GENERATEUR D'IMPULSION DE PRESSION DE FLUIDE DE FOND DE TROU

DOWNHOLE FLUID PRESSURE PULSE GENERATOR

Abrégé anglais

A fluid pressure pulse generator forms part of a tubing string for use in a
wellbore. The
generator includes a tubular stator and a tubular rotor disposed for rotation
within the stator
to periodically align rotor transverse openings with stator transverse
openings to permit fluid
communication from a rotor longitudinal bore to a stator outer surface. The
rotor is disposed
longitudinally between bearing members to define a pair of end gaps sized for
creation of end
fluid film bearings. The stator inner surface defines a plurality of
longitudinally extending
grooves. The rotor transverse openings are adapted to direct fluid away from
the rotor
longitudinal bore in a direction having a tangential component in respect to
the rotor
longitudinal bore, and into the grooves. The stator transverse openings are
adapted to direct
away from the stator outer surface in at least six different directions.

Revendications

CLAIMS
1. A fluid pressure pulse generator for forming part of a tubing string for
use in a
wellbore, the fluid pressure pulse generator comprising:
(a) a pair of longitudinally spaced apart annular bearing members, wherein
each
of the bearing members comprises an annular bearing surface, and defines a
bearing member opening for fluid communication with the tubing string; and
(b) a tubular stator and a tubular rotor disposed for rotation within the
stator to
periodically align at least one rotor transverse opening with at least one
stator
transverse opening to permit fluid communication from a rotor longitudinal
bore to a stator outer surface;
(c) wherein the rotor is disposed longitudinally between the bearing
members with
the rotor longitudinal bore in fluid communication with the bearing member
openings, and wherein rotor longitudinal ends and the bearing surfaces define
therebetween a pair of end gaps in fluid communication with the bearing
member openings and sized for creation of end fluid film bearings.
2. The fluid pressure pulse generator of claim 1, further comprising a pair
of crossover
subs adapted for connecting the stator to the tubing string, and wherein each
bearing
member is disposed longitudinally between and in abutting relationship with
one of
the subs and one of the stator longitudinal ends.

3. The fluid pressure pulse generator of claim 1, further comprising a pair
of
longitudinally spaced apart annular bushings, wherein each bushing is disposed
in an
annular space defined between a stator inner surface and a rotor outer
surface, and
wherein the rotor outer surface and bushing inner surfaces define therebetween
a pair
of inner annular gaps in fluid communication with the bearing member openings
and
sized for creation of inner annular fluid film bearings.
4. The fluid pressure pulse generator of claim 1, wherein the stator inner
surface and
bushing outer surfaces define therebetween outer annular gaps in fluid
communication
with the bearing member openings and sized for creation of outer annular fluid
film
bearings.
5. The fluid pressure pulse generator of claim 3, wherein the end gaps
extend between
bushing longitudinal ends and the bearing surfaces.
6. A fluid pressure pulse generator for forming part of a tubing string for
use in a
wellbore, the fluid pressure pulse generator comprising:
(a) a tubular stator defining at least one stator transverse opening, and
comprising
a stator inner surface defining a plurality of longitudinally extending
grooves;
and
(b) a tubular rotor defining at least one rotor transverse opening adapted
to direct
fluid away from a rotor longitudinal bore in a direction having a tangential
component in respect to the rotor longitudinal bore, wherein the rotor is
21

disposed for rotation within the stator to periodically align the at least one
rotor
transverse opening with the at least one stator transverse opening to permit
fluid communication from the rotor longitudinal bore to an outer surface of
the
stator, followed sequentially by alignment of the at least one rotor
transverse
opening with the grooves.
7. A fluid pressure pulse generator for forming part of a tubing string for
use in a
wellbore, the fluid pressure pulse generator comprising a tubular stator and a
tubular
rotor disposed for rotation within the stator to periodically align at least
one rotor
transverse opening with at least six stator transverse openings to permit
fluid
communication from a rotor longitudinal bore to a stator outer surface,
wherein the at
least six stator transverse openings are adapted to direct away from the
stator outer
surface in at least six different directions.
8. The fluid pressure pulse generator claim 7, wherein the at least one
rotor transverse
openings comprises at least one pair of rotor transverse openings, wherein the
pair of
transverse openings are positioned on the rotor such that rotation of the
rotor within
the stator aligns the pair of rotor transverse openings simultaneously with a
pair of the
at least six stator transverse openings.
9. The fluid pressure pulse generator of claim 7, wherein each of the
stator transverse
openings has a different longitudinal position on the stator.
22

Description

DOWNHOLE FLUID PRESSURE PULSE GENERATOR
FIELD OF THE INVENTION
[0001] The present invention relates to oil and gas production from wellbores,
and more
particularly to a fluid pressure pulse generator and methods of using the
same.
BACKGROUND OF THE INVENTION
[0002] In the field of oil and gas production, fluid pressure pulse generators
are used to
stimulate produced fluids from a wellbore, enhance cleaning of the wellbore,
and enhance
injection sweeps in the wellbore. A typical pulse generator is connected to a
tubing string,
whether made of pipe segments or coiled tubing. The pulse generator includes a
tubular stator,
a tubular rotor, and an external motor (e.g., a submersible well motor) that
drives rotation of
the rotor within the stator to periodically align transverse openings defined
by them. Fluid is
pumped down the tubing string and exits transversely through the periodically
aligned
openings into the wellbore, thereby creating a fluid pressure pulse in the
wellbore.
[0003] One limitation associated with pulse generators is that high fluid
pressure acting on
the rotor increases the bearing force of the rotor on its bearing surfaces.
This increases the
rotational friction acting on the rotor, which impedes rotation of the rotor
and accelerates wear
of the rotor and the bearing surfaces. Another limitation is that the
mechanical coupling
between the external motor and the rotor may degrade or fail. Another
limitation is that the
stator typically has pulse openings that emit fluid pressure pulses in only
one or two transverse
directions, which may limit the pulse generator's efficacy for certain
applications.
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SUMMARY OF THE INVENTION
[0004] The present invention comprises a fluid pressure pulse generator for
forming part of a
tubing string for use in a wellbore. The fluid pressure pulse generator
comprises a tubular
stator and a tubular rotor disposed for rotation within the stator to
periodically align at least
one rotor transverse opening with at least one stator transverse opening to
permit fluid
communication from a rotor longitudinal bore to a stator outer surface.
[0005] In one aspect, a fluid pressure pulse generator comprises a pair of
longitudinally
spaced apart annular bearing members, wherein each of the bearing members
comprises an
annular bearing surface, and defines a bearing member opening for fluid
communication with
the tubing string. The rotor is disposed longitudinally between the bearing
members with the
rotor longitudinal bore in fluid communication with the bearing member
openings. Each rotor
longitudinal end and a bearing surface define an end gap which is in fluid
communication with
the bearing member openings and sized for creation of end fluid film bearings.
[0006] In one embodiment, the fluid pressure pulse generator also comprises a
pair of
crossover subs adapted for connecting the stator to the tubing string. Each
bearing member is
disposed longitudinally between and in abutting relationship with one of the
subs and one of
the stator longitudinal ends.
[0007] In one embodiment, the fluid pressure pulse generator also comprises a
pair of
longitudinally spaced apart annular bushings. Each bushing is disposed in an
annular space
defined between a stator inner surface and a rotor outer surface. The rotor
outer surface and
bushing inner surfaces define therebetween a pair of inner annular gaps in
fluid
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communication with the bearing member openings and sized for creation of inner
annular
fluid film bearings. The stator inner surface and bushing outer surfaces may
define
therebetween outer annular gaps in fluid communication with the bearing member
openings
and sized for creation of outer annular fluid film bearings. The end gaps may
extend between
bushing longitudinal ends and the bearing surfaces.
[0008] In another aspect, the pulse generator comprises a stator having an
inner surface which
defines a plurality of longitudinally extending grooves. The at least one
rotor transverse
opening is adapted to direct fluid away from the rotor longitudinal bore in a
direction having
a tangential component in respect to the rotor longitudinal bore. The rotor is
disposed for
rotation within the stator to periodically align the at least one rotor
transverse opening with
the at least one stator transverse opening, followed sequentially by alignment
of the at least
one rotor transverse opening with the grooves.
[0009] In another aspect, the at least one stator transverse opening includes
at least four or six
stator transverse openings. The at least four or six stator transverse
openings are adapted to
direct away from the stator outer surface in at least four or six different
directions.
[0010] In one embodiment, the at least one rotor transverse openings comprises
at least one
pair of rotor transverse openings. The pair of transverse openings are
positioned on the rotor
such that rotation of the rotor within the stator aligns the pair of rotor
transverse openings
simultaneously with a pair of the at least four or six stator transverse
openings.
[0011] In one embodiment, each of the stator transverse openings has a
different longitudinal
position on the stator.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the drawings shown in the specification, like elements may be
assigned like
reference numerals. The drawings are not necessarily to scale, with the
emphasis instead
placed upon the principles of the present invention. Additionally, each of the
embodiments
.. depicted are but one of a number of possible arrangements utilizing the
fundamental concepts
of the present invention.
[0013] Figure 1 shows a top perspective view of an embodiment of the pulse
generator of the
present invention.
[0014] Figure 2 shows an exploded top perspective view of the pulse generator
of Figure 1.
[0015] Figure 3 shows a cross-sectional view of the pulse generator of Figure
1 along its
longitudinal midline.
[0016] Figure 4 shows the uphole portion of Figure 3 at an enlarged scale.
[0017] Figure 5 shows a top view of the stator of the pulse generator of
Figure 1.
[0018] Figure 6 shows a cross-sectional view of the stator of Figure 5 along
longitudinal
section line A-A of Figure 5.
[0019] Figure 7 shows an elevation view of the stator of Figure 5 from the
perspective of line
B-B of Figure 5.
[0020] Figure 8 shows an elevation view of the stator of Figure 5 from the
perspective of line
C-C of Figure 5.
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[0021] Figure 9 shows a top view of the rotor of the pulse generator of Figure
1.
[0022] Figure 10 shows a cross-sectional view of the rotor of Figure 9 along
longitudinal
section line A-A of Figure 9.
[0023] Figure 11 shows a cross-sectional view of the rotor of Figure 10 along
transverse
section line B-B of Figure 10.
[0024] Figure 12 shows a cross-sectional view of the rotor of Figure 10 along
longitudinal
section line C-C of Figure 10.
[0025] Figure 13 shows a side elevation view of the pulse generator of Figure
1 in a tubing
string in a wellbore.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0026] Definitions. Any term or expression not expressly defined herein shall
have its
commonly accepted definition understood by a person skilled in the art.
[0027] As used herein, "longitudinal" means aligned with the axial direction
of tubular
elements associated with the invention, and "transverse" means a direction
that is substantially
perpendicular to the longitudinal direction.
[0028] As used herein "uphole" and "downhole" are used to describe relative
longitudinal
positions of parts in the wellbore. One skilled in the art will recognize that
wellbores may not
be strictly vertical or horizontal, and may be slanted or curved in various
configurations.
Therefore, the longitudinal direction may or may not be vertical (i.e.,
perpendicular to the
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plane of the horizon), and the transverse direction may or may not be
horizontal (i.e., parallel
to the plane of the horizon). Further, an "uphole" part may or may not be
disposed above a
"downhole" part.
[0029] As used herein, "fluid" means either a liquid, a liquid mixed with
solids and/or
entrained gases, or a gas. Non-limiting examples of fluids that may be used in
conjunction
with the present invention include drilling fluids conventionally referred to
as "drilling mud",
and nitrogen gas.
[0030] As used herein, "tubing string", refers to any tubular structure in a
wellbore that may
be used to convey fluid in a wellbore. Non-limiting examples of tubing string
include rigid
pipe segments, and coiled tubing.
[0031] Pulse generator. Figures 1 to 4 show an embodiment of a fluid pressure
pulse
generator (10) of the present invention. In this embodiment, the pulse
generator (10) includes
a tubular stator (20), a tubular rotor (40), annular bushings (60), annular
washers (80), annular
bearing members (100), 0-ring gaskets (120), and crossover subs (140). In this
embodiment,
the uphole bushing (60a), washer (80a), annular bearing member (100a), 0-ring
gasket (120a)
and crossover sub (140a) are the same as the corresponding downhole components
(60b, 80b,
100b, 120b, 140b), such that this embodiment of the fluid pressure pulse
generator (10) is
substantially symmetric about its longitudinal center.
[0032] Stator. The stator (20) defines a stator longitudinal bore (28) (Figure
6) that receives
.. the rotor (40), the bushings (60), and washers (80). The stator (20) also
defines stator
transverse openings (32) that permit fluid communication from the rotor
transverse openings
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(52) (Figures 10 to 12), when aligned with the stator transverse openings
(32), to outside of
the stator (20).
[0033] In one embodiment, as shown in Figures 5 to 8, the stator (20) is made
of stainless
steel (e.g., American Iron and Steel Institute (AISI) grade 4330 or 4340 alloy
steel) and is in
the form of a cylindrical tubular member having a total longitudinal length of
about 4.125
inches and an outer diameter of about 1.7 inches. The length and diameter may
be varied in
different embodiments. In this embodiment, as shown in Figure 6, the stator
(20) is formed
from a stator inner mandrel (22) surrounded by a stator outer sleeve (24). The
stator inner
mandrel (22) has a stator inner surface (26) that defines the stator
longitudinal bore (28). The
stator outer sleeve (24) defines a stator outer surface (30). In other
embodiments, the stator
(20) may be formed from one piece rather than from the stator inner mandrel
(22) and the
stator outer sleeve (24).
[0034] In this embodiment, the stator (20) defines six stator transverse
openings (32a to 320
permitting fluid communication from the stator inner surface (26) to the
stator outer surface
(30). Each stator transverse opening (32) has a diameter of about 7/32 inches
(0.219 inches)
at the stator outer surface (30). The angular distance between adjacent stator
transverse
openings (32) is about 60 degrees. Stator transverse openings (32a, 32d) are
separated by
about 180 degrees from each other. In general, the stator transverse openings
(32) have a
diameter of about 0.219 inches at the stator inner surface 926), except that
stator transverse
openings (32a, 32d) have an enlarged diameter of about 0.600 inches at the
stator inner surface
(26) to accommodate fluid exiting the rotor radial openings (52a, 52b, 52c)
tangentially to the
rotor longitudinal bore (44) as discussed below. Stator transverse openings
(32a, 32d) are
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positioned at about the longitudinal center of the stator (20). Stator
transverse opening (32b)
is about 0.424 inches below the longitudinal center of the stator (20). Stator
transverse opening
(32c) is about 0.812 inches above the longitudinal center, of the stator (20).
Stator transverse
opening (32e) is about 0.813 inches below the longitudinal center of the
stator (20). Stator
transverse opening (320 is about 0.408 inches above the longitudinal middle of
the stator (20).
In other embodiments, the stator (20) may have a different number and
arrangement of stator
transverse openings (32).
100351 In this embodiment, as shown in Figure 5, the stator inner surface (26)
has a grooved
portion (34) which defines a plurality of elongate grooves that extend
longitudinally for about
0.30 inches on either side of the longitudinal center of the stator (20). It
will be understood
that the grooved portion (34) extends around the stator inner surface (26) to
the longitudinal
cross-section opposite to that shown in Figure 5. The grooved portion (34)
enhances rotation
of the rotor (40) within the stator longitudinal bore (28), as described
below.
100361 Rotor. The rotor (40) defines rotor transverse openings (52) that
permit fluid
communication from the rotor longitudinal bore (44) to the stator transverse
openings (32)
when the rotor transverse openings (52) are aligned with the stator transverse
openings (32).
In embodiments, some or all of the stator transverse openings (32) also permit
fluid
communication from the rotor longitudinal bore (44) to the grooved portion
(34) of the stator
inner surface (26).
100371 In one embodiment, as shown in Figures 9 to 12, the rotor (40) is made
of stainless
steel (e.g., AISI grade 4330 or 4340 alloy steel), and is in the form of a
cylindrical tubular
member having a total longitudinal length which is just slightly shorter than
the total length
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of the stator (20), as discussed below. The rotor (40) has a rotor inner
surface (42) defining a
rotor longitudinal bore (44), and a rotor outer surface (46). A rotor middle
portion (48) fits
within close tolerance of the stator inner surface (26) without preventing
rotation of the rotor
(40) within the stator longitudinal bore (28). In comparison with the rotor
middle portion (48),
the rotor end portions (50a, 50b) have a reduced outer diameter so that they
and the stator
inner surface (26) define an annular space therebetween for the bushings (60a,
60b) and
washers (80a, 80b), as may be seen in Figures 3 and 4.
100381 In this embodiment, the rotor (40) defines three rotor transverse
openings (52a, 52b,
52c) permitting fluid communication from the rotor inner surface (42) to the
rotor outer
surface (46). The rotor transverse openings (52a, 52b, 52c) may have a
diameter of about 5/64
inches (0.078 inches). The angular distance between adjacent rotor transverse
openings (52a,
52b, 52c) is about 120 degrees. As shown in Figure 11, the rotor transverse
openings (52a,
52b, 52c) are adapted to direct fluid away from a rotor longitudinal bore (44)
in a direction
having a tangential component relative to the rotor longitudinal bore (44) so
that fluid flowing
from the rotor longitudinal bore (44) through the rotor transverse openings
(52a, 52b, 52c)
causes the rotor (40) to rotate. In this embodiment, the rotor transverse
openings (52a, 52b,
52c) are oriented tangentially to the rotor longitudinal bore (44). However,
the rotor transverse
openings (52a, 52b, 52c) may be adapted to direct fluid away from a rotor
longitudinal bore
(44) in a direction having a tangential component relative to the rotor
longitudinal bore (44),
so long as the rotor transverse openings (52a, 52b, 52c) direct fluid in a
direction that is non-
perpendicular to the rotor outer surface (46). In other embodiments, the rotor
(40) may be
driven by a motor mechanically coupled to the rotor (40). The rotor transverse
openings (52a,
52b, 52c) are positioned at about the longitudinal center of the rotor (40).
Accordingly, the
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rotor transverse openings (52a, 52b, 52c) will periodically align, one at a
time, with one of the
stator transverse openings (32a, 32d) and the grooved portion (34) of the
stator inner surface
(26) as the rotor (40) rotates within the stator longitudinal bore (28).
[0039] In this embodiment, the rotor (40) also defines four rotor transverse
openings (52d,
52e, 52f, 52g) permitting fluid communication from the rotor inner surface
(42) to the rotor
outer surface (46). The rotor transverse openings (52d, 52e, 52f, 52g) have a
diameter of about
3/16 inches (0.188 inches). The angular distance between adjacent ones of the
rotor transverse
openings (52d, 52e, 52f, 52g) is about 90 degrees, with rotor transverse
opening 52(d) being
in angular alignment with the rotor transverse opening (52a) on the rotor
outer surface (46).
[0040] In this embodiment, the rotor transverse opening (52d) is
longitudinally aligned with
the stator transverse opening (32c), and rotor transverse opening (52g) is
longitudinally
aligned with stator transverse opening (32e). The angular distance between
rotor transverse
openings (52d, 52g) is about 180 degrees, and the angular distance between
stator transverse
openings (32c, 32e) is also about 180 degrees. Accordingly, periodic alignment
of openings
(32c, 52d) will coincide with periodic alignment of openings (32e, 52g), as
the rotor (40)
rotates within the stator longitudinal bore (28).
[0041] In this embodiment, the rotor transverse opening (52e) is
longitudinally aligned with
the stator transverse opening (320. The rotor transverse opening (520 is
longitudinally
aligned with stator transverse opening (32b). The angular distance between
rotor transverse
openings (52e, 520 is about 180 degrees, and the angular distance between
stator transverse
openings (32f, 32b) is also about 180 degrees. Accordingly, periodic alignment
of openings
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(32f, 52e) will coincide with periodic alignment of openings (32b, 520, as the
rotor (40)
rotates within the stator longitudinal bore (28).
[0042] Bushings and washers. In one embodiment, the bushings (60) provide
annular and
end bearing surfaces for the rotor (40). The washers (80) avoid direct
frictional contact
=
between the end bearing surfaces of the bushings (60) and the rotor (40).
[0043] In one embodiment, as shown in Figures 2 to 4, the annular bushings
(60) are made of
a suitably durable and low-friction polymer material, such as polyether ether
ketone (PEEK),
and are in the form of a cylindrical tubular member, which may have a
longitudinal length of
about 0.935 inches. PEEK is advantageous as it is known to exhibit excellent
chemical
resistance, low permeability, and low moisture absorption.
[0044] The washers (80) may also be made of a suitable polymer or metal. In
one
embodiment, the washers (80) are made of stainless steel (e.g., NitronicTM
alloy (AK Steel,
West Chester Township, Ohio, United States)), and may have a longitudinal
dimension
(thickness) of about 0.062 inches.
[0045] Figure 4 shows the uphole portion of the fluid pressure pulse generator
(10) at an
enlarged scale. It will be understood that the downhole portion of the pulse
generator is
substantially the same, but as a mirror image. In this embodiment, after the
rotor (40) is
inserted in the stator longitudinal bore (28), the washers (80) are inserted
into the stator
longitudinal bore (28) in abutting relationship with the shoulder of the rotor
(40) formed at
the junction of the rotor middle portion (48) and one of the rotor end
portions (50).
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Subsequently, the bushings (60) are inserted into the stator longitudinal bore
(28) in abutting
relationship with the washers (80).
100461 Annular bearing member, 0-ring gaskets, and crossover subs. The uphole
annular
bearing member (100a) defines an uphole annular bearing member opening (102a)
that
permits fluid communication between an uphole portion of a tubing string into
the rotor
longitudinal bore (44). The downhole annular bearing member (100a) defines a
downhole
annular bearing member opening (102a) that permits fluid communication between
the rotor
longitudinal bore (44) and a downhole portion of a tubing string. The bearing
members (100)
also define annular bearing surfaces (104a) in relation to the end of the
rotor (40), as shown
in Figure 4. In one embodiment, the annular bearing members (100) are made of
stainless steel
(e.g., Nitronic TM alloy). The outer periphery of the annular bearing member
(100a) abuts
against the end of the stator (20). The annular bearing member (100a) has a
central tubular
portion that extends into the rotor longitudinal bore (44) for fluid
communication between the
crossover sub bore (142a) and the rotor longitudinal bore (44) via the bearing
member opening
(102a).
100471 The 0-ring gasket (120a) seals between the annular bearing member
(100a) and the
crossover sub (140a), so as to prevent fluid flow between the interfacing
surfaces, and are
made of a suitable elastomer (e.g. rubber, or Viton 75TM fluorocarbon
elastomer; DuPont
Company, Wilmington, Delaware, United States). In this embodiment, the gasket
(120a) is
received in an annular grooves defined by the annular bearing member (100a).
100481 The crossover subs (140) connect the stator (20) to uphole and downhole
portions of
a tubing string, and define a crossover sub bore (142) permitting fluid
communication between
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the tubing string portions to the rotor longitudinal bore (44) via the annular
bearing member
openings (102). In one embodiment, the crossover subs (140) are made of
stainless steel (e.g.,
AISI grade 4330 or 4340 alloy steel), and are in the form of a cylindrical
tubular members.
Each crossover sub (140) has a threaded "box" end for attachment to a
complementary
threaded "pin" end of the stator (20), and a threaded "pin" end for attachment
to a
complementary threaded "box" end of a tubing string.
[0049] In this embodiment, after the bushings (60) are inserted into the
stator longitudinal
bore (28), the annular bearing members (100) and 0-ring gaskets (120) are
placed into the
"box" end of the crossover subs (140). The threaded "box" ends of the
crossover subs (140)
are then screwed tightly onto the threaded "pin" ends of the stator (20), so
that the 0-ring
gaskets (120) create a fluid-tight seal at the interfacing and abutting
surfaces of the annular
bearing members (100) and the crossover subs (140).
[0050] Fluid film bearings. In embodiments of the present invention, the
device is configured
with at least one fluid bearing, created by gaps between adjacent surfaces.
Preferably, the gap
is less than about 0.01 inches, and more preferably less than about 0.008
inches. Figure 4
shows a cross-sectional view of an uphole portion of the pulse generator of
Figure 1, at an
enlarged scale relative to Figure 3. Again, it will be understood that the
downhole portion of
the pulse generator is substantially the same, but longitudinally inverted. In
this embodiment
of the pulse generator (10), the total length of the stator (20) is 4.125
inches, whereas the total
length of the rotor (40) is about 4.119 inches, for a difference in length of
about 0.006 inches.
Preferably, this difference in length is less than about 0.01 inches, and more
preferably less
than about 0.008 inches. Accordingly, when the rotor (40) is longitudinally
centered within
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the stator longitudinal bore (28), the rotor (40) and the bushing (80) are
separated from the
annular bearing surface (104) of the bearing member (100) by an end gap (160a)
having a
longitudinal length of about 0.003 inches. The size of the gap (160a) in
Figure 4 has been
exaggerated for clarity and is not shown to scale. Fluid under pressure can
flow into the end
gap (160a) to form a thin film of pressurized fluid that separates the rotor
(40) and bushing
(60a) from the annular bearing surface (104) of the annular bearing member
(100). This thin
film of pressurized fluid provides a fluid film bearing for the rotor (40) and
bushing (60a). In
other embodiments, the size of the gap (160a) may be different. A person
skilled in the art
may be able to determine the size of the gap needed to create a fluid film
bearing having regard
to the mechanical properties and pressure of a particular fluid. In the
embodiment shown in
Figure 4, the inner diameter of the annular bushing (60a) and the washer (80a)
are thousandths
of an inch greater than the outer diameter of the rotor end portion (50a) to
create an inner
annular gap (162a) therebetween. Their outer diameters are thousandths of an
inch less than
the diameter of the portion of the stator inner bore (28) in which they reside
to create an
annular outer gap (164a) therebetween. In use, the inner annular gap (162a)
and outer annular
gap (162a) allow for the creation of an inner annular fluid film bearings, and
an outer annular
fluid film bearing, respectively. Further, as shown in Figure 4, the combined
longitudinal
length of the bushing (60a) and the washer (80a) may be thousands of an inch
less than the
longitudinal distance between the annular bearing surface (104) and the
shoulder of the rotor
(40), such that fluid film bearings may also be created between these parts.
[0051] Use and operation. Figure 13 shows an exemplary use of the pulse
generator (10) of
the present invention to stimulate a wellbore (200). The pulse generator (10)
is connected to
uphole and downhole portions of a tubing string (202) by the crossover subs
(140). The uphole
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portion of the tubing string (202) is connected to a pump (204) that
pressurizes fluid (e.g.,
drilling fluid or nitrogen gas) down the tubing string (202) and into the
rotor longitudinal bore
(44) so that the fluid pressure inside the rotor longitudinal bore (44) is
higher than the fluid
pressure in the wellbore (200).
.. [0052] Accordingly, fluid flows from the rotor longitudinal bore (44) out
of the rotor
transverse openings (52a to 52e). Flow of fluid out of the rotor transverse
openings (52a, 52b,
52c) causes the rotor (40) to rotate within the stator longitudinal bore (28)
on account of these
openings being oriented tangentially to the rotor longitudinal bore (40).
Impingement of the
fluid exiting rotor transverse openings (52a, 52b, 52c) on the grooved portion
(34) enhances
this rotational effect by allowing some fluid to exit the rotor transverse
openings (52a, 52b,
52b) regardless of the angular position of the rotor (40) relative to the
stator (20).
[0053] When one of the rotor transverse openings (52a to 52e) aligns with one
of the stator
transverse openings (32a to 32f), a pulse of fluid flows from the rotor
longitudinal bore (44)
through the aligned openings to outside of the stator (20) to create a fluid
pressure pulse in the
.. wellbore. The frequency of the pulses depends on the rotational speed of
the rotor (40) within
the stator (20). The amplitude of the pulses depends on the pressure
differential between the
pressure in the rotor longitudinal bore (44) and the portion of the wellbore
proximate to the
apparatus (10). In the embodiment of the pulse generator (10) shown in the
Figures, the
provision of six stator transverse openings (32a to 32f) with equal angular
spacing between
.. them allows for the creation of pulses that effectively surround the stator
(20).
[0054] The pressurized fluid also flows into the end gap (160a) (Figure 4) to
create a fluid
film bearing between the rotor (40) and the bushing (60), and the annular
bearing surface (104)
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of annular bearing member (100). Such a fluid bearing is created at the uphole
end of the rotor
(40) which tends to push the rotor (40) in the downhole direction, and another
such fluid
bearing is created at the downhole end of the rotor (40) which tends to push
the rotor (40) in
the uphole direction. Accordingly, any momentary increase of fluid pressure
acting on the
uphole end of the rotor (40) that pushes the rotor (40) downwards will be
accompanied by a
reduction of the size of the downhole end gap (160). This reduction in size of
the downhole
end gap (160) will be accompanied by a momentary increase the fluid pressure
therein, thus
pushing the rotor (40) in the uphole direction. Accordingly, the uphole and
downhole fluid
bearings will tend to maintain the rotor (40) in an equilibrium position in
which the uphole
and downhole ends of the rotor (40) do not contact the annular bearing surface
(104) of the
annular bearing member (100). This avoids direct rotational friction between
the rotor (40)
and the annular bearing surface (104) of the annular bearing member (100),
allowing the rotor
(40) to rotate freely, which in turn allows for reliable generation of fluid
pressure pulses under
varying fluid flow and pressure conditions. As fluid flows through the pulse
generator (10)
from the uphole end to the downhole end, fluid film bearings are likewise
created in the gaps
between the bushing (60) and the washer (80), between the bushing (60) and the
stator inner
surface (26), between the bushing (60) and the rotor outer surface (46),
between the washer
(80) and the stator inner surface (26), and between the washer (80) and the
rotor outer surface
(46).
100551 The pulse generator may be used in any scenario where pulsed fluid jets
are desirable
or required downhole in a wellbore. For example, the pulse generator may be
used to stimulate
hydrocarbon flow from formations bearing oil and gas, clean out sand, scale or
other
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I]
impediments to fluid flow in a tubular or in a formation, or clean out or
reopen ports or
openings in a tubular, such as a frac port.
[0056] Interpretation. References in the specification to "one embodiment",
"an
embodiment", etc., indicate that the embodiment described may include a
particular aspect,
feature, structure, or characteristic, but not every embodiment necessarily
includes that aspect,
feature, structure, or characteristic. Moreover, such phrases may, but do not
necessarily, refer
to the same embodiment referred to in other portions of the specification.
Further, when a
particular aspect, feature, structure, or characteristic is described in
connection with an
embodiment, it is within the knowledge of one skilled in the art to affect or
connect such
module, aspect, feature, structure, or characteristic with other embodiments,
whether or not
explicitly described. In other words, any module, element or feature may be
combined with
any other element or feature in different embodiments, unless there is an
obvious or inherent
incompatibility, or it is specifically excluded.
[0057] It is further noted that the claims may be drafted to exclude any
optional element. As
such, this statement is intended to serve as antecedent basis for the use of
exclusive
terminology, such as "solely," "only," and the like, in connection with the
recitation of claim
elements or use of a "negative" limitation. The terms "preferably,"
"preferred," "prefer,"
"optionally," "may," and similar terms are used to indicate that an item,
condition or step being
referred to is an optional (not required) feature of the invention.
[0058] The singular forms "a," "an," and "the" include the plural reference
unless the context
clearly dictates otherwise. The term "and/or" means any one of the items, any
combination of
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the items, or all of the items with which this term is associated. The phrase
"one or more" is
readily understood by one of skill in the art, particularly when read in
context of its usage.
[0059] The term "about" can refer to a variation of 5%, 10%, 20%, or +
25% of the
value specified. For example, "about 50" percent can in some embodiments carry
a variation
from 45 to 55 percent. For integer ranges, the term "about" can include one or
two integers
greater than and/or less than a recited integer at each end of the range.
Unless indicated
otherwise herein, the term "about" is intended to include values and ranges
proximate to the
recited range that are equivalent in terms of the functionality of the
composition, or the
embodiment.
[0060] As will be understood by one skilled in the art, for any and all
purposes, particularly
in terms of providing a written description, all ranges recited herein also
encompass any and
all possible sub-ranges and combinations of sub-ranges thereof, as well as the
individual
values making up the range, particularly integer values. A recited range
includes each specific
value, integer, decimal, or identity within the range. Any listed range can be
easily recognized
as sufficiently describing and enabling the same range being broken down into
at least equal
halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each
range discussed
herein can be readily broken down into a lower third, middle third and upper
third, etc.
[0061] As will also be understood by one skilled in the art, all language such
as "up to", "at
least", "greater than", "less than", "more than", "or more", and the like,
include the number
recited and such terms refer to ranges that can be subsequently broken down
into sub-ranges
as discussed above. In the same manner, all ratios recited herein also include
all sub-ratios
falling within the broader ratio.
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[0062] The corresponding structures, materials, acts, and equivalents of all
means or steps
plus function elements in the claims appended to this specification are
intended to include any
structure, material, or act for performing the function in combination with
other claimed
elements as specifically claimed.
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