Evaluating [Formula: see text] breakthrough in a shaly a caprock material: a multi-scale experimental approach

Area of Science:

• Geological Engineering
• Material Science
• Geochemistry

Background:

• Underground CO2 storage requires effective caprock sealing.
• Shales, like Opalinus Clay, show promise as caprock materials due to favorable hydro-mechanical properties.
• Understanding caprock response to CO2 injection is crucial for safe storage design.

Purpose of the Study:

• To assess the sealing capacity of Opalinus Clay to CO2 injection.
• To understand the geomechanical response of Opalinus Clay to CO2 injection at different scales.
• To relate lab-measured properties to field-relevant parameters for safe CO2 storage design.

Main Methods:

• CO2 breakthrough tests on Opalinus Clay at meso- and micro-scales.
• Meso-scale tests under oedometric conditions with varying effective stress and CO2 phase (gaseous/liquid).
• Micro-scale tests using in-situ X-ray tomography to visualize CO2 breakthrough and volumetric response.

Main Results:

• Demonstrated the impact of CO2 phase and open porosity on entry pressure.
• Correlated measured entry pressure with absolute permeability.
• Identified CO2 breakthrough using X-ray tomography, revealing anisotropic material response.

Conclusions:

• Opalinus Clay's sealing capacity to CO2 injection is dependent on hydro-mechanical properties.
• In-situ X-ray tomography provides critical insights into CO2 breakthrough mechanisms.
• Findings are vital for the representative modeling and safe design of geological CO2 storage.