The complicated flow behaviors of multiphase fluids in shale reservoirs are significantly influenced by fluid-fluid and fluid-rock interactions due to the non-negligible intermolecular forces at the nanoscale, which is crucial for the effective development and efficient extraction of shale oil. The complexity of multiphase fluid distribution and flow behaviors in shale reservoirs is further increased by low porosity, low permeability, poor connectivity, high inhomogeneity, and multi-component minerals, making the development process more challenging. Molecular dynamics simulation is widely to precisely capture the intermolecular forces and effectively explain the complex distribution and flow behaviors of these fluids under fluid-fluid and fluid-rock interaction forces. In this review, the characteristics of mineral composition, pore structure, porosity, permeability, and fluid types are first elaborated to illustrate the particularity of shale reservoirs and fluids compared to conventional scale reservoirs. The results show that shale minerals are composed of inorganic and organic matter with extremely low porosity and permeability, and nanoscale pore size, in which the complicated oil-water-CO multiphase fluid types are caused by the primary underground water, fracturing water and injected CO. The research progress of molecular simulation on the fluid-fluid and fluid-rock interaction mechanisms and on multiphase shale fluids flow behaviors are then reviewed in detail. The strong intermolecular interaction forces can result in the different occurrence states of fluids, the fluid-fluid interfacial slip, the fluid-rock boundary slip and heterogeneous fluid viscosity/density, significantly exacerbating the complexity of fluids flow. Meanwhile, the injected CO in the formation becomes a supercritical state with high diffusivity and strong solubility, and causes oil expansion, density and viscosity reduction, interfacial tension reduction, wettability alteration and molecular diffusion, which effectively replaces adsorbed hydrocarbon components by competitive adsorption behaviors, and promotes oil flow. The challenges and outlook of molecular simulation research and upscaling applications are finally discussed. This review aims to provide a microscopic understanding of the distribution characteristics and flow behaviors of multiphase shale fluids in nanoconfined space for both unconventional oil and gas researchers and industry professionals.

中文翻译：

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页岩纳米孔中的多相流体-岩石相互作用和流动行为：综合综述


由于纳米尺度上不可忽略的分子间力，页岩储层中多相流体的复杂流动行为受到流体-流体和流体-岩石相互作用的显着影响，这对于页岩油的有效开发和高效开采至关重要。低孔、低渗、连通性差、非均质性高、矿物成分多等特点进一步增加了页岩储层多相流体分布和流动行为的复杂性，使得开发过程更具挑战性。分子动力学模拟广泛用于精确捕获分子间力，并有效解释这些流体在液-液和液-岩相互作用力下的复杂分布和流动行为。本文首先阐述了页岩储层的矿物成分、孔隙结构、孔隙度、渗透率和流体类型等特征，以说明页岩储层和流体相对于常规规模储层的特殊性。结果表明，页岩矿物由无机质和有机质组成，孔隙度和渗透率极低，孔径为纳米级，原生地下水、压裂水和注入CO导致复杂的油-水-CO多相流体类型。详细综述了流体-流体、流体-岩石相互作用机制以及多相页岩流体流动行为的分子模拟研究进展。强烈的分子间相互作用力会导致流体存在不同的状态、流体-流体界面滑移、流体-岩石边界滑移以及非均质流体粘度/密度，显着加剧流体流动的复杂性。 同时，注入地层中的CO成为扩散性高、溶解性强的超临界状态，引起原油膨胀、密度和粘度降低、界面张力降低、润湿性改变和分子扩散，通过竞争吸附行为有效取代吸附的烃组分，并促进油的流动。最后讨论了分子模拟研究和升级应用的挑战和前景。本综述旨在为非常规油气研究人员和行业专业人士提供对纳米有限空间中多相页岩流体的分布特征和流动行为的微观理解。