Occurrence Of Methane Research Articles

Methane occurrence is associated with sodium‐rich valley waters in domestic wells overlying the Marcellus shale in New York State

AbstractPrior work suggests spatial parameters (e.g., landscape position, distance to nearest gas well) can be used to estimate the amount of dissolved methane in domestic drinking water wells overlying the deep Marcellus Shale. New York (NY) provides an opportunity to investigate methane occurrence prior to expansion of high‐volume hydraulic fracturing because unconventional gas production is currently banned in the state. We sampled domestic groundwater wells for methane in 2013 (n = 137) across five counties of NY bordering Pennsylvania, and then resampled a subset of those wells in 2014 for methane concentrations and δ13C‐CH4 and δD‐CH4. The majority of waters from wells sampled (77%) had low concentrations of methane (<0.1 mg/L), and only 5% (n = 7) had actionable levels of methane (>10 mg/L). Dissolved methane concentrations did not change as a function of proximity to existing vertical gas wells, nor other parameters indicating subsurface planes of weakness (i.e., faults or lineaments). Methane levels were significantly higher in wells closer to hydrography flow lines, and most strongly correlated to Na‐HCO3 water type. The distribution of methane between Ca‐HCO3 (n = 76) and Na‐HCO3 (n = 23) water types significantly differed (p < 0.01), with median methane concentrations of 0.002 and 0.78 mg/L, respectively. Combined classification of sampled waters based on the dominant water cation, well topographic position, and geologic unit of well completion effectively identified wells with a greater than 50% probability of having methane concentrations exceeding 1 mg/L. Such classification schemes may be useful as a screening tool to assess natural versus gas production‐related sources of methane in domestic wells.

Occurrence and origin of methane in groundwater in Alberta (Canada): Gas geochemical and isotopic approaches

To assess potential future impacts on shallow aquifers by leakage of natural gas from unconventional energy resource development it is essential to establish a reliable baseline. Occurrence of methane in shallow groundwater in Alberta between 2006 and 2014 was assessed and was ubiquitous in 186 sampled monitoring wells. Free and dissolved gas sampling and measurement approaches yielded comparable results with low methane concentrations in shallow groundwater, but in 28 samples from 21 wells methane exceeded 10mg/L in dissolved gas and 300,000ppmv in free gas. Methane concentrations in free and dissolved gas samples were found to increase with well depth and were especially elevated in groundwater obtained from aquifers containing coal seams and shale units. Carbon isotope ratios of methane averaged −69.7±11.1‰ (n=63) in free gas and −65.6±8.9‰ (n=26) in dissolved gas. δ13C values were not found to vary with well depth or lithology indicating that methane in Alberta groundwater was derived from a similar source. The low δ13C values in concert with average δ2HCH4 values of −289±44‰ (n=45) suggest that most methane was of biogenic origin predominantly generated via CO2 reduction. This interpretation is confirmed by dryness parameters typically >500 due to only small amounts of ethane and a lack of propane in most samples. Comparison with mud gas profile carbon isotope data revealed that methane in the investigated shallow groundwater in Alberta is isotopically similar to hydrocarbon gases found in 100–250meter depths in the WCSB and is currently not sourced from thermogenic hydrocarbon occurrences in deeper portions of the basin. The chemical and isotopic data for methane gas samples obtained from Alberta groundwater provide an excellent baseline against which potential future impact of deeper stray gases on shallow aquifers can be assessed.

Reply to Ryan et al. comment on “Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario”

Reply to Ryan et al. comment on “Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario”

Dissolved gas ‘concentrations’ or ‘concentration estimates’ – A comment on “Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario, Canada” by Jennifer C. McIntosh, Stephen E. Grasby, Stewart M. Hamilton, and Stephen G. Osborn

Dissolved gas ‘concentrations’ or ‘concentration estimates’ – A comment on “Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario, Canada” by Jennifer C. McIntosh, Stephen E. Grasby, Stewart M. Hamilton, and Stephen G. Osborn

Evidence for methane in Martian meteorites.

The putative occurrence of methane in the Martian atmosphere has had a major influence on the exploration of Mars, especially by the implication of active biology. The occurrence has not been borne out by measurements of atmosphere by the MSL rover Curiosity but, as on Earth, methane on Mars is most likely in the subsurface of the crust. Serpentinization of olivine-bearing rocks, to yield hydrogen that may further react with carbon-bearing species, has been widely invoked as a source of methane on Mars, but this possibility has not hitherto been tested. Here we show that some Martian meteorites, representing basic igneous rocks, liberate a methane-rich volatile component on crushing. The occurrence of methane in Martian rock samples adds strong weight to models whereby any life on Mars is/was likely to be resident in a subsurface habitat, where methane could be a source of energy and carbon for microbial activity.

Occurrence of abiotic methane in the eastern United Arab Emirates ophiolite aquifer

Methane with carbon and hydrogen isotope composition diagnostic of abiotic gas related to serpentinization of peridotites has been detected for the first time in the ophiolitic aquifer in the United Arab Emirates (UAE), along the Wadi Ham fault. This methane is isotopically similar to that previously reported in serpentinization-related springs in Oman, in the same Semail ophiolite nappe. Abiotic gas may be widespread in these ophiolitic rocks. Conventional thermogenic gas fields in the sedimentary basin overthrusted by the ophiolite could be “contaminated” to some extent by this abiotic gas. This may confound the accurate characterization of these thermogenic gases (origin, type of source rock type and maturity) and thus the associated petroleum system model.

From shale oil to biogenic shale gas: retracing organic-inorganic interactions in the Alum Shale (Furongian-Lower Ordovician) in southern Sweden

Methane-rich gas occurs in the total organic carbon–rich Alum Shale (Furongian to Lower Ordovician) in southern Sweden. The lower part of the thermally immature Alum Shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the Carboniferous to the Permian. Organic geochemical data indicate that the migrated bitumen is slightly degraded. In the upper Alum Shale, where methane is the main hydrocarbon in thermovaporization experiments, centimeter-size calcite crystals occur that contain fluid inclusions filled with oil, gas, or water. The Alum Shale is thus considered a mixed shale oil–biogenic shale gas play. The presented working hypothesis to explain the biogenic methane occurrence considers that water-soluble bitumen components of the Alum Shale were converted to methane. A hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation. The modeling results reproduce the present-day gas and mineralogical composition. The conceptual model applied to explain the methane occurrence in the Alum Shale in southern Sweden resembles the formation of biogenic methane in the Antrim Shale (Michigan Basin, United States). In both models, melting water after the Pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids (TDS) in basinal brines. Such pore waters with low TDS contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane. Today, biogenic methane production rates, with shale as the substrate using different hydrocarbon-degrading microbial enrichment cultures in incubation experiments, range from 10 to 620 nmol per gram and per day.

Occurrence, characteristics and formation mechanisms of methane generated micro-pockmarks in Dunmanus Bay, Ireland

A small gas pockmark field in Dunmanus Bay, SW Ireland was surveyed and ground-truthed to assess its activity, geomorphology, explore its formation mechanisms and to investigate its potential influence on the benthic community. The field consisted of 121 circular, shallow units ranging from 5 to 17m in diameter and not exceeding 1m in relief. Sub-bottom profiles revealed broad acoustic signatures typical of shallow gas accumulation in the subsurface in addition to vertically elongated signals of ascending bubbles captured in the echo sounder data. The pockmarks show strong correlation with the depth of sub-surface gas fronts. However methane concentrations in the water column and directly above the features were close to typical marine, background values and did not exceed 15nM. This suggests a very mild, periodic venting scenario. Sediment core samples revealed permeable sandy layers with slightly elevated methane concentrations indicative of stratified, diffusive flow. Pore-water sulphate and chloride data show no sign of pore water freshening and thus suggest that methane gas is the sole fluid responsible for formation of these pockmarks. Benthic infauna distributions showed reduced diversity in pockmarked regions, primarily influenced by the sediment composition. Few species utilising chemosymbiotic associations were identified, and there was little indication of a community influenced by methane venting in Dunmanus Bay.

Paleozoic-aged microbial methane in an Ordovician shale and carbonate aquiclude of the Michigan Basin, southwestern Ontario

Interest in the origin and migrational history of methane in low permeability shales reaches beyond that of resource potential to include the evaluation of such formations as geological barriers for the purposes of isolating surface environments from the impacts of deep exploitation and the deep disposal of waste. Here, we present detailed isotope and geochemical profiles of porewaters and methane from an Ordovician shale and carbonate aquiclude on the eastern flank of the Michigan Basin, where a deep geological repository for low and intermediate level nuclear waste is proposed. The solute concentrations and stable isotopes of water (δ18O and δD) indicate that this aquiclude hosts saline brine (39% TDS), originating as evaporated seawater. Methane concentrations are < 4mmol/g in the shale section, with negative δ13C and δD signatures that are consistent with archaeal methanogenesis and are accompanied by a well defined positive excursion in δ13C of CO2. Below the aquiclude, porewaters contain lower concentrations of methane with a thermocatalytic signature, consistent with regional methane elsewhere in the Michigan Basin. No evidence for archaea was identified by microcosm experiments or through PCR rRNA analysis, suggesting that the microbial methane present in these sediments is not the result of recent microbial activity. Based on these results and considering that archaeal activity has not been observed in such hypersaline brines with low water activities (< 0.75), it is concluded that the methane likely formed prior to the infiltration of hypersaline Silurian seawater. The methane has since remained in place, making it, perhaps, the oldest documented occurrence of biogenic methane. This is consistent with helium isotope data, which also suggests authigenic production and accumulation in this aquiclude since the Paleozoic.

Proposed sources of methane along the Dead Sea Transform

The concentrations and isotopic compositions of methane, higher alkanes, dissolved inorganic carbon (DIC) and CO2 were studied in fresh groundwater, brines and springs along the Dead Sea Transform (DST), from the Hula Valley in the north to the Dead Sea (DS) basin in the south. Although the occurrence of methane along the DST was documented before, this is the first time that comprehensive research was conducted on the methane provenance and the post-genetic reactions involved. The methane stable carbon isotopic composition (δ13CCH4) shows a distinct geographic pattern. In the northern part of the DST studied, in the Hula valley and Lake Kinneret, where recent marshy and lacustrine environments exist, the methane source seems to be related to intense shallow depth methanogenesis. This microbial methane shows low 13C values in the range of δ13CCH4 between −58‰ and −72‰ and high alkane ratios (C1/C2+C3) between 100 and 1000. The isotope fractionation α CO2–CH4 of 1.065‰ suggests the domination of hydrogenotrophic methanogenesis rather than acetoclastic methanogenesis. In the waters of Hammat Gader and Tiberias hot spring, whose source is the Cretaceous aquifer, δ13CCH4 has high values of −28‰ and −56‰, respectively, with low alkane ratios of ~40 in both sites. The high δ2HCH4 values of Hammat Gader, in addition to the isotopic composition of the DIC and the difference between CO2 and CH4, reject the possibility of local microbially produced methane and suggest a sub-surface thermogenic source of an initial stage of thermal degradation of bituminous chalk of Senonian age. Similarly, methane in groundwater from the DS basin is also interpreted to be of thermogenic origin. In accordance with the local geology context in the DS basin of buried asphalt, and due to the low geothermal gradient in the region, it is speculated that methane is produced from slight heating of the asphalts. In general, it seems that there is a thermogenic methane contribution along the entire DST, which is locally masked by high microbial activity in shallow organic-rich environments, such as Lake Kinneret and the Hula basin.

The effect of sedimentary redbeds on coalbed methane occurrence in the Xutuan and Zhaoji Coal Mines, Huaibei Coalfield, China

The lithologies and permeabilities of caprocks have significant effects on coalbed methane (CBM) preservation. To study the controlling effects of redbeds deposits on CBM occurrence in the Xutuan and Zhaoji Coal Mines of the Huaibei Coalfield in China, the variations in mineralogical composition, microstructure, pore structure, permeability and diffusion among the redbeds caprock samples, Neogene clay rock and ordinary coal measure strata (sandstone, mudstone and siltstone) have been investigated. The results indicate that redbeds are porous rocks with weaker sealing capabilities than coal strata caprocks, allowing CBM to escape from the coal seam. The formation of the lithological properties of the redbeds is closely related to their mineralogical composition and diagenesis. Redbeds are mainly composed of illite (57–64%), calcite (25–33%), quartz (6–12%), muscovite (3–8%) and pyrite (<1%). The high content of fragile minerals and the later formation age of this rock lead to unapparent compaction and cementation, resulting in a loose structure, low degrees of consolidation and pore structure development. Mercury intrusion experiments show that the porosity of redbeds is 3.8–5.2 times higher than that of sandstone and 8–13 times higher than those of mudstone and siltstone; the pore size distribution of this rock is primarily centralized in transition pores (57.82%–74.72%) and mesopores (9.08%–22.51%), which favors gas diffusion. The permeability and diffusion coefficient tests demonstrate that the sealing capability of redbeds is much weaker than that of coal strata caprocks. Although the origins of the CBM gas pool in the Huaibei Coalfield remain controversial, the findings of this study along with the mining practices indicate that the deposition of thick redbeds can be treated as indicative of low gas contents in the coal mines, which has a significant meaning for the engineering of coal mine gas control.

Geological conditions of coal bed methane occurrence in Handan - Fengfeng Mining area

The coal bed methane resources distribution of Handan - Fengfeng Mining area has the features of "richness in the midland and north while poorness in the south, and richness in the east while poorness in the west. Through the analysis of the geological factors causing the above phenomena, we get that: the coal metamorphism and hydrogeological condition are the major controlling factors, the former controls the north and south difference of coal bed methane resources distribution from the two aspects covering gas-generated quantity and adsorption capacity, while the latter controls the east and west difference of coal bed methane resources distribution; syncline and good cap rock conditions are necessary conditions for coal bed methane enrichment, but not the reason for causing the difference of coal bed methane resources distribution.

Differences in coal bed methane occurrence for different regions of igneous erosion in the Haizi coal mine, Huaibei coalfield, China

Igneous erosion would change the coal bed methane (CBM) occurrence in coal. Based on the different occurrences of magma rock at the II101 and II102 mining areas in the Haizi coal mine of the Huaibei coalfield in China, coal bed methane occurrence in different regions of igneous erosion was studied by collecting and categorizing CBM parameters during the establishment and mining of the II101 and II102 mining areas. The CBM pressure gradient, CBM content, and CBM emission during mining the workface for the II102 mining area with more stable and thicker magmatic rock were larger than those of the II101 mining area. The CBM pressure gradients for the II101 and II102 mining areas were 0.02397 MPa/m and 0.03736 MPa/m, respectively. With increasing depth, the CBM contents of both the II101 mining area and the II102 mining area increased and the CBM content of the II102 mining area was greater than that of the II101 mining area. The absolute CBM emission (AE) gradient and the relative CBM emission (RE) gradients for the II101 mining area were 0.012 m3/min/m and 0.023 m3/t/m, respectively. Additionally, the AE gradient and the RE gradient for the II102 mining area were 0.031 m3/min/m and 0.055 m3/t/m, respectively. Partition management for different regions of igneous erosion should be used.

Fluid flow and methane occurrences in the Disko Bugt area offshore West Greenland: indications for gas hydrates?

The present study is the first to directly address the issue of gas hydrates offshore West Greenland, where numerous occurrences of shallow hydrocarbons have been documented in the vicinity of Disko Bugt (Bay). Furthermore, decomposing gas hydrate has been implied to explain seabed features in this climate-sensitive area. The study is based on archive data and new (2011, 2012) shallow seismic and sediment core data. Archive seismic records crossing an elongated depression (20×35 km large, 575 m deep) on the inner shelf west of Disko Bugt (Bay) show a bottom simulating reflector (BSR) within faulted Mesozoic strata, consistent with the occurrence of gas hydrates. Moreover, the more recently acquired shallow seismic data reveal gas/fluid-related features in the overlying sediments, and geochemical data point to methane migration from a deeper-lying petroleum system. By contrast, hydrocarbon signatures within faulted Mesozoic strata below the strait known as the Vaigat can be inferred on archive seismics, but no BSR was visible. New seismic data provide evidence of various gas/fluid-releasing features in the overlying sediments. Flares were detected by the echo-sounder in July 2012, and cores contained ikaite and showed gas-releasing cracks and bubbles, all pointing to ongoing methane seepage in the strait. Observed seabed mounds also sustain gas seepages. For areas where crystalline bedrock is covered only by Pleistocene–Holocene deposits, methane was found only in the Egedesminde Dyb (Trough). There was a strong increase in methane concentration with depth, but no free gas. This is likely due to the formation of gas hydrate and the limited thickness of the sediment infill. Seabed depressions off Ilulissat Isfjord (Icefjord) previously inferred to express ongoing gas release from decomposing gas hydrate show no evidence of gas seepage, and are more likely a result of neo-tectonism.

Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario, Canada

Natural gas reservoirs in organic-rich shales in the Appalachian and Michigan basins in the United States are currently being produced via hydraulic fracturing. Stratigraphically-equivalent shales occur in the Canadian portion of the basins in southwestern Ontario with anecdotal evidence of gas shows, yet there has been no commercial shale gas production to date. To provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production, such as leakage of natural gas, saline water, and/or hydraulic fracturing fluids, and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general, this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern Ontario. An extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow, domestic wells in bedrock and overburden aquifers throughout southwestern Ontario was utilized. In addition, select wells (n=36) were resampled for detailed dissolved gas composition, δ13C of CH4, C2, C3, and CO2, and δD of CH4. Dissolved gases in groundwater from bedrock and overburden wells were composed primarily of CH4 (29.7–98.6mol% of total gas volume), N2 (0.8–66.2mol%), Ar+O2 (0.2–3.4mol%), and CO2 (0–1.2mol%). Ethane was detected, but only in low concentrations (<0.041mol%), and no other higher chain hydrocarbons were present, except for one well in overburden overlying the Dundee Formation, which contained 0.81mol% ethane and 0.21mol% propane. The highest methane concentrations (30 to >100 in situ % saturation) were found in bedrock wells completed in the Upper Devonian Kettle Point Formation, Middle Devonian Hamilton Group and Dundee Formation, and in surficial aquifers overlying these organic-rich shale-bearing formations, indicating that bedrock geology is the primary control on methane occurrences. A few (n=40) samples showed Na–Cl–Br evidence of brine mixing with dilute groundwater, however only one of these samples contained high (>60 in situ % saturation) CH4. The relatively low δ13C values of CH4 (−89.9‰ to −57.3‰), covariance of δD values of CH4 and H2O, positive correlation between δ13C values of CH4 and CO2, and lack of higher chain hydrocarbons (C3+) in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin. The presence or absence of alternative electron acceptors (e.g. dissolved oxygen, Fe, NO3, SO4), in addition to organic substrates, controls the occurrence of microbial CH4 in shallow aquifers. Microbial methane has likely been accumulating in the study area, since at least the Late Pleistocene to the present, as indicated by the co-variance and range of δD values of CH4 (−314‰ to −263‰) and associated groundwater (−19‰ to −6‰ δD-H2O).

Abiogenic Fischer–Tropsch synthesis of methane at the Baogutu reduced porphyry copper deposit, western Junggar, NW-China

Methane is widely developed in hydrothermal fluids from reduced porphyry copper deposits, but its origin remains enigmatic. The occurrence of methane in fluid inclusions at the Late Carboniferous Baogutu reduced porphyry copper deposit in western Junggar, Xinjiang, NW-China, presents an excellent opportunity to address this problem. A systematic study including fluid inclusion Laser-Raman and CO2–CH4 carbon isotope analyses, igneous and hydrothermal mineral H–O isotope analyses, and in situ major, trace element and Sr isotopic analyses of hydrothermal epidote was conducted to constrain the origin of CH4 and CH4-rich fluids. The δ2H and δ18O of water in equilibrium with igneous biotite ranges from −65.0‰ to −66.0‰ and +7.2‰ to +7.4‰, respectively, indicating notable degassing of probably supercritical fluids in the magma chamber. The wide range of δ2H (−58.0‰ to −107.0‰, n=23) for water within quartz suggests the existence of significant hydrothermal fluid boiling. Water–rock interaction is the most likely mechanism leading to the wide range of δ18O values for water in vein quartz with water/rock ratios (wt.% in O) of 0.15 to 0.75 and 0.13 to 0.46 for a closed and open system, respectively. Detailed Laser-Raman analyses indicate CO2 in apatite included in granodiorite porphyry phenocrystic biotite that records the carbon species of the early stage magmatic stage, whereas later hydrothermal fluids containing CH4 with trace or without CO2 are found in inclusions of vein quartz. We propose that CH4 is probably transformed from CO2 by Fischer–Tropsch type reactions at 500°C, assumed from CO2–CH4 C isotope equilibrium. The (87Sr/86Sr)i of hydrothermal epidote yields values of 0.70369–0.70404, consistent with that reported for the whole rocks. The δ13CCH4 (−28.6‰ to −22.6‰) and δ2HCH4 (−108.0‰ to −59.5‰) are characteristic of abiogenic methane. The measured δ13CCO2 shows a slightly depleted 13C (−13.5‰ to −7.2‰) relative to upper mantle (−6‰), probably due to the combined effects of minor (less than 0.5%) sedimentary organic matter contamination in the mantle and carbon isotope fractionation occurring during late degassing.Combining the results indicates that CO2 likely originated from the upper mantle with trace addition of sedimentary organic matter. During the uplift or emplacement of the granitoids, significant degassing caused the depletion of 13C and 2H. As the granitoids cooled, notable hydrothermal fluid boiling and water–rock interaction produced the depletion of 2H and 18O, respectively, and the magmatic CO2 was reduced to CH4 by Fischer–Tropsch type reactions that probably occurred during Ca–Na and potassic hydrothermal alteration.

Strategies to cope with methanogens in hydrogen producing UASB reactors: Community dynamics

Methane occurrence is a common concern in hydrogen producing reactors. This study presents the analysis of the microbial community structure during the application of operational strategies to decrease methane production, in three different up-flow anaerobic sludge blanket hydrogen-producing reactors. Cloning and denaturing gradient gel electrophoresis approach were used to establish the presence of homoacetogens, methanogens and hydrogen producers. The results showed that homoacetogenic organisms related to Blautia hydrogenotrophica and Oscillibacter valericigenes, and the hydrogen producer Enterobacter aerogenes where favored during pH decreasing strategies (5.6 to 4.5). The increment of the organic loading rate from 20 to 30 g chemical oxygen demand/L-d, selected hydrogen producers similar to Clostridium tyrobutyricum, Citrobacter freundii and E. aerogenes; further increments caused inhibition of hydrogen production due to the high undissociated acids concentration. Methane production was inhibited completely only when the biomass of the reactor was heat treated for a second time, this strategy selected hydrogen producers capable to sporulate, but homoacetogens were also favored. In all reactors the methanogenic activity was attributed to hydrogenotrophs related to the genera Methanobrevibacter and Methanobacterium.

CBM a Pathfinder of Petroleum System?

The present study aims to understand if there is any relation of commercial methane in CBM producers with oil producing kerogen. This is necessary because methane in coal, by default, is assigned to be sourced by bacterial/thermal actions on biomass during coalification process but critical analysis suggests it cannot be commercial because coal bears a ratio of molar concentrations of Hydrogen to Carbon (H/C) around 0.8 whereas methane require H/C = 4.0. A simple calculation reveals 1Tcf of methane generation may come from around 25 trillion tonnes of coal, suggesting commercial methane cannot be sourced only from coal. Generation of methane can be biogenic or thermogenic, either from coal or related organic biomass or from oil generating kerogen. Technically, we can distinguish biogenic methane from thermogenic but we cannot distinguish same methane either from coal or from oil generating kerogen unless it is evident that one is distinctly biogenic and the other is thermogenic. Further, a review of successful major CBM projects also reveals that most of them are geologically associated with some producing petroliferous basin. This suggests that a close genetic relationship between the occurrence of coal bed methane and petroliferous basin probably exists whereby adsorbed methane in coal bed is possibly sourced from the same oil generating kerogen in the basin. Therefore, discovery of commercial coal bed methane may suggest possible existence of mature source rock in the basin and may act as pathfinder of possible new petroleum system attached to it.

The impact of faults on the occurrence of coal bed methane in Renlou coal mine, Huaibei coalfield, China

The fault has an important impact on coal bed methane (CBM) occurrence. The complexity of the fault exacerbates the variability of CBM occurrence, which increases the difficulty of mine gas prevention and thus threats to mining safety seriously. The coal-bearing strata in the Renlou coal mine located in the Linhuan mining area of the Huaibei coalfield have undergone three transformations caused by major tectonic movements since its formation. In addition, the large-angle tectonic stress superposition leads to structure characteristic and mechanical properties of faults transform in the area or just make it become multiplicity. The normal faults F3 and F7 and reverse fault F5 in southern Renlou coal mine are open structures. The coal seam between faults F7 and F5 is in the emission range of the two faults (partially in the superimposed range) in which a significant amount of gas escapes. The formation between faults F5 and F7 is horst, and it turns from NS to EW. The stress in the formation is large, which results in the presence of numerous fractures and cleats. Therefore, there is difference of methane occurrence between the two regions. Between faults F7 and F5, the gas pressure gradient of coal seam No. 72 is 0.00356 MPa/m with a maximum value of 0.39 MPa (−633.5 m). However, the gas pressure gradient of coal seam No. 72 between faults F3 and F2 is 0.00726 MPa/m and the maximum measured gas pressure is 1.7 MPa (−692 m). The relative methane emission (RME) of working face 7257 located between faults F7 and F5 was 2.01 m3/t on average with a maximum value of 4.96 m3/t. The average RME of working face ІІ7211 located between faults F3 and F2 reached 12 m3/t in the area of 0–600 m away from F3 fault and increased to 30 m3/t in the region of >600 m away from fault F3.

Geochemical and acoustic evidence for the occurrence of methane in sediments of the Polish sector of the southern Baltic Sea

This paper presents the results of geochemical and acoustic investigations of sediments in the Polish sector of the southern Baltic Sea. Its objective was to indicate areas of gas bubble formation and the occurrence of methane. Over 3000 nautical miles of transects were recorded using a variety of hydroacoustic instruments, and five coring points were selected for further analyses of pore waters (CH4, SO42−, H2S, NH4+, total alkalinity) and sediments (grain size distribution, Corg, Ntot, LOI and WC). Gas turned out to be present at shallow depths in different forms such as recent and buried pockmarks, and gas-saturated sediments (including gas pockets and seepages). It was found that methane was widespread in the sediments of the study area, both in the surface sediments, e.g. in the vicinity of the Hel Peninsula or in the central Gulf of Gdańsk, and in deeper sediment layers, e.g. in the Gdańsk Deep and the Słupsk Furrow. Chemical analysis showed that as a result of the rapid decomposition of organic matter, sulphates were depleted in the top 20cm layer of sediments and that methane was produced at relatively shallow depths (in some areas even at depths of 20–30cm bsf) compared to other regions of the Baltic, reaching concentrations of>6mmol l−1 in the 30–40cm layer below the sediment surface. The sulphate-methane transition zone (SMTZ) was 4–37cm thick and was situated in the uppermost 50cm of the sediments.