EP0812977B1 - Process to reduce the tendency to agglomerate of hydrates in production effluents containing paraffinic oils - Google Patents

Description

The invention relates to a method for reducing the tendency to agglomerate. hydrates of natural gas, petroleum gas or other gases within a fluid comprising water, one of said gases and at least one paraffinic oil

It relates more particularly to a process in which a mixture of at least two additives, including at least one block copolymer polyisobutene - polyethylene glycol and at least one alkyl (meth) acrylate copolymer - nitrogen monomer

The gases which form hydrates can in particular comprise at least one hydrocarbon chosen from methane, ethane, ethylene, propane, propene, n-butane and iso-butane, and optionally H ₂ S and / or CO ₂ .

These hydrates are formed when water is in the presence of gas, i.e. the free state, or in the dissolved state in a liquid phase, such as a hydrocarbon liquid, and when the temperature reached by the mixture in particular of water, gas and eventually liquid hydrocarbons, such as oil, becomes lower than the thermodynamic hydrate formation temperature, this temperature being given for a known gas composition and when their pressure is fixed.

Hydrate formation can be feared, especially in industry oil and gas, for which hydrate formation conditions can be reunited. Indeed, to decrease the cost of producing crude oil and gas, both from an investment point of view and from an operational point of view, a envisaged, particularly in offshore production, is to reduce, or even eliminate, the treatments applied to crude or gas to be transported from the deposit to the coast and in particular to leave all or part of the water in the fluid to be transported. These treatments at sea are generally carried out on a platform located on the surface proximity to the deposit, so that the effluent, initially hot, can be treated before the thermodynamic hydrate formation conditions are affected by cooling the effluent with seawater.

However, as practically happens when the conditions thermodynamics required to form hydrates are met, the agglomeration hydrates leads to the blocking of transport lines by creating plugs that prevent any passage of crude oil or gas.

The formation of hydrate plugs can cause production to stop and thus cause significant financial losses. In addition, the return to service of the installation, especially if it involves production or transport at sea, can be long, because the decomposition of the hydrates formed is very difficult to achieve Indeed, when the production of an underwater natural gas or oil and gas deposit with water reaching the surface of the sea floor and then being transported to the bottom from the sea, it happens, by lowering the temperature of the effluent produced, that the thermodynamic conditions are met for hydrates to form, clump together and block the transfer lines. The temperature at the bottom of the sea can be, for example, 3 or 4 ° C.

Favorable conditions for the formation of hydrates can also be met in the same way on land, for pipes not (or not deep enough) buried in the earth, when for example the ambient air temperature is Cold.

To avoid these drawbacks, attempts have been made in the prior art to use products which, when added to the fluid, could act as inhibitors by lowering the thermodynamic temperature of hydrate formation. These include alcohols, such as methanol, or glycols, such as mono-, di- or tri- ethylene glycol. This solution is very expensive because the amount of inhibitors to be added can reach 10 to 40% of the water content and these inhibitors are difficult to recover completely.

It was also recommended to insulate the transport lines, so as to prevent the temperature of the transported fluid from reaching the formation temperature hydrates under the operating conditions. Such a technique is also very costly

In addition, various nonionic or anionic surfactant compounds have been tested for their effect of delaying the formation of hydrates within a fluid containing a gas, in particular a hydrocarbon, and water. We can cite for example the article by Kuliev et al: "Surfactants Studied as Hydrate Formation Inhibitors." Gazovoe Delo No. 10 1972, 17-19, reported in Chemical Abstracts 80, 1974, 98122r.

The use of additives capable of modifying the mechanism has also been described. hydrate formation, since, instead of rapidly agglomerating each other others and form plugs, the hydrates formed disperse in the fluid without clumping and without obstructing the pipes. We can cite in this regard: Patent application EP-A-323774 in the name of the applicant, which describes the use non-ionic amphiphilic compounds chosen from polyol and acid esters carboxylic, substituted or unsubstituted, and imide functional compounds; the patent application EP-A-323775, also in the name of the applicant, which describes in particular the use of compounds belonging to the family of diethanolamides fatty acids or fatty acid derivatives; US-A-4956593 which describes the use of surfactants such as organic phosphonates, phosphate esters, phosphonic acids, their salts and esters, inorganic polyphosphates and their esters, as well as polyacrylamides and polyacrylates; and patent application EP-A-457375, which describes the use of anionic surfactants, such as alkylarylsulfonic acids and their alkali metal salts.

Amphiphilic compounds obtained by reaction of at least one derivative succinic chosen from the group formed by polyalkenyl acids and anhydrides succinics on at least one polyethylene glycol monoether have also been proposed to reduce the tendency towards agglomeration of natural gas hydrates, petroleum gas or other gases (patent application EP-A-582507).

Likewise WO-A-9 604 348 describes the use of the products hydrate formation inhibitors, for use in drilling.

We have now found that to reduce the tendency to agglomerate hydrates in the transport of a fluid comprising water, gas and an oil paraffinic, it was possible to advantageously use a mixture of two, or more, copolymer additives, as will be defined in the description which follows.

Thus, the invention provides a method for reducing the tendency to agglomeration of hydrates in the transport of a fluid comprising at least water a gas and paraffinic oil, under conditions where hydrates can form at from water and gas, characterized in that one incorporates into said fluid a composition of additives comprising at least two organically soluble constituents, of which at least one polyisobutene-polyethylene glycol block copolymer and at least one alkyl (meth) acrylate copolymer - nitrogenous monomer.

By paraffinic oil is meant in the invention a crude oil containing paraffinic constituents capable of crystallizing when the temperature is lowered. Such oils are characterized by their starting crystallization temperature (denoted T _c ), determined by differential enthalpy analysis, the content and distribution of n-paraffins, determined by gas chromatography, and their rheological behavior as a function of temperature ( in particular the temperature T _B from which the flow is no longer Newtonian).

The paraffinic oils considered in the invention are more particularly those whose starting crystallization temperature T _c is greater than 10 ° C, the temperature T _B is greater than 5 ° C and the content of n-paraffins from 10 to 40 atoms of carbon is greater than 5% by mass

Polyisobutene - polyethylene glycol block copolymers organosoblubles used in the composition of mixtures used as additives in the process of the invention can be defined as containing sequences derived from polyisobutenyl succinic anhydrides and sequences derived from polyethylene glycols or alkyl monoethers of polyethylene glycols. Such Block polymers have been widely described in the literature. They can be prepared for example as described in patent application EP-A-582507 to name of the applicant, by reaction of polyisobutenyl succinic anhydrides and polyethylene glycols or alkyl monoethers of polyethylene glycols. The polyisobutenyl succinic anhydrides for example have molecular weights number averages of around 500 to 5000 and preferably from 800 to 2000 polyethylene glycols and the polyethylene glycol alkyl monoethers have usually a number average molecular weight of about 100 to 1000.

dans lesquelles R₁ représente un atome d'hydrogène ou un radical méthyle, R₂ représente un groupement (CH₂)_pCH₃, dans lequel p a l'une des valeurs 15, 17, 19 et 21, et R₃ représente un groupement contenant de l'azote.The allyl (meth) acrylate-nitrogenous monomer copolymers considered in the additive compositions used in the process of the invention can be defined more particularly as formed by units of formula A and units of formula B:

in which R ₁ represents a hydrogen atom or a methyl radical, R ₂ represents a group (CH ₂ ) _p CH ₃ , in which p has one of the values 15, 17, 19 and 21, and R ₃ represents a group containing nitrogen.

The type A monomer is chosen from acrylates and alkyl methacrylates of 18, 20, 22 or 24 carbon atoms. The type A monomers used in the constitution of alkyl (meth) acrylate - nitrogen monomer copolymers are the more often mixtures of monomers with different R ₂ values.

The type B monomer can be chosen from N-vinyl-pyrrolidone, the vinyl-pyridines and N-vinyl-imidazole, or among the acid derivatives acrylic or methacrylic containing nitrogen groups, such as for example dimethylaminoethyl acrylate or methacrylate.

The content of type B monomer units in the copolymers alkyl (meth) acrylate - nitrogenous monomer is generally between 2 and 50%, of preferably between 5 and 30 mol%.

These copolymers can have a number-average molecular mass from 10,000 to 100,000, preferably from 20,000 to 70,000.

These copolymers have been widely described in the literature. They can be prepared for example by radical copolymerization in solution of at least one type A monomer with at least one type B monomer

In their use as additives to reduce the tendency to agglomeration of hydrates, blends of copolymers of the types described above can be added to the fluid to be treated at concentrations generally ranging from 0.05 to 5% by mass, preferably 0.2 to 2% by mass, relative to water. The proportions of the copolymers in these mixtures are more particularly from 50 to 96 % of polyisobutene - polyethylene glycol block copolymer for 4 to 50% of alkyl (meth) acrylate copolymer - nitrogenous monomer.

The following examples illustrate the invention but should not in any way be considered limiting. Examples 1, 3 and 4 are given as comparative.

Examples

In each of the examples presented below, to test the effectiveness of the mixtures according to the invention and mixtures tested for comparison, we simulated the transport of hydrate-forming fluids, such as petroleum effluents and we have carried out tests for the formation of hydrates from gases, paraffinic oil and of water, using the apparatus described below.

The apparatus has a 10-meter loop made up of inner diameter equal to 7.7 mm; a 2 liter reactor comprising an inlet and an outlet for the gas, a suction and a discharge for the mixture: oil, water and additive originally introduced. The reactor puts the loop under pressure.

Tubes of diameter similar to those of the loop ensure the circulation of fluids from the loop to the reactor, and vice versa, via a pump gears placed between the two. A sapphire cell integrated into the circuit allows a visualization of the liquid in circulation, and therefore of the hydrates, if they have formed

To determine the effectiveness of the additive mixtures according to the invention, we introduces the fluids (water, oil, additive) into the reactor; installation is then brought under a pressure of 70 bars The homogenization of liquids is ensured by their circulation in the loop and the reactor, then only in the loop. In depending on the pressure drop and flow variations, a rapid reduction is imposed from the temperature, from 17 ° C to the hydrate formation temperature, this is then kept at this value.

The duration of the tests can vary from a few minutes to several hours: a efficient additive keeps circulation of the hydrate suspension with stable pressure drop and flow.

Example 1 (comparative)

In this example, the operation is carried out with a fluid composed by volume of 20% water and 80% paraffinic oil (Tc = 26 ° C, T _B = 10 ° C). The gas used comprises 98% methane and 2% ethane by volume. The experiment is carried out under a pressure of 7 MPa, kept constant by adding gas. Under these conditions, the formation of a plug in the coil is observed 10 minutes after the start of the formation of hydrates.

Example 2 (according to the invention)

In this example, the procedure is as in Comparative Example 1, with the same fluid, the same gas and at the same pressure, but to the circulating fluid is added 1.2% by mass relative to the water of a blend of copolymers consisting of 1% polyethylene glycol polyisobutenyl succinate having an average molecular weight close to 1500 and a polyisobutene / polyethylene glycol mass ratio close to 2.5, and 0.2% of alkyl acrylate-N-vinyl copolymer -pyrrolidone in which the distribution of the alkyl groups is as follows. C ₁₆ 5% weight C ₁₈ 40% weight C ₂₀ 11% weight C ₂₂ 44% weight the N-vinyl-pyrrolidone content of the copolymer being 12% by weight and its number average molecular mass being close to 55,000

Under these conditions, an increase in the pressure drop is observed during the formation of hydrates at 4 ° C, followed by its reduction and stabilization for more than 24 hours.

Examples 3 (comparative)

All other things being equal, we repeat Example 2 using 1.2% in mass relative to water of the polyethylene glycol polyisobutenyl succinate used in Example 2, in the absence of an alkyl acrylate-N-vinyl-pyrrolidone copolymer Under these conditions, the formation of a plug in the coil 20 is observed. minutes after the start of hydrate formation

Example 4 (comparative)

All other things being equal, we repeat Example 2 using 1.2% in mass relative to water of the alkyl acrylate-N-vinyl-pyrrolidone copolymer used in Example 2, in the absence of polyethylene glycol polyisobutenyl succinate Under these conditions, the formation of a plug in the coil.

Example 5 (according to the invention)

If in Example 2, all other things being equal, the copolymer alkyl acrylate - N-vinyl-pyrrolidone is replaced by an acrylate copolymer alkyl - 4-vinyl-pyridine of average composition and molecular weight equivalent, it is observed under these conditions, as in Example 2, that the fluid circulation is maintained for 24 hours with a pressure drop and a stable flow.

Example 6 (according to the invention)

If in Example 2, all other things being equal, the copolymer alkyl acrylate - N-vinyl-pyrrolidone is replaced by an acrylate copolymer alkyl - N-vinyl-imidazole of composition and average molecular weight equivalent, it is observed under these conditions, as in Example 2, that the fluid circulation is maintained for 24 hours with a pressure drop and a stable flow.

Claims (11)

1. A process for inhibiting or retarding the formation, growth and/or agglomeration of hydrates in the transport of a fluid comprising at least water, a gas and a paraffin oil, under conditions in which hydrates can form from the water and the gas, characterized in that an organosoluble additive composition comprising at least two constituents is incorporated into said fluid, namely at least one polyisobutene - polyethyleneglycol block copolymer and at least one copolymer of an alkyl (meth)acrylate and a nitrogen-containing monomer, in which said alkyl (meth)acrylate is selected from alkyl acrylates and methacrylates containing 18, 20, 22 or 24 carbon atoms.
2. A process according to claim 1, characterized in that said polyisobutene - polyethyleneglycol block copolymer comprises blocks derived from polyisobutenyl succinic anhydrides and blocks derived from polyethyleneglycols or alkyl monoethers of polyethyleneglycols.
3. A process according to claim 1 or claim 2, characterized in that said polyisobutene - polyethyleneglycol block copolymer is derived from at least one polyisobutenyl succinic anhydride with a number average molecular mass of about 500 to 5000 and at least one polyethyleneglycol or at least one polyethyleneglycol alkyl monoether with a number average molecular mass of about 100 to 1000.
4. A process according to any one of claims 1 to 3, characterized in that said copolymer of an alkyl (meth)acrylate and a nitrogen-containing monomer is formed of units of formula A and units of formula B:

   

   where R₁ is a hydrogen atom or a methyl radical, R₂ is an alkyl radical containing at least 10 carbon atoms and R₃ is a group containing nitrogen.
5. A process according to claim 4, characterized in that monomer B is selected from N-vinylpyrrolidone, vinylpyridines, N-vinylimidazole and acrylic or methacrylic acid derivatives containing nitrogen-containing groups.
6. A process according to claim 5, characterized in that monomer A consists of a mixture of monomers with different values of R₂.
7. A process according to any one of claims 1 to 6, characterized in that said copolymer of alkyl (meth)acrylate - nirtrogen-containing monomer has a number average molecular mass of 10000 to 100000.
8. A process according to any one of claims 1 to 7, characterized in that said paraffin oil has a crystallisation onset temperature T_c of more than 10°C, a temperature from which flow is no longer newtonian T_B of more than 5°C and the amount of n-paraffins containing 10 to 40 carbon atoms is more than 5% by weight.
9. A process according to any one of claims 1 to 8, characterized in that in the copolymer mixture, the proportions of copolymers are 50% to 96% of polyisobutene - polyethyleneglycol block copolymer for 4% to 50% of the copolymer of an alkyl (meth)acrylate and a nitrogen-containing monomer.
10. A process according to any one of claims 1 to 9, characterized in that the mixture of copolymers is added to the fluid in a concentration of 0.05% to 5% by weight with respect to the amount of water.
11. A process according to claim 10, characterized in that said concentration is 0.2% to 2% by weight with respect to the amount of water.