zvi koren - Academia.edu (original) (raw)

Papers by zvi koren

5th International Congress of the Brazilian Geophysical Society, 1997

61st EAGE Conference and Exhibition, 1999

An interactive method for the refinement of interval velocities and interface depths is presented... more An interactive method for the refinement of interval velocities and interface depths is presented. The updating algorithm is based on the tomographic principle which relates perturbations in layer slowness and interface depths to traveltime changes along CRP rays.

56th EAEG Meeting, 1994

This paper describes a tomographic approach for determining subsurface models for depth migration... more This paper describes a tomographic approach for determining subsurface models for depth migration. The definition of a good depth model is currently a subject of debate. This study employed the objective of producing velocity-depth models which yield flat prestack depth migration panels. The algorithm operates directly on multi-offset common reflection point (CRP) gathers. The calculations start from an initial model and produce updates giving an improved model which yields flatter panels.

EAGE/SEG Workshop - Depth Imaging of Reservoir Attributes, 1998

The proposed reflector migration is a fast and accurate prestack depth migration designed for int... more The proposed reflector migration is a fast and accurate prestack depth migration designed for interval velocity and depth interface determination and for AVO analysis. The output of the migration consists of CRP gathers in windows centered at the reflecting horizons (CRP migrated panels) and the corresponding CRP ray paths for the given output offsets. Related approaches for 2D data were described in a patent by Johnson (1990), Landa and Sorin (1993) and Kosloffet et. al. (1995). This work is designed for 3D complex geological structures with a special treatment for obtaining true amplitude reflection events.

Geophysical Journal International

SUMMARYReflector-normal angles and reflector-curvature parameters are the principal geometric att... more SUMMARYReflector-normal angles and reflector-curvature parameters are the principal geometric attributes used in seismic interpretation for characterizing the orientations and shapes, respectively, of geological reflecting surfaces. Commonly, the input data set for their computation consists of fine 3-D grids of scalar fields representing either the seismic-driven reflectivities (e.g. amplitudes of 3-D seismic migrated volumes) or model-driven reflectivities, computed, for example, from the derived elastic impedance parameters. Conventionally, the computation of curvature parameters at each gridpoint is based on analysing the local change in the inline/crossline dips, considering the potential existence of a local quadratic reflecting surface in the vicinity of that point. This assumption breaks down for subsurface points in the vicinity of either complex reflecting surfaces (e.g. brittle/rough/tilted synclines/anticlines, ridges/troughs and saddles) and/or sharp, discontinuous geol...

Geophysical Prospecting, Sep 3, 2015

We suggest a new method to determine the piecewise‐continuous vertical distribution of instantane... more We suggest a new method to determine the piecewise‐continuous vertical distribution of instantaneous velocities within sediment layers, using different order time‐domain effective velocities on their top and bottom points. We demonstrate our method using a synthetic model that consists of different compacted sediment layers characterized by monotonously increasing velocity, combined with hard rock layers, such as salt or basalt, characterized by constant fast velocities, and low velocity layers, such as gas pockets. We first show that, by using only the root‐mean‐square velocities and the corresponding vertical travel times (computed from the original instantaneous velocity in depth) as input for a Dix‐type inversion, many different vertical distributions of the instantaneous velocities can be obtained (inverted). Some geological constraints, such as limiting the values of the inverted vertical velocity gradients, should be applied in order to obtain more geologically plausible velocity profiles. In order to limit the non‐uniqueness of the inverted velocities, additional information should be added. We have derived three different inversion solutions that yield the correct instantaneous velocity, avoiding any a priori geological constraints. The additional data at the interface points contain either the average velocities (or depths) or the fourth‐order average velocities, or both. Practically, average velocities can be obtained from nearby wells, whereas the fourth‐order average velocity can be estimated from the quartic moveout term during velocity analysis. Along with the three different types of input, we consider two types of vertical velocity models within each interval: distribution with a constant velocity gradient and an exponential asymptotically bounded velocity model, which is in particular important for modelling thick layers. It has been shown that, in the case of thin intervals, both models lead to similar results. The method allows us to establish the instantaneous velocities at the top and bottom interfaces, where the velocity profile inside the intervals is given by either the linear or the exponential asymptotically bounded velocity models. Since the velocity parameters of each interval are independently inverted, discontinuities of the instantaneous velocity at the interfaces occur naturally. The improved accuracy of the inverted instantaneous velocities is particularly important for accurate time‐to‐depth conversion.

Geophysical Prospecting, Nov 6, 2015

Proceedings, Jun 12, 2017

Summary Considering all types of pure-mode and converted waves, we derive the azimuthally-depende... more Summary Considering all types of pure-mode and converted waves, we derive the azimuthally-dependent normal moveout (NMO) series coefficients of near normal-incidence reflection waves in general anisotropic (triclinic) horizontally layered media, for a leading error term of order six. The NMO series can be either a function of the invariant horizontal-slowness (slowness domain) or the surface-offset (offset domain). The NMO series coefficients of different orders, also referred to as effective parameters, are associated with the corresponding azimuthally-dependent NMO velocity functions. We distinguish between local (single-layer) and global (overburden multilayer) effective parameters, where the local and global effective parameters are related by forward and inverse Dix-type transforms. We first consider the case in which the reciprocity assertion for incidence and reflected waves holds, i.e. pure-mode waves for general anisotropic horizontally-layered media, and converted waves for anisotropic horizontally-layered models sharing a common horizontal symmetry plane. Considering reciprocity, the odd-power coefficients of the NMO series cancel, and the remaining coefficients are zero-offset time, three second-order and five fourth-order effective parameters. Next we consider converted waves in general anisotropic media, where reciprocity no longer holds. Twelve additional parameters are required: two firstorder, four third-order and six fifth-order effective parameters.

Proceedings, Jun 12, 2017

Summary Considering reciprocity where the traveltime is an even function of the offset or horizon... more Summary Considering reciprocity where the traveltime is an even function of the offset or horizontal-slowness, the fourth-order normal moveout (NMO) series are governed by the normal-incidence time and eight effective parameters: three second-order and five fourth-order. Local effective parameters are related to the individual layers, while the global effective parameters are related to the overburden multi-layer model. Local and global parameters are related by forward and inverse Dix-type transforms. The NMO formulae are different in the slowness and offset domains, but the eight parameters are the same in both cases. We suggest a new set of intuitive normalized effective parameters, classified into two “azimuthally isotropic” and six “azimuthally anisotropic” parameters. We provide feasible ranges for the normalized parameters, thus allowing their used for controlled inversion.

Proceedings, Jun 11, 2018

Proceedings, 2014

In this work we study the hyperbolic moveout approximations for shear and converted waves in a la... more In this work we study the hyperbolic moveout approximations for shear and converted waves in a layered orthorhombic medium with flat interfaces in the horizontal plane of symmetry, distinguishing two types of conversion - PS1 and PS2, with different shear polarizations. Note that the azimuthally dependent NMO velocity function for shear or converted waves is similar to that of compression waves - only the coefficients are different. Given a package of orthorhombic layers with different parameters, one can establish an equivalent effective model consisting of a single layer with the same vertical time as the original package, described by the fast and slow effective NMO velocities, the effective azimuth of the slow velocity, and the vertical compression velocity. The latter is normally obtained from non-seismic information such as check-shot or well logs. Note that the effective azimuths are different for models describing PP, PS1 and PS2 waves.