Opportunities for large-scale CO2 disposal in coastal marine volcanic basins based on the geology of northeast Hawaii

Abstract This paper presents an initial evaluation and concept description of an approach to CO2 storage where the reservoir rocks are volcanic terrains that have been built up from the seafloor and consist of several kilometers of stacked lava, pyroclastic, and volcano-sedimentary rocks, and where CO2 could be injected in large quantities in the supercritical or liquid state. These coastal “Saline Volcanic Basins” (SVB) have massive volume, heterogeneous internal structure, and relatively low temperatures. SVB's occur in island arcs and so-called hot spots such as Hawaii and Iceland. In both settings, the volcanic formations are exceedingly thick, border the ocean, are below sea level, and are saturated with seawater at storage depths. Many SVB reservoirs are accessible with onshore wells within which intercalated high and low-permeability layers and low temperatures can keep supercritical CO2 in a relatively high-density state and promote solution and capillary trapping, in addition to mineralization. Some regions of the subsurface may be at low enough temperature to allow for CO2 hydrate formation as an additional trapping mechanism. Our initial assessment of storage potential focuses on the northeast portion of the island of Hawaii, where there is direct information about the subsurface volcanic stratigraphy and hydrology based on observations made during two scientific drilling projects that penetrated to 3.5 km with continuous coring. Initial analysis, including simulations of a 50 Megaton injection of supercritical CO2, suggests that this region could be effective for permanent storage, and potentially for gigatons of CO2.