FR2767068A1 - Inhibition of formation, growth and agglomeration of hydrates in natural gas and petroleum - Google Patents

Abstract

A process is claimed for the retardation of the growth and/or agglomeration and formation of hydrates in a fluid comprising water and a gas, in conditions favourable to their formation. A mixture of macromers and/or polymacromers is used.

Description

1 2767068

  The invention relates to a method for inhibiting or delaying the formation, growth or / and agglomeration of hydrates of natural gas, petroleum gas or other gases, by using at least one additive. 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

  Possibly H2S and / or CO2.

  These hydrates are formed when the water is in the presence of gas, either in the free state or in the dissolved state in a liquid phase, such as a liquid hydrocarbon, and when the temperature reached by the mixture in particular d water, gas and possibly liquid hydrocarbons, such as oil, becomes lower than the thermodynamic temperature of hydrate formation, this temperature being

  given for a known composition of gases and when their pressure is fixed.

  Hydrate formation can be feared, especially in the oil and gas industry, for which hydrate formation conditions can be met. Indeed, to reduce the cost of producing crude oil and gas, both from the point of view of investments and from the point of view of exploitation, one way envisaged, in particular in production at sea, is to reduce, even remove, the treatments applied to the crude oil or to the 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 near the deposit, so that the effluent, initially hot, can be treated before the thermodynamic conditions for hydrate formation are

  affected by cooling the effluent with seawater.

  However, as practically happens, when the thermo-

  dynamics required to form hydrates are combined, the agglomeration of hydrates causes the transport pipes to be blocked by creating plugs which

  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 is a question of 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 deposit of natural gas or oil and gas comprising water reaches the surface of the sea floor and is then transported to the bottom of the sea, it happens, by lowering the temperature of the effluent produced, that the thermodynamic conditions are met so that hydrates form, agglomerate and block the transfer pipes, The temperature at the bottom of the sea

  can be, for example, 3 or 4 C.

  Conditions favorable to the formation of hydrates can also be met in the same way on the ground, for pipes which are not (or not deep enough) buried in the ground, when for example the temperature of the ambient air is cold. To avoid these drawbacks, attempts have been made in the prior art to use products which, added to the fluid, could act as inhibitors by lowering the thermodynamic temperature for the formation of hydrates. These include

  alcohols, such as methanol, or glycols, such as mono-, diou 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 has also been recommended to insulate the transport lines, so as to prevent the temperature of the transported fluid from reaching the hydrate formation temperature under the operating conditions. Such a technique is also very

expensive.

  The use of additives capable of modifying the hydrate formation mechanism has also been described, since, instead of rapidly agglomerating each other and forming plugs, the hydrates formed disperse in the fluid without agglomerate and without obstructing the pipes. Mention may be made in this regard: patent application EP-A-323774 in the name of the applicant, which describes the use of nonionic amphiphilic compounds chosen from polyol esters of substituted or unsubstituted carboxylic acids , and the imide functional compounds; patent application EP-A-323 775, also in the name of the applicant, which describes in particular the use of compounds belonging to the family of diethanolamides of fatty acids or derivatives of fatty acids; US-A-4856593 which describes the use of surfactant compounds such as organic phosphonates, phosphate esters, phosphonic acids, their salts and their esters, inorganic polyphosphates and their esters, as well as homopolyacrylamides and acrylanmide copolymers -acrylates; 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 succinic derivative chosen from the group formed by polyalkenylsuccinic acids and anhydrides on at least one polyethylene glycol monoether have also been proposed to reduce the tendency to agglomerate hydrates of

  natural gas, petroleum gas or other gases (patent application EP-A582507).

  Furthermore, the use of additives capable of inhibiting or delaying the formation and / or growth of hydrates has also been recommended. Mention may be made in this regard of patent application EP-A-536950, which describes the use of tyrosine derivatives, international application WO-A9325798, which describes the use of homopolymer and copolymer compounds of N-vinyl- 2-pyrrolidone and their mixtures, international application WO-A-9412761 and patent US-A-5432292 which describe the use of poly (N-vinyl-2-pyrrolidone), hydroxyethyl cellulose and their

  mixtures or of a terpolymer based on N-vinyl-2-pyrrolidone, N-vinyl-E-

  caprolactam and dimethylaminoethyl methacrylate, marketed under the name of GAFFIX VC-713. International application WO-A-9519408 more generally describes the use of aliphatic polymers containing carbonylated N-heterocycles in complex formulations. The same applies to international application WO-A-9532356, which describes in particular the use of terpolymer with

  base of N-vinyl-2-pyrrolidone, of acrylamide methyl propane sulfonate and of acrylamide.

  Finally, international applications WO-A-9517579 and WO-A-9604462 describe the use of ammonium, sulfonium and phosphonium derivatives alkylated either alone or

  mixed with a corrosion inhibitor.

  It has now been discovered that certain essentially water-soluble compounds based on polyoxyalkylene glycol macromomers, polymerized or not, make it possible, at low concentrations, to retard the growth and / or the agglomeration of hydrates of natural gas, petroleum gas or the like. gas, with very high efficiency. Optionally, these compounds also have an inhibitory effect on

hydrate formation.

  Thus, the invention provides a method for retarding growth and / or agglomeration and optionally for delaying the formation of hydrates in a fluid comprising water and a gas, under conditions where hydrates can form (from water and gas), characterized in that at least one macromer or a polymer composed of one or more macromers of

  essentially water-soluble polyoxyalkylene glycol.

  The polyoxyalkylene glycol macromers are defined by the general formula (A) below: R1 I

CH2 C

C O (CH2- CHO) 2 - CH2- CHOH (A)

  o R2 R2 in which RI represents a hydrogen or an alkyl group comprising from I to 6 carbon atoms and preferably from I to 4 carbon atoms; R2 represents a hydrogen atom or an alkyl group; n represents the degree of polymerization

  and has a value between 1 and 140.

  The macromers defined by the general formula (A), essentially water-soluble and comprising at least one polyoxyalkylene glycol chain,

  can be used either as a mnacromer or polymerized.

  The polymers are either homopolymers, that is to say sequences of a single macromer unit, or copolymers, that is to say polymers consisting of at least two different units defined by the formula (AT). These copolymers are polymacromers composed of at least two macromers which differ by the side groups linked to the oxyalkylene groups R2, and / or by the groups R I linked to the macromolecular skeleton and / or by the number

  of n sequences of groups (CH2-CHOR2) present on the macromer.

  The macromers and polymers described in the invention have masses

  molecular weights which can vary between 160 g.mol-1 and several millions.

  In the process of the invention, the macromers, homo and copolymers as described above can be added to the fluid to be treated alone or in the form of mixtures of two or more of them. When several macromers, homopolymers or copolymers are used as a mixture, they may be macromers, homopolymers or copolymers which differ from each other for example

  by the nature of the motifs which compose them and / or by their molecular mass.

  The macromeres, homo or copolymers, as well as their mixtures in all proportions can be added to the fluid to be treated at concentrations generally ranging from 0.05 to 5% by mass, preferably from 0.1 to 2% by mass , compared to

  the water present in the fluid to be treated.

  Furthermore, the macromers, homo or copolymers recommended as additives in the invention can be mixed with one or more alcohols (monoalcohols or polyols) containing, for example, from I to 6 carbon atoms, more particularly mono-, di- or triethylene glycol, ethanol or methanol, the latter being the preferred alcohol. This alcohol (or these alcohols) is (are) added (s) in general in proportions ranging from 0.5 to 20% by mass, preferably from I to 10% by mass, relative to the water present in the fluid to be treated. The macromer (s), homopolymer (s) or copolymer (s) considered in the invention can then be dissolved beforehand in a hydroalcoholic medium and then added to the medium to be treated, so as to obtain final concentrations in macromer (s), homopolymer (s) or copolymer (s) generally ranging from 0.05 to 5% by mass, preferably from 0.1 to 2%

  in mass relative to the water present in the fluid to be treated.

  The presence in the medium of additive (s) retarding growth and / or agglomeration and possibly having an inhibiting effect on formation such as macromer (s), homo or copolymer (s) or alternatively mixtures of these recommended compounds in the invention and of alcohol (s) such as for example methanol, makes it possible, by their combined actions, to obtain delays in the growth of hydrates and a strong slowing down of the formation of plug in the pipes, on the one hand, by reducing the quantities of additives used (alcohol and polymers) and, on the other hand, by

  especially allowing to operate in a much lower temperature range.

  The essentially water-soluble macromers, homo or copolymers considered in the invention can be used either in pure water medium, for example in water of condensation, or in saline medium, for example in water of

  production, in seawater or in brine.

  The invention will be better understood on reading the following experiments, which are in no way limitative. Examples 4 to 9 are given for comparison and do not

part of the invention.

FEXEMPLE1

  The experimental procedure for the selection of additives is carried out on tetrahydrofuran hydrates (THF). A pure water / THF solution (80/20 by mass) forms hydrates under atmospheric pressure at 4 C (see: "Kinetic Inihibitors of

  Natural Gas Hydrates ", Sloan, ED. Et al .; 1994).

  The device used consists of tubes with a diameter of 16 mm, into which are introduced 8 ml of an aqueous solution at 20% by mass of THF optionally containing the additive to be tested. A glass ball with a diameter of 8 mm is introduced into each tube, in order to ensure correct mixing of the solution. The tubes are placed on a rotary agitator, which rotates at 20 rpm. The latter is placed in

a 2 C refrigerated enclosure

  The principle of this test is to determine the time At necessary to form a given quantity of hydrates. This time At corresponds to the interval measured between the moment when the formation of hydrates is observed (appearance of a disorder) and the

  moment when a hydrate plug 1 cm thick forms in the tube.

  Each series of tests is carried out in the presence of a reference mixture containing no additive, and the At supplied for an additive correspond to an average

times measured on 16 tests.

  Under the operating conditions described above, the pure water / THIF solutions

have an average At of 17.0 minutes.

  Under the operating conditions used, the addition of 0.5% by weight of polyethylene glycol monomethacrylate comprising 6 ethylene glycol sequences, referred to as M in the text below, clearly slows down the growth rate of the THF hydrate crystals . The average At goes from 17 minutes for water to 21.4 minutes in the presence of an additive. From this macromer M two homopolymers of different average molecular mass were synthesized by radical polymerization in aqueous phase. These polymers are respectively named homopolymer A and homopolymer B and respectively contain on average 45 macromer units and macromer units. The addition of 0.5% of homopolymer A in the medium prolongs the At to 30.7 minutes, while the average At obtained during the addition of

  0.5% of homopolymer B is 25.4 minutes.

  The macromere M has also been copolymerized with a macromer unit of the polypropylene glycol monoacrylate type comprising 3 side-chain propylene glycol sequences. The copolymer C obtained contains on average 25 macromer units in proportions of (75/25 respectively in macromer M and in macromer of propylene glycol). Under the test conditions implemented, the At

  average determined for copolymer C is 31.2 minutes.

EXAMPLE 2

  The experimental procedure of Example I is repeated, replacing the pure water with a mixture of pure water + 5% methanol by mass and lowering the

  refrigerated cabinet temperature at -1 C.

  Under these conditions, the average At of pure water solutions + 5% of

  methanol / THF in the absence of an additive is 23.0 minutes.

  The addition of 0.5% by mass of macromere M, prolongs the average At to

26.3 minutes.

EXAMPLE 3

  The experimental procedure of Example I is repeated, replacing the pure water with a NaCl solution 3.5% by mass, the temperature of the refrigerated enclosure is lowered to -1 C. Under these conditions, the mean At of NaCl / THF solutions in

  the absence of additive is 22.3 minutes.

  The mean At values determined respectively for the macromer M, the homopolymer A and the copolymer C are respectively 27.1 minutes,

33.1 minutes and 29.8 minutes.

  EXAMPLES 4. 5. 6. 7. 8 and 9 (comparative) Different additives outside the scope of the invention were tested for comparison under the conditions described above (examples 1, 2 and 3): Ex, 4: Polyvinylpyrrolidone (weight average molecular weight: 1.5 million; 0.5% by mass) Ex. 5; Polyacrylamide (weight average molecular weight: 1.0 million; 0.5% by mass) Ex. 6; Acrylamide / acrylic acid copolymer -40 / 60- (weight average molecular weight: 1.0 million; 0.5% by weight) Ex. 7: GAFFIX VC - 713 (N - vinyl - 2 - pyrrolidone / Nvinyl-e- caprolactam / dimethylaminoethyl methacrylate; 0.5% by mass) Ex. 8 GAFFIX VC - 713 (0.3% by mass) Ex. 9 Copolymer acrylic acid / butyl acrylate -55 / 45- (weight average molecular weight: 8 , 0 million; 0.5% by mass) Under the test conditions used, these additives have At significantly shorter than the substances mentioned in the invention, as shown by the results collected in the table below Additive Concentration Operating conditions At (mol% of the units) (% by mass) (min) Ex. 1: - without additive I pure water / THF at 2 C 17.0 - Macromer M 0.5 .... 21.4 Homopolymer A 0.5 .... 30.7 - Homopolymer B 0.5 .... 25.4 - Copolymer C 0.5 .. 31.2 Ex. 2: - without additive / water + 5% 23.0 MeOHITHF - Macromer M 0.5 -C 26 , 3 Ex. 3: - without additive / 22.3 NaCl 3.5% I THF à - Macromèrec M 0,5 -l C 27.1 - Homopolymer A 0.5 .., 33.1 - Copolymer C 0.5 .... 29.8 - without pure water additiveITHF à 2 C 17 Ex. 4: 0.5 ... 19 Ex. 5 : 0.5 ... 17.1 Ex. 6: 0.5.7.7 Ex. 7: 0.5 .... 12.9 Ex. 8: 0.3. 12.9 Ex. 9: 0.5. 13.1 - without additive I NaCl 3.5% ITHF at 22.3 -1 C Ex. 9: 0.3 .... 20.4 It

EXEMPLEM1

  To test the efficacy of the products used in the process of the invention, in the presence of methane hydrates, hydrate formation tests were carried out.

  from gas and water, using the equipment described below.

  The apparatus comprises a 10-meter loop made up of tubes with an internal 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 water and additive mixture initially introduced. . The reactor puts the loop under pressure. Tubes of diameter similar to those of the loop ensure the circulation of the fluid from the loop to the reactor, and vice versa, by means of a gear pump placed between the two. A sapphire cell integrated into the circuit allows visualization of the liquid

  circulating and hydrates when they form.

  To determine the effectiveness of the additives according to the invention, the fluid (water and additive) is introduced into the reactor. The installation is then brought under a pressure of 7 MPa. The solution is homogenized by its circulation in the loop and the reactor for one hour at 20 C. The pressure is kept constant by adding methane, and a gradual decrease in temperature (0.5 C / min) is imposed by

   C to 3 C, which corresponds to the chosen experimental temperature.

  The principle of these tests is to determine, on the one hand the temperature of formation of methane hydrates in the loop and on the other hand to evaluate the growth rate and the quantity of hydrate crystals formed. The detection of hydrate formation is detected by exotherm and an increase in the

gas consumption.

  In the absence of an additive (medium: deionized water), the methane hydrates are formed at a temperature in the region of 10.8 C. From the formation of the first crystals, two phases are observed with regard to the consumption of gas. In the first phase (approximately S minutes) the gas supply is very low, then, in the second phase it becomes extremely important (maximum opening of the flow meter) until complete blocking of the circulation of the fluid + hydrates mixture in the loop + reactor assembly. The second phase, corresponding to the growth and agglomeration of the crystals lasts 28 minutes and the total consumption is

average of 17 normal liters.

  The addition of 0.5% by mass of the macromere M, relative to the water, slightly decreases the temperature of formation of methane hydrates (10.3 C), under the pressure and temperature conditions imposed for this test and gas consumption also has two phases. The first phase is analogous to that observed in pure water, the second phase takes place over an average duration of 50 minutes, the opening of the flow meter is approximately 50% of its maximum capacity. In fine,

  total consumption is almost identical.

Claims (10)

  1 Method for retarding growth and / or agglomeration and optionally for delaying the formation of hydrates in a fluid comprising water and a gas, under conditions where hydrates can be formed from water and gas, characterized in that said fluid incorporates at least one polyoxyalkylene glycol macromer or a polymer formed on at least one macromer of   polyoxyalkylene glycol, essentially water-soluble.   2. Method according to claim 1, characterized in that at least one macromere of polyoxyalkylene glycol defined by the general formula is used: RI R1 CH2 C C O (CH2- CHO) - CH2 CHOH (A) II I O R2 R2   in which RI represents a hydrogen or an alkyl group comprising from 1 to 6 carbon atoms; R2 represents a hydrogen atom or an alkyl group   and n which represents the degree of polymerization has a value between 1 and 140.   3. Method according to claim 1, characterized in that at least one homopolymer of polyoxyalkylene glycol macromer defined by the general formula Ri E1 is used CH2 C C O (CH2- CHO) - CH2- CHOH (A)   II I o R2 R2 in which RI represents a hydrogen or an alkyl group comprising from I to 6 carbon atoms; R2 represents a hydrogen atom or an alkyl group; and n which represents the degree of polymerization has a value between I and 140. 4. Method according to claim 1, characterized in that at least one copolymer of at least two polyoxyalkylene glycol macromers defined by the general formula I is used CH2 C C -O (CH2- CHO) - CH2 CHOH (A)   IlI nI o R2 R2 in which R] represents a hydrogen or an alkyl group comprising from I to 6 carbon atoms; R2 represents a hydrogen atom or an alkyl group;   and n which represents the degree of polymerization has a value between 1 and 140.   5. Method according to one of claims 1 to 4, characterized in that said   macromer, homopolymer or copolymer has an average molecular weight of g.mol-1 to several million.   6. Method according to one of claims 1 to 5, characterized in that said   macromere, homopolymer or copolymer is added to the fluid to be treated at a   concentration of 0.05 to 5% relative to the water present in the fluid to be treated.   7. Method according to claim 6, characterized in that said concentration is   0.1 to 2% by mass relative to the water present in the fluid to be treated.   8. Method according to one of claims I to 7, characterized in that said   macromer, homopolymer or copolymer is mixed with at least one alcohol chosen from monoalcohols and polyols containing from 1 to 6 carbon atoms, in one   proportion of 0.5 to 20% by mass relative to the water present in the fluid to be treated.   9. Method according to claim 8, characterized in that said alcohol is mono-,   di- or tri-ethylene glycol, ethanol or methanol.   10. Method according to one of claims 8 and 9, characterized in that said   macromer, homopolymer or copolymer is dissolved beforehand in a hydro-   alcoholic then added to the medium to be treated, so as to obtain a final concentration of macromer, homopolymer or copolymer of 0.05 to 5% by mass relative to   the water present in the fluid to be treated.