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77th EAGE Conference and Exhibition - Workshops
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
101 - 128 of 128 results
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Quantifying Seismic Interpretation and Modeling Uncertainties while Building Salt Caverns
By B. OttoSummaryAs part of building a new salt cavern gas storage facility within a complex Zechstein salt canopy next to the village of Jemgum (Lower Saxony basin, Germany) a detailed geological site characterization was requested. Key input was a reprocessed anisotropic (TTI) controlled beam 3D prestack depth migration were 5D data regularization has been applied in advance of migration to improve seismic imaging. 3D velocity building was further supported by integration of 3D gravity data. In order to precisely determine the distance between cavern edges and salt interface various different salt models have been created by applying different workflows (manual seismic interpretation, adaptive seismic geobody building, supervised neural network building). Subsequently, instead of purely visual assessment, Hausdorff metrics have been calculated to numerically determine mesh differences of the salt interface. These numerical values have then been draped over the mesh to better visualize and efficiently detect mesh differences. Deployed methods and workflows have a very positive impact on spatial precision. It furthermore accelerates model building considerably.
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Estimation of Spatial Uncertainties in Tomographic Images
By M. JordanSummaryVelocity models derived from the inversion of seismic (or other) data often lack a clear indication of the associated spatial uncertainties, which are as important for the interpretation as the velocity models themselves.
Most common model appraisal methods only address the amplitudes of the velocity model parameters but are not able to estimate the error distribution of the location of the retrieved anomalies very well. We also expect that the distribution of the spatial uncertainties is not isotropic, but reflects the data coverage of the model space.
The approach presented here was designed as a test to study if accurate and quantitative estimates of spatial uncertainties (e.g., in meters) could be obtained from the analysis of equivalent models (similar models with the same data fit)
Our uncertainty analysis consists of a Monte Carlo-type perturbation of the velocity model to obtain a range of equivalent models. These equivalent models, taken collectively, indicate the spatial uncertainty. Due to the otherwise extremely large computational cost, the perturbations are guided by the a posteriori covariance matrix.
This presentation focuses on the method and its requirements, the lessons learned and the consequences for the application to third-party velocity models.
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Geostatistical Velocity Models for Assessing Seismic Uncertainty - An Application to Sub-salt Imaging
More LessSummaryWhile seismic data is used to interpret the structural framework, the uncertainties associated with the seismic data itself are often neglected for computational reasons. Structural uncertainty studies are often limited to perturbing horizons and faults around a single interpretation. We propose a method to assess the uncertainty in the seismic image itself through geostatistical randomization of the 3D seismic velocity model. A novel fractal algorithm is used to generate multiple 3D velocity models. To mitigate the computational costs of migrating all generated models, a model selection procedure is applied to select a representative subset of the models. Image registration techniques are applied to the resulting set of migrated images, providing uncertainty maps and as well as a distribution of structural elements, thereby yielding more realistic assessments of structural uncertainty. An application to 3D sub-salt imaging is provided.
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Modeling Structural Uncertainty in Depositional Domain Using Structural Analogs
Authors O. Aydin and J.K. CaersSummaryStructural model has a zeroth order impact for flow through porous media. Although seismic image is used extensively to understand structure and is increasing in quality, it may not able to resolve the structure (faults and horizons) in areas of interest due to low image quality. However, there can be areas in seismic data where structure can be extracted. In this paper, we propose ways to use the structure we observe in seismic image to model the structural uncertainty in area(s) of interest for which structure cannot be resolved. We make use of GeoChron to take the structural features from the physical domain they are defined into depositional domain to generate and evaluate fault realizations. This transformation makes generating multiple structural models with different fault groups, breakage patterns and hierarchies an easier task since. Ideas in this paper are elaborated on field data from offshore Japan, namely Kumano Basin, using the seismic data taken at the plate boundary at which there is complicated and partly unresolved structure.
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New Imaging of the Messinian Salinity Crisis - Uncovering a Salt Giant
Authors C. Gorini, L. Montader, M. Rabineau and J.L. RubinoSummaryThrough several examples we show that following sea-level fall and marginal erosion during the Messinian salinity crisis (MSC), clastic inputs into the eastern and western Mediterranean Sea are not distributed evenly in space and time but are mainly limited to the lower section of the Messinian salinity crisis depositional megasequence. Significant similarities around the Mediterranean Basin allow us to propose a Mediterranean Messinian salinity crisis depositional model. In the eastern and western deep basins the falling stage is illustrated by an early lowstand characterized by massive clastic inputs and meteoric waters from major Messinian rivers (the Rhone, Nile, and Antalya Gulf rivers)and deposited in an over-saturated sea-water. A late lowstand, started by rapid deposition of massive halite. The transition between the two lowstands is interpreted as the peak of the "salinity" crisis and the maximum dispersal of sands into the deep Mediterranean basins. The upper part of the evaporites is evidence for a transition between the late lowstand stage and an early transgressive stage.
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The MSC Salt Giant - Open Questions, Depositional Scenarios, Impacts in Term of Exploration, and ongoing IODP DREAM Drill
Authors J. Lofi, A. Camerlenghi and D.R.E.A. M. TeamSummaryAmong the main open questions dedicated to the Messinian Salinity Crisis, one concerns the causes, timing and emplacement mechanisms of the halite now observed in the deep basins. Several contradictory conceptual models have been proposed to account for its genesis.The deposition mechanisms and magnitude of the sea-level drawdown involved in these scenarios have various impacts on the sedimentary and tectonic evolution of the Mediterranean basins and margins, and the associated traditional plays. In order to answer some of these open questions, we propose to drill, core and log a shallow-to-deep transect on the Balearic Promontory in the framework of an IODP drilling proposal entitled: DREAM (Deep-Sea Records of the MSC; coordination: J. Lofi, Géosciences Montpellier & A. Camerlenghi, OGS Trieste).
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Messinian Salinity Crisis - Facts, Theories, Open Problems and their Implications for Mediterranean Exploration
Authors M. Roveri, R. Gennari, S. Lugli, V. Manzi, N. Minelli, M. Reghizzi and B.C. SchreiberSummaryA large consensus has been reached on a three-stage evolutionary model of the Messinian salinity crisis (MSC), each of them characterized by a peculiar association of evaporitic deposits, which record changes in the Mediterranean basin hydrology.
However, a general agreement on what actually happened during the MSC, and particularly in the deepest settings of the Mediterranean basin, is still far from being obtained and several scenarios of the crisis have been proposed, with different implications for hydrocarbon exploration.
The current MSC paradigm - the “shallow-water deep-basin” model - implying high-amplitude sea-level oscillations (>1500 m) of the Mediterranean up to its desiccation, is often considered as a fact. Actually, the different MSC scenarios so far proposed should be considered as theories needing to be proved. In recent times the desiccation theory has been questioned on its main arguments. We suggest an alternative, deep-water, non-desiccated scenario implying the permanence of a large water body in the Mediterranean throughout the whole MSC with strongly reduced Atlantic connections. The model has important implications for the exploration of the deep Mediterranean and the assessment of its hydrocarbon systems. In particular, its impact for a better definition of source rock generation and distribution, as well as of the magnitude of water unloading processes and their effects on hydrocarbon accumulations, should be carefully considered and evaluated.
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Mediterranean Halokinesis and Hydrocarbon Plays - Much Ado about Everything
Authors N.A. Hodgson and K.R. KarynaSummaryThe seismic characteristics and mechanisms of deformation of the Messinian Formation in the East and West Mediterranean Basins are discussed using offshore seismic from Lebanon and Spain.
The consequences for hydrocarbon plays in either basin are discussed.
Above the depositional limit of the Messinian salt, structuration can also be dominated by salt through the dominance of the mesozoic evaporite halokinetic fabric (examples from Adriatic etc). Evidence for the widespread occurrence and influence of Triassic salt is discussed, and interactions with the messinian hydrocarbon system presented.
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Messinian Salinity Crisis in the Mediterranean Basin: A reference model for evaporitic basin margins?
Authors Jean Gerard, Raphael Bourillot, Mateu Esteban and Philippe RazinSummaryEvaporite basins are commonly rimmed by a wide range of facies made of complex depositional lithologies later affected by various diagenetic processes along the basin margins in response to recurrent fluctuations of relative sea level and associated water chemistry. The example of the Messinian of SE Spain is presented as a potential reference model for other salt basins.
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Traditional and New Potential Hydrocarbon Plays in the NW Mediterranean
Authors P. Granado, F. Sàbat, J.A. Muñoz, N. Mazzuca, G. Griffi and R. GambiniSummaryA regional hydrocarbon play concept diagram has been produced for platform to deep water regions, including the Miocene rifting hyperextension processes (i.e., sub salt plays), a sequential stratigraphy approach for the sedimentary products of the Messinian Salinity Crisis, and suprasalt plays related with post-rift salt tectonics. In addition, plays related with the Mesozoic-Cenozoic evolution of the Valencia Trough are also included. A large degree of uncertainty is present is the deep water area of this salt giant but many geological factors point to similarities with the prolific South Atlantic Salt Basins and to potential large hydrocarbon accumulations.
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Evidence of Messinian Channels Deposits in the Valencia Basin from 3D Seismic Analysis - A Possible Messinian New Play
Authors N. Ibrihen, H. Gonzalez, L. García, L. Perez, L. Abushaala, B. Krpan and A. PonteSummaryIn the light of this work, we could recognize the different Messinian unconformity surfaces documented in the Mediterranean Sea and the paleo-drainage system which consists of a major NW-SE oriented valleys network and 1700m as a minimum of erosion.
So far, most of the discoveries in the Valencia Basin are related to the Mesozoic play, the carbonates reservoirs fed from the Langhian/Burdigallian source rocks.
In addition, our study of the wells in the area of the Casablanca field has shown that most of them had gas/oil shows, fluorescence, in practically all of the Tertiary section. This reveals that the fluids could migrate vertically from the mature deep source rocks, most probably via faulting.
Today, we believe that the Messinian play has been overlooked in the past and that is likely to work. In fact, the expected good reservoirs of Messinian age filling the Messinian channels evidenced by the seismic attributes generated from a good 3D seismic quality, have an excellent chance of being filled by the deeper source rocks, particularly where they are cut by the faults that characterize the paleohighs affecting the Mesozoic platform.
Importantly, the seismic attributes revealed that none of the wells penetrated the channels.
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Tectonics, Erosion, and Climate Interacting at the Mediterranean Gateways - A Mechanistic View of the Messinian Crisis
Authors D. Garcia-Castellanos, F. Sierro, S. Ledesma and A. CamerlenghiSummaryThe isolation of the Mediterranean leading to the Messinian Salinity Crisis (MSC) is thought to be the result of the interplay between global sea level oscillations and a gradual tectonic uplift of the connecting seaways between the Mediterranean and the Atlantic, in the Gibraltar Arc region. There is no full consensus, however, on whether a kilometric drawdown ever took place and when, or whether it may have occurred in multiple occasions. The main reasons behind these uncertainties are 1) the absence of drillings that cross the entire evaporitic sequence in the deep basins; 2) the lack of a direct correlation between marginal and deep stratigraphy; and 3) the shortage for quantitative, process-based, mechanistic models that aim to account for the vast amount of multidisciplinary observations available on the MSC.
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The Messinian Salinity Crisis in the West-mediterranean Sea - Some Previous Results about the Messinian Events
Authors M. Dal Cin, F. Accaino, A. Camerlenghi, A. Del Ben, R. Geletti, A. Mocnik, N. Wardell and F. ZgurSummaryA large seismic dataset has allowed us to regionally study the West Mediterranean Sea with particular focus on the West Sardinia and South Balearic continental margins and adjacent oceanic basins. The main seismic and geological evidences are related to the presence of the Messinian Trilogy in the deep basins and lower slopes, and coeval erosional truncation on the intermediate and upper margins. During the deposition of the upper Messinian sequence (UU), a thin salt layer has been highlighted, thanks to the high resolution of recent profiles. This salt layer, precipitated during the initial re-filling of the Mediterranean Sea, has been correlated to an erosional surface on the lower slope inner the UU and interpreted as the effect of a temporary sea level drop. The underlying salt layer (MU) shows halokinetic deformations in the deep basins which started since the Upper Messinian and developed principally during the Pliocene, sometimes until the Present, as testified by sea bottom piercings. The halokinetics has affected by different intensity, on the base of its original thickness, of the sediments and water load, and of the proximity of the lower slopes, where the sliding of salt toward the deep basin determined compressive stress and enhancing diapirism.
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Palaeoenvironmental Evolution and Exploration Hydrocarbon Potential of the Messinian Tripoli in Sicily
SummaryWith the aim to evaluate the hydrocarbon potential of the Messinian Tripoli Formation widely outcropping in the Sicily structural evaporitic basins, nineteen field sections sited mostly in Central Southern Sicily have been investigated in a cooperation program with ENI. Many of these basins are part of the Gela accretionary wedge, the highest and more recent tectonic element of the Sicily Fold and Thrust Belt. The study evidentiates the tectonic involvement of the several Tripoli-Evaporites sections, originally deposited in an area now occupied by the Tyrrhenian Sea. A restoration of the surface and subsurface setting images the Tripoli as deformed in large, buried asymmetrical synclines and surface tight anticlines with limbs eroded in outcrop.
With reference to the well-known Tripoli chronology (nine bioevents constrained by cyclostratigraphy), each section has been assigned (referred) to a well defined biostratigraphic and chronologic interval. On the ground of the micropaleontological associations the palaeoenvironmental evolution has been restored in order to recognize the occurrence of openly marine to restricted domains.
Finally geochemical analyses helped to recognize and evaluate an unexpected hydrocarbon potential for the exploration of the Tripoli Formation in Sicily.
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Architecture and Stratigraphy of Messinian Deposits (Abu Madi Fm.) at the Mouth of Messinian Nile Canyon, Offshore Egypt
Authors J.L. Rubino, E. Crouzy, R.M. Campo, C. Jardiné, M. Khalil, T. Rives and T. RossiSummaryFor the first time, subsurface data, i.e. well and 3D seismic establish that a sand rich fan delta is deposited during the Messinian Salinity Crisis at the mouth of the Nile Messinian canyon in the offshore. The Abu Madi Formation displaying an overall backstepping architecture; correlations can be made with gas fields develop updip into the infill of subaerial canyon.
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The Characteristics of the Messinian Salt and their Effect on the Pre-salt Exploration over the Eastern Mediterranean Ba
More LessSummaryThe large gas reservoirs, recently found in the Eastern Mediterranean basin are situated below a thick Messinian salt layer. The unique characteristics of this salt body, known to have been deposited over a very short period of time, are described using detailed depth imaging and well data.
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Why Are there no Messinian Evaporites in the Black Sea?
More LessSummaryThe suggestion of a very large (1,600 ml) sea-level drop in the Black Sea during the Messinian Salinity Crisis (MSC) is primarily based on the findings of shallow-water clastics and carbonates in DSDP wells 380 and 381. However, the re-interpretation of the core data from these wells, including the integration of recently acquired long-offset seismic data, clearly show that both of these wells penetrated gravity-driven mega-slumps and mass transport complexes. Therefore the interpreted shallow water MSC units in these deepwater wells do not represent in-situ rock formations, but rather allochthonous strata derived from the basin margin. This explains the lack of Messinian evaporites in the Black Sea as this large basin never got desiccated during the MSC, unlike the Mediterranean Basin.
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Creating Virtual Receivers from Drill-bit Noise
Authors Y. Liu, D. Draganov, K. Wapenaar and B. ArntsenSummaryIn the field of seismic interferometry using noise, surface waves and body waves between receivers have been retrieved by crosscorrelating recordings of uncorrelated noise sources to extract useful subsurface information. When the positions of the noise sources are known, inter-source interferometry can be applied to retrieve the wavefileds between sources, thus turning sources into virtual receivers. Previous applications of this form of interferometry assume impulsive point sources or transient sources with similar signatures. We investigate the requirements of applying inter-source seismic interferometry using drill-bit noise to retrieve the reflection responses at those positions. We show that an accurate estimate of the source function is essential for such application. The preprocessing involves using standard seismic-while-drilling procedures, such as pilot crosscorrelation and pilot deconvolution to remove the drill-bit signatures in the data, and then applying crosscorrelation interferometry. Provided that pilot signals are reliable, drill-bit data can be redatumed from surface to the depth of boreholes using this inter-source interferometry approach without any velocity information of the medium. We show that a well-positioned image below the borehole can be obtained with just a simple velocity model using these reflection responses. We also discuss some of the practical hurdles that restrict its application offshore.
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Imaging Near-surface Heterogeneities by Natural Migration of Back-scattered Surface Waves
Authors A. AlTheyab, E. Workman, F.C. Lin and G.T. SchusterSummaryWe present a surface-wave natural migration method that does not require velocity models to migrate backscattered surface waves to their projected locations on the surface. This method uses recorded Green's functions instead of simulated Green's functions. The key assumptions are that the scattering bodies are within the depth interrogated by the surface waves, and the Green's functions are recorded with dense receiver sampling. This natural migration takes into account all orders of multiples, mode conversions, and non-linear effects of surface waves in the data. The natural imaging formulas are derived for both active source and ambient-noise data, and computer simulations show that natural migration can effectively image near-surface heterogeneities with typical distributions of ambient-noise sources. We also present the results of applying natural migration to Long-Beach and US-Array passive data. The migration images highlight known discontinuities in surface-wave tomograms and correlate well with some of the prominent geological boundaries at two different scales: (1) the tectonic scale such as the edge of the Atlantic Plain Province in southeastern US and (2) the regional scale structure under Long Beach, California. The migration images provide complementary high-wavenumber information to the smoother surface-wave tomograms and can be used to refine the tomographic models.
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4D Surface Wave Tomography Using Ambient Seismic Noise
Authors F. Duret and E. ForguesSummaryIn 4D land seismic and especially for Permanent Reservoir Monitoring (PRM), changes of the near-surface induce unwanted signal variations that interfere with the 4D signal recorded from the reservoir. A three-month PRM pilot was carried out for Shell on the Peace River heavy oil field in Alberta, Canada in 2009. During this period, reservoir production was monitored using active buried sources and buried receivers. We took advantage of this continuous seismic recording to extract surface waves from recorded ambient noise using cross-correlation techniques. Surface wave tomography is then applied to produce daily time-lapse surface wave velocity maps that monitor velocity variations within the near-surface. We provide an image of the shallow subsurface velocities showing generally higher values in the southern part of the area. This pattern correlates fairly well with the known presence of swamp (muskeg) in the area and the wells pad location. Calendar observation of velocity maps shows stronger variation at low frequencies with good spatial coherence. In the case of PRM and continuous seismic monitoring, these findings could help to discriminate, at least qualitatively, contributions due to near-surface variations from actual reservoir 4D variations.
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Estimating the Location of a Tunnel Using Interferometric Times of Rayleigh-wave Scattering
Authors A. Kaslilar, U. Harmankaya, K. Wapenaar and D. DraganovSummaryInspired by a technique called seismic interferometry, we estimate the location of a scatterer using scattered waves. We isolate the scattered wavefield and evaluate the result of correlating scattered waves at different receiver locations. The cross-correlation eliminates the travel path between a source and a scatterer, making the estimation of the scatterers’ locations dependent only on properties between the receivers and the scatterer. We illustrate the potential of this method by locating a tunnel from seismic field data, recorded along a line with multiple source and receiver locations. As near-surface scatterers are potential weak zones and may pose risk for the environment, to mitigate geo- and environmental hazards, this method can be an efficient alternative in detection of such structures.
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Feasibility Study of Seismic Interferometry for CO2 Storage Monitoring - An Example from the Ketzin Site
More LessSummarySeismic interferometry is a relatively low cost method compared with conventional seismic monitoring methods and can be performed together with microseismic and reservoir monitoring. These features make it a new potential tool for carbon dioxide storage monitoring. In this study, we acquired 6 nights of ambient noise data were recorded at the Ketzin experimental CO2 injection Site located in Ketzin, west of Berlin, Germany, in August 2013. An active survey was also acquired at the same time along of one line for a source test. Passive seismic interferometry was applied to the recorded noise data to reconstruct common shot gathers. The virtual shot gathers was processed to obtain a stacked section. The results show that the passive stacked sections are less coherent and low resolution compared with the active stacked section. However, we could also find some similar features to both the passive and active stacked sections in the shallow parts and even some agreement in the deeper parts.
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Feasibility of Retrieving Time-lapse Reflection Signals Using Ambient-noise Seismic Interferometry at Ketzin, Germany
Authors B. Boullenger, A. Verdel, B. Paap, J. Thorbecke and D. DraganovSummaryAmbient-noise seismic interferometry (ANSI) applied to passive body-wave measurements retrieves an estimate of the reflection response as if from a source at a receiver position. Often, the limited compliance with theoretical assumptions causes erroneous absolute amplitudes of the retrieved physical reflections, and additional artefacts. Nevertheless, the retrieved reflection data may be further used for time-lapse interpretation, since the latter exploits relative amplitude differences. Here, we study the feasibility of applying ANSI to time-lapse passive seismic data to extract the time-lapse reflection signal produced by the exploitation of a reservoir. We base our study on the case of the demonstration site for CO2 storage at Ketzin, Germany. With numerical experiments, we apply ANSI to two passive datasets using a base and a repeat scenario (after velocity decreases in the CO2 reservoir) and modelled by random distributions of band-limited noise sources. We show that the retrieval of an unambiguous time-lapse signal is enabled by increased common illumination between the two datasets. Finally, we apply ANSI by auto-correlation to Ketzin field data and show the retrieval of responses consistent with modelled and active field data. We conclude that ANSI applied to field data has the potential for time-lapse differences extraction and interpretation.
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A Study on the Effect of Least-squares Datuming on VSP Multiple Imaging
Authors A. Aldawood, I. Hoteit, G. Turkiyyah and T. AlkhalifahSummaryInterferometric transformations are widely applied to transform seismic data from one acquisition geometry to another. We used a correlation-type interferometric transformation to redatum vertical-seismic-profiling surface-related multiples into surface-seismic virtual primaries. Conventional redatuming, based on the cross-correlation of seismic traces, yields virtual surface-seismic records that suffer from correlation artefacts, wavelet distortion, and low-temporal resolution. These effects are mainly caused by the limited recording aperture, the band-limited nature of the source wavelet, and the coarse source-receiver sampling. Least-squares migration of the virtual surface-seismic gathers can partially enhance the seismic resolution of the final migrated sections. However, our results demonstrate that the least-squares datuming step remarkably helps suppress the cross-correlation artefacts, enhance the resolution of the seismic events, and properly deconvolve the source wavelet. Therefore, the computed migrated sections suggest that least-squares datuming can be an essential processing step to apply to VSP surface-related multiples prior to imaging subsurface structures.
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A Review of Tangent-phase Interferometry Method and Applications
Authors F. Poletto, B. Farina and G. BöhmSummarySeismic interferometry makes it possible to reconstruct redatumed signals creating virtual sources at receivers. The conventional method utilizes the crosscorrelation of recorded signals from a plurality of sources to estimate the Green’s function between receivers. Great advantages are to remove the propagation effects outside the representation zone, and redatum signals without the need of velocity model. The seismic interferometry method requires an appropriate and complete distribution of seismic sources around the receivers for signal representation with stationary conditions. Lack of coverage may results in ghost and artefacts. However, the condition to have only partial coverage by sources is common. Recently, a method was proposed to overcome these limitations and to extend the stationary conditions for selected events. The tangent-phase interferometry (TPI) corrects the phase in the cross-correlations before integral representation. This approach requires identification of the signal trends for selected events in the cross correlations, and corresponds to move the virtual source from receiver positions to projected points on the signal wavefronts. We present a review of TPI applications, with the analysis of emerging aspects in different examples. This review is aimed at evaluating advantages and critical issues in the joint use of TPI with other inversion and imaging methods.
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Use of Seismic Interferometry to Improve the Imaging of a Heterogeneous Landfill
Authors L.A. Konstantaki, D. Draganov, R. Ghose and T. HeimovaaraSummaryIn this study we investigate the application of seismic interferometry (SI) to seismic reflection data recorded over a landfill. Landfills represent strongly heterogeneous subsurfaces making the seismic reflection imaging challenging. We show that SI improves the imaging of high-density areas, which create scattering events in the recorded data. In addition, we use SI to subsequently predict surface-wave energy and remove it from the original data to improve the imaging of reflectors. The combined interpretation of the conventional reflection seismic data, SI and reflection data with surface waves removed improves the understanding of the landfill body.
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Scatterer Characterization from Correlated Surface Wave Coda
Authors T.E. Blum, T.D. Mikesell, K. van Wijk, R. Snieder and H. SatoSummaryThe accuracy of scattered Rayleigh waves estimated using an interferometric method is investigated. Summing the cross correlations of the wave fields measured all around the scatterers yields the Green's function between two excitation points. This accounts for the direct wave and the scattered field (coda). The correlations themselves provide insights into the location of the scatterers as well as which scatterer is responsible for particular parts of the coda.
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Analysis of Rayleigh Wave Ellipticity in the Iberian Peninsula and Morocco Using Ambient Noise and Teleseismic Records
Authors C. Gómez-García, A. Villaseñor, A. Ugalde and B. GaiteSummaryWe combine Rayleigh wave ellipticity, or H/V (horizontal to vertical) amplitude ratios, measurements obtained using teleseismic earthquake recordings and ambient noise cross correlations to provide improved constraints on the crustal models across the Iberian Peninsula and Morocco. To obtain the H/V ratios, we use more than 250 shallow (h<40 km) teleseismic events with magnitudes Mw>6.0 recorded atmore than 450 seismic stations. We also use all the multicomponent ambient noise cross correlations computed for each station pair for the time period 2010 to 2012. Periods between 20 and 100 seconds are investigated. We observe a good agreement between the uppermost geological features of the crust and the obtained Rayleigh H/V ratios, with low values in major mountain ranges and high ratios in sedimentary basins. Combination of Rayleigh H/V ratio measurements from both earthquakes and ambient noise data with phase velocities and other types of seismic data will help to better constrain the Earth’s structure at different crustal levels.
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