Frigg Cessation Project

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 148626, ’The Frigg Cessation Project,’ by Jean-Claude Berger, Total S.A., prepared for the 2011 SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, 6-8 September. The paper has not been peer reviewed. The Frigg Cessation Project included the removal of six topsides, three steel jackets, and sealines with an estimated weight of 87 000 t. The project is unique because the field straddles the border between Norway and the UK. Both Norwegian and British statutes apply, depending on the location of the platforms. The main execution phases are described, from the offshore latch down, removal, and transportation to the onshore disposal of the installations. Introduction The Frigg field was a natural-gas reservoir on the North Sea continental shelf. The field was discovered in June 1971 in the Norwegian Block 25/1. In April 1972, gas was encountered in the neighboring UK Block 10/1. In July 1973, the Frigg licensees signed a unitization agreement regulating the split of the reserves between Norway and the UK. In May 1976, the Norwegian and British governments signed an agreement, known as the Frigg Treaty, under which Elf Norge (now Total E&P Norge) was defined as the operator of the Frigg field while Total Oil Marine (now Total E&P UK) was defined as operator of the gas-export system. Development of the Frigg field took place between 1973 and 1977 and consisted of five platforms (Fig. 1). Three platforms were in UK water—one drilling-and-production platform (CDP1), a treatment platform (TP1), and a living-quarters platform (QP). The two other installations were in the Norwegian sector—one drilling-and-production platform (DP2) and one treatment-and-compression platform (TCP2). Three of the platforms, TP1, QP, and TCP2 were linked permanently and formed what was known as the Frigg Central Complex. Three of the platforms—CDP1, TP1, and TCP2—and the intermediate platform MCP01 had concrete gravity-base substructures; QP and DP2 had steel-jacket substructures. The topsides of all platforms consisted of steel decks supporting several modules and pieces of equipment. First gas was produced from Frigg to St. Fergus in September 1977. In October 2004, the Frigg reservoir was finally shut in, having delivered approximately 192×109 std m3 of gas to the UK domestic market.