GB2184214A - Firing of well perforation guns - Google Patents

Abstract

A method and apparatus for actuating a perforating gun by pressure includes a pressure actuated gun firing head (60) disposed on the perforating gun for detonating the shaped charges of the gun to complete an underwater well. The gun is attached (at 88) to a pipe string and located downhole adjacent the formation to be perforated. The pressure actuated firing head includes a housing (62) with a plug (160) and piston (120). The piston has a firing pin (140) adapted for engagement with the initiator (90) of a perforating gun upon reciprocation within the housing. initially, the piston is pressure balanced until the time of actuation. The plug is responsive to fluid pressure of a predetermined magnitude at the time of the actuation of the gun firing head. Upon effecting pressure on the plug, the plug unbalances the piston causing the piston to move downwardly. Upon such movement of the piston, the firing pin engages the initiator to detonate the shaped charges of the perforating gun. Pressure may be effected on the firing head through the pipe string, or the annulus around the pipe string, or both. The firing head includes a plurality of passageways, as well as the plug and piston, arranged in a manner whereby should leakage of well fluids into the firing head inadvertently occur, the apparatus is rendered inoperative and therefore the firing head cannot inadvertently be fired due to the occurrence of unforeseen intervening circumstances. <IMAGE>

Description

1 GB 2 184 214 A 1

SPECIFICATION

Firing of well purforation guns 1 After a well bore has been formed into the ground and the casing has been cemented into place, the hydrocarbon containing zone usually is communicated with the casing interior byforming a plurality of perforations through the casing which extend rad- ially awayfrom the casing and out into the formation, thereby communicating the hydrocarbon producing zone with the interior of the casing.

It is common practice to run a jet perforating gun downhole and to fire the gun bythe employment of a gun firing head which is actuated by a bar dropped down through the interior of thetubing string. Completion techniques involving this known completion process are setforth in U.S. Patents 3,706,344 and 4,009,757.

A bar actuated firing head cannot be used in certain situations and sometimes it is desirableto be able to detonate the charges of a perforating gun withoutthe use of a bar. Particularly itwould be advantageous to actuate the gun by effecting a pres- sure within the pipe string or annulus or both, but a gun firing head which could be detonated in responseto pressure effected within the borehole has been considered to be highly dangerous by many logging and completion engineers forthe reason that leakage across some of the critical seals of the firing head could inadvertently detonatethe firing head and prematurely explode the shaped charges of the gun. Should this misfire occur at an inappropriate time, untold damage could be done to the wellbore if, for example, the explosion occurred while running the gun into the hole, or if the explosion occurred before properflow passageways back to the surface had been provided forthe completed formation. If a pressure actuated gun is to be safe, it is necessary that the firing head be unable to detonatethe shaped charges until the gun has been lowered downhole and properly located relative tothe formation to be completed.

U.S. Patent 3,189,094to Hyde discloses a hydraul- ically operated firing apparatus on a gun perforator for purposes of formation testing. The firing apparatus assembly includes a tubing string having a conventional formation testervalve in a housing and a conventional packer secured belowthe housing. Fir- ing apparatus housings, along with the gun perforator, are series connected tothetubing string below the packer. In conducting a formation test, the assembly is lowered into a fluid filled wellbore so that, externally, all parts of the assembly are sujected to the submergence pressure exerted bythefluid in the well. Theformation testervalve is initially closed so thatthe pressure within the emptytubing string is essentially at atmospheric pressure. When the packer is set, the zone opposite the gun is isolated from the region above the packer. Thereafter, when the formation testervalve is opened, the zone opposite the gun is exposed essentially to atmospheric pressure, or at leastto a pressure which is greatly lowerthan the submergence pressure of the fluid in the well. Although various embodiments of the firing apparatus are disclosed, all of the embodiments utilizethe submergence pressure to arm thefiring apparatus during descent of the assembly and then utilize the low pressure condition created when the packer has been set and the formation testervalve opens to cause a pressure differential which operates thefiring apparatus and fires the gun. The gun perforator penetrates the surrounding formation so thatthe formation fluids flow into the tubing string to 76 complete the formation testing operation.

The present invention seeks to overcomethe deficiencies of the prior art.

This invention provides a method of firing a perforating gun which is suspended within a well atthe end of a pipe string, comprising the steps of:

(1) Communicating a fluid flow path from the surface to a firing head adjacentthe perforating gun; (2) effecting a predetermined pressurethrough the fluid flow pathto the firing head; (3) closing a passageway through a movablewall reciprocally mounted in a chamberwithin thefiring head in responsetothe predetermined pressure of step (2); (4) opening a valve in the f luid flow path forfluid communication with one side of the movable wall in the chamber in response to the predetermined press u re of step (2); (5) effecting the predetermined pressure on the one side of the movable wall to cause the movable wall to move; and (6) using the movement of the movable wall of step (5) for detonating the charges of the perforating gun.

The invention also provides a method of firing a perforating gun which is suspended downhole in a borehole on the end of a tubing string, wherein the gun includes shaped charges which are connected to an initiator so thatthe initiator can be activated to detonate the charges, comprising the steps of:

(1) elevating the tubing pressureto a first downhole pressure value; (2) moving a first member in responseto the pressure of the value of step (1); (3) using the member movement of step (2) for closing a passageway which extends into a piston; (4) effecting the pressure of the value of step (1) on one side of the piston to cause the piston to move; (5) using the movement of the piston set forth in step (4) for activating the initiator and thereby det- onating the charges of the gun.

The latter method may further includethe steps of:

forming a first chamber above and a second chamber belowthe piston; and, conducting well fluid which may inadvertently leak intothe gun into thefirst chamber, through the piston, and intothe second chamberto thereby preclude a pressure differential across the piston.

The invention further provides a method of detonating a perforating gun located on a pipe string and positioned downhole in a borehole, comprising the steps of:

(1) arranging the perforating gun in a manner to be detonated by an initiator; (2) placing a f irst and a second piston, respectively, in spaced relationship within a first and a second 2 GB 2 184 214 A 2 cylinder, respectively; (3) positioning the initiator, first and second pistons and first and second cylinders to form a first chamber between the initiatorand the first piston, and to form a second chamber between thefirst piston and the second cylinder; (4) forming a passageway along the axial centerline of thefirst piston into which one end of the second piston can be sealingly received; (5)forming a flow path which extendsfrom the interiorof thetubing string, intothe second cylinder, and into the second chamberwhen the second piston is sealingly reciprocated intothe passageway of thefirst piston, thereby providing a means by which an increased pressure effected within thetubing string also effects a pressure differential across thefirst piston,thereby driving thefirst piston downwardlyand exploding the initiator.

The latter method may further include the steps of:

arranging thefirst and second pistons,the first and second cylinders, thefirstand second chambers, and the initiatoralong a common axial centerline and within a common body.

The method mayfurther include the steps of extending the second piston upwardly into theflow path which is in communication with the interiorof thetubing; and, impacting one end of the second piston with sufficientforceto movethesecond piston intosealed relationship with the passageway so that pressure subsequently effected within the tubing string also provides a pressure differential acrossthefirst piston.

Said passageway may extends from the second chamber,through thefirstpiston, and intothefirst chamber so that inadvertent leakage of incompressible well fluids intothesecond chamberprovidesafluid on theopposed sidesof thefirst piston and prevents the first piston from moving.

The method may include the further steps of extendingthe upperend ofthesecond piston upwardly into an area which is in communication with the interior of thetubing; and, running a mass downhole through thetubing str- ing and impacting one end of the second pistonto move the second piston into sealed relationship with the passageway so that pressure subsequently effected within thetubing string also provides a pressure differential acrossthefirst piston.

The method may also includethe steps of:

arranging a portthrough the second piston; receiving the second piston in the second cylinder priorto effecting the pressure differential across the first piston; sealing the portto fluidflowfrom theflow path when the second piston is received in the second cylinder; communicating the flow path with the second chamberthrough the port upon the second piston moving into the passageway of the first piston.

The method may also include the additional steps of:

forming a portthrough the second piston; receiving the second piston in the second cylinder priorto effecting the pressure differential across the 130 first piston; conducting well fluid which may inadvertently leak between the second piston and cylinderthroughthe port and into the second chamberto preclude a pre- mature movement of the second piston in the second cylinder.

The invention also provides a method of completing a highly deviated well comprising the stepsof:

suspending a perforating gun on a pipe string ex- tending down into the highly deviated well; setting a packer disposed on the pipe string above the perforating gun; communicating a fluid flow path from the surface to a firing head adjacentthe perforating gun; effecting a predetermined pressurethrough the flow path to the firing head; opening a valve in theflow path forfluid communication with one side of a movable memberreciprocally disposed in a chamber in thefiring head in response to the predetermined pressure; effecting the predetermined pressure on the one side of the movable memberto cause the movable memberto move; and using the movementof the movable memberto actuatethe perforating gun.

The lattermethod mayfurther includethe steps of:

forming thefluidflow path in theflow bore of the pipestring andfillingthe pipe string with afluid prior to detonation of the gun.

13. The method may also includethe steps of:

opening the pipe string at a point belowthe packer to the flow of hydrocarbons from the well formation; reducing the predetermined pressure in theflow path; and flowing hydrocarbons from theformation and through theflow bore of the pipe string tothesurface.

The invention also provides a method of testing a formation in a well comprising the steps of:

mounting a perforating gun and firing head on the exterior of a pipe string extending down into the wall; setting a packer disposed on the pipe string above the perforating gun; communicating the firing head with afluid flow path to the surface; locating the perforating gun adjacent the formation to be tested; effecting a predetermined pressure through the flow path to thefiring head; effecting the predetermined pressure on one side of a movable member reciprocably disposed in a chamber in thefiring head to causethe movable memberto move; and usingthe movementof the movable memberto actuate the perforating gun.

The lattermethod may includethe stepsof:

forming the fluidflow path intheflow bore ofthe pipestring and communicating thefiring headwith flowbore;and filling the pipe string with a fluid priorto detonation of the gun; and may include the steps of:

opening the pipe string at point below the packer to the flow of hydrocarbons from the formation to be tested.

e--" 3 GB 2 184 214 A 3 More specifica I ly the method may include the steps of:

mounting another perforating gun and f iring head on the exterior of the pipe string prior to extending the pipe string into the well; setting another packer to isolate the formation of the first mentioned perforating gun from the formation of said other perforating gun; communicating the firing head of said other per- forating gun with the fluid flow path to the surface; effecting another predetermined pressure greater than thefirst mentioned predetermined pressure through theflow path to thefiring head of said other perforating gun; effecting the another predetermined pressure on one side of a movable member reciprocably dis posed in a chamber in the firing head of said other perforating gun to causethe movable memberto move; and using the movement of the movable memberto 85 actuate said other perforating gun.

In accordance with a further aspect, the invention provides a method of firing a perforating gun which is suspended within a well on a pipe string, compris- ing the steps of:

communicating a f low path from the surface to a firing head adjacentthe perforating gun; filling the flow path with a fluid; effecting a predetermined pressure through the flow path to the firing head; lowering a mass through the pipe string to close a passageway through a movable wall reciprocably mounted in a chamberwithin the firing head and to open a valve in the flow path forfluid communica tion with one side of the movable wall in the chamber; effecting the predetermined pressure on the one side of the movable wall to causethe moveablewall to move; and using the movement of the movable wall fordet- 105 onating the charges of the perforating gun.

The latter method mayfurther includethe steps of:

raising the pressure down the flow path to a level above the predetermined pressure in case the mass fails to close the passageway or open the valve; effecting the additional pressure onto a piston member in the valve; moving the piston memberto open the valve; and effecting the additional pressure and pred etermined pressure on the one side of the movable member.

There follows, byway of example, a description of specific embodiments of the invention, reference being made to the accompanying drawings in which:

Figure 1 is a fragmentary, partly schematic, partly diagrammatic, partly cross-sectional view of a well with a substantially vertical borehole and an appar atus made in accordancewith the present invention associated therewith; Figure 2 is an en larged cross-sectional view of pa rt of the apparatus disclosed in Figu re 1 prior to actua tion; Figure 3 is a cross-sectiona 1 view of the apparatus disclosed in Figure 2 after partial actuation; Figure 4 is a cross-sectional view of the apparatus disclosed in Figure 3 afterfull actuation and detonation of the perforating gun; Figure5is an enlarged cross-sectional view of an- other embodiment of the apparatus disclosed in Figures 2 through 4; Figure 6is a cross-sectional viewtaken along line 6-6 of Fig u re 5; Figure 7is an enlarged cross-sectional view of the embodiment of Figure 5 after partial actuation; Figure 8 is an enlarged cross-sectional view of the embodiment of Figure 5 afterfull actuation and detonation of the perforating gun; Figure 9 is a fragmentary, partly schematic, partly diagrammatic, partly cross-sectional view of a highly deviated well and an apparatus made in accordance with the present invention associated therewith; Figure 10 is a partly schematic, partly diagrammatic view of a well for perforation of multiple portions of the cased borehole using a plurality of apparatus made in accordance with the present invention associated therewith; and Figure 11 is a fragmentary, partly schematic, partly diagrammatic, party cross-sectional view of a well and a perforating gun having both a bar-actuated firing head and the apparatus of the present invention.

Referring initially to Figure 1, there is disclosed a typical well having borehole 10 extending downhole f rom the surface 12 of the ground through a hydro- carbon-containing formation 14. The borehole 10 is cased by a string of casing 16 hung from wellhead 18 and within surface casing 20. Casing string 16 is cemented into borehole 10 and casing 20 as shown at 22. Casing 16 isolates the wellbore 24from formation 14.

Astring of production tubing 26 is suspended within casing 16 and extends from the surface 12 axially through casing 16. Tubing 26 within casing 16forms borehole annulus 28, and packer30, disposed on tubing 26, dividesthe borehole annulus 28 into an upperannulus 32 and a lower annulus 34. Suitable outlets are provided atthe surface 12 forthetubing flow bore and each annulus formed by adjacentcasing strings with each of the outlets being provided with suitable valves and the like, including valve 36 forthe outlet communicating with the borehole annuius 28 and valves 38,39 forthe outlet communicating with theflow bore 40 of tubing string 26. A lubricator 42 is provided for accessto tubing flow bore 40 forthe use of slick linetools.

In orderto complete the well or test the formation, it is necessaryto access the hydrocarbons in form ation 14with the wellbore 24. This is accomplished by supporting a perforating gun 50 atthe lowerend of thetubing string 26. Gun 50 is preferably a jetcas- ing gun, but it should be understood thattheterm is intended to include any means for communicating the hydrocarbon-producing formation 14with lower annulus 34. Thejet perforating gun of the casing type shoots metallic particles into theformation 14to form perforations 44 and corresponding channels or tunnels 46. Numerals 44 and 46 broadly indicate a few of a plurality of perforations and tunnelswhich are formed when the charges 52 of gun 50 are detonated. Perforating objectives include perforations of a desired size and configuration, prevention of 4 GB 2 184 214 A 4 furtherformation invasion and contamination during the perforating process, and maximum capacity to movethe hydrocarbons from formation 14to lowerannulus34.

During the drilling of the borehole 10, theformation pressures are controlled byweighted drilling fluidAltrate and perhaps fines which invade theformation, interacting with in situ solids and fluidsto create a contaminated zone 48, reducing per- meability, and leaving on theface of formation 14a low-permeability filter cake. The cementing operation also includesfluids and fines which invade and damagethe formation 14 atthe contaminated zone 48. Thus,thejet perforating gun 50 of the casing type using shaped charges 52 must penetrate deeply into theformation 14to form tunnels 46 that pass through casing 16, cement 22, and contaminated zone 48 and into the uncontaminated orsterile zone 54 of formation 14. Perforations 44and tunnels 46 form the final passageways which enablethe hydrocarbonsto flowfrom theformation 14,through tunnels 46 and perforations 44and into lowerannulus 34for movementto the surface 12.

Varioustool strings may be included with tubing string 26, packer 30, and gun 50 to complete thewell and/ortestthe formation. Figure 1 illustrates onevariation of a tool string to compietethe well and transportthe hydrocarbons contained in formation 14to the surface. As shown, the tool string includestubing string 26, a perforated nipple orvent assembly 56, a releasable coupling device 58, packer30, a pressure actuatedfiring head 60 in accordancewith the presentinvention, and casing perforating gun 50.

Ventassembly56 is located in underlying relation- ship relativeto packer30 and made of the designs described in U.S. Patents 4,151,830; 4,040,485 and 3,871,448. Although not essential, it is sometimes desirable to include a releasable coupling 58, such as described in U.S. Patent 3,966,236, to release gun 50 after detonation.

Perforating gun 50, such as disclosed in U.S. Patents 3,706,344 or4,140, 180, is connected to the lower end of tubing string 26 and includes shaped charges 52 of known design, which, when detonated, form perforations 44through the sidewall of casing 16 and form tunnels 46which extend radiallyfrom borehole 10 and back up into the sterile zone 54 of formation 14.

In thetool string shown in Figure 1, pressurefiring head 60formsthe upperend of perforating gun 50. Pressure actuated firing head 60 connectsthe housing or charge carrier of gun 50tothe lowerend of tubing string 26; and,tubing string 26, casing 16, packer 30, vent assembly 56, releasable coupling 58, gunfiring head 60, andjetfiring gun 50 areall more or less arranged along a common axial centerline. in some instances, borehole 10 may be deviated, or slanted almost backto the horizontal as shown in Figure 9, and in that instance,the apparatus orthe tool string may instead be eccentrically arranged relative to one another. This invention can therefore be used in vertical as well as slanted boreholes and is especially adapted for use where difficulty is experienced in actuating the gun firing head, as for ex- ample in instances where a bar cannot be gravitated downhole, orwhere a slick line cannot be used in conjunction with a bar orfishing tool in orderto detonate the gun firing head by impact.

Although various methods of operation will be hereinafter setforth, briefly, the well istypicallycompleted bysetting packer 30 and opening vent assembIV56, pressurizing the fluid in flow bore 40 of tubing string 26 to actuate firing head 60, detonating gun 50, perforating formation 14, and flowing hydro- carbons into the lower annulus 34, through open vent assembly 56, and up tubing flow bore 40tothe outletvalve38.

Referring nowto Figure 2 fora description of one embodiment of the present invention,the pressure actuated firing head 60 includes a tubular housing 62 composed of an upper cylinder64and a lower mandrel 66. Cylinder64 has an outer cylindrical surface 68which is of the same diameter as the outercylindrical surface 72 of mandrel 66. An axial fluid passage- way 70 extends the length of cylinder 64 and includes a counterbore forming box 74 atthe lower end thereof. Reference to "lower" and "upper" parts of the present invention refers to their position shown on the drawings attached hereto for convenience and does not necessarily indicate their position during actual operation. Although firing head 60 is shown positioned in one direction in the well as shown in Figure 1, head 60 is positioned in the opposite direction as shown in Figure 11. Thus re- ferences to "lower" or "upper" are notto be limiting.

Mandrel 66 includes a reduced diameter portion or pin 76 which is telescopingly received within box74 of cylinder64. Pin 76 isthreadingly engaged to box 74 at78 by external threads on pin 76 and internal threads on box74. Pin 76forms an annularshoulder 82 forseating the lower end of cylinder 64 upon complete attachment. Set screws 84 are provided in threaded bores in the lower end of cylinder 64 to engage the outer surface of pin 76 and prevent any in- advertent disengagement of cylinder 64 and mandrel 66. Pin 76 has annular seal grooves in which are disposed sealing members 11 2,114for sealing engagement with the internal surface of box 74to prevent leakage at connection 78.

At the upper end of cylinder 64 is a tapered threaded in 86 and tapered shoulder 88 for making connection with one of the pipe members making up tubing string 26. The pipe member of string 26 adjacent pin 86 has a threaded boxwhich threadingly receives pin 86for mounting firing head 60 onto tubing string 26. Pipe readily available atthe well site is often usedfortubing string 26. Since that pipe may often be drill pipe or drill collars, the connection on the upper end of housing 62 may be a rotaryshoul- dered connection compatible with such pipe.

Mandrel 66 includes a lowerthreaded box end 92 forthreadingly receiving a sub 51 on the upper end of perforating gun 50. Pin 76, extending above box end 92 ' has a central bore 80 generally having the same internal diameter as axial passageway 70 in cylinder 64. Central bore 80 has a lower counterbore 94 adjacent box end 92 for receiving initiator 90 as hereinafter described, and is restricted by an inwardly directed annular shoulder 96 located nearthe upper end of pin 76. Annular shoulder 96 includes an GB 2 184 214 A 5 upwardly facing seat 98 forming an insert counterbore 102 with the upper portion of bore 80 and a downwardly facing seat 104forming a chamber 100 with the lower portion of bore 80. Insert counterbore 5 102 receives closure assembly 110, hereinafterdescribed, and chamber 100 houses piston 120, hereinafter described. The upper end of bore 80 is bevelled at 106for receiving closure assembly 110, and pin 76 is reduced in outer diameter at 108 along its upperend.

Piston 120 is slidingly received by chamber 1 00for reciprocation therein and has annular grooves housing upperand lower 0-ring seals 116,118, respectively, forsealing engagement with the internal cylindrical surface of chamber 100.

Initiator90 is mounted within a bore 122 in an initiator support 124which is telescopingly received within lower counterbore 94 of central bore 80. Support 124 has 0-rings 126 disposed in annular grooves therearound for sealing with the internal surface forming counterbore 94. Counterbore 94 and bore 80form a downwardly facing annularshouider 128 for abutting the upperface 130 of support 124. As the sub 51 of perforating gun 50 is threaded into box end 92, the upper end of the sub 51 engagesthe lowerface 132 of support 124 and the lower end of initiator 90 to secure support 124 and initiator 90 within lower counterbore 94. Initiator 90 supports a plurality of seal rings 134 on its exterior for sealing engagement with the inner surface of bore 122 and has an elastomeric ring 135 on its upper end to take up any end play as sub 51 is threaded into end 92. A prima cord 53 extends from initiator 90 to the shaped charges 52 of gun 50 whereby upon the initiation of initiator 90, charges 52 are detonated. The upper end of bore 122 is reduced in diameterforming an entry bore 136fora firing pin to be described.

Piston 120 includes a reduced diameter lowerend 138which supports a firing pin 140 positioned on piston 120to be received by entry bore 136when piston 120 is moved to its lowermost position. Firing pin 140 has threads on one end which isthreaded into a hole at 142 in the lowerface of end 138 and secured by a set screw (not shown), and a point 146 for impacting and setting off initiator 90. As best shown in Figure 2, initially piston 120 is secured by shear pins 150 in an uppermost position against lower seat 104 in chamber 100. Shear pins 150 are sized to shear upon the application of a pred- etermined pressure force on the upperface of piston 115 120.

Closure assembly 110 is mounted on pin 76to open and closefluid communication with chamber 100. Assembly 110 includes a generally cylindrical bonnet 152 having a lowerthreaded end 154 and an outwardly extending radial annularflange 156. The aperture through annularshoulder 96 of pin 76 is threaded to threadingly engage at 155 end 154 and secured closure assembly 110 to the upper end of pin 76. Annularflange 156 is slidingly received by insert counterbore 102 and includes an 0-ring seal 158 received in an annular groove in the radial circumference of shoulder 156to seal with the internal wall forming insert counterbore 102.

Closure assembly 110 further includes a piston member or a plunger or a plug 160 reciprocably received in a cylinder 162 formed by cooperating blind bores 164,166 in bonnet 152 and piston 120, respectively, having a common inner diameter. Each mouth of blind bores 164,166 is conically tapered for ease of passage of plug 160 between bores 164,166. Bonnet bore 164, as shown, opens downwardly opposite the upwardly facing open end of piston bore 166. The bottom 172 of bonnet blind bore 164 has a hole 168forslidably receiving a shaft or stem 174 on plug 160 extending upwardly therethrough. Stem 174 has a stop shoulder 176 which engages bottom 172 to limitthe upward movement of plug 160within bonnet bore 164. A stem head 178 may bethreaded at 179 onto the uppermost end of stem 174where auxiliary bar actuation of head 60 may be desirable. The piston portion of plug 160 has annulargrooves therearound in which are housed 0-ring seal members 182, 184for sealingly engaging the cylindrical walls of cylinder 162 as plug 160 reciprocates therein.

Bonnet bore 164 is part of a fluid flow path which ultimately extends tothe surface 12. A plurality of radial fluid ports 180, located adjacent bottom 172 of bonnet bore 164, extend from blind bore 164tothe exteriorof bonnet 152 and axial fluid flow passageway 70 of cylinder 64. Shoulder 176of stem 174 prevents plug 160 from moving over bonnet ports 180 so asto damage 0- ring seal members 182,184. Init- ially, as shown in Figure 2, plug 160 is inthe upper and bonnet portsealing position preventing any fluidflowfrom passageway70to chamber 100. Plug 160 is held in the upper position by shear pin 188 sized to shear upon the application of a predetermined fluid pressure in passageway 70through bonnet ports 180 and that portion of bonnet bore 164 above plug 160. Roll pins 189 pass through closure assembly 110 to hold shear pin 188 in position.

Shear pins 188 determine the amount of fluid pres- sure required in passageway 70 to actuatefiring head 60. Where head 60 isto be actuated solely by fluid pressure, i.e. withoutthe use of a bar, shear pins 188 are sized to shear at a predetermined pressure approximately 2000 to 3000 psi above hydrostatic pressure. The hydrostatic pressure is the heavierof the hydrostatic head in the easing annulus 28 orthe tubing flow bore 40. If the predetermined pressure were calculated based on the tubing flow bore hydrostatic and the casing annulus hydrostatic greaterthan the predetermined pressure setto shear pins 188, a leakfrom the casing annulus into thetubing flow bore might raisethe fluid pressure in passageway 70 to the predetermined pressure and prematurely detonate gun 50. Thus, shear pins 188 must be heavy enough to insure that pins 188will not be sheared bythe largest hydrostatic head in the well.

Piston bore 166 also has a plurality of radial fluid ports 190 located adjacentthe bottom 192 of piston bore 166 permitting fluid flow between that portion of chamber 100 above piston 120, i.e. upperchamber 100A, and that portion of chamber 100 below piston 120, i.e. lowerchamber 100B. So long as piston ports 190 are open,thefluid pressureswill be equal in upperand lowerchambers 100A, 100B since ports 190 will permit equalizing flowtherebetween. This 6 GB 2 184 214 A 6 flowpathway between chambers 100A, 100B provides a pressure balancing meansacross piston 120to preventthe inadvertentand premature detonation of gun50dueto a pressure buildup in upperchamber 100A. Forexample, if plug seals 182,184orbonnet seal 158wereto leakfluidfrom axialfluid passageway70 into upper chamber 1 OOA, such a pressure increasewould merely equalize across piston 120 due to flow through piston ports 190into lower chamber 10013.

Referring nowalsoto Figure3showing partial actuation, shear pin 188issheared byincreasingthe fluid pressure in axial passageway 70 which, when appliedtothe cross-sectional area of stem 174pro- jecting into passageway70 andtothe remaining cross-sectional area of plug 160 in that portion of bonnet bore 164 above plug 160 via bonnet ports 180, the force will reach the predetermined amount which will shear pin 188. The pressure on plug 160 and stem 174 causes plug 160 to move downwardly in cylinder 162, passing from bonnet bore 164 where bonnet ports 180 are sealed to piston bore 166 where seal members 182,184 of plug 160 sealingly engage the cylindrical wall of piston bore 166 and seal off piston ports 190.

Referring now also to Figure 4, pressure actuated firing head 60 is shown fully actuated. By unsealing bonnet ports 180, the f luid from axial passageway 70 nowf lows into upper chamber 1 OOA. Further, be- cause plug 160 has now sealed piston ports 190, a pressure differential is effected across piston 120. Upon the application of this increased fluid pressure onto the upperface of piston 120 and the impact of plug 160 engaging bottom 192 of piston bore 166, pins 150 are sheared. Shear pins 150 for piston 120 may be largerthan shear pins 188 for plug 160 because the cross-section of piston 120, i.e. pressure area, is greaterthan the cross-section of plug 160. Since piston 120 issubstantially heavierthan plug 120, pins 150 needto be largerto passthe droptest.

Pins 150 are notstrong enough to withstand the hydrostatic head and would shear.

Upon shearing pins 150, piston 120 moves down wardly in chamber 100 with the point 146 of firing pin 140 impacting initiator90 to detonate charges 52 of perforating gun 50. Piston 120 snaps downwardlyto provide a substantial impact of pin 140 with initiator 90. The lowerface of piston 120 engages the upper face 130 of support 124to arrestthe downward movement of piston 120. - In operation, fluid pressure is effected into pas sageway70 to actuate head 60. Although normally the fluid pressure will be hydraulic pressure from a liquid, it is possiblethata gas may be used to actuate head 60. Further, fluid pressure may be effected in passageway70 by pressuring down the flow bore40 of tubing string 26, or pressuring down the casing annulus 28, or pressuring down both thetubing flow bore 40 and casing annulus 28, or pressuring down a flow path made up of portions of tubing flow bore 40 and casing annulus 28 to communicate with pas sageway 70.

The pressure effected into passageway 70 is hydrostatic pressure plus a safety margin pressure such as 20% of hydrostatic pressure or about 2000 to 130 3000 psi. Again the heaviest hydrostatic pressure in the well is used to calculatethe predetermined pressure required to actuate firing head 60. Once thefluid pressure in passageway 70 exceedsthe predetermined pressure limitfor shear pins 188, pins 188 shear and free plug 160 to move downwardly.

A substantial pressure differential is created across plug 160. On the upperface of plug 160 and stem 174 is hydrostatic pressure plus 2000to 3000 psi and on the lowerface of plug 160 is atmospheric pressure since cylinder 162 and chamber 100 are at atmospheric. As plug 160 moves downward under the pressure differential, seal 182 continuesto seal with bonnet 152 until after lower seal 184 has seal- ingly engaged the walls of cylinder 162 of piston 120. As plug 160 moves into cylinder 162, anytrapped pressure is exhausted through piston ports 190. Once plug 160 is received within cylinder 162 and seal 184 has sealed with piston 120, ports 190 in piston 120 are closed preventing freefluid flow between upper and lower chambers 1 OOA and 10013. At thattime upperseal 182 disengageswith bonnet 152 and permitsthe fluid pressure of passageway 70to pass into upper chamber 1 OOA and be applied to the cross-section of piston 120. Fluid from passageway 70 flows through hole 168 between stem 174and bonnet 152 and through bonnet ports 180 into blind bore 164 in bonnet 152. The fluid then passesfrom bore 164 into upper chamber 100A.

Upon the application of thefluid pressurefrom passageway 70to piston 120, a pressure differential is created across piston 120.Thefluid pressurefrom passageway70 is applied to the upperface of piston 120 and atmospheric pressure is on the lowerface of piston 120 since lower chamber 1 OOB is atatmospheric. This large pressure differential causes piston 120 to snap downwardly. The lower reduced diameter portion around piston 120 prevents any pressure lock as piston 120 moves downward to causefiring pin 140 to impact initiator 90.

Theforce of impact between pin 140 and initiator 90 ignites prima cord 53which in turn detonatesthe shaped charges 52 of jet perforating gun 50. Theformation 14 is perforated forming perforations 44 and tunnels 46 to permitthe hydrocarbons of formation 14toflow into annulus 28.

Figures 5-8 illustrate another embodiment of the present invention. Referring initiallyto Figures 5 and Che other embodiment of the pressure actuated gun firing head 200, as illustrated, is seen to include a main body composed of an upper main body part 202 substantially the same as cylinder64 of thefirst embodiment including a cylindrical axial passageway 70 formed on the inside thereof, which enlarges in diameter into an internally threaded surface 203, and terminates in a circumferentially extending edge portion 204.

The main body includes a lower main body part 206terminating in a femalethreaded interiorsurface 208, hereinafter also called "a box ora box end". The box end 210 has a circumferentially extending lower terminal edge portion 212.

The box end 210 includes an axial bore 214which is reduced in diameter at 216. The outside diameter of the upper end of the lower main body part 206 is c 7 GB 2 184 214 A 7 reduced in diameter commencing at 204 to provide reduced diameter part 218. Outer surface 218 and inner surface 220 are made in close fitting relationship relative to one another so that one slidably re- ceives the other in a telescoping man nertherewithin. The before mentioned coacting threaded areas 203 releasably fasten the upper and lower main body parts 202,206togeth er.

An annular boss 224 projects inwardly from hous- ing 200 and is internally threaded at 226. The boss 224increases in diameter to provide a cylindrical portion 228,which again increases in inside diameter at 230 top rovidethe i I I ustrated upper constant diameter inner surface which terminates at the upper terminal end thereof in the form of a shoulder 232.

The upper main body part 202 includes a shoulder 234which is slightly spaced from the confronting shoulder 232. Axial passageway 70 is in communication with the interior of the tubing string 26. Tri g g er device 236 is positioned within the axial passageway 70 and includes a shaft 238.

Shaft 238 is slidably received in closetolerance relationship within a bore 240 in bushing 242. 0-ring 244 seals the interface between the bore 240 and the shaft 238. Shaft 238 is screwed into the upper end of piston plug 250 which is of larger diameter than shaft 238. O-ring 246 seals the interface between the enlarged bore 248 and piston plug 250. The lowerend of piston plug 250 is larger in diameterthan the upper end providing a transition portion at 251. Circumferentially extending grooves on piston plug 250 house an upper 0-ring 252 and a lower O-ring 254. 0-ring sealswith further enlarged bore 256 of bushing 242. Numeral 258 indicates the lowerterminal end of piston plug 250.

As best shown in Figure 5, bushing 242 is secured to lower body part 206, and is provided with a contoured entrance at 260. Bushing 242 further includes an outersurface area defined by outside diameter 262. The bushing is spaced from the wall of axial bore 70, therebyforming an upwardly opening annulus 264. The annulus 264 communicates with bore 256 by means of the illustrated radial passageway 270. The upper reduced diameter end of piston plug 250 includes at least one radial passageway 272 which communicate with an axial passageway 274 which leads to a lower radial passageway 276. Radial passageway 276 communicates, via axial passageway 274, with the upper end of piston plug 250which is isolated from well fluids by means of the spaced O-rings 244 and 246.

Should well fluids leak past seal 244 or246to act on the upper end of piston plug 250, itwill also be conducted by passages 272,274,276to lower end 258 of piston plug 250 and exertthere a balancing force so that piston plug 250 will not be moved. The upper end of piston plug 250 is releasably affixed to bushing 242 by means of radially disposed shear pins 278. Shear pins 278 are selected to fail upon the application of a predetermined force, as will be more fully discussed hereinafter.

In this embodiment of the present invention, shear pins 278 may be somewhat smaller. Because that portion of bore 248 between seals 244,246 corn- rnunicates with upper chamber 284, via ports 272, 274,276, there is atmospheric pressure on both sides of the small diameter portion of plug 250 having little tendencyfor moving plug 250. The only down force on plug 250 is the difference in cross-sectional area between the larger lower portion of piston 250 and the smaller upper portions of piston 250. Thus the smaller pins 278 can pin against a high hydrostatic.

Larger piston 280 has an upwardly opening passageway 282formed therewithin which is in communication with an upper chamber 284when thefiring head is in the:standby configuration as shown in Figure 5. Lateral ports 286 placethe lower chamber 288 in communication with piston passageway 282.

Initiator support 292 underlies the piston 280 and has an outside diameter 294fitting closelywithin the before mentioned axial bore 214. The support 292 is provided with an axial bore 296 which sealingly receives the initiator 290 in sealed relationship therewithin, noting the plurality of spaced O-rings located between the initiator 290 and the bore 296. O-rings 298 seal the interface between outside diameter 294 and axial bore 214. Piston 280 is reduced in diameter at lower end 302thereof. The upperface 304of piston 280 is disposed within the interior of chamber 284. Lower face 308 of piston 280 is disposed within lower chamber 288. The lower end of piston 280 is again reduced at 310 to provide a firing pin 300 atthe lower extremity thereof.

Radial shear pins 312 are formed through the side wall of the lower main part 206 and extend into bores formed in a sidewall of piston 280. Shear pins 312 are sized to insure that pins 312 do not shear dueto the weight of piston 280 or due to head 60 being accidentally dropped. O-rings 314 seal againstfluid flow across the shear pins 312 and across thethreads 203. 0-rings 316 further seal againstf lowwhich may occur across shear pins 312 orfrom upper chamber 284 into lower chamber 288 under certain conditions of operation, as will be further discussed later on in this disclosure.

Locking screws 318 prevent inadvertent relative motion between the upper and lower main body parts 202 and 206. Prima cord 320 is routed through passageway 322 of sub 51 associated with gun 50.

The prima cord 320 is attached to the initiator290, and to the shaped charges 52 so thatwhen thefiring pin 300 strikesface 324of initiator290, initiator290 explodes, which in turn explodes prima cord 320, and this action instantaneously detonates all of the shaped charges 52 associated with the gun 50. In actual practice, the initiator explodes and thereafterthe prima cord 320 is progressively exploded, with each of the shaped charges 52 being sequentially exploded; however, thetime framewithin which this ex- plosivetrain occurs is of such a short duration that one could call this action "instantaneous", although those skilled in the art of measuring phenomena that occurwithin a millisecond would probably consider thatthe explosion train requires a time duration.

Referring nowto Figure 7 showing partial actuation, shear pin 278 is sheared by increasing the fluid pressure in passageway 70 which,when applied to the cross-sectional area of shaft 238 projecting into passageway 70 and to the remaining cross-sectional area of piston plug 250 in bore 256 8 GB 2 184 214 A 8 via ports 270, the force will reach the predetermined amountwhich will shear pins 278. As piston plug 250 and shaft 238 move downwardly, the lower end of piston plug 250 with O-ring seal 254 enters piston passageway 282 where O-ring seal 254 sealing ly engages piston plug 250 and large piston 280 to close off lateral ports 286 in large piston 280. Then, O-ring seals 244 on shaft 238 and seal ring 246 on the upper end of piston plug 250 move into enlarged bushing bores 248,256, respectively whereby seals 244,246 disengage their sealing engagementwith bushing 242. Further, as piston plug 250 moves out of bore 256 of bushing 242, O-ring seal 252 also unsealswith bushing 242. However, priortothe disengagement& seals 244,246 and 252,the lower seal 254on piston plug 250 sealing ly engage the cylindrical wall of bore 282 in piston 280 which in turn seals off piston ports 286. When plug 250 bottoms in cylinder 282 of piston 280, radial ports 272 are in communication with ports 270.

As illustrated in Figure 7, the fluid in passageway 70 is nowfree to f low around bushing 242 in annulus 264 and through bushing ports 270. Further, the f luid in passageway 70 can flow down bushing bore 240 between shaft 238 and bushing 242. Once thefluid from passageway 70 reaches enlarged bushing bore 256 from either bore 242 or ports 270, the fluid can pass through passageways 272,274 and 276 in plug 250 into upper chamber 284 or through bushing bore 256 between piston plug 250 and bushing 242 into upper chamber284.

Referring nowto Figure 8, pressure actuated firing head 200 is shown fully actuated. By unsealing ports 270 and unsealing shaft 238 and piston plug 250 with bushing 242, thefluid pressure from passageway70 is applied in upper chamber 284. Further, because piston plug 250 has now sealed off piston ports 286, a fluid pressure differential is effected across large piston 280. Upon the application of this increased fluid pressure onto the upperface 304 of piston 280, and the impact of piston plug 250 engaging the bottom of piston bore 282, pins 312 are sheared and piston 300 moves downwardly in lower chamber 288 with firing pin 300 impacting initiator 290 and thereby detonate charges 52 of perforating gun 50. Piston 280 snaps downwardlyto provide a substantial impact between firing pin 300 and initiator290.

Should it be necessaryto remove thetool string from thewell for some reason such as thefailure of the gun to discharge, the packer may be unseated and thetool string raised. An inadvertent activation of the firing head is notof concern. The previously discussed safetyfeatures renderthefiring head safe.

The pressure effected on the firing head is reduced asthetubing string is raised and the large piston remains pressure balanced.

The present invention may be used in a varietyof applications. Figure 9 illustrates the use of the present invention in a highly deviated well where a bar-actuated firing head cannot be used becausethe barwill nottravel down the tubing string with enough speed to sufficiently impact a baractuated 5ring head. As shown in Figure 9, casing 16 extends downwardly in the vertical direction and then is turned to a substantially horizontal position. Atool string consisting of a packer 30, vent assembly 56, pressure actuated firing head 60, and jet perforating gun 50 suspended on a tubing string 26 is lowered into casing 16 until gun 50 is adjacent formation 14. Tubing string 26 is filled with a fluid. Packer30 isset and vent assembly 56 is opened. Itshould be understood that a perforated nipple may be used ratherthan a vent assembly. Pump pressure is applied down theflow bore 40 of tubing string 26to actuatefiring head 60 and fire gun 50. The pump pressure is bled off to produce formation 14. In this application, the perforating gun 50 is actuated withoutthe use of a bar.

Another application of the present invention is illustrated in Figure 10. In this application the present invention is used to test a plurality of payzones through a single tubing string. Referring to Figure 10, there is shown a casing 350 extending through a plurality of payzones such as upper payzone 352 and lower payzone 354. The tool string includes an upper packer 356, an upper vent 358, an upper pressure actuated firing head 360, an upper perforating gun 362, a lower packer 366, a lowervent 368, a lower pressure actuated firing head 370, a lower perforating gun 372 and a bull plug 364, all suspended on tubing string 374. Bull plug 370 closes the lowerend of tubing string 374. Although only two payzones and corresponding perforating guns are shown, itshould be understood that any number of payzones could be tested by adjacent perforating guns mounted on tubing string 374. Upperand lower pressure actuated firing heads 360,370 and upper and lower perforating guns 362,372 are mounted on the exterior of tubing string 374. Each pressure actuated f iring head is in fluid communication with the tubing flow bore of tubing string 374 by means of a ported connector whereby pressure effected down the tubing flow bore of string 374 is applied to the respective plugs of firing heads 360,370. Vents358, 368 may be sliding sleeves or one-wayvalves forthe passage of production fluids into thetubing flow bore of string 374 after perforation. It should be obvious that a bar cannot be used in this situation since the perforating guns are disposed outside the tubing string. The shear pins 188 in firing heads 360,370 are set at 500 psi intervals wherebythe lowest firing head 370 and gun 372 will be actuated first. Thus lower pressure actuated firing head 370 has shear pins 188 setto shear at a predetermined pressure 500 psi lowerthan the predetermined pressure setto shearthe pins 188 in upper pressure actuated firing head 360. In operation, lower packer 366 is set to isolate payzone 354. When the invention is used in a newwell such thatthe annulus below packers 356,366 can be pressurized, lower vent 368 maybe a sliding sleeve which is opened using a wireline priorto perforating. Pressure isthen effected down tubing string 374 until shear pins 188 of lowerfiring head 370 are sheared and gun 372 is detonated. Prduction isthen permitted into tubing string 374via lowervent368. After lower payzone 354 istested, lowervent368 is closed and upper packer356 is set if it has not already been set, Upper vent 358 is then opened and 11 i 9 GB 2 184 214 A 9 pressure is again applied through tubing string 374 until pins 188 in upperfiring head 360 are sheared and payzone 352 is perforated fortesting. Production is then permitted into tubing string 374via upper vent 358. Wherethe annulus below packers 356,366 cannot be pressurized, as for example where there are existing perforations already in payzones 352, 354, vents 358,368 may be one-wayvalves which are opened to the flow of production fluids after perforation either by bleeding the pressure off from tubing string 374 or swabbing string 374to open the one-wayvalve.

A still another application of the present invention is with a workover operation where the well has previously been perforated. As shown in Figure 1, a tool string with a packer 30, vent assembly 56, releasable coupling 58, pressure actuated firing head 60, and jet perforating gun 50 suspended on tubing string 26 is run into the well with the ventassembly 56 closed. Tubing string 26 isfilled with fluid. Packer is hydraulically set. Pump pressure is applied down theflow bore 40 of tubing string 26 to actuate firing head 60 and fire gun 50. Vent assembly 56 is then opened, and the pump pressure is bled off or the tubing string is swabbed to bring in the well. Vent assembly 56 could not have been opened priorto detonation due to the old perforations in the payzone. Vent assembly 56 may be a sliding sleeve or a checkvalve which opens when the pressure in thetubing string is reduced. No underbalance, i.e.

downhole pressure lessthan formation pressure, is used. The same procedure may be used in a newwell where an overbalance is desired, i.e. downhole pressure greaterthan formation pressure. Gun 50 may be dropped by using releasable coupling 58.

In another application, the activation of head 60 is initiated by dropping a bar. Where a bar may be dropped down tubing string 26, a tool string with packer 30, vent assembly 56, firing head 60, and gun 50 suspended on tubing string 26 is run into the well with vent assembly 56 closed. Tubing string 26 is filled with a lightfluid such as water creating a hydrostatic head substantially less than the formation pressure so as to create an underbalance.

However,the shear pins 188 in the piston plug 160 require a force in excess of the hyarostatic head in the casing annulus 28 plus a safety margin pressure.

In order to maintain the underbalance, it is necessary to actuate head 60 without pressuring down the tubing flow bore 40 an amount necessary to shear pins 188 since such a pressure would cause an overbalance situation. Thus, a bar is dropped down the tubing string 26 to open vent assembly 56 and impact head 178 on stem 174 of plug 160 to shear pins 188 and open upper chamber 1 00Ato the hydrostatic head of the fluid in tubing flow bore40.

Although the hydrostatic head in tubing flow bore40 is insufficientto shear pins 188, it is sufficient, when applied to the larger pressure area of piston 120,to shear pins 150 and actuate head 60. Thus, the barand hydrostatic head are used in combination to actuate head 60.

In this application, firing head 160 also acts as a fail safe device. if, after dropping the bar, the head does not actuate because, for example, there is debris in 130 the tubing string preventing the barfrom having sufficient impact on head 178 to shear pins 188, the operator has a second chance. Ratherthan attempting to fish outthe bar or unseatthe packer and remove the tubing string, pump pressure is added to the hydrostatic head in thetubing flow bore 40. Oncethe pressure in the tubing flow bore40 reaches the predetermined pressure, pins 188 are sheared and firing head 60 is actuated by pressure.

Although the underbalance is lost, the operator is still able to achieve a well completion.

In a variation to the above, the bar initiates activation of the pressure actuated firing head but additional pressure must be added to thetubing flow bore to complete actuation. The tool string is lowered into the well with a normally closed vent assembly. In operation a bar is dropped downhole. The bar opens vent assembly 56 and impacts against head 178,thereby driving the plug 160 into the piston passageway 162 and forming a flow path from the tubing string into the upper chamber 1 OOA. The gun firing head 160 now is the "armed" or "cocked" position and the gun 50 is readyto fire upon the addition of sufficient pressure being effected within thetubing string 26. The vent56 can be opened using wireline, bar, or packer actuated devices. Further pressure is then applied. This preferably is accomplished using N2, C02, orflue gases, although a liquid could be employed to elevate the tubing hydrostatic head orfluid pressure to the valve required to shearthe piston pin 150. Afterthe pressure differential acrossthe piston 120 has sheared the piston pins 150, the piston 120 strokes downhole, thus forcing firing pin 146to strikpthe initiator 90, and explode the prima cord 53,which detonatesthe individual shaped charges 52. After the casing 16 has been perforated, thetubing is swabbed until production is achieved. In some instances it may be necessaryforthe well to be put on a pumpjack unit because of the low downhole formation pressure. In the above example, it is, of course, necessaryto contain the downhole pressure bythe provision of a hydrostatic head achieved by the use of a suitable well fluid.

A still another application of the present invention is shown in Figure 11 where a pressure actuated firing head is used as an alternate firing head. Referring nowto Figure 11, there is shown a casing 380 extending though a formation 382. Atoof string with a packer384, vent assembly 386, releasable coupling 388, bar actuated firing head 390, perforating gun 392, and pressure actuated firing head 394 suspended on a drill string 396, is lowered in the borehole until the perforating gun 392 is adjacent formation 382. The packer384 is setto isolate formation 382 and a bar is dropped to actuate bar actuated firing head 390. Vent assembly386 is either packer actuated or bar actuated. IfJorsome reason, bar-actuated firing head 390 does not actuate, pressure actuated firing head 394 may be actuated by pressuring down tubing string 396 and through open vent assembly386 into lower annulus 398. Pressure actuated firing head 394 is in fluid communication with the lower annulus 398, and therefore pressure is effected on pressure actuated GB 2 184 214 A firing head 394to detonate gun 392. Thus, pressure actuated firing head 394serves as a back-upfiring head.

Those skilled in the art, having digested the above 5 description of this invention, will appreciate thatthe gunfiring head can be actuated by (1) elevated pressure of a predetermined magnitude; (2) bar and pressure combination; or(3) barand elevated tubing pressure in two distinctsteps.

One advantage of the present invention isto fire a perforating gun or guns under conditions which prevent firing with a bar. One such condition would beto pressure the tubing orthe annulus to firea lowergun priorto firing an upper gun with the upper gun and lower gun priorto firing an upper gun with the upper gun and lower gun being attached to one another. The uppergun can thus befired by dropping a bar. Therefore, the presentinvention enablesthe charges of a casing gun to be detonated commencing atthe bottom-most charge and proceeding uphole until the uppermostcharge has been fired. This may be accomplished by inverting the gun and gun firing head, thereby locating the gun firing head on the bottom of the gun 1ooking downhole". Thevent assembly bythe lower gun must be opened in ordertofire the lowergun by elevating the bottom hole pressure as in (1) above. A barcannot be used as in (2) above in this instance.

An unusual feature of this invention lies in the plug, piston and passageways being arranged wherebythere is one large aperture piston within which a plug must be sealingly received in orderfor the head to be detonated. The plug and piston are selectively moved by pressure, impact, or a combination thereof. Leakage of incompressible well fluids into the head is equalized across the piston and thereafterthere can be no pressure differential developed thereacross because of the presence of the piston passageway. Leakage of well fluids into the sealed off area is bled off to equalize the leakage pressure on the plug.

In theforegoing, the invention has been described primarilywith reference to shape and structure. It can be further described from the standpoint of function.

It is desired to detonate the gun hydraulically (or conceivably by anyfluid pressure, including gas). To that end a so called hydraulic cylinder, Le, a cylinder in which moves a piston, is employed. Since circular cross-section is merely usual but not essential, the cylinder may be referred to as an expansible chamber having a movable wall (the piston).

It is desired to admit pressure fluid to the interior of the expansible chamberto move its movable wall to detonate the gun by means of a firing pin carried by the wall. So an inlet fluid passage is provided through a fixed wall of the expansible chamber and a valve is placed in the inlet. In the present casethe small plug 160 and bushing 152 provide such a valve.

Radial ports 180 arethis valve inlet. The cylindrical surface of piston bore 166 is the valve seat. Large piston 120 is the valve closure. The valve outlet isthe lowerend of cylinder 164, which discharges into upper chamber 1 00Awhen the valve is open, as shown in Figures 3,4 and 7. In Figures 2 and 5this valve is shown in closed position.

Should this primaryvalve leak and fluid enterthe expansible chamber, the movablewall would move thefiring pin to detonate this gun. This isthe problem faced and solved bythis invention.

An equalizing passage is provided through the movable wall communicating the interior of the expansible chamberwith the outside of the movable wall. As long asthis equalizing passage is open, no differential pressure can build up on opposite sides of the movablewall and the gun will notfire sincethe movablewall is held fixed by shear pins.

To arm the firing head, the equalizing fluid passage must be closed. This is achieved by means of an auxiliaryvalve which, in the present case, includes a valve closure provided bythe lower end of the small plug 160, such valve closure cooperating with a valve seat provided bythe inner peripheryof cylinder 162 in the large piston 120.

Itwill be seen thatthe two valves are connected together or interlocked so thatwhen the primary or supplyvalve is closed, the auxiliary orequilizervalve is open, as shown in Figures 2 and 5; whenthe primary of supplyvalve is open,the auxiliary or equilizervalve is closed, as shown in Figures 3,4 and 7. Furthermore, the seal spacing, referring to seals 182 and 184, is such thatthe auxiliary valve (seal 134) closes beforethe primaryvalve (seals 182) opens, so that opening of the primary or supplyvalve will not admitfluid to the outside of the expansible chamber (belovithe big piston) and hydraulically lockthe firing head.

Recapitulating, according to the invention a perforating gunfiring head comprises a pipe nipple to be connected at its lowerend to a gun and at its upper end to a pipe string. The nipple has a transverse wall at its upper end and a detonator mounted in its lower end. A piston is secured in the nipple between its ends by lower shear pins. The piston carries a firing pin on its lower side and has a pressure equalizing fluid passage from its upper side to its lower side. Thetransverse wall has a fluid supply passagefrom its uppersideto its lowerside to admit pressurefluid from the pipestring tothe upperside of the piston.Avalve in thefluidsupply passage includes a plunger normally closing the supply passage and held in closed position by upper shear pins, the lower end of the plunger moving to close the pressure equalizing passagewhen the uppershear pins are sheared and the plunger moves to open thefluid supply passageto admit pressure fluid to the upperside of the piston. The plungeris moved down and the uppershear pins sheared either by pressure on an area of the plunger or bya hammer blow on an anvil connected by a stem tothe upperend of the plunger. Anotherarea around the plunger belowthe stem is sealed off from pressure fluid and passages in the plungerequalize pressure between the sealed area and the lower end of the piston.

It isto be understood that although it is preferred thatthe uppershear pins break at a higher pressure than the lowershear pins, as that operation without the use of a bar, i.e. all pressure operation,will cause a snap action of the firing head, it would also be 11 GB 2 184 214 A 11 possible to provide a firing head in which the upper shear pins sheared at a lowertubing pressure than the lower shear pins, whereby a two stage a I I pressure operation could be achieved, the headfirst being armed by raising thetubing pressureto a certain valueto shearthe uppershear pins and thereafter at any time the pressure could be raisedto a higher pressure sufficientto shearthe lowershear pins and movethe lowerpiston to detonatethe gun.

Itwould also be possibleto providethatthe upper and lowershear pins both shearatthesame pressure.

While a preferred embodiment of the invention has been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit of the invention.

Claims (20)

1. Method of firing a perforating gun which is 85 suspended within a well atthe end of a pipe string, comprising the steps of:

(1) Communicating a fluid flow path from the surface to a firing head adjacentthe perforating gun; (2) effecting a predetermined pressurethrough the 90 fluid flow path to the firing head; (3) closing a passageway through a movable wall reciprocally mounted in a chamberwithin thefiring head in responseto the predetermined pressure of step (2); (4) opening a valve in thefluid flow path forfluid communication with one side of the movable wall in the chamber in response to the predetermined pressure of step (2); (5) effecting the predetermined pressure on the one side of the movable wall to cause the movable wall to move; and (6) using the movement of the movablewall of step (5) for detonating the charges of the perforating gun.

2. Method of firing a perforating gun which is suspended downhole in a borehole on the end of a tubing string, wherein the gun includes shaped charges which are connected to an initiatorsothat the initiatorcan be activated to detonatethe charges, comprising the steps of:

(1) elevating the tubing pressure to a first downhole pressure value; (2) moving a f irst member in response to the pressure of the value of step (1); (3) using the member movement of step (2) for closing a passageway which extends into a piston; (4) effecting the pressure of the value of step (1) on one side of the piston to cause the piston to move; (5) using the movement of the piston setforth in step (4) for activating the initiator and thereby detonating the charges of the gun.

3. The method of claim 2 wherein there is further included the steps of:

forming a first chamber above and a second chamber belowthe piston; and, cnoducting well fluid which may inadvertently leak into the gun into thefirst chamber, through the piston, and into the second chamberto thereby preclude a pressure differential across the piston.

Q

4. Method of detonating a perforating gun located on a pipe string and positioned downhole in a borehole, comprising the steps of:

(1) arranging the perforating gun in a mannerto be detonated by an initiator; (2) placing a first and a second piston, respectively, in spaced relationship within a first and a second cylinder, respectively; (3) positioning the initiator,first and second pistons and first and second cylindersto form a first chamber between the initiator and the first piston, and to form a second chamber between thefirst piston and the second cylinder; (4) forming a passageway along the axial centerline of the first piston into which one end of the second piston can be sealingly received; (5) forming a flow path which extendsfrom the interiorof thetubing string, into the second cylinder, and into the second chamberwhen the second piston is sealingly reciprocated into the passageway of the first piston, thereby providing a means by which an increased pressure effected within the tubing string also effects a pressure differential across thefirst piston, thereby driving thefirst piston downwardly and exploding the initiator.

5. The method of claim 4 and further including the steps of:

arranging the first and second pistons, the first and second cylinders, the first and second chambers, and the initiator along a common axial centerline and within a common body.

6. The method of claim 4or5, andfurther including the steps of extending the second piston upwardly into the flow path which is in communication with the interior of the tubing; and, impacting one end of the second piston with sufficient force to move the second piston into sealed relationship with the passageway so that pressure subsequently effected within the tubing string also provides a pressure differential across the first piston.

7. The method of any of claims 4to 6, wherein said passageway extends from the second chamber, through the first piston, and into the first chamber so that inadvertent leakage of incompressible well fluids into the second chamber provides a fluid on the opposed sides of the f i rst piston and prevents the first piston from moving.

8. The method of claim 7 and further including the steps of:

extending the upper end of the second piston upwardly into an area which is in communication with the interiorof thetubing; and, running a mass downhole through thetubing string and impacting one end of the second piston to move the second piston into sealed relationship with the passageway so that pressure subsequently effected within the tubing string also provides a pressure differential across the first piston.

9. The method of any of claims 4to 8 and further including the steps of:

arranging a port through the second piston; receiving the second piston in the second cylinder priorto effecting the pressure differential acrossthe firstpiston; 12 GB 2 184 214 A sealing the portto fluidflowfrom theflow path when the second piston is received in the second cylinder; communicating the flow path with the second chamberthrough the port upon the second piston moving into the passageway of the f irst piston.

10. The method of any of claims 4to 9 and further including the steps of:

forming a portthrough the second piston; receiving the second piston in the second cylinder priorto effecting the pressure differential across the first piston; conducting well fluid which may inadvertently leak between the second piston and cylinderthrough the port and intothe second chamberto preclude a premature movement of the second piston in the second cylinder.

11. Method of completing a highly deviated well comprising the steps of:

suspending a perforating gun on a pipe string extending down into the highly deviated well; setting a packer disposed on the pipe string above the perforating gun; communicating afluidflow path fromthesurface to afiring head adjacentthe perforating gun; effecting a predetermined pressurethrough the flow path tothefiring head; opening a valve intheflow path forfluid communication with oneside of a movable member reciprocally disposed in a chamberin thefiring head in responsetothe predetermined pressure; effecting the predetermined pressure on the one side of the movable memberto cause the movable member to move; and using the movement of the movable memberto actuatethe perforating gun.

12. The method of claim 11 further including the steps of:

forming the f lu id f low path in the f low bore of the pi pe stri ng a nd f il Ii ng the pipe string with a f lu id prior 105 to detonation of the gun.

13. The method of claims 12 further including the steps of:

opening the pipe string at a point belowthe packer to the flow of hydrocarbons from the well formation; reducing the predetermined pressure in the f low path; and flowing hydrocarbons from the formation and through the flow bore of the pipe string to the surface.

14. Method of testing a formation in a well comprising the steps of:

mounting a perforating gun and firing head on the exterior of a pipe string extending down intothe wafl; setting a packer disposed on the pipe string above the perforating gun; communicating the firing head with a fluid flow path to the surface; locating the perforating gun adjacentthe formation to be tested; effecting a predetermined pressure through the flow path to thefiring head; effecting the predetermined pressure on one side ofa movable member reciprocably disposed in a 12 chamber in the firing head to cause the movable memberto move; and using the movementof the movable memberto actuatethe perforating gun.

15. The method of claim 14further including the steps of:

forming the fluid flow path in the flow bore of the pipe string and communicating the firing head with flow bore; and filling the pipe string with a fluid priorto detonation of the gun.

16. The method of claim 15 further including the steps of:

opening the pipe string at point below the packer to the flow of hydrocarbons from the formation to be tested.

17. The method of any of claims 14to 16 further including the steps of:

mounting another perforating gun and firing head on the exterior of the pipe string prior to extending the pipe string into the well; setting another packer to isolate the formation of the first mentioned perforating gun from the formation of said other perforating gun; communicating thefiring head of said other perforating gun with thefluid flow path to the surface; effecting another predetermined pressure greater than thefirst mentioned predetermined pressure through theflow path to thefiring head of said other perfo;ating gun; effecting the another predetermined pressure on one side of a movable member reciprocably disposed in a chamber in thefiring head of said other perforating gun to causethe movable memberto move; and using the movement of the movable memberto actuate said other perforating gun.

18. Method of firing a perforating gun which is suspended within a well on a pipe string, comprising the steps of:

communicating a f low path from the surface to a firing head adjacentthe perforating gun; filling the flow path with a f luid; effecting a predetermined pressure through the flow path to the firing head; lowering a mass through the pipe string to close a passageway through a movable wall reciprocably mounted in a chamberwithin the firing head and to open a valve in the flow path forf luid communication with one side of the movable wall in the chamber; effecting the predetermined pressure on the one side of the movable wall to causethe moveablewall to move; and using the movementof the movablewall for detonating the charges of the perforating gun.

19. The method of claim 18 and further including the steps of:

raising the pressure down the flow path to a level above the predetermined pressure in case the mass fails to close the passageway or open the valve; effecting the additional pressure onto a piston member in the valve; moving the piston memberto open thevalve; and c 13 GB 2 184 214 A 13 effecting the additional pressure and predetermined pressure on the one side of the movablemember.

20. A method of firing a perforating gun in a well, substantially as hereinbefore described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (L) K) Ltd,4187, D8991685. Published by The Patent Office, 25Southampton Buildings, London, WC2A l AY, from which copies maybe obtained.

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