GB2618994A

GB2618994A - Apparatus for raising or lowering a load in a body of water

Info

Publication number: GB2618994A
Application number: GB2205560.2A
Authority: GB
Inventors: Scullion Callum; Joseph Collins Patrick
Original assignee: Italmatch Chemicals GB Ltd
Current assignee: Italmatch Chemicals GB Ltd
Priority date: 2022-04-14
Filing date: 2022-04-14
Publication date: 2023-11-29
Also published as: WO2023199073A1; GB202205560D0

Abstract

An apparatus comprises a support frame for attachment to the load and one or more rigid ﬁrst compartments 1 supported on the support frame which can be alternatively ﬁlled with a first compressible gas such as air, or ﬁlled with a second ﬂuid such as water. The second ﬂuid has a density greater than the ﬁrst gas. A ﬁrst conduit, usually with a valve, is connected between the, or each, ﬁrst compartment and a ﬁrst reservoir 15 for the ﬁrst gas. A second conduit, usually with a valve, is connected between the, or each, ﬁrst compartment and a second reservoir for the second ﬂuid, which may simply be the surrounding water e.g. seawater. The ﬁrst compartments may be buoyant in water and may be made from carbon ﬁbre. A further buoyancy tank 11 maybe partially filled with a fluid such as water, and partially filled with a further buoyant liquid possibly containing microspheres, allowing for controlled fine adjustment of buoyancy.

Description

Apparatus for raising or lowering a load in a body of water This invention relates to apparatus and a method for raising or lowering a load in a body of water.

Currently two main techniques are available for placing, moving and retrieving objects underwater in a controlled manner; a crane mounted on a vessel which lifts and places objects over the side or a bag filled with air creating a buoyant force counteracting the weight of an object in water allowing it to be retrieved to the surface. While these techniques are effective they each present a number of drawbacks.

A vessel crane is a complex piece of engineering and very expensive. Because the vessel is mostly operated in marine conditions a means of dynamic positioning of the vessel and motion compensation of the crane is required if lifts are to be conducted. As a consequence, such equipment can only be operated in benign weather conditions and sea states, with vessels often required to wait on weather.

Subsea engineering increasingly requires that instead of placing or retrieving objects subsea they are moved into discrete positions often in close proximity to each other, for installation. Although this is possible with a crane it is difficult and time consuming to the extent that such operations constitute the bulk of subsea activity.

In order to work, the vessel-mounted crane needs to be directly above the work site -in some cases this is not possible for instance when lifts need to be conducted underneath or closes to existing offshore structures.

Furthermore, as water depths increase to exceed 1000 metres the weight of the suspending "wire" starts to impact the lifting capacity of the crane meaning that a much larger crane vessel may be needed.

While air bags are a much cheaper and simpler solution they cannot be practically used to lower objects and move them subsea since as the loaded is lowered the increase in hydrostatic pressure with increasing depth causes the volume of the bag to reduce, lowering the buoyancy. Unless additional air is injected to increase the pressure to match the hydrostatic pressure control of the load is lost and it falls to the seabed. Conversely unless the airbag is able to discharge air when travelling to the surface the bag will expand and the load will accelerate to the surface in an uncontrolled manner.

Recently a number of patents have been filed which seek to deal with these short comings. W02018/051064 (Collins) discloses the use of an incompressible low density gel. Contained in a bag the gel can have a density as low as 550 kgs/ma. Containers filled with this gel are buoyant in water with the degree of buoyant force being directly proportional to the volume of fluid pumped. This means that a constant buoyant force regardless of depth is attained enabling loads to be made neutrally buoyant and so easily and safely used subsea.

This technique requires a volume of gel more than twice as great as a volume of air is used to give the same degree of buoyancy. This fluid needs to be pumped into and out of the bag through an umbilical line running to the surface where it is stored on the vessel. This can take a long time particularly when large volumes of gel need to be pumped. In long umbilical's a significant pressure drop is created when pumping fluids limiting the pump rate. There is also sometimes a requirement to make an break this flowline subsea meaning that some gel is lost to the environment.

W02015/181314A1 (Wilson) discloses a method of governing the elevation, attitude and structural integrity of a pressure-containing vessel in a body of liquid, the method comprising the steps of: selecting a flotation medium which is capable of increasing the buoyancy of the vessel; selecting an incompressible ballast medium which is capable of decreasing the buoyancy of the vessel; dividing the vessel into reciprocal serial hydraulically discrete compartments, one compartment for containing the selected flotation medium and the other compartment for containing the selected incompressible ballast medium; counterbalancing the selected flotation medium in the flotation medium compartment against the selected incompressible ballast medium in the ballast medium compartment; and varying the quantity of incompressible ballast medium in the ballast medium compartment to control the elevation of the pressure-containing vessel in the body of liquid.

Wilson's device comprises of a long tube wound into a coil, the tube is filled with air.

Ballast fluid is introduced at one end of the tube separated from the air by a pig which is capable of moving along the tube varying the buoyancy by compressing the air. Although this technique is effective at or close to the sea bed it is less successful when used to move up and down through the water column as the changes in hydrostatic pressure can result in crushing the tube or an ingress of water into the tube compressing the air with a consequent loss of buoyancy.

It is in this context that the present disclosure has been conceived.

In accordance with the present disclosure there is provided apparatus for raising or lowering a load in body of water. The apparatus comprises: a support frame for attachment to the load; one or more first compartments supported on the support frame, the one or more first compartments being substantially rigid and each configured to be provided in a first configuration filled with a first gas having a first density and in a second configuration filled with a second fluid having a second density different from the first density; a first conduit in fluid communication with the, or each, first compartment and providing a first gas communication pathway between a first reservoir for the first gas and the, or each, first compartment; and a second conduit in fluid communication with the, or each, first compartment and providing a second fluid communication pathway between a second reservoir for the second fluid and the, or each, first compartment. The first gas is a compressible gas.

Thus, the raising or lowering of a load secured at the support frame can be controlled using the filling of the one or more first compartments with either the first gas or the second fluid. Of course, where the one or more first compartments is a plurality of first compartments, it will be understood that some of the first compartments can be filled with the first gas whilst the rest of the first compartments can be filled with the second fluid. By forming the one or more first compartments to be substantially rigid, the first gas can be made compressible without causing any change in volume of the compartment housing the first gas with variations in external pressure. Thus, the buoyancy of the apparatus can be substantially independent of depth, providing a particularly simple and controllable apparatus. Typically, a portion of the apparatus other than the one or more first compartments, or the combination of the portion and the load will have a density greater than the surrounding water in the body of water. Therefore, at least one of the first gas and the second fluid will be chosen such that a density of the relevant compartment(s) is/are less than the surrounding water to ensure substantially neutral buoyancy of the apparatus and/or the combination of the apparatus and the load.

Although the first compartment, or each first compartment, when provided in the first configuration, is described as being filled with a first gas, which is a compressible gas, it will be understood that substantially any flowable material, such as any fluid (liquid or gas) can be used as the first gas, providing it is compressible.

The phrase "substantially rigid" as applied to the one or more first compartments will be understood to mean that the one or more first compartments are substantially inflexible, unlike bags, for example air bags, as has been used for retaining compressible buoyancy gases previously. In other words, the volume of the one or more first compartments will not be changeable with changing external pressures applied thereto, even when the one or more first compartments are filled with a compressible gas, for example air.

The one or more first compartments may have an empty mass less than a notional mass of water to be displaced by submersion of the one or more first compartments in water. 35 Thus, each of the one or more first compartments is suitable for use as a buoyancy compartment, sometimes referred to as a buoyancy tank. It will be understood that typical rigid pressure vessels capable of storing gases at high pressure are typically bulky and heavy, making them generally unsuitable for use to provide buoyancy when filled with a buoyant gas, such as air.

The one or more first compartments may be buoyant in water.

The one or more first compartments may be formed from carbon fibre. Thus, the pressure vessel forming the one or more first compartments may be formed from a strong, lightweight material.

The apparatus may be capable of operation at an operational depth of greater than 100 metres below a surface of the body of water. At 100 metres below a surface of the water, the pressure is typically approximately 1,000 kilopascals (10 bar). The apparatus may be capable of operation at an operational depth of greater than 1000 metres below a surface of the body of water. At 1000 metres below a surface of the water, the pressure is typically approximately 10,000 kilopascals (100 bar). Traditional metal, such as steel, rigid pressure vessels are generally incapable of safely containing such gases without such reinforcement as would mean that the mass of the material forming the pressure vessel itself would be so great that the pressure vessel could not function efficiently or even at all as a buoyancy compartment. In some examples, the apparatus may be capable of operation at an operational depth of greater than 2000 metres below a surface of the body of water. The apparatus may be capable of operation at an operational depth of greater than 3000 metres below a surface of the body of water.

It will be understood that the operational depth is the maximum depth at which the apparatus is capable of operating.

In the first configuration, the first gas may be at a pressure at least equal to a hydrostatic pressure in the body of water at the operational depth. In the first configuration, the first gas may be at a pressure greater than the hydrostatic pressure in the body of water at the operational depth. In some examples, in the first configuration, the first gas may be at a pressure substantially equal to the hydrostatic pressure in the body of water at the operational depth. Thus, the one or more first compartments may be pressurised to a substantially constant pressure in the first configuration. By pressurising the one or more first compartments to substantially the same pressure as at the operational depth, the one or more first compartments can be safely opened to the external environment at the operational depth to facilitate transfer between the first gas and the external environment. When the second fluid is water, the water can be sourced from the external environment. Thus, the one or more first compartments can be easily and safely filled with the water providing the second fluid, from the body of water at the operational depth, whilst the compressible gas providing the first gas is released into the body of water. In this way, it can be seen that the effective buoyancy of the apparatus is decreased, because less water is now displaced. Viewed another way, the effective mass of the apparatus is increased by replacement of the compressed gas with the water.

The one or more first compartments may be to be provided in the first configuration when 5 the apparatus is above the operational depth. Thus, the one or more first compartments may be configured such that it is possible for the one or more first compartments to be safely pressurised even when the apparatus is not yet at the operational depth.

The one or more first compartments may be to be provided in the first configuration when the apparatus is substantially at the surface of the body of water. Thus, the one or more first compartments may be configured such that it is possible for the one or more first compartments to be safely pressurised ready for the operational depth even when the apparatus is still at or near the surface of the body of water. Importantly, this allows the one or more first compartments to be filled with the first gas at the surface and then lowered down to the operational depth without any change in the volume of the first gas in the one or more first compartments.

The first gas may be air. Thus, the first gas is easy to obtain at the surface of the body of water.

The apparatus may further comprise the first reservoir. The first reservoir may be supported on the support frame. Alternatively, the first reservoir may be provided off the apparatus. In one example the first reservoir may be provided at a surface of the body of water, such as on a support vessel. Altematively, the first reservoir may be provided at the bed of the body of water, such as on the seabed. It will be understood that the first reservoir may be provided by the atmosphere where the first gas is air.

The second fluid may be water. The second reservoir may be the body of water. The second fluid may be seawater, and the second reservoir may be seawater. In other examples, the second density may be greater than water. Thus, the resultant buoyancy of the apparatus can be manipulated by filling one or more of the one or more first compartments with the first gas or the second fluid.

The, or each, of the one or more first compartments may be provided with a first valve in the first conduit to selectively permit flow of the first gas from the first reservoir into the respective first compartment. The, or each, of the one or more first compartments may be provided with a second valve in the second conduit to selectively permit flow of the second fluid from the second reservoir into the respective first compartment. Thus, movement of the first gas and the second fluid can be controlled. Typically, the first valve and the second valve are controllable valves. In other examples, at least one of the first valve and the second valve may be passive valves.

In the first configuration, the second valve may be further configured to substantially prevent flow of the first gas from the respective first compartment. Thus, the second valve can be used to selectively prevent escape of the first gas from the first compartment through the second valve when the first compartment is filled with the first gas. Thus, in some instances, the first gas can be prevented from escaping the first compartment via the second valve. When the first valve and the second valve are closed, the first compartment may be a substantially closed compartment. In other words, the first compartment may not be in fluid communication with the first reservoir or the second reservoir or, to the extent that it is different, the body of water.

The apparatus may further comprise a first pump to pump the first gas into the one or more first compartments. The first pump may be provided in the first conduit between the first reservoir and the one or more first compartments. In some examples, each of the one or more first compartments may comprise a separate first pump. Alternatively, the first pump may be used to pump the first gas into each of the one or more first compartments.

The apparatus may further comprise a controller to control movement of the first gas between the one or more first compartments and the first reservoir. The controller may be to control movement of the second fluid between the one or more first compartments and the second reservoir. For example, the controller may be to control operation of the first pump. The controller may be to control operation of the first valve and/or the second valve. The controller may be to control operation of a plurality of pumps.

The apparatus may further comprise: a second compartment supported on the support frame and configured to retain a third fluid in at least a portion thereof; and a third conduit in fluid communication with the second compartment and providing a third fluid communication pathway between a third reservoir for the third fluid and the second compartment. The third fluid may be substantially incompressible. The third fluid may have a third density different from the second density. Thus, the second compartment can be used in combination with the one or more first compartments to provide an effective apparatus for raising and/or lowering loads in a body of water. As will be described in more detail elsewhere herein, at least some of the one or more first compartments are filled with the first gas to make the combination of the apparatus and the load have a buoyancy closer to neutral buoyancy. The one or more first compartments are either completely filled with the first gas or completely filled with the second fluid. The second compartment is then at least partly filled with the third fluid, provided from a third reservoir typically located off the portion of the apparatus to be movable for raising and/or lowering the load, to fine-tune the buoyancy of the combination of the apparatus and the load to control movement of the load.

The second compartment may be configured to retain a fourth fluid in at least a further portion thereof, wherein the apparatus further comprises a fourth conduit in fluid communication with the second compartment and providing a fourth fluid communication pathway between a fourth reservoir for the fourth fluid and the second compartment, and wherein the fourth fluid is substantially incompressible and has a fourth density greater than the third density. Thus, the second compartment can be filled with the third fluid, the fourth fluid, or a combination of the third fluid and the fourth fluid.

The fourth density may be at least the density of water. In some examples, the fourth fluid may be water. Alternatively, the fourth fluid may be a fluid heavier than water.

The third density may be less than a density of water. The third density may be greater than the first density, which may be that of air. Thus, where the density of the third fluid is between that of air and water, it will be understood that the majority of the buoyancy can be provided by compressed air, with the remaining buoyancy being provided by the third fluid. It will be understood that a greater volume of third fluid would be required compared to air to achieve the same buoyancy.

The third fluid may comprise microspheres.

The third fluid may sometimes be referred to as a buoyant fluid. The buoyant fluid typically comprises a base fluid, microspheres, and a viscosifying agent. The viscosifying agent normally comprises a block copolymer. The third fluid may be a gel.

The buoyant fluid is typically a liquid. The buoyant fluid is typically incompressible or at least substantially incompressible. The buoyant fluid is normally a liquid and thereby incompressible. It may be an advantage of the present disclosure that when the buoyant fluid is underwater, the buoyant fluid is incompressible and therefore the volume of a fixed quantity of the buoyant fluid does not change or at least does not substantially change with a change in underwater depth and therefore also pressure. This provides an operator with greater control of the apparatus underwater that contains the buoyant fluid compared to using, for example, a gas. The volume of a fixed quantity of a gas changes substantially with a change in underwater depth and pressure.

The buoyant fluid typically comprises from 40 to 70% vol/vol base fluid, optionally from 50 to 60% vol/vol base fluid and normally 53% base fluid.

The base fluid may have a relatively low viscosity, that is a viscosity of from 1 to 5cSt at 400C. The flash point of the base fluid may be from 75 to 125oC. The base fluid may have a relatively high flash point, that is a flash point of more than or equal to 90oC. The base fluid may be sheen free.

The base fluid may have a density of from 0.7 to 1 kg/I at 15oC. The lower the density of the base fluid the less microspheres are required to provide the buoyant fluid with the required buoyancy. The density of the base fluid may be from 0.7 to 1g/cc, typically 0.76g/cc. The base fluid may have a specific gravity of more than 0.40g/cm3, optionally more than 0.45g/cm3, and may be more than 0.50g/cm3. The pour point may be from 0 to less than -48oC.

The base fluid may be an oil. The oil may be a mineral oil. The oil is typically a liquid.

The oil may be the majority component vol/vol or wt/wt of the base fluid.

The oil is preferably a low toxicity oil, such as a hydrocarbon, an alkane, an aliphatic oil, poly-alpha-olefin, alkyl ester and/or vegetable oil. The base fluid may have a very low toxicity to marine life, the aquatic toxicity for fish LC50 being greater than or equal to 1000mg/I. The base fluid may be referred to as having a low and/or relatively low aromaticity. The base fluid may be SIPDRILLTM.

The oil may be biodegradable, for example vegetable oil. Thus for certain embodiments of the invention, the inherent risk of environmental damage posed by the buoyant fluid leaking from a chamber is mitigated and therefore not a significant concern because the biodegradable oil used does not present an environmental risk or concern to wildlife.

In an alternative embodiment the base fluid may comprise water.

The buoyant fluid typically comprises from 0.5 to 5% vol/vol viscosifying agent, optionally from Ito 3% vol/vol viscosifying agent and typically 1.6% vol/vol viscosifying agent.

The viscosifying agent typically increases the viscosity and/or changes the rheobgical profile of the buoyant fluid. The viscosity of the buoyant fluid comprising the viscosifying agent typically decreases with an increase in shear rate. The decrease in viscosity with an increase in shear rate may be referred to as shear thinning. Typically when the buoyant fluid is subjected to shear forces, for example when being pumped and/or transferred from one container to another, the viscosity of the buoyant fluid reduces and the buoyant fluid flows relatively freely. Typically when the shear forces are removed, for example when the buoyant fluid is being stored in a container, the viscosity increases, helping to keep the buoyant fluid a homogeneous mixture of the base fluid, microspheres, viscosifying agent and dispersant when present.

The viscosifying agent typically helps to suspend the microspheres in the buoyant fluid.

The block copolymer of the viscosifying agent typically comprises two or more homopolymer subunits joined together with one or more covalent bonds. There may be a junction block between the two or more homopolymer subunits. The block copolymer may be a diblock copolymer with two distinct blocks.

The block copolymer of the viscosifying agent may be a linear diblock copolymer of styrene and one or more of ethylene, propylene and butadiene. The styrene content of the linear diblock copolymer may be between 20 and 35%, typically 28% wt/wt. The viscosifying agent typically forms a plurality of micelles. The plurality of micelles typically provides the shear thinning characteristics described above. The viscosifying agent may be KRATONTM.

The plurality of micelles typically comprise a core of poly(styrene) heads and a corona of poly(ethylene-co-propylene) and/or hydrogenated p(isoprene) tails.

The plurality of micelles may be formable after the viscosifying agent has been added to the base fluid and the mixture heated to more than or equal to 50oC, typically more than or 15 equal to 60oC and normally more than or equal to 70oC.

Alternatively the viscosifying agent may be a polysaccharide. The viscosifying agent may comprise a plurality of pentasaccharide repeat units. The plurality of pentasaccharide repeat units typically comprise one or more of glucose, mannose, and glucuronic acid. The viscosifying agent may be xanthan gum.

The microspheres are normally mixed with the viscosifying agent and/or a mixture of the viscosifying agent and the base fluid. The mixture may be referred to as a viscosified base fluid. The mixture may also contain a dispersant. The mixture may be referred to as buoyant fluid. One or more of the base fluid, microspheres, viscosifying agent, dispersant when present, and buoyant fluid may be heated to at least 70oC. Heating one or more of the base fluid, microspheres, viscosifying agent, dispersant when present, and buoyant fluid typically helps to make the buoyant fluid a homogenous mixture of two or more of the base fluid, microspheres, viscosifying agent and dispersant.

The buoyant fluid comprising the viscosifying agent is typically a stable mixture in the temperature range of from -10 to 100oC, typically from 0 to 70oC. It may be an advantage of the present invention that the buoyant fluid is typically a stable mixture. The buoyant fluid is a stable mixture when the components of the buoyant fluid do not separate or split from one another over time and/or with an increase in temperature.

The microspheres may each have a sealed chamber containing a gas or an at least a partial vacuum. The microspheres may be from 1pm to 5mm in diameter, optionally from 5 to 500pm in diameter and typically from 20 to 200pm in diameter.

The microspheres are typically rigid and so are incompressible at underwater pressures. The microspheres may be obtained from 3MTM. The microspheres may be rated to over 2,000kPa (300psi), normally over 31,000kPa (4500psi), preferably over 41,000kPa (6000psi) and optionally over 55,000kPA (8000psi). Other microspheres with different strengths and densities may be used and generally stronger microspheres have higher densities. The higher the rating of the microspheres, the deeper the water and/or deeper in the water that they can be used in.

The microspheres may be glass microspheres. The microspheres may lower the density of the buoyant fluid to a density of approximately 530 kg/m3 at room temperature.

The buoyant fluid typically comprises from 25 to 60% vol/vol microspheres, optionally from to 50% vol/vol microspheres and typically less than 55% vol/vol microspheres. The vol/vol of microspheres used is typically chosen to match the buoyancy required. If the vol/vol microspheres is however too high, the microspheres may contact one another and thereby be damaged or break so reducing the buoyancy they provide.

The vol/vol of microspheres used typically varies depending on the depth rating of the buoyant fluid. The vol/vol of microspheres used is normally a balance between the density of the buoyant fluid required and the depth rating of the buoyant fluid.

The grade of microspheres is also important. The sealed chamber of each microsphere is typically defined by a wall. The grade of the microspheres refers to the thickness of the wall.

The microspheres may be referred to as rigid containers. The sealed chamber of each microsphere may be referred to as a sealed void or may contain a gas.

The buoyant fluid typically also comprises a dispersant. The buoyant fluid typically comprises from 0 to 3% vol/vol dispersant, optionally from 0.5 to 2% vol/vol dispersant and typically 0.6% vol/vol dispersant. The dispersant typically helps to mitigate coagulation of the microspheres. Dispersion rather than coagulation of microspheres increases the flowabifity of the buoyant fluid, that is the ability of the buoyant fluid to flow.

The dispersant may be an imidazoline. The imidazoline is normally derived from an imidazole by the addition of H2 across one of two double bonds. The imidazoline is typically one or more of 2-imidazolines, 3-imidazoline and 4-imidazoline.

The dispersant may be a surfactant. The dispersant may be poly(ethylene glycol) (PEG) dioleate having the formula: CH3(CH2)7CH=CH(CH2)7C0(OCH2CH2)n020(CH2)7CH=CH(CH2)7CH3.

The PEG dioleate typically interacts with a hydrophilic outer surface of the microspheres and hydrophobic oil of the base fluid.

The dispersant may be a combination of an imidazoline and poly(ethylene glycol) (PEG) dioleate.

The buoyant fluid may have a specific gravity of less than 0.70g/cm3, optionally less than 0.65g/cm3, typically less than 0.60g/cm3, and often less than 0.55g/cm3.

The buoyant fluid may have a viscosity of from 9000 to 12000mPans at a shear rate of 1.1s-1 at 293K and 900 to 1200mPa.s at a shear rate of 113s-1 at 293K.

The viscosities detailed herein were determined using a Chandler 35 rotational viscometer with a number 1 spring and R1 B2 rotor-bob configuration, this allows the shear rate to be calculated as (0.37723*RPM) and viscosity as (300/RPM*8.91*dial reading).

The buoyant fluid normally provides lift of from 200 to 600 kg/m3, typically from 425 to 500 kg/m3.

In an alternative embodiment the dispersant may have from 50 to 100% m/M (mass/Molecular mass) of a polyamine amide salt and/or from 12.5 to 20% m/M of 2-butoxyethanol. The dispersant may be BYK-W 980TM. This dispersant is preferable when the buoyant fluid is water-based.

The third reservoir may be provided off the support frame. Thus, the third reservoir is not arranged to be raised or lowered with the load. The third reservoir may be provided at a surface of the body of water. Alternatively, the third reservoir may be provided on a bed of the body of water, such as the seabed when the body of water is the sea.

The apparatus may be configured to provide a fluid communication path from the second compartment to the body of water, in use. Thus, in some examples, the second compartment can be filled with the third fluid and water from the body of water. Typically, the pressure in the second compartment is the same as ambient pressure surrounding the apparatus. In some examples, the second compartment may be filled with a combination of the third fluid, the fourth fluid and water from the body of water.

A combined volume of the one or more first compartments may be greater than a volume of the second compartment. In other words, filling the second compartment may have less of an effect on buoyancy than filling all of the one or more first compartments. In some examples, the volume of the second compartment is sufficient that the difference in buoyancy caused by filling to a maximum capacity, a second compartment containing none of the third fluid, with the third fluid, is equal or greater than the difference in buoyancy caused by filling a single one of the one or more first compartments, filled with the second fluid, instead with the first gas to replace the second fluid. It will be appreciated that this depends on the specific fluids used, as well as the operating depth (and therefore operating pressure) of the apparatus. Thus, the second compartment can always be used in combination with the one or more first compartments to achieve any buoyancy force between a maximum buoyancy when all of the one or more first compartments are filled with the first gas and a minimum buoyancy when all of the one or more first compartments are filled with the second fluid. Typically, the volume of the second compartment is greater than a volume of a single one of the one or more first compartments.

The controller may be to control movement of the third fluid between the second compartment and the third reservoir.

The apparatus may further comprise a second pump to pump the third fluid between the second compartment and the third reservoir. The second pump may be to pump the fluid from the third reservoir to the second compartment. The second pump may be to pump the fluid from the second compartment to the third reservoir.

The apparatus may further comprise a non-varying buoyancy component supported at the support frame. The non-varying buoyancy may sometimes be referred to as semipermanent buoyancy. Typically, the buoyancy provided by the non-varying buoyancy will not change during, or even immediately before or after an operation to raise or lower the load in the body of water. The non-varying buoyancy may be substantially incompressible.

The non-varying buoyancy may be solid buoyancy. The non-varying buoyancy may be syntactic buoyancy.

In accordance with another aspect of the present disclosure, there is provided a method for raising or lowering a load in a body of water. The method comprises: providing the apparatus as described hereinbefore, having at least one of the one or more first compartments filled with the second fluid; securing the load at the support frame of the apparatus; filling at least one of the one or more first compartments with the first gas instead of the second fluid such that a combination of the apparatus and the load are at least mostly neutrally buoyant; and raising or lowering the apparatus and the load to a desired position in the body of water.

Thus, the apparatus described herein can be used to raise and/or lower the load in the body of water.

It will be understood that the securing the load and the filling the at least one of the one or more first compartments with the first gas may be performed in the claimed order. Alternatively, the securing the load and the filling the at least one of the one or more first compartments with the first gas may be performed in the reverse of the described order.

In some examples, such as where a load is to be lowered, the at least one of the one or more first compartments may be filled with the first gas instead of the second fluid at a surface of the body of water. When the load has been lowered, the one or more first compartments may be flooded with the second fluid to render the apparatus substantially neutrally buoyant, before removal of the load.

Where a load is to be raised, the at least one of the one or more first compartments may be filled with the first gas instead of the second fluid at the operating depth of the apparatus, such as at a depth of the load, after the apparatus has been lowered to the operating depth and secured to the load.

Where the apparatus include the second compartment, the method may further comprise at least partially filling the second compartment with the third fluid.

The second compartment may be at least partially filled with the third fluid to control the raising or lowering of the combination of the apparatus and the load. Typically, the composition of the fluids in the second compartment, being the proportion of the third compartment filled with the third fluid, is varied in a raising operation or a lowering operation after the one or more first compartments have been filled with a determined configuration of the first gas and the second fluid. In other words, the filling of the one or more first compartments is typically not changed once the raising operation or the lowering operation has begun.

When the one or more first compartments are to be filled with the first gas, the at least one of the one or more first compartments may be filled with the first gas to a pressure at least equal to a hydrostatic pressure at a maximum operating depth of the apparatus. The at least one of the one or more first compartments may be filled with the first gas to a pressure greater than the hydrostatic pressure at a maximum operating depth of the apparatus.

Viewed from another aspect, the present disclosure extends to a buoyancy compartment to be used underwater and for retaining a first gas therein at a maximum operating pressure greater than 1,000 kilopascals (10 bar). The buoyancy compartment is substantially rigid. The buoyancy compartment may be for retaining a first gas therein at a maximum operating pressure greater than 10,000 kilopascals (100 bar). It will be understood that such buoyancy compartments were typically not thought possible prior to now as, were they to be constructed from, for example, steel, in order for the compartment to be sufficiently strong to withstand the pressure of the first gas therein, such a quantity of steel would need to be used that the compartment would be incapable of being buoyant.

Although some potentially suitable metal materials were known, such as titanium, the cost and complexity of constructing a buoyancy compartment from titanium was considered prohibitive, meaning this was not a viable option.

A mass of the buoyancy compartment when filled with air at the maximum operating pressure is typically less than a mass of water to be displaced by submersion of the 5 buoyancy compartment in a body of water.

The maximum operating pressure may be greater than 20,000 kilopascals (200 bar). The maximum operating pressure may be greater than 30,000 kilopascals (300 bar).

The buoyancy compartment may be formed from carbon fibre.

Viewed from a further aspect, the present disclosure extends to the use of a compartment, 10 as described herein, as a buoyancy compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a compartment in accordance with the present disclosure; Figure 2 shows a plurality of the compartments shown in Figure 1, mounted within a frame; Figures 3a and 3b each illustrate an assembly showing two different types of compartment in accordance with the present disclosure; Figure 3c shows a compartment and associated reservoirs in accordance with the

present disclosure; and

Figures 4 to 6 show 3 different apparatus in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

There follows a detailed description of embodiments of compartments and apparatus for use in raising or lowering a load in a body of water.

Figure 1 depicts a compartment 1, in the form of a gas buoyancy tank 1, having a first opening 2 in the form of a top opening 2 and a second opening 3 in the form of a bottom opening 3. The opening at the top 2 allows a gas, usually but not necessarily air, to be pumped into or out of the tank 1. A first valve 4 is fitted to the top opening 2 to control flow of gas into and out of the tank 1. The bottom opening 3, being at the base of the tank 1 allows water to fill or drain the tank. A second valve 5 is fitted to opening 3 to control the flow of water into and out of the tank 1. The tank 1 is typically rigid, in that it is substantially incompressible, even when filled with a compressible gas, such as air.

In one embodiment, a plurality of such tanks 1 are mounted within a frame 6 (as shown in fig 2). The top opening 2 of each tank 1 is connected to a first conduit 7a in the form of a first manifold 7a, such that each top opening 2 of the plurality of tanks 1 can be connected to an air supply via the first manifold 7a. The bottom opening 3 of each tank 1 is connected to a second conduit 7b in the form of a second manifold 7b, such that each bottom opening 3 of the plurality of tanks 1 can be connected to a water supply via the second manifold 7b. The first valves 4 and the second valves 5 ensure that each tank can be opened and closed independently.

Each tank 1 needs to be capable of withstanding the pressure of the air or other gas inside the tank 1. The tank 1 must be constructed of a material strong enough to withstand an intemal pressure but light enough such that when filled with air under water at the internal pressure, the tank 1 is buoyant. It is advantageous if the tank 1 can be at an internal pressure that matches the hydrostatic pressure at an operating depth to which the load will be lowered or from which the load will be raised. Thus, fluid exchange in the tank 1 at the operating depth between the gas in the tank and the water surrounding the tank can take place at substantially matching pressures. However, it is most efficient to pressurise the tank 1 to the required pressure at or near the surface of the body of water. Therefore, it is important that the tank 1 is capable of withstanding an internal pressure matching the hydrostatic pressure at the operating depth, even when the tank 1 is at the surface. Of course, it will be understood that when the tank 1 is at the surface, the external pressure acting on the tank 1 is substantially atmospheric. Thus, the material must have sufficient tensile strength to prevent ruptures in the tank. At the operational depth, substantially the same high pressure force will be acting on an outside of the tank as on the inside of the tank. Therefore, the material must also be crush-resistant. Typically, the pressure on the inside of the tank will always exceed the pressure on the outside of the tank at any given depth, down to the operating depth. A variety of materials can be used for this function but it is likely that the tank is manufactured from a composite material such as glass reinforced resin composite or carbon fibre composite or a combination of both. Whilst tanks have been constructed from carbon fibre composite to transport gases at pressures as great as 300 bar, buoyancy tanks have not. The applicants have realised that tanks formed from the composite materials described herein can be formed as buoyancy tanks suitable to be operated at a depth of up to 3000 metres. Up until recently it has not been possible to fabricate pressure vessels other than out of steel making them very heavy and unsuitable for buoyancy.

Were the tank 1 instead to be lowered to the operating depth before pressurisation, the pressure inside the tank 1 would be lower than the pressure outside the tank 1, exposing the tank 1 to significant compressive forces, which may damage the tank 1.

Thus, the inventors has realised that the tank 1 is suited to the situation where the pressure inside the tank 1 is greater than the pressure outside the tank I. When used as a buoyancy tank 1, the pressure inside the tank 1 should never be lower than the pressure outside the tank 1, as discussed hereinbefore.

As to construction of the buoyancy tanks 1 from composite material. It will be understood that one suitable example may have a tank of approximately 1 metre in diameter and 2.5 metres in length, with bowed ends. Thus, the mass of water displaced by the tank is approximately 2000 kilograms. An average thickness of the carbon fibre is 24 millimetres. Thus, using carbon fibre having a bulk density of approximately 1,750 kilograms per cubic metre, the mass of the tank would be approximately 350kgs in air, or 150kgs in water, taking into account that the mass of water displaced by the carbon fibre material of the tank is approximately 200kgs. Therefore, the maximum buoyancy force created by such a tank would be around 1,850 kilograms, calculated by taking the weight of the tank in water away from the total weight of water displaced by the tank. Thus, a plurality of similar tanks can provide significant lifting capacity. In this instance, the tank is suitable for pressures up to 1,000 kilopascals (10 bar), though it will be understood that thicker layers of carbon fibre may be used, and/or tanks having a smaller diameter, to safely contain gases at higher pressures.

These tanks, when filled with gas, comprise a significant element of the buoyancy, but they cannot easily be used to provide fine control. Typically, the tanks are arranged to be either full of gas or full of water. When the tanks have water inside, the second valve 5 is typically left open, allowing the inside of the tank Ito be in fluid communication with the body of water. Thus, the pressure of the water inside the tank 1 is the hydrostatic pressure at the depth of the tank, which will change as the tank 1 is raised or lowered Accordingly, the tank 1 must be fully filled with air, and sealed from the water, with at least the second valve 5 closed, to prevent reduction of buoyancy and the associated problems. For this reason, it can be seen that the use of the tanks 1 can provide buoyancy control equivalent to the volume of one tank. Although all the gas tanks shown in Fig 2. are the same size this is not a requirement and in some cases a variety of different sized gas filled buoyancy tanks may be used. The gas can either be supplied from the surface via a compressor or from tanks filled with gas at pressure. In either case, the tank 1 is considered to be filled from a gas reservoir, which can be atmosphere or a gas supply tank, as described further hereinafter.

As such this element of the buoyancy can be described as the dumb buoyancy since, although it can provide most of the buoyancy variation required by the apparatus for raising or lowering a load, it typically has only a limited capability for control. A means of fine control of buoyancy is often required. Nevertheless, it will be understood that in some examples, the buoyancy tanks 1 described in relation to Figure 2 may be used as the sole elements of variable buoyancy in apparatus for raising or lowering a load in a body of water.

Figure 3a depicts a fine control element of the described apparatus. A further compartment 8 in the form of a tank 8 is disclosed for retaining a further fluid therein. In this example, the tank 8 comprises a bag 9 with a volume less than or equal to the volume of tank 8 for retaining the further fluid therein. In fig 3a the bag 9 is fixed to a top of the tank 8 and can be filled with the further fluid, for example low density buoyant gel 10, such as that described herein, and further in W02018/051064, having a density less than water and being substantially incompressible. The gel 10 is pumped from a reservoir either on a vessel or a reservoir placed subsea. The reservoir is to be located off the apparatus. The bag 9 and the tank 8 are sized such that, when the bag 9 is filled with buoyant gel 10, it creates a buoyant force at least as great as one of the gas filled buoyancy tanks 1. The buoyant force created by the gel 10 in the bag 9 is directly proportional to the volume of gel pumped providing fine control of the buoyancy. In this way, it can be understood that the buoyancy of the apparatus can be easily fine-tuned by pumping gel 10 between the reservoir off the apparatus to the bag 9 in the tank 8.

Typically, the base of the tank 8 is open to the external environment such that as the bag 9 fills it displaces water from the bottom of the tank 8, thereby increasing the volume of water displaced by the apparatus which increases the buoyancy of the apparatus. Adjustment of the volume of gel in tank 8 allows significant flexibility in buoyancy to be achieved since the buoyancy is directly proportional to the volume of fluid pumped.

It will be understood that the bag 9 is optional and in some examples, particularly where the gel 10 is immiscible, the gel 10 can be retained directly within the tank 8, without use of a separate bag 9.

Fig 3b shows a similar arrangement except that in this case tank 8 contains a bag 11 full of ballast fluid 12. Such fluid could be high density, for example having a density higher than water and being substantially incompressible, such that when the bag 11 is filled with ballast fluid 12 it ads as ballast counteracting the buoyancy created in one of the gas buoyancy tanks. Equally it is apparent that by adjustment of ballast fluid 12 within tank 8 complete flexibility in buoyancy can be achieved since once again ballasting is directly proportional to the volume of ballast fluid pumped.

Fluids of high density could be brines such as Sodium or Potassium Formate or Acetate, Sodium or Calcium Bromide or Calcium Chloride or brines containing weighting material such as barite or haematite.

As previously, the ballast fluid 12 can be pumped between a reservoir either on a vessel or a reservoir placed subsea. The reservoir is located off the apparatus.

Also as previously, it will be understood that the bag 11 is optional and in some examples, particularly where the ballast fluid 12 is immiscible and where water can enter or leave the tank 8 away from the bottom of the tank 8, the ballast fluid 12 can be retained directly within the tank 8, without use of a separate bag 11.

In an alternative embodiment, there is provided a subsea crane device such as that described in W02018/051064. In particular, in this variant depicted in figure 3c, instead of the tank 8 containing only one bag and either gel 10 or ballast fluid 12, tank 8 contains both gel and ballast fluid. In this example, each of the gel and the ballast fluid are contained in separate bags. Thus, the tank 8 contains two bags, a first bag 9 containing buoyant fluid 10 in the form of buoyant gel 10 and a second bag 11 containing ballast fluid 12 in the form of brine 12 such that the bags fill tank 8. It will be understood that the tank 8 may still be open to the external environment outside any bags 9, 11, and therefore the tank 8 may also contain water outside the bags 9, 11. The assembly is connected by an upper conduit 14a, sometimes referred to as an upper umbilical hose 14a, and a lower conduit 14b, sometimes referred to as a lower umbilical hose 14b, to a reservoir assembly 13, for example placed underwater close to the apparatus, sometimes referred to as a lifting unit, but not on the lifting unit. For instance, tank 13 could be placed on the seabed as a skid, mounted on an ROV, or the ROV tether management system. Fluid, for instance, ballast fluid 12 is pumped from the ballast fluid bag 11 in tank 13 to the ballast bag 11 in tank 8 via the lower umbilical hose 14b, displacing buoyant fluid 10 from tank 8 to tank 13 via the upper umbilical hose 14a, therefore varying the buoyancy on the lifting unit.

In some examples, the tank contains both buoyant fluid (such as buoyant gel) and ballast fluid, though only one bag to contain either the buoyant fluid or the ballast fluid. In this way, it can be seen that the bag provides a separating membrane between the buoyant fluid and the ballast fluid in the tank.

An example of apparatus for raising or lowering a load in a body of water, sometimes referred to as a lifting device, is shown in fig 4. The lifting device comprises a frame structure 6 with a plurality of lifting points (not shown) to enable the lifting device to be transported and placed in the water. A plurality of gas buoyancy tanks 1, in this example assembled vertically next to each other, are connected via an upper manifold 7a and a lower manifold 7b, as described with reference to figure 2 hereinbefore, such that some or all these tanks can be filled with gas to create buoyant force. It is preferable that these tanks are filled from a pressurised gas tank 15. or a plurality of pressurised gas tanks, mounted on the lifting device or situated elsewhere subsea (such skid mounted on an ROV). This allows the lifting device to operate without a dedicated fluid communication pathway, such as provided by a hose, to the surface which may be advantageous. In another example, the gas tanks could be filled with air from an air compressor mounted on a vessel at the surface, and transported to the lifting device via a conduit, such as a hose.

Additionally, the lifting device of figure 4 incorporates a fine control element, as described with reference to figures 3a, mounted at the lifting frame. In this example, the fine control element is preferably mounted substantially in the centre of the lifting unit for structural stability of the lifting device. The reservoir of buoyant gel is located elsewhere, either on a vessel at the surface or subsea. In figure 4 fine buoyancy control is achieved with a buoyant gel, as described with reference to figure 3a. In figure 5 fine buoyancy control is achieved with a ballast fluid, as described with reference to figure 3b. In fig 6 buoyancy control is achieved used an underwater lifting device, as described with reference to figure 3c.

In some examples, permanent syntactic buoyancy can be fitted to the unit in addition to the variable buoyancy provisions described elsewhere. The permanent buoyancy can be located to ensure that the unit is orientated correctly within the water column.

In this example, a sling is mounted below the lifting device, which is to be attached to the load to be placed, moved or recovered subsea.

The operation of the lifting unit in the field is now described. It will be appreciated that there are a number of tasks that any subsea lifting device preferably need to be able to perform to function as a subsea lifting device.

A lifting device preferably needs to be able to travel from the surface of the ocean to the seabed in a controlled manner with a load to place the load on the seabed. Once the load is placed on the seabed the lifting device preferably needs to be able to return to the surface without the load, in a controlled manner.

The lifting device also typically needs to be able to travel from the surface to the sea bed without a load and collect a load and retrieve it to the surface in a controlled manner.

Finally, the lifting device preferably needs to be able to pick up a load off the seabed and render it neutrally buoyant allowing the load to be moved from one location on the sea bed to another without having to return to the surface. The load preferably needs to be able to be placed and released from the lifting device in a controlled manner. As will be described hereinafter, the disclosed lifting device can be used to perform all of the required tasks.

Returning again to figure 4, it depicts a lifting device for raising or lowering a load in an underwater environment. The lifting device consists of a load-bearing frame 6 enclosing multiple gas buoyancy tanks 1 mounted within the frame, manifolded and having valves operable to allow the tanks to fill with water when placed in the sea at the surface of the sea. The tanks 1 are also further manifolded to allow them to be filled with gas, for example from a pressurised tank 15 on the lifting device or for a gas compressor on the vessel, in a manner that allows one some or all of the tanks Ito be completely filled with gas to replace the water. The tanks preferably need to be filled to a pressure at least matching or even exceeding that of the hydrostatic pressure at the seabed. This is to stop them being crushed by the pressure at the seabed. Typically, the tanks are designed to operate in tension to retain gases therein at pressure, and may not be able to operate under compression where the external pressure is greater than the internal pressure.Tanks that are not filled with gas are flooded with water and effectively open to the marine environment. Typically, sufficient tanks are filled with gas instead of water to render the lifting device as close as possible to neutral buoyancy, with the final portion of buoyancy (or ballast) required to make the lifting device perfectly neutrally buoyant being provided from the further buoyancy tank 8, sometimes referred to as the smart buoyancy tank 8, as described hereinafter.

The bag 9 in the smart buoyancy tank 8 is partially filled with a substantially incompressible fluid, for example either buoyant gel or ballast material such that the rifting device is stable on the surface of the water or more preferably maintains a neutral buoyancy in the water column some metres below the surface. The lifting device can be fitted with permanent syntactic buoyancy at the top of the device to maintain a predetermined vertical orientation in the water at all times.

The load to be placed on the seabed is placed in the water and attached to the lifting device while remaining attached to the vessel. Sufficient gas filled buoyancy tanks 1 are pressurised with gas to provide a buoyancy equivalent to approximately the mass of the load less the buoyancy of one tank, if gel is used or equivalent to the mass of the load plus the buoyancy of one tank if ballast fluid is used. The lifting device is adjusted to achieve substantially neutral buoyancy by adding or removing the buoyant gel or ballast fluid to the further buoyancy tank (buoyancy tank 8), at which point the load is detached from the vessel and hangs free below the lifting device, with the whole assembly of the lifting device and the load being substantially neutrally buoyant. Then, the load and the lifting device can be lowered through the water to the required position. For example, ballast is either added or buoyant gel removed from the bag 9 and the load and the lifting device can be lowered with a small crane or winch or allowed to sink to the sea bed, typically while remaining tethered to the vessel. As the lifting device and the load approach the seabed the volume of fluid in the bag is adjusted such that the load is placed in a controlled manner on the seabed. For example, the rate of descent can be slowed by removing ballast fluid or adding buoyant gel to the further buoyancy tank 8.

At this point, the load can be left on the seabed and the lifting device returned to surface or the load can be made neutrally buoyant and moved to a new location to form for instance a subsea installation. In some cases where an environmentally acceptable ballast fluid such as a formate brine is employed for fine tuning buoyancy it can be discharged to the environment.

The lifting device is returned to the surface in the following manner. Once the load has been placed in position the gas tanks are opened to release the gas from the lifting device, thereby flooding the tanks with water to reduce the buoyant force between the lifting device and the load such that it can be disconnected safely. After disconnection between the lifting device and the load, the lifting device is either slightly buoyant whereupon it floats to the surface or slightly heavy in the water and can be retrieved to the surface by the winch. As previously, ballast fluid and/or buoyant gel can be added or removed from the buoyancy tank 8 to control the ascent of the lifting device to the surface.

If a load needs to be retrieved to the surface, then the following procedure is employed.

The lifting device is placed in the water the gas tanks 1 are flooded and the buoyancy in the buoyancy tank 8 is adjusted such that the lifting device is either neutrally buoyant or slightly heavier in water such that it sinks and is then lowered to the seabed. Typically, the lifting device is arranged such that all of the gas tanks 1 will need to be flooded with water for the lifting device to sink, though this is not essential.

At the seabed the device is attached to the load and at least some of the gas buoyancy tanks 1 are filled with gas with the water discharge valve 5 being opened to allow the gas to cause the water to be displaced from the gas buoyancy tanks 1 through the bottom opening 3, sometimes referred to as the water discharge line 3. Sufficient tanks are filled with gas to make the lifting device and the load almost buoyant. Buoyant gel 10 is then pumped into the bag 9 in the buoyancy tank 8 until the lifting device together with the load is either neutrally buoyant or very slightly buoyant. At this point the load can be retrieved to the surface or moved to another location on the seabed. As described elsewhere herein, the exact buoyancy of the lifting device can be controlled by addition or removal of fluid, such as buoyant gel or ballast fluid, from the buoyancy tank 8.

As the load is brought to the surface the second valve, sometimes referred to as the water discharge valve 5, can be opened allowing gas to escape via the seawater discharge line, maintaining the pressure in the gas buoyancy tanks 1 to be equal to the hydrostatic pressure in the water column. This way when the lifting device is returned to surface it does not contain gas at a pressure which will need to be released. In some examples, it will be understood that when the gas is pumped into the buoyancy tanks Ito displace the water out of the buoyancy tanks 1 through the bottom opening 3, the second valve 5 is never closed, such that air constantly leaks out of the buoyancy tanks 1 as the lifting device and the load rises. In some examples, the second valve 5 may be configured to operate in a one-way configuration in which air is permitted to pass out of the valve to the water, but water is not permitted to pass through the second valve into the buoyancy tank When the lifting device is at the surface it has a comparatively low mass with the buoyancy tanks 1 filled with air instead of water, and so it can be retrieved to the vessel easily.

Furthermore, the lifting device can be formed to be of a dimension that it can easily be shipped by vessels or road transport. In some examples, multiple lifting devices can be employed to lift heavy objects subsea. A slave lifting device which consists only of dumb buoyancy can be employed to increase the lifting capacity further. It will be understood that the term "dumb buoyancy" refers to buoyancy tanks that can either be filled completely with gas, such as air, or completely with denser liquid, such as water, where the proportions of gas and liquid in the buoyancy tanks are typically not adjusted during raising or lowering of the buoyancy tanks.

Control of the manifolded valves allows significant modification of the buoyancy to accommodate the degree of lift. In some examples, one or more pump to add or remove fluids from the buoyancy tanks 1, 8 may be located onboard the lifting device. One or more pumps may be located off the lifting device, such as on a vessel or on a subsea structure, for example in the same location as the reservoir of the buoyant fluid and/or the ballast fluid.

It can be appreciated that adding ballast is more effective for lowering loads while adding buoyancy is more effective for raising loads. It will be understood that this is at least partly because a pump for pumping ballast fluids is typically located at the surface, and is more capable of pumping the ballast fluids down to the apparatus than sucking the ballast fluids up from the apparatus. Conversely, a pump for pumping buoyancy can both pump buoyancy gas down to the apparatus and easily suck the buoyancy gas up from the apparatus. A combination of buoyancy and ballast such as that disclosed in W02018/051064, is most effective for moving loads on the sea bed, where raising and lowering of loads is required.

In summary, there is provided an apparatus for raising or lowering a load in a body of water. The apparatus comprises: a support frame (6) for attachment to the load; and one or more first compartments (1) supported on the support frame (6). The one or more first compartments (1) are substantially rigid and each configured to be provided in a first configuration filled with a first gas having a first density. The one or more first compartments are further configured to be provided in a second configuration filled with a second fluid having a second density greater than the first density. The apparatus further comprises: a first conduit (7) and a second conduit (7), each in fluid communication with the, or each, first compartment (1). The first conduit (7) provides a first gas communication pathway between a first reservoir (15) for the first gas and the, or each, first compartment (1). The second conduit (7) provides a second fluid communication pathway between a second reservoir for the second fluid and the, or each, first compartment (1). The first gas is a compressible gas.

Claims

CLAIMS1. An apparatus for raising or lowering a load in a body of water, the apparatus comprising: a support frame for attachment to the load; one or more first compartments supported on the support frame, the one or more first compartments being substantially rigid and each configured to be provided in a first configuration filled with a first gas having a first density and in a second configuration filled with a second fluid having a second density greater than the first density; a first conduit in fluid communication with the, or each, first compartment and providing a first gas communication pathway between a first reservoir for the first gas and the, or each, first compartment; and a second conduit in fluid communication with the, or each, first compartment and providing a second fluid communication pathway between a second reservoir for the second fluid and the, or each, first compartment, wherein the first gas is a compressible gas.
2. The apparatus as claimed in claim 1, wherein the one or more first compartments are buoyant in water.
3. The apparatus as claimed in claim 2, wherein the one or more first compartments 20 are formed from carbon fibre.
4. The apparatus as claimed in any preceding claim, further comprising the first reservoir supported on the support frame.
5. The apparatus as claimed in any preceding claim, further comprising a first pump to pump the first gas into the one or more first compartments.
6. The apparatus as claimed in any preceding claim, further comprising a non-varying buoyancy component supported at the support frame.
7. The apparatus as claimed in any preceding claim, further comprising a controller to control movement of the first gas between the one or more first compartments and the first reservoir and movement of the second fluid between the one or more first compartments and the second reservoir.
8. The apparatus as claimed in any preceding claim, wherein the, or each, of the one or more first compartments is provided with: a first valve in the first conduit to selectively permit flow of the first gas from the first reservoir into the respective first compartment; and a second valve in the second conduit to selectively permit flow of the second fluid from the second reservoir into the respective first compartment.
9. The apparatus as claimed in claim 8, wherein, in the first configuration, the second valve is further configured to substantially prevent flow of the first gas from the respective first compartment.
10. The apparatus as claimed in any preceding claim, further comprising: a second compartment supported on the support frame and configured to retain a third fluid in at least a portion thereof; and a third conduit in fluid communication with the second compartment and providing a third fluid communication pathway between a third reservoir for the third fluid and the second compartment, wherein the third fluid is substantially incompressible and has a third density different from the second density.
11. The apparatus as claimed in any of claims 10, wherein the third reservoir is provided off the support frame whereby the third reservoir is not arranged to be raised or lowered with the load.
12. The apparatus as claimed in claim 10 or claim 11, further comprising a second pump to pump the third fluid between the second compartment and the third reservoir.
13. The apparatus as claimed in any of claims 10 to 12, wherein the apparatus is configured to provide a fluid communication path from the second compartment to the body of water, in use.
14. The apparatus as claimed in any of claims 10 to 13, wherein a combined volume of the one or more first compartments is greater than a volume of the second compartment.
15. The apparatus as claimed in any of claims 10 to 14, when dependent on claim 7, wherein the controller is further to control movement of the third fluid between the second compartment and the third reservoir.
16. The apparatus as claimed in any of claims 10 to 15, wherein the second compartment is configured to retain a fourth fluid in at least a further portion thereof, wherein the apparatus further comprises a fourth conduit in fluid communication with the second compartment and providing a fourth fluid communication pathway between a fourth reservoir for the fourth fluid and the second compartment, and wherein the fourth fluid is substantially incompressible and has a fourth density greater than the third density.
17. The apparatus as claimed in any of claims 10 to 16, wherein the third density is less than a density of water.
18. The apparatus as claimed in claim 17, wherein the fourth density is at least the density of water.
19. The apparatus as claimed in claim 17 or 18, wherein the third fluid comprises microspheres.
20. The apparatus as claimed in any preceding claim, wherein the apparatus is capable of operation at an operational depth of greater than 100 metres below a surface of the body of water.
21. The apparatus as claimed in claim 20, wherein, in the first configuration, the first gas is at a pressure substantially equal to a hydrostatic pressure in the body of water at the operational depth.
22. The apparatus as claimed in claim 21, wherein the one or more first compartments can be provided in the first configuration when the apparatus is above the operational depth.
23. The apparatus as claimed in claim 22, wherein the one or more first compartments can be provided in the first configuration when the apparatus is substantially at the surface 20 of the body of water.
24. The apparatus as claimed in any preceding claim, wherein the first gas is air.
25. The apparatus as claimed in any preceding claim, wherein the second fluid is water and wherein the second reservoir is the body of water.
26. A method for raising or lowering a load in a body of water, the method comprising: providing the apparatus as claimed in any preceding claim, having at least one of the one or more first compartments filled with the second fluid; securing the load at the support frame of the apparatus; filling at least one of the one or more first compartments with the first gas instead of the second fluid such that a combination of the apparatus and the load are substantially neutrally buoyant; raising or lowering the apparatus and the load to a desired position in the body of water.
27. The method as claimed in claim 26, wherein the apparatus is as claimed in claim 1501 any of claims 16 to 25 when dependent on claim 15, further comprising at least partially filling the second compartment with the third fluid.
28. The method as claimed in claim 27, wherein the second compartment is at least partially filled with the third fluid to control the raising or lowering of the combination of the apparatus and the load.
29. A buoyancy compartment to be used underwater and for retaining a first gas therein at a maximum operating pressure greater than 1,000 kilopascals (10 bar), wherein the buoyancy compartment is substantially rigid.
30. The buoyancy compartment of claim 29, wherein a mass of the buoyancy compartment when filled with air at the maximum operating pressure is less than a mass of water to be displaced by submersion of the buoyancy compartment in a body of water.
31. The buoyancy compartment of claim 29 or claim 30, wherein the maximum operating pressure is greater than 10,000 kilopascals (100 bar).
32. The buoyancy compartment of any of claims 29 to 31, wherein the buoyancy compartment is formed from carbon fibre.