GB2579092A

GB2579092A - Method

Info

Publication number: GB2579092A
Application number: GB1818908.4A
Authority: GB
Inventors: Joseph Collins Patrick
Original assignee: Aubin Ltd
Current assignee: Aubin Ltd
Priority date: 2018-11-20
Filing date: 2018-11-20
Publication date: 2020-06-10
Anticipated expiration: 2038-11-20
Also published as: GB201818908D0; GB2579092B; WO2020104795A1

Abstract

The present invention relates to a method of preparing an offshore structure 10 for movement, especially a structure i.e. an oil rig used in the oil and gas industry. The method comprises adding a foam 25 comprising a base mixture 21 and a gas 24 to the offshore structure and allowing the foam to form a foamed gel. The foamed gel may have a 'mousse-like consistency and is more viscous than the base mixture. The presence of foamed gel helps retain any pollutants in the offshore structure allowing it to be moved, for example to port, where it can be cleaned and dismantled more efficiently. Later embodiments relate to a method of recovering an offshore structure, the method comprising moving the offshore structure comprising the foamed gel, cleaning or dismantling such an offshore structure having foamed gel, and a chemical blend. In this way, an offshore structure can be decontaminated in port rather than offshore, which saves significant costs.

Description

Method This invention relates to a method and blend for preparing, moving and/or dismantling offshore structures, especially those used in the offshore oil and gas industry.

Offshore structures used in the oil and gas industry are complex systems comprising many facilities such as processing equipment, pipes and vessels. Over the number of years that an offshore structure is in use, vast amounts of fluids including hydrocarbons and water pass through these facilities, which leads to a gradual build-up of deposits of potentially hazardous and environmentally harmful substances within the structures. These include hydrocarbon deposits, scale that may comprise naturally occurring radioactive material (particularly in water-producing facilities) and sometimes also deposits of highly hazardous pyrophoric substances.

At the end of the economic life of a structure it undergoes a process of decommissioning, during which it is dismantled and removed. In order for that to be carried out safely, and with minimal impact to the environment, the structure needs to be drained and thoroughly cleaned prior to dismantling offshore to prevent pollutants escaping into the environment.

An object of embodiments of the present invention is improve the current procedures for moving and/or dismantling such structures especially for decommissioning.

According to a first aspect of the invention, there is provided a method of preparing an offshore structure for movement, the method comprising: adding a foam comprising a base mixture and a gas to the offshore structure in order to retain pollutants; -allowing the foam to form a foamed gel.

In this way, any pollutants can be retained in the offshore structure, allowing it to be moved, for example to port, where it can be cleaned and dismantled more efficiently. This is preferable to existing techniques where extensive cleaning and/or dismantling is undertaken offshore, and/or where movement of the offshore structure can cause localised pollutants to spread to other areas, requiring further clearing and decontamination at a later date.

The viscosity of the base mixture before adding to the offshore structure may be in the range of 0.1 Pa.s to 5 Pa.s before the gas is combined with the base mixture and before any thickening agent or cross-linker is added.

The foamed gel may have a 'mousse'-like consistency and will be much more viscous than the base mixture. Therefore, the dynamic viscosity when formed into the foamed gel is typically more than 1000 Pa.s or considerably in excess of 1000 Pa.s, such as ranging above 2000 Pa.s to essentially solid materials which do not flow and thus have a viscosity of over 5,000,000 Pa.s.

Normally the foamed gel will be removed at a later date. Accordingly, the strength of the formed gel should not be too strong, so that removal is convenient. The compressive strength therefore is normally less than 500psi, may be less than 50psi, optionally less than psi, more optionally less than 10psi, and even more optionally less than 2psi.

The foam and/or foamed gel may have a gas volume to total foam/foamed gel volume ratio respectively of at least 60%, and preferably more than 70% The foam and/or foamed gel may have a gas volume to total foam/foamed gel volume ratio of at most 85%, and preferably at most 75%.

The foam may comprise gas bubbles where at least 90% have a diameter smaller than 1mm, optionally smaller than 100 pm.

Expansion ratio is a parameter used to determine quality of foam. The foam may be a medium expansion foam. The expansion ratio may be greater than 2 and less than 100, optionally 10 to 90 Drainage time is a measurement of the rate at which foam solution drains out of a finished foam. This can provide an indication of the stability of the foam. Preferred embodiments have a long drainage time so that the foamed gel can be left for weeks or months until movement of the offshore structure can be undertaken. For example, the time taken for 25% of the base mixture to have drained from the foam or foamed gel can be measured. For preferred embodiments of the present invention, this time is at least a day, preferably at least a week, or at least one month or indeed indefinitely -ideally there is essentially no drainage from the foam or foamed gel. It is therefore normally much longer than the curing time for the foam to become a foamed gel.

The method may include at least one step of flushing the offshore structure with a fluid prior to adding the foam. For example, it may be flushed with a liquid such as water. At least one second flush may also be performed. A low-density non-flammable liquid may be used, such as a brine. This may assist in removing trapped oil. Furthermore, gas may be added to drain the structure and displace trapped fluids, also before adding the foam.

The foamed gel may be made by cross-linking a polymer. The combination of a cross-linker and polymer may be done at site.

The cross-linker may be added to a base mixture comprising a solvent and the polymer. The combined mixture may then be foamed, for example, by passing through a foaming machine. Inert gas, such as carbon dioxide or nitrogen, may be used to create the foam. The mixture and the resulting foam is typically non-flammable.

In certain embodiments, the cross-linker is added to the base mixture immediately before foaming, that is, within 30 minutes, preferably within 15 minutes, more preferably within 5 minutes.

In turn, for certain embodiments, the foam is added to the offshore structure within 30 minutes of being foamed, preferably within 15 minutes, more preferably within 5 minutes.

The amount (or rate of injection) of the inert gas may be varied in order to control the ratio of liquid to gas formed. The ratio may be within 1:1 and 1:10 by volume. Normally, the foam cures in order to form the foamed gel.

The base mixture may comprise water, brine or other suitable solvent. The solvent comprising substantially water is preferred.

The base mixture may further comprise surfactants and/or a pH modifier Examples can include any class of Bronsted acid, i.e. proton-donating acids, such as inorganic acids (for example hydrochloric acid, sulfuric acid and phosphoric acid), organic acids (for example carboxylic acids and phenols), sulfonated organics (such as alkylsulfonic acids), phosphorylated acids (such as alkylphosphonic acids), phosphate esters (such as mono-or di-esters of phosphonic acid), and other common proton donors, typically with a pKa less than 10 in water at room temperature.

Thus, the base mixture typically comprises a polymer, such as a long chain polymer.

Preferred polymers have 1,2-or 1,3-alcohol groups. One suitable polymer is polyvinyl alcohol. Other polymers that may be used include polysaccharides and cellulosics.

Further options include water-based polymers which contain functional groups that can crosslink such as copolymers of PVA, polyacrylamide and its copolymers, polypeptides; preferably the functional group of the polymer is not too reactive to survive within an aqueous environment and may include carbon-carbon double bonds, carbon-oxygen double bonds, carbon-carbon triple bonds, alcohols, amines, thiols and/or esters.

Typically, the weight average molecular weight range of the polymer is 100,000 to 200,000, optionally 146,000 to 186,000.

The hydrolysis of the polymer can be 80 to 100%, typically 85% to 90%.

One class of suitable cross-linkers is dialdehyde and one example in the class is glutaraldehyde. Other cross-linkers may be used, especially those used in fracking, such as borates, zirconates, and other metals/mixed metals.

The cross-linker is typically added at the time of adding the foam to the offshore structure, as it will gradually start to set thereafter to form the foamed gel.

A foaming agent is normally included in the base mixture.

Suitable foaming agents include: anionics/sulfonates (e.g. sodium lauryl sulfate), betaines (e.g. cocoamidopropyl betaine, cocoamidopropyl hydroxy sultaine), amine oxides (e.g. cocoamidopropylamine oxide), and nonionics (APGs, alcohol ethoxylates).

A pH modifier may be included in the base mixture. Optionally, this may be added at the same time as the cross-linker in order to allow for an improved shelf life of the base chemical or other benefits.

The invention also provides a chemical blend comprising: * a water solvent * a polymer capable of cross-linking; * a foaming agent; and optionally * a pH modifier.

An advantage of certain embodiments of the invention is that the foamed gel inhibits contamination from one area of the structure to another. Accordingly, contaminated areas can be effectively isolated so that extensive clean is later required only in these areas.

The polymer, foaming agent and pH modifier may be any of those described herein.

The offshore structure is typically an oil and gas platform and the transportation may be required at the end of the economic life of this structure. The structure is typically an offside topside oil and gas structure. The foamed gel thus typically fills facilities in the structure such as pipes and vessels. The foam preferably provides a low density inert material rendering the structure safe to be moved, where it may be broken up. Thus, the method according to the aspects of the present invention, may be a method for decommissioning an offshore structure.

In due course, after adding the foam, the structure may be moved. This may be at least 30 minutes after adding the foam. However, it may be much longer, such as weeks or months later, depending on, for example, the logistics of moving the structure. Thus the first aspect of the invention may include the step of moving the offshore structure with the foam that has been added.

According to a second aspect of the invention, there is provided a method of recovering an offshore structure, the method comprising: moving an offshore structure, the offshore structure comprising a foamed gel added thereto in order to retain pollutants.

The foamed gel of the second aspect of the invention is preferably the foamed gel described herein for other aspects of the invention.

Thus, the foamed gel can inhibit loss of pollutants whilst moving the offshore structure. In this way, the structure can be moved closer to shore where dismantling of the structure tends to be safer, more cost effective, less time consuming and/or better for the environment. The structure may be moved to a dismantling facility.

After moving the structure, the method may include removing the foamed gel thereon or therein. This may be done by mechanical removal, such as cutting or grinding; and/or chemical removal, such with a breaker fluid to break down the cross-linked polymer. The structure is then typically dismantled.

According to a third aspect of the invention, there is provided a method of cleaning and/or dismantling an offshore structure having foamed gel thereon or therein to retain pollutants, the method comprising: * removing the foamed gel, * cleaning and/or dismantling the offshore structure.

Preferably removing the foamed gel and/or dismantling the offshore structure is done onshore or at, or proximate, the shore, such as within 1 km, preferably 500 m, preferably 250 m of the shore.

The portion of the offshore structure cleaned is typically the portion which included the foamed gel.

Embodiments may therefore make safe facilities such as production equipment and pipework of a structure prior to decommissioning which may involve removing hydrocarbon deposits from the structure by flushing, and providing and introducing into the structure a foamed inert gel which fills the structure rendering it safer for removal.

An embodiment of the present invention will now be described by way of example only and with reference to Figure 1 which is a schematic representation of steps of a method according to the present invention.

Before recovering an offshore structure 10 back to a port or onshore, a foam is introduced into the structure 10 and allowed to gel in order to hold environmental pollutants which could otherwise escape during transport onshore. The structure can therefore be transported safely and with minimal environmental impact, and cleaned and dismantled onshore, where the costs and convenience of doing so are usually better, as well as improved environmental benefits; compared to extensive cleaning offshore.

In use at an offshore structure 10, the facilities 11 of the structure 10 are first flushed with water in order to displace out any easily removeable debris such as certain hydrocarbon deposits. The structures 11 are then treated with a non-flammable liquid to remove any hydrocarbons trapped in the structures 11 that were not displaced during flushing The structures 11 are then drained by displacing the non-flammable liquid or other liquids of fluids mixed with an inert gas such as nitrogen.

Figure 1 outlines a method 20 involved in providing and introducing a stable foamed inert gel 26 into a pipe 11 of the structure 10. A base mixture 21 is provided comprising a solvent, surfactants and a long chain polymer capable of being cross-linked through reaction with a cross-linking agent 22. The cross-linking agent 22 is added to the base mixture 21 immediately prior to its passing through a foam generation device 23 which is linked to a supply of an inert gas 24 to create foam 25. When the foam 25 is put in place, the polymer cross-links, cures and a stable foamed gel 26 is created.

The foam 25 generated may have a ratio of fluid to foam of between 1:1 and 1:10 especially between 1:1 and 1:4, with a working time of approximately 20 minutes from the addition of the cross-linking agent 22 The working time is defined as the time after which the structure of the foam setting into foamed gel no longer allows for it for it to be introduced into the facility. The time of formation of a stable gel, after which the facility may be displaced, may be referred to as the curing time. A stable foamed gel 26 forms within a curing time of 60 minutes of the addition of the cross-linking agent 22.

The mixture generated is pumped into the structures 11 of the structure 10 where it fills the available volume over a period of minutes before setting or curing into a stable foamed gel 26. The foamed gel 26 fills all the all the structures 11 of the structure 10 with a low density inert material rendering the structure 10 safe to be removed to the shore, where it can be dismantled more conveniently.

The rate of formation of the stable foamed gel 26 can be controlled by regulating the amount of the cross-linking agent 22, and also by adding brine or pH modifier; or a combination of these.

The process of filling the structure 10 with foam 25 can be completed in several days and once filled the stable foamed gel 26 can be left for an extended period of time, such as weeks or months.

The structure 10 can then be moved to the shore using conventional techniques. On arrival, the foamed gel 26 can be removed either mechanically or by the addition of a breaker chemical which breaks the gel allowing the foam to collapse and the resultant fluid can be collected for disposal. As the dominant component of the base mixture 21, and consequently the foamed gel 26, is water, in the latter case most of the resultant liquid may be reduced by boiling it off.

Various polymers and other chemicals can be used for different embodiments of the invention. In the present embodiment, the base mixture 21 is prepared with water which acts as the solvent for the polymer and the surfactants solution (foaming agent).

Specifically, the base mixture 21 comprises 10 percent Ghosenol GH-23 and an 86.5% -89% partially saponified polyvinyl alcohol, to which is added a 30 percent solution of Sodium N-Lauroylsarconsinate such as Surfacare L30, Additionally the base mixture 21 comprises a mixture of mono-and diphosphate ester such as P208 from JW VVhewell and a Calcium Chloride brine with a density of 1.08 g/cm3, which act as foaming rate modifiers. The ratios of the substances in the base mixture 21 are provided in Table 1.

Table 1 -Base Mixture Additive Purpose Percent additive Water solvent 72.0 Ghosenol GH23 polymer 8.0 Surfacare L30 Foaming agent 1.0 JW Whewell P208 pH modifier 3.0 Calcium Chloride brine density 1.08 g/cm3 (or for Rate modifier 15 example sodium chloride brine) In this embodiment, a 4% w/w of 50% glutaraldehyde solution is provided to act as the cross-linking agent 22, and the foam generation device 23 comprises inert gas supply 24, wherein the gas is nitrogen gas. Such embodiments of the present invention offer an advantage of a controllable working time and subsequent curing time during the process of formation of the stable foamed gel 26. Thus, the formation of stable foamed gel 26 may be brought forward, or delayed, to meet the specific requirements at a given structure 10. For example, depending on the size and layout of the structure 10, it may be beneficial to prolong the working time and/or the subsequent curing time to allow for all desired structures 11 within the structure 10 to be filled before the formation of the stable foamed gel 26.

It is further beneficial that the stable foamed gel 26 it is a foam-based material, and therefore it adds very little weight to the weight of the structure 10 to be lifted for removal to the shore.

Testing methods Compressive Strength To determine compressive strength the compressive strength test for polystyrene foam can be followed, based on ASTM 1621. This avoids any restriction on the radius of the sample and measures the forces acting axially only using cube or cylindrical moulds. The pressure required for 10% deformation can be used to assess the compressive strength of foamed gels disclosed herein.

Viscosity The viscosity of the foamed gel may be determined, for example, using a dropped ball method based on a modification of ASTM D1343-96 (2000), by measuring the rate at which a stainless-steel ball falls a predetermined distance and applying this figure to a Stokes law calculation. The foam may be placed into calibrated vessels and allowed to cure into foamed gel. The stainless-steel ball may then be placed on the surface of the foamed gel, preferably centered with respect to the walls of the vessel. The ball's rate of fall through the foamed gel may be determined by measuring either the time it takes the base of the ball to pass between two calibrated points or the time it takes for the ball to pass from the base to the top of the ball at one calibrated point. A number of readings may be taken and the average may be used to calculate the viscosity using Stokes equation as follows: V = (2gr2) (dl-d2)/9y where V = velocity of fall (cm sec-1), g = acceleration of gravity (cm sec-2), 980 cm sec r ="equivalent" radius of ball (cm), dl = density of particle (g cm-3) t d2 = density of medium (g cm-3), and y = viscosity of medium (dyne sec cm-2). This can be rearranged to give y = (2gr2) (dl-d2)/90V as Pascal seconds (Pa.$) Drainage For the drainage tests, International Standard ISO 7203-1 can be followed to determine the drainage time.

Expansion Ratio A description on how to determine the expansion ratio can be found in the International Standard ISO 7203-1 Improvements and modifications may be made without departing from the scope of the invention. For example, whilst this embodiment makes use of specific chemical substances, alternative and/or additional substances of similar properties may be used without departing from the scope of the present invention. For example, different quantifies and concentration of the substances may also be used, for example the amount of the cross-linking agent, brine and/or the pH modifier may be altered in order to control the rate of formation of the foam and, subsequently, that of formation of the foamed gel.

Claims

CLAIMS1 A method of preparing an offshore structure for movement, the method comprising: adding a foam comprising a base mixture and a gas to the offshore structure; and, allowing the foam to form a foamed gel.
2. A method as claimed in claim 1, wherein the compressive strength of the foamed gel is less than 50psi.
3 A method as claimed in any preceding claim, wherein the dynamic viscosity of the base mixture is in the range of 0.1 Pa.s to 5 Pa.s after the gas is combined with the base mixture.
4. A method as claimed in any preceding claim, wherein the dynamic viscosity of the foamed gel is more than 1000Pa.s.
A method as claimed in any preceding claim, wherein the foam and/or foamed gel has a gas volume to total foam/foamed gel volume ratio of at least 50% optionally at least 70%.
6 A method as claimed in any preceding claim, wherein the foam and/or foamed gel has a gas volume to total foam/foamed gel volume ratio up to 85% optionally up to 75%.
7 A method as claimed in any preceding claim, wherein the foam and/or foamed gel comprises gas bubbles, at least 90% of said bubbles having a diameter smaller than 1mm.
8. A method as claimed in any preceding claim, wherein the time taken for 25% of the base mixture to have drained from the foam and/or foamed gel is more than a day.
9. A method as claimed in any preceding claim, including at least one step of flushing the offshore structure with a fluid prior to adding the foam.
10. A method as claimed in any preceding claim, wherein the base mixture comprises a cross-linkable polymer.
11. A method as claimed in claim 10, wherein the polymer has 1,2-and/or 1,3-alcohol groups.
12. A method as claimed in claim 10 or claim 11, wherein the polymer comprises polyvinyl alcohol.
13. A method as claimed in any one of claims 10 to 12, wherein the weight average molecular weight range of the polymer is 100,000 to 200,000, optionally 146,000 to 186,000.
14. A method as claimed in any one of claims 10 to 13, wherein the hydrolysis of the polymer is 80 to 100%, optionally 85% to 90%.
15. A method as claimed in any one of claims 10 to 14, wherein a cross-linker is added to cause the foam to form a foamed gel, the cross linker being at least one of a dialdehyde and glutaraldehyde.
16. A method as claimed in claim 15, wherein the crosslinker is added to the base mixture immediately before foaming with the gas, that is within 30 minutes.
17. A method as claimed in any preceding claim, wherein the foam is added to the offshore structure within 30 minutes of being formed by the combination of gas and the base mixture.
18. A method as claimed in any preceding claim, wherein the base mixture is a water-based base mixture.
19. A method as claimed in any preceding claim, wherein the base mixture comprises a pH modifier.
20. A method as claimed in any preceding claim, wherein the base mixture comprises a foaming agent.
21. A method as claimed claim 20, wherein the foaming agent comprises one selected from the group consisting of: anionics/sulfonates (e.g. sodium lauryl sulfate), betaines (e.g. cocoamidopropyl betaine, cocoamidopropyl hydroxy sultaine), amine oxides (e.g. cocoamidopropylamine oxide), and nonionics (APGs, alcohol ethoxylates).
22. A method as claimed in any preceding claim, wherein the offshore structure is an oil and gas platform.
23. A method as claimed in any preceding claim, wherein the structure is moved after adding the foam to form the foamed gel.
24. A method as claimed in claim 23, comprising removing the foamed gel thereon or therein.
25. A method as claimed in claim 24, comprising cleaning at least a portion of the offshore platform where the gel was provided.
26. A method as claimed in any one of claims 21 to 25, comprising dismantling the offshore structure.
27. A method of recovering an offshore structure, the method comprising: moving an offshore structure, the offshore structure comprising a foamed gel added thereto in order to retain pollutants.
28. A method of cleaning or dismantling an offshore structure having foamed gel thereon or therein to retain pollutants, the method comprising: removing the foamed gel, cleaning and/or dismantling the offshore structure.
29. A chemical blend comprising: a water solvent; a polymer capable of cross-linking, the polymer comprising has 1,2-and/or 1,3-alcohol groups; a foaming agent comprising one selected from the group consisting of: anionics/sulfonates (e.g. sodium lauryl sulfate), betaines (e.g. cocoamidopropyl betaine, cocoamidopropyl hydroxy sultaine), amine oxides (e.g. cocoamidopropylamine oxide), and nonionics (APGs, alcohol ethoxylates) and optionally, a pH modifier.