Liwei Zhang

and 5 more

Xiuxiu Miao

and 4 more

The combination of X-ray imaging and CT image‒based computational fluid dynamics (CFD) simulation allows study of flow in fractured porous media. In this study, X-ray imaging was employed to unveil the morphological and aperture alterations of artificial fractures in wellbore cement cores that were exposed to CO2-saturated brine under geologic carbon sequestration (GCS) conditions. Direct pore-scale modelling of fluid flow through 3D fractures reconstructed from CT images was carried out to reveal velocity distribution in the fracture and for estimation of local and average permeability of the fracture. Varying-radius pipe representations of the fractures were established using the optimal characteristic radius formulation that was determined from the relation of flow cross-section shape and conductivity based on direct pore-scale modelling. Varying-radius pipeline modelling of fluid flow through simplified fractures was also implemented and the local and average permeability results based on varying-radius pipeline modelling were compared against those based on direct pore-scale modelling. The fracture after CO2 exposure in the reactive diffusion process was covered by substantial precipitated calcite, and the permeability of the fracture decreased from 4.15×10-8 m2 to 2.96×10-8 m2. In contrast, the fracture after CO2 exposure in the reactive flow process underwent significant dissolution, a large number of tensile micro-fractures were formed at the surface of the fracture, and the permeability of the fracture increased from 3.91×10-8 m2 to 4.23×10-8 m2. The relative error of the average fracture permeability obtained from direct pore-scale modelling (-7.33%‒4.05%) was comparable with that obtained from varying-radius pipeline modelling (-7.77%‒10.64%).