Periodic Reporting for period 1 - MEDIA (Modelling the Effect of DIspersion on convection in porous mediA)
Reporting period: 2023-09-01 to 2025-08-31
Global warming attracts great social, economic, political and scientific attention. A major proportion of the carbon dioxide (CO2) emitted in the atmosphere is due to anthropogenic activities and represents one of the main causes of this global problem. A possible solution is represented by carbon sequestration: CO2 is captured from power plants and injected in underground geological formations, where it dissolves into the resident fluid (brine) and can be safely stored for hundreds of years. In this frame, the properties of the rocks play a key role: after injection, CO2 follows sinuous pathways among the rock grains and spreads in a complex manner, making predictions on the long-term dynamics hard to obtain. For this reason, the identification of suitable sequestration sites and the design of the injection process is still a challenging task. Moreover, injection of CO2 takes place at depths between 1 and 3 km beneath the earth surface, which makes in-situ measurements hard to obtain: simulations and lab-scale experiments are essential. To make practical and prudent decisions about the future energy production strategies, the European Union (EU) must be able to accurately identify its carbon storage capacity. This research work improves our understanding and design capabilities of carbon storage processes in geological formations. This study focused on the analysis and interpretation of experiments and simulations of convection in porous media. The results are used to develop models that describe the rock properties, contributing also to improve commercial reservoir simulators. I (1) examined the effect of dispersion via innovative experiments in bead packs, (2) quantified the effect of dispersion with state-of-art numerical pore-scale simulations, and (3) identified appropriate models of dispersion for large-scale simulations.
An extensive review of existing studies on convection in porous media has been performed and made available to the entire community as a journal paper. An innovative experimental setup has been developed to study convection in porous media in bead packs. With the aim of comparison against the experiments, state of art numerical simulations have been performed in the same configuration, at unprecedented values of the flow parameters. Combining these findings, physical models have been proposed to explain in detail the phenomena observed. The flow has been also analyzed from a rigorously theoretical viewpoint: combining consolidated theories (Grossmann-Lohse) to numerical simulations, the physics has been explored and the flow dynamics explained in terms of global transport properties. The software developed to carry out this research, allowing to explore unprecedented values of the Rayleigh numbers with efficient and parallel simulations, has been made publicly and freely available to the entire community. The role of the three-dimensional flow structures in determining the dissolution of CO2 in brine has been thoroughly characterized for the first time, shedding new light on the role of the dimensionality of the system on its long-term flow evolution, with huge implications for the development of carbon injection and storage strategies. The role of additional solute redistribution due to the effect of mechanical dispersion has been also studied via Darcy simulations. For the first time, Rayleigh-Taylor-Darcy simulations with dispersion have been performed at large Rayleigh numbers, and the results have been exploited to derive a physical understanding of the underlying flow dynamics.
For the first time direct numerical simulations and experiments have been performed to study convection in bead packs within the same range of flow parameters. This allowed to explore in detail both flow and concentration fields, making the modelling considerably simpler and reliable. The Grossmann-Lohse theory applied to this problem allowed to reconcile an apparent discrepancy existing between theoretical predictions and experiments in 2D and 3D porous media convection. To achieve these results, a very efficient code has been developed, and made freely available to the entire community. Innovative numerical methods combined to consolidated theoretical modelling has allowed to explore a wide range of three-dimensional flows, and to develop original models to predict convection in porous media, and in porous media with dispersion. Additional three-dimensional numerical simulations would be required to explore in further detail the dynamics at the pore-scale and at the Darcy-scale with dispersion.