Note: Descriptions are shown in the official language in which they were submitted.
CA 02433475 2003-06-26
Drilling Fluid Treatment Tank
Field of the Invention
The present invention is directed to a drilling fluid tank and in particular
to a tank
for the treatment of drilling fluid.
Background of the Invention
Drilling fluid, which is also termed mud, is circulated through a wellbore
during
drilling to lubricate the drill bit and to carry drilled cuttings to surface.
A selection
of drilling fluid is made depending on various parameters including the nature
of
the formation being drilled through, the depth of the borehole and the speed
under which the drilling is being progressed. In North America, it is possible
to
use a less expensive water-based drilling fluid initially, during spudding,
before
moving to a polymer based mud as the hole depth is increased.
Environmental concerns, as well as cost, have urged operators to move to
closed
loop systems, wherein the drilling fluid is recycled during use, rather than
discarding it. In so doing, the drilling fluid must be treated in various
ways. First,
the drilling fluid must be treated to remove the drilled cuttings it contains
when
returning to surface. Polymer-based drilling fluids must, in addition to
solids
settling, be treated initially to mix the polymers into the carrying fluid.
During
polymer drilling it often becomes necessary to have supply of drilling fluid
available.
Traditionally, a tank has been used for the settling or stripping of water-
based
drilling muds. The tank permits a settling area for solids separation from the
fluid. During this process other components must be brought in such as polymer
injection units, pumps and lines. Once the drilling is moved to a polymer
based
fluid, the settling tank is removed and replaced with one or more tanks for
mixing
and handling the polymer-based fluids. This results in considerable equipment,
space and transport requirements.
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CA 02433475 2003-06-26
Summary of the Invention
A drilling fluid treatment tank has been invented that can be used for both
water-
based drilling fluid and for polymer-based drilling fluid. As such, the tank
can be
employed to manage the fluid from spudding to rig release, when the borehole
is
complete. The tank is substantially self-contained including, for example,
fluid
handling tanks, pre-mix tanks and polymer storage tanks, and possibly also
pumps, pump controls and fluid circulation lines.
In accordance with a broad aspect of the present invention, there is provided
a
drilling fluid treatment tank system comprising; a tank including walls for
containing liquid drilling fluid, weirs spaced along the tank dividing the
tank into a
plurality of compartments and a liquid passage positioned adjacent an upper
edge of each weir permitting liquid to flow from compartment to compartment,
the
tank including means for providing conversion between use for solids settling,
use for stripping drilling mud and use for polymer-based drilling mud pre-
mixing.
In accordance with a broad aspect of the present invention, there is provided
a
drilling fluid treatment tank system comprising; a tank including walls for
containing liquid drilling fluid, weirs spaced along the tank dividing the
tank into a
plurality of compartments and a liquid passage in each weir permitting liquid
to
flow from compartment to compartment; and a fluid mixing system positioned to
act in at least some of the compartments.
In such an embodiment, the fluid mixing system can include a fluid circulation
system for evacuating the fluid from the tank and reintroducing the fluid to
the
tank substantially without further treatment thereof. The fluid circulation
system
can include lines and a pump. The fines can be, for example, a slotted suction
tube extending along a bottom of the tank in communication with an outlet line
in
the tank. The mixing system can alternately or in addition, include jet guns
mounted in at least some of the compartments.
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In one embodiment, the tank includes a mixer for mixing additives into any
contained fluid in the tank. The mixer can be mounted in a fluid circulation
line to
introduce the additives to fluid circulating through the line. The fluid
circulation
line can include a feed line for evacuating fluid from the tank and a
discharge line
for reintroducing the additive-containing fluid to the tank after it has
passed
through the mixer.
In accordance with a broad aspect of the present invention, there is provided
a
drilling fluid treatment tank system comprising a skid, a tank mounted on the
skid
and including walls for containing liquid drilling fluid, weirs spaced along
the tank
dividing the tank into a plurality of compartments and a liquid passage in
each
weir permitting liquid to flow from compartment to compartment; and an
additive
premixer selected from an inline mixer andlor a polymer injection tank, a
fluid
circulation pump and/or an additive injection pump mounted on the skid.
In accordance with a broad aspect of the present invention, there is provided
a
drilling fluid treatment tank comprising a tank including side walls, a first
end wall
and a second end wall for containing liquid-based drilling fluid, a tank
separation
wall positioned within the tank between the end walls to separation the tank
into
a first section and a second section, the tank separation wall restricting
liquid flow
therepast between the first section and the second section except through a
closable opening in the wall; at least one weir spaced between the first end
wall
and the tank separation wall, dividing the first section into a plurality of
compartments; and a liquid passage in the weir permitting liquid to flow from
compartment to compartment.
In such an embodiment, the tank system can include a first material conveyor
in
the first section and a second material conveyor in the second section. The
tank
system can also include a fluid circulation system for moving fluid between
the
first section and the second section. The fluid circulation system can include
lines and a pump. The fluid circulation system can, in addition or
alternately,
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4
includes lines for evacuating fluid from one of the sections and reintroducing
the
fluid to that section.
In accordance with another aspect of the invention, there is provided a method
for treating drilling fluid comprising: providing a tank system capable of
solids
settling and of mixing drilling mud, using the tank system to treat a drilling
fluid by
solids removal therefrom and using the tank to mix an additive into a liquid
to
form a polymer-based drilling fluid.
Detailed Description of the Drawings
Figure 1 is an end perspective view of a tank system according to the present
invention.
Figure 2 is a top perspective view of the tank system of Figure 1, with a side
wall
cut away to facilitate illustration of the inner tank components.
Figure 3 is an enlarged top perspective view of the pump and polymer mix areas
useful in a tank system according to the present invention.
Figure 4 is a sectional view along line IV-IV of Figure 2, showing a flow path
generated by operation of a jetting gun.
Figure 5 is a schematic flow diagram of a method of using the system of the
present invention.
Figure 6 is a schematic flow diagram of another method of using the system of
the present invention.
Figure 7 is a schematic flow diagram of another method of using the system of
the present invention.
Figure 8 is a top perspective view of another tank system according to the
present invention.
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Figure 9 is an enlarged perspective view of a portion of the tank system of
Figure
8.
Detailed Description of the Invention
Tanks according to the present invention are useful for drilling fluid
treatment
from drilling start up to drilling completion. The tanks can handle water-
based
and polymer-based drilling fluids and can handle batch treatments and closed
loop systems.
One embodiment of a tank system 10 according to the present invention is
shown in Figures 1 to 3. The system is built for drilling fluid management. It
can
be used for dewatering of drilling mud, for solids removal and stripping (also
known as dewatering) for clear water drilling and for mixing polymer-based
fluids
for later well drilling operations. As such, the system can be used throughout
the
entire drilling operation, with simple conversion, when needed, to handle the
various types or processing requirements of drilling mud.
The system is elongate having a first end and a second end and includes a skid-
type base 12, on which the other components are mounted. The second end has
positioned thereon a mechanical section 14 containing controls and pumps 16,
18 and an arrangement of mixers 20 and mix tanks 22.
A tank 24 capable of containing liquid extends from the first end to the
mechanical room. The tank can be sized, as desired. The tank has sidewalls
24a and end walls 24b, 24c. The end walls are positioned one 24b at the first
end of the system and the other 24c adjacent the mechanical room and mix
tanks at the second end. The tank sidewalls extend between the end walls and
converge at the their lower ends such that the tank narrows towards its bottom
end.
There is a plurality of vertically oriented weirs 26a, 26b connected between
the
sidewalls. The weirs are spaced apart along the length of the tank such that a
plurality of compartments 28, 28a, 28b are set up, which are separated by the
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6
weirs. In the illustrated embodiment, the tank is-separated into 10
compartments
by 9 weirs. However, other numbers of weirs can be provided, as desired. The
weirs each contain an opening 30 adjacent their upper ends to permit flow
communication of a liquid through the weirs. The positions of the openings on
the weirs alternate from a position adjacent one and then the other sidewalls
in
series. One of the centrally positioned weirs 26b includes a gate 32 oriented
to
permit opening 30 therein to be closed and sealed against liquid flow
therethrough, if desired. The gate can be connected in various ways for
closing
the opening. For example, the gate can be pivotally connected to the weir or
slidably positioned. The gate can include a sealing member 34 such as an
elastomeric ring that assists in the sealing action of the gate over the
opening.
The weirs 26a each extend down adjacent the bottom end of the tank but are
spaced therefrom to form a lower opening 36 permitting liquid flow under the
weirs. Weir 26b, supporting gate 32, is sealingly disposed between the side
walls and the bottom of the tank such that no flow is permitted therepast
except
through opening 30, when the gate is open. '
As such, weir 26b creates a tank separation wall that can separate the tank
into
two sections. In particular, the weir with gate 32 can provide convertability
to the
tank system to permit tank 24 to operate, when gate 32 is open, as one liquid
containing area or to operate, when gate 32 is closed, as two separate smaller
volume tanks with no or only controlled communication therebetween. Due to
the ability of weir 26b to be used to separate the tank into two large
compartments, it is preferably positioned centrally, although this is not
essential.
The compartment adjacent the first end 28a, which will be termed herein the
first
compartment, includes an air union 38 in its upper end or sidewalls. The air
union can accept connection or passage through of liquid supply tubes (not
shown) to provide a flow of liquid, such as drilling mud, to the first
compartment.
An arrangement of slotted suction tubes 40a, 40b, 40c extend beneath the weirs
in the bottom of the tank. There are three slotted suction tubes in the
illustrated
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embodiment. However, any arrangement can be used to act as material
conveyors in the bottom of the tank. A first slotted suction tube 40a is open
to
the first three compartments including compartment 28a, a second slotted
suction tube.40b is open to the fourth compartment and the fifth compartment,
which is adjacent weir 26b, and a third slotted suction tube 40c is open to
the five
compartments, including compartment 28b, closest to the second end of the
system and on the opposite side of weir 26b from suction tubes 40a, 40b. The
first and second suction tubes each extend out of the tank through first end
24b
and have outlet ends 42a, 42b to which suction devices (not shown), such as
pumps, can be connected. The suction tubes are used for removing settled
solids, for fluid circulation and for complete emptying of the tank.
Other means are also provided for liquid evacuation from the tank. In
particular,
in the illustrated embodiment, the feed side of pump 16 has connected thereto
a
valve-controlled port 43 opening into compartment 28b and a valve-controlled
line 44 opening into the compartment adjacent solid weir 26b toward end 24b.
Liquids drawn through pump 16 are discharged through fine 39 for recirculation
or for returning to the rig, as will be discussed herein after. Alternately, a
submersible pump (not shown) could be positioned in any of the compartments
to draw liquid therefrom. A hoist 45 is provided to facilitate handling of
heavy
equipment such as, for example, a submersible pump.
An injection gun 46 is provided in each campartment to jet fluid into the
compartment for mixing. The injection guns, in the illustrated embodiment, are
formed with a perforated elongate end 46a joined in configuration to a pipe
46b
extending down into the compartment. Injection guns 46 can be used to
facilitate
material conveyance and, in such an embodiment, are positioned with end 46a
close above the slotted suction tubes. The elongate end extends with its long
axis substantially parallel to the long axis of the slotted suction tube above
which
it is positioned. Straps and/or brackets 47 can be used to maintain the
selected
positioning of the injection guns. Of course, other configurations can be
used.
However, with reference to Figure 4, this configuration permits a flow path 41
to
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CA 02433475 2003-06-26
be. set up in the tank that facilitates solids evacuation with the slotted
suction
tubes, for example 40b. In particular, jet ports 46c open substantially along
the
sides of the elongate end 46a such that fluid jetting out therefrom is
directed
substantially laterally and against the angled side walls, where the flow is
diverted upwardly by the side walls and then down past the end 46a as driven
by
the low pressure region generated by operation of the suction tubes. This flow
path permits settling of the solids leaving a clearer water upper layer, while
the
settled solids remain entrained in liquid and, thereby fluid, to facilitate
their
evacuation.
A supply pipe 48 is in fluid flow communication with the guns 46 and flow
control
to each gun is provided via a valve 49. Thus, flow can be shut off or reduced
to
certain guns by closing their valves while flow to other guns is selected by
opening their valves. Pipe 48 receives fluid via line 39 from pump 16
discharge.
In the illustrated embodiment, pump 16 is arranged such that fluid can be
drawn
though third suction tube 40c, port 43 or line 44 for supplying pipe 48 and
guns
46. However, other arrangements can be used for fluid supply to pipe 48, as
desired.
Pipe 48 can also be used to convey large flows of liquid to the rig and/or to
recirculate or move large flows through the tank. In particular, pipe 48
includes
valued-connectors 48a for connection of return lines to the rig or to other
drilling
mud/liquid facilities or disposal sites. Pipe 48 also has secured thereto in
fluid
communication therewith a first outlet pipe 50 opening to ~ compartment
between end 24b and solid weir 26b and a second outlet pipe 52 opening to a
compartment between end 24c and solid weir 26b. Valves 54, 56 are provided
on first outlet pipe 50 and second outlet pipe 52, respectively, to control
flow
therethrough. Pipe 48 with outlet pipes 50, 52, used independently or
together,
can be used to rapidly fill selected sides of the tank about weir 26b or the
entire
tank, when gate 30 is open on the solid weir.
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Mixer 20 is mounted on the skid to provide for mixing of drilling mud
additives
such as those for adjusting the solids-carrying properties of the mud, for
example, bentonite or viscosity adjusting polymers. Mixer 20 in the
illustrated
embodiment, includes an inline mixer and a hopper. In the illustrated
embodiment, mixer feed liquid comes from line 39 via a line 54 to the inline
mixer. A valve is provided to control flow through pipe 48 to the inline
mixer. In
this way, liquid from the system can be used to produce the additive-
containing
liquid. Discharge of additive-containing liquid from the mixer is conveyed
through
pipe 56 to the tank and is bifurcated to permit flow, as controlled by valves
58,
into a compartment between end 24b and solid weir 26b and/or into a
compartment between end 24b and solid weir 26b.
A tank 22 with a driven mixer 60 disposed therein is also provided for the
preparation additive-containing liquid such as flocculants. Tank 22 can
include a
steam,line for heat input. Liquid from the system or otherwise can be added to
the tank for hydrating the additive. The tank is sized to hold a reserve of
hydrated flocculent, for a period of operation. Once prepared, the hydrated
flocculent is withdrawn by pumps 18. Sufficient pumps can be provided to have
a pump dedicated to the supply of each process step where the additive is
required to be injected. For example, in the illustrated embodiment, three
pumps
are provided so that flocculent can be injected independently to the tank
input
and one or possibly two centrifuges.
Pumps 18 can be positive displacement pumps, or any other pumps that can
withstand the operational and flow requirements of the additive supply. Pump
16
can be a centrifugal pump, or any other pump that can withstand the
operational
and flow requirements of rig supply/tank recirculation. The operation of the
pumps and other components can be controlled through an electrical control
panel or other control systems, as desired.
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Mechanical section also includes a heater 70 fior heating the mechanical room
in
which the pumps and controls are located, to reduce the risk of freeze up and
downtime.
Walkways 72 are provided about 24 tank to facilitate operation fior example to
permit access to the valves on pipe 48 and to permit observation of the
liquids
within the compartments.
The system can be powered by rig power or any other power source, with the
required modifications.
As noted, the system can be used in a method for solids separation from
drilling
mud, for dewatering drilling mud and/or for pre-mixing of borehole additives.
With reference to Figure 5, when used for solids removal in a closed loop
operation, the system is set up near the drill rig 73 to receive drilling mud,
which
is at this stage usually water-based. For use in solids separation, piping 74
is
connected to the air union to convey drilling mud from the rig to compartment
28a. Depending on the rig circulation rate, pump 16 is readied to evacuate
water
through port 43 or a submersible pump assembly is positioned in one of the
compartments, for example, that compartment 28b closest to the second end,
and a line 75 is installed to feed the rig from pump 16 and pipe 48 or from
the
submersible pump. Unless the solids content and mud circulation rate are such
that quick settling can be achieved, gate 32 is opened to permit flow from
compartment 28a to compartment 28b. The system is used with a centrifuge 76
and, therefore, one is positioned nearby and lines 77 are connected between
the
outlets 42a, 42b and the centrifuge. A centrifuge liquid outlet 78 extends to
the
rig or to empty into tank 24. Flocculants are hydrated in tank 22 and lines
79a,
79b are connected between pumps 16 and piping 74 connected to the air union
and to the centrifuge lines 77.
Drilling mud, from the rig, with the injected flocculants are then introduced
to the
first compartment 28a. The drilling mud begins to fill the tank, with the
major
portion of the flow from compartment to compartment being through openings 30.
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11
Once the tank is filled, the drilling mud is withdrawn from the last
compartment
and pumped to the rig. This causes the drilling mud to slowly move from the
first
compartment to the last compartment by a flow through the openings. Because
of the positioning of the openings, the flow along the tank follows a sinuous
path.
The slow movement of the drilling mud permits settling of sediments toward the
bottom of the tank, such that the liquid in the last compartment 28b is
generally
free of sediments.
To ensure that the sediments remain fluid, mud, withdrawn from the later
compartments through suction tube 40c and/or port 43 can be jetted through the
one or more injection guns 46, as controlled by valves 49, to create
turbulence in
the lower portions of their compartments (see Figure 4) adjacent the first end
24b. The need to jet will depend on the accumulation of sediments in the
compartment, as determined by circulation rate, rate of penetration, hole size
and
flocculent effectiveness.
Suction means are operated to draw the settled sediments into the first and
second suction tubes 40a, 40b and to move it to the centrifuge. In one
embodiment, suction tube 40a is evacuated more regularly than tube 40b, since
generally more sediments accumulate in .the earlier compartments. The
collected sediments are treated in the centrifuge to remove the solids from
the
liquids. The solids are collected and the liquids are returned to the tank or
sent
to the rig.
In this way, the tank system is operated, with the use of a centrifuge, a
suction
means and additional lines to remove solids from the drilling mud to provide
clear
mud, for reuse in a drilling operation, directly from compartment 28b, and
possibly also directly from a centrifuge attached to tireat the settled
solids.
Once the closed loop water-based drilling is complete, the tank can be readied
for the next drilling mud procedure or can be cleaned out.
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The tank system 10 can also be used for stripping drilling mud, which is a
batch
method of solids removal as shown schematically in Figure 6. 1n this system,
the
full tank can be used or the gate 32 on weir 26b can be closed to reduce the
volume to correspond to the batch size.
The tank system is set up in a manner similar to that described above with
respect to a closed loop settling system and an amount of drilling mud with
flocculants is introduced to the tank. The drilling mud is then permitted to
settle,
with the solids being removed through the suction tubes 40a, 40b until
acceptable clear water is achieved. Liquid for jetting through guns 46 can be
withdrawn through line 44. The clear water is removed via line 44 through pump
16, line 39, pipe 48 and valued-connectors 48a.
If only one section of the tank is being used for stripping, the other side
can be
used for stripping another batch of drilling mud, for storage of cleaned mud
from
the first section or for other mud procedures such as for the premix of
polymer-
based muds.
Once the need for stripping drilling mud is complete, the tank can be readied
for
the next drilling mud procedure or can be cleaned out.
Premix of polymer based mud can also be achieved using the tank system 10 of
the present invention. In particular, with reference to Figure 7, when used
for the
preparation of a polymer-based mud, the system is set up near the drill rig
73,
pump 16 is readied to evacuate water from the tank for recirculation and
passage
through mixer 20 and a line 75 is installed to connector 48a to feed the rig,
when
the mud is ready. Gate 32 is often closed to reduce the volume of the tank.
The selected section of the tank is then filled with a liquid. As the tank is
filled,
liquid is withdrawn, sent through mixer 20, where additives are introduced
through the mixer hopper, and returned to the tank through pipe 56, for
example,
into the end including compartment 28b, by opening valve 58a and closing valve
58b.
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13
To ensure that the polymer becomes, and remains, mixed, the fluid can continue
to be run through the mixer lines for circulation or the fluid can be
withdrawn from .
the later compartments through suction tube 40c and/or port 43 can be jetted
through the one or more injection guns 46 to create turbulence in their
compartments. !f desired, considerable turbulence can be generated in a
compartment by opening the gun"s valve 49 to greater levels.
In this way, the tank system is operated to premix drilling mud and to
maintain
the drilling mud in a mixed condition until it is desired to provide the mud,
through
pump 16 and line 75, to the rig.
Once the drilling mud pre-mix operation is complete, the tank can be readied
for
the next drilling mud procedure or can be cleaned out.
Cleaning is facilitated by use of guns 46 and suction tubes 40a, 40b, 40c,
such
that very little manual work is required to clean out the tank.
Referring to the remaining Figures, another embodiment of a tank system 10a
according to the present invention is shown. This tank system is similar to
the
system of Figure 1, except with a few differences.
In particular, the first and second slotted suction tubes (40a, 40b of Figure
1 )
have been replaced with a plurality of smaller, divided, slotted suction
tubes. In
the illustrated embodiment, there is one slotted suction tube 40d opening into
both the first compartment 28a and its next adjacent compartment and one
slotted suction tube 40e, 40f, 40g in each of the next three compartments.
Slotted tube 40d has an output port 42c passing through the first end wall and
an
output tube 42d extending out through the sidewall 24a. Slotted suction tubes
40e, 40f, 40g each have an output tube 42e - 42g, respectively, extending out
through the sidewall 24a. The materials in the first two compartments can be
pumped out of the tank by either applying suction at output port 42c or by
applying suction at output tube 42d extending through the sidewall. Output
tubes
42e - 42g include connectors at their ends for connection to a source of
suction
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CA 02433475 2003-06-26
14
so that the compartment into which they extend can be cleaned out. This
permits
conveyance of solids out of selected compartments only, together or
compartment by compartment. Thus, the heaviest mulls can be treated
selectively offering the most effective use of treatment apparatus, such as
centrifuges.
A liquid spillway 80 extends along the length of the flank above the weirs
26a,
26b and has a plurality of closeable openings 82 through which liquid can flow
into selected compartments. The spillway is configured to permit liquids
returning from the centrifuge to be introduced, via the spillway, to selected
compartments along the tank, depending on the clarity of the liquid.
System 10a also includes lower floodgates 86 operable to seal enlarged
openings at the bottom ends thereof 36. Handles 88 extend to permit operation
of the floodgates, when desired to permit a greater flow through the bottom
portion of the tank.
In addition to polymer mix tank 22, a second polymer mix tank 23 is provided.
So
that greater volumes of additives can be prepared and, if desired, two batches
can be readied so that a constant controlled solution can be available.
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