U.S. patent application number 13/342924 was filed with the patent office on 2012-04-26 for system and method for aquifer geo-cooling.
This patent application is currently assigned to AltaRock Energy, Inc.. Invention is credited to Susan Petty.
Application Number | 20120098277 13/342924 |
Document ID | / |
Family ID | 41255833 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120098277 |
Kind Code |
A1 |
Petty; Susan |
April 26, 2012 |
SYSTEM AND METHOD FOR AQUIFER GEO-COOLING
Abstract
A geo-cooling system of specified cooling capacity for cooling a
known heat load is disclosed. The system includes a cool water
aquifer, a cool water production well and a heated water injection
well. The cool water production well is open to the cool water
aquifer and in hydrologic communication with a subterranean heat
exchange area that provides requisite cooling capacity to a known
heat load. The heated water injection well is in hydrologic
communication with the subterranean heat exchange area and open to
the cool water aquifer at a prescribed distance from the cool water
production well. The prescribed distance between the cool water
production well and the heated water injection well is at least
based on the available size of a subterranean heat exchange area
including a portion of the cool water aquifer that hydrologically
communicates between the heated water injection well and the cool
water production well.
Inventors: |
Petty; Susan; (Shoreline,
WA) |
Assignee: |
AltaRock Energy, Inc.
Sausalito
CA
|
Family ID: |
41255833 |
Appl. No.: |
13/342924 |
Filed: |
January 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12433611 |
Apr 30, 2009 |
8109094 |
|
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13342924 |
|
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|
61049295 |
Apr 30, 2008 |
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Current U.S.
Class: |
290/1R ;
165/45 |
Current CPC
Class: |
Y02E 10/46 20130101;
F24T 10/20 20180501; Y02E 10/10 20130101; Y02E 10/14 20130101 |
Class at
Publication: |
290/1.R ;
165/45 |
International
Class: |
H02K 7/18 20060101
H02K007/18; F24J 3/08 20060101 F24J003/08 |
Claims
1. A system comprising: at least one cool water production well
open to a cool water aquifer and in hydrologic communication with a
subterranean heat exchange area that provides requisite cooling
capacity to a known heat load; and at least one heated water
injection well in hydrologic communication with the subterranean
heat exchange area and open to the cool water aquifer at a
prescribed distance from the cool water production well, wherein
the prescribed distance is based at least on the available size of
the subterranean heat exchange area including a portion of the cool
water aquifer that hydrologically communicates the heated water
injection well with the cool water production well.
2. The system as recited in claim 1, wherein cool water produced
from the cool water aquifer is used in a cooling heat exchanger to
condense a vaporized working fluid exiting a turbine in a
geothermal electricity generating system.
3. The system as recited in claim 2, wherein the geothermal
electricity generating system is one of a flash steam power plant
and a binary power plant.
4. The system as recited in claim 2, wherein the geothermal
electricity generating system is a solar thermal power plant and
the vaporized working fluid entering the turbine is vaporized by
the sun.
5. The system as recited in claim 1, wherein cool water from the
cool water aquifer is produced from a plurality of production wells
and injected into the cool water aquifer through a plurality of
injection wells.
6. The system as recited in claim 2, wherein the temperature of the
cool water from the cool water aquifer is at least 40 degrees
Celsius lower than the temperature of the working fluid entering
the turbine.
7. The system as recited in claim 2, wherein the vaporized working
fluid of the turbine is steam generated by vaporizing geothermally
heated water.
8. The system as recited in claim 2, wherein the vaporized working
fluid of the turbine is a fluid having a vaporization point lower
than water and which has been vaporized in a vaporizing heat
exchanger with geothermally heated water.
9. The system as recited in claim 1, wherein the system is an
essentially closed fluid flow course having substantially no fluid
evaporation losses therefrom.
10. The system as recited in claim 1, wherein the cool water
aquifer is a porous matrix aquifer and the prescribed distance
between heated water injection well and the cool water production
well is determined at least by the thermal properties of a rock
matrix within the cool water aquifer, the initial temperature of
cool water in the cool water aquifer and the temperature of heated
fluid injected into the cool water aquifer.
11. The system as recited in claim 1, wherein the cool water
aquifer is a naturally fractured aquifer.
12. The system as recited in claim 1, wherein the cool water
aquifer is a fractured aquifer developed through artificially
stimulating a low permeability aquitard.
13. A method comprising: providing at least one cool water
production well open to a cool water aquifer and in hydrologic
communication with a subterranean heat exchange area that provides
requisite cooling capacity to a known heat load; and providing at
least one heated water injection well in hydrologic communication
with the subterranean heat exchange area and open to the cool water
aquifer at a prescribed distance from the cool water production
well, wherein the prescribed distance is based at least on the
available size of the subterranean heat exchange area including a
portion of the cool water aquifer that hydrologically communicates
the heated water injection well with the cool water production
well.
14. The method as recited in claim 13, wherein cool water produced
from the cool water aquifer is used in a cooling heat exchanger to
condense a vaporized working fluid exiting a turbine in a
geothermal electricity generating system.
15. The method as recited in claim 14, further comprising sourcing
heat used to vaporize the working fluid entering the turbine in the
geothermal electricity generating system locally from a separate
and warmer aquifer than the cool water aquifer.
16. The method as recited in claim 14, wherein the geothermal
electricity generating system is one of a flash steam power plant,
a binary power plant and a solar thermal power plant.
17. The method as recited in claim 13, wherein the cool water
aquifer is a porous matrix aquifer and the prescribed distance
between heated water injection well and the cool water production
well is determined at least by the thermal properties of a rock
matrix within the cool water aquifer, the initial temperature of
cool water in the cool water aquifer and the temperature of heated
fluid injected into the cool water aquifer.
18. The method as recited in claim 13, wherein the cool water
aquifer is a naturally fractured aquifer.
19. The method as recited in claim 13, wherein the cool water
aquifer is an artificially fractured aquifer in a low permeability
aquitard developed by stimulation through injection of water under
pressure.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/433,611, filed on Apr. 30, 2009, which claims the benefit of
and priority to U.S. Provisional Application No. 61/049,295,
entitled "SYSTEM AND METHOD FOR AQUIFER GEO-COOLING," filed on Apr.
30, 2008, each of which is incorporated by reference in its
entirety, for all purposes, herein.
FIELD OF TECHNOLOGY
[0002] The present application is directed to systems and methods
for exchanging heat between a fluid and a subterranean
formation.
BACKGROUND
[0003] Conventional geothermal heat recovery systems are employed
to extract thermal energy from subterranean heated formations
through heat exchange with rock using water as the heat exchange
medium. In the same way, fluids from the high temperature side of
any thermal process can be cooled through heat exchange with
cooling water from cool subterranean formations.
[0004] Heat exchangers are used in industrial processes to cool
heated process fluids before discharging the fluids to the
environment. For instance, heat exchangers are used in thermal
cycle power plants to decrease the discharge temperature of working
fluid exiting a turbine that drives an electrical generator. The
efficiency of the thermal cycle increases as the discharge
temperature of the working fluid decreases. Water is commonly used,
in wet cooling cycles because water has a high heat capacity.
However, water is not always available and is often allocated for
other uses including irrigation, drinking and/or other industrial
uses. Water is particularly scarce for cooling uses in projects
located in arid areas.
[0005] Current wet cooling cycles used in thermal cycle power
plants include once through cooling cycles and evaporative cooling
cycles. Once-through cooling involves circulating water from a
water body or an aquifer through the cooling cycle and then
disposing of the heated water into the same or other water body.
Evaporative cooling involves circulating cooling water between the
cooling cycle and an evaporative cooling tower where the water is
cooled.
[0006] In once-through cooling cycles, water is not usually
consumed and water temperature generally increases less than
10.degree. C. However, large volumes of water are necessary for
cooling. Once through cooling cycles require between four and
twelve gallons of cool water per minute per kilowatt electricity
generated. Heated water is returned to surface water bodies which
can adversely impact plant and animal life that is sensitive to
minor variations in water temperature.
[0007] Evaporative cooling cycles result in approximately 70 to 80
percent water loss on an annual basis, which is equivalent to one
to three gallons per minute per kilowatt electricity generated.
Recirculation of cooling water through the evaporative cooling
tower increases the concentration of dissolved solids and minerals
that are common in water and brine produced from geothermal wells.
Scale and corrosion inhibitors and other chemicals are required to
prevent scale, corrosion and growth of organisms such as algae in
the oxygen rich cooling cycle. This water, if disposed of to
surface water bodies, can cause environmental damage.
[0008] Current cooling systems and methods that are used in
industrial processes including, but not limited to, flash steam
power plants, binary power plants and solar thermal power plants
are inefficient, require large volumes of water and are harmful to
the environment.
SUMMARY
[0009] A geo-cooling system of specified cooling capacity for
cooling a known heat load is disclosed. The system includes a cool
water aquifer, a cool water production well and a heated water
injection well. The cool water production well is open to the cool
water aquifer and in hydrologic communication with a subterranean
heat exchange area that provides requisite cooling capacity to a
known heat load. The heated water injection well is in hydrologic
communication with the subterranean heat exchange area and open to
the cool water aquifer at a prescribed distance from the cool water
production well. The prescribed distance between the cool water
production well and the heated water injection well is at least
based on the available size of a subterranean heat exchange area
including a portion of the cool water aquifer that hydrologically
communicates between the heated water injection well and the cool
water production well.
[0010] The foregoing and other objects, features and advantages of
the present disclosure will become more readily apparent from the
following detailed description and figures of exemplary embodiments
as disclosed herein.
DEFINITIONS
[0011] The term "aquifer" is defined herein as a formation, group
of formations, or part of a formation that contains sufficient
saturated permeable material to yield economical quantities of
water to wells and springs.
[0012] The term "aquifer stimulation" is defined herein as a type
of development in semiconsolidated and completely consolidated
formations to alter the formation physically to improve its
hydraulic properties.
[0013] The term "aquitard" is defined herein as a saturated, but
poorly permeable bed, formation or group of formations that does
not yield water freely to a well or spring. However, an aquitard
may transmit appreciable water to or from adjacent aquifers.
[0014] The term "confined aquifer" is defined herein as a formation
in which the groundwater is isolated from the atmosphere at the
point of discharge by impermeable geologic formations; confined
groundwater is generally subject to pressure greater than
atmospheric.
[0015] The term "permeability" is defined herein as the property or
capacity of a porous rock, sediment, or soil for transmitting a
fluid and a measure of the relative ease of the fluid flow under
unequal pressure.
[0016] The term "transmissivity" is defined herein as the rate at
which water is transmitted through a unit width of an aquifer under
a unit hydraulic gradient.
[0017] The term "unconfined aquifer" is defined herein as an
aquifer wherein the water table is exposed to the atmosphere
through openings in the overlaying materials.
[0018] The term "well screen" is defined as a filtering device used
to keep sediment from entering the well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Embodiments of the present application are described, by way
of example only, with reference to the attached Figures,
wherein:
[0020] FIG. 1 illustrates an exemplary geo-cooling system for
cooling a known heat load according to one embodiment;
[0021] FIG. 2 illustrates the temperature along a distance (d)
between a cool water production well and a heated water injection
well in an exemplary geo-cooling system;
[0022] FIG. 3A illustrates an exemplary geo-cooling system for
cooling a heat load of a geothermal electricity generating system
according to one embodiment; and
[0023] FIG. 3B illustrates an exemplary geo-cooling system in a
stimulated, engineered or enhanced aquifer for cooling a heat load
of a geothermal electricity generating system according to another
embodiment.
DETAILED DESCRIPTION
[0024] It will be appreciated that for simplicity and clarity of
illustration, where considered appropriate, reference numerals may
be repeated among the figures to indicate corresponding or
analogous elements. In addition, numerous specific details are set
forth in order to provide a thorough understanding of the example
embodiments described herein. However, it will be understood by
those of ordinary skill in the art that the example embodiments
described herein may be practiced without these specific details.
In other instances, methods, procedures and components have not
been described in detail so as not to obscure the embodiments
described herein.
[0025] FIG. 1 illustrates an exemplary geo-cooling system 100 for
cooling a known heat load according to one embodiment. The heat
load may be generated by any industrial process including, but not
limited to, a flash steam power plant, a binary power plant, a
solar thermal power plant, a coal fire power plant and/or any other
industrial process known in the art for generating a heat load. The
geo-cooling system 100 includes a cool water aquifer 102, a cool
water production well 122 and a heated water injection well 124.
The cool water aquifer 102 may be confined by an aquitard 123 below
the water table 119. A water table aquifer 101 may exist above the
aquitard 123. The cool water aquifer 100 may also be an unconfined
aquifer. The cool water production well 122 is drilled to a depth
sufficient to penetrate the cool water aquifer 102. The heated
water injection well 124 is drilled a predetermined distance (d)
from the cool water production well 122 and to a depth sufficient
to penetrate the cool water aquifer 102. A well screen 160 may be
provided at the bottom of the cool water production well 122 and/or
the heated water injection well 124 to prevent sediment from
entering the wells 122, 124.
[0026] Cool water 104 enters the cool water production well 122
through a slotted or perforated production interval 103. A downhole
pump 125 may be provided within the cool water production well 122
to pump or circulate cool water 104 up the production tubing 107
and production piping 108 and into a cooling heat exchanger 110 for
cooling and/or condensing a known heat load. The heat load may be a
working fluid used in any industrial process including, but not
limited to, a flash steam power plant, a binary power plant, a
solar thermal power plant or a coal fire power plant. Heated water
105 is discharged from the cooling heat exchanger 110 and into
heated water injection piping 114.
[0027] Heated water 105 may be injected or pumped through the
heated water injection piping 114 and into the heated water
injection well 124 with an injection pump 126. Heated water 105
enters the cool water aquifer 102 through a slotted or perforated
completion interval 116. The heated water 105 follows a tortuous
fluid path that defines a subterranean heat exchange area 126
wherein heat from the heated water 105 is transferred to the
adjacent matrix of rock in the cool water aquifer 102 without a
significant increase in the overall temperature of water in the
cool water aquifer 102.
[0028] The adjacent rock matrix, wherein heated water 105 is
cooled, may be a porous rock matrix, a naturally fractured rock
matrix or a rock matrix fractured by aquifer stimulation. The
subterranean heat exchange area 126 includes a portion of the cool
water aquifer 102 that hydrologically communicates between the
heated water injection well 124 and the cool water production well
122. The temperature gradient across the subterranean heat exchange
area 126 is substantially constant except proximate the injection
completion interval 116 where the injection of heated water 105
causes the temperature to rise. Heated water 105 is cooled in the
subterranean heat exchange area 126 and is re-circulated through
the cool water production well 122 and into the cooling heat
exchanger 110 to cool the heat load.
[0029] The prescribed distance (d) between the cool water
production well 122 and the heated water injection well 124 is
based at least on the heat absorption characteristics of the cool
water aquifer 102 including the thermal conductivity of cool water
104, the heat capacity of the rock matrix and the available size of
the subterranean heat exchange area 126 in the cool water aquifer
102. Preferably, the prescribed distance (d) between the cool water
production well 122 and the heated water injection well 124 is
selected to maintain a constant temperature of water proximate the
cool water production well 122 over the economic life of the
industrial process. In cool water aquifers 102 having a porous rock
matrix the prescribed distance (d) between cool water production
well 122 and the heated water injection well 124 is governed by the
following conservation of energy equations:
( 1 - .phi. ) ( .rho. C p ) s .differential. T .differential. t = (
1 - .phi. ) .gradient. ( K s .gradient. T ) + ( 1 - .phi. ) q s ( 1
) .phi. ( .rho. C p ) t .differential. T .differential. t + ( .rho.
C p ) l ( V l .gradient. ) T = .phi. .gradient. ( K l .gradient. T
) + .phi. q l ( 2 ) ##EQU00001##
[0030] .phi. is the porosity of the rock matrix,
(.rho.C.sub.p).sub.s is the thermal capacity of the rock matrix, T
is the temperature of the rock matrix, K is the thermal conductance
of the rock matrix and q.sub.s is the thermal source intensity of
the rock matrix within the cool water aquifer 102.
(.rho.C.sub.p).sub.t is the thermal capacity of the liquid, K.sub.l
is the thermal conductance of the liquid, V.sub.l is the volume of
liquid, q.sub.l is the thermal source intensity of the liquid
within the cool water aquifer 102 and t is time. The combination of
Equations (1) and (2) yields Equation (3).
( .rho. C p ) t .differential. T .differential. t + ( .rho. C p ) l
( V l .gradient. ) T = .gradient. ( K t .gradient. T ) + q t ( 3 )
##EQU00002##
[0031] (.rho.C.sub.p).sub.t is the total thermal capacity of the
cool water aquifer 102, K.sub.t is the total thermal conductance of
the cool water aquifer 102 and q.sub.t is the total thermal source
intensity of the cool water aquifer 102. By assuming radial flow
and a heat flux
.differential. T .differential. t ##EQU00003##
that is constant with time an analytical solution to Equation (3)
takes the form of Equation (4).
q T ( a , t ) = 4 .pi. K R r ( T R - T F ) { erfc ( r - a ) 2 ( K t
) 1 2 - exp [ ( r - a ) a + Kt a 2 ] erfc [ ( r - a ) ( 2 Kt ) 1 2
+ ( Kt ) 1 2 a ] } - 1 ( 4 ) ##EQU00004##
[0032] K.sub.R is the thermal conductance of the rock matrix, a is
the depth within the cool water aquifer, r is the radial distance
from the wall of subterranean well 100, t is time, T.sub.R is the
initial temperature of the rock matrix at a depth a in the cool
water aquifer 102, T.sub.F is the final temperature of the rock
matrix at a depth a in the cool water aquifer 102, and .kappa. is
the thermal diffusivity of the rock matrix in the cool water
aquifer 102. Using the simplified conservation of energy Equation
(4) the distance (d) between the cool water production well 122 and
the heated water injection well 124 can be calculated in order to
maintain a substantially constant temperature of the cool water
aquifer 102 throughout the economic life of the industrial
process.
[0033] FIG. 2 illustrates the temperature along a distance (d) in a
subterranean heat exchange area 126 between a cool water production
well 122 and a heated water injection well 124 in an exemplary
geo-cooling system 100. A cool water aquifer 100 that has an
initial temperature of 10.degree. C. and temperature of 50.degree.
C. proximate the heated water injection well 124 must have a
prescribed distance (d) of 150 meters between the cool water
production well 122 and the heated water injection well 124 in
order to maintain a constant temperature proximate the cool water
production well 122 for at least a 30 year period of an industrial
process that generates a known heat load.
[0034] In accordance with the example embodiment illustrated in
FIG. 1, the geo-cooling system 100 may be a closed-loop system
wherein water is brought to the surface from the cool water aquifer
102, used to cool a known heat load, re-injected back into the cool
water aquifer 102 and re-circulated through the system 100 without
being exposed to the atmosphere. By forming a closed-loop
geo-cooling system 100 with the cool water aquifer 102, the
consumption, evaporation and loss of water is prevented during
cooling operations. In most cases, the groundwater chemistry of
cool water aquifers 102 is benign and treatment for scale and
corrosion is not necessary. Treatment chemicals including scale or
corrosion inhibitors may be cycled through the closed-loop
geo-cooling system 100 if the water composition in the cool water
aquifer 102 is corrosive or impure. Treatment chemicals including
scale or corrosion inhibitors may be injected directly into the
cool water aquifer 102 with minimal environmental impact if the
water contained in the cool water aquifer 102 is non-potable
groundwater. Water may be extracted from the cool water aquifer
102, circulated through the geo-cooling system 100 and injected
back into the cool water aquifer 102 by pump, thermal siphon
gravity or any other method known in the art for circulating water
to and from an aquifer.
[0035] While the exemplary geo-cooling system 100 illustrated in
FIG. 1 includes a cool water production well 122 and a heated water
injection well 124, the geo-cooling system 100 may include a
plurality of cool water production wells and a plurality of heated
water injection wells spaced at a prescribed distance apart
sufficient to prevent heating of the water in the plurality of
production wells over the life of the industrial process. The
number of production and injection wells is governed in part by the
magnitude of the heat load generated by the industrial process, the
thermal conductivity of water within the cool water aquifer, the
heat capacity of the rock matrix of the cool water aquifer within
which the production and injection wells are located, the available
size of the subterranean heat exchange area, and the transmissivity
of the subterranean heat exchange area.
[0036] FIG. 3A illustrates an exemplary geo-cooling system 200 for
cooling a heat load of a geothermal electricity generating system
according to one embodiment. The geo-cooling system 200 includes a
cool water aquifer 202, a cool water production well 222 and a
heated water injection well 224. The cool water aquifer 202 may be
confined by an aquitard 223 below the water table 219. A water
table aquifer 201 may exist above the aquitard 223. The cool water
aquifer 200 may also be an unconfined aquifer. The cool water
production well 222 is drilled to a depth sufficient to penetrate
the cool water aquifer 202. The heated water injection well 224 is
drilled a predetermined distance (d) from the cool water production
well 222 and to a depth sufficient to penetrate the cool water
aquifer 202. A well screen 260 may be provided at the bottom of the
cool water production well 222 and/or the heated water injection
well 224 to prevent sediment from entering the wells 222, 224. Cool
water 204 enters the cool water production well 222 through a
slotted or perforated production interval 203. A downhole pump 225
may be provided within the cool water production well 222 to pump
or circulate cool water 204 up the production tubing 207 and
production piping 208 and into the tube-side inlet 217 of a cooling
heat exchanger 210 for cooling and/or condensing a known heat load
of a geothermal electricity generating system.
[0037] Heated water 205 is discharged from the tube-side outlet 218
of the cooling heat exchanger 210 and into heated water injection
piping 214. Heated water 205 may be injected or pumped through the
heated water injection piping 214 and into the heated water
injection well 224 with an injection pump 226. Heated water 205
enters the cool water aquifer 202 through a slotted or perforated
completion interval 216. The heated water 205 follows a tortuous
fluid path that defines a subterranean heat exchange area 226
wherein heat from the heated water 205 is transferred to the
adjacent rock matrix in the cool water aquifer 202 without a
significant increase in the overall temperature of the water in the
cool water aquifer 202. The adjacent rock matrix, wherein the
heated water 205 is cooled, may be a porous rock matrix a naturally
fractured rock matrix or a rock matrix fractured by aquifer
stimulation. The subterranean heat exchange area 226 includes a
portion of the cool water aquifer 202 that hydrologically
communicates between the heated water injection well 224 and the
cool water production well 222. The temperature gradient across the
subterranean heat exchange area 226 is substantially constant
except proximate the injection completion interval 216 where the
injection of heated water 205 causes the temperature to rise.
Heated water 205 is cooled in the subterranean heat exchange area
226 and is re-circulated through the cool water production well 222
and into the tube-side inlet 217 of the cooling heat exchanger 210
for cooling a known heat load of a geothermal electricity
generating system. Water may be extracted from the cool water
aquifer 202, circulated through the geocooling system 200 and
injected back into the cool water aquifer 202 by a pump, thermal
siphon, gravity or any other method known in the art for
circulating fluids to and from an aquifer.
[0038] In accordance with FIG. 3A, the geothermal electricity
generating system may be a flash steam power plant including a heat
producing well (not shown) drilled in a geothermal formation (not
shown), a pressure separator 221 and a turbine 228. Geothermal
brine, water and/or steam 240 may be produced from the heat
producing well and separated into liquid 229 and vapor components
in the pressure separator 221. The liquid component 229 of the
geothermal brine, water and/or steam 240 may be re-injected into
the heat producing well or circulated to a second stage flash. The
vapor component of the geothermal brine, water and/or steam 240 may
be used as the working fluid 242 of a turbine 228 to generate
electricity in the flash steam power plant.
[0039] The working fluid 242 discharged from the turbine 228 enters
the shell-side inlet 230 of the cooling heat exchanger 210 where it
is cooled and/or condensed by cool water 204 from the aquifer 202
entering the tube-side inlet 217 of the cooling heat exchanger 210.
The cooled and/or condensed working fluid 242 is discharged from
the shell-side outlet 244 of the cooling heat exchanger 210 and may
be re-injected for heating into the geothermal formation through an
injection well. The working fluid 223 may then be produced from the
heat producing well and re-circulated through the flash steam power
plant for producing electricity. Water, brine and/or steam 240 may
be extracted from the heat producing well and circulated through
the flash steam power plant by a pump, thermal siphon, gravity or
any other methods known in the art for circulating fluids. The
flash steam power plant may be a closed-loop system wherein the
geothermal brine, water and/or steam 240 produced from the heat
producing well is brought to the surface, separated into liquid and
vapor components in the pressure separator 221, used to drive the
turbine 228, cooled in the cooling heat exchanger 210, re-injected
back into the heat producing well and re-circulated through the
flash steam power plant without being exposed to the
atmosphere.
[0040] The geo-cooling system 200 may derive cooling capacity from
any aquifer having a fluid and/or rock temperature lower than
temperature of the working fluid exiting the turbine 228. The
geo-cooling system 200 may derive cooling capacity from a cool
water aquifer 202 such as a confined aquifer, unconfined aquifer, a
porous matrix aquifer, a naturally fractured aquifer or an aquifer
fractured by aquifer stimulation. During aquifer stimulation,
naturally occurring fractures in a fractured aquifer in the
geo-cooling system 200 may be artificially developed through
stimulation of a low permeability aquitard 223. These fractures may
be developed by pumping water under pressure sufficient to relieve
the stresses on the rocks in the aquitard 223, thus allowing the
rock to shift along plains of weakness and create shear fractures.
These fractures may enhance the naturally low permeability of the
aquitard 223 or may create permeability in rock which has little to
no permeability. Cool water aquifers having substantially constant
year round groundwater temperatures between 5.degree. C. and
25.degree. C. are capable of cooling a heat load such as the
working fluid 242 exiting the turbine 228 of a flash steam power
plant throughout the economic life of the power plant.
[0041] The efficiency of the flash steam power plant is in part
controlled by the difference between the temperature and pressure
of the heated working fluid 242 entering the turbine 228 and the
temperature and pressure of the cooled working fluid 242 discharged
from the cooling heat exchanger 210. This temperature difference
may be governed by the fluid and/or rock temperature of the cool
water aquifer 202 from which the cool water 204 is sourced. Cool
water aquifers 202 with lower fluid and/or rock temperatures
provide greater cooling capacity and geothermal formations with
higher fluid and/or rock temperatures provide greater heating
capacity for generating electricity. The cooling capacity of the
geo-cooling system 200 is also affected by the distance (d) between
the heated water injection well 224 and the cool water production
well 222. By increasing the distance (d) between the heated water
injection well 224 and the cool water production well 222, a larger
flow rate of heated water 205 can be returned to the cool water
aquifer 202 for cooling without causing a significant increase in
the overall temperature of the cool water aquifer 202. To maintain
a substantially constant water temperature of the cool water
aquifer 202 over the typical 30-year life of a flash steam power
plant, the increase in temperature of the cool water 204 passing
through the heat exchanger 210 must be minimized. To increase the
efficiency of the flash steam power plant, the decrease in
temperature of the working fluid 242 passing through the heat
exchanger 210 must be maximized. In an example embodiment, the
temperature increase of the cool water 204 passing through the
subterranean cooling heat exchange area 226 is maintained at about
10.degree. C. or less.
[0042] Geothermal electricity generating systems deriving heat from
geothermal formations with higher fluid and/or rock temperatures
require a larger flow rate of cool water 204 from the cool water
aquifer 202 to cool and/or condense the working fluid 242 driving
the turbine 228 of the electricity generating system. Geothermal
electricity generating systems having higher flow rates of working
fluid 242 driving the turbine 228 also require a larger flow rate
of cool water 204 from the cool water aquifer 202 to cool and/or
condense the working fluid 242. The cooling capacity of the
geo-cooling system 200 is related not only to the thermal
conductivity of the rock matrix of the cool water aquifer 202 and
the porosity of the fluid filled portion of the cool water aquifer
202, but also to the initial temperature of the cooling water
aquifer 202.
[0043] FIG. 3B illustrates an exemplary geo-cooling system 200 for
cooling a heat load in a geothermal electricity generating system
according to another embodiment. The geo-cooling system 200
includes a cool water aquifer 202, a cool water production well 222
and a heated water injection well 224. The cool water aquifer 202
may be confined by an aquitard 223 below the water table 219. A
water table aquifer 201 may exist above the aquitard 223. The cool
water aquifer may also be an unconfined aquifer. The cool water
production well 222 is drilled to a depth sufficient to penetrate
the cool water aquifer 202. The heated water injection well 224 is
drilled a predetermined distance (d) from the cool water production
well 222 and to a depth sufficient to penetrate the cool water
aquifer 202. A well screen 260 may be provided at the bottom of the
cool water production well 222 and/or the heated water injection
well 224 to prevent sediment from entering the wells 222, 224. Cool
water 204 enters the cool water production well 222 through a
slotted or perforated production interval 203. A downhole pump 225
may be provided within the cool water production well 222 to pump
or circulate cool water 204 up the production tubing 207 and
production piping 208 and into the tube-side inlet 217 of a cooling
heat exchanger 210 for cooling and/or condensing a known heat load
of a geothermal electricity generating system.
[0044] Heated water 205 is discharged from the tube-side outlet 218
of the cooling heat exchanger 210 and into heated water injection
piping 214. Heated water 205 may be injected or pumped through the
heated water injection piping 214 and into the heated water
injection well 224 with an injection pump 226. Heated water 205
enters the cool water aquifer 202 through a slotted or perforated
completion interval 216. The heated water 205 follows a tortuous
fluid path that defines a subterranean heat exchange area 226
wherein heat from the heated water 205 is transferred to the
adjacent rock matrix in the cool water aquifer 202 without a
significant increase in the overall temperature of the water in the
cool water aquifer 202. The adjacent rock matrix, wherein the
heated water 205 is cooled, may be a porous rock matrix, a
naturally fractured rock matrix or a rock matrix fractured by
aquifer stimulation.
[0045] The subterranean heat exchange area 226 includes a portion
of the cool water aquifer 202 that hydrologically communicates
between the heated water injection well 224 and the cool water
production well 222. The temperature gradient across the
subterranean heat exchange area 226 is substantially constant
except proximate the injection completion interval 216 where the
injection of heated water 205 causes the temperature to rise.
Heated water 205 is cooled in the subterranean heat exchange area
226 and is re-circulated through the cool water production well 222
and into the tube-side inlet 217 of the cooling heat exchanger 210
for cooling a known heat load of a geothermal electricity
generating system. Water may be extracted from the cool water
aquifer 202, circulated through the geocooling system 200 and
injected back into the cool water aquifer 202 by a pump, thermal
siphon, gravity or any other method known in the art for
circulating fluids to and from an aquifer.
[0046] In accordance with FIG. 2B, the geothermal electricity
generating system may be a binary power plant including a heat
producing well (not shown) drilled in a geothermal formation (not
shown), a vaporizing heat exchanger 250 and a turbine 228.
Geothermal brine, water and/or steam 240 may be produced from the
heat producing well and circulated into the shell-side inlet 232 of
the vaporizing heat exchanger 250 to vaporize a working fluid 242
entering the tube-side inlet 236 of the vaporizing heat exchanger
250. Preferably the working fluid 242 has a vaporization point
lower than the geothermal brine, water and/or steam 222 used to
vaporize the working fluid 223. Suitable working fluids for use in
binary power plants include, but are not limited to, isobutane or
other organic liquids having a boiling point lower than geothermal
brine and/or water produced from the heat producing well. The
geothermal brine, water and/or steam 240 is discharged from the
shell-side outlet 238 of the vaporizing heat exchanger 250,
re-injected into the geothermal formation for heating through an
injection well, produced from the heat producing well and
re-circulated into the vaporizing heat exchanger 250. The vaporized
working fluid 242 is discharged from the tube-side outlet 234 of
the vaporizing heat exchanger 250 and circulated into a turbine 228
to generate electricity. The production of electricity and the
efficiency of the binary power plant increases as the temperature
of the working fluid 242 discharged from the turbine 228
decreases.
[0047] The working fluid 242 discharged from the turbine 228 enters
the shell-side inlet 230 of the cooling heat exchanger 210 where it
is cooled and/or condensed by cool water 204 from the aquifer 202
entering the tube-side inlet 217 of the cooling heat exchanger 210.
The cooled and/or condensed working fluid 242 is discharged from
the shell-side outlet 244 of the cooling heat exchanger 210 and may
be re-circulated into the tube-side inlet 236 of the vaporizing
heat exchanger 250 where it is vaporized. Water, brine and/or steam
240 may be extracted from the heat producing well and circulated
through the binary power plant by a pump, thermal siphon, gravity
or any other method known in the art for circulating fluids. The
binary power plant may be a closed-loop system wherein the
geothermal brine, water and/or steam 222 produced from the heat
producing well is brought to the surface, circulated in the
vaporizing heat exchanger 250, re-injected back into geothermal
formation, produced from the heat producing well and re-circulated
through the binary power plant without being exposed to the
atmosphere.
[0048] The geo-cooling system 200 may derive cooling capacity from
any aquifer having a fluid and/or rock temperature lower than
temperature of the working fluid exiting the turbine 228 of the
binary power plant. The geo-cooling system 200 may derive cooling
capacity from a cool water aquifer 202 such as a confined aquifer,
unconfined aquifer, a porous matrix aquifer, a naturally fractured
aquifer or an aquifer fractured by aquifer stimulation. During
aquifer stimulation naturally occurring fractures in a fractured
aquifer in the geo-cooling system 200 may be artificially developed
through stimulation of a low permeability aquitard 223. These
fractures may be developed by pumping water under pressure
sufficient to relieve the stresses on the rocks in the aquitard
223, thus allowing the rock to shift along plains of weakness and
create shear fractures. These fractures may enhance the naturally
low permeability of the aquitard 223 or may create permeability in
rock which has little to no permeability. Cool water aquifers
having substantially constant year round groundwater temperatures
between 5.degree. C. and 25.degree. C. are capable of cooling a
heat load such as the working fluid 242 exiting the turbine 228 of
a binary power plant throughout the economic life of the power
plant.
[0049] The efficiency of the binary power plant is in part
controlled by the difference between the temperature and pressure
of the heated working fluid 242 entering the turbine 228 and the
temperature and pressure of the cooled working fluid 242 discharged
from the cooling heat exchanger 210. This temperature difference
may be governed by the fluid and/or rock temperature of the cool
water aquifer 202 from which the cool water 204 is sourced. Cool
water aquifers 202 with lower fluid and/or rock temperatures
provide greater cooling capacity and geothermal formations with
higher fluid and/or rock temperatures provide greater heating
capacity for generating electricity. The cooling capacity of the
geo-cooling system 200 is also affected by the distance (d) between
the heated water injection well 224 and the cool water production
well 222. By increasing the distance (d) between the heated water
injection well 224 and the cool water production well 222, a larger
flow rate of heated water 205 can be returned to the cool water
aquifer 202 for cooling without causing a significant increase in
the overall temperature of the cool water aquifer 202. To maintain
a substantially constant water temperature of the cool water
aquifer 202 over the typical 30-year life of a binary power plant,
the increase in temperature of the cool water 204 passing through
the heat exchanger 210 must be minimized. To increase the
efficiency of the binary power plant, the decrease in temperature
of the working fluid 242 passing through the heat exchanger 210
must be maximized. In an example embodiment, the temperature
increase of the cool water 204 passing through the subterranean
heat exchange area 226 is maintained at about 10.degree. C. or
less.
[0050] In another exemplary embodiment, the geo-cooling system 200
may be used to cool a working fluid exiting a turbine for
generating electricity in a solar thermal power plant. The working
fluid entering the turbine for generating electricity in a solar
thermal power plant is vaporized by the sun.
[0051] Example embodiments have been described hereinabove
regarding improved geocooling methods and systems for cooling a
known heat load. Various modifications to and departures from the
disclosed example embodiments will occur to those having skill in
the art. The subject matter that is intended to be within the
spirit of this disclosure is set forth in the following claims.
* * * * *