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

Abstract

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.