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54th EAEG Meeting
- Conference date: 01 Jun 1992 - 05 Jun 1992
- Location: Paris, France
- ISBN: 978-90-73781-04-7
- Published: 01 June 1992
61 - 80 of 405 results
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High resolution seismic stratigraphy: a new approach showing new possibilities of seismic profiling
Authors N. Ya. Kunin and A. G. BudagovSeismic sequences analysis elaborated by the US scientists (P. Vail et al) has been promoted in many countries . In the Russian Federation this analysis is widely applied. In this presentation we shall discuss some results of theoretical and practical investigations . High resolution (fine-layer) seismic stratigraphy operates with objects smaller than a seismic sequence . According to their size magnitude the odjects are classified as sesmic packages and seismic quanta, the explanation of these terms being Biven .
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Seismic stratigraphy or structural formational interpretation of seismic data, or both?
Authors I. A. Mushin, E. A. Kozlov and L. Yu. BrodovEvidently, there are now two approaches in geologic interpretation of geophysical data that can be considered as dominating ones . One of them is the well known and widely used seismic stratigraphy (SS) . Another one is the structural-and-formational interpretation (SFI) elaborated by Russian geophysicists. Up to now, the application of the SFI was restricted to oil and gas provinces of Russia, Kazakhstan, Turkmenia, and recently - Pakistan and Ethyopia .
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Recent advances in onboard seismic QC systems
Authors D. Pajot, H. Bragstad and J. H. BarschModern marine seismic acquisition techniques have drastically reduced the acquisition colt per unit of subsurface coverage . Today modern seismic versels typically record 6 subsurface lines in one vessel traverse; the seismic data volume acquired every 8 seconds may be in exces of 20 Mega bits . However the complexity of the most advanced configurations and the amount of gear deployed at sea have kept the high acquisition costs per unit of time . This lead rome operators to re-think the way seismic data quality must be assessed in the field, evolving from a basic signal to noire ratio evaluation done on single fold data to more sophisticated analysis dove on stacked/filtered data . In the case of bad weather operators sometimes hold the decision to suspend the acquisition until the noise becomes unacceptable on stacked sections processed in a commercial data processing center .
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Evaluation of 3D coverage specs - a case study
Authors M. Brink, B. Ursin-Holm and K. KolbjørnsenIt is common practice in 3-D seismic surveying to specify criteria for CMP coverage in terms of minimum acceptance levels fór different parts of the streamers . In case these minimum levels are not met, infill seismic data are acquired in addition to the socalled primary seismic data . Depending on sea currents the infill percentage is often between 10 and 25 percent . The need for infill is also depending on the extent of flexible binning which is considered acceptable . For different levels of infill in combination with fixed and flexible binning the seismic results of a 3-D seismic survey have been analysed, in order to assess the relevante of these infill specifications . The main results of this analysis are presented in this paper . It comprises full 3-D seismic processing including 3-D migration of the primary dataset with and without the infill dataset . For this processing botte fixed binning and flexible overlapping binning has been used . In addition the effects on seismic data quality of less accurate navigation by omitting the acoustic network, has been investigated .
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An examination of tapered binning in 3D marine data acquisition
Authors B. O‘Sullivan and L. LuIn this paper we will examine different techniques used during 3D marine data acquisition to reduce the amount of additional "infill" data required. In particular, we will look at how tapered binning is applied, its underlying assumptions, and the geophysical and economic concerns resulting from using tapered binning. We will also examine how tapers are applied in the field, the consequences and subsequent effects on processing techniques. In relation to this, the effects on stacking, DMO, AVO, and migration of a data set before and after tapering process are discussed .
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Source array design to attenuate multiples in a hardwater bottom area - conclusions from an experimental seismic survey carried out on the North-West shelf of Australia
Authors C. R. T. Ramsden and C. CooperThe North West Shelf of Australia is a difficult data area . The seafloor and near surface comprises a Tertiary carbonate wedge which thickens away from the coast. Strong multiple sequences are generated between the sea surface, the seafloor and other strong reflectors in the near surface. The absorption of the primary energy by the carbonate wedge and the low reflectivities in the zone of interest results in the masking of these reflectors by the multiple train. Back scattered energy is not a severe problem because the seafloor is generally smooth and flat .
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Field testing of a seismic G.I. gun array
More LessDuring the last decades the airguns have become a standard energy source for seismic surveys in the industry. Sleeve guns were introduced a number of years ago and are widely used today. This paper aims at comparing the results of a testline shot with a sleeve gun array to the results of a testline shot with the newly developed G.I. gun array . These data were shot in the summer of 1991 . The data were acquired in Norwegian waters in quadrant 16. An airgun shot line from the same area, acquired in 1989, is also available for comparison .
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A demonstration of efficient exploitation of airgun interaction
Authors M. H. Safar and V. B. HewettIn a paper presented at the 60th Annual International SEG Meeting in San Francisco, 1990, and also at the 53rd EAEG Meeting Florence Italy, 1991, Safar et al showed from the measured far field signatures radiated by a 4 x 40 cu.in. compact sleeve gun array (cluster), that higher values of Primary-to-Bubble ratio are achieved at the expense of radiating considerably lens energy flux. Consequently, it was suggested that the importante of the Primary-to-Bubble ratio as a design criterion should be reconsidered and the radiated energy flux should be given a serious consideration in the design of compact gun arrays. This is because the strength of the reflected signal is essentially determined by the radiated energy flux.
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Experimental study of temperature effects on air gun signatures
Authors J. Langhammer and M. LandroMarine seismic sources have been studied extensively during the last two decades. Both experimental and theoretical studies of air guns and water guns have been performed. One of the main theoretical issues have been to onderstand the damping mechanisme for the bubble oscillations in an air gun pressure signature . Both Ziolkowski (1990) and Laws et al . (1990) pointed out that condensation and evaporation of water vapour across the bubble wall are essential procesnes involved in the damping mechanism. Since these processen are driven by pressure and temperature gradients across the bubble wall, we decided to investigate the influence of changing the temperature of the water surrounding an air gun . From measurements it is well known that the bubble time period changes when the sea temperature changes . However, this knowledge is of qualitative nature, and how other signature characteristics like primary to bubble ratio is influenced by a change in the water temperature is not so well known. In order to quantify these effects, we performed a controlled tank experiment . We used a water tank of approximately 850 litres . In order to attenuate reflections From the walls and the bottom of the tank, absorbers of 5cm thickness were placed inside the tank . The source was a BOLT 6 00 B air gun with a chamber volume of 1.9 cu.in. In all the experiments the firing pressure was 100 bar . The gun was placed at 0.5 m depth, and the hydrophone was placed 0 .22 m from the gun ports.
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Screw seismic sources
Authors K. Davies, G. Hampson, H. Jakubowicz and J. OdegaardIn this paper we propose a novel method of acquiring marine seismic data in which screw noise is used as the seismic source. This approach has many potential advantages and might be suitable for seismic acquisition beneath the ice-cap in polar regions .
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Layer-based oriented full wave inversion
Authors F. Jurado, V. Richard and M. CuerWe present a 3-D inverse method for wave propagation in horizontally layered elastic isotropic media. The direct modeling uses a Hankel transform in the horizontal direction. We have previously introduced in the inversion problem a parameter reducing formulation based on a layered medium assumption (Jurado et x1,1991). In this paper we present a travel-time formulation of the problem to reduce coupling between velocity and depth. These two formulations are viewed as a change of variable or reparameterization on the usual depth formulation in the roversion problem. A synthetic example illustrates the interest of botte formulations .
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Statistical methodology for the geological calibration of a 2D seismic data set
Authors F. Fournier and J. -F. DerainMore and more sophisticated techniques such as stochastic simulations are used to build the reservoir model, which is mainly based on well data. These data are often not sufficient for a reliable reservoir description because of the well scarcity or poor spatial distribution. Indeed, reservoir description would greatly be improved by accounting for some extra geological information between the Wells. Such geological knowledge may be derived Erom the seismic data which are welt spatially distributed over the field. In particular, multivariate statistical techniques could be applied to achieve this goal (Thadani et al ., 1987, Fournier, 1989) .
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Wave equation based seismic processing: in which domain?
More LessThe forward model of prestack data that we use in our seismic inversion project DELPHI (Berkhout and Wapenaar, 1990) is based on a number of matrix multiplications. In its simplest form, (i.e. after pre-processing), it is given by P = W RW+S+ Where S+ contains the downgoing (source) wave fields at the surface, W+ describes downward propagation into the subsurface. W describes upward propagation to the surface and, finally, P contains the upgoing wave fields at the surface
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Hume, popper, bayes and geophysical inverse problems
Authors G. G. Drijkoningen and A. M. ZiolkowskiWe distinguish two approaches to geophysical inverse problems. One is the opposite, or inverse, of the forward problem. Signature deconvolution and migration are examples of this kind of inversion. The data are inverted to arrive at the Barth model. The other approach is iterative forward modeping, in which we try to match the measured data with synthetic data created with a model and the given theory. In recent years Bayes's rule has been a popular way to measure the quality of the result obtained by iterative forward modelling. We focus on the philosophical arguments for the two approaches and on the difficulties in applying them to geophysical inverse problems.
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Constrained AVO inversion
Authors G. Roberts and P. N. ArmstrongMuch AVO (Amplitude versus Offset) analysis involves linearised inversion of simplified Zoeppritz equations (Smith and Gidlow, 1987) . The approximations are only valid for small changes of physical properties, and for angles of incidence significantly leas than critical. Therefore, weighted stack AVO analysis is only applicable over a restricted range of conditions .
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Bright spot anomalies studies: an integrated approach
Authors A. Bruneton, D. T. van Nhieu and D. WloszczowskiAn integrated lithological and seismic interpretation method has been used in a real case study of seismic amplitude anomalies ("bright spots") related to shallow gas Bands encased in marine shales. Using a statistical analysis of geological and petrophysical data from core and wire-line logs data, the distribution of parameters to which seismic reflection is sensitive such as acoustic and elastic properties and bed thicknesses, is determined for the encountered lithologies . Qualitative interpretation of reprocessed seismic data witti we amplitude recovery before stack, quantitative seismic modelling and inversion are carried out . The results of this study calibrated on wells serve as guide lines in prospect evaluation whose expressions on conventional seismic sections are "bright spots".
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Porosity and lithology mapping from seismic data
Authors H. Özdemir, L. Jensen and A. StrudleyMapping of the reservoir zones and reservoir parameters between the Wells is needed at the field development stage, and later for reservoir characterization as inputs to reservoir simulations. Increasing use of horizontal Wells has also emphasized the need for detailed delineations of reservoir zones using surface seismic data. Improvements in the resolution obtained Erom seismic measurements can be achieved through post stack inversion scheures to assist in drilling prognosis. Key issuses in such inversion procedures are a relative amplitude proceseed surface seismic data set and a reliable method of wavelet extraction Erom surface seismic data over the zones of interest. Well seismic calibration is required at key well5 for calibration of inverted acoustic impedance and for the most rubast wavelet extraction scheures which make use of well acoustic impedance.
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Direct and inverse problem estimating of reservoir structure
Authors E. M. Chesnokov and V. V. TertychnyiThis report is a review of recent results obtained through the study of physical parameters carbonate reservoirs, which is presented by pore-cracked model under stress . As a basic model of cracked solid, we assume a linear elastic matrix with some system of distributed penny-shaped of ellipsoidal inclusions. The distribution function of inclusions with respect to orientation angle and aspect ratio is considered to be a function of applied stress. The latter predicts non-linear elastic behaviour of cracked solid and theoretically determines the dependence of effective elastic modules, heat and electrical conductivity on applied stress and fluid pressure .
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Seismic physical modelling facility at Delft university
Authors E. A. Koek and G. FaberThe use of physical modelling as a research tool in 3D-seismology has been known and used for several years. The choice of model scaling factors was mainly limited by the availability of high frequency transducers. Common transducers used for investigations were usable up to a maximum frequency of 300 kHz and showed rather poor directivity. As a result a maximum reduction in model size was limited to a factor of 1 :12,000 requiring also velocity scaling. The models used in these experiments are still rather large and thus expensive.
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Borehole coupling in cross-well wave propagation
More LessWe present the results of large-scale simulations aimed at studying the propagation and scattering of elastic waves in cross-well seismic experiments and their influence on the migrationinversion algorithms used in processing the data. The objective of this study is twofold: • To understand coupling phenomena in order to better design the experiment and interpret the observed data; • To providé realistic 3D elastic synthetics to be used in algorithmic validation of inversion techniques .
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