Research on Depressurization Gas Extraction Techniques and Identification of Gas Sources in Goaf Based on Carbon and Hydrogen Isotope Tracing

Stable carbon and hydrogen isotope technology is used in determining gas sources in coal mines. Coal measures at the Shuangliu mine mainly contain nine coal seams (i.e. No. 2 to No. 10) and five limestone layers (namely, L1 to L5). The coal seams are interbedded with the limestone layers. A large amount of methane is adsorbed in the limestone layer, and the actual measured maximum gas pressure is 1.3 MPa, posing a serious gas emission safety risk in roadway excavation in the coal measures. In order to effectively manage the safety risk of gas emissions, it is necessary to determine gas sources and take necessary control measures. In this study, 50 gas samples were taken from the coal seams and 10 gas samples were collected from the limestone layers. These samples were measured for their composition and stable carbon and hydrogen isotopes. Stable carbon and hydrogen isotope tracer separation technique and multi-source linear calculation methods were used to analyze the measurement results. The study shows that 84% of gas in the L1, L2 and L3 limestone layers comes from the No. 8 coal seam and 11% from the No. 9 coal seam; gas in the L4 limestone layer is mainly from the No. 8 (44%), No. 7 (37%) and No. 6 coal seams (16%), and gas in L5 limestone layer mainly comes from the No. 6 (59%), No. 7 (23%) and No. 8 coal seams (13%). The research results can guide the design of gas drainage boreholes before roadway tunneling, so it has important guiding significance in the formulation of comprehensive gas control schemes.

Stable hydrogen and carbon isotopic ratios of coal-derived gases from the Turpan-Hami Basin, NW China

Microbial methane from in situ biodegradation of coal and shale: A review and reevaluation of hydrogen and carbon isotope signatures

Three wood isotopic reference materials for δ2H and δ13C measurements of plant methoxy groups

Stable hydrogen and carbon isotope ratios of methoxy groups (OCH3 ) of plant organic matter have many potential applications in biogeochemical, atmospheric and food research. So far, most of the analyses of plant methoxy groups by isotope ratio mass spectrometry have employed liquid iodomethane (CH3 I) as the reference material to normalise stable isotope measurements of these moieties to isotope-δ scales. However, comparisons of measurements of stable hydrogen and carbon isotopes of plant methoxy groups are still hindered by the lack of suitable reference materials. We have investigated two methyl sulfate salts (HUBG1 and HUBG2), which exclusively contain carbon and hydrogen from one methoxy group, for their suitability as methoxy reference materials. Firstly, the stable hydrogen and carbon isotope values of the bulk compounds were calibrated against international reference substances by high-temperature conversion- and elemental analyser isotope ratio mass spectrometry (HTC- and EA-IRMS). In a second step these values were compared with values obtained by measurements using gas chromatography/isotope ratio mass spectrometry (GC/IRMS) where prior to analysis the methoxy groups were converted into gaseous iodomethane. The 2 H- and 13 C isotopic abundances of HUBG1 measured by HTC- and EA-IRMS and expressed as δ-values on the usual international scales are -144.5 ± 1.2 mUr (n = 30) and -50.31 ± 0.16 mUr (n = 14), respectively. For HUBG2 we obtained -102.0 ± 1.3 mUr (n = 32) and +1.60 ± 0.12 mUr (n = 16). Furthermore, the values obtained by GC/IRMS were in good agreement with the HTC- and EA-IRMS values. We suggest that both methyl sulfates are suitable reference materials for normalisation of isotope measurements of carbon of plant methoxy groups to isotope-δ scales and for inter-laboratory calibration. For stable hydrogen isotope measurements, we suggest that in addition to HUBG1 and HUBG2 additional reference materials are required to cover the full range of plant methoxy groups reported so far.

Equilibrium headspace analysis of toluene for δ2H isotopic composition by continuous flow compound specific isotope mass spectrometry was determined to have an accuracy and reproducibility of ±5‰. Using this analytical approach, the hydrogen isotope fractionation produced by anaerobic biodegradation of toluene was evaluated in laboratory experiments using a mixed methanogenic consortium. A large, reproducible 2H-enrichment in the residual toluene of greater than 60‰ was observed at greater than 95% degradation, reflecting the preferential biodegradation of molecules containing the light (1H) isotope. Recent studies evaluating the magnitude of carbon isotope fractionation produced during biodegradation of aromatic hydrocarbons have documented heavy isotope (13C) enrichment in the residual contaminant approximately an order of magnitude smaller than those reported here for 2H. The very large isotopic enrichment in 2H suggests that under anaerobic conditions compound specific hydrogen isotope analysis may provide a more reliable means of validating intrinsic bioremediation of aromatic hydrocarbons than stable carbon isotope analysis. Combined application of stable carbon and hydrogen isotope analysis in an anaerobic groundwater has the potential to provide two important diagnostic tools. Relatively insensitive to biodegradation by mixed consortia, stable carbon isotope values may provide information about different sources of contaminant, while hydrogen isotope values provide an assessment of the degree of attenuation due to biodegradation.

Stable carbon and hydrogen isotopic fractionation of individual n-alkanes accompanying biodegradation: evidence from a group of progressively biodegraded oils

Geochemistry and origin of continental natural gas in the western Sichuan basin, China

Stable carbon and hydrogen isotope fractionation of volatile organic compounds caused by vapor-liquid equilibrium

The non-linear dynamics of stable carbon and hydrogen isotope signatures during methane oxidation by the methanotrophic bacteria Methylosinus sporium strain 5 (NCIMB 11126) and Methylocaldum gracile strain 14 L (NCIMB 11912) under copper-rich (8.9 µM Cu2+), copper-limited (0.3 µM Cu2+) or copper-regular (1.1 µM Cu2+) conditions has been described mathematically. The model was calibrated by experimental data of methane quantities and carbon and hydrogen isotope signatures of methane measured previously in laboratory microcosms reported by Feisthauer et al. [1] M. gracile initially oxidizes methane by a particulate methane monooxygenase and assimilates formaldehyde via the ribulose monophosphate pathway, whereas M. sporium expresses a soluble methane monooxygenase under copper-limited conditions and uses the serine pathway for carbon assimilation. The model shows that during methane solubilization dominant carbon and hydrogen isotope fractionation occurs. An increase of biomass due to growth of methanotrophs causes an increase of particulate or soluble monooxygenase that, in turn, decreases soluble methane concentration intensifying methane solubilization. The specific maximum rate of methane oxidation υm was proved to be equal to 4.0 and 1.3 mM mM−1 h−1 for M. sporium under copper-rich and copper-limited conditions, respectively, and 0.5 mM mM−1 h−1 for M. gracile. The model shows that methane oxidation cannot be described by traditional first-order kinetics. The kinetic isotope fractionation ceases when methane concentrations decrease close to the threshold value. Applicability of the non-linear model was confirmed by dynamics of carbon isotope signature for carbon dioxide that was depleted and later enriched in 13C. Contrasting to the common Rayleigh linear graph, the dynamic curves allow identifying inappropriate isotope data due to inaccurate substrate concentration analyses. The non-linear model pretty adequately described experimental data presented in the two-dimensional plot of hydrogen versus carbon stable isotope signatures.

Summary1. Stable carbon isotope studies have been an essential component of research regarding the contribution of methane (CH4)‐derived carbon to freshwater food webs and results have suggested that benthic macroinvertebrates in billabongs, streams and lakes may be partially, and in some instances, significantly ‘fuelled’ by methanotrophic biomass. However, the singular use of carbon isotopes can lead to ambiguous interpretations concerning the origin of carbon, especially in systems where phototrophs are likely to be using carbon respired sources and hence show more 13C‐depleted values.2. These uncertainties can be further resolved by the inclusion of additional isotopic data. Stable hydrogen isotopes are being increasingly used in food web studies with a marked advantage that sources may be isotopically distinct by one or two orders of magnitude greater than stable carbon or nitrogen, the isotopes most commonly used to delineate trophic interactions. By using hydrogen as a second biogeochemical tracer we provide further supportive evidence for the assimilation of methanotrophic microbial biomass by chironomid larvae.3. Moreover, the hydrogen and carbon isotope values we found in chironomid tissues appear to reflect the original substrate used during methanogenesis; either acetate fermentation or carbonate reduction. Use of the former tends to result in relatively heavy carbon and light hydrogen isotope values due to kinetic isotope effects, whereas use of the latter results in relatively lighter carbon and heavier hydrogen isotope values.4. We provide preliminary evidence to suggest that hydrogen and carbon isotope values in macroinvertebrates may be used to distinguish between CH4 formation pathways and help to explain inter‐depth and inter‐specific differences between co‐existing chironomid species found in the same lake.

Gas disaster in goaf (by goaf, we mean the area behind the working face after coal mining) of coal mine has always been the key research object of mine safety. A large amount of gas will flood into the goaf during coal mining work, and accurate identification of its gas source is of great significance for clarifying the focus of gas prevention and optimizing mine gas control. In this paper, the 28 118 working face of the Tunlan coal mine is taken as the research object, and the distribution characteristics of carbon and hydrogen isotopes in desorption gas of each coal seam are revealed by field sampling and experimental determination. The results show that the main contribution form of gas source is the coal seam and the lower adjacent layer. The COMSOL numerical simulation software was used to study the distribution law of gas concentration in goaf under different extraction parameters of large-diameter boreholes. The optimal borehole spacing of large-diameter borehole technology was determined to be 20 m, the extraction negative pressure was 10 kPa, and the borehole diameter was 550 mm. On this basis, the comprehensive prevention and control technology of gas in goaf with large-diameter borehole and directional long borehole is proposed. Compared with buried pipe extraction, the proportion of gas concentration in goaf and lower adjacent layer is reduced by 41.5% and 40.2%, respectively, and the gas concentration in upper corner is reduced by 46.77%. The comprehensive prevention and control technology inhibits the emission of main gas sources in goaf and effectively reduces the gas concentration in upper corner, which fundamentally prevents the gas accumulation and overrun in working face.

<p>Hydrogen isotope ratios of leaf waxes are used to reconstruct past hydroclimate because they are correlated to meteoric/growth water hydrogen isotopes. The interpretation of these signatures from ancient sedimentary archives relies on a thorough understanding of the drivers of modern isotope variability. Studies in the high latitudes, regions that are particularly valuable in light of their vulnerability to rapid climate change, are scarce. We studied modern vegetation (22 plants) in two areas in the Northwestern Territories (Canada): Herschel Island and Peel Plateau, to understand the stable isotope variability found in plants of Arctic regions. Bulk biomass stable carbon isotope and radiocarbon composition have been measured as well as fatty acids (wax lipids coating the plant leaves) stable carbon and hydrogen isotopes. Furthermore, lake surface sediments and river bank sediments from the Mackenzie River Delta (surrounded by the same plants) have been similarly studied. Bulk carbon isotope composition of the plants show strong difference between plant type, i.e. herbs, shrubs, lichen and moss, as shown in previous studies. Whereas the commonly used average chain length (ACL) is not useful to differentiate the plants. In term of compound-specific isotope ratios, herbs are generally <sup>2</sup>H-enriched in comparison to shrubs as shown in other regions of the world, and the C<sub>28</sub> fatty acid present the most differences amongst plant type (from ~ -207‰ for herbs to ~ – 240‰ for shrubs). No major difference between the areas is noted indicating that the ~ 250 km (Herschel Island 69.5⁰N and Peel Plateau 67.3⁰N) have no impact on the hydrogen isotope composition of the fatty acids. As such we decided to compare the plant with the lake surface sediments (from the Mackenzie Delta, located between Herschel Island and the Peel Plateau). Short-chain fatty acids, sourced from organisms growing in the lake, from isolated lakes shows <sup>2</sup>H-enriched isotopic values indicating the effect of increased evaporation in the lake during summer plant growth. Whereas long-chain fatty acids do not show any differences and are enriched compared to the shorter-chain (~ -260‰ for long-chain vs ~ -260‰ to - 280‰ for short-chain). In conclusion, differences between plant fatty acids seems to be best represented by the C<sub>28</sub> fatty acid, indicating the potential to reconstruct past vegetation and hydrological conditions in the region using lacustrine archives.</p>

Geochemical characteristics and source of natural gases from Southwest Depression of the Tarim Basin, NW China

Peatland degradation indicated by stable isotope depth profiles and soil carbon loss