Physical Analogue Experiment of Microstructure and Variation Law of Permeability within Faults in High-Porosity Sandstone
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摘要: 在油气勘探过程中,对于小位移断层分隔油水封闭能力的控制因素研究尚浅,野外也难以获得不同变形过程的断层带结构及其渗透性变化规律.因此,以高孔隙度纯净砂岩人造岩心为研究对象,采用自主研发的“高压~低速环形剪切装置”开展实验,实验后样品取心分别进行覆压孔渗测试、纳米CT扫描、铸体薄片分析等分析测试.以有效正应力和断层位移为实验变量开展了多组环剪实验,其研究结果表明:宏观上断层面上可观察到明显擦痕与粉末状碎裂岩,微观上确定了断层带内碎裂作用导致的颗粒粒度降低与颗粒的定向排列是孔渗降低的主要原因,断层带渗透率小于10 mD,较母岩降低2~3个数量级.随着断层有效正应力或断层滑动位移增加,断层带碎裂程度增大且粒径和孔径减小,断层带厚度增大,孔隙度和渗透率逐渐减小.这一结果可为小位移断层侧向封闭能力与油气勘探领域的研究奠定理论基础.Abstract: The research on the controlling factors of the oil and water sealing capacity of small-displacement faults to oil and water just scratches the surface of the problem in the process of oil and gas exploration, and it is difficult to obtain the internal structure and permeability change laws of the fault zone in different deformation processes in the field outcrop. Therefore, in this study it takes the artificial core of pure sandstone with high porosity as the research object, and uses the independently-developed "high-pressure and low-speed ring shear laboratory equipment" to carry out the experiment. After the experiment, the samples are cored for different analysis tests according to the needs, including permeability and porosity tests with overburden pressure, nano-CT scan, casting thin section analysis, etc. we have carried out several groups of ring shear experiments with effective normal stress and fault displacement as experimental variables. The research results show that macroscopically, obvious scratches and powdery cataclastic rock can be observed on the fault surface. Microscopically, the main reason for the decrease of porosity and permeability is the reduction of particle size and the directional arrangement of particles caused by the cataclastic in the fault zone. The fault zone permeability is less than 10 mD, 2~3 orders of magnitude lower than that of the host rock. With the increase of effective normal stress or sliding displacement, the cataclastic degree of fault zone increases, the particle size and pore diameter decrease, the thickness of fault zone increases, and the porosity and permeability decrease gradually. The study results lay a theoretical foundation for the study of the lateral sealing capacity of small-displacement faults in oil and gas exploration.
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表 1 实验参数设定
Table 1. Experimental parameter settings
实验编号 应力大小
(MPa)旋转角度
(°)断层位移(mm) 1 2 30 30.1 2 2 60 60.2 3 2 90 90.3 4 2 120 120.4 5 2 150 150.5 6 2 190 190.6 7 1 90 90.3 8 1.5 90 90.3 9 2.5 90 90.3 10 3 90 90.3 表 2 颗粒直径统计数据
Table 2. Statistics of particle diameter
频数分布区间 频数 频数分布区间 频数 0~0.05 50 0.25~0.30 21 0.05~0.10 0 0.30~0.35 11 0.10~0.15 3 0.35~0.40 12 0.15~0.20 13 0.40~0.45 5 0.20~0.25 23 0.45~0.50 3 -
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