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Quick and Dirty VSP Delivers Clean Image of Complex Geology Offshore BrazilNormal access

Authors: R. Guerra, A. Martinez, M. Pinheiro and E. Wielemaker
Event name: 81st EAGE Conference and Exhibition 2019
Session: Borehole Seismic Methods I
Publication date: 03 June 2019
DOI: 10.3997/2214-4609.201901249
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 3.31Mb )
Price: € 20

Summary:
The term “Dirty VSP” has been coined in the USA for decades to signify a 'quick and dirty' approach to VSP acquisition which is not as rigorous as a fully sampled VSP but is quick, cheap and still fit for purpose. Dirty VSPs do not have the dense regular receiver spacing of a proper VSPs and they are usually recorded with only one or two tools. They are not as sparse as standard Checkshot surveys, recording enough waveform data for lower resolution VSP processing. They represent an attractive solution for wells where only a Checkshot survey is planned, providing more information for similar amount of rig time. We demonstrate the value of a “Dirty VSP” survey recorded offshore Brazil, producing quality depth images of a salt dome 1.3 km away from the well, not fully imaged by surface seismic data. It also delivered accurate velocities, robust well to seismic tie and seismic attenuation parameters. Advanced sonic measurements allowed assessing the VTI anisotropy and its possible impact on depth imaging accuracy. In a time when the pressure on Operators is high to reduce costs, such cost-effective solutions may help some geophysicists overcoming internal resistance to record standard VSPs.


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