U.S. patent application number 11/114926 was filed with the patent office on 2006-10-26 for earth boring tool.
This patent application is currently assigned to Dennis Tool Company. Invention is credited to Mahlon D. Dennis, Thomas M. Dennis, Roy Powell, Eric M. Twardowski.
Application Number | 20060237234 11/114926 |
Document ID | / |
Family ID | 37185680 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060237234 |
Kind Code |
A1 |
Dennis; Mahlon D. ; et
al. |
October 26, 2006 |
Earth boring tool
Abstract
An earth boring tool includes two coaxially-aligned, positive
displacement motors. One motor turns a pilot bit and the other
turns a reamer concentric with the pilot bit. The central bit bores
the center of the hole and the reamer enlarges it. The central bit
is rotated relatively faster, while rotation of the larger diameter
reamer is relatively slow. The tool can thus be used to bore larger
diameter holes without slowing drilling rates or adversely
affecting performance of the cutter elements due to higher
tangential velocities.
Inventors: |
Dennis; Mahlon D.;
(Kingwood, TX) ; Dennis; Thomas M.; (Kingwood,
TX) ; Twardowski; Eric M.; (Spring, TX) ;
Powell; Roy; (Estes Park, CO) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
Dennis Tool Company
|
Family ID: |
37185680 |
Appl. No.: |
11/114926 |
Filed: |
April 25, 2005 |
Current U.S.
Class: |
175/95 ;
175/406 |
Current CPC
Class: |
E21B 4/16 20130101; E21B
7/28 20130101; E21B 4/02 20130101; E21B 10/26 20130101 |
Class at
Publication: |
175/095 ;
175/406 |
International
Class: |
E21B 10/36 20060101
E21B010/36; E21B 4/00 20060101 E21B004/00; E21B 10/26 20060101
E21B010/26 |
Claims
1. A drilling tool comprising: a body have a central axis; a
central bit mounted for rotation about the central axis, on which
is disposed a first plurality of cutters, the central bit having a
first cutting diameter; a sleeve-shaped reamer mounted for rotation
about the central axis, on which is disposed a second plurality of
cutters, the reamer having a second cutting diameter greater than
the first cutting diameter; a first motor coupled with the central
bit for rotating the central bit; a second motor coupled with the
first motor and the reamer for rotating the first motor and reamer,
the first motor being configured to turn the central bit at a first
angular velocity relative to the body of the drilling tool; the
second motor being configured to rotate the reamer at a second
angular velocity relative to the body, the magnitude of the first
angular velocity being greater than the magnitude of the second
angular velocity.
2. The drilling tool of claim 1, wherein the first and second
motors are positive displacement motors powered by drilling fluid
pumped under pressure through the tool.
3. The drilling tool of claim 1, wherein the first motor is
comprised of a first positive displacement motor (PDM); and the
second motor is comprised of a second positive displacement motor
(PDM); the second PDM having a internal stator having a
non-rotational relationship with the body of the tool and an
external rotor; the first PDM have an external stator coupled in
fixed relationship with the external rotor of the second PDM and an
internal rotor coupled with the central bit for rotation of the
central bit.
4. The drilling tool of claim 3, wherein the first and second PDMs
are aligned such that the drilling fluid flowing into the tool
flows into the second PDM, exits the second PDM and flows into the
first PDM.
5. The drilling tool of claim 3, further comprising unsealed
bearings for supporting the first PDM within the body for rotation
relative to the body, the bearings having surfaces comprised of a
hard or super hard material and being lubricated by the drilling
fluid.
6. The drilling tool of claim 5, wherein the bearings are thrust
bearings.
7. The drilling tool of claim 1, wherein the reamer is connected to
the first motor.
8. The drilling tool of claim 1, wherein the first motor rotates a
first direction and the second motor rotates a second
direction.
9. A drilling tool comprising: a body have a central axis; a
central bit mounted for rotation about the central axis, on which
is disposed a first plurality of cutters, the central bit having a
first cutting diameter; a sleeve-shaped reamer mounted for rotation
about the central axis, on which is disposed a second plurality of
cutters, the reamer having a second cutting diameter greater than
the first cutting diameter; a first positive displacement motor
(PDM) coupled with the central bit for rotating the central bit; a
second PDM coupled with the first motor and the reamer for rotating
the first PDM and reamer; wherein the first PDM being configured to
turn the central bit at a first angular velocity relative to the
body of the drilling tool; the second PDM being configured to
rotate the reamer at a second angular velocity relative to the
body, the magnitude of the first angular velocity being greater
than the magnitude of the second angular velocity; and the first
and second PDMs are aligned such that drilling fluid flowing into
the tool under pressure flows into the second PDM, exits the second
PDM and flows into the first PDM; the second PDM having an internal
stator having a non-rotational relationship with the body of the
tool and an external rotor; the first PDM having an external stator
coupled in fixed relationship with the external rotor of the second
PDM and an internal rotor coupled with the central bit for rotation
of the central bit.
10. The drilling tool of claim 9, further comprising unsealed
bearings for supporting the first PDM within the body for rotation
relative to the body, the bearings having surfaces comprised of a
hard or super hard material and being lubricated by the drilling
fluid.
11. The drilling tool of claim 10, wherein the bearings are thrust
bearings.
12. The drilling tool of claim 9, wherein the reamer is connected
to the first PDM.
13. The drilling tool of claim 9, wherein the first PDM rotates a
first direction and the second PDM rotates a second direction
opposite the first direction.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to tools for forming bores in the
earth, especially rock, and particularly to rotary drill bits for
use in oil and gas exploration and mining.
[0002] Drag bits for drilling through rock are typically outfitted
with hard, durable cutters. To improve wear, the cutters often
possess contact surfaces made from diamond, typically in the form
of polycrystalline diamond compact (PDC). PDC is an extremely hard
and wear resistant material.
[0003] Although PDC cutters are known to have one of the lowest
rates of wear when operated at cooler temperatures, thermal damage
to the diamond layer of the cutter begins at temperatures of
approximately 700 degrees Celsius. Thermal damage lowers wear
resistance and the PDC cutters become more susceptible to abrasive
wear and breakage from impact.
[0004] Greater tangential cutter velocity causes more friction,
thus generating more heat. Cutters moving at higher tangential
velocities will thus tend to operate at higher temperatures. At
some velocity, frictional heat reaches a level sufficient to cause
cutter wear rates to accelerate, reducing the life of the cutters.
In conventional PDC drag bits, the tangential velocity of a cutter,
when measured relative to the material being cut, depends on the
distance of the cutter from the center of rotation of the drill
bit. For a given angular velocity, the tangential velocity of
cutter increases with the distance of the cutter from the bit's
axis of rotation. Thus, a PDC cutter's intolerance of high
temperatures limits, in practice, the diameter of the bit.
[0005] Increased application of force also generates more heat.
Cutters require more force to penetrate harder rock. Cutters
dragging through harder rock have higher wear rates due to the
increased application of force. Therefore, the critical point at
which the wear rate begins to accelerate is also a function of
hardness of rock in addition to the rotational velocity of the
drill bit to which the cutter is attached. In softer rocks,
accelerated wear rates do not occur until higher rotational speeds
are used; in harder rocks, acceleration of the wear rate occurs at
much lower rotational speeds.
[0006] A number of additional factors also shorten the life of PDC
cutters.
[0007] First, a cutter's abrupt contact with rock formations also
increases the rate of wear of PDC cutters. Drilling with
conventional PDC drag bits require application of weight and torque
to a drill string to turn the drilling tool face and drive the face
into the formation. Torque rotates the bit, dragging its PDC
cutters through the formation being cut by the cutters. Dragging
generates chips, which are removed by drilling fluids, thereby
forming a bore or drilled hole. The drilling action causes a
reverse, corresponding torque in the drill string. Because of the
length of the drill string, the torque winds the drill string like
a torsion spring. If a bit releases from consistent contact with
the formation being drilled, the drill string will unwind and
rotate backward. Changing the tension in the drill string causes
the drill bit to come into irregular, abrupt contact either with
the sides of the bore or the exposed formation surface being cut.
These irregular contacts can cause impact damage to the
cutters.
[0008] Second, drill strings will also vibrate, sometimes severely.
Under typical drilling conditions, a drill string rotates at 90 to
150 rpm. These vibrations can also damage a drill bit, including
the cutters, as well as the drill pipe, MWD equipment, and other
components in the drilling system.
[0009] Third, "bit whirl" further contributes to impact loads on
PDC cutters. This complex motion of the drill bit is thought to
occur due to a combination of causes, including lateral forces on
the drill bit due to vibration of the drill string vibration,
heterogeneous rock formations, bit design, and other factors in
combination with the radial cutting ability of PDC bits. Whirl of a
drill bit in a bore subjects PDC cutters on the bit to large impact
loads as the bit bounces against rock or other material in the
bore. Cutters on these drill bits will lose large chips of PDC from
impact, rather than from gradual abrasion of the cutter, thereby
shortening the effective life of the cutters and the drill bit.
[0010] Drilling tools disclosed in U.S. Pat. No. 6,488,103 of
Dennis et al., and in U.S. application Ser. No. 10/988,722, filed
Nov. 15, 2004, both of which are incorporated herein by reference,
address these problems by reducing the thermal and impact stresses
on the cutters. The tools employ a plurality of satellite mills
surrounding a central pilot bit. The satellite mills reduce the
tangential velocity of the cutters along the periphery of the bore
hole.
SUMMARY OF THE INVENTION
[0011] The invention pertains to an earth boring tool, or aspects
thereof, having PDC cutters that overcomes one or more of these
problems by combining on the same rotational axis a central bit and
a relatively larger diameter reamer that extends beyond the central
bit. In effect, the central bit bores the center of the hole and
the reamer enlarges it. By turning the reamer at a relatively low
angular velocity relative to the earth, the tangential velocity of
the cutters on the reamer are kept low enough to reduce wear and
other adverse affects associated with higher tangential velocities
of the cutters. The central bit is allowed to rotate relatively
faster, thereby permitting larger diameter holes to be bored
without adversely affecting cutter performance or drilling rate.
Cutting speed can be optimized, allowing the maximum efficiency
without excess wear of the cutters.
[0012] Several additional benefits are possible with such a tool.
It will tend to create less vibration and chatter. Less force on
the drilling tool is required for cutting. This in turn lowers the
torque on the drill string, lessening the chance of the drill
string of wrapping up. Lighter force applied to the tool also
permits use of a lighter tubing having thinner walls to be
used.
[0013] Details of an example of such an earth boring tool are
described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a highly simplified, schematic representation of
the drive system for turning a pilot bit and reamer for the
drilling tool shown in FIGS. 2 and 3.
[0015] FIG. 2 is a side, elevation view of a first example of a
drilling tool, sectioned its entire length along its axis.
[0016] FIG. 3 is a side, elevation view of a second example of a
drilling tool, sectioned its entire length along its axis.
DETAILED DESCRIPTION
[0017] In the following description, like numbers throughout the
figures refer to like elements.
[0018] Briefly, in the following example of an earth boring tool,
the pilot bit and reamer are each driven by a separate motor,
thereby avoiding the complexities of gears and problems occasioned
by them. Examples of such problems include structural complexities
necessary to have seals, with the attendant potential for failure.
If seals are not used, there is a substantial risk of gear failure
or jamming that is not easily addressed by merely hardening the
gears.
[0019] FIG. 1 schematically illustrates the functional and spatial
relationships between two motors 10 and 12, a drill string 14,
reamer 16 and a central bit 18 within an earth boring tool 20. The
reamer and central bit each possess a plurality of cutters 21 along
exterior cutting surfaces. The central bit drills a pilot hole; the
sleeve-shaped or donut-shaped reamer, since it has an wider
diameter, widens the hole. These cutters are wear-resistant, and
may be made from carbide, polycrystalline diamond or other super
hard materials. Motor 10, the casing (not shown) of tool 20 and
drill string 14 to which the tool is attached are in a fixed
relationship and do not rotate with respect to each other. Motor 10
has a rotating output 22, with which motor 12 is in a fixed
relationship. Thus, motor 10 effectively turns motor 12. Reamer 16
has a fixed relationship with the rotating output 22 as well as
motor 12. Whether the reamer is connected with motor 12 or output
22, it is in effect turned by motor 10. Rotating output 24 of motor
12 turns central bit 18. Depending on the direction of rotation of
the outputs of the motors, their rotations can be additive, meaning
that angular velocity of the bit 18, relative to the tool and the
earth through which the tool is boring, is the sum of the angular
velocity of the rotating output of each motor. Thus the central bit
will naturally turn at a relatively higher rate of rotation than
the reamer. The relative angular velocity of the pilot bit to the
reamer will depend on the rate of rotation of the output 24 of
motor 12.
[0020] Counter-rotating the reamer and drill bit will reduce torque
on the string and stress on the cutting tool. With this
configuration, the angular velocity of motor 12 must overcome the
opposite rotation of the output 22 of motor 10. Preferably, the
central, high-speed bit rotates right, to tighten threaded
connections, and the low-speed reamer turns left.
[0021] Using conventional positive displacement motors (PDMs)--also
called "mud motors"--for motors 10 and 12 permits the motors to be
powered by drilling fluid pumped down a drilling string. With their
axes aligned with each other and the tool, drilling fluid will flow
from one into the next, and then out the end of the tool in a
manner to cool the cutters and clear cutting debris. A central
stator of the first mud motor, motor 10 in the preceding schematic,
remains stationary with respect to the casing of the tool and the
drill string. An outer, sleeve-shaped rotor functions as output 22.
This outer rotator is then coupled with an outer, sleeve-shaped
stator of the second mud motor, which corresponds with motor 12.
The construction of the second motor is the inverse of the first
mud motor: the stator, or stationary part, is disposed on the
outside of the mud motor, with the rotor formed on an internal,
rotating shaft. This inverse construction or arrangement allows the
two motors to be coupled for drilling fluid to flow straight from
one into the other. It also permits the reamer to be easily coupled
to the rotor of the first motor or the stator of the second
motor.
[0022] FIGS. 2 and 3 illustrate details of two examples of such an
earth boring tool. These examples share certain characteristics and
elements, which will be discussed first. Unless otherwise noted or
apparent from the context, each element is symmetrical about the
tool's central axis 28. Each has a top connection subassembly 30
having a threaded rod box 32 for connection to a drill string.
Connected to the top connection subassembly by support pin 34, is a
flex joint 36. The flex joint has fixed relationship with (i.e.,
does not substantially rotate with respect to) the drilling string
and tool, and extends down into a main body of each of the tools.
The main body is defined in part by an outer tool casing 39.
[0023] Mounted within the main body of each of the tools include an
upper positive displacement motor (PDM) 40 and a lower PDM 42. One
purpose of PDM 40 is to provide a relatively low-speed rotational
output for turning a reamer. One purpose of PDM 42 is to provide a
relatively high-speed rotational output for turning a pilot bit.
However, PDM 42 is rotated by PDM 40 and, therefore, the true
angular velocity of the "high speed" PDM 42 may not necessarily be
higher than the angular velocity of the output of the upper, "low
speed" PDM 40.
[0024] The upper, low speed PDM is coupled to a lower end of the
flex joint 36 in a substantially non-rotating or fixed relationship
by attaching stator 44 to flex joint 36. Rotor 46 of upper PDM 40,
which is an elastomer, rotates an outer body 48 of the upper PDM
40. Fluid under pressure flows from the drilling string (not shown)
into passage 50, which in turn carries it to the upper PDM 40,
causing the rotor 48 and, thus also, body 52 of the upper PDM to
turn. Small arrows throughout the figures indicate the direction of
fluid flow during operation.
[0025] Body 54 of the lower PDM 42 connects to body 52 of the upper
PDM. This connection is, in the example, threaded, though other
types of connections may be used. The connection causes the body of
the lower PDM to rotate with the body of the upper PDM. Stator 56
of the lower PDM 42 is thus coupled to, and turns with, the rotor
48 of the upper PDM 40. Rotor 58 of the lower PDM is connected to a
flex shaft 59, which in turn is connected to lower shaft 60. The
flex shaft provides, in essence, a flexible coupling between the
output of the lower PDM and the lower shaft that accommodates the
eccentric movement of the rotor 58 with respect to the center line
of the tool. A drill bit 62, on which a plurality of cutters (not
shown) are mounted, is attached to the free end of shaft 60. The
shaft includes a passageway 64 through its center. A portion of the
drilling fluid exiting the lower PDM is diverted through the
passageway to the drill bit.
[0026] Reamer 66 couples to body 54 of the lower PDM 42 through
inner bearing housing 68. In the illustrated embodiments, reamer 66
is attached to inner bearing housing 68 by a threaded connection,
and the bearing housing 68 is connected to the body 54 of the lower
PDM by a threaded connection.
[0027] Several sets of radial bearings support rotating components
within the body of the tool, namely radial bearing assemblies 70
and 78 support the relative rotation of the upper and lower PDMs in
each of the tools, and radial bearing assemblies 71 and 73 support
rotation of the lower shaft. Radial bearing assembly 70 includes a
radial bearing 72 and a bearing wear surface layer 76 disposed
between the tool casing 39 and upper bearing housing 74. The upper
bearing housing is connected to body 52 of the upper PDM, and thus
rotates with the body of the upper PDM. Bearing assembly 78
includes a radial bearing 80 disposed between lower bearing housing
68 and outer bearing housing 82. The outer bearing housing is
connected to casing 39 of the tool, preferably by a threaded
connection. Bearing assemblies 71 and 73 are located at opposite
ends of the lower shaft 60. They include radial bearings 75 and 79,
respectively, each with a wear surface 79.
[0028] A set of thrust bearings limit movement of rotating
components along the axis of the tool. Upper thrust bearing
assembly 84 include a pair a fixed bearings 86 and 88, and a pair
of moving bearings 90 and 92, each having a wear surface 113.
Spacer 94 acting against radial bearing 72 prevents upward movement
of the fixed bearing 86, and thus also of thrust bearing assembly
84. Locking nut 96 stops upward movement of the radial bearing.
Ledge 98, which is integrally formed in casing 39, prevents
downward movement of fixed bearing 88 and thus also of the thrust
bearing assembly. Moving bearings 90 and 92 are trapped by the
fixed bearings. Ledge 100 transfers the load on the rotating
components to the thrust bearing assembly. Some amount of lateral
movement of elements of the thrust bearing assembly is desirable,
as it permits drilling fluid to migrate into and down through outer
passageway 102, through the upper radial bearing assembly and then
through the upper thrust bearing assembly. Spacer 103 prevents
downward movement of bearing wear surface layer 76.
[0029] Lower thrust bearing assembly 105 has a construction similar
to that of the upper thrust bearing, with fixed bearings 106 and
108 and moving bearings 110 and 112, each with a wear surface 113.
The thrust bearing is trapped by the set of radial bearings 71 and
73, with shoulder or ledge 114 stopping upward lateral movement of
the bearings. Spacers are used to space apart the bearings and
facillitate flow of drilling fluids through the bearings. Spacer
116 keeps fixed bearings 106 and 108 spaced apart at the correct
distance. Lock nut 118 screws onto a threaded interior surface of
inner bearing housing 68 to prevent downward movement of the radial
bearing assemblies 71 and 73 and thrust bearing assembly 105. Like
the other radial and thrust bearings, this thrust bearing assembly
is also lubricated and cooled by drilling fluid. However, it is
cooled by fluid exiting lower PDM 42.
[0030] It is preferred that at least the thrust bearings, due to
expected high loading, be made of a wear resistant material, such
as a polycrystalline diamond compact or similar material.
[0031] The bearing assemblies are, in the example tools described
above and shown in FIGS. 2 and 3, not sealed. Drilling fluid pumped
through the tool lubricates and cools the bearings. As indicated by
arrows, a portion of the drilling fluid flowing into the tool is
diverted into for lubricating the radial bearing assemblies 70 and
87 and thrust bearing assembly 84. The fluid travels through
passageway 102 to bearing assembly 78 before it exits through
opening 104 between the bottom end of outer bearing housing 82 and
a shoulder of the inner bearing housing 68. Similarly, a portion of
drilling fluid exiting lower PDM 42 flows, as indicted by the
arrows, through radial bearing assemblies 71 and 73, and thrust
bearing assembly 105, before exiting the bottom of the tool.
[0032] Referring now just to FIG. 2, central, high speed bit 62,
which turns at a high speed relative to the tool, extends beyond
the end of tool, in front of the reamer. It forms a pilot hole
having a relatively smaller diameter, and the reamer enlarges it.
In the embodiment of FIG. 3, reamer 66 leads the central bit, the
reamer first cutting an annular bore and then the central bit
subsequently crushing the core.
* * * * *