A1 Magnús Þór Jónsson Fracture Characterization at Reykjanes Using Time-Lapse Electric...

Fracture Characterization at Reykjanes Using Time-Lapse Electric Potential

Data

Lilja Magnúsdóttir and Magnús Þór JónssonGEORG Geothermal Workshop 2016

Lilja Magnúsdóttir and Magnús Þór Jónsson

Outline

Introduction

Electrical Resistivity

iTOUGH2 Simulations

Electric Field Solved Using

iTOUGH2

Inverse Analysis

Summary

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Introduction

Fracture characterization is crucial

to ensure adequate supply of

geothermal fluids and efficient

thermal operation of wells

Interconnected conductive fractures

control mass and heat transport in

the system

IDDP-2 is expected to be drilled

down to 5 km depth at Reykjanes

Proposed project and workplan

discussed for characterizing

fracture networks at Reykjanes

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Source: iddp.is

Lilja Magnúsdóttir and Magnús Þór Jónsson

Objective

Water with less electrical conductivity than the brine will be

injected into the reservoir

Electrical potential will increase as the injected water fills

fracture paths

Time-lapse electric potential data is related to the

connectivity of the fracture network

Estimate fracture connectivity at Reykjanes using direct

current electric potential measurements during water

injection

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Electrical Resistivity

Fractures initially filled with

brine (sea water)

Water injected to enhance

contrast in resistivity between

rock and fractures

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Source: Ucok et al., 1980

Lilja Magnúsdóttir and Magnús Þór Jónsson 6

Electrical Resistivity

Direct current

injected and

electric potential

measured

Electric potential

difference/Resistivity

changes between

wells as fluid is

injected

Lilja Magnúsdóttir and Magnús Þór Jónsson

Electrical Resistivity

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Source: Northwest Geophysical Associates

Lilja Magnúsdóttir and Magnús Þór Jónsson

Simulations using iTOUGH2

Develop a model of Reykjanes to a depth of >5 km

Use EOS1SC in iTOUGH2 to model heat source

Develop a discrete fracture model of Reykjanes using an

approach by Karimi-Fard et al.

iTOUGH2 used to simulate the flow of injected water

iTOUGH2 used to simulate electric

field

Inverse analysis used with resistivity

measurements to estimate fracture

network

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Electric Field Solved Using iTOUGH2

Ohm’s law:

Darcy’s law:

Analogy between Darcy’s law and Ohm’s law

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VJ

IQm

Darcy’s law: Ohm’s law:

Flux of: Water q Charge J

Potential: Pressure p Voltage V

Medium

property:

Hydraulic

conductivity

k/μ

Electrical

conductivity

σ

Source: Hyperphysics, Georgia State University

pk

q

k

Lilja Magnúsdóttir and Magnús Þór Jónsson

Inverse Analysis

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Summary

Proposed project and workplan discussed for estimating

fracture networks at Reykjanes

Resistivity will be measured as water is injected into the

reservoir

iTOUGH2 will be used to model the flow of water in the

reservoir as well as the electric field as the resistivity

changes

Inverse analysis used with resistivity measurements to

estimate fracture network

We thank the Icelandic Research Fund for the

support

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Acknowledgements

Icelandic Research Fund

IDDP

DEEPEGS

HS orka

ÍSOR

Vatnaskil

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Lilja Magnúsdóttir and Magnús Þór Jónsson

Questions?

Cust

omiz

e