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71st EAGE Conference and Exhibition - Workshops and Fieldtrips
- Conference date: 08 Jun 2009 - 11 Jun 2009
- Location: Amsterdam, Netherlands
- ISBN: 978-94-6282-103-3
- Published: 08 June 2009
41 - 60 of 112 results
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Anti-Aliasing, Anti-Leakage Fourier Transform
Authors M. Schonewille, A. Klaedtke and A. VignerThe anti‐leakage Fourier transform (ALFT) is a robust and easy to implement regularisation method. In this talk first several aspects of the ALFT are illustrated using simple synthetic signals. The key observations are: 1) When the Fourier spectrum is sparse, very good results can be obtained using the ALFT with a limited number of iterations; 2) When the spectrum is not sparse, but data are well sampled, a very large number of iterations can be required for a similar quality reconstruction of the data as with Least Squares Fourier regularisation; 3) Sparsely sampled data with a sparse spectrum can be handled by the ALFT if the sampling is irregular, but results strongly degrade if the sampling is (close to) regular. To improve the handling of sparsely sampled data it is proposed to derive a weighting function in the spatial Fourier domain from the lower temporal frequencies. The weighting function is extrapolated to the higher frequencies where the data may be spatially aliased, and instead of selecting the strongest Fourier component in each iteration (as done in the standard ALFT), the component that would be strongest after weighting is selected. The advantages are shown on synthetic and field data.
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Five Dimensional Interpolation in Practice
By D. TradComputer power growth has made possible to extend interpolation algorithms to many dimensions, which has proven to be essential to deal with the increase of dimensions of seismic data, from two to three dimensions and from narrow to wide azimuth. Simultaneous interpolation in all five seismic data dimensions has the greatest chance of predicting missing data with correct amplitude and phase variations because well sampled dimensions help to constraint the more poorly sampled dimensions.
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Seismic data regularization for WATS data
More LessThe seismic data regularization, which maps the acquired irregularly sampled seismic traces to a regular grid, is an important processing for preparing the data for regular sampling based algorithm, such as wave equation migration, 3D SRME etc. The wide azimuth seismic data generally contains the shooting locations covering a patch over a 2D surface and the geophone locations as well. Combining with the recording time, the seismic data is fully represented in a five dimensional coordinate. Conventional data regularization scheme splits the five dimension problem in to two pass three dimensional procedures. The interpolation algorithm in higher dimension generally gives better chance to fill the acquisition holes. In this paper, we generalized the anti‐leakage Fourier Transform algorithm to five dimensions, which regularizes the seismic data in one pass. The initial tests on Gulf of Mexico data demonstrate promising results.
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Interferometric interpolation of missing seismic data
Authors Y. Wang, Y. Luo and G. T. SchusterWe present an interferometric interpolation method for filling in trace gaps in common shot gathers. There are two steps for implementation: first, virtual traces are created in the trace gaps by cross-correlation of recorded traces in a shot gather followed by summation of correlated trace pairs over all shot positions; secondly, a 1-D matching filter is applied to the predicted events to correct for the wavelet and amplitude distortions. By using a 1- D assumption (assuming a layered medium around the midpoint in a common midpoint gather), the interferometric interpolation method can be applied to common midpoint gathers.
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Highlights of the EAGE 2008 Vibroseis Workshop
Authors C. Bagaini, J. Meunier, P. Pecholcs, J. Sallas and P. ScholtzMore than 100 geophysicists and engineers participated to the EAGE-sponsored Vibroseis Workshop (Prague, 13-15 October 2008). The conveners plan to share the highlights of this workshop with the participants to the annual EAGE meeting.
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Near-surface model building: Are first breaks enough?
By F. ErnstEstimation of a near-surface model for the derivation of long-wavelength statics is one of the long-standing problems in land seismic data processing. First arrivals are currently the main source of information for building a near-surface model and computing the resulting statics. Alternatively, ground roll and guided waves can be used for near-surface model building. I present a case study on a data set from the south of Oman where both inversion methodologies are applied. While the statics maps are similar, the underlying near-surface models differ significantly, and the first-arrival model is not consistent with the near-surface wavefield arriving after the first breaks. Hence, if the near-surface model is to be used for any purpose beyond statics, additional information on the near-surface wavefield such as dispersion curves should be incorporated into the inversion.
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Geomorphology – Understanding the Near-surface Impact on Seismic Data
Authors A. Laake, A. Zaghloul and C. StrobbiaSurface seismic data are significantly affected by the properties of the near-surface strata. We propose to integrate information extracted from geomorphology into the seismic processing workflow. Topography classification of the elevation and lithology information of satellite imagery allows mapping formation tops, which in turn, provide the basis for 3D near-surface modelling. The lithology class map can be converted into a surface velocity map for the estimation of coherent noise velocities. The 3D geologic model can be converted into an elastic model using standardized velocities. The result is a model of the statics estimates, which can be generated prior to data acquisition. The comparison of the model with refraction statics from data processing reveals that the estimate matches the refraction statics in areas with homogeneous surface lithology. In terrain with heterogeneous surface lithology such as isolated limestone ridges and steep cliffs with rapidly changing lithology, differences are observed, which are yet to be explained.
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Schoonebeek 3D Hi-Res Acquisition & Processing: How dense spatial sampling leads to excellent well ties
Authors M. Reinier, S. Goldesbrough, H. Dankbaar, M. Bruehl and C. WeltevredeThe Schoonebeek Oil Field, located in the eastern part of the Netherlands, is Europe’s largest onshore oilfield. The field was discovered in 1943, shut in since 1996 and in the final stages of being abandoned. The field STOIIP amounts to 165 mln m3 oil, with to date 40 mln m3 recovered from 599 production and injection wells drilled on a 250 m spacing. The reservoir comprises the 0-50m thick, darcy-permeability Bentheim sands. The Schoonebeek Field is currently re-developed using steam injection through a system of 70+ horizontal injector and producer wells. In the redevelopment area the Bentheim sandstone thickens towards the east, with a relatively constant 16-30m thickness.
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First arrival traveltime tomography for complex near-surface velocity structures
Authors M. Noble, N. Belayouni and H. ChaurisClassical algorithms used for travel time tomography are not necessarily well-suited for handling very large seismic data sets, densely parameterized velocity models and for taking advantage of current supercomputers architecture. We revisit the classical approach of firstarrival travel time tomography by proposing to use a simple gradient-based approach without the need of estimating the inverse of the Hessian of the misfit function. The gradient-based approach is very attractive from a numerical point as it can handle large data sets and velocity models and is very robust with respect to the choice of the initial velocity model.
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Using Modern Processing Technologies to Improve Poor Signal to Noise Ratio - A 3D Land Case Study
Authors P. Plasterie, D. Le Meur and R. PillaiEspecially with land data, often acquired with poor signal to noise ratio, it is important to remove noise in the early phases of the processing sequence. Ground roll in particular needs special attention as the characteristic features of ground roll (low frequency, highly energy) noise in the data can hide near offset reflection data that contains important signal. In this article we review a new adaptive method for ground roll attenuation that could potentially better attenuate noise and at the same time better preserve signal.
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A Survey of Land Data Acquisition and Processing
By O. YilmazWe shall review aspects of acquisition and processing of land seismic data, including spatial sampling requirements for reflected and refracted waves, surface waves and guided waves, use of surface waves to estimate the near-surface S-wave velocities, and processing methods to attenuate surface waves and guided waves, use of wide-angle reflections to image beneath basalt and carbonates, near-surface modeling, and image-based subsurface modeling.
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Rock Physics Issues in Carbonates
Authors M. A. Payne, S. Xu and G. BaechleCarbonates are very complex, increasing the difficulty of developing rock physics models to describe geophysical responses. However, since carbonates make up such a large fraction of the hydrocarbon reserves in the world, it is important to develop such models. In this paper, we discuss a rock physics model that is applicable to clastic and carbonate rocks, and across a range of grain sizes. It incorporates known or relatively easily measurable basic parameters. We demonstrate the impact of several physical effects on geophysical responses.
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Micro-porosity effect on sonic velocity in carbonate rocks
Authors G. Baechle, A. Colpaert and G. EberliIn carbonate rocks, the rock frame and pore space are a function of the depositional environment and the diagenetic history. Cementation, recrystallisation and dissolution processes can change the mineralogy and texture of the original framework and hereby alter the original grain-to-grain contacts and/or occlude pore space. These diagenetic alterations and associated changes of the rock frame and pore structure result in a wide velocity range at a given porosity.
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The Effect of Micrite Content on Porosity, Permeability, and Acoustic Velocity of Carbonate Rocks.
Authors T. Vanorio, J. Dvorkin and G. MavkoCarbonates are highly susceptible to physical, chemical, and biological alterations during sedimentation and post-deposition. This often results in the complexity of trends between geophysical observables and measurable rock properties. Carbonates are classified based on the amounts of allochems (transported grains and fossils), carbonate cement (sparite), and microcrystalline calcite matrix (micrite). These components can strongly affect rock properties. By examining a new dataset comprised of outcrop samples, we concentrate on the effect of micrite on the elastic-wave velocity, porosity, and permeability. The fraction of micrite is quantified from micro-CT images subject to subsequent image processing to delineate calcite grains, micrite patches, and macroscopic pore space.
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What do we really understand about pore systems in carbonates?
By C. HollisThe construction of 3D reservoir models that are capable of confidently predicting flow behaviour in carbonate reservoirs requires that the porosity distribution in the reservoir is characterised appropriately and related to a robust conceptual geological model. Porosity is at the root of both reservoir characterisation and reservoir modelling, but its measurement and description remains an area of uncertainty since in many fields there is a discrepancy between core and log derived reservoir properties. In addition, robust conceptual models to predict reservoir properties in the interwell area of carbonate reservoirs are often weak. This largely reflects an immaturity in the tools available to predict the effects of diagenesis on porosity. The aim of this paper is to establish a picture as to where we currently stand with regard to the characterisation of carbonate pore systems and identify emerging technologies that will improve confidence in future models. The case is made here for a genuinely interdisciplinary approach to reservoir characterisation, but also for a return to truly geological models to increase confidence in the predictive capacity of 3D reservoir models. Central to this is a recommendation to more consistently consider the diagenetic process responsible for porosity development.
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Ultrasonic velocities in carbonates: laboratory data versus a new squirt-flow dispersion model
Authors O. de Paula, B. Gurevich, M. Pervukhina and D. MakarynskaUnderstanding elastic properties of fluid saturated carbonates is a major challenge in quantitative interpretation of seismic data. In particular, the validity of Gassmann’s equations for carbonates is sometimes unclear. This complexity is belived to be caused by diversity of their pore geometries. One of the ways to study the impact of pore geometry is by measuring ultrasonic velocities. In this paper we compare the measured velocity as a function of pressure against a recently developed simple squirt flow model. This allows us to estimate effective aspect ratio of compliant pores. The resulting value of about 0.01 appears to be common for a number of samples examined.
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What we have learnt about fluid substitution and velocity pressure dependence on Early Cretaceous carbonate rocks from the Middle East?
By S. VegaFluid substitution and pore pressure changes are the main factors affecting time-lapse 4D seismic. Fluid changes are often predicted by Gassmann, which works generally well in clastic rocks. However, the applicability of Gassmann in carbonates is not well understood yet. Changes in pore pressure due to production might become important under certain conditions of reservoir production and injection. In addition, to be able to identify accurately these fluid and/or pressure changes in a time-lapse 4D seismic, uncertainty of the seismic signature should also be evaluated. Therefore, it is important to determine and quantify the effect of these factors to have a full understanding of the changes in the 4D seismic data. In this paper, we present a summary of preliminary results of different studies of pressure changes, fluid substitution, and seismic uncertainty analysis in a carbonate reservoir and surrounding facies from two different producing oil fields in the Middle East.
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The Challenge of Predicting Fluid Properties in Carbonate Rocks
By I. BrevikPredicting fluid phase from geophysical (i.e. normally seismic) data in carbonate reservoir rocks is a challenging task, especially in exploration problems with limited data access and uncertain geological process understanding. This is due to the frequent occurrence of poor seismic amplitude quality in these high velocity and heterogeneous environments, lack of predictive capabilities of rock properties in the complex compaction processes and methodological doubt in how various fluid types and mixes control the seismic properties and in turn the seismic reflectivity caused by carbonate reservoir rocks.
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Recent Advances in Imaging and Computational Rock Physics and Applications.
By A. NurThe need for rock physics information is exploding as we aspire to improve geo-steering; recovery; wellbore management; and reservoir simulation. The most reliable source of this information is experimentation. However, physical measurements on rock fragments are slow and cumbersome, and often impossible to conduct or conduct well. Even when available, such data are sparse -- required are properties not for tens but for thousands or tens of thousands of samples.
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Iso-frame modeling of elastic moduli of calcite – dolomite sedimentary rocks
Authors I. L. Fabricius, T. Vanorio, C. Scotellaro and G. MavkoCarbonate grainstones from Apulia in Italy with varying degree of dolomitisation and calcite cementation have a wide range of porosity, permeability and elastic moduli. In general, elastic moduli increase with decreasing porosity and stiffening frame. By using the effective medium iso-frame model, the effect of frame stiffening due to cementation may be quantified independently of mineralogy and porosity. We find that for carbonate samples with less than 15% porosity, variation in elastic moduli is rather due to change in porosity than in change in pore stiffness. For samples with porosity over 20%, we rather find that for variation in elastic moduli, changes in pore stiffness plays a distinct role.
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