当前，油气资源的供需紧张已成为制约我国经济发展、制造产业升级的关键矛盾，高对外依存度使我国工业发展时刻可能陷入“卡脖子”困境，能源系统的安全是关系工业主动脉的重大战略问题。另一现状是，我国的页岩油气储量位居世界前列，可利用空间巨大，突破非常规油气的开发问题，对推进能源自由意义重大。因此，页岩油气高效开发的相关问题研究十分重要。干酪根作为地球上分布最广、含量最丰富的有机碳存在形式，是页岩油气至关重要的来源。其结构研究是评价储层油气潜力的重要基础。干酪根成熟度是资源富集储层评价的重要指标，但常见成熟度指数受到多种地质因素的制约。而我国储层普遍存在干酪根成熟发育不充分的问题，原位转化技术是页岩油气开发的重点方向。因此，厘清干酪根演化规律，发展新的成熟度评价指标，建立干酪根演化动力学模型十分必要。另外，干酪根作为沉积岩中的主要有机组分，其力学性能对储层物性有显著影响，开展干酪根的力学响应研究对储层的压裂设计有重要意义。

  基于以上背景，本文针对干酪根的结构构建、成油成气机理、热演化过程及力学性能几个方面开展研究。主要关注两个关键科学问题：干酪根生烃化学-力学耦合效应及成熟度演化，采用实验观测、跨尺度模拟及理论分析，针对深部页岩样品展开研究工作。

  针对干酪根结构认知不清晰的问题，通过一系列物理化学实验，厘清了干酪根的类型及其包含的结构信息，构建了具有统计意义的矿区干酪根二维大分子模型，结合分子力学和分子动力学 (molecular dynamics, MD) 的退火算法，建立能量最小化的三维干酪根大分子模型。使用反应力场的分子动力学 (reactive force field molecular dynamics, ReaxFF-MD) 厘清了温度和升温速率对干酪根热解的影响，提出了干酪根热解典型反应机理。通过混合 MD 和力偏倚蒙特卡罗的计算方法，实现了在实验温度下计算机时间尺度内的干酪根热解反应的发生，为实验温度下的热解模拟提供了一种可靠方法。

  基于热演化过程中有机大分子结构的变化，提出了一种干酪根成熟度指数“分子成熟度指数 (molecular maturity index, MMI)”。厘清了 MMI 与传统成熟度评价指标镜质体反射率的关系，建立了随 MMI 升高的失重率变化规律。通过 MMI 引入了新的转换率，得到了活化能与 MMI 间的函数关系，建立了干酪根成熟度演化的活化能随成熟度变化的动力学模型 (kinetic model of the maturity evolution, MEKM)，描述了时间-温度-成熟度之间的关系。MEKM 模型形式简单，便于工程应用，为人工催熟储层的温度和时间选择提供了理论模型。

  通过热解-气相色谱/质谱联用实验，厘清温度与干酪根热解产物种类和相对含量的关系。基于提出的干酪根热解典型反应机理，结合密度泛函计算，将热解产物反演接入干酪根大分子热解位点，提出了干酪根重构的物理力学反演法 (physico-mechanical inversion method, PMIM)。通过物理力学反演法建立了一组具有更多矿区特征干酪根分子，分子量符合高斯分布，为进一步研究干酪根的性质提供了模型基础。基于建立的分子群，揭示了不同压强情况下的干酪根孔隙率变化规律，阐述了温度和孔隙尺寸对结构中甲烷分子吸附的影响。

  基于物理力学反演法，以构造的干酪根分子群为基础，建立干酪根纳米尺度的团聚体。通过 Reaxff-MD 计算不同的应变率下干酪根的力学响应，厘清了应变率对干酪根性能的影响。考虑化学键与非化学键的变化，得到了干酪根力学行为与微观机制间的关系。建立了可描述不同应变率下干酪根力学行为的可压缩超弹性-黏弹性本构关系，得到了干酪根团聚体的力学参数，有助于从微观角度理解页岩储层的力学行为。

  本文研究了干酪根的结构性质，从分子层面探索了干酪根的成油成气机理、成熟度演化规律及力学行为的微观机制，并建立了相关的理论模型，为人工原位催熟开发提供理论指导。

  The contradiction between supply and demand of oil and gas resources has become a key factor restricting the economic development and manufacturing industry upgrading in China. High degree of foreign dependence makes that the industrial development may be stuck in a bottleneck. The energy security is a strategic issue related to the industrial layout. The shale oil and gas reserves are among the highest in the world, which are with huge available space. It is of great significance to the promotion of energy freedom breaking through the development of unconventional oil and gas. Kerogen is the most widespread and richest form of organic matter in crust, and is the vital source of shale oil/gas. The study on kerogen structure is an important basis for evaluating the oil and gas potential of the reservoirs. And the maturity of kerogen is a key evaluation for the resource reservoir. However, the common maturity index is restricted by a variety of geological factors. The immature reservoirs are widespread in China. The in-situ conversion technology is a key direction of the shale oil and gas development. Therefore, it is necessary to clarify the evolution of kerogen, develop a new maturity index and establish the maturity evolution kinetic model. As kerogen is the main organic component in sedimentary rock, its mechanical properties directly impact on the physical properties of the reservoirs. The study of the mechanical response of kerogen is very significant for the fracturing design of the reservoir.

  In this dissertation, the researches on the structure, the mechanism of oil/gas formation, the evolution process and mechanical properties of kerogen are conducted. It mainly focuses on two key academic issues: The chemo-mechanical coupling effect in hydrocarbon generation by kerogen; the evolution of maturity. The study is carried out by using the experiments, the multi-scale simulations and the theoretical analysis.

  The molecular information of kerogens is obtained by a series of experiments. The statistical macromolecular models of kerogens are established. Then, the reasonable three-dimensional macromolecular models are obtained by molecular mechanics and molecular dynamics (MD). The effects of temperature and heating rate on the chemical kinetics of kerogen pyrolysis are studied by reactive force field (ReaxFF). And the mechanisms of typical reactions of kerogen pyrolysis are proposed. By hybrid MD/force-biased Monte Carlo (MD/fbMC) approach, kerogen pyrolytic reaction at the experimental temperature occurs in the computer time scale. It provides a reliable simulation method for the pyrolysis of kerogen at the experimental temperature.

  On the base of the thermal evolution of organic matter, a kerogen maturity index (molecular maturity index, MMI) is proposed. The relationship between MMI and the vitrinite reflectance is revealed. And the change of weight loss with MMI is obtained. The functional relationship between the activation energy and MMI is clarified by introducing a new conversion rate. And a new chemical kinetic model of kerogen thermal maturity is established based on MMI (kinetic model of the maturity evolution, MEKM), which describes the time-temperature-MMI relationship. The MEKM equation is with a simple form and is convenient for engineering applications. It lays a theoretical foundation for the choice of temperature and time on artificial maturity.

  By using the pyrolysis-gas chromatography/mass spectrometry, the relative contents of kerogen pyrolytic products are clarified. The pyrolytic products are inverted into kerogen macromolecules at the pyrolytic sites. The sites are selected by combining the typical reaction mechanism with density functional theory. The physico-mechanical inversion method (PMIM) of kerogen reconstruction is proposed. A kerogen molecular group are established by PMIM, which have much characteristic of the reservoirs. The molecular weight conforms to the Gaussian distribution. It provides a model basis for further research on kerogen properties. Then, the change of pore in kerogen with pressure is revealed. The influence of temperature and pore size on the adsorption of methane in kerogen is discussed.

  Based on the PMIM, a nano-scale kerogen aggregate is constructed. Kerogen mechanical response is obtained with different strain rates. The effect of strain rate on the mechanical properties of kerogen is clarified. By considering the changes of chemical/non-chemical bonds, the microscopic mechanism for the mechanical behavior of kerogen is revealed. A compressible hyper-viscoelastic constitutive relationship of kerogen is developed, which describes the mechanical behaviour of kerogen with different strain rates. The mechanical parameters of kerogen are obtained, which is helpful to understand the mechanical behavior of the shale reservoirs.

  In this dissertation, the structural properties of kerogen are studied. The mechanism of kerogen to oil/gas, the maturation evolution and the micro mechanism of mechanical behavior are discussed, and the related theoretical models are established. It provides theoretical guidance for the development of artificial maturation technology.