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53rd EAEG Meeting
- Conference date: 26 May 1991 - 30 May 1991
- Location: Florence, Italy
- ISBN: 978-90-73781-03-0
- Published: 28 May 1991
201 - 250 of 315 results
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Considerations on the meaning of bouguer anomalies in areas with complex morphology and density
Authors M. Bernabini, P. Favoro and L. OrlandoBouguer anomaly is usually worked out considering the zones above zero level as masses with constant density or with a density varying according to the outeropping rocks' density. Although subsequent elaborations are made considering Bouguer anomalies at station level, the masses between the topographic surface and zero level are no longer taken into account.
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Inversion of 2D gravity data by a relative entropy algorithm
By A. BassreiA stochastic approach, called MRE (minimum relative entropy) principle, is used here to invert 2-D gravity data. The main idea of this work lies on the concept of relative entropy, first defined by KuIlback and Leibler (1951). Among several applications of this principle - minimum relative entropy, we quote the interesting application of the MRE in the field of speetral analysis, as a inverse procedure (Shore, 1981), who also have studied the principle in a axiomatic manner (Shore and Johnson, 1980). This approach was already applied in several geophysical inverse problems, both in fundamental and exploration geophysics: inversion of interval velocities, seismic transmission tomography, potential data (gravity and magnetics), correction of the effect of aliasing, band limited extrapolation, and the recovering of the density profile within the earth (Bassrei, 1990a; Bassrei, 1990b; Ulrych et alii, 1990).
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Two applications of space-variable convolution filters reducing to the pole within a large survey area and continuation from or to an irregular surface
Authors P. Andrieux, A. Galdeano and A. TheraThe purpose of this presentation is to demonstrate that variable filters can be used economically, when required, in the space domain. Two applications are considered.
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Radon transform application to 2D processing of potential field data
Authors Y. Zhou, C. V. Reeves and P. ZeilWe have been trying to make use of the Radon transform, a tool for plane-wave decomposition in reflection seismology, in evaluating anomaly trend information from parallel airborne geophysical profile maps, in order to improve the quality of line-to-line interpolation. During our research exercise, we find that this transform has a great application potential in 2D potential field data processing and image processing. In this paper we show how the Radon transform can be generalized and used as a new approach for directional filtering on a gridded data set.
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Extensions to Euler's method for three-dimensional potential field interpretation
Authors K. A. Whaler, C. Neil and A. B. ReidReid et al.'s (1990) method for interpreting magnetic survey data in grid form to give source locations and depths uses Euler's homogeneity relation. The relation is formulated in terms of a 'structural index' by which geological constraints are imposed - the index represents the rate of fall-off of the field with distance, which can be calculated for a given source type (thin dyke, finite step, etc.). Reid et al. (1990) used a least squares technique to solve for the source position (lateral coordinates and depth) and regional field value at each grid point, using a window of surrounding values at which the field gradients were known, and the structural index specified. Solutions were accepted or rejected using a criterion which compared the calculated source depth to its standard deviation.
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A method to estimate the total magnetization direction from a distortion analysis of magnetic anomalies
Authors M. Fedi, G. Floria and A. RapollaThe knowledge of the declinations and inclinations of the total and induced magnetization vectors is normally required, in the interpretation of magnetic anomalies. While the direction of the last (i.e. : its declination, AF, and inclination, IF) can be likely recovered by some appropriate I.G.R.F. model, the declination and the inclination of the total magnetization vector (AT and IT) are more difficult to be determined, depending on the loc al direction of the remanent magnetization vector too.
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Norway offshore - Lista and Kristiansand volcanic areas controlled by 3D interactive magnetic modelling
More LessFollowing the regional high sensitivity aeromagnetic surveys performed by NORGES GEOLOGISKE UNDERSOEKELSE (NGU) in 1974-75 for oil exploration and re-processed by AMAROK in 1989-90, it has been possible to identify and reconstruct the most important anorogenic volcanoes of the Lower Tertiary (Paleocene) in the passive margin of the southern Norwegian offshore, covering an area of approximately 27,000 Km2•
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CQSO: Marine pulse source quality control
By A. RegnaultThe use of various marine source synchronizers has yielded a number of ideas which have now been applied to developing new technology, introducing parameters that had not previously been utilized, and thus opening the way to more sophisticated quality control. The new source synchronizer discussed here is an open system, allowing for further development.
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A Drill-bit source experiment using a 2D array
More LessA number of authors have used the drill bit as a seismic source. In one type of study (Rector et al, 1989), an accelerometer is placed on the drill string, giving an estimate of the signature of the drill bit source. Crosscorrelating this estimate with the data recorded by one or more geophones enhances drill-bit energy in the recorded traces and gives results whose quality is comparable to VSP data.
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Seismic study of the dynamic response of rock to cylindrical charges fired in a half and a quarter space geometry
Authors S. K. Reamer and K. -G. HinzenA series of controlled seismic experiments was performed a limestone quarry in southem Germany to study seismic effects of cylindrical charges fired in both a half space (HS) (burden 63 m) and quarter space (QS) (burdens of 3 and 3.5 m) geometry. Charge columns contained from 20--32 kg of explosives and initiated frorn the bottom. The explosives formed a cylinder 4 rn (20 kg) and 5 rn (32 kg) high and 90 rnrn in diameter at depths from 3-8 rn below ground level. Prior to each of the larger explosions, srnall charges of 0.12 kg seisrnogelit were fired at 4 m and 8 m depths in the same boreholes.
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The shallow reflection profiling (SRP) method for field statics
Authors R. D. Tinsley and M. G. BarbierThere are many areas where simple LVL refraction statics are invalidated by complex near-surface geological conditions, for example, velocity inversions. Uphole drilling is often carried out in these circumstances, but it is a costly business and yields only a single control point with no information about the geological structure around the hole.
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Complex geophysical prospecting of a terrigenous oil field
Authors G. G. Tenchov, W. Hubanov and G. WassilevThe present paper offers the geophysical part of the case history of a terrigenous oil field. The investigated area is situated in the Northem Central part of Africa. The geological and geophysical investigations include seismic and well logging methods and drilling information. The seismic common - depth - point reflection method was used with a profile density of about 3 line km/sq.km..
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Biharkeresztes lower-pannonian natural gas field, Hungary - Interpretational case-study
Authors E. Loboczki and J. ViszkokBiharkeresztes natural gas field is located in east-Hungary, by the Romanian border. Natural gas was first found in the metamorphic rocks and was then detected in lower-Pannonian beds. The sequence at Biharkeresztes consists of Precambrian metamorphite, , Miocene fine-grained sandstone and Pannonian deposits of Paratethys. The reservoir rock is fine-grained, light-grey sandstone, varying from 0.2 to several metres in thickness. The overlying bed is siltstone. The reservoir contains many small gas lenses.
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Objectivised interpretation of seismic sections by tools of artificial intelligence
Authors B. Rugenstein and V. WittkopfThe "Knowledge Based Interpretation System" KnowBIS is our successful first step to computerise the geological interpretation of migrated seismic sections by some rule-based tools of the so-called AI.
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Automated horizon picking by multiple target tracking
Authors E. Harrigan and T. S. DurraniGeophysical horizons are of interest to the interpreter as an indicator of geological boundaries and structures. As such, they are also important for accurately obtaining the earth's velocity model. Horizon picking is still commonly done by hand, a process which is error-prone and time consuming. Attempts to automate the process are hindered by the absence of a clear, robust and universal picking algorithm.
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Computer aided fault pattern analysis (CAFPA): A prototype of an expert system for seismic data contouring
Authors C. Chiaruitini, P. Galuppo, M. Pipan and V. RobertoDrawing structural maps of seismic horizons is a task that requires the efficient management of a large amount of input data. Artificial Intelligence techniques can help the geophysical interpreter in the analysis and synthesis of the information available. CAFPA aims at providing an intelligent assistance to the interpreter by means of Knowledge Based System (KBS).
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Integration of 3D subsurface models of different scales
Authors I. L. Ritsema, P. N. Nobili and J. L. MalletThe integration of 3D subsurface rnodels derived from geophysical, petrophysical and geological data on computers bas always been a problem in Exploration and Production of Oil and Gas. Especially the discrepancy between the various geometrical scales used for the various geophysical and geological properties has prohibited the availability of a fully integrated computerized facility to build, rnanipulate and view the 3D subsurface model geometry with their properties at all scales. An extension has been constructed to the GOCAD interactive 3D modelling facility to handle models at different scales describing different properties in an integrated way.
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2D Synthetics and interpretation of deep seismic profiling data from Skagerrak
Authors O. A. Sandvin, E. S. Husebye, B. Rosland and J. E. LieThe evolutionary history of a basin is in general attempted reconstructed on the basis of the relative distribution of sedimentary strata as a function of the geological history. Associated basin extension models, say of the McKenzie type, presume a homogeneous crust subject to uniform stretching. The validity of such a hypothesis can be examined on the basis of deep (16-40 sTWT) seismic reflection data and is the topic of this presentation.
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Non-standard P-and S-wave experiments at the KTB deep drilling site: Nature of reflections and seismic anisotropy of crystalline rocks
Authors E. Lüschen, W. Söllner, A. Hohrath and W. RabbelThe interpretation of standard 2D-reflection profiling data collected in crystalline areas often suffers from the lack of direct calibration. Deeper crustal reflections differ significantly from those known from industrial sedimentary basin surveys. Although they are often very bright, reflections from crystalline rocks appear discontinuous and of chaotic or, in the lower crust, of laminated character.
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Shear wave investigations at the KTB deep drilling site
Authors W. Rabbel, E. Lüschen, W. Söllner and A. HohrathIn 1989, after the pilot hole of the Continent al Deep Drilling Project (KTB, Oberpfalz, F.R.G.) had beed finished, an extensive seismic survey was carried out at the KTB site by the German DEKORP group. Besides a 3D-reflection survey a large number of special experiments were realized in order to get a comprehensive petrophysical description of the rocks in the KTB surrounding. Parts of the data basis of this so - called Integrated Seismics Oberpfalz (ISO 89) had been presented during the last EAEG meeting in Copenhagen, Denmark. Meanwhile first interpretations are available.
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A high-density 3-component reflection-refraction survey across an exposed lower crust in Southern Italy
Authors E. Lüschen, M. Romanelli, J. Feddersen, R. Nicolich and L. CernoboriThe outcropping crystalline basement of the Serre Mountains in Calabria (Southern Italy) presents a tilted block containing a nearly complete section of the continentallower crust (granulites, metabasites). This has been regarded as key area to study the structure, composition and evolution of the Hercynian lower crust in a multidisciplinary approach. Petrological, petrophysical and structural data are available from surface mapping and laboratory experiments at varying P-T conditions on rock samples. Using these data as direct input for modelling techniques, the seismic in-situ characteristics, e.g. the reflectivity and the P- and S-wavevelocities can be interpreted. Since direct observations of the actual lower crust are not possible, this calibration of a fossil lower crust is expected to provide a better understanding of deep seismic results.
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Shot gathers amplitude and frequency processing and fast prestack depth migration. Application to ECORS deep reflection seismic data
Authors A. Bitri, D. Rappin and J. M. MarthelotStacked sections of ECORS deep reflection seismic profiles are characterized by: - an important variability in the lateral continuity of the reflections, - the presence of transparent zones, - the occurrence of highly dipping reflections, - the often strong and complex reflectivity of the lower crost. The CDP stacking procedure may not be well adapted because: - the quality of the shot gathers is quite variable, - the reflection events are assumed to have continuous hyperbolic moveout, - the lateral smearing of the CDP on dipping reflectors is large since the spreads used are long, - normal moveout is a dip selective procedure.
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The application of shear waves to studying the upper part of section with view to detecting the karst zones
Authors T. I. Oblogina and D. A. KouchenevThe shear SR-waves were used for studying the upper part of the geological section in the Moscow region. The field observations were carried out by the refraction and reflection surveys.
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Algebraic reconstruction for 3D seismic quality control
More LessDerived from medical applications, algebraic reconstruction techniques (ART) were first implemented by geophysicists for crosswell tomography (Bois et al, 1972 ; Bishop et al, 1985 ; Paulson et al, 1985; lvansson, 1985). 2-D refraction cases were recently studied (krajewski et al, 1989 ; Ruhl and Luschen, 1989), using a particular ART variant known as Simultaneous Iterative Reconstruction Technique (or SIRT), whereby each model bin slowness is modified when all raypaths pertaining to that bin have been taken into account .
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Two case histories of diffraction tomography applied in engineering geophysics
More LessThis paper presents the application of diffraction tomography to real data in engineering geophysics. In the past many papers developed the theory of diffraction tomography and discussed possible applications (Devaney and Beylkin, 1984; Wu and Toksöz, 1987). This new inversion technique is based on the acoustic wave equation. It tries to reconstruct the velocity perturbation against a constant background (constant density assumed) from a scattered, diffracted wavefield. In contrast to traveltime tomography where only picked times of some phases are inverted diffraction tomography uses the full wavefield.
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Deep and shallow aquifer modelling from gravity and reflection seismic data in Southwestern Denmark
Authors S. Thomsen, H. Lyke-Andersen, B. H. Jacobsen and R. FribordGravimetry is efficient and cost effective as a means for revealing the horizontal geometry of shaIlow as weIl as deep aquifers. Depth resolution of this method however is poor.
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Integration of mineral exploration data using fuzzy set theory
Authors W. M. Moon and P. AnThe traditional geophysical information processing theory is founded on Boolean logic and in Euclidean space. However, accurate assessment of given sets of multiple layer exploration data requires that one must define preciseness of one's knowledge as precisely as possible. Fuzzy logic provides a theoretical means of quantifying imprecise information, which was first utilized as early as 1965 and has been extensively applied since in engineering and related sciences. Fuzzy set theory is tested and applied to integrate geophysical, geological and remote sensing data sets in this research.
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A combined square array resistivity and magnetic survey in the archaelogical site of Noville, Coruna, Spain
Authors M. J. S. Matias and F. E. R. AlmeidaGeophysical exploration techniques have been adapted to archaeological exploration successfully. The use of Exploration Geophysics in Archeology has proved to be a fast and economical tooI in excavation planning of archaeological sites.
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Bedrock fractures as seismic reflectors
By O. OkkoThis paper presents the interpretation of reflections from same very shallow fracture zones located at the depth of less than 250m and recorded in soundings carried out on bedrock outcrops and in boreholes. The resolution of the seismic reflection method is compared to the corresponding acoustic logs and other geophysical and geological investigations.
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Conventional and modern seismic investigations for elastic properties determination in gneiss-schist. A case history
Authors J. Louis, T. Papadopoulos, G. Drakatos and P. PantzartzisRefraction seismics and modern tomographic surveys were employed at Platanovrissi damsite on Nestos river in Northern Greece in an effort to investigate the dynamic elastic properties and rockmass condition of gneiss-schist which outcorps in the area and it is prone for a hydroelectric dam construction.
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3-component colored 'attribute seismograms'
Authors H. Steentoft and S. WendeAn integrated system for recording, processing and interpretation of seismic data has been developed in order to increase the resolution in near - surface measurements and to perform first analysis during the field measurements. An extensive 3 - component - processing software - package was installed on a 68000 CPU micro - computer for completion of this processing system.
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Test park for environmental geophysical measurements
More LessIn the last decade the role of geophysics has been increasing in prospecting and prevention of environmental damages in Hungary. The reason is that geophysical methods are the most effective, quick and economical tools and what is similarly important, they can be used without causing damages to the environment. Inspite of these favourable features these methods have not spread in the expected degree, because theory for application of geophysical methods in environmental protection has not developed sufficiently and application has not been proved with practical measurements.
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Geoel: An IBM PC algorithm for the automatic processing and graphic presentation of geoelectric data
Authors G. -A. Tselentis and G. DelisThis paper addresses the problem of automatic processing and interpretation of geoelectric data with personal computers. The main algorithm is divided into two processing stages. During the first processing stage, the field curve is aproximated by a group of layers which are determined automatically by the program in such a way that the resulting theoreticaI curve describes as close as possible the field curve. This operation is performed in the resistivity - space domain and the optimum number of layers needed to describe the resistivity distribution versus depth is determined from the algorithm.
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Model curves for vertical electrical sounding over 2D structures
Authors J. Pous and P. QueraltVertical electrical sounding is one of the most used electrical methods in Geophysical Prospecting and its application is restricted to those problems according to structures that do not differ strongly from stratified media. Even in these situations the simplicity of a near one dimensional earth approach is sometimes not reached and some important lateral resistivity variations may appear.
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Borehole-to-surface D.C. resistivity and time domain electromagnetics monitoring of contaminant plumes. A model study
Authors A. Zerilli and B. A. JamesContamination of ground water and soils is one of today's most pressing problem. It has its origin in a number of causes, such as improperly buried wastes, poor effluent disposal and improper use of agricultural and industrial chemicals and spillages. The waste migrate along paths determined by subsurface soil types, stratigraphy and presence of faults, shear zones and fracture zones.
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Transient airborne EM applied to geological mapping
By A. P. AnnanGEOTEM is a high performance time domain airborne EM (AEM) system developed for mineral exploration and geological mapping applications. The historical focus for transient AEM has been on direct detection of massive sulfide type targets or other mineralized zones which have intrinsically high electrical conductivity. A bi-product of airborne EM surveys, particularly transient airborne EM surveys, has been a wealth of data which has considerable potential for mapping geology but which has seen limited use. With the advent of high quality digital GEOTEM data, new applications are being addressed.
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Ground penetration radar survey design criteria
Authors A. P. Annan and S. W. CoswayGround penetrating radar (GPR) is now becoming a weIl accepted geophysical technique. Basic criteria for the design and execution of surveys as weIl as the processing of data subsequent to these surveys have yet to be established in any satisfactory form. Experience from many sites over the past 15 years have provided many useful guidelines for survey design and data presentation. In this paper, criteria which are helpful to the new user in this field are presented.
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The TRH procedure for transient soundings. Practical results and some new ideas
By K. L. KakasOn the Oostende meeting of EAEG in 1986, a simple depth inversion of transient (time-domain EM) soundings was suggested by the author for the CIL (coincident loop) layout. This procecure (called TRH, because the transformation goes from the time to depth via resistivity) has been proved serviceable for preliminary interpretation of sounding curves, and combined with master curves and/or interactive curve fitting, the results seem to be stables and geologically acceptable.
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Magnetic interpretation using the 3D analytic signal
Authors W. R. Roest, M. Pilkington and J. VerhoefWith the availability of large digital datasets of magnetic data (e.g. Committee for the Magnetic Anomaly Map of North America, 1988) the need for automated techniques for the analysis of magnetic anomalies is growing. Several methods have been developed that have been successful in predicting source characteristics, using certain assumptions.
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Apparent density mapping from gravity data using the walsh transform
Authors P. B. Keating and M. PilkingtonThe purpose of apparent density mapping is the identification of uniform density areas that can be related to geological units. Apparent density maps are usually calculated by linear filtering in the Fourier domain (Gupta and Grant, 1985). The Earth model is then a set of right rectangular blocks extending to depth d, below which significant contributions to the residual gravity anomaly do not arise.
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Depth determination from gravity gradients
Authors M. M. Gobashy, E. M. Abdelrahman and A. I. BayoumiEstimation of the depth to a buried structure from the horizontal or vertical gravity gradients (Hammer and Anzoleaga, 1975; and Stanley and Green, 1976) has drawn considerable attention. The simplest and most widely used method to determine the depth of a buried structure from gravity gradients is the Xe-rule (Piek et al., 1973).
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An efficient 2D resistivity inversion technique and its application
By H. ShimaFor two-dimensional (2-D) resistivity analysis, a number of inversion techniques have already been proposed (e.g., Shima,1990). However when underground is close to a horizontally layered structure, an one-dimensional (1-D) assumption is considered to be more effective in arriving a further accurate solution. To make the 1-D assumption more useful, I propose a filtering procedure that improves the sensitivity characteristics of the potenrial data obtained by a pole-pole array.
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Regional tectonics derived from gravity gradients
Authors E. Kilenyi and Z. SzaboTwo-dimensional filtering of Bouguer anomaly maps enhances different 'wavelengths' according to the applied parameters. The meaning of wavelength in gravity can be interpreted in a more familiar way: long waves - regional anomalies, short waves residual anomalies, very short waves - derivatives.
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Magnetic-anomaly map of the Republic of Yemen
More LessA standardised composite magnetic-anomaly map of the Republic of Yemen is presented. This has been compiled from 23 airborne surveys of widely differing specifications undertaken between 1975 and 1985. The airborne magnetic surveys flown on behalf of the Natural Resources Project of the Ministry of Oil and Mineral Resources over the central parts of the Republic of Yemen in 1985, which included a high altitude regional coarse grid survey, completed the magnetic coverage of the Republic. The magnetic-anomaly map of the Republic of Yemen has been produced by The Robertson Group plc for the Natural Resorces Project. The surveying and compilation was primarily financed by loans from the Arab Fund for Economic and Social Development with technical assistance from the United Nations Department of Technical Co-operation and Development (UN/DTCD).
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A new view of the gravity and aeromagnetic fields in the UK
Authors I. F. Smith, M. K. Lee, C. A. Green, A. J. W. McDonald and K. E. RollinPublished maps showing the regional coverage of both gravity and aeromagnetic data for the land and parts of the sea areas of the UK have been available for a number of years. These data are now available in digital form, which allow the geophysicist to take advantage of advanced analytical and imaging techniques. Horizontal and vertical derivatives, inversions, grey-scale and colour shaded relief plots are startlingly effective in defining structural trends and characteristic anomaly pattems.
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Integrated interpretation of borehole investigations for structural modelling of crystalline bedrock
By P. PitkanenThe poster presents an integrated approach to use various borehole investigation methods in order to analyze structural and hydrological properties of crystalline bedrock. Geological and geophysical borehole data are interpreted to obtain engineering geological structures of the rock mass. The results are applied for the creation of three-dimensional bedrock models. The structural interpretations are also used as a basis for geohydrological modelling.
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Integrated presentation of all data from well
More LessThe goal of this paper is to illustrate what can be achieved by using all available information in integrated form with the help of composite log, for correlation, formation evaluation and documentation.
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Multiple offset VSP and multiple component VSP data processing to improve structural definition
Authors E. del Pino and E. RamirezA flower structure with two prospective blocks was drilled in the northem central part of Lake Maracaibo. In order to define the structural position of the fault plane separating the two blocks and its distance from a well driIled into the upper block, a multi offset 3 component VSP was acquired immediately upon penetration of the top of the structure.
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VSP and steep reflectors: A case history of data processing and interpretative modelling
Authors F. Ogliani and J. MullerIn the presence of dipping reflectors, a zero-offset VSP allows a lateral investigation far from the well. In data processing, such property is routinely exploited when reflectors are gently dipping or involved in salt tectonics. Some aspects, however, may become not familiar or problematic, when structural dips exceed 45 degrees.
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Evaluation of the VSP technique in the northern part of the Oseberg Field - A case history
Authors H. Rutledal, S. E. Johnstad and V. DanielsenThe Oseberg Field was discovered in 1979 and is located in the North Sea Norwegian Blocks 30/6 and 30/9 about 140 km west-northwest of Bergen. The field is a fault trap reservoir with about 600 m of structural relief at top reservoir level, and consists of three major eastwardly rotated fault blocks: Alpha, Gamma and Alpha North.
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