Variation Of Gas Content Research Articles

Research on an Equivalent Algorithm for Predicting Gas Content in Deep Coal Seams

This document introduces a novel equivalent algorithm for forecasting gas content within deep coal seams, which is subject to constraints stemming from the advancements and precision achieved in well and roadway engineering endeavors. This algorithm meticulously acknowledges that coal seam gas content comprises three fundamental components: the inherent gas emission rate of the equivalent stratum, the residual gas content retained within the coal seam itself, and the influence imparted by the gas content within the coal seam. Furthermore, the approach thoroughly considers variations in the level of porosity development within the coal seam and its surrounding rock formations, as well as the occurrence of gas within these structures. The equivalent layer is classified into two distinct groups: the sandstone zone and the clay zone. The sandstone zone utilizes pertinent parameters pertaining to fine sandstone, whereas the clay zone distinguishes between clay rock and thick mudstone. The influencing factor considerations solely encompass natural elements, such as the coal seam’s occurrence and geological structure. The residual gas content employs either existing measured parameters or acknowledged experimental parameters specific to the coal seam. Based on this predictive approach, an intelligent auxiliary software (V1.0) for mine gas forecasting was devised. The software calculates the gas content of deep coal seams within the mine at intervals of 100 m × 100 m, subsequently fitting the contour lines of gas content across the entire area. The gas content predictions derived from this equivalent algorithm demonstrate robust adaptability to variations in gas content caused by construction activities, and the prediction results exhibit an acceptable level of error on-site. Notably, the prediction process is not constrained by the progress of tunnel engineering, ensuring that the prediction outcomes can accurately represent the distribution characteristics of deep coal seam gas content. After a year of application, the prediction results have consistently met on-site requirements, providing a scientific foundation for the implementation of effective gas prevention and control measures in the mining area. Furthermore, this approach can effectively guide the formulation of medium- and long-term gas prevention and control plans for mines.

Petrophysical and Geochemical Investigation-Based Methodology for Analysis of the Multilithology of the Permian Longtan Formation in Southeastern Sichuan Basin, SW China

Against the backdrop of the national strategic goals of carbon peaking and carbon neutrality, the imperative for China’s low-carbon new energy transformation is evident. Emerging as an efficient and clean new energy source, the coal-based “three gases” (coalbed methane, tight sandstone gas, and shale gas) have gained prominence. Nevertheless, the current exploration of the coal-based “three gases” is limited to individual reservoirs, posing challenges to achieving overall extraction efficiency. The primary obstacle lies in the conspicuous disparities in gas content among different reservoirs, with the causes of such disparities remaining elusive. To address this issue, this study focused on the Permian Longtan Formation (coal, shale, and tight sandstone) in the southeastern Sichuan Basin. Through a comparative analysis of the mineral composition, organic geochemical features, and pore structure characteristics, this study aimed to delineate reservoir variations and establish a foundation for the simultaneous exploration and exploitation of the coal-based “three gases”. The research findings revealed that the differences in reservoir characteristics account for the variations in gas content among coal, shale, and tight sandstone. The mineral composition of the rock formations in the study area primarily consists of quartz, feldspar, clay minerals, pyrite, calcite, and dolomite. By comparison, the coal samples from the four major coal seams in the study area exhibited relatively large pore sizes, which are favorable for gas accumulation.

Study on gas content variation and main controlling of low-rank coal in Huanglong Jurassic coalfield

In order to study the controlled factors and variation of gas content in deep low-rank coal reservoirs, taking No.4 coal of Jurassic Yan’an Formation in Huanglong coalfield as an example, collects the production data and prepares the coal samples. Carrying out the coal rock and coal quality test and multi-temperature methane isothermal adsorption experiment to explore the influence of different temperature and pressure conditions on coal adsorption capacity, and analyzes the variation characteristics of gas content with burial depth combined with geological conditions. The results show that the sedimentary, structural and hydrogeological conditions have a certain influence on the formation and preservation of coalbed methane. The gas content increases with the increase of coalification degree and vitrinite content, and decreases with the increase of inertinite content, ash yield and volatile yield. With the increase of moisture, the gas content increased first and then decreased. When the pressure is less than 4 MPa, the adsorption capacity increases about 4-4.7m3/t with the increase of pressure, and the increasing trend slows down when the pressure is greater than 4 MPa. The adsorption capacity decreased more obviously with the increase of temperature when the temperature increased from 25°C to 35°C. Based on the prediction model of saturated adsorption capacity of deep coal reservoirs, it is found that there is a gas content critical conversion depth 800-900 m. The gas content shows a process of rapid increase (<800 m)-slow increase (800–900 m)-gradual decrease (>900 m) with the increase of burial depth. Below 800 m, the positive effect of reservoir pressure is dominant, and the gas content increases with burial depth. Above 900 m, the negative effect of reservoir temperature is dominant, and the gas content decreases with burial depth. The study results provide a theoretical basis for the development of deep low-rank coalbed methane resources.

Characterization of chemical and carbon isotopic compositions of gases during thermochemical sulfate reduction and implications for gas origin and content

For identifying the occurrence and extent of thermochemical sulfate reduction (TSR) reaction of natural gas and better understanding the chemical and carbon isotopic variations in natural gas reservoirs, high-pressure hydro-pyrolysis with a special designed apparatus was performed using natural gas and various amounts of MgSO4·7H2O at up to 360 °C. The yields, chemical and isotopic compositions of the gases produced during TSR and thermal cracking were measured. As the extent of TSR reaction increased, the concentrations of CH4, CO2 and H2S increased in a nonlinear way, while those of C2H6 and C3H8 decreased. According to the variation of gas content, the TSR reaction of alkane gases can be divided into an uncatalyzed and a catalyzed stage, which is different from previous studies that treated the TSR reaction of alkane gases as a non-autocatalytic reduction process. As the concentration of MgSO4·7H2O increased, the rate of TSR reaction with hydrocarbon gases increased. The concentrations of HSO4− and volume of aqueous phase could be responsible for the different TSR reaction rates in the catalyzed stage. The co-variation of ln(C1/C2) and ln(C2/C3) could be related to the TSR reaction of alkane gases. Our study provides clues for understanding the compositional variations in natural conditions.

Characteristics and Origins of the Difference between the Middle and High Rank Coal in Guizhou and Their Implication for the CBM Exploration and Development Strategy: A Case Study from Dahebian and Dafang Block

The coalbed methane (CBM) geology in Guizhou is characterized by a high gas content, pressure and resource abundance, indicating superior CBM resource potential. However, there are also many unfavorable factors, such as complex structure geology, significant regional differences in CBM geology, the widespread development of tectonically deformed coal, and the unclear understanding of the configuration of geological factors for CBM enrichment and high yield, which restrict the increase in CBM production and a large-scale development. Taking the Dahebian Block in Liupanshui coal field and the Dafang Block in Qianbei coal field as examples, this study presented the CBM geological differences between middle- and high-rank coals; their origins were analyzed and the effect of depth on gas content and permeability was discussed. A CBM enrichment and high-yield model was illustrated, and the geologic fitness-related exploration and development methods for Guizhou CBM were finally proposed. The results show that (1) significant differences between the middle- and high-rank coals occur in coal occurrence and distribution, coal qualities, and coal reservoir properties. Compared to Dahebian coal, Dafang coal has a higher coal rank, vitrinite content, and gas content, but a lower number of coal layers and permeability. (2) The sedimentary–tectonic evolution of the Longtan coal-bearing sequence is the fundamental reason for CBM geological differences between the Dadebian Block and Dafang Block, consisting of coal occurrence, qualities, maceral, rank, structure, and their associated reservoir properties. (3) The coordinated variation of gas content and permeability contributes to a greater depth for CBM enrichment and a high yield of the middle-rank coal. It is suggested that the best depths for CBM enrichment and high yield in Guizhou are 600–800 m for the middle-rank coal and 500 m for the high-rank coal, respectively. (4) Considering the bottleneck of inefficient CBM development in Guizhou, we proposed three CBM assessment and development technologies, including the CBM optimization of the classification–hierarchical optimization–analytical hierarchy, multiple coal seams commingling production with the pressure relief of tectonically deformed coal, and surface–underground CBM three-dimensional drainage development. The aim of this study was to provide new insights into the efficient exploration and development of CBM in Guizhou.

Tracing the evolution of dust-obscured activity using sub-millimetre galaxy populations from STUDIES and AS2UDS

ABSTRACT We analyse the physical properties of 121 SNR ≥ 5 sub-millimetre galaxies (SMGs) from the STUDIES 450 μm survey. We model their UV-to-radio spectral energy distributions using magphys+photo-z and compare the results to similar modelling of 850 μm-selected SMG sample from AS2UDS, to understand the fundamental physical differences between the two populations at the observed depths. The redshift distribution of the 450-μm sample has a median of z = 1.85 ± 0.12 and can be described by strong evolution of the far-infrared luminosity function. The fainter 450-μm sample has ∼14 times higher space density than the brighter 850-μm sample at z ≲ 2, and a comparable space density at z = 2–3, before rapidly declining, suggesting LIRGs are the main obscured population at z ∼ 1–2, while ULIRGs dominate at higher redshifts. We construct rest-frame ∼180-μm-selected and dust-mass-matched samples at z = 1–2 and z = 3–4 from the 450 and 850-μm samples, respectively, to probe the evolution of a uniform sample of galaxies spanning the cosmic noon era. Using far-infrared luminosity, dust masses, and an optically thick dust model, we suggest that higher redshift sources have higher dust densities due to inferred dust continuum sizes which are roughly half of those for the lower redshift population at a given dust mass, leading to higher dust attenuation. We track the evolution in the cosmic dust mass density and suggest that the dust content of galaxies is governed by a combination of both the variation of gas content and dust destruction time-scale.

Hydro-mechanical modelling of multiphase flowin naturally fractured coalbed using a multiscale approach

This paper presents a multiscale model developed for the modelling of multiphase flow in fractured reservoirs, particularly in coal seams during coalbed methane recovery (or carbon dioxide storage). The variation of gas content in the matrix induces a shrinkage/swelling of the material which is likely to affect the fractures and thus the permeability of the rock. In addition, the permeability is also sensitive to the effective stress evolution. In order to simulate the reservoir production taking into account the cleat-scale phenomena on their specific length, a cleat-scale model is used for the modelling of the Representative Elementary Volume (REV at microscale). This cleat-scale model is integrated in a multiscale approach using the finite element square method. It consists to localize the macroscale deformation to the microscale by applying appropriate boundaries, then resolve the boundary value problem on the microscale with finite elements, then homogenize the microscale stresses with appropriate averages to compute macroscopic quantities, and finally resolve the boundary value problem on the macroscale with finite elements. This approach has the advantage that it does not require to write some constitutive laws at the macroscale but only at the REV-scale. The model is developed and implemented in a finite element code and then used for reservoir modelling. A synthetic case is first considered to demonstrate the ability of the model to obtain some bell-shape production curves as expected for unconventional reservoirs. Finally, a history matching exercise is carried out.

Controls on Gas Domains and Production Behaviour in A High-Rank CSG Reservoir: Insights from Molecular and Isotopic Chemistry of Co-Produced Waters and Gases from the Bowen Basin, Australia

This paper uses hydrochemical and multi-isotope analysis to investigate geological controls on coal seam gas (CSG) saturation domains and gas well production performance in a high-rank (vitrinite reflectance (Rv) > 1.1) CSG field in the north-western Bowen Basin, Australia. New hydrochemical and stable isotope data were combined with existing geochemical datasets to refine hypotheses on the distribution and origins of CSG in two highly compartmentalized Permian coal seams. Stable isotopic results suggest that geographic variations in gas content, saturation and production reflect the extent of secondary microbial gas generation and retention as a function of hydrodynamics. δ13C and δ2H data support a gas mixing hypothesis with δ13C-CH4 increasing from secondary biogenic values to thermogenic values at depth (δ13C −62.2‰ to −46.3‰), whereas correlated methane and carbon dioxide carbon isotope compositions, Δ13C(CO2–CH4) values and δ13CDIC/alkalinity trends are largely consistent with microbial CO2 reduction. In addition, below 200 m, the majority of δ13C-CO2 values are positive (δ13C: −1.2‰ to 7.1‰) and δ13CDIC shows an erratic increase with depth for both seams that is characteristic of evolution via microbial activity. The progression of carbon isotope values along the CO2 reduction fractionation line suggests progressive depletion of the CO2 reservoir with increasing depth. Faults clearly segment coal seams into areas having significantly different production, with results of geochemical analysis suggesting that pooling of biogenic gas and waters and enhanced methanogenesis occur north of a faulted hinge zone.

Predicting gas content in high-maturity marine shales using artificial intelligence based seismic multiple-attributes analysis: A case study from the lower Silurian Longmaxi Formation, Sichuan Basin, China

Abstract Gas content is the most important index used to evaluate shale gas reservoirs. Compared to the North American marine shales, the marine shales of China are older, characterized by high thermal maturity, and have experienced multiple stages of tectonism. There is no clear positive correlation between the gas content and TOC content for marine shales in China; therefore, it is not feasible to indirectly predict the gas content by predicting TOC content, as has been extensively done for the North American shales. In this study, the geophysical responses of reservoirs with high gas contents, the factors that influence the gas content have been determined based on well log interpretation and seismic rock physics analysis. The seismic attributes and elastic parameters that are sensitive to the gas content have also been investigated. Additionally, a pre-stack seismic inversion has been carried out through a combination of well log and 3D seismic data to obtain the data volumes of the seismic elastic parameters, which are highly sensitive to variations in gas content. A seismic multiple-attribute analysis based on neural networks of AI (artificial intelligence) technology has been applied to determine the type and the combination of elastic parameters for computing the gas content data volume. This kind of analysis has been carried out based on pre-stack inversion of seismic data. The results suggest that the lower Silurian Longmaxi Formation, a high-quality gas-rich reservoir, is characterized by its low density, low Poisson's ratio and low velocity. A combination of six parameters or attributes optimally predicts gas content. The studied block, W202, generally has a high gas content. Two classes of sweet spots have been predicted in the study area based on these results. The application of neural networks has provided a precise prediction for the spatial distribution of gas saturation in the shale reservoir, serving as a basis for locating and designing horizontal wells for shale gas development.

Geological controls on variable gas concentrations: A case study of the northern Gujiao Block, northwestern Qinshui Basin, China

A systematic investigation was performed on the variation of gas content and its geological controls based on the diverse geological data and the experimental results of 72 coal samples from 24 coalbed methane (CBM) wells in the northern Gujiao Block, NW Qinshui Basin, China. Coal rank varies from low-volatile bituminous coal to medium-volatile bituminous coal, with maximum vitrinite reflectance (Ro,max) ranging from 1.21 to 1.92%. CBM in the northern Gujiao Block is mainly produced from the relatively thick coal seams (∼1.0 m-7.0 m), which are distributed in the Upper Carboniferous Taiyuan formation and Lower Permian Shanxi formation. The total gas content of coal seams ranges from 3.83 to 16.82 m3/t, with increasing gas content from marginal to central areas. Highly variable gas content reflects the comprehensive effect of various geological factors and coal reservoir properties. The results of the study show that the structural types, roof lithology, burial depth and hydrodynamic conditions are key factors controlling the gas content, whereas coal thickness and coal properties have no or little correlation with the gas content. In the northern Gujiao Block, three geological features controlling gas content are identified: 1) hydrodynamic trapping of gas in the graben structure with an adequate burial depth and impermeable roof, 2) gas loss by hydrodynamic flushing and normal faults in the syncline structure, and 3) gas migration by intensive movement of groundwater in the shallow burial area. The first mechanism is considered to cause the high gas content of central study area, whereas the other two mechanisms can explain the low gas content in the north-western and south-eastern regions.

Contribution of non-coal facies to the total gas-in-place in Mannville coal measures, Central Alberta

The contribution of non-coal, organic rich, fine grained lithofacies to total gas-in-place and producible gas in the Upper Mannville Group coal measures, has been investigated in the producing and prospective coalbed methane fairway in Alberta. Petrophysical well logs, core, fluid, and gas analyses of organic rich rocks have been evaluated in order to quantify the total gas-in-place resource that may be accessed by a horizontal well(s) completed in the thickest coal seam. Within a ±20m stratigraphic interval of the completed seam, significant additional gas storage exists in coal seams too thin to warrant separate completions and in organic rich, fine grained facies. Such gas, although not currently attributed to producible reserves, can reasonably be expected to be produced.Three non-coal, organic reservoir facies are recognised based on core desorption and laboratory analysis and are identified on log, through mainly a combination of the bulk density and gamma ray logs. The reservoir facies are carbonaceous mudstone (1.5–2.0g/cm3), organic rich mudstone (2.0–2.2g/cm3), and organic mudstone (2.2g/cm3–2.4g/cm3). The gas storage in the mudstone reservoir facies, similar to the coal, is mainly in the adsorbed state with minor amounts in solution within the water/brine, and in the free state within the pores and fractures. The average gas content from canister desorption of carbonaceous mudstone is 147scf/t,111cm3/g (SI unit) ≈ 34scf/t (oil field units, 15.6°C and 101kPs). organic rich mudstone is 83scf/t, and organic mudstone is 54scf/t. Gas in solution ranges from about 5scf/t for the carbonaceous mudstones to a low of 0.5scf/t for the organic mudstone reservoir facies. The measured as received porosity of the mudstones ranges from 2.5 to 14%.The organic matter in all lithologies is dominated by particulate carbonaceous material derived from vascular plants (Type III kerogen/vitrinite). The gas capacity of non-coal facies, as determined by adsorption isotherms, and gas content as determined by desorption analysis of core, increase with thermal maturity (rank), and percentage organic matter. Values for the carbonaceous mudstone approach those of coal.Regionally, the gas capacity and content of the coals and non-coal reservoir facies increases from northeast to southwest in parallel with the increase in current depth of burial and level of organic maturation (coal rank), although local variations exist. The gas composition of the coal and non-coal reservoir facies in the producing fairway is similar: the highest carbon dioxide contents occur in areas of highest and lowest maturity, whereas the percentage of heavier gases (C2–C5) increases with maturity/depth of burial. Anomalously high C2–C5 hydrocarbons (up to 10%) occur in the shallowest coal measures, which, in the absence of an alternate explanation, is attributed to migration. Isotopic composition of the methane has a thermogenic signature in the deepest strata, through mixed thermogenic–biogenic, to biogenic signatures at shallower depths.In order to quantify the stratigraphic and areal variation in gas content of the non-coal lithofacies in wells where no core exits, a protocol was developed that allows extrapolation of data from cored wells to non-cored wells of similar maturity and depth of burial using petrophysical logs. In the producing and prospective fairway within ±20m of the main coal seam, the net thickness of the carbonaceous mudstone facies varies from 0.3 to 9.3m and averages 2.7m. In this interval the organic rich mudstone ranges up to 7m thick and averages 2.6m and, the organic mudstone, ranges up to 7m thick and averages 2.7m thick.The total gas resource in the current area of production and in prospective areas was determined by applying the measured and calculated gas density (gas per unit volume) of the reservoir facies at estimated high median and low values to the net thickness of each facies in some 203 wells across the study area. The average well in the study area, using the estimate medium gas content, has a resource of 10.2BCF/mi2 (billions of cubic feet per square mile). Of the 10.2BCF/mi2, the contribution to the total gas-in-place of the thickest coal seam is 21%, the total cumulative coal is 57%, the carbonaceous mudstone facies is 21%, organic rich mudstone is 13%, and the organic mudstone is 9%.Most producing coalbed methane formations are similar to the Mannville coal measures in that they include non-coal organic rich lithologies that can be anticipated to have generated and retained hydrocarbons similar to coal. How much the non-coal lithologies will contribute to the producible ‘coalbed’ will vary with geology of the coal measures and the drilling and completion methods utilised. Not considering the contribution of non-coal facies to the gas resource and producible gas, will under value the resource and result in non-optimal field development.

Vertical and lateral variation of gas content associated with coal seams

Vertical and lateral gas content variation associated within a coal seam and its relation to porosity and geology was researched. Several seams of high sub-bituminous and bituminous coal volatile C from Amaga formation were selected. Channel samples were taken and were subdivided into the different plies (lithotypes associations), performing proximal analysis; Petrographic (maceral counting and determining the vitrinite reflectance); furthermore desorption testing and porosity.The higher gas content was in intermediate plies. It was possible to identify that the gas content, and micropores and mesopores has a direct relationship; also, there is a direct relationship between the content of liptinites macerals and gas content. In some cases, these relationships were not clear, since there is influence of geological factors such as the presence of faults favor migration and degassing of the mantles studied.

Stable isotopic and molecular composition of desorbed coal seam gases from the Walloon Subgroup, eastern Surat Basin, Australia

This study used compositional and stable isotopic analysis to test hypotheses on the distribution and origins of Walloon Subgroup coal seam gas (CSG) in the eastern Surat Basin, Queensland, Australia. The Middle Jurassic Walloon Subgroup play differs from many other low-rank CSG plays—particularly in methane carbon isotopic signature, i.e., the CSG is not as ‘microbial’ as could be expected. The carbon isotope compositions of desorbed methane from three cored appraisal wells fall within the generally accepted range for thermogenic or mixed gas (δ13C −58.5‰ to −45.3‰). The δ13C–CH4 values from stratigraphically placed coal core samples increased (became more ‘thermogenic’) from the top of the upper (Juandah) coal measures to the base of the Tangalooma Sandstone. Below the Tangalooma Sandstone, in the lower (Taroom) coal measures, the δ13C–CH4 values decreased with increasing depth. These positively parabolic δ13C profiles tracked total measured gas content in two out of the three wells studied. The third well displayed lower variance of δ13C–CH4 and gas content increased uniformly with depth.A genetic classification based on methane stable carbon isotopes alone might interpret this pattern as a transition from microbially- to thermogenically-sourced methane in the central coal seams. However, a δ13C–CO2 profile for one well tracks total gas content and δ13C–CH4, and exhibits an inverse relationship with δD–CH4. These results, together with the mostly dry nature of the gas samples [(C1/(C2+C3)) ratios up to ~10,000] and relatively uniform δD–CH4 values (δD −238‰ to −202‰), suggest that microbial CO2 reduction is the primary source of Walloon Subgroup methane. As such, stratigraphic variations in gas content mainly reflect the extent of microbial methanogenesis. We suggest that peak microbial utilisation of H2–CO2 occurred at the Tangalooma Sandstone level, enriching the residual CO2 pool and derived methane in 13C. Carbon [Δ13C(CO2–CH4)] and deuterium isotopic differences [ΔD(H2O–CH4)], and cross-plots of δD–H2O and δ18O–H2O are also consistent with kinetic isotope fractionation during microbial-mediated carbonate reduction. The results are relevant for applying microbially enhanced coal bed methane (MECoM) in the Surat Basin.

Application of ground‐penetrating radar to measure near‐saturation soil water content in peat soils

The presence and flux of biogenic methane‐rich free phase gas that is eventually released to the atmosphere influence water content (θ) of peat soils below the water table. Small variations in gas content in peat soils at near‐saturation θ could be inferred by changes in dielectric permittivity, but detailed measurements in that range of θ needed to develop calibration functions are lacking. Our experiment uses a new method for varying θ in the sample using elevated pressure to reduce the naturally occurring volumetric gas content in a manner similar to what occurs in situ under atmospheric pressure change, which relevant to understanding carbon gas cycling in peatlands. We recorded dielectric permittivity using a 1.6 MHz ground‐penetrating radar antenna at multiple water contents between 0.87 and 0.95 m3 m−3 on four peat monoliths with varying levels of humification and with <5% gas content as is commonly observed in the field. We identified empirical equations that were linear over the range of θ investigated and optimized a dielectric mixing model for estimating θ from GPR. These results indicate that there are differences in the permittivity‐θ relationships developed between peat samples and suggest that variability in dielectric relationships may be attributed to peat structure and particle orientation. The empirical relationships developed in this study confirm the utility of previously applied multiphase mixing models for estimating peat properties using methods sensitive to dielectric permittivity. This work is relevant to studies of gas content in peat and the role of peatlands in the carbon cycle.

Geophysical evidence for the lateral distribution of free phase gas at the peat basin scale in a large northern peatland

[1] Northern peatlands contribute to the global carbon cycle by way of gas emissions in the form of biogenic carbon dioxide and methane originating in the subsurface. Determining how much gas is present and where it is trapped is essential to understanding the role of northern peatlands on the global carbon cycle, particularly in regard to methane cycling. In this study, spatial variability in free phase gas content was estimated using ground penetrating radar (GPR) along a 1.4 km transect crossing distinct peat landforms including a bog crest, midslope lawn, and fen. Variations in gas content and distribution were observed in landforms crossed by this transect. Estimated gas content up to 25% by volume was observed in landforms dominated by woody surface vegetation. In areas of the midslope lawn, the estimated gas content was greater than 15%, while estimated gas contents between 0% and 7% were found in the fen. Changes in estimated gas content of up to 20% were observed over distances of 100 m across a transition between a stand of 10 m tall trees and an adjacent fen. The mean of the estimated errors in gas content is 1.3%, suggesting that these large changes in estimated gas content between landforms can be clearly determined using geophysical methods. A geophysical image of the distribution of free phase across this transect reveals evidence for gas storage in deep peat in intervals as thin as 0.35 m. These data support conceptual models based on accumulation and storage of free phase gas in deep peat.

Gas composition of the surface air in Moscow during the extreme summer of 2010

In summer 2010, anomalously hot weather occurred in the European part of Russia. It was caused by a blocking anticyclone of an unusually high intensity. West winds were stopped in the whole column of the troposphere, from the Earth's surface up to the lower stratosphere, for two months. During this entire period, the concentration of gaseous and aerosol pol� lutants grew in the nearsurface air. In the end of July and the first half of August, this extreme situation become even more complicated due to the arrival of air masses from the areas of forest, peat, and grass fires to Moscow. By the measurements data from the station of the Institute of Physics of the Atmosphere, Russian Academy of Sciences (IPA RAS), the concentrations of reactive gases NO, NO 2 , CO, and O 3 exceeded both the average daily and the general maximum permissi� ble concentration (MPC). The concentrations of greenhouse gases CO2, CH4, and other hydrocarbons were also excessive. Analysis of variation in gas content in the nearsurface air and in the atmospheric bound� ary layer has shown a close dependence on vertical stratification of the atmosphere. The blocking anticyclone above the European part of Russia recorded in summer 2010 significantly exceeded all the previously recorded ones in its dura� tion. According to (1), the duration of summer block� ing anticyclones in the Northern and Southern Hemi� spheres has not exceeded three weeks for the last forty years, while the longest periods of anticyclonic weather in winter have not lasted more than a month. Anomalies in the frequency and intensity of atmo� spheric blockings were recorded most often in the years of El Nino/La Nina phenomenon, including 2010 (see, for instance, (2)). The formed hot weather lead to the outbreak of numerous forest and peat wildfires. In total, 29 000 wild� fires were recorded in summer 2010 with a total burned area of 1.2 million ha (3). And though the wildfire intensity in 2010 was weaker than in some other years (e.g., 40 000 wildfires with a total burned area of about 1.5 million ha were recorded in 1972; 28 000 wildfires of 4.2 million ha, in 1998; 29 000 wildfires of 2.4 mil� lion ha, in 2009), the economic, ecological, and social consequences were more significant. The most important consequence of the emer� gency situation that appeared in summer 2010 was change in the chemical composition of the atmo� sphere above the European territory of Russia and West Siberia. Cities and settlements were covered with a dense haze when they happened to be in smoke trails of forest and peat wildfires. The presence of obviously extreme quantities of aerosols in the nearsurface air caused extreme concern and a demand for introduc� tion of required protective activities (3). No less nega� tive an effect on people's health and ecosystems was made by a significant change in gas composition of the atmosphere.

Variation of Gas Content in Coalbed Methane Development

At present, the variation of gas content resulted from the surface coalbed methane (CBM) development has not been reported at home. It is introduced that adopting the CBM-SIM software and combining with the key oil and gas special research task, the productivity prediction and reservoir simulation analysis of the impact and variation of the CBM in the surface CBM development process are conducted respectively in the Sihe north block and Chengzhuang block of the Jincheng mining area. Combined with the measured results of the gas content in the inspect well on the drainage effect after 5 years on the surface CBM development in the Sihe north block, the variation rules of the CBM in the surface coalbed methane development process are discussed and researched.

Variations in pore characteristics in high volatile bituminous coals: Implications for coal bed gas content

Abstract The Seelyville Coal Member of the Linton Formation (Pennsylvanian) in Indiana was studied to: 1) understand variations in pore characteristics within a coal seam at a single location and compare these variations with changes occurring between the same coal at different locations, 2) elaborate on the influence of mineral-matter and maceral composition on mesopore and micropore characteristics, and 3) discuss implications of these variations for coal bed gas content. The coal is high volatile bituminous rank with R 0 ranging from 0.57% to 0.60%. BET specific surface areas (determined by nitrogen adsorption) of the coals samples studied range from 1.8 to 22.9 m 2 /g, BJH adsorption mesopore volumes from 0.0041 to 0.0339 cm 3 /g, and micropore volumes (determined by carbon dioxide adsorption) from 0.0315 to 0.0540 cm 3 /g. The coals that had the largest specific surface areas and largest mesopore volumes occur at the shallowest depths, whereas the smallest values for these two parameters occur in the deepest coals. Micropore volumes, in contrast, are not depth-dependent. In the coal samples examined for this study, mineral-matter content influenced both specific surface area as well as mesopore and micropore volumes. It is especially clear in the case of micropores, where an increase in mineral-matter content parallels the decrease of micropore volume of the coal. No obvious relationships were observed between the total vitrinite content and pore characteristics but, after splitting vitrinite into individual macerals, we see that collotelinite influences both meso- and micropore volume positively, whereas collodetrinite contributes to the reduction of mesopore and micropore volumes. There are large variations in gas content within a single coal at a single location. Because of this variability, the entire thickness of the coal must be desorbed in order to determine gas content reliably and to accurately calculate the level of gas saturation.

EFFECT OF GAS CONTENT ON THE OSCILLATION OF A LASER-INDUCED CAVITATION BUBBLE

The oscillation of a cavitation bubble and the effect of gas content inside a cavity on the bubble motion are investigated by theory and experiment. Based on the cavitation model, the numerical study yields the gas content dependence of the amplitude and duration of the bubble oscillation in liquids. In experiment, the temporal oscillation of a single laser-induced cavitation bubble is obtained by means of a sensitive fiber-optic sensor based on optical beam deflection. The characteristic bubble parameters are determined, including the maximum (minimum) radii, oscillation duration and bubble energy, which all decrease with the oscillation. Besides, combining the cavitation theory with experimental data, the variation of gas content within the bubble during each oscillation is estimated, which increases with the oscillation cycle. Our results reveal the competitive interplay of the bubble energy and gas content during the bubble motion and the bubble energy in effect outweighs the latter.

An X‐Ray Survey of Galaxies in Pairs

Results are reported from the first survey of X-ray emission from galaxies in pairs. The sample consists of fifty-two pairs of galaxies from the Catalog of Paired Galaxies Karachentsev (1972) whose coordinates overlap ROSAT Position Sensitive Proportional Counter pointed observations. The mean observed log l_x for early-type pairs is 41.35 +/-0.21 while the mean log l_x predicted using the l_x-l_b relationship for isolated early-type galaxies is 42.10 +/-0.19. With 95% confidence, the galaxies in pairs are underluminous in the X-ray, compared to isolated galaxies, for the same l_b. A significant fraction of the mixed pair sample also appear similarly underluminous. A spatial analysis shows that the X-ray emission from pairs of both types typically has an extent of ~10 - 50 kpc, much smaller than group intergalactic medium and thus likely originates from the galaxies. CPG 564, the most X-ray luminous early-type pair, 4.7x10^42 ergs/sec, is an exception. The extent of it's X-ray emission, >169 kpc, and HWHM, ~80 kpc, is comparable to that expected from an intergalactic medium. The sample shows only a weak correlation, ~81% confidence, between l_x and l_b, presumably due to variations in gas content within the galaxies. No correlation between l_x and the pair velocity difference, separation, or far-infrared luminosity is found though the detection rate is low, 22%.