US3842919A

US3842919A - Apparatus for venting gases from an enclosed perforating carrier

Info

Publication number: US3842919A
Application number: US00399657A
Authority: US
Inventors: R Dermott
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1973-09-21
Filing date: 1973-09-21
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22
Also published as: GB1483505A

Abstract

In the preferred embodiments of the present invention disclosed herein, an enclosed-carrier perforating gun is provided with a passage between the sealed interior of the carrier and the exterior thereof and a valve member is cooperatively arranged to shift from a normal passage-closing position to a passage-opening position whenever the pressure inside the carrier is greater than that outside of the carrier for venting highly pressured well bore gases which may be retained in the carrier should the perforating gun be returned to the surface without having been actuated.

Description

I United States Patent [191 [111 3,842,919 Dermott 1 Oct. 22, 1974 [54] APPARATUS FOR VENTING GASES FROM 3,246,707 4/1966 Bell 175/454 AN ENCLOSED PERFORATING CARRIER 3,311,178 3/1967 McElheny 175/454 3,327,630 6/1967 Bell l75/4.6 X

[75] Inventor: Raymond W. Dermott, Houston,

Tex.

[73] Assignee: Schlumberger Technology Corporation, New York, NY.

[22] Filed: Sept. 21, 1973 [21] Appl. No.: 399,657

[52] US. Cl. 175/454 [51] Int. Cl E2lb 43/116 [581 Field of Search 175/454, 4.55, 4.58, 4.59, 175/2, 4.6; 102/20, 24 AC [56] References Cited UNITED STATES PATENTS 2,191,781 2/1940 Turechek 175/454 2,760,408 8/1956 Taylor 3,057,297 1011962 Brown 175/4.6

Primary Examiner-David H. Brown Attorney, Agent, or FirmErnest R. Archambeau, Jr.; William R. Sherman; Stewart F. Moore ABSTRACT In the preferred embodiments of the present invention disclosed herein, an enc1osed-earricr perforating gun is provided with a passage between the sealed interior of the carrier and the exterior thereof and a valve member is cooperative1y arranged to shift from a normal passage-closing position to a passage-opening position whenever the pressure inside the carrier is greater than that outside of the carrier for venting highly pressured well bore gases which may be retained in the carrier should the perforating gun he returned to the surface without having been actuated.

15 Claims, 4 Drawing Figures PAIENIEB III 221974 mania FIG. 4

APPARATUS FOR VENTING GASES FROM AN ENCLOSED PERFORATING CARRIER The perforating guns most commonly used in present-day well-completion operations are typically comprised of an elongated fluid-tight tubular body or a socalled enclosed carrier which houses one or more longitudinally spaced shaped explosive charges and the necessary accessories for selectively detonating these charges from the surface. In those situations where the perforator must be lowered through a production string to reach the interval of the well that is to be perforated, these enclosed carriers are usually made up of an integral section of thin-walled, small-diameter steel tubing having complementally fitted heads that are secured in place and fluidly sealed in the upper and lower ends of the tubing section by seals such as elastomeric O-rings and the like. As fully described in US. Pat. No. 3,048,l02, these thin-walled carriers are considered expendable since their walls will be punctured by the perforating jets respectively developed upon detonation of the enclosed shaped charges. On the other hand, where there is no production string limiting access to the well interval that is to be perforated, a larger thickwalled carrier such as shown in US. Pat. Nos. 3,329,2l8 or 3,7l7,207 is generally used. Since these large-diameter carriers are reused as many times as possible, each of the shaped charges in these non expendable carriers is respectively aligned with an access opening or threaded side port in the carrier that is closed by an expendable port plug. In addition to the heads which seal off the upper and lower ends of these carriers, each of the port plugs is fluidly sealed in its respective port by conventional seals such as an elastomeric O-ring. It is also common practice to provide additional access openings in the sides of some nonexpendable carriers for installing detonators, making internal wiring connections, and the like. These access openings are also typically closed with replaceable threaded plugs that are similarly sealed by O-rings or the like.

Accordingly, it will be recognized that any enclosed carrier whether it is expendable or non-expendable will be entirely dependent upon the integrity of several critical fluid seals for preventing the unwanted entrance of well bore liquids into the carrier before the shaped charges are detonated. Those skilled in the art will appreciate, however, that although various present-day sealing materials are well suited for blocking the entry of liquids even under adverse well bore conditions, there is no satisfactory non-metallic material known today that will reliably prevent highly pressured gases from permeating through the several seals of an enclosed carrier as the gun is being positioned. Thus, whether a well bore is gas-filled or contains liquids with dissolved gases therein, it is inevitable that by the time a perforating gun reaches a particularly deep well bore interval that is to be perforated, the interior of the enclosed carrier will be filled with these highly pressured gases.

Ordinarily, no problem is presented by the infusion of well bore gases into an enclosed carrier. Once the gun is successfully actuated, the interior of the carrier will be opened to the well bore by way of the holes made in the carrier wall or port plugs by the perforating jets. Thus, once the gun is withdrawn from the well bore. the pressure of any fluids in the carrier will be at atmospheric pressure and the gun can be safely disassembled.

A wholly difierent situation is presented, however, when the gun must be recovered for some reason with its shaped charges being undetonated so that the carrier is still nominally sealed. Experience has shown that although gases will readily permeate through the seals and fill the carrier as it is lowered into a gas-bearing well bore, these gases will escape from the carrier at a considerably slower rate as it is returned to the surface. As a result, once the gun is at the surface, the interior of the carrier may be filled with highly pressured gases and disassembly of the gun may be extremely risky. For instance, with a gas-filled non-expendable carrier, as the first port plug to be removed is loosened, it may be suddenly blown out of the gun. Similarly, removal of the heads from either type of enclosed carrier can also present a definite hazard to nearby workers and equipment. These problems are even further complicated since it is never known for sure whether or not the carrier of a recovered perforator is under pressure. Thus, if it is unwisely assumed that there is little or no pressured gas in an enclosed carrier, a serious accident can easily occur if the gun is carelessly disassembled.

Accordingly, it is an object of the present invention to provide new and improved enclosed-carrier perforating apparatus which will be reliably purged of any entrapped high-pressure gases should the apparatus be returned to the surface with its shaped charges undetonated.

This and other objects of the present invention are attained by cooperatively arranging normally closed valve means on an enclosed-carrier well perforator adapted for venting pressured fluids from the interior of the carrier whenever the perforator is returned to the surface without having been actuated.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts a preferred embodiment of new and improved enclosed-carrier perforating apparatus as it appears with its carrier-venting valve means in a normal or closed position;

FIG. 2 is a view similar to FIG. I but showing the valve means for that apparatus in a carrier-venting or open position; and

FIGS. 3 and 4 depict an alternate embodiment of the present invention which may be used either alone or in conjunction with perforating apparatus as shown in FIG. 1.

Turning now to FIG. I, the lower portion is shown of new and improved perforating apparatus 10 incorporating the principles of the present invention. To illustrate the invention, the new and improved perforating apparatus 10 is depicted as including an expendable thin-walled carrier ll such as the one fully described in US. Pat. No. 3.048,l02. It will, of course, be recognized that the carrier ll could just as well be a thickwalled re-usablc perforating carrier either with individual charge compartments as shown in US. Pat. No. 3,329,218 or with an elongated longitudinal bore for housing a group of shaped charges as shown in US.

Pat. No. 3,717,207 without being outside of the scope of the present invention.

As is typical, the perforating apparatus includes one or more shaped charges, as at 12, which are mounted in spaced holes on a support or elongated strip 13 so as to be longitudinally spaced along the length of the enclosed charge chamber defined by the internal bore 14 of the tubular carrier 11. To detonate the shaped charges, as at 12, the new and improved perforating apparatus 10 is provided with detonating means such as an electrically actuated detonator 15 which is coupled to a length of explosive detonating cord 16 that is secured to the support 13 and cooperatively positioned so as to be in detonating proximity of each of the shaped charges, as at 12.

As illustrated in U.S. Pat. No. 3,048,l02, the upper end of the thin-walled carrier H is closed with a suitably sized closure member or head (not shown in the present drawings) which is sealingly disposed within the carrier and arranged as necessary for connection either to other tools thereabove or to the lower end of a typical armored electrical cable (also not shown) having at least one conductor 17 that is sealingly passed through the head and connected to the detonator 15. The lower end of the carrier ll is similarly closed by a closure member or head, as at 18, which is fitted into the carrier and sealed in relation thereto by sealing means such as one or more elastomeric O-rings 19.

In contrast to the prior-art heads such as shown in US. Pat. No. 3,048,102, in the preferred embodiment of the present invention illustrated here the lower head 18 is provided with a venting passage, such as a longitudinal bore 20 formed in the head, which is terminated by a slightly enlarged counterbore 21 for defining a valve seat. To cooperatively control fluid communication through the venting passage 20, a valve member 22 is cooperatively arranged to be complementally seated within the counterbore 21 and to normally be sealingly engaged therewith by fluid seals such as one or more elastomeric O-rings 23. To prevent loss of the valve member 22 once it moves to its open position, the valve member is loosely confined within a hollowed nose piece 24 having an enlarged chamber 25 and one or more ports, as at 26, which are arranged downstream of the valve seat 21 to communicate the chamber with the well bore exterior of the perforating apparatus 10.

Accordingly, it will be appreciated from FIG. 1, that so long as the valve member 22 remains in its depicted normal passage-closing position. fluids cannot enter the internal bore 14 of the carrier 11 by way of the passage 20 except, of course, for whatever well bore gases that permeate into the carrier through the O-rings such as at 19 or 23. it should be noted that since the internal bore 14 of the carrier ll is initially at atmospheric pressure, as the perforating apparatus 10 is lowered into a well bore the pressure of the fluids in the well bore will be effective for maintaining the valve member 22 in its illustrated passage-closing position.

As discussed above, it is generally expected that well bore gases will gradually permeate into the internal bore 14 of the carrier 11 as the perforating apparatus I0 is being lowered to a formation interval that is to be perforated. This will naturally pose no problem ordinarily since the frictional engagement of the valve member 22 and its seals 23 within the counterbored valve seat 2! will retain the valve member in its passage-closing position even should the internal bore 14 of the carrier 11 become filled with gases at the same pressure as that of the well bore fluids exterior of the carrier.

There is, of course, ordinarily no problem where the perforating charges, as at 12, are subsequently detonated since their respective perforating jets will puncture the walls of the carrier 11 so that its internal bore 14 will be exposed to the well bore exterior of the carrier. However, as previously discussed, it is not uncommon for the charges, as at 12, to not be detonated for any one of several reasons. Should this occur, it will be recalled from the previous discussion that whatever gases that have already entered the carrier ll will be at a substantially-elevated pressure which may be as high as that of the well bore fluids at the depth the perforating apparatus 10 is then located. Thus, although withdrawal of the perforating apparatus 10 from the well bore will ultimately result in the highly pressured gases entrapped in the carrier 11 being at a higher pressure than that exterior of the carrier, there is usually insufficient time for these gases to permeate back through the various seals, as at 19, on the carrier so as to reduce the pressure in the internal bore 14 to a safe level.

Accordingly, it will be recognized that should the unactuated perforating apparatus 10 be returned to the surface with highly pressured well bore gases trapped in the internal bore 14 of the carrier 11, there will be some point in the ascent of the tool where the pressure differential acting across the valve member 22 will be sufficient to move it from its passage-blocking position shown in FIG. 1 to its passage-opening position shown in FIG. 2. When this occurs, it will be appreciated that any entrapped gases in the carrier 11 will be quickly vented into the well bore by way of the venting passage 20 and the ports 26. Thus, once the perforating apparatus 10 is returned to the surface, it can be reasonably expected that the carrier 11 will be purged of highly pressured gases so that the perforating apparatus can be safely disassembled.

Although the valve member 22 will normally function to vent any entrapped gases from the carrier ll should the unactuated perforating apparatus 10 be returned to the surface, it will be appreciated that there may be occasional situations where the valve member may inadvertently become jammed in the valve seat 21. Accordingly, to avoid any possibility of such an event being undetected when the perforating apparatus 10 is recovered, it is preferred to provide the valve member 22 with a manual actuator such as rod 27 which is dependently secured to the valve member and extended through a longitudinal bore 28 in the lower end of the nose piece 24. In this manner, should the valve member 22 still be in its normal passage-closing position when the perforating apparatus 10 is returned to the surface without having been actuated, the valve member can be readily opened such as by inserting a hook or the like into a hole 29 formed in the lower end of the actuating rod 27 and pulling on it to shift the valve member to its passage-opening position.

It should also be noted that by extending the actuating rod 27 below the lower end of the nose piece 24, the position of the rod in relation to the nose piece will provide a reliable indicator as to the operating position of the valve member 22. This will, of course, have the dual advantage of indicating the position of the valve member 22 both before the perforating apparatus is lowered into a well bore as well as after the perforator is recovered without having been actuated.

Those skilled in the art will, of course, appreciate that various perforating operations often necessitate the placement of individual perforations at different selected depths during a single trip into a well bore. in such instances, nonexpendable perforating apparatus such as the-gun shown in U.S. Pat. No. 3,329,218 may often be used. On the other hand, where the perforating apparatus must enter the interval to be perforated by way of small-diameter production tubing, it is common practice to use a number of expendable guns (such as that shown in U.S. Pat. No. 3,048,102) individually carrying only one or two shaped charges and which are tandemly coupled to one another in an assembly of convenient length. To selectively control the individual firing of these several guns, control arrangements such as those shown in U.S. Pat. Nos. 3,246,707 or 3,246,708 are typically employed. It will be recognized, therefore, that should one of these tandemly arranged guns be employed, an arrangement such as described above by reference to FIGS. 1 and 2 would be effective for venting only the lowermost gun in that particular assembly since the several inter-carrier arming switches (such as shown generally at "47" in U.S. Pat. No. 3,246,708) would prevent free pressure communication between the other carriers.

Accordingly, to provide means for venting of all of the carriers in an assembly of two or more carriers which have little or no pressure communication therebetween, apparatus incorporating the principles of the present invention is preferably arranged as shown in FIG. 3. As depicted in the partial view shown there, the new and improved perforating apparatus 50 includes upper and

lower carriers

51 and 52 which are respectively arranged as described in U.S. Pat. No. 3,048,102 with each carrying one or more shaped charges and a suitable detonating device (none of which shown in FIG. 3). To couple the

carriers

51 and 52 to one another, a suitably arranged body 53 is secured within the adjacent ends of the carriers and sealed thereto by seals such as O-

rings

54 and 55. To provide for electrical interconnections between the two

carriers

51 and 52, a pressure-actuated arming switch 56 such as described in U.S. Pat. No. 3,246,708 is mounted in a complementally enlarged portion of a longitudinal bore 57 formed in the intermediate coupling body 53 and connected to

electrical conductors

58 and 59 respectively leading to the detonators (not shown) in the

carriers

51 and 52.

It will, of course, be recognized that if the carrier 52 is the lowermost one in the assembly of carriers included in the perforating apparatus 50, the lower end of this carrier will be provided with venting apparatus such as shown in H65. 1 and 2 so that carrier will be vented as already described. To provide for venting of the carrier 51, the longitudinal bore 57 is intersected with an enlarged transverse bore 58 which is communicated by way of the longitudinal bore to the shaped charge chamber defined by the interior bore of that carrier. Although the enlarged lateral bore 58 need not extend fully across the body 53, it is preferred that it do so for providing a convenient a ess opening to the electrical conductor 58. To close the enlarged bore 58, a typical port plug 59 is threadedly secured and fluidly sealed in one end of the lateral bore.

As best seen in FIG. 4, the other end of the lateral bore 58 is closed by a threaded plug 60 and fluidly sealed as by an O-ring 61. To provide valve means for venting the carrier 51, the plug 60 is drilled, as at 62, to define a valve seat adapted to receive a valve member 63 having one or more seals, as at 64, mounted therearound. To limit the inward movement of the valve member 63 beyond its illustrated passage-closing position, a stop member such as a transverse pin 65 is mounted on the outer portion of the valve member and arranged to engage an outer face or stop 66 defined by the bottom of an enlarged counterbore 67 in the outer end of the threaded plug 60. The outermost end of the plug 60 is upset or turned over, as at 68, to provide a second stop for limiting the outward travel of the valve member 63 beyond a passage-opening position sufficient to completely withdraw the valve seal 64 from the valve seat 62.

It will, of course, be recognized that the valve member 63 will operate in the same manner as the valve member 22. Thus, whenever the pressure of any en trapped gases in the carrier Sl exceed the pressure exterior of the carrier, the valve member 63 will be urged outwardly from its passage-closing position in the valve seat 62 to the passage-opening position defined by the engagement of the stop pin 65 against the upset stop or shoulder 68. To provide for manual actuation of the valve member 63, its outer face is shaped to form a keyshaped projection, as at 69, and a hole, as at 70, is placed in the projection to allow a hook or the like to be used to open the valve member. It will, of course, be recognized that either the transverse pin 65 or the projection 69 will also effectively serve as a visual indicator of the particular position that the valve member 63 is then occupying.

Accordingly, it will be recognized that the two abovedescribed embodiments of enclosed-carrier perforating apparatus arranged in accordance with the principles of the present invention are each cooperatively arranged to prevent the undetected retention of highly pressured gases in the carrier should the apparatus go unactuated and be returned to the surface intact. By arranging the valve means as depicted in the drawings, the usual situation will be that the carrier will be automatically vented once the apparatus is returned to a higher elevation in the well bore where the outwardly acting pressure differential is sufficient to shift the valve member to its passage-opening position. More over, by providing the valve means with their respec tively illustrated valve actuators, in addition to serving as a position indicator the actuator will enable the operator to shift the valve member to its passage-opening position so as to be certain that the interior of the carrier is completely vented before it is disassembled.

While only particular embodiments of the present in vention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

l. Perforating apparatus adapted for perforating earth formations traversed by a well bore containing pressured gases and comprising:

a carrier including a body member having an interior chamber for receiving at least one perforating device and at least one opening therein providing access to said chamber, and a closure member in said access opening and sealingly coupled to said body member for blocking the entrance of well bore liquids into said chamber;

a venting passage arranged on at least one of said members for communicating said chamber with the exterior of said carrier; and

valve means normally blocking communication through said venting passage and cooperatively arranged for movement from a normal passageelosing position to a passage-opening position in response to a pressure in said chamber greater than the pressure exterior of said carrier for venting whatever pressured well bore gases may have entered said chamber.

2. The perforating apparatus of claim 1 further including:

actuating means coupled to said valve means and adapted for manually moving said valve means to said passage-opening position.

3. The perforating apparatus of claim 1 further including:

means operatively associated with said valve means and adapted for providing a visual indication representative of said valve means being in at least one of said positions.

4. The perforating apparatus of claim I further including:

means coupled to said valve means and adapted for manually moving said valve means to said passageopening position as well as for providing a visual indication representative of at least the movement of said valve means to said passage-opening position.

5. The perforating apparatus of claim 1 further including:

means coupled to said valve means and adapted for selectively moving said valve means either to said normal passage-blocking position or to said passage-opening position as well as for providing a visual indication representative of said valve means being in each of said positions.

6. The perforating apparatus of claim 1 wherein said venting passage is in said body member.

7. The perforating apparatus of claim 1 wherein said venting passage is in said closure member.

8. Perforating apparatus adapted for perforating earth formations traversed by a well bore containing pressured gases and comprising:

an enclosed carrier including a body member having an interior chamber defined therein, an opening in said body member providing access to said chamber, a closure member adapted for closing said access opening, and non-metallic sealing means adapted for fluidly sealing said closure member in relation to said body member to prevent the entrance of well bore liquids into said chamber;

perforating means in said chamber and cooperatively arranged for actuation for perforating an earth formations; and

means cooperatively arranged for venting pressured well bore gases from said chamber which may have permeated through said sealing means and become entrapped in said chamber whenever the pressure of such entrapped gases exceeds the pressure exterior of said carrier.

9. The perforating apparatus of claim 8 wherein said gas-venting means include:

a gas passage in at least one of said carrier members for providing communication between said chamber and the exterior of said carrier;

means in said gas passage defining a valve seat; and

a valve member cooperatively arranged for movement from a normal passage-closing position where said valve member is sealingly engaged with said valve seat to a passage-opening position away from sealing engagement with said valve seat in response to a greater pressure in said chamber upstream of said valve seat than the pressure exterior of said carrier downstream of said valve seat.

10. The apparatus of claim 9 further including:

actuating means coupled to said valve member and adapted for manually moving said valve member to its said passage-opening position.

11. The apparatus of claim 9 further including:

means operatively associated with said valve member and adapted for providing a visual representation representative of said valve'member being in at least one of its said positions.

12. The apparatus of claim 9 further including:

means coupled to said valve member and adapted for manually moving said valve member to its said passage-opening position as well as for providing a visual indication representative of the movement of said valve member to its said passage-opening positron.

13. The apparatus of claim 9 further including:

means coupled to said valve member adapted for manually moving said valve member to either its said passage-opening position or its said passageclosing position as well as for providing a visual representation of the position of said valve member.

14. The perforating apparatus of claim 9 wherein said gas passage has at least one portion thereof extending through said closure member, and said valve seat is located in said one passage portionv 15. The perforating apparatus of claim 14 wherein said access opening is in the end of said body.

* k s: a a

Claims

1. Perforating apparatus adapted for perforating earth formations traversed by a well bore containing pressured gases and comprising: a carrier including a body member having an interior chamber for receiving at least one perforating device and at least one opening therein providing access to said chamber, and a closure member in said access opening and sealingly coupled to said body member for blocking the entrance of well bore liquids into said chamber; a venting passage arranged on at least one of said members for communicating said chamber with the exterior of said carrier; and valve means normally blocking communication through said venting passage and cooperatively arranged for movement from a normal passage-closing position to a passage-opening position in response to a pressure in said chamber greater than the pressure exterior of said carrier for venting whatever pressured well bore gases may have entered said chamber.

2. The perforating apparatus of claim 1 further including: actuating means coupled to said valve means and adapted for manually moving said valve means to said passage-opening position.

3. The perforating apparatus of claim 1 further including: means operatively associated with said valve means and adapted for providing a visual indication representative of said valve means being in at least one of said positions.

4. The perforating apparatus of claim 1 further including: means coupled to said valve means and adapted for manually moving said valve means to said passage-opening position as well as for providing a visual indication representative of at least the movement of said valve means to said passage-opening position.

5. The perforating apparatus of claim 1 further including: means coupled to said valve means and adapted for selectively moving said valve means either to said normal passage-blocking position or to said passage-opening position as well as for providing a visual indication representative of said valve means being in each of said positions.

8. Perforating apparatus adapted for perforating earth formations traversed by a well bore containing pressured gases and comprising: an enclosed carrier including a body member having an interior chamber defined therein, an opening in said body member providing access to said chamber, a closure member adapted for closing said access opening, and non-metallic sealing means adapted for fluidly sealing said closure member in relation to said body member to prevent the entrance of well bore liquids into said chamber; perforating means in said chamber and cooperatively arranged for actuation for perforating an earth formations; and means cooperatively arranged for venting pressured well bore gases from said chamber which may have permeated through said sealing means and become entrapped in said chamber whenever the pressure of such entrapped gases exceeds the pressure exterior of said carrier.

9. The perforating apparatus of claim 8 wherein said gas-venting means include: a gas passage in at least one of said carrier members for providing communication between said chamber and the exterior of said carrier; means in said gas passage defining a valve seat; and a valve member cooperatively arranged for movement from a normal passage-closing position where said valve member is sealingly engaged with said valve seat to a passage-opening position away from sealing engagement with said valve seat in response to a greater pressure in said chamber upstream of said valve seat than the pressure exterior of said carrier downstream of said valve seat.

10. The apparatus of claim 9 further including: actuating means coupled to said valve member and adapted for manually moving said valve member to its said passage-opening position.

11. The apparatus of claim 9 further including: means operatively associated with said valve member and adapted for providing a visual representation representative of said valve member being in at least one of its said positions.

12. The apparatus of claim 9 further including: means coupled to said valve member and adapted for manually moving said valve member to its said passage-opening position as well as for providing a visual indication representative of the movement of said valve member to its said passage-opening position.

13. The apparatus of claim 9 further including: means coupled to said valve member adapted for manually moving said valve member to either its said passage-opening position or its said passage-closing position as well as for providing a visual representation of the position of said valve member.

14. The perforating apparatus of claim 9 wherein said gas passage has at least one portion thereof extending through said closure member, and said valve seat is located in said one passage portion.

15. The perforating apparatus of claim 14 wherein said access opening is in the end of said body.