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Copyright of Mining Report is the property of GVSt,GesamtverbandSteinkohlee.V. 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 Mining Report is the property of GVSt,GesamtverbandSteinkohlee.V. 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 Mining Report is the property of GVSt,GesamtverbandSteinkohlee.V. 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.)

This paper presents the results of a statistical analysis study for the influence of air humidity on the ignition sensitivity of gaseous explosive atmospheres in underground firedamp mines. The first half of the paper briefly presents the experimental results used. Since the results are probabilistic, methods of statistical analysis have been used. The second section presents the results of statistical analysis of experimental data. [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]

The risk of uncontrolled escape of firedamp is one of the major manifestations of closing coal mines in the Ostrava -- Karviná District in the Czech Republic. Mining activity was also carried out in areas close to urban or suburban development in the city of Ostrava, including its historical district. The article presents aspects of dealing with the hazards as well as measures that have been implemented with respect to the risk of uncontrolled escape of firedamp. It outlines some of the applied approaches and equipment, which can eliminate this hazard. The figures included in the article document the current state of the solution. [ABSTRACT FROM AUTHOR]

Highlights • A transfer coefficient ratio was defined as the conversion node of gas transport. • The influence of various factors on the evolution of stage characteristic was analyzed. • The transfer coefficient ratio was used to analyze the best distance of borehole. Abstract Diffusion and seepage play a significant role in the mine gas extraction, while their influence degree is dynamic with the change of time or location, showing a notable dynamic stage characteristic. Therefore, it is significant to master the conversion node of gas transport for improving the gas production. However, it is difficult to determine the conversion node and master controlling roles during mine gas extraction due to the lack of judgment index. In this work, a dual-porosity model was constructed to describe the gas transport in coal seam. Then, a transfer coefficient ratio between gas diffusion and gas seepage was used to define as the conversion node. Furthermore, our model was validated by comparing with the previous model, showing that our model can better describe the evolution of gas pressure under different stress conditions. The influence of stress, initial permeability and initial diffusion coefficient on the conversion node were investigated. Results showed that the initial permeability shows the most notable influence on the conversion node, followed by the stress. The initial diffusion coefficient has the relatively complex effect on the conversion node depending on the specific reservoir conditions. Finally, the transfer coefficient ratio was used to determine the best distance of boreholes for improving the gas production. The research results are important for CBM and mine gas extraction. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen energy can be generated by steam methane reforming method, and methane production from coal seams is important to ensure the abundance of hydrogen energy generation. The gaseous compound of hydrogen and carbon production performance analysis is important and pressure transient analysis can be used to analyze the flow characteristics in the development of gaseous compound of hydrogen and carbon in coalbed reservoir. The computational models on vertical wells, vertically fractured wells and horizontal wells have been studied intensively in coalbed reservoir to predict gaseous compound of hydrogen and carbon production behavior. For a thin coalbed methane reservoir, it will be more effective to develop through forming horizontal fractures near the wellbore. However, such model has not been established. To analyze gaseous compound of hydrogen and carbon production performance for horizontal fractures in coalbed methane reservoirs, this paper presents a 3D point-sink model and the corresponding solution is obtained through using Laplace transform and Fourier transform methods. The point-source integral method is used to obtain the general solutions of gaseous compound of hydrogen and carbon flow through horizontal fractures. The pressure transient solution have been compared with numerical simulation to validate its accuracy. Type curves are established to analyze the flow characteristics of gaseous compound of hydrogen and carbon, which can be divided into four regions, i.e., linear flow region, transition flow region, inter-porosity flow region, and radial flow region. The sensitive analysis of the key model parameters on type curves has been conducted. Highlights • A novel production performance model in coalbed reservoir with horizontal fractures is developed. • The accuracy of the derived pressure transient analytical solution is validated with numerical simulation. • The production performance for horizontal fractures in CBM reservoirs is analyzed. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a comprehensive semi-analytical model was presented to investigate pressure transient behavior for asymmetrically fractured wells in organic compound reservoir of hydrogen and carbon with dual-permeability behavior. Stehfest inversion algorithm can be used to transform it back into time domain to obtain pressure solution. The presented solution was validated well with numerical solutions. Flow characteristics for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon were divided into five regime. The effects of some important parameters on dimensionless pressure and its derivative curves were analyzed in details, including inter-porosity flow coefficient from matrix to natural fractures λ , storage coefficient ω , fracture asymmetry factor θ and permeability ratio κ. The presented model can be used to predict production performance and do well test analysis in the development of dual-permeability organic compound reservoir of hydrogen and carbon. Highlights • A dual-permeability model for asymmetrically fractured wells is presented. • The Lapalace-transform semi-analytical solution is developed. • The presented solution was validated through using numerical simulation. [ABSTRACT FROM AUTHOR]

Abstract With the continuous expansion, exploration and development of unconventional natural gas resources, mainly coalbed methane, shale gas and tight gas, some areas overlapped by two or three types of unconventional natural gas reservoirs are explored, e.g., the Linxing, Shilou and Linfen blocks located in the east margin of the Ordos Basin, China. Gas extraction from an individual reservoir becomes not economic as gas resources are not fully recovered; thus, gas coproduction from two or multiple layers is an effective method for improving gas production. In this work, a mathematical model of gas and water two-phase flow for the coproduction of coalbed methane and tight gas is developed. The adsorption characteristics, stress-sensitive and matrix shrinkage effects on coal permeability, and the stress-sensitive effect of tight sandstone are all considered in the model. The gas production related parameters, such as bottom hole flowing pressure, reservoir pressure differences, reservoir properties (e.g., permeability, cleat compressibility of coal, and Langmuir isotherm parameters) are discussed and compared with different geological conditions. The results show that the gas and water flow from the coalbed and sandstone reservoirs show no interference between each other under a constant pressure drainage system; the sandstone reservoirs show a fast pressure drawdown with a high gas production rate decline, while the coalbed reservoir is slow in pressure drawdown and the gas production rate increases gradually. The properties of a specific reservoir have a great influence on its own gas production performance, but with no influence on the other reservoirs. It was found that a lower constant drainage pressure should be adopted in the case of stress-sensitive effects, and coal with a lower cleat compression coefficient and Poisson's ratio value is better for higher gas production. The production contribution from each layer can be acquired if a specific production rate is set. If the reservoir pressure difference between the two reservoirs is too high (for instance at least > 3 MPa in the cases studied in this work), gas and water intrusion may happen, but the reservoirs would be balanced quickly. Thus, the coproduction of coalbed methane and tight gas from one well bore is feasible, and more work should be conducted on proposing a proper drainage strategy to improve the gas resource recovery efficiency in coal-bearing strata. Highlights • A mathematical model of two phase flow from both CBM and tight sandstone formations was proposed. • Sensitivity of the reservoir properties on gas production was studied. • Production contribution from each formation can be distinguished. • Interferences of the two formations were discussed. [ABSTRACT FROM AUTHOR]

Abstract Three geologic sections along the main coal seam (MCS) of the Middle Jurassic (Bathonian) Safa Formation of Maghara mine are examined. Samples collected have been studied. The fuel analyses of coal samples were conducted to determine their Rank characteristic. Fuel analysis classified the studied Maghara MCS as high grade coal, medium rank (D) of para-bituminous class based on its average values of ash content 7.1% (dry-base; d.b), gross calorific value (29 Mj/kg; moist ash free) and random vitrinite reflectance 0.43%. Synonym nomenclature of the studied Maghara coal based to ASTM classification is high volatile (C) class of bituminous group with agglomerating character attributed to their values of gross calorific value 30 Mj/kg-(moist-mineral-matter-free; mmmf), fixed carbon 45% (dry-mineral-matter-free; dmmf) and volatile matter 54.8% dmmf. Elemental ratio of H/C versus O/C indicate that majority of the studied Maghara coal samples occupy the area of vitrinite genesis pathway on Van-Krevelen diagram, and within the area of per-hydrous in Seyler chart of dominated anoxic condition. Studied coal seam is a type III kerogen corresponding to humic characteristic, within the immature and mature zones of coalification. [ABSTRACT FROM AUTHOR]

Mine gas overflow is a serious threat to the safe and efficient longwall mining of gassy coal seams. Based on the field mining conditions and gas extraction of the fully mechanized top-coal caving face of a gassy coal mine, the space volume fraction distribution and emission (extraction rate) of gas in the face were tested by an arrangement of measuring points in the stereo grid. The isograms of gas volume fraction distribution for each measurement section and air direction in the face are drawn. The research shows that each measurement section gas volume fraction distribution is presented for an asymmetric concave curve along the vertical direction of the coal wall in the air-inlet side and the air-return side of the face; on the working face air-return side, the determination of gas volume fraction distribution of the section appears as falling straight line along the vertical direction of the coal wall. Before the first weighting, the absolute quantity of gas emission in the working face increased with the advancing of the working face, reached the maximum at the time of the first weighting, and then remained stable. [ABSTRACT FROM AUTHOR]

Coal and gas outburst accidents occurring in underground coal mines generally cause great casualties and economic losses, especially in construction areas of coal seams where the outburst risks are not accurately evaluated. Therefore, accurately identifying the outburst risks of coal seams is necessary and critical to prevent and control outbursts. In order to improve the prediction accuracy for outbursts in working faces of coal roadways, a self-designed drilling device that can simulate the in-situ outburst prediction of coal roadways was used in this study. We used the coal samples with different coal ranks to adsorb CO 2 and N 2 with different pressures in the laboratory, so as to simulate the coal seams with different outburst risks. Finally, boreholes for predicting the outburst risk were drilled in the simulated coal seams to study the correlation between common dynamic phenomena (e.g. gas and coal being ejected from the borehole (GCEB) and drill pipe being stuck by coal mass in the borehole (DPSC)) and outburst risks. The results show that the greater the outburst risks of coal seams, the more frequent the occurrence of GCEB and DPSC is. The GCEB phenomenon for outburst prediction is attributed to small-sized coal and gas outbursts in boreholes, while the occurrence of DPSC phenomenon does not affirm that there definitely are outburst risks on working faces. The DPSC phenomenon indicating outburst risks is generally accompanied with GCEB, which form a linkage system and are triggered successively. [ABSTRACT FROM AUTHOR]

In view of the local extreme problem of the gradient descent algorithm, which makes the working face of mine gas emission prediction uncertainly, this paper combined Wolf pack algorithm (WPA) with complex neural network nonlinear prediction method to the established new prediction model. The WPA shows good global convergence and computational robustness in the solving process of complex high-dimensional functions. Working face in a coal mine as a case, this paper selects seven factors as input variables of the mine gas emission prediction, uses training data to mature prediction model and adopted it to predict six group gas emission data. Research results show that the mean absolute percentage value of the complex neural network model which has been optimized by WPA is 0.06%, the root mean square error value is 0.0191, the mean absolute error value is 0.0175 and the equal coefficient value is 0.9979. The prediction results are very close to the real value, and the change trend is highly consistent with the actual situation. [ABSTRACT FROM AUTHOR]

Gas outburst has always affected the safety of coal mining. To eliminate this risk by high-efficiency extraction of coalbed methane (CBM) in 4102 working face of number 3 coal seam in Hebi Number 3 coal mine, a model of CBM extraction in working face was established which was considering the mining impact of adjacent 4101 working face. In this model, the coupling relationships between stress, desorption, and migration of methane were analyzed. Moreover, we also studied the changes of methane pressure, plastic failure scope, and permeability of coal during the mining and then verified the results with the field data. And on this basis, a stimulation solution for methane extraction by injecting air into coal seam was presented, and the extraction effect was simulated. The simulation results show that the injection of air decreases the effective stress of coal which increases the permeability of coal and promotes the methane migration within the coal seam fractures. Besides, affected by the velocity of gas migration, the pressure drop between fractures and matrix will reduce with time while air injection can provide extra power for gas migration in fractures which causes the desorption and diffusion of methane in the matrix. So this stimulation solution can enhance the efficiency of gas extraction of coal seam and prevent gas outburst of the working face. [ABSTRACT FROM AUTHOR]

Coalbed methane has emerged as a viable natural gas resource in India since 2007. The understanding of gas genesis kinetics, storage mechanisms and the geological controls is vital for exploration and successful recovery of gas in a cost-effective manner. In this respect, a multidisciplinary analytical approach including gas content, stable isotopes ( δ 13 C 1 ), hydrocarbons distribution, reconstruction of original organic matter, chemical properties, sorption kinetics and the role of petrographic constituents have been assessed. The volatile matter content varies from 20.2 to 32.1 wt%; indicating medium volatile to high volatile bituminous rank of coal with the maximum vitrinite reflectance (VR o %) ranging from 0.63 to 0.98%. The studied coals are vitrinite rich and contains vitrinite group macerals in the range of 41–65 vol%. Dendritic micro-fractures are confined to vitrite microlithotype, and secondary mineralization helps preserve fracture connectivity. The average gas content of coal seams is 2.06 cc/g. The increase in gas content values per 100 m is about 0.38 cc/g emphasizing escape and migration of hydrocarbons during restructuring and tectonic activities in the basin. The relationship of C3/C1 and C2/C1 ratios is indicating that the hydrocarbons in desorbed gas originated from the thermogenic process. The large concentration of methane in desorbed gas and its stable isotope signatures ( δ 13 C 1  < −40‰) also indicates the thermogenic origin of gases in coal seams. Few desorbed gas samples have been found in the mixed gas region, which may be due to the influx of fresh water carrying bacteria leading to the generation of biogenic gases and subsequent mixing with the sorbed thermogenic gases. The values of S1 (0.19–0.78 mg HC/g) and S2 (10.31–25.63 mg HC/g) indicate excellent source rock potentials. The positive correlation of original hydrogen index (HI O ) with present-day hydrogen index (HI PD ) and original organic content (TOC O ) with present-day organic content (TOC PD ) suggests uniform consistency in organic carbon conversion to hydrocarbons. The gas content compared with sorption capacity reveals the undersaturation of coal seams. The experimental results summarize that the low gas content is a critical issue. Similarly, the low, quality and quantity of CH 4 may affect the exploration and recovery of methane in the long term into this basin. But, the low values of sorption time (0.12–6.65 days) signifies good diffusion characteristics that may support the recovery of gas. Finally, it is concluded that depth of occurrence, maturity and pore/cleats associated with microconstituents control the gas accumulation and transport in coal seam reservoirs of South Karanpura coalfield. [ABSTRACT FROM AUTHOR]

The enhancement of coalbed methane extraction by repeatedly injecting CO2 has been investigated for many decades, mostly focusing on the fracturing and flooding effect in numerous lab experiments, simulations, and field applications, whereas the effect of the accompanying heat transfer during cyclic liquid CO2 (LCO2) injection has rarely been studied. In this paper, the influence of the cyclic injection of cryogenic LCO2 with different cycle numbers and time on the coal pore variation was explored using low-field nuclear magnetic resonance to extract the T2 spectral information. The results have shown that as the cycle number increased, the adsorbed water (AW) decreased while the capillary water (CW) and bulk water (BW) values increased, and the pore volumes were magnified greatly based on the tendencies of fitted polynomial curves of Isa1 values and fitted exponential curve of Isa2 values. With increasing cycle time, the increase ratios of AW, CW, and BW were not independent but mutually influenced, and the Isa1 values approximately displayed a “rapid increase-slow increase” tendency, while Isa2 roughly showed fluctuating or “increase-decrease” tendencies. The changes in the IWS and FWS showed that the increased pore connectivity could allow more water to infiltrate into the pores at the saturation state and accelerate the removal of fluid water during the centrifugation state. The φe and φr variations indicated that longer cycle time coupled with a larger cycle number could cause damage generation and enhance the pore connectivity. [ABSTRACT FROM AUTHOR]

To enhance desorption of coalbed methane and increase extraction efficiency, a technique using microwave irradiation is proposed. Methane desorption experiments without and with microwave irradiation were carried out in the laboratory using an experimental system developed to study methane desorption. The experimental results show that microwave irradiation causes the total quantity of methane desorbed to increase from 1.91 to 3.92 times larger than the quantity desorbed without MI. Two hour trials were performed, applying microwaves for 4, 8 or 16 min, equivalent to output energies of 192, 384 and 768 kJ. These results show that 1 kJ of microwave energy can cause methane desorption to increase by 0.0088 ml per gram of coal. Under successive microwave irradiations of 40 s, the desorption rate increases by a factor of 10.2. Kinetic analysis also found that microwave irradiation enhances the methane diffusion coefficient and decreases the attenuation coefficient. Regardless of which diffusion model is used to determine the diffusion coefficient, the quantity of gas desorbed increases as the microwave irradiation time increases. The pore and surface features of coal samples exposed to microwaves were determined by using mercury intrusion porosimetry and nitrogen adsorption and specimens were examined by scanning electron microscopy. Methane desorption evidently results from both the microwave thermal effect and structural damage to the coal. The results reported herein reveal the mechanisms that promote methane desorption by microwave irradiation and suggest a new field technique for extracting coalbed methane. [ABSTRACT FROM AUTHOR]

The study was performed on 4 different coals of varied rank. Pyrolysis was conducted on coals of different ranks in gold capsules, with the yield and stable carbon isotopic values of selected gas components and liquid hydrocarbons separately measured to investigate the hydrocarbon generation chemistry, isotopic compositions, and kinetic parameters in coal. With increasing heating temperature, the methane concentrations and total gaseous hydrocarbons increase consistently with temperature. The liquid hydrocarbon concentrations first increase to maximum values and then decrease with temperature. Coals of higher ranks are more likely to primarily produce methane, while coal with low maturity is more likely to produce wet gases. The compositional differences of the four coals become similar at the late stage of the pyrolysis experiment, with a methane content >95%. All of the experiments show a similar isotope trend δ 13 C 1  < δ 13 C 2  < δ 13 C 3 at the same temperature. The δ 13 C values of ethane and propane became less negative with increasing temperature for all four experiments. The gap between δ 13 C 1 and δ 13 C 2 is greater than that between δ 13 C 2 and δ 13 C 3 . There is a linear relationship between ln(C 1 /C 2 ) versus ln(C 2 /C 3 ). When ln(C 2 /C 3 ) increases sharply as ln(C 1 /C 2 ) increases, the decomposition rates exceed the generation rates for C 4   +5 , C 3 , and C 2 as secondary oil cracking occurs. At high temperatures, both parameters are larger. The activation energy distribution of 48–72 kcal/mol for Yilan coal is slightly higher than 55–66 kcal/mol for Xinjing coal, but significantly higher than the distribution of 46–61 kcal/mol for Qinan coal and 51–67 kcal/mol for Shitai coal. [ABSTRACT FROM AUTHOR]

Gas desorption and transport in coal matrix plays pivot roles to estimate in situ gas content, forecast gas production from coalbed methane (CBM) wellbores, classify the gas/coal outburst proneness of coal seams and estimate gas emission rate for active mine ventilation planning. Only using Fick’s law to depict methane transport in coal matrix may result in an erroneous prediction because it uses only adsorbed phase gas to calculate methane concentration gradient. In this study, a series of coal-methane ad/desorption experiments were carried out under different pressure boundary conditions. Following this, an effort is made to propose a semi-empirical desorption model describing the entire methane diffusion process and discuss its superiority and applicability by comparing to various commonly used models. The proposed approach includes two different theoretical models (Fick diffusion model, assuming concentration-difference transports gas; and Density model, assuming density-difference transports gas), to model methane diffusion corresponding to the experimental sections conducted in this study. Afterward a series of comparisons between the experimental desorption data and two sets of simulated desorption data obtained by numerically calculating the two theoretical models were conducted, and it shows that Density model exhibited a higher accuracy over Fick model. The proposed Density model is more effective in describing the non-linear gas diffusion behavior in coal matrix for the experimentally studied coals. Essentially, the Density model covers and promotes the Fick diffusion model, and is competent in mathematically modeling both adsorbing gas and non-adsorbing gas transport behavior in porous media. Moreover, the Density model can be directly incorporated to the existing dual-porosity model to model methane migration in coal matrix in coal seam. [ABSTRACT FROM AUTHOR]

Longwall chock support failures seriously restrain the safety and high-efficiency of mining of extra thick coal seams, as well as causing a great waste of coal resources. During longwall top-coal caving (LTCC), the influential effect of the properties and the movement regulation of top-coal on strata behavior cannot be ignored, since the top-coal is the medium through which the load of the overlying strata is transferred to the chock supports. Taking Datong coalfield as an example, the mechanism of a chock support failure in the LTCC face was investigated. Research findings indicated that the hard top-coal and insufficient chock support capacity were primary reasons for chock support failure accidents. On account of the field-measured results, a new method to determine support capacity was proposed, which fully took the impact of the top-coal strength into consideration. The calculation revealed that the required support capacity had exceeded the existing production maximum, at about 22,000 KN. Since it was unrealistic to simply increase chock support capacity, other approaches, according to the theoretical analysis, were proposed, such as lowering the integrity and strength of the top-coal, and upgrading its crushing effect to weaken the support load effectively during the weighting period, which reduces the likelihood of chock support accidents occurring. Based on this, hydraulic fracturing for hard top-coal and optimization of the caving process (chock supports raised up and down repeatedly by manual operation before moving forward) were presented. The proposed solutions were successfully applied in LTCC-west8101 for subsequent mining and achieved substantial benefits. The above research provides valuable references and ideas for the control of strata behavior to ensure safe and highly efficient mining in extremely thick and hard coal seams with the LTCC method. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) resources are abundant in Gujiao blocks, Xishan coalfield, China. However, there is little previous geological research regarding coalbed methane. Using a quantitative and qualitative index, the hydrocarbon source rocks and preservation conditions of No. 2, 8 and 9 coalbed methane systems in Gujiao blocks were evaluated through a multi-level fuzzy method. On this basis, the comprehensive favourable area of three CBM systems and multi-layer commingled production were predicted. The results showed that the comprehensive score trend of hydrocarbon source rocks in Gujiao blocks gradually increases from southeast to northwest. The comprehensive score trend of preservation conditions increases gradually from north to south. The No. 2 coalbed methane system of the Shanxi formation is given priority over level II, which is distributed in the central and southern study area. The No. 8 coalbed methane system of the Taiyuan formation is given priority over level III, followed by level IV. The No. 9 coalbed methane system of the Taiyuan formation is given priority over level II and level III, which is distributed in the central and southern study area. Most of the area is suitable for individual CBM exploitation of No. 8 coal. The favourable area for the No. 2+8 coal layer is located in parts of the central, south-western and south-eastern study area. The favourable area for No. 8+9 coal layer is located in the Dongqu well field and the southern Tunlan well field. The favourable area for No. 2+8+9 coal layer is located in the eastern Yang Zhuang well field. [ABSTRACT FROM AUTHOR]

Backfill mining is an effective way to control ground subsidence and govern gangue. To solve the problem of thin coal seam mining under villages, a new thin seam backfill mining technology was proposed. This paper investigated a reasonable proportion of filling materials by experiments, designed the filling system and introduced key technologies for thin seam working face filling. Finally, an industrial test of thin seam backfill mining technology was carried out in the C1661 working face, Beixu Coal Mine. The results show that the developed filling material meets both the pumping liquidity and strength requirements of the filling body during the early and late stages. The design and equipment selection of the paste filling system were reasonable. By using the key technologies for thin seam working face filling, the time needed for working face filling, the connection and disconnection of the filling pipeline and gob-side entry retaining were all greatly shortened. The labor intensity of the workers was reduced, and the mechanization level of the mine was improved. A fill mining length of 480 m was successfully completed. With effective roof subsidence control, the ground subsidence can be reduced, and good results can be achieved. This study can contribute to the development of backfill mining in thin coal seams. [ABSTRACT FROM AUTHOR]

In order to solve the problem of reciprocating motion in no beam supported mining machines, putting energy saving as a starting point in Coal Bed Methane (CBM) exploitation, this paper designs a completely non-circular gear automatic reversing vertical drainage machine based on the theory of non-circular gear transmission. In the field of CBM exploitation, the use of non-circular gears is an attempt at an innovation. First of all, according to the working conditions of the pump and use requirements, a scheme is established whereby the one-way rotary motion of the motor is changed into reciprocating motion so that it could drive the oil pumping rod to achieve the upper and lower mining. Secondly, this paper has designed a new type non-circular gear reversing box as the core component to replace the traditional four beam linkage mechanism and also provides elaborate calculations. Finally, the movement simulation of the non-circular gear reversing gear system is completed. Comparing the motion simulation results with the theoretical ones, the correctness of our theoretical analysis can be verified. Compared with the traditional devices, the new coal seam gas drainage machine model design has nearly 11% higher efficiency, which has obvious energy saving effects and reduces the cost of mining coal seam gas. [ABSTRACT FROM AUTHOR]

As a new technology, characterised by an absence of pollution and low energy consumption, ultrasonic waves have been widely used to promote the fracturing of oil-bearing and coal bed methane reservoirs, so as to increase their permeability. The propagation of ultrasonic waves in coals, and its influencing factors, is the key factors determining ultrasonic wave behaviour in promoting the permeability of coal seams. In this research, a device for measuring the attenuation of the ultrasonic waves in coal and rock masses was used to measure the attenuation coefficient of ultrasonic waves in coal briquettes with different properties. The standing wave method was used to fit the attenuation curves of the ultrasonic waves in the coal briquettes with different variables. Meanwhile, a dynamic strain instrument was used to record the energy attenuation experienced by ultrasonic waves in fractured coals with different moisture contents. The experimental results demonstrated that increases in the number of the fractures, and the content and size of the impurities in the coal briquettes, all led to an increased attenuation coefficient of the ultrasonic waves. Meanwhile, the attenuation coefficient was positively correlated with the cube of the number of fractures, and the content and size of the impurities. Besides, it was discovered that with the increase in the moisture content in coal briquettes, the attenuation coefficient of the ultrasonic waves increased firstly, followed by a decrease, and the energy consumed by the ultrasonic waves was increased firstly before a reduction as it penetrated through the fractured coals of the same length and increased moisture content. Additionally, it was found that by injecting water into the coals fractured by ultrasonic waves, the attenuation coefficient of the ultrasonic waves in coals can be reduced. Therefore, the propagation distance of the ultrasonic waves in coals was increased. [ABSTRACT FROM AUTHOR]

Internal structure of coalbed methane (CBM) reservoirs can be evaluated through ultrasonic measurements. The compressional wave that propagates in a fractured coal reservoir may indicate the internal coal structure and fluid characteristics. The P-wave propagation was proposed to study the relations between petrophysical parameters (including water saturation, fractures, porosity and permeability) of coals and the P-wave velocity (V p ), using a KON-NM-4A ultrasonic velocity meter. In this study, the relations between V p s and water saturations were established: Type I is mainly controlled by capillary of developed seepage pores. The controlling factors on Type II and Type III are internal homogeneity of pores/fractures and developed micro-fractures, respectively. Micro-fractures density linearly correlates with the V p due to the fracture volume and dispersion of P-wave; and micro-fractures of types C and D have a priority in V p . For dry coals, no clear relation exists between porosity, permeability and the V p . However, as for water-saturated coals, the correlation coefficients of porosity, permeability and V p are slightly improved. The V p of saturated coals could be predicted with the equation of V p -saturated = 1.4952V p -dry–26.742 m/s. The relation between petrophysical parameters of coals and V p under various water saturations can be used to evaluate the internal structure in fractured coals. Therefore, these relations have significant implications for coalbed methane (CBM) exploration. [ABSTRACT FROM AUTHOR]

Owing to the gas content is an important indicator in coal and gas outburst prevention, we set up a gas adsorption and desorption experimental system with temperature controlling, and draw out a method combining with experimental analysis, theoretical calculation and project inspection to determine the critical value of gas content in coal and gas outburst prediction. This paper takes D6 coal seam in Pingdingshan No.1 coal mine as an example, sets up the powder function equations among the gas content, gas pressure and gas desorption of drill-cuttings (Δh2). The gas content minimum is calculated as 5.04m3/t as the gas pressure and Δh2 reach their critical values respectively, which is lower than the critical value of gas content (5.19m³/t) determined by Langmuir formula, considering a deformed coal with a thickness of 0.6m exists in D6 coal seam, the critical value of gas content is determined as 5.0 m3/t finally, and its accuracy is proved well in engineering application. [ABSTRACT FROM AUTHOR]

Understanding permeability evolution in coal is critical for the prediction of coalbed methane (CBM) production and prevention of mine gas disasters. The primary objective of this study is to investigate the influences of gas pressure and temperature on the permeability and steady-state time of a Chinese anthracite coal. Using a self-developed coal and rock steady-state permeability testing system, the permeabilities of Chinese anthracite coal samples with CH 4 , CO 2 and helium were measured under various gas pressures and temperatures. Meanwhile, the relationships between the steady-state time and gas pressure and temperature were examined. The results indicate that the changes of methane and carbon dioxide permeability with respect to gas pressure do not always monotonically increase or decrease. A tendency of an initial decrease, and subsequent increase is observed. For a seepage system, the time required to achieve a steady state increases nonlinearly with the increment of gas pressure, which indicates the typical characteristics of the Langmuir model. If other conditions are held constant, the time required to reach a steady state is longer for higher confining pressures. Carbon dioxide takes longer to reach the steady state than methane. The relationship between permeability and temperature is relatively complicated. Temperature affects the permeability by influencing the thermodynamic expansion of coal, gas molecular dynamics and adsorption/desorption. The actual permeability depends on the influence of the leading factor. We believe that this research will have a substantial guiding significance for field CO 2 -ECBM and the prevention of mine gas disasters. [ABSTRACT FROM AUTHOR]

An evaluation of the ability of the stretched exponential (SE) equation to describe the sorption kinetics and the rate of expansion/contraction of hard coal in coal–carbon dioxide, coal–methane and coal–CO 2 /CH 4 mixture systems was performed. In order to address this issue the adequate sorption experiments were carried out at high pressure by means of the volumetric method on a cubicoid solid samples. Simultaneously the kinetics of coal sorption-induced swelling were monitored. For two coals under investigation a linear and a non-linear relation between coal expansion and the amount of sorbed gas was observed. The SE equation shows a very good agreement with the sorption experimental data obtained for both coals, it is also able to accurately describe the sorption-induced-swelling of lower rank coal and the CH 4 -induced swelling of higher rank coal however it does not give a reasonable fit to swelling kinetics induced by sorption of CO 2 and CO 2 \CH 4 mixtures on higher rank coal. The highest characteristic rate parameter k was found for CO 2 sorption on lower rank coal, the lowest was calculated for CH 4 sorption on the same coal and the values of k for higher rank coal are in between. The values of stretching parameter b for higher rank coal are greater than for lower rank coal, i.e. between 0.55 and 0.75 and < 0.5, indicating a relatively narrow and a relatively broad distribution of characteristic relaxation times of sorption processes, respectively. Generally, the values of parameters k and b calculated for CO 2 , CH 4 and CO 2 \CH 4 mixture sorption-induced swelling are lower for lower rank coal. The values of parameter b for swelling phenomena are not compatible with these of sorption processes. [ABSTRACT FROM AUTHOR]

With the increasing demand for coal resources, coal mining has gradually entered into the deep strata of coal seams. Although the increase in mining depth improves energy security, it is associated with severe hazards, especially coal and gas outburst. Protective seam mining is an efficient method for gas control and has been widely used in major coal-producing countries. However, studies on deep ultra-thin protective seam (thickness 0.1-1 m, average thickness 0.5 m) mining and its related problems have been rarely reported. Focusing on the challenges resulting from deep mining (mining depth >1100 m) and the research gap, a coal and gas co-exploitation technique, which combines the gas control technology and green mining (including coal preparation and backfilling), has been proposed in this work. Significant benefits have been achieved in the twelfth coal mine of the Pingdingshan coalfield (study area) following the implementation of this technique. The application of the gas control technology markedly improved the gas drainage efficiency, promoted increased gas utilization, and reduced the greenhouse gas emission, providing notable economic and environmental benefits. In addition, implementation of green mining improved the coal quality, relieved the burden of the transport system, and, in particular, effectively prevented surface subsidence, thus protecting the ecological environment of the mining area, which offered significant economic, environmental, and social benefits. The practice in the twelfth coal mine could be used as a valuable example for coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]

In deep coal mines, coal and gas outbursts are common disasters because of the high in situ stress and high gas pressure in coal seams. To eliminate the outburst risk, gob-side entry driving is proposed during the roadway excavation. To analyse the outburst risk of gob-side entry driving in a coal seam, this study employed an innovative model that incorporates a stress equilibrium equation and gas transport equation. On the basis of numerical simulations, the distribution law of displacement and stress and gas pressure in the solid coal on both sides of the gob were determined. Specifically, the gas content distribution in the solid coal along the gob, and gas emissions law during the excavation with gob-side entry driving technique were measured. Both the R index method and three-parameter index method were used for outburst risk predictions during roadway excavation with gob-side entry driving. Results showed that the surrounding rock stress, coal seam displacement, and gas pressure and gas content all were significantly reduced on both sides of the gob, and both the R index method and three-parameter index yielded values less than the outburst risk critical values. These findings verify that gob-side entry driving is an effective method for outburst-prone coal seam excavation in deep mines. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) wells tend to produce large volumes of water, especially when there is hydraulic connectivity between coalbed and nearby formations. Cross-formational flow between producing coal and adjacent formations can have significant production and environmental implications, affecting economic viability of production from these shallow reservoirs. Such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well. The aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis. A reservoir model is constructed to investigate the production performance of a CBM well when cross-formational flow is present between the coalbed and the overlying formation. Results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity. Due to hydraulic connectivity, water saturation within coalbed does not considerably change for a period of time, and hence, the peak of gas production is delayed. Upon depletion of the overlying formation, water saturation in coalbed quickly decreases. Rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production. As an important consequence, when cross-flow is present, gas and water relative permeability curves, derived from simulated production data, have distinctive features compared to the initial relative permeability curves. In the case of cross-flow, signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation, followed by rapid increase afterward for water and gas, respectively. The results and analyses presented in this work can help to assess the impact of cross-formational flow on reservoir variables derived from production data analysis and can also contribute to identifying hydraulic connectivity between coalbed and adjacent formations. [ABSTRACT FROM AUTHOR]

This research investigates a rural community’s perceptions of their future at two time-points during a major onshore gas project in the Surat Basin, Australia. The study site is a region in southern Queensland economically centred on agriculture. Using qualitative methods, the research found that the construction phase was dominated by residents’ concerns about the future and uncertainty about how community well-being might be affected. By the end of the construction phase, there were emerging signs of adjustment and adaptation to change. Factors such as a developing sense of collective efficacy, previous experience with the resources sector, a return to prior levels of acquaintanceship density and recognition of social and economic benefits may have contributed to this adjustment, although landowners remained concerned about water and the future of their farms. [ABSTRACT FROM PUBLISHER]

In this study, the sorption capacities of hard coals with reference to gases present in the mine atmosphere: carbon dioxide, methane, ethane, ethene, propane, propene, carbon monoxide and hydrogen were examined. For laboratory tests, 4 samples of hard coals collected from exploitable coal seams were selected. Among considered gases the mostly sorbed is carbon dioxide, in slightly smaller amounts are sorbed unsaturated hydrocarbons: ethene and propene. Their large sorption results from i.a. interactions of π electrons in the double bond between carbon atoms in the ethene or propene molecules with energetic centers of the coal surface. The amounts of the sorbed saturated hydrocarbons: ethane and propane are small, which is probably related to the adsorption mechanism of their sorption by coals. In the smallest amounts are sorbed hydrogen and carbon monoxide, the values of their sorption being maximum 5% of hard coals sorption capacity in relation to carbon dioxide. Based on the experiments it was found that the largest amounts of gases are sorbed by low-rank, highly porous coals with high oxygen content. The process of sorption of unsaturated hydrocarbons: ethene and propene can lead to a reduction in concentration of those gases in the mine atmosphere and thus may affect correctness of the self-heating phenomenon assessment. [ABSTRACT FROM AUTHOR]

The development height of a gas conducting fracture zone (GFZ) in the gob overlying strata is crucial to the gas drainage and safe production of a coal mine. In order to address the issues of excessive gas concentration and uncertain GFZ height in No. 7435 Face overlying strata of Kongzhuang Coal Mine, China, the caving characteristics of overlying strata were explored using both physical experiments on similar materials and numerical simulations of Particle Flow Code (PFC) software and verified each other. The relationship of cracks development to porosity changing characteristics was introduced to quantitatively determine the height of the local GFZ. The quantified GFZ heights were compared with those measured using the in-situ drilling flow method. The results showed that 1) PFC software could accurately simulate the overlying strata caving behaviors, thus saving manpower, materials and financial resources needed for related physical experiments, and 2) the temporospatial distribution characteristics of porosity could be used to forecast GFZ height, and are of significant importance for determination of GFZ. Overall, the conclusions are of engineering significance for accurate arrangement of boreholes for gas drainage and reduction of mine gas disasters. [ABSTRACT FROM AUTHOR]

During the mining of coalbed methane, the temperature, overburden pressure, and pore pressure increase with the depth, leading to a decline in permeability and making the mining more difficult. Many researches are devoted to get more accurately changing mechanism of permeability by measuring sorption-induced strain. However, the presently huge facilities and complex process make the test quite inconvenient. Therefore, based on common laboratory equipment, we have developed an optical observation device with the function of multi-field coupling, which is a pioneered design in China. It realises the contrast experiment of the sorption-induced strain under free absorption inflation and restrained strain with axial direction. Through carbon dioxide and methane adsorption experiments with this device, the pressure - strain curve and time - strain curve is obtained, from which we observe that coal is more sensitive to CO2 adsorption than methane adsorption. The Langmuir equation can satisfactorily simulate experimental data. The adsorption experiment can be divided into three phases: rapid, slow and stable. Adsorption-induced strain of CO2 is two to four times than that of methane. Through those experiments, we have verified the previous research results and proved the feasibility of the device. [ABSTRACT FROM AUTHOR]

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This study was to investigate whether working in conditions of elevated concentrations of mine gases (CO 2 , CO, CH 4 , DMS) and dust may result in oxidative stress. Coal miners ( n =94) from the Velenje Coal mine who were arranged into control group and three groups according to a number of consecutive working days. 8-isoprostane as a biological marker of oxidative stress was measured in exhaled breath condensate (EBC). Miners who worked for three consecutive days had higher 8-isoprostane values in EBC compared to the control group. Gas/dust concentrations and exposure time of a single/two day shift seem too low to trigger immediate oxidative stress. [ABSTRACT FROM AUTHOR]

High-pressure hydraulic fracturing technology in coal and coal bed methane mines can lead to roof and floor damage, and fracture initiation disorder that leads to a "blank area", and other issues. A new method of hydraulic fracturing is proposed to increase the homogeneous permeability of coal in underground coalmines. Numerical and other simulation tests for different forms of a tree-type, branched borehole model are presented. The results show that the branched array causes cracks to initiate from the bottom of the array, and these extend along the direction of the adjacent boreholes. Generally, as the number of branched boreholes increases, the coal seam fracture network also increase, improving the distribution of the fracture network, making the fracturing effect better. The branched boreholes appear to reduce initiation pressure and, with increasing branches, the initiation pressure decreases. A model with four tree-type, branched boreholes leads to a reduction in initiation pressure of 69%. In terms of permeability improvement technology in underground coalmines, a branched hydraulic fracturing borehole array has the advantages of reducing initiation pressure, controlling crack initiation and extension, enhancing the fracturing effect and reducing the destruction of the roof and floor. [ABSTRACT FROM AUTHOR]

The protective seam mining technology is the most effective and economical method in realizing the safe mining of outburst-prone coal seams. To study the effects of remote lower protective seam mining on coal mine gas control, a typical case (average layer spacing: 78 m) taken from the Zhuxianzhuang Coal Mine was investigated by a comprehensive evaluation through numerical simulation, gas extraction data statistics, residual gas pressure/content measurements and recovering gas emission analysis. The results indicate that after the recovery of the protective seam, the unloading effects could lead to a maximum expansion deformation rate of the protected seam by 33.4‰, which remarkably increases the permeability of the coal seam by 4320 times. Combining with the pressure-relief gas extraction methods, considerable amount of the gas (about 78.58%) was extracted from the protected seam, resulting in the maximum residual gas pressure and content of 0.26 MPa and 4.29 m 3 /t respectively, which indicate that the outburst risk has been completely eliminated. Additionally, among the gas extraction methods, the penetrating borehole extraction presents the best drainage effect, accounting for 42.58%–55.09% of the total extracted pressure-relief gas. The effect of the surface wells extraction is closely related to the number of wells and whether the wells can work properly or not. However, the effect of interception boreholes extraction is poor and the extracted amount is almost negligible. Moreover, a protected range extension phenomenon is noticed, which demonstrate that the protected area generated by the protective seam mining is larger than that of the theoretical predicted one, and thus a further study is needed. [ABSTRACT FROM AUTHOR]

The Qinshui Coalfield is one of the most important coalbed methane (CBM) coalfields in China with vast CBM resources, in which the Carboniferous Taiyuan Formation is one of the main coal-bearing sequences. Eleven CBM production gas samples and associated production waters were collected from the Taiyuan Fm. in the karstic collapse column (KCC) area of Sijiazhuang mining area, Qinshui Coalfield. The gas molecular and isotopic compositions and water quality, water carbon and hydrogen isotope compositions were analyzed. Results in this study reveal that CBM from Taiyuan Fm. of Sijiazhuang is dominated by CH 4 (95.9–99.4 mol%, air-free basis) with minor amounts of N 2 (average: 1.07%), CO 2 (average: 0.25%), and ethane (average: 0.02%). The carbon isotope ratios of the production CH 4 range from − 40.8‰ to − 33.2‰, with an average of − 37.1‰, and the corresponding hydrogen isotope ratios of CH 4 − 196‰ to − 178‰, with an average of − 186‰ ( n = 11). Thermogenic methane is the primary source of CBM from the Taiyuan Fm. of Sijiazhuang, and its estimated proportion is calculated to range from 72% to 95%. The type of CBM production water is Na–HCO 3 , and the concentrations of total dissolved solids range from 1282 mg/mL to 1718 mg/mL, with an average of 1417 mg/mL. The δ D values of the water samples range from − 74.8‰ to − 61.1‰, the δ 18 O values from − 9.6‰ to − 8.0‰. The isotope compositions of water samples fall to the right of the GMWL, suggesting a combination of fluid–rock interaction under high temperature conditions and evaporation. There is a good correlation between the distribution of KCCs and the isotopic compositions of CBM production gases and waters in the study area. KCCs in this area can be the free pathways going through the surface, the limestone beds and the 15# coal seam of Taiyuan Fm. KCC presence makes the CH 4 carbon isotopic composition become more enriched in 13 C in shallower areas, because of the stronger desorption–diffusion–migration isotope fraction effect of CBM in the north of Sijiazhuang mining area. In contrast, the δ 13 C 1 and δ 13 C CO 2 values are lighter in deeper areas in the southwest of the study area. This could be due to the stronger groundwater stripping process in that area. The results can be used for CBM exploration and exploitation in KCC areas. [ABSTRACT FROM AUTHOR]

The Integrated Ocean Drilling Program (IODP) Expedition 337 was the first expedition dedicated to subseafloor microbiology that used riser-drilling technology with the drilling vessel Chikyu. The drilling Site C0020 is located in a forearc basin formed by the subduction of the Pacific Plate off the Shimokita Peninsula, Japan, at a water depth of 1180m. Primary scientific objectives during Expedition 337 were to study the relationship between the deep microbial biosphere and a series of ~2 km deep subseafloor coalbeds and to explore the limits of life in the deepest horizons ever probed by scientific ocean drilling. To address these scientific objectives, we penetrated a 2.466 km deep sedimentary sequence with a series of lignite layers buried around 2 km below the seafloor. The cored sediments, as well as cuttings and logging data, showed a record of dynamically changing depositional environments in the former forearc basin off the Shimokita Peninsula during the late Oligocene and Miocene, ranging from warm-temperate coastal backswamps to a cool water continental shelf. The occurrence of small microbial populations and their methanogenic activity were confirmed down to the bottom of the hole by microbiological and biogeochemical analyses. The factors controlling the size and viability of ultra-deep microbial communities in those warm sedimentary habitats could be the increase in demand of energy and water expended on the enzymatic repair of biomolecules as a function of the burial depth. Expedition 337 provided a test ground for the use of riser-drilling technology to address geobiological and biogeochemical objectives and was therefore a crucial step toward the next phase of deep scientific ocean drilling. [ABSTRACT FROM AUTHOR]

Gas drainage for the single and low gas permeability coal seam is the key technical problem hampering efficient coal mine gas drainage and without which mining safely cannot be realised in China. To solve this problem, this paper presents an engineering method for enhanced coalbed methane recovery based on high-pressure hydraulic flush from floor tunnels. The first step is to evaluate when the likelihood of coal and gas outburst reaches dangerous levels according to coal seam parameters (including coal seam gas contents, gas pressure, permeability and geological conditions). With these parameters in place, the second step is to determine and optimise borehole parameters, such as the effective influencing radius of hydraulic flush, hydraulic flush space between drills and borehole number to make sure that the coal seam stress is fully released and permeability is dramatically increased. What is also included in this step is the employment of a high-pressure hydraulic flush of coal from boreholes drilled from tunnels developed in the floor of the coal seam. Parameters of water pressure, water flow rate and the volume of coal flushed out are selected based on on-site testing and numerical modelling. Finally, numerical modelling and onsite testing are employed to validate the effects of enhanced coalbed methane recovery, which is whether or not coal and gas outburst danger is eliminated according to the national standards of China. The results show that the technology could improve the permeability of a coal seam and that the gas seepage coefficient was increased by about 10.50 times, the pre-gas drainage ratio was up to 35.5–70.4% and the borehole gas drainage experienced a process of increase-steady-decrease, which delayed 15–20 days of the attenuation time. [ABSTRACT FROM PUBLISHER]