Patent Application
20130263426
The invention relates to a method for offshore installation of a system for recovering hydrocarbons escaping from an underwater installation.
With the increasing number of offshore oil wells, there is an increasing risk of ecological accidents associated with hydrocarbons leaking from an underwater installation such as a wellhead or pipe, for example. The environmental consequences for the ecosystem can be irreversible and it is therefore necessary to intervene as quickly as possible to confine and recover the fluids escaping from the underwater installation in order to limit the environmental consequences linked to the outflow of these hydrocarbons into the marine environment.
To this end, it is known to deploy vertically above the damaged underwater installation bells having the shape of an inverted funnel to channel hydrocarbons escaping from the installation and recover them on a ship by means of a recovery pipe connecting the recovery bell and the hydrocarbon recovery ship.
Application WO2005/038145 in the name of the applicant discloses a recovery device comprising a rigid canopy of very large area intended to be deployed vertically over the underwater installation from which hydrocarbons are escaping. The area of the roof of the canopy is of the order of 100 to 10 000 m2. The canopy consists of two dihedral surfaces and is mounted on telescopic anchoring legs for stabilizing the position of the canopy over the underwater installation. It is connected to a flexible hydrocarbon raising pipe that is connected at the bottom to the canopy and extends up to the hydrocarbon recovery and storage ship. Moreover, a collecting chamber is disposed at the apex of the canopy, the flexible pipe being connected directly to the collecting chamber. There are carried out in the collecting chamber all operations beneficial to facilitating raising of the hydrocarbons, which may be very viscous and therefore difficult to raise to the surface via the pipe. These operations may consist in fluidizing the hydrocarbons by heating with electrical elements or by circulating hot water. They may also consist in diluting the hydrocarbons by adding dilutants or in mechanical stirring of the hydrocarbons in the collecting chamber. This recovery system is then towed to site and lowered in vertical alignment with the underwater installation, the buoyancy of the canopy being monitored and adjusted during its descent. The legs of the canopy are then deployed to stabilize the canopy on the seabed and vertically above the underwater installation.
A flexible pipe is then deployed from a pipelaying ship at the destination site. Unmanned submersibles are then used to connect the pipe to the collecting chamber and then to the surface installation.
The complete installation of such a recovery system may take months (two to three months) because it requires steps that are carried out in sequence and the sequential mobilization of a number of ships at the destination site.
These installation methods are therefore unsatisfactory because it is necessary to confine the leaking hydrocarbons as soon as possible to limit the impact on the environment.
Accordingly, the present invention proposes a method of installing a recovery system including an assembly for raising hydrocarbons to a surface installation that is faster to install at the destination site in a very short time, of a few days.
To this end the method of the invention includes the following steps:
The method in accordance with the invention is also characterized in that steps 3 and 4 of assembling the upper assembly (26) at sea and towing it to site are effected simultaneously with step 1 and/or step 2.
Thus the upper or fluid raising assembly is assembled and towed to the surface installation in what is otherwise dead time.
In accordance with another feature of the invention, the installation method is characterized in that assembling the upper assembly (26) includes the following steps:
According to other features of the invention, the method in accordance with the invention is characterized in that, at the destination site, the upstream end (34) of the first flexible pipe (30) provided with the collecting chamber (32) is deployed toward the seabed by paying out a disposable line (72) and is then connected to the canopy (27) of the lower assembly (25).
Other features and advantages of the invention will emerge from the description of one embodiment of the invention given hereinafter illustrated by the following figures:
In the remainder of the text, the terms “upstream” and “downstream” are to be understood as relative to the direction of flow of the fluids when the fluid recovery system is operational.
The underwater installation (21) may for example be an underwater oil well, an underwater pipe that has been damaged or a ship for storing or transporting hydrocarbons that has sunk.
The recovery system comprises a first or lower assembly (25) comprising a rigid canopy (27) of large area. This canopy is the shape of an inverted funnel and includes compartments (29) for adjusting the buoyancy of the canopy during its installation over the underwater installation (21). It further includes legs that can be deployed toward the seabed in the direction A-A′ to anchor the lower assembly (25) to the seabed (11). This rigid canopy is protected by international patent application WO2005/038145 in the name of the applicant.
The function of this lower or recovery assembly is to channel hydrocarbons escaping from the underwater structure (21) toward a flexible pipe (30) in order to recover them in a storage ship (13) such as a tanker, for example.
Accordingly, the canopy advantageously takes the form of two dihedral surfaces forming at their apex a trough leading to the upper part of the canopy to which is connected an upper or hydrocarbon raising assembly (26).
The upper or hydrocarbon raising assembly (26) of the recovery system includes a first flexible pipe (30) extending substantially vertically along the axis A-A′. The first flexible pipe (30) is connected at its upstream end (34) to a collecting chamber (32) and at its downstream end (35) to a buoy (40) immersed under the surface of the water that exerts an upward traction force in the direction A-A′ on the first flexible pipe to maintain it in a substantially vertical position. A shorter second flexible pipe (33) connects the downstream end (35) of the first flexible pipe (30) to the surface installation (13). It preferably extends in the form of a catenary between the buoy (40) and the surface installation (13) in order to accommodate movements of the surface installation (13). Here the fluidic connection (41) between the upstream end (38) of the second flexible pipe (33) and the downstream end (35) of the first flexible pipe (30) is made above the buoy (40) by means of a U-shaped rigid pipe connector (41). Flanges or other ad hoc elements connect the ends of the rigid connector (41) to the ends of the flexible pipes (30, 33).
The collecting chamber (32) at the apex of the canopy (27) of the lower assembly (25) is connected to the upstream end of the first flexible pipe (30). The collecting chamber (32) thus on one side connects the volume under the canopy and the interior of the first flexible pipe (30). It collects the hydrocarbons under the canopy before they are raised to the ship (13) via the flexible pipes (30, 33, 41).
This chamber preferably includes means for facilitating raising the hydrocarbons in the first flexible pipe (30). These means may be mechanical stirring elements, electrical heating means or heating means that circulate hot water in small serpentine pipes, or means for injecting dilutants. The collecting chamber is described in application WO2005/038145 in the name of the applicant. Thus it will not be described in detail in the present application.
In the context of the invention, the term “hose” or “flexible pipe” refers to a pipe consisting of a plurality of layers that may be bounded or unbounded. These pipes are described in the standards API17j and AP RP 17B published by the American Petroleum Institute (API).
The flexible pipe or hose may advantageously consist of a composite “bundle” comprising at least one flexible pipe for conveying fluids and a set of electrical or optical cables for transmitting electrical or optical power and possibly also including small ancillary pipes for feeding/injecting chemical products into the mixture of hydrocarbons.
A method in accordance with the invention for installing the hydrocarbon recovery assembly (10) will now be described with reference to
The lower or recovery assembly (25) including the rigid canopy (27) previously constructed on land in a shipyard is launched in the vicinity of its place of construction. By virtue of its double-wall hull and caisson type design, the rigid canopy is able to float on the surface of the water. The deployable anchor legs (22) are in their upwardly retracted position.
Referring to
To this end, the lower assembly is connected to two tugs (53) via towlines (65, 66). The buoyancy of the recovery or lower assembly (25) is then adjusted (by partially filling the caissons of the canopy) to sink it a few meters below the surface of the sea. Weights (68) are also added to the cables in order for the towlines to be deployed under the lower or recovery assembly (25) and thereby contribute to stabilizing the position of the lower assembly (25) under the surface of the water.
The lower assembly (25) is then towed in the direction of the arrow to the destination site between the two tugs (53).
Once arrived at the destination site, in a second step of the installation method, the lower assembly (25) of the recovery system is ballasted so that it sinks progressively in the water. The towlines (65, 66) are paid out simultaneously to guide the lower assembly (25) toward the seabed. These lines (65, 66) are also used to control the descent of the lower assembly (25) toward the seabed.
On approaching the seabed (11), as shown in
Referring to
This assembly process includes a step of bringing a buoy (40) to the body of water. This buoy floats on the surface of the water essentially by virtue of its own resources. It is preferably of cylindrical and flat shape, which gives it better stability at sea. By a flat buoy is meant one in which the ratio of its height along the axis A-A′ to its diameter D is less than 1.5. A pipelaying ship (52) on which a flexible pipe is stored in a rack or on a storage reel is brought up to the vicinity of the buoy (40). The pipelaying ship also transports the collecting chamber (32) on deck. A first flexible pipe (30) is paid out from this pipelaying ship (52). The downstream end (35) of the first flexible pipe is then connected to the buoy (40). The first flexible pipe (30) extends at this stage in a U-shape or double catenary shape between the buoy (40) and the pipelaying ship (52), which retains the upstream end (34) of the first flexible pipe (30). Alternatively, the downstream end (35) of the first flexible pipe is retained by a tug and the pipelaying ship (52) can be stood down.
A second flexible pipe (33) shorter than the first flexible pipe (30) is connected to the buoy; its upstream end (38) is connected to its final location in a space provided in the buoy and the downstream end (37) of the second flexible pipe is retained temporarily at the periphery of the buoy.
The buoy (40) advantageously has a height (H)/diameter (D) ratio less than 1.5. Accordingly, the first and second flexible pipes may be connected to the buoy after a pulling-in operation carried out from the upper surface of the buoy and the fluidic connection between the first and second flexible pipes may be established on top of the buoy using a rigid pipe connector (41).
A towline (70) connects the buoy (40) to a tug (53). The upper assembly (26) is towed in the direction of the arrow F by the tug 53 and the pipelaying ship (52) moves in the same direction at a speed matched to that of the tug.
This third step of assembling the upper assembly (26) is advantageously carried out in what is otherwise dead time, during the phase of installing the lower assembly (25), namely during step 1 and/or step 2 of the installation method described above. Accordingly, by carrying out a plurality of steps simultaneously, the time necessary to render the recovery assembly (10) operational is reduced.
When the upper assembly (26) nears the destination site, the collecting chamber (32) is connected to the upstream end (34) of the first flexible pipe (30). It is then connected to a cable (72) of a winch disposed on the ship (52), as shown in
As shown in
The upper assembly (26) is then connected to a surface installation (13).
To this end, and as shown in
Finally, the downstream end (37) of the second flexible pipe (33) is recovered and connected to the surface installation (13). It extends in the form of a catenary between the buoy and the ship (13).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10/04858 | Dec 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2011/052947 | 12/12/2011 | WO | 00 | 6/27/2013 |
