Comparative Analysis of Multi-Layer and Single-Layer Injection Methods for Offshore CCS in Saline Aquifer Storage

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Abstract
The aim of this study is to compare the performance of the multi-layer and the single-layer CO2 injection methods used in offshore carbon capture and storage (CCS) through TOUGH-FLAC numerical simulations. Four key indicators, namely CO2 saturation, pore pressure, vertical displacement, and Coulomb Failure Stress (CFS), are employed as indices to assess the storage capacity of reservoirs and the mechanical stability of caprocks. Numerical simulation results show that the multi-layer injection method increases the CO2 migration distance and reduces CFS values compared with the single-layer injection method. After 1 year of injection, the combined CO2 migration distance across two aquifers in Case 3 is 610 m, which is greater than that obtained using single-layer injection in Cases 1 and 2 (350 m and 380 m, respectively). Additionally, deep saline aquifers demonstrate superior CO2 storage capacity due to higher overburden pressure, which also reduces the risk of caprock failures. After 30 years of injection, in Cases 1 and 2, the maximum CFS values are 0.591 and 0.567, respectively, and the CO2 migration distances are 2400 m and 2650 m, respectively. Overall, the findings of this study indicate that the multi-layer injection method, particularly in deep saline aquifers, provides a safer and more efficient CO2 injection approach for offshore CCS projects.
Funding Information
  • National Natural Science Foundation of Chin (U24A20609, 42477144, DH-2022ZY0007)
  • The Science Foundation of Donghai Laboratory (U24A20609, 42477144, DH-2022ZY0007)

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