Packer, downhole tool, and wellbore treatment method

Abstract

Provided is a plug that can maintain a plugged state for a prescribed period even in a fluid or water having a high temperature and a low salt concentration. A plug (5) for temporarily blocking the flow of a fluid in a well, the plug being provided with a resin molded body formed of a polyglycolic acid resin composition containing polyglycolic acid and a cyclic carbodiimide compound, the concentration of carbodiimide groups being 15 eq / t or more, or the plug being composed of the resin molded body.

Description

TECHNICAL FIELD

[0001] The present application relates to a plug, a downhole tool, and a well treatment method. BACKGROUND

[0002] As a well treatment operation for recovering a hydrocarbon resource from the ground, for example, fracturing and washing of a well can be cited. When fracturing is performed, it is necessary to use a downhole tool or a plug to block the passage of fluid in the well. Furthermore, in the case of washing of a well and stimulation of a formation before fracturing, in the washing, it is necessary to isolate the flow path of the fluid for washing with a downhole tool so that the fluid for washing does not mix before and after the washing. Meanwhile, after the washing, in order to stimulate the formation, it is necessary to set an opening portion by disassembling a specific position of the downhole tool so as to apply water pressure to the well wall.

[0003] Moreover, after any well treatment, these downhole tools need to be removed quickly by some method. Thus, it is required that the downhole tool or the plug can maintain the hole blocking only for a prescribed period.

[0004] In this regard, in Patent Literature 1, a method of treating a well using particles of a decomposable raw material containing a stabilizer is disclosed. In Patent Literature 2, it is disclosed that the decomposition of a resin is inhibited if the acid group concentration of the resin is reduced, and the decomposition of the resin is promoted if the acid group concentration is increased. In Patent Literature 3, a molded body of a polyglycolic acid resin is disclosed, which has a constant thickness reduction rate with respect to time in water. In Patent Literature 4, a treatment method using a tool provided with a plug having corrosiveness in an electrolyte is disclosed.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: U.S. Patent No. 2017 / 0342306 Specification

[0008] Patent Literature 2: Japanese Patent Application Publication No. 2015-160872 Specification

[0009] Patent Literature 3: International Publication No. 2013 / 183363

[0010] Patent Literature 4: International Publication No. 2015 / 199647 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] However, the prior art described above is not a technique of decomposing a molded body having a wall thickness capable of withstanding a pressure at the time of fracturing in water. Also, in the prior art document described above, a specific decomposition retardant having an effect of slowing down a reduction speed of thickness and a composition are not disclosed. Furthermore, the higher the temperature around polyglycolic acid, the faster the hydrolysis reaction speed, and thus, a plug including a polyglycolic acid member has a problem that a hole plugging cannot be maintained for a target period in a well of high temperature. Also, in a plug including a corrosive metal member, a corrosion speed is strongly dependent on a salt (electrolyte) concentration in a fluid, and the corrosion is slow in a fluid or water of low salt concentration. Thus, a plug including a corrosive metal member has a problem that a hole plugging is not released even if a target period elapses.

[0013] Thus, a plug in which a hole plugging maintaining time is sufficient even in a well of high temperature and in which a hole plugging can be reliably released even in a fluid or water of low salt concentration is desired.

[0014] Therefore, the present application is achieved in view of the above-described problems, and an object thereof is to provide a plug in which a hole plugging can be maintained only for a prescribed period even in a fluid or water of high temperature and low salt concentration.

[0015] Technical Solution

[0016] To solve the above-described problems, the plug of the present application is a plug for temporarily blocking a flow of a fluid in a well, the plug including a resin molded body formed of a polyglycolic acid resin composition including polyglycolic acid and a cyclic carbodiimide compound, a concentration of a carbodiimide group being 15 eq / t or more, or the plug being composed of the resin molded body.

[0017] Further, the downhole tool of the present application includes a cylindrical body having an opening portion for communicating the inside and the outside of the cylindrical body on a peripheral surface thereof, and the plug described above engaged with the cylindrical body so as to plug the opening portion.

[0018] The well treatment method of the present application includes: temporarily plugging one or more regions of at least one of a well and a downhole tool using the plug described above; and removing the plug by decomposing the resin molded body of the plug to change a flow path of a fluid in the region.

[0019] The well treatment method of the present application includes: setting the plug described above in a well to block a flow of a fluid in the well; and decomposing the resin molded body to restore the flow of the fluid.

[0020] The well treatment method of the present application includes: introducing a downhole tool into a well, the downhole tool having a first opening at a leading end, a second opening at a trailing end, and a third opening between the leading end and the trailing end, the third opening being plugged by the plug; pressurizing a fluid from the ground through the first opening into the downhole tool, and ejecting the fluid from the second opening into the well to clean the well; and after the cleaning, decomposing the resin molded body of the plug to enable the circulation of the fluid between the inside and outside of the downhole tool through the third opening.

[0021] Advantages

[0022] According to the plug of the present application, the plugging can be maintained for a prescribed period even in a fluid or water having a high temperature and a low salt concentration. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic view of a cross section of a downhole tool to which the first aspect of the plug of the embodiment of the present application is applied.

[0024] Figure 2 is a schematic view of a part of a cross section of a downhole tool to which the first aspect of the plug of the embodiment of the present application is applied, enlarged.

[0025] Figure 3 is a schematic view of a part of a cross section of a downhole tool to which the first aspect of the plug of the embodiment of the present application is applied, enlarged.

[0026] Figure 4 is a schematic view of a cross section of a downhole plug at a prescribed position in a well according to the embodiment of the present application.

[0027] Figure 5 is a schematic view of a cross section of a downhole plug when plugging a well according to the embodiment of the present application. DETAILED DESCRIPTION

[0028] 1. Plug

[0029] The plug of the present embodiment refers to a member or device for temporarily blocking the circulation of a fluid in a well. There is no limitation on the form of the plug as long as it is a plug for temporarily blocking the circulation of a fluid in a well, and it can be, for example, a ball, a dart, a disc, a screw, a frac plug, a bridge plug, or a packer.

[0030] The plug of the present embodiment is provided with a resin molded body formed of a polyglycolic acid resin composition, or the plug of the present embodiment is composed of a resin molded body formed of a polyglycolic acid resin composition. "Composed of a resin molded body" means that no other constituent element other than the resin molded body is included.

[0031] In the case of a plug having a resin molded body formed from a polyglycolic acid resin composition, the use of any specific constituent element is not limited as long as the obstruction to fluid flow is eliminated by decomposition of the resin molded body. Detailed examples of specific plugs will be described later.

[0032] There are no particular restrictions on the shape of the resin molded body; it should be appropriately designed according to the plug or the component in the plug that is being used.

[0033] (Polyglycolic acid resin composition)

[0034] The resin molded body used in the plug of this embodiment is formed from a polyglycolic acid resin composition. The polyglycolic acid resin composition in this embodiment contains polyglycolic acid and a cyclic carbodiimide compound. Furthermore, the concentration of carbodiimide groups in the polyglycolic acid resin composition is 15 eq / t or more. It should be noted that, unless otherwise specified, "cyclic carbodiimide compound" in this specification refers to a cyclic carbodiimide compound that does not react with polyglycolic acid.

[0035] The content of the cyclic carbodiimide compound in the polyglycolic acid resin composition is preferably 0.4% by mass or more. The content of the cyclic carbodiimide compound can be appropriately adjusted according to the desired pore-clogging retention period of the resin molded body formed from this composition. From the viewpoint of reliably reducing the thickness reduction rate of the molded body, the content of the cyclic carbodiimide compound is more preferably 0.7% by mass or more, and even more preferably 1% by mass or more. Furthermore, from the viewpoint of stably melt-blending the polyglycolic acid resin composition, the content of the cyclic carbodiimide compound is preferably 30% by mass or less, and more preferably 25% by mass or less.

[0036] The polyglycolic acid used in the polyglycolic acid resin composition of this embodiment is a polymer containing repeating units represented by -(-O-CH2-CO-)-. Polyglycolic acid can be a homopolymer of glycolic acid or a copolymer of glycolic acid with other monomeric components. Other monomeric components used in the copolymer include, for example, hydroxycarboxylic acids such as L-lactic acid, D-lactic acid, 3-hydroxybutyric acid, and 1-hydroxyhexanoic acid; ester compounds composed of diols and dicarboxylic acids, such as condensates of 1,4-butanediol and succinic acid and condensates of 1,4-butanediol and adipic acid; cyclic esters and lactones formed by intramolecular condensation of the aforementioned monomeric components; and cyclic carbonates such as trimethylene carbonate.

[0037] When polyglycolic acid is a copolymer of glycolic acid and other monomeric components, the content of constituent units derived from glycolic acid is 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more.

[0038] When polyglycolic acid is a copolymer of glycolic acid and other monomeric components, the melt viscosity of the copolymer is preferably lower than that of a glycolic acid homopolymer with the same molecular weight as the copolymer. With a copolymer having such a melt viscosity, when using a polyglycolic acid resin composition for curing extrusion molding or injection molding, it is not necessary to increase the melt temperature to suppress the decrease in the molecular weight of polyglycolic acid, thus enabling the production of high-strength downhole tool components.

[0039] When polyglycolic acid is a homopolymer, its weight-average molecular weight preferably exceeds 20,000. By exceeding 20,000, the water vapor barrier properties of polyglycolic acid are guaranteed. This delays the penetration of water into the resin molded body used in the plug, thus preventing the plug from decomposing. Furthermore, from the viewpoint of obtaining a high-strength downhole tool component, the weight-average molecular weight of the polyglycolic acid homopolymer is preferably 50,000 or more, more preferably 70,000 or more, and even more preferably 150,000 or more. While there is no particular upper limit to the weight-average molecular weight of the polyglycolic acid homopolymer, from the viewpoint of enabling curing extrusion molding or injection molding, it is generally preferred to be 500,000 or less, more preferably 300,000 or less.

[0040] The ends of polyglycolic acid are preferably capped with a cyclic carbodiimide compound. Here, "the ends of polyglycolic acid are capped with a cyclic carbodiimide compound" means having a structure obtained by reacting the carboxyl groups at the ends of the polyglycolic acid with the cyclic carbodiimide compound. In the case of polyglycolic acid being capped with a cyclic carbodiimide compound, the capping may not necessarily occur in all of the polyglycolic acid ends.

[0041] When at least a portion of the polyglycolic acid is capped by a cyclic carbodiimide compound, the concentration of the carboxyl terminus of the polyglycolic acid in the polyglycolic acid resin composition is preferably 10 eq / t or less, more preferably 8 eq / t or less, and even more preferably 6 eq / t or less. There is no particular limitation on the lower limit of the concentration of the carboxyl terminus of the polyglycolic acid, but it is generally approximately 0.1 eq / t or more. By keeping the concentration of the carboxyl terminus of the polyglycolic acid within the above range, the decomposition of the polyglycolic acid in the pit environment can be suppressed.

[0042] The concentration of the carboxyl terminus of polyglycolic acid in the polyglycolic acid resin composition can be calculated by titration using a neutralization reaction. Specifically, the following method can be cited as an example: The polyglycolic acid resin composition is dissolved in a solvent such as DMSO, a pH indicator is added, and an alkaline solution is added dropwise while observing the color change of the mixed solution. The addition is stopped when the color of the mixed solution no longer changes, and the carboxyl concentration is calculated based on the amount of alkaline solution added. It should be noted that, for example, a DMSO solution of 1,8-diazabicyclo[5,4,0]undec-7-ene can be used as the alkaline solution. The matrix concentration of the alkaline solution can be appropriately adjusted according to the concentration of the carboxyl terminus of the polyglycolic acid.

[0043] The cyclic carbodiimide compound used for end capping can typically be the same compound as the cyclic carbodiimide compound contained in the polyglycolic acid resin composition, or it may not have to be the same compound.

[0044] By capping the ends of polyglycolic acid with cyclic carbodiimide compounds, the decomposition of polyglycolic acid can be suppressed in pit environments.

[0045] The cyclic carbodiimide compound contained in the polyglycolic acid resin composition of this embodiment is a compound having the following cyclic structure, wherein the cyclic structure is formed by the bonding of the first nitrogen and the second nitrogen of the carbodiimide group through a bonding group. The cyclic carbodiimide compound can be represented, for example, by the following formula (Ⅰ).

[0046]

[0047] In Formula (I), R represents one or more divalent bonded groups selected from the group consisting of aliphatic groups, alicyclic groups, and aromatic groups. Furthermore, in Formula (I), R optionally contains heteroatoms. Examples of heteroatoms include oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P). Moreover, R optionally contains a ring structure, which optionally contains a carbodiimide structure. The type and number of atoms constituting the main chain of the ring structure can be appropriately determined within the range that yields the effects of this embodiment. For example, the number of atoms directly constituting the ring structure is preferably 8 or more, more preferably 10 or more. Furthermore, the number of these atoms is preferably 50 or less, more preferably 20 or less.

[0048] Furthermore, R may also have a monovalent substituent within the range that achieves the effects of this embodiment. More specifically, R may be an aliphatic group with 1 to 20 carbon atoms in a divalent to tetravalent state, an alicyclic group with 3 to 20 carbon atoms in a divalent to tetravalent state, an aromatic group with 5 to 15 carbon atoms in a divalent to tetravalent state, or a combination thereof. Examples of such combinations include alkylene-arylene groups formed by the bonding of an alkylene group to an arylene group.

[0049] Examples of aliphatic groups in R include: alkylene groups with 1 to 20 carbon atoms, trialkyl alkane groups with 1 to 20 carbon atoms, and tetraalkyl alkane groups with 1 to 20 carbon atoms.

[0050] Examples of alkylene compounds include: methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, dodecylene, and hexadecylene.

[0051] Examples of alkane triaryl groups include: methane triaryl, ethane triaryl, propane triaryl, butane triaryl, pentane triaryl, hexane triaryl, heptane triaryl, octane triaryl, nonane triaryl, decane triaryl, dodecane triaryl, and hexadecane triaryl.

[0052] Examples of alkyl tetrayl groups include: methane tetrayl, ethane tetrayl, propane tetrayl, butane tetrayl, pentane tetrayl, hexane tetrayl, heptane tetrayl, octane tetrayl, nonane tetrayl, decane tetrayl, dodecane tetrayl, and hexadecane tetrayl.

[0053] Examples of alicyclic groups in R include: cycloalkylene groups with 3 to 20 carbon atoms, cycloalkane trimethyl groups with 3 to 20 carbon atoms, and cycloalkane tetramethyl groups with 3 to 20 carbon atoms.

[0054] Examples of cycloalkylene compounds include: cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, cycloheptylene, cyclooctylene, cyclononylene, cyclodecylene, cyclododecylene, and cyclohexadecylene.

[0055] Examples of cycloalkane trimethyl groups include: cyclopropane trimethyl, cyclobutane trimethyl, cyclopentane trimethyl, cyclohexane trimethyl, cycloheptane trimethyl, cyclooctane trimethyl, cyclononane trimethyl, cyclodecane trimethyl, cyclododecane trimethyl, and cyclohexadecane trimethyl.

[0056] Examples of cycloalkane tetrayl groups include: cyclopropane tetrayl, cyclobutane tetrayl, cyclopentane tetrayl, cyclohexane tetrayl, cycloheptane tetrayl, cyclooctane tetrayl, cyclononane tetrayl, cyclodecane tetrayl, cyclododecane tetrayl, and cyclohexadecane tetrayl.

[0057] Examples of aromatic groups in R include: arylene groups with 5 to 15 carbon atoms, triarylene groups with 5 to 15 carbon atoms, and tetraarylene groups with 5 to 15 carbon atoms. The aromatic group optionally contains heteroatoms.

[0058] Examples of aryl groups include phenylene and naphthylene.

[0059] Examples of trivalent aromatic compounds include phenyltrimethyl and naphthyltrimethyl.

[0060] Examples of tetravalent aromatic compounds include phenyltetramethyl and naphthyltetramethyl.

[0061] Examples of substituents optionally present in R include: alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 15 carbon atoms, halogen atoms, nitro groups, amide groups, hydroxyl groups, ester groups, ether groups, and aldehyde groups.

[0062] Among the aforementioned cyclic carbodiimide compounds, from the viewpoint of preventing the deterioration of the working environment caused by the distinctive odor of isocyanate compounds, it is preferable to use a compound having only one carbodiimide group within a cyclic structure. This is because, with this structure, even if the cyclic carbodiimide reacts with the carboxyl group at the end of polyglycolic acid, a compound containing an isocyanate group will not be released.

[0063] Examples of the cyclic carbodiimide compounds mentioned above include compounds represented by formula (II) or formula (III) below.

[0064]

[0065] In addition to the aforementioned cyclic carbodiimide compound, the polyglycolic acid resin composition may also contain, for example, derivatives of the cyclic carbodiimide compound generated by reacting with the carboxyl terminus of polyglycolic acid.

[0066] Furthermore, the carbodiimide group contained in the polyglycolic acid resin composition has the structure of the following formula (Ⅳ).

[0067] -N=C=N-(Ⅳ)

[0068] The concentration of carbodiimide groups in the polyglycolic acid resin composition of this embodiment is 15 eq / t or more. This concentration can be appropriately designed according to the required pore-closing retention time of the resin molded body of this embodiment. For example, from the viewpoint of reducing the thickness reduction rate of the resin molded body of this embodiment, this concentration is preferably 18 eq / t or more, more preferably 30 eq / t or more, and even more preferably 50 eq / t or more. Furthermore, from the viewpoint of maintaining the tensile strength of the resin molded body of this embodiment at 80 MPa or more, this concentration is preferably 900 eq / t or less, more preferably 800 eq / t or less, and even more preferably 650 eq / t or less. If the concentration of carbodiimide groups is within this range, a pore-closing device that can maintain pore clogging for a desired period of time under high temperature conditions can be realized.

[0069] The concentration of the carbodiimide terminus in the polyglycolic acid resin composition can be determined, for example, by using dimethyl sulfone as a standard. 1 It was calculated by H NMR measurement.

[0070] It should be noted that the polyglycolic acid resin composition of this embodiment may also include heat stabilizers, antioxidants, impact modifiers, crosslinking agents, organic fillers, inorganic fillers, colorants, and other additives, as long as the desired effect of the plugger of this embodiment is not lost.

[0071] When a polyglycolic acid resin composition contains a cyclic carbodiimide compound, the hydrolysis of the polyglycolic acid contained in the composition is inhibited. The higher the content of the carbodiimide compound, the more inhibited the hydrolysis. This is because water also reacts with the carbodiimide groups; therefore, the more carbodiimide groups are contained in the polyglycolic acid resin composition, the more water is consumed in the reaction with the carbodiimide groups, and as a result, less water participates in the hydrolysis of the polyglycolic acid.

[0072] Regarding the polyglycolic acid resin composition of this embodiment, by having a carbodiimide group concentration of 15 eq / t or higher, the hydrolysis of polyglycolic acid contained in the resin molded article formed from this composition can be moderately suppressed in a high-temperature pit environment. Therefore, with such a resin molded article, pore plugging can be maintained for a desired period of time in a high-temperature environment. In this specification, "high temperature" refers to a temperature of 80°C or higher.

[0073] It should be noted that even resin molded bodies formed from polyglycolic acid resin compositions that do not contain cyclic carbodiimide compounds can have their plugging retention time extended by increasing their thickness. However, due to design constraints of downhole tools, the thickness is not solely determined by considering decomposition. In this embodiment, the thickness of the plug used to achieve the same plugging retention time is less than that of a resin molded body formed from a polyglycolic acid resin composition that does not contain cyclic carbodiimide compounds. As a result, the design scope and freedom of downhole tools can be broadened. For example, as shown in one plug design described later, in the case of a plug used in an insertable cylindrical member, the inner diameter of the downhole tool can be further increased by reducing the wall thickness of the cylindrical body to match the thickness of the plug. As a result, fluid transport efficiency is improved. The application of the plug of this embodiment can also contribute to such an increase in fluid transport efficiency.

[0074] (Manufacturing method of resin molded articles)

[0075] The resin molded article of this embodiment can be manufactured by mixing polyglycolic acid with a cyclic carbodiimide compound and then curing and extruding or injection molding the mixture. The mixture can be formed by melt-blending polyglycolic acid and the cyclic carbodiimide compound and then granulating it. In the case of melt-blending, from the viewpoint of suppressing the thermal decomposition of polyglycolic acid, the temperature is preferably 220°C to 280°C, more preferably 230°C to 260°C.

[0076] Furthermore, by mixing polyglycolic acid with a cyclic carbodiimide compound at the aforementioned temperature, a portion of the cyclic carbodiimide compound reacts with the terminal carboxyl groups of the polyglycolic acid. As a result, the ends of the polyglycolic acid are capped by the cyclic carbodiimide compound.

[0077] The amount of the cyclic carbodiimide compound added to polyglycolic acid is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, relative to 100 parts by mass of polyglycolic acid. When manufacturing the molded article by curing extrusion molding or injection molding, or when granulating polyglycolic acid by melt-blending with the cyclic carbodiimide compound, a portion of the added cyclic carbodiimide compound reacts with the terminal carboxyl groups of the polyglycolic acid, serving as end-capping for the polyglycolic acid. A portion of the remaining cyclic carbodiimide compound decomposes or disappears due to heat. By adjusting the amount of the added cyclic carbodiimide compound as described above, the concentration of carbodiimide groups in the final resin molded article can be adjusted to 15 eq / t or more. Furthermore, the content of the cyclic carbodiimide compound in the resin molded article can also be adjusted to 0.4% by mass or more. There is no upper limit to the amount of the added cyclic carbodiimide compound, but it can be, for example, 30 parts by mass or less, and even more preferably 20 parts by mass or less.

[0078] It should be noted that, generally, if a resin molded article is formed by adding, for example, 20 parts by mass of a low-molecular-weight compound, the tensile strength of the resin molded article tends to decrease. However, in the resin molded article of this embodiment, which is produced by adding a cyclic carbodiimide compound, no decrease in tensile strength is observed even when the amount of the cyclic carbodiimide compound added is 30 parts by mass. Therefore, it is preferably used in downhole tools or components thereof where strength is required even when a large amount of the cyclic carbodiimide compound is added.

[0079] The preferred temperature for curing, extruding, or injection molding the resin molded body is 220°C to 280°C, and more preferably 230°C to 260°C.

[0080] (Decomposition of resin molded parts)

[0081] The resin molded body of this embodiment comprises a resin molded body formed from a polyglycolic acid resin composition, or the resin molded body of this embodiment is composed of a resin molded body formed from a polyglycolic acid resin composition, thus it is appropriately decomposed even in fluids or water with low salt concentration. When the resin molded body of this embodiment is immersed in water, the polyglycolic acid in the surface portion of the resin molded body decreases in molecular weight due to hydrolysis caused by the water. As a result, the surface portion of the resin molded body becomes brittle. The polyglycolic acid with reduced molecular weight permeates through water, thus the polyglycolic acid gradually hydrolyzes from the surface portion to the center of the resin molded body, thereby causing the resin molded body to become brittle. When the polyglycolic acid with reduced molecular weight is further reduced in molecular weight through further hydrolysis, oligomers or glycolic acid generated as hydrolysis products dissolve into the water, resulting in the resin molded body losing its shape. Thus, the resin molded body is ultimately decomposed. Through the decomposition of the resin molded body, the pore blockage achieved by the resin molded body is relieved.

[0082] In this specification, the time from the moment the resin molded body is immersed in water until the moment when the polyglycolic acid in the surface layer of the molded body begins to hydrolyze and the thickness of the molded body begins to decrease is called the "decomposition lead time". The resin molded body retains its shape immediately before immersion in water at least after the decomposition lead time.

[0083] Furthermore, due to the hydrolysis of polyglycolic acid, the molecular weight of polyglycolic acid decreases, resulting in the resin molded body becoming brittle; this condition is called "embrittlement." The brittle portion within the resin molded body is called the embrittlement layer.

[0084] In this embodiment, the decomposition lead time and the rate of embrittlement of the resin molded body when immersed in water at 80°C depend on the hydrolysis rate of polyglycolic acid and can be appropriately adjusted according to the desired pore-clogging retention time. Hereinafter, unless otherwise specified, "the hydrolysis rate of polyglycolic acid and the rate of embrittlement of the resin molded body" will be abbreviated as "decomposition rate".

[0085] The optimal decomposition lead time when the resin-molded body is immersed in water at 80°C depends on the design of the downhole tool using the resin-molded body, and therefore cannot be generalized. However, from the viewpoint of extending the plugging retention time and minimizing the volume of the resin-molded body, a longer decomposition lead time is preferred. From the viewpoint of increasing the design flexibility and range of motion of the downhole tool, minimizing the volume of the resin-molded body is also preferable.

[0086] The decomposition lead time can be, for example, 2 hours or more, more preferably 10 hours or more, and even more preferably 16 hours or more. Furthermore, in this case, the decomposition lead time is preferably 72 hours or less, more preferably 48 hours or less, and even more preferably 40 hours or less.

[0087] The decomposition lead time can be extended by increasing the content of cyclic carbodiimide compounds or the concentration of carbodiimide groups in the resin molded body. This is because water molecules in contact with the resin molded body react first with the cyclic carbodiimide compounds or carbodiimide groups, thus inhibiting the hydrolysis of polyglycolic acid on the surface of the resin molded body.

[0088] Furthermore, when the resin molded body of this embodiment is immersed in water at 80°C for 48 hours, a central portion and a surface portion with a lower weight-average molecular weight than the central portion are formed. As an example, the weight-average molecular weight of the polyglycolic acid in the central portion of the resin molded body after immersion in water at 80°C for 48 hours is 70,000 or more. On the other hand, the weight-average molecular weight of the polyglycolic acid in the surface portion of the resin molded body after immersion in water at 80°C for 48 hours is 20,000 or less.

[0089] The thickness of the central portion and the surface portion of the resin molded body after impregnation also depends on the overall thickness of the resin molded body, as described below. Specifically, when the thickness of the resin molded body is approximately 5 mm, the difference between the thickness of the central portion and the thickness of the resin molded body before impregnation is preferably 0.1 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more. Furthermore, this thickness difference is preferably 2.0 mm or less, more preferably 1.9 mm or less, and even more preferably 1.8 mm or less.

[0090] The weight-average molecular weight of polyglycolic acid (PGA) decreases as hydrolysis proceeds. The carboxyl terminus of PGA is acidic, thus acting as a catalyst for ester bond hydrolysis; therefore, the decomposition rates differ between the central and surface portions of the resin molded body. The decomposition of the central and surface portions can also be delayed, similar to the lead time, by increasing the content of cyclic carbodiimide compounds or the concentration of carbodiimide groups in the resin molded body.

[0091] In this specification, the rate of embrittlement of the resin molded body is defined as the thickness reduction rate. The thickness reduction rate is the rate at which the thickness of the unembrittled portion of the resin molded body decreases. Embrittlement proceeds from the surface of the resin molded body towards the center, and the thickness of the unembrittled portion decreases from the surface side. Therefore, the rate of embrittlement is positively correlated with the thickness reduction rate.

[0092] The thickness reduction rate of the resin molded article in this embodiment after the decomposition lead time in water at 80°C is preferably 0.1 μm / hr or more, more preferably 1 μm / hr or more, and even more preferably 5 μm / hr or more. Furthermore, this thickness reduction rate is preferably less than 64 μm / hr, more preferably less than 61 μm / hr, and even more preferably less than 50 μm / hr.

[0093] The resin molded body of this embodiment is formed from a polyglycolic acid resin composition. Polyglycolic acid has high water vapor barrier properties; therefore, in order for water molecules to reach the center of the resin molded body, they must first pass through a brittle layer formed by surface hydrolysis. Thus, the resin molded body of this embodiment does not experience central hydrolysis and brittleness until the surface layer becomes brittle, and therefore brittleness does not occur rapidly.

[0094] Furthermore, the resin molded article of this embodiment contains a cyclic carbodiimide compound or a carbodiimide group. Water molecules that have passed through the embrittlement layer first react with the cyclic carbodiimide compound or the carbodiimide group, thus further inhibiting the diffusion of water molecules. As a result, the embrittlement process is further delayed.

[0095] Thus, the resin molded body of this embodiment can delay hydrolysis and embrittlement even after the decomposition advance period, thereby extending the pore-blocking retention time even under high temperature conditions.

[0096] Furthermore, by adjusting the decomposition rates of the central portion and the surface portion, the pore-clogging retention time of the resin molded body in this embodiment can be more appropriately adjusted. Examples include: immersing the molded body in preheated water to reduce the molecular weight of the polyglycolic acid only in the surface portion; and performing multilayer molding using different polyglycolic acid resin compositions in the central and surface portions. Furthermore, by adjusting the thickness and shape of the molded body, or by appropriately combining these conditions, the pore-clogging retention time under high-temperature conditions can also be more appropriately adjusted. The resin molded body of this embodiment maintains its function as a pore-clogging agent during the target period, and even after this period, decomposition proceeds at an appropriate rate in fluids with low salt concentrations (e.g., water with low salt concentrations). As a result, while suppressing decomposition to maintain its function, the problem of pore clogging not being resolved even after the target period can be eliminated.

[0097] (Other physical properties of resin molded articles)

[0098] Regarding the resin molded article in this embodiment, from the viewpoint of withstanding the high pressure inside the pit and maintaining the plugging effect, the tensile strength is preferably 80 MPa or more, more preferably 90 MPa or more, and even more preferably 100 MPa or more. Furthermore, from the viewpoint of ease of molding, the tensile strength is preferably 400 MPa or less, more preferably 370 MPa or less, and even more preferably 350 MPa or less. Here, the tensile strength of the resin molded article is determined using a type 1A tensile test piece, according to ISO 527, at 23°C and a stretching speed of 50 mm / min.

[0099] Furthermore, regarding the resin molded body in this embodiment, from the viewpoint of suppressing plastic deformation under high pressure in the pit and maintaining plugging, the compressive yield stress is preferably 100 MPa or more, more preferably 110 MPa or more, and even more preferably 120 MPa or more. Furthermore, from the viewpoint of ease of molding, the compressive yield stress is preferably 450 MPa or less, more preferably 420 MPa or less, and even more preferably 400 MPa or less. Here, the compressive yield stress of the resin molded body is measured using a 5 mm cube resin molded body, compressed at a speed of 1 mm / min in an environment of 23°C using a compression testing machine.

[0100] 2. Specific solutions for the blocker (the first solution for the blocker)

[0101] As a first embodiment of the plugging device, a plugging device is described that blocks an opening on the circumference of a cylindrical member inserted into a well, allowing communication between the inside and outside of the cylindrical member. Such a plugging device can be, for example, a ball, dart, disc, screw, or packer used in downhole tools. Furthermore, examples of downhole tools using these first-ideal plugging devices include flushing pipes used for cleaning wells or stimulating formations before fracturing.

[0102] The following uses Figure 1 The solution is described when the plug is a screw used in downhole tools. Figure 1 This is a schematic cross-sectional view of a downhole tool that uses the plugging device of the first aspect of the present invention.

[0103] Figure 1 The downhole tool 1 shown is inserted into the pit and has a cylindrical body 14 as a cylindrical component. The downhole tool 1 has a first opening 16 at the beginning and a second opening 17 at the end, and has one or more third openings 18 between the beginning and the end.

[0104] The third opening 18 is located on the circumferential surface of the cylindrical body 14, allowing communication between the inside and outside of the cylindrical body 14. A screw-shaped plug 11 is inserted into the third opening 18 to block it, and the plug 11 engages with the third opening. In this way, the third opening 18 of the cylindrical body 14 is blocked by the plug 11.

[0105] Here, the "starting end" of a downhole tool refers to the end located on the entrance side of the well when the downhole tool is positioned inside the well, and is the last end inserted when the downhole tool is inserted into the well. The "ending end" is the end on the opposite side of the starting end, and is the end located on the inside side when the well is viewed from the entrance, and is the first end inserted when the downhole tool is inserted into the well.

[0106] like Figure 1 As shown, the plug 11 is a screw-shaped plug that blocks the opening on the circumference of the cylindrical member that connects the inside and outside of the cylindrical member. The plug 11 is made of a resin molded body according to this embodiment.

[0107] The plug 11 is inserted into the third opening 18 of the cylindrical body 14, thereby blocking the flow of fluid from the inside of the cylindrical body 14 to the outside through the third opening 18. Then, by disintegrating the plug 11, which is made of resin molding, the third opening 18 is opened, resulting in the flow of fluid from the inside of the cylindrical body 14 to the outside through the third opening 18.

[0108] The size of the plug 11 can vary depending on the thickness of the cylindrical body 14 to which it is applied. As an example, when the plug 11 is embedded in the cylindrical body 14, the shortest distance L1 between the first surface 121 of the plug 11 exposed on the outside of the cylindrical body 14 and the second surface 122 of the plug 11 exposed on the inside of the cylindrical body 14 can be more than 6 mm and less than 65 mm.

[0109] (Variation 1 of the first scheme)

[0110] use Figure 2 A variation of the first scheme of the blocker in this embodiment will be described. Figure 2 This is an enlarged schematic diagram of a portion of the cross-section of a downhole tool of a modified example 1 of the first embodiment of the plugger applied according to the present invention. The downhole tool 2 of modified example 1 is the same as the downhole tool 1 described above, and the third opening 28 of the cylindrical body 24 is plugged by a screw-shaped plugger 21.

[0111] like Figure 2As shown, the plug 21 of Modified Example 1 is the same as the plug 11 described above, and is a plug that blocks the opening on the circumference of the cylindrical member that connects the inside and outside of the cylindrical member. However, the plug 21 of Modified Example 1 differs from the plug 11 in the following aspects: the plug 21 is composed of a main body 22 and an annular molded body 23, the main body 22 is formed of a resin molded body of this embodiment, and the annular molded body 23 is formed of a non-degradable material.

[0112] In Modification 1, the annular molded body 23 is an annular member covering the periphery of the main body 22 and having threaded teeth on its outer peripheral surface. Here, the main body 22 is configured to be disposed inside the ring of the annular molded body 23. The annular molded body 23 in Modification 1 is formed of a non-degradable material such as SUS303 and SUS304. Here, "non-degradable material" refers to a material whose weight or thickness does not easily decrease in a pit environment. The annular molded body 23 is preferably formed of a material whose weight or thickness does not substantially decrease in a pit for more than 30 days.

[0113] In Modification 1, the plug 21 is inserted into the third opening 28 of the cylindrical body 24, thereby blocking the flow of fluid from the inside of the cylindrical body 14 to the outside through the third opening 28. Then, by disassembling the main body 22 of the plug 21, which is made of resin molding, the third opening 28 is opened, resulting in the flow of fluid from the inside of the cylindrical body 24 to the outside through the third opening 28, and more specifically, through the inside of the ring of the annular molding 23.

[0114] The size of the main body 22 is the same as that of the blocker 11, and can be appropriately set by those skilled in the art.

[0115] (Variation 2 of the first scheme)

[0116] use Figure 3 A variation 2 of the first scheme of the blocker of this embodiment will be described. Figure 3 This is an enlarged schematic diagram of a portion of the cross-section of a downhole tool of a modified example 2 of the first scheme of the plugging device applying an embodiment of the present invention. Figure 3 The downhole tool 3 has a cylindrical body 34, with a third opening 38 on its circumference that connects the inside and outside of the cylindrical body 34. A plug 31 is engaged inside the cylindrical body 34.

[0117] The plug 31 in Modification 2 of the first embodiment is the same as the plug 11 of the first embodiment described above. It can also be applied to a cylindrical member having an opening on its circumferential surface that allows communication between the inside and outside. However, it differs from the plug 11 in that the plug 31 is not inserted into the opening. In Modification 2, the plug 31 engages with the cylindrical member on the inner side of its circumferential surface in a way that blocks the opening. Thus, the third opening 38 is blocked from the inside by the plug 31 engaging with the inner side of the cylindrical body 34. This prevents fluid from flowing from the inside of the cylindrical body 34 to the outside through the third opening 38. Furthermore, by partially disintegrating the resin-molded portion of the plug 31, the third opening 38 is exposed, allowing fluid to flow from the inside of the cylindrical body 34 to the outside through the third opening 38.

[0118] (Second option for the blocker)

[0119] As a second embodiment of the plugging device, examples include downhole plugs (downhole tools) such as fracturing plugs or bridge plugs inserted into the wellbore. In the downhole plugging device of this embodiment, the resin molded body is used in the form of downhole tool components such as a mandrel, load ring, cone, casing, and bottom, but is not limited to these. Hereinafter, the following will be described... Figure 4 The second embodiment of the plugging device, a downhole plugging device, will be described. Figure 4 This is a schematic cross-sectional view of a downhole plug at a predetermined location within a pit, according to an embodiment of the present invention. It should be noted that... Figure 4 The image shows only one side of the axisymmetric cross-section of the downhole plug.

[0120] Figure 4 The downhole plug 5 shown includes: a mandrel 51 corresponding to the cylindrical component, a ball 53, a central element 52 assembled around the outer circumference of the mandrel 51, a sleeve 54, cones 55a and 55b, sliding bodies 56a and 56b, balancing rings 57a and 57b, a load ring 58, and a bottom 59. The downhole plug 5 as a whole has a cylindrical shape.

[0121] Here, the mandrel 51a functions as the central axis supporting other components (hereinafter referred to as side components) arranged around the outer periphery of the mandrel 51, and as the receiving body of the ball 53. The central element 52 is an annular rubber component in the downhole plugger 5 used to plug the well by filling the gap between the mandrel 51 and the well wall 20, and deforms due to load.

[0122] The casing 54, cone 55, sliding body 56, balance ring 57, and load ring 58 are all elements that, when the downhole plug 5 is working in the pit, are used to directly or indirectly transfer the load applied by the setting tool to the central element 52.

[0123] The load ring 58 is a pressing clamp that transfers the load applied by the setting tool to other side components. The cone 55 has the function of promoting circumferential expansion towards the slider 56 and compressing the central element 52. The sleeve 54 has the function of preventing the central element 52 from flowing out to the inside when viewed from the inlet pit.

[0124] The bottom 59 has the following functions: to prevent the downhole plug 5 from colliding with the pit wall 20 during the delivery of the downhole plug 5 into the pit, and to fix other side components during installation.

[0125] 3. Application in pit and well treatment

[0126] The plug described above is a plug that temporarily blocks the flow of fluid within a pit well and can be used for pit well treatment. In this embodiment, the pit well is preferably a casing well.

[0127] Well treatment includes using a plug to temporarily block the flow path of fluid in at least one area of ​​the well or downhole tools; and removing the blockage by decomposing the resin molded body of the plug, thereby altering the flow path of fluid in that area. The following describes the application of a first approach to well treatment and the application of a second approach to well treatment.

[0128] When applying the first scheme of "2. Specific Scheme of the Plugging Device" to wellbore treatment, the area where the plugging device temporarily blocks the fluid flow path is the downhole tool. Specifically, the cylindrical member inserted into the well corresponds to the downhole tool. In this case, the fluid flow path is a third opening provided on the circumference of the cylindrical member of the downhole tool, which connects the inside and outside. The fluid flow is either from the inside of the cylindrical member, i.e., from the inside of the downhole tool, through the opening to the outside, or from the outside of the downhole tool, through the opening to the inside.

[0129] When the second scheme of "2. Specific scheme of plugger" above is applied to pit well treatment, the flow path of the fluid in which the plugger temporarily blocks the hole is the pit well, and the area in the flow path where the hole is temporarily blocked is a part of the pit well.

[0130] Other solutions for well treatment include: placing a plug in the well to block the flow of fluid within it; and decomposing the resin molded material constituting the plug to restore fluid flow. In well treatment, the resin molded material constituting the plug is decomposed by the water contained in the fluid present in the well, thus the well is blocked and fluid flow is restored.

[0131] (Scenario 1)

[0132] As a more specific method for treating pitted wells using the plugging device from the first approach, for using Figure 1 The document describes the cleaning of pitted wells and the treatment of formation irritation using the downhole tools shown. Figure 1 The pitting treatment method for the downhole tool shown is as follows: as a first option, a screw-shaped plug 11 temporarily plugs the third opening 18 on the circumference of the cylindrical body 14 of the downhole tool 1.

[0133] The cleaning of the pit aims to improve the recovery efficiency of hydrocarbon resources. Before fracturing, it is carried out in the following sequence: First, the downhole tool 1 is introduced into any position within the pit using fluids such as water. Next, a fluid such as water is pumped from the surface through the first opening 16 into the cylindrical body 14, causing the fluid to be sprayed into the pit from the second opening 17, thereby cleaning the pit. The fluid used is typically a liquid such as water, oil, or emulsion, and sometimes contains a few ppm to tens of percent of salts. At this time, the third opening 18 is plugged by the plugger 11, so the fluid pumped from the first opening 16 is not sprayed from the third opening 18. The fluid sprayed into the pit from the second opening 17 then passes through the gap between the outside of the downhole tool 1 and the pit wall 20, and is recovered on the surface along with sand and scale accumulated on the inner wall of the pit.

[0134] Here, by plugging the third opening 18 with the plug 11, fluids containing sand and scale from the cleaning process can be prevented from entering the interior of the downhole tool through the third opening 18. Therefore, it is possible to prevent a decrease in the efficiency of the cleaning operation. Thus, maintaining the plug 11 is important to prevent the plugging of the third opening from being removed during the cleaning operation.

[0135] After cleaning, when the resin molded body of the plug 11 that plugs the third opening 18 is disassembled, the inside and outside of the cylindrical body 14 can be connected through the third opening 18. Thus, fluid can flow through the inside and outside of the downhole tool 1.

[0136] Next, the treatment of stimulating the formation will be explained. From the viewpoint of improving the recovery efficiency of hydrocarbon resources recovered from the formation, the treatment of stimulating the formation is preferably carried out after cleaning the pit well. During the stimulation of the formation, it is preferable to allow the flow of fluids inside and outside the downhole tool 1 through the third opening.

[0137] The formation stimulation process is described below. First, a stimulating fluid is injected from the surface into the cylindrical body 14 through a first opening 16. The injected stimulating fluid is then sprayed onto the wellbore wall 20 through a third opening 18, stimulating the formation. This stimulation increases the amount of hydrocarbon resources recovered from the formation, thus contributing to increased production efficiency.

[0138] After the formation has been stimulated, the production fluid containing hydrocarbon resources flowing from the formation into the pit can be recovered to the surface via the third opening 18 and the first opening 16.

[0139] According to the plugger of this embodiment, a plugger is obtained that can maintain a high-temperature environment in multiple areas of downhole tools within a well for a desired period of time, and that appropriately decomposes even in fluids or water with low salt concentration after the desired period has elapsed. Therefore, plugging can be performed more reliably for the desired period of time, and the risk of blockage at the plugging location is reduced.

[0140] (The second option)

[0141] As a more specific example of a method for treating pitted wells using the second approach plug, for using... Figure 4 and Figure 5 The method for fracturing using the downhole plug shown will be explained. This is a well treatment method when the downhole plug corresponding to the plug of the second scheme is used to temporarily plug the well. Figure 4 This is a schematic cross-sectional view of a downhole plug at a predetermined position within a pit, according to an embodiment of the present invention. Figure 5 This is a schematic cross-sectional view of a downhole plugging device used for plugging pits and wells, according to an embodiment of the present invention. It should be noted that... Figure 4 and Figure 5 The image shows only one side of the axisymmetric cross-section of the downhole plug.

[0142] First, use fluid or similar means to guide the downhole plug 5 from the surface to any location within the pit. Then, operate the setting tool, such as... Figure 5 The central element 52 is deformed as shown, thereby setting and fixing the downhole plug 5 in the pit wall 20.

[0143] Next, the beginning of the mandrel 51 of the downhole plug 5 is blocked to complete the plugging. One method of plugging the hole is, for example... Figure 5 As shown, the following method can be used: a ball 53 supplied to the beginning of the downhole plug 5 is positioned at the beginning of the mandrel 51, thereby blocking one end of the mandrel 51. This allows the space at the entrance of the well to be separated from the space at the inner side, with the downhole plug 5 as the boundary. It should be noted that the ball 53 can also be positioned at the beginning of the mandrel 51 by allowing the ball 53 to flow in from the surface along with fluid.

[0144] Next, a fluid containing water or water is injected from the surface, applying high pressure to the space of the pit closer to the inlet side than the downhole plug 5, causing the fractures within the pit to expand / propagate. This method of using fluid injection to expand fractures is called hydraulic fracturing.

[0145] After fracturing, by contacting the downhole plug 5 with a water-containing fluid, part or all of the resin molded body constituting the downhole plug 5 decomposes. As a result, the downhole plug 5 loses its original shape, and the wellbore plugging is released. The downhole plug 5 equipped with the resin molded body of this embodiment decomposes even in the high-temperature environment within the well, for example, within a desired short period such as 5 to 30 days, thus releasing the plugging. When the temperature within the well is 80°C or higher, the plugging is released in an even shorter period.

[0146] The plugger according to this embodiment can maintain the plugging function in multiple areas of a well in a high-temperature environment for a desired period of time, and can also properly decompose even in fluids or water with low salt concentration after the desired period has elapsed. Therefore, plugging can be reliably performed for the desired period of time, and the risk of blockage at the plugging location can be reduced.

[0147] 〔Summarize〕

[0148] As described above, the plug of the present invention is used to temporarily block the flow of fluid in a pit or well. The plug comprises a resin molded body formed of a polyglycolic acid resin composition, or the plug is composed of the resin molded body, wherein the polyglycolic acid resin composition contains polyglycolic acid and a cyclic carbodiimide compound, and the concentration of the carbodiimide group is 15 eq / t or more.

[0149] Furthermore, it is preferred that the concentration of carboxyl termini in the polyglycolic acid resin composition is 10 eq / t or less.

[0150] Furthermore, it is preferable that the tensile strength of the above-mentioned resin molded article is 80 MPa or higher.

[0151] Furthermore, it is preferable that the compressive yield stress of the above-mentioned resin molded article is 100 MPa or more.

[0152] Furthermore, preferably, the resin molded body is a resin molded body that, after being immersed in water at 80°C for 48 hours, comprises a central portion with a weight-average molecular weight of 70,000 or more and a surface portion with a weight-average molecular weight of 20,000 or less, wherein the thickness of the central portion differs from the thickness of the resin molded body before immersion by 0.1 mm or more and 2.0 mm or less.

[0153] Furthermore, it is preferred that the aforementioned plug is a ball, dart, disc, screw, or packer.

[0154] Furthermore, preferably, the plug is used to block the opening on the circumference of the cylindrical member that connects the inside and outside of the cylindrical member, and the resin molded body has: a first surface that is exposed on the outside of the cylindrical member when the plug is used; and a second surface that is exposed on the inside of the cylindrical member when used, wherein the shortest distance between the first surface and the second surface is 6 mm or more and 65 mm or less.

[0155] Furthermore, preferably, the resin molded body is at least partially covered by other molded bodies made of non-degradable materials.

[0156] Furthermore, preferably, the other molded body is a ring-shaped molded body with threaded teeth on its outer peripheral surface, and the resin molded body is disposed inside the ring of the ring-shaped molded body.

[0157] Furthermore, it is preferable that the aforementioned plug is a fracturing plug or a bridge plug.

[0158] The downhole tool of the present invention comprises a cylindrical body and the aforementioned plug, wherein the cylindrical body has an opening on its circumferential surface that allows communication between the inside and outside, and the aforementioned plug engages with the cylindrical body in such a way as to block the opening.

[0159] The pit treatment method of the present invention includes: temporarily plugging at least one area of ​​a pit and a downhole tool using the above-mentioned plug; and eliminating the plug by decomposing the above-mentioned resin molded body of the plug, thereby changing the flow path of the fluid in the area.

[0160] The pit treatment method of the present invention includes: temporarily plugging at least one area of ​​a pit and a downhole tool using the above-mentioned plug; and eliminating the plug by decomposing the above-mentioned resin molded body of the plug, thereby changing the flow path of the fluid in the area.

[0161] The pit treatment method of the present invention includes: placing the above-mentioned plug in the pit to block the flow of fluid in the pit; and decomposing the above-mentioned resin molded body to restore the flow of the fluid.

[0162] The pit treatment method of the present invention includes: introducing a downhole tool having a first opening at a starting end and a second opening at a terminal end, and a third opening between the starting end and the terminal end, the third opening being plugged by the aforementioned plug; injecting fluid from the surface through the first opening into the downhole tool, causing the fluid to be sprayed into the pit from the second opening to clean the pit; and after cleaning, decomposing the resin molded body of the plug to allow fluid to flow through the third opening inside and outside the downhole tool.

[0163] The following embodiments are provided to further illustrate the implementation of the present invention. It is self-evident that the present invention is not limited to the following embodiments, and various solutions may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the disclosed technical means are also included within the technical scope of the present invention. In addition, all documents described in this specification are incorporated herein by reference.

[0164] Example

[0165] <Manufacturing of Resin Molded Components and Tensile Test Pieces>

[0166] 100 parts by weight of polyglycolic acid (Kureha Co., Ltd. "Kuredux 100R90", weight average molecular weight (Mw): 210,000) were mixed with 0, 1, 3, 5, or 20 parts by weight of cyclic carbodiimide (Teijin Co., Ltd. "Carbosista (trademark)", grade "TCC-NP"). The mixture was then fed into the feed section of a twin-screw extruder mixer with the screw section temperature set to 210°C–240°C for melt mixing, resulting in a granular polyglycolic acid resin composition. It should be noted that two samples were prepared using this mixture of 5 parts by weight of cyclic carbodiimide mixed with 100 parts by weight of polyglycolic acid.

[0167] The granules of the polyglycolic acid resin composition were fed into an injection molding machine with the screw temperature set at 210℃~255℃, and injection molded at a mold temperature of 100℃ to obtain a cubic resin molded body with a side width of 12.5mm and a dumbbell-shaped tensile test piece.

[0168] <Determination of the concentration of carboxyl terminus in polyglycolic acid>

[0169] The concentration of the carboxyl terminus of the polyglycolic acid used was calculated based on a titration using a neutralization reaction. First, 100 mg of granular polyglycolic acid resin composition was weighed into a vial, and then 10 mL of dehydrated DMSO was added. The vial was immersed in an oil bath at 160°C and heated to dissolve the granules. Then, the vial was cooled to room temperature, and 10 μL of a 1% BTB / DMSO solution was added. Next, while observing the color change of the mixed solution using a colorimeter, a 0.001 mol / L solution of 1,8-diazabicyclo[5,4,0]undec-7-ene DMSO was added dropwise as an alkaline solution. The addition was stopped at the point where the color of the mixed solution no longer changed, and the concentration of the carboxyl terminus was calculated based on the amount of alkaline solution added. The results are shown in Table 1.

[0170] <Decomposition Test>

[0171] The decomposition test of the resin molded body was carried out according to (1) to (5) below, and the thickness reduction rate and decomposition lead time were calculated. The results are shown in Table 1.

[0172] (1) After annealing the prepared cubic resin molded body at 120°C for 5 hours, the length, width and height of the resin molded body were measured.

[0173] (2) Add 50 mL of deionized water to a 50 mL bottle and let it stand in an 80°C constant temperature bath to prepare it to 80°C.

[0174] (3) Put the resin molded body into the small bottle of (2), immerse it in 50 mL of deionized water, and then let it stand in a constant temperature bath at 80°C for a specified time before taking it out.

[0175] (4) After drying the resin molded body under atmospheric pressure in an oven at 80°C for 2 hours, remove the brittle layer of the resin molded body and measure the length, width and height of the remaining part. The brittle layer is removed by cutting with a cutting tool.

[0176] (5) For the acquired data, a graph was created with time (hr) on the horizontal axis and thickness reduction on the vertical axis. The slope of the straight line calculated using the least squares method and the intersection point with the horizontal axis (the intercept of the horizontal axis) were calculated. The slope of the obtained straight line represents the thickness reduction rate (μm / hr), and the intercept of the horizontal axis represents the decomposition lead time (hr). Here, the thickness reduction is the average difference between the length, width, and height of the resin molded body before and after impregnation. It should be noted that points with a thickness reduction of less than 0.01 mm may contain errors in length measurement and are therefore excluded from the calculation.

[0177] <Determination of the content and concentration of cyclic carbodiimide compounds>

[0178] The prepared resin molded body and dimethyl sulfone (DMSO) used as an internal standard were dissolved in DMSO-d6 at 160°C for 2 minutes. After dissolution, the mixture was cooled to room temperature, filtered, and then... 1 The content and concentration of cyclic carbodiimide compounds were determined by H NMR.

[0179] Tensile Test

[0180] Tensile tests were performed to determine the maximum tensile stress of the manufactured resin molded parts. Type 1A tensile test specimens were used, and the stress was determined according to ISO 527 at 23°C and a speed of 50 mm / min. The results are shown in Table 1.

[0181] <Determination of compressive yield stress>

[0182] The compressive yield stress of the resin molded parts was determined. The determination was performed by cutting cubes with a side length of 5 mm from the resin molded parts and compressing them at a speed of 1 mm / min using a compression testing machine at 23°C. The results are shown in Table 1.

[0183] [Table 1]

[0184]

[0185]

[0186] When comparing Example 2 with Example 4, it is evident that even with the same amount of cyclic carbodiimide compound added, the thickness reduction rate was slower in Example 2, where the content of the cyclic carbodiimide compound was higher, compared to Example 4. In Example 4, it can be assumed that more cyclic carbodiimide compound reacted with the carboxyl groups at the ends of the polyglycolic acid, resulting in a lower concentration of carboxyl-terminal polyglycolic acid and carbodiimide groups in the composition compared to Example 2.

[0187] Symbol Explanation

[0188] 1, 2, 3 Downhole tools

[0189] 5. Downhole plug

[0190] 11, 21, 31 Blockers

[0191] 14, 24, 34 tubular body

[0192] 16 First opening

[0193] 17 Second opening

[0194] 18, 28, 38 Third opening

[0195] 20 pit well wall

[0196] 22 Main body

[0197] 23 Ring-shaped moldings

[0198] 51 mandrels

[0199] 52 central components

[0200] 53 goals

[0201] 54 tubing

[0202] 55, 55a, 55b cones

[0203] 56, 56a, 56b sliding bodies

[0204] 57, 57a, 57b balance rings

[0205] 58 load ring

[0206] 59 bottom

[0207] 121 First Page

[0208] 122 Second page

Claims

1. A plug for temporarily blocking the flow of fluid within a pit or well. The plugger comprises a resin molded body formed from a polyglycolic acid resin composition, or the plugger is composed of the resin molded body thereof, wherein the polyglycolic acid resin composition comprises polyglycolic acid and a cyclic carbodiimide compound, wherein the concentration of the carboxyl terminus of the polyglycolic acid is 10 eq / t or less, the concentration of the carbodiimide group is 50 eq / t or more and 650 eq / t or less, and the content of the cyclic carbodiimide compound is 0.4% by mass or more and 30% by mass or less. The content of the cyclic carbodiimide compound and the concentration of the carbodiimide group are obtained by heating and dissolving the prepared resin molded body and dimethyl sulfone as an internal standard in DMSO-d6, then cooling to room temperature, filtering the liquid components, and using... 1 It was obtained by H NMR measurement. The cyclic carbodiimide compound is a compound represented by formula (I). The resin molded body is as follows: after being immersed in water at 80°C for 48 hours, it comprises a central portion with a weight-average molecular weight of 70,000 or more and a surface portion with a weight-average molecular weight of 20,000 or less, wherein the thickness of the central portion differs from the thickness of the resin molded body before immersion by 0.1 mm or more and 2.0 mm or less. In formula (I), R represents one or more divalent bonded groups selected from the group consisting of aliphatic groups, alicyclic groups, and aromatic groups. Furthermore, in formula (I), R optionally contains heteroatoms selected from oxygen (O), nitrogen (N), sulfur (S) and phosphorus (P).

2. The blocker according to claim 1, wherein, The tensile strength of the resin molded body is above 80 MPa.

3. The blocker according to claim 1, wherein, The compressive yield stress of the resin molded body is above 100 MPa.

4. The blocker according to claim 1, wherein, The stopper is a ball, dart, disc, screw, or packer.

5. The plugger according to claim 1, wherein, The plug is used to block the opening on the circumference of the cylindrical member that allows communication between the inside and outside of the cylindrical member. The resin molded body has: a first surface exposed on the outside of the cylindrical member when the plug is used; and a second surface exposed on the inside of the cylindrical member when in use. The shortest distance between the first surface and the second surface is more than 6 mm and less than 65 mm.

6. The blocker according to claim 1, wherein, The resin molded body is at least partially covered by other molded bodies made of non-degradable materials.

7. The plugger according to claim 6, wherein, The other molded body is a ring-shaped molded body with threaded teeth on its outer peripheral surface, and the resin molded body is disposed inside the ring of the ring-shaped molded body.

8. The blocker according to claim 1, wherein, The plug is a fracturing plug or a bridge plug.

9. A downhole tool comprising a cylindrical body and a plug as claimed in claim 1. The cylindrical body has an opening on its circumferential surface that allows communication between the inside and outside. The plug engages with the cylindrical body in a manner that blocks the opening.

10. A method for treating pits and wells, the method comprising: Using the plugger as described in claim 1, temporarily plug at least one area of ​​at least one of the pit well and downhole tools; as well as The blockage is eliminated by decomposing the resin molded body of the plug, thereby altering the flow path of the fluid in the region.

11. A method for treating pits and wells, the method comprising: The plug as described in claim 1 is placed in the pit well to block the flow of fluid in the pit well; as well as The resin molded body is decomposed to restore the flow of the fluid.

12. A method for treating pits and wells, the method comprising: The following downhole tool is introduced into the pit, the downhole tool having a first opening at the beginning and a second opening at the end, and a third opening between the beginning and the end, the third opening being plugged by the plugger as described in claim 1; Fluid is forced from the ground through the first opening into the downhole tool, and then the fluid is ejected from the second opening into the pit to clean the pit; as well as After cleaning, the resin molded body of the plug is decomposed, allowing fluid to flow through the third opening inside and outside the downhole tool.

Images