EP0046114A1 - Perforation apparatus for boreholes - Google Patents

Abstract

The device comprises an elongated support (22) formed by a series of sections with planar faces and explosive charges (23) mounted perpendicular to the planar faces. Detonating cords are connected to the charges for their ignition. Each section of the support has two close fixing holes adapted to receive respectively the rear parts of two loads mounted in opposite directions on either side of this section. The support is formed by a tube crushed transversely so as to form the sections with flat faces. Spacers are inserted between each load and the support for large diameter casings. The load envelopes have a ceramic cover and a spun steel body which flourishes under the effect of the explosion instead of breaking into pieces. Device with high charge density for the preparation of gravel screens.

Description

The invention relates to perforation devices for the production of boreholes and more particularly to a hollow charge device of the semi-recoverable type.

The semi-recoverable perforation devices comprise an elongated support along which are fixed encapsulated hollow charges directed radially. The assembly is lowered in a borehole to the depth where it is desired to perforate the casing and, after firing, the support and, if necessary, the parts of envelopes of charges which have remained fixed to the support, are brought up to the surface. The parts of the envelopes broken by the explosion constitute debris which remains in the borehole but this quantity of debris is limited thanks to the recovery of the support.

The supports used are often in the form of an elongated bar comprising fixing holes intended to receive the loads. Such devices are described, for example, in United States Patent No. 2,756,677 (J.J. McCullough). For certain applications it is desirable to make perforations of large diameter and in large numbers. Such an application is for example the preparation of a tubing producing area for the constitution of a gravel screen (gravel pack). These devices with high charge density impose numerous constraints which until now have not been resolved by the techniques of the prior art.

Supports have been made consisting of a helically twisted bar to obtain loads directed in several radial directions. The support described in the already mentioned patent does not allow a high density of charges to be mounted by its very design and as a result of its lack of robustness. Such a support is twisted along its length after fixing the loads. As the holes are also deformed by torsion, it is possible that the maintenance of loads is not ensured with sufficient firmness. In addition, if the known devices are used for casings of different diameters, the same quality of performance is not obtained everywhere. In casings of large diameter, only the loads which come to bear on the casing exhibit good performance. The other charges, the front face of which is relatively far from the wall. lose a considerable part of their effectiveness. In the perforation devices intended for the preparation of gravel screens, it is particularly important to obtain perforations of large diameter (2 cm for example) as evenly spaced as possible _. in all directions. With the known devices which make it possible to reach, for example, a density of four strokes per 30 cm, one could obtain a double density by lowering two of these devices to the same depth but we do not know how to interpose them to make perforations with a regular distribution.

It is therefore desirable to produce perforation devices capable of receiving a high density of charges and having excellent robustness with, however, a low manufacturing cost. This low cost is important because in general, after a shot, the supports are deformed or made fragile and cannot be reused.

The object of the invention relates to a perforation device in a borehole which is particularly desirable for producing a high density of perforations of large diameter with regular distribution.

The object of the invention also relates to a perforation device whose load carrier is particularly simple and robust. A disadvantage of known devices of the semi-recoverable type is the large amount of debris left in the borehole after firing. Indeed, the explosion breaks into fragments almost all of the envelopes of charges leaving on the support only the part of these envelopes, fixed in the support. This drawback is particularly troublesome in the case of devices with a high charge density.

Another object of the invention is to reduce the amount of debris obtained with such a perforating device.

According to the invention, a perforation device for soundings comprises: an elongated support formed by a series of sections with planar faces angularly offset around the longitudinal direction and pierced with longitudinally spaced fixing holes and explosive charges having sealed envelopes fixed in the fixing holes with their axes substantially perpendicular to the planar faces. Electrically controlled detonation means are connected to the shells for their ignition. Each support section has two fixing holes spaced, longitudinally, by a distance less than the maximum diameter of a load perpendicular to its axis, and the envelopes of the loads have rear parts of reduced diameter adapted to engage in the holes of fixing for mounting two loads in opposite radial directions on each of said sections.

Preferably the support is formed by a tube which is successively crushed edge to edge in predetermined radial directions to form the sections with planar faces.

The detonation means comprise an electrically controlled detonator to detonate two detonating cords respectively connected one to a first series comprising a charge from each section and the other to a second series comprising the other charge from each section. The two cords are ignited simultaneously thanks to an explosive relay and possibly synchronized by other explosive relays.

The envelope of each load comprises a metal body offering sufficient resistance for fixing and a cover made of a brittle material, for example ceramic. The rear part of the body of the charges has a slot for the passage of the ignition cord.

The body of each load envelope is made of spun steel having sufficient resistance in the direction of the axis of the load and less resistance perpendicular to this axis so that for the most part the bodies of the loads open under the effect of the detonation while remaining attached to said support by their rear part after firing.

For large boreholes, spacers are placed between the support and the base of the load envelopes. Each spacer comprises a reinforced annular part adapted to receive this rear part. Inside said annular part, the spacer comprises a transverse part adapted to be inserted in the passage passage of the cord when the rear part of a load envelope is placed in the spacer, in order to reduce the volume. of sounding fluid inside the annular part while ensuring a suitable transmission of the explosion of the cord to the load thanks to a good application of this cord against the envelope of the load.

• - la figure 1 est une vue d'ensemble d'un dispositif de perforation selon l'invention représenté dans un sondage';
• - les figure 2A et 2B sont une vue en coupe partielle du dispositif de la figure 1 ;
• - la figure 3 est une coupe suivant 3 - 3 de la figure 2A ;
• - la figure 4 est un détail du support des charges de la figure 1 ;
• - la figure 5 est une vue en perspective du support de charges ;
• -.les figures 6 et 7 sont respectivement une coupe longitudinale et une vue arrière d'une charge encapsulée -utilisée dans le dispositif ;
• - les figures 8 et 9 sont des coupes transversale et longitudinale d'une entretoise utilisée pour les tubages de diamètre élevé ; et
• - la figure 10 est une coupe transversale après le tir d'un mode de réalisation du dispositif de perforation selon l'invention.

The characteristics and advantages of the invention will emerge more clearly from the description which follows, given by way of nonlimiting example with reference to the appended drawings in which:

• - Figure 1 is an overview of a perforation device according to the invention shown in a survey ';
• - Figures 2A and 2B are a partial sectional view of the device of Figure 1;
• - Figure 3 is a section along 3 - 3 of Figure 2A;
• - Figure 4 is a detail of the load carrier of Figure 1;
• - Figure 5 is a perspective view of the load carrier;
• - Figures 6 and 7 are respectively a longitudinal section and a rear view of an encapsulated load -used in the device;
• - Figures 8 and 9 are cross-sectional and longitudinal sections of a spacer used for casings of large diameter; and
• - Figure 10 is a cross section after firing an embodiment of the perforation device according to the invention.

Referring to Figure 1, a perforation device 11 suspended from the end of a cable 12 is shown in a borehole 13 coated with a casing 14 which passes through formations 15. To put into production a certain zone containing hydrocarbons , we want to prepare this area for the installation of a gravel screen and, to do this, punch a large density of large diameter holes in this area. The perforation device 11 produced for this result is fixed to a conventional cable head 16 by means of a detector 17 of casing joints making it possible to pinpoint the depths. The perforation device comprises an upper head 18, an adapter 20, one (or more) connection member 21, one (or more) support 22 for loads 23 and a lower end piece 24.

Referring to Figures 2A and 2B, the upper head 18 of cylindrical shape carries a thread 26 allowing its attachment to the lower end of the detector 17 of casing joints. An electrical connector 27 mounted in an isolated and sealed manner in the axis of the head is connected at its lower part to an insulated conductor 28. The head 18 is fixed for example by screws 30 to the adapter 20 formed by a sleeve 31 eccentrically welded to a plate 32. Lateral reinforcements 33 are welded between the sleeve 31 and the plate 32. It is preferable that the head 18 is eccentric in the borehole so that the joint detector 17 is close to the wall of the casing 14 and thus provide a better signal. The plate 32 is connected to the support 22 by the connection member 21. This connection member 21, shown in more detail in FIG. 3, is formed by two half-shells 35 and 36 fixed to one another by screws 37. Each half-shell (for example 35) is formed by a segment of angle iron whose wings are rounded and on which is welded a spar 40 of square section so that the two half-shells after mounting allow a limited angular movement between the head 18 and the support 22. Each half-shell further comprises a projection transverse 41 on which can be fixed a detonating cord or an explosive relay and the electrical conductors.

The support 22, also shown in FIGS. 4 and 5, comprises a series of sections with planar faces angularly offset by 90 ° around the longitudinal direction AA '. Each section (see Figure 4) is pierced with two fixing holes 44-45 longitudinally spaced to receive the rear of the loads. Each fixing hole such as 44 has two transverse flats 46, 47 and two oblique flats 48, 49 to prevent the corresponding load from rotating about its axis. The distance d between the centers of the two fixing holes 44 and 45 of a section is much less than the maximum diameter of a load taken perpendicular to its axis in order to allow a high density of loads. The loads are then mounted with opposite directions on either side of each section. Preferably the holes 44 and 45 are as close together as possible while leaving between them a minimum metal strip sufficient to allow good fixing of the loads. In one embodiment, the distance d was approximately 2 cm for charges of diameter approximately 5 cm, the metal strip left between the two holes being 8 mm wide.

The support 22 (Figure 5) is made from a steel tube of suitable diameter (4 cm in the example above) crushed in two radial directions so as to form successive sections with flat faces. To do this, place the tube under a press to crush a section with a force of about 100 tonnes and then advance the tube a section length, by rotating it 90 ° around its axis before crushing the next section. The fixing holes are then cut by punching.

Before introducing charges into the fixing holes of the support, a first detonating cord 62 is placed (FIG. 2A) in the slots 60 of a first series of charges formed by the upper charge of each section, and a second detonating cord 63 in the slots 60 of a second series of loads comprising the other (lower) load of each section. Each detonating cord (62-63-) is arranged in a helix around the support. And extends downwards to an explosive relay 64. The explosive relay 64 connected via another detonating cord 65 to a detonator 66 has the purpose of igniting the two cords 62 and 63 simultaneously. The detonator 66 comprises two electrical firing wires 67 and 68 connected upwards along the support 22, one to the insulated conductor 28 and the another to a second conductor 70 connected to ground. The detonator 66, the detonating cords, and consequently all of the charges 23 are ignited by sending a suitable electric current between the connector 27 and the ground via the cable 12.

Conventionally, it is preferable that the firing takes place from the bottom up. Indeed, with a reverse firing direction, a partial failure of the device would result in a stack of debris on the lower loads not pulled, which could jam the device in the casing when it is brought to the surface.

To obtain perforations over a long length, several supports 22 can be fixed end to end by connection members 21. So that the detonation of the two cords 62 and 63 remains simultaneous, a relay is inserted at each connection member 21 explosive which, at the start of each support 22, synchronizes the detonation of these two cords.

The support 22 is fixed to the lower end piece 24 by a connecting member 71 identical to the member 21 of FIG. 3. The end piece 24 is constituted by a tube 72 crushed at its upper part to present a flat connection section 73 adapted to be placed in the connecting member 71. Windows 74 are cut from the tube and a plug 75 is welded at its lower end. Three rods 76 are welded at their ends to the top and bottom of the tube 72 so that their middle parts are distant from the axis and center the bottom of the device in the casing. The detonator 66 is placed inside the tube 72.

Each load 23 shown in more detail in Figures 6 and 7 comprises a metal body 52 and a ceramic cover 53 mounted in leaktight manner on the body. The body is made of metal to be securely attached to the support. The cover is made of sintered alumina to be split into small debris by explosion. The body 52 of axis B.B 'contains an explosive bar 50, the front face of which is hollowed out in the shape of a cone covered with a metallic coating 51.

The body 52 comprises a rear part 56 (or foot) of reduced section connected to a cylindrical front part 55 by a frustoconical part 54. The foot 56, the section of which is complementary to that of the fixing holes, comprises two opposite flats 57, 58. In the foot 56 are cut a slot 60 for the passage of a detonating cord and a transverse hole 61 adapted to receive a locking pin. Preferably, the slot 60 which extends as far as the frustoconical part 54 is inclined at approximately 45 ° relative to the plane of the flats 57, 58. The body is produced by spinning, that is to say by plastic deformation of a steel cylinder under the action of a punch moved by a suitable force in the direction of the axis of the body. This spinning is carried out so as to produce a body having an anisotropic mechanical resistance, that is to say a better resistance in the direction of the axis B.B 'of the load than perpendicular to this axis. In this way, under the effect of the explosion, the body 52 breaks along longitudinal lines and expands while deviating from the axis but remains attached to the foot 56 as shown in FIG. 10.

The steel used must have sufficient strength and malleability so as not to break into pieces under the effect of the explosion. Good results have been obtained with low brittle steels such as XC 32F, XC 18F and 20 MB5. Appropriate heat treatments can improve the desired qualities of the steel chosen.

A perforation device as shown in FIGS. 2A and 2B is suitable for a given series of casings such as, for example, casings with an outside diameter of 17.8 cm (7 inches). To perforate casings of different diameter such as casings with an outside diameter of 24.5 cm, the same support 22 is used but the loads 23 are mounted on this support by means of spacers to reduce the distance between the casing and the front side of the loads. Such a spacer 80 represented in FIGS. 8 and 9 comprises an annular part 81 reinforced in thickness, in which the foot 56 fits with a load envelope, and a rear part 82 of reduced cross section complementary to that of the holes fixing 44 or 45 of the support 22. The annular part 81 has a transverse hole 83 adapted to receive a locking pin 85 (FIG. 10) for fixing the foot 56 of a load in the spacer. The rear part 82 has a transverse hole 84 adapted to receive a locking pin 86 for fixing the spacer on the support 22.

Inside the annular part 81, a transverse part 87 is produced which is adapted to be inserted in the slot 60 for passage of the detonating cord, when the foot of an envelope is placed in the spacer 80. The face before this transverse part 'maintains the detonating cord over its entire length at the bottom of the slot 60, thus ensuring proper transmission of the detonation of the cord to the explosive bread of the charge. In addition, the presence of this transverse part minimizes the volume of fluid inside the spacer. Without this transverse part, the spacer would contain a large volume of fluid filling the slot 60 for passage of the cord. This fluid would then transmit the explosion to the walls of the spacer at the risk of bursting the latter and lose in the survey the foot of the load envelope. In large boreholes, where these spacers are necessary, the above embodiment therefore makes it possible to considerably reduce the amount of debris left in the borehole.

The embodiment which has just been described can obviously be the subject of numerous variants without however departing from the scope of the invention.

Claims (13)

1. Perforation device for soundings comprising: - an elongated support formed by a series of sections with planar faces angularly offset around the longitudinal direction and pierced with longitudinally spaced fixing holes; - explosive charges having sealed envelopes fixed to said support in the fixing holes with their axes substantially perpendicular to the flat faces; and - detonation means electrically controlled and connected to said charges to ignite said charges; characterized in that each support section has two longitudinally spaced fixing holes, of a distance between centers less than the maximum diameter of a load perpendicular to its axis, and in that the envelopes of the loads have rear portions of diameter reduced adapted to engage in the fixing holes so as to mount two loads in opposite radial directions on each of said sections. 2. A perforation device according to claim 1, characterized in that said support is formed by a metal tube, the said sections of which are made by crushing edge to edge of the successive parts of the tube in predetermined radial directions. 3. A perforation device according to one of claims 1 and 2, characterized in that two successive sections of said support are offset by 90 ° around the longitudinal direction so as to obtain explosive charges oriented in four radial directions at 90 °. 4. Perforation device according to one of claims 1 to 3, characterized in that the envelope of each load comprises a metal body offering sufficient resistance for fixing in a hole in the support and a fixed cover in front of the body and made of a brittle material to reduce the size of debris after explosion of said charge. 5. A perforation device according to claim 6, characterized in that said cover is made of ceramic. 6. A perforation device according to one of claims 4 and 5, characterized in that said load body is made of spun steel having better breaking strength in the direction of the axis of the load than perpendicular to this axis , so that for the most part, said bodies open out under the effect of the detonation while remaining attached by their rear part to said support after firing. 7. A perforation device according to one of claims 1 to 6, characterized in that it comprises removable spacers capable of being interposed between the charges and said support for perforating boreholes equipped with casings of large diameter with reduced clearance between the front parts of the loads and the casing. 8. A perforation device according to claim 7, characterized in that it comprises several types of removable spacers of different predetermined lengths for boreholes equipped with casings of different diameters. 9. A perforation device according to one of claims 7 and 8 in which the rear part of each charge comprises a passage slot for a detonating firing cord, characterized in that each of said spacers comprises an annular part adapted to surround the rear part of the body of a load, and, inside this annular part, a transverse part adapted to engage in said slot for passage of the cord, when the rear part of a load is placed in the spacer, in order to reduce the volume of fluid inside the spacer, while ensuring proper application of the cord against the body of the load. 10. A perforation device according to claim 9, characterized in that said annular part of each spacer has a reinforced thickness. 11. A perforation device according to one of claims 1 to 10, characterized in that said detonation means comprise an electrically controlled detonator for igniting two detonating cords respectively connected one to a first series of charges comprising a charge of each section and the other to a second series of charges comprising the other charge of each section. 12. A perforation device according to claim 11, characterized in that it comprises an explosive relay triggered by the detonator for the simultaneous firing of the two detonating cords. 13. A perforation device according to claim 12, characterized in that it comprises several explosive relays longitudinally spaced along the support and to which are connected the two detonating cords to maintain the simultaneous detonation of the two detonating cords.

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