Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TELESCOPIC FRAC7NK
FIELD
[0001] This specification relates to liquid storage tanks,
particularly frac tanks, and to
hydraulic fracturing and well stimulation operations.
BACKGROUND
[0002] The following discussion is not an admission that anything
described below is
common knowledge in the field or citable as prior art.
[0003] Hydraulic fracturing, also called fracking or hydrofracking,
involves pumping
pressurized water, typically mixed with a proppant, down a well bore and into
an
underground formation. The water pushes open fractures in the formation, and
the proppant
helps keep the fractures open after the pressurized water is removed. Opening
the fractures
allows additional oil to be removed from a reservoir, or allows natural gas,
shale gas or coal
bed gas to be produced. A similar process used in more permeable reservoirs
may be
referred to as well stimulation, but for the purposes of this specification
well stimulation will
be included in the term hydraulic fracturing unless discussed separately.
[0004] A hydraulic fracturing site requires tanks, typically called
"frac tanks", sufficient
to store large volumes of water. The volume of water required may range from
roughly
50,000 gallons for a well stimulation operation to one or two million gallons
or more for a
high-volume hydraulic fracturing operation. After the fracturing operations,
used frac water
(alternatively called blowback or brine) needs to be stored in the frac tanks
until it can be
treated for discharge or re-used. The frac tanks must be transported to the
site, set up, and
later removed. The site may be a remote lease, beyond the reach of ordinary
roads. The
lease, and particularly the prepared drilling pad area of the lease, is often
barely larger than
the frac tanks and other equipment used on the site, with large vehicles
moving about the
site.
[0005] A standard rectangular frac tank is a 21,000 gallon (500
barrels) steel walled
tank. These tanks are roughly 45 feet long, 8 or 9 feet high, and 10 or 11
feet wide. These
tanks often have a rear axle which allows them to be moved by a fifth wheel
tractor truck.
Some examples are shown in US Patent Application Publication 2011/0186581 and
US
Patent 7,997,623 B2. At the site, these tanks are placed on a mat foundation
typically made
of squared timbers bolted together.
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[0006] Another type of tank is an inflatable bladder, or pillow
tank. These tanks may
be a few feet high, with various lengths and widths. The bladder is
transported in a deflated
state on a truck. At the site, a thick membrane is placed on the ground to
cover sharp spots
in the earth and the tank is folded out over the ground cover membrane.
[0007] A third type of tank is a round surface tank. These tanks are made
by
fastening many steel panels together to form a ring on the ground over a
ground covering
membrane. The seems between the panels are not watertight to each other or the
ground
and a second membrane is installed in the ring to contain the water. The tanks
may be up to
11 feet high and over 100 feet in diameter, with capacities ranging from about
10,000 to
40,000 barrels.
[0008] A fourth type of tank is a cylindrical 400 barrel tank of
about 12 feet in
diameter. This type of tank has skid rails on its bottom and along one side.
The skid rails
allow the tank to be transported on a winch truck. The tank is transported to
the site on its
side, balanced on the rear roller for placement at the site, and then tipped
to stand vertically
on a mat foundation. The need to tip the tank up during unloading, and to pull
the tank back
down on reloading, requires a skilled driver and limits the height of these
tanks to about 20
feet.
[0009] The choice between frac tanks is influenced by trucking
costs, set up time, site
constraints and safety. In many remote areas, such as Northern Alberta, there
are no proper
roads to the site and the work must be done in the winter when the ground is
frozen. The
cost of transporting a 400 barrel cylindrical tank from Calgary to Fort
McMurray is about
$5,000 in 2012. Shipping costs for standard rectangular frac tanks are
similar. Since up to
100 of these tanks may be required for a large frac operation, the trucking
costs are
significant. Further, cylindrical and rectangular tanks must often be placed
on the drilling pad
essentially one at a time to give room for the truck movements required to
unload a tank.
This increases the set up time required, particularly for the cylindrical
tanks which require a
multi-step unloading and tip up procedure. The cylindrical 400 barrel tanks
are higher than
standard rectangular tanks, but they do not double the liquid storage per unit
area of ground
covered because cylindrical tanks inherently do not cover the ground as
efficiently as
rectangular tanks, and some clearance room is required for tipping the
cylindrical tanks in
place.
[0010] Pillow tanks can be moved by smaller trucks but they must be
unfolded on
site, they occupy a large land area per unit volume, and the membrane is
directly exposed to
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the environment and UV degredation. Fear of leaks makes these tanks unpopular,
particularly for use in holding brine. Brine can cause more environmental
damage than un-
used frac water if there is a spill.
[0011] Round surface tanks can hold large volumes of water, but they
require many
hours of high priced on-site labour to fasten the panels together and, for
very large tanks, to
weld membrane pieces together. The large size of these tanks helps to
efficiently cover the
ground by avoiding spaces between multiple tanks, but this is offset by the
circular shape
which creates unusable spaces in the corners of the site. The size of the tank
also inherently
increases the risk that a tank failure, caused for example by a truck hitting
the tank wall,
could cause environmental harm. Another disadvantage is that these tanks have
no drain
ports. The tanks must be filled and emptied by siphon tubes over the side of
the tank. This
can cause pumping problems or prevent a complete drain of the tank. Canadian
Patent
Number 2692016 describes a panel fastening system that is used by one surface
tank
manufacturer.
INTRODUCTION TO THE INVENTION
[0012] The following discussion is intended to introduce the reader
to the invention
and the detailed description to follow, but not to limit or define the claims.
[0013] A liquid storage tank described in this specification has two
or more
telescoping sections. Each of the sections may be rectangular and the tank may
be
transported, for example by truck, with its sections collapsed. When an upper
section is lifted
on site, the telescoping tank has about twice the height of a standard
rectangular frac tank.
Accordingly, the amount of space occupied on site, and the area of mat
foundation, are
approximately cut in half. Optionally, the tank may be fitted with an attached
lifting system
such that the telescoping operation involves only a small amount of on-site
labour. The lifting
system may use one or more hydraulic rams which may be mechanically pinned
after the
upper section of the tank is raised to avoid the need to maintain hydraulic
pressure.
[0014] An inflatable seal, optionally located within a boxed space
formed between
flanges and the walls of the telescoping sections, allows the telescoped
sections to contain
water. Alternatively, a membrane inside the tank unfolds when the tank is
telescoped and
contains the water. Optionally, but preferably, both containment systems are
used. In this
way, the telescoping frac tank provides a double barrier containment system
with a rugged
outer shell and a UV and impact protected inner membrane. This reduces the
risk of a leak
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allowing frac water to reach the environment. The telescoping frac tank may be
used to hold
brine. Optionally, a sensor at the bottom of the tank between the membrane and
the tank
wall allows a leak in the barrier to be detected before water leaks from the
outer walls of the
tank.
[0015] The telescoping frac tank is adapted to be transported by a winch
truck and
rolled off the bed of the truck at the site. This mode of delivery is similar
to the way in which
large skids are delivered to the site. There is no need to tip the tank, or
even to tilt the tank
onto a rear axle, and so the telescoping frac tank can be made 45 or 50 feet
long or more.
The tank may be made to the maximum size allowed for transportation through
rural Alberta.
When the upper section of the telescoping frac tank lifted, the height may be
15 or 20 feet or
more. Total volume may be 1500 or 2000 barrels or more. This is sufficient to
handle many
well stimulation operations with a single tank, and to handle high-volume
fracking operations
with a manageable number of tanks.
[0016] Because the telescoping tank is rectangular and tall, it
provides more storage
per unit land area than any of the tanks discussed in the background section.
Transportation
costs and truck movements on the drilling pad are reduced relative to typical
400 and 500
barrel tanks. The number of hydraulic connections is also reduced, while
optional large ports
of 8 inches or more in diameter allow the telescoping frac tank to be filled
and emptied
quickly.
FIGURES
[0017] Figure 1 is a side view of a frac tank in a telescoped
position.
[0018] Figure 2 is an end view of the frac tank of Figure 1.
[0019] Figure 3 is a top view of the frac tank of Figure 1.
[0020] Figure 4 is an enlarged cross-section of an inflatable seal of the
frac tank of
Figure 1.
[0021] Figure 5 is an enlarged view of a hydraulic ram of the frac
tank of Figure 1.
[0022] Figure 6 is a schematic cross-section view showing an
internal membrane of
the frac tank of Figure 1.
[0023] Figure 7 is an orthographic projection and one detailed view of a
second frac
tank in a telescoped position.
[0024] Figure 8 is a front, cross section and two detailed views of
the tank of Figure
7.
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[0025] Figure 9 is an elevation, cross-section and two detailed
views of the tank of
Figure 7.
[0026] Figure 10 is an isometric view of the tank of Figure 7.
[0027] Figure 11 is an orthographic projection and one detail view
of the tank of
Figure 7 in a collapsed position.
[0028] Figure 12 is a front, cross section and two detail views of
the tank of Figure 7
in a collapsed position.
[0029] Figure 13 is an elevation, cross-section and two detailed
views of the tank of
Figure 7 in a collapsed position.
[0030] Figure 14 is an isometric view of the tank of Figure 7 in a
collapsed position.
[0031] Figure 15 is a front view of a skid assembly for the tank of
Figure 7.
[0032] Figure 16 shows plan, elevation, cross sections and a detail
view of the skid
assembly of Figure 15.
[0033] Figure 17 is an isometric view of the skid assembly of
Figure 16.
[0034] Figure 18 is a front view of a base-plate for the tank of Figure 7.
[0036] Figure 19 is a plan, elevation and cross section of the base-
plate of Figure 18.
[0036] Figure 20 is an isometric view of the base-plate of Figure
20.
DETAILED DESCRIPTION
[0037] Figures 1 to 3 show a liquid storage tank 10, or frac tank, having a
lower
section 20 and an upper section 30. The overall length of the tank 10 is 57
feet. Its overall
width is 12'4". Its overall height in the raised or telescoped position shown
is 22 feet. Height
when collapsed is about 11'. The tank 10 holds about 370 KL of water.
[0038] The tank 10 is transported in a collapsed position with the
upper section 30
lowered and nested over the lower section 20. The upper section 30 rests on
the lower
section 20. On site, the tank 10 may be placed on a rig mat foundation. The
tank 10 has a
pair of slings 34 at each end which allow the tank 10 to be attached to a
cable. The tank 10
may be placed on a skid frame, or the bottom of the tank 10 may be reinforced
so that the
tank 10 can operate as a skid itself. The tank 10 is transported by a truck,
which may be a
tractor trailer combination, having a flat bed. Vehicles of this type may be
called a bed truck,
winch tractor, winch truck or similar names. The bed has a first roller at one
end and,
typically, a second roller part way along the length of the bed. The front of
the bed, or the
tractor, has a winch.
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[0039] The tank 10 is loaded by backing the bed of the truck up to
the end of the tank
and connecting the winch cable to the slings 34 or to a skid frame below the
tank 10.
Pulling in the winch cable first pulls the truck back towards the tank 10 and
then lifts one end
of the tank 10 up and over the first roller. The tank 10 is then moved further
on to the bed by
5 backing up the truck. When the first roller is near the middle of the
tank 10, the tank 10
pivots downwards to lie flat on the bed. A slight forward movement can soften
the fall of the
tank 10 onto the bed. The winch cable can be pulled in further to advance the
tank 10 along
the bed if the tank 10 will be transported over a long distance.
[0040] Alternatively, to move the tank 10 a short distance or
position it on a site, the
10 winch cable can be brought in by a small amount while the tank 10 is
leaning against the first
roller to balance the tank 10 on the first roller rather than dropping the
tank 10 on to the bed.
The tank 10 can be moved in this position and easily unloaded by loosening the
winch cable
until one end of the tank 10 touches the ground and then driving the truck
away.
[0041] To unload the tank 10 from a fully loaded long distance
transport position, the
truck is reversed and its brakes applied hard. The momentum of the tank 10
causes it to roll
backward on the bed. Two or three repetitions of these steps may be required
until one end
of the tank 10 travels to the end of the winch line, which is set to allow the
tank 10 to pivot on
the first roller. The tank 10 can be moved into a final position while it
balances on the first
roller. Letting the winch cable out further allows one end of the tank 10 to
contact the
ground. The truck then drives ahead to complete unloading the tank 10.
[0042] Referring to Figures 1 to 4, the bottom of the upper section
30 of the tank 10
has an opening that is defined by an upper section flange 36. This opening is
larger than the
outside of lower walls 44 of the lower section 20 except at a lower section
flange 38. The
ends of the flanges 36, 38 have bushings or wheels 40 made of a slippery
plastic such as
Teflon T" or a high molecular weight plastic. The bushings 40 of the upper
section flange 36
bear against the outside of lower walls 44. The bushings 40 of lower section
flange 38 bear
against the inside of upper walls 46. The bushings 40 help the sections 20, 30
move relative
to each other when the upper section 30 is raised or lowered.
[0043] The flanges 36, 38 also help to contain an inflatable seal 42
between an outer
surface of the lower section 20 and an inner surface of the upper section 30.
The inflatable
seal 42 expands when filled with compressed air to seal between the flanges
36, 38,
between the lower walls 44 and upper walls 46, or both. An air inflation valve
is closed when
the seal 42 has been inflated to a suitable pressure. Suitable inflatable
seals 42 are sold, for
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example, by Mechanical Research & Design Inc. under the Sea!fast trade mark.
These seals
are made from durable elastomer extrusions and can provide a pressure tight
closure to 500
psig. The seal 42 prevents water from leaking between the upper section 30 and
lower
section 20.
[0044] The upper section 30 may have an open top, but it is preferably
covered with
a roof 48. The roof 48 provides strength for the upper section 30. The roof 48
also isolates
the contents of the tank 10 from UV radiation and reduces chemical transfers
between the
inside of the tank 10 and he environment. One or more vents 50 are provided in
the roof 48
to allow the tank 10 to be filled and emptied. One or more hatches 52 are
provided in the
roof 48 to allow for repairs and servicing.
[0045] The tank 10 is filled and emptied through a port 54 at the
bottom of one end of
the tank 10. The port 54 connects a flange 56 with the inside of the tank 10,
or the inside of
bladder 70 (see Figure 6) if one is used. The port 54 may be a section of pipe
with a
diameter of 8" or more. The flange 56 is configured to be bolted to a header
(not shown).
The header is a pipe, preferably with a diameter of 12" or more. The port 54
is preferably
located at an end of the tank so that the port 54 is exposed when several
tanks 10 are
arranged side by side in a row.
[0046] Referring to Figure 5, hydraulic rams 34 are placed at the
four corners of the
tank 10. Optionally, additional rams 34 may be placed along the length of the
tank 10. The
rams 34 are driven by a hydraulic compressor, which is typically available on
site for other
purposes. A lower end of the ram 34 is attached to a base 60 extending
outwards from
below the floor 62 of the lower section 20. An upper end of the ram 34 is
attached to the side
of the upper section 30. Alternatively, mechanical or electrical lifting
columns may be used.
[0047] The rams 34 are preferably linked to a controller (not shown)
which is further
linked to position sensors in each ram 34. The controller monitors the
position of each ram
34 and adjusted the flow of hydraulic fluid to the rams 34 as required to have
them rise or
lower at equal rates. This reduces binding of the upper section 30 against the
lower section.
When the upper section 30 has been fully raised, one or more pins 64 are
inserted through
part of the ram 34 to maintain the ram 34 in an extended position when
hydraulic pressure is
removed. The inflatable seal 42 is then inflated and closed to maintain a seal
between the
upper section 30 and the lower section 20. The rams 34 may be welded to the
tank 10.
Optionally, quick connect fittings may be provided on the rams 34 and tank 10,
and a set of
portable rams 34 may be moved from tank 10 to tank 10 as required. In this
case, pins are
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inserted into sockets in the lower section 20 at the bottom of the upper
section 30, or posts
are inserted between the base 60 and the upper section 30, to support the
upper section 30
when the rams 34 are removed.
[0048] The tank 10 is constructed primarily of carbon steel.
Optionally, the tank may
be galvanized or epoxy coated to inhibit rusting. Further, referring to Figure
6, an optional
bladder or membrane 70 within the tank 10 can be used to prevent corrosive
chemicals from
contacting the metal of the tank 10.
[0049] The bladder 70 also creates a second containment barrier
preventing water
from leaking from the tank. Either of the bladder 70 or the inflatable seal 42
may be used to
hold water within the tank 10, but it is preferable to use both to provide a
double wall
containment system. Further, a water sensor 72 may be added near the bottom of
the tank
10 to send an alert if water appears between the bladder 70 and the inside of
the tank 10. In
this way, a leak in the bladder can be found and fixed before any water 10
leaks from the
tank 10 as a whole. Optionally, the water sensor 72 may be connected to a
pressure guage
on the inflatable seal 42 to send a further alert if the seal 42 is not at its
required pressure
when a leak is detected, or to run a pump that adds air to the inflatable seal
42 through a one
way valve if a leak is detected.
[0050] All structural reinforcing, such as corrugation or bracing,
is preferably built on
the outside of the tank 10. The inside surfaces of the tank 10 can therefore
be kept smooth
to reduce stresses on the bladder 70. The bladder 70 is held in position in
the tank 10
primarily by a supporting frame 74 bolted to the roof 48 of the tank 10
through holes with
grommets in the bladder 70. Optionally, additional straps 76 between the
outside of the
bladder 70 and the inside of the tank 10 may be added to reduce wrinkles in
the bladder 10
as the tank is emptied or filled. The frame 74 may end inside of the inner
surfaces of the
lower section 20. In this way, when there is no water in the upper section 30,
the bladder 70
will drape into the lower section 20 rather than resting on the lower section
flange 38. This
prevents the bladder 70 from being pinched between the lower section flange 38
and the
inside of the upper section walls 46 when the upper section 30 is lowered. The
frame 74
also surrounds openings in the top of the bladder 70 corresponding with the
hatches 52.
[0051] The bladder 70 is made of a flexible geomembrane material that is
resistant to
any chemicals expected to be in the liquid stored in the tank 10. The bladder
70 does not
need to be UV resistant if the tank 10 has a roof 48. Suitable materials
include low density
polyethylene (LPDE), high density polyethylene (HPDE) and polyvinyl chloride
(PVC).
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Another suitable material is linear low density polyethylene (LLDPE) as used
in Enviro Liner
4000TM liners sold by Layfield Environmental Systems Corp. The bladder 70 may
be about
0.5 to 1.0 mm thick,
[0052] Figure 7 to 20 show another tank generally similar to tank
10. As shown in
detail D on Figure 9, rollers are not required in the seal between the two
parts of the tank.
Optionally, a non-inflatable seal may be used. As shown in Figures 18-20, the
tank may
have a base plate with sloping sides and a drainage channel leading an inlet
nozzle. As
shown in Figure 15 to 17, that tank may be combined with a skid assembly.
[0053] The tank 10 described in Figures Ito 6 and the tank of
Figures 7 to 20 are
intended to provide examples of embodiment of the claims, and to help provide
an enabling
disclosure of the claimed inventions, but the claims are not limited to the
tank 10 of Figures 1
to 6 or the tank of Figure 7 to 20.
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