GB2348674A - Device for pumping slurry - Google Patents

Abstract

A device 1 which may be lowered into a slurry tank 3 and used to pump out a drill cuttings slurry comprises a progressing cavity pump 12 located above a macerator 4 having two horizontally disposed counter-rotating shafts upon which are provided a series of alternating toothed cutter wheels 9 and spacers 10. The spacers 10 are axially thicker than the cutter wheels 9, creating gaps 11 between counter-rotating cutter wheels 9 through which small solids 2 of a size acceptable to the pump 12 can pass, but leaving larger solid particles 5 to be broken up. Impellers 6 agitate the slurry.

Description

2348674 DEVICE FOR PUMPING SLURRY The present invention relates to a

device for pumping slurry, for example the waste slurry produced by drilling operations.

When drilling for oil, the drill cutting head is frequently driven by a mud motor, which is powered by mud pumped down the drill shaft and which returns to the surface up the drilled bore. The mud motor is commonly of the progressing cavity type in which a helical rotor rotates and orbits inside a stator having a helical bore of the same pitch as the stator but one more, or one less, starts. The returning mud or slurry is normally discharged into a tank and contains a large proportion of foreign bodies and tramp materials which settle out in the tank. There is a wide variety of foreign bodies in the slurry, including rock, bits broken from the cutting head, pieces of polymer broken from the stator of the mud motor and often rubbish from the drilling rig such as nuts, bolts and spanners. Once the slurry tank is full it is taken away and used as landfill. For off-shore drilling rigs, the slurry tank is commonly provided on a barge which is taken to a lagoon where the tanks are emptied.

Because of the high proportion of hard and abrasive foreign bodies in the slurry it is a particularly difficult medium t pump and -it is particularly difficult fully to empty the slurry tank, since the proportion of foreign bodies increases towards the bottom as they settle out, According to the present invention there is provided a device for pumping slurry comprising: a pump for pumping said slurry and having an inlet; and a screen covering said inlet, said screen being adapted to pass only particles of less than a predetermined size and to break up particles of greater than or equal to said predetermined size.

The combined screen and grinder prevents blockages and damage to the pump, by reducing those particles which are too large to pass through the pump, rather than simply rejecting them thereby necessitating their removal by other means.

The pump is preferably of the progressing cavity-type and may have a single start rotor, with a two start stator.

The invention will be described further below with reference to an exemplary embodiment and the accompanying drawings, in which:

Figure 1 is a partly cross-sectioned schematic side-view of a first embodiment of the present invention; Figure 2 is a schematic enlarged plan-view of the grinding screen of the first embodiment; and Figure 3 is a further enlarged prospective view of part of the counter- rotating shafts of the grinding screen of Figure 2.

In the drawings, like parts are indicated by like references.

Figure I shows a pumping device I according to a first embodiment of the present invention which is adapted to pump a drill cuttings slurry out of a tank 3 that may be provided on a barge or similar. At the suction end of the pumping device 1, a screening device 4 is provided. This lets through particles 2 in the slurry that are small enough to be pumped by the pumping element 12 and breaks up any larger particles 5. The pumping element 12 is, in this embodiment, of the progressing cavity type with a single-start helical rotor and a two-start helical bore in the stator.

It is driven by motor 12a via drive-shaft 12b and pumps slurry from funnel shaped chamber 4a above the grinding screen 4 into the drive-shaft chamber 12c from whence it is discharged via suitable conduits (not shown) to its ultimate destination.

Pumping device I is also provided with impellors 6 which are disposed adjacent to and on a level with the grinding screen 4. The impellors 6 serve to agitate the drill cuttings slurry and keep the solid particles therein suspended.

Figure I shows only the grinding screen 4 and impellors 6 submersed in the slurry, however the entire device can optionally be made submersible by provision of appropriate proofing. The pumping device I can be provided on the end of a boom or suspended from a crane, so that it can be lowered into the slurry tank and swept across the bottom to remove all of the slurry and foreign bodies.

The grinding screen 4 is shown enlarged and ftom below in Figure 2. As can there be seen, the grinding screen 4 comprises two counter-rotating shafts which are driven to rotate via motor 4b and gears 4c. The shafts are horizontally disposed and extend between side walls of the screen, leaving only two narrow apertures 14 around the outside, and a centre aperture 13 between them. The sense of rotation indicated by arrows in the Figure, is such as to attract particles to the centre aperture 13 rather than the outside apertures 14.

Each shaft consists of a series of cutter wheels 9 held apart by cylindrical spacers 10. The spacers 10 are axially thicker than the cutter wheels 9 which are of greater diameter and are interleaved, so as to create gaps I I through which small solids 2 can pass. Each cutter wheel 9 has At least one tooth 9a and preferably a plurality, e.g. seven as in this embodiment. The size of the gaps I I will be determined by the size of solids that the pumping clement 12 can accept and in a prefer-red embodiment of the invention is of the order of 8mm axially. Solid particles 5 that are too large to pass through the gaps I I are broken up by the cutter wheels 9 until they are small enough to pass.

Claims (1)

1. 4CLAIMS

   1. A device for pumping slurry comprising: a pump for pumping said slurry and having an inlet; and a screen covering said inlet, said screen being adapted to pass only particles of less than a predetermined size and to break up particles of greater than or equal to said predetermined size.

   2. A device according to Claim 1, wherein said screen comprises a macerator, comprising a macerating chamber having side walls and first and second parallel counter-rotatable shafts extending within said side walls, a plurality of alternating cutters and spacers mounted on each of said first and second shafts, the cutters of the first shaft being interleaved with those of the second shaft and at least one tooth being provided on each of said cutters.

   3. A device according to Claim 2 wherein the axial thickness of said spacers is greater than the axial thickness of said cutters.

   4. A device according to Claim 3 wherein the axial thickness of said spacers is greater than said axial thickness of said cutters by an amount in the range of from about I to about 50mm, preferably from 5 to 20mm.

   5. A device according to any one of Claims 3 and 4 further comprising a motor for driving one of said shafts and gears inter-connecting said shafts so that they counter-rotate.

   6. A device according to any one of the preceding Claims wherein said pump is a progressing cavity pump.

   7. A device according to any one of the preceding Claims, wherein:

   said screen is disposed generally horizontally, said screen having an inlet in its lower surface and an outlet in its upper surface; and said pump is disposed above said screen; and further comprising a funnel shaped chamber connecting said outlet of said screen to said pump.

   8. A device according to any one of the preceding Claims further comprising at least one impeller disposed proximate said screen.

   9. A device for pumping slurry, the device comprising:

   a macerator having a macerating chamber having sidewalls and open upper and lower faces, two parallel, substantially horizontally disposed, shafts extending between opposite sidewalls of said macerating chamber, alternating cutter wheels and spacers disposed on said shafts, said cutter wheels having a greater diameter than said spacers and said cutter wheels on one of said shafts being interleaved with said cutter wheels on the other of said shafts, and means for driving said shafts to counter-rotate; a funnel chamber having upper and lower openings, said lower opening of said funnel chamber being larger than said upper opening thereof and communicating with said open upper face of said macerating chamber; and a pump of the progressing cavity type comprising a helical rotor of N starts and a stator having a helical bore therethrough complimentary to the rotor and having N I starts, said stator being generally vertically arranged and an inlet end of it being in communicaiion with the upper opening of said funnel chamber; wherein in use said pump is operated to pump slurry out of said funnel chamber and thereby draw slurry in through said macerator, and said shafts of said macerator are counter-rotated so as to pass particles of less than a predetermined size and to break up particles of a greater than said predetermined size, said predetermined size being a size acceptable to said pump.

   10. A device according to anyone of the preceding Claims, said device being adapted to be operable when submerged in a slurry.

   11. A device according to any one of the preceding Claims mounted on the end of a movable boom.

   13. A device according to any one of the Claims 1 to 12 having attachment means to enable it to be suspended from a crane.

   14. A device constructed and arranged to operate substantially as in herein before described with reference to the accompanying drawings.