Research And Application Of The Partial Common Refection Surface Stack Method

With seismic exploration is turning to apply in area with more complex geologicalconformation,it is not easy any more to get satisfying image result by conventional processingmethod. So many new image technologies in time domain and pre-stack migration methodscome out, one of which is CRS (common reflection surface) stack. The original mind of CRSstack is by Hubral in1983. The main advantage of the CRS stack is the utility of analyticalformulae that describe the kinematic reflection response of inhomogeneous media with curvedinterfaces based on the theory of paraxial ray. It is dependent on the near surface velocity andforeign to the macroscopic velocity model. It considers the local feature of reflector and thewhole reflect of the first Fresnel zone, hence it utilizes all the information of multiplecoverage reflect data effectively.However,the CRS stack improves only the quality of the stacked sections, this thesispresent the new partial CRS stack method, which allows to improve the quality of prestackseismic reflection data. The method is based on the multiparameter CRS traveltime formula,and uses the results of the automatic CRS stack. The partial CRS stack uses the informationabout local dip and curvature of each reflector element, and sums up the amplitudes of alltraces contributing to that element. The true reflector is locally approximated by the reflectionsurface. Depending on the chosen size of the surface, the number of traces used during thepartial stacking may vary. Due to the constructive summation of coherent events, the partialCRS stack enhances the signal and attenuates random noise. Moreover, missing traces can begenerated and the acquisition can be regularised, if the approximating surface contains usefulevents from neighbouring traces. The latter can be considered as an improved interpolationtechnique using a simple and robust summation algorithm. This also allows generating regulartraces with equidistant intervals, which may be helpful for further processing of the data, e.g.,by wavefield methods. Partially-stacked CRS supergathers are superior to conventional CMPgathers in areas of complex geological behaviour. They are regularised and have a higher S/Nratio compared to the original seismograms. Reflections in CRS supergathers appear clearerand continuous, which is preferable for the velocity analysis and quality control of depth migration.