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Description
Carbon storage (CS) in geological formations is a promising technology for mitigating climate change (IPCC, 2021). Historically, sandstone have been targeted for CS, but in the specific case of Denmark, chalk represents a more promising storage medium as it has a much higher storage potential (Bonto et al., 2021). Chalk, however, has a much higher reactivity with CO$_2$-saturated brines than sandstone. The interaction between the CO$_2$-saturated brine and the chalk can result in the dissolution and subsequent weakening of the chalk. This weakening can cause subsidence, which is detrimental to CO$_2$ storage (Liteanu et al., 2013). It is, therefore, imperative that the properties of chalk is studied in detail to verify its suitability for CS.
We designed a novel triaxial flow cell (shown in fig. 1) to enable in situ imaging of chalk. The cell is capable of maintaining up to 300 bar of pressure at 90 $^{\circ}$C, which allows for the simulation of specific reservoir conditions. The central part of the cell is made of aluminium to maintain X-ray transparency. This is strictly necessary as it reduces the exposure time needed, which improves temporal resolution.
The temporal resolution of the CT scans is further improved by using the reconstruction algorithm presented by Rasmussen et al. (2021). This algorithm makes it possible to reduce exposure time and the number of projections without sacrificing image quality by utilising a high-quality reconstruction of the chalk sample. The high-quality reconstruction constrains the reconstruction of the in situ data, which improves image quality. Using this algorithm provides us with a temporal resolution of approximately 15 to 20 minutes.
The cell has been used for a series of non-reactive and reactive core flooding studies on reservoir chalk cores. Figure 2 shows the transport of a radiotracer (Cs$_2$CO$_3$) in a chalk sample. In the figure, we see two reconstructions of the chalk sample at different points in time. Note the bright band to the right in both figures is due to density variation in the chalk and is not caused by the radiotracer, unlike the bright region to the left in the images, which clearly advances during the experiment.
In fig. 3, we see the results from a triaxial compaction study. In this study, we slowly increased the triaxial pressure on a chalk core until it fractured, which occurred at approximately 82 bar based on the pressure drop recorded in fig. 3a. The fracture can easily be seen in fig. 3b, which shows a reconstruction of the sample after compaction. This study is valuable as it provides us with a baseline on which chalk weakened by CO$_2$ injection can be compared.
We demonstrate that our setup, in conjunction with the previously mentioned reconstruction algorithm, provide valuable insights into the suitability of chalk as a medium to store CO$_2$.
References
[1] M. Bonto et al. “Challenges and enablers for large-scale CO2 storage in chalk formations”.
In: Earth-Science Reviews 222 (2021), p. 103826. issn: 0012-8252. doi: https://doi.
org/10.1016/j.earscirev.2021.103826. url: https://www.sciencedirect.com/
science/article/pii/S0012825221003275.
[2] IPCC. “Summary for Policymakers”. In: Climate Change 2021: The Physical Science
Basis. Contribution of Working Group I to the Sixth Assessment Report of the Inter-
governmental Panel on Climate Change. Ed. by V. Masson-Delmotte et al. Cambridge,
United Kingdom and New York, NY, USA: Cambridge University Press, 2021, pp. 3–32.
doi: 10.1017/9781009157896.001.
[3] E. Liteanu, C.J. Spiers, and J.H.P. de Bresser. “The influence of water and supercritical
CO2 on the failure behavior of chalk”. In: Tectonophysics 599 (2013), pp. 157–169. issn:
0040-1951. doi: https://doi.org/10.1016/j.tecto.2013.04.013. url: https:
//www.sciencedirect.com/science/article/pii/S0040195113002576.
[4] Peter Winkel Rasmussen et al. “Improved dynamic imaging of multiphase flow by con-
strained tomographic reconstruction”. In: Scientific Reports 11.1 (June 2021), p. 12501.
issn: 2045-2322. doi: 10.1038/s41598- 021- 91776- 1. url: https://doi.org/10.
1038/s41598-021-91776-1.
| Participation | In-Person |
|---|---|
| Country | Denmark |
| MDPI Energies Student Poster Award | No, do not submit my presenation for the student posters award. |
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