Design and Development of Electric and Hydraulic Cables for Subsea Wellhead Control in the North Sea

Abstract

Summary This paper presents a development program, from design formulation to field test, for North Sea wellhead-control cables. Typical design considerations, desired performance data, and actual test results are included for both electric and hydraulic cables. Jointing, terminating, and installation techniques also are discussed. Introduction Subsea wellheads operating remotely from a tower or manifold center require electric and hydraulic power and control lines. These systems, some for North Sea installation from 1980 onward, require specially developed cables and terminations. These cables must maintain a stipulated performance and withstand handling and installation performance and withstand handling and installation operations. They must withstand seabed conditions and, in the unfortunate event of damage by trawler or anchor, be capable of recovery and repair. Cables against one of several contracts have been manufactured and installed in the North Sea during 1980. This paper discusses the general cable design requirements specified and the prototype development program. The values and design parameters given are not specific to any particular system and should be considered as purely typical results from a wide-ranging program. Typical Cable Specification Requirements Typical design and performance data, for both hydraulic and electric cables, are given in Tables 1 and 2 (Figs. 1 and 2). Various hose liners for the hydraulic cables may be specific for compatability with methanol, glycol, synthetic hydraulic fluids, and mineral oils. Cold flexibility and flammability tests also are called for in some specifications. Cable Environmental and Installation Requirements The following list summarizes some of the typical requirements.System operational life of up to 25 years.Both minimum and maximum breaking strains for the cables, about 20 and 40 tons (18 and 36 Mg), to give adequate strength but avoid damage to subsea structures if the cable is dragged.Adequate cable modulus for the water depth of installation, typically about 4 naut. miles (7.4 km).Torque-balanced cable due to J-tube and wellhead cable installation.System life resistance to corrosion and abrasion, and adequate weight in water to give stability.The significant but variable trawl and anchor fault hazard to cables in the North Sea calls for monitoring ship control. Suitably maneuverable cable ploughs now exist. Cable Design and Development Background The development team was able to draw on many years of worldwide company experience in the design, development, testing, and installation of underwater electromechanical cables. JPT P. 413