我国页岩气勘探开发潜力巨大，对国民经济发展具有重大战略意义。甲烷气体赋存在页岩的原生纳米孔中，在开采过程中依次经历在干酪根有机质纳米孔隙中的脱附、孔隙网络中的扩散、天然或压裂裂缝中的渗流。页岩的流动空间尺度分布宽广，气体的可压缩性、孔隙表面的吸附效应和在纳米尺度流道内流动的稀薄效应相互耦合，气体运移规律异常复杂。认识和掌握气体在页岩岩心纳米孔隙中的气体吸附和运移机理，对正确开展岩心分析实验、正确解释测量数据具有重要意义，能有效提高储层评价准确度，降低页岩气勘探开发的风险。本文构造了用于描述我国涪陵地区高成熟度页岩有机质的碎片化干酪根分子，提出了在原子尺度构造任意形状和尺寸微孔和介孔的“刀具原子群”方法，生成了孔径在 10 nm 以下的准球形干酪根孔。进而在复杂三维纳米孔隙中开展了巨正则系综蒙特卡罗模拟，获得了单组分气体在孔隙内的含气量和分子空间分布。本文提出了一种基于系综密度分布的分子模拟后处理方法，定量表征了复杂孔隙的气体分布，正确识别了吸附态气体，获得了气体的等温吸附线。本文设计并搭建了高温高压在线核磁共振实验系统，对页岩孔隙内甲烷吸附气和游离气的进行直接探测，测得了纳米孔隙中游离气的横向弛豫信号。结合等温吸附的体积法测量原理解释了含气页岩横向弛豫时间谱的含义，并定量测得了基于核磁共振的吸附量，其结果与体积法测量结果符合很好。本文在多孔介质孔隙尺度的 Navier-Stokes 方程组中考虑速度滑移边界，研究了孔隙尺度下气体稀薄效应对岩心尺度表观渗透率的影响。运用体积平均理论严格推导了多孔介质滑移流动的体积平均方程及渗透率封闭问题，基于理论分析和数值模拟阐明了变截面的、迂曲的孔隙几何形貌对表观渗透率的影响，提出了通用滑移区渗透率 (General Slip Regime,GSR) 模型，并与常用的Klinkenberg 模型和unified 模型进行了比较。本文提出的 GSR 模型物理意义明晰，在滑移区适用性更强。针对具有超低渗透率的页岩多孔介质，建立了考虑气体可压缩性、吸附和稀薄效应的颗粒样品压力衰减数学模型，系统地提出了渗透率拟合/反演的误差分析方法。改进了颗粒样品压力衰减法的标准实验系统，设计并搭建了以耐高压、小量程压差传感器为核心的新型实验系统，提高了压力衰减曲线的测量精度，拓展了基质渗透率测试的压力范围，测得了符合岩心分析要求的页岩基质渗透率数据。
The Shale gas exploration and development potential in China is huge, which can greatly promote the economic and society development. Methane gas is generated and stored in shale nanopores, whose production process goes through three stages: desorption on organic matter pore surfaces, diffusion in nanopore networks and flow in natural or hydraulic fractures. The widely spreading flow scales and the strongly coupling of gas compressibility, adsorption and rarefaction effects lead to an extremely complex transport behavior of shale gas. Better understanding of gas adsorption and transport mechanisms in shale cores will improve the qualities of core analysis experiments and the corresponding data explanations, which can significantly promotes the accuracy of reservoir evaluation and the reduction of exploration risks.Fragmented kerogen molecules were generated to represent the organic matter in highly matured shale from Fuling. A micro-/meso-pore reconstruction method, the cutter atoms method, was invented to make kerogen nanopores with arbitrary shapes and sizes. Up to 10 nm quasi-spherical nanopores were successfully generated, in which a series of Grand Canonical Monte Carlo (GCMC) simulations were carried out to provide gas molecule distributions in 3-dimensional nanopores. A post processing method was proposed to characterize the gas distribution in a nanopore, which was based on the ensemble averaged gas density. The whole molecular simulation workflow successfully recognized the adsorbed gas in the pores and provided their adsorption isotherms. A Nuclear Magnetic Resonance (NMR) apparatus working under high pressures and temperatures was constructed to directly detect the adsorbed and free gas in shale nanopores, which recorded the transverse relaxations of the free methane H atoms. The explanations of the T2 spectrum of methane in shale was further validated with assists from the conventional volumetric method. The combination of NMR technique and volumetric method provided an adsorption isotherm defined by the NMR theory, which fit well with the results from the standard volumetric adsorption isotherm tests.The up-scaling impacts on porous core permeability from pore-scale gas rarefactioneffects was investigated starting from the Navier-Stoke equation with slip velocity boundary conditions at pore-scale. The volume-averaging equations and the corresponding closure problems for porous medium flow were derived rigorously. The impacts of cross section varying and tortuous pore channel geometry were clarified by theoretical analysis and numerical simulations. A General Slip Regime (GSR) model with clearer physical mechanism and better feasibility for slip flow in porous media was established and then compared to the commonly used Klinkenberg and unified models. Focused on the shale samples with ultra-low permeabilities, a grain sample pressure decay model with gas compressibility, adsorption and rarefaction effects was established. The error analysis method for permeability fitting and inversion in grain sample pressure decay experiments was proposed. A new apparatus for pressure decay experiments of grain samples, with a differential pressure transducer was invented. This new apparatus improves the pressure decay curve measurement accuracy and expands the pore pressure range for shale matrix permeability measurement, compared to the conventional apparatus.
