Note: Descriptions are shown in the official language in which they were submitted.
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TORQUE REDUCING TUBING COMPONENT
The present invention relates to a component for insertion in a tubing string
to
reduce torque when the tubing string is inserted in to a bore hole. In
particular the
component is for use within the oil, gas and mining industries especially, but
not
exclusively, for drilling of high angle, horizontal and extended reach wells.
In order to drill a well, a drill string is assembled by connecting lengths of
drill
pipe above a drill bit. The drill string is used to transfer rotary motion
from the surface
equipment to the drill bit, thereby causing the drill bit to rotate and
penetrate formation.
The torque required at surface to cause rotation of the drill bit is
substantial due to the
friction caused by contact between the drill string and the wall of the bore.
An inherent part of this drilling process also involves the pumping of
drilling
fluid (mud) down the bore through the inside diameter of the drill string.
This process
is carried out to improve the drilling performance of the bit, to assist with
cooling and
lubrication of the bit as well as to provide a means for the transfer of the
drill cuttings to
surface. It is known to those skilled in the art that the conveyance of the
drill cuttings is
a function of well depth, well profile, shape and size of drill cuttings,
mechanical
properties of the drilling fluid and the capacity of surface mud pumps.
Accumulation of
drill cuttings in the well bore, resulting in the formation of a cuttings bed,
is a major
obstacle in any drilling operation. Such an accumulation of cuttings results
in an
increased down hole torque and in some instances can lead to a drill string
getting stuck
in the bore hole. Therefore, an efficient drilling fluid circulation process
for the
removal of such cuttings is essential for an efficient drilling operation.
It is an object of at least one embodiment of the present invention to provide
a
method of hydra-mechanically agitating a cuttings bed in order to improve the
efficiency of a circulating drilling fluid.
A further object of at least one embodiment of the present invention is to
provide a tubing component which reduces the rotational friction surface area
of the
drill string, therefore reducing torque.
A yet fiu-ther object of at least one embodiment of the present invention is
to
provide a robust, fail safe mechanical, stand-off within the drill string so
as to minimise
the rotational contact between the drill string and the bore wall.
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According to a first aspect of the present invention there is provided a
torque
reducing tubing component for insertion in a tubing string, the component
comprising a
generally tubular body having an inner bore on a longitudinal axis
therethrough, first
and second ends for connecting the component in the tubing string, and an
outer surface
including one or more upsets, the one or more upsets being located
longitudinally along
the body and extending circumferentially around the body.
Preferably the upsets are integral with the tubular body.
Thus the component may be of unitary construction.
Preferably the component is made of steel. Alternatively the component rnay be
made of titanium, aluminium or the like. Advantageously the component is made
of the
same material as the tubing string to which it is attached.
The one or more upsets may be stand-off upsets. Preferably the stand-off
upsets
have an outer diameter greater than those of the connections on the first and
second
ends. In this way the outer surface of the stand-off upsets are the only
points of the
tubing string in contact with the bore hole wall.
Preferably upon the outer surface of each stand-off upset are located a
plurality
of longitudinally extending arc grooves. More preferably the arc grooves
spiral around
the tubular body in a helical pattern. The arc grooves may provide 360 degree
coverage
on the outer surface of the stand-off upset.
Preferably each arc groove comprises, in the direction of rotation of the
tubing
string, a first leading edge, an arc or cylindrical bed of the groove and a
first trailing
edge, wherein each edge connects the cylindrical bed to the outer surface of
the stand-
off upset at an edge angle. More preferably the first leading edge includes a
positive
leading edge angle. Preferably the positive leading edge angle is greater than
ninety
degrees. More preferably the first trailing edge includes a positive leading
edge angle
also.
Alternatively the one or more upsets may be agitator upsets. Preferably the
agitator upsets have an outer diameter smaller than the outer diameter of the
stand-off
upsets. Thus the agitator upsets do not contact the wall of the bore hole when
in use.
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Preferably upon the outer surface of each agitator upset are located a
plurality of
longitudinally extending notch grooves. More preferably the notch grooves
spiral
around the tubular body in a helical pattern. The notch grooves may provide
360 degree
coverage on the outer surface of the agitator upset.
Preferably each notch groove comprises, in the direction of rotation of the
tubing
string, a second leading edge, a notch or 'V' bed of the groove and a second
trailing
edge, wherein each edge connects the notch to the outer surface of the
agitator upset at
an edge angle. More preferably the second leading edge includes a negative
leading
edge angle. Preferably the negative leading edge angle is less than or equal
to ninety
degrees. More preferably the second trailing edge includes a positive leading
edge
angle.
More preferably the one or more upsets are a combination of stand-off upsets
and agitator upsets. Preferably each stand-off upset is bounded longitudinally
by one or
more agitator upsets.
Preferably the first and second ends comprise threaded pin and box connections
respectively as are known in the art. Preferably also the connections include
joint stand-
off upsets. The joint stand-off upsets may have a smaller outer diameter than
the stand-
off upsets. Advantageously the joint stand-off upsets are integral with the
component.
Alternatively the joint stand-off upsets are made of chromium carbide or
tungsten
carbide in mild steel or equivalent matrix or like material.
In the preferred embodiment of the present invention there are five upsets;
two
joint stand-off upsets located at the first and second ends of the component
respectively
and three combination upsets located equidistantly along the tubular body
between the
first and second ends. More preferably the combination upsets comprise a stand-
off
upset and two agitator upsets, one positioned on either side of the stand-off
upset.
The component may be a short collar, a short drill pipe and/or a short sub.
Alternatively the component may be a casing or liner. In the preferred
embodiment the
component is a drill pipe, having a length approximately equal to the length
of a single
joint of drill pipe as is known in the art.
According to a second aspect of the present invention there is provided a
method
of circulating fluid in a bore hole, the method comprising the steps of
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(a) inserting a tubing string into the bore hole, the tubing string including
a torque
reducing tubing component;
(b) pumping fluid down at least the inner bore of the torque reducing tubing
component;
(c) nimiing the tubing string to cause the torque reducing tubing component to
hydra-mechanically agitate the fluid; and
(d) returning at least a portion of the fluid to the surface via a path over
the outer
surface of the torque reducing tubing component.
Preferably the torque reducing tubing component is according to the first
aspect.
In a preferred embodiment of the present invention, the tubing string is a
drill
string, the fluid is drilling mud and the portion of fluid returned to the
surface includes
drill cuttings.
In a further embodiment of the present invention, the tubing string is a
casing
and the fluid is cement as would occur when cementing a casing.
In step (c) of the method the tubing string may be reciprocated within the
bore
when run. Preferably the tubing string is rotated in the bore when run.
In order to provide a better understanding of the invention, embodiments of
the
invention will now be described by way of example only with reference to the
accompanying figures in which:
Figure 1 a side view of a torque reducing tubing component in accordance with
a first embodiment of the present invention;
Figures 2 (a), (b) and (c) are consecutive longitudinal side views of a torque
reducing tubing component according to a preferred embodiment of the present
invention;
Figure 3 a cross sectional view taken through section AA of the component of
Figure 2; and
Figure 4 a cross sectional view taken through section BB of the component of
Figure 2.
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Referring initially to Figure 1, there is illustrated a torque reducing tubing
component, generally indicated by reference numeral 10, according to a first
embodiment of the present invention. The component 10 comprises a generally
tubular
or cylindrical body 12 having an inner bore (not shown) on a longitudinal axis
extending through the length of the component 10.
At a first end 14 of the component 10 is located a conical threaded pin 16 as
is
known in the art. At a second end 18 of the component 10 is located a box
section 20 as
is known in the art. Pin 16 and box section 20 are used to attach the
component 10 to
adjacent sections of a tubing string (not shown).
Also shown in Figure 1 are raised portions or upsets 22-30. The upsets 22-30
are
located on the outer surface 32 of the component 10. Each upset 22-30 is
located
longitudinally on the tubular body I2 and each upset 22-30 is arranged
circumferentially around the body 12.
The component 10 is of unitary construction being machined from a single piece
of steel, as is known in the art for tubing.
At the first end 14 and the second end 18 over the conical threaded pin 16 and
box section 20, there are located upsets 22, 30. Upsets 22, 30 are joint stand-
off upsets.
The joint stand-off upsets 22, 30, provide a contact bearing surface at each
end 14, 18 of
the component 10. Such a contact surface provides a support at the joint
between the
end 14, 18 of the component 10 and adjacent tubing components in the tubing
string.
Located equidistantly between the first 14 and second 18 ends of the component
are three upsets 24, 26, 28. Each of the upsets 24, 26, 28 are equivalent.
Each upset
24, 26, 28 comprises a stand-off upset 34 centrally located the stand-off
upset 34 being
bounded on each side by an agitator upset 36, 38. These upsets 24, 26, 28 will
be
described with reference to a single upset, 24 say. The stand-off upset 34 has
an outside
diameter which is greater than any other diameter on the component 10. Thus,
in
operation the stand-off upsets 34 located on each of the upsets 24, 26, 28
will provide
the only contact points between the tubing string and bore wall. The reduced
contact
surface area between the tubing string and the bore wall reduces the friction
between the
tubing string and the bore wall, and consequently reduced torque is required
to rotate
the tubing string or to reciprocate the tubing string within the bore.
Agitator upsets 36,
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38 bounding the stand-off upset 34 provide a profile on the component 10 which
assists
in directing fluid around the outside surface 32 of the component 10. As shown
in
Figure 1, the stand-off upsets 34 and agitator upsets 36, 38 comprise a smooth
outer
surface which is parallel to the longitudinal axis of the component 10 and
taper to the
diameter of the component 10, thus there are no significant ledges within the
tubing
component to increase friction between the tubing string and the bore hole
wall.
Reference is now made to Figures 2(a), (b) and (c) of the drawings in which is
shown a preferred embodiment of the present invention. The tubing component in
the
preferred invention is based on a length of drill pipe, this drill pipe
component being
generally indicated by reference numeral 40. Like parts to those of the
embodiment of
Figure 1 have been given the same reference numeral but are now suffixed "a".
The
drill pipe 40 comprises a tubular body 42 onto which is mounted a number of
upsets.
Reference is first made to Figure 2(a) which shows an upper section of the
drill
pipe component 40. Starting at the second end 18a of the drill pipe component
40 there
is illustrated a box section 20a onto which is mounted a joint stand-off upset
22a, as
described hereinbefore with reference to Figure 1. The joint stand-off upset
22a tapers
to the tubular body 12a. The tubular body 12a between the box section 20a and
an
upset 24a is length of a drill pipe 42. Upset 24a comprises from the upper
side an
agitator upset 36a, a stand-off upset 34a and a further agitator upset 38a.
The outer
diameter of the stand-off upset 34a is greater than both the outside diameter
of agitator
upsets 36a, 38a and the joint stand-off upset 22a. Therefore, when the drill
pipe 40
component is installed on the drill string, only the outer surfaces of the
stand-off upset
34a will be in contact with the bore hole wall for this section of the drill
pipe component
40.
In this embodiment, stand-off upset 34a includes on its outer surface 44 five
longitudinally extending arc grooves 46. The arc grooves 46 spiral around the
tubular
body 12a in a helical pattern. The arc grooves 46 provide 360° coverage
on the outer
surface 44 of the stand-off upset 34a.
Each arc groove 46 comprises a first leading edge 48, an arc or cylindrical
bed
50 and a first trailing edge 52. Each edge 48, 52 connects the cylindrical bed
50 to the
outer surface 44 of the stand-off upset 34a at an edge angle 54, 56
respectively. This is
shown more clearly in Figure 3, which shows a section through Line A-A of
Figure 2,
which is a section through the stand-off upset 34a.
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In Figure 3 there is seen the tubular body 12a, outer surface 44 and a central
inner bore 58. On the outer surface 44 are five arc grooves 46. Each arc
groove
comprises a cylindrical bed 50 with a first leading edge 48 and first trailing
edge 52,
bounding the bed 50 and connecting the bed 50 to the outer surface 44. Also
illustrated
are edge angles 54, 56. As is seen in the diagram, edge angles 54, 56 are
positive edge
angles, being acute. That is edge angles 54, 56 are both less than 90°.
In use, the depth, shape and angle of the arc grooves 46 on the outer surface
44
of the stand-off upset 34 relative to the longitudinal axis direct the flow of
the drilling
fluid around the stand-off upset 34 at a relatively high velocity in such a
way so as to
create a film of fluid between the stand-off upset 34 and the bore wall. This
has the
effect of creating a marine bearing film between the two surfaces, resulting
in the
reduction of torque and drag co-efficient friction, as well as reduction in
wear on the
bore wall, when the bore wall is cased.
Referring again to Figure 2(a), the stand-off upset 34a is bounded by agitator
upsets 36a, 38a. Each agitator upset 36a, 38a has a smaller outer diameter
than the
stand-off upset 34a, and therefore the agitator upsets 36a, 38a do not contact
the wall of
the bore hole when in use. A description of a single agitator upset, 36a say
will now be
given, although it will be appreciated that this description is relevant to
all agitator
upsets within the preferred embodiment shown in Figure 2.
Agitator upset 36a has an outer surface 60 upon which is located five
longitudinally extending arc grooves 62. Each of the arc grooves 62 spiral
around the
tubular body 12a to provide 360° coverage on the outer surface 60 of
the agitator upset
36a. Each arc groove 62 comprises, in the direction of rotation of the drill
string, a
second leading edge 64, a notch 66 which is a v-bed of the groove 62 and a
second
trailing edge 68. Each edge 64,68 connects the notch 66 to the outer surface
60 of the
agitator upset 36 at an edge angle 70, 72 respectively (as will be described
hereinafter
with reference to Figure 4). Further, in a longitudinal direction each of the
notch
grooves 62 taper in width as they spiral upwards towards the second end 18a of
the drill
pipe component 40.
In order to have a clearer understanding of the notch groove 62, we refer to
Figure 4 which illustrates a sectional view through Line B-B of Figure 2. This
cross
sectional view of agitator upset 36a includes the inner bore 58 of the tubular
body 12a
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with the outer surface 60. Each notch groove 62 has a second leading edge 64
and a
second trailing edge 68. Between the edges 64,68 is located a notch or v-
groove 66.
The v-groove 66 is created by the edge angles 70, 72. Edge angle 70 is a
positive or
acute angle, being less than 90°, while edge angle 72 is an obtuse
angle, being greater
than or equal to 90°.
In use during a rotary drilling operation, the relationship between the
leading
edge 64 and the trailing edge 68 of the notch grooves 62 of the agitator
upsets 36 causes
the creation of differential pressure zones. These differential pressure zones
serve to
attract drill cuttings away from the well bore wall and into the mainstream
flow of the
drilling fluid, therefore resulting in a more effective conveyance of the
drill cuttings to
the surface. This is achieved as the drill pipe component 40 is rotated within
a well
bore, in conjunction with the drill string, it forms a hydra-mechanical
agitation means to
move fluid within the well bore.
It will be appreciated that the upsets 26a and 28a shown in Figures 2(b) and
2(c)
are substantially identical to the upset 24a shown in Figure 2(a) and
described
hereinbefore. Referring to Figure 2(c), it is seen that at the lower or first
end 14a of the
drill pipe component 40 there is a conical threaded pin 16a for connecting the
drill pipe
component 40 to adjacent drill pipe lengths within the drill string. Located
at the end
14a of the drill pipe component 40 is a joint stand-off upset 30a, which is
similar in
description to the joint stand-off 22a, discussed previously. Joint stand-offs
22a, 30a
are manufactured by machining small spiral grooves around the outer surface,
so as, in
use, they reduce interference with the annulus flow cross sectional area at
the ends 14a,
18a of the drill pipe component 40. In the preferred embodiment, joint stand-
offs 22a
and 30a are formed integrally with the drill pipe component 40. Alternatively,
they
could be made of chromium carbide or the like laid over the outer
circumference of the
ends 14a, 18a.
The drill pipe component 40 of the preferred embodiment has a length
approximately equal to the length of a single joint of drill pipe. Thus, the
present
invention differs from conventional arrangements of upset tubular designs in
so far as it
incorporates hydra-mechanical spirally profiled agitator zones on both ends of
each
stand-off upset, therefore resulting in a longer agitator zones) compared with
conventional arrangements, yet ensuring zero contact between the agitator
zones and the
well bore wall. This unique feature makes the present invention a very
effective tool for
cuttings bed agitation at low circulation pressure drilling environment,
whether in rotary
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or sliding (reciprocating) drilling modes.
A principal advantage of the present invention is therefore that it provides a
tubing component which provides a hydra-mechanical means of agitating the
cuttings
bed in a well bore, and so inherently has the effect of improving the drilling
fluid
circulation when drilling a bore hole.
A further advantage of the present invention is that it reduces the rotational
friction surface area of a tubing string, therefore reducing the torque
required to rotate
the tubing string.
The present invention also has the advantage that it is a robust, fail safe,
mechanical, stand-off element that forms part of a tubing string, thereby
minimising the
rotational contact between the tubing string and the bore wall, such a stand-
off reduces
the downhole torque and drag and also prevents damage or wear to a drill
string and a
cased section of a well bore if in place.
Further modifications and improvements may be incorporated to the invention
hereinbefore described without departing from the scope thereof. For example,
the
preferred embodiment described is with reference to a drill pipe in a drill
string,
however the tubing component may equally be formed from a section of casing,
thus the
stand-off upsets would reduce friction as the casing is run into the bore
hole, while the
agitator upsets would provide efficient mixing and agitation of the cement
during
cementing of the casing. It will also be appreciated that the features of the
tubing
component could be adapted onto a short collar, a short drill pipe and/or a
short sub.
