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GCRock
Physics
and the Case for Multicomponent Seismic Data*
By
Bob Hardage1, Diana Sava1, Randy Remington1, and Michael DeAngelo1
Search and Discovery Article #40273 (2008)
Posted February 7, 2008
*Adapted from the Geophysical Corner column,
prepared by the authors, in AAPG Explorer, January, 2008, and entitled
“Rock-
Physics
Theory a Help.” Editor of Geophysical Corner is Bob A. Hardage.
Managing Editor of AAPG Explorer is Vern Stefanic; Larry Nation is
Communications Director.
1Bureau of Economic Geology, The University of Texas at Austin ( [email protected] )
General Statement
Examples of P-P and P-SV seismic images of deep geologic targets across the northern shelf of the Gulf of Mexico (GOM) are illustrated in Figure 1, with the P-SV data warped to P-P image-time coordinates. This time warping is a first-order depth registration of P-P and P-SV images, implemented by using an averaged VP/VS velocity ratio function for the area to adjust P-SV image time to P-P image time.
This first-order adjustment of P-SV image time to P-P image time is sufficiently accurate to allow equivalent geology to be identified in side-by-side comparisons of P-P and P-SV data. Comparing the seismic responses at the primed and unprimed number locations in each image space shows that each elastic wave mode provides different – but equally valid – sequence and facies information about subsurface geology, which is a fundamental principle of elastic wavefield stratigraphy.
uFigure CaptionsuP-P vs. P-SV imagesuApplicationuAcknowledgment
uFigure CaptionsuP-P vs. P-SV imagesuApplicationuAcknowledgment
uFigure CaptionsuP-P vs. P-SV imagesuApplicationuAcknowledgment
uFigure CaptionsuP-P vs. P-SV imagesuApplicationuAcknowledgment
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P-P Images vs. P-SV ImagesStructural features A and B (Figure 1) are interpreted to be depth equivalent. The time-warping process positions A and B in time-warped P-SV space to within 100 ms of their positions in P-P image space. A salt structure blanks out both P-P and P-SV images approximately midway between CDP coordinates 19,600 and 21,000. Features 1 through 4 on the P-SV image indicate a cyclic depositional process that is not obvious in the P-P image (1’ through 4’). Feature 5 is an example of P-SV data showing strata that are not present in the P-P data (position 5’). Feature 6 is an example of the P-P mode providing a better image of high-dip strata than does the P-SV mode (event 6’) along this particular profile. On other profiles in the area, the P-SV mode often images high-dip strata better than does the P-P mode.
Application of Rock-
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