A transient electromagnetic signal is recorded in an earth formation while drilling at multiple times. Data for subsequent interpretation is transmitted via a hydrochannel with a narrow bandwidth, for that reason the amount of transmitted information is limited. Therefore, data compression is an indispensable element of processing. It is important to determine what parameters and how many of them are necessary to describe the measured EMF curve. The idea is to transfer to the surface only significant parameters allowing to restore the recorded curve with a given accuracy. The paper proposes simple and fast data compression methods based on the spline approximation of the signal. Also, an orthogonal basis in the measurement space is used to describe each signal by a linear combination of vectors from this basis. We analyze transient curves and consider various magnetic field components. Numerical experiments show how many parameters are required to describe and reconstruct the signal of a deep-reading electromagnetic tool.

A low resistivity annulus appearing near the well due to reservoir fluid displacement by mud filtrate is a reliable indicator of movable oil presence in the reservoir. In practical cases estimation of low resistivity annulus parameters is possible based on high-frequency induction logging data analysis. When interpreting practical data of other resistivity logging methods its influence on signals is usually not taken into account. The paper discusses the results of the 5IK and VIKIZ logs numerical simulation which substantiate the possibility of identifying low resistivity annulus according to multi-probe low-frequency induction logging in geoelectric conditions typical for the Cretaceous mixed-saturation reservoirs of the Imilorskoye oilfield.

Properties of the ground force signal complicated by harmonics are studied. It is shown that the adaptation filters, that enable matching the amplitude- and phase- frequency characteristics of harmonics in the corresponding frequency range, have a simple form. The problem of focusing a signal containing harmonics using correlation and deconvolution is discussed. An example of using harmonics to expand the signal spectrum is given.

An algorithm for separating a vibroseis signal from its harmonics implies preliminary prediction of harmonics with their subsequent adaptive subtraction from the correlogram. To obtain the adaptation filter estimates, a statistical criterion is used that minimizes the energy of the subtraction result. The amplitudes of the signals in a seismic trace decay due to geometrical spreading, which leads to statistical inhomogeneity in the objective formed. Therefore, an increase in the statistical reliability of estimation should be associated with an increase in signal amplitudes at large recording times. On the other hand, the source records always contain additive noise, and the signal-to-noise ratio decreases at longer times. In order to provide a compromise between the growth of signal amplitudes and maintaining a satisfactory signal-to-noise ratio in the operator adjusting gate, self-tuning weighting functions are included into the objective. A method for modifying the objective is proposed, which enables increased performance of the algorithm.

Refinement of the geodynamic situation in the area of the Lena River delta is relevant for understanding local geological processes. Previously, source seismology for this area was provided only by remote regional seismic stations. This paper shows the results of processing data from detailed seismological observations for 2018–2021. The distribution of earthquake hypocenters and their focal mechanisms are presented. The results of processing largely confirm the a priori geological data and do not contradict the results of regional observations. The accumulation of earthquakes in the area of the Kharaulakh Range most likely refers to the Primorsky Fault, which extends along the coast of the Bykovskaya channel. According to geological studies, the Primorsky Fault is a fault, which is confirmed by the focal mechanisms of earthquake sources in this area.

The database of relaxation characteristics of core samples from the parametric well was created. It includes their main petrophysical parameters, the NMR signal and the results of its processing and interpretation. A comparative analysis of the obtained data with the results of lithological and stratigraphic analysis was carried out. Using the example of a parametric well, it is shown that NMR data can be used to quickly obtain information on the distribution of reservoir properties of core samples both along the section as a whole and separately for each suite.

The article describes a new approach to seismic modeling that combines calculations using traditional finite difference methods with the deep learning tools. Seismograms for the training data set are calculated using a finite difference scheme with high-quality spatial and temporal discretization. A numerical dispersion mitigation neural network is trained on the training dataset and applied to inaccurate seismograms calculated on a raw grid with a large spatial spacing. The paper presents a demonstration of this approach for 2D model; it is showing a tenfold acceleration of seismic modeling.

The results of a complex interpretation of seismic and gravity data along a part (500 km long) of the 3DV profile located in the transition zone from the Siberian Platform to the Verkhoyano-Kolyma fold system are considered. It crosses the Priverkhoyansk advanced trough, the Sette-Daban tectonic zone with access to the folded region [Tectonics…, 2001; Kashubin et al., 2016]. The structure of the crust of the eastern margin of the Siberian craton is interest, which, according to structural and tectonic criteria, belongs to the Mesozoic passive continental margin [Parfenov, 1991; Sokolov, 1991; Tectonics..., 2001] in order to find signs of superimposed folding in the structure of the Earth's crust according to seismic and gravitational data. The depth of the crystalline basement in the Priverkhoyansk trough is also debatable, depending on the nature of the rocks at a depth of 18–23 km at a velocity of 6.2–6.3 km/s, possibly belonging to the Proterozoic.

The practice of two-dimensional inversion of electrolog signals leads to the conclusion that the results obtained to a large extent depend on the set of devices. Russian geophysical companies mainly use lateral logging (measuring by a set of gradient sondes), focusing lateral logging, high-frequency electromagnetic sounding and low-frequency induction logging, including multi-sonde tool. The article considers the possibilities of determining the parameters of permeable formations by two-dimensional inversion of synthetic signals for these tools, on the example of a geoelectric model of the Lower Cretaceous deposits in Western Siberia. The model includes permeable formations with mud filtrate invasion zones. The different starting value of the invasion depth determines the accuracy of estimating the parameters of the invaded zone by inverting the data of various sets of sonde signals.

In the records of autonomous seismological observations occurrence of quartz watch clock drift often leads to incorrect time records. This paper presents a method for detecting such errors in a seismic station network based on the analysis of ambient seismic noise cross-correlation functions using Monte-Carlo Markov chain (MCMC) approach without using a reference signal. The proposed method was tested on the seismic data of a temporary seismic network installed on Paramushir Island in 2021-2022 for which time shifts were successfully estimated and corrections to the cross-correlation functions were made.