A mobility attribute calculation method based on pre-stack seismic data

The extraction of fluid mobility (FM) attributes from low-frequency information contained in post-stack seismic data has yielded promising results for reservoir prediction and fluid identification.Pre-stack seismic data contain more information about reservoirs and fluids than post-stack data.To extract FM information from pre-stack data, a pre-stack FM prediction method based on the synchro-squeezed generalized S-transform is proposed herein to improve the prediction accuracy.In this method, the relationship between FM and incident angle was established by combining the dispersion amplitude-versus-offset (AVO) analysis with the FM calculation method.In this step, FM information in pre-stack seismic data was extracted and expressed in terms of FM variation with offset.By establishing an AVO theoretical model, the FM of carbonate reservoirs with water and oil was calculated based on pre-stack data.Clear variations could be evaluated in the pre-stack-based mobility value obtained from the variation of amplitude in corner gathers.The time-frequency analysis method offers a different accuracy for mobility calculation, thereby verifying the theoretical effectiveness of the proposed method.An application of the method to actual seismic data in the Tarim Basin was conducted to compare the performance of the pre-and post-stack mobility methods.Although the relative mobility value can be successfully obtained from post-stack mobility attributes, calibration of the threshold value of the mobility value through drilled wells is necessary to quantify the fluid properties.Moreover, these properties can be directly determined by analyzing the positive and negative values of the changes in the mobility value.Therefore, it can be concluded that the pre-stack method offers a superior capability in predicting fluid properties compared with that by the post-stack method.