GEORG Geothermal Workshop 2016 SESSION A1, Upstream

1. Fracture Characterization at Reykjanes
Using Time-Lapse Electric Potential
Data
Lilja Magnúsdóttir and Magnús Þór Jónsson
GEORG Geothermal Workshop 2016

2. Lilja Magnúsdóttir and Magnús Þór Jónsson
Outline
Introduction
Electrical Resistivity
iTOUGH2 Simulations
Electric Field Solved Using
iTOUGH2
Inverse Analysis
Summary
2

3. 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
3
Source: iddp.is

4. 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
4

5. 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
5
Source: Ucok et al., 1980

6. 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

7. Lilja Magnúsdóttir and Magnús Þór Jónsson
Electrical Resistivity
7
Source: Northwest Geophysical Associates

8. 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
8

9. 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
9
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
p
k
q 

k

10. Lilja Magnúsdóttir and Magnús Þór Jónsson
Inverse Analysis
10

11. 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
11

12. Lilja Magnúsdóttir and Magnús Þór Jónsson
Acknowledgements
Icelandic Research Fund
IDDP
DEEPEGS
HS orka
ÍSOR
Vatnaskil
12

13. Lilja Magnúsdóttir and Magnús Þór Jónsson
Questions?
Cust
omiz