The Theory of Inductive ProspectingBy
- A.A. Kaufman, Department of Geophysics, Colorado School of Mines, Golden, CO, 80401 USA
- P.A. Eaton, Newmont Mining Corporation, 10101 E. Dry Creek Road, Englewood, CO, 80112 USA
An update to a classic reference published fifteen years ago, this publication concerns the theoretical aspects of inductive electromagnetic methods applied in geophysical prospecting. From first principles, the electromagnetic responses of several models are derived and analysed in order to form a strong basis for understanding such phenomenon in practice. The original work has been extended by using modern 3-D modeling capabilities with a special emphasis on airborne applications.
Exploration and research geophysicists will appreciate the numerous closed-form and asymptotic electromagnetic expressions for spherical and clylindrical conductors contained within non-conductive and conductive hosts which are described in this volume. Responses based on such expressions are often presented in graphical and tabular form in order to help the reader visualise the significance of the results and in order to facilitate comparisons with physical and numerical modeling results.
In contrast to the first edition, key results are summarised at the end of each chapter and old material that has been retained in the new edition has been clarified and in many instances corrected.A new chapter has been written in which an extensive evaluation of several different airborne electromagnetic systems is described. The evaluation was based on the utilization of an advanced 3-D modeling program to simulate complex geoelectrical situations that are of interest in exploration and in airborne resistivity mapping.
Methods in Geochemistry and Geophysics
Published: January 2001
- List of symbols.Chapter 1 Introduction. Preface to the new edition. Introductory remarks adapted from the first edition. References.Chapter 2 Basic Electromagnetic Laws and Maxwell's Equations. Introduction. Coulomb's Law. Biot-Savart Law. The postulate of conservation of charge and the distribution of charges in a conducting medium. Faraday's Law and the first Maxwell equation. Electromagnetic field equations. Relationships between various EM field components. Summary. References.Chapter 3 Frequency and Time-Domain Behavior of the Field Caused by Currents Induced in a Confined Conductor. Introduction. A conductive sphere in a uniform stationary magnetic field (frequency domain). A conductive sphere in a uniform non-stationary magnetic field (time domain). A conductive sphere energized by the magnetic field of a circular loop with axial symmetry. Equations for the frequency and time-domain fields caused by induced currents in a spherical conductor with axial symmetry. A right circular cylinder in a uniform magnetic field. A right circular cylinder in a field created by an infinitely long current filament. Equations for the frequency and time-domain fields caused by induced currents in a cylindrical conductor with an arbitrary cross-section. The characteristics of the frequency and transient responses caused by a cylindrical conductor with an arbitrary cross-section. A conducting sphere in the field of an arbitrarily oriented magnetic dipole source. A circular cylinder in the field of an arbitrarily oriented magnetic dipole source. Summary. References.Chapter 4 Resolving Capabilities and Depth of Investigation of Inductive Methods when Geologic Noise is a Confined Inhomogeneity. Introduction. Frequency-domain methods. Time-domain methods. Comparing resolution and depth of investigation in the frequency and time domains using spheroid models. Summary. Chapter 5 The Effect of Induced Currents in the Host Medium of the Frequency and Transient Responses Caused by a Confined Conductor. The normal field due to currents in the host medium. The influence of currents induced in the host medium on the secondary electromagnetic field of a confined conductor. An approximate method for calculating the fields caused by vortex currents. Summary. References. Chapter 6 The Effect of Surface Electrical Charge on the Behavior of Secondary Electromagnetic Fields. Introduction. General expressions for the electromagnetic fields of a conductive sphere. A conductive sphere in a plane wave field. A conductive sphere in a magnetic dipole field. A conductive cylinder in the field of an infinitely long current filament parallel to the axis of the cylinder. A conductive cylinder in the field of a magnetic dipole. Summary. References. Chapter 7 Resolving Capabilities of Airborne Inductive Methods. Introduction. The signal-to-geologic-noise ratio. Airborne electromagnetics. Description of the study. Layered-earth modeling results and analysis. Three-dimensional modeling results and analysis. Recommendations for airborne electromagnetic prospecting systems. References. Subject index.