Abstract

Dissolution trapping is one of the most dominant mechanisms for secure storage of CO2 injected in porous subsurface formations saturated with brine. This study uses a 2D visual Hele-Shaw cell to investigate and visualize the impact of CO2 injection locations, reservoir dipping angle, permeability heterogeneity, and brine with different initial ionic concentrations on the density-driven convection during CO2 dissolution (Chapter 2). Also, the role of complex heterogeneity, i.e., irregular permeability distribution in CO2 dissolution, is investigated using a novel experimental approach to create medium permeability heterogeneity in Hele-Shaw cells (Chapter 3). We observed that the presence of salts resulted in an earlier onset of convection and a larger convective finger wavelength than the case with no dissolved salts. Additionally, a higher lateral mixing between CO2 fingers is observed when dipping is involved. The CO2 dissolution, indicated by the area of the pH-depressed region, depends on the type and concentration of the ions present in the brine and is observed to be 0.38-0.77 times compared to when no salt is present. Although convective flow is slowed in the presence of salts, the diffusive flux is enhanced, as observed from both qualitative and quantitative results. The effect of discrete high- conductivity fractures within the flow barriers is also investigated, which showed an uneven vertical sweep and enhanced flow channeling. Complex subsurface transport phenomena such as preferential dissolution path, CO2 sweep efficiency, changes in finger morphology, and CO2 concentration distribution are visualized by creating heterogeneous media. Experimental results showed reservoir permeability heterogeneity causes significant channeling effects and poor sweep efficiency. A scaling relationship between average finger growth rate (Gr) and permeability (k) was obtained as πΊπ‘Ÿ [m.𝑠-1] = 266.8π‘˜ [m2 ] + 1.20 Γ— 10-6. Furthermore, the mass of CO2 dissolved is calculated using the spectrophotometric method to characterize the convective instability. The convective flux was analyzed by comparing experimental dissolution flux with theoretical diffusion flux, calculating a maximum Sherwood number of 6.8. The study's findings improve the current understanding of the CO2 convection morphology, allowing better assessment of long-term CO2 storage.

Date of publication

Fall 12-9-2023

Document Type

Thesis

Language

english

Persistent identifier

http://hdl.handle.net/10950/4469

Committee members

Aaditya Khanal; Fernando Resende; Mohammad Biswas

Degree

Master of Science in Mechanical Engineering

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