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60th EAGE Conference and Exhibition
- Conference date: 08 Jun 1998 - 12 Jun 1998
- Location: Leipzig, Germany
- ISBN: 978-90-73781-09-2
- Published: 08 June 1998
1 - 100 of 489 results
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Tomography and Depth Imaging
By R. BloorBuilding a depth velocity model for prestack depth migration is a time consuming and complicated task . To assist this talk we require as much a priori information as possible. Additionally we use the simplest methods which will address the problem of building the vetocity model for the current structure (Bloór et al. 1997, Stork et al. 1997). However, as structure becomes more complicated we have to resort to more complex methods to determine the vetocity model.
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Testing the Behaviour of Differential Semblance for Velocity Optimization
Authors H. Chauris, M. Noble and P. PodvinBackground velocity estimation is a critical step for the depth imaging process. Because of constant increase of acquired 3D data volumes, this velocit estimation, cast as an inverse problem, should be automated (no picking).
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Velocity Macro Model Estimation by Stereotomography - Application to Real Data
Authors F. Billette, G. Lambaré and P. PodvinIn [1] and [2], we introduced a. new tomographic method, Stereotomography, for estirnating velocity macro rnodels from seismic reflection data.
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Dispersion of 3D Velocity Estimators
More LessWe study the dispersion of the estimators of a 3D velocity model in presence of white noise and with a limited range of azimuths available.
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CRP-Scan - Solving 3D PreSDM Velocity Analysis with Zero-Offset
Authors F. Audebert, P. Guillaume, X. Zhang and I. JonesMigration velocity analysis (MVA) should allow interpreters to check and improve the complex velocity models required for 3D pre-stack depth imaging
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3D Adaptive Tomography by the Fresnel Criterion
Authors P. Galuppo, G. Böhm and A. VesnaverSeismic tomography adopts usually ray tracing as the forward modelling tool for the traveltime inversion.
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Estimation Laterally Varying Velocity Models Using Focusing Operators
Authors R. F. Hegge and J. T. FokkemaThe estimation of macromodels containing laterally varying velocities presents no problem for the method which is based on on the global inversion of focusing operators.
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Practical Anisotropic Imaging
Authors R. Schmid, P. Butler and R. VestrumThere is a strong resurgence and renewed interest in the study of anisotropy. Most of the excellent research involves the theoretical aspects, studying anisotropy in flat lying beds, or using shear wave anisotropy in fracture detection. It is natural and fitting that anisotropy research is performed in the depth domain. However, most depth imaging is performed in complex structural environments, typically for thrustbelt or subsalt imaging. Therefore, truly practical depth imaging which attempts to correct for anisotropic affects must deal with dipping anisotropic geologie formations.
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Pattern Recognition and Subtraction of Coherent Noise
By S. SpitzA crucial issue when processing seismic data is the ability to remove coherent noise while preserving the amplitudes of the signal. Strong noise (multiple reflections, ground roll, converted waves in compression mode analysis) interferes with the signal and can lead to incorrect pre stack attributes and to erroneous interpretations of the final images at target level.
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Tests of a Two-Step Correction Procedure for Long-Offset Data
Authors F. K. Levin and R. C. ChambersThe use in recent years of offset-to-reflector depth ratios of two or three rather than the unity common earlier has resulted in traveltime-offset curves that are not hyperbolic. For long offsets or where anisotropy is important, a need to include a quartic term in the squared traveltime-squared offset function has been established. Long offsets are common today for AVO analysis in areas such as the Gulf of Mexico.
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Traveltime Picking in 3D Data Volumes
Authors N. Bienati and U. SpagnoliniTomography, seismic imaging, and statics require the estimation of traveltimes from 3-D pre-stack data volumes. Manual interpretation is known to be time consuming and not free of errors. We propose here an automatic and robust traveltime picking of 3-D data volumes that avoids (or at least aids) manual intepretation
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Is Common-Offset Common-Azimuth DMO Really That Bad?
By R. FerberThe cross-spread is the basic subset of the orthogonal geometry. It is a single-fold 3D data set which was shown by Vermeer et al. (1995) to be suitable for DMO. This was good news, because DMO was usually regarded as an operation on common-offset common-azimuth (COA) subsets of the acquisition geometry.
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Interactive Polarization Filtering of Nine-Component Seismic Data
By A. H. BalchSome areas of geologic and economic importance are so hostile to seismic investigations, that processing and interpretation of data obtained there remain difficult or impossible, despite the best state-of-the art field and processing procedures
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Practical Wave Equation Datuming
By M. StanleyApplication of Wave Equation Datuming (WED) can produce dramatically improved seismic images. However the technique has not received the degree of acceptance it probably deserves for a number of reasons
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A New Cost-Effective Approach to Statics in Sand Dunes Areas
Authors P. Storer, A. Corrao and M. PastoriStatics computation for reflection seismic in areas covered by sand dunes still remains a challenging problem in the hydrocarbon exploration activity
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A Novel Approach to Cost Effective 4C/4D - the Teal South Experiment
Authors D. Ridyard, P. Maxwell, G. Fisseler and S. RocheUntil quite recently, multicomponent recording has been a minor part of the seismic market, and systems have required expensive and time consuming adaptation to facilitate 4-C recording (three component velocity plus a pressure transducer). The cost and inconvenience of these adaptations has lead to a cost premium in 4-C. As the value of 4-C is becoming apparent, from numerous experimental surveys, it is now time to rethink some of the basic system design concepts to address the practicalities of efficient 4-C recording.
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Seismic Detector Positioning in a 4D/4C OBC Survey Using Both Acoustics and First Breaks
More LessIn the summer of 1997 Texaco conducted, over their Teal South field, the first time-lapse (4-D), multicomponent (4-C), ocean bottom cable (OBC) seismic survey in the Gulf of Mexico.
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4C Sea Bottom Receiver Evaluation
Authors J. Meunier, J-J. Chameau, J. Bijou and J. MaidaSummary not available
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On-Board Processing of Ocean Bottom Cable Multicomponent Data
Authors N. Jones, J. E. Gaiser and E. AngererHistorically, observations of shear-waves in the marine environment began with the work of oceanographic institutes in their investigations of ocean-crust velocity structure.
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t-p Domain Combination of Dual-Sensor Ocean Bottom Cable Data
By R. WombellOBC data is usually processed assuming normal incidence and ignoring angular variations in the geophone response, water bottom reflectivity and reverberation period. A z-p domain decomposition allows the angular variations within the data to be separated and handled. An approach to handling the ghost attenuation is described
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An Essential Processing Correction for Seabed Recording
By C. MacBethThe processing of recordings made at, or near, the seabed is rendered inaccurate by naturally occuring amplitude and phase changes
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Azimuthal Moveout Analysis for Fracture Detection in Marine Streamer Data
By X-Y. LiIn dual-sensor ocean-bottom-cable surveys both pressure and velocity data are recorded. Both data sets contain the up-going energy convolved with their corresponding receiver-ghost operators. The ultimate goal of dual-sensor processing is to eliminate the ghost response and the water bottom reverberation
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Hydrophone-Geophone Deghosting of OBC Data in the t-p Domain
By R. BaleThe receiver ghost for ocean bottom recording, unlike a towed streamer ghost, generates notches in the seismic passband. Fortunately, the positioning of dual or multi-component sensors on the sea bottom presents an opportunity for removing the receiver ghost and reverberation sequence whilst producing a single combined output from the hydrophone and geophone
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3D Target-Oriented AVO Inversion of Data from the Statfjord Field
Authors S. Østmo, E. Tjåland, A. Buland and R. SollieStratigraphic full waveform AVO-inversion is a powerful technique for determining P- and S-wave velocities and densities from seismic pre-stack data
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AVO Behaviour at the Top of a Class-4 Sand - a Case Study of the Maitland-1 Well
More LessThe Maitland gas field is located in the Barrow Sub-basin, offshore Western Australia. The well Maitland-1 was drilled in September 1992 on a strong amplitude anomaly. It intersected a 23m thick land with gas saturation. The well was plugged and abandoned as a gas discovery (Sit).
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Improved Seismic Resolution of the Ty Reservoir by AVO-Processing, Sleipner Øst Field
Authors K. Duffaut, T. Erling and K. HorpestadThe field has its main production from a Paleocene deepwater sandstone reservoir . The main geophysical challenges in the field have been to identify the top reservoir, the reservoir pinch-out zone and internal reservoir geometry. To understand the seismic response at reservoir level a geophysical modeling study (including AVO-modeling) was performed. Well data and pre-stack data from 10 lines were used in the modeling. The modeling showed that the mis-tie between synthetic seismograms and surface seismic data in the hydrocarbon bearing part of the reservoir was caused by an AVO effect. Both the modeled and the real CMP-gathers showed a rapid decrease of the amplitude with offset including a polarity reversal. To avoid the effect of this polarity reversal on the stacked data the concept of Intercept-stack was introduced. The Intercept-stack is an extrapolation of the near offset reflectivity to zero offset.
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Postcritical-Angle AVO for Carbonate Reservoirs
Authors O. K. Youn, H-W. Zhou, S. A. Hall and R. E. SheriffMost carbonate reefs under shale have small critical angle and small amplitude variation with offset (AVO) in the precritical offset range.
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AVA and Residual Moveout
By I. MooreIt is well known that residual moveout can cause large errors in the estimate of amplitude versus angle (AVA) attributes, and in particular in the estimate of gradients. This paper illustrates the problem and proposes two complementary approaches to reducing the effect. Synthetic data are used to assess the effectiveness of these methods, which have also been applied to real data.
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Are Near-Offset Shear Wave Conversions Useful?
By C. MacBethIt is standard to record near-or zero-offset VSP with three-component receiver tools. However, the principal use of these data is to determine model velocities and a high resolution section as an aid to interpretation of surface seismic data. These objectives are fulfilled using only the vertical component recordings.
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Amplitude Versus Offset for Refracted Waves
Authors P. Borejko, E. Brückl and W. ChwatalThe analysis of amplitude versus offset (AVO) is widely used in reflection seismic processing and interpretation. By this technique lithological information (S-wave velocity and density) can be extracted from P-wave reflection coefficients.
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Viscoacoustic Asymptotic Waveform Inversion of Ultrasonic Laboratory Data
Authors A. Ribodetti, H. -P. Valero, S. Operto, J. Virieux and D. GilbertIn this study, we test asymptotic diffraction tomography for viscoacoustic medium imaging by scaled model ultrasonic experiment. Diffraction tomography (namely, the inverse scattering problem) is a useful technique to save various classes of problems involving non destructive evaluation such as seismic exploration and ultrasonic medical imaging . Diffraction tomography is used to image the discontinuities of parameters describing the medium both in terms of localization and true amplitude of the discontinuities.
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Joint 3D Inversion of Direct and Reflected Arrivals from Surface and SWD Seismic Data
Authors G. Rossi, P. Corubolo, G. Böhm, P. Dell‘Aversana and E. CeragioliVertical Seismic Profiles (VSP) provide an effective tie between well information (as logs and core analysis) and surface seismics, by linking the local geology to the Earth reflectivity. Seismic tomography gets similar benefits from the joint inversion of direct and reflected arrivals, recorded both at the surface and in a well.
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Stochastic Inversion of Seismic Data by Evaluation of Pseudo-Wells
Authors B. Bril and P. De GrootA seismic inversion method is described based upon the ranking of realistic local subsurface models. Real wells and/or stochastically simulated pseudo-wells are scored at real seismic locations for seismic response and geostatistical probability. The resulting scores are analysed to yield both detailed local and generalised spadal information on geological and petrophysical subsurface properties.
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Statistical Reservoir Thickness Estimation
By A. G. SenaWith the increasing availability of 3D seismic data, good quality amplitude maps can be generated for prospective horizons. In interpreting these maps the quantification of how much pay is involved is essential and difficult to obtain. By analyzing reflection amplitudes from nearby well log data, a systematic analysis of the amplitude variation with respect to lithology, porosity, hydrocarbon pore fluid saturation, bedding geometries, and reservoir thickness con be carried out.
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Spatially Varying Wavelet in Seismic Inversion
Authors K. B. Rasmussen, H. Wagner and J. M. PedersenWith the introduction of relatively fast globally aptimized post-stack seismic inversion it is now possible to apply post stack seismic inversion of large seismic data volumes. Large seismic data volumes challenge the normal assurnption that a constant wavelet can be used to describe the relationship between acoustic impedance reflectivity and the seismic data for the whole tube. For this reason the determination and use of a spatially varying wavelet has been developed. It is presented below.
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A High-Order Pertubative Approach - Examples of Inversion
Authors A. Druzhinin and A. HanygaA common procedure in nonlinear seismic inversion involves least squares optimization (LSO) [6,8] implemented by various Newton type iteratie algorithms [4]. Recent papers [2,3] indicate that the highorder perturbations can overcome the problems of the LSO concerning initial guess, a priori information, CPU/acquisition costs, etc. The purpose of this paper is to show how such additional constraints can be incorporated into the available LSO algorithms without their special modification.
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Can we Image Complex Structures with Ray-Born Inversion?
Authors S. Xu, S. Operto and G. LambaréSummary not available
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GPR Theory and Simulation in 3D Realistic Media
Authors J. M. Carcione, F. Cavallini and M. SchoenbergThe increasing use of ground-penetrating radar (GPR) for solving a wide range of engineering and environmental problems has been pushed by the application of seismic standard techniques, such as multi-fold coverage and processing.
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Multisource Prestack Depth Migration - an Application of GPR Data
Authors M. Barsotelli-Botelho and I. MuftyThe method of reverse-time migration is widely know for high-quality results as well as extremely high computational colts.
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Filtering of Radargram-Traces with the Wavelet-Transform
Authors C. Seegraef and B. ForkmannGround penetrating radar measurements represent a relatively new, fast and high-resolution investigation method for near surface objects. To explain and to interpret phenomena occurring in nature preliminary investigations with synthetically made radargrams have to be done.
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Influence of Hydrogeologic Properties on the Dielectric Permittivity of Sand Cray Mixtures
Authors T. Heßland, E. Moise and P. SchikowskyPorosity, internal surface area, pore filling, grain size, and temperature have great influence on the velocity of propagation of electromagnetic waves in granular soil. Therefore we investigated these parameters in laboratory to estimate their relevante for field measurement with Ground Penetrating Radar (GPR). Furthermore we verified the applicability of a whole range of mixing formulae which are important for the computation of water content from the propagation vetocity of radar waves.
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Imaging Structures under a Steel-Reinforced Concrete Floor
Authors J. B. U. Haldorsen, D. E. Miller and F. GilbertWe had undertaken a study aimed at assessing the quality of images obtained with ground-penetrating radars (GPR). Using the commercial, impulsive pulseEKKO 1000 from Sensors & Software, and non-standard acquisition geometries, we had collected several 3-D datasets in a natural, suburban environment in Newtown, Connecticut. When approached by the building manager at our Ridgefield research center who needed to break open a floor in one of the workshops for the construction of a new elevator, we thought it a challenging opportunity, particularly considering the steel rebars we expected to find in the floor of the workshop.
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Cavity Identification with GPR Using Variable Offset and Antenna Orientation
Authors A. Helm and U. YaramanciIn GPR, exploration it is of major interest to identify reflector lithology directly using their reflection characteristics. Investigations have been made with simple reflectors especially on cavities in a mine in saliniferous surrounding. The detection of cavities is not only important for mine security but also for eliminating disturbances in the GPR section.
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Verification of Subsurface Pollution Barriers Using Ground-Penetrating Radar
Authors J. B. U. Haldorsen, F. Gilbert, D. E. Miller and L. PellerinDuring August 1997, a project organized by Lawrence Berkeley National Laboratory was carried out on the grounds of Brookhaven National Laboratory. The purpose of the project was to test the feasibility of controlling buried contaminants by injecting colloidal silica (CS) gel to form an impermeable barrier around the contaminants. Geophysical techniques such as ground-penetrating radar (GPR) may be used in an attempt to verify the structural integrity, extent and bulk hydraulic conductivity of a subsurface barrier.
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Induced Polarization Effects in Frequency and Time Domain Electromagnetic Soundings
Authors S. Krylov, N. Bobrov and B. WächterBoth frequency and time domain electromagnetic soundings are widely employed for solving various near-surface geotechnical problems. The experience of field work has shown that the results of soundings often can be distorted by the frequency dispersion of resistivity which is caused by induced polarization (IP).
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Using PRBS-Sequences as Source for TEM-Measurements
By S. L. HelwigThe transient electromagnetic method (TEM) is a well known tool to investigate the subsurface distribution of electrical resistivity
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TEM Measurements in Bolivia - Comparison of Different Fast Interpretation Methods
Authors S. Greinwald, S. Dautel, C. Grisseman and A. HördtA geophysical survey using Audiomagnetotellurics (AMT), Transient-Electromagnetics (TEM) and Induced-Polarisation (IP) measurements was carried out near the former silver mine at Pulacayo, Bolivia, in 1995. The aim of the survey was to support a structural geology investigation of the mineralized volcanic stock. TEM soundings seem to present the most useful information.
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CMP Method Applied to Multichannel Transient Electromagnetic Data
Authors A. Ziolkowski and B. HobbsWe propose a methodology to enable seismic data processing methods to be applied to MTEM data. In particular, horizontal stacking can be applied to common mid-point gathers of MTEM data in the logarithmic-time domain for signal-to-noise enhancement and (in principle) resistivity estimation. In practice, source static corrections must be very precise.
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Analysis of Time-Lapse TEM Data for Underground Gas Storage
More LessNatural gas is an increasingly important energy resource in Europe. Companies are seeking new storage sites, such as depleted reservoirs or deep aquifers. Monitoring of changes in gas volume is crucial to avoid losses and to use the site at its optimum, capacity. The standard method to monitor the gas movements is to drill monitor wells, which are expensive and give information only about the near vicinity of the well. Electromagnetic (EM) methods have the potential to support the monitoring from the surface and to save drilling costs. They are sensitive to changes in electrical conductivity, and thus to movements in the gas/water contact. To demonstrate the feasibility of EM methods to monitor changes in underground gas storage sites, two transient EM surveys were conducted over a gas storage in France. The aim was to use the differences in the data from the two surveys to detect changes in the subsurface.
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Magnetotelluric Investigation in the Polish Western Carpathians
Authors J. Miecznik, E. Jaword, A. Pepel and A. WajdaObjectives of the magnetotelluric survey in the Carpathians (southern Poland) include identification of the structure of the Carpathian orogen and the topography of the crystalline basement as well as prospecting for hydrocarbons.
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A Trial Application of Streaming Potential to Detecting Underground Water Movement while Pumping up
Authors H. Sato, H. Shima and T. ToshiokaWe are researching about the streaming potential for the purpose of detecting groundwater-flow utilizing the electrical potential clistribution generated by watermovement. Sill(1983) theoretically calculated the streaming potential ctistribution, and Ishido and Mizutani (1981) investigated the theoretical basis and carried out experimental studies. At a geothermal area, the streaming potential is used to investigate the geothermal heat-flow. From an engineering point of view, the determination of groundwater-flow or permeability using the streaming potential distribution seems an attractive technique. We investigated the streaming potential in field and laboratory experiments and investigated its nature during water-extraction at a well.
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Effect of Pore Aspect Ratio on the Seismic Wave Attenuation in Porous Rocks
Authors B. Gurevich and J-L. AuriaultSeismic wave attenuation in porous rocks is an important parameter for the characterization of hydrocarbon reservoirs. The two main physical mechanisms of the attenuation in saturated porous media are associated with the viscous forces caused by the so-called global and local fluid flows of the pore fluid, respectively.
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Permeability from Acoustic Impedance and the Characterization of Fracture Flow
More LessIt is becoming increasingly important to provide a better understanding of the mechanisms of fluid flow through low permeability fractured rock systems and to satisfy the ever more sophisticated needs of hydrocarbon exploration and production
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Inversion for the Tensor of Permeability Using Fluid-Injection-Induced Seismic Emission
Authors S. Shapiro, J-J. Royer and P. AudiganeDuring fluid-injection tests in boreholes a spontaneons seismic emission (microearthquakes) can be induced in rocks. We assume that these seismic microevents are due to the perturbation of the porous pressure caused by the fluid injection.
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Controlling Fluid Extraction from Reservoirs by Monitoring Ground Deformation
Authors K. Lehmann and H. -J. KümpelTo assess rock matrix effects from fluid extraction (like subsidence, compaction, pore fluid depletion), numerical modelling is often used. For this purpose, the knowledge of adequate petrohydraulic parameters is essential.
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Rock Physics for Exploration West of Shetlands
Authors J. Bingham, A. Andrea, J. Hook, R. Simm and J. GallagherSummary not available
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A Comparison of Prestack Migration Gathers Formed by Equivalent Offset Migration (EOM) and DMO-PSI
Authors J. C. Bancroft, G. Margrave and H. D. GeigerConventional prestack migration methods that incorporate some form of velocity analysis, use either constant offset sections, or source gathers (shot records). When the velocities are known, these methods should give identical migrated .images. When the velocities are not known, velocity analysis is attempted by applying inverse NMO (INMO) based on arbitrary assumptions of offset, and with the prestack migration gathers formed at CMP locations.
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An Introduction to the Common Reflection Surface Stack
More LessThe success of standaxd seismic reflection imaging routines, such as Prestack Depth Migration or NMO/DMO/stack depends on the required macro-velocity model. Since their Kirchhoff type implementations collect all possible measured reflections events belonging to either a point in the time or in the depth domain they cannot account for the correct shape of the reflector. In contrast, a common-reflection surface (CRS) stack is a selective stack which depends only on the near-surface velocity. The CRS stack provides a new powerful approach to construct simulated zero-offset (ZO) sections from multicoverage reflection data. It accounts for arbitrary reflector shapes and enables us to establish the macro velocity model after the zero-offset simulation.
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Interval Velocities Inversion Using NIP Wave Attributes
Authors J. C. R. Cruz and H. L. MartinsA new inversion procedure to estimate the interval velocities model is presented in this paper. This is based on the search of two normal-incidence point (NIP) wavefront attributes, namely the radius of curvature and the incidente angle. These attributes are determined with help of one coherency analysis, that is applied to a set of seismic traces pertaining to the multicaverage reflection data corresponding to one common-reflection- point, the so-called Common -Reflecting-Element (CRE) gather.
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Three Dimensional Traveltimes Using the Fast Marching Method
Authors M. Popovici and J. SethianA fast, accurate and unconditionally stable 3-D traveltime algorithm is an important tool in seismic imaging. Applications of a robust traveltime computation module are not limited to 3-D Kirchhoff prestack and poststack migration, but also can be used for 3-D velocity analysis, 3-D Kirchoff modeling, 3-D Kirchhoff datuming, and 3-D variable velocity migration to zero-offset.
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Resolution of the 3D Eikonal Equation Parameterized in Celerity in Weak TI Media
By A. PicaEikonal equation solutions are widely used as an approximation of the Green's function in 3D prestack depth migration processing using the Kirchhoff integral method. They represent in many cases an accurate and cost effective way of computing traveltimes. Nevertheless, the increasing size of acquisition surfaces to be modeled, as well as the increasing depths of the required targets, imply that this stage of depth processing, is not negligable at all in global turnaround. This fact is even more critical as this operation has to be iterated several times for image gather analysis used in macro-model construction.
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Prestack Elimination of Complex Multiples - a Gulf of Mexico Example
Authors G. Cambois and A. GuittonThe complexity of salt structures in the Gulf of Mexico imposes the use of prestack depth migration tor subsap imaging. As exploration moves to deeper water, the presence of surface multiples makes subsalt imaging even more difficult. Standard prestack multiple elimination techniques, such as Radon transforms, fall in the presence of complex structures. The surface multiple elimination technique popularized by the DELPHI consortium offers an attractive alternative since it is theoretically independent of subsurface structure.
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Three Dimensional Multiple Moveout Transformation for the Removal of Water Bottom Seismic Multiples
Authors B. M. Hartley, M. G. Lamont and N. F. UrenA two-dimensional wave-field transformation which is useful for pre-conditioning shot records to enhance removal of multiples has been described previously [1]. This wave-field transformation renders water bottom multiple reflections in a shot record into equally spaced horizontal events.
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Non-Wiener Filter, or Sharp Deconvolution in Elimination of Multiples
Authors G. Ryzhikov and M. BiryulinaThe problem of multiple suppression is of interest up to now despite of its long-standing. A new approach for attenuation of multiples in "locally 1-D" environment is suggested, which is illustrated here with well-controlled processing of synthetic data.
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Wave Equation Prediction and Removal of Interbed Multiples
More LessThe succes of multiple suppression for seismic data often hinges on the accuracy with which the multiple behaviour can be predicted. This is especially true for interbed multiples where small details can be essential for distinguishing the multiples from surrounding primaries. In this paper we describe a new wave equation method of predicting interbed multiples from primary events. This scheme can be used to estimate multiples directly from measured data and has been incorporated into a new suppression technique.
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PEG-LEG Attenuation in Ocean Bottom Acquisitions
By R. SoubarasSeveral methods for processing hydrophone and geophone ocean-bottom acquisitions have been proposed in recent years. The aim of this paper is to examine the way in which these methods address the peg-leg attenuation problem, and compare with streamer data peg-leg attenuation methods. The main conclusion is that the peg-leg attenuation problem is basically the same for ocean-bottom as for streamer acquisitions, and that we should take advantage of our experience in peg-leg attenuation of streamer data far ocean-bottom processing.
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Overburden Removal for Marine Walkaway VSP
Authors M. Higgins, C. MacBeth and A. ZiolkowskiSummary not available
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Migration in Transversely Isotropic Media by Cascading Isotropic Operators
By D. RistowIsotropic migration algorithms for seismic data from anisotropic media produce onder certain conditions large position errors for steep reflectors.
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Anisotropy Effects in a Three-Component 3D VSP
Authors G. Rossi and A. VesnaverFractured rocks with a regional trend of faults constitute several hydrocarbon reservoirs. Often, their cracks cannot be observed directly by seismic waves: then, an equivalent medium with an azimuthal anisotropy is the only reliable way for estimating their presence. The crack directions decide the fluid movements in the reservoir: thus, the detection of the anisotropy type allows optimising the depletion wells for oil and gas production.
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Prestack Anisotropic Imaging
Authors Y. Le Stunff and J-P. JeannotAnisotropic pre-stack depth migration is likely to improve image quality and depth calibration in area where anisotropy has been identified (e.g. Sena and Taksóz,1993). It is rather straightforward to implement the kinematic effects of week anisotropy in a Kirchhoff migration algorithm.
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A Case Study of the Application of 3D Seismic to Mine Planning
By R. BjoroyIn die 1980s high resolution seismic reflection was utilised as an investigation technique in the Waikato coalfields. The results from the Huntly Coalfield were disappointing, mainly due to the poor design of the acquisition parameters.
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3D Seismic Imaging of a Deep Massive Sulfide Deposit
Authors B. Milkereit, E. K. Berrer, A. Watts and B. RobertsThe Sudbury Basin is the richest nickel producing area in the world with significant by-products in copper and precious metals. The Basin hosts numerous mines along the outer rim of the Sudbury Igneous Complex (SIC), a differentiated sequence of norite, gabbro and granophyre overlain by breccias and metasedimentary rocks.
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Geophysics for an Exhausted Cromite Field, Kayseri, Turkey
More LessInvestigation site takes place in middle Taurus region, near Kayseri, where ophiolites occupies the whole field. There are numbers of mines, in the area, producing cromite from Anatolian polyform type mineralization nested in ultrabasic rocks situated at the bottom of ophiolitic series.
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Lateral Effects Problem in Shallow Refraction Seismic Interpretation
By H. H. SeisaThe first and probably the most important step in shallow refraction seismic measurements is to decide in the field whether there are lateral changes along refracting interfaces or along the overburden layer(s), while the second step is how to detect these lateral variatians with a minimum number of profiles. The problem associated with lateral variations along the overburelen layer(s) is considered to be a very difficult problem for the shallow refraction seismic technique. This is because the head wave traveltime elements recorded from the lower refractor have pseudo apparent refractor velocities, pseudo inflection points and usually an increase or decrease in their number. Surprisingly, this problem is rarely discussed in literature, and if ever, it is often without suggestions for identification or solution, so the name lateral effects is used to define it.
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Dispersive Waves and their Applications in Civil Engineering
Authors J-L. Mari, F. Glangeaud and J. -L. LacoumeIn surface seismic survey, the ground roll is composed of surface waves which are pseudo- Rayleigh waves and Love waves. The waves are dispersive and the analysis of their dispersive curves is useful to evaluate the mechanical parameters of the layers near the surface. Love waves consist of horizontally polarized shear waves trapped in the superficial layer which propagate by multiple total reflections.
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Geomechanical Paramters of Overburden Dumps from Seismic Wave Velocities
Authors T. Roth and P. SchikowskySeismic measurements combined with drop penetration tests have been completed to investigate geomechanical parameters of overburden dumps of operacast coal mines.
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The Application of Electrical Tomography in Geotechnical Investigations
Authors S. Abdul Nassir, M. H. Loke and C. Y. LeeIn conventional site investigations a large number of boreholes has to be deployed over the site in order to obtain sufficient information about the subsurface structure. The subsurface conditions between these boreholes are assumed by correlation (Clayton, et al., 1982). If a large number of boreholes is required the cost of the investigation can becorne prohibitive. The Electrical Tomography (imaging) technique (Griffiths and Barken, 1993) is an equivalent data acquisition technique that can be used to provide detailed information fan the surveyed area at a lower cost.
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An Application of Traveltime Anisotropic Seismic Tomography for Archaeological Purpose
Authors E. Cardarelli and R. de NardisIn the last few years, the knowledge of the preservation's degree of important monuments has become an important topic. In order to plan the restoration, it is important to know the main physical characteristics of the monument itself and its degree of decay.
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Comparison of Global and Local Optimization Techniques in Electromagnetic Applications
Authors B. Kriegshäuser and P. de LugaoIn this paper we compare the performances of global and local optimization techniques in electromagnetic inversion. Global optimization schemes, e.g., genetic algorithms, Nelder-Mead simplex method, simulated annealing, are becoming increasingly popular in geophysical applications, because they search the whole parameter space for the global extremum.
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Effects of Regularisation in the Inversion of Surface NMR Measurements
Authors U. Yaramanci, G. Lange and K. KnödelSurface Nuclear Magnetic Resonance (SNMR) is a new method for exploration of ground water recently put to regular operation with a field equipment which is now commercially available. The method is based on excitation of hydrogen protons by artificial magnetic fields oscillating with the local Larmor frequency and on recording the magnetic fields emitted by relaxation of precessing protons using the transmitter loop (Beauce et al. 1996).
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Assessment of the Reliability of 2D Inversion of DC Apparent Resistivity Data
Authors A. I. Olayinka and U. YaramanciThe objective in the two-dimensional (2-D) inversion of de apparent resistivity data is to determine the true subsurface resistivity distribution over any arbitrarily shaped 2-D structure. To do this successfuliy, it is essential that a good inversion scheme be able to simultaneously minimize the data rms misfit and the model rms misfit. With field data the true model is rarely, if ever, known precisely. Through model studies, such as is presented here, where the true solutions are known, realistic and assessment of the robustness of the inversion can be accomplished. The models investigated, for the Wenner array, include horizontal layering, fault, low and high resistivity fills, localised inhomogeneities, as well as the influence of noise contamination.
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3D Finite-Element - Simulation and its Application to the Mise á la Masse Method
Authors A. Radinger and J. PichlerIn the wide field of ground - water exploration there are some problems that have been brought to a solution by cooperation of geophysics and software engeneering.
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Nonlinear 3D Inversion of Crosswell Electrode Loggind Data
Authors A. Adubakar and P. M. Van den BergElectrode logging as known in the oil industry is a method for determining the electrical conductivity distribution around a borehole or between two boreholes from the electrostatic field (dc) measurements in the borehole. In this paper we discus the reconstruction of the conductivity in a three-dimensional Romain between two boreholes. The electric current density integral equation will be taken as point of departure. This vector integral equation leads to substantially better results than inversion based on the scalar integral equation for the electric potential. We will use a nonlinear inversion scheme based on a new method, the so-called Contrast Source Inversion method (CSI), recently introduced by Van den Berg and Kleinman (1997).
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Modelling of Three-Component EM Borehole Measurements to 3D Target
Authors R. Mononen, M. Oksama and H. SoininenThis paper summarizes results of the numerical modelling made for an EM borehole-system, in which both the magnetic dipole transmitter and three component receiver are in the same borehole (Lebedkin). Coil separation is fixed to values from 30 m to 120 m and the frequency range is from 20 Hz to 10000 Hz. Calculations were made by using MARCO software (Amira, Australia), which is based on volume integral equation formulation.
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Depth of Penetration of Frequency-Domain Airborne Electromagnetic Methods
More LessDepth of penetration for airborne electromagnetic (AEM) methods is defined as the maximum depth from which a given conductive body gives a recognizable anomaly when surveyed by a given AEM system.
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Impedance Estimation from Magnetic Field Measurement
Authors M. Gharibi and L. B. PedersenIn the VLF method, the ratio between the vertical and the horizontal magnetic field (the tippet) are measured to detect localized changes in electrical conductivity contrasts. The measurements themselves do not give a direct estimation of electrical conductivity contrasts. The tipper is merely an indicator of the presence of a conductivity contrast by exhibiting a well-defined response across a contact and decaying on either side.
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P- and S-Wave Velocities Measured in Dry and Saturated Sandstones and Predicted by Gassmann
Authors M. S. King, J. S. Marsden and J. W. DennisIn the area of oilfield reservoir management, recent developments in single borehole and cross-well seismology are now making it feasible to conduct high-resolution surveys to detect pockets of unswept oil and to monitor the progress of enhanced oil recovery processes.
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