Note: Descriptions are shown in the official language in which they were submitted.
CA 02298912 2000-02-17
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
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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
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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
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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
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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.
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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
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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.
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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.
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