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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.