Time-lapse surface seismic inversion with thin bed resolution for monitoring CO₂ sequestration: A case study from Cranfield, Mississippi

The feasibility of carbon dioxide sequestration research at Cranfield, Mississippi is studied by injecting millions tonnes of CO₂ into the lower Tuscaloosa sandstone Formation over a two year period. Time-lapse surface seismic surveys were recorded at pre-(2007) and post-(2010) injection stages to monitor the subsurface fluid plume. The injection interval, appearing as a thin layer in the well-log data, shows very weak signature of CO₂ injection in the time-lapse seismic amplitude data. In order to improve the capability of tracking CO₂ plume movement using seismic data, we have applied a basis pursuit inversion (BPI) method to the post-stack seismic datasets. This method of inversion incorporates a priori information as a wedge dictionary and employs a L₁-norm optimization for obtaining solutions with improved resolution. The inverted time-lapse acoustic impedances show a strongly decreasing trend mostly at the top of the injection interval, which is in agreement with well-log measurements for CO₂ saturation. Improved resolution time-lapse impedance mapping therefore is an effective tool for imaging the displacement of the CO₂ plume.