Date of Award

12-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Science

Advisor

Falta, Ronald

Committee Member

Murdoch, Lawrence

Committee Member

Benson, Sally

Committee Member

Lee, Cindy

Abstract

The goal of this Dissertation is to further the understanding of secondary trapping mechanisms in geologic CO2 storage systems to improve storage design and security. This Dissertation takes the form of three chapters. The objective of the first chapter was to analyze the storage performance of supercritical and brine saturated CO2 injection strategies to determine their advantages and disadvantages on distribution and immobilization of CO2 and pressure buildup. Results showed dissolved CO2 injection was favorable in terms of storage security in all cases as it resulted in smaller areal extents on the caprock and did not migrate appreciably beyond the injection period. However, the distribution of dissolved CO2 was more influenced by formation heterogeneities than supercritical CO2. In cases with high permeability zones, the storage efficiency of dissolved CO2 was less than supercritical CO2. Supercritical CO2 injection was favorable in highly heterogeneous dipping formations where trapping was enhanced. The second chapter presents results from an experimental investigation of hysteresis in residual trapping and relative permeability of CO2 in a CO2/water system at 50°C and 9 MPa in a Berea sandstone core. Three flooding cycles were completed at a constant total volumetric flow rate by incrementally increasing and decreasing the fractional flow rates of supercritical CO2 and water. Results showed the CO2 saturations trapped during wetting-phase imbibition increased with the maximum CO2 saturations reached during each cycle. A linear model with coefficient 0.5 describes the nonwetting trapping relationship. The CO2 relative permeability data can be represented well by making a minor modification to the Van Genuchten-Burdine relative permeability data to account for hysteresis. The third chapter demonstrates a practical approach to optimizing CO2 storage design by determining economically efficient injection strategies that increase storage security through enhanced secondary trapping mechanisms. Optimizations considered 5 different water/CO2 co-injection strategies. These strategies were all compared to a base case of standard supercritical CO2 injection. Results showed SWAG, WAG, and water flush strategies reduced costs and increased secondary CO2 trapping. Dissolved CO2 injection was unable to reduce the cost, but trapped the most CO2 by secondary mechanisms of any method. Ultimately, results may be used to design CO2 injection strategies that take advantage of CO2 trapping behavior at targeted depths.

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