This paper describes a new concept for steel tube umbilical, with an integrated optional methanol or service line. The theoretical basis of the umbilical concept is established, based on existing experience form flowline bundle developments.
The umbilical characteristics are calculated. In particular the characteristics of the static Integrated Service Umbilical for the Troll Oil development in the Norwegian sector of the North Sea is given as an example.
The steel tube umbilical termination design is described. This design is based on a mechanical hang-off of the different elements in the umbilical.
The steel tube umbilical concept is taken through an extensive qualification test program in a purpose built test set-up, to verify the behaviour during manufacturing and installation. A thorough description the test program and the results will be presented.
The steel tube umbilical is manufactured in continuous lengths in a dedicated manufacturing plant. Capacities and limitations of the manufacturing plant are presented. In addition, experiences from manufacturing of the first lengths of the static Integrated Service Umbilicals for the Troll Oil development are presented.
The steel tube umbilical concept is applicable for remote control of subsea production systems in all known water depths. The present design is qualified for static applications.
The paper presents results from the qualification tests, and limitations of the concept is given.
The axial strength provided by the steel tubes eliminates the need for a separate tensile armouring. Thus it is less complex to manufacture.
The concept fits hydraulic, electrohydraulic and integrated umbilicals. Limitations of the concept with respect to number of lines, sizes, etc. in the cross-section are presented.
Manufacturing capabilities are discussed. With respect to conventional thermoplastic umbilicals the steel tube umbilical concept presented is an improved design, allowing full control of the stresses and strains.
The current trend among oil companies is a move towards extensive use of subsea production systems to develop new fields. These production systems are remotely operated from an adjacent manned installation via electro-hydraulic umbilicals.
Early subsea completions involved single satellite wells at short step-out distances. Lately the pattern of subsea development has changed considerably, with the introduction of many more satellite wells at much greater step-out distances, and multi-well templates which necessitate dozens of separate control functions.
Conventional umbilicals use thermoplastic hydraulic hoses. This design has met a number of problems which range from minor ones not influencing the operation, to major failures causing service interrupts. Typical problems are:
chemical attack on the thermoplastic hose
diffusion of fluids through the liner wall
hose collapse
service life time
The high frequency of failures observed with thermoplastic umbilicals obviously calls for a new design. Based on experience gained in flowline bundle development, a novel concept for umbilicals is developed, in which metal tubes replaces the thermoplastic hoses.
