Timothy Dai, Negar Nazari, Luiz Eduardo Bittencourt Sampaio, Anthony Kovscek
The increasing demand for carbon capture and storage as a means to address escalating atmospheric carbon dioxide levels prompts new studies to understand miscible and immiscible fluid interactions in the subsurface. As anthropogenic CO2 emissions are stored in saline underground formations or repurposed for hydraulic fracturing and enhanced oil recovery applications, supercritical CO2 and other subsurface fluids interact, convect, and diffuse through microscopic, connected pores, rock fissures, and fractures. A better understanding of fluid mixing and miscibility behaviors on the microscale thereby assists in predicting and controlling underground fluid injection as well as improves the rate of success and efficiency of such processes.
This project investigates fluid interactions and scrutinizes the development of microscopic mixing as fluid flows through microchannels. Computational fluid dynamics are used to study such phenomena and explore possible relationships between the rate of injection and the development of miscibility. Additional parameter testing include viscosity, the presence of obstacles, and the pattern of obstacles. The results of this study are used to construct a quantitative model to explain the miscibility behavior between different fluids.
For the purpose of this study, a micro-capillary loop (500 µm wide by 30 µm deep by 1.18 m long) is reproduced and used as input to a fluid dynamics simulator, OpenFOAM. Simulations are designed incorporating two liquids of different colors, injected through Y-shaped inlets allowing them to flow in parallel through the entire length of the channel as they visibly mix due to diffusion. The velocities are chosen so that a small Reynolds number (< 1), comparable to those of porous media, is maintained. Each case is simulated several times with progressively tighter levels of mesh refinement and tolerance to ensure accuracy. The phase value alpha (0-1, where 0.5 indicates a completely mixed area) is recorded at incremental distances from the inlet. Exponential curves are fitted through the simulation results and are used to predict the relationship between each test result and the rate of mixing.