Dynamic Monitoring of Co2 Sequestration and Plume Motion with Advanced Seismic Imaging
Ping TONG#+
Nanyang Technological University, Singapore

Geological storage of CO2 in a deep saline aquifer is a promising way to reduce the emission of greenhouse gas to the atmosphere. This is a critical approach for the success of the Net-Zero 2050 goal set by many major industrial countries. Storage of CO2 requires monitoring of the induced seismicity, the plume extent and the potential stratigraphic seal failure. All of these can be accomplished by using advanced seismic imaging techniques.                           Seismic traveltime tomography is a routine imaging technique to investigate structural heterogeneities and geodynamics of the Earth’s interior. Ray-based seismic traveltime tomography is simple and easy to be implemented. But ray tracing may be inaccurate even in mildly heterogeneous model. Full waveform inversion is physically more correct and maintains its accuracy in complex media. However, a good knowledge of earthquake sources and structure is an essential requirement for the accurate measurement of the misfit between synthetic and observed waveforms. In addition, full waveform inversion is computationally expensive. We present a third form of seismic traveltime tomography, which is neither ray-based nor wave-equation-based. In detail, seismic traveltime tomography is formulated as an eikonal equation-constrained optimization problem, which is solved by the adjoint-state method. For both isotropic and anisotropic media, we discuss adjoint-state absolute traveltime tomography, adjoint-state common-source double-difference traveltime tomography, and adjoint-state common-receiver double-difference traveltime tomography. The advantages of these methods include (1) accurate computation of traveltime fields in complex media, (2) using the most reliable seismic data – traveltime, (3) correctly reflecting the relation between the traveltime data and subsurface structure, and (4) the double-difference traveltimes have strong resolving ability of the subsurface heterogeneities. All these imaging techniques will be applied to monitor the dynamics of CO2 storage and plume motion.