Reflektionsseismik Flashcards
(15 cards)
What are some seismo-acoustic sources?
Airgun/luftkanon
Sparker
Sub-bottom profiler (boomer, pinger)
Ekkolod
Vibroseis
Side-scan sonar
What is Huygens principle?
Principle and geometrical method for finding or predicting a wavefront’s location at a given time based on the envelope of the secondary wavefront
Fungerer lidt som hvis man smed en sten i vand —> bølger spreder sig derfra —> bølger møder ny forhindring (fx ny sten) —> nye bølger spredes derfra
What is acoustic impedance?
Describes a material’s acoustic properties i.e. how seismic energy is transported through the material/rock
What is the formula for the reflection coefficient (R)?
R = (z_2 - z_1) / (z_2 + z_1)
where z = acoustic impedance, z = rho * V
What does a positive reflection coefficient (R) / an impedance increase signal?
Water to sediment
Sediment to salt
Sediment to carbonate
What does a negative reflection coefficient (R) / an impedance decrease signal?
Shallow gas sands
Salt to sediment
Carbonate to sediment
What does time-domain show?
Normal time-series representation of the waveform
(If something is extended in time domain, it is shortened in frequency domain)
What does frequency-domain show?
The wavelet is described through amplitude and phase spectra
(If something is extended in time domain, it is shortened in frequency domain)
What is bandwidth?
Range of frequencies present in a wavelet
Width between the ‘lines’ of the wavelet at 50% the height of the peak value
What is the ideal wave?
The Ricker wavelet
What is the Nyquist frequency (f_ny)?
Defined as the highest frequency that can be reconstructed at a particular sample interval (Δt)
What is RMS velocity (V_rms)?
A form of average velocity to reflectors calculated from seismic data i.e. for areas where we do not have well control
Hvad er vigtigt ift. kvalitet af dataindsamling?
Land or marine seismic data
* Noise (weather, traffic, waves, low velocity layers,
topography)
Seismic source
* Frequency and resolution
* Noise (ex. depth in water – sparker vs arigun)
* Shooting interval (fold coverage, signal stacking)
Receivers
* 2D versus 3D
* Fold coverage (distance between and numbers of receivers)
* Noise (water vs land surface)
* Receiver grouping (signal stacking)
Recording
* Digital vs analogue
* Sampling rate
* Recording length
Hvad er top muting?
Bruges til at fjerne den direkte bølge
What is a Pycnocline?
boundary separating two liquid layers of different densities induced by differences in both temperature and salinity
