 |
Claims  |
|
|
What is claimed is:
1. A downhole tractor, comprising:
a housing;
a first wheel assembly coupled to the housing and being operable to
translate away from the housing in a first direction, the first wheel
assembly having a first electric motor and a first wheel coupled to the
first electric motor;
a second wheel assembly coupled to the housing and being operable to
translate away from the housing in a second direction that is opposite to
the first direction, the second wheel assembly having a second electric
motor and a second wheel coupled to the second electric motor; and
means for selectively translating the first and second wheel assemblies
toward and away from the housing.
2. The downhole tractor of claim 1, wherein the first and second wheel
assemblies are pivotally coupled to the housing.
3. The downhole tractor of claim 2, comprising a pivot arm pivotally
coupled to the housing, the first and second wheel assemblies being
coupled to the pivot arm.
4. The downhole tractor of claim 3, wherein each of the first and second
wheel assemblies is pivotally coupled to the pivot arm.
5. The downhole tractor of claim 1, wherein each of the wheel assemblies
comprises a reduction gear assembly coupled to a given electric motor and
a given wheel.
6. The downhole tractor of claim 1, wherein each of the first and second
electric motors comprises a hub having an internal bore, a stator coupled
to the hub, a rotor positioned in the hub, and a reduction gear coupling
the rotor to a given wheel.
7. The downhole tractor of claim 6, wherein the wheel comprises a mandrel
having a portion positioned in the hub and a first rim and a second rim
positioned in spaced-apart relation outside the hub.
8. The downhole tractor of claim 6, wherein the hub has a set of internal
gear teeth, the rotor has a an elliptical cross-section with a major
elliptical axis, and the reduction gear comprises a flexible cylindrical
cup having a set of external teeth, the elliptical cross-section of the
rotor causing first and second portions of the set of external teeth to
engage third and fourth portions of the set of internal teeth at two
opposite zones across the major elliptical axis.
9. The downhole tractor of claim 8, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
10. The downhole tractor of claim 1, wherein each of the first and second
electric motors comprises a rotor having an internal bore, a hub
positioned in the internal bore, a stator coupled to the hub, and a
reduction gear coupling the rotor to a given wheel.
11. The downhole tractor of claim 10, wherein the wheel has a set of
internal gear teeth, the rotor has an elliptical cross-section with a
major elliptical axis, and the reduction gear comprises a flexible
cylindrical cup having a set of external teeth, the elliptical
cross-section of the rotor causing first and second portions of the set of
external teeth to engage third and fourth portions of the set of internal
teeth at two opposite zones across the major elliptical axis.
12. The downhole tractor of claim 11, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
13. The downhole tractor of claim 1, wherein the means for selectively
translating the first and second wheel assemblies toward and away from the
housing comprises a hydraulic ram coupled to the housing and the first and
second wheel assemblies.
14. The downhole tractor of claim 13, comprising a hydraulic fluid pump and
reservoir positioned in the housing for supplying pressurized hydraulic
fluid to the hydraulic ram.
15. The downhole tractor of claim 1, wherein the means for selectively
translating the first and second wheel assemblies toward and away from the
housing comprises a first hydraulic ram coupled to the housing and the
first wheel assembly, and a second hydraulic ram coupled to the housing
and the second wheel assembly.
16. The downhole tractor of claim 1, wherein the means for selectively
translating the first and second wheel assemblies toward and away from the
housing comprises a powered worm gear coupled to the housing and the first
and second wheel assemblies.
17. The downhole tractor of claim 1, comprising a first controller
electrically connected to the first electric motor and a second controller
electrically connected to the second electric motor for controlling the
supply of electrical current to the first and second electric motors.
18. The downhole tractor of claim 17, comprising a power supply and a third
controller for controlling the supply of current to the first and second
controllers.
19. The downhole tractor of claim 18, comprising a fourth controller for
controlling the supply of current to the third controller.
20. The downhole tractor of claim 19, wherein the fourth controller
comprises a computer positioned at ground level.
21. A wheel assembly for a downhole tractor, comprising:
an electric motor having a hub, a stator coupled to the hub, and a rotor
coupled to the hub;
a wheel coupled to the rotor; and
a reduction gear assembly coupled between the rotor and the wheel.
22. The wheel assembly of claim 21, wherein the rotor has an internal bore
and an elliptical cross-section with a major elliptical axis, the hub is
positioned in the internal bore, the wheel has a set of internal gear
teeth, and the reduction gear comprises a flexible cylindrical cup having
a set of external teeth, the elliptical cross-section of the rotor causing
first and second portions of the set of external teeth to engage third and
fourth portions of the set of internal teeth at two opposite zones across
the major elliptical axis.
23. The wheel assembly of claim 22, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
24. The wheel assembly of claim 21, wherein the hub has a set of internal
gear teeth, the rotor has an elliptical cross-section with a major
elliptical axis, and the reduction gear comprises a flexible cylindrical
cup having a set of external teeth, the elliptical cross-section of the
rotor causing first and second portions of the set of external teeth to
engage third and fourth portions of the set of internal teeth at two
opposite zones across the major elliptical axis.
25. The downhole tractor of claim 24, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
26. The wheel assembly of claim 21, comprising a first controller
electrically connected to the electric motor for controlling the flow of
electrical current thereto.
27. The wheel assembly of claim 21, comprising a power supply and a second
controller for controlling the supply of current to the first controller.
28. The wheel assembly of claim 25, wherein the wheel comprises a mandrel
having a portion positioned in the hub and a first rim and a second rim
positioned in spaced-apart relation outside the hub.
29. A downhole tractor, comprising:
a housing;
a first wheel assembly coupled to the housing and being operable to
translate away from the housing in a first direction, the first wheel
assembly having a first electric motor, a first wheel, and a first
reduction gear assembly coupled between the first electric motor and the
first wheel;
a second wheel assembly coupled to the housing and being operable to
translate away from the housing in a second direction that is opposite to
the first direction, the second wheel assembly having a second electric
motor, a second wheel, and a second reduction gear assembly coupled
between the second electric motor and the second wheel;
a fluid ram coupled to the first and second wheel assemblies for
selectively translating the first and second wheel assemblies toward and
away from the housing; and
a first controller for controlling the flow of current to the first and
second electric motors.
30. The downhole tractor of claim 29, wherein the first and second wheel
assemblies are pivotally coupled to the housing.
31. The downhole tractor of claim 30, comprising a pivot arm pivotally
coupled to the housing, the first and second wheel assemblies being
coupled to the pivot arm.
32. The downhole tractor of claim 31, wherein each of the first and second
wheel assemblies is pivotally coupled to the pivot arm.
33. The downhole tractor of claim 29, wherein each of the first and second
electric motors comprises a hub having an internal bore, a stator coupled
to the hub, and a rotor positioned in the hub, the given reduction gear
assembly coupling the rotor to a given wheel.
34. The downhole tractor of claim 33, wherein the wheel comprises a mandrel
having a portion positioned in the hub and a first rim and a second rim
positioned in spaced-apart relation outside the hub.
35. The downhole tractor of claim 33, wherein the hub has a set of internal
gear teeth, the rotor has a an elliptical cross-section with a major
elliptical axis, and the reduction gear comprises a flexible cylindrical
cup having a set of external teeth, the elliptical cross-section of the
rotor causing first and second portions of the set of external teeth to
engage third and fourth portions of the set of internal teeth at two
opposite zones across the major elliptical axis.
36. The downhole tractor of claim 35, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
37. The downhole tractor of claim 29, wherein each of the first and second
electric motors comprises a rotor having an internal bore, a hub
positioned in the internal bore, a stator coupled to the hub, and a
reduction gear coupling the rotor to a given wheel.
38. The downhole tractor of claim 37, wherein the wheel has a set of
internal gear teeth, the rotor has an elliptical cross-section with a
major elliptical axis, and the reduction gear comprises a flexible
cylindrical cup having a set of external teeth, the elliptical
cross-section of the rotor causing first and second portions of the set of
external teeth to engage third and fourth portions of the set of internal
teeth at two opposite zones across the major elliptical axis.
39. The downhole tractor of claim 38, wherein the set of internal teeth
comprises N teeth, the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
40. The downhole tractor of claim 29, comprising a fluid pump and reservoir
positioned in the housing for supplying pressurized fluid to the fluid
rain.
41. The downhole tractor of claim 40, wherein the fluid is hydraulic fluid.
42. The downhole tractor of claim 29, comprising a second controller
electrically connected to the first electric motor and the first
controller, and a third controller electrically connected to the second
electric motor and the first controller for controlling the supply of
current from the first controller to the first and second electric motors.
43. The downhole tractor of claim 29, comprising a power supply positioned
in the housing for supplying current to the first and second electric
motors.
44. The downhole tractor of claim 43, comprising a fourth controller for
controlling the supply of current to the first controller.
45. The downhole tractor of claim 44, wherein the fourth controller
comprises a computer positioned at ground level.
46. A downhole tractor, comprising:
a housing;
a drive structure carried by the housing and operative to propel the
housing along a surface exterior thereto, the drive structure having a
rotatable portion operative to engage the surface; and
a motor disposed within the rotatable portion and operative to rotate it.
47. The downhole tractor of claim 46 wherein the drive structure includes a
wheel defining the rotatable portion and being directly engageable with
the surface.
48. The downhole tractor of claim 46 wherein the motor is an electric
motor.
49. The downhole tractor of claim 46 wherein:
the drive structure includes a wheel assembly, and
the motor is disposed within the wheel assembly.
50. The downhole tractor of claim 49 wherein the motor is an electric
motor.
51. The downhole tractor of claim 50 wherein:
the wheel assembly includes:
a hub, and
a wheel associated with the hub for rotation relative thereto, and
the electric motor disposed within the wheel assembly includes:
a stator held stationary relative to the hub,
a rotor rotatable relative to the hub and stator and drivingly coupled to
the wheel.
52. The downhole tractor of claim 51 wherein the rotor is positioned within
the stator.
53. The downhole tractor of claim 51 wherein the rotor is drivingly coupled
to the wheel by a reduction gear structure.
54. A downhole tractor, comprising:
a housing;
a wheel assembly carried by the housing and being useable to propel it
along a surface, the wheel assembly including a wheel rotatable relative
to the housing; and
a motor disposed within the wheel assembly and drivingly coupled to the
wheel.
55. The downhole tractor of claim 54 wherein the wheel assembly is
translatable toward and away from the housing.
56. The downhole tractor of claim 55 further comprising translation
apparatus for selectively translating the wheel assembly toward and away
from the housing.
57. The downhole tractor of claim 56 wherein the wheel assembly is
pivotally coupled to the housing.
58. The downhole tractor of claim 54 wherein the motor is an electric
motor.
59. The downhole tractor of claim 54 wherein:
the wheel assembly includes a hub on which the wheel is rotatably
supported, and
the electric motor is disposed within the hub.
60. The downhole tractor of claim 59 wherein the electric motor includes:
a stator anchored to the hub, and
a rotor rotatable relative to the stator and drivingly coupled to the
wheel.
61. The downhole tractor of claim 60 wherein the rotor is drivingly coupled
to the wheel by a reduction gear structure.
62. The downhole tractor of claim 60 wherein the rotor is disposed within
the stator.
63. The downhole tractor of claim 54 wherein the wheel is directly and
drivingly engageable with the surface.
64. A wheel assembly for a downhole tractor, comprising:
a hub;
a wheel rotatable relative to the hub; and
a motor disposed within the hub and operative to rotationally drive the
wheel relative to the hub.
65. The wheel assembly of claim 64 wherein the motor is an electric motor.
66. The wheel assembly of claim 65 wherein the electric motor is drivingly
coupled to the wheel by a reduction gear assembly.
67. The wheel assembly of claim 65 wherein the electric motor includes:
a stator anchored to the hub, and
a rotor rotatable relative to the stator and drivingly coupled to the
wheel.
68. The wheel assembly of claim 67 wherein the rotator is disposed within
the stator.
69. A wheel assembly for a downhole tractor, comprising:
a hub;
an electric motor carried within the hub and including a stator and a rotor
rotatable relative to the stator;
a wheel rotatable relative to the hub; and
a reduction gear assembly drivingly coupling the rotor to the wheel.
70. The wheel assembly of claim 69 wherein:
the rotor has an internal bore and an elliptical cross-section with a major
elliptical axis,
the hub is positioned in the internal bore,
the wheel has a set of internal gear teeth, and the reduction gear assembly
comprises a flexible cylindrical cup having a set of external teeth,
the elliptical cross-section of the rotor causing first and second portions
of the set of external teeth to engage third and fourth portions of the
set of internal teeth at two opposite zones across the major elliptical
axis.
71. The wheel assembly of claim 70 wherein:
the set of internal teeth comprises N teeth,
the set of external teeth comprises N-2 teeth, and
rotation of the rotor in a first direction causes rotation of the flexible
cylindrical cup in a second direction opposite to the first direction.
72. The wheel assembly of claim 69 wherein:
the hub has a set of internal gear teeth,
the rotor has an elliptical cross-section with a major elliptical axis, and
the reduction gear comprises a flexible cylindrical cup having a set of
external teeth,
the elliptical cross-section of the rotor causing first and second portions
of the set of external teeth to engage third and fourth portions of the
set of internal teeth at two opposite zones across the major elliptical
axis.
73. The wheel assembly of claim 72 wherein:
the set of internal teeth comprises N teeth,
the set of external teeth comprises N-2 teeth, and rotation of the rotor in
a first direction causes rotation of the flexible cylindrical cup in a
second direction opposite to the first direction.
74. The wheel assembly of claim 69 further comprising a first controller
electrically connected to the electric motor for controlling the flow of
electrical current thereto.
75. The wheel assembly of claim 74 further comprising a power supply and a
second controller for controlling the supply of current to the first
controller.
76. The wheel assembly of claim 69 wherein the wheel comprises a mandrel
having a portion positioned in the hub and a first rim and a second rim
positioned in spaced-apart relation outside the hub. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to downhole tools, and more particularly
to a downhole tractor for propelling working strings and wirelines in a
wellbore.
2. Description of the Related Art
Subterranean operations in petroleum wells involve the conveyance of pipe,
coiled tubing and wireline supported tools from the surface into well
bores and vice versa. In vertical wells, and in those wells having only a
few degrees of deviation, the axial thrust necessary to convey pipe or
coiled tubing strings, or wireline tools, is supplied by gravity. In these
situations, the downward thrust applied to the string is equal to the
weight of the drill string, minus any buoyancy force due to fluid
downhole. For pipe strings in relatively deep wells, this downward axial
thrust can be quite formidable, sometimes exceeding 500 tons. Although the
weight of a conventional coiled tubing string will be significantly less
than a comparably sized drill pipe string, additional axial downward
thrust is routinely applied to coiled tubing strings by a coiled tubing
injector positioned at the surface.
The retrieval of pipe and coiled tubing strings, and wireline assemblies in
vertical and slightly deviated wells is accomplished by applying upward
axial thrust to the pipe string, coiled tubing string or wireline assembly
as the case may be. In coiled tubing operations, this is routinely
accomplished by reversing the direction of travel of the coiled tubing
injector. In pipe strings, the pipe string is pulled from the well bore by
platform mounted machinery. In wireline operations, though, the wireline
conveyed tool or tool assembly is pulled from the well bore by retrieving
the wireline or a cable that often is lowered into the well with the
wireline assembly.
The situation is more complex in highly deviated and horizontal wells. In
these types of wells, gravity can sometimes be relied upon to convey pipe
and coiled tubing strings, and wireline assemblies into deviated sections,
depending on factors such as the inclination of the well, the weight of
the string and the magnitude of buoyant forces acting on the string.
However, in most deviated well situations, the string will drag against
the walls of the well bore at some point below the commencement of the
deviated portion of the well. At this point, the string will not move
downward further without the input of additional downward axial thrust. In
pipe strings, additional downward thrust may be applied to the pipe string
by means of surface equipment in order to advance the string through the
deviated or horizontal section. The compressive load capacity of
conventional pipe string is such that fairly significant levels of
downward thrust may be applied without inelastically deforming or
fracturing any of the pipe sections.
The relatively small outer diameters and wall thicknesses of coiled tubing
place severe limits on the amount of surface-supplied downward thrust that
can be applied to a coiled tubing string without buckling the tubing. Some
surface supplied downward thrust is possible, and is usually imparted to
the coiled tubing string via the coiled tubing injector.
As the skilled artisan will appreciate, a wireline itself is of little
value in applying downward thrust to a wireline assembly. Other measures
must be applied to deploy such downhole assemblies in highly deviated and
horizontal wells.
Retrieval of pipe and coiled tubing strings, and wireline assemblies is
also more complex in deviated and horizontal wells. During retrieval, the
string or wireline assembly may bind against the inner walls of the well
bore until the string is completely clear of the deviated section. As a
consequence, an upward force exceeding the weight of the string or
wireline assembly must commonly be applied during retrieval while the
string or wireline assembly is within the deviated section. The capacity
of the string or wireline assembly to withstand the overpull necessary to
move such assemblies upward through a deviated well section is largely a
function of the tensile strength of the string or wireline assembly.
Conventional pipe strings can routinely withstand fairly significant
tensile loads. Thus, their retrieval is largely a function of the power
output of platform mounted retrieval machinery. Coiled tubing strings and
wireline assemblies are more problematic in that their capacity to
withstand tensile loads can be quite limited, particularly for wireline
assemblies. If the tensile limit of a coiled tubing string or wireline
assembly is exceeded, a costly fishing operation may be required to clear
the wellbore.
Downhole propulsion machines, often referred to as "tractors", have been
used for several years to facilitate the conveyance of wireline
assemblies, and more recently, coiled tubing strings into a well bore.
Most conventional tractors can be loosely grouped into two groups, namely,
powered-wheel and crawlers. Most conventional wheeled-powered tractors
consist of a tubular housing and two or more powered wheels that project
from the housing and are designed to engage the inner walls of the casing,
string or open hole, as the case may be, to propel the tractor and any
portions of pipe or tubing or wireline tools connected thereto. Designers
have developed several different types of wheeled tractor designs, some
employing electrically powered wheels and some employing hydraulically
powered wheels. In contrast, conventional crawlers typically consist of a
housing and a reciprocating crawler mechanism that rhythmically engages
and disengages the inner walls of the casing, string or open hole, as the
case may be, to propel the tractor and any portions of pipe or tubing or
wireline tools connected thereto.
Conventional wheeled tractors present certain shortcomings. One
disadvantage common to many conventional designs is the lack of redundancy
in power output to the propulsion wheels. In many conventional designs, a
single power motor is encased within a tubular housing and coupled to
multiple wheels by one or a plurality of mechanical linkages. These
linkages typically consist of some form of complex shaft and U-joint
arrangement with or without gearing, or a chain drive of some type. The
difficulty with such designs is that power failure in the single drive
motor result | | |
