Patent Application
20070253778
The present invention relates to a power umbilical for transfer of large quantities of electric power, fluids and electric current/signals from the sea surface to equipment located on the sea bed, in particular in deep waters, comprising a number of power conducting cables, pipes and electric conductors/wires collected in a bundle, a filler material arranged at least partly around and between the pipes, cables and conductors/wires, and a protective sheath enclosing the pipes, cables, conductors/wires and the filler material.
In the later years it has been more common to locate the production equipment for oil and gas wells on the sea bed. For operation thereof supply of electric power is required, not only electric conductors to control operations, but also heavy cables for transmission of electric power to electric driven equipment like huge booster stations performing conveyance of recovered oil and/or gas.
Such heavy cables, normally manufactured of copper wire, are now integrated into the more traditional umbilical, which in turn is under continuous development and alter its construction and functions according to actual needs. These heavy electric cables having substantial transversal cross section provide the umbilical with considerable added weight due to the specific gravity of copper. Knowing that the copper material has a very poor load carrying capacity, the water depth at which the umbilical with its traditional construction can be used is very limited.
The traditional umbilicals of this type are constructed as a composed structure which is able to transfer hydraulic liquids, chemicals, fluids, electric and optical signals and electric power between equipment on the sea bed and on the sea surface. An early version of such umbilicals is known from WO 93/17176. Typical for this umbilical is that most of the load transfer took place in a centrally located steel pipe of substantial dimension. Further examples of prior art are disclosed in GB 2 326 177 A and GB 2 326 758 A, all having the same assignee as the present invention.
It is to be understood that in the present description and patent claims it is made a clear distinction between electric cables, i.e. the heavy ones having a large transversal cross section area, and the electric conductors and wires, i.e. the thinner ones having small cross section area. Each electric cable is able to transmit large quantities of electric power, while the electric conductors or wires are used to transmit small quantities of current and control signals.
Instantly it appears that steel rope could be used as load carrying elements. This, however, do not solve the problem in considerable extent. Steel rope also ads substantial weight and in combination with the heavy copper cables, one do not reach large depths before the power umbilical achieves yield stresses and are torn off due to its own weight.
Substantial efforts and resources have been used in order to find a solution on how to be able to transmit large quantities of electric power down to the sea bed at real large sea depths, such as 1500 meters and more.
This is now solved by combining a technology that is developed by the assignee of the present invention, viz. the technology that is used for tension legs of floating platforms. See for example WO 02/057560 A1.
Thus, according to the present invention a power umbilical of the introductory said kind is provided, which is distinguished in that the power umbilical comprises separate load carrying elements, which load carrying elements are light weighted rods of composite material. The light weight rods of composite material may preferably be carbon rods having embedded strength fibers. The rods can either be collected in bundles or appear individually or in a combination thereof.
Composite material has that excellent property that the material has approx. the same load carrying capacity as steel, at the same time as the weigh is reduced to about 10% of that of steel. Thus the load carrying elements do not contribute substantially to the total weight of the power umbilical which thereby provides an option to use the power umbilical in deep waters. One may get so much deeper as the weight reduction allows.
One recognize the use of rods of composite materials also in the traditional umbilical, even if the invention was conceived with regard to that the umbilical should be in the form of a power umbilical designed to transmit substantial quantities of electric power. This is dealt with in simultaneously filed International patent application no. PCT/NO05/00216.
In one embodiment the filler material, the pipes, the cables and the conductors/wires can be laid in a helix or spiral configuration about the longitudinal axis of the power umbilical.
In a second embodiment the filler material, the pipes, the cables and the conductors/wires can be laid in a substantially rectilinear configuration without any essential twisting or spiraling.
The load carrying elements of the power umbilical can be collected in a twisted or spiraling bundle that is located centrally as a core element within the power umbilical.
As an alternative the load carrying elements of the power umbilical can be distributed to a number of bundles located peripheral relative to the longitudinal axis of the umbilical.
As an alternative the power umbilical can also include weight elements in order to ad mass/weight to the umbilical, either in all its extent or in some sections. Weight elements will be used in those instances where the umbilical has a tendency to become buoyant such as in shallow waters.
The filler material, the pipes, the cables and the conductors/wires can be laid in several layers viewed in a radial direction.
In some embodiments the power cables can be collected in groups in the cross section.
In one embodiment the load carrying elements can consist of single rods that are distributed within the transversal cross section, and some may possibly be located adjacent to each other without thereby being collected in a bundle.
Even if not strictly necessary, the filler material will in a suitable embodiment be in the form of elongated channel elements that are able to at least partly enclose the respective pipes, cables and electric conductors/wires in order to keep these in position relative to each other.
Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which are given for the purpose of description, and given in context with the appended drawings where:
It is to be understood that it is possible with two variants of the transversal cross section of the umbilicals shown in
The power umbilical according to
The power umbilical according to
The reference number 9′ can denote a friction material, like a rubber sheath, lying around the load carrying element 7.
These elements are repeatedly found in most of the figures and are denoted with the same reference number in the respective figures. However, it is to be noted that
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004 2557 | Jun 2004 | NO | national |
| 2004 4671 | Oct 2004 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO05/00215 | 6/17/2005 | WO | 1/30/2007 |
