双重介质是指孔隙结构表现为多重尺度的油气储层，包含微纳尺度的孔隙和微米到千米尺度的裂隙，在本文研究中，考虑微米到毫米量级的微裂隙。双重介质中的两相渗流问题是低渗、致密油气开发中的典型问题。微裂隙的存在一方面增加了储层中阻力较小的渗流通道，改善了储层渗透率低下的状况；另一方面引起多孔介质中局部压力场和流场的变化，导致流体优先通过微裂隙渗流，而产生基质孔穴和喉道中水相波及范围减小，驱油效率降低的现象。双重介质的微观渗流特性在微观渗流力学和相关的油气资源开发工程中具有重要的价值。

孔隙尺度渗流模型是基于逾渗理论和孔隙、微裂隙中的微观渗流机制所建立，其目的是采用易通过实验获取的多孔介质基本特征（例如孔隙结构、连通性等）和流体参数（例如流体黏度、密度等）来预测实验条件和现场条件下难以测量的性质，例如相对渗透率，驱替相波及范围等。此外，通过模型可以很容易地预测孔隙结构或流体性质的改变造成的流动特性的变化。

本文在对孔隙-裂隙双重网络模型渗流研究详细调研的基础上，建立了基于真实岩心孔隙结构和裂隙结构统计数据，并包含微裂隙动态开裂的双重网络模型；建立了一套实验方法，研究了岩心力学性质与应力敏感性的关系及裂缝的产生对应力敏感性的影响；开展了含闭合微裂隙岩心中的动态开裂实验研究。通过数值模拟方法和辅助的物理实验手段，得到了微裂隙参数对孔穴中流体压力分布的变化、主导流动通道的变化、孔隙中油相动用率的变化以及相渗曲线的变化等水驱油微观渗流特性的影响规律，该研究工作不仅具有物理意义，而且对油气开采工程实际具有一定的参考价值。

本文取得的主要创新成果如下：

（1）采用核磁共振、微米CT等设备获得岩石的孔径分布特征，基于真实岩心孔隙、裂隙统计数据和多孔介质中喉道和微裂隙流动机理，建立了考虑多个微裂隙参数的孔隙-裂隙双重网络模型。运用量纲分析，得到了考虑含基质孔隙和微裂隙动态开裂的双重介质的渗流无量纲控制参数，并通过模拟获得了无量纲控制参数对渗流的影响规律，可为含微裂隙网络致密油藏的有效开发提供理论指导（第2章）。

（2）研究了微裂隙的长度、密度、方向、位置、间隔以及微裂隙长度分形参数对绝对渗透率和驱油效率的影响，发现了由于微裂隙存在导致储层中出现水窜或者死油区的原因（第3章）。

（3）提出了含微裂隙多孔介质应力敏感性的实验分析方法，采用高压三轴测量致密油藏岩心的应力应变关系（弹性模量和强度参数），并制备含微裂隙的双重介质。将数值模拟与实验研究相结合，研究了力学性质与应力敏感性的关系以及裂缝产生对岩石应力敏感性的影响，为致密油藏开采过程的分析解释提供了基本依据（第4章）。

（4）开展了动态裂缝微观渗流机理实验研究，利用恒速注入的水压诱导微裂隙的开裂和扩展，获得动态开裂的临界压差和平稳压差，并建立了含微裂隙动态开裂的孔隙-裂隙双重网络模型，进行了临界压差、驱替压力等对含微裂隙动态开裂的双重介质的微观渗流影响规律的研究（第5章）。

Dual porous media is the reservoir with multi-scale of pore and fracture structure. The two-phase seepage in dual porous media is a typical problem in the exploitation of low-permeability, tight oil and gas. The existence of micro-fractures have many influences on the reservoir. On the one hand, it can increase the number of channels with low resistance in the reservoir and improves the permeability; on the other hand, it will lead to the fluids preferentially flow through the micro-fractures, resulting in the decrease of the sweep efficiency and the displacement efficiency. Therefore, the microscopic seepage characteristics of the fractured dual porous media are important in the microscopic seepage mechanics and oil/gas resource exploitation.

The purpose of pore-scale modeling based on percolation theory is to predict the properties which are difficult to measure laboratory experiments and in-situ tests, such as relative permeability, sweep efficiency, displacement efficiency, etc. according to the available core data (e.g. pore structure) and fluid parameters (e.g. fluid viscosity, density, etc.) .In addition, changes in flow characteristics can be easily predicted by the model when the pore structure and the fluid properties change.

In this dissertation, the research work of the pore-fracture dual network model was summarized first. A dual network model based on pore and fracture statistics data of cores was established considering the dynamic cracking of micro-fractures. A set of experimental methods were established to study the relationship between mechanical properties and the stress sensitivity of cores, and the effects of fractures generation on the stress sensitivity. The dynamic cracking in micro-fractured cores was also studied by experiments. By numerical simulation and physical experiments, the influences of the microscopic percolation characteristics of water flooding were obtained, such as the changes of the distribution of fluid pressure in the pores, the dominant flow channels, the oil utilization rate and the relatively permeability curves.

The main innovations achieved in this dissertation are as follows:

(1) The distribution of pore and fracture were obtained by using nuclear magnetic resonance and micrometer CT. Based on the statistics data of real cores pore and fracture and flow mechanism in throats and micro-fractures, a pore-fracture network model considering various micro-fracture parameters was established. The dimensionless parameters in the problem were proposed. A series of simulations were carried out and the influences of the dimensionless parameters on the percolation was obtained, which can be used for tight reservoirs with micro-fractured networks (Chapter 2).

(2) The influences of fracture factors (e.g. length, density, direction, position and gap, the fractal parameters of the micro-fracture length) on the absolute permeability and oil displacement efficiency were investigated. The reason for the occurrence of water channeling and dead oil zones in the reservoir due to the presence of fractures was found. (Chapter 3).

(3) A set of experimental methods for studing the stress sensitivity of porous media containing micro-fractures were proposed. The stress-strain relationship (elastic modulus and strength parameters) of the cores was measured by using a high-pressure triaxial apparatus. The dual porous media containing micro-fractures were prepared by this apparatus. Combining numerical simulation with experiments, the relationship between mechanical properties and stress sensitivity and the influence of fracture generation on rock stress sensitivity were studied, which can provide the analysis and interpretation for the production process of tight oil reservoir (Chapter 4).

(4) An experimental study was carried out on the micro-seepage mechanism of dynamic fractures. The rate-controlled water pressure was used to induce cracking and expansion of micro-fractures to obtain the critical pressure difference and steady pressure difference of dynamic fractures. A dual pore-fracture network model with dynamic cracking of micro-fractures was established, which can perform the influences of critical pressure difference, displacement pressure, steady pressure difference, etc. The micro-seepage characteristics of the dual porous media with dynamic cracking of micro-fractures had been investigated (Chapter 5).