Conoco Inc.

Gregory L Loumos

Shein S Wang

David W Bell

Thomas R Stoeckley

Stephen J Hill

A hybrid velocity model is used to image the subsalt reflector. A method for imaging subsalt reflectors includes receiving seismic data and depth migrating the raw data. Generated seismic P-waves are assigned a first P-wave velocity for travel outside a salt wedge. Prior to entering the salt wedge, the wave is treated as a compressional wave. Upon entering the salt wedge, the P-wave is treated as a converted S-wave and a corresponding S-wave velocity is assigned to the converted wave. When the converted S-wave exits the salt wedge, it is again converted, this time back to a P-wave. As this wave travels through the subsalt layer to a reflector interface, it is assigned a P-wave velocity. Thus, a velocity model which includes both P-wave and S-wave velocities is used to image reflectors below salt wedges.

Method for using P-S converted waves as a subsalt imaging tool

A method for static correction includes a three step process which eliminates the problems of assuming hyperbolic moveout curves and forming base traces from common midpoint gathers while addressing long spatial wavelength variations. First, after calculating and applying an approximate high-frequency static correction to the individual shot and receivers (using traditional automatic methods), depth migration iterations are employed to coarsely tune the near-surface velocity layer. Second, after applying this correction, the remaining statics are incorporated into the model by tomography, which accounts for the velocity and thickness of the weathering layer and buried anomalies. Third, any residual misalignments are addressed using a multi-windowed statics adjustment within the common image point (CIP) gathers.

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Ponca City, OK, United States of America

Gregory L Loumos