Constraining Reservoir Models to Production And 4D Seismic Data - Application to the Girassol Field, Offshore Angola

Time lapse seismic provides a source of invaluable information on the evolution in the space and time of the distribution of hydrocarbons inside reservoirs. Seismic monitoring thus makes it possible to optimize the recovery of hydrocarbons by a better comprehension of the production mechanisms. Although in rise, the use of 40 seismic by oil companies remains often qualitative, by lack of suitable interpretation techniques. Recent modeling experiences have demonstrated that the integration of 40 seismic data for updating reservoir flow models is feasible. However, methodologies based on sequential interpretation of 40 seismic data, trial and error processes and fluid flow simulation tests require a lot of efforts for integrated teams. In this context, the development of assisted history matching techniques represents a significant improvement towards a quantitative use of 40 seismic data in reservoir modeling. This paper proposes an innovative methodology based on advanced history matching solutions to constrain 3D stochastic reservoir models to both production history and 40 seismic attributes. In this approach, geostatistical modeling, upscaling, fluid flow simulation, downscaling and petro-elastic modeling are integrated in the same history matching workflow. Simulated production history and 40 seismic attributes are compared to real data using an objective function, which is minimized using a new optimization algorithm based on response surface fitting. The gradual deformation method is used to constrain globally or locally the facies model realization at the fine scale. Moreover, a new method is proposed to update the facies proportions during the optimization process according to 40 monitoring information. A successful application to the Girassol field is presented. Girassol is a large, complex and faulted turbidite field located offshore Angola. A detailed geostatistical geological model has been build first to describe the reservoir heterogeneity at the fine scale, in good agreement with 3D base seismic data. In a second phase, this model has been constrained to production data and 40 seismic attributes, using the gradual deformation of facies realizations and the calibration of facies proportions. The integration of 40 seismic data led to better production forecasts and improved predictions of a new seismic survey shot two years after the history matching period. The 40 seismic data has also made it possible to better characterize the spatial distribution of heterogeneities in the field. As a result, the underlying fine scale geological model has been improved in a consistent way with the fluid flow simulation model and observed data.