GB2213933A - Method for monitoring polyacrylic scale-inhibitor content in the presence of interfering polyvalent cation - Google Patents

Description

t F-4672 J "' 2 13 '/'3 ' D FOR MONITORING POLYACRYLIC SCALE-INHIFITOR

CONTENT IN IBE PRESENW OF INTERFERING POLYVALM CATION Scale deposits frequently occur in the production of water, oil and gas from subterranean formation and can result in plugged well bores, plugged well casing perforations, plugged tubing - strings, stuck downhole safety valves as well as other valves, stuck downhole pumps and other downhole and surface equipment and lines, scaled formations and fractures in the vicinity of the well. Scale formation can occur as a result of mixing incompatible waters in the well which produce precipitates, or as a result of temperature and pressure changes and the like in the produced waters during production. Generally, incompatible waters occur in waterflooding, as injected sea water mixes with formation water in the borehole during water breakthrough. The more common concern is scale deposited due to changes in supersaturation or solubility of minerals in the formation or produced waters caused by pressure and temperature changes, or changes in other physical and chemical environments such as gas compositions, ratio of gas/oil/water. Scale formation is also a problem in aqueous systems used in cooling towers, boilers and the like. Precipitation frequently encountered as scale include calcium carbonate, calcium sulfate, barium sulfate, magnesium carbonate, magnesium sulfate, and strontium sulfate.

Scale formation can be reduced by the introduction of inhibitors into the formation. Various inhibitors are known including a widely used class of materials which are carboxylated polymers. Typically, these are polymers and copolymers of acrylic or methacrylic acids, commonly referred to as polyacrylic acids.

As disclosed in U.S. Patent 4,514,504, it is desirable to have a method for monitoring the polyacrylic acid content of aqueous systems to make economical decisions in the field concerning the

C, need for adding polyacrylic acids to maintain optimum levels. U.S.

F-4672 Patent 4,514,504 discloses a monitoring system which I have found is unsatisfactory where the aqueous system containing polyacrylic acid also contains ions having a valence greater than 2, such as iron (III), Cr (III) and Al (III), which forr complexes with the polyacrylic acid.

Accordingly, this invention constitutes an improvement on the monitoring method disclosed in U.S. Patent 4,514,504 in which quantitative monitoring of polyacrylic acids of aqueous systems also containing ions of a valence greater than 2 is possible.

The polyacrylic acid content of an aqueous system containing an interfering poiyvalent cation is quantitatively determined by contacting the polyacrylic acid complexed with polyvalent cation with an ion-exchange resin to substantially remove the interfering polyvalent cation and then analyzing the aqueous C, system in the conventional way for its polyacrylic acid content. Interfering polyvalent cations have a valence greater than or equal to 2 and include Fe (III), Cr (III) and Al (III).

Fig. I contains plots of absorbance vs. content of polyacrylic acid inhibitor in the absence of Fe (III), and in the presence of 25 ppm Fe (III) obtained without the use of the ion-exchange step in accordance with this invention.

Fig. 2 contains plots of absorbance vs. content of polyacrylic acid inhibitor in the presence of Fe (III), Cr (III) and Al (III) obtained using the ion-exchange step of this invention.

Polyacrylic acid inhibitors which can be quantitatively analyzed in accordance with this invention include all homopolymers or copolymers composed of two or more co-monomers -containing as one of its components, an alpha, beta-ethylenically unsaturated acid monomer such as acrylic acid, methacrylic acid, diacids such as maleic acid (or maleic anhydride), itaconic acid, fumaric acid, mesoconic acid, citraconic acid and the like, monoesters of diacids with alkanols having 1-8 carbon atoms, and mixtures thereof. When the inhibitor is a copolymer, the other component monomers can be any alpha, beta -ethyl en ically unsaturated monomer with either 1 1 Jl> A 1 1 1 F-4672 non-polar groups such as styrene or olefinic monomers or polar funtional groups such as vinylacetate, vinyl chloride, vinyl alcohol, acrylate ester, vinylpyridine, vinyl pyrrolidone, acrylamide or acrylamide derivatives, etc., or with ionic functional -groups such as styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylsulfonic acid, vinyl phos phonic acid. The polyacrylate inhibitor includes modification of the polymers described above such as phosphinopolyacrylic acid sold under the tradename "Belsperse 16111 or "Belasol S29" by Ciba Geigy. The preferred polyacrylate inhibitor is phosphinopolyacrylic acid.

The step of treatment of the inhibitor solution with cationic exchange resin which is essential to this invention is conducted in the known manner. Generally, the sample to be analyzed, preferably adjusted to a pH of 2, is slowly eluted in a column packed with the ion exchange resin, e. g., over a period of 5 to 60 minutes. The column is rinsed with a measured quantity of water and the rinse water is collected with the exchanged sar[q)le for conventional analysis.

Suitable cation-excbange resins are commercially available. They are generally strong-acid resins which are typically sulfonated copolymers of styrene and divinylbenzene. Such resins are available from DOW under the trademark "DOWTV'.

The steps of analysis subsequent to treatment with ion-exchange resin are conventional and described in U.S. Patent 4,514,SO4. Broadly, the conventional steps comprise adsorbing the cation-exchanged sample at a pH of 2 to 3.5 on a" non-polar adsorbent such as non-polar, bonded phase silica gel and rigid, ipacroreticular styrene -d ivinylbenz ene polymer; desorbing the polyacrylic acid from the adsorbent with a displacement fluid such as methanol or aqueous sodium hydroxide; and determining the carboxyl content of the polyacrylic acid content by the iron-thiocyanate method.

The iron-thiocyanate method is based on the formation of a colorless complex between iron (III) and polyacrylic acids wbile a F-4672 6 complex formed between iron (III) and thiocyanate ions is red. Therefore, a decrease in the color of iron-thiocyanate complex, upon complexing of iron with polyacrylic acids, is directly proportional to the polyacrylic acid concentration.

After the iron (III) has been allowed to complex with the polyacrylic acids to form the colorless complex, potassium thiocyanate is added as an aqueous solution to the complex. The thiocyanate (SCN-) ions will react with non-complexed iron (III) ions to form the red iron-thiocyanate complex.

Therefore, the color of the resulting solution can be correlated with the quantity of iron (III) and thiocyanate ion added to arrive at the concentration of the polyacrylic acids. The color of the resulting solution, in terms of the percentage of light transmitted therethrough, is an accurate measure of the polyacrylic acid concentration.

The invention is illustrated Ly the following non-limiting example in which all parts are by weight unless otherwise specified.

COMPARATIVE EXPTLE 1 Belsperse 161, a commercial phosphiDo-polyacrylic acid from Ciba Geigy was used as the model polyelectrolyte inhibitor. A master brine solution containing the following salts was prepared.

Salt M9C12 6H20 CaCI 2 2 H 2 0 BaCI 2 2 H 2 0 SrCl 2 6 H 2 0 Kcl NaCl deionized H 2 0 to 1 1 iter grams/liter 0.770 2.000 0.240 0.530 0.658 49.190 The prior art procedure was conducted on 30 cc of sample solutions as follows. The pH of the sample solution was adjusted and buffered

0i :5 a 4 9 F-4672 --5-- to 2.5. The low pH suppresses ionization of the inhibitor for better adsorption to the LC cartridge. The non-polar LC cartridge (Sep-PAK C18) is pre-conditioned by eluting with 20 cc of water at pH 2.5. The adsorption was accomplished by attaching the top of the LC cartridge to the fitting of a 3-way syringe valve. one end of the valve was connected to a 30 cc Luer-Lock syringe while the other end was attached to a flexible tubing used to aspirate or to discard liquids. After pre-rinsing the syringe with 5 cc of sample solution, 20 cc of sample solution was aspirated and pumped thru the LC cartridge over at least 15 seconds to adsorb the inhibitor. The eluted solution was discarded. The syringe was rinsed with 5 cc of de-ionized water and then with 5 cc of cluant (60% methanol solution in water). 15 cc of the eluant was then aspirated and pumped thru the LC cartridge over at least 45 seconds. The eluant was diluted with de-ionized water to a final weight of 25 grams. A color reaction was started with the diluted eluant by adding 1 cc of reagent 1 (which contains ferric ions to complex with the inhibitor), then waiting 5 minutes before adding 1 cc of reagent 2 (potassium thiocyanate). After 5 more minutes, the absorbance of the thus treated sample was measured at 480 nm using de-ionized water as reference. The concentration of the carboxylated inhibitor is detected by its interference of full color development of the ferri-thiocyanate complex in which Fe III is quantitatively complexed.

Analysis of Belsperse 161 in the absence of Fe (III) or other trivalent metal ions using the prior art method was conducted using 2, 5 and 10 ppm standard solutions of Belsperse 161 in the master brine solution. No Fe (III) or other trivalent cations were introduced. In the absence of Fe (III), or other trivalent ions, a linear standard plot was obtained from 2 to 10 ppir as shown in the lower plot in Figure 1. The 6 ppm point which fit into the standard plot was obtained by loading three times the volume of 2 ppm standard inhibitor sample thru the LC column.

F-4672 --6-- COWARATIVE EXMPLE 2 Samples containing trivalent ion were prepared by adding 25 ppm of Fe (III) to each of the standard solutions of the Comparative Example 1. The normal prior art procedure was unable to detect the presence of any Belsperse 161. This result suggests that Fe (III) forms a complex with Belsperse 161 even at low pH, that the complex is positively charged and does not adsorb on the non-polar adsorbent. Thus, the normal procedure is not capable of analyzing a carboxylated polyelectrolyte when an ion with a valence greater than 2, such as iron, is present.

EXAMPLE I

This example illustrates the quantitative analysis of polyacrylic acid which is present in a solution which also contains trivalent ion.

An ion exchange column was prepared with 30.0 graws of sulfonic acid cation-exchange resin (Dowex 50 x 8 with exchange capacity of 5 meq/g in the hydrogen form). Sample solutions at p14 2 containing trivalent ion were eluted in a column containing the ion exchange resin over 10 minutes. A 3S cc portion of a pH 2 de-ionized water is added to the column to rinse. The entire collected ion exchanged sample is brought to pF 2.5 and put through the prior art procedure described in the Comparative Examples. The results summarized in Figure 2 show that in the presence of 25 ppm Fe (III), an excellent calibration curve is obtained over the range of zero to 15 ppm Pelsperse 161 concentration in the brine solution. No interference is seen even when the FO (III) is raised by a factor of 4 to 100 ppm. This ion-exchange method is of general usage and works well when Fe (III) is replaced by either Cr (III) or Al (III), also as shown in Figure 2.

i J 9 F-4672

Claims (1)

1. CLAIMS:

   1. A method for determining the concentration of polyacrylic acid in a solution containing polyvalent cation having a valence greater than or equal to 2 and capable of complexing with, said polyacrylic acid comprising (a) contacting polyacrylic acid complexed with polyvalent cation with an ion-exchange resin to substantially remove said polyvalent cation from said polyacrylic acid; and (b) analyzing the ion-exchange treated solution for its polyacrylic acid content.

   2. The method of claim I in which said polyvalent cation is Cr (III), Fe (III) or Al (III).

   3. The method of claiin 1 in which the concentration of polyacrylic acid is determined by the iron-thiocyanate colorimetric procedure.

   4. The method of claim I in wbich said polyacrylic acid is a water soluble polymer selected from homopolymers of acrylic acid, methacrylic acid, and maleic acid, and copolymers from at least 50 weight percent acrylic acid, methacrylic acid, or maleic acid and less than 50 weight percent of a different copolymerizable monomer.

   S. The method of claim 3 in which said-polyacrylic acid is a water soluble polymer selected from the group consisting of homopolymers of acrylic acid, methacrylic acid, and maleic acid, and of copolymers from at least 50 weight percent acrylic acid, methacrylic acid, or maleic acid and less than 50 weight percent of a different copolymerizable monomer.

   F-4672 --8-- 6. A method for determining the concentration of polyacrylic acid in an aqueous solution containing polyvalent cation having a valence greater than or equal to 2 and capable of complexing with said polyacrylic acid comprising: (a) adjusting the pH of said aqueous solution to suppress ionization of said polyacrylic acid; (b) contacting the polyacrylic acid complexed with polyvalent cation with an ion-exchange resin to substantially remove said polyvalent cation; (c) selectively adsorbing said ion suppressed polyacrylic acid on a non-polar adsorbent; (d) desorbing said adsorbed, ionization suppressed, polyacrylic acids from said adsorbent with a suitable displacement fluid; and (e) measuring the concentration of the desorbed polyacrylic acid.

   7. The method of claim 6 in which said polyvalent cation is Cr (III), Fe (M) or Al (III).

   8. is Fe (M).

   The method of claim 7 in which said polyvalent cation 9. The method of claim 6 in which the concentration of polyacrylic acid is determined by the iron-thiocyanate colorimetric procedure.

   10. The method of claim 6 in which said polyacrylic acid is a water soluble polymer selected from the group consisting of homopolymers of acrylic acid, methacrylic acid, and maleic acid, and copolymers from at least 50 weight percent acrylic acid, metbacrylic acid, or maleic. acid and less than 50 weight percent of a different copolymerizable monomer.

   4421h/0403h Published 1988 at The Patent Office. State House. 66'71 High Holborr.. London WC1R - 4TP. Ptirther copies may be obtained from The Patent Office.

   tedty Multip,ex techniques Md. St Ma-y Crky Kcn, Con 187 Sales Branch, St Mary Cray. Orpington. Kent BR5 3RD Prir 1 v