CO2 invasion into the confining formations as a result of dry-out in the storage formation: Insights from numerical simulations

Abstract

This study investigated the combined effects of dry-out in storage formation in the presence of confining formations on fluid flow during geological carbon sequestration. Numerical simulations demonstrated that dry-out significantly decreased the liquid pressure in the storage formation, and this led to a capillary-driven backflow of water from the confining formations to the storage formation, causing a gradual decrease in the liquid pressure in the confining formations. Finally, CO₂ invaded the confining formations, despite the gas pressure buildup in the storage formation by CO₂ injection being maintained below the capillary entry pressure of the confining formations. Long-term simulations demonstrated that invaded CO₂ in confining formations can almost completely dissolve into unsaturated formation water after shut-in, indicating almost no long-term risk for safe storage or the effectiveness of structural trapping. Sensitivity analysis demonstrated that the permeability of the confining formations and maximum capillary pressure are crucial for controlling the quantity of CO₂ invasion and that injecting CO₂ from a deep section of the storage formation can prevent or sustain CO₂ invasion into the overlying formation. These findings provide valuable insights for optimizing CO₂ storage operations and ensuring the long-term stability of geological carbon sequestration.