A Petroleum Geologist's Guide to Seismic Reflection

by Ashcroft, William

• ISBN13: 9781444332636
• ISBN10: 1444332635
• Edition: 1st
• Format: Paperback
• Copyright: 2011-05-06
• Publisher: Wiley-Blackwell

Summary

This book is written for advanced earth science students, geologists, petroleum engineers and others who want to get quickly 'up to speed' on the interpretation of reflection seismic data. It is a development of material given to students on the MSc course in Petroleum Geology at Aberdeen University and takes the form of a course manual rather than a systematic textbook. It can be used as a self-contained course for individual study, or as the basis for a class programme. The book clarifies those aspects of the subject that students tend to find difficult, and provides insights through practical tutorials which aim to reinforce and deepen understanding of key topics and provide the reader with a measure of feedback on progress. Some tutorials may only involve drawing simple diagrams, but many are computer-aided (PC based) with graphics output to give insight into key steps in seismic data processing or into the seismic response of some common geological scenarios. Part I of the book covers basic ideas and it ends with two tutorials in 2-D structural interpretation. Part II concentrates on the current seismic reflection contribution to reservoir studies, based on 3-D data.

Author Biography

After gaining his geology degree, Dr Ashcroft worked with Seismograph Service Ltd on seismic parties in the Middle East and Nigeria,  then went on to do research at Birmingham University. He  joined the Department of Geology, University of Aberdeen in 1966, teaching Applied Geophysics to BSc students and to the MSc class in Petroleum Geology.  His research interests included large-scale magnetic surveys in the Scottish highlands and studies based on seismic data released from the petroleum industry.  He retired as Senior Lecturer in 1999, but has remained active, teaching geophysics at the University of Glasgow and carrying out magnetic surveys over the Rhynie Basin as well as writing this book and developing its tutorial software.

Table of Contents

Preface

Acknowledgements

Basic Topics and 2-D Interpretation

Introduction and overview

Exploration geophysics in petroleum exploration

The principle of seismic reflection surveying

Overview of the seismic reflection industry

Brief history of seismic surveying

Societies, books and journals

Geophysical Signal Description

Overview

Cosine waves

Signals and spectra

Periodic waveforms: Fourier series

Seismic wavelets

Wavelet characteristics: time and frequency domains

Digitization of signals

Fourier description of space-dependent quantities

Consolidating ideas of frequency and phase shift

Fourier summation of a periodic waveform

The transition from periodic waveform to wavelet: program FOURSYN

Amplitude and phase-shift changes in the wavelet: program FOURSYN

Data acquisition

General points

Seismic sources and receivers

Static corrections

Recording and presentation of data

Common mid-point (CMP) shooting

The attack on noise

3-D surveys

Seismic wave propagation

Introduction

P-wave

Controls on P-wave velocity

P-wave waveforms

Shear waves and surface waves

P-wave attenuation

P-wave transmission paths

P- and S-wave particle motion on screen: program PSWAVE

Basic measurements of time, velocity and depth

Drawing the reflection wavefront from Huyghen's principle

Calculating typical reflection coefficients from well data

The process of reflection

Introduction

Fresnel zones

Fresnel zones and the seismic reflector

Faults and diffractions

Hyperbolae on stacked time sections

The reflection as a summation of hyperbolae

Resolution of the seismic reflection method

Multiple reflections: common modes

Multiples: the scale of the problem

Seismic expression of a "point" reflector

Water-layer multiples spoil a deep reservoir interval: program CMPGATHER

Velocity analysis, CMP stacking and post-stack migration

General points

Definitions of seismic velocity: well data

Velocities from seismic data: Vrms

Velocities from seismic data: Vstack

Velocity analysis

Errors in seismic-derived velocities

Multiple suppression by CMP stacking

Stacking the whole section: a make-or-break process

Some stacking refinements

Migration: the fundamental idea

Full-waveform migration

Migration example: 2-D section

Velocities from well data

NMO correction, CMP stacking and velocity analysis: program NMOSTAK

Picking stacking velocities from a velocity spectrum: programs VELSPEC and SEGY2D

Suppression of multiples by CMP stacking: program NMOSTAK

How multiples appear on a velocity spectrum: program VELSPEC

Migration by ray-tracing

Interpretation of two-dimensional (2-D) surveys for structure

Introduction

Linking well geology to seismic section

Choosing reflections to pick

Picking reflections

Sideswipe

A sideswipe example: fault diffractions

Preparing structure maps in TWT

Time to depth conversion

Examples of time-depth conversion

Constructing a synthetic seismogram from well-log data: program SYNTH

Matching a synthetic seismogram to seismic data: program IMAGES

Picking reflections along a 2-D section from the Moray Firth, Northern North Sea basin

Time to depth conversion, West Sole Field, Southern North Sea Basin

Seismic Input To Reservoir Characterisation

Better subsurface imaging

Introduction

Reflection point dispersal, conflicting dips and DMO

Prestack time migration (PSTM)

Prestack depth migration (PSDM)

Anisotropy: the ultimate refinement in velocity

Velocity-depth ambiguity

Future migration technique: Kirchhoff or wave extrapolation?

3D migration

3D seismic interpretation

Growth and impact of 3D surveys

Reflection point dispersal

Lateral mis-location from time migration

3D data: vertical section and time-slice

Modifying the seismic waveform

Introduction

Testing an electronic filter: the impulse response

Digital filters: convolution

Cross-correlation and auto-correlation

Frequency filtering by convolution

The seismogram as a convolution

Deconvolution

Designing deconvolution operators

Predictive deconvolution

Wavelet processing

Frequency-domain processing

Data processing and the fragility of bandwidth

Digital filtering by hand

The power of the vibroseis technique: program SIGPROC

Testing the seismic response of a geological model: program SYNTH

Refining reservoir environment and structure

Introduction: the reservoir model

Refining reservoir environment: seismic stratigraphy and facies analysis

Refining reservoir structure: vertical seismic profiling (VSP)

Refining reservoir structure: seismic attributes

Seismic forward modelling

Section limits in walkaway VSP

Forward modelling of fault shadow: program SYNTHSEC

Seismic input to mapping reservoir properties

Introduction

Reflection amplitude

Acoustic impedance (AI) inversion

Amplitude variation with offset (AVO)

AVO intercept and gradient

Fluid Factor

AVO inversion to rock properties

AVO inversion to P- and S-wave impedance

Elastic impedance: AVO made easy?

Best fluid indicator?

Instantaneous seismic attributes

Usage of seismic attributes

Predicting log properties from seismic attributes

4C and 4D surveys

AVO for typical lithological interfaces

Tutorial Answers

References

Index

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