CA1182394A - High temperature insulated casing - Google Patents

Abstract

HIGH TEMPERATURE INSULATED CASING

ABSTRACT OF THE DISCLOSURE

An insulated casing assembly for use in injecting steam into wells or transmitting steam from the generating source to the wellhead is disclosed.
A plurality of interconnected casings are used, each casing having outer and inner tubular sections and an annular spacing between the two sections containing either multilayered thermal insulation or glass microspheres, enveloped in a low conductivity gas.
Rigid thrust rings connect and prevent relative movement between the corresponding ends of the two sections. A pressure sealing ring disposed between adjacent inner tubular sections prevents ingrees of steam into the coupling cavity. An insulation assembly between adjacent casings includes coupling cavity insulation fitted tightly over the thrust rings and a gap insultating ring disposed between adjacent outer tubular sections. A threaded coupling screwed onto threaded ends of outer tubular sections of adjacent casing joins them.

Description

~ 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 ~ 3~ ~5AE-0081 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 ~ 3~ 25AE-0081 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 ~ 3~ 25AE-0081 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 ~ 3~ 25AE-0081 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 ~ 3~ 25AE-0031 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

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, ~ 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 ~ 3~ 25AE-0081 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.

Claims (8)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. In an insulated casing assembly for conveying a heated fluid, said casing having spaced, concentrically positioned inner and outer tubulars with insulation sealed therebetween, an improved joining arrangement comprising:
a rigid thrust ring joining the inner and outer tubulars at each end of said casing;
said thrust ring joined to said inner tubular near its end and to the outer tubular at a location spaced a substantial distance from its end whereby a long path for heat transfer by conduction from the inner to the outer tubular exists;
the annular space between the outer surface of said thrust ring and the inner surface of said outer tubular constituting a coupling cavity;
coupling cavity insulation contained in said coupling cavity;
said outer tubular having threads at eaeh end;
a threaded coupling ring for joining threaded ends of adjacent outer tubulars;
a seal ring sized to fit within said inner tubular and having a centrally positioned radially outwardly extending rib sized to fit between the ends oE adjacent inner tubulars;
and a gap insulation ring contoured to fit in the gap between the coupling cavity insulation of similar adjacent casings.

2. An insulated easing assembly in accordance with claim 1 wherein:
the second thrust ring of each casing is secured to join the inner and outer tubulars when the inner tubular is elongated.

3. An insulated casing assembly in accordance with claim 1 wherein:
said thrust rings are welded to or threaded onto said inner and outer tubulars.

4. An insulated casing assembly in accordance with claim 1 wherein:
the space between said inner and outer tubulars contains a gas enveloping said insulation.

5. An insulated casing assembly in accordance with claim 4 wherein:
said insulation comprises alternating layers of reflec-tive aluminum radiation shields and low conductivity, loose weave, random oriented, long-fiber glass fiber material.

6. An insulated casing assembly in accordance with claim 4 wherein:
said insulation comprises glass microspheres.

7. An insulated casing assembly in accordance with claim 5 or 6 wherein:
said gas is from the group consisting of argon, krypton, xenon and combinations thereof.

8. An insulated casing assembly in accordance with claim 1 wherein:
the space between said inner and outer tubulars contains annular centralizers to aid in maintaining the desired distance between said tubulars.