Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SLURRY RECOVERY PROCESS
FIELD OF THE INVENTION
This invention relates generally to a process for the recovery and recycling
of slurry
materials produced in well drilling operations, such as frac sand or aqueous
liquid for
transporting frac sand; or both.
BACKGROUND OF THE INVENTION
A number of processes employ sand having specific qualities. In some cases the
particular sand is only available from a small number of sources, and may have
to be
transported over relatively long distances, at significant expense, to the
site where it is to be
employed. The sand may have specific qualities with respect to size, hardness
or strength,
resistance to chemical attack, roundness, or other properties that are
required for the
particular process in question.
One such process involves the introduction of frac sand into wells under
pressure. In
the operation of a well, such as an oil or gas well, it may generally be
desirable for the
stratum, or strata, of the producing zone from which the oil or gas is to be
extracted to have a
number of cracks or fissures running generally away from the well bore. The
general
premise is that the larger the cracks, and the farther they run away from the
well bore, the
easier it is for the gas or oil in the stratum to migrate toward the well
bore, whence it can
flow, or be drawn, to the well-head at the surface.
One way to promote, or enhance, this process is to encourage the creation of a
large
number of cracks, and to try to force cracks in the stratum to open up, to
lengthen, and to
stay open so that the oil or gas can flow out. One method of doing this is to
raise the
pressure in the well, so that the adjacent cracks may tend to open up, and to
force a
"proppant" into the cracks the have been opened, so that when the raised
pressure is
removed, the cracks may tend to stay propped open. It is important that the
propant be
strong enough to keep the crack in the stratum open, and yet not fill the
crack so tightly that
the path for migration of oil or gas be thereby blocked. That is, the propant
material must
also let the oil and gas flow out.
One type of proppant material widely used in the oil and gas industry is a
type of
silica sand of a particular range of size and roundness. The roundness of the
sand is
advantageous since the grains, when stacked together, are interstitially
porous. That is, the
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paths between the stacked, rounded grains, are sufficiently porous to permit
the oil and gas
to migrate through the spaces between the grains toward the well bore. It is
not
advantageous to use sharp particles that stack tightly together. The
desirable, rounded sand
of appropriate size is available from only a relatively small number of
suppliers, and tends to
be relatively expensive. When the propant insertion process is completed, the
residue in the
well bore is produced and, heretofore, discarded. Inasmuch as this residue
contains a
significant amount of frac sand propant, and inasmuch as frac sand is
relatively expensive to
buy and transport, it would be advantageous to recover frac sand from the
residue produced
from the well.
However, frac sand has not been recovered in the past for a number of reasons.
First,
the residue produced from the well includes not only frac sand, but may also
include
undesirable materials such as metal particles, drilling mud, and liquid frac
sand Garner. The
metal particles may tend to be steel filings worn from the drill string by the
abrasive action
of the frac sand, or other abrasive material, within the drill string itself.
Alternatively the
iron particles may be abraded from the casing of the bore, or from particles
separated from
the casing by a well perforating gun. The drilling mud tends to be a residue
left over from
the drilling of the well in the first place. The liquid frac sand carrier
arises from the frac sand
process itself.
The frac sand process involves mixing dry, clean frac sand with a carrier. It
is
important that the frac sand be distributed reasonably evenly in suspension in
the carrier, as
opposed to settling out, so that it will be relatively well dispersed for
entering a multitude of
cracks along the producing zone of the well bore. Therefore, at the time of
mixing at the
well-head, the carrier has the form of gel, or gel like substance in which the
frac sand is
suspended. The mixture is then forced down the well bore under high pressure.
The
pressure may tend to force the cracks in the producing stratum to open, and in
opening to
admit both the gel and the frac sand suspended in the gel. When the pressure
is reduced to
the pre-existing level, the cracks in the producing stratum attempt to close,
but are held (that
is, propped) open by the frac sand. Once the frac sand is in place, it is
desirable that the gel
Garner be removed. Therefore the gel has a limited duration, and after a time
it returns to a
thin, predominantly watery liquid form. As such it drains back into the well
bore, and leaves
most of the proppant sand behind. The excess proppant also remains in the well
bore.
In due course, the material that drains into the well bore is pumped out,
typically as a
slurry of several components, namely: the liquid Garner; the excess frac sand;
left-over
drilling mud; and whatever else may have collected in the bore. In former
times, the slurry
produced from a new well at completion was extracted from the well and sprayed
over
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terrain adjacent to the well head. This is not necessarily a desirable method
of disposal, and
has fallen out of favour in more recent times. The liquid carrier of the
slurry from the
completed well may well be a brine, and it is not desirable to spray various
chlorides over
adjacent agricultural lands. It would be preferable to recover the frac sand
and to re-inject
the iron laden aqueous solution back into the ground at an injection well.
While it is desirable to re-use the frac sand, it is undesirable to
reintroduce into the
well proppant sand that is contaminated with metal particles, since the metal
particles may
tend to then be forced into, and to block, the interstitial spaces in-between
the sand granules
that are needed to permit oil or gas to drain out. Similarly, it is
undesirable to reintroduce
proppant that is contaminated with drilling mud, since the drilling mud (and
any undersized,
cracked particles of proppant) will tend to block, i.e., stopper up, the
cracks as well. It is
thought that it may also be undesirable to re-introduce proppant that is
contaminated with
used Garner fluid. It would be desirable, then, to extract the frac sand
residue, remove
contaminants such as metal particles, drilling mud, broken or undersized
particles of frac
sand, or used carrier fluid, and dry the recovered frac sand so that it is
ready for re-use. It
would also be desirable to re-condition the aqueous solution that carnes the
frac sand to the
surface to permit it to be discharged benignly as approved, or used in other
operations, such
as inj ection wells.
Injection wells have been used to extend production from existing wells. It
may be
that a producing well produces a mixture of water and oil. At the surface the
water is
separated from the oil. The oil is transported to a refinery, and the water
remainder is then
disposed. One form of disposal for the water is to re-inject it under pressure
back into the oil
or gas bearing stratum whence it came. The reinjected water is chemically
treated before
reinjection, the chemical treatment process typically including a biocide.
Over a period of
years, the repeated action of treating and re-injecting water may tend to
result in a build up
of sulphuric acidity in the water pumped from the producing well.
At the same time, the waste water from a new well frac sand completion process
may tend to transport abraded iron particles that may tend to be small and to
have a
relatively high ratio of surface area to mass. Further, the solubility of iron
in a salt solution
may tend to be higher than in fresh water. If the aqueous solution of
chlorides and iron from
the new well, and low concentration sulphuric acid solution from the producing
well are
mixed, a black iron sulphate precipitate may tend to form. It is undesirable
to direct this
precipitate back into the injection well. First, the pumps of the injection
well may be
damaged by the precipitate, and second, over a period of time it is not
desirable to clog the
pores of the well with solid precipitate. In that light, it is desirable to
treat the waste water
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by-product solution of the frac sand cleaning process to discourage the black
precipitate
from forming, and to mechanically filter the waste water output by passing it
through a
relatively fine filter. In particular, it may be desirable to introduce a
modest concentration of
citric acid, such as in a soluble anhydrous powder form, into the frac sand
waste water
output to form a soluble ferric citrate from which black ferric sulphate may
have less
tendency to form when the solutions are mixed.
Washing and drying systems for sand may tend to use washwater, and produce a
quantity of dust. It would be advantageous to recycle at least part of the
wash water, and
thereby to reduce overall water consumption as compared to using only fresh
water. It
would also be advantageous to employ a dust collector, or collectors, to
reduce the amount
of dust given off in the process.
SUMMARY OF THE INVENTION
In an aspect of the invention there is a process comprising the steps of
collecting
frac sand after it has been used in a well bore, washing the frac sand, drying
the frac sand
and accumulating the washed and dried frac sand for re-use.
In an additional feature of that aspect of the invention, the process includes
the
step of segregating the frac sand by size before accumulating the washed and
dried frac
sand for re-use. In another additional feature, the process includes the step
of mixing the
washed and dried frac sand with a suspension agent and injecting the suspended
frac sand
into a well. In still another additional feature, the process further includes
the step of
collecting includes the step of collecting a slurry, a portion of the slurry
being frac sand,
settling the slurry, and decanting free liquid from the settled slurry.
In another aspect of the invention, there is a process for recovering used
frac sand
from a well, comprising the steps of extracting a slurry from the well, the
slurry including
at least frac sand and a carrier liquid, separating free liquid from the
slurry to leave a first
remainder, washing the first remainder in a washing facility, extracting a
second
remainder of wet solids from the washing facility, drying the wet solids,
separating re-
usable, dried frac sand from other solids and accumulating the re-useable frac
sand.
In an additional feature of that aspect of the invention, the step of washing
includes introducing the first remainder into a tub. In another additional
feature, the step
of washing includes directing wash water at the first remainder. In still
another additional
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feature, the process further includes the step of re-cycling at least a
portion of the wash
water. In yet another additional feature, the step of recycling includes the
step of settling
the used wash water. In still yet another additional feature, the step of
settling the used
wash water is followed by the step of decanting clear wash water for re-use.
In another additional feature, the step of setting includes introducing used
wash
water into a settling tank, allowing solids to settle out, and removing
settled solids from
the tank. In still another additional feature, the process further includes
the step of
chemically treating the wash water before directing it to the washing facility
again. In a
further additional feature, the process includes discarding a portion of the
used wash
water. In still yet a further additional feature, the process includes the
step of directing an
outflow of wash water from the washing facility along a path having at least
one weir,
and passing the flow over at least one weir.
In yet another additional feature, there is a settling zone upstream of the
weir, and
the process includes the step of passing the outflow through the settling zone
on the way
to the weir. In still another additional feature, there is a cascade of a
plurality of weirs
along the path, and the process includes removing precipitated material from
upstream of
the weirs. In yet another additional feature, the process includes the step of
directing the
outflow to a settling tank downstream of the weirs. In still another
additional feature, the
process includes decanting wash water for re-use from the settling tank. In
another
additional feature, the step of extracting includes raising the frac sand with
an inclined
screw.
In yet another additional feature, the step of drying includes the step of
introducing at least a portion of the second remainder extracted from the
washing facility
into a rotating drum and introducing hot air into the drum to dry the second
remainder. In
a further additional feature, the step of drying includes passing exhaust air
from the drum
through a dust collector. In yet a further additional feature, the step of
washing includes
magnetic separation of metal particles from the slurry.
In yet another additional feature, the process includes the step of screening
the
solids to remove oversize particles. In still another additional feature, the
process
includes the step of screening the solids to exclude undersized particles. In
a further
additional feature, the process includes the step of screening the solids to
exclude both
oversize and undersize particles. In still yet a further additional feature,
the process
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includes the step of screening the solids by size, and the step of screening
includes the
step of collecting dust arising from the step of screening.
In a further aspect of the invention, there is a process for recovering used
frac sand
from a well completion operation. The process includes the steps of extracting
a slurry
from the well, the slurry including at least frac sand, drilling mud, and a
liquid Garner;
passing at least a portion of the slurry through a washing facility to
separate the drilling
mud and the liquid carrier from at least a portion of the frac sand; removing
at least the
portion of the frac sand from the washing facility, drying at least the
portion of the frac
sand; and passing at least the portion of the frac sand through a sizing
apparatus to yield a
re-usable remainder.
In a still further aspect of the invention, there is a process for recovering
re-usable
frac sand from a hydrocarbon well completion operation. The process includes
the steps
of extracting a slurry from a well bore of a well, the slurry including a
carrier liquid, frac
sand, and drilling mud; passing at least a portion of the slurry into a
washing facility;
washing the drilling mud off the frac sand to yield a frac sand rich
remainder; extracting
the frac sand rich remainder from the washing facility; passing the frac sand
rich
remainder through a dryer; and passing the frac sand rich remainder through a
sizing
apparatus to yield re-usable washed, dried and sized frac sand.
In an additional feature of that aspect of the invention, the step of passing
at least
a portion of the slurry into the washing facility includes a step of passing
the portion of
the slurry through an input sizing apparatus to reject oversize solids, and
then washing the
portion of the slurry, less the oversize solids. In another additional
feature, at least some
of the slurry is at least partially settled to yield a free liquid portion and
a solid rich
portion, and the process includes the step of decanting the free liquid
portion before
introducing the solid rich portion of the slurry into the washing facility.
In a further additional feature, an input sizing apparatus is mounted to
receive the
portion of the slurry, the input sizing apparatus including a reciprocating
screen. The
washing facility includes a water delivery apparatus mounted to spray water
over the
portion of the slurry and the reciprocating screen. The process includes the
steps of
passing at least the portion of the slurry through the input sizing apparatus
to reject off
spec solid material, spraying water on the solid rich portion as the solid
rich portion is
passed through the reciprocating screen.
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In a yet further additional feature, the washing facility includes a magnetic
element and the process includes the step of operating the magnetic element to
extract
ferro-magnetic particles.
In another feature, the washing facility includes a washwater supply, an
outflow,
and a settling system, the outflow being located to discharge into the
settling system. The
process includes the steps of providing washwater from the washwater supply to
wash the
drilling mud from the frac sand; and transporting at least a portion of the
drilling mud in
suspension in sand washwater through the outflow into the settling system. In
still
another feature, the process includes the steps of accumulating a sludge of
drilling mud in
the settling system and removing the accumulated sludge of drilling mud. In a
further
feature, the process may include re-using the drilling mud sludge in a down-
hole drilling
operation. In a still further feature, the outflow system includes a plurality
of settling
tanks arranged in series. A first of the settling tanks is located to receive
the discharge
from the outflow of the washing facility. A second of the settling tanks is
located to
receive a discharge from the first settling tank. A weir is located between
the first and
second settling tanks. The discharge from the first settling tank flows across
the weir, and
the process includes the step of skimming water from the settling system and
re-using at
least a portion of the water skimmed from the settling system.
In an additional feature, the process further includes the step of re-
directing at
least a portion of the water skimmed from the settling system to the washing
facility. In
another additional feature, the process further includes the step of directing
at least a
portion of the water skimmed from the settling system to an injection well.
In yet another feature, the washing facility includes a bath and a screw
mounted at
least partially within the bath, the screw being operable to urge the frac
sand rich
remainder from the bath toward the dryer. In a further additional feature, a
chute is
mounted to direct the frac sand rich remainder discharged from the screw to
the dryer,
and the process includes the stop of directing air from the dryer into the
chute.
In still another feature, a dust extraction apparatus is connected to the
dryer and
the process includes the step of directing hot air exhaust from the dryer to
through the
dust extraction apparatus. In a further feature, a cooling apparatus is
connected to receive
at least a portion of the hot, dried frac sand rich remainder from the dryer
and the process
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includes the step of passing the portion of the hot, dried frac sand rich
remainder through
the cooling apparatus. In still yet another feature, the second, or output,
sizing apparatus
includes a means for rejecting oversized particles, a means for rejecting
undersized
particles, and a discharge for "on-spec" particles and the process includes
the step of
accumulating and storing the "on-spec" particles for re-use.
In a still further aspect of the invention, there is a process for recovering
re-usable
frac sand from a hydrocarbon well completion operation. The process includes
the steps
of extracting a slurry from a well bore of a well, the slurry including a
carrier liquid, frac
sand, and drilling mud; settling the slurry to produce a free liquid portion
and a solid rich
portion; removing the free liquid portion; passing the solid rich portion
through a first
sizing apparatus to reject oversize solids; passing the solid rich portion,
less the rejected
oversize solids, into a washing facility; washing the drilling mud off the
frac sand of the
solid rich portion to yield a frac sand rich remainder; extracting the frac
sand rich
remainder from the washing facility; passing the frac sand rich remainder
through a dryer;
and passing the frac sand rich remainder through a second sizing apparatus to
yield re-
usable washed, dried and sized frac sand.
In still another aspect of the invention, there is an apparatus for re-cycling
used
frac sand. The apparatus has machinery operable to collect used frac sand, and
to
transport the used frac sand; a washing facility for washing the frac sand,
located to
receive transported frac sand; a drying facility for drying the frac sand
mounted to receive
washed frac sand from the washing facility; a sizing machine for segregating
the frac sand
from off spec material, the sizing machine being located to receive the frac
sand from the
drying facility; and a storage container for holding frac sand, the storage
container being
located to receive on-spec frac sand from the sizing machine.
In a still further aspect of the invention, there is the use for re-cycling of
frac sand
of an apparatus having machinery operable to collect used frac sand, and to
transport the
used frac sand; a washing facility for washing the frac sand, located to
receive transported
frac sand; a drying facility for drying the frac sand mounted to receive
washed frac sand
from the washing facility; a sizing machine for segregating the frac sand from
off spec
material, the sizing machine being located to receive the frac sand from the
drying
facility; and a storage container for holding frac sand, the storage container
being located
to receive on-spec frac sand from the sizing machine.
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In still another aspect of the invention there is a process for the treatment
of slurry
waste water from a well completion operation. The process includes the step of
extracting a slurry from a well bore. The slurry includes at least an aqueous
liquid, and
solids suspended in the liquid; the solids including sand; iron in at least
one form chosen
from the set of: (a) iron in solution in the aqueous liquid, and (b) iron
particles suspended
in the aqueous liquid amongst other solids. The process further includes the
steps of
separating the aqueous liquid from at least the majority of the solids by
using a
mechanical separation apparatus to produce a remainder including at least some
of the
aqueous solution and some of the iron; converting at least some of the iron in
the
remainder to a compound form; mechanically filtering the remainder to remove
iron
particles from suspension to produce a treated output solution; mixing the
treated output
solution with a solution of re-cycled hydrocarbon field production water; and
re-injecting
the mixture of the treated output solution and the re-cycled hydrocarbon field
production
water into a hydrocarbon producing stratum.
In an additional feature of that aspect of the invention, the step of
converting
includes adding citric material to the remainder.
These and other aspects and features of the invention may be understood with
the
assistance of the Figures and description as provided hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a plan view of a sand recovery installation according to the
present
mvent><on;
Figure 2A is a first portion of a pictorial schematic diagram of the sand
recover
installation of Figurel;
Figure 2B is a second portion of a pictorial schematic diagram of the sand
recover
installation of Figurel;
Figure 2C is a third portion of a pictorial schematic diagram of the sand
recover
installation of Figurel;
Figure 2D is a fourth portion of a pictorial schematic diagram of the sand
recover
installation of Figurel; and
Figure 2E is a fifth portion of a pictorial schematic diagram of the sand
recover
installation of Figurel; and
Figure 3 shows a block diagram representation of a process employing the
installation of Figure 1.
Detailed Description Of The Invention
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The description which follows, and the embodiments described therein, are
provided by way of illustration of an example, or examples of particular
embodiments of
the principles of the present invention. These examples are provided for the
purposes of
explanation, and not of limitation, of those principles and of the invention.
In the
description which follows, like parts are marked throughout the specification
and the
drawings with the same respective reference numerals. The drawings are not
necessarily
to scale and in some instances proportions may have been exaggerated in order
more
clearly to depict certain features of the invention.
Figure 1 shows a plan view, or map, of a frac sand recovery installation,
indicated
generally as 20. It is located some distance from a well field 22 from which
frac sand is to
be recovered. A battery of wastewater injection wells 24 is also located some
distance away
in an old, existing producing well field, 23 (Figure 2B). Old, exiting
producing wells are
indicated as 25. A road 26 links installation 20 with well field 22 and
injection wells 24. A
pipe system 28 also links injection wells 24 and frac sand recovery
installation 20.
Operation of the frac sand recovery installation 20 is controlled and directed
from a
control trailer, 21. Describing installation 20 in the order in which material
would be
processed, input material arnves at the site of sand recovery installation 20
by truck 30. The
material is generally obtained in one of two ways.
First, well 32 in producing field 22 has been subject to a well completion
treatment
to introduce frac sand. That is, well 32, typically being a new well, has been
pressurised to
open cracks in the adjacent mineral bearing stratum. Frac sand has been mixed
with a gel
carrier, and has been introduced under pressure into well 32, and forced under
pressure into
the cracks and fissures of the adjacent stratum. Then the pressure in the well
has been
reduced to its previous level. The Garner has reverted to a liquid form, and
has drained back
into the well, leaving the majority of the frac sand in place as a proppant to
keep the cracks
open. The remainder of the frac sand, the liquid carrier, and other matter,
such as drilling
mud with any metal shards or particles abraded from the drill string, collect
in the well bore
sump. The material from the well bore has been collected by producing it from
the well
using collection apparatus in the nature of pumps and collection tanks as may
be suitable,
and transferred to the frac sand recovery site using transport machinery such
as truck 30.
Truck 30 is most typically a vacuum truck for transporting the collected
material in the form
of a slurry.
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Second, the collected material may have been recovered from an old pit or dump
34.
That is, formerly, the slurry produced from wells after introduction of
proppant has usually
been produced from the well, and then discarded, typically being collected at
the well head
and then discharged into a pit or dump 34 from which the liquid eventually
evaporates or
drains away. As the opportunity to re-cycle potentially valuable frac sand is
made available,
the formerly discarded material can be mined from existing dump sites.
Material collected,
such as by mining from a dump site, can be transported in either vacuum truck
30 if wet, or
in a gravel truck 36 if drained, as may be appropriate. While preferred, it is
not necessary
that the free water be drawn off. Decanting off the free water first may tend
to reduce the
quantity of liquid poured into the bins noted below.
If the material to be treated arrives in a vacuum truck 30, as is most
typical, it will
generally have settled during the trip, and vacuum truck 30 may be equipped
with a
vibration unit to enhance this settling. This may result in a first portion of
the water, or
watery liquid, in vacuum truck 30 forming a layer of "free water" from which
the solids
have settled out. As such, as a preliminary optional step, the free water is
decanted off the
slurry in vacuum truck 30 to a sloop tank 38. This leaves a first remainder in
truck 30, the
first remainder including the solids and the balance of the liquid remaining
after the free
water has been decanted off. The free water from well 32 may tend typically to
be a salty
chloride brine with iron in solution, or possible an amount of very fine iron
particles in
suspension.
Sloop tank 38 is a semi-buried open top tank having a liner - that is, tank 38
is
equipped with an external secondary containment liner and has a monitoring
well 40 placed
at one end of the tank. Monitoring well 40 can monitor the interstitial space
42 between the
tank and the liner. Water collected in sloop tank 38 can be removed for
treatment elsewhere,
can be directed into the wash-water system described below, or can be used
elsewhere for
other purposes, as may be permitted, or may be discarded in an approved
manner.
Once the free water has been removed, the solids rich remainder of the
material in
the vacuum truck 30 (or the material in gravel truck 36, as may be) is weighed
at weigh scale
44, adjacent to scale control trailer 45, and emptied at either of a pair of
first and second
offload pits 46, 48. Offload pits 46, 48 are also semi-buried tanks that each
have a
secondary containment liner and a leak detection system in the nature of an
interstitial
monitoring well, also indicated as 40, as noted above. Pits 46, 48 (i.e., the
semi-buried
tanks) are sloped to prevent any free fluids from running out. A monitoring
well 40 is again
positioned at the low point to permit effective leak detection. Truck 30, (or
36, as may be),
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now empty, is re-weighed, and the difference between the full and empty
weights calculated,
that difference being the weight of wet sand material deposited in the offload
pit.
The material from offload pits 46, 48, is transported to an inlet hopper 52 of
the
washing facility, indicated generally as 50. Transport may be by a conveyor
or, as in the
preferred embodiment, by a front-end loader 54.
A conveying device in the nature of a rotating sand screw, or auger 56 feeds
material
from hopper 52 onto a reciprocating (that is, vibrating) wash deck 58 mounted
above a tub
60 of washing facility 50 (Fig. 2A). In the preferred embodiment hopper 52 is
a 10' x 10'
hopper, and auger 56 is a 24 inch sand screw. A wash water delivery system 62
includes
nozzles or water jets 64 located to direct an inflow of wash water against the
solids rich
material fed from auger 56 onto wash deck 58. The wet material, and the wash
water, fall or
drain, through a '/2 inch grid screen 66 of wash deck 58, and into tub 60.
Oversized material
rejected by screen 66 such as stones inadvertently included in material
recovered from old
storage pits is discarded through a discharge chute to an oversize bin 68. Bin
68 is
periodically emptied as required.
Tub 60 has two exits. The first exit is by an inclined dehydrating screw 70,
described below. The second exit is by an outflow passage 72 leading to a
settling system in
the nature of a three compartment, high level overflow rig tank 74 (Fig. 2B).
Tub 60 has a
high level weir 71 leading to passage 72. Rig tank 74 has a series, or set, of
weirs 76 and 78
of decreasing height. Although two such weirs are shown, a greater number
could also be
used. There are respective settling, or low velocity, zones 80, 82, 84, in
each of the three
compartments, in which a sludge of heavier solid particles 67 silts out over
time. The
outflow from tub 60 may tend generally to transport away the drilling mud in
suspension,
and the resultant accretion of sludge 67 collected upstream of weirs 76, 78 in
settling zones
80, 82, 84 is largely, if not entirely, drilling mud. The collected mud is
routinely removed
from each of the three compartments.
The wash water is recycled through rig tank 74, on average, up to about four
times.
That is, the ratio of the flow through re-circulation pump 75 and re-
circulation line 77 from
the most downstream settling zone, namely zone 84, back to washing tub 60 is
about four
times as great (+/-) as the flow out through pump 85 and pipes 86. The wash
water is
skimmed off the rig tank and moved, (that is, pumped through pipes 86), into
one of three
alternately selectable waste water holding tanks, 88, 90, 92. Fines are
allowed further time
to settle in holding tanks 88, 90 and 92. While one tank is selected, waste
water is being
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settled in one or both of the others. Tanks 88, 90 and 92 are periodically
cleaned or flushed
to remove accumulated fines.
The settled wastewater is treated for downhole compatibility with additives as
shown
schematically at 87, drawn from a settled tank, whichever it may be. The
relatively clean,
treated output wastewater is then passed through a filter 89 before being sent
either to the
battery of injection wells 24 for re-injection into the mineral bearing
stratum, or for other
use, or for discard in an approved manner. The chemical additives may include
citric acid in
a soluble anhydrous powder form such as may tend to combine with the iron in
solution in
the wastewater. The quantity of citric additive is also modest, in one
embodiment being of
the order of a quart per 400 bbl settling tank. The quantity of additive
required may tend to
vary according to the condition and dilution of the waste water as received
from truck 30.
Filter 89 may typically have filter elements for trapping solid particles of
greater than 20
microns in size, the trapped material being removed at 91. The volume of water
directed to
the battery wells, or discarded, is measured and monitored for solid
precipitants.
Treated, filtered wastewater sent by pipe 24 to old producing field 23 is
mixed with
treated, re-cycled water obtained when the material produced from old well 25
is separated
into oil 95 and watei 97. The recycled water from well 25 has been treated
with biocide, and
may tend to have a somewhat sour, sulphuric acidic nature, depending on the
condition of
well 25. The mixture is then injected into well 24 under pressure, as provided
by pump 93.
Inasmuch as the metal particles tend to be predominantly, if not wholly, steel
from
the drill string, they also tend to be ferro-magnetic in nature. Metal
particle removal
apparatus, in the nature of magnetic heads 94 mounted at the outflow lip of
high level weir
71 of tub 60 and at weirs 76 and 78, where the flow is shallow, to attract the
metal particles
that may have been entrained in the slurry. Magnetic heads 94 are periodically
removed and
cleaned of accumulated metallic material.
Returning to tub 60, the second exit is by a lifting device in the nature of
inclined de-
watering screw 70 mounted within an inclined channel, or casing 73 that is
manufactured as
an inclined extension of the main body of tub 60. The sand and wash water that
fall through
screen 66 fall on dewatering screw 70 and into tub 60. Over time, the use of
the wash water
and the agitation of the sand by dewatering screw 70 tends to clean the frac
sand, such that
the sand eventually raised by dewatering screw 70 and thus extracted from tub
60 is
relatively clean frac sand.
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The wet sand discharged from the upper end of dewatering screw 70 is directed
through a chute 96 into a drying facility, namely rotating drum dryer 100 fed
from chute 96
by auger 97(Fig. 2C). In the preferred embodiment dryer 100 is 5 ft in
diameter and 40 ft
long. Dryer 100 is supplied with heated air by a burner 102. The inside of
dryer 100 has
S baffles 104 that lift and turn the sand and allow it to fall in the heated
airflow as the dryer
drum 106 turns. The incline of the dryer is such as to urge the sand gently
from the elevated
inlet end at chute 96 to the somewhat lower outlet end at burner 102 over a
period of time,
such that the sand may tend to be dry by the time it reaches the exit.
In the preferred embodiment dryer 100 operates at about 700 F. Dryer 100 is a
counter-flow dryer operating on a negative air system. That is, the direction
of the airflow,
from burner 102, through rotating drum 106, is generally in the opposite, or
counter-flow
direction to the progress of the sand that enters from chute 96. The sand
proceeds along
rotating drum 106 to a sand discharge auger 108 located adjacent to the air
inlet opening 110
1 S into which burner 102 is directed. The negative air system, rather than
blowing air into
dryer 100, draws it through dryer 100 at a negative pressure relative to
ambient, by use of an
air mover, or fan, in the nature of a centrifugal blower 112.
Blower 112 (Fig. 2D) is mounted to draw the heated air through drum 106, from
inlet 110 at burner 102, as noted above, and to extract the hot air exhaust
and entrained dust
from the end of dryer 100 adjacent to the chute 96. The air and dust extracted
are drawn first
into a large, dry cyclone 114. Settled off spec undersized sand particles and
fines are
discharged from dry cyclone 114 through a discharge chute 116 for collection
in a
receptacle, or containment bin in the nature of an above ground shale sloop
118, and either
sent to a waste management facility or reused as may be appropriate.
The air exhaust from dry cyclone 114 is drawn through ducting 113 into a wet
dust
collection apparatus, or scrubber 122. In a first portion 115 of wet scrubber
122, the exhaust
air from dry cyclone 114 is drawn downwardly through a large chamber 117 in
which it has
relatively low downward velocity. Water is drawn from a settling tank 124
through a pump
119 and piping 120 to be sprayed as a mist from an array of nozzles 121 into
the passing still
relatively warm, dry air. The now moistened air, and any unevaporated spray,
then passes
through a throat leading to a check valve 123. Check valve 123 permits the wet
air to pass
into the second portion of scrubber 122, namely a bath, 127 that is filled
with water. When
the pressure in bath 127 at check valve 123 is lower than in portion 115, the
air, and
entrained dust particles, will be drawn into bath 127, the air bubbling upward
to the surface
of the water. The water level of bath 127 is maintained by a spring loaded
release valve 129
that operates to release water from bath 127 when the internal level exceeds a
"full" height.
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The released water is returned to tank 124. Wet discharge from scrubber 122
passes through
a solid discharge chute 131 to be collected in settling tank 124. The moisture
laden air
exhaust from wet scrubber 122 is extracted through ducting 126 by blower 112
and is
discharged to the atmosphere through a stack 133.
A lifting device in the nature of a bucket elevator 128 (Fig. 2C) transports
the hot,
dry sand from the discharge of dryer 100 to the top of a cooling facility in
the nature of a
counter-flow cooling tower 130. Tower 130 has a sand inlet at the top, and a
sand discharge
at the bottom. An array of baffles 132 inside tower 130 causes the sand to
fall through the
airflow several times before reaching the bottom. Ambient, relatively cool air
is introduced
at the base of tower 130 and is drawn upward to encounter the cascading,
downward falling
sand. The air is forced out the top of tower 130 and then through a dust
collector cyclone
134 by a blower 136. The fines from cyclone 134 are collected in an open ended
tank 138,
and are disposed of in a suitable manner.
The sand leaving the bottom end of cooling tower 130 is at a moderate
temperature,
in the range of 150 F, with variation depending on the ambient temperature.
The sand
leaving through the discharge chute of cooling tower 130 falls into a
receptacle in the nature
of an open ended tank 140, where it collects. The sand is then transported to
a sizing facility
in the nature of a system of moving screens, most preferably a rotary screener
142. Rotary
screener 142 rejects remaining small stones and over spec sand. This leaves a
remainder of
washed, dried, on-spec sand that is transported by an elevator 144 to one of
four storage
receptacles in the nature of bins 146, 148, 150 and 152. This sand is ready to
be loaded by a
transport means such as movable conveyor 154 onto trucks, such as gravel truck
158,
weighed on scale 44 (empty and full, as above, to permit the difference to be
calculated) and
sent back to well completion sites for use as frac sand. The oversize, off
spec sand from
screener 142 is accumulated in a bin 156 and then transferred, typically by
truck, for landfill
or for use in sand and gravel operations more generally. Both the volume of
material stored
in bins 146, 148, 150 and 152 and the weight of material sent out from
recovery facility 20
are monitored, as for example when departing trucks 158 with clean frac sand
are weighed
empty and full. The frac sand can then be used, as described above, by mixing
with the gel
carrier, introduction under pressure into a well, and so forth.
In this system, fresh water is provided from an external source, such as a
lake or
river, and is introduced by means of a pump 160 and pipe 162 at the wet
scrubber setting
tank 124, from which it is forced by pump 61 and line 63 pumped to wash water
delivery
system jets 64, as noted above. The decanted water from sloop tank 38 is
pumped into the
first settling region, 80, of rig tank 74 by means of a pump 164 and pipe 166.
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Embodiments of the invention have now been described in detail. Since changes
in
and or additions to the above-described best mode may be made without
departing from the
nature, spirit or scope of the invention, the invention is not to be limited
to those details, but
only by the appended claims.
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