Downhole cable

Abstract

The present invention pertains to a cable comprising: —at least one conductor coated by an insulation coating layer, —a first protective layer surrounding said insulation coating layer, said first protective layer at least comprising, but preferably being made of a tetrafluoroethylene (TFE) copolymer comprising from 0.8% to 2.5% by weight of recurring units derived from at least one perfluorinated alkyl vinyl ether having formula (I) here below: CF.sub.2═CF—O—R.sub.f, wherein R.sub.f is a linear or branched C.sub.3-C.sub.5 perfluorinated alkyl group or a linear or branched C.sub.3-C.sub.12 perfluorinated alkyl group comprising one or more ether oxygen atoms, said TFE copolymer having a melt flow index comprised between 1.0 and 6.0 g/10 min, as measured according to ASTM D1238 at 372° C. under a load of 5 Kg [polymer (F)]; —optionally, a second protective layer surrounding said first protective layer, and —an armor shell surrounding said first or second protective layer. The invention also pertains to use of the cable in downhole wells.

Claims

1. A cable comprising: at least one conductor coated by an insulation coating layer; a first protective layer surrounding said insulation coating layer, said first protective layer being made of polymer (F), wherein polymer (F) is a tetrafluoroethylene (TFE) copolymer consisting essentially of: from 1.3% to 1.8% by weight of recurring units derived from at least one per-fluorinated alkyl vinyl ether having formula (I):
CF.sub.2═CF—O—R.sub.f  (I),  wherein R.sub.f is a linear or branched C3-C5 perfluorinated alkyl group or a linear or branched C3-C12 perfluorinated alkyl group comprising one or more ether oxygen atoms, and, from 98.1% to 98.7% by weight of recurring units derived from TFE, said polymer (F) having a melt flow index comprised between 1.0 and 6.0 g/10 min, as measured according to ASTM D1238 at 372° C. under a load of 5 Kg and a melting point comprised between 312° C. and 318° C.; optionally, a second protective layer surrounding said first protective layer, and an armor shell surrounding said first or second protective layer; wherein the first protective layer is free from high molecular weight polytetrafluoroethylene (PTFE) or low molecular weight PTFE.

2. The cable according to claim 1, wherein polymer (F) has a melt flow index comprised between 1.5 and 5.5 g/10 min, as measured according to ASTM D1238 at 372° C. under a load of 5 Kg.

3. The cable according to claim 2, wherein polymer (F) has a melt flow index comprised between 2.0 and 5.0 g/10 min, as measured according to ASTM D1238 at 372° C. under a load of 5 Kg.

4. The cable according to claim 2, wherein the perfluorinated alkyl vinyl ether complies with formula (II):
CF.sub.2═CF—O—R′.sub.f  (II) wherein R′.sub.f is a linear or branched C3-C5 perfluorinated alkyl group.

5. The cable according to claim 4, wherein the insulated conductor is selected from copper, copper-nickel alloys, aluminum, alloys, fiber electric hybrid materials, fiber optical materials, stranded or woven conductors.

6. The cable according to claim 1, wherein the perfluorinated alkyl vinyl ether complies with formula (II):
CF.sub.2═CF—O—R′.sub.f  (II) wherein R′.sub.f is a linear or branched C3-C5 perfluorinated alkyl group.

7. The cable according to claim 1, wherein the perfluorinated alkyl vinyl ether is perfluoropropyl vinyl ether (PPVE).

8. The cable according to claim 1, wherein polymer (F) has a heat of fusion of greater than 1 J/g, as measured according to ASTM D3418 using Differential Scanning Calorimetry at a heating rate of 10° C/min.

9. The cable according to claim 1, wherein the insulated conductor is selected from copper, copper-nickel alloys, aluminum, alloys, fiber electric hybrid materials, fiber optical materials, stranded or woven conductors.

10. A downhole well comprising the cable according to claim 1.

11. A method for communicating a signal between the bottom of a downhole well and the top of the downhole well, the method comprising communicating a signal with a cable according to claim 1.

12. A method for providing electrical power to the bottom of a downhole well, the method comprising providing electrical power with a cable according to claim 1.

13. A cable comprising: at least one conductor coated by an insulation coating layer; a first protective layer surrounding said insulation coating layer, said first protective layer being made of polymer (F), wherein polymer (F) is a tetrafluoroethylene (TFE) copolymer consisting essentially of: from 1.3% to 1.8% by weight of recurring units derived from at least one per-fluorinated alkyl vinyl ether having formula (I):
CF.sub.2═CF—O—R.sub.f  (I),  wherein R.sub.f is a linear or branched C3-C5 perfluorinated alkyl group or a linear or branched C3-C12 perfluorinated alkyl group comprising one or more ether oxygen atoms, and, from 98.1% to 98.7% by weight of recurring units derived from TFE, said polymer (F) having a melt flow index comprised between 1.0 and 6.0 g/10 min, as measured according to ASTM D1238 at 372° C. under a load of 5 Kg and a melting point comprised between 312° C. and 318° C.;  a second protective layer surrounding said first protective layer, wherein the second protective layer comprises a thermoset or thermopolymer material; and  an armor shell surrounding said second protective layer; wherein the first protective layer is free from high molecular weight polytetrafluoroethylene (PTFE) or low molecular weight PTFE.

14. The cable according to claim 13, wherein the second protective layer is a semi-crystalline fluoropolymer such as ethylene-chlorotrifluoroethylene and ethylene-tetrafluoroethylene.

Description

EXAMPLE 1

TFE/PPVE 99.1/0.9 (Weight Ratio)

(1) In an AISI 316 steel vertical 22 litres autoclave, equipped with stirrer working at 400 rpm, after the vacuum has been made, were introduced in sequence: 13.9 litres of demineralised water; 18.0 g of perfluoropropylvinylether (PPVE); 138.0 g of a of a microemulsion prepared according to Example 1 of U.S. Pat. No. 4,864,006 (AUSIMONT S.P.A.) 5 Sep. 1989 having a pH of about 7.5. The autoclave was then heated up to reaction temperature of 60° C. and, when this temperature was reached, 0.72 bar of ethane were introduced. By a compressor a gaseous mixture of TFE/PPVE in nomi-nal molar ratio of 99.6/0.4 was added until reaching a pressure of 21 bar.

(2) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 95.9% TFE, 1.3% PPVE, 2.8% ethane. Then, by a metering pump, 100 ml of a 0.035 M ammonium persulphate solu-tion were fed.

(3) The polymerization pressure was maintained constant by feeding the above mentioned monomeric mixture; when 8.8 g of the mixture were fed, the monomer feeding was interrupted. The reactor was cooled to room temperature, the latex was dischar-ged and coagulated with HNO.sub.3 (65% by weight) and the polymer was washed with H.sub.2O and dried at about 220° C.

(4) Determination of the obtained polymer:

(5) Composition (IR analysis): PPVE: 0.9% by weight

(6) MFI: 5.0 g/10 min

(7) Second melting temperature (T(II) melting point): 320° C.

EXAMPLE 2

TFE/PPVE 98.6/1.4 (Weight Ratio)

(8) The same procedure as detailed under Example 1 was followed but: 25.0 g of PPVE were fed; 0.62 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.4/0.6 was added.

(9) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 94.1% TFE, 3.4% PPVE, 2.5% ethane.

(10) Determinations on the obtained polymer:

(11) Composition (IR analysis): PPVE: 1.4% by weight

(12) MFI: 5.0 g/10 min

(13) Second melting temperature (T(II) melting point): 317° C.

EXAMPLE 3

TFE/PPVE 98.2/1.8 (Weight Ratio)

(14) The same procedure as detailed under Example 1 was followed but: 32.0 g of PPVE were fed; 0.6 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.2/0.8 was added.

(15) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 95.9% TFE, 2.0% PPVE, 2.1% ethane.

(16) Determinations on the obtained polymer:

(17) Composition (IR analysis): PPVE: 1.8% by weight

(18) MFI: 5.0 g/10 min

(19) Second melting temperature (T(II) melting point): 314° C.

EXAMPLE 4

TFE/PPVE 98.2/1.8 (Weight Ratio)

(20) The same procedure as detailed under Example 1 was followed but: 32.0 g of PPVE were fed; 0.40 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.2/0.8 was added.

(21) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 96.6% TFE, 1.5% PPVE, 1.9% ethane.

(22) Determinations on the obtained polymer:

(23) Composition (IR analysis): PPVE: 1.8% by weight

(24) MFI: 2.0 g/10 min

(25) Second melting temperature (T(II) melting point): 314° C.

EXAMPLE 5

TFE/PPVE 98.6/1.4 (Weight Ratio)

(26) The same procedure as detailed under Example 1 was followed but: 25.0 g of PPVE were fed; 0.50 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.4/0.6 was added.

(27) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 96.9% TFE, 1.55% PPVE, 1.55% ethane.

(28) Determinations on the obtained polymer:

(29) Composition (IR analysis): PPVE: 1.4% by weight

(30) MFI: 3.0 g/10 min

(31) Second melting temperature (T(II) melting point): 317° C.

EXAMPLE 6

TFE/PPVE 98.3/1.7 (Weight Ratio)

(32) The same procedure as detailed under Example 1 was followed but: 28.0 g of PPVE were fed; 0.50 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.3/0.7 was added.

(33) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 96.5% TFE, 2.0% PPVE, 1.5% ethane.

(34) Determinations on the obtained polymer:

(35) Composition (IR analysis): PPVE: 1.7% by weight

(36) MFI: 4.0 g/10 min

(37) Second melting temperature (T(II) melting point): 315° C.

EXAMPLE 7

TFE/PPVE 98.6/1.4 (Weight Ratio)

(38) The same procedure as detailed under Example 1 was followed but: 25.0 g of PPVE were fed; 0.40 bar of ethane were fed; a gaseous mixture of TFE/PPVE in nominal molar ratio of 99.4/0.6 was added; 150 ml of a 0.035 M ammonium persulphate solution were fed.

(39) The composition of the gaseous mixture present at the autoclave head (as determined by GC analysis) was formed of the following compounds in the indicated molar percentages: 96.2% TFE, 1.7% PPVE, 2.1% ethane.

(40) Determinations on the obtained polymer:

(41) Composition (IR analysis): PPVE: 1.5% by weight

(42) MFI: 2.0 g/10 min

(43) Second melting temperature (T(II) melting point): 316° C.

(44) As shown in Table 1 here below, thermal shock tests were carried out at 280° C. following VDE 0472-608 standard test method after a six-hours thermal cycle on AWG 20 cables obtained according to procedure as detailed above. No crack was observed using polymers (F) of Examples 1 to 6 according to the invention.

(45) TABLE-US-00001 TABLE 1 PPVE MFI Tm Thermal Run [% wt.] [g/10 min] [° C.] shock Example 1 0.9 5.0 320 No crack Example 2 1.4 5.0 317 No crack Example 3 1.8 5.0 314 No crack Example 4 1.8 2.0 314 No crack Example 5 1.4 3.0 317 No crack Example 6 1.7 4.0 315 No crack

(46) As shown in Table 2 here below, reporting the results of yield strength tests at 280° C., the polymers (F) according to the invention advantageously exhibited improved yield stress values at temperatures up to 280° C. as compared with commercially available products of comparative Examples 1 and 3.

(47) TABLE-US-00002 TABLE 2 PPVE MFI Tm Yield stress Run [% wt.] [g/10 min] [° C.] [MPa] Example 3 1.8 5.0 314 3.6 Example 5 1.4 3.0 317 3.5 C. Example 1 3.8 2.5 307 2.8 C. Example 3 3.3 2.5 310 3.2

(48) As shown in Table 3 here below, reporting the results of the creep strain tests, the polymers (F) according to the invention advantageously exhibit lower creep strain values as compared with commercially available products of comparative Examples 1 to 3.

(49) TABLE-US-00003 TABLE 3 MFI Creep Creep Creep PPVE [g/10 Tm 250° C. 280° C. 300° C. Run [% wt.] min] [° C.] 1.5 MPa 1.0 MPa 1.0 MPa Example 5 1.4 3.0 317 6.4% 11.8% — Example 2 1.4 5.0 317 6.8% — — Example 7 1.5 2.0 316 —  9.3% 20.0% C. 3.8 2.5 307 17.0% — — Example 1 C. 3.8 13.0 307 19.0% — — Example 2 C. 3.3 2.5 310 12.0% 17.8%  >40% Example 3

(50) It has been thus found that the cables of the present invention comprising a first protective layer at least comprising, but preferably being made of, the polymer (F) according to the invention advantageously withstand high-pressure downhole environments up to temperatures of 300° C. and exhibit an improved resistance to deform plastically and to squeeze out of the armor shell of the cable under the influence of external pressure impacts, thus being particularly suitable for use in drilling operations.