OPTIMIZING SCHEMES OF FREQUENCY-DEPENDENT AVO INVERSION FOR SEISMIC DISPERSION-BASED HIGH GAS-SATURATION RESERVOIR QUANTITATIVE DELINEATION

摘要

Previous works demonstrate that dispersion properties can be deduced fromfrequency-dependent AVO inversion (FDAI). The optimal selection ofdispersion-related fluid factors is of great importance to improve the accuracy of fluididentification. In order to quantitatively delineate the reservoir with high gas saturation,we propose an optimal scheme of FDAI to pursue the optimal dispersion factor which isthe most sensitive to the high gas saturation reservoir. First, within the seismic frequencyband, we construct an objective function to determine the optimal reference frequencyby using the dispersion factors calculated from the pre-stack seismic data nearbyborehole. Then, we can directly get the optimal dispersion factor related to gas-saturatedreservoir according to the fluid indication coefficient. At last, we apply optimalparameters to calculate the dispersion results for seismic data volume. Numericalanalysis indicates that the dispersion degree of fluid-saturated reservoir shows anapproximate linear increase characteristic with increasing gas saturation. It provides anevidence for the delineation of high gas-saturation reservoirs by using the dispersionanomalies. The seismic field data results illustrate that the dispersion factors inverted bythe optimal reference frequency can highlight the dispersion anomalies of gas-saturatedreservoirs. Meanwhile, the optimal dispersion factor can delineate the reservoirs withhigh gas-saturation more accurate while less affected by the background interference ofelastic layers than conventional methods. The proposed optimal workflow can improvethe accuracy of FDAI and it is feasible to detect the location and spatial distribution ofhigh gas-saturation reservoirs.