US20090038790A1 - Downhole tool with slip elements having a friction surface - Google Patents

Abstract

Slip segments with a friction medium are used to anchor a downhole tool in a well. Each slip segment has a slip segment body made of a drillable material. A friction medium is applied to the outer surface of the slip segment body so that the outer surface of the slip segment has an increased holding capability in the well.

Description

BACKGROUND
• Downhole tools for use in oil and gas wellbores often have drillable components made from metallic or non-metallic materials, such as soft steel, cast iron, engineering grade plastics, and composite materials.
• In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. It thus becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.
• Bridge plugs isolate the portion of the well below the bridge plug from the portion thereabove. Bridge plugs therefore may experience a high differential pressure and must be capable of withstanding the pressure so that the bridge plug seals the well and does not move in the well after it has been set.
• Bridge plugs make use of metallic or non-metallic slip segments, or slips, that are initially retained in close proximity to a mandrel but are forced outwardly away from the mandrel of the tool upon the tool being set to engage a casing previously installed within an open wellbore. Upon the tool being positioned at the desired depth, or position, the slips are forced outwardly against the inside of the casing to secure the packer, or bridge plug as the case may be, so that the tool will not move relative to the casing when, for example, operations are being conducted for tests, to stimulate production of the well, or to plug all or a portion of the well.
• Cylindrically shaped inserts, or buttons, may be placed in such slip segments, especially when the slip segments are made of a non-metallic material such as plastic composite material, to enhance the ability of the slip segments to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into, the surface of the well casing which is typically steel. However, especially in the case of downhole tools being constructed of materials that lend themselves to being easily drilled from the wellbore once a given operation involving the tool has been performed, the buttons must not be so hard or so tough to resist drilling or fouling of the cutting surfaces of the drilling bit or milling bit. The buttons will at times tear, rupture, or otherwise alter the slip segments, and thereby become loosened from the slip segments. When the buttons become loose, the slip segments may lose some gripping capability, and are therefore susceptible to movement in the well due to the high pressures experienced in the well.
• While current slip elements work well in many circumstances, there is a continuing need to increase the holding capability of the slips.
SUMMARY
• A downhole tool has a mandrel and an expandable packer element disposed thereabout for sealingly engaging a well. Slip assemblies are positioned on the mandrel above and below the packer element to anchor the downhole tool in the well. Each slip assembly comprises a slip ring movable from an unset position to a set position in which the slip ring engages the well. The slip ring comprises a plurality of slip segments. Each slip segment is retained about the mandrel and is movable radially outwardly so that it will engage the well and anchor the well tool in the well. The slip segments comprise a slip segment body with a friction medium applied to the outer surface. A plurality of inserts, or buttons may be secured to the slip segments, and will extend outwardly from the outer surface thereof. The friction medium increases the ability of the slip segment to hold the well tool in the well and to withstand pressures experienced in the well. The surface of the slip segment with the friction medium thereon may be a sandpaper-like surface.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a cross section of a downhole tool disposed in a well.
• FIG. 2 is an enlarged cross-sectional side view of a slip segment with a friction medium applied to the outer or engagement surface thereof.
• FIG. 3 is an exploded end view of two slip segments with friction medium applied to the outer or engagement surface thereof.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
• Referring to the drawings,FIG. 1 shows well10 comprising awellbore12 with acasing14 cemented therein.Downhole tool16 comprises amandrel18 with anouter surface20 and aninner surface22. The tool inFIG. 1 may generally be referred to as a bridge plug sincedownhole tool16 has anoptional plug24 pinned withinmandrel18 by radially orientedpins26.Plug24 has aseal28 located betweenplug24 andmandrel18. The overall tool structure would be suited for use as and referred to as a packer ifplug24 was not incorporated and fluid communication was allowed through the tool. Other components may be connected so that the packer, withoutplug24 may be used, for example, as a frac plug.
• Aspacer ring30 is mounted tomandrel18 with apin32. A slip assembly34 is disposed aboutmandrel18 andspacer ring30 provides an abutment which serves to axially retain slip assembly34.Downhole tool16 has two slip assemblies34, namely a first slip assembly and second slip assembly which are shown in the drawings and are designated in the drawings as first andsecond slip assemblies34a and34b for ease of reference. The slip assemblies will anchordownhole tool16 in well10. The structure of slip assemblies34aand34bis identical, and only the orientation and position ondownhole tool16 are different. Each slip assembly34 includes a slip ring36 and slip wedge38 which is pinned into place with pins40.
• Slip ring36 is an expandable slip ring36 which has aband42 disposed ingrooves44. Retainingband42 will retain slip ring36 in an unset position aboutmandrel18 whendownhole tool16 is lowered into the well. Slip rings36 may be moved or radially expanded from the unset to the set position which is seen inFIG. 1 in which the first and second slip rings36 engagecasing14 to holddownhole tool16 in the well.
• Slip rings36 are comprised of a drillable material, for example a molded phenolic. Afriction medium37, such as for example aluminum oxide, is applied to the outer surface of the phenolic material, so that theouter surface46 of slip ring36 comprises the friction medium. Slip rings36 may be made from other drillable materials as well such as drillable metals, composites and engineering grade plastics. The remainder of the slip assembly and other components of the tool may likewise be made from drillable materials. A plurality of inserts orbuttons48 are secured to slip ring36 by adhesive or by other means and extend radially outwardly fromouter surface46. The buttons are comprised of material of sufficient hardness to partially penetrate or bite into the well casing and may be comprised, for example, of tungsten carbide or other materials. The buttons may be, for example, like those described in U.S. Pat. No. 5,984,007. In the set position as shown inFIG. 1,buttons48 will engage or gripcasing14 to holdtool16 in place.
• Each slip ring36 is preferably comprised of a plurality ofslip segments50.Slip segments50 haveinner surface52,outer surface54 and first andsecond sides56 and58, respectively.Outer surface54 of each slip segment comprises a portion ofouter surface46 of slip ring36.Slip segments50 are shown inFIGS. 3 and 4. Slip rings36 may include, for example, six to eightslip segments50 thatencircle mandrel18. Slip ring36 may include more or less than six or eight segments, and the examples herein are non-limiting.
• Slip segments50 include aslip segment body60 which hasfriction medium37 applied to theouter surface62 thereof so that theouter surface54 of each slip segment comprisesfriction medium37. Whenouter surface54 engagescasing14,friction medium37 will engagecasing14 to increase the holding capability ofslip segment50 over the holding capability of a bare slip segment (i.e., a slip segment with no friction medium applied to the slip segment body). At least one and preferably all ofslip segment bodies60 are comprised of a drillable material, for example, a molded phenolic. The friction medium may be applied to one or more of theslip segment bodies60 to increase the coefficient of friction between theslip segments50 andcasing14.Friction medium37 may be for example crushed ceramics, carbide particles, steel particles, granite particles and, as set forth above, aluminum oxide in the described embodiment. The aluminum oxide may be applied to slipsegment body60 for example by molding aluminum oxide into the phenolic slip segment body. Slipsegments50 will preferably have a sandpaper-likeouter surface54.
• A packer element assembly64 which includes at least one expandable packer element66 is positioned between slip wedges38. Packer shoes68 may provide axial support to the ends of packer element assembly64.
• In operation,downhole tool16 is deployed in well10 using known deployment means such as for example jointed or coiled tubing.Downhole tool16 will be in an unset position whereintool16 does not engage well10. Thus, neither slip ring36, nor packer element assembly64 will engage casing14 in the unset position. In the unset position,spacer ring30,slip ring36aandslip wedge38aare all in an initial position aboutmandrel18 and are positioned axially upwardly and radially inwardly from the set position shown inFIG. 1. Whendownhole tool16 reaches a desired location in the well, each ofslip rings36aand36bare moved radially outwardly to the set position shown inFIG. 1, andtool16 may be left inwell10.Downhole tool16 separates well10 intoupper well portion10aandlower portion10b. The upper andlower portions10aand10bare isolated from one another bywell tool16 which in the embodiment shown is a bridge plug.Tool16 will typically experience high differential pressures in well10 which will try to move thewell tool16 in well10 aftertool16 has been set. The gripping engagement betweenslip segments50 andcasing14 will hold thewell tool16 in place.Friction medium37 at theouter surface54 ofslip segments50 will increase the coefficient of friction over that which is seen with the material that comprises the slip segment body, and as such increases the holding capability over a bare slip segment body.
• When welltool16 is set in well10,buttons48 will bite, or cut intocasing14 asslip segments50 move radially outwardly from the unset position.Outer surface54 of at least a portion ofslip segments50 will engage casing14 in the set position.
• It is known thatbuttons48 may tear or rupture theslip segment body60 or otherwise become loosened fromslip segment body60. When this occurs, slipsegment surface54 may contact casing14 so that all or most ofsurface54 is in contact withcasing14, and friction becomes a greater component of the holding ability of slip rings36 inwell10. The likelihood of slippage may increase in such cases. While slip segment bodies with no friction medium applied thereto provide some gripping capability, they do not provide the holding force that is provided with the slip segments described herein.
• The increased coefficient of friction between friction medium37 atouter surface54 andcasing14 is such that an increased holding capability is supplied byslip segment50. Slip rings36 comprised ofslip segments50 will hold welltool16 in place at pressures higher than is possible with bare slip segments. For example, a tool utilizing phenolic slip segments with no friction medium applied thereto can typically withstand differential pressures less than 10,000 psi without slippage. Tests have shown that a well tool with phenolic slip segments utilizing aluminum oxide as a friction medium as described herein can withstand differential pressures of greater than 10,000 psi with no slippage.
• Thus, it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.

Claims (24)

1. Apparatus for anchoring a downhole tool in a well comprising:

a plurality of slip segments disposed about a mandrel of the downhole tool and movable to a set position wherein the slip segments engage the well, at least one of the slip segments made of a drillable material with a friction medium applied to the outer surface thereof for increasing the gripping capability of the slip segment to the well.

2. The apparatus ofclaim 1, wherein the slip segment has a sandpaper-like outer surface.

3. The apparatus ofclaim 1, the at least one slip segment comprising a phenolic slip segment body, the friction medium being applied to the outer surface of the slip segment body.

4. The apparatus ofclaim 3, wherein the friction medium is molded to the phenolic slip segment body.

5. The apparatus ofclaim 3, wherein the friction medium comprises aluminum oxide.

6. The apparatus ofclaim 1, wherein the slip segments have at least one button secured thereto and extending outwardly from the outer surface thereof for gripping the casing.

7. The apparatus ofclaim 1, wherein the plurality of slip segments are comprised of a non-metallic material.

8. The apparatus ofclaim 7, wherein the plurality of slip segments are comprised of a phenolic.

9. The apparatus ofclaim 8, the friction medium comprising aluminum oxide applied to the outer surface of the phenolic.

10. The apparatus ofclaim 8, wherein all of the slip segments include the friction medium at the outer surface thereof.

11. A downhole tool for use in a well comprising:

a mandrel;

a slip ring movable from a set to an unset position, wherein in the set position the slip ring grippingly engages the well, the slip ring comprising a drillable material with a friction medium applied on the outer surface thereof for increasing the gripping capability of the slip ring to the well.

12. The downhole tool ofclaim 11 wherein the slip ring comprises a plurality of slip segments, at least a portion of the slip segments having the friction medium on an outer surface thereof.

13. The downhole tool ofclaim 12, wherein the friction medium comprises aluminum oxide.

14. The downhole tool ofclaim 12, wherein the slip segments are comprised of a phenolic.

15. The downhole tool ofclaim 11 comprising an expandable packer element disposed about the mandrel and first and second slip rings, one of the slip rings positioned above the packer element and the other positioned below the packer element.

16. The downhole tool ofclaim 15, wherein the first and second slip rings comprise a plurality of slip segments grippingly engageable with the well.

17. The downhole tool ofclaim 16, wherein at least a portion of the slip segments comprises inserts extending outwardly from an outer surface thereof.

18. The downhole tool ofclaim 17 wherein the slip segments comprise a phenolic slip segment body with aluminum oxide applied to an outer surface thereof.

19. A downhole tool for use in a well comprising::

a mandrel;

an expandable element disposed about the mandrel;

a first slip ring disposed about the mandrel movable from an unset to a set position wherein the first slip ring grippingly engages the well in the set position;

a second slip ring disposed about the mandrel movable from an unset to a set position wherein the second slip ring grippingly engages the well in the set position, wherein at least one of the first and second slip rings has a friction medium on the outer surface thereof so that the gripping ability of the slip ring is greater than the gripping ability of a bare slip ring.

20. The downhole tool ofclaim 19, the first and second slip rings comprising a plurality of slip segments retained on the mandrel and movable to the set position wherein an outer surface of at least a portion of the slip segments engages the well in the set position.

21. The downhole tool ofclaim 20, wherein at least a portion of the slip segments comprises a phenolic slip segment body with the friction medium applied thereto.

22. The downhole tool ofclaim 21, the friction medium comprising aluminum oxide.

23. The downhole tool ofclaim 19, the slip rings comprising a phenolic having the friction medium applied to the outer surface thereof.

24. The downhole tool ofclaim 19, the friction medium comprising aluminum oxide.

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