Rubber composition for downhole tools, rubber molded article, member, and well treatment method

Abstract

The present disclosure provides a technique for achieving a well treatment by a member for downholes, which can achieve both mechanical properties and decomposability at appropriate levels. In the present disclosure, as a rubber member for downhole tools in a downhole tool to be used in a well treatment method, a rubber member comprising a rubber molded article is used, wherein the rubber molded article is produced using a rubber composition for downhole tools as a material therefor, and the rubber composition contains a polyester-based polyurethane, methyl p-toluenesulfonate, a carbodiimide compound, and an aromatic amine resin in specified amounts.

Description

Rubber composition, rubber molded article, component for downhole tool, and well treatment method

[0001] The present invention relates to a rubber composition, a rubber molded article, a component, and a well treatment method for downhole tools.

[0002] One known technique for extracting underground hydrocarbon resources is hydraulic fracturing, which involves drilling a hole (also called a "well" or "downhole") that leads to a productive layer of hydrocarbon resources underground, pumping water downhole, and increasing the pressure of the water to create fractures in the productive layer. In hydraulic fracturing, a downhole tool is inserted into the downhole, which is then sealed with downhole components, and various treatments for hydraulic fracturing are carried out. The downhole tool is placed deep underground and is usually not easy to retrieve. Therefore, the downhole components attached to the downhole tool are required to have sufficient mechanical properties to enable the various treatments described above and to be degradable downhole.

[0003] Known rubber compositions for downhole tools for such downhole components include those containing a polyester polyurethane, which is a degradable rubber, and a p-toluenesulfonic acid ester, which is a decomposition accelerator (see, for example, Patent Documents 1 and 2). Also known rubber compositions for downhole tools include those containing a polyester polyurethane, which is a decomposable rubber, a p-toluenesulfonic acid ester, which is a decomposition accelerator, and a carbodiimide compound, which is a decomposition inhibitor (see, for example, Patent Document 3).

[0004] International Publication No. WO 2015 / 133545 International Publication No. WO 2017 / 110609 International Publication No. WO 2018 / 216334

[0005] In downhole components, if the amount of the decomposition accelerator methyl p-toluenesulfonate added is increased in order to enhance decomposition, the decomposition ability is improved, but the surface hardness of the downhole component may become insufficient. Thus, the conventional technology leaves room for further study from the viewpoint of achieving both mechanical properties and decomposition ability of downhole components.

[0006] An object of one aspect of the present invention is to provide a technology for realizing well treatment using a downhole component that can adequately achieve both mechanical properties and degradability.

[0007] In order to solve the above problems, a rubber composition for downhole tools according to one embodiment of the present invention contains a polyester-based polyurethane, 3 to 10 parts by mass of methyl p-toluenesulfonate per 100 parts by mass of the polyester-based polyurethane, 0.1 to 2 parts by mass of a carbodiimide compound per 100 parts by mass of the polyester-based polyurethane, and 0.1 to 5 parts by mass of an aromatic amine resin per 100 parts by mass of the polyester-based polyurethane.

[0008] In order to solve the above problems, a rubber molded product for a downhole tool according to one embodiment of the present invention is molded using the above rubber composition for a downhole tool as a material, and has an initial durometer A hardness of 70 or more, and a rate of thickness reduction of 0.15 mm / h or more after 24 hours when immersed in water at 49°C.

[0009] In order to solve the above-mentioned problems, a downhole tool component according to one aspect of the present invention includes the above-mentioned rubber molded article for a downhole tool.

[0010] In addition, in order to solve the above-mentioned problems, a well treatment method according to one embodiment of the present invention temporarily seals the well using a downhole tool including the above-mentioned downhole tool component, and by contacting the downhole tool component with a fluid in the well environment, at least a portion of the downhole tool component is decomposed to unseal the well.

[0011] According to one aspect of the present invention, a technology can be provided that realizes well treatment using a downhole component that can adequately achieve both mechanical properties and degradability.

[0012] 1A and 1B are diagrams for explaining a cross section of a sample in an embodiment of the present invention, and are diagrams for explaining an observation target region in a sample in an embodiment of the present invention.

[0013] [Rubber Composition for Downhole Tool] A rubber composition for a downhole tool (hereinafter also simply referred to as "rubber composition") according to an embodiment of the present invention contains a polyester-based polyurethane, methyl p-toluenesulfonate, a carbodiimide compound, and an aromatic amine resin.

[0014] Polyester polyurethane is a type of rubber material that has a urethane bond (—NH—CO—O—) in its molecule, and is a polymer compound with a molecular structure formed by a condensation reaction between an isocyanate compound and an ester compound having a hydroxyl group. Polyester polyurethane has an ester bond in its main chain.

[0015] Polyester-based polyurethanes are degradable. In this specification, "degradable" refers to biodegradability, i.e., decomposition by microorganisms in soil; hydrolysis, i.e., decomposition by solvents such as fracturing fluid, particularly water, and optionally by acid or alkali, particularly by water at a predetermined temperature or higher; or chemical decomposition by some other method. Furthermore, "degradability" in this specification also refers to the fact that the strength inherent to polyester-based polyurethanes is reduced due to, for example, a decrease in the degree of polymerization, making them brittle and losing their shape (disintegrability). Therefore, polyester-based polyurethanes can exhibit disintegrability. Disintegrability refers to the fact that, as a result of the polyester-based polyurethanes becoming brittle as described above, a specific form of a polyester-based polyurethane component is easily disintegrated and loses its shape when extremely small mechanical forces are applied. Polyester-based polyurethanes are preferred from the viewpoint of ease of control of decomposition and disintegration.

[0016] The polyester polyurethane may be one or more types, and may be synthetic or commercially available. Examples of polyester polyurethane include Pandex® 390E, Pandex® 380E, Pandex® 370E, and Pandex® 356E (manufactured by DIC Corporation), and Takenate® L-1300 (manufactured by Mitsui Chemicals, Inc.).

[0017] [Methyl p-toluenesulfonate] Methyl p-toluenesulfonate has a p-toluenesulfonate ester structure and generates an acid (p-toluenesulfonic acid) upon hydrolysis. This acid acts as a catalyst to promote the hydrolysis reaction that cleaves the bonds in the main chain of polyester-based polyurethane. As a result, it promotes the decomposition of rubber compositions or rubber molded articles for downhole tools (hereinafter simply referred to as "rubber molded articles"). Methyl p-toluenesulfonate is also hydrolyzed by moisture in the air. Methyl p-toluenesulfonate hydrolyzes more easily than other p-toluenesulfonate ester compounds with a larger number of alcohol-derived carbon atoms, making it advantageous from the perspective of enhancing the decomposability and disintegrability of polyester-based polyurethanes.

[0018] If the content of methyl p-toluenesulfonate in the rubber composition of this embodiment is too low, the decomposition rate of the polyester-based polyurethane may be slowed, and the decomposition ability of the molded rubber article may be insufficient. If the content of methyl p-toluenesulfonate in the rubber composition of this embodiment is too high, the curing process may be slowed when the rubber composition is molded into a molded rubber article. As a result, bubbles generated in the system due to decomposition of urethane bonds or the like grow large, and numerous bubbles of a size (e.g., 1.2 mm in diameter) that substantially affects the mechanical strength of the molded rubber article may be generated in the molded rubber article. As a result, tears originating from the bubbles may occur in downhole components including the molded rubber article. Therefore, when used in downhole tools, the properties required for the downhole component (e.g., sealing ability) may not be fully realized.

[0019] From the viewpoint of sufficiently enhancing the degradability of the rubber molded article, the content of methyl p-toluenesulfonate is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the polyester polyurethane. Furthermore, from the viewpoint of sufficiently enhancing the mechanical properties of the rubber molded article, the content of methyl p-toluenesulfonate is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of the polyester polyurethane.

[0020] [Carbodiimide Compound] The carbodiimide compound functions as a decomposition inhibitor in the rubber composition of this embodiment. One or more carbodiimide compounds may be used, and examples include N,N'-diisopropylcarbodiimide and N,N'-2,6-diisopropylphenylcarbodiimide. From the viewpoint of suppressing the generation of bubbles in a rubber molded article, N,N'-diisopropylcarbodiimide is more preferred.

[0021] In this embodiment, it is preferable that an appropriate amount of carbodiimide compound is contained in the rubber composition from the viewpoint of increasing and maintaining the surface hardness of the resulting molded rubber article. If the content of the carbodiimide compound in the rubber composition is too low, the carbodiimide compound's effect of inhibiting the decomposition of the molded rubber article may be insufficient. If the content is too high, the surface hardness of the molded rubber article may be insufficient, and the rubber composition may not cure during the production of the molded rubber article. In order to obtain a sufficient effect of inhibiting the decomposition of the molded rubber article, the content of the carbodiimide compound in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, per 100 parts by mass of polyester polyurethane. Furthermore, in order to obtain a sufficient surface hardness of the molded rubber article, the content of the carbodiimide compound in the rubber composition is preferably 2 parts by mass or less, more preferably 1.8 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of polyester polyurethane.

[0022] [Aromatic Amine Resin] In the rubber composition of this embodiment, the aromatic amine resin accelerates the curing of the rubber composition during the production of a molded rubber product. As a result, the curing reaction time during the production of the molded rubber product is shortened, and the generation and growth of bubbles in the molded rubber product is suppressed. Furthermore, the aromatic amine resin accelerates the decomposition of the molded rubber product in a fluid containing water.

[0023] The aromatic amine resin may be a polymer compound having the functions of promoting curing during molding and promoting decomposition in water, as described above, and may be one or more types. For example, the aromatic amine resin may be a compound represented by the following formula (1): １ ~R ５ each independently represents hydrogen or an alkyl group having 1 to 18 carbon atoms which may have a substituent. The alkyl group may be linear or branched. A preferred example of such an aromatic amine resin is represented by the following formula (2). In formulas (1) and (2), n represents an integer of 1 or greater.

[0024]

[0025] The aromatic amine resin may be a synthetic product or a commercially available product, examples of which include Kayahard® AA (K-AA) manufactured by Nippon Kayaku Co., Ltd., and 4,4'-methylenebis(2-ethylaniline).

[0026] The content of the aromatic amine resin in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of polyester polyurethane, from the viewpoint of sufficiently accelerating the curing of the rubber composition during molding and from the viewpoint of sufficiently accelerating the decomposition of the molded rubber article in a fluid containing water. Furthermore, the content of the aromatic amine resin in the rubber composition is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of polyester polyurethane, from the viewpoint of ensuring uniformity of the components during mixing of the rubber composition.

[0027] [Other Components] The rubber composition of this embodiment may be substantially composed of only the polyester polyurethane, methyl p-toluenesulfonate, carbodiimide compound, aromatic amine resin, and curing agent described above. The rubber composition of this embodiment may further contain other components in addition to the above components, as long as the functions and effects described above are exhibited by the above components. The other components may be one or more, and examples include stabilizers, colorants, reinforcing agents, curing agents, and curing accelerators. The other components may be blended into the rubber composition in amounts that further exhibit the effects of the other components.

[0028] For example, examples of curing agents include 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), dimethylthiotoluenediamine, isophoronediamine, piperazine, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, hydroquinone di(2-hydroxyethyl ether), 1,1,1-trimethylolpropane, and glycerin. The content of the curing agent in the rubber composition of this embodiment may be 1 to 30 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the polyester polyurethane.

[0029] For example, the curing accelerator may be any known one, including stannous octoate, etc. From the viewpoint of safety, stannous octoate is particularly preferred.

[0030] [Manufacturing Method] The rubber composition of this embodiment can be prepared by mixing the various components described above. The production of this rubber composition can be carried out using known equipment, such as a known stirring device. In the production of this rubber composition, the various components described above may be added to the mixing system in an appropriate order, or two or more of the various components may be added simultaneously, if necessary, depending on the manufacturing conditions, such as the equipment used. Examples of methods for mixing the various components include an automatic elastomer injector or a method using a hand mixer. However, a method in which the various components are simultaneously stirred is preferred. However, if the specific gravities of the various components are significantly different and mixing is insufficient, the components may be mixed and stirred in multiple batches. When using MOCA as the curing agent and K-AA as the curing accelerator and mixing the various components in multiple batches, it is more preferable to add MOCA and K-AA simultaneously and stir them in order to efficiently promote the curing reaction. Here, the stirring conditions for handling using a hand mixer are preferably 300 to 3,000 rpm and 10 seconds to 5 minutes. Furthermore, when an automatic injector is used, it is preferable that the stirring conditions in the mixing section of the automatic injector be conditions that can obtain dispersion efficiency of the various components similar to the stirring conditions when handling using the hand mixer described above.

[0031] [Rubber Molded Article for Downhole Tool] The rubber molded article for downhole tools according to an embodiment of the present invention is molded using the rubber composition according to the present embodiment as a material. The molding method for producing the rubber molded article may be a known molding method, examples of which include cast molding, injection molding, extrusion molding (including solidification extrusion molding), centrifugal molding, and compression molding. For example, when molding a rubber molded article for downhole tools by cast molding, the rubber composition for downhole tools is poured into a mold of the desired shape, and the mold is heated at a temperature of 70 to 110°C for 1 to 2 hours to temporarily cure the rubber composition for downhole tools, thereby obtaining a molded article with increased hardness to the extent that it can be demolded from the mold. The molded article is then demolded from the mold, and further heated at 70 to 110°C for 4 to 24 hours to secondary cure the rubber composition for downhole tools, thereby obtaining a rubber molded article for downhole tools according to the present invention with the desired initial hardness. If the secondary curing time in the above-mentioned secondary curing step is set to 24 hours or more, the initial hardness of the rubber molded product for downhole tools may be significantly reduced due to decomposition during the manufacturing process. Therefore, in order to maintain the initial hardness, the secondary curing step is preferably performed at 70 to 110°C for 4 to 24 hours.

[0032] A molded article according to one embodiment of the present invention is a molded article obtained by curing the aforementioned composition. There are circumstances in which it is impossible or practical to directly identify a molded article obtained by curing the composition based on its structure or properties. The molded article according to one embodiment of the present invention has both mechanical properties and degradability. While this function may be achieved by a three-dimensional molecular structure formed by the mutual reaction of components in the composition, it is impossible to determine in general terms what state the three-dimensional molecular structure must be in to achieve this function. Furthermore, while identifying the three-dimensional molecular structure that achieves this function may be possible by comparing and examining a large number of three-dimensional molecular structures in various states, this requires enormous time and cost, and is therefore highly impractical given the nature of patent applications, which require rapidity.

[0033] The shape of the rubber molded product is not limited, and may be the shape of the intended downhole tool component (hereinafter also simply referred to as "component") described below, or may be a shape that can be obtained by processing such as cutting, milling, drilling, etc. Examples of such shapes include a rod, plate, cylinder, and ring.

[0034] The rubber molded article of this embodiment preferably has a mechanical strength appropriate for its intended use. The mechanical strength of the rubber molded article of this embodiment can be determined, for example, by its Durometer A hardness in its initial state (hereinafter also referred to as "initial hardness"). The "initial state" here refers to the surface hardness of the rubber molded article before substantial decomposition occurs, for example, before immersion in water. For example, if the intended use of the rubber molded article is as a component for a downhole tool used in the aforementioned hydraulic fracturing method, the initial hardness of the rubber molded article is preferably 70 or more, more preferably 75 or more, and even more preferably 80 or more, in Durometer A hardness. Furthermore, the initial hardness of the rubber molded article can be determined from the viewpoint of being able to fully exhibit rubber elasticity appropriate for the intended use, and may be, for example, 100 or less.

[0035] Furthermore, the mechanical strength of the rubber molded article of this embodiment can be determined by the state of the bubbles inside the rubber molded article. For example, if the rubber molded article is used as a downhole tool component, the diameter of the largest bubble contained inside the rubber molded article is preferably 1.20 mm or less, more preferably 1.10 mm or less, and even more preferably 1.00 mm or less. Having sufficiently small bubbles inside the rubber molded article is advantageous from the perspective of preventing cracks originating from the bubbles. The smaller the bubbles, the better, and they may even be absent. The diameter of the bubbles can be determined within a range in which the bubbles are unlikely to become the starting point for crack initiation, and may be, for example, 0 mm or more.

[0036] Furthermore, it is preferable that the rubber molded article of this embodiment have a sufficiently small number of bubbles, not only from the viewpoint of preventing the occurrence of cracks as described above, but also from the viewpoint of sufficiently increasing the mechanical strength of the rubber molded article. For example, from the viewpoint described above, the bubble occupancy rate in the entire rubber molded article is preferably 2.0% or less, more preferably 1.0% or less, and even more preferably 0.5% or less. The smaller the bubble occupancy rate, the better, and from this viewpoint it may be greater than 0%, or even 0%.

[0037] The diameter of the largest bubble among the bubbles inside the rubber molded article and the above-mentioned bubble occupancy rate are determined by analyzing a three-dimensional CT scan image of the rubber molded article, as described in the Examples below. Furthermore, both the diameter of the largest bubble and the bubble occupancy rate tend to decrease by shortening the curing time during the production of the rubber molded article.

[0038] Furthermore, the rubber molded article of this embodiment preferably has appropriate degradability depending on its intended use. The degradability of the rubber molded article of this embodiment can be determined by its state after immersion in water at a predetermined temperature for a certain period of time. For example, if the intended use of the rubber molded article is a downhole tool component, the thickness reduction rate of the rubber molded article after immersion in water at 49°C for 24 hours is preferably 0.15 mm / h or more, more preferably 0.16 mm / h or more, and even more preferably 0.18 mm / h or more. The thickness reduction rate of the rubber molded article can be determined appropriately from the viewpoint of suppressing decomposition during use in the desired application, and may be, for example, 1.00 mm / h or less.

[0039] As described in the Examples below, the thickness reduction rate is determined by maintaining the temperature of a sufficient amount of water in which a rubber molded article is immersed at 49°C using a thermostat, immersing the rubber molded article in this water for 24 hours or more, measuring the surface hardness (Durometer A hardness) of the rubber molded article after 24 hours (for example, 24 to 96 hours), and removing the portion of the rubber molded article that is equal to or less than a specific value, and then determining the change in dimension before and after removal.

[0040] [Downhole Tool Component] A downhole tool component according to an embodiment of the present invention includes the rubber molded product of the present embodiment described above. The component may include a portion of the rubber molded product, may be the rubber molded product itself, or may further include a portion other than the rubber molded product (e.g., a reinforcing member or a reinforcing structure such as a rib). Because the component includes the rubber molded product described above, it is suitable as a tubular sealing component for sealing low-temperature wells and is also suitable for disassembly after use. The component may have any shape appropriate for its intended use, such as a sheet (e.g., a thin film, a thick plate, etc.), a rod (e.g., a round bar, a rectangular column, etc.), a rectangular parallelepiped (including a cubic shape), a ball, or other block (e.g., a regular or irregular shape). For example, if the downhole tool component is a degradable sealing component for a downhole tool, the component may be composed of an annular or tubular rubber molded product. The component can be manufactured by known methods, for example, by machining, such as cutting or drilling, a rubber molded product.

[0041] [Well Treatment Method] A well treatment method according to an embodiment of the present invention includes a step of temporarily sealing the inside of a well using a downhole tool including the downhole tool component according to the present embodiment described above.

[0042] [Downhole Tool] The downhole tool in this embodiment includes the downhole tool component described above. The type, shape, and size of the downhole tool are not limited. The components described above may be included in the downhole tool as sealing or protective components. Examples of such sealing components include sealing components in a sleeve system (frac sleeve), sealing components such as ball valves and flapper valves in the downhole tool, sealing components that are placed in openings between the downhole tool and the casing and can temporarily block fluids, and sealing components that cover metal downhole tool components, sensors, flow paths, etc. to provide protection or sealing, and that seal the wellbore by expanding the diameter of these metal parts, etc.

[0043] From the viewpoint of more effectively demonstrating both the mechanical properties and degradability that are the characteristics of the above-mentioned components, the downhole tool is preferably a well drilling plug, and more preferably a frac plug or a bridge plug.

[0044] The well drilling plug includes, for example, a mandrel and various downhole tool components placed on the outer peripheral surface of the mandrel perpendicular to the axial direction. The mandrel may have a hollow portion, or may have a shape whose diameter changes along the axial direction, or may have a fixing portion, a step portion, a recessed portion, or a protruding portion on its outer surface. The downhole tool component is, for example, an expandable annular seal component that can be expanded in diameter to close the space between the well drilling plug and the casing and seal the fluid. In addition to the downhole tool component, the well drilling plug may further include known components such as a sensor.

[0045] [Sealing] The downhole tool applies a force in the axial direction of the mandrel to compress the downhole tool component, which is a sealing member, in the axial direction and expand the diameter in a direction perpendicular to the axial direction of the mandrel. The sealing member then abuts the inner wall of the downhole, and the inner part in the direction perpendicular to the axial direction abuts the outer peripheral surface of the mandrel. In this way, the inside of the wellbore is temporarily sealed using the downhole tool of this embodiment.

[0046] [Removal of seal] The well treatment method of this embodiment further includes a step of contacting the downhole tool component with a fluid in a well environment, thereby decomposing at least a portion of the downhole tool component and removing seal in the well.

[0047] The fluid may be a fluid originally present in the well, such as groundwater, or a fluid supplied into the well after the downhole tool is inserted. When the downhole tool plugging the well comes into contact with the fluid, the downhole tool components also come into contact with the fluid. Therefore, depending on the well environment (temperature, etc.), the downhole tool components (e.g., seal members) decompose and disintegrate. As a result, the plugging of the well by the downhole tool is eliminated.

[0048] It is preferable that other components constituting the downhole tool besides the downhole tool components are also degradable from the viewpoint of enhancing the disintegration property of the entire downhole tool and reliably eliminating plugging. Examples of other components include a mandrel, a slip, and a ring. Such other degradable components can be realized by constructing them from a degradable material (such as a biodegradable resin).

[0049] [Others] The well treatment method of this embodiment may further include other steps in addition to the aforementioned plugging step and unplugging step, as long as the effects of this embodiment can be obtained. For example, the well treatment method may further include a step of supplying a temperature control medium (e.g., water) to the well after plugging to adjust the temperature of the downhole tool component in the downhole tool plugging the well. Such a temperature adjustment step can accelerate or delay the onset of decomposition of the downhole tool component in the well by adjusting the ambient temperature of the downhole tool component to a higher or lower level. Therefore, the temperature adjustment step is preferable from the viewpoint of performing the unplugging step at a desired timing.

[0050] The well treatment method may further include a step of recovering disassembled parts resulting from the disassembly and collapse of the downhole tool by recovering fluids in the well after unplugging. Such a recovery step makes it possible to easily recover the disassembled parts in the well, and is advantageous from the viewpoint of suppressing the occurrence of well plugging in the production of hydrocarbon resources.

[0051] In addition, the downhole tool described above can be applied to other methods that require some kind of sealing, such as inspection or repair of piping, in addition to its use in producing underground hydrocarbon resources, and can also achieve the effects described above when applied to other methods.

[0052] The well treatment method of this embodiment facilitates the implementation of various well treatment methods that require sealing operations, such as fracturing in low-temperature well environments. Furthermore, this well treatment method reliably maintains the sealing function during the sealing operation for a desired period of time, and enables the sealing to be released at the desired time. Therefore, this well treatment method can contribute to reducing costs and shortening the process in such hole-sealing operations, and can contribute to improving production efficiency.

[0053] [Summary] A first aspect of the present invention is a rubber composition for downhole tools, comprising a polyester-based polyurethane, 3 to 10 parts by mass of methyl p-toluenesulfonate per 100 parts by mass of the polyester-based polyurethane, 0.1 to 2 parts by mass of a carbodiimide compound per 100 parts by mass of the polyester-based polyurethane, and 0.1 to 5 parts by mass of an aromatic amine resin per 100 parts by mass of the polyester-based polyurethane. According to the first aspect, a technology can be provided for realizing well treatment using a downhole component that can adequately achieve both mechanical properties and degradability.

[0054] In a second aspect of the present invention, the carbodiimide compound in the first aspect is N,N'-diisopropylcarbodiimide or N,N'-2,6-diisopropylphenylcarbodiimide, which is even more effective in improving and maintaining the hardness of the rubber molded article.

[0055] A third aspect of the present invention is a rubber molded article for a downhole tool, which is molded using the rubber composition for a downhole tool of the first or second aspect as its material, and which has an initial durometer A hardness of 70 or more and a rate of thickness reduction of 0.15 mm / h or more after 24 hours when immersed in water at 49° C. According to the third aspect, the balance between the mechanical properties and degradability of the rubber molded article is appropriately adjusted, and a technology can be provided for realizing well treatment using a downhole component that can moderately achieve both mechanical properties and degradability.

[0056] A fourth aspect of the present invention is the third aspect, wherein the diameter of the largest bubble contained therein is 1.20 mm or less. The fourth aspect is even more effective from the viewpoint of improving the mechanical properties of the rubber molded article.

[0057] A fifth aspect of the present invention is the third or fourth aspect, wherein the air bubble occupancy rate in the entire rubber molded article for a downhole tool is 2.0% or less. The fifth aspect is even more effective from the viewpoint of improving the mechanical properties of the rubber molded article.

[0058] A sixth aspect of the present invention is any one of the third to fifth aspects, wherein the void occupancy rate in the entire rubber molded article for a downhole tool is 0.5% or less, which is even more effective from the viewpoint of improving the mechanical properties of the rubber molded article.

[0059] A seventh aspect of the present invention is a downhole tool component including the rubber molded article for a downhole tool according to any one of the third to sixth aspects. According to the seventh aspect, a technique for realizing well treatment using a downhole component that can adequately achieve both mechanical properties and degradability can be provided.

[0060] An eighth aspect of the present invention is a well treatment method that temporarily seals a well using a downhole tool including the downhole tool component of the seventh aspect, and unseals the well by contacting the downhole tool component with a fluid in a well environment, thereby degrading at least a portion of the downhole tool component. According to the eighth aspect, well treatment can be achieved using a downhole component that can adequately achieve both mechanical properties and degradability.

[0061] According to an aspect of the present invention, a downhole component that satisfies both mechanical properties and degradability can be provided, and its use can improve the efficiency of work involving well treatment. The present invention, which has such effects, is expected to contribute to the achievement of, for example, Goal 9 of the Sustainable Development Goals (SDGs) proposed by the United Nations, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and promote inclusive and sustainable industrialization."

[0062] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0063] An embodiment of the present invention will now be described.

[0064] [Material Preparation] The following materials were prepared as materials for the rubber composition for downhole tools: Polyester polyurethane (PEPU, Pandex (registered trademark) 390E) Polyester polyurethane (PEPU, Pandex (registered trademark) 356E) Methyl p-toluenesulfonate (MPTS) Carbodiimide compound 1 (N,N'-diisopropylcarbodiimide (DIC)) Carbodiimide compound 2 (N,N'-2,6-diisopropylphenylcarbodiimide (DIPC)) Aromatic amine resin (KAYAHARD (registered trademark) A-A (K-AA)) Curing agent 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA)

[0065] Example 1 Preparation of Rubber Composition for Downhole Tool Pandex 390E was heated to 80 to 100°C, methyl p-toluenesulfonate (MPTS) to 20 to 60°C, diisopropylcarbodiimide (DIC) to 20 to 45°C, 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA) to 120 to 140°C, and aromatic amine resin (K-AA) to 20 to 60°C.

[0066] Next, N,N'-diisopropylcarbodiimide (DIC) was added in an amount of 0.5 parts by mass per 100 parts by mass of Pandex 390E, and the mixture was stirred using a hand mixer at 300 to 3,000 rpm for 10 seconds to 5 minutes. The resulting mixture was heated at 80 to 100°C and degassed by evacuating, and then allowed to stand for 10 to 15 minutes.

[0067] Subsequently, 5.3 parts by mass of methyl p-toluenesulfonate, 13 parts by mass of 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), and 1.1 parts by mass of aromatic amine resin (K-AA) were simultaneously added to 100 parts by mass of Pandex 390E to the degassed mixture, and the mixture was stirred at 80 to 100°C using a hand mixer at 300 to 3,000 rpm for 10 seconds to 5 minutes. In this way, a rubber composition for downhole tools was prepared.

[0068] [Production of Rubber Molded Article for Downhole Tool] The obtained rubber composition for downhole tools was poured into a pipe-shaped mold having an outer diameter of 100 mm, an inner diameter of 50 mm, and a height of 80 mm. The mold was then heated at a temperature of 70 to 110°C for 1 to 2 hours to temporarily cure the rubber composition for downhole tools. The rubber composition was then demolded from the mold and further heated at 70 to 110°C for 4 to 24 hours to secondary cure the rubber composition for downhole tools, producing a pipe-shaped rubber molded article for downhole tools having a height of 80 mm. A molded article having a height of 50 mm was then cut out from the lower part of the mold of the rubber molded article for downhole tools. In this way, a pipe-shaped sample having an outer diameter of 100 mm, an inner diameter of 50 mm, and a height of 50 mm was obtained.

[0069] Example 2 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that the amount of DIC added was changed to 1 part by mass per 100 parts by mass of Pandex 390E.

[0070] Example 3 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that the amount of MPTS added per 100 parts by mass of Pandex 390E was changed to 7.5 parts by mass and the amount of DIC added per 100 parts by mass of Pandex 390E was changed to 1 part by mass.

[0071] Example 4 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that the amount of MPTS added per 100 parts by mass of Pandex 390E was changed to 7.5 parts by mass and the amount of DIC added per 100 parts by mass of Pandex 390E was changed to 1.5 parts by mass.

[0072] Example 5 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that the amount of MPTS added per 100 parts by mass of Pandex 390E was changed to 9.9 parts by mass and the amount of DIC added per 100 parts by mass of Pandex 390E was changed to 1 part by mass.

[0073] Example 6 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that N,N'-2,6-diisopropylphenylcarbodiimide (DIPC) was used instead of DIC.

[0074] Example 7 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 6, except that the amount of DIPC added was changed to 1 part by mass per 100 parts by mass of Pandex 390E.

[0075] Example 8 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 1, except that Pandex 356E was used instead of Pandex 390E.

[0076] Comparative Example 1 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 2, except that K-AA was not added.

[0077] Comparative Example 2 A rubber composition for a downhole tool was obtained in the same manner as in Example 1, except that the amount of DIC added per 100 parts by mass of Pandex 390E was changed to 3 parts by mass. An attempt was made to produce a rubber molded article for a downhole tool in the same manner as in Example 1. However, even when the mold was heated, the rubber composition for a downhole tool did not solidify but remained in a viscous liquid state and was foamed, so a rubber molded article for a downhole tool could not be obtained, and therefore no pipe-shaped sample could be obtained.

[0078] Comparative Example 3 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Example 6, except that K-AA was not added.

[0079] Comparative Example 4 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Comparative Example 3, except that the amount of MPTS added was changed to 7.5 parts by mass per 100 parts by mass of Pandex 390E.

[0080] Comparative Example 5 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Comparative Example 3, except that the amount of MPTS added per 100 parts by mass of Pandex 390E was changed to 7.5 parts by mass and the amount of DIPC added per 100 parts by mass of Pandex 390E was changed to 1 part by mass.

[0081] Comparative Example 6 A rubber composition for a downhole tool and a pipe-shaped sample were obtained in the same manner as in Comparative Example 3, except that the amount of MPTS added per 100 parts by mass of Pandex 390E was changed to 7.5 parts by mass and the amount of DIPC added per 100 parts by mass of Pandex 390E was changed to 1.5 parts by mass.

[0082] [Evaluation] (1) Initial Hardness (Hi) The surface hardness of a pipe-shaped sample that was not immersed in water was measured using a Durometer Type A (GS-719N, manufactured by Teclock Corporation). The value 3 seconds after applying a load of 5 kg was measured, and this value was taken as the initial hardness (Hi).

[0083] (2) 49°C Thickness Reduction Rate (Rtr, mm / hr) A rubber molded article for a downhole tool that had not been immersed in water was cut into a 20 mm cube to prepare a cube-shaped sample, and the width, depth, and height of the cube-shaped sample were measured. Next, the cube-shaped sample and 200 ml of ion-exchanged water were placed in a wide-mouth glass bottle and stored in a constant temperature incubator at 49°C for a certain period of time. The cube-shaped sample was removed from the wide-mouth glass bottle over time and subjected to solid-liquid separation using a filter.

[0084] The cube-shaped sample obtained after separation was placed in a dry room with a dew point of -40°C or less and dried for 12 hours. After drying, the adhesive layer or embrittlement layer having a durometer A hardness of less than 60 was peeled off from the surface of the cube-shaped sample using a cutter, and a core layer having a durometer A hardness of 60 or more was extracted. The width, depth, and height dimensions of the core layer were measured, and the amount of change from the initial dimensions was calculated. The average value of the changes in width, depth, and height was calculated, and this was taken as the amount of thickness reduction.

[0085] A graph was created by plotting the obtained data with time (hr) on the horizontal axis and thickness reduction (mm) on the vertical axis, and the slope of the line calculated by the least squares method was taken as the 49°C thickness reduction rate (mm / hr). Note that, since there may be samples with a lead time until a change in thickness occurs, in order to accurately determine the slope of the line, the 49°C thickness reduction rate (Rtr) was calculated using data from at least two points, one at 24 hours and one thereafter (immersion time of 24 to 96 hours).

[0086] (3) Observation of bubbles A pipe-shaped sample that was not immersed in water was irradiated with X-rays using a CT scanning device, NAOMi-CT 3D-L, manufactured by RF Corporation, at a tube voltage of 80 kV, to obtain a three-dimensional CT scan image.

[0087] Next, a specific area of ​​a specific cross section in the 3D CT scan image was set. That is, as shown in Figure 1, a cross section obtained by cutting the pipe-shaped sample on an arbitrary plane including the center of gravity and the axis of the sample was set as the cross section. Then, as shown in Figure 2, a 400 mm ２ Any one of the above regions was set as the observation target region, and its area (Aoa) was calculated.

[0088] Next, voids with a diameter of 0.1 mm or more observed in the observation area in the 3D CT scan image were detected as bubbles, and the number of bubbles in the observation area (Nb), the total area of ​​the bubbles in the observation area (TAb), and the diameter of the largest bubble in the observation area (Dmb) were measured.

[0089] Next, the total area of ​​the bubbles was divided by the area of ​​the observation region to calculate the bubble occupancy rate per unit area (ORb, %). Based on the concept of stereology, the area rate per unit area of ​​bubbles contained in a molded product is equal to the volume rate per unit volume of bubbles contained in the molded product. Therefore, it can also be said that the bubble occupancy rate per unit area is equal to the volume rate of bubbles relative to the total volume of the molded product. In addition, the number of bubbles in the observation region was calculated based on the area (mm ２ ) and divide by 100 (mm ２ The number of bubbles per unit area (Nbua) was calculated by multiplying the area by 100 mm ２ Number of bubbles per 1cm ２ Since the number of bubbles per unit area in Table 1 is equal to the number of bubbles per unit area, the unit of the number of bubbles per unit area is (bubbles / cm ２ )

[0090] Table 1 shows the composition of the rubber composition for a downhole tool in each of the above examples and the evaluation results of the rubber molded article for a downhole tool.

[0091] In Table 1, "PEPU type" indicates the number in the product name of the polyester polyurethane, "MPTS" indicates methyl p-toluenesulfonate, "DIC" indicates carbodiimide compound 1 (N,N'-diisopropylcarbodiimide), "DIPC" indicates carbodiimide compound 2 (N,N'-2,6-diisopropylphenylcarbodiimide), and "K-AA" indicates aromatic amine resin (KAYAHARD A-A). Furthermore, "Hi" represents the initial hardness of the sample not immersed in water, "Rtr" represents the rate of thickness reduction at 49°C of the sample, "Aoa" represents the area of ​​the observation region when observing bubbles in the sample, "Nb" represents the number of bubbles in the observation region, "TAb" represents the total area of ​​the bubbles in the observation region, "ORb" represents the bubble occupancy rate per unit area in the observation region, "Nbua" represents the number of bubbles per unit area in the observation region, and "Dmb" represents the diameter of the largest bubble in the observation region.

[0092]

[0093] [Discussion] As is clear from Table 1, all of the rubber compositions for downhole tools in Examples 1 to 8 contain methyl p-toluenesulfonate as a decomposition accelerator, a carbodiimide compound as a decomposition inhibitor, and an aromatic amine resin as a cure accelerator. As a result, the generation of coarse bubbles in the rubber molded product for downhole tools is suppressed. This is thought to be because the inclusion of the aromatic amine resin as a cure accelerator shortens the curing reaction time in the production of the rubber molded product for downhole tools from the rubber composition.

[0094] Furthermore, as is clear from the comparison between Example 1 and Example 8, it is possible to adjust the initial hardness of the rubber composition for a downhole tool by changing the type of polyester polyurethane.

[0095] Furthermore, as is clear from a comparison between Examples 1 to 8 and Comparative Examples 1 to 6, the use of an aromatic amine resin as a material for the rubber composition for downhole tools has the effect of accelerating the decomposition of the rubber material in the rubber molded product for downhole tools obtained from the rubber composition, and increasing the rate of thickness reduction after 24 hours when immersed in water at 49°C.

[0096] Furthermore, as is clear from a comparison between Example 1 and Comparative Example 2, for example, by setting the amount of carbodiimide compound added as a decomposition inhibitor within an appropriate range, the hardness of the rubber molded product for downhole tools after manufacture can be maintained high.

[0097] Furthermore, as is clear from a comparison of Examples 1 to 5 and Comparative Example 1 with Examples 6, 7, and Comparative Examples 3 to 6, it is clear that among carbodiimide compounds, DIC is superior in terms of suppressing the generation of bubbles. Furthermore, as is clear from a comparison of Example 2 with Comparative Example 1, it is clear that the inclusion of an aromatic amine resin in the rubber composition is effective in further suppressing the generation of bubbles.

[0098] As described above, a downhole tool component, such as a seal component, made from the rubber composition for a downhole tool of the present invention exhibits favorable sealing performance in a low-temperature well and can be decomposed favorably.

[0099] The present invention can be suitably used in the production of hydrocarbon resources from wells.

Claims

1. A rubber composition for downhole tools comprising: a polyester-based polyurethane; 3 to 10 parts by mass of methyl p-toluenesulfonate per 100 parts by mass of the polyester-based polyurethane; 0.1 to 2 parts by mass of a carbodiimide compound per 100 parts by mass of the polyester-based polyurethane; and 0.1 to 5 parts by mass of an aromatic amine resin per 100 parts by mass of the polyester-based polyurethane.

2. The rubber composition for downhole tools according to claim 1, wherein the carbodiimide compound is N,N'-diisopropylcarbodiimide or N,N'-2,6-diisopropylphenylcarbodiimide.

3. A rubber molded product for downhole tools, which is molded using the rubber composition for downhole tools described in claim 1 or 2 as its material, has an initial durometer A hardness of 70 or more, and exhibits a rate of thickness reduction of 0.15 mm / h or more after 24 hours when immersed in water at 49°C.

4. The rubber molded product for downhole tools according to claim 3, wherein the diameter of the largest air bubble contained therein is 1.20 mm or less.

5. A rubber molded product for downhole tools according to claim 4, wherein the air bubble occupancy rate in the entire rubber molded product for downhole tools is 2.0% or less.

6. The rubber molded product for downhole tools according to claim 5, wherein the air bubble occupancy rate is 0.5% or less.

7. A component for a downhole tool comprising the rubber molded article for a downhole tool according to claim 3.

8. A well treatment method comprising: temporarily sealing a well using a downhole tool including the downhole tool component according to claim 7; and unblocking the well by contacting the downhole tool component with a fluid in a well environment, thereby decomposing at least a portion of the downhole tool component.

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