An Exercise in Geothermal Assessment - Long Valley Caldera

UC Davis Geology Dept

Geology of Geothermal Resources Course

Fall 2010

PROFESSORS:Bill GlassleyJim McClainPeter SchiffmanRobert Zierenberg

GRADS:Katrina ArredondoScott BennettAustin ElliottAndrew FowlerJoy HinesMaia KostlanMaya Wildgoose

UNDERGRADS:Adam Asquith Lauren AustinLesley Barnes Carolyn CantwellDerek DavisKevin DelanoDominique Garello

Samuel HawkesRachael JohnsonTucker LanceRita MartinAlexander MorelanThomas MykytynKevin RenlundDaniel Sousa

Ten week class2 hours per week of lecture and discussion

Guest Lecturers

Gene Suemnicht (EGS, Inc.)Mike Sorey (USGS)

Colin Williams (USGS)Tom Box (Calpine)

Field Trips Mammoth Area and

Casa Diablo Geothermal SiteBrigette Martini and Charlene Wardlow (Ormat)

Geysers Geothermal FieldTom Box and Karl Urbank (Calpine)

Mammoth Area Research Projects

One Day in the Field

Research TeamsGeophysicsStructure

Fluid SamplingCore Logging

One MonthAnalyze Samples

Interpret Data Present Results

Restricted to In House EquipmentLow Cost Analysis

A Geothermal Assessment-- Long Valley Caldera --

UC Davis Geology Dept

Geology of Geothermal Resources Course

Fall 2010

PROFESSORS:Bill GlassleyJim McClainPeter SchiffmanRobert Zierenberg

GRADS:Katrina ArredondoScott BennettAustin ElliottAndrew FowlerJoy HinesMaia KostlanMaya Wildgoose

UNDERGRADS:Adam Asquith Lauren AustinLesley Barnes Carolyn CantwellDerek DavisKevin DelanoDominique Garello

Samuel HawkesRachael JohnsonTucker LanceRita MartinAlexander MorelanThomas MykytynKevin RenlundDaniel Sousa

• Located between Sierra Nevada and Basin & Range provinces

• Straddles step-over between normal faults

• Formed during large (~600 km3) eruption ~760 ka (Bailey et al., 1976)

• Younger, recent volcanism in western caldera

– provides thermal energy to active geothermal system

Henry et al. (2007)

USGS

Long Valley Caldera

Long Valley Caldera

Bailey (1989)

Suemnicht (2006)Early Rhyolite

Megabreccia

Bishop Tuff

Pre-Caldera Rx

Active Tectonics Study of the Long Valley Caldera

Scott Bennett

Tectonics Study #1Discovery (Dry Creek) Dome

Tectonics Study #2Hilton Creek Fault Splay

Bailey (1989)

USGS

Fault Mapping (1): Discovery Dome

GOALS

• Confirm presence of NE-SW striking fault

• Looking for evidence of geothermal fluid flow

METHODS

• mapping of brittle faults

• search for and collect samples of mineral precipitates

Discovery Dome

Suemnicht & Varga (1988)

FLUID FLOW ON FAULT HANGING WALL amorphous

silica

Discovery Dome

Fault Mapping (2): Hilton Creek Fault

GOALS

• Examine and compare style of faulting inside and outside the caldera

• distributed faulting can provide conduits for geothermal fluid flow

METHODS

• mapping of Quaternary deposits and faults

• measure fault scarp profiles with ‘slope scopes’ USGS

Hilton Creek Fault Entering the Caldera

USGS

moraine

HILTON CREEK FLT NORTH

HILTON CREEK FLT SOUTH

HILTON CREEK FLT (MCGEE CREEK)

ROUND VALLEY FLT (PINE CREEK)

5X VERTICAL EXAGGERATION

Meters

Meters

Meters

Meters

Meters

Meters

Meters

Meters

NO VERTICAL EXAGGERATION

NO VERTICAL EXAGGERATION

NO VERTICAL EXAGGERATION

survey by Bruce Perez

survey by Bruce Perez & Derek Davis

survey by Rachael Johnson & Kevin Delano

DEM survey by Austin Elliott & Alex Morelan

42 m

22 m

13 m

10 m

Conclusions

• (1) Discovery Dome

– Confirmed existence of NE-SW faults at Discovery Dome

– Fluid flow and mineral precipitation observed on faults

• (2) Hilton Creek fault

– fault system splays upon entry to Long Valley Caldera

– upper crust in Long Valley Caldera may be warmer, allowing more distributed faulting

– splays potentially create multiple conduits for subsurfacegeothermal fluid flow

Alteration and Petrology of the Long Valley Caldera:

Study of Core BC 12-31

Maya Wildgoose

Bailey (1989)

Goals1) Assess the spatial and temporal relations of alteration mineralogy in this core hole

2) Investigate the origin of the Megabreccia unit

3) Determine if the Megabreccia exhibits characteristics that would make it an effective hydrologic barrier

Core Logging

Mix of undergraduate and graduate students and faculty

Photos courtesy of Andrew Fowler

Core

Core stored at the Casa Diablo shed; logged 8 boxes (~80 feet of core)

Early Rhyolite

1248

1248

1251

Megabreccia1400

14161416

1418

Bishop Tuff1441

1891

1891

ResultsEarly Rhyolite: Silicification followed by carbonate veining and illitization

Megabreccia: Chloritiziation and illitization of the matrix has effectively cemented the breccia, with late generation of carbonate veins; makes it an effective hydrologic barrier between hotter hydrothermal fluids above and cooler fluids below

Bishop Tuff: Upper portion is unwelded and similar to Early Rhyolite. Lower portion is densely welded, but cut by large fractures lined with hydrothermal quartz and illite.

QUARTZ

ILLITEILLITE

CHLORITEILLITE

ALBITE

Temperature Calculations

• Illite in upper Bishop Tuff (Bishop and Bird 1987 method): ~ 2000C, which is consistent with current downhole temperatures

• Chlorite in upper Bishop Tuff (Inoue 2009 method): ~ 2500C (sampled from matrix chlorite)

Fluid Rock Interaction:A Study of Core BC12-31

Andrew Fowler

Fluid GroupGoal

• Determine subsurface

temperatures from

geochemical analyses of fluid

and mineral samples

Outcome

• Evidence for evolution of the

geothermal system in core

BC12-31

• Chlorite and illite temperatures

are key evidence

Hot Spring Sampling – Hot Creek

Sampling

• Hot spring and creek fluid samples– Major elements– Trace elements– δ18O– δ2H

• Surface travertine sample• Vein carbonate BC 12-31

– δ13C and δ18O

Travertine

Geothermometers – Hot Creek

• Well LV86-9 data used as a control (Shevenell et al 1987)• Quartz and Na-K-Ca fit LV86-9 measured temp. best• Quartz shows lower temp. than Na-K-Ca for Hot Creek

Geothermometer Hot CreekLV86-9

(RDO-8)

Measured Temperature 202°C

SiO2 (Quartz) 162°C 207°C

Na-K-Ca 192°C 209°C

SiO2 (Amorphous silica) 135°C 82°C

K-Mg 154°C 168°C

Na-K 191°C 242°C

Activity Diagrams

• Mineral stability diagrams generated for 200°C• LV 86-9 fluid plots in equilibrium with muscovite• Consistent with presence of illite in BC12-31• Illite temperatures modern phenomenon

δ18O Temperature - Travertine

fluid – calcite oxygen isotope fractionation (O’Neil 1969):

– δ18O Calcite [0.19 to -0.33‰+

– δ18O Fluid [-14.4‰+

– Temperature

Travertine Calculated Temperature: 124-130°C

Travertine δ18O at 93°C: -17.5 to -18.1‰

≈ 3.0 ‰ lighter than current fluids in Hot Creek area

Current fluid in BC 12-31 [-15.69 ‰+ (personal communication LBNL)

Carbonate veins in BT and ER [-7.6 to -8.0 ‰+:

– Either higher temps than present [227 to 237˚C+ – Or 1.3‰ lighter fluid than present *-17.0 ‰ ]–Currently unresolved

Carbonate veins in Megabreccia *0.3 to 8.7 ‰+:

–Either lower temps than present [46 to 110˚C+–Or heavy δ18O fluids [-9.5 to -1.1 ‰ +

δ18O Temperature – BC 12-31

– MB veins formed at hot temperatures: isotopically heavy fluids– Two distinct vein temps: consistent with microprobe results– Hotter fluid inclusion group consistent with BT and ER δ18O Temp.

Fluid Inclusion Temps -Megabreccia

Convict Lake Formation

Mount Morrison Sandstone

δ13C

δ18O

δ13C Calcite – BC 12-31

– Roof pendant carbonate and volcanic calcite veins distinct

– Megabreccia carbonate plots in distinct groups; clasts and veins

– MB veins appear to have formed from heavy δ18O fluids

– Low water-rock ratio in Megabreccia

Conclusions

• Quartz underestimates Hot Creek temperatures

• Na-K-Ca indicates deeper reservoir temp

• Travertine formed from light (glacial?) fluid

• MB contains detrital roof pendant carbonate

• Veins in MB from heavy fluid (rock dominated fluids)

• Evidence for long-term cooling trend in system– Higher chlorite temps than (current) illite temps

– Two fluid inclusion temp. clusters trend toward current temps

Geophysics: MT Field survey + geophysical synthesis

Maia Kostlan

Outline(1) Magnetotellurics field survey

– Methods

– Field work

– Data and results

– Interpretations

(2) Study of previous Geophysical work in LVC

– Pribnow et al., 2003

– Onacha, 2006

– used for assessment

(1) Magnetotellurics field survey

Goal

• To familiarize the group with electromagnetic tools that can be valuable for geothermal exploration

Expectations

• Anisotropy in the subsurface

• Variable resistivity

Magnetotelluric Survey

• Magnetotellurictechnique

• Geophysical applications include resistivity measurements of the subsurface

Photo courtesy of Lesley Barnes

Resistivity• Subsurface resistivity

decreases as the following factors increase:

–Fluid content

–Salinity

–Porosity (if fluids present)

–Clay content

• Resistivity values can help locate regions of potential hydrothermal flow and/or alteration in the subsurface

Photo courtesy of Rita Martin

Methods

• Geometrics Stratagem EH4 MT survey equipment

– Receiver

– Transmitter

– Recording box

Photos courtesy of Lesley Barnes and Rita Martin

North-South Direction

East-West Direction

Bailey, 1986

Low Frequency Band

Bailey (1989)

High-Frequency Band (0.75-92khz)

Interpretations

• N-S measurements higher than E-W measurements imply higher conductivity in the E-W direction

– Possibly due to the E-W oriented faults?

• Resistivity is highest at the surface, decreases until a depth of 250-300m where it remains roughly constant

(2) Geophysics Synthesis

Goal

• To estimate the volume of the potential geothermal reservoir using previously collected geophysical data and temperature bore-hole data

E-W Resistivity Profile

Pribnow et al., 2003

Resistivity Contours

20Ωm cut off

Modified from Pribnow et al., 2003

Temperature Boreholes & Contours

(Suemnicht and Varga, 88)

Inyo – 4 44-16

Resistivity, Temperature and Geothermal Reservoir

Area = 3.12km2

Avg Thickness = 0.7 km

Geophysical and temperature data

Resistivity and Temperature Contours

Resistivity, Temperature and Geothermal Reservoir

Area = 3.05 km2

Avg Thickness = 0.48 km

Map-view Extent of Reservoir

Area =

27.5 km2

Map Area = 27.5 km2

Avg Thickness = 0.59 km

Volume = 16.23 km3

Map-view Extent of Reservoir

• Combining temperature and resistivity data can help define 2D limits of a geothermal reservoir

• Using intersecting geophysical transects can provide 3D constraints for volume estimates

• Synthesis of existing data allows for a volume estimate of the Long Valley geothermal resource

Conclusions

National Geothermal Student Competition

• …”A competition that challenges students to advance their understanding of geothermal energy's potential as a significant contributor to the nation's energy portfolio in the coming decades.”

• Student teams conduct an assessment of the geothermal energy potential of the Rio Grande Rift in southern Colorado and northern New Mexico

• Each collegiate team will assess a number of factors, such as geologic, engineering, environmental, land use, policy and culture

Participating Schools* Colorado School of Mines * Oregon Institute of Technology * Pennsylvania State University* San Diego State University * Stanford University * Texas A&M University * University of California, Davis * University of Idaho * University of North Dakota * University of Utah * Virginia Polytechnic Institute and State University

UC DavisProject

Location: Valles Caldera, near Los Alamos, NM

Proposal: Use unique approach to managing complex geothermal datasets with a re-

evaluation of the geothermal system using a 3-D visualization environment = KeckCAVES

Valles Caldera Subsurface Temperature Extrapolation

MeetingWhen: June 23-24

Where: Santa Fe, NM

• Our presentation will include (hopefully) a 3-D TV or 3-D video of what we’ve done in the KeckCAVES with our data; If we win, we get $$ and a trip to San Diego for the GRC 2011 meeting

Acknowledgments

• Janice Fong (UC Davis)

• Brigette Martini (Ormat)

• Gene Suemnicht (EGS, Inc.)

• SNARL

Instructor’s Conclusions

Strong Student Interest In Geothermal

Instructor’s Conclusions

Strong Student Interest In Geothermal

Field Trips and Research Projects

Instructor’s Conclusions

Strong Student Interest In Geothermal

Field Trips and Research Projects

Top quality, highly motivated UCD students using in house analytical resources are a cost

effective means of producing relevant research results

Questions?

Interpretation of TEM-measurements in Krafla Field 300 m under sea level .

Vítismór

VVííttiissmmóórr

Krafla

KRAFLA STATION

Sandabotnar

V-02

V-01

Leirhnjúkur

Vestursvæ_i

Figure 3. A resistivity map of the Hengill central volcano at 850 m b.s.l. showing variations in resistivity. The cross-hatched areas define high resitivity cores below low resistivity, and are interprted to indicate alteration temperatures of over 200°C.