Patent Description:
Known methods to install elongated elements into ducts make use of a propelling fluid, to generate drag forces along all the length of the elongated element. It is known to introduce the propelling fluid into the duct under pressure via a pressure chamber connected to the entry of the duct. Then, the elongated element has to be pushed into the pressure chamber to enter the duct. However, the pressure to be applied to the propelling fluid at the entry of the duct depends on the full length of the duct. For very long distances (several kilometers), the required entry pressure of propelling fluid (liquid) might be of tens or of hundreds of bar. Such values become an issue, as the elongated element cannot be pushed into the pressure chamber without buckling. Document <CIT> discloses a method of laying marine bottom optical fiber cable. Document <CIT>discloses an optical transmission line laying method. Document <CIT> discloses an optical fibre installation. Document <CIT> discloses systems and methods for controlling duct pressurization for cable installation.

The present invention aims to address the above mentioned drawbacks of the prior art, and to propose first a method for laying an elongated element into a submarine duct, which allows to operate in simple manner variety of sizes of elongated element into a variety of conditions.

In this aim, a first aspect of the invention is a method for installing an elongated element, such as a cable or a fibre, in a submarine duct, the submarine duct having an entry port located at or above a surface level or at a first depth in an outer liquid and an exit port located in the outer liquid at a second depth, the method comprising the steps of:.

wherein the method comprises a step of sucking propelling liquid out of the exit port of the duct with an immerged suction pump immerged in vicinity of exit port, presenting an inlet connected to the exit port and an outlet, the immerged suction pump being operated at a predetermined suction pressure drop of propelling liquid between the immerged suction pump inlet and the immerged suction pump outlet so that the predetermined suction pressure drop applied to propelling liquid is smaller than a hydrostatic pressure outside the duct at the location of the immerged suction pump. According to the above embodiment, a suction pump is installed at the exit port location, and connected to the exit port. Then, the pump is operated to suck the propelling liquid out of the duct, applying a pressure drop to the propelling liquid. The installation is now possible even for great lengths, as the pressure drop is applied at the exit port, so that the elongated element can be easily introduced into the entry port. One should note that the pressure chamber is not mandatory anymore: one can directly introduce the elongated element into the duct, as the propelling liquid can be introduced at no entry pressure. It should be noticed that the predetermined suction pressure drop applied to propelling liquid created by the suction pump is smaller than a hydrostatic pressure at the exit port: the pressure, in dynamic conditions, inside the duct is always positive, avoiding generation of bubbles or voids.

According to one aspect, the entry port might be located at a higher position/altitude than the exit port. In other words, the entry port might be at the surface level, a bit higher or even under the surface. It has to be noted that the method is not limited to the above, and the entry port might be located at a deeper depth than the exit port.

Advantageously, the predetermined suction pressure drop applied to propelling liquid is greater than <NUM> bar, preferably greater than <NUM>% and more preferably greater than preferably <NUM>% and even more preferably <NUM>% of the hydrostatic pressure at the location of the exit port and/or immerged suction pump.

Advantageously, the entry port is connected to a pressure chamber, and:.

Advantageously, the predetermined suction pressure drop applied by the immerged suction pump to propelling liquid is smaller than the hydrostatic pressure at the location of the immerged suction pump. The pressure inside the duct is always positive, so that cavitation, bubbles or voids are not generated.

Advantageously, the threshold entry pressure is set to be lower than <NUM> bar, and preferably lower than <NUM> bar. The elongated element can be easily introduced into the duct at these pressures with a pushing unit comprising caterpillars for example, as the contra pressure force applied to the elongated element will not exceed pushing force achieved by caterpillar pushing unit.

Advantageously, the threshold entry pressure is set to be lower than <NUM>%, and preferably lower than <NUM>%, of the predetermined suction pressure drop applied to the propelling liquid by the immerged suction pump. Again, the elongated element can be easily introduced into the duct at these pressures with a pushing unit comprising caterpillars for example, as the contra pressure force applied to the elongated element will not exceed pushing force achieved by caterpillar pushing unit.

However, the method is not limited to the two above embodiments, and entry pressures of higher range might be held as well, up to <NUM> bar for example. In the later case the reel with elongated element might also be placed inside a pressure tank, in pressure communication with the pressure chamber.

Advantageously, the elongated element is pulled into the pressure chamber with pulling means arranged inside the pressure chamber.

Advantageously, the elongated element is pushed into the pressure chamber with pushing means arranged outside of the pressure chamber.

Advantageously, the elongated element presents a cross section area and is pushed or pulled into the pressure chamber at a given pushing or pulling force, and wherein the predetermined entry pressure is set to be equal to or lower than the pushing or pulling force divided by the cross section area.

Advantageously, the elongated element is freely inserted into the entry port, that is to say without pushing unit or pulling unit (caterpillars). The installation equipment is very simple and does not require any pressure chamber and not any sophisticated driving unit for driving the elongated element into the duct.

Advantageously, the elongated element is inserted into the entry port via a supply tube, the supply tube having an input and an output, the output of the supply tube being in connection with the entry port of the duct, a given fluid under pressure being fed near the input of the supply tube, and the elongated element being conducted into the input of the supply tube and being propelled through the supply tube by the entraining force of the given fluid, at least part of the given fluid being discharged from the supply tube at the output of the supply tube and, at the entry port of the duct, the propelling liquid being fed. Due to said measures, the pressure drop at the input of the tubular section (supply tube + duct) may be overcome without utilizing mechanical means which might damage the elongated element.

Advantageously, the method comprises the steps of:.

Advantageously, the method comprises an initial step of providing a T junction at the exit port, so as to:.

Alternatively to coupling the elongated element arriving to the exit port for pulling its foremost end to the surface level, the method comprises a preparation phase, executed before introducing the elongated element into the duct, comprising the step of coupling the elongated element to a precursor line selected to have at least similar density to that of propelling liquid and/or greater flexibility to that of the elongated element, wherein the exit port of the duct is connected via a T-junction to a riser duct leading near or to the surface, so that the method comprises the step of introducing the precursor line into the duct before installing the elongated element, and the step of leading a foremost end of the precursor line to or through an exit of the riser duct simultaneously to, or preferably before, the foremost end of the elongated element arrives to the exit port of the duct.

Advantageously, the method ends with the step consisting in lifting up the elongated element to the exit of the riser duct by pulling the precursor line.

Advantageously, the coupling of the precursor line to the elongated element is executed before introduction of the precursor line into the duct.

Alternatively, the coupling of the precursor line to the elongated element is executed after a significant part of the precursor line (at least <NUM>%, preferably at least <NUM>%, and more preferably all length but <NUM> meters) has been introduced into the duct.

Advantageously, the predetermined suction pressure drop is set so as to define a propelling liquid level in the riser duct to be located strictly above the pump, by a distance of e.g. <NUM> or more.

Advantageously, the exit port is located at a depth greater than <NUM>, preferably greater than <NUM>, and more preferably greater than <NUM>.

Advantageously, the duct presents a length greater than <NUM>, preferably greater than <NUM>, and more preferably greater than <NUM>.

It is to be understood that all the above technical features can be combined together or dissociated from each other, provided there is no technical contradiction and they are within the scope of the invention as defined by the appended claims.

Other features and advantages of the present invention will appear more clearly from the following detailed description of particular non-limitative examples of the invention, illustrated by the appended drawings where:.

In <FIG> a schematic representation is given of the prior art to install an elongated element <NUM> by floating into a duct <NUM> almost fully immerged in an outer liquid OL. As example a depth of <NUM> and a total length of <NUM> is given.

The duct <NUM> presents an entry port <NUM> connected to a pressure chamber <NUM>, the elongated element <NUM> is pushed into the entry port <NUM> via the pressure chamber <NUM> with a pushing unit <NUM> (caterpillars). The entry port <NUM> in the example is located at altitude H1, but it could be located under the sea surface at a first depth. In case when the entry port <NUM> is located under the sea surface, it would be at a first depth, and reference H1 used for altitude would turn into reference D1 on the figures.

The duct <NUM> presents also an exit port <NUM>, located well under the surface level, on the sea bed, at a second depth D2. In the given example, the exit port <NUM> is subjected to a hydrostatic pressure Phydro corresponding to the height of the outer liquid column C.

To insert the elongated element <NUM> into the duct <NUM>, a propelling liquid PL is introduced at a pressure ΔPentry. In detail, as this entry pressure ΔPentry is generated by a pump, it is a difference of pressure or a pressure drop.

As shown <FIG>, the pressure outside the duct <NUM> increases linearly from <NUM> to <NUM> bar in the vertical part. Regarding the pressure inside the duct <NUM>, at the entry port <NUM> the applied pressure ΔPentry is <NUM> bar, also <NUM> bar higher than outside the duct <NUM> at the entry port <NUM>, and at the end of the duct <NUM>, inside pressure is equal to outside of the duct <NUM> (<NUM> bar). The virtual pressure in the duct <NUM> (here also duct relative pressure) decreases linearly from <NUM> to <NUM> bar. The slope of the virtual pressure, which obeys Blasius' law for the turbulent flow, is a measure for the elongated element <NUM> drag force.

In order to insert the elongated element <NUM> into the pressure chamber <NUM> at <NUM> bar, the elongated element <NUM> must be pushed with a force at least equal to this pressure ΔPentry, multiplied by the cross-sectional area of the elongated element <NUM> (pushing the cork). For an elongated element <NUM> with e.g. a diameter of <NUM> this would require a pushing force of at least <NUM> N. This effort becomes a clearly limiting factor in case the depth and length are higher than in this given example. For example if depth and length are <NUM> times greater a pressure of <NUM> bar is needed, leading to <NUM> N pushing force. Far more than machines for Floating and Blowing cables of this size usually give (they are usually rated to maximum <NUM> bar or less and a maximum pushing force of about <NUM> N). Increasing the pushing force can, in principle, be done by using a number of pushers in tandem, but this is limited by elongated element <NUM> buckling risk. This could, in principle, be avoided by placing the pushers inside the pressure chamber (so they pull instead of pushing, avoiding buckling). This would not only make the pressure chamber very long, there is still risk for buckling in the duct when the elongated element <NUM> installation is blocked while the propelling liquid pressure is released and the pushers still pushing. For installation of small elongated element <NUM> and optical fibres in small steel tubes this has been solved by placing the entire elongated element <NUM> reel inside a tank, at the same pressure as and in communication with the pressure chamber. For a <NUM> elongated element <NUM> of <NUM> long, the <NUM> bar pressure tank would be enormous!.

To avoid the above drawbacks, and to allow installation in very long (more than <NUM>, <NUM> or even <NUM>) and very deep ducts (<NUM> depth) <FIG> illustrates a method according to the invention, involving placing an immerged suction pump <NUM> at the exit port <NUM> of the duct <NUM>. This immerged suction pump <NUM> can have its outlet just in the surroundings of the exit port <NUM>. Now the relative pressure over the duct <NUM> is negative for a part of the duct <NUM>, see <FIG> (now also relative pressure shown), where the immerged suction pump <NUM> is operated at <NUM> bar. In this case <NUM> times larger virtual inside pressure gradient is obtained, resulting in a <NUM> times higher drag force on the elongated element, or about <NUM> times longer installation length. According to the invention, the immerged suction pump <NUM> is operated at the duct exit port <NUM> with a pressure drop (<NUM> bar) below the hydrostatic pressure (<NUM> bar) at the sea bed to avoid pumping too hard and/or creating vacuum sections without water in the duct <NUM>. In particular, the immerged suction pump <NUM> applies to the propelling liquid a predetermined suction pressure drop ΔPpump , the outer liquid applies to the duct <NUM> a hydrostatic pressure Phydro generated by the outer liquid column C, for which the following relation shall apply: <MAT>.

Another example is described <FIG>, where the elongated element <NUM> is pulled up to the surface after being installed into the duct <NUM>. In this aim, the exit port <NUM> is connected to the immerged suction pump <NUM> and a riser duct <NUM> via a T junction, and a winch rope <NUM> pulled by a winch unit <NUM> are also provided.

In the given example of <FIG>, the elongated element <NUM> is installed into a <NUM>/<NUM> microduct to be installed between two marine platforms distant by eight kilometers. According to regular floating technique, e.g. <NUM> bar of pressure for the propelling liquid at the pressure chamber <NUM> would be required. The sea in between the platforms is <NUM> deep. As an example for the microduct (the duct <NUM> of <FIG>), a standard dimension ratio SDR <NUM> microduct can be subjected without implosion risk to a short time outer pressure of <NUM> bar (at <NUM>, much more at deep sea temperature of e.g. <NUM>). The immerged suction pump <NUM> is at a depth of <NUM> (<NUM> bar hydrostatic pressure) and connected by a T-junction at the exit port <NUM> (already or almost already in the vertical riser <NUM>) at the vertical of the second (arrival) platform. Pumping is limited to apply a predetermined suction pressure drop at the immerged suction pump <NUM>ΔPpump of <NUM> bar (to avoid implosion of the microduct), so also respecting the criteria: <MAT>
so vacuum and/or cavitation are avoided. At the injection side (entry port <NUM>) the applied propelling liquid pressure ΔPentry is <NUM> bar (relative inside pressure in a duct can be higher than relative outside pressure, <NUM> bar inside pressure no problem for SDR <NUM> microduct for short time), so the total applied pressure drop over the eight kilometers pipe is higher than the required forty bar to install the cable. When the elongated element <NUM> arrives at the immerged suction pump <NUM>, it is picked up by the winch rope <NUM> to which it is hooked.

According to an aspect of the invention, the propelling liquid in the riser duct <NUM> is ten meters above the T-junction, the difference between the <NUM> depth and the <NUM> "equivalent hydrostatic depth" of the <NUM> bar pumping pressure ΔPpump. These ten meters is a safeguard that the propelling liquid pumping is not disturbed by air. So, the vertical <NUM> the elongated element <NUM> has to be pulled up by the winch, of which <NUM> are without buoyancy assistance. As this length is only short there will be no high forces involved. Optionally, as an extra safety against air (e.g. due to oscillations of the U-column of water), a receiving (bi-directional) pig might be placed, attached to the winch rope <NUM> and waiting for the elongated element <NUM> to hook on. In order to avoid high pull up forces this pig might have a valve that opens at low pressure.

In detail to ensure that the immerged suction pump <NUM> will always be immerged and will not suck air via the riser duct <NUM>, the operation conditions are set as : <MAT>.

<FIG> represent an alternative embodiment for pulling up the elongated element <NUM> back to the surface. In this embodiment, as show <FIG> representing the elongated element <NUM> without the environment of <FIG>, the elongated element <NUM> is connected to a precursor line <NUM>, to form a composite element <NUM>. The precursor line <NUM> is chosen to have similar density to that of the propelling liquid PL (the densities could be equal at ± <NUM>%), and/or the precursor line <NUM> is chosen to have higher flexibility than the elongated element (flexibility could higher by at least <NUM>%). Consequently, with reduced friction (because of neutral buoyancy provided by equal densities) and/or reduced capstan effect (provided by high flexibility), precursor line <NUM> is easily passed through the duct <NUM> and through riser duct <NUM> and their bends.

Length of precursor line <NUM> is chosen to be at least slightly greater than depth of exit port <NUM>, so that the precursor line <NUM> will exit out of the riser duct <NUM> for providing a pulling line to pull the elongated element <NUM> up to the surface after the elongated element <NUM> has reached the exit port <NUM>.

The main aspect of this embodiment is that the coupling of the elongated element <NUM> to the precursor line <NUM> is performed before the introduction of the elongated element into the duct <NUM>. In other words, the coupling of the elongated element <NUM> to the precursor line <NUM> is performed at the surface level, which is an easy operation.

First option is to execute this coupling in vicinity to the installation equipment, preliminary or during installation operations. Second option is to execute this coupling far before installation, in a manufacturing factory for example.

One possibility is to introduce almost all the precursor line <NUM> into the duct (with same operating condition as the ones planed for the elongated element <NUM>), then connecting the rear end of precursor line <NUM> to the foremost end of the elongated element <NUM>, and then installing the elongated element <NUM> into the duct <NUM>. Two reels will be necessary in this case.

Second possibility is to connect the precursor line <NUM> to the elongated element <NUM> before any installation, so that the composite element <NUM> will be provided already reeled on a single reel.

Reverting to the installation method, the precursor line <NUM> is first entered and laid into the duct <NUM>, followed by the connected elongated element <NUM>. Therefore, the precursor line <NUM> will be passed through the entire duct <NUM> and riser duct <NUM> before the foremost end of the elongated element <NUM> arrives at the exit port <NUM>, with same or slightly adjusted operating conditions at least for pump <NUM>, and/or pressure chamber <NUM>. When the foremost end of the elongated element <NUM> arrives at the exit port <NUM>, it is then possible to catch the precursor line <NUM> already arrived at surface level, to pull the rest of precursor line <NUM> and the elongated element <NUM> up to the surface as shown <FIG>.

To assist travel of precursor line <NUM> through riser duct <NUM>, it is possible to plan that a part of the pumping flow generated by the pump <NUM> has to be directed into the riser duct <NUM>. Alternatively, a second pump (not shown) could be provided at the surface and a inlet hole could be provided in riser duct <NUM> at a given distance of exit port <NUM>, so that the second pump could generate a flow of liquid into the riser duct <NUM> (different from the flow conditions applied into the duct <NUM>). The rest of <FIG> is identical to <FIG> and will ne be described again here.

Claim 1:
Method for installing an elongated element (<NUM>), such as a cable or a fibre, in a submarine duct (<NUM>),
the submarine duct (<NUM>) having an entry port (<NUM>) located at or above a surface level or at a first depth in an outer liquid (OL) and an exit port (<NUM>) located in the outer liquid (OL) at a second depth,
the method comprising the steps of:
- introducing the elongated element (<NUM>) into the entry port (<NUM>),
- introducing propelling liquid (PL) into the entry port (<NUM>) of the duct (<NUM>),
characterized in that the method comprises a step of sucking propelling liquid (PL) out of the exit port (<NUM>) of the duct (<NUM>) with an immerged suction pump (<NUM>) immerged in vicinity of exit port (<NUM>), presenting an inlet connected to the exit port (<NUM>) and an outlet, the immerged suction pump (<NUM>) being operated at a predetermined suction pressure drop (ΔPpump) of propelling liquid (PL) between the immerged suction pump (<NUM>) inlet and the immerged suction pump (<NUM>) outlet so that the predetermined suction pressure drop (ΔPpump) applied to propelling liquid (PL) is smaller than a hydrostatic pressure (Phydro) of the outer liquid (OL) at the level of the second depth.