煤层甲烷扩散物理模拟实验及其机理研究

发布时间：2018-01-25 15:18

本文关键词： 甲烷扩散物理模拟控制机理　出处：《河南理工大学》2014年博士论文　论文类型：学位论文

【摘要】：煤中甲烷产出需经过解吸、扩散和渗流三个阶段,其中扩散不仅是衔接瓦斯解吸和渗流的纽带,而且是控制瓦斯最终产出速度的必要条件。以往针对煤中瓦斯扩散的研究,主要集中在对煤屑采用解吸实验进行扩散表征和构建扩散数学模型上,缺乏对煤中瓦斯扩散过程的完整描述和表征。论文在借鉴前人已有研究成果的基础上,采集山西沁水盆地中南部的潞安矿区碎裂煤为研究煤样,分析研究区的地温、地应力、储层压力等地层条件,选用规则块状煤样品并结合气相色谱法开展煤中甲烷的扩散实验,探寻孔隙结构、扩散路径、围压、气压和温度等多因素对对扩散特征影响规律及控制机理。论文研究主要取得了以下进展:(1)采用液氮吸附和冷场发射扫描电镜实验,获取了微观扩散孔隙的新特性,建立了微观扩散孔隙几何模型,为揭示煤中甲烷扩散控制机理奠定了基础。①高煤级贫煤主要以微孔隙(10nm)为主,占总孔容的45%以上,其次为过渡孔,中孔孔容最小;微孔比表面积占总比表面积的90%以上,微孔对甲烷的吸附/解吸/扩散起决定性作用;微孔阶段的分形特征分析表明:煤样的综合分形维数随比表面积增大而增大,二者呈线性正相关关系,而与孔容、孔隙率没有明显的线性关系。②煤样中未发现贯通孔隙,段状连通孔隙主要以近似平行层理方向不规则分布。在平行层理方向上,煤的微孔隙结构主要由段状连通孔隙和孤立孔隙组成,存在个别孔径在100nm的独立大孔;在垂直层理方向中,未发现段状连通孔隙,仅存在独立孔隙。(2)采用规则块状煤样结合气相色谱法测试了煤中甲烷的扩散系数,探讨了地层条件下煤中甲烷扩散的新特性及其控制机理。①高温高压条件下,实验区煤中甲烷的扩散系数表现出动态变化规律。即伴随微孔数量、围压和气压增大而减小,伴随孔隙度和温度升高而增大;同时扩散系数呈现出明显的矢量性,并与扩散路径密切相关,同一样品中甲烷在平行层理方向所测的扩散系数远比垂直层理方向所测的扩散系数大1~2个数量级。②随着围压增加,煤体的有效应力不断增加,由于煤体强度较低的因素,引起煤体变形不断增大,最终导致煤体孔隙率下降,扩散系数显著减小;随着压力升高,煤对甲烷的吸附性增强,孔隙的有效应力降低从而导致煤粒吸附变形增大,扩散系数减小;随着温度升高,甲烷分子运动速度加快,分子运动活力增加,由高浓度到低浓度的运动速度增加,扩散速度加快,最终导致扩散系数呈逐渐上升的趋势。(3)综合实验结果分析,筛选出地应力、地温、储层压力和扩散路径方向性作为影响甲烷扩散的主要因素,建立了基于数量化理论I的煤中甲烷扩散耦合数学模型,经理论和实践检验模型精度较高。
[Abstract]:In coal methane output after desorption, diffusion and seepage in three phases, in which diffusion is not only the link between gas desorption and seepage, and is a necessary condition for the control of gas output speed. Previous research on gas diffusion in coal, mainly concentrated in the desorption experiments of cinder diffusion characterization and construction of diffusion model and the lack of complete characterization and description of gas diffusion in coal. On the basis of previous studies on the acquisition of Lu'an mining area of Shanxi coal fragmentation in central southqinshui basin for the study of coal, geothermal, study area stress, reservoir pressure formation conditions, combined with the massive coal sample selection rules carry out the gas diffusion experiment in coal methane chromatography, explore the pore structure, the diffusion path, confining pressure, pressure and temperature on the multiple factors on the diffusion characteristics of the influence rule and control mechanism. This thesis mainly made the following progress: (1) using liquid nitrogen adsorption and scanning electron microscopy experiments, obtain the new characteristics of micro pore diffusion, a microscopic diffusion pore geometry model, lay a solid foundation for studying the coal methane diffusion control mechanism. The high rank coal mainly in the micro pore (10nm). Accounted for more than 45% of the total pore volume, followed by the transition hole, hole in the Kong Rong minimum; micro total surface area of more than 90% specific surface area, adsorption / desorption / diffusion of methane on micropores play a decisive role; fractal characteristics of micropore phase show that the fractal dimension of coal samples with larger surface area and increases, there is a positive correlation between the two, and Kong Rong, the porosity has no obvious linear relationship. Through the pore was not found in coal samples, mainly in the pore section shape approximate parallel direction of irregular distribution in parallel direction. On the micropore structure of coal is mainly composed of segments connected pores and isolated pore composition, the existence of individual aperture in a separate 100nm big hole in the vertical direction; and found no segmental connectivity only independent pores. (2) the rule of lump coal with gas chromatography to test the diffusion coefficient of coal methane, discusses the new diffusion characteristics of methane in coal and its control mechanism under formation conditions. The high temperature high pressure conditions, the diffusion coefficient of methane in coal experimentation area showed a dynamic change rule. With the number of micropores, confining pressure and increasing air pressure decreases with increasing temperature and porosity and the diffusion coefficient; showing a vector of the obvious, and the diffusion path is closely related to the diffusion coefficient of 1~2 order of magnitude of diffusion coefficient of methane in the same sample measured in parallel direction than the vertical direction are measured. The confining With the increase of effective stress of coal is increasing, due to factors of coal strength low, caused by coal deformation increases, resulting in coal porosity decreased, the diffusion coefficient decreased; with the increase of pressure, the adsorption of methane in coal increased, effective pore stress resulting in reduced coal particle adsorption deformation increase of diffusion coefficient decreases with the increase of temperature; molecular velocity of methane is accelerated, molecular motion activity increased from high concentration to low velocity of increasing concentration, diffusion speed, resulting in diffusion coefficient showed a gradual upward trend. (3) a comprehensive analysis of the experimental results, the screening of stress, temperature, pressure and reservoir the diffusion path direction as the main factors affecting methane diffusion, established the quantitative theory of methane diffusion coupled mathematical model of I in coal based on theory and practice, the test accuracy of the model is high.

【学位授予单位】：河南理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TD712

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