Earth boring – well treating – and oil field chemistry – Preventing contaminant deposits in petroleum oil conduits
Reexamination Certificate
1997-11-24
2002-04-09
Medley, Margaret (Department: 1714)
Earth boring, well treating, and oil field chemistry
Preventing contaminant deposits in petroleum oil conduits
C507S103000, C507S130000, C507S242000, C507S260000, C137S013000, C166S310000, C210S698000
Reexamination Certificate
active
06369004
ABSTRACT:
FIELD OF INVENTION
This invention relates to the use of water-soluble polymers for inhibiting formation of gas hydrates in pipes containing oil or gas. This is relevant for both drilling and production of oil and gas.
BACKGROUND OF THE INVENTION
Gas hydrates are clathrates (inclusion compounds) of small molecules in a lattice of water molecules. In the petroleum industry natural gas and petroleum fluids contain a variety of these small molecules which can form gas hydrates. They include hydrocarbons such as methane, ethane, propane, isobutane as well as nitrogen, carbon dioxide and hydrogen sulphide. Larger hydrocarbons such as n-butane, neopentane, ethylene, cyclopentane, cyclohexane and benzene are also hydrate forming components. When these hydrate forming components are present with water at elevated pressures and reduced temperatures the mixture tends to form gas hydrate crystals. For example, ethane at a pressure of 1 MPa forms hydrates only below 4° C. whereas at 3 MPa gas hydrates can only form below 14° C. These temperatures and pressures are typical operating environments where petroleum fluids are produced and transported.
If gas hydrates are allowed to form inside a pipe used to transport natural gas and/or other petroleum fluids they can eventually block the pipe. The hydrate blockage can lead to a shutdown in production and significant financial loss. The oil and gas industry uses various means to prevent the formation of hydrate blockages in pipelines. These include heating the pipe, 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 costly to implement and maintain. The most common method used today is adding antifreezes. However, these antifreezes have to be added at high concentrations, typically 10-40% by weight of the water present, in order to be effective. Recovery of the antifreezes is also usually required and is a costly procedure.
Consequently, there is a need for alternate cheap methods for preventing hydrate blockages in oil and gas drilling and production.
An alternative to the above methods is to control the gas hydrate formation process using nucleation and crystal growth inhibitors. These types of chemicals are widely known and used in other industrial processes. The advantage of using these chemicals to control gas hydrate formation is that they can be used at concentrations of 0.01 to 2% which is much lower than for antifreezes.
It is an object of this invention to provide an additive and a method of controlling gas hydrate formation using said additives added at low concentrations to a stream of at least some light hydrocarbons and water.
SUMMARY OF INVENTION
According to the present invention we provide the use of polymers which comprise structural elements of the formula
wherein
each R is independently H or C
1
-C
5
-alkyl;
X is H, an alkaline or earth alkaline metal or a quarternary ammonium group;
R
1
is H or C
1
-C
18
-alkyl; and
R
2
is C
1
-C
18
-alkyl;
and wherein the alkyl groups represented by R
1
and R
2
may carry a hydroxy or amino substituent;
and, if desired, a minor proportion of structural elements of the formula
wherein R
1
, R
2
and X are as above, and Alk is a C
1
-C
5
-alkylene chain, and, if desired, also other structural elements formed from ethylenically unsaturated monomers;
the molecular weight of the polymer being in the range from 500 to 2,000,000, as an additive for inhibiting the formation of gas hydrates in connection with hydrocarbon production and transportation.
When reference is made to formula I in the following, this may also include minor amounts of II.
The polymers preferably have a molecular weight in the range 1000-1,000,000. The units of formula I may be different, and there may also be other units which are different from formula 1. Such other units may be present in the polymer in amounts up to 90% of the polymer based on the total 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 having units of formula I and said other units in a ratio of 2.1 to 1:2 may also be preferred. The distribution of the units in the polymer may be random or an exact alternation (in particular when the ratio is 1:1).
The polymer can contain more monomers giving rise to units of formula I in a polymer formed by reaction of one or more primary or secondary amines having 1-18 carbon atoms with polymers or copolymers of maleic anhydride. Additionally the polymer can be made by reacting one of more monoamines having 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 ethers, (meth)acrylates, hydroxyalkyl (meth)acrylates, vinyl carboxylates, alkenes, vinyl lactams, vinyl amides, acrylamidopropylsulphonic acid (AMPS), vinylsulphonic acid, alkyl(meth)acrylamides, styrene, allyl amides, vinylphosphoric acid and styrenesulphonic acid.
Instead of amidating the maleic anhydride polymer it is also possible to amidate the corresponding maleic anhydride to form a compound of the formula
wherein
each R is independently H or C
1
-C
5
-alkyl;
X is H, an alkaline or earth alkaline metal or a quaternary ammonium group;
R
1
is H or C
1
-C
18
-alkyl, hydroxyalkyl or aminoalkyl; and
R
2
is C
1
-C
18
-alkyl, hydroxyalkyl or aminoalkyl.
This monomer may then be subjected to polymerisation, if required together with a comonomer.
Examples of alkylamines that can be reacted 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-aminoethylamino)ethanol, 2-(2-aminoethoxy)ethanol, dimethylethanolamine, 3-(dimethylamino)-1-propanol, 1-(dimethylamino)-2-propanol, N,N-dibutylethanolamine and 1-amino-2-propanol as well as polyglycols of ethylene oxide, propylene oxide and butylene oxide having one 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 since a disubstituted amino group cannot react with the maleic anhydride.
Examples of alkyl diamines which can be added to the reaction mixture of alkylamine and maleic anhydride polymers include 3-dimethylaminopropylamine and 3-diethylaminopropylamine.
At least one of the alkylamines to be reacted with maleic anhydride polymers is preferably chosen from C
3
-C
4
-alkylamines, in particular n-propylamine, iso-propylamine, n-butylamine and isobutylamine. Thus, one of R
1
or R
2
is preferably n-propyl, iso-propyl, n-butyl or iso-butyl.
Two or more amines can be reacted with the maleic anhydride polymer to increase performance or for compatibility with the aqueous phase. Two examples to illustrate this but which are not meant to limit the scope of application include a mixture of isobutylamine and a hydroxyamine or a mixture of isobutylamine and methylamine.
The amidated maleic anhydride monomers can be structurally part of copolymers comprising other comonomers such as alkenes, alkyl vinyl ethers, (meth)acrylates, hydroxyalkyl (meth)acrylates, vinyl carboxylates, vinyl lactams, vinyl amides, acrylamidopropylsulphonic acid (AMPS), vinylsulphonic acid, alkyl(meth)acrylamides, styrene, alkyl amides, vinylphosphoric acid and styrenesulphonic acid. Examples of alkenes include 1-alkenes having 2-24 carbon atoms and iso-butylene.
Examples of (meth)acrylates include acrylic acid and acrylate salts, methacrylic acid and salts, C1-24 alkyl acrylates, C1-24 alkyl methacrylates, dimethylaminoethyl (meth)acrylate and trimethylammonium-ethyl (meth)acrylate chloride.
Examples of hydroxyalkyl (meth)acrylates include hyd
Kelland Malcolm
Klug Peter
Hanf Scott E.
Jackson Susan S.
Medley Margaret
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