U.S. patent application number 10/594157 was filed with the patent office on 2007-09-20 for downhole apparatus for mobilising drill cuttings.
Invention is credited to William Barron Bieldside, Alistair Bertram Clark, lan Alastair Kirk.
Application Number | 20070215388 10/594157 |
Document ID | / |
Family ID | 34553799 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070215388 |
Kind Code |
A1 |
Kirk; lan Alastair ; et
al. |
September 20, 2007 |
Downhole Apparatus for Mobilising Drill Cuttings
Abstract
Apparatus for mobilising drill cuttings in a well, comprising 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 apparatus is provided to
alleviate the problem of drill cuttings clumping together downhole.
The or each vane (12) can be provided on a sleeve (5). The blades
(15) can be mounted on a bushing (7) that is rotatably mounted on
the sleeve (5).
Inventors: |
Kirk; lan Alastair;
(Milltimber, GB) ; Bieldside; William Barron;
(Aberdeen, GB) ; Clark; Alistair Bertram;
(Westhill, GB) |
Correspondence
Address: |
MIDDLETON & REUTLINGER
2500 BROWN & WILLIAMSON TOWER
LOUISVILLE
KY
40202
US
|
Family ID: |
34553799 |
Appl. No.: |
10/594157 |
Filed: |
March 24, 2005 |
PCT Filed: |
March 24, 2005 |
PCT NO: |
PCT/GB05/01199 |
371 Date: |
September 26, 2006 |
Current U.S.
Class: |
175/327 |
Current CPC
Class: |
E21B 17/1057 20130101;
E21B 17/22 20130101; E21B 21/00 20130101 |
Class at
Publication: |
175/327 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2004 |
GB |
0406782.3 |
Nov 23, 2004 |
GB |
0425663.2 |
Claims
1. Apparatus for mobilizing drill cuttings in a well, comprising at
least one vane, and at least two blades defining at least one fluid
conduit between adjacent blades, the blades and vane being
rotatable relative to one another.
2. Apparatus according to claim 1, wherein the blades are
configured to create a pressure difference in a fluid flowing
through the at least one fluid conduit.
3. Apparatus according to claim 1, comprising a sleeve adapted to
fit over a drill string in the well.
4. Apparatus according to claim 3, wherein the at least one vane is
provided on the sleeve.
5. Apparatus according to claim 1, wherein the blades project
radially outward to a greater extent than the at least one
vane.
6. Apparatus according to claim 3, wherein the blades are mounted
on a bushing that is rotatably mounted on a sleeve.
7. Apparatus according to claim 3, wherein the sleeve has an axis
of rotation, and wherein the blades are arranged substantially
parallel to the axis of rotation of the sleeve.
8. Apparatus according to claim 6, wherein the bushing has an axis
of rotation and wherein the blades are offset with respect to the
axis of rotation of the bushing such that the blades extend
helically around the bushing.
9. Apparatus according to claim 8, wherein the blades are offset at
an angle of 3-10.degree. with respect to the axis of rotation of
the bushing.
10. Apparatus according to claim 3, comprising a fixing device for
attaching the sleeve to the drill string.
11. Apparatus according to claim 10, wherein the fixing device
comprises a clamp means.
12. Apparatus according to claim 11, wherein the clamp means
comprise an annular clamp.
13. Apparatus according to claim 1, wherein the at least one vane
is rotationally fixed to a drill string such that rotation of the
drill string causes rotation of the at least one vane.
14. Apparatus according to claim 1, wherein the at least one vane
is configured to create thrust when rotated in a fluid.
15. Apparatus according to claim 1, wherein the blades have an
asymmetric profile.
16. Apparatus according to claim 1, wherein the blades are shaped
in the form of foils, so that the fluid conduits defined between
adjacent blades on the bushing change in profile between a first
end proximal to the drill bit and a second end distal from the
drill bit.
17. Apparatus according to claim 16, wherein the at least one fluid
conduit is relatively narrow at the first end proximal to the drill
bit and relatively wider towards the other end distal from the
drill bit.
18. Apparatus according to claim 1, wherein the blades have a cross
section in the form of an hour glass.
19. Apparatus according to claim 18, wherein the blades are shaped
to have a wide root radially inner most adjacent the bushing, a
wide top at the radially outermost part of the blade arranged to
bear against the borehole wall, and a narrower cutaway portion
between the root and top.
20. Apparatus according to claim 6, wherein the bushing is formed
from a rigid material.
21. Apparatus according to claim 3, wherein the sleeve has an
annular body to accommodate a tubular therethrough.
22. Apparatus according to claim 21, wherein the annular body has
at least one vane integrally formed therewith.
23. Apparatus according to a claim 21, wherein the sleeve has at
least one vane-receiving recess therein to receive and retain at
least one modular vane.
24. Apparatus according to claim 6, wherein the bushing has blades
integrally formed therewith.
25. Apparatus according to claim 6, wherein the bushing has
blade-receiving recesses therein to receive and retain modular
blades.
26. Apparatus according to claim 3, wherein the sleeve has an axis
of rotation, and therein the at least one vane lies parallel to the
axis of rotation of the sleeve.
27. Apparatus according to claim 3, wherein the at least one vane
is curved so as to scoop fluid from an area surrounding the
vanes.
28. Apparatus according to claim 27, wherein the at least one vane
is configured in a sinusoidal shape.
29. Apparatus according to claim 27, wherein the sleeve has an axis
of rotation, and wherein the at least one vane is offset with
respect to the axis of rotation of the sleeve such that one end of
the at least one vane is circumferentially spaced around the sleeve
from the other end.
30. Apparatus according to claim 29, wherein the direction of
offset of the at least one vane is in an opposite direction to the
offset of the blades.
31. Apparatus according to claim 1, wherein the at least one vane
has a concave surface.
32. Apparatus according to claim 31, wherein the concave surface is
provided on one side of the at least one vane facing the direction
of rotation.
33. Apparatus according to a claim 32, wherein the side of the at
least one vane is shaped to have a greater radius of curvature at
one end than at another end.
34. Apparatus according to claim 1, wherein the at least one vane
has one or more notches cut away from a radially outermost portion
thereof.
35. A drill cuttings agitation assembly, comprising a tubular, at
least one vane, and at least two blades defining at least one fluid
conduit between adjacent blades, wherein the at least one vane and
the blades are rotatable relative to one another.
36. A method of agitating drill fluid in an oil or gas well, the
method comprising passing the drill fluid past at least one vane
rotatable relative to at least two blades.
37. A method according to claim 36, including configuring the
blades to create a pressure difference in fluid flowing through at
least one fluid conduit defined by at least two blades.
38. A method according to claim 36, including providing the at
least one vane on a sleeve.
39. A method according to claim 38, including providing blades on a
bushing and rotatably mounting the bushing with respect to the
sleeve.
40. A method according to claim 36, including mounting and
rotationally fixing the at last one vane on a drill string.
41. A method according to claim 40, including rotating the drill
string to rotate the at least one vane, thereby agitating the drill
fluid in the environment.
42. A method according to claim 41, including centralizing the
sleeve within a bore in which the drill string is located, by means
of the blades.
Description
[0001] The present invention relates to apparatus for mobilising
drill cuttings in an oil or gas well.
[0002] The art of drilling wellbores for recovery of oil and gas is
well known. One particular problem faced by this art is the removal
of cuttings from the well as they are generated by the action of
the drill bit cutting into the formation. The cuttings need to be
removed from the bit and conveyed back to surface as efficiently as
possible, as their persistence in the wellbore hampers drilling
activity, and tends to reduce the productivity of the well.
[0003] Cuttings are washed back to surface by drilling mud or fluid
pumped down the string, out through the bit, and back up the
annulus surrounding the string. This solution is generally
satisfactory, but in long and deviated wells we have found that
cuttings still tend to clump and impede the drilling activity, or
the production of the well.
[0004] According to the present invention there is provided
apparatus for mobilising drill cuttings in a well, the apparatus
comprising at least one vane, and two or more blades defining at
least one fluid conduit between adjacent blades, the blades and
vane being rotatable relative to one another.
[0005] Typically the blades are configured to create a pressure
difference in fluid flowing through the conduit, but this is not
essential, and a fluid drop, if required, can be induced by other
means apart from the blades.
[0006] The apparatus typically comprises a sleeve or collar, which
is typically tubular and is adapted to fit over a string in the
well. The string can be a tubing string, drill string, or casing
string etc. Typically the vanes are provided on the sleeve.
[0007] Typically the blades are mounted on a bushing that is
rotatably mounted on the sleeve.
[0008] However, in certain simple embodiments, it is sufficient to
provide the vanes direct on the tubing string (or on a sleeve
attached to the string) and to provide the blades on an adjacent
part of the string, or on a separate sleeve attached thereto, so
that the blade-bearing bushing is not directly attached to the
vane-bearing sleeve. The blades or the bushing can optionally be
incorporated into a sub in the string, or on a collar that is
separately attached to the string.
[0009] Typically the sleeve is adapted for attachment to a drill
string, and the fixing means typically comprises a clamp means such
as an annular clamp to fix the sleeve over the outer surface of the
drill pipe. However, the sleeve may equally attach to casing or any
other oilfield tubular goods.
[0010] The vanes can be carried direct on the sleeve, or in some
embodiments can be provided on a separate bushing rotationally (or
otherwise) affixed to the sleeve. The vanes typically rotate with
the drill string in normal rotary drilling operations as they are
typically rotationally fixed to the drill string. The rotation of
the vanes agitates the fluid surrounding the apparatus, and creates
thrust tending to drive the fluid past the sleeve. The blades of
the bushing typically create a pressure drop in the fluid as it
flows past the apparatus, driven by the rotation of the
vane(s).
[0011] Typically the bushing is free to rotate relative to the
sleeve, which is affixed to the drill string. Thus, upon rotation
of the drill string (or casing) during normal rotary drilling, the
bushing typically remains stationary relative to the wellbore,
while the drill string rotates.
[0012] Typically the blades on the bushing project radially outward
to a greater extent than the vanes of the sleeve, so that the
radially outermost surface of the blades contacts the inner surface
of the bore within which the string is located, and this
centralises the sleeve within the bore. In preferred embodiments,
the vanes are radially lower than the blades, and can freely rotate
within the bore, as the higher blades provide a stand off against
the inner surface of the bore. The bore can be the unlined
wellbore, or can be the bore of casing, liner or other tubing in
which the apparatus is located.
[0013] The blades can be set parallel to the axis, or can be offset
with respect to it, so that they extend helically around the
bushing. In some embodiments the blades are offset at an angle of
3-10.degree. e.g. 5.degree. from top left to bottom right with
respect to the axis of the bushing. This orientation is useful in
drillstrings that are conventionally rotated to the right, as the
fluid path up the annulus tends to flow in a spiral from bottom
right to top left at around 5.degree. off the axis. Therefore, the
offset blades do not substantially impede the fluid flow rate.
Clearly adjustments can be made to the offset angle to suit the
fluid flow direction in other wells.
[0014] The blades typically have an asymmetric profile, and in
preferred embodiments the blades are shaped in the form of foils,
so that the fluid conduits defined between adjacent blades on the
bushing change in profile. Typically the fluid conduits are
relatively narrow at a lower end (nearest the drill bit) and grow
relatively wider toward the upper end (furthest away from the bit).
The increase in dimension from the bottom of the channel to the top
causes a pressure drop in the fluid flowing through the
channel.
[0015] The blades can have profiled cross sections (i.e. end-on
view) in the form of an hour glass, with a wide root radially
innermost adjacent the bushing, a wide top at the radially
outermost part of the blade that bears against the borehole wall,
and a narrower cutaway portion between the two to facilitate fluid
flow between the blades. This cutaway creates more space for the
fluid to pass between the blades, and helps to avoid impedance of
the fluid flow.
[0016] Typically the bushing can be formed from a rigid material,
such as hard rubber or metal. The sleeve is typically formed from
metal such as steel, alloy, aluminium, etc.
[0017] The sleeve can have an annular body to fit around a tubular
or string of tubulars. The annular body can have the vanes
integrally formed with it, for example by moulding the sleeve and
vanes as a single piece. In alternative (and preferred)
embodiments, the sleeve can have vane-receiving recesses therein to
receive and retain modular vanes, which can be slotted in the
recesses, and retained therein. This has the advantage that several
different sizes of vanes can be used with a single sleeve.
[0018] Likewise, the blades on the bushing can be modular and can
be received within blade recesses in the same manner.
[0019] The vanes can be curved or straight, and can lie parallel to
the axis, but in typical embodiments they cross the axis of the
sleeve so as to scoop the fluid from the annulus. The lower end of
the vane is typically circumferentially spaced around the sleeve
from the upper end, typically in the direction of rotation of the
string, so where the string rotates to the right (as is
conventional in most wells) the vanes are offset across the axis
from top right to bottom left, the opposite configuration from the
offset blades described above.
[0020] In some embodiments the vanes are configured in a sinusoidal
"lazy-s" shape and this helps to agitate the fluid surrounding the
apparatus during rotation. In other embodiments, they are disposed
straight across the axis.
[0021] The vanes can have concave surfaces to assist in the
scooping action, and typically the concave surfaces can be provided
in one side of the vane only, typically on the side of the vane
facing the direction of rotation. The concave surface can be
regular and unchanging along the side of the vane, but in some
embodiments the side vane is shaped to have more of a curve on its
upper end than on its lower end, so that as the fluid moves up the
side of the vane, the increasing curve of the concave surface keeps
the fluid close to the sleeve, where most turbulence will be
generated, thereby keeping the cuttings in suspension for
longer.
[0022] The or each vane can be provided with a notch cut away from
a radially outermost portion of the vane. Several notches may be
provided on each vane. The notches can serve to introduce
additional turbulence or induce a vortex as the vane is rotated to
agitate drill cuttings and entrain them into the flow of fluid up
the annulus.
[0023] The invention also provides a drill cuttings agitation
assembly, comprising a tubular, a vane, and at least two blades
defining at least one fluid conduit between adjacent blades,
wherein the vane and the blades are rotatable relative to one
another.
[0024] The invention also provides a method of agitating drill
fluid in an oil or gas well, the method comprising passing the
drill fluid past a vane rotatable relative to at least two
blades.
[0025] An embodiment of the invention will now be described by way
of example and with reference to the accompanying drawings, in
which:
[0026] FIG. 1 is a side view of apparatus according to the present
invention, mounted on a tubular;
[0027] FIG. 2 is a close up side view of the FIG. 1 apparatus;
[0028] FIG. 3 is a side view of a sleeve of the FIG. 1
apparatus;
[0029] FIG. 4 is a side view of a bushing of a bushing of the FIG.
1 apparatus;
[0030] FIG. 5 is a side view of a clamp of the FIG. 1
apparatus;
[0031] FIGS. 6 and 7 (respectively) plan and underside views of the
FIG. 4 bushing;
[0032] FIG. 8 is a flat view of a bushing half shell;
[0033] FIG. 9 is a side view of a bushing blade;
[0034] FIG. 10 is a plan view of a sleeve;
[0035] FIG. 11 is a sectional view through a clamp;
[0036] FIG. 12 is an outer side view of a second sleeve;
[0037] FIG. 13 is an inner side view of the second sleeve;
[0038] FIG. 14 is a sectional view through the second sleeve;
[0039] FIG. 15 is a perspective view of a modular vane for the
second sleeve;
[0040] FIG. 16 is an underneath view of the FIG. 15 vane;
[0041] FIG. 17 is a plan view of the FIG. 15 vane;
[0042] FIG. 18 is a side view of the same vane;
[0043] FIG. 19 is a side view of a second embodiment of apparatus
mounted on a tubular;
[0044] FIG. 20 is a sectional view from beneath the FIG. 19
apparatus at point A;
[0045] FIG. 21 is a sectional view from beneath the FIG. 19
apparatus at point B;
[0046] FIG. 22 is a plan of a vane;
[0047] FIG. 23 is a plan view of a second vane; and
[0048] FIG. 24 is a plan view of a vane having a cut-out
portion.
[0049] Referring now to the drawings, apparatus for mobilising
drill cuttings in a well comprises a sleeve 5, a bushing 7 and a
clamp 9. All of these components are generally tubular, but are
axially divided into two separate leaves that are hinged together.
The leaves of the sleeve 5 are hinged at three locations 5h, and
its two leaves pivot around those hinges to enable the sleeve 5 to
be opened and closed around a tubular T such as drill pipe or
casing. The two halves of the sleeve are locked together by one or
more bolts 5b at a position diametrically opposite to the hinge 5h,
so that the sleeve 5 can be tightly fastened to the tubular T by
means of the bolts.
[0050] The hinges 5h are located on an upper part of the sleeve 5,
beneath which is a bearing region 6 having a reduced outer diameter
as compared with the nominal diameter of the upper region. An
annular groove 6g is formed on the lower end of the bearing region
6, and a shoulder 6s divides the upper and bearing regions of the
sleeve.
[0051] The bushing 7 is also formed as two separate leaves that are
connected together at diametrically opposed positions by
interlocking castellations and connecting pins 7p, about which the
two leaves can pivot. The two leaves of the bushing 7 are typically
closed around the bearing region 6 of the sleeve, at which point
the leaves are connected together by inserting the pins 7p into
axially aligned bores on the interlocking castellations to close
and lock the bushing 7, so that the bushing 7 is connected to the
sleeve 5.
[0052] After the bushing 7 has been locked in place around the
bearing region 6 of the sleeve 5, the clamp 9 is then placed around
the lower end of the bearing region 6, so that an annular lip on
the internal surface of the clamp 9 engages in the external annular
groove 6g on the lower part of the bearing region 6. The clamp 9 is
then closed and fastened by means of bolts (not shown) in the same
manner as the bolts 5b that lock the sleeve closed around the
tubular T.
[0053] When thus assembled, the tightening of the bolts in the
sleeve 5 and the clamp 9 securely connects the sleeve to the
tubular, so that the two are rotationally connected, and thus the
sleeve rotates with the tubular.
[0054] The bushing 7 is fixed to the bearing area 6 of the sleeve,
and is prevented from axial movement by the shoulder 6s above it,
and the clamp 9 below it; however, the bushing 7 is free to rotate
around its axis relative to the sleeve and the clamp, and the
tolerance of the outer diameter of the bearing region 6 and the
inner diameter of the bushing 7 are chosen to permit a degree of
play between the two, and allow rotation of the bushing 7 around
the axis of the sleeve 5.
[0055] The sleeve 5 has vanes 12 mounted on the upper large
diameter section. As best shown in FIG. 10, two vanes 12 are
mounted on each leaf of the sleeve, and the vanes are spaced apart
on the circumference of the assembled sleeve 5 at equal distances,
so that the vanes 12 are arranged in diametrically opposed
pairs.
[0056] The vanes 12 have a generally sinusoidal "lazy-S" shape with
a lower scoop 12s, a generally axial mid-region 12m, and an upper
deflector portion 12d.
[0057] In side profile, the vanes 12 are generally arcuate in the
scoop and deflector regions, rising from the plane of the sleeve 5
in a regular arc until a plateau is reached at the mid-section 12m.
FIG. 18 shows the side profile of a typical vane 12. The vanes 12
project radially from the outer surface of the sleeve 5, so as to
create between adjacent vanes 12 a fluid path that is generally
sinusoidal in shape.
[0058] The bushing 7 has blades 15. Typically, there are three
blades arranged on each leaf of the bushing 7, and typically these
are circumferentially spaced at equal distances, so that the blades
15 are arranged in three diametrically opposed pairs, as best shown
in FIGS. 6 and 7. Each blade 15 is arranged generally parallel to
the axis of the assembled bushing 7, and in plan view, each blade
15 is in the general shape of a foil or wing, as best shown in
FIGS. 2 and 8. In detail, each blade 15 has a lower end 15l that
widens from the lowermost tip of the blade to an apex 15a, from
where it tapers through a mid-section 15m, to an upper end 15u, and
finally to a slim point at the upper end. Shaping adjacent blades
like foils in this manner creates a flow path between adjacent
blades that rapidly narrows to a throat at the level of the apex
15a of the blades, and then gradually widens as the passage passes
the upper ends 15u of the blades.
[0059] As best shown in FIG. 9, the side profile of each blade 15
rises from the plane of the bushing 7 at the tips and is arcuate in
the upper 15u and lower 15l ends, and forms a plateau in the
mid-section 15m.
[0060] The nominal external diameter of the bushing 7 is generally
very close to the nominal external diameter of the upper part of
the sleeve 5, and also matches that of the clamp 9, so that apart
from the vanes 12 and the blades 15, there are no upsets on the
outer surface of the apparatus.
[0061] The radial extent of the blades 15 typically exceeds the
radial extent of the vanes 12, so that the mid-section 15m of the
blades contacts the inner surface of the bore in which the
apparatus is deployed, thereby spacing the vanes 12 from the inner
surface of the bore.
[0062] In preferred embodiments, the blades 15 are integrally
formed with the leaves of the bushing 7, and in typical
embodiments, the two leaves can be cast or moulded each in a single
piece with their respective blades. Alternatively, the blades can
be formed separately and attached to the body of the bushing 7 as
required.
[0063] The vanes 12 can also be cast or moulded integrally with the
separate leaves of the sleeve, but in preferred embodiments, the
vanes 12 (and optionally the blades 15) can be separately cast or
otherwise formed from the same or a different material, and can be
assembled with the sleeve prior to use in a modular fashion.
[0064] One such arrangement is shown in FIGS. 12 to 18.
[0065] In this embodiment, the sleeve 5 has a vane-receiving
portion 20, which comprises a region with an increased inner
diameter. Each vane 12 has a base plate 12b attached to its
radially innermost face as shown in FIG. 15. The base plate 12b is
curved, with an outer diameter that matches the inner diameter of a
vane-receiving portion 20 of the sleeve.
[0066] When the sleeve 5 is to be assembled with the modular vanes
12, the radially outermost mid-portion 12m of each vane is offered
to a vane-shaped slot 18 in the vane receiving portion 12, so that
the mid-portion 12m passes from the inner surface of the sleeve 5
through the vane receiving slot 18, and extends radially outward
from the outer surface of the sleeve 5. The curved radially outer
face of the base plate 12b of each vane 12 matches the inner
diameter of the vane receiving portion 20, and the depth of each
base plate 12b is chosen to match the step between the nominal
inner diameter of the sleeve 5 and the nominal inner diameter of
the vane receiving portion 20, so that when the modular vanes are
assembled with the sleeve 5, the base plates 12b are accommodated
within the vane-receiving portion 20, and the inner diameter of the
sleeve and base place are contiguous. The assembled sleeve with
modular vanes 12 can then be clamped onto the tubular T as
previously described.
[0067] Modular vanes 12 give the advantage that worn vanes can be
replaced easily, and different sizes or profiles of vanes 12 can be
used with the same sleeve body. Also, vanes of different materials
or properties can be provided on a generic sleeve 5, and if
desired, modular vanes 12 having different characteristics can even
be provided on the same sleeve 5.
[0068] It will be appreciated that modular blades 15 can be
provided for the bushing 7 in the same way.
[0069] Typically the bushing 7 and blades 15 are formed from a hard
material such as a hard rubber or plastic. Metals are also useful
for the formation of the bushing 7, and aluminium, zinc alloy, or
austemperised ductile iron can be used for this purpose.
[0070] The sleeve 5 and vanes 12 need not be formed from the same
material as the bushing 7 and blades 15, and in preferred
embodiments, metals or plastics can be used for the vanes 12 and/or
the sleeve 5.
[0071] In use, when the apparatus is clamped to a tubular T such as
a drill string that is being used to drill a well, the device is
typically deployed at regular intervals along the bore, and can be
used from a position relatively close to the drill bit right up to
the top of the bore. The weight of the string T typically forces
the mid-portion 15m of the blades 15 against the inner surface of
the wellbore, so that the string is spaced away from the inner
surface of the wellbore by the radial extent of the blades 15.
Since the sleeve 5 is securely rotationally fastened to the drill
string T, the sleeve 5 and hence the vanes 12 rotate in the
direction of arrow A in FIG. 1, ie clockwise when viewed from the
top of the string. However, since the weight of the string is
pressing the blades 15 against the inner surface of the wellbore,
and since the bushing 7 is rotatable on the bearing area 6, the
bushing 7 remains stationary relative to the wellbore, and the
sleeve and vanes 12 rotate relative to the bushing 7 along with the
string.
[0072] The radial dimensions of the blades 15 exceed those of the
vanes 12, and thus the vanes 12 are spaced from the inner surface
of the bore, and are not impeded from rotating by contact with the
inner surface of the wellbore. The rotation of the vanes 12 and the
speed of the string (typically 120-180 rpm with normal rotary
drilling, but sometimes as slow as 20 rpm with casing drilling)
generates turbulence in the drill fluid in the annulus between the
string and the wellbore. The sinusoidal arrangement of the vanes 12
generates thrust in the drill fluid in the region of the apparatus,
and in particular, the scoops 12s drive the drill fluid up through
the fluid passageways between adjacent vanes, and the deflectors
12d accelerate it out of the top of the fluid passage. In addition
to creating thrust in the fluid and pumping the fluid from the
lower end of the apparatus to the upper end, this also creates
turbulence in the fluid, tending to break up clumps of drill
cuttings, to keep the fluid in a liquid phase.
[0073] The rapid rotation of the vanes 12 in the drill fluid
creates a pressure drop in the area between the vanes 12 and the
blades 15, which draws more fluid up through the channels between
adjacent blades 15. As the fluid passes the apex 15a in the
channels between adjacent blades 15 on the stationary bushing 7, it
experiences a further pressure drop created by the expansion in
volume of the fluid passageway as each blade narrows towards its
upper end. The pressure changes occurring as a result of this
speeds up fluid flow from the bit to the surface, and also suspends
cuttings in the liquid phase, which makes it easier to return them
to surface.
[0074] An additional advantage of the non-rotating bushing 7 is
that it reduces torque for rotation of the string T within the
hole, and the bearing surface between the sleeve 5 and the bushing
7 is typically lubricated by the drill fluid passing the apparatus.
In addition to this advantage, the smooth outer surface of the
blades 15, and particular the rounded profile of the ends of the
blades 15u and 15l, can reduce drag while running in the hole,
thereby also reducing casing wear, and enhancing the penetration of
the drill bit. If the bushing 12 is manufactured from materials
having a low co-efficient of friction then additional advantages in
running in the hole are also achieved. Notably, plastics, rubber
and zinc alloys give useful secondary advantages in this
respect.
[0075] The provision of the non-rotating bushing also reduces drill
string harmonics, and can help to prevent differential sticking of
the string.
[0076] FIG. 19 shows a further embodiment of apparatus for
mobilising drill cuttings in a well comprising a sleeve 5', a
bushing 7' and a clamp 9' similar to that previously described for
the first embodiment, and assembled onto the string T in the same
way.
[0077] The sleeve 5' has vanes 22 mounted on the upper large
diameter section. Only one vane 22 is mounted on each leaf of the
sleeve, and the vanes are spaced apart on the circumference of the
assembled sleeve 5' at equal distances, so that the vanes 22 are
diametrically opposed to one another.
[0078] The vanes 22 are generally straight, but are attached to the
sleeve 5' at an angle that is offset with respect to the axis of
the sleeve 5', from top right to bottom left at around 5.degree.
wrt the axis. Each vane 22 typically has a concave surface on one
side, typically that facing the direction of rotation, as best seen
in FIG. 20. The concave surface typically acts as a scoop to create
turbulence in the fluid flowing up the annulus between the sleeve
5' and the borehole. The radius of curvature of the concave surface
changes with the axial position on the vane, as shown in FIGS. 20
and 21, so that at the lower end of the blade (see B in FIG. 19)
the concave surface has a small curvature with the radially
outermost part of the blade being nearly perpendicular to the
tangent of the circumference of the sleeve 5'; whereas at the upper
end of the blade (see A at FIG. 19) the radially outermost part of
the blade is more curved and approaches a tangent to the
circumference of the sleeve 5'. This graduation in the radius of
curvature of the concave surface guides the fluid flowing past the
vane 22 towards the sleeve 5', where turbulence and flow rates are
highest, and this keeps the cuttings in suspension for longer.
[0079] In some other embodiments of vanes, the change in the radius
of curvature is not required, and a simple regular concave surface
as shown in FIGS. 22 and 23 will suffice. The vane shown in FIG. 22
can be modified by cutting out a small portion towards the centre
of the radially outermost edge of the vane. Such an embodiment of a
vane 22' is shown in FIG. 24. In an alternative embodiment, several
notches 90 may be provided on the vane 22'. The notch 90 or notches
can introduce additional turbulence or create a vortex to assist in
the pick-up and agitation of drill cuttings to facilitate their
inclusion in the flow regime.
[0080] The bushing 7' has blades 25. Typically, there are three
blades arranged on each leaf of the bushing 7', and typically these
are circumferentially spaced at equal distances, so that the blades
25 are arranged in three diametrically opposed pairs. Each blade 25
is offset at a 5.degree. angle wrt the axis of the assembled
bushing 7', from top left to bottom right, in an opposite
configuration to the offset of the vanes 22.
[0081] In side profile, as shown in FIG. 19, each blade 25
comprises a central plateau region and radially lower ends. The
width of the blades are consistent throughout their length unlike
the earlier embodiments.
[0082] The nominal external diameter of the bushing 7' is generally
very close to the nominal external diameter of the upper part of
the sleeve 5', and also matches that of the clamp 9', so that apart
from the vanes 22 and the blades 25, there are no upsets on the
outer surface of the apparatus.
[0083] The radial extent of the blades 25 typically exceeds the
radial extent of the vanes 22, so that the plateau sections of the
blades contact the inner surface of the bore in which the apparatus
is deployed, thereby spacing the vanes 22 from the inner surface of
the bore.
[0084] The blades 25 have profiled cross sections (i.e. end-on
views) in the form of an hour glass as best shown in FIGS. 20 and
21, with a wide root radially innermost adjacent the bushing, a
wide top at the radially outermost plateau of the blade that bears
against the borehole wall, and a narrower cutaway portion radially
between the two to facilitate fluid flow between the blades. This
cutaway creates more space for the fluid to pass between the
blades, and helps to avoid impedance of the fluid flow.
[0085] In use the operation of the second embodiment is similar to
the first, but the vanes 22 keep the drill fluid and cuttings close
to the wall of the sleeve as the scoops drive the drill fluid up
through the fluid passageways between adjacent vanes. In addition
to creating thrust in the fluid and pumping the fluid from the
lower end of the apparatus to the upper end, this also creates
turbulence in the fluid, tending to break up clumps of drill
cuttings, to keep the fluid in a liquid phase.
[0086] Modifications and improvements can be incorporated without
departing from the scope of the invention.
* * * * *