Hydrate And Wax Prevention of Risers By Electrical Heating

The traditional methods for hydrate prevention by use of chemical treatments have considerable operation costs and represent a risk to the environment. Especially for deep-water fields electrical heating of pipeline systems is attractive. Norwegian oil companies have since 1986 been investigating alternative electrical heating methods for prevention of hydrates and wax plugging the pipelines. A joint industry project "Concept Verification - Direct Heating of Oil & Gas Pipelines" was initiated in 1996 and terminated in October 1999. During this work the electrical heating system was proved to be feasible on several fields in the North Sea and is installed on 7 flowlines of 13% chromium (Crl3) material with a length between 6 km and 16 kin. The work is continued to implement electrical heating of rigid steel risers. Flexible risers with hot water heating - IPB (Integrated Production Bundles) - have been developed and tested for application in shallow and deep water. Electrical heating of flexible risers is being reviewed in the present programme. Different configurations of steel risers are studied with individual and simultaneous heating of random selected risers. Some development work of cable and connector technology is scheduled for application in 2000 m water depth. The single-phase power supply to the heating system is based on commercially available components and connected to the platform power supply. Application of a frequency converter is evaluated for optimising the heating system. The electrical heat is used to maintain or raise the thermally insulated steel riser temperature above the critical value for hydrate (typically 15 – 25°C) or wax formation (typically 20 - 40°C). Both heating during planned shutdowns and continuous heating are evaluated. Melting of plugs are considered, but must be handled carefully due to differential pressure problems.