Carbon capture and sequestration (CCS) in a deep saline aquifer is one of the most promising technologies to mitigate anthropologically emitted carbon dioxide. Accurately quantifying the mass transport of CO₂ at pore-scales is crucial but challenging for successful CCS deployment. Here, we conduct high-pressure microfluidic experiments, mimicking reservoir conditions up to 9.5 MPa and 35 °C, to elucidate the microfluidic mass transfer process of CO₂ at three different states (i.e., gas, liquid, and supercritical phase) into water. We measure the size change of CO₂ micro-bubbles/droplets generated using a microfluidic T-junction to estimate the volumetric mass transfer coefficient (k_La), quantifying the rate change of CO₂ concentration under the driving force of concentration gradient. The results show that bubbles/droplets under high-pressure conditions reach a steady state faster than low pressure. The measured volumetric mass transfer coefficient increases with the Reynolds number (based on the liquid slug) and is nearly independent of the injection pressure for both the gas and liquid phases. In addition, k_La significantly enlarges with increasing high pressure at the supercritical state. Compared with various chemical engineering applications using millimeter-sized capillaries (with typical k_La measured ranging from ≈0.005 to 0.8 s⁻¹), the microfluidic results show a significant increase in the volumetric mass transfer of CO₂ into water by two to three orders of magnitude, O (10²–10³), with decreasing hydrodynamic diameter (of ≈50 μm).

中文翻译：

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高压下二氧化碳的微流体传质：对深部咸水层碳储存的影响

深盐水层中的碳捕获和封存 (CCS) 是减轻人类排放二氧化碳的最有前途的技术之一。在孔隙尺度上准确量化 CO ₂的质量传输至关重要，但对于成功部署 CCS 而言具有挑战性。在这里，我们进行了高压微流体实验，模拟高达 9.5 MPa 和 35 °C 的储层条件，以阐明 CO ₂在三种不同状态（即气态、液态和超临界相）进入水中的微流体传质过程。我们测量了使用微流体 T 型接头产生的 CO ₂微气泡/液滴的尺寸变化，以估计体积传质系数 ( k _L a)，量化浓度梯度驱动下CO ₂浓度的变化率。结果表明，高压条件下的气泡/液滴比低压条件更快地达到稳定状态。测得的体积传质系数随雷诺数（基于液段塞）而增加，并且几乎与气相和液相的注入压力无关。此外，k _L a在超临界状态下随着高压的增加而显着增大。与使用毫米级毛细管的各种化学工程应用相比（典型的k _L a测量范围从 ≈0.005 到 0.8 s ^-1)，微流体结果显示 CO ₂向水中的体积传质显着增加了两到三个数量级，O (10 ² –10 ³ )，流体动力学直径减小（≈50 μm）。