Opendtect
Instantaneous
Name
Instantaneous - Attribute that returns a value at a single sample location.
Description
Instantaneous attributes are computed sample by sample, and represent instantaneous
variations of various parameters. Instantaneous values
Volumetric Dip and Azimuth
Study conducted to compare multi window estimates of
volumetric dip with conventional dip maps made from
interpreted horizons from survey acquired in the Fort Worth
Basin, Texas, U.S.A., and examine two horizons Pennsylvanian-a
Quantitative Amplitude Analysis
Minimum Phase, Zero Phase, Linear Phase
Figure shows four waveforms which
have the same amplitude spectrum
but different phase spectra.
Figure (a) is zero phase, recognized
by the symmetry about the maximum
at t = 0; it is
Volume curvature
Volume curvature attributes are geometric attributes
computed at each sample of a 3D seismic volume from local
surfaces fitted to the volume data in the region of the sample.
The curvature attributes respond to bends and breaks in
seism
Curvature
Curvature - Osculating circle
In differential geometry of curves,
the osculating circle of a sufficiently
smooth plane curve at a given
point p on the curve has been
traditionally defined as the circle
passing through p and a pair of
additional
Impedance, Reflectivity, & Amplitude
Frequencies, Periods,
Wavelengths, and Wavenumbers
Period T is the time of
repetition of a periodic wave,
the time for a wave crest to
travel one wavelength
Frequency f - is the
repetition rate of the periodic
wave,
Seismic Attributes
Instantaneous, Dip, Azimuth
Seismic Attributes
An attribute is necessarily a derivative of a basic seismic
measurement.
All the horizon and formation attributes available are not
independent of each other but simply different ways of
p
3-D Seismics
2D vs 3D
3D Seismic Significance
Line 6
Line 6
Line 6
Model of two anticlines and one fault with seismic data along
Line 6 showing comparative effects of 2D and 3D migration
3D Data Volume
3D Data Volume - Inline, Crossline, and Seiscrop sect
Seismic Data Acquisition
Land and Marine
Source, Receiver
Streamer, Cable
Geophone array
Line Layout
Recording Instrument
Polarity Convention
Seismic Data Acquisition
Target zones can vary from shallow to deep
Scale of the problem varies
Land and
Traveltime
Refraction and Reflection
Ray Path Geometry
Vp1 = 4000 m/s
Vs1 = 4000 m/s / 1.75 = 2286 m/s
Vp2 = 6000 m/s
Vs2 = 6000 m/s / 1.75 = 3429 m/s
P-critical angle [ic] = sin-1 (4000/6000) = 41.8
For a P-wave at incident angle [ip] = 30
Reflected P-wa
Energy Partitioning
Seismic waves will be reflected at interfaces with discontinuities in elastic properties
A new ray emerges, heading back to the surface
Energy is partitioned some energy is reflected, some energy is transmitted,
according to
(where Z =
Partitioning at an Interface
In Figure, the angles for
incident, reflected and
transmitted rays
synchronous at the
boundary are related
according to Snells law by:
where P1V = P-wave velocity in medium 1, P2V = P-wave velocity in
medium 2; S1V = S-wave ve
Seismic Resolution
Resolution
Resolution refers to the minimum separation between two
features such that we can tell that there are two features
rather than only one.
With respect to seismic waves, we may think of
(a) how far apart (in space or time) two
Frequencies, Periods,
Wavelengths, and Wavenumbers
Period T is the time of
repetition of a periodic wave, the
time for a wave crest to travel one
wavelength
Frequency f - is the repetition
rate of the periodic wave,
reciprocal of period (1/T)
Wave length
Common Midpoint (CMP) Method
The basic objective is to sample each subsurface point more than
once
For horizontal reflectors, the reflection point is halfway between shot
and receiver (at the midpoint)
Survey is organized to sample midpoints repeatedly
The Law Of Reflection Using Huygens Principle
The angle between the normal to the interface and the
normal to the incident wavefront is called the angle of
incidence (i); the angle between the normal to the
interface and the normal to the reflected wavefr
Huygens principle
Huygens principle can be stated: All points on a wavefront can be regarded as point
sources for the production of new spherical waves; the new wavefront is the tangential
surface (or envelope) of the secondary wavelets.
Application of Hu
The SEG Polarity Standard
The SEG polarity standard (Thigpen et al., 1975) implies,
when using for display a minimum-phase wavelet from a
compressive source, that a P-P reflection from an
interface with a positive P-P reflection coefficient (RPP >
0) wil