Abstract:
An improved apparatus and method are provided for effecting a sealed connection to an upstanding end of a tubular member in a subterranean well where the upstanding end of the tubular member is of irregular configuration at one end. A connecting housing is lowered by a tubing string over the upstanding end of the tubular member and is provided internally with an annular elastomeric seal element and two pairs of cooperating slip elements respectively disposed above and below the annular seal. The actuation of the slip elements to engage the housing with the tubular member is such that a predetermined amount of compression force can be applied to the annular seal to insure that the seal will resist the normal fluid pressures encountered in the well operation, but forces in excess of such predetermined limit are not applied to the seal by the manipulative movements of the reconnected tubing string. The apparatus may include scrapers for scraping the upstanding end of the tubular member to remove particulates adhering thereto prior to effecting the engagement of the annular seal and the various slip elements therewith.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and apparatus for effecting a sealed connection of a tubing string to a tubular member positioned down hole in a subterranean well which has had the top end portion thereof severed by either acid, explosion, or the like, hence presenting an irregular, unthreaded or partially threaded upstanding end surface. 
     2. Description of the Prior Art 
     It occasionally becomes necessary to effect the severance of a tubing string in a subterranean well at a down hole point in the well by either acid cutting, by an explosive method, or the like. These drastic methods of effecting the severing of the tubing string may be required if the packer or other tool is stuck in the well. 
     Utilization of acid or explosive cutting of the tubing string at a down hole position necessarily results in the tubing remaining down hole having an irregularly shaped, top end portion. Connectors for such down hole tubing, collaquially called a &#34;pack-off over shot,&#34; have heretofore been provided comprising an annular elastomeric sealing element which is mounted within a housing and lowered on the tubing string to a position surrounding the top end of the tubular member. Slips are provided in the housing which are cam actuated to respectively expand and contract into engagement with the inner wall of the housing and the outer wall of the tubular member, and to concurrently impart an axial compressive force on the annular elastomeric material. 
     In such prior art connectors, the amount of axial force imposed upon the annular elastomeric seal is in no manner limited, and the greater the axial force that is applied through the connector, the greater will be the axial compression force on the seal. This inherently results either in undesirable extrusion of the elastomeric seal material, or an axial collapsing of a portion of the wall of the tubular member tubing engaged by the seal or the blowing out of the wall of the housing containing the seal. 
     There is, therefore, a need for a sealed connection for an irregular shaped upstanding end of down hole tubular member which will impose sufficient axial compression force on the annular seal to insure that the seal will maintain its integrity under any fluid pressures encountered in the operation of the particular well, yet limits the application of excessive compression forces to the seal by the subsequent manipulative movement of the tubing string. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved apparatus, and method for operating such apparatus, for effecting a sealed connection to an upstanding end of a down hole tubular member. The connection and seal apparatus comprises a tubular housing mounting an annular elastomeric seal within an appropriate interior recess. Also mounted in such recess are two pairs of slip elements respectively disposed both above and below the annular elastomeric seal. Lowering of the housing over the upstanding end of the tubular member results in the annular elastomeric seal surrounding an end portion of the tubular member. The reversal of the movement of the connecting housing to raise the housing relative to the tubular member effects an immediate engagement of an upper slip element with the top end of the tubular member tubing while the lower slip elements have ratchet shaped internal teeth which do not bite into the tubing and hence move upwardly, imparting a compressive force to the annular elastomeric seal. The compressive force imposed on such a seal is backed up by a two piece force transmitting ring which is disposed between the top end of the elastomeric seal and the upper engaged slip element. An annular shear element secures the two piece force transmitting ring in assembly and, when a desired amount of axial compressive force has been imparted to the annular elastomeric seal, such shear element shears and the one portion of the force transmitting ring moves upwardly to force another upper slip element outwardly into biting engagement with the inner wall of the connecting housing. This slip element, as well as one of the lower slip elements, has external teeth that are shaped to prevent any further upward movement of the connecting housing with respect to the tubular member, and thus the compressive force in the annular elastomeric seal remains constant and trapped therein between the various slip elements. Moreover, the application of additional upward or downward force to the connecting housing by manipulation of the tubing string will not change the amount of compressive force exerted on the annular elastomeric seal. 
     In accordance with a modification of this invention, the interior surfaces of the annular elastomeric seal and the various slip elements are covered by a sleeve which is slidably mounted within the connecting housing but maintained in its protective position by one or more shear pins until a downwardly facing shoulder on such sleeve engages the top end of the tubular member. Such engagement effects the shearing of the shear pins and the movement of the protective sleeve upwardly as the connecting member is lowered into surrounding relationship with the upper end of the tubular member. Additionally, the bottom end of the connecting member may be provided with a plurality of radially contractible scrapping elements which snugly engage the external periphery of the tubular member and effect a scraping of such tubing to remove encrustation therefrom prior to the engagement of the slip elements and the annular seal with the top portions of the tubular member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic vertical sectional view of a sealable connector with the elements thereof in their positions prior to engagement with the upstanding irregular end of a piece of tubular member. 
     FIG. 2 is a view similar to FIG. 1 showing the elements of the connector in engaged and sealed position with the upstanding end of the tubular member. 
     FIGS. 3A and 3B are enlarged scale views of the portion of FIG. 1 containing the slip elements and annular seal, FIG. 3B being a vertical continuation of FIG. 3A. 
     FIG. 4 is a cross-sectional view taken along section 4--4 in FIG. 1. 
     FIG. 5 is a cross-sectional view taken along section lines 5--5 in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, the numeral 1 indicates the casing of an oil or gas well. Disposed within the lower portions of such casing is the upstanding irregular end 2 of a down hole tubular member which for whatever reason, had to be severed by either acid cutting, explosive techniques, or otherwise. 
     To reconnect the downhole tubing 2 to a new tubing string, a connecting apparatus 10 embodying this invention is provided. Connecting apparatus 10 includes a main housing 11 defined by an elongated cylindrical element which is threadably secured at its top end by threads 11a to a connecting sub 12 with threads 12a which in turn is provided at its top end with internal threads for connection to the bottom end of the new tubing string (not shown). A set screw 12b anchors this threaded connection and an O-ring seal 12c prevents fluid leakage therebetween. 
     At its lower end, the tubular housing 11 is provided with an internal, axially elongated recess 11b which terminates in an internally threaded portion 11c. This portion is threadably engaged with the upper end of an intermediate connecting sleeve 13. The top end 13a of sleeve 13 thus defines the bottom end of the housing recess 11b. One or more radially disposed set screws 13b are provided to effect the locking of this threaded connection. 
     Connecting sleeve 13 in turn is provided at its lower end with internal threads 13c which engage external threads provided on the upper end of a guide sleeve 14 which has a bottom outwardly flared conical surface 14a to effect the guiding of the sleeve 14 into surrounding relationship with the irregularly shaped end of the tubular member 2. Sleeve 13 is also provided at its lower end with a counter bore 13d and this counter bore, in cooperation with the top end 14b of the guide sleeve 14, provides a retention mounting for a plurality of resiliently expansible scraper elements 15 having internal scraping edges 15a. Each of the scraping elements 15 is fabricated from spring material and is of C-shaped configuration so that it tends to maintain its minimum diameter or closed position wherein the diameter of the scraping edges 15a is less than the exterior diameter of the tubular member 2, thus insuring a vigorous scraping action on the external surface of tubular member 2 as the connection housing 11 is lowered thereover. 
     Within the axially elongated recess 11b, an annular elastomeric seal element 16 of conventional configuration is mounted and is disposed between a pair of lower slip elements 17 and 18 and a pair of upper slip elements 19 and 20. All of these slip elements are conventionally formed from spring material in a C-shaped configuration. The lowermost slip element 17 and the uppermost slip element 20 are radially contractible, while the intermediate elements 18 and 19 are radially expansible. The internal teeth 17a of the contractible lowermost slip element 17 are shaped so as to permit only relative upward movement of slip 17 with respect to the external surface of the tubular member 2 with which they will be eventually engaged, as illustrated in FIG. 2, through the application of an axially derived camming force. The internal teeth 20a of the uppermost slip element 20 are oppositely inclined so as to permit only relative downward movement of the connecting housing 11 with respect to the tubular member 2, and to engage such tubing and block relative upward movement with respect thereto. 
     The slip 18 is provided with external teeth 18a which are dimensioned to engage the inner walls of the housing recess 11b to prevent relative downward movement of the housing 11 with respect to the slip 18. Lastly, the slip 19 is provided with external teeth 19a which are proportioned to prevent relative upward movement of the housing 11 with respect to the slips. The slips 17 and 18 are additionally provided with cooperating conical surfaces 17b and 18b which, upon the application of an axial force to either of said slips, intensifies the biting engagement of the teeth 17a and 18a with the tubular member 2 and the wall of housing recess 11b respectively. 
     The upper slip elements 19 and 20 also have opposed conical faces 19b and 20b but these faces are not directly abuttable. Instead, they respectively abut the similarly shaped surfaces 21a and 21b of a thrust transmitting ring element 21 which is secured to a second thrust transmitting ring element 22 by an axially shearable ring element 23 which has a T-shaped cross-section. To permit the assemblage of ring element 23 between the thrust transmitting rings 21 and 22, it may be fabricated as a compressible C-shaped spring element which surrounds the lower extremities of thrust transmitting ring 21 and has a radially projecting annular stem portion 23a thereof inserted within an internal slot 22a provided in the second thrust transmitting ring 22. While so connected, the assemblage functions as a unitary, two piece thrust transmitting ring which transmits an upward axial force only to the uppermost slip 20. 
     Intermediate the bottom end of the thrust transmitting ring 22 and the top end of the annular elastomeric seal 16, a solid thrust transmitting ring 24 is provided. Similarly, between the lower end of the annular elastomeric seal 16 and the top end of the slip 18, a solid thrust transmitting ring 25 is provided. Thus, any axial upward displacements of the lower set of slip elements 17 and 18 with respect to the upper slip elements 19 and 20 will result in the imposition of a compressive force on the annular elastomeric seal element 16. 
     The apparatus thus far described is capable of effecting a mechanical sealed connection between the housing 11 and the upstanding end of the tubular member 2. It is well known, however, that as the housing 11 is lowered into the well, undesirable particulates may tend to accumulate on the internal surfaces of the slip elements and the elastomeric seal. Accordingly, in accordance with a preferred modification of this invention, an inner sleeve 30 is provided which is axially slidably mounted within the bore 11d of the main housing 11. The sleeve 30 is of sufficient length so that when positioned in a lower position by one or more radially disposed shear screws 31 it will completely overlie all of the slip elements and the elastomeric seal, thus protecting the internal surfaces of such elements from deposit of undesirable particulates. The number and strength of shear screws 31 determines the shearing force required. 
     The internal bore 30a of the inner sleeve 30 is of smaller diameter than the external diameter of the tubular member 2. A counterbore 30b is provided in the bottom end of the inner sleeve 30 having a diameter which will permit such bottom end portion to slide over the extreme top end portion of the tubular member 2. The downwardly facing shoulder 30c provided at the top end of counterbore 30b then abuts the top irregular surface of the tubular member 2. Upon such abutment, the further downward movement of the housing 11 would be prevented until sufficient downward force is applied by the operator to the housing 11 to effect the shearing of the shear screws 31. 
     Upon the shearing of such screws, the inner sleeve 30 moves upwardly within the bore 11d of the main housing 11 to the position illustrated in FIG. 2 wherein its bottom end is disposed entirely above the recess 11b of housing 11, hence above the upper slip element 20. During this upward movement, the counterbore 30b provides protection for the irregular end of the tubular member 2. 
     As previously mentioned, the ratchet shape of the teeth 17a and 20a of the contractible slips 17 and 20 permits such relative upward movement of the inner sleeve 30 because no axial force is being applied to any of the slip elements and the teeth 20a of slip 20 are so shaped as to permit the outer surface of inner sleeve 30 to freely slide thereby. 
     When, however, the inner sleeve 30 reaches its uppermost position wherein its top end abuts the end face of the top sub 12, further downward movement of the housing 11 is interrupted and this provides a signal to the operator to begin the setting operation. 
     As the housing 11 is lowered over the upstanding end of the tubular member 2, the radially expandable scraping elements 15a  engage the exterior surface of the tubing 2 and scrape it free of any undesirable particulates adhering thereto, thus providing a smooth, clean surface for engagement by the slips 17 and 20 and the inner surface of the annular elastomeric seal 16. 
     The setting operation is accomplished through the simple expedient of raising the tubing string and thus raising the housing 11 relative to the now inserted end of the tubular member 2, as specifically illustrated in FIG. 2. The first effect of such raising movement is to cause the teeth 20a of the uppermost slip 20 to bite into the adjacent exterior wall of the tubular member 2 due to the resilient contraction of the slip 20. At the same time, the lowermost slip element 17 is being raised by the end surface 13a of the intermediate sleeve 13 and the interaction of conical surfaces 17b and 18b produces an upward displacement of these lower slip elements to apply a compressive force to the annular elastomeric seal through the ring 25 which is resisted by the upper torque transmitting ring 24, the united thrust transmitting rings 21 and 22 and the anchored upper slip 20. 
     Any desired degree of compressive force may thus be imposed upon the annular elastomeric seal 16, with the limits of such force being determined by the shearing of the axially shearable connecting ring 23 which is provided between the two thrust transmitting rings 21 and 22. Upon such shearing, the ring 22 is free to move upwardly and this force produces an engagement of the teeth 19a of the slip 19 with the inner wall of recess 11b and prevents further relative upward movement of the housing 11 with respect to the slip 19. Accordingly, the housing is effectively locked to the upper end of the tubular member 2 by the combined interaction of lower slip elements 17 and 18 and upper slip elements 19 and 20. 
     Further manipulation of the tubing string by the operator may then be accomplished without in any manner affecting the amount of compressive force applied to the annular elastomeric seal element 16. The upper slips 19 and 20 effectively prevent any relative upward movement of the housing 11 with respect to the tubular member 2 and the lower set of slips 17 and 18 effectively prevent any downward relative movement of the housing with respect to the tubular member 2. 
     It is accordingly apparent that the method and apparatus of this invention provides a convenient, economical method for effecting a sealed connection to a down hole tubular member having an irregular end. Most importantly, the tensile strength of the connection is substantially equal to the tensile strength of the tubing string and large tensile and/or compressive forces may be applied to the connection without in any manner disturbing the amount of compression trapped in the annular elastomeric seal. The selection of this amount of compression is predetermined by the selection of the shear strength of axially shearable ring element 23 which interconnects the two thrust transmitting rings 21 and 22. 
     Although the invention has been described in terms of specified embodiment which has been set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.