Novel experimental/numerical approach to evaluate the permeability of cement-caprock systems

• A novel laboratory-scale experimental/numerical approach is presented.
• The approach enables permeability estimation of defects in cement-shale interfaces.
• The approach combines μ-CT, flow experiments and numerical modelling.
• The approach may facilitate understanding of well integrity problems.

This study presents a novel laboratory-scale experimental/numerical approach that contributes to our understanding of micro-annular flow paths in cement-caprock interfaces. The approach is based on studying single-phase fluid flow in composite specimens with imperfect bonding between cement and caprock. Imperfect bonding and defect zones in the cement were initially characterized by X-ray micro computed tomography. Subsequently, the bulk permeability of the specimens was determined through single-phase fluid permeability measurements. Permeability was also evaluated numerically by finite-element modelling of steady single-phase flow in the specimens. The numerical modelling revealed that the average permeability of defect zones mapped from μ-CT images was likely to be within 1–10 D (0.1 × 10−11 to 1 × 10−11 m2). If a connected region of elevated permeability is established in situ, it can create a potential well integrity risk by providing a flow path up the annulus of the well. The integrated experimental and numerical framework employed in this study can form the basis for future systematic evaluation of leakage risks related to well integrity issues during underground CO2 storage, as well as in other applications such as drilling and completion of geothermal wells.