Attachment device for a slip gripping mechanism with floating cone segments
BACKGROUND OF THE INVENTION 
     1. Cross Reference to Related Applications 
     The present application is related to the pending application of John L. Baugh, et al, Ser. No. 06/876,515, filed June 20, 1986, entitled &#34;SLIP GRIPPING MECHANISM&#34;, now U.S. Pat. No. 4,711,326, to the pending application of Sidney Kenneth Smith, Jr., et al, Ser. No. 943,531, filed Dec. 18, 1986, entitled &#34;MECHANICALLY ACTUATED SLIP GRIPPING MECHANISM&#34;, and to the pending application of Sidney Kenneth Smith, Jr., Ser. No. 077,559, entitled &#34;SLIP GRIPPING MECHANISM WITH FLOATING CONE SEGMENTS&#34; filed concurrently herewith. 
     2. Field of the Invention 
     This invention relates to improvements in well tools of the type having slip assemblies for grippingly engaging surrounding cylindrical conduits. 
     3. Description of the Prior Art 
     Slip assemblies for well packers and liner hangers are actuated in order to support a conduit within the cased bore of a well. Prior art slip gripping mechanisms have generally included a plurality of wedge-shaped slip elements carried in circumferentially spaced-apart relation about a generally conically shaped expander surface on the tool body. More particularly, the lower surface portions of the slips are slidable over complimentary surfaces on the expander so as to cause teeth on the upper surfaces of the slips to be moved between expanded and contracted positions in response to relative axial movement of the slip elements and expander. This relative movement can be induced hydraulically or by mechanical actuation of telescopingly arranged, axially reciprocal members of the tool to which the slips and expanders are connected. 
     One disadvantage in the prior art gripping mechanisms lies in the fact that the loading imposed by the cylindrical conduit is transmitted radially from the expanders to the slips and radially into the surrounding well casing. At times, the loading can cause the casing to burst. 
     Prior arts slip gripping mechanisms have generally formed a part of a special hanger body or sub which included an internal mandrel that required consideration in determining the maximum support load of the tool. The hanger body was usually manufactured from special high strength material which differed from the material of the remainder of the cylindrical conduit being supported in the well bore. 
     The present invention has as its object the provision of a slip gripping mechanism for supporting a string of conduit within the interior bore of a circumscribing conduit which distributes the load being supported in a circumferential direction, rather than imposing a radial load. 
     Another object of the invention is the provision of a slip gripping mechanism which can be received upon the exterior surface of a standard string of cylindrical conduit and which does not require the presence of a special sub or hanger body within the string. 
     Another object of the invention is the provision of a unique slip and cone gripping arrangement which includes floating cone segments that allow the metal of the gripping mechanism to flex more equally, thereby reducing stress build-up during high load applications and consequently reducing the chance of permanent deformation of the slip and cone components of the mechanism. 
     Another object of the invention is the provision of an attachment device for fixing the cones against axial movement with respect to the cylindrical conduit without imposing radial loading upon the cylindrical conduit during use. 
     Additional objects, features and advantages will be apparent in the written description which follows. 
     SUMMARY OF THE INVENTION 
     The slip gripping mechanism of the invention is used for supporting a string of cylindrical conduit within the interior bore of a circumscribing conduit in a well bore. The gripping mechanism includes a cone retaining ring which is supported in the string of cylindrical conduit. Preferrably, the cone retaining ring has an internal bore which is sized to slidingly receive the cylindrical external diameter of one of the joints of the cylindrical conduit which is to be supported from the circumscribing conduit, whereby the cone retaining ring is received directly on the cylindrical external diameter of the cylindrical conduit. 
     The gripping mechanism also includes a plurality of individual cone segments. Each cone segment has side edges with lower edge surfaces and an engagement end. The engagement end is adapted to be engaged by the cone retaining ring for supporting each of the cone segments in spaced circumferential locations. The side edges of adjacent cone segments define a plurality of circumferentially spaced, longitudinally disposed slots when the cone segments are received on the exterior of the cylindrical conduit. 
     A plurality of circumferentially spaced, vertically shiftable slips are carried on the cylindrical conduit in the longitudinally disposed slots. Each slip has side edges which engage mating profiles formed in the longitudinally disposed slots. The mating profiles comprise converging ramp surfaces which present a tapered incline in the range of about 2  to 10 degrees with the respect to the slot lower edge surfaces whereby the slots form guideways for the slips for shifting the slips upwardly and outwardly between a set position engaging the circumscribing conduit and an unset position. 
     Each slip has an arcuate lower surface as defined radially from the longitudinal axis of the cylindrical conduit. An imaginary center line can be drawn which bisects the lower surface longitudinally. The lower surface center line is disposed above the cylindrical conduit exterior surface in both the set and unset positions, wherein movement of the slips upwardly and outwardly relative to the cone segments within the longitudinally disposed slots serves to impose circumferential loading upon the adjacent cone segment side edges. 
     The cone retaining ring is internally threaded and engages a mating externally threaded surface on the cylindrical conduit to fix the cone segments and prevent axial movement with respect to the cylindrical conduit. 
     The above as well as additional objects, features, and advantages of the invention will become apparent in the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1A is a side, cross-sectional view of the top portion of a gripping mechanism of the invention in the running-in position. 
     FIG. 1B is a downward continuation of the tool of FIG. 1A. 
     FIG. 2 is a profile, perspective view of the slip gripping mechanism of the invention in the unset position. 
     FIG. 3 is an exploded view of the mechanism of FIG. 2 showing the floating cone segments and the gripping slips. 
     FIG. 4 is a close-up view of an individual slip and cone segment showing the mating ramp surfaces thereof. 
     FIG. 5 is an isolated view of the slip and cone segments of the gripping mechanism in the unset position. 
     FIG. 6 is a view similar to FIG. 5 showing the slip and cone segments in the set position. 
     FIG. 7 is a cross-sectional view of the slip and cone segments taken along lines VII--VII in FIG. 5. 
     FIG. 8 is a cross-sectional view taken along Lines VIII--VIII in FIG. 6. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1A shows the upper portion of a slip gripping mechanism of the invention designated generally as 11. The slip gripping mechanism 11 is used for supporting a string of cylindrical conduit, such as a liner, within the interior bore of a circumscribing conduit, such as the casing, in a well. 
     The gripping mechanism includes a central mandrel 13 having an exterior surface 15 and an internal bore 17. The central mandrel 13 also has an upper connecting end 19 and is engaged by a conventional running tool for running the gripping mechanism into position within the well bore. One such commercially available running tool is shown, for instance, in U.S. Pat. No. 4,598,774, issued July 8, 1976, and assigned to the assignee of the present invention. Connecting end 19 is a &#34;box&#34; connection having internal threads 20 for engaging the external threads 22 of the central mandrel 13. The connecting end 19 also has an externally threaded surface 24 and an internally threaded bore 27. Unlike prior gripping mechanisms, the central mandrel 13 can be a standard joint of cylindrical conduit identical to the joints of conduit in the remainder of the string which is to be supported in the well bore. An opposite connecting end 21 can be used to support the depending string of cylindrical conduit, such as a liner to be hung within a cased well bore. 
     The gripping mechanism includes a cone retaining body, such as ring 23 which has an internal bore 25. The bore 25 is sized to slidingly receive the cylindrical external diameter 15 of the joint of cylindrical conduit 13 which is to be supported from the circumscribing conduit (casing) whereby the cone retaining ring 23 is received directly on the cylindrical external diameter 15 between the threaded connecting ends 19, 21. It is not necessary that the cylindrical conduit 13 be made from special materials or that it have a greater wall thickness than the cylindrical conduit in the remainder of the pipe string. The bore 25 of the cone retaining ring is threaded and engages the mating externally threaded surface 24 of the connecting end 19. This threaded connection fixes the ring 23 against axial movement with respect to the mandrel 13. 
     As shown in FIGS. 1A, 2 and 3, a plurality of individual, floating cone segments 41, 43, 45 are engaged by the cone retaining ring 23. Each of the cone segments has side edges 47, 49 and an engagement end 51. The engagement end 51 can be provided with a groove 53 which is engaged within a mating recess (55 in FIG. 1A) in the cone retaining ring 23 whereby the cone segments are supported in spaced, circumferential locations on the external surface 15 of the cylindrical conduit 13. As shown in FIG. 2, the side edges 47, 57 of adjacent cone segments 41, 45 along with the ring 23 define a plurality of circumferentially spaced, longidutinally disposed slots. 
     A plurality of circumferentially spaced, vertically shiftable slips 61, 63, 65 are carried on the cylindrical conduit 13 in the longitudinally disposed slots 59. Each slip has side edges 67, 69 which engage mating profiles formed in the longitudinally disposed slots, whereby the slots form guideways for the slips 61, 63, 65 for shifting the slips upwardly and outwardly between an unset position, as shown in FIG. 5 and a set position, as shown in FIG. 6, engaging the circumscribing conduit. 
     As shown in FIGS. 2, 5 and 6, the slot profiles 47, 57 comprise converging ramp surfaces which present a tapered incline or &#34;ramp angle&#34; which is preferably in the range from about 2 to 10 degrees with respect to the slot lower edge surface 71. As a result, any upward vertical travel of the slip 63 within the slot 59 results in outward radial movement of the slip upper surface 73. With reference to FIG. 4, it will be noted that the side edge 47 of the cone 41 is tapered to slant inwardly 2 to 10 degrees along the entire lower edge 71 from the engagement end 51 to the opposite end 75. The mating surface 67 of the slip 63 is also tapered to slant outwardly 2 to 10 degrees along the entire length of the lower edge surface 77 from the engagement end 79 to the opposite end 81 thereof. Each slip 63 is preferably provided with protruding ribs 83 on the side edges 67 which are received within mating grooves 85 provided in the side edges 47 of the mating cones 41. The rib and groove arrangement prevents &#34;slop&#34; as the gripping mechanism is being run into the well bore. However, the ribs and grooves are not necessary for the functioning of the gripping mechanism once the mechanism has entered the interior bore of the circumscribing conduit. As the slips move from the unset position shown in FIG. 5 to the set position shown in FIG. 6, it is the mating side edges 47, 57 which provide the outward radial movement of the slips and which are loaded circumferentially during the slip actuation. 
     Each slip 61, 63, 65 has a leading edge 87 (FIG. 3) and a trailing edge 89 which is preferably provided with a T-shaped connecting region 91. As shown in FIG. 4, each slip 63 has an arcuate lower surface 93 which forms a flow area with a respect to the external cylindrical surface 15 of the conduit 13. An imaginary center line 95 can be drawn which bisects the slip upper and lower surfaces 73, 93 longitudinally. The lower surface longitudinal line includes the point 97 in FIG. 8 which is disposed above the cylindrical conduit 13 exterior surface 15 in both the unset position of FIG. 7 and the set position illustrated in FIG. 8. In prior art slip gripping mechanisms, the lower surface 93 generally contacted the expander surface of the hanger body for shifting the slip upwardly and radially outwardly with respect to the hanger body. 
     As shown in FIGS. 1 and 2, the slip T-shaped connecting regions 91 are received within mating openings provided in a slip retaining ring 99. The retaining ring 99 forms the upper extent of a drag spring assembly 101. The drag spring assembly 101 has a plurality of drag springs 103 which bow outwardly from the central mandrel 13 and make frictional contact with the interior bore of the circumscribing conduit (105 in FIG. 7) as the gripping mechanism is run into position within the well bore. Each spring has an upper end 107 and a lower end 109 (FIG. 1B). The spring ends are engaged by upper and lower retaining rings 111, 113 respectively. The retaining rings 111, 113 are carried on the outer surface 115 of a cylindrical spring support 117 which surrounds the mandrel 13. The spring support 117 is connected at its upper extent to the slip retaining ring 99 by means of a square wire 119 received in a key way formed between the spring support 117 and the retaining ring 99. The spring support 117 also includes a downwardly extending lower extent 121 which surrounds the mandrel 13 and which is provided with helical shaped J-slots 123 (FIG. 3). 
     As shown in FIG. 1B, a make-up nut 125 is carried about the mandrel 13 below the drag spring assembly 101. A portion of the make-up nut is spaced apart from the mandrel exterior surface 15 and has an internal thread profile 127. A body lock ring 129 is located on the interior thread profile 127 between the make-up nut 125 and the mandrel 13 and is provided with an external thread profile 131 which engages the mating profile 127. The body lock ring 129 also has a lower serrated surface 133 for gripping the mandrel exterior. The body lock ring 131 is split at one circumferential location to allow radial contraction and expansion. 
     The internal thread profile 127 of the make-up nut engages an external thread profile 135 of an actuating sleeve 137. Movement of the make-up nut 125 up the external profile 135 results in inward radial movement of the body lock ring 129 whereby the serrated surface 133 grips the exterior surface 15 of the mandrel 13. This fixes the sleeve 137 against axial travel with respect to the mandrel 13. The actuating sleeve 137 has an upper extent 139 which is spaced apart from the mandrel exterior to form an annular recess 141. A J-pin 143 is mounted on the interior of the actuating sleeve 137 and extends radially inward into the annular recess 141 in the direction of the mandrel exterior 15. Preferably, a plurality of J-pins are located at spaced circumferential locations about the actuating sleeve and are received within mating recesses of the drag spring lower extent 121. 
     The operation of the device will now be described. As shown in FIG. 3, the J-slot 123 has an axial leg 145 which extends generally parallel to the longitudinal axis of the device, and an intersecting helical leg portion 147. The device is run into position in the well bore with the drag spring assembly and J-pin assembly as shown in FIGS. 1A and 1B. The frictional engagement between the drag spring assembly 101 and the surrounding casing 105 causes the J-pin 143 to ride at the upper end of the axial leg 145. Once the desired depth has been reached in the well bore, the running tool and associated pipe string leading to the well surface is raised a few inches and turned to the right which allows the J-pin 143 to move down the helical portion 147 to unlatch the J-assembly. The running-in string is then lowered to transfer the liner weight to the slips causing the slips to move from the retracted position to the extended gripping position. 
     The slip dimensions are selected to allow controlled bending or flexing of the slip in the direction of the circumscribing conduit as the slip moves from the unset to the set position. As shown in FIGS. 7 and 8, the imaginary center line 95 which bisects the top arcuate surface 73 of the slip 63 defines the first area of contact with the surrounding casing during the setting step. This area is indicated by the area F1 in FIG. 8. As the setting operation continues, the slip flexes and contacts the surrounding casing at points F2, F2&#39; followed by points F3, F3&#39;. This action also results in force being exerted in a circumferential direction, indicated by arrows F4, F4&#39;. In other words, the setting action of the present slip gripping mechanism results in a compressive circumferential loading on the adjacent cone segments 41, 43, 45. In prior art slip gripping mechanism, the setting load resulted in force being applied radially between the slip and the casing bore. By properly selecting the slip dimensions and ramp angle, the slip will flex and conform to the shape of the casing interior bore without imposing burst loads upon the casing or collapse loads on the cylindrical conduit. The &#34;floating&#34; nature of the cones enables the slips to flex more equally and distributes the load more evenly about the gripping mechanism. 
     The slip gripping mechanism of the invention is designed to control the maximum load applied to the surrounding casing through the flexing action of the slip. The thickness, width, contour, material, and condition of the slips are controlled to allow control of the loads imparted to the casing by the slips. If the maximum acceptable load on the casing is &#34;P&#34; (pounds per square inch) then the slip is designed to carry the maximum rated load without exceeding &#34;P&#34;. As the load increases, the slip gripping mechanism allows the area of the slip in contact with the casing to increase without exceeding load &#34;P&#34;. Length L (FIG. 6) × width indicated by F2&#39; to F2 ×&#34;P&#34; indicates the maximum load which can be applied to the casing without damage. As the area in contact increases to L×F3&#39; to F3×&#34;P&#34;, the load which can be supported also increases. The flex of the slip can be controlled to be less than or equal to &#34;P&#34; up to the maximum rated capacity of the slip system. The cylindrical conduit 13 does not support any radial loads and is therefore eliminated from the hanger load limiting factors. The loads can be controlled for use with any casing or conduit grade from steel to plastic without damage to the conduit. 
     EXAMPLE 
     A slip gripping mechanism of the invention was tested in 95/8&#34; P-110 oil well casing having a weight/ft. of 53.5 lbs./ft. P-110 casing has a performance rating (P) of 10,900 lbs./sq. in. Each slip in the gripping mechanism had a length (L) of 7 inches. The distance F2&#39; to F2 was 2 inches and the distance F3&#39; to F3 was 4 inches. The area in each slip in contact with the casing is 4×7=28 sq. in. The slip gripping mechanism utilized 3 slips mounted at 120 degree circumferential locations, as shown in FIGS. 1, 2, and 3. Thus there were 3 slips×28 sq. in.=84 sq. in. total slip area in contact with the surrounding casing. The calculated maximum load which can be supported by the casing is 84×10,900=915,600 pounds without damage to the casing. Using a 5 degree ramp angle, this translates into a vertical load capability of 364,000 pounds. In an actual test a 364,000 pounds load was applied to the slip gripping mechanism without damage to the casing. 
     Because of the flexing action of the slips in conforming to the shape of the circumscribing conduit, the gripping surfaces 73 can be designed as other than serrated surfaces. For instance, &#34;hard facing&#34; treatments can be applied to the metal surface 73 to provide a roughened surface capable of gripping the circumscribing conduit. Hard facing metal treatments are known to those skilled in the art. For instance, See U.S. Pat. No. 3,800,891 to WHITE, ET AL, issued Apr. 2, 1974 and U.S. Pat. No. 2,939,684 to PAYNE, issued June 7, 1960. Also, because of the unique action of the slip gripping mechanism, the gripping surface 73 can have a &#34;soft facing&#34; of a deformable nature, such as a layer of copper which would tend to assume the shape of any irregularity of the bore in the circumscribing conduit. 
     An invention has been provided with several advantages. The slip gripping mechanism can be quickly and easily installed on the exterior of a string of well tubing, casing or liner. The modular design eliminates the need for a separate liner hanger body or sub to be made up in the pipe string. This eliminates problems in matching threaded connectors in premium threaded pipe strings. It also eliminates the need for a hanger body made of a heavier walled, more expensive pipe material. Because of the unique circumferential loading action of the gripping mechanism, the support load is not imposed radially in toward the pipe. As a result, heavier loads can be supported without the danger of bursting the surrounding casing or the need to provide a heavy walled hanger body. The gripping mechanism of the invention can be provided in a shorter length and yet support heavier loads than prior art devices. The slip upper surface has a smaller radius than the circumscribing conduit diameter and the slip dimensions are selected to allow the slips to flex and conform to the diameter of the surrounding casing. The setting action begins with a line contact at the center of the slip upper surface with the contact moving out evenly on either side of the initial center line contact. By providing the cone elements as floating segments, the metal is allowed to flex more equally, thereby reducing stress build-up during high load applications and reducing the chance of permanent deformation of the metal parts. The attachment device for the cone segments fixes the cones against axial travel with respect to the cylindrical conduit without imposing radial loads on the conduit in use. All loading on the cone retaining ring caused by the weight of the depending string of conduit is in an axial direction. 
     While the invention has been described in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes and modifications without departing from the spirit thereof.