Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: DOWNHOLE GAS GENERATOR WITH MULTIPLE COMBUSTION CHAMBERS AND
METHOD OF OPERATION
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION:
This invention relates generally to gas generators, and more particularly to a
downhole
gas generator having multiple independently controlled combustion chambers.
DESCRIPTION OF RELATED ART:
The prior art teaches gas generators for use in oil recovery systems.
Challacombe, U.S.
3721297, for example, teaches a system for cleaning wells that includes a
series of gas
generating modules and explosive caps interconnected in a string and arranged
so that the
burning or explosion of one element of the string will, itself, initiate the
burning or
explosion of the succeeding element, thus eliminating the need for multiple
control lines.
Carr, U.S. 4382771, teaches a gas generator for use in generating electricity.
The
generator includes a linear series of combustion chambers, and each combustion
chamber
is provided with a reduced nozzle-type outlet for creating great pressures and
temperatures within the respective chambers.
Hill et al., U.S. 4633951, teaches multiple combustion gas generating units
that each use
rocket fuel type propellants disposed in a well casing. The gas generating
units are
simultaneously ignited to generate combustion gasses and perforate the well
casing.
Other references include the following: Tilmont et al., U.S. 8387692, Ryan et
al., U.S.
4558743, Fox, U.S. 4385661, Griffin et al., U.S. 20040069245, Couto, U.S.
20110000666, Tilmont, et al., U.S. 2011/0127036; Retallick, et al., U.S.
2008/0053655;
Kraus et al., U.S. 2006/0000427; and Person, U.S. 1993/5,259,341
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The prior art systems struggle to adjust the amount of gas injected so that
the formation
pressure does not fracture the formation. The prior art does not teach a gas
generator
having multiple combustion chambers that can be independently controlled, so
that the
output of gasses can be controlled to not exceed predetermined pressures. The
present
invention fulfills these needs and provides further advantages as described in
the
following summary.
SUMMARY OF THE INVENTION
The present invention teaches certain benefits in construction and use which
give rise to
the objectives described below.
The present invention provides a multiple chamber gas generator system for
generating
gasses in a borehole for use in the recovery of petroleum products. The
multiple chamber
gas generator system includes a plurality of gas generators shaped to fit
within the
borehole, each of the gas generators having an elongate combustion chamber; a
gas flow
control system operably installed for supplying gas to the elongate combustion
chambers
of each of the gas generators; and a control computer having a computer
processor, a
computer memory, and a control program operatively installed in the computer
memory.
The control program functions to control the operation of the gas flow control
system and
to selectively turn on or off each of the gas generators to regulate the
volume of gasses
being generated in response to changes in pressure within the borehole.
In another embodiment, the present invention provides a method for generating
gasses in
a borehole for use in the recovery of petroleum products. The method comprises
the steps
of providing a multiple chamber gas generator system comprising a plurality of
gas
generators each having an elongate combustion chamber. The multiple chamber
gas
generator system is positioned in the borehole, and the operation of each of
the plurality
of gas generators is controlled to selectively turn each of the gas generators
on or off, to
regulate the volume of gasses being generated in response to changes in
conditions within
the borehole.
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A primary objective of the present invention is to provide a multiple chamber
gas
generator system and method having advantages not taught by the prior art.
Another objective is to provide a multiple chamber gas generator system that
includes
multiple combustion chambers that can be independently controlled, so that the
output of
gasses into the formation can be controlled to maintain pressure within the
borehole
within a predetermined range of pressures.
Another objective is to provide a multiple chamber gas generator system that
can function
within a heterogeneous reservoir that includes areas of low permeability,
without
fracturing the reservoir.
Another objective is to provide a method for generating gasses in a borehole
that utilizes
a multiple chamber gas generator system that includes multiple combustion
chambers that
can be independently controlled, so that the output of gasses into the
formation can be
controlled to maintain pressure within the borehole within a predetermined
range of
pressures.
A further objective is to provide a method for generating gasses that is
functional within a
heterogeneous reservoir that includes areas of low permeability, without
fracturing the
reservoir.
A further objective is to provide a method for generating gasses that
optimizes the
recovery of petroleum products without fracturing the reservoir
Other features and advantages of the present invention will become apparent
from the
following more detailed description, taken in conjunction with the
accompanying
drawings, which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the present invention. In such drawings:
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FIGURE 1 is a perspective view of a gas generator according to one embodiment
of
the present invention, the gas generator having a combustion end and an
exhaust end;
FIGURE 2 is a perspective view of the combustion end of the gas generator;
FIGURE 3 is a sectional view thereof taken along line 3-3 in Figure 2;
FIGURE 4 is a sectional view similar to Fig. 3, illustrating an oxygen
injection port
and a hydrogen injection port of Fig. 3;
FIGURE 5 is a sectional view of the gas generator taken along line 5-5 in
Figure 1;
FIGURE 6 is a perspective view of the gas generator further including
additional
water injectors and annular ribs through which the additional water injectors
are mounted;
FIGURE 7 is close up of the exhaust end of the gas generator, illustrating the
restricted orifice and the additional water injectors;
FIGURE 8 is a sectional view of the gas generator operably mounted in a steam
injection tube in a borehole;
FIGURE 9 is a block diagram of one embodiment of a control system for the gas
generator;
FIGURE 10 is a top perspective view of a multiple chamber gas generator system
according to another embodiment of the invention;
FIGURE 11 is a bottom perspective view of a bottom portion of the multiple
chamber
gas generator system;
FIGURE 12 is a sectional view of the multiple chamber gas generator system,
illustrating the multiple chamber gas generator system operably mounted in the
steam
injection tube;
FIGURE 13 is a graph of gas pressure vs. mass flow rate for a single gas
generator in
a high permeability reservoir;
FIGURE 14 is a graph of gas pressure vs. mass flow rate for multiple gas
generators
in a low permeability reservoir;
FIGURE 15 is a flow chart of the operation of the multiple chamber gas
generator
system operation; and
FIGURE 16 is a close up of the exhaust end of one embodiment of the gas
generator,
wherein the gas generator includes an inline steam valve.
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DETAILED DESCRIPTION OF THE INVENTION
The above-described drawing figures illustrate the invention, a gas generator
10 for
extracting petroleum products present in an underground reservoir. The gas
generator 10
enables a method of recovering petroleum products that provides advantages.
FIGURE 1 is a perspective view of one embodiment of a gas generator 10. As
shown in
Fig. 1, the gas generator 10 includes a combustion housing 20 for containing a
combustion process which makes high-pressure steam for injection into the
reservoir.
m The combustion housing 20 may be an elongate combustion housing 20. The
elongate
combustion housing 20 includes a combustion end 22 and an exhaust end 24,
which are
described in greater detail below. The gas generator 10 burns a fuel and an
oxidizing
agent to produce the high pressure gasses that are used to extract the
petroleum products.
In the current embodiment, the fuel is hydrogen, and the oxidizing agent is
oxygen. In
the following disclosure we refer to the use of hydrogen and oxygen, but it
should be
understood that alternative fuels (e.g., natural gas, other hydrocarbons,
etc.) may be used,
and alternative oxidizing agents (e.g., ozone, hydrogen peroxide, etc.) may be
used,
according to the knowledge of one skilled in the art.
For purposes of this application, the term "petroleum products" is broadly
defined to
include any form of hydrocarbons, chemicals, and/or any other similar or
related fluids
that may be desirable to extract from underground formations.
As illustrated in Fig. 1, the elongate combustion housing 20 is operably
connected with
supply lines 40, in this case a hydrogen line 41, an oxygen line 42, and an
inlet water line
44. There is also an outlet water line 45 for the removal of heated water from
the
elongate combustion housing 20. The supply lines 40 are used to transfer gases
and/or
liquids from the surface to the gas generator 10, as described in greater
detail below. In
this embodiment, the hydrogen line 41 and the oxygen line 42 are used to
provide the fuel
and the oxidizing agent for combustion, and the inlet water line 44 is used to
provide
coolant for cooling the elongate combustion housing 20.
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The combustion end 22 generally refers to where hydrogen and oxygen from the
hydrogen line 41 and the oxygen line 42 mix and combustion originates. The
exhaust end
24 is the end where the gasses exit the elongate combustion housing 20 and are
injected
into the reservoir. While Fig. 1 illustrates one embodiment of the gas
generator 10, those
skilled in the art may devise alternative embodiments, and these alternative
or equivalent
are considered within the scope of the present invention.
FIGURE 2 is a perspective view of the combustion end 22 of the gas generator
10.
FIGURE 3 is a top perspective sectional view thereof taken along line 3-3 in
Fig. 2. As
illustrated in Figs. 2 and 3, the gas generator 10 includes an ignition system
30 for
initially igniting the oxygen and hydrogen in the combustion chamber 50. In
the present
embodiment, the ignition system 30 is a device which accepts gas from the
hydrogen line
41 and the oxygen line 42 and combines them into a mixture. The flammable
mixture is
then ignited by a pulsed electrical current, wherein the gas ignites and
expands into an
elongate combustion chamber 50 for initiating combustion within the gas
generator 10.
While one embodiment of the ignition system 30 is shown, alternative ignition
devices
known in the art may also be used, and should be considered within the scope
of the
present invention.
Also as shown in Fig. 2, the inlet water line 44 may include an inline water
valve 47 for
controlling the water flow therethrough. The inline water valves 47 may be any
form of
valve, mass flow controllers for fine control of water flow, or any other
equivalent type of
device. While one embodiment of the inline water valves 47 is shown, those
skilled in
the art may devise alternative embodiments, and these alternative or
equivalent are
considered within the scope of the present invention.
Also as shown in Figs. 2 and 3, the hydrogen line 41, the oxygen line 42,
and/or any other
gas lines, may contain inline gas valves 43. The inline gas valves 43 are used
for
controlling the gas flow rate through a gas line. The inline gas valves 43 may
be any
form of valve, mass flow controller (for fine control of gas flow), or any
other equivalent
mechanism. While one embodiment of the inline gas valves 43 is shown, those
skilled in
the art may devise alternative embodiments, and these alternative or
equivalent are
considered within the scope of the present invention.
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FIGURE 4 is a bottom perspective sectional view similar to Fig. 3, only at an
upward
angle to illustrate an oxygen injection port 52 and a hydrogen injection port
54. As
illustrated in Figs. 3-4, the hydrogen line 41 and the oxygen line 42 (shown
in Fig. 3)
direct the gas to the to the oxygen injection port 52 and the hydrogen
injection port 54,
respectively (shown in Fig. 4). As illustrated in Figs. 3-4, in this
embodiment the gasses
are directed, along the way, through various structures to prepare the gasses
for
combustion.
In the embodiment of Figs. 3-4, the hydrogen line 41 and the oxygen line 42
may enter
into the gas generator 10 via an injection manifold 60. The injection manifold
60 is for
directing the oxygen and hydrogen to the oxygen injection port 52 and the
hydrogen
injection port 54, respectively, of the elongate combustion chamber 50 where
they are
combined into a mixture. The injection manifold 60 includes an oxygen
injection
chamber 61, a hydrogen injection chamber 62, a hydrogen feedthrough 64, an
oxygen
feedthrough 65 and an injection manifold water cooling jacket 66.
The oxygen injection chamber 61 and the hydrogen injection chamber 62 serve as
a
plenums to reduce pressure fluctuations from the oxygen and hydrogen supply
lines 42
and 41. In this embodiment, the oxygen injection chamber 61 serves as a
conduit
between the oxygen line 42 and the oxygen feedthrough 65, and the hydrogen
injection
chamber 62 serves as a conduit between the hydrogen line 41 and the hydrogen
feedthrough 64. While one embodiment of the oxygen injection chamber 61 and
the
hydrogen injection chamber 62 are shown, those skilled in the art may devise
alternative
embodiments, and these alternative or equivalent embodiments are considered
within the
scope of the present invention.
In the embodiment of Figs. 3 and 4, the oxygen feedthrough 65 is a tube
extending from
the oxygen injection chamber 61 to the oxygen injection port 52 in the
combustion end 22
of the elongate combustion housing 20. In this embodiment, the hydrogen
feedthrough
64 is provided by slots surrounding the oxygen feedthrough 65. The slots 64
may be
coaxial with the oxygen feedthrough 65, and extend to the hydrogen injection
port 54.
The slots 64 of this embodiment are not azimuthally contiguous but consist of
a plurality
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of curved segments for the purpose of restraining the oxygen feedthrough 65.
This
structure facilitates the mixing of the two gasses into a readily combustible
mixture.
While one embodiment of the oxygen injection port 52 and the hydrogen
injection port 54
are shown, those skilled in the art may devise alternative embodiments, and
these
alternative or equivalent are considered within the scope of the present
invention.
It is important to note that in alternative embodiments, the oxygen and
hydrogen lines
may be interchanged with no loss of functionality regarding the operation of
the gas
generator 10. All of the uses of the term hydrogen and oxygen are hereby
defined to
include the inverse, so that a mere reversal of these structures is explicitly
within the
scope of the claimed invention.
Also shown in Figs. 3-4, the injection manifold 60 further includes the
injection manifold
water cooling jacket 66 within the combustion end 22 of the elongate
combustion housing
20. The injection manifold water cooling jacket 66 is a space for water from
the inlet
water line 44 to circulate for cooling the combustion end 22 of the elongate
combustion
housing 20. Water enters the injection manifold cooling water jacket 66
through the inlet
water line 44 and exits through the outlet water line 45. While one embodiment
of the
injection manifold water cooling jacket 66 is shown, those skilled in the art
may devise
alternative embodiments, and these alternative or equivalent are considered
within the
scope of the present invention.
FIGURE 5 is a section view of the gas generator 10 taken through line 5-5 of
Fig. 1. As
shown in Fig. 5, the gas generator 10 includes a plurality of annular cooling
jacket
segments 70 that are adapted to receive water from the water inlet line 44 for
cooling the
elongate combustion housing 20. The elongate combustion housing 20 includes
apertures
71 that communicate with the annular cooling jacket segments 70, so that water
from the
annular cooling jacket segments 70 can flow over an inner surface 72 of the
elongate
combustion chamber 50 for cooling the elongate combustion housing 20 and
protecting it
from the extreme temperatures generated within the elongate combustion chamber
50.
As illustrated in Fig. 5, water from the inlet water line 44 is fed through an
inlet port 73
into one of the annular cooling jacket segments 70 via an inlet flow control
valve 74. As
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water flows through the annular cooling jacket segment 70, it absorbs heat
from the walls
of the elongate combustion housing 20. The heated water then exits the annular
cooling
jacket segment 70 at an outlet port 75 connected to the outlet water line 45,
through an
outlet flow control valve 76. While we refer to the inlet water line 44 being
operably
connected to the inlet ports 73, and the outlet water line 45 being operably
connected to
the outlet ports 75, these terms are also expressly defined to include
functionally similar
embodiments that utilize multiple lines. The segregation of each of the
annular cooling
jacket segments 70 serves to increase the control over the temperature of the
elongate
combustion housing 20 and reduce the occurrence and severity of hot spots
forming due
to the combustion in the elongate combustion housing 20 during normal use.
While one
embodiment of the inlet ports 73 and the outlet ports 75 are shown, those
skilled in the art
may devise alternative embodiments, and these alternative or equivalent are
considered
within the scope of the present invention.
The present embodiment includes independent control of the flow rate of water
into and
out of each of the annular cooling jacket segments 70. The water flow through
the inlet
74 and outlet flow control valves 76 may be varied independently to control
the amount
of water going through the annular cooling water jacket segment 70, and also
through the
apertures 71 and into the elongate combustion chamber 50. For example, if more
water is
desired to flow through the jacket, to reduce the elongate combustion chamber
50 wall
temperature, the flow through the inlet flow control valve 74 and outlet flow
control valve
76 is increased. However, if additional water is desired to go into the
elongate
combustion chamber 50 for the purpose of making steam, only the inlet flow
control
valve 74 is adjusted to allow more water flow in (and/or the flow through the
outlet flow
control valve 76 may be reduced).
In the current embodiment, the flow control valves described above may be mass
flow
controllers. In alternative embodiments, the flow control valves may be any
form of
valve, regulator, or equivalent device for controlling the flow of water
through the
annular cooling jacket segments 70 as described herein.
The independent control of the annular cooling jacket segments 70 allows the
operator to
control internal axial temperature gradients within the elongate combustion
housing 20.
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These thermal gradients may cause undesirable thermal instabilities that may
reduce
operational efficiency or even damage the device. While Fig. 5 illustrates one
embodiment of the annular cooling jacket segments 70, those skilled in the art
may devise
alternative embodiments, and these alternative or equivalent are considered
within the
scope of the present invention.
In the embodiment of Fig. 5, the apertures 71 that extend through from the
elongate
combustion chamber 50 to the annular cooling jacket segments 70. The axis of
the
apertures 71 in the present embodiment are normal, that is radial, relative to
the gas
generator axis 26 of the gas generator 10, taken to be in the vertical
direction. This
orientation is one possible orientation, their axes may have a vertical
component to impart
a vertical component to the injection of water into the elongate combustion
chamber 50.
While Fig. 5 illustrates one embodiment of the apertures 71, those skilled in
the art may
devise alternative embodiments, and these alternative or equivalent are
considered within
the scope of the present invention.
As illustrated in Fig. 5, the exhaust end 24 is where the combustion products
and steam
are ejected at high velocity into the reservoir. The exhaust end 24 is shown
in the present
embodiment as a narrowing of an annular cooling jacket segment 70 into a
conical shape.
Though the illustrated shape is that of a frustum of a cone it could be
ellipsoid or any
other narrowing shape and would be considered within the scope of the present
invention.
One purpose of narrowing the exhaust end 24 is to maintain sufficient pressure
within the
gas generator 10 such that the produced steam is able to escape into the
reservoir. The
narrow end of the annular cooling jacket segment 70 contains a restricted
orifice 78 for
ejecting the high velocity steam into the reservoir. While Fig. 5 illustrates
one
embodiment of the exhaust end 24, those skilled in the art may devise
alternative
embodiments, and these alternative or equivalent are considered within the
scope of the
present invention.
FIGURE 6 is a perspective view of one embodiment of the gas generator 10 that
further
includes support ribs 80 and secondary water lines 46. As shown in Fig. 6, the
support
ribs 80 are for seating the gas generator 10 in the steam injection tube 12
(Shown in Fig.
8), as well as supporting and protecting the water lines (the inlet water line
44, the outlet
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water line 45, and the secondary water lines 46). The support ribs 80 of the
present
embodiment are cylindrical plates shaped to fit within the steam injection
tube 12 (Shown
in Fig. 8). Each support rib 80 has a gas generator aperture 81 shaped to fit
an annular
cooling jacket segment 70, as well as a plurality of water line apertures 82
shaped to be
threaded by the water lines (and/or other mechanical structures). In the
present
embodiment the water line apertures 82 are shaped to be threaded by the inlet
water line
44, the outlet water line 45, or steam injection water supply lines 40. While
Fig. 6
illustrates one embodiment of the support ribs 80, those skilled in the art
may devise
alternative embodiments, and these alternative or equivalent are considered
within the
m scope of the present invention.
As illustrated in Fig. 6, the secondary water lines 46 inject additional water
into the steam
plume at the exhaust end 24 to provide additional steam generation as well as
temperature
control over the steam plume. The secondary water lines 46 may terminate at
water
supply line nozzles 48. In the present embodiment, the water supply line
nozzles 48
direct the water coaxially with the gas generator 10. In another embodiment,
the water
supply line nozzles 48 may be directed either towards or away from the gas
generator axis
26 of the gas generator 10 to alter the density or temperature profile of the
steam plume.
While Fig. 6 illustrates one embodiment of the water supply line nozzles 48,
those skilled
in the art may devise alternative embodiments, and these alternative or
equivalent are
considered within the scope of the present invention.
FIGURE 7 is close up of the exhaust end 24 of the gas generator 10,
illustrating the
restricted orifice 78. As shown in Fig. 7, the restricted orifice 78 restricts
the flow of the
gases from the elongate combustion chamber 50 (shown in Fig. 5), in this case
steam and
combustion gases. In the embodiment of Fig. 7, the restricted orifice 78 is
shaped to
allow a desired flow of steam to escape from the elongate combustion chamber
50, while
maintaining desired pressures within the combustion chamber 50. In this
embodiment,
the exhaust end 24 is narrowed to form a frustum of a cone. While Fig. 7
illustrates one
embodiment of the exhaust end 24 and the restricted orifice 78, those skilled
in the art
may devise alternative embodiments, and these alternative or equivalent are
considered
within the scope of the present invention.
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Fig. 7 also illustrates the water supply line nozzles 48 discussed above. The
water supply
line nozzles 48 may further include inline valves (not shown) to prevent
material from
within the reservoir from backflowing into the water lines or elongate
combustion
chamber 50 when no water or steam injection is taking place through the water
supply
line nozzles 48 or the restricted orifice 78. The inline valves may include
check valves,
spring valves, gate valves, ball valves. Those skilled in the art may devise
alternative
embodiments of the inline valves and these alternative or equivalent are
considered within
the scope of the present invention.
FIGURE 8 is a sectional view of the gas generator 10 operably mounted in a
steam
injection tube 12 in a borehole 18. As shown in Fig. 8, the gas generator 10
includes a
steam injection tube 12 and a packer 14 positioned between the steam injection
tube 12
and the borehole 18, in this case a well casing 16 of the borehole 18. The
packer 14
functions to keep steam from escaping up the borehole 18 between the steam
injection
tube 12 and the well casing 16. For purposes of this application, positioning
the packer
14 "between the steam injection tube 12 and the borehole 18" is defined to
include
between the steam injection tube 12 (or the actual gas generator(s) 10, if no
steam
injection tube 12 is used), and the physical rock/dirt of the borehole 18, or
the well casing
16 (if present), and/or any other similar or equivalent installation that may
be required
and/or devised by one skilled in the art.
As illustrated in Fig. 8, the gas generator 10 may be positioned at a top end
of the steam
injection tube 12. The steam injection tube 12 may have a tube length TL that
is
significantly longer than a device length DL of the gas generator 10. In one
embodiment,
the tube length TL of the steam injection tube 12 in the present embodiment is
approximately 5 meters, which is more than twice the length of the device
length DL, and
it may be about three times the length thereof While Fig. 8 illustrates one
embodiment of
the steam injection tube 12, those skilled in the art may devise alternative
embodiments,
and these alternative or equivalent are considered within the scope of the
present
invention.
FIGURE 9 is a block diagram of one embodiment of a control system 90 for the
gas
generator 10. As shown in Fig. 9, the control system 90 includes a control
computer 91,
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pressure sensors 160 and 162, temperature sensors 166 and 168, a gas flow
control
system 98, a water flow control system 99, and an ignition system 30. These
various
elements are discussed in greater detail below.
As illustrated in Fig. 9, the control computer 91 includes a computer
processor 92,
computer memory 93 and a control program 94 operably installed on the computer
memory 93. The control program 94 receives data from the pressure sensors 160
and
162, and the temperature sensors 166 and 168, to operably control the
generator 10, as
discussed in greater detail below. The control program 94 utilizes an
algorithm to
determine what changes need to be effected to a gas flow control system 98, a
water flow
control system 99, and the ignition system 30. An example of the control of
water flow
through the annular cooling jacket segments 70 was given in the detailed
description of
Fig. 5. The function of these sensors in conjunction with the control program
94 is more
fully described in the discussions of Fig. 12.
FIGURE 10 is a top perspective view of a multiple chamber gas generator system
130
according to another embodiment of the invention. FIGURE 11 is a bottom
perspective
view of a bottom portion of the multiple chamber gas generator system 130. As
shown in
Figs. 10-11, the multiple chamber gas generator system 130 is a combination of
individual gas generators 10, for providing additional control of the
steam/water pressure
in the steam plume. The multiple chamber gas generator system 130 includes gas
generators 10, a primary water line 140, and support ribs 150.
Unless otherwise noted, the individual gas generators 10 may be substantially
similar in
construction and operation to the single gas generator 10 described above in
Figs. 1-8, or
they may have a different construction, as selected by one skilled in the art.
The parallel
construction of the gas generators 10 provides advantages which will become
apparent,
with their use described during the discussion below. The multiple chamber gas
generator system 130 may contain two, or a plurality, of gas generators 10
arranged to be
operated in parallel for the purpose of increased control in injecting steam
or water. Their
arrangement is taken mostly to be symmetric in the azimuthal direction around
a multiple
chamber gas generator system axis 132 of the multiple chamber gas generator
system
130, however alternate embodiments including any number of individual gas
generators
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and their arrangement is considered equivalent and within the scope of the
present
invention.
As shown in Figs. 10-11, the primary water line 140 is for providing a source
of water for
5 several components within the multiple chamber gas generator system 130.
The primary
water line 140 is attached to the inlet water lines 44, one for each of the
gas generators 10,
for providing water for cooling and steam generation. Also, the primary water
line 140
extends axially from the combustion end 22 to the exhaust end 24, between the
individual
gas generators 10. Though Figs. 10-11 show the primary water line 140 being
along the
10 multiple chamber gas generator system axis 132 of the multiple chamber
gas generator
system 130, other embodiments are possible, such as the primary water line 140
being
offset radially to make room for other components, or having it coil around
the individual
gas generators 10 for the purpose of drawing heat from the elongate combustion
housing
by conduction, etc. While Figs. 10-11 illustrate one embodiment of the primary
water
15 line 140, those skilled in the art may devise alternative embodiments,
and these
alternative or equivalent are considered within the scope of the present
invention.
Also as shown in Figs. 10-11, the primary water line 140 may be connected to a
primary
water line outlet tree 142. The primary water line outlet tree 142 is
comprised of a central
20 outlet tree water line 144 and four tertiary outlet tree water lines
146, with additional or
fewer lines possible depending on the application. In the present embodiment,
each line
of the primary water line outlet tree 142 terminates in a water supply line
nozzle 48.
Water flows through the primary water line 140, through each line of the
tertiary outlet
tree water lines 146, and out the water supply line nozzles 48 to inject
additional water
into the reservoir. In the present embodiment, the primary water line outlet
tree 142
replaces the secondary water lines 46 shown in Fig. 6. Alternate embodiments
could have
secondary water lines 46 in addition to the primary water line 140. The
tertiary outlet tree
water lines 146 may be "L" shaped, with one end connected to the primary water
line 140
and the other end pointing axially in the direction of the steam plume. In
another
embodiment, valves or mass flow controllers could be placed on each line of
the primary
water line outlet tree 142 in order to correct or induce azimuthal variations
in the steam
plume. In yet another embodiment, additional water supply line nozzles 48
could be
added radially along each tertiary outlet tree water line 146 in order to have
radial profile
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control of the water injection flow. The number of branches, their
configuration,
orientation, and any variations thereof by one skilled in the art are
considered equivalent
and within the scope of the present invention. While Figs. 10-11 illustrate
one
embodiment of the primary water line outlet tree 142, those skilled in the art
may devise
alternative embodiments, and these alternative or equivalent are considered
within the
scope of the present invention.
FIGURE 12 is a sectional view of the multiple chamber gas generator system
130,
illustrating the multiple chamber gas generator system 130 operably mounted in
the steam
injection tube 12, with the steam injection tube 12 and one of the gas
generators 10 shown
in cross-section.
As shown in Fig. 12, the multiple chamber gas generator system 130 includes
pressure
sensors 160 and 162, and temperature sensors 166 and 168, for sensing pressure
and
temperature at various points in and around the system 130. In the present
embodiment,
the system 130 includes at least one chamber pressure sensor 160 positioned
within the
combustion chamber 50, for sensing pressure within the chamber 50.
In this embodiment, the system 130 also includes a borehole pressure sensor
162 for
sensing pressure within the borehole 18. The borehole pressure sensor 162 of
this
embodiment is mounted on an outer surface of the exhaust end 24 of the
elongate
combustion housing 20, although it may also be mounted on one of the support
ribs 150,
on an inner surface 13 of the steam injection tube 12, it could be mounted
elsewhere in
the formation, and/or on any other suitable location determined by one skilled
in the art.
For purposes of the location of the pressure and temperature sensors, the term
"borehole"
is defined to include any external point, either on the outer surface of the
system 130, in
the steam injection tube 12, or elsewhere in the formation, for sensing
pressure being
generated within the borehole/formation by the system 130. The pressure
sensors may be
may be diaphragms sensors, optical sensors, and/or any other equivalent sensor
devices
known to those skilled in the art. The use of the pressure data gathered is
discussed in
greater detail below.
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Temperature sensors 166 and 168 are provided in a manner similar to the
pressure
sensors. A chamber temperature sensor 166 may be operably mounted in the
chamber 50,
and a borehole temperature sensor 169 may be operably mounted in or around the
borehole 18, as discussed above. The temperature sensors 166 and 168 are
operably
connected to the control computer 91 (shown in Fig. 9) so that the control
program 94
(shown in Fig. 9) can receive temperature data and control the operation of
the inlet flow
control valves 74 and the outlet flow control valves 76 (both shown in Fig.
9), as
discussed above, to prevent hotspots from forming in the system 130.
The temperature sensors 166 and 168 may be thermocouple sensors, optical
temperature
sensors, and/or any other equivalent sensor devices known to those skilled in
the art. The
use of the temperature data gathered is discussed in greater detail below.
The sensors 160, 162, 166, and 168 are operably mounted to provide data on the
pressure
and temperature conditions in the elongate combustion chamber 50 and also
within the
steam injection zone. The data from the sensors 160, 162, 166, and 168 is
utilized by the
control program 94 to control the various operations of the system 130. The
control
program 94 (of Fig. 9) interprets the data and adjusts the flow of water
through the
various water lines and through the fuel supply lines and oxidizer supply
lines, until the
pressure and temperature readings are suitable for stable operation. The
control program
94 of the control computer 91 receives the pressure signal from the at least
one borehole
pressure sensor 160, and functions to selectively turn on or off each of the
gas generators
10 in response, so that pressures within the borehole 18 are maintained within
a
predetermined range of pressures. This may be done either in an open-loop
control
method, or a closed-loop control method by using the sensor data in a feedback
loop.
Additionally, individual gas generators 10 may be powered on or off if they
are needed to
be for stable operation of the overall system.
In use, for example, all four gas generators 10 may initially be used to
produce as much
petroleum output as possible. If the formation permeability is low, pressure
within the
reservoir may rise, which can result in a fracture of the reservoir. In this
case, when the
borehole pressure sensor 162 senses the rise in pressure, the control computer
91 (of Fig.
9) may function to turn off one or more gas generators 10, to lower the
pressure.
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Similarly, if pressure readings get too low, one or more of the gas generators
10 may be
brought back online.
As shown in Figs. 10-12, the individual gas generators 10 in the multiple
chamber gas
generator system 130 are supported by at least one support rib 150, in this
embodiment
multiple support ribs 150. As shown in Fig. 12, the support ribs 150 also may
function
for seating the gas generator 10 in the steam injection tube 12, as well as
supporting and
protecting the inlet water lines 44 and the outlet water lines 45. The support
ribs 150 of
the present embodiment are cylindrical plates with an outer perimeter 151
shaped to fit
securely against the steam injection tube 12. Each of the support ribs 150 may
have gas
generator apertures 154 shaped to fit one of the gas generators 10. The
support ribs 80
may also have one or more water line apertures 156 shaped to be threaded by
the water
lines (and/or other mechanical structures coaxial with the gas generator 10).
In the
present embodiment the water line apertures 156 are shaped to be threaded by
inlet water
lines 44, outlet water lines 45, or the primary water line 140. Variations in
the number
and location of the support ribs 150 are considered equivalent and within the
scope of the
present invention. While Figs. 10-12 illustrate one embodiment of the support
ribs 150,
those skilled in the art may devise alternative embodiments, and these
alternative or
equivalent are considered within the scope of the present invention.
FIGURE 13 is a graph of pressure vs. mass flow rate for the throat pressure
and the
downhole steam injection zone with a single gas generator 10. A preliminary
discussion
of some terminology and background is needed before further describing Fig.
13. A gas
generator 10 has a primary function of ejecting mass, preferably gas such as
steam and
other combustion gasses, into a borehole for the purpose of adding
hydrodynamic
pressure to a reservoir. This pressure facilitates extraction of the material
(e.g., petroleum
products) in the reservoir from the borehole or well, typically in another
location. The
pressure of the fluid just outside the gas generator, in what is called the
steam injection
zone, is referred to as the downhole steam injection zone pressure (PD). This
pressure,
PD, is the result of forcing mass, either steam or water, into the confined
space of the
steam injection tube/borehole/reservoir. The throat pressure (PT), is the
pressure in the
elongate combustion chamber 50 immediately on the combustion side of the
restricted
orifice 78. The pressure within the restricted orifice 78 is much lower due to
the small
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size of the orifice and the high velocity of the injected steam or water. In
order to avoid a
backflow of material into the elongate combustion chamber we require
PD
¨ < 1. (1)
PT
If material from the reservoir were to backflow into the elongate combustion
chamber 50
it could cause contamination of the elongate chamber 50, instabilities in the
combustion
process, or even stop the combustion process altogether.
There are two types of mass being injected into the reservoir, water and
steam. The steam
injection mass flow rate (Ms) is the mass of the injected steam through the
restricted
m orifice 78
per unit time. The water injection mass flow rate (Mw) is the sum of the mass
of the water injected through the restricted orifice 78 per unit time, and the
water injected
through the outlet water lines 45, secondary water lines 46, central outlet
tree water line
144, or tertiary outlet tree water lines 146 per unit time. The total downhole
steam mass
flow rate (nip) is the sum of the two rates,
niD = niS TriW = (2)
As shown in Fig. 13, the curve for the rocket steam flow relates ins to PT,
with a typical
operation point shown. Once we define a ifis we may then read off the
corresponding
value of T. Similarly, the curve for the total downhole steam injection flow
(for a
reservoir of typical permeability) allows us to again determine the PD for a
given nip. In
the case shown in Fig. 13, we have a single gas generator 10 and the condition
in Eq. 1 is
satisfied, thus under standard operation there will be no backflow of material
into the
elongate combustion chamber 50.
Another requirement is flow through the restricted orifice 78 is always
choked. Choked
means that the exhaust speed of the injected water or steam is greater than
the local sound
speed of the water or steam. This is important for stable operation of the gas
generator
10, because in the choked condition, acoustic waves cannot propagate up into
the
elongate combustion chamber 50. Were they to do so, they could incite
instabilities in the
combustion process which could lead to hot spots in the elongate combustion
chamber 50,
decreased efficiency of combustion, or a disruption of the combustion process.
The
approximate pressure ratio for the choked condition, is
¨PD <0.577. (3)
PT
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This puts an upper bound on the allowable pressure in the steam injection zone
more
restrictive than just the backflow pressure limit given by Eq. 1, thus
requiring strict
control over the amount of mass flowing into the steam injection zone.
FIGURE 14 is a graph of pressure vs. mass flow rate for the throat and the
downhole
steam injection zone for multiple gas generators 10 in a low permeability
reservoir.
Multiple gas generators 10 may be needed to create sufficient pressure in the
reservoir. In
the case of a reservoir with low permeability, the pressure in the reservoir
builds up faster
for a given mass flow injection rate. This is shown by the slope of the line
for the
reservoir being larger than for the high permeability reservoir shown in Fig.
13. In this
figure we have a family of curves showing the pressure vs. mass flow rate for
the case of
1, 2, 3, or 4 gas generators. This applies when using the multiple chamber gas
generator
system 130 where one or more gas generators 10 may be off As in the discussion
of Fig.
13, we define the steam mass flow rate of one gas generator 10 as Tits,' four
gas
generators 10 as rits,4, the total mass flow rate of one gas generator 10 as
ThD,1, and the
total mass flow rate of four gas generators 10 as ThDA. As before, the curves
define the
throat pressure as a function of mass flow rate depending on how many gas
generators 10
are active. We also take the throat pressure (PT) as independent of the number
of gas
generators 10 being used. For the given operating points shown in the figure,
when
considering one gas generator 10, we see that the steam pressure buildup,
PD,1, is lower
than the corresponding throat pressure PT, and also satisfies the choked
condition.
However, with four gas generators 10 operational, the steam pressure buildup,
P
D,4,
exceeds PT, satisfying neither the constraint of no backflow, Eq. 1, nor the
choked
condition, Eq. 3. Though not shown in Fig. 14, the total downhole pressure is
the sum of
the pressure introduced by the gas generators 10 and the base pressure of the
reservoir.
One cannot simply reduce the flow rates arbitrarily as the reservoir pressure
would
exceed the choking condition. The only way to reduce the flow rates beyond a
certain
point is to entirely turn off one or more gas generators 10. As an example,
one possible
condition is when the total downhole pressure imparted by the gas generators
10, when
running at a minimum mass flow rate while still choked, exceeds the maximum
reservoir
pressure. In this case, individual gas generators 10 need to be turned off to
reduce the
pressure. This illustrates the need for being able to turn off individual
generators 10
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depending on the conditions in the reservoir. The present invention satisfies
this need
with the parallel design of the multiple chamber gas generator system 130.
FIGURE 15 is a flow chart of the operation of the multiple chamber gas
generator system
130 operation. The purpose of this flow chart is to illustrate a simplified
control scheme
that can be used to take advantage of the operational flexibility in the
present invention in
varying the pressure in the steam injection zone. In this flow chart we
consider a scenario
of an over-pressure in the steam injection zone. First, the injection process
is initiated,
and one or more gas generators 10 ignite and begin to inject steam and water
into the
steam injection zone. During the process the pressure and temperature are read
by the
pressure sensors 97 and the temperature sensors 160 and 162 to determine both
the
absolute pressure in the elongate combustion chamber 50 and in the steam
injection zone.
Monitoring the pressure in the elongate combustion chamber 50 is critical for
not
damaging the gas generators 10. The pressure differential is critical for
maintaining the
no backflow condition (Eq. 1) and the choked condition (Eq. 3). If the
pressure is out of
range, the control program 94 determines if rilD is at a lower operational
limit. Recall that
we have lower bounds for pressure in the combustion chamber. If rilD is not at
a lower
limit, then it may be reduced and the pressure and temperature rechecked as
before. If
rilD is at a lower limit, then a single gas generator 10 may be turned off
entirely, with the
other gas generators 10 adjusting their flow rates to minimize any
instantaneous pressure
discontinuities due to the shutoff The pressure and temperature are then
reread and the
loop continues with the gas generators 10 adjusting their output until the
choked
condition is satisfied for all gas generators 10 presently in operation. At
this point the
process is considered stable and the feedback loop continues to monitor
pressure and
temperature for any changes. It should also be noted that this particular
control loop is
also valid for the operation of a single gas generator 10 as described in
Figs. 1-9. With a
single gas generator 10, if the pressure cannot be made to be in an acceptable
range, the
gas generator 10 shuts down and other steps will need to be taken.
FIGURE 16 is a close up of the exhaust end 24 of another embodiment of the gas
generator 10, illustrating an inline steam valve 79 connected to the exhaust
end 24 of the
elongate combustion housing 20. The inline steam valve 79 is for sealing the
elongate
combustion chamber 50 (Shown in Fig. 5) when the gas generator 10 is not
ejecting
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steam. This serves to keep material from backflowing through the restricted
orifice 78
into the elongate combustion chamber 50 causing contamination that would
inhibit the
combustion process. It also prevents material from the reservoir from causing
obstructions in the hydrogen injection port 54, the oxygen injection port 52
(Shown in
Fig. 5), the apertures 71 (Shown in Fig. 5), the inlet ports 73 (Shown in Fig.
5), or the
outlet ports 75 (Shown in Fig. 5). The inline steam valve 79 may be any type
of valve
suitable for use in such an environment, including gate valves, check valves,
etc. As
shown in Fig. 16, the inline steam valve 79 is on the steam injection zone
side of the
restricted orifice 78. In other embodiments, the inline steam valve 79 may be
within the
restricted orifice 78 or within the elongate combustion chamber 50 abutting
the restricted
orifice 78, and such placement of the inline steam valve 79 by those skilled
in the art are
considered equivalent and within the scope of the present invention. In yet
another
embodiment, the inline steam valves 79 may be of a construction that uses the
thermal
expansion of constituent materials to open the valve, thus reducing or
eliminating the
need for moving mechanical parts, as well as providing a normally closed
condition that
would passively seal the elongate combustion chamber 50 in the event of a
combustion
failure or intentional shut-off While Fig. 16 illustrates one embodiment of
the inline
steam valve 79, those skilled in the art may devise alternative embodiments,
and these
alternative or equivalent are considered within the scope of the present
invention.
As used in this application, the terms computer, processor, memory, and other
computer
related components, are hereby expressly defined to include any arrangement of
computer(s), processor(s), memory device or devices, and/or computer
components,
either as a single unit or operably connected and/or networked across multiple
computers
(or distributed computer components), to perform the functions described
herein.
As used in this application, the words "a," "an," and "one" are defined to
include one or
more of the referenced item unless specifically stated otherwise. Also, the
terms "have,"
"include," "contain," and similar terms are defined to mean "comprising"
unless
specifically stated otherwise. Furthermore, the terminology used in the
specification
provided above is hereby defined to include similar and/or equivalent terms,
and/or
alternative embodiments that would be considered obvious to one skilled in the
art given
the teachings of the present patent application.
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