Reviewing the Impact of Attenuation under Thick Karst and the Implications for Survey Design and Processing

Q-profiles extracted from rig sourced VSPs in an area with thick heavily karstified intervals are used to confirm that the upper frequency limit for all surface acquired seismic in this area (towed streamer or ocean-bottom) may be predicted by earth attenuation on the input source spectrum.

To mitigate the effective resolution loss at our reservoir interval, we designed a verydense survey with much better sampling, to lower the noise floor and increase the usable bandwidth after Q-compensation. Creating a 3D Q-model and correcting for attenuation in migration does not appear to be fully robust workflow at this stage, but we found that the FWI derived velocity model was useful to guide the irregular shallow gas Q-anomalies, and we used this hybrid Q-model in a two-step processing flow: QPreSDM to include shallow gas, and post-stack compensation using the VSP derived Q properties.

Processing tools alone are insufficient to compensate for strong earth attenuation and acquisition design also needs to be considered when subsurface resolution is an important objective. Resolution in the final seismic dataset is not just a factor of the earth attenuation, it is related to how well the acquisition and processing compensate for the effect.