CO₂ mineralization in volcanogenic sandstones: geochemical characterization of the Etchegoin formation, San Joaquin Basin [CO2 mineralization in volcanogenic sandstones: geochemical characterization of the Etchegoin formation, San Joaquin Basin]

Volcanogenic sandstones are typically rich in volcanic rock fragments that can provide reactive minerals for CO2 mineralization in a scenario of CO2 sequestration. To quantitatively evaluate the extent and time scale of CO2 mineralization in potential reservoir formations, we characterized example high-porosity volcanic sand from the San Joaquin Valley of southern Central California. Samples were collected from the volcanic-rich members of the Etchegoin Formation in the San Joaquin Basin near Coalinga, California. Thin sections made from these samples were examined under petrographic microscope to identify mineral compositions, and then scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) were used to gather quantitative information on mineral abundances, distribution, and reactive surface areas. Porosity and permeability were also measured using core plugs made from outcrop samples. Results show that the Etchegoin volcanic sandstone has a high percentage (10-15%) of reactive minerals (pyroxenes, Fe-Ti spinel and clays), and high reactive surface areas at about 1 m(2)/kg. Reactive transport modeling is conducted and shows that these reactive minerals could mineralize 92% of injected and capillary-trapped CO2 within 1000 years of injection. Possible effects of heterogeneity on CO2 injection and mineralization are also studied using the reactive transport code TOUGHREACT. Vertical heterogeneity of mineralogy and hydrology increases both CO2 injectivity and mineralization. Available volcanogenic sandstones worldwide like the Etchegoin sandstone are summarized from the literature, with formations from the western USA that have CO2 sequestration potential emphasized.