Basic Geophysics

Course Description

The overall objective is to introduce to entry level geophysicists, seismic interpreters and geologists, petrophysicists, and reservoir engineers the key concepts and principles of seismic data acquisition, seismic data processing and seismic interpretation, that form the technical basis for value added seismic applications in exploration, field appraisal and reservoir management. Emphasis is on the fundamental and practical understanding of the technical requirements for extraction of geophysical, geological and rock property information. Data examples and exercises are used to illustrate key concepts, practical issues and pitfalls as they affect seismic data quality and interpretation. 

 

The course starts with an introduction in elasticity theory, rock physics, wave phenomena, and signal analysis. These are necessary topics for a proper appreciation of the seismic method.   

 

Data acquisition deals with seismic survey design and instrumentation, i.e. sources and receivers, for land and marine environments. Acquisition parameters and their impact on subsequent processing and interpretation will be discussed, as well as acquisition in terms of the spatial sampling of a surface wavefield, and in terms of illumination of subsurface targets.
New developments in acquisition – survey design as well as instrumentation – will also be discussed; e.g. long offset full azimuth field design and broadband seismic acquisition.

 

Data processing can be characterised as a sequence of processing steps that start with the field data and ends with an image in depth of the subsurface structure together with a velocity model and, ideally, amplitudes that can be used for further applications.
Each of these processing steps has a number of alternative implementations and for each implementation there is a choice of parameters.
During this course all processing steps will discussed together with their alternative implementations, parameter choices and strong and weak points.

 

Data interpretation uses the depth image and velocity information for structural interpretation. Amplitude information, provided this information is preserved during processing, can be used for the subsequent derivation of lithological information, i.e. rock physics attributes, as well as used as direct hydrocarbon indicators (DHIs). The procedures like AVO (= amplitude versus offset) and seismic inversion will be discussed. In addition other procedures to exploit the seismic data will be discussed: time-lapse seismic (or 4D seismic), the derivation of seismic attributes like dip and azimuth, coherence, curvature and spectral decomposition.


Developments like multi-component seismic, including OBC (ocean bottom cable) acquisition and processing together with their contribution to structural and lithological interpretation will be discussed. Anisotropy and fracture characterisation is naturally part of this discussion. 


Course Objectives

At the end of this course the participants will have a working knowledge of the full range of processes of the seismic method: acquisition, processing, and interpretation.
He or she is fully capable to arrive at a proper assessment of the seismic input in multi-disciplinary teams.  

  
Geophysicists – acquisition and processing – at the beginning of their career will have an excellent starting point for subsequent more advanced courses. 

 

 

Continuing Professional Development

35 HOURS CPD

 


Course Content

Day 1
1. Stress-strain relationships and elastic constants


. Deformation and the strain tensor 
. Traction and the stress tensor
. Stress-strain relations: Hooke’s law
. Symmetry properties of the strain tensor, stress tensor and stress-strain tensor
. The equation of motion and the wave equation
. Definitions of elastic constants
. Relationships between elastic constants

 

2. The wave equation, wave phenomena, rock physics and the Gassmann equation
. The acoustic wave equation
. The elastic wave equation
. Rays and raytracing
. P-waves and S-waves
. The boundary conditions
. Rock properties
. The Gassmann equation to calculate effects of fluid substitution

 

 

Day 2
3. Signal analysis


. Fourier analysis and filtering
. Sampling, the Z-transform and digital filters
 
4. Seismic data acquisition


. Acquisition geometries and parameters for land and marine seismic
. Sources and receivers with their properties for land and marine seismic
. Spatial sampling
. Arrays and point receivers
. Data partitioning and offset vector tiling (OVT)
. New developments in receivers:
-    MEMS (micro electro-mechanical system) devices
-    Dual-sensor cables - GeoStreamer (PGS)
-    Variable depth streamer – Broadseis (CGGVeritas)
-    ObliQ – sliding notch acquisition (Schlumberger)
-    UniQ – point receivers (WesternGeco)
-    Isometrix – multi-sensor towed streamer (WesternGeco)
. New developments in sources:
-    low-frequency and high-frequency vibrators
-    productivity enhancement for vibrator seismic (e.g. slip sweep)
-    Time and depth distributed source – GeoSource (PGS)
-    low frequency sources
-    simultaneous sources (blended seismic)
. New developments in acquisition geometries:
-    multi-azimuth (MAZ) and full-azimuth (FAZ) marine seismic
-    coil shooting
-    long offsets

 

Day 3
5. Seismic data processing  


. The processing sequence
. Various types of velocities: definition and way of measurement
. Identing and quality control
. Static corrections
. Stacking velocities: behaviour and determination
. Signal analysis and deconvolution
. Signal-to-noise enhancement
. Multiple elimination
. Migration (or seismic imaging), principles and algorithms:
-    Kirchhoff or summation migration
-    Wave equation migration
-    RTM (reverse time migration)
-    Gaussian beam migration
-    Migration and demigration
. Velocity model building, principles and algorithms:
-    CIGs (common image gathers) and their application
-    Traveltime inversion and Stereotomography
-    Tomographic velocity model building
-    FWI (Full Waveform Inversion)


Day 4
6. Quantitative interpretation for rock properties and DHIs
AVO/AVA


. Factors affecting amplitudes
. The Zoeppritz equations for reflection and transmission coefficients
. Approximate expressions for the reflection coefficients
. AVO modelling
. Processing for AVO analysis
. Estimation of AVO parameters
. Crossplotting of AVO attributes and AVO classification
. Elastic inversion based on AVO behaviour

 

Seismic inversion
. From reflectivity to acoustic impedance
. Least-squares estimation methodology
. Singular value decomposition (SVD)
. Resolution matrix and Covariance matrix
. AVO inversion or elastic inversion
. Probability theory and Bayesian approach to inversion
. Deterministic inversion and stochastic inversion

 

Day 5
7. Additional developments for enhanced interpretation
Multi-component seismic and OBC/OBN seismic


. The data matrix
. The hodogram and polarization analysis of 3C (three-component) data
. Polarization filtering
. Rotation of sources and receivers
. Characteristics of P-, SV-, and SH waves
. P-SV converted waves: occurrence and processing
. P- and S-wavefield separation methods:
-    VSP data
-    Surface seismic data
. Elastic wavefield decomposition

. OBC (ocean bottom cable) and OBN (ocean bottom node) 4C features
. Technical advantages of wide-azimuth ocean-bottom seismic
. Generation of P-to-S converted waves
. Acquisition geometries for ocean-bottom seismic
. Processing of OBC data – PS converted data
. Hydrophone and vertical geophone summation for deghosting and dereverberation
. Wavefield decomposition with various combinations of receivers
. Case studies

 

Anisotropy
. Introduction and definition of anisotropy
. The stress tensor, the Voigt notation and symmetries
. Plane wave solutions and the Christoffel equations
. Phase velocity and group velocity
. Relationship between Wave surface and Slowness surface
. Raytracing, reflection and transmission in anisotropic media
. Shear-wave splitting
. Definitions pertaining to anisotropy
. Transverse isotropy (TI):
-    Angle dependency of velocities in VTI (Vertical TI) media
-    Thomsen’s notation for weakly anisotropic media
-    Crack and fracture properties
-    VTI parameters for finely layered media (Backus averaging)
-    HTI (Horizontal TI) and TTI (Tilted TI) media and azimuthal anisotropy
. Anisotropy from seismic survey design and processing

 

Time-lapse seismic or 4D seismic


. Objectives and feasibility analysis
. Rock physics
. Fluid substitution with the Gassmann equation
. Measurement of traveltime differences and amplitude differences
. Quantification of repeatability of acquisition and processing
. Methods to assess the comparison of  different datasets
. Methods for cross-equalization of two datasets
. 4D modelling of different scenarios
. The 4D workflow

 

Seismic attributes


. Introduction to attributes, definitions and historical overview
. Attribute classification
. The geometric attributes dip and azimuth
. The coherency attribute
. Curvature and reflector shape
. Spectral decomposition and its applications

 

 

 

Location

Date

 

London, United Kingdom

 

 

17-21 July 2017

 

Houston, Texas, United States

 

 

11-15 September 2017

 

Dubai, United Arab Emirates

 

 

5-9 November 2017