4-D uncovers more oil

July 8, 1999, 10:00 CEST

Hidden oil pockets in the Gullfaks field are to be uncovered with the help of four-dimensional seismology.

The method which is new and relatively untried, compares data from three-dimensional surveys performed in the same field at different points of time. Time is the fourth dimension.

"This is pioneering work," says Lars Kristian Strønen, staff geophysicist in Statoil's Gullfaks organisation.

The last time 3-D seismic was shot in the Gullfaks field was in 1996. The seismic vessel Geco Topaz recently completed an identical survey in the same area. Once the data from this survey has been processed, Statoil's specialists will have two new sets of seismic data from different periods of time. By interpreting the charts it will be possible to "read" what has taken place in the reservoir during the past three years.

"Four-dimensional seismology is an important tool for enhancing recovery from the Gullfaks field. It will help us to position new production wells optimally, in relation to where the oil is situated in the reservoir, " says Mr Strønen. He adds that two drilling teams are engaged in drilling new production wells from the three platforms at any given time.

The Gullfaks reservoir is complex and contains many faults. The main field consists of a number of smaller fields that are connected with each other. It is therefore important to increase understanding of the reservoir, according to Mr Strønen.

He believes that 4-D seismic will be adopted mainly in a reservoir's problem areas.

Since it started up in 1996, the Gullfaks field has produced about 1.6 billion barrels of oil. Recovery will increase from about 2.1 billion barrels to about 2.3 billion barrels by 2016. Roughly 245 million barrels will be recovered by raising the recovery rate from 54 to 61 per cent.