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Given the suboptimal physical properties and distinctive geological conditions of deep coalbed methane reservoirs, any reservoir damage that occurs becomes irreversible. Consequently, the protection of these deep coalbed methane reservoirs is of paramount importance. This study employs experimental techniques such as scanning electron microscopy, X-ray diffraction, and micro-CT imaging to conduct a comprehensive analysis of the pore structure, mineral composition, fluid characteristics, and wettability of coal seams 3# and 15# in the northern Qinshui Basin of China. The objective is to elucidate the types of reservoir damage induced by fracturing fluid intrusion along with potential contributing factors. This research is critical for ensuring safe drilling practices, effective gas injection, and efficient development strategies for coalbed methane reservoirs. The findings indicate that the mineral composition of the coal rock consists of 18.52% clay minerals, 34% quartz, and 8.98% calcite. Furthermore, hydrophilicity and natural fractures within the coal rock may lead to water-sensitivity, velocity- sensitivity, alkali- sensitivity, and acid- sensitivity damages to the coalbed methane reservoir. There exists good compatibility between fracturing fluids and both coal rock as well as formation water. The fine particles generated from hydraulic fracturing are prone to transport through the coal seam while obstructing pore throats. Thus exhibiting pronounced velocity sensitivity characteristics in this reservoir type. Coal rock demonstrates pronounced stress sensitivity. As the effective stress escalates from 2 MPa to 10 MPa, there is a marked decrease in the permeability of coal rock. With increasing effective stress, the pore structure and natural fractures within the coal rock are compressed more tightly, resulting in a diminished permeability of the coal rock. When exposed to fracturing fluid saturation, not only does the volume of these particles expand but they can also cause blockages that result in up to a 60% reduction in fracture flow capacity. These insights are vital for optimizing fracturing designs aimed at protecting reservoir integrity. [ABSTRACT FROM AUTHOR]

【Objective】Aromatic compound metabolism is considered a limiting factor for the generation of biogenic coalbed methane. To increase biomethane production from coal, the compounded microflora (CM) was obtained by compounding raw inoculum (RI) with ability of producing methane by degrading coal and phenanthrene-degrading functional microflora enriched from produced water. 【Method】A combined metagenome and metatranscriptome approach was used to analyze the differences in the community structure and metabolic pathways of CM and RI. 【Result】The methane yield of CM increased significantly by 114.55%. Compounding significantly increased the proportion of aromatics-degrading bacteria, such as Pseudomonas, accounting for 63.49%, and also increased the metabolic activity of the dominant bacteria as well as the synthesis and expression of the key enzymes in the metabolic pathway of aromatic compounds. Gene abundance of the aromatics-degrading pathway in CM was 1.65 times higher than that of RI, and the gene expression abundance was 6.34 times higher than that of RI (P<0.05). The gene abundance and expression abundance of EC:1.13.11.2 were 2.24 and 62 times higher than those of RI, respectively. The increased expression abundance of these enzymes prompted the transformation of aromatic compounds to pyruvate. Compounding also enhanced the gene expression during the process of pyruvate metabolism to acetyl-CoA. The expression abundance of EC: 1.2.4.1 reached 14.70-fold of the RI in CM. The gene expression abundance of the respective methanogenic pathways in CM was 2.66 to 7.10-fold of the RI. 【Conclusion】The compounding enriched the aromatics-degrading bacteria and significantly increased gene abundance, especially gene expression abundance, in the whole metabolic pathway of degrading aromatics to methane generation, resulting in the increased methane production. [ABSTRACT FROM AUTHOR]

The complex fracture network provides the main channel for coalbed methane seepage, and its structural characteristics significantly affect the productivity of coalbed methane. In view of the lack of fracture network connectivity in existing coalbed methane seepage models, based on topological graph theory, the connectivity characteristics of fracture network were analyzed, and the expression of power law relation of fracture branch length was derived. Combined with fractal geometry, a permeability model considering fracture network structure characteristics was established on the basis of classical cubic law. The model shows that the permeability of fracture network is a function of fractal dimension, porosity, tortuosity fractal dimension, scale coefficient, connectivity, maximum fracture branch length, azimuth angle, dip angle and feature length. The permeability evolution of fracture network under true triaxial stress was analyzed. The results show that with the increase of the principal stresses σ1, σ2 and σ3, the fractures in coal are gradually compressed and the gas seepage channel becomes narrow. The permeability of fracture network shows a negative exponential decrease with the increase of the principal stresses σ1, σ2 and σ3. Based on the experimental rules and results, the fracture network fractal permeability model and S&D model (Shi-Durucan) were combined to establish the fracture network permeability calculation model under true triaxial stress. The effectiveness of the model was verified by the experimental data. The obtained permeability variation trend is consistent with the process of loading the three principal stresses, which can reflect the influence trend of the change of three-way stress on the permeability. Compared with the S&D model, it can better reflect the anisotropy characteristics of the permeability of the fracture network.

The influence of cleat permeability and porosity on the cumulative gas produced is studied. The cleat parameters are weighed for producing reserve in the least time and the minimum breakdown pressure requirement to create fractures. The reservoir is stimulated. The breakdown pressure required is more to create fractures at closer spacing than needed to increase the width of new fractures. The non-linear hyperbolic partial differential equations (PDE) are solved by the implicit finite difference method. Cleat permeability has a more significant influence on the gas produced than the porosity. Optimized values of 300 mD and 0.03 porosity sweep more area in a short time. Due to the faster propagation of drainage, the adsorbed gas is not recovered to nearly complete before the entire reservoir/pay zone length is drained. Fracturing a formation can be successful if the same adsorbed gas is spread over a larger area, and length is insufficient to accommodate the gas in place. The pay zone length needs to be larger than the present value. The novel approach of checking both the economic feasibility of fracturing a formation and its relation with the length of the reservoir, is discovered and solved here. [ABSTRACT FROM AUTHOR]

In the process of coalbed methane development, drilling fluid and fracturing fluid cannot achieve absolute compatibility with formation. The incompatibility between the working fluid and reservoir will lead to the intrusion of working fluid into the reservoir and cause reservoir pollution. This is a very common phenomenon. There is a large amount of pulverized coal in the coal seam, and the intrusion of working liquid will be combined with the pulverized coal to form cement to block the seepage space in the reservoir. Since pressure relief and fracturing fluid backflow will be performed at the first time after fracturing, the intrusion range of the working fluid is small, generally reaching 10 m to 50 m. Compared with a conventional gas reservoir or shale gas reservoir, the working fluid loss during CBM development will seriously affect the subsequent production project and even make the gas well lose production capacity. On the other hand, in order to avoid this phenomenon, measures such as acidification or volumetric fracturing are sometimes used to improve the seepage environment near the well and near the fracture. The purpose of this study is to quantitatively evaluate the impacts of working fluid filtration and reservoir reconstruction on production. In this study, a single well productivity evaluation model and sensitivity analysis method considering drilling fluid filtration loss, fracturing fluid filtration loss, reservoir reconstruction and other processes is proposed. The formation mechanism of fluid loss during drilling and fracturing is described, and the productivity evaluation model considering fluid loss is combined with the Langmuir isothermal adsorption equation, steady-state diffusion law, Darcy's seepage law and Duhamel convolution formation. Combined with the distribution of actual gas reservoir flow characteristics, the sensitivity of single well productivity to gas reservoir porosity, gas reservoir permeability, coal seam adsorption coefficient, working fluid filtration loss and reservoir reconstruction measures are analyzed. Through the analysis and fitting of the actual production data on site, the relationship curve can better fit the field production data, and the evaluation results are in line with the drilling and fracturing conditions at that time and the subsequent production conditions, with small errors. The obtained method is suitable for predicting the productivity of fractured vertical wells in different working conditions and provides a basis for the development and productivity prediction of CBM reservoirs in China and in international cooperation. [ABSTRACT FROM AUTHOR]

Guizhou has a large amount of coal resources, which have been mined for a long period of time, resulting in the formation of a large area of goaf. There is a large amount of coalbed methane resources in the goaf, but the exploitation and utilization rate are low, mainly because of the complex ground conditions, the large longitudinal span of coal measure strata, and the thin development of coal seam in Guizhou. When extracting pressure relief gas from overlying coal seam and coalbed methane from goaf using drilling wells passed through goaf, it is difficult to form wells using conventional drilling technology and is prone to complex underground accidents, which leads to less exploitation and utilization of gob coalbed methane resources in Guizhou. In order to extract pressure relief gas from the overlying coal seam and make full use of the goaf coalbed methane resources, it is particularly important to explore the longitudinal development characteristics of the superimposed “three zones” of overlying coal strata and the stress variation law of the bottom bulge coal strata after multi-seam mining. Taking Shanjiaoshu Mine, Panjiang mining area, Guizhou as an example, a directional test well passing through goaf with multiple coal seams was carried out. The results shown that the implementation of directional well to extract pressure relief gas from overlying coal seam and underlying goaf coalbed methane under special geological conditions in Guizhou had great economics. Meanwhile, through the successful implementation of the well, the longitudinal development characteristics of the superimposed “three zones” in Panjiang mining area after multi-seam mining were firstly verified. Secondly, the key geological and engineering technical parameters of coalbed methane extraction from the underlying coal seam in the coal mining goaf were also successfully obtained, and the utilization of coalbed methane resources in the goaf had been maximized. The project provided valuable engineering experience and technical support for the subsequent development of extracting pressure relief gas in gob and coalbed methane from underlying coal seam in Panjiang mining area and even in the whole Guizhou region.

In the eastern edge of the Ordos Basin in China, coalbed methane geological resources are very abundant, and efficient extraction of coalbed methane has become an important demand for energy development strategies and coal safety production. Therefore, this article uses IoT detection technology to optimize the coal seam pressure fracturing fluid system in this area, in order to improve its efficiency and reliability. Through on-site experiments, the relationship between different concentrations of fracturing fluid systems and coal seam permeability was studied. Divide the architecture of the Internet of Things to achieve more efficient information transmission and application. Based on the actual situation of the coal industry, we have constructed a system architecture for the Internet of Things in coal mines. Based on in-depth research on the occurrence characteristics of coalbed methane in the eastern edge of the Ordos Basin and the characteristics of underground fracturing fluid technology in coal mines, we have obtained the viscosity, rheological properties, viscoelasticity of underground fracturing fluid in coal mines, as well as specific requirements for the action of coalbed methane. On this basis, an interaction model between coal seam fracturing proppant and coal reservoir was established, and its mechanical response process was analyzed using numerical simulation methods. Selecting the optimal fracturing fluid ratio can significantly improve the surface wettability and strength of coal samples, while reducing the content of clay minerals and increasing the porosity of coal samples.

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In order to ensure the stability of flow rate and valve pressure difference during gas-water-coal mixture lifting, a multivariable non-singular terminal composite sliding mode (MNTCSM) controller based on accurate feedback linearization is proposed. The multi-input multi-output nonlinear system with time delay and coupling is transformed into a multi-input multi-output uncoupled linear system by using an improved Smith predictor and accurate feedback linearization. At the same time, the MNTCSM controller is designed to make the flow and pressure tracking errors of the decoupling system converge to zero in a finite time. Finally, simulations and experiments are designed for different control methods to verify the feasibility and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the importance of the diffusion mechanism of CH4 and CO2 in coal for the development of coalbed methane, the aim of this paper is to reveal the influence mechanism of pressure, temperature, water content and other factors on the molecular diffusion behavior of gas at the molecular level. In this paper, non-sticky coal in Chicheng Coal Mine is taken as the research object. Based on the molecular dynamics method (MD) and Monte Carlo (GCMC) method, the diffusion characteristics and microscopic mechanism of CH4 and CO2 in coal under different pressures (100 kPa–10 MPa), temperatures (293.15–313.15 K) and water contents (1–5%) were analyzed in order to lay a theoretical foundation for revealing the diffusion characteristics of CBM in coal, and provide technical support for further improving CBM extraction. The results show that high temperature is conducive to gas diffusion, while high pressure and water are not conducive to gas diffusion in the coal macromolecular model. [ABSTRACT FROM AUTHOR]

Green synthesis of metal-organic frameworks (MOFs) in water with alleviated environmental influence and reduced cost is an essential step to transfer laboratory MOFs research to industrial application. Switching from the commonly used organic solvents to pure water encounters challenges of the poor solubility of organic linkers, slow reaction kinetics, and the formation of polymorphic products. So far, a universal MOFs synthetic strategy in water system has yet to be developed. This study reports the seed-aided synthesis of eleven MOFs with diverse compositions and structures while pure water serving as solvent. The corresponding reaction temperature and time of using this new strategy were reduced compared with original synthetic approaches, while the products maintain porous structure and high crystallinity. The success of this strategy relies on the addition of parent MOFs as seeds which could promote crystallization process by skipping the time-consuming induction period and avoiding the formation of polymorphic impurities.

Coal Bed Methane (CBM) is natural gas occurring in coal seams. It can be used for domestic (heating and cooking) and industrial purposes, electricity generation, transportation (as compressed natural gas or liquefied natural gas), and in boilers supporting mining operations. It is established that Zimbabwe has CBM in the North-Western region. At the time of this study, only one organization (Industrial Development Corporation) has reported an Original Gas in Place (OGIP) estimate for the region as 765 Bm3. In this study we use Monte Carlo Simulation (MCS) to estimate the range of OGIP values for the region. MCS is a widely used probabilistic method, preferred over deterministic methods in which only best-estimate values of parameters are used to predict a single OGIP value. This single OGIP value may be either positively (overestimated) or negatively skewed (underestimated). However, the probabilistic approach using MCS accounts for the uncertainty in values of parameters. This is done by incorporating appropriate range and probability distributions (e.g. triangular, normal, uniform, etc.) of input parameters (e.g. target area, formation thickness, coal bulk density, and adsorbed methane content), and repeating calculations to generate a cumulative distribution curve for the OGIP. The generated curve provides statistical confidence levels represented as probability distributions, i.e. P10, P50, and P90 represents low, mid, and high probability estimates, respectively. Our results show that P10, P50, and P90 values for the North-Western region OGIP are 5699 Bm3, 2347 Bm3, and 706 Bm3, respectively. The Resource Density (RD) estimation is found to range from 0.015 Bm3/km2 to 0.113 Bm3/km2 over the geographic area. This range is comparable to Alberta plains shallow and deep basins in Canada which boosts a higher level of confidence for CBM potential in Zimbabwe. The results are encouraging for further exploration and planning of exploitation of CBM in Zimbabwe.

The key to coordinated development of coal mine methane and coal is to coordinate the spatio-temporal relationship between coal mining and coal mine methane development. During the “11th Five-Year Plan” and “13th Five-Year Plan” period, relying on the overall implementation of the national major science and technology project “Development of large oil and gas fields and coal mine methane”, the coordinated development mechanism of coal mine methane and coal in coal mining areas has made great progress. The development mechanism of coal mine methane in coal mine area is formed by “gas drainage”, “coal mine methane extraction”, “combination of ground development and underground extraction” and so on to ensure the safety of coal mine production. By defining the scope of coordinated development of coal mine methane and coal, establishing the evaluation method of coordinated development of coal mine methane and coal, forming the optimization decision-making platform of coordinated development of coal mine methane and coal, the concept of coordinated development of coal mine methane and coal in coal mine area based on “coordinated development, quality and efficiency improvement, technical support, platform decision-making, integrated demonstration” was put forward. Relying on the coordinated development technology system of coal mine methane and coal, as well as a complete set of technologies such as efficient extraction and effective utilization of coal mine methane in coal mining areas, Formation of coal-bed methane mining area in shanxi area “four linkage” global coordination development mode, huaibei mining area coal seam group of coal mine methane (CBM) three-dimensional joint development pattern, the complex soft Songzao mining area coal seam ahead of anti-reflection coordinated development pattern, Xinjiang mining area coal group “trinity” of large dip Angle coordinate development mode, leading to the coal mining area of coal bed methane development practice. The coordinated development mechanism, model and application of coal mine methane and coal in coal mine area have led the scientific and technological innovation of coal mine methane industry in coal mine area, and significantly improved the level of coal mine methane development and utilization in coal mine area. With the adjustment of national energy strategy, the implementation of the strategy of “double carbon” and the new requirements of the new situation, such as construction of ecological civilization coal mining area of coal bed methane development faces new challenges, new demand on promoting fine coal mining area of coal mine methane geological exploration and underground coal bed methane efficient development, abandoned mine coal mine methane extraction, such as coal gas together, a total of mining technology research and development, To construct a new technology body for clean and efficient development of coal mine methane and coal in coal mine area

Physical similarity simulation is one of the best methods for improving coal bed methane extraction efficiency, and the development of reasonable materials is important for improving physical similarity simulation testing results. This study aimed to investigate the mechanical properties of coal-like materials in a solid–gas coupled physical simulation test experiment. A new type of material with sand as aggregate, cement gypsum as cement, and silica gel as adsorbent was developed by an orthogonal design method. ANOVA and theoretical analysis were used to investigate the sensitivity and effects of different content ratios on the volumetric weight, uniaxial compressive strength, and elastic modulus of coal-like materials. The results of the investigation showed that the order of volumetric weight sensitivity ranging from large to small was the contents of silica gel, gypsum, and cement. The order of the sensitivity of uniaxial compressive strength and elastic modulus ranging from large to small was the ratio of the contents of silica gel, cement, and gypsum. Furthermore, the volumetric weight, uniaxial compressive strength, and elastic modulus of coal-like materials increased linearly and exponentially with the increase of cement and gypsum contents, respectively, whereas they decreased exponentially with the increase of silica content. Based on the results and analysis, a comprehensive model for the characteristic parameters of coal-like materials was established, and the prediction error was controllable to within 25%. [ABSTRACT FROM AUTHOR]

To enhance the extraction of methane gas from coal beds, hydraulic fracturing technology is used. However, stimulation operations in soft rocks, such as coal beds, are associated with technical problems related mainly to the embedment phenomenon. Therefore, the concept of a novel coke-based proppant was introduced. The purpose of the study was to identify the source coke material for further processing to obtain a proppant. Twenty coke materials differing in type, grain size, and production method from five coking plants were tested. The values of the following parameters were determined for the initial coke: micum index 40; micum index 10; coke reactivity index; coke strength after reaction; and ash content. The coke was modified by crushing and mechanical classification, and the 3–1 mm class was obtained. This was enriched in heavy liquid with a density of 1.35 g/cm3. The crush resistance index and Roga index, which were selected as key strength parameters, and the ash content were determined for the lighter fraction. The most promising modified coke materials with the best strength properties were obtained from the coarse-grained (fraction 25–80 mm and greater) blast furnace and foundry coke. They had crush resistance index and Roga index values of at least 44% and at least 96%, respectively, and contained less than 9% ash. After assessing the suitability of coke material for proppants in the hydraulic fracturing of coal, further research will be needed to develop a technology to produce proppants with parameters compliant with the PN-EN ISO 13503-2:2010 standard. [ABSTRACT FROM AUTHOR]

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.

Coalbed methane exploitation can optimize the energy composition, help to achieve carbon neutrality and carbon peak. As a key factor affecting the effect of coalbed methane production, fracturing fluid can greatly improve the micropore structure of the coal seam and the effect of gas desorption, and improve the efficiency of gas extraction. Due to the ordinary physical and chemical reaction rate between fracturing fluid and coal and the short effective extraction time, it is difficult to achieve an effective extraction effect. A novel ultrasonic promoting fracturing technology is proposed in this paper to increase gas production, that is, applying an ultrasonic field to the coal seam during the fracturing and extraction stage to enhance the fracturing effect, the desorption effect, and the integrity of the seepage channel. This technology uses the mechanical, cavitation, thermal and chemical effects of ultrasonic waves to strengthen the interaction effect of fracturing fluid and coal and gas extraction rate. In the ultrasonic–temperature–pressure multiple fields experiments, it is found that after the application of ultrasonic, the effect of the fracturing fluid was greatly improved, the diameter of the macropores was significantly increased, and a large number of new micropores were generated. Compared with the effect of only fracturing fluid, the pore volume, fractal dimension, and permeability of coal were increased by 14.1 %, 15.9 %, and 26.9 %, respectively. The experimental results prove the feasibility and effectiveness of the ultrasonic promoting fracturing technology.

Demand for a cleaner source of energy is increasing in India. In the search for alternate energy sources, coal bed methane gas receives considerable attention for its potential as a good energy source. During the coalification process, methane gas is captured in the coal seams and later released during coal mining operations. Coal bed methane separation is crucial for both economic benefit and methane emission reduction. The methane production from seams is an efficient way to reduce greenhouse emissions and provide a safe mining operation environment. In India, the production of coal bed methane on a commercial scale has been recently observed. In the present paper, an attempt is made to understand and establish a 3-D excavation of coal bed methane from reservoir simulation (COMET3) for Gondwana coal seams in the Sitarampur block of the Raniganj coalfield in India. The simulation study was carried out for a period of 25 years for the recovery of methane from the reservoir. It is observed from the simulation study that 372 million cubic meters CO2 equivalent greenhouse gas emissions can be prevented by the extraction of methane with space and time. The fracture gas concentration increases with time, and it is observed that fractures are fully saturated with gas in 3000 days.

Underground mining, including underground coal mining, is accompanied by accidents and fire hazards that pose a threat to the life safety of miners. The fire hazard increases with an increase in the mining depth. Currently, most accidents in coal mines are mine fires. The cost of eliminating mine fires is 80–95% of the cost of eliminating all accidents occurring at mining enterprises. Therefore, the problem of developing a new methodology for modeling the ventilation network parameters of the mine to increase the reliability of controlling the aerogas mode at the excavation site is very relevant. The comprehensive analysis and assessment of gas-dynamic processes in coalmines under study were carried out using the methods of probability theory and mathematical statistics. Spatial data were processed using spline interpolation in "gnuplot". As a result, a generalized expression for the transfer functions of coalmine objects, taking into account delays, was developed, including the description of dynamic properties of mining sites under various operating modes. The principal possibility of using a graphical method for estimating additional parameters of the sections of the ventilation system branches has been proved due to the alignment of their profiles at an equivalent distance relative to an arbitrary analogue. The improved method of spatial modeling was used to determine the gas-dynamic characteristics through additive gas-dynamic processes. The studies have been carried out and the method for managing the process of changing connections between devices (controllers–switches) of the technical system was developed in order to obtain greater reliability for safe mining. In subsequent studies, there is an issue of more detailed clarification of the peculiarities concerning the interrelations between the studied parameters in several projections of the response space. [ABSTRACT FROM AUTHOR]

The production of ultra-light weight coke proppants for fracturing coal bed methane deposits is presented. The raw material is blast-furnace coke, foundry coke and a coke breeze. The method used obtains coke proppants that meet all the requirements of the ISO 13503-2:2006/Amd.1:2009 standard for proppants used in hydraulic fracturing, with the exception of crush resistance. They have porosity up to 40 % and they are mainly macroporous materials, containing predominantly cylindrical, less frequently bottle-shaped or wedge-shaped pores. The proppants with the lowest crush rate were obtained from the blast furnace coke (CSR > 65 %). • A coke modification to obtain proppant for hydraulic fracturing. • Proppants with the best properties were obtained by modifying blast furnace coke. • Coke proppant is suitable for fracturing shallow CBM deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anthracite is the most suitable site for gas sequestration in three coal ranks. • Dominant factor shifts from energy effect to filling effect as gas loading rises. • Adsorption site competition determines CO 2 (NO)/CH 4 selectivity. • Major competitive sites for CO 2 /CH 4 are OH in anthracite and C O C in other coal. • NO and CH 4 primarily compete for OH adsorption sites in three coal slits. A new method of injecting CO 2 -rich industrial waste gas (CO 2 -rich IWG) to displace coal bed methane (CBM) is proposed for energy conservation and green growth. In this study, the adsorption mechanisms of this method were studied by the Giant canonical Monte Carlo and molecular dynamics methods in macromolecular coal models with three ranks (brown, bituminous, and anthracite coal). It is found that the proportion of gas molecules in the adsorbed state is higher in the anthracite coal slit than in the brown and bituminous slits, indicating that anthracite coal seams are more appropriate for waste gas sequestration. The adsorption selectivity of NO and CO 2 is consistent among the three coal ranks, with the order of brown > bituminous > anthracite > 1.0, and that of N 2 orders as 1.0 > bituminous > anthracite > brown. This is due to the different dominant factors affecting the competitive adsorption between different waste gas components and CBM, namely competition for adsorption sites in the NO and CO 2 systems and the filling effect in the N 2 system. There is a positive correlation between the number of major competitive adsorption sites and the adsorption selectivity of the CO 2 (NO) system. CO 2 and CH 4 compete for C O C structures in brown and bituminous coal and OH structures in anthracite coal, and OH structures in the three coals are the major adsorption sites for NO systems. Our work advances the understanding of the microscopic adsorption mechanisms of CO 2 -rich IWG in the CBM reservoirs, which provides a theoretical basis for CO 2 -rich injection-enhanced CBM recovery technology. [ABSTRACT FROM AUTHOR]

Methane is an economic energy resource and potent greenhouse gas. Distinguishing secondary microbial methane from thermogenic gas is important for natural gas exploration and consideration of subsurface microbial activity in the global carbon cycle, but remains challenging. To understand controls on methane origins in natural gas systems, we investigated the methane clumped isotopologue distributions in the Qinshui Basin high-thermal maturity coal bed methane (CBM) reservoir. Here, near-equilibrium clumped isotopologues distribution (Δ13CH 3 D and Δ12CH 2 D 2) inferred a temperature interval of 21.6–252.3 °C. The high-temperature thermodynamic equilibrium most likely represents original thermogenic CBM characteristics during coalification. The low-temperature equilibrium clumped isotopologue distributions suggest microbial alteration to CH 4 isotopic bond ordering by increased enzymatically catalyzed isotopic exchange. The independent constraints from clumped isotopes, integrated with other geochemical and genomic evidence, confirm notable secondary microbial methane from biodegradation in the highly mature reservoir. Thus, methane clumped isotopes can be used as unequivocal tracers to distinguish secondary microbial methane from thermogenic gases and hence provide the ability to incorporate them separately into global methane budgets. [ABSTRACT FROM AUTHOR]

Coal bed methane is mainly used for combustion, which has low efficiency and low added value. Based on the microwave plasma chemical vapor deposition (MPCVD) technique, the concept of producing gem-quality single crystal diamond from coal bed methane was proposed, and the corresponding industrialization process route was designed. CVD diamond production technique starts late in China and high-end equipment mainly depends on imports. Here, five generations of MPCVD diamond equipment have been independently developed and a special process for producing gem-quality diamond from coal bed methane was also developed. The fifth-generation equipment has been industrialized. Using home-made equipment and corresponding process, multiple single crystal diamonds can be prepared synchronously in an special enclosed substrate holder. Besides, large area single crystal diamonds can also be prepared by “mosaic” growth method. The industrialization demonstration base can mass-produce rough diamonds within 20 carats. When processed into loose diamonds, they have good color, high clarity, and perfect cutting, and are deeply welcomed by the market. The results show that the production of gem-quality diamond from coal bed methane has realized its high value-added transformation. The continuous promotion of industrialization can not only boost the consumption and comprehensive utilization of coalbed methane, but also help the development of CVD diamond industry in China.

Abstract Some of the most promising potential applications of nanotechnology to hydraulic fracturing of coal seam gas (CSG) are reviewed with a focus on Australian CSG wells. Three propitious applications were identified: (1) Nanoparticle enhanced viscoelastic surfactants (VES) fracturing fluids to prevent fluid loss by up to 30%, made possible by the formation of pseudo-filter cakes and reducing the viscosity of the VES fluids. Besides, there is no requirement of clay control additives or biocides. (2) Nano-proppants to extend fracture networks and reduce proppant embedment by introducing them prior to the emplacement of larger proppants. Fly Ash nanoparticles can be particularly effective because of their high sphericity and mechanical strength. (3) Nanoparticle-coated proppants, to mitigate the migration of particle fines by restricting them close to their source by adsorption, with MgO being the most effective. The use of nanotechnology in hydraulic fracturing applications is currently hindered due to a discordant regulatory environment compounded by the cost of the nanoparticles themselves, as well as, a lack of field data to validate the technology under real downhole conditions. Although the necessary field tests are unlikely to be conducted for as long as abundant natural gas is available, exploratory studies could pave the way for future applications. Graphical abstract

Microbial generation of coal bed methane (CBM) represents a significant source of natural gas on Earth. While biostimulation has been demonstrated in batch cultures, environmental parameters such as overburden pressure and formation water flow need to be tested at the laboratory scale to understand in situ potential. We designed and constructed a high-pressure (HP) flow-through reactor system that simulates in situ conditions of underground coal seams. Two stainless-steel columns contained coal from the Powder River Basin (PRB), USA, or a coal/sand mixture to represent the interface of coal seams with sandstone layers, which are hypothesized to exhibit higher methanogenesis rates in situ. The system was filled with CBM formation water, inoculated with a methanogenic enrichment from PRB coal beds, and stimulated with algal biomass as a nutrient. The reactors were incubated under pressure (5.4 atm) and flow of CBM water (0.01 mL/min), and control batch cultures were incubated at ambient pressure and without flow (± amendment). Dissolved and headspace methane concentrations were analyzed over time by gas chromatography for 75 days. The pressurized reactors exhibited longer latency periods than ambient pressure controls, but methane production did not reach a plateau phase, which might reflect the impact of scale on the inoculum. The coal/sand reactor exhibited higher methane production than the coal-only reactor, a pattern also observed in the corresponding controls, suggesting an interface effect on methanogenesis. This study indicates that the HP flow test system we designed is well suited for the study of methanogenesis and provides a successful demonstration of CBM generation from the PRB in field-relevant laboratory conditions as a precursor to meso‑scale demonstrations.

The rapid depletion of conventional hydrocarbons has shifted the industry's focus to other sources of energy which are uncommon. Unconventional opportunities are more important than the conventional opportunities, and they require high capital levels to be achieved. This analysis intends to fill a gap in the market with a modern and concise overview of Coal Bed Methane for students and newcomers to the business. This study discusses the various categories of coal rankings and the different generations of CBM. It covers the background of CBM industry along with its journey throughout these years. Considering India's increasing economic and population growth, innovative approaches to optimize sources of energy is an urgent need. As a result, India has been actively researching and improving its CBM capital through international tendering processes over all these years. CBM is an unconventional natural gas source and is currently being evaluated as a potential option for fulfilling India's increasing energy demands. Therefore, complete analysis of the Indian CBM Market has been conducted discussing various CBM extraction techniques. An evaluation of the impact of India's geography on CBM market has been performed. The study concludes with discussion of the future of CBM in India and throughout the world. [ABSTRACT FROM AUTHOR]

Coal bed methane (CBM) is a gas resource associated with and symbiotic with coal, which refers to the hydrocarbon gas stored in the coal seam, with methane as the main component, which belongs to unconventional natural gas. The development and utilization of CBM has the effect of achieving multiple things in one fell swoop: clean energy, commercialization can produce huge economic benefits. At present, rod pump, screw pump and other lifting technologies commonly used in CBM drainage and production have poor adaptability, short pump inspection period, and it is difficult to enter horizontal section in horizontal well. Aiming at this problem, a new method of efficient CBM lifting is proposed by adopting dual-pipe gas lift technology. In this paper, the basic principle of double tube gas lift is analyzed, the optimization design of gas injection volume, coiled tubing size and coiled tubing running depth is carried out, and the field technology application of vertical and horizontal Wells is carried out. The results show that the dual tube gas lift technology has good adaptability in the deliquification of CBM, and the field application has achieved good production results. After the process modification, gas production of CBM Wells increases continuously, while water production decreases gradually, with the maximum gas rate exceeding 2400 m3/d. According to the latest production data, well L31 has been in steady production for more than 9 months, with an average gas rate of 1294.56 m3/d, which greatly exceeds the capacity before the transformation. Because there are no moving parts in the wellbore, the pump inspection period is greatly improved, and it has the potential to be widely applied in CBM. [ABSTRACT FROM AUTHOR]

The geomechanical modeling turned out to be an essential component of the hydrocarbon exploration assisting reduction of risk of drilling issues and optimization of hydraulic fracturing treatment. This study provides a workflow of critically stressed fracture (CSF) analysis dedicated for coal layers. The main focus of the paper is applying the 1D mechanical models and following modelling of hydraulic fracturing treatment to describe the fracture behavior under the impact of the stresses at the wellbore scale. Another objective of presented study is demonstration of benefits of 1D and 3D CSF analysis to understand fracture contribution to gained volume of hydrocarbon after fracturing of coal seam. Interpretation of fracture orientation and their behavior is vital to effective development of coal bed methane (CBM) resources as the CSF can be responsible for considerable part of CBM production. Natural fractures and faults contribute to fluid flow through rock. It is often noted that natural fractures may not be critically stressed at ambient stress state. However, during stimulation the optimally oriented natural fracture sets have an inclination to become critically stressed. Hence, understanding of the recent stress state and fracture orientations is significant for well planning and fracturing design. The outcome of this study are comprehensive 1D mechanical Earth models (MEMs) for analyzed wells and explanation of behavior of identified CSF under variable stress state as well as understanding of the connectivity of natural fractures within zone subjected to fracturing treatment. [ABSTRACT FROM AUTHOR]

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Demand for a cleaner source of energy is increasing in India. In the search for alternate energy sources, coal bed methane gas receives considerable attention for its potential as a good energy source. During the coalification process, methane gas is captured in the coal seams and later released during coal mining operations. Coal bed methane separation is crucial for both economic benefit and methane emission reduction. The methane production from seams is an efficient way to reduce greenhouse emissions and provide a safe mining operation environment. In India, the production of coal bed methane on a commercial scale has been recently observed. In the present paper, an attempt is made to understand and establish a 3-D excavation of coal bed methane from reservoir simulation (COMET3) for Gondwana coal seams in the Sitarampur block of the Raniganj coalfield in India. The simulation study was carried out for a period of 25 years for the recovery of methane from the reservoir. It is observed from the simulation study that 372 million cubic meters CO2 equivalent greenhouse gas emissions can be prevented by the extraction of methane with space and time. The fracture gas concentration increases with time, and it is observed that fractures are fully saturated with gas in 3000 days. [ABSTRACT FROM AUTHOR]

The present investigation aims to evaluate the coal bed methane (CBM) potential of the Permian coal deposits in the Son-valley Basin, India, using a series of geochemical, organic petrological, and gas adsorption experiments. The results of the proximate analysis and the relation between atomic hydrogen to carbon (H/C) and oxygen to carbon (O/C) ratios mark the sub-bituminous to bituminous rank of these coals, which are suitable for generating CBM. The thermally cracked hydrocarbons released under the Rock–Eval S2 curve (77.29–168.54 mg HC/g rock) along with the TOC (total organic carbon) content (TOC: 42.53–71.42 wt%) reflect excellent source rock potential for hydrocarbon generation. The hydrogen index (HI) and oxygen index (OI) ranging from 110 to 332 mg HC/g TOC and from 3 to 9 mg CO2/g TOC, respectively, indicate the presence of type III kerogen with the mixture of type II and III kerogen. The Rock–Eval Tmax and estimated vitrinite reflectance values mostly suggest an early mature to peak mature phase of oil/wet gas generation. Besides, the studied coals are dominated by ligno-cellulosic vitrinite (39.71–56.83 vol.%), with a substantial volume of inertinite (30.54–45.49 vol.%), and labile liptinite (9.71–22.15 vol.%) macerals (on mineral matter-free basis), which may advocate gas-prone nature of these coals. The relations of the Langmuir volume (VL: 17.4–21.6 cc/g on a dry ash-free basis) with organic and inorganic constituents of the coals reveal the integrated influence of organic matter, minerals, and thermal maturity of kerogen on gas sorption capacity. [ABSTRACT FROM AUTHOR]

As one of the most essential clean energy sources, the extraction and utilization methods of Coal Bed Methane (CBM) have been widely investigated and analyzed. A good understanding of the CBM seepage behavior in complex reservoir fracture–matrix structure is fundamental to the exploitation. In this study, we propose a new approach to investigate the interactions between macroscopic behavior and reservoir microstructure by the following parameters: (1) matrix fractal dimension; (2) fracture fractal dimension; (3) maximum fracture length; (4) maximum pore diameter. The results indicate that the fractal seepage model proposed in this study is more effective than the classical cubic seepage model for investigating thermal conduction, seepage and fracture–matrix interactions in coal seam. When the fractal dimension increases by 0.4, the permeability increases by about 10%. In addition, reservoir permeability is inversely proportional to coal seam temperature and directly proportional to fracture–matrix fractal dimension, maximum fracture length and maximum pore diameter. Furthermore, we also investigate the evolution of reservoir permeability with the extraction process, coal seam temperature and gas pressure under various microstructural parameters. It can be concluded that different structural parameters will draw various effects on coal seam gas seepage, which cannot be obtained by the cubic permeability model. Highlights: Relationship of fracture-matrix structure and macroscopic behavior is proposed. A new cross-scale coupled hydrological-thermal–mechanical model is developed. The impacts of the macroscopic behavior on the microstructure is analyzed. Permeability of unconventional reservoir is enhanced by 10.05% to 27.40%. [ABSTRACT FROM AUTHOR]

Air leakage in borehole not only seriously restricts the development and utilization of coal bed methane (CBM) but also affects gas disaster prevention and underground safety mining. Several triaxial-seepage experiments were conducted to analyze the seepage characteristic change of raw coal under different loads in consideration of the above-mentioned problems. On this basis, a dynamic multifield coupling model, including coal permeability evolution, creep mechanical, and binary gas flow system, was proposed to describe the CBM drainage process. Based on this fully coupling model, factors influencing air leakage flux were investigated by numerical method. Findings show that the dynamic change of air leakage flux is determined by stress and permeability variation. Therefore, in practical work, grouting method can be adopted to decrease coal permeability and softening modulus as well as increase coal residual strength and support stress, so as to reduce air leaking in borehole. Furthermore, we also proposed a new remedy method, including self-developed GP material and corresponding sealing–plugging integrative device, for preventing borehole leakage. The field test results indicate that the gas concentration of the boreholes was effectively enhanced after the leakage treatment by this method, and a great drainage level was still maintained at the late period. The results in this work can provide a remedy method for improving borehole sealing and drained gas quality. Such method is important for enhancing the CBM utilization, reducing greenhouse gas emission, and ensuring mining safety. [ABSTRACT FROM AUTHOR]

In the present investigation, composite coal seam III–IV of the Ramagundam coalfield of the Godavari Basin has been studied through scanning electron microscopy (SEM), optical microscopy, Fourier transform infrared spectroscopy (FTIR), proximate and ultimate analyses, porosimetry and permeametry. Vitrinite reflectance ( R ¯ r from 0.38 to 0.49%) and proximate parameters put sub-bituminous rank to this coal. Vitrinite (48.3% mmf basis) and inertinite (37.2% mmf basis) are abundant while liptinite (14.5% mmf basis) occurs in subordinated amount. Cleats and the fractures are more in the vitrain band but they are partially filled with mineral matter. Dead-end types of pores are common. Open and unmineralized cell pores and cavities in the fusain band offer adsorption sites and micro-permeability, but at places, they are broken, homogenized and mineral filled, which eventually reduce the permeability. Porosity (1.88–2.75%) and permeability (0.017–0.029 millidarcy, mD) substantiate the availability of adsorption sites but poor methane migration in coal seam. The compressive strength value (24.28–29.55 megapascal, MPa) gradually increases from the top towards the bottom of the coal seam and leads to compaction, and lesser permeability and porosity in the coal seam. The elastic modulus value suggests less cleat development (face and butt cleat). The studied coals are thermally less mature and yet to approach the oil window. Most of the samples show a volatile matter content more than 37.8%, a value below which thermogenic methane generation begins. Nevertheless, FTIR supports a moderate hydrocarbon-generating potential. Besides, the biogenic gases are likely to occur in variable quantity. [ABSTRACT FROM AUTHOR]

Coal bio-gasification is one in situ coal gasification technology that utilizes the digestion of organic components in coal by methanogenic bacteria. It is not only an effective technology to enhance the recoverable reserves of coalbed methane, but also an important technical method to promote clean coal utilization. Relevant laboratory researches have confirmed the technical feasibility of anthracite bio-gasification. However, in the complex environment of coal bed, whether in situ gas can be yield with methanogenic bacteria needs to be verified by in situ experiments. In this study, a vertical well and a horizontal well were used in Qinshui basin to perform field experiments to confirm the technical industrial feasibility. The concentration of Cl− ion and number changes of Methanogen spp. were used to trace nutrition diffusion. Gas production changes and coalbed biome evolution were used to analyze technical implementation results. The trace data and biome evolution identified that: (1) The development of Methanoculleus spp. has a significant positive correlation with culture medium diffusion; (2) the structure of coalbed microbial community was significantly changed with the injection of nutrition, and the newly constructed methanogenic community was more suitable for fermentation of coal; and (3) the evolution of dominant microflora has further enhanced bio-gasification of coal. Gas production data showed that the gasification of coal lasted 635 and 799 days and yielded 74,817 m3 and 251,754 m3 coalbed methane in Z-159 and Z-7H wells, respectively. One nutrition injection in coalbed achieved an average of 717 days of continuous gas production in experimental wells. Results confirmed that coalbed methane enhancement with bio-gasification of coal is a potential technology to achieve the productivity improvement of coalbed methane wells. And the findings of this study can help to further understand the mechanism of in situ coal bio-gasification and provide theoretical support for the development of biomining of coal. [ABSTRACT FROM AUTHOR]