GB2428718A - Ball arrester, seat and resetable actuation mechanism - Google Patents

Abstract

A ball arrester 90 dissipates the pressure and energy behind a ball 68 as it leaves a ball seat. The arrester 90 presents a non-linear pathway to the ball 68 which can be in the convoluted form of a number of transverse ledges 100 and longitudinal slots 102. Each ledge can have a trailing, concave ramp 101 which guides the ball 68. Each impact with a ledge slowing the ball 68 as is passes down through the arrester 90. Fluid can pass around the ball 68 as it passes through the arrester 90. A ball seat can comprise two part cylindrical sleeves which can shuttle longitudinally relative to one another (figures 7) . When the sleeves are together the ball locates on the seat. When the sleeves are longitudinally extended relative to one another the ball can pass through the seat. Actuation mechanisms for a downhole tool can comprise a ball acting against and passing through a deformable ball seat (figure 3), or a ball acting against and passing through a sleeve with a helical channel (figure 5), each moving against a biasing means. On release of the ball from the deformable seat or helical channel the biasing mechanism will return the seat or sleeve to its original position.

Description

1 Dowrihoj.e Tool 3 The present invention relates to the selective

operation 4 of downhole tools as used in the oil and gas industry and in particular, though not exclusively, to a re-settable 6 circulation tool operated by a drop ball mechanism.

8 While many downhole tools operate continuously through a 9 well bore e.g. scrapers and brushes as disclosed in US 6,227,291, it is more desirable to provide a tool which 11 performs a function only when it has reached a preferred 12 location within a well bore. An example of such a tool 13 would be a circulation tool as disclosed in WO 02/061236.

14 The tool provides a cleaning action on the walls of the casing or lining of the well bore. The cleaning action 16 may be required after the casing has been brushed or 17 scraped and thus the tool is designed to be selectively 18 actuated in the well bore. Such tools provide the 19 advantage of allowing an operator to mount a number of tools on a single work string and operate them 2]. individually on a single trip in to the well bore. This 22 saves significant time in making the well operational.

1 Tools which are selectively actuable in a well bore 2 commonly operate by having an element which can be moved 3 relative to the tool when in the well bore. In the 4 circulation tool of WO 02/061236, the element is a sleeve located in the cylindrical body of the tool. When run in 6 the well, the sleeve is held in a first position by one 7 or more shear screws. To actuate the tool, a drop ball 8 is released from the surface of the well through the work 9 string. On reaching the sleeve, the ball blocks the flow of fluid through the tool and consequently pressure 11 builds up until the shear screws shear and the sleeve is 12 forced downwards. The movement of the sleeve is then 13 stopped when a lower ledge of the sleeve contacts a 14 shoulder on the internal surface of the tool body.

16 Such tools have a number of disadvantages. The tools are 17 generally limited to one actuable movement. If two 18 sleeves are incorporated to overcome this, the shear 19 screws of the second sleeve can operate prematurely under the shock created to shear the shear screws of the first 21 sleeve. Additionally, the reduced bore diameter of the 22 lower part also effects the flow rate achievable through 23 the tool.

One tool which has been developed to operate repeatedly 26 is that disclosed in US 4,889,199. This tool comprises a 27 tubular body having a radial port into which is located a 28 sleeve having a matching radial port. The sleeve is 29 slidably mounted and its action controlled from a deformable drop ball biasing the sleeve against a spring.

31 Initially the spring biases the sleeve to a closed 32 position in which the ports are misaligned. The drop ball 33 causes the sleeve to move to a position where the ports 1 align due to a build up of pressure behind the ball, and 2 fluid is discharged radially through the ports. A small 3 steel ball is then dropped into the tool which seals the 4 radial ports and the consequential pressure build up extrudes the deformable ball through the ball seat. The 6 steel ball will drop with the deformable ball and both 7 are retained in a ball catcher at the base of the tool.

8 When the balls drop together the spring biases the sleeve 9 back to the closed position and the tool can be operated repeatedly.

12 A disadvantage of this tool is that it requires both a 13 deformable ball and a smaller metal ball to operate. Care 14 must then be taken to ensure the balls are dropped in the correct order. The smaller metal ball must lodge in the 16 second, radial, outlet in order to stop flow and thus the 17 tool is restricted to having a single radial port. This 18 limits the amount of cleaning which can be performed.

It is an object of the present invention to provide a 21 downhole tool which obviates or mitigates at least some

22 of the disadvantages of the prior art.

24 It is a further object of at least one embodiment of the present invention to provide a circulation tool which is 26 re-settable and operated by similar drop balls.

28 It is a further object of at least one embodiment of the 29 present invention to provide an actuation mechanism to move a sleeve within a downhole tool.

32 According to a first aspect of the present invention 33 there is provided a downhole tool for selectively 1 performing a task in a well bore, the tool comprising a 2 substantially cylindrical body having a central bore 3 running axially therethrough, a sleeve located within the 4 bore, the sleeve including a ball seat, a plurality of balls, each ball having substantially similar dimensions 6 and each ball arresting a majority of fluid flow through 7 the bore when located in the ball seat, mechanical 8 biasing means located between the sleeve and the body to 9 bias the sleeve in a first direction, and functional means on the body to perform a task in the well bore, the 11 functional means being operable on relative movement of 12 the sleeve, wherein the functional means has at least a 13 first and a second operating position, each change in 14 position being effected by passing a said ball through the sleeve in a reverse direction, and wherein the said 16 changes form a cyclic pattern such that the functional 17 means can be cycled back to the first operating position.

19 The tool can therefore be operated a number of times while located in a well bore. Further all operations are 21 controlled by dropping identical balls through the tool 22 and thus there is no co-ordination required in dropping 23 the balls.

It will be appreciated that while the term ball has been 26 used, this represents any shaped projectile which can be 27 dropped into the fluid flow, travel to and seat in the 28 ball seat, and further travel through the ball seat. Such 29 projectiles may be plugs, bombs darts or the like.

31 Preferably the ball seat releasably retains each ball.

32 Preferably the ball seat is a ledge or shoulder located 33 on an inner surface of the sleeve means. The ball 1 therefore rests on the shoulder until sufficient pressure 2 builds up to force the ball past the shoulder.

4 In a first embodiment, the balls are deformable. In this way each ball can be released by passing through the ball 6 seat when sufficient pressure is applied to it.

8 When a ball is dropped in the body, the ball will locate 9 in the ball seat. The ball will block the fluid path through the tool and consequently pressure will build up 11 on the ball by fluid prevented from travelling through 12 the body. This pressure will be sufficient to move the 13 ball and sleeve together against the mechanical bias and 14 force the sleeve in the reverse direction. When the limit of the bias is reached, increased pressure will cause the 16 ball to deform and pass through the ball seat. On release 17 of the ball, pressure drops and the sleeve is biased in 18 the first direction. The movement of the sleeve actuates 19 the tool and moves the functional means to an operating position.

22 In a second embodiment, the ball seat may be a deformable 23 ball seat. Preferably the deformable ball seat includes a 24 part conical surface having an aperture therethrough.

Advantageously the aperture has a diameter less than a 26 diameter of the ball. Preferably the deformable ball seat 27 is made of a flexible material, so that at a 28 predetermined pressure it flexes to release the ball.

29 Advantageously the deformable ball seat is made of a metal so that the seat is not prone to wear during use.

32 The deformable ball seat may comprise a spring such as a 33 disc spring. Preferably the deformable ball seat has 1 sufficient elasticity such that it returns to its 2 original dimensions once a ball has passed therethrough.

3 Optionally the deformable ball seat may be of a layered 4 structure. Preferably the layered structure comprises a plurality of disc springs.

7 Throughout this specification the term deformable refers 8 to the ability of an element to change shape within its 9 own volume as it deforms. This is in contrast to expandable wherein the element must get bigger i.e. 11 extend beyond its outer diameter.

13 Preferably the balls of the second embodiment are 14 spherical. More preferably the balls are of a non-pliable material and thus cannot deform. Advantageously the balls 16 are made of steel.

18 In the second embodiment, when a ball is dropped in the 19 body, the ball will locate in the deformable ball seat.

The ball will block the fluid path through the tool and 21 consequently pressure will build up on the ball by fluid 22 being impeded in travelling through the body. This 23 pressure will be sufficient to move the ball and sleeve 24 together against the mechanical bias and force the sleeve in the reverse direction. When the limit of the bias is 26 reached, increased pressure will cause the seat to expand 27 against the pressure of the ball. The ball will pass 28 through the expanded ball seat. On release of the ball, 29 pressure drops and the sleeve is biased in the first direction. The movement of the sleeve actuates the tool 31 and moves the functional means to an operating position.

1 In a third embodiment the ball seat may comprise a 2 helical channel on an inner surface of the sleeve.

4 Preferably the helical channel has curved walls. This will prevent damage to a ball passing through the 6 channel. Preferably also the ball is sized to provide a 7 restricted fluid by-pass around the ball when in the 8 channel. This ensures a positive pressure is maintained 9 behind the ball and prevents chattering of the ball in the channel.

12 The helical channel may be considered as a screw thread.

13 Thus the channel has a left hand thread so that a ball 14 travels in the opposite direction to the rotation of the tool on a work string. Preferably a pitch of the thread 16 is greater than or equal to a diameter of each ball.

18 Preferably the balls are spherical. More preferably the 19 balls are of a non-pliable material and thus cannot deform. Zdvantageously the balls are made of steel.

22 Preferably also the sleeve includes a conical surface at 23 an entrance to the channel. This funnels the ball into 24 the channel and ensures it travels into the helical path.

26 For this embodiment, when a ball is dropped in the body, 27 fluid will drive the ball into the channel and into the 28 helical path. As the ball is sized for the channel it 29 will block the majority of the fluid path through the tool and consequently pressure will build up behind the 31 ball. This pressure will be sufficient to move the ball 32 and sleeve together against the spring and force the 33 sleeve in the reverse direction. On release of the ball 1 from the channel the sleeve is biased in the first 2 direction. The movement of the sleeve actuates the tool 3 and moves the functional means to an operating position.

Preferably the mechanical biasing means is a strong 6 spring. The spring may be helical, conical or the like. A 7 strong spring will prevent the sleeve moving in the 8 reverse direction by fluid flow in the central bore.

9 Preferably also the mechanical biasing means is located in a chamber created between the sleeve and the body.

11 Advantageously the chamber includes an exhaust port such 12 that fluid can enter and be dispelled from the chamber by 13 relative movement of the sleeve and the body. This 14 provides a damping effect which prevents shock movements in the tool.

17 Preferably a choke ring is located around the sleeve.

18 Preferably the ring has an extended portion in the 19 longitudinal plane to provide an extended surface area to match the outer surface of the sleeve for fluid to flow 21 therebetween. The shape of the ring, assists in 22 providing a damping action as the sleeve moves in the 23 reverse direction. Fluid which has to pass the sleeve as 24 it moves downwards is forced to take a route having a restricted flow path in the first direction. This 26 damping helps prevent the mechanical bias e.g. a spring 27 or other parts, from bouncing' into a location which 28 could result in the functional means being moved to an 29 unwanted operating position.

31 Preferably the tool further comprises engagement means to 32 control relative movement between the sleeve and the 1 body. Preferably also the mechanical bias biases the 2 sleeve against the engagement means.

4 Preferably said engagement means comprises at least one index pin located in a profiled groove. Preferably the at 6 least one index pin is located on the body and the 7 profiled groove is located on an outer surface of the 8 sleeve. In this way, an index sleeve is produced with the 9 groove determining the relative position of the sleeve to the body. Advantageously the groove extends 11 circurnferentially around the sleeve, this enables the 12 tool to be continuously cycled through a number of 13 operating positions.

Preferably the tool further includes a ball non-return 16 element. Preferably the element is a split ring located 17 in the bore below the sleeve. Advantageously the ring is 18 located at the base of a ramp on an inner surface of the 19 body. Preferably the ramp is arranged such that if a ball pushes against the ring in the first direction, the 21 ring will travel up the ramp and thereby reduce in 22 diameter as edges of the split are forced together. This 23 reduction in diameter will prevent a ball from travelling 24 in a first direction back up through the tool.

26 Advantageously the tool includes a ball arrester.

27 Preferably the arrester is located below the ball seat.

28 The inner surface of the sleeve may be shaped to provide 29 the ball arrester. Preferably the ball arrester comprises a plurality of surfaces transversely arranged 31 to the central bore. Preferably the surfaces provide a 32 convoluted path which a ball must take through the 33 sleeve. Preferably the path is sized such that fluid may 1 pass around the ball during its passage. In this way, the 2 momentum of the ball as it passes through the seat is 3 dissipated before the ball reaches any further ball seats 4 in the tool or in the work string to which it is attached. This prevents the ball exploding' through 6 restrictions in the bore and allows restrictions, such as 7 further ball seats, to be mounted relatively closely to 8 the ball seat.

Preferably the tool further comprises a second ball seat.

11 The second ball seat is located below the sleeve and 12 allows the central bore to be blocked in any operating 13 position, if desired.

The second ball seat may comprise a collet including a 16 plurality of fingers directed in the first direction.

17 Preferably the collet is closed and the fingers are 18 brought together by the action of the sleeve locating 19 between the fingers and the body. In this way, when the sleeve is moved in the reverse direction the passage 21 through the central bore is restricted as the collet 22 closes. A ball is then arrested on the collet. When the 23 sleeve moves in the first direction by a predetermined 24 distance the collet opens and the ball is released to travel through the tool.

27 Alternatively the second ball seat may comprise a trapped 28 C' ring, or split ring. Again movement of the sleeve 29 between the ring and the body will cause the ring to be compressed wherein its diameter reduces. A ball will 31 therefore be prevented from passing through the bore and 32 be impeded at the ring. Movement of the sleeve in the 33 first direction by a predetermined direction will free 1 the ring and, by expansion, the ball can pass through the 2 now increased aperture.

4 Advantageously the second ball seat is a shuttle arrangement. The shuttle arrangement comprises a 6 plurality of part cylindrical sleeves. Preferably the 7 sleeves combine to form a complete sleeve which is 8 located in the body. Preferably at least a first part 9 cylindrical sleeve is connected to the sleeve, such that it moves with the sleeve. Preferably at least a second 11 part cylindrical sleeve is attached to the body arid is 12 prevented from longitudinal movement in the bore.

13 Preferably the part cylindrical sleeves overlap in the 14 bore at all times, such that movement of the sleeve brings them into sliding engagement. More preferably, 16 when the sleeves are brought together, the internal bore 17 created has a diameter smaller than the diameter of the 18 balls, but that one or more balls can pass between a part 19 cylindrical sleeve and an inner surface of the body.

Preferably a free end of each part cylindrical sleeve 21 includes a funnel portion. More preferably the funnel 22 reduces the diameter of the part cylindrical sleeve from 23 that of substantially the body to that of the inner bore.

24 The funnel may be stepped. In this way, only when then the funnels of each part cylindrical sleeve are aligned 26 can balls pass through the second ball seat.

28 Preferably the tool is a circulation tool. The 29 functional means may comprise at least one first port arranged substantially transversely to the central bore 31 through the body, and at least one second port arranged 32 transversely to the central bore through the sleeve, such 33 that aligrunenc of the ports causes fluid to be discharged 1 from the central bore and wherein alignment of the ports 2 is controlled by relative movement of the sleeve.

4 More preferably there are a plurality of said first and said second ports. Advantageously there are three or more 6 said first and said second ports. Preferably also said 7 first and said second ports are spaced equidistantly 8 around the body and sleeve respectively.

Preferably also the tool includes ball collecting means.

11 The ball collecting means may be an element located in 12 the casing means to prevent passage of the ball through 13 the tool, but allowing passage of fluid through the tool.

According to a second aspect of the present invention 16 there is provided a method of circulating fluid in a 17 borehole, the method comprising the steps: 19 (a) inserting in a work string a tool comprising a tubular body including a plurality of first radial 21 outlet ports in which is located a sleeve including 22 a plurality of second radial outlets; 23 (b) running the work string and tool into a borehole, 24 with the sleeve in a first position relative to the body wherein the first and second radial outlets are 26 arranged in a first operating position; 27 (c) dropping a ball into the work string such that the 28 ball lands on the sleeve and forces the sleeve into 29 a second position relative to the casing wherein the first and second radial outlets are arranged in an 31 intermediate operating position and fluid flow is 32 restricted by the ball; 1 (d) increasing pressure behind the ball to cause the 2 ball to pass through the sleeve, the releasing 3 pressure allowing the sleeve to move to a third 4 position relative to the body wherein the first and second radial outlets are arranged in a second 6 operating position; and wherein the ports are 7 aligned in either of the operating positions and 8 misaligned in the other operating position.

In this way, the tool can be run into the borehole with 11 the ports in an open or closed configuration. The 12 intermediate position is a position where the tool is 13 primed between he first and second operating positions.

Preferably the method further includes the steps of: 17 (e) dropping a second ball, substantially similar to the 18 first ball, into the work string such that the 19 second ball lands on the sleeve and forces the sleeve into the second position relative to the body 21 wherein the first and second radial outlets are 22 arranged in the intermediate operating position and 23 fluid flow is restricted by the second ball; and 24 (f) increasing pressure behind the second ball to cause the second ball to pass through the sleeve, the 26 releasing pressure allowing the sleeve to move to 27 the first position relative to the body wherein the 28 first and second radial outlets are arranged in the 29 first operating position.

31 With the sleeve and body back in the first position, the 32 steps (c) to (f) can be repeated. In this way the tool 33 can operate in a cyclic manner.

1 Preferably the method includes the step of moving the 2 sleeve against a mechanical bias.

4 Preferably the method includes the step of controlling movement of the sleeve relative to the body by use of an 6 index sleeve.

8 Preferably the method includes the step of decelerating 9 the ball as it passes from the sleeve to dissipate the pressure.

12 Preferably the method includes the step of stopping the 13 ball in a second ball seat after it has passed through 14 the sleeve. Preferably this step further includes the step of preventing fluid flow through the work string 16 while directing it through the radial ports.

18 Preferably also the method includes the step of catching 19 the dropped balls in the work string.

21 According to a third aspect there is provided a ball 22 arrester for dissipating momentum of a ball after it has 23 passed through a ball seat, the arrester comprising a 24 substantially cylindrical body in which is located a non- linear pathway through which the ball is guided.

27 Preferably the pathway comprises a plurality of surfaces 28 transversely arranged to a central bore. Preferably each 29 transverse path has a curved ramp extending therefrom to the next transverse surface. Preferably also each 31 transverse surface extends across a portion of the bore 32 so that the ball can pass between the surfaces.

33 Advantageously adjacent surfaces are off-set so chat the 1 ball is forced to run along each surface before 2 travelling to the next surface. Preferably the surfaces 3 provide a convoluted path which a ball must take through 4 the body. Preferably the path is sized such that fluid may pass around the ball during its passage. In this way, 6 the kinetic energy of the ball as it passes through the 7 seat is dissipated before the ball reaches any further 8 ball seats in a tool or in the work string to which it is 9 attached. This prevents a ball exploding' through restrictions in the bore and allows restrictions, such as 11 further deformable ball seats, to be mounted relatively 12 closely to the ball seat.

14 According to a fourth aspect of the present invention there is provided a ball seat for a dowrihole tool, the 16 ball seat comprising a plurality of part cylindrical 17 sleeves which can shuttle with respect to each other, 18 longitudinally in the tool, wherein a ball can only pass 19 through the seat when the sleeves are located at their longitudinal extent.

22 Preferably the sleeves combine to form a complete sleeve 23 which is located in a cylindrical bore of the tool.

24 Preferably at least a first part cylindrical sleeve is moveable within the tool. Preferably at least a second 26 part cylindrical sleeve is attached to the tool and is 27 prevented from longitudinal movement in the bore.

28 Preferably the part cylindrical sleeves overlap in the 29 bore at all times, such that movement of the first brings them into sliding engagement by a shuttle motion. More 31 preferably, when the sleeves are brought together, the 32 internal bore created has a diameter smaller than the 33 diameter of a ball directed at the seat, but that a ball 1 can pass between a part cylindrical sleeve and an inner 2 surface of the tool. Preferably a free end of each part 3 cylindrical sleeve includes a funnel portion. More 4 preferably the funnel reduces the diameter of the part cylindrical sleeve from that of substantially the body to 6 that of the inner bore. The funnel may be stepped. In 7 this way, only when the funnels of each part cylindrical 8 sleeve are aligned can balls pass through the ball seat.

According to a fifth aspect of the present invention 11 there is provided an actuation mechanism for a downhole 12 tool, the mechanism comprising a substantially 13 cylindrical body having a central bore running axially 14 therethrough, a sleeve located within the bore, the sleeve including an deformable ball seat, 16 mechanical biasing means located between the sleeve and 17 the body to bias the sleeve in a first direction and a 18 ball, wherein the deformable ball seat releasably retains 19 the ball to prevent fluid flow through the sleeve and cause the sleeve to move in the reverse direction 21 relative to the body and wherein on release of the ball 22 the seat returns to its original dimensions.

24 Preferably the mechanical bias is a strong spring. The spring may be helical, conical or the like. A strong 26 spring will prevent the sleeve moving in the reverse 27 direction by fluid flow in the central bore.

29 Preferably the deformable ball seat includes a part conical surface having an aperture therethrough.

31 Advantageously the aperture has a diameter less than a 32 diameter of the ball. Preferably the ball seat is made of 33 a flexible or elastic material, so that at a 1 predetermined pressure it flexes to release the ball.

2 Advantageously the ball seat is made of a metal so that 3 the seat is not prone to wear during use. The ball seat 4 my comprise a spring such as a disc spring.

6 Optionally the ball seat may be of a layered structure.

7 Preferably the layered structure comprises a plurality of 8 disc springs.

Preferably the ball is spherical. More preferably the 11 ball is of a non-pliable material and thus cannot deform.

12 Advantageously the ball is made of steel.

14 According to a sixth aspect of the present invention there is provided an actuation mechanism for a downhole 16 tool, the mechanism comprising a substantially 17 cylindrical body having a central bore running axially 18 therethrough, a sleeve located within the bore, the 19 sleeve including a helical channel on an inner surface, mechanical biasing means located between the sleeve and 21 the body to bias the sleeve in a first direction and a 22 ball, sized to run in the helical channel in a reverse 23 direction to prevent a majority of fluid flow through the 24 sleeve and cause the sleeve to move in the reverse direction relative to the body.

27 Preferably the mechanical bias is a strong spring. The 28 spring may be helical, conical or the like. A strong 29 spring will prevent the sleeve moving in the reverse direction by fluid flow in the central bore.

32 Preferably the helical channel has curved walls. This 33 will prevenc damage to the ball. Preferably also the ball 1 is sized to provide a restricted fluid by-pass around the 2 ball when in the channel. This ensures a positive 3 pressure is maintained behind the ball and prevents 4 chattering of the ball in the channel.

6 The helical channel may be considered as a screw thread.

7 Thus the channel has a left hand thread so that the ball 8 travels in the opposite direction to the rotation of the 9 tool on a work string. Preferably a pitch of the thread is greater than or equal to a diameter of the ball.

12 Preferably the ball is spherical. More preferably the 13 ball is of a non-pliable material and thus cannot deform.

14 Advantageously the ball is made of steel.

16 Preferably also the sleeve includes a conical surface at 17 an entrance to the channel. This funnels the ball into 18 the channel and ensures it travels into the helical path.

Embodiments of the present invention will now be 21 described, by way of example only, with reference to the 22 following Figures, of which: 24 Figure 1 is a part cross-sectional view of a downhole tool in a first position according to an embodiment of 26 the present invention; 28 Figures 2(a)-(c) are schematic illustrations of an index 29 pin positioned in a groove of the tool of Figure 1 for the first, second and third positions respectively; 32 Figures 3(a)-(c) are part cross-sectional views of a 33 downhole tool according to a first embodiment of the 1 present invention illustrating a change in operating 2 position from (a) a firstoperating position to (C) a 3 second operating position; Figures 4(a)-(c) are part cross-sectional views of a 6 downhole tool according to a second embodiment of the 7 present invention illustrating a change in operating 8 position from (a) a first operating position to (c) a 9 second operating position; 11 Figures 5(a)-(c) are part cross-sectional views of a 12 downhole tool according to a third embodiment of the 13 present invention illustrating a change in operating 14 position from (a) a first operating position to (c) a second operating position; 17 Figure 6 is a schematic view of a ball arrester according 18 to an embodiment of the present invention; and Figures 7(a)-(c) are part cross-sectional views of a ball 21 seat according to an embodiment of the present invention 22 illustrating a change in operating position from (a) a 23 first operating position to (c) a second operating 24 position.

26 Reference is initially made to Figure 1 of the drawings 27 which illustrates a downhole tool, generally indicated by 28 reference numeral 10, in accordance with an embodiment of 29 the present invention. Tool 10 includes a cylindrical body 12 having an upper end 14, a lower end 16 and a 31 cylindrical bore 18 running therethrough. The body 12 has 32 a box section 20 located at the upper end 14 and a pin 1 section 22 located at the lower end 16 for connecting the 2 tool 10 in a work string or drill string (not shown).

4 The body 12 further includes five radial ports 24 located equidistantly around the body 12. The ports 24 are 6 perpendicular to the bore 18.

8 Within the bore 18 there is located a sleeve 30. Sleeve 9 30 is an annular body which includes five radial ports 32 located equidistantly around the sleeve 30. The ports 32 11 are perpendicular to the bore 18. The ports 32 are of a 12 similar size to the ports 24 in the body 12.

14 On an outer surface 44 of the sleeve 30 there is located a longitudinal recess 45. Arranged through the body 12 is 16 a pin 47 which locates in the recess 45. Relative 17 longitudinal movement of the pin 47 and recess 45 ensures 18 that the ports 24 in the body will align with the ports 19 32 in the sleeve 30. The sleeve 30 is sealed against body 12 by 0-rings 31a-d at the ports 24,32.

22 A ball seat 34 is located on the sleeve 30 at an upper 23 end 36. The ball seat comprises an aperture or throat 40 24 sized for a ball 68 to rest against and form a seal. The throat 40 also has a diameter less than the diameter of 26 the bore 42 of the sleeve 30. The sleeve includes a 27 conical surface 38 at the upper end 36 to direct the ball 28 68 with minimal turbulence towards the seat 34.

Located between the outer surface 44 of the sleeve 30 and 31 the inner surface 46 of the body 12 is a space forming a 32 chamber 48. The upper edge of the chamber is formed from 33 a ledge or stop 50 on the outer surface 44 of the sleeve 1 30. The lower edge of the chamber 48 is formed from the 2 ledge 28 of the body 12. A strong spring 52 is positioned 3 within the chamber 48 and compressed to bias against the 4 ledge 50 of the sleeve 30. A similar chamber 49 can be created between the sleeve 30 and the body l2at other 6 locations in the tool. The restricted passage of fluid 7 into and through these chambers 48,49 provides a 8 hydraulic damping effect during movement in the tool 10.

Further an engagement mechanism, generally indicated by 11 reference numeral 56, couples the sleeve 30 to the body 12 12 and controls relative movement there between.

13 Engagement mechanism 56 comprises an index sleeve 58, 14 being located with respect to the sleeve 30, and a matching index pin 60 located through the body 12 towards 16 the sleeve 30. Though only one index pin 60 is 17 illustrated the tool 10 would typically have three or 18 more pins to distribute load over the mechanism 56. Index 19 sleeve 58 includes a profiled groove 62 on its outer surface 57 of the sleeve 30 into which the index pin 60 21 locates.

23 Reference is now made to Figure 2 of the drawings which 24 illustrates the groove 62 of the index sleeve 58. The groove 62 extends circumferentially around the sleeve 58 26 and consequently the sleeve 30 in a continuous path. The 27 groove 62 defines a path having a substantially zig-zag 28 profile to provided axial movement of the sleeve 30 29 relative to the body 12. Indeed, spring 52 biases the sleeve 30 against the index pin 60. The path includes an 31 extended longitudinal portion 64 at every second upper 32 apex of the zig-zag. Further a stop 66 is located at the 33 apexes of the zig-zags to encourage the index pin 60 to 1 remain at the apexes and provide a locking function to 2 the tool 10. The stops 66 are in the direction of travel 3 of the pin 60 along the groove 62.

Further features of the tool 10 will be described 6 hereinafter with reference to later Figures.

8 In use, tool 10 is connected to a work string using the 9 box section 20 and the pin section 22. As shown in Figures 1 and 2(a), the spring 52 biases the sleeve 30 11 against the index pin 60 such that the pin 60 is located 12 in the base of longitudinal portion 64 of the groove 62.

13 This is referred to as the first position of the tool 10.

14 In this position, sleeve ports 32 are located above body ports 24, thus preventing fluid flow radially through 16 these ports due to their misalignment. All fluid flow is 17 through bores 18,42 of the tool 10. The tool 10 is then 18 run into a bore hole until it reaches a location where 19 cleaning of the bore hole casing or circulation of the fluid through the tool is required.

22 Drop ball 68 is then released through the bore of the 23 work string from a surface. Ball 68 travels by fluid 24 pressure and/or gravity to the ball seat 34 of the sleeve 30. The ball 68 is guided by the conical surface 38 to 26 the ball seat 34. When the ball 68 reaches the seat 34 27 it effectively seals the bore 12 and prevents axial fluid 28 flow through the tool 10. Consequently fluid pressure 29 builds up behind the ball 68 and the sleeve 30, including the ball 68, moves against the bias of the spring 52, to 31 an intermediate position. The spring 52 is compressed 32 into a now smaller chamber 48. Fluid has been expelled 33 from the chamber 48. The index pin 60 is now located at 1 the apex 63 of the groove 62 next to the longitudinal 2 portion 64. This is as illustrated in Figure 2(b).

3 Consequently the sleeve ports 32 have crossed the body 4 ports 24 and are now located below them. Fluid flow through the bores 18,42 is prevented by the ball 68.

7 As pressure increases on the ball 68 it is released from 8 the ball seat 34 by passing through the throat 40. The 9 ball 68 travels by fluid pressure until it is stopped further through the tool 10 or the work string. On 11 release of the pressure, spring 52 moves the sleeve 30 12 against the index pin 60 such that the sleeve travels to 13 a second position. Fluid has been drawn into the chamber 14 48 and this drawing and expelling of fluid provides a hydraulic damping effect on the impact on the pin 60.

16 Index pin 60 is now located in a base 65 of the groove 62 17 and the ports 24,32 are aligned. This is illustrated in 18 Figure 2(c). In this second position fluid is expelled 19 radially from the tool 10 through the now aligned ports 24,32. The tool 10 is locked in this position by virtue 21 of the stop 66 on the groove 62 which prevents movement 22 of the sleeve 30 for small variations in fluid pressure.

24 In order to close the ports 24,32, a second ball is dropped from the surface through the work string. The 26 second ball, and indeed any ball subsequent to this, is 27 identical to the first ball 68. The second ball will 28 travel to rest in the ball seat 34. On the build up of 29 fluid pressure behind the ball, sleeve 30 will move downwards against the bias of the spring 52. Consequently 31 the index pin 60 will be relocated into the next apex 63 32 of the groove 62 and thus the tool is returned to the 33 intermediate position. When the ball passes through the 1 throat 40, the pin 60 and sleeve 30 will move relatively 2 back to the first position and the ball will come to rest.

3 by the first ball 68. The index pin 60 has located in the 4 next longitudinal portion 64. Effectively the tool is reset and by dropping further balls the tool 10 can be 6 repeatedly cycled in an open and closed manner as often 7 as desired. The intermediate position can be considered 8 as a primed position.

It will be appreciated that although the description 11 refers to relative positions as being above' and 12 below', the tool of the present invention can equally 13 well be used in horizontal or inclined boreholes and is 14 not restricted to vertical boreholes.

16 Reference is now made to Figure 3 of the drawings which 17 illustrates a downhole tool, generally indicated by 18 reference numeral 10, in accordance with a first 19 embodiment of the present invention. Tool 10 has similar features to the tool 10 of Figure 1 and those features 21 have been given the identical reference numerals for ease 22 of interpretation. Tool 10 is a circulation tool 23 operated by the alignment of the radial ports 24,32 of 24 the sleeve 30 and the body 12. Movement is controlled via an engaging mechanism 56, as for Figures 1 and 2.

27 In this embodiment, located on an inner surface 26 of the 28 body 12 are two opposing ledges 26, 28 used to limit 29 axial movement of the sleeve 30 located within the body 12. The ball seat 34 is located on the sleeve 30 at an 31 upper end 36. The ball seat comprises a conical surface 32 38 facing the upper end 14 of the tool 10. A throat 40 is 33 provided at a base of the conical surface 38, the throat 1 having a diameter less than the diameter of the bore 42 2 of the sleeve 30.

4 Located between the outer surface 44 of the sleeve 30 and the inner surface 46 of the body 12 is a chamber 48. An 6 exhaust port 54 is located through the sleeve 30 at the 7 chamber 48 to allow fluid from the bore 42 to pass in to 8 and out of the chamber 48 as the sleeve 30 is moved 9 relative to the body 12.

11 Figure 3(a) illustrates the tool 10 when run into a well 12 bore. Figure 3(b) illustrates the tool 10 with a ball 68 13 located in the bore 42. Ball 68 is sized to rest on 14 surface 38 and be of a deformable material e.g. rubber so that under force it changes shape within its own volunie 16 to pass through the throat 40. Figure 3(c) of the 17 drawings illustrates the tool 10 with the ball 68 exiting 18 the sleeve 30 into the bore 18. Body 12 includes a pin 70 19 located into the bore 18. Pin 70 is a ball retainer pin which blocks the passage of the ball 68 through the bore 21 18. Ball 68 will come to rest at the pin 70 and therefore 22 be retrievable with the tool 10. Pin 70 does not prevent 23 the flow of fluid through the bore 18 and from the tool 24 10 into the work string below. The pin 70 and the space 72 in the bore 18 immediately above it may be considered 26 as a ball catcher.

28 In use, tool 10 operates as for the tool described in 29 Figures 1 and 2. When drop ball 68 it travels by fluid pressure and/or gravity to the ball seat 34 of the sleeve 31 30. The ball 68 rests on the conical surface 38 and 32 prevents axial fluid flow through the tool 10.

33 Consequently fluid pressure builds up behind the ball 68 1 and the sleeve 30, including the ball 68, moves against 2 the bias of the spring 52, to the intermediate position.

3 This position is illustrated in Figures 3(b) and 2(b).

4 The spring 52 is compressed into a now smaller chamber 48. Fluid has been expelled from the chamber 48 through 6 the exhaust port 54. The index pin 60 is now located at 7 the apex 63 of the groove 62. Consequently the sleeve 8 ports 32 have crossed the body ports 24 and are now 9 located below them. Fluid flow is prevented form passing through the bores 18,42, by the obstruction of the ball 11 68.

13 As pressure increases on the ball 68 it is extruded 14 through the throat 40 by deforming. The ball 68 travels by fluid pressure until it is stopped by the pin 70 and 16 is held in the space 72. On release of the pressure, 17 spring 52 moves the sleeve 30 against the index pin 60 18 such that the sleeve travels to the second position. The 19 second position is illustrated in Figures 3(c) and 2(c).

Fluid has been drawn into the chamber 48 and this drawing 21 and expelling of fluid provides a hydraulic damping 22 effect on the impact on the pin 60. Index pin 60 is now 23 located in the base 65 of the groove 62 and the ports 24 24,32 are aligned. In this third position fluid is expelled radially from the tool 10 through the now 26 aligned ports 24,32. The tool 10 is locked in this 27 position by virtue of the stop 66 on the groove 62 which 28 prevents movement of the sleeve 30 for small variations 29 in fluid pressure.

31 In order to close the ports 24,32, a second ball is 32 dropped from the surface through the work string. The 33 second ball, and indeed any ball subsequent to this, is 1 identical to the first ball 68. The second ball will 2 travel to rest in the ball seat 34. On the build up of 3 fluid pressure behind the ball, sleeve 30 will move 4 doiriwards against the bias of the spring 52. Consequently the index pin 60 will be relocated into the next apex 63 6 of the groove 62 and thus the tool is returned to the 7 intermediate position. When the ball is extruded through 8 the throat 40, the pin 60 and sleeve 30 will move 9 relatively back to the first position and the ball will come to rest by the first ball 68. Effectively the tool 11 is reset and by dropping further balls the tool 10 can be 12 repeatedly cycled in an open and closed manner as often 13 as desired.

Reference is now made to Figure 4 of the drawings which 16 illustrates a downhole tool, generally indicated by 17 reference numeral 10, in accordance with a second 18 embodiment of the present invention. Tool 10 includes 19 features in common with the tool illustrated in Figure 3 and thus like parts have been given the same reference 21 numerals to aid clarity. Tool 10 is a circulation tool 22 operated by the alignment of the radial ports 24,32 of 23 the sleeve 30 and the body 12. Movement is controlled via 24 an engaging mechanism 56 as for Figures 1 and 2.

26 In this second embodiment, ball seat 34 is a deformable 27 ball seat. The seat 34 is located at an upper end 36 of 28 the sleeve 30. A conical surface 38 of the seat 34 faces 29 the upper end 14 of the tool 10. The conical surface 38 is part of a disc spring 33 mounted at the upper end 36 3]. of the sleeve 30. A perpendicular portion 41 of the 32 spring 33 sits proud of the inner surface 39 of the 33 sleeve 30. The spring 33 is placed in the first direction 1 such that it operates opposite to its typical 2 arrangement. Spring 33 may comprise a stack of disc 3 springs selected to provide a deflection or flex in 4 structure at a desired pressure. Disc springs, and in particular disc springs formed from conical shaped 6 washers (sometimes referred to as Belleville washers) as 7 used here, are well known to those skilled in the art.

8 Such springs are available from, for example, Belleville 9 Springs Ltd, Redditch, United Kingdom. An advantage of these springs is that they return to their original shape 11 following deflection.

13 Figure 4(a) illustrates the location of the ball seat 34 14 as the tool is run in a well bore. The tool 10 is in a first operating position with the radial ports 24,32 16 misaligned and the sleeve 30 biased fully upwards by the 17 spring 52. Figure 4(b) illustrates the tool 10 with a 18 ball 68 now located in the bore 42. Ball 68 is located on 19 the deformable ball seat 34 and is sized to block the bore 42. In this way the ball 68 is arrested and pressure 21 builds up behind the ball 68. This pressure moves the 22 ball 68 and sleeve 30 together within the body 12 to the 23 position illustrated. At this point the spring 52 is 24 compressed fully, this being the maximum distance of travel for the sleeve 30. Any additional pressure will 26 now cause the disc spring 33 to flex and release the ball 27 to travel through the sleeve 30 and into the bore 18.

29 The ball is of a hard material which is non-pliable.

Ideally the ball is made of a metal such as steel.

32 Reference is now made to Figure 4(c) which illustrates 33 the tool 10 with the ball 68 now exiting the sleeve 30 1 into the bore 18. Exit of the ball is in an identical 2 manner to that of Figure 3(c).

4 In use, tool 10 operates identically to the earlier tools. When ball 68 travels by fluid pressure to the 6 conical surface 38 at the upper end 36 of the sleeve 30.

7 The ball 68 lands on the seat 34 where its progress is 8 arrested. As the ball 68 is now blocking the fluid flow 9 through the bore 42, fluid pressure will build up behind the ball and allow sufficient pressure to build up on the 11 ball 68 and sleeve 30 such that they can move in the 12 direction of applied pressure against the bias of the 13 spring 52. Consequently the sleeve 30 and ball 68 move to 14 an intermediate position. This position is illustrated in Figure 4(b) and 2(b). On increasing fluid pressure on the 16 ball 68, with the sleeve 30 now arrested, pressure is 17 exerted on the ball seat 34. The disc spring 33 will 18 deflect under this increased pressure and ejects the ball 19 68 into the bore 42 below the seat 34. The seat 34 has deformed within its own volume and now returns to its 21 original shape. The ball 68 exits the seat 34 and free 22 falls from this point. On release of the pressure, spring 23 52 moves the sleeve 30 against the index pin 60 such that 24 the sleeve travels to a second position. The second position is illustrated in Figures 4(c) and 2(c). The 26 ports 24,32 are aligned for fluid to be expelled radially 27 from the tool 10.

29 In order to close the ports 24,32, a second ball is dropped from the surface through the work string. As with 31 the previous embodiments the tool 10 is reset and can be 32 cycled between the first and second operating position a 33 number of times. The number of times may be dependent on 3. the number of balls which can be caught in the work 2 string.

4 Reference is now made to Figure 5 of the drawings which illustrates a downhole tool, generally indicated by 6 reference numeral 10, in accordance with a third 7 embodiment of the present invention. Tool 10 has 8 identical features and operates in an identical mariner to 9 the earlier embodiment except that it incorporates an alternative ball seat 34 comprising a helical channel 35.

12 At an upper end 36 of the sleeve 30 is located a conical 13 surface 38 facing the upper end 14 of the tool 10.

14 Downwardly extending from the conical surface is a helical channel 35. The channel 35 comprises a continuous 16 spiral groove, having curved walls 41, which takes the 17 path of a screw thread on the inner surface 39 of the 18 sleeve 30. The handedness of the screw thread is left 19 handed.

21 Figure 5(b) illustrates the tool 10, now with a ball 68 22 located in the bore 42. Ball 68 is sized to travel along 23 the helical channel 35. Ideally the ball 68 is sized to 24 have a diameter less than or equal to the pitch of the screw thread forming the walls 41 of the channel 35. In 26 this way when the ball 68 travels along the channel 35 a 27 restricted by-pass is created between the edge of the 28 ball 68 and the walls 41 of the channel 35. The ball is 29 of a hard material which is non-pliable. Ideally the ball is made of a metal such as steel.

32 In use, tool 10 is connected to a work string and run in 33 a well bore in a first operating position as shown in 1 Figures 2(a) and 5(a), until it reaches a location where 2 cleaning of the bore hole casing or circulation of fluid 3 through the tool is required.

Drop ball 68 is then released through the bore of the 6 work string from the surface of the well bore. Ball 68 7 travels by fluid pressure and/or gravity to the conical 8 surface 38 at the upper end 36 of the sleeve 30. The ball 9 68 is funnelled into the helical channel 35 where its progress is arrested. As the ball 68 is now blocking the 11 majority of fluid flow through the bore 42, fluid 12 pressure will build up behind the ball and force the ball 13 along the helical channel 35. Due to the size of the ball 14 a small amount of fluid will be allowed to by-pass the ball 68. This restrictive fluid by-pass ensures that a 16 positive pressure is maintained behind the ball 68 so 17 that the ball 68 does not flow towards the upper end 14 18 of the tool 10 also prevents the ball 68 from 19 chattering' in the channel 35. As the ball 68 makes its way along the channel 35 it acts as a temporary flow 21 restrictor allowing sufficient pressure to build up on 22 the ball 68 and sleeve 30 such that they can move in the 23 direction of applied pressure against the bias of the 24 spring. Consequently the sleeve 30 and ball 68 move to the intermediate position. This position is illustrated 26 in Figure 2(b) and 5(b). Though the ball 68 is at the top 27 of the channel 35 it will be appreciated that this 28 position can be reached with the ball in this position or 29 when the ball 68 has travelled a distance down the channel 35.

32 On reaching the base of the channel 35, at the sleeve 33 port 32, the ball 68 exits the channel 35 and free falls 1 from this point. The tool then moves to the second 2 operating position as described with reference to the 3 previous figures.

As with the earlier embodiments, the tool can be reset 6 and operated in a cyclic manner by the repeated insertion 7 of identical balls 68 into the bore 42.

9 Returning to Figure 1, the tool of the present invention can advantageously include a number of further features.

12 In the embodiment of Figure 1, there is included a choke 13 ring 51. This lies between the sleeve 30 and the body 12.

14 Alternatively it could form a portion of either the sleeve 30 or the body 12. The ring comprises an elongate, 16 cylindrical portion having at an end a substantially 17 longitudinal portion to provide an L' cross section. The 18 ring 51 is arranged close to the sleeve 30 and the body 19 12 to provide a restricted flow path therebetween. The presence and shape of the ring 51 assists in providing a 21 damping action as the sleeve moves in the reverse 22 direction. Fluid, which has to pass the sleeve as it 23 moves downwards is forced to take the restricted flow 24 path in the first direction. This damping helps prevent the mechanical bias e.g. a spring or other parts of the 26 tool 10, from bouncing' into a location which could 27 result in the functional means being moved to an unwanted 28 operating position.

A split ring 81 is also located in the bore 42 of the 31 tool 10. This ring 81 is located below the ports 24,32.

32 The ring 81 is housed in a recess 83 formed on the inner 33 surface 39 of the sleeve 30. The recess 83 includes a 1 conical portion 85 which provides a ramp whose apex is 2 directed toward the ball seat 34. The ring 81 and recess 3 83 are sized such that the ball 68 can pass easily 4 therethrough as it passes through the sleeve 30 from the S upper end 14 to the lower end 16 of the tool 10. However 6 if the ball 68 is, at any time, directed back up the tool 7 10 the ring 81 will prevent its passage. The ball 68 will 8 be influenced by varying fluid pressure and by turbulence 9 within the bore 42 and these may cause the ball 68 to change direction. If the ball 68 changes direction and 11 heads upwards it will contact the ring 81. The ring 81 12 will be moved up the ramp and consequently edges at the 13 split 87 will be brought together as the bore 42 is 14 restricted. The diameter of the ring 81 will decrease sufficiently to a point where it is smaller than the 16 diameter of the ball 68. At this point the ball 68 will 17 stick at the ring 81 and its passage up the bore 42 is 18 prevented. This provides a one-way or non-return feature 19 for the ball 68 within the tool 10.

21 A problem encountered in drop ball activated downhole 22 tools is that when a ball is released from a ball seat it 23 can have a significant force associated with it. A ball 24 travelling through a work string at high velocity can have sufficient kinetic energy and resulting momentum to 26 explode through any further restraining apertures in the 27 work string. This prevents certain types of drop-ball 28 activated tools, such as those with expandable or 29 deformable ball, seats, being located close to each other on a work string and limits the design of some ball 31 catchers. A ball arrester 90 is located in the tool 10 32 to prevent this. The arrester 90 can be formed as part of 33 the sleeve 30 below the ball seat 34 or can be mounted on 1 the sleeve 30 below the ball seat 34. An embodiment of a 2 ball arrester is shown in Figure 6. The arrester 90 has 3 an upper end 92 and a lower end 94. At the upper end 92 4 there is a recess 96 into which a ball seat 34 may be located.

7 As illustrated the arrester may comprise one or more 8 inner surfaces 98 longitudinally arranged between the 9 ends 92,94. In the embodiment shown two surfaces 98a,b are provided. Such an arrangement is easier to machine.

11 On each inner surface 98 there is located a number of 12 transverse ledges 100. Each ledge 100 has a trailing ramp 13 101 towards the lower end 94. The trailing ramp 101 is 14 concave thereby providing a curvature. This curvature guides a ball 68 along the ledge 100. Additionally 16 longitudinally arranged slots or recesses 102 lie 17 perpendicular to the ledges 100 opposing ends of adjacent 18 ledges 100. The ledges 100 and the slots 102 together 19 define a path through the arrester 90. The path is convoluted in that a ball 68 travelling through the 21 arrester 90 is forced to make each transverse crossing 22 before it can fall downwards through the sleeve 30. Each 23 impact of the ball on a ledge 100 slows the ball down and 24 its energy is consequently dissipated through the arrester 90.

27 The path through the arrester 90 is sized such that fluid 28 may pass around the ball 68 during its passage. In this 29 way, the pressure on the ball 68 as it passes through the seat is dissipated before the ball reaches any further 31 ball seats in a tool or in the work string to which it is 32 attached. This prevents a ball exploding' through 33 restrictions in the bore and allows restrictions, such as 1 further ball seats, to be mounted relatively closely to 2 the ball seat 34.

4 Returning again to Figure 1 there is illustrated a second ball seat, generally indicated by reference numeral 110, 6 according to an embodiment of the present invention. The 7 second ball seat 110 is located towards a lower end 16 of 8 the tool 10, below the sleeve 30. In this embodiment the 9 second ball seat 110 is a collet 112, as is known in the art. Collet 112 comprises twelve fingers 114 which are 11 arranged longitudinally in the bore 18. Any number of 12 fingers 114 could be used. The fingers 114 are fixed at a 13 base by being integral with a sleeve 116. The sleeve 116 14 is held to the body 12 so that the collet 112 cannot move longitudinally in the bore 12. The collet 112 is sized so 16 that the fingers 114 rest on the inner surface 46 of the 17 body 12. Each finger 114 has a curved upper edge so that 18 the sleeve 30 can be pushed over the fingers 114. Thus 19 downward movement of the sleeve 30 will cause the sleeve to be pushed between the collet 112 and the body 12. When 21 the sleeve 30 is around the collet 112, the fingers 114 22 are forced radially inwardly and consequently the bore 18 23 is restricted in diameter at this point.

In use, when the tool 10 is moved to the second operating 26 position, the sleeve 30 will be pushed down against the 27 collet 112 and sit between the collet 112 and the body 28 12. Thus as the ball 68 arrives at the collet 112 the 29 clearance through the bore 12 will have been reduced and there will be insufficient space for the ball 68 to pass 31 there through. As a result the ball 68 will be held in 32 the second ball seat 110. Fluidpassing through the bore 33 18 will be substantially prevented from passing the ball 1 seat 110. Axial fluid flow is substantially prevented and 2 this will ensure all fluid flow is through the radial 3 ports 24,32. When a further ball is released into the 4 tool 10, this will cause the sleeve to move back towards the top 14 of the bore 18 and thus the collet 112 is 6 released and the first ball 68 will fall through the tool 7 10. As the sleeve 30 begins to move towards the top 14, 8 the second released ball will fall and hit the first 9 ball. As the sleeve continues to move the second ball seat 110 opens sufficiently to release both balls.

12 An alternative embodiment for the second ball seat could 13 be a trapped C' ring, or split ring. This would work in 14 a similar way to the non-return split ring 81 presented earlier. The ramp would be replaced by the sleeve 30 16 moving down towards the ring. The end of the sleeve would 17 be shaped to slide in behind the ring. Again movement of 18 the sleeve between the ring and the body will cause the 19 ring to be compressed wherein its diameter reduces. A ball will therefore be prevented from passing through the 21 bore and be stopped at the ring. Movement of the sleeve 22 in the first direction will free the ring and, by 23 expansion, the ball can pass through the now increased 24 aperture.

26 A further embodiment of the second ball seat 110 is 27 illustrated in Figure 7. Like parts to those of Figure 1 28 have been given the same reference numeral to aid 29 clarity. Advantageously the second ball seat of this embodiment is a shuttle arrangement, generally indicated 31 by reference numeral 120. The shuttle arrangement 120 32 comprises two semi-cylindrical sleeves 122a,b. The 33 sleeves 122 combine to form a complete sleeve which is 1 located in the body 12. One sleeve 122a is connected to 2 the sleeve 30 and thus moves with the sleeve 30. The 3 other sleeve 122b is fixed to the body 12 towards the 4 lower end 16. The sleeves 122a,b are arranged to overlap in the bore at all times, such that movement of the 6 sleeve brings them into sliding engagement. The sleeves 7 122a,b are sized such that, when the sleeves 122a,b are 8 brought together, the internal bore created has a 9 diameter smaller than the diameter of the balls 68, but that a ball 68 can pass between a sleeve 122a,b and the 11 inner surface 46 of the body 12. A free end 124a,b of 12 each sleeve 122a,b includes a funnel portion 126a,b which 13 presents a ledge or ramp 128a,b towards the free end 14 124a,b. The ledge 128a,b acts as a ball seat if the clearance through the arrangement 120 is insufficient for 16 a ball 68 to pass.

18 In use, the tool 10 will be run in the well bore with the 19 sleeves 122a,b furthest from each other as the sleeve 30 is towards the top 14 of the tool 10. Funnel portions 21 l26a,b overlap and provide a clearance which is greater 22 than the diameter of a ball 68. This provides maximum 23 fluid flow through the tool 10 during run-in. This is 24 illustrated in Figure 7(a) . When a ball 68 is located in the ball seat 34, the sleeve 30 is forced downwards and 26 consequently the sleeves 122a,b are shuttled together in 27 to a substantially overlapping position. Clearance 28 between the sleeves l22a,b is now reduced and a ball 29 would be prevented from passing therethrough as it will be held on the lower ledge 128b. This is as illustrated 31 in Figure 7 (b) . When the ball 68 is released from the 32 ball seat 34 it travels towards the arrangement 120 while 33 the sleeve and consequently the upper sleeve ll2a move 1 upwards by a distance determined by the index sleeve 58.

2 They come to rest at a position illustrated in Figure 3 7(c) . At this position the ball 68 is caught on the 4 ledge 128 as there is insufficient clearance through the arrangement 120. it will be clear that by dropping a 6 second ball through the tool, the sleeve is moved to the 7 illustrated in Figure 7(a) wherein the funnel portions 8 126a,b meet to provide an aperture through which both 9 balls can exit the tool 10.

11 The principal advantage of the present invention is that 12 it provides a downhole tool which can be repeatedly 13 operated by dropping identical balls through the work 14 string. A further advantage is that it provides a circulation tool which can have a number of radial ports 16 to increase the flow area if desired compared with the

17 prior art.

19 Further as the actuating mechanism is located above the ports, the ports are opened with no flow going across the 21 seals. This effectively saves the seals from excessive 22 wear. An additional advantage is in the ability of the 23 index sleeve to lock the circulating ports in position 24 when aligned. Yet further the entry and exit of fluid in the chamber for the spring advantageously reduces the 26 impact on the index pin via a hydraulic damping effect.

27 The incorporation on a ball non-return element 28 advantageously prevents balls travelling back through the 29 tool, while a lower ball seat allows selective blocking of the axial bore, for instance, when radially 31 circulating fluid. Yet further the use of a ball arrester 32 allows the ball seats to be mounted close together, thus 33 reducing the length of the tool.

1 Various modifications may be made to the invention herein 2 described without departing from the scope thereof. For 3 example, more index pins could be used to provide 4 increased stability to the tool and distribute the load S on the pins. Additional radial ports could be located at 6 longitudinal spacings on the tool to provide radial fluid 7 flow across a larger area when the ports are open. The 8 ports may have varying diameters which may provide a 9 nozzle on the outer surface of the body to increase fluid velocity.

Claims (1)

1 CLAIMS 3 1. A ball arrester for dissipating momentum of a ball 4 after

it has passed through a ball seat, the arrester comprising a substantially cylindrical body 6 in which is located a non-linear pathway through 7 which the ball is guided.

9 2. A ball arrester as claimed in Claim 1 wherein the pathway comprises a plurality of surfaces 11 transversely arranged to a central bore.

13 3. A ball seat for a downhole tool, the ball seat 14 comprising a plurality of part cylindrical sleeves which can shuttle with respect to each other, 16 longitudinally in the tool, wherein a ball can only 17 pass through the seat when the sleeves are located 18 at their longitudinal extent.

4. A ball seat for a downhole tool as claimed in Claim 21 3 wherein at least a first sleeve is stationary 22 while at least a second sleeve moves thereover.

24 5. An actuation mechanism for a downhole tool, the mechanism comprising a substantially cylindrical 26 body having a central bore running axially 27 therethrough, a sleeve located within the bore, the 28 sleeve including a deformable ball seat, 29 mechanical biasing means located between the sleeve and the body to bias the sleeve in a first direction 31 and a ball, wherein the deformable ball seat 32 releasably retains the ball to prevent fluid flow 33 through the sleeve and cause the sleeve to move in 1 the reverse direction relative to the body and 2 wherein on release of the ball the seat returns to 3 its original dimensions.

6. An actuation mechanism as claimed in Claim 5 wherein 6 the ball seat comprises a spring.

8 7. An actuation mechanism as claimed in Claim 6 wherein 9 the spring is a plurality of disc springs in a layered structure.

12 8. An actuation mechanism for a downhole tool, the 13 mechanism comprising a substantially cylindrical 14 body having a central bore running axially therethrough, a sleeve located within the bore, the 16 sleeve including a helical channel on an inner 17 surface, mechanical biasing means located between 18 the sleeve and the body to bias the sleeve in a 19 first direction and a ball, sized to run in the helical channel in a reverse direction to prevent a 21 majority of fluid flow through the sleeve and cause 22 the sleeve to move in the reverse direction relative 23 to the body.

9. An actuation mechanism as claimed in Claim 8 wherein 26 the mechanical bias is a strong spring.

28 10. An actuation mechanism as claimed in Claim 8 or 29 Claim 9 wherein the helical channel has a left hand thread so that a ball travelling through the seat 31 travels in the opposite direction to the rotation of 32 the work string.

1 11. An actuation mechanism as claimed in Claim 10 2 wherein a pitch of the thread is greater than or 3 equal to a diameter of the ball intended to pass 4 therethrough.