Cihan Abdullah, Tokunaga Tetsu K, Birkholzer Jens T
Energy Geosciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.
Langmuir. 2019 Jul 23;35(29):9611-9621. doi: 10.1021/acs.langmuir.9b00813. Epub 2019 Jul 12.
Multiphase flow phenomena in nanoporous media are encountered in many science and engineering applications. Shales, for example, possessing complex nanopore networks, have considerable importance as source rocks for unconventional oil and gas production and as low-permeability seals for geologic carbon sequestration or nuclear waste disposal. This study presents a theoretical investigation of the processes controlling adsorption, capillary condensation, and imbibition in such nanoporous media, with a particular focus on understanding the effects of fluid-fluid and fluid-pore wall interaction forces in the interconnected nanopore space. Building on a new theoretical framework, we developed a numerical model for the multiphase nanoporous flow and tested it against water vapor uptake measurements conducted on a shale core sample. The model, which is based on the density functional approach, explicitly includes the relevant interaction forces among fluids and solids while allowing for a continuum representation of the porous medium. The experimental data include gravimetrically measured mass changes in an initially dry core sample exposed to varying levels of relative humidity, starting with a low relative humidity (rh = 0.31) followed by a period of a higher relative humidity (rh = 0.81). During this process, water vapor uptake in the dry core is recorded as a function of time. Our model suggests that, under low rh conditions, the flow within the shale sample is controlled by adsorption- and diffusion-type processes. After increasing the rh to 0.81, the uptake of water vapor becomes more significant, and according to our model, this can be explained by capillary condensation followed by immiscible displacement in the core sample. It appears that strong fluid-pore wall attractive forces cause condensation near the inlet, which then induces water imbibition further into sample.
纳米多孔介质中的多相流现象在许多科学和工程应用中都会遇到。例如，页岩具有复杂的纳米孔隙网络，作为非常规油气生产的源岩以及地质碳封存或核废料处置的低渗透密封层具有相当重要的意义。本研究对控制此类纳米多孔介质中吸附、毛细管凝结和吸渗过程进行了理论研究，特别关注理解相互连通的纳米孔隙空间中流体 - 流体和流体 - 孔壁相互作用力的影响。基于一个新的理论框架，我们开发了一个多相纳米多孔流数值模型，并根据对页岩岩心样品进行的水蒸气吸收测量对其进行了测试。该模型基于密度泛函方法，明确包含了流体与固体之间的相关相互作用力，同时允许对多孔介质进行连续介质表示。实验数据包括对初始干燥岩心样品在不同相对湿度水平下重量法测量的质量变化，从低相对湿度（rh = 0.31）开始，随后是较高相对湿度（rh = 0.81）的时间段。在此过程中，记录干燥岩心中水蒸气吸收量随时间的变化。我们的模型表明，在低相对湿度条件下，页岩样品内的流动由吸附和扩散型过程控制。将相对湿度提高到0.81后，水蒸气的吸收变得更加显著，根据我们的模型，这可以通过毛细管凝结以及随后岩心样品中的不混溶驱替来解释。似乎强大的流体 - 孔壁吸引力在入口附近导致凝结，进而诱导水进一步渗入样品。
