Estimation of geological dip and reflector curvature from zero-offset seismic reflections in heterogeneous anisotropic media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Depth conversion of selected seismic reflections is a valuable procedure to position key reflectors in depth in a process of constructing or refining a depth-velocity model. The most widespread example of such procedure is the so-called map migration, in which normal-incidence, zero-offset (stacked) seismic data are employed. Since the late seventies and early eighties, under the assumption of an isotropic velocity model, map migration algorithms have been devised to convert traveltime and its first and second derivatives into reflector position, dip and curvatures in depth. In this work we revisit map migration to improve the existing algorithms in the following accounts: (a) We allow for fully anisotropic media; (b) In contrast to simple planar measurement surface, arbitrary topography is allowed, thus enlarging the algorithms applicability and (c) Derivations and results are much simplified upon the use of the methodology of surface-to-surface paraxial matrices.562521531VISTAResearch Council of Norway via the ROSEResearch Council of Norway via NORSAR's SIP [194064/I30]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Wave Inversion Technology (WIT) Consortium, GermanyConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Research Council of Norway via NORSAR's SIP [194064/I30

Estimation of geological dip and curvature from time-migrated zero-offset reflections in heterogeneous anisotropic media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Starting from a given time-migrated zero-offset data volume and time-migration velocity, recent literature has shown that it is possible to simultaneously trace image rays in depth and reconstruct the depth-velocity model along them. This, in turn, allows image-ray migration, namely to map time-migrated reflections into depth by tracing the image ray until half of the reflection time is consumed. As known since the 1980s, image-ray migration can be made more complete if, besides reflection time, also estimates of its first and second derivatives with respect to the time-migration datum coordinates are available. Such information provides, in addition to the location and dip of the reflectors in depth, also an estimation of their curvature. The expressions explicitly relate geological dip and curvature to first and second derivatives of reflection time with respect to time-migration datum coordinates. Such quantitative relationships can provide useful constraints for improved construction of reflectors at depth in the presence of uncertainty. Furthermore, the results of image-ray migration can be used to verify and improve time-migration algorithms and can therefore be considered complementary to those of normal-ray migration. So far, image-ray migration algorithms have been restricted to layered models with isotropic smooth velocities within the layers. Using the methodology of surface-to-surface paraxial matrices, we obtain a natural extension to smooth or layered anisotropic media.602201216VISTAResearch Council of Norway via the ROSENORSAR's SIP [194064/I30]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Wave Inversion Technology (WIT) Consortium, GermanyGeo-Mathematical Imaging Group, USAConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)NORSAR's SIP [194064/I30

Kinematic time migration and demigration of reflections in pre-stack seismic data

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In kinematic time migration one maps the time, slope and curvature characteristics of seismic reflection events, referred to as reflection-time parameters, from the recording domain of the seismic data to the time-migration domain. The inverse process is kinematic time demigration. We generalize kinematic time migration and demigration in several respects: the reflection-time parameters may belong to arbitrary sourcereceiver offsets; local heterogeneity of the time-migration velocity model is accounted for; the mapping operations do not depend specifically on the type of diffraction-time function and the parametrization of the velocity model. Time-migration and time-demigration spreading matrices are obtained as byproducts of the mapping operations. These matrices yield a paraxial expression for the connection between midpoint and image-point gather locations of mapped reflection events. Also, we obtain the time-migration counterpart of the so-called second duality theorem in Kirchhoff depth migration. Diffractions and reflections are assumed to be without conversion, and sources and receivers are located along the same measurement surface. Our framework enables the identification of a full set of first- and second-order reflection-time parameters from time-migrated seismic data followed by a kinematic demigration to the recording domain. The idea of this route is to undo eventual errors introduced by time migration and result in reliable estimation of recording-domain invariants, that is, parameters insensitive to the time-migration velocity model. The developed concepts associated with time migration are of interest in reflection seismic and global earth applications. Two numerical examples demonstrate the potential of kinematic time migration and demigration techniques in seismic time imaging and velocity-model building.189316351666Research Council of Norway [194064/I30]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Wave Inversion Technology (WIT) Consortium, GermanyGeo-Mathematical Imaging Group, USAConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Research Council of Norway [194064/I30