Andrew Lamb1, Kasper van Wijk1, Lee Liberty1 , Mike Batzle2, André Revil2, Kyle Richards2 and

Chuck Diggins3

1 Department of Geosciences, Boise State University, Boise, ID

2 Department of Geophysics, Colorado School of Mines, Golden, CO3 Fusion Petroleum Technologies, Inc., Boulder, CO

Preliminary results for a near surface 3D

seismic survey of a geothermal system in

Colorado

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

Salida

Mt. Princeton

Buena VistaModified from Richards et al., 2010

Rio Grand Rift

Upper Arkansas Valley

Salida

Mt. Princeton

Buena VistaModified from Richards et al., 2010

Rio Grand Rift

Upper Arkansas Valley

Modified from Richards et al., 2010

Heat Source

Upper Arkansas Valley

Salida

Mt. Princeton

Buena Vista

Modified from Richards et al., 2010

Upper Arkansas Valley

Salida

Mt. Princeton

Buena Vista

Modified from Richards et al., 2010

Geothermal Springs

-Why these locations?

Upper Arkansas Valley

Salida

Mt. Princeton

Buena Vista

Sawatch Fault

Modified from Richards et al., 2010

Upper Arkansas Valley

Salida

Mt. Princeton

Buena Vista

Sawatch Fault

Modified from Richards et al., 2010

Upper Arkansas Valley

Salida

Mt. Princeton

Buena Vista

Sawatch Fault

Modified from Richards et al., 2010

Chalk Creek Valley

Chalk Creek Valley

Mt. Princeton

From:

Richards et al. 2010

Chalk Creek Valley

Mt. Princeton

From:

Richards et al. 2010

Mt. Princeton Study Site

Mt. Princeton Study Site

Mt. Princeton

Hot Springs

Resort

Elevation Increase

[200m N = +20m]

Mt. Princeton

The Self Potential Method

OH 2+

O-

O-

O-

OH

OH

+ Na

+

Cl-

O -

O-

Na

+ Na

+ Na

+ Na

+ Na

Cl-

+ Na

EAU LIBRE

Cl-

+ Na

H O2

+

O-

HO

HO

O-

O-

O-

O-

+ Na

COUCHEDE

STERN+ Na

COUCHEDIFFUSE

Cl-

+ Na

+ Na

+ Na

+ Na

Plan d

d ­

VITESSE DU FLUIDE

+ Na

Cl-

MINERAUX

Velocity of the fluid

SternLayer

Diffuselayer

Free water

Ground water flow is responsible for

an electrical field

Mineral grains

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 ElevationAssume Bedrock Velocity ~ 3300 m/s

Self Potential with Bedrock ContoursAssume Bedrock Velocity ~ 3300 m/s

Self Potential with Bedrock ContoursAssume 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.