Yurii Kiselev

Multiple migration of VSP data for velocity analysis

Summary We investigate the new method that combines the migration of VSP data and updating of the velocity model. The method is based on the comparison of subsurface images obtained by using different types of waves: the primary reflections and surface-related multiples. As a measure of similarity of the images we use the functional based on cross-correlation. Estimation of the velocity model parameters is carried out by maximization of this functional. Therefore the resulting velocity model provides the maximal similarity between images obtained by using the primary reflections and surface-related multiples. We develop an iterative procedure to maximize the functional and demonstrate the efficiency of the method using the synthetic walk-away data. The method can be used for very short VSP receiver arrays and allows us to estimate the interval velocities below receivers, which is considered to be a challenge with VSP acquisition geometry.

Velocity analysis for VSP data using multiples

Summary The quality of the subsurface images obtained using VSP data strongly depends on the velocity model used for migration. The velocity model derived from surface seismic is often not accurate enough for VSP imaging and there is a need for its improvement. We propose the method for updating of velocities using VSP data. The main idea is to use the images of the subsurface obtained using different types of waves: primary reflections and surface-related multiples. If the background velocity is correct, then these images will be similar, and they will not coincide, if the velocity model is erroneous. We develop the algorithm of velocity updating based on this criterion. The proposed method allows us to retrieve the velocity below the borehole receivers. This is complementary to first break VSP travel time tomography, which helps to retrieve velocity only above the receivers.

Scattering objects location with cross-well data

Summary Most of conventional imaging techniques are designed to locate the reflecting interfaces in the subsurface. But the scattering objects (diffractors), such as faults or salt inclusions, are also of interest for exploration. Locating these objects may be useful for seismic data interpretation, production monitoring and reservoir characterization. In this paper we propose the technique of diffractor location using the cross-well data. We use Kirchhoff migration with special weights for the diffractor imaging. We demonstrate that the diffractors, invisible with more conventional processing, have been imaged with the proposed technique.

Numerical simulation in diffraction tomography with elastic and electromagnetic sounding signals

The results of numerical simulation on restoration of parameters of local in-homogeneities are considered. Studying of restoration of elastic inhomogeneities and inhomogeneities of electrical conductivity is implemented using elastic and electromagnetic wave fields correspondingly. The direct problem for the Lame and Maxwell equations is solved by the finite difference method. Restoration of parameters is implemented by the diffraction tomography method in the time domain with the help of the first-order Born approximation. In electromagnetic case we study restoration of local inhomogeneity of electrical conductivity using the sounding by diffusion electromagnetic field.