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8th Congress of the Balkan Geophysical Society
- Conference date: October 5-8, 2015
- Location: Chania, Greece
- Published: 05 October 2015
81 - 100 of 124 results
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Drilling Technology Influence on Boreholes Quality with Geophysical Measurements Implications
Authors C Ciuperca, G.T. Jackson, B.M. Niculescu and B.M. PopinaSummaryThe drilling techniques and operations performed during drilling can affect the borehole’s shape and quality, with direct repercussions on the quality of geophysical records, both LWD and wireline. However, wireline measurements are more affected than LWD, due to the operations that occur after drilling the well (e.g., reaming trips, etc.) and the “aging borehole” phenomena (breakouts and fractures become larger, invasion becomes deeper).
The most affected by borehole’s quality and shape are the pad-type geophysical tools: Imaging, Litho-density or Microresistivity, which require a good contact with the formations. Also, the sonic logging readings can be affected by the occurence of quasi-horizontal or inclined fracture systems, due to a strong attenuation of the signal, causing the “time stretch” or even “cycle skipping” phenomena (abnormally long transit time readings).
Different types of fractures induced by drilling operations can create a false invasion appearance, since the resistivity tools with short investigation radii are influenced by the drilling fluid penetrating in these fractures.
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Imaging Folegandros Basin by Using Seismic Reflection Data from a Part of Seismic Line AEG-1
Authors N. Andronikidis, M. Gialitaki, A. Mouchou, G. Kritikakis, E. Manoutsoglou and A. VafidisSummarySeismic reflection data of the part of seismic line AEG-1 which crosses Folegandros basin in the south-central Aegean has been processed in order to image structures within this basin. The processing sequence included band-pass filtering for noise suppression, velocity analysis, tau-p filtering for multiple attenuation, zero phase deconvolution and post stack migration techniques. The seismic reflection method at Folegandros basin provided information about the geological structures at intermediate depths which is possibly related to tectonic elements and structures at greater depth. The evolution of Folegandros basin is explained by the action of wrench tectonics which can contribute to the understanding of multi - direction crustal- extension in the area.
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Anaximander Mountains and Deep Sea Mud Volcanoes South of Turkey
By M. SenozSummaryInitial stages of continental collision in the eastern Mediterranean Sea dominate the tectonic interaction between Africa and Eurasia, represented by the westward extrusion of the Anatolian microplate. The plate boundary is well defined through the Hellenic Arc to the west and through the Cyprus Arc to the east. The offshore Anaximander Mountains are an important link between the Hellenic and Cyprus arcs. They were formed by southeastward rifting from Turkey in post-Miocene time. Gravity data have shown that the eastern part of the Anaximander Mountains is different from the western part; multibeam mapping seems to confirm that the eastern Anaximander Mountains have affinity with the Florence Rise structure (western Cyprus Arc). Faulting along and across the latter feature is characterized in the seismic data by anastomosing faults and pop-up flower structures. It is likely that progressive adjustment to incipient collision developed into a broad zone of NW–SE transpressive wrenching extending towards south Turkey. In contrast, the western mountains are more directly related to the opening of the Rhodes Basin and the Finike Basin, as transtension may have dominated in southwest Turkey since the Pliocene ( A.E. Aksu et al.,2009 ). The connection with onshore Turkey is still unclear, but could be related to the Fethiye—Burdur Fault Zone that defines the western boundary of the complex Isparta Angle. The Anaximander Mountains and the Isparta Angle form together a tectonic accommodation zone between the active deformation in southwestern Turkey and the Aegean region and the tectonically quieter Cyprus region. ( T. A.C. Zitter, 2003 ) In the last years are in this area on tausends of kilometers sonar ; side scan sonar ; multibeam and multichannel seismic track lines new bathymetric data collected ( Lykousıs et al., 2009 ; A. E.Aksu et al., 2009 ). Detailed multibeam, sedimentological, and geophysical surveys provide ample new data to confirm that the Anaximander Mountains (Eastern Mediterranean) are an important area for active mud volcanism and gas hydrate formation. Very detailed morphology maps have been made of the known targeted mud volcanoes (Amsterdam, Kazan and Kula), especially the Amsterdam ‘‘crater’’ and the related mud breccia flows. New mud volcanoes identified on the basis of multibeam backscatter intensity were sampled, documented as active and named ‘‘Athina’’ and ‘‘Thessaloniki’’. Gas hydrates were sampled also in Thessaloniki mud volcano, the shallowest (1264 m) among all the active Mediterranean sites, at the boundary of the gas hydrate stability zone. Biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of Late Cretaceous limestones, Paleocene siliciclastic rocks, Eocene biogenic limestones and Miocene mudstones. Rough estimations of the total capacity of the Anaximander mud volcanoes in methane gas are 2.56–6.40 km3.( Lykoısıs et al. 2009 ).
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Bathymetric Features of the Levant Basin on the Basis of Modern Processing Techniques
Authors E. Kokinou and H. KoppSummaryThe objective of the present work is to determine and partly interpret the sea floor morphological features in the Levant basin based on bathymetric analyses and taking into account previous geological and geophysical studies.
Bathymetry processing has been achieved by applying a new algorithm for the automatic enhancement and the identification of the linear patterns. According to this method, the Slope and Aspect images, as well as their derivatives are initially computed. Then, a rotation and scale-invariant filter produces an image of the automatic detected geomorphologic features in the study area.
The Levant basin comprises a geodynamically active area, where strong tectonic deformation takes part, resulting to the presence of extensional and contractional structures, strike slip motions, submarine landslides and density flows of sediments. All the previous phenomena are identified with sufficient accuracy in position and shape based on the bathymetric analyses of this work.
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A Newton-Raphson Approach for Geophysical Well Logs Interpretation in Complex Lithology Formations
Authors B.M. Niculescu and A. NEGUTSummaryThe paper presents a numerical algorithm that performs accurate lithology corrections for thermal (CNL/ TNPH, CNL/NPHI) and epithermal (SNP) neutron logs, in the whole range of porosities normally encountered in practice. It is known that neutron logs respond not only to a formation’s true porosity, but, to some extent, also to its lithology (the so-called “matrix effect”). Because the matrix effect is nonlinear and varies with true porosity, which is unknown beforehand, an iterative process is needed in order to carry out proper lithology corrections and obtain formation’s porosity.
The relationships between measured neutron porosity and true porosity for the common reservoir lithologies (sandstones, limestones and dolomites), at different formation water salinities, are approximable via suitable regression polynomials. Nonlinear neutron responses thus expressed are combined with the responses of density and sonic velocity logs, together with the volumetric unity constraint, into a system which is solved using a Newton-Raphson root finding routine. The algorithm, implemented as a set of Matlab™ codes, provides optimal petrophysical models for the interpretation of neutron-density-sonic log suites and is easily adaptable in order to include additional linear or nonlinear log response equations. A case study regarding its applicability is also presented in the paper.
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The Use of Magnetotelluric to Exploration the Groundwater in Central of Saudi Arabia
Authors RA ALmutairi, Y.A.A. almutairi, H.H.G. ALGHTANI, K.H.D. ALDAMEGH and E.S.S. ABOUDSummarySaudi Arabia is a desert country with no permanent rivers or lakes and very little rainfall. As such, ground water aquifers are major sources of water in Saudi Arabia. For example, in the Riyadh region (central of Saudi Arabia), several Wadies, including Wadi Nisah, store about 14 × 106 m3 which are extracted for local irrigation purposes. In most of these areas, water wells are as shallow as 200–300m. Wadi Nisah aquifer is important because it is a large subsurface water aquifer that could provide enough water for many years. Accordingly, a Magnetotelluric (MT) survey was conducted (for the first time in the Riyadh region) in order to evaluate the subsurface aquifers at great depths (∼ 2–3km). In this study, we used the available portable broadband sounding receiver system (MT24LF). This system is designed for measuring low frequency signals which penetrate the earth layers and directly related to the subsurface resistivity. MT results indicated that, a low resistivity layer associated with alluvium deposits was defined at depth of about 1–2km and extend horizontally to about 15km. We interpreted this layer as the subsurface ground water aquifer in Wadi Nisah.
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Thermal Water Sources and Features of Seismicity in the Elbasani Zone, Albania
By MR ShatroSummaryIn Elbasani fault zone, hot mineral water (thermal waters) spot out from natural springs which have been known since the 19th century. The thermal water zone correlates in space with seismic activity and compound earthquakes occurred. Activation of thermal water in this fracture zone is probably related to the feature of sismicity in this area. Thermo mineral and mineral waters of the area of Elbasan are located in the transvesal fracture Vlore-Elbasan-Diber. This fracture is one of the most interesting and unique tectonics of the geologic structure of the Albanids.In this area are located major thermal deposits like in Kozan region, where the most important one is Kozan’s Well −8, region of Lixha(Elbasan) and also the resources in the region of Hydraj.Moving southeast there are located the deposits of Galigati and Holta. Apart from the resources of Lixha and Hydraj, that have been known since the roman era, the wells of Kozan region,Galigati’s and Holta’s, have been showing in the surface,as a result of drilling these wells in order to seek for oil and gas.All the studies that were performed until today show that these resources have their origin in depth. Where geological conditions are favourable, rainwater seeps through the surface and becames trapped in vast underground reservoirs so deep below the Earth”s surface that it becomes heated to high temperatures by the low velocity zones. Thermal waters flow out through the contact of conglomerate layer with calcolistolith. The 24 October 2008 Kuturman (Elbasan) earthquakes sequence was a compound earthquake consisting of four nearly identical events. Low velocity layers can be promotore of geothermal energy inside it. Having high temperature in the low velocity layers in this area can creating the thermal-water. The low-velocity layer are characteristic for sizmoactive regions.
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Two Dimensional Inversion of Resistivity Data by an Adaptive Parameterization Approach
Authors I. Akca and C. Öztürk AkcaSummaryAn adaptive model parameterization methodology is used to develop a two dimensional inversion scheme for the direct current resistivity data. Adaptation is realized by a two stage inversion algorithm. The inverted model after the first stage of inversion is clustered to distinguish the target anomalies and the background. In the second stage a new parameter grid is formed by refining the model cells corresponding to the target bodies or structures. This methodology is well suited for the targets such as archaeological ruins, embedded bodies (tanks, bunkers) and cavities. A test with a synthetic data set is carried out to demonstrate the efficiency of the developed method. Results showed that algorithm is able to recover the subsurface image with more detail in comparison with the inversion results of the regular model mesh.
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Lithosphere-asthenosphere System in the Mediterranean Region in the Framework of Polarized Plate Tectonics
Authors R.B. Raykova, G.F. Panza and C. DoglioniSummaryVelocity structure of the lithosphere-asthenosphere system, to the depth of about 350 km, is obtained for almost 400 cells, sized 1°×1° in the Mediterranean region. The models are obtained by the following sequence of methods and tools: surface-wave dispersion measurements and collection; 2D tomography of dispersion relations; non-linear inversion of cellular dispersion relations; smoothing optimization method to select a preferred model for each cell. The 3D velocity model, that satisfies Occam razor principle, is obtained as a juxtaposition of selected cellular models. The reconstructed picture of the lithosphere-asthenosphere system evidences the, globally well known, asymmetry between the W- and E-directed subduction zones, attributed to the westward drift of the lithosphere relative to the mantle. Different relationship between slabs and mantle dynamics cause strong compositional differences in the upper mantle, as shown by large variations of seismic waves velocity, consistent with Polarized Plate Tectonics model.
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Seismic Coherence Driven Sparse Mesh for CSEM Inversion
More LessSummaryMany geophysical inverse problems involve large and dense coefficient matrices that often require an immense amount of computing power. Some methods can be used to reduce the processing time or physical memory required. This paper pose a significant challenge to solve large-scale inverse problems. We have developed a method that combines the adaptive mesh discretization and sparse mesh to reduce the computational complexity of CSEM inverse problems. The sparse mesh is created by Delaunay Triangulations method and constrained by seismic image. The nodes for generating triangular mesh are extracted from seismic coherence map. This sparse mesh is including all the information of geological features which are extracted from seismic image. A synthetic CSEM data are simulated for sparse mesh testing. As a result, the seismic coherence driven sparse mesh has an as high resolution inversion result as normal unstructured triangular dense mesh. Comparing with the same number unstructured triangular sparse mesh, seismic coherence driven sparse mesh has an advantage of vertical resolution.
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Optimization Methods for Least Squares Time Migrations
More LessSummaryLeast Squares Migration (LSM) is well known migration methods, but it is very expensive because of time. There are many optimization methods to improve LSM results. In this paper, five optimization methods, LSQR, Shooting, Grafting, Gauss-Seidel and Conjugate-Gradient are applied to data (SEG/ EAGE salt model) in order to obtain better migration results and to compare them in terms of quality, time and resolution. Tests have shown that the Gauss-Seidel method is the best method yields improved amplitude response, less time and higher resolution compared to others.
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SYstem for Modelling and INterpreting of GRavity ANomalies (SYMINGRAN)
By C.H. TzankovSummaryThe paper comprises new knowledge and at the same time improves cognition about some important issues related to modelling and interpretation of gravity anomalies in gravity exploration.
Useful algorithms for interactive modelling of varying geometric bodies with specific effective gravity attraction are developed. The analytical expressions concerning the form and the spatial relation of some geometrical models such as finite 3D horizontal circular cylinder and finite 2D horizontal elliptical cylinder are improved. This enhanced their technical qualities and flexibility through the modelling process.
In addition, all geometric models as well as the measured and the modelled gravity data are supported with original subroutines for visualization.
Moreover, the elements of the model are captured by a complex algorithm for simple real-time modelling which provides manual control of the model.
The optimization algorithms are based on Tikhonov regularization which means that additional heterogeneous information which stabilizes the solution of the inverse gravity problem could be included in the optimized models during the interpretation process.
The developed algorithms and programs are integrated into a single automated SYstem for Modelling and INterpreting of GRavity ANomalies (SYMINGRAN).
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Effect of Pressure on Compression, Shear and Young’s Moduli
Authors A. Kiss, J. Somogyi Molnar, M. Dobroka, T. Ormos and Á. GyulaiSummaryThe rocks response as perfectly elastic materials in case of rapidly changing stresses. With the assumption of the Hooke body, the elastic moduli describe how rocks resist different deformations. Present investigations covered the examination of pressure dependence of compressional, shear and Young’s moduli. As they can be calculated from the acoustic wave velocities (longitudinal and transverse) it is important to know accurately the velocity-stress function. Therefore the authors developed a petrophysical model, which gives the physical connection between the acoustic velocities and stresses. After estimating the model parameters by joint inversion, where the rock physical parameter is the common parameter, the velocities can be calculated at any arbitrary stresses and the pressure dependent elastic moduli can be derived. To prove the applicability of this method, we measured P and S wave velocities on sandstone samples with an automatic acoustic test system under uniaxial load. This paper includes one sample from these measurements together with literature data of a Berea sandstone sample. The results show that the misfits between measured and calculated data are small, the model can be applied well in practice.
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Laboratory P and S Wave Velocity Measurements to Confirm the Developed Petrophysical Model for Acoustic Hysteresis
Authors J. Somogyi Molnar, M. Dobroka, A. Kiss, T. Ormos, Á. Gyulai and E. PrácserSummaryIt is well known that acoustic wave propagation under pressure is very nonlinear and the elastic properties of rocks are hysteretic, which behavior is important for mechanical understanding of reservoirs during depletion. Pressure strongly influences the elastic parameters of rocks, thus wave velocities too. In this study longitudinal and transverse wave velocities measured in laboratory on sandstone samples under pressure are presented. The uniaxial loading of the samples was carried out by an automatic acoustic test system. Measurement data were processed by a joint inversion technique based on the developed petrophysical model which describes the relationship between acoustic P/S wave velocities and pressure for loading and unloading phases. After Birch we assume that the main factor determining the pressure dependence is the closure of pores. The advantage of the model is that it is not based on simple curve fitting, but gives physical explanation for the process with three-parameter exponential equations. The quality checked joint inversion results showed that the misfits between measured and calculated data are small, proving that the proposed petrophysical model can be applied well in practice.
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RefPick: A GUI Application to Pick First Arrival Times and Data Processing on Seismic Refraction Data
Authors K.H. Coban, M. Senkaya and H. KarslıSummaryThe quantified interpretation of the seismic refraction record depends on correct and confident picking first arrival times. However, traditional first arrival picking techniques are not enough if the refraction data are poor. This study presents the implementation of a GUI interface, RefPick, which has been established to detecting first arrivals on seismic refraction data, also data processing and inversion. While the interface allows picking the first arrival times by semi-automatically based correlation technique and manually, in addition, the seismic data can be filtered by f-k and Butterworth filters. The interface provides to export the first arrivals in the format of common evaluation software. Also, the inversion will be useful to invert the first data set within RefPick interface. By means of the RefPick, a seismic refraction data can be evaluated within one user-friend, open source GUI application.
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Anticlinal Structure Modeling with Feed Forward Neural Networks for Residual Gravity Anomaly Profile
Authors A. Eshaghzadeh and R.S. KalantarySummaryGeologically, Anticlines are the most important geological structures amongst regional studies and hydrocarbon exploration methods. In general, inversion of gravity anomalies is non-unique in the sense that the observed gravity anomalies in a survey can be explained by a variety of density distributions. To resolve such an ambiguity, the anomalous mass should be estimated by a suitable geometry with a defined density contrast.
Since anticlinal structures have mostly two non-isocline skirt, therefore utilization of the isosceles triangular model will be accompanied by a large error in the forward modeling. We have proposed using two adjoining right triangle for resolving mentioned problem. The density has been assumed constant. In this paper, a new method for anticline structure modeling based on feed forward neural network is presented.
The network is trained by synthetic data as input and output. For feed forward neural network training we have used the back-propagation algorithm. The results indicate that feed forward neural networks, if adequately trained, can predict the 2D form of anticline structure. The proposed method was applied to gravity data from Korand in Iran. The modeling results show high similarity with the attained results from seismic operation.
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Analysis of Capture and Surfatron Ultrarelativistic Acceleration of Electrons with Initial Relativistic Energy
Authors N.S. Erokhin, N.S. Erokhin, R.S. Shkevov, N.N. Zolnikova and L.A. MikhailovskayaSummaryThe ultrarelativistic acceleration of electrons in space plasma by an electromagnetic wave packet propagating across an external magnetic field is analyzed on the basis of numerical calculations. Electrons capturing conditions by the wave packet, dynamics of their velocity components and particle momentum are discussed depending on the problem initial parameters, including the size of the wave packet. The phase plane structure of the accelerated electrons is considered. The optimal conditions for the realization of ultrarelativistic surfatron acceleration of electrons by spatially localized wave packet are outlined. The occurrence of deviations and variations of the accelerated ultrarelativistic electron from cosmic rays standard power graph is discussed.
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Empirical Background TOC Model over Bulgaria
By P. KaleynaSummaryA detailed analysis of the variations of the stratospheric and mesospheric ozone over Bulgaria, in the period 1996–2012, is presented in the article on the basis of ground and satellite measurements of the Total Column Ozone (TCO). The move of the most important components has been studied. Their mean values for the period and the existing long-term trends have been found. It has been studied the move of the most basic components of the seasonal course, the existing long-term trends in it and their relations to the stratospheric temperature and quasi-biennial oscillation. Based on these studies and analyses, an empirical model for daily forecast of TCO over Bulgaria has been created. The main aim of the model is monitoring of the ozone layer and, respectively, the biologically harmful ultraviolet radiation of the Sun related to it which has an effect on human health and life.
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Moho Depth Determination of the Adriatic Sea Region Using a New Bouguer Anomaly Database
Authors G.A. Tassis, C.B. Papazachos, G.N. Tsokas, I.N. Tziavos, I. Vasiljević and A. StampolidisSummaryIn the present work we examine the crustal structure in the wider Adriatic Sea region using a newly presented Bouguer database derived from the integration of satellite, marine and inland gravity measurements. The observed large-wavelength Bouguer anomalies clearly correlate with the deeper crustal - upper mantle structural features, revealing new information on the Moho undulations, allowing the quantitative assessments of the Moho geometry in the study area. This task was performed using three different approaches, namely the multiple source Werner deconvolution (MSWD), the isostatic admittance method and the Parker-Oldenburg algorithm. The interpretation of the MSWD estimates was performed along nine selected Bouguer gravity profiles, leading to a pseudo-3D Moho map, as opposed to the other two methodologies from which 3D models are derived. All three maps exhibit similar large scale features but also local differences for the Moho structure in the Adriatic Sea area. Since this region exhibits complex geotectonic features, such as a double plate subduction, the main goal of the present work is to highlight the main areas of crustal thinning and thickening, using the aforementioned results. Moreover, the results provided by the different methods are evaluated against the current geological and geophysical data and models developed for the area.
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Seismic Monitoring for Automatic Rockfall Detection along Transportation corridor
Authors N. Economou, G. Kritikakis, A. Tripolitsiotis, P. Partsinevelos, G. Vlachou, Z. Agioutantis and A. VafidisSummaryThis geophysical research presents the setup and the preliminary results of several experiments conducted to evaluate the performance of seismic monitoring to recognize low energy ground vibrations caused by small rock free fall or rock rolling along a slope. New ideas for automatic rockfall detection based on Short Time Average over Long Time average (STA/LTA) and fractal analysis of the seismic records are introduced. Different events of vibrations were tested, such as random noise, passing cars or people, rolling or throwing rocks or combination of passing car with rockfall. Based on the experimental results it was determined that more than 95% of car stimulated records are discarded while, more than 90 % of rockfalls or simultaneous car passing and rockfalls are successfully recognized.
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