US3800705A

US3800705A - Pressure balanced percussion firing system

Info

Publication number: US3800705A
Application number: US00347324A
Authority: US
Inventors: J Tamplen
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-30
Filing date: 1973-03-30
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

Percussion firing apparatus for firing an explosive charge in a downhole tool without using an electrical system characterized by a chamber and a pressure balancing piston and including a percussion firing head assembly that is set in the well and, on a subsequent trip, a firing prong employed to move the pressure balancing piston downwardly to arm and ultimately fire via a firing pin a charge. After the charge is fired the entire percussion firing apparatus is pulled from the well. The apparatus provides consistent firing regardless of internal and external pressures of variations therein, or of the fluids in the well. Also disclosed are positive safety features; such as, running the percussion firing head assembly with the firing pin disarmed, and a single-fire safety construction that allows only one firing attempt; as well as other advantageous features and specific structure and assembly.

Description

United States Patent [1 1 Tamplen 1 PRESSURE BALANCED PERCUSSION FIRHNG SYSTEM Jack W. Tamplen, RR. 2, Celina, Tex. 75009 22 Filed: Mar. 30, 11973 [21] Appl. No.: 347,324

[76] Inventor:

Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or Firm-Wofford, Felsman & Fails 1 1 Apr. 2, 1974 [57] ABSTRACT Percussion firing apparatus for firing an explosive charge in a downhole tool without using an electrical system characterized by a chamber and a pressure balancing piston and including a percussion firing head assembly that is set in the well and, on a subsequent trip, a firing prong employed to move the pressure balancing piston downwardly to arm and ultimately fire via a firing pin a charge. After the charge is fired the entire percussion firing apparatus is pulled from the well. The apparatus provides consistent firing regard less of internal and external pr essures of variations therein, or of the fluids in the well. Also disclosed are positive safety features; such as, running the percussion firing head assembly with the firing pin disarmed, and a single-fire safety construction that allows only one firing attempt; as well as other advantageous features and specific structure and assembly.

38 Claims, 7 Drawing Figures MTENYEU APR 2 I974 SHEET 2 UP 2 PRESSURE BALANCED PERCUSSION FIRING SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to subsurface well apparatus; and, more particularly, to percussion firing apparatus for firing an explosive charge within a wellbore penetrating subterranean formations.

2. Description of the Prior Art The prior art has seen the development of a wide va riety of apparatus for firing explosive charges downhole in a well penetrating subterranean formations; including firing by wire lines. Such charges were used in' a wide variety of applications. For example, setting tools were operated with such charges to set bridge plugs and/or packers; perforating guns were employed to effect communication between the interior of a conduit in a well and the subterranean formations penetrated by the well; and explosive cut-off tools were employed to sever sections of conduit or the like. Primarily, the apparatus for firing an explosive charge has developed along the lines of either electrically fired systems or thenonelectrical systems that resorted to percussion firing of an igniter. The electrically fired systems require care in connection, handling and transportation, as well as in running; since the electrical systems are subject to stray currents, as from radio frequency transmission towers, static electricity, and the like. Such electrically fired systems are also generally more expensive in operation and are not as readily available in the field as are the nonelectrical wire line units. The percussion firing systems, on the other hand, have required care in handling and have been dangerous because of the danger of an inadvertent blow effecting firing of the charge, either during handling or while being lowered into the well. Moreover, the prior art percussion firing apparatus has been dangerous and unsatisfactory because it could not be ascertained with certainty that it had been fired or disarmed in the wellbore, so that it was risky to go in and retrieve the percussion firing assembly. Expressed otherwise, a sharp blow during the retrieval operation could cause inadvertent firing, sometimes at the incorrect depth with resultant damage to the well casing or conduit. it will be apparent that such inadvertent firing, when the charge is properly located at the correct depth, is not necessarily disadvantageous, since such firing would still achieve the desired result. ln my U.S. Pat. No. 3,710,717, entitled PERCUSSION FIRING SYSTEM, 1 described an improved apparatus that obviated the disadvantages of the prior art. Good as that improved percussion firing system was, however, it still did not afford a completely satisfactory system that had the desirable features delineated hereinafter.

It has been found that, when running explosives to extreme depths in high pressure oil wells, external pressures attempting to enter the explosive chamber is very high; and, on the other hand, when the explosives are ignited, the internal pressures sometimes become extremely high even in the firing pin chamber. The prior art has provided an external firing system which requires a reinforcing disc plus extemely close fits between the parts to prevent the external pressure from deforming the top of the primer shell. Also, when the explosives were ignited, the reinforcing discs would often be blown out permitting the internal pressure to bleed off without completely operating the attached device, such as a pressure setting tool 13. Moreover. the thickness of the reinforcing disc often made it impossible for the firing pin to penetrate the reinforcing disc sufficiently to obtain ignition of the igniter means. Sand, pipe scale, and even heavy muds also adversely affected the chances for success of obtaining firing with an external firing mechanism.

Experience had indicated that a percussion firing apparatus for firing an explosive charge within a well penetrating subterranean formations should have the following features.

I. The percussion firing head assembly should be firable by a direct force and not require speed, thereby:

a. enabling being fired by either wire line, a tubing string, or dropping a sinker bar from the surface; and

b. enabling operation at great depth and in viscous fluids in the wellbore.

2. The percussion firing head assembly should have its arming, firing and safety mechanism contained inside an enclosed firing chamber so as to not be adversely affected by sand, pipe scale, or well fluids.

3. The percussion firing head assembly should have a pressure balancing means to prevent external pressure or internal pressure or sudden changes in these pressures from affecting the downhole arming and firing sequences.

4. The percussion firing head assembly should include an arming mechanism that is run and set in the unarmed condition.

5. The arming mechanism should inlcude releaseable retainer means that must be overcome before the arming sequence can begin.

6. A second releasable retainer means should be included as an additional safety factor to prevent firing before it is overcome.

7. A means should be provided for retaining pressure within the percussion firing head assembly to ensure operation of an attached tool, such as a pressure setting tool, in the event there is a bleeding off, or blow-by," of pressure past the firing pin assembly. In this way operation of the tool is ensured even if there is blowby of fluids, or gases from fired charges.

8. It is desirable that ignition be facilitated by omission of interfering elements between the firing pin and the igniter and with the igniter insulated from wellbore pressure and fluids. This enables employing less sensitive and less expensive ignition caps.

9. The load delivered to the firing pin should be consistent, and invariant for each run, regardless of well conditions, to ensure firing without piercing completely through the firing cap.

10. The arming and firing assembly should be disarmed after one firing attempt for safety in subsequently handling the tools in the event of a mirfire.

l l. The firing pin should have a supplemental safety feature to ensure adequate pentration for ignition but to prevent subsequent ignition in the event of a misfire.

12. The percussion firing head assembly should be adaptable to be employed with either an internal fishing neck or an external fishing neck. 13. The percussion firing head assembly should be adapted to be fired by an inexpensive one-piece firing prong used on a second trip to arm and fire the charge while the percussion firing head assembly is retained, or hung, at a given depth in the wellbore.

14. The percussion firing head assembly, the onepiece prong described immediately hereinbefore, and the associated pulling tool should be designed such that the pulling tool engages the percussion firing head assembly fishing neck before ignition occurs to prevent dropping of the firing head assembly in cases where the explosives move the pulling tool and the percussion firing head assembly up the borehole sufficiently to loosen the slips during ignition.

Accordingly, it is an object of this invention to provide a percussion firing apparatus having an internally contained firing mechanism that obviates the disadvantages of the prior art delineated hereinbefore, and having an additional one or more of the desirable features delineated hereinbefore and not heretofore provided.

It is another object of this invention to provide a percussion firing apparatus for firing an explosive charge within a well penetrating subterranean formations in which the apparatus has all of the desirable features delineated hereinbefore.

These and other specific objects will be apparent from the following descriptive matter when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic elevational view of one embodiment of this invention in a wire line tool string, the tool string being shown within a cased wellbore.

FIG. 2 is a fragmentary longitudinal sectional view of the upper part of the percussion firing head assembly of FIG. 1.

FIG. 3 is a fragmentary longitudinal sectional view of the middle part of the percussion firing head assembly of FIG. 1.

FIG. 4 is a fragmentary longitudinal sectional view of the bottom part of the percussion firing head assembly of FIG. I.

FIG. 5 is a fragmentary longitudinal sectional view of the percussion firing head assembly of FIG. 2 with a firing prong being employed to effect the arming and firing of the firing pin therewithin.

FIG. 6 is a schematic view of an unfolded exterior of the body illustrated in FIG. 3; showing the J-slot arrangement for controlling the means for setting the slips.

FIG. 7 is a partial side elevational view, partly in section, of an embodiment of this invention employing an external fish neck.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, FIG. 1 illustrates a percussion firing head assembly 11, a setting tool 13 and a bridge plug 15, all of which are removably attached to a running tool 17 and suspended by a tool string 19 from a non-electrical wire line 21 in a section of conduit 23, such as casing, in a cased wellbore 25. The elements other than the percussion firing head assembly II are conventional and need not be described in detail herein. For example, the bridge plug and the setting tool 13 are described in US. Pat. Nos. 3,l8(i,485 and 3,266,575, issued to H.D. ()wen. It is sufficient to not that when an explosive charge within the setting tool 13 is fired, the bridge plug is set in the conduit 23 by the 4 setting tool; and the setting tool 13 thereafter shears a shear pin to separate from the bridge plug 15. The setting tool 13 may then be pulled from the wellbore 25.

The setting tool 13 may be fired in response to the firing of an explosive charge, such as the igniter means in the percussion firing head assembly 11.

As illustrated, the percussion firing head assembly 11, with a setting tool 13 and the bridge plug 15 attached thereto, is being emplaced at a predetermined depth in the wellbore 25 with a shear down" running tool. Such shear down" running tools are conventional and have the characteristic that when jarred downwardly to produce a large force, a shear pin is sheared to release the tool from a device with which it is connected, such as the percussion firing head assembly 11. Conversely, a shear up tool has the char acteristic that it will shear a shear pin and release any device with which it is connected when a sufficiently large upwardly acting force is developed, as by being jarred upwardly. Shear down running tools and shear up" pulling tools are employed conventionally with a tool string that has means such as jars for developing upwardly and downwardly acting forces. Moreover, the running and pulling tools have means for engaging the fishing neck means of the percussion firing head assembly 11. After the percussion firing head assembly 11 is emplaced in the conduit 23, a firing prong 26, FIG. 5, is inserted on a second trip and the explosive charge fired to actuated the setting tool and set the bridge plug in place. After the bridge plug is set, the setting tool is sheared off and pulled from the wellbore 25; and the bridge plug is left in the well. If the setting tool 13 fails to shear completely free of the bridge plug 15, it may be sheared therefrom by a jarring force transmitted through the shear up pulling tool because of the preselected relative sizes of the respective shear pins.

Referring to FIGS. 2-4, the percussion firing head assembly 11 comprises pressure balancing means 27 for neutralizing the adverse effects of external pressure and internal pressure and transients, or changes, therein; firing pin assembly 29; igniter means 31; settable hanging means 33; and first connection means 35.

The pressure balancing means 27 includes a chamber 37 and a pressure balancing piston 39. The chamber 37 has an enlarged annular passageway 41 that opens at its bottom end to facilitate insertion of the pressure balancing piston 39. A plurality of ports 43 communicate intermediate the interior of the chamber 37 and the exterior of the outer housing 45 of the percussion firing head assembly 1 l. The outer housing 45 has an internal thread 47 for conformingly and sealingly receiving an external thread 49 of a second and lower housing section 51.

The pressure balancing piston 39 has a lower end 53 that is adapted to engage the upper end 55 of the hammer pin 57, described in more detail hereinafter with respect to the arming means of the firing pin assembly. The pressure balancing piston 39 has an upwardly extending member 59 that has adequate structural strength for pushing the pressure balancing piston 39 downwardly for arming and firing. The upwardly extending member 59 protrudes into the prong receiving chamber M for a length L, that is suflicient to move the pressure balancing piston 39 downwardly sufficiently to arm and fire the firing pin assembly 29 and igniter means'3l. Specifically, the length L, is greater than the distance separating the lower end 53 of the pressure balancing piston 39 and the upper end 55 of the hammer pin 57 to ensure that positive contact is made between the pressure balancing piston 39 and the hammer pin 57 for the arming and firing operation. The upwardly extending member 59 is disposed in and movable reciprocally of a first longitudinally extending bore 63. The upwardly extending member has a first cross sectional area, or first area, 65. As illustrated, the upwardly extending member 59 is cylindrical in shape. Suitable seal means, such as o-rings 67, sealingly engage the upwardly extending member 59 and the internal walls of the bore 63 to seal against flow of fluids therepast. Any pressure on the'respective sides of the piston, therefore, will act against the first area 65.

As illustrated, the outer housing 45 has downwardly and outwardly extending passageways 69 for draining off sand and other types of debris to ensure that a firing prong can be admitted into the firing prong receiving chamber 61. Consequently, the first area 65 is exposed to the pressure of the borehole fluids, creating a downward force on the pressure balancing piston 39.

In order to balance this force, the pressure balancing piston 39 has a large central portion 71 disposed in the chamber 37. As illustrated, the large central portion 71 is cylindrical in shape and has the same diameter as the chamber 37 so as to effect a second cross sectional area, or second area, 73. Suitable seal means, such as o-rings 75, sealingly engage the large central portion 71 and internal walls of the chamber 37 so as to maintain a seal therebetween as the large central portion 71 is moved longitudinally of the chamber 37. Pressure balancing piston 39 has a lower portion 77 that is slidably disposed in a longitudinal bore 79 of the second housing section 51. The lower portion 77 has a third cross sectional area, or third area, 81. As illustrated, the lower portion 77 is also cylindrical in shape. Suitable seals, such as O-rings 83, sealingly engage the lower portion 77 and the internal walls of the longitudinal bore 79 to maintain a seal as the lower portion 77 is moved longitudinally of the bore 79. Thus, it can be seen that the external pressure of the borehole fluids will enter via ports 43 and act against the exposed surface" of the large central portion 71. The exposed surface is the difference between the second area 73 and the third area 81. The exposed surface is made such that it equals the first area 65. Consequently, the external pressure acting on the exposed surface of the large central portion 71 will cancel out and oppose the pressure acting on the first area 65, balancing the force of the external pressure on the pressure balancing piston. Consequently, the piston does not move; even though the external pressures may become very high as a tool is lowered into a wellbore having aqueous based fluids therein.

The pressure balancing piston 39 has a central longitudinally extending bore 87 with branch passageways 89 that communicate with the top portion of the chamber 37. Consequently, the internal pressure within the longitudinal bore 79 acts on the third area 81, either at the lower end 53 or at the top 91, with a third force. The difference between the second area 73 and the third area 81 is also chosen to be the same as the third area 81 such that the internal pressure will also act on the large central portion 71 to generate a fourth force that opposes and cancels out the third force. As a result, the pressure balancing piston 39 is again at pressure equilibrium and does not move as a result of internal pressure either, regardless of whether the internal pressure is less than or greater than the external pressure. As will be appreciated, the internal pressure will normally be at about atmospheric pressure when the tool is being run into the well, by may become very high following the ignition of the charges if there is sufficient blow-by of gases past the firing pin 93 of the firing pin assembly 29. Thus, the pressure balancing piston 39 does not move responsive to pressure, but moves responsive to an external force imposed upon it. This external force may be supplied by any of the means described herein, or any other suitable means.

Moreover, the pressure balancing piston 39, with its seal means, prevents communication between the interior of the percussion firing head assembly 11 and the exterior thereof, both before and after firing; with the numerous advantages delineated herein.

A releasable piston retainer means is employed to prevent premature movement, or creep, of the pressure balancing piston 39 until a force is applied to fire the igniter means 31. The piston retainer means comprises a shear pin ring 113 disposed about the lower portion 77 of the pressure balancing piston 39. The shear pin ring 113 is slidable longitudinally of the lower portion 77, but is releasably connected therewith by shear pins 1 15. As illustrated, two shear pins are diametrically opposed for balanced retention and to afford a balanced force when they are sheared by downward movement of the pressure balancing piston 39. The shear pin ring 113 encounters the top 116 of the second housing section 51 to limit its downward travel for shearing of the shear pins 115.

The firing is accomplished with the firing pin assembly 29. The firing pin assembly 29 comprises the firing pin 93 disposed therewithin and an arming means 94 for arming and firing. The arming means 94 is disposed intermediate the firing pin 93 and the pressure balancing piston 39 such that the firing pin ultimately can be forced sharply downwardly by a downward force on the pressure balancing piston 39.

The firing pin 93 has an enlarged head 95 designed for being repeatedly struck by the hammer pin 57. To prevent the firing pin 93 from being blown up the bore and out of position in the event the igniter means 31 disintegrates, a threaded enlarged portion 97 is screwed through threaded aperture 99 of a hammer pin retainer 101 so as to be slidably disposed within bore 103 of the firing pin retainer 105. Suitable seal means, such as O-ring 106, sealingly engage the firing pin retainer 105 and the walls of the bore into which it is inserted within the lower end of the second housing section 51. As illustrated, the firing pin 93 has a controlled penetrating depth safety feature that assures the adequate penetration for ignition but acts as a safety feature in the unlikely event of a misfire, or failure of the igniter means 31 to fire. Specifically, the controlled penetrating depth firing pin can be repeatedly knocked to the same depth without firing the igniter means 31 if the firing pin 93 fails to fire the igniter means 31 the first time. Moreover, the controlled depth firing pin prevents penetrating completely through the upper sur face of the igniter means 31 and lessens the chances of blow out of the igniter means. In the controlled penetrating depth safety feature, the bottom of the enlarged head 95 encounters the top surface of the bottom of the hammer pin retainer 101 to limit the downward movement of the firing pin 93. If desired, the controlled penetrating depth safety feature may comprise a first annular shoulder 107 dispoed annularly of the small lower end 109 of the firing pin, and a mating second annular shoulder 111 extending concentrically interiorly of the bore 103. Thus, when the first annular shoulder 107 encounters the second annular shoulder 111, downward movement of the firing pin is stopped. The depth penetration is thereby controlled, during and after firing; which, of course, follows the arming by the arming means 94.

The arming means 94 includes the hammer pin 57 disposed intermediate the firing pin assembly 29 and the pressure balancing piston 39. The upper end 55 of the hammer pin 57 has a slot 124 that allows fluid to flow, even ifthe upper end 55 engages the lower end 53 of the pressure balancing piston 39. The arming means 94 also includes a releasable hammer pin retainer means; such as, shear pin 117 in hammer pin retainer, or skirt, 101; and a biasing means, such as spring 1 19.

As illustrated, the shear pin 117 penetrates through matching apertures in the hammer pin 57 and the hammer pin skirt 101 and serves two purposes. First, it serves as a releasable retainer means to retain the hammer pin in its top position until a sufficient force has been generated by the downward movement of the pressure balancing piston 39. The sufficient force is that which is great enough to compress the spring 119 a predetermined amount, effect solid contact between the lower end 53 of the pressure balancing piston 39 and the top 55 of the hammer pin 57, and shear the shear pin 117. Second, it, in combination with the hammer pin skirt 101, forms a single-fire safety. Expressed otherwise, the single-fire safety retains the hammer pin 57 in its top position preparatory to firing, so that it can be snapped downwardly longitudinally of the hammer pin skirt 101 for firing only one time. As illustrated, the hammer pin 57 is cylindrical. The hammer pin skirt 101 comprises a cylindrical tubular skirt that engages the firing pin retainer 105 for affording a positive retaining and stopping force. The hammer pin skirt 101 has a top portion that closely fits the exterior of the bottom of the hammer pin 57. An enlarged bore 104 prevents any dragging or fluid compression effects and allows free and rapid downward movement of the hammer pin 57 once the shear pin 117 is sheared. The hammer pin skirt 101 has a downwardly and inwardly depending portion containing the threaded aperture 99 through which the firing pin 93 is inserted, as described hereinbefore.

The spring 119 is provided to afford a constant and reproduceable firing force each time firing is attempted, regardless of the pressure externally of the percussion firing head assembly 11. Specifically, the spring 119 is not initially compressed, but is compressed by downward movement of the pressure balancing piston 39 to store the constant and reproduceable amount of force before the lower end 53 of the pressure balancing piston 39 contacts the upper end 55 of the hammer pin 57. After contact, a greater force is generated to shear the shear pin 117. Once the shear pin 117 is sheared, the hammer pin 57 moves rapidly downwardly to strike the firing pin 93 and ignite the igniter means 31. It is noteworthy that the hammer pin is accelerated by the constant force stored in the spring 8 119, but relies upon inertia to strike the firing pin 93. The bottom of the spring 119 is stopped before the hammer pin 57 strikes the firing pin 93, as will become apparent from the description of a supplemental safety feature hereinafter.

A supplemental safety feature is provided, in the event there is a misfire. The supplemental safety feature prevents any subsequent compression of the spring 119 from moving the hammer pin 57 downwardly onto the firing pin 93. The supplemental safety feature comprises an annularly disposed washer 121 disposed at the bottom of the spring 119 and an interiorly protruding shoulder 123 of the hammer pin skirt 101. The washer 121 serves as a spring stop when it engages the shoulder 123. Specifically, the downwardly moving washer 121 will encounter the interiorly protruding shoulder 123 and prevent further'downward movement of the bottom end of the spring 119. Thus, even though the pressure balancing piston 39 may creep a little after the first firing attempt has been made, and put a small compressing force on the spring 1 19, the force cannot be transmitted downwardly onto the hammer pin 57 for subsequent downward movement of the firing pin 93.

From the foregoing, it can be seen that the arming means 94 is unarmed during running. It remains unarmed until after the percussion firing head assembly 11 is set in the conduit 23 is the wellbore 25; and the arming and firing attempt is made. Moreover, after the firing attempt has been made, the arming means is also disarmed so as to prevent any further firing attempts to be inadvertently made, as sometimes undesirably happens with conventional apparatus and igniter means.

The igniter means 31 comprises a small explosive charge, such as igniter 127; and is disposed beneath the firing pin 93 so as to be ignited responsive to a downwardly moved firing pin 93. One of the advantages of this invention is that no safety disc is required to be dis posed above the igniter 127, either to prevent its firing or to prevent upward movement of gases from diminishing the power ofa setting tool or the like in the event that the igniter 127 disintegrates. As illustrated, the igniter 127 has an upper flange 129 that is received in a removable ejector cap 131. The ejector cap 13l,is ,disposed on top ofa receiver 133 that carries the igniter 127. The ejector cap 131 will pull the igniter 127 from the receiver 133 when the ejector cap 131 is lifted from the top of the receiver 133. This provides a convenient way of removing the igniters 127 and provides another safety factor when a misfiring of an igniter has occured. As is recognized, rodding from the bottom, as would otherwise be necessary, is dangerous. The ejector cap 131 is received in a recess in the lower end of the second housing section 51. The second housing section 51 is removably connected, as by threaded connection 135, with the receiver 133 for retaining the ejector cap 131 in place. As can be seen, the top of the ejector cap 131 abuts the bottom of the firing pin retainer 105. The igniter means 31 has a percussion cap 137 to initiate firing responsive to a sharp downward force by a small lower end 109 of the firing pin 93. The arming and firing is performed after the percussion firing head assembly 11 is set, or suspended, in the conduit 23.

The settable hanging means 33 is provided for suspending the percussion firing head assembly 11 in the conduit 23. As illustrated, the settable hanging means comprises drag show means 139 and slip means 141.

The drag shoe means 139 are means for dragging on the walls of the conduit 23 so as to move the slip means to the maximum position allowed by a J-slot arrangement opposite the direction of movement of the percussion firing head assembly 11 in the conduit. The slip means 141 serve, as is well known, to removably jam into engagement with the inner walls of the conduit 23 for immobilizing the percussion firing head assembly against a downward force from above.

The drag shoe means 139 contain a guide means, such as guide pin, or ball, 143, that engages a J-slot arrangement 145, FIG. 6. The drag shoe means 139 is otherwise freely movable reciprocally along a portion 147 of the percussion firing head assembly 11. The guide ball 143 is retained in place by a band 149 that is rotatably disposed within the drag shoe housing 151. The drag shoe means 139 has drag shoes 153 for frictionally dragging on the walls of the conduit 23. The drag shoes 153 have, at each end, an extending lip 155 that prevents their being pushed out of the drag shoe means 139 by the springs 157. The guide ball 143 serves to limit the upward and downward movement of the drag shoe means 139, depending upon which slot in the J-slot arrangement 145 it engages. The J-slot arrangement 145 and the guide ball 143 are conventional and allow an operator at the surface to control setting of the slip means 141 by reciprocal movement of the percussion firing head assembly 11 within the conduit 23, as will become more clearly apparent from the operational description hereinafter.

As illustrated in unfolded format in FIG. 6, the .I-slot arrangement 145 is cut peripherally around the portion 147. The .I-slot arrangement 145 is continuous peripherally around the portion 147 for guiding the guide ball 143 through repetitive traverses through 360 around the portion 147. The .I-slot arrangement 145 has an entry slot 159 for entry of the guide ball 143 into the J-slot arrangement 145. The .I-slot arrangement 145 also has an elongate upwardly extending slot 161 for allowing the guide ball 143 to move upwardly for setting the slip means 141.

The slip means 141, FIG. 3, are connected with the drag shoe means 139 so as to be moved upwardly and downwardly responsive to the respective movement of the drag shoe means 139. Expressed otherwise, the drag shoe 153 frictionally drag on the walls of the conduit 23 and bias, through their frictional force, the drag shoe means 139 upwardly or downwardly as the tool is moved respectively downwardly or upwardly. The slip means 141 follow the movement of the drag shoe means 139. An inverted cone means, such as cone 163, is disposed adjacent the slip means 141 when the slip means 141 are at their lower point. The inverted cone 163 is adapted for upward travel of the slip means 141 thereon for extension of the slip means 141 outwardly to engage the walls of the conduit 23 for setting a percussion firing head assembly 11. Expressed otherwise, the slip means 141 are set, or engaged with the conduit 23, by downward movement of the percussion firing head assembly 11 when the guide ball 143 is in the upwardly extending slot 161, FIG. 6, allowing the slip means 141 to run up on the inverted cone 163. The slip means 141 are more rigidly set by a greater downward force. Conversely, the slip means 141 are released by an upward force on the percussion firing head assembly 11 sufficient to pull the inverted cone 163 from beneath the slip means 141.

The first connection means 35, FIG. 4, is provided for connection with a device that is actuated responsive to firing of the igniter means 31. As illustrated, the first connection means 35 comprises a male thread of a threaded connection for joining to a female thread on the device that is to be actuated.

Ordinarily, it will be advantageous to provide a percussion firing head assembly 11 with a fishing neck means 167 for connection with a running and pulling tool. The fishing neck means 167 may comprise either an internal or an external fish neck. The fishing neck means 167 is disposed at the upper end of the percussion firing head assembly 11. As illustrated, the fishing neck means 167 comprises an internal fishing neck means that is adapted for being suspended from a running or a pulling tool equipped for such internal fish necks. Specifically, the fishing neck means 167 is adapted for being suspended from a shear down running tool and for being engaged and pulled upwardly by a shear up pulling tool.

A prong receiving chamber 61 is disposed adjacent the fishing neck means 167 and is adapted for receiving a firing prong 26, as illustrated in FIG. 5. The prong receiving chamber has a length sufficient to receive the prong 26 therewithin and th ensure that the dogs 169 ofa pulling tool 171 will engage the interiorly protruding annular ring 173 of the internal fish neck before the igniter means 31 is fired. The fishing neck means 167 is disposed in the fishing neck sub 177. The fishing neck sub 177 forms a housing defining the prongreceiving chamber 61 and is threadedly connected by a threaded connection 179 with the lower sub, or outer housing, 45.

It has been found advantageous to emplace the igniter means 31 at the upper portion of the percussion firing head assembly for a top firing tool. An elongate detonation passageway 181, FIGS. 2-4, is disposed intermediate the igniter means 31 and the first connection means 35 for downward passage of the shock wave from the ignition of the igniter 127. When an elongate detonation passageway 181 is employed, it is frequently preferably to also employ a shooting adapter 183 at the lower end of the detonation passageway, FIG. 4. The shooting adapter 183 has a third connection means, such as threads 185, for connection with a device to be actuated in response to ignition of the booster pellet 187. The booster pellet 187 increases the likelihood that the device that is to be actuated will be actuated in response to ignition of the igniter 127.

If desired, an elongate prong receiving chamber 61 and elongate firing prong 26 could be employed and eliminate the necessity for the detonation passageway 181. On the other hand, an elongate upwardly extending member 59 can be employed and eliminate the necessity for an elongate prong.

The overall operation has been described hereinbefore with respect to FIG. 1. Detailed considerations will now be described. Assume that the percussion firing head assembly 11 has been assembled as illustrated in FIGS. 2-4 except that the guide ball 143, instead of being at the upper position 189, FIG. 6, is disposed at the lower position 191 and the slip means 141 are below the inverted cone 163, FIG. 3. A running tool 17 is attached to the fishing neck means 167 and the percussion firing head assembly 11 is run into the wellbore 25. As the percussion firing head assembly 11 moves downwardly in the conduit 23, the drag shoe means 139 tend to move upwardly, moving the guide ball 143 to the top 193 of the running slot 195. The running slot 195 maintains the slip means 141 in a position below the inverted cone 163. The path the guide ball 143 follows in the J-slot to reach the top 193 is indicated by the arrows 197. As indicated hereinbefore, the J-slot is relatively conventional and need not be described in detail herein. The running slot 195 and the preparatory slot 199 are somewhat elongated in order to allow for variations in speed in the wellbore and to keep the guide pin in the desired slot. When the desired depth has been reached, the running tool 17 is stopped and pulled upwardly. The guide ball 143 is moved to the bottom 201 of the preparatory slot 199 by the relative downward frictional force of the drag shoes 153 against the conduit 23. Thereafter, the running tool 17 is again lowered. The drag shoe means 139 move upwardly with respect to the percussion firing head assembly 11, moving the guide ball 143 toward the upper position 189 in the upwardly extending slot 161, or as far as the slip means 141 will allow before they engage the walls of the conduit 23. Ordinarily, the slip means 141 will engage the conduit 23 before the guide ball 143 reaches the upper position 189. Thus, the percussion firing head assembly 11 is set in the well. Further downward force merely serves to set it more tightly in the well. By pulling the percussion firing head assembly 11 upwardly, however, the operator can release the slip means 141. The operator can safely set and release the slip means 141 as many times as necessary to obtain the desired setting depth, since the arming means is not armed and the igniter means 31 is protected from being fired by the respective first and second retainer means.

In fact, during running there are several safety factors that are noteworthy in this invention. The pressure balancing piston 39 is prevented from accidentally moving until the shear pins 115 are sheared between it and the shear pin ring 113. Also, the spring 119 of the arming means is not compressed in the run-in position so the arming means is unarmed; but it is compressed only after the shear pins 115 have been sheared and the balancing piston moved downwardly. Moreover, the hammer pin shear pin 117 cannot be sheared until the lower end of the pressure balancing piston 39 engages the upper end 55 of the hammer pin 57.

Once the percussion firing head assembly 11 is set, the shear down running tool 17 is jarred downwardly to shear its shear pin and disengage the fishing neck means 167. The running tool 17 is thereafter pulled from the well.

At the surface a shear up" pulling tool 171 is attached to the tool string 19; and a firing prong 26 is connected to the lower end of the pulling tool 171. The pulling tool 171 and the firing prong 26 are then run into the well. The firing prong 26 is run through the fishing neck means 167 and encounters the upwardly extending member 59 of the pressure balancing piston 39.

As the bottom 175 of the firing prong 26, or similar prong, lands on the upper end of the upwardly extending member 59, downward jarring; or, in fact, any downward force of sufficient magnitude; will move the pressure balancing piston 39, shear pin ring 113 and shear pins 115 downwardly until the shear pin ring 113 encounters the top 116 of the second housing section 51. Further downward force or jarring will shear the shear pins 115, permitting the pressure balancing piston 39 to telescope downwardly through the shear pin ring 113. Further downward movement of the pressure balancing piston 39 compresses the hammer pin spring 1 l9 and brings the lower end 53 of the pressure balancing piston 39 into engagement with the upper end 55 of the hammer pin 57. At this point, the hammer pin spring 119 is fully compressed to deliver a uniform acceleration to the hammer pin 57. Further downward force on the pressure balancing piston 39 will impose force onto the hammer pin 57 and, ultimately, will shear shear pin 1 17. When the shear pin 1 17 shears, the hammer pin 57 will be snapped downwardly onto the firing pin 93, firing the igniter means 31.

A indicated hereinbefore, the dogs 169 on the pulling tool 171 will have engaged the internal fishing neck ring 173 before the prong 26 and pressure balancing piston 31 have moved downwardly sufficiently to shear shear pin 117 and fire the igniter 127. The pulling tool engages the internal fishing neck means 167 to retain the percussion firing head assembly 11 in place, even if there is sufficient upward movement to loosen the slip means 141 as a result of the firing of the setting tool or the like that is connected with the lower end of the percussion firing head assembly 11.

Even if the igniter means is disintegrated so badly that there is blow-by of gases around the firing pin area, as may occur when using high order explosives, the only pressure loss is the small volume of gas required to fill the chamber about the firing pin 93 and the bore 79. Escape exteriorly of the percussion firing head assembly 1 1 is prevented by the pressure balancing piston 39. The feature ensures operation of any pressure actuated tool that is appended to the lower end of the percussion firing head assembly 11. Moreover, any increase in pressure as a result of firing and blow-by imposes a balanced force on the pressure balancing piston 39 by reason of the opposed areas described hereinbefore. Consequently, any blow-by or pressure build does not adversely affect any of the sequency of steps necessary to obtain ignition or diminish the chances of obtaining ingition.

The additional safety feature of the washer 121 encountering the shoulder 123 to stop transmission of a biasing force via spring 119 onto hammer pin 57 has been described hereinbefore. As a further additional safety feature, the shear pin ring 113 is dimensioned such that its upper surface 203 will encounter the bottom shoulder 205 of the pressure balancing piston 39 and prevent movement of the pressure balancing piston 39 downwardly sufficiently to impose a force onto the hammer pin 57 after the shear pin 117 has been sheared once.

After a normal firing has been completed, the pulling tool is jarred upwardly and the shear up pulling tool then pulls the inverted cone 163 from beneath the slip means 141 to disengage the slip means 141 and allow the percussion firing head assembly 11 to be drawn upwardly. As the inverted cone 163 is pulled upwardly,

the drag shoe means 139 and the guide pin 143 move downwardly to the lower position 207, FIG. 6. The pulling tool 171, the percussion firing head assembly 11 and the setting tool 13 are thereafter withdrawn from the well. A shear up pulling tool 171 is also employed to allow the pulling tool 171 to be released from the percussion firing head assembly 11 in the event one or more of the tools should become immobilized; as by collapsed casing or debris, in conjunction with failure of the setting tool-13 to shear off of the bridge plug 15. In such as event, the released pulling tool 171 is pulled from the wellbore 25 and a stronger pulling apparatus is employed to fish" out the percus sion firing head assembly 11 and the setting tool 13.

At the surface, the percussion firing head assembly 11 is prepared for subsequent use by repositioning the respective elements and subassemblies as illustrated in FIGS. 2-4. Specifically, the hammer pin assembly is reconnected as indicated hereinbefore; that is, by extending it to its most elongate condition, punching out the parts of sheared shear pin 117 and inserting a new shear pin 117. The pressure balancing piston 39 is moved'to its uppermost position and the shear pins 115 are replaced by punching out the parts of sheared shear pins 115 and inserting new shear pins 115. The second housing section 51 is unscrewed from the receiver 133 and the ejector cap 131 lifted upwardly, removing the igniter 127. A new igniter 127 may be emplaced in the ejector cap 131 and the tool reassembled as illustrated in FIGS. 24 for an additional firing run in the same or different wellbore.

Although in the embodiment described and illustrated hereinbefore, a setting tool is shown as the de vice to be actuated responsive to firing of the igniter means 31, it should be understood that the invention may be used with various such devices; as for example, jet perforating guns and cut-off tools.

The materials of construction that are ordinarily employed in this art are satisfactory herein and no exotic new materials need be employed.

The percussion firing head assembly 11 is readily adaptable to be connected with either an internal, FIG. 2, or an external fishing neck, 167, FIG. 7. The external fishing neck 167 is connected with the remainder ofthe percussion firing head assembly by conventional means, such as threaded connection 179. When using an outside fishing neck 167, FIG. 7, several options are possible. For example, one can extend the upper end, or upwardly member 59, of the pressure balancing piston to a point above the fishing neck 167, thereby eliminating the need for a prong 26, per se, FIG. 5, or the side sand drain-off holes, or downwardly and outwardly extending passageways 69, FIG. 2.

The embodiment of FIG. 7 is run and pulled with conventional external fishing neck running tools and pulling tools with hollow cores that are presently available on the market and that need not be described herein. The running, arming and firing, and pulling of the embodiment of FIG. 7 are effected substantially as described hereinbefore, except for the apparent difference in the fishing neck structure.

Although the firing has been described hereinbefore by attaching a firing prong 26 onto the bottom ofa pulling tool, or a fishing tool or the like and employing a wire line tool string, one advantage of this invention is that firing can be effected by dropping a bar downwardly through conduit in the well-bore, the bar having a similar firing prong attached to its lower end; or by running a similar prong at the bottom end of a macaroni tubing string or the like. When the igniter means 31 is fired by macaroni tubing string or pump rod string, the entire assembly can be pulled on the ignition trip or can be fired and then pulled on a subsequent trip.

Another advantage of this invention is that the percussion firing apparatus may be employed in conjunction with any of the conventional means for suspending it in a well at a predetermined depth; such as, suspending it via a string of tubing or via emplacement on a landing nipple or the like; whether or not such other means are as convenient and as generally available as the example, or embodiment, disclosed. Thereafter, the arming and firing may be effected by an suitable means, such as a second trip with a firing prong or similar prong at the bottom end ofa macaroni tubing string or the like.

From the foregoing descriptive matter, it can be seen that this invention provides one or more of the desirable features delineated hereinbefore and not heretofore provided. In specific embodiments, this invention provides all of the desirable features delineated hereinbefore. While most of the features are believed to be self-explanatory, some of the features and advantages are worth re-iterating. The pressure balancing design of this invention enables the percussion firing head assembly to be fired by any of the conventionally employed methods and at any depth, even in viscous fluids in the wellbore; since firing is responsive to the degree of force along and not to speed of some falling object, or weight, in the wellbore. The pressure balancing design prevents adverse effects from either high internal or external pressures from affecting the downhole arming and firing sequence. The percussion firing head is set in the wellbore with the arming means unarmed; and, then, armed and fired on a second trip using a simple firing prong. Moreover, after a single attempt at firing, the arming means is disarmed for safety. The new balancing piston design of this invention prevents loss of pressure from a pressure operated tool and thus alleviates difficulties with having tool strings stuck in the wellbore. Ignition can be accomplished more consistently and easier with less expensive ignition caps, because there is no necessity for having a sealing shear disc to retain the pressures of a connected, pressureoperated tool. Moreover, a consistently repeatable degree of acceleration of the hammer pin and, hence, a constant load is delivered to the firing pin for firing regardless of well conditions. Experience with experimental models in the field have shown 100 percent firing compared with only about percent firing for the best comparable nonelectrical prior art type devices. A plurality of safety features are provided to ensure that there is no subsequent firing in the unlikely event there should be a misfire. For example, the firing pin has a controlled penetration depth so as to obtain ignition but not so great as to penetrate completely through the head of the igniter 127. Expressed otherwise, even penetration of the thin ignition cap of a center fire shell is desirable and has not been provided heretofore, but is provided by this invention. In this regard, a cap that had been misfired in a surface experimental setup was attempted to be fired repeatedly, including dropping the entire firing head assembly six times from a height of twelve feet onto concrete without firing the cap. This indicates the high degree of safety that is effected as a result of this feature. Once a cap is deformed to a maximum depth permitted by the controlled depth firing pin without firing, then the same cap cannot be fired thereafter by the same firing pin unless the firing pin is allowed to penetrate further. This is a very important secondary feature.

Although this invention has been described with a certain degree of particularlity, it is understood that the present disclosure has been made only bt way of example and that numerous changes in the details of construction and the combination and arrangement of 5 parts may be resorted to without departing from the spirit and scope of this invention.

What is claimed is:

l. Percussion firing apparatus for firing an explosive charge means within a well penetrating subterranean formations comprising:

a. pressure balancing means for neutralizing adverse effects of external pressure and of internal pressure and changes therein; said pressure balancing means including a pressure balancing chamber and a pressure balancing piston that sealingly excludes fluid communication between a firing pin chamber and the exterior of said percussion firing apparatus;

b. a firing pin chamber having therein a firing pin assembly that includes:

i. a firing pin disposed within said firing pin assembly; and

ii. arming means disposed intermediate said firing pin and said pressure balancing chamber and piston such that said firing pin can be forced sharply downwardly by a downward force on said pressure balancing piston; said arming means being normally unarmed until after said percussion firing apparatus is set in a conduit in said well;

c. igniter means disposed beneath said firing pin so as to be ignited responsive to a downwardly moved firing pin;

d. settable hanging means for suspending said percussion firing apparatus in a conduit within said well; said hanging means being set by a downward force and released by an upward force; and

e. first connection means for connection with a device that is actuated responsive to the firing of said igniter means.

2. The percussion firing apparatus of claim 1 wherein said arming means includes a hammer pin assembly that is disposed intermediate said firing pin and said pressure balancing piston so as to be engaged by said pressure balancing piston when it is moved downwardly for ignition of said igniter means.

3. The percussion firing apparatus of claim 2 wherein a releasable piston retainer means is provided; said releasable piston retainer means holding said pressure balancing piston at a predetermined position longitudinally of said pressure balancing chamber and releasing said pressure balancing piston for downward movement when subjected to sufficient downward force.

4. The percussion firing apparatus of claim 2 wherein there is provided a single-fire safety means interposed intermediate said firing pin and said pressure balancing piston; said single-fire safety means allowing arming said hammer pin assembly such that said downward force on said pressure balancing piston will cause said firing pin to attempt ignition of said igniter means; said single-fire safety means also effecting disarming of said hammer pin assembly after one said attempt.

5. The percussion firing apparatus of claim 4 wherein said single-fire safety means comprises a hammer pin; a hammer pin skirt defining a path directing said hammer pin to said firing pin; said hammer pin being slidably disposed within said hammer pin skirt; and a releasable hammer pin retainer means retaining said hammer pin at the upper portion of said hammer pin skirt prior to attempting ignition of said igniter means by striking said firing pin with said hammer pin; said releasable hammer pin retainer means releasing said hammer pin for striking said firing pin when subjected to sufficient downward force.

6. The percussion firing apparatus of claim 5 wherein said releasable hammer pin retainer means comprises a shear pin extending laterally through said hammer pin skirt and at least into said hammer pin; and said hammer pin skirt has a top portion that closely and conformingly fits the exterior of the bottom of the hammer pin and has an enlarged bore immediately therebelow for preventing any dragging and fluid compression effects and allowing free and rapid downward movement of the hammer pin once the shear pin has been sheared.

7. The percussion firing apparatus of claim 5 wherein said arming means includes a releasable piston retainer means for retaining said pressure balancing piston in place with respect to said hammer pin prior to moving downwardly for effecting firing; and includes a biasing means intermediate said hammer pin said said pressure balancing piston for storing a predetermined amount of energy for accelerating said hammer pin once said respective releasable piston and hammer pin retainer means have been released to ensure that said firing pin is struck sufficiently hard to effect ignition of said igniter means.

8. The percussion firing apparatus of claim 7 wherein said single-fire safety means includes a shoulder on said hammer pin skirt and a stop ring at the lower end of said biasing means for preventing downward movement of the lower end of said biasing means beyond said hammer pin skirt whereby downward force on said hammer pin and said firing pin cannot be exerted by said biasing means after said single attempt at firing.

9. The percussion firing apparatus of claim 8 wherein said biasing means comprises a spring; and said hammerpin and said shoulder are so designed that said stop ring encounters said shoulder before said hammer pin encounters said firing pin whereby said hammer pin is accelerated by said spring, said spring is prevented from acting upon said hammer pin all the way to said firing pin, and said hammer pin relies upon inertial force to strike said firing pin with the correct force.

10. The percussion firing apparatus of claim 8 wherein said single-fire safety also includes an exteriorly protruding shoulder on said pressure balancing piston and an interiorly protruding shoulder for limiting downward motion of said pressure balancing piston to prevent its imposing a force on said firing pin by way of said hammer pin after said releasable hammer pin retainer means has been released for firing.

11. The percussion firing apparatus of' claim ll wherein said pressure balancing piston has an upwardly protruding member that is adapted to be acted on for moving said pressure balancing piston downwardly for effecting arming and firing.

12. The percussion firing apparatus of claim 11 wherein a fishing neck means is disposed at the upper end of said percussion firing apparatus and is adapted for being suspended from a shear down wire line running tool and adapted for being engaged and pulled upwardly by a shear up pulling tool.

13. The percussion firing apparatus of claim 12 wherein said fishing neck means includes an internal fish neck; a housing defines a prong-receiving chamber surrounding said upwardly protruding member on said pressure balancing piston; and apertures are provided in said housing, said apertures having downwardly and outwardly inclined surfaces for draining off trash, debris and the like.

14. The percussion firing apparatus of claim 13 wherein a simple one-piece prong is included, said prong having a connection means at its upper end for connection with a pulling tool and being adapted to fit inside said fishingneck means and having its lower end adapted to contact said upwardly protruding member of said pressure balancing piston for forcing it downwardly.

15. The percussion firing apparatus of claim 13 wherein said prong and said prong-receiving chamber and proportioned such that said pulling tool will have engaged said fishing neck means before said firing pin fires said igniter means responsive to downward pressure of said prong.

16. The percussion firing apparatus of claim 12 wherein said fishing neck means includes an external fish neck and said upwardly protruding member on said pressure balancing piston extends above said external fish neck in the run-in, unarmed position before the arming and firing attempt is made.

17. The percussion firing apparatus of claim 1 wherein said firing pin has a controlled penetrating depth feature that assures adequate penetration for ignition but acts as a safety feature in instances where ignition fails to occur.

18. The percussion firing apparatus of claim 17 wherein said controlled penetrating depth feature includes an enlarged head on said firing pin, said enlarged head having a relatively large flat bottom surface for encountering a second flat surface to limit downward movement thereof; and said firing pin is disposed in an aperture that is surrounded at its upper end by a second, relatively large, flat surface for stopping downward movement of said enlarged head and said firing pin- 19. The percussion firing apparatus of claim 1 wherein said pressure balancing piston is disposed in said pressure balancing chamber; first and second bores communicate with respective ends of said pressure balancing chamber, said first bore communicating with the exterior of said percussion firing apparatus and said second bore communicating interiorly thereof with said firing pin chamber; said pressure balancing piston having an upwardly extending member disposed in said first bore and having a first cross sectional area that is exposed to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a large central portion having a second cross sectional area; an aperture communicating with said pressure balancing chamber near its end closest to said second bore and communicating exteriorly of said percussion firing apparatus for exposing the lower portion of said pressure balancing chamber to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a lower end disposed in said second bore such that said pressure balancing piston is slidable longitudinally of said first and second bores and said pressure balancing chamber; said pressure balancing piston having a longitudinally extending internal passageway communicating intermediate said second bore and an upper portion of said pressure balancing chamber intermediate said enlarged portion of said pressure balancing piston and said first bore for exposing the upper portion of said pressure balancing chamber to pressure interiorly of said percussion firing apparatus; said lower end of said pressure balancing piston having a third cross sectional area; said second cross sectional area being enough larger than said first and third cross sectional areas that pressure interiorly of said percussion firing apparatus will act on exposed said third area and the top exterior portion of said second area and the pressure exteriorly of said percussion firing apparatus will act on said first area and the bottom exterior portion of said second area to create equal and opposing forces that neutralize each other such that said pressure balancing piston is moved responsive to a force other than pressure and the effects of pressure are neutralized.

20. The percussion firing apparatus of claim 1 wherein an elongate detonation passageway is disposed intermediate said igniter means and said first connection means for downward passage of the shock wave from the ignited igniter means; and wherein a shooting adapter and a booster pellet are connected with said first connection means and have a third connection means similar to said first connection means for connecting with a device that is actuated responsive to firing of said booster pellet.

21. Percussion firing apparatus for firing an explosive charge means within a well penetrating subterranean formations, having means for suspending a percussion firing head assembly at a predetermined depth, com prising:

a. pressure balancing means for neutralizing adverse effects of external pressure and ofinternal pressure and changes therein; said pressure balancing means including a pressure balancing chamber and a pressure balancing piston that sealingly excludes fluid communication between a firing pin chamber and the exterior of said percussion firing apparatus;

b. a firing pin chamber having therein a firing pin assembly that includes:

i. a firing pin disposed within said firing pin assembly; and

c. igniter means disposed beneath said firing pin so as to be ignited responsive to a downwardly moved firing pin; and

d. first connection means for connection with a device that is actuated responsive to the firing of said igniter means.

22. The percussion firing apparatus of claim 21 wherein said arming means includes a hammer pin assembly that is disposed intermediate said firing pin and said pressure balancing piston so as to be engaged by said pressure balancing piston when it is moved downwardly for ignition of said igniter means.

23. The percussion firing apparatus of claim 22 wherein a releasable piston retainer means is provided; said releasable piston retainer means holding said pressure balancing piston at a predetermined position longitudinally of said pressure balancing chamber and releasing said pressure balancing piston for downward movement when subjected to sufficient downward force.

24. The percussion firing apparatus of claim 22 wherein there is provided a single-fire safety means interposed intermediate said firing pin and said pressure balancing piston; said single-fire safety means allowing arming said hammer pin assembly such that said downward force on said pressure balancing piston will cause said firing pin to attempt ignition of said igniter means; said single-fire safety means also effecting disarming of said hammer pin assembly after one said attempt.

25. The percussion firing apparatus of claim 24 wherein said single-fire safety means comprises a hammer pin; a hammer pin skirt defining a path directing said hammer pin to said firing pin; said hammer pin being slidably disposed within said hammer pin skirt; and a releasable hammer pin retainer means retaining said hammer pin at the upper portion of said hammer pin skirt prior to attempting ignition of said igniter means by striking said firing pin with said hammer pin; said releasable hammer pin retainer means releasing said hammer pin for striking saidtfiring pin when subjected to sufficient downward force.

26. The percussion firing apparatus of claim 25 wherein said releasable hammer pin retainer means comprises a shear pin extending laterally through said hammer pin skirt and at least into said hammer pin; and said hammer pin skirt has a top portion that closely and conformingly fits the exterior of the bottom of the hammer pin and has an enlarged bore immediately therebelow for preventing any dragging and fluid compressioneffects and allowing free and rapid downward movement of the hammer pin once the shear pin has been sheared.

27. The percussion firing apparatus of claim 25 wherein said arming means includes a releasable piston retainer means for retaining said pressure balancing piston in place with respect to said hammer pin prior to moving downwardly for effecting firing; and includes a biasing means intermediate said hammer pin and said pressure balancing piston for storing a predetermined amount of energy for accelerating said hammer pin once said respective releasable piston and hammer pin retainer means have been released to ensure that said firing pin is struck sufficiently hard to effect ignition of said igniter means.

28. The percussion firing apparatus of claim 27 wherein said single-fire safety means includes a shoulder on said hammer pin skirt and a stop ring at the lower end of said biasing means for preventing downward movement of the lower end of said biasing means beyond said hammer pin skirt whereby downward force on said hammer pin and said firing pin cannot be exerted by said biasing means after said single attempt at firing.

29. The percussion firing apparatus of claim 28 wherein said biasing means comprises a spring; and said hammer pin and said shoulder are so designed that said stop ring encounters said shoulder before said hammer pin encounters said firing pin whereby said hammer pin is accelerated by said spring, said spring is prevented from acting upon said hammer pin all the way to said firing pin, and said hammer pin relies upon inertial force to strike said firing pin with the correct force.

30. The percussion firing apparatus of claim 28 wherein said single-fire safety also includes an exteriorly protruding shoulder on said pressure balancing piston and an interiorly protruding shoulder for limiting downward motion of said pressure balancing piston to prevent its imposing a force on said firing pin by way of said hammer pin after said releasable hammer pin retainer means has been released for firing.

31. The percussion firing apparatus of claim 21 wherein said pressure balancing piston has an upwardly protruding member that is adapted to be acted on for moving said pressure balancing piston downwardly for effecting arming and firing.

32. The percussion firing apparatus of claim 31 wherein a fishing neck means is disposed at the upper end of said percussion firing apparatus and is adapted for being suspended from a tubing string for emplacement in and removal from said well.

33. The percussion firing apparatus of claim 32 wherein said fishing neck means includes an internal fish neck; a housing defines a prong-receiving chamber surrounding said upwardly protruding member on said pressure balancing piston; and apertures are provided in said housing, said apertures having downwardly and outwardly inclined surfaces for draining off trash, debris and the like.

34. The percussion firing apparatus of claim 33 wherein a simple one-piece prong is included, said prong having a connection means at its upper end for connection with a means for imposing a downward force; said prong being adapted to fit inside said fishing neck means and having its lower end adapted to contact said upwardly protruding member of said pressure balancing piston for forcing it downwardly.

35. The percussion firing apparatus of claim 21 wherein said firing pin has a controlled penetrating depth feature that assures adequate penetration for ignition but acts as a safety feature in instances where ignition fails to occur.

36. The percussion firing apparatus of claim 35 wherein said controlled penetrating depth feature includes an enlarged head on said firing pin, said enlarged head having a relatively large flat bottom surface for encountering a second flat surface to limit downward movement thereof; and said firing pin is disposed in an aperture that is surrounded at its upper end by a second, relatively large, flat surface for stopping downward movement of said enlarged head and said firing pin.

37. The percussion firing apparatus of claim 21 wherein said pressure balancing piston is disposed in said pressure balancing chamber; first and second bores communicate with respective ends of said pressure balancing chamber, said first bore communicating with the exterior of said percussion firing apparatus and said second bore communicating interiorly thereof with said firing pin chamber; said pressure balancing piston having an upwardly extending member disposed in said first bore and having a first cross sectional area that is exposed to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a large central portion having a second cross sectional area; an aperture communicating with said pressure balancing chamber near its end closest to said second bore and communicating exteriorly of said percussion firing apparatus for exposing the lower portion of said pressure balancing chamber to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a lower end disposed in said second bore such that said pressure balancing piston is slidable longitudinally of said first and second bores and said pressure balancing chamber; said pressure balancing piston having a longitudinally extending internal passageway communicating intermediate said second bore and an upper portion of said pressure balancing chamber intermediate said enlarged portion of said pressure balancing piston and said first bore for exposing the upper portion of said pressure balancing chamber to pressure interiorly of said percussion firing apparatus; said lower end of said pressure balancing piston having a third cross sectional area; said second cross sectional area being enough larger than said first and third cross sectional areas that pressure interiorly of said percussion firing apparatus will act on exposed said third area and the top exterior portion of said second area and the pressure exteriorly of said percussion firing apparatus will act on said first area and the bottom exterior portion of said second area to create equal and opposing forces that neutralize each other such that said pressure balancing piston is moved responsive to a force other than pressure and the effects of pressure are neutralized.

38. The percussion firing apparatus of claim 21 wherein an elongate detonation passageway is disposed intermediate said igniter means and said first connection means for downward passage of the shock wave from the ignited igniter means; and wherein a shooting adapter and a booster pellet are connected with said first connection means and have a third connection means similar to said first'connection means for'con necting with a device that is actuated responsive to firing of said booster pellet.

Claims

1. Percussion firing apparatus for firing an explosive charge means within a well penetrating subterranean formations comprising: a. pressure balancing means for neutralizing adverse effects of external pressure and of internal pressure and changes therein; said pressure balancing means including a pressure balancing chamber and a pressure balancing piston that sealingly excludes fluid communication between a firing pin chamber and the exterior of said percussion firing apparatus; b. a firing pin chamber having therein a firing pin assembly that includes: i. a firing pin disposed within said firing pin assembly; and ii. arming means disposed intermediate said firing pin and said pressure balancing chamber and piston such that said firing pin can be forced sharply downwardly by a downward force on said pressure balancing piston; said arming means being normally unarmed until after said percussion firing apparatus is set in a conduit in said well; c. igniter means disposed beneath said firing pin so as to be ignited responsive to a downwardly moved firing pin; d. settable hanging means for suspending said percussion firing apparatus in a conduit within said well; said hanging means being set by a downward force and released by an upward force; and e. first connection means for connection with a device that is actuated responsive to the firing of said igniter means.

9. The percussion firing apparatus of claim 8 wherein said biasing means comprises a spring; and said hammer pin and said shoulder are so designed that said stop ring encounters said shoulder before said hammer pin encounters said firing pin whereby said hammer pin is accelerated by said spring, said spring is prevented from acting upon said hammer pin all the way to said firing pin, and said hammer pin relies upon inertial force to strike said firing pin with the correct force.

11. The percussion firing apparatus of claim 1 wherein said pressure balancing piston has an upwardly protruding member that is adapted to be acted on for moving said pressure balancing piston downwardly for effecting arming and firing.

12. The percussion firing apparatus of claim 11 wherein a fishing neck means is disposed at the upper end of said percussion firing apparatus and is adapted for being suspended from a ''''shear down'''' wire line running tool and adapted for being engaged and pulled upwardly by a ''''shear up'''' pulling tool.

14. The percussion firing apparatus of claim 13 wherein a simple one-piece prong is included, said prong having a connection means at its upper end for connection with a pulling tool and being adapted to fit inside said fishing neck means and having its lower end adapted to contact said upwardly protruding member of said pressure balancing piston for forcing it downwardly.

18. The percussion firing apparatus of claim 17 wherein said controlled penetrating depth feature includes an enlarged head on said firing pin, said enlarged head having a relatively large flat bottom surface for encountering a second flat surface to limit downward movement thereof; and said firing pin is disposed in an aperture that is surrounded at its upper end by a second, relatively large, flat surface for stopping downward movement of said enlarged head and said firing pin.

19. The percussion firing apparatus of claim 1 wherein said pressure balancing piston is disposed in said pressure balancing chamber; first and second bores communicate with respective ends of said pressure balancing chamber, said first bore communicating with the exterior of said percussion firing apparatus and said second bore communicating interiorly thereof with said firing pin chamber; said pressure balancing piston having an upwardly extending member disposed in said first bore and having a first cross sectional area that is exposed to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a large central portion having a second cross sectional area; an aperture communicating with said pressure balancing chamber near its end closest to said second bore and communicating exteriorly of said percussion firing apparatus for exposing the lower portion of said pressure balancing chamber to pressure exteriorly of said percussion firing apparatus; said pressure balancing piston having a lower end disposed in said second bore such that said pressure balancing piston is slidable longitudinally of said first and second bores and said pressure balancing chamber; said pressure balancing piston having a longitudinally extending internal Passageway communicating intermediate said second bore and an upper portion of said pressure balancing chamber intermediate said enlarged portion of said pressure balancing piston and said first bore for exposing the upper portion of said pressure balancing chamber to pressure interiorly of said percussion firing apparatus; said lower end of said pressure balancing piston having a third cross sectional area; said second cross sectional area being enough larger than said first and third cross sectional areas that pressure interiorly of said percussion firing apparatus will act on exposed said third area and the top exterior portion of said second area and the pressure exteriorly of said percussion firing apparatus will act on said first area and the bottom exterior portion of said second area to create equal and opposing forces that neutralize each other such that said pressure balancing piston is moved responsive to a force other than pressure and the effects of pressure are neutralized.

21. Percussion firing apparatus for firing an explosive charge means within a well penetrating subterranean formations, having means for suspending a percussion firing head assembly at a predetermined depth, comprising: a. pressure balancing means for neutralizing adverse effects of external pressure and of internal pressure and changes therein; said pressure balancing means including a pressure balancing chamber and a pressure balancing piston that sealingly excludes fluid communication between a firing pin chamber and the exterior of said percussion firing apparatus; b. a firing pin chamber having therein a firing pin assembly that includes: i. a firing pin disposed within said firing pin assembly; and ii. arming means disposed intermediate said firing pin and said pressure balancing chamber and piston such that said firing pin can be forced sharply downwardly by a downward force on said pressure balancing piston; said arming means being normally unarmed until after said percussion firing apparatus is set in a conduit in said well; c. igniter means disposed beneath said firing pin so as to be ignited responsive to a downwardly moved firing pin; and d. first connection means for connection with a device that is actuated responsive to the firing of said igniter means.

25. The percussion firing apparatus of Claim 24 wherein said single-fire safety means comprises a hammer pin; a hammer pin skirt defining a path directing said hammer pin to said firing pin; said hammer pin being slidably disposed within said hammer pin skirt; and a releasable hammer pin retainer means retaining said hammer pin at the upper portion of said hammer pin skirt prior to attempting ignition of said igniter means by striking said firing pin with said hammer pin; said releasable hammer pin retainer means releasing said hammer pin for striking said firing pin when subjected to sufficient downward force.

26. The percussion firing apparatus of claim 25 wherein said releasable hammer pin retainer means comprises a shear pin extending laterally through said hammer pin skirt and at least into said hammer pin; and said hammer pin skirt has a top portion that closely and conformingly fits the exterior of the bottom of the hammer pin and has an enlarged bore immediately therebelow for preventing any dragging and fluid compression effects and allowing free and rapid downward movement of the hammer pin once the shear pin has been sheared.

38. The percussion firing apparatus of claim 21 wherein an elongate detonation passageway is disposed intermediate said igniter means and said first connection means for downward passage of the shock wave from the ignited igniter means; and wherein a shooting adapter and a booster pellet are connected with said first connection means and have a third connection means similar to said first connection means for connecting with a device that is actuated responsive to firing of said booster pellet.