Abstract A robust high precision experimental approach to determine the Dew Point Pressure (DPP) of the gas condensates in a nano-porous medium is presented in this study. Gas condensate reservoirs have been the center of attention for numerous numerical and experimental studies for decades. Therefore, accurate measurement of DPP is crucial in developing long-term production plans for these reservoirs. This paper presents for the first time a proof of concept for a procedure to study the effect of the pore size distribution on the degree and direction of the shift in the saturation pressure of hydrocarbon gas mixtures under confinement over a relevant range of pressures and temperatures. Isochoric method, an indirect high-precision way of phase transition point determination, is commonly used in other disciplines where a clear non-visual determination of phase transition of a fixed volume of fluid is needed. This study provides an insight into using this approach for determining DPP of gas mixtures inside and outside of the porous media. A semi-automated apparatus for measuring and monitoring equilibrium conditions along with fluid properties is designed based on the isochoric method. The apparatus provides constant volume, variable pressure (0–104 bar), and variable temperature (290–410 K) experimental conditions. Pressure and temperature measurements provide a way to detect the phase transition point along the constant-mole-constant-volume line based on the change in the slope of this line at the phase transition point. A packed bed of BaTiO3 nanoparticles, providing a homogenous porous medium with pores of 1–70 nm is used as a representative nano-scale porous medium. The synthesized porous medium is very helpful in uncoupling the effect of pore size from the effect of mineralogy on the observed deviations in behavior, providing a volume more than 1000 times larger than the typical nano channels. The result is a set of isochoric lines for bulk and confined sample, plotted on the mixture's corresponding phase envelope to demonstrate the change in the saturation pressure. Phase envelopes (P-T diagrams) of the same mixture using different equations of state are created and the accuracy of each of these equations of state in providing an estimate of the experimentally detected DPP is discussed. Many attempts in explaining the shift in saturation pressures of the reservoir fluid confined in the narrow pores of unconventional reservoirs compared to those of the bulk can be found in the literature. However, there are some contradictions between the predicted behavior using different mathematical approaches. Experimental data could be substantially helpful in both validating the models and improving the understanding of the fluid behavior in these formations. Contrary to what many published models proposed, our results show that confinement effect shifts the DPP towards higher values compared to the bulk for a fixed temperature in the retrograde region. Capillary condensation is identified as the main source of the deviations observed in the behavior of fluids inside the nanopores. We evaluated some published models, including those based on EoS modifications, by comparing those to the experimental results which provides a quantification of their accuracy in estimating saturation pressure values for the confined mixtures.

中文翻译：

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使用等容装置对大量和受限气体混合物的露点压力进行实验测定

摘要 本研究提出了一种可靠的高精度实验方法，用于确定纳米多孔介质中气体冷凝物的露点压力 (DPP)。几十年来，凝析气藏一直是众多数值和实验研究的关注焦点。因此，准确测量 DPP 对于制定这些油藏的长期生产计划至关重要。本文首次提出了一个程序的概念证明，该程序研究孔径分布对在相关压力和温度范围内限制条件下烃类气体混合物饱和压力变化的程度和方向的影响。等容法，一种间接的高精度相变点测定方法，通常用于需要对固定体积流体的相变进行清晰的非视觉确定的其他学科。这项研究提供了使用这种方法来确定多孔介质内部和外部气体混合物的 DPP 的见解。基于等容法设计了一种用于测量和监测平衡条件以及流体性质的半自动装置。该设备提供恒定体积、可变压力 (0–104 bar) 和可变温度 (290–410 K) 的实验条件。压力和温度测量提供了一种方法来检测沿恒定摩尔恒定体积线的相变点，该线基于相变点处该线的斜率变化。BaTiO3 纳米颗粒的填充床，提供具有 1-70 nm 孔隙的均质多孔介质被用作代表性的纳米级多孔介质。合成的多孔介质非常有助于将孔径的影响与矿物学对观察到的行为偏差的影响分开，提供比典型纳米通道大 1000 倍以上的体积。结果是一组用于大量和受限样品的等容线，绘制在混合物的相应相包络上，以证明饱和压力的变化。使用不同状态方程创建相同混合物的相位包络（PT 图），并讨论了这些状态方程中的每一个在提供实验检测 DPP 的估计中的准确性。在文献中可以找到许多解释非常规储层狭窄孔隙中的储层流体饱和压力变化的尝试。然而，使用不同数学方法的预测行为之间存在一些矛盾。实验数据对于验证模型和提高对这些地层中流体行为的理解都非常有帮助。与许多已发表的模型提出的相反，我们的结果表明，与逆行区域的固定温度相比，限制效应使 DPP 向更高的值移动。毛细管冷凝被确定为在纳米孔内流体行为中观察到的偏差的主要来源。我们评估了一些已发布的模型，