Downhole tool member comprising branched poly(hydroxy acid)

Abstract

The present invention relates to downhole tools that include components that include branched poly(hydroxy acid) polymers that exhibit improved degradation rates when contacted with water.

Description

Technical Field

[0001] Related Applications This application claims priority based on European Patent Application No. 19315161.0 filed on December 18, 2019 in Europe and US Patent Application No. 62 / 950285 filed on December 19, 2019 in the United States, and the entire contents of each of these applications are incorporated herein by reference for all purposes.

[0002] The present invention relates to an article forming a tool itself or a component thereof for forming or repairing a downhole for extracting hydrocarbon resources including oil and gas.

Background Art

[0003] It is known that hydrocarbon resources such as oil or natural gas are produced by excavation from a well (collectively referred to as a "well", including an oil well or a gas well) having a porous and permeable underground layer. In a continuously excavated well, the production layer is stimulated to efficiently and continuously excavate hydrocarbon resources from the underground layer. One method for increasing hydrocarbon extraction relies on the generation of fractures in the production layer using fluid pressure (hereinafter referred to as "hydraulic pressure").

[0004] The hydraulic fracturing method is a method of generating fractures in the production layer by fluid pressure such as hydraulic pressure (hereinafter referred to as "hydraulic pressure"). Generally, after drilling a vertical hole, the vertical hole is curved in an underground layer thousands of meters underground to drill a horizontal hole. Then, a fracturing fluid is supplied to these boreholes (holes provided for forming a well, also referred to as "downholes") at high pressure, and fractures are generated by hydraulic pressure in the deep underground production layer. Thereby, the production layer is stimulated and hydrocarbon resources are extracted from the fractures.

[0005] To perform the above well treatment, usually the following method is used. Specifically, a predetermined section of the borehole or downhole is partially blocked, and a fluid such as a fracturing fluid is supplied thereto at high pressure, or a tool such as a perforating gun containing an explosive compound is used to generate fractures or perforate the production layer. Next, the next predetermined section (usually a section closer to the ground surface, i.e., in front of the previous section) is blocked, and fracturing and the like are performed to advance the fractures and perforations. Thereafter, this process is repeated until the necessary separation, fracturing, etc. are completed.

[0006] In the present invention, the "downhole tool" means a tool that is used to form a downhole (which may be called a "borehole", "wellbore" or "underground drill bore") provided when drilling from the ground (including over water) towards a production reservoir in order to obtain hydrocarbon resources, and functions as a flow path for hydrocarbon resources to recover hydrocarbon resources after the completion of the well.

[0007] The tool used for blocking and fracturing the borehole is a tool known as a "downhole tool". Downhole tools are generally not designed to be recoverable after use and are removed by destruction or by cutting, perforating or otherwise reducing them to small pieces, but cutting, perforating, etc. require considerable cost and time.

[0008] Therefore, it is recommended that the entire tool or at least one of its components (i.e., the downhole tool member) be formed of a degradable polymer so that the tool or tool member is decomposed underground.

[0009] Poly(hydroxy acids) such as poly(glycolic acid) and poly(lactic acid) are polymers known to decompose.

[0010] Downhole tools made of poly(glycolic acid) have already been described. U.S. Patent No. 9,267,351 discloses a downhole tool member comprising a shaped body made of a poly(glycolic acid) polymer having a weight average molecular weight of at least 70,000, an effective thickness that is at least 1 / 2 of the critical thickness of surface degradation, and exhibiting a constant rate of stock removal in water over time. Poly(glycolic acid) is described as a glycolic acid homopolymer consisting only of glycolic acid units (-OCH 2 -CO-) as repeating units, or a glycolic acid copolymer containing at most 50% by weight of other monomer units such as hydroxycarboxylic acid units, preferably lactic acid units. These polymers are thought to have a linear structure.

[0011] To increase the rate of stock removal of the tool member in water over time, U.S. Patent No. 9,574,418 teaches that a composition of poly(glycolic acid) containing a short fiber reinforcing material in an amount of preferably 1 to 50 parts per 100 parts of poly(glycolic acid) is required.

[0012] It has been found that branched poly(hydroxy acids), particularly certain branched poly(glycolic acid) polymers, can be successfully used in the manufacture of downhole tool members that exhibit a rate of stock removal in water that increases over time and is higher than that of downhole tool members made of prior art linear poly(glycolic acid) polymers.

Brief Description of the Drawings

[0013]

Figure 1

Summary of the Invention

[0014] The object of the present invention is (i) at least one hydroxy acid [hydroxy acid (A)] having only one hydroxyl group and only one carboxylic acid group, (ii) Optionally, at least one carboxylic acid [acid (C)] having one or two carboxylic acid groups and no hydroxyl group, and (iii) a. A compound containing at least one epoxy functional group, preferably a compound selected from the group consisting of epoxy silanes and polyepoxides, and b. A mixture containing at least one polyol [polyol (H)] containing at least three hydroxyl groups and no carboxylic acid group, and at least one polyacid [polyacid (O)] containing at least two carboxylic acid groups and no hydroxyl group, and c. A mixture containing at least one polyol [polyol (H)] containing at least three hydroxyl groups and no carboxylic acid group, and at least one alcohol [alcohol (AO)] containing at least one or two hydroxyl groups and no carboxylic acid group At least one polyfunctional reactant [reactant (F)] different from hydroxy acid (A) and acid (C), selected from the group consisting of A downhole tool member comprising at least one element containing a branched poly(hydroxy acid) polymer obtained from a polycondensation reaction of a monomer mixture containing

[0015] Hydroxy acid (A) Any hydroxy acid that can undergo polycondensation, that is, can form a polymer by condensation, that is, can add monomers while removing water, can be used as hydroxy acid (A). Examples thereof include glycolic acid, lactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxypentanoic acid, 5-hydroxypentanoic acid, and 6-hydroxycaproic acid. Generally, hydroxy acids having primary alcohols are preferred because they are more reactive.

[0016] Preferably, hydroxy acid (A) is selected from the group consisting of glycolic acid, lactic acid (L or D isomers, racemic mixture or single isomer), and mixtures thereof. Glycolic acid is particularly preferred.

[0017] The hydroxy acid (A) may consist of glycolic acid. Alternatively, the hydroxy acid (A) may contain glycolic acid and at least one hydroxy acid (A) different from glycolic acid. In the alternative variant, glycolic acid is preferably at least 50 mol%, preferably at least 70 mol%, and more preferably at least 95 mol% of the total amount of the hydroxy acid (A). When a hydroxy acid (A) different from glycolic acid is included, the amount thereof is at most 5 mol%, generally at most 4 mol%, preferably at most 3 mol% with respect to the total number of moles of glycolic acid and hydroxy acid (A), and / or the amount may be a low amount of about 0.1 mol%.

[0018] Acid (C) The acid (C) has one or two carboxylic acid groups and is selected from carboxylic acids that do not contain a hydroxyl group. It is generally understood that better results are obtained by using an acid (C) having a total of at least 4 carbon atoms, preferably at least 5 carbon atoms, and more preferably at least 6 carbon atoms. Generally, the acid (C) has 4 to 36 carbon atoms, preferably 6 to 24 carbon atoms.

[0019] Among the carboxylic acids having one carboxylic acid group that can be advantageously used as the acid (C), especially caprylic acid [CH 3 (CH 2 ) 6 -COOH], capric acid [CH 3 (CH 2 ) 8 -COOH], undecanoic acid [CH 3 (CH 2 ) 9 -COOH], dodecanoic acid or lauric acid [CH 3 (CH 2 ) 10 -COOH], tridecanoic acid [CH 3 (CH 2 ) 11 -COOH], tetradecanoic acid or myristic acid [CH 3 (CH 2 ) 12-COOH], pentadecanoic acid [CH 3 (CH 2 ) 13 -COOH], hexadecanoic acid or palmitic acid [CH 3 (CH 2 ) 14 -COOH], octadecanoic acid or stearic acid [CH 3 (CH 2 ) 16 -COOH], arachidic acid [CH 3 (CH 2 ) 18 -COOH], behenic acid [CH 3 (CH 2 ) 20 -COOH] and the like. The fatty acid (C) that has been shown to provide particularly good results is stearic acid, and thus stearic acid is particularly preferred.

[0020] When acid (C) is an aromatic monocarboxylic acid, it is preferably selected from the group consisting of benzoic acid, naphthoic acid, and phenylacetic acid.

[0021] Among the dicarboxylic acids that can be advantageously used as acid (C), succinic acid [HOOC-(CH 2 ) 2 -COOH], glutaric acid [HOOC-(CH 2 ) 3 -COOH], 2,2-dimethyl-glutaric acid [HOOC-C(CH 3 ) 2 -(CH 2 ) 2 -COOH], adipic acid [HOOC-(CH 2 ) 4 -COOH], 2,4,4-trimethyladipic acid [HOOC-CH(CH 3 )-CH 2 -C(CH 3 ) 2 -CH 2 -COOH], pimelic acid [HOOC-(CH 2 ) 5- COOH], suberic acid [HOOC-(CH 2 ) 6-COOH], azelaic acid [HOOC-(CH 2 ) 7 -COOH], sebacic acid [HOOC-(CH 2 ) 8 -COOH], undecanedioic acid [HOOC-(CH 2 ) 9 -COOH], dodecanedioic acid [HOOC-(CH 2 ) 10 -COOH], tetradodecanedioic acid [HOOC-(CH 2 ) 11 -COOH], octadecanedioic acid [HOOC-(CH 2 ) 16 -COOH] can be mentioned.

[0022] Polyfunctional reactant (F) Compound containing at least one epoxy functional group Notable non-limiting examples of suitable compounds containing at least one epoxy functional group are selected from the group consisting of epoxysilanes, especially glycidyloxypropyltrimethoxysilane or polyepoxides. Among the polyepoxides, epoxidized oils such as bisphenol A diglycidyl ether (BADGE) or epoxidized soybean oil or epoxidized linseed oil can be mentioned.

[0023] Mixture containing at least one polyol (H) and at least one polyacid (O) Polyol (H) The selection of the polyol (H) is not particularly limited, and any polyol containing at least three hydroxy groups and no carboxylic acid group can be used in the preparation of branched poly(hydroxy acids).

[0024] The polyol (H) is - In particular, a triol selected from the group consisting of glycerol, trimethylolpropane, trimethylolbutane, 2,3 - bis(2'-hydroxyethyl)-cyclohexan-1-ol, hexane-1,2,6-triol, 1,1,1-tris(hydroxymethyl)ethane, 3-(2'-hydroxyethoxy)propane-1,2-diol, 3-(2'-hydroxypropoxy)-propane-1,2-diol, 2-(2'-hydroxyethoxy)-hexane-1,2-diol, 6-(2' hydroxypropoxy)-hexane-1,2-diol, 1,1,1-tris-[(2'-hydroxyethoxy)-methylethane, 1,1,1-tris-[(2'-hydroxypropoxy)-methyl-propane, 1,1,1-tris-(4'-hydroxyphenyl)ethane, 1,1,1-tris-(hydroxyphenyl)-propane, 1,1,5-tris-(hydroxyphenyl)-3-methylpentane, trimethylolpropane ethoxylate, trimethylolpropane propoxylate, tris(hydroxymethyl)aminomethane, - In particular, a tetraol selected from the group consisting of diglycerol, di(trimethylolpropane), pentaerythritol, 1,1,4-tris-(dihydroxyphenyl)-butane, - A polyol containing five hydroxyl groups, in particular triglycerol, - A polyol containing six hydroxyl groups, in particular dipentaerythritol, and - A polyol containing eight hydroxyl groups, in particular tripentaerythritol may be selected from the group consisting of.

[0025] Preferred polyols (H) are triols and tetraols. The polyol (H) which has been confirmed to give particularly good results within the framework of the present invention is trimethylolpropane.

[0026] Polyacid (O) The polyacid (O) contains at least two carboxylic acid groups and can be any polyacid that does not contain a hydroxyl group. The polyacid (O) is different from the acid (C), if the acid (C) is included.

[0027] The polyacid (O) contains at least two carboxylic acid groups, particularly 2, 3 or 4 carboxylic acid groups.

[0028] The polyacid (O) can be selected from aliphatic polycarboxylic acids, alicyclic polycarboxylic acids and aromatic polycarboxylic acids.

[0029] Examples of aliphatic polycarboxylic acids are propane-1,2,3-tricarboxylic acid (also known as tricarballylic acid), ethane-1,1,2,2-tetracarboxylic acid, butane-1,2,3,4-tetracarboxylic acid, pentane-1,2,4,5-tetracarboxylic acid. Among them, butane-1,2,3,4-tetracarboxylic acid is preferred.

[0030] Examples of alicyclic polycarboxylic acids are 1,2,3,4-cyclobutanetetracarboxylic acid, 2,2,6,6-tetra-(carboxyethyl)cyclohexanone (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid, cyclohexane-1,2,3,4-tetracarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, cyclohexane-2,3,5,6-tetracarboxylic acid, 3-ethylcyclohexane-1,2,4,5-tetracarboxylic acid, 1-methyl-3-ethylcyclohexane-3-(1,2)5,6-tetracarboxylic acid, 1-ethylcyclohexane-1-(1,2)3,4-tetracarboxylic acid, 1-propylcyclohexane-1-(2,3),3,4-tetracarboxylic acid 1,3-dipropylcyclohexane-1-(2,3),3-(2,3)tetracarboxylic acid, dicyclohexyl-3,4,3’,4’-tetracarboxylic acid.

[0031] Examples of aromatic polycarboxylic acids are phthalic acids such as isophthalic acid and terephthalic acid, 2,5-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, bis(4-carboxyphenyl)methane, 2,2-bis(4-carboxyphenyl)hexafluoropropane, 2,2-bis(4-carboxyphenyl)ketone, 4,4'-bis(4-carboxyphenyl)sulfone, 2,2-bis(3-carboxyphenyl)propane, bis(3-carboxyphenyl)methane, 2,2-bis(3-carboxyphenyl)hexafluoropropane, 2,2-bis(3-carboxyphenyl)ketone, bis(3-carboxyphenoxy)benzene, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, and the like.

[0032] Among aromatic carboxylic acids having three or more carboxylic acid groups, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), trimellitic acid (1,3,5-benzenetricarboxylic acid), trimellitic acid (1,3,4-benzenetricarboxylic acid), benzophenone-3,3’,4,4’-tetracarboxylic acid, tetrahydrofuran-2,3,4,5-tetracarboxylic acid, 4,4’-(hexafluoroisopropylidene)diphthalic acid, 4,4’-oxydiphthalic anhydride, 4,4’-(4,4’-isopropylidenediphenoxy)bis(phthalic acid), 3,3’,4,4’-biphenyltetracarboxylic acid, 2,3,3’,4’-biphenyltetracarboxylic acid, 2,2’,3,3’-biphenyltetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, perylene-3,4,9,10-tetracarboxylic acid; propane-2,2-bis(3,4-dicarboxyphenyl) acid, ethane-1,1-bis(2,3-dicarboxyphenyl) acid, ethane-1,1-bis(3,4-dicarboxyphenyl) acid, phenanthrene-1,8,9,10-tetracarboxylic acid, tetrahydrofuran-2,3,4,5-tetracarboxylic acid, 3,3’,4,4’-benzophenonetetracarboxylic acid, 2,2’,3,3’-benzophenonetetracarboxylic acid, 2,3,5,6-pyridinetetracarboxylic acid, 3,3’,4,4’-tetraphenylsilanetetracarboxylic acid, 2,2’-bis-(3,4-bicarboxyphenyl)hexafluoropropanetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)sulfonic acid, 4,4’-(hexafluoroisopropylidene)diphthalic acid, 3,3’,4,4’-diphenylsulfonetetracarboxylic acid, ethylene glycol bistrimellitic acid, hydroquinone diphthalic acid, pyrazine-2,3,5,6-tetracarboxylic acid, thiophene-2,3,4,5-tetracarboxylic acid can be mentioned.

[0033] The polyacids (O) in which particularly good results have been obtained within the framework of the present invention are phthalic acids, in particular isophthalic acid, tricarballylic acid, 1,2,4,5-benzenetetracarboxylic acid and butane-1,2,3,4-tetracarboxylic acid. Tricarballylic acid and isophthalic acid are particularly preferred.

[0034] A mixture comprising at least one polyol (H) and at least one alcohol (AO) The polyol (H) is as detailed above.

[0035] Alcohol (AO) The alcohol (AO) can be a monoalcohol (MO) containing one hydroxy group, a diol (D) containing two hydroxy groups, or a mixture of a monoalcohol (MO) and a diol (D).

[0036] When the alcohol (AO) is a monoalcohol (MO), it can be selected from aliphatic or aromatic monoalcohols.

[0037] The monoalcohol (MO) is characterized in that its boiling point at atmospheric pressure is advantageously at least 90 °C, preferably at least 100 °C, more preferably at least 125 °C, and most preferably at least 150 °C.

[0038] The aliphatic monoalcohol (MO) is advantageously an aliphatic monoalcohol represented by the following formula: R Hm -OH (wherein R Hm is a monovalent aliphatic group having one or more carbon atoms, in particular having three or more carbon atoms).

[0039] It is generally understood that better results are obtained when using long-chain aliphatic monoalcohols, i.e., aliphatic monoalcohols (MO) in which the total number of carbon atoms is advantageously at least 6. The aliphatic monoalcohol (MO) preferably has 6 to 36 carbon atoms, more preferably 6 to 24 carbon atoms.

[0040] Among the aliphatic monoalcohols (MO) that can be advantageously used in the present invention, in particular, hexanol-1 [CH 3 (CH 2 ) 5 -OH], dodecanol [CH 3 (CH 2 ) 11 -OH], hexadecanol or cetyl alcohol [CH 3 (CH 2 ) 15 -OH], octadecanol or stearyl alcohol CH 3 (CH 2 ) 17 -OH], arachidyl alcohol CH 3 (CH 2 ) 18 -OH], docosanol or behenyl alcohol [CH 3 (CH 2 ) 21 -OH], cyclohexanol and menthol can be mentioned.

[0041] When the monoalcohol (MO) is an aromatic monoalcohol, it is preferably selected from the group consisting of phenol, cresol, naphthol, benzyl alcohol, 2-phenylethanol and 3-phenylpropanol.

[0042] The monoalcohol (MO) is preferably selected from the group consisting of dodecanol, benzyl alcohol, menthol and mixtures thereof.

[0043] When the alcohol (AO) is a diol (D), the diol (D) is characterized in that the boiling point at atmospheric pressure is preferably at least 100 °C, more preferably at least 150 °C, still more preferably at least 200 °C, and most preferably at least 230 °C.

[0044] Non-limiting examples of suitable diols (D) include, in particular, ethylene glycol, 2,2-dimethylpropane-1,3-diol, pentane-1,2-diol, pentane-1,5-diol, hexane-1,2-diol, heptane-1,2-diol, diethylene glycol, hexane-1,6-diol, heptane-1,7-diol, 1,4-cyclohexanediol, cis 1,2-cyclohexanediol, trans 1,2-cyclohexanediol, polyether polyol diol Dianol® 220, 1,4-cyclohexanedimethanol, isosorbide, isoidide, dodecane 1,12-diol, and mixtures thereof.

[0045] The diol (D) is preferably selected from the group consisting of diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, isoidide, dodecane 1,12-diol, and mixtures thereof.

[0046] The diol (D) is more preferably selected from the group consisting of diethylene glycol, 1,4-cyclohexanedimethanol, and mixtures thereof.

[0047] The diol (D) that has been shown to give particularly good results is 1,4-cyclohexanedimethanol, and thus this is particularly preferred, and a cis / trans isomer mixture of 1,4-cyclohexanedimethanol (CAS No. 105-08-8) is particularly preferred.

[0048] The alcohol (AO) is preferably selected from the group consisting of diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, isoidide, dodecane 1,12-diol, dodecanol, benzyl alcohol, menthol, and mixtures thereof.

[0049] Branched poly(hydroxy acid) polymer The branched poly(hydroxy acid) polymer used in the downhole tool member of the present invention is (i) At least one hydroxy acid [hydroxy acid (A)] having only one hydroxyl group and only one carboxylic acid group, (ii) Optionally, at least one carboxylic acid [acid (C)] having one or two carboxylic acid groups and not containing a hydroxyl group, and (iii) At least one polyfunctional reactant [reactant (F)] as detailed above is obtained from the polycondensation reaction of a monomer mixture containing

[0050] The expression "branched polymer" is used herein in the meaning provided by IUPAC, i.e., to identify a polymer whose molecules are branched chains. In this context, the branches are introduced into the polymer chains by the presence of at least one polyfunctional reactant (reactant (F)).

[0051] In a first embodiment of the present invention, the branched poly(hydroxy acid) polymer is selected from those polymers comprising repeating units derived from the polycondensation reaction of a monomer mixture containing at least one hydroxy acid (A) and at least one reactant (F) selected from the group consisting of compounds containing at least one epoxy functional group, preferably compounds selected from the group consisting of epoxysilanes and polyepoxides.

[0052] The polymers of the first embodiment are, for example, those described in WO 2010 / 112602 A1 pamphlet and can be prepared according to the methods described therein.

[0053] In a second embodiment of the present invention, the branched poly(hydroxy acid) polymer is selected from those polymers comprising repeating units derived from the polycondensation reaction of a monomer mixture containing at least one hydroxy acid (A) and at least one reactant (F) selected from the mixture containing at least one polyol (H) having at least three hydroxyl groups and at least one polyacid (O) having at least three carboxylic acid groups.

[0054] In this second embodiment, the hydroxy acid (A) is preferably selected from glycolic acid, lactic acid, and mixtures thereof. More preferably, the hydroxy acid (A) is glycolic acid.

[0055] Advantageously, the mixture containing at least one polyol (H) and at least one polyacid (O) is selected from the mixture of pentaerythritol and butanetetracarboxylic acid, or the mixture of trimethylolpropane and tricarballylic acid.

[0056] The polymer of the second embodiment is, for example, as described in WO 2010 / 112602A1 pamphlet and can be prepared according to the method described therein.

[0057] In the third embodiment of the present invention, the branched poly(hydroxy acid) polymer is selected from those polymers obtained from the polycondensation reaction of a monomer mixture containing at least one hydroxy acid (A), optionally at least one acid (C), and at least one reactant (F) selected from a mixture containing at least one polyol (H) having at least three hydroxyl groups and at least one polyacid (O) having at least three carboxylic acid groups. In particular, this branched poly(hydroxy acid) polymer can be selected from polymers in which the amount of the acid (C) is such that the number of its carboxylic acid groups is from 0.0001 to 0.010% relative to the number of hydroxyl groups of the hydroxy acid (A).

[0058] Preferably, the hydroxy acid (A) is selected from glycolic acid, lactic acid, and mixtures thereof. More preferably, the hydroxy acid (A) is glycolic acid.

[0059] The polyol (H) is usually selected from triols (especially trimethylolpropane) and tetraols (especially pentaerythritol). The polyol (H) that has been found to give particularly good results is trimethylolpropane.

[0060] The polyacid (O) that has been found to give particularly good results is tricarballylic acid, 1,2,4,5-benzenetetracarboxylic acid, and butane-1,2,3,4-tetracarboxylic acid, with tricarballylic acid being particularly preferred.

[0061] Generally, the amounts of polyacid (O) and polyol (H) in the branched poly(hydroxy acid) polymer of the third embodiment are substantially the same when expressed as the number of moles per mole of hydroxy acid (A). The molar ratio of polyacid (O):polyol (H) is in the range of 1.5:1 to 0.5:1, preferably in the range of 1.25:1 to 0.75:1, more preferably in the range of 1.10:1 to 0.9:1.

[0062] When the acid (C) is included, its amount is such that the number of its carboxylic acid groups is included in the range of 0.0001 to 0.010% relative to the number of hydroxyl groups of the hydroxy acid (A). Preferably, the amount is such that the number of carboxylic acid groups of the acid (C) is at least 0.0005%, preferably at least 0.001%, and / or at most 0.010%, preferably at most 0.008%, most preferably at most 0.007%, even more preferably at most 0.006% relative to the number of hydroxyl groups of the hydroxy acid (A).

[0063] The acid (C) is preferably a monocarboxylic acid. Stearic acid is particularly preferred.

[0064] The polymer of the third embodiment is, for example, the one described in WO 2016 / 173640 A1 pamphlet and can be prepared according to the method described therein.

[0065] In a fourth embodiment of the present invention, the branched poly(hydroxy acid) polymer is selected from polymers obtained from a polycondensation reaction of a monomer mixture containing glycolic acid and, optionally, at least one hydroxy acid (A) different from glycolic acid, the hydroxy acid (A) being present in an amount of up to 5 mol% based on the total moles of glycolic acid and hydroxy acid (A), and, optionally, at least one acid (C) having one carboxylic acid group, and at least one reactant (F) selected from at least one polyol (H) containing at least three hydroxyl groups and at least one polyacid (O) selected from aromatic acids containing two aromatic carboxylic acid groups. In particular, the amount of the polyol (H) is such that the number of its hydroxyl groups is 0.050 to 1.200% relative to the total number of carboxyl groups of glycolic acid and hydroxy acid (A) (when included), the amount of the polyacid (O) is such that the number of its hydroxyl groups is 0.050 to 0.750% relative to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (when included), and the amount of the acid (C), when included, is such that the number of its carboxylic acid groups is 0.0001 to 0.010% relative to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (when included).

[0066] The polyol (H) is usually selected from triols (especially trimethylolpropane) and tetraols (especially pentaerythritol). Preferably, the polyol (H) is trimethylolpropane.

[0067] Non-limiting examples of suitable polyacids (O) containing two aromatic carboxylic acid groups include phthalic acids such as isophthalic acid and terephthalic acid, 2,5-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, bis(4-carboxyphenyl)methane, 2,2-bis(4-carboxyphenyl)hexafluoropropane, 2,2-bis(4-carboxyphenyl)ketone, 4,4'-bis(4-carboxyphenyl)sulfone, 2,2-bis(3-carboxyphenyl)propane, bis(3-carboxyphenyl)methane, 2,2-bis(3-carboxyphenyl)hexafluoropropane, 2,2-bis(3-carboxyphenyl)ketone, bis(3-carboxyphenoxy)benzene, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid. Phthalic acid is generally preferred. Isophthalic acid has been shown to provide particularly good results.

[0068] Acid (C) is a monocarboxylic acid. Stearic acid is particularly preferred.

[0069] The polymer of the fourth embodiment is, for example, the one described in WO 2018 / 115008 A1 pamphlet and can be prepared according to the method described therein.

[0070] In the fifth embodiment of the present invention, the branched poly(hydroxy acid) polymer is selected from polymers obtained from a polycondensation reaction of a monomer mixture containing glycolic acid, optionally at least one hydroxy acid (A) different from glycolic acid (where the molar amount of hydroxy acid (A) is at most 5 mol% based on the total moles of glycolic acid and hydroxy acid (A)), optionally at least one acid (C) (said acid (C) having one carboxylic acid group), optionally at least one polyacid (O), and at least one reactant (F) selected from a mixture containing at least one polyol (H) and at least one alcohol (AO).

[0071] Preferably, the branched poly(hydroxy acid) polymer is obtained from a polycondensation reaction of a monomer mixture consisting of glycolic acid, optionally at least one hydroxy acid (A) different from glycolic acid (where the molar amount of hydroxy acid (A) is at most 5 mol% based on the total moles of glycolic acid and hydroxy acid (A)), at least one polyol (H); and at least one alcohol (AO), preferably at least one diol (D).

[0072] Most preferably, the branched poly(hydroxy acid) polymer is obtained from a polycondensation reaction of a monomer mixture consisting of glycolic acid, optionally at least one hydroxy acid (A) different from glycolic acid (where the molar amount of hydroxy acid (A) is at most 5 mol% based on the total moles of glycolic acid and hydroxy acid (A)), at least one polyol (H); and at least one diol (D).

[0073] The hydroxy acid (A) is preferably selected from the group consisting of lactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxypentanoic acid, 5-hydroxypentanoic acid, 6-hydroxycaproic acid, and is preferably lactic acid.

[0074] The preferred polyol (H) is, as detailed above, a triol selected from the group consisting of triols, in particular glycerol, trimethylolpropane and trimethylolbutane, and a tetraol, in particular pentaerythritol.

[0075] The polyol (H) which has been found to give particularly good results is trimethylolpropane.

[0076] The polyol (H) is used in an amount such that the number of its hydroxyl groups is advantageously from 0.050 to 1.200% relative to the total number of carboxyl groups of glycolic acid and hydroxyacid (A) (when included). Advantageously, the polyol (H) is included in an amount such that the number of its hydroxyl groups is at least 0.075%, further at least 0.100%, preferably at least 0.120% relative to the total number of carboxyl groups of glycolic acid and hydroxyacid (A) (when included). The polyol (H) is included in an amount such that the number of its hydroxyl groups is at most 1.000%, further at most 0.750%, preferably at most 0.600% relative to the total number of carboxyl groups of glycolic acid and hydroxyacid (A) (when included).

[0077] When the alcohol (AO) is a monoalcohol (MO), it is preferably selected from the group consisting of dodecanol, benzyl alcohol, menthol and mixtures thereof.

[0078] When the alcohol (AO) is a diol (D), the diol (D) is preferably selected from the group consisting of diethylene glycol, 1,4 - cyclohexanedimethanol, isosorbide, isoidide, dodecane - 1,12 - diol and mixtures thereof, more preferably selected from the group consisting of diethylene glycol, 1,4 - cyclohexanedimethanol and mixtures thereof.

[0079] The diol (D) that has been shown to give particularly good results is 1,4-cyclohexanedimethanol, and is thus particularly preferred, and a cis / trans isomer mixture of 1,4-cyclohexanedimethanol (CAS number 105-08-8) is particularly preferred.

[0080] The alcohol (AO) is preferably selected from diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, isoidide, dodecane 1,12-diol, dodecanol, benzyl alcohol, menthol, and mixtures thereof.

[0081] The alcohol (AO) is more preferably the diol (D), which is preferably characterized by having a boiling point of at least 100 °C at atmospheric pressure and / or is preferably used in the amounts defined below.

[0082] The alcohol (AO) is used in an amount such that the number of its hydroxyl groups is advantageously from 0.010 to 1.200% relative to the total number of carboxylic acid groups of glycolic acid and hydroxyacid (A) (if included).

[0083] The alcohol (AO) is used in an amount such that the number of its hydroxyl groups is advantageously at least 0.010%, preferably at least 0.050%, more preferably at least 0.080%, most preferably at least 0.100% relative to the total number of carboxylic acid groups of glycolic acid and hydroxyacid (A) (if included), and / or is advantageously at most 1.200%, further at most 1.000%, preferably at most 0.750%, more preferably at most 0.700%, most preferably at most 0.650%.

[0084] Advantageously, an alcohol (AO) in an amount such that the number of its hydroxyl groups is from 0.010 to 0.650% relative to the total number of carboxylic acid groups of glycolic acid and hydroxyacid (A).

[0085] The polyol (H) and the alcohol (AO) are used in an amount such that the number obtained by subtracting the total number of moles of the carboxylic acid groups of glycolic acid and hydroxy acid (A) (if included) from the total number of moles of all the hydroxyl groups thereof, divided by the total number of moles of the carboxylic acid groups of glycolic acid and hydroxy acid (A) (if included), is preferably from 0 to 1.0%, more preferably from 0.1 to 1.0%, still more preferably from 0.3 to 0.9%.

[0086] The acid (C) is a monocarboxylic acid. Among aliphatic monobasic acids, stearic acid is particularly preferred. When the acid (C) is an aromatic monobasic acid, it is preferably selected from the group consisting of benzoic acid, naphthoic acid, and phenylacetic acid.

[0087] When the acid (C) is included, it is preferably an aromatic monobasic acid.

[0088] When the acid (C) is included, the acid (C) is a monobasic acid, and the number of its carboxylic acid groups is used in an amount such that it is preferably from 0.010 to 2.0% with respect to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (if included). The acid (C) has the number of its carboxylic acid groups such that it is preferably at least 0.010%, more preferably at least 0.030%, still more preferably at least 0.075% with respect to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A), and / or, with respect to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A), it is preferably at most 2.0%, more preferably at most 1.50%, still more preferably at most 1.20%, most preferably at most 1.00%, and even most preferably at most 0.75%.

[0089] The branched poly(hydroxy acid) polymer according to this fifth embodiment may optionally contain repeating units derived from at least one polyacid (O) as defined above. The polyacid (O) can contain two carboxylic acid groups or three or more carboxylic acid groups, particularly three or four carboxylic acid groups.

[0090] Among suitable polyacids (O), phthalic acid, tricarballylic acid, butane-1,2,3,4-tetracarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) can be mentioned. The polyacid (O) is preferably an aromatic dibasic acid, more preferably phthalic acid, and most preferably isophthalic acid.

[0091] When the polyacid (O) is included, the polyacid (C) is used in an amount such that the number of its carboxylic acid groups is 0.025 to 1.200% relative to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (when included). When the polyacid (O) is included, the polyacid (C) is advantageously at least 0.025%, preferably at least 0.050%, more preferably at least 0.100% relative to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (when included), and / or advantageously at most 1.200%, preferably at most 1.000%, more preferably at most 0.900%, most preferably at most 0.750%, particularly most preferably at most 0.650%. When the polyacid (O) is included, a polyacid (O) in an amount such that the number of its carboxyl groups is 0.150 to 0.550% relative to the total number of hydroxyl groups of glycolic acid and hydroxy acid (A) (when included) has been found to be particularly useful.

[0092] The branched poly(hydroxy acid) polymer detailed above can be obtained by a method comprising polycondensing glycolic acid, optionally at least one hydroxy acid (A), at least one polyol (H), at least one alcohol (AO), optionally at least one acid (C) and optionally at least one polyacid (O). In said method, a polycondensation catalyst can optionally be added to the monomer mixture. Such polycondensation catalysts are well known to those skilled in the art and can be selected, for example, from tin(II) chloride, stannous octoate, zinc acetate, zinc lactate, methanesulfonic acid, orthophosphoric acid, and mixtures thereof. Methanesulfonic acid, and mixtures of methanesulfonic acid with other catalysts (those disclosed above or others) are particularly preferred.

[0093] When adding such a catalyst, it is usually added in an amount of about 0.001 to 2 mol%, particularly about 0.002 to 0.1 mol%, based on the total moles of the monomers in the monomer mixture.

[0094] Preferably, the polycondensation step is at least partially carried out at a temperature such that the mixture of monomers and the growing polymer formed are in the molten phase. Generally, after the polycondensation step in the molten state, a prepolymer may be provided that contains unreacted glycolic acid, hydroxy acid (A) (if included), polyol (H), alcohol (AO), monobasic acid (C) (if included), and polyacid (O) (if included), and then the polycondensation is continued at a temperature such that the prepolymer is in the solid state (this step is hereinafter referred to as solid-state polymerization or SSP).

[0095] Therefore, the method of the present invention generally includes a first step of polymerization in the molten state to form a prepolymer and a second step of solid-state polymerization (SSP) to increase the molecular weight of the prepolymer.

[0096] In the first step, the temperature is selected to maintain the monomer mixture and the prepolymer formed during the progress of the reaction in the molten state.

[0097] Generally, the first step of polycondensation in the molten state is achieved by maintaining the reaction mixture at a temperature in the range of 160 to 240 °C with stirring.

[0098] The prepolymer obtained from the first step of polymerization in the molten state and containing residual monomers as described in detail above, if any, is subjected to a solidification and miniaturization process to provide a particulate prepolymer material in the form of loose particles.

[0099] The particulate prepolymer can be processed from the molten state in the form of pearls or pellets by standard techniques of pelletization and / or pastillation, or recovered as solidified fragments and milled to powder form.

[0100] When recovering a prepolymer that may contain residual monomers as detailed above by solidifying it in the form of fragments, a milling process is required. Such a milling process can be carried out by means known to those skilled in the art, for example, by milling with a high-speed grinder or a rotary mill.

[0101] The SSP process can be carried out by subjecting a prepolymer that may contain residual monomers as detailed above in its solid state, under vacuum or in an inert gas atmosphere (e.g., under nitrogen) or both, for 1 hour or more or over several days, to a temperature higher than the glass transition temperature of the prepolymer that may contain the above-mentioned residual monomers, but lower than its melting temperature. Usually, such an SSP process can be carried out at a temperature of 140 - 240 °C, particularly 150 - 230 °C, for example, about 170 - 220 °C, and at a pressure of less than 50 mbar.

[0102] Depending on the nature of the residual monomers in the prepolymer, their proportions and the target final viscosity / molecular weight, the temperature and pressure during the entire polycondensation process, the duration of the SSP process can be from several hours to 1 week, particularly 6 - 200 hours, for example, about 10 - 150 hours.

[0103] The polycondensation reaction in the melt phase is preferably carried out under vacuum in order to evaporate the water of the reaction and avoid hydrolysis of the polymer chains being formed by water. The polycondensation reaction in the melt phase is started at atmospheric pressure, and it is highly particularly preferred to gradually apply a reduced pressure until a pressure on the order of several mbar, particularly less than 50 mbar, preferably less than 20 mbar, is achieved. The SSP process is usually carried out at a pressure of about 0.1 - 50 mbar, preferably about 0.1 - 20 mbar.

[0104] Downhole tool member An object of the present invention is a downhole tool member comprising at least one element comprising the branched poly(hydroxy acid) detailed above.

[0105] The expressions "downhole tool", "downhole tool member", or "element of a downhole tool member" are used to refer to oilfield equipment used during the drilling, completion, or repair of a downhole, for example, tools used to perform borehole plugging and fracturing.

[0106] Non-limiting examples of note of downhole tools and / or downhole tool members and / or elements of downhole tool members include, for example, frac plugs or dissolvable plugs, bridge plugs, cement retainers, perforating guns, ball sealers, frac balls, divert balls, ball seats, mandrels, slips, wedges, rings, sealing plugs, frac sleeves, fracture sleeve pistons (also known as "pistons" or "piston plugs"), and packers.

[0107] One or more components of a downhole tool, generally referred to as "downhole tool members", may be made from branched poly(hydroxy acids), as detailed above. Alternatively, the entire downhole tool structure may be made from branched poly(hydroxy acids).

[0108] The downhole tool member of the present invention usually includes at least one element made of branched poly(hydroxy acid) alone, but it is also possible to blend the polymer with other polymers. Examples of other polymers 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; modified polyvinyl alcohol; soft polyolefin resins such as ethylene / glycidyl methacrylate copolymer, ethylene / propylene terpolymer, and ethylene / butylene homopolymer; styrene copolymer resins; polyphenylene sulfide resins; polyether ether ketone 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 of these other polymers may be contained in the composition.

[0109] The branched poly(hydroxy acid) may also be blended with a filler.

[0110] Advantageously, the downhole tool member of the present invention may include at least one element containing a composition comprising a branched poly(hydroxy acid) and a filler.

[0111] The nature of the filler is not particularly limited, and any fibrous or whisker-like filler may be used. Fillers other than fibrous or whisker-like fillers, such as sheet-like (lamellar), powdery, or granular fillers, can also be used. Furthermore, fillers of various compositions, such as carbon-based, metal-based, or silicon-based fillers, can be used.

[0112] Specific examples of fibrous or whisker-like fillers that can be used include glass fibers (long fiber type or short fiber type chopped strands, soft fibers, etc.), carbon fibers of the pan type or pitch type, graphite fibers, metal fibers, metal fibers such as aluminum fibers, brass fibers or stainless steel fibers, fibrous fillers such as alumina fibers, zirconia fibers, ceramic fibers, asbestos fibers, gypsum fibers, silicon carbide fibers, silica fibers, titanium oxide fibers and rock wool, and whisker-like fillers such as potassium titanate whiskers, barium titanate whiskers, aluminum borate whiskers, silicon nitride whiskers, zinc oxide whiskers, calcium carbonate whiskers, wollastonite whiskers, aluminum borate whiskers, etc.

[0113] Examples of fillers other than fibrous or whisker-like fillers that can be used include silicates such as silicon oxide (silica, silica sand, etc.), talc, kaolin, aluminosilicates and magnesium silicate; metal oxides such as magnesium oxide, alumina, zinc oxide, zirconium oxide, titanium oxide, iron oxide, antimony oxide, tungstic acid and vanadium; sulfates such as calcium sulfate, barium sulfate and aluminum sulfate; hydroxides such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide; clay minerals such as montmorillonite, kaolinite, beidellite, saponite, nontronite, hectorite, sauconite, vermiculite, halloysite, kanemite, octosilicate, magadiite, kenyaite, zirconium phosphate and titanium phosphate; layered phosphates such as hydroxyapatite; and other sheet-like, granular or powdery inorganic fillers such as glass beads, glass balloons, ceramic beads, glass flakes, glass powder, boron nitride, silicon carbide, calcium phosphate, carbon black and graphite.

[0114] Among these fillers, silicon oxide, silicate, carbonate, clay mineral, inorganic fibrous filler, or inorganic whisker-like filler is preferable, and silica sand, silica, talc, kaolin, mica, calcium carbonate, magnesium carbonate, barium carbonate, barium sulfate, montmorillonite, glass fiber, carbon fiber, or graphite fiber is particularly preferable.

[0115] Two or more kinds of fillers may be used in combination.

[0116] The filler is usually contained in an amount of 10 to 70% by weight, preferably 10 to 60% by weight, more preferably 15 to 40% by weight, based on the total weight of the branched poly(hydroxy acid) and the filler.

[0117] The downhole tool member of the present invention or the downhole tool including the member can be manufactured using known melt processing techniques such as injection molding, extrusion molding, or any other molding or thermoforming technique.

[0118] The branched poly(hydroxy acid) polymer has particularly advantageous degradation behavior, which makes it particularly useful for manufacturing downhole tool members that rapidly degrade underground even at low temperatures.

[0119] If the disclosure of any patent, patent application, and publication incorporated herein by reference conflicts with the description of this application to the extent that it may obscure the terms, the description of this application shall prevail.

[0120] If the disclosure of any patent, patent application, and publication incorporated herein by reference conflicts with the description of this application to the extent that it may obscure the terms, the description of this application shall prevail.

[0121] Here, the present invention will be described in more detail in relation to the following examples, but the purpose is merely illustrative and is not intended to limit the scope of the present invention.

Examples

[0122] Example 1 Into a 7.5 L stainless steel double jacket reactor equipped with a heater, a condenser, temperature and pressure sensors, and a mechanical stirrer, 4500 g (41.420 mol, based on 1.0000 mol) of an aqueous glycolic acid solution containing 70 wt% glycolic acid, 10.004 g (0.075 mol, 0.0018 mol per mol of glycolic acid) of trimethylolpropane, 3.584 g (0.025 mol, 0.0006 mol per mol of glycolic acid) of cyclohexanedimethanol, and 0.536 g (0.006 mol, 0.00014 mol per mol of glycolic acid) of methanesulfonic acid were charged.

[0123] The reactor was then closed and purged three times using vacuum and nitrogen alternately. The reaction solution was rapidly heated to 50 °C under mechanical stirring. The pressure was reduced to 600 mbar and heating was continued from 50 °C to 100 °C over 30 minutes. Steam distillation was started. The temperature was slowly raised to 130 °C over 60 minutes and steam distillation was continued gently. When most of the water had been removed, the temperature was raised more rapidly to 220 °C over 30 minutes.

[0124] When 220 °C was reached, the pressure was gradually reduced to 30 mbar over 30 minutes. Thereafter, the temperature was finally raised to 230 °C and maintained stable during the remaining synthesis. To increase the glycolic acid conversion rate, vacuum was applied for an additional 270 minutes.

[0125] The reaction mixture was then returned to atmospheric pressure using nitrogen. The polymer was taken out of the kettle through the bottom valve and collected on an SS tray on dry ice. The hard solidified polymer mass was taken out and weighed. Crude yield: 2.10 kg (approx. 88%).

[0126] The polymer was ground into small particles with a diameter of less than 2 mm using a high-speed grinder, classified through a 2 mm sieve, and further dried overnight at 90 °C in a vacuum oven.

[0127] To obtain a uniform particle size distribution and homogeneity, the powder was pelletized using a 19 mm diameter BRABENDER extruder equipped with a 25 L / D single screw having a compression ratio of 3:1. The die was a 1-strand die (2 mm holes), and the strands were "die face cut" under dry conditions. The screw speed used was 60 rpm, and the temperature profile was kept low (a flat temperature profile of 195 °C, 4 heating zones in the extruder; 1 heating zone in the die) to cope with the low viscosity of the melt-polymerized prepolymer. The typical output was about 2.1 kg / h. The resulting pellet size was approximately 2 mm in diameter and about 3 mm in length.

[0128] The pellets thus obtained were introduced into a double-wall rotary tumbler unit, uniformly mixed, and further polymerized in the solid phase by heating and evacuating to vacuum. The tumbler used had a total volume of 15 L and an effective volume of 6 L. Approximately 2 kg of polymer was used per batch.

[0129] After closing the tumbler, rotation was started at 8 rpm. The vacuum pump was started to bring the inside of the tumbler to a vacuum of 5 - 10 mbar. At the same time, the tumbler was flushed with nitrogen (flow rate set at 50 L / h). The oil circulating inside the double wall was heated to raise the temperature from room temperature to 214 °C over 16 hours.

[0130] The tumbler was equipped with a sampling valve, and samples with decreasing amounts of polymer were carefully taken out and analyzed using a parallel plate rheometer for the melt viscosity at various points in solid state polymerization (SSP). After the desired melt viscosity was achieved, heating was stopped, SSP was terminated, and the product was cooled.

[0131] After 66 hours of SSP at 214 °C, 1.8 g of poly(glycolic acid) polymer with a melt viscosity of 647 Pa·s at a shear rate of 10 s -1 was obtained.

[0132] The residual methanesulfonic acid in the final polymer after SSP was titrated according to the described method and found to be 0.005 mol% with respect to glycolic acid units.

[0133] Example 2 Using the same apparatus and protocol as in Example 1, 4500 g (41.420 mol, based on 1.0000 mol) of a 70 wt% aqueous glycolic acid solution, 8.892 g (0.066 mol, 0.0016 mol per mol of glycolic acid) of trimethylolpropane, 6.193 g (0.037 mol, 0.0009 mol per mol of glycolic acid) of isophthalic acid, and 0.819 g (0.009 mol, 0.00021 mol per mol of glycolic acid) of methanesulfonic acid were charged and converted to 2.15 kg of a poly(glycolic acid) polymer (crude yield 90%).

[0134] The powder was pelletized and the exact same protocol as in Example 1 for increasing the melt viscosity by SSP was applied.

[0135] After 63 hours of SSP at 214 °C, 1.8 g of a poly(glycolic acid) polymer having a melt viscosity of 582 Pa·s at a shear rate of 10 s -1 was obtained.

[0136] The residual methanesulfonic acid in the final polymer after SSP was titrated according to the described method and found to be 0.005 mol% with respect to glycolic acid units.

[0137] Linear weight loss test By melt processing the polymers of Examples 1 and 2, parts having a bottom surface of 5 cm 2 and a height of 12.7 mm were fabricated. These parts were crystallized in an oven at 120 °C for 1 hour. Then, the parts were placed in an 800 mL bottle filled with deionized water and placed in an oven at 80 °C. The jar was withdrawn at various times and the parts were dried overnight. The next day, the parts were cut and the thickness of the non-decomposed sections was measured.

[0138] Figure 1 is a graph showing the change in thickness over time of the branched poly(hydroxy acid) polymers of Examples 1 and 2.

[0139] The data showed that the degradation rate increased with time, resulting in a non-linear curve of partial weight loss.

[0140] During the first 24 hours of the experiment, the average weight loss rate was about 75 microns / hour. During the last 72 hours of the experiment, the weight loss rate increased to about 130 microns / hour.

[0141] The increase in the weight loss rate has the advantage that the components in the well degrade faster. Therefore, the time required to remove the remaining parts of the tool or tool member in the well is shortened. This is particularly important in wells in North America where the temperature is generally relatively low.

Claims

A downhole tool member comprising at least one element comprising a branched poly(hydroxy acid) polymer obtained from the polycondensation reaction of a monomer mixture, wherein the monomer mixture (i) comprises glycolic acid and, optionally, at least one hydroxy acid (A) different from said glycolic acid having only one hydroxyl group and only one carboxylic acid group, wherein said hydroxy acid (A) is in an amount of 5% or less relative to the total moles of said glycolic acid and said hydroxy acid (A), (ii) optionally comprises at least one carboxylic acid [acid (C)] having one or two carboxylic acid groups and no hydroxyl group, and (iii) a. A mixture comprising at least one polyol [polyol (H)] having at least three hydroxyl groups and no carboxylic acid group, and at least one polyacid [polyacid (O)] selected from aromatic acids having two aromatic carboxylic acid groups and no hydroxyl group, wherein the amount of said polyol (H) is such that the number of its hydroxyl groups is from 0.050 to 1.200% relative to the total number of carboxyl groups of said glycolic acid and said hydroxy acid (A) (if included), and the amount of said polyacid (O) is such that the number of its carboxylic acid groups is from 0.050 to 0.750% relative to the total number of hydroxyl groups of said glycolic acid and said hydroxy acid (A) (if included), and the amount of acid (C) is such that the number of its carboxylic acid groups is from 0.0001 to 0.010% relative to the total number of hydroxyl groups of said glycolic acid and said hydroxy acid (A) (if included); and b. A mixture comprising at least one polyol [polyol (H)] having at least three hydroxyl groups and no carboxylic acid group, and at least one alcohol [alcohol (AO)] having at least one or two hydroxyl groups and no carboxylic acid group at least one polyfunctional reactant [reactant (F)] different from hydroxy acid (A) and acid (C), selected from the group consisting of comprising a downhole tool member. **Claim 2**: The reactant (F) is selected from a mixture comprising at least one polyol (H) and at least one alcohol (AO), the amount of the polyol (H) being such that the number of its hydroxyl groups is from 0.050 to 1.200% relative to the total number of carboxyl groups of glycolic acid and the hydroxy acid (A) (if included), the amount of the alcohol (AO) being such that the number of its hydroxyl groups is from 0.010 to 1.200% relative to the total number of carboxylic acid groups of glycolic acid and the hydroxy acid (A), and the amount of the monobasic acid (C) (if included) being such that the number of its carboxylic acid groups is from 0.010 to 2.0% relative to the total number of hydroxyl groups of glycolic acid and the hydroxy acid (A) (if included). The downhole tool member according to claim 1. **Claim 3** The hydroxy acid (A) is selected from the group consisting of lactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxypentanoic acid, 5-hydroxypentanoic acid and 6-hydroxycaproic acid, preferably the hydroxy acid (A) is lactic acid, and / or the hydroxy acid (A) is included in an amount of at most 4 mol%, more preferably at most 3 mol%, based on the total moles of glycolic acid and the hydroxy acid (A). The downhole tool member according to claim 2. **Claim 4** The polyol (H) is selected from the group consisting of triols, in particular triols selected from glycerol, trimethylolpropane and trimethylolbutane, and tetraols, in particular pentaerythritol, and / or the polyol (H) is used in an amount such that the number of its hydroxyl groups is at least 0.050%, preferably at least 0.075%, more preferably at least 0.100%, most preferably at least 0.120%, and / or at most 1.200%, preferably at most 1.000%, more preferably at most 0.750%, relative to the total number of carboxylic acid groups of glycolic acid and the hydroxy acid (A) (if included). The downhole tool member according to claim 2 or 3. **Claim 5** The alcohol (AO) is a diol (D), preferably a diol (D) characterized in that the boiling point at atmospheric pressure is at least 100°C, preferably at least 150°C, more preferably at least 200°C, and most preferably at least 230°C, and / or the number of its hydroxyl groups is at least 0.010%, preferably at least 0.050%, more preferably at least 0.080%, most preferably at least 0.100%, and / or at most 1.200%, preferably at most 0.750%, more preferably at most 0.650% with respect to the total number of carboxylic acid groups of glycolic acid and the hydroxy acid (A) (when included), and is preferably used in such an amount that the downhole tool member according to any one of claims 2 to 4 is obtained.

6. The alcohol (AO) is a diol (D) selected from the group consisting of diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, isoidide, dodecane 1,12-diol, and mixtures thereof, and the downhole tool member according to any one of claims 2 to 5 is obtained.

7. The acid (C) is of the formula: R Ｈｍ -COOH (wherein R Ｈｍ is a monovalent aliphatic group having one or more carbon atoms, particularly one or more carbon atoms), or an aromatic monobasic acid selected from the group consisting of benzoic acid, naphthoic acid and phenylacetic acid, and / or the polyacid (O) is an aromatic dibasic acid, more preferably phthalic acid, most preferably isophthalic acid, the downhole tool member according to any one of claims 2 to 6.

8. The reactant (F) is selected from a mixture containing at least one polyol (H) and at least one polyacid (O), and the polyol (H) is trimethylolpropane or pentaerythritol, and the downhole tool member according to claim 1 is obtained.

9. The reactant (F) is selected from a mixture containing at least one polyol (H) and at least one polyacid (O), and the polyacid (O) is isophthalic acid or terephthalic acid, and the downhole tool member according to claim 1 is obtained.

10. A downhole tool comprising the downhole tool member according to any one of claims 1 to 9.

11. Selected from the group consisting of a frac plug, a dissolvable plug, a bridge plug, a cement retainer, a perforating gun, a ball seal, a frac ball, a diverter ball, a ball sheet, a mandrel, a slip, a wedge, a ring, a sealing plug, a flux sleeve, a fracture sleeve piston, and a packer, and the downhole tool member or the downhole tool according to any one of claims 1 to 10 is obtained.

12. A method for manufacturing a downhole tool member or a downhole tool according to any one of claims 1 to 11, the method comprising melt processing and injection molding or extrusion molding of a composition comprising the branched poly(hydroxy acid) polymer according to claim 1.

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