In August 2016, the TEN field operated by Tullow Oil Plc produced first oil. We take a look behind the scenes of this impressive ultra-deep offshore project off the coast of Ghana.
Vallourec was selected to supply 15,000 tons of seamless tubes in non-standard dimension and fully integrated services including welding dedicated to the subsea infrastructure in the context of the TEN project in 2014. The abbreviation TEN stands for Tweneboa, Enyenra and Ntomme, the three fields comprising the project operated by Tullow Oil Plc situated in the Tano block, around sixty kilometers offshore Ghana. The reservoirs are spread over 500 square kilometers, and lie in water depths ranging from 1,000 to 2,000 meters. The dimensions and technical complexity of the TEN development plan are impressive: it foresees up to 24 wells connected to a FPSO with a nominal production capacity of 80,000 barrels of oil per day once the project is fully developed. After having produced first oil in August 2016, TEN entered its ramp-up phase.
To accompany its customer in this vast project, Vallourec helped co-design a custom offer comprising products, services and project execution. In particular, Vallourec supplied production flowlines and gas export lines in non-standard dimensions to comply with the customer’s requirements and optimize the weight of the subsea infrastructure. Moreover, Vallourec offered a specifically designed pipe-in-pipe solution that performs outstanding tolerances for both the diameters of the outer pipe and inner pipe, with coating, dedicated sleeves and a unique welding solution realized by welding specialist and Vallourec subsidiary Serimax. In order to guarantee optimal quality and save time on the pipe-laying vessel, the tubes were pre-assemble and welded one to another by Serimax before a partner company proceeded with the PIP assembly, resulting in a final product 24 meters long and ready to be used by the customer.
Stéphane Chrobot, Project Director at the time, explains some of the product’s characteristics: “The PIP solution serves the purpose of thermal isolation. It basically consists of two tubes, one inserted into another. The ends of the outside tube are then welded to the wall of the inner tube, allowing the creation of a vacuum between the inner and the outer tube. It works very much like a thermos, with the exception that in our case, we are dealing with tubes that weigh several tons. This insulation is necessary to ensure that the temperature of fluid flowing through the inner pipe from the wellhead to the FPSO
remains above the temperature at which hydrates or waxy deposits can form and cause an undesired change in the flow characteristics. Operating at the bottom of the ocean, at depths of almost 2000 meters, the temperature differences when oil leaves the well can cause a thermal shock that may lead to obstructions and bottlenecks in the steel tube. The PIP solution allows for a gradual change in temperature. At the same time, the isolation has to withstand all the other mechanical stresses associated with ultra-deepwater offshore operations, such as pressure and corrosion. We could offer a steel PIP product since Vallourec has a vast expertise in this field. In order for everything to work, the tubes have to respect very thigh tolerances in terms of straightness and diameter. Thanks to the knowhow of the teams in our rolling mills, we were able to reach the necessary degree of precision.”
Tullow TEN raised the threshold of subsea offers for Vallourec as it contains not only technical and industrial value, but also a considerable amount of project management, coordination and logistics, making integration the key concept throughout the entire project.
Stéphane Chrobot describes: “Integrated planning, where you can monitor the whole execution, has a great advantage: at any given moment, you can trigger corrective actions and adapt the workflow of all partners consequently. We learned to become more adaptable, predict bottlenecks and foresee risks at a very early stage and better adapt to client modifications or needs. This is the ultimate time-saver. For instance, early in the project, the client decided to increase the quantity of the sleeves . In theory, it was simple, but necessitated nevertheless various adaptations in the production process. In a non-integrated planning organization, we would not have been able to modify all the slots on such short notice: inform the mills, anticipate the workload in the cutting workshop, adapt the coating phase etc. Without wasting time we were able to focus on quality and delivering.”
“The trickiest part was managing the assembly-phase in a workshop in Caen, where we finalized the 24meter long sections with the pipe-in-pipe and welding. We optimized the flow of delivery of the pipes so there wouldn’t be too many pipes at the same time. Remember, the whole order is 15,000 tons, corresponding to hundreds of kilometers. We set up an intermediary platform in the north of France so the products would arrive regularly, according to production and to the project’s real-time schedule. This definitely represents value for the customer, as he has neither bottlenecks in terms of storage nor organization to manage. Just in time is what you want to aim for.”