This paper discusses examples of testing a new implementation of the method of multi-channel surface wave analysis on synthetic data computed for elastic media with complex boundary geometry. The new implementation of the method includes developed algorithms for noise-resistant spectral analysis based on time-frequency domain filtering of seismograms and inversion of dispersion curves of phase velocities based on determination of ranges of possible transverse wave velocity models and application of artificial neural networks. Based on the results of synthetic data processing, the accuracy, lateral resolution limitations and applicability limits of the method under consideration are evaluated.
During drilling, formation fluids are pushed aside by mud filtrate. As a result, the electrophysical properties of rocks near the borehole wall change. Sounding methods are used to determine the resistivity of the part of the reservoir that is remote from the well and unchanged during drilling. Among these methods, electromagnetic logging has the best spatial resolution. However, when analyzing the practical data of electromagnetic sounding, "wrong" ratios of signals from probes of different lengths are often observed, including those showing penetration in impermeable rocks. One of the reasons may be the influence of the shift of the device from the axis of symmetry of the medium. The paper considers the results of numerical simulation of signals from decentralized probes of LWD and VEMKZ instruments in some models.
Within the analyzed observation period (1971–2021), the values of the total magnitude of the scalar seismic moment obtained from the aftershocks of the strongest earthquakes (Мw ≥ 7.6) Asia (φ=20–50 N, λ=60–105° E), are weakly correlated with the total magnitude of the scalar seismic moment of background seismicity in the region of the main earthquake. A high level of seismic activity is manifested in the zones of large active faults and is reflected in the total magnitude of the scalar seismic moment of aftershock sequences. The types of movements in the foci of the main events do not affect the degree of aftershock activity (the total values of the scalar seismic moment) and occur at different background levels. Over the past 50 years, the magnitude of the strongest earthquakes has increased compared to the previous fifty-year period.
This research is aimed at finding out the capabilities of an electromagnetic probe with toroidal coils in geosteering problems. Three-dimensional numerical finite-difference modeling of electromagnetic responses was performed for a probe with toroidal coils, for high-frequency electromagnetic logging probe and side logging sondes in two-layer models with varying resistivity contrast and borehole zenith angle. Based on these calculations, the key features of the toroidal coil electromagnetic sounder (ZET), high-frequency electromagnetic logging (VIKIZ) and side logging (BKZ) signals in detecting the boundary before it is crossed are shown. These features make it possible to determine the approach to the roof of the collector using the signals ZET, VIKIZ and BKZ.
In vibroseismic data, nonlinear signal distortions called harmonics are usually present. The previously proposed method of separating the signal and its harmonics makes it possible to improve the quality of the initial data, as well as to obtain additional information about the geological structure of the earth interior. One of the limitations of the proposed methodology is its initial development for linear frequency-modulated signals. A new method of prediction of harmonics that allows non-linear frequency modulation as well as amplitude variation is proposed.
When vibroseis oscillations are excited, along with the main signal, harmonics are generated. They travel into the Earth and, like the main signal, interact with the target reflectors. Harmonics have a wider than that of the main signal frequency band, so they can be used to increase the resolution of the seismic data. To do this, the signal-related data should be separated from the harmonic-related data. This problem can be successfully solved by the previously proposed optimization recursive filtering algorithm, which, however, was developed only for linearly frequency-modulated signals. In this work, the algorithm is generalized to the case of amplitude modulation and nonlinear frequency modulation. Examples of application of the technique to increase the resolution of real vibroseis data are given.
