Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02549226 2006-06-O1
Agent File No. 282.4
TITLE: HIGH-PRESSURE INJECTION PROPPANT SYSTEM
s FIELD OF THE INVENTION
The present invention relates generally to systems for injecting
substances into underground formations, and in particular relates to novel
systems and methods of combining fluids and proppant under high-pressure,
and for injection of the resultant fluid stream into formations such as coal
beds.
BACKGROUND OF THE INVENTION
The Horseshoe canyon coal formations in Alberta have been difficult to
stimulate for coal bed methane production. These formations have been through
a plethora of conventional stimulation treatments, ranging from foams to
is crosslink polymers. Due to the nature of the low reservoir pressures of
these
coal formations, or seams, and their sensitivity to damage by conventional
stimulation fluids (defined herein as a liquid and/or gas), stimulation fluid
recovery becomes almost impossible. The only other economically viable
choices appear to be straight C02 or N2 gas injection. High rate N2 gas
injection
2o technique is a common practice in North American coal bed methane exploited
plays, and C02 is used as a flood medium.
Although using C02 gas to stimulate a formation works fine, it has certain
drawbacks, including:
1. Costly treatments; and,
zs 2. C02 does not clean up quickly, and since water is commonly produced
during stimulation, it will turn into carbonic acid which is extremely hard on
surface production manifolding.
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Using N2 gas works the same way all fluids do to stimulate a formation,
although extremely high rates are required to create enough stress to overcome
the natural formation mechanics and actually fracture, or "frac", the
formation.
s Enhanced conductivity of a formation relies on the effect of hysteresis,
namely
when the frac faces come back together under stress, that these faces will not
heal back to their original orientation. It would be desirable to use proppant
(e.g.
a sand or orther suitable materials) to hold the fractured, or "fraced", faces
apart
as used in conventional frac theory. However, the problem with this is that N2
is
1o pumped as a gas and will not suspend or carry proppant as do conventional
fracturing fluid systems.
What is desired therefore is a novel method of fracturing, or "fracing", a
target formation (such as a coal or shale formation) using gases and
proppants,
and a novel system for mixing such gasses and proppants in a manner that
is would result in an "impregnated" fluid stream suitable for such fracing.
Preferably, the method and system should be capable of combining N2 gas and
a proppant material, such as sand, to produce a suitable fluid stream for
fracing
a coal formation. The method and system should further provide for
introduction
of surfactants to the fluid stream to further enhance the performance of the
zo proppant in the target formation.
SUMMARY OF THE PRESENT INVENTION
According to the present invention, there is provided in one aspect a high
pressure injection proppant system (also referred to as "HIPS") in which
zs proppant, such as sand, is preloaded into one or more high-pressure
cylindrical
or spherical vessels, and such proppant is delivered into a fluid stream, such
a
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N2 gas stream, via an arrangement, such as a screw auger, which meters the
proppant volumes and rates into the fluid stream.
In another aspect the invention provides two vessels operationally
mounted in parallel which can function separately or concurrently depending on
s the demand for proppant in a particular formation. When operated seperately,
one vessel can be in use for fracing a formation while the other vessel is
isolated, de-pressurized and reloaded with proppant via a pneumatic bulk
proppant system. The other vessel is then ready for operation when the first
vessel is depleted of proppant.
so In yet another aspect the invention provides for the injection of
surfactants
(i.e. chemicals or like substances) into the fluid stream to enhance the
performance of the proppant, to aid in the placement of the proppant into the
fracture network, and to demote proppant flowback during production and
embedment.
15 In another aspect the invention provides a high-pressure injection
proppant apparatus comprising:
at least one pressure vessel;
means for filling the vessel with proppant;
means for delivering a fluid containing nitrogen gas to the vessel and
2o pressuzing the vessel therewith; and,
a metering arrangement operatively coupled to the vessel and in fluid
communication therewith for metering the proppant from the pressurized vessel
into a fluid stream containing nitrogen gas for delivery to a target
formation.
In yet another aspect the invention provides a method of injecting
2s proppant into a target formation comprising:
providing at least one pressure vessel and a metering arrangement
operatively coupled to the vessel and in fluid communication therewith;
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charging the vessel with proppant;
pressurizing the vessel with a fluid containing nitrogen gas; and,
operating the metering arrangement to meter the proppant from the
pressurized vessel into a fluid stream containing nitrogen for delivery to the
s target formation.
Further, the system of the present invention can be operated manualy or
by computer automation to aid in the accuracy of mixing of the components of
the fluid stream.
io BRIEF DESCRIPTION OF THE DRAWING FIGURES
Embodiments of the invention will now be described, by way of example
only, with reference to the accompanying drawings, wherein:
Figure 1 is an elevational side view of a mobile carrier carrying a high-
pressure injection proppant system ("HIPS") according to a first embodiment of
is the present invention, showing the cylindrical pressure vessels of the
system in a
reclined transportation mode;
Figure 2 is a view of the system of fig.1 with the pressure vessels in an
elevated operating mode;
Figure 3 is a plan view of the rig and system of fig.2;
zo Figure 4 is an elevational end view of the rig and system of fig.2;
Figure 5 shows the system of fig.4 in isolation, with the rig omitted;
Figure 6 is a view similar to fig.4, but shows asecond embodiment of the
system of the present invention, in operating mode;
Figure 7 is an elevational side view of the system of fig.h;
2s Figure 8 is a plan view of fig.h with the front portion of the rig omitted;
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Figure 9 is a perspective view, from the rear, of a third preferred
embodiment of the system of the present invention showing a pair of spherical
pressure vessels mounted on a mobile trailer;
Figure 10 is an elevational side view of the system of fig.9;
s Figure 11 is a perspective view, from the front, of a fourth embodiment
similar to the third embodiment, but having a single spherical pressure
vessel;
Figure 12 is an elevational side view showing the vessel and piping of
fig.11 in isolation;
Figure 13 is an elevational side view from the right side of fig.12;
so Figure 14 is an elevational side view from the opposed back side of fig.12;
Figure 15 is an elevational side view from the left side of fig.12; and,
Figure 16 is a plan view from the top of fig.12.
LIST OF REFERENCE NUMBERS IN DRAWINGS
is 10 high-pressure injection proppant system
12 trailer
14 truck
15 hydraulic wet kit
16 axles of 12
20 18 wheels on 12
20 proppant bulk storage tank
22 low-pressure blower pump
24 first low-pressure air line
26 second low-pressure bulk load
line
zs 28 surfactant storage and pumping
assembly
30 delivery tubing for 28
32 hydraulic lift cylinders
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34 pivots
36, 36a,
36b
pressure
gauges
38 densometer
40 pressure vessels)
s 42 outer wall of 40
43 reinforced portion
of 42
44 inner chamber of 40
46 first vessel inlet
for proppant
48 first/top end of 40
50 second vessel inlet/outlet
52 first vessel outlet
53 flange of 52
54 screws)
56 radial inlet of 54
is 57 radial outlet of 54
58 motor of 54
60 piping arrangement
61 high-pressure fluid
stream
62 first inlet of 60
zo 64 first (Y) diverter
66 first fluid stream
68 second fluid stream
70 venturi-type orifice
72 first outlet of 60
zs 74 second (four way) diverter
76 first fluid sub-streams
78 second fluid sub-stream
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80 piping
82 first valves of 60
84 third (T-shaped) diverter
86 third fluid sub-streams
s 87 fourth fluid sub-streams
88 second valves
90 third valves
92 piping
94 Y-joint
96 pressure vessel isolation valve
98 upstream injection port
99 downstream injection port
130 delivery line of second embodiment
140 pressure vessels) of second embodiment
is 142 outer wall of 140
144a first inner chamber of 140
144b second inner chamber of 140
144c third inner chamber of 140
145 first bottomopening of 144a
146 first vessel inlet
147 second top opening of 144a
150 second vessel inlet
152 bottom vessel outlet of 144c
154 screws) of second embodiment
2s 158 motor of 154
160 piping arrangement of second embodiment
162 inlet
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166 first fluid stream
167 Y-shaped diveter
168 second fluid stream
170 orifice
s 183 first valves
190 pressure relief valve
192 piping
196 isolation valves)
220 proppant storage tank
228 storage and pumping assembly
231 lower legs
240 spherical pressure vessels)
254 sand screw
280 valves
is 311 retractable arms
326 proppant supply line
327 proppant supply valve
340 pressure vessel
341 cap
zo 346 proppant supply valve
350 top fluid inlet port
354 screw/auger
357 auger outlet
358 drive motor and seal
assembly
2s 360 piping arrangement
361 high pressure fluid streamline
364 first fluid diverter
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372 outlet
374 second fluid diverter
376 fluid auger by-pass
line
380 piping for fluid by-pass
s 382 fluid by-pass line
valve
388 top fluid supply valve
390 vent valve
391 cap for vent line
393 purge valve
io 394 y-joint (auger outlet
by-pass)
395 choke
396 auger outlet valve
399 surfactant inlet
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DESCRIPTION OF EMBODIMENTS
Reference is first made to figures 1 to 3 which show a high-pressure
injection proppant system, or "HIPS", (generally designated by reference
numeral 10) according to a first embodiment of the present invention. The
s system is mounted on a carrier, which is preferably a wheeled trailer 12
adapted
to be pulled by a motorized vehicle, or truck 14. It will be understood that
the
carrier may take various alternate forms, namely the trailer may itself be
self-
propelled, the truck and trailer may form one non-detachable unit, the system
may be mounted on a skid for transport between sites, or the like. However,
1o since the system is extremely heavy, not all carriers will be suitable for
road
transport as prescribed load limits for roads may be exceeded. Hence, in the
present embodiment, the 24 wheeled trailer 12 is specifically designed to
remain
within such load limits (i.e. is "road legal") by having three axles 16 with
eight
tires 18 per axle. Different axle and wheel combinations and quantities may be
is equally suitable, depending on the load to be transported. Likewise, the
truck is
suitably designed to haul the trailer 12, and should include a hydraulic "wet
kit"
15 to power the system 10 on the trailer.
The preferred system 10 includes a proppant storage means in the form
of a cone-shaped tank 20 located on the trailer 12. A relatively low-pressure
2o blower pump 22, conveniently mounted on the truck 14 close to a power
source
(i.e. the hydraulic wet kit 15), communicates with the tank 20 via a first low-
pressure line 24. The pump 22 permits the bulk transfer of proppant from the
tank 20 at the front of the trailer to the two high-pressure vessels 40 at the
back
of the trailer via at least one second loading line 26 (fig.2). Although one
line 26
2s may be configured for suitable delivery of proppant, each vessel has a
designated line 26 in the present embodiment.
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The system further includes a surfactant storage and high pressure
pumping assembly 28 located on the trailer. This assembly stores one or more
surfactants for injection or "misting" (via a delivery tubing generally
indicated by
30) into the high-pressure fluid stream associated with the pressure vessels
40,
s as will be discussed later. The pumping assembly may employ as many high-
pressure surfactant pumps as required. It is noted that in alternate
embodiments, the assembly may be located elsewhere than on the trailer 12,
such as on another trailer, but must be capable of communicating with the
fluid
stream during operation for the desired misting. Likewise, the proppant
storage
1o tank 20 may be remotely located, but in communication with the vessels 40
during operation.
The surfactant referred to herein should be a chemical or like substance
for enhancing the performance of the fluid stream proppant, for aiding in the
placement of the proppant into a formation's fracture network, and/or for
is reducing proppant flowback during production and embedment. The proppant
should be any material suitable for achieving the desired fracturing, or
"fracing"
of a target formation. The preferred system of the present invention is
specifically geared toward fracing a coal formation for enhancing gas
production
therefrom, and the desired proppant is a form of sand. The use of the terms
zo "proppant", "surfactant", "front", "back" and the like is not intended to
limit the
present system's use or operation, nor the scope of the invention. Further,
when
describing the invention, all terms not defined herein have their common art-
recognized meaning.
Referring now as well to fig. 4 (showing the trailer 12) and fig. 5 (omitting
zs the trailer), a particular aspect of the system is the arrangement at the
back of
the trailer which has a means for directing/diverting a high pressure fluid
stream
61 into the pair of pressure vessels 40 operationally arranged in parallel,
and a
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means for metering/feeding proppant into the fluid stream. Specifically, a
piping
arrangement 60 below the vessels 40 has a first inlet 62 for receiving a
desired
fluid. In a preferred embodiment that fluid is nitrogen gas pumped under high
pressure from a nitrogen source, such as a pumper truck. A first Y-shaped
s diverter 64 downstream of the inlet splits the incoming nitrogen 61 into
first and
second fluid streams 66, 68 respectively. An adjustable venturi-type orifice
70
downstream of the diverter 64 is adapted to create a pressure drop, say in the
range of 300 psi (or other desired amount), in the second fluid stream 68
passing
therethrough. The orifice 70 should have the effect of diverting more volume
of
so fluid into the first stream than the second stream, and for maintaining a
positive
fluid pressure in the screws) 58, as will become apparent later. The second
fluid stream 68 then proceeds under relatively lower pressure toward a first
outlet
72 for discharge to a coiled tubing rig or like apparatus in communication
with the
target formation.
is A second four-way diverter 74 downstream of the diverter 64 allows the
first fluid stream to split again into first and second fluid sub-streams 76
and 78
respectively. Elongate piping 80 carries the second sub-stream 78 toward the
top of the vessels, while the first sub-streams 76 are directed to the bottom
of the
vessels through respective first valves 82. If only the left vessel is
operating,
2o then only the left valve 82 (as viewed in fig.5) is open for fluid entry,
and the right
valve 82 is closed, and visa versa. If both vessels are operating, then both
valves 82 should be open. A third T-shaped diverter 84 further splits the
second
fluid sub-stream 78 into third fluid sub-streams 86 directed to the top of the
vessels through respective second valves 88. The diverter 84 and valves 88
zs also act as a pressure equalization manifold between the vessels 40.
Further,
the piping 80 and associated valves 82, 88 and 90 (discussed below) are used
to
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equalize the fluid pressures at the top and bottom of the vessels 40, and to
de-
pressurize the system to atmosphere when required.
Each pressure vessel 40 is formed by an elongate cylindrical tank having
relatively thick outer walls 42 (e.g. 5 inches solid steel) to accommodate the
high
s operating pressures (up to 9000 psi / 63 MPa or more). The walls form an
elongate interior cavity or chamber 44 for holding the desired proppant. The
proppant is introduced into the chamber through a first vessel inlet 46 (shown
in
fig.2) at a first top end 48 of the vessel. A second vessel inlet 50 is
provided at
the top end of each tank for entry of the respective third fluid sub-streams
86,
1o and to communicate with a respective third pressure relief valve 90 for
bleeding
pressure from the respective vessel to atmosphere prior to receiving proppant
through the proppant inlet 46. A first vessel outlet 52 at the bottom of the
vessel
allows proppant and fluid to exit the vessel's chamber 44 and to encounter the
first fluid sub-stream 76, and to then proceed to the proppant metering means.
It
1s is noted that the identifiers such a "top" and bottom" as used herein refer
to the
vessel in its generally vertically oriented operating position, as shown in
figs 2-5,
rather than when it is reclined about the pivot 34 by the hydraulic lift
cylinders 32
into its generally horizontal transport position (as in fig.1 ). The vessels
should be
reinforced at 43 where they engage the hydraulic cylinders 32 and pivots 34.
2o The proppant metering means is defined by a high pressure sand screw
54 disposed generally perpendicularly to each vessel's longitudinal centerline
and it's outlet 52. Other orientations of the screws should also be suitable.
The
screw has a flanged radial inlet 56 for attachment to a respective flange 53
of the
vessel outlet 52, and for receiving the proppant and fluid therefrom. A
variable
2s rate electric or other suitable motor 58 operates the screw to discharge,
or meter,
a desired amount of proppant through a radial screw outlet 57 into piping 92.
A
Y-shaped joint 94 allows the proppant and fluids exiting the screw 54 to enter
the
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second fluid stream 68 prior to exiting the first outlet 72. A pressure vessel
isolation valve 96 on each piping 92 upstream of the Y joint 94 operates to
isolate a respective vessel from the second fluid stream 68 as desired (e.g.
when
that vessel is inoperative and depressurized for proppant recharging), to
prevent
s fluid backflow into the vessel through the screw. Each screw may be readily
removed from the system for servicing, repair, or switching to a different
screw
size by uncoupling the flanges 53, 56 at one end, and at the other end by
uncoupling from the isolation valve 96.
The piping arrangement 60 further incorporates an "upstream" surfactant
1o injection port 98 at the first inlet 62 for introducing surfactants from
the delivery
tubing 30 into the fluid stream 61 prior to its split into the first and
second fluid
streams 66, 68. Such introduction may also be accomplished further
downstream after the fluid and proppant have been mixed, such as at a
"downstream" surfactant injection port 99 located immediately prior to the
first
is outlet 72. Both ports 98, 99 may also be used concurrently, and other ports
may
be added in the system if required.
An alternate second embodiment of the present invention is shown in
figures 6 to 8 where the screws 154 are located longitudinally within the
pressure
vessels 140. The reference numerals used in these figures are similar to those
2o used to describe the components of the system 10, with the addition of a
prefix
"1 ". Each vessel has in essence three longitudinally aligned chambers. A
first
elongate chamber 144a is defined by the vessel's outer wall 142 for holding
the
proppent received through the first vessel inlet 146 via the delivery line
130. A
pressure relief valve 190 bleeds excess pressure before filling the chamber
zs 144a. A second elongate chamber 144b is longitudinally disposed within the
first
chamber 144a in a parallel relationship, and houses the screw 154 operated by
the motor 158. The bottom end of the second chamber 144b has a first bottom
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opening 145 into the first chamber 144a to allow entry of the proppant. The
screw raises the proppant to the opposed top end where it is discharges out of
a
second top opening 147 into the open end of a hollow third chamber 144c. The
third chamber 144c is also located within the first chamber 144a and extends
s downwardly alongside the second chamber144b and opens at a bottom vessel
outlet 152 where the proppant and high-pressure fluid exit the vessel into the
piping arrangement 160.
The piping arrangement 160 is similar to the piping arrangement 60 in that
high pressure fluid, such as nitrogen gas, enters at the inlet 162 and is
divided
1o into first and second fluid streams 166 and 168 with the aid of orifice
170. The
first fluid stream is then directed to one or both vessels at the Y-shaped
diverter
167 by controlling the first valves 183. The first fluid stream enters the
bottom of
the first chamber 144a via the second vessel inlet 150. The pressurized fluid
is
urged through the proppant and up the screw where it proceeds through the top
is opening 147 and then down the third chamber 144c to exit the bottom outlet
152.
When the screw is activated to discharge proppent through the top opening 147,
the proppant is entrained in the high-pressure fluid flow and is carried down
the
third chamber 144c to the outlet 152. The fluid and proppent exiting the
outlet
152 proceed through piping 192 and the respective pressure vessel isolation
zo valve 196 to rejoin the second fluid stream 168 moving to the first piping
outlet
172.
This system is not preferred over the first embodiment for several
reasons. First, for a given size of pressure vessel, the vessel 140 holds less
proppent than the vessel 40 since internal volume is lost to the second and
third
zs chambers 144b, 144c. Second, a longer and more costly screw must be
employed in the vessel 140, and such screw is more difficult to access or
remove
than in the first embodiment. The screw 154 must lift proppent against
gravity,
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whereas the negative effects of gravity are reduced in the arrangement of the
first embodiment.
The operation and advantages of the present invention may now be better
understood, with reference to the first embodiment. For illustrative purposes
it
s will be assumed that nitrogen and a form of sand are to be pumped into a
coal
formation. In the first embodiment, the rig is brought to the work site in an
advantageous reclined transportation mode (as in fig.1 ) to avoid road
clearance
limitations. The trailer's wheel configuration is also designed to make the
rig
"road legal", despite the extremely heavy weight of the system 10.
1o The vessels 40 and associated components are then elevated into the
operating mode (fig.2) for use. If the vessel chambers 44 require charging
with
sand, then it is pumped from the tank 20 into at least one of the chambers via
the line 26 and through respective first vessel inlet 46. An advantage of this
two
vessel arrangement is that fracing may commence once one vessel is charged
is with sand. There is no need to wait for the second vessel to be filled to
begin
operations. Likewise, there is no need to disrupt ongoing operations once the
first vessel is emptied of sand since pumping may readily switch to the second
filled vessel. In the meantime, the first vessel can be refilled with sand and
be
ready for when the second vessel is emptied. In unusual circumstances where
zo the rate and volume of sand injection requires both vessels to operate
simultaneously, then operations may be disrupted periodically while the
vessels
are refilled.
Assuming that the left vessel 40 in fig.5 is charged and ready for
operation, and the right vessel is not, then the operator should isolate the
right
zs vessel by closing the first and second valves 82, 88 leading to the right
vessel,
as well as the respective (right side) isolation valve 96. Conversely, the
first and
second valves 82, 88 and the isolation valve 96 for the left vessel should be
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opened or activated. Once a high-pressure nitrogen stream 61 is established
from a nearby nitrogen truck into the first inlet 62, the orifice 70 should
provide
the necessary pressure drop and split into first and second nitrogen streams
66,
68. The first stream is then further split into the first nitrogen sub-stream
76 at
s the lower end of the vessel and into the third nitrogen sub-stream 86 which
enters the vessel at the top. The first and second valves 82, 88 control the
relative pressures of the nitrogen gas to ensure that the nitrogen moves
downwardly through the sand in the chamber 44 and does not reverse to force
the sand upwardly, particularly as the sand is being depleted in the vessel.
Both
1o gravity and the nitrogen flowing out of the vessel should urge the sand
from the
chamber 44 toward the screw 54. If the screw is not activated, the nitrogen
should seep through the porous sand and around the stationary screw blades to
escape out of the screw outlet 57. However, once the screw is activated to
carry
sand to the screw outlet 57, the sand should be carried in the fourth nitrogen
is sub-stream 87 to the (unsanded) second nitrogen stream at the Y-joint 94,
where
both streams commingle and exit the first outlet 72 to a coiled tubing rig and
ultimately to the coal formation.
If desired or required, surfactants may be introduced at either one or both
of the upstream and downstream injection ports 98, 99. Injection at the
2o downstream port 99 avoids circulation of the surfactant through the vessels
and
most of the system 10. In contrast, injection into the relatively "dry"
nitrogen
stream at the upstream port 98 will "wet" the sand in the vessels.
This nitrogen and sand combination, mixed potentially with one or more
surfactants, should enhance the stimulation of coal deposits for improved gas
zs production over prior art methods, as discussed earlier.
It is noted that pressure gauges 36 and one or more densometers 38 are
installed at selected locations in the system to monitor pressures and
proppant
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concentrations in the fluid stream exiting the system, to ensure that the
desired
volume and rate of proppant is being delivered to a particular formation. In
particular, the gauge 36a measures the manifold inlet pressure to the screw
58,
and the gauge 36b measures the manifold outlet pressure near the outlet 72. If
s the exiting fluid stream is not satisfactory, then the orifice 70 and/or the
various
described valves and/or the speed of the screws) 58 for proppant delivery may
be adjusted, either manually or preferably remotely by PLC (programmable logic
controller) systems, to obtain the desired mix/values.
Further advantages of the present invention include:
1o the system provides great flexibility for various pumping operations;
the system allows for a wide range of proppant density in the fluid stream;
the system can use various types of proppant;
the system's ability to mix proppant in the fluid stream, and in particular to
mix
sand with a N2 gas stream, provides an important means of enhancing
is production of coal bed methane sales gas;
the system is cost effective to build and operate; and,
the trailer 12 carrying the system 10 is "street" (i.e. weight) legal.
An even more advantageous third preferred embodiment of the present
system is shown in figures 9 and 10. In general, the system of this embodiment
2o in essence functions the same way as the first embodiment, except that the
vessels 240 have a spherical configuration rather cylindrical. The reference
numerals used for this embodiment are similar to those used to describe the
components of the system 10, with the addition of a prefix "2". There are
several
advantages to employing such spheres, including:
2s The sphere is a more efficient shape for confining contents under high-
pressure;
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A greater volume of proppant may be held than in a given cylindrical
configuration; and,
The spherical configuration omits the need for separate operating and
transporation modes. For holding a given volume of proppant, the sphere 240
s need not be as tall as the cylinder 40 (when elevated in an operating
position),
and so the sphere provides a more advantageous road height clearance when
mounted on the trailer. Hence, the spheres 240 are mounted in a single
orientation on the trailer for both transport and operation, and need not be
reclined for transportation nor inclined for operation as the cylindrical
vessels 40.
1o Each spherical pressure vessel 240 has a sand screw 254 located
therebeneath in a manner similar to the first embodiment, and the piping
system
for proppant and nitrogen gas delivery is also similar. However, the location
of
certain features on the trailer 212 have changed, such as placement the
proppant storage tank 220 and the surfactant storage and high pressure
is pumping assembly 228 at the rear of the trailer. Each sphere 240 also has a
plurality of legs 231 spaced about a bottom portion thereof for supporting the
sphere on the trailer, and three valves 280 at a top portion thereof for
connection
to respective piping for delivery of proppant, for delivery of nitrogen gas,
and for
venting.
2o A fourth embodiment of the invention in fig.11 shows a trailer carrying a
single spherical pressure vessel 340 which is of a similar design to the third
embodiment. Some of the reference numerals used for this embodiment are
those used to describe like components of the system 10, with the addition of
a
prefix "3". The vessel's mounting assembly differs from the previous lower
legs
2s 231 in that retractable arms 311 are employed to engage a top portion of
the
sphere to hold it on the trailer. Also, the vessel has a single cap 341 which
accesses the sphere's interior and operatively connects to the proppant and
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nitrogen gas supplies, and has a vent. Valves in either the cap, or in piping
leading to the cap, control the flow of products into the sphere, and for
venting of
the vessel. Further, the auger 354 in this embodiment is inclined for better
ground clearance. A drive motor and seal assembly 354 (shown in outline) is
s coupled to the upwardly inclined end of the auger to operate the auger.
It is noted that a configuration of a single vessel per trailer is not
preferred
as it will present certain disadvantages. If the capacity of the one vessel is
insufficient to treat a particular formation, then fracing operations will
have to be
disrupted as the vessel is refilled with proppant.
io A sample operating sequence of the fourth embodiment will now be set
out, with reference to figs.12-16 which show the vessel 340 and associated
piping 360 in isolation from the trailer. The sequence is described for one
pressure vessel, but is equally applicable to each vessel of a multi-vessel
configuration:
is Lower valves (such as the auger outlet valve 396) under the spherical
pressure vessel are closed. The sand screw, or auger 354, is off
(inoperative). The pressure vessel 340 is empty and unpressurized.
The top proppant supply and vent valves 346, 390 are opened and
proppant is blown or pumped into the vessel until nearly full.
2o The top supply and vent valves 346, 390 (capped at 391 ) are closed.
The top fluid (nitrogen) valve 388 is opened and the pressure vessel is
pressurized up to the line pressure of the main horizontal fluid line 361
running along the bottom of the trailer. In this embodiment the vessel has a
pressure rating up to about 9000 psi, and a proppant capacity of about 5
25 tonnes.
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CA 02549226 2006-06-O1
The outlet valve 396 at the end of the auger 354 is opened and the fluid
(nitrogen) bypass line valve 382 at the auger outlet is opened. This flow of
fluid (nitrogen) clears the auger outlet 357.
The auger is started to bring proppant from the pressure vessel to the
s outlet 357 of the auger.
Since the top and bypass fluid (nitrogen) valves 388, 382 are open, the
high-pressure flow of fluid (nitrogen) assists the flow of, namely helps push,
the proppant through the auger.
Once the pressure vessel is empty, the top fluid (nitrogen) valve 388 is
1o closed, then the auger 354 is stopped, then the bypass fluid (nitrogen)
line
382 is closed and then the auger outlet valve 396 at the discharge 357 of the
auger is closed.
At this point the pressure vessel is vented down to atmospheric pressure
via the vent valve 390 and/or purge valve 393 (& associated choke 395) and
15 then refilled with proppant, and the above sequence is repeated.
The fluid stream, namely all or mostly nitrogen, in the main fluid line 361
across the bottom of the trailer is pumped at very high pressure. With the use
of
in-line restrictors, a portion of the fluid stream is diverted (via the first
diverter
20 364) to the pressure vessel's top fluid inlet port 350 and to the auger
fluid by-
pass line 376 (via the second diverter 374), and another portion to the auger
outlet bypass 394, in a like manner to that shown in fig.5 for the first
embodiment. After the first diverter 364 there is an inlet 399 for the
surfactant
where it is injected at high pressure into the fluid (nitrogen) stream in the
main
zs line 361. After this injection point there is an auger outlet by-pass 394
for
discharging the proppant and combining it with the fluid stream in line 361.
The
resulting fluid stream at the outlet 372 of this line (analogous to the the
first outlet
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72 in fig.5) contains a mixture of nitrogen, suspended surfactant and proppant
for
use in a target formation.
The above description is intended in an illustrative rather than a restrictive
sense, and variations to the specific configurations described may be apparent
s to skilled persons in adapting the present invention to other specific
applications.
Such variations are intended to form part of the present invention insofar as
they
are within the spirit and scope of the claims below. For instance, it may be
possible to employ only one cylindrical vessel 42 per trailer, as in the
fig.11
embodiment, but the single vessel configurations present certain
disadvantages.
so If the capacity of the one vessel is insufficient to treat a particular
formation, then
fracing operations will have to be disrupted as the vessel is refilled with
proppant.
Likewise, three or more pressure vessels might be employed per trailer, but it
is
believed that the third vessel would be redundant, be cost inefficient, and
would
lead to weight restriction issues for the trailer. Any number of trailers with
is pressure vessels mounted thereon may be employed in series or parallel at a
given site, but capacity and cost efficiency are among the factors that will
dictate
the optimal configuration. It should also be appreciated by those skilled in
the art
that, based on the above information, other vessel shapes may also provide
suitable proppant storage and pressure capacities.
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