2024 AIChE Annual Meeting

(432f) Assessment of CO2 Storage and Mineralization in Hawaiian Basalt: Subsurface Characterization and Modeling Results

Authors

Lautze, N., University of Hawaii
Thomas, D., University of Hawaii
Arora, B., LBNL
Xue, Z., RITE
Mito, S., RITE
Zhang, S., Tsinghua University
Lu, X., Stanford University
Most studies of subsurface CO2 storage have focused on sedimentary formations. However, there is increasing interest in using basalt formations for CO2 disposal because of the potential for relatively rapid transformation of CO2 to carbonate minerals, which could decrease long-term leakage risk and monitoring requirements. Basalt formations are widespread in both continental and oceanic regions, but their suitability for CO2 disposal is uncertain. We have been focused on the Hawaiian Islands, which are composed of basalt lavas and clastic rocks piled up on the ocean floor to thicknesses greater than 10 km (DePaolo et al., IJGGC, 2021). The likely target formations are below sea level but accessible with onshore wells and consist of subaerial and submarine lava flows interlayered with low-permeability glassy clastic material. Although the volume of basalt is sufficient for gigatons of CO2 disposal on each island, there is uncertainty about the scale of interconnected porosity and the permeability, both horizontal and vertical. We are working to close the knowledge gaps, first with indirect characterization methods and modeling and then with downhole tests carried out in an existing 3500 meter deep well drilled and cored in 1999 – 2006 in Hilo, HI (Stolper et al., Scientific Drilling, 2009). Geochemical analyses of archived fluids collected from this well, combined with temperature logs, provide information on porosity and fluid residence time. Inversion of water level data with Earth and ocean tides provides information on large-scale permeability below the well casing (3000 meters). Experiments and modeling provide information on likely mineralization timescales. Available data indicate that permeability in the basalt formations varies from several Darcy at 500 to 1000 meters depth (from geochemistry, temperature profiles and hydrological modeling) to less than about 1mD at depth >3000 meters (water level – tidal forcing inversion). Fluid residence time varies from 1000’s of years at shallow depths to >40,000 years below 2000 meters. Reactive transport simulation of an injection of 50 million tons of supercritical CO2 over 100 years at 2500 meters depth suggests all CO2 will be dissolved or mineralized within 400 years, and none leaks to the surface, but this result depends on details of permeability and mineral-fluid reaction kinetics. Most of the horizontal permeability is in relatively narrow zones spaced 10’s of meters apart, an inference based on Sr and O isotopes and widely spaced water entries evident on temperature logs. Experiments aimed at measuring mineralization rates indicate that rates are likely to be high initially but may slow markedly with time, an issue that is applicable to all mineralization strategies. Our indirect approaches will be extended with additional downhole fluid sampling and pump tests combined with temperature logs. More direct measures of permeability are expected to come from downhole injections. Overall assessment is that the basalt formations under the northeast portion of the Island of Hawaii could be suitable for gigaton scale CO2 disposal if the porosity-permeability characteristics prove favorable.