Note: Descriptions are shown in the official language in which they were submitted.
I
SHRINK-FIT CONNECTOR FOR ELECTRICAL
JELL SUBSURFACE HEATING PROCESSES
Background of the Invention
This invention pertains to a special Waldo
electrical insulating connector for electrode wells used
for electrical heating of a subsurface viscous oil bearing
formation. More particularly, this invention concerns an
iron base metal and ceramic insulating connector wherein
the outer surface of the ceramic and the inner surface
of the metal are joined by heat shrink fitting with an
intermediate layer of high expansion, softer, stress
controlling nonferrous metal.
In the recovery of oil from viscous oil bearing
formations it is usually possible to produce only a very
small portion of the original in-place oil by natural or
primary production which relies solely on the natural
forces present in the formation. A variety of artificial
recovery techniques, therefore, have been employed to
increase oil recover. It has been proposed, for example,
in US. Patents, 3,6~2,066; 3,874,450t 3,848,671; 3,948,319;
3,958,636; 4,010,799 and 4,084,637, to use electrical
power to add heat to a subsurface pay zone containing tar
sands or viscous oil to render the viscous hydrocarbons
more plowable. In general, two or more electrodes are
connected to an electrical power source and are positioned
at spaced apart points in contact with the earth in a
manner such that when electric current is passed between
the electrodes it will heat viscous oil in the subsurface
formation. Voltages of 200 volts and up to and exceeding
1000 volts are applied to the electrodes. Currents up
to 1800 amperes are passed between electrode wells.
I.
~2~2~
Most of the heat venerated by power consumption in or
near the formation occurs in and adjacent to the electrode
well and heat transfer outward into the formation by
conduction is slow. This leads to temperatures up to
and possibly exceeding 500~F. This heat is conducted by
the tubing and casing to the Waldo of the electrode
wells. The Waldo fittings, therefore, must be capable
of safely withstanding these elevated temperatures
In subsurface electrical heating processes
whether or not the electricity is flowed through the
casing tubing, the voltages and currents used cause power
leakage flow and discharge to surface equipment if standard
Waldo electrical isolating devices are employed.
Standard Waldo electrical isolating devices have
closely spaced metal parts and thin electrical insulate
in material. The space between the metal parts is
easily shorted by debris, chemicals and the products of
corrosion. The electrical paths around the electrical
insulation allow power leakage and sometimes act as
power consuming resistance paths which generate heat at
the Waldo. It would, therefore, be desirable to
provide a reliable Waldo connector that reduces power
leakage losses and does not provide resistance paths
that act like an electrical resistance heater. it is an
object of this invention to provide a Waldo connector
- which acts as an electrical insulator. It is a further
object of this invention to describe an insulating con-
nectar for a Waldo of an electrode well used in
electrically heating a subsurface formation in which
extreme stresses are relieved or prevented and other
stresses are better controlled. It is still a further
object of this invention to provide an insulating con-
nectar that will safely withstand temperatures up to
and exceeding 500 F.
Summary of the Invention
In accordance with the present invention, there
is provided an insulating connector especially suited
for use in the Waldo of an electrode well used in
electrical heating of a viscous oil bearing subsurface
formation wherein at least one metal well string extends
from the Waldo downward toward the subsurface formation
The connector has good electrical insulating properties
while providing adequate strength and reliability for
the elevated temperatures and high voltages and currents
encountered in heating a subsurface formation by electric
eel power dissipation in the formation. The insulating
connector is capable of withstanding temperatures up to
500F and may be formed to withstand even higher tempera-
lures. The connector is comprised of three essential
elements heat shrink fitted together. The first element
is a generally tubular shaped ceramic member. Ceramic
is a good electrical insulator and a poor conductor of
heat. Two iron base metal members (for example, bolt-type
flange halves especially adapted to this invention) and
- an inner nonferrous second metal are heat shrink fitted
to the ceramic member. The second metal (for example,
copper) has a higher thermal expansion coefficient than
the iron base metal. Ordinary ferrous metals have a
thermal expansion coefficient greater than ceramics. As
the temperature increases the metal members expand greater
~%~32~
than the ceramic and the amount of interference and the
strength of the heat shrink fit are reduced. In order to
obtain sufficient joint strength at elevated temperatures
it is ordinarily necessary to increase the amount of
interference of the heat shrink fitted joint at room
temperature. This stresses the ceramic to below acceptable
safety factors and may even cause failure. In addition,
cycling temperatures create deformation stresses which
tend to be localized and exerted at unsafe levels. The
second metal is positioned and has thermal expansion and
deformation characteristics which reduce peak stresses
and more uniformly distribute the stresses while main-
twining adequate heat shrink joint strength.
Other features which improve the quality and
control of various parameters affecting the heat shrink
fit insulating connector include the amount of interference
required per inch of outside diameter of the ceramic
member, length of interference surface relative to the
outside diameter of the ceramic member, matching slightly
tapered mating surfaces, beveling the outside surface
of the overlapping inner end of the metal members, and
using a ceramic member with a flow passage larger than
the flow passage through the metal members.
Brief Description of the Drawing
The drawing is a side longitudinal cross-
sectional view of an insulating connector using flange-
like members and having all of the features covered by
this disclosure. The drawing is not to scale.
Detailed Description of the Preferred Embodime _
In the heating of a subsurface, viscous oil
~22~
bearing formation by passing electrical current through
the formation, various types of electrode well configurations
have been proposed. In general, the electrode well has
one or more casing strings and a tubing string which
extend downward toward the subsurface formation. The
tubular casing and tubing strings are connected to a
Waldo which has casing and tubing heads which form a
part of a Waldo. The Waldo is also connected to
flow lines leading to various types of injection or
producing equipment and tanks. In some installations, an
electrode is lowered through the casing or tubing on a
cable to an appropriate point from which electrical
current may be passed through the formation. In other
installations, the casing or tubing may be used both as
an electrical conductor and as an electrode.
Regardless of the type of electrode well complex
lion, voltage and electrical current are present in
casing and tubing. As electrical power is consumed,
heat is generated adjacent or in the electrode well
causing increase Waldo temperature. An electrical
insulator that can withstand elevated temperatures is
required in the casing or tubing string. Ordinary ins-
feting gaskets, bolt insulators and insulating washers
are inadequate for the voltages and temperatures en-
countered in electrode wells used in electrical heating
- of subsurface formation. Adequate leak tightness and
pull-out strength approaching steel can be achieved by
heat shrink fitting bolt-type flange halves or other
types of steel fittings to a piece of ceramic pipe. But
the difference in expansion between the ceramic and
I
steel causes a decrease in shrink fit interference as
the temperature increases. For example, for ten inch
diameter ceramic and a shrink-on N-80 steel member it
is necessary to use 0.025 inch interference at room temperature
to have 0.005 inch interference remaining at 500F. The
high interference at room temperature creates considerable
stress in the ceramic and steel. Normally, this problem
would be solved by using less room temperature interference
and donating the insulator to a lower temperature.
Another solution would be to use a higher yield, more
expensive ceramic if a different stronger ceramic is
available. Still another solution is to use a controlled
expansion metal alloy (for example, 42% nickel, or titanium)
to better match the expansion properties of the ceramic,
but such alloys are very expensive and are not readily
available.
In the drawing there is shown a different soul-
lion. There is illustrated a strong heat shrink fitted
ceramic and steel insulating connector using conventional
materials. The Waldo insulating connector is comprised
of tubular ceramic member 11 Stormed of a suitably strong
ceramic material of good electrical insulating properties
and having a thermal coefficient of expansion lower than
that of ordinary iron base metals used in wilds,
flow lines and casing and tubing strings in oil and gas
production. The thermal coefficient of expansion of the
ceramic is 8.7 X 10-6 inch per inch per degree Centigrade
an the thermal coefficient of expansion of steel vary
between 10.5 to 13.5 X 10-6 inch per inch per degree
Centigrade between 60 and 500F. One such ceramic
--6--
material is Corning pyroceram~ This is the type of
ceramic used in nonbreakable chinaware. A more preferred
ceramic material is the Malta ceramics containing 85%
to 95% alumina (for example, Coors-type AD 85 and AD
94). Aluminum oxide ceramics are strong and readily
ground. They are also less susceptible to acid fluids
used in well treatments than the pyroceram ceramics.
The ceramic should be suitable for grinding for perfect
fit purposes for reasons hereinafter made apparent.
Tubular ceramic member 11 has a central generally
cylindrically shaped internal flow passage 12 extending
longitudinally through the ceramic member. This flow
passage permits the insulating connector to be used in
the Waldo of an electrode well as a part of the Waldo
and tubing or casing string. The ceramic member has a
generally cylindrically shaped outer surface 13 which
optionally is slightly tapered at about 0.5 degrees in a
manner such that the outside diameter of the tubular
ceramic member is slightly smaller at its ends. The degree
of taper in the drawing is exaggerated for illustration
purposes.
Shown are two iron base metal members 14 and 15
with tubular sections 16 and 17, respectively, projecting
inwardly overlapping and extending over and around the two
ends of ceramic member 11 and in a manner such that inner
ends 18 and 19 of the tubular sections are spaced apart
and do not touch each other. This electrically isolates
the metal members from each other. Preferably, the ends
of the tubular sections will be separated by a distance
of at least two inches. A spacing ox two or more inches
~292~
assures electrical insulation. Metal members 14 and 15
have central generally cylindrically shaped internal
flow passages 20 and 21, respectively, extending through
the metal members and in line and in communication with
flow passage 12 extending through ceramic member 11.
The diameter of flow passage 12 in the ceramic member is
greater than the diameter of flow passages 20 and 21.
This reduces possible damage to the ceramic member when
tools or cables are lowered into and removed from an
electrode well using the insulating connector of this
invention Metal members 14 and 15 are any sort of
coupling or flange suitable for connection to a well
string or Waldo. Bolt-type flange halves are pro-
furred since they may be connected in the well system
without subjecting the ceramic member and shrink fit
joints to torque. Accordingly, metal members 14 and 15
ens shown as bolt-type flange halves with tubular sections
16 and 17 extending inwardly and toward each other. The
flange halves have mating or outer face surfaces 22 and
23 and inner face surfaces 24 and 25. Illustrated are
standard ring-joint or seal ring flanges which have
standard jolt holes 26, 27, 28 and 29, which are usually
provided in multiples of four with pairs on the same
center or diameter line. The flange members are shown
with ring grooves 30 and 31 for use with a metallic seal
ring. Standard ring joint flanges are usually marked
with the ring groove number. Seal ring flanges are
shown, but it is understood that any type of flange may
be used (for example, male-female flanges and tongue and
groove flanges). Since half flanges are frequently
supplied in matching pairs, it is preferred that half
flange metal members be obtained in matching pairs and
the respective mating halves used with the insulating
connector of this invention.
Tubular sections 16 and 17 are shown inserted
into circular grooves 32 and 33 respectively and welded in
place by inner and outer welds 34, 35, 36 and 37. This
method of attaching is especially suited to the kirk-
touristic of the insulating connector because the bore
diameter and thickness of ceramic member 11 are greater
than normally used with Waldo flange halves. Inner
generally cylindrical walls 38 and 39 of the tubular
sections optionally have slightly tapered surfaces of
about 0.5 degrees so that the diameter of the cylindrical
walls nearest the flange ends is less than the inside
diameter of the tubular sections at ends 18 and 19.
The degree of taper is exaggerated for illustration pun-
poses. This taper matches the taper previously mentioned
of the outer surface of the ceramic member ends. The
matching tapers of the ceramic member and iron base
tubular sections improves the seal between the outer
surface of the ceramic member and the inner walls of the
tubular sections.
The iron base tubular sections are shown heat
shrink fitted to ceramic member 11 with a layer of non-
- ferrous metal 40 and 43 between cylindrical walls 38 and 39
and outer surface 13 where the ceramic and tubular sections
overlap and extend over and into each other. The thickness
of the nonferrous metal may be very thin. the nonferrous
metal has a yield strength less than that of the iron
9~3
base metal. It also has a thermal coefficient of expansion
greater than the thermal coefficient of expansion of the
iron base metal in metal members 14 and 15. The preferred
nonferrous metal is copper which has a yield of about
40,000 psi and coefficient of expansion of 14 to 17.8 X 10-6
inch per inch per degree Centigrade between 60 and 500F
compared to steel having a coefficient of expansion of
10.5 to 13 X 10-6 over the same temperature range and a
yield greater than 70,000 psi. Tin which has a yield of less
than 20,000 psi and a thermal coefficient of expansion of about
2~.9 X 10-6 inch per inch per degree Centigrade may also be
used as the nonferrous metal. The nonferrous metal is
an essential element of this invention. The tubular
sections and nonferrous metal are heat shrink fitted on
the ends of the ceramic members where they overlap and
extend into and over each other. Heat shrink fitting
requires that at room temperature the diameter of inner
generally cylindrical walls be slightly less than the
outside diameter of the ceramic member. The difference
in diameters is called interference and is typically
measured in miss. The amount of interference required
for the heat shrink joint depends on the nature and strength
of the materials joined, the service or working requirements
for the joint, the diameters, ring thicknesses and
coefficients of expansion of the materials joined, the
- lengths of the interference surfaces, and the friction
coefficients between the surfaces of the joints.
For purposes of this invention, it is preferred
that the interference be at least 1 mix per inch of
outside diameter of ceramic member 11 (for example, for
--10--
it
Coors ~D85 alumina ceramic, a room temperature interference
of 19.8 miss for 300F, of 28.3 miss for 400F and of 37
miss for 500F is preferred for 16.5 inch outside diameter
fitted to ASTM AHAB steel) For purposes of this invent
lion, it is preferred that the length of the interference
surfaces be at least one inch for every 2.5 inches of outside
diameter of the ceramic member. For example, for ASTM
AHAB steel shrink fitted to Coors AD 85 ceramic to be
subjected to a service temperature of 500F, there is
preferred a minimum interference length of 1.06 inches
for 2.5 inch OX ceramic, I inches for 10 inch OX
ceramic, and 6.95 inches for 16.5 inch OX ceramic. The
heat shrink fit may be formed by grinding or cutting
the mating surfaces to proper dimensions and tapered
within close tolerances (for example, with 0.0005 inch
and with a number 60 fished). This assumes proper fit
both for seal and stress purposes. The nonferrous metal
layer may be formed by applying a coating of the non-
ferrous metal to the overleaping inner surfaces of the
walls of the generally cylindrical shaped flow passage
of tubular sections 16 and 17 before the ferrous metal
member is heat shrink fitted to the ceramic member.
Thereafter, the ceramic member and the iron base metal
member with an inner nonferrous layer are properly
aligned and the metal members are heated (for example,
with band heaters) to a temperature above the maximum
design service temperature and to a temperature (for
example, ~50F) high enough to expand the iron base metal
until the cylindrical shaped passage through the tubular
sections will allow them to be slipped over the end of
the ceramic member. A suitable sealing cement may be
added to prevent crevice or bimetallic corrosion of the
ferrous material.
In operation, very high tensile and compressive
stresses would result from expansion, shrinking and
bending of the ceramic and ferrous members it it were not
for the intermediate layer of lower yield strength non-
ferrous metal having a thermal coefficient or expansion
greater than the ferrous metal. The properties of the
nonferrous metal causes it to yield cure deform to
compensate for the differences in expansion between the
ferrous metal members and ceramic members The non-
ferrous metal more uniformly distributes the stresses and
thereby reduces the changes for peak localized stresses.
Sometimes the diameters and thicknesses are such that high
stresses may arise in ferrous tubular sections 16 and 17
and ceramic member 11 near inner ends 18 and 19. In such
cases, the magnitude of these stresses may be prevented
by the outer surface of tubular sections 16 and 17 near
ends 18 and 19 to reduce the thickness of these tubular
sections. This is illustrated by beveling surfaces 41
and 42.
The present invention has been described herein
with reference to particular embodiments thereof. It will
be appreciated by those skilled in the art, however, that
- various changes and modifications can be made therein
without departing from the scope of the invention as
present.
