Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OE' THE INVENTION
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Multicomponent electrical cables are used to supply
power -to submersible pumps which lift crude oil and brine to
the surface from depths up to 4,000 to 10,000 feet. These
great depths require that the pumps be driven by motors which
operate at high power le~els, sometimes over 200 horsepower.
The motors are usually a polyphase type requiring a power cable
having three conductors.
These oil well cables must maintain dielectric
strength in the presence of a mixture of crude oil and brine
containing hydrogen sulfide gas, carbonates, chlorides, and
sulfur compounds. Because most oil wells contain conslderable
amounts of brine, there is a high percentage of cable failures
when the brine is absorbed into the cable. In the past,
materials have been selected to make the jacketing impervious
to all liquids so that the insulation surrounding the con-
ductors would keep dielectric integrity. In addition, the
jacketing material was sought to be gas impervious CO that
gases would not diffuse into the cable under the high pressure
and high temperature environment in the depths of the well.
This is not possible with polymeric materials known today.
Materials with low permeability to gases in the well would, it
has been found, be subject to "blow-out" of the cable jacketing
and insulation when the cable was raised from the well.
The power cables usually have an outer metal armor
comprising a continuous band of metal wrapped around the jac-
ket. The band is lapped as it is wrapped so as to provide
flexibility as well as abrasion resistance~ Flexibility of the
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armor, as well as the other cable materials, is required be-
~ause the cables are stored and transported on reels. Abrasion
resistan~e is required because the cable rubs on the well casing
walls as it is inserted through a small opening for several
thousand feet.
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SU~ ~RY OF TH~ INVENTION
The invention provides an electrical power cable
for submersibl- oil well pumps, particularly deep well pumps,
having at least two and normally three electrical conductors
embedded in an ethylene-propylene copolymer or an ethylene-
propylene terpolymer jacket. The conductors are electrically
insulated from one another either by the jacket composition
itself or by ~eparator insulation about the conductors. An
outer armor of metal is wrapped around the jacket to radially
confine the ]acket and provide abrasion--~resistance and
strength with flexibility.
The e~hylene-propylene copolymer or the ethylene-
prop~lene-hexadiene terpol~er compound which forms the jac-
keting material of this invention is, pervious to gases a~d is ¦
selectively permeable to crude oil over brine. These pervious
',properties not only permit the deep well gases to penetrate the ~ ''
~' jacket, but readily permit the escape of the gases when the
pressure is reduced around the cable. Thus, "blow-out" pro-
blems are substantially eliminated. 'Because of the selective
permeability of the terpolymer to the crude oil, a nonpolar
` material~ the ~ielectric strength of the cable is not signifi-
cantly reduced when immersed in the hot liquid of the well.
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The outer armor of the cable provides not only abra-
sion reslstance and strength for the cable, but acts as an in-
direct barrier to the gross penetration of the elements in the
well environment. The metal band is tightly wrapped around
the cable so as to hold the polymer jacket under compression.
This compression reduces the ability of the high pressuré gases
and hot liquids in the well to swell the cable jacket and in-
sulation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary perspective view of a section
of electrical conducting cable for submersible motors illustra-
ting the unitized jacket and insulation;
FIG. 2 is a cross-sectional view of the cable in
FIG. 1 taken generally along the lines 2-2 of FIG. l;
, 15 FIG. 3 is a fragmentary perspective view of a section
.~ ~f electrical conducting cable for submersible motors illustra-
; ting separately insulated conductors embedded in jacketing
-~ material; and
` FIG. 4 is a cross-sectional view of the cable in FIG.
.~, 20 3 taken generally along the lines 4-4.
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DESCRIPTION OF THE PREFERE~D EMBODIMENTS
Referriny to the drawing, there are shown multi-
component electrical conducting cables for submersible pumps
designed for use in high temperature, high pressure oil wells.
FIGS. 1 and 2 show a cable section comprising
--- multistranded conductors 1, surrounded by an insulation
jacket 2, and the entire package pro~ected by armor 3.
Each conductor 1 is formed of strands of wire helical
twisted to prevent separation of the strands and to allow ex-
tensibility of the conductor. These separate strands may bevarnished to minimize chemical interaction between the con- ¦
ductor and the insulating material. The number o~ conductors,
the diameter of the conductor, and the number of wires is
dependent upon the load carrying capabilities required for the
particular application. Illustrative of the several materials
whi~h can be used for conductors in the cable are copper,
aluminum, steel, and var~ous a]loys thereof. Preferred of
; the~e is, of course, copper.
The cable shown in FIGS. 1 and 2 has a unitary
construction intended ~or use in app:Lications whose cabl~e
specifications require the same ethylene-propylene co- or ter-
- polymer compound for both insulation and jac~eting. In this
casel conductor 1 may be encapsulated in the jacket compound
2 by a one-pass extrusion process which achieves simplified~
fabrication, homogeneous encapsulation of the conductors, and
substantial savings in cable production time and cost.
`1 FIGS~ 3 and 4 illustrate a composite-cable
construction for use in applications whose spëcifications require
di~ferent polymeric materials for the conductor insulation and
cable jacket. In this embodimen~ conductors 11 are
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individually coated with insulation 12. Insulation 12 may
be selected from butyl rubber, sllicone rubber, or co- or ter-
polymers of ethylene and propylene, depending upon the pro-
perties sought in the final product. After insulation 12 is
coated onto conductors 11, a cable jacket 13 is applied about
the conductors by extrusion or other suitable means. Jacket
- 13 is selected from an ethylene-propylene copolymer or an
ethylene-propylene terpolymer in which the third constituent
is an unconjugated diene. Whichever cable construction is
used, the unitary insulation-jacket construction of FIGS. 1
and 2 or the separately insulated and jacketed construction
of FIGS. 3 and 4, the minimum distance between the outerpoint
on the conductors and the outermost point on the jacket must
be 75 mils to be rated for 3,000 volts or 80 mils to be rated
for 4,000 volts.
A typical ethylene propylene terpolymer which may be
employed in this invention is an amorphous material sold by
the E. I. duPont de Nemours and Co., Ltd., under the trademark
of "Nordel 1040." This material has a high molecular weight
as shown by its Mooney viscosity value (ML @ 250F) of 40.
The correlation of glass transition temperature with ethylene-
propylene ratio is reported by J. J. Maurer in Rubber Chemistry
and Techno ~ , 38, 979 (1965). This indicates the Nordel
1040 polymer contains about 25 to 30 mole percent propylene,
about 69 to 74 mole percent ethylene, and 1 to 2 mole percent
unconju~ated diene. Several unconjugated dienes may be used
to form this type of terpolymer including dicyclopentadiene,
methylene norbornene, ethyldiene norbornene, and 1,4-hexadiene.
Analytical data reported by K. Kiyimoto and S. Nakade in
Journal of Applled Polymer Science, 13, 1509 (1969~, established
that Nordel 1040 con-tains 1,4-hexadiene as the termonomer.
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In order to reduce material costs and to lmprove
processing, fillers are included into the polymeric composi-
tions in ~'loun~s ranging from approximately 5 percent to 55
percent by weight. Greater or lesser amounts of fillers may
be used; however, the properties of the cable are sufficiently
changed that it is not desirable to go beyond these amounts.
Generally, the preferred amounts will range between 25 and 40
percent by weight.
Chief among the fillers are silicas and non-hydrated
clays. Very minor amounts of other fillers, such as carbon
black or silicates may be included; however, because carbon
blac]c is electrically conducting, the amounts are kept to a
minimum. Silane treatment of some of the clays and silicas
may be required to provide good coupling between the clay and
the surrounding polymer.
A metal band of steel, Monel ~ or other corrosion
resistance metal is tightly wrapped around the polymeric
; portion of the cable so as to hold it under compression. The
band of metal is overlapped as ik is wrapped to provide outer
armor 3 in FIGS. 1 and 2 and 14 in FIGS. 3 and 4, which pro-
tects the cable against abrasion and partially protects the
cable against gross penetration of the high pressure gases
and high temperature liquids in the well. Thus, when ethylene-
propylene terpolymer absorbs the crude oil in the well, the
terpolymer swells until it reaches equilibrium with cable
armor 4 or 14. At this point, no further absorption of crude
oil into the cable takes place. Although the terpolymer
selectively absorbs crude oil in preference to salt water,
the absorption and
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compression of the cable polymers fuxther excludes the possi-
bility of polar materials diffusing into the cable polymer and
lowering the dielectric strength of the cable polymer. Thus,
rather than seeking to select materials which are completely
impervious to the oil well materials, the ethylene-propylene
terpolymer permits absorption of those materials which are
beneficial to the cable properties, and capitalizes upon their
usesO Similarly, the ethylene-propylene terpolymer is per-
meable to the high pressure gases found in the wells. Thus,
while the gases can readily permeate the cable ~acket, the flow
in the opposite direction is equally as free when the pressure
is released by raising the cable from the well. Therefore,
these cable may be raised and lowered rapidly without danger
of "blow-out."
Although a circular configuration is shown in the
drawings, it should be understood that the overall shape or
the arrangement of the components of the cable is not critical
to the present invention. The shape of the cable may be any
form which is convenient for the fabrication and the utility.
; 20 In addition to the round configuration shown in the drawings,~
the present invention contemplates flat cables in which the
conductors are in side-by-side relationship or round cables
which are fabricated according to United States Patent No.
3,2597687.
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