NO342412B1 - Hydraulic Fluids - Google Patents

Abstract

The invention relates to an aqueous hydraulic fluid comprising, in addition to water, at least one phospholipid lubricant, wherein the hydraulic fluid comprises less than 20% by weight of an oil selected from a mineral oil, a synthetic hydrocarbon oil or any mixture thereof. Preferably, the or each phospholipid lubricant comprises a plant-derived lecithin.

Description

This invention relates to aqueous hydraulic fluids, and in particular, but not exclusively, hydraulic fluids for use in the offshore oil and gas industry where the hydraulic fluid has a composition as stated in claim 1.

Background for the invention

During underwater oil drilling, it is normal for a drilling rig to drill a hole in the seabed in search of oil reserves. After drilling down a certain distance, it is common to place a BOP stack on the wellhead on the seabed and then continue drilling through the center of the BOP assembly. The Blowout Preventor (BOP) stack is simply a hydraulically operated safety device that can shut down the well if a gas pocket or oil is detected (an uncontrolled blowout). The device operates by hydraulic pressure that can be used to seal the opening between the drill string (which rotates the head of the drill and is connected to the drilling rig) either by forming a seal against the drill string or to cut through the drill string in more dangerous situations. Sealing and cutting operations are performed by hydraulic pressure forcing large hydraulic rams to close; the fluid is then released into the sea to relieve the pressure after the operation.

The BOP stack and hydraulic control boxes that are on the seabed (or sometimes on board the rig if drilling is done in shallow water) are connected by a hydraulic hose (Umbilical) to the rig where the operation can be controlled via a control panel by rig operators.

The hydraulic system has a large hydraulic fluid reserve tank on board and as the fluid is pressurized and then dumped into the sea, the fluid is removed from the reserve tank.

Many BOP stacks use Type-One (Type-One) BOP hydraulic fluid, which is an aqueous hydraulic fluid concentrate, minus the water (and antifreeze if necessary).

In an effort to minimize the amount of space required to store the hydraulic fluid on board, rig operators tend to take a delivery of the water hydraulic fluid as a concentrate without the water and antifreeze to the site and then add water and antifreeze on board as needed.

Some rigs prefer premixed fluid in some areas for various reasons and it is supplied in the same manner as outlined in Type-Two (Type Two) below.

Other operators use Type-Two production control hydraulic fluids.

This type of water-based hydraulic fluid is typically a pre-mixed version of the BOP fluid mentioned above, sometimes with the addition of antifreeze and stability additives as needed.

This pre-mixed fluid is used to produce oil remotely via a system whereby a subsea hydraulic control system is placed on the well holding and connected back via a hydraulic connection line to the production facility (fixed platform, floating unit or to land).

This system is in many ways similar to the BOP system although in this case it functions at the wellhead control of the flow of oil and other production-related functions and typically uses much smaller valves with greater tolerances and a greater need for stability, fluid purity etc. In addition, it can The hydraulic connection line can be of varying lengths from a few kilometers to several hundred kilometres.

There is a third type of BOP hydraulic fluid, Type-Three (Type Three) water-based ISO equivalent hydraulic oils.

These fluids are based on the same technology as the other fluids described above and usually comprise the basic Type-Two production control fluid described above with added thickeners to suit the ISO hydraulic oil in use.

Functional lubricating fluids are previously known from WO-A-9218586 and WO-A-9814538. A liquid which is suitable as a hydraulic fluid is known from US 6509301 B1.

Many applications on board drilling and production units use standard ISO hydraulic oils, with varying viscosities depending on the application.

Typical performance requirements for offshore hydraulic fluids include

1. Lubrication – it is important that a water-based hydraulic fluid has sufficient lubricity to allow moving surfaces (such as metal-to-metal contact within valves) to slide without seizing or wearing within acceptable limits.

2. Corrosion protection - it is important that a water-based hydraulic fluid has sufficient corrosion protection to protect the metals in the system from corrosion, especially if moderate seawater exposure is likely.

3. Stability additives - it is important that a water-based hydraulic fluid has sufficient stability to ensure that the fluid does not separate in service. The level of importance of this depends on the application as some systems are very prone to such cases. If a product does not have sufficient stability in itself, it is common to use some form of chemical additive that will ensure that the product does not separate.

4. Biocidal protection - it is important that a water-based hydraulic fluid has sufficient biocidal protection to prevent excessive growth of fungi and bacteria within the hydraulic fluid medium.

5. Elastomer compatibility - it is important that a water-based hydraulic fluid does not adversely affect the elastomer present within the system.

6. Anti-freeze protection - it is important that a water-based hydraulic fluid has sufficient anti-freeze protection to allow the product to be used in cold conditions.

7. Viscosity agents – some fluids may need to have their viscosity modified to suit a certain technical profile, this will involve adding additives to increase or decrease the viscosity of the product.

8. Environmental approval - it is important that a water-based hydraulic fluid is sufficiently acceptable environmentally to allow its discharge under the individual regulations in each applicable country under which laws the drilling takes place.

It would be advantageous to provide a water-based hydraulic fluid that does not include large amounts, or particularly any amount, of oil, especially mineral oil or synthetic hydrocarbon oil, which oils create environmental problems especially in offshore applications.

It would further be advantageous to provide aqueous hydraulic fluids that include environmentally friendly lubricants, which lubricants do not rely on mineral or synthetic hydrocarbon oil formulations to work effectively.

It is therefore an object of the preferred embodiments of this invention to overcome or mitigate at least one problem of the prior art.

Summary of the invention

According to a first aspect of the invention, there is provided an aqueous hydraulic fluid comprising, in addition to water, i) a plant-derived lecithin comprising soybean lecithin, castor lecithin, rapeseed lecithin, cottonseed lecithin and combinations thereof, as essentially the only lubricant in the hydraulic fluid; and ii) at least one component selected from a glycol, a glycerol ester and glycerol, wherein the hydraulic fluid is substantially free of a mineral oil, a synthetic hydrocarbon oil or any mixture thereof; and where the aqueous fluid comprises water in an amount of at least 10% by weight and no more than 90% by weight of the total weight of the hydraulic fluid; and where the lecithin is present in an amount from 0.1% by weight up to 40% by weight of the total weight of the hydraulic fluid.

Suitably, the aqueous hydraulic fluid comprises water in an amount of at least 10% by weight, preferably less than 20% by weight, and more preferably at least 30% by weight of the total weight of the hydraulic fluid. Suitably, the aqueous hydraulic fluid comprises water in an amount of no more than 90% by weight, more preferably no more than 80% by weight and most preferably no more than 75% by weight of the total weight of the hydraulic fluid.

A preferred concentration of the water is mainly 30-70% by weight of the total weight of the hydraulic fluid.

Particularly preferred lecithins are those derived from commercial sources such as soybean oil, cottonseed oil and castor seed oil.

A particularly preferred effective mixture of lecithins comprises soybean lecithin and other plant-derived lecithins.

In preferred embodiments, the hydraulic fluid comprises a plate-derived lecithin, such as e.g. soybean lecithin, castor lecithin, rapeseed lecithin, cottonseed lecithin and the like. Particularly preferred is soybean lecithin, preferably comprising soybean oil, phosphoatidylcholine, phosphatidylethanolamine, and phosphatidyinositol.

The plant-derived lecithin lubricant preferably comprises at least 1% by weight of the total weight of the hydraulic fluid, more preferably at least 2% by weight, and most preferably at least 4% by weight. The plant-derived lecithin lubricant preferably comprises no more than 40% by weight of the total weight of the hydraulic fluid. In preferred hydraulic fluids, the total weight of the plant-derived lecithin lubricant comprises substantially 1-30% by weight of the total weight of the hydraulic fluid.

The lecithin lubricant can also serve to act as a corrosion inhibitor. Alternatively or additionally, the hydraulic fluid may comprise at least one separate corrosion inhibitor. The corrosion inhibitor may comprise an alkylamine or alkanolamine. Suitable alkylamines preferably comprise a C6-C20 linear or branched alkyl group. Suitable alkanolamines preferably comprise 1 to 12 carbon atoms, more preferably 6 to 9 carbon atoms. The alkanolamine may comprise more than one alkanol group, e.g. dialkanolamines and trialkanolamines. Preferred alkanolamines include monoethanolamine and triethanolamine. Other corrosion inhibitors include copper corrosion inhibitors such as benzotriazole for example.

The hydraulic fluid may include a stabilizer. Many preferred embodiments of the hydraulic fluid of the invention do not require stabilizers, as they are inherently stable. In contrast, certain additives and ingredients can be unstable in the hydraulic fluid for various reasons, such as ingredients that are insoluble or partially soluble in the aqueous medium of the fluid, or ingredients and ions that form complexes with hard water salts. Therefore, the particular stabilizer or stabilizers used depends on the other ingredients present in the hydraulic fluid and/or the hardness of the aqueous medium in the fluid. Suitable stabilizers include surfactants, which can increase the solubility of the ingredients in the hydraulic fluid. Suitable surfactants include ethoxylate surfactants. Other suitable types of stabilizers are a complexing agent, which is able to form a complex with ions or ingredients that can react with hard water salts in the aqueous medium. Suitable complexing agents include EDTA. The hydraulic fluid may contain a biocidal additive. Biocidal additives useful in the hydraulic fluids of the invention include sulfur-containing biocides and nitrogen-containing biocides. Suitable nitrogen-containing biocides include triazenes and guanidines.

The hydraulic fluid may comprise an antifreeze additive. In some embodiments, a high concentration of the dissolved or suspended ingredients of the aqueous hydraulic fluid can provide sufficient antifreeze effect without the need for additional antifreeze additives. If an antifreeze additive is required in the hydraulic composition, it is preferably a glycol compound, glycerol or a glycerol ester. Suitable glycols include alkylene glycols, preferably having 1 to 12 carbon atoms in each alkylene group, which groups may be linear or branched. The alkylene glycols can be monoalkylene glycols or dialkylene glycols. Preferred glycols include monoethylene glycol and monopropylene glycol for example.

The hydraulic fluid may include further additives such as a viscosity modifier. The viscosity modifier may be an agent capable of increasing the viscosity of the hydraulic fluid or, alternatively, may be an agent capable of increasing the viscosity. The type of viscosity modifier may depend on the application in which the fluid is used, the environmental conditions in which the fluid is used, and other factors. Suitable viscosity modifiers which increase the viscosity of the hydraulic fluid compared to when the modifier is not present include long chain polymer compounds such as high molecular weight ethylene oxide/propylene oxide copolymers and high molecular weight polyacrylic acid polymers. Suitable viscosity modifiers which serve to lower the viscosity of the hydraulic fluid compared to when the modifier is not present include organic solvents such as ethylene glycol ethers and propylene glycol ethers.

The aqueous hydraulic fluid is mainly free of mineral oil and/or synthetic hydrocarbon oil. If an oil is present, it is preferably a natural oil, such as a plant-derived oil for example.

The aqueous hydraulic fluids of the invention are preferably mainly free of phosphorus dithionates.

The aqueous hydraulic fluids of the invention are particularly suitable for use as hydraulic fluids in the offshore, mineral and mining industries.

Examples

For a better understanding of the invention and to show how embodiments of the same may be put into effect, preferred embodiments of the invention will now be described by the following examples: with reference to Figure 1 which illustrates a graph of the results of a Falex Lubricity Test with consideration of the hydraulic fluid of the invention compared to known hydraulic fluids.

Example 1

An aqueous hydraulic fluid of the invention (Formulation A) was prepared by mixing the following ingredients and then homogenizing this mixture under pressure of between 500-5000 psi until a stable dispersion was obtained. The resulting product was then filtered to remove any large particles.

10% w/w soybean lecithin, supplied by Cargill PLC, UK 0.1% w/w Benzotriazole, supplied by Ellis and Everard PLC (UNIVAR), UK

0.1% w/w EDTA, supplied by BASF PLC, UK

10% Decanoic acid (supplied by Multisol, UK)/TEA (supplied by Univar, UK), pre-neutralized salt to pH 8.8

5% w/w Triazene, supplied by Thor Chemicals, UK

40% w/w Monoethylene Glycol, supplied by Ellis & Everard PLC, (Univar), UK

Water for balance

This formulation, hereafter referred to as formulation A, is used as a BOP hydraulic fluid concentrate which is diluted by the consumer before use, typically to a working concentration of 20% volume/volume and antifreeze mixture, depending on the necessary freeze protection. Formulation A provides excellent torque reduction and anti-wear on offshore and extraction hydraulic equipment.

Falex Lubricity test

The falex tester measures the torque experienced on a rotating test needle immersed in the test fluid, as it is exposed to increasing load. The load on the needle is increased in 45 kg (100 lb) increments and the torque is measured at each load increase. When the 227 kg (55 lb) load is reached, the load is held for 30 minutes and the level of wear on the test needle is recorded in units of "wear teeth".

A working version of diluted (20% vol/vol) BOP formulation A containing soybean lecithin was compared on the Falex Lubricity Tester for working concentrations of two main control hydraulic fluid products, Control fluid-One, containing synthetic additives but no mineral/synthetic oils, and Control fluid- Two, containing synthetic hydrocarbon oil.

Comparative torque and wear results for each product are shown in figure 1 and table 1 below:

Table 1

Test data at 500 lb load for 30 min:

These results show that Formulation A, when compared at working concentrations, exhibits superior torque reduction to a control water-based (non-phospholipid, non-mineral/synthetic hydrocarbon containing) Control Fluid-One and superior torque reduction to control synthetic hydrocarbon oil-based Control Fluid-Two.

In terms of anti-wear, formulation A exhibits 25% less wear than Controlfluid-One, and Controlfluid-Two was unable to withstand the test conditions.

These results show that formulation A, which is an example of an aqueous hydraulic fluid of the invention, which includes a natural lubricant in the form of soybean lecithin, exhibits more effective torque reduction and antiwear than the control hydraulic fluids.

In other preferred embodiments of the aqueous hydraulic fluid of the invention, the soybean lecithin may be replaced by an equivalent amount of individual phosphatide, or other natural lecithins as mentioned above.

The hydraulic fluids of the invention may also include various additives including corrosion inhibitors, stabilizers, biocides, viscosity modifiers, antifreezes and the like.

In the hydraulic fluid of the invention, there is no mineral or synthetic hydrocarbon oil present. It can be anticipated that very small amounts of mineral oil or hydrocarbon oil may be present, but these should be kept to a minimum, and not more than 0.01% w/w of the total weight of the hydraulic fluid, if possible.

The soybean lecithin used in formulation A is believed to include the following ingredients:

Soybean oil 37.5%, phosphatidylcholine 15%, phosphatidylethanolamine 13%, phosphatidylinositol 10%, other phospholipids and lipids 19%, and carbohydrates 5%.

Example 2

Another preferred embodiment of the aqueous hydraulic fluid of the invention, formulation B, was prepared by mixing the following ingredients and then homogenizing this mixture under pressure between 500-5000 psi until a stable dispersion was obtained. The resulting product was then filtered to remove all large particles:

2% w/w soybean lecithin

0.01% w/w benzotriazole

0.01% w/w EDTA

0.5% decanoic acid/TEA, pre-neutralized salt to pH 8.8

0.3% w/w triazene

40% w/w monoethylene glycol

Water for balance

The above formulation is hereinafter referred to as formulation B.

Formulation B was subjected to the Falex Lubricity Test as described above, and showed similar performance to formulation A. The results showed that formulation B provided an effective water-based hydraulic fluid for offshore and production fields.

The aqueous hydrocarbon fluid of the invention exhibits excellent environmental characteristics, and prevents the possibility of accidental release of large quantities of synthetic hydrocarbons or mineral oils into an underwater environment or groundwater table.

Claims (10)

Patent claims 1. Aqueous hydraulic fluid for use in an offshore, mineral or mining drilling rig comprising, in addition to water, i) a plant-derived lecithin comprising soybean lecithin, castor lecithin, rapeseed lecithin, cottonseed lecithin and combinations thereof, as essentially the sole lubricant in the hydraulic fluid; and ii) at least one component selected from a glycol, a glycerol ester and glycerol, wherein the hydraulic fluid is substantially free of a mineral oil, a synthetic hydrocarbon oil or any mixture thereof; and wherein the aqueous fluid comprises water in an amount of at least 10% by weight and no more than 90% by weight of the total weight of the hydraulic fluid; and where the lecithin is present in an amount from 0.1% by weight up to 40% by weight of the total weight of the hydraulic fluid. 2. Aqueous hydraulic fluid according to claim 1, comprising water in an amount of at least mainly 20% by weight of the total weight of the hydraulic fluid. 3. Aqueous hydraulic fluid according to claim 1, comprising water in an amount of not more than substantially 80% by weight of the total weight of the hydraulic fluid. 4. Aqueous hydraulic fluid according to claim 1, wherein the plant-derived lecithin is soybean lecithin. 5. Aqueous hydraulic fluid according to any preceding claim, wherein the water is present in an amount of at least 30% by weight and not more than 75% by weight of the total weight of the hydraulic fluid. 6. Aqueous hydraulic fluid according to any preceding claim, wherein the lecithin is present in an amount of up to substantially 30% by weight of the total weight of the hydraulic fluid. 7. An aqueous hydraulic fluid according to any preceding claim, wherein the plant-derived lecithin is present in an amount of at least 1% by weight. 8. Aqueous hydraulic fluid according to any preceding claim, further comprising at least one corrosion inhibitor. 9. Aqueous hydraulic fluid according to claim 8, wherein the corrosion inhibitor comprises an alkylamine or alkanolamine. 10. An aqueous hydraulic fluid according to any preceding claim, which is substantially free of phosphorus dithioates.