U.S. patent application number 09/742514 was filed with the patent office on 2002-06-20 for high speed positive displacement motor.
Invention is credited to Plop, Andrei.
Application Number | 20020074167 09/742514 |
Document ID | / |
Family ID | 24985124 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074167 |
Kind Code |
A1 |
Plop, Andrei |
June 20, 2002 |
High speed positive displacement motor
Abstract
According to the present invention, a downhole motor converts
hydraulic energy from drilling fluid passing through the motor into
mechanical power that is useful to rotate a drillbit. The downhole
motor includes a tubular housing and a stator mounted within the
tubular housing. A rotor is positioned within the stator for
rotation relative thereto. The stator has a central first axis and
the rotor has a central second axis. The rotor is rotated about the
second axis and nutated about the first axis within the stator by
drilling fluid passing through the stator. The rotor further has a
concentric lower end portion thereon. A cylindrical coupling is
disposed within the tubular housing beneath the rotor and has an
axis substantially aligned with the first axis and an inner
cylindrical opening the axis of which is substantially aligned with
the second axis, the opening being adapted for receiving the lower
end portion of the rotor. A first bearing assembly is disposed in
the opening of the coupling for rotatably receiving and supporting
the lower end portion of the rotor, whereby nutation of the lower
end portion of the rotor about the first axis induces rotation of
the coupling about the first axis. A second bearing assembly is
disposed between the coupling and the tubular housing for
supporting rotation of the coupling relative to the tubular
housing. A transmission shaft and bit box are connected to the
coupling for rotation. In this manner, nutation of the rotor about
the first axis results in rotation of the transmission shaft and
the bit box. A related method is also provided.
Inventors: |
Plop, Andrei; (Houston,
TX) |
Correspondence
Address: |
Schlumberger Technology Corporation
ATTN: IP Counsel
200 GILLINGHAM LANE
SUGAR LAND
TX
77478
US
|
Family ID: |
24985124 |
Appl. No.: |
09/742514 |
Filed: |
December 20, 2000 |
Current U.S.
Class: |
175/107 |
Current CPC
Class: |
E21B 4/02 20130101 |
Class at
Publication: |
175/107 |
International
Class: |
E21B 004/00 |
Claims
What is claimed is:
1. A downhole motor for converting hydraulic energy from drilling
fluid passing through the motor into mechanical power that is
useful to rotate a drillbit, comprising: a tubular housing; a
stator mounted within said tubular housing, said stator having a
first axis; a rotor positioned within said stator for rotation
relative thereto, said rotor having a second axis and being rotated
about the second axis and nutated about the first axis within said
stator by drilling fluid passing through said stator, said rotor
further having a concentric lower end portion; a cylindrical
coupling disposed within said tubular housing beneath the rotor and
having an axis substantially aligned with the first axis and an
inner cylindrical opening the axis of which is substantially
aligned with the second axis, the opening adapted for receiving the
lower end portion of said rotor; a first bearing assembly disposed
in the opening of said coupling for rotatably receiving and
supporting the lower end portion of said rotor, whereby nutation of
the lower end portion of said rotor about the first axis induces
rotation of said coupling about the first axis; a second bearing
assembly disposed between said coupling and said tubular housing
for supporting rotation of said coupling relative to said tubular
housing; and a transmission shaft and bit box connected to said
coupling for rotation, whereby nutation of the rotor about the
first axis results in rotation of said transmission shaft and said
bit box.
2. The downhole motor of claim 1, wherein said cylindrical coupling
has a peripheral opening therein for passage of drilling fluid
through said cylindrical coupling.
3. The downhole motor of claim 2, wherein the peripheral opening is
shaped to optimize the structural integrity of said cylindrical
coupling while minimizing the resistance to flow of the drilling
fluid therethrough.
4. In a downhole motor including a tubular stator housing, a
helical stator having a first axis and connected to the stator
housing, and a helical rotor having a second axis, the rotor being
rotated about the second axis and nutated about the first axis
within the stator by drilling fluid passing through the stator, an
apparatus for transmitting torque developed at the rotor to a bit
box, comprising: a pin connected to the lower end of the rotor,
said pin having an axis aligned with the second axis whereby
nutation of the rotor about the first axis induces nutation of said
pin about the first axis; a cylindrical coupling disposed within
the stator housing beneath the rotor and having an axis
substantially aligned with the first axis and an inner cylindrical
opening the axis of which is substantially aligned with the second
axis, the opening adapted for receiving said pin; a first bearing
assembly disposed in the opening of said coupling for rotatably
receiving and supporting said pin, whereby nutation of said pin
about the first axis induces rotation of said coupling about the
first axis; a second bearing assembly disposed between said
coupling and the stator housing for supporting rotation of said
coupling relative to the stator housing; and a transmission shaft
and bit box connected to said coupling for rotation, whereby
nutation of the rotor about the first axis results in rotation of
said transmission shaft and said bit box.
5. The downhole motor of claim 1, wherein said cylindrical coupling
has a peripheral opening therein for passage of drilling fluid
through said cylindrical coupling.
6. The downhole motor of claim 2, wherein the peripheral opening is
shaped to optimize the structural integrity of said cylindrical
coupling while minimizing the resistance to flow of the drilling
fluid therethrough.
7. A method for converting hydraulic energy from drilling fluid
passing through a drill string into mechanical power that is useful
to rotate a drillbit, comprising: placing a tubular housing in the
drill string; mounting a stator within the tubular housing, the
stator having a first axis; positioning a rotor within the stator
for rotation relative thereto, the rotor having a second axis and
being rotated about the second axis and nutated about the first
axis within the stator by drilling fluid passing through the
stator; and converting the nutation of the rotor about the first
axis into rotation of a transmission assembly and bit box.
8. The method of claim 7, wherein the converting step includes:
equipping the rotor with a concentric lower end portion, whereby
nutation of the rotor about the first axis induces nutation of the
lower end portion about the first axis; placing a coupling within
the tubular housing beneath the rotor, the coupling having an axis
substantially aligned with the first axis and an inner opening the
axis of which is substantially aligned with the second axis, the
opening adapted for receiving the lower end portion of the rotor,
whereby nutation of the lower end portion of the rotor induces
rotation of the coupling about the first axis; and applying the
rotation of the coupling to a transmission assembly and bit box to
rotate the transmission assembly and bit box.
9. The method of claim 8, further comprising the steps of: placing
a first bearing assembly in the opening of the coupling for
rotatably receiving and supporting the lower end portion of the
rotor; placing a second bearing assembly between the coupling and
the tubular housing for supporting rotation of said coupling
relative to said tubular housing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to positive displacement
motors (PDMs) for downhole applications in the drilling of oil and
gas wells, and more particularly to the power transmission aspects
of such motors.
[0003] 2. Description of the Related Art
[0004] The use of downhole drilling motors, particularly PDMs, that
convert hydraulic energy from the drilling fluid pumped through a
drill string into mechanical power to rotate a drilling bit at the
end of the drill string is well known in the art. The energy
conversion is accomplished by the reverse application of the
Moineau pump principle. Drilling fluid is pumped into the motor's
power section at a pressure that causes a helical rotor having "n"
lobes to rotate and nutate within a helical stator having "n+1"
lobes. The rotor movement is driven by the passage and the
compression of the drilling fluid through the cavities defined by
the spaces between the rotor lobes and the stator lobes.
[0005] The basic components of a typical PDM power section are
illustrated in FIGS. 1-3. Thus, a three-lobe rotor 11 is shown with
an outer helical profile 4. The center axis 2 of rotor 11 rotates
about center axis 1 within inner helical profile 3 of four-lobe
stator 10. Rotor axis 2 defines a circle .largecircle., the radius
of which is equal to the eccentricity e, as the rotor rotates about
stator axis 1. The eccentricity is dependent on the diameter of
major circle 7 and the diameter of minor circle 5 relative to
stator 10, as well as the diameter of major circle 8 and diameter
of minor circle 6 relative to rotor 11. While rotor 11 is nutating
about stator axis 1, the rotor is also rotating about its own axis
2 as it navigates the stator's inner helical profile 3.
[0006] FIG. 4 illustrates typical PDM power and transmission
sections in elevation. Rotor 11 is shown assembled inside stator
10. The internal surface of the stator is generally made of (or
lined with) an elastomeric material such as rubber, but other
materials such as ceramics and metals are also used in various
applications. The stator is mounted in a housing 9. The lower end
of rotor 11 is connected to transmission shaft 13 via transmission
coupling 12. The axis of the transmission coupling is collinear
with the axis 2 of the rotor. The lower end of the transmission
shaft is connected to drive shaft 15 via second coupling 14. The
second coupling is aligned with drive shaft 15.Drive shaft 15 is
supported within lower housing 18 by thrust and radial bearings 16.
The rotational force developed in rotor 11 is thus transmitted via
transmission coupling 12, transmission shaft 13, second coupling
14, and drive shaft 15 to bit box 17 which directly drives the
drill bit (not shown).
[0007] As mentioned above, the second rotational movement of rotor
11 (about its own axis) is utilized to transmit rotation and torque
to the bit. Problems reside in this mode of transmission, however,
due to the eccentricity inherent in the first rotational movement
of the rotor (about axis 1 of the stator). The eccentricity results
in a misalignment between the rotor axis 2 and the center axis of
the motor, which is collinear with axis 1. This misalignment must
be accommodated in transmission shaft 13 and the result is a
misalignment angle a shown at 19 in FIG. 4. This misalignment
degrades the reliability and solidity of the transmission coupling
between the rotor and the transmission shaft, as well as between
the transmission shaft and second coupling 14.
[0008] To address this shortcoming, it is a principal object of the
present invention to provide a transmission assembly for a PDM that
utilizes the rotation of the rotor about the stator axis to produce
rotational power.
[0009] It is a further object of the present invention to take
advantage of the fact that the rotor speed of rotation about the
stator axis is greater than the rotor speed of rotation about its
own axis, thereby producing higher speeds to transmit from the PDM
power section to the drill bit.
SUMMARY OF THE INVENTION
[0010] The objects described above, as well as various other
objects and advantages, are achieved by a downhole motor for
converting hydraulic energy from drilling fluid passing through the
motor into mechanical power that is useful to rotate a drillbit.
The downhole motor includes a tubular housing and a stator mounted
within the tubular housing. A rotor is positioned within the stator
for rotation relative thereto. The stator has a central first axis
and the rotor has a central second axis. The rotor is rotated about
the second axis and nutated about the first axis within the stator
by drilling fluid passing through the power section. The rotor
further has a concentric lower end portion, or pin, thereon. A
cylindrical coupling is disposed within the tubular housing beneath
the rotor and has an axis substantially aligned with the first axis
and an inner cylindrical opening the axis of which is substantially
aligned with the second axis, the opening being adapted for
receiving the lower end portion of the rotor. A first bearing
assembly is disposed in the opening of the coupling for rotatably
receiving and supporting the lower end portion of the rotor,
whereby nutation of the lower end portion of the rotor about the
first axis induces rotation of the coupling about the first axis. A
second bearing assembly is disposed between the coupling and the
tubular housing for supporting rotation of the coupling relative to
the tubular housing. A transmission shaft is connected to the
coupling for transmission of the rotation to the bit box. In this
manner, nutation of the rotor about the first axis results in
rotation of the transmission shaft and the bit box.
[0011] In a preferred embodiment, the cylindrical coupling has a
peripheral opening therein for passage of drilling fluid through
the cylindrical coupling. The peripheral opening is preferably
shaped to optimize the structural integrity of the cylindrical
coupling while minimizing the resistance to flow of the drilling
fluid therethrough.
[0012] In another aspect, the present invention contemplates a
method for converting hydraulic energy from drilling fluid passing
through a drill string into mechanical power that is useful to
rotate a drillbit. The method includes the steps of placing a
tubular housing in the drill string, and mounting a stator within
the tubular housing. A rotor is positioned within the stator for
rotation relative thereto. The stator has a central first axis and
the rotor has a central second axis. The rotor is rotated about the
second axis and nutated about the first axis within the stator by
drilling fluid passing through the stator. The nutation of the
rotor about the first axis is converted into rotation of a
transmission assembly and bit box.
[0013] In a preferred embodiment, the converting step includes
equipping the rotor with a concentric lower end portion, or pin,
whereby nutation of the rotor about the first axis induces nutation
of the lower end portion about the first axis. A coupling is placed
within the tubular housing beneath the rotor. The coupling has an
axis substantially aligned with the first axis and an inner opening
the axis of which is substantially aligned with the second axis.
The opening is adapted for receiving the lower end portion of the
rotor, whereby nutation of the lower end portion of the rotor
induces rotation of the coupling about the first axis. The rotation
of the coupling is applied to a transmission assembly to rotate the
bit box.
[0014] The method preferably further comprises the steps of placing
a first bearing assembly in the opening of the coupling for
rotatably receiving and supporting the lower end portion of the
rotor, and placing a second bearing assembly between the coupling
and the tubular housing for supporting rotation of said coupling
relative to said tubular housing.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0015] The manner in which the present invention attains the above
recited features, advantages, and objects can be understood with
greater clarity by reference to the preferred embodiment(s) thereof
which are illustrated in the accompanying drawings.
[0016] It is to be noted however, that the appended drawings
illustrate only typical embodiment(s) of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0017] In the drawings:
[0018] FIG. 1 is a sectional plan view of a PDM rotor;
[0019] FIG. 2 is a sectional plan view of a PDM stator;
[0020] FIG. 3 is a sectional plan view of the rotor of FIG. 1
assembled within the stator of FIG. 2;
[0021] FIG. 4 is a sectional elevational view, partly in section,
of the rotor-stator assembly of FIG. 3 connected to a bit box via a
transmission assembly in a conventional manner;
[0022] FIG. 5 is a sectional elevational view, partly in section,
of a rotor-stator assembly connected to a bit box via a
transmission assembly in accordance with the present invention;
and
[0023] FIG. 6 is a sectional plan view taken along line 6-6 in FIG.
5.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Referring now to the FIG. 5, tubular stator housing 9 is
shown having helically profiled stator 10 mounted therein. The
stator has a central first axis 1. Helically profiled rotor 11 is
positioned within stator 10 for rotation relative thereto. The
rotor has a central second axis 2 and is rotated about second axis
2 and nutated about first axis 1 within stator 10 by drilling fluid
passing through the stator. Rotor 11 further has a concentric lower
end portion or pin 23 thereon that is also rotated about second
axis 2 and nutated about first axis 1.
[0025] Cylindrical coupling 22 is disposed within tubular stator
housing 9 beneath rotor 11 and has a central axis substantially
aligned with first axis 1 and includes inner cylindrical opening 31
the axis of which is substantially aligned with second axis 2.
Opening 31 is adapted for receiving lower end portion or pin 23 of
rotor 11. By this positioning, pin 23 transmits the rotor's
nutating movement to coupling 22.
[0026] First bearing assembly 20 includes thrust and radial
bearings and is disposed in opening 31 of coupling 22 for rotatably
receiving and supporting pin 23 of rotor 11. The first bearing
assembly take the rotor hydraulic thrust load, freely supports
rotor 11 during its rotational movement about second axis 2, and
transmits the nutating movement of pin 23 to the coupling 22,
inducing rotation of coupling 22 about the first axis. Rotation of
coupling 22 is supported inside tubular housing 9 by second bearing
assembly 21, including thrust and radial bearings, permitting the
coupling to rotate relative to the tubular housing.
[0027] The bottom end of the coupling is aligned with tubular
housing 9 and first axis 1, and is connected to bit box 17 through
transmission shaft 13. 1. In this manner, nutation of rotor 11
about first axis 1 results in rotation of the transmission shaft
and the bit box.
[0028] FIG. 6 shows a sectional view of coupling 22. Thus, rotor
pin 23 and first bearing assembly 20 (neither of which is shown in
FIG. 6) are disposed inside central bore 31, which is aligned with
second axis 2. Second bearing assembly 21 (not shown in FIG. 6)
supports coupling 22 on the circular outer surface 32 of the
coupling, which is aligned with first axis 1. Peripheral slot or
opening 30 is formed in the body of coupling 22 to allow for the
passage of drilling fluid. The shape of this peripheral opening is
designed to minimize erosion and frictional losses due to the
drilling fluid interaction and to maximize the structural integrity
of coupling 22.
[0029] The present invention therefore utilizes the rotation of
second (rotor) axis 2 about first (stator) axis 1 to transmit power
to bit box 17. Since that rotation is defined relatively to the
first axis, which is the same as the tubular housing axis, no
flexible coupling is needed to transmit the movement and the torque
to the bit, unless a bend is needed in the motor assembly. If no
bend is needed, the rotor may thus be directly linked to
transmission shaft 13 and bit box 17, resulting in the removal of
the longer, conventional transmission section and in the shortening
of the motor assembly as a whole.
[0030] Those skilled in the art will further appreciate that the
combination rotation/nutation movement about two axes 1, 2 is
dictated by the respective numbers of lobes on rotor 11 and stator
10. For the 3:4 lobe PDM shown in FIG. 1-3, the nutational speed of
rotor 11 about stator axis 1 will be three times faster than the
rotational speed of the rotor about its own axis 2. The main
consequence is that the free rotational speed of the transmission
shaft and bit box, as compared to a standard design at the same
flow rate, are increased by an amount which is equal to the number
of lobes on the rotor. This increased speed makes the present
invention suitable for applications with high speed PDC or
diamond-impregnated drill bits.
[0031] Since the bit rotational speed may be increased by a
substantial amount, the invention makes possible the choice of a
downhole motor having a very high number of lobes for normal to
high-speed applications. This in turn greatly improves the
reliability of the power section since a very high number of lobes
stator improves the heat dissipation by reducing the variation in
the thickness of the rubber.
[0032] In view of the foregoing it is evident that the present
invention is well adapted to attain all of the objects and features
hereinabove set forth, together with other objects and features
which are inherent in the apparatus disclosed herein.
[0033] As will be readily apparent to those skilled in the art, the
present invention may easily be produced in other specific forms
without departing from its spirit or essential characteristics. The
present embodiment is, therefore, to be considered as merely
illustrative and not restrictive. The scope of the invention is
indicated by the claims that follow rather than the foregoing
description, and all changes which come within the meaning and
range of equivalence of the claims are therefore intended to be
embraced therein.
[0034] For example, with reference again to FIG. 5, second bearing
assembly 21 may also be used as the main motor bearing assembly
since a conventional transmission assembly (see FIG. 4) is obviated
by the present invention and the motor assembly as a whole becomes
shorter. A longer, conventional transmission assembly may be used
if the motor has to be bent for well directional control, with the
advantage of extending the life of the transmission since there is
no more misalignment (see FIG. 4 again) due to the rotor eccentric
movement.
* * * * *