A SRI 1
SRI
SRI
fault shadow velocity distortion
apparent rollover
salt associated velocity anomalies
.
velocity push down
under shale diapir
velocity anomalies beneath detached listric faults
.
sedimentary features that can have associated seismic velocity anomalies
channels
reefs
two differnet methods for calculating the velocity to a point
Average velocity
Interval velocity
sources of velocity information
calibrated (check shot) sonic log
stacking velocityes (well distribuated but often inaccurate)
advantage and disadvantage of getting velocitys from borehole sonic logs
accurate
single point, generally only on top of structures
3 methods for determination of the spatial velocity field
use well data to determine a single time vs. depth curve
determine average velocity to horizons at well, stacking velocity for gaps between wells
depth conversion scenarios
no dip, not lateral variations: time to depth along vertical rays
dipping events, mild lateral variation: time migration and as before
dipping events moderate
What does the complex seismic trace consist of
the original input trace and a complex trace generated via the Hilbert Transform.
seismic envolope
the maximum value a trace can have when a single phase rotation (in the range 0 - 360º) is applied
instantaneous amplitude
the maximum value of the seismic amplitude
instantaneous phase
the phase rotation that gives rise to the instantaneous amplitude
Pre stack vs. post stack attributes
AVO is pre stack, everything else is post stack
what energy does the real seismic trace measure
the kinetic energy
what energy does the imaginary seismic trace measure
potential energy
what energy does the complex seismic trace measure
real+imaginary=kinetic+potential=total energy of seismic responce
how to generate synthetic wavelet
.
what does dipping structures mean for depth conversion?
you need migration beore time conversion
Isochore
Vertical thickness of the interval
Isopach
True stratigraphic thickness
Static mis-ties
constant bulk shift of seismic at tie point for a match
Dynamic mis-ties
mis-tie varies with TWT eg increasing mist-tie with dip also known as migration mis-ties
4 causes of static mis ties
aPPle NEver DEstroyed PCs
Navigation or surveying Errors
Polarity Conventions - reverse polarity between different vintage lines
Processing Problems - (eg stacking velocities, static corrections, NMO stretch due to different mute patterns, wavelet shape ie min. or zero phase) the major cause of misties
Diffraction Effects near faults
how does migration affect mis ties
unmigrated lines should always tie, so so mis-ties on these lines are of the static variety.
Dynamic misties only affect migrated data.
how to handle dynamic mis ties
Use strike lines only to tie events among the dip lines; map only the dip lines - wasteful on information held in the dip lines. • Explicitly correct strike line data by moving the data to their proper position on the basemap. This can be accomplished graphically eg move strike lines up-dip on the intersecting dip lines until they tie and plot the strike line information at the tie location on the basemap. Note that this correction will vary with dip and TWT.
dynamic mis ties
Shallow low dip events will tie reasonably; mis-ties increase with dip and TWT.
4 methods of contouring
Most People Eat Simple Ingredients
mechanical
parallel
equal space
interpretive
what log represents seismic data
sonic log
Hilbert Transform
filter that shifts all +ve frequencies by -90º and all -ve frequencies by +90º
Attributes
Amplitude
Phase
Frequency
Polaity
Azimuth
Dip magnitude
curvature
what does Spectral Decomposition do
transforms the seismic data to the frequency domain
what does spectral decompostion allows
tunes (in or out) depending on the time thickness of the layers
(good for looking at paleorivers)
DHI
direct hydrocarbon indicators
different DHI's
bright spot (flat spot)
dim spot
polrity reversal
chimney
false bright spots
Igneous intrusions
overpressure
top of diapirs
highly cemented sands
Depth conversion , two types of product
depth map generated from well data
depth converted seismic section (calibrated from wells)
laterally thinning velocity distortion
.
depth variation velocity distortions
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Cartes-fiches
what does dipping structures mean for depth conversion?
you need migration beore time conversion
