore- and fracture-apatites exhibited two trends. In the samples from tuffaceous coals (e.g., Fort Cooper Coal Measures), the pore- and fracture apatites tended to follow the magmatic LREE trend. In the Rangal Coal Measures, the pore- and fracture-apatites have elevated F contents, minimal Cl contents and depleted LREE contents (or Middle REE enrichment). Depletion of LREE could occur through leaching in an acidic environment, which is suggested by the abundance of kaolinite. Apatite precipitates under more neutral conditions although pore-apatites are commonly considered "early" and fracture-apatites "late" or post coalification. Their geochemical similarity suggests they have similar fluid origins and/or timing, with geothermal fluids moving through the porosity afforded by the structured inertinite group macerals and fractures. Verification of that geothermal source still requires further work and a technique that can analyse the isotopic composition—e.g., carbon (13C/12C), oxygen (18O/16O) and strontium (87Sr/86Sr)—of micron-sized crystals in situ. • Four primary modes of apatite occurrence were observed: pore and fracture infill, detrital (in organics and lithics), and encrusting • All apatites analysed by EPMA, regardless of mode, are fluorapatites. • The trace elements from EPMA REY patterns from LA-ICPMS differentiated by mode of occurrence • Results suggest the pore and fracture apatites precipitated or were geochemically over-printed by similar or same fluids. • Verification of source and timing requires the ability to date small (<10 μm) apatite crystals in situ. [ABSTRACT FROM AUTHOR]

The Herrin coal (Western Kentucky No. 11) "ragged edge" is composed of peculiar organic materials, including voids, which defy conventional maceral classification. These materials seem to have originated from natural pyrolysis caused by hot fluids migrating through low-rank coal. However, the observed petrographic patterns and the reflectance analysis were not enough to confirm this hypothesis. In order to obtain for the first time an approximate composition and temperature value of the fluids that may have thermally affected the Herrin coal, the origin of the "ragged edge" of the Herrin coal seam was studied via a combination of analytical techniques mainly focused on the carbonates including optical microscopy, cathodoluminescence, X-ray fluorescence, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, electron microprobe, and Raman microspectroscopy. The sum of indicators is collectively considered evidence that ascending hot fluids thermally affected the coal. These indicators include the ambient reflectance increase due to forced coalification; liptinite fading and "cryptic liptinite" formation at the bottom of the coal seam; the carbonate stable isotopes model temperature that indicates a range of 150 °C to 200 °C, and the Raman spectra proxy of the thermally affected particles indicating a temperature between 160 and 220 °C. • The origin of the "ragged edge" of the Herrin coal seam was studied via a combination of analytical techniques. • The sum of indicators is collectively considered evidence that ascending hot fluids thermally affected the coal. • The carbonate stable isotopes model temperature that indicates a range of 150 °C to 200 °C and the Raman spectra a temperature between 160 and 220 °C. [ABSTRACT FROM AUTHOR]

Coupling carbon and nitrogen isotopes and petrography of coals and related intra-seam carbonaceous mudstone partings from basins in northern China provides insight into regional palaeoenvironments and palaeoclimate during the late Carboniferous–early Permian. The carbon isotopic composition (δ 13C coal , VPDB) of coal samples from the Taiyuan and Shanxi formations of Qinshui and North China-Bohaiwan basins ranges from −25.3‰ to −22.7‰, with an average of −23.7‰. The average δ 13C coal value is −23.6‰ in the late Carboniferous, −23.4‰ in the early Permian and −23.5‰ in the mid–early Permian. By contrast, equivalent early Permian coals in the southern North China-Bohaiwan Basin to the east were found to be significantly more negative at −25.2‰, likely as a function of regional aridity changes. Related δ 15N in coal seams ranges from +2.3‰ to +4.7‰, with an average of +3.7‰. Within the thick, economically important #15coal seam of the Qinshui Basin, δ 15N coal is significantly more negative than δ 15N in mudstone partings (avg. +7.1‰), implying that the coals underwent a stronger degree of microbial degradation during peat formation. δ 15N of mudstone partings varies stratigraphically, with significantly more positive δ 15N (+8.1‰, +8.3‰) for the lower partings and lower δ 15N (+4.8‰) for the upper parting. This may reflect varying degrees of microbial activity, but could reflect higher thermal maturity in the upper part of the seam as indicated in the coal rank profile. δ 13C coal in this region was used to calculate the carbon isotopic composition of atmospheric CO 2 (δ 13C a). Calculated δ 13C a ranges from −6.0‰ to −3.4‰, with an average of −4.5‰, which is more positive than the δ 13C a of modern atmospheric CO 2 (−8.5‰, Graven et al., 2017). Two δ 13C a excursions are noted: a positive one (magnitude 3.7‰) in the late Carboniferous and a tentative negative excursion (magnitude 6.0‰) in the mid–early Permian. The positive shift coincided with a sea-level transgression in the Qinshui Basin. The rise in sea level may have led to the burial of more terrestrial plant debris that decreased photosynthesis and enriched atmospheric CO 2 in 13C. More data are needed to understand mid-early Permian variation in δ 13C, as this could reflect a regional aridity or humidity effect rather than a global signal. Unlabelled Image • C and N isotope analysis of major coal seams in the Taiyuan and Shanxi formations. • Results compared with the existing terrestrial δ 13C org curve for northern China. • δ 13N coal offers insights on short-term environmental changes and microbial activity. [ABSTRACT FROM AUTHOR]