Data QC and filtering Bryce HutchinsonSumit Verma Objective: Consider the frequency range of different seismic features Look for low frequency and high frequency noise. Understand Amplitude and Phase spectrum.

This lab is independent of velocity picking lab, you do not need to be done with velocity picking to start this lab.

1 Hope you remember geometry set up !!!! 2 3 Let us select a gather from middle of the survey to QC. Right click to get this

1 3 Just see Double click..

Figure out: How many receiver lines are active ? How many receivers per line? 1 3 2

Let us recognize some events ! Reflections ? High Amplitude ? ?

Let us apply exponential gain : exp(nt) or e nt, we kept n=2 and t= time.

Accessing Frequency Spectrum 1. Click the Seismic Analysis Window icon in the Seismic Data window 2. From the dropdown menu select Frequency Analysis Window then click the green plus sign. 3. The window on the top right dynamically changes depending on where your mouse is pointed. This window displays the trace frequency spectrum and overall frequency spectrum for the shot. We will understand this panel first! Amplitude Spectrum ! Frequency range at each trace! Phase spectrum!

Zoom in frequency scale ! Now we will just look into the frequency of whole gather (for one shot) 2. This is for one trace, so here we do not want to see amplitude spectrum of every trace separately, but just analyze the amplitude gather of whole shot gather.

What is frequency range of my recorded data? What is source frequency? On our data set Vibroseis sweep was : 8-120Hz

Zoom this !

Lets analyze the data on different frequency bands ! Before any band pass filter This is an image of the raw data. In the next several slides I will display images of the band raw data then band passed data for your consideration. Take note of what stays in the images and what is removed.

Ground roll? Head Wave? Here, we think the high amplitude low velocity events are ground roll and fast velocity events are head wave. We will check the velocity of these events next Band Pass 4-10Hz

Ground roll? Head Wave? Calculating Velocity (linear velocity) linear velocity = Offset / Seismic time

2 Ground roll? Head Wave? Reflections? 1

1 2 Left Click here Drag the mouse Calculate the velocity of this section too What velocity did you get? Ground roll? Head Wave?

Calculate the velocity of reflector manually ! 500ms  3000ft Linear Velocity  6000ft/sec Head wave is faster than ground roll ? We do not calculate the velocity of reflections by this method ?

Observations ! We have head wave in our data set and ground roll at lower frequencies. We may also need to see how much they interfere(and may interfere after migration) with our reflections of zone of interest.

Band Pass 15-20Hz Ground roll? Ground roll is present at this frequency range.

Do it if you like ! Make band pass : – 20-30Hz – 30-60Hz – 60-80Hz – – Just see how it looks.

Noise This has signal and noise!

Data sweep was 8-120! So, can we get any frequency >120? Is it noise ? Band pass filter Out of the source frequency range

We wish to keep reelections and remove noises. But, we may need a good range of frequencies for Seismic inversion, so we do not want to remove the frequencies. But, it will be a good idea to band pass filter the data in the range of source frequency.

Let us calculate the reflection velocity! You can get this display ! 1 Click it to see nmo velocity!

Left Click here Drag the mouse 6600 ft/sec

the reflection velocity at different level! Compare it with your velocity semblance panel!

Band Pass Flow Choose your input as the raw data. Ormsby is the band pass flow command you will use. Set the frequency range as I do in the following slides. Remember we must use a taper! Just keep the source frequency range !

Acknowledgement ! Dr. Kurt Marfurt Marcus Cahoj for giving inspiration for this lab.