[0001] The invention relates to a method for preventing or retarding the formation of hydrates
or for reducing the tendency of hydrates to agglomerate during the transport of a
fluid through a conduit.
[0002] It is well known in the art that the formation of hydrates in a conduit, e.g. a pipeline,
during the transport of oil and gas can be a serious problem, especially in areas
with a low temperature in the winter season or in the sea. Generally the temperatures
are so low that hydrate formation, due to the inevitable presence of coproduced water
in the wells, takes place if no special steps are taken. It is possible to insulate
a pipeline when during transport from the well, the temperature of the fluid in the
pipeline decreases. Insulation decreases the chance of hydrate formation, but on the
other hand it is expensive. If the field is relatively small and at long distance
from the production platform the costs of insulation may be too high to make the field
economically attractive.
[0003] It is also known to control the hydrate formation by addition of chemical compounds
in the fluid which is transported, e.g. by the use of glycols, e.g. ethylene glycol
or diethylene glycol. A disadvantage thereof is that large amounts of glycol are needed
(in the order of 30% by weight calculated on the amount of water).
[0004] In the U.S.S.R. Inventor's Certificate 697696 is disclosed a composition suitable
for the prevention of hydrate formation, which composition comprises diethylene glycol
with a minor amount of alkyl aryl sulphonate (in a quantity of 0.3-0.5% based on the
weight of the diethylene glycol).
[0005] Surprisingly it has been found that alkyl aryl sulphonic acids or alkali metal- or
ammonium salts thereof can be used without glycols, to control hydrate formation.
[0006] The invention relates to a method for preventing or retarding the formation of hydrates
or for reducing the tendency of hydrates to agglomerate in a stream of fluid comprising
water and hydrocarbon during transport of the fluid through a conduit, which method
comprises adding to the fluid an alkyl aryl sulphonic acid or an alkali metal- or
ammonium salt thereof substantially in the absence of glycol flowing in the stream.
[0007] The hydrocarbon may be a liquid or a gas, but is preferably a gas such as methane,
ethane, propane, isopropane, butane or isobutane. The fluid may be produced from oil
wells as well as from gas wells. The fluid may also include natural gas.
[0008] Depending upon the pressure hydrates may be formed at temperatures well above the
freezing point of water. Ethane hydrates, for example, are formed at pressures between
10 and 30 bar (1 and 3 MPa) and temperatures between 4 °C and 14 °C. Formation and
agglomeration of hydrate crystals will thus easily occur in pipelines surrounded by
a cold atmosphere.
[0009] The problem of formation and agglomeration of gas hydrates is not limited to gas
wells, but also occurs in oil wells, if water and gas are present in the fluid.
[0010] The alkyl aryl sulphonic acids or their salts preferably have an aryl group derived
from benzene, toluene, ortho-, meta- or para-xylene. The alkyl group is preferably
a long chain alkyl group, which may be branched or straight. The alkyl group may be
e.g. a C₈-C₂₂-alkyl group.
[0011] Preferred compounds are those of the chemical formula
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0001)
wherein X is H, Na or K and R is a C₈-C₂₂ alkyl group.
[0012] More preferred compounds are those wherein R is a C₁₃ and/or C₁₄ alkyl or a C₁₈-alkyl
group, such as those known under the trade name DOBANAX-320, DOBANAX-313 and DOBANAX-205.
[0013] Other groups of preferred compounds are dialkyl benzene sulphonates of the chemical
structure
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0002)
wherein X is an alkali metal and R₁ and R₂ are the same or different C₂-C₂₀-alkyl
groups, preferably C₆-C₁₄-alkyl groups.
[0014] The alkyl aryl sulphonates are added in quantities from 0.1 per cent to 3 per cent
by weight, calculated on the weight of the water present in the fluid. A preferred
range is from 0.2 to 1 percent, more preferred in the range of from 0.3 to 0.6 per
cent.
[0015] To study the influence of a small quantity of alkyl aryl sulphonates on the nucleation
temperature, kinetics of the crystal growth and morphology of the crystals, a high
pressure, jacketed visual cell was built. The cell was made of stainless steel and
had a cooling jacket to allow a good and easy temperature control of the cell. Two
sapphire windows allowed visual observation of the cell content. The cell was provided
with two valves one for the introduction of liquid and one for gas. At the bottom
of the cell a stirring bar cared for good mixing of the cell content. The inner volume
of the cell was 66.4 ml and dead volumes were reduced to a minimum. The cell was further
tested together with its loading system at a pressure of 100 bar over a period of
80 hours without any pressure drop being observed. The cell usually worked at a pressure
of below 30 bar. The cell was located in a plexiglass cage.
[0016] A personal computer based data acquisition system allowed the measurement of the
temperature and pressure inside the cell once per minute. The set point of a thermostated
bath, connected to the cooling jacket, could be set automatically by the computer.
A steel well went deeply inside the cell in which a platinum resistance thermometer
was introduced. On the cell was mounted a pressure transducer, with a very small temperature
hysteresis and a high accuracy.
[0017] Before a run was made, the cell was rinsed with demineralized water, rinsed with
ethanol and vacuum dried, all without dismounting the cell.
[0018] To carry out the experiment demineralized water and decane were introduced as liquid
into the cell. The water contained 0.5% per cent by weight of alkyl aryl sulphonic
acid or salt thereof, if desired. Ethane was introduced as a gas into the cell. The
run started at 20 °C and the temperature in the cell was dropped, via the jacket connected
to the thermostatic bath by lowering its temperature. The amounts of water, decane
and ethane were 25, 5.8 and 4.7 grams respectively. The pressure was 25 bar at 20
°C, and no ethane hydrates were formed.
[0019] The thermometer sent a digital signal, the pressure meter an analog signal, to the
computer. The computer could also send a set point command to the thermostatic bath.
During each experiment the temperature and the pressure of the cell were recorded,
together with the time, at every minute. Of a given composition, comprising water,
decane and ethane and if desired the alkyl aryl sulphonic acid or salt thereof, a
temperature-time and a pressure-time curve could be made.
[0020] By lowering the temperature, which was accompanied by a pressure drop, to below the
equilibrium temperature point at which hydrates and liquid were in equilibrium, ethane
hydrates were formed. The rather sudden formation of hydrates was read from the temperature-
and pressure-time curve. A relatively steep rise in temperature (about 0.5 °C) and
a pressure drop (about 1 to 5 bar) occurred.
[0021] At the same time the formation of hydrates was seen through a sapphire window. The
formation of hydrate crystals consumes the free ethane molecules. The progressive
drop of the cell pressure that occurs after nucleation has started is a good indication
of the quantity of hydrate formed as a function of time.
[0022] It was further observed that in the hydrate formation the crystals agglomerated in
case that alkyl aryl sulphonate was not added.
[0023] In the method according to the invention, however, the addition of an alkyl aryl
sulphonate prevented the formation of agglomerates of hydrates.
EXAMPLE 1
[0024] 25 g of water, 5.8 g of decane, 4.7 g of ethane and 0.5% by weight, based on the
water, of di-linear C₈-C₁₀-alkyl benzene sulphonate (sodium salt), were used as described
above in the cell. The experiment started at 20 °C and after lowering the temperature
to 8.4 °C crystallization occurred, while at the same time the pressure in the cell
decreased from 22 bar to 13 bar. No agglomeration of the hydrate was observed.
EXAMPLE 2
[0025] 25 g of water, 5.8 g of decane, 4.7 g of ethane and 0.5% by weight, based on the
water, of sulphonated "SOMIL SH" (SOMIL is a Trade Mark) were used as described above
in the cell. The experiment started at 20 °C and after lowering the temperature to
8.4 °C crystallization occurred, while at the same time the pressure in the cell decreased
from 22 bar to 16 bar. No agglomeration of the hydrate was observed.
EXAMPLE 3
[0026] 25 g of water, 5.8 g of decane, 4.7 g of ethane and 0.5% by weight, based on the
water, of C₁₈-alkyl benzene sulphonic acid were used as described above in the cell.
The experiment started at 20 °C and after lowering the temperature to 8.4 °C crystallization
occurred while at the same time the pressure in the cell dropped from 22 bar to 16
bar. No agglomeration of the hydrate was observed.
Comparative Example A
[0027] 25 g of water, 5.8 g of decane and 4.7 g of ethane were used as described above in
the cell. Also in this case the experiment started at 20 °C and after lowering the
temperature to 9.4 °C crystallization occurred and was followed by agglomeration of
the crystals.
1. A method for preventing or retarding the formation of hydrates or for reducing the
tendency of hydrates to agglomerate in a stream of fluid comprising water and hydrocarbon
during transport of the fluid through a conduit, which method comprises adding to
the fluid an alkyl aryl sulphonic acid or an alkali metal- or ammonium salt thereof
in the absence of glycol flowing in the stream.
2. A method as claimed in claim 1 wherein the fluid comprises one or more hydrocarbons
consisting of the group: methane, ethane, propane, isopropane, butane and isobutane.
3. A method as claimed in claim 1 or 2 wherein the fluid comprises natural gas.
4. A method as claimed in one or more of the claims 1-3 wherein is added to the fluid
a C₈-C₂₂-alkyl aryl sulphonic acid or an alkali metal- or ammonium salt thereof.
5. A method as claimed in claim 4 wherein a compound of the chemical structure
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0003)
wherein X is H, Na or K and R is a C₈-C₂₂ alkyl group, is used.
6. A method as claimed in claim 1 wherein a compound of the chemical structure
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0004)
wherein X is an alkali metal and R₁ and R₂ are the same or different C₂-C₂₀-alkyl
groups, preferably C₆-C₁₄-alkyl groups, is used.
7. A method as claimed in one or more of the claims 1-6 wherein the quantity of alkyl
aryl sulphonate ranges from 0.1 per cent to 3 per cent by weight, calculated on the
weight of the water present in the fluid.
8. A method as claimed in claim 7 wherein the quantity of alkyl aryl sulphonate lies
in the range of from 0.2 to 1 per cent.
9. A method as claimed in one or more of the claims 1-8 characterized by the absence
of a glycol.
1. Ein Verfahren zur Verhinderung oder Verzögerung der Bildung von Hydraten oder zur
Herabsetzung der Neigung der Hydrate, in einem Strom einer Flüssigkeit, bestehend
aus Wasser und einem Kohlenwasserstoff, während des Transports der Flüssigkeit durch
eine Leitung zu agglomerieren, wobei das Verfahren das Zugeben einer Alkylarylsulfonsäure
oder deren Alkalimetall- oder Ammoniumsalz zu der Flüssigkeit in Abwesenheit von in
dem Strom fließenden Glykols umfaßt.
2. Ein Verfahren wie in Anspruch 1 beansprucht, wobei die Flüssigkeit einen oder mehrere
Kohlenwasserstoffe umfaßt, bestehend aus der Gruppe Methan, Ethan, Propan, Isopropan,
Butan und Isobutan.
3. Ein Verfahren wie in Anspruch 1 oder 2 beansprucht, wobei die Flüssigkeit natürliches
Gas umfaßt.
4. Ein Verfahren wie in einem oder mehreren der Ansprüche 1 bis 3 beansprucht, wobei
zu der Flüssigkeit eine C₈-C₂₂-Alkylarylsulfonsäure oder deren Alkalimetall-oder Ammoniumsalz
zugegeben wird.
5. Ein Verfahren wie in Anspruch 4 beansprucht, wobei eine Verbindung der chemischen
Struktur
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0005)
in der X Wasserstoff, Natrium oder Kalium ist und R eine C₈-C₂₂-Alkylgruppe ist,
verwendet wird.
6. Ein Verfahren wie in Anspruch 1 beansprucht, wobei eine Verbindung der chemischen
Struktur
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0006)
in der X ein Alkalimetall ist und R₁ und R₂ gleiche oder verschiedene C₂-C₂₀-Alkylgruppen,
vorzugsweise C₆-C₁₄-Alkylgruppen, sind, verwendet wird.
7. Ein Verfahren wie in einem oder mehreren der Ansprüche 1 bis 6 beansprucht, wobei
die Menge des Alkylarylsulfonats im Bereich von 0,1 bis 3 Gew% liegt, berechnet auf
das Gewicht des in der Flüssigkeit vorhandenen Wassers.
8. Ein Verfahren wie in Anspruch 7 beansprucht, wobei die Menge des Alkylarylsulfonats
im Bereich von 0,2 bis 1 % liegt.
9. Ein Verfahren wie in einem oder mehreren der Ansprüche 1 bis 8 beansprucht, gekennzeichnet
durch die Abwesenheit eines Glykols.
1. Une méthode pour empêcher ou retarder la formation d'hydrates ou pour réduire la tendance
d'hydrates à s'agglomérer dans un courant d'un fluide comprenant de l'eau et des hydrocarbures
durant le transport du fluide par une canalisation, cette méthode comprenant l'addition
au fluide d'un acide alcoyl aryl sulfonique ou d'un sel de métal alcalin ou d'ammonium
d'un tel acide en l'absence de glycol dans le courant.
2. Une méthode selon la revendication 1, dans laquelle le fluide comprend un ou plusieurs
hydrocarbures choisis dans le groupe constitué par le méthane, l'éthane, le propane,
l'isopropane, le butane et l'isobutane.
3. Une méthode selon la revendication 1 ou 2, dans laquelle le fluide comprend du gaz
naturel.
4. Une méthode selon une ou plusieurs des revendications 1-3, dans laquelle on ajoute
au fluide un acide C₈-C₂₂-alcoyl aryl sulfonique ou un sel de métal alcalin ou d'ammonium
d'un tel acide.
5. Une méthode selon la revendication 4, dans laquelle on utilise un composé de la structure
chimique
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0007)
où X est H, Na ou K et R est un groupe alcoyle en C₈-C₂₂.
6. Une méthode selon la revendication 1, dans laquelle on utilise un composé de la structure
chimique
![](https://data.epo.org/publication-server/image?imagePath=1993/30/DOC/EPNWB1/EP91200272NWB1/imgb0008)
où X est un métal alcalin et R₁ et R₂ sont des groupes alcoyle en C₂₋₂₀ identiques
ou différents, de préférence des groupes alcoyle en C₆-C₁₄.
7. Une méthode selon une ou plusieurs des revendications 1-6, dans laquelle la quantité
d'alcoyl aryl sulfonate est comprise entre 0,1 pour cent et 3 pour cent en poids,
par rapport au poids de l'eau présente dans le fluide.
8. Une méthode selon la revendication 7, dans laquelle la quantité d'alcoyl aryl sulfonate
est comprise entre 0,2 et 1 pour cent.
9. Une méthode selon une ou plusieurs des revendications 1-8, caractérisée par l'absence
d'un glycol.