Abstract

The Gullfaks Field located in block 34/10 of the Norwegian Sector, is one of the major fields offshore Norway. The field has been in production since 1987. The Gullfaks Field is regarded as a challenge to history match due to its complexity in faulting and communication pattern. In 1993 a project was launched to history match the production from the eastern part of the Brent Group. A joint operator/consultant multi-disciplinary team was established for the task to ensure optimisation and consistency of available data, as well as utilising experience from the field and earlier simulation models. Prior to initialising the model, a thorough data evaluation was performed and a pressure communication model was established. The grid was constructed honouring the geological model, in particular the fault pattern and angles. The simulation model was initialised according to the pre-established communication model, and no major adjustment to the communication pattern was necessary during the history matching. The reservoir energy was history matched as the first step by altering communication across faults, rock compaction and aquifer support. The water production was history matched thereafter, by altering the reservoir transmissibility in well areas, horizontal barriers and relative permeability curves. The history matched simulation model fulfilled the pre-specifications in terms of matching the RFT pressures within +/-5 bars. The water production was matched satisfactorily and water saturation was in accordance with GST and PLT logs. During the history matching process, adjustments in the model were always carefully checked for their physical validity before being implemented in the model. This resulted in a history matched model without artificial, non-physical features. The model is currently in use for production predictions for the Brent Group in the eastern part of the field. Only minor modifications in local transmissibility has been implemented during the one and a half years since this project was finalised.

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