Patent W02016016628A2 - Corrodible downhole article - Google Patents
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`Page 1 of 10
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`WO 2016/016628
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`Patents.
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`W3 29’? 5331 6828 A2
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`l his invention relates to magnesmm alloys editable for use as corrodlbie
`downhole articles, wherein the alloys have a corrosion rate of at least 50mg/‘cm
`2 May in 15% KCl at 93°C and a 0.2% proof strength of at least 50MPa when
`tested usmg standard tensile test method ASTM 5557-10. The invention also
`relates to methods for producing the alloys, downhole tools comprising the
`
`alloys and methods of hydraulic fracturing using the downhole tools.
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`Publication number
`Publication type
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`Publication date
`Filing date
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`inventors
`Applicant
`Export Citation
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`W02016016628 A2
`Application
`PCT/882015052169
`Feb 4. 2016
`Jul 28. 2015
`‘ul
`:-'8 2014
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`r-nesium Eleioron Limited
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`Referenced by .-;; Ciasggscgggws m, Rizal Events iii}
`External Links: F‘atentscopc Especenet
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`DESCRIP1 [UK ii.
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`CORRODiBLE DQWNHOLE ARTECLE
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`(TL/HMS :O'
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`{CC-“ii This invention relates ‘0 a magnesium alloy suitable for use as a
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`‘1“ an alloy, an article
`corrodible downhoie article. a method for making "
`comprismg the alloy and the use of the article
`
`{002) Background [003} The oil and gas industries utilise a technology known as
`hydraulic fracturing or "tracking“ This normally involves the pressurisation with
`..
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`water of a system of boreholes in 0:: and/or gas bearing rocxs in order to
`fracture the rocks to release the oil andi’or gas. £004} in order to achieve this
`pressunsation’ valves may be used to separate different sections of a borehole
`system These valves are referred to as downhole valves. the word downhoie
`
`being used in the context of the invention to refer to an article that is used in a
`well or borehole {005] One way of forming such valves involves the use of
`spheres of materia: known as tracking balls to seal off parts of a borehole.
`Freaking bails may be made from aluminium. magnesium. polymers or
`composites.
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`the use of rack '19 balls rela es to how they are re’hoved
`J06] A problem wt
`once the tracking operation has been completed so order to allow fluid to flow
`
`through the well or borehole, Cine way of doing this is to drill through the
`tracking bali However, this type of drilling process can hamper production. as
`well as being expensive. difficult and therefore undesrrapie. [007] One proposed
`solution to this problem has been to form the tracking ball from a material that
`well dissolve or corrode under the conditions in the well or borehows An issue
`
`that needs to be conSidered in relation to such corrodible articles is ensuring
`_
`,
`,
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`that they corrode at a rate which allows them to remain useable for the time
`period during which they are required to perform their function. but that allows
`them to corrode or dissolve afterwards. {008] Degradable polymers have been
`
`used in order to provide a corrodible arti
`. for use in such methods However.
`these polymers do not generally have particularly high mechanical strength.
`
`1. A magnesium alloy suitable for use as a corrodible downhole article» wherein
`the alloy has a corrosion rate of at least 50mg/cm3i‘day in 15% KCI at 93°C and
`a 0.2% proof strength of at least SOMPa when tested using standard tensile test
`method ASTM 355740
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`2‘ A magnesmm alloy as cla med m 0'3”“ 1 haVlng a corrosion ate 0 at east
`1OOmg/cm2/day in 15% KC! at 93“:-
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`3. A magnesium alloy as claimed in either claim 1 or claim 2 having a 0.2%
`proof strength of at least 150MPa when tested using standard tensile test
`method ASTM 8557-10,
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`4. A magnesium alloy as claimed in any one of the preceding claims comprising
`.
`one or more of Ni. Co, tr, Au. Pd or Cu
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`.ttaa\dtdxmsmsmm“team‘s““mmt-ttt“tt“mm“mm“m“xxma“asx\\x“\msmmmm‘m
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`5 A magnesium alloy as claimed in claim 4 comprising one or more of Ni. Co,
`ir, Au, Pd or Cu in an amount of O 01-15wt%.
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`6. A magnesium alloy as claimed in. either claim 4 or claim 5, wherein the 0.2%
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`proof strength of the magnesrum alloy when the one or more of Ni. Co, lr, Au,
`Pd or Cu has been added is at least 80% of the 0.2% proof strength of the base
`alloy.
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`[0091An alternative corrodibie article is described in US patent no 8.425651 in
`the name of Xu et at. This document describes a powder metal composne
`comprising a nanomatrix. preferably made of Al or Ni or a combination thereof.
`.
`.
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`=r= which are dispersed a plurality of first particles, a plurality of second particles
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`7. A magnesmm alloy as claimed in any one of the preceding claims
`comprising:
`
`g
`{
`(a) 0 01—10wt% of one or more of Ni. Co, :r, Au. Pd or Cu,
`
`fb) i-tOwt% y.
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`(C) 5‘15WW" of at “533‘ one rare earth metal other than \fl and
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`(d) O-lwt% Zr.
`
`and a solid—state bond layer. The first particles comprise Mg, Al. Zn or Mn. or a
`combination thereof, and the second particles comprise carbon nanoparticies.
`The composite may be produced by forming a powder mixture of the required
`components and then applying temperature and pressure to the powder to
`sinter and deform (but not melt) the composers- in order to form a powder
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`Patent W02016016628A2 — Corrodible downhole article - Google Patents
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`Page 2 of 10
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`composite A problem With such powder metallurgical methods is that they are
`compilcated and expensive.
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`8. A magnesium alloy as claimed in claim 7 comprising O.1-8wt% Ni.
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`{0010} A further corrooible article is described in US patent application
`publication no 20120318513 in the name of Mazyar e: at. in this document. the
`corrodible article is described as having a corrodible core and a metallic layer
`covering the core, The core material is described as being a magnesium altoy
`However. it appears that the combination of magnesium and one or more other
`materials in a form which is not an aiioy is also intended to be covered by the
`use of the term "alloy“ in Mazyar et al. For example, this document refers to
`alloys of magnesium with tungsten, whereas it is actually not technically feasrble
`to form a magnesium tungsten alloy Similarly. Mazyer et al also mentions
`powders of magnesium coated with a metal oxide as being useful for forming
`the core. which again would not be magnesium "alloys". Thus. Mazyar et ai
`appears to utii:se the term “magnesium alioy" to mean any way in which
`magnesium and another metal are combined. The metallic layer is described as
`including aluminium or nickel.
`
`{0011} A dissolvabie weilbore isolation device is described in US patent
`application publication no 201410124216 in the name of Haliiburton Energy
`Services, Inc, Although there is minimai description on how the devrce is made,
`it appears that again a powder composite 55 formed instead of an "alloy“ in
`
`addition, this document oniy menti
`magnesium as one of a large list of
`components, with magnesium not being one of the preferred components The
`devrce also requires the presence of an “electrolytic compound" which dissolves
`in the fluid in the welibore. Similarly. related US patent application publication
`no ROM/0190705, also in the name of Hailiburton Energy Services, the. only
`mentions magnesium as one of a large list of components, with magnesium not
`Easing one of the preferred components. This document also requires the
`presence of an "electrolytic compound“ which dissolves in the fluid in the
`wellbore
`
`{0012] Although casting. forging and machining are described in Mazyar et at.
`these are only mentioned :n very generai terms (eg method steps and heating
`temperatures are not stated: and the structure of the resulting materials is not
`described. in addition. the preferred method of forming the corrodible article is
`by compressing the powder into the desired shape for example by cold
`compressmn using a isostatic press, As noted above. such powder metallurgical
`methods are complicated and expensive in addition, the resulting powder
`composites can have poor mechanical properties.
`
`{0013} Thus. there is a need it“: the Oil and gas industries to provide a corrodible
`article which provides the desired corrosion characteristics. whilst also havrng
`Empire‘-
`o' mechanical properties, and at a lower cost than can currently be
`
`achieved. it is also advantageous for the co
`: article to have a relatively
`Sow density (for example. compared to metais in general) This invention seeks
`to ameliorate these problems. {0014} Statement of invention
`
`{0015] This invention relates to a magneSium alioy suitable for use as a
`corrodible downhole e: are, wherein the alloy has a corrosion rate of a: least
`
`9 A magnesium alloy as claimed :5: either claim 7 or claim 8 comprisrng 3,3-
`4.3wt% Y, up to lwt% Zr and 1.5-2.5wtt’i'o Nd.
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`to. A magnesrum alloy as claimed in any one of claims 1—6 comprising:
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`(a) 0.01-10wt% of one or more of Ni, Co, lr, Au, Pd or Cu,
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`fb) l-15wt% Al,
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`to} 0.1~iwt% Mn, and
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`(d) optionatiy one or more of Ca. Sn and Zn.
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`1?. A magnesium aiioy as claimed in cralm 10 comprisrng 0.01-3wt% Ni.
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`1.2. A magnesium alloy as claimed in either claim 10 or claim 11 comprising 2-
`6wt% Sn.
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`13. A magnesrum alloy as claimed in any one of claims 10-12 comprising 02-
`3wt% Zn.
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`14. A magnesium alloy as ciaimed in either claim 10 or claim 11 comprising 1.,
`10wt% Ca.
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`15. A magnesrum alloy as claimed in any one of claims 1—6 comprising.
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`(a) 0.01—15wt% of one or more of Ni, Co, lr, Au, Pd or Cu.
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`(b) l-9wt% Zn. and
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`(c) optionally one or more of Mn and Zr.
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`16. A magnesium alloy as claimed in claim 15 comprising 0.1-th Mn or 0.05—
`lwt% Zr.
`
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`17. A magnesium alloy as claimed in claim 16 comprising 0.1-lwt Mn and 0.1-
`5wt% Cu.
`
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`50mgi'cmzi'day in 15% K61 at 93°C and a O 2% proof strength of at least SOMPa
`when tested usrng standard tensile test method ASTM 3557-10,
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`18, A downhole tool, preferably a tracking ball. comprising a magnesium alloy
`as claimed in any one of the preceding claims.
`
`[0016} in relation to this invention, the term "alioy" is used to mean a
`composttion made by mixing and fusing two or more metallic elements by
`melting them together. mixmg and re—so! ‘:g them
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`19. A method for producing a magnesium alloy as claimed in any one of claims
`1- 17, comprising the steps of:
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`{0017] The term "rare earth metals" is used :n relation to the invention to refer to
`the fifteen lanthanide eiements, as well as Sc and Y. {0018} The magnesium
`alloy preferably comprises one or more of Ni. Co, lr, Au. Pd or Cu in some
`embodiments. Ni is preferred. These metaii:c elements promote the corrosion of
`the alloy in all embod:ments, the alloy preferably comprises one or more of Ni.
`Co, lr. Au, Pd or Cu, more preferably NE,
`in an amount of between . 01% and
`15% by weight (wt‘f/ai and in some a
`more preferably between
`Try the new Soogie intents, with machinouoiassitted Soogie Scholar results. and tisdahmmtaemmadwmus.
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`(a) melting magnesium or a magnesium alloy,
`
`to) adding one or more of Ni, Co, lr, Au, Pd or Cu to the molten magnesium
`or magnesium alloy alloy such that the one or more of Ni. Co, is, Au. Pd or
`Cu melts,
`
`to) mixing the resulting molten magnesium alloy, and
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`Page 3 of 10
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`01% and 10% by weight, even more preferably between 02 fit. by weight and
`8% by weight.
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`20. A method of hydraulic fracturing comprising the use of a downhole tool as
`claimed in claim 18.
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`[00‘l9] Particularly preferred combinations of metals in the magnesium alloy
`include Mg»Ai~Zn-Mn, Mg-Ai—Mn, Mg-Zn-Zr, Mg—Y—RE-Zr. Mg—Zn-Cu-Mn. Mg~
`Nd-de- Zr, Mg—Ag—REZE Mg-Zn-RE—Zr, Mg-Gd-Yer. Mg~Al~Ca-Mn and Mg—Ai-
`Sn-Zn-Mn. These additional elements can be included by forming an alioy of
`magnessum With those elements, and then adding a corrosion promoting metallic element tie Ni. Co, tr, Au, Pd andior Cu)
`to the molten alioy [0020] in a first preferred embodiment, the magnesium alloy comprises (a) 001- towt‘tt: of one or more
`of Ni. Co, tr, Au, Pd or Cu, (bi 5-10wt% Y, to) t-iSwttlb of at least one rare earth metal other than V. and (d). 0-1. win/o Zr
`{0021} in the first embodiment, the magnesium alloy comprises one or more rare earth metais other than Y in an amount of
`5-15vvt% more preferably in an amount of Hewitt, even more preferably in an amount of t 5-5.0wt‘i'é. A preferred rare
`
`earth meta; other than Y is Nd. A pa
`'
`rly preferred amount of Nd in the atloy is i.7-2.5wt%, more preferabiy
`2.0-2.3wt'i3.
`
`{0022] in the first embodiment, the magnesrum elioy comprises Y in an amount of 1,— 1,0wt%, preferably :n an amount of
`2.0~6.0wt‘i"e, more preferably in an amount of 3,0-5.0wt%, even more preferably in an amount of 3.3—4.3wt% or 3.7-4.3wt9/c.
`
`[0023] in the first embodiment. the magnesium alloy comprises Zr in an amount of up to iwt%. in some embodiments, the
`magnesrum alioy comprises Zr in an amount of 005-1 Owt‘Z/o, more preferably in an amount of 0.3-1.0wt%, even more
`preferably in an amount of 0 3-0.6wt% in some embodiments, the magnessum alloy comprises Zr in an amount of up to
`0 6wt%, preferably up to C 3wt%. more preferably up to 0,15wt%. in some embodiments the magnesium alloy is
`substantially free of Zr (eg the magnesium alsoy comprises iess than 0.05wt% Zr), {0024] For all embodiments, preferably
`
`the remainder of the alloy is magnesium and ,
`identai impurities It is preferred that the content of Mg in the magnesium
`alloy is preferably at least 80wt%, more preferably at ieast 85wt‘E/o, even more preferably at ieast 87wt% [0025} A
`particuiarty preferred composition of the first embodiment is a magnesium alloy comprising :3 3~4.3wt% Y, 0.2-1.0wt‘i’a Zr,
`2.0-2.5wt9'2. Nd and optionally 0.3— rams-‘0 other rare earths with N: as the corrosion promoting metaliic element. An
`alternative preferred composition of the first embodiment is a magnesium ailoy ccmprismg 3.3-4.3wt% Y, up to 0.2wt% Zr,
`1 7~2 5wt% Nd and optionally 03- t0 wt% other rare earths with Ni as the corrosion promoting rnetaiiic element. {0026} in
`the first embodiment, the magnesrum ailoy preferably comprises Ni in an amount of between 0 01% and 1.0% by weight,
`more preferably between 0.1% and 8% by weight. even more preferably between 0.2% by weight and 7% by weight. A
`further particuiarly preferred composition is a magnesium alloy comprising 3.3- 4.3wt% Y, 0.2-1 Owl‘i/o Zr, 2.0—2.5wt% Nd
`and 0 2-.7wt% Ni, An alternative further particularly preferred composition is a magnesium alloy comprising 3.3-4 3wt% Y_
`0.2wt0/3; or less Zr, 1.7-2.5wt% Nd and 0 2~7wt% bit.
`it is preferred that the remainder of the alloy is magnesium and
`incidental :mpurities. [0027] in a second preferred embodiment, the magnesium alloy comprises (a) 0 01- 10wt% of one or
`more of Ms, Co, lr Au, Pd or Cu. (b) i~15wt°t~ Ai. (c) 0 TvEWtc/o Mn, and (d) optionally one or more of Ca, Sn and Zn.
`
`{0028] in the second embodiment. the magnesrum aiioy comprises 5-1 5wt% Al, preferably 2—1.2wt% Al, more preferably
`2.5-10wt% A5,
`
`{0029} in the second embodiment, the magnesium aiioy comprises O.1-swt% Mn preferably O.1-0,8wt% Mn. more
`preferably 0 24) 6wt% Mn. [0030] in the second embodiment, the magnesium alioy optionally comprises one or more of
`Ca. Sn and Zn When the alloy comprises Sn, it is preferably in an amount of 2—6wt'i’o, more preferably 3—5wt%. When the
`aiioy comprises Zn. it is preferably in an amount 060.1~3wt%. more preferabiy 0.2-2.5wt%. in some embodiments, the
`alioy comprises both Sn and Zn When the ailoy comprises Ca, it is preferably in an amount of i-‘iOwt‘Vo. more preferably
`2—6wt%.
`
`[0031] in the second embodiment, the magnesium alioy preferably comprises Ni in an amount of between 0.01% and 10%
`by weight, more preferably between 0 01% and 5% by weight, even more preferably between 0.1% by weight and 3% by
`weight. [0032} in a third preferred embodiment, the magnesium alloy comprises {3) 0,01. 15wt% of one or more of Ni, Co,
`tr, Au. Pd or Cu, (b) i-9wt‘Z/o Zn, and (c) optionaily one or more of Mn and Zr. [0033] in the third embodiment, the
`magnesmm ailoy comprises i-th'h; Zn, preferably 5—8wt% Zn. more preferabiy 6-7wt‘i/o Zn,
`
`{0034} in the third embodiment. when the alicy comprises Mn it is preferabty in an amount of 0.1-‘wt%, more preferabiy
`0.5-1.0wt‘5’e, even more preferably 0 7~ 0 9wt%
`
`{0035] in the third embodiment, the magnesium aiioy preferabiy comprises Ni in an amount of between 001% and 10% by
`weight. more preferabiy between 001%. and 7% by weight, even more preferably between 0.1% by weight and 5% by
`weight,
`
`[0036] in the third emitcdimem, the magnesium ailoy may also comprise Cu, preferabiy in an amount of 0 1»5wt°/ti, more
`preferably 0 5-3wt'i’a, even more preferabiy E~2wt°/'o. in some embodiments, the ailoy comprises both Mn and Cu. [0037] in
`the third embodiment, when the magnesium alloy comprises Zr it is preferably in an amount of up to im%. more preferably
`in an amount of G.05~ 1,0wt%, even more preferably in an amount of 0.2-1_0wt%. more preferably in an amount of
`0 3—0.7wt‘ta i0038} it a preferred that the corrosion promoting metaliic element tie Ni, Co. tr, Au, Pd and/or Cu; has a
`tsptfltzdityew anew: mammarmmm hogtiedmegafififinmemme,themdepehxapremefitgimemte_
`
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`https..I'wwwgooglc.com/’patentstO2016016628A2?dq:WO+2016.!‘016628&cl=cn
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`Patent W02016016628A2 - Corrodible downholc article - Google Patents
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`has a solubility of at least 0 5% by weight in molten magnesrum at 850"C more preferably at least 1% by weight. in some
`embodiments, it is preferred that the corrosion promoting metallic element has a solubility of at least 1% by weight in the
`molten magnesium alloy to which it is to be added at 850°C. =n relation to the molten material, the term "solubility“ is used
`to mean that the corrosion promoting metallic element dissolves in the molten magnesium or magnesium alloy
`
`10039] Preferably, the common promoting metaiiic element has a solubility of less than 0.1% by weight, more preferably
`less than 0.01% by weight, in solid magnesium a125°C. in some embodiments, it is preferred that the corrosion promoting
`metallic element has a solubility of less than 0.1% by weight. more preferably less than 0.01% by weight, in the solid
`magnesrum alloy to which it is to be added at 250. in relation to the solid material, the term “solubility" is used to mean
`that atoms of the corrosrori promoting metallic element are randomly distributed throughout the alloy in a single phase (ie
`rather than forming a separate phase)
`
`{0-340} The magnessum alloy preferably has a corrosmn rate of at least 50mg/cm2/day preferably at least 75mg/cm2i'day,
`
`it is preferred that the magnesium alloy has a
`even more preferably at least 100mgicm2iday. in 3% KC1 at 38°C (100F)
`corrosion rate of at least 75mg/cm‘7day, preferably at least 250mgi‘cm2idey, even more preferably at least 500mgi’cm2iday,
`in 1.5% K01 at 93“C (ZOOF). it is preferred that the corrosion rate. in 3% K01 at 38“C or in 15% Km at 93°C (ZOOF), is
`less than 15,000mg/cm‘zlday.
`
`[0041] it is preferred that the magnestum alloy has a 0.2% proof strength of at least 75MPa. more preferably at least
`lOOMF’a, even more preferably at least 150MPa. when tested usmg standard tensile test method ASTM 8557—10, It is
`preferred that the 0.2% proof strength is less than ‘7OOMF’a The proof strength of a material is the stress at which material
`strain changes from elastic deformation to plastic deformation causing the material to deform permanently
`
`{0042] it is preferred that the 0 2% proof strength of the magnesmm alloy when the one or more of Ni, Co, lr, Au, Pd or Cu
`has been added is at least 80%, more preferably at least 90% of the 0.2% proof strength of the base alloy. The term
`"base alloy“ is used to mean the magnesium alloy without one or more of .Ni, Co. ii'. Au, Pd or Cu having been added
`Even more preferably the 0 2% proof strength of the magnesmm alloy when Ni has been added is at least 80%, more
`preferably at least 90%, of the 0.2% proof strength of the base alloy.
`
`{0043} This invention also relates to a corrodible downhole article. such as a downiioie tool, comprismg the magnesium
`alloy described above. in some embodments. the corrodibie downhole article is a tracking ball. plug, packer or tool
`assembly The tracking bait is preferably substantially spherical in shape. in some embodiments, the tracking bali consists
`essentially of the magnesium alloy described above
`
`[0044] This invention also relates to a method for producing a magnesium alloy sortable for use as a corrodible downhole
`article comprising the steps of.
`
`{a} melting magnesium or a magnesium alloy,
`
`(b) adding one or more of Ni. Co, lr, Au, Pd or Cu to the molten magnesium or magneSiurn alloy such that the one or more
`of Ni Co. lr. Au. Pd or Cu melts,
`
`{cl mixing the resulting molten magnesmm alloy, and
`
`id} casting the magnesmm alloy
`
`{0045] Preferably the method is for producing a magnessum alloy as defined above. it is preferred that the melting step :3
`carried out at a temperature of 650° C {re the melting point of pure magnesium) or more, preferably iess than 1090°C (the
`boiling point of pure magnesium). A preferred temperature range is 650K”) to 850°C more preferably 700°C to 800%).
`most preferably about 750°C
`
`£0046] The casring step normally involves pouring the molten magneSium alloy into a mould, and then allowing it to cool
`and solidify The mould may be a die mould, a permanent mould, a sand mould, an investment mould, a direct chill casting
`{DC} mould, or other mould. {0047} After step (c), the method may comprise one or more of the following additional steps,
`id; extruding, (e) forging. if} roiling. (g) machining.
`
`
`a magnesium alloy. Preferably the magnesium alloy of step (3)
`{0048] it is preferred that step (a) comprises met
`comprises one or more of At, Zn, Mn, Zr, Y. rare earth metals. Cu, Nd. Gd. Ca. Sn andior Ag Particularly preferred
`magnesium ailoys for step (a; include Mg-Al-Zn-Mri, Mg-Ai—Mn Mg-Zn-Zr. Mg-Y-RE-Zr. Mg-Zn-Cu-Mn. Mg—Nd-Gd~Zr. Mg-
` in. As noted above, these additional elements can
`Ag-RE-Zr, Mg-Zn-RE—Zr, Mg-Gd—Y-Zr Mg-Al-Ca-Mn and Mg-Ai~Sn- En
`be included by forming an alloy of magnesium with those elements, and then adding the corrosion promoting metallic
`element to the molten alloy.
`
`[0049} =n a first preferred embodiment, the rnagnesmm alloy comprises l—‘tit‘Ve Y,
`
`“:- ":5wt% rare earths other than Y and up to iwt% Zr. A particularly preferred magnesium alloy comprises 3.3-4.3wt% Y,
`
`”if? tglmgisfzt5§igigWhitfield Weigh Etb'cQsaszl(32%ngbflgigwsotg‘rtlggifigflgdfigpallfigbeggtttgcfigiwggbopatsnts.
`
`https:i’i’www.google.comi’patents/WO2016016628A2?dq=WO-i~2016i’016628&cl=en
`
`12/612017
`
`

`

`Patent W02016016628A2 - Corrodibte downhole article - Google Patents
`
`Page 5 of 10
`
`005-“.- Ow‘lt’n, or the alloy may comprise less than GDEwtt/a Zr. Ni is preferably added it". an amount of between (12% and
`7% by weight. it is preferred that the remainder o‘ the alloy is magnesrum and incidental impurities,
`
`50050] in a second preferred embodin
`., the magnesium alloy comprises 1- 15wt% Al and up to 2wt% in total of Zn
`and/or Mn The alloy preferably comprises
`
`- 12M% A: Preferably, the alloy comprises 0.2-1.2wt% in total onn and/or Mn. Ni is preferably added in an amount of
`0.1«3wt%
`
`
`
`{0051} in a third preferred e
`merit. the magnesium alloy comprises lu9wt% Zn and optionally one or more of Mn and
`Zr The alloy preferably comprises 5-8wt% Zn. Ni is preferably added in an amount of 0.1-5wt‘iti. [0052] The composition of
`the magnesmm alloy, in particular those of the first and third embodiments, can be tailored to achieve a desired corrosion
`rate fallng in a particular range. The desired corrosrori rate in 15% K01 at 93°C can be in any of the following particular
`
`ranges 50.4: OOmQI’cmzfday, ioo.2somg/cm’iday. 250— 500mgicm‘i'aay. 500-1000mg/cm2i’day; 1000-3000mg/cm2iday;
`3000-4000 mgi‘crrili’day; 4QOO-5000mg/cmpi‘day; 50004 0,000mgfcrn2ilday. 10.000—15DGG mg/cdeay.
`
`{0053] The method of the invention may also Li's-roams tailoring compositions of the magnesium alloys, in particular of the
`first and third embodiments such that the cast magnesium alloys achieve desired corrosion rates in 15% KC“: at 93°C
`
`faliing in at least two of the following ranges: 50 to 100mgicm3i'day; 100-250mg/crn2/day; 250«500mg/cm2lday: 500~
`
`iiidiimgicmi’idai ; 1000-3000mg/cm2iday; 3000-4000 mg/ami’idagi; 4000-5000mg/cm2/day; 5000-10,000mg.’cm2i’day; and
`10.000- 15.000 mg/cmzi‘day.
`
`{0054] it is preferred that the corrosion promoting metallic element tie Ni. Co, tr, Au, Pd and/or Cu) has a solubility of at
`least 0 1% by weight in molten magneSium at 850°C Preferably, the corrosmn promoting metallic element has a solubility
`of at least (i 5% by weight in molten magnesium at 850%). more preferably at least 1% by weight. in some embodiments. it
`is preferred that the corrosion promoting metallic element has a solubility of at least 1% by weight in the molten
`magnesium or magnesium alioy to which it is added
`
`{0055} Preferably the corrosion promoting metallic element (ie Ni Co. lr. Au, Pd arid/or Cu). has a solubility of less than
`0 1% by weight, more preferably less than 0.01% by weight. in solid magnesnim at 25"-:'.i. in some embodiments. it is
`preferred that the corrosion promoting metallic element has a solubility of less than 0 1% by weight, more preferably less
`than 0.01% by weight, in the molten magnesium or magnesium alloy to which it is added once it has been cooled to 25°C
`and solidified.
`
`[0056} The corrosion promoting metallic element :'~ one or more of Ni, Co. it. Au. Pd or Cu. in some embodiments. Ni is
`
`preferred. 5.
`reie ‘
`. to composnions of the first preferred embodiment, the corrosion promoting metallic element is
`preferably added in an amount of between 0 01% and 10% by weight, more preferably between 0 1% and 8% by weight,
`even more preferably between 0.2% and 7% by weight
`in relation to composrtions of the second preferred embodiment,
`the corrosion promoting metallic element is preferably added in an amount of between D 01% and 15% by weight, more
`preferably between 0.01% and 5% by weight. even more preferably between 0.1% and 3% by weight. in relation to
`compositions of the third preferred embodiment. the corrosion promoting metaiiic element is preferably added in an
`amount of between 0.01% and 10% by weight, more preferably 0.0’i% and 7% by weight, even more preferably between
`0.1% and 5% by weight. {0057] A particularly preferred first embodiment method comprises melting in step (a) a
`magnesium alloy comprissng 3 3-4.3wt°/<i Y. 0.2-1 C‘W‘e/ii Zr. 2.0—2.5wt‘l’o Nd and optionally 03—1 Owt°fa rare earths, and
`adding in step (b) Ni as the corrosion promoting metallic element. it is preferred that in step (2)) Ni is added in an amount of
`between 0 01% and 10% by weight, more preferably between 0.1% by weight and 8% by weight.
`
`iOOSS] This invention also relates to a magnesmm atioy suitable for use as a corrodible downhole article which is
`obtainable by the method described above, [0059; in addition, this invention relates to a magnesium alloy as described
`above for use as a corrodible downhoie article
`
`{0060} This invention also relates to a method of hydraulic fracturing comprising the use of a oorrodible downnole article
`comprieing the magnesium alloy as described above, or a downhoie tool as described above Preferably, the method
`comprises- forming an at least partial seal in a borehole with the corrodible downhoie article The method may then
`comprise removrng the at least partial seal by permitting the corrodible downhole article to corrode, This corrosion can
`occur at a desired rate with certain alloy compositions of the disclosure as discussed above it is preferred that the
`corrodible downhoie article is a tracking ball, plug, packer or tool assembly. The tracking ball is preferably substantially
`spherical in shape. in some embodiments, the tracking ball consists essentially of the magnesium alloy described above.
`
`{0061] This :livention wiii be further described by reference to the followmg Figures which is not intended to limit the scope
`of the :nvention claimed. in which‘
`
`Figure 1 shows a mlcrostiucture of sample DFQQOSD of Example 1.
`
`Figure 2 shows a graph of % loss in proof stress against Ni addition [WW/£2} for the alloys of Examples 3 A, BB and 3C,
`To: the new Georgie Fatents, with machinemlassil‘ied Boogie Scholar results and Japanese and South Korean patonm.
`
`httpsifi’wwwgooglc.comfpatents/WOZO16016628A2?dq=WO+2016/016628&c1:on
`
`12/6/2017
`
`

`

`Patent WO2016016628A2 - Corrodible downhole article - Google Patents
`
`Page 6 of 10
`
`Figure 3 shows a graph of proof stress against l\:i addition i’wt‘B/o) for the alloys of Examples 3 A, SB and 3C. and
`
`Figure 4 shows a graph of corrosion rate against N: addition {wt%) for the alloys of Examples 3 A, SB and BC,
`
`[0062} Examples
`
`[0063} Example 1 — Magnesium Aluminium Alloy
`
`[0064] A base magnesium alloy consisting of the commercial alloy AZBOA which has a typical chemical composition of
`8.5wt% Al, SSW/1% Zn and 0 3wt% 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 root
`
`[0065] 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 3wt% potasstum chloride at a constant temperature of 38“C :11 00F) and
`15wt% potassium chloride aqueous solution at a constant temperature of 93°C (ZOOF)
`
`{0066) The corrosion rates are shown in Table 1 below The samples comprise the standard alloy tie AZBOA without nickel
`added‘i‘ and two samples With different amounts of nickel added Sample lD Nickel Corrosion rate in Corrosion rate in
`concentration 3% KCL at 38°C 15% KCL at 93°C Wt 9:1: (100?, (ZOOF)
`
`twig/cmzlday Mgi‘cml’sday
`
`Standard

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