DOWNHOLE MOTOR FOR A DRILLING APPARATUS

MOTEUR DE FOND POUR APPAREIL DE FORAGE

English Abstract

A drilling motor (20) comprises a stator (21) and a rotor (23) rotatably mounted in a stator
(21). The stator (21) is provided with two opposed rod recesses (75) and two opposed exhaust ports
(33). In use motive fluid is pumped through a central channel (27) in the rotor (23) and through a
plurality of radially extending channels (58) into action chambers (31) between the rotor (23) and
the stator (21). The rotor (23) has two opposed seals (76) which engage the stator (21) and the rod
recesses (75) are each provided with rods (71) which, in use, also form a seal between the stator
(21) and the rotor (23). The seals (76) and rods (71) can be made of a variety of materials including
stainless steel. Two drilling motors (20, 50) can be arranged in parallel with their rotors out of phase
to provide a relatively smooth power output and inhibit stalling.

French Abstract

Un moteur de forage (20) comprend un stator (21) ainsi qu'un rotor (23) monté pivotant dans le stator (21). Le stator (21) est doté de deux évidements opposés (75) destinés à une tige, ainsi que de deux orifices de sortie (33). Lors du fonctionnement de ce moteur, le fluide moteur est pompé à travers une voie d'écoulement centrale (27) dans le rotor (23) ainsi qu'à travers une pluralité de conduits (58) s'étendant radialement à l'intérieur de chambres d'action (31) situées entre le rotor (23) et le stator (21). Le rotor (23) est pourvu de deux joints d'étanchéité opposés (76) entrant en contact avec le stator (21), et les évidements (75) des tiges sont pourvus chacun d'une tige (71) qui, lors de l'utilisation du moteur, forme également un joint entre le stator (21) et le rotor (23). Les joints (76) ainsi que les tiges (71) peuvent être fabriqués dans une pluralité de matériaux, et notamment dans de l'acier inoxydable. On peut disposer en parallèle deux moteurs de forage (20, 50) en déphasant leur rotor afin de procurer une puissance utile relativement régulière et d'empêcher qu'ils ne calent.

Claims

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Claims
1. A drilling motor which comprises a stator and a
rotor rotatably mounted in said stator, wherein said
stator is provided with a rod recess and an exhaust port,
wherein said rotor is provided with a rotor channel and
at least one channel for conducting motive fluid from
said rotor channel to a chamber between said rotor and
said stator, and wherein said rod recess is provided with
a rod which, in use, forms a seal between said stator and
said rotor.
2. A drilling motor as claimed in Claim 1, wherein said
rotor is provided with a seal for engagement with the
stator.
3. A drilling motor as claimed in Claim 1 or 2, wherein
said seal is made from a material selected from the group
consisting of plastics materials, polyethylethylketone,
metal, copper alloys and stainless steel.
4. A drilling motor as claimed in Claim 1, 2 or 3,
wherein said rod is made from a material selected from
the group consisting plastics materials,
polyethylethylketone, metal, copper alloys and stainless
steel.
5. A drilling motor as claimed in Claim 1, 2, 3, or 4,
wherein said stator is provided with a second rod recess,
each of said rod recesses being disposed opposite one
another, a second exhaust port, each of said exhaust
ports being disposed opposite one another, each of said
rod recesses being provided with a respective rod, and
wherein said motor is provided with a first seal and a
second seal which are disposed opposite one another.

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6. A drilling apparatus comprising two drilling motors
as claimed in any one of the preceding Claims, arranged
with their respective rotors connected together.
7. A drilling apparatus as claimed in Claim 6, wherein
said drilling motors are connected in parallel.
8. A drilling apparatus as claimed in Claim 6, wherein
said drilling motors are connected in series.
9. A drilling apparatus as claimed in Claim 6, 7 or 8,
wherein said drilling motors are arranged so that, in
use, one drilling motor operates out of phase with the
other.
10. A drilling apparatus as claimed in claim 9 wherein
said drilling motors each have two chambers, said two
chambers of the first drilling motor being arranged so as
to be 90° out of phase with the two chambers of the
second drilling motor.
11. A drilling rig comprising a drill string
incorporating a drilling apparatus as claimed in Claim 6,
7, 8 or 9 and a well tool rotatable by said drilling
apparatus.
12. A drilling rig as claimed in Claim 11, wherein said
well tool is a drill bit.
13. A pump comprising the motor of claim 1.

Description

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W 0 9511948$ PCT/GB95100069
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Downhole motor for a drilling apparatus
This invention relates to a drilling motor, to a
drilling apparatus including said drilling motor and to
a-drilling rig including said drilling apparatus.
V
Traditionally, well bores are drilled by rotating a
drill string with a motor situated at the surface.
Whilst this technique is quite satisfactory for drilling
vertical bores it is not suitable for deviated drilling
where it may be desired to drill a near horizontal
branch bore from a vertical bore. For this purpose it
is usual to employ a drilling motor which is disposed
near the drill bit and is powered by pumping hydraulic
or pneumatic fluid from the surface to the drilling
motor.
At the present time "Moineau" motors are used for
this purpose.
One of the difficulties with using such drilling
motors is that they do not operate reliably at tempera-
tures above about 120C (250F) and are thus not suit-
able for use in drilling most geothermal wells and other
wells where, the ambient temperature exceeds 120C.
Attempts have been made to replace parts of Moineau
motors with materials which will withstand higher tem-
peratures. However, these attempts have not been en-
tirely successfull.
The aim of at least preferred embodiments of the
present invention is to provide a drilling motor which
is relatively reliable particularly, but not exclusive-
ly, when operating at temperatures in excess of 120C.
According to one aspect of the present invention
there is provided a drilling motor which comprises a
stator and a rotor rotatably mounted in said stator,
' wherein said stator is provided with a rod recess and an
exhaust port, wherein said rotor is
r
id
d
p
ov
e
with a

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rotor channel and at least one channel for conducting
motive fluid from said rotor channel to a chamber be-
tween said rotor and said stator,-and wherein said rod ',
recess is provided with a rod which, in use, forms a
seal between said stator and said rotor.
Although not essential it is highly desirable that
the rotor be provided with a seal for engagement with '
the stator.
Preferably, said seal is made from a material
selected from the group consisting of plastics mater
ials, polyethylethylketone, metal, copper alloys and
stainless steel.
Advantageously, said rod is made from a material
selected from the group consisting of plastics mater- '
ials, polyethylethylketone, metal, copper alloys and
stainless steel.
Preferably, said stator is provided with two rod t
recesses which are disposed opposite one another, two
exhaust ports which are disposed opposite one another,
each of said rod recesses is provided with a respective
rod, and said rotor has two seals which are disposed
opposite one another.
According to another aspect, the present invention
provided a drilling apparatus comprising two drilling
motors in accordance with the invention arranged with
their respective rotors connected together.
Preferably, said drilling motors are connected in
parallel although they could be connected in series if
desired.
Advantageously, said drilling motors are arranged
so that, in use, one drilling motor operates out of
phase with the other. Thus, in the preferred embodiment
each drilling motor has two chambers and the chambers in
the first drilling motor-are 9D° out of phase with the
chambers in the second drilling motor. Similarly, in an

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embodiment in which each drilling motor has four cham-
bers, the chambers in the first drilling motor would
preferably be 45° out of phase with the chambers on the
second drilling motor. This arrangement helps ensure a
smooth power output and inhibits stalling.
The present invention also provides a drilling rig
including a drill string provided with drilling appara-
tus in accordance with the invention and a well tool
rotatable by said drilling apparatus.
The well tool will normally be a drill bit although
it could comprise, for example, a rotatable cleaning
head. The well tool could also be a drill used to dig a
pit (sometimes referred to as a "glory hole") in the sea
bed to house sub-sea well head equipment.
20
30

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For a better understanding of the present invention
reference will now be made, by way of example, to they
accompanying drawings in which:- '
Fig. 1 is a longitudinal cross sectional view of
one embodiment of drilling apparatus according to the'
i
present invention;
Fig. 2A-2D are cross sectional views along line A-A
of Fig. 1 showing the rotor in four different positions; i
Fig. 3A-3D are cross sectional views along line B-B
of Fig. 1 showing the rotor in four different positions;
and
Fig. 4 is a cross sectional view of a typical,
bearing housing and drill bit.
Referring now to Fig. 1, there is shown a drilling
apparatus which is generally identified by reference'
numeral 10. The drilling apparatus 10 comprises a first
motor 20 and a second motor 50.
The first motor 20 comprises a stator 21 and a
rotar 23. A top portion 22 of the rotor 23 extends
through an upper bearing assembly 24 which comprises a
thrust bearing 26 and seals 25.
Motive fluid, e.g. water, drilling mud or gas under
pressure, flows down through a central sub channel 12,
into a central rotor channel 27, and then out through
rotor flow channels 28 into action chambers 31 and 32.
Following a motor power stroke, the motive fluid,
flows through exhaust ports 33, and then downwardly
through an annular channel circumjacent the stator 21~
and flow channels 35 in a lower bearing assembly 34. A,
portion 36 of the rotor 23 extends through the lower
bearing assembly 34 which comprises a thrust bearing 37'.
and seals 38.
The ends of the stator 21 are castellated and the
castellations engage in recesses in the respective upper'
bearing assembly 24 and lower bearing assembly 34'

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PCT/GB95/00069
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respectively to inhibit rotation of the stator 21. The
upper bearing assembly 24 and lower bearing assembly 34
are a tight fit in an outer tubular member 14 and are
held against rotation by compression between threaded
sleeves 16 and 84.
A splined union 39 joins a splined end of the rotor
23 to a splined end of the rotor 53 of the second motor
50. The second motor 50 has a stator 51.
A top portion 52 of the rotor 53 extends through an
upper bearing assembly 54. Seals 55 are disposed be
tween the upper bearing assembly 54 and the exterior of
the top portion 52 of the rotor 53. The rotor 53 moves
on thrust bearings 56 with respect to the upper bearing
assembly 54.
Motive fluid flows into a central rotor channel 57
from the central rotor channel 27 and then out through
rotor flow channels 58 into action chambers 61 and 62.
Following a motor power stroke, the motive fluid flows
through exhaust ports 63 and then downwardly through an
annular channel circumjacent the stator 51 and flow
channels 65 in a lower bearing assembly 64. A portion
66 of the rotor 53 extends through the lower bearing
assembly 64. The rotor 53 moves on thrust bearings 67
with respect to the lower bearing assembly 64 and seals
68 seal the rotor-bearing assembly interface. Also
motive fluid which flowed through the flow channels 35
in the lower bearing assembly 34, flows downwardly
through channels 79 in the upper bearing assembly 54,
past stator 51 and through flow channels 65 in the lower
bearing assembly 64.
The upper bearing assembly 54 and lower bearing
assembly 64 are a tight fit in an outer tubular member
18 and are held against rotation by compression between
threaded sleeve 84 and a lower threaded sleeve (not
shown).

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A lower sub is=threadedly connected to the stator,
51 via threads 70 and provides interconnection with a
drill bit connection/bearing housing S (Fig. 4) and a
typical drill bit D (Fig. 4). A solid plug or a flow
restrictor 78 at the bottom of the rotor 53 may be used
to restrict motive fluid flow to the drill bit D and to
ensure that a desired amount of motive fluid passes
through the motors.
Figs. 2A-2D and 3A-3D depict a typical cycle for
the first and second motors 20 and 50 and show the
status of the two motors with respect to each other at
various times in the cycle. For example, Fig. 2c shows
an exhaust period for the first motor 20 while Fig. 3_c,~,
at that same moment, shows a power period for the second
motor 50.
As shown in Fig. 2A, motive fluid flowing through'
the rotor flow channels 28 enters the action chambers 31
and 32. Due to the geometry of the chambers (as discus-
sed below) and the resultant forces, the motive fluid
moves the rotor in a clockwise direction as seen in Fig.
2B. The action chamber 31 is sealed at one end by a
rolling vane rod 71 which abuts an exterior surface 72~
of the rotor 23 and a portion 74 of a rod recess 75.
At the other end of the action chamber 31, a seal
76 on a lobe 77 of the rotor 23 sealingly abuts an~
interior surface of the stator 21.
As shown in Fig. 2_B, the rotor 23 has moved to a
point near the end of a power period.
As shown in Fig. 2C, motive fluid starts exhausting,
at this point in the motor cycle through the exhaust
ports 33.
As shown in Fig. 2D, the rolling vane rods 71 and
seals 76 have sealed off the action chambers and motive
fluids flowing thereinto will rotate the rotor 23 until ,
the seals 76 again move past the exhaust ports 33.

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PCT/GB95/00069
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The second motor 50 operates as does the first
motor 20; but, as preferred, and as shown in Figs. 3A
3D, the two motors are out of phase by 90° so that as
one motor is exhausting motive fluid the other is provi
ding power.
The seals 76 are, in one embodiment, made of poly-
ethylethylketone (PEEK). The rolling vane rods 71 are
also made from PEEK. The rotors (23, 25) and stators
(21, 51) are preferably made from corrosion resistant
materials such as stainless steel.
When a seal 76 in the first motor 20 rotates past
an exhaust port 33, the motive fluid that caused the
turning exits and flows downward through the stator
adaptor 84 (Fig. 1), then through the channels 79, past
the exhaust ports 63, the flow channels 65, the bearing
housing S (Fig. 4) and subsequently to the drill bit D
(Fig. 4). All motive fluid that enters the top sub 11
finally exits to the drill bit D.
During tests, an apparatus similar to the apparatus
shown in Fig. 1 was shown to develop the same rotational
power as a conventional Moineau motor of approximately
three times the length. This is a most significant
advantage when operating in a deviated well.
The apparatus of Fig. 1 may be used as a pump by
either manually or mechanically turning the drill bit D
or housing S in a direction opposite to that of Fig. 2A;
or by connecting a rotative mechanism to the rotor 53
and rotating it in a direction opposite to that of Fig.
2A. -With the apparatus in a wellbore, this is achieved
by jamming the bit into a formations so it does not turn
and then rotating the tubular string above the apparatus
of Fig. 1.
Various modifications to the embodiment described
are envisaged, for example the seal 76 can be made of
other durable materials such as copper alloys and steels

PCT1GB95I00069 ~~
WO 95119488
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such as stainless steel. Stainless steel is particular-,
ly useful in high temperature environments and has been,
successfully tested at 500°F (260°C). This compares ,
with a maximum operating temperature of 250°F-(121°C) of~
conventional Moineau motors. Whereas the first motor 20
and second motor 50 are shown operating in parallel they
could also be operated in series if desired.
15
25
35

Representative Drawing