Electronic Theses and Dissertations

Title

Influence of Capillary Heterogeneity on Leakage of Co2 From a Borehols

Author

Frank Roecker

Date of Award

2012

Document Type

Dissertation

Degree Name

M.S. in Engineering Science

First Advisor

Robert M. Holt

Second Advisor

Joel S. Kuszmaul

Third Advisor

Gregg R. Davidson

Abstract

We used a modified invasion percolation (MIP) model to examine the effect of capillary heterogeneity, buoyancy forces, and viscous forces on the surface area and saturation of a CO2 plume leaking into a shallow aquifer. The purpose of this study is to provide a better understanding of how CO 2 migrates from a borehole, which is essential in implementing effective simulation and monitoring regimes to accurately detect CO2 leakage from sequestration sites. The MIP model approach will simulate invasion of a light non-wetting fluid (e.g., CO2) into a medium initially saturated with a dense wetting fluid (water). The style of capillary heterogeneity, the strength of buoyancy and viscous forces, and the size of the CO2 source were systematically varied yielding 168 different simulation scenarios. We find that the interplay between capillary heterogeneity, buoyancy forces, and viscous forces controls the surface area and saturation of gaseous CO2 leaking into an aquifer system. In unstructured systems with the absence of buoyancy and viscous forces, the CO2 surface area and saturation are relatively large. In most cases, the CO 2 surface area decreases in weakly stratified systems, and as stratification increases, the CO2 surface area increases and the CO2 saturation decrease. Buoyancy forces stretch the invading CO2 into a narrower structure, resulting in a higher surface area and a lower saturation. Our model implements weak viscous forces which cause CO2 to pool around the leak source until, at a radial distance, either buoyancy or capillary forces begin to dominate CO2 invasion. The dissolution rate of gaseous CO2 into groundwater is proportional to the surface area of the CO2 phase. Our study shows that variations in the style of capillary heterogeneity and the strength of buoyancy and viscous forces can lead to large differences in CO2 dissolution rates.

Concentration/Emphasis

Geological Engineering

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