CA1191454A - Insulated tubular structure - Google Patents
Insulated tubular structureInfo
- Publication number
- CA1191454A CA1191454A CA000419766A CA419766A CA1191454A CA 1191454 A CA1191454 A CA 1191454A CA 000419766 A CA000419766 A CA 000419766A CA 419766 A CA419766 A CA 419766A CA 1191454 A CA1191454 A CA 1191454A
- Authority
- CA
- Canada
- Prior art keywords
- tubular
- pipe section
- pipe sections
- gas
- members
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000007789 sealing Methods 0.000 claims abstract description 16
- 239000012530 fluid Substances 0.000 claims abstract description 15
- 239000011810 insulating material Substances 0.000 claims abstract description 14
- 239000007789 gas Substances 0.000 claims description 15
- 230000008878 coupling Effects 0.000 claims description 14
- 238000010168 coupling process Methods 0.000 claims description 14
- 238000005859 coupling reaction Methods 0.000 claims description 14
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 10
- 229910000831 Steel Inorganic materials 0.000 claims description 10
- 239000010959 steel Substances 0.000 claims description 10
- 239000011343 solid material Substances 0.000 claims description 6
- 229910052786 argon Inorganic materials 0.000 claims description 5
- 210000002268 wool Anatomy 0.000 claims description 5
- 239000000919 ceramic Substances 0.000 claims description 4
- 239000000945 filler Substances 0.000 claims description 4
- 239000011261 inert gas Substances 0.000 claims 4
- 239000000203 mixture Substances 0.000 claims 2
- 238000010793 Steam injection (oil industry) Methods 0.000 abstract description 3
- 239000003129 oil well Substances 0.000 abstract description 3
- 238000009413 insulation Methods 0.000 description 12
- 230000008602 contraction Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 101000959868 Solanum tuberosum Aspartic protease inhibitor 8 Proteins 0.000 description 1
- 230000004308 accommodation Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052743 krypton Inorganic materials 0.000 description 1
- DNNSSWSSYDEUBZ-UHFFFAOYSA-N krypton atom Chemical compound [Kr] DNNSSWSSYDEUBZ-UHFFFAOYSA-N 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000006903 response to temperature Effects 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
- E21B36/003—Insulating arrangements
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L59/00—Thermal insulation in general
- F16L59/14—Arrangements for the insulation of pipes or pipe systems
- F16L59/16—Arrangements specially adapted to local requirements at flanges, junctions, valves or the like
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L59/00—Thermal insulation in general
- F16L59/14—Arrangements for the insulation of pipes or pipe systems
- F16L59/16—Arrangements specially adapted to local requirements at flanges, junctions, valves or the like
- F16L59/18—Arrangements specially adapted to local requirements at flanges, junctions, valves or the like adapted for joints
- F16L59/185—Adjustable joints, joints allowing movement
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Thermal Insulation (AREA)
Abstract
ABSTRACT
An insulated tubular structure for fluid transfer, more particularly for use in downhole oil well steam injection, comprises inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween, thermally insulating material substantially filling the cavity, sealing means at both ends of each pipe section hermetically sealing the ends of the annular cavity, the outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, the end tubular members being rigidly connected to respective ends of the inner pipe section by the sealing means, and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
An insulated tubular structure for fluid transfer, more particularly for use in downhole oil well steam injection, comprises inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween, thermally insulating material substantially filling the cavity, sealing means at both ends of each pipe section hermetically sealing the ends of the annular cavity, the outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, the end tubular members being rigidly connected to respective ends of the inner pipe section by the sealing means, and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
Description
'.3L.f~ rj~
This invention relates to insulated tubular structures for fluid transfer, and is concerned more particularly, hut not exclusively, with downhole tubulars of the type employed in oil well steam injection. Downhole tubular systems are intended to be inserted deep into the ground for downhole fluid transfer, and normally comprise a string of insulated component tubular structures coupled together in vertical end to end alignment, the assembly forming a rigid and leakproof structure~
J
As is well known, downhole tubular systems of the type referred to are subjected to extremely arduous operating conditions and encounter several potentially destructive forces besides being exposed to the corrosive and erosive effects of the steam and other fluids. These conditions can, and from time to time do, result in structural failure. Since the recovery of a failed system is a very expensive and time consuming procedure, it is important that they be designed so as to minimize the risk of structural failure. One might in principle increase structural reliability by making the stress bearing components of the s~stem of a heavier gauge or thickness, but this introduces its own disadvantages.
Apart from the additional cost of the metal that would be rec~uired in making the component str~ctures more stress resistant, the heavier gauge of the components ~L ~ S4 i would increase their weight and so actually add to the axial stresses in the other components from which they are suspended.
The problem of constructing a downhole tubular system which is both structurally and functional]y reliable is greatly increased by the need to insulate the system to prevent heat loss from the steam. Conventionally insulated pipes cannot readily be adapted for oil well steam injection purposes. Damage to the insulation would result in loss of insulatiny properties and consequent damage to structural components due to overstressingO On the other hand, if the insulation is to be encased using a double-walled tubular structure, it is necessary also to allow for differential expansion and contraction of the inner and outer walls of the structure since otherwise additional stresses tending to cause failure would be set up. However, this must be accomplished without loss of structural rigidity of the system as a whole.
In United States Patent No. 4,332,401, Stephenson et al, - issued June 1, 1982, there is disclosed an insulated tubular assembly for fluid transfer which is designed so as to reduce the problems mentioned above. The assembly comprises a plurality of component tubular structures
This invention relates to insulated tubular structures for fluid transfer, and is concerned more particularly, hut not exclusively, with downhole tubulars of the type employed in oil well steam injection. Downhole tubular systems are intended to be inserted deep into the ground for downhole fluid transfer, and normally comprise a string of insulated component tubular structures coupled together in vertical end to end alignment, the assembly forming a rigid and leakproof structure~
J
As is well known, downhole tubular systems of the type referred to are subjected to extremely arduous operating conditions and encounter several potentially destructive forces besides being exposed to the corrosive and erosive effects of the steam and other fluids. These conditions can, and from time to time do, result in structural failure. Since the recovery of a failed system is a very expensive and time consuming procedure, it is important that they be designed so as to minimize the risk of structural failure. One might in principle increase structural reliability by making the stress bearing components of the s~stem of a heavier gauge or thickness, but this introduces its own disadvantages.
Apart from the additional cost of the metal that would be rec~uired in making the component str~ctures more stress resistant, the heavier gauge of the components ~L ~ S4 i would increase their weight and so actually add to the axial stresses in the other components from which they are suspended.
The problem of constructing a downhole tubular system which is both structurally and functional]y reliable is greatly increased by the need to insulate the system to prevent heat loss from the steam. Conventionally insulated pipes cannot readily be adapted for oil well steam injection purposes. Damage to the insulation would result in loss of insulatiny properties and consequent damage to structural components due to overstressingO On the other hand, if the insulation is to be encased using a double-walled tubular structure, it is necessary also to allow for differential expansion and contraction of the inner and outer walls of the structure since otherwise additional stresses tending to cause failure would be set up. However, this must be accomplished without loss of structural rigidity of the system as a whole.
In United States Patent No. 4,332,401, Stephenson et al, - issued June 1, 1982, there is disclosed an insulated tubular assembly for fluid transfer which is designed so as to reduce the problems mentioned above. The assembly comprises a plurality of component tubular structures
2~ coupled together in end to end alignment, each component structure comprising radially spaced inner and outer pipe sections defining an annular space which is filled with thermally insulating material, the ends of the pipe sections being interconnected by axially extending tubular bellows which, in effect, hermetically seal the ends of the annular space containing the insulation.
The outer pipe sections of the component tubular structures àre rigidly coupled together end to end by threaded couplings. In this way not only is the s~
insulation protected, but the assernbly provides an inner fluid-carrying section which is free to expand and contract in response to temperature changes while the outer load-bearing section of the structure remains essentially rigid.
However, the arrangement described in ~nited States Patent No. 4,332,401 has several potential short-comings. In the first place the tubular bellows are exposed to the fluid being transferred. It is true that they are shielded from direct exposure by diffuser sleeves which interconnect the ends of the inner pipe sections, but should a diffuser sleeve fail the tubular bellows are directly exposed and likely to fail mechanically. The mechanical failure of a bellows may have serious consequences. First, since the thermally insulating material will become exposed to the fluid being transferred, it will become impregnated with con-sequent loss of thermal efficiency. Even more serious is the fact that mechanical failure of a bellows will result in loss of mechanical integrity of the string of inner pipe sections, and in consequence it will become - practically impossible to recover the balance of the assembly below the failed component. Another short-coming is that the entire weight of the tubular assembly is borne by the outer pipe sections and their couplings, which means that the wall thickness of these components must be sufficient to withstand the heavy load incurr-ed. But the inner pipe sections must in any case be of substantial wall thickness to withstand the high intern-al fluid pressure and therefore, for a given diameter,the space available to accommodate insulation is limited by the structural considerations for the inner and outer walls. The consequence of this is loss of thermal efficiency or, in the alternative, reliance upon special ~L~ 54L
types o~ insulation which are far more costly than would otherwise be necessary.
By contrast, in a downhole tubular system according to the present invention the entire weight of the system is borne by the inner pipe sect.ions which are rigidly interconnected at their ends, the outer pipe sections being decoupled from stresses transferred via the inner pipe sections by expansion joints which are not subjected to load.
According to one aspect of the present invention there is provided an insulated tubular structure for fluid transfer which comprises: inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween; thermally insulating material substantially filling sai.d cavity; sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity; said outer pipe section compri.sing a main tubular member having a pair of end tubular members extending therefrom; said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means;
and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
Preferably the main tubular member and one end tubular member of the outer pipe section have respective free end portions telescoping one within the other, one such free end portion carrying an annular seal which slidably engages the other to provide the expansion joint.
Alternatively the expansion joint may be provided by a tubular bellows rather than the annular sliding seal, although the latter is usually to be preferred on account of the cost oE the bello~s and risk of their mechanical failure.
According to another aspect o~ the invention there is provided a downhole tubular system comprising a plurality of insulated tubu:Lar structures coupled together in vertical end to end alignment each said tubular structure comprising inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween; thermally insulating material substantially filling said cavity;
sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity;
said outer plpe section comprising a main tubular member having a pair of end tubular members extending therefrom said end tubular members being rigidly connected to respective ends of said inner pipe section by said sea].ing means and one end tubular member being interconnected with the main tubular member by an expansion joint providing a gas-tight seal between said members said tubular structures being coupled together by rigid coupling means rigidly interconnecting the inner pipe sections thereof so as to decouple the outer pipe sections from stresses transferred via the inner pipe sections.
~part from the mechanical integrity ensured by rigidly interconnecting the inner pipe sections while disposing the expansion joints so that they will not be subjected to load stresses, the arrangement has the considerable advantage that the outer pipe sections can be relatively thin-walled. This means that, for a given diameter of the tubular structure, more space can be made available to accommodate the insulation and hence the thermal properties of the design are greatly improved. Thus, ~or a given insulating material the insulation can be S~
made more effective. On the other hand, it is also feasible to use a simpler and less expensive insulating material than would otherwise be required. In a preferred embodiment of the present invention the thermally insulating material is a gas-permeable solid material such as cerarnic wool which is permeated with low conductivity gas such as argon.
Although the present invention is primarily concerned with the structural reliability of downhole tubing of the type discussed above, it has general application to the design of insulated pipe structures used for fluid transfer, wherein expansion joints required to accommodate differential thermal expansion of the inner and outer pipe sections must be shielded from load stresses.
In order that the invention may be readily understood one embodLment thereof will now be described, by way of e~ample, with reference to the accompanying drawings.
In the drawings, which show details of a downhole tubular system comprising a plurality of component tubular structures coupled together in vertical end to end alignment;
Figure 1 is a fragmentary half-sectional elevational view showing one of the component tubular structures and part of an adjacent tubular structure to which it is coupled;
Figure 2 is an exploded fragmentary perspective view of the component elements shown in Figure 1;
Figure 3 is an enlarged half-sectional elevational view showing the coupling in greater detail; and 7 ~ 5~
Figure 4 is an enlarged half-sectional elevational view showing the expansion joint in greater detail.
Referring to the drawings, each of the component tubular structures is essentially a double-walled structure comprising an inner pipe section 10 and an outer pipe section 11, the pipe sections being arranged concentrically one within the other to define an annular space therebetween. The outer pipe section 11 comprises a main tubular casing member 12, which extends for the greater part of the length of the structure, and a pair of end tubular casing members 13, 14 extending from it at each end. As shown in Figure 1, the end tubular members 13, 14 are of smaller diameter than the main tubular member 12. The end member 13 is received at one end within one end of the main tubular member 12, to which it is welded as shown at 15. The other end member 14, on the other hand, has a free end portion which telescopes within a free end portion of the main tubular member 12, being interconnected with the latter by an expansion joint 17 as hereinafter described. The distal ends of the end members 13, 14 are rigidly connected to respective ends of the inner pipe section by means o steel rings 18 which are welded to the ends of the inner pipe section 10 and to which they in turn are welded at their ends. Thus the steel rings 18 hermetically seal the ends of the annular cavity defined by the inner and outer pipe sections.
The annular cavity is itself filled with a thermally insulating material for minimizing heat losses rom the fluid being transferred. This material may comprise a gas permeable solid material permeated with a low conductivity ~as. For example, the insulation may be made up o~ a multilayered insulation as described in ~nited States Patent No. 4,332,~01 permeated with a very low conductivity gas such as krypton. However, since the present design permits space economy without loss of structural integrity, it is feasible to use a less elaborate and less expensive insulation system without loss of thermal efficiency owing to the additional space made available for its accommodation. Thus, in the present example the insulation comprises a ceramic wool 19 substantiall~ filling the annular cavity and back-filled with a low conductivity gas such as argon.
For this purpose a hole is drilled in the main tubular member 12 to permit evacuation of air from the annular cavity in which the ceramic wool has been laid, and then argon gas is introduced via the hole at atmospheric pressure. The hole is then sealed by a weld 20.
As previously mentionedr the end tubular casing member 14 is rigidly connected to one end of the inner pipe section 10 by means of the steel ring 18 to which it is welded, and has a free end portion which telescopes within the cooperating free end portion of the tubular member 12. The expansion joint 17 is formed by an annular sliding seal arrangement which is best illustrated in Figure 4. This consists essentially of a pair of short cylindrical members 21, 22 of the same diameters as the casing members 12, 14 and welded thereto in end ~o end alignment as shown by the welds 23, 24. The cylindrical members 21, 22 telescope one within the other and thus constitute, in effect, the free end portions of the casing members 14 and 12 respectively. The inside surface of the member 22 is machined to provide an annular abutment stop 25 which is positioned to engaye an abutment flanye 26 of the inner member 21 for limiting the extent of slidiny movement one relative to the other. It will be observed that by limiting the extent of sliding movement of the member 22 s~
within the member 21, the deslgn provides additional protection in the event of structural failure of one component.
Also machined in the inside surface of the outer cylindrical member 22 are a pair of annular slots for accor~odating a pair of retaining C-rings 27, 28, and an annular step 29. A pair of circular mechanical seals 30, 31 located by the retaining rings and the step 29 slidably engage the surface of the inner member 21 to provi~e a gas-tight seal while permitting relative movement of the inner and outer members in response to differential thermal expansion and contraction of the pipe sections. For this purpose fluorocarbon seals are well known in the art.
The component tubular structures are coupled end to end to form a rigid string, and details of the coupling between a pair of casing structures 32, 33 are best shown in Figure 3. This figure clearly shows the steel rings 18, 18' by which the end tubular members 14, 13' of the component structures 32, 33 are rigidly connected to the inner pipe sections 10, 10'. The external surfaces of the members 14, 13' are tapered as shown and provided with buttress threads 34, 34'. An internally threaded collar 35 engaging these threads provides the coupling by which the adjacent ends of the casing structures 32, 33 are rigidly coupled together. The inner pipe sections 10, 10' are aligned to form a continuous duct for the fluid to be transferred. A
filler ring or gasket 36 is interposed between the end rings 18l 18', which abut against it, and extends between the pipe ends 37 so as to minimize fluid leakage therefrom. The filler ring is firmly wedged in position within the collar 35 and is frictionally held by the internal th~eads thereof. The purpose of the s~
- ln -filler ring 36, which is made of a tough, heat resistant and steam resistant insulating material, is to prevent a heat short at the join between the two inner pipe sections, as well as to break the flow of steam which would otherwise be damaging to the coupling.
As will be apparent from the construction described, the entire weight of the suspended tubular system is borne by the inner pipe sectons 10, the axial load being transferred from each section to the next via the welded steel end rings 18, to which the tubular casing members 13, 1~ are welded, and the threaded collars 35 by which the cooperating ends of the component tubular structures are coupled together. The inner pipe sections 10 must therefore be of sufficient strength to carry the axial lS load, as must the couplings also, but this requirement is conveniently met since the pipe sections must in any case be strong enough to withstand the internal fluid pressure. On the other hand the outer pipe sections are decoupled from the axial load.
In the embodiment described above the outside diameter of the tubular system is 5.56 inches and each component casing structure is 30 feet long~ The inner pipe sections are of 2 7/8 inch outside diameter seamless steel tubing API-J55. The main tubular members 12 of the outer pipe sections are of standard wall-5 inch diameter line pipe. The end casing members 13, 14, which are specifically designed to withstand the grip of a service rig, are typically 3 feet long and are of 5 inch diameter API-J55 or API-N80 steel casing with API-8 Round Long Threaded and coupled ends. The internally threaded coupling collars 35, which are also of API-J55 or API-~8n steel casing. The specifications of these components are given by way of example only, of course, and for any given application the materials and dimensions of the components must be selected according to the working requirements. Thus, for example, the wall thickness of the outer pipe sections is very much less than that of the inner pipe sections and the load bearing components.
The outer pipe sections of the component tubular structures àre rigidly coupled together end to end by threaded couplings. In this way not only is the s~
insulation protected, but the assernbly provides an inner fluid-carrying section which is free to expand and contract in response to temperature changes while the outer load-bearing section of the structure remains essentially rigid.
However, the arrangement described in ~nited States Patent No. 4,332,401 has several potential short-comings. In the first place the tubular bellows are exposed to the fluid being transferred. It is true that they are shielded from direct exposure by diffuser sleeves which interconnect the ends of the inner pipe sections, but should a diffuser sleeve fail the tubular bellows are directly exposed and likely to fail mechanically. The mechanical failure of a bellows may have serious consequences. First, since the thermally insulating material will become exposed to the fluid being transferred, it will become impregnated with con-sequent loss of thermal efficiency. Even more serious is the fact that mechanical failure of a bellows will result in loss of mechanical integrity of the string of inner pipe sections, and in consequence it will become - practically impossible to recover the balance of the assembly below the failed component. Another short-coming is that the entire weight of the tubular assembly is borne by the outer pipe sections and their couplings, which means that the wall thickness of these components must be sufficient to withstand the heavy load incurr-ed. But the inner pipe sections must in any case be of substantial wall thickness to withstand the high intern-al fluid pressure and therefore, for a given diameter,the space available to accommodate insulation is limited by the structural considerations for the inner and outer walls. The consequence of this is loss of thermal efficiency or, in the alternative, reliance upon special ~L~ 54L
types o~ insulation which are far more costly than would otherwise be necessary.
By contrast, in a downhole tubular system according to the present invention the entire weight of the system is borne by the inner pipe sect.ions which are rigidly interconnected at their ends, the outer pipe sections being decoupled from stresses transferred via the inner pipe sections by expansion joints which are not subjected to load.
According to one aspect of the present invention there is provided an insulated tubular structure for fluid transfer which comprises: inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween; thermally insulating material substantially filling sai.d cavity; sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity; said outer pipe section compri.sing a main tubular member having a pair of end tubular members extending therefrom; said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means;
and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
Preferably the main tubular member and one end tubular member of the outer pipe section have respective free end portions telescoping one within the other, one such free end portion carrying an annular seal which slidably engages the other to provide the expansion joint.
Alternatively the expansion joint may be provided by a tubular bellows rather than the annular sliding seal, although the latter is usually to be preferred on account of the cost oE the bello~s and risk of their mechanical failure.
According to another aspect o~ the invention there is provided a downhole tubular system comprising a plurality of insulated tubu:Lar structures coupled together in vertical end to end alignment each said tubular structure comprising inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween; thermally insulating material substantially filling said cavity;
sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity;
said outer plpe section comprising a main tubular member having a pair of end tubular members extending therefrom said end tubular members being rigidly connected to respective ends of said inner pipe section by said sea].ing means and one end tubular member being interconnected with the main tubular member by an expansion joint providing a gas-tight seal between said members said tubular structures being coupled together by rigid coupling means rigidly interconnecting the inner pipe sections thereof so as to decouple the outer pipe sections from stresses transferred via the inner pipe sections.
~part from the mechanical integrity ensured by rigidly interconnecting the inner pipe sections while disposing the expansion joints so that they will not be subjected to load stresses, the arrangement has the considerable advantage that the outer pipe sections can be relatively thin-walled. This means that, for a given diameter of the tubular structure, more space can be made available to accommodate the insulation and hence the thermal properties of the design are greatly improved. Thus, ~or a given insulating material the insulation can be S~
made more effective. On the other hand, it is also feasible to use a simpler and less expensive insulating material than would otherwise be required. In a preferred embodiment of the present invention the thermally insulating material is a gas-permeable solid material such as cerarnic wool which is permeated with low conductivity gas such as argon.
Although the present invention is primarily concerned with the structural reliability of downhole tubing of the type discussed above, it has general application to the design of insulated pipe structures used for fluid transfer, wherein expansion joints required to accommodate differential thermal expansion of the inner and outer pipe sections must be shielded from load stresses.
In order that the invention may be readily understood one embodLment thereof will now be described, by way of e~ample, with reference to the accompanying drawings.
In the drawings, which show details of a downhole tubular system comprising a plurality of component tubular structures coupled together in vertical end to end alignment;
Figure 1 is a fragmentary half-sectional elevational view showing one of the component tubular structures and part of an adjacent tubular structure to which it is coupled;
Figure 2 is an exploded fragmentary perspective view of the component elements shown in Figure 1;
Figure 3 is an enlarged half-sectional elevational view showing the coupling in greater detail; and 7 ~ 5~
Figure 4 is an enlarged half-sectional elevational view showing the expansion joint in greater detail.
Referring to the drawings, each of the component tubular structures is essentially a double-walled structure comprising an inner pipe section 10 and an outer pipe section 11, the pipe sections being arranged concentrically one within the other to define an annular space therebetween. The outer pipe section 11 comprises a main tubular casing member 12, which extends for the greater part of the length of the structure, and a pair of end tubular casing members 13, 14 extending from it at each end. As shown in Figure 1, the end tubular members 13, 14 are of smaller diameter than the main tubular member 12. The end member 13 is received at one end within one end of the main tubular member 12, to which it is welded as shown at 15. The other end member 14, on the other hand, has a free end portion which telescopes within a free end portion of the main tubular member 12, being interconnected with the latter by an expansion joint 17 as hereinafter described. The distal ends of the end members 13, 14 are rigidly connected to respective ends of the inner pipe section by means o steel rings 18 which are welded to the ends of the inner pipe section 10 and to which they in turn are welded at their ends. Thus the steel rings 18 hermetically seal the ends of the annular cavity defined by the inner and outer pipe sections.
The annular cavity is itself filled with a thermally insulating material for minimizing heat losses rom the fluid being transferred. This material may comprise a gas permeable solid material permeated with a low conductivity ~as. For example, the insulation may be made up o~ a multilayered insulation as described in ~nited States Patent No. 4,332,~01 permeated with a very low conductivity gas such as krypton. However, since the present design permits space economy without loss of structural integrity, it is feasible to use a less elaborate and less expensive insulation system without loss of thermal efficiency owing to the additional space made available for its accommodation. Thus, in the present example the insulation comprises a ceramic wool 19 substantiall~ filling the annular cavity and back-filled with a low conductivity gas such as argon.
For this purpose a hole is drilled in the main tubular member 12 to permit evacuation of air from the annular cavity in which the ceramic wool has been laid, and then argon gas is introduced via the hole at atmospheric pressure. The hole is then sealed by a weld 20.
As previously mentionedr the end tubular casing member 14 is rigidly connected to one end of the inner pipe section 10 by means of the steel ring 18 to which it is welded, and has a free end portion which telescopes within the cooperating free end portion of the tubular member 12. The expansion joint 17 is formed by an annular sliding seal arrangement which is best illustrated in Figure 4. This consists essentially of a pair of short cylindrical members 21, 22 of the same diameters as the casing members 12, 14 and welded thereto in end ~o end alignment as shown by the welds 23, 24. The cylindrical members 21, 22 telescope one within the other and thus constitute, in effect, the free end portions of the casing members 14 and 12 respectively. The inside surface of the member 22 is machined to provide an annular abutment stop 25 which is positioned to engaye an abutment flanye 26 of the inner member 21 for limiting the extent of slidiny movement one relative to the other. It will be observed that by limiting the extent of sliding movement of the member 22 s~
within the member 21, the deslgn provides additional protection in the event of structural failure of one component.
Also machined in the inside surface of the outer cylindrical member 22 are a pair of annular slots for accor~odating a pair of retaining C-rings 27, 28, and an annular step 29. A pair of circular mechanical seals 30, 31 located by the retaining rings and the step 29 slidably engage the surface of the inner member 21 to provi~e a gas-tight seal while permitting relative movement of the inner and outer members in response to differential thermal expansion and contraction of the pipe sections. For this purpose fluorocarbon seals are well known in the art.
The component tubular structures are coupled end to end to form a rigid string, and details of the coupling between a pair of casing structures 32, 33 are best shown in Figure 3. This figure clearly shows the steel rings 18, 18' by which the end tubular members 14, 13' of the component structures 32, 33 are rigidly connected to the inner pipe sections 10, 10'. The external surfaces of the members 14, 13' are tapered as shown and provided with buttress threads 34, 34'. An internally threaded collar 35 engaging these threads provides the coupling by which the adjacent ends of the casing structures 32, 33 are rigidly coupled together. The inner pipe sections 10, 10' are aligned to form a continuous duct for the fluid to be transferred. A
filler ring or gasket 36 is interposed between the end rings 18l 18', which abut against it, and extends between the pipe ends 37 so as to minimize fluid leakage therefrom. The filler ring is firmly wedged in position within the collar 35 and is frictionally held by the internal th~eads thereof. The purpose of the s~
- ln -filler ring 36, which is made of a tough, heat resistant and steam resistant insulating material, is to prevent a heat short at the join between the two inner pipe sections, as well as to break the flow of steam which would otherwise be damaging to the coupling.
As will be apparent from the construction described, the entire weight of the suspended tubular system is borne by the inner pipe sectons 10, the axial load being transferred from each section to the next via the welded steel end rings 18, to which the tubular casing members 13, 1~ are welded, and the threaded collars 35 by which the cooperating ends of the component tubular structures are coupled together. The inner pipe sections 10 must therefore be of sufficient strength to carry the axial lS load, as must the couplings also, but this requirement is conveniently met since the pipe sections must in any case be strong enough to withstand the internal fluid pressure. On the other hand the outer pipe sections are decoupled from the axial load.
In the embodiment described above the outside diameter of the tubular system is 5.56 inches and each component casing structure is 30 feet long~ The inner pipe sections are of 2 7/8 inch outside diameter seamless steel tubing API-J55. The main tubular members 12 of the outer pipe sections are of standard wall-5 inch diameter line pipe. The end casing members 13, 14, which are specifically designed to withstand the grip of a service rig, are typically 3 feet long and are of 5 inch diameter API-J55 or API-N80 steel casing with API-8 Round Long Threaded and coupled ends. The internally threaded coupling collars 35, which are also of API-J55 or API-~8n steel casing. The specifications of these components are given by way of example only, of course, and for any given application the materials and dimensions of the components must be selected according to the working requirements. Thus, for example, the wall thickness of the outer pipe sections is very much less than that of the inner pipe sections and the load bearing components.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An insulated tubular structure for fluid transfer comprising:
inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween, thermally insulating material substantially filling said cavity, sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity, said outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means, and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween, thermally insulating material substantially filling said cavity, sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity, said outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means, and one said end tubular member being interconnected with the main tubular member by a gas-tight expansion joint.
2. An insulated tubular structure according to claim 1, further comprising rigid coupling means at each end of the tubular structure for connecting like structures in end to end alignment, said coupling means rigidly interconnecting the inner pipe sections of said aligned tubular structures so as to decouple the outer pipe sections thereof from stresses transferred via the inner pipe sections.
3. An insulated tubular structure according to claim 2, wherein said end tubular members are externally threaded, said coupling means comprising internally threaded collars engageable with said threaded end tubular members for interconnecting the end tubular members of adjacent tubular structures.
4. An insulated tubular structure according to claim 3, wherein said sealing means comprises a pair of .
steel rings welded directly to the respective ends of the inner pipe section and said end tubular members.
steel rings welded directly to the respective ends of the inner pipe section and said end tubular members.
5. A tubular structure according to claim 1, wherein said one end tubular member has a free end portion telescoping within a respective free end portion of the main tubular member, one said free end portion carrying an annular seal slidably engaging the other free end portion.
6. A tubular structure according to claim 5, wherein said free end portions are formed with annular abutment stops for limiting the extent of movement one within the other.
7. A tubular structure according to claim 1, wherein the thermally insulating material comprises a gas permeable solid material permeated with low conductivity gas.
8. A tubular structure according to claim 7, wherein the gas permeable solid material is ceramic wool.
9. A tubular structure according to claim 8, wherein the low conductivity gas is an inert gas or mixture of inert gases.
10. A tubular structure according to claim 8, wherein the low conductivity gas is argon.
11. A downhole tubular system comprising a plurality of insulated tubular structures coupled together in vertical end to end alignment, each said tubular structure comprising:
inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween.
thermally insulating material substantially filling said cavity, sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity, said outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means, and one end tubular member being interconnected with the main tubular member by an expansion joint providing a gas-tight seal between said members, said tubular structures being coupled together by rigid coupling means rigidly interconnecting the inner pipe sections thereof so as to decouple the outer pipe sections from stresses transferred via the inner pipe sections.
inner and outer pipe sections arranged concentrically one within the other to define an annular cavity therebetween.
thermally insulating material substantially filling said cavity, sealing means at both ends of each pipe section hermetically sealing the ends of said annular cavity, said outer pipe section comprising a main tubular member having a pair of end tubular members extending therefrom, said end tubular members being rigidly connected to respective ends of said inner pipe section by said sealing means, and one end tubular member being interconnected with the main tubular member by an expansion joint providing a gas-tight seal between said members, said tubular structures being coupled together by rigid coupling means rigidly interconnecting the inner pipe sections thereof so as to decouple the outer pipe sections from stresses transferred via the inner pipe sections.
12. A downhole tubular system according to claim 11, wherein said end tubular members are externally threaded, said coupling means comprising internally threaded collars engageable with said threaded end tubular members for interconnecting the end tubular members of adjacent tubular structures.
13. A downhole tubular system according to claim 12, wherein said sealing means of each said tubular structure comprises a pair of steel rings welded directly to the respective ends of the inner pipe section and said end tubular members.
14. A downhole tubular system according to claim 11, wherein the main tubular member and one end tubular member of each outer pipe section have respective free end portions telescoping one within the other, one free end portion carrying an annular seal slidably engaging the other.
15. A downhole tubular system according to claim 14, wherein the telescoping free end portions are formed with respective annular abutment stops for limiting the extent of movement one within the other.
16. A downhole tubular system according to claim 11, wherein the thermally insulating material comprises a gas permeable solid material permeated with low conductivity gas.
17. A downhole tubular system according to claim 16, wherein the gas permeable solid material is ceramic wool.
18. A downhole tubular system according to claim 17, wherein the low conductivity gas is an inert gas or mixture of inert gases.
19. A well casing according to claim 17, wherein the low conductivity gas is argon.
20. A well casing according to claim 11, wherein a filler ring is disposed between the opposed ends of each pair of adjacent casing structures and mounted coaxially therewith.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000419766A CA1191454A (en) | 1983-01-19 | 1983-01-19 | Insulated tubular structure |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000419766A CA1191454A (en) | 1983-01-19 | 1983-01-19 | Insulated tubular structure |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191454A true CA1191454A (en) | 1985-08-06 |
Family
ID=4124383
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000419766A Expired CA1191454A (en) | 1983-01-19 | 1983-01-19 | Insulated tubular structure |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191454A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1986004950A1 (en) * | 1985-02-21 | 1986-08-28 | A/S Raufoss Ammunisjonsfabrikker | Drilling pipe for making a drill string |
| WO1999027228A1 (en) * | 1997-11-24 | 1999-06-03 | Elwood Champness | Tool cooling system |
-
1983
- 1983-01-19 CA CA000419766A patent/CA1191454A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1986004950A1 (en) * | 1985-02-21 | 1986-08-28 | A/S Raufoss Ammunisjonsfabrikker | Drilling pipe for making a drill string |
| WO1999027228A1 (en) * | 1997-11-24 | 1999-06-03 | Elwood Champness | Tool cooling system |
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