Integrated modeling of thermal decarbonation and three-dimensional poroelastic fluid behavior: Assessment of stored CO2 leakage along carbonate fault

Abstract

Estimation of permeability changes and fluid flow is necessary to ensure storage integrity during carbon storage in carbonate formations. This study evaluates the effect of thermal decarbonation driven by seismic slip along a carbonate fault on the leakage of pre-injected CO₂. We constructed a centimeter-scale one-dimensional thermal decarbonation (1D-TD) model to investigate fault geometry and thermochemical effects on porosity evolution with various geomechanical properties. Then, a three-dimensional poroelastic leakage (3D-PL) model was coupled, using permeability structures exchanged with the 1D-TD model, to calculate the leakage rate based on regional-scale fault geometry. The evolved fault permeability is positively correlated with fault depth and friction coefficient, while larger shear zone width and TD activation energy lead to lower permeability. In the 3D-PL model, CO₂ ascends along the fault as fault permeability increases after fault reactivation. The annual leakage rate measured at 0.5 km above the reservoir varies from 0.054 % to 4.56 % of the total injection amount, for the cases of fault depth = 3 and 5 km and shear zone width = 0.005 and 0.001 m, respectively. Our model suggests that the leakage rate > 1 % can occur with a deep fault (5 km) and extremely localized shear zone. Since carbon storage reservoirs are typically between 1 and 3 km deep, fluid leakage due to the TD-driven permeability increase will be minimal. Furthermore, near-surface leakage is negligible as TD effects are attenuated at shallow depth due to low confining stress, limiting the permeability increase by a factor of three or less.