10 Questions
What is the primary objective of interpolating input data to determine the value of YI at points XI?
To improve the Signal-to-Noise Ratio (SNR) in seismic data
What is the purpose of applying Normal Moveout (NMO) correction to seismic data?
To correct for the effects of velocity variations on seismic wave arrival times
What is the primary application of Common MidPoint (CMP) stacking in seismic imaging?
To generate high-resolution seismic images of the subsurface
What is the main benefit of sorting seismic data into offset sections?
To reduce the effects of noise on seismic data
What is the purpose of velocity analysis in seismic imaging?
To determine the velocity structure of the subsurface
What is the primary advantage of using Common MidPoint (CMP) stacking in seismic imaging?
To reduce the effects of noise on seismic data
What is the main difference between onshore and offshore seismic data?
The complexity of the subsurface velocity structure
What is the purpose of generating a Common Offset section?
To visualize the seismic data in a more meaningful way
What is the primary benefit of using velocity analysis in seismic imaging?
To determine the correct velocity model for seismic imaging
What is the main application of seismic imaging in the oil and gas industry?
To identify potential hydrocarbon reservoirs
Study Notes
Depth Stretching after NMO-Stack
- Depth stretching maps the sample at time t0 into the sample at depth.
- NMO removes the additional delay due to offset.
- The corrected depth is calculated using the equation: z = sqrt(t0^2 + (h/V)^2).
NMO-Stack: Imaging for a Flat Earth
- NMO-stack is an imaging algorithm that assumes:
- Reflectors are flat.
- Layer velocities are constant.
- When these assumptions are met, NMO-stack is suitable for imaging.
- One CMP gather contributes to the image for a specific midpoint only.
- NMO-stack is extremely fast and can be used for quick processing QC.
- It is also used when layers are almost flat.
NMO Correction
- NMO correction involves calculating the corrected time using the equation: t_NMO(h) = t + 2h^2 / V^2.
- The corrected time is used to calculate the corrected depth.
CMP Gather
- A CMP gather is a collection of seismic data with a common midpoint.
- The data is sorted into CMPs, and NMO is applied, followed by stacking.
Multiple Layers and Constant Velocities
- In the presence of multiple layers with constant velocities, the NMO correction equation is used to calculate the corrected time.
- The equation is: t_NMO(h) = t + 2h^2 / V^2.
Matlab/Octave Code
- The provided Matlab/Octave code calculates the NMO correction using the equation: dNMO(:,h) = interp1(t, data(:,h), tNMO).
- The code iterates over each offset, calculates the corrected time, and then interpolates the data using the corrected time.
Stack: SNR Improvement
- The NMO corrected CMP gather is stacked to produce a final image.
- The stacking process improves the signal-to-noise ratio (SNR).
- The resulting image shows an improvement in SNR compared to the original CMP gather.
This quiz covers the concept of depth stretching after NMO-stack in seismic exploration. It deals with the relationship between offset and depth.
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