Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1998-11-03
2003-11-18
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S437000, C166S387000, C166S084100
Reexamination Certificate
active
06648335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a metal-to-metal seal assembly and, more particularly, to such an assembly for use in oil and gas production apparatus located in a well.
2. Description of Related Art
It is critically important to properly seal certain components in oil and gas wells during the operation of downhole tools, after completion and testing of the well, and during production. For example, expansion joints, often referred to as “polished bore receptacles,” can be connected in the production tubing string in a completed well to compensate for changes in the axial length of the tubing string due to the effects of relatively large temperature changes in the well. Failure to compensate would otherwise cause a compression deformation or tensile failure. A typical polished bore receptacle includes two tubular members disposed in a telescoping relationship that is move relatively to each other in an axial direction in response to temperature variations, and a continuous dynamic seal is provided between the two members to prevent fluid leakage between the sliding surfaces of the two members.
Elastomer seals have been used in a variety of sealing applications in oil and gas wells, including use in the polished bore receptacles described above. However, the elastomer may lose its resiliency or shape memory after some use, which is necessary for the seal to oppose the imposed forces thereon. Also, elastomer seals tend to deteriorate with exposure to the downhole chemical and relative high temperature environments for long periods of time. Further, significant abrasion of the seal material will occur by the forces generated when there is relative movement between the two members being sealed, as is the case with polished bore receptacles. Although these deficiencies can be compensated for to a certain degree by preloading the seal, the preloading force becomes less as more and more of the seal material abrades, ultimately causing seal leakage and failure.
Therefore, to overcome these problems, metal-to-metal seals have evolved since they, for the most part, do not lose their resiliency and shape memory and are not affected by hostile environments. However, metal-to-metal seals are normally only used as static seals or as safety backup seals since the seal must remain stationary and must be under constant compression to insure that it is not compromised. Therefore, these metal-to-metal seals are not suitable for use in dynamic sealing applications, including the polished bore receptacles described above.
Prior art patents have addressed the need for metal-to-metal seals to some extent. For example, U.S. Pat. No. 5,662,341 which issued to the present inventors, discloses an earlier type of metal to metal seal assembly.
FIGS. 1 and 2
illustrate this prior art seal. Referring to
FIG. 1
of the drawings, the reference numeral
10
refers in general, to the expansion joint, or polished bore receptacle, of the present invention which is adapted to be connected between two tubular sections (not shown) forming a portion of production tubing string in an oil or gas well. The assembly
10
consists of an inner mandrel
12
telescopically received in an outer tubular member
14
. It is understood that the inner bore of the outer tubular member
14
is polished and that the entire lengths of the overlapping end portions of the mandrel
12
and the tubular member
14
are not shown in their entirety for the convenience of presentation.
The respective distal end portions of the mandrel
12
and the tubular member
14
are threaded for connection to the two tubular sections of the tubing string (not shown) in coaxial alignment. The respective inner bores of the mandrel
12
, the tubular member
14
and the tubing string sections are aligned in a coaxial relationship and thus provide a continuous passage for the flow of production fluid upwardly, as viewed in
FIG. 1
, through the lower portion of the tubing string, the tubular member
14
, the mandrel
12
and the upper portion of the string.
The mandrel
12
has a stepped outer surface and the tubular member
14
has a stepped inner surface. As a result, a shoulder
12
a
is defined on the outer surface of the mandrel
12
which, in the assembled condition of the assembly
10
as viewed in
FIG. 1
, abuts against a corresponding shoulder formed on the tubular member
14
. An annular cross-sectional space is defined between the outer surface of the mandrel
12
and the inner surface of the tubular member
14
, which space extends below the shoulder
12
a
and the corresponding shoulder of the tubular member
14
. The reference numeral
14
a
refers to a shoulder defined on the inner surface of the tubular member
14
at which the inner diameter of the latter member increases in a direction from the upper portion to the lower portion, for reasons to be described.
A locking mandrel
16
extends over the upper end portion of the tubular member
14
and has a inwardly-directed flange
16
a
which engages the end of the latter member. A plurality of angularly-spaced, radially-extending openings
16
b
(only one of which is shown in the drawing) are formed through the locating mandrel
16
and align with corresponding openings in the tubular member
14
and the mandrel
12
. A plurality of pins
18
are provided which, during assembly, pass through the openings
16
a
respectively, and extend in the respective aligned openings in the tubular member
14
and the mandrel
12
. This locates the mandrel
12
relative to the tubular member
14
in the position shown and prevents relative axial movement therebetween. The pins
18
are adapted to shear in response to a predetermined shear force between the mandrel
12
and the tubular member
14
, in a conventional manner. A threaded pin
20
extends through a threaded opening in the locating mandrel
16
and into a notch
14
b
formed in the upper surface of the tubular member
14
to secure the locating mandrel to the member.
A bearing ring
24
extends around the mandrel
12
and in the annular space between the mandrel
12
and the tubular member
14
. A wire ring
26
is used to secure the bearing ring
24
in the position shown. Another bearing ring
28
also extends around the mandrel
12
, in the latter annular space, and above the bearing ring
24
in a slightly spaced relation thereto.
A seal ring
30
extends around the mandrel
12
, in the annular space between the mandrel
12
and the tubular member
14
, and between the bearing rings
24
and
28
. As better shown in
FIG. 2
, the seal ring
30
has a substantially “C”-shaped cross section and, in the assembled portion shown in
FIG. 1
, the open portion of the C faces downwardly, i.e., in a direction facing the production fluid as it flows upwardly through the assembly
20
. The “C” configuration defines two parallel sections
30
a
and
30
b
which abut the tubular member
14
and the mandrel
12
, respectively, as will be described in further detail. The seal ring
30
is preferably fabricated from a metal material, and the height of the ring is slightly more than the height of the annular space between the mandrel
12
and the tubular member
14
in the portion of the annular gap in which the ring
30
is installed.
A coiled spring
32
is disposed within the seal ring
30
and extends for its entire circumference. The purpose of the spring
32
is to preload the seal ring
30
as will be described.
A coiled spring
32
is disposed within the seal ring
30
and extends for its entire circumference. The purpose of the spring
32
is to preload the seal ring
30
as will be described. The seal ring
30
has a major diameter defining its circumference, as well as a cross sectional diameter which defines the cross-sectional area of the seal ring
30
.
The assembly
10
is assembled by initially placing the bearing ring
24
over the outer surface of the mandrel
12
and aligning the groove in the inner surface of the ring
24
with the complementary groove in the outer surface
Knight Anthony
Williams Mark
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