U.S. patent application number 09/907003 was filed with the patent office on 2003-01-23 for flow retarder for bearing assembly of downhole drilling motor.
Invention is credited to Robin, Lawrence E..
Application Number | 20030015352 09/907003 |
Document ID | / |
Family ID | 25423385 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030015352 |
Kind Code |
A1 |
Robin, Lawrence E. |
January 23, 2003 |
Flow retarder for bearing assembly of downhole drilling motor
Abstract
A flow retarder is provided for use in the bearing assembly of a
downhole drilling motor. The bearing assembly comprises an inner
tubular mandrel and an outer tubular housing. The flow retarder
comprises: an inner carbide sleeve connected to the rotating
mandrel by a resilient elastomer layer bonded to a driver ring
which is locked on the rotating mandrel; an outer carbide sleeve
affixed to the stationary tubular housing; the sleeves forming a
narrow annular clearance or metering gap between them; a secondary
port extending through the mandrel side wall directly above the
carbide sleeves; and a housing port extending through the housing
side wall below the flow retarder sleeves. Drilling fluid leaks
down from the adapter/adjustable housing clearance and passes
through the metering gap to lubricate the carbide sleeves. Part of
this fluid returns through the secondary port to the main bore of
the mandrel. By providing the elastomer layer, the transmission of
radial loads from the inner sleeve to the outer sleeve is
reduced.
Inventors: |
Robin, Lawrence E.;
(Edmonton, CA) |
Correspondence
Address: |
SHERIDAN ROSS PC
1560 BROADWAY
SUITE 1200
DENVER
CO
80202
|
Family ID: |
25423385 |
Appl. No.: |
09/907003 |
Filed: |
July 17, 2001 |
Current U.S.
Class: |
175/107 |
Current CPC
Class: |
E21B 4/003 20130101 |
Class at
Publication: |
175/107 |
International
Class: |
E21B 004/00 |
Claims
The embodiment of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A flow retarder for use in a downhole drilling motor bearing
assembly used in a well borehole, said bearing assembly comprising
a main clearance through which drilling fluid can move, an inner
rotatable tubular mandrel having a side wall forming a longitudinal
bore, an outer stationary tubular housing having a side wall, an
annular pressure balancing chamber formed between the housing and
mandrel side walls and an annular floating piston seal closing the
bottom end of the chamber, the flow retarder comprising: an
erosion-resistant inner sleeve mounted on a driver ring connected
to rotate with the mandrel, said inner sleeve being secured to the
driver ring by a layer of resilient elastomer positioned between
the sleeve and the driver ring; an erosion-resistant outer sleeve
fixed to the inside surface of the housing side wall; the inner
sleeve being positioned within the outer sleeve, said sleeves
forming a narrow annular metering gap between them, the sleeves
being positioned in the upper end of the chamber and extending
there across; the housing side wall forming a housing port
extending therethrough below the sleeves to connect the pressure
balancing chamber and the lower end of the metering gap with the
borehole.
2. The flow retarder as set forth in claim 1 wherein: the mandrel
side wall forms a secondary mandrel port at the upper end of the
metering gap for connecting the lower end of the main clearance
with the mandrel bore.
3. The flow retarder as set forth in claim 2 comprising: the
mandrel having an outwardly protruding shoulder; the driver ring
being seated on the shoulder and having a frictional engagement
with the mandrel so as to rotate therewith; the elastomer layer
being bonded to the driver ring and the inner sleeve so that the
inner sleeve rotates with the mandrel.
4. The flow retarder as set forth in claim 3 comprising: means for
resiliently pressing the driver ring against the mandrel
shoulder.
5. The flow retarder of claim 1, 2, 3 or 4 wherein: the inner
sleeve has a plurality of circumferential grooves formed in its
outer surface at spaced intervals along its length.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a fluid retarder or
restrictor used in the bearing assembly of a downhole drilling
motor.
BACKGROUND OF THE INVENTION
[0002] A downhole drilling motor and its bearing assembly are known
tools used in well drilling. The present invention is concerned
with improving the bearing assembly.
[0003] A bearing assembly typically includes:
[0004] an inner rotating tubular mandrel connected between the
power unit of the downhole drilling motor and the bit;
[0005] an outer stationary tubular housing co-extensive with the
mandrel and connected with the drill string;
[0006] bearings positioned in a bearing chamber formed between the
mandrel and housing;
[0007] spaced stationary and floating piston seals closing the ends
of the bearing chamber, which is filled with lubricating oil;
[0008] the floating piston seal being positioned at the lower end
of an annular pressure balancing chamber, formed between the
mandrel and housing.
[0009] The bearing assembly is connected at its upper end to the
motor power section by an inner tubular adapter and an outer
tubular adjustment housing. Drilling fluid moving down through the
clearance between the adapter and the adjustment housing enters the
bore of the mandrel through a primary mandrel port. This clearance
can be referred to as the main clearance.
[0010] An assembly referred to as a flow retarder is positioned at
the upper end of the pressure balancing chamber. A small portion of
the drilling fluid moves down to the flow retarder through a
narrower extension of the main clearance. The prior art flow
retarder typically comprises:
[0011] a tungsten carbide inner sleeve affixed to the outside
surface of the rotating mandrel;
[0012] an opposed tungsten carbide outer sleeve affixed to the
inside surface of the stationary housing in opposed relationship to
the inner sleeve;
[0013] a radial port extending through the housing side wall below
the carbide sleeves, for connecting the pressure balancing chamber
with the well borehole;
[0014] the sleeves defining a narrow annular metering gap between
them; and
[0015] the upper end of the gap communicating with the aforesaid
main clearance and the lower end of the gap communicating with the
pressure balancing chamber.
[0016] The two sleeves provide a pressure-resistant hydrodynamic
seal at the upper end of the pressure balancing chamber. The seal
is provided with the objective of isolating the pressure balancing
chamber from the relatively high pressure of the fluid in the main
clearance, so that it experiences only the relatively low pressure
of the wellbore annulus external of the bearing assembly. The gap,
and the leakage of drilling fluid through it, also functions to
ensure lubrication of the two sleeves (one of which is rotating and
one of which is stationary).
[0017] Now, there are problems associated with these known flow
retarders. More particularly:
[0018] wear of the sleeves is substantial and is exacerbated by the
flow of fluid therethrough and radial loading from the rotating
mandrel;
[0019] to minimize wear from radial loading, the gap is
widened--this leads to a significant flow of drilling fluid through
the flow retarder--this increases sleeve and housing port wear and
reduces the volume of fluid reaching the bit; and
[0020] in addition, drilling fluid coarse solids from the main
clearance may pile up at the upper end of the metering gap and
penetrate into the gap, thus causing wear of the sleeves.
[0021] It is the objective of the present invention to provide a
flow retarder in a bearing assembly which addresses these
problems.
SUMMARY OF THE INVENTION
[0022] The present invention is directed to a flow retarder for use
in the bearing assembly of a downhole drilling motor. The flow
retarder is associated with the upper section of the pressure
balancing chamber. As previously stated, the pressure balancing
chamber contains an annular floating piston seal extending around
the rotating inner mandrel. The flow retarder functions to restrict
the flow of drilling fluid through the pressure balancing chamber,
to substantially isolate the balancing chamber from the high
pressure in the drilling fluid moving through the main clearance
and to substantially equalize the pressure internal of the
balancing chamber with the pressure of the wellbore.
[0023] The flow retarder comprises: an erosion-resistant inner
sleeve connected to the rotating mandrel by a layer of resilient
elastomer bonding the inner sleeve to a driver ring which in turn
is locked on the rotating mandrel; an erosion-resistant outer
sleeve fixed to the inside surface of the stationary tubular outer
housing of the bearing assembly; the inner sleeve being positioned
within the outer sleeve, the sleeves forming a narrow annular
metering gap between them; the sleeves being positioned at the
upper end of the balancing chamber and extending there across; a
secondary mandrel port extending through the mandrel side wall
adjacent the upper end of the metering gap, to provide
communication between the lower end of the main clearance and the
bore of the mandrel; and a housing port extending through the
housing side wall to provide communication between the other end of
the metering gap, the balancing chamber and the well bore.
[0024] The layer of resilient elastomer between the inner sleeve
and the mandrel functions as a shock absorber for the radial loads
transmitted to the inner sleeve by the rotating mandrel during
drilling motor operation. As a consequence, wear on the sleeves is
reduced and the annular metering gap can be made narrower, thereby
reducing the loss of drilling fluid through the flow retarder.
[0025] The secondary mandrel port enables drilling fluid moving out
of the main clearance and unable to penetrate through the metering
gap, to circulate into the bore of the mandrel and provide a
flushing function. In prior art flow retarders, particles pile up
at the upper end of the carbide sleeves. These particles ultimately
get ground up in the annular gap between the two sleeves, thus
causing extra wear. In the present flow retarder, the pressure at
the secondary mandrel port will be slightly lower than the pressure
at the primary mandrel ports and the small flow of fluid into the
mandrel bore will wash or flush particles away from the entrance to
the metering gap.
[0026] In a preferred feature, one or more resilient belleville
spring washers are positioned at the upper end of the inner sleeve
and are downwardly biased to apply a downward force on the driver
ring to seat the ring and sleeve on the rotating mandrel. The
spring washers function as a shock absorber for the inner sleeve by
allowing it to move axially a small amount during drilling motor
operation, thereby reducing damage to the inner sleeve caused by
vibrations in the bearing assembly.
[0027] In summary then, the inner sleeve is cushioned both radially
and axially, with consequent wear reduction.
[0028] In another preferred feature, the inner sleeve has a
plurality of circumferential, spaced-apart grooves extending around
its outer peripheral surface. These grooves function to further
restrict and reduce the flow of drilling fluid through the flow
retarder.
[0029] Broadly stated, the invention is directed to a flow retarder
for use in a downhole drilling motor bearing assembly used in a
well borehole, said bearing assembly comprising a main clearance
through which drilling fluid can move, an inner rotatable tubular
mandrel having a side wall forming a longitudinal bore, an outer
stationary tubular housing having a side wall, an annular pressure
balancing chamber formed between the housing and mandrel side walls
and an annular floating piston seal closing the bottom end of the
chamber, the flow retarder comprising an erosion-resistant inner
sleeve mounted on a driver ring connected to rotate with the
mandrel, said inner sleeve being secured to the driver ring by a
layer of resilient elastomer positioned between the sleeve and the
driver ring; an erosion-resistant outer sleeve fixed to the inside
surface of the housing side wall; the inner sleeve being positioned
within the outer sleeve, said sleeves forming a narrow annular
metering gap between them, the sleeves being positioned in the
upper end of the chamber and extending there across; the housing
side wall forming a housing port extending therethrough below the
sleeves to connect the pressure balancing chamber and the lower end
of the metering gap with the borehole.
DESCRIPTION OF THE DRAWING
[0030] FIG. 1 is a cross-sectional side view of a downhole drilling
motor bearing assembly incorporating a flow retarder in accordance
with the invention;
[0031] FIG. 2 is a larger scale side view of part of the bearing
assembly of FIG. 1, showing the flow retarder;
[0032] FIG. 3 is a sectional side view of the inner sleeve,
elastomer layer and driver ring; and
[0033] FIGS. 4, 5 and 6 are sectional side, external side and end
views of the filter ring.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] The bearing assembly 1 shown in FIG. 1 comprises an inner
mandrel 2 and an outer housing 3.
[0035] The mandrel 2 is connected at its upper end with an adapter
4 connectable to the power unit (not shown) of a downhole drilling
motor (also not shown). The outer housing 3 is connected at its
upper end with an adjustment housing 41. An annular main clearance
42 is formed between the adapter 4 and the adjustment housing 41.
Drilling fluid from the motor passes down through the main
clearance 42 and enters the bore 5 of the mandrel 2 through a
primary mandrel port 43. A small portion of the drilling fluid can
penetrate downwardly through a narrow extension 42a of the main
clearance 42, present between mandrel 2 and outer housing 3.
[0036] At its lower end the mandrel 2 is threadably connected with
a bit assembly (not shown).
[0037] In use the mandrel 2 is rotatably driven and transmits
drilling fluid down through its axial bore 5. The drilling fluid in
the main clearance 42 and mandrel bore 5 is at higher pressure than
the drilling fluid in the borehole external of the bearing assembly
1.
[0038] The bearing assembly outer housing 3 comprises a piston
housing 6, a thrust housing 7 and a bearing housing 8, threadably
connected together end to end.
[0039] A journal bearing assembly 9, on bottom thrust bearing 10
and off bottom thrust bearing 11 are positioned between the mandrel
2 and outer housing 3.
[0040] A stationary bottom seal assembly 12 and floating piston
seal 13 seal the ends of the bearing chamber 14 containing the
bearings 9, 10 and 11.
[0041] An annular pressure balancing chamber 15 is formed between
the mandrel 2 and the piston housing 6. The floating piston seal 13
floats at the lower end of the pressure balancing chamber 15.
[0042] The flow retarder 16 is associated with the pressure
balancing chamber 15, the mandrel 2 and the outer housing 3.
[0043] More particularly, the flow retarder 16 comprises a driver
ring 17 which conforms with and seats on a tapered shoulder 18
formed by the mandrel 2. The driver ring 17 has a relatively thick
base 19 and an upwardly extending thin section 20. On its inner
surface, the base 19 carries an O-ring 36 to block the influx of
fluid to the tapered shoulder 18. The mandrel 2 rotatably drives
the driver ring 17.
[0044] An annular disc 21 is seated on the shoulder 22 formed at
the junction of the driver ring base 19 and thin section 20. The
disc 21 is made of aluminum and acts as a thrust cushion for the
inner sleeve 23, which seats on it.
[0045] The annular inner sleeve 23 is formed of hard,
erosion-resistant material such as tungsten carbide. It is bonded
by a layer 24 of elastomer with the thin section 20 of the driver
ring 17 and thus is drivably connected with the mandrel 2. The
layer 24 is formed before assembly of the tool by injection of
nitrile rubber into an annular space defined between the sleeve 23
and the thin section 20.
[0046] The outer surface 25 of the sleeve 23 is formed to provide
circumferential grooves 26 at spaced intervals along its
length.
[0047] An outer sleeve 27, also formed of tungsten carbide or the
like, is affixed to the inside surface 28 of the piston housing 6
with a shrink fit. The outer sleeve 27 is co-extensive with and
extends around the inner sleeve 23. It is positioned opposite the
inner sleeve 23 by a spacer 37 which abuts an inwardly projecting
shoulder 38 of the piston housing 6.
[0048] The sleeves 23, 27 are slightly spaced apart to form a
metering gap 29 having a width in the order of 0.002"-0.004".
[0049] A filter ring 30 is positioned at the upper ends of the
sleeves 23, 27. The filter ring assembly 30 forms transverse slots
31 at spaced intervals at its upper end. The slots 31 are provided
to allow large particles suspended in the drilling fluid to be
carried away through the secondary mandrel port 32. The secondary
mandrel port 32 extends radially through the side wall 33 of the
mandrel 2 at a point just above the upper end of the metering gap
29.
[0050] A housing port 34 extends radially through the side wall 35
of the piston housing 6 at a point below the bottom end of the
metering gap 29 and above the floating piston seal 13. The housing
port 34 enables pressure communication between the lower end of the
metering gap 29 and the annulus or wellbore outside the bearing
assembly 1.
[0051] A ring 37 and a stack of belleville springs 38 are
positioned between the upper face 39 of the filter ring 30 and the
bottom face 40 of the adapter 4. As the adapter 4 is threaded onto
the upper end of the mandrel 2, the face 40 presses down on the
belleville springs 38, thereby resiliently biasing the driver ring
17 down to seat it firmly on the mandrel's tapered shoulder 18.
[0052] From the foregoing, it will be noted that the inner sleeve
23 is cushioned with respect to radial and axial loads.
[0053] In operation, some drilling fluid at relatively high
pressure penetrates down through the narrow extension 42a of the
main clearance 42 and reaches the flow retarder 16. One part of
this fluid moves into the mandrel bore 5 through the secondary
mandrel port 32 and flushes coarse solids away from the top end of
the metering gap 29. Another part of the fluid moves through the
gap 29 to lubricate the sleeves 23, 27. The resilient elastomer
layer 24 acts as a radial shock absorber for side loads originating
from the rotating mandrel 2. The belleville springs 36 act to
cushion the inner sleeve from axial loads. The metering gap 29
substantially isolates the pressure balancing chamber 15 from the
high pressure fluid. And the housing port 34 provides communication
between the pressure balancing chamber 15 and the wellbore
annulus.
* * * * *