Process For Inhibition Of Sulphide Scales

Abstract

The invention provides for the use of a copolymer, comprising a) 0.1 to 10 mol-%, based on the weight of the copolymer, of structural units derived from vinylphosphonic acid or of a salt thereof, b) 40 to 80 mol-%, based on the weight of the copolymer, of structural units derived from compounds of the formula (1)

##STR00001## c) 1 to 50 mol-%, based on the weight of the copolymer, of structural units derived from compounds of the formula (5)

##STR00002##  in which X is OH or NR.sup.3R.sup.4, and R.sup.3 and R.sup.4, independently of one another, are H or C.sub.1-C.sub.4-alkyl,
for the inhibition and/or dispersion of inorganic sulphide scales, and for a process for the inhibition and/or dispersion of inorganic sulphide scales, the process comprising adding to water being within an oil or gas containing formation said copolymer.

Claims

1.-16. (canceled)

17. A process for the inhibition and/or dispersion of inorganic sulphide scales, wherein the process comprises the step of adding a copolymer comprising a) 0.1 to 10 mol-% of structural units derived from vinylphosphonic acid or of a salt thereof, b) 40 to 80 mol-% of structural units derived from compounds of the formula (1) ##STR00009## c) 1 to 50 mol-% of structural units derived from compounds of the formula (5) ##STR00010##  in which X is OH or NR.sup.3R.sup.4, and R.sup.3 and R.sup.4, independently of one another, are H or C.sub.1-C.sub.4-alkyl to water within an oil or gas containing formation.

18. The process according to claim 17, wherein the copolymer comprises additionally 1 to 10 mol-%, based on the weight of the copolymer, of structural units of formula (2) ##STR00011## in which n is 3, 4 or 5.

19. The process according to claim 17, wherein the copolymer further comprises 1 to 10 mol-% of structural units of formula (3) ##STR00012## in which R.sup.1 and R.sup.2, independently of one another, are hydrogen or C.sub.1-C.sub.4-alkyl.

20. The process according to claim 17, wherein the copolymer comprises less than 1 mol-% monomers which comprise an olefinically unsaturated hydrocarbon substituted ammonium salt group, wherein the expression hydrocarbon encompasses groups containing oxygen.

21. The process according to claim 17, wherein in the copolymer the proportion by weight of vinylphosphonic acid or salts thereof is from 0.8 to 6 mol-%.

22. The process according to claim 17, wherein in the copolymer the proportion of structural units which are derived from compounds of the formula (1) is from 45 to 70 mol-%.

23. The process according to claim 17, wherein in the copolymer the proportion of structural units which are derived from compounds of the formula (5) is from 5 to 45 mol-%.

24. The process according to claim 17, wherein formula (5) is acrylic acid and/or acrylamide.

25. The process according to claim 17, wherein formula (5) is acrylamide and the proportion thereof is from 5 to 45 mol-%.

26. The process according to claim 17, wherein formula (5) is a mixture of acrylic acid and acrylamide, and the proportion of acrylic acid is from 1 to 10 mol-%, and the proportion of acrylamide is from 1 to 40 mol-%.

27. The process according to claim 19, wherein the proportion of structural units which are derived from the compound of the formula (3) is from 1 to 10 mol-%.

28. The process according to claim 18, wherein the proportion of structural units which are derived from the compound of the formula (2) is from 1 to 10 mol-%.

29. The process according to claim 17, wherein the molecular weight (number average) of the copolymer is from 100,000 to 10,000,000 g/mol, determined by GPC against polyacrylic acid as standard.

30. The process according to claim 17, further comprising the step of adding a conventional scale inhibitor to the water within an oil or gas containing formation.

31. The process according to claim 17, further comprising the step of adding a composition comprising 0.5-10 wt.-% the copolymer, 25-30 wt.-% water or solvent, 1-25 wt.-% of a conventional scale inhibitor and 5-50 wt.-% of a glycol based solvent, to the water within an oil or gas containing formation.

32. The process according to claim 30, wherein the conventional scale inhibitor is selected from the group consisting of diethylenetriamine penta(methylene phosphonic acid), nitrilo(methylene phosphonic acid), methacrylic diphosphonate homopolymer, acrylic acid-allyl ethanolamine diphosphonate copolymer, SVS (sodium vinyl sulphate)-acrylic acid-allyl ammonia diphosphonate terpolymer, acrylic acid-maleic acid-DETA (diethylene triamine) allyl phosphonate terpolymer, polyaspartic acid, and polycarboxylates.

Description

EXAMPLES

[0063] The following examples are based upon a brine composition as described in Table 1 ata pH of 7.0

TABLE-US-00001 TABLE 1 Brine composition for examples 1-6 Sea Water Cations Anions Final (50:50) Ion [wt.-ppm] Salt [g/l] [g/l] [g/l] Na 10890 NaCl 24.04 24.04 24.04 Ca 428 CaCl.sub.2•2H.sub.2O 3.15 0 1.57 Mg 1368 MgCl.sub.2•6H.sub.2O 22.89 0 11.45 K 460 KCl 1.75 0 0.88 Zn 20 Zn(CH.sub.3COO).sub.2•2H.sub.2O 0.13 0 0.07 Pb 20 Pb(CH.sub.3COO).sub.2•3H.sub.2O 0.07 0 0.04 S 250 Na.sub.2S (anhydrous) 0 1.22 0.61

[0064] It is of course possible to use e.g. Na.sub.2S.3H.sub.2O or Na.sub.2S.9H.sub.2O instead of anhydrous Na.sub.2S.

[0065] The composition of the copolymers used as ZnS/PbS scale inhibitor/dispersant were as follows (percentages denote mol-%):

[0066] Polymer 1:58% AMPS, 38% Acrylic Amide, 2% n-Vinyl Formamide, 2% Vinyl Phosphonic Acid. Number average molecular mass 4-5 Million g mol.sup.−1.

[0067] Polymer 2: 78% AMPS, 38% Acrylic Amide, 2% n-Vinyl Formamide, 2% Vinyl Phosphonic Acid. Number average molecular mass 4-5 Million g mol.sup.−1.

[0068] Polymer 3: 83% AMPS, 5% n-Vinyl Pyrrolidone, 5% n-Vinyl Formamide, 5% Acrylic Amide, 2% Vinyl Phosphonic Acid. Number average molecular mass 0.5-1 Million g mol.sup.−1.

[0069] Separate cation and anion brines were prepared. The cation brine contained NaCl, CaCl.sub.2, MgCl.sub.2, KCl, Zn(CH.sub.3COO).sub.2 and Pb(CH.sub.3COO).sub.2. The anion brine contained only NaS.

[0070] The respective ZnS/PbS scale inhibitor/dispersant copolymer was then added to the anion brine. The cation brine was subsequently mixed with the anion brine at a 50:50 volume mix in a glass jar. The jars were placed into a 90° C. water bath and monitored over 24 hours. The visual appearance was noted and concentrations of Zn and Pb were determined using ICP. These are expressed as Pb or Zn Inhibition Efficiency relative to a blank and control sample of the brine. For this determination, a sample of the liquid which is above the precipitate, if any, is taken. The liquid is analyzed for Zn and Pb content using ICP. The higher the Zn and Pb concentration is, the higher the Efficiency is. The examples 1-12 below use different copolymers/terpolymers as indicated.

[0071] Visual appearance checks on the jars were made to see there was any Zinc Sulphide/Lead Sulphide/Iron Sulphide precipitation. If there was precipitation within the jars a dark solid would be present at the bottom of the jars. This would be seen in the comparative examples which would contain 50% cation brine and 50% anion brine without any ZnS/PbS scale inhibitor/dispersant copolymer. For jars where Zinc Sulphide/Lead Sulphide/iron Sulphide was being successfully inhibited and/or dispersed a solution of high turbidity that was extremely dark in colour (dark grey) is observed. As inhibitor and/or dispersant performance decreases a solution with decreased turbidity is observed, i.e. the solution becomes clearer and solids precipitate and settle at the bottom of the jar.

[0072] Inductively Coupled Plasma (ICP) was used as an analytical method used to measure the elemental composition of fluids. The analyte is introduced via a nebuliser to create a fine spray and in combination with Argon gas creates a plasma. The plasma then passes through a torch, where, depending upon which elements are present within the plasma, emit a characteristic wavelength. The characteristic wavelength is detected using a spectrometer (Optical Emission Spectrometer, OES) that is linked to the ICP instrument. The intensity of the wavelength emission is directly proportional to the concentration of the element that is being studied.

[0073] The results obtained were as follows. The ppm values refer to weight ppm of the respective polymer based on the total weight of the brine.

TABLE-US-00002 TABLE 2 Pb inhibition efficiency in Examples 1-3 Pb Efficiency Example Polymer 10 ppm 50 ppm 100 ppm 500 ppm 1 1 90 116 129 97 2 2 90 115 108 90 3 3 87 108 109 74

TABLE-US-00003 TABLE 3 Zn inhibition efficiency in Examples 4-6 Zn Efficiency Example Polymer 10 ppm 50 ppm 100 ppm 500 ppm 4 1 109 118 114 95 5 2 107 113 107 86 6 3 115 128 108 73

[0074] The efficiencies were calculated according to

Efficiency=(C.sub.t−C.sub.Blank)/(C.sub.control−C.sub.Blank)×100

where: [0075] C.sub.t is equal to the concentration of the ion at a given time (i.e. after 24 hours) [0076] C.sub.Blank is equal to the lowest possible concentration of the ion at a given time (i.e. 24 hours with full amount of scaling) [0077] C.sub.control is equal to the highest possible concentration of the ion at a given time (i.e. 24 hours with no scaling)

[0078] The control values were obtained through analyzing a sample made up of 50% cations and 50% anions by ICP straight away, i.e. without time delay. This of course leads to some scale formation and thus a loss of Zinc and Lead concentration.

[0079] In ICP-OES (inductively coupled plasma optical emission spectrometry) high viscosity and low surface tension fluids can impair sample nebulization and transport of the analytes to the detector, causing inaccuracies especially in samples with high dissolved solids.

[0080] In the examples using 100 or 500 ppm of the polymer, the samples may not have nebulized fully as a result of the higher viscosity from the relatively higher inhibitor concentrations present. This can lead to a reduction in the Zinc and Lead concentrations that are detected by ICP-OES and accounts for the decline in efficiency at higher polymer concentrations.

[0081] Further to this due to the standardization technique employed in the examples was ‘matrix matching’, the concentrations of Zinc and Lead are not corrected from the loss of sample during the nebulization of the sample. If an internal standard was employed the instrument can correct the concentrations of Zinc and Lead. The ‘matrix matching’ correction would account for the salinity interferences of the brine such as spectral interferences and reduced ionisation of the analytes in the plasma, however variation in the nebulisation of the samples would not have been accounted for.

[0082] Examples 7-12 again used copolymers 1-3 as listed above at the same concentrations, as well as the same test conditions, however they use harsher water chemistry, as shown below;

TABLE-US-00004 TABLE 4 Brine composition for Examples 7-12 Sea Final Water Cations Anions (50:50) Ion [wt.-ppm] Salt [g/l] [g/l] [g/l] Na 10890 NaCl 24.04 24.04 24.04 Ca 428 CaCl.sub.2•2H.sub.2O 3.15 0 1.57 Mg 1368 MgCl.sub.2•6H.sub.2O 22.89 0 11.45 K 460 KCl 1.75 0 0.88 Ba 0 BaCl.sub.2•2H.sub.2O 0 0 0 Sr 0 SrCl.sub.2•6H.sub.2O 0 0 0 Zn 400 Zn(CH.sub.3COO).sub.2•2H.sub.2O 2.69 0 1.34 Pb 400 Pb(CH.sub.3COO).sub.2•3H.sub.2O 1.46 0 0.73 SO.sub.4 0 Na.sub.2SO.sub.4 0 0 0 S 250 Na.sub.2S (anhydrous) 0 1.22 0.61

TABLE-US-00005 TABLE 5 Pb inhibition efficiency in Examples 7-9 % Pb Efficiency Example Polymer 10 ppm 50 ppm 100 ppm 500 ppm 7 1 0.05 3.42 24.65 97.05 8 2 27.55 64.42 87.39 93.17 9 3 −0.09 0.64 72.25 81.45

TABLE-US-00006 TABLE 6 Zn inhibition efficiency in Examples 10-12 % Zn Efficiency Example Polymer 10 ppm 50 ppm 100 ppm 500 ppm 10 1 0.32 2.84 18.96 76.40 11 2 7.37 44.13 72.31 72.37 12 3 0.16 93.28 82.41 63.82