A decoupled elastic wave equation for CO2 monitoring and its numerical simulation

Monitoring the migration and potential leakage of carbon dioxide (CO 2 ) is a critical part of carbon capture and storage (CCS). The most widely used monitoring technique is 4D seismic imaging, which involves examining subsurface formations at varying burial depths based on seismic waves, conducting seismic inversion of the acquired data, and then identifying alterations in subsurface structures. Therefore, a thorough understanding of the seismic responses to CO 2 injection and migration is essential, necessitating detailed analysis. In this study, the porosity and saturation parameters related to CCS are transformed into seismic parameters using the Hertz-Mindlin (HM) contact model initially. Then, an elastic wave equation is derived based on the porosity and saturation. To distinctly characterize seismic responses to variations in porosity and saturation, novel decoupled elastic wave equations are introduced. Using these equations, the wavefields and equations associated with porosity and saturation are separated into distinct terms. Through numerical simulation based on a portion of the Marmousi model, this study demonstrates that the proposed decoupled elastic wave equations can effectively identify seismic wavefields and data discrepancies induced by CO 2 migration, thereby enabling their applicability in subsequent inversion processes. • Transformations between saturation, pressure and seismic velocities are derived. • A decoupled elastic wave equation using sat uration and pressure is derived and analyzed. • Simulations show how seismic signals relate to CO 2 injection-induced saturation-pressure changes.