Vibratory separators have been employed for many years to separate particles in a wide array of industrial applications. One common application for vibratory separators is in drilling operations to separate particles suspended in drilling fluids, such as that known as drilling mud. Screens are mounted generally horizontally in a basket or frame on a vibrating mechanism or shaker that imparts a desired motion to the screen. Material from which particles are to be separated is poured onto a back end of the vibrating screens, usually from a pan mounted above the screen.

The material generally flows toward the front end of the screen. Large particles are unable to move through the screen and hence remain on top of the screen and move towards the front of the screen where they are collected.

The smaller particles and fluid flows through the screen and collects in a tank, receptacle or pan beneath the screen.

Typically the screen is resiliently suspended or mounted upon a support in a basket or frame, the basket being caused to vibrate by a vibrating mechanism, such as a an unbalanced weight on a rotating shaft connected to the basket or frame. The screen is 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.

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, such as 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 screen or 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 and/or debris 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 many cases it is difficult if impossible to mount or hang a screen in a vibratory separator or shale shaker so that the lateral plane of its surface is perfectly horizontal.

Material to be separated generally comprises various sized particles in a fluid. It is generally advantageous to remove the fluid as quickly as possible, so that the vibratory separator in order to reduce the weight of material to be separated and to speed up separation of the particles therefrom. It is also advantageous to increase the screening area in a given size vibratory shaker.

In accordance with the present invention, there is provided a vibratory separator comprising a basket having screening apparatus mounted therein, the screening

apparatus having at least a first portion and a second portion, the first portion lower in the basket than the second portion.

Other aspects and features of the present invention are set out in claims 2 to 23.

The present invention also provides a basket and a screen apparatus of the vibratory separator of the invention.

The present invention also provides a method for screening material comprising the steps of introducing material to be screened into a basket of a vibratory separator, said material landing on a screen having a first portion and a second portion, the first portion at a lower height in the basket than the second portion.

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an end view of a prior art screen connected to mounting brackets of a shale shaker; Figure 2 is a perspective view of a prior art shale shaker; Figure 3 is a perspective view of a prior art basket with a screen mounted therein; Figure 4A is a side cross-sectional view of a shale shaker with a screen arranged therein in accordance with the present invention; Figure 4B is an end view of the shale shaker of Figure 4A ; Figure 5A is a side cross-section view of a shale shaker and screen arranged therein in accordance with the present invention ; Figure 5B is an end view of the shale shaker of Figure 5A; Figure 6 to 10 are side cross-sectional views of shale shakers and screens in accordance with the present invention; Figure 11A is a side cross-sectional view of a shale shaker in accordance with the present invention; and Figure 11B is an end view of a part of Figure 11A.

Figure 1 shows a screen S having left and right sides. Each side is provided with hook shaped strips. The screen S is hooked via the hook shaped strips to hooked bolts which are arranged on each side of a basket (not shown) of a shale shaker (not shown). The screen S may be tensioned over formers (not shown) spaced along the interior of the basket. The centre of the screen bulges upwardly from the longitudinal edges of the screen as shown in Fig. 1 (an"over slung"screen as described in

U. S. Patent 4,820,407, incorporated fully herein), in which case the screen is said to be"crowned"or"over slung", or the centre bulges downward in which case the screen is said to be"under slung". A screen that is "crowned"or"over slung" (Fig. 1), causes solids to tend to congregate at the screen's longitudinal edges; if a screen is"under slung", solids tend to congregate at its centre.

Figure 2 shows a typical prior art shale shaker system A with a screen B (comprising screening cloth or mesh as desired) mounted on a vibratable"basket"C. The screen B may be any screen disclosed herein or have any combination of any feature or features of any screen or screen part disclosed herein ; and any such screen may be used with any appropriate shaker or screening apparatus.

The basket C is mounted on springs I (only two shown; two are on the opposite side) which are supported from a frame D. The basket C is vibrated by a motor E and interconnected vibrating apparatus F which is mounted on the basket C for vibrating the basket and the screens.

Elevator apparatus G provides for raising and lowering of the exit end of the basket C. The screen B is any prior art screen, screens, and/or screen assembly.

Figure 3 shows a prior art basket J with a screen K mounted therein with a typical prior art"crown" disposition with a middle crown portion L. Typical mounting rails or channels M are used with typical mounting devices N to releasably secure the screen K in the basket J.

Referring to Figures 4A and 4B, there is shown a shale shaker 10 in accordance with the present invention.

The shale shaker 10 has a basket 12 for retaining screens. Vibrating apparatus 14 is connected to the basket 12. Material to be treated by the shale shaker 10 is introduced into a first end 16 of the basket 12 above

a screen 30 releasably secured within the basket 12 by any suitable known screen securement device and/or structure. Item 18 is a back plate or rear weir.

The screen 30 has a central portion 31 which is higher than either screen end 32,33. A pool 22 of material to be treated is above the screen end 31 and enclosed by sides 13,15 and end 16 of the basket 12.

Fluid 24 (e. g. but not limited to drilling fluid separated from drilled solids, cuttings and debris) separated from the material to be treated falls from the screen 30 into a receptacle or pan 26, and onward through a pipe system for further processing. Alternatively, the basket 12 may be bottomless, such that fluid and small particles fall into a separate receiver or funnel and onward through a pipe system to be processed further before being re-used. The larger particles separated from the fluid and smaller particles, exit from the end 33 of the screen 30 into a skip (not shown) or the like.

It is within the scope of this invention to adjust the height of the screen ends 32,33 as desired and thereby to adjust the size and depth of the pool 22.

This also permits adjustment of the location of the edge of the pool in relation to the discharge end of the screen so that solids can have a longer distance to move on the screen (while liquid escapes and moves through the screen) once they have left the pool. The screen (s) of baskets according to the present invention may be mounted to the basket in any known manner with any known screen mounting apparatus or device. In certain aspects a reverse hook strip tensioning system may be used at either end of the screen (which may be at the first end 16 and discharge end of the basket) and, in one aspect, tension may be applied to a"live"end of the screen with the system at the basket's discharge end. In one particular aspect at the"live"end a normally open

spring actuator is used which is selectively actuated to a closed position to tension and secure the screen. Such an actuator may be manually actuated or operated with appropriate hydraulic and/or pneumatic systems.

Figures 5A and 5B show a shale shaker 40 according to the present invention with a screen mounting basket 42, vibrating apparatus 44 connected to the basket 42.

Material is introduced into a first end 46 of the basket 42 above a screen 50 releasably secured within the basket 42.

The screen 50 has a central portion 51 which is higher than either screen end 52,53. A pool 52 of material to be treated is above the screen end 51 and enclosed by sides 43,45 and end 46 of the basket 42. A flat screen 60 is located with part thereof beneath the end 53 of the screen 50 so that solids flow onto the screen 60 from the screen 50 for further separation of fluid from solids. Fluid (e. g. but not limited to drilling fluid separated from drilled solids, cuttings and debris) separated from the material to be treated falls from the screen 50 into a receptacle or pan 56 or may have an open bottom having a separate receiver arranged therebelow, having no physical connection thereto. Separated materials on the screen top exit from the end 53 of the screen 50.

Figures 6 and 8A-9C show various screens according to the present invention, each in a screen mounting basket 62 of a shale shaker vibrated by vibrating apparatus 64. Figure 7 shows a basket 63.

In the apparatus of Figure 6, two screens 70, 71 are mounted one above the other, each with central portions 70a, 71a respectively which are above screen ends 70b, 70c and 71b, 71c, respectively. Optionally either screen may be deleted or may be substantially horizontal viewed from the sides and ends. A pool 61 is above the screen

end 70b. The upper screen 70 and lower screen 71 may comprise screening material of the same mesh size or the upper screen may comprise screening material of a larger mesh size. The upper screen may be a scalping screen. The screens may be spaced by approximately 10cm.

In Figure 7 the apparatus has a screen 72 (like screen 50, Figure 5A) with a middle portion 72a and an end 72c from which separated materials fall onto a lower screen 73 which itself is curved rather than flat (as is the screen 60, Figure 5A). As shown the lower screen 73 is convex (viewed from the side); but it is within the scope of this invention for the lower screen 73 to be concave as viewed from the side. A pool 63 of material to be treated is above an end 72b of the screen 72. A solid partion, known as a flow back pan, as shown and described in PCT Publication No. WO 96/33792 may be arranged between the upper and the lower screen. The flow back pan is preferably solid and inhibits material and fluid falling through the upper screen 72 to land on the upper surface of the lower screen 73. Alternatively, a simple barrier, as shown in Figure 7, is arranged at the leading end of the lower screen to inhibit large particles from dropping into the receptacle, receiver or sump for the fluid and smaller particles.

As shown schematically in Figure 7, the"crown"or height of the screen 72 may be selectively adjusted by an inflatable bladder 163 with an appropriate inflation system 162 controlled by a system 160 with a control/monitor system 161. Alternatively crown height may be manually adjusted and screens thus adjusted held in place by any suitable means, including, but not limited to: nuts and bolts; support blocks, beams, or members; and/or recesses or grooves in side walls, with or without one or more screen projections or screen frame projections therein.

In the apparatus of Figure 8A a screen 80 has a first end 81 which is lower than the remaining screen portion 82. The remaining screen portion 82 is substantially flat. A pool 65 of material to be treated is above the end 81. Solids on the screen top exit from a screen end 83.

In the apparatus of Figure 8B a screen 84 has a first substantially flat end 85 and a downwardly angled exit end 87 which is lower than the end 85 and central screen portion 86. In the apparatus of Figure 8C a screen 90 has a first end 91 and a second end 93 both of which are lower than a central screen portion 92. A pool 66 of material to be treated is above the end 91. Solids on the screen top exit from the screen end 93.

In the apparatus of Figure 9A a screen 95 has a first screen portion 96 which is lower than the remaining screen portions 97,98. The first screen portion 96 is substantially flat, although may be slanted and may be concave or convex. The remaining screen portions 97,98 are substantially flat and are arranged at a higher level than the first screen portion 96. The remaining screen portions 97,98 may be slanted and may be concave or convex. A connecting portion 99 is arranged between the first screen portion 96 and a leading end of the remaining screen portions 97,98. The connecting portion 99 is substantially vertically arranged and may be either solid or perforated, and made of screen, mesh, or any suitable material. A pool 67 of material to be treated is above the end 96. Larger particles exit from a screen end 97.

In the apparatus of Figure 9B a screen 100 has a first end 101 and a central portion 109 which are higher than a screen exit end 104. A connecting portion 105 is like the portion 99, Figure 9A.

In Figure 9C a screen 110 has a first end 111 lower

than a central screen portion 112. A pool 68 of material is above the end 111. Solids exit from a screen end 113 which is also lower than the central portion 112.

Connecting portions 114,115 are like the portion 99, Figure 9A.

Any screen or screen portion in any screen disclosed herein may be any known screen for a vibratory shaker, including, but not limited to, known two-and three- dimensional screens and screen assemblies. Any screen disclosed herein with portions at different levels may include a separate screen or screens for each portion, the multiple screens mounted adjacent each other in a basket.

In certain embodiments of the present invention a long single screen, initially flat, is bent to produce the"reverse crown"shape (e. g. the shape of the screen in Figure 4A, viewed from the side or of Figures 8A-8C) and is secured in a basket.

Figure 10 shows a basket 120 for a vibratory shaker such as a shale shaker (e. g. but not limited to apparatuses as shown in Figure 2) with ends and side walls which may be like those of any basket described herein. Material to be treated is introduced at a first end 121 of the basket 20 where it forms a pool 122 above part of a screen 123 according to the present invention.

(The screen 123 may be like the screens 31,50, or 72 described above and with any suitable layer or layers of screening material and/or mesh, either two-or three- dimensional bonded together and/or mechanically connected together-as may be any screen or screen assembly herein). Fluid (e. g. but not limited to drilling fluid) separated from the pool 122 flows down into a collection receptacle 124. Fluid that exits the pool 122 in material on the screen top can move through the screen 123 and flow down to contact another screen 130 (which

may be like any screen disclosed herein, including, but not limited to screens 60,73,87 or 93. Fluid separated by the screen 130 flows down into the collection receptacle 124.

A rear barrier or weir 131 contains one end of the pool 122. A barrier 132 (solid or made of screening material) may be used with the screen 130. As shown the barrier 132 may lie below the end of the pool 122 nearest the discharge end 125 of the screen 123. However, the barrier 132 may be positioned further under the pool 122 (to the left in Figure 10) or closer to the discharge end 125 (to the right in Figure 10). Also the screen 130 may extend across the entire length of the basket 120 or any part thereof. Instead of a barrier 131, a screen may be used.

Figure 11A shows a vibratory separator or shale shaker 140 according to the present invention with a basket 150 according to the present invention (e. g., but not limited to like the apparatus of Figure 4A; and like numerals indicate like parts and items). The sides of the shaker 140 incorporate side screens 142 (one side shown in Figure 11A) adjacent the pool 22. Either or both side screens 142 may be deleted. The side screen opposite the side screen 142 in Figure 11A is the same as the side screen 142 shown. Optionally, the basket 150 has an end opening 152 and an end screen 154 adjacent the pool 22. The end screen and side screens may be like any described in pending PCT application No. PCT/GB01/04667.

Such an end screen and/or side screen (s) may be used with any basket disclosed herein. The screens may be two dimensional or three dimensional such as those disclosed in PCT Publication Nos.

In a typical prior art apparatus, a pool formed on the top of the screen has a"horseshoe"or U-shape with side pool potions along side edges of a screen and with

the central raised part of the screen above the pool, or with the pool on a central screen portion relatively shallow compared to the pool at the screen's sides and end. A pool in a system according to the present invention (e. g., but not limited to any of the pools in Figures 4A-11A) extends from one side of the basket to the other with a uniform depth at any particular distance from the basket input end.