CFD Modelling of an Electrically Trace Heated Blanket

Abstract The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties. CFD models of the test set-up have been built to replicate the thermal behaviour of the ETH-Blanket prototype. Once validated against the test results, the final aim of CFD modelling is to be able to calculate the performances of the system in real subsea conditions. The modelling of the prototype includes a 3D geometry of the system including the soil, natural convection of water between the ETH-blanket and the pipe sample and natural convection of fluid in the pipe sample. The present paper focuses on the CFD work performed to match the full-scale thermal test results and to predict the ETH-Blanket performances for real subsea operating conditions. It will describe the various CFD models used, the sensitivities and findings in terms of local and global heat transfer and flow effects and the comparison to the experimental data.