Modeling Subsurface Porous Media Flow in Conventional and Unconventional Formations: Carbon Sequestration, Shale Gas, and Policy Implications

This dissertation is focused on modeling porous media flow in subsurface formations, with applications to carbon sequestration, shale gas, and policy implications at the energy-environment nexus. Carbon capture and storage (CCS) can significantly contribute to climate-change mitigation only if it is deployed at a very large scale. In Chapter 2, a range of models is considered to predict the basin-scale pressure response to specific injection scenarios in the Basal Aquifer of Canada. Results show that single-phase numerical models are good enough to predict the pressure response over a large aquifer; however, a simple superposition of semi-analytical solutions is not sufficiently accurate because spatial variability of formation properties is important in the problem. In Chapter 3, a three-dimensional nano-scale pore-network model is constructed to study the two-phase flow mechanisms in dry gas producing shales. Previous pore-scale modeling studies on shale have been focused on single-phase gas flow. However, it is believed that a large portion of the fracturing fluid imbibes into the shale matrix, and thus two-phase flow occurs. In addition, the system displays spatial heterogeneity of wettability, with the hydrophobic organic material embedded within the water-wet mineral matrix. Other important physics include pressure-dependent gas sorption and slip flow. All of these physics are included in the pore-scale model, which is used to compute continuum-scale properties including relative-permeability curves. In Chapter 4, a synergistic energy system at the water-carbon-energy nexus, including CCS, shale gas, synthetic natural gas (SNG) and solar desalination, is proposed for water-stressed regions such as northwestern China. The pure stream of CO2 from the SNG process can be injected into saline aquifers, while subsurface brine may be pumped to the land surface for water needs associated with SNG and hydraulic fracturing. Abundant solar radiation in water-stressed regions could be used to drive desalination of the produced brine. The synergistic use of subsurface resources allows both the carbon emissions and the water requirements associated with SNG to be addressed effectively. The synergistic energy system closely aligns with recent U.S.-China climate announcements and China’s submitted Intended Nationally Determined Contributions to the United Nations Framework Convention on Climate Change

Research on monitoring methods and technical systems of CO2 mineralization in basalt formation

CO2 storage in basalt formation has received much attention as one of the new CO2 geological storage methods worldwide. It has been successfully implemented in Iceland and the United States. During the process of carbon storage in basalt, CO2 is transformed into solid minerals, which differs significantly from carbon storage in sandstone reservoirs in terms of CO2 injection method, burial depth, and physical property requirements of reservoir cap. Significant differences are also found in both monitoring schemes. By studying the Wallula basalt storage project in the United States and the Carbfix mineralization storage project in Iceland, this study compared and summarized the monitoring schemes of basalt storage for different CO2 injection phases (supercritical and gas dissolved state). The monitoring systems of basalt storage, saline aquifer storage, oil and gas reservoir storage were further compared. The storage monitoring system for sandstone reservoir focuses on the structural integrity of the CO2 reservoir and evaluating the change of CO2 concentration along the potential leakage path. The monitoring period is usually more than 50 years. In contrast, basalt mineralization and storage technology focus on the mineralization reaction of “water-CO2-basalt”. Its monitoring system is mainly to describe the property changing pattern of each substance from downhole fluid (chemical compositions, tracer concentrations, pH, etc.) during the storage cycle. Moreover, it evaluates the degree of mineralization reaction and the storage efficiency of basalt qualitatively and quantitatively. Finally, based on the systematic and comprehensive monitoring scheme of saline aquifer and oil and gas reservoir storage, the basalt-CO2 mineralization storage monitoring technology is analyzed systematically and a complete set of basalt-CO2 mineralization storage monitoring scheme and process is summarized. By comparing different CO2 storage monitoring systems, this study proposes a universal “subsurface-wellbore-surface-ground” monitoring scheme for basalt-CO2 mineralization: monitoring scope, purpose, program, and alert system. This provides basic information for the future basalt-CO2 mineralization storage demonstration project