Time-dependent permeability of fractured Callovo-Oxfordian claystone in laboratory and in situ drift excavation induced damaged zone in the claystone formation: experiment and numerical modeling

This study examines the permeability evolution of the excavation damaged zone (EDZ) in Callovo-Oxfordian argillite (COx claystone) drifts, from excavation to refilling. The aim is to validate the drifts’ EDZ self-sealing capability and assess its suitability for nuclear waste storage. Biot’s model integrated with a swelling–shrinkage criterion is proposed to describe Callovo-Oxfordian argillite deformation due to saturation changes. Using the Nadai criterion, Cubic law, and Darcy’s law, the authors have characterized plasticity, assessed crack permeability, and described flow. Notably, Callovo-Oxfordian argillite fractures, produced by the Brazil splitting test or within EDZ, and their self-sealing from experiments are validated numerically, no matter at laboratory scale or in situ. This is the first model capable of simulating the dynamic development of claystone fractures over time during 3D fracture and pore seepage, laying the groundwork for subsequent analysis of time-dependent thermo-hydro-mechano-chemo (THMC) behaviors and their impact on the self-sealing of fractured Callovo-Oxfordian argillite. Additionally, the model holds potential for assessing time-dependent CO₂ flow within fractures of caprocks which are usually claystone during large-scale geological storage of CO₂. Consequently, the proposed model holds potential application value for evaluating the long-term safety of both nuclear waste and CO₂ geological storage.