Abstract:
A method and apparatus for effecting the perforation of a well casing and the adjoining production formation comprises a tubular housing communicating between a perforating gun housing and the lower end of a tubular string. The perforating gun housing which is adapted to be carriable by the tubular string contains an impact actuated firing head and the tubular housing contains a port normally closed by sleeve valve. The valve is biased towards an open position but is selectively secured in its closed position by a frangible restraining mechanism which extends into the free fall path of a detonating bar dropped through the tubular tool string and is removed by the detonating bar to initiate the opening of the port sleeve valve prior to impacting the firing head. In a modification, the sleeve valve is shifted to its open position by fluid pressure produced in the casing annulus subsequent to the firing of the perforating gun.

Description:
BACKGROUND OF THE INVENTION 
     History of the Prior Art 
     There are many production formations encountered in the drilling of modern oil wells wherein it is desirable to effect the perforating of the casing and the adjoining production formation in an &#34;underbalanced&#34; condition, i.e., where the fluid pressure within the casing immediately adjacent the production formation, and the tubular string connected to such casing region, are maintained at a substantially lower fluid pressure than the anticipated fluid pressure of the production formation. When the perforating gun is fired under these conditions, the production fluid flows rapidly through the resulting perforations into the casing and up the tubular string, carrying with it all debris resulting from the perforating operation, hence cleaning the fractures in the perforated formation for more efficient production flow when the well is completed. 
     In order to efficiently utilize the underbalanced perforating, a packer is generally run into the well on a tubular string and set immediately above the region of the well casing to be perforated. The perforating gun is suspended from the packer by a tubular string which is fluid connected to the tubular work string. Other tools, such as chemical treatment, washing and/or gravel packing tools, may be connected in the same tool string either above or below the packer. In any event, the assembled tool string is run into the well with an essentially dry condition existing in the tool string, thus assuring that the fluid pressure in the tool string is substantially below that anticipated to exist in the formation to be perforated. To permit the free flow of production fluid from the perforated formation, it is necessary that radial ports be opened in the tubular string below the packer and above the perforating gun. It has previously been proposed, for example, in U.S. Pat. No. 4,151,880 (Vann), that a radially ported, wire line actuated sleeve valve be mounted in this position. 
     The utilization of a wire line actuated valve necessarily introduces delay in effecting the opening of the radial ports in the tubing string, thus delaying the initial flow of production fluid from the perforated formation. U.S. Pat. No. 4,299,287 (Vann) proposes to use the freely falling detonating bar to shift the sleeve valve. This can result in slowing the speed of the detonating bar to a level insufficient to fire the gun. 
     SUMMARY OF THE INVENTION 
     This invention provides a method and apparatus for effecting the perforating of a well casing and the adjoining production formation in an underbalanced condition wherein the radially ported sleeve valve disposed between a packer and a perforating gun is automatically opened by the passing therethrough of a free-falling detonating bar for the perforating gun, without extracting any significant amount of kinetic energy from such detonating bar. It is thus assured that the radial ports are fully opened immediately subsequent to the firing of the perforating gun, thus permitting unimpeded fluid flow through the newly formed perforations and up through the tubular string upon which the perforating gun is mounted. 
     More specifically, the radially ported sleeve valve embodying this invention comprises a housing having radial ports formed therein which are closed in the run-in position of the tool by an axially shiftable sleeve valve. In one modification, the sleeve valve is spring biased to its opening position with respect to the ports but is restrained in its port closing position by a latching mechanism which has a portion thereof extending into the path of the freely-falling detonating bar. The impact of the detonating bar with the inwardly projecting portion of the latching mechanism effects the tripping of the latching mechanism and the release of the sleeve valve to move under its spring bias to its port opening position, thus assuring that the radial ports are immediately opened for flow of formation fluid from the newly perforated formation immediately subsequent to the perforating operation. 
     In the one embodiment of the invention, the restraining mechanism for latching the sleeve valve in its port closing position comprises a frangible barrier, such as a tempered glass disc which is held in a transverse position across the bore of the tool and, in such position, maintains the latching mechanism in its engaged position with the sleeve valve, thus holding the sleeve valve in its port closing position. A shattering of the glass disc by the passage of the detonating bar therethrough absorbs very little kinetic energy from the detonating bar, yet is effective to release the latching mechanism and initiate the movement of the sleeve valve to its port opening position under the influence of its spring bias. 
     In another embodiment of the invention, the restraining mechanism for latching the sleeve valve in its port closing position comprises a pair of cooperating collets which are disposed in axially spaced relationship within the tubular housing. The upper collet holds the sleeve valve in its closed position with respect to the radial ports. The latching heads effecting this holding action are restrained in their position by the ring portion of a lower collet having downwardly extending, peripherally spaced spring arms with enlarged head portions projecting partially into the free-fall path of the detonating bar. A shear pin between the ring portion of the lower collet and the housing maintains the collets in their latching relationship with respect to the sleeve valve. 
     Upon impact of the detonating bar with the latching heads of the lower collet, the shear pins are sheared and the lower collet shifted downwardly a slight distance to release the latching heads of the upper collet. The differential pressure existing between the casing annulus in the vicinity of the housing and the bore of the housing is then effective upon the sleeve valve to urge the sleeve downardly to a port opening position, thus permitting the formation fluids to flow freely through the newly formed perforations and upwardly through the tool string. 
     Further advantages of the invention will be readily apparent to those skilled in the art from the following detailed description, taken in conjunction with the annexed sheets of drawings on which is shown two preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A, 1B and 1C collectively constitute a vertical, quarter-sectional view of a valve for connection in a tubular string immediately above a perforating gun to permit the firing of the gun in an underbalanced pressure condition with respect to the production formation, with the components of the valve mechanism being shown in their run-in position. 
     FIGS. 2A, 2B and 2C are views respectively similar to FIGS. 1A, 1B and 1C, but illustrate the position of the components following the passage of a detonating bar therethrough to fire the perforating gun. 
     FIG. 3 is a sectional view taken on the plane 3--3 of FIG. 1B. 
     FIG. 4 is a sectional view taken on the plane 4--4 of FIG. 1C. 
     FIGS. 5A and 5B collectively constitute a vertical, quarter-sectional view of a modified valve embodying this invention wherein fluid pressure is utilized to effect the shifting of the valve following the release of the latching mechanism by a free-falling detonating bar; in these figures, the components of the valve are shown in their run-in position. 
     FIGS. 6A and 6B collectively comprise views similar to FIGS. 5A and 5B but showing the elements of the valve in their open port position following the firing of the perforating gun. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to Figs. 1A-1C, the method of this invention is practiced through the insertion of a valving tool 1 in series relationship between a tubular string (not shown) and the top end of a conventional impact actuated perforating gun, which also is not shown. 
     The valving tool 10 comprises a housing 10 fabricated by the threaded assemblage of three elements, namely, an upper housing 11, an intermediate housing 12 and a lower housing 13. Upper housing 11 is provided with internal threads 11a for conventional connection to the end of the tubular string. The lower end of upper housing 11 is internally threaded as indicated at 11b and the intermediate housing 12 is secured thereto. An O-ring seal 12a seals the threaded connection and a set screw 11c effects the locking of the threaded connection. 
     The lower end of the intermediate housing 12 is provided with threads 12a for connection to the lower housing 13. An O-ring seal 12b seals the threaded connection and a set screw 13a effects securement of the threaded connection. The lower end of the lower housing 13 is provided with external threads 13b for conventional sealed connection to the housing of a perforating gun (not shown). 
     The intermediate portion of the middle housing 12 is provided with a plurality of peripherally spaced, axially extending fluid flow passages 12c and a sliding sleeve valve having spaced O-rings 14a and 14b overlying passages 12c to prevent the flow of fluid therethrough. 
     The sliding sleeve valve 14 is, however, biased to an open position relative to the fluid passage ports 12c by a spring 15. The top end 15a of spring 15 abuts the bottom end of the upper housing 11, while the bottom end 15b of spring 15 abuts the top end of a force transfer or actuating sleeve 16 which is slidably mounted on the exterior of the intermediate housing 12. Sleeve 16 is of skeletonized configuration, having only three axial ribs 16a in its midsection. The actuating sleeve 16 is secured to the valve sleeve 12 for axial movement by a plurality of peripherally spaced bolts 17 which pass through the axially extending fluid passage ports 12c and engage an annular recess 14c provided in the valve sleeve 14. Thus, any movements of the sleeve 16 produced by the compressed spring 15 are immediately transferred to the valve sleeve 14. 
     The lower end of valve sleeve 14 is formed with a plurality of peripherally spaced, axially extending collet arms 14d, each of which terminates in an enlarged head portion 14e. Collet arms 14d are constructed with an inherent radially inward spring bias, but are pushed radially outwardly and maintained in latching engagement with an internal shoulder 13c formed on the lower housing element 13 by a frangible retention member 20 which extends across the internal bore of the valve sleeve 14. Retention barrier 20 preferably comprises a member that is readily frangible when impacted by the downwardly falling detonating bar 25 (FIG. 2C). A tempered glass disc makes an admirable retention barrier since the energy required to shatter the disc is minimal compared to the kinetic energy contained within the falling detonating bar 25. Furthermore, the fact that the glass disc is tempered insures that when it breaks, it will shatter into literally hundreds of small pieces which will not in any way impede the impact blow transferred to the firing mechanism of the perforating gun by the falling detonating bar 25. The frangible retention disc 20 is mounted within an internal slot 14f provided in the enlarged head portion 14e of each collet arm 14d. 
     As best shown in FIGS. 2B and 2C, the apparatus of the invention is operated entirely automatically by the downward movement of the detonating bar 25. As soon as the retention barrier 20 is broken by the detonating bar 25, the collet arms 14d spring inwardly and release from the latching surface 13c provided on the lower housing 13, thus freeing the valve sleeve 14 and the spring pressed actuating sleeve 16 to move downwardly under the bias of the compressed spring 15. 
     In summary, therefore, the method of this invention contemplates the compression of the spring 15 by the actuating sleeve 16 during the intial assemblage of the barrier retention disc 20 between the ends of the collet arms 14d. The spring loaded tool is then assembled in the tubing string immediately above the perforating gun and the assemblage is run into the well on a tubing string. When the perforating gun is positioned opposite the production formation to be perforated, the packer (not shown) carried by the tubing string is set and the pressure within the tubing string, hence within the bore of the tool 10, is reduced to a level below that anticipated for the production fluids contained in the formation to be perforated. The tubing string may be run in dry or just partially filled with fluid. The detonating bar 25 is then dropped and shatters the retention barrier 20, thus releasing the sleeve valve 14 for downward movement to its open position wherein fluid may freely pass from the interior of the housing 10 through the openings formed between ribs 16a of the actuating sleeve 16 and the radial ports 12c. Thus, coincidentially with the firing of the perforating gun, a direct fluid passage is opened to the interior of the tubing string, permitting unrestricted flow of the formation fluids through the newly formed perforations and upwardly into the tubing string. Such flow is fairly rapid due to the underbalanced pressure condition existing in the tubing string at the instant of perforating, and thus the debris inherently encountered in the perforating operation is washed from the perforations and does not impede future production from the perforated formation. 
     Referring now to FIGS. 5A and 5B, there is shown a modified apparatus embodying this invention. In this embodiment, a valve housing 50 is provided comprising an upper connecting sub portion 51, an intermediate tubular portion 52 and a lower connecting sub portion 53. The upper sub portion 51 is provided with internal threads 51a at its upper end for connection to a tubular tool string which generally includes a packer and may include other tools, such as washer, chemical treatment apparatus, and/or gravel packing apparatus. The upper connecting sub portion 51 is connected by threads 51b to the top end of the intermediate portion 52. The threaded connection is sealed by an O-ring 52a and secured by a set screw 51c. 
     The intermediate housing portion 52 is connected by threads 53a to the lower connecting sub portion 53. This threaded connection is sealed by an O-ring 53b and secured by a set screw 53c. The lower extremity of the lower connecting sub 53 is provided with threads 53d for conventional sealed connection to the housing of a perforating gun (not shown) having an impact actuated primer which is detonated by dropping thereon of a detonating bar 25, which is shown in intermediate positions in FIGS. 5B and 6B. 
     The medial portion of the intermediate housing portion 52 is machined to define a plurality of peripherally spaced, axially extending collet arms 52b, each of which terminates in an enlarged head portion 52c. Each collet arm 52b is surrounded by a space 52d which comprises a radial fluid passage or port for the entry of formation fluids into the interior of the tubular tool string, in a manner that will be hereinafter described. 
     The radial ports 52d are normally sealed by a sleeve valve 55 which snugly surrounds the periphery of the intermediate housing portion 52 and is sealably engaged by an O-ring 52e seal in the upper portion of the intermediate housing 52 above the radial ports 52d, and by an O-ring seal 52f in a portion of the intermediate housing 52 located below the radial ports 52d. It should be noted that the diameter of the O-ring seal 52f is substantially greater than that of the O-ring 52e, and the sleeve valve 55 has a reduced thickness lower portion 55a to cooperate with the larger diameter O-ring 52f. 
     Sleeve valve 55 is retained in its sealing position relative to the radial ports 52d by the enlarged head portions 52c of the collet arms 52b. Such head portions engage a downwardly sloped surface 55b communicating between the upper thickwalled portion of the sleeve 55 and the lower thinwalled portion 55a. In turn, the heads 52c of the collet arms 52b are held in their latching relationship with respect to the valve sleeve 55 by the ring portion 56a of a collet 56 which is mounted within the bore of the intermediate housing portion 52. Collet 56 has a plurality of peripherally spaced, downwardly extending spring arms 56b, each of which terminates in an enlarged head portion 56c. The extreme inner portion of 56d of each enlarged head portion 56c projects into the path of the detonating bar 25. 
     The collet 56 is releasably secured in its run-in position illustrated in FIG. 5A by a plurality of shear screws 57 in the wall of housing 52. The intermediate housing portion 52 is provided with an annular recess 52g which will receive the enlarged collet head portions 56c upon downward movement of the collet 56 subsequent to shearing of the shear pins 57. Such downward movement is imparted by the passage of the detonating bar 25 through the bore of the housing 50. It should be noted that the energy extracted from the detonating bar 25 is only that sufficient to effect the shearing of pins 57 and the movement of the collet 56 to its lower position illustrated in FIG. 6B. None of the kinetic energy of the detonating bar 25 is employed to effect the movement of the valve sleeve 55 to its port opening position. 
     The downward movement of the valve sleeve 55 to its port opening position is accomplished entirely by fluid pressure. After the lower collet 56 moves downwardly, the collet arms 52b of upper collet 52 are free to be cammed inwardly by the inclined surface 55b acting on the bulbous heads 52c. The valve sleeve 55 is always subjected to the fluid pressure existing in the casing annulus surrounding the housing 50. This fluid pressure is substantially in excess of the fluid pressure within the bore of the housing 50 for the reason that such bore is deliberately maintained dry or is only partially filled with fluid and the tubing string fluid pressure is thus substantially less than the anticipated fluid pressure of the formation to be perforated. Additionally, the discharge of the perforating gun will, as is well known to those skilled in the art, produce a charge of compressed gases which will also augment the fluid pressure existing in the casing annulus adjacent the valve sleeve 55. Accordingly, because of the differential areas of the valve sleeve 55 exposed to the casing annulus pressure and the internal bore pressures, the valve sleeve 55 will be forced downwardly to its open position, as illustrated in FIG. 6B, thus exposing the radial ports 52d and permitting unrestricted flow of fluid from the newly formed formations through such ports and upwardly through the tool string, due to the underbalanced condition existing at the time of perforating. 
     Although the invention has been described in terms of specified embodiments which are 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.