Statoil Contracts WesternGeco in First 4D Q-Reservoir Survey

Seeking to improve production from their Norne field, North Sea, Statoil has awarded WesternGeco a contract to conduct the world's first 4D Q-Reservoir(a) survey.

WesternGeco performed the baseline Q-Reservoir survey for Statoil on the Norne field in 2001, and the new survey, scheduled to begin in June, will enable the industry's first "Q-on-Q" data comparison.

"Statoil is a pioneer in 4D reservoir applications," said Dalton Boutte, president of WesternGeco. "They were an important contributor in the development of Q-Technology and were among the first to use it. We expect that data comparisons from these two surveys will provide the most accurate picture of the effect of production on the reservoir that the seismic industry can produce today."

Q-Reservoir is the WesternGeco proprietary suite of seismic technologies with marine, land, and seabed applications.

"A key feature of Q is calibrated, repeatable seismic measurements," said Ole Magnar Droenen, Peteksjef (Petroleum Technology Manager) of the Norne field for Statoil. "Our first Q survey on Norne confirmed that the repeatability was accurate enough to undertake a rapid, short-sequence reservoir monitoring campaign.

Western Geco Topaz

"To increase the oil recovery of the Norne field above 50%, it is necessary to use all available data to have a better picture of the drainage efficiency," Droenen said. "4D monitoring is very important in evaluating the oil-water contacts in the different segments, and we needed data with high repeatability and high signal-to-noise ratios. We chose WesternGeco's Q-Technology because of the repeatability provided by streamer steering and minimum azimuth variation between base and monitor surveys. The streamer steering also allowed us to pass closer to the Norne production vessel than we could with a conventional survey, and thus reduce the area of no coverage."

The Norne field has been in production for more than five years. In 2001, the owners Statoil (operator), Norsk Hydro, Agip, Enterprise/Shell, and Petoro decided to use 4D seismic surveys to monitor the oil-water contact and drainage of the field.

"As the field is situated on a flat-lying horst structure, the seismic analysis had to be based on highly repeatable time-lapse difference data," Droenen said. "Based on indications of areas where the oil has not been recovered yet, we can revise our drainage strategy and target where to drill our next oil producer."

"Time is a critical factor in the effectiveness of 4D," said Leif Larsen, marine vice president for WesternGeco. "While 4D has been proven technically, the time between surveys had limited its business value. However, with Q-Reservoir, the operator can take quick action, refine the way a field is managed, and maximize recovery. With only 18 to 24 months between 4D surveys on the Norne field, Statoil is taking full advantage of this capability."

The 4D surveys will allow Statoil to analyze changes in the field over time. Such information reveals how the reservoir is being drained and indicates where to locate new production wells. Use of seismic technology for reservoir monitoring is one of the most important tools oil companies have to increase the recovery and extend the life of the field. Q-Reservoir surveys provide the most enhanced images and repeatability in the industry through the use of steerable streamers, calibrated marine source, and calibrated single-sensor acquisition with a registration density (distance between hydrophones) that is four times greater than conventional systems.