Beyond Conventional Reservoirs: A Mechanistic Review of CO2 Storage in Basalt and Granite

Basalt and granite offer complementary opportunities for geological CO2 storage where conventional sedimentary reservoirs are limited or permanent mineral trapping and geothermal integration are priorities. This review examines how mineralogy, pore and fracture architecture and fluid-rock reactions control storage performance in these crystalline reservoirs. Basalt contains reactive olivine, pyroxene, plagioclase and volcanic glass that release Ca2+, Mg2+ and Fe2+, supporting carbonate precipitation. Field projects including CarbFix and Wallula demonstrate its potential for rapid mineralization. Granite is less reactive and has low primary porosity, making storage dependent largely on natural or engineered fractures. Feldspar alteration and integration with Enhanced Geothermal Systems may nevertheless support combined CO2 storage and heat extraction. In both lithologies, dissolution and secondary precipitation modify porosity, permeability and injectivity, creating a tradeoff between mineral trapping and sustained fluid flow. Laboratory experiments, field demonstrations and reactive transport models are evaluated to identify the principal controls on mineralization and reservoir performance. Key research needs include improved laboratory-to-field scaling, coupled hydrochemical and geomechanical modeling and dedicated granite field validation. Basalt and granite should therefore be considered complementary components of a diversified geological carbon storage portfolio.