Page 8 - Geothermal Energy Systems Exploration, Development, and Utilization

VI Contents
2 Exploration Methods 37
David Bruhn, Adele Manzella, Fran¸cois Vuataz, James Faulds,
Inga Moeck, and Kemal Erbas
2.1 Introduction 37
2.2 Geological Characterization 39
2.3 Relevance of the Stress Field for EGS 44
2.4 Geophysics 52
2.4.1 Electrical Methods (DC, EM, MT) 53
2.4.1.1 Direct Current (DC) Methods 54
2.4.1.2 Electromagnetic Methods 55
2.4.1.3 The Magnetotelluric Method 55
2.4.1.4 Active Electromagnetic Methods 63
2.4.2 Seismic Methods 66
2.4.2.1 Active Seismic Sources 67
2.4.2.2 Seismic Anisotropy and Fractures 71
2.4.2.3 Passive Seismic Methods 73
2.4.3 Potential Methods 76
2.4.3.1 Gravity 76
2.4.3.2 Geomagnetics and Airborne Magnetic 78
2.4.4 Data Integration 80
2.4.4.1 Joint Inversion Procedures 81
2.5 Geochemistry 81
2.5.1 Introduction 81
2.5.2 Fluids and Minerals as Indicators of Deep Circulation and
Reservoirs 83
2.5.3 Mud and Fluid Logging while Drilling 85
2.5.4 Hydrothermal Reactions 86
2.5.4.1 Boiling and Mixing 88
2.5.5 Chemical Characteristics of Fluids 91
2.5.5.1 Sodium–Chloride Waters 92
2.5.5.2 Acid–Sulfate Waters 92
2.5.5.3 Sodium–Bicarbonate Waters 93
2.5.5.4 Acid Chloride–Sulfate Waters 93
2.5.6 Isotopic Characteristics of Fluids 94
2.5.7 Estimation of Reservoir Temperature 97
2.5.7.1 Geothermometric Methods for Geothermal
Waters 98
2.5.7.2 Silica Geothermometer 98
2.5.7.3 Ionic Solutes Geothermometers 99
2.5.7.4 Gas (Steam) Geothermometers 100
2.5.7.5 Isotope Geothermometers 100
2.5.8 Forecast of Corrosion and Scaling
Processes 100
References 103
Further Reading 111