The Permeability Alternation of Shale Fractures due to Sc-CO2 Soaking: Implications for Sc-CO2 Fracturing and Deep CO2 Sequestration in Shale Reservoirs

This article examines the influence of supercritical carbon dioxide (Sc-CO2) on shale fracture permeability—a crucial factor in assessing gas production and deep CO2 sequestration efficacy. Understanding the evolution of shale fracture permeability after Sc-CO2 interaction is essential to gauge the permeability of shale reservoirs and evaluate the long-term sealing capability of shale formations. In the study, the researchers carried out experiments soaking shale fractures in Sc-CO2 for varying durations and subsequently measured the evolution of shale fracture permeability and hydraulic aperture under diverse stress conditions. Advanced techniques like X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, and optical profilometry were employed to quantify chemical compositions, pore attributes, and changes in fracture surface roughness. Key findings suggest that Sc-CO2 immersion significantly enhances the shale fracture permeability and aperture primarily due to the dissolution of calcite and dolomite. This dissolution process, termed free-face dissolution, leads to the removal of mineral particles on the fracture surface, producing larger pores and pronounced peaks and valleys on these surfaces. Interestingly, this chemical process appears to stabilize after roughly seven days. Ultimately, the research offers a detailed microscopic insight into how Sc-CO2 impacts shale fracture permeability by chemically dissolving specific minerals.