3. Magnetic Methods / 62

Transcription

1 Contents Preface to the Second Edition / xv Excerpts from Preface to the FirstEdition / xvii Mathematical Conventions / xix 1. Introduction / 1 Reference / 5 2. Gravity Methods / 6 2. I. Introduction / General/ History of Gravity Exploration / Principles of Gravity/ Newton s Law of Gravitation / Acceleration of Gravity / Gravitational Potential / Potential-Field Equations / Derivatives of the Potential / Gravity of the Earth/ Figure of the Earth/ Gravity Reduction / Densities of Rocks and Minerals / Density Estimates from Field Results / Gravity Instruments / General / Absolute Measurement of Gravity / Relative Measurement of Gravity / Field Operations / Land Surveys / Drift Correction / Marine Surveys / Airborne Gravity / Gravity Data Processing/ Noise, Regionals, and Residuals / Graphical Residualizing / Surface-Fitting Residualizing Methods / Empirical Gridding Methods / Second Vertical Derivative Methods / Wavelength Filtering / Field Continuation / Gravity Interpretation / General / Gravity Effect of a Sphere/ Gravity Effect of a Horizontal Rod / Gravity Effect of a Vertical Cylinder / Gravity Effect of a Thin Dipping Sheet / Gravity Effect of Horizontal Sheets, Slabs, Dikes, and Faults / Applying Simple Models to Actual Anomalies / Gravity Effects of Complex Shapes / The Direct and Inverse

2 VI Contents Problems of Interpretation / Excess Mass / Overburden Effects / Maximum-Depth Rules / Field Examples / Problems / 52 References / Magnetic Methods / I. Introduction / General / History of Magnetic Methods / Principles and Elementary Theory/ Classical versus Electromagnetic Concepts / B-H Relations: The Hysteresis Loop / Magnetostatic Potential for a Dipole Field / The General Magnetic Anomaly / Poisson s Relation / Magnetism of the Earth / Nature of the Geomagnetic Field / Magnetism of Rocks and The Main Field / 68 The External Magnetic Field / 72 Local Magnetic Anomalies / 72 Minerals / 72 Remanent Magnetism / 73 Magnetic Susceptibilities of Rocks and Minerals / 73 Magnetic Susceptibility Measurements / Field Instruments for Magnetic Measurements / General / Flux-gate Magnetometer / Proton-Precession Magnetometer / Optically Pumped Magnetometer / Gradiometers / Instrument Recording / Calibration of Magnetometers / Field Operations / General / Ground Magnetic Surveys / Gradiometer Surveys / 84 Airborne Magnetic Surveys / 81 Shipborne Magnetic Surveys / Magnetic Effects of Simple Shapes / General / The Isolated Pole (Monopole) / The Dipole / Two-Dimensional Features / Dipping Dike (Prism) / Dipping Sheet / Horizontal Sheet (Plate) / Semiinfinite Horizontal Sheet: Fault Approximation / Contact between Beds of Different Susceptibilities / Demagnetization / Processing and Interpretation / General / Crude Interpretation and Structural Aspects / Data Processing Operations: The Fourier Transform / Derivatives / Continuation / Spectral Analysis / Reduction to the Pole/ 109 Use of Master Curves for Dikes of Great Depth Extent / Matched Filtering / Werner Deconvolution / Depth Estimates / Field Examples/ Ground Surveys / Airborne Surveys / Problems / 124 References / 134

3 Contents Vii 4. Seismic Methods / I. Introduction / Importance of Seismic Work / History of Seismic Exploration / Outline of the Seismic Reflection Method / Seismic Theory/ Theory of Elasticity / Wave Equation and Its Solutions / Body Waves: P and S Waves / Surface Waves / Energy of Waves / Wave Motion / Partitioning of Energy at an Interface / Seismic Velocity / Geometry of Seismic Wavepaths/ Reflection Paths in a Constant Velocity Layer / Velocity Gradient and Raypath Curvature / Geometry of Refraction Paths / Characteristics of Seismic Events/ Distinguishing Features of Events / Reflections and Refractions / Diffractions / Multiples / Surface Waves / Effects of Reflector Curvature / Types of Seismic Noise/ 184 Attenuation of Noise / Reflection Field Methods and Equipment / Field Methods for Land Surveys / Field Layouts / Field Equipment for Land Surveys / Marine Equipment and Methods / Measurement of Velocity / Refraction field Methods and Equipment / Comparison of Refraction and Reflection Methods / In-Line Refraction / Broadside Refraction and Fan Shooting / Engineering Surveys on Land / Marine Refraction Work / 212 Refraction Data Reduction / Data Processing / Data Reduction / Introduction to Digital Processing: Fourier Transforms / Convolution / Correlation / Phase Considerations / Frequency Filtering / Velocity Analysis / Common-Midpoint Stacking / Apparent-Velocity (Apparent- Dip) Filtering / The p-r Transform / Relative-Amplitude Processing / Migration or Imaging / 230 Measures of Coherence / 232 Other Types of Processing / Basic Geological Concepts in Petroleum Exploration / Basic Concepts / Objectives of Interpretation / Refraction Interpretation / Interpretation of Refraction Records / Refraction Interpretation Methods / Delay-Time Methods / Wavefront Methods / Engineering Applications / 242

4 ... Vlll Contents Reflection Interpretation / Interpretation Techniques / Modeling: Synthetic Seismograms / Evidences of Faulting / Fold and Flow Structures / Reefs / Unconformities and Seismic Facies Patterns / Use of Velocity Information / Hydrocarbon Indicators / Specialized Methods / Profiling/ Three-Dimensional Methods / 267 Use of Channel Waves / 270 Vertical Seismic Profiling / Shear Waves in Exploration / Variation of Amplitude with Offset / Cross-Hole Methods / Problems / 273 References / Electrical Properties of Rocks and Minerals / I. Classification of Electrical Methods / Electrical Properties of Rocks and Minerals / Electrical Potentials / Electrical Conductivities / Magnetic Permeability / Polarization Potentials / Measurement of Electrical Properties of Rocks and Minerals / Laboratory Measurement of Resistivity / Measurement of Dielectric Constant / Typical Values of Electrical Constants of Rocks and Minerals / Resistivities of Rocks and Minerals / Dielectric Constants of Rocks and Minerals / Magnetic Permeability of Minerals / 292 References / Methods Employing Natural Electrical Sources / I Self- Potential Method / 293 Origin of Potentials / Self-potential Field Equipment / 2% Field Procedure / 2% Interpretation of Self-potential Data / Telluric and Magnetotelluric Methods / Origin and Characteristics of Magnetotelluric Fields and Telluric Currents / 302 Elementary Electromagnetic Theory / 306 Attenuation of EM Fields / 307 Boundary Conditions / 309 Magnetotelluric Fields / 309 Field Equipment and Operations / 311 Interpretation of Telluric Data / 314 Interpretation of Magnetotelluric Data / Field Examples / Self-potential / Tellurics and Magnetotellurics / Problems / 335 References / 342

5 Contents 7. Electromagnetic Methods / EM Field Procedures / I. Introduction and Historical 7.7. Interpretation / 383 Background/ Introduction / Electromagnetic Theory/ Vector and Scalar Potentials / Description of EM Fields; Biot-Savart Law / Field in the Frequency Domain / Combination of FD Fields / Mutual Inductance / Fields in the Time Domain / EM Equipment / General / Power Sources / Transmitter Loops / Receiver Coils / Receiver Amplifiers / Indicators / Compensating Networks / EM Field Systems for Ground Surveys / General / Frequency-Domain Systems; Dip-Angle Measurements / FD Systems for Phase- Component Measurements / Time-Domain EM Ground Systems / Measurement of H / Assessment of EM Ground Methods / Airborne EM Systems/ General / Quadrature Method / Turair System / Airborne VLF / Phase-Component Measurements / 378 Transient (Input) Method / 379 Cryogenic EM System / Assessment of Airborne EM / General Interpretation Procedure / Ground Systems; FDEM over Dipping Sheet / Ground Systems; TDEM over Dipping Sheet / The Sphere Model in FD and TD Ground Systems / Layered Structure: EM Depth Sounding / Interpretation of Airborne EM Data / Turair / Airborne VLF / Phase-Component AEM / Resistivity Mapping / Input AEM / Field Examples / Problems / 504 References / Resistivity Methods / I. Introduction / Elementary Theory/ Potentials in Homogeneous Media / Single Current Electrode at Depth / Single Current Electrode at Surface / Two Current Electrodes at Surface / Current Distribution / Effect of lnhomogeneous Ground / Introduction / Distortion of Current Flow at a Plane Interface / Distortion of Potential at a Plane Interface / Surface Potential due to Horizontal Beds / 529

6 x Contents Potential Due to Buried Sphere / Effect of Anisotropic Ground / Effect of Topography / Equipment for Resistivity Field Work / Power Sources / Meters / Electrodes and Wire / Electrode Layouts and Field Procedure / General / Apparent Resistivity / Electrode Arrays (Spreads)/ Resistivity Field Procedures / Interpretation / Introduction / Resistivity Modeling / Vertical Sounding; Two Horizontal Beds / Vertical Sounding; Multiple Horizontal Beds / Lateral Mapping; Vertical Contact / The Vertical Dike / Mapping Three-Dimensional Anomalies / Measuring Overburden Depth and Resistivity / Field Examples / Problems / 570 References / Induced Polarization / I. Introduction / Sources of the Induced Polarization Effects / General / Membrane Polarization / Electrode Polarization / Equivalent Electrical Circuits / Induced Polarization Measurements / General / Time-Domain Measurements / Frequency-Domain Measurements / 582 Relative Phase Shift and Phase Components / Magnetic Induced Polarization (MIP) Measurements / Relation between Time- and Frequency-Domain IP Measurements / 583 IP Response Examples / IP Field Operations / General / Field Equipment / Field Procedures / Noise Sources / Interpretation / Plotting Methods / General Interpretation / Theoretical and Model Work / 5% 9.6. Field Examples / Problems / 604 References / Radioactivity Method / I. Introduction / Principles of Radioactivity/ Constituents of the Nucleus / Nuclear Disintegrations / Radioactive Decay Processes / Radioactive Equilibrium / Units / Radioactivity of Rocks and Minerals / Age Determination Using Radioisotopes / Instruments / Introduction / Geiger-Muller Counter / 620

7 Contents xi Scintillation Meter / Elastic- Wave (Acoustic) Gamma-Ray Spectrometer / 622 Methods / Miscellaneous Instruments / Elastic Waves in Boreholes / Calibration of Instruments / Sonic Log / 667 Field Operations / Amplitude and Full-Waveform Logs / 670 Interpretation / Borehole Televiewer / Field Examples / Problems / 637 References / Nuclear Methods / Nuclear Processes / Gamma-Ray Logging / Density Log / Neutron Logging / Geophysical Well logging / 645 I I. I. Introduction / Uses of Well Logging/ History of Well Logging/ General Aspects of Well Logging / Rock Property Measurements / Resistivity Methods / Introduction to Resistivity Logging / Normal Resistivity Logging / Lateral Arrangement / Microlog / Focused-Current Logs / Induction Log/ Resistivity Logging in Mineral Search / Self- Potential (SP) Logging/ Sources of SP/ Instrumentation / Uses of SP Curves in Oil-Well Logging / Uses of SP Curves in Mineral Logging / Geological Interpretation of SP / The Dipmeter/ Electromagnetic Wave Propagation Method/ Induced Polarization Logging/ Gravity, Magnetic, and Thermal Methods / Gravity and Magnetic Field Logging / Susceptibility Log / Nuclear Magnetic-Resonance Log / Thermal Logging / Well-Log Interpretation / General / Combining Measurements from Several Logs / I I. Field Examples / Analysis of an Oil Sand / Analysis of Carbonate Section / Coal Identification / Evaporites / Sulfur / Slate and Chert/ Mineral Exploration / Borehole Methods in the USSR / Problems / 690 References / Integrated Geophysical Problems / I. Introduction / Examples and Problems / 701

8 Xi; Contents Appendix A. Mathematical Background / 727 A. I. Determinants / 727 A.2. Matrices / 728 A.3. Vector Analysis / 729 A.3.1. Basic Theory / 729 A.3.2. Vector Products / 730 A.3.3. The Vector Operator v /731 A.3.4. Vector Theorems / 731 A.4. Curvilinear Coordinates / 733 A.5. Taylor s Series; Maclaurin s Series / 735 A.6. Binomial Expansion / 736 A. 7. Complex Numbers / 736 A.8. Method of Least Squares/ 737 A. 9. Fourier Series and Transforms / 738 A.9.1. Fourier Series / 738 A.9.2. Fourier Integral; Fourier Transforms / 738 A.9.3. Digital Functions; z Transforms / 740 A. 10. Convolution / 740 A. I I. Correlation / 741 A.ll.l. Cross-Correlation / 741 A Autocorrelation / 741 A. 12. Laplace Transforms / 741 A Basic Theory / 741 A Calculation of Laplace Transforms / 742 A Transforms of the Error Function and its Derivatives / 742 A. 13. Linear Systems / 743 References / 744 Appendix B. Location Determination / I Direction Determination / 745 Distance Measurement / 745 Elevation Measurement / 745 Angle Measurement / 746 Doppler Measurement of Velocity / 746 Radionavigation / 746 Acoustic and Inertial Positioning/ 748 Satellite Positioning/ 749 Reference / 750 Index / 751