Classifications

• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S422/00—Chemical apparatus and process disinfecting, deodorizing, preserving, or sterilizing
  • Y10S422/901—Polymer dissolver

Definitions

• the present invention relates to a process for preventing, or at least substantially reducing, the formation of scale, and the like, water insoluble deposits on equipment during the dilution of aqueous solutions of polymers such as partially hydrolyzed polyacrylamides.
• the process of the present invention involves the preparation of aqueous polymer solutions having special utility as drive fluids and/or mobility buffers in the secondary or tertiary recovery of oil from subterranean oil-bearing formations or reservoirs.
• Such solutions are generally prepared from a water soluble, ethylenically unsaturated monomer containing at least one vinyl grouping wherein the vinyl is an acrylyl, a vinyl cyanide, a styryl, and water soluble salts thereof.
• the vinyl is an acrylyl it may be represented by the formula: CH2-CY-CO-X
• X is hydrogen, an a ino group ⁇ NH2>r a hydroxy group, a methyl group or an OR group wherein R is a lower alkyl group, and wherein Y is hydrogen or a methyl group.
• suitable monomers include acrylamide, acrylic acid, acrylonitrile, methacrylic acid, methacrylamide, methacrylonitrile, methyl methacrylate, and sodium styrenesulfonate. Of this group of monomers, acrylamide is preferred. Polymerization of the monomer desirably 'is carried out in an aqueous solution containing about 1 to about 20 weight percent, preferably about 2 to about 12 weight percent, and most advantageously about 6 to about 8 weight percent monomer.
• the pH of the solution generally will be about 4 to about 11, usually about 6 to about 9.
• the temperature of the polymerization reaction can range from about 5°C to about 100°C, with a temperature of about 20°C to about 65°C being preferred.
• the time required to complete polymerization of the monomer can vary from about 2 to about 20 hours. With lower concentrations of catalyst, polymerization times can be effectively reduced.
• a free radical generating initiator e.g. azo compounds such as azobisisobutyranitrile and azobisisobutyramidine chloride; peroxides such as hydrogen peroxide,. sodium peroxide and benzoyl peroxide; alkyl and dialkyl
• - no peroxides such as, for example, t-butyl hydrogen peroxides and diethyl peroxide; alkali metal and ammonium persulfates including sodium persulfate, potassium persulfate and ammonium persulfate; and alkali metal bisulfites exemplified by sodium bisulfite and potassium bisulfite.
• alkali metal bisulfites exemplified by sodium bisulfite and potassium bisulfite.
• ammonium persulfate is the preferred free radical generating initiator.
• the concentration of the free radical generating initiator used in the polymerization of the monomer usually will be about 50 ppm to about 500 pp , preferably about 150 ppm to about 300 ppm, based upon the weight of the monomer in the polymerization reaction mixture.
• a preferred polymer solution for use in the secondary and tertiary recovery of oil from an oil- bearing formation is an aqueous solution of a partially hydrolyzed polyacryla ide.
• a hydrolyzing agent is added to the aqueous polymer solution.
• An especially effective agent for this purpose is ' a 50% solution of sodium hydroxide.
• the amount of hydrolyzing agent introduced into the polymer solution desirably is sufficient to hydrolyze approximately 20% to 40% of the amide groups comprising the polyacrylamide.
• One of the by-products of the hydrolysis reaction is ammonia which is generated in a molar amount in substantially direct proportion to the amount of hydrolyzing agent employed. More specifically in this connection, if 30 moles of base are used to hydrolyze the polymer, approximately 30 moles of ammonia will be produced during the
• ⁇ S5 « hydrolysis reaction.
• the pH of the aqueous solution of the partially hydrolyzed polyacrylamide is increased, usually to a level of about 10 to 12, or higher.
• the concentration of the partially hydrolyzed polymer in the aqueous solution will be about 6% to about 7%, and the solution will have a viscosity of about 450,000 cp to about 550,000 cp. It is necessary, prior to final dilution and injection, for example, into an input well of a subterranean oil-bearing formation or reservoir, to dilute the aqueous solution of the hydrolyzed polymer to provide a concentration of the polymer in the solution of about 1% to about 2%. Dilution of the hydrolyzed polymer solution advantageously is achieved by passing the solution through a series of dispersing stations which act to progressively increase the surface area of the polymer.
• the process of the present invention provides an effective, efficient and inexpensive means for eliminating, or at least substantially reducing, scaling in apparatus of the type disclosed in U.S. Patent No. 4,402,916.
• the process can be carried out, moreover, without any alteration in the arrangement of the elements comprising such apparatus, and without, furthermore, in any way adversely affecting the performance capabilities of tne diluted aqueous polymer solution.
• the process in its preferred aspects, involves the use of a gaseous substance which is soluble, or at least partly soluble, in water, and which is characterized in tnat it is capable of altering the pH of tne aqueous polymer solution in a manner to inhibit scale formation in tne dilution apparatus.
• the gaseous substance is further characterized in that it is substantially inert with respect to the polymer comprising the aqueous polymer solution.
• Fig. 1 is a schematic representation, shown in elevation, of an embodiment of an apparatus useful in carrying out the process of the present invention.
• the hydrolyzation of a polymer such as polyacrylamide generates ammonia (NH3) in an amount directly proportional to the number of moles of base employed to hydrolyze the polymer.
• the ammonia remains in solution, and acts to raise the pH of the solution to a level which favors the formation of scale due to the presence of compounds such as calcium carbonate (CaC03> in the aqueous m dium, in accordance with the present invention, it has been discovered that scaling in the dilution apparatus can be eliminated, or substantially reduced, by carrying out the dilution of the partially hydrolyzed polymer solution in the presence of a gas, in particular, carbon dioxide, in an amount sufficient to lower the pH of the solution to a level wnich cends to cause scale forming substances such as calcium carbonate to remain in solution throughout the dilution process.
• a gas in particular, carbon dioxide
• Carbon dioxide apart from its ability to lower the pH of the aqueous polymer solution, is inert with respect to the polymer comprising the solution. Tne relatively low cost of carbon dioxide, and its ease in handling, make it particularly suitable for use in an on-site, in-line aqueous polymer solution preparation operation.
• the carbon dioxide gas advantageously is injected into the water stream prior to the water contacting the partially hydrolyzed polymer solution.
• the gas may be introduced into the inlet end of the dilution apparatus provided it is well dispersed before it reaches the polymer dispersing stations of the dilution apparatus.
• the amount of gas injected should be sufficient to saturate, or nearly saturate, the polymer solution, and, most preferably, should be i jected in an amount of about 1.5 to about 2 times that required to attain saturation.
• greater amounts of gas may be required. This can readily be determined by sampling the polymer solution as it * moves through the dilution apparatus.
• a solution which has been saturated, or nearly so, with the gas, or which contains an amount of the gas in excess of that required for saturation, will have a pH of the order of about 6.5 to about 8.5. It has been found that the highest degree of scale reduction is achieved at a' solution pH of about 6 to about 7, the upper effective limit being a solution pH of about 8.3 to about 8.5.
• the carbon dioxide gas is believed to combine with the ammonia (NH3) present in the aqueous partially hydrolyzed polymer solution, and to increase the bicarbonate level in the aqueous solution thereby acting to reduce the pH of the solution and to maintain scale forming agents such as calcium carbonate (CaCOs) in a soluble state.
• the embodiment of the dilution apparatus illustrated, and designated generally by reference numeral 10 comprises an elongated cylinder or tube 12 provided with openings at inlet end 12a thereof for an aqueous
• the outlet end 12b of"the tube 12 has an opening for receiving an end of a discharge conduit 18.
• the tube 12 defines a chamber 20 in which a plurality of polymer solution dispersing stations 22, 24 and 26 are arranged.
• the chamber 20 also has positioned therein flow control elements 28 and 30 which may comprise static mixers of the type sold under the designations Sulzer ?MX, SMV and SMXL, manufactured by Koch Engineering Company Inc.
• the flow control elements function to maintain and enhance the laminar flow of the polymer solution as its passes from one dispersing station to the next.
• the dispersing stations 22, 24 and 26 each comprise a plurality of perforated- plates and/or screens 22a, 24a and 26a, respectively, the perforations in the plates and the mesh size of the screens at eacn of the stations being different.
• the size of the openings in the plates and the mesh size of the screens are largest at the inlet end of the chamber 20, and smallest at the outlet end thereof.
• the inlet 12a of the tube 12 desirably has a polymer solution distributor 32 which, as shown, includes a coupling 34 which carries a perforated sleeve 36.
• a cap 38 having a plurality of shaped, polymer solution dispersing blades or paddles 40, is secured on the sleeve 36.
• a cone shaped ring 42 is attached to the coupling 34 to increase the velocity of the fluid diluent along the perforated sleeve 36.
• the function and operation of the distributor 32 are essentially the same as the corresponding unit shown in Fig.3 of U.S. Patent No. 4,402,916.
• a gas injection conduit 50 intersects the fluid diluent conduit 16.
• the conduit 50 is in communication with a source (not shown) of gas such as carbon dioxide. Gauges and valves (not shown) advantageously are associated with the gas source to regulate the flow of gas into the water stream to provide a saturated, or near saturated, solution of the gas in the chamber 20. While the gas injection conduit 50, as illustrated, is connected to the diluent conduit 16, the injection .conduit 50 may be connected directly to the chamber 20 preferably at a point adjacent to the distributor 32 to assure uniform and adequate distribution of the gas in the polymer solution entering the chamber 20 through the conduit 14.
• the solution is introduced into the chamber 20 by initially passing it through the distributor 32 to disperse the polymer and increase its surface area. At the same time, the solution is brought into contact with water, saturated with carbon dioxide gas, passing into the chamber 20 through the conduit 16. As the polymer solution continuously and successively passes -through each of the dispersing stations 22, 24 and 26, the surface area of the polymer is increased to expose previously unexposed surface areas of the polymer to the diluent.
• the laminar flow of the polymer solution in the chamber is regulated and maintained by the flow control elements 28 and 30 thereby preventing any turbulence from developing in the chamber whicn otherwise might result in degradation or thinning of the polymer during dilution.
• the pH of the solution is regulated and maintained by the flow control elements 28 and 30 thereby preventing any turbulence from developing in the chamber whicn otherwise might result in degradation or thinning of the polymer during dilution.
• the volume of polymer solution and water introduced into the chamber is controlled so that when the polymer solution reaches the outlet end of the chamber, the polymer will have taken-up or absorbed an amount of water sufficient to reduce the concentration of the polymer in the solution to a predetermined level.
• the volume of wac ⁇ r employed can be in the range of 15 to about 150 times that of the aqueous polymer solution.
• the polymer solution will be introduced at a rate of approximately 1 to about 2 gallons per minutes, while at the same time water will be introduced at the rate of 6 to 7 gallons.
• the pressure drop across the system in such a case will be about 20 to about 30 psi.
• Sufficient carbon dioxide gas is injected to maintain the pH of the polymer solution at a level of the order of about 6.5 to about 8.5, preferably about 7 to about 7.5, throughout the chamber 20.
• the diluted material discharged from the chamber is substantially uniform, and may be further diluted to provide a material of the desired concentration for immediate injection into an input well of an oil-bearing formation.
• the concentration of the polymer in the final diluted solution usually will be about 50 to about 5000 ppm, especially desirably about 500 to about 2000 ppm.
• r xi solution does not in any way adversely affect the injectivity and mobility properties of the solution thereby enabling the solution to meet the performance demands of an oil-bearing formation or reservoir into which it is injected.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Processes Of Treating Macromolecular Substances (AREA)

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• 1984
  • 1984-02-16 US US06/580,967 patent/US4517097A/en not_active Expired - Fee Related
  • 1984-11-16 JP JP59504389A patent/JPS61501553A/ja active Granted
  • 1984-11-16 GB GB08522878A patent/GB2165227B/en not_active Expired
  • 1984-11-16 DE DE19843490623 patent/DE3490623T1/de not_active Withdrawn
  • 1984-11-16 WO PCT/US1984/001866 patent/WO1985003696A1/en not_active Ceased
  • 1984-11-19 CA CA000468142A patent/CA1247284A/en not_active Expired
• 1985
  • 1985-01-23 FR FR858500930A patent/FR2559756B1/fr not_active Expired

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