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.

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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) ??

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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

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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

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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.

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Potential Field Methods in Geothermal Exploration2. Warner Valley, SW Oregon, U.S.

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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.

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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.

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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

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