CO2 injection detection using light time-lapse seismic monitoring
Carbon Dioxide (CO2) injection has been used for Enhanced Oil Recovery (EOR) in the Weyburn field in southeast Saskatchewan in Canada for over 20 years. Since 2000, the Weyburn Unit has sequestered over 34 million tonnes of CO2, with an ultimate storage capacity estimated at 55 million tonnes. Since 1997, time-lapse (4D) seismic has been an essential surveillance tool to ensure safe and optimized development throughout the field. Multiple 4D seismic surveys have been acquired to monitor the evolution of CO2 flooding and identify sweeping inefficiencies and infill drilling opportunities. 4D seismic plays an integral role in understanding the Weyburn Unit’s CO2 flooding performance and helps in strategic planning and time-critical field optimization (Chen et al., 2021).
To maximize the value of information while controlling costs, a novel light seismic monitoring approach has been “blind-tested” on a CO2 use case. The concept requires the use of only one source and one receiver location optimally placed in the field to monitor a spot in the subsurface, using time- lapse shots to detect 4D changes in the zones of interest (Brun et al., 2021). This technology has already shown successful results and is currently being used for several applications: steam monitoring in a heavy oil field, fracking and over a gas storage monitoring area.
The objective of this blind-test was to identify the zones that were affected by a CO2 injection without knowing the injection scenario thanks to the ultra-light time-lapse seismic acquisition system designed. The results were then successfully matched to the 4D time-lapse CO2 amplitude anomalies within the CO2 flood, with the SpotLight technology successfully identifying CO2 swept vs non-swept spots by calculating travel time delays.