4D Seismic Modeling on a Geological Grid and Downscaling of Dynamic Reservoir Properties

We present a 4D seismic modelling study on a field offshore Angola, where real 4D seismic data have been very valuable for monitoring changes in the reservoir. To date the 4D information has been used in a mostly qualitative sense, but the ultimate objective is a quantitative use for reservoir model updates by comparing forward modelled seismic with real 4D seismic data. The study is a pilot using a provisional reservoir model, with the aim of putting an adequate methodology in place and uncovering uncertainties in the forward modelling process. A challenge in the work is the horizontal grid scale, which is required for the modelling in light of geological heterogeneities, being finer than the scale at which full-field reservoir simulation is feasible. Therefore, we downscale the dynamic reservoir properties into the geomodel grid, for which methods are proposed. Independent of the scale issue, the 4D seismic modelling results expose fundamental uncertainties related to the petro-elastic model and global reservoir simulation parameters. Herein lies the value of this pilot, as it points out aspects where uncertainties have to be reduced in the forward modelling, if the 4D data are to be used in any type of seismic history matching process.