Enhanced gas recovery (EGR) is believed to be a promising technology to improve the production of shale gas reservoirs and simultaneously reduce the emissions of greenhouse gas via the injection (sequestration) of carbon dioxide, to which great effort has been devoted by scholars. However, traditional investigations are generally limited to the ideal model of nanochannels and statistic characterization of competitive adsorption, neglecting the nanoporous structure of the kerogen matrix and the complex dynamic behavior during the EGR process. In this work, we present a comprehensive study of the EGR process in a realistic kerogen pore network (matrix) which is obtained from the artificial pyrolysis of bulk kerogen through reactive force field molecular dynamics (ReaxFF MD) simulations. The influence of pore properties (e.g., porosity) of the kerogen matrix under different maturities, and the proportions (i.e., methane and carbon dioxide) of injection gas with various injection pressures are revealed and meticulously discussed. In addition, the underlying mechanisms including diffusion and displacement effects behind the EGR process are analyzed by combining them with with particle trajectory capture technology. In particular, based on the MD simulation results, an analytical model to depict the dynamic recovery process in the kerogen matrix is proposed by coupling consideration of recovery time and capacity, which are examined against the simulation and experimental data. The hybrid recovery strategy is developed by utilizing the advantages of depressurization and gas-injection recoveries to achieve the optimization of both recovery time and capacity. The insights acquired from this work would be helpful for efficient exploitation of shale gas reservoirs and pave the way to capture the realistic EGR processes within the kerogen matrix from molecular and theoretical perspectives.

中文翻译：

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干酪根热解孔网络中提高的气体采收率：分子模拟和理论分析

据信增强的气体采收率（EGR）是一种改善页岩气储层产量并同时通过注入（封存）二氧化碳减少温室气体排放的有前途的技术，学者们已经致力于此。但是，传统的研究通常仅限于理想的纳米通道模型和竞争性吸附的统计特征，而忽略了干酪根基质的纳米多孔结构和EGR过程中的复杂动态行为。在这项工作中，我们对现实的干酪根孔隙网络（基质）中的EGR过程进行了全面研究，该过程是通过反应力场分子动力学（ReaxFF MD）模拟从大量干酪根的人工热解获得的。孔隙特性的影响（例如，揭示并精心讨论了在不同成熟度条件下干酪根基质的孔隙度，以及注入气体的比例（即甲烷和二氧化碳）。此外，通过将其与粒子轨迹捕获技术结合起来，分析了EGR过程背后的包括扩散和位移效应在内的潜在机制。特别地，基于MD模拟结果，通过结合恢复时间和容量的考虑，提出了用于描述干酪根基质中动态恢复过程的分析模型，并针对模拟和实验数据进行了研究。通过利用减压和注气回收的优势来开发混合采收策略，以实现采收时间和产能的优化。