Specifications

University of Pretoria etd – Combrinck, M (2006)
TABLE OF CONTENTS
1 INTRODUCTION......................................................................................................................1
1.1 General overview ...................................................................................................................1
1.2 Objective .................................................................................................................................3
2 OVERVIEW OF ELECTROMAGNETIC THEORY FOR GROUND, IN-
LOOP TDEM DATA.............................................................................................................................4
2.1 Introduction............................................................................................................................4
2.2 System geometry and operating specifications.................................................................4
2.3 Analytical TDEM responses for four common models ................................................5
2.3.1 TDEM central-loop response over a conductive half space..................................7
2.3.2 Thin, conductive sheet (S-layer)...................................................................................9
2.3.3 Finite conductor in a resistive host rock (half space).............................................11
2.3.4 Finite conductor in a conductive host rock (half space) .......................................12
2.4 Conclusion ............................................................................................................................17
3 CONVENTIONAL INTERPRETATION TECHNIQUES....................................18
3.1 Introduction..........................................................................................................................18
3.2 Profiles versus soundings ...................................................................................................19
3.3 Forward Modelling and Inversion....................................................................................20
3.4 Limitations on automation of inversion techniques .....................................................21
3.5 Decay curve analysis............................................................................................................22
3.6 Transforms (Depth imaging).............................................................................................24
3.6.1 Conductivity Depth Images (CDI’s).........................................................................24
3.6.2 Stationary current images (SCI) (SCI - trademark of Geoterrex-Dighem
Pty Limited)..................................................................................................................................24
3.6.3 S-layer differential transform......................................................................................25
3.7 Combining Strategies ..........................................................................................................27
4 AUTOMATED INTEGRATED ANALYSIS OF TDEM DATA.............................28
4.1 An integrated analysis algorithm.......................................................................................28
4.2 Visualization of the field data for rapid anomaly detection.........................................28
4.3 Decay curve analysis............................................................................................................30
4.3.1 Layered earth behaviour..............................................................................................31
4.3.2 Confined conductor behaviour..................................................................................32
4.3.3 IP effect or severe lateral variation in subsurface conductivity............................33
4.3.4 Results, output and presentation ...............................................................................33
4.4 Numerical calculation of the S-layer differential transform........................................33
4.4.1 Defining the S-layer transform...................................................................................33
4.4.2 Numerical differentiation of TEM data ...................................................................36
4.4.3 Comparison of differentiation methods applied to synthetic data......................45
4.4.5 Concluding remarks on numerical differentiation..................................................54
4.5 The S-layer correction factor............................................................................................55
4.5.1 Defining a S-layer correction factor ..........................................................................55
4.5.3 Behaviour of the S-layer transform when applied to synthetic data ...................68
4.5.4 S-layer differential transform compatibility filter....................................................92