Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02448935 2003-11-12
HIGH DENSITY PLASTIC TUBING WITH INCLUDED POWER
TRANSMISSION CABLING FOR DOWNHOLE USE IN PETROLEUM
INDUSTRY
FIELD OF THE INVENTION
The present invention relates generally to provision of electrical power
downhole
to power tools such as pumps, valves, motor-driven drilling tools, grapples
and the like.
More particularly, the present invention relates to the provision of
electrical power and
high-density plastic tubing for use in completion or production techniques in
some oil and
gas production settings, commonly referred to as "coiled" or "endless" tubing.
BACKGROUND OF THE INVENTION
It is known in the art of extraction of petroleum products from formation
through
well-bores to provide a solid walled casing to seal the well-bore from the
earth within
which it resides to protect its integrity and the integrity of the conduit
formed by the
casing from production zone to surface. In recent decades, the technique of
providing a
second conduit within the casing's conduit by insertion of endless or coiled
tubing with
outside diameter less than the inside diameter of the casing structure has
become quite
common. There are several reasons for providing that second, included conduit.
Some of
those reasons are: to provide a conduit from two (or more) different
production zones by
producing from a segregated region within the casing's length directly to the
inserted
tubing, by segregating its opened bottom end from the annulus between casing
and tubing
so that production from that zone can be done through the tubing, while
producing from a
different zone through the annulus; another sample reason is to provide a
conduit of
smaller diameter than the casing so that the produced gas will be forced
through the small
diameter tubing by formation pressure to surface at a much higher velocity,
and thus carry
with it included liquids which would otherwise collect at the well's bottom
end, and
eventually the weight of the column of collected fluids in the wellbore would
overbalance
or shut-in the gas production from formation.
In US6,357,485B2 (Quigley, et al.) is disclosed a method of construction of a
composite endless tubing structure made up of layers of material of different
characteristics; for example, an outer layer which is abrasion resistant, a
middle layer
which has high tensile strength, another middle Layer which is of braided cord
and
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provides enhanced burst strength, and an inner layer providing low friction
for fluid flow,
all while providing a continuous tubing string with bending characteristics to
permit it to
be rolled onto conventional truck-mounted reels for use in the oil industry.
While useful,
this invention addresses requirements for a varied blending of characteristics
of tubing, but
provides no assistance with operating machinery downhole.
In US6,361,299B1 (Quigley et al.) is provided an endless tubing string with
optical
fiber (or similar energy conductor) communicating between an included sensor
(or string
of sensors) in the tubing and the surface such that the state of the sensor
(and thus an
inference of what it is designed to sense) can be communicated to surface
equipment.
Again, this fails to assist with operation of downhole equipment. Likewise,
US6,004,639
provides for a similar sensor and communication conduit system embedded or
included
within the wall of an endless spoolable tubing string for use in the oil
industry.
In US5,920,032 (Aeschbacher et al.) a rigid tubing string is provided with a
centralizer within which power cable and signal conductors are deployed, and
around
which centralizer can be installed insulation, stiffening matter, or
alternatively the voids
within the tubing formed by the centralizes can be used to convey fluid or
fluid pressure
downhole. While of interest, it is to be noted that this system is rigid or
semirigid, is not a
continuous spoolable tubing string, is difficult to manufacture, and provides
quite a large
impairment of free flow within the tubing's central void by interrupting the
space with the
centralizes and conduits.
In US5,554,425 (ICrause et al.) is disclosed a method of manufacturing
continuous
tubing from flouropolymers in several layers using extrusion and then co-
extrusion in
series. While of some interest in providing a mufti-layered composite tube
structure, and
of some interest in the manufacturing process, neither the technique nor the
resulting
product is very helpful in providing endless spoolable tubing strings or
assistance with
operating machinery downhole.
US5,334,801 (Mohn) discloses a method of providing connectable series of pipe
segments with included power cable in or on the pipe segments' walls, to form
a
continuous set of electrical circuits notwithstanding the juncture's coupling
mechanism
must provide for sealing of the pipe segments one to the other, as well as
providing de-
couplable structural joints. Another interesting concept, but this fails to
provide for the
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more efficient continuous spoolable plastic coiled or endless tubing systems
preferred in
modern completion and production settings.
None of the prior art accessible to the inventor succeeds in providing the
desired
characteristics to the art of oil and gas well completion and production using
endless or
coiled tubing made from plastics while at the same time providing means of
assisting in
the operation of machinery downhole.
It is, therefore, desirable to provide a system of coiled tubing made from
plastic
which provides assistance in the operation of machinery downhoIe, and to
overcome the
shortcomings of the prior art.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one
disadvantage of previous systems noted above.
In a first aspect, a coiled tubing string is provided for conducting electric
power to
a downhole location to provide power to downhole machinery. The tubing string
comprises flexible tubing defined by a homogeneous wall of embedding material,
the
tubing wall having an interior surface and an outer surface; and at least one
electrically
conductive cable embedded within the wall between the interior surface and the
outer
surface, the at least one cable extending axially along the tubing for
conducting electric
power along the length of the tubing.
In one embodiment, the cable is copper wire, which may be from about 10 gauge
to about 4 gauge copper wire. Preferably, the wire is insulated, for example
flat ribbon-
cable, with each wire lead separately insulated.
In a further embodiment, the coiled tubing is capable of providing power to a
downhole tool, which may be a pump, a drill, a heater, a sonic source, a
mechanical
energy source, or any other electrically powered tool that may be used
downhole.
In another embodiment, the embedding material is a plastic, preferably a high-
density polyethylene. The thickness of the wall should be similar to that
known in the art,
preferably having a thickness between 0.25 and 5.25 inches.
In a second aspect, a coiled tubing is provided comprising an inner tubing
layer of
a first flexible material; an outer tubing layer of a second flexible
material, and at least one
electrically conductive cable disposed between the inner tubing layer and the
outer tubing
layer such that the cable is effectively embedded between the tubing layers,
the at least
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one cable extending along the entire length of the tubing for conducting
electric power
along the length of the tubing.
In one embodiment, the first or second flexible material is a high-density
polyethylene. Preferably, both the f rst and second materials are high-density
polyethylenes.
In a third aspect, the present invention provides a method of constructing an
endless or coiled tubing string of plastic by two extrusion steps with an
intermediate
wiring step.
A further aspect provides a method to manufacture coiled tubing comprising the
steps of extruding a first flexible tubing, laying at least one electrically
conductive cable
against the outer surface of the tubing such that the cable extends along the
entire length of
the tubing, and passing the flexible tubing and cabling through a co-extrusion
device to
extrude a second layer of flexible tubing over the outer surface of the first
tubing, thereby
embedding the cabling between the first and second flexible tubing layers.
In one embodiment, the co-extrusion device is an extruder and crosshead die.
In
another embodiment, the step of laying the cable over the first tubing layer
occurs while
the first flexible tubing layer is still tacky from the extrusion process,
such that the cable
will adhere to the surface of the first tubing layer.
The coiled or endless tubing string with included power cabling is capable of
conveying electrical power downhole to operate and power machinery in situ
from surface
without having to rely upon pressure or fluid flows or other complex energy
transmission
means such as rods, rotating tools, or the like.
In further aspect, the present invention provides an improved method, using
the
coiled tubing with embedded cabling, of powering tools downhole. Such tools
may
include a pump, a drill, a motor, a heater, a sonic source, a mechanical
energy source or
any other electrically powered tool that may be used downhole.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, with reference to the attached Figures, wherein:
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.~.._...__.._.___.. .. ___....~ _ .. ~~._ ...__.._ ._.... $ _ __
CA 02448935 2003-11-12
Fig. 1 is a cutaway cross-section of the tubing once built
Fig. 2 is a block diagram describing the steps for manufacturing the coiled
tubing
Fig. 3 is a cross-section of the tubing installed within a wellbore casing
DETAILED DESCRIPTI~N
The tubing comprises an outer surface 1, a wall structure made of at least two
parts
and 20 which are formed into one by joining typically by melting at their
interface 10
during the extrusion and co-extrusion process (figure 2), embedded or included
cables 15,
and a smooth inner surface 25 with a conduit or void 30 in the center.
The tubing is constructed by first extruding an inner layer 20 with smooth
interior
surface 25 forming a void or conduit 30 and a temporary outer surface at 10;
electrical
conducting cabling 15 is laid onto the outer surface 10 while that surface is
tacky; the
tubing is pulled through a co-extrusion device (extruder and cross-head die)
and a second
layer of plastic 5 is extruded over the first tubing to form a singIa~walled
tube with
included power cable. The inner diametex and outer diameter, wall thickness
and cable
material and thickness may be varied to obtain desired performance
characteristics for use
in production and extraction of petroleum products from formation using
conventional
coiled-tubing rigs, packers, sealers, and equipment.
When in a wellbore with casing 40, the tubing string 1,5,10,20,15 will have an
inner conduit 30 of appropriate size to, for example, permit high-velocity
production of
gas and included liquids to avoid accumulation of produced liquids in the
wellbore.
Alternatively (or as desired), the annulus between the inside surface of the
casing 45 and
the outside surface of the tubing 1 can be used as a second conduit for
production from the
wellbore, the introduction of pressurized material into the wellbore, or as
otherwise
desired. The invention provides several added power conducting cables 15 to
provide
electrical power from surface to the bottom of the tubing string to operate
relatively
heavy-load equipment such as pumps, drills, and the like. Similarly, the same
conductors
can be used to either simultaneously or separately provide a means of
conducting electrical
or electromagnetic signals either to or from surface and either from or to
sensors or
equipment downhole.
The conductors 15 can be insulated or uninsulated prior to installation in the
manufacturing process. The layers of the plastic extrusion may be more than
two, and may
be of different substances. As noted in the prior art discussion, there may be
layered within
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the tubing composite layers of differing materials to provide different
characteristic mixes
to the final construct, provided that there is embedded wiring between two
extruded layers,
which should preferably bond one to the other without leaving any voids or non-
bonded
surfaces at their place of meeting 10.
The above-described embodiments of the present invention are intended to be
examples
only. Alterations, modifications and variations may be effected to the
particular
embodiments by those of skill in the art without departing from the scope of
the invention.
The tubing is contemplated to be manufactured of higlrdensity polyethylene or
similar plastic extruded in a continuous process, the first step being to
extrude a tubular
shape with an inside diameter (ID) as desired in the final product,
immediately following
that extrusion process, power cabling comprising (typically) electrically-
conductive
metallic power leads which may or may not be separately insulated is laid onto
the outer
surface of the tubing which surface is preferably still tacky from the initial
extrusion
process, and following which the tubing with cabling has a further outer
coating of the
(probably the same but not necessarily so) high-density palyethylene or
similar plastic
extruded onto its outer surface to an outer diameter (OD) desired- in the
finished product,
which may involve milling as a final step. Ideally, the two extrusions of
plastic meld and
form one body with the cabling embedded seamlessly within the body. Other
embodiments may include different layers of laminated plastics of different
types (for
example, outer surface may be abrasion-resistant and inner. surface may be
corrosion-
resistant or load-bearing, or have other characteristics which are
complementary to the
tubing string's eventual purpose).
For utility in the planned application, which is to provide useable electrical
power
(i.e. not signals, but electricity to power mechanical devices) to bottom hole
via a
continuous (or relatively continuous) tubing string to power things like
valves, pumps,
drive motors, etc., the cabling is likely to be minimum 10 gauge wiring to
probably 4
gauge copper wiring. The wiring is preferably pre-manufactured in rolls of
flat ribbon-
cable, each wire lead separately insulated.
The tubing's wall thickness and materials must maintain desirable
claracteristics
within temperature ranges of approximately -40 to +40 degrees Celsius.
Desirable
characteristics include wall strength to withstand a pressure differential
between the
tubing's interior and its exterior of in the range of 2,000 pounds .burst
Pressure. Other
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desirable characteristics include resistance to longitudinal stretching, and
the ability to
bear a longitudinal load. Typical tubing sizes might be from l and i/4" to 6"
OD (typically
3") with ID, respectively relative to the list of ODs above, of 3/4" to 3"
(typically 1"),
resulting in a wall thickness of approximately 0.25 to S,2S inches.
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