Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MAGNETIC SEPARATION IN FLUIDS
FIELD OF THE INVENTION
The present invention relates to an apparatus and methods for recovering
magnetically
attractable articles from fluid, and more particularly to an apparatus and
methods for
recovering magnetically attractable fragments from fluid in oil and gas well
casings to
determine the metal loss from the well casing.
BACKGROUND OF THE INVENTION
Casings used to line wells in oil- and gas-producing formations typically
suffer
damage from erosion, perforation (such as for the purpose of running
additional lines
into such a formation), and ordinary wear and tear from the operation of the
wells.
Since the integrity of well casing is important to the integrity of the well,
monitoring
the condition of well casing is an important part of well maintenance.
Drilling fluid is
circulated in well casing for purposes including removing drill cuttings from
the
casing and the face of the bit, so one way to monitor the condition of the
casing is to
collect and analyze the casing fragments released into the drilling fluid. The
quantity
of casing fragments collected from the drilling fluid is indicative of the
quantity of
fragments being generated down hole.
Solids and cuttings are generally removed from drilling fluids at the surface
by solids
control equipment such as shale shakers and hydrocyclones, which dump solids
into
collection bins. It is known to place a "ditch magnet" into the drilling fluid
system to
collect casing fragments from the drilling fluids. The typical ditch magnet is
heavy,
and requires at least two persons to lower it into the drilling fluid stream.
As metal
fragments adhere to the ditch magnet, the device becomes even heavier and
difficult
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for personnel to remove. Removal of the metal particles from the ditch magnet
is
difficult because of the strong magnetic field, which can also result in the
magnetization of handles or other features of the device. Drilling personnel
usually
run their hands over the surface of the ditch magnet in an effort to strip the
magnetic
materials from the magnet. This process is slow and laborious, and the amount
of
metal fragments retrieved and therefore the accuracy of the calculation of
total metal
loss in the casing depends on the skill and thoroughness of the personnel
removing the
fragments from the ditch magnets. Another known method of fragment removal
employs shrouded or sheathed magnets in a non-magnetic housing which includes
a
lid connectable to the housing so that the magnets are removable from the
housing.
By removing the magnets from the housing, the housing can be demagnetized to
facilitate collection of the metal filings from the exterior surface of the
housing.
However, the connection between the lid and the housing can become fouled by
drilling mud and metal filings so that the reconnection of the lid to the
housing
becomes difficult. There is a need for an apparatus and method for inexpensive
removal of casing fragments from drilling fluids without the disadvantages of
the
known devices and methods.
SUMMARY OF THE INVENTION
The present invention is directed to methods and apparatus for removing casing
fragments from fluids circulated in hydrocarbon-producing wells which meets
the
need identified above. In one aspect, the invention is directed to a method
for
monitoring the condition of well casing by recovering magnetically attractable
casing
fragments from fluid in a vessel having an upper end, including placing a
reusable
magnetic separator in the fluid in the vessel, wherein the separator includes
a magnetic
body, at least one nonmagnetic end contiguous to the body, an exterior surface
spanning the body and nonmagnetic end, and a hanger; retaining the separator
in the
fluid for a selected period of time; removing the separator from the vessel;
and urging
the casing fragments along the exterior surface of the separator to the
nonmagnetic end
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and collecting them. In another aspect, the invention is directed to a
magnetic
separator, having a bare magnet body, at least one nonmagnetic end contiguous
to the
body, and an exterior surface spanning the body and nonmagnetic end.
These and other features and aspects of the present invention will become
better
understood with regard to the following description, appended claims, and
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view of an embodiment of the disclosed invention.
FIG. 2 is an exploded isometric view of an embodiment the disclosed invention.
FIG. 3 shows a side elevation view of an embodiment of the disclosed invention
in
operation.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to FIG. 1, one apparatus according to the invention is a reusable
magnetic
separator l0a for retrieving metal fragments from hydrocarbon well fluids
including a
magnet body 12a contiguous to at least one nonmagnetic end 14a, and an
exterior
surface 16a.
Referring to FIG. 2, a method of the invention includes placing a reusable
magnetic
separator lOb into fluid 28 in a vessel 20, such as a shale shaker, and
retaining the
separator lOb in the fluid 28 for a selected period of time; the magnetic
field separates
the casing fragments 30 and other magnetically attractable materials from the
fluid 28.
After a suitable selected period of time, the separator lOb is removed from
the vessel
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20, and, to release the casing fragments 30 from the separator lOb, the casing
fragments 30 are urged along the exterior surface 16b to the nonmagnetic end
14b. In
addition, the recovered casing fragments 30 may be analyzed (qualitatively
and/or
quantitatively) to assess the condition of the well casing. As shown in FIG.
2, in some
embodiments, the separator lOb may be suspended in the fluid 28 with one or
more
hangers 18a.
Another aspect of the invention is a method for monitoring the condition of
well
casing by recovering magnetically attractable casing fragments from fluid,
wherein the
casing fragments may be generated by use or modification of the well casing.
In this
method, a reusable magnetic separator having a magnetic body and a nonmagnetic
end
contiguous to the body is placed in such fluid contained in a vessel, whereby
magnetically attractable casing fragments are separated from the fluid by the
magnetic
field created by the magnetic body. After a suitable selected period of time,
the
separator is removed from the fluid, and the casing fragments are urged along
the
exterior surface of the separator to the nonmagnetic end. The magnetic
separator used
in some embodiments may include a housing substantially free of protrusions
along its
sides and containing bar magnets, at least one nonmagnetic end, an eye bolt on
the at
least one nonmagnetic end attaching such nonmagnetic end to a hanger (such as
a
chain or other conventional hanger). In some embodiments, the collected casing
fragments may be weighed and the total weight of the recovered casing
fragments may
calculated. The total weight of the casing originally installed in the well
may also be
calculated so that the percent of metal lost from the casing is obtainable for
example
by dividing the total weight of the casing fragments recovered from the well
by the
total weight of the casing originally installed in the well. The casing
fragments may
also be subjected to qualitative assessment, such as by visual inspection.
Yet another aspect of the invention is a method for collecting magnetically
attractable
particles from fluid. This method of the invention includes placing a reusable
magnetic separator in fluid, wherein the separator includes a magnetic body
which in
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turn may have bare magnet, at least one nonmagnetic end contiguous to the
body, and
an exterior surface spanning the body and nonmagnetic end; retaining the
separator in
the fluid for a selected period of time; removing the separator from the
fluid; and,
urging the particles along the exterior surface of the separator to the
nonmagnetic end
and collecting them.
In some embodiments of the invention, the separator may include nonmagnetic
ends at
either side of the magnetic body, such that the magnetically attractable
casing
fragments may be collected by urging them to either nonmagnetic end. In other
embodiments, the separator may be suspended from the upper end of the vessel
with a
hanger, which may include cable, rope, chain, or other conventional materials.
In yet
other embodiments, the separator may be suspended with at least two hangers
for
increased stability; each of these hangers may be disposed away from the other
and
furthermore may each be disposed at a nonmagnetic end. In various embodiments
of
the invention, the length of the hanger may be selected to maintain the
separator above
the bottom of the vessel. The selected length of the hanger may then be fixed
in some
embodiments of the inventive methods so that the separator may be positioned
within
the vessel.
Referring to FIG. 3, in some embodiments of the invention the body 12c may
include
at least one magnet 22, and each magnet 22 may have a bore 26 such that the
bores 26
of adjacent magnets 22 are aligned along an axis and a retainer 24 can be
inserted
through the bore 26 of each magnet 22. At least one end of the retainer 24 may
be
attached to a nonmagnetic end 14c, which nonmagnetic end is further attached
to a
hanger 18.
While the above is a description of various embodiments of the present
invention,
further modifications may be employed without departing from the spirit and
scope of
the present invention. For example, the size, shape, and/or material of the
various
components may be changed as desired. Thus the scope of the invention should
not be
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limited by the specific structures disclosed. Instead the true scope of the
invention
should be determined by the following claims.
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