Subsea Induction Heating Technology Solves Hydrate and Wax Issues in Subsea Flowlines

Abstract

A new technology called local heating offers the possibility of significantly raising the temperature of the multiphase production fluid in order to improve flow assurance and consequently the economics of 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. While other heating technologies such as DEH and Heat tracing are only used under transient operations (start-up, shutdown, preservation), local heating is a different solution, mainly to be used continuously during production and also during transient operations as long as there is fluid circulation in the flowline. The local heating device is a very simple and robust system integrated into a compact subsea module, installed in parallel of the main flowline and which can be retrieved for maintenance or relocated. The technology is compatible with any type of field architecture and can be implemented either on greenfields or brownfields. In the case of greenfields, the use of local heating is a way to mitigate uncertainties on production fluid temperature or solve an unexpected poor thermal performance of the design. The main principles of the local heating technology, as well as a preliminary design performed for a specific case provided by an operator, will be described in the paper. This solution is based on induction and is therefore able to provide very high-power levels (several MW) with a compact module. The temperature is continuously monitored throughout the heating module by means of fiber optic distributed sensors. The technology is fully compatible with preservation by flushing and allows pigging in the event of deposits. The paper will also present the qualification work performed by Saipem to date including heating performance tests performed mid-2018 on a small-scale submerged prototype operated under atmospheric conditions with multiphase fluid. The tests have confirmed the good electrical and thermal behaviour of the system. The next qualification step entails new tests to be performed on a medium scale prototype using crude oil as process fluid. The main objective is to qualify the heating performance tests and the fabrication method of the local heating module under representative conditions: representative process fluid and representative module geometry. The intention is to perform these tests on an existing Brazilian onshore test site in the frame of a JIP.