SHELL PLANS TO REDEVELOP BIG NORTH SEA FIELD

Shell U.K. Exploration & Production plans to redevelop Brent oil and gas field, one of the largest in the U.K. North Sea. The project could cost as much as 1 billion ($1.77 billion). It will involve refurbishing and reequipping platforms and producing the reservoir at lower pressures to achieve top recovery. Walter van de Vijver, Shell petroleum engineering manager in Aberdeen, said the Brent project is unique. "The industry has never attempted anything like it on such a scale. In effect, we

Nov. 25, 1991

4 min read

Shell U.K. Exploration & Production plans to redevelop Brent oil and gas field, one of the largest in the U.K. North Sea.

The project could cost as much as 1 billion ($1.77 billion). It will involve refurbishing and reequipping platforms and producing the reservoir at lower pressures to achieve top recovery.

Walter van de Vijver, Shell petroleum engineering manager in Aberdeen, said the Brent project is unique.

"The industry has never attempted anything like it on such a scale. In effect, we are reversing development of the field."

BRENT'S SIGNIFICANCE

Brent, with four production platforms and reserves of 1.8 billion bbl, is among the most important fields in the U.K. North Sea. A redevelopment that extends its life would be one of the most significant advances on the U.K. continental shelf in several years.

Brent's significance stems from its position as the hub of two major oil and gas pipelines.

It is the offshore terminal for the multiuser Brent oil pipeline to Sullom Voe terminal in the Shetlands Islands. It also is the center of a complex gas gathering network in the area east of the Shetlands that links into the Flags gas pipeline to St. Fergus, Scotland.

Proposals for redevelopment come at the end of a difficult time for Shell. Its oil production last year averaged only 73,000 b/d, and after a period of lengthy offshore shutdowns production has just returned to an average 210,000 b/d.

The field is still capable of producing about the 400,000 b/d level achieved in the mid-1980s. But because of extensive off shore work that will be required by the redevelopment program and refurbishment ahead of that program, production is likely to remain at less than 250,000 b/d.

In 1988, before the field ran into problems with its platforms, Brent associated gas peaked at an average of a little less than 500 MMcfd.

BIG CHANGE

By lowering the reservoir pressure Shell will turn Brent from an oil producer with associated gas into a gas producer with associated oil.

John Struik, Brent field general manager, said redevelopment will yield more oil and gas and extend the field's gas plateau well beyond 2000.

Shell currently injects water into the base of the Brent reservoir to move oil upward for production.

Van de Vijver said, "In future we will pump water out of those same wells to reduce pressure. This depressurization process will allow the gas cap to expand gradually, which will allow additional oil recovery as well as significant gas recovery."

The redevelopment program has been agreed to in principle but still needs final confirmation from the partners in the project, Shell U.K. Ltd. and Esso U.K. Exploration & Production. If this is obtained, detailed design work will start in 1992 with offshore work beginning in 1994.

Stuik said a number of interim upgrades will be needed to ensure reliability of the four platforms before redevelopment work begins. The first upgrade will start on the Brent Delta platform in 1992.

Van de Vijver said because reservoir pressure will be lowered to 40 bar (580 psi) from about 130 bar (1,885 psi), present topside facilities can no longer be used. Vessels will be too small to handle the volumes of gas Shell expects to produce.

Shell will change separation and compression equipment and add equipment to handle more water. The remaining facilities will be refurbished.

That will result in platforms with low pressure option facilities, designed for 20 years of operation.

Only three of the four platforms will be involved in the low pressure production project. Brent Alpha platform, to be upgraded and refurbished, will remain an oil production platform associated with South Brent development.