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OBTAINING INTERVAL VELOCITIES FROM STACKING VELOCITIES WHEN DIPPING HORIZONS ARE INCLUDED *
Author(s) -
EVERETT J. E.
Publication year - 1974
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1974.tb00069.x
Subject(s) - stacking , geology , azimuth , curvature , interval (graph theory) , inverse , offset (computer science) , anisotropy , point (geometry) , geodesy , geometry , optics , mathematics , physics , nuclear magnetic resonance , combinatorics , computer science , programming language
A bstract Common‐depth‐point stacking velocities may differ from root‐mean‐square velocities because of large offset and because of dipping reflectors. This paper shows that the two effects may be treated separately, and proceeds to examine the effect of dip. If stacking velocities are assumed equal to rms velocities for the purpose of time to depth conversion, then errors are introduced comparable to the difference between migrated and unmigrated depths. Consequently, if the effect of dip on stacking velocity is ignored, there is no point in migrating the resulting depth data. For a multi‐layered model having parallel dip, a formula is developed to compute interval velocities and depths from the stacking velocities, time picks, and time slope of the seismic section. It is shown that cross‐dip need not be considered, if all the reflectors have the same dip azimuth. The problem becomes intractable if the dips are not parallel. But the inverse problem is soluble: to obtain, stacking velocities; time picks, and time slopes from a given depth and interval velocity model. Finally, the inverse solution is combined with an approximate forward solution. This provides an iterative method to obtain depths and interval velocities from stacking velocities, time picks and time slopes. It is assumed that the dip azimuth is the same for all reflectors, but not necessarily in the plane of the section, and that the curvature of the reflecting horizons is negligible. The effect of onset delay is examined. It is shown that onset corrections may be unnecessary when converting from time to depth.