HIGH PRESSURE STRIPPING HEADS AND METHODS OF MAKING SAME

Abstract

A stripper element for use with stripping heads includes a one-piece, formed, generally cylindrical elastomer body having a top, a bottom, a central longitudinal through passage defining an inside surface, and an outer surface. The elastomer body includes an upper cylindrical portion and a lower truncated cone portion, the upper cylindrical portion including a cylindrical lip configured to seal against an inside surface of a stripper head. A one-piece, formed, flexible sheet insert (metal, fabric, or combination thereof) is positioned within at least a portion of either the upper cylindrical portion, the lower truncated cone portion, or both of the one-piece, formed, generally cylindrical elastomer body, the one-piece, formed, flexible sheet insert including a plurality of slots or through holes therein. Methods of making the stripper elements.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims domestic priority benefit under 35 U.S.C. § 119 (e) from Applicant's provisional patent application Nos. 63/595,915, filed Nov. 3, 2023, and 63/607,529, filed Dec. 7, 2023, both of which are hereby explicitly incorporated herein by reference.

BACKGROUND INFORMATION

Technical Field

The present disclosure relates to apparatus and methods in the onshore and marine (offshore) hydrocarbon exploration, production, drilling, well completion, well intervention, and leak containment fields. More particularly, the present disclosure relates to high pressure stripping heads.

Background Art

A “stripping head” (or “stripper head”) is a device consisting of a gland and packing arrangement bolted to a wellhead. Stripping heads include a rubber “stripper element” surrounding drill pipe or tubing that removes mud as the pipe is brought out of the hole, and also serves as the pressure-sealing element. Stripping heads are used to seal annular space between tubing and casing to prevent a well, usually a hydrocarbon producing well, from flowing uncontrollably. Industry standards require having a stripping head for every string of pipe in the hole on every rig that is working.

Key rating metrics of stripper heads are the pressure rating and the longevity of the stripper element. In some stripping heads the stripper element rotates with the kelly or drillpipe and lubricant is used, and in others the stripper element is stationary and the kelly or drillpipe rotates within the stripper element and contacts an inner surface of the element. In both, the rubber material longevity decreases the more the drillpipe rotates and/or moves axially.

The pressure rating of known stripping heads varies but typically ranges from about 2400 to about 3500 psi. A need in the art has arisen for stripping elements having significantly longer life than presently available. It is our personal and professional experience that well service companies that drill out frac plugs need more pressure capability than stripper heads rated at 2400 psi.

U.S. Pat. Nos. 10,914,130 and 11,530,593 (Mueller et al.) disclose stripper head assemblies that can hold higher pressures, but are complicated in design, in use, and in maintenance. The disclosed stripper heads include a stripper head, a stripper insert, a stripper rubber, and one or more retention pins. The retention pins hold the stripper insert and stripper rubber within the stripper head. In certain embodiments, the insert includes a plurality of cylindrical stalks that nest into the stripper rubber.

As may be seen, current practice of installing, using, removing, and maintaining known stripping heads may not be adequate for all circumstances. There remains a need for more robust stripping head designs, particularly for more robust stripper elements. The apparatus and methods of the present disclosure are directed to these needs.

SUMMARY

In accordance with the present disclosure, improved stripper elements and stripping heads including same are described, as well as and methods of making the stripper elements and assembling the stripping heads and using same, which reduce or overcome many of the faults of previously known stripper elements, stripper heads, and methods. In particular, we have designed uniquely flexible skeletons positioned within a portion of the rubber to reduce or prevent destruction of the element while rotating and traveling tubing connections under pressure.

A first aspect of the disclosure is a stripper element for use with stripping heads comprising:

• • a) a one-piece, formed, generally cylindrical elastomer body having a top, a bottom, a central longitudinal through passage defining an inside surface, and an outer surface, the generally cylindrical elastomer body comprising an upper cylindrical portion and a lower truncated cone portion, the upper cylindrical portion including a cylindrical lip configured to seal against an inside surface of a stripper head; and
  • b) a one-piece, formed, flexible sheet insert (metal, fabric (Kevlar), or combination thereof) positioned within at least a portion of either the upper cylindrical portion, the lower truncated cone portion, or both of the generally cylindrical elastomer body, the one-piece, formed, flexible sheet insert including a plurality of slots or through holes therein.

In certain embodiments, the one-piece, formed, generally cylindrical elastomer body may comprise one or more natural elastomers, one or more synthetic elastomers, or combinations and mixtures thereof, for example, but not limited to, natural rubber (NR) otherwise known as isoprene, styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile rubber (otherwise known as NBR rubber and Buna-N), hydrogenated nitrile (HNBR), neoprene (CR), ethylene propylene diene monomer (EPDM) rubber, fluoroelastomers, and polyurethanes (AU).

In certain embodiments the one-piece, formed, flexible sheet insert (metal, fabric, or combination thereof) insert may comprise a sheet of metal, fabric, or layered combination thereof having one or more formed slots, round holes, or other shaped through passages therethrough. As used herein the phrase “positioned within” when referring to the flexible sheet insert means that the flexible sheet insert is molded into or otherwise surrounded by the elastomer forming the body of the stripper element. In certain embodiments, the one-piece, formed, flexible sheet insert may be a cylindrical metal ring such as a cylindrical steel ring, where one edge of the ring is welded or brazed to a stripper head insert, which is essentially a steel disk, as described herein.

In certain embodiments the one-piece, formed, flexible sheet insert may be expanded metal sheet. In certain embodiments the one-piece, formed, flexible sheet insert may be stainless steel sheet. In certain embodiments the stainless steel may be type 304. Certain embodiments may have a minimum tensile strength of 515 MPa, a minimum yield strength at 0.2% of 205 MPa, a minimum elongation (% in 50 mm) of 40, a maximum Rockwell B hardness of 92, and a maximum Brinell hardness of 201, all in accordance with ASTM A240/A240M.

Another aspect of the disclosure is a combination stripper element and stripping head body, sometimes referred to herein as a stripping assembly, where the stripping head body is configured for connecting to a drillpipe or other tubular or tool. The connections may be threaded, flanged, or clamped. In certain embodiments the stripper head connections may be Hydril PH6 connections, having an external seal/torque shoulder, an intermediate torque shoulder, and an internal seal.

In certain embodiments the central longitudinal through passage may have an initial diameter smaller than the tubing around which the one-piece, formed, generally cylindrical elastomer body is to seal. Tubing around which the central longitudinal through passage of the one-piece, formed, generally cylindrical elastomer body is to seal may have external diameter selected from 2⅜ inch, 2⅝ inch, 2⅞ inch, and 3½ inch. In certain embodiments, if the external diameter of the tubing is 2⅜ inch, the initial diameter of the central longitudinal through passage may range from about 1.35 to about 1.41 inch. This may be expressed as a “squeeze factor” ranging from about 0.56 to about 0.59. The diameter of the central longitudinal through passage may expand from its initial diameter to the external diameter of the tubing, and any tubing coupling that passes through the central longitudinal through passage. Similar squeeze factors and diameters of the central longitudinal through passage are specified for the other tubing sizes.

In addition to the features already mentioned, stripping head bodies may further comprise a combination of metallurgy and structural reinforcement such as to prevent failure of the stripping head upon exposure to inner pressure up to 1,000 psia, or up to 1,500 psia, or up to 2,000 psia, or up to 2,500 psia, or up to 3,000 psia, or up to 4,000 psi or higher, such as may be experienced during frac plug drilling operations.

Another aspect of the disclosure is a method of making stripper elements of the present disclosure, comprising:

• • a) providing a mold for forming a one-piece, formed, generally cylindrical elastomer body (2) having a top (4), a bottom (6), a central longitudinal through passage (8) defining an inside surface (10), and an outer surface (12), the one-piece, formed, generally cylindrical elastomer body (2) comprising an upper cylindrical portion (14) and a lower truncated cone portion (16), the upper cylindrical portion (14) including a cylindrical lip (18) configured to seal against an inside surface (33) of a stripper head body (32);
  • b) selecting an elastomer;
  • c) selecting a one-piece, formed, flexible insert (22) as described herein;
  • d) positioning the one-piece, formed, flexible insert (22) within the mold;
  • e) filling the mold with an elastomer so that the one-piece, formed, flexible insert (22) is surrounded by the elastomer;
  • f) heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (2); and
  • g) cooling the mold and the elastomer.

Alternatively, another method of making stripper elements of the present disclosure comprises:

• • a) providing a mold for forming a one-piece, formed, generally cylindrical elastomer body (2) having a top (4), a bottom (6), a central longitudinal through passage (8) defining an inside surface (10), and an outer surface (12), the one-piece, formed, generally cylindrical elastomer body (2) comprising an upper cylindrical portion (14) and a lower truncated cone portion (16), the upper cylindrical portion (14) including a cylindrical lip (18) configured to seal against an inside surface (33) of a stripper head body (32);
  • b) selecting an elastomer;
  • c) selecting a one-piece, formed, flexible insert (22) as described herein formed into a cylindrical metal ring;
  • d) welding or brazing an edge of the cylindrical ring to a stripper head insert formed as a steel disk;
  • e) positioning the cylindrical metal ring within the mold;
  • f) filling the mold with an elastomer so that the one-piece, formed, flexible insert (22) is surrounded by the elastomer;
  • g) heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (2); and
  • h) cooling the mold and the elastomer.

An important feature of the apparatus and methods disclosed herein is the modularity, that is, the stripper head may quickly and easily be disassembled, the installed one-piece, formed, stripper element removed, and another stripper element of same or different composition installed, if the original stripper element becomes worn, cracks or otherwise becomes unusable. Another important feature of the apparatus and methods disclosed herein is the one-piece, formed, flexible sheet insert feature of the stripper elements, allowing longer life. We have experience that in certain applications the stripper elements last up to 3 or 4 times longer than the same rubber elements without the one-piece, formed, flexible sheet insert. Moreover, the stripper elements of the present disclosure may be used with multiple stripping heads.

These and other features of the apparatus and methods of the disclosure will become more apparent upon review of the brief description of the drawings, the detailed description, and the claims that follow. It should be understood that wherever the term “comprising” is used herein, other embodiments where the term “comprising” is substituted with “consisting essentially of” are explicitly disclosed herein. It should be further understood that wherever the term “comprising” is used herein, other embodiments where the term “comprising” is substituted with “consisting of” are explicitly disclosed herein. Moreover, the use of negative limitations is specifically contemplated; for example, certain stripper elements, stripper head bodies, stripper head assemblies and combinations, and methods may comprise a number of physical components and features but may be devoid of certain optional hardware and/or other features.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner in which the objectives of this disclosure and other desirable characteristics can be obtained is explained in the following description and attached drawings in which:

FIGS. 1 and 2 are schematic perspective views of two stripper elements in accordance with the present disclosure;

FIG. 3 is a schematic cross-sectional view of the stripper element illustrated schematically in FIG. 1, and FIGS. 3A and 3B are schematic illustrations of two further embodiments of stripper elements;

FIGS. 4 and 5 are schematic perspective views of a stripper assembly illustrated schematically in FIG. 4 in open mode and closed mode in FIG. 5;

FIGS. 6 and 7 are schematic top and cross-sectional views of the stripper assembly schematically illustrated in FIGS. 4 and 5;

FIGS. 8, 9, and 10 are schematical top, cross-sectional, and detail views of the stripper head illustrated in FIGS. 4-7;

FIGS. 11A, 11B, 11C, 11D, 11E, 11F, 11G, 11H, 11I, 11J, 11K, 11L, 11M. 11N, 110, 11P, 11Q, 11R, and 11S are schematic plan views of 19 embodiments of one-piece, formed flexible sheet inserts useful in the stripper elements and stripper assemblies in accordance with the present disclosure;

FIG. 12 is a schematical perspective view of one embodiment of a tubular sheet useful in certain embodiments of the present disclosure; and

FIGS. 13 and 14 are a logic diagrams of two non-limiting methods of making a stripper element of the present disclosure.

It is to be noted, however, that the appended drawings of FIGS. 1-12 may not be to scale and illustrate only typical apparatus embodiments of this disclosure. Furthermore, FIGS. 13 and 14 illustrate only two of many possible methods of this disclosure. Therefore, the drawing figures are not to be considered limiting in scope, for the disclosure may admit to other equally effective embodiments.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to provide an understanding of the disclosed apparatus, combinations, and methods. However, it will be understood by those skilled in the art that the apparatus, combinations, and methods disclosed herein may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. All published patent applications and patents referenced herein are hereby explicitly incorporated herein by reference, irrespective of the page, paragraph, or section in which they are referenced. As used herein, “ASTM” refers to ASTM International, West Conshohocken, Pennsylvania (U.S.A.), formerly known as American Society for Testing Materials.

The primary features of the apparatus, combinations, and methods of the present disclosure will now be described with reference to the drawing figures, after which some of the construction and operational details, some of which are optional, will be further explained. The same reference numerals are used throughout to denote the same items in the figures.

One aspect the present disclosure are stripper elements. Referring to FIGS. 1, 2, and 3, stripper element embodiments 100 and 200 of the present disclosure comprise a one-piece, formed, generally cylindrical elastomer body 2 having a top 4, a bottom 6, a central longitudinal through passage 8 defining an inside surface 10, and an outer surface 12. The one-piece, formed, generally cylindrical elastomer body 2 comprises an upper cylindrical portion 14 and a lower truncated cone portion 16 having a cylindrical lip 18 configured to seal against an inside surface 33 of a stripper head body 32.

As best illustrated schematically in FIG. 3, stripper elements such as embodiments 100 and 200 of the present disclosure feature a one-piece, formed, flexible sheet insert 22, which may comprise metal, fabric (for example Kevlar), or combination thereof) positioned within at least a portion of either the upper cylindrical portion 14, the lower truncated cone portion 16, or both of the one-piece, formed, generally cylindrical elastomer body 2. That is, the elastomer surrounds the flexible sheet insert 22. Some examples of metal sheet that may be used are schematically illustrated in FIGS. 11A, 11B, 11C, 11D, 11E, 11F, 11G, 11H, 11I, 11J, 11K, 11L, 11M. 11N, 110, 11P, 11Q, 11R, and 11S, discussed herein. If the flexible metal sheet is or comprises metal, the metal may be steel, including stainless steels (for example, but not limited to type 304), or steel alloy. Stripper element body 2 may have a cone-shaped top portion 11 and a cone-shaped bottom portion 13. Cone-shaped top portion 11 may have a cone angle “θ” ranging from about 30 to about 60 degrees. Cone-shaped bottom portion 13 may have a cone angle “ρ” ranging from about 30 to about 60 degrees. Angles θ and ρ may be the same or different.

As schematically illustrated in FIG. 11A, flexible sheet insert 22 may include a plurality of slots 24 in certain embodiments (see FIGS. 11G, 11H, 11I, 11J, and 11S). In certain other embodiments, flexible sheet insert 22 may include a plurality of through holes 26 (see FIGS. 11A, 11B, 11C, 11D, 11E, 11F as well as FIGS. 11K, 11L, 11M, 11N, 11O, 11P, 11Q, 11R, and 11S. The embodiment illustrated in FIG. 11S includes both through slots 24 and through holes 26. As indicated in the various figures, through holes may be circular or non-circular, and may be arranged in straight pattern (FIG. 11A) or in staggered pattern (FIGS. 11B and 11C), or even in diagonal pattern (FIG. 11F). Non-limiting examples of non-circular through holes are square (illustrated schematically in FIGS. 11D-F); triangular (FIGS. 11K and 11L); diamond (FIGS. 11M and 11N); hexagonal (FIG. 11O); star (FIG. 11P); oval (FIG. 11Q); and chevron or heart (FIG. 11R). Moreover, through slots 24 may have round ends or square ends, or indeed other shapes. FIG. 12 illustrates schematically a flexible sheet insert formed into a tubular shape having a length “l”, a diameter “d”, and the flexible sheet having a thickness “t”.

In certain embodiments the flexible metal sheet insert may have a minimum tensile strength of 515 MPa, a minimum yield strength at 0.2% of 205 MPa, a minimum elongation (% in 50 mm) of 40, a maximum Rockwell B hardness of 92, and a maximum Brinell hardness of 201, all in accordance with ASTM A240/A240M.

Referring now to FIG. 3A and FIG. 3B, FIG. 3A illustrates schematically another stripper element embodiment 110, having a cylindrical metal ring 23 (in most cases a low-carbon steel, such as 316 stainless steel) having a plurality of through holes 26 therein. In embodiment 110, cylindrical metal ring 23 has an edge 23A that is welded, brazed, friction fitted, or otherwise affixed to a portion 30A of a surface of a stripper insert 30, and adjacent a lip 27 of stripper insert 30. Cylindrical metal ring 25 extends generally parallel to a longitudinal axis LA. FIG. 3B illustrates schematically another embodiment 120, where cylindrical metal ring 30 of embodiment 110 is replaced with a cylindrical metal ring 25 having a lower edge 25A that is welded, brazed, friction fitted, or otherwise affixed to a portion 30A of a surface of stripper insert 30, and adjacent a lip 27 of stripper insert 30. Cylindrical metal ring 25 further has an extension 25B generally parallel to a longitudinal axis LA, and a plurality of through slots 24 in extension 25B having rounded lower corners 24A and open rectangular ends 24B.

Referring now to FIGS. 4-10, stripper head assemblies of the present disclosure comprise a stripper head insert 30, which is essentially a steel disk, a stripper head body 32 also of steel, and a steel hinged clamp 34 configured to clamp the stripper head insert 30 and stripper element body 2 securely into stripper head body 32, whereby the mating cylindrical lip 36 fits into a groove 35, and a swing bolt 38 fits into a main clamp groove 40. A series of bolt holes 42 in a flange 44 accept bolts (not shown) to secure the stripper head assembly to a wellhead.

As illustrated schematically in FIG. 7, stripper head 32 includes an inside surface 33 having diameter 50, where diameter 50 typically ranges from about 6 to about 8 inches. Dashed lines indicate the normal, relaxed, or initial dimensions of elastomeric stripper element body 2 prior to being “squeezed” by tubing 54 and tubing coupling 56. Initial diameter 52 of central through passage 8 of the elastomeric stripper element is much smaller initially than diameter 58 of tubing or the diameter of tubing coupling 56, but as explained herein the element is squeezed so that it contacts tubing 54 and tubing coupling 56 tightly. A chevron seal 60 may be employed, as illustrated in more detail in FIGS. 9 and 10.

FIG. 7 illustrates schematically stripper elements of the present disclosure feature a one-piece, formed, flexible sheet insert 22 positioned within at least a portion of the upper cylindrical portion 14. FIG. 7 also illustrates schematically a cylindrical metal ring 23 welded to an underside of stripper head insert 30. Either one or both of flexible sheet insert 22 and/or cylindrical metal ring 23 may be present, depending on the embodiment. As mentioned previously, cylindrical metal ring 23 is welded or brazed to the underside of stripper head insert 30 before the integrated piece is inserted into a molding machine for forming the one-piece, formed, generally cylindrical elastomer body 2. In certain embodiments, the surface to which the cylindrical metal ring is welded or brazed to is roughened up to provide a stronger bond to the elastomer body 2

Dimensions

Table 1 provides possible broad and arrow ranges of several dimensions mentioned herein for the flexible screen insert.

TABLE 1
Dimensions for flexible screen inserts
	Broad range (millimeters	Less broad range
	unless otherwise	(millimeters unless
Screen Feature	specified)	otherwise specified)
t, thickness	0.4-5	1-3
D, diameter of through	1-25	5-15
holes
C1, spacing of through	2-34	12-18
holes in horizontal
direction
C2, spacing of through	2-34	12-18
holes in vertical direction
β, pitch angle	30-90	degrees	45-60	degrees
l, length of screen insert	3-30	cm	10-20	cm
(tube or sheet)
d, diameter of tubular	50-200	60-90
screen insert
L, length of slot through	10-100	20-50
holes
W, width of slot through	0.1W-0.8W	0.2W-0.3W
holes

Stripper head body 32 is a one-piece, formed, cylindrical, metallic component with no welds, brazing or components welded or brazed thereto. This eliminates the need for pull testing (tensile testing) in offshore applications. In certain embodiments the stripper head body 32 includes one or more lifting features 39 formed therein (FIG. 5) configured to accept one or more manipulator cables or chains (not illustrated), the one or more formed lifting features (for example lifting eyes) positioned such that when the stripper head assembly is lifted by the rig hoist using cables, chains, and like manipulators, it is easily moved over, aligned with, and connected with a working drillpipe or wellhead while minimizing possibility of slipping off the cables or chains. Severe injury to rig workers is thereby avoided, or at least the possibility greatly reduced, compared with previous designs.

FIGS. 4, 6, 8, and 9 illustrate schematically another feature of stripper assemblies of the present disclosure, the provision of an NPT outlet, 70. Outlet 70 may be positioned at an angle “a” ranging from about 40 to about 50 degrees offset from a centerline of the clamp, as best illustrated in FIG. 6.

It will be appreciated that more or less (or other shaped) slots 24 or holes 26 than illustrated in the various figures herein may be provided. It is not necessary that slots 24 be the same length or shape in any flexible screen insert embodiment; however, in order to provide the best weight balance, and therefore best wear performance, it is preferred that slots 24 be a substantial mirror image of each other, with slots 24 of substantially equal dimensions and shape, likewise for holes 26.

FIG. 13 is a logic diagram of a method embodiment 400 of making a stripper element of the present disclosure (Box 402). A first step of method embodiment 400 comprises providing a mold for forming a one-piece, formed, generally cylindrical elastomer body having a top, a bottom, a central longitudinal through passage defining an inside surface, and an outer surface, the generally cylindrical elastomer body comprising an upper cylindrical portion and a lower truncated cone portion, the upper cylindrical portion including a skirt defining a downward facing annulus configured to accept a mating cylindrical lip of a stripper head insert (Box 404); selecting an elastomer (Box 406); selecting a one-piece, formed, flexible insert as described herein (Box 408); positioning the one-piece, formed, flexible insert within the mold (Box 410); filling the mold with an elastomer so that the one-piece, formed, flexible insert is surrounded by the elastomer (Box 412); heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (Box 414); and cooling the mold and the elastomer (Box 416).

FIG. 14 is a logic diagram of another method embodiment 500 of making a stripper element of the present disclosure (Box 502). A first step of method embodiment 500 comprises providing a mold for forming a one-piece, formed, generally cylindrical elastomer body having a top, a bottom, a central longitudinal through passage defining an inside surface, and an outer surface, the generally cylindrical elastomer body comprising an upper cylindrical portion and a lower truncated cone portion, the upper cylindrical portion including a skirt defining a downward facing annulus configured to accept a mating cylindrical lip of a stripper head insert (Box 504); selecting an elastomer (Box 506); selecting a one-piece, formed, flexible insert as described herein formed into a cylindrical metal ring (Box 508; welding or brazing an edge of the cylindrical ring to a stripper head insert formed as a steel disk (Box 510); positioning the cylindrical metal ring within the mold as described herein (Box 512); filling the mold with an elastomer so that the one-piece, formed, flexible insert is surrounded by the elastomer, except for the edge welded to the stripper head insert (Box 514); heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (Box 516); and cooling the mold and the elastomer (Box 518).

Thus the apparatus, combinations, and methods described herein provide long lasting stripper elements, and stripping assemblies having few moving parts.

From the foregoing detailed description of specific embodiments, it should be apparent that patentable apparatus, combinations, and methods have been described. Although specific embodiments of the disclosure have been described herein in some detail, this has been done solely for the purposes of describing various features and aspects of the apparatus, combinations, and methods, and is not intended to be limiting with respect to their scope. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the described embodiments without departing from the scope of the appended claims.

Claims

1. A stripper element for use with stripping heads comprising:

a) a one-piece, formed, generally cylindrical elastomer body (2) having a top (4), a bottom (6), a central longitudinal through passage (8) defining an inside surface (10), and an outer surface (12), the one-piece, formed, generally cylindrical elastomer body (2) comprising an upper cylindrical portion (14) and a lower truncated cone portion (16), the upper cylindrical portion (14) including a cylindrical lip (18) configured to seal against an inside surface (33) of a stripper head (32); and

b) a one-piece, formed, flexible sheet insert (22) (metal, fabric (Kevlar), or combination thereof) positioned within at least a portion of either the upper cylindrical portion (14), the lower truncated cone portion (16), or both of the one-piece, formed, generally cylindrical elastomer body (2), the one-piece, formed, flexible sheet insert (22) including a plurality of slots (24) or through holes (26) therein.

2. The stripper element of claim 1, wherein the one-piece, formed, generally cylindrical elastomer body comprises one or more natural elastomers, one or more synthetic elastomers, or combinations and mixtures thereof.

3. The stripper element of claim 2, wherein the one-piece, formed, generally cylindrical elastomer body comprises natural rubber (NR).

4. The stripper element of claim 2, wherein the one-piece, formed, generally cylindrical elastomer body comprises a synthetic rubber selected from styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile rubber (otherwise known as NBR rubber and Buna-N), hydrogenated nitrile (HNBR), neoprene (CR), ethylene propylene diene monomer (EPDM) rubber, fluoroelastomers, polyurethanes (AU), and combinations, mixtures, and layered versions thereof.

5. The stripper element of claim 1, wherein the one-piece, formed, flexible sheet insert comprises a sheet of metal, fabric, or layered combination thereof.

6. The stripper element of claim 1, wherein the one-piece, formed, flexible sheet insert is molded into or otherwise surrounded by the elastomer forming the body of the stripper element.

7. The stripper element of claim 1, wherein the one-piece, formed, flexible sheet insert is expanded metal sheet.

8. The stripper element of claim 1, wherein the one-piece, formed, flexible sheet insert is stainless steel sheet. In certain embodiments the stainless steel may be type 304. Certain embodiments may have a minimum tensile strength of 515 MPa, a minimum yield strength at 0.2% of 205 MPa, a minimum elongation (% in 50 mm) of 40, a maximum Rockwell B hardness of 92, and a maximum Brinell hardness of 201, all in accordance with ASTM A240/A240M.

9. The stripper element of claim 1, wherein the plurality of slots or through holes in the one-piece, formed, flexible sheet insert are a plurality of round through passages therethrough.

10. A stripping assembly comprising a stripper head insert (30) and the stripper element of claim 1 inserted into a stripper head body (32), the stripping assembly further comprising a hinged clamp (34) configured to clamp the stripper head insert (30) and stripper element body (2) into the stripper head body (32), whereby the mating cylindrical lip (36) fits into a main clamp groove (35), and a swing bolt (38) fits into a clamp groove (40).

11. The stripping assembly of claim 10 wherein the stripper head body (32) is configured to connect to a drillpipe or other tubular or tool through a chevron seal (60).

12. The stripping assembly of claim 10 wherein the stripper head (32) further comprises an NPT outlet (70).

13. The stripping assembly of claim 11 wherein the stripper head body connections comprise Hydril PH6 connections, having an external seal/torque shoulder, an intermediate torque shoulder, and an internal seal.

14. The stripping assembly of claim 10 wherein the central longitudinal through passage of the one-piece, formed, generally cylindrical elastomer body has an initial diameter that is from about 0.56 to about 0.59 times an external diameter of a tubing selected from 2⅜ inch, 2⅝ inch, 2⅞ inch, and 3½ inch.

15. The stripping assembly of claim 11 wherein the stripper head body further comprises a combination of metallurgy and structural reinforcement such as to prevent failure of the stripping head upon exposure to inner pressure up to 1,000 psia, or up to 1,500 psia, or up to 2,000 psia, or up to 2,500 psia, or up to 3,000 psia, or up to 4,000 psi or higher, such as may be experienced during frac plug drilling operations.

16. A method of making a stripper element, comprising:

a) providing a mold for forming a one-piece, formed, generally cylindrical elastomer body (2) having a top (4), a bottom (6), a central longitudinal through passage (8) defining an inside surface (10), and an outer surface (12), the one-piece, formed, generally cylindrical elastomer body (2) comprising an upper cylindrical portion (14) and a lower truncated cone portion (16), the upper cylindrical portion (14) including a cylindrical lip (18) configured to seal against an inside surface (33) of a stripper head body (32);

b) selecting an elastomer;

c) selecting a one-piece, formed, flexible insert (22) including a plurality of slots (24) or a plurality of through holes (26) therein;

d) positioning the one-piece, formed, flexible insert (22) within the mold;

e) filling the mold with an elastomer so that that the one-piece, formed, flexible insert (22) is surrounded by the elastomer;

f) heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (2); and

g) cooling the mold and the elastomer.

17. The method of claim 16 comprising selecting the plurality of through holes from hole shapes selected from circular and non-circular, and selecting the plurality of slots from slot shapes selected from rounded ends and non-rounded ends.

18. The method of claim 16 comprising selecting the elastomer from one or more natural elastomers, one or more synthetic elastomers, or combinations and mixtures thereof.

19. The method of claim 18 comprising selecting the elastomer from styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile rubber (otherwise known as NBR rubber and Buna-N), hydrogenated nitrile (HNBR), neoprene (CR), ethylene propylene diene monomer (EPDM) rubber, fluoroelastomers, polyurethanes (AU), and combinations, mixtures, and layered versions thereof.

20. A method of making a stripper element, comprising:

a) providing a mold for forming a one-piece, formed, generally cylindrical elastomer body (2) having a top (4), a bottom (6), a central longitudinal through passage (8) defining an inside surface (10), and an outer surface (12), the one-piece, formed, generally cylindrical elastomer body (2) comprising an upper cylindrical portion (14) and a lower truncated cone portion (16), the upper cylindrical portion (14) including a cylindrical lip (18) configured to seal against an inside surface (33) of a stripper head body (32);

b) selecting an elastomer;

c) selecting a one-piece, formed, flexible insert (22) as described herein formed into a cylindrical metal ring;

d) welding or brazing an edge of the cylindrical ring to a stripper head insert formed as a steel disk;

e) positioning the cylindrical metal ring within the mold;

f) filling the mold with an elastomer so that the one-piece, formed, flexible insert (22) is surrounded by the elastomer;

g) heating the mold and the elastomer to temperature sufficient to cause the elastomer to flow and form the one-piece, formed, generally cylindrical elastomer body (2); and

h) cooling the mold and the elastomer.