Corrodible downhole article

Abstract

A magnesium alloy suitable for use as a corrodible downhole article. The alloy has a corrosion rate of at least 50 mg/cm.sup.2/day in 15% KCl at 93 C. and a 0.2% proof strength of at least 50 MPa when tested using standard tensile test method ASTM B557-10.

Claims

1. A corrodible downhole article comprising a magnesium alloy which comprises 0.4-10 wt % of a corrosion promoting element Ni, 2-8 wt % Y, 0.1-15 wt % of at least one rare earth metal other than Y, and 0-1 wt % Zr, wherein a balance is magnesium and incidental impurities, wherein the corrodible downhole article has a corrosion rate of at least 643 mg/cm.sup.2/day in 15% KCl at 93 C. and a 0.2% proof strength of at least 50 MPa when tested using standard tensile test method ASTM B557-10.

2. A corrodible downhole article as claimed in claim 1 having a 0.2% proof strength of at least 150 MPa when tested using standard tensile test method ASTM B557-10.

3. A corrodible downhole article as claimed in claim 1 wherein said magnesium alloy comprises up to 8 wt % Ni.

4. A corrodible downhole article as claimed in claim 1 wherein said at least one rare earth metal other than Y includes 2.0-2.5 wt % Nd.

5. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 15,000 mg/cm.sup.2/day in 15% KCl at 93 C.

6. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 1000 mg/cm.sup.2/day in 15% KCl at 93 C.

7. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 3000 mg/cm.sup.2/day in 15% KCl at 93 C.

8. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 4000 mg/cm.sup.2/day in 15% KCl at 93 C.

9. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 5000 mg/cm.sup.2/day in 15% KCl at 93 C.

10. A corrodible downhole article as claimed in claim 1 having a maximum corrosion rate of 10,000 mg/cm.sup.2/day in 15% KCl at 93 C.

11. A corrodible downhole article as claimed in claim 1, said magnesium alloy consisting essentially of: said Ni, Y, at least one rare earth metal other than Y, Zr, and balance of magnesium and incidental impurities.

12. A corrodible downhole article as claimed in claim 1 which is a downhole tool.

13. A corrodible downhole article as claimed in claim 1 with the proviso that it contains no core shell particles.

14. A corrodible downhole article as claimed in claim 1 with the proviso that it contains no coated magnesium alloy powder.

15. A corrodible downhole article as claimed in claim 1, wherein said magnesium alloy comprises 0.4-5 wt % of corrosion promoting element Ni, 2.0-6.0 wt % Y, and 0.1-5.0 wt % of said at least one rare earth metal other than Y.

16. A corrodible downhole article as claimed in claim 1, wherein said magnesium alloy comprises 0.4-5 wt % of corrosion promoting element Ni, 3.7-4.3 wt % Y, and wherein said at least one rare earth metal other than Y includes 2.0-2.5 wt % Nd.

17. A method for producing a corrodible downhole article as claimed in claim 1, comprising the steps of: melting and mixing elements to form said magnesium alloy; and casting the magnesium alloy and solidifying to form said corrodible downhole article.

18. A method as claimed in claim 17 wherein said casting of said magnesium alloy is carried out in a mold without application of compression to said magnesium alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This disclosure will be further described by reference to the following Figures which is not intended to limit the scope of the claimed subject matter, in which:

(2) FIG. 1 shows a microstructure of sample DF9905D of Example 1,

(3) FIG. 2 shows a graph of % loss in proof stress against Ni addition (wt %) for the alloys of Examples 3A, 3B and 3C,

(4) FIG. 3 shows a graph of proof stress against Ni addition (wt %) for the alloys of Examples 3A, 3B and 3C, and

(5) FIG. 4 shows a graph of corrosion rate against Ni addition (wt %) for the alloys of Examples 3A, 3B and 3C.

EXAMPLES

Example 1Magnesium Aluminium Alloy

(6) A base magnesium alloy consisting of the commercial alloy AZ80A which has a typical chemical composition of 8.5 wt % Al, 0.5 wt % Zn and 0.3 wt % Mn, was melted by heating to 750 C. and nickel was added to it in amounts ranging between 0.01% wt to 1% wt. The product was then cast into a billet and extruded into a rod.

(7) In order to simulate the mild and extreme corrosion performance in a well, the material was corrosion tested by measuring weight loss in an aqueous solution of 3 wt % potassium chloride at a constant temperature of 38 C. (100 F.) and 15 wt % potassium chloride aqueous solution at a constant temperature of 93 C. (200 F.).

(8) The corrosion rates are shown in Table 1 below. The samples comprise the standard alloy (ie AZ80A without nickel added), and two samples with different amounts of nickel added.

(9) TABLE-US-00001 TABLE 1 Corrosion rate in Corrosion rate in Nickel 3% KCL at 38 C. 15% KCL at 93 C. concentration (100 F.) (200 F.) Sample ID Wt % Mg/cm.sup.2/day Mg/cm.sup.2/day Standard <0.005 <0.5 <0.5 alloy DF9905B 0.016 113 449 DF9905D 0.61 161 1328

(10) The data in Table 1 clearly shows the increased corrosion level achieved in the samples to which nickel has been added, with a higher nickel content resulting in a higher corrosion rate.

(11) The mechanical properties of the samples were also tested using standardised tension tests (ie ASTM B557-10), and the results are shown in Table 2 below.

(12) TABLE-US-00002 TABLE 2 Nickel 0.2% Proof concentration Strength UTS Sample ID Wt % MPa MPa Elongation % Standard alloy <0.005 219 339 9 DF9905B 0.016 238 334 11 DF9905D 0.61 219 309 14

(13) FIG. 1 shows a microstructure of sample DF9905D (i.e., 0.61 wt % nickel). The dark area of the microstructure, labelled 1, is the -Mg phase (i.e., the phase comprising magnesium in solid solution with the other alloying elements). The light area of the microstructure, an example of which is labelled 2, is the phase comprising the corrosion promoting element (i.e., nickel in this case) and magnesium.

Example 2Magnesium Yttrium Rare Earth Alloy

(14) The procedure of Example 1 was repeated, but with the base magnesium alloy AZ80A being replaced by commercial alloy Elektron 43. A WE43C alloy was used with a composition of 3.7-4.3 wt % Y, 0.2-1.0 wt % Zr, 2.0-2.5 wt % Nd and 0.3-1.0 wt % rare earths.

(15) The corrosion rates are shown in Table 3 below. The samples comprise the standard alloy (i.e., WE43C without nickel added), and five samples with different amounts of nickel added.

(16) TABLE-US-00003 TABLE 3 Corrosion rate in Corrosion rate in Nickel 3% KCl at 38 C. 15% KCl at 93 C. concentration (100 F.) (200 F.) Sample ID Wt % Mg/cm.sup.2/day Mg/cm.sup.2/day Standard alloy <0.005 <0.5 <0.5 DF9911D 0.1 <0.5 94 DF9912A 0.2 78 308 DF9912B 0.4 199 643 DF9912C 0.62 203 929 DF9915C 0.65 302 1075 DF9915D 1.43 542 1811

(17) The data in Table 3 clearly shows the increased corrosion level achieved in the samples to which nickel has been added, with a higher nickel content resulting in a higher corrosion rate.

(18) The mechanical properties of these samples were also tested using standardised tension tests, and the results are shown in Table 4 below.

(19) TABLE-US-00004 TABLE 4 Nickel 0.2% Proof concentration Strength UTS Sample ID Wt % MPa MPa Elongation % Standard alloy <0.005 186 301 15 DF9911D 0.1 197 302 17 DF9912A 0.2 234 337 15 DF9912B 0.4 238 331 14 DF9912C 0.62 230 311 11 DF9915C 0.65 224 305 21 DF9915D 1.43 229 321 20

(20) The data in Table 4 shows that alloys of the disclosure have improved mechanical properties, in particular 0.2% proof strength, when compared to prior art compositions.

Example 3AMagnesium Aluminium Alloys

(21) Further magnesium alloy compositions were prepared by combining the components in the amounts listed in Table 5 below (the balance being magnesium). These compositions were then melted by heating at 750 C. The product was then cast into a billet and extruded to a rod.

(22) TABLE-US-00005 TABLE 5 MgAl Alloy Additions (wt %, balance magnesium) Sample ID Al Ca Sn Zn Mn Ni A1 8.4 0.4 0.2 0.00 A2 8.4 0.4 0.2 0.02 A3 8.4 0.4 0.2 0.15 A4 8.4 0.4 0.2 1.50 A5 6.5 0.7 0.3 0.00 A6 6.5 0.7 0.3 0.05 A7 6.5 0.7 0.3 0.15 A8 6.5 0.7 0.3 0.30 A9 6.5 0.7 0.3 0.60 A10 6.5 0.7 0.3 1.20 A11 3.0 0.7 0.3 0.00 A12 3.0 0.7 0.3 0.05 A13 3.0 0.7 0.3 0.15 A14 3.0 0.7 0.3 0.30 A15 3.0 0.7 0.3 0.60 A16 3.0 0.7 0.3 1.20 A17 3.5 3.0 0.0 0.3 0.00 A18 4.0 5.0 0.0 0.5 0.15 A19 4.0 3.6 0.0 0.4 0.50 A20 3.5 3.0 0.0 0.3 2.00 A21 8.0 4.0 2.0 0.3 0.00 A22 8.0 4.0 2.0 0.3 0.15

(23) The mechanical properties of these samples were also tested using the same standardised tension tests, and the results are shown in Table 6 below.

(24) TABLE-US-00006 TABLE 6 Alloy class: MgAl Percentage Proof Corrosion Rate in 15% 0.2% Proof Strength KCl at 93 C. (200 F.) Sample ID Strength (MPa) remaining (%) (mg/cm.sup.2/day) A1 219 100 0 A2 239 109 449 A3 235 107 1995 A4 220 101 1328 A5 199 100 0 A6 197 99 2078 A7 203 102 2531 A8 198 99 2800 A9 197 99 2574 A10 199 100 2494 A11 211 100 0 A12 196 93 1483 A13 192 91 1853 A14 194 92 1854 A15 197 94 1969 A16 194 92 1877 A17 321 100 0 A18 329 102 3299 A19 312 97 4851 A20 309 96 2828 A21 258 100 0 A22 256 99 1205

(25) This data shows that the addition of nickel to these magnesium-aluminium alloys significantly increases the corrosion rate of the alloys. Advantageously, for these alloys this increase in corrosion rate is provided whilst maintaining the mechanical properties of the alloy (as exemplified by the 0.2% proof strength). Thus, the alloys tested in this example can find use as components in downhole tools due to their combination of high corrosion rates and good mechanical properties.

Example 3BMagnesium Yttrium Rare Earth Alloys

(26) Further magnesium alloy compositions were prepared by combining the components in the amounts listed in Table 7 below. These compositions were then melted by heating at 750 C. The product was then cast into a billet and extruded to a rod.

(27) TABLE-US-00007 TABLE 7 Alloy Additions MgY-RE (wt %, balance Mg) Sample ID Y Nd Zr Ni R1 4.0 2.2 0.5 0.0 R2 3.6 2.1 0.5 0.4 R3 3.6 2.1 0.5 0.6 R4 3.6 2.1 0.5 1.4 R5 3.5 2.1 0.4 1.8 R6 3.5 2.1 0.4 3.5 R7 3.5 2.1 0.4 5.0 R8 3.5 2.1 0.4 6.1 R9 3.7 2.1 0.0 0.4 R10 3.7 2.1 0.0 0.6 R11 3.6 2.1 0.1 1.5 R12 3.9 2.0 0.0 1.1 R13 3.5 1.8 0.0 2.2

(28) The mechanical properties of these samples were tested using standardised tension tests, and the results are shown in Table 8 below.

(29) TABLE-US-00008 TABLE 8 Alloy Class: MgY-RE Corrosion Rate in 0.2% Proof Percentage Proof 15% KCl at 93 C. Strength Strength remaining (200 F.) Sample ID (MPa) (%) (mg/cm.sup.2/day) R1 241 100 0.0 R2 229 95 198.6 R3 235 97 578.5 R4 234 97 1302.3 R5 238 99 2160.0 R6 263 109 6060.8 R7 253 105 7175.7 R8 232 96 7793.1 R9 221 92 636.0 R10 217 90 937.0 R11 206 85 1115.0 R12 209 87 1118.0 R13 256 106 3401.0

(30) This data shows that, as for the magnesium-aluminium alloys, the addition of nickel to these magnesium-yttrium-rare earth alloys significantly increases the corrosion rate of the alloy. Advantageously, for these alloys this increase in corrosion rate is provided whilst maintaining the mechanical properties of the alloy (as exemplified by the 0.2% proof strength). However, in addition to these advantageous properties, for these alloys the increase in corrosion rate is substantially proportional to the amount of added nickel. This can provide the further feature that the corrosion rate of these alloys is therefore tunable and alloys with specific desirable corrosion rates, or ranges of particular corrosion rates, can be produced. Thus, the alloys tested in this example can find use as components in downhole tools due to their combination of high corrosion rates and good mechanical properties.

Example 3CMagnesium Zinc Alloys

(31) Magnesium alloy compositions were prepared by combining the components in the amounts listed in Table 9 below. These compositions were then melted by heating at 750 C. The product was then cast into a billet and extruded to a rod.

(32) TABLE-US-00009 TABLE 9 Alloy Additions MgZn (wt %, balance Mg) Sample ID Zn Cu Mn Zr Ni Z1 6.5 1.5 0.8 0.00 Z2 6.5 1.5 0.8 1.00 Z3 6.5 1.5 0.8 2.00 Z4 6.5 1.5 0.8 4.00 Z5 6.5 0.5 0.00 Z6 6.5 0.15 Z7 6.5 0.30 Z8 6.5 1.00

(33) The mechanical properties of these samples were tested using standardised tension tests, and the results are shown in Table 10 below.

(34) TABLE-US-00010 TABLE 10 Alloy Class: MgZn Corrosion Rate in 15% KCl at 93 C. Sample 0.2% Proof Percentage Proof (200 F.) ID Strength (MPa) Strength remaining (%) (mg/cm.sup.2/day) Z1 312 100 50 Z2 229 73 315 Z3 229 73 5474 Z4 216 69 9312 Z5 223 100 1 Z6 133 59 565 Z7 137 62 643 Z8 142 63 905

(35) This data shows that, as for the magnesium-aluminium and magnesium-yttrium-rare earth alloys, the addition of nickel to these magnesium-alloys advantageously significantly increases their corrosion rate. Magnesium-zinc alloys are known in the art to have high strength values and it is shown in the disclosure that the addition of nickel also increases their corrosion rate. However, the data demonstrates that the mechanical properties of these Magnesium-zinc alloys (as exemplified by the 0.2% proof strength) decrease with increasing nickel content.

(36) This example shows that not all magnesium alloys provide the mechanical strength required for certain uses of the disclosure when nickel is added to them, and that it is in fact difficult to predict how the properties of a particular alloy will be altered when a corrosion promoting element such as nickel is added.

(37) In FIGS. 2, 3 and 4 the mechanical properties of the alloys of Examples 3A, 3B and 3C, have been plotted against the Ni addition (wt %).

(38) FIG. 2 in particular shows that for the magnesium-zinc alloys of Example 3C (MgZn, where zinc is the major strengthening element), between 20% and 40% of the strength is lost when nickel is added. In contrast, the strength of the magnesium-aluminium (MgAl) and magnesium-yttrium-rare earth (MgY-RE) alloys (Examples 3A and 3B) is maintained. FIG. 3 is a plot showing the absolute proof strength values (MPa) against Ni addition (wt %).

(39) FIG. 4 is a plot of corrosion rate against Ni addition (wt %). For the magnesium-yttrium-rare earth alloys, a line has been drawn through the data points which demonstrates the correlation between corrosion rate and Ni addition for these alloys. This shows that the Magnesium-yttrium rare earth alloy, advantageously can be tailored to achieve a desired specific corrosion rate or range of corrosion rates.

(40) Many modifications and variations of the disclosed subject matter will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than has been specifically shown and described.