Local Heating of Subsea Flowlines, A Way to Increase Step Out Distance with Conventional Thermal Insulation

摘要

Innovative flow assurance solutions are required to make new field developments both technically and economically feasible. 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 not be applicable. In this case, heating the flowlines is a way to overcome the thermal constraints, mitigate hydrate and wax risks and provide operational flexibility. Existing heating solutions 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, intending to be used continuously during production. Local heating allows for the integration of the system into a compact subsea station, installed in parallel of the main flowline, which can be retrieved for maintenance or relocated to another location. The technology can be implemented either on new fields or for the extension of existing lines. The purpose of this paper is to present an overview of the local heating technology under qualification by Saipem. The heat is provided using induction. This solution is thus able to provide a very high power density leading to a very compact solution. The internal diameter of the line in the heating station remains unchanged from the main production line, which makes the solution fully compatible with preservation by flushing and allows to pig the system in case of deposits. The temperature is monitored throughout the heating module by means of a network of optical fibers. The paper will introduce the main features of the technology, the main scenarios for which this solution is particularly suitable as well as the impact on the field operations. Information will be based on the results of flow assurance studies performed for various types of oils and field configurations. Some preliminary designs of the subsea station will be given, going up to 3MW of thermal power delivered to the fluid. Finally the paper will present the qualification testing recently conducted on a reduced scale prototype, with a description of the prototype and the main results obtained.