Earth boring – well treating – and oil field chemistry – Preventing contaminant deposits in petroleum oil conduits
Reexamination Certificate
1998-02-02
2001-12-18
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Preventing contaminant deposits in petroleum oil conduits
C507S246000, C585S015000, C585S950000
Reexamination Certificate
active
06331508
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to controlling hydrates, particularly gas hydrates, in fluid mixtures, particularly light hydrocarbons in admixture with water.
BACKGROUND OF THE INVENTION
Clathrate hydrates are crystalline compounds that occur when water forms a cage-like structure around guest molecules, particularly gaseous molecules. Clathrate hydrates, especially in the petroleum industry, are referred to as gas hydrates, gas hydrate crystals, or simply hydrates. In the petroleum industry, gas hydrates pose particular problems with respect to producing, transporting, and processing of natural gas in petroleum fluids. Typical gas hydrates formed in petroleum (hydrocarbon) environments are composed of water and one or more guest molecules such as methane, ethane, propane, isobutane, normal butane, nitrogen, carbon dioxide, and hydrogen sulfate. It is also known that other guest molecules such as ethane, nitrous oxide, acetylene, vinyl chloride, ethyl bromide, oxygen, etc., can also form clathrate hydrates.
It is well established that gas hydrate crystals, when allowed to form and grow, can become a nuisance at best and pose a serious problem at worst. Gas hydrates can block transmission lines and plug blowout preventers, jeopardize the foundations of deep water platforms and pipelines, collapse tubing and casing, and foul process heat exchangers and expanders. To overcome these problems, several thermodynamic measures are possible in principal: removal of free water, maintaining an elevated temperature and/or reduced pressure, or the addition of freezing point depressants (antifreeze). As a practical matter, the last mentioned measure, i.e., adding freezing point depressants, has been most frequently applied. Thus, lower alcohols and glycols, e.g., methanol, have been added to act as antifreezes. However, in order for such substances to be effective, it is necessary that they be added in substantial amounts, e.g., 30% by weight of the water present. Not only is this expensive, it poses an additional problem since the addition of such larger amounts of antifreeze requires that they be recovered prior to further processing of the fluid mixture, e.g., the gas-water mixture.
It has been known for some time that in lieu of antifreezes, one can employ a crystal growth inhibitor that inhibits the formation of the gas-hydrate crystals and/or the agglomeration of the gas hydrate crystallites to large crystalline masses sufficient to cause plugging. Thus, surface active agents such as phosphonates, phosphate esters, phosphonic acids, salts and esters of phosphonic acids, inorganic polyphosphates, salts and esters of inorganic polyphosphates, polyacrylamids, and polyacrylates have been used.
It is also known that poly-N-vinyl-2-pyrrolidone (PVP), which is a well-known water-soluble polymer, is effective, in relatively low concentrations, in interfering with the growth of gas-hydrate crystals. WO94/12761, published Jun. 9, 1994, discloses other additives for inhibiting crystal growth and controlling the formation of gas hydrates in fluid mixtures such as are encountered in the hydrocarbon industry in the production, transportation, and processing of petroleum and natural gas fluids.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved method for controlling the formation and/or growth of gas hydrate crystals in fluid mixtures.
Another object of the present invention is to provide a method for inhibiting the formation and/or growth of gas hydrate crystals in a fluid mixture containing hydrocarbons and susceptible to gas hydrate formation.
Still another object of the present invention is to provide a method for controlling gas hydrate and/or growth formation in hydrocarbon streams such as natural gas streams and other low boiling hydrocarbon fluids.
Still a further object of the present invention is to provide a method for inhibiting gas hydrate and/or growth formation that utilizes relatively small amounts of crystal growth inhibitor, thereby obviating the necessity for recovering such inhibitor.
The above and other objects of the present invention will become apparent from the description given herein and the appended claims.
The present invention provides a method for controlling gas hydrate formation in a fluid mixture containing water and susceptible to the formation of such gas hydrates. In the method according to the present invention, there is added to the fluid mixture an effective amount of a gas hydrate growth inhibitor or additive that can be generally described as a polyoxyalkylenediamine. In particular, the alkoxylated diamines that are useful in the method of the present invention of the general formula:
wherein:
R
1
is independently H,—[—C
n
H
2n
O—]
a
—H, or an alkyl group having from 1 to 24 carbon atoms,
R
2
is independently H or —[—C
n
H
2n
O—]
b
—H,
R
3
is independently—[—CH
2
—]
c
—, or —C
d
H
2d
—[—OC
n
H
2n
—]
e
—,
R
4
is independently H or —[—C
n
H
2n
O—]
l
—H,
R
5
is independently H or —[—C
n
H
2n
O—]
g
—H, and wherein:
a is 1-8,
b+f+g=3-30,
c is 1-6,
d is 1-6,
e is 1-8, and
n is 2 or 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the word “controlling,” when used in reference to gas hydrate crystals or gas hydrates, is used in the context of inhibiting the formation of gas hydrates as well as preventing growth of gas hydrates that have formed; i.e., the additive prevents hydrate masses from forming a mass or masses that become so large as to impede the flow of the fluid stream. Additionally, while it will be understood that the present invention is useful in any fluid mixture wherein gas hydrates can form, it finds particular utility in the control of gas hydrate formation that could occur during the extraction of natural gas and petroleum fluids, e.g., low boiling hydrocarbons, from a producing well, during transportation of such gas and fluids, and during processing of such gas and fluids. Thus, the invention is particularly applicable to controlling the formation of gas hydrates in fluid mixtures that comprise a gaseous phase and an aqueous phase, the gaseous phase being a low boiling hydrocarbon, as, for example, a hydrocarbon containing from about 1 to 4 carbon atoms such as methane, ethane, propane, butane, etc. The invention thus relates, in one aspect, to a method for inhibiting the formation, growth and/or agglomeration of gas hydrate crystals in a mixture containing low boiling hydrocarbons in water.
In performing the method of the present invention, there is admixed with a fluid mixture, which contains water and at least one guest substance, rendering the fluid mixture susceptible to the formation of gas hydrate crystals, an effective amount of an additive having the general formula:
wherein:
R
1
is independently H,—[—C
n
H
2n
O—]
a
—H, or an alkyl group having from 1 to 24 carbon atoms,
R
2
is independently H or —[—C
n
H
2n
O—]
b
—H,
R
3
is independently—[—CH
2
—]
e
—, or —C
d
H
2d
—[—OC
n
H
2n
—]
e
—,
R
4
is independently H or —[—C
n
H
2n
O—]
l
—H,
R
5
is independently H or —[—C
n
H
2n
O—]
g
—H,
and wherein:
a is 1-8
b+f+g=3-30,
c is 1-6,
d is 1-6,
e is 1-8, and
n is 2 or 3.
Preferred are compounds, falling within the above general formula, that have the following formulae:
wherein x=1-4 and R is an alkyl group having from 1 to 20 carbon atoms.
H
2
N—C
d
H
2d
—[—OC
n
H
2n
—]
e
—NH
2
[III]
In a particular preferred embodiment of the present invention, employed are the compounds having the following general formulae:
wherein R has from 16 to 18 carbon atoms.
In the case of compounds having the formula shown in Formula II, it is preferred that the sum of b+f+g be from about 20 to about 30, more especially from about 25 to about 30. Compounds having the structure shown in Formula IV are commercially marketed as Ethoduomeen T/25 by Akzo and are commonly referre
BJ Service Company, U.S.A.
Browning & Bushman P.C.
Tucker Philip
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