Seismic Survey Design, Acquisition and Processing

Course Instructor:    Mangat R. Thapar, Ph.D.

Who should attend?

Geologists, geophysicists, engineers, supervisors, as well as supervisors, and managers involved in the design, execution and monitoring of seismic data acquisition and processing

 

Prerequisites:

Participants should have taken a Basic Geophysics course prior to attending.

 

Course Description:

 

The appropriate design, acquisition and processing of a 3-D seismic survey is vital to the success of any oil and gas exploration and development program. This course covers and emphasizes the equal importance of proper acquisition and processing parameters, utilizing exercises and case histories to teach fundamental principles, and explain limitations and pitfalls.  By the end of the course, participants will be able to participate in the effective planning, execution, and quality control of seismic data acquisition and processing.

 

Appropriate design, acquisition and processing are equally essential to producing a 3-D seismic survey that will effectively impact the success of any oil and gas exploration or development program. During this course, we provide a live demonstration of design using OMNI, acquisition using Cirrus board, I/O Sensors, and processing using VISTA. After detailed discussion/exercise on related topics, the participants are shown live demonstrations to help in understanding and grasping the subject matter.

 

The course content includes:

 

Design and Acquisition

(1)                 Description of fundamentals of P, S, and R waves with intuitive illustrations, demonstrations and examples. How to analyze aliasing in time and 2-D and its effect on seismic data?

(2)                 Details of land data acquisition along with all of the important steps and parameters in data acquisition in the field, thorough discussion of vibroseis and dynamite as sources of energy, and presentation of ground positioning methods for source/receiver stations. Estimation of SNR and its importance to seismic data.

(3)                 Details of marine data acquisition along with all of the important steps and parameters in data acquisition, thorough discussion of airgun arrays, and positioning methods for source/receiver locations.

(4)                 A systematic approach in a step by step procedure is presented for designing a 3-D survey along with most of the available templates and array designs.

 

Processing

(5)                 Basics and importance of correct recording geometry are explained. How to apply the right type of amplitude scaling, and to select the right type of deconvolution and filter.

(6)                 How to conduct velocity analysis and how to monitor or QC velocity analysis? Details of the relationship between NMO and velocity are discussed.

(7)                 Discussion of different components of statics in seismic data and how they are corrected.

(8)                 Explanation and discussion of how to improve SNR with stacking, the relationship between fold and SNR, and migration (pre-stack, post-stack, DMO) of seismic data.

(9)                 Discussion of basic seismic attributes, step by step VSP processing, and the effect of deep water on data acquisition and processing.

 

Exercises

Exercises in this course are designed to further the understanding of basic principles in survey design, data acquisition and processing, and some of these exercises include:

 

Design and Acquisition

(a)     Exercises on how to relate useable offsets and critical angle for major horizons design Vibroseis sweep and calculate related parameters to avoid harmonics interference with data? Exercises on measuring ground roll velocity and frequency from field records to design array patterns and filters, calculation of Aliasing frequency due to sampling and due to dip, calculation of Migration aperture for dipping horizons.

(b)     Design 2-D crossing lines over a structure and calculate all required parameters.

(c)     Design a 3-D survey over a prospect, and calculate all parameters related to the sources and receivers.

Processing

(d)     Exercises on: calculation of absorption effects of P and S waves, how to apply relative amplitude scaling using tn, and how to obtain the value of n from seismic data, and calculate and relate critical angle, incidence angle, offset, and fold for major horizons.

(e)     How to quality control velocity analysis using RMS and Interval velocities?

(f)       Interpret and Identify water bottom and peg-leg multiples, and primaries on the records.

(g)    A group exercise for participants to compare, QC, and select the best seismic section of the same line processed by different companies.

(h)    A group exercise for participants to compare, QC, and select the best seismic section of a line processed by a single company but with different processing flows.

(i)       As a group, participants examine, analyze, and modify an existing acquisition parameter and processing flow to make it suitable for AVO and seismic attribute analysis.

 

 

Course Content:

 

Participants will learn how to:

 

Participants are encouraged to bring data examples or displays related to this course for one on one or group discussion.

 

 

 

Chapter 1 Fundamental Principles

Chapter 2 Recording System

Chapter 3 Signal to Noise Ratio and Recording Parameters

Chapter 4 Survey Planning and Design

Chapter 5 Introduction to Wave Propagation

Chapter 6 Sampling and Recording Geometry

Chapter 7 Amplitude Scaling and Filtering

Chapter 8 Velocity Analysis

Chapter 9 Static Corrections

Chapter 10 Stacking and Migration

Chapter 11 Seismic Processing and Analysis

Exercises Seismic Data Acquisition and Processing

 

Seismic Survey Design, Acquisition and Processing

Chapter 1: Fundamental Principles

Chapter 1 : Fundamentcal Principles  1-1

Elastic Wave Propagation and Principles. 1-3

Dilatational, Longitudinal, Irrotational, Compressional or Simply Primary or P‑Waves. 1-7

Shear, Transverse, Rotational, Tensional, Secondary, or S-Waves. 1-8

Ground Roll or Surface Waves or Rayleigh Waves (R) 1-8

Love Waves (L) 1-9

Stonely Waves. 1-10

Elastic Parameters. 1-10

Bulk Modulus (K) 1-10

Rigidity Modulus (μ) or Shear Modulus. 1-11

Stress. 1-11

Strain. 1-11

Young’s Modulus (E) 1-11

Poisson’s Ratio. 1-11

Partition of Incident Seismic Energy. 1-12

Reflection. 1-12

Refraction. 1-12

Diffractions. 1-14

Transmission and Conversion. 1-14

Reflection Coefficient 1-14

Acoustic Impedance. 1-15

Acoustic Impedance Contrast 1-15

Application of Time Domain Principles to Data Acquisition. 1-17

Source Wavelet and Seismic Trace. 1-17

Reflection Series. 1-18

Convolution. 1-18

Deconvolution. 1-18

Correlation, Cross-Correlation, and Auto-Correlation. 1-18

Application of Frequency Domain Principles to Data Acquisition. 1-18

Amplitude, Phase, Frequency and Phase Spectra, Fourier Transforms. 1-18

Filtering. 1-18

Application of Sampling Theory to Survey Design and Data Acquisition. 1-19

Sampling Seismic Trace (time) 1-19

Aliasing Frequency and Frequency Bandwidth. 1-19

Anti Alias Filter 1-19

Resampling and Interpolation. 1-19

Instrument Noise and Sampling. 1-19

Wave Number F-K Transform (Spatial or 2-D Fourier Transform) 1-23

 


 

 

 Chapter 2: Recording System

Chapter 2 : Recording System   2-1

Recording System.. 2-3

Desirable and Undesirable Source Characteristics. 2-3

Energy Penetration to the Target Horizon Depth. 2-3

Frequency Bandwidth and the Desired Resolution of Seismic Data. 2-3

Signal to Noise Ratio. 2-3

Environmental and Natural Terrain Considerations. 2-3

Availability and Cost of Using an Energy Source in an Area. 2-4

Seismic Energy Sources for Land Data Acquisition. 2-5

Dynamite: 2-5

Buried Primacord: 2-5

Weight Dropping Method: 2-6

Dinoseis. 2-6

Vibroseis. 2-6

Sweep Frequency Control 2-7

Selecting Vibroseis Sweep. 2-7

Summary of Sweep Criterion. 2-8

Receivers (Geophones) 2-20

Geophones for Land Data Acquisition. 2-20

Hydrophones for Marine Data Acquisition. 2-20

Geophone Response. 2-20

Data Recording. 2-21

Shooting Spread Types. 2-21

Ground Roll Attenuation Using Source Array Pattern. 2-21

Important Steps in Seismic Data Acquisition. 2-21

Land: 2-21

Drilling Shot Holes: 2-21

Marine Seismic Data Acquisition – Energy Sources and Receivers. 2-23

Secondary Pressure Pulses or Bubble Effect 2-23

Air Gun. 2-23

Unipulse. 2-24

Vaporchoc or Steam Gun: 2-24

Flexotir 2-24

The Sleeve Exploder Or Aquapulse. 2-24

Aquaseis. 2-24

Imploders. 2-24

Receivers: Hydrophones for Marine Data Acquisition. 2-26

Selecting Air Gun Parameters. 2-26

Streamers in Marine Data Acquisition. 2-27

Streamers or Cables. 2-28

Depth Control 2-28

Depth Indicators. 2-28

Compass Heading. 2-28

Noise. 2-28

Fundamental Principles of Array Design. 2-28

Modeling a Seismic Record and Ground Roll/Surface Waves. 2-29

Receiver Array Design. 2-31

Linear Array. 2-31

Non-Linear or Weighted Array. 2-34

Stack Array. 2-34

Source Array/Pattern Design. 2-34

Instrumentation for Seismic Recording. 2-36

Roll-Along-Switch. 2-36

Preamplifier 2-36

Alias Filter 2-37

Notch Filter 2-37

Multiplexer 2-37

Main Amplifier 2-37

A/D Converter 2-37

Automatic Gain Control (AGC) 2-38

Tape Drive and Storage Media. 2-38

Instrument Noise. 2-38

Number of Recording Channels. 2-38

Using Telemetry in Seismic Surveys. 2-38

Sign-Bit Recording Method. 2-38

Formatter 2-40

 


 

 

 Chapter 3: Signal to Noise Ratio and Recording Parameters

Chapter 3 : Signal to Noise Ratio and Recording Parameters  3-1

Signal to Noise Ratio and Recording Parameters. 3-2

Signal Definition and Analysis. 3-2

Desired Reflected Signal Recognition and Analysis. 3-2

Depth of Target 3-3

Frequency Spectra or Bandwidth of the Reflected Signal 3-4

Signal Enhancement in Data Acquisition. 3-5

Sources. 3-5

Receivers. 3-6

Noise Definition, Recognition and Analysis. 3-8

Frequency Spectra or Bandwidth of Recorded Noise. 3-9

Noise Reduction in Data Acquisition, Noise Tests in the Field. 3-12

Seismic Data Recording/Acquisition Parameters. 3-12

 


 

 

 Chapter 4: Survey Planning and Design

Chapter 4 : Survey Planning and Design  4-1

Survey Planning and Design. 4-2

Review Historical Data for Geology and Geophysics. 4-2

Survey Design Objective and Planning. 4-3

Land Seismic Surveying. 4-3

Source Arrays. 4-4

Cables. 4-4

Cable Difficulties and Problems. 4-4

Positioning of Land Survey. 4-4

Marine Seismic Surveying. 4-5

Air Gun Arrays. 4-5

Streamers. 4-6

Streamer Difficulties and Problems. 4-7

Positioning of Marine Survey. 4-8

Positioning Using Doppler Shift of Satellites Signals. 4-8

Global Positioning System (GPS) 4-8

Radio Navigation. 4-9

Computations Performed During Navigation and Data Acquisition (After Evans, 1998) 4-9

Data Acquisition Configurations. 4-10

Problems and Difficulties in Survey Design. 4-10

3-D Survey Design and Analysis. 4-10

Fundamentals of 3-D Seismic Surveys. 4-10

Fresnel Zone as Applied to Seismic Reflections and Migration. 4-12

Major Steps in Designing 3-D Surveys. 4-16

Survey Design to Meet Processing Objectives. 4-16

Template Design: Number and Length of Receiver Lines. 4-16

Swath Surveys. 4-16

Full 3-D Surveys. 4-16

Loop Surveys. 4-16

Circular Surveys. 4-16

Parallel Surveys. 4-16

Checkerboard Survey. 4-16

Marine Surveys. 4-17

Random Source and Receiver Surveys. 4-17

Transition Zone Surveys. 4-17

Special Surveys. 4-19

Broadside Template. 4-19

Kite Survey. 4-19

Slanted Source Survey. 4-19

Aerial Coverage. 4-19

Bin Size and Fold. 4-19

Source Interval and Source Line Spacing. 4-20

Receiver Interval and Receiver Line Spacing. 4-20

Template Movement 4-21

Estimating Number of Moves for a Template: 4-21

Attribute Analysis. 4-22

Recording Equipment, Seismic Crew and Cost 4-27

Designing a 3-D Survey Example. 4-27

Case Histories. 4-28

Parallel Swath 3-D Survey. 4-28

Marine-Transition-Land 3-D Survey. 4-30

 

 Chapter 5: Introduction to Wave Propagation

Chapter 5 : Introduction to Wave Propagation  5-1

Introduction to Wave Propagation and Seismic Data Processing. 5-2

Principles of Wave Propagation and Application to Data Processing. 5-2

Reflection. 5-3

Transmission and Conversion: 5-3

Refraction: 5-3

P-Waves: 5-4

Shear, Transverse, Rotational, Tensional, Secondary, or S-Waves: 5-4

Ground Roll or Surface Waves or Rayleigh Waves (R): 5-4

Poisson's Ratio. 5-4

Reflection Coefficient 5-4

Acoustic Impedance. 5-6

Acoustic Impedance Contrast 5-6

Factors Affecting Seismic Wave Propagation. 5-6

Interval Velocity and Reflection Coefficients. 5-6

Spherical Divergence and Reflector Geometry. 5-6

Attenuation or Absorption. 5-6

Scattering. 5-6

Reflection and Transmission Loss. 5-7

Factors Affecting Velocity of Seismic Waves: 5-7

Density and Pressure. 5-7

Porosity and Saturation. 5-7

Depth, Age, and Lithology. 5-7

Velocity – Depth Curves. 5-7

Source types: 5-8

Impulsive. 5-8

Vibratory. 5-8

Amplitude. 5-8

Frequencies. 5-8

Phases. 5-9

Definitions of Terms Used in Seismic Data Processing. 5-10

Frequency Spectra. 5-10

Phase Spectra. 5-10

Fourier Transform.. 5-10

Wave Number – Frequency (F-K) Transform (Spatial or 2-D Fourier Transform) 5-10

Source Receiver Configuration Parameters and Definitions. 5-10

Parameters Relating to Geometry of Data Processing. 5-13

Methods Used in Data Correction. 5-13

Filtering and Deconvolution. 5-13

Signal-to-Noise Ratio Enhancement 5-15

Migration and Stacking. 5-19

Post Stack Processing. 5-19

Steps from Recording to Processing. 5-21

Pre-Processing. 5-21

Amplitude Scaling and Filtering. 5-21

Near Surface and Static Corrections. 5-21

DMO and Prestack Migration. 5-21

Velocity Analysis and Stacking. 5-21

Special Topics. 5-21


 

 

 Chapter 6: Sampling and Recording Geometry

Chapter 6 : Sampling and Recording Geometry  6-1

Seismic Data Sampling and Recording Geometry. 6-2

Multiplex. 6-2

Procedure of Digitally Sampling and Recording Seismic Data in the Field. 6-2

Demultiplex. 6-2

Procedure of Extracting and Reordering Recorded Seismic Data into Seismic Traces. 6-2

Recording Geometry. 6-2

Shooting Spread Types. 6-2

Marine Seismic Data Acquisition – Energy Sources. 6-5

Secondary Pressure Pulses or Bubble Effect 6-5

Parameters Relating to Geometry of Data Processing. 6-6

 


 

 

 Chapter 7: Amplitude Scaling and Filtering

Chapter 7 : Amplitude Scaling and Filtering  7-1

Amplitude Scaling. 7-2

Decay Curve and Inverse. 7-2

Determine the Amplitude Decay Curve. 7-2

Calculate the Inverse of the Decay Curve. 7-2

Apply the Scaling or Normalization Function to the Data. 7-4

Filtering and Deconvolution, Signal Enhancement 7-4

Seismic Trace. 7-4

Seismic Wavelet 7-4

Bandpass Filter Wavelet 7-4

Klauder Wavelet 7-4

Ricker Wavelet 7-5

Filtering. 7-5

Convolution. 7-7

Correlation and Cross-correlation: 7-7

Wiener Filter 7-7

Recursive Filter 7-7

Types of Deconvolution    (Inverse Filters) 7-7

Predictive Deconvolution. 7-7

Velocity Filters (Moveout or Dip Filters, Fan Filters) 7-10

Wave Number F-K Transform (Spatial or 2-D Fourier Transform) 7-10

Amplitude, Phase, Frequency and Phase Spectra, and Fourier Transforms. 7-10

Wavelet Phase. 7-10

Minimum Phase or Minimum Delay. 7-10

Maximum Phase or Maximum Delay. 7-10

Mixed Phase or Mixed Delay. 7-10

Zero Phase or Symmetric. 7-10

Seismic Wavelets. 7-11

 


 

 

 Chapter 8: Velocity Analysis

Chapter 8 : Velocity Analysis  8-1

Velocity Analysis. 8-2

NMO.. 8-2

NMO and Velocity Relationship. 8-2

NMO Approximation. 8-2

Higher Order NMO.. 8-2

NMO Correction. 8-2

Velocity Analysis. 8-2

NMO Correction and Wavelet Stretch. 8-8

Automated Velocity Analysis. 8-8

CDP Gather Data and Velocity Functions. 8-8

NMO Correction and Velocities. 8-8

Multiples and Moveout 8-8

Picking Velocities. 8-8

Example of Velocity Analysis Using Synthetic Gathers. 8-12

Methods of Displaying Velocity Analysis Results. 8-12

Effect of Far Offsets on Velocity Analysis. 8-12

Effect of Statics on Velocity Analysis. 8-12

Classification of Seismic Velocities: 8-16

Average Velocity. 8-16

Interval Velocity. 8-16

Instantaneous Velocity. 8-16

Root-Mean-Square or RMS Velocity. 8-16

Stacking Velocity. 8-16

Methods for Seismic Velocity Measurement 8-18

Well Shooting (CVL) or Check Shot Velocity Logs or Sonic Logs. 8-18

Velocities from the Reflection Travel Times: 8-18

Summary of Automated Velocity Analysis Steps. 8-18

NMO and Velocity Analysis. 8-18

NMO of Seismic Reflections from Dipping Reflectors. 8-21

 


 

 

 Chapter 9: Static Corrections

Chapter 9 : Static Corrections  9-1

Static Corrections. 9-2

Weathering Correction for Reflection Seismic Data. 9-2

Correcting Shot and Detector to a Datum Plane: 9-2

Residual Statics. 9-4

Plus-Minus Method of Estimating Statics. 9-4

Calculating velocity Vb 9-4

Least Squares Method of Estimating Statics. 9-5

Automatic Statics with Limited Maximum Shift 9-5

Processing Steps for Static Corrections. 9-6

Dynamic Corrections. 9-8

Shot-Receiver Elevation and Low Velocity Layer Replacement: 9-8

Water Layer Replacement Correction. 9-8

The Dewater Process. 9-8

Dewater Corrections. 9-9

Real Data Example of Dewater Correction. 9-9

List of Corrections Applied to Seismic Data. 9-9

 


 

 

 Chapter 10: Stacking and Migration

Chapter 10 : Stacking and Migration  10-1

Stacking. 10-2

CDP Stacking Processing Flow. 10-2

Common Depth Point (CDP) Stacking. 10-3

Quality Control 10-3

Static Corrections. 10-3

Velocity Analysis and Static Corrections. 10-3

Stack. 10-3

Stacking and Signal to Noise Ratio. 10-3

CDP Stacking and Random Noise. 10-4

Signal/Noise Ratio Enhancement 10-4

Semblance or Coherency Criterion for Stacking CDP Gathers. 10-7

Common Offset Sections. 10-8

Post Stack Migration. 10-8

Relationship between Seismic Reflections and Diffractions. 10-8

Migration and Dipping Reflectors. 10-8

Equal Travel Times Elliptic Curves. 10-9

A Reflector Point Before and After Migration. 10-9

Kirchoff’s Diffraction Summing. 10-9

Maximum Migration Aperture. 10-9

Diffraction Curves for Migration. 10-9

Finite-Difference Wave Equation Migration. 10-14

Frequency-Wavenumber (F-K) Migration. 10-14

Depth Domain Migration. 10-14

Frequency Domain Migration. 10-14

DMO - Dip Moveout Correction (Partial Migration) 10-15

Flat Reflectors. 10-15

Dipping Reflectors. 10-15

Benefits of DMO Correction: 10-16

Factors Affecting Migration. 10-16

Migration Properties. 10-16

 


 

 

 Chapter 11: Seismic Processing and Analysis

Chapter 11 : Seismic Processing and Analysis  11-1

Special Topics. 11-2

Factors Affecting Resolution of Seismic Data. 11-2

Signal 11-2

Noise. 11-2

Vertical Resolution (Recording Sample Rate) 11-2

Spatial or Lateral Resolution. 11-2

Frequency Content of Seismic Signal 11-2

Source Wavelet 11-3

Rock Velocities. 11-3

Stacking Velocities. 11-3

Statics. 11-3

Near Surface Low/High Velocity Layers. 11-3

Dipping Reflectors. 11-3

Depth of Penetration. 11-3

Applications of Tau-P Transforms or Slant Stacks. 11-4

Tau-P Transform.. 11-5

Surface Waves Removal 11-5

Suppression of Multiples. 11-5

Multi-Component Seismic Data Processing. 11-5

Separation of P and S Wave Data. 11-7

Rock Properties from 3-Component Data. 11-7

Seismic Attributes. 11-7

Amplitude. 11-7

Frequency. 11-7

Phase. 11-7

Energy. 11-7

VSP Data Processing and Correlation with Stacked Seismic Data. 11-15

For Vertical Ray Paths Up-going Waves. 11-15

Down-going Waves: 11-15

Stacking of Constant Depth Recordings. 11-16

VSP Data Processing. 11-16

Vertical Summation. 11-16

VSP Data Processing Example. 11-17

Deep Water Seismic Exploration. 11-25

 


 Exercises

 

Exercises: Seismic Data Acquisition and Processing

Seismic Data Acquisition and Processing: Exercises  3

Exercise 1: Elastic Wave Propagation. 3

Incident and Refraction Angles. 3

Critical Angle. 3

Exercise 2: Partition of Incident Seismic Energy. 4

Exercise 3: Time Domain Principle. 5

Exercise 4: Recording System.. 5

Exercise 5: Velocity of P, S, and R (Ground Roll) 6

Ground Roll 7

Exercise 6: Notch Filter 7

Exercise 7: Seismic Trace Recording. 7

Exercise 8: Signal to Noise Ratio. 7

Exercise 9: Fresnel Zone. 8

Exercise 10: Frequency Aliasing. 8

Exercise 11: Migration. 9

Maximum Migration Aperture. 9

Diffraction Curves for Migration. 9

Exercise 12: Frequency vs Wavelength. 10

Exercise 13: Mid-Point Scatter for Dipping Reflectors. 10

Exercise 14: Migration. 11

Exercise 15: Frequency and Wavenumber 11

Exercise 16: Surface Obstacles in 3-D data Acquisition. 11

Close Loop Elevation Survey. 11

Exercise 17: Survey. 12

Exercise 18: Fresnel Zone and Ray Tracing. 12

Exercise 19: Design 2-D Seismic Lines. 12

Exercise 20: Survey Design. 13

(1) Area Dimensions  14

(2) Bin Size  14

(3) No. of Shots per Square Kilometer 14

(4) Source Line Spacing  14

(5) Receivers and Receiver Lines  15

(6) Sources and Source Lines  15

(7) Total Fold  15

(8) Maximum Offset 16

(9) Template Moves  16

Exercise 21: 3-D Survey. 16

Exercise 22: 3-D Transition Survey. 16

Exercise 23: P& S Wave Attenuation. 16

Attenuation of P-Waves. 16

Attenuation of S-Waves. 17

Exercise 25: Bright and Dim Spots. 21

Exercise 26: Multi-Component Recording. 21

Exercise 27: Rock Properties. 21

Exercise 28: Depth Imaging. 21

Exercise 29: Seismic Data Processing Introduction. 21

Exercise 30: Geometry. 21

Exercise 31: Gain. 21

Exercise 32: Convolution. 22

Exercise 33: Corrections. 22

Exercise 34: Stacking. 23

Exercise 35: RMS and Interval Velocities. 24

Calculate Interval Velocities from RMS Velocities. 24

Exercise 36: Special Topics. 25

Exercise 37: DMO – Dip Move-out Correction. 26

Dipping Reflectors. 26

Exercise 38: Design Acquisition/Processing Parameters. 27

Elevation Change. 27

Crooked Line Shooting: 27

Ground Condition: 28

Seismic Data Problems: 28

Statics and Fold. 28

60 Hz Pickup. 28

Ground Roll 29

Target Reservoir: 29

Previous Acquisition Parameters: 30

Previous Processing Sequence on Old Data: 30