Abstract Significant advances have been made in the evaluation of micro- and nano-scale variations of pore structure in low-permeability (unconventional) reservoirs using imaging techniques. In parallel, digital rock physics (DRP) methods have been advanced so that pore structure information extracted from these images may be used, in combination with pore-scale modeling, to predict critical petrophysical rock properties such as porosity and permeability. Recent work using DRP applied to multi-phase flow of unconventional reservoirs has suggested that wettability variations at the micro-scale caused by mineralogical heterogeneity or aging can have a profound effect on simulated capillary pressure and relative permeability curves. However, wettability is typically measured at the macro-scale, with the resulting contact angles used for populating DRP models. Further, fluid imbibition rates are usually measured at the macro-scale to compare, for example, the impact of fracturing fluid additives on oil recovery. This study compares water contact angle measurements made at the micro-scale, using an environmental field emission scanning electron microscope (E-FESEM) combined with innovative procedures for contact-angle extraction, with a conventional macro-scale approach (sessile drop) for low-permeability samples obtained from the Montney Formation in Western Canada. For the first time, quantification of imbibition rates at the micro-scale is demonstrated. Two micro-wettability evaluation procedures developed previously are applied to these samples to evaluate water micro-contact angles: 1) imaging of condensation/evaporation experiments and 2) imaging of injected fluids using a micro-injection system. Micro contact angles were first estimated by extracting sessile droplet profiles (with user-guided software developed in-house) and then fitting a parameterized Young-Laplace equation to the droplet profile. For some of the micro-injection experiments, the geometry of the micro-droplet, as captured with the parameterized Young-Laplace equation, was used to compute the volume of the micro-droplet at different stages of imbibition, which in turn was used to evaluate imbibition rates at this scale. Macro contact angles were evaluated using the parameterized Young-Laplace equation and commercial software. This study suggests that laboratory-derived macro-droplet contact angles cannot be confidently and consistently applied at the micro-scale for use in DRP models for tight heterogeneous formations such as the Montney. Significant errors in simulating fluid displacement processes, fluid saturation distributions, capillary pressure and relative permeability curves using DRP methods will result if micro-scale variations in wettability are not taken into account. Finally, the study demonstrates that fluid imbibition measurements may be performed at the micro-scale, enabling fine-scale rock composition/pore structure controls on fluid imbibition to be explored.

中文翻译：

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非常规储层微观和宏观润湿性测量的比较和微观渗流率评估：对微观多相流建模的意义

摘要 在使用成像技术评估低渗透（非常规）储层孔隙结构的微米和纳米级变化方面取得了重大进展。与此同时，数字岩石物理 (DRP) 方法得到了改进，因此可以使用从这些图像中提取的孔隙结构信息，结合孔隙尺度建模，来预测关键的岩石物理特性，例如孔隙度和渗透率。最近使用 DRP 应用于非常规储层多相流的工作表明，由矿物非均质性或老化引起的微观润湿性变化会对模拟的毛细管压力和相对渗透率曲线产生深远的影响。然而，润湿性通常在宏观尺度上测量，产生的接触角用于填充 DRP 模型。此外，流体渗吸率通常在宏观尺度上进行测量，以比较例如压裂液添加剂对石油采收率的影响。本研究比较了在微观尺度上进行的水接触角测量，使用环境场发射扫描电子显微镜 (E-FESEM) 结合创新的接触角提取程序，与传统的宏观尺度方法（静滴）用于低- 从加拿大西部 Montney 地层获得的渗透率样品。首次证明了在微观尺度上对吸入率进行量化。先前开发的两种微润湿性评估程序适用于这些样品，以评估水的微接触角：1) 冷凝/蒸发实验的成像和 2) 使用微注射系统的注入流体的成像。首先通过提取固定液滴轮廓（使用内部开发的用户指导软件）来估计微接触角，然后将参数化的 Young-Laplace 方程拟合到液滴轮廓。对于一些微注射实验，使用参数化的 Young-Laplace 方程捕获的微液滴的几何形状用于计算不同吸入阶段的微液滴体积，进而用于计算在这个尺度上评估吸水率。使用参数化的 Young-Laplace 方程和商业软件评估宏观接触角。这项研究表明，实验室衍生的宏观液滴接触角不能自信且一致地应用于微观尺度，以用于紧密异质地层（如 Montney）的 DRP 模型。如果不考虑润湿性的微尺度变化，将导致使用 DRP 方法模拟流体驱替过程、流体饱和度分布、毛细管压力和相对渗透率曲线时出现重大错误。最后，该研究表明，流体渗吸测量可以在微观尺度上进行，从而能够探索流体渗吸的精细岩石成分/孔隙结构控制。如果不考虑润湿性的微尺度变化，将使用 DRP 方法得出毛细管压力和相对渗透率曲线。最后，该研究表明，流体渗吸测量可以在微观尺度上进行，从而能够探索流体渗吸的精细岩石成分/孔隙结构控制。如果不考虑润湿性的微尺度变化，将使用 DRP 方法得出毛细管压力和相对渗透率曲线。最后，该研究表明，流体渗吸测量可以在微观尺度上进行，从而能够探索流体渗吸的精细岩石成分/孔隙结构控制。