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75th EAGE Conference & Exhibition - Workshops
- Conference date: 10 Jun 2013 - 13 Jun 2013
- Location: London, UK
- ISBN: 978-90-73834-49-1
- Published: 10 June 2013
51 - 100 of 138 results
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Wavefield Tomography without Low Frequency Data
More LessWaveform inversion (FWI) requires a good starting model and/or data at very low frequency (< 1Hz) for convergence. However, this is not a necessary condition, but an artifact of the objective function defined using differences of observed and simulated data. Image-domain tomographic methods using the same wavefields and wave-equations can converge to a reasonable solution from poor starting models and without long offset and/or low frequency data. Cascading image-domain and data-domain wavefield tomography eliminates the need for extremely low-frequency in the acquired data.
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Ongoing R&D in Ray-based Tomography - Well Worth the Effort
By P. HardyOver the past 20 years, ray-based post-migration reflection tomography has remained largely unchallenged as a velocity model building tool for seismic depth imaging. While other, more mathematically attractive methods have been proposed, they have yet to be adopted into standard workflows. The decisive elements for such tools are: accuracy, resolution, flexibility, ease of use, and turnaround time. The success of depth domain tomography comes from the good balance it offers between those elements. This paper aims to illustrate with a few practical innovations in post migration tomography, that ray based approaches are still making progress and are nowadays finding applications far beyond their expected range of validity.
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A Real-data Example of Automatic Migration Velocity Analysis with Extended Images in the Presence of Multiples
By W. MulderMigration velocity analysis for the two-way wave equation based on focusing extended migration images at zero subsurface offset are sensitive to the presence of multiples. Even after thorough multiple suppression, remnant multiple energy can lead to conflicting events that will focus at different velocities, one for the primary and another for the multiple. An automatic algorithm will produce a velocity in between these two. If the multiples are mainly caused by the presence of a water layer, a bias of the algorithm towards higher velocities may help. Here, an application of this approach to a marine data is presented and the result is compared to a well log.
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Differential Waveform Inversion - A Way to Cope with Multiples?
Authors H. Chauris and R.-E. PlessixIn the context of velocity estimation, we investigate the differential waveform inversion method. The approach is formulated in the data domain and consists of two main steps. First, for a given shot, we derive the optimal reflectivity section. From the result, we then compute the next shot gather. The new formulation measures the differences between the predicted shot and the observed shot at the nextposition. The main interest of the Differential Waveform Inversion strategy resides in the possibility to take into account surface-related multiples. The key point is the iterative migration.
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Wavefield Tomography Based on Local Image Correlations
Authors F. Perrone and P. SavaSeismic imaging includes the estimation of both the position of the structures that generate the data recorded at the surface and a model that describes the propagation in the subsurface. The waves recorded at the surface are extrapolated in the model by solving a wave equation, and they are crosscorrelated with a synthetic source wavefield simulated in the same model. Reflectors are located where the source and receiver wavefields match in time and space. If the velocity model is inaccurate, the reflectors are positioned at incorrect locations. We propose an objective function in the image space that does not require common-image gathers (CIGs). We consider pairs of images from adjacent experiments and reformulate the semblance principle in the physical space, instead of the extended space at selected CIGs. We use penalized local correlations of two images to estimate shifts in the image space.
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High-definition 3D Anisotropic WEM-tomography
Authors O. Holberg, E. Pedersen, J.K. Lotsberg and S.K. FossWe review the challenges and trade-offs involved in coupling shot record WEM with high-definitionanisotropic tomographic inversion, and demonstrate successful application of a 3D WEM-tomography process to improve the imaging of formations partly obscured by shallow velocity anomalies and salt.
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Seismic Reflection Tomography with 3D RTM Angle Gathers
Authors C. Zhou, S. Crawley, D. Whitmore, S. Lin, S. Frolov, Z. Liu and N. Chemingui3D angle domain common image gathers (ADCIGs) from reverse time migration (RTM) provide accurate representation of residual moveout in complex media, especially in the presence of salt. Thus, tomography with residual moveout picked from RTM angle gathers allows us to build accurate models for seismic imaging. However, RTM angle gathers bring some challenges too. Among them are spatial under-sampling and insufficient angular sampling in deep parts of the image. In this paper, we present the approaches to overcome such problems and our complete work flow to build models with 3D RTM angle gathers.
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Tomographic Full Waveform Inversion (TFWI) by Successive Linearizations and Scale Separations
Authors A. Almomin and B. BiondiTomographic Full waveform inversion (TFWI) provides a framework to invert the seismic data that is immune to cycle-skipping problems by extending the velocity model. However, this extension makes the propagation considerably more expensive because each multiplication by velocity becomes a convolution. We provide an alternative formulation which computes the backscattering and the forward scattering components of the gradient separately. The inversion setup includes two steps that maintain the high resolution results of TFWI. First, the linearized residual are updated in a nested inversion scheme. Second, the two components of the gradient are first mixed and then separated based on a Fourier domain scale separation to allow for a fully simultaneous inversion of model scales.
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Waveform Inversion via Nonlinear Differential Semblance Optimization
Authors D. Sun and W.W. SymesThis article describes a nonlinear differential semblance approach to waveform inversion. Nonlinear differential semblance optimization combines the ability of full waveform inversion to account for nonlinear physical effects, such as multiple reflections, with the tendency of differential semblance migration velocity analysis to avoid local minima. It borrows the gather-flattening concept from migration velocity analysis, and updates the velocity by flattening primaries-only gathers obtained via nonlinear inversion. We describe the underlying idea and formulation of this algorithm, and present a layered 2D acoustic inversion excercise for which standard full waveform inversion fails, whereas nonlinear differential semblance succeeds in constructing a kinematically correct model and fitting the data rather precisely.
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Tomographic Full Waveform Inversion (TFWI) by Extending the Velocity Model along the Time-lag Axis
Authors B. Biondi and A. AlmominThe extension of the velocity model along the subsurface-offset axes enables to define a tomographic full waveform inversion that converges robustly towards high-resolution velocity models. However the resulting numerical algorithms are extremely expensive and their performance is uncertain when transmitted events (e.g. diving waves) are present in the data. We discuss the advantages of extending the velocity model along the time-lag axis instead of the subsurface offsets. This extension leads to a linearization of the wave equation that overcomes the well-known limitation of the first-order Born approximation to model large time shifts in the data.
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About ADCIG Residual Moveout
Authors J.-P. Montel and G. LambaréThe increasing usage of wave equation and reverse time migration has motivated investigations about new types of common images gathers. Several types of angle domain common image gathers have then been proposed. While they should have the same aspect (up to specific artefacts) when the exact velocity model is used it appears that they exhibit significant differences in curvature when the velocity model is erroneous. This observation is analysed here by a theoretical analysis in the frame of high frequency asymptotics. This analysis is performed for several types of angle domain common image gathers revealing much more complexity than expected. It demonstrates that some well admitted statements such as the validity of Snell Descartes law for tomographic rays or the idea that the tomographic ray tracing could be limited to lower layers may not be satisfied for all type of angle gathers.
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The Challenge of Short-wavelength, High-contrast Velocity Anomalies
By J. EtgenConventional velocity estimation, based on post migration residual moveout, works very well when the velocity structure of the Earth is smooth enough in the lateral directions. This is true even when the initial velocity model is far from correct. Stated another way, long wavelength lateral velocity errors are not a significant challenge anymore. However, once the velocity varies significantly in the lateral directions at scales approaching or less than a few wavelengths, residual moveout estimation plus reflection tomography will often fail to improve velocity models.
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Unmanned Aircraft Systems for Rapid Near Surface Geophysical Measurements
More LessThis paper looks at some of the unmanned aircraft systems (UAS) options and deals with a magnetometer sensor system which might be of interest in conducting rapid near surface geophysical measurements. Few of the traditional airborne geophysical sensors are now capable of being miniaturized to sizes and payload within mini UAS limits (e.g. airborne magnetics, gamma ray spectrometer). Here the deployment of a fluxgate magnetometer mounted on an UAS is presented demonstrating its capability of detecting metallic materials that are buried in the soil. The effectiveness in finding ferrous objects (e.g. UXO, landslides) is demonstrated in a case study.
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Successful Execution of Remotely Piloted Ocean Vehicles to Conduct METOC and Turbidity Pre-site Survey
More LessThis is to present case studies conducted for Chevron’s Environmental Technology Unit off the coast of North West Australia. Two sorties, first a METOC survey followed by a detailed Turbidity study was conducted over 2 months (Dec 2012 and Jan 2013) to collect baseline data as pre-site survey prior to the start of a full scale dredging operation to lay a pipeline.
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Analysis and Separation of Surface and Body Waves in Onshore-seismic Dual Fields
Authors F. Poletto, A. Schleifer, B. Farina and L. PetronioDual-field seismic data are achieved recording particle velocity and pressure/stress at a same receiver-device location. The dual-field method makes it possible to separate different components of the propagating wavefields activated by a single source. We analyze the results of an onshore seismic application using dual-field measurements in the shallow ground. We acquired the seismic data by reciprocal source-receiver geometry that makes it possible to limit the number of dual-receivers installations and to record dual-field data by a source activated along a seismic line. The data obtained by shallow stress sensors buried in the ground and surface geophone are studied for the characterization of vertically propagating body waves, and of surface waves propagating in the horizontal direction with amplitude decaying in depth. The analysis shows that the surface and body waves can be separated combining the dual signals without needing of multi-dimensional processing. This technique may represent a new approach useful for wavefield analysis in near-surface applications, and not only, easily achievable with reciprocal geometry in shallow seismic acquisition surveys.
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Fusing Multi Source Remote Sensing Data – Selected Aspects on Geometric and Thematic Accuracy
Authors M. Pregesbauer, R. Michel and A. AltenbergerRemote Sensing data is widely used in geosciences for all kind of applications. The user thereby relies on, for his purposes, sufficient accuracy and well calibrated data. Beside standard processing methods geometric accuracy and radiometric calibration can be increased with the aim to enhance the thematic accuracy. With the focus on airborne remote sensing, different strategies for laserscanning and hyperspectral data processing with the focus on the subsequent analysis and interpretation are going to be discussed and an assessment on the possible accuracy is given.
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Seabed Sampling for Stratigraphy and Seep Studies Offshore Greenland and Norway
Authors S. Polteau, S. Planke, R. Myklebust and G. HickmanGravity coring and dredging has been used to obtain extensive seabed sampling of escarpments and potential hydrocarbon seep sites offshore Greenland in the northeast Atlantic. Sampling of sub cropping strata and thin overburden sediments provide consistent information on ages of the strata and the nature of potential active hydrocarbon systems. Our results are the first to document active hydrocarbon systems in the Baffin Bay, the northeast Greenland shelf, and on the southern Jan Mayen Ridge.
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Mapping Palaeorivers from Satellite Radar and Surface-wave Velocities
Authors A. Laake and C. StrobbiaSatellite radar data have revealed the existence of extensive palaeodrainage patterns below sand dunes in the eastern Sahara. So far, studies have focused mainly on the lateral mapping of these so-called radar rivers. We use seismic surface-wave data to estimate the penetration of satellite radar into the ground on a regional scale. We developed a scheme for the classification of radar backscatter intensity that allows the discrimination of direct surface backscatter in areas with hard rock at the surface from areas where the radar data penetrate the surface and provide information about palaeorivers in the subsurface. The estimated radar penetration depth is calibrated with seismic surface-wave velocity profiles. Corendering both data sets in 3D shows the high degree of correlation. The method is demonstrated on an area of about 200 x 200 km in the hyperarid desert of southwest Egypt. A 200-km high-resolution seismic section provides the shallow seismic data. The seismic surface waves confirm the existence of two phases of palaeovalleys in the area: wide valleys of several km in width from the Tertiary and Pleistocene rivers, the channels of which are mapped by the satellite radar data.
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Surface Deformation Monitoring with InSAR Data for Oil & Gas Applications
Authors A. Rucci, A. Ferretti and F. RoccaApart from the environmental impact of subsidence and uplift phenomena induced by fluid injection and/or extraction, recent reservoir optimization techniques ask for timely information about many geophysical parameters, both downhole and on the surface. In particular, surface deformation measurements are lately gaining increasing attention within the reservoir engineer community, which is searching for new monitoring tools to complement seismic surveys. In the last decade, a new remote-sensing technology called PSInSAR™- based on the use of satellite radar data - is receiving an increasing attention, thanks to its capability to provide accurate, large-scale surface deformation measurements. The main advantages of PSInSAR™ data, compared to conventional geodetic networks, are essentially related to the spatial density of measurement points, the temporal frequency of the observations, the precision and the limited cost, at least for the monitoring of large areas. Since the number of radar-mounted satellite platforms is increasing, as well as the accuracy of radar measurements, this source of information will probably become more and more common in projects related to reservoir monitoring and optimization. More in detail, ground deformation measurement can provide valuable information to better understand the fluid/gas flow in the subsurface or to calibrate the geomechanical model of the reservoir/overburden, if properly interpreted and integrated with more conventional data.
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Outcrop Structural Mapping from Hi-res DEM and Worldview Satellite Imagery
Authors B. Baugh and K. NavulurRecent trends in commercial remote sensing imagery point to increased spatial, spectral resolution, and agility of satellites. Satellites are now planned at 1foot pixel resolution allowing for new applications. The global capacity of satellites at these high spatial resolutions has signalled a new market for geological applications. Similarly, the number of spectral bands is evolving from traditional bands to specialized bands designed for specific applications. DigitalGlobe has recently announced that Worldview-3, the next generation satellite, will have 17 bands ranging from VNIR to SWIR region of the spectrum that are suited of variety of geological applications. These spectral bands can detect specific phenomenology of outcrops that are indicators of subsurface minerals. The advent of CMG’s allow for backward and forward scanning, allowing for unprecedented agility for collection of stereo imagery that can be used for creating elevation models. Several research papers show accuracy of DEM’s derived from satellite imagery are around 2 meters LE90. Combing the spectral capabilities of Worldview satellites with elevation models, can be indicators of outcrops for geological mapping. This papers talks about specific phenomenology that can be exploited for outcrop structural mapping from hi-res DEM and Worldview satellite imagery.
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Geoid Determination in the Western Part of Egypt from Gravity Data and Gps/Leveling
By A. RadwanPrecise geoid determination is one of the main current geodetic interests in Egypt. The method of Least-squares collocation (LSC) is used in this research for the computation of geoid in Egypt, combining a geopotentail model complete to degree and order 360 in addition to gravity and GPS/leveling data. No topographic information was taken into account on the area under study.
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Reactive Transport in Carbonate Reservoirs: Seismic and Transport Properties
Authors J.P. Nunes, L.G. Rodrigues and R.R. GuérillotThe recent surge in CO2 rich gas injection activities for both Capture Carbon and Sequestration (CCS) and Enhanced Oil Recovery (EOR) projects have led the oil industry and the academia to explore the implications of rock-fluid interactions at full scale development projects. Some of the main questions are: Do reactions occur? Are they relevant for CO2 capture and/or oil recovery? How to monitor them? To illustrate some of the ways the industry may tackle these questions reactive transport simulations have been made to evaluate the impact of rock-fluid interactions in the seismic, mechanical and flow properties in an outcrop based 3D geocellular model. Changes in elastic properties are evaluated using a flow coupled petroelastic model based on an effective medium approach. Current challenges to develop pore-to-reservoir reactive models will also be addressed.
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Dual Mineral Matrix and Organic Pore Textures in Mature Niobrara Formation, Rocky Mountains, USA – Implications for Tight-Oil Carbonate Reservoir Modeling
Authors C. Laughrey and R. RubleProspective tight-oil reservoirs in the Upper Cretaceous Niobrara Formation B Chalk in the northern Denver basin include elements of hybrid/interbedded and porous mudstone fine-grained systems. We recognize three reservoir/source rock lithologies: 1) argillaceous, organic-rich, pelletal impure chalk; 2) organic-rich pelletal chalk; and, 3) highly organic-rich pelletal impure chalk. Geochemical parameters indicate the rocks belong to Organic Facies B (oil-prone), and are thermally mature with respect to oil generation. We recognize both mineral matrix pores and organic-matter pores in the Niobrara reservoirs. Mineral matrix pores include interparticle and intraparticle voids. Intraparticle pores dominate storage capacity in the rocks and consist of nano- to micro-scale fabric-selective and not-fabric-selective carbonate pore textures preserved within compacted pelletal allochems. Organic porosity is well developed in alginite and liptodetrinite, but is absent in bituminite, and thus may be related to the original kerogen structure. Complex intraparticle pore geometry is readily modeled by 3D FIB/SEM segmentation. Laboratory NMR measurements of the modeled samples appear to discriminate discrete pore and fluid distributions in the tight reservoirs.
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Bi-Directional Interactions between Fluids and Geomechanics in Fractured Reservoirs
By G. CouplesPopular ideas used to explain geomechanical-fluid interactions in fractured reservoirs are inadequate, or wrong, as they are based on assumptions that are incorrect. Poro-elasticity considerations show that predicted aperture effects are highly sensitive to the local boundary conditions, which themselves may change during reservoir operation. The more-general approach is to consider fully-coupled systems of matrix blocks bounded by fractures, and the porefluids. Simulations based on such systems reveal significant insights, as well as surprising outcomes, with effective permeabilities that can vary by more than 1000x due to small changes in conditions. Application of these concepts within reservoir models can be used to improve the results of reservoir flow simulation.
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Carbonate Rock-typing – Diagenesis and Multi-scale Heterogeneity
Authors C. van der Land and Z. JiangCarbonate rock typing methods aim to associate texture with petrophysically similar rocks. Here, we use 2D thin sections of carbonate reservoir rocks to create 3D statistical pore-size distributions and extract pore network models from these to obtain multiphase flow properties. This novel rocktyping method is applied to synthetic depositional rock textures which are progressively altered by a succession of typical diagenetic processes. For each stage in the paragenetic sequence, flow properties were calculated. Secondly, by comparing experimental results with our modelled predictions, we validate our methodology of pore reconstruction, network extraction, stochastic network generation and creation of multi-scale networks.
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Calculating Vertical Stress in Chalk
More LessWhen effective stress is calculated with reference to the grain cross sectional area as defined from Biot’s coefficient, it is simple to illustrate zones of chalk where the stress on the mineral grains is high, and pore collapse would be a challenge during production of hydrocarbons.
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Quantification of Depositional and Diagenetic Geobody Geometries for Reservoir Modelling, Hammam Fauran Fault Block, Sinai Peninsula, Egypt
Authors C. Hollis, H. Corlett, J. Hirani, D. Hodgetts, R. Gawthorpe, A. Rotevatn and E. BastesenOutcrop data has traditionally been used to constrain conceptual models during subsurface reservoir characterisation and geocellular modeling, but published data of depositional and diagenetic geobodies in carbonate systems is lacking. Furthermore, few studies address how these diagenetic bodies, which often cross-cut sedimentary bedding, can be captured in reservoir models, even though diagenetic modification is likely to impart a significant influence on flow behaviour. This paper presents a case study from the differentially dolomitised pre-rift Eocene Thebes Formation on the Sinai Peninsula. It documents the size of depositional and diagenetic geobodies and demonstrates how these data have been incorporated into a 3D geocellular model. The results can be used as input parameters or templates for reservoirs in which fault/fracture controlled dolomite bodies have been described, whilst the workflow could have broader applications to other carbonate reservoirs.
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Modeling and Validation of Fluid Flow-Geomechanics of Mauddud Reservoir in Sabriya Field
More LessIntegrating fluid flow and geomechanics is becoming increasingly important in the oil and gas industry to improve production history matching and forecasting. This is especially the case in carbonate reservoirs due to the heterogeneous nature of the rock and flow properties within the pores and sometimes fractures. During production, carbonate reservoirs are subject to mechanical, hydraulic, and, in some cases, thermal processes. Coupled modeling between these processes helps to better understand the behavior of a carbonate field. When hydrocarbon is produced, the pore-pressure change within the reservoir gives rise to accompanying stress changes, which cause rock deformation that will either reduce or enhance permeability and porosity. A multidisciplinary approach is necessary to integrate geology, petrophysics, fluid flow, and geomechanics within a coupled reservoir simulation. 3D fluid-flow geomechanical modeling was conducted for a carbonate field in order to improve the history match of a reservoir model, and we examined the impact of permeability change and enhancement on well performance. The results showed significant improvement of the reservoir production history matching by including coupled reservoir simulations. The geomechanical changes brought on by production will influence other field-development operations such as in-fill drilling. Geomechanical modeling of the reservoir can be extended to optimize wellbore stability through a 3D mud-weight cube for field-scale in-fill drilling optimization.
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Challenges in Brazilian Pre-Salt Reservoirs Geophysical Characterization
By P. JohannThis paper focuses on the impact that reservoir geophysics has had on the production development of the Brazilian marine carbonate pre-salt fields starting from the first oil discovery in 2005 to 2011. The evolution of three main knowledge areas of reservoir geophysics technology will be detailed, namely: acquisition, processing and interpretation, all oriented towards reservoir characterization and monitoring. Seismic acquisition technology has experienced an increase in “information density” (seismic traces per square kilometer). In the seismic processing domain, the improvement of seismic algorithms and methodologies has allowed for better seismic data quality, resolution and imaging. In particular, the algorithms/techniques of 3-D multiple suppression and 3-D depth migration have significantly evolved in recent years. In the seismic interpretation area, geological context-oriented seismic attributes algorithms/methodologies have made possible better reservoir characterization in the deep and ultra deep-water Brazilian offshore basins. No extended abstract available.
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Land Vibroseis Source Advances towards Low Frequencies
Authors Z. Wei and T.F. PhillipsExtending the frequency bandwidth towards low frequencies using the Vibroseis method has gained a lot of attenation recently. The source (vibrators) becomes one of the obtacles in the success of recording low frequency seismic signals. How do we increase the vibrator ground force at low frequencies (< 10 Hz)? Can the vibrator control electronics effectively supress harmonic distortion at low frequencies? This paper attempts to provide a fresh look at these questions.
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The Impact of the Field Array on Temporal Bandwidth of Land Seismic Data and Its Mitigation in Processing
By R. FerberThe field array is the group of seismic sensors connected to a single recording channel. The impact of field arrays on the spatial bandwidth of the recorded seismic data is described by the array wavenumber amplitude transfer function. In this paper, I discuss, however the impact of the field array on the temporal bandwidth of the recorded data. A requirement for this is an accurate knowledge of the field array geometry. I also propose a novel technique to correct the corresponding signal amplitude distortions in data processing.
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The End of Unblended Acquisition
Authors G. Berkhout, G. Blacquičre and E. VerschuurWe show that deblended shot records have a better S/N than shot records in unblended surveys. We also show that a further improvement in S/N is obtained in the migrated domain. Both improvements increase with increasing blending fold and decreasing survey time. An interesting consequence of this remarkable property is that blended surveys can be carried out under more severe noise conditions than unblended surveys. We conclude with the observation that unblended seismic acquisition may evolve into a technology of the past.
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Land Broadband Seismic from the Receiver Perspective
By D. MougenotThe broadband capability of land receivers is reviewed. On the low-frequency side, two more octaves have been added to the signal using low dwell sweeps. These low frequencies can be recovered below the resonant frequency of the geophones by compensating for their attenuation. However, this inverse filter works well so long as there is adequate signal-to-noise ratio. To avoid amplifying instrument noise, new geophones have been developed with a higher sensitivity and a lower resonant frequency. MEMS accelerometers that display a linear response down to DC seem to be the ideal sensor to capture very low frequencies. Their limitations relating to the instrument noise may be compensated by a high spatial sampling. On the high-frequency side, progress is limited by the absorption that occurs at shallow levels and during propagation. The spurious frequency of geophones occurs above the high-cut used in most of the surveys. MEMS accelerometers benefit from a broadband response, higher sensitivity and lower instrument noise at high frequency. Therefore, the main issue is not related to the receivers but to the possibility of enhancing the signal-to-noise ratio at high frequency.
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On the Use of a Seismic Sensor as a Seismic Source
Authors D.F. Halliday, T. Fawumi, J.O. A. Robertsson and E. KraghWe investigate the use of seismic sensors as small seismic sources. A voltage signal is applied to a number of geophones, forcing the mass within the geophones to move, generating a seismic wavefield that is recorded on a separate array of geophones. We observe higher-frequency (25 Hz and above) surface and body waves propagating from the geophone source at offsets of 10s of metres.
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Interpretation of Single-sensor Data - a Practical Perspective
Authors V. Aarre, A. Poole, B. Mitchell, S. Tan and G. BusanelloLand broadband seismic technology involves not only high-technology acquisition equipment, sophisticated mathematics, and near-surface challenges. Much more than that, the technology provides fit-for-purpose measurements of the subsurface. We present how geological survey objectives dictated a novel broadband single-sensor survey design. We also show how those measurements provided important geological insights that had a material impact on economics and risks, and hence, further development plans for a prospective area in central Australia.
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Onshore Low Frequency Acquisition for Full Waveform Inversion – from Field Trials to State of the Art Production Surveys
Authors G. Baeten, F. ten Kroode, S. Rawahi and S. MahrooqiFollowing a series of field tests, low frequency acquisition and processing and Full Waveform Inversion techniques have been applied successfully in 3D, long offset, Wide Azimuth surveys from the Middle East. The field testing evolved from downhole testing of vibrator sweeps to an extensive high channel count 2D line test. The development of low frequency acquisition techniques has been accompanied by testing and maturation of Full Waveform Inversion techniques, eventually leading to high quality velocity model estimates for state of the art onshore data.
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Is Broadband Land Seismic as Good as Marine Broadband?
Authors M. Denis, M. Denis, V. Brem and F. PradalieTo evaluate the potential of modern land seismic capabilities and further improve the seismic value for the mining industry, AngloGold Ashanti (AGA) has acquired a prospect area of 35 km2. The geological objective of this test is to image the formations above and below the Ventersdorp Control Reef (VCR) and down to the carbon leader reef, for depths ranging from 2.7 to 3.8 km. This test was the opportunity to illustrate how dense broadband seismic can significantly improve land seismic imaging. The benefit of a dense acquisition with a broadband source is illustrated on the AGA prospect. We compare a conventional acquisition (SLI 420m, SI 70m, RLI 300m, RI 50m; 10-90 Hz) with a dense acquisition (SLI 50m, SI 50m, RLI 100m, RI 50m; 10-90 Hz) and a dense acquisition with a broadband source (SLI 50m, SI 50m, RLI 100m, RI 50m; 3-160 Hz). The expectations from dense acquisition are confirmed by an outstanding imaging quality for all depth levels, simultaneously for ultra-shallow and ultra-deep targets. This in turn leads to significantly improved depth velocity models for a simultaneous optimal focalization and positioning of the seismic reflections. This leads to a textured image with unprecedented stratigraphic details available for the interpretation.
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Putting It All Together – Broadband, High-density, Point-receiver Seismic in Practice
Authors J. Quigley, D. Holmes and K. O’ConnellLand seismic technology is advancing rapidly on many fronts. There are challenges in assimilating all the changes and new opportunities. A technical viewpoint may be to analyse each of the component technologies, both acquisition and processing, on their separate merits, but how are we to put it all together in the most technically effective manner, while maintaining cost-effectiveness and, ideally, reducing the overall time to which business decisions are made from the data? Technical development and tighter integration across the full design-to-interpretation workflow should go hand-in-hand and the more we improve our technical capabilities in multiple areas, the greater the imperative to act to integrate those technologies for maximum gain. The presentation will discuss WesternGeco’s several years of practical experience with integrated land seismic acquisition and processing technology delivering high-density, broadband full-azimuth data as a key enabler for improved reservoir characterisation.
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Interpretation of Broadband Land 3D Data from Saudi Arabia
Authors L. Giroldi and B. WallickA broadband, high-density, full azimuth 3D land survey was acquired in 2011 over a producing oil and gas field in the Eastern Province of Saudi Arabia. The survey was designed to test a combination of point receiver sensors and a specially designed low frequency sweep for use in improved reservoir property prediction. Interpretation of this broadband, high density, full azimuth land 3D survey shows the beneficial impact of the increased bandwidth and improved signal- to-noise ratio on the interpretation of seismic data. The recovery of low frequency signals has dramatic implications for seismic inversion, as less reliance can be placed on the initial model. Moreover structural clarity and resolution can be achieved in the interpretation of both shallow and deeper levels. Results from this work indicate that a more accurate representation of the wave field is achieved with this broadband, full azimuth dataset, with the recovery of low frequency signal being one of the most notable aspects. This has a dramatic impact on both the interpretation and the seismic inversion.
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Improving Business Decisions by Evaluating Subsalt Structural Uncertainty and Illumination with Modeling and Re-migration
Authors J. Sinton, P.A. Valasek, J. Zhu, S.K. Towe, S.M. Carlson, T. Kendricks and M. GreenwoodBuilding a salt velocity model is usually an iterative process. Based on seismic character alone there is often a large range of alternative salt models. The iterations can often take on the form of trial-and-error in trying to understand the geologically most likely model. We present a solution to allow integration of geological insight in the velocity model building. The solution consists of a seamless system of flexible model editing and fast migrations. This creates an arena for the geophysicist and the geologist to work together. The crucial component is the interactivity, or the ability to work in the same time frame. This means that several salt models can be created and resulting images analyzed during the course of a working day.
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Subsalt Target-oriented Salt Interpretation in the Gulf of Mexico
By Y. AgnihotriThe conventional method for salt interpretation begins with the search for salt-sediment interfaces, starting with the shallowest depths and progressively moving deeper. This search is typically conducted on intermediate seismic products like sediment flood volumes, salt flood volumes, and overhang sediment and salt flood migrations. However, with this approach, poorly imaged subsalt areas become known only after spending considerable time interpreting intermediate salt features. In this paper, I present a new methodology where a reference salt geometry is obtained early in the salt interpretation process. Having a reference seismic volume helps identify poorly imaged subsalt targets much sooner. A geologic model-based interpretation is performed in these identified areas, and changes in salt geometry are assessed based on their impact on subsalt imaging.
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Houston, We Have a Problem: Geologic Ambiguities Persist on GoM Subsalt Seismic Data
Authors E. Ekstrand and B. Hartled out, and the industry necessarily transitions to less obvious and/or more complex subsalt objectives.Our talk describes three generic subsalt trap styles that comprise a significant portion of remaining play inventory, but which carry increased geologic risks, thereby requiring wholesale improvements in subsalt seismic fidelity if the industry is going to maintain its current favorable success rate: 1) Low relief anticlines situated in the down dip lower slope salt trend. 2) “Bowl weld” truncation traps of the middle to upper slope. 3) “Ribbon truncation closures” that are ubiquitous across the subsalt play fairway. We illustrate the critical velocity sensitivities and imaging challenges associated with each of these trap geometries, and discuss how interpretational ambiguities that endure on current subsalt seismic datasets impede the commercial assessment of these remaining exploration opportunities.
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Interactive and Integrated Salt Model Building
Authors S.-K. Foss, E. Karlsen, A. Osen, M. Rhodes, J. Mispel, D. Michel, N. Kotava, D. Merten, B. Lehnertz and N. EttrichBuilding a salt velocity model is usually an iterative process. Based on seismic character alone there is often a large range of alternative salt models. The iterations can often take on the form of trial-and-error in trying to understand the geologically most likely model. We present a solution to allow integration of geological insight in the velocity model building. The solution consists of a seamless system of flexible model editing and fast migrations. This creates an arena for the geophysicist and the geologist to work together. The crucial component is the interactivity, or the ability to work in the same time frame. This means that several salt models can be created and resulting images analyzed during the course of a working day.
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Keynote 1: Review of the Geology of Deformed Salt Bodies and the Implications for Seismic Imaging
By I. DavisonThis paper reviews new data on the internal structure and external geometry of salt bodies and their interaction with surrounding sedimentary strata, followed by a discussion of teh implications for seismic imaging.
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Workshop Introduction: Pitfalls in Subsalt Imaging
Authors I. Jones and I. DavisonThe physical behaviour of most earth materials is fairly straightforward, both in terms of their deposition and subsequent deformation. Consequently, the geometries to be imaged and interpreted are likewise usually well understood. Salts, however, do not conform to the usual behaviours of earth materials due to the ductile nature of the material. Consequently, in both imaging and interpretation of salt province data, special care needs to be taken. In this work, we review various considerations for velocity model building, migration, and subsequent interpretation of complex salt bodies.
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Advanced Seismic Processing Reveals the Structures Hidden beneath Salt Diapirs on Legacy Data from the Onshore Netherlands
Authors R. Wervelman and J. Pi AlperinBy means of two recent sub-salt imaging projects, using rather old short-cable narrow-azimuth and low-fold seismic surveys acquired two decades plus ago, some new/emerging model-building and imaging technologies will be discussed: - shallow subsurface model-building by 5D data regularization, before migration and by a joint tomographic inversion of deep reflection data and first-break picks; - enhanced structural interpretation of complex salt structures by intermediate RTM’s. The two projects enabled an extensive geophysical comparison between various depth imaging tools: standard and extended Kirchhoff, 1-way WEM and Reverse Time Migration. For one of the projects examining multiple salt-diapir scenarios, depth-imaging using RTM, led to reduced subsurface uncertainties especially regarding the risk of depletion of the target block (towards already producing neighbouring fields to the North and to the East); the imaging project consequently aided plans for a development well planned to spud Q2 2013. In the other project a large reduction in the subsurface uncertainty led to a confident decision not to drill the prospect.
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Challenges in Quantifying Subsalt Structural Uncertainty
Authors K. Osypov, N. Ivanova, Y. Yang, A. Fournier and D. NikolenkoSubsalt deep-water exploration and production (E&P) is one of the most challenging and risky businesses. In particular, drilling in the deep-water environment is becoming increasingly complex and expensive. Uncertainty is inherent in every stage E&P business, and understanding uncertainty enables mitigation of E&P risks. Therefore, quantification of uncertainty is beneficial for decision-making, and uncertainty should be managed along with other aspects of business. For example, decisions on well-positioning subsalt should take into account the structural uncertainties related to non-uniqueness of the velocity model used to create the seismic depth image. Even with our best efforts to combine all available data, there is still intrinsic ambiguity in our velocity models, i.e., multiple feasible models can fit the data equally well. The velocity model ambiguity exacerbates significantly in the presence of salt. The paper discusses the challenges for structural uncertainty analysis for subsalt targets.
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The Impact of Reverse Time Migration on the Evaluation of Mature Southern North Sea Assets
By S. FletcherA case study is presented on the impact of Reverse Time Migration (RTM) on the derivation of a geologically realistic velocity model in a depth imaging sequence applied to a field development in the Southern North Sea. Exceptionally complex salt overhangs in the area make imaging of the Rotliegend target particularly challenging and despite repeated applications of the depth imaging technique since the mid 90’s, with the most recent one carried out in 2008, it has remained challenging to define the reservoir compartmentalisation and reconcile mapped GIIP volumes with well production profiles. The present interpretive processing workflow, with the application of state-of-the-art RTM in the velocity model building stage and a close cooperation of interpreters and depth imagers, has improved the imaging particularly below salt overhangs, yielded a geologically plausible model of the reservoir structure and offered new options for development well placement.
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The Effects of Marine Data Acquisition and Velocity Model Building Practices to Imaging Complex Geological Setting - Modeling Study
By M. CvetkovicInterpreting seismic images in complex geological settings still remains a challenging task. Significant academia and industry effort in the last decade has been devoted to addressing imaging issues in complex marine
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A Decade of Advances in Subsalt Imaging from Exploration to Development on Kaombo
Authors P. Williamson, V. Martin, A. Douillard, L. Lemaistre and V. ClergetAbout two thirds of Block 32, offshore Angola, is covered with allochthonous salt bodies that complexify seismic wave propagation thereby tending to make illumination irregular and accurate imaging difficult. In the early years of exploration of this block, this prevented a good estimation of the resources and their distribution in several subsalt areas. However, in the last decade the industry has seen a dramatic improvement in subsalt seismic imaging capabilities thanks to the significant uplift in illumination offered by wide-azimuth towed-streamer (WATS) data and the improved simulation of seismic wave propagation used in Reverse-Time Migration (RTM), enabled by the increased computing power now available. In this talk we review the evolution of the imaging of Block 32 during this period: we show that, as our images improved, so did our understanding of the geology, which fed back into the model-building, yielding further improvements; and we look at the most recent advances due to full waveform inversion and image post-processing using RTM surface-offset gathers. Cumulatively, these have transformed our vision of, and confidence in, the subsalt reservoirs and allowed the Kaombo multifield development to be launched.
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