Hostile environment joint seal and method for installation

A tubular joint sealing system for use in high pressure and high temperature conditions is provided. The sealing system consists of a shape memory material backup member combined with a compliant seal. The shape memory member is deformed into an intermediate shape that is sufficiently reduced in size so as to avoid abrasive contact with the sealing surfaces of the tubular members during the mechanical makeup of the joint. Thereafter, the shape memory member may be activated to assume its memory shape configuration, which is selected to be sufficient size to form a pressure and fluid-tight seal.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention relates to a joint seal for use in high pressure and 
high temperature conditions, and more particularly to such a seal system 
fabricated out of a metal alloy having shape memory characteristics in 
combination with a compliant seal, which permits seating of the seal 
system after the mechanical makeup or connection has been fully completed. 
2. Description Of The Prior Art 
The exploration for and extraction of natural gas has in some instances 
presented problems not commonly associated with other types of oil and gas 
wells. Extremely high temperatures and especially high pressures 
associated with the deeper gas wells present various problems that could 
not have even been imagined by the earlier drillers of the more shallow 
oil and gas wells. However, with the exhaustion of the more easily 
recoverable oil and gas, it has become necessary to drill deeper into the 
earth, seeking replacement supplies of these vital commodities. The 
hostile conditions present at these greater depths are constantly 
challenging metallurgists and petroleum engineers to develop new systems 
capable of performing under these conditions. 
The drilling method historically employed by the petroleum industry for the 
drilling of exploratory and producing wells utilizes a drill bit attached 
to a rotating string of drilling pipe. Rotation is induced by a rotary 
table located on the surface, which is engaged with the string of pipe by 
a special, uppermost section of drilling pipe, or Kelly. As the drill bit 
bores into the earth, at rates often averaging about five feet per hour 
(1.5 meters per hour) in deep holes, additional sections of drilling pipe 
are added from the top. During both the drilling and production, it is 
vital that connections between the individual lengths of drilling pipe as 
well as other types of well tubulars, including various kinds of casing, 
lining, and tubing, also provide gas and fluid-tight seals. Such sealing 
is necessary to ensure containment during drilling and production of the 
hazardous high pressures existing in deep gas wells. The difficulties in 
maintaining these individual seals is made infinitely more complicated by 
high and widely varying magnitudes of temperature and pressure, and 
frequently, highly corrosive environments. 
In providing pressure-tight joints at ultra-high pressures, whether or not 
in the oil industry, it is typically not possible to utilize compliant 
seal material as the primary seal. Under high differential pressures, such 
material will structurally fail and extrude out through any available 
opening. For this reason, metal-to-metal seals are provided as the primary 
seal. Metal seals are created both through the provision of corresponding 
planar sealing surfaces and through specially designed, tapered threads. 
Use of a compliant sealing material in these circumstances is limited to 
the formation of secondary seals, which are created in protected areas 
located between the metal-to-metal seals. Such metal-to-metal seals have 
been widely used in the past over varying temperature and pressure 
conditions, however at increasing temperatures and pressures, These 
concepts have proven to be unreliable. 
Most sealing systems utilize either the application of a preload or the 
creation of an interference, either of which energizes the seal and 
creates sealing stresses. Because metals have relatively high modulus and 
low compliance, relatively high stresses and preloads are required with 
metal seal systems. Furthermore, stretching of the connection due to 
weight of the tubular, internal pressure, flexing of the tubular, and 
differential thermal expansion can cause unloading of the preload, and 
thus seal failure. To prevent this from occurring, additional, 
compensating preloading is required. After the sealing surfaces have been 
brought together during the mechanical formation of the connection, it is 
necessary to further tighten the members, pressing the sealing surfaces 
tightly together to preload them sufficiently to form a reliable seal. All 
of these additional components of preloading increase the stresses and 
frictional forces in the connection. 
Since the mating or sealing surfaces are also part of the mechanical joint 
system, these surfaces are subjected to rotational sliding, under load, 
during the mechanical makeup of the joint. In fact, the seals are formed 
as a result of the two sealing surfaces sliding past one another under 
increasing stresses. Such a sealing process inevitably creates the 
potential for damage to the sealing surfaces because of the interference 
fit. Minimization of the amount of damage caused thereby requires creation 
of extremely tight tolerances and precise interference fits, which are 
both expensive to obtain and excessively vulnerable to damage. 
The precise interference fits also prevent the effective and reliable use 
of resilient or compliant materials as the primary seal. Such materials 
are unable to withstand the strain placed upon them as the tightly 
confining mating surfaces rotate against them. Bunching, rolling, and/or 
galling is highly probable, and such destructive deformation is 
catastrophic to the formation of a viable seal. Even should the material 
somehow escape damage during the mechanical makeup, it is inevitable that 
gaps will exist within the threads or between sealing surfaces, and at 
high pressures, the sealing material will fail by extruding out of its 
seat and into these gaps. For these reasons, compliant materials, which 
are the most desirable seal materials, are seldom used in forming such 
high pressure seals, and even where used, metal-to-metal seals provide the 
primary sealing means. 
SUMMARY OF THE INVENTION 
The present invention has as an underlying objective, the improvement in 
the hertofore known types of high pressure and temperature sealed 
connections by the provision of a compliant material seal having a 
metal-to-metal seal backup that is formed only after the tubular 
connection itself has been mechanically completed. Up until that point, 
neither the compliant material nor the metal-to-metal backup surfaces have 
been subjected to mechanical or frictional loading or sliding motion, and 
thus the sealing surfaces are not subject to damage while the mechanical 
connection between the tubular members is being formed. 
The separate, post-connection formation of the seal substantially eases the 
design criteria for the connection between members since all of the 
previous, exacting seal considerations have been substantially removed. 
The thread and mechanical surface tolerances are not nearly as critical, 
nor is preloading stress the major design consideration. 
These objectives are inventively achieved by providing a separate sealing 
system constructed of a metallic, shape memory material, and a compliant 
seal. After first being formed into the required dimensions, the shape 
memory member is deformed sufficiently to avoid sliding contact with the 
sealing surfaces during the makeup of the joint connection. After the 
joint is mechanically completed, the sealing system is then caused to 
resume its original dimensions, seating itself and forming the seal. As 
finally formed, the compliant material is enclosed by adjacent 
metal-to-metal backup, which prevents subsequent extrusion of the 
compliant material when subjected to high pressures. 
This remarkable seal system with the ability to seat itself after the 
mechanical makeup of the connection is made possible by the inventive 
utilization of shape memory material. Beginning in the early 1960's, a 
series of engineering alloys possessing this "memory" became known to 
metallurgists. The generic name of one series of such alloys is 
55-Nitinol, where Nitinol is an acronym of: NIckel TItanium Naval 
Ordinance Laboratory. These alloys, having chemical compositions in the 
range of approximately 53 to 57 weight percent nickel, with the balance 
titanium, possess a memory such that under the proper conditions, an 
object formed thereof can be restored to its original shape even after 
permanent deformation. The return to the original or "memory" shape is 
triggered by heating the alloy to a specific transition temperature, which 
can be variably selected within the range of -400.degree. to 330.degree. 
F. (-240.degree. to 165.degree. C.), by adjusting the precise composition 
of the alloy. Further information concerning Nitinol, its composition, 
physical properties, and applications may be found in NASA publication No. 
SP 5110, entitled "55-Nitinol--The Alloy With A Memory: Its Physical 
Metallurgy, Properties, And Applications", published in 1972 by the U.S. 
Government Printing Office. 
Discovery of Nitinol resulted in the issuance of U.S. Pat. No. 3,174,851 to 
Buehler et al. A benevolent licensing program by the assignee, the United 
States Government, has resulted in a number of patents disclosing various 
ways of utilizing this alloy. These uses range in complexity and 
importance from self-erectable structures for aerospace hardware to toys 
and advertising novelties. (See NASA Publication No. SP 5110, supra.) In 
the area of connectors, however, the variety has been somewhat limited. 
U.S. Pat. Nos. 4,149,911 and 4,198,081 to Clabburn and Harrison et al., 
respectively, typify the systems wherein the Nitinol is formed in such a 
manner that upon reassuming its memory shape, it contracts around the 
pipes, clamping them together. U.S. Pat. No. 3,759,552 to Levinsohn et 
al., provides a heat recoverable V-ring seal in addition to the 
above-mentioned clamping seal. 
In Kim et al. (U.S. Pat. No. 4,281,841), an O-ring of Nitinol is utilized 
for sealing two concentric tubes in an ultra-high vacuum system. Upon 
heating, the O-ring expands outwardly, deforming to create a seal as a 
result of ridges formed in the walls of the inner and outer tubes. In 
another expansion-type seal, U.S. Pat. No. 4,001,928 to Schweiso, a 
dish-shaped plug of heat recoverable material is placed in an opening, 
and, upon heating, the plug enlarges to its former "memory" diameter and 
seals the opening. Additional prior patent and bibliographic information 
may be found in the Naval Surface Weapons Center Publication No. NSWC TR 
80-59, entitled "A Source Manual For Information On Nitinol And Niti, 
First Revision", by David Goldstein, Feb. 1, 1980 edition. 
In contrast to this prior art, the present invention utilizes shape memory 
metal to provide a backup to a compliant sealing material. In the context 
of an oil well environment, this is a fundamental difference, as will now 
be described in conjunction with the type of tubular connection utilizing 
a cylindrical outer sleeve. 
The sealing ring fabricated out of a shape memory metal is provided with 
compliant sealing material located in grooves formed in both end faces of 
the alloy ring. Prior to insertion into the sleeve, the sealing ring is 
radially distorted in a manner that effectively reduces its axial length. 
The ring is then placed between the two tubular members, which are 
tightened onto the cylindrical sleeve. After the connection has been 
mechanically completed, the sealing ring is heated, causing the ring to 
return to its original axial dimensions, expanding to fill the previously 
unoccupied spacing gaps between the two tubular members. This axial 
expansion causes the ridge of compliant sealing material located at each 
end face to form a seal with the mating surface of the tubular member 
located adjacent thereto. In addition, the alloy ring material adjacent 
each side of the compliant material forms a zero clearance backup and, 
secondarily, a metal-to-metal seal with the end of the tubular member, 
thus preventing the sealing material from extruding therefrom. 
The Nitinol alloy permits the sealing ring to have an initial axial 
dimension that is sufficiently reduced to avoid any abrasive contact with 
the sealing surfaces on the tubular member during the tightening 
operation. The forceful tendency of the sealing ring to return to its 
original, expanded shape upon heating creates controllable mechanical 
forces that press the compliant material against the sealing surfaces. A 
tight, well-formed seal system results, which is suitable for the high 
temperature and pressure environments commonly associated with the deeper 
drilling operations. Moreover, the minimal hysteresis losses occurring 
during the Nitinol phase changes enable the sealing ring to be repeatedly 
refurbished for the reuse thereof. The many assemblies and disassemblies 
to tubular members required during oil well drilling and production makes 
this ability for recycling extraordinarily advantageous. In addition to 
Nitinol, other shape memory alloys exist and may be utilized in the 
present invention, such as a family of brasses. 
Various other objects, advantages, and features of the present invention 
will become readily apparent from the ensuing detailed description, and 
the novel features will be particularly pointed out in the appended claims 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a sealing ring 1 that is used to form a tubular joint seal in 
accordance with the present invention. The sealing ring 1 consists of a 
shape memory backup ring 2 with a pair of end faces 3 and a 
circumferential ridge of a compliant sealing material forming a compliant 
seal 5 upon each thereof. As more clearly shown in FIG. 2, the compliant 
seal 5 is located in a pair of grooves 4 that are formed in the end faces 
3 of the backup ring 2. 
The shape memory material utilized for the backup ring 2 is, in a preferred 
embodiment, a metal alloy known as Nitinol. The shape memory 
characteristics of Nitinol have long been well known to those skilled in 
the art. This alloy of approximately 55% Nickel and 45% Titanium, posseses 
the ability to be formed into a "memory" shape while in the higher 
temperature crystaline phase; to be cooled and deformed while in the lower 
temperature phase (deformation of up to 10%); and then to reassume its 
original memory shape upon again being warmed into its higher temperature 
phase. Nitinol alloys suitable for the present invention may be obtained 
from such suppliers as Special Metals Corp., New Hartford, N.Y., and 
Raychem Corp., Menlo Park, Calif. 
The backup ring 2 shown in FIGS. 1 and 2, illustrates the "memory shape" 
chosen for the present invention, i.e., the form selected for the higher 
temperature phase. In contrast, the backup ring 2a shown in FIGS. 3 and 4, 
has been deformed and is in its "intermediate shape". (The "intermediate 
shape" will be hereinafter indicated by the addition of an "a" to the 
reference numeral indentifying that same structure when in its "memory 
shape".) As is shown by FIGS. 3 and 4, the precise nature of the 
deformation is not important, it can be a simple radial, inward distortion 
illustrated by FIG. 3, or the more complex ripple shown in FIG. 4. The 
only critical characteristic of the deformation is that the axial length 
B,B.sup.1 after distortion of the backup ring 2a, 2a.sup.1 must be less 
than axial length A of the backup ring 1 in its memory shape. The 
difference between A and B,B.sup.1 can be on the order of 8% to 10%, 
however, in all cases it must be sufficient to avoid abrasive contact of 
the compliant seal 5 and the end faces 3 with their mating surfaces during 
the mechanical makeup of the connection. 
In FIG. 5, a sealing ring 19a, in its intermediate configuration, has been 
installed in a coupled connection 11. The coupled connection 11, aside 
from the sealing ring 19a, consists of an upper tubular member 13 and a 
lower tubular member 14 received by an outer cylindrical sleeve 17. The 
tubular members 13,14 are retained within the cylindrical sleeve 17 by 
threads 15, formed on both the sleeve 17 and the tubular members 13,14. In 
the coupled connection 11 shown in FIG. 5, both of the tubular members 
13,14 have been fully tightened onto the cylindrical sleeve 17. Adjacent 
the sealing ring 19a, the tubular members 13,14 are provided with an upper 
sealing surface 21 and a lower sealing surface 22, respectively. 
As is more clearly shown in FIG. 6, the sealing ring 19a is not in 
compression as between the upper member 13 and the lower member 14. An 
upper gap 23 separates the upper sealing surfaces while a lower gap 24 
separates the lower sealing surfaces 22. When placed in a vertical 
installation, the end face 3 of the sealing ring 19a will rest upon the 
lower sealing surface 22 of the lower tubular member 14. However, the 
mechanical connection between the lower tubular member 14 and the outer 
cylindrical sleeve 17 has previously been completed, and thus after 
installation of the sealing ring 19a, relative motion will only occur 
between the end face 3 of the sealing ring 19a and the upper sealing 
surface 21 of the upper tubular member 13, which are separated by the 
upper gap 23. The presence of either or both the upper and lower gaps 
23,24 between sealing surfaces in relative motion assures that the sealing 
ring 19a and the upper and lower sealing surfaces 21,22 will not be 
damaged during the mechanical makeup of the coupled connection 11. 
Upon the application of heat energy to the sealing ring 19a, the Nitinol 
backup ring 2 will change crystaline phases, and attempt to reassume its 
memory shape. FIG. 7 illustrates the results of such a transformation. The 
upper and lower gaps 23,24 no longer exist as the sealing ring 19 occupies 
the entire space between the upper and lower tubular members 13,14. A 
compliant seal 20 is shown pressed between a zero-clearance backup and 
secondary seal 27. The backup/seal 27 prevents the complaint seal 20 from 
extruding out of the grooves 4 when subjected to high temperature and 
pressure conditions. The actual material utilized to make up the compliant 
seal 20 may consist of any compliant seal material known to the art, such 
as polyfluoroolefin resins such as Teflon, various elastomeric materials, 
and even soft metals. The principal design criteria is the ability of such 
material to retain its integrity and flexibility under the harsh, high 
temperature and pressure conditions to which it will be subjected. A 
present preferred material is a known elastomeric material, Y267 EPDM, 
(ethelyne propylene diene methylene), which may be obtained from Precision 
Rubber Company, Lebanon, Tenn. 
The dimensional configuration of the backup/sealing ring 19 while in its 
memory shape, is carefully designed to obtain a backup/seal with the 
desired design characteristics. The characteristics of Nitinol provide a 
precise control of the extent of the backup ring 2 expansion. The 8-10% of 
expansion available from Nitinol must also take into account dimensional 
changes in the connection due to the influences of pressure and 
temperature. in addition to stretching of the connection caused by various 
forces, including the weight of the string of tubing already in the well 
hole. Presently, it is believed that the maximum possible stretch in the 
connection is approximately 3 mils, or about 0.3%. By tailoring the cross 
section of the sealing ring, the force applied to the adjacent tubular 
members 13,14 can be controlled, and thus overstressing of the joint can 
be prevented, while concurrently providing a slack take-up capability of 
the sealing ring 19 on the order of two to three percent--well in excess 
of the 0.3% due to stretching. Thus, the seal is maintained 
notwithstanding the dimensional changes in the joint due to temperature 
and pressure variations and other outside forces being applied to the 
joint. 
The actual interface between the sealing ring 19 and the tubular member 13 
is clearly shown in FIG. 8. The compliant seal 20 is shown between zero 
clearance backup/seals 27. The backup/seals 27 consist of the 
metal-to-metal backup/seal formed by the end faces 3 of the metal ring 2 
abutting the sealing surface 21 of the tubular member 13. The ability to 
create both the compliant seal 20 and the backup/seal 27 after the coupled 
connection 11 has been mechanically completed, greatly simplifies design 
of the connection. The sealing surfaces are no longer subjected to the 
high abrasive forces created as the connection is being made. Instead, the 
seal shown in FIG. 8 possess sealing surfaces that were essentially not in 
sliding contact prior to the transition of the Nitinol from its 
intermediate shape to its memory shape. 
This inventive shape memory seal may be utilized in a wide variety of 
tubular joints. FIG. 9 illustrates its use in connection with a box-pin 
upset tubular joint 31, so known due to the increase in outer diameter of 
the tubular member about the joint. In the upset joint connection 31, an 
upper tubular member 33 having a pin or male end portion 38, is received 
by a box or female end portion 39 formed in the lower tubular member 34. A 
sealing ring 39 is received between a tip 40 of the pin end portion 38 and 
a base 41 of the box end portion 37. As was the case in the coupled 
connection 11, a seal is formed in the upset joint connection 31 only 
after the joint is mechanically complete. 
FIG. 10 illustrates the utilization of the shape memory seal in conjunction 
with a rock core pressure testing vessel 50. The testing vessel 50 is 
frequently used for geothermal and oil and gas formation permeability 
testing. The testing vessel 50 consists of an outer cylindrical pressure 
vessel 53 with a bottom closing flange 54 and an upper closing flange 55. 
A cylindrical rock core 57 having a center bore 58 is placed inside of the 
pressure vessel 53. A disc-shaped sealing system 61, Z-shaped in 
cross-section, of shape memory material provides the seal between the top 
of the rock core 57 and the closing flange 55. The bottom of the rock core 
57 can easily be firmly attached to the bottom flange 54; however, surface 
irregularities in the rock core 57 and variations in overall size 
invariably produce irregular gaps between the rock core 57 and the upper 
flange 55. Upon activation to its memory shape, the seal system 61 exerts 
upward pressure against the closing flange 55 forming a pressure tight 
seal, thus permitting the creation of a pressure differential between the 
center bore 58 and the space surrounding the rock core 57 within the 
pressure vessel 53. FIG. 11 illustrates the analogous utilization of a 
shape memory member 64 in conjunction with a compliant material 65 in the 
disc-shaped sealing system 61. 
Regardless of the type of tubing connection involved, the method for 
effecting this inventive seal is the same. Where a separate coupling 
member is to be utilized, for example a cylindrical sleeve, the separate 
member is first attached to the lower tubular member. The Nitinol ring 
seal in its intermediate shape is then placed either in the coupling 
portion of the lower tubular member or on top of the lower member when it 
is attached to a separate coupling member. In either case, the upper 
tubular member is then attached. It is only after the connection has been 
mechanically completed that the Nitinol ring is returned to its memory 
shape by the application of heat, which may be applied by any method, for 
example, by combustion of oil or gas, or induction heating. In a preferred 
method, since oil drilling rigs are normally provided with a steam 
generator, and by adjusting the components of the Nitinol alloy in a 
manner well known to the art, it is possible to select an alloy such that 
steam could be used to effect the crystaline structure transition. 
Upon the application of heat, the tubular joint is completed. Even where 
the temperature falls below the memory shape crystaline phase temperature, 
the seal is maintained but at a lower stress. Upon subjecting the joint to 
its high pressure and temperature environment, phase transition and higher 
stresses are again achieved. Independently, the seal is self-energized 
into its correct, designed configuration by the pressure within the 
tubular. Disassembly is no problem and upon the simple refurbishing, the 
seal may be reused any number of times without losing its ability to 
reassume its memory shape. 
While we have disclosed exemplary structures and methods of construction to 
illustrate the principles of the present invention, it should be 
understood that we wish to embody within the scope of the patent warranted 
hereon, all such modifications as reasonably and properly come within the 
scope of our contribution to the art.