Patent Application
20160024858
The present invention relates to the field of oil and gas exploration, and in particular downhole activities, such as, for example, drilling, logging, fishing, completions, etc.
More specifically, the present invention relates to a tool for selectively connecting or disconnecting components of a downhole workstring, comprising a drive shaft and a housing couplable to said drive shaft, said housing comprising a first housing part and a second housing part releasably connected to one another. In particular the invention is a so-called back off sub for release and re-connection of components of a downhole workstring.
Safety subs, also referred to in the industry as back-off safety subs (BOSS), are used in downhole activities to disengage or connect components of downhole string whenever it becomes necessary. This tool is used in various workstrings such as drill, fishing, washover string. During normal downhole activities, the tool transmits torque from the upper string to the equipment below the tool. Disconnection may for example be required to recover the part of the string above the equipment which has been or stuck or otherwise fixed downhole.
Some known safety subs comprise upper and lower mating parts couplable together by way of a thread and a stop device for preventing the thread from loosening until it is required to disengage the mating parts. Such a stop device can comprise a spring or a friction ring or some other stop means which typically maintains bias between the mating parts and thus prevents the mating parts from unscrewing and maintains torsional integrity of the joint between the mating parts. When it is required to disengage the mating parts, the stop device can be acted upon from surface, for example by application of a force overcoming the bias, so as to permit the mating parts to rotate relative to each other. The upper string can then be rotated from surface while the stuck portion remains stationary thus permitting the mating parts to disengage.
Disadvantages associated with such known back off subs include, for example, the risk of accidental disengagement of the mating parts of the back off sub during the normal downhole activity and the associated financial losses due to the non-production time required to re-connect the string.
The aim of this invention is to provide a tool with the features mentioned in the first paragraph of this description, which does not present said disadvantages.
This aim is achieved by providing a tool for selectively connecting or disconnecting components of a downhole workstring comprising a drive shaft and a housing couplable to said drive shaft, said housing comprising a first housing part and a second housing part releasably connected to one another, and further comprising transmission means coupled to the drive shaft, said transmission means being arranged to selectively connect or disconnect the housing parts by rotating the drive shaft.
Preferably, said transmission means are arranged so that the rotation of said drive shaft causes a longitudinal displacement of one of the housing parts, or of an operating member for connecting or disconnecting said housing parts, and that the housing parts are connected or disconnected as a result of said axial displacement.
Advantageously, the tool comprises a kinematic pair which is selected such that said axial displacement occurs for a predetermined disconnection time before the housing parts disengage.
In a further advantageous arrangement, the tool comprises a gear reduction mechanism.
In a first special embodiment of the tool according to this invention, said transmission means comprises a gear mechanism arranged for selectively transmitting the torque of said drive shaft to one of said housing parts, said gear mechanism comprising an output gear element of which a threaded portion is coupled to a threaded portion of an operating member for connecting or disconnecting said housing parts, such that rotational motion of the output gear element results in axial displacement of said operating member.
Preferably, the gear mechanism of said first special embodiment comprises a harmonic drive having a reference gear element, which is fixed to or integrally formed with said housing part, an input gear element fixed to said drive shaft, and an output gear element, such that rotation of the input gear element relative to the reference gear element results in rotation of the output gear element.
In this first special embodiment, the first housing part and the second housing part preferably comprise a set of longitudinally spaced first reception cavities and a set of longitudinally spaced second reception cavities respectively, the connected housing parts are in a relative position wherein the first cavities and the second cavities are aligned in transversal direction, and the tool further comprises
Advantageously, said operating member is longitudinally displaceable between a holding position wherein it is holding each connection member in a respective connecting position, and a releasing position wherein the connection members are allowed to move or to be moved into the disconnecting position.
In a further advantageous embodiment, said operating member comprises a set of longitudinally spaced third reception cavities, such that, when the operating member is placed in the releasing position, each third cavity is aligned with a respective pair of aligned first and second cavities, and the connecting elements are allowed to move or to be moved to a disconnecting position wherein they are removed from the first cavities and extending in the aligned second and third cavities.
In a specific embodiment the first reception cavities are transversal recesses in the first housing part, the second reception cavities are holes in the second housing part, the connection elements are blocks fitting in a respective alignment of a hole and a recess, and the third reception cavities are recesses in the operating member.
In a most preferred embodiment, each pair of aligned first and second reception cavities define a reception space delimited by at least one inclined end surface, such that a connection element, when positioned in its connection position, is transversally moved towards its disconnection position, when a force acting in longitudinal direction pushes said connection element against said inclined surface, said force being the result of gravity and/or the result of a relative longitudinal displacement of the housing parts.
The tool according to said first special embodiment preferably also comprises a coupling member which is selectively displaceable between a coupling position and an uncoupling position wherein the drive shaft and one of the housing parts are coupled and uncoupled respectively.
Further preferably, this coupling member is displaceable in a space which is in communication with a fluid channel of the tool through at least one aperture, the tool further comprises a spring member urging the coupling member towards its coupling position, and an operating assembly for selectively opening or closing said aperture so that, when the aperture is open, a fluid flowing in the fluid channel is allowed to enter the space through said aperture, thereby exerting a force on said coupling member resulting in its displacement into the uncoupling position, and that, when the aperture is closed, the coupling member is moved into the coupling position by said spring member.
Ideally, said operating assembly comprises
said operating assembly being arranged so that, when a fluid is flowing in the fluid channel, the insertion of the object and its resulting position in the trap influences the fluid pressure in the channel such that said sleeve is moved into the opening position, and that, when the object is not positioned in the trap, the sleeve is moved into the closing position by said spring element.
As an alternative for said first special embodiment, and in accordance with this invention, the tool can also be constructed as a second special embodiment, having the following features: a tool for selectively connecting or disconnecting components of a downhole workstring, in particular a downhole back off sub, comprising a housing couplable with a drive shaft, the housing comprising a pair of housing parts arranged to rotate relative to each other about a common rotation axis; the housing parts being engaged together via a kinematic pair arranged to translate the relative rotation of the housing parts into longitudinal displacement of the housing parts relative to each other and relative to the common rotation axis, and a transmission mechanism arranged to selectively transmit the rotation of the drive shaft to at least one of the pair of the housing parts thereby inducing the relative rotation of the housing parts and the resulting relative longitudinal displacement of the housing parts.
Some preferred features of the second special embodiment will now be described hereinafter. Though the first and second special embodiment are presented as alternative embodiments of this invention, It will be apparent that some of the features of the second special embodiment mentioned below are readily available for incorporation in the first special embodiment, and vice versa, even when this has not been explicitly mentioned.
The drive shaft is typically that of a workstring, which can be for example a drillstring, fishing string, washover string, logging string etc. The drive shaft typically is or is connected to a drive shaft of a motor which may be a motor at surface, such as e.g. a top drive. In drilling activities, the rotation of the motor at surface is typically transferred downhole by a drill pipe, i.e. the drill pipe serves as a drive shaft. It is envisaged that in other cases, e.g. in coiled tubing drilling or other downhole activities, the drive shaft may be that of a mud motor, that is, a downhole motor driven by a column of mud within a workstring.
In use, the tool of the invention is assembled with the workstring so that the housing is coupled with the drive shaft via the transmission mechanism.
Preferably, one part of the housing remains stationary during the relative rotation and the other part of the housing rotates about the rotation axis.
Preferably, the transmission mechanism comprises a gear box. Preferably, the transmission mechanism is a reducer.
Preferably, the transmission mechanism includes a locking means for selectively locking or unlocking at least one housing part so as to restrict or permit rotation of the housing part with respect to the drive shaft, wherein the tool is arranged to operate in a locked mode, in which the locking means locks the at least one housing part to the drive shaft whereas the transmission mechanism is engaged, with the result that the housing parts are rotatable as a unit with the drive shaft, so that torque and rotation from the drive shaft can be transmitted to the relevant equipment of the workstring.
Thus, in the locked mode, which is required during normal operation of the workstring (e.g. during drilling), torque and rotation from the drive shaft is transmitted to the relevant equipment downstring of the back off sub.
Further preferably, the transmission mechanism includes an interruption means for interrupting or engaging the transmission mechanism to respectively disable or enable the transmission from the drive shaft to the housing part through the transmission mechanism, wherein the tool is arranged to operate in a back off mode, in which the locking means is actuated and the housing part previously locked to the drive shaft becomes released therefrom, i.e. the housing part becomes unlocked for rotation relative to the other housing part, whereas the transmission mechanism remains engaged, so that torque and rotation from the drive shaft can be transmitted through the transmission mechanism to cause the relative rotation of the housing parts.
Preferably, the locking means and the interruption means are arranged in a cooperative relationship so that the back off sub selectively operates in a number of modes and more preferably, in at least a locked mode and a back off mode. Further preferably, the locking means and the interruption means are arranged in a cooperative relationship so that the back off sub selectively operates in a re-connection mode.
If for whatever reason it is required to disconnect the equipment downstring of the back off sub, e.g. if it has been fixed in place or becomes stuck downhole the back off sub is brought into a back off mode.
Preferably, one part of the housing is in use non-rotatably attached to equipment downstring of the back of sub. Accordingly, this part of the housing, which in use is typically a lower part, remains stationary downhole if the equipment has been fixed in place or becomes stuck downhole, whereas the other part of the housing, which in use is typically an upper part, is rotated by the transmission mechanism. The relative rotation of the housing parts becomes converted into the relative axial movement of the housing parts by the kinematic pair.
Thus, rotation of the drive shaft in one direction, for example, clockwise, causes one housing part (i.e. the upper, rotatable part) to move away and eventually disconnect from the other (i.e. the lower, stationary) housing part. Accordingly, in the back off mode, the drive shaft rotates but does not transmit rotation to the stationary housing part. Rotation of the drive shaft in the opposite direction, e.g. anticlockwise, results in the reversal of the relative rotation of the housing parts, so that the housing parts move axially toward each other and reconnect. The rotation is transferred from the drive shaft to the housing parts at the reduction ratio provided by the transmission mechanism. Thus, if the transmission mechanism is a reducer, as in a preferred embodiment of the present invention, the relative rotation of the housing parts is slower than the rotation of the drive shaft, and a certain time interval elapses before the housing parts disconnect.
Such a delay is advantageous, for example, if the back off action starts accidentally, because the delay provides an operator with extra time to assess the situation and take the necessary steps to prevent the undesired disengagement. The delay, for example, makes possible an attempt to be made to retrieve the stuck portion of the workstring by application of an axially directed force to the stuck portion, e.g. pushing or pulling force or a dynamic force using a jarring tool, while the housing parts are still in the process of disconnecting, i.e. while the workstring is still one-piece. The delay in disconnection of the housing parts also means that the part of the workstring above the fixed or stuck portion of the workstring rotates during the disconnection process. The relative rotation of the housing parts is advantageous during an attempt to retrieve the stuck portion of the workstring because during the application of such an axial force, a considerable amount of friction is created between the workstring and the walls of the wellbore. The rotation of the upper part of the workstring during the retrieval attempts not only provides additional force in the immediate proximity to the stuck portion of the workstring which may help to release the stuck portion, but also reduces friction in the axial direction and thus facilitates the axial movements of the upper part of the workstring during the retrieval attempt.
In the re-connection mode, which is required, for example, when it is necessary to re-connect the housing parts, the locking means locks at least one housing part to the drive shaft whereas the transmission mechanism is interrupted with the result that the housing part locked to the drive shaft is rotatable as a unit with the drive shaft, that is, rotation and torque are transmitted directly from the drive shaft to that housing part. In the re-connection mode, the stationary housing part remains stationary downhole whereas the rotatable part of the housing is rotated directly by the drive shaft. The relative rotation of the housing parts becomes converted into the relative axial movement of the housing parts by the kinematic pair.
Thus, when the drive shaft rotates in one direction, for example, clockwise, one housing part (i.e. the upper, rotatable part) to moves towards and eventually re-connects with the stationary (i.e. the lower, stationary) housing part. The rotation of the drive shaft is transferred from the drive shaft to the rotatable housing part directly, i.e. the angular speed of the rotatable housing part is the same as that of the drive shaft. This is advantageous when it is required to re-connect the housing parts at a speed different than that provided by the transmission mechanism. If the transmission mechanism is a reducer, in the re-connection mode, re-connection of the housing parts occurs quicker than in the back off mode, which is desirable in the production environment. In the re-connection mode, the drive shaft thus rotates but does not transmit rotation to the stationary housing part. Rotation of the drive shaft in the opposite direction, e.g. anticlockwise, results in the reversal of the relative rotation of the housing parts, so that the housing parts move axially away from each other and disconnect. This may be required when, for example, the transmission mechanism is a reducer and for whatever reason it is required to disconnect the housing parts faster than the disconnection time provided for by the transmission mechanism.
Advantageously, the kinematic pair is selected such that the relative axial displacement of the housing parts occurs for a predetermined time before the housing parts disengage. Such an arrangement is advantageous in case, as explained above in connection with the transmission mechanism, the locking means unlocks inadvertently because the prolonged axial displacement provides sufficient time for an operator at surface to detect a lowered torque exerted by the drive shaft indicating that the disengagement process has begun and to take measures to prevent further disengagement and to re-connect the housing parts by switching the direction of rotation of the drive shaft to rotate in the opposite direction or by bringing the back off sub into the re-connection mode in which the drive shaft is coupled directly to the rotatable housing part and thus to cause the housing parts to re-engage. Also as explained above in connection with the transmission mechanism, the delay, combined with relative rotation of the housing parts facilitates an attempt to retrieve a stationary portion of the workstring.
In one preferred arrangement, the kinematic pair is provided in the form of a pair of cooperating threads between the housing parts. Preferably, the pitch of the threads is selected so that the longitudinal displacement of the housing parts per revolution of the drive shaft is relatively small and the housing parts move a relatively small total axial distance during the predetermined time interval as the housing parts engage or disengage. This adds to the compactness of the design of the back off sub of the invention while ensuring that the housing parts remain engaged for the predetermined time interval. Such threads facilitate a slow pace of the axial disengagement of the housing parts compared to the angular speed of rotation of the drive shaft.
In one arrangement, the threads are fine-pitch threads. For the back off sub of the present invention, a pitch of 1 mm, 2 mm or 3 mm would be regarded as a fine-pitch. Combined with appropriately selected length in the axial direction of the threaded connection and transmission ratio of the transmission mechanism, the required disconnection time is achieved.
For example, for 1 mm pitch and 100 mm long thread connection and a 100:1 reduction ratio of the transmission mechanism, rotation at input at 100 rpm results in 50 min thread disconnection (or connection) time involving 50 thread revolutions and 5000 drive shaft revolutions.
Further preferably, the kinematic pair is selected such that it has tensile strength in the axial direction in a state when the kinematic pair has disconnected by about 75-85% approximately the same or greater than the tensile strength of the part of the workstring which becomes stationary downhole. Such an arrangement helps to ensure that the kinematic pair does not break when an attempt is made to retrieve a stuck portion of the workstring while the housing parts of the back off sub are in the process of disconnecting.
Preferably, the housing is tubular and the drive shaft extends axially through the housing. Preferably, the pair of housing parts comprise a pair of sleeves connected end-to-end, preferably, co-axially. Preferably, the transmission mechanism is disposed within the housing and is coupled to each housing part.
In an advantageous embodiment, the transmission mechanism comprises a harmonic drive comprising a wave generator (an elliptical disc, plug or hub sometimes also referred to as an inner gear, albeit without teeth), a flexible gear and an outer gear (also referred to as a circular gear), wherein one of the wave generator, flexible gear and outer gear serves as a rotary input component and another of the wave generator, flexible gear and outer gear serves as a rotary output component; and wherein the harmonic drive is couplable with the drive shaft so that rotation of the drive shaft results in the relative rotation of the housing parts. In principle, in its broader aspect, the present invention is not limited to the use of a harmonic drive as a transmission mechanism and indeed can comprise such various transmission mechanisms suitable for co-axial transmission as would be envisaged by a skilled person, such as, for example only, planetary gearing. However, there are certain advantages associated with the use of a harmonic drive in a back off sub of the present invention.
A harmonic drive is a special type of drive and typically comprises a wave generator, also known as an inner gear, an intermediate gear, also known as a flexible gear, and an outer gear, commonly referred to as an outer gear. In a harmonic drive, when the outer gear is fixed, the wave generator and the flexible gear rotate in opposite directions; when the flexible gear is fixed, the outer gear and the wave generator rotate in the same direction; and when the wave generator is fixed, the outer gear and the flexible gear rotate in the same direction. Due to its unique principle of construction, a harmonic drive provides very high or very low, depending on what is used as an input, transmission ratios (typical ratios include 100:1, 200:1, 300:1 or vice versa etc.) along with high torque transmission (due to a plurality of teeth meshing at the same time), torque multiplication (or reduction depending on what is used as an input), very compact construction, rotation precision, low vibration and absence of backlash. Since harmonic drives are known, it is not necessary to describe its construction and operation in detail.
Preferably, in one arrangement, the wave generator of the harmonic drive is coupled to the drive shaft and thus serves as the rotary input component and the flexible gear and the outer gear are each coupled to one of the housing parts and one of the flexible gear or the outer gear serves as a the rotary output component. Thus, the harmonic drive operates as a reducer (and torque multiplier).
In one particular variation, the wave generator of the harmonic drive is coupled to the drive shaft, the outer gear is coupled the housing part which remains stationary during relative rotation and the flexible gear serves as the rotary output component and is coupled to the part of the housing which rotates about the rotation axis relative to the stationary part of the housing. In this variation, the drive shaft and the flexible gear rotate in opposite directions. It is of course in principle possible to couple the outer gear of the harmonic drive to the rotating part of the housing and the flexible gear to the stationary part of the housing. In this case, the rotating part of the housing will rotate in the same direction as the drive shaft. The kinematic pair between the housing parts must be adapted accordingly to suit the applicable direction of rotation of the rotating housing part.
The considerable reduction and torque multiplication provided by the harmonic drive result in the relative rotation of the housing parts much slower than the rotation of the drive shaft but with higher torque compared to other gear boxes. Low speed at the output is beneficial because it provides for a time delay in case the disconnection has been induced accidentally which allows an operator at surface to detect the undesired disconnection process and to take measures to reconnect the housing parts. Also, the delay in disconnection provides for a possibility of an attempt to be made to retrieve the stuck portion of the workstring, for example, by jarring or by straightforward pushing or pulling, while the housing parts are still connected, while the relative rotation of the housing parts provides extra force for retrieval and friction reduction as described above. Torque multiplication may be necessary to translate the rotary motion of the housing parts into the relative axial movement since the connection (i.e. the kinematic pair) between the housing parts may be such as to require high torque to induce the relative movement of the housing parts
It is further advantageous to include a combination of a harmonic drive as the transmission mechanism and a threaded connection, preferably, a fine-pitched threaded connection, as the kinematic pair between the housing parts to achieve the necessary disconnection time sufficient for an inadvertent disconnection to be detected at surface and prevented while maintaining compactness of the back off sub of the invention. Also, while such an arrangement provides for the desired relatively slow disconnection of the housing parts, the provision of the re-connection mode, provides for a quick re-connection of the housing parts when it is necessary to re-connect the housing parts rapidly compared to the disconnection time.
It will be appreciated that the present invention, in its broader aspect, is not limited to the combination of a threaded connection and a harmonic drive. The required disconnection time, in principle, can be achieved by suitably adapting one or each of the transmission mechanism and the kinematic pair.
Also, preferably, the kinematic pair and/or the transmission mechanism are adjustable to provide for the necessary disconnection time interval.
In one variation, the locking means is provided in the form of a first spline coupling arranged between at least one housing part and the drive shaft to selectively lock and unlock the rotary connection between the housing part and the drive shaft. The splines arrangement may take many forms as will be readily envisaged by a person skilled in the art.
In one variation, the interruption means is provided in the form of a second spline coupling arranged in the transmission mechanism.
Accordingly, in the locked mode, the first spline coupling locks at least one housing part to the drive shaft and the second spline coupling holds transmission mechanism in an engaged mode, with the result that the housing parts are rotatable as a unit with the drive shaft, as described above.
In the back off mode, the first spline coupling is actuated, thus disengaging the first spline coupling, and the housing part previously locked to the drive shaft becomes released therefrom, i.e. the housing part becomes unlocked for rotation relative to the other housing part, whereas the transmission mechanism remains engaged. The first spline coupling can be disengaged by, for example, arranging the drive shaft to move axially within the housing, so that, for example, by pulling the drive shaft towards surface (i.e. applying tension to the workstring) or, as the case may be, pushing it downwardly (i.e. compressing the workstring), away from surface, the first spline coupling becomes disengaged. At the same time, the second spline coupling is preferably configured so that it remains engaged when the first coupling set is disengaged. This can be achieved by selecting appropriate axial dimension and relative position of the second spline coupling taking into account the distance travelled by the drive shaft to disconnect the first spline coupling. Accordingly, torque and rotation from the drive shaft are transmitted through the second spline coupling and through the transmission mechanism to cause the relative rotation of the housing parts at the transmission rate provided by the transmission mechanism, as described above.
In the re-connection mode the first spline coupling locks at least one housing part to the drive shaft, whereas the second spline coupling is interrupted, with the result that the housing part locked to the drive shaft remains rotatable as a unit with the drive shaft, as described above. The second spline coupling can be disengaged by, for example, arranging the drive shaft to move axially within the housing, so that e.g. by pushing the drive shaft downwardly (i.e. compressing the back off sub), i.e. away from surface, or as the case may be, pulling the drive shaft towards the surface (i.e. applying tension to the back off sub), the second spline coupling becomes disengaged while the first spline coupling moves together with the drive shaft and thus remains engaged when the second coupling set is disengaged. This is achieved by selecting appropriate axial dimensions and relative positions of the first spline coupling taking into account the distance travelled by the drive shaft to disconnect the second spline coupling. Accordingly, the stationary housing part remains stationary downhole whereas the rotatable part of the housing is rotated directly by the drive shaft to permit rapid re-connection or disconnection of the housing parts as described above.
Where the transmission mechanism comprises a harmonic drive, the second spline coupling can be provided between the drive shaft and the wave generator. Alternatively, instead of providing a separate second spline coupling, the interruption means can be provided by arranging the wave generator and the flexible gear to be movable axially relative to each other so as to engage or disengage. The wave generator and the flexible gear function in the same manner as described above in connection with the second spline coupling in the locked mode, the back off mode and the re-connection modes.
In the interruption means provided by the wave generator and the flexible gear, the flexible gear preferably includes a flared mouth opening section for receiving and guiding the wave generator into engagement with the flexible gear.
Since the flexible gear and the wave generator are always in register and can be engaged readily irrespective of their relative angular positions (simply by moving the flexible gear and wave generator together so that the wave generator is received within the flexible gear), the use of the wave generator and the flexible gear as the interruption means eliminates the requirement for timing the harmonic drive in order to re-connect interrupted transmission as is the case with a splined type of coupling and, indeed, the need to provide a separate second coupling, whether or not a splined coupling, in the first instance.
Preferably, the flared mouth opening section is configured so that the wave generator is disengaged from the flexible gear when positioned within the flared mouth opening section.
Ideally, the locking means comprises an actuation mechanism adapted to switch the locking means between locked and unlocked modes. Preferably, the actuation mechanism includes a trip mechanism, preferably a hydro-mechanical trip mechanism, actuatable upon a condition indicating that equipment below the back off sub has become stationary and to cause the locking mechanism to unlock.
To detect such condition, a sensor, which may, advantageously, be a mechanical sensor because such a sensor does not require power to operate, is preferably provided sensitive for example to the change in the fluid pressure inside the work string or to the change in the torque, or a specific flow pulse. The trip mechanism can be actuated by application of a force, for example, tensile or compressive force, or upon receipt of a signal which can be provided in the form of a pressure differential, flow pulse, electric, magnetic or electromagnetic field pulse, rate or differential, a specific flow rate or differential. In one specific arrangement, the trip mechanism is configured to induce the axial movement of the drive shaft in relation to the housing upon detection of the condition indicating that the equipment below the back off sub has become stationary. Preferably, the trip mechanism is adjustable to be actuated upon a specific condition.
Ideally, the trip mechanism comprises a delay mechanism configured to prevent the locking means from unlocking for a predetermined time delay interval from the detection of a condition indicating that equipment below the back off sub has become stationary. This prevents the housing parts from beginning to disconnect immediately after the equipment is fixed or stuck. This is advantageous when the equipment below the back off sub is stuck and an attempt to retrieve the stuck objects is necessary or desired, typically by pulling or pushing the workstring from surface with force or by applying a dynamic force, for example, through the use of a jarring tool. If after the predetermined time delay interval the attempt to retrieve the stuck objects is not successful, the trip mechanism causes the locking means to unlock. Preferably, the delay mechanism is adjustable to provide a required time delay interval.
A plurality of such downhole back off subs can be incorporated into a workstring to provide for multiple back off locations along the workstring.
The first and second special embodiment of the invention preferably are made such that the first housing part is connected to an upper workstring, and that the second housing part is connected to a lower workstring or a bottom hole assembly. Preferably, it comprises means for detecting that the second housing part has become stationary.
A further object of this invention is a downhole workstring comprising a tool for selectively connecting or disconnecting components of said workstring, according to this invention.
A still further object of this invention is a method for disconnecting an upper workstring from a stuck lower workstring or a stuck bottom hole assembly of a workstring, wherein a tool according to this invention is used.
In particular, the present invention provides a method of using such a tool, in particular a back off sub, according to the first aspect of the invention, for releasing a part of a workstring which has been deposited downhole or disconnecting parts of workstring downhole, the method comprising
Preferably, the method further comprises
Preferably, the method further comprises
Preferably, the method further comprises
Preferably, the method comprises the step of:
Preferably, the method comprises the step of:
In yet another aspect, the present invention provides a method of using a back off sub according to the first aspect of the invention for releasing a part of a workstring which has been deposited downhole or disconnecting or reconnecting parts of workstring downhole, the method comprising
Preferably, the method comprises the step of:
Preferably, the method comprises the step of:
Preferably, the method comprises the step of:
Preferably, the method comprises the step of:
In still a further aspect, the present invention provides a method of using a back off sub according to the first aspect of the invention for disconnecting or reconnecting parts of workstring downhole, the method comprising
Preferably, the method comprises the step of:
The present invention provides a back off sub which is practically fail safe, i.e. it cannot disengage accidentally. The invention also provides a back off sub which enables an attempt to be made to release a part of the workstring which has been lodged downhole before the back off starts disconnecting by providing a delay between the moment when the workstring part becomes lodged and the initiation of the disconnection process. The invention also provides a back off sub which facilitates attempts to release a part of workstring which has become stationary downhole, by reducing friction and providing extra force for the release attempt. The back off sub of the invention provides sufficient time for an attempt to release the stationary part of workstring in case a part of workstring below the back off sub becomes stuck downhole or to reconnect the back off sub in case the disconnection process has initiated by accident before the disconnection is accomplished. The provision of the cooperating threads, preferably, small pitched threads as a kinematic pair and a harmonic drive as the transmission mechanism provides for a compact configuration which is important downhole. The provision of the harmonic drive further provides for low speed and high torque transmission while at the same time allowing the back off sub to remain compact.
The present invention will now be described by way of examples only, with reference to the accompanying drawings in which:
a, 8b, 8c, 8d show consecutive parts of a tool according to the present invention. Each of these
a, 9b and 9c show an enlarged view of a connection means for connecting a first housing part and a second housing part of the tool according to an embodiment of the present invention, respectively in a connecting position, in a disconnecting position and in an intermediate position.
With reference to
The housing 2 comprises a pair of tubular housing parts, a lower part 21 and an upper part 22. The tubular housing parts 21, 22 are provided in the form of co-axial sleeves, connected end-to-end with each other and arranged to rotate relative to each other about a common rotation axis 23. The drive shaft 3 extends axially through the housing 2. The housing parts 21, 22 are engaged together via a kinematic pair, in this embodiment, cooperating threads 24, provided on each housing part 21, 22 and arranged to translate the relative rotation of the housing parts 21, 22 into longitudinal displacement of the tubular parts 21, 22 relative to each other and relative to the common rotation axis 23. A transmission mechanism 5, provided by in the form of a harmonic drive 51 in the presently described embodiments, as will be described in more detail below, is arranged within the housing 2 to selectively transmit the rotation of the drive shaft 3 to at least one of the pair of the housing parts 21, 22, as will be described in more detail below, in order to induce the relative rotation of the housing parts 21, 22 and the resulting relative longitudinal displacement of the housing parts 21, 22. The housing 2 is mounted on the drive shaft 3 via the transmission mechanism 5, which in the presently described embodiment is coupled to each housing part 21, 22 as will be described below. Seals 61, 62 isolate the interior of the housing 2 from the rest of the workstring.
The transmission mechanism 5 includes a locking mechanism 7, as will be described below, is provided for selectively locking or unlocking the housing part 22 so as to restrict or permit the rotation of the housing part, 22 with respect to the drive shaft 3. The transmission mechanism 5 includes an interruption mechanism 77 for interrupting or engaging the transmission mechanism 5 to respectively disable or enable the transmission from the drive shaft 3 to the housing part 22 through the transmission mechanism 5. Preferably, the locking mechanism 7 and the interruption mechanism 77 are adapted to cooperate so that the back off sub 1 selectively operates in a number of modes, more specifically, in at least a locked mode, a back off mode and, preferably, a re-connection mode.
In a locked mode, the locking mechanism 7 locks the housing part 22 to the drive shaft 3 while the transmission mechanism 5 is engaged, with the result that the housing parts 21, 22 cannot rotate relative to each other and, instead, rotate as a unit together with the drive shaft 3 as indicated by arrows in
If and when it is required to disconnect the equipment below the back off sub 1, typically, if it is stuck downhole or has been installed or fixed in place the back off sub is brought into a back off mode. In the back off mode, the locking mechanism is actuated and the housing part 22 becomes released from the drive shaft 3, whereas the transmission mechanism 5 remains engaged. In the back off mode, the torque and rotation (indicated by arrow A in
Rotation of the drive shaft 3 in the opposite direction, e.g. anticlockwise, results in the reversal of the rotation of the housing part 22, so that the housing parts 21, 22 move axially toward each other and reconnect.
The rotation is transferred from the drive shaft 3 to the housing part 22 at the reduction ratio provided by the transmission mechanism 5. If the transmission mechanism is a reducer, as the harmonic drive 51 of the presently described embodiment, the relative rotation of the housing parts 21, 22 is slower than the rotation of the drive shaft 3, and, accordingly a certain time interval elapses before the housing parts 21, 22 disconnect. This delay is advantageous, for example, if the back off action starts accidentally, because the delay provides an operator with extra time to assess the situation and take the necessary steps to prevent the undesired disengagement. The delay in disconnection of the housing parts 21, 22 also means that the part of the workstring above the fixed or stuck portion of the workstring rotates during the disconnection process. The relative rotation of the housing parts 21, 22 is advantageous during an attempt to retrieve the stuck portion of the workstring because during the application of such an axial force, a considerable amount of friction is created between the workstring and the walls of the wellbore. The relative rotation of the housing parts 21, 22 during the retrieval attempts not only provides additional force in the immediate proximity to the stuck portion of the workstring which may help to release the stuck portion, but also reduces friction in the axial direction and thus facilitates the axial movements of the upper part of the workstring during the retrieval attempt.
Although not shown in
The cooperating threads 24 are selected such that the relative axial displacement of the housing parts 21, 22 occurs for a predetermined time before the housing parts 21, 22 disengage. Such an arrangement, as discussed above, is advantageous in case the locking mechanism 7 unlocks inadvertently or accidentally, because the prolonged disengagement process provides sufficient time for an operator at surface to detect a lowered torque exerted by the drive shaft 3 indicating that the disengagement process between the housing parts 21, 22 has begun, and to take measures to prevent further disengagement, i.e. to re-connect the housing parts 21, 22 by switching the direction of rotation of the drive shaft 3 to rotate in the opposite direction or by bringing the back off sub 1 into the re-connection mode in which the drive shaft 3 is coupled directly to the rotatable housing part 22 with the transmission mechanism 5 being interrupted, and thus causing the housing parts 21, 22 to re-engage. Also as explained above in connection with the transmission mechanism, such a prolonged disconnection time of the housing parts 21, 22, combined with the relative rotation of the housing parts 21, 22 facilitates an attempt to retrieve a stationary portion of the workstring, e.g. by jarring or by simple pushing or pulling.
In the presently described embodiment, the pitch of the cooperating threads 24 is selected so that the longitudinal displacement of the housing parts 21, 22 per revolution of the drive shaft 3 is relatively small and the housing parts move a relatively small total axial distance during the predetermined time interval as the housing parts engage or disengage. This adds to the compactness of the design of the back off sub of the invention while ensuring that the housing parts 21, 22 remain engaged for the predetermined time interval. The threads 24 can be fine-pitch threads. The threads 24 provide for a slow pace of the axial disengagement of the housing parts 21, 22 compared to the angular speed of rotation of the drive shaft 3. For the back off sub of the present invention, a pitch of 1 mm, 2 mm or 3 mm would be regarded as a fine-pitch. Combined with appropriately selected length in the axial direction of the threaded connection and transmission ratio of the transmission mechanism 5, the required disconnection time is achieved. For example, for 1 mm pitch and 100 mm long thread connection and a 100:1 reduction ratio of the transmission mechanism, rotation at input at 100 rpm results in 50 min thread disconnection (or connection) time involving 50 thread revolutions and 5000 drive shaft 3 revolutions.
Furthermore, the threads 24 are selected such that the threaded connection has a tensile strength in the axial direction in a state when the threads have disconnected by about 75-85% approximately the same or greater than the tensile strength of the part of the workstring which becomes stationary downhole. This prevents the threaded connection from breaking when an attempt is made to retrieve a stuck portion of the workstring while the housing parts 21, 22 of the back off sub are in the process of disconnecting.
In the presently described embodiment, the transmission mechanism 5 comprises a harmonic drive 51 comprising a wave generator 52, a flexible gear 53 and a circular (outer) gear 54. The wave generator 52 is mounted on the drive shaft 3 and serves as a rotary input component of the harmonic drive 51. The flexible gear 53 is coupled with the upper housing part 22 and serves as a rotary output component of the harmonic drive 51. The outer gear 54 is coupled with the lower housing part 21. When the harmonic drive 51 is in operation, i.e. when the housing parts 21, 22 are unlocked for relative rotation, the outer gear 54 remains stationary together with the lower housing part 21, which, in turn, is non-rotatably coupled to the equipment below the back off sub 1, while the flexible gear 53 rotates the upper housing part 22. Inherent to the principle of construction of harmonic drive, the wave generator 52 and the flexible gear 53 rotate in opposite directions as indicated by arrows A and B respectively in
Due to the principle of its construction, the harmonic drive 51 provides considerable reduction, which can be for example, 100:1, 200:1, 300:1, which means that the upper housing part 22 rotates very slowly compared to the drive shaft 3 the rotational speed of which is typically 30-150 rpm. The reduction combined with the small pitch threaded connection result in that disconnection of the housing parts 21, 22 does not occur instantly or soon after the disconnection process has begun. Instead, a certain time period elapses before the housing parts 21, 22 are disconnected and this time is sufficient for an operator at surface to become aware that the disconnection process has started and to react by taking measures to stop the disconnection and to re-connect the housing parts 21, 22 in case the disconnection process started accidentally. Also, the delay in disconnection provides for a possibility of an attempt to be made to retrieve the stuck portion of the workstring, for example, by jarring or by straightforward pushing or pulling, while the housing parts 21, 22 are still connected, while the relative rotation of the housing parts 21, 22 provides extra force for retrieval and friction reduction as described above.
Due to the principle of its construction, along with considerable reduction, the harmonic drive 51 provides torque multiplication (which is inversely proportional to the reduction). The plurality of teeth meshing at the same time in the harmonic drive 51 facilitates high torque transmission. High torque is required to rotate the housing parts 21, 22 relative each other via the cooperating threads 24 to translate the rotary motion of the housing parts 21, 22 into the relative axial movement of the housing parts 21, 22. The plurality of meshing teeth also provide for low vibration and absence of backlash, unlike other gear boxes.
Due to the co-axial arrangement of the rotating components of the harmonic drive 51, very compact configuration is achieved which is crucial in downhole tools.
In the embodiment of
When it is required to disengage the housing parts 21, 22 via the harmonic drive 51 the back off sub 1 is switched to a back off mode in which the drive shaft 3 is caused to slide axially in relation to the housing 2 (in the present embodiment, upwardly as indicated by arrow D in
To be capable of operating in the re-connection mode, the back off sub 1 of
The locking mechanism 7 comprises an actuation mechanism 75 for actuating the locking mechanism 7 between locked and unlocked modes. In the presently described embodiment, the actuation mechanism 75 is provided in the form of a trip mechanism, such as a hydro-mechanical trip mechanism, actuatable upon a condition indicating that equipment below the back off sub has become stationary and to cause the locking mechanism 7 to unlock. To detect such condition, a sensor (not shown) can be provided sensitive for example to the change in the fluid pressure inside the drill string or to the change in the torque. The trip mechanism can be actuated by application of a force, for example, tensile or compressive force, or upon receipt of a signal which can be provided in the form of a pressure differential, flow pulse, electric, magnetic or electromagnetic field pulse, rate or differential, a specific flow rate or differential. Upon detection of the condition indicating that equipment below the back off sub 1 has become stationary the trip mechanism 75 induces the axial movement of the drive shaft 3 in relation to the housing 2 as indicated by the arrow D in
Furthermore, the trip mechanism 75 comprises a delay mechanism (not shown) configured to prevent the locking mechanism 7 from unlocking for a predetermined time delay interval (e.g. 30 min or 1 hour) from the detection of the condition indicating that equipment below the back off sub 1 has become stationary. This prevents the housing parts 21, 22 from disconnecting immediately after the workstring has become fixed or stuck. This is advantageous when equipment below the back off sub 1 becomes stuck and an attempt to retrieve the stuck objects is necessary or desired by pulling or pushing the workstring from surface with force, or by applying a dynamic force using a jarring tool. If after the predetermined time delay interval the attempt to retrieve the stuck objects is not successful, the trip mechanism 75 causes the locking mechanism 7 to unlock. In the present embodiment, the drive shaft 3 is caused to slide axially upwardly thereby causing the splines 71, 72 to disconnect thereby permitting the housing parts 21, 22 to rotate relative to each other. The delay mechanism is preferably adjustable to provide a required time delay interval.
In
In
Modifications and improvements are envisaged without departing from the scope of the present invention as defined in the appended claims.
The present invention may be also described as follow. A downhole workstring generally comprises fluid channel or bore extending from the top of the workstring through the bottom of the workstring. A fluid, generally a mud, is allowed to flow through the bore or fluid channel, for example for providing a stream of fluid between the workstring and the walls of the downhole, evacuating the cuttings during a drilling operation, or also for avoiding the drill bit to be stuck into the downhole and for reducting the drag while the workstring is rotating inside the downhole.
The tool of the present invention comprises a drive shaft (3), preferably tubular and forming a part of the bore of the workstring. The tool further comprises and a housing (21,22), advantageously surrounding the drive shaft and couplable to said drive shaft (3). The housing comprises a first housing part (22) and a second housing part (21) releasably connected to one another.
The tool of the present invention is characterized in that it further comprises transmission means (52-54) coupled to the drive shaft (3), said transmission means being arranged to selectively connect or disconnect the housing parts (21),(22) by rotating the drive shaft (3).
Preferably, the transmission means (52-54) are arranged so that the rotation of said drive shaft (3) causes a longitudinal displacement of one of the housing parts (22), (21), or of an operating member (104) for connecting or disconnecting said housing parts, and so that the housing parts (22), (21) are connected or disconnected as a result of said axial displacement.
The tool comprises a kinematic pair which is selected such that said axial displacement occurs for a predetermined disconnection time before the housing parts disengage.
More preferably, the tool comprises a gear reduction mechanism, for example a harmonic drive or a planetary gear.
A preferred embodiment of the present invention is described by reference with the drawings 8a, 8b, 8c, 8d showing consecutive parts respectively from the top of the tool to the bottom of the tool. In an embodiment of the present invention, the housing comprises a first annular portion (106′) extending inside the housing and preferably located near the top of the housing. The first annular portion (106′) is hold by a second annular portion (106) fixed on the drive shaft (3). Preferably, thrust roller bearings (105) are inserted between the first annular portion (106′) and the second annular portion (106). The gear reduction mechanism is arranged for selectively transmitting the torque of said drive shaft (3) to one of said housing parts (21,54), said gear reduction mechanism comprising an output gear element (53) of which a threaded portion (108) is coupled to a threaded portion (107) of an operating member (104) for connecting or disconnecting said housing parts, such that rotational motion of the output gear element (53) results in axial displacement of said operating member (104).
Preferably, the gear reduction mechanism further comprises a reference gear element (54), which is fixed to or integrally formed with said housing part (21), an input gear element (52) fixed to said drive shaft (3), and an output gear element (53), such that rotation of the input gear element (52) relative to the reference gear element (54) results in rotation of the output gear element (53). In
Preferably, as shown in
Preferably, the reception cavities in the first housing part (22) are transversal recesses (101), the reception cavities in the second housing part (21, 54) are holes (102), the connection elements (103) are blocks fitting in a hole (102) and a recess (101) in alignment therewith, and the reception cavities of the operating member (104) are transversal recesses (101′).
Such a connection means between the first and second housing parts (22, 21) has the advantage over threaded connections to be more resistant to failure when the housing parts are disconnected from each other.
As shown at the right side R of the
a, 9b and 9c, show an enlarged view of the reception cavities of the first housing part, of the second housing part and of the operating member, respectively in a connecting position, in a disconnecting position and in an intermediate position. The blocks (103), the recesses (101) of the first housing (22), the holes (102) and the recesses (101′) of the operating member (104) are designed such that:
The cross-section of recesses (101′) of the operating member (104) preferably has a shape comprising an edge (203) forming an acute angle with the second housing (21) and oriented in a manner that when the operating member (104) is moved for connecting the first housing part (22) with the said second housing part (21), the edges push the blocks (103) towards the recesses (101) of the first housing (22), avoiding the stuck of the blocks (103) when the operating member (104) moves respect to the second housing (21).
Preferably, the tool further comprises a coupling member (110) which is selectively displaceable between a coupling position as shown at the left part L of the
The coupling member (110) is displaceable in a space (201) which is in communication with a fluid channel (200) of the tool through at least one aperture or port (119). In an embodiment of the invention as shown in
In an embodiment of the invention, as shown in the
said operating assembly (112,114,115) being arranged so that, when a fluid is flowing in the fluid channel (200), the insertion of the object (114) and its resulting position in the trap (113) influences the fluid pressure in the channel (200) such that said sleeve (112) is moved into the opening position, and that, when the object (114) is not positioned in the trap (113), the sleeve (112) is moved into the closing position by said spring element (115).
Preferably, the tubular sleeve (111) comprises a support (122) that supports the operating assembly (112, 114, 115).
More preferably, the operating assembly further comprises a locking pin (117) that can move through a hole formed in the wall of the tubular sleeve (111) and selectively enter or move out of a recess (118) formed in the coupling member (110). Preferably, the locking pin is mounted on a lever ( ) comprised between the operating sleeve (112), the tubular sleeve (111) and the support (122) so that:
In a preferred embodiment of the invention, the drive shaft (3) comprises an upper end fixed, preferably screw, to a bottom end of the upper work string, and the second housing comprise a lower end fixed, preferably screw, to the upper end of the lower work string or bottom hole assembly.
According to a second aspect of the invention, a method is provided for disconnecting an upper work string from a stuck lower workstring or a stuck bottom hole assembly of a work string, using the tool according to the embodiment of the
When a lower work string or a bottom hole assembly (herein after called BHA) of a workstring is stuck in the down hole, a sensor detects the that the lower work string or BHA is stuck, the drilling operator assesses the situation and may take the decision to activate the disconnection of the lower work string or BHA. In that situation, the drilling operator throws an object (114) for example, a dart or a ball, into the fluid channel (200). The object (114) is dragged by the flow of the fluid flowing in the fluid channel until it is catch by the trap (113) comprised at the top of the operating sleeve (112). The operating sleeve (112), which is initially retained in its closing position by the spring element (115), is moved down to its opening position, wherein:
The drive shaft (3) is therefore uncoupled from the second housing part (21). Since the drive shaft (3) was coupled with the second housing (21) connected to the first housing, and since the stuck lower workstring or BHA is fixed to the second housing, the drive shaft (3) was not able to rotate inside the housing (21, 22) because the coupling member (110) was coupling the drive shaft (3) with the second housing part (21). When the coupling member (110) is in its uncoupling position, the drive shaft (3) is able to move again inside the housing (21, 22) independently from the second housing (21) that comprises the reference gear element (54). Therefore, the input gear element (52) rotates with the drive shaft (3) if a torque or a residual torque is applied on the drive shaft (3), and the rotation of the input gear element (52) respect to the reference gear element (54) results in a rotation of the output element (53) in the opposite direction of the drive shaft (3) and with a very low transmission ratio respect to the rotation of the drive shaft.
The rotation of the output gear element (53) results in an axial movement of the operating member (104) that allows the alignment of the recesses (101′) of the operating members (104) with the holes (102) of the second housing (21) and the recesses (101) of the first housing (22), thereby allowing the first housing to move axially respect to the second housing when the upper workstring is pull off the downhole, the upper workstring being connected to the drive shaft that holds the first housing via the second annular portion fixed on the drive shaft (3).
The upper workstring can be connected or reconnected to the lower workstring or BHA by rotating the drive shaft in the appropriate direction for moving the operating sleeve (104) to its connecting position.
The man skilled in the art can also imagine a tool operating a disconnection of a first housing part from a second housing part with an axial movement of the drive shaft as presented in the embodiments related to the
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2013/000398 | 3/15/2013 | WO | 00 |
