Note: Descriptions are shown in the official language in which they were submitted.
CA 02521287 2008-11-17
DUAL WALL DRILL STRING ASSEMBLY
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates generally to drill string assemblies. More
particularly, the
invention relates to a dual wall drill string assembly for use in subsurface
drilling
applications.
Background and Description of the Prior Art:
Drill pipe is used in various ways and for different applications including
mining for
precious gems, precious metals or coal; installing public and private
utilities; drilling for
oil and various gases including coal methane; creating an avenue to link the
surface to
one or more reservoirs; and linking a location on the surface or the
subsurface with
another surface or subsurface location. Accordingly, drill pipe comes in
specialized
configurations particularly adapted for use in one or more different
applications. For
example, drill pipe may comprise a single wall construction made from exotic
steels to
withstand hostile fluid and gases. Alternatively, drill pipe may comprise a
dual wall
construction adapted for use in reverse circulation drilling applications.
Traditional drill
pipe is "jointed," i.e., it is made up of sections of pipe having opposing
threaded ends.
The pipe string typically is comprised of a series of pipe sections, which are
screwed
together by "tool joints" or upset connections. However, Flush Joint designs
are
becoming popular because of higher performance threads such as the "wedge
threads".
Depending upon the application and environmental issues, a particular type of
drill pipe
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may be preferable to another based upon cost, proven scientific principles,
physical
limitations and the like.
For example, coil tubing drilling is another technique utilized commercially
at the
present time. Coil tubing is not "jointed" in the sense of traditional drill
pipe. Rather, a
continuous length of manufactured tubing having an O.D. on the order of 1- 3%2
inches
is spooled onto, for example, a 40 foot diameter reel. An injector head
utilizing gripper
blocks and a contra-rotating chain drive system is typically used to feed the
coil tubing
into the well bore. Coil tubing offers a number of advantages over
conventional jointed
drill pipe in some situations. These include the ability to drill and trip
under pressure,
faster trips, continuous circulation while tripping pipe, slim hole and thru
tubing
capability, a small location footprint, portability and a safer work area on
the rig site.
More exotic drilling, completion and production operations also continue to
evolve in the
oil and gas industries. For example, drilling operations are now being
conducted in
regions of the arctic permafrost, and other regions, for methane hydrate. One
source of
methane hydrate is the world's sea beds where the combined actions of heat,
pressure and
time on buried organic material produce methane. Over the eons, organic rich
source
beds are converted into large quantities of oil and natural gas. Along with
the oil, the
natural gas (largely methane) migrates upwardly from sea beds due to its
natural
buoyancy. If sufficient quantities reach a zone of hydrate stability, the
methane gas will
combine with formation water to form methane hydrate. In some circumstances,
these
deposits can provide sufficient in-place resources as to be suitable for
economic drilling
and production.
Regardless of the application, conventional single-walled drill pipe and coil
tubing have
traditionally utilized the same basic drilling technique: fluids such as
drilling muds are
pumped down the inside of the pipe and cuttings produced by the drilling
process are
carried with the drilling mud to the earth's surface along the outside of the
drill pipe.
More particularly, the cuttings are carried out of the hole either between the
borehole and
the drill pipe or between a cased hole and the drill pipe. Some exotic types
of drilling
such as under balanced drilling deal with the pressure differential between
the bottom
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hole pressures and the surface pressures. This method of drilling is
controllable, but it is
dangerous.
In addition, single-walled drill pipe exposes the borehole to the drilling mud
or fluids
until the borehole is cased or cemented. Further, when the returned drilling
mud or fluids
and cuttings pass along the drilled hole, the hole can become packed between
the drill
pipe and the hole from the cuttings, thereby limiting the movement of the
drill pipe. One
technique employed to overcome the problem of pipe sticking is to increase the
mud flow
volume and to circulate the borehole before further drilling is performed.
This technique,
however, impacts the earth's formation, for example, by forming or opening
cracks in the
formations. Typically, much, if not all of the additional mud flows into the
cracks and/or
produces additional cracks. In addition, when the hole is close to the
surface, the
additional mud can seep or flow to the surface in a process known as "fracing
out,"
which raises environmental concerns. Also it has been proven that low pressure
gas
wells are being abandoned because this process results in plugging and sealing
off the
avenue of producing natural gas. Reverse circulation air hammer drilling has
produced
low pressure gas wells, where previous standard drilled holes utilizing mud
showed no
evidence gas was present.
Reverse circulation drilling is a distinct drilling technique in which fluids
are pumped to
the drill bit and cuttings are transferred back to the earth's surface within
the drill pipe
assembly. This technique can be very advantageous because the drilling mud or
fluid has
limited exposure to the borehole and creates negligible damming effect. Also,
it is
environmentally-friendly in drilling applications that involve sensitive
aquifers for
drinking water and the like. The drill pipe typically used in reverse
circulation drilling,
however, is very stiff and difficult to steer and bend in a borehole. Thus,
its use is
limited to relatively straight hole applications, and it is not typically used
in deviated hole
drilling applications, which are commonly used in the construction, oil and
gas, and
mining industries.
In conventional drill pipes, wires are typically inserted and spliced inside
each drill pipe
to communicate with a gyroscope or compass transmitter in order to identify
the location
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of the drill bit below the earth's surface. However, these wires are typically
exposed and,
therefore, are vulnerable to damage from short circuiting and breakage during
the drilling
operation.
It would be desirable, therefore, if an apparatus could be provided that would
permit
double-walled drill string pipe sections to be used for reverse-circulation,
horizontal
directional and deviated vertical drilling. It would also be desirable if a
coil tubing
apparatus could be provided which offered the advantages of such a double wall
drill
string. It would also be desirable if such an apparatus could be provided that
would
permit the double-walled drill string pipe sections to bend along the arcuate
path of a
subsurface borehole as freely as a single-walled drill pipe. It would be
further desirable
if such an apparatus could be provided that would convey larger-sized cuttings
and
increased volumes of cuttings from the drilling mechanism to the surface of
the ground.
It would be further desirable if such an apparatus could be provided that
would permit
drilling in soft, medium or hard rock formations as well as corrosive
formations with
reduced negative environmental impact and reduced borehole wall damage. It
would be
a further advantage if an apparatus was provided suitable for permafrost
drilling
operations, such as operations to drill and recover methane hydrate. ,
It would be further desirable if such an apparatus could be provided that
would reduce or
eliminate the risk of short circuiting the conductive wires on the drill
string pipe sections.
It would also be desirable if such an apparatus could be provided that would
permit an
operator at the ground surface to know immediately what rock or soil formation
the drill
is cutting as well as the condition of the drill bit. It would be still
further desirable if
such an apparatus could be provided that would produce a more efficient
drilling
mechanism by decreasing discharge back pressure experienced during drilling
operations
utilizing conventional drill pipe. It would be further desirable if such an
apparatus could
be provided that would achieve longer pilot borehole distances and have a
longer lifespan
in the borehole. It would also be desirable if such an apparatus could be
provided to
electronically sense the hole pressures and differential pressures between the
ID and OD
at close proximity to the drill bit, as well as at other appropriate locations
along the drill
string length. It would be further desirable if an apparatus could be provided
to "smell"
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or detect hazardous gases, such as H2S, in the down hole environment. It would
be still
further desirable if such an apparatus could be provided that would permit the
apparatus
to be more easily assembled and perform drilling more efficiently, more
quickly, and less
costly. It would still further be desirable if such an apparatus could be
provided to have
an electric motor turn the drill bit instead of turning the drill pipe to
limit or raise the
fatigue life of the drill string. It would also be desirable if such an
apparatus could be
provided to be able to adjust the angle of the adjustable bent sub
electrically, which can
enable a bit, after drilling the hole with casing being installed
simultaneously, to pull
through the casing, leaving the casing in place. It would be further desirable
if such an
apparatus could be provided to have an electric motor(s) between the bit and
bent sub, in
order to deviate on a planned path so as to optimize the drilling task.
Advantages of the Invention:
Accordingly, it is an advantage of the invention claimed herein to provide an
apparatus
that includes double-walled drill string pipe sections adapted for use in all
subsurface
drilling applications, it is another advantage of the invention to provide an
apparatus
having an inner tube adapted to bend to the arcuate path of a borehole with
little or no
resistance. It is also an advantage of the invention to provide an apparatus
capable of
conveying larger-sized cuttings and increased volumes of cuttings from the
drilling
mechanism to the surface of the ground. It is also an advantage of the
invention to
provide an apparatus that is capable of drilling in soft, medium or hard
formations,
permafrost formations, as well as corrosive fonmations with reduced negative
environmental impact and reduced borehole wall damage. It is a further
advantage of the
invention to provide an apparatus that reduces or eliminates the risk of short
circuiting
the conductive wires on the drill string pipe sections. It is a still further
advantage of the
invention to provide an apparatus that permits an operator at the ground
surface to know
what rock or soil formation the drill is cutting and the location of the drill
bit. It is also
an advantage of the invention to electronically sense the hole pressures and
differential
pressures between the ID and OD at close proximity to the drill bit, as well
as at other
appropriate locations along the drill string length. It is another advantage
of the
invention to provide an apparatus that can detect the presence of hazardous
gas, such as
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H2S. It is another advantage of the invention to provide an apparatus that
produces a
more efficient drilling mechanism by decreasing the incidence of "fracing out"
of the
subsurface formation. It is yet another advantage of the invention to provide
an
apparatus that achieves longer pilot borehole distances and has a longer
lifespan in the
borehole. It is a further advantage of the invention to provide an apparatus
that is more
easily assembled and performs all subsurface drilling more efficiently, more
quickly, and
less costly. It is a still further advantage to have an electric motor(s) turn
the drill bit
instead of turning the drill pipe to limit or raise the fatigue life of the
drill string. It is a
still further advantage to be able to adjust the angle of the adjustable bent
sub electrically,
which can enable a bit, after drilling the hole with casing being installed
simultaneously,
to pull through the casing, leaving the casing in place. It is a still further
advantage to
have an electric motor(s) between the bit and bent sub, so in order to deviate
on a
planned path so as to optimize the drilling task. Another aspect of the
invention is the
provision of a coil tubing apparatus which utilizes a "tube within a tube"
design to
achieve the aforesaid advantages of dual wall drill pipe. Additional
advantages of the
invention will become apparent from an examination of the drawings and the
ensuing
description.
Explanation of the Technical Terms:
As used herein, the term "arcuate" refers to a curving, bending, turning,
arching or other
non-straight line, path or direction. As used herein, the term "arcuate path
that is
generally horizontal" refers to a borehole having an entry hole and a separate
exit hole
that are connected by a curved path. It is contemplated within the scope of
the term
"arcuate path that is generally horizontal" that the borehole may have a
longer vertical
component than its horizontal component.
As used herein, the term "conductive" means able to convey, transmit or
otherwise
communicate a signal and/or provide electrical current.
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As used herein, the term "fluid" relates to a liquid, air, a gas, or a
combination of liquid,
gas, and/or air. The term "fluid" includes, without limitation, mixtures of
solids and
water, oils, other chemicals and the like.
As used herein, the term "signal" refers to a means for communication between
a
transmitter and a receiver. The term "signal" includes, without limitation,
analog signals,
digital signals, multiplexing signals, light signals and the like.
As used herein, the term "steerable" means the ability to follow the deviated
path of a
planned drilled hole.
As used herein, the term "substantially vertical borehole" refers to a
borehole that is
drilled substantially perpendicular to the earth's surface. The term
"substantially vertical
borehole" includes, without limitation, boreholes that are arcuate, curved and
the like. It
is also contemplated that the term "substantially vertical borehole" refers to
a borehole
that is a combination of vertical and horizontal drilling in relation to the
earth's surface.
As used herein, the term "subsurface drilling" refers to any type of drilling,
including
vertical, horizontal and everything in between, employed by any industry that
uses drill
pipe to drill holes into the earth's formation, including, without limitation,
soil, rock, ice,
permafrost, wetlands, sand and the like.
The term "coil tubing" will be taken to mean any continuously-milled tubular
product
manufactured in lengths which require spooling onto a take-up reel during the
primary
milling or manufacturing process. Conventional coil tubing is constructed of
carbon
steel using the high- frequency induction welding process. Advanced metallic
coil tubing
strings are constructed using corrosion resistant alloys or titanium, with the
seam weld
formed using the TIG process.
The term "coil tubing unit" will be understood to mean an assembly of the
major
equipment components needed to perform a continuous-length tubing service or
drilling
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operation. These basic equipment components generally include as a minimum an
injector, service reel, control console, power supply, and well control stack
assembly.
SUMMARY OF THE INVENTION
A first aspect of the invention provides a dual wall drill string assembly
which allows
dual circulation for any subsurface drilling, said assembly comprising: (A) a
metallic
outer tube having: (1) an outer tube first end; (2) an outer tube second end
opposite the
outer tube first end, and wherein the outer tube comprises a plurality of
rigid outer tube
sections, each of said rigid outer tube sections having a pair of threaded
ends adapted to
be removably connected to a threaded end on another rigid outer tube section;
(B) a
flexible, substantially non-metallic inner tube that is substantially enclosed
within and
generally coaxially aligned with the outer tube, said inner tube having: (1)
an inner tube
first end; (2) an inner tube second end opposite the inner tube first end
which defines a
tube length therebetween; (3) an inner tube diameter which is generally
constant along the
tube length from the inner tube first end to the inner tube second end; (4)
wherein the
flexible inner tube comprises a plurality of flexible inner tube sections,
each of said
flexible inner tube sections having a male connection end and a female
connection end,
each male section end being adapted to be connected to a female connection end
on
another flexible inner tube section and each female connection end being
adapted to be
connected to a male connection end on another flexible inner tube section;
wherein the
inner tube and the outer tube define an annular channel there between, wherein
the non-
metallic inner tube is formed of a material which allows it to bend to an
arcuate path of a
borehole for drilling a deviated wellbore without limiting bending of the
metallic outer
tube; (C) a means for conveying fluid through the annular channel toward the
inner tube
first end; wherein the annular channel is adapted to convey drilling fluid
under pressure
toward the inner tube first end, and the inner tube is adapted to convey
cuttings toward
the inner tube second end.
The drill string assembly also includes a means to detect increases in
formation pressure
and pressures along the length of the drill string as well as a means to
detect the presence
of hazardous gas in the formation. Components of the drill string can have
electric or
mud motor(s) to drill the hole. Also, another component may have an adjustable
bent sub
controlled by electricity.
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In a preferred embodiment of the drill string assembly of the invention
claimed herein, a
conductive element is substantially enclosed within the flexible,
substantially non-
metallic (and if appropriate a substantially non-conductive material) inner
tube and
adapted to convey a signal to allow the operator to control the direction of
the drilling
mechanism. In another preferred embodiment, flexible sleeve(s) with openings
are
provided in the annular channel in order to maintain the outer tube and the
inner tube in
substantially concentric relationship to each other and permit fluid under
pressure to be
conveyed through the annular channel.
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According to the method of the invention claimed herein, the dual wall drill
string
assembly is adapted to produce a subsurface borehole. In a preferred
embodiment, the
assembly is adapted to produce a substantially vertical subsurface borehole, a
substantially horizontal subsurface borehole, or a borehole anywhere between
vertical
and horizontal, having an arcuate path. In another preferred embodiment, the
assembly is
adapted to pull a product into the arcuate path of a subsurface borehole.
A preferred embodiment of the invention utilizes a coil tubing drill string
assembly for
subsurface drilling. The assembly again has inner and outer tubes with an
annular
channel therebetween, as previously described. The outer tube is formed as a
continuously-milled tubular product manufactured in lengths which require
spooling onto
a take-up reel during the primary milling or manufacturing process. When
appropriate, a
centralizer(s) is located in the annular channel formed between the inner and
outer tubes
adjacent each of a surface end and a bit end of the coil tubing, respectively,
to assist in
maintaining the annular channel between the outer tube and inner tube.
The surface end of the coil tubing is also supplied with a fluid supply and
communication
and power transmission adapter which includes an inlet for fluid supply flow
inwardly
and which also includes a conduit opening which accepts communication and
power
transmission connectors leading to a surface control console. The bit end of
the coil
tubing includes a tubing end adapter which has communication and power
transmission
connector(s). Preferably, the inner and outer tubes are separated by the
centralizer(s)
which are located adjacent the bit end and surface end of the coil tubing,
respectively.
The bit end of the coil tubing apparatus can be connected to a downhole
adjustable or
non adjustable bent sub, and/or electric or hydraulic and/or air motor(s).
The annular channel is adapted to convey drilling fluid under pressure toward
the inner
tube first end, and the inner tube is adapted to convey cuttings toward the
inner tube
second end. The coiled tubing is fed from a spool at the surface to an
injector head
which is used to feed the coiled tubing into a well bore to thereby drill a
subsurface
borehole. Pressure sensor(s) are located within the wall of the inner tube
that sense
pressure differentials between the outer and inner tube and also senses
pressure inside the
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inner tube. Additionally, sensors are located within the wall of the inner
tube that detect
the presence of hazardous gas.
In a second aspect of the invention there is provided a method for subsurface
drilling
using dual circulation, said method comprising the steps of:
(A) providing a flexible dual wall drill string assembly, said assembly
comprising:
(1) a metallic outer tube having;
(i) an outer tube first end;
(ii) an outer tube second end opposite the outer tube first end,
wherein the outer tube comprises a plurality of rigid outer
tube sections, each of said rigid outer tube sections having a
pair of threaded ends adapted to be removably connected to
a threaded end on another rigid outer tube section;
(2) a flexible, substantially non-metallic inner tube that is substantially
enclosed within and generally coaxially aligned with the outer tube,
said inner tube having:
(i) an inner tube first end;
(ii) an inner tube second end opposite the inner tube first end
which defines a tube length therebetween;
(iii) an inner tube inner diameter which is generally constant
along the tube length from the inner tube first end to the
inner tube second end;
wherein the inner tube and the outer tube define an annular channel
therebetween,
wherein the non-metallic inner tube is formed of a material which allows it to
bend in an
arcuate path of a borehole for drilling a deviated wellbore without limiting
bending of the
metallic outer tube;
(3) a means for conveying fluid through the annular channel toward
the inner tube first end;
wherein the annular channel is adapted to convey drilling fluid under pressure
toward the
inner tube first end, and the inner tube is adapted to convey cuttings toward
the inner tube
second end; and
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(B) drilling a deviated subsurface borehole, at least a portion of which has
an
arcuate path, by circulating drilling fluid down the annular channel which
is formed between the inner tube and the outer tube and by then returning
cuttings up the inner tube diameter to the surface.
Additional objects, features and advantages will be apparent in the written
description
which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
The presently preferred embodiments of the invention are illustrated in the
accompanying
drawings, in which like reference numerals represent like parts throughout,
and in which:
Figure 1 is a sectional side view of a preferred embodiment of the bit end of
the dual wall
drill string assembly partially in a subsurface borehole in accordance with
the present
invention.
Figure 2 is an enlarged sectional side view of the preferred dual wall drill
string pipe
section shown in Figure 1.
Figure 3 is a sectional side view of an alternative embodiment of the dual
wall drill string
pipe section in accordance with the present invention.
Figure 4A is a sectional side view of a pair of the dual wall drill string
pipe sections
shown in Figure 3.
Figure 4B is a sectional side view of the pair of dual wall drill string pipe
sections shown
in Figure 4A connected to each other.
Figure 5A is a cross-sectional view of a preferred embodiment of the flexible
sleeve in
accordance with the present invention.
Figure 5B is a cross-sectional view of an alternative embodiment of the
flexible sleeve in
accordance with the present invention.
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Figure 6 is a sectional side view of a preferred dual wall drill string pipe
section and a
drilling mechanism.
Figure 7 is a sectional side view of an alternative embodiment of the dual
wall drill string
assembly partially in a subsurface borehole in accordance with the present
invention.
Figure 8 is a sectional side view of an alternative embodiment of the dual
wall drill string
assembly partially in a subsurface borehole in accordance with the present
invention.
Figure 9 is a perspective view of a typical prior art coil tubing injector
unit showing the
tubing being fed from a spool to the well bore.
Figure 10 is a close-up view of a gripper block assembly which is used to grip
and feed
the coil tubing into the well bore.
Figure 11 is a simplified, schematic view of the surface end of a length of
the improved
coil tubing of the invention.
Figure 12 is a simplified, schematic view of the bit or down hole end of the
length of coil
tubing of Figure 11.
Figure 13 is a simplified, exploded view of a portion of the coil tubing of
Figures 11 and
12, showing the inner tube and wire assembly.
Figure 14 is a sectional view of sensors located within the wall of an inner
tube.
Figure 15 is an assembly view of a typical mud motor.
Figure 16 is an assembly view of an electrical motor, similar in function to
Figure 15.
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Figure 17 is an assembly view of the electrical drill motor assembly of Figure
16
combined with an electrical angle adjustment bent sub.
Figure 18 is an assembly view of the electrical drill motor assembly of Figure
16
combined with a mechanical angle adjustment bent sub.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
Referring now to the drawings, the various embodiments of the apparatus of the
invention claimed herein are illustrated by Figures 1 through 18. Figure 1
illustrates a
preferred embodiment of the dual wall, jointed drill string assembly partially
in a
subsurface borehole. The preferred dual wall drill string assembly is
designated
generally by reference numeral 10 and the subsurface borehole is designated by
reference
numeral 12. As shown in Figure 1, the preferred drill string assembly may
comprise a
plurality of dual wall pipe sections 14. It is contemplated, however, that the
drill string
assembly of the invention claimed herein may comprise a single dual wall pipe.
The
preferred drill string assembly may further comprise a drilling mechanism, an
interchange sub, a means for conveying fluid under pressure, a signal source
such as a
transmitter or a source of electricity, a receiver, and a navigation
transmitter as described
in more detail below. It is further contemplated that the assembly may be used
in
connection with any suitable steering mechanism such as a bent sub or a
deflectable drill
bit as will be appreciated by one having ordinary skill in the art. The dual
wall drill
string assembly of the present invention is adapted for use in all subsurface
drilling
applications.
Referring still to Figure 1, in the preferred drill string assembly, a
plurality of dual wall
pipe sections 14 are connected together to produce a dual wall drill string.
As shown in
Figure 1 the preferred dual wall drill string comprising dual wall pipe
sections 14 is
connected to drilling mechanism 16 by interchange sub 18. Drilling mechanism
16 is
adapted to produce cuttings as it drills subsurface borehole 12. Drilling
mechanism 16
may be any suitable drilling mechanism adapted to drill a subsurface borehole
such as a
rotary cutter or a down-the-hole hammer.
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Interchange sub 18 is adapted to direct cuttings from the drilling mechanism
to the dual
wall drill string assembly. More particularly, as discussed below, interchange
sub 18
directs cuttings and fluid under pressure from the subsurface borehole into
the inner tube
of the dual wall drill string. Interchange sub 18 may be any suitable device
adapted to
direct cuttings from the drilling mechanism to the dual wall drill string.
Also, the
interchange sub drilling mechanism or use of a separate interchange sub may
have
communication capabilities such as a location transmitter. It is also
contemplated that
the drill string assembly of the invention may not require an interchange sub
because a
channel through which cuttings may be transferred from the drilling mechanism
to the
drill string may be incorporated into the drilling mechanism.
Still referring to Figure 1, the preferred drill string assembly also includes
a means for
conveying fluid through the dual wall drill string towards the drilling
mechanism such as
pump 20. More particularly, as discussed below, pump 20 is adapted to convey
fluid
under pressure through an annular channel defined by the outer tube and the
inner tube
of the dual wall drill string towards drilling mechanism 16. The flow of fluid
from
pump 20 through the annular channel of the dual wall drill string and,
thereafter, through
interchange sub 18 towards drilling mechanism 16 is designated by arrowed line
22. The
flow of cuttings and fluid from drilling mechanism 16 into interchange sub 18
and,
thereafter, into the inner tube of the dual wall drill string is designated by
arrowed
lines 24. it is contemplated within the scope of the invention that the means
for
conveying fluid through the annular channel of the dual wall drill string
toward the
drilling mechanism may be any suitable means for conveying fluid under
pressure.
As also shown in Figure 1, the preferred embodiment of the dual wall drill
string
assembly includes signal source of electricity 26 adapted to provide an
electrical current
to navigation transmitter 28, which is adapted to indicate the direction of
drilling
mechanism 16. Source of electricity 26 may be any suitable source for
providing an
electrical current. Navigation transmitter 28 may be any suitable device
adapted to
monitor the direction of the drilling mechanism.
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Referring now to Figure 2, an enlarged sectional side view of the preferred
dual wall
pipe section 14 shown in Figure 1 is illustrated. Pipe section 14 includes
metallic outer
tube 30 having outer tube first end 31 and outer tube second end 32 opposite
the outer
tube first end. In a preferred embodiment, drilling mechanism 16 (See Figure
1) is
located adjacent to outer tube first end 31 of a dual wall pipe section such
as pipe
section 14. Outer tube first end 31 is adapted to be connected to the outer
tube second
end of another pipe section such that fluid may be conveyed under pressure in
the outer
tubes of the pipe sections. Outer tube second end 32 is adapted to be
connected to the
outer tube first end of another pipe section such that fluid may be conveyed
under
pressure in the outer tubes of the pipe sections. In a preferred embodiment,
outer tube 30
of each dual wall pipe section 14 is rigid and includes a pair of threaded
ends 33 and 34
adapted to be removably connected to a threaded end on another rigid outer
tube section.
As shown in Figure 2, the preferred dual wall pipe section 14 also includes
flexible,
substantially non-metallic inner tube 40 that is substantially enclosed within
and
generally coaxially aligned with outer tube 30. The non-metallic inner tube 40
can be
formed of a variety of materials depending upon the particular drilling
application at
hand. For example, elastomers such as natural or synthetic rubber,
polyurethane, flexible
plastics, flexible carbon fiber, plastic composites, rubber composites, carbon
composites,
NylonsTM, fiberglass, Rayonrm, TeflonTM, acrylics, polymers, etc., can be
utilized in
some situations. The preferred material for inner tube 40 will be dictated by
the drilling
conditions. For example, if hydrogen sulfide is present in the drilling
environment, the
inner tube material (and outer tube material) must be resistant to the gas.
If carbon dioxide is present, the inner and outer tube must not be harmed by
or absorb
this gas. Rubber is a convenient choice of material in many cases, since it
can be
formulated to specifically withstand the environment at hand.
Inner tube 40 includes inner tube first end 41, inner tube second end 42
opposite the
inner tube first end, and an inner tube inner diameter designated by line 43.
Inner tube
first end 41 is adapted to be connected to the inner tube second end of
another pipe
section such that cuttings and fluid under pressure may be conveyed in the
inner tubes of
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CA 02521287 2005-09-27
the pipe sections. Inner tube second end 42 is adapted to be connected to the
inner tube
first end of another pipe section such that cuttings and fluid under pressure
may be
conveyed in the inner tubes of the pipe sections. More particularly, an inner
tube such as
inner tube 40 is adapted to convey cuttings from drilling mechanism 16 toward
inner tube
second end 42. In a preferred embodiment, the drill string assembly is
comprised of a
plurality of pipe sections 14, each of which includes a flexible inner tube
section 40,
wherein each of the flexible inner tube sections has male connection end 44
and female
connection end 45. Each male connection end 44 is adapted to be connected to a
female
connection end on another flexible inner tube section and each female
connection end 45
is adapted to be connected to a male connection end on another flexible inner
tube
section. It is also preferred that each flexible inner tube section is in
communication (as
hereinafter described) with each adjacent flexible inner tube section.
Still referring to Figure 2, the preferred inner tube 40 also includes
conductive element
46 for conveying a signal such as an electrical signal from source of
electricity 26 (See
Figure 1) to drilling mechanism 16 (See Figure 1). The signal may be used to
indicate
the direction of the drilling mechanism. In a preferred embodiment, conductive
element
46 is continuous from inner tube first end 41 to inner tube second end 42 so
that a
continuous conductive path is provided from one end of the drill string to the
other and
provides an electrical current from the source of electricity to a navigation
device. It is
also preferred that conductive element 46 is substantially enclosed within
inner tube 40.
Furthermore, conductive element 46 preferably comprises at least one metallic
or fiber
optic material. It is also preferred that conductive element 46 includes
metallic wire,
metallic mesh or thin wall pipe. It is contemplated within the scope of the
invention,
however, that conductive element 46 may be any suitable material for conveying
a signal
such as an electrical current.
The preferred inner tube also includes a means for reinforcing the inner tube
such as
mesh 48. Mesh 48 is adapted to provide structural support to the flexible,
substantially
non-metallic inner tube. More particularly, mesh 48 is adapted to enable inner
tube 40 to
withstand greater pressure differentials between the pressure in annular
channel 50 and
the pressure in the inner tube. In other words, mesh 48 provides the inner
tube with
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CA 02521287 2005-09-27
resistance against collapsing when the pressure in the annular channel becomes
significantly greater than the pressure in the inner tube, and resistance
against bursting
when the pressure in the inner tube becomes significantly greater than the
pressure in the
annular channel. In addition, mesh 48 is adapted to minimize the bending
resistance of
the inner tube. As a result, mesh 48 does not significantly impair the
steerability of the
drill string assembly. Mesh 48 may be made from wire mesh, fabric mesh, thin
wall
metallic tube or any other suitable material adapted to provide resistance
against pressure
differentials between the annular channel and the inner tube and minimize
resistance
against bending or steering the inner tube. Typical candidate materials
include steel,
steel alloys, stainless steel, stainless steel alloys, IncoloyTM, copper,
copper based alloys,
brass, brass based alloys, fiberglass, RayonTM, NylonTM, plastics and non-
conductive
materials. An appropriately placed mesh may be utilized as shielding from
cross talk
with respect to the signal canying conductive elements of the apparatus. It is
contemplated that mesh 48 may be located throughout the inner tube or in
designated
areas. It is further contemplated that mesh 48 may be substantially enclosed
within the
inner tube, applied to the exterior or interior surfaces of the inner tube, or
a combination
thereof.
Referring still to Figure 2, outer tube 30 and inner tube 40 define annular
channel 50
there between. The annular channel is adapted to convey fluid under pressure
from the
means for conveying fluid such as pump 20 (See Figure 1) toward the inner tube
first
end. More particularly, annular channel 50 is adapted to convey drilling fluid
under
pressure from inner tube second end 42 toward inner tube first end 41.
As shown in Figure 2, the preferred dual wall pipe section 14 also includes at
least one
centering member such as flexible sleeve 60 that is located in annular channel
50. In a
preferred embodiment, at least one flexible sleeve 60 is adapted to maintain
outer tube 30
and inner tube 40 in a substantially concentric relationship to each other.
Also in a
preferred embodiment, flexible sleeve 60 has at least one opening therein such
as
holes 262 (See Figure 5A). In an alternative embodiment, flexible sleeve 360
includes
apertures 362 (See Figure 5B). It is also preferred that the cumulative area
of the
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CA 02521287 2005-09-27
openings in the flexible sleeves is greater than the cross sectional area
defined by inner
tube inner diameter 43.
Referring now to Figure 3, an alternative embodiment of a dual wall pipe
section is
illustrated. More particularly, Figure 3 illustrates an alternative embodiment
of the male
connection end and the female connection end of the flexible, substantially
non-metallic
inner tube of a dual wall pipe section. As shown in Figure 3, dual wall pipe
section 114
includes metallic outer tube 130 having outer tube first end 131 and outer
tube second
end 132 opposite the outer tube first end. The outer tube also includes a pair
of threaded
connections 133 and 134 adapted to be connected to the threaded connections of
another
pipe section 114. Pipe section 114 also includes flexible, substantially non-
metallic inner
tube 140. Inner tube 140 includes inner tube first end 141, inner tube second
end 142
opposite the inner tube first end, and inner tube inner diameter designated by
line 143.
Inner tube 140 also includes male connection end 144 and female connection end
145
which are adapted to be connected to the female connection end and the male
connection
end, respectively, of an inner tube of another pipe section such that adjacent
pipe sections
are in communication with each other, fluid can be conveyed under pressure
through
annular channel 150, and cuttings and fluid under pressure can be conveyed in
the inner
tubes of the pipe sections.
Inner tube 140 also includes conductive element 146, stiffener 148 and
flexible sleeves
160. While stiffener 148 is shown on the outside surface of preferred inner
tube 140, it is
contemplated within the scope of the invention that one or more stiffeners may
be located
on the inside surface of the inner tube or substantially or entirely enclosed
within the
inner tube. Inner tube 140 has outer pressure sensor 170 which detects
abnormal
pressures or measures pressure to compare the inner pressure sensor readings.
Inner tube
140 has inner pressure sensor 171 which detects abnormal pressures or measures
pressure
to compare to the outer pressure sensor readings.
Referring now to Figures 4A and 4B, a pair of dual wall pipe sections are
illustrated in
nearly-connected and connected disposition, respectively. More particularly,
Figure 4A
shows a pair of pipe sections 114A and 114B in a nearly-connected relationship
to each
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CA 02521287 2005-09-27
other. As shown in Figure 4A, pipe section 114A includes metallic outer tube
130A
having threaded end 133A adapted to be connected to threaded end 134B of outer
tube
130B of pipe section 114B. Pipe section 114A also includes flexible,
substantially non-
metallic inner tube 140A. Inner tube 140A includes male connection end 144A
which is
adapted to be connected to female connection end 145B of inner tube 140B of
pipe
section 114B. Male connection end 144A and female connection end 145B are
adapted
to be connected to each other such that inner tubes 140A and 140B are in
communication
with each other and cuttings and fluid under pressure can be conveyed through
annular
channels 150A and 150B of pipe sections 114A and 114B, respectively.
Referring now to Figure 4B, the preferred pipe sections shown in Figure 4A are
illustrated in connected relationship to each other. More particularly,
threaded ends
133A and 134B of outer tubes 130A and 130B, respectively, are shown in full
threaded
engagement with each other. In addition, male connection end 144A and female
connection end 145B of inner tubes 140A and 140B, respectively, are shown
connected
to each other such that inner tubes 140A and I40B are in communication with
each
other, fluid under pressure may be conveyed through annular channels 150A and
150B,
and cuttings and fluid under pressure may be conveyed through the inner tubes
140A and
140B.
Referring now to Figures 5A and 5B, two cross-sectional views of preferred
embodiments of dual wall pipe sections 214 and 314, respectively, are
illustrated. As
shown in Figure 5A, preferred pipe section 214 includes outer tube 230, inner
tube 240
and flexible sleeve 260. Flexible sleeve 260 includes a plurality of holes
262. Holes 262
are adapted to permit fluid under pressure to be conveyed there through. It is
contemplated that the cumulative area of holes 262 in flexible sleeve 260 may
be greater
than the cross-sectional area defined by inner tube inner diameter 264. It is
also
contemplated that the cumulative area of holes 262 in flexible sleeve 260 may
be less
than or equal to the cross-sectional area defined by inner tube inner diameter
264.
Referring now to Figure 5B, preferred dual wall pipe section 314 includes
outer tube 330,
inner tube 340 and flexible sleeve 360. Flexible sleeve 360 includes a
plurality of
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CA 02521287 2005-09-27
apertures 362. Apertures 362 are adapted to permit fluid under pressure to be
conveyed
there through. It is contemplated that the cumulative area of apertures 362 in
flexible
sleeve 360 may be greater than the cross-sectional area defined by inner tube
inner
diameter 364. It is also contemplated that the cumulative area of apertures
362 in
flexible sleeve 360 may be less than or equal to the cross-sectional area
defined by inner
tube inner diameter 364. While Figures 5A and 5B illustrate flexible sleeve
260 having a
plurality of round holes 262 and flexible sleeve 360 having a plurality of
arched apertures
362, respectively, it is contemplated within the scope of the invention that
one or more
openings of any suitable configuration and location may be provided in the
flexible
sleeves of the present invention.
Referring now to Figure 6, preferred dual wall pipe section 14 is illustrated
in a nearly-
connected relationship to interchange sub 18. Preferred pipe section 14 is
illustrated in
Figures 1 and 2 and described in detail above. As shown in Figure 6, threaded
end 33 is
adapted to be connected to threaded end 66 of interchange sub 18. Drilling
mechanism
16 includes navigation transmitter 28, cutting head 68, fluid channel 70, and
cuttings
channel 72. Drilling head 68 is adapted to drill a subsurface borehole as
illustrated in
Figure 1. Drilling head 68 may be any suitable mechanism for drilling a
subsurface
borehole. Fluid channel 70 is adapted to convey fluid under pressure from
annular
channe150 of pipe section 14 to drilling head 68 of drilling mechanism 16.
Fluid
channel 70 may be of any suitable conventional configuration adapted to convey
fluid
under pressure toward the drilling head of the drilling mechanism. Cuttings
channel 72
is adapted to convey cuttings produced by the drilling head of the drilling
mechanism
from the subsurface borehole to inner tube 40 of pipe section 14. Cuttings
channe172 on
interchange sub 18 may be of any suitable configuration for conveying cuttings
from the
drilling mechanism to the inner tube of one or more dual wall pipe sections.
Referring now to Figure 7, an alternative embodiment of the dual wall drill
string
assembly is illustrated. More particularly, Figure 7 illustrates a preferred
dual wall drill
string assembly utilizing a drilling mechanism commonly known as a down-the-
hole
percussion hammer. As shown in Figure 7, preferred assembly 400 includes a
plurality
of dual wall pipe sections 414 connected to each other. The drill string of
dual wall pipe
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CA 02521287 2005-09-27
sections 414 is connected to drilling mechanism 416 by interchange sub 418.
Drilling
mechanism 416 is adapted to drill subsurface borehole 412. Interchange sub 418
is
adapted to convey cuttings from drilling mechanism 416 to inner tubes 440 of
pipe
sections 414. The flow of fluid conveyed under pressure from annular channels
450 of
pipe sections 414 through interchange sub 418 and, thereafter, towards
drilling
mechanism 416 is designated by arrowed line 420. The flow of cuttings and
fluid under
pressure from drilling mechanism 416 to interchange sub 418 and, thereafter,
to the inner
tubes of pipe sections 414 is designated by arrowed lines 422.
Referring now to Figure 8, an alternative embodiment of the dual wall drill
string
assembly is illustrated. More particularly, Figure 8 illustrates a preferred
dual wall drill
string assembly without an interchange sub. As shown in Figure 8, preferred
assembly
500 includes dual wall pipe section 514 which is connected directly to
drilling
mechanism 516. Drilling mechanism 516 is adapted to drill subsurface borehole
512.
Drilling mechanism 516 includes cuttings channe1519 which is adapted to convey
cuttings from the drilling mechanism to the dual wall pipe section. The flow
of fluid
conveyed under pressure through annular channe1550 of pipe section 514 towards
drilling mechanism 516 is designated by arrowed lines 520. The flow of
cuttings and
fluid under pressure from drilling mechanism 516 to the inner tube of pipe
section 514 is
designated by arrowed line 522. The foregoing describes the operation of a
reverse
circulation down-the-hole hammer.
The dual wall drill string assembly of the invention may also take the form of
a coil
tubing drill string, as will now be described. Turning now to Figure 9, there
is shown a
prior art coil tubing injector unit designated generally as 601. While units
of this general
type have been known in the art for many years, the unit 601 is illustrated in
order to
explain the environment of the improved coil tubing system of the invention.
Unlike the
jointed dual wall pipe discussed up to this point, the coil tubing injector
system of
Figures 9 and 10 utilizes a continuous length of tubing 603 which is dispensed
from a
spool or ree16051ocated at the well surface. Traditional coil tubing is
manufactured in
continuous lengths by fabricating highly ductile steel. The first steels
utilized were high
strength, low alloy materials, and with only minor modifications this type
steel remains
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CA 02521287 2005-09-27
the standard for coil tubing today. Early coil tubing utilized 40,000psi (40-
ksi) and
50,000psi (50-ksi) yield strength steel which was provided in 0.049-in, thick
sheets.
Tubing was milled in 250 to 2,000 foot long sections, and strings were
assembled by
butt-welding the tube sections together using TIG and MIG techniques. The
continuous
tubing was wound onto tubing service reels with 48 inch core diameters being
typical.
As generally shown in Figures 9 and 10, the coil tubing 603 is fed between a
contra-
rotating, hydraulically powered chain drive system (607 in Figure 10) which
carries a
plurality of gripper block assemblies 609. The drive motor is illustrated at
608 in Figure
9. The gripper block assemblies include C-shaped clamp regions 611 and rollers
613.
The rollers 613 ride on the tracks of a vertical run 615. The gripper block
assemblies are
pivoted between disengaged and engaged positions with respect to the coil
tubing being
fed within the vertical run of the injector unit. The gripper block assemblies
and chain
drive provide the gripping force necessary to feed the continuous length of
tubing into
the well bore. The operation of commercially available coil tubing injector
units will be
well understood by those skilled in the relevant arts.
Figures 11-13 show one embodiment of the improved coil tubing of the
invention.
Turning first to Figure 11, there is shown the exit or surface end 617 of the
coil tubing.
As described with respect to the jointed, dual wall drill pipe, the coil
tubing of the
invention has an outer, metallic pipe 619 and an inner non-metallic tube or
layer (621 in
Figure 13). In the embodiment of the invention illustrated in Figures 11-13,
the inner,
non-metallic tube 621 is provided with wire reinforcement (shown in exploded
fashion as
622 in Figure 13). An annular region (generally at 623 in Figures 11 and 12)
separates
the outer pipe 619 and inner tube 621. Fluid and cuttings flow through the
interior of the
inner tube toward an exit at the well surface. The annular space between the
inner tube
and outer pipe allows the fluid flow to be supplied to the cutter or bit.
In the embodiment of Figure 11, a webbed centralizer 636 assists in separating
the inner
tube and outer pipe and lets air or other fluid pass freely. While only one
centralizer 636
is shown in the embodiment of Figure 11, it will be understood by those
skilled in the art
that one or more centralizers 636 may be needed to keep the inner tube and
outer pipe
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CA 02521287 2005-09-27
separated, or the centralizer could be an integral part of the inner tube
throughout the
length thereof. In this case, a plurality of centralizers could be located
throughout the
length of the inner tube. The surface end of the coil tubing is also supplied
with a fluid
supply and communication and/or power transmission adapter 627 which includes
an
inlet 629 for fluid supply flow inwardly from the reel swivel. The adapter 627
also
includes a conduit opening 631 which accepts cabling leading to a control
console. The
length of coil tubing is attached to the adapter 627 by means of a standard
coil tubing
connection (generally at 633) of the customer's preference.
Figure 12 shows the bit end 635 of the coil tubing of the invention. The inner
tube 621
can be used to encase communication and power transmission cables. A second
centralizer 637 is used to ensure the free passage of air or other fluid. In
the embodiment
of Figure 12, the coil tubing is attached to a tubing end adapter 639. The end
adapter 639
has communication and power transmission connectors 641 molded onto the end of
the
inner tube 643. Note that the inner and outer tubes are separated only by the
centralizers
636 and 637 in the embodiment of the invention illustrated in Figures 11 and
12. The
centralizers are located generally adjacent the air and wire adapter 627 at
one end of the
length of tubing and adjacent the bit end at the other extent of the tubing.
The bit end 635 of the coil tubing apparatus shown in Figure 12 would
typically be
connected to a conventional downhole electric, hydraulic and/or air motor (not
shown).
Most downhole motors used in coil tubing drilling operations are smaller
versions of
their jointed pipe versions. Downhole motors consist of a rotor and stator
combination
and use fluid flow to generate torque downhole. Electric motors are more
recent
introductions into the industry but, if incorporated, allow the motor assembly
to be
shortened in order to undertake a tighter turning radius. Additionally, an
electronically
controlled bent sub can be incorporated into the assembly of the invention so
that the
bend angle can be controlled or eliminated when the string is required to
follow a straight
path. The electronically controlled bent sub can also enable the use of
special drilling
techniques so that casing can be run simultaneously during the drilling
operation and
pulled through the casing, leaving the casing in place. The size, number of
lobes and
efficiency of the motor, determine the fluid-flow requirements, the output
torque and
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CA 02521287 2005-09-27
speed. The typical sizes used in coil tubing drilling operations range from 1-
11/16" to
3-1/4" OD. Most motors also incorporate a method for adjusting the bend at the
bottom
of the motor. This mechanical adjustable kick-off angle allows for different
dogleg
severity's depending on the application and well design. For some
applications, drilling
with very high quality foams and mist, turbine motors have also been used to
some
degree. As will be understood by those skilled in the coil tubing arts, the
typical coil
tubing string will include such other components as connectors, shear subs,
float valves,
orienting devices, measurement while drilling devices, dump or equalizer subs,
in
addition to the downhole motor.
Figure 14 is an illustration of an annulus sensor 770 that measures pressure
between the
inner tube 740 and outer tube 730. The annular sensor 771 measures pressure
inside the
inner tube 740. Both sensors are connected to one or more communication
cable(s) 722
to enable communication to the drilling operators console, and/or computer,
and/or
blowout preventer(s). In similar fashion, sensor 772 is a gas detector
connected to
communicate with the conductive element (in this case communication cable 722)
for
communicating information related to the presence or absence of gases along
the drill
string assembly from a subsurface location to a location at the well surface.
These
sensors perform important and sometimes critical functions in "smelling"
important
gases and compliment the action of the pressure sensors 770 and 771 in
monitoring
abnormal pressures that may cause a blowout. This type of detection down hole
rather
than at the well surface offers distinct advantages, since problems such as
high pressure
kicks can be detected earlier before becoming a major problem at the surface.
Also,
because the sensors are electrical sensors, an associated computer or
programmable logic
controller (PLC) can immediately perform safety measures such as closing in
blowout
preventers, dumping of heavy mud down hole, signaling alarms and other related
tasks.
The pressure sensors also can compare the pressure differential to help
monitor the
integrity of the operation. The higher the differential, the less efficient
the drilling
operation. The "Smelling" sensors which are installed can detect certain
problem gases
such as HZS. It is better to detect this gas at its source before it is
detected at the well
surface.
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CA 02521287 2005-09-27
Figure 15 is an illustration of a typical mud motor 750. The mud motor
illustrated in
Figure 15 includes a bent section 751 as a part of the assembly. This bent
section 751
can rotate separately from the remaining straight section 752. This enables
the drill pipe
assembly to drill at an angle relative to the horizontal axis 753 of the
straight section 752.
If the drill pipe is pushed further into the hole without the drill pipe
assembly rotating,
the bent section 751 of the mud motor will continue to drill at an increasing
angle. This
action creates a radius or segmented radius depending upon the drilling
technique being
utilized. If the straight portion 752 of the mud motor is rotated,
theoretically the mud
motor assembly will drill straight ahead, thus drilling a straight hole. Mud
motors are
generally driven by fluids at high volume rates forced through the center of
the
conventional drill pipe. At the intersection between the bent portion and the
straight
portion is a conventional adjustable angular mechanical adjuster (not shown)
that is used
to control the angle of deviation of the drill string. Normally the adjustment
must be
made by loosening bolts and clamps inside the structure. This generally
requires that the
adjustment be performed above ground, normally inside a machine shop or
controlled
shelter.
Figure 16 is an illustration of an electric drill motor assembly 754 similar
in function to
the mud motor 750 of Figure 15. However, in this case, the assembly 754
incorporates
an electric motor 755 which drives the bit 756 rather than being driven by
drilling fluids.
The illustration in Figure 16 shows a simple arrangement for an electrical
drill motor
assembly. In practice, there may be several motors in series to achieve
increased drilling
torque. A major advantage in an electric design is that the length of the
assembly can be
shortened considerably. Also, in the electrical drill motor assembly
illustrated in
Figure 16, the mechanical adjuster would be the same as discussed with respect
to
Figure 15.
Figure 17 is an illustration similar to Figure 16 of an electrical drill motor
assembly 757
including a drill bit 759, an electric motor 761, a bent sub 763 and a second
motor 765 on
the bent sub. The pivot sub 767 can clamp and unclamp electrically so that the
pivot
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CA 02521287 2005-09-27
angle can be controlled while drilling. In this case, it incorporates an
angular adjuster
which would be electrical/mechanical in nature instead of being totally
mechanical in
nature as previously described. This type of design enables the angle
adjustment to be
made down hole. Also, the drill assembly can be adjusted to a straight
position. As a
result, the drill string will not need to rotate in order to drill a straight
hole.
Figure 18 is an illustration similar to Figure 16, except that one or more
electrical
motors 769, 771 are mounted on the straight section 773. These additional
motor(s)
provide the ability to drill without rotating the drill string, which in turn
increases the
fatigue life of the drill string. However, the mechanical adjuster would be
fixed and non
adjustable down hole. Another advantage of eliminating the need to rotate the
drill string
is the ability to run the assembly utilizing coil tubing. Coil tubing is not
normally rotated
during drilling operations.
The electrical motors which are illustrated in Figures 16-18 can have hollow
shafts and
be lined with the same material as the drill string inner tubes. Also the
casing of the
electrical motors can have cooling vents plumbed in order to channel the
fluids to the
hammer bit or conventional bits for cutting.
In operation, several advantages of the dual wall drill string assembly of the
present
invention are achieved, whether with jointed, dual wall pipe or with coil
tubing. First, a
borehole is drilled by the drilling mechanism. The cuttings produced by the
drilling
mechanism are conveyed to the inside of the flexible, substantially non-
metallic inner
tube of the dual wall drill string as fluid under pressure is conveyed through
the annular
channel of the drill string toward the drilling mechanism. Moreover, the dual
wall and
coil tubing drill string assemblies of the invention claimed herein are
adapted for use in
all subsurface drilling applications. The flexible, substantially non-metallic
(and if
practical, non-conductive material) inner tube of the drill string assembly of
the present
invention permits the assembly to be used in all subsurface drilling
applications because
the inner tube is flexible and transmits considerably less bending resistance
to the outer
tube. In addition, the flexible, substantially non-metallic, and possibly non-
conductive
inner tube is adapted to substantially enclose a conductive element for
conveying a signal
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CA 02521287 2005-09-27
to the navigation transmitter. Consequently, the direction of the drilling
mechanism can
be monitored, and short circuiting of the conductive element on the metallic
outer tube is
avoided. Flexible sleeves also contribute to the ability of the preferred
embodiment of
the dual wall and coil tubing drill assemblies of the present invention to
function in any
subsurface drilling applications. Further, according to the method of the
invention
claimed herein, the dual wall and coil tubing drill string assemblies are
capable of
reaming the arcuate path of a borehole in any subsurface drilling
applications. Still
further, the assembly is capable of pulling or pushing a product such as
pipeline, ducts
and the like into the arcuate path of a subsurface borehole. The inner tube
wall also can
have pressure sensors along the length of the string to monitor the pressures
and detect
any abnormal pressures that may be unanticipated from down hole formations.
Additionally, the inner tube wall can have sensors to detect the presence of
hazardous
gas.
Although this description contains many specifics, these should not be
construed as
limiting the scope of the invention but as merely providing illustrations of
some of the
presently preferred embodiments thereof, as well as the best mode contemplated
by the
inventors of carrying out the invention. The invention, as described herein,
is susceptible
to various modifications and adaptations, and the same are intended to be
comprehended
within the meaning and range of equivalents of the appended claims.
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