Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~343135
This in~7ention relates to an improved downhole
drill bit drive apparatus assembly of ~the type employed
in drilling through soil and rock formations.
B KGROUND OF _HE INVENTION
The use of downhole motors in drilling operations
has had limited success due to the short functional life
span of drill bits. The life of a drill bit is related
to the rotational speed of the drill bit and,
10 heretofore, downhole motors arrangements have tended to
rotatably drive the drill bit at relatively hi~h
rotational speeds. As a result, premature drill bit
failure would result and, each time a drill bit would
become worn, valuable drilling hours would be lost as
15 the drill string would be removed from the borehole, the
bit replaced and the drill string reinserted into the
borehole. While the solution, reduction of the
rotational speed of the drill bit, has been recognized
for several years, downhole drill bit drive tools have
20 nevertheless failed to meet expectations. By way of
background and as is well known in the this field, a
drilling fluid, or "drilling mud" as it is known in th~
field, i5 pumped under pressure down the interior of the
drill string to the drill bit and the fluid together
25 with cuttings are returned to the surface along the
exterior of the drill string. The fluid pressure at the
bottom of the bore hole is considerable.
In one prior downhole drill bit drive arrangement,
a controlled amount of drilling mud was allowed to pass
30 through the bearing assemblies. However, the drilling
mud was found to cause premature failure of the bearings
and, accordingly, this approach was deemed an
unsatisfactory solution to the problem. Various
attempts at sealing the bearing and speed reduction
35 mechanism have had little success. The solution to the
problem is known to lie in lubricated systems to prolong
~23 ~3~35
bearing life, however this will require an advance in
seal systems technology.
SUMMARY OF THE INVENTION
___ _ __
The primary object of one aspect of the present
invention is to provide an improved sealing arran~ement
for the bearing assembly of a downhole drill bit drive
apparatus.
Acrording to the present invention there is
10 provided an improvement in a downhole drill bit drive
apparatus haviny a tubular housing adapted to be secured
to the downhole end of a drill string, a mandrel
concentrically disposed within the housing and having
one end adapted to be secured to a downhole rotary drive
- 15 means and an other end adapted to be secured to a drill
bit, bearing means disposed between the housing and the
mandre.l to permit rotation of the mandrel with respect
to the housing and transmit axial and radial loads
between the housing and the mandrel, the housing and the
20 mandrel defining a fluid flow passage for transmitting
drilling fluid to a drill bit secured to the mandrel.
The improvement is comprised of a first seal means at
one end of the bearing means, the first seal means
defining one end of a bearing chamber for housing the
2~ bearing means and a lubricating fluid for lubricating
the hearing means and being operable to seal the chamber
from the fluid flow passage and maintain the pressure in
the flow passage and in the chamber substantially at
equilibrium; second seal means at the other end of the
30 bearing means, the second seal means de~ining the other
end of the bearing chamber and being operable to seal
the chamber from the exterior of the chamber. The first
seal means includes an annular piston chamber, the
housing defining an outer wall of the piston chamber and
35 the mandrel defining an inner wall of the piston
chamber, one end of the piston chamber communicating
with the fluid ~low passage, the other end of the piston
chamber communicating with the bearing chamber, annular
1;~3~3135
-- 3
piston means concentrically disposed within the piston
chamber in sealing el~gagement with the inner and outer
walls of the p:iston chamber, the piston means being
axially movable in the piston chamber in response to a
pressure differential between the flllid pressure in -the
fluid flow passage and the fluid pressure in the bearing
chamber to a position whereat the fluid pressures are
substantially equal; and further including roller
bearing means for rotatingly mounting the piston means
on the mandrel to permit rotation of the mandrel with
respect to the piston.
J~23~38S
-- 4 --
BRIEF DESCRIPTION OF THE DRAWINGS
_,____ __,_ ___ __ __
These and other features of the invention will
become more apparent from the following description in
which reference i5 made to the appended drawings,
wherein:
FIGUR~ 1 is a partially diagrammatic illustration
of a downhole drive apparatus of the present invention
secured to the downhole end of a drill string;
FIGURES 2a - 2e are longitudinal cross-sectional
views of an embodiment of the downhole drive apparatus
of the present without ~peed reduction;
FI~UR~S 3a - 3e are longitudinal cross-sectional
15 views of an embodiment of the downhole drive apparatus
of the present invention with speed reduction;
FIGUR~ 4 is a partially broken, longitudinal
cross-sectional view of an end cap; and
~ IGUR~ 5 is a cross--sectional view ta~en along line
5-5 of FIGUR~ 3.
~;23~38~
DETAILED _ESCRIPTION OF AN EMBODI_~NT
With reference to FIGURE 1 of the drawings, there
i5 diagramma-tically illustrated a downhole, drill bit
drive apparatus, generally designated by reference
numeral 10. The apparatus i5 comprised of a tubular
housing or casing 12 having a string end 14 adapted to
be secured to the downhole end of a conventional drill
string 18. A mandrel 20 is concentrically disposed
within the housing and has a drill string end 22 adapted
to be secured to a downhole rotary drive means (not
10 shown) and a bit end 24 adapted to be secured to a drill
bit 25. Bearing means is disposed between the housing
and the mandrel to permit rotation of the mandrel with
respect to the housing and transmit axial and radial
loads between the housing and the mandrel in a manner
15 explained more fully later. The drill string end 22 of
the mandrel is formed with a plurality of radial fluid
passages 26 for receiving, in a longitudinal internal
channel 28 thereof, drilling fluid delivered by means of
~; surface pumps down the drill string 18 and into the
20 drill string end 14 of the housing. Channel 28 deliv0rs
the drilling fluid to the drill bit secured to the
mandrel, as is well known.
A first seal means 30 is provided at the drill
string ends of the housing and mandrel to define the
25 drill string end of a bearing chamber 3~ which houses
the bearing means, a lubricating fluid for lubricating
the bearing means and a speed reducing mechanism, if the
latter is provided~ As explained more fully later, the
first seal means is operable to seal the bearing chamber
30 from the drilling fluid and maintain the pressure in the
drilling fluid passage and in the bearing chamber
substantially equal. A second seal means 34 is disposed
at the bit end of the bearin~ means and defines the
other end of the bearing chamber. The second seal means
35 is operable to seal the bearing chamber from the
exterior of the chamber.
:I Z3~38S
-- 6
With particular reference to FI~UR~S 2a - 2e, which
illustrate an embodiment of the invention without speed
reduction, the drill string end 14 of the housing 12
will be seen to be threadedly engaged with an adaptor
suh 36 which, in turn, is secured to the downhole end of
the drill string. To permit assembly of the ~earings
and other internal components of the apparatus, the
housing i5 formed in two parts including a top sub 40
and a bearing housing 42, threadedly secured together in
10 end-to-end relation, as shown. An end cap 44 is
threadedly secured to the bit end of bearing housing 42
and houses the second seal means 34 referenced earlier.
The drill string end 22 of the mandrel is
threadedly engaged with a coupling member 46 which, in
15 turn, is threadedly secured to the output shaft 48 of
the downhole motor (not shown). The mandrel is
constructed in two parts including a wash pipe 50 at the
drill string end and a main mandrel 52 at the bit end
threadedly engaged together in end-to-end relation.
With reference to FIGURE 2b, first seal means 30
will be seen as being comprised of an annular piston 60
disposed in a piston chamber 62 having an outer wall 64
formed in top sub 40 and an inner wall 66 formed by wash
pipe 50 of mandrel 20. Drill string end 68 of the
25 piston chamber opens into the drilling fluid ~low
passage while the bit end ~0 of the piston chamber opens
into bearing chamber 32. The piston is formed with
generally cylindrical cuter and inner walls 72 and 74,
respectively, concentrically disposed in the pi~ton
chamber in sealing engagement with the outer and inner
walls of the piston chamber. The piston i5 axially
movable in the piston chamber in response to a pressure
differential between the drilling fluid flow passage and
the bearing chamber whereby to e~ualize the pressure
therebetween. A roller bearing 76 i5 disposed between
the piston and the wash pipe to permit rotation of the
mandrel with respect to the piston and maintain
concentricity between the mandrel, piston and housing.
.
::L23~385
-- 7
The bearing and its races are axially mo~able with the
piston.
A first pair of axially spaced, inner floating
seals 80 and 82 are respectively disposed in seal
grooves 84 and 86 formed in inner wall ~4 of the piston
for sealingly engaging piston chamber inner wall 66
while a second pair of axially spaced, outer floating
~eals 88 and 90, respectively, are disposed in seal
grooves 92 and 94 formed in piston outer wall ~2 for
sealingly engaging piston chamber outer wall 64. A pair
of radial passages 96 (only one is shown) extend between
piston inner wall ~4 and piston outer wall 72 between
the seals 80 and 82 of the inner pair of seals and seals
88 and 90 of the outer pair of seals. A pair of axial
passages 9S (only one is shown) extend from drill string
end face 100 of the piston and each communicates with
one of the radial passages. A grease nipple 102 is
provided in end face 100 for feeding ~rease or like
fluid under pressure into passages 98 and ~6, between
adjacent inner walls 66 and 74 of the chamber and piston
and ad~acent outer walls 64 and 72 of the chamber ~nd
piston and into seal grooves 84, 86, 92 and 94 to urg2
the seals to the distal ends of their respective
grooves. Once the grooves have been filled with an
appropriate fluid, nipple 102 is replaced with a plug
(not shown).
Thus, it will be seen that during the normal course
of operation, a differential in pressure between the
drilling Eluid passage and the bearing chamber will
cause axial displacement of the piston within the piston
chamber in the direction of lower pressure thus tending
to equalize the pressure between the drilling fluid
passage and the bearing chamber. This reduces the
likelihood of leakage of drilling fluid into the bearing
chamber. Further, as the pressure increases on either
end oE the piston, such pressure will be transmitted to
the axial outer faces of the inner and outer seals
against the prea-~ure of the fluid on the inner sides Gf
123~3~3S
~ 8 --
the grooves, thus enhancing the sealing effort of the
seals.
With reference to FIGURE 2e, second seal means 34
will be seen to be housed within end cap 44 which is
threadedly secured in the bit end of bearing housing 42
of housing 12. Seal means 34 is provided with, in bore
108 thereof, a first floating seal 110 disposed in seal
groove 112, a second floating seal 114 disposed in a
seal groove 116, a fixed seal 118 disposed in a seal
; 10 groove 120 and a third floating seal 122 disposed in a
seal groove 124. A seepage passage 126 extends from
seal groove 112 between the bore of the end cap and the
outer surface of main mandrel 52 ~or communicating fluid
under pressure from the exterior of the housing to bit
15 end face 128 of seal 110. The seals are packed with a
suitable fluid or grease with the floating seals being
urged thereby to the positions shown in FIGURE 2e.
Fixed seal 118 is intended to serve as the primary
seal between the bearing chamber and the exterior of the
20 housing while the remaining floating seals are intended
to serve aæ backup seals in the event that seal 118
fails. In addition, seals 110 and 114 are intended to
keep fixed seal 118 properly lubricated by preventing
drilling fluid from reaching and contaminating fixed
25 seal lla.
In lieu of the seepage passage, there may be
provided, as shown in FIGURE 4, an additional groove 130
at the bit end of the end cap 44, a flow restrictor 132
po~itioned therein and a radial fluid passage 134
30 extending between channel 28 and the bit end of face 128
of seal 110. In this manner, drilling fluid under
pressure is communicated directly to seal 110.
: With reference to FIGUR~ 2~, a series of five
cylindrical roller bearings 140 are provided at the bit
end of the b~aring chamber 30 between bearing housing ~2
and main mandrel 52 for transmitting radial forces
between the housing and the mandrel. Each is provided
with an inner race 142 and an outer race 144. Inner
~; :
~ ' ,
~ ' :
3'~3~35
race 142 of the bit end bearing 140 i5 held against a
shoulder 146 ~ormed by a profile on the outer surface of
the main mandrel 52 while outer race 144 thereof is held
against the string end of end cap 44. The inner and
outer races of the other four of bearings 140 are held
in end-to-end relation by the bit ends of an inner
spacer sleeve 150 and an outer spacer sleeve 152. With
reference to FIGURE 2d, a second serie~ of three
cylindrical roller beari~gs 154 are provided generally
10 midway of the length of the housing and mandrel for
transmitting radial forces therebetween. The inner and
outer races 156 and 158 of the bit-end bearing 154 are
held against the drill string ends of inner and outer
spacer sleeves 150 and 152 while the inner race of drill
15 5tring end bearing 154 is held against a retaining ri~g
160 which, in turn, is held in position by a snap ring
162. The outer race of the string end bearing is held
in position by the bit end of a spacer sleeve 164.
With reference to FIGURES 2b and 2c, a third series
20 o~ two cylindrical roller bearings 166 are provided at
the string end of the apparatus between top sub 40 and
wash pipe 50 to transmit radial forces therebetween.
Inner and outer races 168 and 170 thereof are spaced
apart by inner and outer spacer sleeves 172 and 174,
25 re5pectively. The bit end of the outer race of the bit
end bearing is held against a snap ring 176 while the
inner race thereof is held against a shoulder 1~8 formed
on the outer surface of wash pipe 50. The string end of
the outer race of the string end bearing 166 i5 held
30 against a shoulder 180 formed on the inner surface of
top sub 40 of the housing while the inner race thereof
is held against a snap ring 182.
With reference to FIGURE 2d, there is provided a
pair o~ spherical roller bearings 190 and 192 for
35 transmitting axial loads from the drill string and
housing to the mandrel during drilling operations.
Bearings 190 and 192 are arranged in such a manner that
the axial load~ are distributed substantially e~ually
1~23~3~5
-- 10 --
between the two bearings. Bearing 190 i5 provided with
an inner race 194 held against a shoulder 195 formed on
the outer surface of main mandrel 52 and an outer race
196 held against the drill string end of spacer sleeve
164. Bearing 192 is provided with an inner race 198 and
an outer race 200 held against a shoulder 202 formed on
the inner surface of bearing housing 42. Disposed
between outer race 196 of bearing 190 and outer race 200
of bearing 192 are a compression ring 204, which bears
10 against race 196, a pair of disc springs 206 and 208,
and a sleeve 210, the string end of which bears against
outer race 200. Similarly disposed between inner race
194 of bearing 190 and inner race 198 of bearing 192 are
a compression ring 212, which bears against inner race
15 198, a pair of disc springs 214 and 216, and a sleeve
218, the bit end of which bears against inner race 194.
The compression rings serve to evenly and centrally
distribute the spring loads against their respective
races and ~aintain the bearings axially and
20 compressively loaded. A further spherical roller
bearing 220 is provided to support the weight of the
mandrel and associated components when the drill string
is raised. Bearing 220 is provided with an outer race
222 held against the string end 224 of bearing housing
25 42 and an inner race 226 which i5 urged against the
rollers by means of a compression ring 228 and pair of
disc springs 230 and 232 compressed between the
compression ring and the bit end of wash pipe 50.
;Reference will now be made to FIGURES 3a - 3e,
30 which illustrate an embodiment of the invention provided
with a speed reducer. This embodiment, generally
designated by reference numeral 300, i9 substantially
the same as that of FIGURES 2a - 2e except for the
inclusion of the speed reducing mechanism, generally
35 designated by the numeral 310. Thus, embodiment 300 is
; provided with a housing 312 which includes an adaptor
sub 314, a top sub 316 and a bearing housing 318 and a
~ mandrel, generally designated by refer~nce numeral 320,
: .
,
~;Z3438S
including a coupling member 322, a wash pipe 324, and a
main mandrel 326. An annular piston 328 is concentri-
cally disposed in an annular piston chamber 330 at the
string end of the apparatus while an end cap 332, and
associated seals, is provided at the bit end of the
apparatus.
A first series of five cylindrical roller bearings
334 (FIGURES 3d and 3e), a second series of three
cylindrical roller bearings 336 (FIGURF 3d) and a third
series of two cylindrical roller bearings 338 (only one
of which is shown in FIGURE 3a) are provided for
transmitting radial forces between the housing and the
mandrel. A pair of spherical roller bearings 339
(FIGURE 3d) are provided for transmitting drill string
and housing axial loads to the mandrel during normal
drilling operations. The components just referenced are
identical to corresponding components in the embodiment
of FIGURES 2a - 2e and, accordingly, will not be
described in further detail.
With particular reference to FIGURES 3b and 3c,
the housing will be seen to be further comprised of a
stationary gear housing 340 and a barrel member 342
threadedly secured together in end-to-end relation. The
string end of gear housing 340 is threadedly secured
through the bit end of top sub 316 while the bit end of
barrel member 342 is threadedly secured to the bit end
of bearing housing 318.
Mandrel 320 further includes a gear mandrel member
344, the string end of which is threadedly secured to
wash pipe 324 and, thus, is rotatably driven thereby.
Gear mandrel 344 is telescopically received within a
gear cage 346 (FIGURES 3b and 5). A plurality of
bushings 348 are disposed between the gear cage and the
gear mandrel for transmitting radial forces therebetween
while permitting relative rotation thereof. A spherical
roller bearing 350 is positioned between string end 352
of the gear cage and bit end 354 of wash pipe 324. Bit
end 356 (FIGURE 3c3 of the gear cage is threadedly
, .
:. :
'
. .
1~2343l3S
- 12 -
secured to a gear cage coupling 358 which, in turn, is
threadedly secured to main mandrel 326. The cage
csupling serves to transmit torque from the cage
coupling to the main mandrel. A spherical roller
hearing 360, a compression ring 362 and a pair of disc
springs 364 and 366 are positioned between the string
end 368 of bearing housing 318 and bit end 370 of gear
cage 358.
As best shown in FIGUR~ 5, gear mandrel 344 is
10 formed with an external axial spline or gear 37~ which
meshes with three driven planetary gear assemblies 3~6
while gear housing 340 is formed with an internal axial
spline or gear 378 which also meshes with the gears
assemblies. In order to transmit the high torque
15 required, each planetary gear assembly 3~6 is comprised
of three coaxially aligned gear~ 380, 382 and 384 (see
FIGURE 3b) suitably journaled in bearing blocks 386
slidably received in pockets 388 of gear cage 346 for
rotation about their respective axis and epicyclic
20 movements about the axis of the mandrel. The speed
reducer shown provides a speed reduction ratio of 3:1.
It will be understood that various modifications
and alterations may be made to the above described
embodiments of the invention without departing from the
25 spirit of the following claims.
