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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 - 100 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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Surface-wave Analyses in Unconsolidated Granular Models with Increasing Degrees of Complexity
Authors L. Bodet, P. Bergamo, A. Dhemaied, R. Martin, R. Mourgues, S. Pasquet, F. Rejiba, L.V. Socco and V. TournatUsing micrometric glass beads, we build small scale physical models with increasing degrees of complexity in order to address theoretical and methodological issues of seismic methods (velocity gradients, lateral variations, pore overpressure, etc.). We simulate seismic records at the surface of the laboratory models thanks to a mechanical source and a laser-Doppler vibrometer. From recorded seismograms, we are able to invert surface-wave dispersion for one or two-dimensional velocity structures. These experiments are for instance used as benchmarks for processing and inversion techniques, enable the validation of numerical methods, or make it possible to study issues related to pore fluids.
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Near-surface Modelling from Surface and Guided Waves and Its Applications
Authors D. Boiero, C. Strobbia, A. Zarkhidze, E. Wiarda and P. VermeerSurface and guided waves are effective sources of information for near-surface characterization. They constitute a large part of the recorded energy and, with proper acquisition, analysis, and inversion, can be used to model the near surface with surprisingly high resolution. In this role, they can be used for correcting short- to long-wavelength perturbations, building velocity models, and optimizing coherent noise-filtering workflows.
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The Interpacific Project - A Cooperative Exercise for Assessing Reliability and Accuracy of Seismic Methods
Authors F. Hollender, P.Y. Bard, C. Cornou, B.R. Cox, S. Foti, F. Garofalo, M. Ohrnberger and D. SiciliaThe InterPacific (Intercomparison of methods for site parameter and velocity profile characterization) project aims to assess the reliability/variability of seismic site characterization methods (borehole and surface wave methods) used for estimating shear wave velocity (Vs) profiles and corresponding lumped parameters (e.g., Vs,30). The ultimate goal of the project is to determine procedures that can be used for the construction of consistent ground models for seismic studies. Three sites have been selected in France and Italy for the implementation of the project. They are representative of different geological conditions relevant for the evaluation of seismic site response effects: a stiff rock outcrop, a deep soft deposit, and an intermediate case with thick stiff soils and large bedrock depth.
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Deriving P-wave Near-surface Models from Exploration Data
Authors E.J. van Dedem, F. Ernst and J. ShorterAdequate handling of the near surface is crucial for proper imaging of land data, especially for complex overburdens. Recently we introduced modal elastic inversion (Ernst 2013): approximate FWI which inverts P-guided waves to near-surface P-velocity models. We will present two case studies of modal elastic inversion of P-guided waves to obtain near-surface velocity models. The results show that this inversion approach can give realistic results not only for modern high-end densely sampled surveys, but also for sparse legacy dynamite surveys.
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Effects of the Trace Interval on Surface Wave Dispersion and Inversion
Authors T.J. Gong, H.L. Chen, X.D. Li, Y.Q. Ye, J. Liu, H.J. Zhang, C.Z. Ni, G.D. Ding and B.J. LiangIt is the trace interval that determines the spatial frequency property of one shot gather. As the trace interval increases, spatial aliasing emerges and data quality deteoriates. Aliased surface waves in the dispersion energy map have false higher-mode dispersion curves, or low velocity noise, and have missing or pronged dispersion energy trends at certain frequency ranges. Qualitatively, large spacing causes a severe aliasing that smears the dispersion plot, yielding it unusable. As long as spatial aliasing is not dominant, the surface waves can be used to invert the corresponding subsurface structure. We present a synthetic example to test the effectiveness of the high resolution linear Radon transform (HRLRT) and the least squares Radon transform (LSRT), which are used to calculate dispersion curves. Since the HRLRT typically affords a better low frequency response, we use it to map the field example. Effects caused by different spatial intervals in dispersion maps of synthetic and field examples are also shown. A genetic algorithm is used in the inversion to determine the subsurface structure, and these results are then compared with a nearby borehole test. The agreement between the test and the model shows the promising prospect of the surface wave methods.
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Multimodal Rayleigh Wave Dispersion Curve Picking and Inversion to Build Near Surface Shear Wave Velocity Models
More LessThe use of Rayleigh waves to invert for a near surface shear wave velocity model is attractive in converted wave processing, such as the application of receiver side statics correction and PS PSDM. We propose a differential evolution inversion scheme to invert Rayleigh wave dispersion curves, and we apply it on a field dataset with high density acquisition to obtain the underlying shear wave velocity structure. The joint use of a new misfit function, which allows multimodal inversion and reduces the risk of mode misinterpretations, combined with differential evolution inversion is highly likely to converge to the real shallow shear wave velocity structure. A semi-automatic picking method based on the quick thinning algorithm is introduced to extract the dispersion curves from frequency-phase velocity spectra. This greatly reduces the demand on manual labor and improves productivity.
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Surface Wave Analysis - Challenges for Application on an Ultra-shallow Structure Characterisation
Authors C.A. Pérez Solano, D. Donno, H. Chauris and G.P. DeiddaWe discuss several difficulties related to the application of Full Waveform Inversion using surface waves in the context of seismic data acquired on an ultra-shallow ground model (0 — 10 m depth). For instance, the choice of an accurate initial velocity model in the presence of very high velocity contrasts is complicated. The presence of surface waves increases local minima problems in the objective function, preventing from convergence towards the global minimum. For improving convergence, we propose to use an alternative functional, the windowed-Amplitude Waveform Inversion, which is similar to dispersion curve analysis but without any picking step. The source wavelet is iteratively estimated during the velocity model inversion. If previous examples have shown that this methodology is applicable in synthetic data sets, it is less obvious in real data sets as discussed here.
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Thickness Variations in Layered Subsurface Models - Effects on Simulated MASW
Authors S. Bignardi, G. Santarato and N. Abu ZeidSeismic surface wave methods allow to retrieve the shallow subsurface shear wave velocity. Among these, the “Multi-channel Analysis of Surface Waves” is to date one of the most widely adopted non-invasive active-source approaches in the professional world for the evaluation of the stiffness properties of the ground for geotechnical engineering purposes. The method utilizes the dispersive nature of surface waves by constructing the dispersion curve which is then inverted to obtain the shear wave velocity profile. Dispersion curves generation typically requires the transformation of the recorded seismograms into the frequency-velocity (f-V) domain. Commercially available inversion algorithms assume the subsurface model as a stack of homogeneous parallel layers, but unfortunately this may lead to misleading results if the actual soil profile is far from the assumed 1D geometry. We investigate the effects of lateral heterogeneities due to variations of layer thicknesses on the f-V spectrum to assess the limitations of the 1D approach and thus to judge the reliability of such surface waves interpretation
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Geological Setting of the Vaca Muerta Fm, Neuquen Basin - A World class Shale Play
Authors M. Di Benedetto, P. Biscayart, J. Zunino and J. SoldoThe Vaca MuertaFormation, the main proven source rock in the Neuquen basin, has become, in the last two years, a unit that promises an enormous potential as a Non-Conventional Shale Gas and Oil resource play. This unit shows a high geological complexity related, primarily, to its large size and extension. The aim of this work is to characterize the geological features of Vaca Muerta Fm., as an example of a shale play, in order to understand and define the productivity of this type of shale resources.
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Relationships among Porosity, Permeability and Seismic Velocity of Shales
By N.H. MondolThis study focuses on relationships among porosity, permeability and seismic velocity of shales. A total of thirty well characterized, brine-saturated (35000 ppm NaCl) synthetic shale of varying textural and mineralogical compositions were compacted mechanically both in triaxial and oedometer cells under controlled pore pressure and proper drained conditions. Results show that kaolinite dominated shales compact more but have higher permeability and seismic velocity compared to smectite dominated shales at same stress/depth. Permeability differs a maximum five orders of magnitude at the same porosity for different shales. For velocity-permeability relationship between kaolinite- and smectite-dominated shales, a maximum four orders of magnitude are observed. Velocity/porosity can therefore not be good proxy to estimate reliable permeability in shales. Comparison of experimental and published data show a good agreement and illustrated that a better understanding of mineralogical and textural relationships can be significantly improved to establish relationships among porosity, permeability and seismic velocity of shales. In addition to the existing database, the new experimental data (this study) can improve the calibration of fluid flow modeling, seismic and well-log interpretation and evolution of shale rock properties. The experimental results may also be of importance for structural design, slope stability analysis and waste disposal efforts.
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Experimental Studies of Stress Dependence, Static vs Dynamic Behaviour and Mechanical Anisotropies of Shale
Authors R.M. Holt, A. Bakk, A. Bauer, E. Fjær and J.F. StenebråtenLaboratory data from controlled rock mechanical tests with various shales have been used to understand and quantify stress effects on wave velocities of relevance for 4D seismics, and to quantify the difference between static and dynamic mechanical properties and their anisotropies.
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The Effect of Shale Mineralogy on Anisotropy in Unconventional Resources Settings - A Rock Physics Modeling Study
By R. BachrachRock physics modeling provides a mathematical framework that links rock volumetric and microstructural parameters to effective elastic properties. Shales, which are elastically anisotropic, provide a special challenge for rock physics modeling due to the complex nature of their fabric and pore space and the large variations in depositional and diagenetic settings that affect the mineralogical composition, porosity and fabric of the rock.
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3D Relocation Errors of Microseismic Events by Surface and Borehole Receivers for Shale Gas Stimulation
Authors H. Alsahfy, A.L. Vesnaver, M. Jervis and H. KuleliMicroseismic monitoring and mapping of induced hydraulic fractures (frac) is an important tool in unconventional oil and gas exploitation. It is a key technology for completion evaluation which allows for continuous improved frac design, frac effectiveness, and ultimate resources recovery estimation and development. Formation evaluation tools provide accurate measurements of the target formation’s petrophysical and mechanical properties proximal to the borehole only, distal to the borehole though, Microseismic monitoring can be a useful tool to monitor the formation’s response to the frac. Shale response to hydraulic stimulation can be estimated mainly by the local density and pattern of hypocentres. Linear trends of microseismic event and their associated focal mechanisms may highlight the reactivation of faults due to hydraulic stimulation, while the location of events outside the target formation may suggest a need for future Improvements to the completion/ stimulation plan, and in some cases, re-stimulation. However, errors in the hypocentre locations may convert clear trends into “fuzzy” clouds, hampering our understanding of how the simulation interacted with the formation. The accuracy of hypocentral coordinates of micro-earthquakes is critical for understanding and proper planning for the hydraulic stimulation jobs of a shale play.
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The Role of Geomechanics in Reservoir Stimulation Design Procedure
Authors M.M. Slota-Valim and H.B. Jedrzejowska-TyczkowskaHydraulic fracturing treatment preceded with reliable geomechanical analysis of the reservoir, whether carried out immediately after well completion or during late stages of the reservoir lifetime (refracturing among others), helps to avoid near-wellbore area damage and the hydrocarbons production increase, through the creation of the artificial fracture network and therefore enabling free flow of the gas from the unconventional formation into the wellbore. The practice of stimulation treatment by fracturing the geologic formation reaches 1947, but the early application of hydraulic fracturing was not successful due to the problems with diagnosis of the complications and selection of wells that were about to be subjected to the treatment. Over the last two decades numerous cases of successful secondary fracturing were recorded in the hydrocarbons reservoirs in North America, Russia, China, Brazil and Algeria. Obviously the potential for production increase have hydrocarbon deposits around the world, especially those at advanced stage of exploitation. In most of the cases the use of such treatments is much more economical than determining optimal location, well design, drilling and completion of new well.
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Model-based Workflows for Optimal Long-term Reservoir Mangement
Authors O. Leeuwenburgh, P. Egberts, A. Chitu and F. WilschutLife-cycle optimization is the process of finding field operation strategies that aim to optimize recovery or economic value with a long-term (years to decades) horizon. A reservoir simulation model is therefore generally appropriate and sufficient to explore the impact of different recovery scenarios. A number of challenges arise when trying to determining the optimal recovery strategy. We describe a practically feasible model-based optimization workflow that addresses complications associated with computational effort, large numbers of decision variables (controls), and the uncertainty in the properties of the reservoir. A software tool has been developed, in cooperation with industry partners, and applied to several synthetic and real field cases to demonstrate the value and potential benefits of this workflow, such as optimal well operating strategies for multiple wells that increase recovery or economic value, improved well design, and reservoir understanding.
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Marine CSEM - Where Do We Stand and Where Can We Go?
More LessAlthough most of the early problems that plagued commercial marine CSEM data have been addressed, the market for marine CSEM data is shrinking. Reasons include a lack of integration with the rest of the exploration workflow, high cost of data acquisition, and lack of diversity in the marketplace. Small companies are discouraged from competing because of the threat of patent lawsuits, and large companies appear to be looking for a larger commercial opportunity than marine EM currently provides. Data show that the marine CSEM method works, and that very few commercially viable hydrocarbon targets lack a detectable resistivity signature. The existence of the large number of dry wells that support this assertion demonstrates that the method is not being used to best advantage.
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CSEM - Where Do We Stand and Where Can We Go?
More LessCSEM was established as an industry 12 years ago by several service companies that offered 2D CSEM commercially. The presentation will focus on how CSEM has developed as a commercial tool since the first commercial introduction 12 years ago and look into the future. The technology has gone through a significant development. The most important step was from 2D to 3D wide azimuth data enabled by improvements in equipment, operations, inversion and streamlined processing of large data volumes. Both horizontal and vertical resistivity cubes are now inverted, enabling mapping of anisotropy and CSEM is no longer limited to deep-water applications. Wide-azimuth 3D surveys will most likely be the main way to acquire CSEM data also in the future. In future processing and inversion, magnetic field data will be used more to improve imaging, especially in shallow water. In general MT data will also be used more which implies stationary seafloor receivers with both electric and magnetic sensors (Ex, Ey, Hx and Hy). CSEM will see deeper (stronger sources), get better resolution and improved data will be processed jointly with seismic, resulting in improved imaging. Moreover, the data will be used as an important part in the oil companies workflow.
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Increasing Transmitter Current and Reducing Ambient Noise Levels – What Are the Limitations?
Authors R. Mittet, J.P. Morten and H.R. JensenThe marine controlled-source electromagnetic method (CSEM) can detect subsurface hydrocarbon reservoirs because they represent resistors in a conductive medium, i.e. brine-saturated rocks. The limitations on the applicability of the technology are given by target burial depth, lateral extent, and the net pay thickness. Improvements to the acquisition instrumentation can extend the applicability and increase the resolution. However, several factors affect the accuracy of the measured data. To achieve a significant improvement it is important to understand the experimental error contribution from each hardware component in relation to the target effect on the data. We present error propagation analysis for CSEM acquisition, which reveals feasible limitations for target detection. Further, we show how equipment can be optimally improved to extend applicability of the technology.
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Rotate your Dipoles by 90 Degree - the Vertical CSEM Approach
Authors S.L. Helwig, J.M. Børven, K. Eide, Ø. Frafjord, T. Holten and A.W. El KaffasThe acronym CSEM has widely become synonymous for frequency domain Controlled Source ElectroMagnetics with seabed nodes and horizontal towed dipole transmitters. While this incarnation of marine CSEM is certainly the best known CSEM variant, it is not necessarily always the best option for acquisition over a certain prospect. Based on numerical modelling the differences between horizontal FD CSEM and vertical TD CSEM for given models were explored. The results show that time domain CSEM with vertical transmitter and vertical receiver dipoles is a viable alternative that provides high sensitivity, high depth of penetration as well as low disturbance by air wave and 3D structures. It's much smaller transmitter receiver distance creates an advantage in lateral resolution as well as in the detection of narrower or smaller structures. Case studies with comparisons between inverted vertical-vertical CSEM data and well log results show the real world usefulness of the method as well as the necessity for close integration of the results with other geophysical data. We argue that the marine CSEM landscape will become more divers and that acquisition layout and methodology for a given target needs to be evaluated on a case by case basis to achieve optimum results.
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Investigations on Small Scale Targets with Sputnik, a Two Polarization Transmitter System
Authors S. Hölz, A. Swidinsky, M. Sommer and M. JegenSputnik is a novel CSEM transmitter system, which is used for small scale investigations. The system is special in the sense that it can excite two perpendicular TX polarizations at each TX location. It can be shown that this generally increases the sensitivity of measurements to the resistivity structure of the seafloor. This style of experiment requires new approaches for a first pass data interpretation, for which we have adapted the concept of rotational invariants to the marine case. Rotational invariants allow a display of measured data in terms of apparent resistivity sections. They can also be used in the inversion of data. Additionally - using the skew invariant - a dimensionality analysis of the underlying resistivity structure is possible directly from the measured data. Within the past two years the system has been used in three successful experiments for the investigation of methane hydrates and free gas. First results prove that the system is a useful tool for investigations on small targets.
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Anisotropic Inversion of Towed Streamer EM Data in Shallow Waters
By J. MattssonTowed streamer electromagnetic (EM) data along a survey line at the Alvheim Boa oil field in the North Sea has been inverted using an open-source 2.5D inversion code. The electric field data was acquired in 4 kn with a single vessel using a horizontal bipole source at 10 m depth and densely populated electrode pair receivers housed in a towed streamer towed at 50 m depth in water depths between 110 and 125 m. The inversion algorithm is based on a parallel adaptive 2.5D finite element algorithm and uses a regularized variant of a Gauss-Newton minimization algorithm. This inversion method has proven to be fast and efficient for and suitable for towed streamer EM data. In this case, the resulting anisotropic resistivity cross section corresponds well with the high resistive part of the sand layer in the vicinity of the reservoir depocenter. The low noise in the frequency response data and the low navigation and measurement uncertainties made it possible to obtain a final misfit as low as 2 %. The towed streamer EM technology has proven to be a robust and useful CSEM method in shallow waters. The densely sampled frequency response data is suitable for anisotropic inversion.
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Towards Real Earth Models - Computational Geophysics on Unstructured Tetrahedral Meshes?
Authors C.G. Farquharson, P.G. Lelièvre, S. Ansari and H. JahandariUsing unstructured tetrahedral meshes to specify 3D geophysical Earth models has a numer of advantages. Such meshes can conform exactly to the triangularly tessellated wireframe surfaces in the 3D Earth models used by geologists. This offers up the possibility of both geophysicists and geologists working with a single unified Earth model. Unstructured tetrahedral meshes are extremely flexible, and so can accurately mimic arbitrarily complicated subsurface structures and topography. Also, in the context of electromagnetic methods, unstructured tetrahedral meshes can be very finely discretized around sources and yet can transition to a coarse discretization in the extremities of the solution domain without, in principle, affecting the quality of the mesh. However, using unstructured tetrahedral meshes for geophysical Earth models has its challenges. The tessellated surfaces in wireframe geological models are often not immediately suitable for computational techniques as they can contain intersecting facets and facets with extreme aspect ratios. Generating tetrahedral meshes that are of sufficient quality from real wireframe geological models can therefore be difficult. This presentation will aim to discuss the pros and cons of using unstructured tetrahedral meshes for geophysical Earth models, keeping in mind the complexities of the real subsurface that we are ultimately trying to represent.
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Advanced Modeling and Inversion Tools for Controlled Source EM
By E. HaberModeling and invasion of CSEM data is a challenging problem. In this work we present a combination of methodologies that allows for the solution of such problem using reduced in a computational efficient way. Our framework is composed from three main parts 1. An adaptive mesh, that is adapted to the sources and receivers, that decreases the size of each linear system to be solved. 2. A multiscale approach that allows us to use large cells far away from the sources and receivers and correctly average or upscale the conductivity. 3. A stochastic programming approach that allows for the reduction of the number of forward modeling at each step of the inverse problem
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New Advances for a Joint 3D Inversion of Multiple EM Methods
More LessElectromagnetic (EM) methods are routinely applied to image the subsurface from shallow to regional structures. EM methods differ in their sensitivities towards resistive and conductive structures as well as in their exploration depths. Joint 3D inversion of multiple EM data result in significantly better resolution of subsurface structures than the individual inversions. Proper weighting between different EM data is essential, however. We present a recently developed weighting algorithm to combine magnetotelluric (MT), controlled source EM (CSEM) and DC-geoelectric (DC) data. It is known that MT data are mostly sensible to regional conductive structures, whereas, CSEM and DC data are suitable to recover more shallow and resistive structures. Our new scheme is based on weighting individual components of the total data gradient after each model update. Norms of each data residual are used to assess how much weight individual components of the total gradient must have to achieve an equal contribution of all data in the inverse model. A numerically efficient way to search for appropriate weighting factors could be established by applying a bi-diagonalization to the sensitivity matrix. Thereby, the original inverse problem can be projected onto a smaller dimension in which the search of weighting factors is numerically cheap.
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Estimation of the Petrophysical Model through the Joint Inversion of Seismic and EM Attributes
Authors F. Miotti, I. Guerra, F. Ceci, A. Lovatini, M. Paydayesh, G. Milne, M. Leathard and A. SharmaReservoir characterization objectives are to estimate the petrophysical properties of the prospective hydrocarbon traps and to reduce the uncertainty of the interpretation. In this framework, we present a workflow for petrophysical joint inversion (PJI) of seismic and EM attributes to estimate the petrophysical model in terms of porosity and water saturation. This study realizes the joint inversion within the probabilistic structure provided by the Bayesian theory. 3D volumes of estimated porosity and saturation show how the joint inversion of acoustic impedance and electrical resistivity can provide a quantitative description of the reservoir properties and with it a measure of uncertainty, which is consistent with the petrophysical model and observations.
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Joint CSEM–seismic Evaluation of Risky Drilling Task
More LessDue to the complex surface and subsurface exploration conditions, hydrocarbon reservoir distribution is controlled by many unknown factors, such as structure reservoir, lithologic trap reservoir, stratigraphic trap reservoir, and changes of exploration target, etc., any single geophysical exploration method has higher risk to predict and evaluate the hydrocarbon reservoir. Explorationists have high expectation to identify hydrocarbon target using CSEM method, but its wide applications have been limited due to its low resolution and poor accuracy. Recent years, CSEM and seismic constrained or joint inversion has achieved higher accuracy for electrical anomaly target exploration. Based on this trend, we have developed a new exploration method of the joint TFEM (Time and Frequency domain EM) – Seismic evaluation of risky drilling task. When an exploration area not only has confirmed seismic structure trap and reliable AVO anomaly, but also has matched induced polarization (IP) and resistivity anomaly (R) on the potential exploration target, it will have much lower drilling risk. The wide application of this new exploration method in the west of China has significantly improved the drilling success rate through the using the joint TFEM – Seismic method to predict and evaluate the potential hydrocarbon target.
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Marine CSEM for Gas Hydrate Exploration Using a Seafloor-towed Multi-receiver System
Authors K. Schwalenberg, M. Engels, D. Rippe and C. SchollIn the past years BGR – the German Federal Institute for Geosciences and Natural Resources has been developing unique marine CSEM systems to explore the electrical attributes of the shallow seafloor. CSEM data are sensitive to the presence of resistive gas and gas hydrate in the sediment, and provide complementary volume information which, if used in connection with seismic and other exploration methods, e.g. drilling, allow for a better evaluation of the gas or gas hydrate resource potential. The gas hydrate setting differs from the exploration of conventional offshore oil and gas reservoirs as typical gas hydrate deposits are smaller in scale und at shallower depths below the seafloor. Therefore instrumentation and survey configurations need to be adapted. HYDRA, the seafloor-towed, multi-receiver system has been recently refined with a new signal generator and receiver units which both allow for online communication and data transfer. 1D and 2D inversions of CSEM data collected offshore New Zealand result in highly anomalous resistivities over several methane seep sites within the gas hydrate stability field which are believed to be caused by concentrated gas hydrates below the seeps.
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Overview of Marine Controlled-Source Electromagnetic Interferometry by Multidimensional Deconvolution
Authors J.W. Hunziker, E. Slob and K. WapenaarInterferometry by multidimensional deconvolution for marine Controlled-Source Electromagnetics can suppress the direct field and the airwave in order to increase the detectability of the reservoir. For monitoring, interferometry by multidimensional deconvolution can increase the source repeatability. We give an overview over the method and discuss a possible path of research for the future.
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Recent Developments for Land-based Controlled-source Electromagnetic Surveying
Authors K. Tietze, A. Grayver, R. Streich and O. RitterControlled-source electromagnetic (CSEM) surveying has been in use for more than ten years and has become a well-established tool for hydrocarbon exploration in marine environments. On land, however, CSEM methods are rarely applied in a similar manner, since challenges are greater for a range of technical, logistical, and numerical aspects. Over the last five years, the Geo-Electromagnetics working group at the German Research Centre for Geosciences Potsdam (GFZ) has been developing the CSEM method for land-based applications, including a three-phase current transmitter allowing for arbitrary source polarizations, new robust data processing concepts, and 1D to 3D modelling and inversion software. The CSEM hardware and software has been successfully applied in a series of surveys on different targets. We show examples from case studies, including 3D inversion results from the Ketzin CO2 injection test site in Northern Germany.
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Advances in Electromagnetic Survey Instrumentation and the Use of a Cased Borehole for Imaging a Deep Formations
Authors A.D. Hibbs, T.R. Petrov, J. Pendleton, A. Agundes, S. Kouba, T. Hall, D. Boyle, T. Martin, C. Schenkel and H.F. MorrisonElectromagnetic (EM) resistivity imaging methods have the potential to map subsurface fluid distribution in applications ranging from derisking potential prospects to quantifying the propagation of hydrofractures in unconventional reservoirs. However, to date EM surveys have been limited to reservoirs too shallow or too large to be of general applicability in the oil industry. The critical technology issues in extending EM methods are: a) generating an adequate subsurface electrical current, and b) the sensitivity and stability of the EM resistivity measurement apparatus. A borehole provides a physical means to contact to deep hydrocarbon formations. To date boreholes have been exploited by lowering a current injection electrode to the depth of interest and completing the electrical circuit with a counter electrode at the surface. This borehole to surface EM method has been successfully used to image oil-to-water contact in an oil reservoir but has the disadvantage that the well must be opened, and, for a producing reservoir, taken off-line. We have now demonstrated a new approach that uses the borehole casing as a current injection electrode. In addition, we have developed the first capacitive sensors for geophysical use and have adapted them for use with commercial seismic data recorders.
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Utilizing Impressed Current Cathodic Protection as the Source for Electromagnetic Exploration
More LessCentral Europe is criss-crossed by pipelines to transport water, gas and oil. Metal pipelines are routinely protected against electrochemical corrosion with a coating supplemented with an impressed current cathodic protection (ICCP) system. For pipeline integrity tests, the rectified injection current is temporarily switched on and off. The switching scheme effectively generates time-varying electrical currents and induces secondary electric and magnetic fields in the subsurface, which decay spatially and temporally as a function of subsurface electrical resistivity. Here, we describe our first attempts to measure and to analyze the induced electromagnetic fields generated by switched cathodic protection currents in order to determine the subsurface electrical resistivity structure in the upper (few) kilometers depth range. This approach is closely related to controlled source electromagnetics. It may provide a cheap complement to existing electromagnetic geophysical sounding techniques, which is applicable in noisy environments without facing the logistical challenge of the installation a strong current source in the field. The methodology can aid in geophysical subsurface reconnaissance addressed in the exploration and monitoring of resources, reservoirs and geological storages.
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Assimilation of Time-lapse CSEM Data for Fluid Flow Monitoring
Authors M. Lien, T. Mannseth and R. AgersborgThe feasibility of marine CSEM for reservoir monitoring is supported by several model studies suggesting that there may be a detectable time-lapse signal in CSEM data. However, the detectability of these signals for field cases will depend on careful acquisition design and reliable inversion methodology. To mitigate the inherent non-uniqueness associated with these large scale geophysical problems, the integration of additional data types is required. Constraining the solution space by including different data types in the model calibration process can help reducing the model uncertainty and lower production related risk. In this talk, the use of statistical ensemble based methods (EnKF) for the integration of CSEM data and other geophysical data types (i.e. gravimetric data) will be discussed. By the utilization of a statistical inversion method, an assessment of the uncertainty in the estimated flow patterns is obtained as part of the solution.
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Hydro-frac Monitoring Using Ground Time-domain EM
Authors G.M. Hoversten, M. Commer, E. Haber and C. SchwarzbachThis paper explores the sensitivity of surface based time domain electromagnetic systems for monitoring hydraulic fractures. The steel well casing of the frac well acts primarily as a DC current path that charges the conductive fracture zone during the transmitter on-time. This increases the current density in the fracture zone several orders of magnitude above that without the steel well connection. The background resistivity for production environments range from Bakken shale (30 Ohmm) to West Texas carbonates (500 Ohmm). The transient decay response from fracture zones with steel casing produces anomalies between 5% (30 Ohmm background) and 150% (500 Ohmm background) for Ex-Ex coupled surface systems for a 1500 bbl injection (a small frac stage) at 3km below the surface when a conductively enhanced proppant is used. An adequate characterization of hydraulic fractures will no doubt require the integration of multiple disciplines, including production/injection data and other geophysical techniques. EM methods can play an important role because they can sense where fluid and conductively enhanced proppant actually go.
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Non Stationary, Broad-band Waveforms for CSEM - An Analysis with Synthetic Data
Authors M. Neukirch and X. GarciaControlled source electromagnetic (CSEM) methods are sensitive to the subsurface conductivity structure and thus had led to its use in resource exploration. Since the frequency for peak sensitivity and the exact location of an exploration target is normally unknown prior exploration, it is desirable to acquire the transfer functions for a broad range of frequencies and in a wide area. Investigations in both directions have been driven by optimising properties of the Fourier transform in order to enhance the frequency range and the source-receiver distances. Recent research on non-stationary (NS) time series analysis tools significantly enhanced processing of NS time series. This work assesses the possibility of NS source waveforms by presenting a chirp source that is highly customisable in amplitude and frequency range in order to accommodate any frequency range in combination with virtually any amplitude for each frequency (e.g. in order to counter attenuation by decreasing power from low frequencies to increase high frequency power assuming constant energy supply). A numeric example illustrates the NS waveform and that robust NS time series processing may lead reliably to the transfer functions of a 1D conductivity model. Lastly, the advantages of a freely customisable waveform design are discussed.
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The Prospecting Potential of Frequency and Pulse CSEM
Authors P. Barsukov and E. FainbergThe depth of exploration, sensitivity and resolution of two methods of marine electromagnetic soundings using a horizontal electric dipole as a field source are investigated. An inline dipole-dipole setup measuring a horizontal electric field in the frequency domain and the vertical electric field in a pulsed mode (time domain) in the near-field source are analysed. It was found that the sensitivity of the pulse method in shallow water is higher than that of the frequency approach. In water depths exceeding 800 m, the sensitivities of both methods are approximately the same. The horizontal resolution of the pulse method is higher throughout the range of depths studied. A new approach to the inversion of sounding results is demonstrated on a model of the geological section.
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The 3D Forward of Vertical Current Source Electromagnetic Method
More LessA special CSEM in frequency-domain method, using a vertical current source place on the wall of a borehole and measures the horizontal electric fields on the surface, is named Vertical Current Source Electromagnetic (VCSEM) method is introduced in this paper to study the feasibility of the method. The 3D responses calculated using finite difference simulation scheme to analyze the 3D responses in case of the source being buried different depth. The results show that the multiple information about the object can be obtain using the observation data of the different depths of the VCS. Therefore, the vertical CSEM method is a high-precision electromagnetic method and have the potential to be applied in prospecting minerals, predicting water inflow or mapping reservoir boundary and monitoring the variations of oil-gas contact, and so on.
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A Scalable Parallel Edge 3D Finite-lement Approach to Marine Controlled Source Electromagnetic Using a Multifrontal Sol
More LessWe present a Scalable Parallel edge 3D Finite-Element Approach to marine controlled source electromagnetic using a multifrontal solver.By using domain decomposition of METIS grid partition technology,we make the most of each MPI processors.In orde to decompose the matrix system and solve right sides for different sources we use a massive parallel multifrontal solver implementation (MUMPS). The result of 3D CSEM matches very well with the 2.5D CSEM.
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CSEM Monitoring of a CO2 Reservoir Imaged by MT
Authors V. Puzyrev, P. Queralt, J. Ledo, E. Vilamajo, A. Marcuello, J. de la Puente and J.M. CelaDuring the last years, different studies based on numerical simulations have shown the potential of CSEM for CO2 monitoring. In this study, we carried out a set of simulations for CSEM monitoring of CO2 realistic deep saline reservoir in a 3D dome anticline structure. We perform numerical simulations in different scenarios (emission frequencies and surface-to-borehole configurations) in order to investigate the effect on the resolution when the simulations are done considering a baseline geoelectric model resulting from the inversion of MT synthetic data.
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Future Applications for CSEM - Shales and Monitoring
By K.M. StrackCSEM has become again of interest for land applications because of emerging markets such as reservoir monitoring and shale applications. They are sufficient high value to justify dealing with the complexity of a grounded dipole source, necessary to resolve both the resistors (oil reservoirs) and the conductors (host rock) equally well. For shale application, three key applications are: Reservoir depletion, fracture monitoring and geosteering. Since increased accuracy is required at different field development stages, borehole measurements need to be added as depth and accuracy requirements increase. For monitoring, one starts with surface only measurements. Since in more mature fields have borehole data, they should be added for a realistic 3D solution. In all cases, feasibility studies are essential to guide the fieldwork. To estimate the risk correctly, one should acquire noise data as oilfield are likely to have pipes and corrosion protection installed. With that noise data and bounding it by the 3D seismic reservoir boundaries we can illustrate the success chance of CSEM. Because EM responds to fluid contrast, we see more cases where EM is likely to work than not. As in these cases there is often no seismic signature it is likely to track fluid movements even better than seismic.
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Seismic-EM Integration Tackles Deep Water E&P Challenges
Authors A. Zerilli, M.P. Buonora, P.D.L. Menezes, J.L. Crepaldi and T. LabruzzoDeep water is a complex high-risk environment with no shortcuts to success. Joint interpretation of seismic and deep reading electromagnetics (EM) can provide a powerful tool for the risk mitigation process. This work focuses on the advances and challenges in seismic-EM integration and gives case examples of imaging improvements that are consistently proving to lower exploration risk while maximizing knowledge of the prospects in the deep Brazilian offshore where challenges, logistics, and costs can be formidable.
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Industry Adoption and Use of the CSEM Technology
Authors S. Fanavoll and P.T. GabrielsenAfter more than ten years of acquisition of EM data, it is widely accepted that the technology has a significant potential for improving exploration efficiency. However, despite the fact that there is a convincing track record of EM results correlating with well results and some oil companies incorporating EM technology into their workflows, adoption of the technology in the industry overall has not come a long way. This paper discuss some of the challenges faced by the petroleum industry in the interpretation of EM data, as well as necessary improvements of the technolgy in order to enhance the value of incorporating EM data into decision workflows. the current use of EM is illustrated by two examples, one unsuccessful and one successful
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Development of a 3D velocity Model for Improving the Location of Potentially Induced Earthquakes in the Gulf of Valencia
Authors B. Gaite, A. Ugalde and A. VillaseñorOn September 2013, unusual seismic activity was detected around an underwater gas storage plant in the gulf of Valencia (Spain). According to the reports by the Spanish National Geographic Institute, more than 550 occurred during two months, the strongest having a magnitude of Mw=4.2, which took place after the gas injection activities halted. The low magnitude of the events (only 17 earthquakes had magnitudes greater than 3), their long event-to-station distance, and the inhomogeneous station distribution, made the location problem to be a great challenge. Here we present a preliminary relocation of this earthquake sequence using absolute and relative methods. We also present a new 3D shear-wave velocity model estimated from inversion of Ambient Noise Tomography data which will serve to obtain more accurate seismic-wave travel times to improve the earthquakes location in this area. The interpretation of the results in terms of the tectonic structure of the region is in progress.
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Surface Microseismic Monitoring of Hydraulic Fracturing of a Shale-Gas Reservoir Using Low-Frequency Sensors
More LessIn this study, we report results from a surface microseismic monitoring of a 21-stage hydraulic fracturing of a shale gas reservoir along a horizontal well. The depths of hydraulic fracturing range from 2500m to 3020m. A surface array consisting of 45 sensors was deployed around the well, with 27 L22E short-period and 18 CMG-6TD broadband seismometers. For analyzing the continuously recorded microseismic data, we adopted the following steps: (1) event detection, (2) event location, (3) event focal mechanism determination, and (4) microseismic imaging. The double-difference seismic tomography method of Zhang and Thurber [2003] is applied to determine the Vp and Vs anomalies due to the fracturing process. In total, more than 700 events were detected. The events can be categorized into two groups: group I near the wellbore and group II about 500 meters to the east of the wellbore. The group II events are likely induced by the pore pressure increase directly caused by fluid migrated from the fracturing spot or the pressure perturbation caused by undrained response of fluid injection. The velocity tomography shows that the fracturing process causes lower Vp and Vs anomalies around the fracturing zone.
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Small Microseismic Surface Acquisition System Case Study
Authors G.N. Erokhin, V.D. Baranov, A.N. Kremlev, D.N. Gapeev, I.I. Smirnov and S.V. RodinSmall Microseismic Surface Acquisition System for oilfield monitoring is presented. Algorithms for data processing are based on the mathematical theory of inverse problems and the using of the supercomputer calculations. A distinctive feature of the suggested system is high mobility, compactness and universality. The technology based on the this acquisition system is intended not only for hydraulic fracturing monitoring but also for long-duration passive monitoring of fluid injection, for hydrocarbon drainage area estimation and for oilfield block structure mapping. Case Study has more than 50 examples.
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Diffraction Stacking - The Role of Source Mechanisms
Authors O. Zhebel, D. Gajewski and C. VanelleLocalization of seismic events provides us valuable information about structures activated by tectonic stresses, geothermal or volcanic activity, reservoir stimulation, and other subsurface activities. In the last few years automatic stacking-based localization techniques that do not require any picking of phases, have become popular and widely-used localization tools. Localization results obtained by such techniques are influenced by various factors. In this work we illustrate that source mechanisms directly influence the form and resolution of a resulting image function. For this purpose, two numerical examples are presented. The first considered source type is a so-called compensated linear vector dipole source, which is typical for geothermal and volcanic areas. As the most seismic events can be best characterized by a combination of explosive, double-couple (DC) and compensated linear vector dipole (CLVD) components, localization of such a source mechanism is also illustrated.
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The Application of the Microseismic Monitoring in Natural Fracture Detection
More LessMicroseismic monitoring (MSM) is one of the effective and real-time evaluation techniques for the fracturing. The results from in-field real-time MSM always provides the valuable benefits that help us gain an insight into the changes in the reservoir and the status of the fracturing operation. Sichuan area has a complex structure characteristic and many natural fractures are activated by the fracturing.The paper describes the different fracturing responses between the shale and tight sand, reveals its special characteristic of the natural fracture which activated by fracturing and probably provides the method (Relative magnitude), suitable analysis (Radiated pattern, Linear distribution), and interpretation (Integrated fracture interpretation) to detect the natural fracture through MSM and prevent induced fracture propagation towards fault zones.
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Accounting for Seismic Energy Release and Fracture Surface Area Development Associated with Hydraulic Fractures
Authors T.I. Urbancic, A. Cochrane and A. BaigHydraulic fracturing in naturally fractured reservoirs is known to generate seismicity due to the interaction of injected fluids with the pre-existing fracture network. Typically, the observed moment magnitudes for such operations are small, usually with Mw < 0. To map the seismicity during these injections, geophones (typically consisting of only 15 Hz elements) are deployed in arrays in nearby wells. From such configurations information on the relative stimulation volumes and overall fracture dimensions can be obtained. However, the ubiquity of these high-frequency instruments has profound implications for the reliability of magnitude estimates for the largest events associated with these treatments. To address this concern, accelerometers and lower-frequency geophones can be installed to characterize events over a wider magnitude band. Furthermore, these sensors can be combined with the high-frequency downhole geophones to monitor (hybrid sensor network) the full bandwidth of activity that can occur during fracture stimulation programs.
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Auxiliary Media - A Generalized View on Stacking
Authors B. Schwarz, C. Vanelle and D. GajewskiStacking still plays a fundamental role in seismic data processing. While the summation helps to decrease data redundancy and leads to a first interpretable time image with a high signal-to-noise ratio, the estimated stacking parameters form the foundation of many important subsequent processing steps, including depth imaging. Current multi-parameter stacking techniques aim to include higher order terms in the traveltime moveout surface. Without increasing the number of parameters, this goal is commonly achieved by assuming a certain reflector geometry and straight raypaths. In the presence of heterogeneity, as a consequence, moveout is described in an auxiliary medium. Although modern methods are usually based on the same set of parameters, we show that they can be divided into two types of approximations, one assuming an effective medium, the other describing the optical analogue in a medium of constant near-surface velocity. Based on ideas of de Bazelaire and Höcht, we provide a simple but general recipe to transform operators from the effective to the optical medium. As an example, we investigate the optical representation of a nonhyperbolic effective medium operator currently in use. In addition, we clarify the unique role of the multifocusing method and point out distinct advantages of both approaches.
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3D Common Offset CRS for Data Pre-conditioning
More LessCommon Offset CRS allows to enhance S/N and to regularize pre-stack data, to be used for pre-stack migration algorithms, both in time and depth domain
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Prestack Signal Enhancement by Multi-parameter Common Offset MultiFocusing
Authors E. Landa, M. Rauch-Davies, K. Deev and A. BerkovitchImaging in complex areas is of great importance in seismic imaging. First of all it is connected to the ability to extract valuable information from the raw seismic data and to use this information for constructing of a reliable velocity model, which is a crucial step in depth imaging. In such case, time processing is a necessary step to improve signal to noise ratio in the raw data. Moreover, results of time imaging can significantly help to create reliable velocity models and consequent depth images. Improving the quality of prestack data always stays in focus of intensive research. In this paper we follow an approach presented by Berkovich et al. (2011) which proposes using a local COMF approximation for traveltime stacking surface description. It allows for an arbitrary common offset adequately approximate traveltimes of seismic events in the vicinity of a CMP position. The paper presents application of the proposed procedure on synthetic and real data including imaging using the improved seismic data.
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