Note: Descriptions are shown in the official language in which they were submitted.
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01 CONCENTRIC INSULATED TURING STRING
BACKGROUND OF T~IE INVEMTIOM
When steam flooding a subsurface petroleum-
os containing formation, steam is usually yenerated at theearth's surface and injected into the subsurface formation
from a cased well. The steam is usually transporte~ to
the producing formation through a conduit run inside the
casing within the well. In a successful steam flood oper-
ation, the injection of steam into the target formation ismaximized, while the loss of heat from the steam as it is
transported from the surface to the target formation
through the well conduit is minimized. Thermal insulation
between the steam carrying conduit and the formation has
been proposed as a means for reducing heat loss from the
steam conduit to the formation. I'he construction of
insulated conduit sections and the joining of sections of
such insulated conduit into a concentric insulated tubing
string is the subject matter of this invention.
PRIOR ~RT
Prior art systems have disclosed both preinsu-
lated conduit sections and the application of insulation
to the conduit after the conduit has been run into a well.
The application of insulation in place has the
disadvantage of being uninspectable, both for initial
application and subsequent failure. One form of appli-
cation of insulation in place is shown in U.S. Patent
No. 3,525,399.
In prior art preinsulated conduits, concentric
string conduits have been proposed with insulating
materials positioned between concentric tubing sections.
Such prior art concentric tubing sections have included
several schemes for construction including schemes for
accommodating a difference in thermal elongation of the
steam conduit with respect to the insulated conduit of
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the concentric tubing. Concentric tubing for injection
into or produc-tion from a subsurface formation is shown in
U.S. Patent Nos. 3,608,640 and 3,680,631 and is available
from General Electric Company in a product sold under the
tradename of "Thermocase III".
SUMMARY OF THE INVENTION
Various aspects of the invention are as follows:
In apparatus for conducting hot fluid to a sub-
surface earth formation through a well bore penetrating0 said earth formation the improvement comprising:
a heat elongated inner tubing for conducting said
hot fluid,
an outer tubing surrounding said inner tubing and
establishing an annular volume space between the inside of5 said outer tubing and the outside of said inner tubing,
insulating means in said annular volume space,
substantially rigid ring like spacer means position-
ed along said apparatus in said annular volume space,
annular end members first secured to the outer0 surface of said inner tubing adjacent to the ends thereof
and then secured to the inner surface of said outer tubing
adjacent to the ends thereof at locations along said outer
tubing where said heat elongated inner tubing aligns said
end members,
threads cut into the outer surface of said outer
tubing at each end thereof adjacent to the location where
said end members are secured to the inner surface of said
outer tubing thus forming individual sections of concentric
inner and outer tubing,
and coupling members having internal threads match-
ing said threads cut into the outer surface of said outer
tubing to permit said individual sections to be joined to
form said apparatus.
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A coupling for insulated concentric tubing sections
for conducting hot fluids wherein the inner tubing of said
concentric tubing is elongated by thermal expansion, attach-
ed to the inner surface of the outer tubing of said concen-
tric tubing when elongated and insulated from said outertubing by an insulating annular volume space hetween said
tubing, said couplin~ comprising:
a threaded coupling member engaging threads on the
outer surface of the ends of said outer tubing of concen-
0 tric tubing sections to be joinedtan annular insulating member positioned over the
extendiny ends of said inner tubing in concentric tubing
sections to be joined,
and deflector means between said annular insulating5 member and the inner surace of said coupling member,
whereby adjacent sections of said concentric tubing
are joined by said threaded couplings member joining said
outer tubing.
A method for producing an insulated, concentric
tubing, hot fluid conducting apparatus comprising the steps
of:
attaching annular end members to the outer surface
of a first tubing adjacent to the ends thereof,
heating said first tubing to about the temperature
of hot fluids to be conducted in said apparatus to elongate
said first tubing,
inserting said first tubing inside a second tubing
with spacing and insulating materials between the outside
of said first tubing and the inside of said second tubing,
said second tubing having a shorter axial length than said
first tubing when said first tubing is elongated due to
said heating,
securing said annular end members to the inner
surface of said second tubing adjacent to the ends thereof
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when said first tubing is elongated due to said heating and
sealing said inner space between said first and second tubing
containing said spacing and insulating materials,
and threading said second tubing at the outer sur-
faces adjacent to said ends thereof and about where saidannular end members are secured so as to permit multiple
units of said insulated concentric tubing to be joined by
couplings members engaging the second tubing at said thread-
ed surfaces.
The prior art concentric insulated tubing conduits
or strings have been inefficient in field use where steam
flooding has been the objective because of heat loss at the
coupling between sections of conduits. A coupling used to
join the adjacent sections of conduit because heated to sub-
stantially the same temparature as the conduit carrying
the steam and the coupling then is a source of heat loss.
One of the prior art conduits provides threaded
ends at each end of the internal tubing of the conduit
sections and a coupling joining the internal tubing. The
coupling of sections by threads on the internal tubing
places excessive tension strain on the assembled injection
conduit. Mechanical failure and excessive heat loss at
such coupling joints has been observed.
The present invention in one aspect proposes an insu-
lated, concentric tubing, steam injection (or production)conduit wherein the conduit is assembled from sections of
concentric insulated tubing with a coupling that joins the
sections together at threaded portions on the exterior of
the outer tubing. The coupling is adapted to insulate the
inner tubing against heat loss as sections of the concen-
tric tubing are joined together.
Individual concentric tubing sections are manufac-
tured by a procedure that establishes an isolated space
between the outside of the inner tubing and the inside of
the outer tubing. The inner tubing is elongated by heat
01 expansion prior to being attached to ancl insulated from
the outer tubing. The outer tubiny is then dressed and
threaded for cooperation with an external coupling.
The coupliny joininy tubing sections provides
05 insulation at the joint and mechanical strenyth for an
assembled string.
The objects and features of the present inven-
tion will be readily apparent to those skilled in the art
from the appended drawings and specification illustrating
a preferred embodiment.
BRIEF DESCRIPTIOM OF THE DRAWINGS
FIG. 1 is a sectional view through an earth
formation illustrating the apparatus of the present
invention in use.
FIG. 2 is a sectional view of the apparatus of
the present invention showing the coupling of two sections
of insulated concentric tubing conduit.
FIG. 3 is a sectional view of the apparatus of
the present invention intermediate the ends showing the
insulation and spacing between concentric tubing.
FIG. 4 is a sectional view of the inner tubing
prior to its attachment to the outer tubing.
FIG. 5 is a sectional view of the inner and
outer tubing prior to heat expansion.
FIG. 6 is a sectional view of the end of an
assembled insulated concentric tubing section.
FIG. 1 is a sectional view through an earth for-
mation illustrating the present invention in its installed
position within a cased well. As illustrated, a well 10
is drilled from the earth's surface 11 to an oil-bearing
formation 12. A typical oil-beariny reservoir to which
the present invention has application includes a formation
containing viscous crude oil which cannot be produced to
the earth's surface under formation pressure and temper-
ature. A technique for stimulating the production of a
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01 viscous cr~de oil from such a subsur~ace oil reservoiris to inject ste~m into that reservolr through a steam
injection well to heat the oil an~l reduce its viscosity.
As herein illustrated, the injection well includes a metal
05 casing 13 passing through the forma-tion 14 to the sub-
surface horizon of the formation 12. ~ steam injection
conduit 15 is positioned inside the casing 13 and spaced
by suitable spacing means 16 to conduct steam from a
surface steam ~enerating source 17 to the subsurface
formation 12. A packer 1~3 is usually provided at the
downhole end of the steam conduit 15 to prevent steam from
flowing back up the annulus between the conduit and the
casing. The casing is perforated, as at 19, at the
location of the oil-bearing formation to provide conduits
into and out of the permeable oil-bearing formation.
FIGS. 2 and 3 illustrate in sectional form the
construction of the concentric tubing steam injection
conduit as illustrated generally in FIG. 1. It should be
understood that FIG. 2 illustrates the adjacent ends of
two concentric tubing sections adjoined by a coupling
means so as to produce a continuous portion of a steam
injection conduit or string of the type illustrated in
FIG. 1. Each of the individual concentric tubing conduit
sections is made up of an inner tubing 21 havin~ an annu-
lar end member 22 secured to the exterior surface of theinner tubing, as by being welded thereto at 23 and 24.
The outer surface of the annular member 22 is secured to
the inner surface adjacent to the end of an outer tubing
section 25. The connection between the annular end member
22 and the outer tubing 25 is established by welding the
end of the annular member, as at 26, to the end of the
outer tubing section.
The annular space 27 between the outside of the
inner tubing and the inside of the outer tubing is filled
with an insulating material 23. The insu]ating material
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01 may be formed of tubular sections which are inserted over
the outside of the inner tubing when the inner tubing is
inserted into the outer tubin~. The tubular sections of
insulating material may be split longitudinally to fit
05 around the inner tubing during assembly.
; Between sections of the insulating materials,
ring-like spacers 29, shown in FIG. 3, are provided to
maintain positioning of the insulating material 28 and
to prevent the collapse of the outer tubing onto the
insulation and inner tubing, thus destroying the insu--
lating qualities of the insulation material.
- As particularly shown in FIG. 2, individual
sections of the concentric tuhiny string are joined
together by a coupling member generally designated 31.
The coupling is a hollow cylindrical form with female
threads on the inside of each end thereof at 32. The ends
of the outside tubing 25 of the concentric tubing string
are threaded with male threads at 33 to match with the
internal threads of the coupling. Both of these threads
are conventional oil field pipe threads being tapered to
provide a wedge tightening for the coupling. A sealing
ring 34 is positioned in the grooves cut into the interior
of the coupling and the exterior of the outer tubing to
provide both sealing and protection for the mating of the
two threads. The inner tubing 21 of the concentric string
15 extends beyond the threaded end of the outer tubing 25,
as at 35, and is adapted -to be fitted with a deflector
ring 36. An insulating hollow cylinder 37 surrounds the
deflector ring 36 and encloses the ends of the extension
of the inner tubing to insulate the coupling from the hot
fluid which may be pumped down through the inner conduit.
When assembled in the form as shown in FIG. 2,
` the two sections of concentric tubing string may form a
portion of the overall string extending through the earth
formation to carry hot fluids, or steam, through the inner
s
01 conductor in a manner to insulate the temperature of the
inner tubing from the outer tubing. To fur-ther improve
the insulation characteristic of the space between the
inner tubing and the outer tubing, the rernaining space may
05 be filled with an inert gas having low heat carrying char-
acteristics. For that purpose, the outer tubing rnay be
provided with a plug member 38 through which the insulat-
ing gas may be pumped.
FIGS. 4, 5 and 6 illustrate a preferred manner
for constructing the concentric tubing string of the
present invention~ As illustrated in FIG. ~, the inner
tuhing 21 is first provided with an annular end member 22
at each end and the inside surface of each end member 22
is welded at 23 and 24 to the outside surface of the inner
tubing 21 to establish complete sealing of the annular
member against the outer surface of the inner tubing. The
inner tubing 21 is then inserted into the outer tubing 25
as shown in FIG. 5 and insulating material 28 is installed
to surround the inner tubing as the tubing is inserted
into the outer tubing. For that purpose, the cylindrical
insulation may be in the form of a split cylinder to per-
mit it to be placed around the inner tubing as the inner
tubirg is inserted. The spacer members 29 also are placed
around the inner tubing 21 between adjacent insulation
sections. The spacers may be formed as split rings to
permit them to be assembled around the inner tubing.
After a concentric tubing section has been
assemblecl as described, a heating element ~1 connected to
an energy source 42, as schematically illustra~ed in
FIG. 5, is placed within the interior of -the inner tubing
to heat it along its entire length. While FIG. 5 illus-
trates a short portion only of the heating element, it
should be understood that it is preEerred that the entire
length of the inner tubing within the outer tubing is
heated. As the inner tubing becomes heated, it expands in
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01 length. If one end of the lnner tubing is held in place
with respect to the outer tubing, by clamping or by haviny
first been welded thereto, as at 26, the other free end of
the inner tubing will expand axially to extend toward the
05 other end of the outer tubing. When the inner -tubing has
been expanded to a desired length, the outer surface of the
annular end member 22 at the free end is welded at 26 to
the inner surface of the outer tubing. In the welded posi-
tion, the inner t~bing extends a predetermined distance,
shown as d in FIG. 5, beyond the end of the o~ter tubing.
If the fixed end of the inner tubing had only previo~sly
been clamped to the outer tubing, that end is then also
welded, as at 26, to the inside of the outer tubing.
When the welding between the annular end member
22 and the outer tubing 25 is completed to securely fasten
the inner and o~lter tubing sections together, the inner
tubing is in an elongated condition and the heating ele-
ment is then withdrawn permitting the inner tubing member
to cool. When cooled, the inner tubing is placed in ten-
sion as it attempts to contract but it is maintained atits elongated length by its connection at both ends to the
inner surface of the outer tubing. As shown in FIG. 6,
the end of the outer tubing is then dressed at 44 and the
male threads 32 are cut into the outer surface. The slot
accomodating the sealing ring 34 is then machined and the
section of concentric tubing is available for assembly
with other tubing sections.
Because of the manner in which the concentric
tubing sections have been fabricated, placing the inner
member in tension when in cooled condition b~t in relaxed
(expanded) condition when in heated condition, and because
of the insulation between inner and outer tubings, the
assembled concentric tubing string of the present inven-
tion provides a conduit for the conduction of hot fluids
with minimized heat loss and with reduced coupling stress.
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01 A particular feature of the present invention is that the
joint between successive sections of the concentric tubing
strings is formed by coupling the outer tubing of each of
the members, thus providing additional strength to the
05 overall concentric tubing. With the construction here
described, the outer tubing may be made of heavier gauge
pipe capable of supporting greater weight in the assembled
tubing string. Also, because the fabricated sections are
substantially unstressed at operating temperature, the
assembled tubing string is less likely to fail due to
fatigue. When assembled with the coupling, as shown in
FIG. 2, the entire string of concentric tubing sections is
substantially completely insulated from the earth forma-
tion and the interior of the casing, thus reducing the
heat loss in transporting the hot fluids or steam through
the subsurface formation. When the steam has been carried
to the horizon where the oil~bearing formation is found,
the steam may be forced out of the end of the tubing
string and into the formation 12 through the perforations
l9 with the packing gland 18 preventing steam from passing
up through the annulus around the tubing string and inside
of the casing.
While a certain preferred embodiment of the
invention has been specifically disclosed, it should be
understood that the invention is not limited thereto as
many variations will be readily apparent to those skilled
in the art and the invention is to be given its broadest
possible interpretation within the terms of the following
claims.
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