Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION:
Method of reducing wear in a backup seal sealing a bearing chamber of a
downhole
tool
FIELD OF THE INVENTION
The present invention relates to a method of reducing wear in a backup seal
sealing a
bearing chamber of a downhole tool.
BACKGROUND OF THE INVENTION
Many downhole tools used in earth drilling have lubricant filled bearing
chambers in
which are radial bearings, thrust bearings or both. The bearing chambers have
seal assemblies
at each end to contain the lubricant and prevent the entry of drilling fluid
into the bearings. In
some cases more than one seal, positioned at each sealing location, is used to
seal the drilling
fluid out or the lubricant in. If two seals are used to seal the drilling
fluid out, the first or
primary seal encountering the drilling fluid will usually wear more than the
second or backup
seal; but both seals do experience wear. If two seals are used to seal
lubricant in, the primary
seal is sealing pressure and the backup seal is not. The seal which seals the
pressure will
usually wear more, but both seals do experience wear. It is advantageous to
ensure that the
backup seals are subjected to as little wear as possible, until they are
needed. If the backup
2 0 seal is already partially worn by the time it is needed, it will have a
reduced functional life.
SUMMARY OF THE INVENTION
What is required is a method of reducing wear on a backup seal sealing a
bearing
chamber of a downhole tool.
According to the present invention there is provided a method of reducing wear
on a
backup seal sealing a bearing chamber of a downhole tool. The method involves
a first step
of providing a downhole tool used in earth drilling, which includes a tubular
housing having
an inner surface defining an interior bore and a rotating shaft having an
exterior surface. The
3 0 rotating shaft extends into the interior bore of the housing. A bearing
chamber is positioned
between the inner surface of the housing and the exterior surface of the
rotating shaft. The
bearing chamber has a first end and a second end. Annular bearings are
disposed in the
bearing chamber. A first sealing assembly seals the first end of the bearing
chamber. A
second sealing assembly seals the second end of the bearing chamber. A second
step involves
3 5 providing at least one of the first sealing assembly or the second sealing
assembly with a
floating piston which moves axially in the bearing chamber in response to
changes in
pressure. Movement of the floating piston determines positioning of at least
one backup seal.
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A third step involves providing one of the exterior surface of the rotating
shaft or the floating
piston with an undercut which provides a clearance space between the at least
one backup seal
and the exterior surface of the rotating shaft. The at least one backup seal
does not engage the
exterior surface of the rotating shaft until axial movement of the floating
piston occurs to
move the at least one backup seal out of the undercut and into engagement with
the exterior
surface of the rotating shaft.
In applications in which several seals are in sealing engagement with a
rotating shaft,
it is difficult to avoid having the backup seals experience some wear.
However, in
accordance with the teachings of the present invention, the backup seals are
maintained in an
undercut where they experience virtually no wear. A subsequent loss of
lubricant will result in
a shifting of the floating piston, which moves the backup seal out of the
undercut and into
engagement with the rotating shaft.
Once the basic teaching of the present invention is understood, there are
various ways
to put the invention into effect. For example, the undercut can be positioned
either on the
exterior surface of the rotating shaft or on the floating piston. When the
undercut is in the
exterior surface of the rotating shaft, the backup seal can be carried in a
seal groove in the
floating piston. When the undercut is in the floating piston, movement of the
floating piston
2 0 forces the backup seal up an inclined plane on the floating piston into
engagement with the
exterior surface of the rotating shaft.
Similarly, there are various ways that the desired movement of the floating
piston can
2 5 be made to occur. For example, a spring can be provided to act upon the
floating piston, so
that the floating piston is biased by the spring to move the at least one
backup seal out of the
undercut and into engagement with the exterior surface of the rotating shaft
should a loss of
lubricant occur from the bearing chamber. Alternatively, the floating piston
is biased by
lubricant pressure within the bearing chamber to move the backup seal out of
the undercut
3 0 and into engagement with the exterior surface of the rotating shaft should
a loss of lubricant
occur from the bearing chamber downstream of the floating piston. If the
floating piston
forms part of the second seal assembly, it can also be biased by drilling
fluid pump pressure to
move the backup seal out of the undercut and into engagement with the exterior
surface of the
rotating shaft should a loss of lubricant occur from the bearing chamber
downstream of the
3 5 floating piston.
It will be appreciated that there can be any number of backup seals. When more
than
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one backup seal is provided, as one backup seal fails, the floating piston
moves incrementally
further axially in the bearing chamber bringing another backup seal out of the
undercut and
into engagement with the exterior surface of the rotating shaft.
It will also be appreciated, that the various teachings can be combined in
various
ways. Three alternative ways of co~guring the first seal assembly will
hereinafter be
illustrated and described, along with two alternative ways to configure the
second seal
assembly.
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BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following description in which reference is made to the appended drawings, the
drawings are
for the purpose of illustration only and are not intended to in any way limit
the scope of the
invention to the particular embodiment or embodiments shown, wherein:
FIGURE 1 is a side elevation view, in section, of a downhole tool with a
rotary shaft
constructed in accordance with the teachings of the present invention, prior
to primary seal
failure occurring.
FIGURE 2 is a side elevation view, in section, of the downhole tool with the
rotary
shaft illustrated in FIGURE 1, after primary seal failure has occurred.
FIGURE 3 is a detailed side elevation view, in section, of the first seal
assembly of
the downhole tool with the rotary shaft illustrated in FIGURE 1.
FIGURE 4 is a detailed side elevation view, in section, of the second seal
assembly
of the downhole tool with the rotary shaft illustrated in FIGURE 1.
FIGURE 5 is a detailed side elevation view, in section, of a first alternative
embodiment of first seal assembly, with undercut on the exterior surface of
the rotating shaft
and lubricant pressure biasing.
FIGURE 6 is a detailed side elevation view, in section, of a second
alternative
2 0 embodiment of first seal assembly, with undercut on the floating piston
and spring biasing.
FIGURE 7 is a detailed side elevation view, in section, of a third alternative
embodiment of first seal assembly, with undercut on the floating piston and
lubricant pressure
biasing.
FIGURE 8 is a detailed side elevation view, in section, of a first alternative
2 5 embodiment of second seal assembly, with undercut on the exterior surface
of the rotating
shaft and drilling mud pressure biasing.
FIGURE 9 is a detailed side elevation view, in section, of a second
alternative
embodiment of second seal assembly, with undercut on the floating piston and
spring biasing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred method will now be described with reference to FIGURES 1 through
4.
3 5 Structure and Relationship of Parts:
Referring now to FIGURE 1, there is provided a downhole tool indicated
generally by
reference numeral 100 used in earth drilling. The downhole tool 100 comprises
a tubular
CA 02455543 2004-O1-21
housing 102 having an inner surface 104 defining an interior bore 112. There
is also a
rotating shaft 106 having an exterior surface 108, the rotating shaft 106
extending into the
interior bore 112 of the housing 102. A bearing chamber 110 is positioned
between the inner
surface 104 of the housing 102 and the exterior surface 108 of the rotating
shaft 106, the
5 bearing chamber 110 having a first end 114 and a second end 116. Annular
bearings 111 are
disposed in the bearing chamber 110. There is also a first sealing assembly
120 sealing the
first end 114 of the bearing chamber 110 and a second sealing assembly 122
sealing the
second end 116 of the bearing chamber 110. Referring to FIGURE 3, the first
sealing
assembly 120 includes a primary seal 149, as well as a floating piston 124
which moves
axially in the bearing chamber 110 in response to changes in pressure.
Floating piston 124
also has a primary seal 126, as well as two backup seals 128 and 136. Seals
126, 128, and
136 are positioned in seal grooves 126A, 128A and 136A, respectively, in
floating piston 124.
It will be understood that movement of the floating piston 124 determines
positioning of seals
126, 128 and 136. Exterior surface 108 of rotating shaft 106 is provided with
an undercut
130, which provides a clearance space 132 between backup seals 128, 136 and
the exterior
surface 108 of the rotating shaft 106. This means that backup seals 128 and
136 do not engage
exterior surface 108 of rotating shaft 106, until axial movement of floating
piston 124 occurs
to move one of both of backup seals 128 and 136 out of undercut 130 and into
engagement
with exterior surface 108 of rotating shaft 106. It is preferred that there be
provided a spring
2 0 134 acting upon floating piston 124 urging floating piston 124 toward
first end 114 of bearing
chamber 110. Floating piston 124 is biased by spring 134 to move backup seals
128 and 136
out of undercut 132 and into engagement with exterior surface 108 of rotating
shaft 106,
should a loss of lubricant occur from sub-chamber 110A at first end 114 of the
bearing
chamber 110. Pipe plug 150 provides the user access to sub-chamber 110A.
There may be any number of backup seals provided, for purposes of this
description
two are depicted in FIGURE 3. Primary seal 149 is exposed to corrosive
drilling fluids. It is
likely to be the first seal to fail. Upon failure of primary seal 149,
lubricant will leak past
primary seal 149 and be lost from sub-chamber 110A. Once lubricant is lost
from sub-
3 0 chamber 110A, floating piston 124 will slide down behind failed primary
seal 149, with seals
126, 128 and 136 all engaged with exterior surface 108 of rotating shaft 106.
The speed at
which floating piston 124 moves into position depends upon the time interval
over which
lubricant is lost from sub-chamber 110A.
3 5 If, for some reason, primary seal 126, should fail first; the behaviour of
floating piston
124 will be slightly different. Even after primary seal 126 fails, there will
still be lubricant in
sub-chamber 110A. This means that upon failure of primary seal 126, the
floating piston 124
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will only move incrementally further axially toward the first end 114 of the
bearing chamber
110 bringing another backup seal 128 out of the undercut 130 and into
engagement with the
exterior surface 108 of the rotating shaft 106. Backup seal 136 will remain
shielded within
undercut 130 until seal 128 fails. Spring 134 ensures that floating piston 124
moves, as
intended to permit backup seal 128 to assume the sealing function of failed
primary seal 126.
FIGURE 2 shows the downhole tool with floating piston 124 having moved to
first
end 114 of bearing chamber 110 immediately adjacent to primary seal 149. In
this position,
seals 126, 128 and 136 are all engaged with exterior surface 108 of rotating
shaft 106.
to
Referring to FIGURE 4, the second sealing assembly 122 is shown to have a
floating
piston 140 which moves axially in the bearing chamber 110 in response to
changes in
pressure. Floating piston has several primary seals 141, 142 and 143,
positioned in seal
grooves 141A, 142A and 143A, respectively. Primary seals 141 and 142 seal
exterior surface
108 of rotating shaft 106. For ease of assembly and fabrication, instead of
providing rotating
shaft 106 with an irregular profile, there are a number of spacer sleeves and
like components
which rotate with rotating shaft 106. It will be understood that when the
exterior surface 108
is referred to, it will include components which rotate with rotating shaft
106. Primary seal
143 seals against inner surface 104 of tubular housing 102. Floating piston
140 also has
2 0 backup seals 144 and 145 positioned in seal grooves 144A and 145A,
respectively. Exterior
surface 108 of rotating shaft 106 has an undercut 146 which provides a
clearance space 148
between the backup seals 144, 145 and exterior surface 108 of rotating shaft
106. Backup
seals 144 and 145 do not engage exterior surface 108 of rotating shaft 106
until axial
movement of floating piston 140 occurs to move backup seals 144 and 145 out of
undercut
2 5 146 and into engagement with exterior surface 108 of the rotating shaft
106. A spring 172
acts upon floating piston 140 urging floating piston 140 toward the first end
114 of the
bearing chamber 110. Pipe plug 180 provides the user access to bearing chamber
110.
Floating piston 140 is biased by spring 172 to move backup seal 142 out of
undercut 146 and
into engagement with exterior surface 108 of rotating shaft 106 should a loss
of lubricant
3 0 occur from sub-chamber 1 l0A at first end 114 of the bearing chamber 110.
Referring to
FIGURE 2, there is illustrated how floating piston 124 moves should a loss of
lubricant occur
from sub-chamber 110A.
Operation:
3 5 Referring to FIGURE 4, drilling mud enters the drilling tool through ports
166. Most
of the mud travels through the interior 168 of the rotating shaft 106. Some
mud will flow
between the inner surface 104 of the tubular housing 102 and the exterior
surface 108 of the
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rotating shaft 106 as indicated by arrow 175. The mud's flow is restricted by
the flow
restrictor 170, past spring 172, and out side opening 174. Flow restrictor 170
only allows a
small amount of drilling fluid to flow past it, causing most of the fluid to
pass through ports
166 and down through interior 168. This allows fluid chamber 176 above piston
140 to be
pressure balanced with fluid external to the tool through ports 174. Without
flow restrictor
170, far too much fluid would be lost through ports 174. Referring to FIGURE
3, the first
sealing assembly 120 is shown primary seal 149 engaged, as well as primary
seal 126 on
floating piston 124. Backup seals 128 and 136 not engaged. Upon failure of
primary seal 149
at first end 114 of bearing chamber 110, the change in pressure due to the
loss of lubricant
from sub-chamber 110A will cause spring 134 to move floating piston 124.
Floating piston
124 will move to the position illustrated in FIGURE 2, engaging the backup
seals 128 and
136 with exterior surface 108 of rotating shaft 106. Referring to FIGURE 4,
floating piston
140 is shown in the position it would be in prior to the loss of lubricant.
Once the lubricant is
lost, floating piston 140 moves to engage the backup seals 142 and 144 against
the exterior
surface 108 of the rotating shaft 106. Referring to FIGURE 2, the floating
piston 140 is
shown as having moved to engage backup seals 142 and 144.
Variations:
There will now be described alternative embodiments of both the first sealing
2 0 assembly 120 and the second sealing assembly 122.
Referring to FIGURE 5, there is illustrated a first alternative embodiment of
the first
sealing assembly 120. In this embodiment, floating piston 124 is biased solely
by lubricant
pressure toward the first end 114 of the bearing chamber 110. Should primary
seal 149 fail, a
2 5 loss of lubricant will occur from sub-chamber 1 l0A at first end 114 of
bearing chamber 110
downstream of floating piston 124. This will result in a pressure imbalance
and lubricant
pressure will move floating piston 124 to bring backup seals 128 and 136 out
of undercut 132
and into engagement with exterior surface 108 of rotating shaft 106. This
version is not
preferred, as there is nothing to bias floating piston 124, should primary
seal 126 fail first,
3 0 instead of primary seal 149. However, in most applications this embodiment
would be
suitable, as primary seal 149 generally fails first.
Referring to FIGURE 6, there is illustrated a second alternative embodiment of
the
first sealing assembly 120. In this embodiment, the floating piston 124 has an
undercut 160
3 5 which provides a clearance space 162 between backup seal 126 and the
exterior surface 108
of the rotating shaft 106. The backup seal 126 will not engage the exterior
surface 108 of the
rotating shaft 106 until axial movement of the floating piston 124 occurs to
move backup seal
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126 out of the undercut 160 and into engagement with the exterior surface 108
of the rotating
shaft 106. There is also an inclined plane 164 on the floating piston 124
adjacent to the
undercut 160, such that movement of the floating piston 124 forces the backup
seal 126 up the
inclined plane 164 and into engagement with the exterior surface 108 of the
rotating shaft
106. As with the original embodiment, there is a spring 134 acting upon the
floating piston
124 urging the floating piston toward the first end 120 of the bearing chamber
110. The
floating piston 124 is biased by the spring 134 to move the backup seal 126
out of the
undercut 160 and into engagement with the exterior surface 108 of the rotating
shaft 106
should a loss of lubricant occur from the first end 120 of the bearing chamber
110.
Referring to FIGURE 7, there is illustrated a third alternative embodiment of
the first
sealing assembly 120. As with the alternative embodiment described by FIGURE
6, there is
a floating piston 124 with an undercut 160 which provides a clearance space
162 between the
backup seal 126 and the exterior surface 108 of the rotating shaft 106, and an
inclined plane
164 for moving the backup seal 126 into engagement with the exterior surface
108 of the
rotating shaft 106. In this embodiment, as with the embodiment illustrated in
FIGURE 5,
floating piston is biased solely by lubricant pressure toward first end 114 of
bearing chamber
110. Should a loss of lubricant occur from sub-chamber 110A at first end 114
of bearing
chamber 110 downstream of the floating piston 124, lubricant pressure will
move floating
2 0 piston 124. Backup seals 128 and 136 will move out of undercut 160 and
into engagement
with exterior surface 108 of rotating shaft 106.
Referring to FIGURE 8, there is illustrated a first alternative embodiment of
the
second sealing assembly 122. In this embodiment, floating piston 140 is biased
by drilling
2 5 mud pressure toward first end 114 of bearing chamber 110 to move the
backup seals 142 and
144 out of undercut 146 and into engagement with exterior surface 108 of
rotating shaft 106
should a loss of lubricant occur from first end 114 of the bearing chamber 110
downstream of
the floating piston 140.
3 0 Referring to FIGURE 9, there is illustrated a second alternative
embodiment of the
second sealing assembly 122. In this embodiment, spring 172 acts upon the
floating piston
140, urging the floating piston 140 toward the first end 114 of the bearing
chamber 110. The
floating piston 140 has an undercut 190 which provides a clearance space 192
between the
backup seal 142 and the exterior surface 108 of the rotating shaft 106, and an
inclined plane
3 5 194 for moving the backup seal 126 into engagement with the exterior
surface 108 of the
rotating shaft 106. The floating piston 140 is biased by the spring 172 to
move the backup
seal 142 out of the undercut 190 and into engagement with the exterior surface
108 of the
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rotating shaft 106 should lubricant be lost from bearing chamber 110.
In this patent document, the word "comprising" is used in its non-limiting
sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
It will be apparent to one skilled in the art that modifications may be made
to the
illustrated embodiment without departing from the spirit and scope of the
invention as
hereinafter defined in the Claims.
