Oil well pipe threaded joint

Details Oil well pipe threaded joint Oil well pipe threaded joint

1996-07-30

2001-01-23

Arola, Dave W. (Department: 3629)

Pipe joints or couplings

With casing, lining or protector

Lined

C285S334000, C285S355000, C285S369000, C285S910000

Reexamination Certificate

active

06176524

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an oil well pipe threaded joint as a connection portion for tubes used for the excavation of a crude oil or a natural gas. More particularly, it relates to an oil well pipe threaded joint which can prevent the occurrence of looping or squeezing of a ring (also called a “ring-like buffer”) interposed between pins of oil well pipes for improving the sealability of the oil well pipe threaded joint and damage such as corrosion due to a corrosive fluid inside a pipe.
2. Description of the Prior Art
To excavate crude oil or natural gas, it has been customary to drill an oil well (also called an “ore chute”) from the ground surface to an oil layer or a gas layer, to apply a casing round the inner peripheral surface of this oil well so as to prevent the collapse of the oil well and to recover the crude oil or the natural gas through tubing inserted into the casing. Because the depth of the oil well is generally as great as several thousands of meters, steel pipes of a low alloy steel, etc, are fastened to one another by various methods to obtain an elongated pipe. Here, the connection portion of the tubing, etc, is referred to as an “oil well pipe threaded joint”.
Various oil well pipe threaded joints are known as described below. {circle around (1)} Japanese Unexamined Utility Model Publication (Kokai) No. 58-142475 proposes an oil well pipe threaded joint wherein a pin having an outside thread is formed on an outer peripheral surface in the proximity of an end portion of each pipe and a coupling (also called a “sleeve”) having an inside thread on an inner peripheral surface in the proximity of an open portion of a cylindrical member is formed so that the pin of each pipe can be threaded to this coupling. In this case, since the fitting and removal works are repeatedly carried out between each pipe and the coupling, a coating layer is likely to be damaged, and a ring made of a soft thermoplastic resin such as Teflon (trade name) is used. However, there remains the problem that the thermoplastic resin ring cannot play the role of a so-called “torque shoulder” for absorbing a torque acting on the distal end surface of each pipe and between both side surfaces of a protuberance portion at the time of makeup (also called “fastening”) and for reliably securing fixing. {circle around (2)} Japanese Examined Utility Model Publication (Kokoku) No. 6-49989 proposes a threaded joint wherein a pin having an outside thread formed on the outer peripheral surface of one of the pipes in the proximity of the end portion thereof and a pin having an inside thread formed on the inner peripheral surface of the other pipe in the proximity of the end portion thereof are interengaged with each other.
Recently, a so-called “water injection well” which injects water or brine (hereinafter called “injection water”) into the oil layer through the tubing has been widely employed in order to improve a crude oil recovery ratio. When ordinary water or brine is injected into the tubing, however, the tubing (or the oil well pipe) is remarkably corroded due to a high oxygen content of this injection water, and the collapse of the tubing occurs within a relatively short period. Therefore, to economically prevent the collapse of the tubing, {circle around (3)} Japanese Unexamined Patent Publication (Kokai) No. 62-98088, Japanese Unexamined Utility Model Publication (Kokai) No. 4-63884, U.S. Pat. No. 5,236,230, etc, propose a so-called “inner surface coating tubing” which applies a corrosion-resistant material such as a synthetic resin or ceramic to the inner peripheral surface of the oil well pipe made of ordinary steel, etc, as a coating, and protects the tubing from a corrosive fluid inside the tubing such as crude oil.
Nonetheless, the conventional oil well pipe threaded joints described above are not free from detrimental deformation under the environment of use such as looping (also called “buckling” or “jump-out”) and squeezing (also called “swell-out”).
Here, the mechanism of looping is as follows. When the corrosive fluid (also called the “pressure medium”) such as the crude oil or the natural gas inside the tubing enters the gap between a recess
55
defined by the distal end surface
51
h
,
52
h
of a pin
51
a
,
52
a
of each pipe
51
,
52
and a groove
53
f
of a coupling
53
and a ring
54
fitted into this recess
55
and as a result, when the pressure of the pressure medium inside the tubing (also called the “pipe internal pressure) drops with respect to the pressure of the pressure medium (hereinafter called the “back pressure”) as shown in FIG.
1
(
a
), the back pressure is applied to the end surface of the ring
54
on the outside diameter side as indicated by and arrow in FIG.
1
(
a
), so that the ring
54
is pressurized in a direction indicated by an arrow F′ in FIG.
1
(
a
) and partially jumps into the tubing as shown at the portion F in FIG.
1
(
b
).
The mechanism of squeezing is as follows. During the makeup (or “fastening”) work of the oil well pipe threaded joint, the distal end surfaces
51
h
and
52
h
of the pins
51
a
and
52
a
of the pipes
51
and
52
cause the ring
54
to interfere in the same direction as the axial direction of the tubing (hereinafter called the “axial direction”), or the groove
53
f
of the coupling
53
causes the ring
54
to interfere in the inner direction of the pipe as shown in FIG.
2
. As a result, the ring
54
undergoes elastic deformation from the initial shape represented by dash line in
FIG. 2
to the shape represented by solid line in FIG.
2
and swells out at the portion G in
FIG. 2
in the direction represented by arrow G′.
Once such looping and squeezing occur, a tool lowered inside the tubing during a logging (or “drift”) operation is caught by the ring which jumps out or swells out inside the tubing, and the logging operation cannot be carried out smoothly and the operation factor is remarkably lowered. When looping and squeezing occur in the oil well pipe threaded joint, the surface of the pin and the coupling which is originally covered with the ring is exposed, and this exposed surface comes into contact with the corrosive fluid and is eroded. As a result, the collapse of the tubing occurs within a short time, and reliability drastically drops.
To solve the problems described above, {circle around (4)} a method which uses a so-called “retainer ring” by making a spring or a metallic ring composite with a synthetic resin has been proposed. {circle around (5)} On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 59-126191 proposes an oil well pipe joint having the construction wherein a lip portion having a tapered outer peripheral seal surface and a distal end seal surface is formed at an end portion of a pipe having an external thread, a shoulder portion having an inner peripheral seal surface and a butt seal surface corresponding to the outer peripheral seal surface and the distal end seal surface, respectively, is formed at the inner depth of a coupling having an internal thread engaging with the external thread, and stopper portions are formed in the proximity of the outer and inner peripheral seal surfaces in such a manner as to engage with each other.
{circle around (6)} Further, Japanese Examined Utility Model (Kokoku) No. 1-12051 proposes an oil well pipe threaded joint for engaging and connecting the pipe end portions with each other, which can butt the terminal portion of shoulder portion of the pipe end on the external thread side with that of the pipe end of the internal thread, and wherein a clearance is generated between the terminal portion of the shoulder portion of the pipe end on the internal thread side and that of the pipe end on the external thread side at the time of butting and moreover, the distal end outer surface portion at the pipe end on the external thread side and the depth inner surface of the pipe end of the internal thread side can be brought into pressure contact with each other. In this thre

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