Compensating drill string

Abstract

Compensating drill string tool 40 for use in drilling a wellbore that can be locked and unlocked, is configured for connection within a length of drill pipe or between and end of the drill pipe and th

Description

FIELD The present disclosure relates to a compensating drill string tool, particularly a compensating drill string tool for use in drilling subterranean wellbores, and a method of drilling a wellbore. BACKGROUND When drilling a subterranean wellbore, little annular clearance may be provided between the drill string / drill bit and the newly drilled wellbore. Vertical rig movement due to waves may cause the drill string / drill pipe to reciprocate up and down into the wellbore. When the drill string / drill pipe moves downward into the well, a ‘surge’ pressure arises due to the limited clearance between the drill string / drill bit and the newly formed wellbore, when combined with the viscosity of any fluids present within the wellbore. If surge pressure builds to high enough levels, this can cause fracturing of the formation and loss of fluid circulation in the wellbore. If the rig were to move upwards the limited clearance between the drill string / drill bit and the wellbore may also give rise to an issue from ‘swab’ pressure. In other words, ‘swabbing’ may occur as the drill string is pulled from the wellbore, causing a reduced wellbore pressure below the drill bit. Such a reduced pressure may cause an influx of fluid from the formation into the well and / or collapse of the wellbore. Therefore, the ‘surging’ and ‘swabbing’ should be avoided when drilling a wellbore, as these may result in a loss of wellbore fluids, or cause an influx of reservoir fluids which will result in a well-control situation. SUMMARY A first aspect of the invention relates to a compensating drill string tool for use in drilling a wellbore, the compensating drill string tool being configured for connection within a length of drill pipe or between an end of the drill pipe and a drill bit, the tool comprising a locking arrangement configurable between a locked configuration and an unlocked configuration; the tool being further configured to have an axial length, that varies in use, in response to axial forces on the tool, when in the unlocked configuration. The variable length of the compensating drill string tool may accommodate for, and mitigate against, swab and surge pressures within the wellbore when drilling. For example, when a new section of drill pipe is added to the drill string during drilling operations, the drill string may be locked to the drilling rig. Whilst the drill string is locked to the rig, the vertical movement of the drilling rig is transferred to the drill string, which may cause surge and swab pressure differences downhole; potentially causing an influx of wellbore fluids into the wellbore, resulting in a pressure kick in the well. Use of such a compensating drill string tool with a variable in length (which is variable in response to an axial force on the drill pipe of the drill string) as part of a drill string, allows the drill string to move axially within the wellbore, with the drill bit remaining at the bottom / end of the wellbore (e.g. the drill bit remains substantially stationary as the drill string / drill pipe moves axially within the wellbore), thereby preventing creation of a reduced pressure below the drill bit. Therefore, kicks due to swab pressures caused by the retraction of the drill string can be mitigated against. When in the locked configuration the axial length of the compensating drill string tool may be fixed. The compensating drill string tool may comprise a plurality of pipe lengths in telescopic engagement with one another, such that the axial length of the tool may be varied telescopically. The plurality of pipe lengths may arranged concentrically with one and other. Alternatively, the plurality of pipe lengths may be arranged eccentrically with one and other. A flow path is defined through the tool. The flow path may be defined along the axial length of the tool. The flow path may facilitate the flow of fluids downhole, such as drill fluids, cement or the like. The tool may comprise a flow activated lock arrangement. Such a lock arrangement is advantageous as the tool may be held in its locked configuration when drilling fluids are being pumped along the drill pipe (to the drill bit) during drilling operations. When drilling stops (e.g. when a new length of drill pipe needs to be added), the drill string tool will be reconfigured to its unlocked configuration, allowing the length of the drill string tool to be varied. The lock arrangement may be a pressure activated lock arrangement. The lock arrangement may be configurable between the locked and unlocked by variations in static pressure, such as variation in the static pressure of a fluid present in the flow path. Alternatively, the lock arrangement may be configurable between the lock and unlocked configurations by variations in dynamic pressure, such as variations in the dynamic pressure of a fluid present in the flow path. Such a pressure controlled lock arrangement may be advantageous, as varying either the static or dynamic pressure of a drilling fluid present within the drill pipe (e.g. a fluid already being used in drilling operations) can also be used to lock and unlock the compensating drill string tool. The locking arrangement may be resiliently biased towards the unlocked configuration. Resiliency biasing the locking arrangement towards the unlocked configuration means that the drill string tool will default to the unlocked configuration when there is no flow within the flow path, or when the flow or static fluid in the flow path is below a certain pressure. As outlined above, a variable length compensating drill string tool may provide means for compensating for axial forces on the drill pipe / drill string during drilling a wellbore, when the tool is in the unlocked configuration. For example, when the tool is in the locked configuration, its fixed length may allow the tool to transmit sufficient force to a drill bit of a drill string to allow drilling of the wellbore to be progressed. Once the drill string has progressed as far as its length allows, drilling operations may be stopped to allow an additional length of drill pipe to be added to the drill string, if the wellbore is to be advanced. Upon stopping drilling operations, the compensating drill string section may be configured to its unlocked configuration, allowing the length of the compensating drill string section to be varied. By unlocking the compensating drill string tool, and allowing the length of the tool to be varied, the drill string may now act like a reciprocating piston, wherein the length of the drill string section may be determined by axial forces applied to the drill pipe above the compensating drill string section. Therefore, for example, if the drill string / drill pipe above the compensating drill string tool is retracted from the wellbore, the drill bit may remain at the bottom / end of the wellbore. A second aspect of the invention relates to a method of drilling a wellbore. The method comprises assembling a first length of drill string, the length of drill string comprising the compensating drill string tool as described above, connected within a length of drill pipe, or between a length of drill pipe and a drill bit. The method further comprises running the drill string downhole, configuring the compensating drill string tool to a first axial length, locking the compensating drill string tool to fix the first axial length of the tool, drilling a first wellbore section, unlocking the compensating drill string tool to allow the axial length to be varied, retracting the drill string in the first wellbore section thereby extending the tool to a second axial length, assembling a further length of drill pipe to the drill string, configuring the compensating drill string tool to the first axial length of the tool, locking the compensating drill string tool to fix the first axial length of the tool, and drilling a further wellbore section beyond the first wellbore section. Following the step of assembling a further length of drill pipe to the drill string, the compensating drill string tool may be configured to the first axial length by advancing the drill string in the first wellbore section. A flow path may be defined through the compensating drill string tool. Said flow path may facilitate the flow of fluids downhole (e.g. between a drill floor and the drill bit), such as drilling fluids, cement or the like. The method may further comprise comprising locking the tool by flowing a fluid along the flow path of the tool, or flowing a fluid along the flow path of the tool above a predetermined pressure threshold. The method may further comprise unlocking the tool by stopping the flow of fluid along the flow path of the tool, or flowing the fluid along the flow path of the tool below a predetermined pressure threshold. It will be appreciated any of the features defined with respect to the first aspect of the disclosure may be used in combination with the second aspect of the disclosure, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A shows a first embodiment of a compensating drill string tool, according to the present disclosure, in a first configuration. Figure 1B shows the tool of Figure 1A, in a second configuration. Figure 1C shows the tool of Figures 1A and 1B, in a third configuration. Figure 2A shows a second embodiment of a compensating drill string tool, according to the present disclosure, in a first configuration. Figure 2B shows the tool of Figure 2A, in a second configuration. Figure 2C shows the tool of Figures 2A and 2B, in a third configuration. Figure 3A shows the first step in a method of drilling a wellbore using a drill string comprising a compensating drill string tool, according to the present disclosure. Figure 3B shows the second step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3C shows the third step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3D shows the fourth step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3E shows the fifth step in the method of drilling the wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3F shows the sixth step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3G shows the seventh step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. Figure 3H shows the eighth step in the method of drilling a wellbore using a drill string comprising the compensating drill string tool, according to the present disclosure. DETAILED DESCRIPTION Figures 1A to 1C show a first example of a compensating drill string tool 10 according to the present disclosure. Figure 1A shows a first embodiment of the compensating drill string tool 10 in a first configuration. The tool 10 comprises a tool body 15, which is defined by a first (outer) tubular 12 and a second (inner) tubular 14, wherein the inner and outer tubulars 12, 14 are arranged concentrically with one and other. The tool body 15 also defines a flow path 30 therethrough. The tool 10 further comprises a first end 16 and a second end 18. In this example, the first end 16 is disposed uphole of the second end 18. Although not shown in this example, the first end 16 may comprise a connector. Said connector may be configured to allow the first end to be connected to a length of drill pipe (also not shown). Said connector may comprise the female portion of a threaded coupling, or the male portion of a threaded coupling; e.g. the connector may comprise either the box or the pin of a pin and box joint. The second end 18 may also comprise a connector. Said connector may be also be configured to allow the second end to be connected to a length of drill pipe, or to a drill bit (directly, or via a drill collar or the like). As with the connector of the first end 16, the connector of the second end 18 may comprise a female portion of a threaded coupling, or the male portion of a threaded coupling, e.g. the connector may comprise either the box or the pin of a pin and box joint. Further shown are a plurality of locks 25 disposed on the inner tubular 14. Each lock 25 comprises a lock arm 22, and a lock member 24 disposed on the lock arm 22. Each lock member 24 comprises a plurality of surface features to engage with the inner surface 13 of the first tubular 12, which will be described below in greater detail. In the configuration of Figure 1A, the lock members 24 are not in engagement with the inner surface 13 of the outer tubular 12. This may be described as the ‘unlocked’ configuration. In this configuration, relative axial movement between the first and second tubulars 12, 14 is permitted. Figure 1B shows the tool 10 in a ‘locked’ configuration, wherein the lock members 24 have moved into engagement with the inner surface 13 of the first tubular 12. In this configuration, the surface features of the lock member 24 grip or ‘bite’ into the inner surface 13 of the first tubular, thereby locking the inner tubular 14 with respect to the outer tubular 12, and preventing axial movement between the two. The tool 10 may be configured into its locked configuration by flow of fluid 32 within the flow path 30 of the tool 10. For example, flow of fluid 32 within the flow path 30 may act upon the locks 25 to move them radially outwardly (as shown by arrows 23), bringing them into engagement with the inner surface 13 of the outer tubular 12. While not shown, the tool 10 may comprise any suitable means to allow fluid pressure to be communicated from the flow path 30 to the locks 25, and thereby bring the locks 25 into engagement with the inner surface 13 of the first tubular 12. For example, at least one port (not shown) may be provided in the wall of the second tubular 14, allowing pressure communication from the flow path 30 of the tool 10 to the locks 25. In alternative embodiment, the locks 25 may only be brought into locking engagement with the inner surface 13 of the outer tubular 12 when the pressure of the fluid 32 flowing in the flow path 30 of the tool 10 reaches a predetermined pressure threshold. Therefore, when fluid flowing in the flow path 30 of the tool 10 is below said threshold, the tool 10 will remain in the unlocked configuration. Figure 1C shows the compensating drill string tool 10 reconfigured to the unlocked configuration. The inner tubular 14 has extended beyond the outer tubular 12. The inner tubular 14 is able to extend beyond the outer tubular 12 due to the lock members 24 no longer being engaged with the inner surface 13 of the outer tubular 12. In this unlocked state, free axial movement between the first and second tubulars 12, 14 is permitted, causing variations in the axial length between the first and second ends 16, 18 of the tool 10. Therefore, the compensating drill string tool 10 may extend and retract as required in the unlocked state (e.g. in response to pressure forces, such as wellbore pressure forces). Figures 2A to 2C of the present disclosure show a second embodiment of the compensating drill string tool 40. Within this example, all features are the same as those described in relation to the first embodiment, except the locks 55 and engagement means with the inner surface of the first tubular 42. As shown within Figure 2A, this embodiment comprises locks 55 which comprise a lock arm 52 and a key 54 disposed on the lock arm 52. The inner surface of the outer tubular 42 comprises a keyway 53, configured to receive the key 54 of a lock 55. Within Figure 2B, the locks 55 of the compensating drill string tool have been forced radially outwardly (as shown by arrows 56), bringing the keys 54 of the locks 55 into engagement with their respective keyways 53. The actuation means to bring the locks 55 into engagement with their respective keyways 53 are the same as those described in relation to the embodiment of Figures 1A to 1C. In both of the foregoing examples, the locks 25, 55 may comprise biasing means, biasing the locks 25, 55 into the unlocked configuration. For example, when no fluid is flowing along the flow path 30, 60 of the compensating drill string tool 10, 40, or when the fluid flowing along the flow path 30, 60 is below a predetermined threshold, the locks 25, 55 may be biased towards the unlocked configuration. This may prevent the tool 10, 40 from becoming stuck in its locked configuration. The biasing means may be any suitable biasing means. For example, the arms 22, 52 of the locks 25, 55 of each example may be resiliently biased towards the unlocked configuration. Alternatively, the locks 25, 55 may comprise a spring (or the like) to bias the locks 25, 55 towards the unlocked configuration. The compensating drill string tool 10 may comprise one or more seals 29, 49 disposed between adjacent concentric tubulars. Said seals 29, 49 may be any suitable sealing means (such as an O-ring, graphite packing or the like) configurable to prevent the ingress of wellbore fluids between adjacent tubulars of the tool 10. The compensating drill string tool 10 may further comprise a stop arrangement 21a, 41a, 21b, 41b, preventing over-extension of the inner tubular 14, 44 relative to the outer tubular 12, 42, and / or preventing the inner tubular 14, 44 from retracting past the first end 16, 46 of the tool 10, 40. The stop 21a, 41, 21b, 41b may comprise any suitable stopping means within the understanding of one skilled in the art, such as shoulders 21a, 41a, 21b, 41b disposed on both the inner and outer tubulars 12, 42, 14, 44, wherein the shoulders 21a, 41a, 21b, 41b are configured to engage to put a stop to relative axial movement between the inner and outer tubulars 12, 42, 14, 44 in at least one direction, when the tool is in the unlocked configuration. The compensating drill string tool 10, 40, may further comprise dampening means 27, 47 disposed between the inner and outer tubulars 12, 42, 14, 44 configured to dampen the relative axial movement of the tubulars 12, 42, 14, 44. Such a dampening means 27, 47 may comprise any suitable dampening means within the knowledge of one skilled in the art, such as mechanical or compressible fluid springs disposed between the adjacent tubulars 12, 42, 14, 44 of the tool 10. Including dampening means 27, 47 to dampen the relative axial motion between the tubulars 12, 42, 14, 44 may prevent rapid extension and / or retraction of the tool 10, which may thereby prevent damage to the tool. It will be appreciated by one skilled in the art that, while the compensating drill string tools of Figures 1A to 2C have been described as having a body 15, 45comprising two concentrically arranged tubulars, the tool may comprise more than two concentrically arranged tubulars, with a locking arrangement (as described above) disposed between one or more adjacent pairs of tubulars. Figures 3A to 3H show a method of drilling a wellbore using the compensating drill string tool described above. Figure 3A shows a first step of drilling a wellbore 215 in a subterranean formation 220, wherein a drill string has been run into the wellhead. The drill string comprises a first length of drill pipe 205, a second length of drill pipe 210 and a drill bit 200 Disposed between the first and second lengths of drill pipe 205, 210 is the compensating drill string tool 10 as described with reference to Figures 1A to 1C. It will be appreciated that this embodiment of the compensating drill string tool 10 has been used for illustrative purposes, and the embodiment described with reference to Figures 2A to 2C (or variations thereof) may be used instead. The second length of drill pipe 210 is connected to the drive means (not shown) for the drill string for drilling the wellbore 215. It will also be appreciated that while in this example the compensating drill string tool has been included intermediate two lengths of drill pipe 205, 210, the tool 10 may be connected to the drill bit 200 without the use of the first length of drill pipe 205. When the drill string is run into the wellhead, the compensating drill string tool 10 is configured in its ‘collapsed’ position, wherein there is no extension of the compensating drill string tool 10. Figure 3B shows the start of the wellbore drilling process. As shown, drilling fluid 105 is pumped along the flow path of the drill string (via the compensating drill string tool 10) to the drill bit 200. As such, the compensating drill string tool 10 is configured to its locked configuration, preventing relative axial movement of the inner tubular (not shown in this figure) with respect to the outer tubular 12 of the tool 10, and thereby preventing extension of the tool 10. Figure 3C shows the wellbore 215 having been progressed to the point at which a third length drill pipe needs to be added to the drill string in order to progress the wellbore 215 further. At this point, pumping of drilling fluid along the drill string is stopped, and the compensating drill string tool 10 is now configured to its unlocked configuration. Figure 3D shows the drill string being retracted slightly (as shown by arrows 212) from the wellbore 215 and the drill string 212 locked to the drilling rig. The retraction of the drill string 212 may have been a result of movement of the drilling rig induced by sea conditions. As the drill string is retracted 212, and given the compensating drill string tool 10 is in its unlocked configuration, the compensating drill string tool 10 is allowed to extend (as shown by arrows 112), with the drill bit 215 remaining at the bottom of the wellbore (220). The extension is shown by the inner tubular 14 of the tool 10 extending axially beyond the outer tubular 12. As the tool 10 is now in its unlocked configuration, free relative axial motion between the outer and inner tubulars 12, 14 is now permitted, and the compensating drill string tool 10 may extend or retract as needed (for example, to accommodate for weight fluctuations in the drill pipe 210 disposed above the tool 12, or movements of the drilling rig induced by sea conditions). Within Figure 3E, the third length of drill pipe 225 has been assembled to the drill string. The compensating drill string tool 10 remains in its unlocked configuration during this process. Figure 3F shows the compensating drill string tool 10 being reconfigured to its ‘collapsed’ position (as indicated by arrows 114), wherein there is no extension of the inner tubular 14 beyond the outer tubular 12. This is achieved by engaging the drill bit 200 with the bottom of the wellbore 215 by forcing the drill string downhole (as shown by arrows 214) until the compensating drill string tool 10 is in its fully collapsed state. Once the compensating drill string tool 10 is in its fully collapsed stated, and as shown by Figure 3G, the compensating drill string tool 10 is reconfigured to its locked state. This is achieved by again pumping drilling fluid 105 along the drill string, via the compensating drill string tool 10, thereby engaging the locks of the tool 10. Once the 5 compensating drill string tool 10 has returned to its locked configuration, drilling of the wellbore 215 can be progressed. Progression of the next stage of the wellbore 215 is shown in Figure 3H, wherein the drill string, with the compensating drill string tool 10 in its locked configuration, has 10 advanced the wellbore 215 further into the subterranean formation 220.

Claims

1. A compensating drill string tool for use in drilling a wellbore, the compensating drill string tool being configured for connection within a length of drill pipe or between an end of the drill pipe and a drill bit, the tool comprising a locking arrangement configurable between a locked configuration and an unlocked configuration, the tool being further configurable to have an axial length that varies in use, in response to axial forces on the tool, when in the unlocked configuration.

2. The tool according to claim 1 and comprising a plurality of pipe lengths in telescopic engagement with one another, such that the axial length is of the tool is varied telescopically.

3. The tool according to claim 2, wherein the plurality of pipe lengths are arranged concentrically with one and other.

4. The tool of any preceding claim, wherein a flow path is defined through the tool, along the axial length of the tool.

5. The tool of claim 4, wherein the lock arrangement is a flow activated lock arrangement.

6. The tool of claims 4 or 5, wherein the lock arrangement is a pressure activated lock arrangement.

7. The tool according to any preceding claim, wherein the locking arrangement is resiliently biased towards the unlocked configuration.

8. A method of drilling a wellbore, the method comprising:assembling a length of drill string, the length of drill string comprising the compensating drill string tool of any one of the preceding claims connected within a length of drill pipe, or between a length of drill pipe and a drill bit;running the drill string downhole;configuring the compensating drill string tool to a first axial length;locking the compensating drill string tool to fix the first axial length of the tool;drilling a first wellbore section;unlocking the compensating drill string tool to allow the axial length of the tool to be varied;retracting the drill string in the first wellbore section, thereby extending the tool to a second axial length;assembling a further length of drill pipe to the drill string;configuring the compensating drill string tool to the first axial length;locking the compensating drill string tool to fix the first axial length of the tool; drilling a further wellbore section beyond the first wellbore section.

9. The method of claim 8, wherein, following the step of assembling a further length of drill pipe to the drill string, the compensating drill string tool is configured to the first axial length by advancing the drill string in the first wellbore section.

10. The method of claims 8 or 9, wherein a flow path is defined through the compensating drill string tool.

11. The method of claim 10, comprising locking the tool by flowing a fluid along the flow path of the tool, or flowing a fluid along the flow path of the tool above a predetermined pressure threshold.

12. The method of claim 11, comprising unlocking the tool by stopping the flow of fluid along the flow path of the tool, or flowing the fluid along the flow path of the tool below a predetermined pressure threshold.

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