Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02549739 2006-06-09
FLUID DRIVEN DRILLING MOTOR AND SYSTEM
Field of the Invention
The present invention relates to the field of drilling systems, and more
particularly, it relates to an improved mud motor.
Background of the Invention
Conventional rotary drilling operations rotate the drill bit by turning the
entire
drill string at the surface with a rotary table and kelly. However, a down-
hole motor, such as a
down-hole mud motor, utilizes the circulation system and the hydraulic power
of a drilling
fluid to rotate the drill bit without rotating the entire drill string within
the well bore. A down-
hole mud motor system may include drill collars which are larger diameter
pipes attached to
the drill pipe at a lower end of the drill string above the drill bit wherein
the drill collar helps
to add weight to the drill string to ensure there is sufficient downward
pressure to enable the
drill bit to drill through the formation. The drill bit, located at the bottom
end of the drill string
is responsible for breaking up and dislodging the rock formation as small rock
particles
suspended in the fluid as it is pumped back to the surface from the drill bit.
There are different
types of drill bits, such as diamond bits, steel tooth bits, and carbide
insert bits to handle
different drilling conditions, such as the type of underground formation, the
type of drilling,
and the temperature of the Eartli.
A mud motor is typically used in directional drilling operations, especially
in
oil and gas and mining operations. Mud motors are usually used to rotate a
drill bit for bore
hole drilling and coring in the earth. The rotor of the motor rotates the
drill bit with respect to
a stator which is connected to a drill string. The weight of the drill bit and
drill string in
conjunction with the rotary speeds generated by the mud motor enables the
rotating drill bit to
efficiently cut away the formation the drill bit is pushed against. Drilling
fluid, such as so-
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called "mud", supplies the hydraulic power to operate the motor. More
particularly, the inud
motor operates by coinverting the hydraulic energy of the drilling fluid into
mechanical torque
and applying the torque to drive the drill bit into the formation.
The additional main functions of the drilling fluid include cooling and
lubricating the drill bit, stabilizing the wall of the well bore, controlling
well pressure, and
removing debris and cuttings. The composition of the mud drilling fluid used
for any
particular drilling operation depends on the drilling conditions. The mud must
be of light
enough consistency such that it may circulate through the drill bit to cool
and Iubr.icate the
parts, but the mud must also be sufficiently viscous to carry the rock
particulate debris away
from the drill bit when the drill cuttings are circulated back up the well
through the annular
space. Typically, the circulating system pumps the mud drilling fluid down
through the
hollow drill string. The mud supplies the hydraulic power to operate the mud
motor and cools
and lubricates the drill bit as it flows through apertures in the drill bit.
The mud may be a
water-based, synthetic-based or diesel fuel-based product. Once the inud is
circulated back up
to the surface through the annular space, the cuttings are removed from the
mud, for example,
by way of a mesh before the mud is r.eturned to the mud pits to be used again.
As the drilling fluid is pumped down the drill string and through the mud
motor, pressure loss due to friction reduces the amount of pressure supplied
to the motor,
causing a decrease in motor torque and slower boring. Further pressure loss at
the motor due
to narrow flow passages also reduces the efficiency of drilling. By minimizing
the pressure
loss, the overall torque and hydraulic horsepower available to the motor may
be increased. As
such, there exists a need to provide a fluid driven drilling motor and system
wherein pressure
loss as the drilling fluid circulates througli the drilliiig motor and system
may be minimized to
increase the drilling efficiency of the down-hole drilling motor.
Applicant is aware of several apparatus and methods in the art that purport to
improve the efficiency of a down-hole motor. However, none of the prior art
apparatus and
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methods minimize the pressure loss of the drilling fluid in the manner of the
present invention.
For example, applicant is aware of United States Patent No. 6,561,290 to Blair
et al. for a
down-hole mud motor which has an improved bearing mandrel and a bearing stop
to transfer a
larger percentage of the weight of the drill string to the bit. Improved
sealing systems for the
transmission section and bearing section prevent drilling mud from entering
critical
coinponents. A piston stop is provided to prevent the piston from damaging any
parts as the
piston moves under pressure. A compensating pressure disk is placed in the
lower housing to
prevent pressure from building up in the bearing section. A grooved ball seat
is provided in
the transmission to allow for greater flow of lubricant around the ball
bearings.
Applicant is also aware of Canadian Patent No. 2,197,964 which issued to
Sallwasser et al. on December 3, 2002 for a Method and Apparatus for Drilling
with a Flexible
Shaft While Using Hydraulic Assistance. The apparatus and method disclosed
includes
applying thrust weight to a drill bit when drilling with a flexible drilling
shaft while creating
perforations in a cased well. The thrust is applied directly to the drill bit
instead of applying it
to the drill bit through the flexible drilling shaft. A support bracket is
also in contact with a
piston and is in slidable contact with the tool housing. A portion of the
piston is positioned
inside a chamber in the housing and is slidably attached to the chamber walls.
As hydraulic
fluid flows into the chamber opposite the piston, the piston is forced toward
the drill bit. As
the piston moves toward the drill bit, force is exerted on the support bracket
which causes the
bracket to move toward the drill bit. This force is transferred to the drill
bit during the drilling
process, thereby supplying the force needed by the drill bit to effectively
drill through a
desired material.
Applicant is also aware of United States Patent No. 3,982,859 which issued to
Tschirky et al. on September 28, 1976 wherein the operation of hydraulic
motors may be
improved by employing stable flow restrictors which are resistant to corrosion
and maintains a
stable bypass volume of fluid used to lubricate the bearing package.
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Summary of the Invention
A fluid driven drilling motor and system for use in a drill string containing
a
down-hole drilling motor is disclosed. A rotor of the down-hole drilling motor
rotates in a first
direction relative to a stator about the longitudinal axis of a well bore in
which the drill string
is journalled. The rotor is operative under the pressure of a drilling fluid.
In suminary, the
fluid driven drilling motor and system of the present invention. may be
characterized in one
aspect as including a flex shaft mountable to and between the rotor and a
cylindrical flow
collar, the cylindrical flow collar having a cylindrical sidewall and. first
and second opposite
ends. The first end of the cylindrical flow collar is mountable to the flex
shaft. The second
end of the cylindrical flow collar has a bore and is mountable to a drill bit
so that the bore is in
fluid communication with the drill bit.
At least one, and preferably two or more ramped apertures are formed in the
side wall of the cylindrical flow collar. Each ramped aperture includes an
inlet on an outer
surface of the sidewall and a corresponding opening within the cylindrical
flow collar such that
the drilling fluid may be directed to the bore in the second end of the flow
collar. The r.amped
apertures are therefore in fluid communication with the bore such that the
drilling fluid may
enter the bore via the inlets and the openings. Each of the ramped apertures
include inclined
ranzp surfaces and inclined side surfaces extending radially, relative to a
longitudinal axis of
the bore, between the inlets and the corresponding openings. The ramped
surfaces and side
ranip surfaces are formed such that drilling fluid flowing under pressure down
past the flex
shaft may be directed and drawn into the rainped apertures along a fluid flow
path which
spirals downwardly and radially inwardly of the flow collar so as to then flow
into the bore.
The pressure loss associated with drawing the drilling fluid into the ranlped
apertures is
thereby minimized such that increased hydraulic pressure is available to
increase the overall
torque and hydraulic power of the drill motor to increase drilling efficiency.
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In an embodiment of the invention, the cylindrical flow collar includes a
shear
pin positionable and mountable between the flex shaft and the drive shaft such
that the shear
pin may shear in the event of excess torsional stress, thereby inhibiting
breakage of the drive
shaft.
Brief Description of the Drawings
Various other objects, features and attendant advantages of the present
invention will become fully appreciated as the same becomes better understood
when
1.0 considered in conjunction with the accompanying drawings, in which like
reference characters
designate the same or similar parts throughout the several views, and wherein:
Figure 1 is a partial cut away view of the fluid driven drilling motor and
system
according to the present invention.
Figure 2 is partial cut away view of the fluid driven drilling system of
Figure 1
journalled in and along a well bore.
Figure 2a is a sectional view of a lower end of the fluid driven drilling
system.
of Figure 2.
Figure 3 is a front view of a flow collar and a drill bit coaxially mounted
together.
Figure 3a is a sectional view of the flow collar of Figure 3.
Figure 4 is a perspective view of the flow collar of Figure 3.
Figure 5 is a plan view of the flow collar shown in Figure 3.
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Detailed Description of Embodiments of the Invention
With reference to the Figures 1 to 5 wherein similar characters of reference
denote corresponding parts in each view, the fluid driven drilling system
according to the
present invention includes a drill string 2 having a power section 10, a flex
shaft 20, a flow
collar 30, and a drill bit 40 coaxially mountable to each other. Power section
10, which
includes a down-hole drilling motor 12, is coaxially mounted within a drill
pipe (shown in
Figure 2) to flex shaft 20. Flex shaft 20 is coaxially mounted between power
section 10 and
flow collar 30. Down-hole drilling motor 12 is mounted to an upper end of flex
shaft 20.
Flow collar 30 is mounted to an opposite lower end of flex shaft 20. Flow
collar 30 is
mounted between flex shaft 20 and drill bit 40. An upper end of flow collar 30
is mounted to
flex shaft 20. Alternatively, flow collar 30 may form the lower end of flex
shaft 20, as
described below. The lower end of flow collar 30 is configured to coaxially
receive drill bit
40. Drill bit 40 is at the bottom-most end of drill string 2. Drill string 2
is journalled in and
down th.rough a well bore 1 such that drill bit 40 engages and drills the rock
formation 7.
Down-hole drilling motor 12 includes a stator 14 and a rotor 16 disposed in
power section 10 of drill string 2. In an embodiment of the invention, down-
hole drilling
motor 12 is a mud motor or a positive displacement drilling motor that uses
the hydraulic
power of a drilling fluid, such as so-called mud, to rotate drill bit 40, as
described below.
Rotor 16 may be a chrome plated helically splined shaft having a series of
projections that fit
into corresponding channels of helically splined stator 14. Rotor 16 is
rotatably joumalled in
helically splined stator 14 which defines a series of corresponding channels
such that the series
of projections of rotor 16 may mate with the series of channels defined by
stator 14. Stator 14
spirals vertically down the length of power section 10. Stator 14 may be made
of elastomer
coated steel. The number of channels defined by stator 14 exceeds the number
of projections
on rotor 16, thereby creating a progressive series of cavities or spaces that
extend vertically
down the length of power section 10 as rotor 16 rotates relative to stator 14.
As the drilling
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fluid is pumped down drill string 2 and flows through the series of cavities
between stator 14
and rotor 16, the pressure of the drill fluid causes eccentric rotation of
rotor 16 relative to
stator 14 about the longitudinal axis A. of power section 10. The ratio of
rotor 16 projections
and stator 14 channels may be varied to achieve the desired torque and speed.
For example, a
higher number of channels and projections yield a higher torque and slower
speed whereas a
fewer number of channels and projections yield a lower torque and higher
speed.
The upper end of flex shaft 20 is coaxially mounted to the bottom end of rotor
16 by coupling means known in the art, such as a combined splined/threaded
coupling. In an
embodiment of the invention, flex shaft 20 is cylindrical and may be made of
solid alloy steel
or any other heavy duty material such that flex shaft 20 may convert the
eccentric rotation of
rotor 1.6 to smooth concentric rotation at the lower end of flex shaft 20 to
ensure concentric
rotation of a drive shaft 42 to rotate drill bit 40. Flex shaft 20 also
transmits the torque
generated by down-hole drilling motor 12 from power section 10 to flow collar
30 to drive
shaft 42 to rotate drill bit 40.
In an embodiment of the invention, the lower end of flex shaft 20 is coaxially
mounted to upper end of flow collar 30 by for example a threaded coupling or
other coupling
means known in the art. Alternatively, flex shaft 20 and flow collar 30 may be
a single unitary
structure. For example, the lower end of flex shaft 20 may include flow collar
30 such that
flow collar 30 is formed at the lower end of, and as a part of, flex shaft 20.
In the former
embodiment of the invention, flow collar 30 defines an upper bore 34, as seen
in Figure 4, at
an upper end of flow cotlar 30 to receive and mate with a lower portion of
flex shaft 20. Flow
collar 30 may also define a lower bore 36, seen in Figure 3a, to receive and
mate with drive
shaft 42 at the lower end of flow collar 30. In a preferred embodiment of the
invention, flow
collar 30 is cylindrical, having a cylindrical sidewall 32 and a diameter
larger than flex shaft
20. At least one, and preferably two or more ramped apertures 37 are formed in
sidewall 32 of
flow collar 30. Flow collar 30 may be made of steel. Ramped apertures 37 may
be hardened
using a nitride or carbide coating process to inhibit corrosion.
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Each ramped aperture 37 includes an. inlet 39 on an outer surface of sidewall
32
where the drilling fluid may enter flow collar 30. Ramped apertures 37 are in
fluid
communication with lower bore 36 via inlets 39 and openings 39' such that when
the drilling
fluid enters ramped apertures 37 in directions B via inlets 39, the drilling
fluid flows through
openings 39' and into lower bore 36. The drilling fluid continues to flow down
and through
lower bore 36 and drive shaft 42 in direction C to lubricate and cool drill
bit 40 while flow
collar 30 rotates concentrically in direction D relative to longitudinal axis
of rotation E. The
drilling fluid flows out of drill bit 40 via a plurality of apertures such
that the drilling fluid may
transport drill cuttings to the surface through the annular space 44 in
direction F when the
drilling fluid is pumped back up to the surface.
Each of the ramped apertures 37 include inclined ramp surfaces 38 and side
inclined ramp surfaces 38' extending radially, relative to longitudinal axis G
of lower bore 36,
between inlets 39 and openings 39'. Preferably, the drilling fluid flows down
a generally thirty
degree ramp (see angle (x of Figure 3a) of inclined ramp surfaces 38 and a
generally sixty
degree ramp (see angle (3 of Figure 5) of side inclined ramp surfaces 38' into
lower bore 36.
Inclined ramp surfaces 38 and side inclined ramp surfaces 38' are formed such
that drilling
fluid flowing under pressure down the outside of flex shaft 20 in direction H
is directed and
drawn into ramped apertures 37 via inlets 39 along fluid flow path J which
spirals downwardly
and radially inwardly of flow collar 30. In an embodiment of the invention,
ramped apertures
37 are machined in a spiraled configuration such that drilling fluid may be
easily drawn down
inclined ramp surfaces 38 and side inclined ramp surfaces 38' and into lower
bore 36 via inlets
39 and openings 39' due to the pressure difference between the pressure within
lower bore 36
and the flow pressure of the drilling fluid. Advantageously, the pressure loss
associated with
drawing the drilling fluid into ramped apertures 37 is minimal, therefore more
pressure is
available to increase the overall torque and hydraulic power of down-hole
drilling motor 12 to
increase drilling efficiency.
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During the process of converting the eccentric rotary motion of rotor 16 to
concentric rotary motion, a large amount of stress may be induced into flex
shaft 20. More
particularly, the torque generated by the rotation of rotor 16 relative to
stator 14 and the
additional torque generated by the rotation of drill bit 40 creates torsional
or shear stress along
flex shaft 20. Excessive torsional stress may damage the flex shaft 20 or the
drive shaft 42.
Consequently in one embodiment, flow collar 30 includes a shear pin 50 mounted
between
flex shaft 20 and drive shaft 42 such that shear pin 50 shears under excessive
torsional stress,
thereby inhibiting damage to the flex shaft or drive shaft.
As will be apparent to those skilled in the art in the light of the foregoing
disclosure, many alterations and modifications are possible in the practice of
this invention
without departing from the spirit or scope thereof. Accordingly, the scope of
the invention is
to be construed in accordance with the substance defined by the following
claims.
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