Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/52—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning
  • C09K8/528—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning inorganic depositions, e.g. sulfates or carbonates
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
  • C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
  • C02F5/10—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances

Definitions

• the present invention relates to a relatively high molecular weight polyvinyl sulfonate and to a process for inhibiting scale deposition, particularly inorganic sulfate such as barium sulfate, in a subterranean formation utilizing an aqueous solution having the relatively high molecular weight polyv yl sulfonate dissolved therein.
• inorganic salts such as calcium carbonate and calcium, barium, and strontium sulfate
• scale deposits is a persistent and common problem encountered in many field operations for the recovery of hydrocarbons from subterranean formations.
• EOR enhanced oil recovery
• Two or more aqueous fluids are incompatible if each fluid contains distinct ions which form a precipitate and deposit as a scale when the two or more aqueous fluids are commingled.
• the connate water or brine present in a reservoir will contain barium, calcium and/or strontium ions while water injected into the subterranean formation during EOR operations will contain sulfate ions.
• offshore operations may involve the injection of large volumes of sea water containing a relatively large concentration of sulfate ions into a subterranean formation having brine containing relatively large concentrations of barium, calcium, and strontium.
• precipitation of barium, calcium, or strontium sulfate will occur in the formation and the subsurface and surface production equipment and/or tubing.
• Commingling of incompatible aqueous fluids usually occurs within the near production well bore environment of a subterranean formation.
• Injection of carbon dioxide into a subterranean hydrocarbon-bearing formation as an EOR method results in absorption of carbon dioxide by connate water present in the formation.
• some subterranean formation brines such as those found in the North Sea, may naturally contain a relatively large concentration of carbon dioxide.
• pressure is reduced, for example during production, carbon dioxide flashes off to the gas phase thereby increasing the pH of the aqueous fluids and permitting formation of calcium carbonate scale predominantly in the near production well bore environment of the formation and in subsurface and surface production equipment and/or tubing.
• the present invention provides a process for inhibiting scale deposition, particularly inorganic sulfate deposition, from aqueous fluid present in and/or produced from a subterranean formation by contacting such fluid with an aqueous solution having a- novel, relatively high molecular weight polyvinyl sulfonate dissolve i therein.
• the polyvinyl sulfonate has a molecular weight of from about 9,000 to about 30,000, preferably from 10,500 to about 25,000, and more preferably from about 12,000 to about 20,000.
• the polyvinyl sulfonate has a polydispersity of less than about 2.0.
• the aqueous fluid is contacted with the aqueous solution having polyvinyl sulfonate dissolved therein, for example by means of a squeeze treatment via a production well bore in fluid communication with the formation.
• the polyvinyl sulfonate of the present invention is dissolved in an aqueous solution in an amount of from about 0.4 to about 25 volume percent of the total solution.
• the pH of the aqueous fluid is equal to or less than 6.0.
• Figure 1 is a graph illustrating the percent barium efficiency, i.e., barium sulfate scale inhibition, of polyvinyl sulfonate at a pH of 4 and 6 as a function of molecular weight of the polyvinyl sulfonate;
• Figure 2 is a graph illustrating the calorim ' etric titration curves for an uninhibited and several polyvinyl sulfonate inhibited sulfate brines titrated with barium brine;
• Figure 3 is a graph indicating the change in heat of reaction for each of the several polyvinyl sulfonate inhibited sulfate brines which are titrated with barium brine;
• Figure 4 is a graph of the percent barium efficiency, i.e., barium sulfate scale inhibition, of differing molecular weight polyvinyl suifonates at a pH of 4 and 6 as a function of the concentration of polyvinyl sulfonate.
• the present invention relates to a scale inhibitor composition
• a scale inhibitor composition comprising an aqueous solution having a relatively high molecular weight polyvinyl sulfonate dissolved therein and to a process which employs this scale inhibitor composition to effectively inhibit the deposition of scale, particularly inorganic sulfate scale, from aqueous fluids present in a subterranean formation and subsurface and/or surface hydrocarbon production tubing and/or equipment.
• the term "molecular weight” refers to the weight average molecular weight of polyvinyl sulfonate. The weight average molecular weight is determined from experiments in which each molecule or chain makes a contribution to the measured result.
• polydispersity refers to the weight average molecular weight of polyvinyl sulfonate divided by the number average molecular weight of polyvinyl sulfonate. The number average molecular weight is calculated by dividing the sum of the individual molecular weight values by the number of molecules.
• an aqueous solution having a relatively high molecular weight polyvinyl sulfonate dissolved therein is injected into a subterranean formation via a production well in fluid communication therewith to effectively inhibit scale formation in aqueous fluids present in the formation and/or in surface and subsurface production tubing and/or equipment when the well is returned to production.
• a polyvinyl sulfonate having a molecular weight of from about 9,000 to about 30,000 results in an unexpected improvement in the inhibition of scale, particularly inorganic sulfate scale such as barium sulfate, from these aqueous fluids.
• the polyvinyl sulfonate of the present invention has a molecular weight of from about 9,000 to about 30,000, more preferably from about 10,500 to about 25,000, and most preferably from about 12,000 to about 20,000. Preferably, the polyvinyl sulfonate of the present invention has a polydispersity of less than about 2.0.
• the polyvinyl sulfonate of the present invention is thermally stable.
• the polyvinyl sulfonate scale inhibitor of the present invention is prepared by polymerizing a commercially available aqueous solution of vinyl sulfonic acid, sodium salt, such as that manufactured by Air Products & Chemicals, Inc., Aldrich Chemical Co., Inc. or Farbwerke Hoechst AG.
• aqueous solutions of vinyl sulfonic acid, sodium salt are commercially available from Air Products & Chemicals, Inc. and Farbwerke Hoechst AG, respectively.
• the vinyl sulfonic acid, sodium salt, solution may contain a polymerization inhibitor, e.g. 100 ppm of methylether hydroquinone.
• the particular polymerization inhibitor employed can be extracted by passing the monomer, i.e. the vinyl sulfonic acid, sodium salt, slowly through a column packed with a suitable resin as will be evident to a skilled artisan. The monomer solution is purged for about an hour with nitrogen at room temperature while the solution is stirred to remove oxygen therefrom.
• a suitable catalyst such as ammonium persulfate
• ammonium persulfate is also purged with the nitrogen and then added to the monomer solution at room temperature.
• the resulting solution is continually stirred at room temperature for a sufficient period to allow for maximum conversion of the monomer to polyvinyl sulfonate.
• the resultant polymerization solution contains deleterious by-products of sulfonation, such as sulfate ions or hydroxyethyl sulfonate
• polyvinyl sulfonate can be separated from these deleterious by-products of sulfonation by any suitable method as will be evident to the skilled artisan.
• this separation is accomplished by the addition of methanol to effect a liquid/liquid separation of polyvinyl sulfonate from the solution containing deleterious by-products of sulfonation.
• methanol a liquid/liquid separation of polyvinyl sulfonate from the solution containing deleterious by-products of sulfonation.
• This method is described in a commonly assigned, co-pending patent application entitled “Process for Recovering and Purifying a High Molecular Weight Sulfonate" to Richard T. Barthorpe which was filed concurrently herewith.
• the polyvinyl sulfonate scale inhibitor of the present invention is incorporated into an aqueous solution in an amount effective to inhibit the formation of scale in aqueous fluids present in and/or produced from a subterranean formation.
• the aqueous solution having the polyvinyl sulfonate scale inhibitor of the present invention dissolved therein can be introduced into contact with aqueous fluids present in a subterranean formation and/or in surface and/or subsurface production tubing and/or equipment in any suitable manner known to those skilled in the art such as, by metering into aqueous fluid present in a production well bore through a small diameter tube, e.g. 4-I inch, by injection through a gas lift valve, or by introducing encapsulated polyvinyl sulfonate into a production well bore.
• an aqueous solution of the polyvinyl sulfonate of the present invention is injected into a subterranean formation via a production well bore in fluid communication therewith and can be followed by an overflush, for example a brine containing a relatively low quantity of sulfate ions, i.e. a brine which is compatible with formation fluids.
• the production well bore may be shut in for a suitable period, for example, zero to twenty- four hours, and thereafter is returned to production.
• the polyvinyl sulfonate is absorbed within formation matrix during the shut-in period and is subsequently desorbed over a period of time into aqueous fluids present in and produced from the formation to effectively inhibit scale deposition, particularly inorganic sulfate scale such as barium sulfate scale.
• the polyvinyl sulfonate of the present invention should be inco ⁇ orated into an aqueous solution to be squeezed into a subterranean formation in an amount of from about 0.4 to about 25 volume percent, more preferably in an amount of from about 2 to about 20 volume percent, and most preferably in an amount of from about 5 to ' about 10 volume percent, of the solution to effectively inhibit scale formation upon being desorbed into aqueous fluids present in and produced from the formation.
• aqueous fluids produced from the subterranean formation will be analyzed for inhibitor concentration to ensure that an appropriate concentration of inhibitor is present in produced fluids to effectively inhibit scale deposition and to determine the need for subsequent squeeze treatments.
• the process of the present invention can be utilized to inhibit scale, particularly inorganic sulfate scale such as barium sulfate scale, from aqueous fluids contained in and/or produced from any subterranean formation in which incompatible aqueous fluids may commingle, for example, during an EOR operation, and/or in which the aqueous fluids present in the formation contain a relatively large concentration of carbon dioxide.
• scale particularly inorganic sulfate scale such as barium sulfate scale
• the polyvinyl sulfonate scale inhibitor and process of the present invention are employed to effectively inhibit scale from aqueous fluids present in or produced from a subterranean formation which have a pH equal to or less than about 6.0 and more preferably equal to or less than about 4.0.
• the process of the present invention is applicable to a wide variety of subterranean formation temperatures and mineralogies.
• Aldrich Chemical Co., Inc. is passed through a resin column to remove methylether hydroquinone which is employed as a polymerization inhibitor for the vinyl sulfonic acid, sodium salt monomer during transportation. 1000 g of vinyl sulfonic acid, sodium salt is charged to a reaction flask and is purged with nitrogen at room temperature for one hour while stirring to remove oxygen therefrom. Ammonium persulfate is added to 25 ml of nitrogen purged distilled water in an amount to obtain an ammonium persulfate concentration of 0.1g/ml. The mixture is then heated to 50° C.
• Example 1 The polymerization reaction set forth in Example 1 is repeated except that the vinyl sulfonic acid, sodium salt charged to the reactor is reduced to 100 g the concentration of ammonium persulfate present in the reaction solution is increased to 0.50 mg/ml, the reaction temperature is reduced to room temperature, i.e. 22.2° C, and the reaction time is reduced to eight hours.
• This polymerization reaction results in 53.2% conversion of monomer to a polyvinyl sulfonate which is determined to have a molecular weight of about 13,565 and a polydispersity of about 2.0.
• Example 2 The polymerization reaction set forth in Example 2 is repeated except that the concentration of ammonium persulfate catalyst employed in the reaction solution is increased to 1.0 mg/ml and the reaction time is extended to three days. This polymerization reaction results in a 78% conversion of monomer to a polyvinyl sulfonate which is determined to have a molecular weight of about 15,542 and a polydispersity of about 1.99.
• Example 2 The polymerization reaction of Example 2 is repeated except that the concentration of ammonium persulfate catalyst employed in the reaction solution is decreased to 0.25 mg/ml and the reaction time is increased to twenty-four hours. This polymerization reaction results in a 68% conversion of monomer to a polyvinyl sulfonate which is determined to have a molecular weight of about 16,269 and a polydispersity of about 1.70.
• Example 2 The polymerization reaction of Example 2 is repeated except that the concentration of ammonium persulfate catalyst employed in the reaction solution is increased to 1.0 mg/ml, a co-catalyst, triethanolamine, is also employed at a concentration of 1.2 wt % in the reaction solution, and the reaction time is increased to twenty-four hours.
• This polymerization reaction results in a 22% conversion of monomer of a polyvinyl sulfonate which is determined to have a molecular weight of about 18,887 and a polydispersity of about 1.82.
• Example 2 The polymerization reaction of Example 2 is repeated except that the concentration of ammonium persulfate catalyst employed in the reaction solution is decreased to 0.25 mg/ml and the reaction time is increased to five days. This polymerization reaction results in a 72% conversion of monomer to a polyvinyl sulfonate which is determined to have a molecular weight of about 18 902 and a polydispersity of about 1.81.
• Example 2 The polymerization reaction of Example 2 is repeated except that a 37.5 wt % solution of vinyl sulfonic acid, sodium salt, is utilized in lieu of a 25% solution, the concentration of ammonium persulfate catalyst present in the reaction solution is decreased to 0.25 mg/ml and the reaction time is increased to three days.
• This polymerization procedure should result in an adequate conversation of monomer to a polyvinyl sulfonate which is determined to have a molecular weight approximating 25,000 and a polydispersity of less than about 2.0.
• Example 2 The polymerization reaction of Example 2 is repeated except that a
• BaCl2*2H2 ⁇ , 0.157 g of SrCl2*6H2 ⁇ , 3.486 g KCI, and 55.626 g of NaCl per liter is adjusted to a pH of either 4 or 6, depending on the exact pH test being run, by adding hydrochloric acid to lower the pH or sodium hydroxide to raise the pH.
• 100 ppm of the particular polyvinyl sulfonate obtained in Examples 1 -6 above to be tested is added to 100 ml of brine B containing 60.155 g NaCl and 1.597 g of Na2S04 per liter.
• the pH of the resultant brine B mixture is adjusted to either pH 4 or 6, depending on the test to be run, by adding hydrochloric acid to lower the pH or sodium hydroxide to raise the pH.
• Subsequent mixing of equal volumes of brines A and B simulates an 80% formation or connate water and 20% seawater brine which is representative of an aqueous formation fluid obtained when North Sea seawater is utilized as a drive fluid in a Brae field subterranean formation.
• the Brae field is located in the United Kingdom section of the North Sea.
• 0.01 g of barium sulfate, i.e. seed crystals are added to a screw top glass culture tube.
• 5.00 ml of brine B (containing inhibitor) are added to the glass tube using a volumetric pipet.
• the resultant suspension is filtered through a 0.2 micrometer syringe filter to remove solid barium sulfate and approximately 2 g of the filtrate are weighed into a plastic tube containing 5.0 g of deionized water and 0.5 g of basic EDTA solution to chelate the barium contained in the filtrate.
• the remaining suspension is returned in the glass tube to the shaker bath and mixed for an additional hour.
• the resultant suspension is again analyzed as above and the filtered samples are analyzed for barium concentrations by ICAP analysis.
• the percent barium efficiency of the polyvinyl sulfonate inhibitor is calculated by determining the amount of barium ion in the final solution, dividing that amount by the amount of barium ion in the initial brine A + B solution, and multiplying by 100%. The results of this testing are depicted in Figure 1.
• the barium brine was added as a titrant to 50 ml of the sulfate brine containing 0.75 mMole sulfate at a rate of 0.00664 ml per sec. for a total period of 290 sec. A total of about 0.96 mMole of barium was added to the sulfate brine resulting in an excess of 0.21 mMole of barium.
• This calorimeter includes a 600 RPM synchronous motor which drives a glass stirrer to provide thorough mixing.
• the results of this titration of sulfate brine with barium brine are illustrated in Figure 2 as calorimetric titration curve B.
• Line A represents the heat of stirring and heat of dilution of sodium salts which are determined by adding the barium brine as set forth above to a 3 wt % sodium chloride solution.
• the total heat of reaction for the titration performed is calculated by extrapolating the slope of the titration curve B for the first 100 seconds of the test, i.e.
• a premeasured quantity of each polyvinyl sulfonate Fraction is added to separate sulfate brines to inhibit formation of barium sulfate precipitate.
• thermometric titration curves are plotted in Fig. 2 and respectively labeled as curves C-G.
• the total heat of reaction for each titration C-G is calculated and is subtracted from the total heat of reaction for titration B to yield a change in the heat of reaction which indicates the amount of reaction, and therefore barium sulfate precipitation, which is inhibited, by each polyvinyl sulfonate Fraction.
• Example 9 The seeded bottle test procedure set forth in Example 9 above was repeated at six different concentrations and at a pH of 4 and 6 for each of the polyvinyl suifonates obtained from the procedures demonstrated in Examples 1 -4 above.
• the results which are depicted in Figure 4 demonstrate that the concentration of polyvinyl sulfonate scale inhibitor of the present invention in an aqueous fluid in which the formation of scale is to be inhibited should be at least about 50 ppm, more preferably at least about 75 ppm, and most preferably at least about 100 ppm to result in the unexpected increase in the percent barium efficiency at a pH of 4 and 6 of the process of the present invention.
• an aqueous solution containing the polyvinyl sulfonate scale inhibitor of the present invention does not dissolve calcium carbonate scale to any appreciable degree when injected into a subterranean formation via a production well bore. Accordingly, the presence of calcium carbonate scale in a production well bore or the near well bore environment of a formation does not adversely affect the efficiency of the polyvinyl sulfonate scale inhibitor of the present invention. Further, it has been determined that the polyvinyl sulfonate scale inhibitor of the present invention has a significantly greater degree of inhibition of barium sulfate scale on calcium carbonate seeds than conventional polyphosphonate or polycarboxylate scale inhibitors.

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• 1990
  • 1990-08-24 WO PCT/US1990/004824 patent/WO1991006511A1/en active Application Filing
  • 1990-08-24 NL NL9021596A patent/NL9021596A/nl not_active Application Discontinuation
  • 1990-08-24 DE DE19904092063 patent/DE4092063T/de not_active Ceased
  • 1990-08-24 AU AU64018/90A patent/AU6401890A/en not_active Abandoned
• 1992
  • 1992-02-03 GB GB9202274A patent/GB2250738B/en not_active Expired - Lifetime
  • 1992-04-28 NO NO921642A patent/NO303010B1/no unknown

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