Prediction of Shear-Wave Velocities in Carbonate Reservoirs

The purpose of this paper was to propose a method to predict shear-wave velocities in the process of AVO (amplitude variation with offset) inversion, to interpret seismic converted-wave data, and to match reservoir engineering information with seismic data in regions without shear-wave velocities. During CO2 flooding and sequestration, the shear-wave velocity varies with the pressure that is caused by fluid injection. Predictions of how the shear-wave velocity changes with pressure can be used to interpret 4D seismic monitoring data during different stages of CO2 injection. To verify the calculations, the authors used the characteristic parameters of the Marly dolomite and Vuggy limestone units of the Weyburn Oilfield reservoir in Canada. The Digby’s model and Gassmann’s equation were used to evaluate the dependence of the shear-wave velocity on the pressure in the carbonate rock formation. The authors have developed a new method for calculating the coordination number of the model and supplement the results with a shale correction, enabling the prediction to match the measured shear-wave velocities more closely. Our method is verified by dipole sonic logging data and petrophysical test data from the Weyburn Oilfield. When applied to petrophysical test data, the average error is below 5%. When the method is applied to well log data, the average error in the porous media is 3.014% in the Marly unit and 6.288% in the Vuggy unit.