Slip element for use with a downhole tool and a method of manufacturing same

[0001] This invention relates to a slip element for use in connection with a downhole tool for use in wellbores in oil and gas recovery operations.

[0002] In the drilling or reworking of oil wells, it is often desirable to seal casing, or seal tubing or other pipes in the casing, to isolate a zone in the casing, and, to this end, downhole sealing tools, such as bridge plugs, frac plugs; and packers are utilized. These tools typically employ a slip assembly consisting of a plurality of slip elements mounted on a mandrel, or the like, that are initially retained in close proximity to the mandrel but are forced outwardly away from the mandrel upon the tool being set to engage, or grip, the inner wall of the casing. This locates and secures the tool in the wellbore so that sealing, and other wellbore operations, may be performed.

[0003] Some of these slip elements are made with cast iron so that they will readily grip the inner wall of the casing when expanded. However, these cast iron slip elements are relatively heavy and, as a result, have often been replaced with composite slip elements fabricated, at least in part, of a relatively lightweight plastic material. However, the composite slip elements often cannot properly grip the inner casing wall. Therefore, ceramic inserts, or buttons, have been placed in the composite slip elements to bite into the inner casing wall to assist in the gripping action discussed above. Another advantage of the ceramic inserts is that when the tool is no longer needed, the ceramic inserts are easy to drill or mill out with the slip elements when the tool is to be destructively removed from the wellbore. However, the ceramic inserts tend to chip, especially when they are set in the casing, which can compromise the gripping action of the slip elements.

[0004] Metallic inserts have been used in place of the ceramic inserts since they do not chip. However, when the tool is to be removed from the wellbore, it is often drilled or milled out, and it is often difficult to drill or mill out the metallic inserts.

[0005] Thus, there remains a need in the art for a cost-effective slip assembly that includes inserts that grip the casing wall, yet resist chipping and can easily be drilled or milled out.

[0012] Referring to FIG. 1, the reference numeral 10 refers to a wellbore penetrating a subterranean formation F for the purpose of recovering hydrocarbon fluids from the formation F. To this end, and for the purpose of carrying out a sealing operation to be described, a tool 12 is lowered into the wellbore 10 to a predetermined depth by a string 14, in the form of coiled tubing, jointed tubing, wireline, or the like, that is connected to the upper end of the tool 12. The tool 12 is shown generally in FIG. 1 and will be described in detail later.

[0013] The string 14 extends from a rig 16 that is located above ground and extends over the wellbore 10. The rig 16 is conventional and, as such, includes support structure, a motor driven winch, or the like, and other associated equipment for receiving and supporting the tool 12 and lowering it to a predetermined depth in the wellbore 10 by unwinding the string 14 from the winch.

[0014] The upper portion of the wellbore 10 may be lined with a casing 20 which is cemented in the wellbore 10 by introducing cement 22 in an annulus formed between the inner surface of the wellbore 10 and the outer surface of the casing 20, all in a conventional manner.

[0015] Referring to FIG. 2, the tool 12 can be in the form of a bridge plug, a frac plug, or a packer and, as such, includes an elongated tubular mandrel 30 having several components secured to its outer surface in any conventional manner. These components include a plurality of axially spaced packer elements 32 which are angularly spaced around the circumference of the mandrel 30 and are connected to the mandrel 30 in any conventional manner. A pair of wedges 34 and 36 are mounted on the mandrel 30 in any conventional manner and in an axially spaced relation to the packer elements 32. Assuming the wellbore 10, and therefore the mandrel 30, extend vertically, or substantially vertically, the wedge 34 extends above the packer elements 32 and the wedge 36 extends below the packer elements 32. The inner surfaces of the packer elements 32 and the wedges 34 and 36 are curved to conform to the curvature of the mandrel 30, and the outer surfaces of the wedges 34 and 36 are tapered outwardly in a direction towards the packer elements 32.

[0016] A slip assembly 40 is mounted on the mandrel 30 above the wedge 34 and a slip assembly 42 is mounted on the mandrel 30 below the wedge 36. The slip assemblies 40 and 42 will be described in detail. Other components are provided on the mandrel 30 but will not be described since they form no part of the invention.

[0017] As shown in FIG. 3A, the slip assembly 40 consists of eight spaced, arcuate slip elements 44 angularly spaced around the circumference of the mandrel 30. Each slip element 44 is in the form of a body member having a curved inner surface to conform to the curvature of the mandrel 30 and a lower tapered end portion in engagement with the tapered portion of the wedge 34 (FIG. 2).

[0018] One of the slip elements 44 is shown in FIG. 3B and has two spaced grooves, or notches, 44a and 44b, formed in its outer surface for receiving retaining rings, or the like, to secure the slip element 44 to the mandrel 30. A plurality of buttons, or inserts, 46a, 46b, and 46c are provided in corresponding openings formed in the outer surface of each slip element 44. Each insert 46a, 46b, and 46c is in the form of a solid cylinder, or rod, and is secured in its respective opening in any conventional manner. In the example shown in FIG. 3B, the inserts 46a and 46b are horizontally aligned and horizontally spaced to form a horizontal row extending just above the insert 46c. As better shown in FIG. 3C, an end portion of each insert 46a, 46b, and 46c projects outwardly from the outer surface of the slip element 44 and extends downwardly at a slight angle to the horizontal, or transverse, axis of the slip element 44.

[0019] Each slip element 44 is fabricated from a relatively light and inexpensive material, such as a composite matrix consisting of epoxy resin polymers and a glass fiber reinforcement. The inserts 46a and 46b are fabricated from a material, such as ceramic, that is stronger than the material of the slip elements 44 and is strong enough to enable the inserts 46a and 46b to grip the inner wall of the casing 20 (FIG. 1) when set, yet can be drilled or milled out when it is desired to remove the tool 12 from the wellbore 10.

[0020] The insert 46c consists of a material, such as a metallic ceramic composite, that is stronger than that of the above-mentioned ceramic material forming the inserts 46a and 46b, and is strong enough to enable the insert 46c to grip the inner wall of the casing 20 yet will not be as susceptible to chipping as the inserts 46a and 46b. Thus, the insert 46c absorbs forces and loads on all of the inserts 46a, 46b, and 46c that otherwise would cause the inserts 46a and 46b to chip and thus become dysfunctional. Moreover, the provision of only one insert 46c of a metallic ceramic composite associated with each slip element 44 does not significantly impair the ability of the slip elements 44 to be milled or drilled out when it is desired to remove the tool 12 from the wellbore 10.

[0021] It is understood that the remaining slip elements 44 of the slip assembly 40, as well as all of the slip elements of the slip assembly 42, are identical to the slip element 44 shown in FIGS. 3B and 3C and have inserts that are identical to, and are located in the same manner as, the inserts 46a, 46b, and 46c.

[0022] When the tool 12 is lowered to a predetermined depth in the casing 20 (FIG. 1) for the purpose of establishing a seal with the inner wall of the casing 20, the slip assemblies 40 and 42 are set in a conventional manner so that the inserts 46a, 46b, and 46c of the slip assembly 40, as well as the corresponding inserts of the slip assembly 42, move into engagement with the inner wall of the casing 20 (FIG. 1) to grip the latter wall and secure the tool 12 in the casing 20.

[0023] According to the embodiment of FIGS. 4A–4C, the slip assembly 40 is replaced by a slip assembly 50 and the components shown in FIGS. 1 and 2 are otherwise the same. The slip assembly 50 consists of six spaced, arcuate slip elements 52 angularly spaced around the circumference of the mandrel 30. Each slip element 52 has a curved inner surface to conform to the curvature of the mandrel 30 and a lower tapered end portion that engages the tapered portion of the wedge 34 (FIG. 2).

[0024] One of the slip elements 52 is shown in FIG. 4B and has two spaced grooves, or notches, 52a and 52b formed in its outer surface for receiving retaining rings, or the like, to secure the slip elements 52 to the mandrel 30. A plurality of buttons, or inserts 56a, 56b, 56c, 56d and 56e are provided in corresponding openings formed in the outer surface of each slip element 52, and each insert 56a, 56b, 56c, 56d and 56e is in the form of a solid cylinder, or rod, secured in the respective opening in any conventional, manner. The inserts 56a and 56b are horizontally aligned and horizontally spaced to form a horizontal row extending just above a horizontal row formed by the inserts 56c, 56d, and 56e. As shown in FIG. 4C, each insert 56a, 56b, 56c, 56d, and 56e projects outwardly from the outer surface of the slip element 52 and extends downwardly at a slight angle to the horizontal, or transverse, axis of the slip element 52.

[0025] Each slip element 52 is fabricated from a relatively light and inexpensive material, such as a composite matrix consisting of epoxy resin polymers and a glass fiber reinforcement. The inserts 56a and 56b are fabricated from a material, such as ceramic, that is stronger than the material of the slip elements 52 and is strong enough to enable the inserts 56a and 56b to grip the inner wall of the casing 20 (FIG. 1) when set, yet be drilled or milled out when it is desired to remove the tool 12 from the wellbore 12.

[0026] Each insert 56c, 56d, and 56e consists of a material, such as a metallic ceramic composite, that is stronger than that of the above-mentioned ceramic material forming the inserts 56a and 56b, and is strong enough to enable the inserts 56c, 56d, and 56e to grip the inner wall of the casing 20 yet will not be as susceptible to chipping as the inserts 56a and 56b. Thus, the inserts 56c, 56d, and 56e absorb forces and loads on all of the inserts 56a, 56b, 56c, 56d, and 56e that otherwise would cause the inserts 56a and 56b to chip and thus become dysfunctional. Moreover, the provision of only three inserts 56c, 56d, and 56e of a metallic ceramic composite associated with each slip element 52 does not significantly impair the ability of the slip elements 52 to be milled or drilled out when it is desired to move the tool 12 in the wellbore 10.

[0027] It is understood that the remaining slip elements 52 of the slip assembly 50 are identical to the slip element 52 shown in FIGS. 4B and 4C, and that the lower slip assembly 42 of the previous embodiment can also be replaced by the slip assembly 50.

[0028] When the tool 12 is lowered to a predetermined depth in the casing 20 (FIG. 1) for the purpose of establishing a seal with the inner wall of the casing 20, the slip assemblies 50 are set in a conventional manner so that the inserts 56a, 56b, 56c, 56d, and 56e move into engagement with the inner wall of the casing 20 (FIG. 1) to grip the latter wall and secure the tool 12 in the casing 20. It is understood that the above-mentioned lower slip assembly functions in the same manner.

[0029] 1. The number of slip elements can vary and could be in the form of one continuous ring.

[0030] 2. The shape of the slip elements can vary and, for example, could be conical with or without a flat bottom.

[0031] 3. The slip elements can be made of other materials, such as cast iron.

[0032] 4. The shape and size of the inserts can be varied.

[0033] 5. The number of relatively strong inserts, such as the insert 46c of the embodiment of FIG. 3A–3C, utilized in each slip can be varied based on the time allotted for drilling or milling out the slip elements after use.

[0034] 6. The number of relatively strong inserts, such as the insert 46c of the embodiment of FIG. 3A-3C and/or the number of relatively weak inserts, such as the inserts 46a and 46b of the latter embodiment, can be varied, as well as the ratio of these numbers.

[0035] 7. The particular location and pattern of the inserts in each slip element can be varied.

[0036] 8. The material forming the inserts 46a, 46b, 56a, and 56b is not limited to ceramic and the material forming the inserts 46c and 56c, 56d, and 56e is not limited to a metallic ceramic composite. Rather, these materials can be varied as long as all of the inserts grip the casing wall, as long as the material of the insert 46c is more chip resistant than material of the inserts 46a and 46b; and as long as the material of the inserts 56c, 56d, and 56e is more chip resistant than the material of the inserts 56a and 56b, and as long as all of the inserts 46a, 46b, 46c, 56a, 56b, 56c, 56d, and 56e can be drilled or milled out. For example, the material of the inserts 46c, 56c, 56d, and 56e could be made of steel, cast iron, or of a non-metallic material.

[0037] 9. The slip assemblies 40 and 50 can be used on the same tool.

[0038] 10. Spatial references, such as “upper”, “lower”, “vertical”, “angular”, etc. are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above.

[0039] Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many other modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.