EP2341212A1

EP2341212A1 - Downhole perforation tool

Info

Publication number: EP2341212A1
Application number: EP09180919A
Authority: EP
Inventors: Jørgen HALLUNDBAEK
Original assignee: Welltec AS
Current assignee: Welltec AS
Priority date: 2009-12-29
Filing date: 2009-12-29
Publication date: 2011-07-06
Also published as: WO2011080291A3; WO2011080291A2

Abstract

The present invention relates to a downhole perforation tool for detonation of at least one charge (2) downhole to perforate a casing, the tool having a longitudinal direction (I), comprising an outer face (3), at least one recess (4) provided in the outer face of the tool, at least one charge (2) arranged in the recess (4), a plurality of planes transverse to the longitudinal direction (I) of the tool, and a charge holder part (5) for holding at least part of the charge. The invention furthermore relates to a method for perforating a casing downhole.

Description

Technical field

The present invention relates to a downhole perforation tool for detonation of at least one charge downhole to perforate a casing, the tool having a longitudinal direction, comprising an outer face, at least one recess provided in the outer face of the tool, at least one charge arranged in the recess, a plurality of planes transverse to the longitudinal direction of the tool, and a charge holder part for holding at least part of the charge. The invention furthermore relates to a method for perforating a casing downhole.

Background

Perforation of metal casings in a well is very commonly used when retracting oil from a borehole. Over time, many different designs have been developed which suit individual perforation patterns.
The most recently developed tools in perforation technology are designed with an intention to reduce the risk of the tool getting stuck after detonation of charges, and the outer circumference of the tool housing in the area of the charge has therefore been reduced to ensure that remains of the tool housing after a detonation do not extend further radially outwards than the overall circumference of the tool. Other tools have been designed which improve control of the detonations due to a more secure activation design.
The problem with all known tools is that they have to be redesigned in order to be able to be submerged into a well through a lubricator since the lubricator is often not long enough to enclose the entire perforation tool, and thereby unable to perforate the casing in one run. These tools all need to be shortened, which means that several runs are necessary to perforate the entire casing part which is to be perforated.

Description of the invention

It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide a downhole perforating tool whose outer circumference does not increase after detonation.
Furthermore, it is an object of the present invention to provide a downhole perforation tool which, despite its limited extension in a longitudinal direction, is able to perforate a large area of a casing downhole in one run.
In addition, it is an object of the present invention to provide a downhole perforation tool with a flexible design.
The above objects, together with numerous other objects, advantages, and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a downhole perforation tool for detonation of at least one charge downhole to perforate a casing, the tool having a longitudinal direction, comprising

an outer face,
at least one recess provided in the outer face of the tool,
at least one charge arranged in the recess,
a plurality of planes transverse to the longitudinal direction of the tool, and
a charge holder part for holding at least part of the charge,
wherein at least two charges are arranged in the same transverse plane.

The downhole perforation tool may further comprise a driving unit for moving the charge holder part in the time interval between the detonation of two charges.
This driving unit may have means for moving the charge holder part in the longitudinal direction and/or for rotation of the charge holder part around the longitudinal direction.
Furthermore, several charges may be arranged in the same recess.
The recess may extend in the longitudinal direction and/or in the transverse direction of the longitudinal direction.
Furthermore, the recess may be helical (spiral) and extend along the outer face.
Moreover, the recess may be circular, hexagonal, octagonal or square.
The recess may taper towards the centre of the charge holder part.
Additionally, a plurality of recesses may be arranged in the outer face.
In one embodiment, the charges may extend in the longitudinal direction, the recesses being arranged adjacent to each other with a distance smaller than the extension of the charges in that direction.
Each charge may be closed by a cap for protecting the charge.
Furthermore, the charges may be controlled by a control means.
Moreover, the charges may be connected to the control means by means of wires or wireless communication.
In another embodiment, the wires may be positioned inside the charge holder part.
Furthermore, at least four, six or eight charges may be arranged in the same transverse plane.
The charge holder part may be a solid part with the recesses in the outer face and a bore near its centre.
Furthermore, the recesses may be connected to the centre bore of the charge holder part.
Moreover, one or more bore(s) may be arranged between the recess(es) and the centre bore.
In one embodiment, the charge holder part may be made of a material, the strength of which is able to withstand the pressure from the detonation of the charges, such as metal.
Furthermore, the charge holder part may be reusable and rechargeable when the charges have been detonated.
In another embodiment, the outer face of the tool may have a cross-sectional configuration enabling it to be moved inside a downhole casing.
This cross-sectional configuration may be circular, hexagon, octagonal or the like.
The charge holder part may be part of the outer face of the tool.
Furthermore, a housing/sleeve may be arranged outside the charges, the housing/sleeve comprising openings which are aligned with the charges arranged in the recesses.
Furthermore, the charges may be arranged essentially without any intermediate elements between them and an area to be perforated.
The downhole perforation tool may further comprise an anchor tool for anchoring the tool inside the casing or borehole.
Furthermore, the downhole perforation tool may comprise a stroker tool for moving at least part of the charge holder part in the longitudinal direction of the tool.
This invention also relates to a method for perforating a casing downhole, the method comprising the steps of introducing a downhole perforation tool inside the casing, positioning the tool in a first area to be perforated, detonating one or more charges in the first area, positioning the tool in a second area to be perforated by moving the tool along the casing and/or by rotating the charge holder part of the tool, detonating one or more charges in the second area, performing the steps of positioning and detonating in additional areas to be perforated, and retrieving the tool from the casing.
Finally, the tool may be retrieved from the casing subsequent to the detonation of an area, recharged with new charges, introduced into the casing again, and positioned in a new area to be perforated.

Brief description of the drawings

The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which

Fig. 1 shows a downhole perforation tool according to the invention,
Fig. 2 shows a charge holder part,
Fig. 3 shows a cross-sectional view of a the charge holder part of Fig. 2,
Fig. 4 shows another embodiment of the charge holder part,
Fig. 5 shows yet another embodiment of the charge holder part,
Fig. 6 shows the charge holder part of Fig. 4 without charges,
Fig. 7 shows a cross-sectional view of part of the downhole perforation tool, and
Fig. 8 shows part of another embodiment of the perforation tool.

All these figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.

Detailed description of the invention

The invention relates to a downhole perforation tool 1 for detonation of charges 2 in a predetermined pattern to perforate a casing 15 in a well. The tool 1 is submerged into a casing at a predetermined position, either by means of a driving tool, such as a downhole tractor, or by means of coiled tubing or wireline.
The tool 1 has a control means 8 enabling it to detonate the charges 2 in a desired pattern one by one. Each charge 2 is connected to at least one switch 14 through which the firing of the charges is controlled.
In Fig. 1, the tool 1 is lowered into the casing 15 by means of a wireline. The tool comprises an electrical motor 20, a control means 8, a driving unit 6 and a part holding the charges 5. The tool 1 has a cylindrical shape, and the charges 2 are arranged in the circumference of the tool in a charge holder part 5. Each charge 2 is arranged in a recess 4 spaced apart along the outer face 3 of the tool 1, and as can be seen, several charges are arranged in the same cross-sectional plane p of the tool transverse to its longitudinal direction l.
The charges 2 are arranged in a cavity having an open end facing the casing wall, ensuring that when detonated, each charge only penetrates the casing wall and the fluid in the casing 15 and thus not a tool housing. In this way, each charge 2 may be smaller than a charge which has to penetrate both the tool housing and the casing wall. Due to the fact that the charges 2 are smaller than the charges usually used in prior art tools, they can be arranged closer to one another. However, the charges 2 are still arranged in a pattern with a mutual distance between them which is sufficient to ensure that they do not detonate other charges 2 than intended. In this way, the charges 2 are not necessarily arranged in a pattern identical to the perforation pattern, but may both be positioned closer together in the longitudinal direction l and along the circumference of the outer face 3 of the tool 1.
In the event that the charges 2 are not arranged in a pattern conforming to the perforation pattern, the tool 1 comprises a driving unit 6 for moving the charge holder part 5 in the time interval between the detonation of the charges, allowing the tool to perforate the casing 15 in an optional pattern. The driving unit 6 has means for moving the charge holder part 5 in the longitudinal direction I and/or for rotating the charge holder part around the longitudinal direction of the tool 1.
Having a driving unit 6 makes it possible to arrange the charges 2 in the pattern in which they have the smallest longitudinal and circumferential extension since the driving unit can move the charge holder part 5 in between the detonations. In this way, the perforation tool 1 is still able to perforate the casing 15 in any desired standard or non-standard pattern.
Since the charges do not also have to perforate the tool housing before perforating the casing wall, the detonation capacity of each charge can be substantially reduced, and the charges can be positioned closer together in the tool 1. It is thus possible to minimise the diameter of the tool 1 and/or reduce the length of the tool. When lowering the tool 1 in a subsea well, it first enters into a lubricator.
When using prior art tools, the perforation process often takes a long time since the extension of the lubricator limits the extension of the perforation tool 1. Given that the charges of prior art tools are arranged in a pattern in the charge holder identical to the perforation pattern, the extension of the charge holder of the perforation tool is the same as that of the casing part which is to be perforated. If the casing part to be perforated is 40 feet, and the lubricator has room for a perforation tool having a charge holder of 10 feet, the perforation tool 1 has to be lowered into the well four times in order for the entire 40 feet of casing to be perforated. The tool 1 of the present invention substantially reduces the number of reruns into the well.
As can be seen in Figs. 2 and 3, a channel connects the bottom of each recess 4 to a centre hole in the charge holder part 5, and the charges 2 are thereby connected with the control means 8 and the switches 14 via wiring through the channel. The channels are very narrow, meaning that when one charge 2 is detonated, only the wiring to that charge is blown away, and thus, the wiring to the other charges is not affected.
The charge holder part 5 of Figs. 2 and 3 is a solid cylinder positioned between the recesses 4, the channels and the centre bore 11. Each charge 2 is thus protected by a solid part 10 of the charge holder part 5, meaning that the firing of one charge does not affect the other charges. The recesses 4 extend from the outer face 3 towards the centre hole of the charge holder part 5. The recesses 4 all have rounded bottoms but may otherwise have any suitable shape, such as square, hexagonal, octagonal or another cross-sectional shape. When the casing has a non-circular cross-sectional shape, it is no longer able to rotate in the recess 4.
In some prior art tools, the charge holding part is just a frame structure inside a tool housing, and the charges are thus not protected in the same way as with the present solid tool, meaning that the distance between the charges must be increased in these prior art tools.
Furthermore, in some prior art tools, the diameter of the tool housing has been reduced opposite each charge, so that when the casing is perforated, the diameter of the tool is not substantially increased. With the tool 1 of the present invention, there is no risk of increasing the diameter of the tool when detonating the charges 2 since the charges are fired directly into the casing wall.
In Fig. 4, several charges 2 are arranged in the same recess 4 in the outer face 3 of the tool 1 and spaced apart by a switch 14 so that the charge furthest away from the wireline is fired first, and so on. The recess 4 has a longitudinal extension in the longitudinal direction l of the tool 1 and is cut into the hollow cylindrical charge holder part 5. As can be seen in Fig. 6, several channels are bored into the bottom of the recess 4, enabling connection of the charges 2 and switches to the control means 8 by means of wires. The recess 4 may also extend in the transverse direction of the longitudinal direction l of the tool 1 in a hollow or solid cylinder.
In Fig. 5, the recess 4 has a helical or spiral shape extending around the longitudinal direction l of the tool and extending along the outer face 3 of the charge holder part 5. Each charge 2 is closed by a protective cap 7 to ensure that the well fluid does not penetrate the charge and cause it to malfunction.
As shown in Fig. 7, the charges 2 are positioned very close together. Each recess 4 has a width D which is larger than the distance between the recesses 4 when measured from the edge of one recess to the edge of the adjacent recess.
The charges 2 can be arranged in a variety of patterns in the tool 1, more or less corresponding to the desired perforation pattern. In order to increase the distance between two recesses 4, one row of recesses arranged in the same cross-sectional plane p is displaced in relation to the next row of recesses so that a recess in one row is positioned opposite the middle of two recesses in the next row.
Furthermore, the charges 2 may be arranged decentralized in the charge holder part.
Even though the charges 2 are mainly described as being controlled by means of wires, they could also be controlled wirelessly.
In Fig. 5, two charges 2 are arranged in the same plane p, and in Figs. 1 and 4, eight charges are arranged in the same plane. In another embodiment, more or fewer charges 2 may by arranged in the same transverse plane p.
The charge holder part 5 is made of a material, the strength of which is able to withstand the pressure from the detonation of the charges 2, such as metal.
Due to the fact that the charges 2 are arranged in open recesses 4 in the charge holder part 5, the charge holder part is reusable and rechargeable when the charges have been detonated.
In Fig. 1, the perforation tool 1 and thus the charge holder part 5 have a circular cross-section configuration, however, the cross-sectional configuration may also be square, hexagon, octagonal or the like.
The perforation tool 1 may also have a housing/sleeve arranged outside the charges 2 so that the openings in the housing/sleeve are aligned with the charges arranged in the recesses 4.
The charges 2 are essentially arranged without any intermediate elements between them and an area of the casing wall to be perforated, allowing the detonation ability of the charges to be reduced enough to position them close together in the charge holder part 5.
Furthermore, the charges 2 may be arranged in an outer part of the charge holder part which may be rotatable in relation to for instance an inner part of the charge holder part.
As shown in Fig. 8, the downhole perforation tool 1 may also comprise an anchor tool 12 for anchoring the tool inside the casing 15 or borehole. The tool 1 further comprises a stroker tool 13 functioning as a driving unit 6 for moving at least part of the charge holder part 5 in the longitudinal direction l of the tool. The stroker tool 13 is able to quickly replace the charge holder part 5 along the longitudinal direction l of the tool 1 and to rotate the charge holder part in the time interval between the detonation of the charges.
The perforation process is performed by introducing a downhole perforation tool 1 into the casing 15 and positioning the tool 1 in a first area of the casing to be perforated. The charges 2 are detonated one or several at a time, and the tool is subsequently moved and positioned opposite a second area of the casing 15. This movement may be a movement in the longitudinal direction l of the tool 1 and/or a rotation movement of the tool. The movement may be of the entire tool 1 by means of a downhole tractor or a stroker tool 13, or by adjusting the length of the wireline or of part of the tool, e.g. the charge holder part 5, by means of the stroker tool 13. When positioned in the second area, one or more charges 2 are fired again. When the tool 1 has performed its detonations, it is retrieved from the casing 15. If the perforation process is not concluded, the tool 1 is recharged with new charges introduced into the casing 15 again, and positioned in a new area to be perforated.
Thus, when a predetermined perforation pattern of a casing 15 downhole is to be performed, the downhole perforation tool 1 according to the invention is loaded with charges 2 and lowered into the casing. The tool 1 is positioned in the first detonation area, and some of the charges 2 are detonated so that they perforate the casing 15 directly. Subsequently, the tool 1 is moved longitudinally and/or turned so that the other charges 2 face the casing 15 in the position where detonation is intended. The next step is that the intended charges 2 are detonated so that they perforate the casing directly as well. The above sequences are performed until the predetermined perforation pattern is obtained, or until the tool needs to be recharged. The detonation sequence of the tool 1 may advantageously be set up to detonate in the predetermined perforation pattern of the casing 15 by detonating one or more charges 2 in different transverse planes p and subsequently move and/or rotate the tool 1 and detonate one or more other charges in the same planes as the first detonation sequence and/or in other transverse planes.
By a casing is meant all types of pipes, tubings, tubulars etc. used downhole in relation to oil or natural gas production.
By fluid or well fluid is meant any kind of fluid which may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively.
In the event that the tools are not submergible all the way into the casing, a downhole tractor can be used to push the tools all the way into position in the well. A downhole tractor is any type of driving tool capable of pushing or pulling tools in a well, such as a Well TractorⓇ.
Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.

Claims

Downhole perforation tool (1) for detonation of at least one charge (2) downhole to perforate a casing (15), the tool having a longitudinal direction (l), comprising
- an outer face (3),

- at least one recess (4) provided in the outer face of the tool,

- at least one charge arranged in the recess,

- a plurality of planes (p) transverse to the longitudinal direction of the tool, and

- a charge holder part (5) for holding at least part of the charge,
wherein at least two charges are arranged in the same transverse plane.
Downhole perforation tool according to claim 1, further comprising a driving unit (6) for moving the charge holder part in a time interval between the detonation of two charges.
Downhole perforation tool according to claim 2, wherein the driving unit has means for moving the charge holder part in the longitudinal direction and/or for rotation of the charge holder part around the longitudinal direction.
Downhole perforation tool according to any of the preceding claims, wherein several charges are arranged in the same recess.
Downhole perforation tool according to any of the preceding claims, wherein the recess extends in the longitudinal direction and/or in the transverse direction of the longitudinal direction.
Downhole perforation tool according to any of the preceding claims, wherein each charge comprises a cap (7) for protecting the charge.
Downhole perforation tool according to any of the preceding claims, wherein the charges are controlled by a control means (8).
Downhole perforation tool according to any of the preceding claims, wherein the charges are connected to the control means by means of wires (9) or wireless communication.
Downhole perforation tool according to any of the preceding claims, wherein the wires are arranged inside the charge holder part.
Downhole perforation tool according to any of the preceding claims, wherein at least four, six or eight charges are arranged in the same transverse plane.
Downhole perforation tool according to any of the preceding claims, wherein the charge holder part is a solid part (10) with the recesses in the outer face and a bore near its centre.
Downhole perforation tool according to any of the preceding claims, wherein the outer face of the tool has a cross-sectional configuration enabling it to be moved inside a downhole casing.
Downhole perforation tool according to any of the preceding claims, further comprising a stroker tool (13) for moving at least part of the charge holder part in the longitudinal direction of the tool.
Method for perforating a casing downhole, the method comprising the steps of:
- introducing a downhole perforation tool according any of the claims 1 to 13 inside the casing,

- positioning the tool in a first area to be perforated,

- detonating one or more charges in the first area,

- positioning the tool in a second area to be perforated by moving the tool along the casing and/or by rotating the charge holder part of the tool,

- detonating one or more charges in the second area,

- performing the steps of positioning and detonating in additional areas to be perforated, and

- retrieving the tool from the casing.
Method according to claim 14, wherein the tool is retrieved from the casing subsequent to the detonation of an area, recharged with new charges, introduced into the casing again, and positioned in a new area to be perforated.