Review of CO₂ Storage Basalts

Publication Overview

This technical review has been undertaken with the aim of providing a high level overview of the current status of basalts as an option for the geological storage of CO₂. The review also includes a short section on the storage potential of ultramafic rocks.
Two high profile sites, CarbFix in Iceland and the Wallula project in Washington State have both injected and monitored CO₂ storage in basalts since 2012 and research has recently been published for both sites. Basalts are important storage sites to consider for CCS as they comprise approximately 10% of the Earth’s surface and are often located in areas where no other storage options exist. Basalts have a high weight percentage of Ca, Mg and Fe rich minerals which react with CO₂ to form carbonates. At the pilot projects Wallula and CarbFix, in-situ carbonisation has been proven to occur and within much shorter timescales than initially predicted. In conventional deep sandstone aquifer storage sites, CO₂ remains buoyant for 1,000s to 100,000s of years and consequently this form of storage relies predominately on structural and solution trapping within the reservoirs to prevent CO₂ leakage.

Publication Summary

Since IEAGHG’s review on storage in basaltic formations conducted in 2011, two pilot sites have shown the technique to be feasible with safe and efficient injection demonstrated. The porosity and permeability of the formations were found to be suitable with no pressure anomalies encountered (within the formations) and the chemical composition has proved to be beneficial to the mineral trapping of CO₂ on very short timescales.

The CarbFix Project has demonstrated that immediate solubility storage of CO₂ is possible using the novel water injection technique developed at the site. CO₂ storage in a stable mineral phase within basalt formations was also demonstrated and on much shorter timescales (months to a year) than expected. The implications from this study are far reaching given the vast distribution of basalt deposits globally. The solubility trapping prevents the formation of a buoyant CO₂ in a reservoir reducing the risk of leakage. Once the CO₂ has been precipitated in a mineral phase, monitoring requirements should be less onerous as there is limited leakage risk. This increases safety and potentially reduces costs.

The volumes of water required may limit potential large-scale basalt storage onshore as groundwater resources are limited in many areas. Research currently implies that seawater could be used, which would be readily available offshore but this option has not been tested.

The Wallula site injected pure supercritical CO₂ and although instant dissolution trapping was not implemented, mineral trapping still occurred within two years, much faster than the 5 to 10 year predictions made via models and simulations.

The global distribution of flood basalts offer very large CO₂ storage potential provided the technical challenges can be addressed with further pilot and demonstration scale evaluation.

Although many flood basalt provinces are extensive they are often remote from large point sources of CO₂. This study has included two examples of large (2,000 MW) coal-fired power stations in comparatively close proximity to basalt formations.