an exercise in geothermal assessment - long valley caldera · an exercise in geothermal assessment...
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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.