Direct Electrical Heating for Shallow Water Installations during Continuous Operation

摘要

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:rn1. Allow production of fields that earlier is considered as not feasiblern2. Effective solution with high heat inputrn3. Easy to install and operatern4. Reliable componentsrn5. Can be retrofitted on pipelines in operationrn6. Implementation require minor modificationrn7. The running costs are considerably reduced compared to traditional methods utilising chemicalsrnAt 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.rnFor the new fields being planned with DEH there are several challenges due to extended design basis regarding:rn8. Continuously use of DEH during the lifetime of the field.rn9. Flow assurance of waxy unprocessed wellstream, requiring large heat input to the pipeline.rn10. Impact of steel armoured concrete pipe weight coatingrn11. Use in shallow waterrn12. Heating of risers and spool-piecesrnAs 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.rnFurthermore 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.rnIt is necessary to obtain the electrical and magnetic characteristics of steel pipe materials. Both these characteristics determine the pipeline impedance. These data are required input for rating (electrical and thermal) of DEH and the anode design layout.