WO2025061862A1

WO2025061862A1 - Energy transferring system and casing plug

Info

Publication number: WO2025061862A1
Application number: PCT/EP2024/076302
Authority: WO
Inventors: Thomas HIORTH
Original assignee: Interwell Norway As
Priority date: 2023-09-20
Filing date: 2024-09-19
Publication date: 2025-03-27
Also published as: NO348717B1; NO20231007A1

Abstract

The present invention relates to an energy transferring system (50) for transferring energy between a first part (1a) of a well tool (1) and a second part (1b) of the well tool (1). The well tool (1) comprises a mandrel (2) and an outer housing (3) with a first housing section (3a), a second housing section (3b), a third housing section (3c) and a fourth housing section (3d). The energy transferring system (50) comprises a first spring assembly (51), a second spring assembly (55), a delay system (60) and a force multiplier system (70). The delay system is located between the first spring assembly (51) and the second spring assembly (55), and is brought from an initial state to an actuated state when a predetermined condition has been met. The force multiplier system (70) is located between the delay system (60) and the fourth housing section (3d) for transferring energy between the first spring assembly (51) and the second spring assembly (55) when the delay system (60) is in the actuated state.

Description

FIELD OF THE INVENTION The present invention relates to an energy transferring system. The present invention also relates to a casing plug with such an energy transferring system. The present invention also relates to a method for setting a casing plug. BACKGROUND OF THE INVENTION Casing plugs are used in a casing of a well, for the purpose of temporarily closing the well, for the purpose of pressure testing the casing etc. Casing plugs are typically run into the well in a radially retracted state by means of a drill pipe and subsequently radially expanded into contact with the inner surface of the casing by means of the drill pipe. The casing plug may be manipulated by means of the drill pipe by pushing the drill pipe down, by pulling the drill pipe up, by rotation of the well pipe to the left or by rotation of the drill pipe to the right. Typically, the casing plug has an anchoring device for anchoring of the plug to the inner surface of the casing and a sealing device with an elastomeric sealing element for preventing fluid flow between a position below the sealing device and a position above the sealing device. One object of at least some embodiments of the present invention is to provide a casing plug that can be radially expanded into the inner surface of the casing and then radially retracted again multiple times. This is often referred to as a resettable casing plug. The drill pipe is typically made by drill pipe elements that are threadedly connected to each other. Clockwise rotation connects two elements to each other, while counter-clockwise rotation disconnects the two elements from each other. Another purpose of the present invention is to provide a resettable casing plug which can be manipulated by the drill string without any risk of disconnecting drill pipe elements from each other. Hence, one object of at least some embodiments of the invention is that there should be no need for counter-clockwise rotation of the drill pipe in order to manipulate the casing plug. US 4149594 discloses a retrievable well plug which is adaptable to be moved longitudinally within a well conduit. The plug contains normally retracted slip elements which are manipulated into engagement with the conduit by expander elements. An elastomeric packing element, of known construction, is expandable exteriorly around the well tool and is adapted to selectively seal with the well conduit. Booster means are provided for transmitting the compressive force defined by differential pressure acting across the packing element when the slips are in expanded position against the conduit and the packing element is sealed with the well conduit, such that the packing element is maintained in sealing relationship with the well conduit. Another object of at least some embodiments of the invention is to reduce the risk of fluid leakages due to a deformed elastomeric sealing element due to temperature changes. SUMMARY OF THE INVENTION The present invention relates to an energy transferring system for transferring energy between an first part of a well tool and a second part of the well tool, wherein the well tool comprises: - a mandrel; - an outer housing, wherein the outer housing comprises a first housing section, a second housing section, a third housing section and a fourth housing section, wherein the first housing section is belonging to the first part of the well tool and wherein the fourth housing section is belonging to the second part of the well tool and wherein the second housing section and the third housing section are located between the first housing section and the fourth housing section; wherein the energy transferring system comprises: - a first spring assembly; - a second spring assembly; - a delay system located between the first spring assembly and the second spring assembly, wherein the delay system is brought from an initial state to an actuated state when a predetermined condition has been met; - a force multiplier system located between the delay system and the fourth housing section for transferring energy between the first spring assembly and the second spring assembly when the delay system is in the actuated state. The outer housing is provided radially outside of at least parts of the mandrel. The well tool, and hence the energy transferring system, may be defined with a central longitudinal axis. The first part of the well tool may be a slips support. The second part of the well tool may be a seal support. The well tool, and hence the energy transferring system, is configured to be operated from topside by performing the three following actions: - pushing the mandrel down relative to a well bore; - pulling the mandrel up relative to a well bore; - clockwise rotation of the mandrel relative to the well bore. The well bore may be a casing, a production tubing, a production liner etc. of connecting drill string segments to each other, thereby forming a drill string, where clockwise rotation causes drill string segments to be connected/tightened, and counter-clockwise rotation causes drill string segments to be disconnected/loosened from each other. Hence, clockwise rotation of the mandrel will not cause drill string segments to be disconnected from each other. Kinetic energy applied to the well tool in the form of relative longitudinal movement between the first part of the well tool and the second part of the well tool in a direction towards each other may be stored as potential energy in the first spring assembly and in the second spring assembly; wherein the delay system may be configured such that energy is stored in first spring assembly before energy is stored in the second spring assembly. Preferably the delay system is configured such that the first spring assembly reaches a maximum energy storage state before energy is stored in the second spring assembly. The predetermined condition may be a condition indicative of the amount of energy stored in the first spring assembly. The predetermined condition may be a condition indicative of a relative travel distance between elements in the first the spring assembly. It will be appreciated that the first and/or the second spring assembly may store energy in any of a variety of ways, such as by means of mechanical or hydraulic spring elements and such as by spring elements that operate in compression, in tension, or in torsion. The two spring assemblies may both use the same principle to store energy. In one example the spring assembles use compression springs and in that case the predetermined condition may be a condition indicative of the compression state of the first spring assembly. Hence, the delay system is brought from the initial state to the actuated state when elements in first the spring assembly has moved the predetermined relative travel distance. The first spring assembly may comprise a first spring supporting surface, a second spring supporting surface and a first spring located longitudinally between the first spring supporting surface and the second spring supporting surface; wherein the first spring supporting surface of the first spring assembly may be fixed to the first housing section. The predetermined condition may be a condition indicative of a relative travel distance between the first spring supporting surface and the second spring supporting surface of the first spring assembly. The second spring assembly may comprise a first spring supporting surface, a second spring supporting surface and a second spring located longitudinally between the first spring supporting surface and the second spring supporting surface, wherein the second spring supporting surface of the second spring assembly may be secured to the third housing section. The first spring has a first spring constant. The second spring has a second spring constant. The first spring constant may be lower than the second spring constant. The first spring assembly may be located above the second spring assembly. Hence, the first spring assembly may be referred to as an upper spring assembly, while the second spring assembly may be referred to as a lower spring assembly. Also the respective parts of the assemblies may be referred to as respective upper/lower parts. The first spring may be biased between the first spring supporting surface and the second spring supporting surface of the first spring assembly in the initial state. The upper spring may be unbiased in the initial state. The lower spring may be biased between the first spring supporting surface and the second spring supporting surface of the second spring assembly in the initial state. The second spring may be unbiased in the initial state. The biasing force of the first spring may be lower than the biasing force of the second spring. The energy transferring system may be configured such that the first spring is at least partially compressed before the second spring is compressed. Preferably the first spring is ful ly compressed prior to compression of the second spring. The delay system may comprise a deflectable finger having a first end and a second end, wherein the second end may comprise a locking notch, wherein the locking notch may be engaged with the second housing section in the initial state. The locking notch may be engaged with an inclining surface of the second housing section. The locking notch may be brought out of engagement with the second housing section when the predetermined condition may be met. When the locking notch is brought out of engagement with the second housing section, the deflectable finger is allowed to deflect. The deflectable finger may be configured to deflect radially inwards. The second end of the deflectable finger may comprise an inclined surface. The inclined surface and/or the inclined surface may allow the deflectable finger to be pushed radially inwards when the predetermined condition is met. The inclined surface may allow the deflectable fingers to return their position in the initial state. The delay system may comprise a longitudinally displaceable intermediate sleeve located at least partially radially inside the deflectable finger, wherein the intermediate sleeve has a first end, a second end, an outer surface and a reces s provided in the outer surface; wherein the outer surface may be preventing the deflectable finger to deflect and wherein first housing section may comprise an inwardly protruding surface, wherein the predetermined condition may be met by moving the inwardly protruding surface into contact with the intermediate sleeve and further displace the intermediate sleeve to a position in which the locking notch may be allowed to deflect inwardly into the recess. Hence, the locking notch is brought out of engagement with the second housing section. The intermediate sleeve may comprise a spring compartment. The delay system may comprise a spring provided within the spring compartment. The spring may be biased to move the intermediate sleeve to a position in which the locking notch is pushed out from the recess. The delay system may be referred to as a push lock. The direction of the relative travel distance between the elements in the first the spring assembly may be parallel with, or aligned with, the central longitudinal axis. The force multiplier system may comprise one or more link arms and/or one or more cam surfaces. The force multiplier system is for transferring energy between the first spring assembly and the second spring assembly when the delay system is in the actuated state. It may thus be configured to transfer energy from the first assembly to the second spring assembly when the delay system is in the actuated state. The force multiplier system may receive energy from the first spring assembly as mechanica l energy with a first magnitude of force and a first travel distance. The force multiplier system may transfer energy to the second spring assembly with a second magnitude of force and a second travel distance. Where the first spring assembly has a lower spring constant than the second spring assembly then the first magnitude of force is lower than the second magnitude of force and the first travel distance is larger than the second travel distance. The mechanical advantage of the force multiplier mechanism may be equivalent to the ratio of the spring constants of the first spring assembly and the second spring assembly. The force multiplier system comprises: - an upper section secured to the second housing section; - a lower section comprising, or may be connected to the first spring supporting surface of the second spring assembly; - a first arm having a first end and a second end, wherein the first end may be pivotably connected to the upper section; - a second arm having a first end and a second end, wherein the first end may be pivotably connected to the lower section; wherein the second end of the first arm may be pivotably connected to the second end of the second arm. The second end of the first arm may be directly connected to the second end of the second arm. The second end of the first arm is may be connected to the second end of the second arm via an intermediate arm. The first arm and the second arm may be oriented relative to each other with an angle, and wherein the force multiplier system may be configured to be in a folded state and in an unfolded state, wherein the angle may be smaller in the folded state than in the unfolded state. The angle may be 90º 170º in the folded state. The angle may be 170 - 180º in the unfolded state. Preferably, the angle is approximately equal to, or slightly below 180º in the unfolded state. The angle may be measured as the angle between a line between the pivoting axis of the first arm and a line between the pivoting axis of the second arm. The force multiplier system may comprise an actuator for guiding the first arm and the second arm between the folded state and the unfolded state. The actuator may comprise a cam surface for applying a required force and motion to a moving part of one of the link arms. The actuator may be configured to move in translation relative to a stationary part of one of the link arms and it may oscillate between two end points of the translation movement during operation of the energy transferring system. The actuator may comprise a lower sleeve having a cam surface provided in contact with the first arm and/or the second arm, wherein longitudinal movement of the lower sleeve may be guiding the first arm and the second arm between the folded state and the unfolded state. The second end of the first arm and/or the second end of the second arm may be provided with a contact area provided in contact with the cam surface, wherein the cam surface may be provided in contact with a first part of the contact area in the folded state, and wherein the cam surface may be provided in contact with a second part of the contact area in the unfolded state. The first part of the contact area may be different from the second part of the contact area. The contact area may be shaped as a circular arc. The contact surface may have a shape being tangential to the contact area at each point of contact between the contact surface and the contact area. The contact surface may be a continuous surface. The contact surface may be a concave surface, a linear surface or a convex surface. Preferably, the contact surface is a convex surface. The actuator may comprise an upper sleeve, wherein the first end of the deflectable finger may be secured to, or may be connected to, the upper sleeve, wherein the upper sleeve may be engaged by the first housing section when the delay system may be in the actuated state. The upper sleeve may be engaged by the first housing section via the intermediate sleeve when the delay system is in the actuated state. The upper sleeve may be connected to the lower sleeve. The upper sleeve and the lower sleeve may be provided as one single sleeve. The force multiplier system may be locked in the unfolded state. Hence, when releasing a downward pressure on the force multiplier system, the force multiplier system will not return to the unfolded state by itself. This may be achieved by having a friction force, representing the friction between the circular arc and the contact surface in the unfolded state, to be larger than the force applied by the lower spring onto the first spring supporting surface. The invention may be embodied as a well tool comprising the energy transferring system as described above. The well tool may be a casing plug. The well bore may be a casing. The second spring supporting surface comprises, or may be secured to, the third housing section. Energy may be transferred between the third housing section and the fourth housing section or between the second housing section and the fourth housing section. When the delay system is in the actuated state, energy may be transferred between the third housing section and the fourth housing section and/or between the second housing section and the fourth housing section. When the delay system is in the initial state, energy may be transferred between the third housing section and the fourth housing section. When the delay system is in the initial state, energy may be transferred only between the third housing section and the fourth housing section. The present invention also relates to a casing plug for sealing a casing, wherein the casing plug comprises: - a mandrel; - an outer housing, wherein the outer housing comprises a first housing section, a second housing section, a third housing section and a fourth housing section, wherein the first housing section is belonging to the first part of the well tool and wherein the fourth housing section is belonging to the second part of the well tool and wherein the second housing section and the third housing section are located between the first housing section and the fourth housing section; characterized in that the casing plug comprises an energy transferring system according to the above, for transferring energy between the first part of the casing plug and the second part of the casing plug. The casing plug comprises: - a drag block device provided outside of the mandrel; - an anchoring device provided radially outside of the mandrel above the drag block device; - a sealing device provided outside of the mandrel; - a ratchet device for selectively locking parts of the outer housing to the mandrel. The casing plug comprises: an upper housing section located above the first housing section, wherein the sealing device may be provided between the upper housing section and the first housing section. The upper housing section may be referred to as the uppermost housing section as it may form the uppermost part of the outer housing. The upper housing section may be secured to the mandrel. The other housing sections may be longitudinally displaceable relative to the mandrel. The mandrel may comprise a housing support for supporting the weight of the outer housing sections below the upper housing section. The sealing device may comprise an upper seal support, a lower seal support and a sealing element between the upper seal support and the lower seal support. Relative longitudinal movement of the upper seal support and the lower seal support in a direction towards each other is moving the sealing element from a radially retracted position to a radially expanded position. Relative longitudinal movement of the upper seal support and the lower seal support in a direction away from each other is moving the sealing element from the radially expanded position to the radially retracted position. The upper seal support is connected to the upper housing section. The lower seal support may be connected to the first housing section. The sealing element may comprise an elastomeric material. In the radially expanded position, the sealing element prevents longitudinal fluid flow through the well bore. The casing plug comprises: a lower housing section located below the fourth housing section, wherein the anchoring device may be provided between the lower housing section and the fourth housing section. The anchoring device may comprise an upper slips support, a lower slips support and a slips element between the upper slips support and the lower slips support. Relative longitudinal movement of the upper slips support and the lower slips support in a direction towards each other is moving the slips element from a radially retracted position to a radially expanded position. Relative longitudinal movement of the upper slips support and the lower slips support in a direction away from each other is moving the slips element from the radially expanded position to the radially retracted position. The upper slips support is connected to the fourth housing section and the lower slips support are connected to the lower housing section. The slips element may comprise a serrated surface. In the radially expanded position, the serrated surface of the slips element is engaged with the inner surface of the wellbore and prevents longitudinal movement of slips element relative to the wellbore. The lower housing section may be referred to as the lowermost housing section as it may form the lowermost part of the outer housing. The drag block device provides friction between the casing plug and the well bore. The drag block device is secured to the lower housing section. The drag block device comprises one or several friction elements biased radially towards the well bore by means of springs. Hence, a friction force is created when the drag block device is dragged along the inner surface of the well bore. The ratchet device may comprise: - a first hatched area provided on the outside of the mandrel; - a second hatched area provided on the outside of the mandrel below the first hatched area; - a first ratchet ring secured to the lower housing section; - a second ratchet ring secured to the lower housing section below the first ratchet ring; wherein the first ratchet ring comprises a hatched area facing towards the mandrel; wherein the second ratchet ring comprises a hatched area facing towards the mandrel; wherein the hatched area of the first ratchet ring is configured to be engaged with the first hatched area of the mandrel, thereby allowing relative longitudinal movement between the first ratchet ring and the mandrel in a first direction while preventing relative longitudinal movement between the first ratchet ring and the mandrel in a second direction opposite of the first direction; wherein the hatched area of the second ratchet ring is configured to be engaged with the second hatched area of the mandrel, thereby allowing relative longitudinal movement between the second ratchet ring and the mandrel in the second direction while preventing relative longitudinal movement between the second ratchet ring and the mandrel in the first direction; wherein clockwise rotation of the mandrel is configured to move the first ratchet ring in the second direction when the hatched area of the first ratchet ring is engaged with first hatched area of the mandrel; wherein clockwise rotation of the mandrel is configured to move the second ratchet ring in the first direction when the hatched area of the second ratchet ring is engaged with second hatched area of the mandrel. The first ratchet ring may comprise ring segments, each ring segment being biased towards the mandrel. Preferably, the first ratchet ring comprises three, four ring or six segments. The second ratchet ring may comprise ring segments, each ring segment being biased towards the mandrel. Preferably, the second ratchet ring comprises three, four or six ring segments. The ratchet device may be configured to be switched between the following states: - a first ratchet state, in which the hatched area of the second ratchet ring is engaged with the second hatched area of the mandrel; - a second ratchet state, in which the hatched area of the first ratchet ring is engaged with first hatched area of the mandrel; - a third ratchet state; in which the hatched area of the first ratchet ring has been moved along the first hatched area of the mandrel. In the first state, the friction force of the drag block device is not sufficient to allow relative longitudinal movement between the hatched area of the second ratchet ring and the second hatched area of the mandrel. Hence, relative longitudinal movement between the mandrel and the second housing section is prevented. This prevents the anchoring device from being radially expanded. In the second state, the friction force of the drag block device is sufficient to allow relative longitudinal movement between the hatched area of the first ratchet ring and the first hatched area of the mandrel. Hence, relative longitudinal movement between the mandrel and the second housing section is allowed. By pushing the mandrel downwardly, the anchoring device will be set into engagement with the inner surface of the well bore. It is now possible to push the mandrel further down, as the anchoring device now is stationary relative to the wellbore, and the sealing device will be set. The ratchet device is brought from the first state to the second state by rotating the mandrel 2 clockwise, bringing the hatched area of the second ratchet ring out of engagement with the second hatched area of the mandrel, and bringing the hatched area of the first ratchet ring into engagement with the first hatched area of the mandrel. The ratchet device is brought from the second state to the third state by pushing the mandrel further down relative to the anchoring device. This will actuate the energy transferring system. The ratchet device is brought from the third state to the first state again by rotating the mandrel clockwise, bringing the hatched area of the first ratchet ring out of engagement with the first hatched area of the mandrel, bringing the hatched area of the first ratchet ring out of engagement with the first hatched area of the mandrel, and bringing the hatched area of the second ratchet ring into engagement with the second hatched area of the mandrel. The present invention also relates to a method for setting a casing plug in a casing, wherein the casing plug comprises a mandrel and an outer housing provided outside of at least parts of the mandrel, wherein the outer housing comprises a first housing section, a second housing section, a third housing section and a fourth housing section, wherein the second housing section and the third housing section are located between the first housing section and the fourth housing section; wherein the method comprises the steps of: a) lowering the casing plug into the casing while a drag block device of the casing plug is in contact with an inner surface of the casing; b) rotating the mandrel in a clockwise direction, wherein the drag block device is preventing rotation of a lower part of a lower housing section located below the housing sections; c) pushing the mandrel downwardly, wherein the drag block device is preventing downward movement of the lower housing section relative to the casing; thereby causing an anchoring device of the casing plug device above the drag block device to expand into engagement with the inner surface of the casing; d) pushing the mandrel downwardly, wherein the anchoring device is preventing downward movement of the fourth housing section immediately above the anchoring device relative to the casing; thereby causing a sealing device of the casing plug device above the fourth housing section to expand into engagement with the inner surface of the casing. In step a), a ratchet device is in in a first ratchet state. In step b), the ratchet device is brought from the first ratchet state to a second ratchet state. In step c), the ratchet device is in the second ratchet state. In step d) the ratchet device is in a third ratchet state. The method further may comprise the step of: e) pressure testing the casing above or below the sealing device after step d). The method further may comprise the step of: f) rotating the mandrel in the clockwise direction; and g) pulling the mandrel upwardly; thereby causing retraction of the sealing device and the anchoring device from their engagement with the inner surface of the casing. The method further may comprise the step of: - lowering or lifting the casing plug to a different location the casing; - repeating steps a) d). The method may further comprise the initial step of: - connecting an upper end of the mandrel to a tubular string, wherein the step of pushing the mandrel down comprises the step of pushing the tubular string down, wherein the step of pulling the mandrel up comprises the step of pulling the tubular string up and wherein the step of rotating the mandrel in the clockwise direction comprises the step of rotating the tubular string in the clockwise direction. The tubular string may be a drill pipe or a coiled tubing. Step d) may comprise the step of: - transferring energy between a first part of the casing plug and the second part of the casing plug by means of the energy transferring system according to the above. the well tool, when the well position relatively further away from the well opening. These terms apply both when the well has a vertical and horizontal orientation. are used interchangeably for the state/position in which the well tool is lowered to a is engaged with the inner surface of the well at the desired location in the well. e well tool which is radially expanded to be engaged with the inner surface of the well at the desired location in the well. The anchoring device may comprise a serrated surface which prevents the well tool from moving longitudinally within the well when engaged with the inner surface of the well. radially expanded into contact with the inner surface of the well at the desired location of the well. The function of the sealing device is to prevent or reduce longitudinal fluid flow at the desired location in the well, i.e. to prevent or reduce fluid from flowing between a location above the well tool and a location below the well tool. It is commonly known that the anchoring device and/or sealing device are only capable of performing their function in their radially expanded state in the well. Moreover, it should be noted that a well tool is rated to a pressure level or pressure interval and/or a temperature level or temperature interval. LIST OF DRAWINGS Fig. 1 is a cross sectional view of the casing plug in its run state; Fig. 2 is an illustration of the housing sections of the outer housing; Fig. 3 is an enlarged view of the dashed box A of fig.2 Fig. 4 is a cross sectional view of the casing plug during setting; Fig. 5 is a cross sectional view of the casing plug in its set state; Fig. 6 is an enlarged cross sectional view of the energy transferring system; Fig. 7 is an enlarged cross sectional perspective view of the delay system; Fig. 8a-8c illustrates the states of the energy transferring system; Fig. 9a illustrates a force multiplier system with link arms and their actuator in the run state; Fig. 9b illustrates the link arms and their actuator in the set state; Fig. 9c illustrates the contour of the contact surface of the actuator, with the circular arc of the arms at the position of the folded state; Fig. 9d illustrates the contour of the contact surface of the actuator, with the circular arc of the arms at the position of the unfolded state; Fig. 9e illustrates the geometry of the circular arc; Fig. 10a-10c illustrates the states of the ratchet device. DETAILED DESCRIPTION The present embodiment of the invention is a well tool in the form of a casing p lug 1 which is used to plug a well bore (WB) in the form of a casing pipe. The casing plug serves at least two purposes it is used to temporarily seal the casing during pressure testing of the casing, and/or it is used to permanently seal the casing when abandoning the well. The casing plug 1 is shown in fig.1 and comprises a mandrel 2 and an outer housing 3 provided outside of the mandrel 2. In addition, the casing plug 1 comprises a drag block device 10, an anchoring device 20, a sealing device 30, a ratchet device 40 (indicated within a dashed rectangle) and an energy transferring system 50. The above parts of the casing plug 1 will be described in detail below. The operation of the casing plug 1 will also be described in detail below. A longitudinal axis of the casing plug 1 is indicated as a dashed line LA in fig.1. The mandrel 2 In the present embodiment, the mandrel 2 is substantially a cylindrical pipe having an upper connection interface 2a for connection to a string of drill pipe. The mandrel 2 further comprises a lower connection interface 2b, to which drill pipe sections or other equipment may be connected. The mandrel 2 further comprises a housing support 2c below the outer housing 3 for supporting the weight of the outer housing 3 during handling of the casing plug topside etc. The outer housing 3 The outer housing 3 is provided outside of the mandrel 2 and comprises a number of housing sections. The housing sections are shown in fig. 1 and 2, and are listed below in order from top to bottom: - an upper housing section 3U; - a first intermediate housing section 3I1, which is also referred to as a first housing section 3a; - a second intermediate housing section 3I2, which is also referred to as a second housing section 3b; - a third intermediate housing section 3I3, which is also referred to as a third housing section 3c; - a fourth intermediate housing section 3I4, which is also referred to as a fourth housing section 3d; - a lower housing section 3L. It should be noted that the above sections are considered as the main housing sections. However, each of the above housing sections may comprise parts and/or subsections which may be movable relative to other parts and/or subsections of its housing section. The upper housing section 3U is secured to the mandrel 2, i.e. it is longitudinally fixed in relation to the mandrel 2. The other housing sections are longitudinally displaceable relative to the mandrel 2, or have at least some parts and/or subsections that are longitudinally displaceable relative to the mandrel 2. Relative longitudinal movement between at least some of the housing sections will bring the anchoring device 20 and the sealing device 30 between its radially retracted and radially expanded states. Relative longitudinal movement between at least some of the housing sections will also activate the ratchet device 40 and the energy transferring system 50. More details of the outer housing 3 and the housing sections thereof will be described further in detail below. It should be noted that as the upper housing section 3U is fixed to the mandrel 2, the housing support 2c will only support the weight of the housing sections below the upper housing section 3U. The drag block device 10 It is referred to fig. 1 and to fig. 10c. Here it is shown that the drag block device 10 is connected to the lower housing section 3L. The drag block device 10 comprises one or several friction elements 11 biased radially towards the well bore WB by means of springs 12 in order provide friction between the casing plug 1 and the well bore WB. During movement of the casing plug 1 relative to the casing WB, a friction force Fr is created, as the friction elements 11 are dragged along the inner surface of the casing. Friction is provided when the friction elements 11 are dragged both in the longitudinal direction relative to the casing, and when the friction elements 11 dragged in the rotational direction (i.e. rotated) relative to the casing. The friction force Fr in the longitudinal direction may be equal to, or may be different from, the friction force in the rotational direction. The anchoring device 20 It is now referred to fig.1, fig.2and to fig. 10a and 10b. The anchoring device 20 is connected between the lower housing section 3L and the fourth housing section 3d. The anchoring device 20 comprises an upper slips support 21, a lower slips support 22 and a slips element 25 between the upper slips support 21 and the lower slips support 22. The upper slips support 21 is connected to the fourth housing section 3d, while the lower slips support 22 is connected to the lower housing section 3L. Relative longitudinal movement of the upper slips support 21 and the lower slips support 22 in a direction towards each other is moving the slips element 25 from a radially retracted position (fig.10a) to a radially expanded position (fig.10b). Relative longitudinal movement of the upper slips support 21 and the lower slips support 22 in a direction away from each other is moving the slips element 25 from the radially expanded position to the radially retracted position. In fig.10a and fig. 10b, it is shown that the anchoring device 20 comprises a spring 26. The spring 26 is biased to pull the slips element 25 radially inwards when the upper slips support 21 and the lower slips support 22 are moved in a direction away from each other. As shown in fig. 10b, the slips element 25 comprise a serrated surface. In the radially expanded position, the serrated surface of the slips element 25 is engaged with the inner surface of the casing WB and prevents longitudinal movement of slips element 25 relative to the casing WB. The sealing device 30 It is now referred to fig.1 and fig.2. The sealing device 30 is connected between the upper housing section 3U and the first housing section 3a. The sealing device 30 comprises an upper seal support 31 connected to the upper housing section 3U, a lower seal support 32 connected to the first housing section 3a and a sealing element 35 between the upper seal support 31 and the lower seal support 32. Relative longitudinal movement of the upper seal support 31 and the lower seal support 32 in a direction towards each other is moving the sealing element 35 from a radially retracted position to a radially expanded position. Relative longitudinal movement of the upper seal support 31 and the lower seal support 32 in a direction away from each allows the sealing element 35 to retract from the radially expanded position to the radially retracted position. The sealing element 35 comprises an elastomeric material. In the radially expanded position, the sealing element 35 prevents longitudinal fluid flow through the casing WB. The ratchet device 40 In general, a ratchet device is a device which allows relative movement between two parts in a first direction, while it prevents relative movement between the two parts in a second direction, opposite of the first direction. This is achieved by means of a toothed area of the first part being engaged with a toothed area of the second part, and where properties of the toothed areas determine the allowed/prevented movement. In the present casing plug, this allowed/prevented movement is a longitudinal movement. In some cases, the toothed areas comprise teeth provided in parallel with each other. In the present embodiment, the toothed areas are spiral shaped, and hence also serves the purpose of threads. It is now referred to fig. 10a/10c. It should be noted that the purpose of the ratchet device 40 is to temporary lock parts of the outer housing 3 to the mandrel 2 and to subsequently release the locked parts. Hence, some parts of the ratchet device 40 are provided as part of the mandrel 2, while other parts are provided as part of the lower housing section 3L. The ratchet device 40 in the present embodiment comprises a first hatched area 2HA1 provided on the outside of the mandrel 2 and a second hatched area 2HA2 provided on the outside of the mandrel 2 below the first hatched area 2HA1. There is a non-hatched area 2NHA between the first hatched area 2HA1 and the second hatched area 2HA2. As shown in the drawings, the first hatched area 2HA1 are extending over a much larger area than the second hatched area 2HA2. In the present embodiment, the second hatched area 2HA2 is ca 2 cm in the longitudinal direction, the non-hatched area 2NHA is ca 4 times the second hatched area 2HA2 in the longitudinal direction, while the first hatched area 2HA1 is 8 10 times the second hatched area 2HA2 in the longitudinal direction. The ratchet device 40 further comprises a first ratchet ring 41 secured to the lower housing section 3L and a second ratchet ring 45 secured to the lower housing section 3L below the first ratchet ring 41. In the present embodiment, the first ratchet ring 41 and the second ratchet ring 45 both comprises six ring segments, each ring segment being biased towards the mandrel 2 by means of ring-shaped spiral springs 49 provided circumferentially outside of the ring segments. The first ratchet ring 41 comprises a hatched area 41HA facing towards the mandrel 2. The hatched area 41HA of the first ratchet ring 41 is configured to be engaged with the first hatched area 2HA1 of the mandrel 2, thereby allowing relative longitudinal movement between the first ratchet ring 41 and the mandrel 2 in a first direction D1 while preventing relative longitudinal movement between the first ratchet ring 41 and the mandrel 2 in a second direction D2 opposite of the first direction D. Clockwise rotation of the mandrel 2 is configured to move the first ratchet ring 41 in the second direction D2 when the hatched area 41HA of the first ratchet ring 41 is engaged with first hatched area 2HA1 of the mandrel 2 (under the assumption that the lower housing section 3L is held stationary due to friction between the drag block device 10 and the inner surface of the casing WB or due to the anchoring device being engaged with the inner surface of the casing WB). The second ratchet ring 45 comprises a hatched area 45HA facing towards the mandrel 2. The hatched area 45HA of the second ratchet ring 45 is configured to be engaged with the second hatched area 2HA2 of the mandrel 2, thereby allowing relative longitudinal movement between the second ratchet ring 45 and the mandrel 2 in the second direction D2 while preventing relative longitudinal movement between the second ratchet ring 45 and the mandrel 2 in the first direction D1. Clockwise rotation of the mandrel 2 is configured to move the second ratchet ring 45 in the first direction D1 when the hatched area 45HA of the second ratchet ring 45 is engaged with second hatched area 2HA2 of the mandrel 2 (again under the assumption that the lower housing section 3L is held stationary due to friction between the drag block device 10 and the inner surface of the casing WB). It should be noted that when the hatched area 45HA of the second ratchet ring 45 is provided circumferentially outside of the first hatched area 2HA1 of the mandrel 2, these hatched areas 45HA, 2HA1 will not engage each other, and relative longitudinal movement is allowed in both directions. The energy transferring system 50 It is now referred to fig. 1 and fig. 5. The purpose of the energy transferring system 50 is to transfer energy in the form of a pressure applied to the top of the mandrel 2 (either a force applied by a drill string manipulator, and/or a weight of the mandrel 2 and the string of drill pipe) to the sealing device 30 in order to press the sealing element 35 towards the inner surface of the casing in order to improve its fluid sealing properties. Of course, another purpose is to improve the engagement between the anchoring device 20 and the inner surface of the casing and hence to reduce the risk of the casing plug 1 being pushed up/down relative to the casing in the expanded state of the anchoring device. The energy transferring system 50 comprises a first spring assembly 51, a second spring assembly 55 , a delay system 60 located longitudinally between the first spring assembly 51 and the second spring assembly 55 and a force multiplier system 70 which is also located longitudinally between the first spring assembly 51 and the second spring assembly 55. In the present embodiment, the first spring assembly 51 is located above the second spring assembly 55. Hence, the first spring assembly 51 may be referred to as an upper spring assembly 51, while the second spring assembly 55 may be referred to as a lower spring assembly 55. The first and second spring assembly 51, 55 of the energy transferring system 50 The first spring assembly 51 comprises a first spring supporting surface 52, a second spring supporting surface 53 below the first spring supporting surface 52 and a first spring 54 located longitudinally between the first spring supporting surface 52 and the second spring supporting surface 53. The first spring supporting surface 52 is fixed to the first housing section 3a. The second spring assembly 55 may comprise a first spring supporting surface 56, a second spring supporting surface 57 and a second spring 58 located longitudinally between the first spring supporting surface 56 and the second spring supporting surface 57. The second spring supporting surface 57 is fixed to the third housing section 3c. The first spring 51 and the second spring 58 are cup springs. The cup springs of the first spring 54 has a first spring constant K54. The cup springs of the second spring 58 has a second spring constant K58. The first spring constant K54 is here lower than the second spring constant K58. As shown in fig.5, the first spring 51 comprises cup spring elements with a thickness smaller than the cup spring elements of the second spring 58. However, the first spring 51 has a higher number of such cup spring elements than the second spring 58. Hence, the first spring 51 requires relatively lower force but longer travel distance to go from uncompressed state to compressed state, while the second spring 58 requires relatively higher force but shorter travel distance to go from uncompressed state to compressed state. It should be noted that the second spring assembly 55 in addition comprises two cup springs 58a (fig. 6) having a lower spring constant than the cup springs of the first spring 54 to allow some flexibility to the relative movements between the outer housing sections. It should further be noted that the first housing section 3a is provided radially outside of the first spring assembly 51 and partially outside of the delay system 60, while the second housing section 3b is provided radially outside of the second spring assembly 55 and the force multiplier system 70. At an overlap OL in fig. 6, it is shown that the first housing section 3a is provided radially outside of, i.e. is overlapping, the second housing section 3b. Relative longitudinal movement between the first housing section 3a and the second housing section 3b is here enabled, which will be described further in detail below. The delay system 60 of the energy transferring system 50 The delay system 60 is shown in fig. 6 and fig. 7. The delay system 60 comprises a number of deflectable fingers 61. Each deflectable finger 61 has a first end 61a and a second end 61b. At the first end 61a the fingers are secured to their adjacent fingers. Due to the cylindrical property of the well tool, the deflectable fingers 61 can be considered to be a part of a sleeve into which cuts are made to form the deflectable fingers. Hence, the second end 61b is the free end, or the deflecting end of the deflectable finger 61.In fig.7 it is shown that the second end 61b comprises a locking notch 62 which is engaged with an inclining surface 62a of the second housing section 3b, which here is radially outside of the deflectable finger 61. The second end 61b of the deflectable finger 61 further comprises an inclined surface 63. The locking notch 62 protrudes radially outwards from the finger 61, while the inclined surface 63 protrudes inwards from the finger 61. The delay system 60 further comprises a longitudinally displaceable intermediate sleeve 64 located at least partially radially inside the deflectable finger 61. The intermediate sleeve 64 has a first end 64a, a second end 64b, an outer (or outwardly facing) surface 64c and a recess 64d provided in the outer surface 64c. Fig. 7 shows an initial state of the delay system. Here, as the intermediate sleeve 64 is located radially inside of the second end 61b of the deflectable finger 61, the outer surface 64c will prevent the deflectable finger 61 to deflect inwardly. Hence, the deflectable finger 61 is stationary with respect to the second housing section 3b. It is further shown that the intermediate sleeve 64 comprises a spring compartment 64e, in which a spring 64e is provided. The first housing section 3a comprises an inwardly protruding surface 65. By pushing the first housing section 3a (which is done by pushing the mandrel 2) downwardly relative to the second housing section 3b, the first spring 54 will be compressed and the surface 65 will move downwardly. Due to the spring 64e, the second spring supporting surface 53 together with the intermediate sleeve 64 is allowed to move a short distance downwardly. The surface 65 will engage the upper end 64a of the intermediate sleeve 64 and push the sleeve 64 downwardly by compressing the spring 65f until the recess 64d becomes aligned with the inclining surface 63 of the second end 61b of the deflectable finger 61. This is shown in fig.8b. Here, the first housing section 3a will be directly engaged with the second housing section 3b, and the inclining surface 62a of the second housing section 3b will push the second end 61b of the deflectable finger 61 radially inwards into the recess 64d. In fig. 8b, the first spring 54 is fully compressed. It is shown that the overlap OL is increased. This is referred to as a predetermined condition at which the delay system 60 changes its state from the initial state to an actuated state. Now, as shown in fig. 8c, the compressed first spring 54 will be able to push the spring supporting surface 53 down together with the deflectable finger 61 and the intermediate sleeve 64 on the inside of the second housing section 3b. As a result, other parts denoted as 77, 77a, 77b will also be moved down. This will cause the second spring 58 to be compressed. This will be described further in detail below, in the description of the force multiplier system 70. It should be noted that if the mandrel 2 is pulled up, also the first housing section 3a will be pulled up. This will cause the intermediate sleeve 64 to be moved up, and due to the inclining surface 63 of the second end 61b of the deflectable finger 61, the deflectable finger 61 will be pushed out into engagement with the inclined surface 62a of the second housing section 3b again. The intermediate sleeve 64 will be moved further up to a position where deflection of the deflectable finger is prevented by the outer surface 64c of the intermediate sleeve 64 again. Hence, the delay system 60 may be brought between its initial state and the actuated state a number of times. In fig.7 and fig.8a, a distance DR is indicating the travel distance of the surface 65 needed to bring the delay system 60 from the initial state to the actuated state. As a final comment to fig. 7: reference number 69a is a guide pin provided within a guide slot 69b of the first housing section 3a. The purpose is to guide and limit the relative longitudinal movement between the first housing section 3a and the second housing section 3b. The force multiplier system 70 of the energy transferring system 50 It is now referred to fig. 6 and fig. 8a-c and fig. 9a-e. The force multiplier system 70 enables energy transfer between the first spring assembly 51 and the second spring assembly 55 when the delay system 60 is in the actuated state. The force multiplier system 70 comprises an upper section 71 secured to the second housing section 3b and a lower section 72 connected to the first spring supporting surface 56 of the lower spring assembly 55. Between the upper section 71 and the lower section 72, arms are connected. A first arm 75 has a first end 75a and a second end 75b, wherein the first end 75a is pivotably connected to the upper section 71. A second arm 76 has a first end 76a and a second end 76b, wherein the first end 76a is pivotably connected to the lower section 72. The second end 75b of the first arm 75 is pivotably connected to the second end 76b of the second arm 76. The force multiplier system 70 is defined with an folded state shown in fig.8a and fig.9a , and with an unfolded state as shown in fig. 8c and fig. 9b. The folded vs. unfolded is indicating relative difference of an between the arms. In the folded state shown in fig.9a, the is ca 150º. In the unfolded state shown in fig. 9b, the angle is slightly below 180º (i.e. ca 170 179,9º). As shown in the drawings, the is here measured as the angle between a line between the pivoting axis of the first arm 75 and a line between the pivoting axis of the s econd arm 76. The force multiplier system 70 further comprises an actuator 77 for guiding the first arm 75 and the second arm 76 between the folded state and the unfolded state. The actuator 77 is longitudinally movable relative to the upper section 71 and the lower section 72. In fig.6, it is shown that the actuator 77 comprises a lower sleeve 77a and an upper sleeve 77b. In the present embodiment, these two sleeves 77a, 77b are two separate parts secured to each other. The first end 61a of the deflectable finger 61 is connected to the upper sleeve 77b. Typically, there will be more than one finger 61, hence, several fingers 61 is protruding up from the upper sleeve 77b. In the actuated state of the delay system 60, the second spring supporting surface 53 will push the actuator 77 down relative to the upper section 71. The lower sleeve 77a is provided with a cam surface 78 provided in contact with the first arm 75 and the second arm 76. The relative positions and contact areas of the cam surface 78 and the arms 75,76 are shown in fig. 9c and 9d. Here it is shown that the second end 75b of the first arm 75 and the second end 76b of the second arm 76 are defined with respective contact areas 75c, 76c. These contact areas 75c, 76c are provided in contact with the cam surface 78. As can be seen from fig. 9c and fig.9d that the relative position between the contact areas 75c, 76c of the arms and the cam surface 78 changes. However, it should be noted that also the point of contact of the contact areas 75c, 76c changes. In fig.9a, the cam surface 78 is provided in contact with a first part of the contact area 75c, 76c and in fig. 9b, the cam surface 78 is provided in contact with a second part of the contact area 75c, 76c, the first part of the contact area 75c, 76c being different from the second part of the contact area 75c, 76c. In fig. 9e, it is shown that the contact areas 75c, 76c are shaped as a circular arc represented by a radius rd. In the present embodiment, the cam surface 78 has a shape being tangential to the contact area 75c, 76c at each point of contact be tween the contact surface 78 and the contact area 75c, 76c. In the folded state, a first tangent T1 of the contact area 75c, 76c is 30º - 45º, preferably 35º - 38º relative to the longitudinal direction of the well tool 1. In the unfolded state, a second tangent T2 of the contact area 75c, 76c is 0º - 5º, preferably 1º - 3º, relative to the longitudinal direction of the well tool 1. It should be noted that these angles will depend on a number of factors, such as the length of the arms, the diameter of the well tool 1 and hence the diameter of the energy transferring system 50. In the present embodiment, each arm 75, 76 has a length of ca 11 cm. The radius rd of the circular contact area 75c, 76c is ca 20 mm. The cam surface 78 is here a continuous, convex surface. It is now referred to fig. 8c. As the delay system 60 now is in the actuated state, the second spring supporting surface 53 is pushed downwardly by the already compressed first spring 54, pushing the actuator 77 downwardly. This will bring the arms from their folded state to their unfolded state, causing the distance D between the first end 75a of the first arm 75 and the first arm 76a of the second arm 76 to increase (see fig. 9a vs fig. 9b). This will cause the lower section 72 to move down, causing compression of the second spring 58. It is now referred to fig.3 again. As described above, the second spring supporting surface 57 is the upper surface of the third housing section 3c. When the delay system 60 is in the initial state, energy may be transferred between the third housing section 3c and the fourth housing section 3d. When the delay system 60 is in the actuated state, energy may be transferred between the third housing section 3c and the fourth housing section 3d. In addition, energy may here also be transferred between the second housing section 3b and the fourth housing section 3d. The energy transfer will of course depend on the force applied to the mandrel (either from topside or by the weight suspended below the mandrel) and will depend on the fluid pressure difference between the upper side of the sealing device and the lower side of the sealing device when the sealing device is expanded. It should be noted that in some embodiments (for example an embodiment with the upper spring 54 having a spring constant being larger than the spring constant of the lower spring 58), energy may be transferred between the second housing section 3d and the fourth housing section 3d independent of the state of the delay system. Release of the downwardly directed movement of the mandrel 2 will allow the second spring 58 to push the above parts back to their original positions again. Hence, the above actions may be repeated a number of times. In an alternative embodiment, the force multiplier system 70 may be locked in the unfolded state. Hence, when releasing a downward pressure on the force multiplier system 70, the force multiplier system 70 will not return to the unfolded state by itself. This may be achieved by having a friction force, representing the friction between the circular arc 75c, 76c and the contact surface 78 in the unfolded state, to be larger than the force applied by the lower spring 58 onto the first spring supporting surface 56. Here, it is required that the mandrel 2 is actively pushed upwardly to move the above parts back to their original positions again. It should be noted that the above energy transferring system 50 allows that energy is stored in first spring assembly 51 before energy is stored in the second spring assembly 55. Operation of the casing plug The operation of the casing plug 1 will now be described in detail. It should be noted that some of the states and movements of the anchoring device 20, the sealing device 30 and the energy transferring system 50, have already been described above. The casing plug is operated from topside by performing one of the two following actions: - pushing the mandrel down relative to a casing WB; - pulling the mandrel up relative to the casing WB; - clockwise rotation of the mandrel relative to the casing WB. It is now referred to fig. 1 and to fig. 10a, showing the first or run state. Here, only the drag block device 10 is in contact with the casing WB. In fig. 10a, the ratchet device 40 is in a first ratchet state, in which the hatched area 45HA of the second ratchet ring 45 is engaged with the second hatched area 2HA2 of the mandrel 2 in this first state. In this first state, the friction force Fr of the drag block device 10 is not sufficient to allow relative longitudinal movement between the hatched area 45HA of the second ratchet ring 45 and the second hatched area 2HA2 of the mandrel 2. Hence, relative longitudinal movement between the mandrel 2 and the housing sections 3a, 3b, 3c, 3d and 3L is prevented. This prevents the anchoring device 20 and the sealing device 30 from being radially expanded before the casing plug 1 has arrived at a desired location in the casing WB. At the desired location, the mandrel 2 is rotated clockwise, thereby moving the first ratchet ring 41 and the second ratchet ring 45 in the second direction D1, thereby bringing the hatched area 45HA of the second ratchet ring 45 out of engagement with the second hatched area 2HA2 of the mandrel 2, and bringing the hatched area 41HA of the first ratchet ring 41 into engagement with the first hatched area 2HA1 of the mandrel 2. Here, the friction force Fr of the drag block device 10 is sufficient to allow relative longitudinal movement between the hatched area 41HA of the first ratchet ring 41 and the first hatched area 2HA1 of the mandrel 2. Hence, relative longitudinal movement between the mandrel 2 and the fourth housing section 3d is allowed. As described above, the anchoring device 20 is located between the fourth housing section 3d and the lower housing section 3L, and by pushing the mandrel 2 downwardly, the anchoring device 20 will be set into engagement with the inner surface of the casing. This is the end of the second state of the ratchet device 40 as shown in fig. 10b. It should be noted that as the mandrel 2 is secured to the upper housing section 3U, forces are transferred on the outside of the mandrel 3, i.e. from the mandrel 2, via the upper housing section 3U, the first housing section 3a, the second housing section 3b to the anchoring device 20 without setting the sealing device 30 and without compressing the first spring 54 of the energy transferring system 50. The sealing device 30 will not be set due to the properties of the sealing element, where deformation of the elastomeric material of the sealing element requires a sufficient compression force. It should be noted that the cup springs 58a of the second spring 58 may be slightly compressed here. It is now possible to push the mandrel 2 further down, as the anchoring device 20 now is stationary relative to the wellbore. This will initiate the radial expansion of the sealing device 30 and also cause compression of the first spring 54 of the energy transferring system 50 (as described above). This state of the casing plug 1 is shown in fig. 4. It is possible to push the mandrel 2 even further down. Now the delay system 60 will be brought to the actuated state and the force multiplier system 70 will be brought to the unfolded state, thereby compressing the second spring 58. This is referred to as the third state of the casing plug 1 shown in fig. 5. Energy is now stored in the lower spring assembly, and this energy will keep the sealing element 35 and the slips element 25 in their radially expanded states with a force which is larger than the force initially being used to set the sealing element 35. Hence, it is achieved that a plug can be set with a higher force, even if only a smaller force is accessible. Pressure testing of the casing can now be performed as the set sealing device 30 will prevent fluid flow through the casing. The ratchet device 40 is now preventing that the sealing device 30 will return to the retracted state. The ratchet device 40 is brought from the third state to the first state again by rotating the mandrel 2 clockwise, bringing the hatched area 41HA of the first ratchet ring 41 out of engagement with the first hatched area 2HA1 of the mandrel 2, bringing the hatched area 41HA of the first ratchet ring 41 out of engagement with the first hatched area 2HA1 of the mandrel 2, and bringing the hatched area 45HA of the second ratchet ring 45 into engagement with the second hatched area 2HA2 of the mandrel 2. Alternative embodiments The energy transferring system 50 may be used for other well tools than casing plugs.

Claims

CLAIMS 1. An energy transferring system (50) for transferring energy between an first part (1a) of a well tool (1) and a second part (1b) of the well tool (1), wherein the well tool (1) comprises: - a mandrel (2); - an outer housing (3), wherein the outer housing (3) comprises a first housing section (3a), a second housing section (3b), a third housing section (3c) and a fourth housing section (3d), wherein the first housing section (3a) is belonging to the first part (1a) of the well tool (1) and wherein the fourth housing section (3d) is belonging to the second part (1b) of the well tool (1) and wherein the second housing section (3b) and the third housing section (3c) are located between the first housing section (3a) and the fourth housing section (3d); wherein the energy transferring system (50) comprises: - a first spring assembly (51); - a second spring assembly (55); - a delay system (60) located between the first spring assembly (51) and the second spring assembly (55), wherein the delay system (60) is brought from an initial state to an actuated state when a predetermined condition has been met; - a force multiplier system (70) located between the delay system (60) and the fourth housing section (3d) for transferring energy between the first spring assembly (51) and the second spring assembly (55) when the delay system (60) is in the actuated state.

2. The energy transferring system (50) according to claim 1, wherein kinetic energy applied to the well tool (1) in the form of relative longitudinal movement between the first part (1a) of the well tool (1) and the second part (1b) of the well tool (1) in a direction towards each other is stored as potential energy in the first spring assembly (51) and in the second spring assembly (55); wherein the delay system (60) is configured such that energy is stored in first spring assembly (51) before energy is stored in the second spring assembly (55).

3. The energy transferring system (50) according to claim 1 or 2, wherein the predetermined condition is a condition indicative of the amount of energy stored in the first spring assembly (51).

4. The energy transferring system (50) according to any one of claims 1 - 3, wherein the predetermined condition is a condition indicative of a relative travel distance (TR) between elements in the first the spring assembly (51).

5. The energy transferring system (50) according to any one of claims 1 - 4, wherein the first spring assembly (51) comprises a first spring supporting surface (52), a second spring supporting surface (53) and a first spring (54) located longitudinally between the first spring supporting surface (52) and the second spring supporting surface (53); wherein the first spring supporting surface (52) of the first spring assembly (51) is fixed to the first housing section (3a).

6. The energy transferring system (50) according to any one of claims 1 - 5, wherein the second spring assembly (55) comprises a first spring supporting surface (56), a second spring supporting surface (57) and a second spring (58) located longitudinally between the first spring supporting surface (56) and the second spring supporting surface (57), wherein the second spring supporting surface (57) of the second spring assembly (55) is secured to the third housing section (3c) .

7. The energy transferring system (50) according to claim 5 or 6, wherein the delay system (60) comprises a deflectable finger (61) having a first end (61a) and a second end (61b), wherein the second end (61b) comprises a locking notch (62), wherein the locking notch (62) is engaged with the second housing section (3b) in the initial state.

8. The energy transferring system (50) according to claim 7, wherein the locking notch (62) is brought out of engagement with the second housing section (3b) when the predetermined condition is met.

9. The energy transferring system (50) according to claim 7 or 8, wherein the second end (61b) of the deflectable finger (61) comprises an inclined surface (63).

10. The energy transferring system (50) according to claim 9, wherein the delay system (60) comprises a longitudinally displaceable intermediate sleeve (64) located at least partially radially inside the deflectable finger (61), wherein the intermediate sleeve (64) has a first end (64a), a second end (64b), an outer surface (64c) and a recess (64d) provided in the outer surface (64c); wherein the outer surface (64c) is preventing the deflectable finger (61) to deflect and wherein first housing section (3a) comprises an inwardly protruding surface (65), wherein the predetermined condition is met by moving the inwardly protruding surface (65) into contact with the intermediate sleeve (64) and further displace the intermediate sleeve (64) to a position in which the locking notch (62) is allowed to deflect inwardly into the recess (64d).

11. The energy transferring system (50) according to any one of the above claims, wherein the force multiplier system (70) comprises one or more link arms and/or one or more cam surfaces.

12. The energy transferring system (50) according to any one of the above claims, wherein the force multiplier system (70) comprises: - an upper section (71) secured to the second housing section (3b); - a lower section (72) comprising, or being connected to the first spring supporting surface (56) of the second spring assembly (55); - a first arm (75) having a first end (75a) and a second end (75b), wherein the first end (75a) is pivotably connected to the upper section (71); - a second arm (76) having a first end (76a) and a second end (76b), wherein the first end (76a) is pivotably connected to the lower section (72); wherein the second end (75b) of the first arm (75) is pivotably connected to the second end (76b) of the second arm (76).

13. The energy transferring system (50) according to claim 12, wherein the first arm (75) and the second arm (76) are oriented relative to each other with , and wherein the force multiplier system (70) is configured to be in a folded state the unfolded state.

14. The energy transferring system (50) according to claim 11 or 12, wherein the force multiplier system (70) comprises an actuator (77) for guiding the first arm (75) and the second arm (76) between the folded state and the unfolded state.

15. The energy transferring system (50) according to claim 14, wherein the actuator (77) comprises a lower sleeve (77a) having a cam surface (78) provided in contact with the first arm (75) and/or the second arm (76), wherein longitudinal movement of the lower sleeve (77) is guiding the first arm (75) and the second arm (76) between the folded state and the unfolded state.

16. The energy transferring system (50) according to claim 15, wherein the second end (75b) of the first arm (75) and/or the second end (76b) of the second arm (76) is provided with a contact area (75c, 76c) provided in contact with the cam surface (78), wherein the cam surface (78) is provided in contact with a first part of the contact area (75c, 76c) in the folded state, and wherein the cam surface (78) is provided in contact with a second part of the contact area (75c, 76c) in the unfolded state.

17. The energy transferring system (50) according to any one of claims 15 - 16, wherein the actuator (77) comprise an upper sleeve (77b), wherein the first end (61a) of the deflectable finger (61) is secured to, or is connected to, the upper sleeve (77b), wherein the upper sleeve (77b) is engaged by the first housing section (3a) when the delay system (60) is in the actuated state.

18. The energy transferring system (50) according to any one of claims, wherein the second spring supporting surface (57) comprises, or is secured to, the third housing section (3c).

19. The energy transferring system (50) according to any one of claims, wherein energy is transferred between the third housing section (3c) and the fourth housing section (3d) or between the second housing section (3b) and the fourth housing section (3d).

20. The energy transferring system (50) according to any one of claims, wherein, when the delay system (60) is in the actuated state, energy is transferred between the third housing section (3c) and the fourth housing section (3d) and/or between the second housing section (3b) and the fourth housing section (3d).

21. The energy transferring system (50) according to any one of claims, wherein, when the delay system (60) is in the initial state, energy is transferred between the third housing section (3c) and the fourth housing section (3d).

22. A casing plug (1) for sealing a casing (WB), wherein the casing plug (1) comprises: - a mandrel (2); - an outer housing (3), wherein the outer housing (3) comprises a first housing section (3a), a second housing section (3b), a third housing section (3c) and a fourth housing section (3d), wherein the first housing section (3a) is belonging to the first part (1a) of the well tool (1) and wherein the fourth housing section (3d) is belonging to the second part (1b) of the well tool (1) and wherein the second housing section (3b) and the third housing section (3c) are located between the first housing section (3a) and the fourth housing section (3d); characterized in that the casing plug (1) comprises an energy transferring system (50) according to any one of the above claims for transferring energy between the first part (1a) of the casing plug (1) and the second part (1b) of the casing plug (1).

23. The casing plug (1) according to claim 22, wherein the casing plug (1) comprises: - a drag block device (10) provided outside of the mandrel (2); - an anchoring device (20) provided radially outside of the mandrel (2) above the drag block device (10); - a sealing device (30) provided outside of the mandrel (2); - a ratchet device (40) for selectively locking parts of the outer housing (3) to the mandrel (2).

24. The casing plug (1) according to claim 23, wherein the casing plug (1) comprises: an upper housing section (3U) located above the first housing section (3a), wherein the sealing device (30) is provided between the upper housing section (3U) and the first housing section (3a).

25. The casing plug (1) according to claim 23 or 24, wherein the casing plug (1) comprises: a lower housing section (3L) located below the fourth housing section (3d), wherein the anchoring device (20) is provided between the lower housing section (3L) and the fourth housing section (3d).

26. A method for setting a casing plug (1) in a casing (WB), wherein the casing plug (1) comprises a mandrel (2) and an outer housing (3) provided outside of at least parts of the mandrel (2), wherein the outer housing (3) comprises a first housing section (3a), a second housing section (3b), a third housing section (3c) and a fourth housing section (3d), wherein the second housing section (3b) and the third housing section (3c) are located between the first housing section (3a) and the fourth housing section (3d); wherein the method comprises the steps of: a) lowering the casing plug (1) into the casing (WB) while a drag block device (10) of the casing plug (1) is in contact with an inner surface of the casing (WB); b) rotating the mandrel (2) in a clockwise direction, wherein the drag block device (10) is preventing rotation of a lower part (3L) of a lower housing section (3U) located below the housing sections (3a, 3b, 3c, 3d); c) pushing the mandrel (2) downwardly, wherein the drag block device (10) is preventing downward movement of the lower housing section (3L) relative to the casing (WB); thereby causing an anchoring device (20) of the casing plug device (1) above the drag block device (10) to expand into engagement with the inner surface of the casing (WB); d) pushing the mandrel (2) downwardly, wherein the anchoring device (20) is preventing downward movement of the fourth housing section (3d) immediately above the anchoring device (20) relative to the casing (WB); thereby causing a sealing device (30) of the casing plug device (1) above the fourth housing section (3d) to expand into engagement with the inner surface of the casing (WB).

27. The method according to claim 26, wherein the method further comprises the step of: e) pressure testing the casing (WB) above or below the sealing device (30) after step d).

28. The method according to claim 26 or 27, wherein the method further comprises the step of: f) rotating the mandrel (2) in the clockwise direction; and g) pulling the mandrel (2) upwardly; thereby causing retraction of the sealing device (30) and the anchoring device (20) from their engagement with the inner surface of the casing (WB).

29. The method according to any one of the above claims 26 - 28, wherein the method further comprises the step of: - lowering or lifting the casing plug (1) to a different location the casing (WB); - repeating steps a) d).

30. The method according to claim 26, wherein step d) comprises the step of: - transferring energy between a first part (1a) of the casing plug (1) and the second part (1b) of the casing plug (1) by means of the energy transferring system (50) according to any one of claims 1 16.