WO1993020330A1

WO1993020330A1 - Apparatus for detonating well perforators

Info

Publication number: WO1993020330A1
Application number: PCT/GB1993/000664
Authority: WO
Inventors: John L. Schneider; Hugo Miguel Barcia; Leslie Eric Jordan
Original assignee: Phoenix Petroleum Services Ltd.
Priority date: 1992-03-30
Filing date: 1993-03-30
Publication date: 1993-10-14
Also published as: NO934256D0; NO934256L

Abstract

A pressure-activated head for detonating a gun for perforating a well bore casing is suspended on a tubing string for lowering down the well. The head includes a detonating pin (24) biased towards a detonator (16), but restrained by dogs (32) maintained in position by sleeve (31) until detonation is required. Detonation is effected by causing or allowing a pressure differential to develop across pistons (64, 68). When a predetermined differential pressure is reached piston (64) moves to shear pins (35) carrying with it piston (68) until the latter meets the shoulder on cylinder (62). Subsequent travel of the second piston (68) is sufficient to ensure that the consequent displacement of the sleeve (31) is adequate to release the dogs (32) fully.

Description

APPARATUS FOR DETONATING WELL PERFORATORS

This invention relates to detonating apparatus for detonating guns, particularly tubing conveyed perfor¬ ating guns, for explosively perforating the well-bore casing, or perforating guns lowered on a slick line for perforating the tubing string or drill pipe string of wells such as, for example, oil, gas, water and steam wells.

Perforating guns containing explosive charges are frequently positioned within the casing or string of oil wells. Detonating apparatus for detonating a gun for perforating a well bore casing or string commonly comprises a detonating pin biased towards a detonator, restraining means for restraining the pin from movement until detonation is required, and pressure-actuated release means comprising displaceable means arranged for displace¬ ment to release the restraining means under the influence of a predetermined differential fluid pressure, the dis¬ placeable means being fixed against movement by shear pins, which are sheared when detonation is required by shear forces generated when said predetermined pressure is reached. A spring or other energy storage means may be provided to assist subsequent movement of said means to a position in which the retaining means are released.

The displaceable means are typically connected to a piston rod of a piston and cylinder assembly, the piston having first and second fluid reservoirs on res¬ pective sides thereof within the cylinder, with movement of the piston being caused by achievement of said differen¬ tial pressure between the reservoirs. A drawback of such known arrangement is that, after the shear pins have been sheared, sufficient longi¬ tudinal movement of the release means to release the restraining means is not available.

The present invention seeks to overcome the above- described drawback by separating the shearing and displace- ^• ment functions of the pressure-actuated release means.

According to the present invention, the pressure- actuated release means include a cylinder, and a first piston and a second piston arranged for sliding movement therewithin, the movement of said pistons being caused by achievement of a differential pressure thereacross, the travel of said first piston being limited to a distance sufficient to allow shearing of the shear means when detonation is required, and the subsequent travel of the second piston being sufficient to ensure that the consequent displacement of the displaceable means is adequate to release the restraining means fully.

One embodiment of the invention is described, by way of example only, with reference to the accompanying drawings, in which Figures 1, 2 and 3 are sections through a plane including the longitudinal axis of successive lengths of detonating apparatus, according to the inven¬ tion, for detonating tubing conveyed perforating guns.

In the drawings, a tool housing 10 is joined at its upper end, i.e. at the left hand of Figure 1, to the bottom length of a tubing string (not shown) fitted with a ported sub-assembly by a screw thread 11 of an upper outer connector 12. The lower end of the tool 10, i.e. at the right hand of Figure 3, is joined to a perforating gun assembly 13 by a lower threaded connector 14. The perforating gun assembly 13 contains a perfor¬ ating gun (not shown) of known kind, in which an array of outwardly-facing charges of explosive are retained, to be exploded by combination of a boosted primer cord 15 which is itself ignited by a detonator 16 of the kind which detonates on impact. The primer cord 15 and deton¬ ator 16 are retained on the axis of and within the lower connector 14. The booster is designated 16a_.

A co-axial cylinder member 17 is screwed at its lower end to the lower connector 14 and at its upper end to an inner connector 18 which is screwed to the lower end of a lower piston housing 60 which is screwed to an upper piston housing 62. At its upper end the piston housing 62 is connected through a choke housing 20 to an upper reservoir housing 21 which is in turn screwed to an upper connector 22-. The reduced diameter upper end portion of the connector 22 is received in the recessed end portion of an upper inner connector 23 which is a sliding fit in the upper outer connector 12. Throughout the apparatus, O-ring seals are used where appropriate.

The detonator 16 is arranged to be fired by a detonator pin 24, slidable in a central bore 25 in the lower end of the cylinder member 17, and having a pointed end 26. The space 27 between the detonator 16 and the detonator pin 24 is at atmospheric pressure, while the left hand (upper) end of the detonator pin 24 is vented to the pressure of the well bore outside the tool 10 by passages 28,29,30 through the lower connector 14, the cylinder member 17 and an inner sleeve 31, respect¬ ively. The pressure on the detonator pin 24 urges it downwards towards the detonator 16, but such movement is prevented by dogs 32, which engage in a groove in the detonator pin 24 and abut an inner face 33 of the inner sleeve 31. The outer cylindrical face of the sleeve 31 is a sliding fit in a bore of a collar 34 abutting the inner connector 18. The sleeve 31 is secured to the collar 34 by shear pins 35.

A lower central rod 36 is screwed to an upper central tube 40, which is slidable through a central bore of the choke housing 20.

The space within the upper chamber housing 21 between the ends of the choke housing 20 and the upper connector 22 forms an upper reservoir 42 which is divided into an upper part 42a. and a lower part 42b_ by a floating piston 43. The piston 43 separates well fluid above it from hydraulic oil below it and allows expansion of the latter. The space within the piston nousing 19 between the choke housing 20 and the piston 41 forms a middle reservoir 44; and the space between the inner connector 18 and the piston 41 a lower reservoir 45. A passage 46 through the choke housing 20 connecting together the upper reservoir 42 with the middle reservoir 44, has a central choke orifice 47 protected by filters 48 fitted one at each end of the passage 46.

A filtered passage 49 through the lower rod 36 and a passage 50 through the upper rod 40 connect with a passage 51 in the choke housing 20, thereby permitting communication between the middle reservoir 44 and the lower reservoir 45. A choke orifice 52 smaller than the orifice 47, is provided in the passage 51 and is protected by a filter 53.

A passage 54 through the upper outer connector 12 communicates with a passage 55 through the upper inner connector 23 and thence with an axial bore 56 of the upper connector 22; well pressure is thus freely communi- cated to the reservoir 42a_.

A primer cord 57 runs from a position next to a booster at the bottom of the primer cord 15 to a connec¬ tion at the top of the upper outer connector 12 from which a further length 58 of primer cord leads to a firing head (not shown) .

The top of the upper housing 62 is internally recessed to accommodate an annular outer piston 64, the upward travel of which is limited by an internal shoulder 66 on the upper housing 62. An inner annular piston 68 is slidably received within the outer piston 64 which has an internal projection clamped between the lower central rod 36 and the upper central tube 40 so that movement of the inner piston 68 causes corresponding movement of the retaining sleeve 31. Upward movement of the outer piston 64 is transmitted to the inner piston 68 by virtue of the inter-engaging shoulders 70, but subsequent relative upward movement of the inner piston 68 is permitted. Sealing between sliding surfaces is ensured by O-rings in the conventional way.

To perforate the casing the tubing conveyed per¬ forating guns are fired by ignition of the detonator 16 through release of the detonator pin 24. This may be achieved by various methods, two of which are now described.

In one method, a packer is set between the well bore casing and a tubing string equipped with a tester valve. Annulus pressure above the packer is increased to open the tester valve, thus communicating lower pressure already obtaining in the upper part of the tubing string where the tester valve to the lower part of the tubing string below the tester valve; and thus also in the well bore around the detonating head. This reduction in ambient pressure causes a corresponding reduction in the pressure in the upper part 42a. of the upper reservoir 42 by virtue of the communication afforded by the passages 54,55 and the bore 56. The pressure reduction is passed on to the reservoir 42b_ through the floating piston 43, causing oil to bleed from the middle reservoir 44 through the passage 46 and choke 47. As a consequence of the volumes of the reservoirs 42,44, the compressibility and viscosity of the oil therein, the action of the choke 47, and the pressure differential, the pressure in the middle reservoir 44 falls more slowly than well bore pressure, the rate being determined by the above factors. Furthermore, the pressure in the lower reservoir 45 bleeds through the bore 50 and passage 51 even more slowly than that in the middle reservoir 44 because the choke 52 is smaller than the choke 47. Thus, the pistons 64,68 are subject to a pressure differential causing an upward force thereon.

As the pressure differential across the pistons 64 and 68 increases a point is reached, at which the pistons move together to shear the shear pins 35 (Fig. 3) . On shearing the movement of the outer piston 64 is arrested by abutment with the shoulder 66. The length of travel, although short, is adequate to ensure shearing of the pins 35, and, as the overall diameter of the dual piston assembly is maximized, the greatest possible shear¬ ing force is generated for a given pressure differential on the pistons 64,68.

Because only a small amount of the stored energy is used by the piston 64 there is ample energy left to drive the piston 68 sufficiently upwards for the sleeve 31 completely to release the dogs 32. The movement of the rod 36 and sleeve 31 is assisted by the spring 39; however, in applications where a large pressure differen¬ tial is available the spring 39 may be dispensed with, - 1 -

and the energy stored in the compressed fluid used as the sole propelling force.

It will be appreciated that there is also a delay between the time at which the shear pins 35 are sheared and the point at which the detonating piston 24 is re¬ leased.

When the bottom of the sleeve 31 clears the dogs 32, the latter fall away to release the detonator pin 24; the point 26 of the latter then strikes the detonator 16 as the pin 24 is driven by the differential between well bore pressure acting above it and atmospheric pressure on its lower end. Reduction of the tubing pressure may be achieved by running the detonating head with a DST type string and applying pressure to the annulus to open a ball valve to allow communication of the well bore in the region of the tool 10 with a lower hydrostatic pressure above the valve, as previously indicated.

In an alternative method of firing the guns, where it is not desirable or practicable to reduce well bore pressure around the detonating head from ambient, it is possible to obtain detonation by applying additional tubing pressure. Thus, the pressure around the apparatus head and hence in all the reservoirs is increased slowly. The increase in tubing and ambient well bore pressure is then removed, and the apparatus operates as if the well bore pressure had been lowered from its normal value in the manner previously described.

Another method of operation of the detonating head involves the use of nitrogen and the manipulation of various tester and circulating valves in the system, thereby creating the necessary pressure drops required to actuate the detonating head. In a further method of operation the detonating head is run down the well on a tubing string partly filled with fluid, and equipped with a packer and tester valves. After pressure testing the tubing string with nitrogen, but before bleeding off the nitrogen, the tester valve is opened by the application of annulus pressure which allows the well bore around the detonating head to be pressurised by the nitrogen pressure applied to the tubing string. The tester valve is then closed by bleeding off the annulus, ^• and nitrogen above the tester valve is slowly bled off at the surface, during which time the head is pressurised as previously described. When the tester valve is opened by pressurising the annulus, the immediate pressure drop around the head causes the guns to be detonated.

The advantage of using gas pressure (for example nitrogen pressure) is that, although more expensive, it is easily removable by venting, whereas a liquid has to be displaced.

If for any reason the detonator 16 fails to go off the perforating guns may be fired by actuating the firing head at the upper end of the primer cord 58. If the guns fail to detonate the whole detonating head can be rendered safe by allowing well bore pressure to reach the atmospheric chamber below the detonating pin 24 through the route of the primer cords 58,57, It will be appre¬ ciated that the primer cords 57,58 burn out when the apparatus works normally.

Preferably a shaped charge is interposed between the detonator or high temperature initiator (HTI) 16 and the top of the booster 16a_ so that if the charge or the HTI 16 fails a metal barrier will not be breached; if the charge and the HTI 16 do detonate then it may be assumed that perforation has occurred. This arrangement prevents the destruction of components any further back.

Although the differential pressure firing system has been described as run above the guns, it may also run below the guns.

In a modification of the above-described embodiment the system may be used to perforate a tubing or drill pipe string by running it down the string on a slick line, and increasing the pressure in the string to cause detonation.

Claims

CLAIMS :

1. Detonating apparatus for detonating a gun (13) for perforating a well bore casing or a tubing or drill string, the apparatus being for suspension respectively on a tubing string or slick line lowered down the well, and comprising a detonating pin (24) biased towards a detonator (16) , restraining means (32) for restraining the pin (24) from movement until detonation is required, pressure-actuated release means (36,41) comprising dis¬ placeable means (31) arranged for displacement to release the restraining means (32) under the influence of a pre¬ determined differential fluid pressure, the displaceable means (31) being fixed against movement by shear means

(35) which are sheared when detonation is required by shear forces generated when said predetermined differential pressure is reached, characterised in that the pressure- actuated release means include a cylinder (60) , and a first piston (64) and a second piston (68) arranged for sliding movement therewithin, the movement of said pistons

(64,68) being caused by achievement of said differential pressure, the travel of said first piston (64) being limited to a distance sufficient to allow shearing of the shear means (35) when detonation is required, and the subsequent travel of the second piston (68) being sufficient to ensure that the consequent displacement of the displaceable means (31) is adequate to release the restraining means (32) fully.

2. Apparatus as claimed in claim 1, in which the first piston (64) is an annular outer piston (64) arranged for sliding movement within the cylinder (60) , and the second piston (68) is an inner annular piston (68) arranged for sliding movement within the outer piston (64) .

3. Apparatus as claimed in claim 1 or 2, in which initial movement of the first piston (64) is transmitted to said second piston (68) by engagement means (70).

4. Apparatus as claimed in claim 1, 2 or 3, in which the pistons (64,68) have a first fluid reservoir (45) on one side thereof within the cylinder (60) and a second fluid reservoir (44) on the other side thereof within a cylinder (62), the movement of the pistons (64,68) being caused by achievement of said differential pressure between the reservoirs (45,44).

5. Apparatus as claimed in any preceding claim, in which pressure control means (47,52) are provided for causing or allowing said differential pressure to be developed within the apparatus over a period of time.

6. Apparatus as claimed in claims 4 and 5, in which the pressure control means (47,52) are arranged to allow fluid in the second reservoir (44) to bleed through a restrictor orifice into a third, variable-volume reservoir

(42).

7. Apparatus as claimed in claim 6, in which the first and second reservoirs (44,45) are connected by a smaller restrictor orifice (52) which allows fluid to flow from the second reservoir (44) into the first reservoir (45) to allow it to be pressurised, and to flow from the first (45) to the second reservoir (44) while fluid is flowing from the second (44) to the third reservoir (42) , but at a slower rate than the rate of flow from the second (44) to the third reservoir (42) .

8. Apparatus as claimed in claim 6 or 7, in which the third, variable volume reservoir (42) comprises a cylinder (22) and a free-floating piston (43) , the position of one face of which within the cylinder (22) defines defines the volume of the reservoir, and the other face of which is exposed to well bore pressure.

9. Apparatus as claimed in any preceding claim, in which the displaceable means (31) are resiliently loaded (39) to assist subsequent movement of said means (31) to a position in which the restraining means (32) are released.

10. Apparatus as claimed in any preceding claim, in which the restraining means (32) comprise latching members (32) engageable with the detonating pin (24) and the displaceable means (31) include a displaceable element (31) for maintaining the latching members (32) in position.