【作者】 方志明；

【导师】 李小春；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2009， 博士

【摘要】 我国是煤炭工业大国,煤层气资源极为丰富,但目前我国煤层气抽采率还处于较低的水平。煤层气抽采率低的直接后果是煤矿瓦斯灾害频繁、采煤效率低下、资源浪费、环境污染等。提高煤层气采收率具有煤矿瓦斯灾害防治、煤层气规模化利用和温室气体减排的三重效果。针对我国煤层绝大多数渗透率较低的特点和煤矿瓦斯抽采率低的现状,建议采用富N₂混合气体驱替煤层气技术,以提高煤层气产采收率。本文主要在CO₂煤层封存、气体驱替煤层气等技术的现有研究基础上,利用煤层气地质学、岩石力学、固体力学、多孔介质理论、渗流力学、多相流等多学科的理论以及室内试验和现场试验对富N₂混合气体驱替煤层气技术进行了以下几方面的研究:1、简要介绍了煤层气的储层特征及赋存、运移与产出机理,在此基础上分析了CO₂驱替煤层气技术的机理与适用性,针对我国煤层绝大多数渗透率较低的特点和煤矿瓦斯抽采率低的现状建议我国采用富N₂混合气体驱替煤层气技术,分析了其机理和优点。2、建立了混合气体驱替煤层气过程多相渗流流-固耦合理论模型并给出了其数值解法。建立了考虑约束条件和膨胀、收缩效应的煤岩渗透率模型。3、提出了煤岩吸附量-变形-渗透系数同时测量方法并开发了相关试验装置。该方法及装置的优点是:（a）一次即可完成吸附量、变形和渗透系数的测量,较之其它方法更为简便;（b）吸附量、变形和渗透系数同时测量,能更好地分析它们这些参数之间的相互影响关系;（c）采用圆柱形煤样,试验结果有利于和常规岩石力学标准吻合,更有实际价值。4、利用上述装置和方法进行了CO₂、N₂、CH₄单组分气体的吸附、变形和渗流室内试验研究。试验结果表明:（1）煤样对CO₂、N₂、CH₄吸附量的大小关系是:CO₂＞CH₄＞N₂。（2）在保持有效应力不变的情况下,随着孔隙压力的增大,煤岩吸附三种气体后的体应变都会增加,而且体应变大小关系为:CO₂＞CH₄＞N₂。因此,相对于原来被CH₄饱和的煤样而言,注CO₂驱替CH₄后,煤岩会发生膨胀;相反,注N₂驱替CH₄后,煤岩会发生收缩。（3）在保持有效应力不变的情况下,随着孔隙压力的增大,三种气体的渗透系数都有所降低,但是CO₂的渗透系数降低最为明显,降低幅度将近一个数量级;其次是CH₄;N₂的渗透系数降低得最少。因此,相对于CH₄而言,注CO₂会使渗透系数降低,而注N₂则会使渗透系数增加。这也就是N₂的增渗机理。（4）上述注CO₂、N₂、CH₄气体的试验结果显示了所提方法和装置的优点,并展示了良好测试效果。5、进行了井下混合气体驱替煤层气现场试验,试验结果表明,相对于现行单纯抽采方法,混合气体驱替煤层气技术在原理和效果上有较大突破,在技术上可行;注气驱替的影响范围较大,除了对与其相邻的钻孔有效果,对与其相距较远的钻孔也有驱替效果;驱替大幅提高了钻孔瓦斯浓度和流量。6、根据井下混合气体驱替煤层气现场试验结果,考虑煤矿井下现场实际情况,提出了井下采面规模混合气体驱替煤层气工业试验方案。具体方案主要包括:钻孔施工与布置要求、钻孔封孔工艺、钻孔水气分离、驱替过程监测及效果评价等方面。7、利用计算机分别进行了单纯抽采和混合气体驱替过程的数值模拟,分析了实施地面混合气体驱替煤层气的理论效果、方案及其可行性。研究结果表明采用地面混合气体驱替煤层气技术可以大幅提高煤层气采收率、缩短煤层瓦斯预抽时间、提高采煤效率。更多还原

【Abstract】 China is a big coal industrial country with very rich coalbed methane resources. However,the recovery ratio of coalbed methane in China is still at a relatively low level. The direct consequences of low recovery ratio of coalbed methane are gas disaster-prone, inefficient mining,resource waste and environmental pollution.Enhanced coalbed methane recovery ratio has the triple effects of disaster prevention,large-scale use of coalbed methane and greenhouse gas emission reduction.In view of the low permeability characteristic of most coalbed and the current status of low recovery ratio of coalbed methane in China,the N₂-rich gas mixture enhanced coalbed methane（G-ECBM） technology has been suggested for the purpose of enhancing coalbed methane recovery ratio.In this thesis,the G-ECBM technology is studied based on the existing technologies of CO₂ sequestration in coalbed and enhanced coalbed methane production by gas injection, according to the theories of coalbed methane geology,rock mechanics,solid mechanics, porous medium,flow mechanics in porous medium,multiphase flow and the methods of laboratory test and field test.The major contents of this thesis include:1.The characteristic of coalbed methane reservoir and the mechanisms of storage, migration and production of coalbed methane were introduced.In view of the low permeability of most coal and the current status of low recovery ratio of coalbed methane in China,the N₂-rich gas mixture enhanced coalbed methane（G-ECBM） technology was suggested.The mechanism and advantages of G-ECBM technology were analyzed.2.A multiphase flow fluid-solid coupling mathematical model for G-ECBM process was developed,and the numerical solution method was given in detail.A permeability model considering the swelling and shrinkage effects of coal under different constraint conditions was established.3.A method for simultaneously measuring adsorption-strain-permeability and related experimental set-up were developed.The advantages of the method and set-up include:（a） simultaneously measuring adsorption,strain and permeability on one sample,making it more convenient than other methods;（b）adsorption,strain and permeability are measured at the same time,making it better to analyze the relations between these parameters;（c） cylindrical coal sample is used,making the results more valuable and more consistent with the standards of conventional rock mechanics.4.The adsorption,strain and flow tests of single-component gas of CO₂、N₂ and CH₄ were carried out with above method and set up,respectively.The test results showed that:（1） The relationship of the adsorptions of CO₂、N₂ and CH₄ on the same coal sample was:CO₂＞CH₄＞N₂.（2） At constant effective stress,sorption-induced strains of three gases all increased with the increase in pore stress,and the relationship of strains was:CO₂＞CH₄＞N₂. Therefore,compared with the original coal sample saturated by CH₄,coal will swell in CO₂-ECBM and shrink in N₂-ECBM.（3） At constant effective stress,permeabilities of three gases all decreased with the increase in pore stress.The permeability decrease induced by CO₂ was nearly an order of magnitude,which was the most obvious;followed by CH₄;the permeability decrease induced by N₂ was very small.Therefore,compared with the original coal sample saturated by CH₄,coal permeability will decrease remarkably in CO₂-ECBM and increase in N₂-ECBM,which shows the mechanism of permeability-increasing of N₂.（4） The test results above indicated that the proposed method and set-up suitable for simultaneously measuring adsorption,strain and permeability of coal.5.Two different scale underground field tests were carried out.Test results showed that,compared with existing conventional extraction method,G-ECBM technology has great breakthrough in principle and effect,and is technically feasible;gas injection had effect on not only the neighboring production wells but also the a litter far production wells; gas injection enhanced the concentration and flow rate of coalbed methane.6.The industrial test program of underground G-ECBM was proposed,based on the field test results and the actual situation in coal mine.The program includes:construction and layout requirements of wells;drilling sealing process;water and gas separation; monitor and estimation of the test process.7.The theoretical effect,program and feasibility of ground G-ECBM have been studied by contrastive numerical simulation of conventional extraction process and G-ECBM technology.The results showed that,by using G-ECBM technology,coalbed methane recovery ratio can be enhanced substantially,and the time for coalbed methane pre-extraction can be shortened thus improving the efficiency of coal mining.更多还原