GB2412393A

GB2412393A - Apparatus and method for mobilising drill cuttings in a well

Info

Publication number: GB2412393A
Application number: GB0506031A
Authority: GB
Inventors: Ian Alistair Kirk; William Barron; Alistair Bertram Clark
Original assignee: Downhole Products Ltd
Current assignee: Downhole Products Ltd
Priority date: 2004-03-26
Filing date: 2005-03-24
Publication date: 2005-09-28
Anticipated expiration: 2025-03-24
Also published as: NO20064040L; US20070215388A1; AU2005225802A1; EP1727960A1; GB0506031D0; GB2412393B; CA2558471A1; GB0616092D0; WO2005093204A1; GB2427225A; GB2427225B

Abstract

Apparatus for mobilising drill cuttings in a well comprises at least one vane 12 and two or more blades 15. The two or more blades 15 define at least one fluid conduit between adjacent blades 15. The blades 15 and the or each vane 12 are rotatable relative to one another. The or each vane 12 can be provided on a sleeve 5. The blades can be mounted on a bushing 7 that is rotatably mounted on the sleeve 5. The blades 15 may be shaped in the form of foils and a cross section through the blades is in the form of an hour glass. The at least one vane 12 may be curved and have a sinusoidal shape. The invention also includes a drill cutting assembly comprising a tubular, at least one vane, and two or more blades and a method of agitating drill fluid in an oil or gas well comprising passing the drill fluid past at least one vane rotatable relative to two or more blades.

Description

24 1 2393 1 "Apparatus and Method" 3 The present invention relates to

apparatus for 4 mobilizing drill cuttings in an oil or gas well.

6 The art of drilling wellbores for recovery of oil 7 and gas is well known. One particular problem faced 8 by this art is the removal of cuttings from the well 9 as they are generated by the action of the drill bit cutting into the formation. The cuttings need to be 11 removed from the bit and conveyed back to surface as 12 efficiently as possible, as their persistence in the 13 wellbore hampers drilling activity, and tends to 14 reduce the productivity of the well.

16 Cuttings are washed back to surface by drilling mud 17 or fluid pumped down the string, out through the 18 bit, and back up the annulus surrounding the string.

19 This solution is generally satisfactory, but in long and deviated wells we have found that cuttings still 21 tend to clump and impede the drilling activity, or 22 the production of the well.

1 According to the present invention there is provided 2 apparatus for mobilising drill cuttings in a well, 3 the apparatus comprising at least one vane, and two 4 or more blades defining at least one fluid conduit between adjacent blades, the blades and vane being 6 rotatable relative to one another.

8 Typically the blades are configured to create a 9 pressure difference in fluid flowing through the TO conduit, but this is not essential, and a fluid 11 drop, if required, can be induced by other means 12 apart from the blades.

14 The apparatus typically comprises a sleeve or collar, which is typically tubular and is adapted to 16 fit over a string in the well. The string can be a 17 tubing string, drill string, or casing string etc. 18 Typically the vanes are provided on the sleeve.

Typically the blades are mounted on a bushing that 21 is rotatably mounted on the sleeve.

23 However, in certain simple embodiments, it is 24 sufficient to provide the vanes direct on the tubing string (or on a sleeve attached to the string) and 2 6 to provide the blades on an adjacent part of the 27 string, or on a separate sleeve attached thereto, so 28 that the blade-bearing bushing is not directly 29 attached to the vane-bearing sleeve. The blades or 3 0 the bushing can optionally be incorporated into a 31 sub in the string, or on a collar that is separately 32 attached to the string.

J

1 Typically the sleeve is adapted for attachment to a 2 drill string, and the fixing means typically 3 comprises a clamp means such as an annular clamp to 4 fix the sleeve over the outer surface of the drill pipe. However, the sleeve may equally attach to

6 casing or any other oilfield tubular goods.

8 The vanes can be carried direct on the sleeve, or in 9 some embodiments can be provided on a separate bushing rotationally (or otherwise) affixed to the 11 sleeve. The vanes typically rotate with the drill 12 string in normal rotary drilling operations as they 13 are typically rotationally fixed to the drill 14 string. The rotation of the vanes agitates the fluid surrounding the apparatus, and creates thrust 16 tending to drive the fluid past the sleeve.

17 The blades of the bushing typically create a 18 pressure drop in the fluid as it flows past the 19 apparatus, driven by the rotation of the vane(s).

21 Typically the bushing is free to rotate relative to 22 the sleeve, which is affixed to the drill string.

23 Thus, upon rotation of the drill string (or casing) 24 during normal rotary drilling, the bushing typically remains stationary relative to the wellbore, while 26 the drill string rotates.

28 Typically the blades on the bushing project radially 29 outward to a greater extent than the vanes of the sleeve, so that the radially outermost surface of 31 the blades contacts the inner surface of the bore 32 within which the string is located, and this 1 centralises the sleeve within the bore. In 2 preferred embodiments, the vanes are radially lower 3 than the blades, and can freely rotate within the 4 bore, as the higher blades provide a stand off against the inner surface of the bore. The bore can 6 be the unlined wellbore, or can be the bore of 7 casing, liner or other tubing in which the apparatus 8 i s located.

The blades can be set parallel to the axis, or can 11 be offset with respect to it, so that they extend 12 helically around the bushing. In some embodiments 13 the blades are offset at an angle of 3-10 e.g. 5 14 from top left to bottom right with respect to the axis of the bushing. This orientation is useful in 16 drillstrings that are conventionally rotated to the 17 right, as the fluid path up the annulus tends to 18 flow in a spiral from bottom right to top left at 19 around 5 off the axis. Therefore, the offset blades do not substantially impede the fluid flow 21 rate. Clearly adjustments can be made to the offset 22 angle to suit the fluid flow direction in other 23 wells.

The blades typically have an asymmetric profile, and 26 in preferred embodiments the blades are shaped in 27 the form of foils, so that the fluid conduits 28 defined between adjacent blades on the bushing 29 change in profile. Typically the fluid conduits are relatively narrow at a lower end (nearest the drill 31 bit) and grow relatively wider toward the upper end 32 (furthest away from the bit). The increase in - ) 1 dimension from the bottom of the channel to the top 2 causes a pressure drop in the fluid flowing through 3 the channel.

The blades can have profiled cross sections (i.e. 6 end-on view) in the form of an hour glass, with a 7 wide root radially innermost adjacent the bushing, a 8 wide top at the radially outermost part of the blade 9 that bears against the borehole wall, and a narrower cutaway portion between the two to facilitate fluid 11 flow between the blades. This cutaway creates more 12 space for the fluid to pass between the blades, and 13 helps to avoid impedance of the fluid flow.

Typically the bushing can be formed from a rigid 16 material, such as hard rubber or metal. The sleeve 17 is typically formed from metal such as steel, alloy, 18 aluminium, etc. The sleeve can have an annular body to fit around a 21 tubular or string of tubulars. The annular body can 22 have the vanes integrally formed with it, for 23 example by moulding the sleeve and vanes as a single 24 piece. In alternative (and preferred) embodiments, the sleeve can have vane-receiving recesses therein 26 to receive and retain modular vanes, which can be 27 slotted in the recesses, and retained therein. This 28 has the advantage that several different sizes of 29 vanes can be used with a single sleeve.

1 Likewise, the blades on the bushing can be modular 2 and can be received within blade recesses in the 3 same manner.

The vanes can be curved or straight, and can lie 6 parallel to the axis, but in typical embodiments 7 they cross the axis of the sleeve so as to scoop the 8 fluid from the annulus. The lower end of the vane 9 is typically circumferentially spaced around the sleeve from the upper end, typically in the 11 direction of rotation of the string, so where the 12 string rotates to the right (as is conventional in 13 most wells) the vanes are offset across the axis 14 from top right to bottom left, the opposite configuration from the offset blades described 16 above. !

18 In some embodiments the vanes are configured in a 19 sinusoidal "lazy-s" shape and this helps to agitate the fluid surrounding the apparatus during rotation.

21 In other embodiments, they are disposed straight 22 across the axis.

24 The vanes can have concave surfaces to assist in the scooping action, and typically the concave surfaces 26 can be provided in one side of the vane only, 27 typically on the side of the vane facing the 28 direction of rotation. The concave surface can be 29 regular and unchanging along the side of the vane, but in some embodiments the side vane is shaped to 31 have more of a curve on its upper end than on its 32 lower end, so that as the fluid moves up the side of

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1 the vane, the increasing curve of the concave 2 surface keeps the fluid close to the sleeve, where 3 most turbulence will be generated, thereby keeping 4 the cuttings in suspension for longer.

6 The or each vane can be provided with a notch cut 7 away from a radially outermost portion of the vane.

8 Several notches may be provided on each vane. The 9 notches can serve to introduce additional turbulence or induce a vortex as the vane is rotated to agitate 11 drill cuttings and entrain them into the flow of 12 fluid up the annulus. I 13

14 The invention also provides a drill cuttings agitation assembly, comprising a tubular, a vane, 16 and at least two blades defining at least one fluid 17 conduit between adjacent blades, wherein the vane 18 and the blades are rotatable relative to one 19 another.

21 The invention also provides a method of agitating 22 drill fluid in an oil or gas well, the method 23 comprising passing the drill fluid past a vane 24 rotatable relative to at least two blades.

26 An embodiment of the invention will now be described 27 by way of example and with reference to the 28 accompanying drawings, in which: Fig. 1 is a side view of apparatus according to 31 the present invention, mounted on a tubular; 1 Fig. 2 is a close up side view of the Fig 1 2 apparatus; 3 Fig. 3 is a side view of a sleeve of the Fig 1 4 apparatus; Fig. 4 is a side view of a bushing of a bushing 6 of the Fig 1 apparatus; 7 Fig. 5 is a side view of a clamp of the Fig 1 8 apparatus; 9 Figs. 6 and 7 (respectively) plan and underside views of the Fig 4 bushing; 11 Fig. 8 is a flat view of a bushing half shell; 12 Fig. 9 is a side view of a bushing blade; 13 Fig. 10 is a plan view of a sleeve; 14 Fig. 11 is a sectional view through a clamp; Fig. 12 is an outer side view of a second 16 sleeves 17 Fig. 13 is an inner side view of the second 18 sleeve; 19 Fig. 14 is a sectional view through the second sleeve; 21 Fig. 15 is a perspective view of a modular vane 22 for the second sleeve; 23 Fig. 16 is an underneath view of the Fig 15 24 vane; Fig. 17 is a plan view of the Fig IS vane; 26 Fig. 18 is a side view of the same vane; 27 Fig. 19 is a side view of a second embodiment 28 of apparatus mounted on a tubular; 29 Fig. 20 is a sectional view from beneath the Fig. 19 apparatus at point A; 31 Fig. 21 is a sectional view from beneath the 32 Fig. 19 apparatus at point B; l trF 1 Fig. 22 is a plan of a vane; 2 Fig. 23 is a plan view of a second vane; and 3 Fig. 24 is a plan view of a vane having a cut 4 out portion.

6 Referring now to the drawings, apparatus for 7 mobilising drill cuttings in a well comprises a 8 sleeve 5, a bushing 7 and a clamp 9. All of these 9 components are generally tubular, but are axially divided into two separate leaves that are hinged 11 together. The leaves of the sleeve 5 are hinged at 12 three locations 5h, and its two leaves pivot around 13 those hinges to enable the sleeve 5 to be opened and 14 closed around a tubular T such as drill pipe or casing. The two halves of the sleeve are locked 16 together by one or more bolts 5b at a position 17 diametrically opposite to the hinge 5h, so that the 18 sleeve 5 can be tightly fastened to the tubular T by 19 means of the bolts.

21 The hinges 5h are located on an upper part of the 22 sleeve 5, beneath which is a bearing region 6 having 23 a reduced outer diameter as compared with the 24 nominal diameter of the upper region. An annular groove 6g is formed on the lower end of the bearing 26 region 6, and a shoulder 6s divides the upper and 27 bearing regions of the sleeve.

29 The bushing 7 is also formed as two separate leaves that are connected together at diametrically opposed 31 positions by interlocking castellations and 32 connecting pins 7p, about which the two leaves can 1 pivot. The two leaves of the bushing 7 are 2 typically closed around the bearing region 6 of the 3 sleeve, at which point the leaves are connected 4 together by inserting the pins 7p into axially aligned bores on the interlocking castellations to 6 close and lock the bushing 7, so that the bushing 7 7 is connected to the sleeve 5.

9 After the bushing 7 has been locked in place around the bearing region 6 of the sleeve 5, the clamp 9 is 11 then placed around the lower end of the bearing 12 region 6, so that an annular lip on the internal 13 surface of the clamp 9 engages in the external 14 annular groove 6g on the lower part of the bearing region 6. The clamp 9 is then closed and fastened 16 by means of bolts (not shown) in the same manner as 17 the bolts Sb that lock the sleeve closed around the 18 tubular T. When thus assembled, the tightening of the bolts in 21 the sleeve 5 and the clamp 9 securely connects the 22 sleeve to the tubular, so that the two are 23 rotationally connected, and thus the sleeve rotates 24 with the tubular.

26 The bushing 7 is fixed to the bearing area 6 of the 27 sleeve, and is prevented from axial movement by the 28 shoulder 6s above it, and the clamp 9 below it; 29 however, the bushing 7 is free to rotate around its axis relative to the sleeve and the clamp, and the 31 tolerance of the outer diameter of the bearing 32 region 6 and the inner diameter of the bushing 7 are 1 chosen to permit a degree of play between the two, 2 and allow rotation of the bushing 7 around the axis 3 of the sleeve 5.

The sleeve 5 has vanes 12 mounted on the upper large 6 diameter section. As best shown in Fig. 10, two 7 vanes 12 are mounted on each leaf of the sleeve, and 8 the vanes are spaced apart on the circumference of 9 the assembled sleeve 5 at equal distances, so that the vanes 12 are arranged in diametrically opposed 11 pairs.

13 The vanes 12 have a generally sinusoidal "lazy-S" 14 shape with a lower scoop 12s, a generally axial mid region 12m, and an upper deflector portion 12d.

17 In side profile, the vanes 12 are generally arcuate 18 in the scoop and deflector regions, rising from the 19 plane of the sleeve 5 in a regular arc until a plateau is reached at the mid-section 12m. Fig. 18 21 shows the side profile of a typical vane 12. The 22 vanes 12 project radially from the outer surface of 23 the sleeve 5, so as to create between adjacent vanes 24 12 a fluid path that is generally sinusoidal in shape.

27 The bushing 7 has blades 15. Typically, there are 28 three blades arranged on each leaf of the bushing 7, 29 and typically these are circumferentially spaced at equal distances, so that the blades 15 are arranged 31 in three diametrically opposed pairs, as best shown 32 in Figs. 6 and 7. Each blade 15 is arranged 1 generally parallel to the axis of the assembled 2 bushing 7, and in plan view, each blade 15 is in the 3 general shape of a foil or wing, as best shown in 4 Figs. 2 and 8. In detail, each blade 15 has a lower end 151 that widens from the lowermost tip of the 6 blade to an apex 15a, from where it tapers through a 7 mid-section 15m, to an upper end 15u, and finally to 8 a slim point at the upper end. Shaping adjacent 9 blades like foils in this manner creates a flow path between adjacent blades that rapidly narrows to a 11 throat at the level of the apex 15a of the blades, 12 and then gradually widens as the passage passes the 13 upper ends 15u of the blades.

As best shown in Fig. 9, the side profile of each 16 blade 15 rises from the plane of the bushing 7 at 17 the tips and is arcuate in the upper 15u and lower 18 151 ends, and forms a plateau in the mid-section 19 15m.

21 The nominal external diameter of the bushing 7 is 22 generally very close to the nominal external 23 diameter of the upper part of the sleeve 5, and also 24 matches that of the clamp 9, so that apart from the vanes 12 and the blades 15, there are no upsets on 26 the outer surface of the apparatus.

28 The radial extent of the blades 15 typically exceeds 29 the radial extent of the vanes 12, so that the mid section 15m of the blades contacts the inner surface 31 of the bore in which the apparatus is deployed, \ ) 1 thereby spacing the vanes 12 from the inner surface 2 of the bore.

4 In preferred embodiments, the blades 15 are integrally formed with the leaves of the bushing 7, 6 and in typical embodiments, the two leaves can be 7 cast or moulded each in a single piece with their 8 respective blades. Alternatively, the blades can be 9 formed separately and attached to the body of the bushing 7 as required.

12 The vanes 12 can also be cast or moulded integrally 13 with the separate leaves of the sleeve, but in 14 preferred embodiments, the vanes 12 (and optionally the blades 15) can be separately cast or otherwise 16 formed from the same or a different material, and 17 can be assembled with the sleeve prior to use in a 18 modular fashion.

One such arrangement is shown in Figs. 12 to 18.

22 In this embodiment, the sleeve 5 has a vane 23 receiving portion 20, which comprises a region with 24 an increased inner diameter. Each vane 12 has a base plate 12b attached to its radially innermost 26 face as shown in Fig. 15. The base plate 12b is 27 curved, with an outer diameter that matches the 28 inner diameter of a vane-receiving portion 20 of the 29 sleeve.

31 When the sleeve 5 is to be assembled with the 32 modular vanes 12, the radially outermost mid-portion / 1 12m of each vane is offered to a vane-shaped slot 18 2 in the vane receiving portion 12, so that the mid 3 portion 12m passes from the inner surface of the 4 sleeve 5 through the vane receiving slot 18, and extends radially outward from the outer surface of 6 the sleeve 5. The curved radially outer face of the 7 base plate 12b of each vane 12 matches the inner 8 diameter of the vane receiving portion 20, and the 9 depth of each base plate 12b is chosen to match the step between the nominal inner diameter of the 11 sleeve 5 and the nominal inner diameter of the vane 12 receiving portion 20, so that when the modular vanes 13 are assembled with the sleeve 5, the base plates 12b 14 are accommodated within the vane-receiving portion 20, and the inner diameter of the sleeve and base 16 place are contiguous. The assembled sleeve with 17 modular vanes 12 can then be clamped onto the 18 tubular T as previously described.

Modular vanes 12 give the advantage that worn vanes 21 can be replaced easily, and different sizes or 22 profiles of vanes 12 can be used with the same 23 sleeve body. Also, vanes of different materials or 24 properties can be provided on a generic sleeve 5, and if desired, modular vanes 12 having different 26 characteristics can even be provided on the same 27 sleeve 5.

29 It will be appreciated that modular blades 15 can be provided for the bushing 7 in the same way. (A

1 Typically the bushing 7 and blades IS are formed 2 from a hard material such as a hard rubber or 3 plastic. Metals are also useful for the formation 4 of the bushing 7, and aluminium, zinc alloy, or austemperised ductile iron can be used for this 6 purpose.

8 The sleeve 5 and vanes 12 need not be formed from 9 the same material as the bushing 7 and blades 15, and in preferred embodiments, metals or plastics can 11 be used for the vanes 12 and/or the sleeve 5.

13 In use, when the apparatus is clamped to a tubular T 14 such as a drill string that is being used to drill a well, the device is typically deployed at regular 16 intervals along the bore, and car be used from a 17 position relatively close to the dr ll bit right up 18 to the top of the bore. The weight of the string T 19 typically forces the mid-portion 15m of the blades 15 against the inner surface of the wellbore, so 21 that the string is spaced away from the inner 22 surface of the wellbore by the radial extent of the 23 blades 15. Since the sleeve 5 is securely 24 rotationally fastened to the drill string T. the sleeve 5 and hence the vanes 12 rotate in the 26 direction of arrow A in Fig. 1, ie clockwise when 27 viewed from the top of the string. However, since 28 the weight of the string is pressing the blades 15 29 against the inner surface of the wellbore, and since the bushing 7 is rotatable on the bearing area 6, 31 the bushing 7 remains stationary relative to the 1 wellbore, and the sleeve and vanes 12 rotate 2 relative to the bushing 7 along with the string.

4 The radial dimensions of the blades 15 exceed those of the vanes 12, and thus the vanes 12 are spaced 6 from the inner surface of the bore, and are not 7 impeded from rotating by contact with the inner 8 surface of the wellbore. The rotation of the vanes 9 12 and the speed of the string (typically 120-180 rpm with normal rotary drilling, but sometimes as 11 slow as 20 rpm with casing drilling) generates 12 turbulence in the drill fluid in the annulus between 13 the string and the wellbore. The sinusoidal 14 arrangement of the vanes 12 generates thrust in the drill fluid in the region of the apparatus, and in 16 particular, the scoops 12s drive the drill fluid up 17 through the fluid passageways between adjacent 18 vanes, and the deflectors 12d accelerate it out of 19 the top of the fluid passage. In addition to creating thrust in the fluid and pumping the fluid 21 from the lower end of the apparatus to the upper 22 end, this also creates turbulence in the fluid, 23 tending to break up clumps of drill cuttings, to 24 keep the fluid in a liquid phase.

26 The rapid rotation of the vanes 12 in the drill 27 fluid creates a pressure drop in the area between 28 the vanes 12 and the blades 15, which draws more 29 fluid up through the channels between adjacent blades 15. As the fluid passes the apex 15a in the 31 channels between adjacent blades 15 on the 32 stationary bushing 7, it experiences a further 1 pressure drop created by the expansion in volume of 2 the fluid passageway as each blade narrows towards 3 its upper end. The pressure changes occurring as a 4 result of this speeds up fluid flow from the bit to the surface, and also suspends cuttings in the 6 liquid phase, which makes it easier to return them 7 to surface.

9 An additional advantage of the non-rotating bushing 7 is that it reduces torque for rotation of the 11 string T within the hole, and the bearing surface 12 between the sleeve 5 and the bushing 7 is typically 13 lubricated by the drill fluid passing the apparatus.

14 In addition to this advantage, the smooth outer surface of the blades 15, and particular the rounded 16 profile of the ends of the blades 15u and 151, can 17 reduce drag while running in the hole, thereby also 18 reducing casing wear, and enhancing the penetration 19 of the drill bit. If the bushing 12 is manufactured from materials having a low co-efficient of friction 21 then additional advantages in running in the hole 22 are also achieved. Notably, plastics, rubber and 23 zinc alloys give useful secondary advantages in this 24 respect.

26 The provision of the non-rotating bushing also 27 reduces drill string harmonics, and can help to 28 prevent differential sticking of the string.

Fig. 19 shows a further embodiment of apparatus for 31 mobilizing drill cuttings in a well comprising a 32 sleeve 5', a bushing 7' and a clamp 9' similar to 1 that previously described for the first embodiment, 2 and assembled onto the string T in the same way.

4 The sleeve 5' has vanes 22 mounted on the upper large diameter section. Only one vane 22 is mounted 6 on each leaf of the sleeve, and the vanes are spaced 7 apart on the circumference of the assembled sleeve 8 5' at equal distances, so that the vanes 22 are 9 diametrically opposed to one another.

11 The vanes 22 are generally straight, but are 12 attached to the sleeve 5' at an angle that is offset 13 with respect to the axis of the sleeve 5', from top 14 right to bottom left at around 5 wrt the axis.

Each vane 22 typically has a concave surface on one 16 side, typically that facing the direction of 17 rotation, as best seen in Fig. 20. The concave 18 surface typically acts as a scoop to create 19 turbulence in the fluid flowing up the annulus between the sleeve 5 ' and the borehole. The radius 21 of curvature of the concave surface changes with the 22 axial position on the vane, as shown in Figs. 20 and 23 21, so that at the lower end of the blade (see B in 24 Fig. 19) the concave surface has a small curvature with the radially outermost part of the blade being 26 nearly perpendicular to the tangent of the 27 circumference of the sleeve 5'; whereas at the upper 28 end of the blade (see A at Fig. 19) the radially 29 outermost part of the blade is more curved and approaches a tangent to the circumference of the 31 sleeve 5' . This graduation in the radius of 32 curvature of the concave surface guides the fluid <- 1 flowing past the vane 22 towards the sleeve 5', 2 where turbulence and flow rates are highest, and 3 this keeps the cuttings in suspension for longer.

In some other embodiments of vanes, the change in 6 the radius of curvature is not required, and a 7 simple regular concave surface as shown in Figs. 22 8 and 23 will suffice. The vane shown in Fig. 22 can 9 be modified by cutting out a small portion towards the centre of the radially outermost edge of the 11 vane. Such an embodiment of a vane 22' is shown in 12 Fig. 24. In an alternative embodiment, several 13 notches 90 may be provided on the vane 22' . The 14 notch 90 or notches can introduce additional turbulence or create a vortex to assist in the pick 16 up and agitation of drill cuttings to facilitate 17 their inclusion in the flow regime.

19 The bushing 7' has blades 25. Typically, there are three blades arranged on each leaf of the bushing 21 7', and typically these are circumferentially spaced 22 at equal distances, so that the blades 25 are 23 arranged in three diametrically opposed pairs. Each 24 blade 25 is offset at a 5 angle wrt the axis of the assembled bushing 7', from top left to bottom right, 26 in an opposite configuration to the offset of the 2 7 vanes 22.

29 In side profile, as shown in Fig. 19, each blade 25 comprises a central plateau region and radially 31 lower ends. The width of the blades are consistent 1 throughout their length unlike the earlier 2 embodiments.

4 The nominal external diameter of the bushing 7' is generally very close to the nominal external 6 diameter of the upper part of the sleeve 5', and 7 also matches that of the clamp 9', so that apart 8 from the vanes 22 and the blades 25, there are no 9 upsets on the outer surface of the apparatus.

11 The radial extent of the blades 25 typically exceeds 12 the radial extent of the vanes 22, so that the 13 plateau sections of the blades contact the inner 14 surface of the bore in which the apparatus is deployed, thereby spacing the vanes 22 from the 16 inner surface of the bore.

18 The blades 25 have profiled cross sections (i.e. l9 end-on views) in the form of an hour glass as best shown in Figs. 20 and 21, with a wide root radially 21 innermost adjacent the bushing, a wide top at the 22 radially outermost plateau of the blade that bears 23 against the borehole wall, and a narrower cutaway 24 portion radially between the two to facilitate fluid flow between the blades. This cutaway creates more 26 space for the fluid to pass between the blades, and 27 helps to avoid impedance of the fluid flow.

29 In use the operation of the second embodiment is similar to the first, but the vanes 22 keep the 31 drill fluid and cuttings close to the wall of the 32 sleeve as the scoops drive the drill fluid up 1 through the fluid passageways between adjacent 2 vanes. In addition to creating thrust in the fluid 3 and pumping the fluid from the lower end of the 4 apparatus to the upper end, this also creates turbulence in the fluid, tending to break up clumps 6 of drill cuttings, to keep the fluid in a liquid 7 phase.

9 Modifications and improvements can be incorporated without departing from the scope of the invention.

Claims

1 CLAIMS 3 1. Apparatus for mobilising drill cuttings in a 4 well,

comprising at least one vane, and two or more blades defining at least one fluid conduit between 6 adjacent blades, the blades and vane being rotatable 7 relative to one another.

9 2. Apparatus according to claim 1, wherein the blades are configured to create a pressure 11 difference in a fluid flowing through the at least 12 one fluid conduit.

14 3. Apparatus according to claim 1 or claim 2, comprising a sleeve adapted to fit over a drill 16 string in the well.

18 4. Apparatus according to claim 3, wherein the or 19 each vane is provided on the sleeve.

21 5. Apparatus according to any preceding claim, 22 wherein the blades project radially outward to a 23 greater extent than the or each vane.

6. Apparatus according to any of claims 3 to 5, 26 wherein the blades are mounted on a bushing that is 27 rotatably mounted on the sleeve.

29 7. Apparatus according to any of claims 3 to 6, wherein the blades are arranged substantially 31 parallel to an axis of rotation of the sleeve.

1 8. Apparatus according to claim 6, wherein the 2 blades are offset with respect to an axis of 3 rotation of the bushing such that the blades extend 4 helically around the bushing.

6 9. Apparatus according to claim 8, wherein the 7 blades are offset at an angle of 3-10 with respect 8 to the axis of rotation.

10. Apparatus according to any of claims 3 to 9, 11 comprising fixing means for attaching the sleeve to 12 the drill string.

14 11. Apparatus according to claim 10, wherein the fixing means comprises a clamp means.

17 12. Apparatus according to claim 11, wherein the 18 clamp means comprise an annular clamp.

13. Apparatus according to any preceding claim, 21 wherein the or each vane is rotationally fixed to a 22 drill string such that rotation of the drill string 23 causes rotation of the or each vane.

14. Apparatus according to any preceding claim, 26 wherein the or each vane is configured to create 27 thrust when rotated in a fluid.

29 15. Apparatus according to any preceding claim, wherein the blades have an asymmetric profile.

1 16. Apparatus according to any preceding claim, 2 wherein the blades are shaped in the form of foils, 3 so that the fluid conduits defined between adjacent 4 blades on the bushing change in profile.

6 17. Apparatus according to any preceding claim, 7 wherein the at least one fluid conduit is relatively 8 narrow at an end proximal to a drill bit and 9 relatively wider towards another end distal from the drill bit.

12 18. Apparatus according to any preceding claim, 13 wherein a cross section through the blades is in the 14 form of an hour glass.

16 19. Apparatus according to claim 18, wherein the 17 blades are shaped to have a wide root radially inner 18 most adjacent the bushing, a wide top at the 19 radially outermost part of the blade arranged to bear against the borehole wall, and a narrower 21 cutaway portion between the root and top.

23 20. Apparatus according to any of claims 6 to 18, 24 wherein the bushing is formed from a rigid material.

26 21. Apparatus according to any of claims 3 to 20, 27 wherein the sleeve has an annular body to 28 accommodate a tubular therethrough.

22. Apparatus according to claim 21, wherein the 31 annular body has at least one vane integrally formed 32 therewith.

2 23. Apparatus according to a claim 21, wherein the 3 sleeve has at least one vane-receiving recess 4 therein to receive and retain at least one modular vane.

7 24. Apparatus according to any of claims 6 to 23, 8 wherein the bushing has blades integrally formed 9 therewith.

11 25. Apparatus according to any of claims 6 to 23, 12 wherein the bushing has blade-receiving recesses 13 therein to receive and retain modular blades.

26. Apparatus according to any of claims 3 to 25, 16 wherein the at least one vane lies parallel to the 17 axis of rotation of the sleeve.

19 27. Apparatus according to any of claims 3 to 25, wherein the at least one vane is curved so as to 21 scoop fluid from an area surrounding the vanes.

23 28. Apparatus according to claim 27, wherein the at 24 least one vane is configured in a sinusoidal shape.

26 29. Apparatus according to claim 27 or claim 28, 27 wherein the at least one vane is offset with respect 28 to the axis of rotation of the sleeve such that one 29 end of the at least one vane is circumferentially spaced around the sleeve from the other end.

1 30. Apparatus according to claim 29, wherein the 2 direction of offset of the at least one vane is in 3 an opposite direction to the offset of the blades.

31. Apparatus according to any preceding claim, 6 wherein the at least one vane has a concave surface.

8 32. Apparatus according to claim 31, wherein the 9 concave surface is provided on one side of the or each vane facing the direction of rotation.

12 33. Apparatus according to a claim 32, wherein the 13 side of the or each vane is shaped to have a greater 14 radius of curvature at one end than at another end.

16 34. Apparatus according to any preceding claim, 17 wherein the at least one vane has one or more 18 notches cut away from a radially outermost portion 19 thereof.

21 35. A drill cuttings agitation assembly, comprising 22 a tubular, at least one vane, and two or more blades 23 defining at least one fluid conduit between adjacent 24 blades, wherein the at least one vane and the blades are rotatable relative to one another.

27 36. A method of agitating drill fluid in an oil or 28 gas well, the method comprising passing the drill 29 fluid past at least one vane rotatable relative to two or more blades. )

1 37. A method according to claim 36, including 2 configuring the blades to create a pressure 3 difference in fluid flowing through at least one 4 fluid conduit defined by the two or more blades.

6 38. A method according to any of claims 36 or 37, 7 including providing the at least one vane on a 8 sleeve.

39. A method according to claim 38, including 11 providing blades on a bushing and rotatably mounting 12 the bushing with respect to the sleeve.

14 40. A method according to any of claims 36 to 39, including mounting and rotationally fixing the at 16 least one vane on a drill string.

18 41. A method according to claim 40, including 19 rotating the drill string to rotate the at least one vane, thereby agitating the drill fluid in the 21 environment.

23 42. A method according to any of claims 40 and 41, 24 including centralizing the sleeve within a bore in which the drill string is located, by means of the 26 blades.