Title of Invention | "AN IMPROVED PROCESS FOR THE PREPARATION OF PARTIALLY HYDROLYZED POLYACRYLAMIDE USEFUL FOR ENHANCED RECOVERY OF OIL" |
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Abstract | An improved process for the preparation of partially hdrolysed polyacrylamide useful for enhanced recovery of oil which comprises polymerizing acrylamide monomer in aqueous solvent in the ratio of 1:5 to 1:10 using redox pair of initiator in the concentration range of 0.05 to 0.3% of acrylamide monomer weight under nitrogen atmosphere at a temperature in the range of 25 to 45°C partially hydrolyzing the polymer using 10% sodium hydroxide or potassium hydroxide solution at a temperature in the range of 40 to 80°C for a period of 10 to 15 hours, stabilizing the resultant solution using microbial agents such as herein described to obtain partially hydrolyzed polyacrylamide. |
Full Text | This invention relates to an improved process for the preparation of partially hydrolysed polyacryla-mide useful for enhanced recovery of oil. The process particularly relates to preparation of PHPA having improved viscosity and stability of the aqueous solutions for use in enhanced oil recovery and in the treatment of subterranean hydrocarbon containing formations. In the process of the present invention partially hydrolysed polyacrylamide is prepared by homopolymerization of acrylamide by solution polymerization using redox initiators, followed by partial hydrolysis with aqueous sodium hydroxide solution. The solution stability is improved by incorporating antimicrobial agents. This viscous solution can be applied to wells containing fresh water or mono and bivalent brine solution. High molecular weight (>106 ) partially hydrolysed polyacrylamide (PHPA) is extensively used as oil field chemical in various stages of crude oil production and transportation. In enhanced oil recovery technique it is used as a mobility control agent particularly in surfactant polymer flooding or in polymer augmented water flooding process. The injection of polymer solution can significantly increase oil production by providing mobility control and by reducing channeling in the reservoir. It reduces the permeability of reservoir rock to water by increasing the viscosity of aqueous fluid. In some of the wells where high permeable water channels exist, oil and gas are produced along with a large volume of salt water. The cost of the separation and disposal of the salt water from the crude oil could be high resulting in considerable loss in the operation of the wells. In order to reduce the production of salt water from such wells viscous aqueous PHPA solution is used preferentially to reduce water production from portions of the high permeable channels. The high molecular weight PHPA solution plugs the pores of the portions of the formation producing water and thereby substantially reduces the water production. In all the above processes PHPA is utilized as a flooding medium having viscosity in the order of or greater than the viscosity of the oil to be displaced. In surfactant polymer flooding technique PHPA solution is injected following the injection of surfactant slug solution in order to maintain the mobility of the surfactant solution. PHPA is also used in muds with bentonite and barite system both as viscosifier and fluid-loss additive particularly in reservoirs where calcium or trivalent metal salt content is negligible. Use of PHPA in the drilling mud is increasing as it replaces chrome lignosulphonate and chrome lignite which are environmentally unsafe. Several patents describe the synthesis of high molecular weight (>106) polyacrylamide both by solution and emulsion polymerization. In the present disclosure only solution polymerization is discussed. In the US Patent No. 4,645,09 highly viscous polymer was prepared by polymerizing acrylamide monomer in aqueous media using ammonium persulfate and sodium metabisulfite redox pair of initiator at 42-52°C for eight hours. The polymer solution was subsequently hydrolysed at 44°C using 50% aqueous sodium hydroxide. In the US Patent No.4,473,689 aqueous polymerization of acrylamide was carried out using sodium metabisulfite and ferrous sulfate as second redox pair with ammonium persulfate which was added dropwise. The incremental addition of the peroxy compound to polymerization mixtures containing redox pair of initiators prevents the generation of an excessive number of polymer chains preventing the formation of low molecular weight polyacrylamide. In the process described in US Patent No. 4, 103, 080, addition of catalyst atleast in three stages during the polymerisation step was performed. This was to maintain the initiator concentration low enough so as to obtain very high molecular weight polymer. In the US Patent No. 4,439.334 methods of preparing viscous aqueous polymer solution having improved viscosity and stability properties was disclosed. The viscous aqueous polymer solutions were prepared by polymerizing one or more water soluble polymerizable vinyl monomers in an oxygen free aqueous solvent such as fresh water, salt water, oil field brine, sea water and mixtures thereof using persulfate or peroxide initiators and chain transfer agents such as triethanolamine, butyl alcohol, isopropyl alcohol and mixtures thereof. In other patents such as US Pat No. 3,509, 113 and US Pat No. 4,020,256 the information on molecular weight of the polymer is not disclosed. Most of the patents as discussed above do not disclose the information on the percentage of low molecular weight PHPA formed. The low molecular weight compounds could restrict its use for Enhanced Recovery of Oil. Some patents describe the use of distilled water as solvent during polymerization. But it is preferable to use brine water so that it can be polymerized in the oil field using oil field brine. In one of the patents, chain transfer agent was used during polymerization. But use of chain transfer agent could produce uniformly low molecular weight polymer which restricts its use for Enhanced Recovery of Oil. PHPA solution degrades during standing for a prolonged period resulting in loss of solution viscosity. This degradation can be prevented by Incorporating oxygen scavengers, antimicrobial agents etc. According to the Japanese patent JP62, 177052 (1986) the aqueous solution of PHPA was stabilized with organic salts of dithiocarbamic acids. PHPA solution containing 10 percent NaCl and 5% pentamethylenedithiocarbamic acid piperidine salt is claimed to be stable even at 80-90o C. According to another patent JP 81,145,941 (1980) PHPA polymer was stabilized in 3% NaCl with 2.5%, 2-mercaptobenzimidazole Na salt and also with 3,5 di-tertiary butyl 4-hydroxy benzyl alcohol. JP 57,159 839(1982) claimed that acrylamide-Na-acrylate copolymer can be stabilized with 3% NaCl and 0.2 parts of 0.1% 8-quinoline at 75o C in nitrogen atmosphere. The object of the present invention is to provide an improved process for the preparation of high molecular weight (>106 ) and stabilized partially hydrolysed polyacrylamide (PHPA) useful for Enhanced Recovery of Oil. Accordingly, the present invention provides an improved process for the preparation of partially hydrolysed polyacrylamide useful for enhanced recovery of oil which comprises polymerizing acrylamide monomer in aqueous solvent in the ratio of 1:5 to 1:10 using redox pair of initiator in the concentration range of 0.05 to 0.3% of acrylamide monomer weight under nitrogen atmosphere at a temperature in the range of 25 to 45 oC partially hydrolyzing the polymer using 10% sodium hydroxide or potassium hydroxide solution at a temperature in the range of 40 to 80 oC for a period of 10 to 15 hours, stabilizing the resultant solution using microbial agents such as herein described to obtain partially hydrolyzed polyacrylamide. The present invention provides for a process for the synthesis of high molecular weight (>106 ) and stable PHPA solution. Homopolymerization of acrylamide is carried out by solution polymerization using redox initiators. The homopolymer is then partially hydrolysed with aqueous NaOH or KQH solution. The viscous PHPA solution is then stabilized with antimicrobial agents such as monoethanolamine, diethanolamine or triethanolamine in 1% NaCl solution. The decrease in solution viscosity on standing the solution1 at 60 C for a period of two months is negligible. The homopolymerization in the present invention is carried out in distilled water or in 10% inorganic monovalent or bivalent brine solution. The brine is selected from sodium chloride, sodium carbonate, sodium sulfate, magnesium chloride etc. Homopolymer in the present invention is prepared by redox initiation. As already described the slow addition of peroxy compound to a monomer solution containing a second member of redox pair of initiators produces very high molecular weight polyacrylamide. The redox pairs may be selected from sodium metabisulfite-thiourea-potassium persulfate; sodium metabisulfite-ferrous sulfate-potassium persulfate; sodium metabisulfite-ferrous sulfate-ammonium persulfate; sodium metabisulfite- ferrous sulfate-hydrogen peroxide; sodium metabisulfite-thiourea-ammonium persulfate etc. The polymerization in the present process was carried out at 25-40°C preferably at room temperature 30°C. The reaction is carried out under nitrogen atmosphere. Partial hydrolysis of polyacrylamide is carried out at 40-80°C for 10-15 hours with aqueous NaOH solution. Calculated molar quantity of alkali is used during hydrolysis. The final solution is clear and highly viscous. To improve the storage stability of the solution 1% NaCl and 300 ppm mono, di, or tri-ethanolamine is added. The following examples are given to illustrate the invention and should not be constrained to limit the scope of the invention. Example 1 Recrystallized acrylamide (10 g) is dissolved in doubly distilled water (80 ml) containing NaCl(10 g) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. Recrystallized thiourea (0.003 g) and recrystalliaed sodium metabisulfite (O.OO7g) are added and nitrogen gas is bubbled continuously for two hours to expel dissolved oxygen. The whole assembly is put in a thermostatic bath at a temperature of 30°C. Potassium persulfate (0.01 g) is dissolved in 20 ml degassed and deoxygenated water. It is then added from a separating funnel to the reaction flask at the rate of 15 ml per hour. Reaction proceeds slowly and at-the end of the addition a viscous polymer solution is obtained. It is then allowed to stand for another one hour at that temperature with constant stirring. A small sample of the polymer is removed and purified by precipitation with methanol. It is dried in vacuum oven for ten hours. Molecular weight of the polymer as determined by viscometry method is 15 x 106 . To the viscous polymer prepared as above (80 ml) normal sodium hydroxide solution (37 ml) is added along with distilled water (100 ml). The hydrolysis is carried out at 60°C for twelve hours with constant stirring till the evolution of ammonia ceases. Degree of hydrolysis of the polymer is determined by Kjeldahl method. Degree of hydrolysis is found to be 31%. PHPA is then isolated by repeated precipitating in methanol and dried in vacuum oven at 60°C for ten hours. Example 2 Recrystallized acrylamide (10 g), recrystallised thiourea (0.003 g) and recrystallized sodium metabisulfite (0.007 g) are dissolved in double distilled water (80 ml). Nitrogen is bubbled continuously for two hours at 30°C. Ammonium persulfate (0.01 g in 20 ml water) is added from the top of the reaction flask at the rate of 15 ml per hour. Reaction proceeds slowly and allowed to stand for 1 hour after addition. A small sample of the viscous polymer solution is withdrawn and precipitated for the determination of molecular weight. Molecular weight by viscometry method is 10 x 106. To the viscous polymer prepared as above (80ml) normal sodium hydroxide solution (37ml) is added along with distilled water (100ml). The hydrolysis is carried out at 60 c for twelve hours with constant stirring till the evolution of ammonia ceases. Degree of hydrolysis of the polymer is determined by Kjeldahl method. Degree of hydrolysis is found to be 32%. PHPA is then isolated by repeated precipitation in methanol and dried in vacuum oven at 60 c for ten hours. Stabilization of viscous PHPA Solution : Example 3 0.15 g PHPA is dissolved in 100 ml distilled water. 1.09 g NaCl and 0.03 g diethanolamine are added while stirring for 1 hour. The solution was kept at 60°C for 50 days. The viscosity of the PHPA solution determined at 30°C was found to vary only marginally even after 50 days as shown in Table 1. But degradation of solution viscosity was observed when the polymer solution was stored for the same period without the addition of diethanolamine. Later on it was observed that 300 ppm of monoethanolamine or 300 ppm of triethanolamine can also stabilize the PHPA solution as indicated in Table 1. Table 1 Aging Effect on PHPA Solution Viscosity Aging temperation: 60 C. (Table Removed) The main advantages of the process of the present invention are: 1. Homopolymerization of acrylamide is carried out at room temperature (25-45 c). 2. The polymerization can be carried out in distilled water or in 10% inorganic monovalent or bivalent brine solutions. This indicates that in-situ polymerization in the oil field using oil field brine water can be performed. 3. Chemicals used in the process are readily available. 4. Stabilization process is simple. The addition of 300 ppm of the antimicrobial agent is sufficient to stabilize the polymer solution. We claim : 1. An improved process for the preparation of par tially hydrolysed polyacrylamide useful for .enhanced recovery of oil which comprises polymerizing acryla- mide monomer in aqueous solvent in the ratio of 1:5 to 1:10 using redox pair of initiator in the concentra tion range of 0.05 to 0.3% of acrylamide monomer weight under nitrogen atmosphere at a temperature in the range of 25 to 45o C partially hydrolyzing the polymer using 10% sodium hydroxide or potassium hydroxide solution at a temperature in the range of 40 to 80 oC for a period of 10 to 15 hours, stabilizing the resultant solution using microbial agents such as herein described to obtain partially hydrolyzed polyacrylamide. 2. An improved process as claimed in 1 wherein the polymerization is effected in distilled water or in 10% inorganic monovalent or bivalent salt solution such as solution of sodium chloride, sodium carbonate, sodium sulphate, magnesium chloride. 3. An improved process as claimed in claims 1 & 2 wherein the redox pair of initiators used is selected from sodium meta bisulfite -thiourea- potassium per sulphate, sodium meta bisulfite-ferrous sulfate-potas- sium persulfate, sodium meta bisulfite-ferrous sulfate- ammonium persulfate, sodium meta- bisulfite-ferrous sulfate-hydrogen peroxide, sodium meta bisulfite-thiou-rea-ammonium-persulfate. 4. An improved process as claimed in claims 1-3 where in the stabilization is effected using antimicrobial agents such as mono, di or tri-ethanolamine in the range of 200-500 ppm to PHPA in 1% sodium chloride solution. 5. An improved process for the preparation of partial ly hydrolysed polyacrylamide useful for enhanced recov ery of oil substantially as herein described with reference to the examples. |
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548-del-1995-complete specification (granted).pdf
548-del-1995-correspondence-others.pdf
548-del-1995-correspondence-po.pdf
548-del-1995-description (complete).pdf
Patent Number | 188663 | |||||||||||||||
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Indian Patent Application Number | 548/DEL/1995 | |||||||||||||||
PG Journal Number | 43/2002 | |||||||||||||||
Publication Date | 26-Oct-2002 | |||||||||||||||
Grant Date | 01-Aug-2003 | |||||||||||||||
Date of Filing | 27-Mar-1995 | |||||||||||||||
Name of Patentee | COUNCIL OF SCIENTEFIC AND INDUSTRIAL RESEARCH | |||||||||||||||
Applicant Address | RAFI MARG, NEW DELHI-110001, INDIA. | |||||||||||||||
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PCT International Classification Number | C08F 120/56 | |||||||||||||||
PCT International Application Number | N/A | |||||||||||||||
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