Reservoir reconstruction technologies for coalbed methane recovery in deep and multiple seams

Multiple coal seams widely develop in the deep Chinese coal-bearing strata. Ground in situ stress and coal seam gas pressure increase continuously with the increase of the mining depth, and coal and gas outburst disasters become increasingly severe. When the coal is very deep, the gas content and pressure will elevate and thus coal seams tends to outburst-prone seams. The safety and economics of exploited firstmined coal seams are tremendously restricted. Meanwhile, the multiple seams occurrence conditions resulted in different methane pressure systems in the coal-bearing strata, which made the reservoir reconstruction of coal difficult. Given the characteristics of low saturation, low permeability, strong anisotropy and soft coal of Chinese coal seams, a single hydraulic fracturing surface well for reservoir reconstruction to pre-drain the coalbed methane(CBM) of multiple seams concurrently under the different gas pressure systems has not yet gained any breakthroughs. Based on analyses of the main features of deep CBM reservoirs in China, current gas control methods and the existing challenges in deep and multiple seams, we proposed a new technology for deep CBM reservoir reconstruction to realize simultaneous high-efficiency coal mining and gas extraction. In particular, we determined the first-mined seam according to the principles of effectiveness and economics, and used hydraulic fracturing surface well to reconstruct the first-mined seam which enlarges the selection range of the first-mined seam. During the process of mining first-mined seam, adjacent coal seams could be reconstructed under the mining effect which promoted high-efficiency pressure relief gas extraction by using spatial and comprehensive gas drainage methods(combination of underground and ground CBM extraction methods). A typical integrated reservoir reconstruction technology, ‘‘One well for triple use", was detailed introduced and successfully applied in the Luling coal mine. The application showed that the proposed technology could effectively promote coal mining safety and simultaneously high-efficiency gas extraction.     

Exploitation technology of pressure relief coalbed methane in vertical surface wells in the Huainan coal mining area

Exploitation technology of pressure relief coalbed methane in vertical surface wells is a new method for exploration of gas and coalbed methane exploitation in mining areas with high concentrations of gas, where tectonic coal developed. Studies on vertical surface well technology in the Huainan Coal Mining area play a role in demonstration in the use of clean, new energy re-sources, preventing and reducing coal mine gas accidents and protecting the environment. Based on the practice of gas drainage engineering of pressure relief coalbed methane in vertical surface wells and combined with relative geological and exploration en-gineering theories, the design principles of design and structure of wells of pressure relief coaibed methane in vertical surface wells are studied. The effects of extraction and their causes are discussed and the impact of geological conditions on gas production of the vertical surface wells are analyzed. The results indicate that in mining areas with high concentrations of gas, where tectonic coal developed, a success rate of pressure relief coalbed methane in surface vertical well is high and single well production usually great. But deformation due to coal exploitation could damage boreholes and cause breaks in the connection between aquifers and bore-holes, which could induce a decrease, even a complete halt in gas production of a single well. The design of well site location and wellbore configuration are the key for technology. The development of the geological conditions for coalbed methane have a sig-nificant effect on gas production of coalbed methane wells.     

Application of structural curvature of coalbed floor on CBM development in the Zaoyuan block of the southern Qinshui Basin

Based on controls of structural style and the position in coalbed methane(CBM)development,we used a method of curvatures to study its relations with CBM development parameters.We calculated structural curvatures of contours of the No.3coal seam floor of the Shanxi Formation in the Zaoyuan block of the Qinshui Basin and analyzed its relations with development parameters of coalbed methane wells.The results show that structural curvature is negatively related to coal reservoir pressure,while positively related to permeability.With an increase in structural curvature,the average production of coalbed methane wells increases at first and then decreases,reaching the highest production at 0.02 m-1 of structural curvature.Therefore,structural curvature can be an important index for potential evaluation of coalbed methane development and provide a basis for siting coalbed methane wells.     

水文地质条件对煤层气富集的影响

水文地质条件作为煤层气保存及形成超压煤储层主要因素之一。它对煤层气赋存、运移和生产都会产生影响与控制作用,对煤层气的高产富集和开采也起到非常重要的作用,是煤层气富集成藏过程主控因素中的一个关键因素。结合沁水盆地、鄂尔多斯盆地等一些国内煤层气区块,研究水文地质对煤层气富集的影响。     

Method for predicting economic peak yield for a single well of coalbed methane

The development of coalbed methane (CBM) in China poses great difficulties because of high investments, low production and high risks. So a study of the economic effect of a single well at its preliminary stage is helpful for commercial exploitation of CBM. Affected by wellbore flow pressure, initial reservoir pressure, relative permeability, Langmuir pressure and other factors,the trend of declining production of a single CBM well agrees, by and large, with a hyperbolic pattern of decline. Based on Arps'sequation, nearly 200 wells production with different peak yields and initial rates of were simulated. Given the present cost of drilling, gas production and engineering on the ground, the gross investment for the development of a single coalbed methane well was estimated for the Fanzhuang block in central China. Considering the current industrial policies for CBM, we established an economic assessment model and analyzed economic peaks. The results show the economic benefits with or without government subsidies at different peak yields of a single CBM well. The results of the evaluation can be directly applied in the Fanzhuang block. The evaluation method, formulated in our study, can be used to other areas with similar conditions.     

等温吸附曲线方法在煤层气可采资源量估算中的应用

在缺乏煤层气井生产资料的情况下，为了合理利用我国煤田地质勘探中煤层气解吸法所测的煤层气含量，使其计算的煤层气资源量与可采资源量更为接近，根据煤层气解吸特征，煤储层等温吸附特征，通过计算解吸系数，求取煤层气的解吸率．利用等温吸附曲线与煤层气临界解吸压力的关系，估算出煤层气临界解吸压力，并结合煤层气井的枯竭压力，估算出煤层气采收率，进而获得煤层气可采资源量．结果表明，残余气在煤层气开采时基本上是不可能获得的，另外由于生产技术的原因，参考国外煤层气实际生产情况，井深结构所能达到的最低储层压力之下的煤层气也基本上不能被采出．因此通过解吸系数法校正、等温吸附曲线法校正后，计算的煤层气资源量更能反映煤层气的可采潜力．     

煤岩等温吸附曲线特征在煤层气研究中的应用

在煤层气研究过程中,通过对曲线形态进行分析,认为在煤层气开采初期和中期,兰氏体积和兰氏压力越大,对产气越有利,而在开采后期,兰氏压力越小,对产气越有利.同时,也可根据曲线方程估算出煤层气采收率,进而获得煤层气可采资源量.     

华北地区煤层含气性影响因素探讨

煤层含气性是评价煤层气勘探开发前景的决定性因素之一,影响煤层含气性的因素很多,其中较为重要的因素有煤层上覆有效地层厚度、煤的变质程度、断裂构造、盖层条件及煤层厚度等.对此进行了分析探讨,认为:影响煤层含气性的主要地质因素为煤层上覆有效地层厚度和煤的变质程度,次要因素为断裂构造、盖层条件及煤层厚度.     

Effect of coal resources development and compensation for damage to cultivated land in mining areas

The exploitation of coal resources inevitably affects, to different degrees, arable land resources and impacts the socio-economic development in mining areas. Therefore it is of great practical importance to probe the rules of the effect from coal resource exploration on arable land. Suitable and effective measures to compensate for damaged to and loss of arable land resources should be taken on the basis of carrying out green mining and reducing damage to limited arable land resources. We have used GIS in simulating the effect of coal resource exploration on arable land. In light of our simulation of the space-time spectrum, the effect is analyzed. Given the socio-economic development conditions of a mining area, specified rational amounts and opportunities for compensation to arable land in mining areas are explored. Finally, from a policy perspective, relevant proposals for rational arable land resource compensation are proposed to facilitate the coordinated development between coal resource exploitation and socio-economy development in mining areas.     

刘家勘探区煤储层特征及煤层气开发条件研究

研究了刘家勘探区煤储层特征及煤层气开发条件，认为研究区煤储层的煤级，孔隙性和渗透性相对较低，但地质构造简单，煤层气资源丰度高，煤储层厚度，含气量，含气饱和度，甲烷浓度，临储压力比，临界解吸压力等都较高，压力梯度基本正常，可采性以及煤层气开发和利用前景条件较好。并已被煤层气井排采试验结果所初步证实，同时，中也就区内今后的煤层气开发工作提出了某些建议。     

水文地质条件对白额勘探区煤层气富集的影响

地下水水动力场对煤层气富集具有明显影响。在研究区东部,煤储层埋藏浅,地下水的径流作用相对较强,煤层气被径流逸散。研究区西南部,煤储层埋藏深,地下水由本区东北浅部向西南深部顺层径流,对煤层中向上扩散的气体起到了封堵作用。矿区西南部为地下水低水位等势面区域,地下水严重滞留,有利于煤层气富集保存,是煤层气富集的有利区域。研究结构显示,地下水化学场特征同样影响煤层气富集。地下水滞留区域与高矿化度中心一致,同样与区域富气中心分布一致。这说明滞留或弱水力交替地下水是煤层气富集成藏的有利水文地质条件。     

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.     

湖南煤层（瓦斯）气研究现状及开发利用前景

介绍了湖南省煤田地质概况，煤层气赋存规律及特征，矿井瓦斯抽放现状与效果，并对煤层气资源进行了初步评价。     

铁法盆地煤层气成藏模式及产能预测

分析了铁法盆地构造形态、沉积环境和聚煤特征 ;研究了盆地水文地质条件和煤层气赋存规律 ,并提出了铁法盆地煤层气成藏模式 .结果表明 :在不对称向斜盆地中 ,沉积了巨厚的下白垩统煤系地层和煤层 ,煤系地层是一个含水层 ,其顶底部含全区分布的隔水层 ,上覆上白垩统含水层 ,有利于煤层气聚集 .侧向上 ,地下水由浅部补给 ,在深部形成滞流 ,在西部煤层分叉尖灭带和相变带附近 ,形成高势能储层 ,因此 ,盆地西部的大兴井田及大隆到大明井田将是煤层气富集高产区 .     

平顶山矿区煤层气赋存特征及开发潜力

平顶山矿区二1煤层富含煤层甲烷气体,其资源量估算达302亿m3以上．本文通过对控制煤层气赋存的二1煤层的传层几何形态、地质特征、煤质变化、特别是物性特征的研究,指出本区二1煤层渗透性较好,渗透率随着围限压力增加而降低,且与判及发育程度、构造应力变化有密切关系．而二1煤层中的煤层气含量与煤层理深有着密切关系,随着深度增加而增加．通过综合分析指出了开发潜力较好的区块．     

割理方向与煤层气抽放效果的关系及预测模型

以井下地质调查为基础 ,就煤层割理方向性与矿井下钻孔煤层气抽放效果之间耦合关系开展了现场试验 ,并据此建立了煤层气抽放效果预测的数学模型 .结果表明 :垂直面割理方向钻孔的抽放量在任何时刻都明显高于平行面割理方向钻孔的抽放量 ,抽放时间越长 ,两方向抽放量之间差距越显著 ;研究区垂直面割理方向钻孔的极限抽放量是平行面割理方向钻孔的 2 .61倍 ,抽放率高出 4.34倍 ,合理抽放时间在 30 0 d左右 .采用垂直面割理方向布置钻孔的方式 ,可显著地提高煤层气抽放效果 .     

煤层气压裂技术研究

煤层气与常规天然气有较大差异,采用压裂施工可达到煤层气开发的理想效果。根据煤层气的特性,在施工中应注意压裂液、煤粉、压实性等因素所造成的伤害。     

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.     

吐哈盆地沙尔湖地区煤层气钻完井适用技术探讨

在剖析美国圣胡安盆地煤层气空气钻井、裸眼洞穴完井技术及优势的基础上,确定了低煤阶煤层气钻井及裸眼洞穴完井的煤储层条件等,并以吐哈盆地沙尔湖地区低煤阶煤层气为主要研究对象,利用类比法及地质统计法,具体分析了吐哈盆地沙尔湖地区的煤储层厚度、含气量、渗透率、井壁稳定性及储层压力条件等．研究表明,沙尔湖地区煤层厚度大,储层物性好,井壁稳定性好,可采用低成本空气钻井及裸眼完井技术提高钻井效率,保护煤储层,提高煤层气采收率．     

应用瓦斯地质图指导安全生产

本文介绍了半罗山矿的地质概况，探讨了低瓦斯矿井瓦斯漏出的一般规律，论述了瓦斯地质编图对煤矿通风安全及生产的指导意义。