Apparatus

Abstract

A well cleaning tool (100) comprising: an elongate body (102) having a longitudinal axis; a central fluid bore (122) aligned with the longitudinal axis; a cleaning element (110) mounted in a recess (124) in the elongate body (102) and being displaceable with respect to the elongate body (102) in a direction inclined to the longitudinal axis; and a sleeve (146) mounted in the central fluid bore (122) and being displaceable with respect to the elongate body (102) in a direction aligned with the longitudinal axis, wherein displacement of the sleeve (146) enables fluid communication of the central fluid bore (122) with the recess (124).

Description

[0001] APPARATUS

[0002] The present invention relates to well cleaning tools for removing debris accumulated in a well casing.

[0003] A wellbore may be drilled in the earth for various purposes, such as hydrocarbon extraction. After a wellbore is drilled, it is typically lined with a casing. The casing preserves the shape of the wellbore as well as providing a conduit for fluid to be transported to the surface.

[0004] Debris left within the conduit poses a significant risk to well performance and its completion activity. Failure to clean the wellbore increases the risk of well production down-time, which in turn increases remedial costs. Therefore, it is desirable and often necessary in oil, gas and water well production to clean the inner wall of the casing.

[0005] The standard tools used for cleaning casing walls are referred to as casing scrapers and are well known in the art. Such tools are attached to a drill string and lowered into the well to scrape debris from the inner wall of the casing as they progressively traverse the length of the well. As a cleaning run can add considerable time to well operation, representing significant cost, some casing scrapers are used in conjunction with other drill string tools, thereby avoiding the need for a separate cleaning run to be carried out on the well casing. United Kingdom Patent No. 2583120 discloses such a casing scraper that acts continuously in a passive manner to clean the casing wall as the drill string is moved through the wellbore.

[0006] In known passive casing scrapers, the continuous cleaning action can present a problem causing damage to the inner wall of the casing. This problem can be exacerbated where the cleaning action is localised along the length of the wellbore under the normal operation of the drill string. In addition, the mechanical friction caused by the cleaning action can lead to an unwanted increase in temperature in the vicinity of the wellbore which can result in temperature induced stresses and consequently wellbore stability problems. These temperature increases can also lead to a degradation of the casing scraper, adversely affecting its ability to clean the wall of the casing. Therefore, it is an objective of the present invention to provide a cleaning tool that provides a selective cleaning action.

[0007] According to a first aspect of the present invention there is provided a well cleaning tool comprising: an elongate body having a longitudinal axis; a central fluid bore aligned with the longitudinal axis; a cleaning element mounted in a recess on the elongate body and being displaceable with respect to the elongate body in a direction inclined to the longitudinal axis; and a sleeve mounted in the central fluid bore and being displaceable with respect to the elongate body in a direction aligned with the longitudinal axis, wherein displacement of the sleeve enables fluid communication of the central fluid bore with the recess.

[0008] Advantageously, the fluid pressure in the recess can be controlled by displacing the sleeve. The fluid pressure in the recess biases the cleaning elements radially outward into contact with the wall providing selective cleaning action when required. This can be performed during the normal operation of the drill string obviating the need for a separate cleaning run, whilst preventing damage from continuous passive cleaning. The casing scraper may be attached to a completion string and run into a wellbore where it may remain dormant for several years until activated, allowing drill operations and liner hanger preparation to be completed in a single run.

[0009] Preferably, the sleeve is displaceable between a first position, in which the sleeve prevents fluid communication of the central fluid bore with the recess and a second position, in which the sleeve enables fluid communication of the central fluid bore with the recess.

[0010] It is preferred that when the recess is in fluid communication with the central fluid bore, fluid pressure within the recess is applied to the cleaning element.

[0011] In addition, it is preferred that the fluid pressure biases the cleaning element outward in the direction inclined to the longitudinal axis. Preferably, the sleeve is retained in the central fluid bore in the first position by a sheer pin.

[0012] It is further preferred that the sheer pin is arranged to fail upon application of a force exceeding a breakaway load value.

[0013] In addition, it is preferred that upon the sheer pin failing, the sleeve moves towards the second position.

[0014] Preferably, the sleeve comprises a through aperture extending in the direction inclined to the longitudinal axis.

[0015] Preferably, the elongate body comprises a fluid channel extending between an inlet aperture formed on an inner face of the central bore and an outlet aperture formed on an inner face of the recess.

[0016] It is also preferred that the through aperture in the sleeve aligns circumferentially and longitudinally with the inlet aperture.

[0017] In addition, it is preferred that the sleeve comprises an open upper end and a closed lower end.

[0018] Preferably, the sleeve further comprises an aperture forming in the lower end that extends in a direction aligned with the longitudinal axis.

[0019] It is preferred that the sleeve comprises a projection formed on an outer peripheral surface extending radially outward.

[0020] In addition, it is preferred that the projection is received in an elongate recess formed in an inner face of the central fluid bore.

[0021] It is also preferred that the diameter of the sleeve provides a slide fit with the central fluid bore. Preferably, the cleaning element further comprises a fluid channel extending from an inlet aperture formed on an inner face of the cleaning element and an outlet aperture formed on the outer surface of the cleaning element.

[0022] In addition, it is preferred that the recess extends around the entire outer circumference of the elongate body.

[0023] Preferably, the tool comprises a plurality of cleaning elements.

[0024] Preferably, the cleaning elements are identical.

[0025] It is further preferred that the cleaning elements are equiangularly displaced with respect to each other.

[0026] Preferably, the tool is comprised of a dissolvable material.

[0027] It is further preferred that the dissolvable material is magnesium based.

[0028] According to a second aspect of the present invention there is provided system comprising the well cleaning tool of the first aspect further comprising means for obstructing the aperture formed in the lower end of the sleeve.

[0029] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0030] Figure 1 is a perspective view of a casing scraper, in accordance with the present invention;

[0031] Figure 2 is a cross-sectional view of the casing scraper of Figure 1 in a first mode of operation; and Figure 3 is a cross-section view of the casing scraper of Figure 1 in a second mode of operation.

[0032] Referring to Figure 1 of the drawings, a casing scraper 100 has an elongate generally tubular body 102 having an upper end 104, a lower end 106, a tubular central portion 108 extending between the upper and lower ends and four identical scraper blocks 110 disposed on the outer surface of the central tubular portion 108.

[0033] The scraper blocks 110 are displaceable in a radial direction between a first retracted position and a second extended position. The outer diameter of the casing scraper 100 is defined by the position of the scraper blocks 110 with respect to the tubular body 102 such that the outer scraping surface 112 of the scraper blocks 110 scrape the interior surface of a well casing (not shown) when in the second extended position.

[0034] As shown in Figure 1 , the upper end 104 of the tubular body 102 is adapted for connection to the end of a drill string. This may be provided by way of a threaded mandrel 114.

[0035] The plurality of scraper blocks 110 are equiangularly spaced around the periphery of the tubular body 102 so that the scraping surfaces 112 of the scraper blocks 110 collectively operate upon the entire circumference of the well casing. Axially separate, helical grooves 116 are formed in the outer scraping surface 112 of each scraper block 110 and a series of equiangularly spaced fluid outlet apertures 118 are formed in the helical grooves 116. When the casing scraper 100 is assembled, the helical grooves 116 of each scraper block 110 align to form axially separated, helical teeth 120 between the grooves 116 that are inclined towards the longitudinal axis of the casing scraper 100 (represented by line A- A). The edges of the teeth 120 are chamfered to allow them to float more easily over or around unyielding obstacles within the wellbore to reduce scoring or damaging the casing.

[0036] As seen in Figure 2, a central fluid bore 122, which corresponds with the central fluid bore of an attached drill string (not shown), extends between the upper and lower ends 104, 106, and is aligned with the longitudinal axis of the tubular body 102 and allows drill string fluid to flow through the length of the tubular body 102 when the casing scraper 100 is attached to a drill string. It will be understood that the casing scraper 100 is locked on the drill string and cannot therefore rotate relative thereto, nor move longitudinally relative thereto. Therefore, in use, when the casing scraper 100 is connected in a drill string and inserted into a wellbore, the casing scraper 100 will rotate with the drill string and move through the wellbore with the drill string.

[0037] The outer face of the tubular central portion 108 is provided with a recessed waisted portion 124 which extends around the entire outer circumference of the tubular body 102. The scraper blocks 110 are mounted in this recess portion 124 and are equiangularly spaced with respect to the tubular body 102. Each scraper block 110 is provided with upper and lower retaining projections 126 along the upper and lower edges, which are seated in respective peripherally extending recesses 128 formed by overhanging shoulder portions 130 formed in the tubular body 102 at the upper and lower ends of the recessed waisted portion 124.

[0038] The projections 126 on the scraper blocks 110 engage an inner face of the overhanging shoulder portions 130 on the upper and lower ends, so that the maximum outward displacement of the scraper blocks 110 is limited between a first retracted position, in which the scraper blocks 110 move radially inward with respect to the longitudinal axis, and a second extended position, in which the scraper blocks 110 move radially outward with respect to the longitudinal axis. When in the first, retracted position, the outer scraping surfaces 112 of the scraper blocks 110 do not extend beyond the periphery of the tubular body 102 of the casing scraper 100 so as not to come into contact with the inner casing of the wellbore. Conversely, when in the second, extended position, the outer scraping surfaces 112 of the scraper blocks 110 extend beyond the periphery of the tubular body 102 of the casing scraper 100 and into contact with the inner casing of the wellbore.

[0039] The inner face 132 of each scraper block 110 is formed into an elongate centrally disposed intermediate lug 134 extending parallel to the longitudinal axis of the scraper block 110 and projecting radially inwardly. The lug 134 is seated in a complementarily shaped recess 136 formed in the recessed waisted portion 124 of the tubular central portion 108, the lug 134 being a press or interference fit within the recess 136. The side walls of the lug 134 and the corresponding walls of the recess extend radially with respect to the longitudinal axis of the tubular body 102, whereby the scraper blocks 110 are constrained to be displaceable in the radial direction.

[0040] As seen in Figure 2, a series of fluid inlet apertures 138, located radially opposite the series of fluid outlet apertures 140, are formed on the inner face 132 and lug 134 of the scraper block 110, with a fluid channel 142 extending perpendicularly to the longitudinal axis of the casing scraper 110 between each fluid inlet aperture 138 and its corresponding fluid outlet aperture 140.

[0041] The central fluid bore 122 communicates with each recessed portion 124 through a series of apertures 144 formed in the tubular central portion 108 that extend perpendicularly to the longitudinal axis of the casing scraper 100.

[0042] A sleeve 146 is disposed within the central fluid bore 122 and is displaceable in the direction of the longitudinal axis of the casing scraper 100 between a first, retracted position and a second, extended position. The sleeve 146 has a generally tubular body having an upper open end 148 and a lower, rounded closed end 150 and a tubular portion 152 extending between the upper and lower ends. A through aperture 154 is formed in the closed end 150 and extends in the direction of the longitudinal axis of the casing scraper 100 to allow the flow of fluid through the sleeve 146. The diameter of the tubular body of the sleeve 146 is chosen to provide a slide fit with the inner diameter of the central fluid bore 122.

[0043] As shown in Figures 2 and 3, the sleeve 146 comprises a series of identical projections 156 spaced equally arounds its peripheral face and extending radially outward in a direction perpendicular to the longitudinal axis of the casing scraper 100. The projections 156 are received by elongate recesses 158 formed in the inner surface of the central fluid bore 122 which serve to restrict rotational movement of the sleeve 146 relative to the casing scraper 100. The elongate recesses 158 are provided with upper and lower shoulder portions 160, 162, which, in use, engage the projections 156 to restrict the maximum displacement of the sleeve 146 in the direction of the longitudinal axis of the casing scraper 100 between the first, retracted position, in which the projection 156 engages the upper shoulder portion 160 and the second, extended position, in which the projection 156 engages the lower shoulder portion 162. As seen in Figures 1 to 3, the upper end 104 of the tubular body 102 is provided with a series of sheer bolts 164 spaced equally around the peripheral face extending through the tubular body 102 in a direction perpendicular to the longitudinal axis and which are received in corresponding recesses 166 formed in the upper end of the sleeve 146 for securing the sleeve 146 in the central fluid bore 122 in the first, retracted position. The sheer bolts 164 are designed to break on application of a predetermined tension, so that a downward force exceeding the predetermined tension will cause the sheer bolt 164 to break, allowing the sleeve 146 to move from the first, retracted position to the second, extended position. Initially, the sleeve 146 is retained in first, retracted position in the central fluid bore 122 by the sheer bolts 164, but the force applied to the sleeve 146 as a result of fluid pressure in the central fluid bore 122 tends to draw the sleeve 146 downwards towards the second, extended position, against the force of the retaining sheer bolts 164 as seen in Figure 3.

[0044] As best seen in Figure 2, the tubular portion 152 of the sleeve 146 is provided with a series of through apertures 168 extending perpendicularly to the longitudinal axis of the casing scraper 100. The size and spacing between the series of through apertures 168 formed in the tubular portion 152 ofthe sleeve 146 correspond to the size and spacing of the through apertures 144 formed in the tubular portion 108 of the casing scraper 100.

[0045] When in the first, retracted position, the apertures 168 formed in the tubular portion 152 of the sleeve 146 are longitudinally misaligned with the apertures 144 formed in the tubular portion 108 of the casing scraper 100, such that the tubular portion 152 of the sleeve 146 obstructs the apertures 144, preventing fluid communication between the central fluid bore 122 and each recessed waisted portion 124. Conversely, when in the second extended position, the apertures 168 formed in the tubular portion 152 of the sleeve 146 are both circumferentially and longitudinally aligned with the apertures 144 formed in the tubular portion 108 of the casing scraper 100, allowing fluid communication between the central fluid bore 122 and each recessed waisted portion 124 (as best seen in Figure 3).

[0046] In use, the casing scraper 100 is inserted into the wellbore with its scraper blocks 110 in the first, retracted position, allowing the drill string to perform its normal operation without the outer scraping surfaces 112 of the scraper blocks 110 coming into contact with the inner casing of the wellbore. The sheer bolts 164 retain the sleeve 146 in the first, retracted position, thereby preventing the flow of fluid through the series of apertures 168 formed in the tubular portion 152 of the sleeve 146 and into the recessed waisted portions 124. However, the through aperture 154 formed in the closed end 150 of the sleeve 146 provides an internal pathway through the casing scraper 100 for the flow of fluid, preventing a build-up of pressure in the central fluid bore 122 and minimising the so called “plunger effect” which manifests itself as the casing scraper 100 is pushed through a body of fluid and which resists movement of the casing scraper 100 through the fluid.

[0047] Once the normal operation of the drill string is complete, the casing scraper 100 can be selectively activated from the surface to perform a cleaning run by introducing an activating ball 170 into the central fluid bore 122 (as shown in Figure 3). The diameter of the activating ball 170 is sized to allow the ball 170 to travel through the tubular portion 152 of the sleeve 146 and plug the through aperture 154 in the closed end 150 thereby preventing the flow of fluid through the casing scraper 100. A build-up of pressure is created in the central fluid bore 122 behind the activating ball 170 resulting in a downward force acting on the sleeve 146. If the downward force is such that the load transferred to the sheer bolts 164 exceeds the pre-determined break-away load, the sheer bolts 164 fail allowing the sleeve 146 to move towards the second, extended position.

[0048] As best seen in Figure 3, when in the second, extended position, the series of apertures 168 in the sleeve 146 align with the apertures 144 formed in the tubular portion 108 of the casing scraper 100, providing an unimpeded internal pathway (indicted by the dashed arrows) for fluid to pass through the casing scraper 100. The internal pathway allows fluid to pass through the central fluid bore 122 and into each recessed waisted portion 124. The resultant increase in pressure within each recessed waisted portion 124 acts on the inner face 132 of the corresponding scraper block 110 biasing it radially outwardly into the second, extended position towards the inner wall of the casing. With the application of a constant fluid pressure to the central fluid bore 122, the casing scraper 100 can be reciprocated by vertical movement of the drill string over an area to be cleaned. The pressure applied to the central fluid bore 122 can be increased to extend the scraper blocks 110, and conversely, decreased to retract the scraper blocks 110, providing for selective cleaning of the well casing. Fluid pressure can be applied both within the central fluid bore 122 and outside of the casing scraper

[0049] 100 within the wellbore, such that the difference in fluid pressure in the central fluid bore 122 relative to the wellbore can be controlled to create a pressure gradient. In use, increasing the pressure in the central fluid bore 122 relative to the pressure in the wellbore results in the pressure gradient force acting on the inner face 132 of the corresponding scraper block 110, biasing the scraper block 110 radially outward into the second, extended position. Conversely, decreasing the pressure in the central fluid bore 122 relative to the pressure in the wellbore results in the pressure gradient force acting on the outer scraping surface 112 of each scraper block 110, biasing each radially inward into the first, retracted position. In this way, the radial displacement of the scraper blocks 110 can be controlled to selectively engage the inner wall of the casing.

[0050] When increased, the pressure is also applied to the fluid channels 142 resulting in the application of a fluid jet, radially outwardly, which assists in the removal of debris from the helical teeth 120 of the scraper blocks 110 increasing their cleaning action on the inner wall of the casing. The fluid jets also directly remove debris from the inner wall of the casing.

[0051] The flow of fluid through the scraper blocks 110 provides heat removal required to remove waste heat produced by the scraping action of the scraper blocks 110 against the interior surface of the well casing. This extends the life of the scraper blocks 110 and increases the efficiency of the helical teeth 120. In addition, the application of fluid assists in breaking up and dispersing debris from the blades of the scraper blocks, upwards into the circulating well fluids for recovery at the surface.

[0052] The casing scraper 100, including scraper blocks 110 and sleeve 146 may be comprised of any drillable material including, but not limited to, cast iron, tool steel, stainless steel, aluminium alloy or dissolvable material. Similarly, the activating ball 170 can be comprised of any drillable material including, but not limited to, cast iron, tool steel, stainless steel, aluminium alloy, polymer rubber, natural rock or dissolvable material. The type and grade of material composition may be selected based on desired physical properties including, but not limited to, hardness, toughness, wear and resistance, tensile strength and spring constant. Factors affecting the selection of materials include the ability to retain a shape memory and ability to be drilled and or dissolved.

[0053] The characteristics of the activating ball 170, for example, its ability to deform under pressure, can be determined by appropriate selection of the features of the activating ball 170, such as material, structure, shape, hardness, etc., such that additional application of fluid pressure in the central fluid bore 122 beyond a predetermined threshold will cause the activating ball 170 to deform and / or crush, allowing the activating ball 170 to pass through the aperture 154 formed in the closed end 150 of the sleeve 146 where it can be brought upwards into the circulating well fluids for recovery at the surface, effectively resetting the casing scraper 100 to its inactive state, allowing the flow of fluid to pass through the tool in the longitudinal direction, minimising the so called “plunger effect”. This arrangement allows for subsequent use of the casing scraper 100 when needed by simple application of a further activating ball 170 into the central fluid bore 122.

[0054] Magnesium based materials may be selected fortheir ability to dissolve when exposed to oxygen, water and salts. In order to reinforce the magnesium-based materials against the rigors of down-well operation, the casing scraper 100 may be constructed from magnesium-based materials using techniques such as laser shock peening to make the materials harder and stronger and able to withstand corrosion during the initial run. Thereafter, the casing scraper 100 may be left down well to dissolve in a solution of oxygen, water and salts.

[0055] Both a drillable material and dissolvable material are required to be sufficiently strong to satisfy normal handling and service requirements and has the ability to form small chip like cuttings when drilled with a conventional rock bit or the like, so that the bit cuttings can be carried from the well by the return circulation of fluid thereby overcoming the problem associated with drilling of high tensile components such as compression springs, bolts, screws and caps. However, it is also envisioned that the casing scraper 100 and its components may be formed from more durable materials such as hardened steel and or toughened composite materials where a re-useable casing scraper is required, suitable for several re-runs of the down well cleaning operation. The present description is for illustrative purposes only and should not be construed to narrow the breadth of the present disclosure in anyway. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope of the present disclosure. For example, it is envisioned that the lower end 106 of the tubular body 102 could be adapted for connection to a drill string such that the casing scraper 100 is positioned part way along the length of the drill string.

[0056] In addition, it is envisioned that a further biasing force applied to each scraper block 110 may be provided by a plurality of tension springs positioned within the recessed waisted portion 124 and behind the inner face 132 of each associated scraper block 110, which bias each scraper block 110 radially inwardly towards the first, retracted position. In this embodiment, each scraper block 110 is retained in the first retracted, position by the tension springs, but the force applied to the inner face 132 of each scraper block 110 resulting from an increase in pressure within each recessed waisted portion 124 tends to bias each scraper block 110 radially outwardly, towards the second, extended position, against the resistive force of the tension spring.

[0057] In an alternative configuration, the further biasing force could be achieved with compression springs positioned between the upper and lower retaining projections 126 and the corresponding overhanging shoulder portions 130, which act to bias each scraper block 110 towards the first, retracted position.

[0058] In addition, it is envisioned that the sleeve 146 may be sized to provide a location or transition fit with the central fluid bore 122 of the casing scraper 100.

[0059] In another example, the sleeve 146 may be retained to the central fluid bore 122 by any number of sheer bolts 164, including one or more. Similarly, the sleeve 146 may be provided with any number of projections 156 on its peripheral face, including one or more, with an equal number of corresponding recesses 158 formed on the inner face of the central fluid bore 122.

[0060] It is also envisioned that the activating ball 170 could be replaced with a bar or any other obstruction sized to fit down tubular portion 152 of the sleeve 146 and plug the aperture 154. In addition, while the cleaning element of the casing scraper 100 has been described as being formed from helical grooves 116 formed in the outer scraping surface 112 of each scraper block, it is envisages that the cleaning element could comprise a plurality of bristles that engage the wall of the casing.

[0061] It is also envisioned that the size of the apertures 168 formed in the tubular portion 152 of the sleeve 146 need not correspond exactly to that of the apertures 144 formed in the tubular portion 108 of the casing scraper 100. In another example the scraper blocks 110 may be equiangularly and longitudinally displaced with respect to each other around the circumference of the casing scraper 100. In addition, the diameter of the fluid channels 142 may vary along their length to increase / decrease the resultant pressure within the fluid channels 142.

[0062] In addition, it is envisioned that there may be no apertures 168 formed in the sleeve 146. In this embodiment, the sleeve 146 is displaced beyond the apertures 144 formed in the tubular portion 108 of the casing scraper 100 when in the second position such that the sleeve 146 does not obstruct the apertures 144 and permits fluid communication between the central fluid bore 122 and the recess waisted portion 124.

[0063] All reference to the term perpendicular as used herein is considered non-limiting and encompasses any direction that is inclined to the longitudinal axis.

[0064] Other aspects, features and advantages will be apparent upon examination of the attached drawings and appended claims.

Claims

CLAIMS1. A well cleaning tool comprising: an elongate body having a longitudinal axis; a central fluid bore aligned with the longitudinal axis; a cleaning element mounted in a recess on the elongate body and being displaceable with respect to the elongate body in a direction inclined to the longitudinal axis; and a sleeve mounted in the central fluid bore and being displaceable with respect to the elongate body in a direction aligned with the longitudinal axis, wherein displacement of the sleeve enables fluid communication of the central fluid bore with the recess.

2. The well cleaning tool of claim 1 , wherein the sleeve is displaceable between a first position, in which the sleeve prevents fluid communication of the central fluid bore with the recess and a second position, in which the sleeve enables fluid communication of the central fluid bore with the recess.

3. The well cleaning tool of any preceding claim, wherein when the recess is in fluid communication with the central fluid bore, fluid pressure within the recess is applied to the cleaning element.

4. The well cleaning tool of claim 3, wherein the fluid pressure biases the cleaning element outward in the direction inclined to the longitudinal axis.

5. The well cleaning tool of any preceding claim when appended to claim 2, wherein the sleeve is retained in the central fluid bore in the first position by a sheer pin.

6. The well cleaning tool of claim 5, wherein the sheer pin is arranged to fail upon application of a force exceeding a break-away load value.

7. The well cleaning tool of claim 6, wherein upon the sheer pin failing, the sleeve moves towards the second position.

8. The well cleaning tool of any claims 2 to 7, wherein the sleeve comprises a through aperture extending in the direction inclined to the longitudinal axis.

9. The well cleaning tool of any claims 2 to 8, wherein the elongate body comprises a fluid channel extending between an inlet aperture formed on an inner face of the central bore and an outlet aperture formed on an inner face of the recess.

10. The well cleaning tool of claim 9 when appended to claim 8, wherein the through aperture in the sleeve aligns circumferentially and longitudinally with the inlet aperture.11 . The well cleaning tool of any preceding claim, wherein the sleeve comprises an open upper end and a closed lower end.

12. The well cleaning tool of claim 11 , wherein the sleeve further comprises an aperture formed in the lower end that extends in a direction aligned with the longitudinal axis.

13. The well cleaning tool of any preceding claim, wherein the sleeve comprises a projection formed on an outer peripheral surface extending radially outward.

14. The well cleaning tool of claim 13, wherein the projection is received in an elongate recess formed in an inner face of the central fluid bore.

15. The well cleaning tool of any preceding claim, wherein the diameter of the sleeve provides a slide fit with the central fluid bore.

16. The well cleaning tool of any preceding claim, wherein the cleaning element further comprises a fluid channel extending from an inlet aperture formed on an inner face of thecleaning element and an outlet aperture formed on the outer surface of the cleaning element.

17. The well cleaning tool of any preceding claim, further comprising means for biasing the cleaning element inward in the direction inclined to the longitudinal axis.

18. The well cleaning tool of claim 17, wherein the biasing means is a tension spring.

19. The well cleaning tool of any preceding claim, wherein the recess extends around the entire outer circumference of the elongate body.

20. The well cleaning tool of any preceding claim, wherein the tool comprises a plurality of cleaning elements.21 . The well cleaning tool of claim 20, wherein the cleaning elements are identical.

22. The well cleaning tool of any claims 20 to 21 , wherein the cleaning elements are equiangularly displaced with respect to each other.

23. The well cleaning tool of any preceding claim, wherein the tool is comprised of a dissolvable material.

24. The well cleaning tool of claim 23, wherein the dissolvable material is magnesium based.

25. A system comprising the well cleaning tool according to one of any claims 12 to 24, further comprising means for obstructing the aperture formed in the lower end of the sleeve.

26. The system of claim 25, wherein the obstructing means is an activating ball.

27. The system of claim 26, wherein the activating ball is comprised of rubber.

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