articles

 

Forward and inverse wavefield extrapolation significantly broadens the capabilities of traditional approaches to seismic data processing. In complex seismic and geological conditions such problems as multiple prediction, correction for near-surface heterogeneities, velocity-depth model building, seismic migration, etc. require application of the wavefield extrapolation methods. The paper presents the theoretical background of the nonray wavefield extrapolation in layered media. It reveals its relation to the ray-based schemes and describes a devised method for true-amplitude modeling of waves in layered earth with account for reflection and transitions effects at curved boundaries.

Full-waveform inversion (FWI) provides better resolution for inverse problem solutions than ray-based methods. FWI also doesn’t principally require any picking or other manual data treatment. The solution of inverse dynamic problem is reduced to a local iterative minimization of a misfit functional, which evaluates the difference between modeled and observed data. Two most significant challenges in FWI are the requirement for low frequencies in the data and huge computational costs. The bottleneck of time-domain FWI is modeling, which needs to be repeated many times. Finite differences in space and time are most commonly used to perform modeling for FWI. We propose to use pseudo-spectral modeling instead of finite differences, because it allows us to reduce the number of parameters used for the description of seismic media by using sparser spatial grid. The resolution of the grid in low velocity domains of the model matches FWI resolution. To relax the requirements on the low frequency content in seismic records the authors suggest regularization based on the non-stationary filtering of the FWI gradients. Applied to the Marmousi velocity model, the method shows the benefits of pseudo-spectral full-waveform inversion.

For clustering the structure of fractured reservoirs, the authors suggest using a seismic attribute known as synergetic singularities (SS), which indicates seismic data singularities associated with faults, fractures and disintegrated zones. Specifically we use a map (cube) of SS fractal dimension and the derived attributes of SS density, amplitude and directions. Possible applications of the method for structuring fractured reservoirs and estimation of petroleum reserves in Eastern Siberia oil deposits are discussed.

The paper addresses multiscale experimental and theoretical studies of microstructure and elasticity of core samples at ambient and confining pressures. The static elastic moduli and strength parameters of core samples are estimated by means of triaxial compression tests simulating reservoir conditions, in which elasticwave velocities are measured at different directions while the loading-related processes are monitored from acoustic emission responses. The results are used to construct multiscale parametric models of effective elastic properties of reservoir rocks.

The pattern recognition method (cluster analysis) applied to high-resolution 3D seismic data inverted to acoustic impedance (AI) can distinguish zones of facies change in complex reservoirs. The method was tested on Jurassic reservoirs in northern West Siberia (especially, J₂² and J₃) and successfully resolved channel, transitional, and overbank facies deposited by meandering rivers.

Pitfalls due to poor accuracy of starting models used for reference in VSP data acquisition, processing, and interpretation are often neglected but may lead to large errors and inconsistent solutions. The orientations of fracture systems detected by walk-around VSP can be rigorously constrained by modelling on the basis of the effective medium approximation.

This article opens our new series of papers on the different capabilities of seismic layered model
parameterization. It is addressed to the structural instability of the inverse kinematic problem in a layered locally homogeneous isotropic model as well as to the capabilities and limits of this model’s extension through additional heterogeneities. The paper presents a method of heterogeneous layer reconstruction by means of inserting of additional horizon in order to provide the conformity to reflected waves arrival times and available a priori information on the depth position of a reflecting horizon.

The article describes the main competing technologies for obtaining seismic data in broadband marine surveys. These modifications of seismic exploration are currently holding about half of the world market, while on the Russian shelf they are almost never applied. The author analyzes the advantages and disadvantages of each of the methods. The conclusion is that the multisensory technology is advantageous if compared to the other solutions discussed.

Fine imaging of near-surface shelf has become of special importance in a few past decades. 3D highresolution seismic imaging systems operated at different frequency ranges have been developed since the early 1990s due to instrumental advance. The paper provides an overview of the existing marine 3D acquisition systems with examples of their actual use in engineering surveys and in different research projects.

Fold and its variations with depth (offset) depending on template are key acquisition geometry parameters. The fold-of-stack plots and scatter graphs used commonly for presentation and analysis of effective fold in survey design are either complicated or poorly informative. As an alternative, we suggest a new convenient way of imaging effective fold patterns as box-whisker plots which are easy to analyze and can provide detailed information. The applicability of the approach is demonstrated for various 3D geometries.

Vibrator baseplate and reaction mass signals can be useful not only for automatic regulation of seismic vibrator operation, but also for definition of the spectral characteristics of vibration conditions to receive information on vibrator–ground assembly rigidity and harmonic distortions. The result can be adaptation of sweep-signal to changing surface conditions while using cable-free acquisition systems. This also can be useful for separation of the nonlinear phenomena that are related to the medium rather than to the excitation system.

The paper considers the history of a physical modeling method, its reasonability as well as its advantages and disadvantages, and provides an overview of contemporary laboratories with references to the most interesting publications on the subject. It presents the characteristic of a Russian hardware-software complex for physical modeling, developed by the Seismo-Shelf Company, and gives examples of its application.

The history and prospects of high-resolution seismoacoustic surveys designed at the Institute of Applied Physics for engineering applications are considered with a focus on an unconventional approach based on the use of coherent signals. Advantages of coherent transmission are illustrated by examples of crosswell profiling in a layered ground with weakly pronounced layer boundaries, remote monitoring of soil saturation with moisture, and Rayleigh-wave surveys at a site of archaeological excavations.