GB2438405A

GB2438405A - Underwater trenching and excavation apparatus

Info

Publication number: GB2438405A
Application number: GB0610100A
Authority: GB
Inventors: Nicholas Victor Sills
Original assignee: SEAVATION Ltd
Current assignee: SEAVATION Ltd
Priority date: 2006-05-22
Filing date: 2006-05-22
Publication date: 2007-11-28
Also published as: GB0610100D0

Abstract

An underwater trenching and excavation apparatus that is neutrally buoyant in water and can be manoeuvred and operated in a free flying mode when attached to a remotely operated vehicle. The apparatus uses arrays of water jets 13 mounted on articulating jetting swords 12 or static jetting swords 35 to excavate the seabed or dig trenches for pipelines in the seabed and has retro jets that counter balance the reaction or thrust forces generated by the excavating water jets. The apparatus has sets of wheels 22 on opposite sides of the apparatus that when articulated can close around a pipeline to clamp the apparatus to the pipeline and when the wheels are rotated can drive the apparatus along the pipeline. All rotating and reciprocating parts are powered by pressurised water. The apparatus is deployed on drill string and receives pressurised water through a flexible umbilical hose 20.

Description

UNDERWATER TRENCHING AND EXCAVATION APPARATUS

This invention relates to a neutrally buoyant, reactionless, water powered, underwater Irenching and excavation apparatus that can excavate ditches and trenches in the seabed whilst operating in a free flying mode when attached to a remotely operated vehicle and excavate trenches in the seabed for burying pipelines when attached to a pipeline with a set of motorised guide wheels and manoeuvred along the pipeline.

It is common practice to bury underwater pipelines and other conduits in trenches to protect them from damage, against movement and stress by strong currents and to reduce heat loss from products such as oil and gas within some conduits.

Some existing forms of underwater trenching and excavation apparatus use an array of pressurised water jets to cut a trench or ditch in the seabed and suction devices to remove the cut soil from the trench or ditch when manoeuvred across the seabed or along a cable, pipeline or conduit.

In all existing apparatus the array of jets are mounted on hollow tubular structures commonly called jetting swords and the jets are arranged to focus their energy in the direction of the soil surface to be excavated or trenched. When the jet array is activated a reaction force or moment is generated and is transmitted through the jetting swords into the structure of the apparatus. This force or moment must be counteracted in some maimer to prevent the apparatus from being destabilised or moved off course. Several means are used in existing machines to counteract the reaction force or moment depending on the direction in which the force is acting.

If the reaction force is vertically upward the force can be counteracted by weight. The trenching apparatus is landed on the seabed in a negatively buoyant manner and moved across the seabed or along a conduit on tracks, wheels or skis. An upward thrust force generated by the apparatus manoeuvring thrusters is also sometimes used to help maintain contact with the seabed.

If the reaction force is horizontal or at an angle a combination of negative buoyancy and friction with the seabed can be used to counteract the force. Caterpillar tracks or wheels are used to generate friction between the apparatus and the seabed when stationary and to provide grip when the wheels or tracks are rotated to manoeuvre the apparatus across the seabed. On a steeply sloping seabed and in weak soils the use of tracks and wheels becomes increasingly ineffective as a method of resisting reactive forces and at an angle above about 25 degrees the vehicles begin to loose grip and slide making them unstable.

If a pipeline or conduit is present it is possible to clamp the apparatus to the structure with a set of contoured caterpillar tracks or wheels to counteract the reaction force. The amount of force that can be tolerated by a pipeline or conduit is strictly limited. In some apparatus a towing line is attached to the apparatus from the surface and a ship or vessel is used to pull the negatively buoyant apparatus across the seabed or along a pipeline or conduit.

These apparatus generate their jetting water supply with water pumps driven by oil hydraulic or electric motors mounted on the apparatus and because of this encounter increasing technological, operational and economic barriers with increasing jetting horse power and water depth, particularly with regard to power transmission over long distances.

By way of example pumping one thousand kilowatts of hydraulic energy through a closed circuit oil hydraulic umbilical one kilometre long becomes operationally impractical due to the enormous frictional losses and difficulty of handling the umbilical.

Similarly generating one thousand kilowatts of jetting water by way of a one kilometre long electrical umbilical and electric pump is practical at very high voltage and some existing apparatus do this but the electric pumps and control apparatus mounted on the vehicle to generate the jetting water flow become increasingly difficult to handle and operate and meet operational barriers above a certain power because of increasing size and weight. in addition severe operational problems arise in insolating high voltage electrical circuits from the marine environment.

The consequence for these apparatus is that it is not practical to generate further jetting energy to use as retro jets to counteract or balance the induced reaction force from the trenching swords.

Without a reaction force balancing system none of these apparatus can operate in a neutrally buoyant free flying condition as the reaction force or moment generated by the jetting swords alters the trim or position of the apparatus and prevent its use. Without operating in a neutrally buoyant reactionless condition these apparatus cannot operate on steeply inclined seabeds and their weight can cause them to sink into soft soils preventing their use.

This invention provides an underwater trenching and excavation apparatus that comprises a frame means on which is articulated one or more jetting sword means each with an array of jets and a motorised wheel means to attach to a pipeline. Hydraulic ram means are provided to articulate the jetting sword means and wheel means from a horizontal position to a vertical downward position or any position in between. A further static jetting sword means with an array of jets is provided and fixed in a horizontal orientation.

A buoyancy means is provided in the frame so that when the apparatus is submerged in water the apparatus is neutrally buoyant. A latching means is provided on the apparatus to secure the apparatus to a vertical pipe or drill string for deployment and recovery of the apparatus. A further latching means is provided on the apparatus to secure a remotely operated underwater vehicle to the apparatus so that when the remotely operated vehicle is operated it may manoeuvre and position the apparatus on or above the seabed or along a conduit. A flexible water supply umbilical hose means is provided to supply pressurised water from the end of a pipe or drill siring to a water distribution manifold means in the apparatus and to the jetting sword means and thereafter to the arrays of jets.

All moving parts of the apparatus that require motive power such as wheels, rams and balanced thrust excavator are powered hydraulically with water pumped from the surface.

The arrays of jets are arranged in such a fashion that the thrust force generated by one jet or a series of jets is balanced by an equal and opposite force from another jet or series of jets in the manner of a retro jet system. When water is pumped down a drill string or hose and through the water manifold supply means to the jets at any water pressure the net reaction force or moment generated by the jetting sword or swords and the apparatus is zero and does not affect the trim or alter the position of the apparatus. When the apparatus is close to or on the seabed with the jetting swords in a horizontal position the flow of water from the jets will disturb and wash away the seabed soil below the apparatus and within range of the jets. When the jetting swords are articulated from a horizontal position to a vertical position the arrangement and configuration of the array of jets is such that when the apparatus is moved across the seabed or along a pipe it will cause a trench or ditch to be excavated in the seabed or along the axis of the pipe. A balanced thrust underwater excavator (patent number GB 2359103) is mounted on the front of the apparatus for dispersal of loose excavated seabed.

The following is a description of some of the specific embodiments of the invention, reference being made to the accompanying drawings in which:-FIGURE 1 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus showing the principal features of the apparatus.

FIGURE 2 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus latched to a drill string for deployment with a typical remotely operated vehicle illustrated nearby.

FIGURE 3 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus unlatched from a drill string with a remotely operated vehicle latched within the apparatus for the purpose of manoeuvring and positioning the apparatus in a free flying condition.

FIGURE 4 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with a remotely operated vehicle latched within the apparatus showing the apparatus in a free flying condition above a seabed with the first set of articulated jetting swords, wheels and soil eductors removed to more clearly show the static horizontal jetting swords with arrows indicating the direction of water flow from the array of water jets and the direction of travel of the apparatus.

FIGURE 5 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with a remotely operated vehicle latched within the apparatus showing the apparatus in a free flying condition above a seabed with the first set of articulated jetting swords, wheels and soil eductors removed to more clearly show the apparatus with a second set of articulated jetting swords in a position that when energised the flow from the water jets will converge under the apparatus and cut a V shape in the seabed when the apparatus is manoeuvred along a pipeline in a free flying condition with arrows indicating the direction of water flow from the jets and the direction of travel of the apparatus.

FIGURE 6 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with a remotely operated vehicle latched within the apparatus and positioned on a pipeline with the first set of articulated jetting swords lowered to the vertical position for trenching and wheels articulated to clamp the apparatus to a pipeline and with arrows showing the flow of water from the jets, the direction of rotation of the wheels and the direction of travel of the apparatus along a pipeline.

FIGURE 7 is a perspective drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with a remotely operated vehicle latched within the apparatus showing the apparatus in a free flying condition above a seabed with the second set of articulated jetting swords articulated to a further position that obstructs two jets and forms a reactionless two jet sword that when energised the flow from the water jets is parallel to the seabed with arrows indicating the direction of water flow from the jets.

FIGURE 8 is a side view drawing of a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with a remotely operated vehicle latched within the apparatus showing the apparatus in a free flying condition above a seabed and the water manifold in the apparatus and fitted with a balanced thrust underwater excavator (J)atent number GB 2359103) with arrows to show the flow of water from the apparatus.

Figure 1 illustrates a neutrally buoyant reactionless water powered underwater Irenching and excavation apparatus comprising a frame 11 on which is mounted for articulation two or more pairs of jetting swords 12 with lines and arrows 26 showing the axis of articulation. Each of a pair of jetting swords comprises a hollow tube assembly with an array of jetting nozzles 13 attached to the tube. The jetting sword articulating arrangements comprising of hydraulic rams 14 and 38 are attached at one end to the frame 11 and to a hinge at 16 on a jetting sword assembly is mounted for rotation of the assembly from the horizontal position to the vertical position as more clearly shown in figures 3 and 5. A latching arrangement 17 secures the invention to a pipe or drill siring assembly as shown at 27 of figure 2 during deployment and recovery and buoyancy tubes 18 make the apparatus neutrally buoyant when submerged in water. A water manifold as shown at 19 of figure 8 receives pressunsed water through the flexible water umbilical 20 and distributes water to the jetting sword assemblies and rams through flexible hoses. The manifold also supplies water to the wheel motors 21 within the wheels 22 that rotate the wheels. Control panels to operate the rams and control the flow of water to the jet arrays and other facilities are shown at 23 and are mounted for operation by a remotely operated vehicle. A pair of soil eductors 24 are mounted for rotation on frame 11 around axis 26.

When for example rain 25 is extended the eductor moves from storage position to a vertically downward position around axis 26 to suck loose soil from a trench as more clearly shown by arrows 29 in figure 5. The jetting swords, wheels, rams and soil eductors are duplicated on opposite sides of the apparatus as in the manner of a mirror image. A balanced thrust underwater excavation apparatus patent nwnber GB 2359103 is shown at 28 and is mounted to wash loose soil from a trench.

Figure 2 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus showing the apparatus latched to a to a drill string assembly 27 with a free flying remotely operated vehicle 30 close by. Latches 32 are mounted for attachment of the remotely operated vehicle to the apparatus.

Figure 3 illustrates a neutrally buoyant reactionless water powered underwater Irenching and excavation apparatus showing a remotely operated vehicle 30 latched to the apparatus by latches 32 for manoeuvring the apparatus underwater and operating the control panel 23.

With reference to figures 4 to 8 a sequence of events will now be described that will make the use of the apparatus for excavating ditches in the seabed or trenches along a pipeline apparent.

Figure 4 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus in a free flying condition above a seabed with the first set of articulated jetting swords, wheels and soil eductors removed to more clearly show the static jetting sword when the apparatus is being manoeuvred at low altitude across a seabed 33 with the assistance of a remotely operated vehicle 30 with arrows 36 indicating the downward direction of flow of pressurised water from a static jetting sword 35 for excavating a ditch or trench 37 in the seabed and the upward direction of retro jets 34 for counteracting the reaction force generated by the downward jets.

Figure 5 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus with the static jetting sword, wheels and soil eductors removed to more clearly show the apparatus with the second set of articulated jetting swords 12 lowered by ram 38 to a position so that the flow from water jets 40 will converge under the apparatus and cut a V shape in the seabed as shown at 41 when the apparatus is -Il-manoeuvred along a pipeline 39 in a free flying condition with arrows 42 indicating the direction of water flow from the jets and arrow 43 the direction of travel of the apparatus.

Figure 6 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus attached to a pipeline 39 by wheels 22 with trenching swords 12 and wheels lowered to the vertical position by ram 14 and 25 for trenching along the pipeline. Soil eductor 24 is shown in the vertical position for sucking loose soil from the trench with arrows 29 indicating the direction of soil transport. Ram 25 lowers and raises the soil eductor and rear wheel 22 together. An arrow 43 indicates the direction of travel of the apparatus along the pipeline.

Figure 7 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus in a free flying condition above a seabed 33 with the third set of jetting swords 12 articulated to a horizontal position and sealed at 44 with arrows 45 indicating the direction of flow of the water jets. When the jets are activated they will cause a flow of water parallel to the seabed to move loose materials such as boulder 46 in the direction indicated by arrow 47.

Figure 8 illustrates a neutrally buoyant reactionless water powered underwater trenching and excavation apparatus in a free flying condition above a seabed 33 showing the flexible water supply umbilical 20 and water manifold 19 for receiving and distributing the water and with arrows 48 showing the direction of water flow from a balanced thrust excavator apparatus 28 to cause a depression in the seabed at 49 or wash away loose soil.

Claims

IS

CLAIMS

1. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus comprising of a frame with one or more jetting sword means mounted for articulation and a water manifold means to supply pressurised water from a drill siring and flexible umbilical hose means to an array of water jets mounted on the jetting sword means and cause soil to be separated from the seabed in a process termed excavation or trenching when pressurised water is pwnped down the drill string.

2. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim 1 wherein the reaction force generated by an array of one or more water jets mounted on a jetting sword means is counterbalanced by the reaction force generated by another jet or jets in the manner of a retro jet system and the net reaction force of the jetting sword means on the apparatus is effectively zero.

3. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim I and 2 wherein one or more jetting swords can be articulated from a horizontal or storage position to a vertical or working position by ram means.

4. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim I to 3 wherein a latching means is provided to attach the apparatus to a drill string for deployment from a ship or vessel and to release the apparatus from the drill string when in the vicinity of the seabed. 1k.

5. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim 4 wherein the latching means provided to attach the apparatus to a drill string for deployment is unlatched by an underwater remotely operated vehicle.

6. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim 1 to 5 wherein a latching means is provided to attach an underwater remotely operated vehicle to the apparatus for manoeuvring and controlling the apparatus underwater.

7. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim I to 6 wherein sets of opposed wheels are mounted for rotation and articulation in the apparatus and when articulated clamp the apparatus to a pipeline and when rotated the wheels move the apparatus along a pipeline.

8. A neutrally buoyant reactionless water powered underwater trenching and excavation apparatus as claimed in claim I to 7 wherein a flexible umbilical hose means transports pressurised water from the drill string to a water manifold means in the apparatus and thereafter by flexible hoses to the jetting sword means, wheel motor means, ram means and balanced thrust excavator apparatus.

9. A neutrally buoyant reactionless underwater trenching and excavation apparatus as claimed in claim 1 to 8 wherein all rotary or reciprocating devices mounted on the apparatus are activated or powered by pressurised water.