Increasing Methane Concentration Research Articles

Real-time surrogate analysis for potential oil and gas contamination of drinking water resources

Public concerns related to the fast-growing shale oil and gas industry have increased during recent years. The major concern regarding shale gas production is the potential of fracturing fluids being injected into the well or produced fluids flowing out of the well to contaminate drinking water resources such as surface water and groundwater. Fracturing fluids contain high total dissolved solids (TDS); thus, changes in TDS concentrations in groundwater might indicate influences of fracturing fluids. An increase of methane concentrations in groundwater could also potentially be due to hydraulic fracturing activities. To understand the possible contamination of groundwater by fracturing activities, real-time groundwater monitoring is being implemented in the Denver-Julesburg basin of northeast Colorado. A strategy of monitoring of surrogate parameters was chosen instead of measuring potential contaminants directly, an approach that is not cost effective or operationally practical. Contaminant surrogates of TDS and dissolved methane were proposed in this study, and were tested for correlation and data distribution with laboratory experiments. Correlations between TDS and electrical conductivity (EC), and between methane contamination and oxidation–reduction potential (ORP) were strong at low concentrations of contaminants (1 mg/L TDS and 0.3 mg/L CH4). Dissolved oxygen (DO) was only an effective surrogate at higher methane concentrations (≥2.5 mg/L). The results indicated that EC and ORP are effective surrogates for detecting concentration changes of TDS and methane, respectively, and that a strategy of monitoring for easy to measure parameters can be effective detecting real-time, anomalous behavior relative to a predetermined baseline.

Thermodynamic properties and diffusion of water + methane binary mixtures

Thermodynamic and diffusion properties of water + methane mixtures in a single liquid phase are studied using NVT molecular dynamics. An extensive comparison is reported for the thermal pressure coefficient, compressibilities, expansion coefficients, heat capacities, Joule-Thomson coefficient, zero frequency speed of sound, and diffusion coefficient at methane concentrations up to 15% in the temperature range of 298-650 K. The simulations reveal a complex concentration dependence of the thermodynamic properties of water + methane mixtures. The compressibilities, heat capacities, and diffusion coefficients decrease with increasing methane concentration, whereas values of the thermal expansion coefficients and speed of sound increase. Increasing methane concentration considerably retards the self-diffusion of both water and methane in the mixture. These effects are caused by changes in hydrogen bond network, solvation shell structure, and dynamics of water molecules induced by the solvation of methane at constant volume conditions.

Nonoxidative Aromatization of CH4 Using C3H8 As a Coreactant: Thermodynamic and Experimental Analysis

The effect of propane addition to the feed of methane aromatization process was studied both thermodynamically and experimentally. Thermodynamic equilibrium calculations were performed within temperature, pressure, and CH4/C3H8 molar ratio ranges of 673–873 K, 1–10 bar, and 0–20, respectively, considering different constraints according to two alternative reaction network models. Experimental evaluations were conducted in a fixed-bed reactor over Zn/HZSM-5 catalyst under different operating conditions. Methane formation showed an induction period of about 4 h on stream. Aromatic yield slightly increased with increase of methane concentration in the feed. Experimental results showed the best agreement with the thermodynamic model based on a proposed mechanism of methylation of propane-derived aromatics by methane, giving equilibrium methane conversions of about 1% under the above conditions. Both thermodynamic and experimental results revealed that in the presence of propane cofeed, the contribution of met...

Geochemical signature related to lipid biomarkers of ANMEs in gas hydrate-bearing sediments in the Ulleung Basin, East Sea (Korea)

The emission of methane as a greenhouse gas is controlled by the anaerobic oxidation of methane (AOM), which plays an important role in the biogeochemical methane cycle. During the Second Ulleung Basin Gas Hydrate Drilling Expedition (UBGH2), the distribution of lipid biomarkers and their compound-specific stable carbon isotope ratios related to methane were investigated in venting and non-venting sites (UBGH2-3, UBGH2-10) of gas-hydrate-bearing sediments in the Ulleung Basin. The objective of this study was to understand the microbial signatures related to methane cycling in organic-rich sediment in a marginal sea (East Sea/Japan Sea) of the western North Pacific. The concentrations of methane-related specific biomarkers (archaeol and sn-2-hydroxyarchaeol) at the sulphate–methane transition zone (SMTZ; sediment depth in UBGH2-3: 1–2 mbsf, in UBGH2-10: 6.8 mbsf) are typically higher than in other sediment sections and their δ 13C valuesare apparently depleted (−73.3‰ to −102.7‰) in the UBGH2-3 and UBGH2-10 study sites. However, the δ13C values of archaeol and sn-2-hydroxyarchaeol (between −59.6‰ and −66.5‰) are not depleted with the increased methane concentration in the sediments below the SMTZ in UBGH2-3, compared to the δ 13C values (about −60‰) of in situ methane. This suggests that methane production processes should be dominant in the deeper sediment sections (2.7–3.8 mbsf) rather than methane consumption by anaerobic methanotrophs (ANMEs) at the corresponding sediment depths. There were also higher δ 13C values (−47‰ to −32‰) for archaeol and sn-2-hydroxyarchaeol in the 3–6 mbsf sections at UBGH2-10, suggesting the prevalence of methanogenic activities. However, the δ13C values (−89.0‰ to −92.2‰) of archaeol and sn-2-hydroxyarchaeol were unexpectedly depleted in the deeper sediment section (5.2 mbsf) of the venting site (UBGH2-3), indicating that the past AOM occurred under low sulphate concentrations in the corresponding pore water. This study used the biomarker ratio (sn-2-hydroxyarchaeol/archaeol) of Archaea as a tool to demonstrate the different ANME communities, which was supported by 16S rRNA analysis in the sediments of venting and non-venting sites (UBGH2-3, UBGH2-10). Consequently, the biochemical signatures of methanotrophic and methanogenic activity were found at varying sediment depths at both sites.

Clarification of Methane Emission Sources Using WDCGG Data: Case Study of Anmyeon-do Observatory, Korea

Methane concentrations have been monitored at the Anmyeon-do Observatory, Korea, since 1999. In recent years, the methane concentration has increased, but the sources of this increase have yet to be identified. This study was designed to identify the major source contributing to the increase by using World Data Centre for Greenhouse Gases (WDCGG) data and the Greenhouse Gases Emission Presumption (GEP) method. The data were collected at Anmyeon-do between 2003 and 2009 (except 2008), and the analyses showed that the increase in methane concentration originated mainly in rice paddies around the observation point. The annual averagemethane concentration at Anmyeon-do was 1894 ppb, of which 100-103 ppb (5.3-5.4%) was shown to originate mainly from rice paddies. The seasonal fluctuation in methane concentration from May to October estimated by the GEP method was compared with experimental data of previous research conducted on rice paddies. The close match obtained through this comparison shows that the GEP method is effective. The difference in methane concentration was also analyzed in terms of land use and land cover. It was shown that although rice paddies account for only 14.7% of the area surveyed, they accounted for between 69 and 90% of the total increase in methane concentration. These results confirm that rice paddies are the main source of the increase in methane concentration observed at Anmyeon-do.

Arctic methane

What are the risks of a runaway greenhouse effect from methane release from hydrates in the Arctic? In January 2013, a dramatic increase of methane concentration up to 2000 ppb has been measured over the Arctic north of Norway in the Barents Sea. The global average being 1750 ppb. It has been suggested that methane normally trapped under the sea ice is now released more easily, especially in areas with reduced sea-ice extent. These high methane concentrations are possibly related to the destabilization of the methane gas hydrates in the Arctic shelf. Is this the start of a runaway greenhouse effect? Methane gas hydrates are solid, ice-like mixtures of water and methane. They are stable under relatively low temperatures and high pressures. These conditions can be found naturally in permafrost regions or under submarine continental slopes. Hydrates accumulate a large amount of gas. One cubic meter can include up to 160 m3 of methane. Their huge amount of stored energy and the wide geographical distribution make hydrates an attractive potential energy source. However, they are also suspected to be a source of global climate change and geological hazard, but the risk is still uncertain. Due to the quasi-stability of methane hydrates, any intervention in the temperature–pressure equilibrium could trigger hydrate dissociation followed by methane emissions, a runaway greenhouse effect, and potential underwater landslides. Here, some consequences for climate change of methane emissions to the atmosphere are analyzed in a scenario study.

Response of methanogenic archaea to Late Pleistocene and Holocene climate changes in the Siberian Arctic

In order to investigate the link between the methane dynamics in permafrost deposits and climate changes in the past, we studied the abundance, composition, and methane production of methanogenic communities in Late Pleistocene and Holocene sediments of the Siberian Arctic. We detected intervals of increased methane concentrations in Late Pleistocene and Holocene deposits along a 42 ka old permafrost sequence from Kurungnakh Island in the Lena Delta (northeast Siberia). Increased amounts of archaeal life markers (intact phospholipid ethers) and a high variety in genetic fingerprints detected by 16S ribosomal ribonucleic acid gene analyses of methanogenic archaea suggest presently living and presumably active methanogenic archaea in distinct layers predominantly in Holocene deposits, but also in deep frozen ground at 17 m depth. Potential methanogenic activity was confirmed by incubation experiments. By comparing methane concentrations, microbial incubation experiments, gene analysis of methanogens, and microbial life markers (intact phospholipid esters and ethers) to already partly degraded membrane lipids, such as archaeol and isoprenoid glycerol dialkyl glycerol tetraethers, we demonstrated that archaeol likely represents a signal of past methanogenic archaea. The archaeol signal was used to reconstruct the response of methanogenic communities to past temperature changes in the Siberian Arctic, and the data suggest higher methane emissions occurred during warm periods, particularly during an interval in the Late Pleistocene and during the Holocene. This new data on present and past methanogenic communities in the Siberian terrestrial permafrost imply that these microorganisms will respond to the predicted future temperature rise in the Arctic with increasing methane production, as demonstrated in previous warmer periods.

Theoretical investigation of the possibility of using multicomponent (N2-O2-CH4-Y2O) clathrate hydrates for methane recovery from mine gas

Phase equilibria in a multicomponent ice-gas mixture-hydrate system are investigated for a mixture of nitrogen, oxygen, and methane, depending on the gas phase composition, pressure, and temperature. Equilibrium compositions of the formed hydrates are found, depending on the gas mixture composition. Calculations show that with increasing concentration ofmethane in gas phase the pressure of hydrate formation gradually decreases. It is shown that this pressure at considerable methane concentrations approximately corresponds to partial pressure of methane in the gas phase. Conditions of hydrate formation are calculated in the range of temperatures from 258 to 273 K, at pressures from 1 to 350 atm. The obtained results are in agreement with the known experimental data for hydrates of pure gases-nitrogen, oxygen, and methane.

続成作用・変成作用における泥岩残留炭化水素ガスの変化と四万十帯付加体のシェールガスポテンシャル

Change of residual hydrocarbon gases in mudstones and pelitic metamorphic rocks was investigated to evaluate the retention of methane in shale rocks during diagenesis and metamorphism. The samples were collected from borehole MITI-Mishima and outcrops in Shimanto belt, Chichibu belt, and Sanbagawa metamorphic belt exposed in Shikoku region. Concentration of residual methane normalized to total organic carbon content begins to increase when mudstone porosity reaches about 5%. The increased methane concentration at mudstone porosity less than 5% suggests a significant retention of methane in mudstone matrix. The high concentration zone of residual methane corresponds to maturity levels of vitrinite reflectance (Ro) =2 to 3%. Residual methane concentration significantly decreases in the higher maturity levels (Ro>4%), suggesting the graphitization of methane. The maturity levels of Ro=2 to 3% with the highest residual methane concentration is expected to be the favorable stage for shale gas formation, although host rock lithology such as the storage capacity and fissile nature are also related to enhanced shale gas recovery. Many parts of accretionary prism in Shimanto belt are at these maturity levels of Ro=2 to 3% favorable for shale gas formation. Accretionary prism formed under the compressional stress suggests development of gas seal structures and closed fracture systems convenient for shale gas retention, although shale rocks in Shimanto accretionary prism are comparatively poor in organic matter. Several thermogenic gas seepages in Shimanto belt would be another indication of shale gas formation in accretionary prism distributed in wide area along Pacific side of southwest Japan.

Mid- and far-infrared absorption spectroscopy of Titan’s aerosols analogues

In this work we present mid- and far-infrared absorption spectra of Titan’s aerosol analogues produced in the PAMPRE experimental setup. The evolution of the linear absorption coefficient ε (cm−1) is given as a function of the wavenumber.We provide a complete dataset regarding the influence that the concentration of methane vapor in the gas mixture has on the tholin spectra. Among other effects, the intensity of the 2900cm−1 (3.4μm) pattern (attributed to methyl stretching modes) increases when the methane concentration increases. More generally, tholins produced with low methane concentrations seem to be more amine based polymers, whereas tholins produced with higher methane concentrations contains more aliphatic carbon based structures.Moreover, it is shown that the position of the bands around 2900cm−1 depends on the chemical environment of the methyl functional group. We conclude that the presence of these absorption bands in Titan’s atmosphere, as measured with the VIMS instrument onboard Cassini is in agreement with an aerosol contribution.We also compare the far-infrared spectrum of tholin to spectra of Titan’s aerosols derived from recent Cassini-CIRS observations displaying many similarities, particularly with absorption bands at 325cm−1, 515cm−1, and the methyl attributed 1380cm−1 and 1450cm−1 bands.

Optical f iber methane sensor based on SAN f ilm containing cryptophane-E-(OEt)6

A novel long-period fiber grating (LPFG) film methane sensor is designed and applied successfully. The sensor is constructed by depositing a thin styrene-acrylonitrile (SAN) film containing the new compound cryptophane-E-(OEt)6 onto the cladding surface of the LPFG. This film is sensitive to methane gas. Methane causes a change in the refractive index of the sensing film, which can be measured by shifting the resonance wavelength. Experimental results show that the resonant wavelength shifts to the longer wavelength, with increasing methane concentration at a range of 0.0%–3.5% (v/v). A linear relationship is obtained within the test range. Detection limit is estimated at 0.2%, and response time is 60 s. No significant interference is detected from dry air, O2, CO, CO2, and H2. This novel methane sensing material has great application potential due to its advantages.

Phylogenetic Microarray Analysis of a Microbial Community Performing Reductive Dechlorination at a TCE-Contaminated Site

A high-density phylogenetic microarray (PhyloChip) was applied to track bacterial and archaeal populations through different phases of remediation at Ft. Lewis, WA, a trichloroethene (TCE)-contaminated groundwater site. Biostimulation with whey, and bioaugmentation with a Dehalococcoides-containing enrichment culture were strategies implemented to enhance dechlorination. As a measure of species richness, over 1300 operational taxonomic units (OTUs) were detected in DNA from groundwater samples extracted during different stages of treatment and in the bioaugmentation culture. In order to determine active members within the community, 16S rRNA from samples were analyzed by microarray and ∼600 OTUs identified. A cDNA clone library of the expressed 16S rRNA corroborated the observed diversity and activity of some of the phyla. Principle component analysis of the treatment plot samples revealed that the microbial populations were constantly changing during the course of the study. Dynamic analysis of the archaeal population showed significant increases in methanogens at the later stages of treatment that correlated with increases in methane concentrations of over 2 orders of magnitude. Overall, the PhyloChip analyses in this study have provided insights into the microbial ecology and population dynamics at the TCE-contaminated field site useful for understanding the in situ reductive dechlorination processes.

Simulation of the Young’s Modulus Anisotropy in CVD Diamond Film

The relationship between textures and Young’s modulus in CVD diamond films was simulated based on the phenomenological theory, which indicates the textures induce the Young’s modulus anisotropy. The increase of methane concentration changes the density of different fiber textures in diamond films, which induces the increase of Young’s modulus in the directions that parallel to the film surface. Among the textures, {111} texture is of no influence whereas {011} texture has the maximum influence on the Young’s modulus anisotropy of diamond film.

Effect of various medicinal plant essential oils obtained from semi-arid climate on rumen fermentation characteristics of a high forage diet using in vitro batch culture

Eighteen natural medicinal plant essential oils and garlic oil obtained from semi-arid climate were conducted to evaluate their effects on in vitro rumen microbial fermentation and their effectiveness for decrease in vitro ruminal methane production. 50 ml of buffered rumen fluid (1:2; rumen fluid: buffer solution) were introduced in 125 ml serum bottles containing 500 mg of 80:20 alfalfa hay to concentrate as basal diet and or basal diet plus 1 µ/ml of medium of medicinal essential oils or garlic oil (6 replicates for each treatment) and incubated for 24 h at 38.7°C. Head space gas pressure of each bottle was recorded using a pressure transducer at 2, 4, 6, 8, 10, 12, 16 and 24 h of the incubation and a sample was collected to determine methane concentration. In the end of incubation pH measured and samples were collected for ammonia nitrogen concentration and dry matter (DM) and crude protein (CP) disappearance were recorded and feed fermentation efficiency (FFE = mg IDMD/ ml accumulative gas produced at 24 h post incubation) were calculated. Medicinal plant essential oils which caused an increase in FFE and decrease in gas production in-contrast with those in control were selected as the candidates for gas analysis and determine their effects on methane concentration. All essential oils resulted in a significant decrease (P < 0.05) in total gas production (except in Rosemary, Dill, Clove, Fennel, Pistachio hull and black pepper) and both IDMD and ICPD (except in Black pepper, Rosemary and Dill). Of the 19 samples tested coriander, rosemary, cinnamon, red basil, oregano 2, black pepper, cumin, caraway and dill that selected as the candidates for gas analysis and determine their effects on methane concentration increase in FFE and decrease in gas production in contrast with those in control. Increase in FFE was more noticeable for thyme, lemon pulp and cinnamon essential oils (22, 21.95 and 3.2 times more than those of control, respectively). Results indicated that coriander, cinnamon, red basil, oregano 2, cumin, caraway and dill essential oils caused a significant decrease (P < 0.05) in total methane production (1.5, 0.3, 1.0, 1.3, 1.1, 1.1 and 2.0 compared with 2.3 in control as mmol/g DM incubated, respectively). Key words: Semi-arid, essential oil, methane, fermentation efficiency, in vitro, rumen.

Large methane releases lead to strong aerosol forcing and reduced cloudiness

Abstract. The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70 % increase in the atmospheric lifetime of methane, and an 18 % decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing ("enhanced greenhouse effect") of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.

Breakdown Current Density of CVD-Grown Multilayer Graphene Interconnects

Graphene wires have been fabricated from large-area multilayer graphene sheets grown by chemical vapor deposition. As the methane concentration increases, a larger percentage of thicker graphene layers are grown. The multilayer graphene sheets have an average thickness of 10-20 nm with sheet resistances between 500 and 1000 Ω/sq. The sheet resistance shows a strong correlation with the average surface roughness. This letter reports measured breakdown current densities up to 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , where resistive heating is proposed as the main breakdown mechanism. Increasing the uniformity of the graphene layers is important in achieving a higher breakdown current density.

Methane and monsoons

The rising trend in atmospheric concentrations of methane over the past 5,000 years has been attributed to human agency. A modelling study, of a power that has only now become possible, points to another cause. See Letter p.82 The question of how long humans have influenced global climate by greenhouse-gas emissions is fundamental to understanding climate system sensitivity. Hence the interest in an apparent anomalous increase in atmospheric methane concentrations that occurred about 5,000 years ago — as recorded in polar ice cores. Explanations offered for the rise in methane levels include very early agricultural activity and increased natural wetland emissions. A new series of climate and wetland simulations of global methane levels during the last glacial cycle now suggests that the increase in methane concentrations can be explained by natural changes in Earth's orbital configuration, with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation.

Late Holocene methane rise caused by orbitally controlled increase in tropical sources

Considerable debate surrounds the source of the apparently 'anomalous' increase of atmospheric methane concentrations since the mid-Holocene (5,000 years ago) compared to previous interglacial periods as recorded in polar ice core records. Proposed mechanisms for the rise in methane concentrations relate either to methane emissions from anthropogenic early rice cultivation or an increase in natural wetland emissions from tropical or boreal sources. Here we show that our climate and wetland simulations of the global methane cycle over the last glacial cycle (the past 130,000 years) recreate the ice core record and capture the late Holocene increase in methane concentrations. Our analyses indicate that the late Holocene increase results from natural changes in the Earth's orbital configuration, with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation. Critically, our simulations capture the declining trend in methane concentrations at the end of the last interglacial period (115,000-130,000 years ago) that was used to diagnose the Holocene methane rise as unique. The difference between the two time periods results from differences in the size and rate of regional insolation changes and the lack of glacial inception in the Holocene. Our findings also suggest that no early agricultural sources are required to account for the increase in methane concentrations in the 5,000 years before the industrial era.

Seasonal changes in Titan's meteorology

The Cassini Imaging Science Subsystem has observed Titan for 1/4 Titan year, and we report here the first evidence of seasonal shifts in preferred locations of tropospheric methane clouds. South \polar convective cloud activity, common in late southern summer, has become rare. North \polar and northern mid \latitude clouds appeared during the approach to the northern spring equinox in August 2009. Recent observations have shown extensive cloud systems at low latitudes. In contrast, southern mid \latitude and subtropical clouds have appeared sporadically throughout the mission, exhibiting little seasonality to date. These differences in behavior suggest that Titan s clouds, and thus its general circulation, are influenced by both the rapid temperature response of a low \thermal \inertia surface and the much longer radiative timescale of Titan s cold thick troposphere. North \polar clouds are often seen near lakes and seas, suggesting that local increases in methane concentration and/or lifting generated by surface roughness gradients may promote cloud formation. Citation

Active pockmarks in a large lake (Lake Constance, Germany): Effects on methane distribution and turnover in the sediment

In the eastern part of Lake Constance, the second largest prealpine lake in Europe, about 500 pockmarks (morphological depressions on the lake floor) were recently discovered. The diameters of these pockmarks are as large as 16 m, and about 24% of them continuously release methane in the form of visible bubbles. The isotopic composition of the escaping gas indicated that the methane was of biogenic origin and was predominantly produced by the CO2‐reduction pathway. In shallow‐water pockmarks (9 m and 12 m), pore‐water analysis revealed increased methane concentrations of &gt; 1100 µmol L−1 in the sediment. Diffusive methane fluxes and oxidation rates within these shallow pockmarks were much higher than in sediments outside pockmarks. An estimated methane ebullition into the water column of about 40 L h−1 per pockmark showed that methane ebullition is by far the dominant pathway of methane release from these shallow pockmarks. Meiofauna abundance and organic carbon contents of the sediment were also higher in the shallow pockmarks, but there were no differences in macrofauna. In a deep pockmark (80 m), even though bubble release was observed, the sediment inside the pockmark had almost the same methane concentrations and isotopic compositions as a site outside of the pockmark. At both sites, the shallow and deep pockmark act mainly as sedimentation traps, the emanating gas has only minor influence on the methane inventory of the sediments and, therefore, gas bubbles enter the water column essentially unaffected.