WO1997048494A1

WO1997048494A1 - Method and apparatus for separating solids from drilling mud

Info

Publication number: WO1997048494A1
Application number: PCT/AU1997/000377
Authority: WO
Inventors: Richard John Craddock
Original assignee: Richard John Craddock
Priority date: 1996-06-14
Filing date: 1997-06-13
Publication date: 1997-12-24
Also published as: AUPO048196A0

Abstract

Apparatus (20) for separating drilled solids from drilling mud comprising a centrifuge having a hollow axially extending member (22) mounted for rotation about its axis. The member (20) has a permeable peripheral wall (24). A drilling mixture of mud and drilled solids is introduced into the interior of the member (20). The member (20) is rotated by a drive motor (60) at a speed sufficient to effect separation of the mud and drilled solids such that under centrifugal action at least some of the mud passes through the permeable peripheral wall and at least some of the drilled solids are retained in the interior of the member (20). The apparatus is arranged for removal of the separated drilled solids from the interior of the member (22).

Description

METHOD AND APPARATUS FOR SEPARATING SOLIDS FROM DRILLING MUD

This invention relates to a method and apparatus for separating solids from drilling mud.

During the drilling of a well in the search for oil or gas, or in drilling a geothermal well, a drilling fluid, called "mud" is circulated downhole through the inside of the drill pipe, through the drilling bit, and back through the annulus between the open hole and the outside of the drill pipe, or between a steel casing in the drilled hole and the outside of the drill pipe .

The drilling operation carries the mud and entrained drill cuttings to the drilling rig, where the majority are removed by various solids control equipment to enable reuse of the mud. This equipment may include scalping (coarse screen) shale shakers, primary shale shakers (primary solids removal mechanism), hydrocyclones (desanders, desilters, mud cleaners) and centrifuges. Centrifuges of the latter kind generally have liquid impermeable rotary elements and operate on a decanting principle whereby the liquids are removed from the centre and the solids from the outer centrifuge wall. Such devices have limited capacity and use is confined to secondary separation processes.

Shale shakers are the primary solids removal mechanism. Recent developments in shale shaker design have focused on the vibrating motion and inclination of prestressed wire mesh screens.

Efficient removal of the solids as soon as possible is preferable, to reduce the dispersion of the drilled solids into the drilling fluid, and the dilution volume of new mud necessary to maintain the physical properties of the fluid. The reuse of mud is also environmentally desirable to reduce the amount of mud dumped into the sea (in the case of offshore water based drilling) or trucked for disposal (in the case of land drilling). For oil based muds and alternative oil based muds the cost of mud lost with the cuttings on the solids control equipment can be large. In one aspect, the invention provides apparatus for separating drilled solids from drilling mud having a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, means for introducing a drilling mixture of mud and drilled solids into the interior of the member, and means for rotating the member at a speed sufficient to effect separation of the mud and drilled solids such that under centrifugal action at least some of the mud passes through the permeable peripheral wall and at least some of the drilled solids are retained in the interior of said member, the apparatus being arranged for removal of the separated drilled solids from the interior of the member. The invention also provides a drilling rig having a drill, means for circulating drilling mud to a drilling bit and for recovering the mud and drilled solids, in combination with apparatus as last described arranged to receive the drilling mixture of mud and drilled solids, for separation of the mud and drilled solids. The permeable peripheral wall may be formed of a perforate structure, or otherwise provided with suitable openings or apertures, such as in the form of a mesh.

In another aspect, the invention provides a method for separating drilled solids from drilling mud, comprising introducing a mixture of the mud and drilled solids to apparatus having a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, the mixture being introduced into the interior of the member, and the member being rotated at a speed sufficient to effect separation of the mud and drilled solids under centrifugal action such that at least some of the mud passes through the perforations of the peripheral wall and at least some of the drilled solids is retained in the interior of said member, and removing separated drilled solids from the interior of the member.

The invention also provides a method of drilling in which drilling mud is circulated to a drill bit and recovered drilled solids and mud are separated by the method last described.

The method and apparatus of the invention have particular application where employed for first separation of the mixture, or after one or more initial separators such as one or more scalping shakers and/or one or more gumbo slides. The member may be generally cylindrical. The member may be arranged with its axis inclined. In the latter case, the mixture may be introduced into the member at an upper location and the removal of separated solids effected at a lower location.

Generally, the invention is preferably employed as the primary solids control separation equipment or method.

The invention is further described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a drilling rig and associated separating apparatus formed in accordance with the invention;

Figure 2 is a plan view of apparatus for separating drilled solids from drilling mud constructed in accordance with the invention;

Figure 3 is a lengthwise cross-section of the apparatus of Figure 2;

Figure 4 is a cross-section on the line 4-4 in Figure 3 ;

Figures 5, 6 and 7 are perspective views of three respective forms rotatable member useful in apparatus formed in accordance with the invention; and

Figure 8 is a diagram of a modified form of apparatus constructed in accordance with the invention.

Referring first to Figure 1 , there is shown a ground drilling rig 10 having a drill string 12 formed of one or more hollow coaxially extending drill elements 13 secured in end to end relationship. A drilling bit 14 is provided at the lower end of string 12, and the string and bit are in use rotated (by means not shown) to cause the bit to drill into the ground. To facilitate cutting by bit 14, drilling mud 16 is passed down the interior of the string 12 to the bit 14, and used mud rises (by flow around the string 12) together with entrained drilled solids. The mixture of mud and entrained solids 25 which rises to the drilling rig 10, at the ground surface or to the sea surface in off-shore drilling, is passed via a pipeline 48 to a separator apparatus 20 formed in accordance with the invention. Separated mud 16 from the apparatus 20 passes to mud pits 55 from which it is pumped by mud pump 52 through pipeline 54 to the drilling string. Apparatus 20 is shown in more detail in Figures 2 to 5.

The apparatus 20 is in the form of a centrifuge, having an elongate cylindrical member 22 which is shown in more detail in Figure 5. Member 22 is hollow, being formed of a hollow cylindrical wall 24. Wall 24 is perforate, having perforations 26 over substantially the whole thereof, such as by being formed as a mesh. As shown, an outer generally cylindrical support structure 50 may be provided, this being shown here as formed of a coarse wire mesh.

Member 22 is mounted for rotation about its axis, which extends in this case at an angle to horizontal to the ground, being supported for rotation by roller bearings 56, and also by thrust bearing 58. A suitable motor 60 is arranged to drive the member 22 via a gear box 62, pulleys 64, 66 and belt 68, so that it in use rotates at high speed about its axis.

A delivery chute 32 is provided at the upper end of member 22 for delivering mud/solids mixture to the interior of member 22 at its upper end.

In use, under rotation of the member 22 about its axis, mud/solids mixture delivered to the member 22 is separated by centrifugal action thereon, arising pursuant to the rotation of the member. In particular, the mud and solids are pressed under centrifugal force against the inner surface of wall 24. The mud passes through perforations 26, but solids too large to pass through these are retained on the interior surface. The solids migrate to the lower end of the member 22, due to the incline of the axis of the member 22, and eventu ally pass over the free lower edge of the member 22 to accumulate at a dump location 34 as shown. In the illustrated construction, the mud itself is collected within a cowling 35 which surrounds the member 22. This defines a cylindrical wall 70 which is coaxially arranged with the member 22 but spaced outwardly therefrom. A lower part 70a of the wall 70 is formed on a lower housing structure 72 of the apparatus. An upper part 70b of the wall 70 is defined on a cowling member 78 which fits over housing structure 72 in the manner shown. The wall 70a is, as shown, perforate so as to enable the mud to pass downwardly therethrough and to be collected in a collector 38 forming part of housing 72, from which collector it is led via a suitable pipeline 74 to the mud pits 55.

The lower outlet end of the member 22 is positioned slightly over the end of the dump location 34 so that solids from the member 22 fall downwardly for disposal. The cowling 35 may include a cowling part 35c which is arranged to direct solids emerging from the lower end of member 22 to the dump location 34.

The wall 24 may be formed of suitable mesh material such as of mesh size 50 to 300. Preferably the mesh openings are of uniform size. In order to adapt the apparatus for particular operating conditions, it is preferable to arrange that the tilt of the axis of the apparatus may be varied and to arrange that the speed of rotation may be varied.

In Figure 6, the member 22 is shown formed of coarse backing mesh panels 51 which are together conformed to a cylindrical configuration held in position by clamp or other security mechanism 52. There may, for example, be two such mechanisms 52, one at each end of member 22. In any event, the member 22 may be mounted on roller bearings which may, in the case of the construction of Figure 5, be in rolling engagement with the or each security mechanism 52, which in such case presents one or more generally cylindrical outer surfaces coaxial with the axis of member 22. The panels 51 may be otherwise affixed to support structure (not shown) forming the member 22.

In Figure 7, the member 22 has two coaxial walls, the inner wall 24a having a coarser mesh size than the outer wall 24b. The wall 24 is described above as being perforate but, in general, any suitable permeable structure may be employed.

Whereas conventional shale shakers rely on the vibration of the mud and cuttings on top of the screen to assist the separation and passage of the fluid through the screen, the centrifugal separator of the invention utilises centrifugal force generated by the rotation of the cylindrical member 22. Transport of the solids along the member is achieved by virtue of the inclination of the cylindrical screen. The equipment can provide a continuous process, which is often necessary to deal with the flow rates experienced during drilling operations.

Screens used in forming the member 22 may be wire mesh bonded to a coarse backing mesh similar to those employed for conventional shale shaker screens, but cylindrical in shape. Two semi cylindrical screens may be used. The screens may be of flexible and/or resilient shape, such as being rectangular, to enable them to be conformed to singly or collectively to form the required liquid permeable surface. The screens may be formed of any medium having the required permeability, such as sintered glass, metal, ceramic. They may be cylindrical, or for ease of transportation, semi-cylindrical. It is preferred that the inner surface is smooth and any joints do not allow solids through (e.g. they may be butt and groove clamped together).

Instead of being truly cylindrical, the member 22 may be slightly conical to facilitate transport of material along the length thereof. In this case, the larger diameter end may be the discharge end.

The described apparatus 20 can be adapted for any solids/fluid separation such as mineral concentrate (flotation) separation, algae/weed from river water, polymerised oil from water for oil spills (recovered oil and water is treated with polymer in storage and then separated).

The apparatus 20 may also be utilised for solids/solids separation where one solid is of a specific aperture size, e.g. , grape seed recovery from wine making process. While, in the described arrangements, the mud is circulated down the interior of the drill string 12 and thence up the exterior thereof, it is of course immaterial to the present invention how the mud is transported to and from the drill bit, and any known method of achieving thi s may be adopted, such as passing the mud directly down the drilling around the drill string.

The described apparatus 20 is arranged with the axis of member 22 inclined and fixed. The apparatus need not necessary be arranged with the axis of member 22 inclined. Also, it may be desirable in some instances, to arrange the apparatus 20 so that the inclination of at least the axis of the member 22 can be varied. Figure 8 shows the apparatus 20 mounted on a pivotal platform 80 with extendible jack means 82 arranged to vary the inclination of the platform and of the apparatus 20 and member 22. In general, it may be more convenient merely to vary the axis of inclination of the member 22 itself rather than the whole apparatus 20. Arrangements of this nature may be especially useful in enabling setting up of the apparatus for optimum operation to suit the characteristics of particular mixtures to be separated. This is particularly so in the case of apparatus where the speed of rotation of the member 22 is variable. In the latter case control of both rotational speed and the inclination of the member 22 enables particularly convenient set-up for different mixtures. It may be preferable to reverse the arrangement of Figure 8 so that the jack means 82, or other extendible means, is at the output end of the platform 80, with the input end being pivotal, rather than the reverse arrangement as shown.

In most cases, the angle of inclination of the axis of member 22 should be in the range 1 ° to 60°, most preferably in the range 10 to 45°.

The described cowling 35 may be varied. For example, it does not need to necessarily surround the member 22. The lower wall part 70a may for example be omitted.

The described construction has been advanced merely by way of example only and many modifications and variations may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

CLAIMS:-

1. Apparatus for separating drilled solids from drilling mud having a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, means for introducing a drilling mixture of mud and drilled solids into the interior of the member, and means for rotating the member at a speed sufficient to effect separation of the mud and drilled solids such that under centrifugal action at least some of th e mud passes through the permeable peripheral wall and at least some of the drilled solids are retained in the interior of said member, the apparatus being arranged for removal of the separated drilled solids from the interior of the member.

2. Apparatus as claimed in claim 1 wherein the permeable peripheral wall is formed of a perforate structure.

3. Apparatus as claimed in claim 2 wherein said perforate structure is in the form of a fine mesh.

4. Apparatus as claimed in any one of claims 1 to 3 wherein the member is generally cylindrical.

5. Apparatus as claimed in any one of claims 1 to 4 wherein the member is arranged with its axis inclined.

6. Apparatus as claimed in claim 5 arranged for introduction of the mixture into the member at an upper location and the removal of separated solids at a lower location.

7. Apparatus as claimed in any one of claims 1 to 6 including a cowling surrounding at least part of the member, for directing the mud to a collector.

8. Apparatus as claimed in any preceding claim including a cowling disposed for directing said solids to a dump location.

9. Apparatus as claimed in any preceding claim including means for variably setting the inclination of the axis of said member.

10. Apparatus as claimed in any preceding claim wherein said means for rotating is arranged for effecting rotation of the member at a rate of rotation which is selectable.

11. A drilling rig having a drill, means for circulating drilling mud to a drilling bit and for recovering the mud and drilled solids, in combination with apparatus as claimed in any one of claims 1 to 10, arranged to receive the drilling mixture of mud and drilled solids, for separation of the mud and drilled solids.

12. A method for separating drilled solids from drilling mud, comprising introducing a mixture of the mud and drilled solids to apparatus having a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, the mixture being introduced into the interior of the member, and the member being rotated at a speed sufficient to effect separation of the mud and drilled solids under centrifugal action such that at least some of the mud passes through the perforations of the peripheral wall and at least some of the drilled solids is retained in the interior of said member, and removal separated drilled solids from the interior of the member.

13. A method as claimed in claim 12 employed for primary separation of the mixture.

14. A method as claimed in claim 12 wherein the mixture is first passed to one or more initial separators, and then to said apparatus.

15. A method as claimed in any one of claims 12 to 14, wherein said apparatus comprises apparatus as claimed in any one of claims 1 to 10.

16. A method of drilling in which drilling mud is circulated to a drill bit and recovered drilled solids and mud are separated by the method of any one of claims 12 to 15.

17. Apparatus for separating drilled solids from drilling mud substantially as hereinbefore described with reference to the accompanying drawings.

18. Apparatus for separating first and second components from a mixture thereof, comprising a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, means for introducing said mixture into the interior of the member, and means for rotating the member at a speed sufficient to effect separation that under centrifugal action at least some of one of the components passes through the permeable peripheral wall and at least some of the other component is retained in the interior of said member, the apparatus being arranged for removal of the other component from the interior of the member.

19. A method for separating first and second components from a mixture thereof, comprising introducing the mixtureinto apparatus having a hollow axially extending member mounted for rotation about its axis, said member having a permeable peripheral wall, the mixture being introduced into the interior of the member, and the member being rotated at a speed sufficient to effect separation of the components of the mixture under centrifugal action such that at least some of one of the components passes through the perforations of the peripheral wall and at least some of the other component is retained in the interior of said member, and removing the other component from the interior of the member.

20. A method as claimed in claim 19, wherein said other component is particulate.

21. A method as claimed in 19 or claim 20, wherein said one component is a liquid or other fluid.

22. A method as claimed in any one of claims 19 to 21 wherein both said components are paniculate .

23. A drilling rig having apparatus from separating mud and drilled solids, substantially as hereinbefore described with reference to the accompanying drawings.

24. A method for separating drilled solids from drilling mud, substantially as hereinbefore described with reference to the accompanying drawings.

25. A method of drilling, substantially as hereinbefore described with reference to the accompanying drawings.