Classifying – separating – and assorting solids – Sifting – Elements
Reexamination Certificate
1999-10-27
2002-11-26
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Elements
C209S254000, C209S264000, C209S269000, C209S274000, C209S275000, C209S397000, C209S401000
Reexamination Certificate
active
06484885
ABSTRACT:
TECHNICAL FIELD
The invention relates to screens used to filter and control solids, such as screens used to remove solids from drilling mud used in drilling wells such as hydrocarbon wells. More specifically, the invention relates to a design for fluids directional and re-directional system for use with screens and flow direction, preferably with diagonal or other flexible ribs which reduces the build-up of solids on particular areas of the screen, which build-up would otherwise reduce flow rate and increase the propensity of the screen to tear or rip.
BACKGROUND ART
The need for solids control, such as in conjunction with the use of drilling mud in hydrocarbon well drilling, has long been known in the prior art. Drilling mud, typically a mixture of clay and water and various additives, is pumped through the hollow drill string (pipe, drill collar, bit, etc.) down into the well and is ejected through holes in the drill bit. Among other functions, the mud picks up cuttings (rock bits) and other solids from the bottom of the well and carries these solids away from the bit as the mud is pumped upward and out of the well in the space between the well walls and the drill string. At the top of the well, the solids-laden mud is directed to the shale shaker, a device consisting essentially of a series of screens which catch and remove the solids from the mud as the mud passes through the screens. As indicated in
FIG. 1
, each screen is caused to vibrate by vibratory equipment generally shown by the indicator
100
in such a manner as to create a longitudinal flow of trapped solids in either direction on the top surface of the screen for removal and disposal of the solids. This filtering, along with other cleaning processes, allows the mud to be reused.
The fineness or coarseness of the mesh of a screen may vary depending upon such factors as flow rate and the size of the solids to be filtered by the screen. The finer the mesh, the higher is the propensity of the screen to tear. Referring now to the drawings, this propensity to tear is further increased by the tendency of solids trapped by the screen
1
to laterally migrate (by the vibration of the screen) to and congregate at the lowest part of the screen
1
, which is suspended as shown in FIG.
1
. It is virtually impossible to hang a screen
1
so that the lateral plane of its surface is perfectly horizontal; rather, either the center
5
of screen
1
bulges upward laterally from the longitudinal edges
2
of screen
1
as shown in
FIG. 2
, in which case the screen is said to be “over slung”, or the center
5
bulges downward as shown in
FIG. 3
, in which case the screen
1
is said to be “under slung”. If screen
1
is over slung (FIG.
2
), solids tend to congregate at the longitudinal edges
2
; if screen
1
is under slung (FIG.
3
), solids tend to congregate at center
5
.
Screen
1
may comprise a single layer or, as shown in
FIGS. 2
,
3
,
5
, and
6
for illustration, two or more layers, the bottom screen layer
9
having a coarser, stronger mesh to provide support for one or more top screen layers
10
which are primarily responsible for the solids filtering function. Top screen layer(s)
10
, being of a finer mesh, is the more prone to tearing.
As a means to limit screen tearing and to otherwise strengthen and support screen
1
and to hold screen layers
9
and
10
together, it is known in the prior art to construct screens with flexible ribs
6
of polypropylene or similar material. As shown in
FIG. 1
, these ribs
6
, which generally vary in width from {fraction (3/16)} inch to {fraction (5/16)} inch, generally comprise a set of longitudinal ribs
7
running the entire length of screen
1
paralleling longitudinal edges
2
), and shorter lateral ribs
8
running between and perpendicular to adjacent longitudinal ribs
7
, spaced at regular intervals. Each set of lateral ribs
8
running between the same two longitudinal ribs
7
is staggered with adjacent sets of lateral ribs
8
, thereby creating a brickwork pattern of ribs
6
. Ribs
6
are of approximately the same thickness as the screen
1
itself (approximately 0.036 inch) and enclose the full thickness of both bottom screen layer
9
and top screen layer(s)
10
. The intersecting of longitudinal ribs
7
and lateral ribs
8
create panels
11
of screen; a tear in top screen layer(s)
10
beginning in any particular screen panel
11
is prevented from spreading to adjacent screen panels
11
by the ribs
6
that form the edges of the panel
11
in which the tear occurs.
A different, superior pattern of ribs
6
is also known in the prior art which counteracts the tendency of trapped solids to flow laterally to the lowest parts of a suspended screen. See U.S. Pat. No. 4,820,407, to Kenneth Lilie, issued Apr. 11, 1989. It reduces the incidence of screen tearing, increases the filtering surface area of the screen, and enhances the longitudinal flow of trapped solids across the top surface of the screen.
Reference numerals
2
,
3
,
4
and
100
and the parts thereof have the same meaning for
FIGS. 4-6
as they do for
FIGS. 1-3
. As indicated in
FIGS. 4-6
, screen
1
has edges
2
connected to hooking clasp
3
. Hooking clasps members are engaged by clamps
4
to vibratory equipment generally shown by the reference numeral
100
. Referring now to
FIG. 5
, the pattern of ribs
6
comprises a single longitudinal center rib
12
extending the full length of screen
1
and, on either side of center rib
12
, a set of diagonal ribs
13
. Each set of diagonal ribs
13
comprises a series of equally spaced and parallel diagonal ribs
13
, each rib
13
beginning laterally at the longitudinal edge
2
corresponding to such set of diagonal ribs
13
and extending diagonally to center rib
12
. (At the lateral edges
14
and
15
of screen
1
, some diagonal ribs
13
are cut off before actually reaching longitudinal edges
2
or center rib
12
or imaginary extensions thereof, but otherwise are situated the same as and are parallel to full diagonal ribs
13
.) For each diagonal rib
13
of one set of diagonal ribs
13
, there is a corresponding and mirroring diagonal rib
13
of the other set of diagonal ribs
13
, beginning at the other longitudinal edge
2
and extending diagonally and laterally in the same longitudinal direction and ending at the same point on center rib
12
as its corresponding diagonal rib
13
of the other set of diagonal ribs
13
. The thickness of ribs
12
and
13
is greater than the thickness of screen
1
(whether comprising a single layer-or multiple layers), and so in addition to fully enclosing the thickness of bottom screen layer
9
and top screen layer(s)
10
, ribs
12
and
13
are slightly raised above the top surface of screen
1
, such as 0.007 inch above said surface. (Optionally, the entire screen
1
may be bordered with ribs
6
of like construction in order to strengthen the screen
1
.)
Screen
1
is intentionally either over slung (
FIG. 5
) or under slung (FIG.
6
). If screen
1
is over slung, then, referring to
FIG. 4
, the longitudinal flow of trapped solids is directed over the top surface of screen
1
from the far lateral end
14
longitudinally of screen
1
to the hear lateral end
15
. Because ribs
12
and
13
form a slightly raised barrier in relation to top screen layer(s)
10
, diagonal ribs
13
tend to cause trapped solids to move laterally from longitudinal edges
2
to center
5
of screen
1
, thereby counteracting the tendency of solids to congregate at longitudinal edges
2
of an over slung screen (FIG.
5
). If, on the other hand, screen
1
is under slung, then, again referring to
FIG. 4
, the longitudinal flow of trapped solids is directed from near lateral end
15
of screen
1
to far lateral end
14
, in which case diagonal ribs
13
tend to cause trapped solids to move laterally from center
5
to longitudinal edges
2
, thereby counteracting the tendency of solids to congregate at center
5
of an under slung screen (FIG.
6
).
The pattern of the screen in U.S. Pat. No. 4,820,4
Arehart Fred B.
Lilie Glenn T.
CPI Sales & Mfg., Inc.
Ostfeld David M.
Schlak Daniel K
Walsh Donald P.
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