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Active heating technologies can be applied to subsea pipelines to tackle challenging reservoir flow assurance constraints that could take place during production shut down and normal subsea field operation (i.e. hydrate, gelling, wax and/or high oil viscosity). Implementation of active heating to subsea pipelines enables i) field architecture simplification and ii) long subsea tie-backs. The Electrically Trace Heated Pipe-in-Pipe (ETH-PIP) is a standard reelable PIP system enhanced with up to 4-off trace heating cables and 2-off fiber optic (FO) cables, for temperature monitoring purposes, spiraled against the inner pipe and covered by high thermal performance insulation allowing a high thermal system efficiency. The high thermal efficiency combined with a primarily resistive electrical system makes the ETH-PIP the most energy efficient active heating technology. Long power heating/transmission line can be described by the fundamental parameters resistance/inductance of conductor and capacitance/conductance of insulation. The analysis of the overall heating system can be assessed using three alternative models: i) the most simple and compact RL model where only total resistance and total inductance of line is included, ii) more advanced RLC model where the total capacitance of insulation is additionally included and iii) the most advanced distributed RLGC (resistance, inductance, conductance, capacitance) model where total length of line is modelled as a chain of shorter RLGC segment lengths. The accuracy of each model depends on multiple aspects such as: heating/transmission line parameters, required heating power, total length of line, mode of operation, environmental conditions, etc. The proper and careful selection of the appropriate model to ensure effective computation and results accuracy is paramount. The paper includes the detailed description of each heating/transmission line model. Additionally, each model is illustrated on a set of theoretical examples. |
