Project Objective: 

The overall objective of the project is to advance the scientific and technical understanding of fracture microstructure on the flow and mineralization of CO2 injected into fractured basalt. Fractured basalts are one of the formation types being considered by the Department of Energy for geologic carbon sequestration. Their most attractive feature is the high concentrations of reactive minerals that contain divalent cations (Ca2+, Mg2+, and Fe2+) that can lead to mineral trapping of CO2 as precipitated carbonate minerals. Because the available pore volume for carbon storage in basalts is primarily in fractures, there is a need to understand the behavior of CO2 in these fractured reservoirs. Further, the geochemical reactions that involve the dissolution of silicate minerals and precipitation of carbonate minerals can influence the fracture network in ways that may either enhance or inhibit the overall sequestration capacity.

The objective will be pursued through an approach that integrates bench-scale CO2-water-rock testing, geomechanical and geochemical characterization of rock cores, and advanced in situ characterization of the fracture structure and carbon trapping mechanisms. Basalt samples from relevant formations will be used as well as synthetic basalts that are more reproducible specimens for systematic evaluation of the effects of specific variables on CO2 behavior. Laboratory experiments will evaluate the extent and trapping mechanisms of carbon sequestration under both static (i.e. no-flow) conditions that simulate dead-end fractures and dynamic advective fluid flow.

Research Approach:

An array of powerful analytical tools will be used to characterize the evolution of the fracture structure and CO2 behavior before, during, and after exposure of fractured basalt samples to CO2-rich fluids. Novel 13C nuclear magnetic resonance (NMR) and X-ray computed tomography (CT) techniques that have been developed for real-time in situ characterization of inorganic carbon speciation and pore structure will be applied to fractured basalt samples held at elevated temperature and pressure. Post-reaction characterization will include imaging of the fracture structure, assessment of mineral trapping, spectroscopic and microprobe evaluation of mineral alteration, and geomechanical testing.