Extrapolation of flow units away from wells with 3D pre-stack seismic amplitude data:: Field example

We estimate the spatial continuity and lateral extent of lithologic and flow units penetrated by wells, using pre-stack seismic amplitude data and well logs. The approach is based on a stochastic global inversion algorithm that concomitantly honors well logs and multiple partial-angle stacks of seismic amplitude data. Inversion results consist of 3D spatial distributions of elastic properties, litho-types, and petrophysical properties between wells. These distributions have a vertical resolution that is intermediate relative to those of well logs and 3D seismic amplitude data. An example of application is shown with high-quality 3D seismic amplitude data acquired over the Marco Polo Field in the deepwater Gulf of Mexico. Reservoir units in this field consist of stacked turbidite sands. Petrophysical logs, elastic-petrophysical correlations, and four partial-angle stacks of pre-stack seismic amplitude data are input to the stochastic inversion algorithm to estimate 3D distributions of lithotype, porosity, permeability, and fluid saturation. When cross-validated at blind-well locations, the estimated spatial distributions of porosity, permeability, and water saturation of individual sand units agree well with the same properties derived from well logs. Sensitivity analyses indicate that inversion results are slightly conditioned by the choice of variogram model and range, as well as by the assumed global lithology proportions. The uncertainty of the extrapolated lithotypes and petrophysical properties increases with distance away from wells. In addition, we find that the uncertainty of the extrapolation increases when flow units are thinner than the vertical resolution of seismic amplitude data. However, in all of the examples considered in this paper, the joint stochastic inversion of wells and pre-stack seismic data yields more accurate extrapolations of lithologic and flow units than pre-stack seismic data alone.