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/m 2
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: paul.morgan@state.co.us
finis
Hydrothermal Systems Enhanced Geothermal 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
Alligator Farm, Hooper well, San Luis Basin Spas & Pools - 18 sites Space Heating - 15 sites Greenhouses - 4 site Aquaculture - 1 sites District Heating - 1 site Electrical Generation - 0 sites Heber, CA
Criteria for geothermal power potential: High heat flow Quaternary volcanism Quaternary faulting 2 nd largest heat flow anomaly in US >100 mw/m 2 5 Quaternary volcanoes >90 Quaternary faults Colorado is also outstanding in these criteria!
Machette, 2003, USGS OFR 03-417 Quaternary Faults
Quaternary Faults & Neogene/ Quaternary Volcanic Deposits
Number of Thermal Points Thermal Point Distance to Quaternary Faults Thermal Point Distance to Quaternary Faults Unique Unique Spring Spring and Well and Well Areas Areas 35 30 25 29 20 15 10 17 15 8 14 10 5 0 0-10 10-20 20-30 30-40 40-50 >50 Distance (miles)
Number of Thermal Points Thermal Thermal Point Point Distance to to Neogene Recent Volcanism (<23Ma) (<23Ma) Unique Spring and Well Areas 40 35 30 25 20 37 30 15 10 5 12 6 5 3 0 0-10 10-20 20-30 30-40 40-50 >50 Distance (miles)
Temperature (deg C) Temperature (deg C) Temperature Relationships Temp vs Distance to Quaternary Faults Thermal Points Temperature vs Distance to Quaternary Fault All Springs and Wells 100 80 60 40 100 80 Temp vs Distance to Neogene Volcanics Thermal Points Temperature vs Distance to Recent Volcanism (<23Ma) All Springs and Wells 25 mi 60 20 0 10 20 30 40 50 60 70 80 90 100 Distance (miles) 40 50 C 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
Depth (km) South North 0 100 Tomographic P-wave velocity variations Cross-Section View D D ASPEN YSTN 200 300 400 500-800 -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 km 10 km 6.5 km For EGS, Colorado has the one of the best high temp resources in the US. from Tester and others, 2006