A Study on Effect of Number of Low-Permeability Layers on Geological Carbon Sequestration in an Open Aquifer

The use of fossil fuels to fulfill energy demand is responsible for CO₂ emissions, resulting in global warming and climate change. Despite the expansion in renewable energy sources, energy combustion and industrial processes caused a 0.9% increase (321 Mt) in global CO₂ emissions to a record high of 36.8 Gt in 2022. Carbon capture and sequestration (CCS) technology can allow the use of fossil fuel without damaging the environment by storing CO₂ underground, paving the way for a sustainable, low-carbon future. Without fracturing, both homogeneous and low-permeability aquifers can safely accommodate injected CO₂. This study investigates the effect of low-permeability layers composed of sandstone and shale layers on the capacity and performance of CO₂ storage in open saline aquifers. The CO₂ migration, dispersion, and reservoir pressure variations have been numerically investigated in a computational domain representing the Utsira Formation in Sleipner CCS project. In a homogeneous aquifer, rapid vertical migration results in 65% of the injected CO₂ accumulating at the top layer after 30 years. However, the presence of four low-permeability layers reduces this accumulation to 58% over the same period, demonstrating enhanced trapping efficiency. Long-term simulations indicate that CO₂ accumulation at the top surface increases to 75% of the total injected volume over 80 years. CO₂ dissipates and migrates over time, resulting in a decrease in surface pressure. Pressure analyses reveal that the peak injection-induced pressure remains within the fracture pressure limit (20–25 MPa), ensuring safe storage. After 30 years of injection, pressure at the top surface drops by 0.27 MPa (2.72%) within 2 years post-injection and continues to decrease gradually. This investigation contributes to a better understanding of the dynamics of CO₂ storage in open saline aquifers, thereby facilitating the development of effective CO₂ sequestration strategies.