Earth boring – well treating – and oil field chemistry – Preventing contaminant deposits in petroleum oil conduits
Reexamination Certificate
2000-05-02
2003-05-20
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
06566309
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an additive and a process for inhibiting nucleation, growth and/or agglomeration of gas hydrates by adding an effective amount of an inhibitor which contains the amides of polyglycol ether carboxylic acids to a multiphase mixture tending to hydrate formation and comprising water, gas and possibly condensate or to drilling fluid tending to gas hydrate formation.
Gas hydrates are crystalline clathrate compounds of gas molecules in water, which form under specific temperature and pressure conditions (low temperature and high pressure). The water molecules form cage structures around the corresponding gas molecules. The framework formed from the water molecules is by itself thermodynamically unstable and is stabilized only by the inclusion of gas molecules, resulting in an ice-like compound which, depending on pressure and gas composition, can also exist in the freezing point of water (up to more than 25° C.). A view of this subject of gas hydrates is given in Sloan, Clathrate Hydrates of Natural Gases, M. Dekker, New York, 1990.
In the petroleum and natural gas industry, in particular the gas hydrates which form from water and the natural gas components methane, ethane, propane, isobutane, n-butane, nitrogen, carbon dioxide and hydrogen sulfide are of considerable importance. Particularly in present day natural gas production, the existence of these gas hydrates presents a major problem especially when wet gas or multiphase mixtures comprising water, gas and alkane mixtures under high pressure are exposed to low temperatures. Here, owing to their insolubility and crystalline structure, the formation of gas hydrates leads to blockage of a very wide range of transport means, such as pipelines, valves or production systems in which wet gas or multiphase mixtures are transported over long distances at low temperatures, as occurs in particular in colder regions of the world or on the seabed.
In addition, gas hydrate formation can lead to problems also in the drilling process for developing new gas or petroleum deposits under corresponding and temperature conditions by virtue of the fact that gas hydrates form in the drilling fluids.
To avoid such problems, the gas hydrate formation in gas pipelines, during transport of multiphase mixtures or in drilling fluids can be suppressed by using relatively large amounts (two-digit percentage amounts, based on the aqueous phase) of lower alcohols, such as methanol, glycol or diethylene glycol. The addition of these additives of these additives shifts the thermodynamic limit of gas hydrate formation to lower temperatures and higher pressures (thermodynamic inhibition). However, the addition of these thermodynamic inhibitors gives rise to greater safety problems (flash point and toxicity of the alcohols), logistic problems (greater storage tanks, recycling of these solvents) and accordingly high costs, especially in offshore production.
Today, attempts are therefore being made to replace thermodynamic inhibitors by adding, in the temperature and pressure ranges in which gas hydrates can form, additives (amount used <2%) which either delay the gas hydrate formation (kinetic inhibitors) or keep the gas hydrate agglomerates small and therefore pumpable so that they can be transported through the pipeline (so-called agglomerate inhibitors or anti-agglomerates). The inhibitors used either prevent the nucleation and/or the growth of the gas hydrate particles or modify the hydrate growth in such a way that smaller hydrate particles result.
In addition to the known thermodynamic inhibitors, a large number of monomeric as well as polymeric classes of substances which are kinetic inhibitors or agglomerate inhibitors have been described as gas hydrate inhibitors in the patent literature.
(2) Description of the Related Art
WO-A-96/08636 describes surface-active substances as gas hydrate inhibitors, which carry a polar head group and a hydrophobic radical, the hydrophobic radical containing not more than 12 carbon atoms. Sodium valerate, butanol, butyl sulfate and butyl sulfonate, alkylpyrrolidones and a zwitterion of the formula R
2
N(CH
3
)
2
—(CH
2
)
4
SO
3
−
are mentioned as examples. WO-A-96/08456 describes synergistic mixtures of the abovementioned substances with water-soluble copolymers. FR-A-2 407 258 describes amides of carboxymethylated oligomeric polyethylene glycol monoalkyl ethers of the structure RO(CH
2
CH
2
O)
n
CH
2
CONR
1
R
2
, R being an aliphatic radical having 8-20 carbon atoms or a phenyl radical substituted by a C
8
-C
12
-alkyl radical and R
1
and R
2
are hydrogen or alkyl radicals having at least 3 carbon atoms, and their use as corrosions inhibitors, detergent additives or anti-pollution additives for fuels.
U.S. Pat. No. 5,817,898 describes polymers of the formula Hb-A-X-A-Hb as inhibitors of gas hydrate formation, X being a polyoxyalkylene chain, A being a urethane group and Hb being an alkyl, alkylaryl or cycloalkyl group.
SUMMARY OF THE INVENTION
To be able to use gas hydrate inhibitors also with greater supercooling than currently possible, i.e. further within the hydrate region, further increase the effectiveness of the available inhibitors as required. In addition, products improved with respect to their biodegradability and toxicity are required. It was therefore the object of the present invention to provide additives which are further improved and which slow down the formation of gas hydrates (kinetic inhibitors) or keep the gas hydrate agglomerates small and pumpable (anti-agglomerates) in order to be able to replace the thermodynamic inhibitors (methanol and glycols) which are still used at present and give rise to considerable safety problems and logistic problems.
As has now surprisingly been found, modified polymers of glycol ether amides are effective as gas hydrate inhibitors. Depending on the structure, the products suppress the nucleation or the growth or the agglomeration of gas hydrates and reinforce the effect of conventional gas hydrate inhibitors already described.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention therefore relates to the use of compounds of the formula (1)
in which
R
1
is C
1
-C
30
-alkyl, C
2
-C
30
-alkenyl or a group of the formula —CH
2
—CO—NR
2
R
3
or a C
6
-C
18
-aryl radical which may be substituted by a C
1
-C
12
-alkyl group,
R
2
, R
3
independently of one another, are hydrogen, C
1
-C
6
-alkyl or C
5
-C
7
-cycloalkyl, or R
2
and R
3
, including the nitrogen atom to which they are bonded, form a ring of 4 to 8 ring atoms, it being possible for the ring also to contain oxygen or nitrogen atoms in addition to carbon atoms,
A is a C
2
-C
4
-alkylene radical and
n is an integer from 1 to 20,
as gas hydrate inhibitors.
Depending on the type of application, R
1
is preferably C
1
-C
8
-alkyl or C
8
-C
30
-alkyl. R
2
and R
3
are preferably hydrogen or C
1
-C
4
-alkyl. A is preferably an ethylene radical and n is an integer from 2 to 10.
The compounds of the formula (1) are obtainable from polyglycol monoalkyl ethers or polyalkylene glycols by first converting the polyglycol into the corresponding alkylated carboxylic acid. This can be effected by oxidation of the terminal CH
2
OH group to give the carboxyl function or reaction of the glycol ether with chloroacetic acid or acrylic acid derivatives by methods known from the literature.
Examples of glycol ethers suitable as starting materials are polyethylene glycols having molecular weights of 100-1000 g/mol, ethylene oxide/propylene oxide copolymer (block or random copolymers), methylpolyglycols, butylpolyglycols and isobutylpolyglycols as well as glycol ethers based on octanol, 2-ethylhexanol, decanol, isodecanol, dodecanol, tetradecanol, hexadecanol, octadecanol, oleyl alcohol or synthetic or natural fatty alcohol cuts. Glycol ethers based on alkylphenols having a C
1
-C
12
-alkyl group are also suitable.
The ether carboxylic acids obtained are then reacted with the corresponding mono- or dialkylamines with elimination of water
Feustel Michael
Klug Peter
Clariant GmbH
Silverman Richard P.
Tucker Philip
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