WO2024182379A1

WO2024182379A1 - Hardened grappling elements for retrieving downhole tools, grappling tool, method for manufacturing a grappling element of a grappling tool

Info

Publication number: WO2024182379A1
Application number: PCT/US2024/017460
Authority: WO
Inventors: Michael ROSSING; William Bunker; Jr. Daniel Hernandez
Original assignee: National Oilwell Varco LP
Current assignee: National Oilwell Varco LP
Priority date: 2023-02-27
Filing date: 2024-02-27
Publication date: 2024-09-06
Anticipated expiration: 2025-08-27
Also published as: US20240287862A1

Abstract

An annular grappling element of a grappling tool for retrieving a downhole tool includes a body extending between a first end and a second end longitudinally opposite the first end, the body defining an inner surface extending between the first end and the second end and an outer surface also extending between the first end and the second end, herein one or more engagement members for grappling the downhole tool are formed on one of the inner surface and the outer surface of the body, and wherein the body is formed from a base material having a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%.

Description

HARDENED GRAPPLING ELEMENTS FOR RETRIEVING DOWNHOLE TOOLS, GRAPPLING TOOL, METHOD FOR MANUFACTURING A GRAPPLING ELEMENT OF A GRAPPLING TOOL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of U.S. provisional patent application No. 63/448,429 filed February 27, 2023, entitled “Hardened Grappling Elements for Retrieving Downhole Tools”, which is incorporated herein in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED

RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] In drilling a wellbore into an earthen formation, such as for the recovery of geothermal energy as part of a geothermal system, it is typical practice to connect a drill bit onto the lower end of a drill string formed from a plurality of drill pipe joints connected together end-to-end, and then rotate the drill string so that the drill bit progresses downward into the earth to create a wellbore along a predetermined trajectory. In some instances, as the wellbore is being drilled downhole tools connected to the drillstring or a portion of the drillstring may become lodged or otherwise stuck in the wellbore. In such instances, devices known as grappling or fishing tools may be deployed from the surface to latch onto the stuck downhole tool within the wellbore. With the grappling tool attached to the stuck downhole tool, the grappling tool and the stuck downhole tool may be retrieved to the surface.

SUMMARY

[0004] An embodiment of an annular grappling element of a grappling tool for retrieving a downhole tool comprises a body extending between a first end and a second end longitudinally opposite the first end, the body defining an inner surface extending between the first end and the second end and an outer surface also extending between the first end and the second end, wherein one or more engagement members for grappling the downhole tool are formed on one of the inner surface and the outer surface of the body, and wherein the body is formed from a base material having a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%. In some embodiments, the carbon content of the base material is equal to or less than 0.10 Wt%. In some embodiments, the nickel content of the base material is equal to or greater than 1.0 Wt%. In certain embodiments, the base material has a chromium content of between 0.40 Wt% and 0.70 Wt%. In certain embodiments, the body has a surface hardness equal to or greater than 52 on the Hardness Rockwell C (HRC) scale. In some embodiments, the body has a surface hardness equal to or greater than 58 on the Hardness Rockwell C (HRC) scale. In some embodiments, the one or more engagement members comprises a helically extending wicker. In certain embodiments, the one or more engagement members comprise helically extending wickers. [0005] An embodiment of a grappling tool for retrieving a downhole tool comprises an outer housing comprising a first end, a second end longitudinally opposite the first end, and a central passage defined by an inner surface extending between the first end and the second end, the grappling element of described above received in the central passage of the outer housing and coupled to the inner surface of the outer housing whereby the grappling element is permitted to travel longitudinally through the central passage of the outer housing, and an annular grappling control positioned in the central passage of the outer housing and rotationally locked to both the outer housing and the grappling element. [0006] An embodiment of a method for manufacturing a grappling element of a grappling tool for retrieving a downhole tool comprises (a) machining a base material to form a grappling element, (b) performing a carburization process on the base material to form a carburized material, (c) performing an austenitization process on the carburized material to austenitize the carburized material and form an austenitized material, (d) quenching the austenitized material to form a quenched material, (e) tempering the quenched material to form a tempered material, and (f) performing a cryogenic treatment process on the tempered material to form a cryogenically treated material. In some embodiments, the base material has a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%. In some embodiments, the tempered material has a surface hardness equal to or greater than 52 on the Hardness Rockwell C (HRC) scale. In certain embodiments, the cryogenically treated material has a surface hardness equal to or greater than 58 on the Hardness Rockwell C (HRC) scale. In certain embodiments, (b) comprises contacting a surface of the base material with both carbon and nitrogen whereby both the carbon and the nitrogen are adsorbed into the surface of the base material. In some embodiments, (f) comprises maintaining the tempered material at or below a cryogenic temperature for a predefined time period, wherein the cryogenic temperature is less than zero degrees Celsius. In some embodiments, the base material has a nickel content that is equal to or greater than 1.0 percent by weight (Wt%) and a carbon content that is equal to or less than 0.10 Wt%. [0007] An embodiment of a method for manufacturing a grappling element of a grappling tool for retrieving a downhole tool comprises (a) machining a base material to form a grappling element, wherein the base material has a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%, (b) performing a carburization process on the base material to form a carburized material, (c) performing an austenitization process on the carburized material to austenitize the carburized material and form an austenitized material, (d) quenching the carburized material to form a quenched material, and (e) tempering the quenched material to form a tempered material. In some embodiments, the carbon content of the base material is equal to or less than 0.10 Wt%. In some embodiments, the nickel content of the base material is equal to or greater than 1.0 Wt%. In certain embodiments, the base material has a chromium content of between 0.40 Wt% and 0.70 Wt%. BRIEF DESCRIPTION OF THE DRAWINGS [0008] For a detailed description of disclosed embodiments, reference will now be made to the accompanying drawings in which: [0009] Figures 1-4 are a schematic partial cross-sectional view of an embodiment of a well system in accordance with principles disclosed herein; [0010] Figure 5 is a side cross-sectional view of an embodiment of a grappling tool in accordance with principles disclosed herein; [0011] Figure 6 is a perspective view of an embodiment of a grappling element of the grappling tool of Figure in accordance with principles disclosed herein; [0012] Figure 7 is a side cross-sectional view of the grappling element of Figure 6; [0013] Figure 8 is a perspective view of another embodiment of a grappling element in accordance with principles disclosed herein; [0014] Figure 9 is a partial cross-sectional view of the grappling element of Figure 8; [0015] Figure 10 is a perspective view of another embodiment of a grappling element in accordance with principles disclosed herein; [0016] Figure 11 is a partial cross-sectional view of the grappling element of Figure 10; [0017] Figure 12 is a flowchart of an embodiment of a method for manufacturing a grappling element of a grappling tool; and [0018] Figure 13 is a partial, side cross-sectional view of another embodiment of a grappling element in accordance with principles disclosed herein. DETAILED DESCRIPTION [0019] The following discussion is directed to various embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. [0020] In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to… ." Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection as accomplished via other devices, components, and connections. In addition, as used herein, the terms "axial" and "axially" generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms "radial" and "radially" generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the wellbore and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the wellbore, regardless of the wellbore orientation. [0021] As described above, in some instances during the drilling of subterranean wellbores one or more downhole tools used for drilling the wellbore may become stuck therein such that the stuck downhole tool cannot be retrieved using the drillstring connected therewith. For example, the stuck downhole tool may become inadvertently disconnected from the drillstring while positioned within the wellbore. Alternatively, the stuck downhole tool may become lodged against a sidewall of the wellbore or against an inner surface of a tubular string positioned in the wellbore such as a casing string and the like. In such instances, the maximum tension applicable to the drillstring connected to the stuck downhole tool may be insufficient for dislodging the tool, necessitating the activation of a disconnect or release tool positioned between the stuck downhole tool and the surface whereby the portion of the drillstring extending uphole from the release tool may be retrieved to the surface with the stuck downhole tool remaining in the wellbore. While the above discussion pertains to the drilling phase of creating subterranean wellbores, it may be understood that downhole tools may become stuck within the wellbore during a completion phase (e.g., a packer or other completion tool may become stuck downhole) and a production phase (e.g., a downhole pump or other production tool may become stuck downhole) of the wellbore. [0022] With a downhole tool (be it a drilling, completion, or production tool) stuck in the wellbore, the stuck downhole tool must typically be dislodged and retrieved from the wellbore before the given phase of creating the wellbore (e.g., the drilling, completion, and production phases) may proceed. As described above, stuck downhole tools are typically retrieved using a grappling tool deployed into the wellbore from the surface. Particularly, the grappling tool may be attached to a downhole end of a work string and run into and through the wellbore until the grappling tool is positioned in proximity of the stuck downhole tool (sometimes referred to as “fish”). Positioned proximal the stuck downhole tool, a grappling element of the grappling tool is activated whereby engagement members of the grappling element grapples or latches against the stuck downhole tool thereby coupling the grappling tool to the stuck downhole tool. With the grappling tool secured to the stuck downhole tool, tension may be applied to the uphole end of the workstring at the surface to dislodge the stuck downhole tool from the wellbore whereby the grappling tool and the dislodged downhole tool secured thereto may be retrieved to the surface using the work string. [0023] Generally, the surface hardness of the engagement members of the grappling element of the grappling tool must be greater than the surface hardness of the stuck downhole tool to be engaged by the grappling tool to ensure that the engagement members do not become worn down in response to contact with the downhole tool as the downhole tool is retrieved from the wellbore. Particularly, the premature wearing down of the engagement members of the grappling element may result in the downhole tool becoming inadvertently disconnected from the grappling tool as the grappling tool and downhole tool are retrieved to the surface, necessitating the deployment of a second or additional grappling tool to retrieve the lost downhole tool following retrieval of the first or initial grappling tool from the wellbore. [0024] In addition, the surface hardness of downhole tools may vary depending on their given application. As an example, standard downhole tools such as conventional drill pipe joints, casing joints, etc., typically have a surface hardness approximately less than 50 on the Hardness Rockwell C (HRC) scale. For retrieving standard downhole tools, a grappling element including standard engagement members having a surface hardness slightly greater than the surface hardness of the standard downhole tool may be used. However, hardened downhole tools such as, for example, downhole tools having a corrosion resistant coating may have a surface hardness significantly greater (e.g., a surface hardness in excess of 50 on the HRC scale) than the surface hardness of standard downhole tools. A grappling element including standard engagement members may be insufficient for retrieving hardened downhole tools given that the surface hardness of the standard engagement members may be less than the surface hardness of the hardened downhole tool. [0025] Conventionally, well operators and servicers have addressed this issue by utilizing different types of grappling elements depending on the surface hardness of the downhole tool to be retrieved from the wellbore. For example, a first or standard grappling element may be used for retrieving standard downhole tools while hardened grappling elements may be used for retrieving hardened downhole tools, where the base materials of the standard and hardened grappling elements may vary. For example, standard grappling elements may be formed from a medium low- carbon steel such as American Iron and Steel Institute (AISI) 1000 Series steel while hardened grappling elements may be formed from a relatively harder base material such as alloy steels including, for example, AISI 4000 Series steel. As used herein, the term “base material” is defined as the material comprising an element or member (e.g., the material comprising a grappling element) before being subjected to a hardening treatment or process. In addition to being formed from a harder base material, hardened grappling elements may be subjected to a hardening process to increase the surface hardness of the resulting hardened grappling element. As an example, the base materials of some hardened grappling elements are subjected to a nitriding process whereby nitrogen is diffused into the surface of the base material to increase the surface hardness of the base material. Hardened base materials configured specifically for such nitriding processes are sometimes referred to Nitralloy. [0026] An issue with the conventional approach for retrieving both standard and hardened downhole tools is that the approach forces operators or servicers to stock both standard grappling elements and hardened grappling elements, increasing the amount of inventory and the expenses associated with possessing and operating grappling tools. Additionally, the hardened base materials utilized in hardened grappling elements, such as Nitralloys, can cost substantially more than standard base materials while also requiring expensive heat-treating processes before use. Further, such hardened base materials may be substantially more difficult to machine relative to standard base materials. [0027] Accordingly, embodiments of annular hardened grappling elements of grappling tools for retrieving downhole tools are described herein. Embodiments grappling elements described herein include a body extending between a first end and a second end longitudinally opposite the first end, the body defining an inner surface extending between the first end and the second end and an outer surface also extending between the first end and the second end, where one or more engagement members for grappling the downhole tool are formed on one of the inner surface and the outer surface of the body, and where the body is formed from a base material having a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%. [0028] The base material from which embodiments of grappling elements described herein are formed combines a low carbon content with a high nickel content compared to the base materials from which conventional grappling elements are formed. The low carbon content of the base material provides the base material with sufficient capacity for carbon adsorption such that the base material comprises a carburizing grade material. Additionally, the high nickel content of the base material provides the base material with sufficient strength and surface hardness such that the material may be used to retrieve standard downhole tools when subjected to austenitization and carburization treatment processes without the need of subjecting the material to a cryogenic treatment process. However, the base material may in at least some applications, in addition to the austenitization and carburization treatment processes, be subject to a cryogenic treatment process when it is desired to further elevate the surface hardness of the grappling element formed from the base material. For example, in instances where it is desired to retrieve hardened downhole tools using the grappling element, the grappling element may be further subjected to the cryogenic treatment process whereby the surface hardness of the grappling element is elevated to the point of exceeding the surface hardness of the hardened downhole tool to be retrieved using the grappling element. The flexibility offered by the base material from which the grappling element is formed may minimize the costs associated with manufacturing and storing grappling elements of each type (e.g., grappling elements for retrieving standard downhole tools and grappling elements for retrieving hardened downhole tools). [0029] Referring to Figure 1, an embodiment of a well system 10 is shown. Well system 10 is generally configured for drilling a wellbore 16 in an earthen formation 5. In this exemplary embodiment, well system 10 includes a drilling rig 20 disposed at the surface 7, a drillstring 21 extending downhole from rig 20, a bottomhole assembly (BHA) 30 coupled to the downhole end of drillstring 21, and a drill bit 90 attached to the lower end of BHA 30. In this exemplary embodiment, drillstring 21 comprises a plurality of separate drill pipe joints threadably connected end-to-end as the drillstring 21 is run into the wellbore 16. However, it may be understood that in other embodiments drillstring 21 may instead comprise a string of coiled tubing or other conveyance mechanisms. A surface or mud pump 23 is positioned at the surface 7 and pumps drilling fluid or mud through drillstring 21. Additionally, rig 20 includes a rotary system 24 for imparting torque to an upper end of drillstring 21 to thereby rotate drillstring 21 in wellbore 16. In this exemplary embodiment, rotary system 24 comprises a rotary table located at a rig floor of rig 20; however, in other embodiments, rotary system 24 may comprise other systems for imparting rotary motion to drillstring 21, such as a top drive. [0030] In this exemplary embodiment, a downhole mud motor is provided in BHA 30 for facilitating the drilling of deviated portions of wellbore 16. The downhole mud motor of BHA 30 may include a hydraulic drive or power section coupled to a bearing assembly. In some embodiments, the portion of BHA 30 can include other components, such as drill collars, measurement-while-drilling (MWD) tools, reamers, stabilizers and the like. It may be understood that in other embodiments well system 10 may not include BHA 30 and instead the downhole end of the drillstring 21 may connect directly to the drill bit 90. [0031] In this exemplary embodiment, the downhole mud motor of BHA 30 converts the fluid pressure of the drilling fluid pumped downward through drillstring 21 into rotational torque for driving the rotation of drill bit 90. With force or weight applied to the drill bit 90, also referred to as weight-on-bit (“WOB”), the rotating drill bit 90 engages the earthen formation and proceeds to form wellbore 16 along a predetermined path toward a target zone. The drilling fluid or mud pumped down the drillstring 21 and through BHA 30 passes out of the face of drill bit 90 and back up the annulus formed between drillstring 21 and the wall 19 of wellbore 16. The drilling fluid cools the bit 90, and flushes the cuttings away from the face of bit 90 and carries the cuttings to the surface 7. [0032] As described above, during the creation of wellbore 16 it is possible for downhole tools of well system 10 to become lodged or stuck within the wellbore 16 such that they cannot be removed from the wellbore 16 using drillstring 21. As an example, and referring now to Figures 1-4, as wellbore 16 is being drilled by the BHA 30 of well system 10, the BHA 30 may become stuck or lodged within the wellbore 16 such that the BHA 30 must be retrieved to the surface 7 using a grappling tool. The BHA 30 may become separated from the drillstring 21 once becoming stuck against the sidewall 18 of wellbore 16, or may be released from drillstring 21 using a specialized disconnect or release tool coupled between the BHA 30 and the downhole end of drillstring 21. [0033] With the downhole end of drillstring 21 separated from the stuck BHA 30, the drillstring 21 may be retrieved to the surface and a workstring 50 as shown particularly in Figure 2. Connected to a downhole end of the workstring 50 is a grappling tool 60 for grappling or latching onto stuck downhole tools such as the stuck BHA 30. As shown particularly in Figure 3, the workstring 50 is lowered from the surface 7 until the grappling tool 60 intercepts the uphole end of the BHA 30. In this example, the uphole end of the BHA 30 may be received in an inner passage or receptacle of the grappling tool 60 following interception of the grappling tool 60 with the BHA 30; however, it may be understood that in other embodiments the grappling tool 60 may instead be received within an internal passage or receptacle of BHA 30 following interception of the grappling tool 60 with the BHA 30. [0034] Following the interception of the grappling tool 60 with the uphole end of the BHA 30, the grappling tool 60 may be activated (e.g., via a fluid pressure signal communicated through the workstring 50 from the surface 7) whereby the grappling tool 60 grapples or latches onto the uphole end of BHA 30, thereby coupling or securing the grappling tool 60 to the BHA 30. With grappling tool 60 grappled onto the stuck BHA 30, tension may be applied to the workstring 50 from the surface 7 sufficient to dislodge the stuck BHA 30 from the sidewall 18 of wellbore 16, thereby permitting workstring 50 to be retrieved to the surface 7 along with the grappling tool 60 and BHA 30 secured thereto. Following the removal of the stuck BHA 30, a new drillstring 21 coupled to a new BHA 30 (or a redressed version of the original BHA 30) and run into the wellbore 16 to continue the process of drilling wellbore 16. [0035] While in this example the grappling tool 60 grapples a stuck BHA 30 used to drill the wellbore 16, it may be understood that grappling tool 60 may be used to draft other kinds of stuck downhole tools including tubular strings or joints, liners, packers and other sealing devices, casing shoes, cement plugs, and others. It may also be understood that while this example pertains to a BHA 30 used to drill the wellbore 16, in other examples, grappling tool 60 may be used to retrieve completion tools used for completing the wellbore 16 and/or production tools used for producing hydrocarbons or other desired materials from the wellbore 16. [0036] Referring now to Figure 5, an embodiment of a grappling tool 100 for retrieving stuck downhole tools is shown. Grappling tool 100 may comprise an embodiment of the grappling tool 60 shown in Figures 2-4 and described above; however, it may be understood that grappling tool 100 may be used to retrieve a variety of stuck downhole tools other than BHAs. In this exemplary embodiment, grappling tool 100 has a central or longitudinal axis 105 and generally includes a generally tubular outer housing or sub 102, an annular seal assembly 120, an annular grappling element or grapple 140, and an annular grapple control 180. The outer housing 102 of grappling tool 100 has a first or uphole end 103, a second or downhole end 104 longitudinally opposite uphole end 103, and a central bore or passage 106 extending between the uphole end 103 and downhole end 104. Received within the central passage 106 is the seal assembly 120, the grappling element 140, and the grapple control 180. [0037] In his exemplary embodiment, the downhole end 104 of outer housing 102 defines a guide 108 providing the central passage 106 at the downhole end 104 with a greater inner diameter than the inner diameter of central passage 106 at the uphole end 103 of outer housing 102. Additionally, a generally cylindrical inner surface of outer housing 102 defining central passage 106 includes a bowl 110 which couples the grappling element 140 to the outer housing 102. The bowl 110 may comprise one or more inclined engagement surfaces for engaging or contacting the grappling element 140 to secure the grappling element 140 to the outer housing 102. [0038] The sealing assembly 120 of grappling tool 100 is positioned within the central passage 106 of outer housing 102 and includes an annular sealing element or packer 122 positioned along an inner diameter of the sealing assembly 120. The sealing element 122 of sealing against an outer surface or diameter of a stuck downhole tool to be retrieved using the grappling tool 100. By sealing against the outer diameter of the stuck downhole tool, fluid pressure within the portion of central passage 106 extending between seal assembly 120 and the uphole end 103 of outer housing 102 may be pressurized from the surface (e.g., from the surface 7 via a central passage of the workstring 50) for operating the grappling tool 100. It may be understood that in some embodiments the grappling tool 100 may not include a sealing assembly or device such as the sealing assembly 120 shown in Figure 5. [0039] The grappling element 140 of grappling tool 100 is configured to physically contact and latch onto the downhole tool to be retrieved using the grappling tool 100. In this exemplary embodiment, grappling element 140 is configured to contact and grapple an outer surface or diameter of the stuck downhole tool; however, it may be understood that in other embodiments the grappling tool 100 may comprise a grapping element 140 configured to physically contact and grapple an outer surface or diameter of the stuck downhole tool. For example, in some embodiments, the stuck downhole tool may be receivable in a central bore or passage of the grappling element of grappling tool 100 whereby the grappling element is permitted to latch against the outer surface of the downhole tool. Referring to Figures 5-7, additional views of the grappling element 140 of grappling tool 100 are provided in Figures 6 and 7. As shown particularly in Figures 6 and 7, in this exemplary embodiment, grappling element 140 is generally tubular extending between a first or uphole end 143 and a second or downhole end 145. In this exemplary embodiment, grappling element 140 is a “basket” style grappling element having a body 141 extending between the uphole end 143 and downhole end 145 and defining pair of circumferentially spaced openings 146 that extend longitudinally between the opposing ends 143 and 145 of grappling element 140. Openings 146 provide the grappling element 140 with a C-shape that allows for the contraction and expansion of the inner diameter of grappling element 140 as will be discussed further herein. [0040] One or more inner engagement members (indicated generally in Figures 6 and 7 by arrow 150) are formed on the inner surface 142 of grappling element 140 while one or more outer engagement members 152 are formed on the outer surface 144 of grappling element 140. The inner engagement members 150 extend helically along the inner surface 142 of grappling element 140 such that the inner engagement members 150 define a plurality of helical teeth or wickers on the inner surface 142 of grappling element 140. Inner engagement members 150 may thus also be referred to as wickers 150. Wickers 150 selectably grapple or bite into the outer surface of the downhole tool to be retrieved by the grapple tool 100. The outer engagement members 152 of grappling element 140 comprise inclined or frustoconical outer surfaces defining a profile that matches the profile defined by the bowl 110 of outer housing 102. [0041] In this exemplary embodiment, the downhole end 145 of grappling element 140 comprises a slot or receptacle 154 extending longitudinally therein. The receptacle 154 is configured to receive a corresponding key 182 (shown in Figure 5) of the grapple control 180. Relative rotation between grappling element 140 and grapple control 180 is restricted with key 182 of grapple control 180 received in the receptacle 154 of grappling element 140. Additionally, in this exemplary embodiment, the grapple control 180 is coupled to the outer housing 102 of grappling tool 100 whereby relative rotation is restricted between grapple control 180 and outer housing 102. In this configuration, grappling element 140 is permitted to travel axially within the central passage 106 of outer housing 102 while rotation is restricted between grappling element 140 and the outer housing 102 due to the connection formed between grappling element 140 and grappling control 180. [0042] During operation, as an uphole end of a stuck downhole tool enters the downhole end 145 of grappling element 140, the grappling tool 100 may be rotated from the surface encouraging the uphole end of the downhole tool to enter the grappling element 140 with the inner diameter of the grappling element 140 expanding to accommodate the uphole end of the downhole tool. Expansion of the inner diameter of the grappling element 140 is permitted by relative axial movement between the grappling element 140 and the outer housing 102 and the tapered connection formed between the outer engagement members 152 of grappling element 140 and the bowl 110 of outer housing 102. [0043] With the uphole end of the downhole tool received in the grappling element 140, tension may be applied to the grappling tool 100 from the surface to slide downhole through the central passage 106 of outer housing 102, thereby contracting the inner diameter of the grappling element 140 via the tapered connection formed between grappling element 140 and the bowl 110. The contraction of grappling element 140 causes the wickers 150 of grappling element 140 grapple or bite into the outer surface of the downhole tool, thereby securing the grappling tool 100 to the downhole tool such that the downhole tool may be retrieved to the surface using tension applied to the grappling tool 100 from the surface. When it is desired to release the downhole tool from the grappling tool 100, a sharp downward force may be applied to the grappling tool 100 from the surface, causing the grappling element 140 to slide uphole through the central passage 106 of outer housing 102, thereby unlocking or releasing the wickers 150 of grappling element 140 from the downhole tool such that the grappling tool 100 may be rotated from the surface to essentially unscrew the grappling element 140 from the downhole tool. [0044] It may be understood that the configuration of the grappling element of grappling tool 100 may vary from that shown in Figures 5-7. As an example, and referring now to Figures 8 and 9, another embodiment of an annular grappling element 200 is shown. In this exemplary embodiment, grappling element 200 comprises a “spiral” grappling element having a body 201 that extends helically between a first or uphole end 203 and a second or downhole end 205 opposite the uphole end 203. The spiral shape of grappling element 200 allows for the expansion and contraction of the inner diameter of grappling element 200 to accommodate downhole tools therein. [0045] In this exemplary embodiment, grappling element 200 comprises a tapered helical outer surface 202 extending between ends 203 and 205, and a helical inner surface on which one or more inner engagement members (indicated generally in Figure 8 by arrow 210). The inner engagement members 210 extend helically along the inner surface of grappling element 200 such that, similar to the inner engagement members 150 described above, inner engagement members 210 define a plurality of helical teeth or wickers on the inner surface of grappling element 200. Inner engagement members 210 may thus also be referred to as wickers 210. The wickers 210 selectably grapple or bite into the outer surface of the downhole tool in a manner similar to the wickers 150 of grappling element 140 described above. It may also be understood that the helical outer surface 202 may interlock or engage a bowl of the grappling tool comprising the grappling element 200, such as a bowl similar to the bowl 110 of grappling tool 100. [0046] Additionally, in this exemplary embodiment, the downhole end 205 of grappling element 200 defines a longitudinally extending key 212 receivable in a corresponding receptacle of a grappling control configured for use with the grappling element 200. Particularly, the grappling control may be rotationally locked to an outer housing of a grappling tool comprising grappling element 200 such that the insertion of key 212 into the receptacle of the grappling control may restrict rotation between the grappling element 200 and the outer housing while permitting relative axial movement between grappling element 200 and the outer housing. [0047] Referring now to Figures 10 and 11, another embodiment of an annular grappling element 250 is shown. In this exemplary embodiment, grappling element 250 comprises a “spear” grappling element configured to latch against an inner surface or diameter of a stuck downhole tool. Particularly, grappling element 250 has a body 251 that extends generally cylindrically between a first or uphole end 253 and a second or downhole end 255 opposite the uphole end 253. [0048] Grappling element 250 comprises a generally cylindrical outer surface 252 extending between ends 253 and 255, and a tapered inner surface 254. Additionally, similar to grappling element 140 described above, grappling element 250 has a C- shape or cross-section and includes a plurality of circumferentially spaced openings or reliefs 256 extend longitudinally between the uphole end 253 and downhole end 255 of grappling element 250 to allow for the expansion and contraction of the outer diameter of grappling element 250 to accommodate downhole tools thereon. [0049] In this exemplary embodiment, one or more outer engagement members (indicated generally in Figure 10 by arrow 260). The outer engagement members 260 extend helically along the outer surface 252 of grappling element 250 such that, similar to the inner engagement members 150 described above (with the exception of being positioned on the outer surface 252 rather than the inner surface 254 of grappling element 250), outer engagement members 260 define a plurality of helical teeth or wickers on the outer surface 252 of grappling element 250. Outer engagement members 260 may thus also be referred to as wickers 260. The wickers 260 selectably grapple or bite into the inner surface of the downhole tool. In this exemplary embodiment, one or more inner engagement members 265 are formed on the inner surface 254 of grappling element 250. The inner engagement members 265 of grappling element 250 comprise inclined or frustoconical tapered surfaces defining a tapered profile that matches the tapered profile defined by a bowl of an outer housing comprising the grappling element 250. [0050] Additionally, in this exemplary embodiment, the downhole end 255 of grappling element 250 defines a longitudinally extending key 270 receivable in a corresponding receptacle of a grappling control configured for use with the grappling element 250. Particularly, the grappling control may be rotationally locked to an outer housing of a grappling tool such that the insertion of key 270 into the receptacle of the grappling control may restrict rotation between the grappling element 250 and the outer housing while permitting relative axial movement between grappling element 250 and the outer housing. [0051] Embodiments of grappling elements described herein (e.g., grappling elements 140, 200, and 250) are formed from a base material that has been subjected to a hardening process or treatment. In at least some embodiments, the base material from which the grappling elements comprises steel having a relatively high nickel content but a relatively low carbon content compared to other steel alloys such as AISI 4000 Series steel alloys. Additionally, the base material comprises a carburizing grade steel having a low enough carbon content such that the base material may accept additional carbon as part of a carburizing process. As used herein, the term “carburizing grade steel” refers to steels having a carbon content that is less than 1.0 by weight percentage (Wt%). Thus, carburizing grade steels include carbon steels, at least some low alloy steels, but generally exclude stainless steels. The relatively high nickel content provides the base material with a suitably great initial hardness (prior to any hardening treatment) while having a low enough carbon content to still qualify as a carburizing grade steel. [0052] In some embodiments, the carbon content by Wt% of the base material is equal to or less than 0.20. In some embodiments, the carbon content of the base material is equal to or less than 0.18. In certain embodiments, the carbon content of the base material is equal to or less than 0.12. In certain embodiments, the carbon content of the base material is equal to or less than 0.10. In some embodiments, the nickel content of the base material is equal to or greater than 0.60 Wt%. In some embodiments, the nickel content of the base material is equal to or greater than 1.00 Wt%. In certain embodiments, the nickel content of the base material is equal to or greater than 1.50 Wt%. In certain embodiments, the nickel content of the base material is equal to or greater than 2.00 Wt%. In some embodiments, the carbon content of the base material ranges between approximately 0.12 Wt% and 0.18 wt% while the nickel content of the base material ranges approximately between 0.65 Wt% and 2.00 Wt%. [0053] The base material from which the embodiments of grappling elements disclosed herein (e.g., grappling elements 140, 200, and 250) may, in addition to carbon and nickel, contain chromium. Thus, the base material comprises in at least some embodiments a carbon, nickel, and chromium alloy. It may be understood that the addition of chromium in at least some embodiments may increase the strength, hardenability, and/or toughness of the base material. In some embodiments, the base material has a chromium content ranging approximately between 0.40 Wt% and 0.70 Wt%. In some embodiments, the base material comprises PS55 steel as defined in the Society of Automotive Engineer’s (SAE’s) SAE J1081 (2000) standard; however, it may be understood that materials other than PS55 steel may comprise the base material from which the embodiments of grappling elements described herein are formed. [0054] The base material from which the grappling elements are formed are subjected to a hardening treatment to increase the surface hardness of the base material, thereby forming a treated material which comprises the particular grappling element. For example, in some embodiments, the base material may be machined to define a grappling element (e.g., grappling elements 140, 200, and 250) having one or more engagement members or wickers for grappling a stuck downhole tool. The machined base material may then be subjected to the hardening treatment to form the treated material comprising the grappling element. Alternatively, the hardening treatment may be performed on the base material prior to machining to form or define the grappling element. For example, the base material may be subjected to the hardening treatment to form the treated material, and the treated material may be machined to form the grappling element including the one or more engagement members or wickers for grappling a stuck downhole tool. [0055] Referring to Figure 12, an embodiment of a method 300 for manufacturing a grappling element of a grappling tool is shown. At block 302, method 300 comprises machining a base material to form a grappling element of a grappling tool. In some embodiments, block 302 comprises machining a base material to form one of the grappling elements 140, 200, and 250 described herein. However, it may be understood that block 302, and the other blocks of method 300, may pertain to grappling elements which vary in configuration from the grappling elements 140, 200, and 250 described herein. [0056] At block 304, method 300 comprises performing a carburization process on the base material to form a carburized material. In some embodiments, block 304 comprises bringing the base material into contact with a carbonaceous atmosphere whereby carbon containing gases of the carbonaceous atmosphere are adsorbed into and diffused through the surface of the base material to produce the carburized material having a greater carbon content than the base material. In addition to bringing the base material into contact with the carbonaceous atmosphere, block 304 may comprise heating the base material to a temperature at or above a carburization temperature for a predefined period of time referred to as the carburization incubation period. [0057] Generally, the carburization process performed at block 304 forms an outer hardened or carburized layer comprising the carburized material. For example, referring briefly to Figure13, an embodiment of a grappling element 350 formed from a base material is shown. Particularly, the process steps described at blocks 302, 304 and 304 have been performed to the grappling element 350 whereby grappling element 350 comprises an inner core 352 and an outer hardened or carburized layer 365 formed integrally or monolithically with the inner core 352. The material forming or comprising the outer hardened layer 360 of grappling element 350 comprises carburized material while the material comprising the inner core 352 comprises the base material. Thus, the composition of the carburized material of outer hardened layer 360 is different from the composition of the base material comprising inner core 352. Particularly, the carbon content of the carburized material of outer hardened layer 360 is greater than the carbon content of the base material comprising inner core 352 due to the adsorption of carbon from the carbonaceous atmosphere into the outer hardened layer 360. It may also be understood that the composition of at least some of the base material comprising the inner core 352 is the same as the composition of the base material from which the grappling element 350 was formed. [0058] Outer hardened layer 360 defines an outer or external surface 364 of the grappling element 350 and has a depth (referred to herein as a “case depth”) 365 extending from the outer surface 362 into the grappling element 350. The case depth 365 may be influenced by the composition of the base material of grappling element 350 and by the parameters of the process steps of blocks 302, 304, and 304 such as, for example, the composition of the carbonaceous atmosphere, the magnitude of the carburization temperature, and the duration of the carburization incubation period. [0059] Referring again to Figure 12, in some embodiments, the carburization temperature is greater than the austenitization temperature. However, in other embodiments, the carburization temperature may be less than the austenitization temperature. In certain embodiments, the carburization temperature of the base material ranges approximately between 1,500 °F and 1,800 °F. In certain embodiments, the carburization incubation period ranges approximately between less than an hour (e.g., half an hour) and 48 hours. It may however be understood that the carburization temperature and carburization incubation period of block 304 may vary in other embodiments. For example, the carburization temperature and carburization incubation period of block 304 may depend on the desired diffusion rate and the desired case depth (e.g., case depth 365 shown in Figure 13) for the particular grappling element. For example, the carburization temperature and/or carburization incubation period may vary based on the composition of the base material. [0060] In some embodiments, the carbon containing gases of the carbonaceous atmosphere may also include nitrogen as part of a carbonitriding treatment process whereby nitrogen, in addition to carbon, is adsorbed by and diffuses through the surface of the base material. It may be understood that the carbon containing gases may comprise any gases suitable for the formation of nitrides, borides, and/or carbides in the surface of the base material. [0061] At block 306, method 300 comprises performing an austenitization process on the carburized material of the grappling element to austenitize the carburized material and form an austenitized material. In some embodiments, block 306 comprises heating the carburized material to a temperature equal to or greater than the austenitization temperature of the carburized material to promote the formation and development of austenite in the carburized material to form the austenitized material. The carburized material may be held at or above the austenitization material for a predefined period of time which may be referred to as austenitization incubation period. The austenitization temperature of the carburized material and the austenitization incubation period may vary depending on the composition of the carburized material such as, for example, by the carbon content of the carburized material. In some embodiments, the austenitization temperature of the carburized material ranges approximately between 1,500 degrees Fahrenheit (°F) and 1,800 °F. In some embodiments, the austenitization incubation period may be approximately one hour or more depending on the mass of the component. It may be understood that the austenitization temperature and austenitization incubation period of block 306 may vary in other embodiments. For example, the austenitization temperature and/or austenitization incubation period of block 306 may vary based on the composition of the base material and the mass or size of the component comprising the base material being austenitized. [0062] At block 308, method 300 comprises quenching the carburized material to form a quenched material in which austenite formed in the surface of the carburized material is transformed into martensite due to the elevation of the material’s carbon content during the carburization process. An advantage of the process of carburizing and subsequent quenching is that the process of carburizing and quenching the material increases the surface hardness of the material while leaving the inner core of the material (e.g., the inner cores of the grappling element 140, 200, 250, and 350) relatively soft and ductile. In some embodiments, block 308 comprises submerging the carburized material in a suitable quenching medium for a predefined period of time which may be referred to as the quenching time period. The quenching medium may comprise a liquid such as water, oil, polymer, or other fluids that provide for a desired quenching rate (the rate at which the temperature of the material is reduced as part of the quenching process. The quenching rate of block 308 is suitable for achieving the desired surface hardness without inducing quench cracking in the quenched material. [0063] At block 310, method 300 comprises tempering the quenched material to form a tempered material. In some embodiments, block 310 comprises reheating the quenched material to a temperature at or above a tempering temperature for a predefined period of time which may be referred to as the tempering time period. A tempering temperature may be selected that increases the toughness of the tempered material without resulting in a significant degree of decarburization. Following the tempering time period the material may be allowed to cool to room temperature to complete the tempering process of block 310. In certain embodiments, the tempering temperature ranges approximately between 150 °F and 600 °F, and the tempering time period ranges approximately between less than an hour (e.g., half an hour) and 24 hours; however, it may be understood that the tempering temperature and/or tempering time period may vary in other embodiments. [0064] The process of tempering the quenched material may increase the toughness and ductility of the tempered material while retaining a high surface hardness. In this manner, the quenched material may have greater surface hardness, wear resistance, and tensile strength than the base material. In some embodiments, the surface hardness of the quenched material ranges approximately between 50 and 55 on the HRC scale. In some embodiments, the surface hardness of the quenched material ranges approximately between 51 and 53 on the HRC scale. Additionally, in certain embodiments, the quenched material has a tensile strength equal in excess of 100 kilopounds per square inch (Ksi), and a Charpy value of at least 100; however, it may be understood that these values may vary in other embodiments. [0065] In some applications, block 310 may mark the conclusion of method 300. Particularly, the treatment process comprising blocks 302-310 provide the grappling element (e.g., grappling elements 140, 200, and 250) with physical properties (including surface hardness) sufficient for retrieving standard downhole tools. In other words, a grappling element comprising the quenched material possesses a surface hardness in excess of the surface hardness of standard downhole tools, making the grappling element suitable for retrieving standard downhole tools. However, a grappling element comprising the quenched material produced at block 310 of method 300 may have a surface hardness that is less than the surface hardness of hardened downhole tools, making the grappling element comprising the quenched material potentially unsuitable for retrieving hardened downhole tools. Additionally, it may be understood that in at least some embodiments the composition of the quenched material forming the inner core of the grappling element following block 310 is the same as the composition of the base material. Particularly, in at least some embodiments, the carbon content of the quenched material forming the inner core of the grappling element following block 310 is the same as the carbon content of the base material. [0066] In this exemplary embodiment, method 300 includes the optional additional block 312 that comprises performing a cryogenic treatment process on the tempered material to form a cryogenically treated material. Block 312 of method 300 may be performed if it is desired to manufacture a grappling element suitable (e.g., having a sufficiently great surface hardness) for retrieving hardened downhole tools. The cryogenic treatment process may transform retained austenite of the tempered material into martensite, further hardening the surface of the material. In some embodiments, the fraction of retained austenite of the cryogenically treated material ranges approximately 10% or less as compared to the fraction of retained austenite of the tempered material which ranges approximately between 60% or less in some embodiments. [0067] In some embodiments, block 312 comprises exposing the tempered material to a cryogenic environment so as to cool the material to a cryogenic temperature for a predefined period of time which may be referred to as the cryogenic time period. As used herein, the term “cryogenic temperature” is defined as temperatures equal to or less than 0 °F. In certain embodiments, the specific cryogenic temperature of block 312 ranges approximately between -100 °F and -350 °F, and the cryogenic time period is approximately one hour per inch of thickness of the grappling element; however, it may be understood that the cryogenic temperature and/or cryogenic time period may vary in other embodiments. However, it may be understood that the term “cryogenic temperature” as used herein is defined as temperatures equal to or less than zero degrees Fahrenheit. In some embodiments, exposing the tempered material to a cryogenic environment may comprise contacting the tempered material with a cryogenic medium such as liquid nitrogen, solid carbon dioxide, solid ammonia, liquid hydrogen, and/or other cryogenic materials. [0068] The surface hardness of the cryogenically treated material exceeds the surface hardness of even hardened downhole tools, making grappling elements (e.g., grappling elements 140, 200, and 250) comprising the cryogenically treated material suitable for retrieving hardened downhole tools. In certain embodiments, the surface hardness of the cryogenically treated material ranges approximately between 56 and 65 on the HRC scale. In certain embodiments, the surface hardness of the cryogenically treated material ranges approximately between 58 and 60 on the HRC scale. However, it may be understood that the surface hardness of the cryogenically treated material may vary from the exemplary ranges provided herein. Additionally, it may be understood that in at least some embodiments the composition of the cryogenically treated material forming the inner core of the grappling element following block 312 is the same as the composition of the base material. Particularly, in at least some embodiments, the carbon content of the cryogenically treated material forming the inner core of the grappling element following block 312 is the same as the carbon content of the base material. [0069] As described above, method 300 provides a process for manufacturing grappling elements (e.g., grappling elements 140, 200, and 250) suitable for retrieving standard downhole tools (e.g., a grappling element comprising the tempered material formed at block 310 of method 300) and for manufacturing grappling elements suitable for retrieving hardened downhole tools (e.g., a grappling element comprising the cryogenically treated material formed at block 312) from the same base material rather than separate base materials as is the case with conventional practice. [0070] The ability to manufacture both types of grappling elements from the same base material may reduce the overall cost born by the manufacturer and/or user of the grappling elements associated with manufacturing the grappling elements and inventorying or storing the grappling elements. For instance, instead of manufacturing and storing both a first set of grappling elements formed from a first base material for retrieving standard downhole tools and a second set of grappling elements from a second base material (e.g., a base material more suitable than the first base material for the treatment processes required to increase the surface hardness of the material to a level sufficient for retrieving hardened downhole tools) for retrieving hardened downhole tools, only one set of grappling elements formed from a single base material may be manufactured and stored by the manufacturer and/or operator of the grappling elements. A portion or subset of these grappling elements may subsequently undergo the cryogenic treatment process of block 312 of method 300 as needed or on a batch basis, thereby minimizing the amount of inventory of the grappling elements needed for the purposes of retrieving both standard and hardened downhole tools. [0071] While disclosed embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

CLAIMS What is claimed is: 1. An annular grappling element of a grappling tool for retrieving a downhole tool, the grappling element comprising: a body extending between a first end and a second end longitudinally opposite the first end, the body defining an inner surface extending between the first end and the second end and an outer surface also extending between the first end and the second end; wherein one or more engagement members for grappling the downhole tool are formed on one of the inner surface and the outer surface of the body; and wherein the body is formed from a base material having a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%.

2. The grappling element of claim 1, wherein the carbon content of the base material is equal to or less than 0.10 Wt%.

3. The grappling element of claim 1, wherein the nickel content of the base material is equal to or greater than 1.0 Wt%.

4. The grappling element of claim 1, wherein the base material has a chromium content of between 0.40 Wt% and 0.70 Wt%.

5. The grappling element of claim 1, wherein the body has a surface hardness equal to or greater than 52 on the Hardness Rockwell C (HRC) scale.

6. The grappling element of claim 1, wherein the body has a surface hardness equal to or greater than 58 on the Hardness Rockwell C (HRC) scale.

7. The grappling element of claim 1, wherein the one or more engagement members comprises a helically extending wicker.

8. The grappling element of claim 1, wherein the one or more engagement members comprise helically extending wickers.

9. A grappling tool for retrieving a downhole tool, the grappling tool comprising: an outer housing comprising a first end, a second end longitudinally opposite the first end, and a central passage defined by an inner surface extending between the first end and the second end; the grappling element of claim 1 received in the central passage of the outer housing and coupled to the inner surface of the outer housing whereby the grappling element is permitted to travel longitudinally through the central passage of the outer housing; and an annular grappling control positioned in the central passage of the outer housing and rotationally locked to both the outer housing and the grappling element.

10. A method for manufacturing a grappling element of a grappling tool for retrieving a downhole tool, the method comprising: (a) machining a base material to form a grappling element; (b) performing a carburization process on the base material to form a carburized material; (c) performing an austenitization process on the carburized material to austenitize the carburized material and form an austenitized material; (d) quenching the austenitized material to form a quenched material; (e) tempering the quenched material to form a tempered material; and (f) performing a cryogenic treatment process on the tempered material to form a cryogenically treated material.

11. The method of claim 10, wherein the base material has a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%.

12. The method of claim 10, wherein the tempered material has a surface hardness equal to or greater than 52 on the Hardness Rockwell C (HRC) scale.

13. The method of claim 10, wherein the cryogenically treated material has a surface hardness equal to or greater than 58 on the Hardness Rockwell C (HRC) scale.

14. The method of claim 10, wherein (b) comprises contacting a surface of the base material with both carbon and nitrogen whereby both the carbon and the nitrogen are adsorbed into the surface of the base material.

15. The method of claim 10, wherein (f) comprises maintaining the tempered material at or below a cryogenic temperature for a predefined time period, wherein the cryogenic temperature is less than zero degrees Celsius.

16. The method of claim 10, wherein the base material has a nickel content that is equal to or greater than 1.0 percent by weight (Wt%) and a carbon content that is equal to or less than 0.10 Wt%.

17. A method for manufacturing a grappling element of a grappling tool for retrieving a downhole tool, the method comprising: (a) machining a base material to form a grappling element, wherein the base material has a nickel content that is equal to or greater than 0.60 percent by weight (Wt%) and a carbon content that is equal to or less than 0.20 Wt%; (b) performing a carburization process on the base material to form a carburized material; (c) performing an austenitization process on the carburized material to austenitize the carburized material and form an austenitized material; (d) quenching the carburized material to form a quenched material; and (e) tempering the quenched material to form a tempered material.

18. The method of claim 17, wherein the carbon content of the base material is equal to or less than 0.10 Wt%.

19. The method of claim 17, wherein the nickel content of the base material is equal to or greater than 1.0 Wt%.

20. The method of claim 17, wherein the base material has a chromium content of between 0.40 Wt% and 0.70 Wt%.