The oil and gas potential of the north of the Siberian platform and adjacent shelf

The objective of this article is an estimation of the oil and gas potential of the north of the Siberian platform and adjacent shelf. The Siberian platform is characterized by a large concentration of oil and gas resources in the southern and central parts of the platform. The main oil and gas province of the Siberian Platform is the Leno-Tungus oil and gas province. The oil- bearing strata in the Lena-Tungus oil and gas province are confined to the Riphean, Vendian, Lower-Middle Cambrian deposits, in which large oil and gas fields are discovered. In modern contours the Siberian platform in the north and north-west is fringed by the Yenisei-Khatanga regional trough. In the east, the Yenisei-Khatanga regional trough is connected with the Anabar- Lena trough, framing the north-eastern part of the Siberian platform. Analysis of the available geological and geophysical materials shows a fairly high potential of the Anabar-Lena and Yenisei-Khatanga troughs for the discovery of large hydrocarbon fields. The basic understanding of the geologic-tectonic structure and petroleum potential of the northern part of the Siberian Platform and the adjacent shelf of the Arctic zone are currently based on seismic data by the method of the common depth point (CDP), tied to the existing deep search and parametric wells. Representations of the deep structure and oil and gas potential of specific areas, the allocation of targeted promising oil and gas horizons can change dramatically as the depth of seismic acquisition of the method of the common depth point increases and the software for processing and interpreting seismic data is improved. The localized oil and gas resources of the north of the Siberian platform and adjacent shelf are 41017,3, subsequently, 27582,3 - onshore and offshore - 13435 MMT (million tons) of oil equivalent.

Demonstrating multiple attenuation with model-driven processing using neural networks

Some of the key tasks in seismic processing involve suppressing multiples and noise that interfere with primary events. Conventional multiple attenuation on seismic prestack data is time-consuming and subjective. As an alternative, we propose model-driven processing using a convolutional neural network trained on synthetically modeled training data. The crucial part of our approach is to generate appropriate training data. Here, we compute a generic data set with pairs of synthetic gathers with and without multiples. Because we generate the primaries first and then add multiples, we ensure that we have perfect target data without any multiple energy. To compute generic and realistic training data, we include elements of wave propagation physics and implement a randomized flexibility of settings such as the wavelet, frequency content, degree of random noise, and amplitude variation with offset effects with each gather pair. A fully convolutional neural network is trained on the synthetic data in order to learn to suppress the noise and multiples. Evaluations of the approach on benchmark data indicate that our trained network is faster than conventional multiple attenuation because it can be run efficiently on a modern GPU, and it has the potential to better preserve primary amplitudes. Multiple removal with model-driven processing is demonstrated on seismic field data, and the results are compared to conventional multiple attenuation using a commercial Radon algorithm. The model-driven approach performs well when applied to real common-depth point gathers, and it successfully removes multiples, even where the multiples interfere with the primary signals on the near offsets.

Detecting lithospheric discontinuities beneath the Mississippi Embayment using S-wave receiver functions

SUMMARY Identifying upper-mantle discontinuities in the Central and Eastern US is crucial for verifying models of lithospheric thinning and a low-velocity anomaly structure beneath the Mississippi Embayment. In this study, S-wave receiver functions (SRFs) were used to detect lithospheric boundaries in the embayment region. The viability of SRFs in detecting seismic boundaries was tested before computing them using the earthquake data. A careful analysis using a stochastic noise and coda model on the synthetics revealed that a negative velocity contrast could be detected with certainty at low to moderate noise levels after stacking. A total of 31 518 SRFs from 688 earthquakes recorded at 174 seismic stations including the Northern Embayment Lithospheric Experiment, EarthScope Transportable Array and other permanent networks were used in this study. Common depth point stacks of the SRFs in 1° × 1° bins indicated a continuous and broad S-to-P converted phase (Sp) arrival corresponding to a negative velocity contrast at depths between 50 and 100 km. The observed negative Sp phase is interpreted as a mid-lithospheric discontinuity (MLD), and several possible origins of the velocity drop corresponding to the MLD are explored. After quantitative analysis, a combination of temperature, water content and melt content variations are attributed to explain the observed MLD in this study. The observations and interpretations in this study support the previous claims of an MLD in the Central and Eastern US and provide a possible mechanism for its origin.

Early assessment of seismic hazard in terms of Voronezh massif-Moscow Depression contact

Purpose is to develop a system approach for early assessment of areas being of high seismic hazard and characterizing by low stability of rock mass relative to external loads. Methods. Well cores have been assessed down to 30 depth and seismic observations have been accumulated. Complexes of field geophysics methods have been applied for the research as well as remote sensing materials, digital model of surface relief, and techniques of qualitative and quantitative interpretation. Findings. Seismic hazard map has been formed in terms of seismic intensification and ground displacement units. The abovementioned is quite reliable but a cost-based result involving early assessments of high seismic hazard areas to infill network of geophysical measurements in the neighbourhood of the areas for their further quantitative characterization. It has been identified that rare well network and definite geophysical lines, run under conditions of a complex terrain, cannot localize the areas of high seismic hazard to focus builders on the enforcement of certain components of the erected structures. It has been defined that end result of the prognostic developments takes a shape of mapping of local areas with the decreased stability of upper share of the geological section supported by further measurements by means of a common depth point method (CDP). Comparison of potential secondary earthquake sources with high permeability zones makes it possible to predict highly reliable areas of the increased seismic magnitude. Originality.For the first time, interpretation techniques have been adapted to describe parametrically nonpotential geofields (i.e. optical density of remote basis; and relative elevation), accepted during the steps of potential field processing, with the use of wave analogies. Practical implications.The methods have been developed helping optimize field geological and geophysical operations in terms of area and well number as well as measuring stakes under the conditions of the limited prior data amount.

Simulated annealing velocity analysis: automating the picking process

We propose an automated method for velocity picking that allows to estimate appropriate velocity functions for the normal moveout (NMO) correction of common depth point (CDP) gathers, valid for either hyperbolic or nonhyperbolic trajectories. In the hyperbolic velocity analysis case the process involves the simultaneous search (picking) of a certain number of time-velocity pairs where the semblance, or any other coherence measure, is high. In the nonhyperbolic velocity analysis case, a third parameter, usually associated with the layering and/or the anisotropy, is added to the searching process. The proposed technique relies on a simple but effective search of a piecewise linear curve defined by a certain number of nodes in a 2D or 3D space that follows the semblance maxima. The search is carried out efficiently using a constrained very fast simulated annealing algorithm. The constraints consist of static and dynamic bounding restrictions, which are viewed as a means to incorporate prior information about the picking process. This allows to avoid those maxima that correspond to multiples, spurious, and other meaningless events. Results using synthetic and field data show that the proposed technique permits to automatically obtain accurate and consistent velocity picks that lead to flattened events, in agreement with the manual picks. As an algorithm, the method is very flexible to accommodate additional constraints (e.g. preselected events) and depends on a limited number of parameters. These parameters are easily tuned according to data requirements, available prior information, and the user's needs. The computational costs are relatively low, ranging from a fraction of a second to, at most, 1-2 seconds per CDP gather, using a standard PC with a single processor.

On the efficiency of integrated analysis of parameters of ref- racted and reflected waves in prediction of oil-gas bearing of section

Based on the comparative analysis of results of researches carried out via the methods of reflected and refracted waves with the purpose of prediction of geological section, the paper justifies that one of the major evidences in the field of seismic wave in oil-gas fields of geological section is the differentiation of elastic properties of oil-gas bearing reservoirs from the environment. Based on mutual comparison of results of conducted researches, it is shown that in the prediction of geological section the integ- rated analysis of changes of dynamic parameters of the waves reflected from the surface of oil-gas bearing reservoir and transmitted through this surface may further increase the reliability of obtained results. The research surveys carried out in Naftalan-Shimali Naftalan areas via the methods of reflected and refracted waves were simultaneously analyzed. With the aim of comparative analysis, the deposit type anomalies revealed through the method of refracted waves were compared to the results of attributed analysis of seismic cross-sections obtained with the method of common depth point. The correspondence of the signs associated with the oil-gas bearing content in change of dynamic parameters of refracted and reflected waves has been specified. With the purpose of prediction of geological section, a complex research is proposed.

6D phase-difference attributes for wide-azimuth seismic data interpretation

Phase information of seismic signals is sensitive to subsurface discontinuities. However, 1D phase attributes are not robust when dealing with noisy data. In addition, variations of seismic phase attributes with azimuth are seldom explored. To address these issues, we have developed 6D phase-difference attributes (PDAs) derived from azimuthal phase-frequency spectra. For the seismic volume of a certain azimuth and frequency, we first construct stacked phase traces at each common-depth point along a certain decomposed trending direction. Then, the 6D PDA is extracted by calculating the complex-valued covariance at a 6D phase space. The proposed method enables characterization of the subsurface discontinuities and indicates seismic anisotropy. Moreover, we provide one q-value attribute obtained by singular value decomposition to describe the variation intensity of PDA along different azimuths. Simulated and field wide-azimuth seismic data sets are used to illustrate the performance of the proposed 6D PDA and the derived q-value attribute. The results show that PDA at different frequencies can image various geologic features, including faults, fracture groups, and karst caves. Our field data example shows that PDA is able to discern the connectivity of karst caves using large-azimuth data. In addition, PDA along different azimuths and the q-value attribute provide a measurement of azimuthal variations, as well as the anisotropy. Our 6D PDA method can be used as a potential tool for wide-azimuth seismic data interpretation.

Tectonic state and oil-gas prospects of Khidirly-Bandovan structure according to the new gravimetric data

Khidirly-Bandovan structures have been studied through geological mapping, structural exploration drilling, geophysical methods (gravimetric, magnetic, electrical, seismic exploration methods) since the 1930s. Small amount of oil from different wells in the upper part of Productive Series (PS) and huge amount of gas fountain from Middle Absheron sediments have been obtained. As the interest to these areas had not decreased, the geophysical surveys continued during further years. Seismic exploration surveys were executed in Bandovan structure via Common Depth Point (CDP) method in 2004, refracted ray method and gravimetric exploration complex in 2006 and 3D seismic exploration works and gravimetric investigations with “Scintrex CG-5 Autograv” devices in 2016, correspondingly. In the result of analysis of distribution characteristics for local gravimetric anomalies, as well as 3D descriptions of new gravimetric data, up-to-date logs on tectonic state of Khidirly-Bandovan structure have been obtained and as the new oil-gas exploration objects, the west and south-west wings of these structures highlighted.

Multiple attenuation with 3D high-order high-resolution parabolic Radon transform using lower frequency constraints

The parabolic Radon transform is one of the most commonly used multiple attenuation methods in seismic data processing. The 2D Radon transform cannot consider the azimuth effect on seismic data when processing 3D common-depth point gathers; hence, the result of applying this transform is unreliable. Therefore, the 3D Radon transform should be applied. The theory of the 3D Radon transform is first introduced. To address sparse sampling in the crossline direction, a lower frequency constraint is introduced to reduce spatial aliasing and improve the resolution of the Radon transform. An orthogonal polynomial transform, which can fit the amplitude variations in different parabolic directions, is combined with the dealiased 3D high-resolution Radon transform to account for the amplitude variations with offset of seismic data. A multiple model can be estimated with superior accuracy, and improved results can be achieved. Synthetic and real data examples indicate that even though our method comes at a higher computational cost than existing techniques, the developed approach provides better attenuation of multiples for 3D seismic data with amplitude variations.