Velocity Estimates of Injected Carbon Dioxide in 4D Seismic Monitoring by Non-linear Elastic Wavefield Inversion

Abstract

Summary Geologic sequestration by carbon dioxide injection into saline aquifers and others is one of the promising options to mitigate global climate changes. Elastic parameters are fundamental in estimating rock properties, fluid saturation and pore pressure in carbon dioxide injection and 4D seismic survey efficiently provides spatial and temporal changes of elastic parameters as well as baseline parameters. 4D seismic survey data, collaboratively acquired by Japex in 2003 and 2005 on the area of onshore RITE/METI carbon dioxide injection test site in Japan, were analysed incorporated with repeated time-lapse logging data matched in scale by the current method. In this study, 1) newly built the most probable full-scale baseline and monitor elastic wave velocity model of the 4D seismic survey in the depth domain using time scale adjusted and calibrated 4D AI cube in the time domain and 2) examined the feasibility of nonlinear elastic wavefield inversion of synthetic 4D seismic data assuming regular 3D geometry, though the original 3D was covered by irregular geometry, with common smoothest quasi-linear initial macro-velocity model for baseline and monitor surveys. Results of non-linear elastic wavefield inversion (FWI) with frequency-cascade scheme successfully showed estimates of 4D elastic wave velocity changes at excellent quality and accuracy.