Potential Field Methods in
Geothermal ExplorationGaud Pouliquen & Birgit Woods – Geosoft Europe Ltd.
Potential Field Methods in Geothermal Exploration
• What is Potential Field?
• Geophysical methods: gravity and magnetics
• low cost
• covers large area
• How it helps with Geothermal Exploration?
• regional geologic framework
• better understanding of the subsurface
• Integrated modeling
• Guide exploration of the area’s geothermal system – efficient planning
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Potential Field Methods in Geothermal ExplorationCase Studies – Evaluating Geothermal Prospects
1. Roer Valley Graben, the Netherlands
2. Warner Valley, Oregon U.S.
GGW 2018, ReykjavÍk - Upstream
Roer Valley
Graben
(RVG)
Zeeland
Platform
(ZP)
London-
Brabant
Massif
(LBM)
Central
Netherlands
Basin
(CNB)
Maasb
ommel
High
(MBH)
L-
Saxony
Basin
(LSB)
TF
PBFRF ?(Modified after Duin etal., 2006) ??
GGW 2018, ReykjavÍk - Upstream
Dinantian formation - potential
geothermal reservoir?
• Ultra-deep reservoir (>4 km)
• Proven Carboniferous &
Permian O&G reservoir
• Building subsurface model
from existing data
• Integrated modelling
approach
Potential Field Methods in Geothermal Exploration1. Roer Valley Graben, the Netherlands
Depth
(km)
HSW-01-S1
Courtesy: Moser Geophysical Services
New processed PSDM section
N90-09(10006)
Potential Field Methods in Geothermal Exploration1. Roer Valley Graben, the Netherlands
GGW 2018, ReykjavÍk - Upstream
SW NE• 1991 2D seismic
line
• Limited resolution
beyond 3 km
Structural interpretation of Potential
field data
• Gravity data: TNO
• Magnetic data: public
domain Emag2
• Transformative maps
• Basement mapping
-2.448
2.513
-0.619
-0.422
-0.317
-0.242
-0.182
-0.133
-0.092
-0.056
-0.023
0.011
0.045
0.081
0.121
0.165
0.217
0.282
0.369
0.504
BG_BP23-29.5kmmGalTNO
Bouguer Gravity 23-
29,5km BP
Potential Field Methods in Geothermal Exploration1. Roer Valley Graben, the Netherlands
GGW 2018, ReykjavÍk - Upstream
gravity
magnetic
0 km-
1 km-
2 km-
3 km-
4 km-
5 km-
6 km-
?UDG formations?
?
Densities kg/m3
Stratigraphy Density log
Interpreted depth migrated seismic
Preliminary subsurface model
Potential Field Methods in Geothermal Exploration1. Roer Valley Graben, the Netherlands
GGW 2018, ReykjavÍk - Upstream
Permian
DinantianBasement
0 km-
10 km-
20 km-
30 km-
mantle
Lower crust
SWgravity
magnetic
±8km
NE
• Constrained by well
densities, stratigraphy &
seismic – integrated
modeling
• ~8 km of sediments
between well TD and Top
Basement
Potential Field Methods in Geothermal Exploration1. Roer Valley Graben, the Netherlands
GGW 2018, ReykjavÍk - Upstream
Final Gravity model
Warner
Valley
• NW Basin and Range
• High heat flow
• Tectonically complex
Basin-and-Range Province
& Quaternary faults
Heat Flow
(Williams&Deangelo, 2008)
RBF HF
(mW/m2)
<30.0
30.1-40.0
40.1-50.0
50.1-60.0
60.1-70.0
70.1-80.0
80.1-90.0
90.1-100.0
>100.0
Warner
Valley
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Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
Structural controls
Intra-basin structures are
concealed by Quaternary alluvium
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Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
Crump Geyser
-119°30'-120°-120°30'
42°30'
42°CA
NV
OR
Gravity Data
new
existing
Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
GGW 2018, ReykjavÍk - Upstream
Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
GGW 2018, ReykjavÍk - Upstream
normal
reversed
undetermined
no data
Polarity
Lithology
Tb
Tsb
Ttu
Toma
Dep
th (
ft)
Dep
th (
ft)
CG35-34 CG38-34
1000
0
500
2000
2500
3000
1500
1000
0
500
2000
2500
3000
1500
35-34 38-34
38-34
35-34
• Geologic mapping
• Rock properties from outcrops
and drill core
• Paleomagnetic studies
• Seismic surveys
Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
GGW 2018, ReykjavÍk - Upstream
Profile location
2D models constructed along
several intersecting 2D profiles
were used as the initial input to
build the 3D model
Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
GGW 2018, ReykjavÍk - Upstream
3D modeling
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• 3D modeling
• 9 layers extrapolated from 2D
models
• Surfaces geometry is inverted
• Results
• Model reveled deep basins
both north and south of Crump
Geyser
• Thermal fluids are funneled
from south and north
6x10km 3D model area
Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.
Potential Field Methods in Geothermal Exploration
• Potential Field Methods
• aid basin/reservoir characterization &
mapping faults & contacts.
• 2D/3D modelling, integrated with
seismic, well, paleomagnetics, rock
properties reveal basin/reservoir
structures that likely play a critical role
in influencing fluid flow.
• better understanding of the subsurface
= efficient planning & risk mitigation
• low cost method
• What’s next?
• inversion, borehole constraints
GGW 2018, ReykjavÍk - Upstream