A Deterministic Evaluation of eismic Fidelity using Velocity Modeling ...
A Deterministic Evaluation of eismic Fidelity using Velocity Modeling ...
A Deterministic Evaluation of eismic Fidelity using Velocity Modeling ...
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Chapter 4<br />
<strong>Velocity</strong> <strong>Modeling</strong> and PreStack Depth Migration (PSDM)<br />
4.1 Introduction<br />
Pre-stack depth migration (PSDM) has been widely used for large, 3-D s<strong>eismic</strong> marine<br />
surveys. As a result the methods used to develop velocity models for the PSDM have<br />
been primarily based on marine data. Many <strong>of</strong> the same problems observed and<br />
mitigated in marine s<strong>eismic</strong> data <strong>using</strong> PSDM exist in 3-D land surveys, but differences<br />
in 3-D marine data and 3-D land data warrant a reevaluation <strong>of</strong> methods used to generate<br />
velocity models for land data. Reexamining the methods for deriving velocity models for<br />
land PSDM has the potential for establishing a different paradigm for velocity modeling<br />
<strong>of</strong> 3-D land s<strong>eismic</strong> data.<br />
Problems resolved by PSDM in marine s<strong>eismic</strong> data are observed in the pre-stack time<br />
migrated (PSTM) data in the 3-D Vinton Dome s<strong>eismic</strong> survey. Misplaced salt, poor<br />
well ties and the inability to image small fault blocks are problems resulting from low<br />
fidelity <strong>of</strong> the Vinton Dome PSTM s<strong>eismic</strong> data. Two primary reasons for these problems<br />
are strong lateral velocity variations caused by salt, and the related structures in the<br />
sediment section related to salt movement, and anisotropy mainly occurring in the shale<br />
bodies. PSDM <strong>using</strong> an accurate interval velocity model can generate high fidelity<br />
subsurface images in the presence <strong>of</strong> lateral velocity variations. Therefore, estimation <strong>of</strong><br />
an accurate interval velocity model is key to improving the fidelity <strong>of</strong> the subsurface<br />
image at Vinton Dome (Fagin, 1999).<br />
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