A New Look at Geothermal Energy as an
Energy Choice for the Future
W.D. Gosnold, D.F. Merriam, D.D. Blackwell
U. North Dakota
Kansas Geol. Survey
Southern Methodist U.
Outline
Take home message
Geothermal energy overview
What we thought we knew
What has changed
What we now know
Take Home Message
Geothermal energy is an underestimated and
largely untapped resource that could have a
significant impact on the world’s energy future.
Advances in technology make electrical power
generation from low-to-intermediate temperature
geothermal waters a reality.
The power that could be generated from oil field
waste waters alone is enormous.
Combining all potential geothermal resources could
supply all electrical power needs for the US.
Image Source: Geothermal
Education Office, Tiburon CA
The first coordinated assessment of US
geothermal resources involved:
US Geological Survey
– Circular 726 (1975)
– Circular 790 (1979)
– Circular 892 (1983)
DOE - State Coupled Program
– Geothermal resource maps and reports
Industry
– Working power plants
Universities
– SMU, Utah, OIT, MIT, Va Tech, Nebraska, UND, UK, NMSU
– Establishment of laboratories and many
publications
Professional Organizations
– Geothermal Resources Council
Some key definitions
The temperature scheme established by
the U.S. Geological Survey Circular 726
(White and Williams, 1975) categorized
hot water resources as:
– high-temperature (>150°C)
– intermediate-temperature (150°C to 90°C)
– low-temperature (<90°C)
Types of Geothermal Systems
Hydrothermal systems
Conduction dominated systems
Stratabound systems
Geopressured systems
Engineering enhanced geothermal
systems (EGS)
Ground source heat pump
Geothermal Applications
Direct use heat
Electrical power
Ground source heat pumps
1018 = exa so 1 x 1018 J = 1 EJ
1 J = 1 W s 1 EJ = 0.278 TWh
Kilo, Mega, Giga, Tera, Peta, Exa, Zetta, Yotta
Direct Use
Space heating
Aquaculture
Greenhouses
Industrial processes
Although the potential for energy production from
low to intermediate resources is great, actual usage
has been slow to develop.
Lund and Boyd (2000) estimated that direct heat
applications in the United States are 8.478 EJ y-1
(8,044 billion btu y-1).
The accessible resource in sedimentary basins is
more than 3 x 106 greater than the amount in use.
Source: Geothermal Education
Office, Tiburon CA
Source: Geothermal Education
Office, Tiburon CA
Electrical Power
Country
Total
1990
1995
MWe
MWe
5831.72 6833.38
2000
MWe
7974.06
2005
MWe
8912
USA
2774.6
2816.7
2228
2544
Philippines 891
1227
1909
1931
Mexico
700
753
755
953
Indonesia
144.75
309.75
589.5
797
Italy
545
631.7
785
790
Japan
214.6
413.71
546.9
535
Source: Geothermal Education
Office, Tiburon CA
Geothermal Power Plant
Dixie Valley, Nevada
Geothermal Power Plant
The Geysers
Source: Geothermal Education
Office, Tiburon CA
Ground Source Heat Pumps
The potential for geothermal heat pumps (GHP)
applications is enormous and GHPs are one of the
fastest growing renewable energy applications world
wide (Lund et al., 2004).
The global installed capacity is estimated to be 12 GWt
and the annual energy use is about 72 PJ (Lund et al.,
2004).
Lund et al., (2004) determined that coupling GHP
systems with renewable electricity resources results in
an apparent efficiency of 140% with an excess of 40%
over the original energy consumed in generating the
electricity.
What we knew
High-temperature convection systems in the
western U.S. contain 371 EJ (Renner, White, and
Williams, USGS Cir. 726, 1975).
Intermediate temperature systems, which exist
primarily in the western U.S., contain 42 ±13 EJ
(Brook et al., USGS Cir. 790, 1978).
The accessible low-temperature resource base
in the central United States contains 27,000 EJ
(Sorey et al., USGS Cir. 893, 1983).
Undiscovered low temperature resources
contain an additional 7,200 EJ (Sorey et al., USGS
Cir. 893, 1983).
What has changed
More and better data on heat flow and
subsurface temperatures
Technology advances
Global energy economics
Global Heat Flow
Global average heat flow: 87 mW m-2
Total surface heat flux: 44.2 x TW
83% of present surface heat flow is due to
radioactive decay of U, Th, and K
Earth’s mantle is cooling at a rate of 36 °C Ga-1
Average solar flux at the surface: 400 W m-2
Average solar flux at TOA: 1365 W m-2
1984
Geothermal Map of North America,
SMU Geothermal Laboratory, 2004
D. Blackwell and M. Richards, Eds.,
Low-to-intermediate temperature
resources were underestimated
USGS Circular 892: The GRA considered only
one or two potential geothermal aquifers within
well-known sedimentary basins.
Large basins such as the Williston Basin,
Denver Basin, Powder River Basin, Anadarko
Basin, and the US Gulf Coast region contain
more than a dozen potential geothermal aquifers
having temperatures greater than 100 °C.
LTITS Resource: Low-to-intermediate
temperature stratabound resource
LTITS in ND and SD
The estimate in USGS Circular 892, based on only the
principal water producing formations, the Dakota Group and
the Madison aquifer, in the Williston and Kennedy basins
totaled 2,050 EJ.
Analysis of all potential aquifers in South Dakota and North
Dakota indicates that the total accessible resource base in
the two basins is approximately 33,700 EJ.
If the difference between earlier assessments and the
current analysis applies to similar basins, the accessible
resource base for the US may be of the order of 400,000 EJ.
The US LTITS resource was underestimated by 400%.
n
Tz  
i 1
qz i

Calculating the geothermal resource base
q  
Conductive heat flow at
the surface is described
by Fourier’s Law of Heat
conduction
n
Assuming we know heat
flow, temperature at depth
“z” may be calculated by
Tz  
i 1
qzi
i
Generalized Thermostratigraphy of the Williston Basin
Depth
System
Thickness
(meters)
Quaternary
Thermal
Temp.
Top of Unit
Gradient
Temp.
(W m-1 K-1)
(mK m-1)
(°C)
70% of Max.
Thickness Conductivity
(meters)
510
0
1.4
42.9
6.0
Tertiary
1250
357
1.2
49.9
27.9
Cretaceous
1640
1232
1.2
48.2
71.6
Jurassic
395
2380
1.3
44.6
126.8
Triassic
225
2657
1.3
46.2
139.2
Permian
232
2814
2.9
20.7
146.4
Pennsylvanian
175
2976
1.7
35.1
149.8
Mississippian
675
3099
2.9
20.6
154.1
Devonian
770
3571
2.7
22.2
163.8
Silurian
370
4110
3.5
17.1
175.8
Ordovician
400
4369
2.7
22.6
180.3
Cambrian
300
4649
1.7
35.3
186.6
Three T-z profiles measured
in wells in thermal
equilibrium with the
surrounding rocks and a
model T-z profile.
Use the equilibrium temperature not the BHT
The energy resource in Joules is the product of
density*volumetric heat capacity*volume*dT qr = ρcvad (t-tref)
The Madison Fm in western North Dakota contains 1,476 EJ.
Colors are temperature, contours are depth (m), lines are county boundaries
Sediment thickness in the continental United States
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
North Dakota and Eastern Montana
Heat flow in North Dakota and eastern
Montana averages 52 ± 15 mWm-2 (n=40)
and ranges from 45 mW m-2 in eastern
North Dakota to 75 mW m-2 in the
Williston basin in eastern Montana.
The mean accessible LTITS resource
base is approximately 31,800 EJ.
Eastern Colorado
Heat flow east of the Front Range in
Colorado averages 91 ± 19 mWm-2 (n=15).
The mean accessible LTITS geothermal
resource base is 2,640 EJ.
South Dakota
Anomalous heat flow due to heat advection in
topographically driven ground water flow in
regional Paleozoic and Mesozoic aquifers
occurs in an 80,000 km2 area in South Dakota
between the Black Hills and the Missouri River.
Heat flow as low as 20 mW m-2 occurs in the
recharge region near the Black Hills, and heat
flow as high as 140 mW m-2 occurs above the
discharge region in south central South Dakota.
The mean accessible LTITS resource base is
12,250 EJ.
Nebraska
Heat flow in Nebraska averages about 65
± 20 mWm-2 (n = 42), but the north central
and western parts have anomalously high
heat flow (80 to 145 mWm-2 ) due to
regional groundwater flow in confined
aquifers.
The mean accessible LTITS resource
base is 3,720 EJ.
Kansas
Heat flow in Kansas averages about 65 ±
9 mWm-2 (n = 20).
The mean accessible LTITS resource
base is 4,980 EJ.
Oklahoma and Texas
Heat flow averages 52 ± 22 mWm-2 (n = 11) in
Oklahoma and 62 ± 56 mWm-2 (n = 50) in Texas.
The ORC power generation potential using
waters from deep oil-producing formations in the
Anadarko and Arkoma basins and Gulf Coast
regions ranges rom 1,124 to 5,393 MWe in
Oklahoma and 1,094 to 5,252 MWe in Texas
(Blackwell, Negraru, and Richards, 2006).
This amount of energy is a thousand times
greater than the annual electrical energy used in
the entire state of Texas.
Technology Advances
UTC Power and Ormat have reverse engineered
industrial air conditioning systems (Organic Rankine
Cycle - ORC) to create highly efficient turbine power
generators.
organic Rankine cycle binary
generators
According to UTC, the efficiency of the ORC
system is such that 10 MW of heat can be
converted practically into about 1 MW of
electrical power.
Water production at 1000 gpm at
temperatures as low as 90 °C can be used to
produce electricity at rates competitive with
conventional power plants.
UTC’s Pure Cycle-Model 200 provides 200 kW
using 165ºF water at 480 gpm at Chena Hot
Springs Resort, Chena, AK. Electricity cost
dropped from 30¢ / kwh to 7¢ / kwh.
Co-produced Oil Field Fluids
The potential power production using oil field
waste waters with ORC technology is estimated
to be at least 5.9 GW and could be as high as
21.9 GW (McKenna et al., 2005; MIT - 2007).
Requirements are: 1,000 gpm, for a well or a
group of wells in relatively close proximity to
each other.
Temperatures can be as low as 90 ºC (192 ºF).
Opportunities for co-produced oil field
waters
“Collecting and passing the fluid through a binary
system electrical power plant is a relatively
straightforward process.”
“Piggy-backing on existing infrastructure should
eliminate most of the need for expensive drilling
and hydrofracturing operations, thereby reducing
the risk and the majority of the upfront cost of
geothermal electrical power production.”
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Equivalent geothermal power from co-produced hot water associated
with existing hydrocarbon production in the mid-continent.
State
Total Water
Produced Ann.
in 1,000 kbbl
Total Water
Production
Rate, kGPM
Equivalent
Power,
MW @ 100oC
Equivalent
Power,
MW @ 140oC
Equivalent
Power,
MW @ 180oC
Montana
189,899
16
16
47
88
Colorado
487,331
44
44
112
212
North Dakota
182,441
16
17
42
79
South Dakota
6,725
1
1
2
3
102,005
9
9
23
44
6,326,175
572
575
1,456
1,980
Oklahoma
12,423,264
1,124
1,129
2,860
5,393
Texas
12,097,990
1,094
1,099
2,785
5,252
Total Mid-Cont
31,944,930
2,876
2,890
7,327
13,051
TOTAL USA
50,527,333
4,590
4,591
11,631
21,933
Nebraska
Kansas
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
http://www.smu.edu/geothermal/
Geothermal Energy Utilization
Associated with
Oil & Gas Development
Conference
June 12-13, 2007
The Future of
Geothermal Energy The Future of
Impact of Enhanced Geothermal
Systems (EGS) on the United States
in the 21st Century
Massachusetts Institute of
Technology
http://geothermal.inel.gov/
EGS Concept and Application
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Excerpts from MIT Report on EGS
“If we limit our calculation of stored thermal energy in
place to a depth of 10 km beneath the land area of
the United States, then the amount of thermal energy
in the crust is so large (about 14 million quads) that
we can view it as sustainable (see Chapter 2, Table
A.2.1).”
“Even if we were to use it to provide all the primary
energy consumed in the United States, we still would
be depleting only a tiny fraction of it.”
Estimated U.S. geothermal resource
base to 10 km depth by category
Category of Resource
Thermal Energy, in
Exajoules (1EJ = 1018
J)
Reference
100,000* may be
400,000
MIT - 2007
* Excludes Yellowstone
National Park and Hawaii
** Includes methane content
Conduction-dominated
EGS
Sedimentary rock
formations
Crystalline basement
rock formations
Supercritical Volcanic
EGS*
MIT - 2007
13,300,000
USGS Circular 790
74,100
Hydrothermal
Coproduced fluids
Geopressured systems
2,400 – 9,600
USGS Circulars 726
and 790
0.0944 – 0.4510
McKenna, et al. (2005)
USGS Circulars 726
71,000 – 170,000**
and 790
Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.
Summary
Geothermal energy is an underestimated and
largely untapped resource that could have a
significant impact on the world’s energy future.
The LTITS resource base was underestimated
by 400 percent.
Advances in ORC technology make LTITS an
electric power resource.
The energy needed to produce an oil field can
be generated from the heat contained in the
waste water from the field.
The combination of LTITS, hydrothermal, GHP,
and EGS constitutes a sustainable resource that
can provide all United States electrical power
needs.