From seismic data to reservoir changes - inversion approaches in 4D seismic modelling

The proposed SIP will represent a considerable research effort with the main objective to develop a new modelling system for transforming 4D (time lapse) seismic data to reservoir model changes, which can improve the reliability of fluid simulation. The m odelling system will be integrated in an already established modelling framework called SeisRoX. The SeisRoX model contains physical properties for a number of rock layers in a petroleum reservoir zone, and these properties are classified in 3 different d omains: geologic domain (G= reservoir properties like porosity, permeability, lithology, oil/gas content), elastic domain (E= elastic properties like seismic velocities and density), and reflectivity domain (R= reflection properties of seismic waves). In the present forward version one can import a model (e. g. Eclipse) from a fluid simulation (F) at different time steps, and define G at each step. By forward modelling procedures one can do the transformation G->E->R, and from R calculate a seismic respon se (S). This forward procedure is e. g. used for predicting the 4D seismic differences for varying fluid scenarios (4D feasibility studies). The SIP focuses on the inverse work-flow, that is, S->R->E->G->F, aiming at modelling changes in the fluid paramet ers from observed differences in 4D seismic data. To be able to perform the above 'transformations' in a proper (unique) way, assumptions or constraints must be added at critical steps in the process. An important add-on functionality of the SeisRoX syste m is the possibility of perturbing the model parameters in any chosen domain, and calculate the implications in the other domains. This allows valuable sensitivity analysis at all stages of the modelling process within a unified and consistent framework.