Use of modified polyglycolic acid moldings on degradable downhole tools

Abstract

The invention discloses a degradable downhole tool component for oil and gas resource exploitation. The downhole tool component includes a molded body comprising a degradable polymer matrix wherein the downhole tool component has an initial mass loss of about 14% for a retention period of about 2 days in a pressure retention test when held in a downhole fluid at about 80 DEG C.

Description

[0001] Cross-references and priority claims to related patent applications

[0002] This patent application claims priority to U.S. patent application No. 18 / 497,632, entitled “Application of Modified Polyglycolic Acid Molded Articles for Degradable Downhole Tools,” filed on October 30, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention discloses a polyglycolic acid resin compound containing polylactic acid and a compatibilizer and a molded article thereof. More particularly, the present invention relates to a technology regarding a biodegradable polymer compound of modified polyglycolic acid and a molded article for degradable downhole tool applications. Background Art

[0004] Biodegradable materials have many uses in our society, from making biodegradable plastic bags, diapers, and water bottles, to creating biodegradable excipients for drug delivery and biodegradable implants for surgery, to a variety of industrial applications such as soil remediation, agriculture, and oil and gas production.

[0005] For example, degradable materials have been used for fluid loss control, diversion, and temporary plugs in downhole applications for oil and gas production.

[0006] Examples of degradable materials used downhole in oil wells include rock salt, benzoic acid flakes, wax beads, wax buttons, oil-soluble resin materials, etc. In addition to filling and plugging fractures and permeable zones in reservoir formations, degradable materials are also used to form cemented plugs in wellbores that degrade after use, eliminating the need for recovery.

[0007] New materials for such applications are always needed, especially materials that degrade quickly under downhole conditions. Summary of the Invention

[0008] In one aspect, an embodiment discloses a downhole tool component for oil and gas resource extraction. The downhole tool component includes a molded body comprising a degradable polymer matrix. When held in downhole fluid at 80° C., the downhole tool component exhibits approximately 14% initial mass loss over a two-day hold period in a pressure hold test.

[0009] Optionally, in any aspect, the mass loss in said pressure hold test is about 50% over a hold period of 7 days.

[0010] Optionally, in any aspect, the degradable polymer comprises polyglycolic acid resin.

[0011] Optionally, in any aspect, the polymer comprises polylactic acid.

[0012] Optionally, in any aspect, the downhole tool component maintains a pressure of 6,500 psi to 10,000 psi at 93° C. for up to 24 hours in a pressure hold test.

[0013] Optionally, in any aspect, the downhole fluid comprises a KCl solution.

[0014] Alternatively, in any aspect, the polymer comprises a copolymer comprising two or more aliphatic polyester copolymers, the aliphatic polyester copolymer comprising poly(lactic-co-glycolic acid) (PLGA). Alternatively, in one aspect, the copolymer comprises poly(lactic-co-glycolic acid) (PLGA).

[0015] Optionally, in any aspect, the copolymer comprises poly(lactic-co-glycolic acid) (PLGA).

[0016] Optionally, in any aspect, based on 100 parts of polyglycolic acid (PGA) and polylactic acid (PLA), wherein PLA is about 1 part to about 30 parts, the copolymer polylactic-co-glycolic acid (PLGA) is about 0 part to about 6 parts.

[0017] In another aspect, one embodiment discloses a downhole tool component for oil and gas resource extraction. The downhole tool component includes a molded body comprising a degradable polymer matrix. When held in downhole fluid at 80° C., the downhole tool component exhibits approximately 50% mass loss over a 7-day hold period in a pressure hold test.

[0018] Optionally, in any aspect, the downhole tool component, when held in a downhole fluid, has an initial mass loss of about 14% over a 2 day hold period in a pressure hold test at 80°C.

[0019] Optionally, in any aspect, the polymer comprises polyglycolic acid resin.

[0020] Optionally, in any aspect, the polymer comprises two or more aliphatic polyester copolymers.

[0021] Optionally, in any aspect, the copolymer comprises poly(lactic-co-glycolic acid) (PLGA).

[0022] Optionally, in any aspect, the downhole tool component maintains a pressure of 6,500 psi to 10,000 psi at 93° C. for up to 24 hours in a pressure hold test.

[0023] In another aspect, an embodiment discloses a downhole tool component for oil and gas resource extraction. The downhole tool may include a molded body comprising a degradable polymer matrix. The downhole tool component maintains a pressure of 6,500 to 10,000 psi at 93° C. for up to 24 hours in a pressure retention test.

[0024] Optionally, in any aspect, the polymer comprises a copolymer, wherein the copolymer comprises poly(lactic-co-glycolic acid) (PLGA).

[0025] Optionally, in any aspect, the downhole tool component, when held in a downhole fluid, has an initial mass loss of about 14% over a 2 day hold period in a pressure hold test at 80°C.

[0026] Optionally, in any aspect, the downhole tool component, when held in a downhole fluid, has a mass loss of about 50% over a 7 day hold period in a pressure hold test at 80°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments or exemplary technologies of the present disclosure, the following briefly describes the drawings used in the embodiments or the description of the exemplary embodiments. Obviously, the drawings in the following description are only certain embodiments of the present disclosure, and those skilled in the art can obtain other drawings based on the structures shown in the drawings without any creative work.

[0028] Figure 1A A schematic diagram showing a specific example of the designed dissolvable plug;

[0029] Figure 1B is a schematic diagram showing the installation state, wherein Figure 1A The diameter of the circular rubber sealing element of the designed dissolvable plug (with a degradable modified PGA mandrel cone) for the drilling process has swelled to seal;

[0030] Figure 2 A graph showing a 4-hour hold test at 7250 psi (50 MPa) and 93°C (200°F);

[0031] Figure 3 A graph showing a 4-hour hold test at 8700 psi (60 MPa) and 93°C (200°F);

[0032] Figure 4 Shown are a series of images of the mandrel cone of modified PGA at 80°C for different soaking times.

[0033] Figure 5A graph showing the relationship between the mass loss test of the mandrel cone of modified PGA at 80°C and the immersion time is shown.

[0034] The embodiments, functional features and advantages of the present disclosure will be further described with reference to the accompanying drawings. DETAILED DESCRIPTION

[0035] definition

[0036] The term "about" means plus or minus 20%, more preferably plus or minus 10%, even more preferably ±5%, and most preferably 2%.

[0037] The present invention is not limited to the specific methods, protocols, and reagents described herein, as they may vary. In addition, the terminology used herein is intended to describe specific embodiments only and is not intended to limit the scope of the present invention. As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0038] Unless otherwise defined, all technical and scientific terms and any abbreviations used herein have the same meanings as commonly understood by those skilled in the art. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, preferred methods, devices and materials are described herein.

[0039] Unless otherwise specified, all weight percentages expressed herein are based on the total weight of the food.

[0040] The technical means, creative features, purposes and effects of this patent application may be easily understood, and the following examples will further illustrate the patent application. However, the following examples are only preferred embodiments of the present patent application, not all. Based on the examples in the embodiments, other examples obtained by those skilled in the art without creative work should also fall within the scope of protection of the present invention. Unless otherwise stated, the experimental methods in the following examples are conventional methods. Unless otherwise stated, the materials and reagents used in the following examples can be obtained from commercial sources.

[0041] invention

[0042] The downhole tool components described herein may have some abradable parts and some dissolvable parts to extend their service life. The soluble portion of the downhole tool component may be made of or include a degradable or dissolvable material. The terms "degradable" and "dissolvable" are used interchangeably herein. The term "degradable" and all its grammatical variations (e.g., "degrade," "degradation," and "degrading," etc.) refers to the dissolution or chemical conversion of a material into smaller components, intermediates, or end products by at least one of solubilization, hydrolytic degradation, biologically formed entities (such as bacteria or enzymes), chemical reactions (including electrochemical reactions), thermal reactions, or radiation-induced reactions. In some cases, the degradation of a material may be sufficient to reduce the mechanical properties of the material to the point where the material no longer maintains its integrity, essentially breaking down or falling apart. The conditions for degradation or dissolution are typically wellbore conditions, under which external stimuli can be used to initiate or influence the rate of degradation. For example, the pH of the fluid interacting with the material can be changed by the introduction of an acid or base.

[0043] The degradation rate of a given soluble material can be accelerated, rapid, or normal, as defined herein. Accelerated degradation can be in the range of from a lower limit of about 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours to an upper limit of about 12 hours, 11 hours, 10 hours, 9 hours, 8 hours, 7 hours, and 6 hours, including any value or subset therebetween. Rapid degradation can be in the range of from a lower limit of about 12 hours, 1 day, 2 days, 3 days, 4 days, and 5 days to an upper limit of about 10 days, 9 days, 8 days, 7 days, 6 days, and 5 days, including any value or subset therebetween. Normal degradation can range from a low of about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, and 26 days to a high of about 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, and 26 days, including any values ​​or subsets therebetween. Thus, degradation of the dissolvable material can take between about 30 minutes and about 40 days, depending on many factors, including, but not limited to, the type of dissolvable material selected, the conditions of the wellbore environment, etc.

[0044] Suitable soluble materials that can be used according to embodiments of the present disclosure include soluble metals, electro-corrosive metals, degradable polymers, degradable rubbers, borate glass, polyglycolic acid (PGA), polylactic acid (PLA), dehydrated salts, and any combination thereof. Suitable soluble materials may also include epoxy resins exposed to alkaline solutions, glass fibers exposed to acids, aluminum exposed to acidic fluids, and adhesives exposed to alkaline or acidic solutions. The soluble material may be configured to degrade by a variety of mechanisms, including but not limited to swelling, dissolution, chemical changes, electrochemical reactions, thermal degradation, or any combination thereof.

[0045] Swelling degradation involves the absorption of aqueous or hydrocarbon fluids present in the wellbore environment by the dissolvable material, resulting in degradation or failure of the dissolvable material's mechanical properties. In swelling degradation, the dissolvable material continues to absorb aqueous and / or hydrocarbon fluids until its mechanical properties are no longer sufficient to maintain the integrity of the dissolvable material and it at least partially decomposes. In some embodiments, the dissolvable material can be designed to only partially degrade by swelling to ensure that the mechanical properties of the component formed from the dissolvable material are adequately maintained for the specific operation in which it is used.

[0046] Exemplary aqueous fluids that can be used to swell and degrade the soluble material include, but are not limited to, fresh water, brine (e.g., water having one or more salts dissolved therein), brine (e.g., saturated brine), seawater, acid, base, or combinations thereof. Exemplary hydrocarbon fluids that can swell and degrade the soluble material include, but are not limited to, crude oil, crude oil fractions, saturated hydrocarbons, unsaturated hydrocarbons, branched hydrocarbons, cyclic hydrocarbons, and any combination thereof.

[0047] Dissolution degradation involves a dissolvable material that is soluble in or susceptible to aqueous or hydrocarbon fluids, such that the aqueous or hydrocarbon fluid is not necessarily incorporated into the dissolvable material (as in the case of swelling degradation), but rather becomes soluble upon contact with the aqueous or hydrocarbon fluid.

[0048] Degradation by chemical changes may involve breaking or cross-linking the bonds of the dissolvable material's (eg, polymeric) backbone, rendering the dissolvable material brittle and capable of breaking into small pieces upon exposure to even small forces expected in the wellbore environment.

[0049] Thermal degradation of dissolvable materials involves chemical decomposition due to heat, such as that which may be present in a wellbore environment. Thermal degradation of some of the dissolvable materials mentioned or contemplated herein may occur in wellbore ambient temperatures exceeding about 93°C (or about 200°F). More specifically, such PGA-based dissolvable plugs may be readily useful over a wide temperature range of about 80°C to about 120°C, and may even be useful in a range of about 70°C to 130°C, or even about 60°C to 140°C.

[0050] Regarding soluble or electrically corrosive metals used as soluble materials, the metal can be configured to dissolve in the presence of an aqueous fluid or degrade by an electrochemical process, wherein the electrically corrosive metal corrodes in the presence of an electrolyte (e.g., salt water or other saline fluid). Suitable soluble or electrically corrosive metals include, but are not limited to, gold, gold-platinum alloys, silver, nickel, nickel-copper alloys, nickel-chromium alloys, copper, copper alloys (e.g., brass, bronze, etc.), chromium, tin, aluminum, iron, zinc, magnesium, and beryllium. Suitable electrically corrosive metals also include electrical materials of nanostructured matrices. An example of a micro-electrical material of a nanostructured matrix is ​​a magnesium alloy with iron coating inclusions. Suitable electrically corrosive metals also include micro-electrical metals or materials, such as solution-structured electrical materials. An example of a solution-structured electrical material is zirconium (Zr) containing a magnesium (Mg) alloy, wherein different regions within the alloy contain different percentages of Zr. This results in galvanic coupling between these different regions, thereby leading to micro-electrical corrosion and degradation. Slightly electro-corroded magnesium alloys can also be solution-structured with other elements such as zinc, aluminum, nickel, iron, carbon, tin, silver, copper, titanium, rare earth elements, etc. Slightly electro-corroded aluminum alloys can be dissolved in solution with elements such as nickel, iron, carbon, tin, silver, copper, titanium, gallium, etc. Among these electro-corroded metals, magnesium and magnesium alloys may be preferred.

[0051] For degradable polymers used as soluble materials, if the degradation is due to chemical and / or free radical processes in situ, such as hydrolysis, oxidation or ultraviolet radiation, the polymer is considered to be "degradable" or "soluble". Degradable polymers can be natural or synthetic polymers, including but not limited to polyacrylates, polyamides and polyolefins, such as polyethylene, polypropylene, polyisobutylene and polystyrene. Suitable examples of degradable polymers that can be used for embodiments of the present invention include polysaccharides, such as dextran or cellulose, chitin, chitosan, proteins, aliphatic polyesters, polylactic acid, polyglycolide, polycaprolactone, polyhydroxybutyrate, polyanhydrides, aliphatic or aromatic polycarbonates, polyorthoesters, polyamino acids, polyethylene oxide, polyphosphazenes, polyphenylene lactide, polyethylene glycol, copolymers of ethylene oxide / polyethylene glycol, terpolymers of epichlorohydrin / ethylene oxide / allyl glycidyl ether and combinations thereof in any.

[0052] Polyanhydrides are another type of particularly suitable degradable polymer that can be used for embodiments of the present disclosure. Polyanhydrides hydrolyze in the presence of aqueous fluids to release constituent monomers or comonomers, producing carboxylic acids as final degradation products. Erosion times can vary within a wide range of variations in the polymer backbone, including changes in molecular weight, composition, or derivatization. Examples of suitable polyanhydrides include polyadipic anhydride, polysuberic anhydride, polysebacic anhydride, and polydodecane dianhydride. Other suitable examples include, but are not limited to, polymaleic anhydride and polybenzoic anhydride.

[0053] Suitable degradable rubbers include degradable natural rubber (i.e., cis-1,4-polyisoprene) and degradable synthetic rubbers, which may include, but are not limited to, EPDM M-grade rubber, isoprene rubber, isobutylene rubber, polyisobutylene rubber, styrene-butadiene rubber, silicone rubber, ethylene-propylene rubber, butyl rubber, norbornene rubber, polynorbornene rubber, styrene block polymers, styrene-butadiene block polymers, styrene-isoprene block polymers, and any combination thereof. Other suitable degradable polymers include those having a melting point that dissolves them at the temperature of the underground formation in which they are placed.

[0054] In certain embodiments, soluble material can have a thermoplastic polymer embedded therein. Thermoplastic polymer can change the intensity, elasticity or modulus of parts, and can also control the degradation rate of parts. Suitable thermoplastic polymer can include but is not limited to acrylate (for example, polymethyl methacrylate, polyoxymethylene, polyamide, polyolefin, aliphatic polyamide, polybutylene terephthalate, polyethylene terephthalate, polycarbonate, polyester, polyethylene, polyetheretherketone, polypropylene, polystyrene, polyvinylidene chloride, styrene-acrylonitrile), polyurethane prepolymer, polystyrene, o-methylstyrene, poly-m-methylstyrene, polypropylene (p-methylstyrene), poly(2,4-dimethylstyrene) resin, polyvinyl toluene and their combination in any. Each of the above can also include acrylonitrile, vinyl toluene or methyl methacrylate. The amount of the thermoplastic polymer in the soluble material that can be embedded to form parts can be any amount that gives required elasticity without affecting required degradation amount. In some embodiments, the thermoplastic polymer content can range from a low of about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, and 45% to a high of about 91%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, and 45% by weight of the soluble material, including any values ​​or subsets therebetween.

[0055] This exemplary embodiment relates to a molded article for a degradable downhole tool. A modified polyglycolic acid is molded as a mandrel cone for a degradable plug in downhole applications, where the mandrel cone is a key component. The mandrel cone made from the modified polyglycolic acid can withstand pressures up to 8,750 psi at 90°C during a pressure retention test. In the pressure retention test, the mandrel cone made from the modified polyglycolic acid exhibited a mass loss of 14% after 2 days in an 80°C aqueous solution, and approximately 50% after 7 days in an 80°C aqueous solution.

[0056] Polyglycolic acid (PGA) has chemical resistance, high mechanical strength, high temperature performance and hydrolytic degradability in downhole environments. However, PGA is not impact-resistant and has a large shrinkage rate for large molded parts for downhole tool applications.

[0057] Here, PGA can be modified by mixing with other biodegradable polymers, including PLA and PLGA. These modifications aim to reduce molding shrinkage while also reducing brittleness. In PGA / PLA blends with a small amount of PLGA, PLGA (a P(LA-co-GA) copolymer) acts as a compatibilizer between PGA and PLA. By increasing the interfacial bonding between the PGA and PLA phases, PLGA enables the secondary PLA component to be well dispersed within the PGA matrix and maintain a very small domain size. Due to PLA's good dispersibility and low composition, PLA has minimal impact on PGA degradation. Therefore, PLA reduces or delays the degradation rate of PGA while also improving its impact resistance and elongation.

[0058] Polyglycolic acid (PGA) resin

[0059] Biodegradable PGA is an aliphatic polyester that can be biodegraded by enzymes and the like. PGA also tends to undergo hydrolytic degradation in water, aqueous solutions or humid environments. The PGA contained in the PGA composition of the present invention refers not only to a glycolic acid homopolymer composed of glycolic acid repeating units represented by the formula (-O-CH2-CO-) (including a ring-opening polymer of glycolide as a bimolecular cyclic ester of glycolic acid), but also to a polyglycolic acid copolymer (PGA copolymer) containing at least 70% by mass of the above-mentioned glycolic acid repeating units. PGA can be synthesized by a dehydration polycondensation reaction of glycolic acid as an α-hydroxycarboxylic acid. In order to efficiently synthesize high molecular weight PGA, it is synthesized by ring-opening polymerization on glycolide, which is a bimolecular cyclic ester of glycolic acid.

[0060] Examples of comonomers used to prepare PGA copolymers together with the above-mentioned glycolic acid monomers such as glycolide include diol compounds such as ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, glycerol, pentaerythritol, bisphenol A, polyethylene glycol, polypropylene glycol and polytetramethylene glycol; dicarboxylic acids such as oxalic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, bis(( (4-carboxyphenyl)methane, anthracene dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 5-sodium sulfonate and 5-tetrabutylisophenyl diphosphonium; hydroxycarboxylic acids such as lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid and hydroxybenzoic acid; lactide; lactones such as caprolactone, valerolactone, propiolactone, undecanoic acid and 1,5-oxepan-2-one; carbonates such as trimethyl carbonate; a substantially equimolar mixture of an aliphatic diol such as ethylene glycol and 1,4-butanediol with an aliphatic dicarboxylic acid such as succinic acid and adipic acid or their alkyl esters; or two or more thereof. Polymers of these comonomers can be used as starting materials to prepare PGA copolymers together with glycolic acid monomers such as the above-mentioned glycolide. The preferred comonomer is lactic acid, which forms a copolymer of glycolic acid and lactic acid (PGLA).

[0061] The repeating units of glycolic acid in the PGA contained in the PGA composition of the present invention are basically formed by a PGA homopolymer having at least 70 mass%, preferably at least 80 mass%, more preferably at least 90 mass%, even more preferably at least 95 mass%, particularly preferably at least 98 mass%, and sometimes 100 mass% of glycolic acid repeating units. When the proportion of glycolic acid repeating units is too small, the expected hydrolyzability, heat resistance, mechanical properties, etc. of the PGA composition of the present invention deteriorate. The proportion of repeating units other than glycolic acid repeating units is at most 30 mass%, preferably at most 20 mass%, more preferably at most 10 mass%, even more preferably at most 5 mass%, particularly preferably at most 2 mass%, and most preferably at most 1 mass%; and repeating units other than glycolic acid repeating units may also not be used.

[0062] In order to efficiently prepare the desired high molecular weight polymer, the PGA contained in the PGA composition of the present invention is preferably a PGA obtained by polymerizing 70 to 100% by mass of glycolide and 30 to 0% by mass of the above-mentioned other comonomer. The other comonomer can be a bimolecular cyclic monomer or a mixture of the two, rather than a cyclic monomer, but in order to obtain the target PGA composition of the present invention, a cyclic monomer is preferred. The following will describe in detail the PGA obtained by ring-opening polymerization of 70 to 100% by mass of glycolide and 30 to 0% by mass of another cyclic monomer.

[0063] Glycolide

[0064] Glycolide, which forms PGA through ring-opening polymerization, is a bimolecular cyclic ester of glycolic acid. The method for producing glycolide is not particularly limited, but glycolide can generally be obtained by thermal depolymerization of glycolic acid oligomers. Examples of methods that can be used to depolymerize glycolic acid oligomers include melt depolymerization, solid-phase depolymerization, and solution depolymerization. Glycolide obtained as a cyclic condensate of chloroacetate can also be used. Furthermore, glycolide-containing glycolic acid having a maximum glycolide content of 20% by mass can be used.

[0065] The PGA contained in the PGA composition of the present invention can be formed by ring-opening polymerization of glycolide alone, but a copolymer can also be formed by simultaneously ring-opening polymerization of another cyclic monomer as a copolymer component. When the copolymer is formed, the glycolide ratio of the copolymer is at least 70% by mass, preferably at least 80% by mass, more preferably at least 95% by mass, even more preferably at least 95% by mass, particularly preferably at least 98% by mass, and most preferably at least 99% by mass, and it is substantially a PGA homopolymer.

[0066] Other cyclic monomers

[0067] Other cyclic monomers that can be used as copolymerization components with glycolide include bimolecular cyclic esters of hydroxycarboxylic acids, such as lactide; and cyclic monomers, such as lactones (e.g., β-propiolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, δ-valerolactone, β-methyl-δ-pentenoic acid, 6-hexanolactone and trimethylene carbonate, 1,3-dioxane (dioxane). Another preferred cyclic monomer is another bimolecular cyclic ester of a hydroxycarboxylic acid, examples of which include L-lactic acid, D-lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, α-hydroxyhexanoic acid, α-isocaproic acid, α-hydroxyethylheptanoic acid, α-hydroxyoctanoic acid, α-hydroxypropyldecanoic acid, α-hydroxymyristic acid, α-hydroxystearic acid, and alkyl-substituted products thereof. A particularly preferred other cyclic monomer is lactide, which is a bimolecular cyclic ester of lactic acid, which may be in the L-form, D-form, racemic form, or a mixture thereof.

[0068] The ratio of other cyclic monomers is at most 30 mass %, preferably at most 20 mass %, more preferably at most 10 mass %, even more preferably at most 5 mass %, particularly preferably at most 2 mass %, most preferably at most 1 mass %.When PGA is formed by 100 mass % of glycolide, the ratio of other cyclic monomers is 0 mass %, and this PGA is also included in the scope of the present invention. By carrying out ring-opening copolymerization of glycolide and another cyclic monomer, it is possible to improve molding processability by reducing the melting point (Tm, sometimes referred to as "crystalline melting point") of the PGA copolymer, reducing the processing temperature of the product such as molded product produced by the PGA composition, or controlling the crystallization rate. However, when the ratio of the cyclic monomer used is too high, the crystallinity of the PGA copolymer formed is reduced, and its heat resistance, mechanical properties, etc. are reduced.

[0069] Ring-opening polymerization

[0070] The ring-opening polymerization or ring-opening copolymerization of glycolide (hereinafter collectively referred to as "ring-opening (co)polymerization") is preferably carried out in the presence of a small amount of a catalyst. The catalyst is not particularly limited, but examples include tin compounds such as tin halides (e.g., tin dichloride, tin tetrachloride, etc.), organic tin carboxylates (e.g., tin octoates such as tin 2-ethylhexanoate); titanium compounds such as alkoxy titanates; aluminum compounds such as aluminum alkoxides; zirconium compounds such as zirconium acetylacetonate; and antimony compounds such as antimony halides and antimony oxide. The amount of catalyst used is preferably about 1 to 1000 ppm, more preferably about 3 to 300 ppm, based on the mass of the cyclic ester.

[0071] In the ring-opening (co)polymerization of glycolide, proton compounds such as alcohol (which may be a higher alcohol such as lauryl alcohol) or water can be used as molecular weight regulators to control the physical properties such as the melt viscosity or molecular weight of the produced PGA. In addition, glycolide usually contains trace amounts of water and hydroxycarboxylic acid compounds, such as glycolic acid or linear glycolic acid oligomers as impurities, which also have an effect on the polymerization reaction. Therefore, the concentration of these impurities can be quantified as a molar concentration by, for example, neutralization titration of carboxylic acid, and alcohol or water can be added as a proton compound according to the target molecular weight to control the molar concentration of the entire proton compound relative to glycolide, thereby adjusting the molecular weight of the product PGA. In addition, polyols such as glycerol can be added to improve physical properties.

[0072] The ring-opening (co)polymerization of glycolide can be bulk polymerization or solution polymerization, but bulk polymerization is used in many cases. The polymerization apparatus for bulk polymerization can be appropriately selected from various devices, such as extruder type, vertical type with paddle wings, vertical type with spiral wing, extruder or kneader horizontal type, ampoule type, plate type, or tubular type. In addition, various reaction vessels can be used for solution polymerization.

[0073] The polymerization temperature can be appropriately set in the range of 120°C to 300°C according to the intended purpose, which is basically the polymerization initialization temperature. The polymerization temperature is preferably 130 to 270°C, more preferably 140 to 260°C, and particularly preferably 150 to 250°C. When the polymerization temperature is too low, the molecular weight distribution of the prepared PGA tends to become broad. When the polymerization temperature is too high, the prepared PGA tends to undergo thermal decomposition. The polymerization time is in the range of 3 minutes to 50 hours, preferably 5 minutes to 30 hours. When the polymerization time is too short, the polymerization is difficult to proceed fully, which makes it impossible to obtain the set weight average molecular weight. When the polymerization time is too long, the prepared PGA tends to be colored.

[0074] After the prepared PGA is converted to a solid state, solid-phase polymerization can be further performed as needed. Solid-phase polymerization refers to the operation of heating the PGA at a temperature below its melting point to maintain its solid state while performing a heat treatment. Due to this solid-phase polymerization, low-molecular-weight components such as unreacted monomers or oligomers are volatilized and removed. Solid-phase polymerization is preferably performed for 1 to 100 hours, more preferably 2 to 50 hours, and particularly preferably 3 to 30 hours.

[0075] (Weight average molecular weight (Mw))

[0076] The weight average molecular weight (Mw) of the PGA included in the PGA composition of the present invention is generally preferably in the range of 70,000 to 1,000,000, more preferably in the range of 100,000 to 800,000, even more preferably in the range of 120,000 to 500,000 and particularly preferably in the range of 150,000 to 400,000. The weight average molecular weight (Mw) of PGA is measured by gel permeation chromatography (GPC) apparatus. When the weight average molecular weight (Mw) is too low, degradation proceeds rapidly, which may make it difficult to achieve the purpose of the present invention, or mechanical properties such as heat resistance or strength may be insufficient. When the weight average molecular weight (Mw) is too high, it may be difficult to prepare the PGA composition, or hydrolyzability or degradability may be insufficient.

[0077] Molecular weight distribution (Mw / Mn)

[0078] The molecular weight distribution is expressed as the ratio (Mw / Mn) of the weight average molecular weight (Mw) of the PGA contained in the PGA composition of the present invention to the number average molecular weight (Mn). It is preferred to set the molecular weight distribution (Mw / Mn) in the range of 1.5 to 4.0 because the degradation rate can be controlled by reducing the amount of polymer components in the low molecular weight range that are easily degraded in the early stage or the polymer components in the high molecular weight range that degrade quickly. When the molecular weight distribution (Mw / Mn) is too wide, the degradation rate no longer depends on the weight average molecular weight (Mw) of the PGA, which may make degradation difficult to control. When the molecular weight distribution (Mw / Mn) is too narrow, it may be difficult to keep the PGA composition within a specified time. Mechanical properties such as strength. The molecular weight distribution (Mw / Mn) is preferably 1.6 to 3.7, more preferably 1.65 to 3.5. As with the case of the weight average molecular weight (Mw), the molecular weight distribution (Mw / Mn) is determined using a GPC analysis device.

[0079] Melting point (Tm)

[0080] The melting point (Tm) of the PGA contained in the PGA composition of the present invention is generally 180 to 245°C. And it can be adjusted based on the weight average molecular weight (Mw), the type and content ratio of the copolymer components, etc. The melting point (Tm) of PGA is preferably 190 to 240°C. , More preferably, it is 195 to 235°C, and particularly preferably, it is 200 to 230°C. The melting point (Tm) of the PGA homopolymer is generally about 220°C. When the melting point (Tm) is too low, mechanical properties such as heat resistance or strength may be insufficient. When the melting point (Tm) is too high, the processability of the PGA composition may be insufficient, or the formation of the product may not be adequately controlled, which may prevent properties such as hydrolysis or biodegradability from falling within the desired range. The melting point (Tm) of PGA is measured in a nitrogen atmosphere using a differential scanning calorimeter (DSC).

[0081] Glass transition temperature (Tg)

[0082] The glass transition temperature (Tg) of the PGA contained in the PGA composition of the present invention is generally 25 to 60° C., preferably 30 to 55° C., more preferably 32 to 52° C., and particularly preferably 35 to 50° C. The glass transition temperature (Tg) of PGA can be adjusted by weight-average molecular weight (Mw), molecular weight distribution, type and content ratio of copolymer components, etc. The glass transition temperature (Tg) of PGA is measured using a differential scanning calorimeter (DSC) in a nitrogen atmosphere.

[0083] Melt flow rate (MFR)

[0084] The melt flow rate (MFR) of the PGA contained in the PGA composition of the present invention is generally preferably in the range of 0.1 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even more preferably 2 to 20 g / 10 min. The MFR of PGA is expressed as the fluid flow rate (g) per 10 minutes measured at a temperature of 240°C under a load of 2.16 kg. When the MFR of PGA is too high, molding processability may not be ensured according to the production process, or the mechanical properties such as strength of the product obtained from the PGA composition may be insufficient, which may hinder the acquisition of a PGA composition having the desired properties. When the MFR of PGA is too low, it may be difficult to mold the resulting PGA composition.

[0085] Other resins or additives

[0086] The PGA composition of the present invention may further contain other biodegradable resins, other resins or other additives as long as they do not conflict with the purpose of the present invention.

[0087] Other biodegradable resins

[0088] Examples of other biodegradable resins that may be further included in the PGA composition of the present invention include polyhydroxyalkanoates such as polyhydroxybutyrate, polyhydroxyvalerate, polyhydroxyhexanoate, polyhydroxyheptanoate, and poly(hydroxybutyrate / hydroxyvalerate); polyesters formed from dicarboxylic acids and diols such as polyethylene succinate, polybutylene succinate, and polybutylene succinate adipate; polyether esters such as polydioxanone; aliphatic polycarbonates such as polytrimethylene carbonate; polyamino acids such as polyα-pyrrolidone, polyaspartic acid, and polylysine; but PLA is preferred. When the PGA composition of the present invention contains another biodegradable resin, it is possible to adjust degradability, i.e., hydrolysis or biodegradability, as well as processability or mechanical properties such as strength.

[0089] When the PGA composition of the present invention comprises PGA and another biodegradable resin, the proportion of PGA is preferably at least 70 parts by mass, more preferably at least 80 parts by mass, even more preferably 90 parts by mass, and particularly preferably at least 95 parts by mass, with the total amount of PGA and other biodegradable resins being defined as 100 parts by mass.

[0090] Other resins

[0091] Examples of other resins that may be further included in the PGA composition of the present invention include polyolefin resins such as polyethylene and polypropylene; polyamide resins such as poly-L-lysine; acrylic resins; polyethers such as polyethylene glycol and polypropylene glycol; denatured polyvinyl alcohol; soft polyolefin resins such as ethylene / glycidyl methacrylate copolymers, ethylene / propylene terpolymers, and ethylene / butylene homopolymers; styrene copolymer resins; polyphenylene sulfide resins; polyetheretherketone resins; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyacetal resins; polysulfone resins; polyphenylene ether resins; polyimide resins; polyetherimide resins; cellulose esters; polyurethane resins; phenolic resins; melamine resins; unsaturated polyester resins; silicone resins; and epoxy resins. Two or more types of these other resins may also be mixed and included in the composition. The processability or mechanical properties of the PGA composition of the present invention, such as strength, can be adjusted by further including other resins and including or not including another biodegradable resin. When the PGA composition contains other resins, the content of the other resins is generally at most 30 parts by mass, preferably at most 20 parts by mass, more preferably at most 10 parts by mass per 100 parts by mass of PGA, and the content may also be 5 parts by mass or less, or 1 part by mass or less.

[0092] PLA

[0093] Polylactic acid or polylactide (PLA) is a thermoplastic aliphatic polyester that is typically derived from renewable resources. PLA is considered biodegradable under certain conditions and can be degraded through hydrolysis reactions. Generally, amorphous PLA degrades more readily than crystalline PLA, which is typically a purer form of poly-D-lactide or poly-L-lactide.

[0094] D-lactide is a dilactone or cyclic dimer of D-lactic acid. Similarly, L-lactide is a cyclic dimer of L-lactic acid. Meso-D,L-lactide is a cyclic dimer of D- and L-lactic acid. Racemic D,L-lactide comprises a 50 / 50 mixture of D- and L-lactic acid. When used alone herein, the term "D,L-lactide" is intended to include either meso-D,L-lactide or racemic D,L-lactide. Polylactic acid can be prepared from one or more of the above. The chirality of the lactide units provides a means of regulating degradation rates as well as physical and mechanical properties. For example, poly(L-lactide) is a semi-crystalline polymer with a relatively slow hydrolysis rate. Poly(D,L-lactide) is an amorphous polymer with a faster hydrolysis rate. According to the present invention, stereoisomers of lactic acid can be combined individually or copolymerized.

[0095] During the degradation of PLA, an acid is produced that can dissolve or react with downhole materials including, but not limited to, acid-soluble bridging agents (calcium carbonate), polymers (such as pH-reversible gels), and shrinkable clays.

[0096] In some embodiments, the amorphous polylactic acid can be in the form of particles, rods, fibers, sheets, or films.

[0097] Compatibilizer

[0098] A blend is a physical mixture of two or more components that typically offers a compromise between the performance and economics of the individual components. It is well known that the properties and performance of the interfaces between the components in a blend often have a limiting effect on the bulk properties of the multiphase blend. In fact, the physical and mechanical properties of a blend are often inferior to the mathematical average of the properties of the original components. Blend components can be miscible or immiscible in their behavior toward one another.

[0099] Alloys differ from blends. Although they also consist of two or more components, alloys exhibit strong intermolecular forces, whereas the intermolecular bonding between the blend components is provided by a compatibilizer. This bonding, in turn, produces new properties that differ from those of the original components and often exceed the average of the original components. The types of interactions, or "chemical bonds," between the components can include, for example, one or more of the following mechanisms: ionic; covalent; intermolecular permeation; hydrogen bonding; or associative.

[0100] Successful compatibilization through one or more of these interactions results in interfacial adhesion, leading to the formation of cohesive, multiphase, compatibilized alloys with useful properties. Numerous strategies have been developed to achieve compatibilization. In one approach, suitable block or graft copolymers are introduced as macromolecular emulsifiers to provide covalent bonds across and strengthen the blend interface. Block and graft copolymers can be generated in situ by reactive extrusion and blending to produce compatibilized blends.

[0101] In another approach, polymers with nucleophilic functional groups interact with hydrogen-containing compatibilizers to form hydrogen bonds. Ionomers also act as compatibilizers. In some cases, ionic or strong physicochemical interactions occur at the interface, which in turn enhance compatibility.

[0102] Compatibilization can also be achieved by adding similar functional groups using the "like attracts like" principle, such as using chlorinated polyethylene to compatibilize polyvinyl chloride with polyethylene. This is called "associative" bonding. Finally, compatibilization has been demonstrated by adding a third, immiscible phase component that exhibits relatively low interfacial tension with each of the main blend components (i.e., those intended to compatibilize). The compatibilizing effect of mutually miscible components may be due to their tendency to be enriched near the blend interface.

[0103] Alloying provides a tool to reduce the cost of high-performance resins while retaining many desirable properties and / or providing improved performance, such as enhanced processing. The most successful alloying processes produce controlled and stable morphologies with unique thermodynamic profiles. However, in multicomponent systems, even incomplete alloying can still produce useful compositions.

[0104] Compatibilizer poly(lactic-co-glycolic acid) (PLGA) was prepared by ring-opening polymerization of the cyclic monomers lactide and glycolide. The glycolic acid comonomer content in the copolymer ranges from 1% to 50%, preferably 5% to 45%, 10% to 40%, 15% to 35%, etc. The resulting copolymer has an MFR of ~50 and is in the form of a powder, flakes, or granules. When PLGA is added as a compatibilizer, ideally, the compatibilizer is dispersed at the interface between PGA and PLA during melt blending of PGA and PLA. The PLA portion of the PLGA copolymer is mixed with the PLA phase, while the PGA in the PLGA copolymer is mixed with the PLA phase. Therefore, the PLGA copolymer enhances interfacial bonding between the PGA and PLA phases, reducing the size of the small phases and reducing interfacial defects. Therefore, the principle is to use the A-co-B copolymer (as a compatibilizer) to compatibilize the polymer blend A / B.

[0105] Other additives

[0106] Examples of other additives that may be further included in the PGA composition of the present invention are additives that are typically compounded with PGA compositions, such as plasticizers (polyester plasticizers, glycerol plasticizers, polycarboxylic acid ester plasticizers, phosphate plasticizers, polyalkylene glycol plasticizers, epoxy plasticizers, etc.), antioxidants, heat stabilizers, end-capping agents, ultraviolet absorbers, flame retardants (bromine flame retardants, phosphorus flame retardants, antimony compounds, melamine compounds, etc.), lubricants, waterproofing agents, water repellents, release agents, waxes, dyes or pigments and other colorants; fillers other than oxygen absorbers, crystallization promoters, nucleating agents, hydrogen ion concentration regulators and inorganic fillers. Two or more types of these other additives may also be mixed and included in the composition. The content of other additives is typically at most 10 parts by mass per 100 parts by mass of PGA, preferably at most 5 parts by mass, and the content may also be 1 part by mass or less.

[0107] Capping agent

[0108] Among these additives, the incorporation of a carboxyl end-capping agent or a hydroxyl end-capping agent into the PGA composition can, in particular, control the degradability of the PGA composition, in particular the hydrolysis resistance, and can improve the storage property of the PGA composition. That is, by incorporating a carboxyl end-capping agent or a hydroxyl end-capping agent into the composition, the accidental degradation of the resulting PGA composition during storage can be suppressed until it is used for molding or other processes, which can suppress the reduction in molecular weight and regulate the hydrolysis or biodegradation rate of the PGA composition. As an end-capping agent, a compound known as a PGA water resistance improver can be used, which has a carboxyl end-capping effect or a hydroxyl end-capping effect. From the perspective of the balance between hydrolysis resistance or biodegradability and hydrolysis resistance during storage, a carboxyl end-capping agent is preferred as the end-capping agent. Examples of carboxyl-capping agents include carbodiimide compounds such as N,N′-2,6-diisopropylphenylcarbodiimide; oxazoline compounds such as 2,2′-m-phenylenebis(2-oxazoline), 2,2′-p-phenylenebis(2-oxazoline), 2-phenyl-2-oxazoline, and styrene-isopropenyl-2-oxazoline; oxazine compounds such as 2-methoxy-5,6-dihydro-4H-1,3-oxazine; epoxy compounds such as N-glycidylphthalimide, cyclohexene oxide, and tris(2,3-epoxypropyl)isocyanurate; and the like. Among these carboxyl-capping agents, carbodiimide compounds are preferred. Any of aromatic, alicyclic, and aliphatic carbodiimide compounds can be used, but aromatic carbodiimide compounds are particularly preferred, especially high-purity compounds that provide improved water resistance during storage. In addition, diketene compounds, isocyanates, etc. can be used as hydroxyl blocking agents. The carboxyl blocking agent or hydroxyl blocking agent is usually used in a proportion of 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass, more preferably 0.1 to 1 part by mass per 100 parts by mass of PGA.

[0109] In addition, when the PGA composition contains a heat stabilizer, thermal degradation during molding or the like can be suppressed, and the long-term storage property of the PGA composition is improved, which is more preferred. Examples of heat stabilizers include phosphoric acid esters having a pentaerythritol skeleton structure, such as cycloneopentanetetrazolbis(2,6-di-tert-butyl-4-methylphenyl)phosphite, cycloneopentanetrazolbis(2,4-di-tert-butylphenyl)phosphite, and cycloneopentanetrazolbis(octadecyl)phosphite; alkyl phosphoric acid esters or alkyl phosphites, the alkyl groups of which preferably have 8 to 24 carbon atoms, such as monostearyl or distearyl phosphoric acid esters or mixtures thereof [a known commercially available product is a mixture of about 50% by mass of monostearyl phosphoric acid ester and about 50% by mass of distearyl phosphoric acid ester (trade name "AX-71", manufactured by ADEKA Co., Ltd.)]; carbonates such as calcium carbonate and strontium carbonate (which can also serve as inorganic fillers); hydrazine compounds that generally have a -CONHNHN-CO unit as polymerization catalyst deactivators, such as bis[2-(2-hydroxybenzoyl)hydrazine]dodecanoic acid and N,N′-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine; triazole compounds such as 3-(N-salicyloyl)amino-1,2,4-triazole; and triazine compounds. These heat stabilizers can be used alone or in combination of two or more. The heat stabilizer is generally used in a ratio of up to 3 parts by mass, preferably 0.001 to 1 part by mass, more preferably 0.005 to 0.5 parts by mass, and particularly preferably 0.01 to 0.1 parts by mass (100 to 1000 ppm) per 100 parts by mass of PGA.

[0110] Polyglycolic acid resin composition

[0111] The PGA composition of the present invention is a PGA composition containing 50 to 90 mass % of PGA, 50 to 10 mass % of PLA, and a compatibilizer. The reaction product can have a tensile strength of at least about 12,000 psi.

[0112] The PGA composition of the present invention may be in any shape or form, for example, a raw material for molding, such as pellets, strands or powder (including a melt-mixed composition and a composition obtained by melt-kneading using an extruder as described below), a sheet, a film, an extrusion-molded product, an injection-molded product, a compression-molded product, a blow-molded product, or a laminate thereof, or other composite materials thereof.

[0113] Figure 1Ais a cross-sectional view of an exemplary downhole tool component 100 that can incorporate the principles of the present disclosure. The downhole tool component 100, also referred to as a "frac plug," has one or more dissolvable components and is configured to anchor itself to a casing or liner on the inner wall of a wellbore. As described herein, the frac plug 100 can incorporate or otherwise include a closable flow path designed to allow flow from below (i.e., downhole) but prevent flow from above (i.e., uphole), thereby functioning as a temporary one-way check valve.

[0114] As shown, the fracturing plug 100 may include a mandrel cone 120, a sealing element 140, and a slider 160. A sleeve 180 is also shown. Some or all of the above components may be made of any soluble material described herein and may be degradable upon contact with a particular solvent. The various components of the fracturing plug 100 may be designed to dissolve at the same rate or at different rates. Some components may be made of two or more soluble alloys, which causes the alloys along the outside (e.g., farther from the centerline of the fracturing plug 100) to dissolve slowly, while the alloys located on the inside (e.g., closer to the centerline of the fracturing plug 100) dissolve faster, or vice versa. The solubility properties of any component may be affected by pressure, temperature, or solvent concentration.

[0115] In at least one embodiment, some or all components of the frac plug 100 can be made from a dissolvable material comprising a primary metallic material alloyed with other elements and chemically layered into place using advanced powder technology. In some embodiments, the primary metallic material can be magnesium, and the powder composition can be determined by the ratio of magnesium to other metallic powders used to layer the rough material shape of the component. The material can then be consolidated using a combination of heat and pressure, and the resulting material can then be heat treated to a desired material strength.

[0116] The soluble portion of the fracturing plug 100 may dissolve upon contact with fresh or salt water. In at least one embodiment, a strong acid such as hydrochloric acid, sulfuric acid, or perchloric acid can accelerate the dissolution of the fracturing plug 100. In some embodiments, for example, hydrochloric acid can be injected directly above the fracturing plug 100 (at the wellhead) to accelerate the dissolution process.

[0117] Mandrel cone 120 may include, for example, upper end 130, lower end 150, and ball seat 110. Ball seat 110 is sized to receive a frac ball, which in a preferred embodiment may be a degradable metal or a degradable polymer, such as an acid polymer, in a manner known in the art.

[0118] Degradable or soluble means substantially degradable or soluble in the downhole fluid, which may be a naturally occurring fluid or an introduced fluid, such as fresh water, salt water, acid solution, fracturing fluid, or other fluid.

[0119] The mandrel cone 120 may include an inner wall 122 and an outer wall 124 .

[0120] The slider 160 and the sealing element 140 can each extend at least partially over the tapered outer surface of the outer wall 124 of the mandrel cone 120. At least the slip ring 160 and the sealing element 140 can have corresponding inclined inner surfaces that are configured to slidingly engage the tapered outer surface of the outer wall 124 of the mandrel cone 120. The sealing element 140 can be made of any of the degradable rubber materials described herein, but can also be made of non-degradable materials without departing from the scope of the present disclosure. A helically wound component (not shown) can be included that is inserted into the slider 160 and the sealing element 140 and can be used to prevent the elastomeric material of the sealing element 140 from extruding, deforming, or otherwise axially creeping when the frac plug 100 is installed.

[0121] The plug 120 can typically be installed using a ballistic, hydraulic, electric, or mechanical installation tool known in the art. The installation tool typically installs the plug by pulling the bottom of the plug upward relative to the top of the plug. The longitudinal compression of the plug causes the split ring to move radially outward to engage the inner wall of the sleeve 180. Further upward pulling on the bottom of the plug causes the plug to slide, and the wedge (or cone) is longitudinally pressed against the plug split ring, forcing the ring radially outward against the sleeve. Figure 1B As shown, the split or non-split ring sealingly engages the inner wall of the sleeve 180 when radially forced against the sleeve, forming a functional seal that prevents fluid flow between the plug and the sleeve.

[0122] The disclosed embodiments allow for the sealing element 140 to be comprised of a metal split ring, or alternatively, a solid, non-split rubber or rubber-like elastomer. In some disclosed embodiments, a sealing element 140 is shown that does not "clog" the milling head or leave sticky debris in the hole when drilled out. In some disclosed embodiments, the metal or non-metal split ring or non-split ring sealing element does not have to be drilled out, but rather degrades with the plug, typically in the presence of downhole fluids or fluids added at the wellhead.

[0123] Even at relatively low wellbore fluid temperatures, such as approximately 200°F or lower, the swellable split ring functions similarly to a conventional rubber or rubber-like elastomeric seal, sealing the plug to the casing to substantially prevent fluid migration around and through the plug. When compressed between the plug-cone elements and sliding during installation, the outer surface of the swellable split ring, or a non-splitting ring, radially swells against the well casing, sealing the plug to the casing.

[0124] like Figure 2As shown, the plug was placed vertically at room temperature. The initial support force was approximately 23,200 lbs. After installation, water was poured onto the upper area, and no leakage occurred. The plug then passed an ambient pressure test of 7,250 psi.

[0125] Furthermore, the plug successfully passed a test at 200°F (93°C) maintaining a pressure of 7250 psi (50 MPa) for four hours. During post-test inspection, no component extrusion was observed. Some deformation was observed on the PGA cone. The plug did not move down to the bottom of the sleeve.

[0126] like Figure 3 As shown, the plug successfully passed the pressure retention test at 8700 psi (60 MPa) and 93°C (200°F) for 4 hours.

[0127] Figure 4 Photos of modified PGA mandrel cones at different immersion times at 80° C. are shown. The mandrel cones were pressure held at 7250 psi (50 MPa) and 93° C. for 4 hours before being immersed in KCl solution at 80° C. for immersion testing.

[0128] Figure 5 The mass retention test of the modified PGA mandrel cone at 80°C as a function of immersion time is shown. The mandrel cone was pressure-held at 7250 psi (50 MPa) and 93°C (200°F) for 4 hours before being immersed in KCl solution at 80°C for immersion testing.

[0129] After immersion in water at 80°C for 2 days, the mass loss percentage of the PGA in the PGA composition of the present invention (sometimes referred to as "mass loss percentage after 2 days at 80°C") is approximately 14%. Since the mass loss percentage of the PGA of the present invention after 7 days at 80°C is approximately 50%, the composition may have excellent moldability and mechanical properties, as well as excellent heat resistance and hydrolysis resistance.

[0130] The percentage of mass loss of the PGA composition after 7 days at 80°C is determined by the following method. Specifically, a dumbbell-shaped evaluation specimen (the dumbbell shape specification complies with ISO 294) is made by injection molding, and the mass of the evaluation specimen is measured. The mass of PGA in the evaluation specimen (hereinafter referred to as "PGA mass before test") is calculated with reference to the content ratio of the inorganic filler. After the retrieved evaluation specimen is blown with cold air and vacuum dried to remove moisture, the mass of the evaluation specimen is evaluated, and the mass of PGA in the evaluation specimen after the test is measured (hereinafter referred to as "PGA mass after test"). The percentage of mass loss of the PGA composition after 6 days at 90°C is calculated according to the following calculation formula.

[0131] Calculation formula:

[0132] 90°C, mass loss percentage after 6 days (%) = (PGA mass before test - PGA mass after test) / PGA weight before test × 100

[0133] [Melt flow rate (MFR)]

[0134] The melt flow rate (MFR) of the PGA contained in the PGA composition of the present invention is generally preferably in the range of 0.1 to 100 g / 10 min, more preferably in the range of 1 to 80 g / 10 min, and even more preferably in the range of 2 to 20 g / 10 min. The MFR of the PGA composition is expressed as the fluid flow rate (g) per 10 minutes measured at a temperature of 240°C under a load of 2.16 kg. When the MFP of the PGA composition is too high, molding processability may not be ensured according to the production process, or the mechanical properties such as strength of the product obtained from the PGA composition may be insufficient. When the MFR of the PGA composition is too low, it may be difficult to mold the PGA composition, which may prevent products from being obtained from the PGA composition having the desired properties.

[0135] [Mechanical properties]

[0136] The PGA composition of the present invention has an excellent balance of mechanical properties. Specifically, it can meet the following conditions required for mechanical properties:

[0137] (a) Charpy impact strength (according to ISO 179) of at least 3 kJ / m 2 , preferably at least 4 kJ / m 2 , more preferably at least 5 kJ / m 2 ;

[0138] (b) a tensile strength (according to ISO 527) of at least 50 MPa, preferably at least 70 MPa;

[0139] (c) an elasticity (according to ISO 527) of at least 1%, preferably at least 1.5%;

[0140] Preparation method of polyglycolic acid resin composition

[0141] The preparation method of the PGA composition of the present invention is not particularly limited, as long as a PGA composition containing a mixture of polyglycolic acid and polylactic acid and a compatibilizer in a weight ratio of about 100:0 or 99:1 to about 50:50 can be obtained, wherein the tensile strength of the reaction product is at least about 12,000 psi.

[0142] The step of injection molding using an extruder refers to mixing a raw material containing polyglycolic acid and polylactic acid in a weight ratio of about 99 / 1 to about 50 / 50 with a compatibilizer, adding the raw material to an extruder equipped with a screw and a cylinder, heating the raw material based on external heating and shearing, thereby heating and melting the raw material, extruding the material into a rod shape, and if necessary, cutting the material into pellets with a length of about a specified number of millimeters to form a PGA composition having a set material composition.

[0143] In particular, the PGA composition obtained by the production method of the PGA composition including the injection molding step using a single-screw extruder has good dispersion / distribution efficiency and can be formed into PGA composition products having various forms / shapes, such as sheets, films or injection molded products, thereby obtaining products made of the PGA composition having excellent moldability, mechanical properties, heat resistance, hydrolysis and biodegradability, which is preferred.

[0144] An extruder having a main feed port and a side feed port is an extruder having a main feed port provided at a position on one side of the screw drive portion of the extruder for supplying the majority of materials for forming a PGA composition, such as PGA, PLA, and a compatibilizer (generally in solid form), to the extruder, and a side feed port provided at a position intermediate between the main feed port and an extrusion port (nozzle) on the top side of the extruder screw for supplying a portion of the materials for forming the PGA composition to the extruder. With respect to the barrel length (L) of the extruder, the side feed port can generally be provided 0.2 to 0.9 L, preferably 0.4 to 0.8 L, and more preferably 0.5 to 0.75 L from the side of the screw drive portion.

[0145] The supply of PGA from the main feed port and / or the side feed port to the extruder can be achieved by known methods and mechanisms. For example, a method of supplying the material to the extruder through a hopper mounted on the main feed port and / or the side feed port can be used, or a method of supplying the material to the extruder through a feeder or extruder mounted on the main feed port and / or the side feed port can be used.

[0146] As described above, the extruder is provided with a screw and a cylinder, and has the functions of heating, melting the raw materials by external heating and shear heating. Most of the materials used to form the PGA composition supplied from the main feed port, particularly PGA, PLA, and compatibilizers, are in solid form; after the materials are heated and melted by external heating and shear heating, they are delivered to the extrusion port (nozzle) in a molten fluid state. Therefore, in the method for manufacturing the PGA composition of the present invention, the shear heat generation and other thermal history in the PGA composition can be adjusted from the main feed port and the side feed port.

[0147] Example

[0148] The PGA compositions of the present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to these examples. The properties of PGA and PGA compositions were determined by the following methods.

[0149] Preparation and Testing of Composite Samples

[0150] Injection molding was carried out on a Toyo Plastar machine. For the PGA / PLA blends, the material pellets were premixed and then dried to a moisture content of less than 0.025%, and then directly injection molded into tensile bars and flexure specimens according to ASTM D638 standards for further mechanical and degradation testing. Table 1 lists the detailed injection molding conditions.

[0151] Table 1 Injection Molding Conditions

[0152] PGA PGA / PLA blends PLA Barrel temperature (F) 473 473 400 Mold temperature (C) 90 90 100 Injection speed 72％ 72％ 72％ Holding pressure (Psi) 450-500 450-500 350 Holding time (seconds) 13 13 8. Screw recovery 25+％ 8％ 25+％ Backpressure (Psi) 40 40 40

[0153] In addition to injection molding, polymer composites can also be formed by compression molding and extrusion molding.

[0154] (Weight-average Molecular Weight (Mw) and Molecular Weight Distribution (Mw / Mn))

[0155] The weight-average molecular weight (Mw) of PGA was obtained using a GPC analyzer. Specifically, 10 mg of the PGA sample was dissolved in hexafluoroisopropanol (HFIP) containing sodium trifluoroacetate at a concentration of 5 mM to form 10 mL, and then the solution was filtered through a membrane filter to obtain a sample solution. 10 μL of this sample solution was injected into the GPC analyzer, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined based on the results of measuring the molecular weight under the following measurement conditions.

[0156] <GPC Measurement Conditions>

[0157] Instrument: GPC104 manufactured by Showa Denko K.K.

[0158] Columns: Two HFIP-806M columns (connected in series) + one HFIP-LG pre-column, manufactured by Showa Denko K.K.

[0159] Column temperature: 40 °C.

[0160] Eluent: HFIP solution containing sodium trifluoroacetate at a concentration of 5 mM

[0161] Detector: Differential refractometer

[0162] Molecular weight calibration: Five different standard molecular weights of polymethyl methacrylate (manufactured by Polymer Laboratories Ltd.) were used to create calibration curve data for molecular weight.

[0163] (Melting point (Tm) and glass transition temperature (Tg))

[0164] The melting point (Tm) and glass transition temperature (Tg) of PGA were measured using a differential scanning calorimeter (DSC; Q20, TA Instruments) in a nitrogen atmosphere.

[0165] [Melt flow rate (MFR)]

[0166] The melt flow rate (MFR) of PGA and the PGA composition is the fluid flow rate (g) per 10 minutes measured at a temperature of 240° C. and a load of 2.16 kg.

[0167] [Tensile strength and elasticity]

[0168] The tensile strength and elasticity of the PGA compositions were measured according to ISO 527.

[0169] Tensile testing was performed on injection molded tensile bars using an MTS QTest / 50LP equipped with a 2" extensometer. Five random samples were taken and measured according to ISO 527. The width and thickness of the waist region of the samples were measured, and the test speed was 10 mm / min.

[0170] The degradation test was carried out in a glass jar at a designed temperature (eg 90°C) using the same 0.3 wt% KCl aqueous solution.

[0171] Results and discussion:

[0172] Table 2 lists the tensile properties of modified PGA formulations from the same batch of injection molding. The tensile strength of PGA / PLA 95 / 5, 90 / 10, and PGA / PLA / PLGA 90 / 10 / 1 formulations was approximately 2%-7% higher than that of pure PGA. The copolymer PLGA used had a copolymer composition of 75% LA and 25% GA.

[0173] As shown in Table 2, after being blended with PLA into binary blends, the elongation at break of the PGA / PLA blends (95 / 5, 90 / 10, 80 / 20, and 70 / 30) decreased from 7% for PGA to 1.6% for the 70 / 30 PGA / PLA blend. This is due to poor interfacial bonding between the PGA and PLA phases. Therefore, we introduced a PLGA compatibilizer to improve interfacial bonding and thereby increase elongation at break.

[0174] The addition of the compatibilizer copolymer Poly(LA-co-GA) (PLGA) increased the elongation at break of PGA / PLA / PLGA compared to PGA / PLA blends without the compatibilizer PLGA. For the 80 / 20 blend, the elongation increased from 1.8% for PGA / PLA 80 / 20 to over 10.4% for PGA / PLA / PLGA 80 / 20 / 1 and over 16.4% for PGA / PLA-PLGA 80 / 20 / 2 (with the compatibilizer PLGA). For the 70 / 30 blend, the elongation increased from 1.6% for PGA / PLA 70 / 30 to over 12.1% for PGA / PLA / PLGA 70 / 30 / 3 (with the compatibilizer PLGA). For the 90 / 10 blends, the elongation increases from 26% for PGA / PLA 90 / 10 to 3% for PGA / PLA / PLGA 90 / 10 / 1 (with the addition of the compatibilizer PLGA).

[0175] Compared to PGA / PLA 80 / 20 without compatibilizer (1.8%), 80 / 20 / 1 and 80 / 20 / 2 showed significant increases (10.4% or higher). This suggests that the compatibilizer increases the interfacial bonding between the PGA and PLA phases (domains), thereby improving the toughness of the blends. PGA / PLA / PLGA 70 / 30 / 3 (containing compatibilizer PLGA) has the same effect as PGA / PLA 70 / 30 without compatibilizer PLGA (elongation at break of PGA / PLA-PLGA 70 / 30 / 3 is >12.1%, higher than 1.6% for PGA / PLA 70 / 30 without compatibilizer).

[0176] In addition, after adding the compatibilizer PLGA, the elongation at break of PGA / PLA / PLGA increased significantly. Their tensile strength also increased slightly with the addition of the compatibilizer PLGA. For the 90 / 10 blend, the tensile strength increased from 16006 psi for PGA / PLA 90 / 10 to 16159 psi for PGA / PLA / PLGA 90 / 10 / 1 (with the addition of the compatibilizer PLGA). For the 80 / 20 blend, the tensile strength increased from 14367 psi for PGA / PLA 80 / 20 to 14415 psi for PGA / PLA / PLGA 80 / 20 / 1 (with the addition of the compatibilizer PLGA). For the 70 / 30 blend, the tensile strength increased from 12726 psi for PGA / PLA 70 / 30 to 13129 psi for PGA / PLA / PLGA 70 / 30 / 3 (with the addition of the compatibilizer PLGA).

[0177] Therefore, according to the test results of elongation at break and tensile strength, the addition of compatibilizer PLGA can improve the toughness and performance of PGA / PLA.

[0178] Table 2 Tensile properties of the formulations

[0179]

[0180]

[0181] degradation

[0182] Different formulations were subjected to degradation tests in glass jars using a 0.3 wt% KCl aqueous solution at a designed temperature (e.g., 90° C.) The well-dispersed small phases (or domains) did not delay the degradation of the blends.

[0183] morphology

[0184] It is clearly shown that the well-dispersed PLA sphere phase (PGA / PLA 90 / 10, several microns (~5 microns or less)) is located within the PGA matrix. After 7 days of degradation at 70°C, PGA rapidly degrades and is removed from the surface, while PLA still maintains a dispersed phase of spheres (or domains) within the PGA matrix because PLA degrades very slowly at 70°C compared to PGA. This is like an etching process, removing the easily etched first component (here, PGA) and revealing the phase structure of the second component (here, dispersed PLA).

[0185] In addition, the PLA dispersed sphere size of PGA / PLA 90 / 10 is about or less than 5 microns, and the dispersed phase (domain) of PGA / PLA 70 / 30 is about 20 microns. This shows that as the percentage of PLA increases from 10% to 30%, the size of the PLA dispersed phase (domain or droplet) increases significantly from 5 microns to 20 microns.

[0186] A distinct boundary exists between the two phases of the PGA and PLA blend, consisting of the dispersed phase (domain) of PLA and the matrix (continuous) phase of PGA. This indicates very limited interfacial bonding between the two phases. However, after adding the compatibilizer PLGA, the PGA / PLA / PLGA 90 / 10 / 1 blend showed no distinct boundary compared to the uncompatibilized PGA / PLA 90 / 10 blend. Therefore, the compatibilizer does enhance the interfacial bonding between the PGA and PLA phases, resulting in increased toughness, a significant increase in elongation at break, and a slight increase in tensile strength.

[0187] In summary, based on tensile properties, degradation, and morphology studies, the newly developed formulation is suitable for molded (e.g., injection molding, extrusion) degradable components for downhole tool applications.

[0188] The basic principles, main features and advantages of the invention patent application are shown and described above. Those skilled in the art should understand that the invention patent application is not limited to the above-mentioned embodiments. The above-mentioned embodiments and descriptions are only preferred examples of the invention patent application and are not intended to limit the invention without departing from the invention. Under the premise of the spirit and scope, the invention patent application will have various changes and improvements, and these changes and improvements belong to the scope of application of the invention patent claimed for protection. The scope of protection claimed by the invention application is defined by the attached claims and their equivalents.

Claims

1. A downhole tool component for oil and gas resource exploitation, comprising: a shaped body comprising a degradable polymer matrix, The downhole tool component, when held in downhole fluid at about 80° C., has an initial mass loss of about 14% over a holding period of about 2 days in a pressure holding test.

2. The downhole tool component according to claim 1, wherein: In the pressure hold test, the mass loss was approximately 50% over a hold period of approximately 7 days.

3. The downhole tool component according to claim 1 or 2, wherein: The degradable polymer includes polyglycolic acid resin.

4. The downhole tool component according to any one of claims 1 to 3, wherein: The degradable polymer includes polylactic acid.

5. The downhole tool component according to any one of claims 1 to 4, wherein: The downhole tool component maintained a pressure of about 6,500 psi to about 10,000 psi at about 93° C. for up to about 24 hours in a pressure retention test.

6. The downhole tool component according to any one of claims 1 to 5, wherein: The downhole fluid includes a KCl solution.

7. The downhole tool component according to any one of claims 1 to 6, wherein: The degradable polymer includes a copolymer, and the copolymer includes two or more aliphatic polyester copolymers.

8. The downhole tool component according to any one of claims 1 to 7, wherein: The copolymer includes poly(lactic-co-glycolic acid) (PLGA).

9. The downhole tool component according to any one of claims 1 to 8, wherein: Based on about 100 parts of polyglycolic acid (PGA) and polylactic acid (PLA), wherein PLA is about 1 part to about 30 parts, the copolymer polylactic-co-glycolic acid (PLGA) is about 0 part to about 6 parts.

10. A downhole tool component for oil and gas resource exploitation, comprising: a shaped body comprising a degradable polymer matrix, The downhole tool component, when held in downhole fluid at 80° C., has a mass loss of about 50% within a holding period of about 7 days in a pressure holding test.

11. The downhole tool component according to claim 10, wherein: The downhole tool component, when held in a downhole fluid, had an initial mass loss of approximately 14% over a holding period of approximately 2 days in a pressure holding test at 80°C.

12. The downhole tool component according to any one of claims 10-11, wherein: The polymer includes polyglycolic acid resin.

13. The downhole tool component according to any one of claims 10 to 12, wherein: The polymer includes polylactic acid.

14. The downhole tool component according to any one of claims 10 to 13, wherein: The polymer includes two or more aliphatic polyester copolymers.

15. The downhole tool component according to any one of claims 10 to 14, wherein: The copolymer includes poly(lactic-co-glycolic acid) (PLGA).

16. The downhole tool component according to any one of claims 10 to 15, wherein: The downhole tool component maintained a pressure of about 6,500 psi to about 10,000 psi at about 93° C. for up to about 24 hours in a pressure retention test.

17. A downhole tool component for oil and gas resource exploitation, comprising: A shaped body comprising a degradable polymer matrix, wherein the downhole tool component maintains a pressure of 6,500 to 10,000 psi at about 93° C. for up to about 24 hours in a pressure hold test.

18. The downhole tool member according to claim 17, wherein: The polymer includes a copolymer including poly(lactic-co-glycolic acid) (PLGA).

19. The downhole tool component according to any one of claims 17 to 18, wherein: The downhole tool component, when held in downhole fluid at about 80° C., had an initial mass loss of about 14% over a holding period of about 2 days in a pressure holding test.

20. The downhole tool component according to any one of claims 17 to 19, wherein: The downhole tool component, when held in a downhole fluid at about 80° C., has a mass loss of about 50% over a holding period of about 7 days in a pressure holding test.

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