Bergler, Steffen

On the determination and use of kinematic wavefield attributes for 3D seismic Imaging : Bestimmung und Anwendung kinematischer Wellenfeldattribute bei 3D seismischen Abbildungsverfahren

In the last two decades a lot of effort has been directed towardsmethods that have the potential to succeed in imaging complex 3Dsubsurface structures from multi-coverage seismic data. The necessityof an estimate for the wave propagation velocities, required fortransforming the data from the time domain to the depth domain, posesone of the fundamental problems in seismic imaging. Inadequatevelocity models distort the final depth image. So-called data-orientedapproaches are a class of imaging methods that avoid the explicitparameterisation of a velocity model in the first imaging steps.Instead, the data-oriented approaches parameterise the reflectionevents in the time domain and try to obtain as much information aspossible from the measured data. The extracted information is thenused to transform the seismic data into depth.The common-reflection-surface (CRS) stack is one of the data-orientedimaging approaches. This method makes use of second-order traveltimeapproximations in order to describe seismic reflection events in thetime domain. For the processing of data from a 3D acquisition, thetraveltime equations can be used as stacking operators to simulate azero-offset (ZO) volume of high accuracy and high signal-to-noiseratio from multi-coverage prestack data. During the stack, reflectionenergy from the entire five-dimensional data hyper-volume enters intothe construction of one ZO sample. The eight parameters, which expressthe traveltime approximation for the ZO case, relate to kinematicwavefield attributes. These locally describe the propagationdirections and curvatures of specific wavefronts at the Earth'ssurface which have travelled through the subsurface. Thus, thekinematic wavefield attributes constitute integral quantities of themedium's parameters and are suitable to estimate the properties of theEarth's interior. The accurate determination of the wavefieldattributes is, therefore, a crucial step in the CRS processing.In this thesis the derivation of the traveltime approximations ispresented. The kinematic wavefield attributes are introduced by meansof concepts known from geometrical optics. The determination of theeight kinematic wavefield attributes for the ZO case from 3Dmulti-coverage seismic data is elaborated. The applications of theattributes to support and facilitate 3D seismic imaging are discussed.In this context emphasis is put on the utilisation of the kinematicwavefield attributes for the 3D CRS stack. The proposed searchalgorithms are validated on a synthetic data example and have shown tobe successful. Finally, the 3D CRS stack is applied to a real marinedataset. In this way the functionality of the search algorithms oncomplex data is verified. Moreover, the imaging quality of the 3D CRSstack is checked by migrating the simulated ZO volume to depth andcomparing the obtained result with the result from a prestack depthmigration. The comparison shows that the CRS based result iscompetitive to the result of the prestack depth migration. Thus, CRSbased imaging is an alternative to prestack depth migration due to thegood imaging quality and also due to the provided information in formof the kinematic wavefield attributes.