Complex Of Geophysical Methods Research Articles

Possibilities of on-board gravimetric and hydromagnetic survey in solving engineering-geological problems on the shelf

This article shows the possibilities of using on-board gravimetry and hydromagnetometry in combination with high-resolution seismic surveys in the framework of site surveys on the Arctic shelf. Geotechnical surveys were carried out in the southern part of the Kara Sea shelf on a study area of 25 km2 in order to identify potentially hazardous areas for setting up a floating drilling rig. The studies were carried out using a regular network of observations, consisting of 51 line and 26 secant profiles. The length of each profile is 5 km. Gravimetric research were carried out with the Chekan-AM marine on-board gravimeter in conjunction with magnetometric research using SeaSPY 2 towed marine magnetometers. The depth of research when performing engineering and geological surveys using the presented set of methods is the first 100 meters, up to 1 km. In this case, objects and phenomena of both technogenic and geological nature can represent a potential hazard. As the experience of carrying out this type of work in the south of the Arctic shelf shows, paleoincisions and paleovalleys are common hazards of the geological nature of the region under study. These structures are traditionally filled with weakly consolidated, often gas-saturated, sediments with inclusions of coarse-grained material. Paleoincisions are clearly manifested in the high-frequency component of the magnetic field, and the local component of the anomalous magnetic field was calculated to reveal them. As a result of a complex interpretation of gravity field anomalies and magnetic survey data, a curved linear zone was localized, crossing the entire study area. The identified anomalous zone is confined to the boundaries of the paleoincision, which was originally discovered according to seismoacoustic studies. Based on the results of gravity surveys, an area of negative anomalies was identified in the eastern part of the study area. According to the materials of seismoacoustic in this zone, paleocuts of a complex spatial and deep configuration are traced. It is noteworthy that these structures are not manifested in a magnetic field. Based on the obtained values of the gravitational field and seismoacoustic data, a seismic-density section of meridional strike was constructed across the entire area. As a result of 2D density modeling, the densities for the undercut paleoincision were selected and two deconsolidations were found at a depth of 200 meters. One of the model “artifacts” does not appear according to seismoacoustic studies and hydromagnetometry. The detected areas of decompaction can be caused by the gas saturation of the sedimentary strata and must be taken into account when setting up a floating drilling platform. The interpretation of the anomalous gravitational field in the specified complex of geophysical methods with a priori geological information makes it possible to predict the density structure of the studied rock mass and gives recommendations for further research.

Geophysical research for organization and service of the regional permafrost monitoring network in the Yamalo-Nenets Autonomous District

The results of the application of geophysical methods for the organization and maintenance of the regional permafrost monitoring network in the Yamalo-Nenets Autonomous District are described in the paper. Arctic Research Center in 2021 used the method of electrical resistivity tomography to determine the locations of the thermometric well. The consistency and necessity of using geophysical methods to search permafrost with deep top near the border of continuous and discontinuous permafrost zone is confirmed. Ground-penetrating radar was used at the CALM R53 site as an additional tool for determining the thickness of active layer. It is shown that the complex of geophysical methods and traditional measurements with a permafrost probe when studying the active layer in hard lithological conditions is necessary to refine and supplement the data.

Оценка фациальной принадлежности локальных нефтегазоносных объектов по геофизическим данным

In the established practice of geological exploration for oil and gas conclusions about the facies belonging of the rocks of oil and gas basins and individual exploration areas were made mainly on the basis of the study of core material. Recently for this purpose the results of seismic exploration and well logging have been used. Geophysical methods despite their obvious progress are indirect and intermittent core sampling and incomplete coring make facies analysis difficult. Тhe study of cuttings during the well logging process makes it possible to fill this gap through direct continuous observations along the well section. The use of the whole complex of geophysical methods allows one to mutually compensate for the limitations and disadvantages of each of them and more fully and reliably assess the genetic characteristics and reservoir potential of productive deposits. Sequential accumulation, comparison and analysis of heterogeneous geophysical data make it possible to continuously refine apriori facies models and forecast oil and gas content which ultimately allows to optimize the directions and volumes of drilling.

History, current state and outlook for developing Mesozoic complex of Terek-Caspian downfold deposits

The article is devoted to the outlook for oil and gas potential of the Mesozoic complex of the Terek-Caspian downfold. The problem of oil and gas content of great depths has been of interest to scientists and specialists since ancient times. However, it became especially relevant in the second half of the 20th century. With the depletion of the Miocene deposits of the Tersko-Sunzhenskaya oil and gas region being exploited for a long time in the 50s of the 20th century, the question of preparing new hydrocarbon reserves through the development of deep-lying horizons of the Mesozoic has become acute. The main oil production in the Tersko-Sunzhensky oil and gas region has been associated with the Mesozoic complex, in particular the Cretaceous one, for more than 60 years. In the Upper Cretaceous deposits, more than twenty highly productive oil deposits associated with a carbonate reservoir represented by fractured limestones were discovered. Currently, many deposits of the Cretaceous complex are at the stage of depletion. This article briefly covers the development of the Mesozoic deposits. As well, it assesses the current state of the oil complex of the Chechen Republic. The short-term and long-term prospects of oil and gas content associated with Cretaceous and Upper Jurassic deposits have been assessed. For successful operation, it is necessary to have a unified oil and gas production system, whose components are oil production, geological exploration and scientific research. Specific recommendations were given for conducting geological exploration for oil and gas. The article substantiates the necessity of studying the regional structure of the territory under consideration using a complex of geophysical methods and parametric drilling, in particular, aimed at studying the nature of the structure and composition of the Upper Jurassic deposits and determining the location and depth of parametric wells. It is recommended to focus on a number of regional seismic profiles for the study area.

Role of multiple reflections in the formationof wave field in the cretaceous successions of the Middli Kura depression in Azerbaijan

The article is devoted to the elucidation of the nature of the wave field recorded below the supporting-dominant seismic horizon «P» in the Middle Kura depression of Azerbaijan. A brief overview of the work carried out here is given; it is indicated that some geologists and geophysicists of our country, in our opinion, mistakenly assume that the observed wave field below the specified horizon is formed mainly by multiple reflections.
 Since the introduction of the common depth point method into the practice of seismic exploration, individual areas of the Middle Kura depression in Azerbaijan, including the Yevlakh-Agjabedi trough, have been repeatedly studied with varying degrees of frequency tracking. On the basis of this, a fairly large number of promising structures have been identified and mapped. But the structure of the Mesozoic, in particular the deposits of the Upper Cretaceous, still remains insufficiently studied.
 The study of the geological structure of the Mesozoic sediments, which are considered promising in terms of oil and gas content, is an urgent geological task; exploration work was carried out in the studied areas of the Middle Kura depression using a complex of geophysical methods at the modern technical and methodological level and new results were obtained. The constructed seismic sections show a dynamically pronounced and well-traceable seismic horizon corresponding to the Mesozoic surface and located deeper than it, relatively weak, short, discontinuous reflective boundaries that characterize the structure within the Mesozoic deposits. The studies carried out on the basis of modeling and velocity analysis made it possible to prove that the wave field in the time interval corresponding to the Mesozoic deposits owes its origin to intermittent single reflections from volcanic-carbonate deposits of the Upper Cretaceous age.

КАРБОНАТНАЯ ФОРМАЦИЯ ВЕРХНЕГО ТРИАСА ЗАПАДА СКИФСКОЙ ПЛАТФОРМЫ И СЕВЕРНОГО КАВКАЗА

Relevance of the work. Despite the long history of studies of the Triassic deposits of the Western Ciscaucasia and the North Caucasus, the scheme of their lithological-stratigraphic division and the correlation of sections of different tectonic zones remains poorly developed. This is especially true for the Upper Triassic carbonate formation, which is of oil and gas exploration interest. In this regard, the aim of the work is a detailed lithological and stratigraphic study of Upper Triassic sediments, elucidation of their occurrence conditions, and determination of the areal distribution of carbonate strata. Research methods. Macro- and microscopic studies of the core material were performed. Biostrati-graphic analysis of the Upper Triassic sections was carried out. To dissect the section, a complex of geophysical methods of well research was used, including all types of logging. The results of the work and the scope of their application. A detailed lithological and stratigraphic study of a powerful section of the Triassic sediments of the Western Ciscaucasia and the North Caucasus allowed us to identify a Late-Norian carbonate formation (the Velikovechnenskaya formation), to identify the features of its structure, the lithofacial composition of the composing rocks, the conditions of occurrence, to make typical sections in various tectonic zones, and the subsequent correlation - to outline the areal distribution of the strata. The zone of probable development of reef structures is determined. Conclusions. The carbonate formation may be of practical interest in the search for minerals, but the area of its development is characterized by a low degree of geological and geophysical knowledge. To clarify the boundaries of its distribution, to clarify the features of the internal structure, it is necessary to conduct additional seismic studies. Exploratory seismic work on a sparse network of profiles is recommended in the western part of the Kopan syncline, as well as along the north-eastern slope of the Kanevsko-Berezansky shaft from Berezanskaya Square to the Adygeya salient.

EXPERIENCE OF USING ELECTRICAL TOMOGRAPHY, RADON SURVEY AND MICROSEISMIC SOUNDING IN SEARCH FOR PIPES CONTROLLED BY FAULT ZONES

The complex of geophysical methods was successfully applied in the Alakit-Markha kimberlite field of the Yakutsk diamondiferous province. A pipe was identified in the local forecast area specified within the field at the previous stage of prospecting. The studies using electric tomography (ET), radon survey (RS) and microseismic sounding (MS) covered an area of ≈1000⨯500 m. Based on the jointly processed ET and RS plan images and MS profiles, a tubular body was detected in the sedimentary cover. It is confined to a fault node and stands out among the host rocks by low electrical resistivity, increased soil radon concentrations and high spectral ratios of the horizontal and vertical components of microseisms. Its complex shape is manifested at the ground surface by two isometric structures (each being several hundred meters long), which jointly form a dike-like body at a depth of ≈40 m, as shown by the electrical tomography images. According to the MS data, its root part is detected to comprise one or two fractured narrow zones that are traceable to a depth of 2 km and below. The structure of the identified body and its chemical composition will be determined after exploratory drilling is complete. Today there are grounds to conclude that using ET, RS and MS methods jointly as a complex described in the article proved effective for identifying pipes controlled by fault zones in the sedimentary cover areas.

Forecasting of oil and gas deposits by a complex of geophysical methods on the southern side of the Fergana Depression

Forecasting of oil and gas deposits by a complex of geophysical methods on the southern side of the Fergana Depression

FEATURES OF THE GEOLOGICAL STRUCTURE OF SEDIMENTARY COVER OF FROLOVSKAYA MEGADEPRESSION DERIVED FROM THE RESULTSOF GENERALIZATION OF GEOLOGICAL AND GEOPHYSICAL DATA

The article is devoted to the features of the geological structure of Jurassic-Cretaceous deposits of Frolovskaya megadepression. These features are derived from the results of the generalization of the materials of regional seismic profiles, maps of gravity and magnetic prospecting, drilling data. The main petroleum prospects are associated with Jurassic deposits and pre-Jurassic basement. We conclude that it is necessary to intensify further researches with carrying out the entire complex of geophysical methods, including magnetic and gravity prospecting with an increased density of observations.

Application of geophysical methods for solving hydrogeoecological problems in the Southern Kryvbas territory

The geoecological impact of various man-made mining facilities in the Southern Kryvbas territory was studied using a complex of geophysical methods (gravity-magnetic prospecting; electrical exploration by the VES method and interpretation of aero-space photographs). The predetermining role of the tectonic factor in assessing the hydrogeoecological situation in the research area is shown. The prevalence of diagonal and sublatitudinal faults of high ranks (dividing the submeridional extension of metamorphic rocks of the Kryvyi Rih series into a system of small blocks) has been established by detailed geological-geophysical studies. Their vertical movements “unload” periodically arising stresses in the Earth’s crust. A high level of activation of dangerous geoecological (and primarily hydrogeoecological) processes is marked as a result of the interaction of natural geodynamic and technogenic processes. It is shown (based on the complex analysis of hydro-geological and geophysical information) that the highly mineralized mine and open-pit waters of the tailing dumps of the PJSC “Yugok” and the PJSC “Arcelor Mittal Kryviy Rih” and mine water storage pond in the Svistunova ravine of State enterprise “Kryvbasshakhtozakrytiei” have a joint effect on the hydro-geoecological situation of Southern Kryvbas territory. The flooding of the study area by results of the research is not universal; it takes into account modern features of the activation of fault tectonics.

Conjugation with the Central Asian Foldbelt: Interpretation of the 3DV and Tynda–Amurzet Transects

In this paper we consider the results of geological interpretation of 3DV (Tommot–Skovorodino segment) and Tynda–Amurzet geophysical transects crosscutting the Aldan Shield and the Stanovoi Granite–Greenstone Domain of the Siberian Platform; the Selengino–Stanovoi, Mongolia–Okhotsk, and Gobi–Hinggang foldbelts; and the Argun and Mamyn microcontinents with a total extent of sections of about 1000 km and depth of about 40 km. The data of previous studies and follow-up electric conductivity information have been used. The data of geological mapping, subject studies, and insights into the deep-seated structure of the considered territory obtained with a complex of geophysical methods are discussed. It is shown that Mesozoic strike-slip and thrust faults play the leading role in the present-day structure of the territory and in control rifting and mantle diapirism. It is suggested that Californian-type metamorphic nuclei, which are of structure-forming significance for adjacent territories in the west, have also developed in the studied region.

Atmospheric electric effects during the explosion of Shiveluch volcano on November 16, 2014

The development of a volcanic plume from the Shiveluch volcano explosion on November 16, 2014, is analyzed using a complex of geophysical methods. The start of the explosion was detected by seismic data. The World Wild Lightning Location Network (WWLLN) allowed the localization of volcanic lightning discharges that occurred during the first stage of the eruption plume. Satellite IR monitoring data made the plume structure obvious. An electrostatic fluxmeter mounted 113 km apart from the volcano recorded the first disturbances of the atmospheric electrical potential gradient (PG) at a distance of 90 km from the eruption cloud front. Two distinct PG anomalies, of 50 and 32 min in length and of more than 100 V/m in amplitude, recorded in 2 h, indicate two separate eruption formations formed by this time. The propagation velocities of two parts of the plume close to the wind speeds at altitudes of temperature inversions (9–10 and 12 km), according to balloon sensing, point out to the plume layering and propagation at two altitudes.

Integrated Geophysical and Geological Investiga-tions of Karst Structures in Komberek, Slovakia

A complex of geophysical methods were used to investigate a small karst area aimed at the production of detailed geological mapping, to confirm geological localization of known sinkholes, and to find possible continuations of caves and voids below the surface. The dipole electromagnetic profiling and radiometric mapping (the gamma-ray spectrometry method) were applied to determine the spatial distribution of hard carbonate rocks and weathered valley-fill sediments. Detailed high-definition magnetometry was carried out at selected sites in the studied region with the aim of distinguishing between sinkholes and man-made lime-kilns, pits where limestone was heated and transformed into lime. The microgravity and the electrical-resistivity tomography (ERT) methods were used to create high-resolution images of the underground cave. The results of ERT and the geological survey were used as an initial model for gravity modeling. Subsurface cavities of various sizes are contrasting geophysical objects, and the electrical resistivity can range from very conductive to relatively resistive depending on the composition of the filling materials. The interpretation of resistivity properties is not always straightforward. We must distinguish air-filled (high-resistivity) and loamy water-filled (low-resistivity) cavities and fractures. The combined geophysical methodology permits us to determine a more accurate near-surface geological model, in our case the parallel interpretation of a strong conductive anomaly in the ERT inversion and a predominant density decrease in the gravity modelling yield the presence of cavities at depths approximately of 50 to 60 m below the surface.

Localization of Shallow Gas Deposits and Uncontrolled Gas Flows in Young and Unconsolidated Sediments by Geophysical Methods

The great mass of Neogene sediments in the Hungarian basin, where several hydrocarbon accumulations are known, is affected by Pliocene strike-slip movements, resulting in many [open quotes]flower structures.[close quotes] The gas may migrate from the reservoirs upward to the surface along the faults. Thus, shallow gas deposits can be located in the young, unconsolidated sands. There are also several shallow gas deposits derived from uncontrolled gas flows. In Hungary, the shallow gas reservoirs, which are small but increasingly important, have not yet been explored properly. However, the depleting gas may pollute the water in the soil as well as cause explosions. Our purpose is to develop inexpensive, complete, and highly sophisticated field- and data-processing techniques and an integrated complex of geophysical methods in order to define the limits of shallow gas deposits. To avoid anomalous behavior on seismic sections of the depleting gas, we started from uncontrolled gas flows which require special velocity and amplitude vs. offset analyses. In addition, natural and controlled source electromagnetic/electric surveys with various parameters were applied. An industrial-scale seismic section over an uncontrolled gas flow, special sections over flower structures and geoelectric sections, and a magnetic map are presented. The integrated complex of geophysical methodsmore » outlined above is being developed in order to establish the conditions for the exploration of gas reservoirs which have been used close to their locality and which could be recovered inexpensively.« less