Note: Descriptions are shown in the official language in which they were submitted.
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' APPARATUS AND METHODS FOR USE WITH DRILLING FLUIDS
TECHNICAL FIELD
The invention relates to apparatus and associated methods for use with
drilling
fluid. In particular, but not exclusively, the invention relates to apparatus
for
conditioning of a drilling fluid for circulation downhole.
Certain embodiments relates to the apparatus and methods used when milling.
BACKGROUND
In downhole operations, such as in the drilling of bores to access subsurface
reservoirs (e.g. oil and gas reservoirs), drilling fluids are used to, among
other things,
remove drill cuttings and to cool drill bits. Drilling fluid consists
typically of a base liquid
with various chemicals and powdered particles combined together in order to
provide
suitable properties to perform a particular downhole operation. The base fluid
is
generally water or synthetic oil; and the powdered particles are usually clays
(drilling
fluid is often referred to as 'mud).
The various properties of the mud can be split into chemical and physical
properties. For example, chemically the mud can be a particular acidity and
salinity in
order to minimize any chemical damage done by corroding metal parts down-hole
or by
dissolving/swelling various rock types through which the drilling is
occurring. The clays
suspended in the mud are generally there to provide the useful physical
properties for
the mud, including density, viscosity and gel strength. The density can
provide a
hydrostatic pressure overbalance on the fluid pressure in the rock, to prevent
fluid
flowing' out of the surrounding formation and into the well (known as a kick,
the
precursor to a blow-out if left uncontrolled). The viscosity can influence the
ability of the
mud to lift drilled cuttings out of a well, for example, as the mud flows back
up an
annulus between the drill pipe and the hole or the casing. The gel strength
influences
the ability of the mud to `set' when it is not flowing (drilling fluid is
typically thixotropic),
and can prevent the drilled cuttings from dropping back down the hole when the
pumps
are turned off (e.g. whilst making a connection or while tripping into or out
of the well).
,Another factor in lifting the cuttings out of the hole is the speed at which
the
mud is flowing to flush them up and then out of the well. If the mud is thick
and viscous
it will require much energy (by creating back-pressure) to pump it at high
speeds. Mud
pumps have pressure/power limits so if the mud is too thick, the mud is not
pumped
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fast enough. Gel strength can also be linked to viscosity, generally the
higher the
viscosity the higher the gel strength can be.
Drilling fluid normally operates hot because down hole temperatures are
typically 120-140 C (248-284 F) but can get over 200 C (392 F). So the
drilling fluid
acts like a heat exchanger between the hot rock and the cold surface
temperature.
Most Mud is used for drilling, which tends to be a continuous operation with
the mud
circulating and in equilibrium, that is the mud properties are generally
stable. When re-
starting the mud pumps it is common to start the pumps slowly. This is known
as
'breaking circulation' to allow the gel's strength some time to reduce. After
longer
periods of mud stagnation (e.g. after a trip), after breaking circulation,
when starting to
drill it is common to use a slightly lower flow rate as the mud is subject to
shear
thinning and warms up, and in order to prevent excess pressures on the hole
and on
the equipment. A driller can see this effect on his pump pressure gauge; the
pressure
gradually drops off as the mud thins to the correct circulating equilibrium.
Tight nozzles in the drill bit are used to jet the mud at the cutting face;
this
improves the rate of drilling penetration particularly in softer rocks. It is
also known that
that the nozzles assist in the shear thinning of the mud. However, this comes
at a
pressure/power/flow-rate cost to the mud pumps.
Sometimes a rig will simply circulate mud through the string, doing nothing
really productive until the mud is judged to be sufficiently conditioned.
Considerable rig
time can be wasted 'circulating and conditioning' the mud; particularly in
preparation for
a milling operation, during which optimal drilling mud conditioning is
critical for success.
A mill will be used in circumstances where is it necessary to cut the metal
casing, for
example to form a window in the casing, or when a section of casing simply
needs to
be ground away. This is often achieved by rotating a tungsten carbide cutter
or bit/mill
onto the casing to turn the casing into metal shavings/swarf, which then need
to be
flushed out of the hole by the mud. Metal swarf is much denser than normal
drilled
rock, and has a tendency to clump, and thus the mud needs to be thicker and
have a
better gel strength to perform properly. Starting milling before the mud is
not sufficiently
thinned and capable of being pumped at a rate sufficient to carry the the
swarf out of
the bore is likely to lead to blockage of the annulus with swarf, and the mill
and the
associated string becoming stuck in the bore, resulting in considerable damage
to
equipment and considerable and very expensive delay.
This is particularly problematic when milling with extendable cutters: such
cutters are often powered by a very tight nozzle which creates a differential
pressure to
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push piston-actuated cutters outwards radially. This creates several problems
for
conditioning the mud. The tight nozzle significantly limits the possible flow-
rate making
the initial time for a complete drilling mud circulation (from surface through
the drill
string to the cutter, through the mill nozzles, and then back to surface
through the
annulus) very long indeed, also the string cannot be moved (particularly
rotated) while
this is occurring ¨ otherwise milling will effectively start. The combination
of the
viscous drilling fluid used in milling operations and the long circulation
time may require
the drilling fluid to be circulated for an extended period, for example 18
hours or more,
before the fluid has been sufficiently conditioned and its viscosity reduced
to permit the
circulation rate to be increased to a rate sufficient for milling to commence.
This
represents a very significant expense for the rig operator. Furthermore, the
initial
viscosity of the unconditioned drilling fluid places a high load on the fluid
circulation
apparatus, and it is not unknown for an operator to misjudge initial
conditions and find
that it simply is not possible to circulate the unconditioned fluid with the
existing pumps
and other equipment.
This background serves to set a scene to allow a skilled reader to better
appreciate the following description. Therefore, none of the above discussion
should
necessarily be taken as an acknowledgement that that discussion is part of the
state of
the art or is common general knowledge. One or more aspects/embodiments of the
invention may or may not address one or more of the background issues.
SUMMARY
According to an aspect of the invention there is provided a method for
facilitating a downhole operation, the method comprising:
providing a drilling fluid conditioning device in a proximal portion of a
tubular
string providing mounting for a cutting tool on a distal downhole portion of
the tubular
string;
circulating drilling fluid through the drilling fluid conditioning device and
the
tubular string to condition the drilling fluid;
removing the drilling fluid conditioning device from the string; and
.circulating the conditioned drilling fluid through the tubular string and the
cutting
tool.
According to another aspect of the invention there is provided a drilling
fluid
conditioning device comprising a tubular body configured for incorporation in
a proximal
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portion of a tubular string extending to a distal downhole location, the body
configured
to induce shear thinning of fluid passing therethrough.
According to a further aspect of the present invention there is provided
apparatus comprising:
a tubular string providing mounting for a cutting tool on a distal end of the
string;
and
'a drilling fluid conditioning device for coupling with the tubular string at
a
proximal end of the string,
wherein the drilling fluid conditioning device is removable from the tubular
string
prior to operation of the cutting tool.
Although reference is made primarily herein to the use of cutting tools,
aspects
of the invention may be utilised in relation to other downhole tools or
devices.
Rather than physically removing the drilling fluid conditioning device from
the
string ft also possible to modify the device to, for example, remove a flow
restriction
from the device, or redirected fluid around or past the device.
The drilling fluid conditioning device may be configured to induce shear
thinning
of fluid passing therethrough, for example by accelerating the fluid. Thus, if
a drilling
fluid is passed through the device the viscosity of the fluid decreases, and
the fluid is
more easily circulated.
The drilling fluid conditioning device may be incorporated in the circulation
path
for the, drilling fluid only until the drilling fluid is judged to be suitably
conditioned to
permit a downhole operation to commence. Typically, the downhole operation
will be a
cutting operation, such as drilling, reaming or milling. By removing the
conditioning
device from the circulation path the losses associated with the device are
also removed
from the fluid circulation system, reducing the load placed on associated
pumps and
the like, and potentially permitting a higher fluid circulation rate to be
achieved.
A bypass tool may be incorporated in the tubular string, typically towards the
distal end of the string, such that the drilling fluid may bypass the cutting
tool during
initial Circulation. This may facilitate initiation of circulation of more
viscous fluids, as
the circulating fluid bypasses the nozzles in the cutting tool, and may
facilitate higher
circulation rates to accelerate the heating of the drilling fluid to a desired
level. The
presence of an open bypass tool also allows the drilling fluid to be
circulated without
activating or actuating fluid-powered tools located below the bypass tool.
Thus, for
example, the presence of a bypass tool allows circulation of fluid at
relatively high rates
without activating a fluid pressure-actuated cutting tool with extendable
cutting blades
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provided on the string below the bypass tool. This would allow the operator to
rotate or
reciprocate the string as the fluid is circulated, and further accelerate the
conditioning
of the fluid, safe in the knowledge that the cutters would not extend.
According to an aspect of the invention there is provided a drilling fluid
5 apparatus and associated methods. The apparatus and methods may be useful
to
reduce the time to condition mud sufficiently, prior to starting a milling
operation.
The apparatus may be configured to condition a drilling fluid to be supplied
to a
downhole assembly. The apparatus may comprise a conditioning device configured
to
thin the drilling fluid passing therethrough. The apparatus may be configured
to be
positioned at a surface region of a wellbore.
*The conditioning device may be configured to induce a shear flow in the
fluid.
The conditioning device may be configured to induce a turbulent flow in the
fluid. The
conditioning device may be configured to induce an eddy current flow in the
fluid. The
conditioning device may be configured to stimulate, or generate, heating of
the fluid.
The conditioning device may be configured to provide a friction in the fluid.
The
conditioning device may be configured to provide an internal friction in the
fluid. The
conditioning device may be configured to provide an increased internal
friction in the
fluid. The conditioning device may be configured to provide an external
friction with the
fluid, such as a friction between the fluid and the apparatus, or between the
fluid and a
flowpath surface (e.g. a toolstring throughbore). The conditioning device may
be
configured to provide an increased external friction with the fluid.
Conditioning may comprise modifying the drilling fluid. Conditioning may
comprise adapting the drilling fluid. Conditioning may comprise altering a
physical
property of the drilling fluid. Conditioning may comprise adjusting, or
modifying, the
viscosity of the drilling fluid. Thinning may comprise reducing a viscosity of
the fluid.
The conditioning device may comprise a flow restrictor. The conditioning
device
may comprise a valve. The conditioning device may comprise a nozzle. The
conditioning device may comprise a choke. The conditioning device may comprise
a
throttle. The conditioning device may comprise an inlet. The conditioning
device may
comprise an outlet. The outlet may comprise a reduced cross-sectional area
relative to
the inlet.
The conditioning device may be variable. The conditioning device may be
adjustable. The conditioning device may be removable. The conditioning
apparatus
may be configured to permit selective positioning of the conditioning device.
The
conditioning apparatus may be configured to permit removal and/or replacement
of the
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conditioning device without retrieval of a toolstring. The apparatus may be
configured
to provide downhole access, such as to a downhole tool, without requiring
access
through the conditioning device.
The conditioning device may be configured to induce a predetermined thinning
of the fluid. The conditioning device may be configured to induce a
predetermined
relative thinning of the fluid. The conditioning device may be configured to
induce a
predetermined pressure differential in the fluid. The conditioning device may
be
configured to provide a predetermined relative acceleration of the fluid. The
conditioning device may be configured to thin the fluid according to one or
more
characteristics of the fluid supplied to the conditioning device. The
characteristic may
comprise a velocity. The characteristic may comprise a temperature. The
characteristic
may comprise a viscosity.
The conditioning device may be configured to condition a substantially cold
drilling fluid. The conditioning device may be configured to condition a
substantially
thick drilling fluid.
The conditioning device may be configured to receive the drilling fluid from a
pump. The drilling fluid may be supplied to the conditioning device from the
pump. The
conditioning device may be configured to be located proximal to the pump. The
conditioning device may be configured to be located proximal to a BOP. The
conditioning device may be configured to be located proximal to a drill drive.
The
conditioning device may be configured to be located proximal to the surface
region.
The conditioning device may be configured to be located nearer to the surface
region
than to the downhole assembly. The conditioning device may be configured to be
located distal to the downhole assembly.
The apparatus may comprise a plurality of conditioning devices. The plurality
of
conditioning devices may be arranged in parallel, and/or series (e.g. one
after the other
in the direction of flow). The plurality of conditioning devices may be
configured to
provide a sequential thinning of the fluid. The plurality of conditioning
devices may be
configured to provide a gradual thinning from an initial viscosity, uphole of
a first
device; to an exit viscosity downhole of a lowermost device.
The conditioning device may be configured to be located downhole of a drill
drive. For example, the conditioning device may be configured to be located
downhole
of a surface drive, such as a rotary table or a topdrive.
The conditioning device may be configured to be located uphole of a drill
drive.
The conditioning device may be configured to be located upstream of a drill
drive. The
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conditioning device may be configured to be located between a drill drive and
the
pump. For example, the conditioning device may be configured to be located
between
a surface drill drive, such as a rotary table or a topdrive, and the pump. The
conditioning device may be configured to be located uphole of a toolstring.
The conditioning device may form part of a toolstring (e.g. integrally
formed).
The apparatus may be configured to attach to a toolstring. The apparatus may
be configured to be inline with a toolstring throughbore when in use. The
apparatus
may be configured to supply a conditioned fluid to a throughbore. The
apparatus may
be configured to supply the conditioned fluid to a throughbore directly from a
conditioning device outlet. The apparatus may be configured to provide a
substantially
uninterrupted flow of fluid from the conditioning device outlet.
The apparatus may comprise a tubular. The conditioning device may be
configured to be located at an, upper portion of a toolstring; such as a
drillstring or a
milling string. The conditioning device may be configured to be located at an
uppermost
portion of a toolstring; such as in a tubular coupled to a surface drive.
The apparatus may be configured to condition a drilling fluid for a milling
operation.
The apparatus may be configured to condition a drilling fluid for a drilling
operation.
The drilling fluid may comprise a milling fluid. The drilling fluid may
comprise a
mud.
The apparatus may be configured for use with a milling tool. The apparatus may
be configured for use with a bypass tool.
The apparatus may comprise a milling tool. The apparatus may comprise a
bypass tool.
The apparatus may be configured for use with a reaming tool.
'According to an aspect of the invention there is provided a method of
conditioning a drilling fluid to be supplied to a downhole assembly.
The method may comprise positioning a drilling fluid apparatus comprising a
conditioning device at a surface region of a wellbore.
The method may comprise passing a drilling fluid through the conditioning
device.
The method may comprise thinning the drilling fluid that passes through the
conditioning device.
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,The method may comprise pumping the drilling fluid from a fluid source, such
as a mud tank, to the conditioning device.
The method may comprise passing the thinned fluid downhole through a
drillstring to the downhole assembly.
The method may comprise passing the fluid through the conditioning device
remotely from the downhole assembly.
The method may comprise passing the fluid through a substantial portion of the
drillstring subsequent to passing through the conditioning device.
*According to an aspect of the invention there is provided a conditioning
device.
The device may be configured to thin a drilling fluid passing therethrough,
and may
comprising:
an inlet portion; and
an outlet portion, the outlet portion being downhole of the inlet portion.
The outlet may provide a relative flow constriction, compared to the inlet
portion.
.The conditioning device may comprise an exit portion downhole of the outlet
portion. The exit portion may be configured to provide a substantially
unimpeded flow
of fluid. The exit portion may comprise a throughbore to a toolstring. The
exit portion
may comprise a substantially full diameter toolstring throughbore.
According to an aspect of the invention there is provided a drilling fluid
apparatus configured to condition a drilling fluid to be supplied to a
downhole
assembly; the apparatus comprising a conditioning device configured to thin
the drilling
fluid passing therethrough; and the apparatus configured to be positioned at a
surface
region of a wellbore.
According to an aspect of the invention there is provided a method of
conditioning a drilling fluid to be supplied to a downhole assembly.
The method may comprise:
positioning a drilling fluid apparatus comprising a conditioning device at a
surface region of a wellbore;
passing a drilling fluid through the conditioning device; and
'thinning the drilling fluid that passes through the conditioning device.
The invention includes one or more corresponding aspects, embodiments or
features in isolation or in various combinations whether or not specifically
stated
(including claimed) in that combination or in isolation. For example, it will
readily be
appreciated that features recited as optional with respect to the one aspect
may be
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additionally applicable with respect to the other aspects without the need to
explicitly
and unnecessarily list those various combinations and permutations here (e.g.
the
conditioning device of one aspect may comprise features of any other aspect).
In addition, corresponding means for performing one or more of the discussed
functions are also within the present disclosure.
'It will be appreciated that one or more embodiments/aspects may be useful in
conditioning a drilling fluid.
The above summary is intended to be merely exemplary and non-limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in which:
Figure 1 shows a schematic view of an apparatus in accordance with a first
embodiment of the invention;
Figure 2 shows a cross-sectional view of a portion of the apparatus of Figure
1;
and
Figure 3 shows a detail view of the cross-section of Figure 2; and
Figure 4 shows a schematic view of an apparatus in accordance with a second
embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1 shows a schematic view of apparatus 10 in accordance with an
exemplary embodiment. In this example, the apparatus 10 is shown in use in
preparation for a milling operation, and can be considered to be mounted to an
upper
portion 12 of a drill pipe string 14 at a proximal or surface region 16. Here,
the surface
region is a rig floor.
The drill pipe 14 extends into and through a bore 18, and may be, for example,
2,450 to 3,050 metres (8,000 to 10,000 feet) long. In the embodiment shown,
the bore
18 is a cased hole, in which a metal bore-lining casing has been cemented in
place.
The drill pipe 14 has a milling tool 20 mounted at its lower or distal end,
and which
milling tool 20 forms part of a bottom hole assembly (BHA). The milling tool
20 has
cutters 22 powered by a differential piston and including a pressure-
differential creating
nozzle to selectively extend the cutters 22 when milling is desired.
=
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In use, the drill pipe 14 is rotated by a top drive 24 positioned above the
apparatus 10. The drill pipe 14 transfers rotation from the top drive 24 to
the milling tool
20. Drilling fluid (i.e mud) is pumped in from mud pumps (not shown) via a
feed line 26
at the top drive 24. The mud is pumped through the apparatus 10, and through a
5 conditioning device (as will be further described below), downhole
through a central
throughbore 28 of the drill pipe 14 to the milling tool 20.
The mud supplied to the apparatus 10 from the mud pumps is generally
unconditioned when starting the pumps after an extended period of inactivity,
or when
initiating an operation using a fresh batch of drilling fluid, or when
switching drilling
10 fluids. Accordingly, the mud is initially relatively cold and thick. As
the mud is pumped
downhole, the apparatus 10 facilitates conditioning of the mud, as will be
described in
more detail with reference to Figures 2 and 3.
In the embodiment shown, the bore 18 is plugged with a cement plug 17.
Figure 2 shows a cross-sectional view of a portion of the apparatus 10 of
Figure
1; and Figure 3 shows a detail view of the cross-section of Figure 2. The
apparatus 10
is configured to facilitate conditioning of a drilling fluid prior to
actuation of the milling
tool 29. The apparatus 10 comprises a conditioning device 15 configured to
thin the
drilling fluid passing therethrough. The apparatus 10 is configured to be
temporarily
positioned in the drill string at the surface region 16 of the wellbore 18, at
a proximal
portion of the drill pipe string 14. The conditioning device 15 has a tubular
body 40,
which is a relatively short sub in the embodiment shown (facilitating manual
handling),
with a box (female) connection 42 at the top 44 and a pin (male) connection 46
at the
bottom 48. The body 40 may thus be readily incorporated in a drill string. A
throat 50 of
the box connection has a short wider bore section 52 with a 30 degree taper at
the end
54 to 'house and support a nozzle seat ring 56. The nozzle seat ring 56 has
circumferential seals 58 in grooves 60 on its outer diameter to seal on the
shorter wide
bore section 52. The nozzle seat ring 56 has an internal bore 62 and a
.shoulder 64 to
house and support a changeable nozzle 66. The nozzle 66 has seals 68 and
grooves
70 on its outside to effect a seal to the internal bore 62 of the nozzle seat
ring 56. In the
embodiment shown, the nozzle 66 is made of case hardened steel. The case
hardened
steel helps to prevent abrasive damage of the high velocity mud. In
alternative
embodiments, the nozzle is made of tungsten carbide or a hard ceramic or a
steel
spray coated with tungsten carbide.
In use, mud can be pumped from the top 44 towards the nozzle 66, forcing the
mud to speed up significantly as it passes through the nozzle 66. As the mud
exits the
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nozzle 66, the mud flows out into a larger internal diameter 71 than the
internal
diameter of the nozzle 66, creating various eddy currents and swirls in its
wake. This
acceleration and subsequent vigorously turbulent situation causes the shearing
effect
which quickly conditions the mud (e.g. thins the mud for use). There is no
obstruction,
such as a metal member in the path of the mud exiting the nozzle 66.
Accordingly, the
significant energy can dissipate within the mud (without damaging further
apparatus,
such as metal components ¨ e.g. drill bits, cutters, motors, etc.).
As will be appreciated, the apparatus 10 can improve, or speeds up, the time
taken to shear/condition the mud. This is assisted by placing the apparatus
10/conditioning device 15 at the beginning of a mud circulating system, at or
near the
surface region 16, which also facilitates removal of the apparatus 10 from the
string
once the mud has been conditioned sufficiently to permit the downhole
operation, in
this example a milling operation, to commence.
In this example, conditioning of the drilling fluid is further facilitated by
provision
of a bypass tool 29 above the milling tool 20. The bypass tool 29 is operable
to open
bypass ports 30 to allow the mud to exit the drill pipe 14, with minimal
restriction, into
an annulus 32 between the drill pipe 14 and the bore 18, without having to
pass
through the milling tool 22 and the associated nozzles.
In use, the bypass ports 30 are initially opened to facilitate circulation of
the
drilling mud while the mud remains in an initial more viscous condition.
Opening of the
ports 30 also prevents radial extension of the cutters 22 before the mud has
been
suitably conditioned, allowing rotation and reciprocation of the string 14
without the
cutters 22 engaging the casing.
Mud passed through the bypass tool 19 travels uphole in the annulus 32 to
surface, where the mud is returned to the mud pumps via a flow line 34 to be
treated or
filtered and recirculated downhole, passing through the mud conditioning
apparatus 10.
The mud is subject to shear thinning on passing through the apparatus 10 and
as the
mud travels downhole, the mud temperature rises. As the mud returns uphole,
the mud
cools, but is generally still warmer on reaching the surface 16 than surface
ambient
temperature.
Once the mud has been circulated for a time through the string 14
incorporating
the apparatus 10 and the open bypass tool 19 and is in the desired condition
to allow
milling to commence, the apparatus 10 is removed from the string 14 and the
bypass
ports 30 are closed. Subsequent circulation of mud will actuate the milling
tool 20 and
extend the cutters 22. When milling, the mud exits the drill pipe 14 through
nozzles in
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the milling tool 20 to cool the cutters 22, assist removal of cuttings and
swarf, and to
transport the cuttings and swarf to the surface 16. The passage of the fluid
through the
milling tool nozzles also causes shear thinning of the fluid, thus assisting
in maintaining
the viscosity of the drilling fluid at a desirable level.
While incorporated in the string the conditioning device 15 does not restrict
access to down-hole tools such as the bypass tool 19 or the milling tool 20,
for example
for activation by balls or darts, because the string may be broken below the
apparatus
in conventional manner and the darts can be dropped from below the
conditioning
10 device 15.
.Once the process of conditioning the mud has finished, and the mud is judged
to be sufficiently conditioned to allow the miiling operation to commence, the
apparatus
10 can be very quickly removed from the system. Consequently, the power usage
and
flow restriction associated with the apparatus 10 is eliminated. The absence
of flow
restrictions above the milling tool 20 is particularly useful in subsequent
cleaning
operations; the valve 19 may have relatively large unrestricted ports 30 so
that at the
end of the milling phase the tool 19 can be re-opened and used to pump fluid
at a
maximum flow rate to clean out all the swarf from the hole as quickly and
efficiently as
possible. Of course the milling operation may comprise a plurality of milling
phases
interspersed by clean-out phases, when the bypass tool 19 is employed to clear
the
annulus of swarf and other debris.
In the embodiment shown, the sub 40 has an NC50 connection, with a 17.8 cm
(7 inch) OD and a 7.6 cm (3 inch) ID. The nozzle 66 shown has a 2.54 cm (1
inch)
ID/Choke. Thus, the nozzle 66 shown has a ratio of 3:1 in diameter. The cross-
sectional area is 9:1 and the kinetic energy increase at the choke is 81:1. A
typical 10
pound per gallon mud (1.2sg) pumped at 500 gpm (1890LPM) would create a
pressure
drop of about 250 psi (1,724 kPa/17 bar). This is basically pure shearing
energy. In the
embodiment shown, the nozzle is configured for use with a mud pump rated to
have
about 27,579 kPa (4000psi) of usable pressure. In use, the apparatus 10 can
reduce
the time required to condition the mud sufficiently to allow milling to
commence. For
example, where an operation may otherwise require 18 hours circulation to
condition
the mud, the apparatus 10 may condition the mud sufficiently within 6 hours of
circulation. Accordingly, the apparatus 10 can save considerable valuable rig
time.
=
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Here, the nozzle seat ring 56 has a tapered inlet 57. The nozzle 66 has a
tapered inlet 67. The nozzle inlet 67 converges to a minimum inner diameter
(ID/choke)
before the diameter of the throughbore 28 sharply increases at a nozzle outlet
69.
The nozzle 66 is removable from the nozzle seat ring 56, through the box
connection 42. Thus, if a different nozzle diameter is desired, the nozzle 66
can be
removed and a different nozzle with a similar OD and different ID can be
inserted into
the nozzle seat ring 56. Likewise, if the nozzle 66 is damaged or needs
replaced, a
new ncizzle can easily be inserted.
Figure 4 shows a schematic view of an apparatus 110 in accordance with a
second embodiment of the invention. The apparatus 110 shown is generally
similar to
that shown in Figure 1; and as such like features share like reference
numerals,
incremented by 100. Accordingly, the apparatus 110 comprises a conditioning
device
115 with a tubular body 140 and a nozzle 166. In the embodiment shown in
Figure 4,
the tubular body 140 is a sub comprising two additional nozzles 194, 196 in
series with
the first nozzle 166. Accordingly, the mud is sequentially sheared and thinned
as it
passes through the succession of nozzles 166, 194, 196. Because the
conditioning
device 115 is at/near surface 116, it can be quickly and easily installed or
removed as
required.
It will be appreciated that any of the aforementioned apparatus may have other
functions in addition to the mentioned functions, and that these functions may
be
performed by the same apparatus.
The applicant hereby discloses in isolation each individual feature described
herein and any combination of two or more such features, to the extent that
such
features or combinations are capable of being carried out based on the present
specification as a whole in the light of the common general knowledge of a
person
skilled in the art, irrespective of whether such features or combinations of
features
solve any problems disclosed herein, and without limitation to the scope of
the claims.
The applicant indicates that aspects of the present invention may consist of
any such
individual feature or combination of features. It should be understood that
the
embodiments described herein are merely exemplary and that various
modifications
may be made thereto without departing from the scope of the invention. For
example,
in alternative embodiments (not shown), the apparatus may comprise a plurality
of
subs, each sub with a nozzle. The subs may be connected together, or may have
spacer subs located therebetween. In an alternative embodiment (not shown)
with a
nozzle with a 1.9 cm (0.75") choke ID and a similar drill pipe ID would create
a
CA 02880883 2015-02-02
WO 2014/027178 PCT/GB2013/052072
14
pressure drop of around 797ps1 (54 bar) with a typical 10 pound per gallon mud
(1.2sg)
pumped at 500 gpm (1890LPM). Similarly, a typical 10 pound per gallon mud
(1.2sg)
pumped at 500 gpm (1890LPM) would create a pressure drop in a nozzle with an
ID of
2.24 cm (0.88 inches) of around 430psi (29.3 bar) .
In further embodiments, the nozzle/s could be installed within the circulating
system of the rigs pipe-work; or as a bolt-on piece of kit to it as an
addition to or a
replacement for having the conditioning apparatus at the very top of the drill
string near
the drill floor.
=
