Patent Application
20100006280
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.
A retaining ring is disposed about the slip segments, generally in a groove in the slip segments, to hold the slip segments in an unset position prior to the slip segments being forced outwardly into the casing. The retaining ring is intended to prevent the slip segments from moving outwardly prematurely. When the slip segments move radially outwardly, the retaining ring breaks, so that the slip segments can move outwardly to engage the casing to secure the tool in the well. The retaining rings often have a “spring effect” upon breaking which causes the broken retaining band to spring with enough energy to move away from the slip segments. The retaining ring may move or spring enough to wedge between the slip segments and the casing, or other part of the tool and the casing and can prevent the tool from setting, sealing or operating properly in the well. There is a need for a retaining ring that will apply sufficient holding force, but that will have a limited spring effect.
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/or 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 tool in the well. A plurality of inserts, or buttons may be secured to the slip segments, and will extend outwardly from the outer surface thereof to grip casing in the well.
A retaining ring is disposed about the slip ring to retain the slip ring about the mandrel, and may be received in grooves defined in the slip segments that comprise the slip ring. The retaining ring will hold the slip ring in an unset position, and will prevent the slip ring from prematurely moving outwardly to the set position in which the slip ring grippingly engages the casing to hold the tool in the well.
The retaining ring comprises a retaining band with a dampener, which may be referred to as a spring suppressor, affixed thereto. The dampener will dampen, or suppress the spring effect that would occur if the retaining band were used without the dampener. The dampener may be comprised of rubber, and may be bonded or molded to the retaining band. The retaining band may be, for example, a fiberglass composite retaining band. The dampener may be affixed to an outer surface of the retaining band, and may completely encapsulate the retaining band.
Referring to the drawings,
A spacer ring 30 is mounted to mandrel 18 with a pin 32. A slip assembly 34 is disposed about mandrel 18 and spacer ring 30 provides an abutment which serves to axially retain slip assembly 34. Downhole tool 16 has two slip assemblies 34, namely a first slip assembly and second slip assembly which are shown in the drawings and are designated in the drawings as first and second slip assemblies 34a and 34b for ease of reference. The slip assemblies will anchor downhole tool 16 in well 10. The structure of slip assemblies 34a and 34b is identical, and only the orientation and position on downhole tool 16 are different. Each slip assembly 34 includes a slip ring 36 and slip wedge 38 which is pinned into place with pins 40.
Slip ring 36 is an expandable slip ring 36 which has a retaining ring 42 disposed in grooves 44. Retaining ring 42 will retain slip ring 36 in an unset position about mandrel 18 when downhole tool 16 is lowered into the well. Slip rings 36 may be moved or radially expanded from the unset to the set position which is seen in
Slip rings 36 are comprised of a drillable material and may be, for example, a molded phenolic and have an outer surface 46. Slip rings 36 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 or buttons 48 are secured to slip ring 36 by adhesive or by other means and extend radially outwardly from outer surface 46. 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 in
Each slip ring 36 is preferably comprised of a plurality of slip segments 50. Slip segments 50 are shown in cross section in
Retaining rings 42 are disposed about slip rings 36, and may be received in grooves 44. Retaining rings 42 are each comprised of a retaining band 68, and a dampener, or spring suppressor 70. Retaining band 68 may be made from a metal, or may be a composite, such as a fiberglass composite retaining band. The examples provided are not limiting, and retaining band 68 may comprise any material, preferably a drillable material, that will provide adequate strength to prevent premature breakage. Dampener 70 may be made from rubber, for example, a nitrile rubber. Other materials that will dampen or suppress the energy, or spring effect of retaining band 68 may be used. Dampener 70 is affixed to retaining band 68 by, for example, bonding, or molding.
Retaining band 68 may be a ring-shaped band 68, and may have a rectangular cross section with outer surface 72. Outer surface 72 may comprise outer circumferential surface 74, inner circumferential surface 76, and side surfaces 78 and 80. Dampener 70 may be affixed to any or all of surfaces 74, 76, 78 and 80, and may, if desired, completely encapsulate retaining band 68.
In operation, downhole tool 16 is deployed in well 10 using known deployment means such as for example jointed or coiled tubing. Downhole tool 16 will be in an unset position wherein tool 16 does not engage well 10. Thus, neither slip ring 36, nor packer element assembly 60 will engage casing 14 in the unset position. In the unset position, spacer ring 30, both of slip rings 36a and 36b and slip wedges 38a and 38b are all in an initial position about mandrel 18 and are positioned radially inwardly from the set position shown in
Retaining rings 42 will retain slip rings 36 in place about mandrel 18 in the unset position prior to being moved to the set position in
The significant amount of energy released when retaining rings 42 break, in the absence of dampener 70 could cause the retaining rings 42 to move away from slip rings 36, and prevent proper engagement of the slip rings by setting between slip rings 36 and the casing 14. Dampeners 70 dampen, or suppress the spring effect, so that when retaining rings 42 break, they will stay in grooves 44.
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.
