上扬子区龙马溪组页岩微孔缝结构演化与页岩气赋存

发布时间：2018-01-22 01:18

本文关键词： 页岩气微孔缝结构动态演化赋存机理龙马溪组上扬子区　出处：《中国矿业大学》2017年博士论文　论文类型：学位论文

【摘要】：微孔缝结构是页岩储层定量表征的核心内容,同时也是架起研究页岩气微观赋存机理与宏观富集规律的桥梁。本论文以上扬子区下志留统龙马溪组富有机质页岩为研究对象,采用野外调查、实验测试、数值模拟、理论研究等方法,以页岩微孔缝结构演化与页岩气赋存机理为科学问题展开系统研究。主要取得以下认识和成果:龙马溪组富有机质页岩在研究区内广泛发育,基于野外实测剖面、钻孔统计以及前人资料总结,编制研究区龙马溪组黑色页岩厚度平面分布图。识别出龙马溪组主要发育黑色碳质页岩相、钙质页岩相、粉砂质页岩相、泥质粉砂岩相等4种主要岩相类型。通过定量表征龙马溪组页岩地化特征与矿物学组成,发现龙马溪组有机碳含量垂向分异性明显,下段有机质丰度高,页岩矿物组成复杂,主要包含石英、粘土、长石、碳酸盐岩等,矿物分布非均质性强。借助场发射扫描电镜,界定不同类型孔隙形貌特征,提出页岩骨架矿物刚性格架对有机质孔隙的保护机制,揭示层理微缝对页岩气赋存运移的重要意义。进一步有效联合高压压汞、低温液氮和二氧化碳吸附等实验,实现对页岩孔隙结构全尺度定量表征,揭示页岩孔径分布以双峰态-微孔优势型为主,且孔比表面积主要由孔径小于10nm孔隙贡献,而孔体积主要来源于孔径小于200nm孔隙。通过高温高压原位地层仿真热模拟实验,结合场发射扫描电镜技术,系统揭示有机孔、溶蚀孔、粘土矿物孔隙形貌动态演化特征,同时结合高压压汞、低温液氮和二氧化碳吸附等测试技术,定量表征微孔、介孔、宏孔孔隙结构(比表面积、孔容、孔径分布)动态演化特征,基于WX2井沉积埋藏史,反演龙马溪组孔隙动态演化规律,建立孔隙网络随热演化的4段式演化机制。同时借助室内甲烷高压等温吸附实验,从Gibbs吸附量定义出发,解释“倒吸附”现象出现原因。引入过剩吸附量校正项,发现以超临界微孔填充模型(SDR)校正得到绝对吸附量更为合理。结合页岩地化、矿物、孔隙结构特征,揭示页岩吸附含气量的物质主控因素,阐明微孔、介孔孔比表面积对页岩吸附含气量的控制作用。最后基于分子动力学理论,使用巨正则蒙特卡洛法模拟系统研究微孔缝中页岩气微观赋存机理,研究发现随着孔径增大,孔隙单位比表面积吸附量呈阶梯式递增,当孔径大于2nm后,单位面积吸附量趋于定值。揭示微孔尺度内甲烷主要以吸附态形式存在,明确孔径分布对页岩含气量有着至关重要的影响。
[Abstract]:Micropore structure is the core of quantitative characterization of shale reservoir. At the same time, it is also a bridge to study the microcosmic mechanism of shale gas and the law of macroscopic enrichment. This paper studies the organic shale of Lower Silurian Longmaxi formation in Yangzi area, and adopts field investigation and experimental test. Numerical simulation, theoretical research and other methods. Taking the evolution of shale micropore structure and the mechanism of shale gas occurrence as the scientific problems, the following knowledge and achievements have been obtained: the organic matter rich shale of Longmaxi formation is widely developed in the study area. Based on the field measured section, borehole statistics and previous data summary, a plane distribution map of black shale thickness in Longmaxi formation is compiled. The black carbonaceous shale facies and calcareous shale facies are identified in Longmaxi formation. Four main lithofacies types are equal to silty shale facies and shaly siltstone. By quantificationally characterizing geochemical characteristics and mineralogical composition of the shale of Longmaxi formation, it is found that the vertical differentiation of organic carbon content in Longmaxi formation is obvious. The lower part is characterized by high abundance of organic matter and complex composition of shale minerals, including quartz, clay, feldspar, carbonate rock and so on. The mechanism of protecting organic pores by rigid character frame of shale skeleton minerals is proposed to reveal the significance of stratigraphic microfractures in shale gas migration and further effectively combine with high pressure mercury injection. Experiments such as adsorption of liquid nitrogen and carbon dioxide at low temperature achieved the full-scale quantitative characterization of shale pore structure and revealed that the pore size distribution of shale was mainly bimodal and micropore dominant type. The pore specific surface area is mainly contributed by pore size less than 10nm, while the pore volume is mainly derived from pore size less than 200nm. Combined with field emission scanning electron microscopy, the dynamic evolution characteristics of pore morphology of organic pores, dissolution pores and clay minerals were systematically revealed. At the same time, high pressure mercury injection, low temperature liquid nitrogen and carbon dioxide adsorption were used. The dynamic evolution characteristics of pore structure (specific surface area, pore volume, pore size distribution) of micropore, mesopore and macropore are quantitatively characterized. Based on the sedimentary burial history of WX2 well, the pore dynamic evolution law of Longmaxi formation is inversed. The four-stage evolution mechanism of pore network with thermal evolution was established. At the same time, with the help of indoor methane isothermal adsorption experiments, the Gibbs adsorption capacity was defined. The reason for the phenomenon of "backward adsorption" is explained. By introducing the correction term of excess adsorption amount, it is found that it is more reasonable to get absolute adsorption quantity by using supercritical micropore filling model (SDR) correction. The characteristics of pore structure reveal the main controlling factors of shale adsorptive gas content, and clarify the control effect of micropore and mesoporous specific surface area on shale adsorption gas content. Finally, based on molecular dynamics theory. The macroregular Monte Carlo simulation system was used to study the mechanism of shale gas occurrence in micropore fractures. It was found that the adsorption amount of pore unit specific surface area increased step by step with the increase of pore size, when the pore size was larger than 2 nm. The adsorption amount per unit area tends to be constant. It is revealed that methane mainly exists in the form of adsorption state in the micropore scale, and the pore size distribution plays an important role in the shale gas content.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.13

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