Perforating tool for perforating a well casing

Abstract

A perforating tool (2, 136) for perforating a well casing comprises a tool body (8, 138), at least one cutter element (14), a plurality of cylinder units (16), and an drive member (22, 156), wherein the drive member (22, 156) is moveable to move the at least one cutter element (14) between a retracted position and an extended position, wherein the cylinder units (16) are configured to move the drive member (22, 156), wherein a fluid supply duct (24) is formed along the longitudinal axis (90) of the tool body (8, 138) and comprises a plurality of ports (80, 82) in fluid contact with first chamber portions of the cylinder units (16) to enable fluid to flow from the fluid supply duct (24) into each first chamber portion (10, 135), such that by increasing a fluid pressure in the fluid supply duct (24) each of the cylinder units (16) operates to drive the drive member (22, 156), wherein outer elements (20, 142) of the cylinder units (16) engage each other through axially effective, face-side engagement elements (100, 146).(Fig. 1)

Description

Perforating tool for perforating a well casing Field of the inventionThe invention relates to a perforating tool for perforating a well casing.BackgroundPerforation is a technique for creating a passageway between a nearby hydrocarbon reservoir and a wellbore. This typically includes puncturing a hole from inside the wellbore through the casing and any cement lining into a production zone. Alternatively, perforation is used in conjunction with plug and abandonment operations, e.g. during a perforate, wash and cement (PWC) operation. Various methods for perforating a well casing are known. For example, perforating devices may utilize explosives. The working principle of another type of perforating devices may be based on abrasion. Hydraulic perforating devices are known that drive a blade or a cutter element through the well casing.For example, EP 2 616 625 B1 discloses a perforating tool for perforating a downhole well casing by means of radially extendable blades. The tool has a body arranged to be disposed in a well casing and at least one cutter block moveable relative to the body between an inwardly retracted condition and an outwardly deployed condition to cut a perforation in the well casing. A plurality of pistons is arranged to move a drive member relative to the body. The drive member defines a bore disposed along a longitudinal axis of the body, and a plurality of ports are formed in the drive member to enable fluid to flow from the bore to pressure chambers, in which the pistons are arranged. An increase in fluid pressure in the body increases fluid pressure in the pressure chambers to move each of the plurality of pistons relative to the body and cause the drive member to move relative to the body, thereby deploying the blades.The tool may comprise a plurality of interconnected subs to form a perforating tool that can be interconnected in a downhole work string. For allowing fluid to escape from a discharge side of a piston, each of the interconnected subs comprises a plurality of drainage holes. Summary of the invention An object of the invention is to propose an alternative perforating tool for perforating a well casing.The present invention is defined by the appended claims and in the following:In a first aspect, the invention relates to a perforating tool for perforating a well casing, comprising a tool body configured to be placed in a well casing, the tool body having a longitudinal axis, a first longitudinal section and a second longitudinal section, at least one cutter element arranged in and radially moveable relative to the first longitudinal section of the tool body between a retracted position and an extended position to create a perforation in the well casing, an drive member arranged in the second longitudinal section and coupled with the at least one cutter element, a plurality of cylinder units arranged in a row along the longitudinal axis in the second longitudinal section, each cylinder unit having an inner element and an outer element, the inner element dividing a pressure chamber of the respective cylinder unit into a first chamber portion and a second chamber portion, wherein the drive member is moveable relative to the first longitudinal section to move the at least one cutter element between the retracted position and the extended position, wherein the cylinder units are configured to move the drive member relative to the first longitudinal section, wherein a fluid supply duct is formed along the longitudinal axis of the tool body and comprises a plurality of ports in fluid contact with each first chamber portion to enable fluid to flow from the fluid supply duct into each first chamber portion, such that by increasing a fluid pressure in the fluid supply duct each of the cylinder units operates to drive the drive member, wherein the outer elements of the cylinder units engage each other through axially effective, face-side engagement elements.The tool body may generally relate to a structure of the tool that extends from an uphole end to a downhole end. It may have a generally elongated cylindrical shape that is dimensioned to easily fit into the well casing to be perforated. It may consist of a plurality of separate parts that create a chain of components along the longitudinal axis.The longitudinal axis may be a center line that extends from the uphole end to the downhole end. When the perforation tool is placed in the well casing, the longitudinal axis may be substantially parallel to a main extension direction of the well casing. The tool may be drill pipe-conveyed or tubing-conveyed (e.g. coiled tubing or umbilical).The first longitudinal section and the second longitudinal section of the tool body refer to separate portions of the perforation tool. While the first longitudinal section comprises the at least one cutter element, the second longitudinal section primarily comprises the cylinder units. Depending on the design of the cylinder units, the second longitudinal section may be movable or fixed relative to the first longitudinal section, as explained further below.The at least one cutter element may comprise one or, preferably, a plurality of cutter elements. The at least one cutter element is movable in a radial direction, such that it can move into a larger distance from the longitudinal axis, i.e. into an extended position, or into a smaller distance from the longitudinal axis, i.e. into a retracted position. By moving into the extended position, the at least one cutter element radially protrudes away from the tool body to act on the well casing to perforate it.The at least one cutter element is a component that is configured to cut or pierce the well casing. It may be designed as a blade, such that it may comprise a blade-like sharp edge at a radial outer side of the cutter element. As an alternative or in addition thereto, it may have a tip that may be used to pierce into the well casing. The cutter element is configured to be drivable into a well casing to reliably perforate the well casing. It may be radially outwardly curved, kinked or bent.The drive member may be a component that is axially movable relative to the first section and that is coupled with the cylinder units and the at least one cutter element. By driving the drive member towards the at least one blade element through the cylinder units, the at least one blade element moves to radially extend. The design of the drive member depends on a variety of factors. These may include the working principle of the at least one cutter element, the number of cutter elements used, the design of the cylinder units, i.e. whether inner elements or outer elements of the cylinder units move along the longitudinal axis.The term “cylinder unit” may refer to a device that is provided as a part of the tool and that is arranged in the second longitudinal section. The cylinder unit is configured to be pressurized through the fluid supply duct and to drive the drive member that is coupled with the cylinder unit in response to the fluid pressure. The fluid may typically be drilling fluid from the surface.The cylinder unit may generally comprise two main parts that are movable relative to each other, i.e. an inner element and an outer element. For example, the outer element is a cylinder sleeve. Either the inner element or the outer element is movable to drive the drive member, while the other element is static and does not move. As explained further below, the cylinder sleeve as the outer element may comprise an internally arranged annular axial surface that acts as a piston, while a static inner element supports and guides the cylinder sleeve and delimits the pressure chamber inside the cylinder sleeve. In another embodiment, the cylinder sleeve as the outer element may be static, while the inner element moves in response to an applied fluid pressure. The length of the stroke provided by the movable element of a cylinder unit may be less than a meter and may, for example, be in a range of roughly 30 to 40 cm, depending on the diameter of the well casing and / or the diameter of the tool body.The number of cylinder units can be chosen depending on the available fluid pressure and the characteristics of the well casing. If the available fluid pressure is comparably low, a higher number of cylinder units, whose individual pressing forces add up, may be used to achieve a required pressing force. It is conceivable to produce a pressing force in the region of roughly 3 to 4 MN (Mega Newton), comparable to the weight force of 300 to 400 metric tons. For reverting the at least one cutter element into the retracted position, a reverse force directed towards the cylinder units is required. This may be achieved by a biasing element, which may be arranged at a side of the at least one cutter element that faces away from the cylinder units. However, other variants are possible and not ruled out herein. The biasing element may exemplarily comprise one or more coil springs. The biasing element may be dimensioned to create a reverting force of, for example, roughly 10 to 30 kN, depending on the detail design of the perforating tool.The fluid supply duct may extend from the uphole end of the tool to the cylinder units. It may be formed as a bore inside components arranged within the tool body. For example, it may comprise a duct section at an uphole end of the tool, it may comprise a bore inside an element that supports or holds the biasing element, it may comprise a bore inside a block that supports the at least one cutter element, it may comprise a bore inside the drive member and inside a part of the cylinder units. By supplying a fluid pressure at the uphole end of the tool, the fluid flows towards the downhole end into the cylinder units. To reach pressure chambers of the individual cylinder units, suitable ports are provided along the fluid supply duct. The ports create a fluid communication between the fluid supply duct and the respective pressure chamber. It is preferred to provide a plurality of ports for each pressure chamber to maintain a reliable fluid communication and to prevent premature clogging.A lower part of the tool in the region of the downhole end may be provided with a physical restriction, e.g. a valve, an orifice, a plug or the like, which allow a pressure to build up inside of the tool as fluid is supplied.The axially effective, face-side engagement elements at the cylinder units allow to plug the cylinder units onto each other to create a chain or row of cylinder units. Preferably, the outer elements of the cylinder units comprise the face-side engagement elements, which allows to plug the outer elements, such as cylinder sleeves, onto each other. The term “axially effective” is to be interpreted as an engagement that is achieved by axially advancing complementarily shaped engagement elements to mutually interlock.The perforating tool according to the invention is particularly easy to assemble. By using a plurality of separate cylinder units, a user may flexibly add or remove cylinder units upon desire. When the cylinder units are arranged to form a row along the longitudinal axis of the tool, they engage each other. This enables to transfer a torque from the uphole end to the downhole end. At the same time, there is no need for a complex connection between two subsequent cylinder units. In particular, the use of electric or pneumatic screwing tools is not required to create a sufficiently strong connection.By arranging the engagement elements on end faces of the individual cylinder units, they may be placed in radially outermost regions, which significantly increases a transferable torque, while maintaining a simple design of the cylinder units. It is conceivable that the inner elements of the cylinder units do not need to transfer a torque, as the main load path for the torque may run through the outer elements of the cylinder units. Thus, the inner elements may be of a particularly simple design and a connection between consecutive internal elements may be easy to assemble and to disassemble. Preferably, this may also be conducted by simple connection elements that do not require the use of electric or pneumatic screwing tools. A flexible handling of the perforating tool on site is thus possible.The engagement elements may be configured to be inserted into each other axially. By simple advancing the engagement elements of two consecutive cylinder units in an axial direction, the engagement elements fit into each other, and they do not need to be intertwined. The engagement elements may be formed as positive locking means. The engagement elements of two consecutive cylinder units thus provide a form-fit engagement. This may result in a rotary connection that is substantially free of play or backlash.The engagement elements may comprise fluid-permeable gaps that are in fluid communication with the second chamber portions. Resultantly, the engagement elements do not need to be shaped so precisely that their connection area is completely sealed. Even contrary to that, a leaky connection is desirable, since dedicated radial discharge bores are not required. When the supplied fluid reaches the first chamber portions, the fluid pushes one of the outer element and the inner element towards the drive member in reaction to the fluid pressure. By this motion, the size of the first chamber portion increases, while the size of the second chamber portion decreases. Due to the gaps, a fluid can exit the second chamber portion through the fluid-permeable gaps into the surrounding of the tool. On the other hand, fluid may be suctioned back into the second chamber portion when the drive member is retracted and the pressure in the second chamber portion is decreased. The gaps may result from an axial distance from two axially consecutive engagement elements. Preferably, the engagement elements are located to surround the second chamber portion and in an axial distance to the first chamber portion to avoid leakage from the first chamber portion.The outer elements may be coupled with the drive member, wherein the inner elements of subsequent cylinder units are connected to each other. Consequently, the outer element of the cylinder units act to move the drive member and are thus movable relative to the inner elements. This may be done by integrating an internal surface into the outer elements, which radially projects inwardly. The internal surface may be substantially perpendicular to the longitudinal axis of the tool. The first pressure chamber section may extend from the internal surface to an opposed surface of the inner element of the respective cylinder unit. By providing a fluid pressure into the first pressure chamber section, the internal surface may move in an axial direction. The inner elements are static through the connection. It is to be understood that one of the inner elements, such as the uppermost inner element, is connected to or coupled with the first longitudinal section of the tool.The drive member may comprise a cutter element pusher coupled with the at least one cutter element in the first longitudinal section and a plurality of push rods that are distributed around and arranged parallel to the longitudinal axis and extend from the cutter element pusher into the direction of the second longitudinal section. The fluid supply line may extend along the longitudinal axis and may thus be located in a center of each cross-sectional profile. The push rods allow to transfer a pressing force parallel to the fluid supply line in a radial distance to the longitudinal axis. The cutter element pusher may act as an interface between the push rods and the at least one cutter element. It may preferably comprise an annular surface that surrounds the longitudinal axis, which allows to use a different number of push rods and cutter elements or different orientations. Preferably, the cutter element pusher is provided as a ring-shaped plate.The push rods may be in contact with an end surface of one of the cylinder units, which is closest to the first longitudinal section. Hence, an uppermost cylinder unit may, for example, comprise a planar surface at a top end, which acts onto the push rods. By providing engagement elements at the opposite side, i.e. its bottom side, the other cylinder units may be coupled with the uppermost cylinder unit.The engagement elements are arranged at a radial outer rim of the respective outer element of the respective cylinder unit. Using a radial outer rim maximizes the distance of the engagement elements to the longitudinal axis. This allows to transfer particularly high torques, while still maintaining a simple connection between two consecutive cylinder units. The engagement elements may comprise protrusions and / or recesses extending parallelly to the longitudinal axis. It is conceivable to use recesses in one of the cylinder units, while protrusions are used in the other cylinder unit of a pair of consecutive cylinder units. The protrusions and the recesses may be complementary to each other. Preferably, the protrusions and recesses only comprise delimiting edges that are parallel or perpendicular to the longitudinal axis.The inner elements may be configured to be insertable into each other at their end faces to form an overlapping region in an axial direction, wherein a fastening element may be inserted radially into the overlapping region. One end of an inner element may thus have a smaller dimension than an opposite end. Preferably, the end with the larger dimension may comprise a hole, into which the other end can be inserted to form the overlapping region. The fastening element may preferably be configured to be placed without the need of pneumatic or electric tools.The fastening element may be designed to create a positive connection in a tool-free manner by inserting it into corresponding openings.The perforating tool may comprise a vent port, wherein the vent port is configured to form a fluid connection between the fluid supply duct and the surrounding of the perforating tool when the at least one cutter element is fully extended. A user may recognize a significant drop in pressure when the vent port opens. This can be used as an indication for a full extension of the at least one cutter element.The vent port may be arranged in one of the outer elements of the cylinder units, wherein a connection port may be arranged in a static component of the tool in fluid communication with the fluid supply duct, and wherein the vent port and the connection port may be configured to be spaced apart until the at least one cutter element is about to be fully extended. Thus, when moving the outer element of a cylinder unit or the inner element of a cylinder unit, the axial positions of the vent port and the connection port may match when the at least one cutter element is about to be fully extended. The static component may be any component that does not move along the longitudinal axis.The first longitudinal section and the second longitudinal section may be configured to be twistable about a limited angle into a first state and a second state, wherein the cylinder units may be blocked from driving the drive member in one of the first state and the second state at least once. The tool can be lowered into the well casing without risking an inadvertent extension of the at least one cutter element, which could harm the well casing at positions, in which a perforation is not desired. The longitudinal sections may be twisted relative to each other by introducing a torque into the first longitudinal section. If the second longitudinal section, i.e. a downhole part, experiences a drag, significant friction or the like, a twisting motion can be created. The tool can be brought into two different states, wherein in one of the states a transfer of a driving force to the at least one cutter element is blocked, while in the other one of the states the transfer is released. This may include the use of shearing pins, or other mechanisms.The perforating tool may comprise a plurality of sets of cutter elements spaced apart along the longitudinal axis. Brief description of the drawings In the following description this invention will be further explained by way of exemplary embodiments shown in the drawings:Fig. 1 shows a lateral view of a perforating tool.Fig. 2 shows a sectional view of the perforating tool.Figs. 3 to 5 show details of the sectional view of Fig. 2.Fig. 6 shows an engagement of two consecutive cylinder units.Figs. 7 to 10 show various cross-sectional views of the tool.Fig. 11 shows a lateral view of a perforating tool.Fig. 12 shows a sectional view of the perforating tool of Fig. 11.Figs. 13 to 15 show details of the sectional view of Fig. 12.Fig. 16 shows the tool of Fig. 1 with two sets of cutter elements.Figs. 17a and 17b show two three-dimensional sectional views of a modified transition region between the first and second longitudinal section of the tool according to Fig. 1. Detailed description of the invention In the following, the terms “above”, “top”, “uppermost”, and “below”, “bottom”, “lowermost” are used to indicate a location of a component in the tool. “Above” refers to a location closer to an uphole end of the tool or the surface. “Top” and “uppermost” refer to an uppermost component, which is closest to the uphole end or the surface. “Below” instead refers to a location further away from the uphole end or the surface and closer to a downhole end of the tool. “Bottom” and “lowermost” refers to a location closest to the downhole end or furthest away from the surface. When using these terms, it is assumed that the tool is in use, i.e. inserted into a well casing.Figs. 1 to 6 show an exemplary embodiment of a perforating tool 2 for perforating a well casing. Figs. 3 to 5 show magnified views of a cross-sectional illustration of Fig. 2. The respective selected sections are marked in Fig. 2. In Figs. 1 and 2, the left-hand side of the drawing shows an uphole end 4, while the right-hand side refers to a downhole end 6. The tool 2 has a tool body 8 that extends from the uphole end 4 to the downhole end 6. The tool body 8 is generally cylindrical. In this exemplary embodiment, the tool body 8 is separated into a first longitudinal section 10 and a second longitudinal section 12. In the first longitudinal section 10, a plurality of cutter elements 14 is arranged, which are radially movable relative to a longitudinal axis 90. They can assume a retracted position, in which they are radially closest to the longitudinal axis 90, and an extended position, in which they are furthest away from the longitudinal axis 90. In the retracted position, the cutter elements 14 allow to freely move the tool 2 in the well casing, while in the extended position the cutter elements 14 create a perforation in the well casing. In the second longitudinal section 12, a plurality of cylinder units 16 is provided. The cylinder units 16 are arranged in a row along the longitudinal axis 90. Each cylinder unit 16 has an inner element 18 and an outer element 20. The cylinder units 16 are configured to move a drive member 22 relative to the first longitudinal section 10 to extend or retract the cutter elements. 14. For achieving this, the cylinder units 16 are in fluid communication with a fluid supply duct 24 that extends from a fluid supply inlet 26 to the downhole end 6. By providing a fluid pressure at the fluid supply inlet 26, the cylinder units 16 move. Details of how the tool 2 is operated are shown in Figs. 3 to 5.In Fig. 3, the uphole end 4 is shown. Here, a top portion 28 of the fluid supply duct 24 is illustrated, which widens in a direction towards the fluid supply inlet 26. The top portion 28 is arranged in a top part 30 of the body 8. The top part 30 has a shoulder 32 surrounding a hollow cylindrical insert 34. A main body 36 having a hollow-cylindrical upper end 38 is placed in contact to the shoulder 32 and encloses the insert 34. Exemplarily, the main body 36 is fastened to the top part 30 through screws 40, which are distributed along the upper end 38 of the main body 36. An inner tube 42 is arranged concentrically to the main body 36. An upper end 44 of the inner tube 42 rests inside a tube recess 46 of the top part 30. The inner tube 42 has a sealing ring 48 that is placed between the inner tube 42 and the tube recess 46 for sealing the interface between the inner tube 42 and the tube recess 46. The inner tube 42 has an inner tube fluid channel 50, which is in fluid communication with a bore 25 inside the top part 30, and thus constitutes a part of the internal fluid supply duct 24. The main body 36 and the inner tube 42 define an annular space, in which a plurality of coil springs 52 is arranged. The coil springs 52 are arranged parallel to the longitudinal axis 90 and are distributed around the longitudinal axis 90 in the annular space. For supporting the coil springs 52, spring supports 54 in the form of pins or other elongated components are arranged in each of the coil spring 52. The coil springs 52 are held in place by a spring housing 56.The spring housing 56 has a radial collar 58 that extends in a radial direction from the inner tube 42 to the main body 36 and may act as an interface for all coil springs 52 and a plurality of push rods 60. The push rods 60 are aligned parallel to the longitudinal axis 90 and are distributed around the inner tube 42. With their sides opposite to the coil springs 52, the push rods 60 are inserted into a rod holder 62 that comprises a cutter element support section 64. The cutter element support section 64 is in surface contact with the cutter elements 14 and presses the cutter elements 14 into the direction of the downhole end 6 through the axial force generated by the coil springs 52. As will be explained further below, the coil springs 52 provide a reversing force that leads the cutter elements to reach their retracted positions again.Fig. 4 shows a cylinder unit 16 in more detail. Here, the cylinder unit 16 has a cylinder sleeve 20 with a substantially cylindrical outer surface. At an inner side of the cylinder unit 16, an annular radial protrusion 66 substantially perpendicularly extends from an inner surface 68 of the outer element 20 towards the inner element 18. The cylinder sleeve 20 defines a pressure chamber 68, which is divided by the inner element 18 into a first chamber portion 70 and a second chamber portion 72. The inner element 18 has a central bore 74, which is in fluid communication with the inner tube fluid channel 50 through a connector fluid channel 78 of a main body connector 76. Fluid supplied into the fluid supply inlet 26 reaches the central bore 74 and is supplied into the first chamber portion 70 through ports 80. Thus, the fluid pressure in the first chamber portion 70 will increase when the fluid pressure at the fluid supply inlet 26 is increased. The inner element 18 is fixedly attached to the main body connector 76, which in turn is a fixed part of the first longitudinal section 10. Consequently, the inner element 18 cannot move in an axial direction. When the fluid pressure in the first chamber portion 70 is increased, the annular protrusion 66 is pressed towards the first longitudinal section 10 and the cylinder sleeve 20 will thus move along the inner element 18. When the tool 2 is deployed in a well casing, a top cylinder unit 16a will be the uppermost cylinder unit 16. Just like the cylinder unit 16 it has a first chamber portion 70 that is supplied with fluid through ports 82 from the main body connector 76. The top cylinder unit 16a has an end surface 84 formed as a ring 84, which is in surface contact with a plurality of push rods 86, which are distributed around the main body connector 76. The push rods 86 are in contact with a cutter element pusher 88, which may be an annular component. The cutter element pusher 88 or the combination of push rods 86 and the cutter element pusher 88 may be considered the drive member 22.The cutter element pusher 88 pushes onto cutter element holders 92, which each carry one of the cutter elements 14. The cutter element holder 92 and the cutter elements 14 are distributed around the longitudinal axis 90. They are sandwiched between the cutter element support section 64 and the cutter element pusher 88. Here, they are arranged in a holding block 94 having radial openings 96, through which the cutter elements 14 can protrude. In and radially inwards of the openings 96 a series of inclined grooves 98 is provided, which are in contact with corresponding inclined tongues arranged at sides of the cutter elements 14 that are hidden in Fig. 4. This combination of inclined grooves and inclined tongues leads to a radial outward motion by pushing the cutter element holder 92 towards the uphole end. As explained above, the cutter elements 14 will face an opposite pressing force of the coil springs 52 when they are extended. Thus, the pressing force provided by the cylinder units 16 must be sufficiently large to overcome the spring force as well as the mechanical resistance of the well casing to reliably perforate it. When the pressure in the first chamber portions 70 is reduced after perforating the casing well, the cutter elements 14 will be retracted again.It can be seen in the drawings that a plurality of cylinder units 16 jointly generate the pressing force for extending the cutter elements. All cylinder sleeves 20 are contacting each other, such that the individual pushing forces sum up at the cutter element pusher 88 to a total pushing force. The number of cylinder units 16 arranged one after another along the longitudinal axis 90 can be chosen depending on the required force for extending the cutter elements 14 and the available fluid pressure at the supply inlet 26. The inner elements 20 of the cylinder units 16 are attached to each other, to form a chain of inner elements 20 that remain in a fixed position relative to the first longitudinal section. Exemplarily, two consecutive inner elements 18 create an overlapping region 19, in which an upper inner element 18 is inserted into a lower inner element 18. To secure this arrangement, fastening elements 21 are radially inserted into the overlapping region. When the tool 2 is assembled, one inner element 18 may be connected to a previous inner element 18 and they can be secured to each other. Afterwards, the associated outer element 20 can be placed on it. Then, a subsequent inner element 18 is provided, connected to the previous inner element 18 and the subsequent outer element 20 is provided. This is done, until the desired number of cylinder units 16 is provided.The cylinder units 16 and 16a, engage each other at their end faces facing each other. This is achieved by engagement elements 100, which include recesses 100a and elongated axial protrusions 100b, which are complementarily shaped, as shown in Figs. 1 and 6. However, they are designed to leave a gap 102, such that fluid may flow out from the second chamber portion 72 through the respective gaps 102. When the cylinder sleeves 20 move upwards, the volume of the second chamber 72 is reduced, and fluid that remains in there will be discharged through the gap 102 into the surrounding of the tool 2. When moving back, fluid may enter the second chamber portion 72 again. The gap 102 is caused by an axial distance between a ground portion 101 of the recess 100a and a tip portion 103 of the protrusion 100b.Fig. 5 shows the downhole end 6 with a bottom cylinder unit 16b. A bottom part 104 is attached to the bottom cylinder unit 16b and has a bottom bore 106, which is in fluid communication with the bore 74 of the bottom inner element 18. For enabling a sufficient pressure inside the first chamber portions 70, the bottom bore 106 of the bottom part 104 may be closed by a plug, an integrated valve or an orifice leading to a sufficient pressure for the desired operation. The bottom part 104 may comprise a bottom stopper 108 to hold the cylinder sleeves 20 on the tool 2, when no fluid pressure is provided, to counteract the force of the coil springs 52 and the weight force of the cylinder sleeves 20.Figs. 7 to 10 show various cross-sectional views as indicated in Fig. 1. Fig. 7 shows a cross-sectional view further upwards. Here, keys 110 are shown, which are arranged in key recesses 112 that radially extend from an outer perimeter of the main body towards the center of the cross-section. The keys 110 are in contact with recesses 114 of the main body connector 76. The keys 110 thus couple the main body 36 and the main body connector 76 and are configured to transfer a torque between the main body 36 and the main body connector 76.Fig. 8 shows a cross-sectional view of the push rods 86 in a transition region between the first longitudinal section 10 and the second longitudinal section 12. Here, four pins 126 are distributed over the cross-section between the push rods 86. The pins 126 are inserted into the main body 36 and the top cylinder unit 16a. The pins 126 hold a circlip 122 in place (see Fig. 2). The circlip 122 is shearing off by axial force from the pins 126 on the first activation of the tool 2. The circlip 122 secures the main body 36 and the top cylinder unit 16a in an initial position, i.e. in a fixed distance to each other. This allows to safely lower the tool 2 into the well casing without inadvertently extending the cutter elements 14. After shearing off the circlip 122, the top cylinder unit 16a may be moved towards the uphole end 4 to extend the cutter elements 14.Fig. 9 shows a cross-sectional view of the top cylinder unit 16a with a viewing direction towards the downhole end 6. Here, the main body connector 76 engages with the top cylinder unit 16a through a shaft-hub connection 128. Torque that is introduced into the main body 36 is thus transferred into the main body connector 76 through the keys 110, is transferred along the longitudinal axis 90 towards the top cylinder unit 16a and is then transferred into the top cylinder unit 16a through the shaft-hub connection 128. This provides a reliable torque transfer through the tool 2. Fig. 10 shows a cross-sectional view through a key cover 132 arranged close to the downhole end 6 and in viewing direction towards the downhole end 6. The bottom cylinder unit 16b is coupled with the bottom part 104 through a plurality of keys 134, which radially extend through the bottom cylinder unit 16b into the bottom part 104. To prevent the keys 134 from falling out of respective recesses 130, the key cover 132 in the form of a hollow-cylindrical element is placed to enclose the keys 134.Fig. 11 shows a perforating tool 136 in a lateral view. Fig. 12 shows the perforating tool 136 in a lateral sectional view. Details of the sectional view of Fig. 12 are shown in Figs. 13 to 15, as indicated by dashed lines in Fig. 12. The perforating tool 136 comprises a tool body 138 having an uphole end 4 and a downhole end 6. The tool 136 comprises a first longitudinal section 135 and a second longitudinal section 137. In the first longitudinal section 135, at least one cutter element 14 is arranged in a way comparable to the illustrations of Figs. 1 and 2. In the second longitudinal section 137, a plurality of cylinder units 140 is provided. The cylinder units 140 comprise outer elements 142 and inner elements 144. The outer elements 142 comprise axially effective, face-side engagement elements 146 comparable to the engagement elements 100 shown in Fig. 1. The outer elements 142 are static and do not move along the longitudinal axis 90, while the inner elements 144 are configured to move along the longitudinal axis 90.As shown in Fig. 13, each outer element 142 comprises a pressure chamber 148, divided into a first chamber portion 150 and a second chamber portion 152. Fluid that enters the first chamber portion 150 through ports 154 leads to pushing the inner element 144 into the direction of the uphole end 4. In doing so, a drive member 156, which is arranged above the inner element 144, is pushed towards cutter elements 14. The cutter elements 14 are provided in a way similar to the exemplary embodiment shown in Figs. 1 to 10. The drive member 156 exemplarily comprises a drive tube 158, and a cutter element pusher 88, which may be the same as shown in the previous exemplary embodiment. The drive tube 158 comprises a top shoulder 157, which is in surface contact with the cutter element pusher 88 when being pushed by the inner element 144.The engagement elements 146 may have gaps 160, too. The gaps 160 allow excess fluid to be discharged from the second chamber portions 152 into the surrounding of the tool 136, when the cutter elements 88 are retracted. When retracting the cutter elements 88, fluid may enter the second chamber portions 152 through the gaps 160 again.Fluid is supplied from the uphole end 4 into the inner elements 144 through a fluid supply duct 162, which extends from the fluid supply inlet 26 through a bore 164 in a top part 166 into the drive tube 158. A top portion of the drive tube 158 is slidably arranged in a sliding block 161, which is sandwiched between the top part 166 and the main body 139. The drive tube 158 is configured to slide parallel to the longitudinal axis 90 within the sliding block and maintain a fluid communication with the bore 164. The drive tube 158 comprises a flow channel 159 in a central region of its cross section. The flow channel 159 is directly connected to an internal flow channel 168 of the inner elements. From there, the fluid may enter the respective first chamber portion 150. All inner elements 144 are attached to each other, such that their flow channels 168 are in fluid communication to convey the fluid into each first chamber portion 150. A bottom portion of the bottom inner element 144 is slidably arranged in a bottom part 170. To allow a significant fluid pressure to build up in the first chamber portions 150, a plug, an orifice or a valve may be arranged in the bottom part 170 to prevent or minimize a discharge of fluid. Fig. 16 shows the use of two sets of cutter elements 14 in a perforating tool 136. Here, a top portion of a bottom drive tube 158 is arranged in a bottom sliding tube 161, which is followed by a second drive tube 158, a top portion of which may be slidably supported in a second sliding block 161 arranged further upwards. In the bottom sliding block 161, initially there could be an axial gap 172 between the two drive tubes 158. This allows to generate an initial extension of the lower cutter elements 14 about at least a part of the desired extension motion when the cylinder units 16 are operated. When the bottom drive tube 158 contacts the top drive tube 158, the upper cutter element pusher 88 is moved to extend the upper cutter elements 14.Figs. 17a and 17b show a modified mechanism for securing the perforating tool 2 from inadvertent extension of the cutter elements 14 without pins 126. A three-dimensional sectional view of a transition region between the first longitudinal section 10 and the second longitudinal section 12 is shown in two different states. Each of the push rods 86 that are driven by the cylinder units 16 is divided into an upper push rod section 86a and a bottom push rod section 86b. The main body connector 76 is divided into a top connector section 76a and a bottom connector section 76b. Both sections 76a and 76b are configured to be swivelable about a limited angle of exemplarily 45°, but generally torque-transferring. Hence, the first longitudinal section 10 and the second longitudinal section 12 may be twisted relative to each other in a limited angular range, if a torque is introduced into the first longitudinal section 10 and if the second longitudinal section 12 experiences friction inside the well casing. By twisting the sections 10 and 12 relative to each other, the bottom sections 86b of the push rods 86 may be brought into or out of an alignment with the top push rod sections 86a. Fig. 17a shows the bottom push rod sections 86b in a first state to be flushly aligned with the top push rod sections 86a. In this first state, the push rods 86 may be pushed in an upward direction by the cylinder units 16 and may thus extend the cutter elements 14.Fig. 17b shows the bottom push rod sections 86b in a circumferential offset from the top push rod sections 86a as a second state. Here, the bottom push rod sections 86b are in or close to a contact with a bottom surface 37 of the main body 36. Hence, they cannot be pushed upwards by the cylinder units 16, and thus, the cutter elements 14 cannot be extended. In this state, the tool 2 can be safely lowered into a well casing and an inadvertent extension of the cutter elements 14 can be prevented. Reference numerals 2 perforating tool4 uphole end6 downhole end8 tool body10 first longitudinal section12 second longitudinal section14 cutter element16 cylinder unit16a top cylinder unit16b bottom cylinder unit18 inner element19 overlapping region20 outer element / cylinder sleeve21 fastening elements22 drive member24 fluid supply duct25 bore26 fluid supply inlet28 top portion30 top part32 shoulder34 insert36 main body37 bottom surface38 upper end40 screws42 inner tube44 upper end46 tube recess48 sealing ring50 inner tube fluid channel52 coil springs54 spring support56 spring housing58 radial collar60 push rod62 rod holder64 cutter element support section66 radial protrusion68 inner surface70 first chamber portion72 second chamber portion74 central bore76 main body connector76a, b connector section78 connector fluid channel80 port82 port84 ring86 push rod86a, b push rod sections88 cutter element pusher90 longitudinal axis92 cutter element holder94 holding block96 radial opening98 inclined groove100 engagement element100a recess100b elongated axial protrusion102 gap104 bottom part106 bottom bore108 bottom stopper110 key112key recess114recess126pin128shaft-hub connection130recess132key cover134key135first longitudinal section136perforating tool137second longitudinal section138tool body139main body140cylinder unit142outer element144inner element146engagement elements148pressure chamber150first chamber portion152second chamber portion154ports156drive member157top shoulder158drive tube159flow channel160gap161sliding block162fluid supply duct164bore166top part168internal flow channel170bottom part  

Claims

Claim 1. A perforating tool (2, 136) for perforating a well casing, comprising:a tool body (8, 138) configured to be placed in a well casing, the tool body (8, 138) having a longitudinal axis (90), a first longitudinal section (10, 135) and a second longitudinal section (12, 137),at least one cutter element (14) arranged in and radially moveable relative to the first longitudinal section (10, 135) of the tool body (8, 138) between a retracted position and an extended position to create a perforation in the well casing,an drive member (22, 156) arranged in the second longitudinal section (12, 137) and coupled with the at least one cutter element (14),a plurality of cylinder units (16) arranged in a row along the longitudinal axis (90) in the second longitudinal section (12, 137), each cylinder unit (16) having an inner element (18, 144) and an outer element (20, 142), the inner element (18, 144) dividing a pressure chamber of the respective cylinder unit (16) into a first chamber portion (70, 150) and a second chamber portion (72, 152),wherein the drive member (22, 156) is moveable relative to the first longitudinal section (10, 135) to move the at least one cutter element (14) between the retracted position and the extended position,wherein the cylinder units (16) are configured to move the drive member (22, 156) relative to the first longitudinal section (10, 135),wherein a fluid supply duct (24) is formed along the longitudinal axis (90) of the tool body (8, 138) and comprises a plurality of ports (80, 82) in fluid contact with each first chamber portion (70, 150) to enable fluid to flow from the fluid supply duct (24) into each first chamber portion (70, 150), such that by increasing a fluid pressure in the fluid supply duct (24) each of the cylinder units (16) operates to drive the drive member (22, 156),wherein the outer elements (20, 142) of the cylinder units (16) engage each other through axially effective, face-side engagement elements (100, 146). Claim 2. The perforating tool (2, 136) according to claim 1,wherein the engagement elements (100, 146) are configured to be inserted into each other axially.  Claim 3. The perforating tool (2, 136) according to claim 1 or 2,wherein the engagement elements (100, 146) are formed as positive locking means.Claim 4. The perforating tool (2, 136) according to any of the preceding claims,wherein the engagement elements (100, 146) comprise fluid-permeable gaps that are in fluid communication with the second chamber portions (12). Claim 5. The perforating tool (2, 136) according to claim 1,wherein the outer elements (20, 142) are coupled with the drive member (22, 156), andwherein the inner elements (18, 144) of subsequent cylinder units (20, 142) are connected to each other. Claim 6. The perforating tool (2, 136) according to claim 1 or 2,wherein the drive member (22, 156) comprises a cutter element pusher (88) coupled with the at least one cutter element (14) in the first longitudinal section (10, 135) and a plurality of push rods (86) that are distributed around and arranged parallel to the longitudinal axis (90) and extend from the cutter element pusher (88) into the direction of the second longitudinal section (12, 137). Claim 7. The perforating tool (2, 136) according to claim 6,wherein the push rods (86) are in contact with an end surface (84) of one of the cylinder units (16), which is closest to the first longitudinal section (10, 135).  Claim 8. The perforating tool (2, 136) according to any of the preceding claims,wherein the engagement elements (100, 146) are arranged at a radial outer rim of the respective outer element (20, 142) of the respective cylinder unit (16). Claim 9. The perforating tool (2, 136) according to any of the preceding claims,wherein the engagement elements (100, 146) comprise protrusions (100b) and / or recesses (100a) extending parallelly to the longitudinal axis (90). Claim 10. The perforating tool (2, 136) according to claim 5,wherein the inner elements (18, 144) are configured to be insertable into each other at their end faces to form an overlapping region (19) in an axial direction, andwherein a fastening element (21) is inserted radially into the overlapping region (19). Claim 11. The perforating tool (2, 136) according to claim 10,wherein the fastening element (21) is designed to create a positive connection in a tool-free manner by inserting it into corresponding openings. Claim 12. The perforating tool (2, 136) according to any of the preceding claims, comprising:a vent port,wherein the vent port is configured to form a fluid connection between the fluid supply duct (24) and the surrounding of the perforating tool (2, 136) when the at least one cutter element (14) is fully extended Claim 13. The perforating tool (2, 136) according to claim 12, when dependent on claim 4,wherein the vent port is arranged in one of the outer elements (20) of the cylinder units (16),wherein a connection port is arranged in a static component of the tool (2, 136) in fluid communication with the fluid supply duct (24), andwherein the vent port and the connection port are configured to be spaced apart until the at least one cutter element (14) is about to be fully extended. Claim 14. The perforating tool (2, 136) according to any of the preceding claims,wherein the first longitudinal section (10) and the second longitudinal section (12) are configured to be twistable about a limited angle into a first state and a second state, andwherein the cylinder units (16) are blocked from driving the drive member (22, 156) in one of the first state and the second state at least once. Claim 15. The perforating tool (2, 136) according to any of the preceding claims,comprising a plurality of sets of cutter elements (14) spaced apart along the longitudinal axis (90). 

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