Shear wave velocity prediction during CO2-EOR and sequestration in the Gao89 well block of the Shengli Oilfield

Shear-wave velocity is a key parameter for calibrating monitoring time-lapse 4D seismic data during CO₂-EOR (Enhanced Oil Recovery) and CO₂ sequestration. However, actual S-wave velocity data are lacking, especially in 4D data for CO₂ sequestration because wells are closed after the CO₂ injection and seismic monitoring is continued but no well log data are acquired. When CO₂ is injected into a reservoir, the pressure and saturation of the reservoirs change as well as the elastic parameters of the reservoir rocks. We propose a method to predict the S-wave velocity in reservoirs at different pressures and porosities based on the Hertz–Mindlin and Gassmann equations. Because the coordination number is unknown in the Hertz–Mindlin equation, we propose a new method to predict it. Thus, we use data at different CO₂ injection stages in the Gao89 well block, Shengli Oilfield. First, the sand and mud beds are separated based on the structural characteristics of the thin sand beds and then the S-wave velocity as a function of reservoir pressure and porosity is calculated. Finally, synthetic seismic seismograms are generated based on the predicted P- and S-wave velocities at different stages of CO₂ injection.