CA2298912C

CA2298912C - Method and apparatus for drying particulates

Info

Publication number: CA2298912C
Application number: CA002298912A
Authority: CA
Inventors: Robert E. Merkley; Ron O. Lincz
Original assignee: Newpark Canada Inc
Current assignee: Newpark Canada Inc
Priority date: 2000-02-17
Filing date: 2000-02-17
Publication date: 2002-04-02
Anticipated expiration: 2020-02-17
Also published as: CA2298912A1

Abstract

An improved method and apparatus is provided for reducing the amount of liquid discard in drill cuttings separated from the drilling fluid, the apparatus including a first separator for removing larger cuttings from the drilling fluid, the cuttings having some remaining fluid associated therewith, a centrifugal separator for removing the majority of the remaining fluid from the cuttings, additional centrifuges for removing fine cuttings from the drilling fluid malting the fluid suitable for reuse in drilling operations and a collection point for cuttings from the centrifugal separators.

Description

METHOD AND APPARATUS FOR DRYING PARTICULATES
Field of the Invention The present invention relates to a method and apparatus for separating solids and liquids and more particularly to a method and apparatus for extracting greater quantities of fluid from solid particles separated from a well drilling fluid.
Background to the Invention To explore and produce hydrocarbons, wells are drilled using a drilling fluid that ensures all material cut by the drill bit is completely removed from the well bore. Often the fluid is a hydrocarbon such as diesel or a low toxicity derivative. The cuttings that the drill bit generates are carned to the surface where they are removed from the drilling fluid by some type of separation technique. Historically this separation technique, simply by design, would also discard a significant amount of the drilling fluid trapped on or in the cuttings. In many cases, this volume would be equal to the volume of solids removed. Also, depending on the design of oil based drilling fluid being used, the oil being discarded might have calcium chloride or other salt based brine emulsified internally.
The above liquid discard results in increased product usage and cost to maintain the drilling fluid while the well is being drilled as well as the attendant costs to dispose of the cuttings that are contaminated with oil and in some cases with high levels of salt.
There have been a number of attempts at reducing the above problem. Patents such as U.S.
Patent Nos. 4,809,791 to Hayatdovaudi, 4,911,834 to Murphy and 5,344,570 to McLachlan and 4,192,392 to Messines et al. all discuss methods of cleaning drilling fluid. These patents, however, are primarily concerned with cleaning the fluid and are not concerned with the extracted particles. These patents discuss using conventional means such as shakers to initially clean the larger particles from the fluid, and then using techniques such as centrifugation to clean the remaining particles from the fluid. However, none of the above patents discusses treating the larger particles that are removed from the drilling fluid by the shaker. These particles will still have a large proportion of drilling fluid entrapped on or within them which gets wasted and which pollutes the cuttings, creating disposal issues.
Other U.S. patents such as 4,304,609 to Morns and 4,595,422 to Hill et al.
deal with cleaning cuttings in order to make disposing of these cuttings easier, but do not discuss the recycling of expensive drilling fluid. Furthermore, systems like '609 and '422 use techniques such as heating or chemically treating the solids, creating an expensive process in which vapour needs to be captured or chemicals need to be disposed of.
Summary of the Invention The present invention overcomes the shortcomings of the prior art by providing a system where the majority of drilling fluid is recovered from the cuttings, thereby reducing both the costs of maintaining the drilling fluid and of disposing of the cuttings.
Furthermore, the system requires neither chemical nor heat processes to remove the liquid phase from the cuttings.
The present system first separates the larger solids from the liquid phase in the used drilling fluid using a screen. The system then takes the separated solids and further separates liquid from them, thereby distinguishing the system over the prior art. The solids are introduced into a large particle centrifuge that has been found to remove 70 to 90 percent of the remaining liquid. The liquid recovered in this way is then processed using a system of traditional centrifuges in order to remove the smaller particles.
The above system produces relatively clean particulates, which are easier and less costly to dispose of, and drilling fluid which can be reused in the drilling process.
According to the present invention then, there is provided an apparatus to reduce the amount of liquid discard in drill cuttings separated from a drilling fluid, comprising first separator means for removing larger cuttings from said drilling fluid, said cuttings having some fluid remaining therewith; centrifugal separator means for removing a major portion of said remaining fluid from said larger cuttings; centrifuging means for removing fine cuttings from either or both of said drilling fluid and said remaining fluid whereby a reusable drilling fluid is produced; and receiving means for said cuttings from said centrifugal separator means and from said centrifuging means for disposal.
According to a further aspect of the present invention, there is also provided a method of drying cuttings removed from a drilling fluid, comprising the steps of separating larger cuttings from said drilling fluid, said larger cuttings having some fluid remaining therewith;
centrifuging said larger cuttings to remove a major portion of said remaining fluid from said larger cuttings; and discharging said larger cuttings following the centrifuging thereof for disposal and recovering said remaining fluid for additional treatment to remove fine cuttings therefrom whereby said fluid can be reused during drilling.
Brief Description of the Drawings Preferred embodiments of the present invention will now be described in greater detail and will be better understood when read in conjunction with the following drawings, in which:
Figure 1 is a schematical diagram of an apparatus for drying particulates.
Figure 2 is an upper perspective view of an auger tank forming part of the apparatus of Figure 1; and.
Figure 3 is a schematical, partially sectional side elevational view of a large particle centrifuge forming part of the apparatus of Figure 1.
Detailed Description Referring to Figure 1 of the drawings, there is shown schematically a preferred embodiment of the present system 10 for removing contaminants from cuttings separated from a drilling fluid. In this system, used drilling fluid is separated from larger cuttings in an initial separation process. The cuttings are then further processed to remove entrained liquids.
Finally, smaller particles are removed from the liquid through a second separation process prior to recycling the fluid back to the active drill fluid system.
Drilling fluid mixed with cuttings from the well bore is introduced to the system through flow line 21, which discharges the mixture into shaker box 20. Shaker 20 includes a vibrating screen 22 that separates cuttings larger than the screen's mesh size (typically 100 to 240 mesh) from the fluid, discharging the liquids into a shaker tank 25 and the screened solids into an auger tank 30. The solids deposited into auger tank 30 include a significant proportion of drilling fluid wetting their outer surfaces or absorbed into their pore structure.
Auger tank 30 can best be seen by refernng to Figure 2. Tank 30 is supported on a framework 28 to receive the discharge from shaker box 20. The tank is hopper shaped in cross-sectional shape to gravity feed the cuttings into a bottom mounted screw-type auger 32.
The auger transports the cuttings, which are in the form of a slurry, in the direction of arrow A into a conveying apparatus 35 that in turn moves the cuttings into a large centrifugal dryer as will be described below. Conveying apparatus 35 will typically be a pump (positive displacement or vacuum), but another auger, a bucket conveyor or any other apparatus adapted to transport a slurry will be useful for this purpose.
In a preferred embodiment constructed by the applicant, conveying apparatus 35 is a Nemo NM90 Progressive Cavity Feed Pump. Pump 35 moves the slurry into a conduit 36 which is connected to an inlet 41 of a centrifugal dryer 40. The dryer 40 is a commercially available unit sold by Centrifuge and Mechanical Industries under the trade-mark EBW
Screen-Scroll Centrifuge.
Dryer 40 is shown schematically in Figure 3. It comprises an outer stationary housing 48 that encloses an inner centrifuging rotating screen and flight assembly 47 mounted in the housing for rotation about the vertical axis. The chamber is in fluid communication with inlet 41 for the ingress of the cutting's slurry and a fluid outlet 42 for the discharge of recovered fluid. An underflow outlet 43 is provided for the release of the dried cuttings which discharge into an inclined chute 5 (Figure 1 ) that dumps the cuttings into a sloop 80. The sloop is preferably an open ended container in which the solids accumulate until removed such as by means for example of a front end loader. Chamber 47 is rotated at approximately 800 rpm by a prime S mover 44, typically an electric motor, coupled to the chamber through a gearbox 45.
Dryer 40 accepts the cuttings slurry from the auger tank and through centrifugal action spins out from 70 to 90% of entrained fluids. In operation, the slurry is input to the dryer at a rate of approximately 270 to SSO litres per minute for a total throughput of approximately 30 to 60 tonnes of dried solids per hour.
Centrifuging chamber 47 inside the dryer's housing includes an internally mounted screen that is available in different mesh sizes, for example 0.020 inch (508 microns), 0.015 inch (381 microns), 0.010 inch (254 microns) and 0.008 inch (203 microns). Particles smaller than 0.008 inch cannot be separated from the drilling fluid in the dryer and further processing of the fluid prior to recycling back to the active fluid system is therefore required. This additional processing is advantageously carried out in parallel with the processing of the fluid discharged from shaker box 20 into shaker tank 25 as will now be described in greater detail.
With reference once again to Figure 1, downstream of dryer 40 and shaker tank 25 are two agitator tanks 50 and 55. Agitators are well known in the art and are commonly used for mixing and to maintain solids in suspension to prevent settling.
Agitator 50 receives fluid through a conduit 51 from shaker tank 25 and through a conduit 45 from the dryer's fluid outlet 42. Agitator 50 discharges its contents through an outlet 53 into a line 54 connected to the intake of a feed pump 60. Pump 60 moves the liquid from agitator 50 through line 61 into a centrifuge 70. In a preferred embodiment constructed by the applicant, pump 60 is a 3 x 3 Gorman RuppT"~ centrifuge feed pump, and centrifuge 70 is a Hutchinson-HayesT~~ FVS 5500 Decanting Centrifuge preferably used with a variable frequency drive (VFD) for controlling its speed.

Centrifuge 70 separates particulates from the liquid as known in the art.
Separated solids are discharged from the centrifuge onto an inclined chute 6 that then dumps them into a separate sloop 85 for disposal.
Preferably, the fluid discharged from centrifuge 70 can be directed in one of two ways. If the S fluid is sufficiently cleansed of solids for return to the active mud system, a valve 77 can be opened to discharge the fluid through line 71 into a suction tank 90 for temporary storage.
Conversely, if further processing is required, valve 77 is closed and valve 78 is opened to direct the fluid into a second agitator tank 55 through line 72.
In addition to reprocessing fluid from centrifuge 70, agitator 55 also receives fluid through a line 56 from shaker tank 25. Line 56 can access fluid from various locations from within the shaker tank. Tank 55 receives therefore a narrower range of relatively smaller particles compared to those received into agitator 50. Fluid from tank 55 is delivered to a second centrifuge 75 by means of a pump 65 that moves the fluid through connecting conduits 58 and 66. Pump 65 is again a 3 x 3 Gorman Rupp centrifuge feed pump, and centrifuge 75 is again a Hutchinson-Hayes FVS 5500 or their equivalents. Centrifuge 75 discharges its separated solids onto chute 6 to be added to those from centrifuge 70.
As will be appreciated, if valve 78 is closed and valve 77 is open, centrifuges 70 and 75 work in parallel and will simultaneously discharge treated fluid into suction tank 90. Conversely, if valve 77 is closed and valve 78 is open, the two centrifuges operate in series with a single discharge into the suction tank via line 76 from centrifuge 75.
A flow line 59 between the two agitators near their tops connects with an overflow line 49 that ensures that spillage will not occur should either tank overfill. Overflow line 49 delivers any excess fluid back to auger tank 30 so that the fluid is reprocessed but is not wasted. To prevent backflow towards shaker tank 25, both of lines 56 and 51 include one way check valves 57.
It will be seen that the present system provides a substantial improvement over systems previously used for the cleaning of drilling fluids and cuttings by recovering and recycling more of the fluid while leaving cleaner cuttings for easier and more economical disposal within current environmental regulations. By way of example, in one embodiment constructed by the applicant, cuttings covered from dryer 40 represent approximately 70%
of the total cuttings recovery. These cuttings have a dry weight oil content of between 2.5% and 3.5%.
Cuttings recovered from centrifuges 70 and 75 represent approximately 30% of total waste volume and have a dry weight oil content of between 15% and 25%. The dry weight oil content of the cuttings recovered from centrifugal dryer 40 will typically allow them to be disposed of via landspread on lease with a resulting soil/waste mix hydrocarbon content of around 0.5% which is considered non-toxic. Cuttings from centrifuges 70 and 75 can be disposed off lease, or if the cuttings do not include chlorine, they may be compost treated and then landspread on the lease.
As will be appreciated by those skilled in the art, all electric motors associated with the present system may be equipped with variable frequency drives. This enables the motors to be operated at any speed range from 0 rpm to maximum rpm . For the various feed pumps used in the system, pump flow rates can be tuned to optimum levels for maximum performance of drying centrifuge 40 and centrifuges 70 and 75. This in turn reduces shear stresses within the pumps which minimizes the production of solid fines that would otherwise remain in the active drill system. Variable speed capability for both the front and back drives of the centrifuges allows for bowl/scroll differential adjustments. These adjustments significantly improve the range of solid particle sizes that can be removed.
Yet another advantage of the present system is that it allows smaller particle sizes to be removed from the drilling fluid right at shaker 20. In conventional systems, shaker screen 22 is kept coarse to prevent screen clogging. Obviously, if the screen plugs, much of the drill fluid and most of the solids will travel over the screen for discharge into shaker tank 25. More solids are therefore within the fluid increasing the chance that these particles will become broken down into ultra-fines through shearing which occurs within the various mud pumps and at the bit. Once the solids are broken down into ultra-fines, they cannot be easily removed by conventional techniques. As the ultra-fines build, the active drilling fluid density increases and the dollar value of the drilling fluid system decreases.
_7_ In contrast it is actually desirable in the present system that a certain amount of liquid run off the end of screen 22 in order that the resulting slurry can be properly processed. This need for fluid content promotes the use of a shaker screen having much finer mesh. This results in the separation of smaller solids right at the shaker. These smaller particles will then be removed and dried by dryer 40 before the recovered drill fluid is reintroduced into the active mud system.
The above-described embodiments of the present invention are meant to be illustrative of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present invention. The only limitations to the scope of the present invention are set out in the following appended claims.
_g_

Claims

1. Apparatus to reduce the amount of liquid discard in drill cuttings separated from a drilling fluid, comprising:
first separator means for removing larger cuttings from said drilling fluid, said cuttings having some fluid remaining therewith;
centrifugal separator means for removing a major portion of said remaining fluid from said larger cuttings;
centrifuging means for removing fine cuttings from either or both of said drilling fluid and said remaining fluid whereby a reusable drilling fluid is produced; and receiving means for said cuttings from said centrifugal separator means and from said centrifuging means for disposal.

2. The apparatus of claim 1 further comprising first tank means for receiving drilling fluid from said first separator means and a first agitator tank means for receiving said remaining fluid from said centrifugal separator means and drilling fluid from said first tank means, and means for controllably discharging fluid from said first agitator tank means into said centrifuging means for said removal of said fine cuttings.

3. The apparatus of claim 2 further comprising a second agitator tank means for receiving drilling fluid from said first tank means, and means for controllably discharging fluid from said second agitator tank means into said centrifuging means for said removal of said fine cuttings.

4. The apparatus of claim 3 wherein said centrifuging means comprise first and second centrifuges, said first centrifuge being in fluid communication with said first agitator tank means to receive fluid therefrom, and said second centrifuge being in fluid communication with said second agitator tank means to receive fluid therefrom, each centrifuge having an outlet for the discharge of said fine cuttings and said fluid.

5. The apparatus of claim 4 wherein the fluid discharged from said first centrifuge can be selectively directed either to a reservoir for said fluid or to said second agitator tank means.

6. The apparatus of claim 5 wherein the fluid discharged from said second centrifuge is discharged into said reservoir.

7. The apparatus of claim 6 wherein said outlet for fluid from said first centrifuge includes a valve actuatable to direct said fluid to said second agitator tank means or to said reservoir.

8. The apparatus of claim 7 further including second tank means to receive said cuttings from said first separator means and means associated with said second tank means to transport said cuttings and said fluid remaining therewith into said centrifugal separator means.

9. The apparatus of claim 8 further including conduit means for directing any excess fluid from one or both of said first and second agitator tank means to said second tank means.

10. The apparatus of any of claims 1 to 9 wherein said first separator means is a vibrating screen.

11. A method of drying cuttings removed from a drilling fluid, comprising the steps of separating larger cuttings from said drilling fluid, said larger cuttings having some fluid remaining therewith;
centrifuging said larger cuttings to remove a major portion of said remaining fluid from said larger cuttings; and discharging said larger cuttings following the centrifuging thereof for disposal and recovering said remaining fluid for additional treatment to remove fine cuttings therefrom whereby said fluid can be reused during drilling.

12. The method of claim 11 wherein said additional treatment comprises centrifuging said remaining fluid.

13. The method of claim 12 wherein said remaining fluid is centrifuged a second time for additional removal of fine cuttings prior to reuse.

14. The method of claim 13 including combining said remaining fluid and drilling fluid recovered from the separation of said larger cuttings for centrifuging to remove fine cuttings therefrom.