GB2424234A

GB2424234A - Work string with shaped external flow channel

Info

Publication number: GB2424234A
Application number: GB0605092A
Authority: GB
Inventors: Arthur Stewart
Original assignee: Stable Services Ltd
Current assignee: Stable Services Ltd
Priority date: 2005-03-14
Filing date: 2006-03-14
Publication date: 2006-09-20
Anticipated expiration: 2026-03-14
Also published as: WO2006097706A1; GB0808075D0; GB0505163D0; GB2446085A; GB2424234B; GB2446085B; GB0605092D0

Abstract

A downhole apparatus 10, such as a centraliser, stabiliser, cleaning tool, casing reamer shoe or motor sleeve comprises a tubular main body 12, a flow channel 14b extending at least part way along a length of the body and a flow guide 16b located adjacent an end of the channel. At least one dimension of the channel is non-uniform, and preferably the channel narrows towards its ends. The flow guide may be generally triangular with a vertex adjacent a restriction 32 at an end of the flow channel. In another aspect, the apparatus includes elongate ribs 20a, 20b upstanding from its outer surface 24 defining flow channels there between. Alternatively, the apparatus may comprise a tubing shoe, a sleeve or a cleaning tool having a non-uniform flow channel where an axis of the channel is disposed parallel to the length of the main body.

Description

1 2424234 1 DOWNHOLE APPARATUS 3 The present invention relates to downhole

apparatus for 4 use in the oil and gas exploration and production industry, such as apparatus for use in the drilling and 6 completion of a welibore of an oil or gas well and in 7 subsequent intervention procedures. In particular, but 8 not exclusively, the present invention relates to drill 9 pipe, a centraliser, a stabiliser, a downhole tubing shoe, a reamer, a sleeve or housing of a downhole tool or 11 a tool sub, and/or a cleaning tool.

13 A number of different types of downhole tools and 14 equipment are used in the oil and gas exploration and production industry during the drilling of a weilbore, 16 lining of the drilled bore with a metal casing/liner, and 17 in the subsequent completion of the well to gain access 18 to subterranean hydrocarbon bearing rock formations.

These tools and equipment include, for example, drill 21 strings used in the drilling of a weilbore; stabilisers 22 and centralisers used for centralising equipment in a 23 borehole or downhole tubing; reamers and other cutting S... S...

24 tools used for reaming a drilled borehole wall; and cleaning tools used for cleaning downhole tubing 1 preparatory to completion of a well or in an intervention 2 procedure.

4 In more detail, an oil or gas well is drilled using a drill string which typically comprises lengths of drill 6 tubing sections coupled together end-to-end, with a drill 7 bit at a lower end for performing the task of boring the 8 rock formation. Drill collars, which are relatively 9 heavyweight drill pipe sections, are provided above the bit to assist both in keeping the direction of drilling 11 consistent and to take up much of the loading in the 12 string resulting from the drilling operation. The drill 13 string is typically rotated from surface by a rotary 14 table on a drilling rig, or by a dedicated fluid-driven downhole motor, which drives the drill bit to form a well 16 borehole.

18 During drilling, drilling fluid such as a drilling mud' 19 is pumped into the weilbore through the drill string, exiting through ports in the drill bit and returning to 21 surface along an annulus formed between the drill string 22 and the borehole wall. The drilling fluid serves a 23 number of purposes including cooling the drill bit, and 24 carrying drill cuttings to surface.

26 A number of factors affect the transmission of torque to 27 the bit through the drill string, including vibration of 28 the drill bit; differential sticking due to penetration 29 of clay rich formations; effective removal of cuttings and drilling fluid; and surface friction. * * a t

32 Different downhole tools and aids are typically employed 33 to assist during a drilling operation, and bottomhole 34 assemblies may include stabilisers that provide a stand- 1 off from the welibore walls, the outer surface of the 2 stabiliser providing a snug clearance fit to the weilbore 3 walls. These help to keep the drill pipe and heavyweight 4 drill collar spaced from the weilbore wall, reducing friction and maintaining the drill bit in the correct 6 position within the weilbore, thereby and thus helping to 7 maintain torque on the bit.

9 Known drill string stabilisers are typically cylindrical tubular elements which are fitted around the drill pipe 11 or provided integrally with the pipe, and often include 12 grooves to allow fluid to pass relatively unrestricted 13 upwards through the well borehole. Some known 14 stabilisers have helical groove channels extending around the body of the pipe, which help to remove fluid and 16 debris away from the drill bit or a drill shoe and along 17 the weilbore annulus to surface.

19 In a similar fashion, drill collars of a bottomhole assembly may carry integral stabiliser arrangements of a 21 similar structure, or a stabiliser arrangement of this 22 type may be provided above the drill bit, for a similar 23 purpose of helping to remove fluid and debris away from 24 the bit or shoe to surface.

26 Grooved stabiliser elements are also used during reaming, 27 which is either a secondary drilling process for re- 28 entering an existing welibore, for example for enlarging 29 the weilbore diameter, or for ensuring a drilled borehole is of a desired diameter.

S S

32 Before a weilbore can be completed to gain access to well

I S S...

33 fluids, the well borehole is usually lined with a metal 34 casing, which is cemented in place to prevent the 1 welibore wall from collapsing. The casing typically 2 carries a number of casing centralisers which centralise 3 the casing in the borehole, and ensure that an annulus 4 around the casing outer surface is maintained, to assist in subsequent cementation. Cement is then pumped down 6 the casing and into the annulus, carrying residual 7 drilling fluid ahead of the cement to surface, and it is 8 important that the cement is adequately circulated and 9 distributed around the casing. It is therefore important that casing centralisers allow adequate flow of cement 11 along the annulus.

13 Many casing centralisers are of a type including 14 bowsprings that act against the borehole wall to centralise the casing. However, in a similar manner as 16 for stabilisers, some known centralisers are provided as 17 tubular elements with channels for assisting upward flow 18 of drill fluid and cement, the channels enhancing 19 turbulence of the fluid flowing up the annulus between the casing and the borehole wall.

22 Similar considerations of effectively removing fluid and 23 cuttings from the well bore are pertinent to well 24 cleaning operations that may be performed subsequent to casing the borehole and prior to completion of the well.

27 Although prior art systems have addressed some important 28 issues there remain a number of significant disadvantages 29 with the proposed systems. One particular problem during rotary drilling is differential sticking, where the drill 31 pipe sticks to the wellbore wall. This is particularly 32 common when drilling through clay rich formations, and 33 occurs when the wellbore pressure is greater than the 34 drilled formation pressure. Formations of this type also 1 cause balling' of debris, where solids such as clays 2 stick to the bit and components of the drill string due 3 to fluid clay interaction and pressure.

International Patent Publication No. WO 9105936 6 (Weatherford US, Inc.) discloses a centraliser, 7 stabiliser, or pipe protector with a fluted tubular 8 cylindrical outer surface that directs and channels fluid 9 flow upwards through the wellbore. The tool is designed such that the diameter of the outer surface of the tool 11 varies in order to create regions that produce a nozzle 12 effect on the flow of fluid passed over the tool in the 13 annular space.

The channels are generally elongate in the axial 16 cylindrical direction and may be off-set to the axis, 17 additionally creating a helical path for the fluid. Ribs 18 protrude from the outer surface such that they perform a 19 centralising or stabilising function, creating an annular space between the tubular member and the weilbore wall.

21 The width of the ribs may also vary in order to enhance 22 the nozzle effect on the fluid.

24 Another centraliser is disclosed in US Patent No. 5,881,810 (Weatherford/Lamb, Inc.), which comprises two 26 annular metal members located around a pipe and 27 rectilinear parallel slats attached to the members at an 28 angle to the axis of the weilbore.

A drill tool protector is disclosed in UK Patent 31 Publication No. 2288198 (Hydril), which has a channelled 32 outer surface where two distinct flow paths for fluid are I * SI.

33 provided by diamond shaped protruding elements on the 1 exterior cylindrical and tubular surface of the 2 protector.

4 It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the 6 foregoing disadvantages.

8 According to a first aspect of the present invention, 9 there is provided downhole apparatus comprising: a tubular main body; 11 at least one flow channel, the channel extending at least 12 part way along a length of the body and at least one 13 dimension of the channel being non-uniform; and 14 at least one flow guide located adjacent an end of the channel, the flow guide and the channel together defining 16 a flow path for flow of a downhole medium along the body.

18 The apparatus has a variety of uses in the downhole 19 environment, and is typically coupled to downhole tubing, or provided as part of a downhole tubing string or tool, 21 adapted to be located downhole. In use, the apparatus 22 may be located in an open hole environment (for example, 23 in a drilled borehole), or within existing downhole 24 tubing such as a casing or liner, and downhole medium present in the borehole/tubing may flow past the body 26 along the flow channel.

28 It will be understood that the downhole medium is capable 29 of flow and typically comprises a solids-laden fluids, such as drilling mud (which is utilised, inter alia, to 31 carry drill cuttings to surface); a viscous fluid such as 32 cement; completion fluids; well fluids or the like, or a 33 mixture thereof. It will also be understood that

S S...

34 references herein to at least one dimension of the 1 channel being non-uniform are to said dimension having at 2 least one variation along the length of the channel. The 3 relevant dimensions of the channel may include, for 4 example, one or more of a width, depth and/or length of the channel.

7 By providing downhole apparatus having a flow channel 8 where at least one dimension of the channel is non- 9 uniform, flow characteristics of a downhole medium flowing through the channel (such as velocity, pressure 11 and turbidity) may vary along the length of the channel.

12 This may promote turbulent flow resulting in thorough 13 mixing of constituents of the downhole medium, and/or 14 scouring of surfaces of the channel to prevent adhesion of materials to the channel walls. This may thereby 16 assist in preventing blockage of the channel by, for 17 example, solids such as drill cuttings, mud residues and 18 the like present in the downhole medium. In preferred 19 embodiments, the flow channel may define at least one nozzle, restriction or the like tending to cause an 21 increase in velocity of a downhole medium flowing through 22 the channel, assisting in preventing blockage of the 23 channel by solids in the medium, by jetting the medium 24 through the channel. Furthermore, provision of restrictions of this type may assist clearing of any 26 blockages that may occur, by creating a piston-effect, in 27 use. This is because any blockage will result in an 28 increase in pressure of the medium behind the blockage, 29 tending to urge the blocked solids through the restriction to clear the channel.

32 The apparatus may be dimensioned to be a close fit with a 33 tubing in which the apparatus is located. Where the 34 apparatus is located in open hole, the apparatus may also 1 be dimensioned to be a close fit with the borehole wall, 2 or indeed an interference fit, such that the apparatus 3 may serve for reaming the borehole to a desired diameter.

4 This may be achieved by providing the apparatus with at least one cutting and/or reaming surface, blade or the 6 like. The channel may therefore be adapted to be bound 7 on one side by an internal wall of tubing or the 8 borehole, such that all or most of the flow of downhole 9 medium past the body is directed along the channel.

11 The apparatus may be provided as an integral part of a 12 tool or tubing string, or as a separate component adapted 13 to be coupled to tubing of a tool string or sections of a 14 tubing string such as a length of casing.

16 The apparatus may be a centraliser for centralising a 17 body such as a tubing or tool string within an open hole 18 or within existing downhole tubing such as a casing or 19 liner. For example, during drilling of an oil or gas well, it is necessary to line a drilled borehole with a 21 metal casing, and the apparatus may be a centraliser for 22 centralising such a casing in the drilled borehole prior 23 to cementation. In a variation, the apparatus may be a 24 stabiliser, which may be utilised, for example, for centralising and stabilising a drill string in an open 26 hole during drilling of a borehole. In a further 27 variation, the centraliser/stabiliser may be provided on 28 or as part of a drill collar or other tubing section of a 29 drill string. * * 31 Alternatively, the apparatus may form part of a shoe such 32 as a casing shoe or a drill shoe. A shoe is the 33 lowermost section of a tubing string in a borehole, thus 34 a casing shoe is the lowermost section of a casing string 1 in a borehole. The casing shoe may comprise a drillable 2 lower end, which may be shaped to guide the casing into 3 the borehole, and which may be a jetting nozzle having a 4 jetting port(s) for jetting a fluid into the borehole, to assist passage of the casing. A drill shoe is the 6 lowermost section of a drill string, and may carry a 7 drill bit or the like, or a jetting nozzle; a jetting 8 nozzle may be utilised depending upon the particular rock 9 formation to be drilled, and may be more suitable for relatively soft formations. In a particular embodiment, 11 the apparatus may be a casing shoe reamer which may 12 assist passage of a casing string into a drilled bore, 13 and includes reaming surfaces, such as reaming blades, 14 for reaming the borehole wall. In a similar fashion, the apparatus may alternatively be a drill shoe reamer.

17 Alternatively, the apparatus may be a sleeve or housing 18 of a downhole tool such as a downhole motor and may serve 19 for centralising/supporting the tool within a borehole/downhole tubing. It will be understood that the 21 sleeve may form an outer housing or sleeve of the tool, 22 or may be provided as a separate component adapted to be 23 coupled to the tool. Thus the apparatus may form an 24 outer sleeve or housing of a main part of a motor, or may be provided as a sub adapted to be coupled to a main part 26 of a motor. It will be understood that downhole motors 27 include downhole fluid driven turbines and motors such as 28 Positive Displacement Motors (PDMs). :...:. S...

In a further alternative, the apparatus may be a cleaning 31 tool for cleaning a borehole, and may include at least 32 one of a cleaning or abrading blade, brush, scraper, 33 wiper or the like for cleaning the wall of a downhole 34 tubing.

2 Preferably, the apparatus comprises a plurality of ribs, 3 arms, shoulders or the like, each rib upstanding or 4 extending outwardly from an outer surface of the body, and extending at least part way along a length of the 6 body. The ribs may be spaced around a circumference of 7 the main body, and the channel may be defined between an 8 adjacent pair of ribs. The apparatus may therefore 9 comprise a plurality of channels, and each channel may be defined or bound by an outer surface of the body and side 11 walls of the adjacent ribs. It will be understood that 12 the apparatus may therefore comprise a plurality of flow 13 paths for flow of fluid past the body. In alternative 14 embodiments, the channel may be formed in or by the main body and may therefore be formed in an outer surface of 16 the body.

18 The ribs may have a respective rib main axis, and the 19 ribs may be disposed on the body such that the rib main axes are substantially parallel with one another.

21 Alternatively, at least one of the ribs may be disposed 22 such that the respective rib axis is non-parallel to the 23 rib axis of the other rib, or one or more of the other 24 ribs.

26 Preferably, the ribs are adapted to be coupled to the 27 main body, and may be releasably couplable to the main 28 body to facilitate removal for maintenance and/or 29 replacement. In a variation, part or parts of the ribs..

adapted to contact the borehole/tubing wall may be 31 releasably couplable to a main portion of the rib, for 32 maintenance and/or replacement of said rib part.

33 Alternatively, the ribs may be may be provided as 34 integral parts of the main body. *:::: 2 The apparatus may be adapted to be translated relative to 3 the borehole/downhole tubing with the body in sliding 4 contact with the borehole/tubing wall. To facilitate this movement, the main axis of each rib, and thus of 6 corresponding axes of the channels, may be disposed 7 substantially parallel to a longitudinal axis of the 8 body. Such an arrangement may reduce or avoid generation 9 of a reaction torque in the body due to flow of downhole medium through the channel when the body is translated 11 relative to the borehole/tubing.

13 Alternatively, the main axis of each rib and thus 14 corresponding axes of the channels may be disposed non- parallel to a longitudinal axis of the body, that is, 16 inclined relative to the body axis. For example, in 17 embodiments of the invention, the ribs may be helically 18 oriented and thus may extend in a helical direction 19 around the body. This may be of particular utility where it is desired, for example, to promote turbulence in the 21 downhole medium, which may facilitate cleaning and/or 22 transportation of the medium, in particular any entrained 23 solids, to surface.

The channel may define a corresponding channel axis and 26 the flow guide may be located on or parallel to the 27 channel axis and may be spaced axially along the body 28 relative to the channel. Preferably, the flow guide is 29 located such that downhole medium flowing out of the *: channel impinges on the flow guide (which may assist in 31 preventing blockage of the channel by breaking up and 32 mixing the flow of the downhole medium and thus of the 33 downhole medium constituents), and/or so as to direct 34 downhole medium around the flow guide and into the I channel. It will be understood that the flow guide 2 directs the medium flowing away from or into the channel 3 depending upon the direction of flow of fluid relative to 4 the body.

6 The flow guide may have a first (axially) inward end, 7 relative to the channel, and a second (axially) outward 8 end, relative to the channel. Thus the first end may 9 face inwardly towards the channel and the second end may JO face outwardly. The first end may define a surface 11 facing the channel, the surface having a leading edge or 12 portion and at least two lateral surface portions which 13 extend away from the leading edge and which are inclined 14 relative to the channel axis. For example, the first, inward end of the flow guide may be generally triangular 16 and may be in the shape of an arrow head. The flow guide 17 may therefore form two flow path portions extending 18 around the flow guide for directing medium flowing away 19 from the channel, and/or for directing medium into the channel; it will again be understood that the flow guide 21 directs the medium flowing away from or into the channel 22 depending upon the direction of flow of fluid relative to 23 the body. The flow path portions may be defined between 24 the first end of the flow guide and an adjacent end or area of the main body or ribs forming the channel.

27 Preferably also, the channel has first and second axial 28 ends, and the apparatus comprises two flow guides 29 associated with the channel, one located adjacent to the first end of the channel and the other located adjacent 31 the second end. In this fashion, depending upon the * 32 direction of flow of fluid relative to the apparatus, one 33 of the flow guides may serve for directing fluid into the 34 channel and the other flow guide may serve for directing I fluid flowing out of the channel. Where the apparatus 2 comprises a plurality of channels, the apparatus may 3 comprise at least two flow guides associated with each 4 channel.

6 The channel width and/or depth may be non-uniform along a 7 length of the channel. The channel may define at least 8 one flow restriction where the width and/or depth of the 9 channel is reduced compared to an adjacent portion or area of the channel. This may define a nozzle which may 11 serve, in use, for increasing a velocity of medium 12 flowing therethrough. In a preferred embodiment of the 13 invention, the channel defines two such restrictions, one 14 at or adjacent each end of the channel, with a relatively unrestricted portion (for example, a portion or area of 16 greater width/depth) at a location between the 17 restrictions in a direction along the length of the 18 channel. In this fashion, medium entering the channel 19 may be accelerated through a nozzle (which may promote turbulent flow) and may then enter the area of greater 21 width, where it may slow and mix before being accelerated 22 and jetted through the second restriction (which may 23 again promote turbulent flow). This may successively 24 cause, for example, turbulent, laminar and turbulent flow of the downhole medium.

27 In alternative embodiments, ends of the channel are of 28 greater width relative to a portion or area at a location 29 between the ends in a direction along the length of the channel. However, any other suitable desired 31 arrangement/number of restrictions may be provided in the 32 channel by appropriate shaping thereof. S. *

1 It will be understood that the channel width may be 2 varied according to a spacing between side walls or edges 3 of the channel, whilst the depth (in a radial or outward 4 direction relative to the main body) may be varied according to a wall thickness of the main body and/or 6 depth of the ribs.

8 Where the channel is defined between adjacent ribs, the 9 width of the channel may be varied according to and determined by the shape/dimensions of the ribs. Thus the 11 restrictions in the flow channel may be defined by areas 12 of the ribs of relatively greater width. In preferred 13 embodiments, each rib may have first and second ends of 14 greater width relative to a portion of the rib at a location between said ends. For example, each rib may be 16 elongate and may have ends defining lobes or the like and 17 with a section extending between the lobes of reduced 18 width. Side walls of the ribs may be curved, to define a 19 smooth transition between areas of the rib of larger and smaller width, although in alternative embodiments, it 21 may be desired to provide a sharp transition between said 22 areas of the rib if deemed appropriate in view of desired 23 flow characteristics of medium flowing through the 24 channels.

26 The ribs may define an outer surface adapted to abut an 27 inner wall of a borehole or a tubing in which the 28 apparatus is located, and a diameter described by the 29 ribs may thus be greater than an outer diameter of the main body. The ribs may be shaped such that the ribs are 31 adapted to abut said wall over a majority, for example, 32 75% or more, optionally 90% or more, of an internal 33 circumference of the wall at a selected location or

I S

ISIS

34 locations along the length thereof. This location may I::.

1 correspond to portions of the ribs of greater width.

2 This may, in use, provide improved stability when 3 compared to known apparatus such as prior 4 centralisers/stabilisers. These locations may be spaced apart along the length of the ribs so as to optimise 6 stability of the apparatus, in use. Furthermore, this 7 arrangement of the ribs may facilitate flexing of the 8 apparatus in use, the main body flexing in regions of the 9 body where the ribs are of reduced width.

11 The apparatus may comprise a plurality of flow guides 12 spaced around a circumference of the body, adjacent flow 13 guides defining part of a flow path. Adjacent flow 14 guides may define a circumferential opening therebetween, which may define an inlet and/or outlet of one or more 16 flow path. The openings may be circumferentially spaced 17 or staggered relative to axes of the channels. This may 18 define a tortuous flow path for flow of the downhole 19 medium around the flow guide and through the channel and thus across the body, improving mixing and reducing the 21 likelihood of balling or adhesion of solids in the medium 22 on the apparatus and in particular on the channel walls.

24 Preferably, the apparatus comprises at least one cutting, abrading or reaming surface for abrading the 26 borehole/tubing wall. The rib outer surfaces may each 27 define or carry abrasive particles, such as Tungsten28 Carbide grit, and/or the ribs may define cutting 29 surfaces, for example, edges of the ribs may define cutting blades. The flow guide may have an outer surface 31 carrying abrasive particles, and/or edges of the flow 32 guide may define cutting surfaces. The flow guide may be 33 shaped to define a plurality of cutting surfaces, and one *s..

34 or both of the first and second ends of the flow guide 1 may define a cutting surface. In a particular, preferred 2 embodiment, where the apparatus comprises two flow guides 3 associated with each channel, the second end of one or 4 both of the flow guides may define a relatively aggressive cutting surface, whilst the first end of one 6 or both of the flow guides may define a less aggressive 7 cutting surface. In particular, the second end of the 8 flow guide provided, in use, lowermost on the apparatus 9 may define a relatively aggressive cutting surface. This second end of the lowermost flow guide may face downhole, 11 in use, during running-in of the apparatus. This has a 12 particular utility where the apparatus is a drill shoe or 13 the like, as the aggressive cutting surface forms a 14 reamer that follows a lower drill bit and ensures the drilled borehole is of a desired diameter.

17 According to a second aspect of the present invention, 18 there is provided downhole apparatus comprising: 19 a tubular main body; and a plurality of elongate ribs upstanding from an outer 21 surface of the main body and extending at least part way 22 along a length thereof, adjacent pairs of ribs defining a 23 flow channel therebetween for flow of a downhole medium 24 along the body; wherein the ribs are shaped such that at least one 26 dimension of each channel is non-uniform and such that 27 respective axes of the channels are disposed 28 substantially parallel to a longitudinal axis of the 29 body.

31 According to a third aspect of the present invention, 32 there is provided dohole apparatus comprising: 33 a tubular main body;

I * is.

II I

1 at least one flow channel for flow of a downhole medium 2 along the body, the flow channel having a respective flow 3 channel main axis, the channel extending at least part 4 way along a length of the body and at least one dimension of the channel being non-uniform; and 6 at least one flow guide located adjacent an end of the 7 channel and disposed on the flow channel axis.

9 According to a fourth aspect of the present invention, there is provided a downhole tubing shoe comprising: 11 a tubular main body; 12 at least one flow channel for flow of a downhole medium 13 along the body, the channel extending at least part way 14 along a length of the body, at least one dimension of the channel being non-uniform, and an axis of the channel 16 being disposed substantially parallel to a longitudinal 17 axis of the body.

19 The shoe may be a casing shoe or a drill shoe. The apparatus may define a reamer, thus the apparatus may be 21 a reamer shoe, such as a casing shoe reamer or a drill 22 shoe reamer.

24 According to a fifth aspect of the present invention, there is provided a sleeve for a downhole motor, the 26 sleeve comprising: 27 a tubular main body; 28 at least one flow channel for flow of a downhole medium 29 along the body, the channel extending at least part way along a length of the body, at least one dimension of the 31 channel being non-uniform, and an axis of the channel 32 being disposed substantially parallel to a longitudinal 33 axis of the body. 34 1l

I II Is a

1 According to a sixth aspect of the present invention, 2 there is provided a downhole cleaning tool, the cleaning 3 tool comprising: 4 atubular main body; at least one flow channel for flow of a downhole medium 6 along the body, the channel extending at least part way 7 along a length of the body, at least one dimension of the 8 channel being non-uniform, and an axis of the channel 9 being disposed substantially parallel to a longitudinal axis of the body.

12 According to a seventh aspect of the present invention, 13 there is provided a centraliser comprising: 14 a tubular main body; a plurality of elongate ribs upstanding from an outer 16 surface of the main body and extending at least part way 17 along a length thereof, adjacent pairs of ribs defining a 18 flow channel therebetween, the ribs shaped such that at 19 least one dimension of each channel is non-uniform and such that respective axes of the channels are disposed 21 substantially parallel to a longitudinal axis of the 22 body; and 23 at least one flow guide upstanding from the outer surface 24 of the main body, the flow guide located adjacent an end of the channel such that the flow guide and the channel 26 together define a flow path for flow of a downhole medium 27 along the body.

S.....

28:*::*, 29 According to an eighth aspect of the present invention, there is provided a stabiliser having the features of the 31 seventh aspect of the invention defined above. S... S... 4**S

1 Further features of the second to eighth aspects are 2 defined above in relation to the first aspect of the 3 invention.

Embodiments of the present invention will now be 6 described, by way of example only, with reference to the 7 accompanying drawings, in which: 9 Fig 1 isa perspective view of downhole apparatus in accordance with a preferred embodiment of the present 11 invention; 13 Fig 2 is a repeated view of the downhole apparatus of Fig 14 1 showing certain additional features; 16 Figs 3 and 4 are views of the downhole apparatus of Fig 1 17 viewing in the direction of the arrows B and C of Fig 1, 18 respectively; Fig 5 is a view of part of a drill string in accordance 21 with an alternative embodiment of the invention, shown 22 during drilling of a borehole, the drill string including 23 downhole apparatus similar to the apparatus of Fig 1; Fig 6 is an enlarged, perspective view of part of the 26 drill string of Fig 5; S.....

28 Fig 7 is a perspective view of a drill shoe in accordance 29 with a further alternative embodiment of the invention, including downhole apparatus similar to the apparatus of 31 Fig 1; S...

33 Fig 8 is a perspective view of a casing shoe in 34 accordance with a further alternative embodiment of the.. : 1 invention, including downhole apparatus similar to the 2 apparatus of Fig 1; 4 Figs 9 and 10 are views of the downhole apparatus of Fig 8 viewing in the direction of the arrows G and H of Fig 6 8, respectively; 8 Fig 11 is a perspective view of a cleaning tool in 9 accordance with a further alternative embodiment of the invention, including downhole apparatus similar to the 11 apparatus of Fig 1; 13 Figs 12 and 13 are views of the cleaning tool of Fig 11 14 viewing in the direction of the arrows I and J of Fig 11, respectively; 17 Fig 14 is a further perspective view of the cleaning tool 18 of Fig 11; and Figs 15 and 16 are views of the cleaning tool shown in 21 Fig 14 viewing in the direction of the arrows K and L of 22 Fig 14, respectively.

24 Turning firstly to Fig 1, there is shown a perspective view of a downhole apparatus in accordance with a 26 preferred embodiment of the present invention, the 27 downhole appaiatus indicated generally by reference 28 numeral 10. As will be described in more detail below, 29 the downhole apparatus 10 may take the form of one of a number of different types of downhole tools or equipment.

31 However, in general terms, the downhole apparatus 10 32 comprises a tubular main body 12; at least one flow 33 channel 14, the channel 14 extending at least part-way 34 along a length of the body 12 and at least one dimension 1 of the channel 14 being non-uniform; and at least one 2 flow guide 16 located adjacent to an end 18 of the 3 channel 14, the flow guide 16 and the channel 14 together 4 defining a flow path A for flow of a downhole medium along the body 12.

7 The apparatus 10 serves for promoting improved fluid flow 8 along an annulus defined between the body 12 and the wall 9 of a well borehole or of a tubing in which the apparatus is located. It will therefore be understood that the 11 apparatus 10 may be located in open hole, that is within 12 a drilled borehole of an oil or gas well; within tubing 13 previously located in a borehole such as a casing or 14 liner; or indeed within other tubing such as a tool string. The apparatus 10 therefore has a wide range of 16 potential uses in the downhole environment.

18 There follows a more detailed description of the 19 structure of the downhole apparatus 10, followed by

descriptions of particular tools or equipment

21 incorporating or comprising the apparatus 10.

23 Turning now also to Fig 2, there is shown a further view 24 of the downhole apparatus 10 of Fig 1. Figs 3 and 4 are also referred to, which are views of the downhole 26 apparatus 10 taken in the direction of the arrows B and C 27 ofFigl. * * *

29 The tubular main body 12 includes a plurality, in the illustrated embodiment, three elongate ribs located at 31 120 degree spacings around a circumference of the body 32 12, and two such adjacent ribs 20a, 20b are shown in the 33 drawings. A flow channel 14 is defined between each 34 adjacent pair of the ribs 20, and one such channel 14b is 1 shown and is defined between the ribs 20a, 20b. The 2 channel 14b is bound by respective side walls 22a, 22b of 3 the ribs 20a, 20b and an outer surface 24 of the main 4 body 12.

6 The ribs 20a, 20b are each shaped such that a 7 circumferential width of the channel 14 defined between 8 the rib side walls 22a, 22b varies along a length of the 9 channel 14. In particular, each of the ribs 20a, 20b have respective first and second ends 26 and 28 of a greater 11 circumferential width relative to a central portion 30, 12 and the side walls 22a, 22b are curved along the length 13 of the channel 14.

The respective ends 26a, 26b and 28a, 28b of the ribs 16 20a, 20b define flow restrictions in the form of nozzles 17 32, 34 in the channel 14, which present a restriction to 18 fluid flow, accelerating downhole medium as it enters and 19 exits the channel 14. It will be understood that, in the downhole environment, the downhole medium may typically 21 comprise drilling fluid such as a drilling mud, cement, 22 well fluids, completion fluids and the like or indeed a 23 mixture thereof. These fluids typically carry entrained 24 solids, for example, drilling mud is a mixture of a number of different fluids and abrasive solid particles 26 and, in use, carries solid drill cuttings to surface.

28 In use, a downhole medium such as drilling mud entering 29 the channel 14 is accelerated through the restriction 32, and then slows as it enters a central channel region 36, 31 before being accelerated and jetted through the 32 restriction 34. In this fashion, the drilling mud may 33 transition from laminar flow during approach to the 34 entrance of the channel 14 defining the restriction 32, 1 transitioning to turbulent flow during passage through 2 the restriction 32. The fluid may then return to laminar 3 flow as it enters and travels along the central region 4 36, before again transitioning to turbulent flow during passage through the flow restriction 34. This achieves a 6 thorough mixing of the drilling mud, drill cuttings and 7 the like, which assists in preventing blockage of the 8 channel 14, for example, by adhesion of solids in the 9 drilling mud to the walls of the channel 14. In particular, balling of clay residues is prevented or 11 substantially reduced.

13 The apparatus 10 also includes a set 38 of flow guides 14 16a, 16b, 16c and a further set 40 of flow guides 42a, 42b and 42c, as shown in Fig 2. The three flow channels 16 14 are spaced around the circumference of the main body 17 12 and two of the channels 14a, 14b are shown in Fig 4.

18 Each of the channels 14 includes a respective pair of 19 flow guides and, considering Fig 2, the channel l4b includes a flow guide l6b adjacent the first end and a 21 flow guide 42b adjacent a second end 44.

23 When the apparatus 10 is run into a borehole or downhole 24 tubing, fluid flows upwardly along an annulus between a tool or tubing string (not shown) supporting the 26 apparatus 10, in the direction of the arrow D (Fig 2) 27 The fluid is directed by the flow guide 16b along the S.....

28 flow path A (Fig 1) into the channel 14, flowing out of 29 the second end 44 and directed around the flow guide 42b.

The flow guides 16b and 42b thus serve for directing 31 fluid into the channel l4b, and for directing fluid 32 flowing out of the channel 14b uphole. However, it will *SS 33 be appreciated that fluid flow in an opposite direction E S...

34 will be directed into the channel 14 by the flow guide 1 42b, whilst the fluid flowing out of the channel 14b will 2 be directed by the flow guide 16b.

4 The flow guides 16b, 42b are each located on and thus aligned with an axis 46 of the channel 14b. Each of the 6 flow guides l6b, 42b are shaped to define respective 7 first and second ends 47, 49 as shown in Fig 1. The first 8 end 47 of each guide 16b, 42b forms a surface that faces 9 axially inwardly, towards the channel 14b, whilst the second ends 49 face axially outwardly. The surfaces 47 11 include a leading edge or point 48 that is aligned with 12 the channel axis 46, and lateral surface portions 50, 52 13 that extend away from the leading edge and are inclined 14 relative to the channel axis 46. Accordingly, each flow guide 16b, 42b is generally triangular and in particular 16 is arrow-shaped.

18 In use, fluid flowing in direction D is jetted from the 19 nozzle 34, and impinges upon the leading edge 48, which splits the fluid flow, thoroughly mixing and disrupting 21 the flow of the fluid, to prevent adhesion of solid 22 particles, and directs the fluid along the lateral 23 surface portions 50, 52 and thus away from the body 12.

24 This impinging of the fluid on the leading edge 48 also serves to split or munch' masses of balled or collected 26 solids in the fluid stream, thereby enhancing fluid flow 27 across the body 12. The restrictions/nozzles 32, 34 also 28 assist in clearing any blockages that may occur, by 29 creating a piston-effect, in use. This is because any. : blockage will result in an increase in pressure of the 31 medium behind the blockage, tending to urge the blocked 32 solids through the restriction to clear the channel.

33 This effect may be enhanced in the event of a blockage by 34 repeated advancement and retraction of the apparatus 10 1 up and down the borehole/tubing wall, to create a pumping 2 effect on the blocked materials.

4 Adjacent pairs of the flow guides 16 in the first flow guide set 38 define circumferential openings 6 therebetween, and two such openings are shown in Fig 1 7 and given the reference numerals 54, 56. The flow guides 8 16 are shaped such that the openings 54, 56 also define a 9 flow restriction or nozzle, jetting fluid through the nozzle where it impinges upon an end surface 58 of the 11 rib 20b. In a similar fashion to the flow guide 42b, this 12 enhances mixing of the constituents of the downhole 13 medium. From there, the fluid is directed, for example, 14 along the flow path A between the flow guide 16b lateral surface portion 52 and the rib end surface 58, and thus 16 into the nozzle 32.

18 It will therefore be understood that the arrangement of 19 the first set of flow guides 38, the various channels 14 defined by the ribs 20, and the second set of flow guides 21 42 define a number of flow paths for flow of fluid across 22 the main body 12 of the apparatus 10. These various flow 23 paths provide an efficient mixing of constituents of the 24 downhole medium, and splitting of any balled or accumulated solids in the flowing fluid, thereby 26 preventing blockage of the flow paths and in particular 27 the channels 14, in use. g*s

29 The shape and arrangement of the ribs 20 to define the axially spaced nozzles 32, 34 additionally improves 31 stability of the apparatus 10, in use. This is because 32 the relatively wider sections of the ribs 20 forming the * *** 33 nozzles 32, 34 provide a relatively large circumferential *.S.

34 contact area with a borehole/tubing wall in the locations 1 of the nozzles. Indeed, the ribs 20 may be dimensioned 2 such that the ribs abut the wall over a majority, f or 3 example, 75% or more, optionally 90% or more, of an 4 internal circumference of the wall, at the locations of the nozzles 32, 34. This provides the additional 6 advantage that the apparatus 10 is flexible, in 7 particular in the region 36 where the ribs 20 are of 8 relatively reduced width.

The apparatus 10 additionally defines a number of cutting 11 or abrading surfaces, for reaming a borehole, or for 12 cleaning an inner surface of tubing in which the 13 apparatus is located. In more detail, the end 49 of each 14 flow guide 16 typically forms a relatively aggressive cleaning blade or scraper f or reaming/cleaning during 16 passage of the apparatus downhole. In a similar fashion, 17 the end 49 of each flow guide 42 define less aggressive 18 blades or 3crapers, to provide a reaming/cleaning 19 function when the apparatus is translated uphole. Also, each of the ends 47 of the guides 16 and 42, and the 21 edges of the rib side walls 22, may define blades or 22 scrapers, for providing a rotary reaming/cleaning 23 function. Also, ends of the ribs 20 may define similar 24 such blades. Furthermore, radially outer surfaces of the apparatus 10, such as outer surfaces of the ribs 20 and 26 guides 16, 42 may define or include abrasive particles, 27 and may, for example, be coated with Tungsten-Carbide a.....

28 grit. :*:.

Each of the ribs 20 have respective rib axes 37 (Fig 3), 31 and the ribs 20 are each located on the body 12 such that *.

32 the rib axes 37 are disposed parallel to a longitudinal 33 axis 39 (Fig 4) of the body 12. Accordingly each of the SW 34 corresponding channel axes 46 are similarly disposed *,* : 1 parallel to the body axis 39. Locating the ribs 20 and 2 channels 14 in this fashion improves sliding motion of 3 the apparatus 10 relative to a wall of the borehole! 4 tubing in use, by reducing or avoid generation of a reaction torque in the body 12 due to flow through the 6 channel 14 when the body is translated relative to the 7 borehole/tubing. The shape of the ribs 20 may also be 8 such that the apparatus 10 provides improved contact with 9 a borehole/tubing wall (that is, a greater surface area) when compared to prior apparatus.

12 Also, if desired, a wall thickness of the main body 12 13 may be varied along a length thereof, or in selected 14 locations, to provide variations in the depth of the one or more of the channels 14, creating a similar nozzle 16 effect to the restrictions 32, 34.

18 - There now follows a detailed description of various 19 downhole tools or tubing strings based upon the apparatus 10 of Figs 1-4.

22 Firstly, the apparatus 10 described above may form a 23 sleeve or housing of a downhole tool, in particular, of a 24 downhole motor such as a turbine or PDM. In a variation, the apparatus 10 may form a separate body or sub coupled 26 to such a downhole motor. This may provide improved or 27 enhanced flow of downhole medium, such as drilling fluids *S.S*S 28 and entrained cuttings, along an annulus defined between *.

29 a drill string carrying the motor and the borehole/tubing wall to surface.

31 * *1 $0 ** 32 Fig 5 is a view of part of a drill string 60 shown during 33 drilling of a borehole 62. The drill string is comprised 0 34 of a number of tubing sections 63 coupled together end- 1 to-end with a bottomhole assembly 64 provided lowermost 2 in the string. The assembly 64 includes two or more 3 tubing sections 66, 68 coupled together, the tubing 4 section 68 being coupled in-turn to a number of relatively heavy drill collars, one of which is shown and 6 indicated by reference numeral 70. The drill collars 70 7 are provided above a drill bit (not shown) which is 8 lowermost in the assembly, which is used for drilling the 9 borehole 62. Also, the tubing sections 66, 68 each carry a respective stabiliser 110, 210, each of which is 11 identical in structure and operation to the apparatus 10 12 of Figs 1-4, and the stabiliser 110 is shown in more 13 detail in the enlarged perspective view of Fig 6. Like 14 components of the stabilisers 110, 210 (and indeed of further tools/equipment that will be described below) 16 with the apparatus 10 of Figs 1 to 4 share the same 17 reference numerals incremented by 100, 200 etc. 19 In use, during drilling of the borehole 62, drilling mud is pumped down through a bore 72 of the drill string 60, 21 exiting through nozzles or jetting ports in the drill 22 bit, thereby cooling the bit and carrying drill cuttings 23 to surface along an annulus 74 defined between an outer 24 surface of the string 60 and an inner wall 76 of the borehole 62.

27 The stabilisers 110, 210 each serve to stabilise and 28 centralise the drill string 60 within the borehole 62 and a..

29 to assist in passage of drilling fluid and drill cuttings to surface, as described above. Furthermore, the reaming 31 surfaces and blades of the stabilisers 110, 210 ream the 32 borehole wall 76, to ensure that the borehole is of a 33 desired diameter for subsequent operations including 34 installation of a borehole casing. .. : 2 Turning now to Fig 7, there is shown a perspective view 3 of a drill shoe 80 including a stabiliser 310 of similar 4 structure and operation to the apparatus 10 shown in Figs 1-4. The stabiliser 310 is particularly suited for 6 drilling a borehole in relatively soft formations, for 7 example, clay based formations, and includes a drillable 8 jetting nozzle 82 provided lowermost on the drill shoe 9 310. In use, drilling fluid flows down through an internal bore of the assembly 80, and is jetted in the 11 direction F out of ports in the jetting nozzle 82, one of 12 which is shown in Fig 7 and given the reference numeral 13 84.

In a similar fashion to the stabilisers 110, 210 on the 16 drill string 60 of Fig 5, the stabiliser 310 stabilises 17 the drill string, and reams the borehole to a desired 18 diameter, if required.

Turning now to Fig 8, there is shown a perspective view 21 of a casing shoe 86 having a casing shoe reamer 410 of 22 similar structure to the apparatus 10 of Figs 1-4. The 23 casing shoe 86 is also shown in Figs 9 and 10, which are 24 views taken in the direction of the arrows G and H shown in Fig 8. The casing shoe 86 is essentially similar to 26 the drill shoe reamer 80 of Fig 7. However, the casing 27 shoe 86 is provided lowermost on a string of casing to be 28 run in to a drilled borehole, located in the borehole and 29 cemented in place.

31 The centraliser 410 serves for centralising the casing 32 within the borehole, and a number of such centralisers e..

33 410 are provided spaced along the length of the casing.

34 Also, in a similar fashion to the drill shoe stabiliser 1 310 of Fig 7, the casing shoe centraliser 410 (and indeed 2 the further centralisers 410 spaced along the length of 3 the casing) act as a reamer during passage of the casing 4 along the borehole.

6 The casing shoe 86 includes a jetting nozzle 482 similar 7 to the nozzle 82 of the drill shoe 80, for jetting fluids 8 into the borehole to assist in passage of the casing 9 along the borehole, and the jetting nozzle 482 is drillable to allow subsequent cementation of the casing 11 in the borehole and indeed further downhole procedures.

13 Turning now to Fig 11, there is shown a perspective view 14 of a cleaning tool 510. The cleaning tool 510 is also shown in the views of Figs 12 and 13, which are taken in 16 the direction of the arrows I and J in Fig 11, 17 respectively.

19 The cleaning tool 510 is of similar structure to the apparatus 10 of Figs 1-4. However, each rib 520 of the 21 cleaning tool 510 includes a longitudinal recess 88, 22 shown in Fig 14 and the views of Figs 15 and 16, taken in 23 the directions K and L of Fig 14. The recesses 88 each 24 receive respective cleaning brushes 90, which serve for cleaning an internal wall of a tubing (not shown) in 26 which the cleaning tool is located, by translation and/or 27 rotation of the tool 510 within the tubing. The brushes S.....

28 90 are releasably secured to the ribs 20 within the 29 recesses 88 and may thus be removed for maintenance * : and/or replacement, as required. Also, alternative types 31 of cleaning equipment, such as scrapers, wipers, blades 32 or the like may be mounted in the recesses 88, or a * S..

33 combination of such equipment may be provided. *.. * * S

34 Furthermore, alternative tools or equipment may be 1 located in the recesses 88, such as stabiliser arms, 2 elements or shoulders, to facilitate use of the apparatus 3 within boreholes and/or tubing of varying diameters, by 4 provisions of appropriately sized arms.

6 Various modifications may be made to the foregoing 7 without departing from the spirit and scope of the 8 present invention.

For example, the relevant dimensions of the channel that 11 vary may include a depth and/or length of the channel.

13 The channel may be formed in or by the main body and may 14 therefore be formed in an outer surface of the body.

16 At least one of the ribs may be disposed such that the 17 respective rib axis is non-parallel to the rib axis of 18 the other rib, or one or more of the other ribs.

The ribs may be may be provided as integral parts of the 21 main body.

23 The main axis of each rib and thus corresponding axes of 24 the channels may be disposed non-parallel to a longitudinal axis of the body, that is, inclined relative 26 to the body axis. For example, in embodiments of the 27 invention, the ribs may be helically oriented and thus 28 may extend in a helical direction around the body. This 29 may be of particular utility where it is desired, for example, to promote turbulence in the downhole medium, 31 which may facilitate cleaning and/or transportation of 32 the medium, in particular any entrained solids, to 33 surface.

S S 34 S

1 Ends of the channel may be of greater width relative to a 2 portion or area at a location between the ends in a 3 direction along the length of the channel. However, any 4 other suitable desired arrangement/number of restrictions may be provided in the channel by appropriate shaping 6 thereof.

8 It may be desired to provide a sharp transition between 9 areas of the rib of differing dimensions if deemed appropriate in view of desired flow characteristics of 11 medium flowing through the channels. * I

I * I.. * * I * S * * * S S S. IS ISS* * S ***. S.

Claims

1 Claims 3 1. Downhole apparatus comprising: a tubular main body; 4 at

least one flow channel, the channel extending at least part way along a length of the body and at 6 least one dimension of the channel being non7 uniform; and at least one flow guide located 8 adjacent an end of the channel, the flow guide and 9 the channel together defining a flow path for flow of a downhole medium along the body.

12 2. The apparatus as claimed in Claim 1, wherein the 13 apparatus is dimensioned to be a close fit with a 14 tubing or borehole in which the apparatus is located.

17 3. The apparatus as claimed in Claim 1 or Claim 2, 18 further provided with at least one cutting and/or 19 reaming surface.

21 4. The apparatus as claimed in any of Claims 1 to 3 22 wherein the channel is adapted to be bound on one 23 side by an internal wall of tubing or the borehole, 24 such that all or most of the flow of downhole medium past the body is directed along the channel.

27 5. The apparatus as claimed in any preceding claim, 28 wherein the apparatus is a centraliser for 29 centralising a body such as a tubing or tool string within an open hole or within existing downhole 31 tubing. 4#

33 6. The apparatus as claimed in any of Claims 1 to 4 34 wherein the apparatus is a stabiliser for 1 stabilising a drill string within an open hole or 2 within existing downhole tubing.

4 7. The apparatus as claimed in any preceding claim, wherein the apparatus is provided as an integral 6 part of a drill pipe.

8 8. The apparatus as claimed in any of Claims 1 to 4 9 wherein the apparatus forms part of a shoe such as a casing shoe or a drill shoe.

12 9. Apparatus as claimed in Claim 8 wherein the 13 apparatus forms part of a casing shoe reamer which 14 includes reaming surfaces for reaming the borehole wall.

17 10. Apparatus as claimed in Claim 8 wherein the 18 apparatus forms part of a drill shoe reamer which 19 includes reaming surfaces for reaming the borehole wall.

22 11. The apparatus as claimed in any of Claims 1 to 4, 23 wherein the apparatus is a sleeve of a downhole 24 motor.

26 12. The apparatus as claimed in any of Claims 1 to 4, 27 wherein the apparatus is a wellbore cleaning tool.

S S S

29 13. The apparatus as claimed in Claim 12, further comprising at least one of a cleaning or abrading 31 blade, brush, scraper, or a wiper. IS..

33 14. The apparatus as claimed in any preceding claim, " *1SP 34 further comprising a plurality of ribs, each rib 1 upstanding or extending outwardly from an outer 2 surface of the body, and extending at least part way 3 along a length of the body.

15. The apparatus as claimed in Claim 14, wherein the 6 ribs are spaced around a circumference of the main 7 body, and the channel is defined between an adjacent 8 pair of ribs.

16. The apparatus as claimed in Claim 14 or Claim 15, 11 further comprising a plurality of channels, each 12 channel defined or bound by an outer surface of the 13 body and side walls of the adjacent ribs.

17. The apparatus as claimed in Claim 16, wherein the 16 side walls of each rib are curved to define a smooth 17 transition between areas of the rib of larger and 18 siuallerwidth.

18. The apparatus as claimed in any of Claims 14 to 17, 21 wherein the ribs have a respective rib main axis, 22 and the ribs are disposed on the body such that the 23 rib main axes are substantially parallel with one 24 another.

26 19. The apparatus as claimed in any of Claims 14 to 18, 27 wherein each rib have first and second ends of 28 greater width relative to a portion of the rib at a 29 location between said ends.

31 20. The apparatus as claimed in any of Claims 14 to 19, 32 wherein each rib is elongate and have ends defining 33 lobes with a section extending between the lobes of 34 reduced width. *. ,

2 21. The apparatus as claimed in Claims 14 to 20, wherein 3 the ribs define an outer surface adapted to abut an 4 inner wall of a borehole or a tubing in which the apparatus is located.

7 22. The apparatus as claimed in any preceding claim, 8 wherein the channel defines a corresponding channel 9 axis and the flow guide is located on or parallel to the channel axis and is spaced axially along the 11 body relative to the channel.

13 23. The apparatus as claimed in any preceding claim, 14 wherein the flow guide is located such that a downhole medium flowing out of the channel impinges 16 on the flow guide.

18 24. The apparatus as claimed in any preceding claim, 19 wherein the flow guide has a first inward end, relative to the channel, and a second outward end, 21 relative to the channel.

23 25. The apparatus as claimed in Claim 24 wherein the 24 first, inward end of the flow guide is generally triangular and in the shape of an arrow head.

27 26. The apparatus as claimed in any preceding claim, 28 wherein the channel has first and second axial ends, 29 and the apparatus comprises two flow guides associated with the channel, one located adjacent to 31 the first end of the channel and the other located 32 adjacent the second end. S... *SSS * S.. * S S *. .

1 27. The apparatus as claimed in any preceding claim, 2 wherein the apparatus comprises at least two flow 3 guides associated with each channel.

28. The apparatus as claimed in any preceding claim, 6 wherein the channel width is non-uniform along a 7 length of the channel.

9 29. The apparatus as claimed in any preceding claim, wherein the channel defines at least one flow 11 restriction where the width of the channel is 12 reduced compared to an adjacent portion or area of 13 the channel.

30. The apparatus as claimed in Claim 29, wherein the at 16 least one flow restriction defines a nozzle which 17 serves, in use, for increasing a velocity of medium 18 flowing theiethrough.

31. The apparatus as claimed in Claim 29 or Claim 30, 21 wherein the channel defines two such restrictions, 22 one adjacent each end of the channel, with a 23 relatively unrestricted portion at a location 24 between the restrictions in a direction along the length of the channel.

27 32. The apparatus as claimed in any preceding claim, 28 wherein the apparatus comprises a plurality of flow 29 guides spaced around a circumference of the body, adjacent flow guides defining part of a flow path.

32 33. The apparatus as claimed in Claim 32, wherein the 33 adjacent flow guides define an opening therebetween, S * S. * 1 which define an inlet or outlet of one or more flow 2 paths.

4 34. The apparatus as claimed in Claim 33, wherein the openings are circumferentially spaced or staggered 6 relative to axes of the channels.

8 35. The apparatus as claimed in any preceding claim, 9 wherein the apparatus comprises at least one cutting, abrading or reaming surface for abrading 11 the borehole/tubing wall.

13 36. The apparatus as claimed in any preceding claim, 14 wherein the flow guide is shaped to define a plurality of cutting surfaces, and one or both of 16 first and second ends of the flow guide define a 17 cutting surface.

19 37. The apparatus as claimed in Claim 36 when dependent on Claim 32, wherein the second end of one or both 21 of the flow guides defines a relatively aggressive 22 cutting surface, whilst the first end of one or both 23 of the flow guides define a less aggressive cutting 24 surface.

26 38. The apparatus as claimed in Claim 37, wherein the 27 second end of the flow guide provided, in use, 28 lowermost on the apparatus defines the relatively 29 aggressive cutting surface.

31 39. A downhole apparatus comprising a tubular main body; 32 and a plurality of elongate ribs upstanding from an 33 outer surface of the main body and extending at S...

34 least part way along a length thereof, adjacent

I S S* S

1 pairs of ribs defining a flow channel therebetween 2 for flow of a downhole medium along the body; 3 wherein the ribs are shaped such that at least one 4 dimension of each channel is non-uniform and such that respective axes of the channels are disposed 6 substantially parallel to a longitudinal axis of the 7 body.

9 40. A downhole apparatus comprising: a tubular main body; at least one flow channel for flow of a 11 downhole medium along the body, the flow channel 12 having a respective flow channel main axis, the 13 channel extending at least part way along a length 14 of the body and at least one dimension of the channel being non- uniform; and at least one flow 16 guide located adjacent an end of the channel and 17 disposed on the flow channel axis.

19 41. A downhole tubing shoe comprising: a tubular main body; at least one flow channel for flow of a 21 downhole medium along the body, the channel 22 extending at least part way along a length of the 23 body, at least one dimension of the channel being 24 non-uniform, and an axis of the channel being disposed substantially parallel to a longitudinal 26 axis of the body.

28 42. A downhole tubing shoe as claimed in Claim 41, 29 wherein the shoe is a casing shoe. :**:.

31 43. A downhole tubing shoe as claimed in Claim 41, 32 wherein the shoe is a drill shoe. *0 t a

1 44. A downhole tubing shoe as claimed in Claim 41, 2 wherein the shoe is a reamer shoe.

4 45. A downhole tubing shoe as claimed in Claim 41, wherein the shoe is a drill shoe reamer.

7 46. A sleeve for a downhole motor, the sleeve 8 comprising: a tubular main body; at least one flow 9 channel for flow of a downhole medium along the body, the channel extending at least part way along 11 a length of the body, at least one dimension of the 12 channel being non-uniform, and an axis of the 13 channel being disposed substantially parallel to a 14 longitudinal axis of the body.

16 47. A downhole cleaning tool, the cleaning tool 17 comprising: a tubular main body; at least one flow 18 channel for flow of a downhole medium along the 19 body, the channel extending at least part way along a length of the body, at least one dimension of the 21 channel being non-uniform, and an axis of the 22 channel being disposed substantially parallel to a 23 longitudinal axis of the body.

48. A centraliser comprising: a tubular main body; a 26 plurality of elongate ribs upstanding from an outer 27 surface of the main body and extending at least part 28 way along a length thereof, adjacent pairs of ribs 29 defining a flow channel therebetween, the ribs shaped such that at least one dimension of each 31 channel is non-uniform and such that respective axes 32 of the channels are disposed substantially parallel 33 to a longitudinal axis of the body; and at least one 34 flow guide upstanding from the outer surface of the I main body, the flow guide located adjacent an end of 2 the channel such that the flow guide and the channel 3 together define a flow path for flow of a downhole 4 medium along the body.

6 49. A stabiliser having the features of any of Claims 39 7 to 48 the seventh aspect of the invention defined 8 above. * .

S..... S... * S S

S S * S *5 *S *5S* S...