EXPERIENCE WITH THUMPER, DYNAMITE, AND VIBROSEIS SOURCES IN EP 308, THE EASTERN CANNING BASIN

The aim of Shell's seismic survey was to acquire high resolution data in the shallow part of the section (0.3-1.0 seconds) as an aid to prospect definition. Extensive testing was carried out with Thumper, dynamite, and Vibroseis sources to determine which source would best meet this data requirement. Source and group intervals were set at 24 m. At the experimental stage Seismograph Services Ltd were engaged to provide dynamite and Vibroseis capabilities, and Petty-Ray Geophysical to provide a Thumper source. The Royal Dutch/Shell research laboratory in The Netherlands also provided two sets of downhole geophones to assist with analysis of near surface signal character. Test data, excepting the downhole geophone traces, were processed in the field by Seismograph Services Ltd. Field processing results indicated that the Vibroseis was the best source, although special attention was needed to ensure adequate low frequency energy was input in poor data areas. In-house processing of production and downhole Vibroseis data suggests that low frequency attenuation may still be an area for future concern. Ministack and downhole geophone data suggest that Vibroseis data quality is enhanced at lower drive levels, set at 20 per cent (Seismograph Services Ltd relative scale) for this survey. The results of testing in EP 308 have provided Shell with useful experience for future data acquisition planning in this part of the Canning Basin.