DEPTH CONVERSION, RESERVOIR VOLUMES, SEAL INTEGRITY, AND 4D MONITORING FOR CO2 SEQUESTRATION

This work aims to enhance the efficiency and accuracy of carbon capture, utilization, and storage (CCUS) practices by developing new techniques of depth conversion and velocity uncertainty assessment, gross rock volume (GRV) estimation, fault seal analysis, and 4D seismic monitoring. The V0-k method of depth conversion is investigated with its mathematical foundations and how its parameters can be derived from commonly available depth-time data from wells. The research demonstrates that obtaining reasonable depth estimates is possible even when errors in the input velocities are large. New equations for estimating GRV and its uncertainty for circular paraboloids are developed, which aspire to provide accurate estimates of GRV and geologically reasonable (10% and 90% probability, P10 and P90) surfaces. A case study of the Illinois Basin-Decatur Project (IBDP) is presented, emphasizing the significance of bottom and fault seal analysis in CO2 sequestration. A possible correlation exists between areas of high microseismic activity in the basement rock and seismic attributes. The dissertation also presents fault seal interpretation for the Vette Fault bounding the Alpha Structure in the Sognefjord Formation (North Sea). The fault seal assessment ranges from moderate to a substantial risk of leakage based on the estimated shale gouge ratio (SGR). While the reservoir is completely offset along most of the length of the trap-defining fault, it is juxtaposed against a sandy section near the crest of the trap. The presence of this sand leads to reduced SGR values, as low as approximately 0.4. This indicates that the buoyancy pressure could surpass the fault's sealing potential at the crest of the trap. Additionally, the dissertation explores the significance of 4D seismic monitoring in CCUS projects, particularly in identifying potential CO2 migration pathways and monitoring the effectiveness of CO2 injection. 4D seismic analysis, particularly the qualitative interpretation of 4D seismic data and quantitative 4D inversion, has provided valuable insights into CO2 migration in the Sleipner (North Sea). Without the 4D imaging, insight into the CO2 migration pattern and potential leakage would not have been possible. Thus, it is highly recommended that 4D seismic acquisition and analysis should be part of the standard methodology for CO2 monitoring, especially with baseline surveys undertaken before any injection. In conclusion, this research emphasizes the practical applications and importance of depth conversion, GRV uncertainty, fault seal analysis, and 4D seismic monitoring in CCUS practices. The techniques and findings of this research promise to contribute to sustainable energy development.