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In the Upper Permian coal bearing strata of Liupanshui Coalfield, there were coal seam, shale and sandstone overlaid frequently. In order to have an overall plan and exploration on the natural gas in different reservoir and to favorably reduce the resources wasted and improve the development benefit, with the study on the lithofacies, thickness and source rock geochemistry of the coal measure gas reservoir, the reservoir physical property and the spatial occurrence law, this paper analyzed the reservoir formation potential of the coalbed methane, coal measure shale gas and the coal measure tight gas in Liupanshui Coalfield and discussed the space overlaid relationship and exploration prospects of the coal measure gas. The study results showed that within the coalfield, the coal rank of late Permian coal seam was complete, the thickness was high, the metamorphic grade was generally higher, and the gas content was good. The gross thicknesses of the shale and the sandstone were high, the organic geochemistry and reservoir physical parameters were good. The difference was high in regional and horizon distribution of different lithology, the lithological combination types varied, and the space disposition was beneficial to the development of many vertical natural gas reservoirs. The favorable exploration horizon of the coal measure shale gas was the lower section of the Longtan Formation and the favorable horizon of the coalbed methane and the coal measure tight gas was the Wangjiazhai Formation and the up section of Longtan Formation. Based on the circumstances, totally three major gas reservoir types, including the “resources and storage integration” independent coal measure shale gas reservoir, “resources and storage closed neighbor type” coal measure “three gas combined gas reservoirs” and “bottom resources and top storage type” coal measure “two gases combined gas reservoirs” were summarized and provided. The paper preliminarily concluded that Qinglong Syncline deep section would be the priority exploration zone of the coal measure shale gas, Qingshan Syncline deep section would be favorable to the co-exploration and co-mining of the coalbed methane and the coal measure shale gas, Panguan Syncline and Gemudi Syncline deep section would be favorable to the co-exploration and co-mining of the coalbed methane and the coal measure tight sandstone gas. [ABSTRACT FROM AUTHOR]

Aiming at the problems of low efficiency of coalbed methane extraction in soft and hard coal composite seam and uneven extraction in coal seam longitudinal section, etc，In order to achieve rapid and overall efficient extraction of CBM over a large area. Taking the No. 3 coal seam in Zhaozhuang field of Qinshui basin as an example, this paper analyzes the layered characteristics of soft-hard coal, optimize the local hard coal segment in the composite coal seam. and puts forward the new idea of exploiting CBM through noncementing staged fracturing horizontal wells in layered soft-hard coal seam. On the basis of fracture propagation pattern of fracturing on horizontal wells in layered soft-hard coal seam, the technical measures for the development of CBM by noncementing staged fracturing horizontal wells are investigated. The results show that there are obvious layers of soft and hard coal in No. 3 coal seam. and obvious characteristics of natural gamma and resistivity logging response in soft-hard coal. Horizontal well in hard coal fracturing can form a complex and irregular vertical fracture, which is easy to expand and extend along the roof strata with strong brittleness. Hydraulic fracturing can break both hard and soft coal seam, and can improve the fracturing effect of soft and hard coal seam. The location of horizontal wells in hard coal and fracturing construction discharge have an influence on the effect of fracture expansion, the influence degree of fracturing discharge is large and the horizontal well position is small. In view of this characteristic, four key technologies for the successful development of CBM by horizontal wells of staged fracturing are formed:(1) Optimization technology of perforation and fracturing section in horizontal well;(2) Pipeline transmission large displacement hydraulic jet anti-channeling technology; (3) Technology of slug type water carrying sand fracturing with “large displacement, large scale and medium sand ratio”; (4) Fine drainage and mining technology for simultaneous production of gas and water well separately. The practice proves that this technology can greatly increase the output of horizontal well of coalbed methane, break through the technical bottleneck of low yield of soft and hard coal composite coal seam, and provide a technical way for coalbed methane extraction and gas disaster control of soft and hard coal composite coal seam. [ABSTRACT FROM AUTHOR]

Compared with AC microgrid, DC microgrid has the advantages of few energy conversion devices, simple control structure, no consideration on eddy current and reactive power, and so on. It has become a research hotspot in the field of efficient utilization of distributed energy resources(DERs) and flexible DC distribution. Hwever, most of the research focuses on the application and development of DC microgrids in future residential and intelligent buildings, as well as the optimization and coordination of DERs in DC microgrids, which lacks in-depth research on the DC microgrid system for CBM ground extraction with the application background and self load characteristics of the energy industry. Combined with the power network for coalbed methane(CBM) ground extraction and electrical load characteristics, the DC microgrid hierarchical topology system for CBM ground extraction was proposed in this paper. In addition, the key technologies to build DC microgrid system for CBM ground extraction were summarized and analyzed, and the feasibility of implementing a DC microgrid system for CBM ground extraction was analyzed and overviewed. [ABSTRACT FROM AUTHOR]

To make it a complete system of the mechanism, prediction and control of rockburst, disturbance response instability theory is deeply studied in this paper. Control quantity, disturbance quantity and response quantity of coal rock deformation system is proposed. Rockburst is concluded as a instability phenomenon of coal rock deformed system which happens when disturbance response approaches to infinite and disturbance response instability conditions of rockburst are given,if the coal and rock deformation system is in an unsteady equilibrium state, characteristic displacement of plastic softening deformation area will increase infinitely no matter how small the disturbance increment is. The analytical solution of rockburst happens in circular roadway is derived strictly observe disturbance response instability theory, and it indicates that there are critical indexes for disturbance quantity and response quantity, the critical indexes are determined by control quantity. Monitor and control of rockburst are narrated from the angle of control quantity , disturbance quantity and response quantity. Monitoring methods such as mining stress monitoring are aimed at disturbance quantity, while monitoring methods such as drilling cuttings methods and microseismic methods are aimed at response quantity. Prevent methods such as rational mining layout, mining protective layer, rational coal pillar retention , break roof are aimed at disturbance quantity, while prevent methods such as coal seam drilling, coal seam water injection,coal seam blasting, strengthening support are aimed at disturbance quantity. [ABSTRACT FROM AUTHOR]

There are some technical challenges in hydraulic fracturing for the ductile formations such as shales and coals. This paper introduced some technologies to solve these challenges. In-situ stress and pore pressure control fracture propagation and fracturing efficiency. Pore pressure and in-situ stress in deep porous formations have very different behaviors compared to the shallow ones. The minimum and maximum horizontal stresses have a very important behavior of lithological dependency, which is often ignored. However, this behavior is of critical importance for hydraulic fracturing. The horizontal stresses are also highly dependent on pore pressure; e.g., the overpressure in pore pressure causes an increase in the minimum horizontal stress, but depletion owing to production causes a decrease in the minimum horizontal stress. This directly affects the propagation location and direction of a hydraulic fracture, because a decrease in the minimum horizontal stress causes a significantly reduction in the fracture breakdown pressure, particularly for the reservoir re-fracturing after a certain time of production. In addition, the relationship of three in-situ stress regimes and fracture generation and propagation were analyzed. For a reservoir with a strong tectonic stress, the commonly-used hydraulic fracturing in horizontal wells cannot increase production effectively. A new fracturing method for this case was proposed, i.e., multi-stages and multi-levels of horizontal fracturing in long perforation tunnels of a horizontal well. Shale reservoirs are very anisotropic in gas or oil richness, and this may cause that some wells cannot reach the expected production. The paper presents a method for how to find "sweet spot" in the shale reservoirs. The indirect vertical fracturing of coal seam was also introduced for enhancing efficiency of coalbed methane fracturing. [ABSTRACT FROM AUTHOR]

China is relatively rich in coalbed methane.A better estimation of maximum adsorption capacity and recovery ratio is based on a better understanding of isothermal adsorption curve.This paper is going to make a comparative study on Langmuir equation,the representative theory of monolayer adsorption theory,and DR equation,which is based on micropore filling theory on an attempt to find a more suitable model fitting equation.Data of the coal sample from four different coal ranks (Ro,max from 0.60% to 3.18%) are fitted.The result shows that VL and pL would be more accurate in physical significance and the equation fitting would be more meaningful if the two parameters are calculated before fitted;the accuracy of other parameters is improved while V0 in DR equation is calculated;and Amankwah method is the most suitable method for calculating p0 after a comparison of five calculation methods by introducing the concept of virtual saturated vapor pressure.DR equation works better in fitting effect and comes nearer to the actual data after a comparison between Langmuir and DR equation. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) exploitation feasibility is determined by both hydrogeological conditions and hydraulic fracturing conditions of coal seams.Exploitation feasibility evaluation and reservoir evaluation constitute two important aspects of coalbed methane recoverability.In this paper,through the drainage efficiency comparison between Shouyang and Shizhuang CBM blocks in Qinshui Basin,CBM exploitation feasibility evaluation was discussed from four aspects,including coal measures aquosity,faulting,in-situ-stress state and the lithology combination of coalbed with adjacent rocks.An evaluation flow chart for CBM exploitation feasibility evaluation was finally proposed.The study shows that coal measures aquosity plays an important role in the CBM exploitation feasibility of whole CBM Block.The hydraulic communication between coal seams and surrounding aquifers through faults weakens the closeness of wellbore-fracturing coal system,leading to lower exploitation feasibility of CBM resources near the faults.The stronger the coal measures aquosity is,the greater risk of high water production in wells near faults will take place and the lower exploitation feasibility will be.The in-situ stress state of coalbed and lithology combination of coal seams with adjacent rocks constitute the objective conditions of CBM exploitation feasibility,and a comprehensive evaluation of exploitation feasibility should be done through combining in-situ stress state,the strength of horizontal stress and fracturing volumes.The qualitative/semi-quantitative evaluation method of CBM exploitation feasibility,based on hierarchy analysis considering coal measures aquosity,faults,the in-situ stress state and the lithology combination of coal seams with adjacent rocks,can be applied to CBM block selection and well/coalbeds selection through the whole process of CBM exploration and development. [ABSTRACT FROM AUTHOR]

Previous material balance equations (MBEs) were established under the assumption that the adsorption and desorption process of coalbed methane (CBM) is completely reversible and the adsorption hysteresis phenomenon observed in CBM adsorption/desorption experiment was neglected,which is obviously not consistent with the actual depressurization process of CBM reservoirs by water drainage.This paper proposed the concept of adsorption hysteresis effect based on laboratory observation and analysis of the potential mechanisms.Furthermore,an improved MBE model of CBM reservoirs considering the adsorption hysteresis effect was established,and it was applied in predicting the original gas in place (OGIP),recoverable reserves and recovery factor of some actual CBM reservoir.The results show that MBEs may significantly underestimate the OGIP while overestimating the recovery factor if the adsorption hysteresis effect is not included in the calculations.Conversely,the calculated OGIP and average water saturation are in good agreement with the actual values using the new MBE model that incorporates the adsorption hysteresis effect.Therefore,the validity and accuracy of the new MBE model is proved,and then the proposed material balance method can be potentially applied in evaluating the recoverable reserves and recovery factor of CBM reservoirs,which would also play a major guiding role in the subsequent development planning and adjustment of CBM reservoirs. [ABSTRACT FROM AUTHOR]

In order to understand the influence laws of geologic structure on the gas production of coalbed methane (CBM) well, the paper made the Changzhi Block, Qinshui basin, as an example, and introduced the variation coefficient of coal thickness to express the complexity degree of geologic structure. Then the complexity degree of geologic structure was evaluated and structure network units were divided by means of analytic hierarchy process (AHP). Furthermore, based on the results of fuzzy mathematics analysis on the factors affecting CBM productivity, including the geological condition,reservoir physical property and gas content,the relative evaluation method of AHP-fuzzy mathematics about the influence degrees of geologic structure on the production effect of CBM wells were established. The research showed that Changzhi block could be classified as simple structure area, relative simple structure area and secondary development structure area by the complexity degree of geologic structure. The evaluation scores of productivity of CBM wells from high to low are relative simple area，simple area, secondary development area in order. In other words,there is the greatest productivity of CBM wells in the relative simple area, the second in the simple, and the least in secondary development area. Meanwhile the effect of gas and water production and production curves features show that this evaluation results are in agreement with actual situation. It reflects that the evaluation method of AHP-fuzzy mathematics which is established about the influence of geological structure to CBM productivity is reasonable. Finally the evaluation results could provide references for choosing wells and improving productivity. [ABSTRACT FROM AUTHOR]

A lot of pores and fractures in some coal reservoirs are blocked by minerals or impurities, such as calcite and dolomite. The permeability of those coal seams is low. This paper puts forward a new method to increase permeability by acidification. In order to study the law of meso-structure of coal under the action of acidification, those parameters, such as specific surface area, pore volume, porosity, permeability, pore size distribution and magnetic resonance imaging, are measured by low temperature nitrogen adsorption and NMR experiments. Test results show that the coal samples' saturated water state NMR signal increases, irreducible water state NMR signal cut down, and the changes about mid-large pores peak ( T2>20 ms) is much bigger than small pores peak in T2 spectrum. The parameters that quantified by NMR, such as total porosity, effective porosity, and permeability were increased, and the residual porosity and T2 cut-off values were decreased. The specific surface area and total pore volume were increased, which quantified by the low temperature nitrogen adsorption, and the increase was mainly concentrated at the pore size of 10 nm, but the increase of high rank coal was not obvious. The nuclear magnetic resonance image directly reflects the change characteristics of the internal pore structure before and after the coal sample acidification, which provides a new way to reveal the microscopic evolution law of acidification. The comparison shows that the initial porosity of coal sample is more developed or more carbonate, silicate and other soluble minerals in the pore, the greater the change of the characteristic parameters, the better the effect of acidification. [ABSTRACT FROM AUTHOR]

The characteristics of a CBM well performance is complex due to multiple influencing factors. It is beneficial for well site/layer selection and fracturing design to diagnose the performance of single CBM well. Based on the geological conditions and well performance data of 30 CBM wells producing from No.3 coal seam of Permian Shanxi formation in Shizhuang block，this paper studies the characteristics of CBM Wells performances and the relationship between gas production and water production. A negative enveloping relationship between gas production and water production is revealed，with high water production generally inhibiting high gas production. From a point of view of closeness of system borehole-stimulated coal interval，the mechanism of high water production due to outside water supply from sandstone aquifers is discussed and a hierarchical performance diagnostic method for single CBM well is proposed. The performance of some typical well are diagnosed using this hierarchical method，showing the method provides a tool for understanding the performance of single CBM well in Shizhuang CBM block and the application of this method can be extended to other CBM blocks. [ABSTRACT FROM AUTHOR]

Selected areas evaluation of coalbed methane has always been an important link in the process of coalbed methane (CBM) exploration，in which the evaluation method is the key to favorable area. The methods gradually developed from the qualitative evaluation to quantitative evaluation in recent years. This paper uses southern Junggar Basin as an appraisal area. Firstly，five typical kinds of evaluation methods are discussed，in which the merits and demerits are systematically expounded. It is founded that qualitative evaluations are still practical，although quantitative evaluations have improved the veracity of evaluation，subjectivism and empirical judgments are still existed in the process of quantitative evaluations to some extent. Based on the differences and similarities of the five evaluation methods，principal component analysis (PCA) has been proposed for the purpose that avoids the subjectivism and empirical judgments. The Sigonghe to Dahuangshan area has been selected as a favorable area by PCA method，the same result is generated by the five evaluation methods，which proves that the PCA method is feasible in selecting the favorable CBM areas，and its greatest advantage is to avoid the subjectivism. The authors advocate that the thought of “first qualitative judgment，second quantitative analysis，and final qualitative verification” should be used to select favorable CBM areas. [ABSTRACT FROM AUTHOR]

In order to effectively control gas unbalance phenomenon of gas occurrence in coal mine, this paper put forward the concept of gas enrichment area and gave the general characteristics of gas enrichment area. Based on geological condition in Zhaogu No. 1 Coal Mine, the paper discussed the gas geological features and analyzed the formation mechanism of gas enrichment area in the thick loess-thin bedrock coal seam, and then obtained the recognition method of gas enrichment area by the overlying bedrock characteristic of coal seam. On the basis of which, the gas enrichment area of Zhaogu No. 1 Coal Mine was confirmed, that was the bedrock layer thickness greater than 50 m and coal seam overlying bedrock gradient greater than 0. 06 or the bedrock layer thickness greater than 150 m area. Coal mining practice verified gas enrichment area identification and actual gas occurrence consistency. [ABSTRACT FROM AUTHOR]

Based on a demonstration project of coal-formed gas co-exploration and concurrent production, this paper analysed the occurrence characteristics and development conditions of Longtan coal measure coalbed methane and tight gas, and discussed the suitable technology for the coal-formed gas co-exploration and concurrent production. The results show that coal-formed gas is mainly hosted in the multiple coal seams of Longtan coal measures and closes to the gas bearing formation which contains fine sandstone and siltstone；it has enough resource and favorable development conditions that include the multi-layer commingling development and the concurrent production of coal-formed gas. The coal reservoir with the characteristics of high temperature, overpressure, high gas content and gas supersaturated is suitable to coalbed methane ground development；but some factors including the reservoir fracture closing and mineral filling could lead to the lower original permeability at high ground stress area. Therefore, the coal-formed gas ground development needs to carry out the reservoir reconstruction. The key technology of discovering, recognizing and evaluating the optimization of gas bearing and producing layers in field coal-formed gas co-exploration and concurrent production are gas logging, uncorrected comprehensive logging and the comprehensive evaluation of gas bearing layer. They provide the basis for establishing the coal-formed gas co-exploration and concurrent production scheme. In the development mode of collecting well group, the technologies including the small-layer perforating, group-segment fracturing and multi-layer drainage need to match with the topography and geology conditions of the field. Thus it can significantly improve the engineering effect of the multi-layer commingling development and the coal-formed gas co-exploration and concurrent production. [ABSTRACT FROM AUTHOR]

The unconventional gas resource in coal measures strata is the main part of unconventional gas. At present, the understanding of coalbed methane, shale gas and tight sandstone gas in the coal measures strata is relatively limited. Also, the degrees of resources exploration and development are relatively low. According to the experiences of gas reservoir combined mining, the coal measure strata can be considered as a whole, then the cost of exploration and development on coalbed methane, shale gas and tight sandstone gas in the coal measures strata could be reduced. In addition, the efficiency and single well profit of gas well could be improved. In this paper, the coalbed methane, the shale gas and the tight sandstone gas in coal measures strata are referred to as “the three coal gases”. The commingling possibility of “the three coal gases” and the difficulties that commingling urgently needs were analyzed from the formation lithology distribution characteristics of coal measures strata lithology, accumulation mechanisms, reservoir characteristics, exploitation characteristics, etc. [ABSTRACT FROM AUTHOR]

It is found that there are two difficult problems in China CBM industry. The one is that not only the success rate of drilling and fracking is very low but also gas rates from more than 50% of those producing wells are far less than they are originally designed. The other is that almost all the production activities happen in a very concentrated small area, leaving more than 80% of China CBM resources far away from commercial potentials. A new model of CBM resource classification is established after a full discussion is made on how a soluid of coal-water-gas is built in the long geology history. And technologies applicable to produce gas from the 4 types of reserves in the model is accordingly recommended. Further studies in this paper concludes that CBM resources are different from other natural gas by three aspects. Firstly it is "Non-gas"in underground. Typical CBM is presented in four kinds of Soluids, in which coal-water-gas are coupled together driven by a combination energy of "pressure" and "stress". Secondly gas has to be "Separated and Fostered" before it is drained to the surface. Actually a real independent gas flow cannot be normally delivered from seam until an effective process of "dewater" or "de-coal" is done. Thirdly there is a strong "window longtail effects" in poor CBM reservoir. No appreciable gas could be drained if there is no good engineering control over "time window" on reservoir stimulation, neither is there any sustainable gas flow if "pumping longtail" is not well managed. [ABSTRACT FROM AUTHOR]

According to the results of China’s new round of CBM resource evaluation in 2006, coalbed methane (CBM) resources were mainly concentrated in the deep seams (coal seam depth in 1 000-2 000 m), but studies related to deep CBM theory were limited, and exploration operations were rare. In this paper, based on the main distribution of coalbed methane resources in the deep coal seams in China, the current deep coal seam mining and CBM exploration wells in Erdos basin and Junggar basin indicate that the exploration and development of deep CBM shows some potential, although the appraisal wells of commercial value occur only in a few pilot areas. By comparing different coal seam depth studies in Yanchuannan block in Erdos basin, it could be concluded that the key parameters such as the gas content, gas saturation,reservoir pressure and critical desorption pressure of deep coal seams were commonly higher than in shallow coal seams. In general, it was a complex system engineering to evaluate the factors of deep CBM production, which generally include resource geology and development technology. Geological conditions of deep CBM were more complicated than those of shallow CBM, which resulted in that the development technology applied in these area was difficult. According to the experience of exploration and production in Yanchuannan pilot CBM project, it was fracturing technique adapted for deep geological condition and draining technology that responsible for favorable well production. Based on this study, it is proposed that the improved well production way of deep CBM is to do the evaluation and prediction of sweet point, to study the fracturing technology and to manage drainage working system. [ABSTRACT FROM AUTHOR]

This paper studied how coal powders are produced in wellbore during the CBM production, and how the yield of coal powders from coal seams is enhanced. The CBM-WS,the instrument for simulating the CBM production from wellbores in high pressure coal seam,was used for investigating the factors affecting the yield of coal powders. The results indicate that the yield of coal powders is related to the coal powders from coal seam, gas production rate, and coal powders concentration. When the gas production rate is low,the radius of produced coal powders from wellbore is less than 20 μm, and the most coal powders with radii between 40 and 100 μm cannot be produced; as the gas production rate increases, both the number and radius of coal powders increase significantly; when the flow rate reaches a critical value,the yield of coal powders will not change too much. After adding coal powder dispersant FYXF-30, the large coal powders in wellbores could be pulverized and then produced. [ABSTRACT FROM AUTHOR]

In order to acquire the evolution characteristics of acoustic emission in failure process of coal absorbed methane, the raw coal absorbed gas was used as the object of study in this paper and the acoustic emission behavior evolution characteristics in failure process of coal absorbed gas under different pore pressure was performed by using triaxial servo-controlled press equipment with acoustic emission synchronous detection function for coal absorbed gas. The results show as follows : mechanical parameters of the coal absorbed gas such as elastic modulus, peak strength and peak strain decrease as increase of gas pressure, and the stress-strain curve transfers to "large strain induced by low stress" under the influence of gas; the acoustic emission behavior evolution of coal can be divided into four phases with time, including quiet period, slow acceleration period, acceleration period and stationary period; cumulative ring counts of slow acceleration and acceleration period increases respectively 6.39 and 37.5 times in comparison with quiet period, and energy parameters increases respectively 8.39 and 43.7 times in comparison with quiet period ; the acoustic emission parameters of slow acceleration period and acceleration period in failure process of coal mass under load are obviously higher than coal mass absorbed gas under the same conditions, in addition, the acoustic emission parameters have exponential attenuation relationships with gas pressure in the acceleration period. [ABSTRACT FROM AUTHOR]

Western Guizhou has the most abundant coalbed methane resources in South China. In order to efficiently exploit the coalbed methane in this area, it is important to understand the drainage decompression and orderly development methods of coal seam groups under the control of Unattached multiple superposed CBM-bearing system. This paper took Feitian Block of Zhina coal field in Western Guizhou as the researching area, analyzing the meticulous hydrogeological condition of coal-bearing strata and the difference of development condition of different coal seam groups in vertical. Based on pumping test data from previous coal exploration, useful information was generated, including the apparent reservoir pressure, pressure gradient, unit water inflow, permeability coefficient and radius of influence. The difference of hydrogeological condition in different parts of coal-bearing strata in three-dimensional space was compared. Eventually, the factor of evaluating CBM development priority was established through fuzzy mathematics synthetical judgement. Accordingly, the developing potential and development order of different coal seam groups in vertical of the three coal mine areas was discussed. It is concluded that the Feitian 2 and Feitian 3 mine areas have a better CBM development condition than Feitian 1,among which Feitian 2 medium part, Feitian 3 upper part and medium part are prior for CBM development. Generally, The development order of each part of coal-bearing strata of each coal mine area is : Feitian 3 upper part → Feitian 2 medium part →Feitian 3 medium part →Feitian 3 lower part →Feitian 2 lower part →Feitian 2 upper part →Feitian 1 upper part /Feitian 1 medium part →Feitian 1 lower part. [ABSTRACT FROM AUTHOR]

Currently the seismic exploration technique is mainly used to reveal the structure of coal beds, and cannot be used to evaluate the distribution of deformed coal, the permeability of coal beds and their roof/bottom, which are related to gas outburst. In other words, it cannot evaluate the lithology of coal beds and rock strata. In recent years, some geophysicists suggest to investigate the lithology of coal beds and rock strata, and define the deformed coal distribution and gas concentrated area with AVO technique. In this paper, a 3D seismic cube of deformed coal model was initially obtained using seismic simulation. Subsequently, AVO inversions for the 3D seismic cube were calculated using different Zoeppritz approximate equations, and many AVO attributes were obtained. Through the analysis of AVO attributes, it was proposed that the B-value cube inversed with Aki & Richards approximate equation, and the G-value cube and Δσ cube inversed with Shuey approximate equation are used as the basis of AVO interpretation. Finally, AVO inversions for real 3D coal seismic data were performed to define the distribution of deformed coal and gas concentrated areas using AVO attributes. [ABSTRACT FROM AUTHOR]

High-grade syngas can be produced from the reforming of CH4 with CO2. To achieve efficient conversion of reforming reaction into syngas production, the reforming of CH4 with CO2 for syngas production was conducted in this paper under microwave irradiation, with biomass char as catalyst and microwave absorbing medium. The influences of the conditions including reaction temperature, molar ratio of CO2 and CH4, addition amount of biomass char as well as the introduction of water vapor on the reforming reaction were investigated. The results reveal that an increase in the conversion of reactant gases into syngas production can be achieved through raising reaction temperature, enhancing molar ratio of CO2 and CH4 or increasing addition amount of biomass char. Raising reaction temperature results in a promotion in the ratio of H2 to CO, while enhancing molar ratio of CO2 to CH4 or increasing addition amount of biomass char bring about a decrease in the ratio of H2 to CO. And the introduction of water vapor is not only favorable for the reforming reaction, but also is responsible for an increase in the ratio of H4 to CO. [ABSTRACT FROM AUTHOR]

For the low porosity and pressure coalbed methane ( CBM) reservoirs in China, the paper adopted the technology thought of combining the temporally plugging technology of the nanomaterials with circulative micro foam drilling fluid. Through the methods of evaluation on the stability of foam drilling fluid, performance tests of drilling fluid and microstructure observation, the expansibility, roiling recovery rate and gas permeability test of original coal rock, the ability of micro-foam mud stabilized by nanoparticles on reducing the damage of CBM reservoir was evaluated. We found that firstly, nanoparticles can improve the stability of foam drilling fluids. Furthermore, the micro-foam mud stabilized by nanoparticles have the advantage of high-controllable density (0. 7-1.0 g/cm³) and viscosity, which can adapt to the drilling requirements of the low porosity and pressure coal seam, and which can effectively restrain the adsorption and swelling of coal rock matrix. Finally, the micro-foam mud stabilized by nanoparticles can effectively plug the low porosity and permeability coal seam, while the gas permeability recovery rate of coal is as high as 72% -96% after slice processing for the surface of pollution section of coal rock. With the integrative consideration, the micro-foam mud stabilized by nanoparticles can not only protect coal seam stability, but reduce the reservoir damage of coalbed methane, and is suitable for the low porosity and low pressure coalbed methane reservoirs drilling. [ABSTRACT FROM AUTHOR]

A mathematical model of thermal reversal oxidation of the low concentration methane was established in this paper. The computational fluid dynamics method was used to simulate the temperature distribution and methane concentration distribution under various operating parameters. The calculated values of methane conversion showed good agreement with the corresponding available experimental data. The model was used to investigate the effects of operational conditions such as the approach velocity and equivalence ratio on the oxidation of methane. The results show that the temperature distribution within the bed is substantially M-typed;the high temperature zone and the methane concentration distribution curve along the direction of gas flow move periodically; the greater the inlet methane concentration, the higher the temperature peak, the closer to the inlet end of the temperature curve and the wider the high-temperature region; if the premixed methane gas flow rate increases from 0. 15 m/s to 0. 70 m/s,the maximum temperature peak and the high temperature zone change little, because as the gas flow velocity increases, both the heat releasing in the reaction bed and the heat carried out by the flow increase. [ABSTRACT FROM AUTHOR]

Considering the variable mass pipe flow of the main and branch boreholes, the CBM pinnate horizontal well productivity prediction model was proposed based on 3D gas-water two-phase flow characteristics in the coal seam. The corresponding calculation program is written based on C++ programming language. At the same time, an actual CBM well is simulated as an example. The simulated results are verified by the monitoring data from the actual site. This paper studies the effects of branch symmetry, the locations of branch points, the angle between main and branch bore-holes, branch length, and branch number on gas production per unit length of the CBM well. The comprehensive results demonstrate the high accuracy of the computation model, and its ability to meet the actual needs of the project. The characteristics of gas production per unit length along the main borehole is high on both ends and low in the middle, with local decline at the branch point locations, while the characteristic of gas production per unit length along the branch borehole is high at heel, low at toe and increases gradually in the middle. Gas production per unit length at branch locations along main borehole declines faster when branches are symmetrical than asymmetrical. As branch node moves from heel to toe along the main borehole, peak gas production per unit length also transforms from toe to heel. The angles of the main and branch boreholes have no effect on gas production. At the same time, gas production per unit length reduces as the branch length along main borehole increases. Gas production per unit length increases with the distance from branch node to heel end. Gas production per unit length increases with the increase of branch length and the angle between main and branch boreholes. However, it declines as the number of branches increase. [ABSTRACT FROM AUTHOR]

This paper analysed micropore structure of coal samples from coalmines of Qinshui basin and Huaibei coalfield by using micro-macroscopic observation, Ro testing, and low temperature nitrogen adsorption method. Results indicate that there are five different coal reservoir types in the study areas. High grade metamorphic and relatively strong to strong deformed coal reservoir (type I) and medium grade metamorphic and relatively strong deformed coal reservoir (type III) are favourable for coalbed methane ( CBM) accumulation, but disadvantageous to CBM seepage; high grade metamorphic and relatively weak deformed coal reservoir (type II) and medium grade metamorphic and relatively weak deformed coal reservoir(type IV) are advantageous to CBM accumulation and seepage;low grade metamorphic and strong deformed coal reservoir (type V) is favourable for CBM accumulation, but not advantageous to CBM desorption and seepage. Consequently, southern part of Qinshui basin and south-central of Huaibei coal field are potential areas for coalbed methane exploration and development. [ABSTRACT FROM AUTHOR]

On the basis of actual producing data, combined with the fluid inclusion studies, this paper analyzed the characteristics of water yield and its influence factors during CBM production in Liulin area from the paleo and present hydrogeology, production model and fracturing technology. The results show that the water yield in Liulin area comes from the common action of many factors. The coal seam roof sandstone aquifer of Shanxi Formation,in which the paleo-fluid presents detained feature, has relatively weak water yield property and its present water yield has a direct relationship with the distribution of fracture. The coal seam roof limestone aquifer of Taiyuan Formation has a communication with surface fresh water in the early stages,which has relatively strong water yield property. During the production by different model, under the influence of fracturing strength and the differential communication of coal seam with roof aquifer,the water yield shows gradual increasing by the order of model D,A,B,and C. We further point out that in order to depress influence of hydrogeology,some horizontal wells can be selected in proper area,the production of CBM can be carried out from northeast to southwest which is favorable for drainage and pressure lowering of coal seam, and fracture size can be decreased, especially the height of vertical fractures. [ABSTRACT FROM AUTHOR]

This paper took Haishiwan coalfield as the background and CO2 in the No. 2 coal seam of Haishiwan mine area as the main study object, systematically carrying out study of various aspects on the causes of CO2, CO2 enrichment regularity, CO2 occurrence in coal seam of Yaojie coalfield, adsorption and desorption of CO2 in coal, numerical simulation and engineering practice applied to eliminate the risk of coal and CO2 outburst regionally, making some innovations. During the researches, the authors adopted all kinds of research methods that multi-disciplinary theory includes geochemistry, petrology, structural geology, surface chemistry, rock mechanics, mining engineering, mechanics, numerical simulation, theoretical analysis, laboratory experiments and field engineering practice. The main research content and conclusions are as follows: (1) The CO2 concentration range in the eastern coalfield is 18.79% to 96.6%. The δ13Cco2 values are mainly in the range of -5.0‰ to + 1.0‰ ( PDB ), suggesting an inorganic origin of CO2. The ³He/4 He ratios are (0.6 ~ 25.9) x 108, and the R/Ra is 0. 004 2 ~ 0. 185 0, which is a characteristic of crust-derived CO2 gas. The dynamic-thermal metamorphism of the F19 ductile-brittle shear zone is believed to result in the release of CO2 from basement marble formations, which shows an inorganic source of CO2 in the Haishiwan coalfield. The regional geological evolution and multi-periodical F19 fault movement control the formation, migration, and accumulation of CO2. The F19 fault plays multiple roles in the generation, transport, and sequestration of gas during the CO2 formation. (2) The studies on the characteristics of coal absorbing CO2 or CO2 and CH4 mixed gas are carried out under low pressure. The D-A model can fit the adsorption isotherms of CO2 well under low pressure. At the same time, the authors establish the modified D-A, which fit the present high-pressure adsorption data well. The modified model is applied to analyze the supercritical CO2 adsorption isotherms of Haishiwan coal field and abnormal adsorption isotherms introducing free volume theory of polymer. The result is preliminarily verified by desorption curve. (3) The mining depth of the Haishiwan mine coal is 600 to 1 000 m, where the coal reservoir temperature is in the range of 31.72 to 43.88 °C. The measured mixture gas pressure is not less than 7.3 MPa;the CO2 concentration range in the eastern coalfield exceeded 90%; statistical gas content is in the range of 50 to 60 m³/t. Supercritical CO2 is likely to exist in the No. 2 coal seam of the Haishiwan coalfield according to in situ measurement, experimental determination and theoretical analysis. (4) The numerical simulation results indicate that the range of pressure-relief and dilatational strain of lower coal-rock mass increases along with the pore pressure increases, the maximum absolute and the maximum relative amount of deformity reach 328 mm and 0.5 % under pore pressure of 9 MPa respectively. At the same time, the plastic area also increases along with pore pressure enlargement. It is indicated that the pore pressure plays strengthen role in the protected coal seam pressure relief according to plate theory. (5) High pore pressure acts on pressure relief of coal seam, which has been verified in practice of remote protective coal seam mining and pressure-relief gas drainage. The singe gas drainage flow reaches more than 2 m³/min. The coal seam permeability increases by 878 times. The gas content decreases from 53 m³/t to 12 m³/t. The risk of outburst has been eliminated with regard to the No. 2 coal seam. [ABSTRACT FROM AUTHOR]