Numerical simulation studies of ihe geothermal resource in singapore 1

NUMERICAL SIMULATION STUDIES OF THE
GEOTHERMAL RESOURCE IN SINGAPORE
HENDRIK TJIAWI
NATIONAL UNIVERSITY OF SINGAPORE
2013
NUMERICAL SIMULATION STUDIES OF THE
GEOTHERMAL RESOURCE IN SINGAPORE
HENDRIK TJIAWI
B.Eng.(Hons.), NUS
A THESIS SUBMITTED FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2013








DECLARATION

I hereby declare that the thesis is my original work and it has been written by me in its
entirety. I have duly acknowledged all the sources of information which have been
used in the thesis.
This thesis has also not been submitted for any degree in any university previously.

Hendrik Tjiawi
08 Apr 2014
Acknowledgements
I would like to express my most sincere gratitude to Prof. Andrew C. Palmer for
his kind support in terms of time, knowledge, ideas, encouragements and finance for
this study. My gratitude is also extended to Dr. Grahame J. H. Oliver for his vast
constructing comments, supports, and expertise, without which the study may not
have proceeded this far. The study is mainly supported by ACrF Tier 1 grant R-264-
000-275-133 from the Ministry of Education, Singapore.
I would also like to express my gratitude to the Department of Engineering Science
in the University of Auckland, especially to Prof. Mike O’Sullivan, Dr. Sadiq Zarrouk,
Dr. Juliet Newson, Dr. Adrian Croucher, Ms. Emily Clearwater, Mr. Angus Yeh,
Mr. Jem Austria and other people who have kindly shared their geothermal knowledge
with me during my stay in Auckland, New Zealand.
I also like to acknowledge NUS, especially the Hydraulic, Geo, Structural and
Material, and Air-Conditioning Lab staffs who involved in instrumentation and sample
preparations for the experiments conducted for the study. I also like to thank several
government agencies (JTC, MTI, BCA) for their supportive collaborations to provide
rock samples, information and facilities for several discussions with Chevron.
I am very grateful for the endless support, patience and ideas from my family,
girlfriend, and friends, especially during the difficult times. And most importantly, I
i
would like to give my utmost thanks to God for His endless grace.
This work is dedicated to my parents, sisters and Jessica.
ii
Contents
Acknowledgements i
Contents iii
Abstract viii

List of Tables x
List of Figures xi
List of Symbols xi
1 Introduction 1
1.1 An Overview of Geothermal Technology . . . . . . . . . . . . . . . . . 2
1.2 A Brief History of Geothermal Energy . . . . . . . . . . . . . . . . . . 6
1.2.1 Conventional geothermal resource . . . . . . . . . . . . . . . . . 6
1.2.2 Overview of EGS . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Site Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3.1 Conventional geothermal fields: Indonesia . . . . . . . . . . . . 10
1.3.2 EGS: Soultz, France . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.3 EGS: Cooper Basin, South Australia . . . . . . . . . . . . . . . 13
iii
1.3.4 EGS: Newberry, Oregon . . . . . . . . . . . . . . . . . . . . . . 14
1.4 The Singapore Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.6 Organization of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 Thermal Conductivity 19
2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1 Guarded Hot Plate: Standard method . . . . . . . . . . . . . . 21
2.2.2 Rock core samples . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2.3 Guarded Hot Plate: Modified method . . . . . . . . . . . . . . 24
2.3 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Experiment procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.1 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.2 GHP measurement . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5 Experiment Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.5.1 Instrument validation . . . . . . . . . . . . . . . . . . . . . . . 32
2.5.2 Insulator thermal conductivity . . . . . . . . . . . . . . . . . . 32

2.5.3 Validation for the GHP modified method . . . . . . . . . . . . 33
2.5.4 Results for Jurong rock samples . . . . . . . . . . . . . . . . . . 35
2.5.5 Results for other rock samples . . . . . . . . . . . . . . . . . . . 37
2.5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3 Modelling Methodology & Pre-Processing 41
3.1 Modelling Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2 Existing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
iv
3.2.1 Geological background . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.2 The hot springs . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2.3 Regional heat flow . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.2.4 Rainfall distribution . . . . . . . . . . . . . . . . . . . . . . . . 50
3.2.5 Surface Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.2.6 Groundwater model . . . . . . . . . . . . . . . . . . . . . . . . 51
3.2.7 Seawater salinity . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.3 Conceptual Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.4 Numerical Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.4.1 Methodology of the numerical modelling . . . . . . . . . . . . . 56
3.4.2 TOUGH2 reservoir simulator . . . . . . . . . . . . . . . . . . . 56
3.4.3 Grid structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.4.4 Boundary and initial conditions . . . . . . . . . . . . . . . . . . 62
3.4.5 Justification for the extended lateral boundary . . . . . . . . . 64
3.4.6 Remarks on the 3D flow effects . . . . . . . . . . . . . . . . . . 66
3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4 Natural State Modelling 68
4.1 Baseline Model Calibration . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1.1 Rock properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1.2 Calibration criteria . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.1.3 Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.1.4 Discussion on Baseline Model Calibration . . . . . . . . . . . . 72

4.1.5 Conclusion on the baseline model . . . . . . . . . . . . . . . . . 87
4.2 Improved Model Calibration . . . . . . . . . . . . . . . . . . . . . . . . 87
v
4.2.1 Hot spring flowrate and salinity . . . . . . . . . . . . . . . . . . 87
4.2.2 Thermal conductivity variations . . . . . . . . . . . . . . . . . . 93
4.2.3 Geological variations at Jurong region . . . . . . . . . . . . . . 98
4.3 Conclusion on the natural state calibration . . . . . . . . . . . . . . . 107
5 Fracture Modelling 110
5.1 Grid Refinement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.2 PyTOUGH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.3 Simulation Results with the Refined Grid . . . . . . . . . . . . . . . . 115
5.4 Modelling Production with EGS Method . . . . . . . . . . . . . . . . . 119
5.4.1 EGS model simulation parameters . . . . . . . . . . . . . . . . 120
5.4.2 Results for EGS with Single Porosity Model . . . . . . . . . . . 123
5.4.3 Simulating EGS with Dual Porosity Model . . . . . . . . . . . . 124
5.4.4 Results for EGS with Dual Porosity Model . . . . . . . . . . . 129
5.5 Model Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.5.1 Model with vertical fractures . . . . . . . . . . . . . . . . . . . 129
5.5.2 Model with reduced mass production rate to 20 kg/s . . . . . . 133
5.5.3 Model with porosity variation . . . . . . . . . . . . . . . . . . . 135
5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
6 Discussion & Recommendations 139
6.1 The heat flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.2 Well measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
6.3 A possible hot plume . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
6.4 3D model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.5 Ground elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
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6.6 Deeper wells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
6.7 Hydroshearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

6.8 Fracture modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6.9 Technological Progress . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
7 Conclusions 151
7.1 Input Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
7.2 Natural State Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . 152
7.3 Fracture Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
7.4 Proposed Road Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Bibliography 157
A Core Logging 165
A.1 Core Logging of BH9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
A.2 Core Logging of BH16 . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
B Publications 180
B.1 Geothermal Desalination in Singapore . . . . . . . . . . . . . . . . . . 181
B.2 Natural State Modeling of Singapore Geothermal Reservoir . . . . . . 190
B.3 Engineered Geothermal Power Systems for Singapore . . . . . . . . . . 197
B.4 Geothermal Power for Singapore . . . . . . . . . . . . . . . . . . . . . 206
vii
Abstract
Singapore has a high geothermal heat flow, i.e. 130 mW/m
2
(about twice the Earth’s
average continental heat flow, 65 mW/m
2
). Together with the existing natural hot
spring at Sembawang, these conditions suggest that Singapore has a potential for
geothermal energy development. The underlying rock at depth is unknown, but likely
to consist of mainly the low permeability rock of the Bukit Timah granite in the east
and at the very deep parts, and Jurong sedimentary rock at shallower depths in the
western Singapore. Potential geothermal development at the Sembawang resource is
likely to utilise the Engineered Geothermal System (EGS) concept because of the low

permeability granite.
The study aims to assess the Singapore geothermal resource through numerical
simulations. The simulator is TOUGH2, which uses an ‘integrated finite difference’
(IFD) or a ‘finite volume’ numerical formulation. Input data for the model are ob-
tained from both literatures and measurements. The simulation is performed with
two-dimensional model in consideration of the limited available data at present. The
2D model is calibrated to match the natural state conditions of the observed and ex-
pected geothermal features in Singapore. The 2D model is also used to simulate some
production scenarios.
Thermal conductivities of rock samples from boreholes at the Jurong region and
viii
from ground surface at several locations in Singapore are measured with the modified
Guarded Hot Plate (GHP) method. The measured thermal conductivities from the
rock samples are: Jurong sedimentary 1.4 - 3.6 W/mK, granite and gabbro 1.9 - 3.5
W/mk, and mudstone and slate 0.8 - 1.3 W/mK.
The 2D model for Singapore geothermal reservoir has been developed as a single
porosity model and calibrated to match the natural state conditions. The optimum
natural state model has a high temperature upflow towards the Sembawang hot spring
with temperature of 125 to 150
◦
C at depths of 1.2 to 1.8 km, and another towards
the Jurong region with temperature of 125 to 150
◦
C at depths of 3 to 4 km.
Simulations of production from an EGS project are carried out with both single
and double porosity model. Results from the simulations show that the Singapore
geothermal resource can sustain 25 years heat extraction (average water temperature
of 150
◦
C) with production rate of 20 kg/s. Simulation shows that an EGS system with

a single layer fracture zone can produce 20 kg/s hot water and 0.67 MW of electricity
for 25 years with an average production temperature of 150
◦
C (temperature decline
about 10
◦
C). If production is simulated for a model with a 3 layer fracture zone, then
2 megawatts electricity can be produced.
ix
List of Tables
2.1 Granite and other sedimentary rock samples from surface . . . . . . . 30
2.2 Layer thickness and thermal conductivity of BH9 and BH16 samples . 38
2.3 Thermal conductivity of granites and other rock samples . . . . . . . . 39
3.1 Chemical concentrations in the Sembawang hot spring water . . . . . . 48
4.1 Estimated engineering properties of the rocktypes . . . . . . . . . . . . 71
4.2 Rock permeability and heat flow of selected simulations . . . . . . . . 73
4.3 Summary of parameters calibration for each simulation . . . . . . . . . 80
4.4 Summary of thermal conductivity variations study . . . . . . . . . . . 98
4.5 Summary of parameters for simulation 2D07 . . . . . . . . . . . . . . . 109
5.1 Summary of parameters for EGS model . . . . . . . . . . . . . . . . . 122
5.2 Summary of parameters for EGS with dual porosity model . . . . . . . 128
x
List of Figures
1.1 Worldwide locations of selected hydrothermal sites . . . . . . . . . . . 2
1.2 Geothermal surface features . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Geothermal power plants . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Schematic of geothermal power plant . . . . . . . . . . . . . . . . . . . 5
1.5 Worldwide installed capacity in 2010 . . . . . . . . . . . . . . . . . . . 6
1.6 Use of geothermal heat . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.7 World geothermal installed capacity . . . . . . . . . . . . . . . . . . . 7

1.8 Schematic of EGS system . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.9 Evolution of global EGS projects . . . . . . . . . . . . . . . . . . . . . 9
1.10 Schematic S-N cross section through the Soultz wells . . . . . . . . . . 12
1.11 The Soultz geothermal power plant . . . . . . . . . . . . . . . . . . . . 12
2.1 Simplified schematic for guarded hot plate assembly . . . . . . . . . . 22
2.2 Locations of BH9 and BH16 at the Jurong Sedimentary region . . . . 23
2.3 Locations of granite and other sedimentary rock samples . . . . . . . . 24
2.4 Modified schematic for guarded hot plate assembly . . . . . . . . . . . 25
2.5 Overall setup for λ measurement with GHP method . . . . . . . . . . 27
2.6 Cutting of sample into size . . . . . . . . . . . . . . . . . . . . . . . . . 28
xi
2.7 Thermal paste partly applied to sample flat surface . . . . . . . . . . . 29
2.8 Thermal conductivity with various temperature differences . . . . . . . 31
2.9 Apparent λ of the standard reference material at 30
◦
C . . . . . . . . . 33
2.10 Thermal conductivity of the insulator (styrofoam) at 30
◦
C . . . . . . . 34
2.11 Thermal conductivity of mortar at 30
◦
C with GHP modified method . 34
2.12 Thermal conductivity of Jurong rocks . . . . . . . . . . . . . . . . . . 35
2.13 Highly weathered rock sample from BH9 at 28 m depth . . . . . . . . 36
2.14 Thermal conductivity of Singapore rocks . . . . . . . . . . . . . . . . . 39
3.1 Simplified geological map of Singapore . . . . . . . . . . . . . . . . . . 44
3.2 Detail of Sembawang hot spring site and the wellbores . . . . . . . . . 46
3.3 Interpreted cross-section through Sembawang boreholes . . . . . . . . . 47
3.4 Heat flow contour map of part of SE Asia . . . . . . . . . . . . . . . . 49
3.5 Mean annual rainfall in Singapore . . . . . . . . . . . . . . . . . . . . . 50

3.6 Relief map of Singapore . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.7 Sea water depth around Singapore Island . . . . . . . . . . . . . . . . 52
3.8 Singapore groundwater model . . . . . . . . . . . . . . . . . . . . . . . 52
3.9 Plan view of the conceptual model . . . . . . . . . . . . . . . . . . . . 54
3.10 Sectional view of the conceptual model . . . . . . . . . . . . . . . . . . 55
3.11 Rose diagram for Singapore . . . . . . . . . . . . . . . . . . . . . . . . 55
3.12 2D grid structure of the model . . . . . . . . . . . . . . . . . . . . . . 62
3.13 Boundary conditions of the model . . . . . . . . . . . . . . . . . . . . . 63
3.14 Temperature profiles of models with fully and partially extended BC . 65
3.15 Salinity profiles of models with fully and partially extended BC . . . . 66
4.1 Generated gridblocks with their rocktypes . . . . . . . . . . . . . . . . 70
xii
4.2 Air saturation profile for simulation 2D01 . . . . . . . . . . . . . . . . 74
4.3 Salinity profile for simulation 2D01 . . . . . . . . . . . . . . . . . . . . 74
4.4 Temperature profile for simulation 2D01 . . . . . . . . . . . . . . . . . 75
4.5 Air saturation profile for simulation 2D02, 2D03, 2D04 and 2D05 . . . 75
4.6 Salinity profile for simulation 2D02 . . . . . . . . . . . . . . . . . . . . 76
4.7 Temperature profile for simulation 2D02 . . . . . . . . . . . . . . . . . 76
4.8 Salinity profile for simulation 2D03 . . . . . . . . . . . . . . . . . . . . 77
4.9 Temperature profile for simulation 2D03 . . . . . . . . . . . . . . . . . 77
4.10 Salinity profile for simulation 2D04 . . . . . . . . . . . . . . . . . . . . 78
4.11 Temperature profile for simulation 2D04 . . . . . . . . . . . . . . . . . 78
4.12 Salinity profile for simulation 2D05 . . . . . . . . . . . . . . . . . . . . 79
4.13 Temperature profile for simulation 2D05 . . . . . . . . . . . . . . . . . 79
4.14 Interpreted mass flow for simulation 2D03 . . . . . . . . . . . . . . . . 86
4.15 Plot of pressure recovery from a well at the Sembawang hot spring . . 88
4.16 Updated map of rocktypes: include ‘gran3’ . . . . . . . . . . . . . . . . 90
4.17 Salinity profile for simulation 2D06 . . . . . . . . . . . . . . . . . . . . 91
4.18 Temperature profile for simulation 2D06 . . . . . . . . . . . . . . . . . 91
4.19 Temperature profiles for simulations with varying k of ‘sedim’ . . . . . 95

4.20 Salinity profile for model with ‘sedim’ λ: 2.1 W/mK . . . . . . . . . . 96
4.21 Salinity profile for model with ‘sedim’ λ: 2.5 W/mK . . . . . . . . . . 96
4.22 Salinity profile for model with ‘sedim’ λ: 2.9 W/mK . . . . . . . . . . 97
4.23 Updated map of rocktypes: include ‘queen’ . . . . . . . . . . . . . . . 100
4.24 Salinity profile for model with low ‘queen’ permeability . . . . . . . . . 101
4.25 Salinity profile for model with high ‘queen’ permeability . . . . . . . . 101
4.26 Temperature profile for model with high ‘queen’ permeability . . . . . 102
xiii
4.27 Updated map of rocktypes: include ‘queen’ and ‘murai’ . . . . . . . . . 103
4.28 Salinity profile for unacceptable ‘murai’ model . . . . . . . . . . . . . . 105
4.29 Salinity profile for acceptable ‘murai’ model . . . . . . . . . . . . . . . 106
4.30 Temperature profile for acceptable ‘murai’ model . . . . . . . . . . . . 107
4.31 Interpreted mass flow for simulation with ‘queen’ and ‘murai’ . . . . . 108
5.1 Area of interest for EGS . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.2 Refined grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.3 Rocktypes in the refined grid . . . . . . . . . . . . . . . . . . . . . . . 113
5.4 Faults in Singapore granite . . . . . . . . . . . . . . . . . . . . . . . . 114
5.5 Temperature profiles from old and refined grids . . . . . . . . . . . . . 116
5.6 Salinity profiles from old and refined grids . . . . . . . . . . . . . . . . 117
5.7 Mass flowrate and temperature at hot spring . . . . . . . . . . . . . . 118
5.8 Location of injection and production wells for EGS method . . . . . . 120
5.9 Completed oil, gas, and geothermal well costs . . . . . . . . . . . . . . 121
5.10 Production temperature for EGS with single porosity . . . . . . . . . . 124
5.11 Tempearture profile at the 25
th
year for single porosity model . . . . . 125
5.12 Jointed granite outcrop . . . . . . . . . . . . . . . . . . . . . . . . . . 126
5.13 Subgridding in MINC with 2 continua for dual porosity model . . . . . 127
5.14 Matrix and fracture continua temperature profile . . . . . . . . . . . . 130
5.15 EGS with vertical fracture . . . . . . . . . . . . . . . . . . . . . . . . . 131

5.16 Temperature declines for horizontal and vertical fractures . . . . . . . 132
5.17 Temperature declines for 20 kg/s and 30 kg/s water flow . . . . . . . . 133
5.18 Production with 3 fracture layers configuration . . . . . . . . . . . . . 134
5.19 Results of single porosity model for various porosities . . . . . . . . . . 136
xiv
5.20 Results of dual porosity model for various porosities . . . . . . . . . . 137
6.1 Proposed shallow wells at Sembawang . . . . . . . . . . . . . . . . . . 141
6.2 Temperature from boreholes near Sembawang HS . . . . . . . . . . . . 143
6.3 Singapore geology for 3D model . . . . . . . . . . . . . . . . . . . . . . 145
6.4 Extensive veining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.5 Thermoelectric generator . . . . . . . . . . . . . . . . . . . . . . . . . . 150
7.1 Proposed road map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
xv