Understanding Reactive Flow in Porous Media for CO₂ Storage Applications

The injection of CO2 in geological formations, e.g., sandstone and carbonate formations, disrupts the equilibrium among the resident phases and causes geochemical changes [1]. Determining the safe storage of CO2 in aquifers significantly depends on understanding how fluid phases interact within the porous structure of rocks [2], including rock/fluid interactions at the macro and micro scale, resulting in dissolution or precipitation which may lead to either enhance or impede fluid flow. Sandstones are often chosen for CO2 storage, as they have suitable porosity and permeability [3]. Although there are studies on the role of fluid chemistry, the literature suffers from a deep understanding of the effect of different ionic strengths of brine on rock dissolution during CO2 geological storage. Therefore, the focus of this work is to investigate the reactivity of CO2 saturated brine with different ionic strengths in contact with sandstone at pressure and temperature conditions representative of storage sites.
In this work, we use a systematic combination of different techniques, including hydrothermal tests, Inductive Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray diffractometer (XRD), Environmental Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (ESEM-EDS), and micro-computed tomography (Micro-CT) scanning to understand geochemical behaviour and address the extremely intricate phenomena of flow, transport and reactions occurring over various temporal and spatial scales in sandstone reservoir rocks.
The synthetic brine used in this research work is representative of typical aquifer brine, consisting of NaCl, KCl, CaCl2 and MgCl2. Hydrothermal tests (130 bar and 60 °C) are conducted using a Berea sandstone sample with length and diameter of 3.8cm and 3.8cm, respectively. Mineralogical composition of the Berea sandstone, based on XRD analysis provided by the supplier, indicated that the main mineral present was quartz, with small concentrations of kaolinite and feldspars.
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Micro-CT studies using Micro-CT (Nikon XT H 160) were conducted to evaluate porosity, pore size distribution and pore structure of the core sample before and after hydrothermal testing. Figure 1 presents the Micro-CT images and pore size distribution of (a) top section, (b) middle area, and (c) bottom slice of the unreacted Berea sandstone core sample.
Figure 1. Micro-CT images and pore size distribution of Berea sandstone core plug pre-reaction in the batch reactor system; (a) top section, (b) middle area, and (c) bottom slice
This paper will present a comprehensive characterisation of the test fluid and Berea sandstone core plug before and after the hydrothermal experiments. This will include detailed measurements of porosity, pore size distribution, morphology changes and cation concentration variations. The information gained from the combination of these unique tests, including CT measurements, will allow to build a better understanding of the dominant drivers of CO2 reactive transport in porous media during CO2 storage.
Acknowledgements
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (MILEPOST, Grant agreement no.: 695070). This paper reflects only the authors’ view and ERC is not responsible for any use that may be made of the information it contains.