Abstract Unconventional resources, including tight oil and gas formations and shale plays, have become a vital source of energy all over the world. The unique characteristic of these reservoirs, which has made their development challenging, is the low-to ultra-low- permeability due to the abundance of nano-scale pores. In these tiny pores and pore-throats, phase behavior and saturation pressures of the confined fluid are shifted from those of the bulk fluid within larger pores of the conventional medium-to high-permeability reservoirs. During the past few decades, many scholars attempted to compare this alteration in fluid phase behavior inside the tiny pores of tight formations to that of the bulk by studying the fundamentals behind this behavior through mathematical models, simulations, and experimental studies. Reduced pore size and pore structure, mineralogy, adsorption, and capillary condensation phenomena have been addressed in different studies as the source of this deviation in properties. Attempts to model fluid phase behavior in narrow pores started by applying the knowledge of classical thermodynamics in molecular simulations of the confined fluid, which has an inhomogeneous distribution inside the narrow pores. This was followed by modifying different types of equations of state to capture the difference in saturation pressures and temperatures of the confined fluid and that of the bulk. Experimental efforts in this area cover a wide range of non-visual approaches and precise visual approaches using the lab-on-a-chip techniques. However, conducting experiments at the nano-scale, specifically less than 100 nm, is rare due to many experimental limitations. This review provides a comprehensive summary of the theoretical and experimental studies in this area, highlights the advantages and disadvantages of each method, and indicates a lack of data at the challenging range of pore scales, less than 10 nm, for simulation validation purposes.

中文翻译：

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约束对致密地层相行为影响的综述

摘要 致密油气层、页岩气等非常规资源已成为全球重要的能源来源。由于纳米级孔隙丰富，这些储层的独特特征使其开发具有挑战性，是低渗透至超低渗透。在这些微小的孔隙和孔喉中，封闭流体的相行为和饱和压力与常规中高渗透储层较大孔隙内的大量流体的相行为和饱和压力发生了变化。在过去的几十年中，许多学者试图通过数学模型、模拟和实验研究来研究这种行为背后的基本原理，从而将这种在致密地层微小孔隙内的流体相行为变化与大体积流体相行为进行比较。在不同的研究中，减小的孔径和孔结构、矿物学、吸附和毛细管冷凝现象已被视为这种性质偏差的来源。尝试模拟狭窄孔隙中的流体相行为，首先将经典热力学知识应用到受限流体的分子模拟中，该流体在狭窄孔隙内具有不均匀分布。随后修改了不同类型的状态方程，以捕捉受限流体和整体的饱和压力和温度的差异。该领域的实验工作涵盖了广泛的非视觉方法和使用芯片实验室技术的精确视觉方法。然而，在纳米尺度上进行实验，特别是小于 100 nm，由于许多实验限制，很少见。这篇综述全面总结了该领域的理论和实验研究，突出了每种方法的优缺点，并指出缺乏具有挑战性的孔径范围（小于 10 nm）的数据，用于模拟验证。