A numerical model for gas CO2 migration in a fault zone

Understanding whether fractures and faults impact the CO2 migration through the overburden is critical in the evaluation and monitoring of CO2 geological storage sites. We present a numerical model and workflow to describe the hydraulic behaviour of a fault located in the shallow part of the overburden. This helps to evaluate the sealing potential of the system in case of unwanted CO2 migration toward the surface and to design an efficient monitoring plan. The model configuration is representative of several experiments performed at real sites under quite shallow conditions (50-500 m). The model results, applied to a selected fault outcropping in the Apennines (Italy), show that most of the gas migrates through the high permeable footwall damage zone. A significant amount of gas then dissolves into the water, emphasizing the importance of accurate modelling to assess the hazard of CO2 leakage into near-surface aquifers or to the surface. The occurrence of pressure buildup close to the fault core points out that detailed modelling of the migration conditions is required to predict gas path through a fault zone.