Preliminary results for a near surface 3D seismic survey of a geothermal system in Colorado Andrew Lamb 1, Kasper van Wijk 1, Lee Liberty 1, Mike Batzle 2, André Revil 2, Kyle Richards 2 and Chuck Diggins 3 1 Department of Geosciences, Boise State University, Boise, ID 2 Department of Geophysics, Colorado School of Mines, Golden, CO 3 Fusion Petroleum Technologies, Inc., Boulder, CO
Overview Geophysics Field Camp Geothermal Energy in the US Hypotheses Study Area and Geological Setting Self Potential Survey 3-D High Resolution Seismic Survey Conclusions Future Work
Field Camp 2007-2010 Four years of Joint Geophysics Field Camp Colorado School of Mines Boise State University Imperial College London Geophysical Methods Used Deep and shallow reflection seismic Electrical resistivity Electro-magnetics Self potential Magnetics Gravity Passive seismology Well logging and VSP
Geothermal Energy The United States leads the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants. Current development will increase this to almost 4,000 MW. This represents over 30% of world online capacity and meets the energy needs of approximately 4 million homes. Geothermal is estimated to cost 3.6 cents per kilowatt-hour, versus 5.5 cents per kilowatt-hour for coal (Mims, 2009). Colorado has a target of 30% renewable energy by 2020 (Minard, 2010).
US Heat Flow Map Source: SMU Geothermal Lab (http://smu.edu/geothermal/heatflow/heatflow.htm)
Colorado Heat Flow Map Modified from Colorado Geological Survey, 2010
Hypotheses Explore new joint inversion techniques to image subsurface structure, fractures, faults and fluid temperatures in the Mt. Princeton shallow geothermal system. Explore the possibilities of geothermal power generation in the Upper Arkansas Valley. Reduce exploration risk (1 in 10 success)
Study Area and Geological Setting
Upper Arkansas Valley Modified from Richards et al., 2010 Mt. Princeton Buena Vista Salida Rio Grand Rift
Upper Arkansas Valley Modified from Richards et al., 2010 Mt. Princeton Buena Vista Salida Rio Grand Rift
Upper Arkansas Valley Heat Source Modified from Richards et al., 2010
Upper Arkansas Valley Mt. Princeton Buena Vista Salida Modified from Richards et al., 2010
Upper Arkansas Valley Geothermal Springs -Why these locations? Mt. Princeton Buena Vista Salida Modified from Richards et al., 2010
Upper Arkansas Valley Mt. Princeton Buena Vista Sawatch Fault Salida Modified from Richards et al., 2010
Upper Arkansas Valley Mt. Princeton Buena Vista Sawatch Fault Salida Modified from Richards et al., 2010
Upper Arkansas Valley Mt. Princeton Buena Vista Sawatch Fault Chalk Creek Valley Salida Modified from Richards et al., 2010
Chalk Creek Valley Mt. Princeton From: Richards et al. 2010
Chalk Creek Valley Mt. Princeton Mt. Princeton Study Site From: Richards et al. 2010
Mt. Princeton Study Site Mt. Princeton Elevation Increase [200m N = +20m] Mt. Princeton Hot Springs Resort
The Self Potential Method Ground water flow is responsible for an electrical field Mineral MINERAUX grains VITESSE DU FLUIDE Velocity of the fluid + OH 2 O - OH O - O - O - OH O - + Na Na + Na + + Na Cl - + Na Na + + Na Cl - EAU Free LIBRE water + Na Cl - Cl - + Na Na + Cl - COUCHE Diffuse DIFFUSE layer + Na Na + + Na + Na + H 2 O - O - O COUCHE Stern Layer DE STERN + Na HO - O - O - O HO Plan d d
The Self Potential Method
Self Potential Acquisition Self potential and electrical resistivity studies in the 2008 field camp showed evidence for upwelling of hot water
Interpretation East-West fracture with upwelling hot water anomalies Wells to north and south of fracture have cold & hot water respectively.
3-D High Resolution Seismic Survey A 3-D high-resolution seismic survey was conducted during the 2009 field camp with the following acquisition parameters: Footprint of survey was approximately 240 m x 240 m Source was an Industrial Vehicles Minivib Model T-15000 Total of ~400 shots into a 576 channel Geode recording system
3-D Survey Design 40 Hz vertical phones 5 m inline receiver int. 20 m xline receiver int. 10 m inline source int. 20 m xline source int. 576 channels 1 ms sampling
3-D Seismic Survey Results Review shot records and first arrival events Two layer refraction model Refraction tomography Preliminary reflection stack
Shot Records (North to South) Synthetic Shot Record (North) Field Shot Record
Shot Records (South to North) Synthetic Shot Record Field Shot Record
First Arrivals
First Arrivals
First Arrivals
First Arrivals
Two Layer Refraction Model
Two Layer Refraction Model Sediments Bedrock Sediments Bedrock
Tomography: Bedrock Elevation Assume Bedrock Velocity ~ 3300 m/s
Self Potential with Bedrock Contours Assume Bedrock Velocity ~ 3300 m/s
Self Potential with Bedrock Contours Assume Bedrock Velocity ~ 3300 m/s
Conclusions Bedrock low trends from west-southwest to east-northeast. The bedrock low may have been formed by glacial scouring or is an old river channel. SP upwelling events are located along the bedrock low. The low refraction velocities suggest the granite is heavily fractured and most likely hydrothermally altered.