In this paper, we first present a global heat balance analysis of typical deepwater pipelines for oil and gas production and show that active heating is necessary for long pipelines due to technical limitations of passive thermal insulation systems. Two methods of combined active heating mid passive insulation are then considered. By the first method, active heating is provided by circulating hot water in annulus. Under certain simplifying hypothesis, we provide a close form analytical solution for the temperature profiles of the produced fluid and heat medium. By the second method, active heating is provided by electrical resistance on the inner steel pipe. For this case, we propose a heating method that minimises the power requirement for a given minimum temperature of produced fluid. Numerical results are shown for the second heating method. Significant reduction in power requirement is achieved.

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