SCALE INHIBITION

Abstract: A method of inhibiting barium sulfate scale deposition from water of high barium content, comprising adding to the water an effective amount of a water-soluble polymer, or salts thereof, containing m units of a moiety A, n units of a moiety B and p units of a moiety D, wherein A is a moiety having the formula I The molecular weight of the polymer ranges from 500 to 10,000 while retaining its water solubility.

Description: The present invention relates to scale inhibition and, in particular, to a method of inhibiting barium scale deposition from waters of high barium content e.g. deeper formation waters. Deeper formation water, e.g., those found in the North Sea, have lower pH values of about 3 to 7 and a higher barium content than formation waters which are closer to the earth's surface. In the subsea secondary recovery by water flooding, a great deal of water is required and recourse may be needed to such deeper formation waters for mixing with sea-water derived from upper sea regions. Such mixing of incompatible waters can lead to severe barium sulfate scaling problems in well bore production equipment and conventional anti-scalants e.g. polyacrylates are not effective against this particular scale. From the GB-A 2 152 919 a method became known, to treat scale in pressur­ ised boiler water systems with a copolymer of maleic or fumaric acid and vinyl sulfonic or allyl sulfonic acid. There is no mention of the barium scale from waters of high barium content and the method is restricted to pressurised boiler systems. Another reference, GB-A 2 105 319, describes a treatment of aqueous systems by a composition comprising an aminocarboxylate and a copolymer of maleic acid and styrene sulfonic acid. The composition relies upon the essential use, as co-inhibitor, of an amino-carboxylate compound. In I.E. Woerner and R.A. Holzer, Proc. Int. Water Conf. Eng. Soc. West Pa (81), pages 281-287, volume 42, an experimental sulfonated polymer was found suitable as an inhibitor for BaSO₄-scale. However, no indication of the precise structure of the sulfonated polymer in question could be found. R.W. Mitchell, D.M. Grist and M.J. Boyle in Journal of Petroleum Techno­ logy, (80), pages 904-912, volume 32, number 5, simply describe polymeric scale inhibitors (A and B) and organic phosphonates (C and E) as barium sulfate inhibitors and the effect of adding barium sulfate inhibitors to the seawater. Also, no precise structure of the polymer in question could be found. We have now found that certain water-soluble vinyl sulfonate homo- or copolymers provide excellent barium scale inhibition in waters having a high barium content. Accordingly, the present invention provides a method of inhibiting barium sulfate scale deposition from water of high barium content, comprising adding to the water an effective amount of a water-soluble polymer, or salts thereof, containing m units of a moiety A, n units of a moiety B and p units of a moiety D, wherein A is a moiety having the formula I in which R₁, R₂ and R₃, independently, are hydrogen, CO₂M, C₁-C₄alkyl or phenyl, but preferably R₁, R₂ and R₃ are each hydrogen; and M is hydro­ gen, an alkali- or alkaline earth metal, ammonium or an amine residue; B is a moiety having the formula II in which R₄ and R₅, independently, are hydrogen, phenyl, C₁-C₄alkyl (optionally substituted by an hydroxyl group or a carboxyl group, or interrupted by an oxygen atom or a carbonyl group), SO₃H, halogen, hydroxyl or C₁-C₄alkoxy, R₄ and R₅ preferably each being hydrogen; X is hydrogen or -CO₂M wherein M has its previous significance; and Y is -CO₂M wherein M has its previous significance or X and Y together may form an anhydride group; and D is a moiety different from B and having the formula III wherein R₆ is hydrogen, methyl or a residue -COOR₈ in which R₈ is hydrogen or C₁-C₄alkyl group; R₇ is hydrogen, C₁-C₄alkyl, hydroxymethyl or -COOR₉ in which R₉ is hydrogen, a residue of formula IV or a residue of formula V -[CH₂-CH(R₁₀)O] z H (V) in which R₁₀ is hydrogen, methyl or phenyl and z is an integer from 1 to 20, or R₉ is a straight or branched chain alkyl having 1 to 4 carbon atoms or C₁-C₄alkyl substituted by -SO₃M or by -COOM where M has its previous significance; Z is -COOR₉ where R₉ is as defined above, or Z is a straight or branched alkyl having 1 to 4 carbon atoms or said alkyl substituted by one to three carboxylic acid groups; or Z is phenyl or said phenyl substituted by -SO₃M or by -PO₃M₂; or Z is acetoxy, hydroxy, hydroxymethyl, acetoxy­ methyl, -CH₂SO₃M, -CH₂PO₃H₂, -PO₃M₂, -PO₃M′₂ in which M has its previous significance and M′ is M or alkyl of 1 to 4 carbon atoms; or Z is a residue -CONR₁₁R₁₂ wherein R₁₁ and R₁₂ are the same or different and each is hydrogen, straight or branched chain alkyl having 1 to 4 carbon atoms, hydroxymethyl, -CH(OH)COOM, -C(CH₃)₂CH₂SO₃M, -C(CH₃)₂CH₂PO₃M₂ or -N(R₁₃)COCH₃ in which R₁₃ is hydrogen or straight or branched chain alkyl of 1 to 4 carbon atoms and M its previous significance; m is an integer, n is 0 or an integer and p is 0 or an in integer. Preferably the values of m, n and p being such that the molecular weight of the polymer ranges from 500 to 10,000 while retaining its water solubility. Preferred ratios of moieties A, B and D in the polymer are determined by the preferred requirements that A constitutes 100 % to 10 % of the total polymer; B constitutes 0 to 90 % of the total polymer; and D constitutes 0 to 25 % of the total polymer, each by weight on total polymer. Salts of the polymers used in the method of the invention are products in which some or all of the acidic hydrogens in acidic polymers have been replaced by alkali metal ions, ammonium ions or quaternised amine radicals. These salts also have good activity in inhibiting barium sulfate scale deposition. C₁-C₄alkyl residues R₁, R₂, R₃, R₄, R₅, R₇, R₈, R₉, R₁₁, R₁₂, R₁₃ or Z are e.g. methyl, ethyl, n-propyl, isopropyl or n-butyl residues. Carboxyl-substituted C₁-C₄alkyl residues Z include carboxymethyl, carboxyethyl, carboxypropyl, 1,1-dicarboxymethyl and 2,3,4-tricarboxy­ butyl residues. Alkali metal atoms M or M′ are, particularly, sodium or potassium atoms; alkaline earth metal atoms M or M′ are, preferably calcium, barium or strontium atoms; and amine residues M or M′ are, especially, -N ⁺H(CH₃)₃, -N ⁺H(C₂H₅)₃ or -N ⁺H(CH₂CH₂OH)₃. The polymers used in the method of the present invention may be produced by reacting m moles of C(R₁)(R₂)=C(R₃)SO₃H with n moles of C(R₄)(X)=C(R₅)Y and p moles of CH(R₆)=C(R₇)Z wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, X, Y, Z, m, n and p have their previous significance, under conventional free radical-initiated polymerisation processes. Depending upon the solubility of the respective monomer or monomers, the polymeri­ sation is carried out in an aqueous or partially aqueous solution, for instance water/lower alkanol solution, lower alkanols, such as iso­ propanol, or hydrocarbon solvents e.g. toluene or xylene. Conventional free radical initiators which may be used include peroxides e.g. hydrogen peroxide, benzoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butylhydroperoxide; perdicarbonates; persulfates; azobis-isobutyro­ nitrile; and the so-called redox and heavy metal polymerisation initia­ tors. The polymerisation procedure may also include the use of telogens, or chain-transfer agents e.g. alcohols, mercaptans, hypophosphorous acid or orthophosphorous acids or their salts to control the molecular weight of the polymer product. Examples of comonomers of formula C(R₁)(R₂)=C(R₃)SO₃H include vinyl sulfonic acid, β-styrenesulfonic acid, 1-propene sulfonic acid, 2-propene sulfonic acid, sulfomaleic acid and their salts and preferably vinyl sulfonic acid and their sodium salts. Comonomers of formula C(R₄)(X)=C(R₅)Y include acrylic acid and meth­ acrylic acid, maleic acid or anhydride and fumaric acid. Comonomers CH(R₆)=C(R₇)Z include acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, N-vinyl-N-methylacetamide, N-allylacetamide, N-acrylamidoglycollic acid, methacrylic acid, methyl methacrylate, fumaric acids, maleic acid, maleic anhydride, 2-carboxyethyl acrylate, 3-buten-1,2,3-tricarboxylic acid, dimethyl maleate, diethyl maleate, diethyl fumarate, itaconic acid, dimethyl itaconate, allyl sulfonic acid, 4-styrene sulfonic acid, sodium- or potassium salts of 3-sulfopropyl acrylic acid, 2-acrylamido-2-methyl-propane sulfonic acid, vinyl phos­ phonic acid, styrene phosphonic acid, allyl alcohol, allyl acetate, vinyl acetate, styrene, α-methyl styrene, hexene, octene, N-acrylamidopropane sulfonic acid, glycidyl methacrylate, crotonic acid, ethyl crotonate, polyethylene glycol esters and polypropylene glycol esters of (meth)-­ acrylic acids. Alternatively, a salt of the comonomer may be employed in which the acidic hydrogens have been partially or completely replaced by cations M or M′ derived from a suitable salt forming base. The products of the polymerisation process are obtained as solutions. These may be subjected to partial or complete evaporation under reduced pressure. The unpurified reaction products may be used as the polymeric products in the method of the invention. The reaction products may be purified if desired. The purification procedure may be: i) by evaporation of reaction solvent, dissolving the residue in water, washing with a water-immiscible organic solvent e.g. ether and evapora­ tion of the aqueous solution. ii) by evaporation of reaction solvent, dissolving the residue in methanol and reprecipitation by addition of ether. When the reaction products are employed without purification, the ratio of reactants is important in that the activity of the product varies accordingly. Salts of the polymers used according to the invention in which some or all of the acidic hydrogens in the polymer having been replaced by the cations derived from a suitable salt forming base, may be prepared by mixing an aqueous or alcoholic solution of the polymer with an aqueous or alcoholic solution containing an amount of the requisite base in excess of, equal to or less than the stoichiometric requirement. The solvent may then be removed by evaporation. The polymer is preferably added to the water to be inhibited against barium sulfate scale deposition in an amount ranging from 1 to 200 ppm especially from 1 to 30 ppm, based on the weight of the water to be treated. The polymer scale inhibitor used according to the invention may be used alone or in conjunction with other compounds known to be useful in the treatment of aqueous systems, e.g. corrosion inhibitors; dispersing and/or threshold agents; precipitating agents; oxygen scavengers; sequestering agents; antifoaming agents; biocides; and demulsifiers. Corrosion inhibitor co-additives include for example, water soluble zinc salts; phosphates; polyphosphates; phosphonic acids and their salts, for example, hydroxyethyl-diphosphonic acid (HEDP) nitrilotris methylene phosphonic acid and methylamino dimethylene phsophonoacarboxylic acids and their salts, for example, those described in German Offenlegungs­ schrift 2632774, hydroxyphosphonoacetic acid, 2-phosphonobutane-1,2,4-­ tricarboxylic acid and those disclosed in GB 1572406; nitrates, for example sodium nitrate; nitrites e.g. sodium nitrite; molybdates e.g sodium molybdate; tungstates; silicates e.g. sodium silicate; benzo­ triazole, bis-benzotriazole or copper deactivating benzotriazole or tolutriazole derivatives or their Mannich base derivatives; mercapto­ benzothiazol; N-acyl sarcosines; N-acylimino diacetic acids; ethanol­ amines; fatty amines; and polycarboxylic acids, for example, polymaleic acid and polyacrylic acid, as well as their respective alkali metal salts, copolymers of maleic anhydride, e.g., copolymers of maleic anhydride and sulfonated styrene, copolymers of acrylic acid e.g. copolymers of acrylic acid and hydroxyalkylated acrylic acid, and substituted derivatives of polymaleic and polyacrylic acids and their copolymers. Moreover, in such completely aqueous systems, the corrosion inhibitor used according to the invention may be used in conjunction with dispersing and/or threshold agents e.g. polymerised acrylic acid (or its salts), phosphino-polycarboxylic acids (as described and claimed in British Patent 1458235), the cotelomeric compounds described in European Patent Application No. 0150706, hydrolysed polyacrylonitrile, polymerised methacrylic acid and its salts, polyacrylamide and co-polymers thereof from acrylic and methacrylic acids, lignin sulphonic acid and its salts, tannin, naphthalene sulphonic acid/formaldehyde condensation products, starch and its derivatives, cellulose, acrylic acid/lower alkyl hydroxy­ acrylate copolymers e.g. those described in U.S. Patent Specification No. 4029577, styrene/maleic anhydride copolymers and sulfonated styrene homopolymers e.g. those described in U.S. Patent Specification No. 4374733 and combinations thereof. Specific threshold agents, such as for example, 2-phosphonobutane-1,2,4-tri-carboxylic acid (PBSAM), hydroxyethyldiphosphonic acid (HEDP) hydrolysed polymaleic anhydride and its salts, alkyl phosphonic acid, hydroxyphosphonoacetic acid 1-amino­ alkyl-1, 1-diphosphonic acids and their salts, and alkali metal poly­ phosphates, may also be used. Particularly interesting additive packages are those comprising compounds of formula I with one or more of polymaleic acid or polyacrylic acid or their copolymers, or substituted copolymers, HEDP, PBSAM, triazoles such as tolutriazole, molybdates and nitrites. Precipitating agents used may be alkali metal orthophosphates or -carbonates. Oxygen scavengers include alkali metal sulfites and hydrazines; se­ questering agents may be nitrilotriacetic and its salts; antifoaming agents such as silicones, e.g. polydimethylsiloxanes, distearylsebac­ amide, distearyl adipamide and related products derived from ethylene oxide and/or propylene oxide condensations, in addition to fatty alcohols, such as capryl alcohols and their ethylene oxide condensates; biocides include, e.g. amines, quaternary ammonium compounds, chloro­ phenols, sulfur-containing compounds such as sulfones, methylene bis thiocyanates and carbamates, acrolein, isothiazolones, brominated propionamides, triazines, phosphonium compounds, glutaraldehyde, chlorine and chlorine-release agents and organo-metallic compounds such as tributyl tin oxide, and demulsifiers include alkyl phenol resin ethoxylates derived from butyl-, amyl-, octyl- and nonyl-phenols, ethylene oxide-propylene oxide block copolymers polyalkylene oxide esters of mono- and polycarboxylic acids, alkoxylated alkyl amines, alkoxylated polyamines, sulfonated systems, polysiloxane derivatives and cationic polyacrylamides. The following Examples further illustrate the present invention. Example 1: Vinyl Sulfonic Acid/Acrylic acid copolymer (molar ratio 1:3) A solution of 54 parts by weight of acrylic acid, 130 parts by weight sodium vinyl sulfonate (as a 25 % aqueous solution), and 5.5 parts by weight of sodium hypophosphite in 150 parts by weight of water, is prepared and is designated solution 1. A further solution of 1.5 parts by weight of sodium persulfate in 100 parts by weight of water is prepared and designated solution 2. The two solutions (solution 1 and solution 2) are added synchronously, over 2 hours to a reaction vessel containing 60 parts by weight of water at the reflux temperature (100°C). The reflux temperature is maintained for a further 1 hour to give 500.8 parts by weight of polymer solution having a solids content of 20.85 %. HPLC analysis shows the solution to contain only trace amounts (at most 0.5%) of unreacted monomes. Example 2: Vinyl Sulfonic Acid/Maleic Acid Copolymer (Molar ratio 1:1) A solution of maleic acid mono sodium salt is prepared by the addition of 20 parts by weight of sodium hydroxide to a mixture of 49 parts by weight of maleic anhydride in 50 parts by weight of water. To this, is added 216.6 parts by weight of sodium vinyl sulfonate (as a 30 % aqueous solution) and the resulting solution is heated to the reflux temperature (100°C). A further solution of 5.95 parts by weight of sodium persulfate in 32.1 parts by weight of hydrogen peroxide (30 % w/v) is added, dropwise, over 4 hours at 100°C and the heating further continued for 2 hours, to give 346 parts by weight of a polymer solution having a solids content of 43 %. HPLC analysis showed less than 1 % unreacted monomer. Examples 3 and 4: Barium Sulfate Threshold Test A volume (50 ml) of a sodium sulfate solution is added to an equal volume of a solution containing barium chloride and sodium chloride and which already contains the additive under test. After addition of an acetic acid/sodium acetate buffer to buffer the pH at 5.5, the resultant solution is stored at 25°C for 24 hours, and then filtered. At the end of this time the barium remaining in solution is determined by Atomic Absorption (AA). The results are expressed as % inhibition of barium sulfate precipitation. Reagents 1) Solution 1 0.3518 g/l BaCl₂·2H₂O (A.R. quality) and 40.00 g NaCl (A.R. quality). (This gives 98.9 ppm as B⁺⁺ and 20,000 ppm of NaCl in final 100 ml test solution). 2) Solution 2 0.800 g/l Na₂SO₄. (This gives 270.5 ppm as SO₄ in final 100 ml test solution). 3) Solution 3 Molar acetic acid solution - 6.0 g glacial acetic acid (A.R. quality) are dissolved in distilled water and made up to 100 ml. 4) Solution 4 Molar sodium acetate solution - 13.61 g CH₃COONa, 3H₂O (A.R.) quality) are dissolved in distilled water and made up to 100 ml. 5) Solution 5 0.1 % solids additive solutions - the appropriate weight of additive is dissolved in distilled water and adjusted to pH 5.5 with HCl solution or NaOH solution, and made up to 100 ml. Procedure A constant temperature water bath is set at 35°C. 50 ml of solution (1) is placed in a clean, new 4 ounce (113.4 g) glass bottle. 0.10 ml of solution (3) and 1.00 ml of solution (4) are added using a micro-pipette. 0.60 ml (6 ppm) of the additive solution (solution (5)) is added using a micro-pipette. 50 ml of solution (2) is then added. The screw cap is placed on the bottle and the reagents are mixed. The bottle is placed in the constant temperature water bath at 25°C for 4 hours without agita­ tion. 50 ml of the liquor is filtered through a 0.45 micron mesh filter into a 4 ounce (113.4 g) glass bottle using a 50 ml plastic syringe. 20 ml of the liquor is immediately pipetted into a standard 100 ml volumetric flask and diluted to the mark with distilled water. The Ba⁺⁺ concentration of this solution is then determined by Atomic Absorption (AA). All tests are done in duplicate, including blank tests (no additive). Additionally, for the purpose of AA measurement, a matrix solution minus Ba⁺⁺ is required to standardise the instrument. The matrix solution is prepared by dissolving 2 g NaCl (A.R. quality) in 50 ml distilled water in a 4 ounce (113.4 g) glass bottle. 50 ml of solution (2) are added. The reagents are mixed and 50 ml of the mixture pipetted into a 250 ml standard volumetric flask. 150 ml of distilled water are added, without making up to the mark. Calculation Before calculating I, the AA ppm Ba⁺⁺ readings should be multiplied by the dilution faction (i.e. x 5). I % = percentage of inhibition of barium sulfate precipitation. The results are set out in Table I.

Claims: 1. A method of inhibiting barium sulfate scale deposition from water of high barium content, comprising adding to the water an effective amount of a water-soluble polymer, or salts thereof, containing m units of a moiety A, n units of a moiety B and p units of a moiety D, wherein A is a moiety having the formula I in which R₁, R₂ and R₃, independently, are hydrogen, CO₂M, C₁-C₄alkyl or phenyl, but preferably R₁, R₂ and R₃ are each hydrogen; and M is hydro­ gen, an alkali- or alkaline earth metal, ammonium or an amine residue; B is a moiety having the formula II in which R₄ and R₅, independently, are hydrogen, phenyl, C₁-C₄alkyl (optionally substituted by an hydroxyl group or a carboxyl group, or interrupted by an oxygen atom or a carbonyl group), SO₃H, halogen, hydroxyl or C₁-C₄alkoxy, R₄ and R₅ preferably each being hydrogen; X is hydrogen or -CO₂M wherein M has its previous significance; and Y is -CO₂M wherein M has its previous significance or X and Y together may form an anhydride group; and D is a moiety different from B and having the formula III wherein R₆ is hydrogen, methyl or a residue -COOR₈ in which R₈ is hydrogen or C₁-C₄alkyl group; R₇ is hydrogen, C₁-C₄alkyl, hydroxymethyl or -COOR₉ in which R₉ is hydrogen, a residue of formula IV or a residue of formula V -[CH₂-CH(R₁₀)O]zH (V) in which R₁₀ is hydrogen, methyl or phenyl and z is an integer from 1 to 20, or R₉ is a straight or branched chain alkyl having 1 to 4 carbon atoms or C₁-C₄alkyl substituted by -SO₃M or by -COOM where M has its previous significance; Z is -COOR₉ where R₉ is as defined above, or Z is a straight or branched alkyl having 1 to 4 carbon atoms or said alkyl substituted by one to three carboxylic acid groups; or Z is phenyl or said phenyl substituted by -SO₃M or by -PO₃M₂; or Z is acetoxy, hydroxy, hydroxymethyl, acetoxy­ methyl, -CH₂SO₃M, -CH₂PO₃H₂, -PO₃M₂ or -PO₃M′₂ in which M has its previous significance and M′ is M or alkyl of 1 to 4 carbon atoms; or Z is a residue -CONR₁₁R₁₂ wherein R₁₁ and R₁₂ are the same or different and each is hydrogen, straight or branched chain alkyl having 1 to 4 carbon atoms, hydroxymethyl, -CH(OH)COOM, -C(CH₃)₂CH₂SO₃M, -C(CH₃)₂CH₂PO₃M₂ or -N(R₁₃)COCH₃ in which R₁₃ is hydrogen or straight or branched chain alkyl of 1 to 4 carbon atoms and M its previous significance; m is an integer, n is 0 or an integer and p is 0 or an in integer. 2. A method according to claim 1 in which the values of m, n and p being such that the molecular weight of the polymer ranges from 500 to 10,000 while retaining its water solubility. 3. A method according to claim 1 in which A constitutes 100 to 10 % of total polymer; B constitutes 0 to 90 % of total polymer; and D consti­ tutes 0 to 25 % of total polymer, each by weight of total polymer. 4. A method according to claim 1 wherein A is derived from vinyl sulfonic acid, β-styrenesulfonic acid, 1-propene sulfonic acid, 2-propene sulfonic acid and sulfomaleic acid. 5. A method according to claim 3 wherein A is derived from vinyl sulfonic acid. 6. A method according to claim 1 wherein B is derived from acrylic acid, methacrylic acid, maleic acid or anhydride or fumaric acid. 7. A method according to claim 1 in which the polymer containing units of formula I is added to the water in an amount ranging from 1 to 200 ppm, based on the weight of the water to be treated. 8. A method according to claim 7 wherein the polymer is added in amount ranging from 1 to 30 ppm, based on the weight of water to be treated. 9. A method according to claim 1 in which the polymer containing units of formula I is added to the water together with one or more of corrosion inhibitors; dispersing and/or threshold agents; precipitating agents; oxygen scavengers; sequestering agents; antifoaming agents; biocides and demulsifiers. 10. A method according to claim 9 in which the polymer containing units of formula I is added to the water together with one or more of poly­ maleic acid or polyacrylic acid or their copolymers, or substituted copoylmers, HEDP, PBSAM, triazoles such as tolutriazole, molybdates and nitrites.

Inventors: COOK, BARRY, DR.
Applicants: CIBA-GEIGY AG
Application year: 1988
Main classification: C02F5
IPC codes: C02F5