articles

 

The new computational model for the seismic wave propagation is proposed, the governing equations of which are written in terms of velocities, stress tensor and small rotation of element of the medium. The properties of wavefields in the prestressed medium are studied and some examples showing anisotropy of prestressed state are discussed. The staggered grid numerical method is developed for solving the governing equations of the model and numerical examples are presented.

A model of defect formation and propagation is developed. It is assumed that the defect is a fracture with a nonzero thickness. The axiomatics of mechanics of deformable solid is used for model construction. A concept of a prefracture zone is introduced. The prefracture zone is considered as a part of a solid where the material properties are changed by external forces. The theory of repeated superposition of large deformations and some strength conditions are used. An example of finite element modelling of fracture growth is discussed.

We propose a method for imaging small scale diffraction objects. It is based on separation between specular reflection and diffraction components of the total wavefield in the migrated domain. Reverse-time migration was utilized to produce surface dip-angle common image gathers. We used continuity of diffractions in the dip-angle CIGs as a criterion for separating reflections from diffractions. Synthetic and data examples illustrate efficient application of the method.

We have investigated a local optimization procedure for seismic imaging by full waveform inversion of surface waves. These waves are highly energetic when considering near-surface imaging and present dispersive effects as well as significant forward scattering. These propagation behaviours have led us to consider alternative data domains where the data fitting should be performed. The frequency-slowness domain as well as the frequency-wavenumber domain have been considered. We have shown how to build the gradient of the misfit function in these two domains based on the adjoint approach. The adjoint source term has been estimated with a systematic procedure based on Lagrangian multiplicators, making the cost of the procedure identical to the one formulated in the standard time-offset domain. A simple 2D synthetic example shows that the reconstruction of the shear velocity is possible, although real applications could require a more extensive investigation including windowing and filtering, as a hierarchical strategy appears to be necessary when considering surface waves with high variations in amplitude. A linearised approach is therefore possible and quite efficient. This avoids the picking of dispersion curves and attempts to fill in the velocity spectrum, extending our search domain to models with lateral velocity variations as done previously using global model search.

This paper presents an original approach to numerical simulation of seismic wave propagation in models with complex near surface part and free-surface topography. The idea of the presented algorithm is to combine discontinuous Galerkin method with the finite differences. We suggest using highly accurate but computationally intense discontinuous Galerkin method in the upper part of the model, whereas efficient and computationally cheap finite difference method in applied in the major part of the model. As the result the hybrid approach combines the accuracy of Galerkin approach with the efficiency of the finite differences.

The article presents a true amplitude imaging procedure for anisotropic media. The basis of the algorithm are Gaussian beams and ray method. Here is considered the possibility to determine the elastic parameters on the basis of the obtained images depending on the angle of incidence. Based on the analysis of singular value decomposition is proposed robust optimal AVA (Amplitude Variation with Angle)-inversion with respect to impedances.

Seismic signals reflected from the subsurface horizons and recorded at the receiver points contain information on the orientation of the vectors of wave motion. The methods of selection of seismic waves by the vector of particle motion allow for identification of the waves with vectors insignificantly different (by several degrees) in a rectangular coordinate system. The results of such selection could be represented in the form of multichannel (raster) signal recording. And each line of the raster image would correspond to recording of waves with certain angular orientation of the projections of their vectors on radial or horizontal plane. Such recording would allow for analysis of fine structure of recorded signals and obtain unique wavefield characteristics at the receiver points within the seismic acquisition area.

A model of filtration of compressible fluid mixture with an arbitrary number of phases through the deformable porous medium is developed on the basis of the method of thermodynamically compatible conservation laws. Governing equations are hyperbolic and have divergent forms in the reversible approximation. Numerical analysis was performed by using an algorithm based on the WENO–Runge–Kutta method of high- order accuracy. The model is designed to solve the challenges arising from the multiscale fluid dynamic processes.

The study provides a methodological framework, the results of the interpretation of well log and seismic data for the Talakan field and prediction of the Osa reservoir properties and architecture from neural network analysis.

Due to the growing volume of site-surveys, it is important to improve the quality and reliability of acquired information about the structure of sub-bottom sediments. Relatively rare spatial network of single- and multichannel high resolution seismic surveys does not allow suitable mapping of the most potentially dangerous geological hazards, thereby increasing risks associated with construction and operation of engineering structures. The article describes processing and interpretation of high-resolution marine seismic data results, acquired by the P-Cable 3D system in the Norwegian Sea. According to necessity to achieve the high spatial resolution and preserve true amplitude information for dynamic interpretation, the original approach to the data processing was applied.