Note: Descriptions are shown in the official language in which they were submitted.
CA 02508953 2005-06-O1
Agent File No. 282.2
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,
as 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
so 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.
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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
proppant, such as sand, is preloaded into one or more high-pressure
cylindrical
s vessels, and such proppant is delivered into a fluid stream, such a N2 gas
stream, via a screw auger arrangement 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
so 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.
is 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.
2o 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.
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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
s pressure injection proppant system ("HIPS") according to a preferred
embodiment of the present invention, showing the 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;
1o Figure 3 is a plan view of the rig and system of fig.2;
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 an alternate embodiment of
the system of the present invention, in operating mode;
is Figure 7 is an elevational side view of the system of fig.6; and,
Figure 8 is a plan view of fig.6 with the front portion of the rig omitted.
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LIST
OF REFERENCE
NUMBERS
IN DRAWINGS
high-pressure injection proppant
system
12 trailer
14 truck
s 15 hydraulic wet kit
16 axles of 12
18 wheels on 12
proppant bulk storage tank
22 low-pressure blower pump
io 24 first low-pressure air line
26 second low-pressure bulk load line
28 surfactant storage and pumping
assembly
delivery tubing for 28
32 hydraulic lift cylinders
is 34 pivots
36, 36a,
36b
pressure
gauges
38 densometer
pressure vessels)
42 outer wall of 40
20 43 reinforced portion of 42
44 inner chamber of 40
46 first vessel inlet for proppant
48 first/top end of 40
second vessel inlet/outlet
2s 52 first vessel outlet
53 flange of 52
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54 screws)
56 radial inlet of 54
57 radial outlet of 54
58 motor of 54
s 60 piping arrangement
61 high-pressure fluid stream
62 first inlet of 60
64 first (Y) diverter
66 first fluid stream
so 68 second fluid stream
70 venturi-type orifice
72 first outlet of 60
74 second (four way) diverter
76 first fluid sub-streams
is 78 second fluid sub-stream
80 piping
82 first valves of 60
84 third (T-shaped) diverter
86 third fluid sub-streams
ao 87 fourth fluid sub-streams
88 second valves
90 third valves
92 piping
94 Y-joint
2s 96 pressure vessel isolation
valve
98 upstream injection port
99 downstream injection
port
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130 delivery line of second embodiment
140 pressure vessels) of second embodiment
142 outer wall of 140
144a first inner chamber of 140
s 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
158 motor of 154
160 piping arrangement of second embodiment
162 inlet
166 first fluid stream
167 Y-shaped diveter
168 second fluid stream
170 orifice
zo 183 first valves
190 pressure relief valve
192 piping
196 isolation valves)
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DESCRIPTION OF PREFERRED 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 preferred embodiment of the present invention. The
s system is mounted on a carrier, which in the preferred embodiment is 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
io like. However, 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
is quantities may be 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
so 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), an important 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 the 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
1o 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.
1s 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
2s 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
is 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 78 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
to 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 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 used to
2o 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
2s 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
2o valve 196 to rejoin the second fluid stream 168 moving to the first piping
outlet
172.
This system is not preferred over the first preferred 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
2s third 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
preferred embodiment.
The operation and advantages of the present invention may now be better
understood. For illustrative purposes it will be assumed that nitrogen and a
form
s of sand are to be pumped into a coal formation. In the preferred 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
1s 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
2s 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
io 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
2s 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:
so 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 proppants;
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.
The above description is intended in an illustrative rather than a restrictive
sense, and variations to the specific configurations described may be apparent
zo 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 vessel 42, or three or more vessels 42, in the
present system, but they will present certain disadvantages. If the capacity
of
2s 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.
In the
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latter case it is believed that the third vessel would be redundant and be
cost
inefficient.
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