Why is this research needed?

It is becoming essential to remove a significant amount of CO2 emissions from atmosphere via application of different techniques including carbon capture and storage (CCS). Geological storage of CO2 in deep saline aquifers, basaltic rocks, coal bed methane and shale formations, and depleted hydrocarbon reservoirs is a large-scale promising technique to mitigate CO2 greenhouse gas emissions. Carbon storage is a critical component of the UK strategy towards industrial decarbonisation. Millions of tons of CO2 can be stored in geological formations annually, which makes the largescale mitigation targets achievable.

Although saline formations are the largest potential for CO2 geological storage, they do not exist in all regions. This is also the case for the depleted oil and gas reservoirs. However, large basaltic deposits are available in several regions around the world, both onshore and offshore, which can be considered as storage options. Additionally, for capture technologies like Direct Air Capture (DAC) or for not-so-large carbon emitters which may not meet the large required quantity of CO2 to make the geological storage attractive, the carbon mineralisation technique is event more attractive. Mineral trapping is the dominant trapping mechanism in basaltic formations which makes the storage secure – basically turning CO2 to rock.

Carbon mineralization involves the formation of solid carbonate minerals (e.g. calcite, magnesite and dolomite) through the reaction of CO2 with rocks rich in calcium or magnesium. One of the best sources of Mg and Ca are ultramafic rocks including basaltic lava.

In a process developed by CarbFix, CO2 and water are injected together in basalt formations, inducing a rapid chemical reaction for storing CO2 in carbonized form. Potentially, using this process, it is possible to store up to 100 kg of CO2 in a cubic meter area of basalt. Having said that, this approach is at a lower stage of technological readiness and further investigation required on the lab- and pilot-scales.

What is this research investigating?

Although basalts have shown promising potential for secure and permanent storage (removal) of CO2, there is still uncertainty in which reactions will take place and their timescales.

Basalt samples are used to represent the storage medium. We characterize the samples before and after exposure to CO2-rich brine at a certain range of pressure and temperature to investigate the reactions and their kinetics. The CO2-brine-basalt interaction experiments are performed using a state-of-the-art set of high-pressure and high-temperature reactors constructed at the University of Edinburgh (UoE). The improved design of these high-pressure batch reaction vessels enables us to undertake experiments at in-situ storage reservoir conditions under a range of geochemical conditions, brine chemistries and gasses. The associated monitoring and analysis enable practical investigation of geochemical reactions over long time scales with the possibility of running 32 different experiments at the same time using the eight vessels.

The reference characterisations are performed on the unreacted samples using SEM-EDX and XRD analysis. The samples are then exposed to CO2-rich brine for two (to four) weeks using the HPHT reactors to mimic typical downhole environments. Various analytical methods will be used to investigate the chemical effects of CO2-rich brine on the basaltic samples. The composition, pH, dissolved O2, conductivity of batch reacted ‘reservoir’ fluids will be determined before and after experiments and the composition of the gas phase will be monitored continuously.

What does the research hope to achieve?

The designed experiments hold the potential to dramatically improve the performance of geological CO2 storage, supporting the UK’s commitment to become zero-carbon by 2040.

This collaborative project is expected to lead to a peer-reviewed publication. Results of this project contribute to further developments of this technique and have a great potential for future research growth, PhD proposals and funding opportunities from both UK and EU research councils and industry. Policy makers and funding agency will also benefit from the results of this study.