InterPore2025

Impact of Impurities on CO₂ Transport in Saline Aquifers Using Microfluidic Models

22 May 2025, 15:45

1h 30m

Poster Presentation (MS11) Microfluidics and nanofluidics in porous systems Poster

Speaker

Mr Enoc Basilio (King Abdullah University of Science and Technology (KAUST))

Description

In the context of carbon sequestration in saline aquifers, evaluating storage security and capacity requires a thorough understanding of the interactions between CO₂ and reservoir fluids. While significant research has focused on the solubility of individual gases in brine and water, limited studies have explored the solubility of CO₂–N₂ mixtures, such as those in power plant flue gases, in aqueous solutions.
This study utilizes a wet-etched microfluidic device made from borosilicate glass to investigate the effects of contaminants on CO₂ transport dynamics in brine, mimicking the conditions found in subsurface aquifer reservoirs at 8 MPa pressure and 50°C temperature. The micromodel flow domain emulates the complex pore network of clastic reservoir rocks, offering a realistic platform for observation. The impact of gas stream impurities on CO₂ transport and dissolution dynamics at the pore scale is investigated through a series of comparative experiments. First, the chip is initialized with fluorescent brine and pressurized to 8 MPa. Second, a CO₂–N₂ mixture is injected, and drainage is observed under an inverted fluorescent microscope. Finally, brine is injected in a tertiary mode to observe residual trapping. Throughout the experiment, flow rates, fluid distribution, pressure and temperature are recorded. Dissolution-induced mass transfer is characterized indirectly by pH changes and perturbed brine fluorescence intensity. Injection of both gas and brine is conducted at a constant rate of 0.5 µL/min. Gas composition is varied, ranging from pure CO₂ to CO₂/N₂ ratios of 5:95, 10:90, 25:75, and 50:50. Additionally, brine salinity is varied from 0–1 M NaCl. Through this approach, we investigate CO₂ mass transfer dynamics, solubility equilibrium, and capillary trapping efficiencies in the presence of N2 contaminant.
Our results demonstrate that increasing the mole fraction of CO₂ in the gas phase and decreasing the ionic strength of the brine both enhance the dissolution of the CO₂–N₂ mixture in aqueous solutions. Conversely, higher salinity significantly reduces the dissolution of the mixture, underscoring the importance of ionic interactions in the system. We also report a distinctive phenomenon where CO₂ preferentially dissolves into the brine ahead of N2, leading to CO₂ being effectively stripped at the advancing front of the gas mixture through the aqueous phase, resulting in a complex interplay between dissolution, displacement, and pressure dynamics. In addition, we observed distinct differences in flow behaviour based on gas composition. Mixtures with 5% N₂ impurity exhibited higher dissolution flux and more significant pressure drop at early stages compared to pure CO₂, whereas mixtures with 50% N₂ showed lower dissolution flux and smaller pressure drops under similar conditions. These findings reveal insights into optimizing CO₂ storage under realistic conditions where purity cannot be assured, highlighting the need for tailored approaches based on gas composition and brine characteristics.
This research enhances our understanding of CO₂ behaviour in impure environments and provides critical data for improving carbon capture and storage technologies by addressing how contaminants influence CO₂ dynamics under simulated geological conditions, offering valuable insights into mechanisms that enhance or inhibit solubility and capillary trapping.