Comparison And Analysis Of Single-Sweep Vibroseis And Dynamite Seismic Data, Cooper And Er0manga Basins, South Australia.
Ryan, Sarah E.
Honours Degree, 1989
University of Adelaide
The Cooper-Eromanga Basin, South Australia, is currently in a mature stage of petroleum exploration. The exploration targets have changed from large-scale structural features to more small-scale stratigraphic traps. To find these traps, seismic data must have better vertical and lateral resolution, and a higher signal-to-noise ratio. The majority of seismic data acquired in the basin to date uses Vibroseis as the source.
Line 87-AYC was shot to test various acquisition parameters, including the difference in the data caused by using a dynamite source, rather than Vibroseis. This was done by using the same receiver array, and station positions, so that any differences in the data sets so acquired would be principally due to the source.
The uncorrelated single Vibroseis sweeps in the source array were recorded, which allowed application of processing techniques before correlation and before summation. A technique called Vibroseis whitening (VSW), involving application of an automatic gain control (AGC) before correlating, was applied to the single sweep data. This enhanced the high frequency content of the data, without phase distortion. Application of deconvolution after correlation increased the bandwidth further.
The array responses for the receiver, and Vibroseis single and summed sweep arrays, were calculated, and found to cause quite high attenuation at frequencies above 30Hz for the dynamite data, and 25Hz for the Vibroseis. This could have a significant effect on the quality of signal recorded.
The dynamite data has a larger bandwidth than the Vibroseis, and has the potential for higher vertical resolution, but there are problems with ghosting. This can be reduced in processing by deconvolution, or in the field by use of shaped charges or similar. The lateral resolution of dynamite data is higher than Vibroseis, since it is a point source and not an array.
There are problems, and advantages, with using both of these sources for a seismic survey, and the preferred source will depend on the objective of the survey.