In natural environments, when dissolved CO2 is exposed to reactive silicate rocks, such as basalts, under favorable pH and temperatures carbonation can occur. Carbonate minerals are considered a way to permanently fix CO2. Carbonation can be accelerated by active injection of CO2-rich fluids into reactive silicate sequences. Such injections are considered a method to potentially reduce or neutralize CO2 emissions. However, many lithological sequences that are considered suitable for such injections occur at temperatures where microbial life can thrive (i.e., below 120°C). This may be problematic, because microbial life can convert CO2 into biomass, influence the reduction-oxidation pathways of a system, and locally modify pH.
This thesis examines how microbial life can enhance or disrupt basalt alteration and carbonation. Two novel reactive percolation experiments, one abiotic and the other biotic, were designed to mimic injection of CO2-rich fluids into a basaltic aquifer. These experiments indicate that rock-hosted microbial communities affect mineral dissolution, precipitation and porosity. Geochemical, microimaging, and X-ray tomography techniques were used to compare results of the percolation experiments with natural basalt samples. Both the experiments and the natural samples demonstrate that microbial life can influence basalt alteration and have the potential to alter the fate of injected CO2. This suggests that rock-hosted microbial communities affect rock alteration and may interfere with carbonation. Therefore, future carbon capture and storage projects should account for the influence of microbes during their planning stages.
Key words: basalt, deep microbial life, X-ray computed tomography, carbon storage, reactive percolation, alteration
This PhD project was developed within the framework of ABYSS, an Initial Training Network funded by the European Commission under the Seventh Framework Programme for Research and Technological Development (FP7).