Groningen, Western Europe's biggest onshore gas field, faces upgrade

By the OGJ Online Staff

LONDON, Feb. 19 --
A $1 billion redevelopment program is planned to extend the life of Groningen, Western Europe's oldest and largest gas field, and to maintain its position as the Netherlands' key producer of gas for domestic consumption.

Operator Nederlandse Aardolie Maatschappij (NAM), a 50-50 joint venture of Royal Dutch/Shell Group and ExxonMobil Corp., will install compression equipment to maintain reservoir pressure at Groningen, which was discovered in 1959.

The field is believed to have ultimate reserves of 2.7 trillion cu m, with more than 1.5 trillion cu m already produced. Production from Groningen is now 150 million cu m/day, less than the 450 million cu m/day required by the country's domestic gas network. The drop stems from declining reservoir pressure -- now down to 2,031 psi from its original 5,033 psi.

Peak domestic gas supplies have been guaranteed by the use of underground gas storage facilities that are filled during the summer months.

Project details
NAM has begun installing compression equipment at each cluster of producing wells.

The field produces from 300 wells in 29 clusters, 14 in the southern sector of the field and 15 in the northern area. Each cluster is a standardized design with 5 treatment units. The southern clusters are designed to produce 15 million cu m/day, with the northern clusters capable of producing 25 million cu m/day.

NAM has maintained production at required levels by improving throughput rates at its treatment plants and by reducing flow resistance in wells and production pipelines. It also announced a $300 million program to renovate three well sites in the Slochteren sector of the field (OGJ, Dec. 24, 2001, Newsletter, p. 9).

Compressor installations will start with the larger clusters at a rate of 3 or 4 at a time, with initial work being completed by the end of 2004. The 14 larger clusters will each be equipped with 23 Mw compressors, and the 15 smaller clusters with 12 Mw compressors. Work on the smaller clusters will be scheduled as market conditions develop and on a schedule that will have all clusters fully operational during winter months.

Ironically, the compressors will be supplied with power under a contract NAM and a local utility company negotiated that uses gas from Norway's supergiant Troll gas-condensate field. Groningen gas is 81% methane and 14% nitrogen, which makes it ideal for use in the Netherlands' domestic network, officials said.

Unique compressor application
The option of electric compressors?the whole package being supplied by Siemens AG?was made after NAM conducted a total cost of ownership exercise involving three potential suppliers.

Wim H. de Groot, senior appraisal engineer at NAM, said, "The compressor application for Groningen is rather unique because the compressors will very seldom run at their maximum capacity. Most of the time [they] will even run at loads below 30%. This is mainly due to the balancing role as a gas supplier."

He said, "The environmental requirements in the densely populated Netherlands are extremely high. As large compressors need a lot of energy, it wouldn't be acceptable if we selected an energy-inefficient solution."

The turbines also are subject to stringent noise requirements. Because it operates in a flat landscape, the height of the installation is important. For safety, it is preferable to install the compressors in the open air, so there are no roofs and walls to affect maintenance, said De Groot.

The compressors utilize magnetic bearings and dry seals, so there is no need for oil skid equipment under the compressors, further reducing installation height.

LNG application
Statoil is evaluating use of electric compressors for its Snøhvit LNG project in northern Norway, where emissions have to be kept to a minimum under the development plan that is to be approved by the Norwegian government Mar. 1 (OGJ Online, Feb. 4, 2002).

Frank Stieler, head of industrial applications at Siemens, said the potential market for electric compressors in the exploration and production sector could be worth as much as $80 billion/year over the next 10 years.

He said, "The LNG market could grow dramatically over the next 10 years, and here again the energy conversion needs of these facilities provide opportunities to apply our technology and solutions. LNG plants need a utility-sized power station to produce the electricity needed for liquefaction and regasification processes. On [an] LNG platform, the compression trains could all utilize variable-speed electric drives. This concept makes the all-electric LNG plant one of the best examples of energy conversion solutions."