Seismic Refraction Training 2-1 | Data Processing - Pickwin Module

Summary

This tutorial guides users through the processing of seismic refraction data using Geometrics' Size Imager software. It begins with an overview of the data setup, including 24-channel lines and shot point arrangements. The tutorial demonstrates the process of picking first arrivals, addressing challenges such as noisy data and dead channels, and adjusting for spherical divergence. Through detailed steps, the user learns how to handle noisy traces, adjust gain, and utilize secondary arrivals to accurately pick first breaks, ensuring precise data processing across multiple shot points.

Takeaways

• 😀 The tutorial demonstrates how to process seismic refraction data acquired in the field using software called Size Imager by Geometrics.
• 😀 Data was collected using three 24-channel lines, with geophone locations ranging from 1 to 72 across the lines, and shot points distributed at key positions.
• 😀 The first step in data processing involves picking the first arrival times, a critical part of seismic refraction analysis.
• 😀 The software used allows for easy adjustment of the display, such as resizing and increasing amplitude, to better view the waveform data.
• 😀 Some geophones were malfunctioning or obstructed, leading to a reduction in the number of active channels, but this was managed during processing.
• 😀 A useful feature in the software allows the automatic picking of first arrival times, though manual adjustments are often needed for accuracy.
• 😀 As seismic waves propagate, the signal strength decreases with distance from the shot point, which requires gain adjustments on the data traces for visibility.
• 😀 The program allows for viewing and editing noisy or unusable portions of the data, such as dead channels or malfunctioning geophones.
• 😀 Secondary arrivals, which are often larger in amplitude than first arrivals, can be used as a reference for accurately picking the first arrival time in noisy traces.
• 😀 The process of picking first arrivals is repeated for each shot point in the dataset, which involves multiple files, ensuring accuracy across all channels.
• 😀 Overall, seismic data processing requires attention to detail, with adjustments to both the display and the gain to ensure that the first arrivals are picked accurately.

Q & A

What is the purpose of the tutorial?

The purpose of the tutorial is to demonstrate how to process seismic refraction data acquired in the field using software called Size Imager, provided by Geometrics.

What kind of data setup was used in the field for this seismic survey?

The field data setup involved three separate 24-channel lines, each with geophone locations from 1 to 24, 25 to 48, and 49 to 72, respectively. These three datasets were collected and processed as one continuous line.

How does the data setup for this seismic survey work?

The data setup consists of three 24-channel spreads, with each spread having shot points at various locations. The first, second, and third spreads have shot points at specific positions, and the data will be processed as if it was acquired using a 72-channel instrument.

What is the first step in processing seismic refraction data?

The first step is to pick the first breaks in the seismic data, which involves identifying the travel times of seismic waves as they first arrive at each geophone.

What software is used to pick the first breaks in the seismic data?

The software used to pick the first breaks in the seismic data is called 'Pick One,' which is supplied by Geometrics.

What kind of information does the waveform file provide when opened?

The waveform file provides information such as the number of required traces, the sampling time in seconds and milliseconds, and the number of data points (samples) for each channel.

What challenges are encountered when picking first arrivals in the data?

Challenges include identifying first arrivals on traces that are farther from the shot point, where the signal is more diffused and harder to distinguish due to the spherical divergence of seismic waves.

What is the role of the 'Pick One' software in the first arrival picking process?

The 'Pick One' software assists in automatically identifying the first breaks (arrivals) in the seismic data, but adjustments are often needed by the user for greater accuracy.

How does noise impact the seismic data processing?

As the distance from the shot point increases, the amplitude of the seismic signals decreases, and noise becomes more prominent, particularly in the traces furthest from the shot point. This noise can be exacerbated by increasing the gain on those traces.

What strategy is used to deal with noisy traces when picking first arrivals?

A strategy involves looking at secondary arrivals in the noisy traces and using the trend of these arrivals to estimate the first arrival's time, as secondary arrivals tend to have larger amplitudes than the first arrivals.