Seismic Modeling Case Studies

Hickory Discovery

Right: 3-D visualization of Hickory discovery in Grand Isle South 116. The top and base of salt are shown, along with well bores, a small patch of a seismic depth slice, and clouds showing the locations of the highest seismic amplitudes. The sub-salt amplitude penetrated by the straight well is a tested discovery.  But the deeper amplitude penetrated by the deviated wellbore proved to be a false HCI because no hydrocarbons were found there.  3-D raytrace modeling predicted correctly the false bright spot before the wells were drilled (Muerdter et al., 1998).00

 Tanzanite Discovery

Below:  3-D Visualization of the relatively thin dipping salt slabs in the Tanzanite discovery area in Eugene Island Block 346.  View is from the southeast.  Salt slabs are color coded by depth (red = shallow, blue = deep).  A section from the 3-D PreSDM volume is shown behind the well bore.  To the left (west) the seismic section intersects a translucent velocity section from the 3-D velocity volume (blue = low velocity, red = high). 

Below right:  Map of seismic amplitude illumination on a sub-salt reflector shows the shadow area under the edge of salt where most of the seismic energy strikes the salt/sediment interfaces at greater than critical angle. The seismic data in the salt shadow have noisy but somewhat coherent reflectors.  The modeling analysis indicates that these may be multiples, mode conversions, or migration sweeps and should not be trusted. 

 Salt Edge Models

 Poorly imaged areas under salt edges can masquerade as salt suture zones.

Features that could be interpreted as salt suture zones  are commonly seen directly under edges of salt bodies.

Above: East-west 3-D pre-stacked depth migrated (PreSDM) section through salt body in Green Canyon. Note the poor imaging and discontinuities under the edges of salt.  The top of salt has a dip greater than 40 degrees on the west side and greater than 35 degrees on the east, both greater than the critical angle for the sediment-salt interface.
Above Right: CRP gather results for simple 2-D near-vertical salt-edge model show that poor imaging occurs under salt edges. These areas will have low signal to noise, and migration sweeps can fill these areas giving them the appearance of discontinuities,  salt welds, or sutures.



Copyright 2002 by Emerald Geoscience Research Corporation