Convective dissolution is a perennial trapping mechanism of carbon dioxide in geological formations saturated with an aqueous phase. This process, which couples dissolution of supercritical CO₂, convection of the liquid containing the dissolved CO₂, and mixing of the latter within the liquid, has so far not been studied in two-dimensional porous media. In order to do so, two-dimensional (2D) porous micromodels (patterned Hele-Shaw cells) have been fabricated from UV-curable NOA63 glue. NOA63 is used instead of PDMS, which is permeable to CO₂ and does not allow for a controlled no flux boundary condition at the walls. The novel fabrication protocol proposed here, based on the bonding of a patterned photo-lithographed NOA63 layer on a flat NOA63 base, shows good reproducibility regardless of the patterns' typical size, and allows for easy filling of the cell despite the small value of the gap. A pressure chamber allows pressurizing the CO₂ and outside of the flow cell up to 10 bars. Experiments were performed in 11 different porous media geometries. As expected, a gravitational fingering instability is observed upon injection of gaseous carbon dioxide in the cell, resulting in the downwards migration of dissolved CO₂ plumes through the 2D porous structure. The initial wavelength of the fingers is larger in the presence of a hexagonal lattice of pillars. This effect can be correctly predicted from the theory for the gravitational instability in a Hele-Shaw cell devoid of pillars, provided that the permeability of the hexagonal porous medium is considered in the theory instead of that of the Hele-Shaw cell. Fluctuations around the theoretical prediction observed in the data are mostly attributed to a hitherto unknown weak locking of the wavelength on the distance between closest pillars.

中文翻译：

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二维微模型，用于研究二氧化碳在二维水饱和多孔介质中的对流溶解

对流溶解是二氧化碳在被水相饱和的地质构造中的常年捕集机制。这一过程耦合了超临界 CO _{2的溶解、含有溶解的 CO 2}的液体的对流以及后者在液体中的混合，迄今为止尚未在二维多孔介质中进行研究。为了做到这一点，二维 (2D) 多孔微模型（图案化的 Hele-Shaw 细胞）已由可紫外线固化的 NOA63 胶水制成。使用 NOA63 代替可渗透 CO _{2的 PDMS}并且不允许在壁上有受控的无通量边界条件。此处提出的新颖制造协议基于在平面 NOA63 基底上结合图案化光刻 NOA63 层，无论图案的典型尺寸如何，都显示出良好的重现性，并且尽管差距。压力室允许对 CO ₂和流通池外部加压高达 10 巴。在 11 种不同的多孔介质几何形状中进行了实验。正如预期的那样，在细胞中注入气态二氧化碳时观察到重力指法不稳定性，导致溶解的 CO _{2向下迁移}羽流穿过二维多孔结构。在存在六方晶格的柱状物的情况下，手指的初始波长更大。如果在理论中考虑六方多孔介质的渗透性而不是 Hele-Shaw 单元的渗透性，则可以根据没有柱体的 Hele-Shaw 单元的重力不稳定性理论正确预测这种效应。在数据中观察到的理论预测的波动主要归因于迄今为止未知的波长在最近的柱子之间的距离上的弱锁定。