Stochastic and global sensitivity analyses of uncertain parameters affecting the safety of geological carbon storage in saline aquifers of the Michigan Basin

Geological carbon storage (GCS) has been proposed as a favorable technology to reduce carbon dioxide (CO2) emissions to the atmosphere. One of the main concerns about GCS is the risk of CO2 escape from the storage formation through leakage pathways in the sealing layer. This study aims at understanding the main sources of uncertainty affecting the upward migration of CO2 through pre-existing “passive” wells and the risk of fissuring of target formation during GCS operations, which may create pathways for CO2 escape. The analysis focuses on a potential GCS site located within the Michigan Basin, a geologic basin situated on the lower Peninsula of the state of Michigan. For this purpose, we perform a stochastic analysis (SA) and a global sensitivity analysis (GSA) to investigate the influence of uncertain parameters, such as: permeability and porosity of the injection formation, passive well permeability, system compressibility, brine residual saturation, and CO2 end-point relative permeability. For the GSA, we apply the extended Fourier amplitude sensitivity test (FAST), which can rank parameters based on their direct impact on the output, or first-order effect, and capture the interaction effect of one parameter with the others, or higher-order effect. To simulate GCS, we use an efficient semi-analytical multiphase flow model, which makes the application of the SA and the GSA computationally affordable. Results show that, among model parameters, the most influential on both fluid overpressure and CO2 mass leakage is the injection formation permeability. Brine residual saturation also has a significant impact on fluid overpressure. While influence of permeability on fluid overpressure is mostly first-order, brine residual saturation's influence is mostly higher-order. CO2 mass leakage is also affected by passive well permeability, followed by porosity and system compressibility through higher-order effects.