Research And Application Of Common Reflection Surface Stack And Its Parameters In Areas With Complex Structures

With the increasing complexity of the reservoir, it is increasingly difficult for the seismicexploration and we should continually improve and enhance the techniques to satisfy therequirement of oil/gas exploration and development. The stack imaging is one importanttechnique in the seismic data processing, however, it is difficult to obtain the satisfying resultsin areas with complexity using the classical stacking methods and it becomes one of thefactors which restrict the level of seismic data processing.Some geophysicists have developed the multi-parameters stacking methods which areindependent of macro velocity models since the late1980s and the typical technique isCommon Reflection Surface (CRS) Stacking method. The CRS stacking operator accounts forthe local geological characteristics of the subsurface reflector and all the information of thereflection points on the surface near the target point is corrected and stacked in the process ofstacking, which significantly improves the quality of seismic data. Since the CRS operatorcontains multi stacking parameters, the multilevel optimization strategy is applied to improveefficiency during the practical stacking. However the situation of intersecting events in thestacked section, which implies several events might contribute to one and the same ZOlocation, can not be addressed with the classical parameter searching algorithm. This paperestablishes the extended parameter searching strategy and introduces the coherence thresholdto obtain the global and local maximum for the target imaging point, which effectivelyresolves the situation of several events intersecting in the same ZO location. The kinematicwavefield attributes reflecting the subsurface information can be obtained by the CRS stackand can be used for the further application. The projected first Fresnel zone in the time domain corresponding to the reflector segment in the depth domain can be obtained using thestacking parameters, which can be used as the optimized stacking aperture to improve theamplitude and lateral resolution of stacking sections. This paper also establishes the thresholdequation in terms of wavefield attributes to effectively separate the reflection and diffractionevents, which can be used in the subsequent processing procedure such as velocity modelbuilding and migration based on diffractions.The Common-Offset Common-Reflection-Surface (CO CRS) Stack can be viewed as thegeneralization of the ZO CRS stack and effective range of the stacking operator is larger,which can fully utilize the far-offset information to obtain the stacked section of thesubsurface in complicated geological condition. Since arbitrary finite-offset rays can beviewed as the central rays, CO CRS stack can handle converted reflections. The2D CO CRSstacking operator involves five stacking parameters and this paper establishes the splitstrategy for searching parameters, which reduces the calculation time of CO CRS stack. Forthe seismic data of low quality, this paper proposes the partial CO CRS stacking method andestablishes the algorithms and procedures for implementation. After the seismic gathers beingprocessed by the partial CRS stack, the reflection events are much easier to be identified andtraced and the quality of imaging sections is improved. The model test and practical dataprocessing results show the evident effects.The quality of the multi-parameter stacking results heavily relies on the accuracy of thetraveltime moveout description. Hyperbolic CRS stacking operator reduces to the NMOhyperbola in the CMP gather, which does not consider the curvature of the reflector. TheNMO hyperbolic moveout is only exact for the case of a planar dipping reflector beneath ahomogeneous overburden. The most intuitive generalization of the planar dipping reflector isthat of a circular reflector beneath a constant velocity overburden and any reflection point onthe circle can be determined by the reflection angle. This paper derives the implicit traveltimeformula in terms of reflection angle, which is recursive stacking operator (RSO). To allow formaking use of the existing CRS stacking procedures, two different parameterizations for RSObased on the kinematic wavefield attributes are introduced. Test results show that RSOprovides superior accurate for all the considered curvatures, not only nearly planer reflector but also diffractor and the model tests show the good results.