This session is dedicated to studies investigating all or part of these THMC interactions by means of experimental, analytical, numerical, multi-scale, data-driven and artificial intelligence methods. Studies focusing on laboratory characterization and on monitoring and interpreting in-situ geological and geophysical evidence to validate or calibrate the multi-physical behavior of rocks and clays are also welcome. Applications in carbon capture and storage (CCS), radioactive waste storage, gas storage, energy storage, mining, geothermal systems, reservoir monitoring and management and geotechnical applications would be relevant.
Session assets
In the field of radioactive waste confinement, the question of gas transfers in clay formations is a crucial issue. A certain amount of gas, such as Hydrogen may be generated during the exploitation phase in the nearfield by the deterioration of the metal components of the system. As the host medium is characterised by a very low permeability, various gas transport processes could occur as a function of gas accumulation and pressurization [1], including the development of preferential gas pathways through the sound rock mass, which could lead to undesirable changes in the favourable containment properties of the host rock.
There is a growing body of experimental evidences [2, 3] that natural heterogeneities and pre-sxisting fractures in clay-rich materials represent preferred weaknesses for the process of opening discrete gas-filled pathways. Capturing the related transport mechanisms therefore requires to go from macroscopic to microscopic scale. Hence, a multi-scale modelling approach that models the micro-scale effects explicitely on their specific length scale and couples their homogenized effects to the macro-scale is proposed in the present work. Based on a periodicity assumption of the microstructure, a relevant Representative Element Volume (REV) is defined based on experimental data, which makes it possible to idealise the flow behaviour of the material microstructure with different families of discontinuities, and an assembly of tubes substituting the porous matrix blocks. This complete hydraulic constitutive model is solved at the scale of the microstructural constituents, and is directly affected by the mechanical effects tackled at the macroscopic scale, which makes the whole model hydro-mechanically coupled.
This model has been subsequently applied to simulate a gas injection test parallel and perpendicular to the bedding of initially saturated samples of Boom Clay [3]. This analysis provides a rather good agreement with the experimental results in terms of pressure response, outflow volume and average axial strain. In addition, it allows to simulated the creation of a preferential flow pathway along the sample axis (Figure 1b, top), which serves as basis to numerically reproduce the development of random pathways through the sample in plane strain state (Figure 1b, bottom), and aims to improve the mechanistic understanding of the gas transport processes at play in clayey barriers.
[1] P. Marschall, S. Horseman, and T. Gimmi. Characterisation of Gas Transport Properties of the Opalinus Clay, a Potential Host Rock Formation for Radioactive Waste Disposal. Oil & Gas Science and Technology Rev. IFP, 60(1):121-139, 2005.
[2] Harrington, J.F., Milodowski, A.E., Graham, C.C., Rushton, J.C., & Cuss, R.J. (2012). Evidence for gas-induced pathways in clay using a nanoparticle injection technique. Mineralogical Magazine, 76(8):3327–3336.
[3] Gonzalez-Blanco, L., Romero, E., Jommi, C., Li, X. & Sillen, X. (2016). Gas migration in a Cenozoic clay: Experimental results and numerical modelling. Geomechanics for Energy and the Environment, 6:81–100.
How to cite: Corman, G. and Collin, F.: A multi-scale model to study gas transport processes in clay materials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16823, https://doi.org/10.5194/egusphere-egu24-16823, 2024.
The successful deployment of carbon dioxide (CO2) geological sequestration in porous media is reliant on the sealing efficiency of the overlying, clay-rich caprock to act as a physical barrier. Clay-rich caprock formations are considered favorable materials to act as a seal due to them characteristically consisting of small pores providing high capillary entry pressures, hence preventing the intrusion of a non-wetting fluid.
The juxtaposition and availability of deep seated (buried) caprock-reservoir systems to carbon capture and storage clusters may not be available. Therefore, the assessment of shallow seated, weakly consolidated caprock-reservoir systems (e.g., Sleipner) will be required. Our experimental campaign tests analogous caprock geomaterials which have relatively high compressibility, representative of shallow seated (buried or less indurated) clay-rich caprocks.
Past experimental campaigns demonstrate that CO2 breakthrough is dominated by the creation of very localized channels across the sealing barrier which occur at pressures far lower than the one predicted by the Laplace’s equation [1]. However, limited data characterizing these pathways exists. Furthermore, the physical indicators of susceptibility which underly the micro-mechanisms of failure (e.g., fracturing), are still only postulated for clay-rich geomaterials.
where Pc* is the capillary breakthrough pressure [kPa], ψ, reflects pore shape [-], Ts, interfacial tension between water and gas (e.g., CO2), and θ, represents wettability [°].
An innovative experimental set-up which allowed for the onset of surface crack formation to be captured during gas injection (representing the non-wetting fluid in CO2 geological sequestration) into intact clay-rich geomaterials is presented. This allowed for the investigation of physical indicators of susceptibility to gas breakthrough via localized pathways.
Results on different fracture patterns when non-wetting gas (i.e., air) is injected into consolidated clay show the formation of large fractures that nucleate from within the sample. Upon air pressurization, before fracture formation, the sample undergoes volumetric deformation (i.e., consolidation), as the resulting action of the vertical stress applied at the air-water interface (menisci). Once a fracture forms deformation stops and breakthrough occurred at lower pressures than traditionally recorded. The mechanisms of air intrusion are expected to be of a similar nature as CO2 intrusion. Post-mortem assessment of the internal nature of these localized pathways was then visualized using xCT imaging.
As a continuum mechanics framework will not predict fracture formation under our test conditions, it appears that the experimental evidence support the underlying hypothesis that disjoining pressure governs the mechanisms that ultimately control fracture formation and thus, eventually CO2 breakthrough. The disjoining pressure is governed by the electrostatic double-layer interactions, van der Waal’s dispersion forces, structural forces, and solvation forces.
If the pore size distribution is such that high gas pressures are required to overcome capillarity, the gas pressure will force single clay particles apart, displacing water form adjacent interparticle spaces. This represents a localized failure mechanism at the clay interface, resulting in fracture nucleation. It is expected that clay displaying large swelling pressures will subsequently display high gas entry pressure, termed “pathway dilation”. Therefore, pressurized gas will enter a dilated pathway at lower pressures than anticipated.
How to cite: Allsop, C., Pedrotti, M., and Tarantino, A.: Insight into the micromechanisms of gas breakthrough in water-saturated clay-rich geomaterials – Implications for CO2 sequestration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17117, https://doi.org/10.5194/egusphere-egu24-17117, 2024.