Numerical Study of a Hybrid Thermal Insulation With Phase Change Material for Subsea Pipelines

Flow assurance is critical in offshore oil and gas production. Thermal insulation is an effective way to reduce heat loss from subsea pipelines and avoid the formation of hydrates or wax deposits that could block the flowlines. This paper presents a hybrid thermal insulation model with a combination of phase change material (PCM) and conventional insulating layers. The idea is to use PCM to store thermal energy with normal oil and gas production and release heat back to the fluids during a shut-in operation. Melting and solidification of the PCM layer is analyzed for different thicknesses at both working and shut-in conditions. The model is developed numerically using a Finite Volume Method (FVM) and an enthalpy porosity technique. It accounts for heat conduction with liquid-solid phase changes, as well as natural convection in the PCM. In this study, paraffin is implemented as PCM with temperature dependent properties while Aerogel is used as the conventional insulation layer. The results show that ticker PCM layer than conventional insulating layer can significantly improve thermal insulation performance, with extended cool-down time during flow line shut in.