JP2010270170A - Oil recovery chemical and method for producing the same, and injection liquid for recovering oil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the further improvements in the performance of oil recovery chemicals have been demanded, because the deterioration of oil recovery chemicals are accelerated, the injectability of the chemicals into oil strata, the mechanical shearing properties of the chemicals and the stability of the chemicals at high temperatures are insufficient in recent years, when crude oils are recovered from the deep oil strata of underground oil fields in severe conditions of high temperatures, high pressures, and the like. <P>SOLUTION: There is provided an oil recovery chemical comprising a water-soluble copolymer which is obtained by copolymerizing 2-acrylamido-2-methylpropane sulfonic acid (salt) monomer having a 2-methyl-2-propenyl-1-sulfonic acid content of ≤120 wt.ppm, and has a GPC top peak mol.wt. of 2,000,000 to 30,000,000. The oil recovery chemical has stable oil recovery performance even in conditions having a high salt concentration, largely variable pH, high temperature, and high pressure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is excellent in handling properties, good in salt resistance and thermal stability, and particularly in oil recovery agents with little thermal deterioration in the oil layer and mechanical shear deterioration in the pump, a method for producing the same, and an injection liquid for oil recovery About.

As a method of recovering oil from underground oil reservoirs, so-called primary recovery of oil production by self-injection has been performed for a long time, but secondary oil is forced to recover oil by injecting fluid into the oil reservoir as the oil extraction rate decreases. And tertiary recovery came to be performed.
In the water flooding method, which is a representative example of secondary recovery, oil is recovered by injecting water into the oil layer. However, there was a problem that the recovery efficiency was not improved as expected. Therefore, in recent years, a polymer attack method using a polymer aqueous solution instead of water has been carried out as a tertiary recovery method.
Depending on the depth of the oil layer, the polymer aqueous solution that has been press-fitted in the polymer flooding method slowly moves to the production well over a period of several months to several tens of months after the press-fitting at a high temperature of 40 ° C to 100 ° C. Polymers used in polymer flooding are those that have excellent water solubility and high viscosity at low concentrations, but polymer aqueous solutions such as polyacrylamide, polyalkyl (meth) acrylate, poacrylonitrile, and xanthan gum are heated at high temperatures. It deteriorated and the viscosity was further lowered in the presence of salts, which had a big problem in practical use.

In order to suppress this thermal deterioration, a method of adding a stabilizer such as sodium bisulfite (USP 2960486, USP 3757939) has been proposed. In addition, decomposition of acrylamide polymers with additives such as benzotriazole (Japanese Patent Publication No. 49-27658), 2-mercaptobenzimidazole (Japanese Patent Publication No. 58-47414), and methionine (Japanese Patent Publication No. 6-57722). A method for suppressing the above has been proposed.
On the other hand, there has been proposed a method for suppressing thermal degradation by using a copolymer having good thermal stability of the polymer itself, not an additive (for example, GB2110744).

  In addition, by using a copolymer of 2-acrylamido-2-methylpropanesulfonic acid, the metal salt contained in the underground layer is less susceptible to mechanical shear degradation and does not cause adsorption of the polymer to the bedrock of the oil layer. There are also proposed methods for suppressing the precipitation phenomenon of the polymer due to the above (for example, Japanese Patent Application Laid-Open Nos. 59-223710 and 62-283185).

U.S. Pat. No. 2,960,486 US Pat. No. 3,753,939 Japanese Patent Publication No.49-27658 Japanese Patent Publication No. 58-47414 Japanese Patent Publication No. 6-57722 British Patent No. 2110744 JP 59-223710 A Japanese Patent Laid-Open No. 62-283185

  However, in any of the above methods, the oil layer becomes deep underground and the conditions such as high temperature and high pressure become severe, and the deterioration of the oil recovery chemical is accelerated, and the oil layer can be injected, mechanically sheared, and heated. Became unstable. Therefore, further improvement in performance of oil recovery chemicals has been demanded.

  As a result of diligent investigation focusing on the impurities normally contained in the sulfonic acid (salt) group-containing monomer, the present inventor has copolymerized a sulfonic acid (salt) group-containing monomer that does not contain a specific component or more. The oil recovery agent composed of the high molecular weight water-soluble copolymer obtained in the above has been found to have a high salt concentration, a large pH fluctuation, and stable oil recovery performance even under high temperature and high pressure conditions. Completed.

That is, the first of the present invention is the following monomer (A) 15 to 80% by weight, monomer (B) 20 to 85% by weight, and optionally monomer (C) 0 to 40%. A water-soluble copolymer obtained by radical copolymerization of wt% (however, monomer (A) + (B) + (C) = 100 wt%), and has a top peak molecular weight of 200 It is a chemical for oil recovery that is 10-30 million.
(A) 2-acrylamido-2-methylpropanesulfonic acid and / or a salt thereof, wherein the content of 2-methyl-2-propenyl-1-sulfonic acid is 120 ppm by weight or less.
(B) Acrylamide.
(C) A vinyl monomer selected from (meth) acrylic acid and / or a salt thereof, (meth) acrylic acid ester, N-vinyl amide, N-substituted acrylamide and N, N-disubstituted acrylamide.
In the second aspect of the present invention, the monomer (A) is continuously mixed by mixing acrylonitrile and fuming sulfuric acid in the first reaction tank and supplying the mixed liquid to the second reaction tank to react with isobutylene. The agent for oil recovery according to the first invention, which is 2-acrylamido-2-methylpropanesulfonic acid and / or a salt thereof produced in 1.
Moreover, 3rd of this invention is described in 1st or 2nd invention whose content of 2-methyl- 2-propenyl- 1-sulfonic acid in a monomer (A) is 60 weight ppm or less. It is a chemical for oil recovery.
Moreover, 4th of this invention is described in 1st or 2nd invention whose content of 2-methyl- 2-propenyl- 1-sulfonic acid in a monomer (A) is 30 weight ppm or less. It is a chemical for oil recovery.
The fifth aspect of the present invention is the oil recovery according to any one of the first to fourth aspects, wherein the monomer (C) is a vinyl monomer selected from acrylic acid and / or a salt thereof and N-vinylamide. Drugs for use.
A sixth aspect of the present invention is a method for producing an oil recovery agent according to any one of the first to fifth aspects, wherein the monomers (A), (B) and, if necessary, (C) are gel-polymerized. .
The seventh aspect of the present invention is the oil recovery agent 0.005-0.5% by weight, inorganic salt 0.01-25% by weight and water 99.98-75% by weight according to any one of the first to fifth. It is a press-fit liquid for oil recovery composed of%.

  The oil recovery agent of the present invention increases the viscosity of the aqueous solution that is pressed into the oil layer, and its thickening effect is not greatly affected by mechanical shearing during dissolution or impurities in the water, and is maintained at a high level. Furthermore, chemical stability and thermal stability in the oil reservoir are superior to conventional oil recovery chemicals, and efficient and economical increase in crude oil production is possible.

  The oil recovery agent of the present invention has a molecular weight at the top peak of GPC (based on polyacrylic acid as a reference substance) obtained by radical copolymerization of the monomers (A) to (C) described below. It is a water-soluble copolymer having an abbreviated top peak molecular weight of 2 million to 30 million. If necessary, other monomers can be copolymerized to 20% by weight or less of the total monomers.

さらに、本発明者らは、ＩＢＳＡを一定量以下に制御したＡＴＢＳを用いて製造した石油回収薬剤が、驚くべきことに、機械的剪断劣化性や高温化での長期安定性を向上させるとともに、耐塩性も優れたものとなることを見出した。
その理由は、定かではないが、ＩＢＳＡは不飽和結合を含んでいるため、共重合体の成分として取り込まれるが、ＡＴＢＳよりスルホン酸基の長さが短く且つアミド基を含まないため、性能の低下に繋がったと考えられる。また、退化的連鎖移動によってポリマー末端に結合するＩＢＳＡ単位はポリマーの熱安定性を低下させると推定されるが、この不安定末端が減少することによって長期安定性が向上した可能性もある。 ○ Monomer (A)
The sulfonic acid (salt) group-containing monomer of the present invention is 2-acrylamido-2-methylpropanesulfonic acid (hereinafter abbreviated as ATBS) and / or a salt thereof.
The monomer is usually produced using acrylonitrile, sulfuric acid or isobutylene. These three components react stoichiometrically in equimolar amounts, but acrylonitrile is used in a large excess because it also serves as a reaction medium. Since ATBS is sparingly soluble in acrylonitrile, the product is in the form of a slurry. First, a crude ATBS is separated from the slurry and purified in the next purification step. The ATBS thus produced contains impurities, and there is a problem that the molecular weight of the polymer varies depending on the content of the substance.
The inventors of the present invention have confirmed that the impurity is 2-methyl-2-propenyl-1-sulfonic acid (hereinafter abbreviated as IBSA) represented by the following formula (1).

Furthermore, the present inventors have surprisingly found that an oil recovery agent produced using ATBS in which IBSA is controlled to a certain amount or less improves mechanical shear deterioration and long-term stability at high temperatures, It has been found that the salt resistance is also excellent.
The reason for this is not clear, but IBSA contains an unsaturated bond, so it is incorporated as a component of the copolymer. However, since sulfonic acid groups are shorter than ATBS and do not contain amide groups, This is thought to have led to a decline. Moreover, although it is presumed that the IBSA unit bonded to the polymer terminal by degenerative chain transfer decreases the thermal stability of the polymer, the long-term stability may be improved by reducing this unstable terminal.

In the present invention, the content of IBSA in ATBS needs to be 120 ppm by weight or less, preferably 60 ppm by weight or less, and more preferably 30 ppm by weight or less. If the IBSA content in ATBS exceeds 120 ppm by weight, the viscosity of the oil recovery agent produced will decrease, and the agent will be adsorbed on the rock in the soil, resulting in a decrease in oil recovery rate and long-term stability of the agent. Also decreases.
The ATBS used in the present invention is produced continuously by mixing acrylonitrile and fuming sulfuric acid in the first reaction tank, supplying this mixed liquid to the second reaction tank, and reacting with isobutylene. Preferably there is.

  The weight ratio in the copolymer of the monomer (A) used by this invention is 15 to 80 weight%, and 20 to 60 weight% is preferable. When the weight ratio of the monomer (A) is less than this value, salt resistance and heat stability are lowered, and when this value is exceeded, the stability of the aqueous solution is lowered.

○ Monomer (B)
The monomer (B) that can be used in the present invention is acrylamide. The weight ratio of the monomer (B) used in the present invention in the water-soluble copolymer is 20 to 85% by weight, preferably 40 to 80% by weight.
If the weight ratio of the monomer (B) is less than this value, the thickening is reduced and the oil recovery efficiency is lowered, and if this value is exceeded, the salt resistance and heat stability are lowered.

○ Monomer (C)
Monomers (C) that can be used in the present invention are (meth) acrylic acid and / or a salt thereof, (meth) acrylic acid ester, N-vinylamide, N-substituted acrylamide and N, N-disubstituted acrylamide. It is a vinyl monomer selected from In the present invention, (meth) acrylic acid means acrylic acid or methacrylic acid.
As (meth) acrylic acid and / or a salt thereof, acrylic acid and / or a salt thereof is preferably used. Salts include metal salts such as lithium, sodium, potassium, calcium, barium, iron, cobalt, nickel, copper, zinc, aluminum, and ammonia, trialkylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, etc. Organic ammonium salts are mentioned, and one kind can be used in combination.

Specific examples of (meth) acrylic acid esters include (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. , Esters of (meth) acrylic acid with polyhydric alcohols such as ethylene glycol, polyethylene glycol, propyne glycol and butanediol, allyl (meth) acrylate, and glycidyl (meth) acrylate.
Specific examples of N-vinylamide include chain amides such as N-vinylformamide and N-vinylacetamide and cyclic amides such as N-vinylpyrrolidone.
Specific examples of N-substituted acrylamides include N-alkyl acrylamides such as N-methyl acrylamide, N-ethyl acrylamide and N-isopropyl acrylamide.
Specific examples of N, N-disubstituted acrylamides include N, N-dialkylacrylamides such as N, N-dimethylacrylamide and N, N-diethylacrylamide.
The weight ratio in the copolymer of the monomer (C) used in the present invention is 0 to 40% by weight, preferably 0 to 30% by weight. When the weight ratio of the monomer (C) exceeds this value, salt resistance and heat stability are deteriorated.
The polymerization ratio of the monomer of the present invention is (A) + (B) + (C) = 100%.

○ Other monomers The copolymer of the present invention is not limited to the monomers (A), (B) and (C) described above, and is within the range of 20% by weight or less of the total monomers. Monomers can be used.
Examples of other monomers include (anhydrous) polyfunctional unsaturated carboxylic acids (anhydrides) such as maleic acid, fumaric acid and itaconic acid or salts thereof, vinyl acetate, carboxylic acid vinyl esters such as propyl acetate, ATBS Other than (meth) acrylamide alkylalkanesulfonic acid, vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, unsaturated sulfonic acid such as 2-hydroxy-3-allyloxypropanesulfonic acid or salts thereof, (meth) acrylonitrile, styrene , Styrene monomers such as α-methyl styrene, p-methyl styrene, chloromethyl styrene, vinyl pyridine, vinyl imidazole, and allylamine. These may be used alone or in combination.
The amount of these monomers used is preferably within 15% by weight, and more preferably within 10% by weight.

-Top peak molecular weight of copolymer The top peak molecular weight of the copolymer of this invention is 2 million-30 million, and a preferable top peak molecular weight is 4 million-20 million. If the top peak molecular weight is less than this range, the oil recovery rate decreases, and if it exceeds this range, the viscosity of the oil recovery agent becomes too high to be dissolved. The molecular weight of the copolymer is, as described above, the molecular weight at the maximum point of the peak curve obtained by aqueous gel permeation chromatography (hereinafter abbreviated as GPC) using polyacrylic acid as a reference substance.

O Production method of oil recovery drug The water-soluble copolymer of the present invention is used for oil recovery drug.
There are many known methods for producing oil recovery chemicals, such as gel polymerization, aqueous solution polymerization, and reverse phase suspension polymerization, which are used in usual polymer synthesis methods.
The synthesis of the high molecular weight water-soluble copolymer is preferably a gel polymerization method because the polymer can be easily made to have a high molecular weight and the polymerization operation and the molecular weight can be easily adjusted. The polymerization operation may be batch or continuous. Specific examples of the continuous gel polymerization method include a continuous belt polymerization method in which an aqueous monomer solution is continuously polymerized on a movable belt.

As the polymerization initiator, a redox polymerization initiator is preferable. Instead of the redox polymerization initiator, a monomer aqueous solution containing a photopolymerization initiator may be irradiated with active energy rays such as ultraviolet rays to be radically polymerized. .
Specific examples of the polymerization initiator include alkali metal persulfates such as sodium persulfate and potassium persulfate, persulfates such as ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, benzoyl peroxide, and t-butyl peroxide. , Organic peroxides such as benzoyl peroxide, 2,2′-azobis (4-cyanovaleric acid), 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2 Azo compounds such as 2,2'-azobisisobutyronitrile. At this time, it is preferable to use together a reducing agent for redox formation such as transition metal salt, bisulfite, L-ascorbic acid (salt), erythorbic acid (salt), amine compound and the like.
The amount of the polymerization initiator to be added is adjusted according to the type of polymerization initiator used, the composition of the target polymer, the degree of polymerization, the viscosity, etc., but is based on the total amount of all monomers. 5 to 10,000 ppm by weight is used. Preferably it is 10 to 5000 ppm by weight, and more preferably 15 to 3000 ppm by weight.
In the present invention, as a result of reducing the content of IBSA that also functions as a chain transfer agent, the amount of polymerization initiator used can be reduced.

The gel polymerization method used in the production of the oil recovery drug of the present invention is a polymerization method employed in a polymer production method such as for organic flocculants in order to obtain an extremely high molecular weight water-soluble polymer. According to this, the resulting polymer is obtained as a gel.
The technical characteristics of the gel polymerization method are that the aqueous solution concentration of the monomer is about 20 to 50% by weight, and the amount of the polymerization initiator used is very small, that is, 1000 ppm by weight or less. Under such conditions, when the polymerization is started at an initial reaction liquid temperature of 5 to 10 ° C., the reaction liquid is converted into a highly viscous gel, and stirring and removal of reaction heat can no longer be performed in the middle of the reaction. By leaving it for a certain period of time, the polymerization is usually completed after the maximum temperature of 80 to 100 ° C., and the desired high molecular weight water-soluble polymer is obtained.
In the polymerization reaction by the gel polymerization method, a preferable polymerization start temperature is 0 to 30 ° C, more preferably 5 to 20 ° C, and a preferable polymerization arrival temperature is 70 to 105 ° C, more preferably 80 to 100 ° C. What is necessary is just to adjust a monomer density | concentration so that it may enter into the range of this superposition | polymerization start temperature and superposition | polymerization attainment temperature. The preferred polymerization time is about 30 minutes to 6 hours.

○ Pressurized liquid for oil recovery The water-soluble copolymer of the present invention described above is used as an oil recovery agent.
The oil recovery press-fitting liquid of the present invention comprises 0.005 to 0.5% by weight of an oil recovery agent, 0.01 to 25% by weight of an inorganic salt, and 99.98 to 75% by weight of water. Preferably, it is composed of 0.01 to 0.3% by weight of an oil recovery agent, 0.05 to 15% by weight of an inorganic salt, and 99.94 to 85% by weight of water, and more preferably 0.02 to It is composed of 0.2% by weight, 0.1 to 10% by weight of inorganic salt and 98.8 to 89.8% by weight of water.
The oil recovery efficiency is low when the amount of the oil recovery agent added is less than the above value, and the economy is reduced when the amount is more than the above value. Moreover, when the content of the inorganic salt is equal to or less than the above value, the cost of the press-fit liquid is high, and when the content is higher than the above value, the stability of the press-fit liquid is low.

  Examples of the inorganic salt that is a component of the oil recovery press-fitting liquid of the present invention include sodium chloride, calcium chloride, potassium chloride, magnesium chloride, sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, sodium sulfate, potassium sulfate, and calcium sulfate. , Magnesium sulfate, ammonium sulfate, sodium hydrogen sulfate, sodium hydrogen carbonate, sodium bromide, potassium bromide and the like, which may be present in the oil recovery intrusion liquid, alone or in combination with a plurality of inorganic salts.

  Additives such as surfactants, antioxidants, bactericides, and anticorrosives can be used in combination in the oil recovery press-fitting liquid of the present invention as necessary. For example, organic acid salts such as sodium acetate and sodium lactate, surfactants such as polyethylene oxide, polyoxyethylene nonylphenol ether, and dioctyl sulfosuccinate soda, and stabilizers such as hydroquinone, catechol, guanidine sulfate, and thiourea as needed To add. The amount of these additives is usually 20% by weight or less based on the oil recovery agent.

  The water used for preparing the oil recovery press-fit liquid is not particularly limited, and a wide range of water can be used. If necessary, suspended particles may be filtered. Even if water containing a large amount of polyvalent metal ions is used, a sufficient effect can be obtained, so water that can be obtained around the oil field without using high-quality water, such as seawater or groundwater, can be used. . In conventional oil recovery polymers, it was necessary to use high-purity water as dissolution water, and thus cost was required for water procurement and purification. The point that the recovery efficiency is not affected by the water quality is a great feature of the oil recovery agent of the present invention. As already mentioned, the water for preparing the oil recovery injection liquid of the present invention can be easily obtained around the oil field, and the inorganic salt content in the water is within the concentration range shown above. There is no need to add another inorganic salt.

In the case of conducting the polymer attack with the oil-recovered injection liquid, the oil layer suitable for the method is not particularly limited, but a sandstone layer and a limestone oil layer having a permeability of 10 mdar or more are preferable, and a sandstone layer and a limestone oil layer of 50 mdar or more are further provided. preferable.
A conventionally known method may be used as a method for dissolving the oil recovery agent, a method for dilution after dissolution, and a method for press-fitting into the oil layer. Further, the oil recovery agent of the present invention can be applied not only to the usual polymer attack method but also to the Myceller polymer attack method, and can also be applied in combination with other known techniques such as the channeling block method.

The amount of the oil recovery agent of the present invention added is preferably 0.001% to 0.5% by weight, more preferably 0.01% to 0.3% by weight, based on the water used. If the addition amount is less than this value, the oil recovery efficiency is low, and if it exceeds this value, the economic efficiency is lowered.
A conventionally known method may be used as a method for dissolving the oil recovery agent, a method for dilution after dissolution, and a method for press-fitting into the oil layer. Further, the oil recovery agent of the present invention can be applied not only to the usual polymer attack method but also to the Myceller polymer attack method, and can also be applied in combination with other known techniques such as the channeling block method.

  Additives such as inorganic salts, surfactants, antioxidants, bactericides, and anticorrosives can be used in combination with the injected water using the oil recovery agent of the present invention as necessary. For example, inorganic salts such as sodium carbonate, potassium carbonate, ammonium carbonate, sodium sulfate, ammonium sulfate, organic acid salts such as sodium acetate and sodium lactate, surfactants such as polyethylene oxide, polyoxyethylene nonylphenol ether, sodium dioctylsulfosuccinate, A stabilizer such as hydroquinone, catechol, guanidine sulfate, and thiourea may be added as necessary. The amount of these additives is usually 20% by weight or less based on the water-soluble copolymer.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
In each of the following examples, “%” when not specifically displayed means “% by weight”.

The synthesis example of ATBS of the present application and the production example of the oil recovery agent will be specifically described. The concentration (weight ppm) was quantified by HPLC.
HPLC conditions; Waters high performance liquid chromatograph column; GL Science ODS-3
Eluent: 0.03% aqueous trifluoroacetic acid / acetonitrile Eluent flow rate: 0.8 ml / min
Detection wavelength: 200 nm

○ Synthesis Example 1
Two glass reactors equipped with a stirrer and an inlet pipe and an outlet pipe were connected, acrylonitrile and fuming sulfuric acid were charged into the first reactor under the following conditions, and after mixing acrylonitrile and fuming sulfuric acid, Two reactors were fed. In the second reactor, isobutylene gas was blown into the mixture to synthesize the target product. The above reaction was carried out continuously.
The amount of acrylonitrile supplied was 11 mol and the amount of isobutylene supplied was 0.9 mol per mol of fuming sulfuric acid. During the reaction, the reaction solution was collected, the concentration of IBSA was measured by HPLC, and the supply amount of fuming sulfuric acid was adjusted as shown in Table 1.
In addition, the concentration of sulfur trioxide in fuming sulfuric acid is 0.6%, and the concentration is adjusted by mixing concentrated sulfuric acid after adding moisture brought from raw materials such as acrylonitrile to commercially available 20% fuming sulfuric acid. is doing. The first reactor is maintained at -5 to -15 ° C and the residence time is 10 minutes. The second reactor is maintained at 30-50 ° C. and the residence time is 90 minutes.
The ATBS slurry obtained in the above production was suction filtered with a glass filter to obtain a cake on the glass filter. The amount of acrylonitrile described in Table 1 with respect to the cake weight was poured into the cake and suction filtered again to wash the cake.
The cake was transferred to a tray and dried at a drying temperature of 80 ° C. for 90 minutes.
When the obtained ATBS powder was subjected to HPLC analysis and the concentration of IBSA was measured, the concentration of IBSA in ATBS was 100 ppm by weight. Table 1 shows.

Next, ATBS and acrylamide were copolymerized using ATBS obtained in Synthesis Example 1.
First, 40 g of ATBS was dissolved in 60 g of water, and the pH was adjusted to 8 by adding a 48 wt% NaOH aqueous solution. Water was added to adjust the concentration to 35% by weight. 55.6 g of 40% by weight acrylamide aqueous solution was added, and further 5.2 g of water was added to make the monomer concentration 35% by weight. After adjusting the liquid temperature to 30 ° C. while blowing nitrogen into this monomer aqueous solution, 0.7 g of ammonium persulfate, 0.7 g of sodium sulfite, 0.6 g of an aqueous copper chloride solution containing 10 ppm by weight of copper ions, a diazo radical As a polymerization initiator, 0.7 g of a 10% by weight aqueous solution of V-50 (manufactured by Wako Pure Chemical Industries, Ltd.) was added. After 2 hours, the reaction was completed and the copolymer was taken out.

The top peak molecular weight of this copolymer determined by GPC measurement conditions was 102.50 million.
○ GPC conditions Using an aqueous solution containing sodium sulfate (1.33 g / l) and sodium hydroxide (0.33 g / l) as a solute as a solvent, polyacrylic acid (AMERICA POLYMER STANDARDDS CORP. Molecular weight 9 million, 555 Calibration curves were created using 10,000, 1.14 million, 440,000, 131200, 7900, and 2400) as reference materials. The elution rate was 0.6 ml / min and the detector used was Tosoh RI detector TI-8020. The molecular weight of the peak top (inflection point) with the highest detection intensity was defined as the top peak molecular weight.

After 1.15 g of the copolymer was dissolved in 393 g of water, 23.4 g of sodium chloride was added to obtain a sample solution for viscosity measurement (copolymer concentration: 0.25% by weight). When the UL viscosity was measured under the following conditions, it was 3.3 mPa · s.
Viscometer: Brookfield digital viscometer Rotor rotation speed: 60 rpm
Measurement temperature: 25 ° C

○ Synthesis Example 2
In Synthesis Example 1, the same operation was carried out except that the amount of acrylonitrile used for washing the cake was changed to 3 times, and the drying temperature of the cake was changed to 110 ° C., and the resulting ATBS powder was subjected to HPLC analysis. However, the IBSA concentration was 60 ppm by weight. Table 1 shows.

  A copolymer was produced in the same manner as in Synthesis Example 1 using the above ATBS. The obtained copolymer had a top peak molecular weight of 11 million and an UL viscosity of 3.6 mPa · s.

○ Synthesis Example 3
The synthesis reaction was carried out by changing the reaction residence time in Synthesis Example 2 to 120 minutes. The cake was dried at 110 ° C. for 180 minutes. When the obtained ATBS powder was analyzed by HPLC, the IBSA concentration was 20 ppm by weight. Table 1 shows.
The copolymer produced from ATBS had a top peak molecular weight of 11.7 million and an UL viscosity of 4.2 mPa · s.

Comparative Comparative Example Synthesis was performed according to a conventionally known ATBS synthesis method. That is, ATBS was synthesized continuously, but the initial charge ratio was maintained without HPLC analysis of the concentration of IBSA during the reaction. After completion of the reaction, the reaction solution was collected and the IBSA concentration was measured by HPLC analysis. The IBSA concentration was 15000 ppm by weight. The obtained ATBS slurry was suction filtered with a glass filter to obtain a cake on the glass filter. The cake was washed by pouring acrylonitrile twice the cake solid weight on the cake and suction filtering again. The cake was transferred to a tray and dried at a drying temperature of 60 ° C. for 90 minutes. When the obtained ATBS powder was analyzed by HPLC, the IBSA concentration was 200 ppm by weight. Table 1 shows.
The copolymer produced from ATBS had a UL viscosity of 1.6 mPa · s and a top peak molecular weight of 7 million.

○ Manufacture of oil recovery chemicals]
The production example of the oil recovery chemical will be specifically described below.

○ Example 1
50% by weight aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid sodium salt (hereinafter referred to as ATBS-Na) obtained in Synthesis Example 1, 36% by weight aqueous solution of sodium acrylate (hereinafter referred to as ANa), acrylamide ( (Hereinafter referred to as AAm) and pure water were mixed so as to have a monomer weight ratio shown in Table 2 to prepare 1 kg of an aqueous solution having a monomer concentration of 38% by weight. This aqueous monomer solution was charged into a stainless steel dewar (reaction vessel), and nitrogen bubbling was performed for 30 minutes while adjusting the temperature in the reaction vessel to 10 ° C. Subsequently, as a polymerization initiator, 30 weight ppm of t-butyl hydroperoxide (converted to the weight standard with respect to the total amount of all monomers, the same applies hereinafter), sodium persulfate 200 weight ppm and sodium erythorbate 30 weight ppm Then, the mixture was left as it was for 8 hours to perform adiabatic standing redox polymerization. After the completion of the reaction for 8 hours, the produced hydrogel polymer was taken out from the reaction vessel, put into a chopper and chopped into ground meat. The chopped water-containing gel was dried with a hot air dryer, and further pulverized with a pulverizer to obtain a desired powdery oil recovery agent. The results are shown in Table 2.

○ Examples 2 to 5 and Comparative Example 1
A powdery oil recovery agent was obtained in the same manner as in Example 1 except that the charged weight ratios of ATBS-Na, ANa, and AAm were changed as shown in Table 2. The results are shown in Table 2.

Example 6
A powdery oil recovery agent was obtained in the same manner as in Example 5 except that ATBS-Na derived from ATBS having an IBSA concentration of 60 ppm by weight obtained in Synthesis Example 2 was used. The results are shown in Table 2.

Example 7
A powdery oil recovery agent was obtained in the same manner as in Example 5 except that ATBS-Na derived from ATBS having an IBSA concentration of 20 ppm by weight obtained in Synthesis Example 3 was used. The results are shown in Table 2.

○ Comparative Example 2
A powdery copolymer was obtained in the same manner as in Example 5 except that ATBS-Na derived from ATBS having an IBSA concentration of 200 ppm obtained in Comparative Synthesis Example was used. The results are shown in Table 2.

  In addition, the viscosity and the top peak molecular weight (Mtop) whose data are shown in Table 2 were measured according to the following method.

1) Viscosity: 1.0 g of each of the oil recovery agents obtained in Examples 1 to 7 and Comparative Examples 1 and 2 was added to 500 ml of pure water, stirred for 3 hours, and sufficiently dissolved to have a concentration of 0.2% by weight. An aqueous solution was prepared. The viscosity of this aqueous solution was measured with a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd., model: BM type) at a rotor rotational speed of 30 ° C. and 30 rpm.
2) Top peak molecular weight (Mtop)
It was determined by GPC under the same conditions as in Synthesis Example 1.

○ Evaluation as oil recovery agent ○ Evaluation Examples 1-8 and Comparative Evaluation Examples 1-2
The copolymers produced in Examples and Comparative Examples were dissolved in brine containing 3% sodium chloride and 1% calcium chloride, and the solution viscosity and screen factor were measured. The concentration of the copolymer is as shown in Table 3.
The solution viscosity was measured at 25 ° C. using a B-type viscometer according to the method already described.
The screen factor is a ratio of the passage time of a 20 mesh screen to the passage time of the solvent alone using a screen viscometer. Measured at 25 ° C.
In addition to the initial values, the solution viscosity and screen factor also show the values after storage for 30 days in a thermostatic bath at 50 ° C. The results are shown in Table 3.

○ Evaluation Example 9 and Comparative Evaluation Example 3
Saturate 2% salt water in a core made by filling Berea sandstone in a cylindrical glass with a diameter of 2.5 cm and a length of 20 cm until oil with a viscosity of 26 mPa · s (25 ° C.) is not generated. Infused with a pump.
At this time, the core volume was 88 mL, the porosity was 25%, the oil saturation was 73%, and the oil content of the core was 16.1 ml.
An aqueous solution (concentration 0.6%) of the copolymer of Example 7 and Comparative Example 2 was injected into the oil-containing core using a micro metering pump. When 30 ml of the effluent was taken from the beginning and the amount of oil in the effluent was examined, 10.0 ml (recovery rate 62%) was obtained for the aqueous copolymer solution of Example 7, and 7.7 for the aqueous copolymer solution of Comparative Example 2. It was 7 ml (recovery rate 48%), and it was found that there was a large difference in oil recovery rate.

  According to the present invention, oil handling chemicals with excellent handling properties, good salt resistance and thermal stability, and less oil deterioration especially in oil reservoirs can be easily obtained. Oil can be recovered efficiently.

Claims (7)

The monomer (A) shown below is 15 to 80% by weight, the monomer (B) is 20 to 85% by weight, and the monomer (C) is optionally 0 to 40% by weight (provided that the monomer ( A) + (B) + (C) = 100% by weight)), a water-soluble copolymer obtained by radical copolymerization and having a top peak molecular weight of 2 million to 30 million. Drugs.
(A) 2-acrylamido-2-methylpropanesulfonic acid and / or a salt thereof, wherein the content of 2-methyl-2-propenyl-1-sulfonic acid is 120 ppm by weight or less.
(B) Acrylamide.
(C) A vinyl monomer selected from (meth) acrylic acid and / or a salt thereof, (meth) acrylic acid ester, N-vinyl amide, N-substituted acrylamide and N, N-disubstituted acrylamide. The monomer (A) was prepared by continuously mixing acrylonitrile and fuming sulfuric acid in the first reaction tank, and supplying the mixed liquid to the second reaction tank to react with isobutylene. The agent for oil recovery according to claim 1, which is methylpropanesulfonic acid and / or a salt thereof. The agent for oil recovery according to claim 1 or 2, wherein the content of 2-methyl-2-propenyl-1-sulfonic acid in the monomer (A) is 60 ppm by weight or less. The agent for oil recovery according to claim 1 or 2, wherein the content of 2-methyl-2-propenyl-1-sulfonic acid in the monomer (A) is 30 ppm by weight or less. The oil recovery agent according to any one of claims 1 to 4, wherein the monomer (C) is a vinyl monomer selected from acrylic acid and / or a salt thereof and N-vinylamide. The method for producing a petroleum recovery agent according to any one of claims 1 to 5, wherein the monomers (A) and (B) and, if necessary, (C) are gel-polymerized. Oil recovery comprising 0.005-0.5 wt% of oil recovery agent according to any of claims 1 to 5, 0.01-25 wt% of inorganic salt and 99.98-75 wt% of water Press-fit liquid.