Visualizing pore scale alterations in artificial materials by CO2 exposure using HRXCT

Abstract

Sequestration of CO2 in geological reservoirs is a transitional solution to reduce the concentration of greenhouse gases in the atmosphere, pending sufficient renewable energy alternatives. Carbonation at the earth’s surface can also be used to sequestrate CO2 in industrial processes, to stabilize mineral waste or even to transform waste into new innovative building materials. A thorough understanding of the mineral-CO2 interactions is therefore essential in the advances of industrial carbonation processes and the upscaling of geological storage. Due to the complexity and heterogeneity of reservoir rocks and minerals waste materials used in laboratory experiments, it is often a challenge to compile a model for reactive transport from physico-chemical data, deducted from reactor experiments, and even more difficult to calibrate or validate this model. This research aims to unravel the processes that occur when a CO2-enriched fluid reacts with different mineral phases in porous media and to quantify the influence of physico-chemical changes on the porosity and permeability of the rock. In order to deduct the influence of different parameters like mineralogy, reactive surface, porosity and permeability as unambiguously as possible, homogeneous artificial porous materials are used. These artificial materials are created from chemically pure mineral powders, with controllable petrophysical parameters (porosity, permeability, reactive surface, composition) and exposed to CO2-enriched fluid in batch and flow through reactors. The physico-chemical changes in the material are analysed using traditional methods and High Resolution X-ray Computed Tomography (HRXCT). HRXCT is a non-destructive technique that allows a complete characterization of the artificial rocks in 3D up to sub-micron resolution (400 nm). The non-destructive nature of this technique allows quantifying the changes (dissolution/precipitation) through time. By combining experimental results from traditional methods and the 3D HRXCT images with the models for reactive transport through porous media, the models can be validated and eventually calibrated. This will help also to better understand more complex experiments on complex reservoir materials and to optimize of the carbonation processes for the stabilisation of mineral waste and the production of innovative building materials