Multiscale Reactive Transport in Carbonate Rocks
Underground mineral dissolution reaction has significant impacts on numerous geo-engineering applications. Dissolution reactions between acid and carbonate minerals is of great relevance in the context of acidification of underground formation water from CO2 sequestration. Dissolution reaction systems are characterized by a complex interplay between various mechanisms, such as multiphase reaction, transport of reacted minerals, and alterations to rock morphology. Each mechanism has very different characteristic length and time scales, which renders the observation of these coupled phenomena complex.
In the Multiscale Physics in Energy Systems Group, we employ various experimental techniques to unravel the complexity of these reactive systems across different scales. Some scientific questions we strive to address include: what is the impact of mineral heterogeneity and reactive surface accessibility on reaction rates and porosity-surface area correlations in real rock samples? Or what is the impact of the evolution of multiphase reaction on the progression of the dissolution reaction?
Currently, the experimental techniques used to characterize dissolution reactions largely rely on utilizing static images, e.g., X-ray micro-CT images. Such static images are limited to characterizing only the pre- and post-reaction states, preventing direct and real-time observation of how dissolution reactions progress within heterogeneous geological media.
Microfluidic experiments overcome these challenges. Coupled with high-resolution optical microscopy, we can directly observe interactions that occur at real rock interfaces characterized by high heterogeneity and complex morphology over multiple temporal and length scales at an unprecedented temporal and spatial resolution.
We are currently looking at the dissolution reaction of carbonate minerals by HCl solution. Cylindrical carbonate-rich samples are placed inside a reaction chamber of a microfluidic device as shown in Figure 1. The dissolution reaction is complicated by the formation of CO2 gas phase as represented by the below chemical reaction.
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
Figure 1. Graphical representation of the sample-embedded microfluidic device
We use microfluidic images recorded in real-time, non-optical imaging and image processing algorithms to study the impact of rock composition on the interplay between advection, reaction, diffusion and to perform direct measurements of time resolved porosity-surface areas correlations as a function of rocks carbonate content. In particular, we developed an experimental platform that uses optical imaging to characterize the reactive sample during acidification reactions and non-optical imaging to perform pre- and post-reaction characterization as shown in Figure 2. The combination of optical and non-optical imaging allows us to reach both high spatial and temporal resolution over wide fields of view.
Figure 2: (A) Composition of the experimental samples considered; (B) Structure of the rick-embedded microfluid chip; (C) Process of sample preparation and workflow of pre-reaction, in operando and post-reaction characterization. Reproduced from Ling et al., PNAS (2022).
Image processing allows us to experimentally determine porosity-surface area correlations for samples with different carbonate content, which can be used in reactive transport codes (Figure 3).
Figure 3: Data image analysis allows us to experimentally determine porosity-surface areas correlations as a function of rocks carbonate content. Reproduced from Ling et al., PNAS (2022).
With a combination optical imaging and image processing techniques and we also investigate and quantify how the formation of CO2 can cause reaction rate laws to deviate from their single-phase counterpart (Figure 4).
Figure 4. Recorded images of CO2 bubble formation around Marcellus carbonate-rich shale and their corresponding segmented images [videos: courtesy of Jun Hwang].
References
[In preparation] J. Hwang, S. Yu, C. M. Ross, B. Ling, I. Battiato, ‘Mineral Dissolution of Carbonate-rich Rocks Investigated through Microfluidic Image Analysis’
S. S. Datta, I. Battiato, M. Ferno, R. Juanes, S. Parsa, V. Prigiobbe, E. Santanach-Carreras, W. Song, D. Sinton, ‘Lab on a Chip for a Low Carbon Future’. Under review in Lab on a Chip (2023)
B. Ling, M. Sodwatana, A. Kohli, C. M. Ross, A. Jew, A. R. Kovscek, I. Battiato, ‘Probing Multiscale Dissolution Dynamics in Natural Rocks through Microfluidics and Compositional Analysis’, Proceedings of the National Academy of Sciences, DOIVol. 119, No. 00 e2122520119 (2022).
B. Ling, M. Sodwatana, A. Kohli, C. M. Ross, A. Jew, A. R. Kovscek, I. Battiato, Supplementary Information to “Probing Multiscale Dissolution Dy- namics in Natural Rocks through Microfluidics and Compositional Analysis”, DOI(2022).
B. Ling, M. Sodwatana, A. Kohli, C. M. Ross, A. Jew, A. R. Kovscek, I. Battiato, Image Supplement for “Probing Multiscale Dissolution Dynamics in Natural Rocks through Microfluidics and Compositional Analysis” Stanford Data Repository, DOIhttps://purl.stanford.edu/fc236gc0777, (2022).
B. Ling, Battiato, I., ‘Module-fluidics: Building blocks for spatio-temporal micro-environment control’, 13(5), 774, DOIMicromachines (2022).
B. Ling, H. J. Khan, J. Druhan, Battiato, I. ‘Multiscale microfluidics for transport in shale fabrics’, 14, Energies (2020).
Ling, B., Oostrom, M., Tartakovsky, A. M., Battiato, I., ‘Hydrodynamic dispersion in thin porous channels with controlled microtexture’, Phys. Fluids, 30, 076601, Editor’s Pick (2018).