裂缝型多孔介质渗流特性的分形分析

发布时间：2018-10-08 11:20

【摘要】：裂缝型多孔介质是由基质孔隙和嵌入基质的裂缝网络组成的双重介质。其中,孔隙和裂缝的空间分布是随机和无序的。这样的多孔介质在自然界中广泛存在如蕴含油气、地下水资源和地热资源的岩层、干裂的土壤、人和动物体组织与器官、植物等。研究其渗流特性对水库的选址、核燃料的存储、化石资源的开采、地下水资源的开发、污染治理、以及肿瘤治疗等有重要意义。然而,由于裂缝型多孔介质中的孔隙和裂缝空间方位具有随机和无序特征,渗流通道迂曲复杂,这给研究者带来巨大的困难,直到现在,流体在其内部的输运的微观机理仍未弄清。20世纪80年代,非线性科学之一的分形几何理论的出现,为我们研究流体在随机分布的孔隙和裂缝中输运规律提供了难得的机遇。已有研究发现嵌入基质材料中孔隙和裂缝网络尺度满足分形的特征。本文基于多孔介质分形基本理论,建立了分形裂缝网络模型,并研究了分形裂缝网络,基质孔隙,裂缝型多孔介质中的渗流特征。本文的主要工作属于理论物理、地球物理和复杂性科学的交叉领域研究热点之一。主要完成了下列工作：把分形多孔介质理论拓展到裂缝网络,建立了分形裂缝网络理论；然后,基于分形裂缝网络理论,提出了裂缝网络的面密度的分形模型,该模型联系了裂缝网络的结构参数如分形维数,孔隙率等,并通过和用自回避随机行走的方法得到二维裂缝网络数值模型的结果进行了验证；提出了牛顿流体在分形裂缝网络中的渗透率模型,该模型和实验数据符合较好；最后,提出了页岩气在页岩中裂缝网络中分形渗透率模型,重点分析了裂缝微观参数对滑移流和连续流渗透率的影响,并通过实验验证模型正确性。裂缝-孔隙双重介质的基质和裂缝网络孔隙率,孔隙,裂缝尺度等对渗透率有重要影响。基于分形多孔介质和分形裂缝网络理论研究了裂隙型多孔介质的渗流特性,并通过与实验结果的对比验证了模型的正确性。研究发现基质最大孔隙直径和裂缝最大长度的相对大小是决定渗流特性的主要因素。球向渗流是油气藏开采过程中的常见的流动方式,本文考虑了毛细压效应,根据分形多孔介质理论,得到了多孔介质中单相流和两相流的相渗透率解析式,并详细讨论了毛细压力对相渗透率的影响,该模型预测和实验结果相符合,证实了模型的正确性。根据分形多孔介质理论,本文还研究了常见的、且复杂的段塞流,提出了单根直毛管中两相段塞流模型,研究中考虑了气液耦合的毛细压力,得到了由直毛管中形成的多孔介质的段塞流的渗透率模型,本文的模型预测与实验数据符合很好,表明我们的模型是正确的,并探讨了段塞流的微观参数,如毛细管数、耦合毛细压力和气液两相的动力粘度系数对渗透率的影响。
[Abstract]:Fractured porous media is a dual medium composed of matrix pores and fracture networks embedded in matrix. The spatial distribution of pores and fractures is random and disordered. Such porous media exists widely in nature, such as rock layers containing oil and gas, underground water resources and geothermal resources, dry soil, human and animal tissues and organs, plants and so on. The study of its percolation characteristics is of great significance to the location of reservoir, the storage of nuclear fuel, the exploitation of fossil resources, the exploitation of groundwater resources, the treatment of pollution, and the treatment of tumor. However, due to the random and disordered orientation of pores and fractures in fractured porous media, the percolation channel is complicated, which brings great difficulties to the researchers until now. The microscopic mechanism of fluid transport in its interior is still unclear. In the 1980s, the appearance of fractal geometry theory, one of the nonlinear sciences, provides us with a rare opportunity to study the fluid transport law in the random distribution of pores and fractures. It has been found that the scale of pore and fracture network in the matrix material satisfies the fractal characteristics. Based on the fractal theory of porous media, a fractal fracture network model is established, and the seepage characteristics of fractal fracture network, matrix pores and fractured porous media are studied. The main work of this paper is one of the research hotspots in the cross field of theoretical physics, geophysics and complexity science. The main work is as follows: the fractal porous media theory is extended to the fracture network, and the fractal fracture network theory is established, and then, based on the fractal fracture network theory, the fractal model of the surface density of the fracture network is proposed. The structural parameters of the fracture network such as fractal dimension, porosity and so on are connected, and the results of the two-dimensional fracture network numerical model are verified by using the self-avoidance random walk method. The permeability model of Newtonian fluid in fractal fracture network is put forward, which is in good agreement with experimental data. Finally, the fractal permeability model of shale gas in fracture network is proposed. The influence of fracture micro parameters on slip flow and continuous flow permeability is analyzed, and the correctness of the model is verified by experiments. The porosity, porosity and fracture size of the matrix and fracture network in the dual medium of fracture and pore have important influence on the permeability. Based on the theory of fractal porous media and fractal fracture network, the percolation characteristics of fractured porous media are studied, and the correctness of the model is verified by comparing with the experimental results. It is found that the relative size of the maximum pore diameter of matrix and the maximum length of fracture are the main factors determining the percolation characteristics. Spherical percolation is a common flow mode in the process of oil and gas reservoir production. The capillary pressure effect is considered in this paper. According to the theory of fractal porous media, the analytical expressions of phase permeability of single-phase flow and two-phase flow in porous media are obtained. The effect of capillary pressure on the phase permeability is discussed in detail. The prediction of the model is in agreement with the experimental results, and the correctness of the model is verified. Based on the fractal porous media theory, the common and complex slug flow is also studied, and a two-phase slug flow model in a single straight capillary tube is proposed. The gas-liquid coupling capillary pressure is considered in the study. The permeability model of slug flow in porous media formed in straight capillary tube is obtained. The model prediction in this paper is in good agreement with the experimental data, which shows that our model is correct, and the microscopic parameters of slug flow, such as capillary number, are discussed. The effect of coupled capillary pressure and the dynamic viscosity coefficient of gas-liquid phase on permeability.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE312

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