Seismic Data Processing
GEOS 469/569 – Spring 2006
„
GEOS 469/569 is a mix of digital filtering theory and
practical applications of digital techniques to assemble
and enhance images of subsurface geology.
„
Digital filtering theory applies to virtually any sampled
information in time (e.g., seismic data, CAT scans,
climate data) or space (e.g., gravity and magnetic data,
satellite imagery).
„
Seismic Data Processing uses both the concepts of
geometrical optics and the powerful techniques of
Fourier Analysis.
Seismic Data Processing
GEOS 469/569 – Spring 2006
„
Assumes knowledge of basic seismic reflection
techniques and knowledge of trigonometry and
calculus
„
We will use complex numbers and some of the ideas
of complex analysis as tools, but will develop these
as we go.
„
Same with Fourier Analysis
Seismic Data Processing
GEOS 469/569 – Spring 2004
Main tasks of seismic data
processing are to:
„ Correct for recording
strategies and ray-path
geometries
„ Take advantage of the
information that recording
techniques provide
„ Enhance S/N
„ Provide the clearest
possible image of the
subsurface
Digital Signal Analysis
Goals:
„ Analyze the “information content” of signals
* Amplitude, Frequency & Phase
„ Recognize noise and signal
„ Provide the tools to increase resolution:
* Broaden frequency spectrum
* Filter noise
* Improve signal characteristics
„ Contribute to the “best” possible subsurface image
Refraction & Reflection of Light Rays
Analogous to seismic waves in layers of rock within the Earth.
Convolutional Model of the Earth (1)
For a single reflector, the
seismogram we would
record (with a coincident
source and receiver) is
simply the seismic
wavelet scaled by the
Reflection Coefficient,
"hung off" the RC spike
with some noise added.
Convolutional Model of the Earth (2)
Where more
reflectors are
present, the
seismogram is the
sum of the response
of each individual
reflector.
Mathematically, this
process is called
convolution.
Note that if we can “deconvolve” the seismic trace, we can
recover the earth’s reflectivity function! We need to understand
digital-signal-analysis techniques to be able to do this.
Shot Record – Where It All Starts
Simple Shot Record
ƒ
ƒ
Many types of
seismic arrivals are
recorded, only
some of which are
used in subsurface
reflection imaging.
Travel times are
recorded as a
function of offset
Shot Records
Normal Moveout
(NMO) is the
result of how the
data are
acquired: travel
times are
recorded as a
function of offset
„
Corrections are applied
to remove the NMO
curvature of reflections
Shot with NMO Correction
CMP Stacking
„
„
Common-MidPoint (CMP)
Profiling permits
“stacking of
edited, NMOcorrected traces
Addition of traces
improves signalto-noise ratio
(S/N)
Shot Record in Color
CMP Gathers
CMP Gathers with NMO
CMP Gathers with NMO and Mute
Stacked Section (CMP “Stack”)
Stacked Section (Color)