Elements of 3D Seismology Second Edition

Transcription

1 Elements of 3D Seismology Second Edition Copyright c All rights reserved Christopher L. Liner Department of Geosciences University of Tulsa August 14, 2003

2 For David and Samantha And to the memory of Ruben Liner, Sr. June 18, August 8, 2003 i

3 Contents Acknowledgements Seismic data and software Changes from the first edition xv xv xvi Figures xvii Errata xvii Introduction xviii Scope xviii A brief history of seismology xviii Why 3D? xx Getting started xx I Waves: The foundation of seismology 1 1 General properties of waves Mechanical waves ii

4 1.2 Particle motion Polarization Elastic properties Wavespeed Display of wavefield data Waveform Impulse response Reciprocity Source and receiver directivity Wavefront and rays Huygens principle Fermat s principle Snell s law Critical angle Dimensional effects Waveform Energy density and geometric spreading Waves in fluids Why fluids? Parameters Equation of motion The big picture Velocity variation iii

5 2.6 What about density? Fine layering Understanding seismic events Half space Uncertainty analysis applied to direct waves Reflection Travel time Reflection coefficient Fresnel zone Head wave The point source: Tying it all together Diffraction Ghost Velocity layering More events Multiples Classification Reservoir Fluid Properties Pressure and Temperature Range Gas Oil Brine iv

6 4.5 Fluid Mixture Waves in solids Strain Stress Hooke s law and elastic parameters Equations of motion Wave types and speeds Mode conversion Snell s law and critical angles Velocity layering Elastic reflection coefficient Reflection coefficient approximations Anisotropy Waves in porous solids Rock as a porous solid Empirical relationships Parameters Equation of motion Wave types Rock density Gassmann theory and wave speeds Attenuation and dispersion v

7 6.9 Rock velocity ranges II Acquisition: Gathering seismic data D Land acquisition Historical summary hardware Source Receiver Recording system Field procedure Vertical stack Roll and cabling SEGY headers and sorting Financial Aspects of 3D Seismic The Big Picture: Stock Price Economics The Exploration Process A Savings/Gain Model Savings Gains Net value, profit, and rate of return vi

8 8.5 Some Industry Trends Survey predesign Acquisition Parameters Time sample rate Offset range Listen time Spatial sampling and aliasing Total signal-to-noise improvement Land shooting geometry Coordinates and related quantities Cross spread method Swath method Fringe Perimeter or loop method Cabling, template shooting, and fold Crooked line 2D Land 3D design optimization Optimization and inversion Assumptions, target variables, and constraints A direct method Method Examples vii

9 12 Marine acquisition methods Towed receiver systems Receiver cable Source array Acquisition geometry Flip-flop shooting Positioning Cable feathering Fixed receiver systems Marine acquisition and the environment Data dimensionality and components 257 III Data processing: Creating the seismic image Processing and binning overview Why Do We Need to Process Seismic Data? Filtering and noise removal Processing Flow Bins Bin Size Calculation Effects of Fold and Offset Variation Anatomy of a Bin viii

10 15 Computing RAM and Disk Storage D Survey Size D Survey Size Processing Speed Speed and 3D Migration Creating the CMP stack Gain Deconvolution Sorting Normal moveout Dip moveout Common midpoint stacking Statics Migration I: Concepts Constant velocity migration and modeling pairs Dip from Seismic Slope Migration Distance Variable velocity migration and modeling pairs D Migration D and 3D Lateral Resolution Survey design for Linear v(z) ix

11 18 Migration II: Classification and velocity analysis Kinds of migration Stolt migration theory Overview of algorithms Kirchhoff depth migration methodology Migration velocity analysis Historical perspective Progress in seismic processing Dip moveout Anisotropy D processes Depth migration A brief account of dip moveout Dip moveout just isn t normal Velocity variation Anisotropy IV Color Plates 378 V Interpretation: Extracting geologic information from seismic data Synthetic seismogram, tuning, and resolution 402 x

12 20.1 Creating the synthetic seismogram Earth model Travel times Reflection coefficients Wavelet Convolutional model Examples Transmission loss Tuning Resolution Introduction to Interpretation What Does It Mean to Interpret Seismic Data? Background Information Interactive Interpretation Systems Interactive Interpretation Project Components Data Volume Data 2D subsets Display of Seismic Data Interpretation Products Structure Fault detection and mapping Time structure and horizon tracking xi

13 23.3 Time-to-depth conversion methods A vertical ray case history Structural uncertainty Extreme velocity variation Stratigraphy Stratigraphy and 2D seismic data Stratigraphy and 3D seismic data Stacked Channel Systems Stratigraphy and structure: A case history Carbonates Seismic attributes Definition and history Classification schemes General and relative Dimensional Reflection characteristic Procedural Prediction of reservoir properties Procedure Case history Multiattribute analysis Selected general attributes xii

14 Complex trace Dip, azimuth, curvature, and gradient Coherence Spectral decomposition Impedance Spice Amplitude in space, time, and offset Prestack amplitude factors Stack amplitude and R Predictive rock model Calibrated rock model for Glenn sandstone Lateral and time-lapse effects Gas Porosity Oil saturation Lithology: Sandstone-limestone Temperature (steamflood) Lithology: Sandstone-clay Permeability Summary and discussion Time-lapse 3D seismic Offset effects (AVO) xiii

15 A Fourier Transform 528 A.1 Definitions A.2 Frequency domain A.3 Spike input A.4 Properties of the Fourier transform A.5 Two spikes A.6 The discrete case A.7 Detection of periodic signals A.8 2D Fourier transform B Glossary of Terms 545 C Conversion Factors 556 D Bibliography 557 xiv