Subsea Local Heating, a Versatile Thermal Booster to Optimize Flow Assurance

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 tiebacks, 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 have been designed mainly to operate under transient operations (start-up, shutdown, preservation), this heating technology can be operated continuously during production and also during transient operations as long as there is fluid circulation in the flowline. The device is a very simple and robust system integrated into a compact subsea module, installed in parallel or in-line with the main flowline and which can be retrieved for maintenance or relocated. It 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 could also be a way to mitigate uncertainties on production fluid temperature or solve an unexpected poor thermal performance of the design. 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 main principles of the technology will be described in the paper, as well as a preliminary design performed for a specific case provided by an operator. The paper will also present the qualification work recently performed including heating performance lab tests using 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 paper finally describes the last qualification phase the objective of which is to install a subsea pilot to be connected to a subsea production system on a field located in Brazil. The intention is to perform this work in the frame of a Joint Industry Project.