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Wave Equation Prestack Depth Migration

for Deep Gulf Coast Prospecting



Morgan Brown, Joe Higginbotham, and Cosmin Macesanu


Wave Imaging Technology Inc., 11777 Katy Frwy., Ste. 156, Houston, Texas  77079





The shallow section in the Gulf Coast normally exhibits a simple, depth-Previous HitvariableNext Hit Previous HitvelocityNext Hit profile, which implies that prestack time migration (PSTM) methods generally suffice to produce a drillable image.  In recent years, however, an exciting frontier has opened in the deep section, with high geopressure preserving reservoir prospectivity.  Geopressure is a double-edged sword.  In addition to being a drilling hazard, geopressured sediments often exhibit seismic velocities below the compaction trend.  Complexity in the Previous HitvelocityNext Hit field causes focusing effects in the propagated wave fields, and challenges all the assumptions behind PSTM.  Even if a PSTM image contains a seismic reflection (not a given), the image time may no longer accurately represent the geology in depth.


For these reasons, prestack depth migration (PSDM) methods have been employed successfully for some time to image the deep section when pressure is an issue.  Provided that the Previous HitvelocityNext Hit complexity can be encoded into a migration Previous HitvelocityNext Hit model, PSDM can provide a more accurate picture of the geologic structure, in situations like fault shadow.


Typically, Kirchhoff PSDM algorithms have been used in the Gulf Coast.  When the Previous HitvelocityNext Hit complexity is severe, such as under Gulf of Mexico salt, it is generally agreed that Wave Equation PSDM (WEM) algorithms produce superior imaging results.  For deep Gulf Coast prospecting, the uplift from WEM over Kirchhoff might be more subtle, but the main difference is likely to be in the amplitudes.  WEM algorithms can more naturally handle the amplitude variations due to Previous HitvelocityTop focusing effects.  Because of this, there is a good reason to use WEM for amplitude-versus-angle (AVA) analysis, but until recently, it was not known how to efficiently decompose WEM images into angle “gathers.”


We show how a quality shot record WEM algorithm, combined with a recently developed efficient angle decomposition scheme, can produce compelling results on deep Gulf Coast imaging examples.



Brown, M., J. Higginbotham, and C. Macesanu, 2009, Wave equation prestack depth migration for deep Gulf Coast prospecting:  Gulf Coast Association of Geological Societies Transactions, v. 59, p. 125.


AAPG Search and Discover Article #90093 © 2009 GCAGS 59th Annual Meeting, Shreveport, Louisiana