Method for inhibiting gas hydrate blockage in oil and gas pipelines

Abstract

This invention relates to a method for inhibiting the agglomeration of gas hydrates, comprising the injection of an anti-agglomerant comprising a N,N-dialkyl-ammoniumalkyl fatty acid amide represented by the formula (I) ##STR00001##
wherein R.sup.1 is an alkyl or alkenyl group having from 7 to 21 carbon atoms, R.sup.2 and R.sup.3 are each independently an alkyl group containing 1 to 10 carbon atoms, or together form an optionally substituted ring having 5 to 10 ring atoms, wherein the ring may carry up to 3 substituents, R.sup.4 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R.sup.5 is hydrogen or an optionally substituted hydrocarbyl group having 1 to 22 carbon atoms and A is an alkylene group having two or three carbon atoms,
into a fluid comprising gas, water and oil under conditions prone to the formation of gas hydrates,
wherein the N,N-dialkyl-ammoniumalkyl fatty acid amide represented by formula (I) is produced by the aminolysis of an ester of a fatty acid and a C.sub.1- to C.sub.4-alcohol with an N,N-dialkylamino alkyl amine and subsequent neutralization with a carboxylic acid.

Claims

1. A method for inhibiting the agglomeration of gas hydrates, comprising the step of injecting at least one anti-agglomerant comprising at least one N,N-dialkyl-ammoniumalkyl fatty acid amide represented by the formula (I) ##STR00008## wherein R.sup.1 is an alkyl or alkenyl group having from 7 to 21 carbon atoms, R.sup.2 and R.sup.3 are each independently an alkyl group containing 1 to 10 carbon atoms, or together form an optionally substituted ring having 5 to 10 ring atoms, wherein the ring may carry up to 3 substituents, R.sup.4 is hydrogen or an alkyl group having 1 to 6 carbon atoms, R.sup.5 is hydrogen or an optionally substituted hydrocarbyl group having 1 to 22 carbon atoms and A is an alkylene group having two or three carbon atoms, into a fluid comprising gas, water and oil under conditions prone to the formation of gas hydrates, wherein the at least one N,N-dialkyl-ammoniumalkyl fatty acid amide represented by formula (I) is produced by the aminolysis of a fatty acid ester of at least one fatty acid and at least one monohydric C.sub.1 to C.sub.4-alcohol with at least one N,N-dialkylamino alkyl amine and subsequent neutralization with at least one carboxylic acid, wherein the fatty acid ester of the at least one fatty acid with the at least one monohydric C.sub.1-C.sub.4-alcohol has the formula (III)
R.sup.1—COOR.sup.6  (III) wherein R.sup.1 is defined above, and R.sup.6 is an alkyl group having 1 to 4 carbon atoms, and wherein the at least one N,N-dialkylamino alkyl amine has the general formula (V) ##STR00009## wherein R.sup.2, R.sup.3, R.sup.4 and A are each independently defined above.

2. The method according to claim 1, wherein R.sup.1 is an alkyl or alkenyl group having 12 or 14 carbon atoms.

3. The method according to claim 1, wherein at least 60 mol-% of the at least one fatty acid has 12 to 14 carbon atoms.

4. The method according to claim 2, wherein the molar ratio of the fatty acid having 12 carbon atoms and the fatty acid having 14 carbon atoms is between 1:9 and 9:1.

5. The method according to claim 1, wherein R.sup.1 is a linear alkyl or alkenyl group having from 7 to 21 carbon atoms.

6. The method according to claim 1, wherein the at least one monohydric C.sub.1-C.sub.4-alcohol is selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert.-butanol and mixtures thereof.

7. The method according to claim 1, wherein the at least one fatty acid and the at least one N,N-dialkylaminoalkylamine are reacted in a molar ratio of between 3:1 and 1:3.

8. The method according to claim 1, wherein the at least one carboxylic acid is selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, pivalic acid, hexanoic acid, octanoic acid, 2-ethyl hexanoic acid, decanoic acid neodecanoic acid, undecanoic acid, neoundecanoic acid, dodecanoic acid, neododecanoic acid, tridecanoic acid, iso-tridecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, acrylic acid, methacrylic acid and mixtures thereof.

9. The method according to claim 1, wherein the at least one fatty acid and the at least one carboxylic acid are different.

10. The method according to claim 9, wherein the at least one fatty acid and the at least one carboxylic acid differ in at least one parameter, wherein the parameter is selected from the group consisting of alkyl chain length, acid value, degree of branching, and degree of unsaturation.

11. The method according to claim 1, wherein the at least one anti-agglomerant is essentially free of glycerol.

12. The method according to claim 1, wherein the at least one anti-agglomerant is injected into the fluid prone to the formation of gas hydrates prior to formation of hydrates.

13. The method according to claim 1, wherein the compound according to formula (I) is combined with at least one polymeric gas hydrate inhibitor.

14. The method according to claim 1, wherein the compound according to formula (I) is combined with at least one thermodynamic gas hydrate inhibitor.

15. The method according to claim 1, wherein the fluid has a pH value of below 8.0.

Description

EXAMPLES

(1) Materials Used:

(2) For synthesis of the N,N-dialkylammoniumalkyl fatty acid amides the fatty acid esters, N,N-dialkylaminoalkylamines and solvents characterized in table 1 were used. They were of commercial grades.

(3) TABLE-US-00001 TABLE 1 Characterization of reactants used C.sub.12/14 methyl Mixture comprising 67% C.sub.12 and 21% C.sub.14 methyl ester ester; saponification number 251 mg KOH/g Coco fatty Methyl ester of coconut oil; C.sub.8-C.sub.18 ester partially acid methyl unsaturated, comprising as main component 46 wt.-% ester C.sub.12 saturated fatty acid methyl ester; saponification number 254 mg KOH/g Palm kernel Methyl ester of a mixture of C.sub.8-C.sub.18 fatty methyl ester acids, comprising as main components 48 wt.-% C.sub.12 saturated fatty acid methyl ester and 13 wt.-% C.sub.18 mono-unsaturated fatty acid methyl ester; saponification number 241 mg KOH/g C.sub.8/10 acid Methyl ester of a mixture of fatty acids, containing as methyl ester main components 83% C.sub.8 and C.sub.10 essentially saturated fatty acid methyl esters; saponification number 324 mg KOH/g Methyl Methyl ester of oleic acid (technical grade having 74% oleate purity, further comprising stearic acid and linoleic acid); saponification number 188 mg KOH/g Coconut Triglyceride of C.sub.8-C.sub.18 fatty acids, comprising as oil main components 45% C.sub.12 saturated fatty acid and 9% unsaturated fatty acids. Free fatty acids content 1%. DBAPA N,N-Dibutylamino propyl amine (≥98%) DMAPA N,N-Dimethylamino propyl amine (>98%) MSA methane sulfonic acid Solvent Mixture of aromatic hydrocarbons having carbon Naphtha numbers predominantly in the range of C.sub.9 through (SN) C.sub.11 and boiling in the range of from 177° C. to 216° C.

(4) Saponification numbers were determined according to DIN/EN/ISO 3681.

(5) Starting from the raw materials characterized in table 1 the N,N-dialkylammoniumalkyl fatty acid amides were produced according to the following general procedure:

(6) A 4-necked flask, equipped with a Dean-Stark apparatus, overhead stirrer, thermometer and nitrogen-purging line was charged with the fatty acid ester, the N,N-dialkylaminoalkylamine, and 0.5 wt.-% of sodium methoxide. The mixture was heated to 140-180° C. for a period of 6 to 12 hours. The alcohol liberated during aminolysis was distilled off. The conversion was monitored by amine value distribution titration; the reaction was stopped when the primary amine value was <6 mg KOH/g. For the comparative examples (using a triglyceride) the reaction was stopped when a primary amine number of less than 15 mg KOH/g was obtained.

(7) Following the aminolysis reaction the reaction product was cooled to below 80° C. and diluted with a solvent (methanol or solvent naphtha). Subsequently the organic acid was added in such a manner that the temperature of the reaction mixture did not exceed 50° C. to form the final N,N-(dialkylammoniumalkyl)carboxylic acid amide salt. Details of the various syntheses are given in table 2.

(8) TABLE-US-00002 TABLE 2 Reactants and reaction pathways for the preparation of N,N-dialkylaminoalkyl fatty acid amides (II) and N,N-(dialkylammoniumalkyl)carboxylic acid amide salts (I) N,N-dialkylaminoalkyl fatty acid amide (II) Ammonium salt (I) Solution Ammonium fatty acid N,N-dialkylamino- molar ratio carboxylic molar ratio active salt ester (IV) alkylamine (V) (IV):(V) acid (VI) (II):(VI) solvent concent AS 1 C.sub.8/10 methyl ester DBAPA 1:1 acrylic acid 1:1 methanol 85% AS 2 C.sub.12/14 methyl ester DBAPA 1:1 acrylic acid 1:1 SN 85% AS 3 methyl cocoate DBAPA 1:1 acrylic acid 1:1 methanol 60% AS 4 palm kernel methyl DBAPA 1:1 acetic acid 1:1 ethylene 60% ester glycol AS 5 methyl oleate DMAPA 1:1 acrylic acid 1:1 methanol 60% AS 6 coconut oil DBAPA 1:1 acrylic acid 1:1 methanol 85% (comp.) AS 7 coconut oil DBAPA 1:1 acrylic acid 1:1 SN 85% (comp.) AS 8 Coconut oil DBAPA 1:1 acetic acid 1:1 methanol 60% (comp.) AS 9 C.sub.12/14 acid methyl DBAPA 1:1 MSA 1:1 SN 60% (comp.) ester

(9) The dynamic viscosities of the samples according to table 1 were determined by using a rheometer from Anton-Paar at the given temperature at a shear rate of 106.Math.s.sup.−1. The results are given in table 3.

(10) TABLE-US-00003 TABLE 3 Viscosities of the N,N-(dialkylammoniumalkyl)carboxylic acid amide salts measured in different solvents N,N-(dialkyl- ammoniumalkyl) Exam- carboxylic active Viscosity Viscosity ple acid amide salt solvent content @10° C. @20° C. 1 AS 3 methanol 60% 1 <1 2 AS 4 methanol 60% 2 <1 3 AS 5 methanol 60% 1 <1 4 AS 9 SN 60% 148 86 (comp.) (comp.) 5 AS 8 methanol 60% 22 5 (comp.) (comp.) 6 AS 1 methanol 85% 153 101 7 AS 6 methanol 85% 295 144 (comp.) (comp.) 8 AS 2 SN 85% 466 218 9 AS 7 SN 85% 835 365 (comp.) (comp.)

(11) For evaluation of the performance of the presently disclosed N,N-dialkylammoniumalkyl fatty acids amide salts (I) as low dose gas hydrate inhibitors, a rocking cell test was used. The rocking cell test is a commonly used test in the art for assessing the performance of anti-agglomerant chemistry. Briefly, additives are evaluated based on their ability to effectively minimize the size of hydrate particle agglomerates and then to disperse those particles into the hydrocarbon phase. The results were classified as “pass” or “fail” based on whether hydrate blockages were detected. Performance is evaluated by determining the minimum effective dose (MED) required to register as a “pass” in the rocking cell test. The effective dosages (MEDs) were screened for 5.0 wt.-% NaCl brine at 50 vol.-% watercut and 138 bar at 4° C.

(12) The rocking cell apparatus (“rack”) is comprised of a plurality of sapphire tubes, each placed within a stainless-steel support cage. Each assembled sapphire tube and steel cage (hereby referred to as a rocking cell) is typically loaded with a fluid containing a hydrocarbon phase and a brine phase, along with a stainless-steel ball for mixing. The rocking cell can withstand pressures of up to 200 bar (2900 psi). The rocking cell, once loaded with the fluids, is then mounted on the rack with gas injection and pressure monitoring. During testing, as the gases cooled, and hydrates formed, the consumed gas was substituted via a high-pressure syringe pump to maintain the system at constant pressure.

(13) The rack was loaded with 10 rocking cells in a 2×5 configuration (two cells wide and 5 cells tall). The center position on the rack (between two cells) was fixed and allowed to rotate while the outer positions on the rack were moved vertically up and down. This vertical motion allowed the rocking cells to rotate into a positive or negative angle position. The steel ball placed inside the sapphire tube moved from one end of the cell to the other during a rocking motion. The rack rocked up and down at a rate of about 5 complete cycles (up and down) every minute. The rack was further contained within a temperature-controlled bath attached to a chiller with temperature control from −10° C. to 60° C.

(14) The rocking cells were filled with three components: hydrocarbon, aqueous phase, and gas. First, each rocking sapphire tube was filled with 5 ml of dodecane and a 5 ml of 5% NaCl brine (water cut 50 vol.-%) for a total liquid loading of 50% total tube volume (20 ml total). The anti-agglomerants according to table 2 were added at dose rates in percent, by volume of water (vol.-%). Green Canyon gas was used for this testing with its composition given in Table 4.

(15) TABLE-US-00004 TABLE 4 Green Canyon gas composition Component Name Chemical Symbol Amount (mol) Nitrogen N.sub.2 0.14 Carbon Dioxide CO.sub.2 0 Methane C.sub.1 87.56 Ethane C.sub.2 7.6 Propane C.sub.3 3 i-Butane i-C.sub.4 0.5 n-Butane n-C.sub.4 0.8 i-Pentane i-C.sub.5 0.2 n-Pentane n-C.sub.5 0.2

(16) Rocking Cell Test Procedure: A. Pretest Steps: Once the rack has been loaded with the rocking cells containing hydrocarbon fluid, brine and the anti-agglomerant, the rocking cells are evacuated with a vacuum pump for 15-20 minutes. While evacuating, the bath temperature is increased to the starting test temperature of 49° C. Once the bath has reached 49° C., the cells and the syringe pump are pressurized with Green Canyon gas to 138 bar and the syringe pump is switched on to maintain pressure during initial saturation. B. Saturation Step: The apparatus is set to rock at 5 rocks per minute for 2 hours to ensure the hydrocarbon fluids and brine loaded in the cell have been saturated with gas. This testing is performed at constant pressure and the syringe pump remains switched on and set at 138 bar for the remainder of the test. C: Cooling Step: While maintaining a rocking rate of 5 rocks per minute, the system is cooled from 49° C. to 4° C. over 6 hours. D. Steady State Mixing Step before Shut-in: At the constant temperature of 4° C., the apparatus is kept rocking at 5 rocks per minute for 12 hours to ensure complete hydrate formation. E. Shut-in Step: The apparatus is set to stop rocking and to set the cell position to horizontal and kept at a constant temperature of 4° C. for 12 hours. F. Steady State Mixing Step after Shut-in: At the conclusion of the shut-in period, the apparatus is restarted at the rate of 5 rocks per minute at the constant temperature of 4° C. for 4 hours. G. Test Completion: At the conclusion of the experiment, the apparatus is set to stop rocking and the cells are set at a negative inclination to keep fluids away from the gas injection port. The chiller bath is set to 49° C. to melt any formed hydrates and allow for depressurization and cleaning.

(17) To determine the relative performance of each inhibitor or dose rate of inhibitor, visual observations were made during the steady state mixing step after shut-in (period F) and correlated with an interpretation of the time required for the ball within the cell to travel between two magnetic sensors. Each experiment was conducted in duplicate to confirm reproducibility. Table 5 below shows the results (average values) of the rocking cell tests.

(18) TABLE-US-00005 TABLE 5 Test results as anti-agglomerant in rocking-cell tests Ammonium Minimum Effective Dose Rate Test salt (wt %, based on water cut) 10 AS 1 0.35% 11 AS 2 0.35% 12 AS 3 0.45% 13 AS 4 0.55% 14 AS 5 0.55% 15 AS 1 + 0.40% AS 3 (1:1) 16 AS 6 0.70% (comp.) 17 AS 8 0.75% (comp.) 18 AS 9 0.90% (comp.)
Testing of Water Quality Upon Phase Separation of Gas and Fluid Phase

(19) For assessment of the water quality obtained upon depressurization and separation of the gas form hydrocarbon and aqueous phase, samples (25 resp. 45 ml) of the crude oils characterized in table 6 where filled into graduated 120 ml glass bottles and filled to 100 ml with tap water. The bottles were placed in a heating bath of 100 F (37.8° C.) for 1 hour. Afterwards, the amount of anti-agglomerant given in tables 7 and 8 was added and the bottles where combined in a box and shaken 200 times. Afterwards, the bottles were placed again in the heating bath. The water separation (measured in mL) and the water quality were rated after 5 min and 120 min of incubation time. Water quality was rated visually using the following grading: water quality: 1=Clear and bright 2=Slight Haze 3=Hazy 4=Opaque

(20) TABLE-US-00006 TABLE 6 Characterization of test oils Oil A Oil B API gravity 30.9° 21.8° Saturates 23.11% 27.82% Aromatics 32.36% 54.71% Resins 35.08% 14.50% Asphaltenes 7.27% 2.97%

(21) The oils were further characterized by their contents of saturates, aromatics, resins and asphaltenes. The SARA analysis was made using a latroscan TLC-FID according to standard method IP 469.

(22) As can be recognized from the test results, the method using N,N-dialkylammoniumalkyl fatty acid amide salts produced by aminolysis of a N,N-dialkylaminoalkylamine with a fatty acid ester according to the invention requires lower additive dosage rates than comparable methods according to the state of the art. Furthermore, the reduced viscosity of these amide salts eases application to the fluid to be treated. Additionally, the method allows for an improved water quality upon phase separation. These are distinct improvements over the prior art.

(23) TABLE-US-00007 TABLE 7 Test results on water quality in Oil A Water/oil (75:25 vol.-%) Water/oil (55:45 vol.-%) Ammonium Dosage water separation water quality water separation water quality Test salt [wt.-%] 5 min 120 min. 5 min 120 min. 5 min 120 min 5 min 120 min 19 AS 1 0.5 51 ml 70 ml 1 1 42 ml 51 ml 1 1 20 AS 1 1.0 55 ml 71 ml 1 1 43 ml 52 ml 1 1 21 AS 2 0.5 53 ml 73 ml 1 1 45 ml 51 ml 1 1 22 AS 2 1.0 58 ml 69 ml 1 1 38 ml 53 ml 1 1 23 AS 5 0.5 59 ml 71 ml 1 1 40 ml 52 ml 1 1 24 AS 5 1.0 59 ml 71 ml 1 1 43 ml 53 ml 1 1 25 AS 6 0.5 44 ml 65 ml 3 2 40 ml 50 ml 1-2 1 (comp.) 26 AS 6 1.0 47 ml 68 ml 3 2 35 ml 45 ml 2-3 1-2 (comp.) 27 AS 9 0.5 40 ml 59 ml 3 3 37 ml 46 ml 2 1-2 (comp.) 28 AS 9 1.0 42 ml 63 ml 4 3 31 ml 41 ml 3 2 (comp.)

(24) TABLE-US-00008 TABLE 8 Test results on water quality in Oil B Water/oil (75/25 vol.-%) Water/oil (55/45 vol.-%) Ammonium Dosage water separation water quality water separation water quality Test salt [wt.-%] 5 min 120 min. 5 min 120 min. 5 min 120 min 5 min 120 min 29 AS 1 0.5 43 ml 59 ml 3 1 20 ml 25 ml 1 1 30 AS 1 1.0 50 ml 60 ml 2 1 23 ml 32 ml 2 1 31 AS 1 2.0 54 ml 65 ml 2 1 27 ml 38 ml 2 1 32 AS 3 0.5 41 ml 55 ml 2 1 18 ml 23 ml 1 1 33 AS 3 1.0 48 ml 59 ml 2 1 22 ml 26 ml 2 1 34 AS 3 2.0 52 ml 63 ml 3 1 25 ml 30 ml 2 1 35 AS 4 0.5 40 ml 57 ml 2 1 20 ml 25 ml 1 1 36 AS 4 1.0 45 ml 62 ml 2 1 22 ml 27 ml 1-2 1 37 AS 4 2.0 40 ml 63 ml 3 1 25 ml 31 ml 2 1-2 38 AS 6 0.5 40 ml 50 ml 4 2 n.d. 20 ml 4 2 (comp.) 39 AS 6 1.0 45 ml 52 ml 3 2 n.d.  5 ml 4 3 (comp.) 40 AS 6 2.0 42 ml 49 ml 4 3 n.d.  5 ml 4 3 (comp.) n.d. = not detectable