Patent Publication Number: US-11035197-B2

Title: Anchoring extrusion limiter for non-retrievable packers and composite frac plug incorporating same

Description:
FIELD OF THE INVENTION 
     This invention relates in general to anti-extrusion limiters for non-retrievable packers, commonly called “frac plugs” which are used to isolate selected zones in cased well bores for the purposes of well completion or recompletion, and, in particular, to an anchoring extrusion limiter for non-retrievable packers, and a composite frac plug incorporating same. 
     BACKGROUND OF THE INVENTION 
     Packers for isolating fluid pressures in cased well bores are well known in the art. Many such packers are single-use packers that are not retrievable from the well bore. One example of a single-use packer is the frac plug, used to isolate fracturing fluid pressure during hydrocarbon well completion or recompletion operations. Once a frac plug is set it can only be removed from the well bore by drilling out the frac plug using a drill bit on a tubing work string. The drill-out operation is facilitated by providing a frac plug made entirely of composite materials. Once such frac plug is described in Applicant&#39;s co-pending U.S. patent application Ser. No. 15/935,163 entitled Composite Frac Plug which was filed on Mar. 26, 2018, the entire specification of which is incorporated herein by reference. Frac plugs must contain extreme fluid pressures within cased well bores, generally at elevated temperatures. The fluid pressure can cause the main sealing element of frac plugs to extrude and lose their fluid sealing contact with the well bore casing. Anti-extrusion inhibitors help control sealing element extrusion and maintain the sealing element in sealing contact with the well bore casing. Anti-extrusion rings are one type of anti-extrusion inhibitor that has proven to be effective in inhibiting sealing element extrusion. However anti-extrusion rings can be deformed or displaced by an extruding main sealing element. An anchoring extrusion limiter that engages the casing to resist main sealing element extrusion pressure is therefore desirable. 
     Extreme fluid pressures also tend to displace the frac plug within the cased well bore. The frac plug is provided with “slips” that bite and grip the casing to anchor the frac plug within the well bore. The slips ride up a slip ramp to a set condition, so the greater the fluid pressure on the frac plug, the more the slips bite and grip the casing to anchor the frac plug in the well bore. However, the thrust load on the slips may exceed a material strength of the slip bodies or anchor elements. A backup anchor to the frac plug slips is therefore also desirable. 
     There therefore exists a need for an anchoring extrusion limiter and a frac plug incorporating same. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an anchoring extrusion limiter and a composite frac plug incorporating same. 
     The invention therefore provides a anchoring extrusion limiter for a main sealing, element of a non-retrievable packer, comprising a plurality of ring segments held together by at least one fracture band that is designed to fracture when the anchoring extrusion limiter is expanded as the non-retrievable packer is shifted from a run-in condition to a set condition, each ring segment having a top surface with least one embedded ring segment insert adapted to bite and grip a well casing in which the non-retrievable packer is set. 
     The invention further provides a anchoring extrusion limiter for a main sealing element of a non-retrievable packer comprising a plurality of ring segments respectively being substantially V-shaped in cross-section and at least one ring segment insert adapted to bite and grip a well casing embedded in a top surface thereof, the respective ring segments being held together by a pair of fracture bands that are received in respective ring segment grooves respectively located on opposite sides of the respective ring segment inserts, the respective fracture bands being adapted to fracture when the anchoring extrusion limiter is expanded as the non-retrievable packer is shifted from a run-in condition to a set condition. 
     The invention yet further provides a composite frac plug, comprising: a composite mandrel with a central passage, the composite mandrel further having an up-hole end and a downhole end with a mandrel hub on the up-hole end, and an end sub securely affixed to the downhole end; an elastomeric gripper assembly mounted to the mandrel, the elastomeric gripper assembly having an insert groove with a plurality of circumferentially spaced-apart inserts that bite and grip a casing of a cased wellbore when the composite frac plug is in, a set condition; a main sealing element downhole of the elastomeric gripper assembly; a sliding cone downhole of the main sealing element; an anchoring extrusion limiter downhole of the main sealing element, the anchoring extrusion limiter comprising a plurality of ring segments held together by at least one fracture band that fractures when the anchoring extrusion limiter is expanded as the composite frac plug is shifted from a run-in condition to the set condition, each ring segment having a top surface with at least one embedded ring segment insert adapted to bite and grip a well casing in which the composite frac plug is set, to inhibit downhole movement of the anchoring extrusion limiter and the composite frag plug after the composite frac plug has been shifted to the set condition; a slip hub downhole of the anchoring anti-extrusion limiter; and a slip assembly downhole of the slip hub, the slip assembly comprising a plurality of slips adapted to slide up the slip cone to bite and grip the casing of the cased wellbore when the composite frac plug is shifted from the run-in condition to the set condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of one embodiment of an anchoring extrusion limiter accordance with the invention, in an unexpended or “run-in” condition; 
         FIG. 1A  is a perspective view of a composite frac plug incorporating the anchoring extrusion limiter shown in  FIG. 1 ; 
         FIG. 2  is a perspective view from the left of section  2 - 2  of the composite frac plug shown in  FIG. 1A ; 
         FIG. 3  is a right end elevational view of the section  2 - 2  of the composite frac plug shown in  FIG. 2 , within a well casing; 
         FIG. 4  is a cross-sectional view of the section  2 - 2  of the composite frac plug taken along lines  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a perspective view of the composite frac plug shown in  FIG. 1A  in a set condition; 
         FIG. 6  is a perspective view of section  6 - 6  of the composite frac plug shown in  FIG. 5 ; 
         FIG. 7  is a right end elevational view of the section  6 - 6  of the composite frac plug shown in  FIG. 6 , within the well casing; 
         FIG. 8  is a cross-sectional view of the section  6 - 6  of the composite frac plug taken along lines  8 - 8  of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides a novel anchoring extrusion limiter and a composite frac plug incorporating same. The anchoring extrusion limiter inhibits an extrusion of a main sealing element of the composite frac plug. The anchoring extrusion limiter is constructed from a plurality of identical ring segments. Each ring segment has a top surface that is provided with at least one ring segment insert adapted to bite and grip a well casing when the composite frac plug is shifted from a “run-in” to a “set” condition. This ensures that the anchoring extrusion limiter is very strongly inhibited from displacement in the cased well bore by frac fluid pressure contained by a main sealing element of the composite frac plug. The anchoring extrusion limiter is very effective in inhibiting packer element extrusion under high temperature and fluid pressure conditions, while providing back-up anchoring in a cased well bore to the anchoring slips of the frac plug. The ring segments are readily constructed from rigid plastic, or composite material using injection molding, casting, composite tape laying or 3-D printing techniques well known in the art. In one embodiment, the ring segment inserts are ceramic cylinders. In one embodiment, the ring segments are held together by a pair of pre-scored fracture bands that are adapted to fracture as the anchoring extrusion limiter is expanded, from the run-in to the packer-set condition. 
     
       
         
           
               
            
               
                   
               
               
                 PARTS LIST 
               
            
           
           
               
               
               
            
               
                   
                 Part No. 
                 Part Description 
               
               
                   
                   
               
               
                   
                 10 
                 Anchoring extrusion limiter 
               
               
                   
                 12 
                 Ring segments 
               
               
                   
                 14 
                 Ring segment inner surface 
               
               
                   
                 16 
                 Ring segment top surface 
               
               
                   
                 18 
                 Ring segment side surface 
               
               
                   
                 20 
                 Ring segment inserts 
               
               
                   
                 22 
                 Fracture bands 
               
               
                   
                 24 
                 Fracture band grooves 
               
               
                   
                 26 
                 Fracture band scores 
               
               
                   
                 30 
                 Composite frac plug 
               
               
                   
                 32 
                 Composite mandrel 
               
               
                   
                 34 
                 Composite mandrel hub 
               
               
                   
                 36 
                 Composite mandrel passage 
               
               
                   
                 38 
                 Shear screw bores 
               
               
                   
                 40 
                 Gauge load ring 
               
               
                   
                 42 
                 Gauge load ring retainer pins 
               
               
                   
                 44 
                 Elastorneric gripper assembly 
               
               
                   
                 46 
                 Elastomeric gripper assembly groove 
               
               
                   
                 48 
                 Ceramic inserts 
               
               
                   
                 50 
                 Main sealing element 
               
               
                   
                 51 
                 Sliding cone 
               
               
                   
                 52 
                 Slip hub 
               
               
                   
                 54 
                 Slip cone 
               
               
                   
                 56 
                 Anti-extrusion cone 
               
               
                   
                 58 
                 Slip hub retainer pins 
               
               
                   
                 60 
                 Slip assembly 
               
               
                   
                 62 
                 Slip retainer bands 
               
               
                   
                 64 
                 Composite slips 
               
               
                   
                 66 
                 Ceramic slip inserts 
               
               
                   
                 68 
                 Lower end sub 
               
               
                   
                 70 
                 Lower end sub retainer pins 
               
               
                   
                 72 
                 Frac ball 
               
               
                   
                 74 
                 Well casing 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 1  is a perspective view of an embodiment of an anchoring extrusion limiter  10  in accordance with the invention, in an unexpanded or the run-in condition. The anchoring extrusion limiter  10  is constructed using a plurality of identical ring segments  12  that are substantially V-shaped in cross-section (see  FIG. 4 ). Each ring segment  12  has an inner surface  14 , a top surface  16  and side surfaces  18 . In one embodiment, mating ring segment end faces are radially-flat surfaces. However, it should be understood that this is a matter of design choice and the mating ring segment end faces can be 2-dimensionally curved surfaces, or 3-dimensionally curved surfaces as described in Applicant&#39;s co-pending U.S. patent application Ser. No. 16/561,385 entitled Single-Set Anti-Extrusion Ring with 3-Dimensionally Curved Mating Ring Segment Faces filed Sep. 5, 2019, the entire specification of which is incorporated herein by reference. 
     Each ring segment  12  also has at least one ring segment insert  20  embedded in a top surface  16  thereof. In one embodiment, each ring segment  12  includes three equally-spaced ring segment inserts  20  and the ring segment inserts  20  are ceramic cylinders, though this is also a matter of design choice. Any other fracture-resistant and abrasion-resistant material that is harder than well casing, such as a steel alloy, a carbide or the like, may also be used for the ring segment inserts  20 . Each ring segment insert  20  is embedded in the top surface  16  at an angle offset from a radius of the anchoring extrusion limiter  10  so that an edge of each ring segment insert  20  adjacent one side of the of the anchoring, extrusion limiter  10  projects above the top surface  16  (see  FIG. 4 ). When a non retrievable packer is assembled using the anchoring extrusion limiter  10 , the edge of the anchoring extrusion limiter  10  with the projecting ring segment inserts  20  is oriented to be opposite a main sealing element of the non-retrievable packer (see  FIGS. 4 and 8 ), so that the respective ring segment inserts  20  will bite and grip the well casing to inhibit movement of the ring segments  12  after the anchoring extrusion limiter  10  is shifted from the run-in condition to the set condition. 
     In one embodiment, the respective ring segments  12  are bound together in the run-in condition by a pair of fracture bands  22 . In one embodiment, each fracture band  22  is a rigid ring that is substantially square in cross-section and has a plurality of spaced-apart fracture band scores  26 . The respective fracture bands  22  are received in respective fracture band grooves  24  located on opposite sides of the ring segment inserts  20 . The fracture band scores  26  provide weakened areas in the fracture bands  22  to promote breakage of the respective fracture bands  22  when the anchoring extrusion limiter  10  is shifted from the run-in to the packer-set condition to permit the anchoring extrusion ring  10  to expand outwardly into contact with a well casing, as will be explained below. 
       FIG. 1A  is a perspective view of a composite frac plug  30  equipped with the anchoring extrusion limiter  10  shown in  FIG. 1 , in the run-in condition. The composite frac plug  30  is one embodiment of composite frac plugs and a method of setting same described in detail in Applicant&#39;s co-pending U.S. patent application Ser. No. 15/935,163 entitled Composite Frac Plug, which was filed on Mar. 26, 2018, the entire specification of which is incorporated herein by reference. 
     The composite frac plug  30  has a composite mandrel  32  with a composite mandrel hub  34 . A composite mandrel passage  36  provides fluid communication through an entire length of the composite mandrel  32 . Shear screw bores  38  in the composite mandrel hub  34  receive shear screws (not shown) that connect the composite frac plug  30  to a frac plug setting sleeve (not shown) that is, in turn connected to a surface-located wireline setting tool (a Baker style size 20, for example, not shown) used to set the composite frac plug  30  in a cased well bore in a manner well known in the art and explained in detail in Applicant&#39;s above-referenced co-pending, patent application. A gauge load ring  40  downhole of the composite mandrel hub  34  is connected to the composite mandrel  32  by gauge load ring preset retainer pins  42 . The gauge load ring preset retainer pins  42  secure the gauge load ring  40  in the run-in position shown in  FIG. 6  until the composite frac plug  30  is pumped down to a desired location in a wellbore. The gauge load ring preset retainer pins  42  shear when the composite frac plug  30  is shifted from the run-in condition to a packer set condition, as explained in Applicant&#39;s co-pending patent application referenced above, Downhole of the gauge load ring  40  is an elastomeric gripper assembly  44  with a circumferential elastomeric gripper assembly groove  46 . Circumferentially distributed in the elastomeric gripper assembly groove  46  are a plurality of ceramic inserts  48  designed to bite and grip a well casing when the composite frac plug  30  is moved to the set condition shown in  FIG. 5 . In the run-in condition shown  FIG. 1A , the ceramic inserts  48  are recessed within the elastomeric gripper assembly groove  46  and do not contact a casing of a cased well bore. 
     Adjacent a downhole side of the elastomeric gripper assembly  44  is an elastomeric main sealing element  50 . The main sealing element  50  provides a high-pressure seal against a well casing  74  (see  FIGS. 3 and 4 ) when the composite frac plug  30  is in the set condition (see  FIGS. 5-8 ). Adjacent a downhole side of the main sealing element  50  is a sliding cone  51 , the structure and function of which will be described below with reference to  FIG. 4 . Adjacent a downhole side of the sliding cone  51  is the anchoring extrusion limiter  10 , described in detail above. The anchoring extrusion limiter  10  inhibits extrusion of the main sealing element  50  when the composite frac plug  30  is in the set condition and subjected to high fluid pressures, and helps anchor the composite frac plug  30  in a cased well bore when the composite frac plug  30  is in the set condition, as will be explained below with reference to  FIGS. 5-8 . Adjacent a downhole side of the anchoring extrusion limiter  10  is a slip hub  52 . The slip hub  52  is secured to the composite mandrel  32  by slip hub retainer pins  58 , which shear when the composite frac plug  30  is shifted from the run-in condition to the set condition. The slip hub  52  provides a slip cone  54  for a slip assembly  60  that, in one embodiment, is a frangible slip assembly that includes six composite slips  64  that are bound together by slip retainer bands  62  while the frac plug  30  is in the run-in condition. In one embodiment each composite slip  64  includes three ceramic slip inserts  66 . Adjacent a lower end of the slip assembly  60  is a lower end sub  68 . The lower end sub  68  is secured to the lower end of the composite mandrel  32  by lower end sub retainer pins  70  arranged in two staggered rows. A frac ball  72  inhibits fluid flow through the composite mandrel passage  36  of the composite mandrel  32  while the composite frac plug  30  is being pumped down a cased well bore and while the composite frac plug is pressure isolating a well bore zone being stimulated using fracturing fluid, for example. 
       FIG. 2  is a perspective view from the left of section  2 - 2  of the composite frac plug  30  shown in  FIG. 1A . As explained above, a downhole side of the main sealing element  50  abuts the sliding cone  51 , which supports an uphole side of the anchoring extrusion limiter  10 . A downhole side of the anchoring extrusion limiter  10  is supported by an uphole end of the slip hub  52 , as better seen in  FIG. 4 . The slip assembly  60  is carried on a downhole end of the slip hub  52  when the composite frac plug  30  is in the run-in condition. 
       FIG. 3  is a right end elevational view of the section  2 - 2  of the composite frac plug  30  shown in  FIG. 2 , within a well casing  74 . As can be seen, in the run-in condition of the composite frac plug  30 , the ceramic slip inserts  66  of the respective composite slips  64  do not bite or grip the well casing  74 , nor do the ring segment inserts  20  of the anchoring extrusion limiter  10 , as will be explained below. 
       FIG. 4  is a cross-sectional view of the section  2 - 2  of the composite frac, plug  30  taken along lines  4 - 4  of  FIG. 3 . As explained above, the anchoring extrusion limiter  10  is supported on the uphole side by the sliding cone  51  and on the downhole side by an anti-extrusion cone  56  on an uphole end of the slip hub  52 . In the run-in condition the ring segment inner surfaces  14  of each ring segment  12  rest against the composite mandrel  32 , which is shown in dashed lines for purposes of illustration. As can be further seen, in the run-in condition, the projecting edge of each ring segment insert  20  is on a side of the respective ring segments  12  opposite the main sealing element  50  and spaced below respective top edges of the sliding cone  51  and the anti-extrusion cone  56 . 
       FIG. 5  is a perspective view of the composite frac plug  30  shown in  FIG. 1A  in a set condition. As can be seen, in the set condition, the elastomeric gripper assembly  44  is compressed to an extent that the ceramic inserts  48  are forced upwardly out of the elastomeric, gripper assembly groove  46  (see  FIG. 1A ) into biting and gripping contact with the casing, as explained in Applicant&#39;s co-pending application Ser. No. 15/935,163 referenced above and shown in  FIG. 8 . The main sealing element  50  is compressed and forced outwardly into high-pressure sealing contact with the well casing  74  (see  FIG. 8 ), and the anchoring extrusion limiter  10  is expanded to an extent that the respective fracture bands  22  have broken at one or more of the fracture band scores  26 , and the mating faces  19  of the respective ring segments  12  have separated, moving the ring segment inserts  20  into biting and gripping contact with the well casing  74 , as also shown in  FIG. 8 . As well, the respective composite slips  64  have been forced up the slip cone  54  of the slip hub  52  and the ceramic slip inserts  66  are forced into biting and gripping contact with the well casing  74  (see  FIG. 8 ). As understood by those skilled in the art, in the set condition, the elastomeric gripper assembly  44  holds the main sealing element in the set condition, i.e. in high-pressure sealing contact with the well casing  74 . Whereas, the composite frac plug  30  must be held in the set location in the well casing  74  against frac fluid pressure, which can exceed 15,000 pounds per square inch (psi). Without the anchoring extrusion limiter  10 , all of the fluid pressure load must be borne by the composite slips  64 . However, with the anchoring extrusion limiter  10 , not only is extrusion of the main sealing element  50  resisted by the casing biting and gripping anchor of the anchoring extrusion limiter  10 , the fluid pressure load on the composite frac plug  30  is shared by the anchoring extrusion limiter  10  and the composite slips  64 , ensuring that the composite frac plug  30  can contain very high fluid pressures within the well casing  74  without being displaced. 
       FIG. 6  is a perspective view of section  6 - 6  of the composite frac plug  30  shown in  FIG. 5  in the packer-set condition. As can be seen, the main sealing element has expanded above a top of the sliding cone  51  and contacts the anchoring ant-extrusion limiter  10 , which has expanded into tight contact with the well casing  74  (see  FIG. 8 ) to inhibit extrusion of the main sealing element in response to frac fluid pressure in the well casing  74 . 
       FIG. 7  is a right end elevational view of the section  6 - 6  of the composite frac plug  30  shown in  FIG. 6 , within the well casing  74 . As explained above, in the packer-set condition the respective ceramic slip inserts  66  bite and grip the well casing  74  to anchor the composite frac plug  30  in the set location within the well casing  74 . 
       FIG. 8  is a cross-sectional view taken along lines  8 - 8  of  FIG. 7 . As can be seen, in the packer-set condition the sliding cone  51  has been pushed down the mandrel  32  by the compressed main sealing element  50 , forcing the ring segments  12  of the anchoring anti-extrusion ring  10  against the anti-extrusion cone  56  of the slip hub  52  and upwardly, fracturing the respective fracture bands  22  and urging the ring segments  12  into tight contact with the well casing  74 . When the respective ring segments  12  contact the well casing  74 , the ring segment inserts  20  bite and grip the well casing  74  to anchor the respective ring segments  12  of the anchoring extrusion inhibitor  10 , and to back up the anchoring bite of the ceramic slip inserts  66  of the composite slips  64 . 
     The explicit embodiments of the invention described above have been presented by way of example only. Other embodiments of the anchoring extrusion limiter are readily constructed with minor alterations, as will be understood by those skilled in the art. As well, the anchoring extrusion limiter has been described with reference to a composite frac plug, but may be used to limit the extrusion of a main sealing element of any non-retrievable downhole packer of a compatible type. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.