Column 1
A vector measurement measures magnitude and direction. (Yes or No)
Yes.
In which components can we see the Shear wave energy?
Z, X, Y
What is another name for Up/down Deconvolution?
Amundsen method
Water support shear wave transmission.
No, Water doesn’t support shear wave transmission, so they are not recorded by a hydrophone in towed streamer.
Geophones measure velocity and can detect direction the wave is traveling and the upward and downward going wave
Yes
Ocean Bottom Cables have good _______ coupling, but variable_______ coupling.
Inline, Crossline
What multiples are typically predicted using WEM_MOD in OBS processing?
Source side water layer multiples
What does UDD, WEMM and DGD stand for?
UDD- Up/Down Deconvolution
DGD- Downgoing Deconvolution
WEMM- Wavefield Extrapolation Multiple Modelling
Which new literal will be used to identify the specific components (P, X, Y, or Z) after this flow has been run?
→DATA_TRACE_TYPE= 333 Z data
→DATA_TRACE_TYPE= 334 P data
→DATA_TRACE_TYPE= 331 X data
→DATA_TRACE_TYPE= 332 Y data
Which sorting provide you the Receiver gather:
DETECT_LINE_ID/SOURCE_POINT_ID/DETECT_POINT_ID;
DETECT_LINE_ID/DETECT_POINT_ID/SOURCE_POINT_ID
→DETECT_LINE_ID/DETECT_POINT_ID/SOURCE_POINT_ID
How can the PS wave or converted wave help us better understand the geology?
→The S wave is less sensitive around fluid so doesn’t show a dramatic change in amplitude when in the presence of lithology. (Thus if the P wave shows a change in amplitude, one can look at the S wave to see if this is in fact an indicator of gas.
→A change in amplitude in the S wave indicates its gas. If the S wave doesn’t show a change in amplitude, then it is a change in lithology.
What is the SWC process and what are the factors we can estimate?
The SWC process simultaneously accounts for the various timing delays (or Acquisition Perturbations) observed in the data.
Source positioning (X,Y), receiver position (X,Y,Z), water velocity, clock drift. You can also choose if you want these factors applied to the upgoing and downgoing wavefield or not.
Water velocity variation is most affected in _______ marine environments.
Deep
What is an important assumption to keep in mind when running the Voronoi process on deep water OBN data?
Voronoi estimates the scalars based on the midpoint values. The midpoint value is halfway between the source and receiver positions in towed streamer but this is not true for deep water OBN. This is due to the dual surfaces acquisition and even more if we consider the downgoing wavefield.
Why is bubble energy stronger in OBS data than towed streamer data?
→Raw data is rich in low frequencies and is free from receiver side ghost and has receiver side free surface multiple energy.
When do we run the PZ Calibration process with Cross-ghosting for OBS projects?
For water depths less than 50m, it is hard to create a large enough window separating the refraction with the upgoing energy only.
Clipping generally occurs in ______ when the source is too strong.
Shallow water, P component
What are the two most common directions to orient the converted waves/horizontal components? Which direction is then taken through for imagining?
Radial and Transverse
Radial direction is only used for further processing
How does tidal static correction differ for OBC versus Towed Streamer acquisition?
→Receivers are on the seabed so we are 1*tidal static for OBC instead of 2X tidal static for towed streamer
→Downgoing data is 3*tidal static because it is the receiver side first multiple
What are factors that affect the coupling of a geophone in the marine environment?
Water current, seabed surface, sediments
What are the two most common summation methods to sum P and Z?
Method #1 Scale Z and sum with P. Formula: Sum = (P + (1+R)/(1-R)*Vz)
• Method #2 Scale Z and summation with delay operator. Formula: Sum = (P + Vz )*(1+RZ)2
Rotate the x and y horizontal components to radial and transverse directions with _____________?
respect to the source-detector azimuth
What is the difference between General Source Mode vs Point Source Modelling?
General Source Mode - uses recorded data as input to produce surface multiple model. Produces different order multiples at the same time.
Point Source Mode - uses synthetic data and models each multiple one at a time.
What is the issue with running GSMP on mid and deep water OBN Data?
-The source and receiver have a different datum but GSMP assumes the datum is the same. The data must be redatumed which is only possible in shallow water.
-For deep OBN data reciprocity cannot be used due to datum difference, but reciprocity can still be used on the towed streamer leg, GSMP creates MCG (Multiple Contributing Gather) from convolutions between the towed streamer and OBN data.
Please list down the key features of UDD. (including limitation)
•Spectral division / deconvolution
•Supresses all free surface multiples
•Output can be shaped to any desired wavelet.
•Full 3D source deghosting if a ghost free wavelet is chosen
•Up down decomposition ‘above seabed’ using P and Vz, no information about the seabed reflectivity is needed.
•UDD process is robust to the 1D medium assumption, where the seabed is relatively flat