Using a Well-Controlled Heterogeneous Permeability Field to Study Its Role on Miscible Density-Driven Convection in Porous Media

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Injection of carbon dioxide (CO2) into deep saline aquifers is a promising solution to lessen global climate change. Injected CO2 dissolves in aquifer water and increases its density. Increased density affects the water flow and the mobility of the injected CO2. This mobility is also influenced by the permeability of the aquifer. The permeability of deep aquifers varies greatly in space and affects the ways in which the fluids move. This research uses 3D printing technologies to build experimental setups that can reproduce the complex characteristics of deep aquifers and study how variable permeability influence the density-driven movement of fluids in porous media. Results from this research will benefit society by providing needed information for efficient management of CO2 injection in deep aquifers. This is critical to understanding the feasibility of using carbon capture and storage in deep aquifers as a viable technology to mitigate CO2 emissions, global warming and climate change. The project will also serve to broaden the education and training of graduate and undergraduate students, increase public scientific literacy, engage women and minority students, and develop partnership with industry and local business.The research objective of this project is to use high-resolution 3D printing technologies to overcome the challenges encountered by conventional experimental methods, in order to: 1) validate the influence of permeability on the critical Rayleigh-Darcy number and critical time for the onset of miscible density-driven convection, 2) construct a known and well-controlled heterogeneous permeability field to study its role on the onset of miscible density-driven convection, and 3) investigate how heterogeneous permeability fields dictate the later-time flow patterns and mass transfer rates. Specifically, computer modeling is used to generate particle assemblies, which are referred to as "digital sediment" blocks. The pore structural information will be imported into a lattice Boltzmann simulator as internal boundary conditions of flow modeling for permeability calculation. These "digital sediment" blocks will then be fabricated using high-resolution 3D printing to construct the desired permeability structure. In this project, the heterogeneity structure of a permeability field is characterized by permeability variation and correlation length. An experimental analogue fluid system equipped with high-speed cameras will be used to measure the convective mass transfer rate under various combinations of permeability variance and correlation length. The 3D-printed "digital sediment" blocks have known and well-controlled permeabilities and are reusable for a different heterogeneous permeability field. These advantages facilitate the construction of heterogeneous porous media and thus increase the total number of laboratory experiments that can be conducted, which is critical for satisfying the ergodicity requirement and makes the fluid system a valuable experimental analogue for validating analytical and numerical findings. Generated knowledge is transformative and will contribute to the study of other density-driven convection processes in heterogeneous porous media. Reinforced by the research plan, the outreach plan will target different educational settings to increase public scientific literacy, engage women and minority students in STEM, and prepare students to contribute to a modern workforce.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.