Introduction

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 geological storage of CO_2.

The majority of work has been carried out regarding onshore basalt storage of CO₂, but some studies have considered the feasibility of storage offshore, which has the added benefits of blanketing deep-sea sediments forming a low-permeability stratigraphic barrier, in the case of leakage at such a depth hydrates are likely to form thereby trapping the leaked CO₂ and at water depths greater than 2700m there will be gravitational trapping as the CO₂ will be more dense than seawater.

It is highly uncertain when basalt storage could be possible on a commercial scale; even assuming the pilot projects described above are successful. If compared to storage in deep saline formations (DSF), for which research started almost 30 years ago, then it may similarly be decades before basalt storage reaches the same level. However some learning from DSF may be applicable to basalt storage, shortening the time for commercialisation.

Conclusions and Recommendations

In-situ mineralisation of CO₂ in basalts is potentially feasible and has been demonstrated in laboratory experiments and modelling studies, but has yet to be tested at the pilot scale. Adequate storage capacity and injectivity is possible due to the porosity and permeability caused by fracturing in the top layers of each basalt flow. However, as there is currently no real life injection data; there is still high uncertainty related to injectivity.

The Wallula and CarbFix pilot projects have carried out extensive site investigation and experimentation and modelling. These projects are very different in nature, with the CarbFix project intending to inject pre-dissolved CO₂ into a 400m deep aquifer and the Wallula project intending to inject supercritical CO₂ at a depth of 900m.

Though injection has not yet started at either injection site, there has been much progress through site characterisations and laboratory and modelling studies and therefore, increased understanding of the CO₂-rock reactions expected to take place. However, while reactions of aqueous CO₂ are considered to be very well understood, knowledge of supercritical CO₂ – rock reactions, while improved greatly, is still considered a knowledge gap. This is in regards to the type of minerals expected to be produced and the reaction rates to be expected. Further research in all these areas is ongoing.

Injection dates at both sites have been repeatedly pushed back, but injection is expected to commence sometime this year.

The majority of work has been carried out regarding onshore basalt storage of CO₂, but some studies have considered the feasibility of storage offshore, though these studies are still theoretical at this stage.

It is uncertain how long it will be before basalt storage will be possible on a commercial scale; assuming it is proved viable in the pilot projects. If compared to storage in DSF, for which research started almost 30 years ago, then it may be a couple of decades before basalt storage reaches the same level. However some learning from DSF may be applicable to basalt storage, shortening the time for commercialisation.

Basalt storage is an active area of research and while not possible in all locations, it may be of significance in regions where this may be the main option for CO₂ storage, therefore IEAGHG should keep updated on developments on basalt storage.

Both current pilot projects have not started injection, giving an absence of real-life data; therefore it is recommended that IEAGHG consider further assessment of basalt storage as and when result from the pilot projects become available.