Abstract:
A composite packer or bridge plug includes substantially all nonmetallic components. The design allows the setting tool metallic components to be retrieved after the bridge plug is set. The slips contain flats with mating flats on the cones which extend to one end of the cones and guides for the slips to facilitate proper slip movement into engagement with the wellbore. A lock ring rides on the nonmetallic mandrel and secures the set, using a buttress-type thread to engage into the mandrel body. Alternative designs are revealed for backup to the sealing elements to prevent extrusion. In one design, split rings are axially compressed so that they grow in radial dimension to act as extrusion barriers. In another design, tapered scored rings are rotationally locked against each other and are axially compressed so that they bend into contact with the wellbore to act as extrusion barriers. Axial travel to obtain an extrusion barrier is minimized. The slips are made of a cohesive component and separate from each other upon advancement with respect to the cone. Mandrels of different plugs can lock together to facilitate mill-out in multi-plug installations.

Description:
FIELD OF THE INVENTION 
     The field of this invention relates to downhole packers and bridge plugs which contain principally nonmetallic components so that the packer or plug structure can be easily drilled out. 
     BACKGROUND OF THE INVENTION 
     In many applications where a packer or bridge plug is to be used, there exists a need at some point in time for subsequent removal of the plug. Packers or plugs made primarily from metallic substructures which involve resilient seals, which are compressed in a sealing relationship with the wellbore, generally take a long time to drill or mill out. Accordingly, a need has developed in the past to construct a packer of materials which are more easily drilled out than the traditional metallic structural components of packers and bridge plugs. Accordingly, bridge plugs have been made with wooden mandrels and metallic slips, as illustrated in U.S. Pat. No. 1,684,266. Other designs have featured nonmetallic mandrels and/or slips. These designs are illustrated in U.S. Pat. Nos. 5,224,540; 5,390,737; 5,540,279; 5,271,468; and 5,701,959. Other designs have simply featured softer materials or other design components so as to make the overall packer or bridge plug easy to drill out. These packers include those disclosed in U.S. Pat. Nos. 2,589,506; 4,151,875; and 4,708,202. Additionally, wiper plugs used primarily in cementing have been made of nonmetallic materials to facilitate rapid drill-out. An example of a nonrotating plug of this nature is illustrated in U.S. Pat. No. 4,858,687. 
     When trying to use as few metallic components as possible in a packer or bridge plug, problems develop which are not normally dealt with when constructing a mostly metallic packer. One of the difficulties is the mechanism to hold the set once the packer or bridge plug is set. Accordingly, one of the objectives of the present invention is to simplify the locking mechanism for a packer or bridge plug having primarily nonmetallic components. Another problem with composite bridge plugs or packers is to guard against extrusion of the sealing element using as few components as possible, yet providing sufficient structural strength on either side of the element to retain it in proper set position without significant extrusion due to pressure differential. Accordingly, another object of the present invention is to provide a simple, functional design which will minimize relative axial travel required to make functional the backup assemblies that retain the sealing element against extrusion. Guiding systems for slips are an important feature in a composite packer, and one of the objectives of the present invention is to provide an improved system for guiding the slips from the retracted to the set position. Composite packers will still be run into the well on a setting tool which is metallic. One of the objectives of the present invention is to provide a design which removes the components of the setting tool left behind in prior designs as a result of setting a composite packer. Thus, the objective is to retrieve metallic components of the setting tool after the set, so that subsequent milling will not be lengthened by having to mill through the residual component of the setting tool after the packer or bridge plug is set. 
     In another objective of the present invention, each of the composite plugs has a clutching feature or an extending tab on at least one of the top and bottom. Thus, when there are multiple composite bridge plugs set in the wellbore and they need to be drilled out, they can be pushed against one another to interlock to facilitate the milling of the top most packer or bridge plug while it is held to a lower plug which is still set. These and other features will become apparent to those of skill in the art from a description of the preferred embodiment below. 
     SUMMARY OF THE INVENTION 
     A composite packer or bridge plug is disclosed. The design features substantially all nonmetallic components. The design allows the setting tool metallic components to be retrieved after the bridge plug is set. The slips contain flats with mating flats on the cones which extend to one end of the cones and guides for the slips to facilitate proper slip movement into engagement with the wellbore. A lock ring rides on the nonmetallic mandrel and secures the set, using a buttress-type thread to engage into the mandrel body. Alternative designs are revealed for backup to the sealing elements to prevent extrusion. In one design, split rings are axially compressed so that they grow in radial dimension to act as extrusion barriers. In another design, tapered scored rings are rotationally locked against each other and are axially compressed so that they bend into contact with the wellbore to act as extrusion barriers. Axial travel to obtain an extrusion barrier is minimized. The slips are made of a cohesive component and separate from each other upon advancement with respect to the cone. Mandrels of different plugs can lock together end-to-end to facilitate mill-out in multi-plug installations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS.  1   a-c  illustrate the preferred embodiment of the composite packer of the present invention. 
     FIG. 2 is a perspective view of the cone which guides the slips. 
     FIG. 3 is a section view through the slip assembly showing all the slips retained to each other. 
     FIG. 4 is a view of FIG. 3 showing the slip ring in an end view. 
     FIG. 5 is section view through the lock ring. 
     FIG. 6 is a detail of the engaging thread on the lock ring which engages the mandrel. 
     FIGS. 7,  8  and  9  are section views of an assembly of rings which act as backup and deter extrusion of the sealing element with the ring of FIG. 7 being closest to the sealing element, FIG. 8 between FIGS. 7 and 9 when fully assembled, as shown in FIG.  1   b.    
     FIGS. 10 and 11 are, respectively, section and end views of an alternative embodiment which is preferred for the sealing element backup assembly showing slotted beveled rings being used. 
     FIG. 12 shows in two different positions the overlapping rings which are scored and rotationally locked in the run-in position and the set position. 
     FIG. 13 is the view of FIG. 12 looking at a side view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The packer or bridge plug, which will be referred to as plug P, is shown in the assembly drawing of FIGS.  1   a-c , a known setting tool  10  which can be a metallic structure. The setting tool  10  has a setting sleeve  12  which bears down on spacer washer  14 . Spacer washer  14  is preferably made of a fiber glass/epoxy laminate. Mandrel  16 , which is preferably made of fabric laminated fiber glass or filament wound with high-temperature epoxy resin, supports the slip molding  18 . Slip molding  18  is made preferably of glass-reinforced phenolic moulding compound such as Fiberite® FM 8130E. The slip molding  18  is shown in more detail in FIGS. 3 and 4. As can be seen in FIGS. 3 and 4, the slip molding  18  is a unitary ring featuring individual slips  20  held together by tabs  22 . Each of the slips  20  has a flat portion  24  which rides on a flat  26  of the cone  28  shown in FIG.  2 . Cone  28  has a plurality of guides  30  which guide edges such as  32  and  34 , as shown in FIG.  3  and is made from filament-wound or fabric-laminated epoxy. Referring to FIGS.  1   b  and  1   c , slip molding  18  is in the lower position while slip molding  36  is oppositely oriented in the upper position. The mandrel  16  has a shoulder  38  which supports the slip molding  18 . Cone  28  is shown in the lower position adjacent slip molding  18 , while cone  40  is in the upper position adjacent slip molding  36 . The cones  28  and  40  are identical but mounted in opposite directions. Slip moldings  18  and  36  are also identical but mounted in opposite directions. 
     Referring now to FIG. 3, the slip molding  18  and slip molding  36  each contain inserts  42  which preferably are of a serrated design, as shown in FIG. 3, and made of a hard carbon steel. Alternative metallics or nonmetallics can be inserted as the insert  42  without departing from the spirit of the invention. Each insert  42  which appears on each slip  20  has serrations  44  to help with getting a bite into the casing when the plug P is set. Those of skill in the art will appreciate that the tabs  22 , shown in FIG. 4, will all break as the slip molding  18  or  36  is advanced on its respective cone  28  or  40  because the slips  20  will move away from each other and radially outwardly as they are ramped with flats  24  sliding on flats  26 . By making the slip molding  18  in a single piece, it is easier to produce. Additionally, the design is preferred to using individual slips and holding them in position with a band spring as in the prior art. The use of tabs such as  22  fixes the position of all the slips to each other, plus facilitates assembly of the plug P for run in. 
     Referring again to FIGS.  1   a-c , a lock ring  48 , which is made preferably of aluminum with a maximum yield strength of 35,000 psi, is retained by sleeve  50 , which can be of the same material as the lock ring  48  or a nonmetallic component, such as the material used for mandrel  16 . The unique features of the lock ring  48  and its interaction with the mandrel  16  can be better seen by an examination of FIGS. 5 and 6. The lock ring  48  is longitudinally split and has an internal serration, preferably in the form of a buttress thread  52 . It is preferred that the pitch be fairly long in the order of at least about eight threads per inch. The profile of the thread which is machined into the ring is shown in FIG.  6 . It is further preferred that the relaxed diameter of the split lock ring  48  internally, as represented by the dimension between opposing ridges  54 , be somewhat smaller than the diameter of the mandrel  16  on which the lock ring  48  is assembled so that a preload of stress of about 200-500 psi is seen by the lock ring  48  in its installed position within sleeve  50  upon assembly. The details of the buttress thread  52  can be seen in FIG.  6 . Extending from ridge  54  is preferably a surface  56  which is preferably perpendicular to surface  58 . Surface  58  is parallel to the longitudinal axis  60 . Surface  62  is sloped preferably at about 20°. Ridge point  54  is defined by surfaces  56  and  62 , respectively, and the length of surface  56  is the depth of the ridge  54 , which indicates the maximum penetration of ridge  54  into the mandrel  16  when the plug P is set. The preferred length of surface  56  is in the order of about 0.015-0.020″ for a plug to fit through a 3½″ O.D. opening. 
     Referring to FIG.  1   b , it can be seen that the serration or thread  52  rides on a smooth surface  64  of mandrel  16  and penetrates surface  64  to hold the set. 
     Referring again to the setting tool  10 , there is an upper tension mandrel  66  to which is connected a tension mandrel sleeve  68 . A release stud  70  connects the upper tension mandrel  66  to the lower tension mandrel  72 . An upper sleeve  74  is secured to mandrel  16 . Upper sleeve  74  is preferably made of fabric-laminated fiberglass with high-temperature epoxy or filament-wound fiberglass with high-temperature epoxy. It is secured to the mandrel  16  by high-temperature adhesive and shear pins  76  which are preferably fiberglass rod. The same pins that hold the upper sleeve  74  also retain the plug  78  to seal off bore  80  in mandrel  16 . Plug  78  can be blown clear by breaking pins  76  to equalize plug P before it is milled out. Alternatively, plug  78  can simply be drilled out to equalize the plug P. Plug  78  is preferably made of carbon-filled PEEK or other reinforced composite materials and is secured within bore  80  of mandrel  16  in a sealing relationship due to rings  82  and  84 . Connected to lower tension mandrel  72  are collet fingers  86  which are trapped by tension mandrel sleeve  68  in the position shown in FIG.  1   b . Thus, the lower tension mandrel  72  is held to the upper sleeve  74  when the collets  86  are trapped to the upper sleeve  74 . The collets  86  are released from sleeve  74  to allow retrieval of the setting tool  10 . When the setting tool  10  operates, a tensile force is exerted on release stud  70 , causing it to shear at the necked down portion  88 . At the same time, the setting sleeve  12  bears down on spacer washer  14 , with a net result of setting the packer due to relative movement. In the course of this operation, the release stud  70  breaks to allow the setting tool  10  to be retrieved. Upward movement on the setting tool  10  allows shoulder  90  on tension mandrel sleeve  68  to engage shoulder  92  on lower tension mandrel  72  so as to retrieve the lower tension mandrel  72  and that portion of the release stud  70  which is affixed to it. Accordingly, one of the advantages of the present invention is that the metallic portions of the setting tool are retrieved from above the plug P when the setting tool  10  is removed after set, as opposed to prior art designs which left metallic components of the setting tool above the nonmetallic packer or plug as a result of setting such a device. 
     Referring now to FIGS.  1   b  and  c , a sealing element  94  is shown retained by an anti-extrusion assembly comprising a beveled packing element retainer ring  96 , which is seen in greater detail in FIG.  7 . It is a complete ring and preferably has no longitudinal split. Stacked behind the retainer ring  96 , which is preferably made of a phenolic composite material called Resinoid 1382, is a packing ring  98 , as seen in FIG.  8 . This ring is longitudinally split and is shaped to accept in a nested manner the cone ring  100 , which is shown in FIG.  9 . The packing ring  98  and cone ring  100  are preferably made of Amodel 1001 HS, a high-performance thermoplastic material. The longitudinal splits in the packing ring  98  and cone ring  100  are offset. Accordingly, when there is relative longitudinal compression, such as when the setting tool  10  is actuated, spacer washer  14  moves closer to shoulder  38 . This longitudinal compression radially expands packing ring  98  and cone ring  100  so as to allow them to reach the casing and guard against extrusion of the element  94 . The sealing element  94  has similar assemblies above and below, as illustrated in FIGS.  1   b  and  1   c . In an alternative and preferred design of an anti-extrusion assembly illustrated in FIGS.  10 - 13 , the assembly of rings  96 ,  98 , and  100  are replaced with a plurality of overlapping beveled rings such as  102  and  104 , shown in FIG.  12 . These rings  102  and  104  are slotted radially, with a plurality of spaced-apart slots  106 , which are also shown in FIG.  10 . On the other side of each of the rings and spaced between the slots  106  are tabs  108 , also best seen in FIGS. 10 and 11. It can be seen that the tabs  108  of one ring extend into the slots  106  of the adjacent ring such that the slots are offset in the run-in position shown on the left-hand side of FIG.  12 . The extension of the tabs  108  into the slots  106  prevents relative rotation between rings such as  102  and  104 . As shown in the right-hand side of FIG. 12, when exposed to axial compression, the slots  106  spread apart as the beveled rings are moved toward a flattened position so that the outside diameter of each of the rings grows until it makes contact with the tubing or casing  110 . The same effect is shown in a side view in FIG.  13 . Two or more rings such as  102  and  104  can be used without departing from the spirit of the invention. The operation of rings  102  and  104  is distinctly different from the assembly of rings  96 ,  98 , and  100  described and shown in FIGS. 7,  8 , and  9 . In the design employing the rings  96 ,  98 , and  100 , a greater degree of axial travel is necessary to open up the longitudinal splits in rings  98  and  100  sufficiently far to encounter the tubing or casing  110 . On the other hand, using two or more of the slotted rings, such as  102  or  104 , S allows such rings to contact the tubing or casing  110  with a far lesser amount of axial relative movement during the setting process. This occurs because the rings  102  and  104  are actually bent toward a flattened position due to relative axial movement by an angular bending which opens up the slots  106 , as shown in FIGS. 12 and 13 in the right-hand portion. Thus, the bending in rings  102  and  104  occurs about the center of the rings and down toward a plane perpendicular to the centerline of those rings, as opposed to the rings  98  and  100  which must be spread radially until contact with the casing or tubing  110 . In many situations with available running tools or setting tools  10 , the amount of relative axial movement is limited, thus creating a distinct advantage for the anti-extrusion back-up system illustrated by using the radially slotted rings such as  102  and  104 . 
     In another feature of the present invention, the plug P has at least one of top and bottom end clutching feature which is shown in FIG.  1   c , for example, at the bottom of the plug P as item  112 . In an installation involving multiple packers or plugs P, they can be pushed one against the other and interlocked due to the conforming mating shapes which prevent relative rotation. Thus, one plug P which has been released can fall and be engaged by the next lower plug P in a manner where no relative rotation can occur to facilitate the further milling of the plug P in the wellbore. The clutching or nonrotation feature can be accomplished in a variety of ways, including matching slanted tapers or other types of lug arrangements. 
     Those skilled in the art will now appreciate that there are several advantages to the plug P as described above. One of the features is the ability to engage the remaining portions of the setting tool  10  below the tensile failure so that they can be retrieved after the plug P is set. By actuation of the setting tool  10 , the mandrel  16  is brought up with respect to the spacer washer  14  and the lock ring  48  holds the set position between the mandrel  16  and the sleeve  50 . The outer sloping surface  114  (see FIG. 5) of the lock ring  48  engages a mating sloping surface internally on sleeve  50  to further assist the ridge  54  of the buttress thread  52  to dig into the smooth surface  64  of mandrel  16 . Thus, the locking device is simple in its operation and is easily drilled out, being made of a relatively soft aluminum material which can interact with the smooth surface  64  of the mandrel  16  to hold the set of the plug P. At the same time, the removal of the setting tool  10  entails the recapture of the severed component parts so that subsequent milling out of the plug P is facilitated by the absence of durable metallic parts left over from the setting operation. The alternative designs which have been depicted for extrusion resistance of the element  94  allow expansion so that rings  98  and  100  extend fully against the casing or tubular  110 . In the alternative preferred embodiment, using the beveled rings with radial slots  106 , the feature of full bore protection against extrusion is accomplished with far less relative longitudinal movement than it takes to set the rings  98  and  100  against the tubing or casing  110 . 
     The interaction between the individual slips  20  and the flat surface  26  on the cone  28 , for example, allows a greater flexibility in manufacturing of the slip molding  18  and a broader versatility in size ranges as the slips  20  can cover a greater extension due to the interaction of the flat surface  24  on the slips  20  with the corresponding surface  26  on the cone such as  28 . The design is to be contrasted with cones of prior designs where the flat segments on the cones come to a point whereas in cone  28 , for example, the flat segments  26  are cut clean to the end, assuring a more uniform contact with each of the slips  20  and the tubing or casing  110 . Depending on the downhole environment, the slip molding  18  can be made from Fiberite FM 8130 or 5083, or E7302 Resinoid 1382X. Finally, the clutching feature, in a multiple installation, allows taking advantage of the fact that the lowermost plugs P are still fixed to ease in the milling of those plugs P which are above due to the ability of one plug P to interconnect with an adjacent plug in a manner preventing relative rotation. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.