articles

 

Quantitative assessment method of geo-technological success and risks by factor analysis is proposed for the oil and gas seismic exploration. The seismic and drilling results on 579 oil and gas exploration projects for the distributed subsoil fund of three regions of the Russian Federation were processed with the approach. It is shown that, in spite of the virtually reached double overstating of the existing resources, the expected growth of hydrocarbon reserves in Russia until 2021 (in the assumption of realization of all prepared-to-drilling exploration projects) may amount 109 % to actually achieved reserves upside in 1992–2011.

Original technology of data filtration and interpolation on the base of optimized statistic sliding window filtration is presented in the paper. Window form, size and positioning are determined with use of complex criteria, including the root mean square deviation minimization. Mapping details depend on the chosen set of statistical filters (variations of window size). This technology is shown to be effective to solve classic interpretational problems.

The method of AVOA-analysis is based on Ruger approximation equation for the P-wave reflection coefficient at the interface of the isotropic and anisotropic (HTI) half-spaces. In this paper we analyze the conditions allowing to use Ruger approximation. For this purpose the exact PP-plane-wave reflection coefficients and their linearized approximations were calculated for both theoretical models and for Siberian medium models. It is shown that the approximation formulas are suitable for AVOA-inversion (with the definition of all model parameters) only in case of weak anisotropy with elastic parameters contrast at the interface of ≤ 15 % (positive contrast) and ≤ 10 % (negative contrast). At the same time, the azimuth of the symmetry axis is determined with sufficient accuracy for all models if signal to noise ratio ≥ 10.

The numerical modelling of full wavefield was performed to synthesize the multi-offset vertical profiling data and the data of OPV (Common Source Point Technique) for multilayered elastic media with the high-velocity layer. The wave field structure and properties of the transmitted and reflected seismic fields depending on the epicentral distances and the thickness of high-velocity layer were studied. Joint interpretation of data from synthetic seismograms and wavelet analysis has revealed that structure of wavefields and their features are strongly dependent on thickness of layer and on the epicentral distances. In agreement with theoretical studies by Yu.A. Voronin the screening effect appears weakly in dynamics and kinematics of transmitted and reflected waves for the small thickness of high-velocity layer. An important feature of wave fields in the case of relatively thick high-velocity layers is the formation of the intensive converted PS-waves when the angle of incidence of longitudinal wave is greater than the critical angle. PS-wavefield can propagate within a layer over long distances in the form of interfering wave packets and convert into PSP- and PSS- waves at the boundaries. The frequency of converted passing shear waves is approximately two times lower than the frequency of longitudinal waves. The results of numerical simulation are generally consistent with the results of previous studies made on the basis of the interpretation of the experimental NVSP data.

The article presents numerical modeling of elastic wave propagation in 3D model of layered geological medium. The model was created based on the geological data specified for Archangelsk region. The modeling was performed using the grid characteristic method. The results of two different approaches application were compared: explicit boundary correction and shock-capturing method. The quality wave patterns match, the coincidence of the kinematic characteristics of the signal (time arrival of response) and the significant difference in the dynamic characteristics of the signal (amplitude of response) were obtained.

The elastic properties of the fluid-saturated isotropic-fractured rock are discussed with consideration of propagation of the slow and dispersive Krauklis wave within individual fractures. The presence of the Krauklis wave in fractures tends to increase P-wave velocity dispersion and attenuation. The results of calculations exhibit a significant difference of the reflectivity of the fractured layer in comparison with a layer without fractures.

In the paper Faust’s equation for the acoustic velocities prognosis from the log data was verified with typical logging data from East and West Siberia. It was shown that the application of the equation is acceptable only for limited part of the West Siberian sedimentary cross section. As an alternative decision of velocity estimation multivariate linear regression method was used. The later approach provided us with satisfactory solutions of acoustic logging curve recovery forthe considered sections.

The paper deals with possible anisotropy caused by surface topography. The possible reason of S wave’s splitting is anisotropy of the upper part of the seismic section. Nevertheless, mentioned phenomenon can be caused by other reasons. The calculation of stress-strain state and second invariant of the strain tensor deviator can be used for clarifying of the topography induced anisotropy. For the strain calculation boundary element method was used. In the paper we treated object with maximal effective tangential strain more than 10¯⁴ as a crack.

The results of the analysis of changes in dynamic characteristics of wavelets in marine seismic investigation with high resolution are presented. The analysis was provided on the basis of data from the offshore area of White Sea. This study was conducted with use of the direct, propagating in the water seismic wave wavelet. The variation of the energies, amplitudes and spectral components of the signals were investigated. Often, these variations seem to be insignificant and are not considered in seismic data processing and interpretation. On the other hand the results of our study demonstrate the importance of such variations, indicating a high relevance of methods accounting for the changes in dynamic parameters of real signals development. The particular importance of these methods is in improving the of the dynamic analysis efficiency and of inverse dynamic problems solution in seismic.

The article presents an example of acquisition system parameters selection for seismic and geological conditions of Western Siberia. The ray tracing technology allowed to determine optimal seismic survey parameters in order to address the particular geophysical objectives. Optimal parameters of acquisition system enhance the value of the recorded seismic data due to the conformity to the requirements of modern processing and interpretation technologies.

The chemical (petrophysical in application to earth crust) heterogeneity coefficient (η) after Bullen and Magnitsky aimed to diversify effects of rock fracturing and mineral association changes with depth is used in the paper. The rock samples under hydrostatic compression up to 1500 MPa were explored for testing of this method. We found that for different rock mineral associations the values of η are also different but generally decrease with pressure increase, approaching to 1 (at 500 MPa) and correlate with fractures closure. A similar stabilization of η changes at depth of 15–20 km was obtained by interpretation of seismic and density data. Detected deviations from the average trend of fractures show extended local anomaly of material composition changes which is traced up to a depth of 20 km. They are correlated with faults according to geological data.

Temporal variations of the seismic waves velocities ratio and b-value beneath Klyuchevskaya volcano group are compared. The interpretation of the observed correlation is shown, the mechanism of changes in the medium state during the volcanic group activation is proposed. Frequency-magnitude relation is studied using GIS-EEDB program.