Wave-equation velocity replacement of the low-velocity layer for overthrust-belt data
- Exxon Production Research Co., Houston, TX (United States)
- Stanford Univ., CA (United States). Dept. of Geophysics
- Exxon Exploration Co., Houston, TX (United States)
Seismic land data are commonly plagued by nonhyperbolic distortions induced by a variable near-surface, low-velocity layer (LVL). First-arrival refraction analysis is conventionally employed to estimate the LVL geometry and velocities. Then vertical static time shifts are used to replace the LVL velocities with the more uniform, faster velocities that characterize the underlying refracting layer. This methodology has earned a good reputation as a geophysical data processing tool; however, velocity replacement with static shifts assumes that no ray bending occurred at the LVL base and that waves propagated vertically through the LVL. Wave-equation datuming may be used to perform LVL velocity replacement when statics are inadequately. This method extrapolates the seismic data from the surface to the LVL base with the LVL velocities. Then it extrapolates the data from the LVL base to an arbitrary datum, with the replacement velocity field. Application of wave-equation datuming to land data is difficult because of certain common characteristics of land data and because the LVL estimation procedure is considerably more difficult. The authors demonstrate wave-equation velocity replacement on land data from a western US overthrust belt. The LVL in this region was particularly thick and complicated and ideal for a wave-theoretical velocity-replacement procedure. Standard refraction analysis techniques were employed to estimate the LVL, then wave-equation datuming was used to perform the velocity replacement. Their derived LVL model was not perfect, so some imaging errors were expected because wave-equation datuming is highly dependent upon the LVL model. Nevertheless, their results show that wave-equation datuming generally allowed better shallow reflector imaging than could be achieved with conventional statics processing.
- OSTI ID:
- 37134
- Journal Information:
- Geophysics, Vol. 60, Issue 2; Other Information: PBD: Mar-Apr 1995
- Country of Publication:
- United States
- Language:
- English
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