Summary The object of the research is a three-dimensional digital seismic-geological model of a real geological object and the corresponding field observations, both by the method of vertical seismic profiling and surface acquisition. The purpose of the work is as follows: 1. Construction of a digital structural model and its verification by comparing field observations and individual synthetic data sets; 2. Constructing a synthetic data set for a structural model for an areal excitation and registration system with a given overlap; 3. Construction of a model of a fractured medium based on the use of DFN and application of the concept of ideal seismic images. 4. Calculation of total wave fields for a fractured medium and analysis of the contribution made by the presence of fracturing.

Summary The current level of development of numerical methods and high-performance computer systems opens way to obtain detailed information about the structure of geological objects using 3D seis-mic study. A universally recognized necessary component that ensures the successful develop-ment of modern high-tech technologies for acquiring, processing and interpreting geophysical data is the complete digital models of geological objects - their digital counterparts. It is on this basis that a detailed assessment of the resolution and information content of the proposed meth-ods and their comparison with the already known processing and interpretation algorithms using the example of a specific geological object becomes possible. In this paper the main efforts are paid to the construction of a realistic three-dimensional seismo-geological model containing a family of faults, as well as clusters of cavities and fracture corri-dors. After constructing such an inhomogeneous multi-scale model, we perform finite-difference numerical simulation of the formation and propagation of three-dimensional seismic wave fields. The data obtained are processed using the original procedures for extracting scattered / diffracted waves with the subsequent construction of images of the corresponding small-scale objects, which generate these waves. We perform the detailed analysis of the results obtained.

Summary Common Middle Point seismic sections and their successive time migration provide extremely important knowledge about the internal structure of the 3D heterogeneous geological media and are key elements for successive geological interpretation. Full scale numerical simulation, that is one which starts with single shot seismograms, provides a deep understanding how the features of the image are linked with its subsurface prototype. Unfortunately, this kind of simulations for realistic geological media and 3D seismic surveys needs huge computer resources, especially for simulation of seismic waves’ propagation through multiscale media like cavernous fractured reservoirs. In order to significantly reduce the query of computer resources we propose to model these 3D seismic cubes directly rather than shot-by-shot simulation with subsequent CMP stacking. In order to do that the well known “exploding reflectors principle” is modified for 3D heterogeneous multiscale media. Its parallel implementation allows modeling of realistic 3D Common Middle Point stacks with reasonable computational costs. Numerical results for simulation of Common Middle Points sections and their time migration are presented and discussed.

В работе численно исследуется формирование сейсмического волнового поля в тонкой неоднородной ледяной пластине, лежащей на воде. Эта ситуация моделирует сейсмические наблюдения в транзитных зонах в зимний период. Исследуется влияние на волновое поле параметров среды, характера неоднородностей во льду, способов возбуждения волнового поля и т.д. Установлено, что основные характеристики волнового поля в однородной пластине, полученные в расчетах, хорошо согласуются с результатами, полученными в других работах асимптотическими методами. При наличии неоднородностей во льду, например, в виде шероховатости нижней границы льда и возбуждении волн на поверхности льда возникает интенсивная случайно-коррелированная помеха, объясняющая шум наблюдаемый при реальных наблюдениях. Объяснена природа этой помехи.

Abstract The interaction of seismic waves with cavernous/fractured reservoirs is analyzed on the base of finite-difference simulation with grids locally refined in time and space. The necessity to use such grids is caused by significantly differing scale of heterogeneities in the background (coarse grid) and reservoir (fine grid). Computations for each subdomain are carried out in parallel. The data exchange between each subdomain within a group is implemented using nonblocking iSend/iReceive MPIcommands in order to guarantee high scalability of the algorithm. The data exchange between the two groups is donecommands in order to guarantee high scalability of the algorithm. The data exchange between the two groups is done. Over the last decade the use of scattered waves won a significant place among the wide range of seismic techniques. But so far the main area of application of scattered waves is narrowed to spatial localization of micro heterogeneities clusters, likecracked and fractured areas, cavities and so on. In other words these waves are using just to say "yes" or "no" to the presence of a microstructure. At the same time more detailed knowledge about fine structure of hydrocarbon reservoirs, likeorientation of fracture corridors and fluid saturation of micro heterogeneities (especially cavities) is extremely important in the design phase of deep and horizontal wells. In order to be able to predict this microstructure one must possess a detailed knowledge of the particular features of interaction of seismic waves with cavernous fractured reservoirs, manifestation of fluid saturation especially. We have developed justified, verified and implemented for supercomputers with parallel architecture the reliable instrument for the studying complicated processes of waves' propagation in realistic 3D heterogeneous multiscale models of geological media – the special finite-difference method with local mesh refinement in time and space. On this base is possible to deal with realistic models and acquisitions and take into account both small scale heterogeneities of a reservoir and mesoscale variations in overburden. This software was applied for simulation of seismic waves' propagation through realistic digital model developed on the base of all available data for some East Siberian oil field. We have found that orientation of fracture corridors and fluid saturation of reservoir microstructure has very specific impact in synthetic images of scattered waves which can be used as predictive criteria in real life data processing and interpretation. These criteria are verified by comparison of predictions with well log data (fracture orientation) and permeability (fluid saturation) of a collector by test results.

In order to simulate interaction of seismic waves with cavernous/fractured reservoirs the finite-difference technique based on locally refined in time and space grids is used. The need to use these grids is due to essentially different scales of heterogeneities in the reference medium and in the reservoir. Parallel computations are organized on the base of 3D Domain Decomposition into elementary subdomains in the both reference medium (coarse grid) and reservoir (fine grid). Each elementary subdomain is assigned to its specific Processor Unit forming two groups – for reference medium and for reservoir. The data exchange between PU within the same group is performed in a standard manner – by nonblocking iSend/iReceive commands. The data exchange between two groups is done simultaneously with coupling of coarse and fine grids and is controlled by specially designated master PU. Results of numerical simulation for a realistic model of the carbonate reservoir are presented and discussed. On the base of numerical simulation an approach to recovery of orientation of fracture corridors is proposed and verified by comparison with direct observation of fractures within a well.

A preconditioned iterative method for solving frequency domain elastic wave equations is presented. Our method is based on Krylov type linear solvers. Its distinctive feature is the use of a right preconditioner, obtained as a solution of the damped elastic wave equations in a vertically heterogeneous medium. We represent the actual differential operator as a perturbation of the preconditioner. As a result, a matrix-by-vector multiplication of the preconditioned system is effectively evaluated via the fast Fourier transform in horizontal direction(s) followed by the solution of a number of systems of ordinary differential equations in the vertical direction. To solve these equations we introduce a piecewise constant 1D background medium and search for the exact solution in the 1D medium as a superposition of upgoing and downgoing P- and S- waves. The method has excellent dispersion properties because it does not use any finite-difference approximation of derivatives and converges reasonably fast.