CORRODIBLE DOWNHOLE ARTICLE

Abstract

A corrodible downhole article includes a magnesium alloy. The magnesium alloy includes: 1-9 wt % Zn; 1-2 wt % Cu; 0.5-1.0 wt % Mn; and 0.1-5 wt % of a corrosion promoting element (e.g., Ni). The alloy can have a 0.2% proof strength of at least 150 MPa when tested using standard tensile test method ASTM B557-10.

Claims

1. A corrodible downhole article comprising a magnesium alloy, the magnesium alloy comprising: 1-9 wt % Zn; 1-2 wt % Cu; 0.5-1.0 wt % Mn; and 0.1-5 wt % of a corrosion promoting element.

2. The corrodible downhole article of claim 1 wherein said corrosion promoting element includes Ni.

3. The corrodible downhole article of claim 1 comprising 5-8 wt % Zn.

4. The corrodible downhole article of claim 1 comprising Zn, Cu, Mn and said corrosion promoting element, wherein the remainder is said magnesium and incidental impurities.

5. The corrodible downhole article of claim 1 wherein the corrodible downhole article is a downhole tool.

6. The corrodible downhole article of claim 1 wherein the alloy has a 0.2% proof strength of at least 150 MPa when tested using standard tensile test method ASTM B557-10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] 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:

[0065] FIG. 1 shows a microstructure of sample DF9905D of Example 1,

[0066] FIG. 2 shows a graph of % loss in proof stress against Ni addition (wt %) for the alloys of Examples 2 and 3,

[0067] FIG. 3 shows a graph of proof stress against Ni addition (wt %) for the alloys of Examples 2 and 3, and

[0068] FIG. 4 shows a graph of corrosion rate against Ni addition (wt %) for the alloys of Examples 2 and 3.

EXAMPLES

Example 1—Magnesium Aluminium Alloy

[0069] 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.

[0070] 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.).

[0071] 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.

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

[0072] 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.

[0073] 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.

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

[0074] FIG. 1 shows a microstructure of sample DF9905D (i.e., 0.61 wt % nickel). The dark area of the microstructure, labelled “1”, is the α-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 2—Magnesium Aluminium Alloys

[0075] Further magnesium alloy compositions were prepared by combining the components in the amounts listed in Table 3 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.

TABLE-US-00003 TABLE 3 Mg—Al 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

[0076] The mechanical properties of these samples were also tested using the same standardised tension tests, and the results are shown in Table 4 below.

TABLE-US-00004 TABLE 4 Alloy class: Mg—Al 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

[0077] 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 3—Magnesium Zinc Alloys

[0078] Magnesium alloy compositions were prepared by combining the components in the amounts listed in Table 5 below. These compositions were then melted by heating at 750° C. The product was then cast into a billet and extruded to a rod.

TABLE-US-00005 TABLE 5 Alloy Additions Mg—Zn (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

[0079] The mechanical properties of these samples were tested using standardised tension tests, and the results are shown in Table 6 below.

TABLE-US-00006 TABLE 6 Alloy Class: Mg—Zn 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

[0080] This data shows that the addition of nickel to these magnesium-aluminium 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.

[0081] 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.

[0082] In FIGS. 2 and 3 the mechanical properties of the alloys of Examples 2 and 3, have been plotted against the Ni addition (wt %).

[0083] FIG. 2 in particular shows that for the magnesium-zinc alloys of Example 3 (“Mg—Zn”, 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 (“Mg—Al”) alloy (Example 2) is maintained. FIG. 3 is a plot showing the absolute proof strength values (MPa) against Ni addition (wt %).

[0084] FIG. 4 is a plot of corrosion rate against Ni addition (wt %).

[0085] 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.