JP2017206569A - Method for liquefying water-absorbing resin in water-retaining condition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a breaker for a water-absorbing resin used in stratum hydraulic fracturing and a method for liquefying the water-absorbing resin in a water-retaining condition using the breaker.SOLUTION: A breaker is provided for a water-absorbing resin including an iron ion-containing material and/or ascorbate, and/or persulfate, the resin to be used in stratum hydraulic fracturing. A kit to be used in stratum hydraulic fracturing is also provided, the kit including a swelling agent including a water-absorbing resin, an iron ion-containing material and ascorbate.SELECTED DRAWING: None

Description

  The present invention relates to a breaker for a water-absorbing resin used in hydraulic fracturing of a formation, more specifically in hydraulic fracturing of a formation containing an iron ion-containing substance and / or ascorbic acid and / or persulfate. The invention relates to a break agent for the water-absorbing resin used. The present invention also relates to a method for liquefying a water-containing water-absorbing resin using the break agent of the present invention.

  Hydraulic crushing of formations in shale gas mining has been practiced since ancient times. In excavation by hydraulic fracturing, guar gum is used as a thickener. In this method, it is necessary to remove the water absorbent resin press-fitted into the fracture after the proppant is fed. As a removal method, it can be performed by feeding a break agent and dissolving guar gum.

Patent Documents 1 to 4 (International Publication Nos. 2012/050187, 2014-1434090, 2014-1432091 and International Publication No. 2014/092146, respectively) use a water absorbent resin for excavation. Is disclosed.
On the other hand, Patent Document 5 (Japanese Patent No. 5143073) discloses the use of a water absorbent resin for paper diapers, and discloses that the decomposition of the water absorbent resin is suppressed by capturing iron ions by a chelating agent.

  Patent Document 6 (International Publication No. 2013/112664) discloses a method of liquefying a polymer material.

  Patent Documents 7 to 8 (Japanese Patent Application Laid-Open No. 2006-055833 and US Patent Application Publication No. 2007/0066167) disclose a method of liquefying a water absorbent resin.

International Publication No. 2012/050187 JP 2014-134090 A JP 2014-132091 A International Publication No. 2014/092146 Japanese Patent No. 5143073 International Publication No. 2013/112664 JP 2006-055833 A US Patent Application Publication No. 2007/0066167

  On the contrary, as a result of searching for conditions necessary for the decomposition (liquefaction) of the water-absorbent resin, the inventors have liquefied the water-absorbent water-absorbent resin and the water-absorbent used in the hydraulic crushing of the formation. A breaker for the resin was found.

  As a result of searching for conditions necessary for the decomposition (liquefaction) of the water absorbent resin, the inventors have found that the amount of ascorbic acid is highly dependent. It was also found that iron-containing minerals (vermiculite) decompose when ascorbic acid coexists. It was also found that persulfate has the same effect. Based on these considerations, a method for liquefying the water-absorbing water-absorbing resin and a break agent for the water-absorbing resin used in hydraulic crushing of the formation were developed.

The present invention also provides the following items.
(Item 1)
A break agent for a water-absorbing resin used in hydraulic fracturing of a formation, comprising an iron ion-containing substance and / or ascorbic acid and / or persulfate.
(Item 2)
The break agent according to the above item, wherein the persulfate is sodium persulfate or ammonium persulfate.
(Item 3)
The break agent according to any one of the above items, wherein the iron ion-containing substance is iron chloride, iron sulfate, or vermiculite.
(Item 4)
The break agent according to any one of the above items, comprising an iron ion-containing substance and ascorbic acid.
(Item 5)
The break agent according to any one of the above items, wherein the water-absorbent resin contains an iron ion-containing substance, and the break agent contains ascorbic acid.
(Item 6)
The break agent according to any one of the above items, wherein the water-absorbent resin is capable of absorbing water at least as much as its own weight.
(Item 7)
The break agent according to any one of the above items, wherein the water absorbent resin is selected from the group consisting of the following (a) to (i):
(A) a partially crosslinked polymer obtained by polymerization of a water-soluble ethylenically unsaturated monomer;
(B) Starch grafted polyacrylate;
(C) acrylamide / acrylic acid copolymer and salts thereof;
(D) Starch graft acrylamide / acrylic acid and its salts;
(E) an isobutylene / maleic anhydride copolymer;
(F) sodium and potassium salts of carboxymethylcellulose;
(G) a crosslinked salt of polyaspartic acid;
(H) Chitosan / polyvinylpyrrolidone combination and chitosan / polyethyleneimine combination; and (i) sulfonic acid group-containing monomer, (meth) acrylic acid amide, (meth) acrylic acid, (meth) acrylate A partially crosslinked polymer obtained by polymerization of two or more monomers.
(Item 8)
The break agent according to any one of the above items, wherein the water absorbent resin is a polyacrylic resin.
(Item 9)
The gel residual ratio of the water-absorbent resin is 30 (g / g) or less, provided that the gel residual ratio (mass%) = (gel mass after addition of break agent-containing aqueous solution / gel mass after addition of pure water) × 100. The break agent according to any one of the above items, which is 100.
(Item 10)
The water-absorbent resin is a compound having two or more unsaturated groups in one molecule, repeating units derived from at least one monomer component (A) selected from the group consisting of unsaturated carboxylic acids and salts thereof Any one of the above items, characterized in that the repeating unit is derived from the compound (C) having two or more functional groups capable of reacting with a carboxyl group in one molecule. Breaking agent described in 1.
(Item 11)
The break agent according to any one of the above items, wherein the hydraulic fracturing is for shale gas mining.
(Item 12)
A kit for use in hydraulic crushing of a formation comprising a swelling agent containing a water absorbent resin, an iron ion-containing substance, and ascorbic acid.
(Item 13)
A kit for use in hydraulic crushing of a formation comprising a swelling agent containing a water-absorbent resin and an iron ion-containing substance and ascorbic acid.
(Item 14)
The kit according to any one of the above items, wherein the water absorbent resin has the characteristics according to any one of items 6 to 10.
(Item 15)
The kit according to any one of the preceding items, wherein the hydraulic fracturing is for shale gas mining.
(Item 16)
A method for hydraulic fracturing of a formation, the method comprising:
A) a step of press-fitting a water-absorbing resin from a perforated portion of the formation with a proppant as necessary, crushing a rock as a reservoir to form a fracture; and B) from the perforated portion, an iron ion-containing substance and A method comprising injecting ascorbic acid and / or persulfate into contact with the fracture.
(Item 17)
The method according to any one of the above items, wherein the water absorbent resin has the characteristics according to any one of the above items.
(Item 18)
The method according to any one of the preceding items, wherein the hydraulic fracturing is for shale gas mining.
(Item 19)
The water-absorbent resin is a compound having two or more unsaturated groups in one molecule, repeating units derived from at least one monomer component (A) selected from the group consisting of unsaturated carboxylic acids and salts thereof Any one of the above items, which is a water absorbent resin having a repeating unit derived from (B) and a repeating unit derived from a compound (C) having two or more functional groups capable of reacting with a carboxyl group in one molecule. Breaking agent described in 1.

  In the present invention, it is contemplated that the one or more features may be provided in further combinations in addition to the explicit combinations. Still further embodiments and advantages of the invention will be recognized by those of ordinary skill in the art upon reading and understanding the following detailed description as needed.

  According to the present invention, a method for liquefying a water-containing water-absorbing resin and a break agent for a water-absorbing resin used in hydraulic crushing of a formation have been developed.

FIG. 1 is a photograph of a gel before and after heating when Fe 50 ppm + L-as 0.1% is added in an experiment of liquefaction of a water absorbent resin. The left side is a photograph before heating, and the right side is a photograph after heating. FIG. 2 is a photograph of the resulting gel with 1% ammonium persulfate (NH ₄ PS) added.

  The present invention will be described below. Throughout this specification, it should be understood that the singular forms also include the plural concept unless specifically stated otherwise. Thus, it should be understood that singular articles (eg, “a”, “an”, “the”, etc. in the case of English) also include the plural concept unless otherwise stated. In addition, it is to be understood that the terms used in the present specification are used in the meaning normally used in the art unless otherwise specified. Thus, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

  The definitions of terms particularly used in the present specification are described below.

[1] Definition of terms (1-1) "Water absorbent resin"
The “water-absorbent resin” in the present invention refers to a water-swellable, water-insoluble polymer gelling agent and satisfies the following physical properties. That is, as “water swellability”, CRC specified by ERT441.2-02 is 5 g / g or more, and as “water-insoluble”, Ext specified by ERT470.2-02 is 50% by weight or less. It refers to a polymer gelling agent that satisfies the above.

  The water-absorbent resin can be appropriately designed according to its use, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. Moreover, the whole amount (100 weight%) is not limited to the form which is a polymer, The water absorbing resin composition containing the additive etc. may be sufficient in the range which satisfies the said physical property (CRC, Ext).

  Furthermore, the water-absorbent resin in the present invention is not limited to the final product, but is an intermediate in the manufacturing process of the water-absorbent resin (for example, a water-containing gel-like crosslinked polymer after polymerization, a dried polymer after drying, a water absorption before surface crosslinking). In combination with the above water-absorbent resin composition, all of which are collectively referred to as “water-absorbent resin”. Examples of the shape of the water absorbent resin include a sheet shape, a fiber shape, a film shape, a particle shape, and a gel shape. In the present invention, a particulate water absorbent resin is preferable.

(1-2) "Polyacrylic acid (salt)"
The “polyacrylic acid (salt)” in the present invention refers to polyacrylic acid and / or a salt thereof, and acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”) as a main component. A polymer containing a repeating component and a graft component as an optional component.

  The “main component” means that the used amount (content) of acrylic acid (salt) is usually 50 to 100 mol% based on the entire monomer (excluding the internal crosslinking agent) used for polymerization, Preferably it is 70-100 mol%, More preferably, it is 90-100 mol%, More preferably, it means substantially 100 mol%.

(1-3) “EDANA” and “ERT”
“EDANA” is an abbreviation for European Disposables and Nonwovens Associations, and “ERT” is an abbreviation for a method for measuring water-absorbent resin (EDANA Recommended Test Methods) of the European standard (almost world standard). In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured according to the original ERT (revised in 2002 / known literature).

(1-3-1) “CRC” (ERT441.2-02)
“CRC” is an abbreviation for Centrifugation Retention Capacity (centrifugal retention capacity), and means the water absorption capacity of the water absorbent resin under no pressure (sometimes referred to as “water absorption capacity”).

  Specifically, 0.2 g of the water-absorbing resin was put in a non-woven bag, and then immersed in a large excess of 0.9 wt% sodium chloride aqueous solution for 30 minutes to freely swell, and then centrifuged (250 G ) Is the water absorption rate (unit: g / g) after draining.

(1-3-2) “AAP” (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure, which means the water absorption capacity of a water absorbent resin under pressure.

Specifically, after swelling 0.9 g of water-absorbing resin with a large excess of 0.9 wt% sodium chloride aqueous solution for 1 hour under a load of 2.06 kPa (21 g / cm ² , 0.3 psi) Of water absorption (unit: g / g). In some cases, the load condition is changed to 4.83 kPa (49 g / cm ² , 0.7 psi).

  In addition, ERT442.2-02 describes “Absorption Under Pressure”, which has substantially the same content.

(1-3-3) "PSD" (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution, and means a particle size distribution of a water-absorbent resin measured by sieving classification.

  The weight average particle diameter (D50) and the logarithmic standard deviation (σζ) of the particle size distribution are described in US Pat. No. 7,638,570 “(3) Mass-Average Particle Diameter (D50) and Logical Standard Deviation (σζ) of”. It measures by the method similar to "Particle Diameter Distribution."

(1-3-4) “Ext” (ERT470.2-02)
“Ext” is an abbreviation for Extractables, which means the water-soluble component (water-soluble component amount) of the water-absorbent resin.

  Specifically, it refers to the amount of dissolved polymer (unit:% by weight) after adding 1.0 g of water-absorbing resin to 200 ml of 0.9 wt% aqueous sodium chloride solution and stirring at 500 rpm for 16 hours. The amount of dissolved polymer is measured using pH titration.

(1-3-5) “Moisture Content” (ERT430.2-02)
“Moisture Content” means the water content of the water-absorbent resin.

  Specifically, it refers to a value (unit:% by weight) calculated from loss on drying when 4.0 g of water-absorbent resin is dried at 105 ° C. for 3 hours. In some cases, the water-absorbent resin is measured at 1.0 g and the drying temperature is changed to 180 ° C.

(1-3-6) “Residual Monomers” (ERT410.2-02)
“Residual Monomers” means the amount of monomer (monomer) remaining in the water-absorbent resin (hereinafter referred to as “residual monomer”).

  Specifically, it refers to the amount of residual monomer (unit: ppm) after adding 1.0 g of water-absorbing resin to 200 ml of 0.9 wt% sodium chloride aqueous solution and stirring at 500 rpm for 1 hour. The amount of residual monomer is measured using high performance liquid chromatography (HPLC).

(1-3-7) “FSC” (ERT440.2-02)
“FSC” is an abbreviation for Free Well Capacity, which means the water absorption capacity of a water absorbent resin suspended under no pressure.

  Specifically, after 0.200 g of the water-absorbing resin is put in a non-woven bag, it is immersed freely in a large excess of 0.9 wt% sodium chloride aqueous solution for 30 minutes, and then suspended for 10 minutes. It refers to the water absorption ratio (unit: g / g) after draining. Unlike the CRC, the amount of liquid retained between the water absorbent resin particles (gap) can be evaluated.

(1-3-8) Other properties of water-absorbing resin specified by EDANA “pH” (ERT400.2-02): means pH of water-absorbing resin.

  “Flow Rate” (ERT450.2-02): The flow rate of the water-absorbing resin.

  “Density” (ERT460.2-02): means the bulk specific gravity of the water-absorbent resin.

  “Respirable Particles” (ERT480.2-02): Respirable area dust of water absorbent resin.

  “Dust” (ERT490.2-02): means dust contained in the water absorbent resin.

(1-4) “Water absorption speed”
The “water absorption rate” of the water absorbent resin in the present invention means the water absorption rate measured by “Vortex” (unit: second).

(1-5) “Swelling agent”
The “swelling agent” in the present invention means a material that is press-fitted from a perforated part in hydraulic crushing of the formation. By press-fitting the swelling agent, the rock as the reservoir can be crushed to form a fracture. The swelling agent may be included in the fracturing fluid for forming the fracture.

(1-6) "Propant"
“Propant” in the present invention means a sand-like substance for supporting the fracture formed in the hydraulic fracturing of the formation, and is used as a support material in the fracture. The proppant supports the fracture after completion of the press-fitting and prevents the complete closing, so that a gas flow path from the reservoir can be secured.

(1-7) “Breaking agent”
The “breaking agent” in the present invention means a material capable of decomposing (liquefaction) the injected water-absorbing resin in hydraulic crushing of the formation. When the break agent is injected into the fracture after the formation of the fracture, the water-absorbent resin in the fracture can be decomposed, liquefied, or deteriorated.

(1-8) Others In this specification, “X to Y” indicating a range means “X or more and Y or less”. Further, unless otherwise noted, “t (ton)” as a unit of weight means “Metric ton”, and “ppm” means “weight ppm” or “mass ppm”. Furthermore, “weight” and “mass”, “part by weight” and “part by mass”, “% by weight” and “% by mass” are treated as synonyms. Further, “˜acid (salt)” means “˜acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”.

  In addition, “liter” may be described as “l” or “L”, and “wt%” may be described as “wt%” for convenience. Further, in the case of measuring a trace component, N.sub. Described as D (Non Detected).

[2] Production method of polyacrylic acid (salt) -based water-absorbing resin Hereinafter, production steps (2-1) to (2-1) of polyacrylic acid (salt) -based water-absorbing resin as the water-absorbing resin that can be used in the present invention. It shows about 2-9).

(2-1) Preparation Step of Monomer Aqueous Solution This step is a step of preparing an aqueous solution containing acrylic acid (salt) as a main component (hereinafter referred to as “monomer aqueous solution”). In addition, although the slurry liquid of a monomer can also be used in the range by which the water absorption performance of the water-absorbing resin obtained does not fall, in this section, monomer aqueous solution is demonstrated for convenience.

  In addition, the above “main component” means that the amount (content) of acrylic acid (salt) used is usually based on the whole monomer (excluding the internal crosslinking agent) subjected to the polymerization reaction of the water-absorbent resin. It means 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more (the upper limit is 100 mol%).

(Acrylic acid)
Acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”) is used as a monomer from the viewpoint of physical properties and productivity of the obtained water-absorbent resin.
The above “acrylic acid” may be a known acrylic acid, preferably a methoxyphenol as a polymerization inhibitor, more preferably p-methoxyphenol, from the viewpoint of the polymerization of acrylic acid and the color tone of the water-absorbent resin. It may contain 200 ppm or less, more preferably 10 to 160 ppm, and still more preferably 20 to 100 ppm. In addition, compounds described in US Patent Application Publication No. 2008/0161512 are also applicable to impurities in acrylic acid.

  In addition, the “acrylic acid salt” is obtained by neutralizing the acrylic acid with the following basic composition, and as the acrylic acid salt, a commercially available acrylate salt (for example, sodium acrylate) may be used. What was obtained by neutralizing in the manufacturing plant of a water absorbing resin may be used.

(Basic composition)
The “basic composition” refers to a composition containing a basic compound, such as a commercially available sodium hydroxide aqueous solution.

  Specific examples of the basic compound include alkali metal carbonates and hydrogen carbonates, alkali metal hydroxides, ammonia, and organic amines. Among these, strong basicity is desired from the viewpoint of the physical properties of the obtained water-absorbent resin. That is, hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide are preferable, and sodium hydroxide is more preferable.

(Neutralization)
As neutralization, either neutralization to acrylic acid (before polymerization) or neutralization (after polymerization) to a hydrogel crosslinked polymer obtained by crosslinking polymerization of acrylic acid (hereinafter referred to as “post-neutralization”) Can be selected or used in combination. These neutralizations may be continuous or batch-type, and are not particularly limited, but are preferably continuous from the viewpoint of production efficiency and the like.

  In addition, about conditions, such as the apparatus which performs neutralization, neutralization temperature, residence time, the conditions described in international publication 2009/123197 and US Patent application publication 2008/0194863 are applied also to this invention. .

  The neutralization rate is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, still more preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol% with respect to the acid group of the monomer. is there. When the neutralization rate is less than 10 mol%, the water absorption ratio may be significantly reduced. On the other hand, when the neutralization rate exceeds 90 mol%, a water absorbent resin having a high water absorption capacity under pressure may not be obtained.

  The neutralization rate is the same even in the case of post-neutralization. Moreover, the said neutralization rate is applied also about the neutralization rate of the water absorbing resin as a final product. The neutralization rate of 75 mol% means a mixture of 25 mol% acrylic acid and 75 mol% acrylate. Moreover, this mixture may be called an acrylic acid partial neutralized material.

(Other monomers)
The “other monomer” refers to a monomer other than the acrylic acid (salt), and can be used in combination with acrylic acid (salt) to produce a water-absorbing resin.

  Examples of the other monomers include water-soluble or hydrophobic unsaturated monomers. Specifically, the compounds described in US Patent Application Publication No. 2005/0215734 (excluding acrylic acid) are also applicable.

(Internal crosslinking agent)
As internal cross-linking agents used, the compounds described in US Pat. No. 6,241,928 are also applicable to the present invention. From these, one or more compounds are selected in consideration of reactivity.

  Further, from the viewpoint of water absorption performance and the like of the obtained water absorbent resin, preferably a compound having two or more polymerizable unsaturated groups, more preferably a compound having thermal decomposability at the following drying temperature, more preferably (poly) alkylene. A compound having two or more polymerizable unsaturated groups having a glycol structural unit is used as an internal cross-linking agent.

  The polymerizable unsaturated group is preferably an allyl group, a (meth) acrylate group, more preferably a (meth) acrylate group. Moreover, polyethylene glycol is preferable as the (poly) alkylene glycol structural unit, and the n number is preferably 1 to 100, more preferably 6 to 50.

  Therefore, (poly) alkylene glycol di (meth) acrylate or (poly) alkylene glycol tri (meth) acrylate, more preferably (poly) ethylene glycol di (meth) acrylate is used.

  The amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, based on the entire monomer. A desired water-absorbing resin can be obtained by setting the amount used within the above range. In addition, when there is too little this usage-amount, it exists in the tendency for gel strength to fall and a water soluble content to increase, and since there exists a tendency for a water absorption factor to fall when this usage-amount is too much, it is unpreferable.

  A method in which a predetermined amount of an internal cross-linking agent is previously added to the monomer aqueous solution and a cross-linking reaction is performed simultaneously with the polymerization is preferably applied. On the other hand, in addition to this method, a method of adding an internal cross-linking agent during or after polymerization and post-crosslinking, a method of radical cross-linking using a radical polymerization initiator, radiation using active energy rays such as electron beams and ultraviolet rays A method of crosslinking and the like can also be employed. Moreover, these methods can also be used together.

(Other substances added to the monomer aqueous solution)
From the viewpoint of improving the physical properties of the resulting water-absorbent resin, the following substances may be added during preparation of the monomer aqueous solution.

  Specifically, hydrophilic polymer such as starch, starch derivative, cellulose, cellulose derivative, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked product, preferably 50% by weight or less, more preferably Is added in an amount of 20% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less (the lower limit is 0% by weight), foaming agents such as carbonates, azo compounds and bubbles, surfactants, chelating agents. An agent, a chain transfer agent and the like are preferably added at 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.5% by weight or less (the lower limit is 0% by weight).

Moreover, the said substance may be added not only in the form added to monomer aqueous solution but in the middle of superposition | polymerization, and these forms can also be used together.
When a water-soluble resin or a water-absorbing resin is used as the hydrophilic polymer, a graft polymer or a water-absorbing resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) is obtained. It is done. These polymers and water-absorbing resin compositions are also within the scope of the present invention.

(Concentration of monomer component)
In this step, each of the above substances is added when preparing an aqueous monomer solution. Although it does not specifically limit as a density | concentration of the monomer component in this monomer aqueous solution, From a viewpoint of the physical property of a water absorbing resin, Preferably it is 10 to 80 weight%, More preferably, it is 20 to 75 weight%, More preferably, it is 30. ~ 70 wt%.

  Moreover, when employ | adopting aqueous solution polymerization or reverse phase suspension polymerization, solvents other than water can also be used together as needed. In this case, the type of solvent is not particularly limited.

The “monomer component concentration” is a value obtained by the following formula (1). The weight of the monomer aqueous solution includes the hydrophobicity in the graft component, the water-absorbing resin, and the reverse phase suspension polymerization. Solvent weight is not included.
[Equation 1]
(Concentration of monomer component (% by weight)) = (Weight of monomer component) / (Weight of monomer aqueous solution) × 100

(2-2) Polymerization step In this step, the acrylic acid (salt) monomer aqueous solution obtained in the monomer aqueous solution preparation step is polymerized to form a hydrogel crosslinked polymer (hereinafter referred to as "hydrogel"). It is a process of obtaining.

(Polymerization initiator)
The polymerization initiator to be used is not particularly limited because it is appropriately selected depending on the polymerization form and the like. For example, the thermal decomposition polymerization initiator, the photodecomposition polymerization initiator, or the decomposition of these polymerization initiators is promoted. Examples thereof include a redox polymerization initiator combined with a reducing agent. Specifically, one or more of the polymerization initiators disclosed in US Pat. No. 7,265,190 are used. From the viewpoint of handling of the polymerization initiator and physical properties of the water-absorbent resin, a peroxide or an azo compound is preferably used, more preferably a peroxide, and still more preferably a persulfate.

  The amount of the polymerization initiator used is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the monomer. The amount of the reducing agent used is preferably 0.0001 to 0.02 mol% with respect to the monomer.

  In addition, it may replace with the said polymerization initiator and may irradiate active energy rays, such as a radiation, an electron beam, and an ultraviolet-ray, and may implement a polymerization reaction, and these active energy rays and a polymerization initiator may be used together.

(Polymerization form)
The polymerization form to be applied is not particularly limited, but from the viewpoint of water absorption characteristics and ease of polymerization control, preferably spray droplet polymerization, aqueous solution polymerization, reverse phase suspension polymerization, more preferably aqueous solution polymerization, reverse phase. Suspension polymerization, more preferably aqueous solution polymerization is mentioned. Among these, continuous aqueous solution polymerization is particularly preferable, and either continuous belt polymerization or continuous kneader polymerization is applied.

  As specific polymerization forms, continuous belt polymerization is disclosed in U.S. Pat. Nos. 4,893,999 and 6,241,928 and U.S. Patent Application Publication No. 2005/215734, and continuous kneader polymerization is disclosed in U.S. Pat. Nos. 6,987,151 and 6,710,141. , Respectively. By adopting such continuous aqueous solution polymerization, the production efficiency of the water-absorbent resin is improved.

  Moreover, as a preferable form of the continuous aqueous solution polymerization, “high temperature initiation polymerization” and “high concentration polymerization” can be mentioned. “High temperature initiation polymerization” means that the temperature of the aqueous monomer solution is preferably 30 ° C. or higher, more preferably 35 ° C. or higher, still more preferably 40 ° C. or higher, particularly preferably 50 ° C. or higher (the upper limit is the boiling point). “High concentration polymerization” means that the monomer concentration is preferably 30% by weight or more, more preferably 35% by weight or more, still more preferably 40% by weight or more, and particularly preferably 45% by weight or more. The upper limit is a saturation concentration. These polymerization forms can also be used in combination.

  Moreover, although superposition | polymerization can also be performed in an air atmosphere, it is preferable to superpose | polymerize in inert gas atmosphere, such as nitrogen and argon, from a viewpoint of the color tone of the water absorbing resin obtained. In this case, for example, the oxygen concentration is preferably controlled to 1% by volume or less. The dissolved oxygen in the monomer aqueous solution is also preferably replaced with an inert gas (for example, dissolved oxygen; less than 1 mg / l).

  Moreover, it can also be set as foaming polymerization which superpose | polymerizes by disperse | distributing a bubble (especially said inert gas etc.) to monomer aqueous solution.

Moreover, you may raise solid content concentration during superposition | polymerization. The solid content increase degree is defined by the following formula (2) as an index of such solid content increase. In addition, as a raise degree of this solid content concentration, Preferably it is 1 weight% or more, More preferably, it is 2 weight% or more.
[Equation 2]
(Solid content rise (wt%)) = (Solid content concentration of water-containing gel after polymerization (wt%))-(Solid content concentration of monomer aqueous solution (wt%))
However, the solid content concentration of the monomer aqueous solution is a value obtained by the following formula (3), and the components in the polymerization system are the monomer aqueous solution, the graft component, the water absorbent resin, and other solids (for example, water). Insoluble fine particles, etc.) and does not include a hydrophobic solvent in reverse phase suspension polymerization.
[Equation 3]
(Solid content of monomer aqueous solution (% by weight)) = (weight of (monomer component + graft component + water absorbent resin + other solids)) / (weight of components in polymerization system) × 100

(2-3) Gel pulverization step In this step, the hydrogel obtained in the polymerization step is subjected to gel pulverization with a screw pulverizer such as a kneader or meat chopper, or a gel pulverizer such as a cutter mill. This is a step of obtaining a hydrous gel (hereinafter referred to as “particulate hydrous gel”). In addition, when the said superposition | polymerization process is kneader polymerization, the superposition | polymerization process and the gel grinding | pulverization process are implemented simultaneously. Further, when a particulate hydrous gel is obtained directly in the polymerization process, such as gas phase polymerization or reverse phase suspension polymerization, the gel pulverization step may not be performed.

  Regarding gel grinding conditions and forms other than those described above, the contents disclosed in International Publication No. 2011/126079 are preferably applied to the present invention.

(2-4) Drying step This step is a step of obtaining a dry polymer by drying the particulate hydrogel obtained in the polymerization step and / or the gel grinding step to a desired resin solid content. The resin solid content is determined from loss on drying (weight change when 1 g of water-absorbent resin is heated at 180 ° C. for 3 hours), preferably 80% by weight or more, more preferably 85 to 99% by weight, and still more preferably 90%. It is -98 weight%, Most preferably, it is 92-97 weight%.

  The method for drying the particulate hydrous gel is not particularly limited. For example, heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, azeotropy with a hydrophobic organic solvent. Examples include drying by dehydration and high-humidity drying using high-temperature steam. Among these, hot air drying is preferable from the viewpoint of drying efficiency, and band drying in which hot air drying is performed on a ventilation belt is more preferable.

  The drying temperature (hot air temperature) in the hot air drying is preferably 120 to 250 ° C, more preferably 150 to 200 ° C, from the viewpoint of the color tone of the water absorbent resin and the drying efficiency. The drying conditions other than the drying temperature, such as the speed of the hot air and the drying time, may be set as appropriate according to the moisture content and total weight of the particulate hydrous gel to be dried and the desired resin solid content, When performing band drying, various conditions described in International Publication Nos. 2006/100300, 2011/025012, 2011/025013, 2011/111657 and the like are appropriately applied.

  By setting the above-described drying temperature and drying time within the above ranges, the CRC (water absorption ratio) of the obtained water absorbent resin can be set to a desired range (see [3] below).

(2-5) Grinding step, classification step In this step, the dried polymer obtained in the drying step is pulverized (pulverization step), adjusted to a predetermined particle size (classification step), and water-absorbing resin powder ( This is a step of obtaining a powdery water-absorbing resin before surface cross-linking for the sake of convenience as “water-absorbing resin powder”.

  Examples of the equipment used in the pulverization step include a high-speed rotary pulverizer such as a roll mill, a hammer mill, a screw mill, and a pin mill, a vibration mill, a knuckle type pulverizer, and a cylindrical mixer. .

  The particle size adjustment method in the classification step is not particularly limited, and examples thereof include sieving classification using JIS standard sieve (JIS Z8801-1 (2000)), airflow classification, and the like. The particle size adjustment of the water-absorbing resin is not limited to the above pulverization step and classification step, but a polymerization step (especially reverse phase suspension polymerization or spray droplet polymerization), other steps (for example, granulation step, fine powder collection step) ).

  The obtained water-absorbent resin powder has a weight average particle diameter (D50) of preferably 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 250 to 500 μm, and particularly preferably 350 to 450 μm. The ratio of particles having a particle diameter of less than 150 μm is preferably 10% by weight or less, more preferably 5% by weight or less, and further preferably 1% by weight or less. The ratio of particles having a particle diameter of 850 μm or more is preferably 5% or less. % By weight or less, more preferably 3% by weight or less, still more preferably 1% by weight or less. The lower limit of the ratio of these particles is preferably as small as possible in any case, and is preferably 0% by weight, but may be about 0.1% by weight. Furthermore, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and still more preferably 0.27 to 0.35. These particle sizes are measured using a standard sieve according to the measurement methods disclosed in US Pat. No. 7,638,570 and EDANA ERT420.2-02.

  The particle size described above is applied not only to the water-absorbent resin after surface crosslinking (hereinafter sometimes referred to as “water-absorbent resin particles” for convenience) but also to the water-absorbent resin as the final product. Therefore, in the water-absorbent resin particles, it is preferable that the surface cross-linking treatment (surface cross-linking step) is performed so as to maintain the particle size in the above range, and the particle size is adjusted by providing a sizing step after the surface cross-linking step. preferable.

(2-6) Surface cross-linking step This step is a step of providing a portion having a higher cross-linking density in the surface layer of the water-absorbent resin powder obtained through the above-described steps (portion of several tens of micrometers from the surface of the water-absorbent resin powder). It is composed of a mixing step, a heat treatment step and a cooling step.

  In the surface cross-linking step, a water-absorbing resin (water-absorbing resin particles) surface-crosslinked by radical cross-linking, surface polymerization, cross-linking reaction with a surface cross-linking agent, etc. on the surface of the water-absorbent resin powder is obtained. What is necessary is just to implement suitably according to the performance requested | required.

(Surface cross-linking agent)
Although it does not specifically limit as a surface crosslinking agent used, An organic or inorganic surface crosslinking agent is mentioned. Among these, an organic surface cross-linking agent that reacts with a carboxyl group is preferable from the viewpoint of the physical properties of the water-absorbing resin and the handleability of the surface cross-linking agent. Examples thereof include one or more surface cross-linking agents disclosed in US Pat. No. 7,183,456. More specifically, polyhydric alcohol compounds, epoxy compounds, haloepoxy compounds, polyvalent amine compounds or their condensates with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. Can be mentioned.

  The surface crosslinking agent is used in an amount of 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water absorbent resin powder. It is. Moreover, it is preferable to add this surface crosslinking agent as aqueous solution, In this case, the usage-amount of water becomes like this. Preferably it is 0.1-20 weight part with respect to 100 weight part of water absorbent resin powder, More preferably, it is 0.00. 5 to 10 parts by weight. Furthermore, if necessary, when using a hydrophilic organic solvent, the amount used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, with respect to 100 parts by weight of the water-absorbent resin powder.

  In addition, each additive added in the “rehumidification step” described later is added to the surface cross-linking agent (aqueous solution) within a range of 5 parts by weight or less, or added separately in the main mixing step. You can also.

(Mixing process)
This step is a step of mixing the water absorbent resin powder and the surface cross-linking agent. The method for mixing the surface cross-linking agent is not particularly limited, but a surface cross-linking agent solution is prepared in advance, and the liquid is preferably sprayed or dropped on the water-absorbent resin powder, and more preferably sprayed. And mixing them.

  An apparatus for performing the mixing is not particularly limited, but a high-speed stirring type mixer is preferable, and a high-speed stirring type continuous mixer is more preferable.

(Heat treatment process)
In this step, heat is applied to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder.
The apparatus for performing the crosslinking reaction is not particularly limited, but preferably includes a paddle dryer. The reaction temperature in the crosslinking reaction is appropriately set according to the type of the surface crosslinking agent to be used, but is preferably 50 to 300 ° C, more preferably 100 to 200 ° C.

(Cooling process)
This process is a process installed as needed after the heat treatment process.

  The apparatus for performing the cooling is not particularly limited, but is preferably an apparatus having the same specifications as the apparatus used in the heat treatment step, and more preferably a paddle dryer. It is because it can be used as a cooling device by changing the heat medium to a refrigerant. In the cooling step, the water-absorbent resin particles obtained in the heat treatment step are forcibly cooled to 40 to 80 ° C., more preferably 50 to 70 ° C. as necessary.

(2-7) Arbitrary Rehumidification Step This step is performed by adding the following polyvalent metal salt compound, cationic polymer, chelating agent, inorganic reducing agent, α-hydroxy to the water absorbent resin particles obtained in the surface cross-linking step. It is a step of adding at least one additive selected from the group consisting of carboxylic acid compounds.

  In addition, since the said additive is added with aqueous solution or slurry liquid, a water-absorbent resin particle is swollen with water again. For this reason, this process is referred to as a “rehumidification process”. As described above, the additive can be mixed with the water-absorbent resin powder simultaneously with the surface cross-linking agent (aqueous solution).

(Polyvalent metal salt and / or cationic polymer)
It is preferable to add a polyvalent metal salt and / or a cationic polymer from the viewpoint of improving the water absorption rate, liquid permeability, hygroscopic fluidity and the like of the obtained water absorbent resin.

  As the polyvalent metal salt and / or cationic polymer, specifically, compounds disclosed in “[7] Polyvalent metal salt and / or cationic polymer” of International Publication No. 2011/040530 and the amount of use thereof Applies to the present invention.

(Chelating agent)
It is preferable to add a chelating agent from the viewpoint of the color tone (coloring prevention) and deterioration prevention of the water-absorbing resin obtained.
As the chelating agent, specifically, the compounds disclosed in “[2] chelating agent” of WO 2011/040530 and the amount used thereof are applied to the present invention.

(Inorganic reducing agent)
It is preferable to add an inorganic reducing agent from the viewpoint of color tone (coloring prevention), deterioration prevention, residual monomer reduction, and the like of the water-absorbing resin obtained.
As the inorganic reducing agent, specifically, compounds disclosed in “[3] Inorganic reducing agent” of WO 2011/040530 and the amount used thereof are applied to the present invention.

(Α-hydroxycarboxylic acid compound)
From the viewpoint of the color tone (coloring prevention) of the resulting water-absorbent resin, it is preferable to add α-hydroxycarboxylic acid. The “α-hydroxycarboxylic acid compound” is a carboxylic acid having a hydroxyl group in the molecule or a salt thereof, and is a hydroxycarboxylic acid having a hydroxyl group at the α-position.

  As the α-hydroxycarboxylic acid compound, specifically, the compounds disclosed in “[6] α-hydroxycarboxylic acid compound” of International Publication No. 2011/040530 and the amount used thereof are applied to the present invention. .

(2-8) Other additive addition process In order to add various functions to water-absorbent resin, additives other than the additive mentioned above can also be added. Specific examples of such additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic fine particles, organic powders such as metal soaps, deodorants, antibacterial agents, pulp and thermoplastics. Examples thereof include fibers. The surfactant is a compound disclosed in International Publication No. 2005/077500, and the water-insoluble inorganic fine particles are disclosed in International Publication No. 2011/040530 “[5] Water-insoluble inorganic fine particles”. Each applied compound is applied.

  The use amount (addition amount) of the additive is appropriately determined depending on the application and is not particularly limited, but is preferably 3 parts by weight or less, more preferably 1 part per 100 parts by weight of the water absorbent resin powder. Less than parts by weight. Moreover, this additive can also be added at a process different from the said process.

(2-9) Other steps In addition to the steps described above, a granulation step, a sizing step, a fine powder removal step, a fine powder reuse step, and the like can be provided as necessary. Moreover, you may further include 1 type, or 2 or more types of processes, such as a transport process, a storage process, a packing process, and a storage process. In addition, the “granulating step” includes a step of performing classification and pulverization when the fine powder removing step after the surface cross-linking step and the water absorbent resin are aggregated and exceed a desired size. In addition, the “fine powder recycling step” includes a step of adding the fine powder as it is as in the present invention to a large water-containing gel and adding it to any step of the production process of the water absorbent resin.

[3] Physical properties of polyacrylic acid (salt) water-absorbing resin The polyacrylic acid (salt) water-absorbing resin obtained by the production method according to the present invention includes the following (3-1) to (3-10). Of the listed physical properties, it is desired to control at least one or more, preferably two or more including CRC, more preferably three or more including CRC, and most preferably all physical properties within a desired range. .

  In addition, the polyacrylic acid (salt) -based water absorbent resin obtained by the above production method is not particularly limited with respect to its shape, but is preferably in the form of particles. In this section, the physical properties of the particulate water-absorbing resin which is a preferred embodiment will be described. In addition, the following physical property was measured based on EDANA method unless there is particular notice.

(3-1) CRC (absorption capacity under no pressure)
The CRC (water absorption capacity under no pressure) of the water-absorbent resin is usually 5 g / g or more, preferably 15 g / g or more, more preferably 25 g / g or more. The upper limit is not particularly limited and is preferably as high as possible. However, from the viewpoint of balance with other physical properties, it is preferably 80 g / g or less, more preferably 70 g / g or less, and still more preferably 65 g / g or less.

  When the CRC is less than 5 g / g, the amount of absorption is small and it is not suitable for hydraulic fracturing. CRC can be controlled by an internal crosslinking agent, a surface crosslinking agent, or the like.

(3-2) AAP (absorption capacity under pressure)
The AAP (water absorption capacity under pressure) of the water absorbent resin is preferably 20 g / g or more, more preferably 22 g / g or more, still more preferably 23 g / g or more, particularly preferably 24 g / g or more, and most preferably 25 g / g. That's it. The upper limit is not particularly limited, but is preferably 30 g / g or less.

  AAP can be controlled by particle size, surface cross-linking agent, and the like.

(3-3) Particle size (particle size distribution, weight average particle size (D50), logarithmic standard deviation (σζ) of particle size distribution)
The particle size (particle size distribution, weight average particle size (D50), logarithmic standard deviation of particle size distribution (σζ)) of the water absorbent resin is controlled so as to be the same as the particle size of the water absorbent resin powder before surface crosslinking. The

(3-4) Ext (water-soluble component)
The Ext (water-soluble content) of the water-absorbent resin is usually 50% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less, and further preferably 15% by weight or less. Although it does not specifically limit about a lower limit, Preferably it is 0 weight%, More preferably, it is about 0.1 weight%.

  When the Ext exceeds 50% by weight, the gel strength is weak and there is a possibility that the water-absorbent resin is not suitable for hydraulic crushing. Ext can be controlled with an internal cross-linking agent or the like.

(3-5) Water content The water content of the water-absorbent resin is preferably more than 0% by weight and 15% by weight or less, more preferably 1 to 13% by weight, still more preferably 2 to 10% by weight, and particularly preferably 2%. ~ 9 wt%.

  By setting the moisture content within the above range, a water-absorbing resin excellent in powder characteristics (for example, fluidity, transportability, damage resistance, etc.) can be obtained.

(3-6) Residual monomer The residual monomer contained in the water-absorbent resin is preferably 500 ppm or less, more preferably 400 ppm or less, and still more preferably 300 ppm or less, from the viewpoint of safety. Although it does not specifically limit about a lower limit, Preferably it is 0 ppm, More preferably, it is about 10 ppm.

(3-7) Vortex (water absorption speed)
The Vortex (water absorption rate) of the water absorbent resin is preferably 80 s or less, more preferably 75 s or less, still more preferably 70 s or less, and particularly preferably 65 s or less. Although it does not specifically limit about a lower limit, Preferably it is 5 s or more, More preferably, it is 15 s or more.

[4] Typical explanation of the hydraulic fracturing technology of the formation The hydraulic fracturing technology is to pressurize the fluid filling the well at high pressure, artificially destroy the reservoir rock near the well and place it in the reservoir layer. This is a technology that secures fluid flow paths by artificially forming and extending fractures. The generated fractures (cracks) can improve the permeability (fluidity of fluid flow) in the vicinity of the well, expand the effective inflow cross section to the well, and improve the productivity of the well.

An exemplary procedure for the hydraulic fracturing technique is as follows.
1. A highly viscous fluid (gel) is press-fitted from the perforated part, and the rock as the reservoir is crushed to form a fracture.
2. Continue to press-fit the gel and increase the length and width of the fracture.
3. In order to support the formed fracture semipermanently, sand granular material called proppant is gradually mixed and pressed into the gel.
4). Increase the concentration of proppant gradually.
5. When the specified amount of proppant has been sent, stop the press-fit pump.
6). Since the injected gel is decomposed by heat and penetrates into the reservoir, the formed fracture tends to close gradually. However, since the proppant supports the fracture and prevents it from closing completely, a gas flow path is ensured.
7). Gas accumulated in a small gap in the reservoir flows into the well through the fracture, and economical productivity can be ensured.
The generated fracture must prevent closure and be maintained over a long period of time. Therefore, a granular object called proppant is injected into the generated fracture.
Proper injection fluid and proppant design is necessary to create and maintain the proper fracture. The efficiency of the injected fracturing fluid can be defined as:
Fluid efficiency = (Fracture volume when sealed) / (Pressure amount of crushing (fracturing) fluid)
A typical procedure for hydraulic fracturing work is as follows.

<Typical procedure for hydraulic fracturing>
(1) Fracturing work [fracture formation, fracture extension]
・ Fluid injection: Pre-pad (for high-viscosity fluid, fracture generation), pad (for gel fluid, fracture extension), proppant transport fluid (mixture of high-viscosity fluid and proppant)
-Well sealing, pressure behavior monitoring (fracture closure)
(2) Post-fracturing work and well cleaning (fracturing fluid polymer bond breakage, backflow)
In order to know the direction of the generated fracture, the acoustic noise (AE) at the time of fracture extension is monitored. A technology (micro seismic technology) that installs a three-dimensional seismometer in a nearby well or a well that has been subjected to hydraulic fracturing, investigates the sound source of AE, and investigates the spread of fractures is also used.
The choice of proppant material and particle size is important. The diameter of the proppant should be about 1/4 or less of the generated fracture width, and the possibility of screen-out (excluded from the fracture) becomes larger.
The points to be noted in the hydraulic fracturing work are as follows.

<Points to note in hydraulic crushing work>
(1) Fracturing fluid is roughly classified into the following three types.
1. Dissolved polymer in water (medium viscosity)
2. Dissolved polymer in water and cross-linked (high viscosity)
3. Water-oil emulsion.

The main characteristics to be provided as a fracturing fluid are the following four points.
1. 1. Create a fracture in the formation conditions and have viscosity to carry the support material. Appropriate fluid efficiency (less leak-off)
3. 3. Compatibility with formation or formation water Decomposes rapidly after processing

(2) After the support material hydraulic crushing operation is completed, the support material is subjected to a clogging pressure from the surface of the crack, but it is important that the crack is destroyed and the support material is not buried in the formation.

(3) Press-in pressure and required horsepower (wellhead press-in pressure / pump discharge pressure) = (crushed pressure) + (friction loss in the pipe) + (pressure loss in the drilled portion) − (hydrostatic pressure).
The necessary horsepower of the pump is calculated by the wellhead press-fit pressure × press-fit speed, and the required number of pumps is obtained in consideration of efficiency.

(4) Securing the passage of the fracturing fluid Acid treatment is usually performed as pretreatment for hydraulic fracturing. Perforation cleaning is also performed. It is also effective to confirm that the crushing pressure is not significantly different from the expected value in the latter half of the cleaning process.

(5) Press-in speed Before the hydraulic fracturing, many data are estimated values, but it is possible to eliminate troubles caused by uncertain factors by securing a sufficient press-in speed.

(6) Press-in operation The press-in operation starts with a low viscosity acid (15% hydrochloric acid) or brine (2% potassium chloride) as a prepad. The fracturing fluid (without supporting material) that is subsequently press-fitted is called a pad, and this amount greatly affects the work results. The pad always enters the deepest part of the crack and destroys the formation with the pressure transmitted from the following. However, when the pad is consumed due to leak-off or the like, the development of the crack stops and the sand of the support material settles in the well, causing the operation to be stopped. It is said that at least 20% of the predetermined amount of fracture fluid should be used as a pad. In the case of a gas layer, the ratio of pads increases. It is also important to improve the conductivity in the vicinity of the well and to reduce the loss due to the sand buried in the formation.

[5] Description of Preferred Embodiments Hereinafter, preferred embodiments of the present invention will be described. The embodiments provided below are provided for a better understanding of the present invention, and it is understood that the scope of the present invention should not be limited to the following description. Therefore, it is obvious that those skilled in the art can make appropriate modifications within the scope of the present invention with reference to the description in the present specification. It will also be appreciated that the following embodiments of the invention may be used alone or in combination.

(Breaking agent for water-absorbing resin used in hydraulic crushing of formation)
In one aspect, the present invention provides a break agent for a water-absorbing resin for use in hydraulic fracturing of formations comprising an iron ion-containing material and / or ascorbic acid and / or persulfate. It is understood that any material can be used as the iron ion-containing material. It is understood that ascorbic acid can be used in any form (for example, a derivative of any salt such as sodium ascorbate and calcium ascorbate). It will be understood that any counterion salt may be used as the persulfate.

  In one preferred embodiment, the persulfate is sodium persulfate, potassium persulfate or ammonium persulfate.

In a preferred embodiment, the iron ion-containing material is first iron oxide (FeO), second iron oxide (Fe ₂ O ₃ ), iron chloride, iron sulfate, or vermiculite. Water-absorbing resin has the property of adsorbing moisture in the atmosphere, and usually silica fine particles (Aerosil, etc.) are added, but the same effect can be obtained by using vermiculite instead. It is thought that. Typical metals contained in vermiculite are Mg, Fe, and Al.

  In a further embodiment, the break agent comprises an iron ion-containing material and ascorbic acid. Although not wishing to be bound by theory, it is observed that liquefaction is promoted by including both substances.

  In still another embodiment, the water absorbent resin contains an iron ion-containing substance, and the break agent contains ascorbic acid. This is because when both substances are mixed at once, liquefaction proceeds, so that it is advantageous to use them as separate agents when it is necessary to control this.

  In one embodiment, the water-absorbent resin is capable of absorbing water at least as much as its own weight. Preferably, the water-absorbent resin is at least 2 times its own weight, at least 5 times its own weight, at least 10 times its own weight, at least 20 times its own weight, at least 50 times its own weight, at least 100 times its own weight, at least 200 times its own weight It may be capable of absorbing water at least 500 times its own weight, at least 1000 times its own weight, and at least 2000 times its own weight, but is not limited thereto. In another embodiment, the water-absorbing resin is a water-absorbing water-containing resin. In another embodiment, the water absorbent resin may be provided as a dispersion. In yet another embodiment, the water absorbent resin is, for example, as described in US Patent Application Publication No. 2004/0059054.

In a specific embodiment, the water absorbent resin is:
(A) a partially crosslinked polymer obtained by polymerization of a water-soluble ethylenically unsaturated monomer;
(B) Starch grafted polyacrylate;
(C) acrylamide / acrylic acid copolymer and salts thereof;
(D) Starch graft acrylamide / acrylic acid and its salts;
(E) an isobutylene / maleic anhydride copolymer;
(F) sodium and potassium salts of carboxymethylcellulose;
(G) a crosslinked salt of polyaspartic acid;
(H) Chitosan / polyvinylpyrrolidone combination and chitosan / polyethyleneimine combination; and (i) sulfonic acid group-containing monomer, (meth) acrylic acid amide, (meth) acrylic acid, (meth) acrylate Selected from the group consisting of partially crosslinked polymers obtained by polymerization of two or more monomers.

  In a further embodiment, the water absorbent resin is a polyacrylic acid resin.

  In one embodiment, the gel residual ratio of the water-absorbent resin is 30 (g / g) or less, provided that the gel residual ratio (mass%) = (gel mass after addition of break agent-containing aqueous solution / pure water addition) Later gel mass) × 100.

  In another embodiment, the water-absorbent resin is a repeating unit derived from at least one monomer component (A) selected from the group consisting of an unsaturated carboxylic acid and a salt thereof, and an unsaturated group in one molecule. It is characterized by comprising a repeating unit derived from a compound (B) having two or more compounds and a repeating unit derived from a compound (C) having two or more functional groups capable of reacting with a carboxyl group in one molecule.

  In still another embodiment, the water-absorbent resin is a repeating unit derived from at least one monomer component (A) selected from the group consisting of an unsaturated carboxylic acid and a salt thereof, and is unsaturated in one molecule. A water-absorbent resin having a repeating unit derived from a compound (B) having two or more groups and a repeating unit derived from a compound (C) having two or more functional groups capable of reacting with a carboxyl group in one molecule .

  In one embodiment, the hydraulic fracturing is for shale gas mining. In another embodiment, the hydraulic fracturing is for shale oil mining.

  In another aspect, the present invention provides a kit for use in hydraulic fracturing of a formation comprising a swelling agent containing a water absorbent resin, an iron ion-containing substance, and ascorbic acid.

  In yet another aspect, the present invention provides a kit for use in hydraulic crushing of a formation comprising a swelling agent comprising a water absorbent resin and an iron ion-containing substance and ascorbic acid.

  In one embodiment, the water-absorbent resin in the kit has any of the above characteristics.

  In another embodiment, the hydraulic fracturing in the kit is for shale gas mining. In yet another embodiment, the hydraulic fracturing in the kit is for shale oil mining.

(Method of hydraulic fracturing of the formation)
In a further aspect, the present invention provides a method for hydraulic fracturing of a formation. The method
A) a step of press-fitting a water-absorbing resin from a perforated portion of the formation with a proppant as necessary, crushing a rock as a reservoir to form a fracture; and B) from the perforated portion, an iron ion-containing substance and Injecting ascorbic acid and / or persulfate into contact with the fracture. The water-absorbing resin, iron ion-containing substance, ascorbic acid and persulfate used here are described in the section of this specification (Breaking agent for water-absorbing resin used in hydraulic crushing of the formation). It is understood that any can be used.

  Accordingly, in one embodiment, the water-absorbent resin in the method has any of the features or combinations thereof in the section (Breaking agent for water-absorbent resin used in hydraulic crushing of formations).

  In another embodiment, the hydraulic fracturing in the method is for shale gas mining. In yet another embodiment, the hydraulic fracturing in the method is for shale oil mining.

In yet another aspect, the present invention provides a method for hydraulic fracturing of a formation. The method
i) a step of pressing a high-viscosity fluid from the perforated portion of the formation and crushing the rock as a reservoir to form a fracture;
ii) continuing the press-fitting of the highly viscous fluid to increase the length and width of the fracture;
iii) a step of gradually mixing and pressurizing the proppant into the highly viscous fluid to semipermanently support the formed fracture;
iv) gradually increasing the concentration of the proppant until a defined amount of the proppant is delivered;
v) A step of injecting iron ion-containing material and / or ascorbic acid and / or persulfate from the perforated portion so as to contact the fracture;
vi) stopping the press-fit pump;
vii) the step of closing the fracture by the intrusion of the highly viscous fluid by the iron ion-containing substance and / or the ascorbic acid and / or the persulfate soaking into the reservoir, wherein Preventing the proppant from supporting and closing the fracture completely; and viii) collecting the gas remaining in the reservoir gap flowing into the fracture;
Is included.

  In one embodiment, in the above method, the order of step (vi) and step (vii) may be reversed.

In one embodiment, the highly viscous fluid is a gel.
In another embodiment, the highly viscous fluid includes a water absorbent resin, a swelling agent comprising a water absorbent resin, or a swelling agent comprising a water absorbent resin and an iron ion-containing material.
In still another embodiment, the water-absorbent resin in the method has any of the above characteristics.

In one embodiment, the proppant is a sand granular material.
In yet another embodiment, the hydraulic fracturing in the method is for shale gas mining.

  Thus, since the water-absorbent resin used in the present invention can be pressed into the basement and then the water-absorbent resin can be liquefied, the target underground resource can be obtained by, for example, hydraulic crushing as a fracturing fluid. Can be excavated.

  Specifically, a well is formed by excavating the formation where the target underground resource exists to form a pit, and then excavating in the horizontal direction to form a horizontal hole.

  Fracturing is performed by filling the well formed in this way with the above-described drilling dispersion liquid containing proppant and pressurizing the well. More specifically, due to this pressurization, the water-absorbing resin and / or proppant permeates in the vicinity of the horizontal hole, and the water-absorbing resin is liquefied and disappears to form a pillar structure. After the remaining liquid is aspirated, recovery of underground resources such as gas and oil is started.

When the dispersion for excavation of the present invention is hydraulically crushed using a fracturing fluid, the water-absorbing resin is quickly liquefied, so that it can be efficiently performed in a short time. Other than fracturing fluid, it is also used as a plug or breakdown material.
Moreover, when excavating with a drill while recirculating muddy water, it can be used as a water loss adjusting agent in the finishing fluid, so that an acid treatment in a subsequent step is not necessary. In addition, there is no clogging and production trouble does not occur.

  Furthermore, this water-absorbent resin can also function as a sealant that blocks the flow path in the well, but since it liquefies after that, problems such as clogging due to sedimentation of the sealant can be avoided, and production efficiency can be avoided. Can be increased.

  In the present invention, the excavation dispersion liquid described above is injected into the underground well in a form in which the water-absorbing resin and other materials are dispersed in water, but a break agent for liquefaction is added later. It is also possible to do. For example, an aqueous solution of a break agent can be supplied later after a liquid in which components other than the break agent are dispersed in water is injected into the well.

  References such as scientific literature, patents and patent applications cited herein are hereby incorporated by reference in their entirety to the same extent as if each was specifically described.

  The present invention has been described with reference to the preferred embodiments for easy understanding. Hereinafter, the present invention will be described based on examples. However, the above description and the following examples are provided for illustrative purposes only and are not provided for the purpose of limiting the present invention. Accordingly, the scope of the invention is not limited to the embodiments or examples specifically described herein, but is limited only by the claims.

  The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not construed as being limited thereto, and examples obtained by appropriately combining technical means disclosed in each example. Are also included in the scope of the present invention.

  In addition, as long as there is no comment, the electrical device (including the physical property measurement of a water absorbing resin) used by an Example and a comparative example used the power supply of 200V or 100V. Further, the physical properties of the water-absorbent resin of the present invention were measured under conditions of room temperature (20 to 25 ° C.) and relative humidity of 50% RH unless otherwise noted.

[Measurement of physical properties of water-absorbing resin]
(A) CRC (absorption capacity under no pressure)
The CRC (water absorption capacity under no pressure) of the water absorbent resin of the present invention was measured according to the EDANA method (ERT441.2-02).

[Production of water-absorbing resin]
The water absorbent resin of the present invention was obtained by the method of Production Example 1 below.

(Production Example 1)
In 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% (monomer concentration: 38% by mass), 1.7 g of trimethylolpropane triacrylate was dissolved to obtain a reaction solution. Next, the reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere, and then a reactor formed by attaching a lid to a double-armed jacketed stainless steel kneader having two sigma-shaped blades with an internal volume of 10 L. The reaction solution was supplied, nitrogen gas was blown into the reactor while maintaining the reaction solution temperature at 30 ° C., and nitrogen substitution was performed so that the dissolved oxygen in the system was 1 ppm or less.

  Subsequently, 29.8 g of a 10% by weight aqueous solution of sodium persulfate and 21.8 g of a 0.2% by weight aqueous solution of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. A polymerization peak temperature of 86 ° C. was exhibited 17 minutes after the start of the polymerization, and a hydrogel polymer was taken out 60 minutes after the start of the polymerization.

  The obtained hydrogel polymer was subdivided into particles of about 1 to 5 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried in hot air at 180 ° C. for 45 minutes to obtain a dried product.

  Next, the dried product was pulverized with a roll mill, and further classified continuously with a metal mesh having openings of 850 μm and 106 μm. The particles of 850 μm or more were pulverized again with a roll mill to obtain irregularly crushed water-absorbent resin particles. The CRC of the water-absorbent resin powder (water absorption capacity under no pressure) was 54.5 [g / g].

  Next, 100 parts by mass of the obtained water-absorbent resin particles were mixed with 0.02 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1,4-butanediol, 0.5 parts by mass of propylene glycol, and 2.8 water. 3.62 parts by mass of a surface cross-linking agent aqueous solution consisting of parts by mass was mixed. The above mixture was heat-treated in a mortar mixer heated to 195 ° C. for 40 minutes to obtain a water absorbent resin.

  Particulate water-absorbing resin was obtained by adding 0.3 part by mass of fumed silica AEROSIL200 manufactured by Nippon Aerosil Co., Ltd. to 100 parts by mass of water-absorbing resin and mixing them uniformly.

[Liquefaction experiment of water-absorbing resin]
The following example was performed about liquefaction of the water absorbing resin.

Example 1
The liquefaction of the water-absorbent resin by adding Fe and L-ascorbic acid (L-as) was examined. Based on the results of Example 1, only 600 μm was used as the sieve.

<Experimental procedure>
1. 0.25 g of the water-absorbent resin prepared in Production Example 1 was added to 450 g each of pure water and an aqueous solution of Fe 100 ppm derived from iron sulfate, Fe 50 ppm + L-as 5%, 10% or 20% (swelled 1800 times), 1 Swelled for hours.
2. The above 1 was heated in a dryer at 60 ° C. for 1 day.
3. The heat-degraded gel was filtered through a 600 μm sieve.
4). The weight of the gel remaining on the sieve was measured.

  <Result>

* Residual rate = (Gel weight in degraded solution / Gel weight in pure water) x 100
-Deterioration progressed more when L-as was added than when Fe alone was added.
-Even when the amount of L-as was increased from 5% to 20%, the degree of deterioration was the same.

(Example 2)
Add iron sulfate-derived Fe, L-ascorbic acid (L-as), vermiculite (typical metals contained: Mg, Fe, Al), sodium persulfate (NaPS), or ammonium persulfate (NH ₄ PS) The liquefaction of the water-absorbent resin produced in Production Example 1 was investigated. Here, an experiment was conducted to determine the effect of addition of vermiculite and the minimum amount of L-as.

  <Result>

* Residual rate = (Gel weight in degraded solution / Gel weight in pure water) x 100
-Addition of 1% vermiculite hardly deteriorated as with pure water.
-In the experiment which adds L-as to Fe50ppm, it turned out that the minimum L-as amount exists between L-as amount 0.01% and 0.1%.
FIG. 1 shows photographs of the gel before and after heating when Fe 50 ppm + L-as 0.1% was added. It was found that the gel was liquefied after heating.

Note) Vermiculite 1% + L-as 0.1% on 600 μm [g] is the weight obtained by subtracting the weight of vermiculite.
* Residual rate = (Gel weight in degraded solution / Gel weight in pure water) x 100
-By adding L-as to 1% vermiculite, the residual rate of the gel was greatly reduced.
-At L-as 0.01%, the gel degradation was the same even when the Fe content was increased from 50 ppm to 100 ppm. From this result, it is considered that the L-as amount has a greater influence on the deterioration of the gel than the Fe amount.
In the persulfate aqueous solution, the residual rate was less than about 5%, and the degree of deterioration was the same as when 0.1% or more of L-as was added. However, as shown in FIG. 2, the gel was one lump of yellowish white.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, it is understood that the scope of this invention should be construed only by the claims. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

  As a result of searching for conditions necessary for the decomposition (liquefaction) of the water-absorbing resin, the inventors have found that the water-absorbing water-absorbing resin is liquefied and the break agent for the water-absorbing resin used in the hydraulic crushing of the formation. I found. Therefore, the present invention is effective in the field of formation hydraulic crushing.

Claims (18)

A break agent for a water-absorbing resin used in hydraulic fracturing of a formation, comprising an iron ion-containing substance and / or ascorbic acid and / or persulfate. The break agent according to claim 1, wherein the persulfate is sodium persulfate or ammonium persulfate. The break agent according to claim 1, wherein the iron ion-containing substance is iron chloride, iron sulfate, or vermiculite. The break agent of Claim 1 containing an iron ion containing substance and ascorbic acid. The break agent according to claim 1, wherein the water absorbent resin contains an iron ion-containing substance, and the break agent contains ascorbic acid. The break agent according to claim 1, wherein the water-absorbent resin is capable of absorbing water at least as much as its own weight. The break agent according to claim 1, wherein the water absorbent resin is selected from the group consisting of the following (a) to (i):
(A) a partially crosslinked polymer obtained by polymerization of a water-soluble ethylenically unsaturated monomer;
(B) Starch grafted polyacrylate;
(C) acrylamide / acrylic acid copolymer and salts thereof;
(D) Starch graft acrylamide / acrylic acid and its salts;
(E) an isobutylene / maleic anhydride copolymer;
(F) sodium and potassium salts of carboxymethylcellulose;
(G) a crosslinked salt of polyaspartic acid;
(H) Chitosan / polyvinylpyrrolidone combination and chitosan / polyethyleneimine combination; and (i) sulfonic acid group-containing monomer, (meth) acrylic acid amide, (meth) acrylic acid, (meth) acrylate A partially crosslinked polymer obtained by polymerization of two or more monomers. The break agent according to claim 1, wherein the water absorbent resin is a polyacrylic acid resin. The gel residual ratio of the water-absorbent resin is 30 (g / g) or less, provided that the gel residual ratio (mass%) = (gel mass after addition of break agent-containing aqueous solution / gel mass after addition of pure water) × The break agent according to claim 1, which is 100. The water-absorbent resin is a compound having two or more unsaturated groups in one molecule, repeating units derived from at least one monomer component (A) selected from the group consisting of unsaturated carboxylic acids and salts thereof The repeating unit derived from (B), comprising a repeating unit derived from a compound (C) having two or more functional groups capable of reacting with a carboxyl group in one molecule. Agent. The break agent according to any one of claims 1 to 10, wherein the hydraulic crushing is for shale gas mining. A kit for use in hydraulic crushing of a formation comprising a swelling agent containing a water absorbent resin, an iron ion-containing substance, and ascorbic acid. A kit for use in hydraulic crushing of a formation comprising a swelling agent containing a water-absorbent resin and an iron ion-containing substance and ascorbic acid. The kit according to claim 12 or 13, wherein the water absorbent resin has the characteristics according to any one of claims 6 to 10. The kit according to any one of claims 12 to 14, wherein the hydraulic fracturing is for shale gas mining. A method for hydraulic fracturing of a formation, the method comprising:
A) a step of press-fitting a water-absorbing resin from a perforated portion of the formation with a proppant as necessary, crushing a rock as a reservoir to form a fracture; and B) from the perforated portion, an iron ion-containing substance and A method comprising injecting ascorbic acid and / or persulfate into contact with the fracture. The method according to claim 16, wherein the water-absorbent resin has the characteristics according to any one of claims 6 to 10. The method of claim 16, wherein the hydraulic fracturing is for shale gas mining.