Review of CO2 storage via in-situ mineralisation in mafic-ultramafic rocks

Overview

Mafic and ultramafic rocks, such as basalt and peridotite, are widely distributed across the globe and can be generally associated with: oceanic crust; large igneous provinces, such as the Deccan traps (India), the Columbia River Basalt Group (USA) and the Parana-Etendeka province (Brazil,  Namibia); ophiolitic complexes e.g. Samail ophiolite (Middle East) and Coast range ophiolite (California); exhumed mantle assemblages; subduction zones and volcanic arcs; and layered intrusions.  Their widespread distribution offers an alternative storage opportunity for the permanent sequestration of CO₂ compared to storage in a conventional sedimentary basin setting (i.e. saline aquifers or depleted oil and gas reservoirs). They largely rely on rapid in-situ mineralisation of injected CO₂.

Recent field experiments in mafic-ultramafic rocks demonstrate the potential for such storage opportunity, and IEAGHG felt it timely to commission a critical evaluation of the technology at this point, to understand the progress made to date and some of the factors necessary to scale up to industrial volumes necessary to impact climate targets. Despite growing research, total injected CO₂ through subsurface mineralisation remains around 100,000 tonnes, primarily from CarbFix projects, but claims of total storage resources range upwards of gigatons to teratons.

This report evaluates progress, barriers, and knowledge gaps, and provides stakeholders, regulators, and investors with a comprehensive summary of current knowledge and understanding of subsurface carbon mineralisation in mafic-ultramafic reservoirs.

Key Messages

• The current storage of mafic and ultramafic remains underdeveloped, with a large resource potential. To date, ~100,000 tonnes of CO₂ have been injected into mafic-ultramafic reservoirs globally, with the majority at CarbFix.
• A consistent approach to storage resource estimation is needed to support more accurate assessments of resource potential. Current storage resource estimates, from 10 countries, range from gigatons to teratons (and vary depending on the approach taken).
• 31 reactive transport models to predict the fate of injected CO₂ in mafic and ultramafic reservoirs were reviewed. The accuracy of the models depends on rock properties, selection of primary minerals, accurately predicting secondary mineralization and scale of the model (pore versus reservoir scale). 
• 10 active or completed CO₂ injection field sites have been reviewed from the literature and discussions with industry experts, across the USA, Iceland, Oman, Saudi Arabia and the UAE.
• The growing commitment to CO₂ mineralization as a scalable carbon storage solution is reflected in the development of 17 planned and prospective CO₂ injection sites across nine countries and six continents. Of these, seven sites are preparing for future injections, while the remaining ten are in the feasibility, drilling, or permitting phases. These projects aim to expand carbon mineralisation into diverse mafic and ultramafic formations.
• A variety of injection schemes are possible with pros and cons to each. For example, aqueous injection demands high levels of water resources which may inhibit scale-up to commercial volumes. Recent water usage estimates from the Coda Terminal in Iceland state that approximately 3000 Litres per second (greater than 1.63 million barrels per day) will be required for a 3 million metric tonnes per year (MMT/yr) CO₂ injection scenario.
• If properly selected and characterized, mafic-ultramafic reservoirs pose no greater risk (potentially less) of harmful reaction products (e.g. to potable water sources) than sedimentary reservoirs.
• Injected CO₂ may be converted to microbial biomass or methane, and requires further work to evaluate potential consequences.
• In theory any subsurface injection, including CO₂ sequestration, can trigger seismic activity due to increased reservoir pressures and resulting fault activation. Thus far, field projects have not seen induced seismicity as a result of CO₂ injection given the care taken in site selection, monitoring and stepwise development of storage sites. However, large-scale projects will increase uncertainty in pressure dynamics and mineralisation effects, possibly raising seismic risks.
• The complex, fractured, and heterogeneous nature of mafic-ultramafic formations, along with CO₂ -fluid-rock interactions which drive mineral trapping, require tailored monitoring technologies to ensure storage security. These rely increasingly on geochemical rather than geophysical methods.
• Regulatory clarity is critical for scaling CO₂ mineralisation projects. While no major legal barriers exist under current CCUS regulations, targeted guidance and incentives could further accelerate deployment. Early projects will help navigate regulatory gaps and challenges under different frameworks.
• Scaling CO₂ mineralisation storage requires overcoming technical, economic, and potential regulatory hurdles. Lessons from the hydrocarbon, mining, and geothermal industries can help optimize processes, while stable revenue models and improved site characterization and MRV will be key to commercial success.