湖相富有机质泥页岩自生石英形成及其页岩油地质意义

Shale oil is an important kind of unconventional hydrocarbons. The hydrocarbons held up in source rock form shale oil, which experienced no migration or only short distance primary migration. This is different from the "shale oil" distilled from the oil shale by dry distillation at the low temperature. With the increasing demand for oil and gas resources, shale oil will undoubtedly become another significative exploration and development fields after shale gas. In lacustrine facies shale, the quartz, one of brittle mineral, is constitutive of clastic quartz and authigenic quartz. The formation process and content of authigenic quartz plays an important role on the formation and stimulation of shale oil reservoir. But in the process of shale diagenetic evolution, it is still unclear about the formation mechanism of authigenic quartz, the main controlling factors and the influence mechanism for shale oil reservoir properties. In view of this weak links, the present study planed to undertake micro-analysis of abundant lacustrine facies shale samples. Then combined with detailed inorganic geochemical and organic geochemical experiments, the study will analyze the formation mechanism of authigenic quartz in organic-matter-rich shale, and illustrate the formation environment and main influencing factors of authigenic quartz. On the strength of experiments of shale reservoir, the study will also interpret the influence of authigenic quartz on shale oil reservoir properties (porosity, permeability, pore distribution, parameters of lithomechanics property). In order to complete the experiment test accurately, all the following method will be used, such as SEM in the field emission environment, electron probe, CL-analysis, permeability test devices based on pulsed stress attenuation method, pore distribution analysis by nitrogen adsorption method. Based on the above research, the shale oil geological significance of the formation of the authigenic quartz will be pointed out with the consideration of thermal evolution of organic matter and oil-bearing.

页岩油为未经运移或经历短距离初次运移而滞留于泥页岩层系中的液态烃类，不同于油页岩干馏后获得的页岩油。随着油气资源需求量的不断加大，页岩油必将成为继页岩气之后又一重要勘探开发领域。湖相富有机质泥页岩中脆性矿物石英，一部分为碎屑石英，另一部分为自生石英，其中自生石英含量及分布对页岩油储层的形成与可改造性（脆性）起着重要作用。但泥页岩成岩演化过程中自生石英的形成机理和主控因素，以及对页岩油储层性质的影响机制还不清楚。针对这一薄弱环节，本次研究拟通过大量湖相富有机质泥页岩样品的扫描电镜微观分析，结合无机地球化学、有机地球化学的实验测试等，分析富有机质泥页岩中自生石英形成机理，明确自生石英的形成环境及其影响因素，阐明自生石英对泥页岩储层性质（孔隙度、渗透率、吼道半径、岩石力学性质）的影响。在上述研究基础上，结合有机质热演化史和含油性，评价自生石英形成的页岩油地质意义。

该基金项目以鄂尔多斯盆地延长组泥页岩和三塘湖盆地芦草沟组泥页岩为研究对象，通过大量的有机地球化学、储层性质及微观观察与统计等方面的实验测试，阐明了富有机质泥页岩中二氧化硅的赋存状态，确定了富有机质泥页岩中自生石英的形成机理及影响因素，建立了定量计算不同赋存状态二氧化硅的方法。在此基础上，明确了自生石英对泥页岩储层物性、力学性质等的影响，阐明了自生石英页岩油形成过程中地质意义。.①鄂尔多斯盆地延长组泥页岩和三塘湖盆地芦草沟组泥页岩二氧化硅主要是以非晶态二氧化硅、自生石英和碎屑石英三种状态存在。.②鄂尔多斯盆地延长组泥页岩二氧化硅主要来自于粘土矿物转化和石英碎屑颗粒的溶蚀。三塘湖盆地芦草沟组泥页岩二氧化硅主要来源于凝灰质脱玻化作用。缺乏生长空间是泥页岩储层中非晶态二氧化硅难以生长为自生石英的根本原因。.③以延长组泥页岩样品为研究对象，通过全岩X衍射与微区矿物定量分析相结合的手段，建立了非晶态二氧化硅的定量分析方法。以芦草沟组泥页岩样品为研究对象，利用全岩X衍射和Image-Pro Plus软件分析相结合，建立了自生石英的定量分析方法。两种方法的结合可以有效地确定非晶态和自生石英的含量。.④自生石英的形成降低了储层的比表面积，可能不利于吸附气的富集。但是自生石英的形成提高了储层的物性，为烃类的富集提供了空间，同时增强了储层的抗压强度和脆性，易于形成裂缝，利于压裂开发。