Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This apparatus lies in the field of filter apparatus.
More particularly, it lies in the field of filter apparatus for
separating particulate matter from a flowing fluid stream.
Still more particularly, this invention relates to a
filtering apparatus for screening out sand from oil and gas
flowing into a well, by permitting the oil and gas to flow
through the permeable walls of the tubular elements and into
the well tubing to the surface.
In the prior art there are a number of designs of
sand screens for use in oil fields wherein a rigid skeleton
structure is provided around which a wire is wound with
suitable tension and suitable spacing, to permit the flow
of oil without the flow of sand of sizes greater than a
selected minimum. These designs typically require the use
of a gravel pack sized to retain the formation sand which
bridges and restrains the passage thereof into the production
tubing.
Because of the large diameter and surface area
of the prior art devices, the skeleton must be extremely
rigid and strong to resist the forces acting radially
inward on the wall by the sand, which compacts itself
around the outside of the wire screen. Furthermore,
in the prior art this single large diameter screen has a
maximum diameter which is the function of the dizmeter
of the casing. There is no way of increasing the area
except to make the device longer and longer, which entails
considerable difficulty in providing suitable strength to
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the skeleton on which the wires are wound.
According to the invention there is provided a filter
apparatus for separating particulate matter from fluid flowing
from a formation within a well comprising: (a) a plurality
of small diameter, rigid tubular filter elements, the walls
of said tubular elements having gauged openings for the flow
of said fluid thereacross into the center of said elements;
(b) means to support said plurality of tubular elements,
such that their axes are substantially parallel to the axis
of said well and with their outer surfaces unencased and
openly exposed to said formation; and (c) at least one plenum
means to which said center space inside said tubular elements
are in communication; and (d) tubing means connected to the
plenum to conduct said filtered fluid to the surface of said
well.
This invention is particularly adapted to be used
for screening sand from oil flowing into a well at the
bottom of a casing inside a borehole. It will therefore be
described in detail in this application, which is solely
for illustrative purposes, since the invention can be used
in many other forms, in many other materials.
Generally speaking, the limitations of the prior
; art are overcome in this invention by providing an assembly
including a plurality of small diameter tubular filter elements
of selected outer diameter and length. These elements are held
in a supPort apparatus which includes two header plates which
have counterbored openings. The openings are substantially
equal in diameter to the inner diameter of the cylindrical
elements, while the counterbores are of a diameter substantially
equal to the outer diameter of the elements. Tension means
are provided to hold these elements in a selected, two-dimensional
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array, between the two headers so that at least a part of the
outer surface is exposed to the flow of particulate matter-
laden fluid.
One convention array is to provide a plurality of
coaxial circular arrays of tubular elements. For example,
one array might hold six elements and another coaxial array
might hold twelve elements, with a tension means such as a
bolt positioned at the axis of the two arrays. Of course,
more than two circular arrays are possible.
The header assembly at one end can be a closure
or header plate, having a plurality of counterbored openings
into which the ends of the tubular elements are inserted.
The header assembly is designed with a plenum inside, which
is connected through the openings in the header Plate so that
the flow of liquid through the perforations or openings in
the walls of the tubular elements passes into the inside of
; the elements and through the openings in the header plate
into the plenum. The liquid is then carried through a
well tubing up the well to the surface or to a pump
which forces the liquid up to the surface.
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The cylindrical elements can be constructed in many
ways, such as by using sintered metal, or perforated thin
walled cylinders supported around a skeleton or by any of
the commercial means for making wire wound screens in the
prior art. The principal feature of the invention lies
in the use of a plurality of small diameter tubular elements,
which in total provide a greater surface area for the flow
of fluid than does a single large diameter wire screen which
would circumscribe the plurality of tubular elements as in
the conventional sand screens.
For the purpose of illustration but not of
limitation the invention will be hereinafter described with
reference to the accompanying drawings, in which:
Figures 1 and 2 show an elevation section and a plan
section of the invention.
Figure 3 shows an alternative second positioning and
clamping means to hold the tubular elements.
Figures 4 and 5 show two views of one method of
construction of the tubular elements.
Figures 6 and 7 show additional details of the
construction of the cylindrical elements of Figures 4 and S.
Figure 8 shows an alternative type of cylindrical
element which may be used in place of the wire wound strain
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and is particularly adapted to the filtering of materials
other than sand-laden oil.
Referring now to the drawings and in particular to
FIGURES 1 and 2, there are shown two views of the invention
indicated generally by the numeral 10. FIGURE 1 is a
vertical section taken along the plane 1-1 of FIGURE 2
and FIGURE 2 is a cross-section taken along the plane 2-2
of FIGURE 1. The device includes a header structure
indicated generally by the numeral 12, which comprises a
header plate 16 which is connected to a pipe coupling 15
having internal threads 14, which may be welded to the
plate 16 by means of an intermediate cylinder 13. The
internal volume 19 constitutes a plenum.
The diameter 17 is such as to be suitable for
introduction into a casing in an oil well. The length 31
is chosen to provide a suitable surface area to the plurality
of tubular elements 46 so as to provide sufficient filtering
area. The length might range from several inches to several
feet or more.
The header plate 16 includes a plurality of openings 18
in a selected two dimensional array such as illustrated in
FIGURE 2 for example. These openings 18 are counterbored
to a diameter 20, which is slightly greater than the outer
diameter of the tubular elements 46. The inner diameter of
the tubular elements 46 is substantially equal to the
diameter of the openings 18.
The tubular elements 46 are constructed in any
selected way which will provide a rigid tubular element of
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a selected outer diameter and selected length with a
selected permeability for the flow of fluid through the
cylindrical wall of the tubular element.
As will be explained later, the diameter of the counter-
bore is slightly greater than the outer diameter of the
elements to permit rotation of the elements while keeping
the annular space between the elements and the counterbore
wall small enough to exclude sand.
A suitable permeability can be provided in any desired
way, such as for example by drilling or otherwise perforating
a thin-walled metal cylinder, by wire wrapping a rigid
skeleton with a selected spacing between the turns of the
wire, by preparing a small diameter cylinder of fritted
glass beads of a selected diameter to provide a selected
permeability, by using powder metallurgy to provide a metal
tube having a selected permeabity to the flow of gases
or liquids or by other means.
The manner of construction of one type of tubular
element will be described in detail in connection with
FIGURES 4, 5, 6 and 7.
There is a second support or header plate 22 which
has the same diameter 17 as the header plate 16 of the header
assembly 12. This plate 22 has a plurality of openings of
diameter of the counterbores 20 in the same two dimensional
spacing as the plate 16. Thin circular discs 24 of suitable
diameter and thickness are placed over the ends of the
elements 46 in the openings 23 in the plate 22. These discs
and the tubular elements are held within the plate 22 by a
second plate 26 and by means of a bolt or other tension means
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28. Bolt 28 is locked to the plate 16 by means of a nut
32 in an axial opening 30. The plates 22 and 26 are
held by means of nuts 34 and 36 as would be understood
by one skilled in the art. By tightening the nut 36 to
securely hold the plates 22 and 26 against the nut 34
the spacing between plates 16 and 22 is maintained at a
selected value, whereas the actual spacing of the tubular
element within its opening may permit it to have a very
slight freedom to move longitudinally and to rotate within
the openings 20 and 23.
It will be clear that the structure of plates 22 and
26 with openings 23 and discs 24 can be replaced with shallow
holes of the same diameter 23 in a single plate like 22.
This freedom to rotate under the influence of a high
velocity stream of sand-laden oil and gas is a distinct
advantage of this invention since as the fluid stream
impinges on the tubular element it will tend to erode the
: surface to the point where the wires may be cut and openings
enlarged to permit the sand to flow into the tubular elements.
In the case of the prior art screen which is a larger
diameter screen which is rigidly clamped to the tubing, there
is no freedom to rotate. Furthermore, the surface is sub-
stantially perpendicular to the radial flow of oil and
sand against it so that at the perforations through the
casing where a high velocity flow exists it is relatively
easy for the stream to erode openings through the old-fashioned
screen. However, with the small diameter screen, the high
speed flow of oil and sand is not directed against a
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substantially flat wall but against a small diameter
cylinder so that the beam can be deflected easily.
Furthermore, the force of the stream on the element can
cause the element to rotate and to present a different area
to the flow so that the depth of erosion at any one point
can be minimized.
The design illustrated in FIGURE 1 is one in which
the length 31 can be varied but there is only a single
assembly of cylindrical elements which can be connected
to the tubing.
FIGURE 3 illustrates a second embodiment of the
header assembly 38 such as can be placed on the lower end
of FIGURE 1 to replace the header plates 22 and 26. The
bottom header plate 42 is similar to that of 16, but the
complete header is made in two parts, the header plate 42
and the header 38. They may be removably attached as by
screw threads or other means. In assembling the device
instead of the plates 22 and 26 the header plate 42 is
used and the nut 36' is tightened against the nut 34' on
the central bolt 28. The header 38 is then screwed to the
plate 42 by means of threads 44. Thus, a short length of
tubing can be screwed into the thread 41' to support another
assembly 10 etc. Thus, a plurality of these filtering devices
can be connected in series with the plena 19 in each of the
ends of the filter devices being in series flow condition
to the well tubing which carries the liquid to the surface.
There are a number of ways which have been followed in
the industry for constructing sand screens of the prior art
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type, namely those in which there is a single wire wound
surface which is wrapped around a rigid skeleton of
suitably large diameter to support the wire turns. There
are also other ways of making the prior art screens which
need not be discussed at this time.
FIGURES 4 and 5 illustrate a way of constructing
the tubular elements 46. This comprises a plurality of
longitudinal rods 56 which are placed in a selected circular
pattern and held between plates 58 and 58' as shown in
FIGURE 6. There are indentations on the inside walls of
the plates 58 and 58' which receive the ends of the rods 56.
The rods are further supported on the inside by a mandrel 60
which is indicated by the dashed line 60' of FIGURE 4. The
plate 58' is tightened to hold the rods 56 rigidly in their
recesses in the insides of the plates 58, 58' by means of a
nut 64 on the threaded portion 62 of the rod 60. The rod
60 is then placed in a lathe and by attaching one end of a
wire 52' to one of the rods 56, the assembly of FIGURE 6
can then be rotated as shown. In which case, the wire 52'
can be held under tension and will be wound tightly around
the rods 50 as the assembly turns in accordance with arrow 63.
Means are provided to spot weld with electrode 66
each contact between the wire 52 on the edge 56 of the
elements 50. This electrode 66 is pressed to the outside
of the wire opposite each point 56 and a current is passed
from a transformer 68, powered by a suitable voltage E,
through leads 70 and switch 72 to the electrode 66 and
to the mandrel 60. Thus, the wire 52' is spot welded to
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the rods 50, forming a wire screen 52 which forms with
the rods 50 a rigid tubular structure.
While the assembly rotates in the lathe and the
turns increase, means are provided to move the welding
electrode 66 and the wire 52' toward the left, in accordance
with arrow 61 to the position 66'' and 52'' and so on to the
final position adjacent the plate 58. The wire 52' is then
cut off, the assembly is removed from the mandrel and the
ends are ground off etc. to provide a finished element.
Of course, other ways can be employed to manufacture
these elements of any selected diameter and any selected
spacing within the diameter permitted for the diameter 17.
As mentioned previously, other ways of constructing the
tubular elements can be to provide a sintered tube of metal
of suitable metallurgy and of selected permeability to the
flow of fluid. For other fluids which are corrosive the
filter elements can be made of fritted glass spheres of
selected small size to provide the suitable permeability
or of porcelain and so on.
Such a tubular element is shown 46' in FIGURE 8. A
tube 76 has an outer diameter 80 and an inner diameter 82
and is of a selected length 84 and is constructed of a
material having suitable interstices or perforations or
openings 78 to provide a desired filtering effect and
overall cross-sectional area for fluid flow through the wall
that may be desired.
While this invention has been described in detail for
use in a well borehole for the flow of sand laden oil and
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gas and is in the class of oil field equipment known as
sand screens, it is described solely for the purpose of
illustration and is adapted for use in substantially any
form where a plurality of small diameter elements can be
held in parallel position and parallel flow conditions
for filtering any selected liquid or gas and any selected
particulate matter.
While I have spoken of a selected size or diameter of
opening or a selected permeability to the flow of fluid
through the walls of the tubular elements, nothing has
been said as to whether these dimensions are the same for
all elements. While in most cases all elements will have
the same openings, there may be times when some of the elements
will have openings or permeabilities different from the others.
One example where such might be desirable is in the
area of sand screen filters. The larger the openings, the
longer it will take to build up a sand pack around the
elements. Consequently, a combination of arrays of elements
of small and large openings might provide a more suitable
combination than to have all elements with the same size of
openings. A typical construction is where the outer ring
array of elements are of a screen of larger opening size,
e.g., .008" while the inner ring array are of smaller openings,
e.g., .004". Any combination, however, is within the purview
of this invention.
While the invention has been described with a certain
degree of particularity it is manifest that many changes may
be made in the details of construction and the arrangement
of components without departing from the spirit and scope of
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this disclosure. It is understood that the invention is
not limited to the embodiments set forth herein but is to
be limited only by the scope of the attached claim or
claims, including the full range of equivalency to which
each element thereof is entitled.
