4D seismic monitoring of CO 2 sequestration based upon spectral‐element and adjoint methods: comparison of acoustic, elastic and poroelastic theories

Abstract

The key issues in CO2 sequestration monitoring involve accurate monitoring, from the injection stage to prediction & verification, of CO2 movement over time for environmental considerations. A natural non‐intrusive monitoring technique is referred to as “4D seismics”, which involves 3D time‐lapse seismic surveys. The success of monitoring the CO2 movement is subject to a proper description of the physical properties of the structure. We realize time‐lapse migrations comparing acoustic, elastic, and poroelastic simulations of 4D seismic imaging to characterize the storage zone, based solely upon the first arrival traveltime anomaly arising from the injection of CO2. This approach highlights the influence of using different physical theories on interpreting seismic data, and, more importantly, on extracting the CO2 signature from the seismic wave field. Simulations are performed using a spectral‐element method, which allows for highly accurate results. Biot's equations are implemented to account for poroelastic effects. The sensitivity of observables to the model parameters is quantified based upon finite‐frequency sensitivity kernels calculated using an adjoint method.