Methane Reserves Research Articles

ОБҐРУНТУВАННЯ КОМПЛЕКСНОГО ПРОЕКТУ ВИРОБНИЦТВА ТЕП-ЛОВОЇ ТА ЕЛЕКТРИЧНОЇ ЕНЕРГІЇ З ВИКОРИСТАННЯМ МЕТАНУ ЗА-КРИТИХ ШАХТ

The article deals with the issue of methane extraction from closed mines for its further use as an alternative energy source. A substantiated and developed method of methane extraction from the dome of the collapse of closed mines, while a mobile surface degassing unit is used to extract methane from the installed places of gas collectors. The use of the proposed method of methane extraction will improve the environmental safety of the man-made and natural environment, solve the issue of disposal and use of methane as fuel for cogeneration plants. To ensure the company's own production of electricity and thermal energy, a gas-piston cogeneration power plant has been justified and selected.At the first stage of the project, methane reserves of closed mines are calculated. As a result of the collapse of the roof layers above the created space in the mountain massif, a displacement vault and a "collapse dome" are formed. Methane accumulates under the collapse dome. The parameters of the vault depend on the depth of the cleaning work and the size of the created space. At the second stage, a mobile surface degassing unit is used to extract methane from closed mines from established places of methane accumulation. The advantage of a mobile surface degassing unit is its mobility, which makes it possible to install it in the necessary places, as well as carry out degassing and achieve significant volumes of capted gas with a methane content of up to 80%. To obtain a gas-air mixture of the required concentration (from 25% to 40%), a methane concentration increaser is used. The third stage is the substantiation of the type of power plant for the design of a gas turbine or gas piston mini thermal power station, taking into account individual conditions and technical tasks.

Differential enrichment mechanism of helium in the Jinqiu gas field of Sichuan Basin, China

Helium is extensively utilized in aerospace, healthcare, electronics, semiconductors, advanced science, and renewable energy sectors, playing a pivotal role in the advancement of human technology. Presently, helium is primarily extracted from natural gas as an associated resource. The cost of extraction decreases with an increase in the helium concentration within the gases. Therefore, understanding the mechanisms involved in helium generation, migration, and accumulation underground is vital. This article delves into the differential enrichment mechanism of helium in the Jinqiu gas field, situated in the Sichuan Basin of China, by analyzing the molecular and isotopic composition characteristics of the major gases and noble gases, employing gas dissolution and diffusion models. Compared with other Jurassic gas reservoirs in the Sichuan Basin, the Jinqiu gas field contains a significantly higher helium concentration, displaying unique enrichment patterns within its area. The majority of hydrocarbon gases originate from the local underlying Triassic Xujiahe Formation source rocks. Specifically, the western section of the Jinqiu field is primarily supplied by the higher maturity Xujiahe Formation source rocks located in the western Sichuan Basin. Notably, there is no significant contribution of mantle-derived volatile components in the Jinqiu field. Helium and argon are primarily radiogenic, whereas neon primarily originates from atmosphere. The good linear correlation between 4He and 20Ne suggests that their transfer is primarily facilitated through groundwater. The solubility calculation reveals that the helium exsolved from the in-situ pore water of the reservoir, due to stratigraphic uplift during the Himalayan movement, comprises only 0.04%–0.11% of the existing reserves. This suggests that gas desolvation plays a relatively minor role in helium enrichment in the Jinqiu field. Additionally, the calculation results of gas diffusion indicate that diffusion's contribution to helium enrichment in the Jinqiu gas field remains minimal. Finally, our analysis of methane reserve changes suggests that the combined effect of differential loss and dilution of hydrocarbon gases is the primary mechanism for helium's differential enrichment in the Jinqiu field. Notably, methane and carbon dioxide depletion may be a significant factor in helium enrichment within the crustal natural gas system.

European Climate Policy in the Context of the Problem of Methane Emissions from Coal Mines in Poland

This paper presents a thorough examination of methane capture from Polish coal mines, contextualized within the framework of the European Union’s (EU) climate policy objectives. Through a strategic analysis encompassing the interior of coal mines, the surrounding environment, and the macro environment, this study elucidates the complex dynamics involved in methane emissions and capture initiatives. The key findings include a declining trend in absolute methane emissions since 2008, despite fluctuations in coal extraction volumes, and a relatively stable level of methane capture exceeding 300 million m3/year since 2014. The analysis underscores the critical role of government support, both in terms of financial incentives and streamlined regulatory processes, to facilitate the integration of methane capture technologies into coal mining operations. Collaboration through partnerships and stakeholder engagement emerges as essential for overcoming resource competition and ensuring the long-term success of methane capture projects. This paper also highlights the economic and environmental opportunities presented by methane reserves, emphasizing the importance of investment in efficient extraction technologies. Despite these advancements, challenges persist, particularly regarding the low efficiency of current de-methanation technologies. Recommendations for modernization and technological innovation are proposed to enhance methane capture efficiency and utilization.

Numerical study of the gas production process from a gas hydrate deposit in the presence of thermal and depression effects

Today the issue of gas production technology from existing gas hydrate deposits discovered on the shelf of the World Ocean and in permafrost areas is still very significant since the methane reserves in the free state are significantly inferior to its reserves in the form of its gas hydrates. One of the tasks for possible gas production from a hydrate-containing porous medium is to study the process of gas hydrate decomposition under thermal and depression effects since they are most commonly used ones. It is necessary to conduct a theoretical study including the development of a mathematical mode and its algorithmization, the creation of a computational program and the conduct of numerical experiments. The paper presents one-dimensional axisymmetric problem of heating and/or pressure reduction at the bottom of a well passing through the entire thickness of a porous formation when its pores are initially filled with methane and its hydrate. The utilized mathematical model includes the continuity equations for methane, its hydrate and water; the equation of the gas phase motion in a porous medium as the Darcy filtration law; the state equation of methane and water, the energy conservation equation considering the Joule–Thomson effects and adiabatic cooling for gas, the latent heat of the “gas hydrate  methane + water” phase transition. A numerical implementation of the proposed mathematical model and a numerical study of the thermal and/or depression impact on the studied hydrate-bearing deposit are carried out. The results of calculations show that the size of a zone containing only the gas hydrate decomposition products (gas and water) slightly increases with a smaller length of a porous layer. They also show that the thermal effect (increasing the temperature at the bottomhole of production well) on the hydrate-saturated reservoir simultaneously with the depression effect is not efficient enough due to the intensive flow of cold gas (with a temperature equal to the initial temperature of the reservoir) from the hydrate-containing deposit to the well.

Changes in mineral fraction and pore morphology of coal with acidification treatment: contribution of clay minerals to methane adsorption.

The accurate calculation of the contribution which provided by clay minerals in coal on methane adsorption not only bares a significant importance for evaluating the effectiveness of acid stimulation in improving permeability and estimating the coalbed methane reserves but also serves a guide for the governance and utilization of methane resources. In this study, hydrochloric acid (HCl) and hydrofluoric acid (HF) were used to remove specific minerals in Qingdong coal samples. We firstly analyzed the mineral compositions of coal samples with different acidification treatments based on the X-ray diffraction (XRD) experiments, together with analysis of the changes in pore morphology and adsorption capacity. The results showed that acidification did not significantly change the shape of the pores, which remained slit-/plate-like pore. However, the altered adsorption capacity of the coal samples was attributed to changes in pore structure and mineral distribution. Acid erosion of mesopores promoted the transition from mesopores to macropores, contributing to an increase of 8.4% and 24.36% in the percentage of macropores in coal samples treated with HCl and HF, respectively. Fractal dimension D1 grew from 2.2193 to 2.3888 and 2.2572, respectively, but D2 decreased from 2.6146 to 2.5814 and 2.5433, indicating an increment in pore surface roughness and a simplification of the pore structure. The mineral richness of the coal seams should be taken into consideration when applying acid stimulation to increase permeability due to that the acidification products may block the passage of gas migration when the mineral content is slight, which can hinder gas extraction. The aim of this study is to quantitatively determine the contribution rate of clay minerals in coal to methane adsorption with a calculation method is provided by combining pore parameters and limit adsorption capacity, resulting in a contribution rate of 15%.

A novel tail: One story from the rare taxa of the coal seam microbiome

A substantial portion of global coal seam methane reserves are biogenically produced. To enhance methane production, recent research has focussed on genetic surveying of the microbial life inhabiting these coal seams. These surveys have revealed that the most abundant organisms in these microbial communities are taxa specialised in metabolism of various simple substrates, and are typically methanogens, their (presumably) syntrophic acetate-oxidising bacterial partners, and other bacterial taxa associated with biomass recycling. Although abundant, these microbes are incapable of directly accessing the vast majority of recalcitrant carbon contained within the coal geopolymer. Instead, these more abundant taxa likely rely on the low abundance but diverse taxa, known as the ‘rare taxa’, to transform the carbon within coal into simpler, more labile substrates. Since these rare taxa typically have low taxonomic resolution, their probable activities within the coal seam environment are difficult to infer using the standard 16S rDNA community surveys. Therefore, the present study aimed to develop a method for identifying and characterising these rare taxa using a metagenomic approach. Using this method, a near-complete genome from a Deltaproteobacteria sp. (CSMB_808; designation taken from the Coal Seam Microbiome reference set) was recovered from a metagenome sampling the Surat Basin, Australia, and comprised only 0.5% of the total 16S rDNA sequences recovered from this metagenome. Genetically, CSMB_808 appears to be a motile fatty acid and possibly alkane-degrader within the coal seam environment, and may play an important role in the coal-to-methane degradative pathways. Despite the near-completeness of the recovered genome, the taxonomic resolution of this deltaproteobacterium was unable to be clarified due to insufficient described close relatives. Together, the low taxonomic resolution, relatively low 16S rDNA abundance, and ability to degrade putative upstream metabolites that may facilitate methanogenesis in the coal seam environment, indicates that this method of analysis can assist in understanding other important but uncharacterised rare taxa of the coal seam microbiome. A clearer understanding of the function of these taxa would allow targeted strategies to enhance methane production, as well as contributing valuable knowledge of carbon cycling in the terrestrial subsurface.

Thermocatalytic Decomposition of Methane: A Review on Carbon-Based Catalysts.

The global initiatives on sustainable and green energy resources as well as large methane reserves have encouraged more research to convert methane to hydrogen. Catalytic decomposition of methane (CDM) is one optimistic route to generate clean hydrogen and value-added carbon without the emission of harmful greenhouse gases, typically known as blue hydrogen. This Review begins with an attempt to understand fundamentals of a CDM process in terms of thermodynamics and the prerequisite characteristics of the catalyst materials. In-depth understanding of rate-determining steps of the heterogeneous catalytic reaction taking place over the catalyst surfaces is crucial for the development of novel catalysts and process conditions for a successful CDM process. The design of state-of-the-art catalysts through both computational and experimental optimizations is the need of hour, as it largely governs the economy of the process. Recent mono- and bimetallic supported and unsupported materials used in CDM process have been highlighted and classified based on their performances under specific reaction conditions, with an understanding of their advantages and limitations. Metal oxides and zeolites have shown interesting performance as support materials for Fe- and Ni-based catalysts, especially in the presence of promoters, by developing strong metal-support interactions or by enhancing the carbon diffusion rates. Carbonaceous catalysts exhibit lower conversions without metal active species and largely result in the formation of amorphous carbon. However, the stability of carbon catalysts is better than that of metal oxides at higher temperatures, and the overall performance depends on the operating conditions, catalyst properties, and reactor configurations. Although efforts to summarize the state-of-art have been reported in literature, they lack systematic analysis on the development of stable and commercially appealing CDM technology. In this work, carbon catalysts are seen as promising futuristic pathways for sustained H2 production and high yields of value-added carbon nanomaterials. The influence of the carbon source, particle size, surface area, and active sites on the activity of carbon materials as catalysts and support templates has been demonstrated. Additionally, the catalyst deactivation process has been discussed, and different regeneration techniques have been evaluated. Recent studies on theoretical models towards better performance have been summarized, and future prospects for novel CDM catalyst development have been recommended.

Bituminous Coal Sorption Characteristics and Its Modeling of the Main Coal Seam Gas Component in the Huaibei Coalfield, China

Knowledge of the gas sorption and permeability characteristics of a coal provides an essential basis for the evaluation of coalbed methane reserves and their recoverability. Thus, the gas excess sorption capacities of the main gas component of coal seam gas (CSG) in bituminous coal samples derived from the Xutuan Coal Mine in the Huaibei Coalfield, in the Anhui Province of China, were measured using a volumetric method. The results showed that under the same equilibrium pressure, the order of excess sorption capacity was CO2 > CH4 > N2. Furthermore, the sorption capacity ratios of coal from the Xutuan Mine for CO2, CH4, and N2 were approximately 6.0:2.3:1. It was also demonstrated that the sorption capacity during depressurization was always larger than that of the adsorption process, which is indicative of desorption hysteresis. The behaviors of three adsorption models, Langmuir, BET, and D-R, all of which include two parameters, are considered in this paper. The different gas sorption measurement data were fitted by the three models. For the bituminous coal samples, the fits of the D-R equation of all three different gases are higher than 0.99, the fits of the Langmuir equation are higher than 0.985, while the fits of the BET equation for CH4 and N2 absorption are higher than 0.95. However, the fits of the BET equation for CO2 absorption are only about 0.5. Coal sorption has an apparent influence on coal permeability; the permeability of the same coal sample to N2, CH4, and CO2 gases was tested and analyzed. The result shows that the permeability of CO2 was found to be lower than that of other coal seam gas constituents, CH4 and N2, due to their different adsorption abilities.

The effect of organics transformation and migration on pore structure of bituminous coal and lignite during biomethane production.

Biomethane generation by coal degradation not only can increase coalbed methane (CBM) reserves, namely, microbially enhanced coalbed methane (MECBM), but also has a significant effect on the pore structure of coal which is the key factor in CBM extraction. The transformation and migration of organics in coal are essential to pore development under the action of microorganisms. Here, the biodegradation of bituminous coal and lignite to produce methane and the cultivation with inhibition of methanogenic activity by 2-bromoethanesulfonate (BES) were performed to analyze the effect of biodegradation on coal pore development by determining the changes of the pore structure and the organics in culture solution and coal. The results showed that the maximum methane productions from bituminous coal and lignite were 117.69μmol/g and 166.55μmol/g, respectively. Biodegradation mainly affected the development of micropore whose specific surface area (SSA) and pore volume (PV) decreased while the fractal dimension increased. After biodegradation, various organics were generated which were partly released into culture solution while a large number of them remained in residual coal. The content of newly generated heterocyclic organics and oxygen-containing aromatics in bituminous coal was 11.21% and 20.21%. And the content of heterocyclic organics in bituminous coal was negatively correlated with SSA and PV but positively correlated with the fractal dimension which suggested that the retention of organics contributed greatly to the decrease of pore development. But the retention effect on pore structure was relatively poor in lignite. Besides, microorganisms were observed around fissures in both coal samples after biodegradation which would not be conducive to the porosity of coal on the micron scale. These results revealed that the effect of biodegradation on pore development of coal was governed by the combined action of organics degradation to produce methane and organics retention in coal whose contributions were antagonistic and determined by coal rank and pore aperture. The better development of MECBM needs to enhance organics biodegradation and reduce organics retention in coal.

Interpretation Method for Lost Gas in Deep Coalbed and Its Application

The gas loss time during the deep coalbed coring process is long. The measured desorption curve does not meet the application conditions for the classical United States Bureau of Mines (USBM) method. However, the industry still lacks a reliable interpretation method, which affects identifying deep coalbed methane reserves and optimizing sweet spots. (Method) The classical double-porosity and double-permeability theoretical model was adopted, and the influence of reservoir permeability, water saturation, and temperature on gas output in the coalbed desorption process was considered. Based on the measured field desorption data of the P1 sample of the No. 8 coal in the Benxi Formation on the eastern margin of Ordos, the entire process for the deep coalbed gas content test was numerically simulated. (Results) The simulation results show that the lost gas in the P1 sample accounts for 24.7% of the total gas, reaching 8.64 m3/t, including 18.81% of loss in wellbore lifting and 5.88% of loss during surface exposure. The total gas content of the sample is 35.34 m3/t. The P1 sample contains free gas, with a content of 9.71 m3/t, and the ratio between adsorbed and free gas is close to 7:3. Matrix permeability, initial gas saturation, and lifting time are the key factors that determine the amount of lost gas. The results of deep coalbed gas loss calculated by the USBM method were excessively large, approximately twice that calculated using the new method. The total gas content calculated based on multiple parameters is consistent with the interpretation results of the new method, with an average error of approximately 7%. (Conclusion) The interpretation method of gas loss in deep coalbeds has acceptable reliability and can be applied in shale gas content testing.

ДИНАМИКА ЗМІН КОЕФІЦІЄНТА ФОЛЬМЕРІВСЬКОЇ ДИФУЗІЇ МЕТАНУ, АДСОРБОВАНОГО У МІКРОСОРБЦІЙНІЙ СТРУКТУРІ ПРУЖНОЇ ЗОНИ ОПОРНОГО ТИСКУ ВУГІЛЬНОГО ПЛАСТА

Purpose. Set the possible change in the coefficient of Volmer diffusion of methane in the microsorption structure of the elastic zone of the supporting pressure of the coal seam. Methodology. The energy of the sorption bond of methane with the coals, the activation energy of the Volmer diffusion in the porous expanse of coal, as well as the stresses of the elastic zone and its effect on the change of the Volmer porosity, was taken into account. In the calculations, such parameters as the diameter of the Volmer micropores and the length of the descending branch of the support pressure diagram were varied. Results. Approximation of calculations made it possible to establish both the pairwise dependences of the Volmer diffusion coefficient on the listed parameters and its multifactorial relationship with them. It was concluded that the diffuse process of methane in the elastic support pressure zone is not blocked by rock pressure, as previously thought, but is actively developing. In this case, the diffusion of free methane will be determined by the established pattern of change in the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure. Calculations showed that as the distance from the maximum reference pressure increases, the Volmer diffusion coefficient of methane in the coal seam increases, which is due to a decrease in rock pressure in the descending branch of the reference pressure graph. However, this growth is not strong due to the weak compressibility of pores. Therefore, for pores of the same diameter, the Volmer diffusion coefficient in the elastic zone of the supporting pressure of the coal seam for the given mining geological conditions can be considered a constant. For depths of, for example, 1000 m and pore diameters of 10 Å, the value of the Volmer diffusion coefficient will be approximately 3.77×10-8 m2/s. Scientific novelty. Calculations of the Volmer diffusion coefficient of methane adsorbed in the micropores of coal in the elastic zone of the supporting pressure of the coal seam, which, of course, is under significant compressive stresses, have been performed. The established phenomenon confirms that methane gas release is determined not only by free gas filtration, but also by Volmer diffusion of adsorbed methane. Practical significance. Since adsorbed methane reserves are known to be the main methane reserves in coal, the regularity established in the article makes it possible to more accurately calculate the volumes of methane that will be released from the coal massif during mining operations for the assessment of safe working conditions for coal deposits and for the development of technologies for the production of shale methane.

Regularity of change in the volmer diffusion coefficient of methane adsorbed in the microsorption structure of the elastic zone of the coal seam bearing pressure

The Volmer diffusion coefficient of methane adsorbed in the micropores of coal in the elastic zone of the coal seam bearing pressure, which normally is under conditions of significant compressive stress, was calculated with taking into account the energy of the methane sorption connection with coal, the energy of Volmer diffusion activation in the porous space of coal, and the stressed state of the elastic zone with its influence on the change of Volmer porosity. During the calculations, such parameters as the diameter of Volmer micropores and the length of the descending branch of the bearing pressure diagram were varied. As a result of the approximation of these calculations, both pairwise dependences of the Volmer diffusion coefficient on the listed parameters and its multifactorial relationship with them were established. Therefore, it is concluded that the process of methane diffusion in the elastic zone of bearing pressure is not blocked by the rock pressure, as previously thought, but is actively developing. The diffusion of free methane will be determined by the established regularity of changes in the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure. The calculations show that as the distance from the maximum of the bearing pressure increases, the Volmer diffusion coefficient of methane in the coal seam increases, which is due to a decrease in the pressure of rocks in the descending branch of the bearing pressure diagram. However, this growth is not great due to the weak compressibility of pores. Therefore, for pores of the same diameter, the Volmer diffusion coefficient in the elastic zone of the coal seam bearing pressure for the given mining geological conditions can be considered a constant. For depths of, for example, 1000 m and pore diameters of 10 Å, the value of the Volmer diffusion coefficient will be approximately 3.77·10-8 m2/s. This confirms that methane gas release is caused not only by filtration of free gas, but also by Volmer diffusion of adsorbed methane. In turn, the reserves of the latter are known to be the main reserves of methane in coal. Therefore, the established regularity makes it possible to more accurately calculate the volumes of methane, which will be released from the coal massif during mining operations, in order to assess safety of conditions for coal deposits mining and to develop technologies for coal mine methane production.

Response of Shallow Gas‐Charged Holocene Deposits in the Yangtze Delta to Meter‐Scale Erosion Induced by Diminished Sediment Supply: Increasing Greenhouse Gas Emissions

AbstractRiver deltas have long been considered important carbon sinks. However, the presence of shallow gas and the processes of delta erosion caused by diminished sediment supplies could reduce the strength of the carbon sink. In this study, based on historical bathymetric data and a data set obtained from a seismic survey, we investigate the response of gas‐charged deposits in the Yangtze subaqueous delta to seabed erosion. A conservative estimate of the total methane reserves of 0.55–4.35 × 1011 mol was obtained in the delineated gassy area of ∼3,800 km2. The seismic and bathymetric data reveal a prominent erosional belt at water depths ranging from 5 to 20 m and extending from the southwestern to northeastern nearshore areas of the Yangtze subaqueous delta. Erosion is severe in the south and slight in the north due to differences in the hydrodynamic conditions, sediment erodibility, and sensitivity to sediment reduction. Seabed erosion reduces the thickness of the cap bed and the overburden pressure at the gas front, making it easier for gas to seep through the sediment column and bypass the anaerobic oxidation of methane. The good agreement between the elevated methane concentrations and the erosional belts and the spatial coincidence between the shallower gas front and pockmarks indicate that seabed erosion accelerates gas seepage activities. In the context of global deltaic degradation, the increasing greenhouse gas emissions from deltaic deposits are worthy of further attention.

Modelling the impact of coal seam methane on the Mongolian economy

Energy independence is one of the most important issues for almost every country and the world. Mongolia strives to have various types of energy sources and reduce energy dependence. Energy dependence always influences economic dependence of any country. Utilising its own country’s resources is optimal to reduce energy dependence. In recent years, the Mongolian Government has been encouraging unconventional oil and gas exploration and foreign investment and implementing supporting policies, such as coal bed (seam) methane. As a result of these activities, unconventional oil and gas investment and exploration have been intensified in the last few years in Mongolia, especially during pandemics. There are 32 oil and gas blocks in Mongolia and coal bed methane exploration and foreign investments have been invested in eight blocks. In 2022, some foreign investment companies are going to introduce proven reserves of coal bed methane to the Mongolian Government and Parliament. Therefore, we have to model the positive and negative impacts of coal bed methane on the Mongolian economy and find methods to increase the positive sides. Unfortunately, there is no experience in any situation for unconventional oil and gas exploration, extraction, and field development. Because of it, we have cooperated with Australian scientists and experts and completed some studies for making a model of the impact of coal seam methane on the Mongolian economy. For today’s condition, the Mongolian Government or Mongolian private companies can’t process coal bed methane activities because of lack of capital expenses and experience. To raise the positive impacts of coal bed methane, foreign investment is of course very important. There are some main purposes to model the impact of coal seam methane on the Mongolian economy.

Recovery of greenhouse gas as cleaner fossil fuel contributes to carbon neutrality

Under the context of carbon neutrality of China, it is urgent to shift our energy supply towards cleaner fuels as well as to reduce the greenhouse gas emission. Currently, coal is the main fossil fuel energy source of China. The country is striving hard to replace it with methane, a cleaner fossil fuel. Although China has rich geological resources of methane as coal bed methane (CBM) reserves, it is quite challenging to utilize them due to low concentration. The CBM is however mainly emitted directly to atmosphere during coal mining, causing waste of the resource and huge contribution to greenhouse effect. The recent work by Yang et al. demonstrated a potential solution to extract low concentration methane selectively from CBM through using MOF materials as sorbents. Such kind of materials and associated separation technology are promising to reduce greenhouse gas emission and promote the methane production capability, which would contribute to carbon neutrality in dual pathways.

A Method to Evaluated Gas Content with Coalbed Methane Reservoir Based on Adsorption Theory and Production Analysis

In the process of coalbed methane development, the gas content not only determines the reserves of methane in coal reservoir but also is the most important geological parameter affecting the production of coalbed methane. The gas content directly determines whether coalbed methane can be developed efficiently. However, in the current development evaluation process, it is very difficult to accurately predict the gas content in coal seams. An efficient and accurate method to predict gas content has not been found yet. This is mainly restricted by the development mode and technology of coalbed methane. In the current low-cost development model, gas content test data are relatively scarce. Under such circumstances, it is difficult to accurately evaluate the distribution of CBM gas content in the whole area. At the same time, the gas content of coalbed is the key parameter for efficient development of coalbed methane. Under normal circumstances, gas content heterogeneity will result in a large gap between development effects in different regions. At present, there is no evaluation method for gas content parameters of coal reservoir. Under this background, the key parameters of coalbed methane development in southern Qinshui Basin were evaluated. On the basis of systematically summarizing and understanding the development law of coalbed methane in different types of coal reservoirs, a gas content evaluation method based on adsorption theory and production dynamic analysis is proposed. Combined with the coalbed methane production model and isothermal adsorption model, the critical desorption pressure can be calculated accurately by using the bottom hole pressure when casing pressure occurs in production wells. The critical desorption pressure correction model of coalbed methane was innovatively established. Langmuir equation was used to accurately characterize the adsorption characteristics of coalbed methane. Forming a new method for gas content prediction in the case of fewer coring wells. The gas content evaluation technology coupled with isothermal adsorption theory and production dynamic analysis saves the development cost of coalbed methane and improves the prediction accuracy of coal seam gas content in noncoring wells. At the same time, there is a good relationship between the predicted results and the measured gas content at well points. The coincidence rate reached 97.37%. This technology can effectively improve the prediction accuracy of coal seam gas content. This technique is suitable for the productivity evaluation of coalbed methane reservoir. It can also provide scientific basis for the development and reserve evaluation of coalbed methane reservoirs at home and abroad.

In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments: Key input for understanding the dynamics of subsea permafrost

Significant reserves of methane (CH4) are held in the Arctic shelf, but the release of CH4 to the overlying ocean and, subsequently, to the atmosphere has been believed to be restricted by impermeable subsea permafrost, which has sealed the upper sediment layers for thousands of years. Our studies demonstrate progressive degradation of subsea permafrost which controls the scales of CH4 release from the sediment into the water-atmospheric system. Thus, new knowledge about the thermal state of subsea permafrost is crucial for better understanding of the permafrost -hydrate system and associated CH4 release from the East Siberian Arctic Shelf (ESAS) – the broadest and shallowest shelf in the World Ocean, which contains about 80% of subsea permafrost and giant pools of hydrates. Meanwhile, the ESAS, still presents large knowledge gaps in many aspects, especially with respect to subsea permafrost distribution and physical properties of bottom sediments. New field data show that the ESAS has an unfrozen (ice-free) upper sediment layer, which in-situ temperature is −1.0 to −1.8 °C and 0.6оС above the freezing point. On one hand, these cold temperature patterns may be related to the presence of subsea permafrost, which currently primarily occurs in the part of the ESAS that is shallower than 100 m, while ice-bearing sediments may also exist locally under deeper water in the Laptev Sea. On the other hand, the negative bottom sediment temperatures of −1.8 °C measured on the Laptev Sea continental slope sediments underlying water columns as deep as down to 330 m may result from dissociation of gas hydrates or possibly from dense water cascading down from the shelf. In contrast, data collected on recent expeditions in the northern Laptev shelf, zones of warmer bottom temperatures are coinciding with methane seeps, likely induced by seismic and tectonic activity in the area. These warm temperatures are not seen in the East Siberian Sea area, not even in areas of methane seeps, yet with little seismic activity.The thermal conductivity and heat capacity of bottom sediments recorded in the database of thermal parameters for the ESAS areas mainly depend on their lithification degree (density or porosity), moisture content, and particle size distribution. The thermal conductivity and heat capacity average about 1.0 W/(m·K) and 2900 kJ/(m3·K), with ±20% and ±10% variance, respectively, in all sampled Arctic sediments to a sub-bottom interval of 0–0.5 m.

ALGORITHM FOR SOLVING THE PROBLEM OF METHANE HYDRATE DECOMPOSITION IN A CLOSED HYDRATE-CONTAINING REGION OF A POROUS MEDIUM

Russia has a law on limiting greenhouse gas emissions, signed by the President of the Russian Federation in July 2021. The list of greenhouse gasses includes methane, and its reserves in the form of gas hydrates largely prevail over the reserves of free methane. The formation of gas hydrates occurs at sufficiently low temperatures and high pressures. A significant part of the “sleeping giants”, as journalists dubbed the methane-containing deposits, are in the Arctic region, and they are very sensitive to warming. The release of this greenhouse potential would have very negative consequences for the Earth’s climate. Thus, it is necessary to study the process of gas hydrate decomposition under thermal impact on a hydrate-containing porous medium. It is worth noting the importance of theoretical research to solve this problem, which includes the construction of a mathematical model of the process under study, algorithmization, software implementation and computational experiments. The paper presents a two-dimensional approximation of the formulated problem of heating at the upper boundary of the porous medium’s closed region containing methane and its hydrate initially. A mathematical model is presented, which is based on the mass conservation equations for methane, water and gas hydrate; Darcy’s law for the motion of the gas and liquid phases; the equation of a real gas state, the energy conservation equation considering thermal conductivity, convection, adiabatic cooling, the Joule-Thomson effect and absorption of latent heat during hydrate formation. An algorithm for the numerical implementation of the mathematical model is constructed and a computer code is developed to calculate main parameters of the process in the work, the computer program is updated to calculate the main parameters of the process researched in the article.

ОЦІНКА СОРБЦІЙНОЇ РІВНОВАГИ МЕТАНУ ПРИ ЙОГО ГЕНЕРАЦІЇ У ВУГІЛЬНОМУ ПЛАСТІ

Purpose. Study the adsorption equilibrium of adsorbed during the generation of methane in coal massif to determine the conditions for its implementation at different depths of mining operations. Methods. The thermodynamic research methodology, numerical calculation methods, mathematical processing of research results using approximation methods. Results. The entropy change of the «adsorbed methane – coal» system shows that the initial state of adsorbed methane during its generation in a coal seams determined by the depth of the seam and the degree of filling of its pores with methane. The results of the calculation showed, that the sorption equilibrium of the “methane – coal” system in the mountain massif is energetically most probable at the degree of filling of the pores with methane, which is θ = 40%. When θ < 40 % an irreversible spontaneous process of adsorption of methane by coal occurs, but when θ > 40% – its desorption, the degree intensity of which can be estimated by the ratio obtained in the work. It has been established that at the depth of the coal seam there is only low-intensity process, and at Н > 500 m – the process is more intensive. Therefore, when methane is generated at depths of Н < 500 m, it is likely that due to weak desorption and high sorption bond energy, the pores tend to be filled with methane almost completely. When Н > 500 m they tend to sorption equilibrium, so they are filled with methane by only 40%. The rest of the volume of gas generated in the coal seam at depths greater than 500 m, as a result of an intensive desorption process, migrates into the intervening rock seam. Scientific novelty. As opposed to a priori accepting opinions about what the initial state of methane adsorbed in coal is always characterized by the complete filling of pores with gas, numerical calculations dedicated to this issue have been performed for the first time in the paper. Calculations are based on modern ideas about the generation of methane in coal with the help of the separation of methyl group and hydrogen atoms from aliphatic fringes, which combine to form methane molecules. At the same time, the dependence of the change in the entropy of the “adsorbed coal – methane” system on the depth of occurrence and the degree of filling of its pores with methane during the generation of methane in the coal seam has been established. Practical significance. The research results make it possible to obtain fundamentally new regularities of the processes of mass transfer and filtration of methane in the mountain massif at great depths. The use of new laws makes it possible to adjust the existing technologies of mine ventilation and methods of safe mining operations in emission-hazardous and highly gas-bearing coal seams, to develop fundamentally new technologies in this direction, as well as to make more accurate calculations of methane reserves in various rocks of the mountain massif.

Experimental study on gas adsorption and drainage of gas-bearing coal subjected to tree-type hydraulic fracturing

Exploiting coalbed methane can optimize the energy mix and improve safety in coal mines. Coalbed methane production commonly requires that the coal’s permeability be enhanced. However, conventional permeability enhancement techniques commonly used at present have their own shortcomings, such as a limited range of permeability enhancement or high fracture initiation pressures Tree-type fracturing is one of the new techniques that are expected to eliminate the above-mentioned shortcomings and allow the efficient exploitation of coalbed methane reserves. The unclear of gas migration mechanism in tree-type fracturing limits the development of this technology. For this paper, a fluid–solid–gas coupling experimental system was assembled to study the changes in gas pressure and gas flow in gas-bearing coal after hydraulic fracturing. In the experiments, tree-type branch boreholes can effectively connect hydraulic fractures and surrounding natural cracks, increasing the scope and rate of gas extraction. The degree of connectivity of fractures (cracks and pores) will affect the gas desorption rate, which makes the gas flow trace “U” shaped lines. Tree-type hydraulic fracturing can increase the coal’s permeability by factors of 3.1 to 3.9, increase the effective drainage rate by factors of 1.23 to 1.41, and increase the proportion of gas drained by 3.7% to 5.5%. These results provide a reliable basis for additional research on tree-type fracturing and can aid in its engineering application.