Microfluidics Underground: A Micro-Core Method for Pore Scale Analysis of Supercritical CO₂ Reactive Transport in Saline Aquifers

Carbon sequestration in microporous geological formations is an emerging strategy for mitigating CO₂ emissions from fossil fuel consumption. Injection of CO₂ in carbonate reservoirs can change the porosity and permeability of the reservoir regions, along the CO₂ plume migration path, due to CO₂-brine-rock interactions. Carbon sequestration is effectively a microfluidic process over large scales, and can readily benefit from microfluidic tools and analysis methods. In this study, a micro-core method was developed to investigate the effect of CO₂ saturated brine and supercritical CO₂ injection, under reservoir temperature and pressure conditions of 8.4 MPa and 40 °C, on the microstructure of limestone core samples. Specifically, carbonate dissolution results in pore structure, porosity, and permeability changes. These changes were measured by X-ray microtomography (micro-CT), liquid permeability measurements, and chemical analysis. Chemical composition of the produced liquid analyzed by inductively coupled plasma-atomic emission spectrometer (ICP-AES) shows concentrations of magnesium and calcium in the produced liquid. Chemical analysis results are consistent with the micro-CT imaging and permeability measurements which all show high dissolution for CO₂ saturated brine injection and very minor dissolution under supercritical CO₂ injection. This work leverages established advantages of microfluidics in the new context of core-sample analysis, providing a simple core sealing method, small sample size, small volumes of injection fluids, fast characterization times, and pore scale resolution.