WO2015118319A1 - Method of producing a buoyant material - Google Patents

Method of producing a buoyant material

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Publication number
WO2015118319A1
WO2015118319A1 PCT/GB2015/050295 GB2015050295W WO2015118319A1 WO 2015118319 A1 WO2015118319 A1 WO 2015118319A1 GB 2015050295 W GB2015050295 W GB 2015050295W WO 2015118319 A1 WO2015118319 A1 WO 2015118319A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
buoyant
fluid
wax
microspheres
container
Prior art date
Application number
PCT/GB2015/050295
Other languages
French (fr)
Inventor
Patrick Collins
Original Assignee
Aubin Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

Links

Classifications

    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21BEARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B17/00Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods ; Cables; Casings; Tubings
    • E21B17/01Risers
    • E21B17/012Risers with buoyancy elements
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/58Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising fillers only, e.g. particles, powder, beads, flakes, spheres
    • B29C70/66Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising fillers only, e.g. particles, powder, beads, flakes, spheres the filler comprising hollow constituents, e.g. syntactic foam
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B63SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63BSHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
    • B63B22/00Buoys
    • B63B22/18Buoys having means to control attitude or position, e.g. reaction surfaces or tether
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL
    • B29KINDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS
    • B29K2105/00Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B29K2105/16Fillers
    • B29K2105/165Hollow fillers, e.g. microballoons, expanded particles

Abstract

A method of providing buoyancy. The method including the steps of transporting a buoyant fluid to a given location, the buoyant fluid comprising a base fluid, microspheres and a wax. The method also including the steps of heating the buoyant fluid at the given location to melt the wax, adding the buoyant fluid to a container, and cooling the buoyant fluid to at least partially solidify the wax, thereby producing a buoyant material. There is also described a method of producing a buoyant material.

Description

METHOD OF PRODUCING A BUOYANT MATERIAL

The present invention relates to a method of producing a buoyant material and method of providing buoyancy.

The subsea industry employs a variety of different subsea technologies and infrastructure. The equipment used that is not fixed to the seabed often requires, or is aided by, the provision of buoyancy modules. Subsea risers for example carry produced fluids from a subsea wellhead through the water column to a surface facility, such as an offshore platform.

Subsea risers often have syntactic buoyancy modules attached thereto. At enhanced depths the subsea riser is so heavy that it cannot support its own weight in the water and there is a significant risk of failure.

Syntactic buoyancy modules are often used to reduce this "top tension" on subsea risers or other subsea elements by providing distributed support. Syntactic buoyancy modules can also assist in shaping the underwater configuration of subsea risers to facilitate flow of the produced fluids, and allow enough slack in the subsea riser to cope with the heave or other movement of a floating surface facility caused by the surface conditions.

Also, remotely operated vehicles (ROVs) often have large syntactic buoyancy modules provided therein. Buoyancy is added to ROVs to render them neutrally buoyant. This reduces the power required to maintain and manoeuvre the ROV in the water.

Whilst generally satisfactory, the inventor of the present invention has noted some limitations of syntactic buoyancy modules. In accordance with a first aspect of the present invention there is provided a method of producing a buoyant material, the method comprising the steps of:

mixing a base fluid, microspheres and a wax to produce a buoyant fluid; and cooling the buoyant fluid to at least partially solidify the wax.

During the cooling step, the wax is normally dispersed, that is more dispersed compared to the wax before the cooling step. It may be an advantage of the present invention that the step of cooling the buoyant fluid to at least partially solidify the wax typically fixes or at least helps to fix the microspheres as a suspension in the base fluid.

The step of cooling the buoyant fluid to at least partially solidify the wax typically produces the buoyant material.

The step of mixing the base fluid, microspheres and wax may comprise two steps, the step of mixing the microspheres with the base fluid and then adding the wax to the mixture of base fluid and microspheres.

After the mixing step the buoyant fluid is typically a homogenous mixture of the base fluid, microspheres and wax. The microspheres are normally suspended in the base fluid after the mixing step. The inventors of the present invention have appreciated that after an extended period of time, for example more than 10 or 20 years, the

microspheres may move or migrate through the base fluid such that the buoyant fluid is no longer a homogenous mixture. The wax is typically added to the mixture of base fluid and microspheres to mitigate the effects of time on the homogeneity of the mixture. The wax may therefore increase the useful lifetime of the buoyant material.

The method typically includes a step of heating and/or warming the buoyant fluid to melt the wax. The wax is typically added to one or more of the base fluid,

microspheres and mixture of the base fluid and microspheres as a solid or at least in a partially solid state. The wax is typically in a solid or at least in a partially solid state both before the step of heating and/or warming the buoyant fluid, and after the step of cooling the buoyant fluid.

However before cooling (and before warming, if a warming step is done) the wax is provided in a discrete form, and the buoyant fluid with any wax behaves largely as a liquid; for example, it is normally pourable. However after the cooling step, the wax solidifies and is dispersed and the overall properties of the buoyant fluid change to that of a far more viscous, normally solid material i.e. the buoyant material; which is not normally pourable. It may be an advantage of the present invention that the buoyant fluid is relatively easy to move about and/or between locations compared to a syntactic buoyancy module. The buoyant fluid can be relatively easily converted into the buoyancy material at a given location. There is typically no need for the buoyant fluid to be mixed at the given location. The buoyant fluid can be transported pre-mixed.

In an alternative embodiment the wax may be heated and/or warmed to melt the wax before it is added to one or more of the base fluid, microspheres and mixture of the base fluid and microspheres. In this alternative embodiment the wax is normally added to one or more of the base fluid, microspheres and mixture of the base fluid and microspheres as a liquid. One or more of the base fluid, microspheres and mixture of the base fluid and microspheres may be heated and/or warmed before the melted and/or liquid wax is added. A heat exchanger is typically used to heat and/or warm one or more of the base fluid, microspheres, wax and buoyant fluid. The heat exchanger may have a first and a second fluid circuit. The first fluid circuit may contain warm water. The second fluid circuit may contain one or more of the base fluid, microspheres, wax and buoyant fluid. Heat from the water is typically transferred to one or more of the base fluid, microspheres, wax and buoyant fluid.

The step of at least partially solidifying the wax may include hardening and/or be referred to as hardening the wax. The at least partially solidified wax may be a solid. When the buoyant fluid is cooled to at least partially solidify the wax the buoyant fluid is also typically solidified. The buoyant fluid is typically a liquid. The buoyant fluid is typically cooled to solidify the wax, thereby producing solid buoyant material. The step of at least partially solidifying the wax may help to fix the dispersion of microspheres in the base fluid of the buoyant material. The step of cooling the buoyant fluid to at least partially solidify the wax is typically achieved by allowing the buoyant fluid to cool to the ambient temperature, for example a temperature of from 15 to 25°C. A chiller or cooler may be used to cool the buoyant fluid. A ribbon blender is typically used to mix the base fluid, microspheres and wax to produce the buoyant fluid. The buoyant material normally provides lift of from 200 to 600 kg/m3, typically from 425 to 480 kg/m3. The wax may be a synthetic or naturally occurring wax. The wax may be a product of a Fischer-Tropsch process. The wax is typically an organic compound. The wax is typically a lipid. The wax may be one or more of a mineral wax, paraffin wax, petroleum wax, vegetable oil, palm oil, coconut oil, and bees wax. The wax may be an ester comprising one or more long-chain carboxylic acids and one or more long-chain alcohols.

The wax may comprise one or more straight chains of carbon atoms. The wax may comprise one or more branched chains of carbon atoms. The wax may comprise a mixture of straight and branched chains of carbon atoms. The one or more straight or branched chains may have from 20 to 80 carbon atoms, typically from 20 to 50 carbon atoms and normally from 22 to 50 carbon atoms.

The buoyant fluid typically comprises from 3 to 25 percent, normally from 8 to 15 percent and may be 15 percent wt/wt of wax.

The step of heating and/or warming the buoyant fluid to melt the wax or heating and/or warming the wax to melt the wax before it is added to the base fluid and/or microspheres normally involves raising the temperature of the buoyant fluid and/or wax by from 5 to 100°C, typically from 5 to 50°C and normally from 5 to 30°C.

The method may further include the step of adding the buoyant fluid to a container. The method may include the step of lowering the container into water. The water is typically seawater. The method may further include the step of sealing the container. The container may be sealed before it is lowered into the water. The step of lowering the container into the water is typically after the step of adding the buoyant fluid to the container but the buoyant fluid may be added to the container when the container is already located in the water. The step of cooling the buoyant fluid to at least partially solidify the wax is typically after the step of adding the buoyant fluid to the container.

The method of producing the buoyant material is normally reversible, that is the solid buoyant material can be warmed to increase the temperature of the buoyant material to produce liquid buoyant fluid, also referred to as buoyant liquid. It may be an advantage of the present invention that when the buoyant material has been used, it can be removed from its container for recycling or safe disposal, separate from recycling or safe disposal of the container.

The buoyant material is typically thermally insulative.

The invention may provide a convenient method of adding buoyancy to a structure including the container because it can first be added as a fluid with a relatively low viscosity and then after cooling, the wax in the buoyant fluid solidifies to form the buoyant material. The buoyant material may be a solid or at least partially solid and/or may have the viscosity of a thick paste. The viscosity of the thick paste is such that the buoyant material will remain in, for example, a 500ml jar when the jar is inverted. The container may be part of a structure that, in use, is located subsea. The container may be referred to as a buoyancy module. The container may be tubular-shaped. The tubular-shaped container may be part of a frame of the structure. The structure may be part of equipment used subsea and may, for example, be a pipe and/or cable laying plough and/or skid.

The method may include the step of sinking the structure after the buoyant fluid has been added to the container. In an alternative embodiment buoyant fluid may be added to the container and/or structure when it is already in place subsea. It can be very difficult to place conventional buoyancy subsea because the material is buoyant and needs to be weighed down or pulled into place particularly if the buoyancy needs to be placed at depth.

The buoyant material, produced by cooling the buoyant fluid to at least partially solidify the wax, may have a viscosity of greater than 14,000mPa-s at a shear rate of 0.8s 1 at 293 K. 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 viscosities render the buoyant material, that is the cooled buoyant fluid, unpumpable. This is in sharp contrast and against the teaching of EP 1 867 564 where a buoyant fluid is provided for a different purpose and is a much less viscous fluid and is pumpable to manipulate and vary buoyancy.

Increasing the viscosity of the buoyant fluid may take from 1 hour to 24 hours, normally from 1 hour to 3 hours. The time taken to increase the viscosity of the buoyant fluid is generally proportional to the volume of buoyant fluid. The greater the volume the longer it takes to cool.

The buoyant material may remain in the container for at least 10 years, typically at least 20 years. It may be the increased viscosity of the buoyant material that helps keep the material in the container for this extended period of time, even if the container is damaged. If the buoyant material was a liquid, any damage to the container would likely result in leakage of the buoyant material from the container and subsequent contamination of the surrounding environment.

It may be an advantage of the present invention that one or more of the base fluid, microspheres, wax and buoyant fluid can be relatively easily tested and/or certified. In contrast, syntactic buoyancy modules need to be tested in large purpose built hydro- facilities. This increases the cost of syntactic buoyancy modules.

In accordance with a second aspect of the present invention there is provided a method of providing buoyancy, the method comprising the steps of:

transporting a buoyant fluid to a given location, the buoyant fluid comprising a base fluid, microspheres and a wax;

heating the buoyant fluid at the given location to melt the wax;

adding the buoyant fluid to a container; and

cooling the buoyant fluid to at least partially solidify the wax, thereby producing a buoyant material. The inventor of the present invention has appreciated that buoyancy can be conveniently provided using the steps of the above method. The container and buoyant fluid can be conveniently transported to the given location and the heating step can be performed locally. In this way, the viscosity of the buoyant fluid can be increased which may provide a variety of benefits, for example transportation costs can be reduced compared to moving large syntactic buoyancy modules of odd shapes and sizes.

The step of heating the buoyant fluid at the given location to melt the wax may be before or after the step of adding the buoyant fluid to the container.

The buoyant fluid may be transported to the given location in the container.

The given location may be a surface vessel, such as ship or an offshore platform. The given location may be onshore, but preferably close to an area of use. The given location is preferably within 100 miles, optionally within 20 miles of the area of use.

The given location may be underwater and/or subsea. When the given location is underwater and/or subsea the buoyancy, also referred to as permanent buoyancy, can be installed in situ.

In one embodiment the container may be pre-filled with a starter fluid such as water. The container may have at least one inlet and at least one outlet. The buoyant fluid may be added to the container through the at least one inlet, thus displacing the starter fluid through the at least one outlet. This may make it easier to locate and/or place the container in situ because the container is less buoyant.

For certain embodiments the container is attached to a structure on which it is to be used, before the buoyant fluid is added. In this way it can be much easier to attach the container when it does not have the fluids therein.

The container may be a bag. Preferably the container is at least partially deformable. A variety of containers with different shapes can be used to form the shapes required for the different applications of the buoyancy, for example to attach to a subsea riser or to fit to an ROV. One suitable shape is a tubular shape. The container may be one or more of flexible, malleable, deformable and bendable. When the buoyant material is in the container the viscosity and/or pressure of the buoyant material in the container may add to the rigidity of the container but the container will typically remain one or more of flexible, malleable, deformable and bendable.

It may be an advantage of the present invention that the flexibility, malleability, deformability and/or bendability of the container with the buoyant material inside means that in the event of an object colliding with the container, the container can absorb some of the impact of the collision without the lift provided by the container being compromised. Other known and/or regular buoyancy modules are not able to absorb the force of an impact in this way. The flexibility, malleability, deformability and/or bendability of the container with the buoyant material inside may mean that in the event of an impact, the risk of damage to the container and/or object is reduced and/or the container remains in place rather than being dislodged from where it is secured. The container may not itself need to be robust enough to withstand the impact of the collision, rather the buoyant material inside the container may provide the container with sufficient strength to withstand the impact of the collision. The container may further comprise a bladder to help absorb some of the impact of a collision between an object and the container.

It may also be an advantage of the present invention that the container need only be filled with the required amount of buoyant fluid. If the amount of buoyant fluid added to the container is too much and therefore the buoyancy it provides is too much, some of the buoyant fluid can be removed from the container before the buoyant fluid cools. Alternatively, the buoyant material can be reheated to produce the liquid buoyant fluid, also referred to as buoyant liquid, that can then be pumped or otherwise removed from the container. In contrast, a portion of a syntactic buoyancy module would have to be cut off to reduce the buoyancy it provided. This is difficult, if at all possible, and cannot be reversed.

The buoyant fluid is typically incompressible. The buoyant material is typically incompressible. Optionally the buoyant fluid has a specific gravity of less than 0.70g/cm3, may be less than 0.65g/cm3, typically less than 0.60g/cm3, and often less than 0.55g/cm3. 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 base fluid typically comprises an oil. The oil is typically the major and/or majority component 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 oil may be a triglyceride such as one having the structure:

Figure imgf000011_0001
wherein R1, R11 and R111 are typically hydrocarbon chains with a chain length of from C12 to C22 to give a range of fatty acids. The hydrocarbon chains may have from zero to three double bonds.

Preferably the oil is naturally occurring. The oil may be biodegradable, for example vegetable oil. Thus for certain embodiments of the invention, the inherent

environmental risk of the buoyant fluid and therefore also the base fluid including the oil leaking from the container 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 oil is synthetic.

The base fluid may also comprise a viscosifying agent such as an organophilic clay, dispersed silica, long chain polymeric materials, surfactants and/or mixtures thereof. The viscosifying agent typically helps to suspend the microspheres in the buoyant fluid. The viscosifying agent normally helps to increase the viscosity of the base fluid. The viscosifying agent may be a styrene butadiene block copolymer, bentonite, attapulgite, fumed silica, phosphate ester, xanthan gum or carrageenan. In use the styrene butadiene block copolymer typically forms large worm-like micelles. Clay-type materials such as the bentonite or attapulgite and fumed silica typically have a very high surface area. When the viscosifying agent is a phosphate ester it may be combined with an iron cross-linker. The xanthan gum or carrageenan may be particularly useful in water based systems.

The microspheres may each have a sealed chamber containing a gas or at least a partial vacuum. The microspheres may be from 1 pm 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 3M. The microspheres may be rated to over 31 ,000kPa (4500psi), preferably over 41 ,000kPa (6000psi). Other microspheres with different strengths and densities may be used and generally stronger microspheres have higher densities. The microspheres may be rated to over 2,000kPa (300psi) and thereby suitable for a water depth of 120meters. The microspheres may be rated to over 3,500kPa (500psi) and thereby suitable for a water depth of 200meters. The microspheres may be rated to over 10,000kPa (3000psi) and thereby suitable for a water depth of 1 ,500meters. The microspheres rated to over 41 ,00kPa (6000psi) may thereby suitable for a water depth of 3,000meters. The microspheres may be rated to over 55,000kPa (8000psi) and thereby suitable for a water depth of 4,000meters.

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 comprising a base fluid, microspheres and a wax is typically stable at room temperature.

The method of providing buoyancy may further comprise the step of pre-stressing the microspheres. The step of pre-stressing the microspheres typically involves breaking the weaker microspheres. The step of pre-stressing the microspheres typically therefore involves breaking the weaker microspheres to leave the stronger and/or more robust microspheres. It is an advantage of the present invention that the microspheres of the buoyant fluid used in the method of providing buoyancy are strong and/or robust because the buoyancy provided by the microspheres is less or not affected by subsequent treatment and/or use of the buoyant fluid. It may be an advantage of the present invention that the microspheres of the buoyant fluid are not damaged in or the buoyancy affected by the present method of providing buoyancy. It may be an advantage of the present invention that the step of pre-stressing the microspheres means that the volume of the buoyant fluid does not change when the buoyant fluid is used in the present method of providing buoyancy.

It is generally accepted that when the microspheres have a rating, of for example to over 41 ,000kPa (6000psi), that equal to or more than 90% of the microsphere will have this rating. The step of pre-stressing the microspheres deliberately breaks and/or crushes the remaining equal to or less than 10% of the microspheres. The step of pre- stressing the microspheres typically results in equal to or less than 5% of the microspheres having a rating of less than the stated rating. For example, if the microspheres with a rating of over 41 ,000kPa (6000psi) are pre-stressed, then equal to or more than 95% of the resultant microspheres will have a rating of over 41 ,000kPa (6000psi).

The step of pre-stressing the microspheres may result in equal to or less than 2% of the microspheres having a rating of less than the stated rating. The step of pre- stressing the microspheres normally results in equal to or less than 1 % of the microspheres having a rating of less than the stated rating.

The step of pre-stressing the microspheres is typically before the step of transporting the buoyant fluid to a given location. The step of pre-stressing the microspheres is typically before the buoyant fluid is produced.

It may be an advantage of the present invention, that by pre-stressing the

microspheres the buoyancy of the buoyant fluid is not degraded in use, so the amount of buoyancy at depth is the same as that on the surface.

The buoyant fluid typically comprises from 25 to 60% vol/vol microspheres, optionally from 30 to 50% 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, damaging the microspheres and thereby reducing the buoyancy they provide. The optional features of the second aspect of the present invention can be

incorporated into the first and third aspects of the present invention and vice versa. In accordance with a third aspect of the present invention there is provided a method of adding buoyancy to a subsea structure, the method comprising adding a buoyant fluid including a base fluid, microspheres and a wax to a bore of a tube, the tube being part of a tubular frame associated and/or integral with the subsea structure. The subsea structure may be a plough, a pipe connector, or another piece of subsea equipment.

The buoyant fluid according to the third aspect of the invention is normally the buoyant fluid described herein with reference to the other aspects of the present invention and may be the buoyant material when the buoyant fluid has been cooled.

The optional features of the third aspect of the present invention can be incorporated into the first and second aspects of the present invention and vice versa.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows a bag attached to a subsea riser to create a catenary bend in the subsea riser, the bag filled with a buoyant material;

Figure 2 shows a plastic shell fitted around a vertical riser, the plastic shell filled with buoyant material;

Figure 3 shows an element to create a bend in a pipeline, the element filled with buoyant material;

Figures 4A and 4B show a bag filled with buoyant material face on and edge on respectively;

Figure 4C shows two bags filled with buoyant material and fitted to a subsea skid to make the skid neutrally buoyant; and

Figure 5 is a subsea pipe connector, the frame of which has been filled with buoyant material.

Figure 1 shows a bag 16 filled with a buoyant material (not shown) attached to a subsea riser 12 to create a catenary bend in the subsea riser.

A base liquid, microspheres and solid wax chips are mixed together to produce a buoyant liquid including solid wax chips. The buoyant liquid is transported to a given location by boat. An empty bag is also transported to the given location by boat. It is relatively easy to move the pre-mixed buoyant liquid containing the solid wax chips between locations compared to a syntactic buoyancy module. The buoyant liquid is then heated in a heat-exchanger to a temperature of 60°C. The bag 16 is then filled with the buoyant liquid at 60°C (which has an overall liquid state) before the buoyant liquid is allowed to cool, such that the wax solidifies and disperses, thus providing a buoyant material with solid properties. The buoyant material assumes the shape of the bag.

The mixture of buoyant liquid/material has a composition of 65% linear paraffin, 2% polymer, 19% glass microspheres, 14% paraffin wax wt wt.

The compositions can be varied as required and in particular, the amount of glass microspheres can be varied depending on the buoyancy required and the depth of intended use. These examples are rated to a depth of 1 ,500 metres. Other compositions may be rated to a depths of 3,000 or 4,000 metres.

Table 1 below shows the viscosity of the base liquid and buoyant liquid (including the wax) measured before the buoyant liquid is heated and cooled.

Figure imgf000016_0001

Table 1 To determine the shear rate based on the RPM a Chandler 35 rotational viscometer was used 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 viscosity of the buoyant material is difficult to measure. As a material becomes more viscous it behaves more like a solid and as such it is increasingly difficult to measure the viscosity of the material. It is typically not possible to measure of the viscosity of the buoyant material using a Chandler 35 rotational viscometer because the material is too viscous.

In an alternative embodiment a mixture of base liquid and microspheres is heated in a heat-exchanger to a temperature of 60°C. Wax is separately heated in a heat- exchanger to a temperature of 60°C to melt the wax and produce liquid wax. The liquid wax is then added to the heated mixture of base liquid and microspheres to produce the buoyant liquid.

The bag 16 is then filled with the buoyant liquid at 60°C (which has an overall liquid state) before the buoyant liquid is allowed to cool, such that the wax solidifies and disperses, thus providing a buoyant material with solid properties.

Figure 1 shows a vessel 10 receiving a riser 12 that transports fluids from a subsea well (not shown) to the vessel 10. The riser or subsea riser 12 has a bag 16 (also referred to as a container or buoyancy module) attached thereto which reduces the weight of the riser 12 felt by the vessel 10 and also provides sufficient slack in the subsea riser 12 to allow for safe movement of the vessel 10 due to surface conditions.

Figure 2 shows a plastic shell 17 fitted around a vertical riser 12. The plastic shell 17 is filled with buoyant material (not shown) to provide buoyancy.

Figure 3 shows an element 18 to create a bend in a pipeline 14. The element 18 is filled with buoyant material (not shown) to provide buoyancy. Figures 4A and 4B show a bag 20 filled with buoyant material (not shown). Figures 4A and 4B show the bag 20 face on and edge on respectively. The bag is surrounded by an edging 22. The edging 22 has attachment points 24 to secure the bag 20 to another object (not shown). Figure 4C shows two bags 20a, 20b filled with buoyant material (not shown). The two bags 20a, 20b are fitted to a subsea skid 30 to make the skid neutrally buoyant.

Figure 5 is a subsea pipe connector 50. The subsea pipe connector 50 has a frame 60 which has been filled with buoyant material (not shown). Syntactic buoyancy units 40 are secured to the subsea pipe connector 50 to provide buoyancy subsea. The internal spaces 62 of the frame 60 act as a container for the buoyant material (not shown) which is added thereto. The buoyant material reduces, and in some cases removes, the requirement for syntactic buoyancy units 40. The subsea equipment is therefore smaller and subsequently easier to move because less space needs to be reserved for the syntactic buoyancy units 40. Moreover, the frame 60 can be rated to a lesser strength because the internal spaces 62 of the frame 60 are filled with the buoyant material (not shown) that provides support to the frame, providing a closer pressure balance between the internal space and the exterior environment.

Modifications and improvements can be incorporated herein without departing from the scope of the invention.

Claims

1. A method of providing buoyancy, the method comprising the steps of:
transporting a buoyant fluid to a given location, the buoyant fluid comprising a base fluid, microspheres and a wax;
heating the buoyant fluid at the given location to melt the wax;
adding the buoyant fluid to a container; and
cooling the buoyant fluid to at least partially solidify the wax, thereby producing a buoyant material.
2. A method according to claim 1 , wherein the step of heating the buoyant fluid at the given location to melt the wax is before the step of adding the buoyant fluid to the container.
3. A method according to claim 1 or claim 2, wherein the given location is a ship or an offshore platform.
4. A method according to any preceding claim, wherein the container is attached to a structure on which it is to be used before the buoyant fluid is added.
5. A method according to any preceding claim, wherein the container is one or more of at least partially deformable, flexible, malleable and bendable.
6. A method according to any preceding claim, wherein the buoyant fluid further comprises a viscosifying agent.
7. A method according to claim 6, wherein the viscosifying agent is styrene butadiene block copolymer, bentonite, attapulgite, fumed silica, phosphate ester, xanthan gum or carrageenan.
8. A method according to any preceding claim, wherein the microspheres have a compressive strength of more than 31 ,000kPa.
9. A method of producing a buoyant material, the method comprising the steps of: mixing a base fluid, microspheres and a wax to produce a buoyant fluid; and cooling the buoyant fluid to at least partially solidify the wax.
10. A method according to claim 9, the method further including the step of heating the buoyant fluid to melt the wax.
11. A method according to claim 10, wherein the wax is in at least a partially solid state both before the step of heating the buoyant fluid, and after the step of cooling the buoyant fluid.
12. A method according to claim 9, the method further including the step of heating the wax to melt the wax before it is added to one or more of the base fluid,
microspheres and mixture of the base fluid and microspheres.
13. A method according to claim 12, wherein the one or more of the base fluid, microspheres and mixture of the base fluid and microspheres is heated before the melted liquid wax is added.
14. A method according to any of claims 9 to 13, the method further including the step of pre-stressing the microspheres such that equal to or less than 5% of the resultant microspheres have a rating of less than the stated strength rating.
15. A method according to any of claims 9 to 13, the method further including the step of pre-stressing the microspheres such that equal to or more than 95% of the resultant microspheres have a rating of over 31 ,000kPa (4500psi).
16. A method as claimed in any of claims 9 to 15, wherein the wax is more dispersed after the cooling step compared to before the cooling step.
17. A method according to any of claims 9 to 16, wherein the buoyant material is at least partially solid.
18. A method according to any of claims 9 to 17, wherein the step of mixing the base fluid, microspheres and wax comprises two steps, the step of mixing the microspheres with the base fluid and then adding the wax to the mixture of base fluid and microspheres.
19. A method according to any of claims 9 to 18, wherein when the buoyant fluid is cooled to at least partially solidify the wax the buoyant fluid is also at least partially solidified.
20. A method according to any of claims 9 to 19, wherein the step of cooling the buoyant fluid to at least partially solidify the wax is achieved by allowing the buoyant fluid to cool to the ambient temperature.
21. A method according to any of claims 10 to 20, wherein the wax melts, that is becomes a liquid, when heated to above 45°C.
22. A method according to any of claims 9 to 21 , the method further including the step of adding the buoyant fluid to a container.
23. A method according to claim 22, wherein the step of cooling the buoyant fluid to at least partially solidify the wax is after the step of adding the buoyant fluid to the container.
24. A method according to claim 22 or claim 23, wherein the container is part of a frame of a structure that, in use, is located subsea.
25. A method according to claim 24, the method further including the step of sinking the structure after the buoyant fluid has been added to the container.
26. A method according to any of claims 9 to 25, wherein the buoyant fluid further comprises a viscosifying agent.
PCT/GB2015/050295 2014-02-04 2015-02-04 Method of producing a buoyant material WO2015118319A1 (en)

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GB0312781D0 (en) * 2003-06-04 2003-07-09 Ythan Environmental Services L Method
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US3531233A (en) * 1968-04-17 1970-09-29 John K Max Method for raising submerged objects
US4021589A (en) * 1976-04-28 1977-05-03 Emerson & Cuming, Inc. Buoyancy materials
US4144658A (en) * 1976-09-16 1979-03-20 Hanson Industries Inc. Viscous, flowable, pressure-compensating fitting materials and their use, including their use in boots
US4728551A (en) * 1987-02-24 1988-03-01 Jay Eric C Flowable pressure compensating fitting materials
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GB2524868A (en) 2015-10-07 application

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