Evaluation Qualification of Electrical Heat Trace Pipe In Pipe for a SS Flow Line and Selection for an Application on a Subsea Field in UK, ISLAY

摘要

Long tie-backs are increasingly being considered for deepwater field developments with intermediate or smaller reserves andrnflow assurance issues. The architecture of the Flowline then becomes a key feature of the development. The Total group hasrnreviewed several solutions for flowline optimizion and, among the different technologies available, has identified the ElectricalrnHeat Trace Pipe In Pipe (EHT-PIP) as an interesting option, with higher energy efficiency, which could limit the impact on thernhost platform. This paper presents the technology of EHT-PIP, and its evaluation-qualification prior its selection for a firstrnapplication, Islay field, offshore UK.rnEHT-PIP technology involves the inclusion of heat tracing cables in a standard PIP, between the outer wall of the inner pipe,rnand the thermal insulation. Once installed, it can be used safely and with good operability in the different required modesrn(maintaining the fluid temperature above critical points, or as a controlled warm-up, or for heating the fluid duringrnproduction).rnFor flow assurance reasons (hydrates, wax, pour points), subsea flowlines generally require highly effective insulation but longrntie-backs push to the limit the conventional passive insulation solution, unless a dual loop configuration is adopted. Anotherrnsolution is to implement an active heating system. Various alternatives for this, such as the direct electrical heating systemsrn(DEH) and hot water circulation (HWC), have been analyzed, but they showed poor energy efficiency. They also presentedrnlimits for long term usage, either linked to the higher electrical current required – heavy qualification of connection andrninsulation material, for example- or operational issues-, although past applications include some positive experiences, on shortrnterm usage. In comparison, the EHT-PIP, requires significantly lower voltage and offers greater efficiency. However, althoughrnit has been proven in surface, the solution is less mature for subsea flowline. Total has undertaken an “EvaluationrnQualification” on this emerging technology. This in-house method is used to improve Total’s capacity to select innovativerntechnology, while adequately addressing the risks and uncertainties before an implementation. Several future applications ofrnEHT-PIP were being considered, in the UK (one with a 6-km flowline presenting a hydrate issue, Islay, another 27 km long,rnetc.) and in another deepwater areas. The assessment resulted in a list of 12 technical uncertainties to be resolved. Therncorresponding program - RMP (Resolution Management Plan) - was discussed with 2 contractors developing this technologyrn(ITP and Technip), and subsequently executed. The results (with full validation of the thermal model, demonstration ofrnreliability and long-term cable ageing test, etc.) were positive and the technology was considered valid with both contractorsrndesign for application on the first full-scale industrial project, ISLAY, for the 6-km flowline. Here, the EHT-PIP will berndeployed as a secondary hydrate prevention method. During the life of the field, the system will be operated and monitored atrnregular intervals. Once proven on this subsea flowline, it will be deployed on 6 similar potential subsea tie-backs, where itrncould improve the economics, and eliminate methanol injection. The validation of this technology therefore offers to TOTAL arntechnically and economically optimized solution, for future long subsea tie-backs with greater operability, even with difficultrnfluids and isolated, distant reservoirs.