Feasibility Assessment of Tiltmeter Monitoring for an Offshore Monoclinal Dipping Saline Aquifer CCS Site: Insights from Coupled Geomechanical Modeling

Abstract This study investigates the feasibility of tiltmeter monitoring for an offshore monoclinal dipping saline aquifer CCS site. The objective is to quantitatively evaluate the response of seabed deformation that can be monitored by tiltmeters through coupled geomechanical modeling. Additionally, the study explores the potential of integrating tiltmeter data with coupled geomechanical modeling to provide insights into pressure propagation and potential plume movement during CO2 injection. A 3D geomechanical model was constructed by applying a machine learning technique to a 1D geomechanical model and seismic attribute data. This model was coupled with a reservoir simulation model to perform one-way coupled analysis, simulating the injection of CO2 at a constant rate over 25 years. The analysis involved extracting predicted deformation amounts on the seabed and calculating tilt changes. The predicted seabed tilt changes were then compared with the CO2 plume and pressure front to investigate their correlations. As a result of coupled simulation, the predicted seabed deformation was consistently found to be less than 1 centimeter and within the expected range of similar injection operations. The tilt changes were also very small, on the order of several hundred nanoradians. The predicted deformation of the seabed and tilt changes were observed even though pressure changes occurred only within the reservoir. The regions exhibiting tilt changes aligned with the CO2 plume and pressure propagation areas, indicating that continuous tilt monitoring could capture spatial and temporal CO2 advancement behavior. Notably, there is a point where the trend of the tilt change over time varies in the tiltmeter near the injection well. At the timing when the trend of tilt change deviates, pressure changes gradually propagate towards shallower depth, and it is observed that pressure progresses to the secondary seal formation. The results indicate the potential for monitoring local vertical pressure propagation through tiltmeter monitoring. This study demonstrates that utilization of tiltmeters as monitoring tools not only allows for the measurement of seabed deformation induced by CO2 injection but also enables the prediction of the advancement behavior of the CO2 plume and pressure front when interpreted in conjunction with coupled geomechanical simulation.