Note: Descriptions are shown in the official language in which they were submitted.
~ 25AE-0081
HIGH TEMPERATURE INSULATED CASING
1. FIELD OF THE INVENTION
This invention relates generally to insulated
casings .Eor hot fluid transfer and more particularly to
a new and improved insulated casing assembly for oil
well steam injection or above ground steam transport
which greatly reduces heat transfer between the ~luid
and the casing components, provides increased
structural integrity and reliability, and permits the
outer sections of plural casings to be repeatedly
and rigidly coupled together, using standard oil.
field equipment without Eluid leakage while the inner
sections of the casings absorb the lengthwise
expansion/contraction loads in response to the
temperature changes of the fluid which they carry
with minimal relative motions.
2. DESC IPTION OF THE PRIOR ART
Casing assemblies utilized to transfer fluids
downhole must be contructed so as to be structurally
rigid and leakproof while being capable o:E cycli.c
response to temperature changes of the fluid flowing
around them. This is particularly true when the
casing assembly is used to inject very h:igh temperature
steam into all oil well. The purpose of steam injection
is to lower the viscosity of heavy crude oil so that
it can be pumped or forced to the surface and thus
extend recovery. The casing ~e~lies which are
used in such a manner, however, are subject to several
potentially destructive forces. Very high static
i.nternal and external pressure forces are exerted on
the casing walls and the couplings when the assemblies
are inserted deep into the ground. Each casing is
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subjected to the axially directed force of the weight
oE the other casings suspended below it in the casing
string. The corrosive effects, the erosive effects,
and the pressure forces caused by the steam itself
on the internal components of the casing as well as
the differential thermal expansion of such components
caused by the high temperature of the steam and
contamination by downhole Eluids can cause structural
Eailure of the casing assembly. Insulated assemblies
currently used for transporting fluids of less extreme
temperatures cannot be readily adapted for oil well
steam injection purposes because of the severe conditions
encountered downhole in the well. Conventionally
insulated flowtubes leave the insulation susceptible
to contamination by downhole fluids causing loss of
insulating properties and potential failure of the
permanent well casing due to overstressing. Another
prior art approach encases the majority oE the in-
sulation in a sealed metal jacketing but leaves the
jo.int area completely uninsulated to allow for jo:int
makeup tooling. This un:insulated portion allows high
hea-t transfer locally to the permanent well casing
thus producting potential failure stresses in that
casing. Another~prior art approach encases the entire
length with conventional insulation of moderate
K-factor but fastens the inner and outer tubular with
a high conductivity coupling resulcing iIl excessive
heat loss and high -temperatures at the outer tubular
threads. Early systems have no provision for
accommodating thermal expansion of the flowtube which
may amount to more than 10 feet in moderate depth
wells and present very difficult sealing problems for
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the bottom hole packer. A previous system accommodated
thermal expansion by means of a thin flexible bellows
which also sealed the inner to outer pipe insulation
tsee U.S. Patent ~,130,301!. The necessity for
flexibility in the sealing bellows makes it susceptible
to physical damage. The accommodation of pipe
elongation wi-thout a corresponding insulation elongation
produces thermal insulation gaps. Elonyation of the
pipes also produces a variable length coupling cavity
:LO which dictates the use o:E compressible cavity insulation
and exposure of the coupling to live steam pressures
and temperatures.
A primary objective the present invention is
therefore to provide a new and improved insulating
casing assembly for transferring fluids in which
elongation due to temperature changes of an inner
fluid-carrying section of each casing is restrailled
by the rigid outer casing. Loads induced in the inner
section due to temperature changes are transEerred
~n to the outer caslng with negligible change in length
through an elongated thrust ring which minimizes heat
losses through the structural connection.
Another object of the present invention is
to provide an insulated casing assembly in which
insulation separating the fluid-carrying portion of
each casing from the rigid portions is isolated and
thus protected from the fluid.
Another object of the present invention is
to minimize heat transfer by conduction from the inner
pipe to the outer casing through the thrust ring at the
coupling area.
Another object of the present invention is to
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provide a fixed coupling cavity volume which does not
vary si.gnificantly with temperature or pressure change
so that a rigid insulation, capable of withstanding
the high temperature and pressure from live steam can
be used in the coupling cavity area.
Another objective of the present invention
is to provide a primary steam seal on the inner pipe
which would effectively prevent egress of the live
steam into the coupling cavity and would thus prevent
.1.0 contact of the steam with the casing coupling and
coupling cavity insulation.
~ nother object of the present invention is
to provide an insulated casing assembly in which couplings
used to join adjacent casings provide a secondary seal
which i.s normally protected from the high temperature
fluid by the primary seal ring on the inner pipe
assembly.
Another object of the present invention is
to provi.de an insulated casing assembly which
.insulates along its entire length thus avoiding
h.i~h heat losses at -the coupling area.
Another object of the present invention is
to provide an insulated casing with a substantially
lower overall thermal conductivity than presently
available.
Another object of the present invention is
to provide an insulated casing assembly with threaded
sections which can be easily repaired without
violation of the sealed insulation annulus.
Still another object of the present invention
is to provide an insulated casing assembly capable of
withstanding radial and longitudinal static and dynamic
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shipping handling and installation forces wi-thout
casing assembly failure.
SUMMARY OF THE IN~ENTION
The present invention, in accordance wi-th one
embodiment thereof, comprises an insulated casing
assembly includlng a plurality of insulated casings
which, when coupled or strung together, permit fluids
oE high temperatures and presses to flow therethrough
with low heat loss and without leakage. Each casing
1~ comprises radially spaced ou-ter and inner tubular
sections defining an annular space therebetween.
The annular space is filled with thermal insulating
material, preferably a high efficiency multilayered or
microsphere insulation, and a filling point in the
outer tubular section permits the annular space to be
evacuated oE air and back-Eilled with a low conductivity
~as to envelop the insulation and thus improve the
insulating characteristics of the casing. A fluidt:ight
load bearing thrust ring at each end of the casinc~,
~n seals the outer and inner tubular sections and transfers
the thermal expansion/contraction loads from the inner
tubular to the outer tubular section while also
protecting the insulatio~ within the annular space
from the fluid. Each of the thrust rings is joined to
the inner tubular section. Thereby, when two casings
are joined, a sealing ring can be fitted over spaced
opposing ends of adjacent inner tubular sections to
prevent steam migration through the coupling
insulation. Additionally, an insulated filler ring
is fitted into -the coupling cavity to inhibit heat
transfer from the inner pipe to the outer casing
coupling. A threaded coupling is screwed onto the
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ends of adjacent casings to rigidly maintain them in
a longitudinally coaxial relationship.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1 is a fra~mented cross~sectional view
of an insulated casing according to the present
invention .
FIG 2A is a cross-sectional view of an
insulated casing incorporating multi-layered insulation
within the annular space, taken along lines 2-2 oE
1() FIG 1.
FIG 2B is a cross-sectional view of an
insulated easing incorporating mierosphere insulati.on
within the annular space, taken along lines 2-2 of
FIG. 1.
FIG. 3 is a Eragmentary cross-sectional
view of the i.nsulated casing assembly including two
easin~s and eoupl.ing means according to the present
invention.
DESCRIPTION OF THE PREFER:RED EMBODIMENT
Refer.ring now to FIG 1, there is shown
insulated casinc3 10. Casing 10 can be joined
to other insulated casings, in a manner to be described
here~ a~ter, to establish a conduit for transporting
Eluids, particularly high tempera-ture fluids over long
distances with low heat loss and without lea~age.
The outer wall of easing 10 is formed by
outer tubular section 12. The inner wall of the casing,
which forms a flowtube through which fluids flow, is
formed by inner tubular section 1~. The inner and outer
tubular sections are concentric and radial spacing of
the inner and outer section walls is such as to provide
annu.Lar space 16 therebetween.
~ ~8~3~ 25AE-0081
The specific material from which the tubular
sections are made, as well as its grade andthickneSS,
will vary with the conditions to which the casing is
subjected. Several Eactors must be considered. The
tubular sections should be constructed of a material
which provides adequate s-tructural support for -the
casing. When a primary use for the casing is to
inject high pressure steam deep in-to the earth, -the
material must also be capable of withstanding the
10 eEfects of excessive pressure, temperature, and
corrosion. Further, if the tubular sections undergo
welding during manufacturing, a material with a
suitable weldability must be selected. Steel a]loys
of various types are examples of ma-terial suitable Eor
use in forming the tubular sections 12 and 14.
The regions is annular space 16 at each end
o:E casing 10 constitutes coupling cavity 18. Within
cavity 1~ is located fluid-tight thrust ring 20.
The purpose of thrust rings 20 is to seal the corresponding
ends of the tubular sections while transferring the
the.r~al expansion and contraction induced loads from
inner tubular section 14 to outer tubular section 12.
Tlle sealing prevents any fluid which enters coupling
cavity 18 from entering annular space 16 and prevents
back fill gas contained in the annulus from escaping
and thereby adversely affecting insulation value of the
material therein. To accomplish this, one end of
thrust ring 20 is sealingly connected to the inner
surface oE outer tubular section 12 at point sub-
stantially spaced axially inwardly from the end ofsection 12 and the other end is similarly connected
to the outer surface of inner tubular section 14 near
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3~ 25AE-0081
its end.
Thrust ring 20 can be made of any material
which is sufficient to withstand the stresses induced
by the thermal loading and steam pressure coupled with
the downhole corrosive environment. Another
consideration for the choice of thrust ring material
is that when the casing is used to convey high
temperature fluidsl particularly steam under pressure,
the thrust ring must be able to function properly ~or
numerous thermal cycles despite the adverse effects
of such temperature, pressure, load cycles, and
corrosion factors.
An example of a suitable thrust ring material
when the casings are used for injection of high
temperature steam into wells is a corrosion resistant
steel such as AISI type 316. For lower -temperature
conditioned s-team, an alloy such as 4130 steel may be
satisfactorily substituted.
The shape of the thrust ring should be such
as to minimize heat transfer between the hot inner
p:ipe and the cooler outer pipe. As such, the cross-
sectional area of the thrust ring should be as small
as feaslble whilst the length of the ring should be
ade~uate to provide a long thermal path, maximizing
the temperature drop along its length.
Thrust rings 20 are connected to the
corresponding ends of tubular sections 12 and 14 by
means appropriate to the materials of which thrust
ring 20 and tubular sections 12 and 14 are made. More
specifically, when the thrust ring and tubular sections
are made of AISI 4130 steel and API 5A N-~0 grade
tubing, respectively~ connection may be made, for
~ 3~ 25AE-0081
example, by welding the respective ends of the thrust
rlng to the tubing, by the use of a high strength
corrosion resistance filler wire such as G.E~
B50A678-B3 chrome-moly steel alloy. Welding of both
thrust rings to the inner tubular and of one thrus-t
riny to the outer tubular can be accomplished in a
normal shop environment; however, the final closeout
weld of the second thrust ring must be made while
the inner tubular is elongated to a dimension equivalent
to approximately halE the nominal expansion which would
be expected for an unrestrained inner tubular a-t
maximum operating temperature. This pre-tensioning
operation is required to preven-t overstressing (in
compression) the inner tubular during normal steam
staxtup operation and can be accomplished by performing
the final closeout weld while the temperature difference
between the inner and outer pipe is approximately half
the nominal operational temperature difference or by
mechanically stretching the inner tubular. To
Eacilitate making the weld between the second thrust
~n xing ~0 and outer tube 12, the threaded end section
15 :is not attached until a;Eter this weld is made.
The thrust rings can also be connected -to
tlle inner and/or outer tubulars by threading the ring
and the tubulars. A seal weld to prevent thread
leakage is recommended at the steam end of the threads.
The thrust rings are designed to carry the
nominal operational thrust loads at worst case
temperature differentials with minimal yielding of
creep of the material. The thrust ring overlaps the
butt weld area of the outer tubular providing an
effective backing ring which produces an excellent
three-way weld. Repair or replacement of threaded
~ 3 ~ 25AE-0081
section 15 may be accomplished by cutting the outer
tubular at the three-way weld and adding a new threaded
sectlon withou-t violating the insulation cavity.
Cen-tralizers 21, which preferably have a
plurality of holes therethrough to minimize transfer
of heat from inner tubular 14 to outer tubular 12,
are spaced at intervals along the length of the inner
tubular are are used to help maintain the desired
spacing between the inner and outer tubulars.
:L0 The remainder of the annular space 16 is
fi.lled with a -thermal insulating material 22. The
appropriate insulating material utilized is
determined by the use, by the available annular volume,
and particularly by the extremes of temperature,
to which the casing assembly is to be subjected. For
example, when the casing assembly is to be used to
i.nject steam into a well wlth a limited cross section,
a high ef:eiciency multilayered or multicellular
insulation is appropriate.
One type oE multilayered insulation which
i~ suitable is shown in FIG 2A and comprises layers
of re:Elective aluminum radiation shie].ds 2~ separated
~y a low concl~lctivi.ty, loose weave, random--oriented,
long~fiber fiberglass spacer material 26~ FIG 2s
shows a typical multicellular insulation 28 in a low
conductivity gas or vacuum environment. However, as
was indicated above, any other insulating material
can be utilized which possesses the proper thermal
insulating qualities required by the use to be made of
the casing assembly. The multilayered insulation used
can be manufactured in the shape of a tube and
inserted into the annular space 16. Alterna-~ively,
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~ 25AE-0081
it can be manufaetured into a flat blanket and
wrapped around the inner tubular section, over-
lapping itself sufficien-tly to negate gap heat loss.
Multicellular insulation can be poured and packed
in the annulus by conventional methods, or can be
fabriacted by the use of a binding agent into
cylindrical tubes or segments thereof to facilitate
assembly procedures.
As an additional insulation measure in the
.L0 eas:ing 10, a partial vacuum can be effected in the
annular space 16 through a filling point 30, FIG 1,
after the insulation is placed therein, and then the
annular space is baek-filled through the same filling
point 30 with a low conductivity gas, seleeted from
the group consisting of argon, krypton, xenon, and
combinations thereof. After the back-filling is
eomplete, annular spaee 16 is hermetical]y sealed at
Eilling point 30. The gas envelops the insulation
within annular space 16 and thereby improves its
insulating efficiency.
FIG 3 shows insulated casings lOA and IOB
eonnected together in such a manner that fluid
Elowing through the inner tubular seetion oE one
easing ean eontinue to Elow in~o the inner tubular
seetion of the adjaeent easing without leakage.
When easings lOA and lOB are properly joined, the
ends of the inner tubulars compress seal ring 32 and
form a pressure seal which prevents fluid flowing in
the inner tubular from entering the coupling eavity.
The sealing ring is recessed into the inner tubular
inside diameter sufficiently to allow down hole tools
to pass unobstrueted. The ring is made of an appropriate
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alloy which can be one of several corrosion resistant
materials such as 17-4PH stainless steel or similar.
The ring may be sized to seal by compression/crushing
between the ends of the inner pipe or by pressure
against the inside lip of the inner pipe. When
sealing is effected by pressure against the inside
lip, the lip must be protected from corrosion and/or
oxidation in the elevated temperature environment
by an appropriate plating or coating over the exposed
steel alloy. A plating such as electrodeposited
nic]cel over hard copper has been successfully used
for this application, however a welded overlay of
corrosion resistant alloy is equally suitable.
Filler insulation 34A and 34s is fitted
over the thrust rings 20A and 20B to minimize heat
loss through the coupling cavity area from the thrust
rings to the coupling. The filler insulation may be
cast in place during assembly with material such as
"Fiberfrax LDS moldable" by the Carborundum Company
or may be inserted at installation using "Fiberfrax
T-30" insulation tubes or similar materials offered
by others.
The gap between the coupling cavity
insulation 34A and 34B which is le-ft vacant is
filled with gap insulation 36. The gap insulation,
like the coupling cavity insulation, may be cast in
place, using Fiberfrax LDS during manufacture of
the casing or it may be field installed using
Fiberfrax T-30 tube insulation or Fiberfrax Vaccucast
pre-molded insulation. The purpose of gap insulation
36 is to provide a thermal barrier between the inner
portion of the tubing and coupling 38. Since seal
~ 25AE-0081
ring 32 effectively prevents leakage into the gap, the
insulation in -the gap and the coupling cavities operates
at near atmospheric pressure resulting in maximum
thermal efficiency for the insulation.
Adjacent casings 10A and 10B are connected
by su.itable couplings 38 which join by fixed position
rather than by torque. Couplings with standard API
buttress threads may be satisfactorily used for this
application. Once satisfactorily jointed in the proper
fixed, longitudinally coaxial, end-to-end relationship,
the relative position of the weldments and seal rinys
remain unchanged during operation.
Two casings, each containing an outer tubular
12, and inner tubular 14, thrust rings 20, centralizers
21, and insulating material 22, 34 and 36 are joined
to comprise a completed insulated casing assembly as
follows. Thread coupling 38 is screwed onto the
threads on the end of outer tubular 12 of a first
casing. Seal ring 32 is slipped on the inner tu~ular
section of the first casing. The second casing is
then stabbed into the coupling 38 and the coupling
is screwed tightly onto the outer tubular section o:E
the second casiny. As a result, the two casings are
maintained in a fixed, longitudinally coaxial
relationship. In this arrangement, the sealing riny
32 provides a pressure seal between the inner tubulars 14.
It is to be understood that this invention
is not limited to the particular embodiment disclosed,
and it is intended to cover all modifications coming
within the true spirit and scope of this invention as
claimed.
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