Precommissioning offshore Libya

The company’s Pipeline & Specialty Services division began work on this contract, worth approximately $4.5 million, in September, 2004.

The Bahr Essalam pipelines and the Sabratha platform are located in the NC-41 field, 110-km off the Libyan coast, in waters approximately 220m deep. Gas from the subsea production wells and pipeline manifold structures passes through a 22-in gas pipeline and 8-in insulated pipe to the Sabratha platform for initial processing. Products are then exported from the production platform to the Mellitah onshore facility via a 107-km, 36-in gas pipeline, and a 10-in condensate pipeline. Final processed gas is compressed and sent to Europe via the Greenstream pipeline. A 4-in service line was also included in the pre-commissioning package.

The workscope was divided into two phases: the first comprised simultaneous onshore and offshore flooding, cleaning, gauging, and initial hydrotesting of all the lines. The second phase involved testing of the pipelines after final tie-ins, including further hydrotesting, dewatering, air drying of the export pipelines, methane-rich-gas swabbing of the infield pipelines, and nitrogen purging and packing of all the pipelines.

Given the difficulties in sourcing a reliable supply of cryogenic nitrogen in Libya, Weatherford’s membrane nitrogen technology was ideally suited to this project. Based on the Sabratha platform, the membrane nitrogen units occupied much less space than nitrogen tanks, and provided an unlimited source of nitrogen for purging and packing of the export and interfield pipelines.

Part of Weatherford’s temporary air compression station (TACS), previously deployed for Saipem during the Greenstream project, was used offshore for the dewatering operations, and another part of the TACS was used onshore, at the Mellitah terminal, for the dewatering of the 36- and 10-in export pipelines.

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