Patent Publication Number: US-4646827-A

Title: Tubing anchor assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Cross-Reference to Related Application 
     This application is a Continuation-In-Part of my copending Patent Application Ser. No. 06/545,530, filed Oct. 26, 1983 now U.S. Pat. No. 4,554,971. 
    
    
     2. Field of the Invention 
     This invention relates to devices and equipment for suspending tubing in an oil or gas well and more particularly, to a new and improved tubing anchor assembly for suspending coiled or conventional tubing in a well without the necessity of &#34;killing&#34; the well. The tubing anchor assembly of this invention is characterized by multiple, shaped slip segments located in the slip bowl of a conventional tubing head, each of the slip segments provided with a bevelled top face and a vertically-oriented dove tail slot. The dove tail slot cooperates with the frustro conical tip of a slip retainer screw threaded in the tubing head and projecting into the slip bowl, to facilitate release of the slip segments after a length of tubing has been inserted into the well, in order to support the tubing in the well. 
     As the down-hole pressure in oil and gas wells decreases with time, it is sometimes desirable or necessary to insert tubing in the well in order to provide a means for more readily removing fluids from the well and prolonging the life of the well. Traditionally, it has been necessary to &#34;kill&#34; the well or terminate production by application of hydrostatic pressure in the well, in order to achieve this objective. The well is &#34;killed&#34;, or production is terminated from the well by pumping a fluid such as water into the producing interval to create a hydrostatic head of sufficient magnitude in the well to overcome the well pressure, thereby terminating production. One of the problems inherent in &#34;killing&#34; a producing well which is characterized by relatively low pressure, is the difficulty and sometimes impossibility, of restoring the well to production after the desired swabbing or cleaning operation has been accomplished. Such cleaning and swabbing and other well maintenance operations are expensive, generally because of the time required to remove the &#34;christmas tree&#34;, set up the necessary apparatus for maintaining the well, place tubing in the well (where such tubing is deemed necessary), place a tubing head on the master valve, set the slip segments and the necessary packing, replace the &#34;christmas tree&#34; and subsequently attempt to bring the well back into production. It is apparent that if the well cannot be brought back into production, then the time and money expended for placing the tubing in the well, as well as the maintenance effort, has been wasted. 
     3. Description of the Prior Art 
     Slip assemblies and related equipment have been employed for many years in the oil field for suspending pipe and tubing in oil and gas wells. Such assemblies usually consist of multiple, segmented wedges which are tapered and are provided with horizontally extending teeth located on curved inner surfaces, which teeth are designed to engage and cut into the pipe or tubing to prevent relative movement between the tubing and the slips. The slips are usually wedged-shaped and curved in order to conform to the shape of a tapered, usually conical slip bowl provided in a tubing head, and facilitate engagement of the slips radially about the pipe or tubing when the slips are released inside the slip bowl responsive to contact between the wedge-shaped rear surfaces of the slips and the slip bowl in the tubing head. Lowering of the pipe or tubing after release of the slips results in a radial compressive force which urges the segments against the pipe or tubing until the teeth cut into the pipe or tubing wall sufficiently to support the weight of the tubing in the tubing head. Generally speaking, the teeth provided in the curved inner face of each slip segment are configured and oriented to engage and cut into the pipe or tubing in an optimum manner, in order to prevent relative movement between the slip segments and the suspended pipe or tubing. 
     Various devices are known in the prior art for supporting casing and tubing in oil and gas wells. An early &#34;Casing Head&#34; is detailed in U.S. Pat. No. 1,400,940, dated Dec. 20, 1921, to C. S. Clarke. The Clarke device includes a clamping member which is adapted to grip a pipe by wedging into engagement with the pipe responsive to the weight of the pipe. A Combination Tubing Spider and Support is set forth in U.S. Pat. No. 1,568,198, dated Jan. 5, 1926, to S. P. Tschappat. This tubing support includes a housing containing a pair of slips with transverse recesses defining interfitting parts which are adapted to support the tubing. A &#34;Pipe Holding Device&#34; is disclosed in U.S. Pat. No. 1,836,596, dated Dec. 15, 1931, to J. E. Hoffoss, et al. The &#34;Pipe Holding Device&#34; detailed in this patent includes a single slip which is adapted to entirely surround the pipe and the device includes multiple jaws which are so mounted and constructed that they can be handled by one workman to engage the pipe uniformly and evenly on all sides. U.S. Pat. No. 3,051,513 to J. D. Watts, et al, dated Aug. 28, 1962, discloses a &#34;Hanger Assembly and Seal Therefor&#34;, which includes a wrap-around hanger assembly having upper and lower segmental members cooperating to define a tubing support bowl and a casing head engaging ring, respectively. The segmental members forming the bowl and ring are interconnected in pairs by an improved construction which provides limited vertical movement between the ring and bowl and allows relative rotational movement between these two elements. A &#34;Slip Assembly&#34; is disclosed in U.S. Pat. No. 2,874,435, dated Feb. 24, 1959, to H. Allen. The &#34;Slip Assembly&#34; of this invention is characterized by a slip bowl constructed in two sections, each of which is substantially semicircular in configuration, in order to permit separation for ease of placing the assembly in position around a pipe to be suspended. Semicircular portions of the bowl are secured around the pipe by cap screws and define a bowl which is, in effect, a completely circular structure having inner and outer tapered surfaces which are substantially parallel to each other. A plate which serves as a slip retainer is also provided on lateral edges of the slip bowl segment. A &#34;Casing Hanger and Stabilizer&#34; is disclosed in U.S. Pat. No. 4,334,342, dated June 15, 1982, to Gregory G. Hall, which device includes a pair of generally wedge-shaped slip segments having mating faces and removably joined at the faces by a pair of plates. The device is further provided with interior slip threads or teeth for engaging the surface casing and a plurality of slots in the longitudinal exterior surface to permit the pumping of drilling mud or other fluid between the supporting conductor pipe and the suspended surface casing prior to cementing the surface casing in the conductor pipe. A &#34;Well Casing and Tubing Suspension Assembly&#34; is detailed in U.S. Pat. No. 3,090,640, dated May 21, 1963, to L. G. Otteman, et al. This suspension assembly includes a section having multiple slips suspended therein at various levels for engaging pipe or tubing and suspending the pipe or tubing in a well. U.S. Pat. No. 2,887,754, dated May 26, 1959, to C. F. Johnson details a &#34;Pipe Anchor&#34; for suspending pipe in a well, which device includes a support with a central opening for the pipe, wedges disposed in a conical bowl in the support and screws inserted in the support wall and engaging the wedges. The screws are sheared when the wedges are forced downwardly against a length of pipe inserted for suspension in the support. U.S. Pat. No. 3,287,035, dated Nov. 22, 1966, to J. A. Greenwood discloses a &#34;Pipe Hanger&#34; which includes a hanger in which a casing gripping jaw is forced into engagement with a casing by radial expansion of a resiliently deformable body, which expansion is caused by axial compression of the body. A &#34;Casing Hanger and Stabilizer Apparatus and Method&#34; is disclosed in U.S. Pat. No. 4,326,587, dated Apr. 27, 1982, to Charles J. Gauthier, et al. This device includes a cylindrical, separable hanger body with half-sections having tapered exterior walls and an interior bore with serrated teeth for gripping a pipe located in the bore. A locking means is provided to secure the hanger body sections together. Canadian Pat. No. 650,818, dated Oct. 23, 1962, to John Beson, et al, details a &#34;Casing Hanger&#34; which includes a body having a cylindrical opening therethrough, a conical seat defining an annulus around the opening, an annular hanger body with a slip seat therein for seating on the conical seat, and a plurality of slip members disposed around the slip seat for engaging the slip seat and a pipe extending through the cylindrical body opening, with compression and packing rings also provided for sealing the pipe. 
     It is an object of this invention to provide a new and improved tubing anchor assembly for suspending tubing in a well in a safe, fast, efficient and cost-effective manner without the necessity of reducing production pressure in the well prior to insertion of the tubing. 
     Another object of this invention is to provide a tubing anchor assembly for suspending tubing in an oil or gas well, which assembly is characterized by multiple slip segments, each having a tapered or bevelled top face and a dove tail slot provided therein for engagement with the shaped end of one of several slip retainer screws which are threaded radially in a tubing head, to facilitate controlled release of the slip segments in the slip bowl of the tubing head and support tubing placed in the well while production pressure is maintained in the well. 
     Yet another object of this invention is to provide a new and improved tubing anchor assembly for use in tubing heads to suspend tubing in oil and gas wells without &#34;killing&#34; the wells, which assembly includes, as a first element, multiple slip segments having bevelled top faces and clustered in a slip assembly by a retainer ring and disposed in the slip bowl of the tubing head, each of which slip segments is also provided with a dove tail slot in the rear surface thereof, and as a second element, slip retainer screws radially threaded in the tubing head wall and extending into the slip bowl and engaging the slots in the slip segments, to selectively release the slip segments in concert and support the tubing after the tubing is introduced into the well. 
     Yet another object of this invention is to provide a tubing anchor assembly for use in conventional tubing heads, which assembly includes at least two slip segments loosely joined by a ring and having bevelled top faces and vertically-oriented dove tail slots provided in the outside surfaces thereof and positioned in the slip bowl of the tubing head. A slip retainer screw is provided for each slip segment, each of which slip retainer screws are threadably and radially pressure-sealed in the tubing head and are each further provided with a frustro conical tip having a bevelled tip base, each tip designed to extend into the slip bowl and engage a dove tail slot in the slip segments, to selectively retain the slip segments in the slip bowl of the tubing head, threadably extend the slip segments into the slip bowl and allow the slip segments to release from the frustro conical tips of the slip retainer screws by operation of gravity, to engage and support the tubing in the tubing head while pressure is maintained in the well. 
     A still further object of this invention is to provide a tubing anchor assembly which includes slip segments having bevelled top faces and dove tail slots for receiving the bevelled top face, frustro conical tips of threaded slip retainer screws, wherein the frustro conical tips are adapted to engage the dove tail slots only at the centers and outer edges of the tips, and are designed to again engage the bevelled top faces of the slips after the slips are released, in order to securely seat the slips against upward movement due to pressure in the well. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are provided in a new and improved tubing anchor assembly which, in a preferred embodiment, is characterized by multiple, wedge-shaped slip segments positioned in the slip bowl of a tubing head, each of the slip segments provided with a bevelled top face, a horizontal groove and a vertically-oriented dove tail slot in the rear surface thereof, the dove tail slot extending to the horizontal groove. Multiple slip retainer screws are radially threaded in the tubing head and are each fitted with bevelled faced, frustro conical tips extending into the slip bowl for engaging the dove tail slots in the slip segments, to facilitate the support of coiled tubing in a well without reducing pressure in the well. The slip segments are released from the slip retainer screws by manipulating the slip segments toward the tubing through threadable manipulation of the slip retainer screws, to cause release of the slip segments from the frustro conical tips of the retainer screws, engagement of the tubing by the slip segments and retention of the slips against the tubing and in seated configuration by engagement of the frustro conical tips of the slip retainer screws against the bevelled top faces of the slips. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the accompanying drawing, wherein: 
     FIG. 1 is a sectional view of a tubing head with the tubing anchor assembly in functional position engaging and supporting a length of tubing; 
     FIG. 2 is a sectional view of the tubing head illustrated in FIG. 1, more particularly illustrating the open position of the slip segments prior to engagement with the tubing; 
     FIG. 3 is perspective, partially exploded view of a preferred slip assembly, more particularly illustrating the bevelled top faces of the slips; 
     FIG. 4A is a plan view, partially in section, of the tubing head with two slip segments in functional, closed position in the slip bowl; 
     FIG. 4B is a plan view, partially in section, of the tubing head with three of the four slip segments in functional, closed position, in the slip bowl; 
     FIG. 4C is a plan view of the tubing head with all four slip segments, which comprise an entire slip assembly, in functional, closed position in the slip bowl; 
     FIG. 5 is a perspective view of a preferred slip retainer screw which is used for supporting the slip segments in the slip bowl of the tubing head; and 
     FIG. 6 is a plan view of three slip segments assembled as a slip assembly, in open configuration. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIGS. 1, 2 and 5 of the drawings, the tubing anchor assembly of this invention is generally illustrated by reference numeral 1, and includes multiple slip retainer screws 23, the retainer screw shanks 24 of which are each threadably and radially spaced and seated in the top flange 53 of the tubing head body 52 of a conventional tubing head 37, by means of shank threads 26. The frustro conical tip 28 of each of the slip retainer screws 23 projects inside a slip bowl 59, shaped in the tubing head 37 and extends from a guide flange 33 at a tip recess 31, as is more particularly illustrated in FIG. 5 of the drawings. In a preferred embodiment of the invention the tip base 30 of the frustro conical tip 28 is bevelled from the center to the tip shoulder 29, for reasons which are more fully hereinafter developed. The slip retainer screws 23 are each sealed in the top flange 53 of the tubing head 37 by means of a retainer screw O-ring 36, fitted in an O-ring groove 27 and by a gland nut 49, which is threadably inserted in an internal thread aperture (not illustrated) in the top flange 53. A pair of packing rings 50, spanning a supply of packing 42 and cooperating with the gland nut 49, serve to seal the retained screw shank 24 against well pressure in the slip bowl 59. Similarly, referring again to FIG. 1 of the drawings, the packing screws 44, each having a packing screw shank 45 fitted with packing screw threads 46, are threadably and radially inserted in spaced relationship in a pack-off flange 38, mounted on the top flange 53 in the tubing head 37. Each packing screw shank 45 is sealed in the pack-off flange 38 by another gland nut 49, engaging the first of a pair of spaced packing rings 50 and including a quantity of packing 42, disposed between the packing rings 50. The packing screw head 47 of the packing screw 44 is tapered to define a bevelled face 48, which is in contact with a matching junk ring face 35 of an upper junk ring 41, provided in the packing bore 51 of the pack-off flange 38, in order to compress the upper junk ring 41 against a quantity of packing 42. The packing 42 is also disposed in the packing bore 51 and is supported by a lower junk ring 43, which is positioned adjacent and above the slip bowl 59. Accordingly, it will be appreciated that as the packing screws 44 are rotated in the clockwise direction by placing a wrench on the wrench flats 25, provided in the extending end of the packing screw shank 45, the upper junk ring 41 is forced against the packing 42 and the packing 42 is squeezed between the upper junk ring 41 and the lower junk ring 43 and against the tubing 65, to seal the packing bore 51 from fluid pressure in the tubing head 37. Furthermore, in a preferred embodiment of the invention the lower junk ring 57 is larger than the diameter of the lower end of the packing bore 51 and fills an enlargement in the pack-off flange 38 and the top of the slip bowl 59, in order to seat against the pack-off flange 38. This design prevents undesirable compression of the packing 42 due to well pressure. The pack-off flange 38 is joined to the top flange 53 of the tubing head 37 by means of a top flange stud 56, provided with stud threads 57 and a stud nut 58 secured to the lower array of stud threads 57, as illustrated. A flange O-ring 39 is positioned in a groove located in the face of the top flange 53 to seal the packing bore 51 and the slip bowl 59, and the pack-off flange apertures 40, provided in the pack-off flange 38, are internally threaded to facilitate mounting a valve or other equipment on the pack-off flange 38. A bottom flange 54 is also provided on the tubing head body 52 and is fitted with flange apertures 61, for flanging to a master valve in a &#34;christmas tree&#34; system, according to procedures well known to those skilled in the art. A flanged outlet 55 is provided in the tubing head body 52 at a point intermediate the top flange 53 and the bottom flange 54 and, like the pack-off flange 38 and the bottom flange 54, is fitted with O-ring seats 62, for sealing a connection with a production or other line (not illustrated) which may extend from the flanged outlet 55. It will be appreciated that the outer bore 63 of the flanged outlet 55 communicates with the bore 60 in the tubing head body 52, in order to facilitate a flow of hydrocarbons and well fluid from the well through the bore 60 and the outlet bore 63 to a pipeline or storage facility, as desired. It will be further appreciated that fluids can also be pumped in the reverse direction through the outlet bore 63 and the bore 60 and into the well, as deemed necessary by those skilled in the art. The flanged outlet 55 is typically attached to the tubing head body 52 by means of a weld 64. 
     Referring again to FIG. 1 of the drawings, a length of tubing 65, having a tubing bore 66, is illustrated extending through the packing bore 51 of the pack-off flange 38 and the slip bowl 59 of the top flange 53 and into the well through the bore 60. As a first element of the tubing anchor assembly of this invention, the slip segments 2 are illustrated in functional configuration positioned in the lower end of the slip bowl 59 and engaging the tubing 65 to support the tubing 65 in the slip bowl 59 and the bore 60 of the tubing head 37. 
     Referring now to FIGS. 3, 5 and 6 of the drawings, in another preferred embodiment of the invention, the slip segments 2 are each designed with a tapered body portion 3, having a retainer ring groove 14 laterally disposed across the outside surface thereof and located intermediate the bevelled top face 4 and the bottom edge 5 of the slip segment 2. The bevelled top face 4 is tapered downwardly from the top edge 16a, bordering the top bevel 16, to the outside ridge edge 3a. A dove tail slot 6 is provided in each of the slip segments 2 in the approximate center of the upper segment of the body portion 3 and extends between the top face 4 and the retainer ring groove 14. The dove tail slots 6 are each further characterized by a slot base 7, which is vertically oriented when the slip segments 2 are in the position illustrated in FIGS. 1 and 2 of the drawings. Furthermore, the slot base 7 is parallel to the inner edges 13 of the body portion 3. The top shoulders 8 define the maximum depth of the dove tail slots 6, which depth varies along the length of the dove tail slots 6 and is equal to the varying width of the slot sides 11. The slot edges 9 extend between the top shoulders 8 and bottom shoulders 10, respectively, in spaced, diverging relationship, as illustrated in FIG. 3. Since each of the slip segments 2 are provided with a downward vertical taper 17 on the outer surface of the body portion 3 between the bevelled top face 4 and the bottom edge 5, the distance between the top shoulders 8 is less than the distance between the bottom shoulders 10 and the slot edges 9 diverge from the top shoulders 8 to the bottom shoulders 10. Furthermore, in another preferred embodiment, the slot sides 11 are at a maximum width at a point between the top shoulders 8 and the slot base 7, and taper to the slot base 7 at the bottom shoulders 10, as a result of the vertical taper 17, when the angle of taper of the vertical taper 17 is about 9.5 degrees, which matches the taper of the slip bowl 59. Each of the slip segments 2 is further provided with multiple teeth 15, shaped in the concave inner surface of the body portion 3 between the inner edges 13. Each bevelled top face 4 is further provided with a slip aperture 18, which is fitted with internal slip aperture threads 19, to facilitate the location of threaded studs in the slip segments 2, in order to remove the slip segments 2 from the position illustrated in FIG. 1 when it is desired to dismantle the tubing anchor assembly 1. Each of the slip segments 2 is further provided with a top bevel 16, extending from the top face 4 downwardly to shape the first of the teeth 15 in the curved inside surface of the body portion 3. 
     Referring now to FIGS. 3 and 6 of the drawings, and initially to FIG. 3, four slip segments 2 are assembled in close proximity to shape a round slip assembly 12, disposed in open configuration and a split retainer ring 21, having retainer ring ends 22, is expanded over the bottom edges 5 of the slip segments 2 and inserted in the retainer ring groove 14, to maintain the four slip segments 2 approximately in alignment with each other and to shape the slip assembly 12. As illustrated in FIG. 6, it will be appreciated by those skilled in the art that various numbers of the slip segments 2 can be used to shape the slip assembly 12 in the tubing anchor assembly 1 and the three slip segments 2 illustrated therein are also joined by a retainer ring 21 in the loose, open configuration illustrated. Various other combinations of slip segments 2, ranging from two such slip segments 2 upward, can be utilized in the tube anchor assembly of this invention, according to the knowledge of those skilled in the art. It will be further appreciated from a consideration of the four slip segments 2 illustrated in FIG. 3 and the three slip segments 2 illustrated in FIG. 6, that the retainer ring 21 is fitted in the retainer ring groove 14 with sufficient tension to prevent any of the slip segments 2 from slipping out of the slip assembly 12, but sufficiently loosely to allow relative radial movement of the slip segments 2 with respect to each other when the slip assembly 12 is oriented in functional configuration, as hereinafter described. 
     Referring now to FIGS. 1, 2 and 4a-4c of the drawings and initially to FIGS. 1 and 4A-4C, the relative positions of the slip segments 2 inside the slip bowl 59 of the tubing head 37 and in engagement with the retainer ring 24 are illustrated in closed, supporting configuration to more particularly detail a slip assembly 12, which is illustrated in completed orientation in FIG. 4C. When the slip assembly 12 is completed, a slip bore 20 is defined by the curved teeth 15 of the slip segments 2. Furthermore, when the slip assembly 12 is placed in the slip bowl 59 of the tubing head 37 with a frustro conical tip 28 of each slip retainer screw 23 in registration with a corresponding dove tail slot 6 in a cooperating one of the slip segments 2, respectively, the slip segments 2 are suspended in the slip bowl 59 as a slip assembly 12 in open configuration, as illustrated in FIG. 2. Each frustro conical tip 28 touches a corresponding dove tail slot 6 at the tip shoulder 29 edges of the tip sides 32 and at the center of the bevelled tip base 30 and holds a corresponding slip segment 2 against the wall of the slip bowl 59. Accordingly, the tubing 65 is easily inserted through the slip bore 20 of the slip assembly 12, the bore 60 of the tubing head 52 and into the well, as also hereinafter described. 
     Referring again to FIGS. 3 and 5 of the drawings in a most preferred embodiment of the invention, each slip retainer screw 23 is threaded in the top flange 53 of the tubing head 37 in horizontal configuration and in perpendicular orientation with respect to the vertically positioned tubing 65. Furthermore, each frustro conical tip 28 is provided with a bevelled tip base 30, defined by a round tip shoulder 29, as heretofore described, which tip base 30 engages the slot base 7 in the dove tail slot 6 of a slip segment 2 at the center of the tip base 30, such that the inner edges 13 of each of the slip segments 2 project substantially vertically downwardly in the slip bowl 50, generally parallel to the tubing 65. Accordingly, referring again to FIGS. 1 and 2 of the drawings, when the tubing head 37 is oriented as illustrated, with the tubing 65 inserted therein in vertical relationship, the retainer screw shank 24 of the slip retainer screw 23 is in horizontal disposition with respect to the vertically oriented inner edges 13 and the slot base 7 of a cooperating slip segment 2. Furthermore, referring to FIG. 5, the tip sides 32 of each of the frustro conical tips 28 are bevelled from the tip shoulder 29 to the tip recess 31 and the angle of bevel conforms substantially to the angle of bevel of the slot sides 11 in the dove tail slots 6, with sufficient clearance provided between the tip base 30 and the slot base 7 to facilitate sliding movement of the frustro conical tips 28 in the dove tail slots 6, respectively. Accordingly, as a frustro conical tip 28 engages a corresponding dove tail slot 6 and the tip sides 32 engage the slot sides 11, the common angle of bevel in the slot sides 11 and the cooperating tip sides 32 and the close proximity of the center of the tip base 30 to the slot base 7, serve to maintain essentially perpendicular alignment between the slip retainer screws 23 and the slot base 7 of each dove tail slot 6. This alignment also facilitates substantially vertical orientation of the inner edges 13 of the slip segments 2 in the slip bowl 59. This alignment is important, since the slip segments 2 must be free to slide in concert as a slip assembly 12 from engagement with the slip retainer screws 23 at the proper time, to engage and support the tubing 65 in the tubing head 37. This ease of release is aided by engagement of only the center portion of the tapered tip base 30 of the frustro conical tip 28 with the slot base 7 in each dove tail slot 6. Accordingly, referring again to FIGS. 2 and 6, when the slip segments 2 are initially placed in the slip bowl 59, the slip retainer screws 23 have already been threadably retracted in the top flange 53 to the point where the frustro conical tips 28 are adjacent the wall of the slip bowl 59. When the slip retainer screws 23 are in this retracted position, the slip segments 2 in the slip assembly 12 can be manipulated such that each dove tail slot 6 is engaged with the frustro conical tip 28 of a cooperating slip retainer screw 23 and the slip assembly 12 is prevented from dropping further into the slip bowl 59 by the close proximity of the frustro conical tips 28 to the wall of one slip bowl 59. Accordingly, the slip segments 2 are constrained in concert as a slip assembly 12, to remain in the position illustrated in FIGS. 2 and 6, in order to define a slip bore 20 which is sufficiently large to permit the insertion of tubing 65 therethrough and position the tubing 65 in the well. 
     In operation, referring again to FIGS. 1, 2 and 6 of the drawings, under circumstances where it is desired to insert a length of tubing 65 into a well without reducing the pressure, or &#34;killing&#34; the well, the master valve (not illustrated) in a conventional &#34;christmas tree&#34; (not illustrated) is initially closed. The &#34;christmas tree&#34; is then removed from the master valve and if the well is not equipped with a tubing head, a tubing head 37 is then installed on the master valve in place of the &#34;christmas tree&#34; by inserting bolts through the flange apertures 61 in the bottom flange 54 and bolting the bottom flange 54 to the top flange of the master valve. It will be appreciated that the tubing head 37, which is so installed on the master valve, is equipped with multiple slip retainer screws 23, extending radially in spaced relationship from the top flange 53 of the tubing head 37, as illustrated in FIG. 1. Slip segments 2, which have been assembled using a retainer ring 21 to define a slip assembly 12, are then suspended from the frustro conical tips 28 of the slip retainer screws 23 by engaging the dove tail slots 6 with corresponding frustro conical tips 28, respectively, as illustrated in FIG. 2. This configuration of the slip segments 2 creates a slip bore 20, which is sufficiently large to permit the tubing 65 to be inserted entirely through the center of the tubing head 37, as illustrated in FIG. 6 of the drawings. The tubing 65, which is typically wound on a drum positioned in cooperation with a tubing running unit (not illustrated) designed to insert the tubing 65 in a well, is then positioned near the well location and an appropriate blowout preventer system (not illustrated) is mounted on the tubing head 37 in association with the tubing 65, in accordance with procedures well known to those skilled in the art. The tubing running unit is then set up for inserting one end of the tubing 65 into the well and the well is &#34;packed off&#34; or sealed above the blowout preventers, in order to prevent the working pressure in the well from escaping around the tubing 65 when the tubing 65 is inserted in the tubing head 37. The inserted end of the tubing 65 is first closed by means of a plug and the plugged end of the tubing 65 is extended through the packing bore 51 of the pack-off flange 38 and the slip bore 20 of the slip assembly 12, to the closed master valve. The packing in the tubing running unit is then tightly compacted, the master valve opened and the tubing 65 unwound from the drum and extended into the well to the desired depth. 
     When the tubing 65 has been inserted in the well to the desired depth and while it is supported by the tubing running unit, the slip assembly 12 is released from the respective frustro conical tips 28 of the retainer screws 23, by placing a wrench on the wrench flats 25 of each retainer screw shank 24 and rotating the slip retainer screws 23 in the clockwise direction. This action causes the frustro conical tips 28 to move inwardly, away from contact with the walls of the slip bowl 59 and toward the tubing 65, and terminates contact between the center of the tip base 30 and the tip sides 32 of the frustro conical tips 28 and the slot base 7 and slot sides 11 of the dove tail slots 6, respectively. When the last of the slip retainer screws 23 is rotated in the clockwise direction for a distance of approximately 2 to 21/2 complete revolutions, the entire slip assembly 12 falls downwardly under the influence of gravity, as the dove tail slots 6 of the slip segments 2 disengage the frustro conical tips 28 of the slip retainer screws 28, respectively. This action allows the slip assembly 12 to settle in the slip bowl 59 to the position illustrated in FIG. 1. It will be appreciated by those skilled in the art that the slip segments 2 drop in concert to the position illustrated in FIG. 1 because of the retainer ring 21, which loosely joins each of the slip segments 2 together, as illustrated in FIG. 3 of the drawing and as heretofore described. Accordingly, it will be further appreciated that rotation of all but the last one of the slip retainer screws 23 in the clockwise direction simply loosens all but the last of the slip segments 2 on the frustro conical tips 28, respectively, and the entire slip assembly 12 will not slide and drop into the position illustrated in FIG. 1 until the last one of the slip retainer screws 23 is rotated. In the event that the slip segments 2 fail to seat properly in the slip bowl 59 after disengaging the slip retainer screws 23, the slip retainer screws 23 can be further rotated in the clockwise direction to engage the tip shoulders 29 with the corresponding bevelled top faces 4, respectively, of the slip segments 2, to force the slip segments 2 downwardly into a seated position in the slip bowl 59. This positioning of the slip retainer screws 23 also insures that the slip segments 2 will not become unseated in the slip bowl 59 by gas pressure in the well. When the slip segments 2 are properly seated, the tubing running unit is adjusted to reduce the supporting force on the tubing 65 and as the weight of the tubing 65 in the well is brought to bear on the teeth 15 of the slip segments 2, the teeth 15 penetrate the outer surface of the tubing 65 and the slip assembly 12 supports the tubing 65 in the well. The slip retainer screws 23 are then rotated in the opposite, or counter-clockwise direction to retract the slip retainer screws 23 in the tubing head 37 and relocate the frustro conical tips 28 against the sides of the slip bowl 59 and away from the slip assembly 12. Alternatively, the tip shoulder 29 of each frustro conical tip 28 can be left in contact with the top faces 4 of the slip segments 2, in order to prevent unseating of the slip assembly 12 from the slip bowl 59 as a result of pressure in the well. The packing screws 44 are then rotated in the clockwise direction to cause the bevelled faces 48 of the packing screw heads 47 to exert pressure on the junk ring face 35 of the upper junk ring 41, which action tightens the packing 42 located between the upper junk ring 41 and the lower junk ring 43, to seal the tubing 65 in the tubing head 37. When this is accomplished, the tubing 65 is considered to be &#34;packed off&#34; in the tubing head 37 and the pressure of the well is tested above the tubing head 37 to insure that the packing 42 located between the upper junk ring 41 and the lower junk ring 43 is holding the well pressure. The tubing running unit and the blowout preventers are then removed from the tubing head 37. The tubing 65 is cut at a point about six inches above the tubing head 37, the bottom valve carried by the &#34;christmas tree&#34; is flanged to the pack-off flange 38 of the tubing head 37, in conventional fashion, and this bottom valve becomes the new master valve. The flow or producing lines are then reattached as required and nitrogen is pumped through the &#34;christmas tree&#34; into the severed open end of the tubing 65 to remove the plug from the opposite end of the tubing 65 which extends into the well. The well is then ready to produce hydrocarbons through the bore 60 of the tubing head body 52, the outlet bore 63 of the flanged outlet 55 and through the tubing bore 66 of the tubing 65. 
     Referring again to FIGS. 3, 4C and 6 of the drawings, it will be further appreciated by those skilled in the art that when it is desired to remove the tubing head 37 from the well after depletion, the new master valve carried by the &#34;christmas tree&#34; can be first removed from the pack-off flange 38 and the tubing head 37 is then removed from the bottom master valve by unbolting the bottom flange 54 from the old master valve flange, in the customary manner. The pack-off flange 38 is then removed from the top flange 53 in the tubing head 37 by removing the stud nuts 58 and the packing screws 44 are adjusted in the counter-clockwise direction to remove the packing screw head 47 from contact with the upper junk ring 41. The upper junk ring 41, packing 42 and the lower junk ring 43 are then removed from the packing bore 51 to expose the slip assembly 12, and threaded studs or eye bolts (not illustrated) are threadably inserted in the slip apertures 18 of the slip segments 2, to remove the slip assembly 12 from the slip bowl 59. The tubing head 37 is then ready to be cleaned and the slip segments 2 reinserted on the frustro conical tips 28 of the slip retainer screws 23, in the manner illustrated in FIG. 2 and heretofore described, for use on another well. 
     It will be appreciated by those skilled in the art that the tubing anchor assembly of this invention offers many advantages over prior art equipment for inserting tubing, and coiled tubing in particular, in an oil or gas well. Since the working pressure of the well does not need to be neutralized in order to insert the tubing in the well, there is no necessity for using a workover rig or special tools and equipment. Furthermore, the tubing anchor assembly can be used to place tubing in the well under pressure, and under circumstances where terminating the pressure might cause permanent loss of production and where the only alternative to effect continued production is use of a pumping unit, sucker rod string and down-hole pump. The tubing anchor assembly of this invention can be used on wells of substantially any depth to support tubing under circumstances where the use of such tubing is feasible. Furthermore, since use of the tubing anchor assembly results in faster, more efficient insertion of tubing in a well, the operation is rendered safer and less expensive, due to the reduced time of exposure to the well by the operators. An added positive feature is the capability of reworking the tubing anchor assembly of this invention in the field by resetting the slip retainer screws 23 and slip segments 2 without the necessity of replacing shear pins and other component parts of conventional devices at a distant point of origin. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.