Surface and Shallow Temperature Measurements
Exploration Workshop
Geothermal Resources Council Annual Meeting
San Diego, CA. Sept. 8, 2006
Mark Coolbaugh, Chris Sladek, Jim Combs, Rick Zehner
Great Basin Center for Geothermal Energy
University of Nevada, Reno
Funding: U.S. Department of Energy, Assistant Secretary Energy Efficiency and Renewable
Energy under DOE Golden Field Office Financial Assistance Award DE-FG36-02ID14311
Surface Features Related to Geothermal Activity
- hot springs, fumaroles, and mud pots
- gas discharge zones
- anomalous spring/groundwater geochemistry
- hydrothermal eruption breccias
- mineral deposition:
silica, calcium carbonate, sulfates, borates
- hydrothermal alteration: advanced argillic alteration
- fault scarps
- vegetation anomalies
- shallow temperature anomalies
- young volcanic rocks
Wet climates and thick vegetation can conceal hot springs
and gas discharges
Meager Mountain area, British Columbia
Hot springs and seeps can be difficult to find in dry desert
climates, where smaller thermal springs and seeps are
sometimes ephemeral, appearing only during wetter, cooler
winter months
Examples from
Salt Wells, NV
It took a week to find 7 groups
of hot springs over a 5 km zone
in the Salt Wells area, NV
Borax Hot Spring, 81°C
Unnamed (unknown) hot springs, 57°C, north end Salt Wells
Spring and well
sampling for
temperatures and
geochemistry
Finding the upwelling zone in a wetland can be difficult,
but is important in order to get accurate temperatures
and geochemistry
K-type thermocouple
connected to Data Logger
(with digital storage capability)
Advantages:
cheap and rugged
Disadvantage: poor calibration
Resistance temperature devices (RTDs)
with platinum resistors (data logger on left)
Advantage: electronics insensitive to temperature
Disadvantage: more fragile than K-type thermocouples
For measurement of temperatures in existing wells, this
equipment pays for itself very quickly
Depth meter
Down-hole temperature probe with 2,000 ft of wire cable
and platinum RTD with temperature-resistant seals
Surface Features Related to Geothermal Activity
- hot springs, fumaroles,and mud pots
- gas discharge zones
- anomalous spring/groundwater geochemistry
- hydrothermal eruption breccias
- mineral deposition:
silica, calcium carbonate, sulfates, borates
- hydrothermal alteration: advanced argillic alteration
- fault scarps
- vegetation anomalies
- shallow temperature anomalies
- young volcanic rocks
Down-hole temperature gradient measurements are key
for geothermal exploration
Successful Application of Shallow Temperature
Measurements (almost everywhere it is tried?):
- Soda Lake, NV. (1 meter) Olmsted, 1977
- Upsal Hogback, NV. (1 meter) Olmstead, 1977
- Fly Ranch, NV. (1 meter) Crewdson, 1978
- Stillwater, NV. (1 meter)
- Coso, CA. (2 meters) LeShack and Lewis, 1983
- Humboldt House/Rye Patch, NV. (2 meters)
- Hawthorne, NV. (2 meters) Trexler et al., 1981
- Pumpernickel Valley, NV. (2 meters) Trexler et al., 1982
- Astor Pass and Smoke Creek Desert, NV. (2 meters)
Temperatures at a 1 m depth
Stillwater Geothermal Area,
Nevada, USA
From USGS Open File
Report 82-345 (1982)
Shallow Temperature Measurements:
1) Surface Temperature Measurements (Remote Sensing)
2) Below-surface Temperature Measurements:
a) 30 cm depth
b) 1 meter depth
c) 2 meter depth
Most previous work 1-2 m
Advantages:
- cheap, rapid
Disadvantages
- can’t see below water
table
Daily temperature variations at the surface damp out
quickly with depth.
Ground Temperatures 14-16 Aug. 2001 South of Desert Queen Mine, Hot
Spring Mtns., NV.
surface
70
Soil Temp (deg C)
60
50
1-meter-depth
40
30
20
10
8/14/2001
0:00
8/14/2001
12:00
8/15/2001
0:00
8/15/2001
12:00
8/16/2001
0:00
8/16/2001
12:00
Time of Day
Andesite Outcrop
Soil depth 33.5 in.
Sandy Soil
Soil Depth 32.5 in.
8/17/2001
0:00
15
14
13
Temperature (C)
12
At a 30 cm (1 ft) depth, the 24hour solar cycle is almost
completely damped out
11
10
Series1
9
8
7
6
5
6:00 AM
12:00 PM
6:00 PM
12:00 AM
6:00 AM
12:00 PM
6:00 PM
Date and Time
Salt Wells, NV, Feb. 26, 2006, after an unseasonably sunny, warm day
Playa (shallow groundwater…shallow temperature measurements)
Piedmont
(deeper groundwater)
(alteration mapping)
Very shallow temperature measurements (30 cm depth)
can be effective in areas like playas where groundwater
is upwelling to the surface
Salt Wells, NV
When the contrast between anomalies and background
temperatures is high, K-type thermocouples can be used
Advantages:
cheap and rugged
Disadvantage:
poor calibration
Shallow 12 in (30 cm)
Temperature Measurements
at Salt Wells, NV
(made in Feb., 2005)
1,000 measurements made in 10 days
Soft playa sediments easy to penetrate
Rapid temperature equilibration in wet
sediments
Because of the shallow depths involved,
many more measurements could be
made, greater improving the
identification of thermal structures
4-ft copper grounding rod (for
driving holes) and 5-ft steel rod
with K-type thermocouple
Measuring groundwater temperature
at a 1-m depth at borate-rich portion
of Teels Marsh, Nevada
1” dia., 1 meter long probe with Hobo temperature logger
It is possible to measure temperatures in 2-m-deep auger holes
immediately on an interactive basis to optimize the design of hole
locations, but errors are higher than if thermocouples or RTDs are
left in the hole for longer periods of time
UNR is currently designing a power hammer-driven 2-meter
hole driving system that should work more rapidly in harder
ground. The goal is to generate 30-50 measurements per day.
Temperatures in 2-meter-deep auger
holes were used to minimize the number
of temperature gradient wells drilled
CONCLUSIONS
1) Surface and shallow temperature measurements can play
a key role in geothermal exploration
2) A number of details should be addressed to obtain the
best data
3) Shallow temperature measurements can augment amd
support deeper temperature gradient drilling
The End