Drift tool

Abstract

There is provided a wellbore drift tool (10) including an elongate outer housing (20) and a mandrel (40) received within the elongate outer housing (20) such that the mandrel (40) and elongate outer housing (20) are axially movable relative to one another. A plurality of drift keys (30) are movably mounted on the outer housing (20), protrude from an outer surface thereof and are radially displaceable relative to the outer housing (20). The mandrel (40) includes a stepped profile (42) interengaging the drift keys (30) and mandrel (40) such that the radial position of the drift keys (30) is determined by the relative axial position of the mandrel (40) and drift keys (30). In use, axial movement of the mandrel (40) relative to the outer housing (20) adjusts the interengagement of the stepped profile (42) and drift keys (30).

Description

[0001] DRIFT TOOL

[0002] TECHNICAL FIELD

[0003] The present invention relates to a drift tool. More specifically, although not exclusively, the present invention relates to a drift tool for carrying out a wellbore drifting operation. The invention further relates to a method of running a wellbore drift tool past a wellbore restriction.

[0004] BACKGROUND

[0005] Prior to carrying out a well intervention a wellbore may be drifted in order to determine the minimum internal or inside diameter (ID) on a path between the surface and the target depth at which the intervention operation is to take place. Whilst casing and production strings generally have standardised IDs, it may be the case that during the life of the well deposits, e.g. scale deposits, cement residue or collapsed tubing strings reduce the actual ID.

[0006] By determining the actual minimum ID prior to running intervention equipment into the wellbore, the risk of equipment becoming stuck or being unable to be run to target depth is reduced.

[0007] It is therefore a first non-exclusive object of the invention to provide a wellbore drift tool that overcomes, or at least mitigates, on or more disadvantages associated with the prior art, such as described herein or elsewhere.

[0008] SUMMARY OF THE INVENTION

[0009] According to an aspect of the invention there is provided a wellbore drift tool, comprising: an outer housing; a mandrel received within the outer housing, wherein the mandrel and outer housing are axially movable relative to one another: a plurality of indicator keys protruding from an outer surface of the outer housing; wherein the indicator keys are radially displaceable relative to the outer housing, in use; wherein the mandrel comprises an indexing profile configured to engage the indicator keys; wherein the extent to which the indicator keys protrude from the outer surface of the housing is dependent on a position of the indexing profile relative to the indicator keys; wherein, in use, axial movement of the mandrel relative to the outer housing adjusts the position of the indexing profile relative to the indicator keys.

[0010] According to an aspect of the invention there is provided a wellbore drift tool, comprising an elongate outer housing; a mandrel received within the elongate outer housing, wherein the mandrel and elongate outer housing are axially movable relative to one another: a plurality of drift keys movably mounted on the elongate outer housing and protruding from an outer surface thereof; wherein the drift keys are radially displaceable relative to the elongate outer housing; wherein the wellbore drift tool comprises an indexing profile interengaging the drift keys and mandrel; wherein the radial position of the drift keys is determined by the relative axial position of the mandrel and drift keys.

[0011] The wellbore drift tool, outer housing and / or mandrel may comprise a central axis or a longitudinal axis. It will be appreciated that the term axially may refer to a direction along or parallel to the central axis or longitudinal axis.

[0012] The wellbore drift tool may comprise an uphole end and a downhole end. The uphole end may be an end of the wellbore drift tool closer than the downhole end to the surface. The uphole end may be an end of the wellbore drift tool further than the downhole end to a target depth.

[0013] The uphole end may be or may be referred to as an upper end. The downhole end may be or may be referred to as a lower end.

[0014] In some embodiments, in use, axial movement of the mandrel relative to the elongate outer housing is configured to adjust the interengagement of the indexing profile and / or the position of the indexing profile relative to the drift keys.

[0015] In some embodiments, in use, axial movement of the outer housing relative to the mandrel is configured to adjust the interengagement of the indexing profile and / or the position of the indexing profile relative to the drift keys.

[0016] The elongate outer housing and mandrel may be slidably mounted relative to one another. The mandrel may be slidably mounted within the elongate outer housing.

[0017] The indexing profile may be or may form part of an indexing assembly. The indexing profile may comprise a stepped profile. The indexing profile may comprise a staircase. The indexing profile may comprise a ratchet or a tapered engagement surface. The stepped profile may determine the radial position of the drift keys. The stepped profile may determine the extent to which at least one of the drift keys protrudes from the outer surface of the elongate outer housing.

[0018] The indexing profile or stepped profile may be arranged such that the extent to which the indicator keys protrude from the outer surface of the housing decreases as the mandrel moves axially relative to the elongate outer housing in a downhole direction.

[0019] The stepped profile may comprise a plurality of steps. Each step may be or may comprise an increment. Each of the plurality of steps may extend axially. Each of the plurality of steps may comprise an engagement surface for engagement with one or more indicator keys or the mandrel. The or each engagement surface may extend generally parallel to the longitudinal axis or central axis. A distance from the central axis or longitudinal axis to each respective step or engagement surface may increase from an uphole end to a downhole end. The height of the steps of the stepped profile may increase from an uphole end to a downhole end.

[0020] The difference in height between adjacent steps may be between 0.05 and 0.15 inches, for example between 0.075 and 0.125 inches. The difference in height between adjacent steps may be 0.1 inches. The or each stepped profile may comprise between five and fifteen steps, for example six steps, ten steps or thirteen steps.

[0021] The indexing profile or stepped profile may be provided on the mandrel. The indexing profile or stepped profile may be formed integrally with the mandrel. The indexing profile or stepped profile may be attached or otherwise connected to the mandrel.

[0022] The indexing profile or stepped profile may be provided on each of the drift keys, e.g. in inner surface of the drift keys.

[0023] An indexing profile or stepped profile may be provided on each of the mandrel and the drift keys.

[0024] The indexing profile or stepped profile may comprise an axial guide, groove or slot. The axial guide, groove or slot may be configured to receive a rib or protrusion, e.g. an elongate rib or protrusion, to guide relative movement of the mandrel and drift keys and / or guide relative movement of the mandrel and elongate outer housing. When the indexing profile or stepped profile is provided on the mandrel, the drift keys may be provided with a rib or protrusion on an inner surface thereof.

[0025] The wellbore drift tool may comprise a plurality of indexing profiles or stepped profiles configured to interengage the drift keys and mandrel. The mandrel may comprise a plurality of indexing profiles, e.g. circumferentially spaced from one another and / or axially spaced from one another.

[0026] The extent to which the drift keys protrude from the outer surface of the elongate outer housing may be dependent on a position of the indexing profile and / or mandrel relative to the drift keys.

[0027] In use, axial movement of the mandrel relative to the elongate outer housing may adjust the position of the indexing profile relative to the drift keys. In use, axial movement of the mandrel relative to the elongate outer housing may adjust the engagement of the indexing profile with the drift keys. In use, axial movement of the mandrel relative to the elongate outer housing may adjust the part or portion of the indexing profile in engagement with the drift keys.

[0028] The elongate outer housing may comprise, retain and / or house the drift keys. The elongate outer housing may comprise one or more openings in receipt of the drift keys. The elongate outer housing may comprise a plurality of openings. Each opening may be in receipt of a respective drift key. The elongate outer housing may be or may comprise a sleeve or tubular body.

[0029] The drift keys may alternatively be referred to as indicator keys. The drift keys may be in contact with the mandrel. Each drift key may comprise an outer surface, e.g. a radially outer surface, configured to contact an inner wall of a wellbore. Each drift key may comprise an inner surface, e.g. a radially inner surface, configured to engage the mandrel and / or indexing profile. Each drift key may comprise one or more engagement profiles configured to engage the indexing profile or stepped profile of the mandrel. The inner surface of the drift keys may comprise the indexing profile or stepped profile. The mandrel may comprise a protrusion or engagement profile configured to engage the indexing profile or stepped profile of the drift keys. An inner surface, e.g. a radially inner surface, of the drift keys may be in contact with the mandrel, indexing profile and / or stepped profile. One or more or each of the drift keys may be elongate. One or more or each of the drift keys may extend axially. One or more or each of the drift keys may comprise curved, filleted and / or radiused corners. One or more or each of the drift keys may comprise a curved and / or arcuate outer surface. One or more or each of the drift keys may be pill shaped. One or more or each of the drift keys may be magnetic. One or more or each of the drift keys may comprise a magnet, e.g. on a radially inner surface thereof. One or more or each of the drift keys may comprise a magnet on each step or portion of the indexing profile or stepped profile.

[0030] One or more or each of the drift keys may comprise retaining holes, e.g. for receipt of retaining pins. The retaining holes and / or retaining pins may be configured to retain the drift keys in a predetermined radial position, e.g. relative to the elongate outer housing and / or mandrel.

[0031] The wellbore drift tool may comprise a first set of drift keys. The drift keys of the first set of drift keys may be circumferentially spaced, e.g. around the elongate outer housing. The drift keys of the first set of drift keys may be evenly circumferentially spaced around the elongate outer housing. The wellbore drift tool may comprise a second set of drift keys. The drift keys of the second set of drift keys may be circumferentially spaced, e.g. around the elongate outer housing. The drift keys of the second set of drift keys may be evenly circumferentially spaced around the elongate outer housing.

[0032] The drift keys of the first set of drift keys and the drift keys of the second set of drift keys may be axially spaced from one another. The drift keys of the first set of drift keys and the drift keys of the second set of drift keys may axially overlap. The drift keys of the first set of drift keys and the drift keys second set of drift keys may be devoid of axial overlap. The drift keys of the first set of drift keys and the drift keys of the second set of drift keys may circumferentially overlap, e.g. such that they provide full circumferential coverage around the wellbore drift tool. The respective central or longitudinal axes of the drift keys of the first set of drift keys may be circumferentially offset from the respective central or longitudinal axes of the drift keys of the second set of drift keys.

[0033] Each set of drift keys may comprise the same or an equal number of drift keys. Each set of drift keys may comprise four drift keys equally circumferentially spaced from one another, e.g. comprising spacing of 90 degrees. Each set of drift keys may be circumferentially offset from one another by 90 degrees. The wellbore drift tool may comprise a pair of diametrically opposed drift keys. One or each set of drift keys may comprise a respective pair of diametrically opposed drift keys. One or each set of drift keys may comprise at least one pair of diametrically opposed drift keys. One or each set of drift keys may comprise a plurality of respective pairs of diametrically opposed drift keys.

[0034] The maximum distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be 3 inches. The distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be adjustable due to the indexing profile or stepped profile to between 3 inches and 2.4 inches, e.g. in 0.1 inch increments. The indexing profile or stepped profile may comprise six steps.

[0035] The maximum distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be 3.9 inches. The distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be adjustable due to the indexing profile or stepped profile to between 3.9 inches and 2.9 inches, e.g. in 0.1 inch increments. The indexing profile or stepped profile may comprise ten steps

[0036] The maximum distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be 4.8 inches. The distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be adjustable due to the indexing profile or stepped profile to between 4.8 inches and 3.8 inches, e.g. in 0.1 inch increments. The indexing profile or stepped profile may comprise ten steps.

[0037] The maximum distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be 6 inches. The distance or diameter measured between the outer surfaces, e.g. radially outer surfaces, of diametrically opposed drift keys may be adjustable due to the indexing profile or stepped profile to between 6 inches and 4.7 inches, e.g. in 0.1 inch increments. The indexing profile or stepped profile may comprise thirteen steps. The wellbore drift tool may comprise a biasing means, e.g. a spring. The biasing means may be pre-loaded. The biasing means may be a compression spring. The biasing means or spring may be pre-loaded in compression. The biasing means or spring may be an emergency release spring. The biasing means or spring may be a bottom end spring. The biasing means or bottom end spring may be located between the elongate outer housing and the mandrel. The biasing means or bottom end spring may be located between the elongate outer housing and a sub or connector connected to a downhole end of the mandrel. The sub or connector may be or may comprise a spring stop. The biasing means or bottom end spring may be located between the elongate outer housing and a spring stop connected to a downhole end of the mandrel. The biasing means or bottom end spring may be arranged to propel or bias the mandrel in a downhole direction. The biasing means or bottom end spring may be configured to propel or bias the elongate outer housing and / or drift keys in an uphole direction. The biasing means or bottom end spring may be configured to propel or bias the mandrel axially in a downhole direction, e.g. relative to the elongate outer housing and / or drift keys. The biasing means or bottom end spring may be configured to propel or bias the elongate outer housing and / or drift keys axially in an uphole direction, e.g. relative to the mandrel.

[0038] The wellbore drift tool may comprise a spring stop, sub or connector connected at a downhole end of the mandrel. The spring stop, sub or connector may comprise a shoulder. The biasing means or bottom end spring may be located between the elongate outer housing and the spring stop, sub or connector, e.g. the shoulder thereof. The elongate outer housing may comprise a shoulder at or proximate a downhole end thereof. The shoulder may extend from an inner surface of the elongate outer housing. The shoulder may extend radially. The biasing means or bottom end spring may be located between the shoulder of the elongate outer housing and the spring stop, sub or connector. The biasing means or bottom end spring may extend axially along a space defined between the elongate outer housing and mandrel.

[0039] The wellbore drift tool may comprise an increment control mechanism or a locking mechanism (hereinafter increment control mechanism). The increment control mechanism may be separate from the indexing profile or stepped profile. The increment control mechanism may be axially spaced from the indexing profile or stepped profile. The increment control mechanism may be configured to restrict relative movement of the mandrel and elongate outer housing. The increment control mechanism may be configured to restrict the adjustment of the position of the indexing profile or stepped profile relative to the elongate outer housing and / or drift keys.

[0040] The increment control mechanism may have a first state or first condition in which axial movement of the mandrel relative to the elongate outer housing is prevented, restricted or limited. The increment control mechanism may have a second state or second condition in which axial movement of the mandrel relative to the elongate outer housing is permitted. In the first state the mandrel may be permitted to move axially relative to the elongate outer housing a lesser amount than in the second state.

[0041] In the first state the increment control mechanism may be configured prevent, restrict or limit axial movement of the mandrel relative to the elongate outer housing due to or in response to the or a biasing means, e.g. an increment spring or an increment control spring as described below and / or a bottom end spring described above. In the second state the increment control mechanism may be configured to permit axial movement of the mandrel relative to the elongate outer housing due to the biasing means , e.g. an increment spring or an increment control spring as described below and / or a bottom end spring described above. In the first state the mandrel may be permitted to move axially relative to the elongate outer housing due to or in response to the biasing means, e.g. an increment spring or an increment control spring as described below and / or a bottom end spring described above, a lesser amount than in the second state.

[0042] The increment control mechanism may comprise a sleeve. The sleeve may have an engagement feature or an engagement profile (hereinafter “engagement feature”) on an inner or internal surface, e.g. radially inner, (hereinafter “inner surface”) thereof. The sleeve may be connected to an uphole end of the elongate outer housing. The sleeve may be constrained to move axially with the elongate outer housing. The sleeve may be axially fixed with respect to the elongate outer housing. The mandrel may be configured to move axially relative to the sleeve. The elongate outer housing may comprise the sleeve.

[0043] The increment control mechanism may comprise a key in engagement with or in contact with the engagement feature in the first state. The key may be out of engagement with or out of contact with the engagement feature when the increment control mechanism is in the second state. The engagement feature may comprise a plurality of circumferentially extending grooves or protrusions. The grooves may be axially spaced from one another along the sleeve. In the first state the mandrel may be permitted to axially move relative to the elongate outer housing to the extent that the key contacts or engages adjacent circumferentially extending grooves or protrusions.

[0044] The axial spacing of the circumferentially extending grooves may be generally equal to the axial length of each of the plurality of steps of the stepped profile and / or the axial length of the engagement surface of each of the steps. The axial spacing of the circumferentially extending grooves may be generally equal to the axial length of each increment of the indexing profile.

[0045] The increment control mechanism may comprise two keys or a pair of keys axially spaced from one another. The two keys or pair of keys (hereinafter “pair of keys”) may form or comprise a set of keys. It will be appreciated that the term “pair of keys” need not suggest that the keys are identical or complementary. The increment control mechanism may comprise one or more further sets or pairs of keys, e.g. circumferentially spaced from one another. The increment control mechanism may comprise four sets of keys circumferentially spaced, e.g. equally spaced, from one another. The increment control mechanism may comprise any other suitable number of pairs or sets of keys circumferentially spaced, e.g. equally spaced, from one another.

[0046] The or each key may be or may comprise a floating key, a lock-dog or a floating lock-dog. The key may be or may comprise a locking key. The term “key” will be used hereinafter, but it will be appreciated that the or each key may take another form as set-out above.

[0047] The or each key may be generally saddle-shaped or H-shaped when viewed perpendicular to an axial direction or longitudinal axis. The key may have an inner recess, e.g. a radially inner recess. The key may have an outer recess, e.g. a radially outer recess.

[0048] When the wellbore drift tool is in a neutral state one of the keys, e.g. one of the two of keys and / or one of each set of keys, may be in engagement with or in contact with one or more of the engagement features. The or at least one key may be radially movable. It will be appreciated that “at least one” in reference to the keys may also encompass all keys. The or at least one key may have a deployed or activated state or configuration (hereinafter “deployed state”). The or at least one key may have a withdrawn or inactivated state or configuration (hereinafter “withdrawn state”). The or at least one key may be radially movable with respect to the sleeve, elongate outer housing and / or mandrel. A key in the deployed state may be located radially outward of a key in the withdrawn state.

[0049] The or at least one key may be in contact with or engagement with one or more of the engagement features in the deployed state. The or at least one key may be come into contact with or engagement with one or more of the engagement features in the deployed state, e.g. in response to relative movement between the mandrel and / or elongate outer housing or sleeve or relative movement between the activation member and / or elongate outer housing or sleeve. The or at least one key may be out of contact with or engagement with one or more or all engagement features in the withdrawn state. All keys may be out of contact with or engagement with all engagement features in the withdrawn state. The mandrel may be free to move axially relative to the elongate outer housing, e.g. due to the biasing means or increment control spring, when all keys are in the withdrawn state. One or more of the engagement features may be received within or located within the outer recess when a key is in the deployed state. The mandrel may be free to move axially relative to the elongate outer housing an axial distance equivalent to the axial distance between adjacent circumferentially extending grooves when the increment control mechanism is in the second state.

[0050] A first of the pair of keys may be in deployed state and a second of the pair of keys may be in the withdrawn state when the increment control mechanism is in the first state. The first key may contact or engage one or more of the engagement features when the increment control mechanism is in the first state, e.g. to prevent, limit or restrict axial movement of the mandrel relative to the sleeve and / or elongate outer housing.

[0051] The first of the pair of keys may be in the withdrawn state and the second of the pair of keys may be in the deployed state when the increment control mechanism is in the second state. The second key may be free to move axially relative to the sleeve and / or elongate outer housing an axial distance equivalent to the distance between adjacent circumferentially extending grooves, e.g. due to or in response to an increment spring or an increment control spring, when the increment control mechanism is in the second state.

[0052] One of the pair of keys may always be in the deployed state and / or the other of the keys may always be in the withdrawn state.

[0053] The key of the pair of keys in the deployed state may alternate between the first state and the second state of the increment control mechanism. The key of the pair of keys in the withdrawn state may alternate between the first state and the second state of the increment control mechanism.

[0054] A first of the pair of keys may be located uphole of a second of the pair of keys.

[0055] One or each of the keys may comprise a respective protrusion configured to engage or contact an engagement feature.

[0056] The wellbore drift tool may comprise an activation member or activation sleeve (hereinafter “activation member”). The increment control mechanism may comprise the activation member. The activation member may be configured to engage the or at least one key so as to move it between the deployed state and the withdrawn state. The activation member may be configured to move axially relative to the key(s). The activation member may be configured to move axially relative to all keys. The activation member may be configured to engage each of the pair of keys.

[0057] The activation member may comprise a cam profile. Additionally or alternatively, the activation member may comprise a biasing means, e.g. a spring.

[0058] The or at least one key may be moved between the deployed state and the withdrawn state in response to relative axial movement between the activation member and the or at least one key. Each of the pair of keys may be moved between the deployed state and the withdrawn state in response to relative axial movement between the activation member and the pair of keys. The cam profile may be configured to radially propel a, the or at least one key in response to relative axial movement between the activation member and the key(s). The activation member may comprise two cam profiles, each configured to engage a respective one of the pair of keys. The activation member may comprise two parts. The two parts may be axially movable relative to one another. The two parts may be constrained to move axially with one another, e.g. via a connector. Each of the two parts may comprise a respective cam profile. The two cam profiles may be axially movable relative to one another, e.g. in response to shearing of the connector or a connection provided therebetween. The connector or connection may comprise a shear ring. The activation member may comprise a plurality of cam profiles each configured to engage a respective key. Each part of the activation member may comprise one or more respective cam profiles.

[0059] The or each cam profile may comprise one or more protrusions or cam surfaces, e.g. axially spaced along the activation member. The cam surfaces may comprise axially extending ramps. One or more cam surfaces may be received within the inner recess of the or at least one key when said key is in the withdrawn state. Axial movement of the activation member and / or cam surface relative to the at least one key and / or the mandrel may be configured to cause the at least one key to ride the cam surface or an axially extending ramp, e.g. to move the at least one key from the withdrawn state to the deployed state and / or vice-versa.

[0060] The or at least one key may be moved between the withdrawn state and the deployed state in response to a jarring force applied to the mandrel and / or activation member, e.g. in a downhole direction. One of the pair of keys may be moved from the withdrawn state to the deployed state in response to a jarring force applied to the mandrel and / or activation member, e.g. in a downhole direction. The other of the pair of keys may be moved from the deployed state to the withdrawn state in response to a jarring force applied to the mandrel and / or activation member, e.g. in a downhole direction.

[0061] The increment control mechanism may be changed from the first state to the second state in response to a jarring force applied to the mandrel and / or activation member, e.g. in a downhole direction.

[0062] The interengagement of the indexing profile or mandrel may be configured to adjust by a single step or single increment in response to the jarring force applied to the mandrel and / or activation member in a downhole direction. The mandrel and / or indexing profile may be configured to move axially a distance equivalent to the axial distance between adjacent engagement features in response to the jarring force applied to the mandrel and / or activation member in a downhole direction.

[0063] The position of the indexing profile and / or mandrel relative to the elongate outer housing and / or drift keys may be configured to move or adjust by a single step or single increment or an axial distance equivalent to the axial distance between adjacent engagement features in response to a jarring force applied to the mandrel and / or activation member in a downhole direction.

[0064] The, each or at least one key may be located between the activation member and the sleeve. The, each or at least one key may be supported by or retained within a carrier sleeve or a carrier sub (hereinafter “carrier sleeve”). The, each or at least one key may be constrained to move axially with the carrier sleeve. The, each or at least one key may be radially movable relative to the carrier sleeve. The increment control mechanism may comprise the carrier sleeve.

[0065] The or at least one key may be constrained to move axially with the mandrel. The carrier sleeve may be connected to a downhole end of the mandrel. The carrier sleeve may comprise a collar received over an end of the mandrel. The mandrel may comprise the carrier sleeve. The carrier sleeve may be constrained to move axially with the mandrel. The activation member may be axially movable relative to the mandrel and / or carrier sleeve. The activation member may be axially movable relative to the mandrel, e.g. via or against a biasing means or increment spring or increment control spring (described below). The mandrel may be constrained to move axially with the activation member. The mandrel may be axially movable with or relative to the activation member.

[0066] The or at least one key may be moved from the withdrawn state to the deployed state in response to axial movement of the activation member relative to the mandrel in a downhole direction. Each of the pair of keys may be moved from the withdrawn state to the deployed state in response to axial movement of the activation member relative to the mandrel in a downhole direction.

[0067] The wellbore drift tool may comprise a biasing means, e.g. a spring, between the mandrel and the activation member. The biasing means or spring may be an increment spring or an increment control spring. The increment control mechanism may comprise the biasing means or increment control spring. The activation member and mandrel may be connected via a spring or increment control spring. The increment spring or increment control spring may be or may comprise a die spring.

[0068] The biasing means or increment control spring may be pre-loaded. The biasing or increment control spring means may be a compression spring. The biasing means or increment control spring may be pre-loaded in compression. The biasing means or increment control spring may be arranged to propel or bias the mandrel in a downhole direction due to or as a result of axial movement of the activation member, e.g. in a downhole direction and / or towards the mandrel. The biasing means or increment control spring may be configured to propel or bias the mandrel axially in a downhole direction, e.g. relative to the elongate outer housing and / or drift keys. The biasing means or increment control spring may be sized such that the mandrel moves axially a single increment or a single step of the indexing profile or stepped profile due to or as a result of axial movement of the activation member. The biasing means may control the movement of the mandrel such that it moves axially a single increment or a single step of the indexing profile or stepped profile due to or as a result of axial movement of the activation member. The biasing means or increment control spring may be sized such that the mandrel moves axially a distance equivalent to the axial distance between adjacent engagement features of the sleeve due to or as a result of axial movement of the activation member.

[0069] The wellbore drift tool may comprise a release function. In response to a jarring force applied to the mandrel and / or activation member in an uphole direction at least one or each of the two keys may be moved to the withdrawn state. In response to a jarring force applied to the mandrel and / or activation member in an uphole direction all keys, e.g. all keys in a deployed state, may be moved to the withdrawn state.

[0070] The release function may comprise shearing or breaking a connection between the two parts of the activation member. The two cam profiles may be moved axially towards one another, e.g. in response to shearing of the connector or connection. The two cam profiles may be moved axially towards one another due to or in response to the increment control spring. The two cam profiles may be moved towards one another to move the second key from a deployed state to a withdrawn state. The sleeve may be connected to an uphole end of the elongate outer housing. The sleeve may be constrained to move axially with the elongate outer housing. The sleeve may be axially fixed relative to the elongate outer housing. The elongate outer housing may comprise the sleeve.

[0071] The wellbore drift tool may comprise a travel limiter. The travel limiter may be configured to limit or restrict the axial movement of the mandrel and / or activation member relative to the elongate outer housing. The travel limiter may define a reset position for the wellbore drift tool. The travel limiter may comprise a shoulder and a protrusion configured to abut the shoulder. The shoulder may be provided on an internal surface of the elongate outer housing or sleeve. The shoulder may be provided proximate an uphole end of the elongate outer housing or sleeve. The protrusion may be provided on or extend from the mandrel and / or activation member.

[0072] The wellbore drift tool may comprising a top sub or shear sub connected to an uphole end of the activation member. In use, when the wellbore drift tool is being run into a wellbore, the drift keys may be configured to contact a restriction within the wellbore to thereby prevent or restrict further movement of the elongate outer housing and drift keys in a downhole direction. The wellbore drift tool may be configured such that when the elongate outer housing and / or drift keys is / are prevented from moving in a downhole direction due to a restriction in the wellbore, the activation member is configured to move relative to the elongate outer housing and / or mandrel in a downhole direction, e.g. against the increment control spring located between the mandrel and activation member. Movement of the activation member may cause movement of the cam surfaces, causing the increment control mechanism to enter the second state. The second key may move from a deployed state to a withdrawn state and the first key may move from the withdrawn state to the deployed state.

[0073] The wellbore drift tool may be for determining an minimum internal or inside diameter of a wellbore.

[0074] According to an aspect of the invention there is provided a wellbore drift tool, comprising: an upper end, a lower end and a longitudinal axis extending therebetween; an outer housing; an indexing assembly comprising: a plurality of indicator keys protruding from an outer surface of the outer housing; wherein the indicator keys are displaceable relative to the outer housing in a direction perpendicular to the longitudinal axis; an indexing profile configured to engage the indicator keys, wherein the indexing profile is movable relative to the outer housing along the longitudinal axis; wherein the extent to which the indicator keys protrude from the outer surface of the housing is dependent on the portion of the indexing profile in engagement with the indicator keys; wherein, in use, movement of the indexing profile along the longitudinal axis relative to the outer housing adjusts the portion of the indexing profile in engagement with the indicator keys.

[0075] According to an aspect of the invention there is provided a method of running a wellbore drift tool past a wellbore restriction, the wellbore drift tool comprising: an elongate outer housing; a mandrel received within the elongate outer housing, wherein the mandrel and elongate outer housing are axially movable relative to one another: a plurality of drift keys movably mounted on the elongate outer housing and protruding from an outer surface thereof; wherein the drift keys are radially displaceable relative to the elongate outer housing; wherein the wellbore drift tool comprises an indexing profile interengaging the drift keys and mandrel; wherein the radial position of the drift keys is determined by the relative axial position of the mandrel and drift keys; wherein, the method comprises axially moving the mandrel relative to the elongate outer housing when one or more drift keys contact a wellbore restriction so as to adjust the relative axial position of the mandrel and drift keys to thereby reduce the extent by which the indicator keys protrude from an outer surface of the outer housing.

[0076] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0077] The invention includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. For example, it will readily be appreciated that features recited as optional with respect to the first aspect may be additionally applicable with respect to the other aspects without the need to explicitly and unnecessarily list those various combinations and permutations here (e.g. the apparatus or device of one aspect may comprise features of any other aspect). Optional features as recited in respect of a method may be additionally applicable to an apparatus or device; and vice versa.

[0078] BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0080] Figure 1 shows a side view of a wellbore drift tool according to an embodiment of the invention;

[0081] Figure 2 shows a longitudinal cross section through plane A-A of Figure 1 ;

[0082] Figure 3 shows a detail view of region B of Figure 2;

[0083] Figure 4 shows an end view of the wellbore drift tool of Figure 1 ;

[0084] Figure 5 shows a perspective view of the mandrel and drift keys of Figure 1 ;

[0085] Figure 6 shows a detail view of region C of Figure 5;

[0086] Figure 7 shows a part cutaway view of the increment control mechanism of the wellbore drift tool of Figure 1 ;

[0087] Figure 8 shows a detail view of the increment control mechanism when operating a release function;

[0088] Figure 9 shows a longitudinal cross section through the plane A-A of Figure 1 during a reset sequence of the wellbore drift tool; and

[0089] Figure 10 shows a detail view of region D of Figure 9. DETAILED DESCRIPTION

[0090] Referring now to Figure 1 , there is shown a wellbore drift tool 10 for carrying out a drift or drifting operation of a wellbore. The wellbore drift tool 10 is configured to determine the minimum internal or inside diameter of a wellbore, e.g. prior to carrying out a well intervention operation. The wellbore drift tool 10 has a central or longitudinal axis L (hereinafter “longitudinal axis”) extending between an uphole end 10a and a downhole end 10b. The wellbore drift tool 10 includes an elongate outer housing 20, which is a generally tubular body in this embodiment.

[0091] A plurality of drift keys 30 are movably mounted on the elongate outer housing 20, protrude from an outer surface 22 thereof and are radially displaceable relative thereto. The drift keys 30 are arranged to contact an inner wall of a wellbore and move radially in response to a change in internal diameter of the wellbore, in use. As such, the radial position of the drift keys 30 can provide an indication the internal diameter of the wellbore. In the present embodiment, the plurality of drift keys 30 are axially fixed relative to the elongate outer housing 20. In the present embodiment, it will be appreciated that axial movement is movement along or parallel to the longitudinal axis L.

[0092] A mandrel 40 is received within the elongate outer housing 20 and is configured to axially move relative thereto. The mandrel 40 includes an indexing profile, which is a stepped profile 42 (Figures 5 and 6) in this embodiment. The indexing profile engages the drift keys 30 such that the radial position of the drift keys 30 is determined by the relative axial position of the mandrel 40 / indexing profile and drift keys 30. In the present embodiment, and as will be described in greater detail below, as the drift keys 30 are axially fixed relative to the elongate outer housing 20, it will be appreciated that the radial position of the drift keys 30 is dependent on the relative axial position of the elongate outer housing 20 and the mandrel 40.

[0093] The wellbore drift tool 10 also includes an increment control mechanism 50 configured to ensure that in response to a jarring force being applied to the mandrel 40 in a downhole direction (upwards in Figure 1), interengagement between drift keys 20 and the stepped profile 42 only adjusts by a single increment or single step.

[0094] Referring now to Figures 1 and 2, the elongate outer housing 20 is formed of two parts in this embodiment, a lower part 20a and an upper part 20b. The parts 20a, 20b may be connected by an interference fit, or may be threadedly engaged. A radially extending internal shoulder 24 is defined proximate the interface between the parts 20a, 20b and is configured to provide an abutment surface for a pre-loaded compression spring S, which is an emergency release spring in this embodiment. A spring stop 44 is connected at a downhole end of the mandrel 40, and the spring S is compressed between the shoulder 24 and a shoulder of the spring stop 44. A bottom sub 80, e.g. for connecting the wellbore drift tool 10 to a drill string or wireline, is connected to a downhole end of the spring stop 44, such that the spring stop 44 is provided between the mandrel 40 and bottom sub 80. The spring S is configured to bias the mandrel 40 axially in a downhole direction relative to the elongate outer housing 20, in use, and when the drift keys 30 contact a restriction within a wellbore such that the elongate outer housing 20 is prevented from further travel downhole.

[0095] The elongate outer housing 20 has a plurality of openings each in receipt of a respective drift key 30. The drift keys 30 are provided in two sets in this embodiment, a first set of drift keys 30a and a second set of drift keys 30b. Each set of drift keys 30a, 30b includes a plurality of drift keys 30. The drift keys of the first set of drift keys 30a are equally circumferentially spaced around the elongate outer housing 20 and the drift keys of the second set of drift keys 30b are equally circumferentially spaced around the elongate outer housing 20.

[0096] The drift keys of the first set of the drift keys 30a and the drift keys of the second set of drift keys 30b are axially spaced from one another and the drift keys 30 of the respective sets 30a, 30b are devoid of any axial overlap in this embodiment. In the present embodiment, respective central or longitudinal axes of the drift keys 30 of the first set of drift keys 30a are circumferentially offset from the respective central or longitudinal axes of the drift keys 30 of the second set of drift keys 30b, i.e. none of the drift keys 30 of the first set of drift keys 30a are axially aligned with any of the drift keys 30 of the second set of drift keys 30b. Each set of drift keys 30a, 30b includes four drift keys 30 spaced 90 degrees apart. Furthermore, each set of drift keys 30a, 30b is circumferentially or rotationally offset by 90 degrees.

[0097] As can be seen more clearly in Figure 4, drift keys 30 of the first set of drift keys 30a and the drift keys 30 of the second set of drift keys 30b circumferentially overlap such that the drift keys 30 provide full circumferential coverage around the wellbore drift tool 10 and / or elongate outer housing 20. Referring now to Figures 5 and 6, each drift key 30 is elongate and has an arcuate radially outer surface 32 configured to contact an inner wall of a wellbore and a radially inner surface 34 configured to engage the stepped profile 42. The radially inner surface 34 of each drift key 30 includes a pair axially spaced engagement profiles 36 having a recessed portion 38 therebetween. The engagement profiles 36 engage the stepped profile 42 of the mandrel 40. Each of the drift keys 30 is provided with an axially extending rib or protrusion 37 on the radially inner surface 34 configured to guide relative movement of the drift keys 30 and / or elongate outer housing 20 and the mandrel 40. Furthermore, each of the drift keys 30 has a pair of axially spaced retaining apertures 39 each extending transverse to the longitudinal axis L. The retaining apertures 39 are configured to receive retaining pins (not shown) to prevent radial movement of the drift keys 30 when carrying out a resetting operation on the wellbore drift tool 10.

[0098] The wellbore drift tool 10 includes a plurality of stepped profiles 42 formed integrally with the mandrel 40 and each configured to engage a respective drift key 30. Each stepped profile 42 includes a plurality of steps or increments 43. More specifically, in the present embodiment the stepped profile 42 includes pairs of identical sets of steps 45 axially spaced from one another. Each of the plurality of steps 43 extends axially and includes a generally planar engagement surface 46 for engagement with an engagement profile 36 of the drift keys 30. Each of the pair of axially spaced engagement profiles 36 is configured to engage one of the pairs of steps 45. Each step 43 has an abutment surface 43a at a downhole end thereof to prevent or resist movement of the mandrel 40 in an uphole direction and / or the elongate outer housing 20 in a downhole direction.

[0099] The height of the steps 43 of the stepped profile 42 increases from the uphole end to the downhole end of the wellbore drift tool 10. As such, as a drift key 30 engages the stepped profile 42, the amount by which it protrudes from the elongate outer housing 20 reduces the mandrel 40 and stepped profile 42 moves in a downhole direction. Each stepped profile 42 includes an axial guide, groove or slot 47 in receipt of the axially extending rib or protrusion 38 of a respective drift key 30.

[0100] Referring now to Figures 3 and 7, there is shown the increment control mechanism 50 in greater detail. As will be described in greater detail below, the increment control mechanism 50 has a first state or first condition in which axial movement of the mandrel 40 relative to the elongate outer housing 20 in response to or as a result of the preloaded spring S and a increment control spring 66 is prevented in this embodiment and a second state or second condition in which axial movement of the mandrel 40 relative to the elongate outer housing 20 in response to or as a result of the preloaded spring S a increment control spring 66is permitted.

[0101] The increment control mechanism 50 includes a sleeve 52 having an engagement feature on an inner surface 54 thereof. The engagement feature in the present embodiment includes a plurality of circumferentially extending protrusions 56 axially spaced from one another along the sleeve 52. Adjacent protrusions 56 are axially spaced an equal amount to the axial length of each step 43 of the stepped profile 42. The sleeve 52 is connected to an uphole end of the upper part 20b of the elongate outer housing 20 and is axially relative thereto.

[0102] A carrier sleeve 58 is located radially inward of the sleeve 52 and is connected to an uphole end of the mandrel 40. The carrier sleeve 58 supports a plurality of keys in such a way that the keys are floating keys in this embodiment. The increment control mechanism 50 includes a plurality of sets of keys 60, wherein each set of keys 60 includes a first key 60a and second key 60b downhole of the first key 60a. The keys 60a, 60b form or define a pair of axially spaced keys. The sets of keys 60 are circumferentially spaced from one another. In the present embodiment, the increment control mechanism 50 includes four sets of keys 60 equally circumferentially spaced from one another. The carrier sleeve 58 is constrained to move axially with the mandrel 40, and the keys 60a, 60b are constrained to move axially with the carrier sleeve 58 and are radially movable relative to the carrier sleeve 58 and sleeve 52.

[0103] As will be described in greater detail below, the increment control mechanism 50 is arranged such that in the first state the second key 60bis in engagement with or in contact with one of the protrusions 56 of the sleeve 52 so as to prevent movement of the mandrel 40 relative to the elongate outer housing 20 in a downhole direction. In the second state the first key 60a comes into contact or into engagement with a protrusion 56 of the sleeve 52 as the mandrel 40 moves axially relative to the elongate outer housing 20 and sleeve 52. Each key 60a, 60b is generally saddle-shaped or H-shaped when viewed perpendicular to the longitudinal axis L, e.g. as shown in Figure 3. Each key 60a, 60b has a radially inner recess 62a and a radially outer recess 62b.

[0104] The increment control mechanism 50 includes an activation member 64 located radially inward of the sleeve 52 and carrier sleeve 58. The activation member 64 is configured to engage each of the keys 60a, 60b so as to move them radially between a deployed state, in which they engage or contact one of the protrusions 56 of the sleeve 52, and a withdrawn state in which they are out of engagement with or out of contact with the protrusions 56 of the sleeve 52.

[0105] In the arrangement shown in Figure 3, the second key 60b closest the downhole end 10b is shown in the deployed state whereby it is in contact with a protrusion 56 and the second key 60a closest the uphole end 10a is shown in the withdrawn state. During operation of the wellbore drift tool, one of the keys 60a, 60b is always in a deployed state and the other in a withdrawn state.

[0106] The activation member 64 includes two parts, an outer part 64a and an inner part 64b interconnected by a shear sub or shear sleeve 74b (hereinafter “shear sub”) and is configured to axially move relative to the mandrel 40, carrier sleeve 58 and keys 60a, 60b. The increment control spring 66, in the form of a die spring in this embodiment, is provided between an uphole end of the mandrel 40 and the activation member 64. The spring 66 interconnects the mandrel 40 and activation member 64 such that they are axially movable relative to one another. The activation member 64 includes a respective cam profile 68 on each part 64a, 64b, including a plurality of cam surfaces axially spaced along an outer surface thereof. The cam profiles 68 are axially spaced form one another. The cam surfaces include axially extending ramps 70 and when a key 60a, 60b is in the withdrawn state a cam surface is received within the inner recess 62a. Axial movement of the activation member 64 relative to a key 62 is configured to cause the key 62 to ride a cam surface, and more specifically an axially extending ramp 68, to move or radially propel the key 60a, 60b from the withdrawn state to the deployed state and vice-versa.

[0107] In the present embodiment, a key 60a, 60b is moved between the withdrawn state and the deployed state in response to a jarring force applied to the mandrel 40 and / or activation member 64 in a downhole direction. The wellbore drift tool 10 includes a top sub 74 connected to an uphole end of the activation member 64. The top sub 74 includes an enlarged portion 75. The top sub 74 or activation member 64 includes a stop sub 74a and the shear sub 74b.

[0108] The wellbore drift tool 10 also includes a travel limiter configured to limit or restrict the axial movement of the mandrel 40 relative to the elongate outer housing 20. The travel limiter also defines a reset position for the wellbore drift tool 10. The travel limiter includes a shoulder 76 formed on an inner surface of the sleeve 52 and a protrusion 78 extending from the activation member 64 and configured to abut the shoulder 76.

[0109] In use, the wellbore drift tool 10 is run into a wellbore on a string or wireline. The wellbore drift tool 10 will be in an unset configuration whereby the second key 60b of each pair of keys 60 will be in the deployed position and the first key 60a will be in the withdrawn position, such that axial movement of the mandrel 40 relative to the elongate outer housing 20 is prevented. The mandrel 40 and stepped profile 42 will be will be positioned at an uphole position with respect to the elongate outer housing 20, and the drift keys 30 may protrude from the outer surface 22 of the elongate outer housing 20 to a maximum extent.

[0110] If the wellbore drift tool 10 encounters a restriction in the wellbore as it is being run-in, the one or more of the drift keys 30 will contact said restriction. As such, the elongate outer housing 20 is unable to travel any further downhole into the wellbore. At this point, when the increment control mechanism 50 is in the first state as shown in Figure 3, a jarring force is applied to the mandrel 40 and activation member 64 in a downhole direction causing the activation member 64 to move axially relative to the elongate outer housing 20, sleeve 52, carrier sleeve 58 and mandrel 40, thereby compressing the increment control 66. Axial movement of the activation member 64 relative to the carrier sleeve 58, and therefore keys 60a, 60b, causes the first key 60a to ride the cam profile 68 and move radially outwards from the withdrawn state to the deployed state. The second key 60b rides the cam profile 68 and moves radially inwards from the deployed state to the withdrawn state, such that the cam surface is received within the inner recess 62a of the second key 60b. At this stage, none of the keys 60a, 60b are in engagement with the protrusion 56 and the increment control mechanism 50 is in the second state such that the mandrel 40 is free to move axially relative to the elongate outer housing 20 a distance equivalent to the axial distance between adjacent protrusions 56. Compression of the increment control spring 66 results in axial movement of the mandrel 40 and activation member 64 downhole until the first key 60a contacts the next protrusion 56 in a downhole direction. The preloaded spring S between the elongate outer housing 20 and the mandrel 40 may also cause or assist axial movement of the mandrel 40, and activation member 64 relative to the elongate outer housing 20. Axial movement of the mandrel 40 causes the position of the stepped profile 42 relative to the elongate outer housing 20 and drift keys 30 to change by a single step, e.g. until the first key 60a contacts the next protrusion 56 in a downhole direction. . The drift keys 30 engage a single step further uphole, i.e. a lower step, than previously, and thereby protrude from the outer surface 22 of the elongate outer housing 20 a lesser amount. When the jarring force is removed, the increment control spring 66 biases the activation member 64 in an uphole direction relative to the keys 60a, 60b to thereby restore the first key 60a to a withdrawn position and the second key 60b to a deployed position whereby it is in contact with a protrusion 56.

[0111] If further adjustment of the wellbore drift tool 10, and drift keys 30, is necessary, the force applied to the mandrel 40 and / or activation member 64 in a downhole direction can be removed and a jarring force as above re-applied in order to repeat the aforementioned process.

[0112] Referring now to Figure 8, there is shown the wellbore drift tool 10 when a release function or an emergency release operation is carried out. The release function or emergency release operation may be carried out if debris falls behind the wellbore drift tool 10, e.g. from an uphole location, when it is being run into a wellbore.

[0113] In this case, a jarring force applied to the mandrel 40 and / or activation member 64 in an uphole direction. As such, the connection between the parts 64a, 64b of the activation member 64 is sheared and the inner part 64b moves relative to the outer part 64b due to the increment control spring 66 and the cam surfaces 68 are brought closed to one another.. The second key 60b also moves radially into the withdrawn state. Therefore, the mandrel 40 is free to move axially relative to the elongate outer housing 20. The pre-loaded spring S or emergency release spring also acts to bias the elongate outer housing 20 and drift keys 30 in an uphole direction relative to the stepped profile 42 so as to reduce the extent to which the drift keys 30 protrude from the elongate outer housing 20. Referring now to Figures 9 and 10, there is shown a release sequence or process for the wellbore drift tool 10. The release sequence or process is carried out after the wellbore drift tool 10 has been used during a drift operation, the mandrel 40 has moved relative to the elongate outer housing 20 so as to adjust the radial position of the drift keys 30 and the tool has been retrieved to the surface.

[0114] The bottom sub 80 and spring stop 44 are removed from the mandrel 40. The shear sub 74b is then moved in a downhole direction away from the stop sub 74a to release tension in the spring 66 due to movement of the inner part 64b of the activation member 64 relative to the outer part 64a of the activation member 64. A magnet is used to pull the drift keys 30 radially outwards and retaining pins are inserted through the retaining apertures 39. The elongate outer housing 20 is then moved axially relative to the mandrel 40 until the protrusion 78 meets the shoulder 76. The shear sub 74b is then moved in a downhole direction towards the stop sub 74a to compress the spring 66 and reset the keys 62. The bottom sub 80 and spring stop 44 are then reconnected to the mandrel 40 and the retaining pins are removed from the drift keys 30.

[0115] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention.

[0116] It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1 . A wellbore drift tool, comprising: an elongate outer housing; a mandrel received within the elongate outer housing, wherein the mandrel and elongate outer housing are axially movable relative to one another: a plurality of drift keys movably mounted on the outer housing and protruding from an outer surface thereof; wherein the drift keys are radially displaceable relative to the outer housing; wherein the mandrel comprises a stepped profile interengaging the drift keys and mandrel; wherein the radial position of the drift keys is determined by the relative axial position of the mandrel and drift keys; wherein, in use, axial movement of the mandrel relative to the outer housing adjusts the interengagement of the stepped profile and drift keys.

2. A wellbore drift tool according to claim 1 , comprising an increment control mechanism having a first state in which axial movement of the mandrel relative to the elongate outer housing is restricted, and a second state in which axial movement of the mandrel relative to the elongate outer housing is permitted.

3. A wellbore drift tool according to claim 2, comprising an increment biasing means between the mandrel and the increment control mechanism, wherein the increment biasing means is configured to propel the mandrel in a downhole direction when the increment control mechanism is in the second state.

4. A wellbore drift tool according to claims, wherein in the first state the increment control mechanism is configured restrict axial movement of the mandrel relative to the elongate outer housing due to the increment biasing means, and in the second state the increment control mechanism is configured to permit axial movement of the mandrel relative to the elongate outer housing due to the increment biasing means.

5. A wellbore drift tool according to any one of claims 2 to 4, wherein the increment control mechanism comprises:a sleeve having an engagement feature on an inner surface; a key in contact with the engagement feature in the first state and out of contact with the engagement feature in the second state.

6. A wellbore drift tool according to claim 5, wherein the engagement feature comprises a plurality of circumferentially extending grooves axially spaced from one another along the sleeve wherein adjacent grooves are axially spaced a distance generally equivalent to the axial length of a step of the stepped profile.

7. A wellbore drift tool according to claim 5 or claim 6, comprising a first key and a second key axially spaced from one another.

8. A wellbore drift tool according to claim 7, wherein when the wellbore drift tool is in a neutral state only one of the first and second keys is in contact with one or more of the engagement features.

9. A wellbore drift tool according to claim 7 or 8, wherein each of the first and second keys is radially movable and has a deployed state and a withdrawn state.

10. A wellbore drift tool according to and one of claim 9, wherein the first key is in the deployed state and the second key is in the withdrawn state when the increment control mechanism is in the first state and the second key is in the deployed state and the first key is in the withdrawn state when the increment control mechanism is in the second state, wherein the second key is free to move axially relative to the sleeve and / or elongate outer housing an axial distance equivalent to the distance between adjacent circumferentially extending grooves when the increment control mechanism is in the second state.11 . A wellbore drift tool according to claim 9, wherein one of the first key and second key is in contact with one or more of the engagement features in the deployed state and out of contact with one or more engagement features in the withdrawn state.

12. A wellbore drift tool according to claim 11 , wherein the other of the first key and second key is configured to come into in contact with one or more of theengagement features in the deployed state due to axial movement of the mandrel relative to the elongate outer housing.

13. A wellbore drift tool according to claim 9, wherein the key of the pair of keys in the deployed state alternates between the first state and the second state of the increment control mechanism.

14. A wellbore drift tool according to any one of claims 7 to 13, comprising an activation member configured to engage each of the first and second keys so as to move them between the deployed state and the withdrawn state.

15. A wellbore drift tool according to claim 14, wherein the activation member comprises a cam profile.

16. A wellbore drift tool according to claim 14 or claim 15, wherein each key is movable between the deployed state and the withdrawn state in response to relative axial movement between the activation member and each key.

17. A wellbore drift tool according to any one of claims 7 to 16, wherein one of the first and second keys is moved from the withdrawn state and the deployed state in response to a jarring force applied to the mandrel and / or activation member in a downhole direction and the other of the first and second keys is moved from the deployed state and the withdrawn state in response to a jarring force applied to the mandrel and / or activation member in a downhole direction.

18. A wellbore drift tool according to claim 17, wherein the interengagement of the drift keys and the stepped profile is configured to adjust by a single step in response to the jarring force applied to the mandrel and / or activation member in a downhole direction.

19. A wellbore drift tool according to any one of claims 7 to 18, wherein each key is located between the activation member and the sleeve.

20. A wellbore drift tool according to any 14, wherein each key is constrained to move axially with the mandrel, and the activation member is axially movable relative to the mandrel.

21. A wellbore drift tool according to claim 20, wherein each key is moved from the withdrawn state to the deployed state in response to axial movement of the activation member relative to the mandrel in a downhole direction.

22. A wellbore drift tool according to claim 20, comprising a release function, wherein in response to a jarring force applied to the activation member and / or mandrel in an uphole direction each of the two keys is moved to the withdrawn position.

23. A wellbore drift tool according to any one of claims 5 to 22, wherein the sleeve is connected to an uphole end of the outer housing and is axially fixed relative thereto.

24. A wellbore drift tool according to any preceding claim, comprising a first set of circumferentially spaced drift keys and a second set of circumferentially spaced drift keys, wherein the first set and the second set are axially spaced from one another.

25. A wellbore drift tool according to any preceding claim, comprising a biasing means located between the outer housing and the mandrel, wherein, in use, the biasing means is configured to bias the mandrel axially in a downhole direction.

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