The interest in Direct Electrical Heating (DEH) is increasing and the system is being planned for flow assurance in development of oil fields on continental shelf around the world. The DEH system is selected due to several advantages:
Allow production of fields that earlier is considered as not feasible
Effective solution with high heat input
Easy to install and operate
Reliable components
Can be retrofitted on pipelines in operation
Implementation require minor modification
The running costs are considerably reduced compared to traditional methods utilising chemicals.
At present it is installed on several subsea pipelines in the North Sea and DEH is applied actively to prevent hydrate formation during shut downs for a total accumulated use of 1 year during the lifetime of the field. For the new fields being planned with DEH there are several challenges due to extended design basis regarding:
Continuously use of DEH during the lifetime of the field.
Flow assurance of waxy unprocessed wellstream, requiring large heat input to the pipeline.
Impact of steel armoured concrete pipe weight coating
Use in shallow water
Heating of risers and spool-pieces.
As the pipeline is an active conductor in the heating system a special anode design is required, both to ensure sufficient grounding for the heating system and for corrosion protection regarding ac (alternating current). The design of the anode system is strongly related to time of use. This is one of the main challenges with continuous operation of DEH. Furthermore the design of the electrical cables is important regarding mechanical and thermal stresses. The lifetime of the cable depends on several factors. The lifetime of the DEH installation decreases with increasing cable temperature and with frequent use.
