Geology and Geothermal Energy Potential in the San Luis Valley Paul Morgan Colorado Geological Survey for Workshop: Geothermal Uses in the San Luis Valley February 27, 2010 Presentation Outline: • General geology (an geologic history) of Colorado • What is important for geothermal resources • The Geology of the San Luis Valley • Geothermal resources in the San Luis Valley . 130 m.y. Paleogeography from Prof. Ron Blakey, NAU 90 m.y. 75 m.y. 65 m.y. 30-35 m.y. 15-20 m.y. 5-10 m.y. Geology of Colorado Heat Flow Map Blackwell and others, SMU Geothermal Lab, 2004 High Heat Flow >80 mW/m2 High Heat Flow is generally important for good geothermal potential Causes of high heat flow: 1) Thinner lithosphere (plate) 2) Igneous plutons at depth (young volcanism) ? 3) Residual heat (extended geologically-recent volcanism) 4) Upwelling of deep, heated groundwater – locally 5) Concentration of radioactive elements ? Effects of geological extension (basin formation) and compression (mountain building) on heat flow Deep groundwater circulation Geothermal Potential of the San Luis Valley • Regional High Heat Flow (thin lithosphere, residual heat, concentration of radioactive elements ) – Gives low-grade geothermal resources, typically < 200 F in most areas at depths up to 5000 feet • Upwelling of deep heated groundwater – May give low-grade geothermal resources at significantly shallower depths, < 200 F as shallow as 2000 feet, and higher-grade resources at currently economic depths, > 250 at < 8,000- 10,000 feet. Examples of Shallow Temperatures Studies Northern San Luis Valley Heat Flow Data Map Gradient range: 1.6 to 4.2 F/100 ft, Predicting ~128 to ~258 F at 5,000 ft The San Luis Basin has complex subsurface structure that causes groundwater to move up and down giving cold and hot spots A geothermal test well was drilled in the early 1980s Alamosa Well #1 In general the basin becomes a poorer aquifer with depth Alamosa Well # 1 The test well demonstrated encouraging temperatures San Luis Valley Oil-well Bottom-Hole Temperature Data confirm high temperatures at depth Typical: 300+ F at 10,000 feet From here to there: maximizing the geothermal potential of the San Luis Valley • There are some very creative folks in the Valley – geothermal is a mature resource, but ideas and technology continue to evolve • Ground-source heat pumps (geoexchange) – are the most efficient, clean form of heating, but swamp cooler are cheaper for cooling in the arid southwest. Use hot water to make ground-source heat pump heating even more efficient. From here to there, concluded • For direct use (< 200 F) hot water is to be found everywhere at depth in the valley – Look for places, upflow zones, where it may be hotter at a shallower depth • High-grade resources (>250 F definitely exist at depth but the permeability may be low. – As with direct use, the depth to these higher temperature probably varies with location. Reservoirs may need stimulation to produce sufficient fluids to produce electricity. CGS Geothermal web page: http://geosurvey.state.co.us Home page> Programs & Projects > Mineral & Energy Resources > Geothermal Paul Morgan: [email protected] finis Enhanced Hydrothermal Geothermal Systems Systems Geothermal Education Association <10,000 ft (<3 km) 10,000-30,000 ft (3-10 km) Hot/Warm Springs & Wells Wuanita Hot Spring, Gunnison Valley Yampah Hot Spring, Glenwood Springs Cottonwood Hot Springs, Buena Vista Mt. Princeton Area, Nathrop • Spas & Pools - 18 sites • Space Heating - 15 sites • Greenhouses - 4 site • Aquaculture - 1 sites • District Heating - 1 site Alligator Farm, Hooper well, San Luis Basin Electrical Generation - 0 sites Heber, CA Criteria for geothermal power potential: • High heat flow 2nd largest heat flow anomaly in US >100 mW/m2 • Quaternary volcanism 5 Quaternary volcanoes • Quaternary faulting >90 Quaternary faults Colorado is also outstanding in these criteria! Quaternary Faults Machette, 2003, USGS OFR 03-417 Quaternary Faults & Neogene/ Quaternary Volcanic Deposits Thermal PointThermal Distance Point Distance to Quaternary to Quaternary Faults Faults UniqueUnique Spring Spring and Welland WellAreas Areas 35 29 30 25 20 17 15 14 15 10 10 8 5 Number of Thermal Points 0 0-10 10-20 20-30 30-40 40-50 >50 Distance (miles) ThermalThermal Point Point Distance Distance to to Neogene Recent Volcanism Volcanism (<23Ma) (<23Ma) UniqueUnique SpringSpring andand WellWell Areas 40 37 35 30 30 25 20 15 12 10 6 5 Number of Thermal Points 5 3 0 0-10 10-20 20-30 30-40 40-50 >50 Distance (miles) Temperature Relationships Temp vs Distance to Quaternary Thermal Points TemperatureFaults vs Distance to Quaternary Fault All Springs and Wells 100 Temp vs Distance to Neogene 80 Thermal Points Temperature vs Distance to Recent Volcanism (<23Ma) VolcanicsAll Springs and Wells 100 60 25 mi 80 Temperature Temperature (deg C) 40 60 20 0 10 20 30 40 50 60 70 80 90 100 50°C Distance (miles) Temperature (deg C) 40 20 0 10 20 30 40 50 60 70 80 90 100 Distance (miles) Tomographic P-wave velocity variations Map at 100 Km Depth Yellow/red = Low Velocity Material from Dueker, Yuan, & Zurek, 2001 Tomographic P-wave velocity variations Cross-Section View South North D D’ ASPEN YSTN 0 100 200 300 400 Depth (km) Depth 500 -800 -600 -400 -200 0 100 200 400 600 Distance (km) from Dueker, Yuan, & Zurek, 2001 Interpretive Heat Flow Map Heat Flow Map – Mt. Princeton Heat Flow Map – Rico Heat Flow Map – Trinidad Bottom Hole Temps – Denver Basin Denver Bottom Hole Temps – San Juan Basin Durango In Summary: • Colorado is prospective • Multiple lines of evidence • The more we look … … the better the prospects Geothermal Gradient Map >50 C/km or >2.7 F/100 ft San Luis Basin at Alamosa Back of the Envelope Analysis I • Like most sedimentary basins in Colorado, San Luis Valley has high geothermal gradients (~ 2.4 ̊F/100 ft; ~50 ̊C/km) – good geothermal prospects. • Porous/permeable sediments are relatively thin (1500 ft; 500 m) around Alamosa – deeper volcanic fill is low permeability. • Effects of Alamosa horst and its faults are relatively unknown. Back of the Envelope Analysis II • Hindsight: Alamosa Geothermal Well # 1 (early 1980s) may have had more success if logs could have been run on the hole to find a permeable zone • Techniques are now more advanced to increase permeability, primarily hydrofracing – expensive, but high returns • This is one of the directions of the future! Isostatic Gravity Anomaly Map (from Oshetski and Kucks, 2000; USGS OFR-00-42) MIT Study - Enhanced Geothermal Systems Table 2.2. High-grade EGS areas (>200 C at depths of about 4 km) from Tester and others, 2006 MIT Study - Enhanced Geothermal Systems 3.5 6.5 Forkm EGS, Coloradokm has the one of the best high temp resources in the 10 km US. from Tester and others, 2006.