Note: Descriptions are shown in the official language in which they were submitted.
CA 02887196 2015-04-01
COMPONENT OF BOTTOM HOLE ASSEMBLY HAVING UPWARLY-DIRECTED FLUID
CLEANING FLOW AND METHODS OF USING SAME
BACKGROUND
[0001] The field of endeavour relates to a stabilizer and a drill bit for use
in a drill string. The
stabilizer and drill bit preferably, but not exclusively, forms part of a
bottom hole assembly of
the drill string.
[0002] In the drilling of a borehole in the construction of an oil or gas
well, a drill bit is arranged
at a lower end of a drill string, which is rotated to bore the borehole
through a formation. A
drilling fluid, referred to herein as "drilling mud," is pumped through the
drill string to the drill
bit to lubricate the drill bit and returns carrying drill cuttings in an
annulus between an outer wall
of the drill string and the borehole. As the drill bit progresses through the
formation, stands of
drill pipe are added to the drill string. Stands of drill pipe typically
comprise two, three or four
joints of drill pipe threadedly connected together in a mousehole in a
drilling rig floor using an
iron roughneck. The stand is then set back in a fingerboard pipe rack. A joint
of drill pipe is
typically 31ft 6inches long (9.65m). Each joint of drill pipe has a hollow
cylindrical body with a
lower threaded pin end and an upper threaded box end. As the drill bit
progresses in the
borehole, the drill string moves downwardly. When an upper end of the drill
string nears the rig
floor, a stand is pulled out of the fingerboard pipe rack. The top of the
stand is placed in an
elevator, and the lower end aligned with a top of the drill string at well
centre. A lower threaded
pin end of the stand of drill pipe is stabbed into an upper box of the drill
string and threadedly
connected using the iron roughneck. Drilling then continues using rotation of
a top drive, a rotary
table or downhole motor. The drill string can be many hundreds or thousands of
metres long.
[0003] The borehole may be substantially vertical and may comprise deviated
portions. A
deviated portion of a borehole may be horizontal. A horizontal portion of a
bore may be several
kilometres long.
[0004] The drill bit is usually arranged in a Bottom Hole Assembly at the
bottom end of a drill
string. The drill bit has a pin end with a male thread and has a flow bore
leading to a body of the
drill bit. The body of the drill bit has a number of cutting elements with a
plurality of nozzles
therebetween. Drilling mud flows down through the flow bore and out through
the nozzles to
inter alia carry drill cuttings from the drill bit through the annulus.
CA 02887196 2015-04-01
[0005] The drill bit is usually threaded into a box end of a stabilizer. The
stabilizer attempts to
reduce vibration induced by the drill bit progressing through the formation
and to improve
directional stability. The stabilizer is generally a thick walled tubular with
a plurality of spaced
blades thereabout which may be arranged in parallel curved paths which may be
helical, or
spiral. The spaced blades define interleaved valleys. The valleys may also
follow a helical or
spiral path to inter alia facilitate the flow of drill cuttings laden drilling
mud in the annulus
around and along the bottom hole assembly. The stabilizer usually has an upper
box end into
which further components of a Bottom Hole Assembly are attached. Such
components may
include: a Measurement While Drilling (MWD) tool, for obtaining data; a
Logging While
Drilling tool, for logging the data; further stabilizers; drill collars for
providing weight to
facilitate Weight On Bit (WOB); ajar for providing a shock to BHA if a tool or
drill bit becomes
stuck in the borehole; and cross-over subs having pin-to-pin connectors.
[0006] The drill string may be pulled out of the borehole for many reasons,
such as: to change
the drill bit; to allow for a string of casing to be lowered into the borehole
for casing the
borehole; to hang a liner; to set a whipstock for deviated drilling; to lower
milling tools; to fish
for stuck tools; to clean the borehole; and prepare the borehole for
production. The step of
pulling the drill string out of the borehole is known as "tripping-out" and
the step of lowering the
drill string back into the borehole is known as "tripping-in". During
tripping, the string of drill
pipe is not rotated or only rotated slowly in order to facilitate a smooth
movement along a
borehole, which may be vertical, deviated or partly horizontal.
[0007] As the drill string is pulled out of the borehole, a stand of drill
pipe is disconnected using
an iron rough neck and the stand placed back into the fingerboard pipe rack,
usually using a pipe
handling tool, such as a racker.
[0008] During tripping-out, circulation of drilling mud through the drill
string may be
maintained to inter alia maintain a constant head of drilling mud in the well,
inhibit solids
suspended in the drilling mud from settling out; and to maintain a constant
pressure in the
borehole to inhibit the borehole collapsing. During tripping out more drilling
mud will be added
to the well to replace the drill pipe removed from the borehole. During
tripping-in drilling mud
will be displaced from the borehole as the drill string is lowered into the
well.
[0009] It is common to stop circulation of drilling mud during tripping.
Although it is common
during tripping to circulate drilling mud between making or breaking a
threaded connection
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between a stand of drill pipe and the drill string. It is also possible to
have a continuous
circulation of drill mud during tripping using a Continuous Circulation System
to maintain
continuous circulation of drilling mud through the entire drill string during
making or breaking a
connection,
SUMMARY OF THE DISCLOSURE
[0010] A stabilizer incorporates a plurality of blades with interleaved
valleys and may have a
ring or ring segments between the blades over the valleys forming flow
passages. Upon upward
movement of the stabilizer, such as being lifted, reciprocated or upon
tripping-out, an upper face
of the ring may scrape along a wall of the borehole, collecting small solids,
such as clay
particles, which can agglomerate to form clumps, known as balling. Once a
small clump forms,
solids suspended in the drilling mud may additionally land on the clump,
increasing the clump's
size. The clumps stick to the stabilizer, possibly blocking flow passages and
can also fall into the
well. The clumps can build up in parts of the borehole and in a worse case,
block the borehole.
Upon tripping-in and during drilling, a bottom face of the ring may scrape
along a wall of the
borehole, collecting small solids, such as clay particles, which can
agglomerate to form clumps,
known as balling. Once a small clump forms, solids suspended in the drilling
mud may
additionally land on the clump, increasing the clump's size. These clumps may
block or partially
block the flow passages defined by the ring and the valleys.
[0011] Furtheiinore, the balling may occur around the ring or ring segment
during drilling.
[0012] There is disclosed a stabilizer for use in drilling a borehole, the
stabilizer comprising a
cylindrical body having an inner wall defining a flow bore and a plurality of
blades extending
outwardly from said cylindrical body with a valley disposed between adjacent
blades, the
stabilizer further comprising at least one ring segment spaced from said
cylindrical body over at
least one valley to define a flow passage characterised in that said
cylindrical body further
comprises at least one fluid passageway or "hole" therein for conveying
drilling mud from said
flow bore to between the blades.
[0013] The hole may provide a flow path for fresh drilling mud to flow out of
the flow bore and
direct the flow to inhibit clumps of drill cuttings and other solids from
forming, particularly but
not exclusively around the ring segment. The flow through the hole exits the
hole as a jet of fresh
drilling mud. The jet may be sufficient to break up clumps of drilled cuttings
and other solids
which have already formed.
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[0014] The hole may have any suitable cross-sectional shape, such as circular,
oval, square,
rectangular, slot-like or polygonal. There may be more than one hole under
each ring segment.
The holes may be pointed in different directions.
[0015] Optionally, the hole comprises an entrance in said inner wall and an
exit in the at least
one valley. Having the exit positioned in the valley facilitates direction of
the flow of fresh
drilling mud therefrom in a radial direction. Optionally, the hole has an exit
directed through at
least a portion of the flow passage. The flow of fresh drilling mud through
the flow passage may
facilitate fluidizing solids knocked, scraped or reamed from the formation
surrounding the
borehole by the ring segment. The flow of fresh drilling mud through the flow
passage may
encourage a smooth flow of solids-laden drilling mud therethrough. Optionally,
the exit of the
hole is located underneath the ring segment, which may encourage solids-laden
drilling mud to
be pulled through as well as pushing solids through the ring, and may prevent
solids from
settling on the ring. Preferably, the exit of the hole is located underneath
the ring segment,
towards a bottom face thereof, which may allow the jet to develop and have a
spread which
facilitates removal of settled solids and solids about to settle on and about
the ring segment.
[0016] Optionally, the hole is lined with a liner. The liner may provide
erosion resistance in the
body around the entrance, exit and along the length of the hole. Optionally,
the liner projects into
the flow bore of the stabilizer, which may help reduce the risk of erosion of
the body around the
entrance to hole. Optionally, the liner is made from a wear resistant
material, such as tungsten
carbide. Optionally, the hole comprises a nozzle having a nozzle bore through
which drilling
fluid flows. The nozzle provides a jet having known qualities, such as spread
pattern and speed.
The nozzle may also be used to facilitate direction of the jet of fresh
drilling mud. The nozzle
bore has a length and a cross-sectional flow area which changes along the
length. A change in
cross-sectional bore area may induce different jet speeds and spread patterns.
Optionally, the
nozzle bore has a fluid entry end which has a first flow area and a fluid exit
end which has a
smaller flow area. The nozzle preferably reduces in diameter between the fluid
entry end and
fluid exit end. The nozzle bore may have a smooth internal surface which
follows a curved path.
The nozzle may be replaceable, so that the nozzle can be replaced with a
nozzle having different
flow characteristics, such as a different ratio of entry and exit flow areas.
Optionally, the nozzle
has a thread and the hole has a corresponding thread, such that the nozzle can
be threaded into
the hole in the body of the stabilizer.
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[0017] Optionally, the body has a wall that varies in thickness, and includes
a thick wall in the
valley along a portion of the length of the blades and a thin wall under the
ring or ring segment.
Thus, a greater flow area may be obtained under the ring, whilst structural
strength may not be
excessively reduced thanks to additional support provided by the ring or ring
segment, including
a structural component that may be employed therein. Optionally, the hole is
arranged in a
transition zone between the thick wall portion and a thin wall portion. The
hole is thus placed in
a position which minimises reduction of structural integrity, whilst being
placed in a position
which provides a flow of fresh drilling mud to inhibit solids from forming
clumps on the ring
segment. Optionally, the stabilizer has a lower end provided with a box for
receiving a pin of a
drill bit. Optionally, an entrance to the hole is ananged in the body between
the box and the ring.
[0018] Optionally, the hole is arranged at an obtuse angle to the direction of
flow of drilling mud
through the flow bore. The obtuse angle provides an acute angle at the exit
when the hole is
formed along a linear path. The acute angle at the exit, in use, provides a
trajectory for the jet of
fresh drilling mud. Optionally, the hole is arranged at between 140 degrees
and 170 degrees to
the direction of flow of drilling mud through the flow bore, and optionally,
between 150 degrees
and 160 degrees.
[0019] Optionally, the ring segment is arranged between every adjacent blade
to form a complete
ring about the stabilizer. Thus each blade has two ring segments, one to the
left and one to the
right. A complete ring may increase stability. Optionally, only one ring
segment spans between
adjacent blades, such that on a stabilizer with four blades there are only two
ring segments, each
on an opposing side. Optionally, the blades are curved about a central axis of
the stabilizer. The
curved blades may curve about the axis by an angle such that the angle of all
blades adds up to at
least 360 degrees. Thus a complete 360 degree contact with the borehole is
possible along the
length of the blades. With such blade contact, only one ring segment per blade
may be provided,
whilst maintaining vibration control of the drill bit.
[0020] Optionally, the ring or ring segment is arranged on a part of each of
the blades, which
may be a part axially aligned with a main axis of the stabilizer. This may
allow the flow passage
to have sides which are substantially axially aligned. Optionally, the
stabilizer further comprises
an upper portion of thick walled pipe. Optionally, the thick walled pipe has a
box in an upper end
to facilitate connection in a bottom hole assembly. Optionally, the upper
portion has a recess
therein for holding a measuring while drilling ("MWD") device.
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[0021] There is disclosed a stabilizer for use in drilling a borehole, the
stabilizer comprising a
cylindrical body having an inner wall defining a flow bore and a plurality of
blades extending
outwardly from the cylindrical body with a valley formed between adjacent
blades, the stabilizer
further comprising at least one ring or ring segment spaced from the
cylindrical body
characterised in that the cylindrical body further comprises at least one hole
therein for
conveying drilling mud from the flow bore.
[0022] A drill bit incorporates a plurality of blades with interleaved valleys
and may have a ring
or ring segments between the blades over the valleys forming flow passages.
Upon upward
movement of the drill, such as being lifted, reciprocated or upon tripping-
out, an upper face of
the ring may scrape along a wall of the borehole, collecting small solids,
such as clay particles,
which can agglomerate to form clumps, known as balling. Once a small clump
forms, solids
suspended in the drilling mud may additionally land on the clump, increasing
the clump's size.
The clumps stick to the drill bit, possibly blocking flow passages and can
also fall into the well.
The clumps can build up in parts of the borehole and in a worse case, block
the borehole. Upon
tripping-in and during drilling, a bottom face of the ring may scrape along a
wall of the borehole,
collecting small solids, such as clay particles, which can agglomerate to form
clumps, known as
balling. Once a small clump forms, solids suspended in the drilling mud may
additionally land
on the clump, increasing the clump's size. These clumps may block or partially
block the flow
passages defined by the ring and the valleys.
[0023] Furthermore, balling may occur around the ring or ring segment during
drilling.
[0024] There is disclosed a drill bit for use in drilling a borehole, the
drill bit comprising a
cylindrical body having an inner wall defining a flow bore for conveying fresh
drilling mud and
a plurality of blades extending outwardly from the cylindrical body with a
valley disposed
between adjacent blades, the drill bit further comprising at least one ring
segment spaced from
the cylindrical body over at least one valley to define a flow passage through
which cuttings-
laden drilling mud flows, the cylindrical body further comprises at least one
fluid passageway or
"hole" therein for conveying drilling mud from the flow bore, characterised in
that the hole has
an exit directed to provide fresh drilling mud with a trajectory passing
through at least a portion
of the flow passage.
[0025] There is disclosed a drill bit for use in drilling a borehole, the
drill bit comprising a
cylindrical body having an inner wall defining a flow bore for conveying fresh
drilling mud and
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a plurality of blades extending outwardly from the cylindrical body with a
valley disposed
between adjacent blades, the drill bit further comprising at least one ring
segment spaced from
the cylindrical body over at least one valley to define a flow passage through
which cuttings
laden drilling mud flows, the cylindrical body further comprises at least one
fluid passageway or
"hole" therein for conveying drilling mud from the flow bore, characterised in
that the hole has
an exit in the flow passage.
[0026] There is disclosed a drill bit for use in drilling a borehole, the
drill bit comprising a
cylindrical body having an inner wall defining a flow bore for conveying fresh
drilling mud and
a plurality of blades extending outwardly from the cylindrical body with a
valley disposed
between adjacent blades, the drill bit further comprising at least one ring
segment spaced from
the cylindrical body over at least one valley to define a flow passage through
which cuttings
laden drilling mud flows, the cylindrical body further comprises at least one
fluid passageway or
"hole" therein for conveying drilling mud from the flow bore, characterised in
that the hole is
arranged at an obtuse angle to the direction of flow of drilling mud through
the flow bore.
[0027] Optionally, the hole comprises an entrance in the inner wall and an
exit in the at least one
valley. Optionally, the hole has an exit directed through the flow passage.
Optionally, the exit of
the hole is located beneath the ring segment. Optionally, the exit of the hole
is located
underneath the ring segment, preferably towards a bottom face thereof.
Optionally, the hole is
lined with a liner. Optionally, the liner projects into the flow bore of the
drill bit. Optionally, the
liner is made from a wear resistant material, such as tungsten carbide.
Optionally, the hole
comprises a nozzle having a nozzle bore through which drilling fluid flows.
Optionally, the
nozzle bore has a length and a cross-sectional flow area which changes along
the length.
Optionally, the nozzle bore has a fluid entry end which has a first flow area
and a fluid exit end
which has a smaller flow area. The nozzle optionally reduces in diameter
between the fluid entry
end and fluid exit end. The nozzle bore optionally has a smooth internal
surface which follows a
curved path. Advantageously, the nozzle is replaceable, so that the nozzle can
be replaced with a
nozzle having different flow characteristics, such as a different ratio of
entry and exit flow areas.
Optionally, the nozzle has a thread and the hole has a corresponding thread,
such that the nozzle
can be threaded into the hole in the body of the drill bit.
[0028] Optionally, the body has a thick wall in the valley along a portion of
the length of the
blades and a thin wall under the ring or ring segment. Optionally, the hole is
arranged in a
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transition zone between the thick wall portion and thin wall portion.
Optionally, an exit of the
hole is arranged under the ring. Preferably, the hole is arranged at an obtuse
angle to the
direction of flow of drilling mud through the flow bore. Optionally, the hole
is arranged at
between 140 degrees and 170 degrees to the direction of flow of drilling mud
through the flow
bore and optionally, between 150 degrees and 160 degrees.
[0029] Optionally, the ring segment is arranged between every adjacent blade
to form a complete
ring about the drill bit. Thus each blade has two ring segments, one to the
left and one to the
right. Optionally, only one ring segment spans between adjacent blades, such
that on a drill bit
with four blades there are only two ring segments, each on an opposing side.
[0030] Optionally, the ring or ring segment is arranged on a part of each of
the blades.
Optionally the part of each blade is axially aligned with a main axis of the
drill bit.
[0031] Also disclosed is a bottom hole assembly comprising a stabiliser and/or
a drill bit in
accordance with an embodiment of the present disclosure.
[0032] Also disclosed is a method of tripping using a stabilizer and/or drill
bit in accordance
with an embodiment of the present disclosure, the method comprising the steps
of circulating
drilling mud through the flow bore, a portion of the drilling mud passing
through the hole and
through the flow passage.
[0033] Thus solids which are scraped off the wall of the borehole or have
otherwise collected
on the ring segment, are fluidised or inhibited from forming clumps. The solid
particles are thus
suspended in the drilling mud and circulated as any other solids in the
drilling mud, such as drill
cuttings. Clumps which may have already formed may be broken up by the jet of
fresh drilling
mud. The drill cuttings-laden drilling fluid in the flow passage is diluted
with fresh drilling mud
by a small amount.
[0034] Optionally, the drilling mud is circulated between threading
operations. Optionally, the
drilling mud is also circulated during threading operations with a circulating
head. Optionally,
the circulating head comprises a seal which seals inside the drill string or
about the drill string, so
that a threaded connection does not have to be made in order to circulate
drilling mud through
the drill string. Optionally, the drill string is threadedly connected to a
rotor of a top drive and the
drilling mud circulated therethrough. Optionally, a continuous circulation
system is used to
maintain circulation of drilling mud throughout tripping.
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[0035] Also disclosed is a method of drilling a borehole using a drill bit or
stabilizer in
accordance with an embodiment of the present disclosure, the method comprising
the steps of
circulating drilling mud through the flow bore, a portion of the drilling mud
passing through the
hole and through the flow passage. Optionally, the drilling mud is circulated
continuously during
drilling.
[0036] Also disclosed is a method of drilling a borehole using a drill bit in
accordance with an
embodiment of the present disclosure, the method comprising the steps of
circulating drilling
mud through the flow bore, a portion of the drilling mud passing through the
hole and through
the flow passage. Optionally, the drilling mud is circulated continuously
during drilling.
[0037] Also disclosed is an apparatus for use in a bottom hole assembly in
drilling a borehole,
the apparatus comprising a cylindrical body having an inner wall defining a
flow bore and a
plurality of blades extending outwardly from the cylindrical body with a
valley disposed between
adjacent blades, the apparatus further comprising at least one ring segment
spaced from the
cylindrical body over at least one valley to define a flow passage,
characterised in that the
cylindrical body further comprises at least one hole therein for conveying
drilling mud from the
flow bore. The apparatus may be one of a drill bit, stabilizer, on-gauge sub
or other BHA
component..
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] For a better understanding of the disclosed exemplary embodiments of
the invention,
reference will now be made to the accompanying drawings, in which:
[0039] Figures IA and 1B show a schematic view of a drilling rig constructing
a wellbore with a
drill string comprising a stabilizer in accordance with certain of the
embodiments disclosed
herein;
[0040] Figure 2 is a perspective view of a stabilizer in accordance with a
disclosed embodiment
, the stabilizer shown before a layer of hardfacing material has been applied;
[0041] Figure 3 is a side view of the stabilizer shown in Figure 2;
[0042] Figure 4 is an end view of the stabilizer shown in Figure 2;
[0043] Figure 5 is an enlarged view in section of a part of the stabilizer
shown in Figure 2 taken
along line V-V, shown with a layer of hardfacing material applied to parts
thereof, showing
details of a nozzle;
[0044] Figure 6a is a side view of the nozzle shown in Figure 5;
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[0045] Figure 6b is an end view of the nozzle shown in Figure 6a;
[0046] Figure 6c is a view in section taken along line VIc-VIc shown in Figure
6b;
[0047] Figure 7 shows an alternative to the part of the stabilizer shown in
Figure 5;
[0048] Figure 8 shows a further alternative to part of the stabilizer shown in
Figure 7;
[0049] Figure 9 is a perspective view of the stabilizer shown in Figure 2 with
hardfacing
material applied to parts thereof;
[0050] Figure 10 is a drill bit in accordance with an exemplary embodiment
disclosed herein;
and
[0051] Figure 11 is a view in cross-section of part of the drill bit shown in
Figure 10.
DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS
[0052] Referring to Figures 1 a and lb there is shown a drilling rig generally
identified by
reference numeral I. The drilling rig 1 has a derrick 2 arranged on a drill
floor 3 supported on
legs 4. The legs 4 are seated on a substructure 5 on ground 6.
[0053] A top drive apparatus 7 is arranged on a carriage 10' raised and
lowered with a travelling
block 8 on line 9 along a vertical track 10. The line 9 passes over a crown
block 11 located at a
top of the derrick 2 and down to a drawworks 12 on the rig floor 3 for reeling
the line 9 in and
out. A stand of drill pipe 13 depends from an elevator 14. The elevator 14
depends from links 15
which are looped over ears 16 of a swivel 16a of the top drive apparatus 7.
[0054] A drill string 17 passes through a spider 18 in the drill floor 3,
through a wellhead 19 into
a borehole 20 in formation 21. A bottom hole assembly 22 is arranged on a
lower end of the drill
string 17. The bottom hole assembly 22 comprises a drill bit 23 connected to a
stabilizer 100 on
a lower end thereof. The bottom hole assembly also comprises a Measurement
While Drilling
tool 24, a further stabilizer 25 and a drill collar 26. A mud motor may also
be incorporated into
the bottom hole assembly. An annulus 29 is defined between the borehole 20 and
the bottom
hole assembly 22.
[0055] A flow line 30 is fluidly connected at one end to an annulus 29 at the
wellhead 19 and the
other end to an active mud system 31. The annulus 29 is an annular flow
passage defined by the
formation 21 (or casing (not shown) if the borehole is cased) and an outer
surface of the drill
string 17 or bottom hole assembly 22. Returned solids-laden drilling mud DM
flows from the
annulus 29, through wellhead 19, into flow line 30 and to the active mud
system 31, which
cleans and processes the solids-laden drilling mud DM to produce fresh
drilling mud M. The
CA 02887196 2015-04-01
active mud system 31 comprises a trip tank, an active mud tank and a series of
pieces of mud
processing equipment, such as: a shale shaker, a degasser, a mud conditioner,
and a centrifuge.
Fresh drilling mud M is pumped with a mud pump MP at a pressure up to between
200 bar and
1000 bar at between 300 and 4800 litres per minute from the active mud system
31 through a
hose 32 to a goose neck connection 33 on top drive 34 of the top drive
apparatus 7. Processed
and now fresh drilling mud flows through the goose neck connection 33 into a
main rotating
shaft 35. The drilling mud continues to flow through an Internal Blow Out
Preventer (IBOP) 36
and sub 37 and through the drill string 17, when connected.
[0056] An iron rough neck 38 is arranged on the rig floor 3 for rotating the
stand of drill pipe 13
relative to the static drill string 17 to thread the stand of drill pipe 13 to
the drill string 17 or
unthread the stand of drill pipe 13 from the drill string 17.
[0057] The stand of drill pipe 13 is threaded and torqued to the drill string
17 using the iron
roughneck 38. The sub 37 of the top drive apparatus 7 is threadedly connected
to the top of the
connected stand of drill pipe 13. The top drive 34 is activated to rotate the
drill string 17, if
desired. The drill bit 23 drills through the formation 21 extending the
borehole 20. The drilling
mud M is circulated through the drill string 17 and out of nozzles in the
drill bit 23, washing
drilled solids through the annulus to the active mud system 31. Rate Of
Penetration of the drill
bit 23 in a formation may vary dramatically, but may often be in the order of
30 metres per hour.
[0058] When required, the drill string 17 is tripped-out of the borehole 20.
During tripping-out,
the sub 37 of the top drive apparatus 7 is not usually threadedly mated with
the drill string 17,
thus the top drive 34 is not rotationally connected to the drill string 17 or
stands of drill pipe 13.
The elevator 14 is used to raise the drill string 17 until typically two,
three or four joints of drill
pipe are above the rig floor 3. The iron roughneck 38 is used to disconnect a
stand of drill pipe
13. A single joint elevator system 46 may be used to set the stand of drill
pipe 13 back into a
finger board pipe rack 44, which stores a multiplicity of stands of drill pipe
45. The elevator 14 is
then lowered with the top drive apparatus 7 until it is just below the box end
of the stem 49 of the
drill string 17. The elevator 14 is opened and clamped or slideably looped
around the stem 49 of
the drill string 17 above the rig floor 3. The operation is repeated until the
entire drill string 17
and bottom hole assembly 22 are out of the borehole 20. Accordingly, tripping-
out is usually
very quick and can be carried out at 600 metres per hour with modern rigs and
experimental rigs
expect tripping-out at up to 3,600 metres per hour.
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[0059] When required, the drill string 17 is tripped-in to the borehole 20.
During tripping-in, the
sub 37 of the top drive apparatus 7 is not usually threadedly mated with the
drill string 17, thus
the top drive 34 is not rotationally connected to the drill string 17 or
stands of drill pipe 13. A
single joint elevator system 46 may be used to pull a stand of drill pipe 13
from the finger board
pipe rack 44, which stores a multiplicity of stands of drill pipe 45 and is
placed in an elevator 14
hanging above stem 49 at well-centre. The iron roughneck 38 on the rig floor 3
is used to
connect the stand of drill pipe 13 to the stem 49. The elevator 14 is raised
with the top drive
apparatus 7 to lift the drill string 17 a little to allow the spider 18 to be
released. The elevator 14
is then lowered with the top drive apparatus 7 until only a stem 49 of the
drill string 17 is above
the rig floor 3. The operation is repeated until the entire drill string 17
and Bottom Hole
Assembly 22 are at the bottom of the borehole 20. Accordingly, tripping-in is
usually very quick
and can be carried out at 600 metres per hour with modern rigs and
experimental rigs expect
tripping-out at up to 3,600 metres per hour.
[0060] Optionally, the sub 37 of the top drive apparatus 7 is threadedly mated
with the drill
string 17 to allow circulation of drilling mud.
[0061] Optionally, a circulating head 50 is connected to the sub 37. Reference
is made to WO
2009/098473, WO 2009/098474, WO 2009/098478, WO 2009/098482, WO 2010/089572,
WO
2010/089573 which are hereby incorporated by reference for all purposes. The
circulating head
50 has a spear 51 which moves axially into a sealing engagement with the top
end of the stand of
drill pipe 13 held in the elevator 14, which has been threadedly connected to
the drill string 17.
Thus a continuous flow path between the goose neck 33 and the drill string 17
is now provided to
allow drilling mud to circulate through the drill string 17 from the goose
neck 33. As the drill
string 17 is raised when tripping-out or lowered when tripping¨in, drilling
mud can circulate.
The sealing engagement is rated to approximately 5,000 psi (320 bar) to allow
circulation.
[0062] Optionally, a continuous circulation system may be used, such as the
continuous
circulation system (CCS) 55 manufactured by the National Oilwell Varco, which
provides a
continuous circulation of drilling mud during tripping-in and tripping-out.
Reference is made to
WO 98/16716, which is hereby incorporated by reference for all purposes. The
CCS 55 is moved
to well-centre and fits about the pipe stub 49. A lower seal seals about the
stem 49 and allows
drilling mud to flow from the MS into the stem 49 of the drill string 17 via a
flow line even when
the stand of drill pipe 13 is disconnected from the stem 49. The bottom end of
the stand of drill
12
CA 02887196 2015-04-01
pipe 13 is lowered into the CCS 55 and an upper seal seals thereabout. A
middle seal is opened
which provides a flow path for drilling mud to flow from the goose neck 33
through the top drive
34 into the drill string 17. The flow of drilling mud through the flow line is
stopped, and the
stand of drill pipe 13 in threaded to the stem 49. The drill string can then
be tripped-in. The
reverse procedure is used when tripping-out.
[0063] Referring to Figures 2 to 5 and 9, there is shown a stabilizer 100 in
accordance with an
exemplary embodiment of the disclosure. The stabilizer 100 has an upper
portion 101 of heavy
weight pipe and a lower portion 102. The lower portion 102 has a body 103 made
from a single
piece of steel, such as a steel comprising chromium and/or molybdenum and to
the standard
AISI 4145. The body 103 has a flow bore 104 extending from a top end 106 to a
bottom end 108
of the body 103, which provides a drilling mud flow path from the drill string
17 to the drill bit
23. The flow bore 104 is preferably of circular cross-section and has a
constant diameter along at
least a portion of the length of the lower portion 102. The drilling mud M
flows in a downward
direction MA along axis AX. A stub connector 105 is located at the top end 106
of the lower
portion 102 to provide a connection with the upper portion 101. The stub
connector 106 has an
external surface which is welded to the upper portion 102. An internally
threaded box 107 is
provided at the bottom end 108 of the body 103. The internally threaded box
107 has a thread
109 for providing a connection with a pin end (not shown) of drill bit 23.
[0064] The body 103 has four equally spaced blades 110, 111, 112 and 113
defining four valleys
114, 115, 116 and 117. Each blade 110, 111, 112 and 113 has a curved portion
which extends in
a curved path about the axis AX, which may be a helical or spiral path from
the bottom end 108
towards the top end 106 in a clockwise direction when viewed from the bottom
end as shown in
Figure 4. Each curved portion of each blade 110, 111, 112 and 113 has a width
which circums
approximately 40 degrees and extends along the curved path to circum
approximately 90
degrees, when viewed from the bottom end as shown in Figure 4. All four blades
110, 111, 112
and 113 follow the curved path to circum approximately ninety degrees each to
complete 360
degrees of the circumference of the body 102. Each blade 110, 111, 112 and 113
has a lead end
118, 119, 120 and 121 and a trailing end 122, 123, 124 and 125. Each lead end
118, 119, 120,
121 has a sloped lead face rising from the bottom end 108 at a first perimeter
126, up to a table
portion 127, 128, 129 and 130 located and following an outer perimeter. The
table portion 127,
128, 129 and 130 follows an outer diameter. A step 131, 132, 133 and 134 is
provided between a
13
CA 02887196 2015-04-01
top of the sloped lead face and the table portion 127, 128, 129 and 130. The
table portion 127,
128, 129 and 130 is hardfaced. Beads of hardfacing material 135 are shown on
blade 110 in
Figure 5 and Figure 9. Beads of hardfacing material 135 may be applied by a
plasma transfer arc
or a tungsten powder spray or any other suitable means. The hardfacing
material may have
diamonds inserted therein. The outer ridges of the beads of the hardfacing
material 135
preferably has the same diameter as the diameter of a gauge 136 of the drill
bit 23, as shown in
Figure 10.
[0065] A ring segment 140 is arranged between trailing ends 122 and 123 of
blades 110 and 111.
The ring segment 140 lies transverse to the main axis AX of the body 103. The
ring segment 140
forms a bridge over the valley 114 defining a cuttings-laden drilling mud flow
path 142 between
the body 103 and the ring segment 140, as best shown in Figure 5. The valley
114 circums
approximately 50 degrees when viewed from the end, as shown in Figure 4. The
cross-sectional
area available in which the cuttings-laden drilling mud flows at any given
point along the length
of the stabilizer 100 is known as a Junk Slot Area, the units of which is
square inches (or square
mm). The Junk Slot Area at any point under the ring segment 140 is typically
between 9 and 14
sq inches (5,800 to 9,000 sq mm).
[0066] A ring segment 144 is arranged between trailing ends 124 and 125 of
blades 112 and 113.
The ring segment 140 lies transverse to the main axis AX of the body 103. The
ring segment 144
forms a bridge over the valley 116 defining a cuttings-laden drilling mud flow
path, like ring
segment 140. The valley 116 circums approximately 50 degrees when viewed from
the end, as
shown in Figure 4. The Junk Slot Area at any point under the ring segment 144
is typically
between 9 and 14 sq inches (5,800 to 9,000 sq mm) and is, in this example, the
same as cuttings-
laden drilling mud flow path 142.
[0067] An outer surface 141 of the ring segment 140 has a ring perimeter which
is the same as
the outer perimeter of the table surface 127, 128, 129 and 130. The ring
segments 140 and 144
are hardfaced. Beads of hardfacing material 135 may be applied by a plasma
transfer arc or a
tungsten powder spray or any other suitable means. The hardfacing material may
have diamonds
inserted therein. The outer ridges of the beads of the hardfacing material 135
in this example has
the same diameter as the diameter of gauge 136 of the drill bit 23 and may be
1/8" (3.2mm)
smaller than the diameter of the borehole 20. Optional cutters 145 and 146 may
be arranged on a
rotationally leading end 147 and 148 of the ring segments 140 and 144.
14
CA 02887196 2015-04-01
[0068] The trailing ends 122 and 123 of the blades 110 and 111 have an axial
portion 149 and
150 between the curved portion and respective ends of the ring segment 140. An
inclined leading
radial land 151 is defined by part of an end face 152 of the curved portion of
blade 111, a part of
a bottom face 153 of the ring segment 140, the outer diameter and a line above
the base of the
valley 114. An end face 155 of the curved portion of blade 110 forms an
inclined trailing radial
land, bound at a top corner by a part of a bottom face 153 of the ring segment
140, the outer
diameter and a curved inclined line above the base of the valley 114.
[0069] The trailing ends 124 and 125 of the blades 112 and 113 have an axial
portion 156 and
157 between the curved portion and respective ends of the ring segment 144. An
inclined leading
radial land 158 is defined by part of an end face 159 of the curved portion of
blade 113, a part of
a bottom face 160 of the ring segment 144, the outer diameter and a line above
the base of the
valley 116. An end face 161 of the curved portion of blade 112 forms an
inclined trailing radial
land, bound at a top corner by a part of a bottom face 160 of the ring segment
144, the outer
diameter and a curved inclined line above the base of the valley 116.
[0070] The ring segment 140 has a top face 166, which is of a smaller radial
thickness than
bottom face 153, but has the same outer diameter. The body 103 has a reduced
thickness B under
a portion of the ring segment 140 and a corresponding increased cross-
sectional flow area 142
therebetween. The floor of the valleys 114 and 116 curves downwardly
undulating down
underneath the ring segment 140 and 144 respectively and upwardly after the
respective ring
segment 140 and 144. Thus the thickness of the body 103 undulates from
thickness A below the
ring segment 140, 144 to the smaller thickness B under the ring segment 140,
144 to thickness C
above the ring segment 140, 144.
[0071] At least one system is arranged in the body 103 that comprises a hole
170 in a sloped
region in which the body 103 decreases in thickness from thickness A to
thickness B. The hole
170 follows a linear path from the flow bore 104 through the body 103 to an
exit in the valley
114. In this manner, hole 170 is a fluid passageway between flow bore 104 and
the borehole
annulus 29. The hole 170 is disposed at a obtuse angle to the general
direction of flow of drilling
fluid through the flow bore 104, of optionally between one hundred and fifty
to one hundred and
sixty degrees. As is used herein, an angle that is obtuse relative to the
general direction of flow of
drilling fluid through the flow bore means the angle existing between the hole
170 and the
direction of the drilling fluid in the flow bore 104 after it has passed by
hole 170 and is moving
CA 02887196 2015-04-01
towards the bottom of the borehole 20, not as the fluid is approaching the
hole 170. The hole
170 comprises an inner portion 171 having a smooth inner wall having a first
diameter, and an
outer portion 172 of a larger diameter, with a shoulder 173 therebetween. A
liner, for example a
sleeve 175 has a smooth inner surface defining a bore 176 and smooth outer
surface with an
outwardly projecting flange 177 at a proximal end. The sleeve 175 is
insertable through the
upper portion 172 of the hole 170 and slid therein until the flange 177 abuts
the shoulder 173.
The upper portion 172 of the hole 170 is at least partly internally threaded.
A nozzle 180 is
threaded into internal threads of the upper portion 172 of the hole 170 which
locks the sleeve 175
in place. A first end of the sleeve 175 projects into the flow bore 104, and
this end may have an
upper point in line with the bore of the borehole 204 and a lower part
projecting in to the flow
bore 204. The sleeve 175 is preferably made from a tungsten-carbon material,
resistant to
erosion. The sleeve 175 inhibits erosion in the body 103 around the hole 170
induced by the flow
of drilling mud through the flow bore 104 and through the hole 170. The hole
170 may be
between lOmm to 25mm in diameter and in this example 17mm to 20mm in diameter.
[0072] The nozzle 180 is shown in more detail in Figures 6a to 6c, which has a
cylindrical body
181 of circular cross-section having an entrance portion provided with a male
thread 182 for
threaded engagement in the female threads of hole 170. An exit portion 183 is
castellated having
four upstands 184 with interleaved notches 185. A nozzle bore 186 has a large
diameter at the
entrance, converging non-linearly to a small diameter bore at the exit.
[0073] A corresponding system may be provided on the other side of the
stabilizer 100 for ring
segment 144.
[0074] When the bottom hole assembly 22 is at the bottom of the borehole 20,
the drill bit 23
and stabilizer 100 are rotated, either by the top drive 34, a rotary table
(not shown) or a mud
motor (not shown) to extend the borehole 20. Mud pump MP is used to pump fresh
drilling mud
M through the drill string 17, which flows through the flow bore 104 of the
stabilizer 100. The
majority of the fresh drilling mud M continues on to the drill bit 23, through
nozzles therein and
washes drill cuttings up through the annulus 29 back to the mud system 31
located at surface 6.
However, a small portion of the fresh drilling mud M passes through the hole
170 in the body
103 of the stabilizer 100. The pressure in the flow bore 104 may be different
from the pressure in
the cuttings-laden drilling mud in the annulus 29 at the flow path 142, at the
exit of the hole 170.
The pressure is typically higher in the fresh drilling mud M in the flow bore
104 than in cuttings-
16
CA 02887196 2015-04-01
laden drilling mud in the annulus 29 at the exit of the hole 170. Fresh
drilling mud M flows from
the flow bore 104 through hole 170 into the flow path 142 defined by the ring
segment 140 and
the valley 114.
[0075] A fast jet of fresh drilling mud M is induced by a reduction in the
diameter of the hole
170 by nozzle 180. The hole 170 and nozzle 180 are directed upwardly through
the cuttings-
laden drilling mud flow path 142 and optionally, at a region above the top
face 166 of the ring
segment 140. The jet of fresh drilling mud may facilitate maintaining
suspension of drill cuttings
and other solids in the cuttings-laden drilling mud. This may reduce the risk
of solids forming
clumps on the top face 166 of the ring segment 140.
[0076] Upon the bottom hole assembly 22 being tripped-out of the borehole 20,
fresh drilling
mud M may flow through the hole 170. If the drilling fluid is circulated
through the drill string
17 as herein described, the flow of drilling mud through the flow bore 104 at
the flow rate and
pressure produced by the mud pump MP is intended to induce a better flow
through the hole 170.
A good flow rate through the hole 170, induces a jet of fresh drilling mud
directed through the
cuttings laden drilling mud flow path 142. As the stabilizer 100 is pulled
through the borehole
20, the top surface 166 of the ring segment 140 may scrape along the wall of
the borehole 20
scraping solid particles therefrom. The solid particles may collect to form a
clump on the ring
segment 140. However, the jet of fresh drilling mud through the cuttings-laden
drilling mud flow
path 142 will stimulate the solids, inducing the solids to fluidize and other
drill cuttings and
solids to remain suspended in the drill mud.
[0077] Upon the bottom hole assembly 22 being tripped-in to the borehole 20,
fresh drilling mud
M may flow through the hole 170. If the drilling fluid is circulated through
the drill string 17 as
hereinbefore described, the flow of drilling mud through the flow bore 104 is
intended to induce
a better flow through the hole 170. A good flow rate through the hole 170,
induces a jet of fresh
drilling mud directed through the cuttings-laden drilling mud flow path 142.
As the stabilizer 100
passes down through the borehole 20, the bottom face 153 of the ring segment
140 may scrape
along the wall of the borehole 20 scraping solid particles therefrom. The
solid particles may
collect to form a clump on the ring segment 140. However, the jet of fresh
drilling mud through
the cuttings-laden drilling mud flow path 142 will stimulate the solids,
inducing the solids to
fluidize and other cuttings and solids to remain suspended in the drill mud
and pull them through
the cuttings-laden drilling mud flow path 142.
17
CA 02887196 2015-04-01
[0078] Such methods for circulating drilling mud through the drill string
whilst tripping include
threadedly connecting the drill string to a sub 37 of the top drive apparatus
7 during tripping.
This may be carried out between each connection or disconnection of a stand of
drill pipe 13, or
once every two, three or more connections or disconnections.
[0079] Alternatively, circulating drilling mud through the drill string whilst
tripping may be
employed using a circulating whilst tripping tool, which allows circulation
between making and
breaking threaded connections, without the need for making a threaded
connection with the sub
37.
[0080] Alternatively, circulating drilling mud continuously through the drill
string 17 whilst
tripping may be employed using a Continuous Circulation System 55, such as the
CCSTM
manufactured by the National Oilwell Varco.
[0081] Figure 7 shows a further exemplary embodiment in which reference
numerals in the two
hundred series are used for similar parts referred to previously in the one
hundred series. The
system 269 comprises a fluid passageway or hole 270 through the body 203 which
is partly lined
with a sleeve 275. The sleeve 275 is arranged at an obtuse angle to the
direction of flow in flow
bore 204. The sleeve 270 has an inner portion 271 which is of a smaller
diameter than a threaded
outer portion 272, with a shoulder therebetween. A proximal end of the sleeve
275 has a threaded
flange 277 threaded into the threaded outer portion 272 and is seated on the
shoulder 273. A first
end of the sleeve 275 extends into the flow bore 204. The first end may have
an upper point in
line with the bore of the borehole 204 and a lower part projecting in to the
flow bore 204.
Alternatively, the sleeve 275 may line the entire length of the hole 270. The
system 269 may be
used in the stabilizer 100 or drill bit 23. A flow axis of the sleeve 275 is
directed through a
cuttings-laden drilling mud flow path 242 defined by the ring segment 240 and
the body 203.
[0082] In use, fresh drilling mud M flows from flow bore 204, through the
sleeve 275 and exits
the sleeve 275 as a jet of fresh drilling mud directed upwardly through the
cuttings- laden drilling
mud flow path 242. Optionally the jet has a trajectory aimed at a region above
the top face 266 of
the ring segment 240 which may reduce the risk of solids forming clumps on the
top face 266
and bottom face 253 of the ring segment 240.
[0083] Figure 8 shows a yet further exemplary embodiment of the invention, in
which reference
numerals in the three hundred series are used for similar parts referred to
previously in the one
hundred series. The system 369 comprises a fluid passageway or hole 370
through the body 303
18
CA 02887196 2015-04-01
which is arranged at an obtuse angle to the direction of flow in flow bore
304. The system may
be used in the stabilizer 100 or drill bit 23. A flow axis of the hole 370 is
directed through a
cuttings-laden drilling mud flow path 342 defined by the ring segment 340 and
the body 303.
[0084] In use, fresh drilling mud M flows from flow bore 304, through the hole
370 and exits the
hole 370 as a jet of fresh drilling mud directed upwardly through the cuttings
laden drilling mud
flow path 342. Optionally, the jet has a trajectory aimed at a region above
the top face 366 of the
ring segment 340 which may reduce the risk of solids forming clumps on the top
face 366 and
bottom face 353 of the ring segment 340.
[0085] Figure 10 shows an example of a drill bit made in accordance with
certain of the
principles disclosed herein. The drill bit 23 comprises a bit body 403 having
a series of curved
blades (two shown) 410 and 411 with a valley (one shown) 412 therebetween. The
blades 410
and 411 curve around a forward end of the drill bit 23. Each blade 410 and 411
has a rotationally
leading face 413 and 414 each provided with a plurality of cutting elements
415 for boring the
borehole 20. A ring segment 416 is arranged between trailing ends 417 and 418
of respective
blades 410 and 411 spanning over valley 412 to define a cuttings- laden
drilling mud flow path
542 between bit body 403 and ring segment 416.. The ring segment 416 has
cutting elements
thereon at a rotational leading edge and trailing edge, which may be set at a
gauge diameter 136.
[0086] A system 569 is arranged in the body 403. The system 569 is shown in
more detail in
Figure 11, in which reference numerals in the five hundred series are used for
similar parts
referred to previously in the one hundred series. The system 569 comprises a
hole 570 that is a
fluid passageway arranged in the body 403 on a slope in a region in which the
body 403
decreases in thickness from thickness A to thickness B. The fluid passageway
or hole 570
follows a linear path from the flow bore 504 through the body to an exit in
the valley 414. The
hole 570 is disposed at an obtuse angle to the direction of flow of drilling
fluid through the flow
bore 504, which in this example is between one hundred and thirty and one
hundred and fifty
degrees. The hole 570 comprises an inner portion 571 having a smooth inner
wall having a first
diameter and an outer portion 572 of a larger diameter with a shoulder 573
therebetween. A liner,
such as sleeve 575 has a smooth inner surface defining a bore 576 and smooth
outer surface with
an outwardly projecting flange 577. The sleeve 575 is insertable through the
upper portion 572 of
the hole 570 and slid therein until the flange 577 abuts the shoulder 573. The
upper portion 572
of the hole 570 is at least partly internally threaded. A nozzle 580 is
threaded into internal
19
CA 02887196 2015-04-01
threads of the upper portion 572 of the hole 570 which locks the sleeve 575 in
place. A bottom of
the sleeve 575 projects into the flow bore 504. The sleeve 575 may be made
from a tungsten-
carbon material, resistant to erosion. The sleeve 575 inhibits erosion in the
body 403 around the
hole 570 induced by the flow of drilling mud through the flow bore 504 and
through the hole
570. The hole 570 may be between 10mm to 25mm in diameter and in this example
approximately 17mm to 20mm in diameter.
[0087] When the bottom hole assembly 22 is at the bottom of the borehole 20,
the drill bit 23
and stabilizer 100 are rotated, either by the top drive 34, a rotary table
(not shown) or a mud
motor (not shown) to extend the borehole 20. Mud pump MP is used to pump fresh
drilling mud
M down through the drill string 17, through flow bore 504 of the drill bit 23.
The majority of the
fresh drilling mud M continues on to flush out of nozzles forwardly in front
of the blades 410
and 411. However, a small portion of the fresh drilling mud M flows out
through the hole 570 in
the body 403 of the drill bit 23. There may be a pressure difference between
the pressure of the
fresh drilling mud M in the flow bore 504 and in cuttings-laden drilling mud
in the annulus 29 at
the flow path 542, at the exit of the hole 570. The pressure may be higher in
the fresh drilling
mud M in the flow bore 504 than in cuttings laden drilling mud in the annulus
29 at the exit of
the hole 570. Fresh drilling mud M flows from the flow bore 504 through hole
570 into the flow
path 542 defined by the ring segment 416 and the valley 412.
[0088] A fast jet of fresh drilling mud M is induced by a reduction in the
diameter of the hole
570 by nozzle 580. The hole 570 and nozzle 580 are directed upwardly through
the cuttings
laden drilling mud flow path 542 and preferably, at a region above the top
face 566 of the ring
segment 416. The jet of fresh drilling mud may facilitate maintaining drill
cuttings and other
solids suspended in the cuttings-laden drilling mud flow path 542. This
preferably reduces the
risk of solids forming clumps on the top face 566 of the ring segment 416.
[0089] Upon the bottom hole assembly 22 being tripped-out of the borehole 20,
fresh drilling
mud M may flow through the hole 570. If the drilling fluid is circulated
through the drill string
17 as hereinbefore described, the flow of drilling mud through the flow bore
504 at the flow rate
and pressure produced by the mud pump MP is intended to induce a better flow
through the hole
570 and nozzle 580. A good flow rate through the hole 570 and nozzle 580,
induces a jet of fresh
drilling mud directed through the cuttings laden drilling mud flow path 542.
As the drill bit 23 is
pulled through the borehole 20, the top surface 566 of the ring segment 416
may scrape along the
CA 02887196 2015-04-01
wall of the borehole 20 scraping solid particles therefrom. The solid
particles may collect to form
a clump on the ring segment 416. However, the jet of fresh drilling mud
through the cuttings-
laden drilling mud flow path 542 will stimulate the solids, inducing the
solids to fluidize and stay
suspended in the drill mud.
[0090] Upon the bottom hole assembly 22 being tripped-in to the borehole 20,
fresh drilling mud
M may flow through the hole 570. If the drilling fluid is circulated through
the drill string 17 as
hereinbefore described, the flow of drilling mud through the flow bore 504 is
intended to induce
a better flow through the hole 570. A good flow rate through the hole 570,
induces a jet of fresh
drilling mud directed through the cuttings-laden drilling mud flow path 542.
As the drill bit 23
passes down through the borehole 20, the bottom face 553 of the ring segment
416 may scrape
along the wall of the borehole 20 scraping solid particles therefrom. The
solid particles may
collect to form a clump on the ring segment 416. However, the jet of fresh
drilling mud through
the cuttings laden drilling mud flow path 542 will stimulate the solids,
inducing the solids to
fluidize and stay suspended in the drill mud and pull them through the
cuttings laden drilling
mud flow path 542.
[0100] The drill string usually comprises a multiplicity of threaded joints of
drill pipe. However,
the drill string may comprise a multiplicity of threaded sections of other
kinds of pipe, such as
casing, which is known as drilling with casing.
21
