Time-lapse Seismic Analysis for Gao89 Area of CO2-EOR Project in SINOPEC Shengli Oilfield, China

Based on the time-lapse seismic data of CO2-EOR project in Gao89 area of Shengli Oilfield in China, this paper carries out the calibration of time-lapse seismic data and the analysis of amplitude differences before and during CO2 injection. From well-log based forward model, we applied Hertz-Mindlin formula and combined it with Gassmann's equation to predict the P-wave velocity, S-wave velocity and density logs at different effective pressure and CO2 fluid saturation. Then we made time-lapse synthetic seismogram to calibrate time lapse seismic data and analyzed amplitude differences from forward model. Our study shows that the effective pressure is the dominant factor for the changes of elastic parameters and seismic amplitudes at the early time of CO2 injection because the reservoir pressure was much lower than that of in-situ pressure. The deficit of reservoir pressure was caused by oil producing. In addition, CO2 saturation also affects the elastic parameters of reservoir and seismic amplitude. Finally, we calibrated the RMS amplitude of time-lapse seismic data at CO2 injection layers and caprocks in Gao89 CO2 injection area. The difference of time-lapse seismic amplitudes reflects low pressure zone of reservoir which is also the migration path and the distribution of CO2.