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Reservoir Model Update Using 4-D Seismic Data


Lefeuvre, Frederick, P. Sexton, J. M. Jourdan, P. Berthet, A. Veillerette, R. Deboaisne, Total, Pau Cedex, France


The Girassol field is located in Angolan deep water of Block17 and consists of large ver­tically stacked turbidite complexes. The reservoir extends over approximately 200 km2 and the water depth varies between 1300 and 1400 meters. In this context High Resolution 3D seismic is a valuable tool to describe and monitor the reservoir. Light oil production started end 2001 and has been maintained at an average rate above 200000 barrels per day. Production gas recycling has been included in the development plan and reservoir engineers have to take into account re-injection of gas into the reservoir top. Monitoring of this injec­tion was the main reason to shoot the first 4D extremely early in the life of field, end 2002. Thanks to a very carefully controlled acquisition-repeatability and, despite the complexity of interpretation due to multi-phase fluid situation and pressure effects, the first 4D images were of high quality. More was visible than expected and the first monitor data was success­fully used to update and refine the reservoir flow model. For instance, the reservoir model has been updated to better represent the gas bubble extension and the water injection responses. Because of these good results and to go further in the field monitoring, a sec­ond 4D was shot end 2004, to continue monitoring gas injection but also to monitor water injection, contact movements and homogeneity of the oil production. The new 4D data will be used to validate and further refine the reservoir model.