NO347771B1

NO347771B1 - A hole forming tool and method of forming a plurality of holes in a tubular wall

Info

Publication number: NO347771B1
Application number: NO20190372A
Authority: NO
Inventors: Morten Lerbrekk; Sigurd Goa
Original assignee: Ti Teknologi As
Priority date: 2016-09-09
Filing date: 2019-03-19
Publication date: 2024-03-18
Also published as: NO20190372A1; WO2018048311A1; GB2568432A; GB2568432B; NO20161434A1; GB201903691D0

Description

A hole forming tool and a method of forming a plurality of holes in a tubular wall

Field of the invention

The invention concerns the field of producing hydrocarbons from a subterranean reservoir. More specifically, the invention concerns a tool for forming a plurality of holes in a tubular, as specified in the preamble of claim 1, and a method of forming a plurality of holes, as specified by the preamble of claim 14.

Background of the invention

Hydrocarbon fluids such as oil and natural gas are obtained from subterranean geologic formations, referred to as reservoirs, by drilling wells that penetrate the reservoirs. Hydrocarbon wells for the exploitation of oil and/or gas from a reservoir normally consist of an upper and outer conductor, which forms the base of the well, an upper casing arranged into and in extension of the conductor, and further down in the well more casings which are arranged into and overlaps the above casing. A production tubing string is located in the middle of the well for transporting petroleum from the bottom of the well to the earth<'>s surface or – in the case of a subsea well – to the seabed. Annuli will then be formed between the different casings.

The use of cementing operations in the extraction of hydrocarbons from subterranean reservoirs is well known. In that context, cementing operations usually mean the preparation and pumping, from an uphole location, cement into one or more zones in a subterranean bore. Cement is widely used as a barrier substance in subterranean wells, to form a seal between nested casings and between the outer well casing and the surrounding formation (as a part of the well completion), and as a plugging substance inside liners or/and in annuli between downhole tubulars (e.g. when the well is to be plugged and abandoned).

In plugging operations, it is important to place the plugging substance (e.g. concrete, resins, epoxy) as accurately as possible in designated sections in the annuli between downhole tubulars (or between a tubular and the surrounding formation). The plugging substance is normally introduced into the well via production tubing, and is placed in the adjacent annulus through holes in the liner or through milled-out sections of the liner.

A number of tools for forming holes in a tubular exist. These include tools having drilling or milling means, or hydraulic jetting nozzles. It is also known in the art per se to form holes in tubulars by means of explosive charges (e.g. perforation guns), but as explosive charges tend to form holes of imprecise diameters and shape, and furthermore may induce cracks and fissures in the pipe wall, they are unsuitable for forming holes to be used in relation to plugging operations as described above.

The prior art includes US 2015/0260020 A1, which describes a multi-directional drilltype device that can be shuttled vertically through well casings of various diameters to add new perforations at the desired spacing and positions along the casings to optimize well performance. The apparatus is especially suited to add perforations to well casings of existing vertical landfill gas (LFG) extraction wells. The apparatus comprises a centralizing skid and includes an electrical motor in a housing that is purged with inert gas and with an output shaft that rotates around a first axis. The motor output shaft drives plural drill assembly modules that have drill bits that rotate around an axis normal to the first axis and which reciprocate into and out of the apparatus. A plurality of individual drill assembly modules may be stacked atop one another, in which case one drill bit is associated with each drill assembly module and each drill assembly module is rotated relative to its adjacent module(s) so that the drill bits are driven in different directions, toward desired points around the cylindrical well pipe.

The prior art also includes US 2066 409, which describes an apparatus configured for being lowered into a well and equipped with a plurality of radial drills with means for rotating the drills and simultaneously moving them outwardly to drill perforations through the surrounding pipe or casing in the well. The drills are powered by a transmission shaft coupled to uphole driving means.

The prior art also includes US 4185 705, which describes a well-perforating tool for drilling holes in a well casing substantially from and at right angles to a vertical well bore within which the casing is disposed. The tool includes an elongate housing for insertion within the casing and having a detachable boot at one end thereof for centralizing the longitudinal axis of the tool within the casing. Two electric motors are disposed within the housing for rotating a flexible drill shaft, and advancing and retracting the flexible drill shaft with respect to the interior wall of the casing. The entire tool is supported by a cable which also includes power supply and signal lines for independently activating the motors from an above-ground control station and ascertaining the depth of drill shaft penetration. In one embodiment, the tool comprises gears and opposing shafts configured for simultaneous drilling of two opposed holes.

The prior art also includes US 4368 786, which describes a downhole drilling apparatus for drilling holes at right angles to a vertical well hole. The apparatus includes a tubular housing capable of being inserted in the well hole and containing at least one elbow tube or guide, and multiple tapered and splined, interlocking drilling segments which are rotatably stacked and nested as a segment string in the guide tube with the bottom one of the drilling segments designed for drilling through the well casing, the cement sheathing and into the production interval, and the top one of the segments cooperating with electric drive means to effect rotation of the nested segments inside the guide. The guide tube extends from the tubular housing wall upwardly and telescopes at the top of the segment string to permit slidable movement of the drive means inside the tubular housing and slidable and rotatable movement of the nested segments inside the guide tube and into the production interval. In a preferred embodiment of the invention a pair of guide tubes and cooperating segment strings is provided in the tubular housing for drilling two transverse drain holes simultaneously.

The prior art also includes US 2008/0135226 A1, which describes a milling assembly which can be delivered downhole on wireline. Once at the desired location, a processor extends centralizing and driving wheels to initially position the assembly. The assembly has a cutter end with one or more mills or cutters that can be selectively radially extended. The entire cutter end can be rotated in an arcuate manner over a predetermined range. One or more cutter can be extended at a time and driven. The wheels are driven either in an uphole or downhole direction at the same time the arcuate motion can take place. Using a processor, different shapes in a surrounding tubular can be made such as windows for laterals, a plurality of openings for production or interior locator surfaces to properly position subsequent equipment with respect to openings already made by the device.

The prior art also includes US 4421 183, which describes an apparatus for penetrating boreholes in oil wells. The apparatus includes a shaft rotatable by power means. First means may be operatively associated with the shaft and a rod to obtain a rotation of the rod by the shaft. Second means obtain a linear movement of the rod at each instant in accordance with a load imposed upon the rod at that instant. The second means may include means providing a slippage between the rotary movements of the shaft and the linear movements of the rod in accordance with the load on the rod. Third means are operatively coupled to the rod and are adaptable in configuration and position in accordance with the configuration of the bore hole to be penetrated. The third means may include an outer casing, a flexible boom movable within the outer casing and resilient means disposed within the flexible boom and movable within the outer casing. Means may rotate the resilient means in accordance with the rotation of the rod. Means may move the flexible boom linearly in accordance with the linear movement of the rod. Fourth means may be coupled to the flexible boom and the resilient means for operation in accordance with the linear movements of the flexible boom and the rotary movements of the resilient means. The fourth means penetrate the bore hole.

The prior art also includes US 1070 336, which describes an apparatus for perforating casings. The apparatus comprises rotary perforating wheels, whereby a plurality of longitudinal perforations may be formed in the casing when the apparatus is moved in one direction.

The prior art also includes US 2013/0319651 A1, which describes a hydro-mechanical slot-type perforator for simultaneously performing at least two slots in a production column. The perforator includes a casing, upper and lower pistons movable within the casing, a cutting unit driven by the pistons and carrying extendable cutting tools, and, optionally, a retractable mechanism fixing the perforator for transportation. The extension is provided by rotatable shackles, or balance beams, or a combination thereof. The lower piston is moved by pressurized fluid supplied through hydraulic channels or a hydraulic system, made in the casing. The shackles rotate around axles being spaced apart, or coincided. The cutting tools can be mounted on the shackles' movable parts, and, when mutually interacted, oppositely extend the cutting tools during countermovement of the pistons. The cutting tools can be mounted in the balance beam's shoulders, or can represent sharp edges thereof.

The prior art also includes US 2015/0233218 A1, which describes a cutting tool for carrying out complete or partial peripheral cuts, and possible perforations, through a pipe wall, from internally in the pipe body. A hole is formed through a pipe wall of a first, innermost pipe body in a well, and without cutting through or significantly damaging a pipe wall of a second pipe body located outside and around the first pipe body in the well. The hole is formed by a hydraulic cutting tool having at least one cutting section provided each with outwardly directed discharge openings connected in a flow communicating manner to said internal flow channel for supply of an abrasive fluid, wherein each discharge opening is configured in a manner allowing it to form a discharging cutting jet of the abrasive fluid for cutting through the pipe wall.

There is a need for an improved device for making multiple perforations in a wellbore tubular, such as an inner casing, in a controlled and efficient manner, without damaging an outer casing in which the inner casing is nested.

Summary of the invention

The invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention.

It is thus provided a hole forming tool having a longitudinal axis and configured for operation inside a first tubular having a wall, and comprising:

- a plurality of drill bits, rotatably connected by drive means to at least one motor; whereby said drill bits may be extended to penetrate said wall and thus form respective holes through said wall, and retracted;

- wherein at least two of said drill bits are arranged in the same plane, perpendicular to the longitudinal axis, characterized by:

- a guide receptacle for each drill bit; each guide receptacle arranged between support members each having an inclined slot;

- each drill bit comprising a guide peg which is slidably arranged in a respective inclined slot;

whereby

- when the support members are moved in one direction, the slot-and-peg connection advances the drill bits radially and out of the tool housing, and

- when the support members are moved in the opposite direction, the slot-and-peg connection retracts the drill bits into the tool housing.

In one embodiment, the hole forming tool further comprises a drive shaft that terminates in a bevel gear wheel which meshes with individual bevel gear wheels on each drill bit, whereby a rotation of the drive shaft will rotate each drill bit simultaneously, and all drill bits are rotated at the same rotational speed.

In one embodiment, at least two of said drill bits are arranged in opposite directions in the same plane. The hole forming tool may comprise three or more drill bits, arranged circumferentially with respect to a housing perimeter. In one embodiment, the drill bits and hydraulic motor are arranged in a tubular housing, said housing having openings configured to correspond with respective drill bit locations.

In one embodiment, the hole forming tool comprises drill bits arranged in multiple planes substantially perpendicular to the longitudinal axis, and wherein each plane comprises two or more drill bits. The at least one motor may be a hydraulic motor.

In one embodiment, the hole forming tool further comprises a common actuation mechanism imparting a common actuation force, by means of which the drill bits in the same plane simultaneously and synchronously may be extended.

The hole forming tool may comprise a plurality of hydraulic motors, drivingly connected to drill bits via drive means, and each motor being connected to a flow manifold via piping.

In one embodiment, the drill bits are arranged at regular intervals around the tool periphery and hence provide for a self-centralizing tool, without the need for anchors, slips, skids, and the like.

In one embodiment, the hole forming tool further comprises bores arranged in the drill bits, said bores being connected to a tool-internal reservoir or an external reservoir.

In one embodiment, the drill bits are extendable and retractable and comprises release/pull-back capabilities. The release/pull-back capabilities may comprise pullback (overpull), reversing rotation, or drill bit weak zone (pull or rotate tool to break).

It is also provided a method of forming a plurality of holes in a tubular wall of a first tubular by means of the tool according to the invention, characterized by the steps of: a) placing the tool at a position inside the tubular; and

b) rotating and extending the plurality of drill bits to penetrate the wall and forming a respective plurality of holes.

In one embodiment, the method comprises, following step b), based on sensed data or predetermined data, retracting the plurality of drill bits before they abut on an outer tubular in which the first tubular is nested. In one embodiment, the plurality of drill bits are rotated and extended simultaneously and synchronously.

In one embodiment of the method, following step b), a sealant material is flowed from the tool and into a first annulus outside said first tubular. Also, following step b), a sealant material (T) may be flowed from the tool and into a second annulus between said first tubular wall and said tool housing. The sealant may be flowed through a bore of at least one drill bit. In one embodiment, at least a portion of the tool is abandoned at said position inside the tubular following the flowing steps.

The invented tool and method are particularly useful for forming multiple holes in the same plane in a liner or casing installed in a subterranean wellbore. The invented tool and method provides for forming (e.g. drilling, milling) multiple penetrations in the liner or casing without damaging the wall beyond the actual hole being formed (i.e. without cracks or fissures in the liner or casing wall) and without damaging other liners or casings, such as outer casings. The invented tool has a considerably higher capacity that the prior art tools, in that is capable of forming multiple holes in one operation.

Brief description of the drawings

These and other characteristics of the invention will become clear from the following description of embodiments, given as non-restrictive examples, with reference to the attached schematic drawings, wherein:

Figure 1 is a part-sectional side view of an embodiment of the invented tool, in operation in a wellbore;

Figure 2 corresponds to figure 1, and illustrates the invented tool having been moved a distance inside the wellbore;

Figure 3 is a part-sectional side view of another embodiment of the invented tool, in operation in a wellbore;

Figures 4a, 4b and 4c are cross-sectional drawings of the tool housing, illustrating various drill bit configurations;

Figure 5 is side view of an embodiment of the invented tool, comprising five individual tool modules;

Figure 6 is a side view of an embodiment of the invented tool furnished with circumferential sealing pads;

Figure 7 is a side view of an embodiment of the invented tool, comprising four individual tool modules and each tool module furnished with circumferential sealing pads;

Figure 8 is a side view of an embodiment of the invented tool, comprising four individual tool modules and the upper and lower tool modules being furnished with respective circumferential sealing pads;

Figure 9 is a side view of an embodiment of the invented tool, in operation in a wellbore;

Figure 10 is a side view of an embodiment of the invented tool, having formed holes in a wellbore casing and expanded circumferential sealing pads;

Figure 11 is a side view of an embodiment of the invented tool, in which a sealant material is injected into a well annulus via the drill bits;

Figure 12 is a side view of an embodiment of the invented tool, in which a sealant material is injected into a well annulus;

Figure 13 is a side view of an embodiment of the tool forming a foundation for a wellbore plug, and the manifold is in the process of being retrieved from the well; Figure 14 is a side view of internal component of an embodiment of the invented tool, showing various drill bit configurations and drill bit guide receptacles;

Figures 15a and 15b are sectional views of sections A-A and B-B, respectively, of figure 14; and

Figures 16a and 16b are principle sketches of one embodiment of the drill bit configurations , shown in retracted and extended positions, respectively.

Detailed description of a preferential embodiment

The following description will use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ”upper”, “lower”, “above”, “below”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

Figure 1 illustrates an embodiment of the invented tool 1, in operation in a wellbore W. The wellbore W is formed in a subterranean formation S, and is lined with an outer casing 4, installed in a manner known in the art. An inner casing 5 is installed inside the outer casing, also in a manner known in the art. The annulus A formed by the casings may be filled with cement (not shown). Although the invented tool in the following is illustrated in a vertical wellbore, it should be understood that the invention is equally applicable for use in tubulars having other inclinations, such as, but not necessarily limited to, casings and liners installed in inclined and horizontal wellbores.

The tool 1 is conveyed inside the inner casing 5 on a drillpipe 3 extending from an uphole assembly (not shown). The tool comprises a tool housing 2, inside of which a plurality of penetration units 9 in the form of drill bits is arranged. The skilled person will know that a drill bit is a cutting tool which is used, by rotation, to remove material to form a hole. The drill bit is rotated by a mechanism (e.g. a motor), commonly referred to as a drill. The drill bits 9 are arranged in a designated housing 8. The drill bits is thus capable of forming a hole in the casing wall 5a in a controlled manned, without damaging other parts of the wall.

Several drill bits 9 are arranged in the same plane (perpendicular to the tool longitudinal axis Y-Y). In the embodiment illustrated in figure 1, four (only three shown; the fourth unit is hidden) drill bits 9 are arranged, at regular intervals, in three different planes P1, P2, P3. It should be understood that the invented tool may comprise a plurality of drill bits in fewer or more planes. That is, when assembling the tool for a given application, the number of planes (P1 to Pn), and hence the length of the tool, is determined based on the given requirements (e.g. the length of casing to be perforated). The tool may be configured such that drill bits 9 within each plane may be operated independently of each other, but – as explained below – drill bits in a common plane may also be interconnected so as to be operated simultaneously and synchronously.

Referring also to figure 4a, the drill bits 9 may be extended and retracted (out of and into the tool housing 2) independently of each other. In another embodiment, illustrated in figures 14 – 16b, the drill bits 9 may be extended and retracted (out of and into the tool housing 2) simultaneously and synchronously by means of a common actuation mechanism.

In general, required control means and sensing means are not illustrated, as such means are known in the art. Figure 4b illustrates an alternative embodiment, in which two drill bits 9 are arranged in the same plane. Figure 4c illustrates yet another embodiment, in which three drill bits 9 are arranged in the same plane. It should be understood that more drill bits may be arranged in the same plane. A common feature of these embodiments is that the drill bits are arranged at regular intervals around the tool periphery and hence provide for a self-centralizing tool, without the need for anchors, slips, skids, extending arms, and the like. The tool may also have a radial dimension such that the distance between the tool body and the inner casing wall is small. A typical tool radial dimension (OD) is 1⁄4” less than the inner casing inner diameter. This gives a 1/8” clearance on all sides. The invention shall not, however, be limited to such dimensions. It should also be understood that the tool housing 2 is stationary with respect to the casing wall during the operation of the drill bits. The tool housing may be suspended by a non-rotating drillpipe 3, or other suitable suspension means. Although not illustrated in figures 1-3, movable pads or slips may be fitted to the tool housing in order to immobilize the tool housing during the operation of the drill bits. These pads or slips may be retracted when the tool is moved to another location, and set (extended) before commencement of the hole-forming operation.

Also, again referring to figures 1 and 2, arranged inside the tool housing 2 is a hydraulic motor 6, connected via an axial drive shaft 7 (and required gears; not shown) to each of the drill bits 9. The hydraulic motor 6 is powered by fluids, for example pressurized drill fluids, water or other fluids, supplied e.g. via the drillpipe 3 in a manner known in the art. It should be understood that the fluids may also be supplied via coiled tubing or other pipe or tubing. Although not illustrated, it should be understood that the drill bit optionally may be powered by other means, such as electric motors.

Arranged on the tool housing outer and lower side is a magnet 13, configured to collect cuttings and swarf created by the drilling operations.

Figure 2 illustrates how the tool 1 has formed a plurality of holes H in the casing wall 5a, and been relocated to a new location in order to form a new set of holes.

Figure 3 illustrates another embodiment of the invented tool. Here, the drill bits 9 are powered (extended, rotated and retracted) by two smaller hydraulic motors 6’, via an axial drive shaft 7’ and radial drive shafts 11. Each of the motors 6’ are connected to a flow manifold 10 via piping 12. It should be understood that the tool may comprise more than two hydraulic motors 6’, as well as other motor types.

In operation, the tool 1; 1’ may be activated to form multiple holes in the inner casing wall 5a, thus providing access to the annulus A (for flushing operations, etc.). The tool comprises sensors and control means (not illustrated) to ensure that the drill bits 9 are only extended sufficiently far as to penetrate the casing wall 5a, but not as far as to come into contact with the outer casing 4. Such sensors and control means may comprise any applicable device known in the art, key control parameters being the amount (length) of which the drill bit has extended out of the tool housing, the distance between the tool housing and the casing 5 inner wall, and the distance between the casing 5 outer wall and the outer casing 4 inner wall.

Yet another embodiment of the invented tool will now be described with reference to figures 5-13. Unless otherwise noted, the features and functions of the embodiments described above may also be incorporated in the embodiments described in the following.

Figure 5 illustrates an embodiment of the invented tool 1’’ which is made up of several individual tool modules and a manifold 10’. The figure shows five individual tool modules 1a-e, but it should be understood that the tool may have fewer (e.g. one or two) and more tool modules. Each tool module comprises mechanical connectors, hydraulic connectors and electrical connectors (not shown) that per se are well known in the art, and by means of which a tool module may be connected to an adjacent connector.

Therefore, in addition to connecting two adjacent tool modules mechanically, respective hydraulic lines, electrical wiring, control cables, etc. may be connected – in any manner known in the art, when two tool modules are interconnected. The same connection interface is arranged on the manifold 10’, whereby fluids, electrical power and control/feed-back signals may be conveyed from a location inside or above the manifold, through the manifold and into each one of the interconnected tool modules. The above mentioned connectors are releasable, such that the manifold may be disconnected from a tool module, and each tool module may be disconnected from an adjacent tool module. Such disconnect means (e.g. overpull, rotation) are well known in the art, and need therefore not be described in more detail here.

Each tool module 1a-e comprises a plurality of drill bits 9 arranged in the same plane, as described above with reference to figures 1-4. In the embodiment illustrated in figure 5, each tool module 1a-e comprises four (only three shown; the fourth unit is hidden) drill bits 9 arranged at regular intervals, in the same plane.

In figure 5, the drillpipe is connected to a manifold 10’. It should be understood that the manifold may comprise a central hydraulic motor (not shown) similar to the motor 6 described above with reference to figure 1, in which case the individual drill bits 9 in each tool module is driven by mechanical transmission systems from the manifold. Alternatively, each tool module comprises one or more hydraulic motor, in which case hydraulic fluid is supplied to the tool modules from the manifold, via hydraulic piping in the tool modules. As noted above, other motor types (e.g. electrical) may be used instead.

The manifold comprises movable pads (or slips) 14 which may be extended against the pipe wall in order to support the tool when the drill bits 9 are operating. Figure 5 shows the pads 14 in a retracted position.

Figure 7 corresponds to figure 5, but shows an embodiment of the tool having four tool modules 1a-d, and each tool module comprises circumferential sealing pads 15, arranged on both sides of the drill bits 9. The circumferential sealing pads 15, which are shown in a retracted position, may be extended to seal against a surrounding pipe wall (see e.g. figure 10). Figure 8 shows yet another embodiment of the tool, in which only the upper 1a and lower 1d tool module are furnished with circumferential sealing pads 15. On the upper tool module 1a, the circumferential sealing pad 15 is arranged above the drill bits 9, while on the lower tool module 1d, the circumferential sealing pad 15 is arranged below the drill bits 9.

Figure 6 illustrates an embodiment of the tool which corresponds to the embodiment illustrated in figures 1 and 3, but the manifold 10’ is releasably connected to the tool housing 2 in a manner corresponding to the embodiments described above with reference to figure 5. In the embodiment shown in figure 6, circumferential sealing pads 15 have been added. One circumferential sealing pad 15 is arranged above the upper coplanar drill bits 9’, and one circumferential sealing pad 15 is arranged below the lower coplanar drill bits 9’’.

Various applications of the invented tool will now be described with reference to figures 9-13. These figures show an embodiment of the tool corresponding to the one illustrated in figure 6, but it should be understood that the other embodiments described above may be used instead.

Figure 9 shows the invented tool arranged in a wellbore. The tool is held (suspended if vertical or inclined wellbore) by a non-rotating drillpipe 3 inside the inner casing 5. The drill bits 9 have formed holes H in the inner casing 5, but are not interfering with the outer casing 4 due to the sensor and control means described above. It should be understood that certain dimensions have been exaggerated in the figures, for illustration purposes. The pads 14, shown in dotted lines as they are optional, have been extended to abut against the inner casing 5.

In figure 10, the drill bits have been retracted from the holes H and the circumferential sealing pads 15 have been set against the inner casing 5.

Figures 11 and 12 illustrate two methods of using the invented tool to inject a sealant material (e.g. cement, resin, epoxy). The sealant may be stored in a container inside the tool housing or may be supplied from an external reservoir via the manifold. In figure 11, the sealant material T is injected from the manifold and through bores (not shown) in the drill bits and into the annulus A formed between the inner 5 and outer 4 casings. Although not illustrated in figure 11, it should be understood that an obstruction preferably is in place inside the annulus below the lowermost drill bits in order to retain the sealant material in the region of the holes H.

In figure 12, the drill bits have been retracted, whereby the sealant T is also poured into the annular volume A’ defined by the circumferential sealing pads 15, the tool body and the inner casing 5. In this embodiment, the sealant material may be channeled through the aforementioned bores in the drill bits or through separate, designated, bores.

Figure 13 shows a plug formed by sealant material T and the tool body, thus forming a foundation for a wellbore plug. The manifold 10’ is in the process of being retrieved from the well.

As mentioned above, in one embodiment, the drill bits in a common plane may be interconnected so as to be operated simultaneously and synchronously. Figures 14 – 16b illustrate one such embodiment. Figure 14 illustrates a drill bit support structure 17. In normal operations, this structure 17 is enclosed by the tool housing 2, with only the drill bits 9 extending out from the housing through designated housing openings (not shown in figure 14). In figure 14, some of the drill bits have been removed in order to visualize the guide receptacles 16 in which they may reciprocate. It will be understood that the illustrated embodiment comprises five drill bits 9 in each plane, and a total of four planes P1 – P4. The guide receptacles are arranged between support members 18.

Figures 15a and 15b illustrate how rotation is transferred from the motor(s) (not shown) to each drill bit in a common plane. The drive shaft 7’’ terminates in a bevel gear wheel 19 which meshes with individual bevel gear wheels 20 og each drill bit 9. A rotation of the drive shaft 7’’ will thus rotate each drill bit 9 simultaneously, and all drill bits are rotated at the same rotational speed.

One embodiment of components for extending and retracting the drill bits (out of and into the tool housing) is illustrated in figures 16a and 16b. Here, for clarity of illustration, the support members 18 are displayed side by side, instead if in the circular configuration of figure 14. Also, in figures 16a,b, drill bits in only one plane are shown. Each drill bit 9 comprises a guide peg 21 which is slidably arranged in an inclined slot 22. When the support members 18 are moved in one direction (upwards in figures 16a,b), the slot-and-peg connection advances the drill bits radially (sideways in figures 16a,b) and out of the tool housing. Conversely, when the support members 18 are moved in the opposite direction, the slot-and-peg connection retracts the drill bits into the tool housing. The arrow denoted “F” indicates a common actuation force, imparted by a member (not shown) in a manner which per se is known in the art, whereby the drill bits are extended (and subsequently retracted) simultaneously and synchronously. One advantage of extending the drill bits synchronously when drilling though the inner casing wall, is that the swarf generated by the drilling is finer and shorter.

In any of the embodiments described above, the drill bit 9 is extendable and retractable and comprises release/pull-back capabilities such as pull-back (overpull), reversing rotation, or drill bit weak zone (pull or rotate tool to break). This is a useful feature in the event that one or more drill bits are jammed in the casing wall.

Although the invention has been described in relation to forming holes in a liner or casing installed in a subterranean wellbore, it should be understood that the invention may also have other applications.

Claims

1. A hole forming tool (1) having a longitudinal axis (Y-Y) and configured for operation inside a first tubular (5) having a wall (5a), and comprising:

- a plurality of drill bits (9), rotatably connected by drive means (7; 7’, 11; 7”, 19, 20) to at least one motor (6; 6’), whereby said drill bits (9) may be extended to penetrate said wall and thus form respective holes (H) through said wall (5a), and retracted;

- wherein at least two of said drill bits (9) are arranged in the same plane (P1) perpendicular to the longitudinal axis, characterized by:

- a guide receptacle (16) for each drill bit; each guide receptacle arranged between support members (18) each having an inclined slot (22);

- each drill bit (9) comprising a guide peg (21) which is slidably arranged in a respective inclined slot (22);

whereby

- when the support members (18) are moved in one direction, the slot-and-peg connection advances the drill bits radially and out of the tool housing, and

- when the support members (18) are moved in the opposite direction, the slot-and-peg connection retracts the drill bits into the tool housing.

2. The hole forming tool of claim 1, further comprising a drive shaft (7") that terminates in a bevel gear wheel (19) which meshes with individual bevel gear wheels (20) on each drill bit (9), whereby a rotation of the drive shaft (7") will rotate each drill bit (9) simultaneously, and all drill bits are rotated at the same rotational speed.

3. The hole forming tool of claim 1, wherein at least two of said drill bits (9) are arranged in opposite directions in the same plane (P1).

4. The hole forming tool of claim 1, wherein said three or more drill bits (9) are arranged circumferentially with respect to a housing perimeter.

5. The hole forming tool of any one of claims 1-4, wherein the drill bits (9) and motor are arranged in a tubular housing (2), said housing having openings configured to correspond with respective drill bit locations.

6. The hole forming tool of any one of claims 1-5, further comprising drill bits arranged in multiple planes (P1 - Pn) perpendicular to the longitudinal axis, and wherein each plane comprises two or more drill bits.

7. The hole forming tool of any one of claims 1-6, wherein the at least one motor (6; 6’) is a hydraulic motor.

8. The hole forming tool of any one of claims 1-7, further comprising a common actuation mechanism (18, 21, 22) imparting a common actuation force (F), by means of which the drill bits (9) in the same plane simultaneously and synchronously may be extended.

9. The hole forming tool of any one of claims 1-8, further comprising a plurality of hydraulic motors drivingly connected to drill bits via drive means (7’, 11), and each motor is connected to a flow manifold (10) via piping (12).

10. The hole forming tool of any one of claims 1-9, wherein the drill bits are arranged at regular intervals around the tool periphery and hence provide for a selfcentralizing tool, without the need for anchors, slips, skids, and the like.

11. The hole forming tool of any one of claims 1-10, further comprising bores in the drill bits, said bores being connected to a tool-internal reservoir or an external reservoir.

12. The hole forming tool of any one of claims 1-11, wherein the drill bits (9) are extendable and retractable and comprises release/pull-back capabilities.

13. The hole forming tool of claim 12, wherein the release/pull-back capabilities comprise pull-back (overpull), reversing rotation, or drill bit weak zone (pull or rotate tool to break).

14. A method of forming a plurality of holes in a tubular wall (5a) of a first tubular (5) by means of the tool of any one of claims 1-13, characterized by the steps of: a) placing the tool (1) at a position inside the tubular (5); and

b) rotating and extending the plurality of drill bits (9) to penetrate the wall (5a) and forming a respective plurality of holes (H).

15. The method of claim 14, wherein, following step b), based on sensed data or predetermined data, retracting the plurality of drill bits before they abut on an outer tubular (4) in which the first tubular (5) is nested.

16. The method of any one of claims 14-15, wherein the plurality of drill bits are rotated and extended simultaneously and synchronously.

17. The method of any one of claims 14-16, wherein, following step b), a sealant material (T) is flowed from the tool (1) and into a first annulus (A) outside said first tubular.

18. The method of any one of claims 14-16, wherein, following step b), a sealant material (T) is flowed from the tool (1) and into a second annulus (A’) between said first tubular wall and the housing of said tool.

19. The method of any claim 17 or claim 18, wherein the sealant is flowed through a bore of at least one drill bit.

20. The method of any one of claims 17-19, wherein at least a portion of the tool is abandoned at said position inside the tubular (5) following the flowing step of claim 14 or claim 15.

21. Use of the method of any one of claims 14-20, for forming a plug in a tubular.