Local heating of subsea flowlines is a new technology block which can improve the economics of new field developments. Heating the flowlines is a way to overcome the thermal constraints, mitigate hydrate & wax risks and provide operational flexibility. Indeed in the case of long distance tie-backs, very deepwater applications or when the fluid temperature at the wellhead is too low, conventional flow assurance solutions might be very expensive or even not applicable.
Several heating solutions are already field proven. They are based on distributed heating technologies (DEH and Heat tracing) and are mainly considered for hydrate management under transient operations (start-up, shutdown, preservation). Local heating is a different solution, intended to be used continuously during production. A local heating device can be integrated into a compact subsea station, installed in parallel of the main flowline and which can be retrieved for maintenance or relocated to another place. The compactness is made possible by the use of induction heating which allows for the transfer of a high power density. The technology can be implemented either on new fields or for the extension of existing lines. It is fully compatible with preservation by flushing and allows pigging in case of deposits.
This paper will present an overview of the local heating technology, some preliminary designs and will then provide information on the prototype tests that are on-going. The main objectives of these tests are to confirm heating levels and heating efficiency for several heating power levels (up to 100 kW), estimate heat transfer coefficients under 2-phase flow regimes and validate cooling of heating coil by surrounding water.
A dedicated test loop has been built for these tests in order to operate the prototype (4 inch OD pipe) under a wide range of air & water 2-phase mixture at atmospheric pressure. The prototype is submerged in a fresh water tank in order to be as representative as possible for the cooling of the inductors.
The prototype is composed of 6 induction heating sections thermally insulated and is equipped with optical fiber network and thermocouples for the monitoring of the temperatures of the flowline, the process fluid and the heating coils.