The critical step necessary to model seismic response for composite deep-water fan sequences is creation of “pseudowell” logs using high-quality outcrop data. The “laboratory” outcrop model can be built to generate “pseudologs” of gamma ray, resistivity, density, and velocity from outcrop descriptions. Synthetic acoustic impedance, reflectivity, and synthetic seismo-gram curves then are generated on the same scale as measured thicknesses. Extrapolation from outcrop to seismic data is completed by resorting to geophysical data from depositionally similar basins under study, such as the deepwater of the Gulf of Mexico. By varying fluid and rock properties itera-tively, it is possible to “forward-model” hydrocarbon presence and its influence on seismic attributes (e.g., AVO) calibrated with rock and log data.
The Permian Skoorsteenberg Formation of the Tanqua Karoo Basin in South Africa is a natural “laboratory” in which to demonstrate how detailed outcrop data can be used to improve rock-calibrated seismic analysis of prospective deepwater fan exploration targets.