GB2357098A

GB2357098A - A packer assembly

Info

Publication number: GB2357098A
Application number: GB0026908A
Authority: GB
Inventors: Gary D Jordan
Original assignee: TIW Corp
Current assignee: TIW Corp
Priority date: 1999-11-05
Filing date: 2000-11-03
Publication date: 2001-06-13
Also published as: CA2325105A1; GB0026908D0

Abstract

A packer assembly includes a packer body (42, 43), a packer element (12) and a mandrel (40) both supported on the packer body (42, 43). The packer element (12) supports a rigid formation ring (15) which has tapered surfaces (17, 18) that act to minimise the axial compressive force required to set the packer (fig 2). Shearable rings (30, 31) may also be present which further enhance the seal. Deformation of the packer element (12) can be controlled with malleable deformation control rings (20, 21). A hydraulically set version of the packer is also described.

Description

2357098 DOWNHOLE PACKOFF ASSEMBLY

Field of Invention

This invention relates generally to a downhole packoff assembly of the type commonly used to seal the annulus between two substantially concentric strings of pipe and, in particular, to packoffis for isolating a select zone or annulus between strings of tubing or 0 between a tubing and a easing.

BackWound of Invention After a gas or fluid producing well is drilled, it is commonly completed and then produced undercontrolled conditions necessitating isolation of pressures and fluids between the inside of a string of pipe and the annulus surrounding the pipe, or between different strings. This is commonly accomplished through. the use of various of downhole tools or assemblies which utilize a packoff type seal which is actuated at the desired position in the well to effect the seal. For example, a downhole tool commonly referred to as a packer, which utilizes a packoff element, may be run in the well on a tubing string, positioned inside of the casing and placed above a producing zone to protect that zone from fluids or pressures in the annulus between the tubing and casing. This may be useful in well completion and production operations for enabling a wellbore to contain a full column of fluid, thereby maintaining integrity of the casing and tubing, inhibiting corrosion and facilitating monitorin. of the annulus for chanaes.

Conversely, the packoff may also protect the tubing-casing annulus from fluids and pressure of the producing formation and from loss of a desirable column of fluid in the annulus. This fluid may be useful in protecting tubing and casing strings from abnormally gh pressures or from exposure to corrosive fluids. In addition. the annular seal effected by hig.

C:kclient\Tlk'\-17-pat appin.wpd the packoff may enhance the ability of the well to produce either under natural conditions or under various types of artificial lift.

Most packoff type tools, including both those using a single sealing element and those using multiple sealing elements, require significant axial or rotational force to effectively set or engage the packing elements against the inner wall of the pipe. Also, in any given application, the differential pressure across the packoff may be very high and the ability of the packoff to effect a seal may vary with setting conditions, including type of fluid W in the hole, hole angle, wellbore tortuosity, depth, casing and tubing size, weight, grade and 0 age, the durometer of the packoff element(s) and downhole temperature. Due to these variables, axial or rotational forces applied at the surface to effectively engage or set the tool may fail to effectively reach the tool downhole, thereby resulting in an ineffective packoff seal. The forces required at the surface for effective actuation of the packoff elements at the tool rilay exceed the yield strength, thereby resulting in plastic deformation, tensile yield parting, reduced burst or collapse strength, excessive joint makeup torque, and/or other Is damage to the pipe string.

The positioning of the tool and packing elements in the wellbore may effect the scaling ability ofthe packoff, thus requiring additional setting forces to effect and maintain a positive seal. If the tool is latched or hooked to the casing wall, then no movement of the packing element is expected. However, if the tool landed or set off on a load bearing surface in the casing string or merely hanging on the tubing and permitted to slide unrestricted, > -.> I> C 1 1 1 1 movement of the packing elements is anticipated with fluctuations in producing and ZY operating characteristics of the well. Such movement of the packoff elements against the casing wall necessitates having adequate energy availability at the tool to maintain a positive seal, should force be applied which tend to axially move the tool. In these instances, a packoff tool requiring large setting forces may potentially fail to engage the packing elements in a fully set position.

C:\clicnt\TIW-17-pat appin.wpd Numerous types of packoffs have been devised. U.S. Patent No. 4,628,997 discloses a packoff using a radial energizing ring to deflect a pair of opposing packing elements into a sealing position when the tool is set. This tool utilizes the movement and engagement of multiple elements, thereby incurring additional complexity and cost, and has increased susceptibility to deformation failure of a packing element. The tool also uses the frictional movement of each packing element at non-congruent angles to the energizing ring, thus resulting in an additional energy loss above that required for the plastic deformation of a given packing element to set the packer. This additional energy loss results in an increased net force requirement at the tool to achieve a given packoff seal effect, necessitating an increased force application at the surface, thereby risking forces above the mechanical or hydraulic limitations of the tubing.

An improved packoff design has long been desired to facilitate an effective seal at a reduced downhole setting force than has been possible according to the prior art. The disadvantages of the prior art are overcome by the present invention, which has a particular utility in downhole packoff applications requiring reduced setting forces.

Z C:\cIient\TI%V\'_)7-pat appIn.wpd Summa[y of The Invention In an exemplary embodiment, the packoff assembly of this invention comprises four primary elements which work both singularly and in combination to improve the performance of packoff type tools in applications desiring reduced setting forces and/or improved differential pressure capacity. These primary elements have application in both single-set and multiple-set tool applications, although the invention has been designed initially for only single set applications.

A suitable embodiment of a packoff assembly according to the present invention includes a single elastomeric packing element mounted around a tool mandrel, such as a 0 packer mandrel, with a shaped formation ring located on the tool mandrel substantially adjacent the axial center and radially inward of the packing element. Each end of the packing element is capped with a malleable metallic ring, which provides support to the packing clemcilt and aids in increased differential pressure capacity. In addition, a pair of expandable backup rings are provided. An expandable ring may be located on the low pressure end of the scaling assembly adjacent to the sealing caps, and the other adjacent the tool setting sleeve on the high pressure end, to further assist in differential pressure capacity.

These backup rings may be designed to shear when subjected to setting forces and expand Outward against the casing wall. These backup rings shall commonly be referred to herein as shearable rings. An additional component, an inner support ring, may be positioned on O either or both sides of the shearable ring to enhance engagement with adjacent components.

The packer is run in the unset position to the desired setting depth where a mechanical or hydraulic setting force may be applied, transmitting axially opposing forces on the packing element through the opposing movement of the mandrel and/or setting sleeve. The axial force on the packing element creates a lateral deflection of the element radially outward 0 Z5 from the mandrel until the packing element may be engaged against the wall of the casing, I.

creating the desired pressure seal. The seal cups, the inner support ring and the shearable CAchen6TINV\217-pat appin.wpd 1-11 r ring which may each be positioned on each side of the elastomeric packing element may aid in controlling deformation of the packing element under high pressure differential, As the required differential pressure rating of the seal may be reduced, one or more of each component may be omitted aLs desired. Opposing sets of slips on the packer may set against the casing wall when the packing element is expanded and may thereby maintain a fluid tight seal. Alternatively, if the packer or tool is of a type that does not include slips, the seal may be otherwise maintained by the yielding and deformation of the materials or by any other means.

A primary objective of the invention is to provide an effective packoff or fluid tight seal, which requires a setting force that is significantly less than is required according to the prior art and which may be reliably engaged. This invention provides an improved packoff tool that is capable of reliably withstanding a high differential pressure. The reduced force requirement may be obtained by utilizing a shaped ring, referred to as a formation ring.

axiallY centered and radially inward of a single packing element. The formation ring functions to redirect the axial setting force radially outward to the center of the packing element. The tapered surfaces ofthe ring are mated with matching tapers on the packoff, creating an area of reduced thickness in the center of the packing element ftom which the radial expansion of the packing element initiates. This may result in a reduced axial force that is required to effect a seal.%-hich is lower than the axial force required to deform an analogous packing, element that does not contain the formation ring, and provide a similar seal for a similar tool. The formation ring may be constructed of a metallic, composite or 00 plastic-based material.

A feature of the invention provides lateral support to the packing element, thereby Z further supporting its ability to withstand a high differential pressure. The element may be radially mated at each end by a malleable copper cup, sometimes referred to as a Gold SeaL The Gold Seal in this application is distinguishable from the prior art in that it extends the

CAcIicntM%V"X27-pat appin.wpd cup axially along a portion of the packoff element. The extension is ofsufficient length such that when the packoff is set, the Gold Seal extension may be flared radially to make contact with the casing wall, thus providing circumferential and radial support across the entirety of the annular area upon which the pressure differential acts. This increased support may allow use of lower durometer elastomeric elements than would otherwise be required for that same application using an unsupported packoff element, thus further reducing the setting force requirements. Also, the Gold Seal conforms to the interior of the casing pipe, adding a metal to metal seal to the packoff element.

In addition, a shearable ring is included as another feature of the invention. The 0 shearable ring may provide rigid support in the annular area to the packoff element and the Gold Seal. The shearable ring may be located adjacent to an inner support ring which may be located adjacent to the Gold Seal. The shearable ring may thus be shouldered on one side by a tool body and on the other by the inner support ring. In one embodiment, during actuation of the packoff, the shcarable ring may be fractured in one or more radial segments or sections, each of which may expand radially outward from the previously unsheared position to engage the casing wall and provide rigid support for the packoffelement and the Gold Seal, thus also contributing to the ability of the packoff to function properly under increased differential pressure. Because the shearable ring may provide rigid support across the entire annular area, undesirable deformation or eruption of the elastomeric packing M element may be abated, thereby allowing use of a more malleable, lower durometer, easier setting material for the packoff element. Thus, the packoff element may be less rigid and need not depend solely upon its own rigidity or,de formation resistance to withstanding relatively high differential pressures. This benefit of the shearable ring may enhance the tool's ability to withstand increased differential pressure while concurrently facilitating reduced axial setting force requirements for setting the packoff, through the use of less rigid packoff element material.

C:\clicnt\TM217-put appin.wpd During actuation of a packoff tool, when axial setting forces are applied to the tool, the mandrel may pull the lower packoff body against a static or upper packoff body in an opposing fashion. Alternatively, the upper packer body may move against the moving lower packer body or the lower packer body may remain static while the upper packer body moves against the lower packer body. In some embodiments the mandrel may be static relative to either or both of the tool bodies. The opposing movement of the tool bodies results in compression and radial expansion of the packoff assembly located between the two bodies.

The major components of this invention may each contribute to a reduction in the axial force required at the tool to set the packoff element and may also contribute to the differential pressure rating of the packoff assembly.

This invention has several other desirable features inherent in the design of the tool and its application, including high reliability and simplicity due to the use of a single packing 0 0 element and reduced setting force requirements. The packing element reinforcement features nlay increase the reliability of the seal in high differential pressure applications. This invention uses relatively few parts, each being of simple design and thus a low manufacturing cost. Because ofthe simple design of this invention, assembly and operation of the packer or tool making use of this invention requires very little special skill or training.

These and further objects, features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

CAdient\TINV\27-pat appln.wpd Brief Description of the Drawings:

Figure 1 is a side view, in cross section, depicting a formation ring, a packoff element, deformation control rings, inner support rings and shearable rings between tool bodies on a mandrel, with the assembly being positioned within a casing in an unset position.

Figure IA extends the upper and lower view of Fig. 1 to demonstrate a slip arrangement.

Figure 2 is a side view, in cross section, depicting the formation ring, the packoff element, the deformation control rings, the inner support rings and shearable rings as shown 0 in Fig. 1, in a set position.

Figure 2A illustrates an embodiment of the packoff components in a set position similar to that shown in Fig. 2, with an additional set of inner support rings provided, such that a set of inner support rings may be positioned on each side of a shearable ring.

Fi-ure 3 is a half section view of the formation ring shown in Fig. 1.

C.\client\TIS17-pat appin.%vo Detailed Description of the Preferred Embodiments

Reference is made to the attached drawings for the purpose of illustrating preferred embodiments and related components of the invention and not forthe purpose of limitingthe same. Figs. I and 2 illustrate a suitable embodiment of a packoff assembly 10 in half-section view. The assembly 10 may be substantially comprised of a packoff element 12, a rigid formation ring 15, a tool mandrel 40, a pair of deformation controlling rings 20, 2 1, a pair of supporting shearable rings 30, 3 1, a pair of inner support rings 81, 82 and packer body components 42, 43. Alternatively, an additional set of inner support rings 83, 84 may be included as illustrated in Fig. 2A, such that a pair of inner support rings 81, 82 and 83,84 may oppose each other on each side of the shearable rings 30,31. Fig. 2A illustrates an embodiment of the invention as adapted for use with tool bodies 85 and 86 having surfaces 87 and 88, respectively, which may not be coplanar with the shearable rings 30 and 3 1. As such, a second pair of inner stipport rings 83 and 84 may be included to, among other uses, assist with propcr force loading against the shearable rings 30, 31. It may be apparent to those skillcd in the art that the application and shape of the inner support rings 81, 82, 83 or 84 may bc fashioned in any of various forms as required by an the application of the invention to any particular tool.

I illustrates an embodiment of a packoff assembly 10 having a substantially Fig circular cross section with a through bore therein and positioned within a cylindrical wellbore casing 50, in the unset position as, for example, when running a packer into a Nvellbore. The packoff assembly 10 may be suspended in the casing 50 by any type of oilfield wire line or tubular string (not shown). Fol. the embodiment illustrated in Figs. I and

2, the packo ff assembly 10 is positioned within a well including a large diameter casing 50 and a smaller diameter tubing string (not shown), substantially concentrically positioned within the casing 50. The term "packoff assembly" as used herein is intended in its broad sense to include doNxmhole tools commonly referred to as packers, packoffs, plugs, retainers, CAcHcnt\T1\V\27-pat appln.wpd 10- hangers, seal assemblies and related tools. Fig. 2 illustrates an embodiment of the same packoff assembly positioned within the casing 50 in the set position. In either configuration, set or unset, the well casing 50 may be filled with a fluid 14 above and/or below the packer, A packer and packoff assembly 10, and related components thereof, each mayhave a relative "upper" end and "lower" end. In the embodiment as illustrated in Figs. I and 2 and in this specification, the term "upper" refers to an axial end nearest the surface in a vertical well bore and the term "lower" refers to an axial end farthest from the surface in a vertical wellbore, with any upper component being relatively positioned axially above a corresponding lower component.

0 For the embodiment illustrated in Fig. 1, the packer or packoff assembly 10 may generally include agencrally cylindrical mandrel 40, which may have a through bore therein along its central axis 62 and a generally cylindrical upper packer body 42 and a generally cylindrical, lower packer body 43), with each of a packer body 42 and 43 also having a through bore along its central axis 62, with each of the aforementioned components substantially sharing the same central axis 62. In altemative tool embodiments, the generally cylindrical mandrel 40 may not have a complete through bore or ma have no through bore, 0 y as for example in a bridge plug. The upper packer body 42 may be positioned concentrically ZD around the mandrel 40 and above the lower packer body 43 with the upper packer body 42 and the lower packer body 43 being axially separated by a selected distance. The mandrel 0 40 may concentrically pass through the ID of the upper packer body 42 and may generally be engaged with the lower packer body 43 such that an axial force applied along the central axis 62 and acting upon the mandrel 40 may cause t4e mandrel 40 to telescope or reciprocate through the upper packer body 42, thereby imparting telescopic displacement or movement in the lower packer body 43 relative to the upper packer body 42. In alternative embodiments, either packer body 42 or 43 may remain static relative to the other 42 or 43, or both packer bodies 42,43 may move relative to the other, or the mandrel 40 may not move C:\clienffl\\-17-pat app1n.%vpd while either or both of the packer bodies 42, 43 may move relative to the mandrel 40.

As previously stated, the upper packer body 42 and lower packer body 43 may be separated by a selected distance, such that a substantially cylindrical packoff assembly 10 may be positioned between the packer bodies 42 and 43. The packoff assembly 10 generally encompasses the OD of the mandrel 40. The components of the packoff assembly 10 may each move axially along or rotate radially about the central axis 62 of the mandrel 40. When axial setting forces are applied, in one embodiment the lower packer body 43 may move in relative opposition to the upper packer body 42 and the packoff assembly 10 may be compressed between the upper packer body 42 and lower packer body 43. The packoff assembly 10 absorbs the energy of the axial setting force that was imparted to the mandrel C' 40. This energy absorption may alter or deform the shape and/or axial and/or radial position of some or all of the components of the packoff asscrnbly 10, causing some or all of the packoff assembly 10 components to deform and engage the inner surface 26 of the casing 50 and/or the outer surface 41 of the mandrel 40. A fluid tight annular seal may thus be effected within the annulus between the mandrel 40 and the casing 50, substantially isolating annular pressure above the packoff assembly 10 from annular pressure below the packoff assembly to.

This invention relates particularly to a packoff assembly 10 which, when set, may effect a fluid tight, annular seal in the casing. A preferred embodiment of this invention is illustrated in Figs. I and 2, exhibiting, some general components of a packoff assembly 10 including an elastomeric element 12, a rigid ring 15, upper and lower deformation control C 0 rings 20 and 2 1, respectively, and upper and lower shearable rings 30 and 3 1, respectively, and upper and lower inner support rings 8 1 andS2, respectively. In this embodiment, each of these generally ring-shaped components may be positioned axially between the upper packer body 42 and the lower packer body 43 and may radially encompass the external surface 41 of the mandrel 40, with the rigid ring 15 being axially centered near the axial CAc1icnt\T1NVQ7-pat appln.wpd 12- midpoint between the lower end 56 of the upper packer body 42 and the upper end 57 of the lower packer body 43. The rigid ring 15 may be axially moveable about the cenLral axis 61 of the mandrel 40. The rigid ring 15 may be metallic, but altematively could be non metallic. The dgid ring 15 may have a radially outward upper tapered surface 17 and a radially outward lower tapered surface IS, wherein each of the upper tapered surface 17 and lower tapered surface 18 are tapered relative to a centerline 62 of the mandrel 40 in a preferred embodiment from about 25 degrees to 30 degrees, and an inner surface 16 that is substantially aligned with and may be substantially coplanar with an inner surface 19 of the elastomeric element 12. In other embodiments of the rigid ring 15, the upper tapered surface 17 and the lower tapered surface 18 of the packoff element 12 may be substantially aligned with and tapered relative to a centerline 62 of the mandrel 40 by as much as 60 degrees or a I Ittle as 15 degrees.

In the Fig. I embodiment, the rigid ring 15 may engage the elastomeric element 12.

The elastomcric element 12 generally includes a radially inward first surface and a radially inward second Surface, substantially forming a radial concave recess in the packoffelement 12, near the axial midpoint of the packoff element 12. The elastomeric element 12 may be configured forsubstantial radial, coplanar engagement with the upper tapered surface 17 and the lower tapered surface 18 of the rigid ring 15 when the packer is unset. The elastomeric element 12 may also include an outer surface 29 that, in the unset position, may be substantially aligned with and may be coplanar with both an outer surface 44 of the upper packer body 42 and the outer surface 45 of the lower packer body.

The elastomeric element 12 may also include a semi-rounded, radialb., tapered upper end 46 which may be engaged with and conform to an upper defomiation control ring 20.

0 0 The elastomenc element 12 may also include a semi-rounded, radially tapered lower end 47 that may be engaged with and conform to a lower deformation control ring 2 1. The upper end 46 of the elastomeric element 12 may provide a recess 36 to facilitate substantial axial C:\c1icnt\T1W\27-pat appInmN 13- alignment and coplanar engagement with the outer surface 38 of the upper deformation control ring 20 with the outer surface 29 of the elastomeric element 12. The lower end 47 of the elastomeric element 12 may provide a recess 37 to facilitate substantial axial alignment and coplanar engagement with the outer surface 39 of the lower deformation control ring 21 with the outer surface 29 of the elastomeric element 12.

The upper and lower deformation control rings 20 and 21, respectively, of this embodiment maybe comprised of a malleable metallic material and may each have a through bore which radially encompasses the outer surface 41 of the mandrel 40. The upper deformation control ring 20 may be shaped with a radially curved outer surface 38, which may begin with a tangent line that is perpendicular to the central axis 62 of the packoff assembly 1 0 and curves in planar engagement with the curved surface 48 at the upper end 46 of the clastomeric clement 12 toward the opposite end 47 of the clastomeric element 12 until the tangent line of the curve of the deformation control ring20 is axially parallel to the central axis 62 of the packoff assembly 10. The deformation control ring 20 may extend axially parallel to the central axis 62, along the outer surface 29 of the elastorneric element for a selected distance that may be of sufficient length such that the upper deformation control ring 20 may, when the packoff assembly 10 is set, engage and conform with the inner surface 26 of the casing 50. The lower deformation control ring 21 may be partially shaped Z with a radially curved outer surface 39, which is in radial engagement with the lower end 47 of the elastomefic element 12, and which may mirror image the shape and curvature of the upper deformation control ring 20 but curves in the opposite direction toward the upper deformation control ring 20. The lower deformation control ring 21 may also extend axially parallel to the packer centerline 62, then along the outer surface 29 of the elastomeric element 12 for a selected distance.

In a preferred embodiment, as illustrated in Fig. 1, the outer surface 38 of the upper deformation control fing 20 may be adjacent to or engaaCd against an upper, inner support 0 0 0 CAc1icnt\T1N%'\-17-pat app1n.wpd 14ring 81 which may act to provide a rigid component between the upper shearable ring 30 and the upper deformation control ring 20 to as an aid in shearing the shearable ring 30 and to provide awedge-like force to encourage radial expansion of the uppershearable ring 30 upon shearing expand radially to engage the casing 50. In addition, a lower, inner supporting ring 82 which may be positioned between the outer surface 39 of the lower deformation control ring 21 and the lower shearable ring 3 1, may act upon the corresponding lower components in similar fashion to the action of the upper, inner support ring 81 against the corresponding upper components. In alternative embodiments, as illustrated in Fig. 2A, an upper pair of inner support rings 81, 83 may centrally engage an upper shearable ring 30 and a lower pair of inner support rings 82, 84 may centrally engage a lower shearable ring 3 1.

0 In the Fig. I embodiment, the outer surface 38 of the upper deformation control ring may be adjaccilL to or engaged against a rigid, metallic or non-metallic, tipper, inner ID Support ring 8 1, which may be engaged against a rigid, metallic or non- metallic, upper shearable ring 30, located above the upper deformation control ring 20. The upper, inner Support ring 8 1, having a through bore with the same axial center as the central axis 62 of 0 the mandrel 40, may radially encompass the exterior surface 41 ofthe mandrel 40 and may be movable axially along and rotationally about the mandrel 40. The upper shearable ring 30, having a through bore with the same axial center as the central axis 62 orthe mandrel 40, may radially encompass the exterior surface 41 of the mandrel 40 and may be movable axially along and rotationally about the mandrel 40. The other side of the upper shearable ring 30 may be engaged against the lower end surface 56 of the upper packer body 42, sandwiching the upper shearable ring 30 between the packer body 42 and the upper deformation control ring 20. As illustrated in Fig. 2A, and as discussed above, in alternative embodiments the upper shearable nng 30 may be centrallylocated between a pair of inner support rings 81 and 83. The upper shearable ring 30 may also have an outer radial surface that, in the unset position, as illustrated in Fig. 1, is substantially coplanar to and axially C:\c1icnt\T1W\_17-pa( app1n.wpd - aligned with the outer surface 44 of an upper packer body 42. The axial length of the OD of the upper shcarable ring 30 may be greater than the axial length of the ID of tile upper shearable ring 30 such that the surface 52 of the upper shearable ring 30, which connects the OD with the ID, may be curvilinear, substantially angular to or perpendicular with respect to the central axis 62 of the packoff assembly 10. The other surface 54 which connects the OD with the ID of the upper shearable ring 30 may be curvilinear, angular to or perpendicular with respect to a line perpendicular to the central axis 62 of the packoff assembly and may, in various embodiments, substantially conform to the shape of the angled or curved outer surface 38 of the upper deformation control ring 20 or with a surface of the upper, inner support ring 81. The upper shearable ring 30 may also have one or more cuts or notches which may pen-nits the radius and OD of the upper shearable ring 30 to enlarge or circumferential expand when it is sheared. In alternative embodiments, the slicarable ring or 31 may be designed with a cut, which may permit the circumference of the shearable rin- 30 or 31 to enlarge at the cut without shearing, as the packoff assembly 10 may be set.

The lower inner support ring 82, having a through bore with the same axial center as tile central axis 62 of the mandrel 40, may radially encompass the exterior surface 41 of tile mandrel 40 and may be movable axially along and rotationally about the mandrel 40. A lower shearable ring, 3 1, as illustrated in Figs. 1 and 2, may be generally located near the end of the packoff assembly 10 which is opposite from the previously described upper shearable ring 30. The lower shearable ring I may be sandwiched between the lower, inner support ring 82 and the upper surface 53 of the lower packer body 45. As illustrated in Fig. 2A, and as discussed above, in alternative embodiments the lower shearable ring 31 may be centrally located between a pair of inner support fings 82 and 84. The lower shearable ring 31 may Z be a mirror image of the upper shearable rinor 30, in shape, orientation and position relative C.

to an axial mid-point of the elastomeric element 12 along the central axis 62 of the packoff assembly 10. The upper and lower shearable rings 30 and 31 may be fabricated from a CAc1icnt\T1\V'\_17-pat app1n.wpd mctallic or non-mctallic matcrial.

In a preferred embodimentof the packoff assembly 10 as illustrated in Figs. I and2, as force directed axially along the centcrline 62 may act upon the mandrel 40, and/or either or both of the packer bodies 42, 43 for the purpose of setting the packoff assembly 10, in an embodiment the force may be imparted upon the lowerpacker body 45 through engagement between the lower packer body 45 and the mandrel 40. The lower packer body 45 may move upward i n axial opposition to downward movement or static positioning of the upper packer body 42. As the packoff assembly 10 is compressed between the upper packer body 42 and the lower packer body 43, the lower packer body 43 compressively engages the lower shearable ring 3 1, which in turn compressively engages a lower, inner support nng 82, which in turn compressively engages a lower deformation ring 21, which is engaged against the lov.-er end 47 of the clastonieric element 12. Conversely and simultaneously, the upper packer body 44 may compressively engage the upper shearable ring 30 with the upper deformation control ring 20 which, in turn, may be engaged with the upper end 46 of the clastomeric element 12. The elastomeric element 12 may partially absorb the compressive energy, causing convergent displacement of the components of tile packoff assembly 10 twvard a radial plane located near the axial center of the elastorneric element 12. This compression may also cause the elastomeric element 12 to compressively engage simultaneously with the rigid ring 15 and the packer mandrel 40, such that axial forces in the axial center of the elastomeric element may be directed radially outward and perpendicularly away from the axial centerline 62 of the packoff assembly 10, thereby consurning annular space between the unset OD of the packoff asseMbly 10 and the inner surface 26 of the casing g 50 with the clastomeric element 12 and other components of the packoff assembly 10, including the upper and lower shearable rings 30 and 3 1, respectively and the upper and I lower deformation control rings 20 and 2 1, respectively. The generally convex shape of the rigid ring 15 may act to engage the generally conforming concave recess located near the C:\cIicnt\TI%N'\-'7-pat appinmpd 17- axial mid-point of the clastomeric clement 12 to provide a substantially radial supporting plane near the axial mid-point of the elastomeric element 12 from which outward deformation or expansion of the elastomeric element 12 in the direction of the casing 50 may be encouraged. The rigid ring 15 and corresponding concave radial recess in the elastomeric:

element 12 may have a ring 15 height or recess depth of less than onehalf of the thickness of the elastomeric clement 12, but more than ten percent of the thickness of the elastomeric element 12. The thickness of the elastomeric element 12 may be defined as one half of the difference between the OD and the ID of the elastomeric; element 12 as measured at a point where the OD is at a maximum and the ID is at a minimum.

When the packoff assembly 10 is being set, the tapered surfaces 17 and 18 of the rigid ring 15 may provide a wedge-like effect against the inner surface 19 of the elastomeric clement 12 as the inner surface 19 slips along the tapered surfaces 17 and 18 of the rigid ring 15, thus assisting in radially displacing the clastomeric cleme nt 12 outward in order that the clastomeric clement 12 may then engage and seal against the inside surface 26 ofthe casing 50. In addition, the rigid ring 15 may also act to reduce any void space which may otherwise tend to be created between the inside surface 19 of the elastomeric clement 12 and tile outer surface 41 of the mandrel 40, thus providing rigid support for the deformed elastomeric:

element 12.

In the Fig. I embodiment, as the packoff assembly 10 is further compressed, the malleable upper deformation ring'70 and the malleable lower deformation ring 21 may be flared radially outward toward the inner surface 26 of the casing 50, thereby engaging the wall of the casing. The deformation rings 20 and 2 1 maybe plastically deformed to remain in engagement with the casing 50 for the purpose of enhancing the fluid tight seal with the casing 50 by supporting the deformed elastomcric element 12 and reducing risk of unwanted extrusion of the elastomeric element 12, which may thereby enhance the differential pressure seating capability of the elastomeric clement 12.

CAc1icnt\T1W\27-pat appln.wpd 18- Also, in a preferred embodimcnt,duHng compression of the packoff assembly 10, the upper shearable ring 30 and the lower shearable fing 31 may be sandwiched between their respective upper or lower packer body 42 or 43 and their respective upper or lower inner supporting rings 81 or 82. The respective upper or lower inner support fings 81 or 82 may be sandwiched between the respective upper or lower shearable rings 30 or 31 and the deformation control ring 20 or 21. The intended result is to cause the respective upper and lower shearable ring 30 or 3 1, to shear fracture at one or more positions and expand at each fracture until the OD of the shearable ring 30 or 31 changes from an OD in the unset position that may be substantially the same as the OD of the packer body 43 or 44 to an OD that is substantially the same as the ID of the casing 50, thus expanding the shearable ring 30 or 31 to internal engagement with the ID of the casing 50. This expansion of the shearable rings ZD C2 t> and 3 1 may provide rigid support in the annular area between the mandrel 40 and the casing 50, to both the elastomeric element 12 and the malleable deformation control rings and 2 1.

As compression of the packoff assembly 10 progresses, deformation of the clastonicric element 12, expansion ofthe deforniation control rings 20 and 2 1. and expansion oftheshearable rings 30 and 31 each may progress until substantially all axial setting force energy is consurned by the packoff assembly 10. In one embodiment, as illustrated in Fig.

I A, when the axial setting force may be relaxed, a pair of slips 66 and 67 or other holding mechanism, which may be fixed to the packoff assembly 10 but may be located elsewhere, may eng-age with the casing 50 to retain large portion of the setting energy which may be stored within the set packoff assembly 10. In other. embodiments the plastic defomiation of the components may be sufficient to retain the setting position and forces. Other mechanisms, such as pipe weight or otherwise may also be utilized to retain the setting forces in the packoff assembly.

C:\cUentMN%'\27-pat appln.wpd It is a feature of the present invention that the axial force required to initiate and complete deformation of an elastomeric element 12 and set the packoff assembly 10 may be less than the force required to set analogous components which do not include a rigid ring and/or the radial concave recess as partially defined by surfaces 27 and 28. As an axial setting force may be applied to the elastomeric element 12, radially outward deformation of the elastomeric element 12 should initiate near the axial center of the elastomeric element 12, with outward deflection propagating simultaneously, axially up and down along the elastomeric element 12 beginning near the axial midpoint of the elastomeric element 12, so as to engage the casing 50, and should continue outward scaling deformation with continued force application. This reduced setting force requirement may be facilitated in part by the rigid ring 15 and the radial inward surfaces 27 and 28 of the elastomeric element 12.

It is also a feature of the present invention to maintain a fluid tight seal at relatively high di fficrential pressure, including pressure in excess of 10,000 psia. As needed or desired based partially upon setting force requirements and pressure rating ofthe packoff seal, the components of this invention may each be selectively included or excluded ill any number of embodiments or configurations, cacti and all of which are within the scope of this invention. In addition, it is a feature of the invention to utilize a single elastomeric element 12 within each packoff assembly 10, not withstanding the fact that a packer or tool could utilize more than one packoff assembly.

Referring also to Fig. 1, Fig. 3 generally illustrates in cross section, an embodiment 1:1 In of a enerally cylindrical rigid ring 15 having a through bore along its central axis 62 with 9 C' 0 an upper tapered surface and a lower tapered suface, a substantially conical outer surface connecting the tapered surfaces, and a substantially straight inner surface parallel with the central axis. In this embodiment, a small perpendicular lip 72 and 73 is included and illustrated at each end between the inner surface and tapered surface. The height or thickness of this lip may vary from non-existent to twenty percent of the thickness of the ring 15, as C:\chent\T1W\217-pat app1n.wpd defined previously. Other embodiments of a rigid ring may include variations of angles, profiles, lengths, heights, material, size and shape of the ring. Fig. 3 is illustrative only and is merely representative of one embodiment of the invention. Those skilled in the art will appreciate that other variations in the dimensions and materials of the other components of the packoff assembly, including the shearable rings, inner support rings, deformation control rings and the elastomeric element may be made without variation from the scope and spirit 0 of this invention.

Those skilled in the art will also appreciate that the components of the present invention of the packoff assembly 10, namely the rigid ring 15, the deformation control rings 20 and 2 1, the inner support rings 81 and 82, and the shearable rings 30 and 3 1, may each be embodied as illustrated in the preferred embodiments or may be embodied, separately or in any combination thereof, in other embodiments.

In addition, othcr embodiments may include a packoff assembly utilizing components oCthis invention wherein setting forces may be imparted to act upon an upper packer body as opposed to a lower packer body, or the forces may act simultaneously upon both bodies, imparting movement Into each packer body, as for example in a hydraulic set packer. In other embodinicrits, the mandrel may not move and/or the packer bodies may each or both move with respect to one another. Other embodiments may employ a mandrel that is engaged with neither packer body, employing other methods for actuating the packoff C assembly. Setting forces may be generated mechanically, hydraulically, thermally or pneumatically, and may be imparted axially, rotationally or otherwise to effect setting the I packoff assembly. This invention may be embodied for use with packer, retainers, plugs or ariv other oilfield or related tools or instruments, or unrelated applications. Although a preferred embodiment described herein illustrated components of the invention employed in a well bore in a generally vertical orientation, this invention or any combination of its components may have utility in various applications, including deviated or horizontal well C:\c1ient\T1M-'7-pjr appln.wpd bores and may have uses other than in well bores, including pipelines or any other generally cylindrical conduit.

While preferred embodiments of the present invention have been described and illustrated in detail, it is apparent that still further modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, which is set forth in the following claims.

CAcIicnt\TINN'\1-7-pat appin.wN

Claims

What is claimed is:

I. A packoff assembly for use in a wellbore to seal off a flow path having a substantially circular cross-section, the packoff assembly comprising:

a packoff assembly body; a packoff element supported on the packoff assembly body, the packo,ff element including an elastomeric element for sealing against a wall defining the flow path; a mandrel supported on the packoff assembly body and axially moveable relative to the packoff assembly body for exerting a compression force on the elastomeric element to set the packoff assembly; and the packoff element supporting a rigid internal ring thereon, the elastomeric element extending continuously from above the rigid ring to below the rigid ring and acting to minimize an axial force required to set the packoff assembly in the wellbore.

2. The packoff assembly as defined in Claim 1, wherein the elastomeric element is a substantially homogenous element.

3. The packoff assembly as defined in Claim 1, wherein the elastomeric element is substantially sleeve-shaped and wherein the rigid ring is substantially centered axially between an upper end of the elastomeric element and a lower end of the elastomeric element.

4. The packoff assembly as defined in Claim 1, wherein the rigid ring is formed from metal.

5. The packoff assembly as defined in Claim 1, further comprising:

the rigid ring having a radially outward upper tapered surface and a radially outward lower tapered surface.

Q\cHcnt\TtNV\27-pat appln.wpd 6. The packoff assembly as defined in Claim 5, wherein each of the upper tapered surface and lower tapered surface are tapered relative to a centerline of a packoff assembly body at from about 15 degrees to about 60 degrees.

7. The packoff assembly as defined in Claim 6, wherein each of the upper tapered surface and lower tapered surface are tapered relative to a centerline of a packoff assembly body at from about 25 degrees to about 30 degrees.

8. The packoff assembly as defined in Claim 1, wherein an inner surface of the rigid ring is substantially aligned with and is co-planar with an inner surface of the elastomeric element.

9. The packoff assembly as defined in Claim 1, further comprising:

D a malleable deformation control ring adjacent each end of the elastomeric element and circumfercncially encompassing the mandrel, each control ring being in planar engagement with a corresponding end of the elastomeric element when the packo Ff assembly is set.

10. The packoff assembly as defined in Claim 9, wherein each deformation control ring extends radially outward from the packoff assembly mandrel in planar engagement with a corresponding end of the elastomeric element and has a radially outward C 0 portion spaced from the mandrel and parallel wit.a central axis of the mandrel such that the deformation ring will be in circumferential engagement with the wall when the pack-off assembly is set.

CAcIicnt\TIN%'\27-pat appln.wpd 11. The packoff assembly as defined in Claim 9, fur-ther comprising:

a backup ring adjacent the control ring and circumferentially encompassing the mandrel.

12. The packoff assembly as defined in Claim 11, wherein the backup ring has a first side in planar conformity with the control ring and a second side in planar conformity with the packoff assembly body.

13. The packoff assembly as defined in Claim 11, wherein the backup ring includes an upper backup ring and lower backup ring, each backup ring being a metallic ring and having a shearable portion to allow for expansion of the backup ring when the packoff to assembly is set.

14. The packoff assembly as defined in Claim 1, further comprising; a scaling element adjacent the mandrel; a gripping mechanism adjacent the mandrel; and a hydraulically actuated mechanism including at least one piston exposed to a is controllable hydraulic pressure on one side and a lesser hydraulic pressure on an opposing side, such that a hydraulic force moves the piston to compress the elastomeric element and set the packoff assembly.

15. The packoff assembly as defined in-Claim 1, wherein the packoff assembly body has a through bore therein.

C:\client\TIS-17-pat appin.wpd 16. A packoff element for use in a packoff assembly to sea] against a flow path having a substantially circular cross-section, the packoff assembly including the packoff assembly body and a mandrel supported on the packoff assembly body and axially moveable while exerting a compressive force on the packo ff element, the packoff element comprising:

an clastorneric element for sealing against a wall defining the through bore; and a rigid internal ring, the elastomeric element extending continuously from above the rigid ring to below the rigid ring.

17. The packoff element as defined in Claim 16, wherein the elastomeric element is a substantially homogenous element.

to 18. The packoff clement as defined in Claim 17, wherein the clastomeric clement is substantially sleeve-shaped and wherein the rigid ring is substantially centered axially between an upper end of the clastomeric element and a lower end of the clastomeric element.

19. The packoff element as defined in Claim IS, further comprising:

the elastomeric element having a radially inward first surface and a radially inward C second surface, the first surface configured for substantial planar engagement with the upper I I 4_1 tapered surface when the packoff assembly is unset and the second surface configured for substantially planar ensgagement with the lower tapered surface when the packoff assembly is unset.

CAdicnATMA-17-pat appin.%qA 20. A method of setting a packoff assembly in a wellbore to seal against a flow path having a substantially circular cross-section, the method comprising:

providing a packoff assembly including apackoff assembly body, a packoff element having an elastomeric element for sealing against a wall defining the flow path, and a mandrel moveable relative to the packoff assembly body for exerting a compressive force on the packoff element to set the packoff assembly; supporting a rigid internal ring on the elastomeric element, the rigid ring being positioned axially between an upper end of the elastomeric element and a lower end of the elastomeric element; 0 applying an axial force to set the packoff assembly; and in response to the axial force, causing a portion of the elastomeric element radially outward of the control ring to move radially outward and initially engage and seal with the wellbore.

21. The method as defined in Claim 20, further comprising; in response to additional axial force, causing an upper portion of the elastomeric element and a lower portion of the elastomeric element above and below the control ring., respectively, to move radially outward and subsequently engage and seal - with the wellbore.

22. The method as defined in Claim 20, further comprising:

forming the elastomeric element as a substantially homogenous element.

!0 2 33. The method as defined in Claim 20, further comprising:

C positioning the intemal ring substantially midway between an upper end of the elastomeric element and a lower end of the elastomeric element.

CAchcnt\TIN%'\_17-pat appIn.%vpd 24. The method as defined in Claim 20, further comprising:

forming the rigid ring with an outward upper tapered surface and an outward lower tapered surface; and forming the elastomeric element with a radially inward first surface and a radially inward second surface, the first surface being in substantial planar engagement with the upper tapered surface with the packoff assembly is unset and the second surface being in substantially planar engagement with the lower tapered surface when the packoff assembly is unset.

25. The method as defined in Claim 20, further comprising:

providing a malleable deformation control ring adjacent each end of the elastomeric element and having a circumferentially encompassing the mandrel, each control ring being in engagement with a corresponding end of the elastomeric element when the packoff assembly is set.

26. A packoff assembly substantially as hereinbefore described with reference to Figs. 1, 1 A, 2 and 3 or Fig. 2A.

27. A packoff element for use in a packoff assembly substantially as hereinbefore described with reference to Figs. 1, 1 A, 2 and 3 or Fig.

2A.

28. A method of setting a packoff assembly in a well bore substantially as hereinbefore described with reference to Figs. 1, 1 A, 2 and 3 or m Fig. 2A.