【作者】 刘长江；

【导师】 桑树勋； Victor Rudolph； Geoff Wang；

【作者基本信息】 中国矿业大学 ， 地球化学， 2010， 博士

【摘要】 以高压超临界CO₂地球化学反应器模拟CO₂在煤储层中的储存过程为研究平台,选择不同煤级、不同粒度煤作为模拟储存的样品,以压汞分析、扫描电子显微镜分析、电感耦合等离子体质谱仪和电感耦合等离子体发射光谱仪等分析测试技术为手段,对实验反应前后煤样品的密度、总孔容、比表面积、孔径分布等参数进行分析测试和对模拟储存过程中的元素地球化学迁移进行了研究,并对煤在CO₂储存过程中的压缩性、膨胀性以及孔裂隙的演化进行了探讨。本次研究所取得的主要研究成果如下:（1）建立了CO₂地质储存的模拟实验研究方法体系,并论证了其可行性以高压超临界CO₂地球化学反应器为模拟平台,采用不同煤级、不同粒级的煤作为模拟样品,从不同矿物在不同时间阶段溶出的差异性特征入手,对煤样进行不同时间的CO₂模拟地质储存实验,并对反应后的煤样和水样进行分析测试,很好的实现了CO₂的模拟地质储存过程,并从模拟装置的稳定性、实验环境参数选择的合理性以及样品处理的规范性等方面论证了模拟实验方法的可行性。（2）CO₂的地质储存过程对煤储层具有明显改造作用CO₂地质储存后,孔隙体积的增大使得煤样品的真密度有增加趋势,而矿物质的溶出则使得视密度呈下降趋势;各煤级样品的总孔容、比表面积和孔隙度均在反应后表现出了明显的增大,其中以无烟煤表现最为突出。煤储层本身固有属性的发育特征也影响了CO₂储存后煤孔隙结构的变化,无烟煤微孔相对发育,微孔占有比例从反应前的76.95%增加到88.98%,而大孔比例相对下降;褐煤大孔发育,反应后大孔比例从14.40%增加到24.25%,微孔比例变化相对较小。CO₂地质储存对煤储层的改造还表现出地球化学反应后煤储层“软化”的趋势;分形维数的计算结果表明,煤的压缩性直接与煤级相关,即煤级越高相对越难被压缩,同时CO₂的储存过程使得煤中矿物质大量溶出,从而使得煤较储存前更易被压缩。（3）CO₂地质储存过程中发生了煤中元素地球化学的规律性迁移CO₂储存前后元素由于各自活性的不同而表现出分期分批优势组合的迁移特征,元素的活性主要取决于煤中与之赋存相关的无机矿物,Ca、Mg、Mn、Sr、Zn、Co、Ba、As、Cr、Cu等与碳酸盐矿物相关的元素在CO₂储存的整个过程中均表现出了较强的迁移能力,与硫化物矿物或者硫酸盐矿物赋存相关的元素则在反应的中后期表现出迁移特征,而Si、Zr、Be、Sc、Ga和Rb等与硅酸盐矿物相关的元素则在反应后期才表现出一定的迁移能力,溶解迁移是CO₂储存过程中元素迁移的最主要方式;同时,CO₂的储存过程也促使了煤中As、Mo、Zn等生态微量元素的迁移,表现出了很强的迁移特征,迁移率分别为31.15%、23.87%和48.87%,在反应后的水中浓度高度富集。因此,CO₂注入煤储层后,有必要对Pb、As、Cu和Cr等具有较强污染作用的元素进行监测。（4）煤储层结构演化与元素迁移存在耦合关系,并构建了孔裂隙演化的地球化学模式煤储层孔裂隙的演化主要表现为3个方面,即煤基质内孔隙的增大和连通、原有裂隙的扩展以及新裂隙的产生,元素或元素组合的优势迁移特征可以反应出煤体结构的变化,特别是具有较大迁移率的Ca、Mg、Mn、Sr、Zn、Co、Ba等元素组合可以反应出煤中碳酸盐矿物受到了强烈的改造,具体体现在对以充填形式存在于煤中的碳酸盐的溶出所导致的煤孔隙度和渗透率的改造上。基于储层应力分布变化、矿物溶解迁移和元素组合迁移特征建立了CO₂地质储存过程中孔裂隙演化的地球化学模式,CO₂储存的不同时期孔裂隙表现出不同的演化特征,具体为初期渗透率变低、短暂渗透率稳定、中期渗透率增大和后期渗透率稳定4个阶段。储层中应力分布的变化和矿物质的溶解特征是控制孔裂隙演化的关键因素。CO₂的储存过程较大的改善了煤储层的孔裂隙结构,使得其开启性和连通性均得到了有益的改善,CO₂的注入改变了煤层中气体成分和浓度的分布、改变了各气体组分的分压,从而导致了CH4的解吸,渗透率的改变加快了气体扩散和渗流的通道和速度,加速了CH4的解吸和扩散,从而使得整个解吸-扩散-渗流得到了较好的改善,提高了煤层气的采收率,也实现了CO₂的储存。更多还原

【Abstract】 High pressure supercitical CO₂ geochemical ractor was employed to simulate CO₂ geological storage into coal seam reservoir process. Different coal samples with different coal rank and grain sizes were choosen in the experiments. True density, total pore volume, specific surface area, pore distribution and element geochemical migration were studied before and after the ScCO₂-H2O treatment with different analysing methods like mercury porosimetry, scanning electron microscope, inductively coupled plasma source mass spectrometer, inductively coupled plasma optical emission spectrometer and X-ray fluorescence spectrometer. Coal compressibility, swelling and evolution of pore-fracture structure were also discussed in this dissertation. The main research achievements are concluded as follows:（1） New method system of simulating CO₂ geological storage into coal seam reservoir has been established and the feasibility is demonstrated.The high pressure supercritical CO₂ geochemical reactor was used to simulate CO₂ geological storage into coal reservoir with different coal rank and grain sizes samples. The simulated experiments were carried out based on the different dissolution characteristics of different minerals in coal at different stage. Coal samples before and after the ScCO₂-H2O treatment and water samples after the treatment were analyzed. The CO₂ geological storage was simulated in labratory as expected. The feasibility was demonstrated from the stability of the simulation apparatus, rationality of the selected environmental parameters and normativity of sample preparation.（2） Coal structures are largely changed after the CO₂ geological storage process.True densities are all increased because of the increased pore voume in coal after the CO₂ geological storage, while bulk densities are all decreased because of the dissolution of coal minerals. Total pore volume, specific surface area and porosity are all largley increased in all the samples especially the anthracite coal. Changes of pore structure are also influenced by the intrinsic property of coal seam reservoir. Micropores are highly developed in anthracite which accordingly resulted in that the proportion of micropores after the ScCO₂-H2O treatment increased from the untreated sample of 76.95% to the treated sample of 88.98% while the macropores are decreased slightly . On the contrary, macropores are very developed in lignite which accordingly resulted in the proportion of macropores increased from the untreated sample of 14.40% to the treated sample of 24.25% while the micropores are not changed largely.The soften phenomenon of coal reservoir was also observed after the CO₂ geological storage. According to the calculation of fractal dimensions, the compressibility of coal is directly related to coal rank i.e. higher rank coal is harder to be compressed than the lower rank one. With the dissolution of coal minerals the treated samples are easier to be compressed than the untreated one.（3） Regularity of elements migration is observed during the CO₂ geological storage.The ability of element migration before and after the CO₂ geological storage is due to the difference of their activity which mainly decided by their occurrence in inorganic mineral matter in coal. Elements such as Ca, Mg, Mn, Sr, Zn, Co, Ba, As, Cr and Cu which interrelated with carbonate mineral and sulfide minerals have the strongest migration ability during the whole geological storage process but elements such as Si, Zr, Be, Sc, Ga and Rb which interrelated with silicate minerals only show their migration ability in the later stage of geological storage. The primary way of elements migration is dissolution migration. Meanwhile, some ecological elements such as As, Mo, Zn also show strong migration ability with migration rate of 31.15%、23.87% and 48.87% respectively. As a result, attention should be paid to the monitor to the elements with high contamination effects such as Pb, As, Cu and Cr.（4） Coupling relationship is found between reservoir structure evolution and element migration and also the geochemical model of pore-fracture evolution has been established.The evolution of pore-fracture structure are mainly represented in 3 aspects, i.e. enlarge and connectivity of pores in the coal matrix, extend of the original fractures and new-forming fractures. Changes of coal structure can be reflected by elements migration or elements combination migration especially those with high migration rate, for instance, elements combination of Ca, Mg, Mn, Sr, Zn, Co and Ba can be a reflectance of reforming of carbonate minerals.Based on the changes of stress distribution in the coal reservoir, dissolution and migration of minerals and migration characteristics of elements combination, the geochemical model of pore-fracture structure during the CO₂ geological storage has been established. The behaviors of pore-fracture evolution at different stage are shown as different characteristics, i.e. decrease of permeability in the initial stage, briefly stability of permeability, increase of permeability in the middle stage and stable permeability in the later stage. Changes of stress distribution in coal reservoir and dissolution characteristics of minerals in coal are the key factors which control the pore-fracture structure evolution. When pores and fractures are changed during the CO₂ geological storage process, their opening and connecting characteristics are greatly improved. Gas components, gas concentrations and partial pressure of different gases are all changed because of the injection of CO₂ which resulted in the desorption of CH4. Desorption and diffusion of CH4 are largely improved because the permeability of coal reservoir are increased. These processes all contribute to the enhanced coalbed methane recovery and the geological storage of CO₂ into coal seam reservoir.更多还原