Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02335694 2001-02-13
OILWELL PERFORATOR HAVING METAL COATED
HIGH DENSITY METAL POWDER LINER
BACKGROUND OF THE INVENTION
The present invention relates generally to explosive shaped charges and,
in an embodiment described herein, more particularly provides an oilwell
perforator having a metal coated high density metal powder liner.
Oilwell perforators are used to perforate casing or liner lining a wellbore,
to
thereby provide a path for production, or injection, of fluids therethrough.
In order
to achieve an acceptably deep perforation tunnel in hard rock having high
density
and high compressive strength, it is generally recognized that it is desirable
to
form a liner of an oilwell perforator from a relatively dense material.
In general, deep penetrating oilwell perforators have liners made of partially
sintered metal powder, or blends of various metal powders. If different metal
powders are used, extreme care must be taken to prevent segregation of the
different powders. This segregation may be due to different particle shapes,
densities and sizes in the different powders. A liner made of segregated metal
powders is undesirable because it will not form an appropriately shaped metal
jet
when the perforator is detonated.
A metal powder having a suitably high density for use in a deep penetrating
perforator is made up of tungsten metal particles. Unfortunately, the tungsten
particles in the powder are relatively hard, and so the particles do not
readily
adhere together when the powder is pressed into a liner shape. The ability of
a
pressed metal powder to resist deformation prior to being partially or fully
sintered
is known as the "green" strength of the pressed powder.
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A sufficiently high green strength is required for handling and other
manufacturing processes. A present solution to the problem of low green
strength
in liners made from tungsten powder is to blend the tungsten powder with other
metal powders which, although they may be less desirable in some respects than
tungsten for use in deep penetrating perforators, enhance the green strength
of
the pressed metal powder. Due to the presence of the other metal powders in
the
liner, segregation problems occur and the tungsten content of the liner is
reduced
to less than about 95% of the liner by weight.
Therefore, it may be seen from the foregoing that it would be desirable to
provide a perforator with a liner that has an increased proportion of tungsten
or
other high density metal therein and which has a reduced tendency for
segregation of metal powders therein, but which has sufficient green strength.
SUMMARY OF THE INVENTION
In carrying out the principles of the present invention, in accordance with an
embodiment thereof, a shaped charge is provided which includes a liner formed
from metal coated high density metal powder. A method of using the shaped
charge as a perforator in a well is also provided.
In one aspect of the present invention, a perforator is provided which has a
liner formed of a metal powder wherein particles thereof are coated with
another
metal. The metal powder may be tungsten and the metal coating may be, for
example, copper, lead, molybdenum, tin, nickel or silver. The metal coating
enhances the green strength of the liner and significantly reduces the
possibility of
segregation of the metals as opposed to a mere blending of metal powders.
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In another aspect of the present invention, a perforator is provided which
has a liner formed of a tungsten powder wherein particles thereof are coated
with
a less dense metal. Nevertheless, the liner has an increased proportion of
tungsten therein, and therefore has an increased density as compared to
conventional liners with tungsten powder therein, and the metal coating
permits
the tungsten powder particles to be pressed into a liner shape with sufficient
green
strength.
These and other features, advantages, benefits and objects of the present
invention will become apparent to one of ordinary skill in the art upon
careful
consideration of the detailed description of a representative embodiment of
the
invention hereinbelow and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a method of oilwell perforating
embodying principles of the present invention;
FIG. 2 is an enlarged scale cross-sectional view of an oilwell perforator
embodying principles of the present invention, the perforator being usable in
the
method of FIG. 1; and
FIG. 3 is an enlarged scale cross-sectional view of a metal coated metal
powder particle of the perforator of FIG. 2.
DETAILED DESCRIPTION
Representatively illustrated in FIG. 1 is a method 10 which embodies
principles of the present invention. In the following description of the
method 10
and other embodiments of the invention described herein, directional terms,
such
as "above", "below", "upper", "lower", etc., are used for convenience in
referring to
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the accompanying drawings. Additionally, it is to be understood that the
various
embodiments of the present invention described herein may be utilized in
various
orientations, such as inclined, inverted, horizontal, vertical, etc., without
departing
from the principles of the present invention.
In the method 10, a perforating gun 12 is conveyed into a wellbore 16 and
positioned opposite a formation or zone 14. As depicted in FIG. 1, the gun 12
is
conveyed on a tubular string 18, but other conveyances, such as wireline,
etc.,
may be used.
The perforating gun 12 is fired, detonating shaped charges known to those
skilled in the art as perforators within the gun, and forming perforations 20
extending from the wellbore 16 and into the zone 14. Fluid may now be flowed
between the wellbore 16 and the zone 14. However, it is to be clearly
understood
that principles of the present invention may be incorporated in other methods
in
which fluid flow between a wellbore and a zone is not the intended or actual
result.
For example, shaped charges may be used in wells to perforate tubing, provide
detonation transfer between guns, etc.
Referring additionally now to FIG. 2, a perforator 24 embodying principles
of the present invention is representatively illustrated. The perforator 24
may be
used in the method 10 in the gun 12, or may be used in other methods.
Additionally, aspects of the perforator 24 described herein may be
incorporated
into other types of shaped charges, without departing from the principles of
the
present invention.
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The perforator 24 includes an outer case 26, an inner liner 28 and an
explosive material 30 retained between the case and liner. The liner 28 is
formed
from a fully or partially sintered metal coated high density pressed metal
powder.
For example, the metal powder may be tungsten, with particles thereof coated
with one or more of copper, lead, molybdenum tin and silver. Of course, other
metal powders and other metal coatings may be used without departing from the
principles of the present invention. In FIG. 3 is representatively illustrated
a metal
powder particle 34 with a metal coating 36.
The liner 28 has a content by weight of approximately 95% to less than
100% tungsten. Preferably, the tungsten content by weight is greater than 90%,
but less than 100%. This content of tungsten produces a liner which has
enhanced performance in creating a metal jet that forms a deep perforation
tunnel.
The present applicants have solved the problem of low green strength in
high tungsten content pressed metal powders by coating the tungsten powder
particles with relatively ductile metal, such as copper, lead, molybdenum,
tin,
silver, nickel etc. Thus, the metal coated metal powder adheres well when
pressed and has a sufficient green strength for a perforator liner, even
though it
has a high tungsten content.
The present applicants have also solved the problem of segregation
between metals in a powdered metal liner having more than one metal therein.
Specifically, by providing the high density metal powder particles with a
metal
coating, the metals are unable to segregate due to their different shapes,
densities, size, etc.
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It is to be clearly understood that other metals and combinations of metals
may be used without departing from the principles of the present invention.
For
example, the powder metal particles in the liner 28 may be other than tungsten
and may be a combination of metals, and the metal coating may be other than
copper, lead, molybdenum, tin, nickel or silver and may be a combination of
metals. Additionally, it is not necessary for the metal coating to be less
dense or
more ductile as compared to the metal powder particles.
Of course, a person skilled in the art would, upon a careful consideration of
the above description of representative embodiments of the invention, readily
appreciate that many modifications, additions, substitutions, deletions, and
other
changes may be made to these specific embodiments, and such changes are
contemplated by the principles of the present invention. Accordingly, the
foregoing detailed description is to be clearly understood as being given by
way of
illustration and example only, the spirit and scope of the present invention
being
limited solely by the appended claims.
WHAT IS CLAIMED IS:
