Matching of Production History and 4D Seismic Data—Application to the Girassol Field, Offshore Angola

Abstract

Abstract This paper presents an advanced history matching methodology for constraining 3D stochastic reservoir models to both production history and 4D seismic attributes. The proposed approach is based on an optimization loop which integrates geostatistical modeling, upscaling, fluid flow simulation and petro-elastic modeling in the same workflow. Simulated production history and 4D seismic attributes are compared to real data using a single objective function, which is minimized using a new optimization algorithm based on response surface fitting. Inversion parameters can be selected throughout the entire modeling workflow, to update the facies spatial distribution, the petrophysical properties and fluid flow parameters. Advanced parameterization techniques are used to constrain the fine scale geostatistical model. The gradual deformation method allows smooth transformations of the facies model realization while conserving the overall statistical characteristics. In addition, a new history matching technique has been implemented to constrain the average facies proportions over given regions. As an example, new geologically-based parameters like shale proportions in flow barriers or sand proportions in channel sequences can be considered in the inversion process. A successful application to the Girassol field is presented. Girassol is a large, complex and faulted turbidite field located offshore Angola. A detailed geostatistical model was built first from 3D high resolution seismic data. The major challenge was to integrate 4D seismic data to constrain the reservoir model in a quantitative way. The gradual deformation method has shown a major impact on production history, since the changes in the facies distribution affect the connectivity in sandy channels and the position of shaly barriers. A good match of water and gas breakthrough was obtained over one year of production data. The addition of new geological constraints allowed us to better honor the 4D seismic information (extent of gas injection and of depleted zones). This was achieved by constraining average sand and shale proportions over channel and levee regions. Improved predictions of future production and of a new seismic survey have been obtained using the matched model.