NO316402B1 - Use of water degree polymeric polymer to inhibit the formation of gas hydrates, method of inhibiting gas hydrate formation and use of a chemical compound as an additive - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to the use of water-soluble polymers to inhibit the formation of gas hydrates in pipelines containing oil or gas. This is relevant both for exploration and production of oil and gas. Furthermore, the invention relates to a method for inhibiting gas hydrate formation and the use of a chemical compound as an additive

BACKGROUND OF THE INVENTION

Gas hydrates are clathrates (inclusion compounds) of small molecules in a lattice of water molecules Within the oil industry, natural gas and crude oil fluids contain a number of certain small molecules that can form gas hydrates They include hydrocarbons such as methane, ethane, propane, isobutane as well as nitrogen, carbon dioxide and hydrogen sulfide Larger hydrocarbons such as n-butane, neopentane, ethylene, cyclopentane, cyclohexane and benzene are also hydrate-forming compounds. When these hydrate-forming compounds are present with water at elevated pressures and reduced temperatures, the mixture tends to form gas hydrate crystals. For example, ethane forms at a pressure of 1 MPa only hydrates below 4°C while at 3MPa gas hydrates can only form below 14°C These temperatures and pressures are typical operating conditions where crude oil fluids are produced or transported

If gas hydrates can form in pipelines used to transport natural gas and/or crude oil fluids, they can possibly block the pipeline. The hydrate blockage can lead to a vapor in production and significant financial loss. The oil and gas industry uses various aids to prevent the formation of hydrate blockages in pipelines. These include heating the line, reducing the pressure, removing the water and adding antifreezes such as methanol and ethylene glycols, which act as melting point depressants Each of these methods is expensive to implement and maintain The most common method used today is the addition of antifreezes However, these must antifreezes are added in high concentrations, typically 10-40% with respect to the weight of the water present, to be effective Recycling of the antifreezes is also usually necessary and is an expensive procedure

As a consequence, there is a need for alternative, cheap methods to prevent hydrate blockages during oil and gas drilling and production

An alternative to the methods mentioned above is to control the gas hydrate formation process by using nucleation and crystal growth inhibitors. These types of chemicals are well known and are used in other industrial processes. The advantage of using these chemicals to control gas hydrate formation is that they can be used in concentrations of 0.01 to 2% which is much lower than for antifreezes

DE-A-39 41 561 describes cold-stable crude oil intermediates containing copolymers which essentially consist of structural units derived from monoamides of maleic acid, and in which the amide residue is substituted with straight-chain C14-C24 alkyl residues

WO-95/32356 describes a method for preventing clathrate formation, where the system showing a tendency for clathrate formation is added to an additive comprising a copolymer in which at least one repeating unit contains a nitrogen atom which is bonded to a carbonyl carbon atom, and where the nitrogen atom is at least an organic group with 1 to 4 carbon atoms

It is an object of the present invention to provide an additive and a method for controlling gas hydrate formation by using said additives added in low concentrations to a stream of at least some light hydrocarbons and water

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, the use of polymers comprising structural elements of the formula is provided

who

each R independently is H or C 1 -C 8 alkyl,

X is H, an alkali or alkaline earth metal or a quaternary ammonium group,

R 1 is H or C 1 -C 1s alkyl, and

R 2 is C 1 -C 18 alkyl,

and wherein the alkyl groups represented by R1 and R2 may carry a hydroxy or amino substituent,

and if desired, a smaller proportion of structural elements of the formula

where R 1 , R 2 and X may have the meanings as above, and Alk is a C 1 -C 8 alkylene chain,

order of magnitude as an additive to inhibit the formation of gas hydrates 1 connection with hydrocarbon production and transport

When reference is made to formula 11 below, this may also include smaller amounts of n

The polymers preferably have a molecular weight in the range of 1,000-1,000,000 The units of formula I may be different and there may also be other units different from formula I Such other units may be present in the polymer in amounts up to 90% of the polymer based on the number of units in the polymer Sometimes it may be advantageous to have as little as 1% of such other units in the polymer A polymer with units of formula I and mentioned other units in a ratio of 2 1 to 1 2 may also be preferred The distribution of the units in the polymer can be random or an exact alternation (especially when the ratio is 1 1)

The polymer may contain several monomers which give rise to units of formula 11 en

polymer formed by reacting one or more primary or secondary amines with 1-18 carbon atoms with polymers or copolymers of maleic anhydride. Furthermore, the polymer can be formed by reacting one or more monoamines with 1-18 carbon atoms and one or more hydroxyamines with polymers or copolymers of maleic anhydride The polymer can be a homopolymer or a copolymer with other ethylenically unsaturated monomers including alkyl, vinyl ether, (meth)acrylates, hydroxyalkyl (meth)acrylates, vinyl carboxylates, alkenes, vinyl lactams, vinyl amides, acrylamidopropylsulfonic acid (AMPS), vinylsulfonic acid, alkyl(mct)acrylamides, styrene, allyl amides, vinyl phosphoric acid and styrene sulphonic acid

Instead of amidation of the maleic anhydne dpo lymer, it is also possible to amidate the corresponding maleic anhydnd to form a compound of the formula

where

each R independently is H or C 1 -C 8 alkyl,

X is H, an alkali or alkaline earth metal or a quaternary ammonium group,

R 1 is H or C 1 -C 1s alkyl, hydroxyalkyl or aminoalkyl, and

R 2 is C 1 -C 8 alkyl, hydroxyalkyl or aminoalkyl

This monomer can be subjected to polymerization, if required together with a comonomer

Examples of alkylamines which can react with maleic anhydride and polymers thereof to form the desired product include methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, iso-propylamine, iso-butylamine and n-butylamine

Examples of hydroxyamines that can be added to the reaction mixture of alkylamine and maleic anhydride polymers include 2-amino-2-methyl-1-propanol, 2-aminoethanol, 2-(2-aminoethoxy)ethanol, dimethylethanolamine, 3-(dimethylamino)-1-propanol, 1-(dimethylamino)-2-propanol, N,N-dibutylethanolamine and l-amino-2-propanol as well as polyglycols of ethylene oxide, propylene oxide and butylene oxide with an amine end group

When a hydroxydialkylamine, such as 3-(dimethylamino)-1-propanol is used, the reaction with the maleic anhydride groups will always result in structural elements of formula II due to the fact that a distributed amino group cannot react with the maleic anhydride

Examples of alkyldiamines that can be added to the reaction mixture of alkylamine and maleic anhydride polymers include 3-dimethylaminopropanolamine and 3-diethylaminopropylamine

At least one of the alkylamines to be reacted with maleic anhydride polymers is preferably selected from C3-C4 alkylamines, especially n-propylamine, iso-propylamine, n-butylamine and isobutylamine. Thus, one of Ri or R2 is preferably n-propyl, iso-propyl, n- butyl or iso-butyl

Two or more amines may be reacted with the maleic anhydride polymer to increase performance or for compatibility with the aqueous phase. Two examples illustrating this include a mixture of isobutylamine and a hydroxyamine or a mixture of isobutylamine and methylamine.

The amidated maleic anhydride monomers can be structural parts of copolymers comprising other comonomers such as alkanes, alkyl vinyl ethers, (meth)acrylates, hydroxyalkyl (meth)acrylates, vinyl carboxylates, vinyl lactams, vinyl amides, acrylamide propyl sulfonic acid (AMPS), vinyl sulfonic acid, alkyl (meth)acrylamides, styrene, allyl amides, vinyl phosphoric acid and styrene sulfonic acid Examples of alkenes include 1-alkenes with 2-24 carbon atoms and iso-butylene

Examples of (meth)acrylates include acrylic acid and acrylate salts, methacrylic acid and salts, Cl-24 alkyl acrylates, Cl-24 alkyl methacrylates, dimethylaminoethyl (meth)acrylate and trimethylammonium ethyl (meth)acrylate clone

Examples of hydroxyalkyl (meth)acrylates include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and polyglycol esters of acrylic acid

Examples of alkyl methyl esters include methyl vinyl ether and isobutyl vinyl ether

Examples of vinyl carboxylates include vinyl acetate

Examples of N-vmyllactams include N-vinylcaprolactam, N-vinylpipedone and N-vinylpyrrolidone

Examples of vinyl amides include N-vinylacetamide, N-vinyl-N-methyl-acetamide and N-vinylformamide

Examples of alkyl(meth)acrylamides include acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-ethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-isobutylacrylamide, acryloylpyrrolidine, methacryloylpyrrolidone, N- octyl acrylamide, stearyl acrylamide, N-methylol(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-isobutoxymethyl-(meth)acrylamide, dimethylaminepropyl(meth)acrylamide and trimethylammonium propyl-(meth)acrylamide chloride Depending on the chemical structure of the comonomers the effect of the resulting polymer can be either to inhibit one or more of the following processes during gas hydrate formation, nucleation or crystal growth. In addition, the polymers have a deposition-inhibiting effect

The present invention further provides a method for inhibiting gas hydrate formation in a system for oil and gas drilling, extraction and/or transport, characterized in that it comprises the addition to the system of an additive comprising a water-soluble polymer as mentioned above, in an amount of 0, 01 to 2% by weight based on the water present in the system

Furthermore, the present invention includes the use of a chemical compound of the formula

where

each R independently is H or C 1 -C 8 alkyl,

X is H, an alkali or alkaline earth metal or a quaternary ammonium group,

R 1 is H or C 1 -C 1s alkyl, hydroxyalkyl or aminoalkyl, and

R2 is C1-C8 alkyl, hydroxyalkyl or aminoalkyl,

as an additive to inhibit the formation of gas hydrates in connection with hydrocarbon extraction and transport

The polymers used according to the present invention are preferably prepared by reacting polymers and copolymers of maleic anhydride with one or more amines containing 1-18 carbon atoms with or without added hydroxy acids, at a temperature low enough to prevent less water-soluble cyclic amide products from forming the amine can be a monoamine or diamine If one mole of amm is used per mole of maleic anhydnd, the product is X = H Although not necessary, these monocarboxylate products can be made more water soluble by the addition of a base, such as NaOH If two or more moles of alkylamine are used per mole of maleic anhydnd is the product

X = RNH3 These products are more ionic and therefore more water soluble than those formed by using one mole of amine and no base Furthermore, the R2NH3 ion also has some activity of its own to prevent hydrate formation, especially if R2 has 4-5 carbon atoms

Water solubility can be increased by using maleic anhydride copolymers comprising comonomers with polar and/or ionic groups, by using less than 1 molar equivalent of alkylamine reacted with the maleic anhydride polymer or by reacting a mixture of hydroxyamine and an alkylamine with the maleic anhydride polymer

As mentioned above, the polymers used according to the present invention are suitable as additives for inhibiting the formation of gas hydrates in connection with hydrocarbon production and transport

The additives according to the present invention can, in addition to the polymers used according to the present invention, also contain other components such as a liquid or solid carrier or additive

The amount of the polymers used according to the present invention that must be added is generally between 0.05 and 5% by weight, preferably between 0.05 and 0.5% by weight based on the amount of water in the hydrocarbon-containing mixture. The polymers can be added to a stream of light hydrocarbons and water either as a powder or preferably 1 concentrated solution

The polymers used according to the present invention can also be used together with various other ingredients, called synergists, to improve the overall performance of the product

These synergists are

a) Polymers and copolymers of N-vinylcaprolactam, N-vmylpyrrolidone, alkylated vinylpyrrohodones, acryloylpyrrolidine and polyamino acids such as polyaspartates b) Butoxyethanol and 2-butoxypropanol which can also be used as a solvent medium c) Tetrabutylammonium salts, tetrapentylammonium salts, tnbutylamine oxide, tnpentylamine oxide and compounds containing di - and the tnalkylammonium group,

where alkyl is preferably butyl or pentyl and doubly ionic compounds with at least one butyl or pentyl group on the quaternary ammonium nitrogen atom such as BualNT-Cfk-COO"

These synergists from classes a), b) and c) are preferably added in an amount between 0.01 and 2.0% by weight based on the water content

An example of a synergist-containing product is formed by adding 1 part Gaffix VC713

(a terpolymer of N-vinylcaprolactam, N-vinylpyrrolidone and dimethylaminoethyl acrylate)

ul 4 parts of the reaction product of "Gantrez AN-119-BF" (a methyl vinyl ether-maleic anhydride copolymer) and isobutylamine

The polymers used according to the present invention can be formulated with a solvent such as water, a glycol or lower alcohol or a mixture of such solvents. Other production chemicals such as corrosion inhibitors, scale inhibitors and defoamers can be formulated with the polymers used according to the present invention. The polymers used according to the present invention is also suspected of having anti-corrosion and anti-seize properties itself

Particular preference is given to products formed by reacting a polymer built up from maleic anhydride and one or more substituted or unsubstituted olefins R<3>R<4>C=CH2, with one or more non-cyclic C2- Ci8 diamines and, if desired, with one or more primary or secondary Ci-Ci2 monoamines,

where R<3> and R<4> are independently hydrogen or a C1-C12-alkyl, C2-C12-alkenyl or C6-C12-aryl radical which may be interrupted by oxygen or -CO-O- or -O- CO- and R<J>can also be -COOH

The incorporation of the diamine makes it possible to prepare polymers that are water-soluble over a wide pH range, because simpler reaction products of polymers based on maleic anhydride with aliphatic monoamines are polymers with carboxylate functions that become water-soluble in an acidic medium as a result of the protonation of the carboxylate groups and therefore precipitates from the aqueous solution When suitable diameters are incorporated the polymer assumes a canonical charge in the acidic region and thus remains anhydrous

These polymers can be alternating polymers and maleic anhydnd and the corresponding olefin, which are formed especially by low-pressure processes, or else random polymers with olefin maleic anhydnd molar ratios of > 1 or < 1 that are formed mainly by high-pressure processes Preference is given to a molar ratio of olefin to maleic anhydnd of 1 1 to 10 1

Many of these polymers are commercially available or can be synthesized in a simple way. Thus, polymers of maleic anhydnd and vinyl esters are obtained under the name Gantrez AN (ISP), Gantrez ES (GAF), Viscofras (ICI) or Sokalan (BASF)

Polymers of maleic anhydride and the corresponding olefins are obtainable by methods known from the literature A summary of these syntheses is given in "Methoden der Orgamschen Chemie", Volume E 20 (Makromolekulare Stoffe)", pages 1234-1250, Georg Thieme Verlag, Stuttgart, 1987

The synthesis of alternating ethylene-maleic anhydride polymers and of random polymers of maleic anhydride and ethylene is described in the reference above and also in "Polymer Science US S R" Vol 25, No 9, pages 2151-2160, 1983

The molecular weight of these polymers can usually be within the range 1000->10<6> g/mol, but preference is given to molecular weights of 1000-40000 g/mol

Diamine components that can be used are dialkyl-substituted diamines with 2-18 carbon atoms in the molecule, preferably with a primary and a tertiary amino group, e.g. N,N-diethylaminopropylamine, N}N-dimethylaminopropylamine, N,N-dipropylaminopropylamine and N,N-dibutylaminopropylamine Preference is given to dialkyl-substituted diamers with 4 to 12 carbon atoms in the molecule, 3-dimethylaminopropylamine is particularly very suitable

Suitable monoamine constituents are monoamines with a primary or secondary amino group and 1 to 12 carbon atoms in the molecule Preference is given to amines of the formula R<S>NH2 where R<5> is an unsubstituted, branched or unbranched alkyl radical with 1 to 12, preferably 1 to 5 carbon atoms Examples are methylamine, ethylamine, propylamine, isopropylamine, n-butylamine, isobutylamine, the isomerpentylamines and hexylamines, as well as octylamine and dodecylamine

The polymers used according to the present invention are produced, for example, by reacting the polymer which is built up from maleic anhydride and one or more olefins with the above-mentioned monoamines and diamers in an aqueous or aqueous-alcoholic medium, the polymer is introduced slowly to the solution of the amines Suitable alcoholic solvents are water-soluble monoalcohols, e.g. methanol, ethanol, propanols, butanols and oxyethylated monoalcohols such as butylglycol and butyldiglycol

The sum of the molar amounts of the diamines and monoamines is 80-200% based on the anhydride content in the polymer However, the diamines and monoamines are preferably added in such amounts that the sum of the amounts of diamines and monoamines corresponds to the anhydride content in the polymer The molar ratio of diamine to monoamine is 100 0 to 10 90

The reaction temperature can be chosen from 0°C to the boiling point of the solvent, but is preferably chosen as low as 50°C to enable the formation of monoamide structures and to suppress coupling reactions that form the cyclic amide. Clear solutions of the modified polymers are formed.

The above-mentioned synergists comprise mixtures of polyamides with one or more different polymers with a carbon main chain and amide bonds in the side chains

These include in particular polymers such as polyvinylpyrrolidone, polyvinylcaprolactam, polymers of vinylpyrrolidone and vmylcaprolactam and also terpolymers of vinylpyrrohdone, vmylcaprolactam and further ammonium, cationic and uncharged comonomers with a vinyl double bond, e.g. 1-olefins, N-alkylacrylamides, N-vinylacetamide , acrylamide, sodium 2-acrylamide-2-methyl-1-propanesulfonate (AMPS) or acrylic acid Mixtures include homopolymers and copolymers of N,N-dialkylacrylamides such as N-acryloylpyrrolidine, N-acryloylmorphol and N-acryloylpipenidine are also suitable Likewise suitable are mixtures comprising alkyl polyglycosides, hydroxyethyl cellulose, carboxymethyl cellulose and other ionic or non-ionic surface-active molecules Particularly suitable mixtures are those comprising quaternary ammonium salts, especially tetrabutylammonium bromide and amine oxides such as tert-butyl ammonium oxide

Example 1

9.15 g (89.5 mmol) of 3-dimethylaminepropylamine and 6.55 g (89.5 mmol) of isobutylamine initially become completely 150.7 g of butyl glycol and 101.4 g of water at 25°C and 35.0 g (179 mmol) of an ethylene-maleic anhydride polymer with a maleic anhydride content of 50% by mass (molecular weight according to gel permeation chromatography about 10,000) in powder form is added over a period of 2 minutes. The reaction mixture is heated to 50°C and after the exothermic the reaction is complete, stir for a further 12 hours at 50°C This gives a yellow, fluid solution with a content of 25% and a pH (1% in deionized water) of 8.0 The product has a solubility of

1% in deionized water at pH 1, pH 3 and pH 11

Example 2

18.3 g (179 mmol) of 3-dimethylaminepropylamine was initially mixed with 153.3 g of butyl glycol and 106.6 g of water at 25°C and 35.0 g (179 mmol) of an ethylene-maleic anhydride polymer with a maleic anhydride content of 50% with regard to mass (molecular weight according to GPC approx. 10000) in powder form was added over a period of 2 minutes. The reaction mixture was heated to 50°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C. This gave a yellow, fluid solution with a content of 25% and a pH (1% in deionized water) of 9.4 The product had a solubility of 1% in deionized water at pH 1, pH 3 and pH 11

Example 3

7.15 g (70.0 mmol) of 3-dimethylaminepropylamine and 5.12 g (70.0 mmol) of isobutylamine were initially completely 147.3 g of butyl glycol and 94.5 g of water at 25°C and 35, 0 g (140 mmol) of an ethylene-maleic anhydride polymer with a maleic anhydride content of 40% with respect to mass (molecular weight according to GPC approx. 10000) in powder form was added over a period of 2 minutes. The reaction mixture was heated to 50°C and after the exothermic the reaction was complete, the stirring was continued for a further 2 hours at 50°C. This gave a yellow, fluid solution with a content of 25% and a pH (1% in

deionized water) of 8.9 The product had a solubility, to obtain a transparent solution, of 1% in deionized water at pH 1, pH 3 and pH 11

Example 4

8.33 g (81.5 mmol) of 3-dimethylaminepropylamine and 5.96 g (81.5 mmol) of isobutylamine were initially completely 144.3 g of butyl glycol and 88.6 g of water at 25°C and 35.0 g (140 mmol) of a vinyl acetate-maleic anhydride polymer (molecular weight according to GPC about 15000) in powder form was added over a period of 2 minutes. The reaction mixture was heated to 45°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C This gave a yellow, fluid, slightly cloudy solution with a content of 25% and a pH (1% in deionized water) of 5.8 The product had a solubility, to obtain a clear solution, of 1% in deionized water at pH 1, pH 3 and pH 11

Example 5

7.76 g (76.0 mmol) of 3-dimethylaminepropylamine and 5.56 g (76.0 mmol) of isobutylamine were initially completely 143.3 g of butyl glycol and 86.6 g of water at 25°C and 30, 0 g (152 mmol) of an alternating vinyl isobutyl ether-maleic anhydride polymer (molecular weight according to GPC approx. 18000) in powder form was added over a period of 3 minutes. The reaction mixture was heated to 48°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C This gave a clear, orange, fluid solution with a content of 25% and a pH (1% in deionized water) of 6.2 The product had a solubility, to obtain a clear solution, of 1% in deionized water at pH 1, pH 3 and pH II

Example 6

15.5 g (152 mmol) of 3-dimethylaminepropylamine was initially poured into 45.5 g of butyl glycol and 91.1 g of water at 25°C and 30.0 g (152 mmol) of an alternating vinyl n-butyl ether -maleic acid anhydride polymer (molecular weight according to GPC approx. 16000) in powder form was added over a period of 3 minutes. The reaction mixture was heated to 42°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C. This gave a cloudy, yellow hg solution with a content of 25% and a pH (1% in deionized water) of 7.0 The product had a solubility, to obtain a clear solution, of 1% in deionized water at pH 1, pH 3 and pH 11

Example 7

7.76 g (76.0 mmol) of 3-dimethylaminepropylamine and 5.56 g (76.0 mmol) of isobutylamine were initially completely 143.3 g of butyl glycol and 86.6 g of water at 25°C and 30, 0 g (152 mmol) of an alternating vinyl n-butyl ether-maleic anhydride polymer (molecular weight according to GPC about 16000) in powder form was added over a period of 3 minutes. The reaction mixture was heated to 48°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C This gave a clear, orange solution with a content of 25% and a pH (1% in deionized water) of 5.9 The product had a solubility, to obtain a clear solution , of 1% in deionized water at pH 1, pH 3 and pH 11

Example 8

7.76 g (76.0 mmol) of 3-dimethylaminopropylamine and 4.5 g (76.0 mmol) of isopropylamine were heated starting with all 142.3 g of butyl glycol and 84.5 g of water at 25°C and 30, 0 g (152 mmol) of an alternating wine isobutyl ether-maleic anhydride polymer (molecular weight according to GPC about 18000) in powder form was added over a period of 3 minutes. The reaction mixture was heated to 48°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C This gave a clear, pale yellow fluid solution with a content of 25% and a pH (1% in deionized water) of 6.2 The product had a solubility, to obtain a clear solution, of 1% in deionized water at pH 1, pH 3 and pH 11

Example 9

7.76 g (76.0 mmol) of 3-dimethylaminepropylamine and 5.40 g (76.0 mmol) of a 63.5% strength aqueous ethylamine solution were mixed with a total of 143.2 g of butyl glycol and 86.4 g water at 25°C and 30.0 g (152 mmol) of an alternating vinyl n-butyl ether-maleic anhydride polymer (molecular weight according to GPC approx. 16000) in powder form were added over a period of 3 minutes. The reaction mixture was heated to 45°C and after the exothermic reaction was complete, stirring was continued for a further 2 hours at 50°C This gave a clear, pale yellow solution with a content of 25% and a pH (1% in deionized water) of 6.0 The product had a solubility, for to obtain a clear solution, of 1% in deionized water at pH 1, pH 3 and pH 11

Efficiency of the polymers

The effectiveness of the polyamides was studied using a THF hydrate test Since natural gas hydrates only exist at high pressures which are only achievable with difficulty under laboratory conditions, the formation of clathrates of THF (tetrahydrofuran) and water is used as a model These hydrates are formed at atmospheric pressure at 4°C at a water THF molar ratio of 17 1 If an additive kinetically inhibits the formation of THF hydrates or keeps the formed THF hydrates stirrable, then this additive should have a similar effect on naturally occurring gas hydrates

As can be seen in the experimental examples below, the lack of inhibitors leads to the rapid onset of THF hydrate formation under the experimental conditions and leads to the formation of THF hydrates with a needle-like or plate-like shape, which very quickly causes the entire test solution to solidify. Addition of the polymer significantly increases THF hydrate formation slower and/or changes the crystal form of the hydrates that are formed

All polyamides used make THF hydrate formation significantly slower

The THF test was performed as follows

Experiment without inhibitor

A short Pasteur pipette (1 = 140 mm) is fixed in a drilled cork in such a way that the tip of the pipette protrudes 120 mm from the cork A drop of a THF/water mixture (1 17) is then taken up into this pipette by capillary forces , the pipette (with cork stopper) is weighed and refrigerated for at least 2 hours at -20°C

A 3.5% strong sodium chloride solution is mixed with THF in a ratio of 4 to 1. 30 ml of this solution is placed in a test tube (150 x 30 mm) and cooled for 25 minutes at 0°C in a cooling bath (the test tube is immersed in the cooling bath to a depth of 60 mm)

The frozen pipette is taken from the freezer, quickly dried (to remove crystal seeds from the outside of the pipette and thus achieve uniform starting conditions) and immediately dipped to a depth of about 15 mm into the above-mentioned THF/water/natnum clone mixture with THF hydrates that form after a short time (a few minutes)

After 60 minutes, the pipette is very carefully removed from the test tube and the pipette together with the cork and adhering hydrates are immediately weighed. The rate of THF hydrate formation (in g/h) is calculated from the difference between initial and final weights and the elapsed time

Examples 1-9:

The blank determination procedure is repeated, but 5000 ppm (based on the water content of the mixture) of the appropriate inhibitor is added to the test solution The evaluation is carried out as above

The results are collected in table 1 and show the effectiveness of the compounds used

In addition, the effectiveness of the polymers used according to the present invention was studied by means of autoclave experiments under isoconic conditions (at constant volume) using water/gas mixtures

For this purpose, in reference experiments, deionized water was treated in an autoclave with about 50 bar of a natural gas that forms structure II hydrates (mainly methane, n-propane content > 1%) and cooled under stirring (stirring speed 250 rpm) according to a temperature program ( see below) The pressure changes indicate nucleation and crystal growth of the gas hydrates and the torque produced, which represents a measure of the hydrate agglomeration, is measured using a torque sensor

As can be shown in the experimental examples below, gas hydrate formation develops rapidly without an inhibitor under the experimental conditions and leads to a large increase in torque, so that one can conclude the formation of large hydrate agglomerates

In contrast, the addition of small amounts (in all examples 500 ppm = 0.05%) of the polymers used according to the present invention leads either to a significant delay in hydrate formation (example 1) or to a complete inhibition of gas hydrate formation during the entire course of the experiment (example 4/5)

The apparatus for measuring gas hydrate inhibition is described in D Lippmann, Thesis, Tech Universitat Clausthal, 1995

The test products were dissolved in 188 ml of deionized water in a stirred steel autoclave equipped with temperature control and a torque sensor (stirring speed 250 rpm) with a volume ratio of gas to water phase of 8 2 and the autoclave was pressurized with gas to 49-53 bar From an initial temperature of 17 .5°C, the contents of the autoclave were cooled to 2°C over a period of 2 hours, then stirred for 20 hours at 2°C and again heated to 17.5°C over a period of 2 tuner During cooling it was first observed a small reduction in pressure corresponding to the thermal contraction of the gas As the formation of gas hydrate atoms occurred, the measured pressure fell and an increase in the measured torque was observed, without the presence of an inhibitor, further crystal growth and increasing agglomeration of these hydrate atoms rapidly lead to a further increase in the measured torque The time from reaching the minimum temperature of 2°C to the first drop in gas pressure is referred to as the induction time When heating ming of the reaction mixture, the gas hydrates were finally broken down again, so that at the end of the experiment the initial state was restored

The agreement between the THF test results and the experimental examples under high pressure conditions shows that the behavior of an inhibitor in the THF test is a correct measurement of its effectiveness under high pressure conditions

To demonstrate the increased salt water compatibility of the modified maleic anhydride copolymers used according to the present invention compared to conventional products based on polyvinylpyrrolidone/polyvinylcaprolactam, the mixing points for 1% strength solutions of the corresponding polymers in a 3.6% strength sodium chloride solution were measured (% = weight -%)

Additional examples

Equipment and test procedure

To evaluate the performance of the hydrate inhibitor polymers used according to the present invention, the examples given use high-pressure sapphire cells and methods for using them described in MA Kelland, TM Svartaas and LA Dybvik, Proe SPE Annual Techmcal Conference/Production Operations and Engineenng, 1994, pages 431-438

The equipment used is illustrated in flg 1

The sapphire cell was placed in a cooling bath The sapphire cell consists of a sapphire tube 1 placed in a holder between two stainless steel end pieces The cell has an inner diameter of 20 mm, a height of 100 mm and a wall thickness of 20 mm 15 mm of the top piece and 13 mm of the bottom piece protrude into the cell and the total volume between top and bottom pieces is 22.6 ml The sapphire cell is equipped with a stirring mechanism A stirring blade 2 is connected to a magnetic cabinet at the bottom of the end piece via an axis An externally rotating magnetic field 3 created by a laboratory magnetic stirrer is used to regulate the stirring speed The reciprocating motor can be regulated to maintain a constant speed (regardless of motor load) in the range from 0 to 1700 rpm The regulator/amplifier unit has output connections for both torque and rotational speed readings Reciprocating speed readings are calibrated using a stroboscope

The sapphire cell is placed inside separate double-walled, transparent carbonate plastic cylinders with four separate windows at 0, 90, 180 and 270° for visual observations Temperature control of the cell is achieved by circulating water in the plastic cylinders and through a cooler/heating unit 8 connected to a temperature control unit 9 The cell system is equipped with two temperature sensors for measuring the temperature inside the cell 5 (in the gas phase) and in the water bath 6 The pressure is measured with a pressure signal converter through the inlet pipe connected to the top end of the cell The temperature is measured with an accuracy of ±0.1 DC and the pressure is measured at a accuracy of ±0.2 bar Video recording of the experiments was also done All data was collected in a data logger 10 The data could be output on a printer/plotter 11

The same procedure for conducting the experiment and filling the cell was followed in all experiments All tests were performed on fresh synthetic seawater (SSW = 3.6%) and synthetic natural gas (SNG) Condensate was added in experiments 23-25

A description of the general test procedure is given here

1) The polymer to be tested was dissolved or dispersed in synthetic seawater (SSW) to the desired concentration 2) The magnetic chamber sat on the cell was filled with an aqueous solution containing the inhibitor to be tested The magnetic chamber sat was then placed in the bottom end of the cell, which was then attached to the manifold and the cell holder 3) The desired amount of the aqueous solution containing dissolved inhibitor was placed in the cell (above the cell bottom) using a pipette The top end piece was put in place and the cell was placed in the cooling bath (plastic coolers) 4) The temperature of the cooling bath was adjusted to 2 -3°C outside the hydrate range at the pressure conditions to be used in the experiment 5) Before filling the cell with hydrocarbon gas or condensate, it was first purged twice with SNG used in the experimental hydrocarbon fluid 6) The data logging and video recording was started and the cell was filled with the hydrocarbon fluid to the desired pressure while stirring at 700 rpm Normal was the hydrocarbon fluid SNG

When the temperature and pressure in the cell had stabilized, the experiment began

All nucleation/crystal growth experiments, called "kinetic inhibition" experiments, were carried out at constant temperature. After the temperature and pressure had stabilized after filling the cell, the stirring was stopped. The closed cell was then cooled to the experiment temperature, resulting in a drop in pressure. When the temperature and the pressure had stabilized again, stirring at 700 rpm was started. The induction time, ten, for hydrate formation was measured from the time of the start of stirring at the experiment temperature. The time from initial hydrate formation to the time when rapid growth of hydrates resulted was called the crystal growth delay time, St-1 The procedure stated for the synthesis of polymers by reaction of amines with maleic anhydride copolymers are only examples of possible synthesis techniques that can be used for the methods according to the present invention

Examples 10-19 are carried out using SNG and brine at 90 bar and 7.5°C (AT = 13.8°C)

Example 10

Several kinetic inhibition experiments were performed without additives. The total delay time before rapid gas uptake occurred (ie, the induction time t, plus the crystal growth delay time St-1) was less than 3 minutes in all experiments Example 11

Ethylene-maleic anhydride copolymer was added as a fine powder to a solution of n-PrNH21 diethyl ether at room temperature and stirred for one hour. One mole of n-PrNH2 was used per mole of maleic anhydride copolymer. The slurry was evaporated to dryness to leave a white solid. When tested for kinetic inhibition at 0.5 wt% in 3.6 wt% SSW gave the product tt = 137 minutes and St-1 = 37 minutes

Example 12

Ethylene-maleic anhydride copolymer was added as a fine powder to a solution of i-BuNH21 diethyl ether at room temperature and stirred for 11 hours 1 mole of i-BuNH2 was used per mole of maleic anhydride in the copolymer The slurry was evaporated to dryness to leave a white solid When tested for kinetic inhibition at 0.5 wt% 13.6% SSW gave the product t, = 885 minutes and St-1 = 183 minutes

Example 13

Ethylene-maleic anhydride copolymer was added slowly as a fine powder to an excess pure solution of isopropylamine at room temperature and stirred for 11 hours. The slurry was evaporated to dryness to leave a beige-white solid. When tested for kinetic inhibition at 0.5 wt% 13.6% SSW, gave the product t, = 115 minutes and St-1 = 15 minutes

Example 14

Ethylene-maleic anhydride copolymer was added slowly as a fine powder to an excess pure solution of n-butylamine at room temperature and stirred for 11 hours. The slurry was evaporated to dryness to leave a beige-white solid. When tested for kinetic inhibition at 0.5% by weight in 3, 6% SSW, gave the product t, = 1175 minutes and St-1 = 55 minutes in a first experiment and t, = 190 minutes and St-1 = 37 minutes in another experiment

Example 15

Ethylene-maleic anhydride copolymer was added slowly as a fine powder to an excess pure solution of isobutylamine at room temperature and stirred for 11 hours. The slurry was evaporated to dryness to leave a beige-white solid. When tested for kinetic inhibition at 0.5 wt% 13.6% SSW, gave the product t, = 103 minutes and St-1 = 171 minutes in a first experiment and t, = 118 minutes and St-1 = 153 minutes in a second experiment

Example 16

Ethylene-maleic anhydride copolymer was added slowly as a fine powder to an excess pure solution of isopentylamine at room temperature and stirred for 11 minutes. The slurry was evaporated to dryness to leave a beige-white solid. When tested for kinetic inhibition at 0.5 wt% 13.6% SSW, gave the product t, = 21 rmnuts and St-1 = 27 minutes

Example 17

A product formed by reaction between Gantrex AN-119-BF (methyl vinyl ether-maleic anhydride copolymer) and isobutylamine was tested for kinetic inhibition at 0.5% by weight in 3.6% SSW The product gave t, - 48 minutes and St-1 = 43 minutes

Example 18

A corresponding product to Example 8 was formed by reaction between Gantrex AN-169-BF (methyl vinyl ether-maleic acid armydnd copolymer) and isobutylamine was tested for kinetic inhibition at 0.5 wt% 13.6% SSW The product gave t, = 106 minutes and St -1 = 60 minutes in the first experiment and t, = 256 minutes and St-1 = 69 minutes in another experiment

Example 19

A product formed by reacting Gantrex AN-169-BF (methyl vinyl ether-maleic anhydride copolymer) with an excess of isobutylamine and ethanolamine in a 4 1 molar ratio was tested for kinetic inhibition at 0.5% by weight in 3.6% SSW. > 1212 minutes

Example 20

A product formed by reacting isobutyl vinyl ether-maleic anhydride copolymer with a mixture of isobutylamine and dimethylaminopropylamine was tested for kinetic inhibition at 0.5 wt% 13.6% SSW The product gave t, = 795 minutes and St-1 = 192 minutes

Example 21

The polymer product used in example 11 was tested for kinetic inhibition at 0.4% by weight 13.6% SSW with an addition of 0.1% vinylpyrrolidone-vmylcaprolactam 1 1 copolymer The product gave t, = 1222 minutes

Example 22

The polymer product used in Example 11 was tested for kinetic inhibition at 0.4 wt% 13.6% SSW with an addition of 0.1 wt% tertbutylamine oxide The product gave t, = 1059 minutes and St-1 = 32 minutes

Examples 23-25 were carried out using a North Sea condensate and the same SNG and brine as in examples 1-13, at 90 bar but at different temperatures Example 23

The polymer product used in example 3 was tested for kinetic inhibition at 0.5% by weight in 3.6% SSW at 8.8°C (DT = 9.7°C). The product gave t, = 621 minutes and St-1 = 48 minutes 1 a corresponding experiment at 6.8°C (DT = 11.7°C) the result was t, = 28 minutes and St-1 = 10 minutes Without an additive this system stops with hydrate in less than 5 minutes at either 8.8°C or 6.8°C

Example 24

The polymer product used in example 3 was tested for kinetic inhibition at 0.5% by weight 13.6% SSW at 6.8°C with the addition of 0.1% polyvinyl caprolactam. The product gave t, = 480 minutes and St-1 = 300 minutes

Example 25

The polymer product used in example 3 was tested for kinetic inhibition at 0.5% by weight in 3.6% SSW at 6.8°C with the addition of 0.1% tetrabutylammonium bromide. The product gave t, = 145 minutes and St-1 = 25 minutes

Claims (26)

1 Application of a water-soluble polymer comprising structural elements of the formula who each R is independently H or C 1 -C 8 alkyl, X is H, an alkali or alkaline earth metal or a quaternary ammonium group, Ri is H or OCis alkyl, and R 2 is C 1 -C 1 -C 1 alkylJ and wherein the alkyl groups represented by R1 and R2 may carry a hydroxy or amino substituent, and if desired, a smaller proportion of structural elements of the formula where R1, R2 and X can have the meanings as above, and Alk is a Ci-Cj alkylene chain, as an additive to inhibit the formation of gas hydrates in connection with hydrocarbon recovery and transport 2 Use of a polymer according to claim 1, where the molecular weight is 1,000-1,000,000 3 Use of a polymer according to any one of claims 1 or 2 comprising different structural elements of formula (I) and, if desired (H) 4 Use of a polymer according to any one of claims 1-3 comprising units of formula (I) and, if desired (H) 1 wherein R is H 5 Use of a polymer according to any one of claims 1-4 comprising units of formula (I) and, if desired (H) in which Rj is H and R2 is C3-C4 alkyl 6 Use of a polymer according to any one of claims 1-5 comprising units of formula (I) and, if desired (II) in which X is H 7 Use of a polymer according to any one of claims 1-6 comprising in addition to units of formula (I) and, if desired (II) also other units corresponding to ethylenic unsaturated comonomers 8 Use of a polymer according to claim 7 comprising up to 90 mol% of such other units 9 Use of a polymer according to claim 8, where the ratio between the number of units of formula (I) and, if present (H) to the number of other units is in the range from 2 1 ul 1 2 10 Use of a polymer according to claim 1, which is formed by reacting a starting polymer made up of maleic anhydride and one or more substituted or unsubstituted olefins R<3>R<4>C=CH2, with non-cyclic C2- C 18 diamines and, if desired, primary and/or secondary C 1 -C 12 monoamines, wherein R<3> and R<4> are independently hydrogen or a C 1 -C 12 alkyl, C 2 -C 12 alkenyl - or Cs-Cu aryl radical which can be interrupted by oxygen or -CO-O- or -O-CO- and R<1> can also be - COOH 11 Use of a polymer according to claim 10, where the polymer is made up of maleic anhydride and ethylene 12 Use of a polymer according to claim 10, where the polymer is built up of maleic anhydride and one or more vinyl ethers 13 Use of a polymer according to claim 10, where the polymer is made up of maleic anhydride and vinyl acetate 14 Use of a polymer according to claim 10, where the polymer is made up of maleic anhydride and styrene 15 Use of a polymer according to claim 10, where the diamine is non-cyclic, has a primary or tertiary amine group and 4-12 carbon atoms in the molecule 16 Use of a polymer according to claim 10, where the diamine is 3-dimethylaminopropylamine 17 Use of a polymer according to claim 10, where the monoamine is a monomeric monoamine with 1-12 carbon atoms in the molecule 18 Use of a polymer according to claim 10, where the monoamine is a monomeric monoamine with 1-5 carbon atoms in the molecule 19 Use of a polymer according to any one of claims 10-171 a mixture with one or more polymers built up from a main carbon chain, obtained by polymerisation and amide bonds in the lateral chains and in a mixture with quaternary ammonium salts and amine oxides 20 Method for inhibiting gas hydrate formation in a system for oil and gas drilling, extraction and/or transport, characterized in that it comprises adding to the system an additive comprising a water-soluble polymer according to any one of claims 1-191 an amount of 0, 01 to 2% by weight based on the water present in the system 21 Method according to claim 20, characterized in that the synergist is added in combination with said polymer 22 Method according to claim 20, characterized in that the synergist is selected from polymers and copolymers of N-vinylcaprolactam, N-vinylpyrrolidone and alkylated vinylpyrrohodones 23 Application of a chemical compound of the formula where each R independently is H or C 1 -C 8 alkyl, X is H, an alkali or alkaline earth metal or a quaternary ammonium group, R 1 is H or C 1 -C 6 alkyl, hydroxyalkyl or aminoalkyl, and R 2 is C 1 -C 6 alkyl, hydroxyalkyl or aminoalkyl, as an additive to inhibit the formation of gas hydrates in connection with hydrocarbon extraction and transport 24 Use of a chemical compound according to claim 23, where each R is H 25 Use of a chemical compound according to either claim 23 or 24, where Ri is H and R2 is C3-C4 alkyl 26 Use of a chemical compound according to any one of claims 23-25, wherein XerH