Occurrence Of Methane Research Articles

An NMR Study of the Ratio between Free and Sorbed Methane in the Pores of Fossil Coals

Theoretical and experimental data on the concentrations of methane in different phase states in the porous structure of coals from the Donets Basin are reported. On the saturation of coal samples with methane, the natural conditions of the occurrence of methane in coal beds were simulated for the equilibrium coal–gas system. The amounts of methane dissolved in a solid matrix and adsorbed on the pore surfaces of coal matter were measured by broad-band NMR spectroscopy. The values obtained did not exceed 20% of the total methane absorbed by the sample in an equilibrium state at a pressure of 10 MPa. Sorbed methane was the predominant phase state only upon the opening of a high-pressure chamber after the emission of methane from filtration channels.

Magnetic Mineral Diagenesis in a High Temperature and Deep Methanic Zone in Izu Rear Arc Marine Sediments, Northwest Pacific Ocean

AbstractMagnetic mineral diagenesis is an important process in sediments that is responsible for the partial or total destruction of records of Earth's magnetic field variations and also plays an important part in iron and sulfur cycling. A rock magnetic study has been carried out at International Ocean Discovery Program Expedition 350 Site U1437 in the Izu Bonin rear arc to investigate magnetic mineral diagenesis in deeply buried sediments from ~775 to ~1,002 m below sea floor (mbsf) with burial temperatures ranging from ~67 to 85 °C. Nonsteady state geochemical environments occur within an unusual deep methanic zone (below 850 mbsf) because of a release of sulfate below the shallow sulfate reduction zone. A drastic decline in magnetic susceptibility and remanence is observed at ~850 mbsf due to a decrease in ferrimagnetic iron oxide contents. Reduction of (titano)‐magnetite and pyritization occur at this inferred deep sulfate‐methane transition zone. Below ~850 mbsf, lower magnetic mineral contents coincide with further methane release. Geochemical analyses support a change in redox conditions and secondary precipitation of iron sulfides and carbonates in the methane‐rich zone. Magnetic mineral alteration is enhanced in zones where methane accumulates underneath low porosity intervals that act as seals. Although geochemical processes due to methane occurrence are likely dominant, more than one mechanism, possibly involving microbial activity, is probably responsible for the observed magnetic mineral assemblage changes.

Porewater dissolved organic and inorganic carbon in relation to methane occurrence in sediments of the Gdańsk Basin (southern Baltic Sea)

The impact of methane occurrence on carbon forms dissolved in pore waters was investigated in the present study. The cores were collected at three geochemically different stations in the Gdańsk Basin area (southern Baltic Sea). Sediments were analyzed for methane, total particulate carbon (TPC) and particulate organic carbon (POC). In pore waters extracted using Rhizon samplers the following parameters were measured: sulfate, total dissolved sulfide (TDS), dissolved inorganic (DIC) and organic carbon (DOC). Concentrations of DIC and DOC in pore water profiles were up to 5 times higher at stations with methane compared to the station without methane in shallow sediments. Average fluxes of DIC and DOC were calculated for three separate sediment layers at each station (surface layer – benthic flux, flux in sulfate-methane transition (SMT) or in intermediate layer and flux below SMT/intermediate). Benthic DIC and DOC fluxes were highest at one of the stations with shallow SMT (7–20 cm): 8.71 mmol m−2 d−1 and max. 1.48 mmol m−2 d−1, respectively. Additionally, we found strong dependences between DIC and DOC in sediments of stations with methane (R2 = 0.98). The relationship between methane and DOC in sediment profiles was described by exponential regression (R2 = 0.83). The contribution of particulate inorganic carbon (PIC) in TPC was significantly higher at the methane station with highest DIC concentration and fluxes.

Methanogenic archaea associated to Microcystis sp. in field samples and in culture

Cyanobacterial mass developments impact the community composition of heterotrophic microorganisms with far-reaching consequences for biogeochemical and energy cycles of freshwater ecosystems including reservoirs. Here we sought to evaluate the temporal stability of methanogenic archaea in the water column and further scrutinize their associations with cyanobacteria. Monthly samples were collected from October 2009 to December 2010 in hypereutrophic Pampulha reservoir with permanently blooming cyanobacteria, and from January to December 2011 in oligotrophic Volta Grande reservoir with only sporadic cyanobacteria incidence. The presence of archaea in cyanobacterial cultures was investigated by screening numerous strains of Microcystis spp. from these reservoirs as well as from lakes in Europe, Asia, and North-America. We consistently determined the occurrence of archaea, in particular methanogenic archaea, in both reservoirs throughout the year. However, archaea were only associated with two strains (Microcystis sp. UFMG 165 and UFMG 175) recently isolated from these reservoirs. These findings do not implicate archaea in the occurrence of methane in the epilimnion of inland waters, but rather serve to highlight the potential of microhabitats associated with particles, including phytoplankton, to shelter unique microbial communities.

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York.

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south-central New York. All samples were collected ≫1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [4 He], thermogenic [CH4 ], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon-rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.

Microscopic characteristics of the methane occurrence state in coal

Microscopic characteristics of the methane occurrence state in coal

Microscopic characteristics of the methane occurrence state in coal

The regulation of methane occurrence is critical for gas control. Through liquid nitrogen adsorption, isothermal adsorption/desorption of methane and electrical experiments with undeformed and deformed coal, this paper studies the microscopic characteristics of methane occurrence. The results show: the median-pore-dominant deformed coal has less specific surface area and pore volume than the undeformed coal, which has mainly micropores and small pores; the deformed coal has greater methane absorption ability than the undeformed coal, and the negative influence of temperature on the former is more notable; the resistivity of deformed coal is three to seven times that of undeformed coal, and when adsorbing the resistivity of both coals decreases before being stable, whereas their dielectric constant rises first, then slightly declines. The results of the three experiments are in good accordance. The research is basic for coalbed gas and may provide a new thought for gas control.

Analysis of coalbed methane occurrence in Shuicheng Coalfield, southwestern China

This article is the result of authors’ long-term efforts to evaluate the occurrence of coalbed methane (CBM) for CBM exploration and coal gas disaster prevention in Shuicheng Coalfield (SCC). A relatively large program of exploratory drilling to determine the content of CBM, geological surveys and laboratory experiments, including coal proximate analysis, coal physical properties analysis and methane adsorption were conducted. The results show that the coals from the SCC contain 21.42–41.34% volatile, 0.24–1.44% moisture and 6.27–38.1% ash yield, with coal porosity in the range of 5.97–14.89%. The type of coal structure ranges from II to IV. The sedimentary characteristics, tectonic evolution, geological structure, coal reservoir conditions and hydrodynamics were studied via geological surveys, field research and laboratory tests. The relationships between these factors and gas content are explained and analyzed in this present paper. The formation of the Shuicheng coal basin was formed under the control of the Ziyun fracture and the Luoping fracture. Ejective folds and synclines that evolved from inverted geological structures in the stage of Yanshan movement affect CBM occurrence. Folds generated in coal bearing strata play an important role in methane accumulation in the period of Himalayan movement. A positive relationship is observed between gas content and coal burial depth, coal thickness, and hydrodynamics. CBM easily concentrates because of the separation between coal bearing strata and Maokou enrich aquifer. We divide the SCC into three methane geological units, the Ertang syncline unit, the Dahebian syncline unit and the Xiaohebian syncline unit. Furthermore, gas content spatial distributions were predicted in the SCC. The probability of CBM exploration was evaluated based on coal permeability and gas flow attenuation coefficient. These research results could contribute to CBM exploration and coal gas disaster prevention in the SCC.

Evaluation of pore development in different coal reservoirs based on centrifugation experiment

Pore development in a coal reservoir is closely related to the coalbed methane (CBM) occurrence. Therefore, an experimental study on the properties and characteristics of coal pores is critical for CBM exploration and production. In this paper, capillary pressure data from six coal samples with coal ranks ranging from medium volatile bituminous to anthracite were obtained using centrifugation, which is fast, convenient, non-toxic and harmless compared with other experimental methods. The centrifugation capillary pressure curves can be classified into three types. Type A refers to the medium-low volatile bituminous with a wide platform on its capillary pressure curve, indicating the pores have a good connectivity. The fractal analysis show that the fractal structure of macro- and mesopores are more complicated than that of transition pores. Thus the pore structure has a good capacity for gas seepage. Type B and C refer to the semi-anthracite to anthracite with steeper capillary pressure curves, suggesting that they both contain large numbers of micropores. However, the maximum and average pore diameters of type B are larger than those of type C, indicating that type B has more macropores than type C. Therefore, type B has both gas flow and adsorption capacities, while type C is only favorable for methane storage. Mercury porosimetry and scanning electron microscopy (SEM) were also performed on the six samples to verify the results of centrifugation. The capillary pressure curves obtained using mercury porosimetry also indicate the three types of pore structures. The pore size distributions evaluated from mercury intrusion show a consistency with those from centrifugation. As the assessment of pore development using centrifugation is limited to quantity, SEM can help to visually reveal the genesis of pores in different types of coal reservoirs.

Methane in aquifers used for public supply in the United States

In 2013 to 2015, 833 public supply wells in 15 Principal aquifers in the U.S. were sampled to identify which aquifers contained high methane concentrations (>1 mg/L) and determine the geologic, hydrologic, and geochemical conditions associated with high concentrations. This study represents the first national assessment of methane in aquifers used for public supply in the U.S. and, as such, advances the understanding of the occurrence and distribution of methane in groundwater nationally. Methane concentrations >1 and > 10 mg/L occurred in 6.7 and 1.1% of the samples, respectively. Most high concentrations occurred in aquifers in the Atlantic and Gulf Coastal Plain regions and upper Midwest. High methane concentrations were most commonly associated with Tertiary and younger aquifer sediments, old groundwater (>60 years), and concentrations of oxygen, nitrate-N, and sulfate <0.5 mg/L. Concentrations of methane were also positively correlated (p < 0.05) with dissolved organic carbon and ammonium. Case studies in Florida, Texas, and Iowa were used to explore how regional context from this data set could aid our understanding of local occurrences of methane in groundwater. Regional data for methane, Br/Cl ratios, sulfate, and other parameters helped identify mixing processes involving end members such as wastewater effluent-impacted groundwater, saline formation water, and pore water in glacial till that contributed methane to groundwater in some cases and supported methane oxidation in others.

Comments: Hydraulic Fracturing Studies

Editor's column Several recent studies have shown that there is no evidence that hydraulic fracturing in unconventional plays harms groundwater. These reports follow a very detailed 5-year study released earlier this year by the US Environmental Protection Agency (EPA) that found no “widespread impact” but was cautious in its conclusions. In April, results from a 3-year study conducted by Duke University, Ohio State University, Penn State, Stanford University, and the French Geological Survey concluded that unconventional oil and gas extraction using hydraulic fracturing and horizontal drilling caused no groundwater contamination in five Northern Appalachian Basin counties in West Virginia. The study monitored water wells both before and after the installation of shale gas wells. The authors observed: “[Our report] provides a clear indication for the lack of groundwater contamination and subsurface impact from shale gas drilling and hydraulic fracturing. Saline groundwater was ubiquitous throughout the study area before and after shale gas development, and the groundwater geochemistry in this study was consistent with historical data reported in the 1980s.” But the study also concluded that accidental spills of waste water from fracturing could threaten surface water in the region. The peer-reviewed study, which was published in the European journal Geochimica et Cosmochimica Acta, showed that methane and saline groundwater were found in some samples, but they occurred naturally in the region’s shallow aquifers and were not caused by shale activity. Similarly, in late May the US Geological Survey released its findings after studying the impact of unconventional activity in parts of Louisiana, Arkansas, and Texas. Included in the study were the prolific production areas covering the Eagle Ford, Haynesville, and Fayetteville formations. That study concluded that unconventional oil and gas production in those areas is not a significant source of methane or benzene in drinking water wells. This was the first study to determine the presence of those chemicals in drinking water wells in relation to the age of the groundwater. “Understanding the occurrence of methane and benzene in groundwater in the context of groundwater age is useful because it allows us to assess whether the hydrocarbons were from surface or subsurface sources,” the study said. “The ages indicated groundwater moves relatively slowly in these aquifers. Decades or longer may be needed to fully assess the effects of unconventional oil and gas production activities on the quality of groundwater used for drinking water.” The 5-year EPA study was an update of a 2015 study that concluded that no harm to groundwater had been done by shale activity. The new study is more cautious, saying that hydraulic fracturing can contaminate water “under some circumstances.” But it said that the incidents that had occurred had been few, especially compared with the number of wells it studied. Controversy surrounding these studies and their conclusions will continue. Additional studies are under way examining not only fracturing’s potential impact on groundwater, but on methane releases and seismic activity. And the resiliency of US unconventional activity during the price downturn indicates that this sector is here to stay.

Surface interpolation of environmental factors as tool for evaluation of the occurrence of high methane and nitrous oxide fluxes

AbstractGreenhouse gas (GHG) emissions from wetlands typically exhibit extended low‐flux phases accompanied by distinct high‐flux events. Prediction and explanation of flux occurrence is hindered by various interactions of the underlying environmental predictors. Here, a novel approach is described to gain insight in patterns of environmental factors, which lead to elevated emissions. Natural neighbor interpolation was utilized to construct flux intensity maps based on two environmental predictors, the ground water level and soil temperature. Further, the effect of inhomogeneous data density was considered by filtering estimates for sufficient information content. The practical application was exemplified by CH4 and N2O flux field data of three years from two fen sites in southwest Germany. This approach considered factor interactions as well as the fluxes occurring as rare events. The application can be useful for the delineation of driving conditions for high‐flux events as well as for wetland management practice.

Evaluation of geological conditions for coalbed methane occurrence based on 3D seismic information: a case study in Fowa region, Xinjing coal mine, China

The research on geological conditions of coalbed methane (CBM) occurrence is of great significance for predicting the high abundance CBM rich region and gas outburst risk area pre-warning. The No. 3 coal seam, in Yangquan coalfield of Qinshui basin, is the research target studied by 3D seismic exploration technique. The geological factors which affect CBM occurrence are interpreted based on the 3D seismic information. First, the geological structure (faults, folds, and collapse columns) is found out by the 3D seismic structural interpretation and the information of buried depth and thickness of the coal seam is calculated by the seismic horizons. Second, 3D elastic impedance (EI) and natural gamma attribute volumes are generated by prestack EI inversion and multi-attribute probabilistic neural network (PNN) inversion techniques which reflect the information of coal structure types and lithology of the roof and floor. Then, the information of metamorphic degree of seam and hydrogeology conditions can be obtained by the geological data. Consequently, geological conditions of CBM occurrence in No. 3 coal seam are evaluated which will provide scientific reference for high abundance CBM rich region prediction and gas outburst risk area pre-warning.

Controls on Methane Occurrences in Aquifers Overlying the Eagle Ford Shale Play, South Texas.

Assessing natural vs. anthropogenic sources of methane in drinking water aquifers is a critical issue in areas of shale oil and gas production. The objective of this study was to determine controls on methane occurrences in aquifers in the Eagle Ford Shale play footprint. A total of 110 water wells were tested for dissolved light alkanes, isotopes of methane, and major ions, mostly in the eastern section of the play. Multiple aquifers were sampled with approximately 47 samples from the Carrizo-Wilcox Aquifer (250-1200 m depth range) and Queen City-Sparta Aquifer (150-900 m depth range) and 63 samples from other shallow aquifers but mostly from the Catahoula Formation (depth <150 m). Besides three shallow wells with unambiguously microbial methane, only deeper wells show significant dissolved methane (22 samples >1 mg/L, 10 samples >10 mg/L). No dissolved methane samples exhibit thermogenic characteristics that would link them unequivocally to oil and gas sourced from the Eagle Ford Shale. In particular, the well water samples contain very little or no ethane and propane (C1/C2+C3 molar ratio >453), unlike what would be expected in an oil province, but they also display relatively heavier δ13 Cmethane (>-55‰) and δDmethane (>-180‰). Samples from the deeper Carrizo and Queen City aquifers are consistent with microbial methane sourced from syndepositional organic matter mixed with thermogenic methane input, most likely originating from deeper oil reservoirs and migrating through fault zones. Active oxidation of methane pushes δ13 Cmethane and δDmethane toward heavier values, whereas the thermogenic gas component is enriched with methane owing to a long migration path resulting in a higher C1/C2+C3 ratio than in the local reservoirs.

Methane Occurrences in Aquifers Overlying the Barnett Shale Play with a Focus on Parker County, Texas.

Clusters of elevated methane concentrations in aquifers overlying the Barnett Shale play have been the focus of recent national attention as they relate to impacts of hydraulic fracturing. The objective of this study was to assess the spatial extent of high dissolved methane previously observed on the western edge of the play (Parker County) and to evaluate its most likely source. A total of 509 well water samples from 12 counties (14,500 km2 ) were analyzed for methane, major ions, and carbon isotopes. Most samples were collected from the regional Trinity Aquifer and show only low levels of dissolved methane (85% of 457 unique locations <0.1 mg/L). Methane, when present is primarily thermogenic (δ13 C 10th and 90th percentiles of -57.54 and -39.00‰ and C1/C2+C3 ratio 10th, 50th, and 90th percentiles of 5, 15, and 42). High methane concentrations (>20 mg/L) are limited to a few spatial clusters. The Parker County cluster area includes historical vertical oil and gas wells producing from relatively shallow formations and recent horizontal wells producing from the Barnett Shale (depth of ∼1500 m). Lack of correlation with distance to Barnett Shale horizontal wells, with distance to conventional wells, and with well density suggests a natural origin of the dissolved methane. Known commercial very shallow gas accumulations (<200 m in places) and historical instances of water wells reaching gas pockets point to the underlying Strawn Group of Paleozoic age as the main natural source of the dissolved gas.

Controls on Methane Occurrences in Shallow Aquifers Overlying the Haynesville Shale Gas Field, East Texas.

Understanding the source of dissolved methane in drinking-water aquifers is critical for assessing potential contributions from hydraulic fracturing in shale plays. Shallow groundwater in the Texas portion of the Haynesville Shale area (13,000 km2 ) was sampled (70 samples) for methane and other dissolved light alkanes. Most samples were derived from the fresh water bearing Wilcox formations and show little methane except in a localized cluster of 12 water wells (17% of total) in a approximately 30 × 30 km2 area in Southern Panola County with dissolved methane concentrations less than 10 mg/L. This zone of elevated methane is spatially associated with the termination of an active fault system affecting the entire sedimentary section, including the Haynesville Shale at a depth more than 3.5 km, and with shallow lignite seams of Lower Wilcox age at a depth of 100 to 230 m. Thelignite spatial extension overlaps with the cluster. Gas wetness and methane isotope compositions suggest a mixed microbial and thermogenic origin with contribution from lignite beds and from deep thermogenic reservoirs that produce condensate in most of the cluster area. The pathway for methane from the lignite and deeper reservoirs is then provided by the fault system.

Abiotic and biotic controls on methane formation down to 2.5 km depth within the Precambrian Fennoscandian Shield

Despite a geological history characterised by high temperature and pressure processes and organic carbon deprived crystalline bedrock, large amounts of hydrocarbons are found in deep groundwaters within Precambrian continental shields. In many sites, methane comprises more that 80% of the dissolved gas phase reaching concentrations of tens of mmoll−1. In this study, we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the Fennoscandian Shield. The main study sites were the Outokumpu Deep Drill Hole and the Pyhäsalmi mine in Finland, both of which allow groundwater sampling down to 2.5km depth and have been previously studied for their groundwater chemistry and microbiology. We show that the differences in the amount and isotopic composition of methane are related to the availability of carbon sources as well as processes behind the incorporation of hydrogen and carbon via abiotic and biotic pathways into hydrocarbon molecules. Supported by previously reported occurrences and isotopic data of deep groundwater methane in lithologically different locations in Finland and Sweden, we show that methane formation is controlled by microbial methanogenesis and abiotic reactions, as well as lithology with the metasedimentary environments being the most favourable for methane occurrence. Rather than a thermogenic relic, crustal methane within the Fennoscandian Shield is more likely the result of low temperature formation from ancient organic compounds or their inorganic intermediates such as graphite. Such crustal gases are characterised by the lack of major amounts of C2+ hydrocarbons and 13C-rich methane. Further, microbiological and isotopic geochemical evidence suggest that microbial methane is more common at depths shallower than 1.5km.

Groundwater methane in relation to oil and gas development and shallow coal seams in the Denver-Julesburg Basin of Colorado

Unconventional oil and gas development has generated intense public concerns about potential impacts to groundwater quality. Specific pathways of contamination have been identified; however, overall rates of contamination remain ambiguous. We used an archive of geochemical data collected from 1988 to 2014 to determine the sources and occurrence of groundwater methane in the Denver-Julesburg Basin of northeastern Colorado. This 60,000-km(2) region has a 60-y-long history of hydraulic fracturing, with horizontal drilling and high-volume hydraulic fracturing beginning in 2010. Of 924 sampled water wells in the basin, dissolved methane was detected in 593 wells at depths of 20-190 m. Based on carbon and hydrogen stable isotopes and gas molecular ratios, most of this methane was microbially generated, likely within shallow coal seams. A total of 42 water wells contained thermogenic stray gas originating from underlying oil and gas producing formations. Inadequate surface casing and leaks in production casing and wellhead seals in older, vertical oil and gas wells were identified as stray gas migration pathways. The rate of oil and gas wellbore failure was estimated as 0.06% of the 54,000 oil and gas wells in the basin (lower estimate) to 0.15% of the 20,700 wells in the area where stray gas contamination occurred (upper estimate) and has remained steady at about two cases per year since 2001. These results show that wellbore barrier failure, not high-volume hydraulic fracturing in horizontal wells, is the main cause of thermogenic stray gas migration in this oil- and gas-producing basin.

PEaCH4 v.2.0: A modelling platform to predict early diagenetic processes in marine sediments with a focus on biogenic methane – Case study: Offshore Namibia

The modelling of early diagenetic processes in marine sediments is of interest in marine science, and in the oil and gas industry, here, especially with respect to methane occurrence and gas hydrate formation as resources. Early diagenesis in marine sediments evolves from a complex web of intertwining (bio)geochemical reactions. It comprises microbially catalysed reactions and inorganic mineral–water–gas interactions. A model that will describe and consider all of these reactions has to be complex. However, it should be user-friendly, as well as to be applicable for a broad community and not only for experts in the field of marine chemistry. The presented modelling platform PeaCH4 v.2.0 combines both aspects, and is Microsoft Excel©–based. The modelling tool is PHREEQC (version 2), a computer programme for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. The conceptual PEaCH4 model is based on the conversion of sediment-bound degradable organic matter. PEaCH4 v.2.0 was developed to quantify and predict early diagenetic processes in marine sediments with the focus on biogenic methane formation and its phase behaviour, and allows carbon mass balancing. In regard to the irreversible degradation of organic matter, it comprises a “reaction model” and a “kinetic model” to predict methane formation. Both approaches differ in their calculations and outputs as the “kinetic model” considers the modelling time to integrate temperature dependent biogenic methane formation in its calculations, whereas the “reaction model” simply relies on default organic matter degradation. With regard to the inorganic mineral–water–gas interactions, which are triggered by irreversible degradation of organic matter, PEaCH4 v.2.0 is based on chemical equilibrium thermodynamics, appropriate mass-action laws, and their temperature dependent equilibrium constants. The programme is exemplarily presented with the example of upwelling sediments off Namibia, ODP Leg 175, Site 1082. The application demonstrates that the modelling platform PEaCH4 v.2.0 provides a user-friendly, but complex scientific tool that delivers retraceable information about early diagenetic processes and products in marine sediments.

Environmental Factors Associated With Natural Methane Occurrence in the Appalachian Basin.

The recent boom in shale gas development in the Marcellus Shale has increased interest in the methods to distinguish between naturally occurring methane in groundwater and stray methane associated with drilling and production operations. This study evaluates the relationship between natural methane occurrence and three principal environmental factors (groundwater redox state, water type, and topography) using two pre-drill datasets of 132 samples from western Pennsylvania, Ohio, and West Virginia and 1417 samples from northeastern Pennsylvania. Higher natural methane concentrations in residential wells are strongly associated with reducing conditions characterized by low nitrate and low sulfate ([NO3- ] < 0.5 mg/L; [SO42- ] < 2.5 mg/L). However, no significant relationship exists between methane and iron [Fe(II)], which is traditionally considered an indicator of conditions that have progressed through iron reduction. As shown in previous studies, water type is significantly correlated with natural methane concentrations, where sodium (Na) -rich waters exhibit significantly higher (p<0.001) natural methane concentrations than calcium (Ca)-rich waters. For water wells exhibiting Na-rich waters and/or low nitrate and low sulfate conditions, valley locations are associated with higher methane concentrations than upland topography. Consequently, we identify three factors ("Low NO3- & SO42- " redox condition, Na-rich water type, and valley location), which, in combination, offer strong predictive power regarding the natural occurrence of high methane concentrations. Samples exhibiting these three factors have a median methane concentration of 10,000 µg/L. These heuristic relationships may facilitate the design of pre-drill monitoring programs and the subsequent evaluation of post-drill monitoring results to help distinguish between naturally occurring methane and methane originating from anthropogenic sources or migration pathways.