Seismic Exploration in the Era of Big Data
Reflection seismic generally use waves to set off artificial earthquakes. It’s an ingenious strategy, but the industry is constantly pushing for ever-growing and higher-dimension data sets, so “ingenious” isn’t always good enough. Signal acquisition systems must gather seismic signals that bubble up from the deepest bowels of the earth. Once digital recordings have been gathered, they must remove unwanted noise without losing important subsurface imagery. Only with accurate data processing methods can seismic testing equipment provide reliable geological interpretations.
Today’s signal acquisition systems must handle the tiniest form factors, so yesterday’s signal acquisition equipment will no longer do when it comes to accurate vibration testing. The seismic method remains one of the most important strategies used in gas and oil exploration. Fortunately, technology is rising to demand, and vibrator tests are one of its key solutions. Today’s sandwich box seismic testing equipment relies on independent accelerometers to perform independent analysis. Verif-i’s system can assess time differences between truck reference sweep delays and vibrations. That tiny difference has exponential effects on accuracy. Vibrator timing errors have never been this controlled.
Data Processing Interfaces
Even the finest vibrator QC system will fall short without an intuitive interface, so the Verif-i seismic testing equipment combines powerful acquisition and processing software with user-friendliness. The equipment is compatible with Windows operating systems all the way from Vista to Windows 10. Software is provided on a thumb drive or can be downloaded from Verif-i’s website at https://verif-i.com/upgrades-and-downloads/. All acquisition signals are monitored on real-time displays to ensure error free acquisition and data can then be saved in SEG-D format for later processing and archival; data can also be saved in SEG-Y format to allow processing by third party software.
Once the data has been acquired, the Sandwich Box processing software is used to analyse the vibrator sweep; a harmonic intensity plot and flexible displays make it one of the most comprehensive vibrator analysis systems in the land seismic systems niche.
Verif-i understands that there is no single testing method, so the Sandwich Box can be used in a range of different ways. Basic analysis can be performed on a single vibrator in stand alone mode to verify vibrator performance or the system can be connected to the source controller and recording instrument to provide a comprehensive vibrator check out, including vibrator start time accuracy and polarity.
In addition, test signals output by the vibrator electronics can be recorded and scaled by the Sandwich Box so that you can easily compare your results with those from the source controller.
Hardware
Seismic exploration doesn’t take place in comfortable, temperature-controlled office blocks, but in tough environments that are exposed to extreme climates. For that reason, Verif-i’s Sandwich Box is housed in durable Peli box casing and has powerful overvoltage and power supply reverse voltage protection. The quality control system uses magnetically-mounted accelerometers and sophisticated evaluation options. A 25-metre cable is used to connect the vibrator to the Sandwich Box allowing the user to keep away from the noise and dust of the operating vibrator.
Each channel uses its own seismic grade A/D converter for signal fidelity and to eliminate sample skew. All of the eight input channels come with switchable current source, so you can finally enjoy the benefits of multi-accelerometer recording and analysis.
The unit uses an internal test signal generator to test all eight acquisition channels, leaving you to concentrate on more important tasks. The test signals are routed directly to the front panel connectors, so no part of the signal path is left unexamined. The self test data is automatically processed by the system and any errors flagged; the test data and results can also be saved to provide an audit trail.
Working with Parameters
The Verif-i Sandwich Box lets you choose your own parameters, including:
- Trigger types: The Sandwich Box can be triggered by either a digital timebreak signal or using a threshold voltage on any of the acquired signals.
- Digital triggering resynchronises the A/D converters when the trigger is received providing sweep to sweep repeatability.
- A pre-trigger delay can be used with the analogue triggers to accommodate long tapers or allow pre T0 recording.
- Data acquisition length, from 1 to 128 seconds and sample intervals from ¼ to 4 ms are available. The linear-phase anti-alias filter is automatically selected by the system to optimise the recorded bandwidth of the selected sample interval.
- There is no low-cut filter is used to remove accelerometer bias voltage as this is done in software to preserve low frequency accuracy.
The Importance of Distortion Calculation
Sweep distortion is by no means easy to calculate. The Sandwich Box software separates each sweep into a range of overlapping time segments and calculates distortion in each segment; these are then joined together to give a distortion graph for the whole sweep.
When working with very low sweep frequencies the harmonics are tightly spaced and can overlap, so a different algorithm can be used. The low-frequency distortion option enables meaningful distortion measurements to be made even at low sweep frequencies.
Verif-i’s Mk3 sandwich box offers independent accelerometers and bandwidth up to 1600 Hz with no low-cut filter. There is simply no better way to evaluate vibrator operation.
Get in touch
If you’d like to know more about our seismic testing equipment, you can call us on +44 118 972 2236 or write to us via our website Contact Us page.
