Note: Descriptions are shown in the official language in which they were submitted.
CA 02715867 2010-09-28
TITLE
[0001] Method and apparatus for earth drilling at an angle
FIELD
[0002] There is described a method and associated apparatus for earth drilling
at an angle
with particular application for drilling horizontal well bores for hydrocarbon
producing wells.
BACKGROUND
[0003] A typical drilling motor assembly used in earth drilling has a power
section that
uses a moineau motor with a rotor and stator. In operation, drilling fluid is
pumped down a
drill string to the power section and, as the drilling fluid passes the rotor,
the rotor rotates in
an eccentric manner. A universal joint coupling is used to translate the
eccentric output from
the moineau motor into a concentric output that is used to rotate a drill bit.
[0004] In order to drill at an angle, an apparatus referred to as a "bent sub"
is placed
above the power section. The bent sub has an angular offset, which creates a
drilling angle
for the drilling motor assembly. This angular offset may be as little as a
fraction of a degree
to as much as three or even four degrees. In order to drill a straight hole,
the bent sub is
removed.
[0005] There will hereinafter be described an alternative method and apparatus
for
creating that offset angle that provides advantages over what is presently
being used, as will
hereinafter be further described.
SUMMARY
[0006] According to one aspect there is provided an apparatus for earth
drilling at an
angle which includes a tubular outer housing and a tubular inner mandrel. The
outer housing
has a concentric longitudinal axis and an interior surface defining an
interior bore. The
interior bore has an offset axis that is offset from the concentric
longitudinal axis. The inner
mandrel is positioned within the interior bore and has an exterior surface.
Bearings
positioned between the interior surface of the outer housing and the exterior
surface of the
inner mandrel support the inner mandrel for concentric rotation about the
offset axis of the
interior bore.
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[0007] According to another aspect there is provided a method for earth
drilling at an
angle. The method involves coupling a drill bit to a coupling apparatus having
a housing with
a concentric longitudinal axis that is co-axial with a drill string and a
concentrically rotating
output that rotates about an offset axis that is offset from the concentric
longitudinal axis of
the housing. With this type of coupling, the drill bit drills at an angle to
the drill string
defined by the offset axis.
[0008] The above described method and apparatus places the "bend" right at the
drill bit,
rather than above the power section. This positioning allows for the drilling
motor to
potentially drill a hole that deviates from vertical to horizontal within a
shorter radius.
[0009] The above described method and apparatus allows for more flexibility
when
drilling. If a relatively small angular offset is used, such as three quarters
of one degree, the
drill string will deviate when left in one rotational position and will drill
straight when rotated.
[0010] When being used with a power section having a moineau motor it is
preferred that
a universal joint coupling be provided within the outer housing to convert
eccentric rotation of
the moineau motor power section into concentric rotation of the inner mandrel.
It must be
remembered that there are other types of power sections that can be used, such
as turbines. A
turbine has a concentric output and does not need a universal joint coupling
to convert
eccentric rotation to concentric rotation. However, a turbine power section
may need a speed
reduction gear assembly to slow down the output of the turbine to a rotational
output better
suited for the drill bit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
[0012] FIG. 1 is a side elevation view, in section, of an apparatus for earth
drilling at an
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angle.
[0013] FIG. 2 is a detailed side elevation view, in section, of the tubular
outer housing
from the apparatus illustrated in FIG. 1.
[0014] FIG. 3 is a simplified side elevation view, in section, of the
apparatus of FIG. 1
attached as part of a drill string which includes a drill bit and a moineau
motor power section.
DETAILED DESCRIPTION
[0015] A apparatus for earth drilling generally identified by reference
numeral 10, will
now be described with reference to FIG. 1 through FIG. 3.
Structure and Relationship of Parts:
[0016] Referring to FIG. 1, apparatus 10 includes a tubular outer housing 12
and a
tubular inner mandrel 14. For ease of assembly outer housing 12 is shown as
having several
components 12a, 12b, and 12c that are connected by pin and box threaded
connections 16a
and 16b. Referring to FIG. 2, outer housing 12 has a concentric longitudinal
axis shown by
broken line 18. Outer housing 12 also has an interior surface 20 defining an
interior bore 22.
Interior bore 22 has an offset axis shown by broken line 24 that is offset
from concentric
longitudinal axis 18. Referring to FIG. 1, inner mandrel 14 is positioned
within interior bore
22 and has an exterior surface 26. For ease of assembly, inner mandrel 14 is
shown as having
several components 14a and 14b that are connected by pin and box threaded
connections 28a
and 28b. Radial Bearings 30 and thrust bearings 32 are positioned between
interior surface
20 of outer housing 12 and exterior surface 26 of inner mandrel 14. Both
radial bearings 30
and thrust bearings 32 support inner mandrel 14 for concentric rotation about
offset axis 24 of
interior bore 22. Radial bearings 30 are primarily intended to bear radial
loads. Radial
bearings 30 are illustrated as being a bushings. Thrust bearings 32 are
primarily intended to
bear axial loads. Two types of thrust bearings are provided 32a and 32b.
Thrust bearing 32a
bears an axial load when weight is being placed on drill bit 200, as shown in
FIG. 3, and
thrust bearing 32b bears off-bottom load when drill bit 200 is lifted off
bottom and suspended
by drill string 300. Belville springs 34 are used to place a preload upon
thrust bearings 32.
[0017] Referring to FIG. 1, this particular embodiment of apparatus 10 was
constructed
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for use with a power section having a moineau motor 400, as illustrated in
FIG. 3. For that
reason, a universal joint coupling, generally indicated by reference numeral
100, was included
within outer housing 12 to convert eccentric rotation of the moineau motor
power section into
concentric rotation of the inner mandrel 14. It will be appreciated that if
apparatus 10 had
been constructed for use with a power section having a turbine, universal
joint coupling 100
would not be necessary. It will also be appreciate, that apparatus 10 could be
coupled to an
existing coupling apparatus that already has incorporated within it a
universal joint coupling.
An eccentric rotor adaptor 102 is provided through which eccentric rotational
input is
received from the moineau motor power section 400, as shown in FIG. 3, into
universal joint
coupling 100. A concentric rotor adaptor 104 is provided through which
concentric rotational
output is transmitted from universal joint coupling 100 to mandrel 14. The
illustrated
universal joint coupling 100 is of conventional construction including a shaft
106 with
bulbous ends 108 and 110. Bulbous end 108 is received in a socket 112
positioned within
eccentric rotor adaptor 102. Bulbous end 110 is received in a socket 114
positioned within
concentric rotor adaptor 104. Drive balls 116 are positioned in bulbous ends
108 and 110.
Drive balls 116 are received in pockets 118 in sockets 112 and 114. Rotational
force is
transmitted from eccentric rotor adaptor 102 to shaft 106 by the engagement
between drive
balls 116 and pockets 118 in socket 112. Similarly, rotational force is
transmitted from shaft
106 to concentric rotor adaptor 104 by the engagement between drive balls 116
and pockets
118 in socket 114. Omni-directional movement required to translate eccentric
input into a
concentric output is accommodated by movement of bulbous end 108 within socket
112 and
bulbous end 110 within socket 114. Sealing boots 120 are clamped in position
to create
lubrication chambers 122 to hold lubrications to facilitate movement of
bulbous ends 108 and
110 within sockets 112 and 114, respectively. Lubrication is pumped into
lubrication
chambers 122 through grease passages 124.
Operation:
[0018] The use and operation of apparatus 10 will now be described. Referring
to FIG 3,
apparatus 10 is incorporated as part of a drill string 300 with moineau power
section 400
attached to housing 12 and drill bit 200 attached to mandrel 14. When attached
to moineau
power section 400, concentric longitudinal axis 18 of outer housing 12 is co-
axial with drill
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string 300. Drilling fluid is pumped down drill string 300 and serves to cause
eccentric
rotation of moineau motor power section 400. Referring to FIG. 1, this
eccentric rotational
input is input into universal joint coupling 100 through eccentric rotor
adaptor 102. A
concentric output is then output from universal joint coupling 100 into
mandrel 14 though
5 concentric rotor adaptor 104. Mandrel 14 rotates with a concentric rotation.
Referring to
FIG. 2, this concentric rotation is about offset axis 24 that is offset from
concentric
longitudinal axis 18 of outer housing 12. Referring to FIG. 3, this rotational
input from
apparatus 10 results in drill bit 200 drilling at an angle to drill string
300, as defined by offset
axis 24.
Advantages:
[0019] The above described method and apparatus places the "bend" right at the
drill bit,
rather than above the power section. If the offset axis 24 is offset by three
degrees, this
positioning allows for the moineau motor power section 400 to drill a hole
that deviates from
vertical to horizontal within a shorter radius.
[0020] The above described method and apparatus also allows for more
flexibility when
drilling. If a relatively small angular offset is used, such as three quarters
of one degree, the
drill string will deviate when left in one rotational position and will drill
straight when rotated.
This allows for steering of the drill bit using measuring while drilling
tools. It also avoid
having to trip out of the hole when shifting to straight drilling as one now
does with bent
housings.
[0021] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
[0022] The following claims are to be understood to include what is
specifically
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illustrated and described above, what is conceptually equivalent, and what can
be obviously
substituted. Those skilled in the art will appreciate that various adaptations
and modifications
of the described embodiments can be configured without departing from the
scope of the
claims. The illustrated embodiments have been set forth only as examples and
should not be
taken as limiting the invention. It is to be understood that, within the scope
of the following
claims, the invention may be practiced other than as specifically illustrated
and described.
