Retrofit Installation of Direct Electrical Heating for Deep Water Flow Assurance

摘要

Flow assurance is increasingly challenging as the oil and gas industry is moving towards deeper water and longer transport distances. Formation of hydrate and ice plugs in the pipelines will have major cost impact and must be avoided as removal of plugs is a challenging and time consuming operation. At deeper water plug removal by depressurization may be impossible. As a mitigation measure active heating may be applied. Direct Electrical Heating (DEH) is now in use on several pipelines on the Norwegian Continental Shelf. Studies are being carried out for application of this method as a retrofit installation, to be performed from a vessel for the cable installation and power supply to the heating system. A retrofit DEH system may be used in an emergency situation where hydrate and ice plug removal is required. When installing the DEH cable along the pipeline it is important to keep the distance (gap) to the pipeline small in order to limit the required supply current. Installation evaluation confirms that a maximum average gap of 0.5 meters between cable and pipeline is feasible. Calculation of required current and voltage confirms compliance with established cable design. In this paper an assessment on retrofit DEH for ice plug melting in deep water is made. Results from FEM analyses confirm the feasibility of melting ice plugs with DEH even for large diameter pipelines with high U-values. Dynamic analysis using state-of-the-art FEM shows that a cable without metallic armour can be designed to bear its own weight in rough weather during deep water installation and be connected to the pipeline using an ROV.