PhD Dissertation - Safety and Water Challenges in CCS: Modeling Studies to Quantify CO2 and Brine Leakage Risk and Evaluate Promising Synergies for Active and Integrated Water Management

Abstract

Carbon dioxide Capture and Sequestration, or CCS, is the only technology available to mitigate the high CO2 emissions from coal-fired electricity production. Since coal is projected to continue to dominate worldwide electricity production, any global atmospheric CO2 concentration stabilization strategy will need to include CCS. There is therefore a strong need to increase the number and scale of CCS projects by several orders of magnitude over the next two decades. Such a ramp-up in CCS projects, however, faces several potential barriers. This dissertation focuses on two such barriers: the previously identified issue of CO2 sequestration safety, and the newly identified CCS issue of water management coupled to CCS operations. In regard to safety, this dissertation advances the capability to model CO2 injection and migration, and the associated pressure build-up to quantify large-scale CO2 and brine leakage risk. Limitations associated with different modeling approaches are evaluated. Regarding water issues, this dissertation improves the current CCS paradigm by considering water requirements for the overall CCS operations and identifying beneficial synergies associated with coupled carbon and water managements. The first part of this dissertation (Chapters 2 through 4) addresses one of the outstanding unanswered CO2 sequestration safety questions, identified by the 2005 IPCC Special Report on CCS, of how to develop reliable quantitative risk assessments of CO2 and brine leakage. In North America, the century-long legacy of oil and gas exploration and production has left millions of old oil and gas wells. Many of these wells are co-located with otherwise good geological sequestration sites, and because the hydraulic properties of the well materials are uncertain, quantitative assessment is challenging. Chapter 2 reviews the hierarchy of vertically-integrated CO2 injection and migration models recently developed to provide such a risk assessment. Chapter 3 presents the quantification of field-scale CO2 and brine leakage risks through abandoned wells of an industrial CO2 injection using a specialized sharp-interface model that is computationally very efficient. Model comparison to results from the industry-standard model ECLIPSE are presented in Chapter 4 to better understand when this vertically-integrated modeling approach is applicable and when the sharp-interface assumption is valid, focusing respectively on the time scale of brine drainage and the spatial scale of capillary effects. The second part of this dissertation (Chapters 5 and 6) presents a paradigm shift in the way a CCS system is considered. We argue that the CCS surface facility and subsurface environment ought to be considered jointly, and that their respective implementation challenges, particularly concerning water management, should be examined collectively across all CCS operations. Retrofitting an existing power plant to capture CO2 implies a doubling of cooling-water requirements. This additional water requirement can be technically challenging and highly publicly sensitive in water-stressed areas. At the same time, the extensive area of subsurface pressure perturbation and the CO2 and brine leakage risks of the CO2 sequestration operation will present regulatory and public acceptance challenges. Chapter 5 therefore provides a complete review of water, sequestration, legal, and public acceptance CCS implementation barriers and proposes a novel active and integrated CCS operation management framework to address them. Examining these barriers and challenges collectively allows us to identify multiple potentially advantageous synergies. Active management of water resources, including production and treatment of subsurface brines, can synergistically provide additional surface cooling water while reducing both the subsurface leakage risk and pressure perturbation, which will facilitate regulatory permitting and increase public acceptance. Chapter 6 quantifies the advantageous impacts of three of these identified synergies coupling simultaneous brine production to a large-scale CO2 geological sequestration operation. Brine production can reduce the injection well pressure, which enables higher injectivity potential; can reduce the extent of the Area of Review; and can reduce the risk of CO2 and brine leakage. This dissertation provides novel and important contributions in advancing the fields of CO2 sequestration safety modeling focusing on leakage risk, and in addressing CCS potential implementation barriers with a focus on water challenges. By integrating modeling progress and the broader considerations of the CCS surface and subsurface environments, presented in this dissertation, future work has the potential to provide a more complete understanding of both the CCS system and implementation barriers. The exploitation of all the identified synergies provides the best possibilities for successful large-scale implementation of CCS.