- Home
- Conferences
- Conference Proceedings
- Conferences
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
1 - 50 of 112 results
-
-
How could the CSEM experiment be improved ?
By L. LosethIn conventional marine CSEM for hydrocarbon exploration, the source is towed behind a vessel without active steering, and a set of receivers are positioned on the seafloor. Traditionally, the receivers have been positioned along the towline which leads to the socalled inline source-receiver geometry. In the last few years, the industry has moved towards using 3D receiver grids. A major advantage with 3D is that the subsurface is explored with the inline source-receiver geometry in several directions. Another added value is that one also gets additional broadside data in some of the directions (directions where the source can be decomposed into two components).
-
-
-
Dealing with complexity of the interpretation of marine controlled source EM surveys.
Authors M. Darnet, R. E. Plessix, M. Rosequist, P. Van Der Sman and J. VoonSubsurface resistivity mapping based on Controlled Source Electromagnetic (CSEM) measurements are attractive for Shell because they offer the possibility to distinguish between hydrocarbon and brine bearing reservoirs where conventional seismic methods are sometimes inconclusive. Indeed, the resistivity of a reservoir rock is directly related to the amount and type of fluid filling the pores while its acoustic properties are rather insensitive to it. CSEM can therefore be a valuable tool to compliment seismic data for prospect evaluation. In Shell, we have applied the CSEM method on a worldwide scale since 2003 to both de-risking and portfolio polarization in a marine settings.
-
-
-
CSEM technology in oil exploration - limitations or opportunities ?
Authors J. Hesthammer and M. BoulenkoOver the past years, Rocksource has studied and tested the application of Controlled Source Electromagnetic (CSEM) surveys for hydrocarbon detection in numerous shallow and deep water settings, mainly in the Norwegian continental shelf, the UK continental shelf, offshore West Africa, and offshore East India.
-
-
-
Marine CSEM for the future.
By F. MaaoLooking back from the very first test of using CSEM to detect hydrocarbon reservoirs in 2001, we have seen a tremendous improvement in technology and processing. We have moved from 2D lines to true 3D acquisition and from attribute analysis to 3D inversion. We have seen significant improvements in data quality and acquisition efficiency, and we have seen an increased effort in integrating EM data with seismic data. All these improvements have contributed to better resolution, deeper penetration, less ambiguity, and, as a consequence, better interpretation and understanding of the subsurface.
-
-
-
Marine CSEM in time and frequency domain: some ways to enhance reservoir response.
More LessThe efficiency, depth investigation and the spatial resolution of Controlled-Source Electromagnetic (CSEM) measurements in shallow and deep water environments are studied in both time- and frequency-domain.
-
-
-
EM in the Barents sea: strategic use of EM measurements in the process of license application.
Authors S. Fanavoll, M. Silva and F. GianninoThe Barents Sea represents tremendous geologic challenges in oil and gas exploration. This is illustrated by drilling of numerous disappointing wells, emphasizing the need for new exploration techniques. Previous CSEM experiences in the Barents Sea showed that EM can detect commercial hydrocarbon accumulations, while clearly non‐economic accumulations do not give significant EM responses. Therefore resistivity measurements could be a valuable indicator of commercial volumes of oil and gas in the region, allowing a possible reduction in the number of dry and non‐productive wells.
-
-
-
Integrated interpretation of EM and seismic data: challenges, open questions, possible solutions.
More LessThe main objective of a well posed integrated approach should be to reduce the level of uncertainty and indetermination about the knowledge of the system under study. That is the desirable result when complementary geophysical disciplines, such as seismic and electromagnetic methods, are combined with each other through an integrated interpretation work flow.
-
-
-
Integrated analysis of CSEM, seismic and well log data for reservoir characterisation.
By B. HartleyImproved reservoir management and production optimisation demands require accurate characterisation of reservoir properties and their changes through time. Advances in geophysical data acquisition and interpretation have led to significant improvements in the remote imaging of earth structure and properties. However, when only a single data type is considered, ambiguities in the interpretation can remain. Integration of disparate geophysical data types allows the strengths of each to be exploited. Here we will concentrate on three contrasting methods: surface seismic, marine controlled source electromagnetic (CSEM) and well-log data.
-
-
-
3D/4D realistic monitoring considerations - is it possible ?
More LessTotal with the assistance of WesternGecoEM acquired a rich 3D marine Controlled Source Electromagnetic (CSEM) dataset offshore West Africa toward the end of 2006 (Figure 1.). This dataset was intended to be a definitive validation of the technique or proof of concept over a well understood target for which definitive measures could be made of many different types of analysis and inversion. The dataset was also acquired at the beginning of the fields’ life so that the opportunity remained for monitoring the production development electrically.
-
-
-
Full field reservoir surveillance using electromagnetics
Authors K. Strack, S. Dasgupta and G. YuIncreasing production efficiency and monitoring water/CO2 floods are key issues to be addressed with borehole and surface technologies. At the same time linking the information to 3D surface seismic data and borehole data is required to extrapolate in the inter-well space and find the sweat spots between wells and in the 3D reservoir space. Electromagnetic has the strongest coupling to the fluid content of the reservoir while seismic can delineate impedance contrasts or lithological boundaries.
-
-
-
Incorporating seismic horizons in inversions of CSEM data.
Authors K. R. Hansen and R. MittetTo improve the interpretation of CSEM data, information from seismic data can be included in a CSEM inversion. The higher resolution of the seismic image makes it possible to accurately determine the location of potential resistivity contrasts.
-
-
-
Description, Objectives and Deliverables
Authors G. Williams, O. Gosselin, J. Ovens and F. VergaThe workshop will be concerned with current practice and new developments in conditioning reservoir models to dynamic data. Aspects covered include: case studies; importance in making robust decisions; getting the static model right; matching 4D seismic data; and assisted history matching. The objectives of this workshop are to share knowledge, understand current practice and discuss new developments on conditioning reservoir models to dynamic data. The deliverable from the workshop will be a summary document from discussions posed by keynote speakers.
-
-
-
Advances in surface-wave processing for nearsurface characterisation in land seismic
Authors C. Strobbia, P. Vermeer, A. Glushchenko and A. LaakeThe analysis of surface waves can be a powerful tool for characterising the near-surface down to penetration depth. In this framework, the surface wave analysis is part of the data processing workflow, and the surface waves are considered signal and not noise. After having extracted the information the surface waves carry, they become unwanted signal to be removed. The resulting near-surface model can be used for short- to long-wavelength statics and perturbation corrections, for velocity model building, and for better filter design which can take into account the complexity of near-surface phenomena.
-
-
-
Surface wave inversion in complex systems
Authors L. V. Socco, D. Boiero and M. MaraschiniDispersion curves estimated from field data can be inverted to supply near surface velocity models. Since the problem is hill posed, strongly non linear and mix-determined, the inverse problem suffers from strong solution non uniqueness particularly for complex velocity models. Global search methods explore the solution space and supply a “picture” of the solution non uniqueness enabling a proper model parameterization to be used for linearised inversion. A possibility for reducing the broadness of the possible equivalent solutions is the introduction of constraints to the solution. Constraints are traditionally obtained from other geophysical tests or boreholes, but significant improvement in the inversion results can be obtained also introducing the higher modes of propagation or inverting simultaneously the dispersion curves relative to different locations in the case of complex 2D/3D systems.
-
-
-
Non destructive non contact air-coupled concrete cover evaluation by ultrasound surface waves using an automated device
Authors B. Piwakowski and P. SafinowskiMany reinforced concrete structures are suffering from deterioration occurring earlier than their expected service life. The first barrier against attacks of external environmental agents is the concrete cover. The damage mechanisms depend on the microstructure of the cover concrete. This microstructure can be assessed with various measurements. The paper presents the automated device designed for the non destructive control of the concrete using the ultrasonic surface waves. The measurements are carried out without any contact with tested sample. The increase of signal level, required for such solution, is obtained using the frequency swept signals, so called “chirps”. The recorded signals are processed using special software which permits to obtain the attenuation and the velocity dispersion of surface waves. These parameters can be next used in order to determine the parameters of concrete cover. Especially the inversion of velocity dispersion characteristics using the approaches developed for the multichannel analysis of surface waves (MASW) technique, enables to evaluate the variations of shear velocity as a function of the concrete cover depth. The potential possibilities of this approach are shown on an example of laboratory measurements carried on the cement slab especially manufactured, displaying the increasing porosity as a function of depth, and on the example of in-site measurements carried out in order to evaluate the depth of deterioration of a concrete platform in maritime port.
-
-
-
The use of the SASW method to determine the shear wave velocity and the material damping ratio of shallow soil layers
Authors M. Schevenels, S. A. Badsar and G. DegrandeThis paper focuses on the Spectral Analysis of Surface Waves (SASW) method for the determination of stiffness and damping parameters of shallow soil layers. The paper consists of three parts, addressing (1) the in situ SASW test, (2) the determination of the dispersion and attenuation curves from the measurement data, and (3) the inverse problem where the soil profile is identified. The existing practice is critically reviewed, and a number of improvements to the SASW method are presented. These include a technique to improve the efficiency of the in situ test, and a new method to determine the experimental attenuation curve. The efficiency of the test is improved by monitoring the signal-to-noise ratio during the experiment. The experimental attenuation curve is determined by means of a frequencywavenumber analysis, using the half-power bandwidth method.
-
-
-
Retrieving surface wave dispersion curve from 3D seismic acquisition scheme
By D. BoieroThree-dimensional (3D) seismic surveys are always more often used both in oil prospection and in near surface problems to handle complex geological structures. At the same time surface wave methods are often coupled to other seismic techniques (2D seismic reflection or refraction) where it is possible the use of seismic data to retrieve dispersion curve along the seismic line. In this work the possibilities and the limits of retrieving dispersion curves from 3D seismic acquisition scheme are analysed. Several tests based on synthetic and real data show that the estimated dispersion curves are in agreement with the dispersion curves estimated through the traditional methods. Furthermore, in case of “cross-spread” acquisition schemes, the proposed processing approach can be used to retrieve 3D subsoil models, also for inaccessible areas.
-
-
-
Surface-wave dispersion inversion in an unconsolidated granular medium
Authors L. Bodet, X. Jacob, V. Tournat, R. Mourgues and V. GusevSurface-wave methods offer relative straightforward experimental, signal processing and inversion procedures to infer materials one-dimensional shear-wave structures. Dispersion inversion can moreover be considered particularly efficient when strong {a priori} information about the probed medium is available. The laboratory experiment presented here shows its ability to estimate the shear-velocity gradient power-law exponent in an unconsolidated granular medium.
-
-
-
Enhanced multi-offset phase analysis of surface wave data for detection of lateral heterogeneities
Authors G. Vignoli and G. CassianiSurface wave methods are based on the inversion of observed Rayleigh wave phase-velocity dispersion curves. The goal is to estimate mainly the shear-wave velocity profile of the investigated site. The model used for the interpretation is 1D, hence results obtained wherever lateral variations are present cannot be considered reliable. In this paper, we consider synthetic models having a lateral heterogeneity. When we process the entire corresponding seismogram with a traditional f-k approach, the resulting 1D profile is representative only of the subsurface structure of the largest part of the considered model. This result shows that classical analysis disregards evidences of sharp lateral velocity changes even when they show up in the raw seismograms. In our research, we implemented a novel robust automated method to check the appropriateness of the 1D model assumption and locate the discontinuities. The method has been tested over synthetic models. This new approach is a development of the recent Multi- Offset Phase Analysis (MOPA) with the advantages that it does not need a-priori noise evaluation nor more than one shot. Only once the discontinuities are clearly identified, we confidently perform classical f-k dispersion curve extraction and inversion separately on either side of the discontinuity. Thus the final result, obtained by putting side by side the 1D profiles, is a correct 2D reconstruction of the discontinuous S-wave distribution, with no need for additional ad-hoc hypotheses.
-
-
-
Feasibility of surface waves analysis to characterize the damaged zone of an underground gallery (EDZ)
Authors L. Donatienne, P. Côte, K. Ben Slimane, J. Cabrera-Nunez and C. Gélised by seismic phases velocity analysis. In this aim, we performed an experimental study in the experimental platform of Tournemire (Aveyron, France), which is a site that is operated by IRSN (Institute for Radiological Protection and Nuclear Safety). A comparison between the hammer source and a vibrator source showed the efficiency of the vibrator that improved the accuracy of evaluation of the phases velocity. A numerical study showed that the phases velocity of seismic surface waves is sensitive to the EDZ characteristics under the layer of concrete. In this way we have been able to invert the phases velocity picked between 200 Hz and 480 Hz. The inversed velocity profile includes an EDZ layer 60 cm thick with a velocity gradient from 300 m/s to 600 m/s. However, introducing the second mode in the inversion process does not give satisfactory results. This disagreement is probably due to the artifact introduced by the way we calculate the dispersion diagram that can lead up to define “effective mode”.
-
-
-
Imaging scattered seismic surface waves with nonuniform receiver arrays
Authors A. Kaslilar and X. CampmanSurface waves are widely used for determining properties of the subsurface on different scales. In most applications, the dispersion of surface waves is analyzed to yield depthdependent velocity profiles. However, the heterogeneity of the shallow subsurface complicates such an analysis because of the scattering it causes. Here, we use an inverse scattering method to determine the location and properties of the heterogeneity. First, we illustrate this method, using a regular receiver array. A synthetic example shows that the scatterer is imaged at the correct location with good resolution. In practice, we may want to take advantage of existing non-uniform arrays, such as those deployed for global seismic studies. In our next example, we generate scattered data at irregularly spaced locations. By simultaneously inverting the scattered wave field excited by different sources, we observe that the image is well focused on the scatterer. Further work is on the way to better understand the influence of non-uniform (and sparse) sampling on the image quality and what are the sampling requirements.
-
-
-
Multimodal Inversion of Surface Wave Data at Sites with Shallow Bedrock
Authors C. Cesare, F. Sebastiano and M. MargheritaIn this paper results of a characterization campaign, conducted by means of surface wave tests, are presented. Tests are conducted on sites with shallow bedrock and the presence of stiff seismic interfaces. The sites are the location of some stations of the Italian Accelerometer Network in the Liguria Region (Italy) and the experimental tests are part of a the development of the Italian strong motion database. Due to the peculiar shear wave velocity profile of the sites, a multimodal inversion is required because the effective dispersion curve is strongly affected by the presence of higher modes of propagation. Three examples are presented, in order to show that a multimodal inversion is of paramount importance in order to increase investigation depth, avoid errors in the retrieved soil profiles due to mode misidentification and improve the resolution on shallow layers, particularly in situations in which the effect of higher modes could be relevant (i.e. velocity inversions or strong seismic contrasts). The used inversion algorithm is a stochastic algorithm, which demonstrates its ability of properly taking into account higher modes of propagation allowing for a correct definition of seismic velocities and interfaces depth in different stratigraphic conditions. Combined refraction interpretation performed on the same seismic dataset provides an useful comparison to assess the reliability of the results.
-
-
-
Love and Rayleigh waves dispersion analysis from microtremor measurements at Bevagna (Italy)
Authors K. Tokeshi, S. Foti, S. Parolai, M. Picozzi, R. Puglia, M. Massa and E. D’AlemaIn the last decades, researchers focused their attention on using the Rayleigh waves dispersion characteristics to estimate the shear wave velocity profile of a site, since their dispersion characteristics can be extracted also from only one component recordings (namely the vertical ones) of active and passive seismic tests. In particular, inverse analysis of empirical surfacewaves dispersion curves from microtremor measurements (passive seismic test) is a very attractive tool since it allows to keep the cost of investigation relatively low and to avoid the use of active sources that might be prohibitive in urban areas. However, until now the full potential of seismic noise array methods was not fully exploited, and, in particular, the possibility of better constraining the subsoil structure by extracting also the Love wave part from microtremors recordings has not been fully investigated.
-
-
-
Global surface wave tomography
By J. TrampertI will present an overview of the state-of-art surface wave analysis which consists of three steps: (i) The measurement of the average dispersion between source and receiver (or between two receivers on the same great circle path) based on a non-linear waveform inversion. (2) The construction of anisotropic phase velocity maps which summarises the measurements on the sphere. (3) The local depth inversion of the phase velocity maps for elastic parameters. At each step, uncertainties are evaluated and all parameters are expressed in terms of probability density functions. Examples will show a global crustal model, transition structure and probabilities of anisotropy in the upper and lower mantle.
-
-
-
Time-lapse monitoring of surface waves
Authors P. Hatchell, P. Wills and C. DidragaObservations of surface and near-surface waves show that shallow velocities change significantly in response to reservoir compaction that often takes place thousands of meters deeper. The compacting reservoir induces vertical and horizontal displacements and strains at the seafloor that lead to anisotropic changes in the shallow p- and s-wave velocities. Analyzing permanent OBC data from the Valhall field we observe large changes in the arrival times and phase velocities of Scholte and critically refracted compressional waves between several surveys acquired over a 5 year interval. The changes in the shallow velocities are compared with seafloor strains predicted by geomechanical models and a reasonable agreement is found. Shallow waves present us with an excellent laboratory for calibrating the stress and strain dependence of our rock physics models and are useful for constraining geomechanical models and monitoring the compaction of deep reservoirs.
-
-
-
SASW measurements in civil engineering applications: using wavelengths to tailor profiling depths from 5 cm to 500 cm
By K. H. StokoeField seismic testing is an active and growing area in Civil Engineering, especially in the subdisciplines of geotechnical, transportation, and structural engineering. Traditionally, intrusive seismic methods have been used. Over the past 15 years, nonintrusive surface-wave methods have undergone significant developments. One surface-wave method, the spectral analysis of surface waves (SASW), is briefly discussed. Development of the SASW method began in the mid-1980’s out of needs in geotechnical earthquake engineering to determine shear wave velocity (Vs) profiles in hard-to-sample soils (e.g. liquefiable gravelly soils) and in pavement engineering to evaluate stiffness profiles without boreholes. Because the method is nonintrusive, applications within Civil Engineering have mushroomed. A brief background of the SASW method is presented. Case histories illustrating the range in applications and profiling depths are discussed. Some examples are: (1) detection of the onset of fatigue cracking in the asphaltic surface layer of a pavement using 2- to 20-cm long wavelengths, (2) evaluation of the improved zone in a liquefiable sand due to dynamic compaction using 0.3- to 30-m long wavelengths, and (3) determination of Vs profiles at Yucca Mountain, Nevada using 1- to 1000-m long wavelengths.
-
-
-
Attenuating scattered surface wave: two faces of interferometry
Authors D. F. Halliday, A. Curtis and K. FinlaySurface wave interferometry is the process of estimating inter-receiver surface waves by cross-correlation, cross-convolution or deconvolution of wavefields recorded at each receiver. We study seismic interferometry of scattered surface waves in attenuating media. One of the starting assumptions for interferometry by correlation is that the medium of interest is lossless, however the near surface of the Earth is often strongly attenuating. On the other hand interferometry by convolution makes no assumptions about medium losses. By investigating both correlation-type and convolution-type interferometry we identify how to successfully approach the problem of estimating inter-receiver scattered waves, and illustrate our findings using real and synthetic examples. Such estimates have applications in the attenuation of scattered ground roll and in near surface imaging and characterization.
-
-
-
Verification of Rayleigh-wave dispersion characteristics using synthetic microtremors
Authors K. Tokeshi and L. V. SoccoAn attempt to verify the characteristics of experimental Rayleigh-wave dispersion curve from passive microtremor measurements is carried out through synthetic microtremors. As case study, array microtremor measurements were performed at an Alpine site. The average experimental vertical Rayleigh dispersion curves obtained by the f-k spectral method was used to estimate subsoil models by random search (Monte Carlo inversion). Also, the predominant frequency of experimental H/V spectral ratio was calculated to improve the inversion process. Several researchers have reported that the fundamental frequency of theoretical H/V spectral ratio or the predominant frequency of experimental H/V spectral ratio would represent an approximate threshold for the lowest frequency of experimental vertical Rayleigh dispersion curve. However, the highest velocity of the experimental Rayleigh dispersion curve occurred at a frequency higher than the value of the experimental H/V predominant frequency. In consequence, this experimental high velocity would not correspond to the fundamental Rayleigh dispersion curve. For verifying purposes, synthetic microtremors using a similar array to the one used at the site, were calculated for one of the subsoil models estimated through Monte Carlo inversion. The synthetic vertical Rayleigh dispersion curve was in good agreement with the experimental one, verifying the above assumptions.
-
-
-
On the feasibility of surface waves approximation to interpret ambient vibrations wave field
Authors D. Albarello and E. LunedeiRandom vibrations monitoring and analysis represents a cheap and effective tool for the seismic characterization of the subsoil. A standard approach to the physical interpretation of ambient vibrations measurements is based on the hypothesis that surface waves dominates the relevant wave field. To evaluate the reliability of this hypothesis, a general physical model for ambient vibrations generated by anthropic activities has been. In this model, the complete wave field generated by a random distribution of independent point loads at the surface of a weakly dissipative layered Earth has been considered. Horizontal to Vertical Spectral Ratios computed from the complete wave field solution have been compared with those deduced in the surface waves hypothesis. This comparison suggests that this approximation supplies reliable only results in the frequency range above the resonance frequency of the local subsoil. At the resonance frequency, a reasonable agreement is obtained when a source-free area exists around the receiver with a radius of the order of few tens of meters.
-
-
-
The role of intermodal cross terms in seismic interferometry
Authors W. P. Kimman and J. TrampertThe exact interferometric equation gives the relation between the retrieved Green’s function and signals arriving from an enclosed surface integral of sources (monopole and dipole sources). This relation is exact, even for complicated media. If only monopole sources are assumed as needs to be done for all practical cases, retrieval can be far from perfect in heterogeneous media. We show that this is due to intermodal cross terms that will appear even if the source distribution is perfect. Especially when sources are present at the free surface only, cross terms have the potential to overwhelm higher modes completely. Luckily one-bit correlation overcomes this problem by the amplifying higher modes.
-
-
-
Marine surface wave investigation in a harbour in southern Sweden
Authors R. Wisén and M. SvenssonA marine surface wave seismic investigation was performed in order to characterize the sediments and bedrock in Ystad harbor, southern Sweden. The dispersive nature of Sholte waves was analyzed and fundamental mode dispersion curves extracted. Using inverse modelling a few layer shear wave velocity, Vs, profile was successfully retrieved to a depth of 5-10 m below sea bottom. The seismic results were confirmed with result from geotechnical probing. The measurements were made with a 12-channel neutral buoyancy streamer with 2 m hydrophone separation. A small number of led plates were attached to the streamer in order to make it sink and for each measurement the ends of the streamer were fixed on the bottom using small concrete blocks. The streamer was pulled up on the vessel before moving to the next measurement position. As energy source a small amount of explosives was detonated on the sea bottom with the shot positioned at 15-30 m distance from the nearest hydrophone and inline with the streamer. The production rate of this approach was 30 measurements in one field day, which should be compared to the 1 or 2 geotechnical soundings that can be achieved at the same time.
-
-
-
Dispersion accuracy using Slant Stack transformation
More LessLast decencies show the increasing interest in using Multichannel Spectral Analysis of Surface Waves (MASW) for ground structure recovery. Using MASW the dispersion characteristics of surface wave field is often determined using so called p−τ transformation known as Slant Stack (SL). It is commonly assumed that the acquisition geometry can affect the dispersion results and several general rules in current MASW practice are observed when this geometry is designed. They suggest for example to observe the minimum offset in order to avoid the interferences of surface waves with the body waves, the maximum offset in order to reach the required depth and maximum geophone spacing in order to avoid spatial aliasing. In the same time there are few reports on the influence of the array geometry on the resolution (i.e. accuracy) who deal with the array involved uncertainty of a dispersion curve. This paper aims a more detailed assessment of above problem: The accuracy of the SL procedure is studied as the function of the acquisition system like receiver spacing, receiver number, aperture length, sampling rate and signal frequency. It is shown how the not adequate array geometry design can corrupt the dispersion result and lead to erroneous interpretation. The easy to use criteria are formulated.
-
-
-
Developments in seismic interpolation and regularization and their applications to acquisition and processing
By R. L. AbmaBecause of the cost, seismic data are seldom acquired with a sampling that is optimal for seismic processing. To produce data with optimal sampling, interpolating or regularizing the seismic data may be used, not only to improve the resolution of the results, but to reduce the cost of acquiring seismic surveys. Multi‐dimensional interpolation methods that allow seismic data to be de‐aliased can provide significant improvements in quality and ease‐of‐use over older interpolation methods.
-
-
-
Accurate data reconstruction through simultaneous application of statistical and physics-based constraints to multiple geophysical datasets.
Authors A. Baumstein and R. NeelamaniSpatial aliasing is the key problem that affects seismic data interpolation techniques. Although existing methods can interpolate data "beyond aliasing" under certain assumptions, their performance degrades as shot and receiver sampling become coarser. Most existing data interpolation techniques overcome aliasing by making assumptions regarding either the statistical properties of the data or the physics that explains the data.
-
-
-
Four methods of data regularization
More LessWhen seismic data regularization is formulated as an inverse problem, it requires mathematical regularization, a method for imposing constraints on the reconstructed data. Mathematical regularization can take four different forms: a differential operator (such as a prediction-error filter or a plane-wave destructor), an integral operator (such as a recursive inverse of prediction-error filtering or a plane-wave constructor), a sparseness constraint in a special domain (such as Fourier or seislet), or a shaping operator. Similar results can be achieved with different methods but at a different computational cost. Using both onedimensional toy examples and seismic field data applications, we compare and illustrate properties of the four methods of data regularization.
-
-
-
Beating Nyquist by randomized sampling
Authors G. Tang, R. Shahidi and F. J. HerrmannSeismic exploration is rooted in the paradigm of regular Nyquist sampling. Recent developments in the area of “compressive sensing” have shown that regular-Nyquist sampling may not be most favorable for signals that are compressible, e.g., by curvelets. In that case, appropriate randomization of the acquisition; such as by jittered1 sampling, creates favorable recovery conditions from data collected at a limited number of randomly placed sources and receivers. By virtue of the randomization, and the subsequent nonlinear recovery by transform-domain sparsity promotion, significant improvements can be made in the frequency content and quality of regularly sampled data volumes obtained from highly undersampled randomized measurements. In this new paradigm, the effective sampling rates are no longer dictated by Nyquist but by transformdomain sparsity. Consequently, twice as compressible signals can be recovered from only halve the randomized sample points. This removes a major impediment of acquisition where costs are proportional to sample rates and survey areas. During this talk, we will discuss multidimensional and continuous2 (opposed to gridded) extensions of randomized jitter sampling. These will include investigations of Poisson disk sampling3 and Farthest Point sampling4 and we will demonstrate that these randomized schemes perform better than the wellestablished regular sampling protocol.
-
-
-
Operator-oriented CRS interpolation
Authors G. Hoecht, P. Ricarte, S. Bergler and E. LandaIn common-reflection-surface (CRS) imaging the reflection arrival time field is parameterized by a kinematic description of the recorded wavefield. Using the CRS approach locally in the unmigrated prestack data domain opens a potential for trace regularization and interpolation. The presented CRS interpolation operates in the original prestack data domain and accounts for irregular geometries. A distinction to existing methods is the use of local operators of the second order which are less sensitive to aliasing but imply a considerable increase of the computational expense.
-
-
-
Improving old tricks: FX interpolation beyond alias for irregularly sampled data, for data with large gaps and for data with spatially variant dips
Authors M. Naghizadeh and M. SacchiFor almost two decades, FX prediction filtering (Spitz, 1991) and FK interpolation (Gülünay, 2003) have provided a robust route to interpolate aliased seismic data. These are probably the only two interpolation methods that were built on sound and solid arguments for the interpolation of aliased events. They both have precise assumptions that one must honor to optimally interpolate seismic data. In essence, the data must be composed of a finite superposition of events with linear moveout. The latter is often validated by windowing the data. In addition, both methods require regularly sampled data and a good SNR in the low frequency portion of the spectrum where the vital non‐aliased Fourier coefficients reside.
-
-
-
Seismic data reconstruction with application to SRME for walkaway VSP data
Authors E. Otnes and K. HokstadInterferometry is used to reconstruct surface data from Walkaway VSP data. Together with a common receiver gather of a WVSP experiment we formulate a data-driven surface demultple scheme for WVSP data. The theory will be presented together with real data examples from the Nordkapp basin in the Barents Sea, an area well known for its complex geological structures.
-
-
-
Green's theorem framework for data reconstruction
By A. RamirezThere is a tremendous and pressing need to improve our ability to effectively extrapolate, interpolate and regularize seimic data. That drives the interest in methods of data reconstruction in general.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-
-
-
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.
-