Geothermal Systems: Geologic Origins of a Vast Energy Resource Energy From the Earth Energy-Land-Water Connections Speaker Series James E. Faulds, PhD Nevada State Geologist and Professor Nevada Bureau of Mines and Geology University of Nevada, Reno Tuesday, September 15, 2015 Longworth House Office Building
What is Geothermal Energy? Geothermal = Earth s heat Heat sources? Residual heat left over from earth s formation Earth s core is about the same temperature as the surface of the Sun or ~6000 C (>10,500 o F) Earth loses heat continuously Normal geothermal gradient ~25 C/km (77 o F/3300 ft) Elevated gradient in some areas Volcanism Extending or thinning crust
Where are Geothermal Resources? Ring of Fire Country MW United States 3500 Philippines 1904 Indonesia 1333 Mexico 1005 Italy 901 New Zealand 895 Iceland 664 Japan 537 Tectonic Plate Boundaries & Geothermal Power Plants
Geothermal Contribution to U. S. Energy Budget? ~0.5% of energy produced. Potential for >10% - 20x current. Nevada already 10-15% 1 MW powers ~750-1000 residential homes or ~3k people. So why change? Huge resource! (Annual heat flow = 10x annual energy consumption of U. S.) Nil greenhouse gases Improved energy independence Desert Peak, Nevada McGinness Hills, Nevada
Source: GEO How Does a Geothermal System Work?
Geothermal System Anatomy Typical Geothermal Reservoir Hot, permeable fractured rock Deep levels far below fresh-water aquifers 300 to 2,900 m (1,000 to 9,000 ft) Reinject water with minimal loss Freshwater Aquifer Water Wells Geothermal Injection Well Geothermal Production Well fractured rocks Geothermal Reservoir
Typical Geothermal Footprint and Infrastructure Power plant (~500 ft) Well field Production wells generally 1 to 6 wells Injection wells generally < 5 wells Monitor wells Well pads Service roads Connecting power line Layout and size differ for each system Salt Wells, Nevada Salt Wells, Nevada
Major Types of Geothermal Systems Fault controlled most common in U.S. Volcanic related Deep sedimentary hosted EGS Engineered geothermal system in hot dry rocks Volcanic New Zealand Deep basins Western Utah Fault controlled Great Basin, Western U.S. EGS Soultz, France Hot impermeable rocks Hydraulically stimulated reservoir
Great Basin Region Richest part of U.S. for geothermal resources Warm crust extending or pulling apart As crust thins, hot rocks get closer to surface Mainly fault controlled systems Faults allow hot water to reach shallow levels 550 MW from ~24 power plants Greater potential 30,000 MW Cannot drill 6 km deep (20,000 ft) economically Most systems blind or hidden with no surface hot springs Must find hot water pathways using geological techniques Cold Ground water Reservoir Schematic Cross Section Heated Ground water Hot Rocks
Exploration Challenges Exploration Challenges Spring directly above upflow from deep source (uncommon) Outflow from source (common) Hidden or blind systems (common) Results significant drilling risk Blue Mt., Nevada Non-Productive Well Productive Well Hot dry wells Overturn in down-hole temperatures Improving conceptual models to: Locate areas of upflow Avoid typically less productive outflow zones Productive wells commonly proximal to non-productive wells Non-Productive Well Productive Desert Peak, Nevada Productive Well Non-Productive From Richards and Blackwell, 2002 Non-Productive
Characteristic Fault Patterns Geothermal Systems Most fields not on major fault segments Stress relieved periodically by major earthquakes Rocks pulverized into clay-size particles, which limits permeability Most on less conspicuous extensional faults Most systems in areas where multiple closely spaced faults: Fault tips: Terminating, horse-tailing faults Steps in normal fault zones Intersecting faults dilational quadrants Accommodation zones: Overlapping opposing faults Most Common Setting Step-Overs or Relay Ramps
Exploration Work Flow: 3D Modeling Geologic Map Subsurface Data Productive Wells Non-Productive Well Drill Target Favorable Faults - Fluid Flow Fault Density in 3D
Next Steps Geothermal Potential Map, Central Nevada Continue characterization of existing systems to better define geothermal signatures New generation of geothermal potential maps Begins with detailed studies of surface geology and Improving techniques to understand subsurface 3D modeling critical Develop EGS technologies through FORGE initiative Frontier Observatory for Research in Geothermal Energy McGinness Hills, Nevada 78 MW new power plants Potential EGS FORGE Site Fallon, Nevada
Carson Sink, Nevada Geothermal Country Fallon EGS FORGE Site Power Plants Known Hot Systems Blue = blind system N 10 miles
Geothermal Systems: Geologic Origins of a Vast Energy Resource Energy From the Earth Energy-Land-Water Connections Speaker Series Thank You James E. Faulds, PhD jfaulds@unr.edu 775-682-6650 www.nbmg.unr.edu Tuesday, September 15, 2015 Longworth House Office Building