Time-lapse (4-D) seismic data is often able to detect changes related to the injection of CO2. However, to quantify these changes is problematic. Understanding the CO2 injection process is critical to relating the seismic response to changes within the reservoir. In most CO2 injection projects, a pure liquid CO2 is initially injected into an oil reservoir, combining with the oil, resulting in the oil swelling and becoming more mobile. Reservoir changes include variations in fluid saturation, compressibility, phase and density along with changes in reservoir temperature and pressure.
Time-lapse (4-D), multi-component (9-C) seismic data has been acquired, processed and interpreted in three oil fields that have undergone CO2 injection. Vacuum field has been monitored with four seismic surveys during an EOR project in the San Andres formation with CO2 being injected over a 200 meter zone. Weyburn field has been monitored with three seismic surveys during an EOR project in the fractured Midale member of the Mission Canyon Formation with an approximately 20 meter thick zone. West Pearl Queen field has been monitored with two seismic surveys during a CO2 sequestration test in a 12 meter thick Queen Formation.
Combining the geologic, geophysical and petroleum engineering data allows an integrated approach to interpreting the time-lapse anomalies associated with CO2 injection. Integrating the multi-component seismic data allows the separation of the fluid changes from the pressure changes, allowing a much more definitive interpretation of the anomalies associated with the CO2 injection process. Multi-component seismology is critical in monitoring CO2 movement in the Vacuum, Weyburn, and West Pearl Queen fields.