Monitoring of injected CO2 using the seismic full waveform inversion for 2-D elastic VTI media

Abstract:

To monitor the injected CO₂ in the subsurface, seismic monitoring techniques are extensively applied because of its high resolution. Among the seismic monitoring techniques, seismic full waveform inversion (FWI) has high applicability because it can delineate parameter changes by injected CO₂. When seismic FWIs are applied, subsurface media can be generally assumed to be isotropic. However, most subsurface media are not isotropic, and shale is a representative anisotropic medium, particularly vertical transversely isotropic (VTI) medium, which is often encountered as a barrier to injected CO₂. Thus, anisotropic properties of subsurface media are important for monitoring of injected CO₂. For these issues, we need to consider anisotropy of subsurface media when seismic FWIs are applied as a monitoring tool for CO₂ sequestration. In this study, we performed seismic FWI for 2-D elastic VTI media to investigate the effects of anisotropic properties in CO₂ monitoring. For this numerical test, we assumed a geological model, which copies after one of CO₂ storage prospects in Korea. We also applied seismic FWI algorithm for 2-D elastic isotropic media for comparison. From this comparison, we noticed that we can obtain more reliable results when we apply the anisotropic FWI algorithm. Numerical examples indicate that we should apply the anisotropic FWI algorithm rather than the isotropic FWI algorithm when we interpret seismic monitoring data acquired in anisotropic media to increase the success of monitoring for injected CO₂. Our numerical results can also be used as references for real seismic monitoring of the Korea CO₂ sequestration projects in the near future.  

Acknowledgements

This work was supported by the Human Resources Development program (No. 20134010200510) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government Ministry of Trade, Industry, and Energy and by the “Development of Technology for CO₂ Marine Geological Storage” grant funded by the Ministry of Oceans and Fisheries of Korea.