Liquid purification or separation – Filter – Movable medium
Reexamination Certificate
2001-10-11
2003-01-28
Lithgow, Thomas M. (Department: 1724)
Liquid purification or separation
Filter
Movable medium
C210S489000, C210S499000, C209S401000, C209S403000, C175S066000, C175S072000
Reexamination Certificate
active
06510947
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to screens for use on a vibratory separator to treat fluid introduced to the vibratory separator; and, in certain particular aspects, to such screens for use on shale shakers; and other particular aspects to such screens for treating drilliing fluid with drilled cuttings therein.
2. Description of Related Art
A wide variety of vibratory separators are used in various industries to separate components of material fed to the vibratory separator. Often the material is a slurry which includes liquid and solids entrained therein and it is desired to separate some, the majority of, or all of the solids from the liquid. One or more screens is typically mounted on the vibratory separator and the material to be treated is introduced onto the screen(s). Liquid, and perhaps some solids, flows through the screen and is collected and solids that do not flow through the screen move off the top of the screen. In other systems, solids of one size flow through the screen(s) and solids of another size flow off the top of the screen.
The need for solids control in drilling mud used in hydrocarbon well drilling is well known in the prior art. Drilling mud, typically a mixture of clay and water and various additives, is pumped down through a hollow drill string (pipe, drill collar, bit, etc.) into a well being drilled and exits through holes in a drillbit. The mud picks up cuttings (rock) and other solids from the well and carries them upwardly away from the bit and out of the well in a space between the well walls and the drill string. At the top of the well, the solids-laden mud is discharged over a shale shaker, a device which typically has a series of screens arranged in tiered or flat disposition with respect to each other. The prior art discloses a wide variety of vibrating screens, devices which use them, shale shakers, and screens for shale shakers. The screens catch and remove solids from the mud as the mud passes through them. If drilled solids are not removed from the mud used during the drilling operation, recirculation of the drilled solids can create weight, viscosity, and gel problems in the mud, as well as increasing wear on mud pumps and other mechanical equipment used for drilling.
In some shale shakers a fine screen cloth is used with the vibrating screen. The screen may have two or more overlying layers of screen cloth. The prior art discloses that the layers may be bonded together; and that a support, supports, or a perforated or apertured plate may be used beneath the screen or screens. The frame of the vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by a vibrating mechanism, e.g. an unbalanced weight on a rotating shaft connected to the frame. Each screen may be vibrated by vibratory equipment to create a flow of trapped solids on top surfaces of the screen for removal and disposal of solids. The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.
Often in drilling a wellbore, the circulation of drilling fluid to and then away from the drill bit ceases due to the porosity of the formation and/or due to fracturing of the formation through which the wellbore is being drilled. Drilling fluid pumps into the fractured formation rather than being returned to the surface. When circulation is lost, it is usually supposed that the lost circulation occurred at some specific depth where the formation is “weak”, and that the fracture extends horizontally away from the borehole. Expressions used to describe rocks that are susceptible to lost returns include terms like vugular limestone, unconsolidated sand, “rotten” shale, and the like. Whether fractures induced by excessive mud pressure are parallel to the axis of the borehole (vertical) or perpendicular to the axis of the borehole (horizontal) is a subject of some controversy.
To fill or seal off a porous formation or to fill or seal off a wellbore fracture so that a proper route for drilling fluid circulation is re-established, a wide variety of “lost circulation materials” have been pumped into wellbores. For purposes of classification, some lost circulation materials can generally be divided into fibers, flakes, granules, and mixtures.
In certain prior art screens, square mesh wire cloths have been used with relatively fine wire diameters in multiple layers because of their resistance to blinding, e.g. with one or more support layers and two screening layers. The ratio between these meshes has generally been between about 1.1 and 1.7. Certain of these screen combinations have difficulty in handling LCM material and the material often blinds these screens. Oblong opening meshes with length to width ratios between 1.55 and 2.0 have also been used in the past for their resistance to blinding. As the ratio increases between the meshes, blinding decreases but strength also decreases. As the wire diameter increases, the resistance to blinding decreases, but the strength increases. However, when multiple layers of oblong cloths have been used in certain prior art screens, the ratio of the length of the openings at adjacent layers has been 2 or greater and of the width of the openings of adjacent layers has been 1.6 or greater. Attempts have been made to use oblong meshes with increasingly large ratios.
Typical known shale shaker screens or screen assemblies with square mesh openings often are clogged when attempts are made to separate lost circulation materials from a mixture of them with fluid that has been pumped down a wellbore. Stringy, fibrous, and/or fibril material (“fibrous” material) can wrap around a wire of a screen and/or bridge a mesh opening without passing through the screen. In certain particular circumstances there have been problems with commercially available ULTRA-SEAL lost circulation material that has fibrous material in it. If components of this material which swell are caught between two screen mesh layers, they swell and plug the screen rather than going through the screen with the drilling fluid (while drilled cuttings, debris, etc. move on the top of the screen assembly and exit the shaker or vibratory separator apparatus). Although the prior art discloses the use of screens with non-square openings for use on shale shakers for treating mixtures of drilling fluid and drilling solids, the present inventors are unaware of the use of prior art screen(s) and/or screen assemblies with non-square mesh openings in methods for separating fluid and fibrous lost circulation materials from drilled cuttings and believe it is not obvious to use screens with non-square openings with relatively more opening area to successfully treat such fluids.
FIGS. 1A and 1B
show a prior art screen
22
as disclosed in U.S. Pat. No. 2,723,032 with a coarse mesh wire screen, or cloth
23
that provides a backing screen or cloth of the unit. A fine mesh wire screen
24
is superimposed or mounted upon the backing screen
23
. The screen unit
22
has its coarse backing wire mesh or cloth coated or covered preferably with rubber or some suitable rubber or synthetic rubber composition. The strands are indicated at
25
and the covering or coating at
26
. Since all of the strands
23
are coated or covered, there is, of course, rubber-to-rubber contact between these strands of the coarser mesh screen
23
. The backing screen of cloth
23
is of the roller flat-top type and of any coarse size such, for example, as three or four mesh. The mesh of the finer mesh wire screen
24
varies, in accordance with the separating job to be done. For example, the mesh of the fine wire screen or cloth
24
may vary fro the order of minus 20 (−20) to the order of minus 325 (−325).
FIGS. 2A and 2B
disclose a screen
30
as disclosed in U.S. Pat. No. 4,696,751 with a first mesh screen with rectangular dimensions of width and length. A second screen
38
is held in superimposed abutting relationship to the first screen
32
. The second
38
has width
Adams Thomas C.
Largent David W.
Schulte David L.
Lithgow Thomas M.
McClung Guy
Varco I/P Inc.
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