Methane Saturation Research Articles

Occurrence and Potential for Coalbed Methane Extraction in the Depocenter Area of the Upper Silesian Coal Basin (Poland) in the Context of Selected Geological Factors

Coalbed methane (CBM) is the only unconventional gas in Poland with estimated recoverable resources. The prospects for developing deep CBM have been explored in recent years by drilling deep exploration wells within the depocenter of the Upper Silesian Coal Basin. The purpose of this study is to analyze the occurrence and potential for CBM extraction in this area of the basin, which can be considered prospective due to the confirmed presence of significant amounts of gas and thick coal seams at depths > 1500 m. The study examined the vertical and horizontal variability of the gas content in the studied area, the coal rank in the seams, thermal conditions, and coal reservoir parameters. The gas content in the seams, reaching more than 18 m3/t coaldaf at a depth of 2840 m, and indicative estimated gas resources of 9 billion m3 were found. The high gas content is accompanied by positive thermal and coal rank anomalies. The permeability and methane saturation of the coal seams are low, and therefore, potential methane production may prove problematic. However, the development of CBM extraction technologies involving directional drilling with artificial fracturing may encourage gas production testing in the study area.

Forecast of the Maximum Methane Concentration in the Longwall Outlet and in the Ventilation Roadway. Case Study

Abstract The mining process of the coal seam wall is accompanied by the release of methane into the mine atmosphere. This process is highly variable and depends on the methane content in the seam and the methane saturation of the rocks surrounding the seam. This is the specificity of the Polish hard coal mining industry. In the article, prognostic formulas for the maximum methane concentration at the outlet of the longwall ventilation gallery were developed. In the presented article, these formulas were used to predict methane concentration at the longwall outlet and in the ventilation gallery at a distance of up to 10 m in front of the longwall. In order to assess the accuracy of the forecasts, their results were compared with the forecast at the exit of the ventilation roadway. The obtained results are so accurate that it is worth repeating this type of check also using measurements in other longwalls. It will allow to reduce the risk of methane explosion during operation.

Direct method to estimate the gas loss characteristics and in-situ gas contents of shale

The commonly used direct methods for the lost gas and in-situ gas content estimation of shale usually follow the assumptions and mathematical models that were originally established for coalbed. The essential differences in formation fluid compositions, coring and on-site desorption processes, governing equations on gas release, and model parameters between shale and coal are not comprehensively analyzed for these available direct methods, therefore, they cannot fully reflect the gas loss characteristics of shale and are also inaccurate for geological reserves calculation. In this paper, the modified lost gas content calculation method is constructed by analyzing the general coring and on-site desorption processes of shale. This method simultaneously depicts the loss characteristics of free and adsorbed gas. It can be summarized that the initial adsorbed gas concentration, time-dependent gas diffusion coefficient, time-dependent desorbed gas concentration at the core boundary, core size, porosity, methane saturation, formation temperature, and formation pressure are the influencing parameters for accurate in-situ shale gas content calculation. Herein, the estimation or optimization methods for some of these parameters are presented. The fitting results manifest that the newly presented method shows satisfactory applicability in gas loss curve prediction and in-situ gas content estimation based on single and twice heating on-site desorption data. It is found that some existing direct methods may exhibit anomalies or stability problems in shale gas loss curve characterization, therefore, the assumption reasonability and mathematical-physical law consistency of these methods should be further confirmed. By contrast, the assumptions of the new method are closer to the practical shale coring, especially the simultaneous loss of free and adsorbed gas as well as the introduction of time-dependent parameters, laying the foundation for a more accurate gas loss curve prediction and geological reserves calculation for shale.

Study of CO2 injection to enhance gas hydrate production in multilateral wells

Multilateral wells offer promising opportunities for the commercial development of natural gas hydrates. The reservoir strength and stiffness weaken as hydrates decompose during the depressurization production process, potentially leading to formation subsidence, seabed inclination, and other associated geomechanical risks. Thus, understanding the geomechanical issues surrounding the wellbore is crucial for attaining safe and efficient hydrate development. This paper develops a three-dimensional numerical model to simulate the production capacity of hydrate reservoirs through CO2 injection in multilateral wells. The study compares the pressure and temperature response of the reservoir, the characteristics of gas and water production, the variation in hydrate and methane saturation, the productivity, and the geological subsidence patterns during the extraction process. Results indicate that hydrates generated through CO2 injection inhibit methane hydrate decomposition, with delayed injections resulting in higher cumulative yields. CO2 injection can restore reservoir pressure and mitigate formation subsidence. The combined depressurization method, which involves CO2 injection in multilateral wells, can increase hydrate production while preserving formation stability, offering a potential approach for commercial hydrate exploitation. This approach is anticipated to advance the industrialization of gas hydrate extraction and propose a new possibility for CO2 utilization to curb climate change.

Leakage and diffusion behavior of a buried pipeline of hydrogen-blended natural gas

Buried pipelines are one method of conservation transfer for widely used gases such as natural gas and hydrogen. The safety of these pipelines is of great importance because of the potential leakage risks posed by the flammable gas and the special properties of the hydrogen mixture. Estimating the leakage behavior and quantifying the diffusion range outside the pipeline are important but challenging goals due to the hydrogen mixture and presence of soil. This study provides essential information about the diffusion behavior and concentration distribution of underground hydrogen and natural gas mixture leakages. Therefore, a large-scale experimental system was developed to simulate high-pressure leaks of hydrogen mixture natural gas from small holes in three different directions from a pipeline buried in soil. The diffusion of hydrogen-doped natural gas in soil was experimentally measured under different conditions, such as different hydrogen mixture ratios, release pressures, and leakage directions. The experimental results verified the applicability of the gas leakage mass flow model, with an error of 6.85%. When a larger proportion of a single component was present in the hydrogen-doped natural gas, the leakage pressure showed a greater diffusion range. In addition, the diffusion range of hydrogen-doped natural gas in the leakage direction was larger at 3 o'clock than that at 12 o'clock. The hydrogen blend carried methane and diffused, which shortened the methane saturation time. Moreover, a quantitative relationship between the concentration of hydrogen-doped natural gas and the diffusion distance over which the hydrogen-doped natural gas reached the lower limit of the explosion was obtained by quantitative analysis of the experimental data.

Dissolved Methane in Coastal Waters of the Northeastern Black Sea

As the largest methane reservoir in the world, the Black Sea is characterized by significant variability in its dissolved methane distribution patterns. Aerobic waters in the coastal regions are influenced by various factors governing the biogeochemical processes in the water column; however, their impact on the distribution pattern of dissolved methane is not always well studied, especially in the shallow areas of the northeastern Black Sea, which have hitherto not been thoroughly covered by observations. Here, we consider the measurements of methane content in several regions of the northeastern Black Sea carried out from 2013–2017 with large and detailed spatial coverage in order to identify the key factors determining the dissolved methane pattern in each region of the study area. The CH4 pattern in the region of Sochi is dominated by the impact of river flow. The increased methane saturation in surface waters of the southeastern Crimean shelf (up to 40 nM) is caused by the influence of the Azov Sea outflow. The waters of the Feodosia Bay and to the south of it are mainly characterized by an increase in methane content towards the bottom (up to 100 nM), which is associated with water–sediment interactions and gas emission from the bottom.

Shelf-Sourced Methane in Surface Seawater at the Eurasian Continental Slope (Arctic Ocean)

This study traces the pathways of dissolved methane at the Eurasian continental slope (ECS) and the Siberian shelf break based on data collected during the NABOS-II expedition in August-September, 2013. We focus on the sea ice-ocean interface during seasonal strong ice melt. Our analysis reveals a patchy pattern of methane supersaturation related to the atmospheric equilibrium. We argue that sea ice transports methane from the shelf and that ice melt is the process that causes the heterogeneous pattern of methane saturation in the Polar Mixed Layer (PML). We calculate the solubility capacity and find that seasonal warming of the PML reduces the CH4 storage capacity and contributes to methane supersaturation and potential sea-air flux in summer. Cooling in autumn enhances the solubility capacity in the PML once again. The shifts in the solubility capacity indicate the buffering capacity for seasonal storage of atmospheric and marine methane in the PML. We discuss specific pathways for marine methane and the storage capacity of the PML on the ECS as a sink/source for atmospheric methane and methane sources from the Siberian shelf. The potential sea-air flux of methane is calculated and intrusions of methane plumes from the PML into the Cold Halocline Layer are described.

Геохімія флюїдів: інноваційне вирішення фундаментальної проблеми

First of all, was developed a reliable mass spectrometric method for studying fluid inclusions in minerals (on the basis of the author’s certificate of the USSR No. 454446 of 1974 for the invention of the “device for cleaning the content inclusions of solid materials”). Were created and published new scientific directions: 1. Thermobarometry and geochemistry of gases of veinlet-impregnated mineralization in sediments of oil and gas regions and metallogenic provinces. 2. Bowels of the Earth – natural physicochemical reactor. Was developed a “method (technology) for determining the prospects of oil and gas bearing of the local area” and “a method (technology) of local forecasting of enriched areas of gold-ore fields” (together with M. M. Davydenko). Was established unknown before, but objectively existing phenomenon of the material world: 1) “lack of molecular hydrogen in inclusions in minerals in the bowels of the planet Earth” (together with V. A. Kaliuzhny). Independently were established: 2) previously unknown “property of deep abiogenic methane-termobar high-temperature fluid decompose-convert natural organic residues into layers of coal with their simultaneous methane saturation and its conservation in the earth’s crust of the planet Earth”; 3) previously unknown natural “phenomenon of arbitrary formation of natural carbon methane in the coal layers of the earth’s crust of the planet Earth under the influence of abiogenic methane-containing high-temperature fluid with their conservation in them”; 4) previously unknown different chemical properties of carbon isotopes in natural processes of synthesis-formation of various carbon-containing compounds ...; 5) “previously unknown pattern of natural processes of synthesis of perfect diamond crystals from astenospheric carbon dioxide ions...”. Was justified “a new way to determine the calorification of natural gas supplied to consumers and its cubic-metre barometry”.

Effects of Methane Saturation and Nitrogen Pressure on N2–Enhanced Coalbed Methane Desorption Strain Characteristics of Medium-Rank Coal

To understand the characteristics of medium-rank coal reservoir desorption in N2–enhanced coalbed methane (N2–ECBM), three groups of nitrogen injection–sealing–desorption strain tests, including atmospheric pressure and successive decreasing outlet pressure (SDOP) desorption, methane saturation and I/A pressure ratio tests (nitrogen injection pressure/methane adsorption pressure), were carried out with four coal samples using an adsorption/desorption strain instrument designed in-house. The results showed that atmospheric pressure desorption cannot represent the samples’ desorption characteristics during the process of reservoir drainage, and the test data for desorption shrinkage strain were 20–40% less than the SDOP desorption data. The average shrinkage/swelling strain ratios (SSRs) during the nitrogen sealing of the samples were directly proportional to the sample saturation. The shrinkage strain in samples with high methane saturations was assumed to arise from methane desorption in the micropore system. When the I/A pressure ratios were 2.3, 1.75 and 1.4, the cumulative SSR of the nitrogen sealing and the SDOP desorption were 198.01%, 118.07%, and 104.06%, respectively; the shrinkage strain was produced mainly during the nitrogen sealing stage. The relationship between the shrinkage/swelling strain and the volume of adsorbed/desorbed gas was a polynomial, while the relationship between the shrinkage strain and time was a negative exponential function. The shrinkage strain rate (the relationship between shrinkage strain and time) was affected by gas saturation and I/A pressure ratio. With increasing gas saturation, the shrinkage strain rate gradually decreased and then increased with increasing I/A pressure ratio. N2–ECBM was more effective for high-saturation and low-gas-content coal reservoirs. This work revealed the properties of desorption rate and strain deformation in N2–ECBM, providing guidance for N2–ECBM of medium-rank coal.

Mathematical model of methane driven by hydraulic fracturing in gassy coal seams

During hydraulic fracturing in gassy coal, methane is driven by hydraulic fracturing. However, its mathematical model has not been established yet. Based on the theory of ‘dual-porosity and dual-permeability’ fluid seepage, a mathematical model is established, with the cleat structure, main hydraulic fracture and methane driven by hydraulic fracturing considered simultaneously. With the help of the COMSOL Multiphysics software, the numerical solution of the mathematical model is obtained. In addition, the space–time rules of water and methane saturation, pore pressure and its gradient are obtained. It is concluded that (1) along the direction of the methane driven by hydraulic fracturing, the pore pressure at the cleat demonstrates a trend of first decreasing and later increasing. The pore pressure gradient exhibits certain regional characteristics along the direction of the methane driven by hydraulic fracturing. (2) Along the direction of the methane driven by hydraulic fracturing, the water saturation exhibits a decreasing trend; however, near the cleat or hydraulic fracture, the water saturation first increases and later decreases. The water saturation in the central region of the coal matrix block is smaller than that of its surrounding region, while the saturation of water in the entire matrix block is greater than that in the cleat or hydraulic fracture surrounding the matrix block. The water saturation at the same space point increases gradually with the time progression. The space–time distribution rules of methane saturation are contrary to those of the water saturation. (3) The free methane driven by hydraulic fracturing includes the original free methane and the free methane desorbed from the adsorption methane. The reduction rate of the adsorption methane is larger than that of free methane.

Analysis of methane hazard in longwall working equipped with a powered longwall complex

Most of currently exploited hard coal seams has a very high degree of methane saturation. Consequently, the mining process of such deposits generates substantial amounts of methane. This in turn increases the risk of fire and/or explosion of this gas. Methane hazard is currently one of the most dangerous threats occurring in the process of underground mining exploitation. In particular, this applies to longwall excavations where the rock mass mining process generates the highest level of this gas. Commonly used high-performance longwall complexes cause an increase in the amount of coal output, which also causes an increase in the amount of methane released. In order to prevent hazardous concentrations, appropriate ventilation systems and atmosphere monitoring in mining excavations are used. The paper discusses currently used methods designed to limit risks caused by methane such as methane drainage. The paper presents an example of the use of an innovative method of analysing methane risk status and measures aimed at minimizing it. The developed method is based on air parameters in the actual mining area which were then used to create a method of ventilation for such excavations. The method combines advanced model analysis and experience of mine employees and integrates academic and practical knowledge. The main objective of the activities presented in the article was to improve the safety of mining operation

Bulk density and bulk modulus of adsorbed coalbed methane

The bulk density and bulk modulus of adsorbed coalbed methane are required to calculate the undrained bulk and shear moduli as well as the fluid-saturated density of the coal reservoir. We derived the formula for the bulk modulus and bulk density of adsorbed methane using the Langmuir equation for isothermal adsorption. The bulk density of adsorbed methane is positively correlated with the gas pressure and Langmuir volume, but it is negatively correlated with the Langmuir pressure and adsorbed methane saturation. The bulk density of adsorbed methane is greater than that of free-state methane for the same gas pressure. The bulk modulus of adsorbed methane is positively correlated with the gas pressure and negatively correlated with the Langmuir pressure; it is much larger than that of free methane, but it is still much smaller than that of water within the normal gas pressure range. Coal samples from the study area demonstrate that the water saturation is less than 95%. Considering adsorbed methane as a pseudosolid, calculations yield a very small difference in the bulk modulus of coal under room-dry conditions. Considering adsorbed methane as a gas, calculations based on spatially uniform or patchy saturation indicate that multiphase fluid saturation produces a very small difference in the elastic parameters and wave velocity of the fluid-saturated coal from the dual-phase fluid (water and free methane).

Adaptation of fluid inclusion techniques for investigating gas charge – examples from the Caswell Sub-basin, Browse Basin, Australia

Abstract Palaeoformation water trapped in quartz cements in sandstone during diagenesis is typically of interest for constraining the temperature history, cementation and timing of hydrocarbon charge. Recent progresses in developing methods for salinity measurement, gas detection (CH 4 , CO 2 , N 2 , H 2 S) and fluid modelling of the CH 4 –H 2 O–NaCl system by combining conventional microthermometry techniques with Raman spectroscopy provide powerful tools for investigating formation water and its evolution in gas-bearing basins. Samples from the aquifer, in the Plover Formation and in the Brewster Member in the Upper Vulcan Formation, underlying large gas accumulations in the Caswell Sub-basin provided an opportunity to test these new techniques and generate data on formation water evolution. Temperature of homogenization, salinity and gas content of water inclusions show that the salinity of the palaeoformation waters decreased with increasing methane content and temperature. Detection of CO 2 shows, however, that water inclusions with dissolved CO 2 , often in association with CH 4 , do not follow the same salinity trend. These inclusions are often associated with higher trapping temperatures. The salinities associated with water reaching methane saturation (coeval with free gas) are between 8500 and 24 000 ppm eq. NaCl (0.8–2.4 wt%). An influx of meteoric water from the Ashmore Platform in the north is presented as a hypothesis on the origin of the low salinities of the formation water in the Plover Formation in the Browse Basin, supported by the distribution of the lowest palaeowater salinities, but still remains problematic.

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

Comparison of Methane Control Methods in Polish and Vietnamese Coal Mines

Methane hazard often occurs in hard coal mines and causes very serious accidents and can be the reason of methane or methane and coal dust explosions. History of coal mining shows that methane released from the rock mass to the longwall area was responsible for numerous mining disasters. The main source of methane are coal deposits because it is autochthonous gas and is closely related with carbonification and forming of coal deposits. Degree of methane saturation in coal deposits depends on numerous factors; mainly on presence or lack of insulating layers in cover deposit that allow or do not on degasification and easily methane outflow into surroundings. Hence in coal mining there are coal deposits that contain only low degree of methane saturation in places where is lack of insulating layers till high in methane coal deposits occurring in insulating claystones or in shales. Conducting mining works in coal deposits of high methane hazard without using of special measures to combat (ventilation, methane drainage) could be impossible. Control of methane hazard depends also on other co-occuring natural dangers for which used preventive actions eliminate methane hazard. Safety in mines excavating coal deposits saturated with methane depends on the correct estimation of methane hazard, drawn up forecasts, conducted observations, hazard control as well as undertaken prevention measures. Methane risk prevention includes identification and control methods of methane hazards as well as means of combating the explosive accumulation of methane in longwall workings. The main preventive actions in underground coal mines are: effective ventilation that prevents forming of methane fuses or placed methane accumulation in headings ventilated by airflow created by main fans and in headings with auxiliary ventilation, methane drainage using drain holes that are drilled from underground headings or from the surface, methanometry control of methane concentration in the air; location of the sensors is defined by law, additional ventilation equipment used in places of lower intensity of ventilation and places where methane is concentrated.

Comparison of Three Key Marine Shale Reservoirs in the Southeastern Margin of the Sichuan Basin, SW China

This study performs a comprehensive comparison of three key marine shale reservoirs in the southeastern margin of the Sichuan Basin, and explains why commercial gas production was only achieved in the Lower Silurian Longmaxi (LSL) and Upper Ordovician Wufeng (UOW) formations, but not in the Lower Cambrian Niutitang (LCN) formation. The experimental methods included in situ gas content and gas composition tests, methane adsorption analysis, low-pressure N2 adsorption, field emission scanning electron microscopy (FE-SEM), and total organic carbon (TOC) and vitrinite reflectance (Ro) analyses to evaluate the lithology, mineralogy, physical properties of the reservoir, organic geochemistry, in situ gas content and methane adsorption capacity characteristics of the three shales. The LCN shale has lower quartz and clay mineral contents and a low brittleness index, but higher contents of feldspar, pyrite and carbonate minerals than the LSL and UOW shales. The porosity and permeability of the LSL and UOW shales are higher than those of the LCN shale. The primary contributions to the high permeability in the LSL shale are its well-developed fractures and organic matter pores. In contrast, the over-mature LCN shale is unfavorable for the development of organic pores and fractures. Although the LCN shale has a higher methane sorption capacity than the LSL and UOW shales, the gas content and methane saturation of the LCN shale are distinctly lower than those of the LSL and UOW shales. This is primarily due to gas migration from the LCN shale, resulting from the activities of tectonic uplift and the unconformable contact between the LCN shale and the Dengying formation. When compared with gas shale in North America, the LSL shale is the most favorable shale reservoir out of the three Sichuan shales, while the combination of the LSL and UOW shales is also potentially productive. However, the individual single layer production of the UOW or LCN shales is still limited due to poor resource potential and/or reservoir physical characteristics in the study area.

High pressure rheological measurements of gas hydrate-in-oil slurries

Gas hydrates are ice-like solids that may form in crude oil flowlines under high pressure and at low temperature, resulting in the formation of viscous hydrate-laden oil slurries. The magnitude of the slurry viscosity has been suggested as a primary means of determining the risk and severity of flow blockage, but there is a dearth of data available to calibrate predictive models of hydrate-in-oil slurry viscosity. This work deploys a controlled-stress, high-pressure rheometer to characterize the rheological properties of methane hydrate-in-crude oil slurries, which were generated in situ from water-in-oil emulsions. A vane blade rotor was found to maintain sufficient methane saturation in the oil phase during the hydrate growth period to allow near full conversion of the water. Dynamic measurements with the rheometer were able to separate the contributions to the viscosity change as the emulsion converted to a hydrate slurry due to (i) formation of the solid particles and (ii) reduction of the methane content in the oil continuous phase. For 5–30 vol% watercut systems, the slurry viscosity increased between 20 and 60 times during hydrate growth, whereas, under equivalent conditions for a 20% watercut emulsion, the viscosity increase due to the desaturation of methane from the oil phase was less than a factor of two. The steady-state hydrate-in-oil slurry demonstrated shear thinning behavior at both 1 and 5° C. The measured slurry relative viscosity deviated between 12 and 212% from the current industry-standard hydrate-in-oil slurry viscosity model, indicating the need for model improvement. After an eight-hour annealing period to simulate subsea shut-in, the yield stress of the hydrate-in-oil slurries varied between 3 and 25 Pa over 5 to 25 vol% hydrate.

Permeability from time dependent methane saturation monitoring in shales

In this paper, we demonstrate the possibility to monitor the methane gas saturation of a shale sample down to fraction of percent porosity using a standard low field NMR core analyser instrument with a proton Larmor frequency of 2.2 MHz. The spontaneous shale gas production at ambient condition, following a saturation at 2000 psi (138 Bar), is monitored in near real time with T2 distributions acquired every few minutes for several days. The obtained dataset shows that gas produces with multiple characteristic rates even for single T2 populations. A model to convert remaining gas signal decays into permeability values is proposed, allowing to determine multiple permeabilities for each T2 and whole samples. The permeabilities calculated on full signal are in reasonably good agreement with pressure decay measurements on the same cores.

Influence of infrastructure on water quality and greenhouse gas dynamics in urban streams.

Streams and rivers are significant sources of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) globally, and watershed management can alter greenhouse gas (GHG) emissions from streams. We hypothesized that urban infrastructure significantly alters downstream water quality and contributes to variability in GHG saturation and emissions. We measured gas saturation and estimated emission rates in headwaters of two urban stream networks (Red Run and Dead Run) of the Baltimore Ecosystem Study Long-Term Ecological Research project. We identified four combinations of stormwater and sanitary infrastructure present in these watersheds, including: (1) stream burial, (2) inline stormwater wetlands, (3) riparian/floodplain preservation, and (4) septic systems. We selected two first order catchments in each of these categories and measured GHG concentrations, emissions, and dissolved inorganic and organic carbon (DIC and DOC) and nutrient concentrations biweekly for 1 year. From a water quality perspective, the DOC : NO3 - ratio of streamwater was significantly different across infrastructure categories. Multiple linear regressions including DOC : NO3 - and other variables (dissolved oxygen, DO; total dissolved nitrogen, TDN; and temperature) explained much of the statistical variation in nitrous oxide (N2O, r2 = 0.78), carbon dioxide (CO2, r2 = 0.78) and methane (CH4, r 2 = 0.50) saturation in stream water. We measured N2O saturation ratios, which were among the highest reported in the literature for streams, ranging from 1.1 to 47 across all sites and dates. N2O saturation ratios were highest in streams draining watersheds with septic systems and strongly correlated with TDN. The CO2 saturation ratio was highly correlated with the N2O saturation ratio across all sites and dates, and the CO2 saturation ratio ranged from 1.1 to 73. CH4 was always supersaturated, with saturation ratios ranging from 3.0 to 2157. Longitudinal surveys extending form headwaters to third-order outlets of Red Run and Dead Run took place in spring and fall. Linear regressions of these data yielded significant negative relationships between each gas with increasing watershed size as well as consistent relationships between solutes (TDN or DOC, and DOC : TDN ratio) and gas saturation. Despite a decline in gas saturation between the headwaters and stream outlet, streams remained saturated with GHGs throughout the drainage network, suggesting that urban streams are continuous sources of CO2, CH4, and N2O. Our results suggest that infrastructure decisions can have significant effects on downstream water quality and greenhouse gases, and watershed management strategies may need to consider coupled impacts on urban water and air quality.

The Repeatability of Sorption Processes Occurring in the Coal-Methane System during Multiple Measurement Series

The aim of this paper was to investigate the repeatability of sorption processes occurring in the coal-methane system during multiple measurement series. For research purposes, three granular samples of coal sorbent were used. The samples were subjected to a series of three measurements, each time performed under the same conditions. During each series of measurements, the following stages took place: outgassing the sample in a vacuum, and then saturating it with methane under the pressure of 1, 3, and 10 bar. Sorption capacities and the values of effective diffusion coefficients were compared. The studies into the repeatability of measurements of sorption capacities, conducted by means of the IGA-001 (Intelligent Gravimetric Analyzer) gravimetric instrument for three measurement cycles, showed that the obtained measurement discrepancies in relation to the mean value did not exceed 1.23%. The discrepancies in question approximated the measurement uncertainty of the IGA-001 device. The evaluation of the recurrence of determining the values of effective diffusion coefficients showed that the obtained discrepancies were no larger than 10%, which might have resulted from problems with fulfilling most of the assumptions of the applied unipore diffusion model. The authors did not observe any changes of the sorption parameters of hard coal during consecutive cycles of methane saturation.