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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
21 - 40 of 500 results
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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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