Guralp’s new Seismic Array for Downhole Investigations, CMG-SADI, has passed its first deployment with flying colours. Ordered by a Turkish company to be used in the exploration for coal, the tool was recently installed at 825 m depth in a borehole in Western Turkey. GSL cooperated with our regional distributor, Sentez Earth and Structure Engineering Ltd., during the deployment and the intensive testing.
The downhole tool, CMG-SADI, can be used for classic Vertical Seismic Profiling (VSP), but also in a continuous sampling mode for ambient noise studies. The tool is very versatile: It currently has 24 elements but it can easily be extended with up to 128 independent seismometers. Passive geophones can be used as well as our newly developed miniature broadband feedback sensors, which have a flat frequency response to acceleration between 10 sec and up to 300 Hz. Each element has its own downhole digitiser with sampling rates down to 0.25 msec. The synchronisation accuracy between the digitisers is better than 3 mircoseconds. With an outer diameter of only 50 mm, it fits into almost any borehole (see image).
During the test phase, CMG-SADI was operated in VSP-Mode with seismic energy being generated either by Vibroseis sweeps (20-200 Hz, sine wave sweeps) or by shots. The picture below shows all traces recorded at the same geophone for all shots over the line. The data shown are completely unfiltered and no processing corrections have been applied. Click the image for a larger version.
We also have developed a new data-gathering and quick-view software for CMG-SADI. The software, called “VSP Viewer”, is based on our successful SCREAM software for regular data acquisition. The image below shows a screen shot of VSP Viewer with highlights of some features of the software. Click the image for a larger version.
For more information, email sales@ideaasgroup.com
