METHOD FOR ASSESSING THE COMPATIBILITY OF PRODUCTION FLUID ADDITIVES

Abstract

A method of determining the suitably of corrosion inhibitors, or other additives in the presence of corrosion inhibitor, for a given fluid environment. The method including determining if there is a difference in the presence or level of micelles between a fluid sample to which corrosion inhibitor has been added either alone or to which corrosion inhibitor and at least one additional fluid additive or additives have been added. The method can be used to determine the compatibility of fluid additives.

Claims

1. A method of determining the suitability of corrosion inhibitors, or other additives in the presence of corrosion inhibitor, for a given fluid environment comprising: determining if there is a difference in the presence or level of micelles between a fluid sample to which corrosion inhibitor has been added either alone or to which corrosion inhibitor and at least one additional fluid additive or additives have been added.

2. A method according to claim 1 wherein the method of determining the presence of micelle comprises: a) obtaining a fluid sample to which corrosion inhibitor is to be added; b) adding to the fluid sample either corrosion inhibitor alone or corrosion inhibitor and at least one additional to the fluid additive or additives; c) adding a marker solution comprising an optically detectable marker to the fluid sample; d) determining the presence or level of micelle in the sample of the fluid; and e) determining the suitability of corrosion inhibitor, or other additive, for a given fluid environment, based on the difference in the presence or level of micelles between fluid samples comprising corrosion inhibitor alone or corrosion inhibitor and at least one additional fluid additive or additives.

3. A method according to claim 2, wherein the fluid sample in mixed after step b).

4. A method according to claim 2, wherein the optically detectable marker is selected from a list comprising NanoOrange®, 9-diethylamino-5-benzo[α]phenoxazinone, 6-Dodecanoyl-2-Dimethylaminonaphthalene, N-(3-Trethylammonuimpropyl)-4-(6-(4-(Diethylamino) Phenyl Hexatrienyl) Pyridinium Dibromide and 2-Anilinonaphthalene-6-sulfonic acid, meropolymethines, pyridinium-N-phenolate betaines, phenoxazones, N,N-dialkylaminonaphthalenes, N,N-dialkylaminostyrenes, N,N-dialkylaminonitrobenzenes, coumarins, N,N-dialkylindoaniline, vinylquinoliums, and arylaminonaphthalene sulfonates.

5. A method according to claim 1, wherein presence of micelle is determined using laser diffraction, interferometry or imaging, spectroscopic means, hyperspectral imaging, or flow cytometry.

6. A method according to claim 2, wherein the fluid sample is taken from, or representative of, a fluid environment of a conducting and containment system used to screen test, produce, transport and process oil and/or gas and their products.

7. A method according to claim 1, wherein the fluid additive is an intended fluid additive comprising an alternative corrosion inhibitor, biocides, foamers, defoamers, paraffin control agents, emulsifiers, demulsifiers, anti-swelling agents, hydrate inhibitors, anti-caking agents, scale dissolvers or inhibitors, wetting agents, or wax control agents.

8. A method according to claim 1, wherein the fluid additive is an unintended fluid additive and comprises solid particles.

9. A method according to claim 8, wherein the solid particles comprise sand, kaolin, limestone, illite, iron (II)(Ill) oxide, iron(II) sulfide, barium sulfate, or calcium sulfate.

10. A method according to claim 1, wherein determining the presence of micelle in the sample of the fluid is performed after separation of the aqueous and hydrocarbon phases or wherein determining the presence of micelle in the sample of the fluid is performed without separation of the aqueous and hydrocarbon phases.

11. A method according to claim 10, wherein separation of the aqueous and hydrocarbon phases is performed by settling through density, centrifugation, heating, and/or chemical treatment.

12. A method according to claim 1, wherein a concentration series of corrosion inhibitor is created by adding an increasing concentration of corrosion inhibitor to two or more fluid samples, wherein the presence of micelle is determined for each of the two or more samples in the concentration series.

13. A method according to claim 1, wherein a concentration series of corrosion inhibitor is created by adding corrosion inhibitor sequentially to a fluid sample to create a concentration series, wherein the presence of micelle is determined after each sequential addition of corrosion inhibitor.

14. A method according to claim 12, wherein a concentration series of corrosion inhibitor alone and a concentration series of corrosion inhibitor and fluid additive at a fixed concentration is compared to determine the suitability of corrosion inhibitors, or fluid additive for a given corrosion inhibitor, for a given fluid environment, in a fluid conducting and containment system.

15. A method according to claim 1, wherein a concentration series of the second fluid additive is created by adding an increasing concentration of fluid additive to two or more fluid samples, wherein the presence of micelle is determined for each of the two or more samples in the concentration series.

16. A method according to claim 1, wherein a concentration series of fluid additive is created by adding corrosion inhibitor sequentially to a fluid sample to create a concentration series, wherein the presence of micelle is determined after each sequential addition of corrosion inhibitor.

17. A method according to claim 15, wherein corrosion inhibitor alone at a fixed concentration and a concentration series of second fluid additive and corrosion inhibitor at a fixed concentration is compared to determine the suitability of corrosion inhibitors for a given fluid environment in a fluid conducting and containment system.

18. A method according to claim 1, wherein the method further comprises the additional step of using the presence or level of micelles to determine corrosion inhibitor aqueous phase partitioning in a fluid sample and/or the presence or level of reverse micelle to determine corrosion inhibitor hydrocarbon phase partitioning in a fluid sample.

19. A method according to claim 1, wherein an aqueous fluid is added to the fluid sample to form a predetermined ratio of aqueous fluid to hydrocarbon fluid.

20. A method according to claim 19, wherein the aqueous fluid is water or a brine solution.

21. A method according to claim 8, wherein the predetermined ratio of aqueous fluid to hydrocarbon fluid is 0.5% to 99.5% of aqueous fluid.

22. A method according to claim 8, wherein the predetermined ratio of aqueous fluid to hydrocarbon fluid is 10%, 50%, and/or 90% of aqueous fluid.

23. A method according to claim 2, wherein the mixing of step e) comprises mixing and equilibrating to between 60° C. and 80° C., before being allowed to cool to ambient temperature.

24. A method according to claim 18, wherein a concentration series of corrosion inhibitor is created after addition of the aqueous fluid to form a predetermined ratio of aqueous fluid to hydrocarbon fluid.

25. A method according to claim 18, wherein the method comprises determining the presence of micelle formation in an aqueous phase and/or the presence of reverse micelle formation in a hydrocarbon phase.

26. A method of determining the suitability of corrosion inhibitors for a given fluid environment comprising: a) obtaining a fluid sample to which corrosion inhibitor is to be added; b) adding to the fluid sample either corrosion inhibitor alone or corrosion inhibitor and at least one additional to the fluid additive or additives; c) adding a marker solution comprising an optically detectable marker; d) determining the presence and level of micelle; and e) determining the suitability of the combination of corrosion inhibitors and at least one additional fluid additive or additives for a given fluid environment based on the difference in the presence or level of micelles between a fluid sample comprising corrosion inhibitor alone and corrosion inhibitor and at least one additional to the fluid additive or additives.

27. A method of determining the suitability of corrosion inhibitors for a given fluid environment comprising: a) obtaining a fluid sample to which corrosion inhibitor is to be added; b) adding a corrosion inhibitor at, or to slightly above, its critical micelle concentration; c) creating a concentration series of increasing amounts of at least one solid; d) adding a marker solution comprising an optically detectable marker; e) determining the presence of micelle; and f) determining the suitability of corrosion inhibitors for a given fluid environment based on the difference in the presence of micelles between samples in the concentration series of increasing amounts of at least one solid in the presence of a corrosion inhibitor at, or close to, its critical micelle concentration and a control of corrosion inhibitor at, or close to, its critical micelle concentration alone.

28. A method of determining the suitability of corrosion inhibitors to at least partially partition to an aqueous phase for a given fluid environment comprising: a) obtaining a fluid sample to which corrosion inhibitor is to be added; b) creating a concentration series of increasing concentration of corrosion inhibitor; c) adding a marker solution comprising an optically detectable marker; d) determining the presence of micelle formation in the aqueous phase and/or the presence of reverse micelle formation in the hydrocarbon phase.

29. A method according to claim 28, wherein an aqueous fluid is added to the fluid sample prior to step b) to form a predetermined ratio of aqueous fluid to hydrocarbon fluid.

30. A method according to claim 29, wherein the aqueous fluid is water or a brine solution.

31. A method according to claim 28, wherein the fluid sample is mixed after addition of the aqueous fluid and equilibrated at a temperature of 50° C. to 90° C., before being allowed to cool to ambient temperature.

Description

[0037] The invention will now be described by way of example with reference to the figures.

[0038] FIG. 1 is a graph of LPR corrosion rate for corrosion inhibitor 30-60% fatty acid amine condensate, acetates solution containing 10-30% 2-Butoxyethanol at 25 ppm, 50 ppm, and 100 ppm;

[0039] FIG. 2 is a graph of LPR corrosion rate for corrosion inhibitor 30-60% fatty acid amine condensate, acetates solution containing 10-30% 2-Butoxyethanol at 25 ppm, 50 ppm, and 100 ppm in the presence of a 25 ppm dose of scale inhibitor;

[0040] FIG. 3 is a graph of a concentration series of surfactant-containing corrosion inhibitor formulated in sodium thiosulphate, IPA (1-10%), glycol and sodium chloride in brine;

[0041] FIG. 4 is a graph of a concentration series of surfactant-containing corrosion inhibitor formulated in sodium thiosulphate, IPA (1-10%), glycol and sodium chloride in 9:1 brine:petroleum ether;

[0042] FIG. 5 is a graph of a concentration series of surfactant-containing corrosion inhibitor formulated in sodium thiosulphate. IPA (1-10%), glycol and sodium chloride in 9:1 brine:peregrino oil;

[0043] FIG. 6 is a graph of micelle index for surfactant-containing corrosion inhibitor formulated in sodium thiosulphate. IPA (1-10%), glycol and sodium chloride in 6:4 brine:petroleum ether;

[0044] FIG. 7 is a graph of micelle concentration of surfactant-containing corrosion inhibitor formulated in sodium thiosulphate, IPA (1-10%), glycol and sodium chloride in 6:4 brine:oil;

[0045] FIG. 8 is graph of corrosion inhibitor 1—1M NaCl (21° C. 20 hours equilibration):

[0046] FIG. 9 is a graph of corrosion inhibitor 2—1M NaCl (21° C., 20 hours equilibration);

[0047] FIG. 10 is a graph of corrosion inhibitor 3—1M NaCl (21° C. 20 hours equilibration); and

[0048] FIG. 11 is a graph of corrosion inhibitor 4—1M NaCl (21° C., 20 hours equilibration).

EXPERIMENT 1: COMPATIBILITY OF CORROSION INHIBITORS AND A SECOND FLUID ADDITIVE

[0049] Samples were taken from LPR tests corrosion rate in which scale inhibitors and/or corrosion inhibitors had been dosed. Sample bottles were filled to the top and lids replaced as soon as possible in order to minimise oxygen ingress. The average micelle result from each set of tests is shown.

[0050] The conditions for the LPR tests were as follows:

TABLE-US-00001 Temperature 50° C. Brine 1 M NaCl (100% aqueous) Gas CO.sub.2 Pre-Corrosion 2 hours Sweep Rate: −10 mV to +10 mV at 10 mV.min.sup.−1 Coupon material: C1018 Coupon Type X65 Carbon Steel

[0051] The test was run for a minimum 16 hours

[0052] Two hours after pre-corrosion, cells were dosed with 25, 50 or 100 pm of a 30-60% fatty acid amine condensate, acetates solution containing the corrosion inhibitor 10-30% 2-Butoxyethanol. Immediately after the corrosion inhibitor dose a 25 ppm dose of scale inhibitor was added. LPR measurements were continued until the following morning.

[0053] Corrosion inhibitor after 2 hours pre-corrosion and then immediately following the corrosion inhibitor dose, the scale inhibitor dose was added. To determine the presence of micelles, 1.98 mL of sample was taken, to which 20 μL of 0.1 mM Nile Red was added, and optical signal determined.

[0054] As shown in Table 1 and FIG. 1, no micelles were present in the samples at 25 and 50 ppm corrosion inhibitor and the final corrosion rate is higher than that of the 100 ppm sample. Micelles are present in the 100 ppm sample and a final corrosion rate of 0.03 mm/yr is achieved.

TABLE-US-00002 TABLE I LPR corrosion rate for corrosion inhibitor 30-60% fatty acid amine condensate, acetates solution containing 10-30% 2-Butoxyethanol at 25 ppm, 50 ppm, and 100 ppm. Peak corrosion rate before Final Inhibitor Test Inhibitor inhibitor dosage Corrosion Efficiency No. combination (mm/yr) rate (mm/yr) (%) Micelle? 1  25 ppm 4.58 1.25 72.83 No 2  50 ppm 3.22 0.14 95.69 No 3 100 ppm 4.47 0.03 99.26 Yes

[0055] As shown in Table 1 and FIG. 1, the results shows that a concentration of 100 ppm of the corrosion inhibitor comprising 30-60% fatty acid amine condensate, acetates solution containing 10-30% 2-Butoxyethanol is the optimal concentration for protection, as it has reached the CMC and micelles were detected.

TABLE-US-00003 TABLE 2 LPR corrosion rate for corrosion inhibitor 30-60% fatty acid amine condensate, acetates solution containing 10-30% 2-Butoxyethanol at 25 ppm, 50 ppm, and 100 ppm in the presence of a 25 ppm dose of scale inhibitor. Peak corrosion Final rate before Corrosion Inhibitor Test Inhibitor inhibitor dosage rate Efficiency No. combination (mm/yr) (mm/yr) (%) Micelle? 4 corrosion 4.54 4.17 8.08 No inhibitor 25 ppm & scale inhibitor 25 ppm 5 corrosion 3.72 4.03 −8.28 No inhibitor 50 ppm & scale inhibitor 25 ppm 6 corrosion 4.00 3.74 6.39 No inhibitor 100 ppm & scale inhibitor 25 ppm

[0056] As shown in Table 2 and FIG. 2, the results show that the scale inhibitor at 25 ppm rendered the corrosion inhibitor completely inefficient for corrosion protection at any of the dose rates tested. This inefficiency was reflected in micelle presence, with no micelles detected in any of the samples when scale inhibitor was present.

EXPERIMENT 2: DETECTION OF CORROSION INHIBITOR PARTITIONING BETWEEN AQUEOUS AND HYDROCARBON PHASES

[0057] The partitioning of an amine derivative surfactant in 10-20% ethanol in a heavy field oil were tested. The oil was stored at 60° C. for at least four hours prior to analysis and was mixed regularly to ensure homogeneity. The aqueous phase was based on a synthetic field brine and consisted of the following quantities of each salt dissolved in 1 L of deionised water.

TABLE-US-00004 TABLE 3 Composition of synthetic field brine. Salt Mass (g) CaCl.sub.2 .Math. 6H.sub.2O 16.6 MgCl.sub.2 .Math. 6H.sub.2O 5.6 KCl 1.0 NaCl 112.5

[0058] A 1% v/v (10,000 ppm) stock of the surfactant was prepared in brine and used to create a concentration series of 0-250 ppm in each of the following (i) brine only (ii) 9:1 (v/v) brine:petroleum ether (b.p. 180-280° C.) (iii) 9:1 (v/v) brine:field oil. Samples were mixed well and equilibrated at 60° C., before being allowed to cool to ambient temperature.

[0059] A 0-250 ppm series of the surfactant in 6:4 (v/v) brine:petroleum ether (b.p 180-280° C.) and 6:4 (v/v) brine:field oil (b.p 180-280° C.) was then analysed. In this case, the samples were mixed well and equilibrated to 80° C., before being allowed to cool to ambient temperature.

[0060] For the samples containing only brine, the surfactant was added directly to the aqueous phase. The surfactant was added to the organic phase of the 9:1 matrix when hydrocarbon was present.

[0061] FIGS. 3-7 show graphical representations of the results for surfactant in brine, brine and petroleum ether, and brine and field oil at water cuts of 90% and 60%.

TABLE-US-00005 TABLE 4 Summary of the estimated CMCs of surfactant in brine, brine and petroleum ether, and brine and field oil. Sample Water Cut (%) T (° C.) CMC (ppm) Brine 100 60  70-80  Brine: Petroleum 90 60  50-60  Ether 60 80  30-40  Brine: Field Oil 90 60  70-100 60 80 100-250

[0062] The presence of petroleum ether led to a lowering of the CMC compared to the brine-only samples. This effect was stronger the higher the proportion of petroleum ether was present, with the lowest CMC observed at the lowest (60%) water cut. This behaviour is typical of water soluble corrosion inhibitors, especially when the dosage is based upon the volume of total fluids. A higher concentration of the water-soluble corrosion inhibitor components will be present in the aqueous phase of the fluids in this case.

[0063] Conversely, the presence of field oil was shown to significantly increase the CMC. Again, this effect was more pronounced with a higher proportion of field oil present; the highest CMC was observed with a 60% water cut. This suggests that the surfactant partitions to the hydrocarbon and such losses in the aqueous phase mean a higher concentration of corrosion inhibitor is needed to achieve micelle formation.

EXPERIMENT 3: THE EFFECT OF SOLIDS ON CORROSION INHIBITION

[0064] FIGS. 8 to 11 show the results of a corrosion inhibitor parasitisation test with a variety of solids. The CMCs of four commercial corrosion inhibitor formulations were determined in 1 M NaCl. 1.98 mL of the sample was transferred to a cuvette, to which was added 20 μL of the micelle detection marker. The cuvette was sealed and gently inverted to mix and read for optical signal. Data is presented as a Micelle Index (MI) of the sample: a normalized indicator of micelle presence, where a gained value above 0.5 signifies the occurrence of surfactant aggregation.

[0065] The CMC of all four inhibitor formulations was determined to be <100 ppm. Each chemical was then prepared as 100 ppm solutions in 1 M NaCl. A 20 mL sample of an inhibitor solution was transferred to a vial charged with a known mass of the test solid, sealed and gently agitated at hourly intervals for 5 hours. The solutions were then allowed to equilibrate for a further 15 hours before micelle analysis. Tested solids were selected based on a range of formation, corrosion and scale products likely to be observed in the field. The sand contained well packed silicon dioxide with low surface area. Experiments carried out using calcium and barium sulfate required the pre-saturation, and filtration to 0.45 μm, of the 1 M NaCl solution prior to use to negate the sparing solubility of the salts in water.

[0066] All chemicals showed varying losses of surfactant chemicals to the solids tested, except in the case of the tested sand. The sand, as well as having low surface area, is expected to have low metal ion content, particularly on its surface. Higher losses were observed in solids that contained metal ions.

[0067] The highest attritions were observed in Inhibitors 1-3, where formation clays and scale solids proved to be particularly effective at eliminating available chemical from the bulk. Corrosion by-products also presented alternative surfactant binding sites, with iron oxide affecting the test chemicals to a greater degree than iron sulphide. Inhibitor 1 performed best overall in the experiments but was susceptible to higher concentrations of formation clays.

[0068] The simple micelle detection method employed here showed there were variations in the extent to which different inhibitors responded to different types of solids and micelles and demonstrates that this method is informative in understanding the effects solids play in a field context.