【作者】 王立国；

【导师】 程远平；

【作者基本信息】 中国矿业大学 ， 安全技术及工程， 2013， 博士

【摘要】 CO₂是温室效应最主要的贡献者，利用深部不可开采煤层封存CO₂可同时实现CO₂大规模减排和增加煤层气资源产量（CO₂-ECBM），具有巨大的发展潜力。然而我国煤层的渗透率普遍较低，传统的煤气层开采方法，排放煤层气藏中的水分，降低气藏的压力，促使煤层气解吸出来，这种方法只能回收20～60%的CH₄，还有相当多的煤层气滞留在煤层中。为了实现这部分资源的开采，在增加煤层透气性基础上，开发了气体驱采煤层CH₄技术，但是这种技术还处于探索阶段。本文基于表面化学、渗流力学、有限元数值分析等理论和方法对CO₂驱替深部煤层CH₄动态过程开展了较系统的实验与模拟研究；以及现场连续采取煤样和气样开展在距离注入点不同尺度中的原始煤层中气体组分浓度及碳同位素的变化，煤体的物理化学结构特性演变研究，获得地质时间内煤层条件CO₂封存的煤体-气体结构的演化规律。对窑街煤田海石湾煤样进行了煤对CO₂、CH₄及二元气体吸附解吸实验。煤对CO₂的吸附量明显大于煤对CH₄的吸附量，约1.36～2.1倍，煤样对CO₂/CH₄混合气体的总吸附量介于煤对CO₂和CH₄吸附量之间。随着CO₂比例逐渐越高，煤对混合气体的总的吸附量逐渐增大。二元气体的游离相和吸附相组分比例关系，揭示了CO₂-CH₄二元气体解吸时CH₄优先解吸，解吸速度由快转慢；而吸附时，CO₂会优先吸附，吸附速度由快转慢，上述结论是煤层中二元气体竞争吸附和CO₂驱替煤层CH₄的重要依据。自主研发了一套考虑地应力条件注气驱替煤层CH₄实验系统，并利用此实验系统开展了不同注气压力（1.5、1.8、2.2MPa），不同应力条件下（14、19MPa）CO₂、N₂驱替煤层CH₄实验研究。结果表明注入0.5个置换体积比后，N₂突破出气口，随着注气压力的升高，突破时间逐渐提前，而且N₂突破出气口后，其浓度缓慢增加。CO₂驱替CH₄实验，驱替效率较高，煤层里的CH₄基本被驱替出来。注入1.4～2.4个置换体积比，CO₂突破出气口，气体突破以后CO₂浓度迅速在90%以上。随着注气压力的增加，CO₂突破时间减小。地应力增加，导致渗透率减小。CO₂在煤体中的渗流速度变缓，CO₂就能充分的跟煤体发生吸附作用，致使CO₂的突破时间明显变缓了，由地应力为14MPa时的1.4个置换体积比到地应力为19MPa时的2.4个置换体积比了。地应力显著影响气体的驱替效果。在物理模拟实验基础上建立了反映二元气体竞争吸附、竞争扩散、气体渗流数学模型。应用COMSOL Multiphysics求解并建立了数值模拟平台，在此数值模拟平台上分别对CO₂、N₂注入煤层后驱替煤层CH₄进行了数值模拟研究。相同的条件下N₂先突破出气口，而CO₂先驱替完煤层中的CH₄。随着注气压力的提高，渗流速度加快，缩短了注气时间。窑街煤田煤层中深部CO₂注入煤层驱替CH₄的这一良好的地质背景为研究提供了独特的视角，采用CO₂吸附和压汞法，进行煤的物理结构分析；同时采用质谱仪与色谱仪进行气体的CO₂的δ13C和气体组分、浓度分析，采用傅里叶红外光谱仪进行煤的化学结构分析。实验室试验及现场试验表明，随着远离CO₂注入点，系列煤样的微孔、介孔及大孔有逐渐减小的趋势。井田东部到西部CO₂浓度逐渐减小，CH₄浓度逐渐增大。系列煤样的红外光谱谱图显示：吸收峰在2800～3000cm-1，2270～2413cm-1，1000～1200cm-1波段吸收峰强度变化较大。高压CO₂甚至超临界CO₂在运移的过程中从煤基质中萃取了部分脂肪烃及矿物质，改变了对应官能团的数量，导致吸收峰强度有所减弱，即化学结构发生改变。更多还原

【Abstract】 CO₂contributes the most to the greenhouse effect of the earth. CO₂sequestrationin deepunminable coal seam is a potential management option for greenhouse gas emissions,reducing CO₂emission meanwhile enhancing coalbed methane recovery, which has has greatpotential for development. And coal seam permeability is generally in China lower,traditional recovery methods of methane by depressurization of coalbeds yield only20～60%of CH₄in place and generally produce large volume of water at the same. There is aconsiderable number of methane in the coal seam. In order to recovery this part of theexploitation of resources, on the basis of increasing coal seam permeability, the technologythat CH₄is recovered by injecting another gas. But this technology is still in the exploratorystage. Based on the theories and methods of surface chemistry, fluid flow mechanics, finiteelement numerical analysis, CO₂flooding for deep coal CH₄dynamic process carried out bysystematic experiment and simulation study. The coal samples and gas samples were selectedcontinuously. Laboratory and field measured methods were used to carry out the gascomponent concentration and carbon isotope change, evolution of the physical and chemicalstructure characteristics of the coal. Coal-gas structure evolution was obtained in the originalseam away from the injection points over the geological time.Single gas adsorption isotherms and binary gas adsorption and desorption isotherms oncoal samples from Haishiwan coal mine in the Yaojie coalfield, were experimentally observed.The adsorption amount of CO₂on coal was significantly greater than the adsorption amountof CH₄on the coal, approximately1.36～2.1times. The total amount of adsorption ofCO₂-CH₄mixed gas on coal samples is between adsorption amount of pure CO₂andadsorption amount of pure CH₄, with the higher the proportion of CO₂gradually, the totalamount of adsorption of mixed gas on the coal gradually increases. According to theseparation information of binary gas composition both in free phase and adsorptive phase,CH₄tends to be desorbed preferentially, which however slows down with desorptionproceeding. On the contrary, CO₂adsorbs preferentially on coal. But the velocity of CO₂adsorption slows down as well. Above findings are regarded as the fundamental theories forcompetitive adsorption of binary gas and displacing the coalbed methane by CO₂injection.Experimental platform was developed independently to use to displace coalbed CH₄by gasinjection. Using this platform, we carry out displacing coalbed CH₄by CO₂or N₂the underdifferent injection pressure （1.5,1.8,2.2MPa） and different stress conditions （14,19MPa）.Theresearch results show that after injection of0.5displaced volume, N₂break through outlet, as the injection pressure increases, the breakthrough time gradually advance, after N₂breakthrough the gas outlet, its concentration increased slowly to100%. In the CO₂displacing CH₄experiments, there was high efficiency of displacement, the coalbed CH₄canbe all drive completely, after1.4～2.4replacement volume being injected, the CO₂breaksthrough gas outlet, and CO₂concentration quickly reach100%, with increasing the injectionpressure, CO₂breakthrough time is reduced. After increasing stress, the permeability reduces,which results in lower flow velocity of CO₂in the coal, CO₂can be sufficiently adsorbed oncoals. The breakthrough time is only1.4displaced volume under the stress of14MPa,however the breakthrough time increases to2.4displaced volume under stress of19MPa. Thestress significantly influences on the gas displacement.The mathematicoal model was established, which consists of the competitive adsorptionof binary gas, the competitive proliferation, the gas flow equation; COMSOLMultiphysicswas adopted to solve and built numerical simulation platform, CO₂, N₂respectively wasinjected into the coal seam to displace coalbed CH₄in this numerical simulation platform.Under same conditions, N₂first breaks through outlet, but the coalbed CH₄was recoveriedcompletely by CO₂injection first. With the improvement of the gas injection pressure,seepage velocity increases, shortening the displacing time.Good geological background of Yaojie coalfield provides a unique perspective for thestudy that displacing CH₄by CO₂injection. The physical structure of the coal was analysedby CO₂adsorption and mercury porosimetry. Gas composition and concentration wasdetermined using mass spectrometry and chromatography. The chemical structure of the coalwere analysed by fourier transform infrared spectroscopy. The results show that away fromthe injection points, the pore volumes of micropores, mecropores and macropores decreasegradually, and the CO₂concentration decreased, whereas the CH₄concentration increasedgradually. According to the FIR spectra of series of coal samples, the absorption peakschange significantly in the2800～3000cm-1,2270～2413cm-1, and1000～1200cm-1regions. Injection of CO₂into deep coal beds, particularly at conditions near the CO₂criticalpoint, may displace aromatic hydrocarbons from the coal matrix during migration, resultingin the absorption peak intensity weakened, and changing the corresponding to the number offunctional groups, which indicates the chemical structure of coal changed.更多还原