ABSTRACT: Gullfaks Oil Field--from Challenge to Success
Henrik Carlsen, Ole Nygaard
The giant Gullfaks oil field was discovered in 1978. The field contains oil reserves in excess of 1.3 billion bbl. The field is located in the northeastern part of Block 34/10 in the Norwegian sector of the North Sea.
Gullfaks represents the shallowest structural element of the Tampen Spur and was formed during the Late Jurassic to Early Cretaceous as a sloping high with a westerly structural dip gradually decreasing toward the east. The major noah-south-striking faults, with easterly sloping fault planes, divided the field into several rotated fault blocks. Central and eastern parts of the structure have been eroded by the Early Cretaceous transgression.
The reservoir sandstones are comprised of the Middle Jurassic delta-deposited Brent Group, the Lower Jurassic shallow-marine sandstones of the Cook Formation, and the Lower Jurassic fluvial channel and delta-plain deposits of the Starfjord Formation.
The presence of gas in the post-Jurassic section and a variable water depth have complicated seismic interpretation. However, the improved quality of the 1985 three-dimensional seismic survey and deliberate deepening of development wells have resulted in a more accurate and complete structural interpretation.
The Brent reserves in the western pan of the field currently are being developed by the Gullfaks A and B platforms. The eastern pan of the field is developed by a third platform, Gullfaks C. Water injection is the major drive mechanism maintaining reservoir pressure above the bubble point.
One of the most important factors in the reservoir development has been the effect of fault transmissibilities on lateral and vertical pressure distributions. A comprehensive data acquisition program, including permanent downhole pressure gauges, have enabled accurate monitoring of the strategic injection and production plan. To characterize fluid movement, radioactive tracer has been injected into selected water injection wells.
Long-term field development planning using a full-field simulation model has been supplemented successfully though the use of smaller
detailed fault block models. Well locations and drilling schedules are continuously updated incorporating information from new wells and the latest production data.
AAPG Search and Discovery Article #91000©1990 AAPG Conference-Giant Oil and Gas Fields of the Decade 1978-1988 Conference, Stavanger, Norway, September 9-12, 1990