High-Resolution Time-Lapse Monitoring of CO₂ Sequestration in a Seven-Meter Reservoir Using Walkaway VSP and Full-Waveform Inversion

He Liu, Xin Fu, Xiaohui Cai, Daniel O. Trad, Kristopher A. Innanen

Vertical seismic profile (VSP) is a powerful technology for monitoring CO₂ injection and sequestration. Applying full-waveform inversion to walkaway VSP data can provide images and time-lapse models of physical properties in the reservoir where CO₂ is injected. One challenge in time-lapse FWI is the non-repeatability in a time-lapse survey, including non-repeatable acquisition geometry, non-repeatable near-surface physical properties, non-repeatable noise, etc, which introduce 4D noise into the time-lapse data and containment the time-lapse result or even make it impossible to detect the time-lapse change. We present a workflow of acoustic FWI applied to walkaway VSP data to identify time-lapse Vp change introduced by injection of 400 t of CO₂ into a 7 m-thick sandstone reservoir at only 300 m depth. The results of both field Snowflake data at CaMI-FRS and synthetic data show that this workflow of applying FWI can detect a minor time-lapse velocity change and achieve high-resolution time-lapse monitoring of CO₂ sequestration.