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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
1 - 50 of 142 results
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Improving Subsalt Imaging by Image Conditioning and Enhancement with RTM Vector Image Partitions - A GoM Case Study
Authors C. Zhao, O. Zdraveva, A. Gonzalez, R. King, R. Gu and S. ChenSubsalt imaging remains challenging despite a growing need for more accurate subsalt characterization. Long offsets, wide-azimuth (WAZ), and full-azimuth (FAZ) acquisition technologies have provided step-change improvements in illumination, multiple attenuation and signal-to-noise ratio. Recently developed more advanced anisotropic velocity model building techniques, have also greatly enhanced our ability to build accurate salt models and reduce velocity error. Reverse-time Migration (RTM) has become the preferred imaging algorithm due to its superior tolerance for complex salt geometry compared with traditional ray-based Kirchhoff migration. However, even with these developments, subsalt imaging still remains a significant challenge. Recently, Vector Image Partitions (VIPs) from RTM have proven valuable for enhancing the image of challenging subsalt structures. In this paper, we present a new method for optimizing the final migrated image through enhancement of the consistent signal and suppression of noise among VIPs. We demonstrate the effectiveness of this method with a case study from the Gulf of Mexico. The result shows great improvements in the subsalt image quality in terms of signal to noise ratio, reflector continuity, and wavelet consistency along reflectors.
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Highly Detailed Reservoir Imaging by Using Sparse Layer Inversion in a Complex N.Sea Turbidite
Authors D.D. Mann, R.H. van Eykenhof, J.P. Castagna and C.P. AshtonSparse layer inversion (SLI), like sparse spike inversion (SSI), invokes a sparse reflectivity solution for the reconstruction of noisy seismic traces in the presence of a known, band-limited wavelet. However, solving for layers, i.e. dipoles, rather than individual interfaces, holds the potential for achieving increased detail and lateral stability over that usually achieved with SSI. In this paper, we present the method and show the application of SLI to a complex turbidite reservoir in the UK Central North Sea.
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Keynote Speech - Broadband Seismic - The Interpreters Dream Come True?
By J.E. LieBroadband seismic (BBS) has without doubt increased seismic resolution through a sharper wavelet with less side lobe artefacts. The low frequency richness of BBS has improved our estimation of rock properties through inversion. Full Waveform Inversion velocities derived from BBS data have improved both imaging and inversion results. This is all really sweet, but BBS data still contain noise, multiples and phase issues, and now they all come in broadband. In this talk we will be sharing some of our experiences with a variety of broadband seismic techniques and how Lundin Petroleum have dealt with whole new set of real world opportunities and problems that BBS has given
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Broadband Seismic - Uplift to the Interpreter
Authors N.A. O'Dowd and P.G. CarolanThe geophysical uplift of broadband data is widely reported as are the benefits it brings to reservoir characterisation. However there are also benefits to the qualitative interpreter which go beyond improved resolution and structural imaging. In addition to the benefits to efficiency and accuracy whilst auto-picking, the manual interpreter can gather more geological information from the texture within the data than just having improved confidence in the structural and stratigraphic image. The broad bandwidth of frequencies within the data produce a texture to the data which can highlight geological packages which may have been previously masked within conventional data. There is geological understanding and information which may be inferred and when accurately tied to well information can increase confidence in model building and help to focus further quantitative interpretation.
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Broadband - The Interpreter's Friend?
Authors M. Francis and C. CunnellThe positive impact of broadband acquisition and processing methods on the interpretation of seismic volumes has been well documented in recent years. While most gains have been achieved by extending low-frequency content, potential pitfalls exist for interpreters at both ends of the frequency spectrum, and care must be taken to understand the effective bandwidth of data. In addition, the handling of spatial frequencies (or wavenumbers) is as important as considerations for temporal aliasing. A complex earth creates a complex seismic wavefield in all directions, and so demands a revised definition of broadband with an emphasis on spatial resolution. We contend that the time has come to adopt the concept of effective spatial broadband based on high-resolution interpretation independent of orientation, and move towards the next level in geological understanding from our seismic volumes.
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Improvements to Frequency Decomposition Methodologies for Use with Broad Bandwidth Seismic Datasets
Authors J. Lowell, A. Eckersley, T. Kristensen, P. Szafian and N.J. McArdleBroadband technology, in its different guises has been developed to extend the spectral width of seismic data giving more sensitivity to the features imaged at high and low frequencies. This has lead to problems using existing frequency decomposition techniques with this data. We have adapted our existing code to meet these demands.
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Benefits of Broadband Seismic Data for Reservoir Characterization - Santos Basin, Brasil.
Authors E. Kneller, L. Zekian, T. Coleou, J.P. Coulon and Y. LafetQuantitative interpretation teams face two challenges when using model-based inversion: to extract meaningful wavelets and to build accurate low frequency models. The lack of low frequencies in conventional seismic data means that a low frequency model must be incorporated in the inversion process in order to recover absolute impedance values. Typically, low frequency models are obtained from low-pass filtered impedance logs. If well-logs are sparse and the geology complex, the well-derived low frequency model may be inaccurate and cause biased inversion results. One option to improve the low frequency model is to use seismic velocities. However, while seismic velocities provide information at very low frequencies (0-5 Hz), they are not usually suitable to provide information for the missing frequencies in the range from 5 to 10 Hz with conventional seismic data. Seismic data acquired using variable depth streamers are ideally suited for inversion as they provide directly these missing low frequencies, hence removing the need to build low frequency initial models from well data. In order to quantify the impact of the low frequency content on seismic inversion, comparative elastic inversion tests have been conducted using 3-D seismic data from conventionally towed Constant Depth Streamer (CDS) acquisition and broadband Variable Depth Streamer (VDS) acquisition. Both datasets from offshore Brasil, Santos Basin were acquired at different time. The CDS survey was acquired and processed in 2000, the VDS was acquired in 2012 and this paper uses fasttrack processing results. The VDS survey was acquired with streamer depth ranging from 10 to 50m.
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Fast Track Broadband Seismic Inversion Workflows
Authors A. Geisslinger and H.H. HamzahThis talk will focus on how Fast Track Reservoir Characterization approaches based on broadband data are being applied on a regional seismic data set of 7000km2 delivering Calibrated Impedance and Fluid Cubes for the entire regional volume, thus enabling Exploration and Development teams to readily harvest value of the improved rock property characterization through broadband seismic. 1 - Calibrated Impedance The much improved low frequency content of the broadband data together with higher frequency content of the velocity model generated by modern processing techniques allows us to close the conventional frequency gap at around 1-8 Hz. A seismic velocity model based low frequency P-Impedance model and reflectivity derived bandlimited impedance cube can be merged seamlessly into a calibrated impedance volume. 2 - Fluid Cube Using Broadband Seismic Data and an operator based Coloured Inversion workflow, followed by weighted stacking of the results, fluid cubes can be generated in a very efficient way. This allows their usage in prospect identification timely after end of a processing project and very early in the exploration interpretation workflows. Having fluid cubes early, is of particular value in the geology of Brunei Darussalam, where prospects are distributed over thousands of milliseconds of sand-shale sequences.
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Using Inversion to Estimate the Impact of Broadband Data on Elastic Property Uncertainties
Authors J.V.R. Townend and A.J. CherrettWe present a comparison of broadband and conventional data using joint elastic inversion to quantify posterior uncertainties. The uncertainty can be quantified at different scales, for example according to temporal frequency or layer thickness. Our observations confirm that enhancements to the usable bandwidth in extreme high and low seismic frequencies give rise to a quantifiable uplift in resolution across a full range of scale lengths.
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The Benefits of Broadband Seismic Data
By B. KrokanTo improve bandwidth and resolution in seismic data has been a priority since the early days of the seismic method. The last years the industry has made great strides forward in terms of providing techniques that contribute to enhanced seismic resolution, deeper penetration into the earth, more quantitative and reliable reservoir inversion, simplified interpretation and clearer facies discrimination. This presentation provides evidence for the improvements by case studies with recently acquired marine broadband data. It will also address a few R&D challenges.
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Addressing Obstacles to Adoption of Broadband Seismic by Asset Team Interpreters
Authors T. Bird, C. Reiser, E. Anderson and M. WhaleyBroadband seismic data is distinctively different from conventional ‘band-limited’ seismic data in appearance as a result of broader information content. Common reactions from interpreters encountering broadband seismic data for the first time are addressed. This paper illustrates these concerns and responds with suggestions to overcome these obstacles to broader adoption. Broadband has been promoted as a resolution solution, causing interpreters to anticipate higher frequencies at depth than is possible given the frequency-dependent attenuation of the earth. Broader frequencies result in a sharper wavelet with less side-lobe energy, causing some reflectors that were artifacts of side-lobe energy to disappear, radically changing the appearance but giving better ties to well data. The additional low frequencies of broadband data are crucial in delivering more stable and higher fidelity inversion results. Popular frequency-related seismic attributes such as ‘sweetness’ are also significantly improved by the additional low frequencies. Once seismic interpreters understand the reasons for the radically different appearance of broadband seismic data and start taking advantage of the additional information content and higher fidelity, it can be expected that this data will be demanded as standard.
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Reghosted 4D and 3D Reservoir Characterization Using a Broadband Monitor on a Deep Offshore Turbiditic Field
Authors C. Deplante, F. Jeanjean, V. Sebastiao and S. SagederOn a turbiditic deep offshore field covered by a recent yet conventional 4D baseline, a non-conventional route has been decided for the first monitor, to obtain seismic information related to dynamic heterogeneities but also better characterize reservoirs. The strategy decided for the first monitor (M1), one year after first oil, was to shoot broadband and process twice: - One 4D-dedicated processing mapped to conventional (with a Fast Track and a Full Processing phase) in order to match the baseline characteristics and obtain quality 4D signal to help understanding the early dynamic behaviour of the field. - One 3D broadband processing aiming to improve the existing seismic for reservoir characterization purposes. The superior resolution of the 4D signal over conventional data helps pushing the interpretation below the 3D resolution limits and has helped identifying sedimentary features which have confirmed the interpretation model but are also difficult to map accurately. Using the 3D broadband processing results, small scale geological details previously guessed from conventional data and locally underlined by 4D signal (but only at places impacted by changes in saturation and pressure), can now be seen more clearly: a more comparable resolution is achieved for 3D and 4D.
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Couy-1 Well, Paris Basin, France - An Open Window on the Toarcian Series for Organic Rich Shale Characterization
Authors C. Rigollet, D. Bonijoly, A. Hofmann, M. Power and M. SimpsonThe COUY-1 well (scientific well drilled in 1987, program “Géologie Profonde de la France”) presents a complete log data set, continuous cores and a well known geological context. Consequently, it is an appropriate case study to test the new technologies and workflows for organic rich shale characterization. This well is an open window on the Lower Toarcian shale: “Schistes Cartons” in France, lateral equivalent of the famous “Posidonia Shale”. The integration of various analyses from COUY-1 logs, cores and cuttings (geochemistry, mineralogy, geomechanic, logs...) led us to update the characterisation of the Lower Toarcian organic rich shales, despite the age of the dataset (almost 30 years). These new analytic approaches (QEMSCAN, CT-Scan, Nano-indentation...), coupled to common analysis in an optimized workflow, allow to consider larger studies with heterogeneous databases, long as geoscientists have access to cuttings. The main analysis recently performed from the COUY-1 dataset by SGS, with BRGM support, will be presented during the WS04 EAGE Workshop and compared with previous studies in Dutch North Sea and SW Algeria.
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How to Maximize Wellsite Information for Assessing Tight Hydrocarbon Opportunities
Authors M. Simpson, D. Bonijoly, M. Power and C. RigolletFor many years mud rich lithologies were largely ignored at the well site. Mud rich formations or shales, were simply the rock that had to be penetrated in order to reach the reservoir target. However mud rich rocks when examined properly at the wellsite are very important when investigating tight hydrocarbon domains. Mud rich formations can be characterized onsite to obtain quickly a first evaluation of the potential sweet spots. In further studies, these valuable first data accessible in the “mudlog”, must be systematically considered and integrated to the working dataset. The rate of penetration (ROP), Rotary torque, onsite analysis (methyl blue tests, calcimetry, fluorescence, isotopic analysis…), cuttings description (mineralogy, lithology, size, shape and morphology) and gas show bring enough information to make a first evaluation of the mud rich formation properties (rock strength, fracture presence, flow unit, TOC presence, maturity…) and hydrocarbon potential. The EAGE WS04 workshop will set out to look at the key characteristics of mud rich lithologies that can be identified at the well site and how some of these parameters can be determined. These parameters are integrated in a way that possible hydrocarbon potential can be identified so that follow up work can be initiated.
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Integrated Log-core Calibrated Approach for Petrophysical and Geomechanical Characterization of Source-rocks
Authors A. Di Matteo, D. Bonijoly, M. Power, C. Rigollet and M. SimpsonThe prediction of mineralogy, TOC, grain density, porosity and gas saturation in organic rich shale is a challenging process that needs to rely on the integration of several measurement methodologies usually performed at different scale and by different disciplines. LECO analysis data can be used to measure the TOC values on core scale. Such values can drive the logs in estimating the TOC on a well scale. QEMSCAN measurements on core and cuttings provide accurate information about the shale composition. This information can be used, along with the TOC content, routine core data and the petrophysical deterministic analysis, to solve a probabilistic petrophysical model that allows characterizing the mineralogy and the organic content of the shale of interest along the whole well path. Once estimated the rock composition, the Brittleness Index can be estimated by assuming a multi-variable dependence between BI and the shale mineral composition. The BI calculated from the mineral composition can be further calibrated by using site specific rock cuttings and by correlating the BI values based on mineral components with the geomechanical response based on nano-indentation measurements. This methodology will be illustrated during the EAGE WS04 workshop with the Toarcian shale (COUY-1 well, Paris Basin, France).
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The Role of Mineralogy (QEMSCAN) in the Facies Heterogeneity Characterization of Organic Rich Shale
Authors M. Power, D. Bonijoly, A. Hofmann, C. Rigollet and M. SimpsonDue to the increased complexity of unconventional plays, existing workflows, developed for more conventional reservoirs, are not always applicable. A better understanding of the rock matrix is critical for the development of improved models for the exploration and exploitation of these resources. As minerals control fundamental parameters such as grain density and directly or indirectly influence many of the wireline responses e.g. density, resistivity, spontaneous potential, gamma ray etc, accurate determination of the mineralogy is a vital input to petrophysical models. In addition, the composition and fabric of the reservoir rocks control geomechanical properties such as well bore stability and fracking potential. Therefore, accurate and reproducible quantification of the mineralogy and texture of the rock matrix is a particularly important factor in exploitation and development workflows for tight and / or unconventional resources. QEMSCAN analyses on the COUY-1 well cores and cuttings (Toarcian Shale, Paris Basin, France) provide quantitative mineralogical data, textural data and mineral maps of each cutting/core sample, thereby allowing for the detailed characterisation and determination of the nature and distribution of the inorganic sample components. The particles are lithotyped in order to quantify the variations between the samples and brittleness indices were calculated from the modal mineralogy.
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Shale Geomechanics - A Nano-indentation Application
Authors M. De Block, D. Bonijoly, A. Hofmann, M. Power, C. Rigollet and M. SimpsonNano-indentation is a technique developed to determine the mechanical properties of small samples. It is based on a hard tip, which is pressed into the surface of a rock sample. The ratio between the applied load and the displacement of the tip into the sample is used to calculate the hardness and Young’s modulus. Additionally, the load-displacement plot obtained from nano-indentation measurements can be used to define three areas which describe the plastic work done on the sample and the elastic work done on the sample. This work-of-indentation approach is a good predictor for the brittleness of shale formation. For the study, core samples were collected from the Toarcian shale formation of the Paris Basin (Couy-1 scientific well) and merged in epoxy resin blocks. First, mineralogical analysis was performed on each block (QEMSCAN analysis) and secondly blocks are used for nano-indentation measurements. Using nano-indentation, for each subsample the Young’s modulus and the hardness are determined. The work-of-indentation approach is utilized in order to predict the brittleness of the samples. Integrating the nano-indentation results with the QEMSCAN data the relation between the mineralogy and the mechanical properties is investigated. Results will presented in details and discussed during the EAGE WS04 workshop.
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Seismic Prospecting of Geothermal Reservoirs in Hard Rock Environment - General Concept and Field Study
Authors W. Rabbel and E. SzalaiovaWe are presenting an approach for finding realistic estimates of geothermal and hydraulic properties of deeply faulted and folded crystalline crust . The approach is based on 3D seismic reflection and geophysical borehole data. It is presented using the example of the 9.1 km deep Continental Deep Drillhole (KTB). This site contains all elements that make seismic prospecting in crystalline environ-ment often more difficult than in sedimentary units – basically complicated tectonics, spatially low-coherent strata, small scale fracturing, strong random component in the seismic velocity field, often rather scattering than reflected arrivals. Considered together these circumstances lead to a statistic approach in deriving underground models that have to be evaluated and calibrated by hydro-thermal modelling. In order to determine model uncertainties distribution functions need to be derived for all geophysical properties involved. The work concept followed during the geothermal potential assess-ment of the KTB site is applicable also for other reservoirs located in similar environment.
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3D Focused Seismic Imaging for Geothermal Reservoir Characterization in Crystalline Rock (Schneeberg, Germany)
Authors F. Hlousek, O. Hellwig and S. BuskeWe present the results of a high resolution 3D seismic survey acquired in the western Erzgebirge near the city of Schneeberg. The project aims at imaging a major fault zone in crystalline rock at a depth of 4-5 km with expected temperatures between 160 and 180°C, which is supposed to be used as a natural geothermal heat exchanger. We applied advanced imaging methods to the data set. 3D Kirchhoff prestack depth migration delivered a clear structural image of the various fault branches at depths of around 2-5 km. Furthermore we applied the focusing coherency migration method, which uses a coherency function of the data recorded at neighboring traces for imaging. This method even sharpened the image such that the 3D seismic result allows for a profound characterization of this potential geothermal reservoir in crystalline rock.
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3D Lithological and Structural Modeling of the Kevitsa 2D and 3D Reflection Seismic Data - A Case Study
Authors E. Koivisto, A. Malehmir, T. Voipio and C. WijnsThe Kevitsa mafic-ultramafic intrusion in northern Finland hosts a large, disseminated nickel-copper sulphide deposit. We present a 3D lithological and structural model of the Kevitsa area, obtained via modeling of 2D and 3D reflection seismic data from Kevitsa. The Kevitsa 3D model contains modeled surfaces of the contacts between the main lithological units and a model of the magmatic layering within the intrusion. The Kevitsa main mineralization is thought to be controlled by the lateral extents of this discontinuous, smaller-scale magmatic layering within the intrusion. An improved knowledge of the geometry of the intrusion, and in particular of the extent of the internal magmatic layering, provides a framework for near-mine and deep exploration in the area. Better control on the position of the basal contact of the intrusion provides an exploration target for the contact-type mineralization. The original purpose of the 3D seismic survey was to provide a structural framework for geotechnical planning of the mine, and accordingly the 3D seismic data were used to create a structural model of the 3D cube. The modeled structures reveal a complex pattern of fault and fracture zones, some of which will be important for slope stability and operational planning at the mine.
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Seismic Exploration for Volcanogenic Massive Sulphides - The DeGrussa Copper-gold Mine, Western Australia
Authors J. Kinkela, S. Ziramov, A. Dzunic, M. Urosevic and P. HilliardTraditional geophysical prospecting techniques used for mineral exploration rarely provide the resolution required to accurately target orebodies at depth. Based on this, the seismic reflection method was trialled over a known VMS orebody at the DeGrussa copper-gold mine, Western Australia, in the hope of providing a viable exploration tool for deeper depths of investigation. However, a structurally complex geologic setting and a thick, highly variable regolith caused significant challenges in the processing of the seismic data. This paper addresses these challenges and looks at strategies used to overcome them eventually leading to the direct imaging of the orebody.
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In-Mine Seismic Imaging Revisited
Authors B.M. Milkereit, R. Saleh, J.W. Huang and B.V. ValleyCurrently, only microseismicity is used as a proxy for stress near deep mines. However, most of the physical properties of crystalline rocks are highly stress dependent. As such, the nonlinear and anisotropic variability of the in situ P- and S-wave velocities can potentially be linked directly to changes in the stress field. At an in-mine seismic laboratory, multi-component sensor arrays are deployed in multiple locations (3D) allowing for both controlled source and passive recordings. Previous in-mine seismic observatories have experienced a number of challenges with regards to sensitivity and longevity. Hence, the geothermally cool but highly stressed Sudbury mining camp offers a favourable setting for fundamental research in to time-lapse monitoring of seismicity, stress, and stress dependent physical properties at a deep mine.
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Direct VMS Targeting through Preserved Relative Amplitude Processed Seismic Imaging at Neves Corvo, Portugal
Authors S. Yavuz, J. Kinkela, M. Penney, V. Araujo, R. Neto, A. Dzunic and M. UrosevicExploration of deep VMS deposits at the Neves Corvo mine on the Iberian Pyrite Belt was further advanced through a specialised application of surface seismic techniques. The contrast in impedances from elastic property measurements of core samples showed that there should be a significant difference in the seismic response of mineralisation compared to the surrounding host rocks. These results indicated that relative amplitude preservation processing may be of importance to help reduce the ambiguity in direct, seismic amplitude anomaly based targeting of Volcanogenic Massive Sulphides. However, such processing was not easy to implement due to an intrinsically low signal to noise ratio, complex 3D geology, high scattering level and often patchy and poor reflectivity. The newly obtained 3D seismic cube was calibrated with the existing boreholes to show superior ore zonation and precision required for the subsequent deep drilling campaign.
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Mineralization Indicators from Seismic and Full Wave Sonic Data in the Athabasca Basin, Saskatchewan, Canada
More LessSeismic reflection method was successfully introduced, as an exploration tool, in the Athabasca Basin in 2003. Investigations demonstrated that the mineralized zones are associated with basement located shear zones, complex variable sandstone-basement unconformity intervals, and significant alteration zones within the sandstone fill and the basement. All these anomalous zones consistently were associated with diagnostic seismic images, providing a set of primary indicators of mineralization for regions of future exploration interest. Recent Full Wave Sonic surveys illustrated that not only the longitudinal (P) waves, which were exclusively utilized to date, but detectable transverse waves (S) can also observed from the geologic setting of the basin. In most instances, the responses of these elastic disturbances, to geologic irregularities, are recognizably dissimilar. This duality of the specific responses permits derivation of characteristic elastic properties of the lithological units within the investigated area. The knowledge of the depth variations of the P and S wave velocities permits the computations of elastic parameters of rocks such as shear modulus (µ), Lame’s modulus (λ) and Poisson’s ratio (σ). Combinations of these elastic properties facilitate the recognition of fractures with different sizes and their properties, as well as alteration and meta-somatic zones.
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Seismic across Different Mineral Deposits - Does It Work?
By M. UrosevicMany years of application of seismic for mineral exploration in Western Australia provided very rich data base which is used to test and optimise data processing and analysis. High signal to noise ratio enabled investigation into the performance of partial and full pre-stack imaging techniques. On the other end of the scale, very complex geologies and poor seismic response inspired the use of novel technologies and also concurrent use different geophysical techniques. Various case histories are presented and discussed.
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Application of Seismic Interferometry in Crystalline Rocks - A Case Study From the Lalor Mining Area, Canada
Authors S. Cheraghi, J. Craven and G. BellefleurApproximately 300 hours of ambient noise data covering an area of 4 km² were acquired over the Lalor mining area, Canada, to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment. The interferometry survey consists of 336 receivers located along 9 parallel lines oriented southwest-to northeast and 7 southeast-to-northwest lines. Alongside the ambient noise survey, a larger 3D active source seismic survey was also acquired in the area and used to evaluate the interferometry results. The seismic wave field is retrieved by crosscorrelating the noise between all receiver locations in each hourly segment of passive seismic data. The crosscorrelated results of all segments are spatially summed to generate virtual shot gathers. The virtual data is processed along all 2D lines with conventional methods similar to those applied to active 3D data. The DMO-stacked section obtained reveals a number of events, some more coherent than observed on the similarly processed active seismic section. Of particular interest is an event possibly associated with the massive sulphides. A comparable event is also observed on the active seismic data. These results demonstrate the benefits of ambient noise measurements in crystalline rock environment for mineral exploration purposes.
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High-resolution Multicomponent Hardrock Seismic Imaging of Mineral Deposits and their Host Rock Structures
Authors A. Malehmir, S. Wang, J. Lamminen, M. Bastani, C. Juhlin, K. Vaittinen, L. Dynesius and H. PalmAlthough applied in the past, there are only a few cases demonstrating the advantages of multicomponent seismic data for mineral exploration. To illustrate this, a test survey using sixty 3C-digital sensors, spaced between 2 to 4 m and assembled in a 160 m long landstreamer, was carried out to provide information on shallow structures hosting mineralization and also a magnetic lineament with an unknown origin. The survey, totally about 1.3 km long, was complemented by Radio MagnetoTelluric (RMT) measurements. Although an explosive source was used to generate the seismic signal, the seismic data show good quality for all the three components. Supported by the RMT results, clear reflections are observed in the horizontal component data at about 25 m depth, one of them steeply dipping, likely associated with the magnetic lineament. Field static corrections were well estimated thanks to the close shot and receiver spacing and the broadband frequency content of the data. This study demonstrates that multicomponent seismic data can be useful for providing information on shallow structures and linking them to the surface geology. The vertical component data, however, show deeper penetration and better image the crystalline basement and its undulated/faulted surface at about 50 m depth.
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Application of Curvelet Denoising to 3D Post-stack Data Acquired in Hardrock Environment
Authors A. Górszczyk and M. MalinowskiSeismic data acquired in hardrock environment are demanding for processing. Frequently occurring lack of clear coherent events hinders imaging and interpretation. Additional difficulty arises from the presence of significant amount of cultural noise (e.g. associated with exploration and processing of ore) which corrupt the data. For this purpose we demonstrate our noise attenuation approach based on 2D Discrete Curvelet Transform (DCT) by applying it to 3D post-stack seismic data from active mining camp. DCT introduce minimal overlapping between coefficients representing signal and noise in the curvelet domain, hence being well-suited for data denoising. Forward DCT is applied in sequences to inline, crossline and time slice sections. 3D DMO volume after curvelet denoising is much easier to interpret, e.g. it’s easier to follow diffracted energy originating at ore lenses. We believe that the presented approach of running 2D DCT for 3D data might be also a sufficient substitution for a more expensive 3D DCT.
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3D Seismic Imaging of the Ghost-Carbon Leader Reef of the World's Deepest Gold Mine - Mponeng Gold Mine, South Africa
By M. ManziThe re-interpretation of the old 3D seismic data from the world’s deepest gold mine of the Witwatersrand basin, have proven to be effective in enhancing the detection of fault zones and unstable lithologies that are potential mining hazards. Most of the structures identified seem to offset the gold-bearing horizons such as the Ventersdorp Contact Reef (VCR) and Carbon Leader Reef (CLR) with throws below seismic resolution limit (equivalent to one-quarter dominant seismic wavelength (λ/4)). To derive or ghost the seismically transparent Carbon Leader Reef model, we used more than 2000 drillholes that intersect the CLR (within the Central Group), VCR (top of the Central Rand Group) and Crown lava (top of the West Rand Group). The final ghosted CLR shows a very consistent dip with the VCR and Crown lava. The model also shows that 60% of the structures imaged at the VCR level at 2-3 km depth continue and displace the ghosted-CLR at 3.5-4.5 km depth in a similar manner. This model represents the gross-structural architecture that was formed following the massive Platberg age extension on the first-order scale structures.
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3D Seismic Survey in Crystalline Rocks of Saxony, Germany
Authors E. Lueschen, F. Rost, G. Hoecht and R. Thomas3D seismic measurements have been performed in 2012 to explore a petrothermal reservoir in a crystalline environment (granite intrusion, metamorphic cover) within the Erzgebirge in Saxony. The intention and challenge is to image and characterize a steeply dipping fault zone with potentially permeable fracture zones at target depths of 5-6 km and temperatures well above 150 °C. The vibroseis technique was used in the experiment. A suite of imaging methods has been applied, from conventional CMP-stacking, CRS processing to pre-stack migrations.
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Application of the 3D CRS Workflow in Crystalline Rock Environment
Authors K.A. Ahmed, B. Schwarz and D. GajewskiSeismic data from crystalline environments usually exhibit a poor signal-to-noise (S/N) ratio due to low acoustic impedances. Moreover, instead of continuous reflections we observe a lot of steeply dipping events and diffractions. The conventional seismic processing (CMP stack and DMO) is not ideally suited for imaging such type of data. CRS processing considers more traces during the stack than CMP processing and the resulting image displays a better quality. CRS workflow was established as a powerful tool to provide improved images, especially for low fold and S/N data. The application of the workflow to the 3D Schneeberg crystalline rock seismic data shows that images of coherence provided the best results for an initial analysis compared to the CRS stack with poor image quality not suitable for interpretation. For data from environments with low acoustic impedance the coherence may provide an alternative way to image the subsurface. The analysis of the data has shown that without pre-stack data enhancement methods it may not be possible to generate satisfactory stacked images. The first time migration results helped to identify several major fault structures in the data volume which coincide with geological features of the considered area.
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Structural Characterization of a Geothermal Reservoir Using Seismic Depth Imaging Methods
More LessGeothermal reservoirs can be characterized by the analysis of heat transport and fluid migration throughout the target rock volume. A hydrothermal simulation which provides insights into these processes, however, first requires detailed knowledge of the structural parameters of the reservoir. Those can be obtained from reflection seismic measurements. For this purpose, we apply two different prestack depth migration methods, namely the familiar Kirchhoff Prestack Depth Migration (KPSDM) and the recently developed Fresnel Volume Migration (FVM) on five seismic reflection profiles in a target region in Southern Tuscany, Italy. The resulting migrated images capture the important reflectors of the target region and provide a good insight in the potential extend of the geothermal reservoir. Moreover, we demonstrate that FVM produces cleaner images than KPSDM due to its “intelligent” aperture limitation. The obtained results provide the structural base on which a hydrothermal evaluation will be performed.
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The Use of Outcrop Analogue Basement Rocks to Help Seismic Imaging of Buried Reservoirs
Authors L. Bertrand, B. Walter, G. Perry, Y. Geraud and M. DiraisonBasement rocks are well studied nowadays for their exploitation as geothermal reservoirs or for mineral exploration. In these rocks, the matrix permeability is poor and the fluid flow (geothermal resource or linked to mineral precipitation) is mainly controlled by the natural fracture and fault network and associated weathered materials. Unconfortunately, the fracture and fault pattern at reservoir scale in the basement is not well known and is difficult to characterize with the actual geophysical tools. The use of analogue rocks at the outcrop is therefore an important tool for helping to the reservoir characterization. This study present a synthesis of basement outcrops studies in different geological setting linked to crustal extension. The method used was to combine satellite pictures, field studies and laboratory measurement in order to define the faults, fractures and cracks network at the largest range of scales as possible. That have lead us to construct a reservoir’s model composed by blocks of different orders depending on their size bounded themselves by faults with decreasing thickness and lengths. This model is a key tool for the characterisation of fractured buried reservoirs by seismic imaging.
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Volumetric Interpretation of 3D Seismic Data from the Hillside IOCG Deposit in South Australia
Authors M.S. Hossain, M. Urosevic and A. KepicA 3D high-resolution reflection seismic data were acquired to investigate its utilisation for exploration of typically excessively complex IOCG deposits in Hillside, South Australia. Full 3D pre-stack imaging produced results where seismic character well resembled different rock types. Further assessment of the value provided by seismic data required borehole calibration. Unfortunately only core samples were available. These information were enriched by utilising a specific gravity voxet that was extracted from the Rex supplied database. Core sample tests (velocity) and specific gravity information were utilised during the process of volumetric interpretation. We show that faults extracted from variance attribute correlate with the faults extracted using guided-tracking method. However, petrophysical data shows that the boundaries between gabbro and metasediments may not generate acoustic impedance contrast to be clearly detected by seismic reflection method. The tops to the main rock formations however are mappable in depth slices and agree very well with magnetic data. Further work involves correlation of seismic interpretation with the geological cross sections and lithological logs collected from the site.
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Reflection Seismic Characterization of the Grängesberg Iron Deposit and Its Mining-induced Structures, Central Sweden
Authors J.A.P. Place, A. Malehmir, K. Högdahl, C. Juhlin and K. Persson NilssonReflection seismic investigation has been conducted on the Grängesberg apatite iron deposit. At the time of closure in 1989, the mine was operated at about 650 m below the surface. Mining activities might be resumed in the next years, which require better understanding of (1) the ore geometry and (2) the fault network which has developed up to the surface from excavated zones at depth. Two E-W oriented reflection lines with a total length of 3.5 km were acquired. The seismic lines intersect the Grängesberg ore body and open pit, as well as several of the mining-induced faults. A weight drop mounted on an hydraulic bobcat truck was used as a seismic source; both cabled and wireless receivers were used for the data recording. Preprocessing of the data first required the cable- and wireless- recorded datasets to be merged before stacking all data available at each shot point. The dataset exhibits several shallow reflections which are likely to occur on steep lithologic or tectonic structures. Other deeper reflections are recorded; careful processing will be carried out in order to preserve such events in final stacked sections and help with refining the geological model of the area.
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Seismic Exploration for Volcanogenic Massive Sulphides - The Rosebery Zinc, Lead, Copper Mine, Tasmania
Authors J. Kinkela, A. Dzunic, M. Urosevic, R. MacRae and L. WebbAn experimental 3D seismic survey conducted in extreme topographic and weather conditions in Rosebery, Tasmania, Australia -a known VMS province - was aimed at validating the technique for this region as well as prospecting further down dip for additional mineralisation. Significant challenges were faced during the survey design stage stemming from trying to image dipping structures while taking into account extreme topographical variation of up to 400 m using a limited survey grid of approximately 1.5 km². Initial processing results were less than satisfactory with the majority of the target geology being migrated outside of the conventional 3D space. By expanding the geometry additional space for migration was provided, allowing seismic events to migrate to their true spatial position. This unambiguously imaged the controlling structures and achieved the major objectives of the trial survey.
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3D-3C Reflection Seismic Imaging of the Lalor VSM Deposit, Manitoba, Canada
Authors G. Bellefleur, E. Schetselaar, K. Miah and D. WhiteA 3D-3C seismic data set was acquired over the Lalor Lake VMS deposit, located near Snow Lake Manitoba, to provide images of the ore zones and host rocks, and to assess the applicability and potential benefits of P-S waves for deep mineral exploration. An analysis of borehole logging data shows that ore zones associated with pyrite and diorite should produce strong reflection on seismic data. Clear reflections are locally observed at the location of shallower ore zones. Alteration and post-metamorphism increased the P-wave velocity and density of felsic volcanic rocks but the impact of this change has not been clearly identified on seismic data. Many prominent and continuous reflections of lithological origin are observed close to the base of the Chisel sequence. P-S results are not discussed here but will be presented at the workshop.
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Deep Ore Exploration of Sulfides with Seismic Reflection Profiling in Outokumpu, Finland
Authors S.E. Heinonen, S. Aatos, P.J. Heikkinen, N. Hellqvist, M. Kurimo, H. Leväniemi and I.T. KukkonenA network of high resolution seismic reflection profiles was acquired in Outokumpu, Finland. Outokumpu is one of the most important mining regions in Finland where active sulphide exploration is ongoing. Over 5 km long spread with 402 active channels and nominal vibroseismic source point interval of 25 m guarantee high fold and good signal-to-noise ratio of the seismic data. These high quality data have been commercially processed by Vniigeofizika, Moscow with standard hardrock seismic processing flow including careful static corrections. Seismic sections were migrated and depth converted with constant velocity (5400 m/s) that corresponds approximately to the seismic P-wave velocity in the main lithology of the area, mica schist. Additionally to seismic velocities, also densities of the main lithologies have been measured from the 2.5 km long drill hole. This enables estimation of the main sources of reflectivity in the Outokumpu area. Encouragingly, typical ore hosting lithological assemblage was found to be brightly reflective both externally and internally due to interlayers of high acoustic impedance skarns and low acoustic impedance serpentinites. All together nine interconnected seismic profiles combined with the drill hole logging data and other geophysical data, including ZTEM survey, enable the 3D-modeling of the Outokumpu subsurface structures.
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High Resolution Seismic Reflection for Imaging Metamorphic Rocks
By M. JudTo optimize the exploitation of ore deposits it is necessary to know the exact geometry of the ore body, as well as the geometry of any barren rock. In the course of this project the principal applicability of high resolution 2D seismic reflection should be tested. For this purpose we have chosen a magnesite quarry where the geology is known from outcrops and deep mining.
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3D Seismic Processing of Crooked Line 2D Data in the Vicinity of the COSC 2.5 Km Deep Scientific Borehole
More LessTwo crooked line 2D seismic profiles were acquired in the vicinity of the location of the first scientific borehole of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project. The planned depth of the borehole is 2.5 km and drilling will start in mid-Spring 2014. The data were previously processed in 2D and the borehole was located based on the results of this processing. In order to obtain a better image of the subsurface and provide better predictions of the expected lithology at depth the data have been reprocessed as a sparse 3D data set. The 3D processing suggests that a larger mafic lense is expected to be penetrated at about 1000 m depth and the base of a high grade metamorphic unit at about 2.2-2.3 km depth. The upper 500 m is not well imaged due to the acquisition geometry.
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Joining Diverse 3D Geometries in PSTM
Authors S. Ziramov, M. Urosevic, J. Kinkela, A. Dzunic and M. PenneyUnique set of 4 overlapped 3D hard rock seismic surveys was processed jointly after successful merging. All four data sets had significant differences in design parameters so that nominal bin size, fold, source/receiver spacing, source line/receiver line interval, azimuthal and offset distribution were quite diverse. Hence the main objective became to attenuate strong footprint caused these geometrical differences. To do so we firstly utilised unique CMP binning followed by surface consistent processing and relative amplitude preservation. Excellent PSTM results were subsequently achieved by appropriate operations performed in the offset planes and by zeroing all the extrapolated migration artefacts. This comprehensive approach resulted in amplitude consistent, fully merged 3D seismic cube with continuous reflectors across entire area which made interpretation reliable and provided assistance to the drilling program.
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Deep Shear Wave Imaging Using Cross-dipole Wireline Data
Authors T.W. Geerits and A. PrzebindowskaDuring the last three decades significant developments have occurred in the design and application of borehole acoustic measurements. Where during the first decade the main focus has been on slowness analysis and its applications (E.g., porosity, synthetic seismogram, etc.), the last two decades have resulted in more advanced applications: -permeability estimation from Stoneley waves; -intrinsic/stress-induced anisotropy from flexural waves; -and most recently, imaging away from the wellbore. The latter application has great promise in imaging fine structural features away from the wellbore, particularly in hard rock (I.e., less attenuation) and it is complementary to conventional surface seismic. Whereas the seismic method has an imaging resolution of order 10^1 m and a depth of investigation of order 10^3 m, the borehole acoustic method has an imaging resolution of order 10^-1 m and a depth of investigation of order 10^1 m. Furthermore, although the borehole acoustic method has been developed for and applied to mainly wireline configurations, it is considered to have an even greater value in a Logging While Drilling (LWD) setting as a result of its geosteering potential. The cross-dipole acoustic measurement principles, theory and processing steps will be explained in conjunction with two case studies.
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The Application of Borehole Hydrophone Arrays in Hardrock Environments
Authors A.J. Greenwood, M. Urosevic, J.C. Dupuis and A. KepicThe geometry of a VSP survey allows us to understand the characteristics of both the transmitted and reflected wavefields. As such, VSP is an “in-field seismic laboratory”, necessary for understanding the origin of seismic events. VSP enables calibration of surface reflection images and the survey can be designed to produce an image around the borehole at a much higher resolution than the surface reflection method. The main drawback of the method with respect to the mining community is the high logistic cost. Hence the main objective of the research presented here is to look into alternative ways of implementing VSP surveys that are cost effective, readily implementable in slim holes and pose lower risk to equipment in unstable uncased mineral exploration boreholes. As shown in this work, these objectives have been met using a borehole hydrophone array. Presented are two field trials in the Agnew-Wiluna and Kambalda regions of Western Australia. The results of these field experiments demonstrate that a borehole hydrophone array is capable of imaging structure in a complex geologic environment. These results, however, are not easily achieved because of the high sensitivity of hydrophones to acoustic modes in the borehole and the passive coupling to the formation.
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Fracture Detection via Beam Imaging and Image Spectrum Analysis
Authors M. Protasov, V.A. Tcheverda and G.V. ReshetovaAn approach to seismic imaging of fractures by multicomponent surface data is presented and discussed. It is based on a specific imaging procedure, which consists in a weighted summation of multicomponent multishot/multioffset data. These weights are computed by tracing a specially chosen Gaussian beams. In order to get image of fractures these beams are taken in a way forming so called selective images (Pozdnyakov and Tcheverda, 2006; Protasov and Tcheverda, 2011). Their geometry provides suppression of regularly reflected waves and, thus, emphasizes the presence of small-scale heterogeneities that give rise to diffracted/scattered waves. Additionally spectral removal is applied for more essential suppression of regular reflections footprint. Numerical experiments with synthetic data set computed for the typical seismogeological model of Yurubcheno-Tokhomskoye area are presented and discussed.
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Diffraction Imaging in Hard Rock Environments
Authors K.V. Tertyshnikov, R. Pevzner, A. Bóna, F. Alonaizi and B. GurevichHard rock seismic exploration normally has to deal with rather complex geological environments. These types of environments are usually characterized by a large number of local heterogeneities. The seismic data from such environments often have a poor signal to noise ratio because of the complexity of hard rock geology. In such situations, the processing algorithms that are capable of handling data with a low signal/noise ratio and are able to image geological discontinuities and subvertical structures are essential. Herein we present a modification of the 3D Kirchhoff post-stack migration algorithm and diffraction imaging. The modification utilizes coherency attributes obtained by the diffraction imaging algorithm in 3D to weight or steer the main Kirchhoff summation. We applied diffraction techniques to a number of 3D seismic datasets from different hard rock mine sites.
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Surface Wave Dispersion Analysis - From Local 1D Models to Tomography
Authors L.V. Socco, P. Bergamo and F. GarofaloThe analysis of surface wave dispersion represents an important exploration method at different scales. The basic scheme of the method is mainly based on 1D assumption, but laterally varying sites can be resolved if an opportune processing and inversion strategy is applied. Spatially constrained inversion (SCI), joint inversion with P-wave travel times and tomography represent possible techniques to apply to retrieve 2D models.
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Past, Present, and Future of Seismic Interferometry
By R. SniederI give an overview of the long history in of seismic interferometry, starting with Einstein's work in 1906 on Brownian motion, through developments in physics in the 1950's to the surge in seismic interferometry in 2000's. I indicate the possibilities and limitations of the method, and pose a number of challenges.
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Probing Near Surface Shear Velocity Structure from Ambient Noise and Surface Wave Array Tomography
More LessAmbient noise tomography has provided essential constraints on crustal and uppermost mantle (isotropic and anisotropic) shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for tomography of near surface shear velocity structures. This approach provides important information for strong ground motion prediction in urban area and near surface structure characterization in oil and gas fields. Here we first give a brief overview about the methodology of ambient noise tomography in global seismology. Then we focus on some recent developments on recovering near surface shear velocity structure using ambient noise tomography. We propose a new one-step iterative surface wave tomography approach that directly inverts all path-dependent dispersion data for 3-D shear wave speeds, in which we perform surface-wave ray tracing at each period using the fast marching method and update ray paths for the next step tomographic inversion. The proposed approach is more efficient than the traditional two-step surface wave tomography and provides a consistent framework for future joint surface wave and body wave travel time tomography.
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Near-surface Full Waveform Inversion Using Surface Waves and Reflected Waves
Authors I. Masoni, W. Zhou, R. Brossier, L. Métivier, S. Operto and J.M. VirieuxWe investigate the capacity of extracting near-surface shear-wave velocity by considering dispersive surface waves and non-dispersive reflected waves. We show that indeed the full waveform fitting of these waves requires a dedicated approach by using lateral spatial and frequential coherence for surface waves and by explicitely introduces the fitting of reflected waves in the inversion formulation. On a simple example as a two-layers model, lateral variations of the velocity are reconstructed while the low-wavenumber content of the velocity could be improved through reflection waves. Combining these two sources of information on the shear-wave velocity could improve our shear-wave velocity imaging in the near-surface context.
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Challenges for 2-D elastic Full Aaveform Inversion of Shallow-seismic Rayleigh Waves
Authors L. Groos, M. Schäfer, S. Butzer, T. Forbriger and T. BohlenShallow-seismic Rayleigh waves are attractive for geotechnical site investigations. They exhibit a high signal to noise ratio in field data recordings and have a high sensitivity to the S-wave velocity, an important lithological and geotechnical parameter to characterize the very shallow subsurface. In recent years we studied the applicability of the two-dimensional elastic FWI method using numerous synthetic reconstruction tests and two field data examples. Some important challenges are reported here: (1) the accurate correction of the geometrical spreading, (2) the estimation of the source wavelet, (3) the importance of an-elastic attenuation in the forward simulations. We found that Important pre-processing steps for the application of 2-D elastic FWI to shallow-seismic field data are the 3D to 2D correction of geometrical spreading and the estimation of a priori Q-values that must be used as a passive medium parameter during the FWI. Furthermore, a source-wavelet correction filter should be applied during the FWI process. Smooth initial models obtained from the analysis of the first arrivals of body waves are important and seem to be sufficient. Our field data examples indicate that FWI is able to resolve lateral variations of S-wave velocities in the very shallow subsurface.
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