Preferential adsorption behaviour of CH4 and CO2 on high-rank coal from Qinshui Basin,China

In order to better understand the prevailing mechanism of CO₂ storage in coal and estimate CO₂ sequestration capacity of a coal seam and enhanced coalbed methane recovery (ECBM) with CO₂ injection into coal, we investigated the preferential adsorption of CH₄ and CO₂ on coals. Adsorption of pure CO₂, CH₄ and their binary mixtures on high-rank coals from Qinshui Basin in China were employed to study the preferential adsorption behaviour. Multiple regression equations were presented to predict CH₄ equilibrium concentration from equilibrium pressure and its initial-composition in feed gas. The results show that preferential adsorption of CO₂ on coals over the entire pressure range under competitive sorption conditions was observed, however, preferential adsorption of CH₄ over CO₂ on low-volatile bituminous coal from higher CH₄-compostion in source gas was found at up to 10 MPa pressure. Preferential adsorption of CO₂ increases with increase of CH₄ concentration in source gas, and decreases with increasing pressure. Although there was no systematic investigation of the effect of coal rank on preferential adsorption, there are obvious differences in preferential adsorption of gas between low-volatile bituminous coal and anthracite. The obtained preferential adsorption gives rise to the assumption that CO₂ sequestration in coal beds with subsequent CO₂-ECBM might be an option in Qinshui Basins, China.     

煤吸附瓦斯过程温度变化的试验研究

在实验室对不同瓦斯（ＣＯ２,Ｃ４,Ｎ２等）吸附过程中煤体温度的变化进行了研究,证实煤体吸附瓦斯的过程是放热过程;煤体吸附不同的瓦斯时,放出的热量不同：吸附ＣＯ２时最大,ＣＨ４次之,Ｎ２最小;煤对其吸附能力超强的瓦斯,吸附时放出的热量越大,对于同一种瓦斯,吸附的瓦斯压力越大,即瓦斯附量越大,吸附过程放出的热量越大。     

Research on Permeability of Multiphase Medium of Middle to High-Rank Coals

1　 IntroductionCoal reservoir permeability is one of the keyfactors to restrict coalbed methane ( CBM) recoveryon the ground in China.Although some domesticscholars investigated single- phase permeability ofgas- saturated and water- saturated coal samples aim-ing atthe prevention of gas outburst or the preven-tion of smut by water injection[1-3 ] ,the research onrelative permeability of double- phase medium underconfining stress has not been reported.Butsome o-versea scholars,such as Gash (…     

典型煤种CO_2气化过程中产物的析出特性

CO2气氛下在热重分析仪上对3种典型煤种分别进行了气化实验,与便携红外分析仪连用,详细研究了煤气化产物与温度、煤种的关系。结果表明：气化温度在500～800℃之间,C煤的甲烷生成速率较高,但焦炭与水蒸气的气化反应较慢,但温度达到1 000℃时甲烷会分解;在热重分析仪中,高灰分阻碍了气化反应的进行,400～1000℃过程中失重曲线较平缓,在1 000℃之后,TG曲线有了明显的变化;煤化程度越低,越有利于挥发分的析出,有利于提高气化过程中CO和CH4的析出量,而且降低了有机硫（COS）的析出量。     

离子液体溶胀煤体与溶解甲烷研究进展

综述了煤矿瓦斯增抽方法、离子液体溶胀煤、离子液体溶解甲烷的研究现状;分析了目前低透煤层瓦斯增抽主要是采用物理作用破碎煤体来释放CH4,或注CO2或N2置换瓦斯的办法,其效果虽然显著,但对于微孔隙中的甲烷解吸还是存在着局限性．鉴于功能化离子液体溶胀煤及吸收甲烷的协同作用,提出利用离子液体增加煤中孔隙尺寸以吸收煤表面CH4气体的方法,强化抽采过程中的瓦斯解吸,降低了煤层本身的瓦斯含量,提高抽采瓦斯气体的利用效率．最后,阐述离子液体溶胀煤、溶解甲烷的研究进展,以及离子液体应用于瓦斯抽采方面的研究基础．     

Construction of high-pressure adsorption isotherm: A tool for predicting coalbed methane recovery from Jharia coalfield,India

Adsorption isotherm relates the gas storage capacity as a function of pressure at constant temperature. In this paper, adsorption isotherm of two dry borehole samples was constructed in the laboratory using the manometric method. Isotherm was measured for two gases, i.e., CH_4 and CO_2 to pressure up to 8.4 MPa.Before the construction of sorption isotherm, coal was characterized by proximate, ultimate and petrographic analysis. Coalbed gas content of these two samples was found 2.29 m~3/t and 2.75 m~3/t. SEM images were obtained for the pore size distribution of coal using pore image analysis. Prediction of coalbed methane recovery from CH_4 adsorption isotherm showed that these coalbeds are under saturated. CO_2 isotherm was constructed to estimate enhanced coalbed methane(ECBM) recovery. Volume wise CO_2/CH_4 sorption ratio was found 2.09 times to 2.75 times respectively. This paper presents the interpretation of isotherm data to find the recovery factor of methane production from Jharia coalfield.     

高含水煤样的多元混合气体的吸附分析

对高含水煤样进行了三元混合气体（CH4,CO2,N2均为33．3％）的高压等温吸附试验,得出等温吸附曲线,并分析了三元混合气体在吸附过程中各组分体积分数的变化规律．结果表明,吸附曲线在煤样含水量高于5％时不遵循超出煤样平衡水分范围曲线不再变化的规律,而是吸附量低得多;吸附过程中各组分的体积分数是实时变化的,吸附能力强的气体吸附速率先快后慢,吸附能力弱的气体吸附速率先慢后快;在高压时吸附曲线没有明显变化．为更科学地计算煤层气资源量和可采潜力提供参考．     

Ti改性活性炭分离CH_4/N_2的实验研究

针对甲烷气体(煤矿乏风瓦斯)的富集与分离,研究了活性炭吸附材料(AC)的Ti改性方法,讨论了对CH4/N2分离性能的影响.结果表明:Ti改性炭活性在1 100℃、N2保护焙烧后孔径分布更均一;CH4的吸附量达到34.4 mL/g,比未改性的活性炭和160℃水热方法 Ti改性的活性炭增加了51.5%;CH4常压穿透曲线的穿透点比未改性的活性炭和160℃水热方法 Ti改性的活性炭分别滞后了41%和50%.     

用多元气体等温吸附成果评价煤层气开发潜力

针对煤层气中通常含有一定数量非 CH4气体的现实情况 ,进行了纯 N2 、纯 CH4和 CH4- N2二元气体等温吸附实验的对比研究 ,分析了煤层气中的 N2 组分对煤层 CH4吸附性能的影响 .结果表明 ,用纯 CH4气体的等温吸附资料进行煤层气开发潜力的评价 ,可能会产生不完全正确的结论 ;而多元气体的等温吸附曲线 ,可用于进行煤层气开发潜力的正确评价 .     

Mechanism of CO2 enhanced CBM recovery in China: a review

Permeability of coal reservoirs in China is in general low. Injection of CO2 into coal seams is one of the potential ap-proaches for enhancing coalbed methane (CBM) production. The feasibility of this technology has been investigated in China since the 1990s. Advances in mechanism of CO2 enhanced CBM recovery (CO2-ECBM) in China are reviewed in light of certain aspects,such as the competitive multi-component gas adsorption, sorption-induced coal swelling/shrinkage and its potential effect on CBM production and numerical simulation for CO2-ECBM recovery. Newer investigations for improving the technology are discussed. It is suggested that a comprehensive feasibility demonstration in terms of geology, technology, economics and environment-carrying capacity is necessary for a successful application of the technology for CBM recovery in China. The demonstration should be car-ried out after more investigations into such facets as the control of coal components and structure to a competitive multi-component-gas adsorption, the behavior and essence of super-critical adsorption by coal of gas, environmental and safe feasi-bility of coal mining after CO2 injection and more extensive pilot tests for CO2-ECBM recovery.     

Explosive limits of mixed gases containing CH4, CO and C2H4 in the goaf area

The explosive gases CO and C2H4, released mainly flammable gases during the process of coal self-ignition, are of the most important ingredients of the multi-component gases in goaf areas, along with CH4. We have determined some of the parameters of explosive properties of the one-component gases CH4, CO and C2H4 using an explosive trial device of polybasic explosive gas mixtures and emphasized particularly the effect on the limits of explosive concentration of the binary explosive mixed gases CH4+CO, CH4+C2H4, as a function of the amount of CO, C2H4 and inert flame resisting gases (N2, CO2). The experimental results show that the effect of inert gases on the explosive limits of mixed gases, given the property of explosive gas, is obvious: the inert gases (N2, CO2) possess some inhibitory effects on the explosion of the multi-component explosive gas mixtures. The results will provide some experimental support to suppress the occurrence of the gas explosions in goaf areas and provide some directions for designing explosion-proof electric equipment and fire arresters.     

Some parameters of coal methane system that cause very slow release of methane from virgin coal beds(CBM)

In some worldwide hard coal basins recovery of methane from virgin coal beds is difficult. In general,mentioned difficulties are related to geo-mechanical, petrographical and physical-chemical properties of coals in question, occurring for example in the Bowen Basin(Australia) or the Upper Silesian Coal Basin(Poland). Among numerous properties and parameters, the following are very essential: susceptibility of coal beds to deformation connected with coal stress state change and contemporary shrinkage of the coal matrix during methane desorption. Those adverse geo-mechanical and physical-chemical effects are accompanied by essential change of the porous coal structure, which under these disadvantageous conditions is very complex. This study aims to show difficulties, which occur in phase of recognition of the methane-reach coal deposit. Volume absorbed methane(not surface adsorbed) in sub-micropores having minimal size comparable with gas molecule diameter must possess energy allowing separation of the nodes and methane release to micropores.     

煤层气运移分馏机理初探

煤层气的分馏效应是指运移过程中气体组份和同位素值发生变化的现象.分馏机理的探讨对煤层气的运移聚集具有重要指导意义.本文以吸附势理论为指导,以等温吸附实验数据为依据,对甲烷碳同位素和多组分气体分馏机理进行了探讨.确定了4种分馏机理的存在:(1)解吸-扩散-运移不仅造成甲烷碳同位素分馏,而且造成多组分气体分馏.13CH4因其吸附势普遍高于12CH4而具有优先吸附、滞后解吸的特征,12CH4更容易发生运移分馏.二氧化碳与甲烷相比,具有优先吸附、滞后解吸的特征,特别是在高压下,甲烷具有强的分馏效应;(2)发生在地下水径流带的溶解作用使得13CH4被优先溶解并被运移至滞留区聚集,12CH4保留在原地;(3)浅部次生生物气的产生造成甲烷碳同位素变轻的假象;(4)高温裂解气的生成造成甲烷碳同位素变重的假象.4种分馏效应都引起浅部甲烷碳同位素变轻,深部变重,这已为众多的实例所证实.     

液态水对煤吸附甲烷影响的机理分析

为了研究液态水对煤吸附甲烷影响的机理,进行了不同煤级干燥煤样、平衡水煤样和注水煤样等温吸附实验,基于分子间作用力对液态水影响机理进行分析,并用维里方程拟合等温吸附实验结果来验证.结果表明,煤基质的润湿程度是液态水影响煤吸附甲烷的主要因素.干燥煤样中煤与甲烷分子间作用力远大于甲烷分子间作用力,第二维里系数较低,吸附能力强;平衡水煤样中煤与水分子氢键能高于范德华力,气态水分子竞争吸附,第二维里系数偏高,煤基质吸附能力弱;注水煤样中煤与甲烷分子之间长程作用力和甲烷与水分子之间短程作用力之和较小,与甲烷分子间作用力相当,第二维里系数最高,煤基质吸附能力很低.煤级增高,煤基质表面极性及其润湿程度降低,第二维里系数随之降低.     

Adsorption mechanism of different coal ranks under variable temperature and pressure conditions

Variable temperature and pressure adsorption tests were conducted on four coal samples with different coal ranks, under simulated temperatures and pressures corresponding to coal reservoirs at different depths. The regularity of the variation in the amounts of adsorption by coals under variable temperature and pressure and 30 ~C isothermal conditions are compared and the adsorption characteristics of coal under the composite effect of temperature and pressure were obtained. The adsorption test and data processing method of coal under variable temperature and pressure are presented and the effect of the mechanism of tempera-ture and pressure on the adsorption capacity of coal has been studied. The research results are of significant importance in the in-vestigation of coalbed methane storage mechanism and for the prediction of the amounts of coalbed methane at various depths.     

The impact of depositional environment and tectonic evolution on coalbed methane occurrence in West Henan,China

A deeper understanding of the mechanisms by which geological factors(depositional environment and tectonic evolution) control the occurrence of coalbed methane(CBM) is important for the utilization of CBM resources via surface-drilled wells and the elimination of coal-methane outbursts, the latter of which is a key issue for coal mine safety. Based on drill core data, high-pressure isothermal adsorption experiments, scanning electron microscopy experiments, mercury intrusion porosimetry, and X-ray diffraction experiments, the impact of the depositional environment and tectonic evolution on CBM occurrence of the II-1 coal seam of the Shanxi Formation in West Henan was analyzed. Results showed that the depositional environment led to the epigenetic erosion of tidal flat coal-accumulating structures by shallow-delta distributary channel strata. This resulted in the replacement of the original mudstonesandy mudstone coal seam immediate roof with fine-to-medium grained sandstones, reducing methane storage capacity. Epigenetic erosion by the depositional environment also increased coal body ash content(from 6.9% to 21.4%) and mineral content, filling the cleat system and reducing porosity, reducing methane storage capacity. The maximum methane adsorption capacity of the coal body reduced from35.7 cm3/g to 30.30 cm3/g, and Langmuir pressure decreased from 1.39 MPa to 0.909 MPa. Hence, the methane adsorption capacity of the coal body decreased while its capacity for methane desorption increased. Owing to the tectonic evolution of West Henan, tectonically deformed coal is common; as it evolves from primary cataclastic coal to granulitic coal, the angle of the diffraction peak increases, d002 decreases, and La, Lc, and Nc increase; these traits are generally consistent with dynamic metamorphism.This is accompanied by increases in the total pore volume and specific surface area of the coal body, further increasing the capacity for methane storage. Increases in micropore volume and specific surface area also increase the ability of the coal body to adsorb methane.     

注二氧化碳提高煤层甲烷采收率的实验模拟

针对我国煤层气开发中存在的产气率低、回采周期长的问题，开展了注二氧化碳驱替煤层甲烷的实验模拟研究．根据实验数据，利用扩展Langmuir方程计算了驱替过程中CH4组分的产出特征，并与纯CH4的解吸过程进行了比较．结果表明，在CO2驱替实验中，CH4在单位压降下的解吸率，明显高于纯CH4解吸时单位压降下的解吸率．其中晋城煤层CH4单位压降下的解吸率提高了150%，潞安煤层CH4单位压降下的解吸率提高了270％．由此可见，采用二氧化碳注入技术，可以显著提高煤层甲烷的采收率．     

注CO2 驱替煤层气过程的影响因素分析

基于煤储层注CO2 提高煤层气采收率的机理, 从实验模拟研究和现场出发, 总结和分析了注CO2 过程的影响因素。通过研究发现, 影响因素主要有煤质条件、 水和CO2 的注入压力及注入速率。煤质条件中的矿物、煤层中的水因其种类、 含量及分布特点不同而影响注气过程, 在煤中无外来水源补给的自由水状态下, 煤中碳酸盐矿物含量越高, 煤层气采收率越高; 注气压力越大, 煤层气产出的渗流通道越好, 在一定时间内甲烷脱附率随着CO2注入速率的增加而增大。通过层次分析法对各影响因素进行敏感性分析发现, 煤质条件的权重系数为0. 5 5, 在注气过程中起主要作用。     

华北重点矿区煤储层吸附特征及其影响因素

研究华北地区煤储层吸附特征及主要影响因素，对9个重点矿区42件煤样进行了平衡水法等温吸附分析．实验表明：研究区原煤兰氏体积在6．22～43．57m^3／t之间，分布特征受区域煤变质的三带分布规律控制，在中带的沁水盆地最高，焦作、安鹤、永夏和荥巩煤田其次，而在南、北两带的平顶山、大同和两淮地区最低；全区域兰氏压力在0．20～3．83MPa之间，以大同和沁水最高，平顶山次之，其他矿区较低．研究表明，煤级是影响该区煤储层吸附能力的主要因素，随煤级增大，煤储层吸附能力呈多项式关系增强．煤吸附能力随煤中镜质组和惰质组含量总和的增高而增强，其中惰质组的影响较大．煤储层吸附能力随煤中碳组分含量的增高和氢组分含量的降低而增高．煤中水分和灰分的存在会降低煤的吸附性能．     

新疆油田CO2驱提高原油采收率与地质埋存潜力评价

CO2驱油与埋存技术既可以大幅提高原油采收率,又可以有效降低温室气体排放,在世界范围内已得到广泛重视,我国近些年来已开展了深入研究并取得了很大进展．基于分流理论,提出一套CO2驱提高原油采收率与埋存潜力评价方法,并针对新疆油田进行了CO2驱提高原油采收率和地质埋存潜力评价．评价结果显示：水驱后转CO2气驱比连续水驱原油采收率有较大幅度的提高,并且CO2混相驱比非混相驱的采收率和地质埋存潜力大．评价结果表明CO2驱在新疆油田具有较好的应用前景．本研究提出了一种可靠、快捷的CO2提高采收率与埋存潜力评价方法及步骤,将可为全国范围内进一步开展潜力评价提供可靠的方法和技术手段．