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 SI

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

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

would like to give my utmost thanks to God for His endless grace.

This work is dedicated to my parents, sisters and Jessica

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

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

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

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

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

Singapore has a high geothermal heat flow, i.e 130 mW/m2 (about twice the Earth’s average continental heat flow, 65 mW/m2) 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

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

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

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

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

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

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 25th 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

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