Incorporation of geology with rock physics enables subsalt poststack inversion: A case study in the Gulf of Mexico

摘要

One of the main goals of seismic inversion is to obtainhigh-resolution relative and absolute impedance for reservoirproperties prediction. We aim to study whether the results fromseismic inversion of subsalt data are sufficiently robust forreliable reservoir characterization. Approximately 481.25 mi2of poststack, wide-azimuth, anisotropic (vertical transverse isotropic)wave-equation migration seismic data from 50 OuterContinental Shelf blocks in the Green Canyon area of the Gulfof Mexico were inverted in this study. A total of four subsaltwells and four subsalt seismic interpreted horizons were usedin the inversion process, and one of the wells was used fora blind test. Our poststack inversion method used an iterativediscrete spike inversion method, based on the combinationof space-adaptive wavelet processing to invert for relativeacoustic impedance. Next, the dips were estimated from seismicdata and converted to a horizon-like layer sequence field thatwas used as one of the inputs into the low-frequency model.The background model was generated by incorporating the wellvelocities, seismic velocity, seismic interpreted horizons, andthe previously derived layer sequence field in the low-frequencymodel. Then, the relative acoustic impedance volume was scaledby adding the low-frequency model to match the calculatedacoustic impedance logs from the wells for absolute acousticimpedance. Finally, the geological information and rock physicsdata were incorporated into the reservoir properties assessmentfor sand/shale prediction in two main target reservoirs in theMiocene and Wilcox formations. Overall, the poststack inversionresults and the sand/shale prediction showed good tiesat the well locations. This was clearly demonstrated in the blindtest well. Hence, incorporating rock physics and geology enablespoststack inversion in subsalt areas.