Note: Descriptions are shown in the official language in which they were submitted.
CA 02487155 2000-02-02
HYl[~~t LIC UNDERREAMER AND SECTIONS FOR USE THEREIN
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic underreamer and improved sections
for use therein.
A hydraulic underreamer is used to hydraulically wash out or more
typically enlarge a wellbore extending through a subterranean formation to
thereby
create a cavity in the formation. Hydraulic underreaming can be applied to a
coal
formation ("coal seam") to enhance the production of methane flowing from
fractures
("cleats") in such a formation, or to other formations in which enlargement of
a wellbore
is desired.
One type of hydraulic underreamer includes: a packer section for sealing
against a well casing so as to isolate an annulus above the packer section as
defined
between the casing and a work pipe; a cutting section for hydraulically
enlarging a
wellbore below the casing to thereby produce a mixture of liquid and formation
1 S fragments in the resulting cavity; and a jet pump section for pumping
mixture from the
cavity for passage through the above-mentioned annulus to the surface.
SUMMARY OF THE INVENTION
It is an object of the invention to provide improved packer, cutting, and
jet pump sections, as well as a novel mill section, for use in a hydraulic
underreamer.
A packer section is provided which comprises: a tubular drive bushing
having an upper end and a lower end; a tubular packer mandrel having an upper
end and
a lower end, the packer mandrel being mounted on the drive bushing with the
packer
mandrel lower end being closely adjacent to but not connected to the drive
bushing
upper end so that the drive bushing may rotate while the packer mandrel
remains
stationary; at least one tubular sealing element received on and around the
packer
mandrel; a tubular drive mandrel defining a packer section central bore
therethrough and
substantially coaxially extending through the drive bushing and packer mandrel
so as to
define a packer section annulus, the tubular drive mandrel being fixedly
connected to the
drive bushing so that rotation of the drive mandrel rotates the drive bushing.
A cutting section is provided which comprises: an outer pipe; an inner
pipe defining a cutting section central bore therethrough and extending
substantially
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coaxially through the outer pipe to define a cutting section annulus between
the inner
and outer pipes; a cutting nozzle housing extending through the cutting
section annulus
between the inner and outer pipes so as to be fixedly connected thereto, the
cutting
nozzle housing having an inlet portion in communication with the cutting
section central
bore and also having an outlet portion; a baffle mounted in the housing inlet
portion; and
a cutting nozzle mounted in the housing outlet portion. '
A jet pump section is provided which comprises: a body having a
longitudinal axis, a longitudinally extending pump section central bore with
an upper
end defining an inlet and a lower end defining an outlet, and a plurality of
turn chambers
circumferentially spaced around the pump section central bore, each turn
chamber
having at least one inlet passageway, in communication with the pump section
central
bore, and also having an outlet; a plurality of ejector nozzles corresponding
to the
plurality of turn chambers such that each ejector nozzle has an inlet in
communication
with a corresponding turn chamber outlet, each ejector nozzle also having an
outlet; a
plurality of venturis corresponding to the plurality of ejector nozzles such
that each
venturi has an inlet aligned with but spaced above a corresponding ejector
nozzle outlet,
each venturi also having an outlet; wherein the body further has defined
therein a
diffusion chamber surrounding the pump section central bore, the diffusion
chamber
having a plurality of inlets in respective communication with the venturi
outlets and also
having a substantially annular outlet adjacent to the inlet of the pump
section central
bore.
A null section is provided which comprises: a tubular bit sub having an
upper end and a lower end; a tubular primary mill having an upper end,
removably
connected to the bit sub lower end, and also an abrasive lower end; and a
center
assembly having a passageway therethrough and adapted to be received in a mill
section
central bore defined in the bit sub and primary mill, wherein the center
assembly
includes (I) a locking mandrel having an upper end and a lower end and being
selectively lockable in the mill section central bore, (ii) a center mill
having an upper
end removably connected to the locking mandrel lower end and also having an
abrasive
lower end adjacent to the primary mill lower end when the locking mandrel is
locked in
the mill section central bore, and (iii) a mill nozzle connected to the center
mill lower
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end so as to be in communication with the center assembly passageway.
There is also provided a hydraulic underreamer comprising the above-
described sections, as well as an intermediate section, connected together in
a string in a
manner further described below.
Operational advantages of this invention are discussed in the context of
preferred embodiments in the Detailed Description of the Invention.
BRIEF DESCRI~'T~ON OF THE DRAWINGS
FIG. 1 is a schematic representation of an operating hydraulic
underreamer in accordance with the invention and having the various sections
discussed
above.
FIG. 2 is a longitudinal cross-sectional view of a preferred embodiment
of the packer section.
FIG. 3 is a longitudinal cross-sectional view of a preferred embodiment
of the cutting section.
FIG. 4 is a cross-sectional view of the cutting section as viewed along
line 4-4 in FIG. 3.
FIG. 5 is a cross-sectional view ofthe cutting section as viewed along
line 5-5 in FIG. 4.
FIG. 6 is a longitudinal cross-sectional view of a preferred embodiment
of the jet pump secrion.
FIGS. 7-12 are cross-sectional views of the jet pump section as viewed
along lines 7-7, 8-8, 9-9, 10-10, I 1-11, and 12-12, respectively, in FIG. 6.
FIG. 13 is a perspective view of the jet pump section with a portion of its
body broken away to show internal details.
FIG. 14 is a longitudinal cross-sectional view of a preferred embodiment
of the mill section without a center assembly therein.
FIG. 15 shows across section as viewed along line 15-15 in FIG. 14.
FIG. 16 is a view of the mill section showing a cross section similar to
FIG. 14 (but rotated slightly counterclockwise), and with the center assembly
shown in
side view with a lowermost portion broken away to reveal internal details in
cross
section.
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DETAILED DESCRIPTION OF THE INVENTION
The hydraulic underreamer and its operation as described below assumes
that a wellbore is being enlarged to enhance methane production from a coal
seam. It
should be understood, however, that the hydraulic underreamer of the invention
can be
used to enlarge a wellbore for any purpose. Any dimensions in the following
description are provided only as typical examples, and should not be construed
to limit
the invention in any manner.
Referring to FIG. 1, a well casing 10 extends through overburden 12, and
is cemented in the overburden as indicated at 14. The lower end of well casing
10 is
shown as being just above a coal seam 16. A previously drilled wellbore 18
extends
through coal seam 16.
The illustrated hydraulic underreamer comprises a number of sections
connected together in a string. Such sections include (from top to bottom) a
packer
section 20, an intermediate section 22 comprising a coaxial pipe string, a
cutting section
24, a jet pump section 26, and a mill section 28. Packer section 20 has an
associated
drive mandrel 30 connected at its upper end to a work pipe 32, which extends
to the
surface (not shown). Cleaning blades 34 are circumferentially affixed to drive
mandrel
30. Sealing elements 36 and 38 of the packer section function to seal against
well
casing 10 and thereby isolate a casing annulus 40 defined above the sealing
elements.
Packer section 20, as well as the other sections, have substantially straight
and aligned
central bores as schematically indicated between broken lines. An annulus
surrounds
the central bore in packer section 20, intermediate section 22, and cutting
section 24.
When using a 7 inch well casing, it is typical to employ a central bore
diameter of 3 '/~
inches and an annulus outer diameter of 6 inches.
In operation, work pipe 32 is rotated to thereby rotate drive mandrel 30.
As will be explained in detail with reference to FIG. 2, packer section 20 is
constructed
so that sealing elements 36 and 38 do not rotate upon rotation of drive
mandrel 30. This
minimizes wear on the sealing elements so as to require less frequent
replacement than
conventional rotating sealing elements. The hydraulic underreamer can be moved
up or
down without losing the desired seal between the sealing elements and well
casing 10.
Rotation of drive mandrel 30 causes rotation of each of the other sections.
Rotation of
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mill section 28 will drill through possible obstructions lying in or across
wellbore 18,
such as formation fragments or even, on rare occasions, metal "junk".
The liquid used is most typically water with one or more viscosity and/or
density increasing additives. Such liquid is pumped into and through work pipe
32 at a
pressure and flow rate which are selected based upon a number of factors,
including well .
depth, well size, sizes of various nozzles (described below), the methane
pressure in the
coal seam, and also safety considerations. The pressure is typically within
the range of
1000-3000 psi, and the flow rate is typically within the range of 350-1000 gpm
(gallons
per minute).
As indicated by the broken arrows, liquid flows downwardly from work
pipe 32, through the upper portion of drive mandrel 30 and then through a
lower portion
of the drive mandrel defining the central bore of packer section 20, through
the central
bore of intermediate section 22, and through the central bore of cutting
section 24.
Some of the liquid is diverted to flow through diametrically opposed cutting
nozzles to
produce cutting. streams 42 and 44. Such opposed cutting streams, balancing
the forces
on the underreamer to minimize structural stress, impact the surrounding walls
of coal
seam 16 to break off formation fragments. These fragments are referred to
generically
as formation fragments since some formation materials other than coal, such as
shale,
may also be present in coal seam 16. An upper portion of wellbore 18,
indicated by
phantom lines (broken lines with alternating dots), is shown as having been
enlarged by
cutting streams 42 and 44 to form a cavity 46. A mixture of liquid and
formation
fragments results which is indicated at 48.
That liquid not diverted to the cutting nozzles continues its downward
flow into the central bore of jet pump section 26. A portion of this liquid
flows
completely through the pump section central bore, and then through mill
section 28 to
cool its abrasive lower end and to help carry cuttings away from such lower
end.
Another portion of the liquid exits the pump section central bore and changes
in flow
direction to flow upwardly. Mixture is drawn into a portion of jet pump
section 26 (as
indicated by solid arrows) and then flows upwardly through such portion,
providing the
formation fragments are sufficiently small as achieved by the action of
cutting streams
42 and 44 as well by the jet pump section itself by a novel means subsequently
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described. Mixture flows into and through the annulus of cutting section 24,
through
the annulus of intermediate section 22, and through the annulus of packer
section 20 so
as to exit such annulus to flow into casing annulus 40 (as indicated by solid
arrows).
Rotation of cleaning blades 34 keeps the casing annulus 40 cleaned out
immediately
above the packer section annulus to assist in constant and unobstructed flow
therefrom.
Mixture continues its upward flow through casing annulus 40 to the surface
(not shown).
Preferably, jet pump section 26 pumps mixture to the surface at a
su~cient volumetric flow rate to maintain the upper level of mixture 48 Below
cutting
section 24. A gas cap can result between mixture 48 and sealing elements 36
and 38,
through which cutting streams 42 and 44 operate efficiently at greater
distances than
they do through liquid.
After having been pumped to the surface, the mixture of liquid and
formation fragments, also containing some methane, is typically passed into a
pit where
natural separation of the mixture components occurs. The formation fragments
fall to
the bottom of the pit, leaving the liquid on top for recycling if desired.
Methane
escaping from the liquid into the atmosphere is immediately burned for safety
reasons.
The hydraulic underreamer is moved down wellbore 18 through coal seam 16 to
continue the underreaming operation. Upon completion of the operation, the
hydraulic
underreamer is withdrawn from the well, and the well is equipped for
production of
methane in a conventional manner.
Preferred embodiments of packer section 20, cutting section 24, jet pump
section 26, and mill section 28 will now be described. The preferred material
of
construction for each section is a suitable heat treated steel unless
otherwise noted for
certain components. All fixed connections hereafter described are preferably
welded
connections.
Referring to FIG. 2, the illustrated packer section 20 includes a tubular
drive bushing 50 having an externally threaded upper end 52. A tubular packer
mandrel
54 has an externally threaded upper end 56 and a flanged lower end 58 with O-
rings 60
received in a circumferential recess. Packer mandrel 54 is mounted on drive
bushing SO
such that packer mandrel lower end 58 is closely adjacent to but not connected
to drive
bushing upper end 52. As shown, a substantially annular thrust bearing 62
(preferably
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brass) is interposed between drive bushing upper end 52 and packer mandrel
lower end
58.
A bearing housing 64 has an internally threaded lower end 66 threadedly
connected to drive bushing upper end 52, and also an internally threaded upper
end 68
threadedly connected to a bearing housing nut 70. Accordingly, bearing housing
64
surrounds and encases thrust bearing 62 and a lower portion of packer mandrel
54, and
is in sealing contact with O-rings 60. A tubular load bearing 72 (preferably
brass) is
interposed between bearing housing 64 and the lower portion of the packer
mandrel.
Sealing elements 36 and 38 are received on and around packer mandrel
54, and a tubular spacer 74 is received on and around packer mandrel 54
between the
sealing elements. Spacer 74 is preferably held in position by set screws 76. A
packer
mandrel nut 78 is threadedly connected to packer mandrel upper end 56 so that
sealing
elements 36 and 38 are positioned between the packer mandrel nut and bearing
housing
nut 70. There is preferably at least a small space between the lower end of
spacer 74
and the upper end of sealing element 36, and a similar space between the lower
end of
packer mandrel nut 78 and the upper end of sealing element 38. Liquid may
enter
through these spaces for reasons apparent below.
Each of the sealing elements can be composed of a synthetic or natural
rubber. Sealing element 36 has a sealing ring 80 embedded near its lower end,
and
sealing element 38 similarly has a sealing ring 82 embedded near its lower
end. Each
sealing ring comprises a metal ring and an O-ring which seals against the
outer surface
of packer mandrel 54. As shown, each sealing element has an internal diameter
which
tapers from the upper end of the sealing element to the sealing ring.
Therefore, a small
tapered gap exists between the inner surface of the sealing element and the
outer surface
of packer mandrel 54. When beginning operation of the hydraulic underreamer,
flow of
liquid into this gap expands the sealing element sufficiently to seal against
the well
casing.
Tubular drive mandrel 30 defines a packer section central bore 84
therethrough, and coaxially extends through packer mandrel 54 and drive
bushing 50 so
as to define a packer section annulus 86. Drive mandrel 30 is fixedly
connected to drive
bushing SO by means of connecting members 88. Therefore, rotation of drive
mandrel
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_g_
30 rotates drive bushing 50, but packer mandrel 54 and associated sealing
elements 36
and 38 can remain stationary.
The lower ends of drive mandrel 30 and drive bushing 50 are not shown,
but can be provided with any suitable means for connection to the upper end of
intermediate section 22 (FIG. 1 ), such that the intermediate section central
bore and
annulus respectively communicate with packer section central bore 84 and
packer
section annulus 86.
Referring to FIG. 3, the illustrated cutting section 24 includes an outer
pipe 90 and an inner pipe 92. Inner pipe 92 defines a cutting section central
bore 94
therethrough, and extends coaxially through outer pipe 90 to define a cutting
section
annulus 96 between outer pipe 90 and inner pipe 92. An upper cutting nozzle
housing
98 extends through cutting section annulus 96 between the inner and outer
pipes so as to
be fixedly connected thereto. Cutting nozzle housing 98 has an inlet portion
100 in
communication with cutting section central bore 94. A baffle 102 is mounted in
housing
inlet portion 100 by means of bar 104 (as will be further explained below). A
cutting
nozzle 106 (preferably tungsten carbide) is threadedly and removably connected
to
cutting nozzle housing 98 within an outlet portion 108 thereof. As shown,
cutting
nozzle 106 has a passageway tapering from an inlet, adjacent to baffle 102 and
having
an inlet diameter, to an outlet having outlet diameter smaller than the inlet
diameter.
The inlet end of cutting nozzle 106 preferably sealingly engages an O-ring as
shown.
Outer pipe 90 and inner pipe 92 have the same longitudinal axis 110,
hereafter denoted as pipe axis 110. Cutting nozzle housing 98 has a
longitudinal axis
112, hereafter denoted as housing axis 112, substantially perpendicular to and
intersecting pipe axis 110. Cutting nozzle 98 and baffle 102 are aligned along
housing
axis 112, and baffle 102 is substantially perpendicular to housing axis 112.
A lower cutting nozzle housing 114 has, similarly to cutting nozzle
housing 98, a housing axis 116 and has a cutting nozzle 118 and baffle 120
mounted
therein. Housing axes 112 and 116 are substantially coplanar, and cutting
nozzle
housings 98 and 114 are on opposite sides of pipe axis 110. Housing axes 112
and 116
are longitudinally spaced from one another along pipe axis 110. Such
longitudinal
spacing for a 6 inch outer pipe is preferably in the range of about 12-24
inches.
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_g_
A first set of three (only two of which are visible in FIG. 3)
circumferentially spaced centralizers 122, positioned in cutting section
annulus 96 above
cutting nozzle housing 98, extend between and are fixedly connected to outer
pipe 90
and inner pipe 92. A second set of centralizers 124 are similarly provided
below cutting
nozzle housing 114.
Outer pipe 90 has an externally threaded lower end 126, and inner pipe
92 has a lower end 128 with a pair of O-rings 130 in circumferential external
recesses.
As shown, inner pipe lower end 128 steps down in wall thickness below 0-rings
130.
The upper ends of outer pipe 90 and inner pipe 92 are not shown, but can be
provided
with any suitable means for connection to the lower end of intermediate
section 22 (FIG.
1), such that cutting section central bore 94 and cutting section annulus 96
are in
respective communication with the intermediate section central bore and
annulus.
An upper portion of cutting section 24 is broken away, as well as a
middle portion, so that the full length of cutting section 24 is not shown.
However, a
typical length for cutting section 24 is in the range of about S-7 feet.
Referring to FIG. 4, this cross-sectional view shows the manner in which
bar I04 transversely extends across housing inlet portion 100 between opposing
ends
fixedly connected to cutting nozzle housing 98. Baffle 102 is fxedly connected
to bar
104. Two centralizers 124 are shown by solid lines in FIG. 4, as well as a
third
centralizer 124, indicated by broken lines, immediately below cutting nozzle
housing
114.
Referring to FIG. 5, this cross-sectional view shows baffle 102 as being a
disk which is circular in shape. Of course, baffle 120 is also preferably a
disk.
The baffle in each cutting nozzle housing desirably reduces the pressure
required to obtain a desired flow through the cutting nozzle.
Referring to FIG. 6, the illustrated jet pump section 26 includes a body
132 having a longitudinal axis 134 and a longitudinally extending pump section
central
bore 136. Pump section central bore 136 has an upper end defining an inlet 138
and a
lower end defining an outlet 140. For ease of fabrication, body 132 includes
body
portions 142, 144, 146, 148, and 150 fixedly connected together as shown. Body
portion 148 has a generally annular subportion 148a (to which the lower end of
body
CA 02487155 2000-02-02
- 10-
portion 150 is connected) and a tubular body subportion 148b (positioned
inside body
portion 150) integral with body subportion 148a. Body subportion 148b has an
upper
end with a pair of O-rings 151 in internal circumferential recesses. As shown,
the upper
end of body subportion 148b steps down in wall thickness above O-rings 1 S 1.
Finally
with respect to the body, body portion 142 has an internally threaded lower
end.
Refernng to FIG. 6 in conjunction with FIGS. 7 and 8, body portion 144
has defined therein a plurality (six in this particular embodiment) of turn
chambers 152
circumferentially spaced around pump section central bore 136. Each turn
chamber 152
has an inlet passageway 154 in communication with pump section central bore
136.
Each turn chamber 152 also has an outlet 156, and is elongated so as to
longitudinally
extend along side pump section central bore 136. Additionally, each turn
chamber 152
has a longitudinally extending central axis 158. Inlet passageway 154 is
preferably
offset from central axis 158. This produces a spinning effect in liquid
flowing upwardly
through the turn chamber. This effect lowers the pressure loss which naturally
results
from the change in flow direction. Each inlet passageway 154 also preferably
tapers in
width from its lower end to its upper end. This desirably produces
progressively
increasing inlet flow into tum chamber 152 from its upper end to its lower
end_ FIGS. 7
and 8 also show a plurality of external grooves 160 in body portion 144, as
will be
further explained below.
Referring to FIG. 6 in conjunction with FIG. 9, a plurality of ejector
nozzles 162 (preferably tungsten carbide), corresponding to the plurality of
tum
chambers 152, are threadedly and removably connected to and partially within
body
portion 146. Each ejector nozzle 162 has an inlet in communication with a
corresponding turn chamber outlet 156 through a tapered passage 164 in body
portion
146. As shown, the inlet end of each ejector nozzle 162 sealingly engages an O-
ring,
and each ejector nozzle has a passageway which tapers from its inlet, having
an inlet
diameter, to an outlet having an outlet diameter smaller than the inlet
diameter. FIG. 9
also shows notches 166 in each ejector nozzle 162 for engagement by a suitable
nozzle
wrench, and also the continuation of grooves 160 in body portion 146.
Referring to FIG. 6, a plurality of venturis 168, corresponding to the
plurality of ejector nozzles 162, are received by body portion 148. Each
venturi 168 has
CA 02487155 2000-02-02
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an inlet aligned with but spaced (typically about'/Z - 3/4 inch) above a
corresponding
ejector nozzle outlet. Each venturi 168 has a passageway tapering from the
venturi inlet
to a throat 170 (typically about'/z - 3/4 inch in diameter), and flaring from
the throat to a
venturi outlet. In the illustrated embodiment, each venturi 168 is comprised
of a lower
S throat nozzle 168a and an upper throat nozzle 168b oriented end to end so as
to define
the desired venturi passageway having throat 170. An O-ring is located at the
junction
of throat nozzles 168a and 168b. A retainer ring 172 having lips 174, in
conjunction
with lips 176 associated with body subportion 148b, serves to removably secure
the
throat nozzles in position. Retainer ring 172 is best shown in FIG. 10. Screws
178
extend through retainer ring 172 and are threadedly and removably received in
body
subportion 148a (FIG. 6). The periphery of each throat nozzle 168a is
indicated by a
circular broken line. A lip 174 slightly overlaps a portion of such periphery,
and lip 176
overlaps the remaining portion. Throats 170 are also shown in FIG. 10.
In addition to the desired jet pump effect achieved by flow of an ejector
stream into and through a corresponding venturi, the high velocity ejector
stream from
an ejector nozzle outlet will break up an immediately adjacent formation
fragment
which will not otherwise pass through the venturi throat because of excessive
size
and/or irregular shape. This capability of the inventive jet pump section
results in
improved hydraulic efficiency, as compared to the conventional hydraulic
underreamer
which relies entirely on its cutting stream (usually acting at long distances)
to
hydraulically produce formation fragments that will pass through its jet pump.
Referring now to FIG. 6 in conjunction with FIG. 11, a diffusion
chamber 180 between body subportion 148b and body portion 1 SO has a plurality
of
inlets 182 in respective communication with the venturi outlets, and also has
a
substantially annular outlet 184 adjacent to the inlet 138 of pump section
central bore
136. Diffusion chamber 180 includes a plurality of diffusion subchambers 186
and a
substantially annular subchamber 188. Diffusion subchambers 186 are defined by
a
diffuser member 190 fixedly connected between body subportion 148b and body
portion
150. Diffusion subchambers 186 extend from respective diffusion chamber inlets
182 to
annular subchamber 188, and annular subchamber 188 extends to annular outlet
184.
FIG. 11 also shows throats 170.
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FIG. 12 shows a cross-sectional view of body portion 142.
FIG. 13 has a portion of body portion 150 broken away to more clearly
illustrate the structure of diffuser member 190 and the diffusion subchambers
186
defined thereby. As shown, diffusion subchambers 186' flare upwardly. FIG. 13
also
shows a perspective view of the various body portions and subportions, grooves
160,
ejector nozzles 162, and retainer ring 172. In particular, FIG. 13 shows that
each groove
160 longitudinally extends from a lower end to an upper end adjacent to
ejector nozzles
162.
With reference again to FIG. 6 as well as FIG. 3, jet pump section 26 is
connectable to cutting section 24. The upper end of body portion
150 can be threadedly connected to outer pipe lower end 126 so that annular
outlet 184
communicates with cutting section annulus 96, and the upper end of body
subportion
148b can be sealingly connected with inner pipe lower end 128 so that pump
section
central bore 136 communicates with cutting section central bore 94.
Referring to FIG. 14, the illustrated mill section 28' (without center
assembly, which is discussed below) includes a tubular bit sub 192 having an
externally
threaded upper end 194 and an internally threaded lower end 196. Bit sub 192
also has
an internal circumferential recess 198, hereafter denoted as the bit sub
recess 198,
adjacent to bit sub lower end 196.
A tubular insert 200, tightly and securely received in bit sub recess 198,
has an internal circumferential recess 202 which is hereafter denoted as the
insert recess
202. Insert 200 also has three circumferentially spaced and longitudinally
extending
slots 204. Only two of slots 204 are shown in FIG. 14, where one is shown in
cross
section and the other is indicated by a broken line. Each slot 204 extends
from a lower
end to an upper end at which it intersects insert recess 202 to create an
opening 206. In
addition, each slot 204 receives an elongated but slightly curved finger 208
(one in cross
section and the other in broken and solid lines) having a lower end, fixedly
connected to
insert 200 (i.e. with a rivet), and an upper end extending through opening 206
into insert
recess 202. Contact with bit sub 192 in bit sub recess 198 forces finger 208
into this
position from a previously relaxed position the finger assumes prior to
insertion of insert
200 into bit sub recess 198. Each finger 208 is composed of a suitably
flexible and
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resilient material, preferably spring steel.
A tubular primary mill 210 has an externally threaded upper end 212
removably connected to bit sub lower end 196. Primary mill upper end 212 is
suitably
tightened against the lower end of insert 200 to provide a good compression
fit in bit sub
recess 198. Therefore, insert 200 will rotate with bit sub 192 during
operation, as will
be more apparent below. Primary mill 210 also has an internal shoulder 214 and
an
abrasive lower end 216. Abrasive lower end 216 includes a lower abrasive layer
218
composed of a suitably hard material (preferably tungsten carbide brazed onto
steel).
Bit sub 192, insert 200, and primary mill 210 define a mill section central
bore 220 therethrough.
Referring to FIG. 15, this cross-sectional view shows the third finger 208
and its corresponding slot 204. FIG. 15 provides an end view of each of the
forgers
extending into insert recess 202. FIG. 15 also shows shoulder 214.
Referring to FIG. 16, this view of mill section 28 shows a cross section
of bit sub 192, insert 200, and primary mill 210, but rotated slightly
counterclockwise
from that position in FIG. 14. No fingers 208 are visible in FIG. 16. Center
assembly
222 is shown as being received in mill section central bore 220 (FIG. 14). A
central
passageway 224, for receiving downwardly flowing liquid, is indicated by
broken lines.
Center assembly 222 includes a locking mandrel 226 having an upper
head 228. Head 228 has a circumferential tool recess 230 (indicated by broken
lines) for
engagement by a setting tool or retrieval tool. Locking mandrel 226 also has
an
internally threaded (indicated by broken lines) lower end 232. The locking
mandrel, as
well as the setting and retrieval tools, are commercially available from Baker
Oil Tool
Company of Houston, Texas. With head 228 in the illustrated down position (in
solid
lines), three (only two of which are visible in FIG. 16) circumferentially
spaced dogs
234 are in their extended positions so as to extend into the insert recess
202. A side
view of one dog 234 is clearly shown (by a solid line) as extending into
insert recess
202. This represents the locked position for normal operation.
It should be apparent from FIGS. 14-16 that, upon rotation of bit sub 192,
primary mill 210, and insert 200 as an integral unit with respect to locking
mandrel 226,
f ngers 208 will engage respective dogs 234 to impart rotation to center
assembly 222.
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When setting center assembly 222 within mill section central bore 220 in a
locked
position, dogs 234 could happen to extend into contact with the upper ends of
fingers
208 so as to bend them outwardly, causing fingers 208 to straighten somewhat.
However, because fingers 208 are comprised of a flexible and resilient
material, they
will snap back into their desired positions upon their rotation with respect
to dogs 234.
Center assembly 222 also includes a center mill 236 having an externally
threaded upper end 238 (indicated by broken lines) threadedly and removably
connected
to locking mandrel lower end 232. Of course, this connection must be such that
center
mill 236 rotates with locking mandrel 226 as an integral unit. Center mill 236
also has
an abrasive lower end 240 adjacent to primary mill lower end 216 when locking
mandrel
226 is in the locked position as shown. Center mill lower end 240 has an
abrasive lower
layer 242 similar to abrasive lower layer 218 of primary mill lower end 216. A
mill
nozzle 244 (preferably tungsten carbide) is threadedly and removably connected
to and
in center mill lower end 240 so as to be in communication with center assembly
passageway 224. As shown, mill nozzle 244 has a passageway which tapers from
an
inlet, having an inlet diameter, to an outlet having an outlet diameter
smaller than the
inlet diameter. The inlet end of mill nozzle 244 sealingly engages an O-ring.
Center
mill 236 also has a pair of packing rings 246 in circumferential recesses for
sealing
against the inner surface of primary mill 210. A shoulder 248 mates with
shoulder 214
, (FIG. 14).
To remove center assembly 222 from its locked position in FIG. 16, a
retrieval tool is used to engage tool recess 230, and head 228 is pulled up to
its up
position shown in phantom lines. A shaft 250 (also shown in phantom lines) is
connected to head 228 and extends out of locking mandrel 226 when retracting
dogs 234
to their retracted positions. One dog 234 is shown by phantom lines in its
refracted
position. Center assembly 226 can now be pulled upwardly out of mill section
central
bore 220 (FIG. 14) with the retrieval tool.
Center assembly 222 can be reinserted with dogs 234 in their retracted
positions, and then locked in position by using a setting tool to engage tool
recess 230
and push head 228 back down to extend dogs 234 to their extended and locked
positions.
CA 02487155 2000-02-02
-15-
With reference to FIG. 14 as well as FIG. 6, the mill section is
connectable to the jet pump section. Bit sub upper end 194 can be threadedly
connected
to the internally threaded lower end of body portion 142 so that mill section
central bore
220 is aligned with the outlet 140 of pump section central bore 136.
Since the mill section has a center assembly that can be removed, and the
various sections, including the mill section, have substantially straight
central bores
which are aligned when connected together as shown in FIG. 1, a tool can be
lowered by
wireline through the central bores below the mill section after removal of the
center
assembly.
This has particular advantages in connection with well control whenever
it becomes necessary in the course of an underreaming operation
to pull the hydraulic underreamer out of the well. This is sometimes necessary
because
of unanticipated events, such as mechanical problems or plugging of some part
of the
underreamer. Because a gas cap containing methane can form below the packer
section,
as previously discussed, simply pulling out of the "live" well could result in
a sudden
and potentially dangerous release of methane into the atmosphere. The usual
practice is
to first "kill" the well before pulling out by use of a dense liquid or "mud"
which tends
to fill coal seam cleats with particles and decrease future productivity.
The invention, however, allows lowering of an inflatable plug through
the central bores and below the mill section in the well casing after removal
of the center
assembly. After inflation of the inflatable plug to obtain a seal in the well
casing, the
underreamer can be pulled out of the well casing. Using a suitable sealing
mechanism at
the surface, such as a lubricator, the inflatable plug can be deflated, pulled
out of the
well, and replaced with a drillable cast iron bridge plug without losing the
desired seal.
The underreamer, with the center assembly set back in the mill section, is
then lowered
back into the well casing and liquid flow is started, which establishes a seal
of the
packer section in the well casing. While rotating with liquid streaming from
the mill
nozzle, the mill section drills through the bridge plug. Plug fragments which
are
sufficiently small are drawn by the jet pump section upward between its body
and the
well casing. The space between the outer surface of the body and the well
casing is
typically less than 1/4 inch. Therefore, the external grooves (most clearly
shown at 160
CA 02487155 2000-02-02
- 16-
in FIG. 13) in the body allow for larger plug fragments to enter the jet pump
section to
be pumped to the surface. After drilling through the bridge plug, the
underreamer is
lowered into the wellbore to the desired depth and the underreaming operation
can
resume. Note that this operation according the invention did not require
killing the well,
and thus avoids the consequent adverse effect upon productivity.
Finally, with respect to the various nozzles previously described in the
cutting, jet pump, and mill sections, such nozzles are all removable, and thus
changeable. This allows excellent hydraulic control for the purpose of
optimizing
hydraulic efficiency and the ability to adapt the hydraulic underreamer to a
wide range
of well conditions such as, but not limited to, depth of the well, methane
pressure in the
coal seam, and thickness of the coal seam.
Obviously, many modifications and variations of the present invention
are possible in light of the above teachings. For example, although six turn
chambers,
ejector nozzles, and venturis are employed in the above-described preferred
embodiment
of the jet pump section, a fewer or greater number could be used (i.e. three
to eleven). It
is, therefore, to be understood that within the scope of the appended claims,
the
invention may be practiced otherwise than as specifically described.
