DOWNHOLE TOOL MEMBER COMPRISING A BRANCHED POLY(HYDROXYACID)

Abstract

The invention relates to downhole tools comprising members comprising branched poly(hydroxyacid) polymers provided with improved degradation rate when in contact with water.

Claims

1. A downhole tool member comprising at least one element comprising: a branched poly(hydroxyacid) polymer obtained from polycondensation reaction of a monomer mixture comprising: (i) at least one hydroxyacid having only one hydroxyl group and only one carboxylic acid group (hydroxyacid (A)); (ii) optionally at least one carboxylic acid having one or two carboxylic acid groups and being free from hydroxyl group (acid (C)), and (iii) at least one polyfunctional reactant different from hydroxyacid (A) and acid (C), (reactant (F)), selected from the group consisting of: a. compounds containing at least one epoxy functional group; and b. mixtures comprising at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group (polyol (H)) and at least one polyacid comprising at least two carboxylic acid groups and being free from hydroxyl groups (polyacid (O)); and c. mixtures comprising at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group (polyol (H)) and at least one alcohol comprising one or two hydroxyl groups and being free from carboxylic acid group (alcohol (AO)).

2. The downhole tool member according to claim 1 wherein the branched poly(hydroxyacid) polymer is obtained from the polycondensation reaction of a monomer mixture comprising at least one hydroxyacid (A) which is glycolic acid and the reactant (F) which is a mixture comprising at least one polyol (H) comprising at least three hydroxyl groups and at least one polyacid (O) comprising at least three carboxylic acid groups.

3. The downhole tool member according to claim 2 wherein the reactant (F) is selected from a mixture of pentaerythritol and butanetetracarboxylic acid or a mixture of trimethylolpropane and tricarballylic acid.

4. The downhole tool member according to claim 1 wherein the branched poly(hydroxyacid) polymer is obtained from the polycondensation reaction of a monomer mixture comprising at least one hydroxyacid (A) which is glycolic acid; optionally at least one acid (C); and at least one reactant (F) selected from mixtures comprising at least one polyol (H) comprising at least three hydroxyl groups, at least one polyacid (O) comprising at least three carboxylic acid groups, and wherein amount of acid (C), when present, is such that number of carboxylic acid groups thereof is comprised between 0.0001 to 0.010% with respect to the number of hydroxyl groups of hydroxyacid (A).

5. The downhole tool member according to claim 1 wherein the branched poly(hydroxyacid) polymer is obtained from the polycondensation reaction of a monomer mixture comprising glycolic acid; optionally, at least one hydroxy acid (A) different from glycolic acid, in an amount of at most 5% moles, with respect to sum of moles of glycolic acid and hydroxy acid (A); optionally at least one carboxylic acid (C) having one carboxylic acid group; and at least one reactant (F) selected from mixtures comprising at least one polyol (H) comprising at least three hydroxyl groups and at least one polyacid (O) selected from aromatic acids comprising two aromatic carboxylic acid groups and wherein: the amount of polyol (H) is such that number of hydroxyl groups thereof is comprised between 0.050 to 1.200% with respect to overall number of carboxyl groups of glycolic acid and the hydroxyacid (A), if present; the amount of polyacid (O) is such that the number of carboxylic acid groups thereof is comprised between 0.050 to 0.750% with respect to overall number of hydroxyl groups of glycolic acid and of the hydroxy acid (A), if present; and the amount of acid (C), when present, is such that the number of carboxylic acid groups thereof is comprised between 0.0001 to 0.010% with respect to the overall number of hydroxyl groups of glycolic acid and of the hydroxy acid (A), if present.

6. The downhole tool member according to claim 1 wherein the branched poly(hydroxyacid) polymer is obtained from the polycondensation reaction of glycolic acid; optionally, at least one hydroxyacid (A) different from glycolic acid, wherein molar amount of hydroxyacid (A) is of at most 5% moles with respect to sum of moles of glycolic acid and hydroxyacid (A); optionally at least one carboxylic acid (C); optionally at least one polyacid (O); and at least one reactant (F) selected from mixtures comprising at least one polyol (H) and at least one alcohol (AO) wherein the amount of polyacid (O) is such that number of carboxylic acid groups thereof is comprised between 0.025 and 1.200% with respect to overall number of hydroxyl groups of glycolic acid and of the hydroxyacid (A), if present.

7. The downhole tool member according to claim 6 wherein amount of polyol (H) is such that the number of hydroxyl groups thereof is comprised between 0.050 and 1.200% with respect to the overall number of carboxyl groups of glycolic acid and of the hydroxyacid (A), if present; the amount of alcohol (AO) is such that the number of hydroxyl groups thereof is comprised between 0.010 and 1.200% with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present; and the amount of monoacid (C), when present, is such that the number of carboxylic acid groups thereof is comprised between 0.010 and 2.0% with respect to the overall number of hydroxyl groups of glycolic acid and of the hydroxyacid (A), if present.

8. The downhole tool member according to claim 6 wherein the hydroxyacid (A) is selected from the group consisting of lactic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid and 6-hydroxycaproic acid, and/or wherein the hydroxyacid (A) is present in an amount of at most 4% moles with respect to the sum of moles of glycolic acid and of hydroxyacid (A).

9. The downhole tool member according to claim 6, wherein the polyol (H) is selected from the group consisting of: triols selected from the group consisting of glycerol, trimethylolpropane and trimethylolbutane, and tetraols; and/or wherein the polyol (H) is used in an amount such that the number of hydroxyl groups thereof is of at least 0.050%, with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present.

10. The downhole tool member according to claim 6, wherein alcohol (AO) is a diol (D), characterized by a boiling point at atmospheric pressure, of at least 100° C., and/or a diol (D) used in an amount such that the number of hydroxyl groups thereof is of at least 0.010% and/or of at most 1.200% with respect to the overall number of carboxylic groups of glycolic acid and of the hydroxyacid (A), if present.

11. The downhole tool member according to claim 6, wherein the alcohol (AO) is a diol (D) which is selected from the group consisting of diethyleneglycol, 1,4-cyclohexane dimethanol, isosorbide, isoidide, dodecane 1,12-diol and mixtures thereof.

12. The downhole tool member according to claim 6, wherein acid (C) is an aliphatic monoacid of formula: R.sub.Hm—COOH wherein R.sub.Hm is a monovalent aliphatic group having one or more than one carbon atom, or an aromatic monoacid selected from the group consisting of benzoic acid, naphthoic acid and phenylacetic acid and/or wherein polyacid (O) is an aromatic diacid.

13. A downhole tool comprising a downhole tool member of claim 1.

14. A downhole tool member of claim 1 which is selected from the group consisting of ball sealers, frac balls, diverting balls, ball seats, mandrels, slips, wedges, and rings sealing plugs.

15. A method for manufacture of a downhole tool member or of a downhole tool, said method comprising melt processing and injection molding or extruding a composition comprising a branched poly(hydroxyacid) polymer obtained from a polycondensation reaction of a monomer mixture comprising: (i) at least one hydroxyacid having only one hydroxyl group and only one carboxylic acid group (hydroxyacid (A)); (ii) optionally at least one carboxylic acid having one or two carboxylic acid groups and being free from hydroxyl group (acid (C)), and (iii) at least one polyfunctional reactant different from hydroxyacid (A) and acid (C), reactant (F), selected from the group consisting of: a. compounds containing at least one epoxy functional group; and b. mixtures comprising at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group (polyol (H)) and at least one polyacid comprising at least two carboxylic acid groups and being free from hydroxyl groups (polyacid (0)); and c. mixtures comprising at least one polyol comprising at least three hydroxyl groups and being free from carboxylic acid group (polyol (H)) and at least one alcohol comprising one or two hydroxyl groups and being free from carboxylic acid group (alcohol (AO)); to form the downhole tool member or the downhole tool.

16. A downhole tool of claim 13 which is selected from the group consisting of frac plugs, disintegratable plugs, bridge plugs, cement retainers, perforation guns, sealing plugs, frac sleeves, fracture sleeve pistons and packers.

17. The downhole tool member according to claim 1 wherein, the compound containing at least one epoxy functional group is selected from the group consisting of epoxysilanes and polyepoxides.

Description

EXAMPLES

Example 1

[0147] A 7.5 L stainless steel double jacketed reactor, equipped with heater, condenser, temperature and pressure sensors and mechanical stirrer was charged with 4500 g of a 70 wt % of an aqueous glycolic acid solution (41.420 mole, taken as 1.0000 mol basis), 10.004 g of trimethylolpropane (0.075 mole, 0.0018 mol per mol of glycolic acid), 3.584 g of cyclohexanedimethanol (0.025 mole, 0.0006 mol per mol of glycolic acid) and 0.536 g of methanesulfonic acid (0.006 mole, 0.00014 mol per mol of glycolic acid).

[0148] The reactor was then closed and purged three times using alternatively vacuum and nitrogen. The reaction solution was heated rapidly to 50° C. under mechanical stirring. Pressure was reduced to 600 mbar and heating was pursued from 50° C. up to 100° C. over 30 min. The water distillation was started. The temperature was slowly raised to 130° C. over 60 min to gently pursue the water distillation. When most of the water was removed, the temperature was increased faster to 220° C. over 30 min.

[0149] Once 220° C. was reached, the pressure was progressively decreased down to 30 mbar over 30 min. Temperature was then finally raised up to 230° C. and kept steady for the rest of the synthesis. The vacuum was applied for 270 min more to increase the glycolic acid conversion.

[0150] The reaction mixture was then brought back to atmospheric pressure using nitrogen. The polymer was drawn from the kettle through the bottom valve and recovered in SS trays over dry ice. The hard solidified polymer mass was taken out and weighed. Crude yield: 2.10 kg (˜88%).

[0151] The polymer was grinded into small particles with less than 2 mm diameter using a high speed grinder, classified through a 2 mm sieve and further dried in a vacuum oven at 90° C. overnight.

[0152] In order to obtain an homogeneous particle size distribution and consistency, the powder was pelletized on a 19 mm diameter BRABENDER extruder, equipped with a 25 LID monoscrew having a compression ratio of 3:1. The die was a one strand die (2 mm hole) and the strand was “die faced cut” in dry conditions. Screw speed used was 60 rpm and the temperature profile was kept low (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 pre-polymer melt polymerized. Typical output was around 2.1 kg/h. Pellet size obtained was approximately 2 mm diameter and approximately 3 mm length.

[0153] The pellets so-obtained were introduced in a double wall rotary tumbler unit for uniform mixing and further polymerization in the solid state by applying heat and pulling vacuum. The tumbler used had a 15 L total volume/6 L useful volume. About 2 kg of polymer was used per batch.

[0154] After closing the tumbler, rotation was started at 8 rpm. The vacuum pump was started to reach 5-10 mbar vacuum in the tumbler. Simultaneously the tumbler was flushed with nitrogen (flow rate set at 50 L/h). Oil circulating in the double wall was heated in order to ramp up the temperature from room temperature to 214° C. in 16 h.

[0155] The tumbler was equipped with a sampling valve so that a specimen of reduced quantity of the polymer could be carefully taken out to analyze the melt viscosity using a parallel plate rheometer, at different times of solid state polymerization (SSP). After achieving the desired melt viscosity, the heating was stopped, the SSP was discontinued and the product was cooled down.

[0156] After 66 hours of SSP at 214° C., 1.8 kg of a poly(glycolic acid) polymer having a melt viscosity of 647 Pa×sec at a shear rate of 10 sec.sup.−1 was obtained.

[0157] The residual methanesulfonic acid in the final polymer after SSP was titrated according to the described method and found to be 0.005 mol % in regard to glycolic acid units.

Example 2

[0158] Using the same equipment and protocol as for Example 1, a load of 4500 g of a 70 wt % of an aqueous glycolic acid solution (41.420 mole, taken as 1.0000 mol basis), 8.892 g of trimethylolpropane (0.066 mole, 0.0016 mol per mol of glycolic acid), 6.193 g of isophthalic acid (0.037 mole, 0.0009 mol per mol of glycolic acid) and 0.819 g of methanesulfonic acid (0.009 mole, 0.00021 mol per mol of glycolic acid), was converted into 2.15 kg of poly(glycolic acid) polymer (crude yield 90%).

[0159] The exact same protocol to pelletize the powder and increase melt viscosity by SSP was applied as in Example 1.

[0160] After 63 hours of SSP at 214° C., 1.8 kg of a poly(glycolic acid) polymer having a melt viscosity of 582 Pa×sec at a shear rate of 10 sec.sup.−1 was obtained.

[0161] The residual methanesulfonic acid in the final polymer after SSP was titrated according to the described method and found to be 0.005 mol % in regard to glycolic acid units.

[0162] Linear Thickness Reduction Testing

[0163] Parts having a 5 cm.sup.2 base and 12.7 mm height were prepared by melt processing polymers of example 1 and 2. The parts were crystallized in an oven for 1 hour at 120° C. Then the parts were placed into 800 mL bottles with deionised water and placed in an oven at 80° C. Jars were pulled at various times and the parts were dried overnight. The following day, the parts were cut and the non-degraded section thickness was measured.

[0164] FIG. 1 is a graph showing changes in thickness with time for the branched poly(hydroxyacid) polymers of Example 1 and 2.

[0165] The data shows that as time increases, degradation rate also increases, giving rise to a nonlinear curve of part thickness reduction.

[0166] The average thickness reduction rate was around 75 micron/hr for the first 24 hours of the run. The thickness reduction rate increased to around 130 micron/hr for the last 72 hours of the run.

[0167] An increase of thickness reduction rate has the advantage of faster part degradation in the well. Thus the time required for eliminating the residual parts of the tool or tool member in the well are reduced. This is particularly important in North American wells that are generally at a relatively low temperature.