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.

Geothermal energy overview What we thought we knew What has changed Outline Take home message Geothermal energy overview What we thought we knew What has changed What we now know The general outline of the talk is as follows. I want you to have the take home message up front. We will have a bried look at how geothermal energy is defined by those who conduct research and use the resource. We will look at what we knew a few decades ago when finding renewable energy was briefly a priority, and we will look at what has changed. We will look at some of the details of how one determines a resource and at some of the resources that are coming on line. Finally we will look at an analysis of the resource base and in some detail at the midcondintnet region.

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. There are four bullets in the take home message

Image Source: Geothermal Education Office, Tiburon CA Earth’s interior is hot, temperatures increase with depth, the temperature gradient varies with tectonic regime. 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. Space heating could be a major factor Pierre SD Aquaculture is an important aspect – Leo Ray in Idaho

Source: Geothermal Education Office, Tiburon CA

Source: Geothermal Education Office, Tiburon CA

Electrical Power Country 1990 MWe 1995 MWe 2000 MWe 2005 MWe Total 5831.72 6833.38 7974.06 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 Guess the countries that produce the most electrical from geothermal energy.

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%.

Calculating the geothermal resource base Conductive heat flow at the surface is described by Fourier’s Law of Heat conduction Assuming we know heat flow, temperature at depth “z” may be calculated by

Generalized Thermostratigraphy of the Williston Basin Depth Thermal Temp. Top of Unit System Thickness 70% of Max. Thickness Conductivity Gradient   (meters) (W m-1 K-1) (mK m-1) (°C) Quaternary 510 1.4 42.9 6.0 Tertiary 1250 357 1.2 49.9 27.9 Cretaceous 1640 1232 48.2 71.6 Jurassic 395 2380 1.3 44.6 126.8 Triassic 225 2657 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 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 22.6 180.3 Cambrian 300 4649 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 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 MW @ 140oC MW @ 180oC Montana 189,899 16 47 88 Colorado 487,331 44 112 212 North Dakota 182,441 17 42 79 South Dakota 6,725 1 2 3 Nebraska 102,005 9 23 Kansas 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 Source: "The Future of Geothermal Energy," MIT Report, January 22, 2007.

Geothermal Energy Utilization 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 Conduction-dominated EGS Sedimentary rock formations 100,000* may be 400,000 MIT - 2007 Crystalline basement rock formations 13,300,000 Supercritical Volcanic EGS* 74,100 USGS Circular 790 Hydrothermal 2,400 – 9,600 USGS Circulars 726 and 790 Coproduced fluids 0.0944 – 0.4510 McKenna, et al. (2005) Geopressured systems 71,000 – 170,000** * Excludes Yellowstone National Park and Hawaii ** Includes methane content 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.