Wells – Processes – Placing or shifting well part
Reexamination Certificate
2000-07-07
2002-12-31
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S066000, C166S162000
Reexamination Certificate
active
06499541
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method of installing components in a space defined between a cylindrical outer case of apparatus placed down an oil or gas well and a cylindrical inner passage passing through the apparatus.
Throughout this text, the term “component” designates any type of electrical or electronic circuit be it simple or complex, integrated or otherwise, isolated or associated with other items, and also other components such as sensors, motors, etc. . . . .
The invention also relates to a downhole apparatus including components installed by the method.
STATE OF THE ART
In apparatuses that are to stay permanently down a well that is in production, an ever-increasing number of electrical devices such as motors, sensors, actuators, etc. are being used. A consequence of that is to increase the size of the components that need to be installed in such apparatuses.
In the past, when the components were small in size, they could be installed without difficulty in small boxes fixed along the production column defining the cylindrical inner passage of which the hydrocarbon rises. Such an arrangement has been in use for many years, in particular for installing pressure sensors on apparatuses that are designed to remain permanently downhole or on test apparatuses associated with drilling strings.
Because of the ever increasing complexity of components, that type of installation is generally no longer usable since it is unsuited to the largest sizes of such components.
A first conventional solution for solving this new requirement is shown diagrammatically in cross-section in
FIG. 1
of the accompanying drawings.
In that case, the components
1
are installed in an annular space
2
formed between a tubular outer case
3
and a tubular inner production column
4
defining internally a cylindrical inside passage
5
up which hydrocarbon rises. In that arrangement, used in particular for test apparatuses installed on drilling strings, the outer case
3
and the production column
4
are arranged coaxially.
The conventional arrangement shown in
FIG. 1
is generally satisfactory. Nevertheless, it can only be used when the ratio between the diameter of the outer case
3
and the diameter of the inner production column
4
is sufficiently large to define an annular space
2
between them that is capable of housing all of the components
1
that are to be installed in the apparatus under consideration.
When the above-mentioned diameter ratio becomes too small, it is conventional to use a second installation technique which is shown diagrammatically in cross-section in
FIG. 2
of the accompanying drawings.
In that arrangement, the small ratio of the diameters between the tubular outer case of the device and the cylindrical inner passage
5
is compensated by locating the passage eccentrically. In general, the components
1
are then installed in recesses
6
machined externally in a solid metal core
7
. Once the components
1
have been mounted in the recesses
6
, the recesses are closed in sealed manner by covers
8
which are either welded at
9
to the core
7
, or else are closed by a tubular sheath surrounding the core.
That conventional arrangement suffers from numerous drawbacks.
Thus, because of the large radius of curvature of the outer case of the apparatus, the covers
8
or the sheath need to be very thick in order to be capable of withstanding the large pressure difference that exists between the external downhole pressure (frequently 1000 bars to 1500 bars) and the internal atmospheric pressure. The large thickness of the covers or of the sheath significantly reduces the amount of space available for the components, and that goes against the desired objective.
Given the sometimes very large dimensions of the recesses
6
, and in order to avoid excessively increasing the thickness of the covers
8
or of the sheath, use is sometimes made of support props
10
interposed between the cover
8
or the sheath and the bottom of a recess
6
. In order to be effective, such support props must be of large section and they must be relatively close together, thereby likewise reducing the space available for components and requiring modifications to their shapes and above all to their interconnections when they are electronic components. In addition, the presence of support props
10
does not prevent the covers
8
or the sheath from sagging under the effect of the pressure difference in those portions of the covers that are not provided with support props.
When covers are used to close the recesses, another major problem that arises with the conventional arrangement as shown in
FIG. 2
lies in obtaining leakproof sealing between the covers
8
and the core
7
, since the sealing must be capable of withstanding the large difference between the external pressure downhole and the atmospheric pressure that exists inside the recesses
6
.
Thus, achieving such sealing by means of elastomer gaskets is not recommended for use of long duration because such gaskets age. Furthermore, metal-on-metal sealing is difficult to design.
The only technique that can guarantee the desired degree of sealing in the long term is therefore welding. Because of the shapes of the covers, TIG welding is generally preferred over electron beam welding. Nevertheless, that type of welding suffers from the drawback of heating the components and, with some materials, of giving rise to stresses in the steel used for making the core
7
and the covers
8
or the sheath. These stresses can be relaxed only by subsequent heat treatment that certain components are incapable of withstanding. Such an operation is therefore not performed. As a result there is a significant increase in the risk of the core corroding.
Furthermore, for reasons of reliability, some components such as electronic circuits must be maintained as far as possible in an environment that is clean, in particular during manufacture and assembly. When the arrangement shown in
FIG. 2
is used, it is very difficult to satisfy this condition during the step of mounting the circuits. Welding the covers
8
onto the core
7
by means of the TIG technique is an operation that is lengthy, and that takes place in a workshop in an environment that is ill-suited to protecting components.
The way in which the covers
8
are fixed onto the core
7
also makes repairing or replacing the components completely impossible. If a component fails, the core must necessarily be returned to the workshop to be cut up.
Other drawbacks of the technique shown in
FIG. 2
stem in particular from using a core
7
that is in a single piece. That characteristic gives rise to high raw materials and machining costs and to machining operations that are complex and that require, for example, a certain number of bores to be made such as the bore referenced
11
to enable electrical link conductors to pass between components installed in different recesses
6
. The complexity of the machining applied to the core gives rise to a non-negligible risk of it being necessary to remake the piece completely in the event of an error occurring during machining.
Furthermore, the presence of large internal volumes under atmospheric pressure inside the recesses
6
makes it necessary to use high quality alloys so as to withstand the pressure difference. Such alloys are more difficult to machine and above all they are more expensive than traditional alloys.
Finally, because the components
1
are mounted directly on the core
7
which withstands the mechanical forces applied to the production column (tension/compression, twisting, thermal expansion), it is necessary to decouple the components mechanically from the core.
SUMMARY OF THE INVENTION
A particular object of the invention is to provide a method enabling components to be installed in an original manner in downhole apparatus, particularly when the ratio of inside to outside diameters is too small to allow annular installation of the type described above with reference to FIG.
1
.
More precisely, the invention provides a metho
Cantin Gilles
Hiron Stephane
Rayssiguier Christophe
Tourillon Vincent
Bagnell David
Dougherty Jennifer R.
Jeffery Brigitte L.
Schlumberger Technology Corporation
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