Abstract:Reflection signals and high velocity noise change in amplitude and waveform with increasing offset between source and receiver.The reflection coefficient changes with incident angle;the reflectivity of a thin reflecting bed or a thick transition zone changes with incident angle;the effects of transmission and wave type conversion change with incident angle;and the geometric divergence effects for a point source change with offset.These complications of the reflection seismogram are well known,but are normally neglected in our standard models used for system design.The striking effects at very wide angle are muted out in processing.An invariant waveform with hyperbolic moveout is implicitly assumed for the unmated data.Trace balance and automatic gain control are often applied before CDP stack to partially compensate for offset dependent effects. It is the purpose of this paper to demonstrate the importance of these offset dependent effects,and to illustrate methods of analyzing them.Displays of ray parameter versus intercept time(p-τ),and reflection transmission,and conversion coefficients versus ray parameter,aid in the identification of what's important for a specified layered model.p-τplots are constructed as the cumulative sum of simply interpretable ellipses,The slope and intercept in p-τ show where an event will appear in x-t.Curvature in p-τ is simply related to geometric divergence in x-t,since the ray parameter is fixed for any ray path,significant ray parameters and interface combinations for the generation of multiples and converted shear waves can be identified,Synthetic seismograms for each significant class of events may be constructed to aid in analysis and interpretation.The analysis of bigh velocity noise in a layered model with large velocity contrasts,and the analysis of signal in a Tertiary clastic model with low velocity contrasts,illustrate the importance of offset dependent effects.
引用本文:
Milo M. Backus, Franciseo Nepomuceno, 曹景忠. 固体层状介质中的反射地震记录[J]. 石油地球物理勘探, 1983, 18(5): 406-410,442.
Milo M. Backus, Franciseo Nepomuceno. The reflection seismogram in a solid layered earth. OGP, 1983, 18(5): 406-410,442.