Page 7 - Geothermal Energy Renewable Energy and The Environment

vi Contents

Internal Energy ................................................................................................. 31
PV Work ...........................................................................................................33
Enthalpy ............................................................................................................33
The Second Law of Thermodynamics: The Inevitable Increase of Entropy .............34
Efficiency ...............................................................................................................34
Carnot Cycle ..........................................................................................................34
Heat Capacity ........................................................................................................35
Entropy ..................................................................................................................37
Gibbs Function and Gibbs Energy (ΔG) .....................................................................38
The Standard State ................................................................................................39
Thermodynamic Efficiency ........................................................................................40
Case Study: The Thermodynamic Properties of Water and
Rock–Water Interaction ......................................................................................... 41
Synopsis ......................................................................................................................47
References ..................................................................................................................47
Further Information ....................................................................................................48

Chapter 4. Subsurface Fluid Flow: The Hydrology of Geothermal Systems .............................. 51
A General Model for Subsurface Fluid Flow ............................................................. 51
Matrix Porosity and Permeability .............................................................................. 51
Definition of Matrix Permeability .........................................................................54
The Kozeny–Carman Equation .............................................................................55
Hydraulic Conductivity .........................................................................................55
Fracture Porosity and Permeability ............................................................................55
Fracture Permeability ............................................................................................56
Fracture Transmissivity .........................................................................................57
Effect of Depth on Porosity and Permeability ...........................................................58
Hydrologic Properties of Real Geothermal Systems .................................................60
Case Study: Long Valley Caldera .............................................................................. 61
Synopsis ......................................................................................................................65
References ..................................................................................................................65
Further Information ....................................................................................................66

Chapter 5. Chemistry of Geothermal Fluids ...............................................................................69
Why the Geochemistry of Geothermal Fluids Matters .............................................69
Water as a Chemical Agent ........................................................................................70
Components and Chemical Systems ..........................................................................72
Chemical Potentials, μ, and Gibbs Energy............................................................72
Activity, a .............................................................................................................. 74
Saturation and The Law of Mass Action .................................................................... 74
Equilibrium Constants ........................................................................................... 74
Activity Coefficients, γ ..........................................................................................75
Affinity ..................................................................................................................76
Ion Exchange .........................................................................................................77
Kinetics of Geothermal Reactions .............................................................................78
Gases in Geothermal Fluids .......................................................................................80
Gas Partitioning between Liquid and Vapor ......................................................... 81
Fluid Flow and Mixing in Natural Systems ...............................................................83
Simulating Reactive Transport ...................................................................................84