U.S. patent application number 10/813183 was filed with the patent office on 2005-09-29 for system and method for controlling drill motor rotational speed.
This patent application is currently assigned to CDX Gas, LLC. Invention is credited to Zupanick, Joseph A..
Application Number | 20050211471 10/813183 |
Document ID | / |
Family ID | 34963057 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050211471 |
Kind Code |
A1 |
Zupanick, Joseph A. |
September 29, 2005 |
System and method for controlling drill motor rotational speed
Abstract
In one embodiment, a system for controlling drill motor
rotational speed includes a downhole motor disposed in a drill
string and having a rotor operable to be rotated by a flow of
drilling fluid through the motor. The system also includes one or
more by-pass ports operable to allow a portion of the drilling
fluid to exit the drill string into a well bore and a governor
coupled to the rotor and comprising a valve operable to move in
response to the rotational speed of the rotor. The valve movement
controls the amount of drilling fluid allowed to flow through the
by-pass ports and exit the drill string into the well bore. The
valve also directly controls the flow of the drilling fluid into
the motor based on the amount of drilling fluid allowed to flow
through the by-pass ports, thereby controlling the rotational speed
of the rotor.
Inventors: |
Zupanick, Joseph A.;
(Pineville, WV) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
1717 MAIN STREET
SUITE 5000
DALLAS
TX
75201
US
|
Assignee: |
CDX Gas, LLC
|
Family ID: |
34963057 |
Appl. No.: |
10/813183 |
Filed: |
March 29, 2004 |
Current U.S.
Class: |
175/57 ; 175/107;
175/324 |
Current CPC
Class: |
E21B 21/103 20130101;
E21B 4/02 20130101 |
Class at
Publication: |
175/057 ;
175/107; 175/324 |
International
Class: |
E21B 004/02 |
Claims
What is claimed is:
1. A system for controlling drill motor rotational speed,
comprising: a downhole motor disposed in a drill string and having
a rotor operable to be rotated by a flow of drilling fluid through
the motor; one or more by-pass ports formed in the drill string and
operable to allow a portion of the drilling fluid to exit the drill
string into a well bore prior to the drilling fluid flowing through
the motor; a governor coupled to the rotor of the downhole motor
and comprising a valve, the valve operable to: move in response to
the rotational speed of the rotor, the movement of the valve
operable to control the amount of drilling fluid allowed to flow
through the one or more by-pass ports and exit the drill string
into the well bore prior to the drilling fluid flowing through the
motor; and directly control the flow of the drilling fluid into the
motor based on the amount of drilling fluid allowed to flow through
the one or more by-pass ports, thereby controlling the rotational
speed of the rotor; and a rotatable downhole device coupled to the
motor and operable to be rotated by the downhole motor.
2. The system of claim 1, wherein the governor is further operable
to prevent the rotor from exceeding a predetermined rotational
speed.
3. The system of claim 1, wherein the governor comprises two or
more valve weights coupled to the valve, the valve weights operable
to rotate at substantially the same speed as the rotor, an axial
force generated by the rotation of the valve weights operable to
move the valve relative to the one or more by-pass ports.
4. The system of claim 3, further comprising a valve spring
operable to provide an axial force to counteract the axial force
generated by the rotation of the valve weights.
5. The system of claim 4, wherein a spring constant of the valve
spring and a mass of the valve weights are selected based on a
desired maximum rotational speed of the rotor.
6. The system of claim 1, wherein the governor is operable to
control the rotational speed of the rotor regardless of a variable
weight-on-bit of the drill string.
7. The system of claim 1, wherein the one or more by-pass ports are
formed in one or more positions in the drill string such that the
flow of drilling fluid out of the drill string through the one or
more by-pass ports does not substantially affect a weight-on-bit of
the drill string.
8. The system of claim 1, wherein the rotatable downhole device
comprises a drill bit operable to remove portions of a subterranean
zone to form the well bore.
9. The system of claim 1, wherein the governor is disposed at an
inlet of the motor.
10. The system of claim 1, wherein the one or more by-pass ports
are formed in the drill string proximate to an inlet of the
motor.
11. A method for controlling drill motor rotational speed,
comprising: pumping a drilling fluid through a drill string, the
drill string comprising a downhole motor, a governor, and one or
more by-pass ports; rotating a rotor of the motor using the flow of
the drilling fluid through the motor; moving a valve of the
governor in response to the rotational speed of the rotor such that
the movement of the valve controls the amount of drilling fluid
allowed to flow through the one or more by-pass ports and exit the
drill string into the well bore prior to the drilling fluid flowing
through the motor to directly control the flow of the drilling
fluid into the motor and the rotational speed of the rotor.
12. The method of claim 11, further comprising preventing the rotor
from exceeding a predetermined rotational speed.
13. The method of claim 12, wherein: the governor comprises two or
more valve weights coupled to the valve, the valve weights operable
to rotate at substantially the same speed as the rotor; and the
method further comprises: generating an axial force on the valve by
rotating the valve weights; moving the valve relative to the one or
more by-pass ports in response to the axial force to control the
flow of at least a portion of the drilling fluid through the one or
more by-pass ports.
14. The method of claim 13, further comprising providing an axial
force using a valve spring to counteract the axial force generated
by rotating the valve weights.
15. The method of claim 14, further comprising selecting a spring
constant of the valve spring and a mass of the valve weights based
on a desired maximum rotational speed of the rotor.
16. The method of claim 11, further comprising controlling the
rotational speed of the rotor regardless of a variable
weight-on-bit of the drill string.
17. The method of claim 11, wherein the one or more by-pass ports
are formed in one or more positions in the drill string such that
the flow of drilling fluid out of the drill string through the one
or more by-pass ports does not substantially affect a weight-on-bit
of the drill string.
18. The method of claim 11, wherein the rotatable downhole device
comprises a drill bit operable to remove portions of a subterranean
zone to form the well bore.
19. The method of claim 11, wherein the governor is disposed at an
inlet of the motor.
20. The method of claim 11, wherein the one or more by-pass ports
are formed in the drill string proximate to an inlet of the
motor.
21. A system for controlling drill motor rotational speed,
comprising: a motive means disposed in a drill string and having a
rotating means operable to be rotated by a flow of drilling fluid
through the motive means; one or more fluid by-pass means formed in
the drill string and operable to allow a portion of the drilling
fluid to exit the drill string into a well bore prior to the
drilling fluid flowing through the motor; a governing means coupled
to the rotating means of the motive means and comprising a valve
means, the valve means operable to: move in response to the
rotational speed of the rotating means, the movement of the valve
means operable to control the amount of drilling fluid allowed to
flow through the one or more fluid by-pass means and exit the drill
string into the well bore prior to the drilling fluid flowing
through the motor; and directly control the flow of the drilling
fluid into the motive means based on the amount of drilling fluid
allowed to flow through the one or more fluid by-pass means,
thereby controlling the rotational speed of the rotating means; and
a drilling means coupled to the motive means and operable to be
rotated by the motive means.
22. A system for controlling drill motor rotational speed,
comprising: a downhole motor disposed in a drill string and having
a rotor operable to be rotated by a flow of drilling fluid through
the motor; one or more by-pass ports formed in the drill string and
operable to allow a portion of the drilling fluid to exit the drill
string into a well bore prior to the drilling fluid flowing through
the motor; and a governor disposed at an inlet to the downhole
motor and coupled to the rotor of the downhole motor, the governor
operable to prevent the rotor from exceeding a predetermined speed,
the governor comprising: a valve operable to: move in response to
the rotational speed of the rotor, the movement of the valve
operable to control the amount of drilling fluid allowed to flow
through the one or more by-pass ports and exit the drill string
into the well bore; and directly control the flow of the drilling
fluid into the motor based on the amount of drilling fluid allowed
to flow through the one or more by-pass ports, thereby controlling
the rotational speed of the rotor; and two or more valve weights
coupled to the valve, the valve weights operable to rotate at
substantially the same speed as the rotor, an axial force generated
by the rotation of the valve weights operable to move the valve
relative to the one or more by-pass ports.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to systems and
methods for drilling in subterranean zones and, more particularly,
to a system and method for controlling drill motor rotational
speed.
BACKGROUND OF THE INVENTION
[0002] Subterranean drilling operations can expose well bore
drilling equipment to severe operating conditions, which may be
detrimental to the operating life of the equipment. To maximize
drilling efficiency, well bore drilling equipment may be designed
to withstand exposure to severe operating conditions for an
extended period of time. However, a drill motor's operating life
can be substantially affected by exposure to rotational over-speed
conditions caused by inconsistencies in the flow of drilling fluid
used to power the drill motor. Therefore, it is desirable to
prevent or reduce such over-speed conditions.
SUMMARY OF THE INVENTION
[0003] The present invention provides a system and method for
controlling drill motor rotational speed that substantially
eliminates or reduces at least some of the disadvantages and
problems associated with conventional systems and methods for
controlling drilling.
[0004] In accordance with certain embodiments, a system for
controlling drill motor rotational speed includes a downhole motor
disposed in a drill string and having a rotor operable to be
rotated by a flow of drilling fluid through the motor. The system
also includes one or more by-pass ports operable to allow a portion
of the drilling fluid to exit the drill string into a well bore and
a governor coupled to the rotor and comprising a valve operable to
move in response to the rotational speed of the rotor. The valve
movement controls the amount of drilling fluid allowed to flow
through the by-pass ports and exit the drill string into the well
bore. The valve also directly controls the flow of the drilling
fluid into the motor based on the amount of drilling fluid allowed
to flow through the by-pass ports, thereby controlling the
rotational speed of the rotor.
[0005] In accordance with certain embodiments, method is provided
for controlling drill motor rotational speed. The method includes
the step of pumping a drilling fluid through a drill string. The
drill string includes a downhole motor, a governor, and one or more
by-pass ports. The method also includes the step of rotating a
rotor of the motor using the flow of the drilling fluid through the
motor. The method further includes the step of moving a valve of
the governor in response to the rotational speed of the rotor such
that the movement of the valve controls the amount of drilling
fluid allowed to flow through the one or more by-pass ports and
exit the drill string into the well bore prior to the drilling
fluid flowing through the motor to directly control the flow of the
drilling fluid into the motor and the rotational speed of the
rotor.
[0006] Technical advantages of the present invention include an
improved system and method for controlling drill motor rotational
speed to increase the motor's operational life. In particular, a
drill motor governor is operable to directly control the flow of
drilling fluid into a drill motor so as to control the rotational
speed of the drill motor. The use of such a governor can prevent
over-speed conditions that frequently occur when using compressible
drilling fluids such as air, nitrogen, or foam. Such over-speed
conditions can cause excessive wear of the rotor and/or other
components of a drill string. Another technical advantage of the
present invention includes the ability to allow excess drilling
fluid to enter the well bore to clean the well bore without that
drilling fluid passing through the drill motor. Other technical
advantages of the present invention will be readily apparent to one
skilled in the art from the following figures, description, and
claims. Moreover, while specific advantages have been enumerated
above, various embodiments may include all, some, or none of the
enumerated advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of particular embodiments
of the present invention and its advantages, reference is now made
to the following description taken in conjunction with the
accompanying drawings, in which:
[0008] FIG. 1 illustrates an example system for controlling drill
motor rotational speed;
[0009] FIG. 2 is a cross sectional diagram illustrating example
components of the system of FIG. 1; and
[0010] FIG. 3 illustrates a detailed view of an example drill motor
governor of the system of FIG. 1.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0011] FIG. 1 illustrates an example system 10 for controlling
drill motor rotational speed. In certain embodiments, system 10 may
be used in a well bore 20 extending from surface 25 to penetrate a
subterranean zone 30. Although FIG. 1 illustrates a substantially
vertical well bore 20, system 10 may be implemented in articulated
wells, slant wells, or any other types of wells or well systems.
Subterranean zone 30 may comprise an oil or gas reservoir, a coal
seam, or any other appropriate subterranean zone. Subterranean zone
30 may be accessed to remove and/or produce water, hydrocarbons,
and other fluids in subterranean zone 30, to treat minerals in
subterranean zone 30 prior to mining operations, or for any other
suitable purpose.
[0012] System 10 includes a drill string 40 used to form well bore
20. In certain embodiments, drill string 40 includes a drill pipe
45, a motor governor 50, a downhole motor 70, a bit box 85, and a
drill bit 90. Drill pipe 45 couples to motor governor 50 and runs
to surface 25, where it is coupled to pumping equipment to deliver
drilling fluid to motor governor 50. Motor governor 50 is coupled
to downhole motor 70 and may be used to directly control the flow
of drilling fluid into downhole motor 70, thereby controlling the
rotational speed of a drill motor contained in downhole motor 70,
as described in more detail below with reference to FIGS. 2 and 3.
Example downhole motors 70 include turbine motors and positive
displacement motors (PDMs), which are well known in the art.
Downhole motor 70 is coupled to bit box 85 which provides a
mechanical link between downhole motor 70 and drill bit 90, such
that the rotational power generated by downhole motor 70 may be
transmitted to drill bit 90.
[0013] In operation, a drilling fluid, such as drilling mud, is
pumped through drill string 40 from pumping equipment located on
surface 25, or at any other appropriate location, thereby causing
particular components of downhole motor 70 to rotate. This rotation
causes drill bit 90 to rotate, thereby facilitating cutting
portions of subterranean zone 30 to form well bore 20. Drill bit 90
may be a rotary cone drill bit or any other suitable drill bit. In
particular embodiments, drill bit 90 may be replaced with any other
suitable rotatable downhole device that is rotated by drill motor
70. The rotation of downhole motor 70 is also used to rotate
particular elements of motor governor 50 to directly control the
flow of drilling fluid into the inlet of downhole motor 70 and thus
control the rotational speed of the drill motor. Although motor
governor 50, downhole motor 70, bit box 85, and drill bit 90 are
illustrated as having a particular size relative to the other
elements of drill string 40, each element 50, 70, 85, 90 may be of
any appropriate size as circumstances require.
[0014] In certain embodiments, drill string 40 may be used to
create well bore 20 to enable access to subterranean zone 30.
Subterranean drilling operations can expose well bore drilling
equipment, such as drill string 40, to damaging operating
conditions. For example, inconsistencies in the flow of drilling
fluid, such as entrapped air within the drilling fluid or varying
geological conditions may be detrimental to the life of drill motor
70. System 10 may be implemented to provide more efficient drilling
operations by providing a system for directly controlling drill
motor rotational speed, thereby potentially increasing drill motor
operating life, and consequently, the operating life of other drill
string components.
[0015] FIG. 2 is a cross-sectional diagram illustrating example
components of drill string 40. In the illustrated embodiment, drill
string 40 includes motor governor 50, downhole motor 70, bit box
85, and drill bit 90. In certain embodiments, the components of
motor governor 50, and downhole motor 70 may be enclosed within
drill string pipe walls 42 of drill string 40. The illustrated
downhole motor 70 comprises a positive displacement motor (PDM)
having a rotor 72 and stators 74. Drilling fluid 100 is pumped into
drill string 40 using pumping equipment located on surface 25.
Motor governor 50 is operable to directly control the flow of
drilling fluid through downhole motor 70, illustrated as fluid 104,
and to direct a portion of fluid 100 out of drill string 40 and
into well bore 20 illustrated as fluid 102. Drilling fluid 104 is
pumped through channels 76 formed between rotor 72 and stators 74.
Because of the eccentricity of rotor 72 in stators 74, the flow of
fluid 104 imparts a torque on rotor 72 causing rotor 72 to
turn.
[0016] In certain embodiments, rotor 72 may be constructed of a
sufficiently durable and reliable material, such as steel, so that
rotor 72 may be disposed within well bore 20 for use over an
extended period of time without the need to be removed from well
bore 20 for repair or replacement during that time. In certain
embodiments, stators 74 may be made from a deformable and resilient
material, such as an elastomer, to provide an effective hydraulic
seal around rotor 72 while still permitting rotor 72 to turn freely
and permitting drilling fluid 104 to flow through channels 76.
Rotor 72 and stators 74 may be designed and constructed to
withstand the corrosive effects of the minerals and fluids that may
be contained in well bore 20. The use of PDMs in well drilling and
the materials and components used to construct PDMs are well known
in the art.
[0017] Rotor 72 includes a substantially straight shaft portion 73,
which extends from stators 74 through downhole motor 70 and
protrudes from the end of downhole motor 70, as illustrated in FIG.
2. Shaft portion 73 is positioned between bearings 79, which may
comprise thrust bearings or radial bearings operable to withstand
axial and normal loads placed on drill bit 90 during the drilling
process and the loads imparted on shaft portion 73 during its
rotation. O-rings 77 are positioned within downhole motor 70 around
shaft portion 73 to provide an effective hydraulic seal which
prevents drilling fluid 104 from flowing through the annulus formed
between shaft portion 73 and drill string pipe walls 42. O-rings 77
may be made from a deformable and resilient material, such as an
elastomer, to provide an effective hydraulic seal around shaft
portion 73 while still permitting shaft portion 73 to turn
freely.
[0018] In certain embodiments, shaft portion 73 contains one or
more fluid ports 80 and a hollow channel 82. Fluid ports 80 allow
drilling fluid 104 to flow into hollow channel 82 of shaft portion
73 so that drilling fluid 104 may flow through shaft portion 73
towards drill bit 90. Shaft portion 73 includes bit box 85, which
has threads 84 for threadably coupling drill bit 90 to rotor 72.
Although threads 84 are illustrated, any other appropriate
mechanism for coupling bit box 85 to drill bit 90 may be
implemented. Drill bit 90 includes one or more drill cones 92 with
a plurality of drill teeth 94. The rotation of rotor 72, and
consequently the rotation of shaft portion 73 and bit box 85,
rotates drill bit 90, facilitating the removal of material in
subterranean zone 30 to form well bore 20. Drilling fluid 104 flows
through channel 82 of shaft portion 73 and then flows out of drill
string 40 through opening 96 in drill bit 90. In this manner,
drilling fluid 104 may be used to remove drill cuttings created by
drill bit 90 and to provide lubrication to drill cones 92. The
design and construction of the components of drill string 40, such
as bit box 85 and drill bit 90, to withstand the corrosive effects
of the minerals and fluids that may be contained in well bore 20,
is well known.
[0019] In certain embodiments, to prolong the operational life of
the components of drill string 40, and, in particular, the
operational life of the components of downhole motor 70, motor
governor 50 may be used to prevent excessive rotational speeds of
downhole motor 70. As will be discussed in more detail below with
respect to FIG. 3, motor governor 50 is operable to directly
control the flow of drilling fluid 104 entering downhole motor 70,
thereby controlling the rotational speed of rotor 72. For example,
it is desirable to prevent rotor 72 from exceeding a predetermined
rotational speed threshold (a condition known as "over-speeding").
Over-speeding may be caused by an irregularity in the flow of
drilling fluid 104 through downhole motor 70. For example, air may
become entrapped in drill fluid 104, causing a decrease in fluid
resistance. This decrease in fluid resistance may cause the
rotational speed of rotor 72 to drastically increase, potentially
causing damage to the components within drill string 40.
Over-speeding can also be caused by a change in the resistance of
the drill bit as it cuts through subterranean zone 30. When
drilling subterranean zone material, the torque of drill motor 70
causes drill bit 90 to turn at a given rotational speed. When drill
bit 90 is lifted off the bottom of well bore 20 or otherwise loses
contact with the subterranean zone material, resistance to the
torque provided by drill motor 70 is reduced, thus causing an
over-speed condition.
[0020] FIG. 3 illustrates a detailed view of an example motor
governor 50 of system 10. Motor governor 50 is operable to control
the rotational speed of rotor 72 by directly controlling the flow
of drilling fluid 104 entering downhole motor 70. In certain
embodiments, motor governor 50 may include a valve apparatus 51 and
one or more bypass ports 52 formed through drill string pipe walls
42. Valve apparatus 51 may include a sliding valve 54, a valve post
58, a valve spring 60, valve weights 61, and support members 62,
63. The components of valve apparatus 51 may be designed and
constructed to withstand the corrosive effects of the minerals and
fluids that may be contained in well bore 20. The use of drill
string component materials capable of withstanding the conditions
of well bore drilling operations is well known in the art.
[0021] In certain embodiments, sliding valve 54 includes valve
channels 56 formed through sliding valve 54. Valve channels 56
permit drilling fluid 104 to pass through sliding valve 54 so that
the drilling fluid may be used to rotate rotor 72 of downhole motor
70. In certain embodiments, sliding valve 54 may be coupled to
valve post 58 or sliding valve 54 and valve post 58 may be
constructed as a single component. Valve spring 60 surrounds valve
post 58 and is positioned between sliding valve 54 and rotor 72.
Support members 62 may be pivotally coupled to sliding valve 54 at
one end and pivotally coupled to a valve weight 61 at the other
end. Similarly, support members 63 may be pivotally coupled to a
valve weight 61 at one end and pivotally coupled to rotor 72 at the
other end. In a particular embodiment, one end of each of support
members 63 may be pivotally coupled at the same location on rotor
72. In the illustrated embodiment, rotor 72 includes a slot 78 to
receive one end of valve post 58 when sliding valve 54 moves
longitudinally towards rotor 72, as indicated by arrow 69a. In an
alternate embodiment, where valve post 58 is directly coupled to
rotor 72 rather than to sliding valve 54, sliding valve 54 may
include a slot to receive valve post 58 when valve 54 moves
longitudinally towards rotor 72, as indicated by arrow 69a. In
certain embodiments, valve post 58 may be omitted from valve
apparatus 51.
[0022] In operation, rotor 72 rotates as a result of drilling fluid
104 flowing through channels 56 of valve 54 and then through
channel 76 between rotor 72 and stator 74. Because sliding valve
54, support members 62, 63, and valve weights 61 are coupled to
rotor 72, these components rotate at the same speed as rotor 72.
The rotational speed of rotor 72, and consequently, the rotational
speed of valve weights 61, may increase due to an increase in the
flow rate of drilling fluid 104. In addition, inconsistencies in
the flow of drilling fluid 104, such as the presence of entrapped
air within drilling fluid 104, may cause a rapid, undesirable
increase in the rotational speed of rotor 72 due to the reduced
fluid resistance caused by the entrapped air. Likewise, a change in
operational or geological conditions could cause the same
undesirable increase in the rotational speed of rotor 72. As the
rotational speed of rotor 72 increases, the resulting increase in
the rotational speed of valve weights 61 causes valve weights 61 to
spin faster around the longitudinal axis of drill string 40. The
centrifugal force caused by the rotation of valve weights 61
creates an axial force 65 acting through members 62 on valve 54.
When axial force 65 exceeds an axial force 66 exerted by valve
spring 60 against valve 54, valve 54 will move towards rotor
72.
[0023] When rotor 72 is not rotating or has a very low rotational
speed, sliding valve 54 is positioned to block by-pass ports 52 to
prevent the drilling fluid from flowing into well bore 20 through
by-pass ports 52. In the illustrated embodiment, as valve weights
61 move laterally outward, axial force 65 causes sliding valve 54
to be moved longitudinally toward rotor 72, as illustrated by arrow
69a, by the closing "scissoring" action of support members 62, 63.
Valve spring 60 is compressed between valve 54 and rotor 72,
thereby providing axial force 66 opposing the longitudinal movement
of sliding valve 54 towards rotor 72. As sliding valve 54 moves in
the direction of arrow 69a, sliding valve 54 moves past by-pass
ports 52 creating a pathway for some of the drilling fluid to flow
out of by-pass ports 52. As by-pass ports 52 are opened, a portion
102 of drilling fluid 100 flows out of drill string 40 and into
well bore 20. Consequently, the flow of drilling fluid 104 to rotor
72 is reduced. Thus, valve apparatus 51 is operable to redirect the
flow of a portion of drilling fluid outside of drill string 40 to
reduce the flow through rotor 72, thereby reducing its rotational
speed and protecting rotor 72 from an over-speed condition which
may reduce the operational life of the rotor 72 and the other
components of drill string 40. As a result of the re-direction of
fluid 100 out of drill string 40 and into well bore 20, the present
invention may also act in certain cases as a "dump-sub" which
allows excess drilling fluid 100 to enter well bore 20 to clean
well bore 20 without fluid 100 passing through drill motor 70.
[0024] As the flow of drilling fluid 104 is reduced, the rotational
speed of rotor 72 and valve weights 61 decreases. In the
illustrated embodiment, at the rotational speed where the axial
force 65 acting on members 62 generated through the centrifugal
force generated by the rotation of valve weights 61 is exceeded by
the axial force 66 of valve spring 60, the axial force 66 applied
by valve spring 60 onto sliding valve 54 will cause sliding valve
54 to move longitudinally away from rotor 72, as illustrated by
arrow 69b. At the same time, valve weights 61 will be drawn away
from drill string pipe walls 42, as illustrated by arrows 68b, due
to the opening "scissoring" action of support members 62, 63. As
sliding valve 54 moves longitudinally away from rotor 72, it
eventually blocks by-pass ports 52 which reduces or completely
prevents the flow of drilling fluid out of drill string 40 and
increases flow 104 through rotor 72, thus increasing the rotational
speed of rotor 72. In this manner, by-pass ports 52 may be blocked
and un-blocked as needed to directly control the flow of drilling
fluid that enters downhole motor 70 to control the rotational speed
of rotor 72.
[0025] Therefore, the design of governor 50 regulates the
rotational speed of rotor 72 such that it does not exceed a
particular rate. The selection of a valve spring 60 having a
particular spring constant, valve weights 61 having a particular
mass, and support members 62, 63 having particular lengths, are
thus matters of design choice based on the desired maximum
rotational speed of rotor 72.
[0026] In certain embodiments, drill motor governor 50 and by-pass
ports 52 may be located at a sufficient distance away from drill
bit 90 so that the drilling fluid 102 flowing into well bore 20
through by pass-ports 52 does not substantially affect the
weight-on-bit of drill string 40. Therefore, drill motor governor
50 may control the rotational speed of motor 70 by directly
affecting the flow of drilling fluid into motor 70.
[0027] Although the present invention has been described with
several embodiments, a multitude of changes, substitutions,
variations, alterations, and modifications may be suggested to one
skilled in the art, and it is intended that the invention encompass
all such changes, substitutions, variations, alterations, and
modifications as fall within the spirit and scope of the appended
claims.
* * * * *