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55th EAEG Meeting
- Conference date: 07 Jun 1993 - 11 Jun 1993
- Location: Stavanger, Norway
- ISBN: 978-94-6282-135-4
- Published: 08 June 1993
1 - 50 of 500 results
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3D Concentric circle survey - The art of going in circles
Authors G. A. Hird, J. Karwatowski, M. R. Jenkerson and A. EyresExploration for hydrocarbons in the North Sea has been successful for targets below Zechstein salt since the very first few Wells were drilled in the Southern North Sea in the mid -1960's (as described by Brennand & van Hoorn, 1984). Exploration targets above the same salt layers has also been successful. However, exploration in the UK sector of the North Sea has not been as successful for targets which are immediately adjacent to Zechstein salt. It is only within the recent past that seismic acquisition and imaging techniques have advanced to the stage that more wells have been successfully drilled (Rockliffe et al, 1992) . The most critical of these techniques has been the 3D survey. This paper will describe the acquisition of a 3D survey over a salt diapir and it will explain why the concentric circle* method was chosen over the more conventional linear technique. This was the first concentric circle survey to be acquired in Europe.
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3D Concentric circle survey - Processing for steep dip imaging
Authors J. M. Reilly and L. B. ComeauxOptimal imaging of reflection energy in steep dip structural environments requires that the data be acquired and processed in a way to retain, and position (migrate) the seismic reflection information. In certain structural situations, such as salt diapirs, special acquisition geometries can be employed which substantially contribute to the overall goal of enhanced imaging of the subsurface . However, these acquisition geometries can cause unique problems in the subsequent processing of the data. Overcoming these difficulties and producing a high quality product requires retention of steeply dipping energy throughout the processing sequence, specially adapted seismic processing techniques, integration of prior knowledge and a degree of creativity.
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Developments in 3D seismic technology
More LessWe believe that 3D seismic technology is revolutionizing the geophysical industry with far-reaching effect on the exploration and production business worldwide. This belief is corroborated by published statements representing the views of a broad spectrum of the industry ranging from the giants, Shell and Exxon, through companies of intermediate size, to small independents. Although the details vary, the message is always the same.
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Client oriented marine seismic acquisition QC
By M. BrinkIn the last few years great effort has been put into the development of quality control processes, which are applied in connection with marine seismic data collection. This is made possible by both a better understanding of the acquisition proces and the introduction of more powerful and cost-effective computer technology. An increasing amount of quality control data is available to the seismic crew and the client representative in order to made decisions about the further course of the seismic operation. Saga Petroleum has been pioneering novel quality control techniques, which have been presented at previous meetings. However, in order to handle all this information its staff of representatiees onboard the seismic vessel had to be increased .
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Measurements of degradation related to 3D acquisition
By P. MeldahlWe present measurements of degradation in 3-D seismic related to line separation, shot point interval and bin size. The accuracy of a survey planning method will be demonstrated by comparisons of predicted and measured degradation .
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Seismic degradation and mispositioning as a function of random and systematic navigation errors
Authors J. Paffenholz and D. J. MonkA quantitative analysis has been performed to show the effectof navigation errors on marine seismic data . It is found that in some cases large systematic navigation errors can lead to negligible degradation or mispositioning of the seismic data, though this is case dependent. The analysis accounts for the type and magnitude of the mispositioning error, streamer feather, acquisition parameters and subsurface geology. The effects on the seismic data are reported in terms of stack degradation, error in NMO velocity and misposition of the seismic data.
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3D Seismic survey - How big do we need to make the acquisition area
Authors T. L. Armstrong and J. PionIn order to make 3D seismic surveys cost effective, it is essential that our seismic acquisition programme enables us to fully meet our interpretation objectives. Having defined interpretation objectives and the subsurface target to be properly imaged, we estimate the surface area of seismic acquisition which will achieve this.
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Planning 3D seismic surveys using ray tracing on structural models
Authors W. H. Neff and H. K. RidgonThe explorationist must select 3D acquisition parameters that will best image the subsurface target objectives for each potential prospect. The usual starting point in parameter selection is to derive acquisition geometries based on a planer earth model with no dip or with constant dip. It has been found, through ray trace modeling, that acquisition parameters derived this way will not always meet the needed exploration objectives when dealing with a complex geologic structure. In examining numerous cases, complex geological structures scatter the primary reflections in such a manner that what is thought to be imaged and what is "truly" imaged are usually quite different. The explorationist must include, as part of the parameter selection list, the location, orientation, and size of survey that will best image the subsurface objectives in complex geologic settings.
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Seimic monitoring on the Frigg Gasfield (Norway) using AVO attributes and inversion
Authors A. Bossert, J. P. Blanche, P. Capelle, J. Marrauld and E. TorheimOperational objectives: in order to monitor the water-rise and control the reservoir model on the Frigg gas-field (Norway), a 2D seismic survey has been shot in 1991 to be compared with the seismic lines acquired in 1973 before the beginning of the production. This study includes several techniques geophysics, geology, petrophysics and reservoir engineering.
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Troll West - Seismic attributes and optimal locations of horizontal wells in a thin oil leg
Authors K. T. Thon and P. -A. ReksnesThe Troll field, situated in the northern part of the Viking Graben offshore Norway, is primarily a giant gas field. However, underneath one sub-area ,the Troll West gas Province (TWGP), there is a 12m thick oil column, constituting approximately 450 x 10 6 m³ oil in place! In order to maximize recovery from this oil volume, horizontal wells satisfying specific geological requirements are needed.
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The use of 3D seismic data for evaluation of drilling hazards at Heidrun, Haltenbanken
Authors T. J. F. Austin and H. M. HaugvaldstadThe identification of potential hazards for any drilling programme has traditionally ben carried out using 2D High Resolution (or Ultra-High Resolution) Seismic Site Surveys, with lines acquired as a grid over the proposed drilling location. Recently this is changing and it is becoming apparent that many potential drilling hazards, primarily shallow gas, can be identified on 3D exploration seismic data (Gallagher 1991 ; Newman 1990). However, there are some limitations to the use of the low frequency seismic data for the study of the shallow sequence, as it is acquired principally with the aim of resolving deeper reservoir related structures. These will be discussed using examples of both 2D Site survey data and 3D Exploration seismic data which has been collected at the Heidrun Field.
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Prediction of gas-oil and oil-water contacts in Norwegian block 30/8 by means of seismic attribute mapping - A new tool for the interpreters´ arsenal
Authors M. Donelick, M. Bahorich and S. FarmerAmoco recently developed proprietary techniques to quickly extract horizon or interval based response attributes from seismic data residing on interpretative workstations. Following their extraction, maps of the various attributes are generated using vendor software. This new technology enables quick analysis of large volumes of data to ascertain which attributes show significant variation. Forward modelling of well data and physical property data provide a means of "groundtruthing" the attribute variations to lithologic changes, changes in reservoir phase, or to processing artifacts.
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Troll West Gas Province - A reservoir depth conversion study
By M. B. GundemIn this paper a depth conversion study of the top and base of the reservoir in an area in the Troll West Gas Province (TWGP) will be presented. The main objective of the study has been to use different depth conversion methods and vetocity models in order to get an uncertainty estimate of the reservoir rock volume present. The work includes the use of standard 2D- and 3D depth conversion methods as well as more sophisticated techniques. In particular, the GOC-method based on the mapping of the gas-oil contact (GOC) in the area, has been applied as the "base-case" method. The excellent seismic definition of the GOC in the area and the uncertainties associated with the correct time-picking of the GOC has been investigated in detail. The velocity fields used in the depth conversion are generated from different sources of velocities available. This includes well velocities, calibrated stacking velocities (3D) and velocities obtained from both pre-stack and post-stack vetocity modelling on selected 2D-lines.
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How AVO attributes can improve seismic calibration and interpretation on the Heimdal Gasfield (Norway)
Authors Th. Vidaillac, J. P. Blanche, T. Nguyen, J. Marrauld, P. Capelle and P. GrindeInvestigation of the migrated seismic data acquired on the Heimdal Field shows that the seismic correlations between two wells in the gas field are not obvious and the well-to-seismic ties are dubious, mainly on the top of gas hearing sands. In order to solve these misties and picking problems, detailed Amplitude Versus Offset (AVO) processing and analysis are performed on several seismic lines.
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Porosity prediction for a Zechstein-2 carbonate prospect, onshore Netherlands
Authors J. M. M. van de Sande, H. Rebel and N. CassonThe studied Collendoornerveen prospect lies in NE Netherlands. The primary exploration targets are carbonates of Permian (Zechstein) age developed on a platform along the southern margin of the NW European Permian evaporitic basin. Wells drilled on this platform were evaluated as gas-hearing with variable average porosities (4-15%) for the carbonate reservoir. The main objective of this study was to map the porosity distribution over the prospect and adjacent platform areas in order to identify a location for an exploration well and to enable accurate reserves calculations.
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Outline of the Central North Sea overpressured zone based on chalk velocities
By P. JapsenDue to overpressure below the Upper Miocene in the North Sea, seismic velocities below this level are low relative to depth in the central North Sea. The pronounced increase of chalk velocities with depth makes it possible to use deviations in velocities from a normal velocity-depth trend to outline the areal extent of overpressure in the tentral North Sea.
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A Comperative study of post-stack inversion techniques
Authors A. Skalnes, I. Sando, H. Braenshoi and G. MangeroyDuring the past years several post-stack inversion techniques have been published and also made available as commercial software packages. In this study we have made a comparison of different methods with respect to the theoretical formulations and the results on both real and synthetic data.
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A Robust optimisation strategy for parametric inversion of seismic data
Authors R. Bale, P. Farmer, O. Yrke and L. SonnelandStandard seismic processing provides an image of the subsurface which is band-limited. Although the migrated stack is an important tool for structural evaluation, limited resolution creates difficulties in its use for small scale stratigraphic interpretation. Resolution is conventionally defined in terms of Rayleigh's criterion, requiring that two equal amplitude pulses are separated sufficiently to have their centres coincident with the others' first sidelobes of opposing sign. However, it has been noted by many authors (Kallweit and Wood,1982; van Riel and Berkhout, 1985) that the actual discrimination is much better, provided there are known to be a small number of reflectors in the model when compared with the number of data samples.
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Automatic determination of background velocities with lateral variation by multiple migration fitting
Authors C. Jacewitz and G. ChaventAfter structural imaging, inversion for various seismic/rock properties is one of the major desired uses for seismic data. The former has been very successful. Here we are concerned with the latter.
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Complex seismic decomposition - Theoretical aspects
Authors G. M. Mitrofanov, H. B. Helle, V. P. Kovaliev and A. G. MadatovA new spectral-statistical approach to seismic processing and inversion has been developed based on multi-level decomposition of the wave field. Its main application is to obtain details of geological/geophysical characteristics of the medium within a local target zone. Pore pressure and lithological prediction is one of several successful applications of the CSD method. In this paper we will review the theoretical aspects of the method.
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Complex seismic decomposition - Application to pore pressure prediction
Authors H. B. Helle, O. H. Inderhaug, V. P. Kovaliev, A. Madatov and G. M. MitrofanovThe commom approach to pore pressure prediction is made in two main steps: (1)-determine the depth intervals wich contain mainly shale, (2)-evaluate the deviation in the petrophysical properties of the shale from the trend of normal compaction (e.g. Tertzaghi & Peck, 1948). Several alternative methods of velocity estimation from surface seismic data are usually employed at the second step (E.Penibaker, 1968). Some of the methods such as RMS velocity analysis, have low resolution. Other methods such as Pseudo Acoustic lmpedance transformation, do not provide the low frequency components which implies that the overall compaction trend for the shale sequences cannot be determined with sufficient accuracy. Furthermore, velocity based methods do not involve lithological subdivisions (i.e. step 1)
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Recent progress in soft inversion of seismic data for reservoir description
More LessIn recent years there has been considerable interest in the possibility of utilizing seismic data to augment sparse well control information in reservoir characterization problems, while also providing for the robust quantification of uncertainty. This problem poses significant challenges: notably that seismic data has limited bandwidth and resolution, and contains only indirect information about reservoir properties (such as acoustic impedance,porosity,thickness...). The limited information content of the data has fueled interest in Stochastic Imaging approaches for seismic inversion, particularly in view of their potential for (non-parametric) risk assessment.
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Linearized elastic inversion of synthetic data from a gas-bearing sand model
Authors V. Richard, A. Bourgeois, D. Mace and G. EtienneLinearization is a goud approximation if the reference medium is sufficiently close to the actual one. The method we propose deals with a 1D reference medium and has been presented in Macé et al (1992). It is adapted to determine a 2D elastic target zone embedded in an almost laterally invariant elastic background. The method is based on the computation of the Jacobian matrix and uses a conjugate gradient algorithm to solve the optimization problem. In this paper, the linearized inversion method is valuated on synthetic prestack marine data from a gas-bearing sand model.
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Seismic waveform inversion of gas hydrate bottom simulating reflectors
Authors T. A. Minshull and S. C. SinghSeismic reflection profiles across many continent al margins have imaged "bottom simulating reflectors" (BSRs), which are interpreted as marking the base of a methane hydrate stability field. BSRs often have very high amplitude and can be continuous for many kilometres, so they provide an ideal target for a waveform inversion scheme. Knowledge of the detailed velocity structure in the vicinity of the BSR allows us to determine whether it is underlain by a free gas zone, and estimate the thickness of such a zone where present.
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Model driven picking in multilayer refraction statics
More LessIn 1990, Zanzi presented an iterative technique for the computation of refraction statics. The method performs a least squares estimation of the near-surface model in the wavenumber-offset domain according to a linear decomposition of headwave traveltimes. Details on ill conditioning problems and noise sensitivity of the linear model are available in Zanzi and Carlini (1991).
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Determination of shallow-refractor properties by 3D-CMP refraction seismic techniques
By T. RuhlIn 3D land seismic surveys refracted waves from shallow refractors (e.g. base of weathering layer, crystalline basement) are often recorded as first breaks. Automatic picking programs can easily determine first break traveltimes which are used for the computation of static corrections. In 2D reflection seismic surveys refracted arrivals can be evaluated by standard methods based on traveltime curves of shots and reverse shots. In the 3D configuration with an irregular distribution of shots and geophones this approach is impossible or very inconvenient. Tomographic techniques must be used for the inversion of refracted waves in order to obtain the near surface velocity structure.
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The generalized reciprocal method (GRM) - A new approach without first break picking
By O. SelviIs it possible to apply the generalized reciprocal method (GRM) for interpreting seismic refraction data without first break picking?
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A Hybrid genetic algorithm/steepest ascent approach has success with difficult statics
More LessSteepest ascent gradient inversion methods are fast but suffer from finding local maxima and not the desired global maxima. Problems which have complex objective functions with many local minima require the use of a global search mechanism. However, global search mechanisms such as genetic algorithms or simulated annealing suffer from excessive computation cost when they start with a collection of random models that have a large number of parameters. We combine a steepest ascent inversion approach with genetic algorithms into a hybrid method that avoids the pitfalls of these methods. The steepest ascent iterations provides a high graded population to the genetic algorithm and speeds the inversion. The genetic algorithm keeps the steepest ascent methods from getting stuck in a local minima.
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Adaptive dip filtering of seismic data
By S. SpitzCorrect removal of events with dips contained in an assigned interval is an old problem in seismic data processing. Because the simple f-k domain fan filter shows poor results when events in the data set are spatially aliased, the filters used nowadays in the industry are modelbased, as their design requires a range of dips that, hopefully, contain the dips actually present in the data.
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Monoplane filter and applications
More LessSeismic data routinely exhibits conflicting dips where as an ideal seismic image has only one dip at each location. Here I introduce an objective measure of the presence of more than a single dip, This measure is the output of a local filter with enough degrees of freedom that it is able to extinguish a single plane wave but not enough degrees of freedom to extinguish more than one plano. This filter is called a LOcal MOnoPLane ANnihilator (LOMOPLAN). Figure 1 shows a synthetic model and the outputs of an array of LOMOPLANs applied to it. Outputs are patched together to smooth over the seams defining the many local regions.
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Trace interpolation with aliased data
By M. K. ChaseThis paper describes a set of techniques for the spatial interpolation of aliased seismic data. The approach is designed to produce accurate interpolations when more than one dip is present simultaneously, even when weak events are hidden behind strong ones, for example when diffraction energy crosses a set of primaries. The method is simple and robust enough for routine use in data processing.
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A Review of trace interpolation for cost-effective 3D
Authors S. Lancaster and P. J. Whitfield3D data acquisition is now established as a key element in risk reduction ahead of the drill -bit. However, with the present trend towards use of 3D as early as the exploration phase, there is a need to reduce costs and improve turnaround. One parameter that affects both these requirements is the cross-line spacing. If we can acquire with a wider cross-line spacing, then fewer boat traverses are required, achieving a proportionally cheaper and faster survey. The downside is that the cross-line wave field is undersampled, and so trace interpolation is required to counteract spatul aliasing. We need therefore to examine the costlquality trade-off between grid cell dimensions and seismic resolution and interpretability. Our study reviews the technical case for trace interpolation, examines the relative merits of different types of interpolator as currently available from the seismic contractors, and benchmarks algorithms on real data.
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Measurement of phase and group velocities at low frequencies
Authors N. Thirion, J. L. Mari, J. Mars and F. GlangeaudThe dispersive properties of surface waves can be used in a case of exploration technology for weathering calculations. In full waveform acoustic Jogging, the dispersive waves are the Pseudo- Rayleigh waves in fast formations only and the Stoneley modes. The phase velocity of these dispersive waves can be used to evaluate the shear velocity of a formation. The use of dipole tools (Zemanek et al 1991) enables a measurement of the shear velocity in slow formations by studying the dispersion curves of flexural modes (figure 1). The object of this paper is to compare three methods which can be used to evaluate phase and group velocities of dispersive waves. The behavior and the accuracy of the proposed methods are checked on synthetic data. Synthetic data are an acoustic common shot point gather (figure 2).
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Results on low frequency acoustic prediction ahead of the bit by geophone dynamic accelerometers
Authors C. F. Kaspareck, F. Ogliani, F. Abramo and F. MirandaBorehole seismic plays an important role in exploration and development. Standard applications, besides measuring the acoustic velocity fields between the source and the well geophone, aim to reconstruct a subsurface acoustic image around and below the borehole (vertical case, VSP), and away from the borehole (offset and walkaway case, OSP and WSP). The fidelity of this image is related to the correct retrieval and definition of the reflectivity sequence.
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τ-p Domain processing of walkaway VSP data
More LessTraditionally 3-component Walkaway VSP data U(x,t)z (acquired at different geophone levels (z) and with a line of source positions (x) crossing near the rig) are processed by first ordering the traces into successive Fixed Source gathers (U(x,t)z -> U(z,t)x). The gathers are next processed individually in order to enhance the primary reflected P wavefield followed by a recordering to the (x,t)z domain before migration. The main drawback in the processing scheme is that neither periodicity in the up- and downgoing multiples nor the possibility of efficient removal of unwanted shear events are present in the (z,t)x domain. In consequente the usefulness of Walkaway VSP data is regarded with some scepticism.
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Application of the intercept time method to full waveform acoustic data
Authors F. Coppens and J. L. MariThe intercept time method was introduced in the early sixties for the computation of static corrections, when multiple coverage became a usual recording technique. This method gives the velocity of the refractor and the delay times at the shot and receiver positions. These delay times are related to the thickness and velocity of the altered zone. This paper presents a stand alone algorithm for the computation of the formation acoustic slowness and of the delay times from full waveform acoustic data recorded with a multi-receiver tool.
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Optimal array focusing deconvolution for VSP
Authors J. Haldorsen, J. Walsh, D. Miller and H. -J. ZochWe describe a technique for performing deconvolution of VSP data. The method is a two-step process that involves (1) estimating the source signature, and (2) applying a least squares optimum deconvolution operator that minimizes the noise not coherent with the source signature estimate. The optimization is done in the frequency domain, which introduces the frequency domain semblance as an extra factor in the deconvolution operator. Comparison to conventional processing of the data shows that the introduction of the semblance weights can give significantly improved results.
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Processing crosswell seismic data for reflection imaging
Authors W. Cai and G. T. SchusterCrosswell imaging with reflections has been proposed and successfully applied to field data (Lazaratos et al., 1992). Crosswell reflections can provide high resolution images of horizons at and below the well bottom, which is a key advantage of reflection imaging relative to transmission tomography. Crosswell re- flection imaging techniques include stacking, migration, wave equation traveltime plus waveforrn inversion (WTW, Luo and Schuster, 1990) etc., where each method may need different processing procedures.
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Characteristics of crosswell seismic data for reflection imaging
Authors B. A. Smith, J. G. Gallagher, G. M. Hoover and J. M. HuffordPhillips Petroleum Company acquired three tomographic crosswell datasets in early 1992 at the British Petroleum Devine test site, Frio County, TX, using Stanford University's piezoelectric Bender source and hydrophone receivers. These three datasets, recorded with source well to receiver well offsets of 100m, 200m, and 300m, show that the wavefield changes as a function of offset, even though there is little lateral change in the lithology. Onderstanding the nature of the wave propagation at the different offsets is important in determining how to process the data for traveltime tomography and reflection imaging. We find that coherent source related noise (tube waves propagating in both the source and receiver wells is a dominant waveform at all three offsets, especially at later times in the records. At farther offsets, most of the recorded wave field energy appears both as tube waves in the source and receiver wells, and as post-critical reflections from the major lithological interfaces.
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Crosswell reflection migration by a constrained Kirchhoff integral method
Authors F. Qin and G. T. SchusterMigrated crosswell reflections can produce high resolution images of the earth structure. To achieve good imaging several problems must be overcome. First, crosswell reflections can be obscured by a mixture of interfering wave types, such as direct waves, S-waves, converted waves, multiples and tube waves from both wells. Secondly, any crosswell reflection survey has only limited aperture. Thirdly the ray coverage is very uneven in terms of both the number of visiting rays and the ray incident angles. Rays with large incident angles will stretch the source wavelet, and cause loss of resolution in the migrated section.
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Interpreting non-orthogonal split shear waves in multicomponent VSPs
Authors X. -Y. Li, S. Crampin and C. MacBethMany techniques for processing shear-wave splitting in VSP data assume orthogonality of the split shear-waves, and are consequently restricted to zero or near-offset VSPs and symmetry planes (Wintersteen and Meadows 1991; Zeng and MacBeth 1993; among others). Here, we derive equations for multicomponent seismic data (two or three sources recorded by 3C receivers) for non-orthogonal split shear-waves. The equations can be solved by the linear-transform technique (LTT) of Li and Crampin (1993) to determine the shear-wave polarizations in both zero- and offset VSPs . This method is particularly useful where orthogonal techniques often fail when deviation from orthogonality exceeds 5°, or the incidence angle exceeds 1.5°.
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Analysis of split-shear waves from near-offset VSP data using a neural network
Authors D. Hengchang and C. MacbethNeural networks provide a way of recognizing particular patterns and extracting their characteristic parameters. Here they are applied to the different patterns of shear-wave particle motion recorded by orthogonal horizontal geophones. It is postulated that the major component of this particle motion is from shear-wave splitting, and that it can be parameterized as the polarization direction of the leading shear-wave and the time-delay between split shear-waves. The network is trained initially to recognize patterns of shear-wave splitting with known parameters from synthetic seismograms. Once training has been accomplished, the network can now be used to recognize patterns which have unknown characteristics, but which still lie within or not far outside the experience of the network. It is hoped to use the network to rapidly quantity any patterns of shear-wave splitting and to analyse large sets of seismic data.
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A Comparison of two methods for measuring shear wave birefringence from VSP data - Parametric inversion and layer stripping
By J. J. WalshShear wave birefringence has been the subject of considerable study in recent years. A principal application is the determination of fracture orientation from shear wave splitting in multicomponent VSPs. This is accomplished by studying the polarization direction of the lesding shear wave -and the travel time delay between the two split shear waves, which may give a direct indication of the orientation of the anisotropy. Here, we examine two methods for detection and description of fractured zones from shear wave splitting: layer stripping and parametric inversion.
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Processing of single-source split shear waves for imaging
Authors D. R. Watts and M. BoulfoulShear wave splitting may be regarded as a nuisance in the production of a shear wave image. Splitting or diffraction effects in the near surface or the weathering layer will degrade stacks especially if there is a rapid variation in the change of polarization along the survey line. We present a technique that may utilize a single source of indeterminate polarization for shear wave imaging even for the case of splitting in the weathering layer.
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True-amplitude processing of P- and PS- (converted) - Wave data for AVO-analysis
Authors P. Krajewski, C. Krajewski and S. GrummtThe analysis of seismic reflection amplitudes for reservoir characterisation or, more general, for the lithological interpretation of reflection data has become a standard approach in exploration geophysics. However the nonuniqueness of the interpretation of amplitude anomalies in P-wave sections has shown the need for shear-wave velocity information to permit a reliable lithology discrimination. In the paper Processing of PS-reflection data applying a common conversion-point stacking technique by Tessmer et al. 1990 a field data set has been presented which has been generated using three conventional P-wave vibrators as source and in-line horizontal geophones as receivers. This technique of shear wave data acquisition is relatively simple and inexpensive compared to techniques using shear-wave vibrators, because it can be done simultaneously with the routine P-wave recording.
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AVO Versus shearwaves by mode conversion
Authors F. Nieuwland and R. MarschallThis paper describes the results of a field experiment which was conducted in the central part of Friesland - The Netherlands.
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Three component seismic experiment in Saudi Arabia
Authors D. J. Fyfe, B. E. Dent, P. G. Kelamis, K. H. Al-Mashouq and D. A. NietupskiIn 1991, Saudi Aramco conducted an experimental three-component seismic program, over a known oil field, using conventional P-wave vibrators and three component geophones. One of the main objectives of the experiment was to use the converted (P-S) energy to improve the structural and stratigraphic picture of the reservoir sands. We recorded usable P-S energy as expected, but the surprisingly strong, coherent, shear energy generated at or near the vibrators (S-S) gave us a clearer image of the reservoir interval than either the vertical component (P-P) stack or the P-S stack.
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Recording and processing PSSP waves in the Barents Sea
Authors E. de Bazelaire, I. Gausland, O. E. Naess, H. Morizot and J. RavatSeismic profiles shot in Barents Sea cross a number of potential reef features, located between two reliable reflections at the top of Paleozoic and within the Paleozoic, 200 ms deeper. Conventional seismic work using P-waves is unable to separate porous from dry reefs, and all the more to assess the fluid contents.
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Rock properties - The missing link in exploitation and exploration
Authors C. H. Sondergeld and C. S. RaiRelationships between different physical properties of rock permit one to interpret log, seismic, magnetic and gravity data. One relies upon these correlations to infer subsurface properties. To map lithology, porosity, or permeability, for example, one must employ a technique which has sensitivity to the property of interest. These techniques generally produce a one, two, or three dimensional image of some attribute say vetocity or amplitude. Beyond a knowledge of the, physics behind a technique, one must establish the correlation between the attribute mapped and the property desired. In many circumstances these properties can not be linked to the attribute in an ab inito sense. Thus healthy empiricism is required to form the bridge. A case in point, the classical theories of Biot (1956a,b) and Gassmann (1951) require the definition of a porous frame modulus, this for obvious reasons can not be derived from first principles without a priori knowledge. However, once the modulus is defined, the theory permits one to conveniently calculate the influence of various saturants on velocity. Such information is extremely useful in modeling an AVO response, for example. The problems hampering such empiricism to date have been twofold: first, the cost on a per sample basis has been prohibitive and second, the core to be characterized has suffered irreversible degradation. GEM (Geophysical Evaluation Modules) has eliminated both these restrictions. Because GEM is portable, it can be brought to a well site or Gore facility and fresh samples can be characterized. Secondly, because of the high degree of automation and parallel processing concepts, the cost for a rather extensive suite of measurements has been reduced by an order of magnitude.
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The role of core measurements in seismic lithology prediction
By J. BartonCore measurements play an important role in lithology prediction from seismic data by: - Providing an accurate set of geophysical and petrophysical measurements about reservoir and caprock lithologies. - Allowing correlations between petrophysical and elastic parameters to be established. - Enabling key elastic parameters such as shear velocity, shear and bulk moduli to be determined for geophysical modelling. This paper describes how core measurements have helped evaluate and predict reservoir and caprock lithologies in the Paleocene section of Amoco operated fields in the UK Central Graben.
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