bluuebunny/crossref_metadata_2025 huggingface dataset:
γδ T cells for immune therapy of patients with lymphoid malignancies
Authors: Wilhelm Martin , Kunzmann Volker , Eckstein Susanne , Reimer Peter , Weissinger Florian , Ruediger Thomas , Tony Hans-Peter
Published: March 2003

There is increasing evidence that γδ T cells have potent innate antitumor activity. We described previously that synthetic aminobisphosphonates are potent γδ T cell stimulatory compounds that induce cytokine secretion (ie, interferon γ [IFN-γ]) and cell-mediated cytotoxicity against lymphoma and myeloma cell lines in vitro. To evaluate the antitumor activity of γδ T cells in vivo, we initiated a pilot study of low-dose interleukin 2 (IL-2) in combination with pamidronate in 19 patients with relapsed/refractory low-grade non-Hodgkin lymphoma (NHL) or multiple myeloma (MM). The objectives of this trial were to determine toxicity, the most effective dose for in vivo activation/proliferation of γδ T cells, and antilymphoma efficacy of the combination of pamidronate and IL-2. The first 10 patients (cohort A) who entered the study received 90 mg pamidronate intravenously on day 1 followed by increasing dose levels of continuous 24-hour intravenous (IV) infusions of IL-2 (0.25 to 3 × 106 IU/m2) from day 3 to day 8. Even at the highest IL-2 dose level in vivo, γδ T-cell activation/proliferation and response to treatment were disappointing with only 1 patient achieving stable disease. Therefore, the next 9 patients were selected by positive in vitro proliferation of γδ T cells in response to pamidronate/IL-2 and received a modified treatment schedule (6-hour bolus IV IL-2 infusions from day 1-6). In this patient group (cohort B), significant in vivo activation/proliferation of γδ T cells was observed in 5 patients (55%), and objective responses (PR) were achieved in 3 patients (33%). Only patients with significant in vivo proliferation of γδ T cells responded to treatment, indicating that γδ T cells might contribute to this antilymphoma effect. Overall, administration of pamidronate and low-dose IL-2 was well tolerated. In conclusion, this clinical trial demonstrates, for the first time, that γδ T-cell–mediated immunotherapy is feasible and can induce objective tumor responses. (Blood. 2003;102:200-206)
Kirchhoff scattering series: Insight into the multiple attenuation method
Authors: Ikelle Luc T. , Amundsen Lasse , Gangi Anthony , Wyatt Steven B.
Published: March 2003

There are two basic integral equations used to represent wavefields in theoretical seismology: the Lippmann‐Schwinger integral equation and the representation theorem. The Born scattering series currently used for attenuating free‐surface multiples has been derived from the Lippmann‐Schwinger integral equation. Similarly, we have used the representation theorem here to derive a Kirchhoff scattering series for attenuating free‐surface multiples in towed‐streamer data.

The Kirchhoff series for attenuating free‐surface multiples is, in theory, equivalent to the Born series; most important, like the Born series, it does not require any knowledge of the subsurface. However, it still provides useful insight into the multiple‐attenuation methods because the form of some quantities involved in the Kirchhoff series is different from the form in the Born series. For example, in towed‐streamer seismic data, the Kirchhoff series requires measurements of the vertical derivative of the pressure field in addition to the pressure field itself, whereas the Born series requires only the pressure field and tries to obtain its vertical derivative by multiplying the pressure field in the f‐k domain by the vertical wavenumber (generally known, in the context of multiple attenuation, as the obliquity factor).

The existing numerical implementations of the Born scattering multiple attenuation can be easily adapted to the Kirchhoff scattering multiple attenuation. We simply have to replace the computation of the vertical derivative of the pressure field with the recorded one. This is the most important conclusion in this paper for practitioners because they can use the numerically stable implementation of the inverse‐scattering multiple‐attenuation method in the form of a series when the combined measurements of the pressure field and its vertical derivative are available.
Fluid‐property discrimination with AVO: A Biot‐Gassmann perspective
Authors: Russell Brian H. , Hedlin Ken , Hilterman Fred J. , Lines Lawrence R.
Published: March 2003

This analysis draws together basic rock physics, amplitude variations with offset (AVO), and seismic amplitude inversion to discuss how fluid‐factor discrimination can be performed using prestack seismic data. From both Biot and Gassmann theories for porous, fluid‐saturated rocks, a general formula is first derived for fluid‐factor discrimination given that both the P and S impedances are available. In essence, the two impedances are transformed so that they better differentiate between the fluid and rock matrix of the porous medium. This formula provides a more sensitive discriminator of the pore‐fluid saturant than the acoustic impedance and is especially applicable in hard‐rock environments. The formulation can be expressed with either the Lamé constants and density, or the bulk and shear moduli and density. Numerical and well‐log examples illustrate the applicability of this approach. AVO inversion results are then incorporated to show how this method can be implemented using prestack seismic data. Finally, a shallow gas‐sand example from Alberta and a well‐log example from eastern Canada are shown to illustrate the technique.
Converted‐wave seismic exploration: Applications
Authors: Stewart Robert R. , Gaiser James E. , Brown R. James , Lawton Don C.
Published: March 2003

Converted seismic waves (specifically, downgoing P‐waves that convert on reflection to upcoming S‐waves are increasingly being used to explore for subsurface targets. Rapid advancements in both land and marine multicomponent acquisition and processing techniques have led to numerous applications for P‐S surveys. Uses that have arisen include structural imaging (e.g., “seeing” through gas‐bearing sediments, improved fault definition, enhanced near‐surface resolution), lithologic estimation (e.g., sand versus shale content, porosity), anisotropy analysis (e.g., fracture density and orientation), subsurface fluid description, and reservoir monitoring. Further applications of P‐S data and analysis of other more complicated converted modes are developing.
Controls on acoustic properties of Upper Jurassic siliciclastic rocks (Boulonnais, northern France)
Authors: Braaksma Hendrik , Kenter Jeroen A. M. , Proust Jean Noel , Dijkmans Vincent , van Hoek Tomas , Mahieux Geoffroy , Drijkoningen Guy G.
Published: March 2003

More than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of Late Jurassic (Kimmeridgian to Tithonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. Our primary goal was to study the effect of clay (fraction smaller than 8 μm), silt/sand (fraction larger than 8 μm), and carbonate on the acoustic properties. The quantitative nature and volume of the data made it possible to observe four‐dimensional relationships in contoured ternary diagrams. Primary control on the acoustic properties is exerted by porosity, but the trend of this relationship significantly deviates from popular velocity transforms. The contribution of clay, silt/sand, and carbonate particular material and cement explains the remaining variation in acoustic properties. Although no clear linear thresholds are defined, a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties, the influence of clay content progressively increases with decreasing carbonate content, and visa versa. With increasing carbonate content, the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay‐dominated sediment. Traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate.

This study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment. In addition, the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy.
Okak Bay AMT data‐set case study: Lessons in dimensionality and scale
Authors: Jones Alan G. , Garcia Xavier
Published: March 2003

Electromagnetic (EM) exploration for base metals using the natural‐source audio‐magnetotelluric (AMT) technique has increased significantly during the last five years due to enhancements in all aspects of AMT and to the demand for imaging deeper than conventional controlled‐source EM methods. However, regional currents induced by natural sources can be problematic in certain situations, and the appropriate interpretational dimensionality must be known. Herein we demonstrate that a two‐dimensional (2D) interpretation is valid for a defined frequency band, but that the effects of large‐scale three‐dimensional (3D) structures must be considered at lower frequencies. Using an AMT dataset from an area located north of Voisey's Bay, Labrador, Canada, we analyse the responses to determine the appropriate dimensionality and to test them for internal consistency. Maps of the distortion‐corrected data identify the lateral extent of connected conducting mineralization intersected by a drilling program. One‐dimensional (1D) inversions of the corrected data from those sites on top of the mineralized zone show the resolution properties of the data. We constructed a pseudo‐3D model from 2D inversions of the data in the frequency band 1000–10~Hz from all profiles, and this model images the mineralized body sufficiently for exploration purposes. We suggest that the anomalous low‐frequency responses observed at sites close to the mineralized zone are possibly due to charges impinged on the mineralized body's boundaries by currents induced in the Atlantic Ocean some 50 km away. Although 3D numerical modeling studies exhibit some of the effects observed, we are unable to reproduce numerically the observed behavior.
Direct seismic detection of methane hydrate on the Blake Ridge
Authors: Hornbach Matthew J. , Holbrook W. Steven , Gorman Andrew R. , Hackwith Kara L. , Lizarralde Daniel , Pecher Ingo
Published: March 2003

Seismic detection of methane hydrate often relies on indirect or equivocal methods. New multichannel seismic reflection data from the Blake Ridge, located approximately 450 km east of Savannah, Georgia, show three direct seismic indicators of methane hydrate: (1) a paleo bottom‐simulating reflector (BSR) formed when methane gas froze into methane hydrate on the eroding eastern flank of the Blake Ridge, (2) a lens of reduced amplitudes and high P‐wave velocities found between the paleo‐BSR and BSR, and (3) bright spots within the hydrate stability zone that represent discrete layers of concentrated hydrate formed by upward migration of gas. Velocities within the lens (∼1910 m/s) are significantly higher than velocities in immediately adjacent strata (1820 and 1849 m/s). Conservative estimates show that the hydrate lens contains at least 13% bulk methane hydrate within a 2‐km3 volume, yielding 3.2 × 1010kg [1.5 TCF (4.2 × 1010 m3] of methane. Low seismic amplitudes coupled with high interval velocities within the lens offer evidence for possible methane hydrate “blanking.” Hydrate bright spots yield velocities as high as 2100 m/s, with bulk hydrate concentrations predicted as high as 42% in an approximately 15‐m thick layer. Our results show that, under certain circumstances, hydrate in marine sediments can be directly detected in seismic reflections but that quantification of hydrate concentrations requires accurate velocity information.
Centroid phase slowness as a tool for dispersion correction of dipole acoustic logging data
Authors: Geerits Tim W. , Tang Xiaoming
Published: March 2003

We develop a simple and efficient method for correcting the borehole flexural‐wave slowness dispersion effects. We demonstrate its validity on synthetic and field data. The theory underlying the method is derived from first principles and shows the general result that semblance‐derived wave slowness is a spectral‐amplitude weighted average of the wave‐slowness dispersion curve. The theory also explains that a dispersion correction on the borehole flexural wave slowness is not necessary if the source frequency content is sufficiently low.
Velocity‐permeability relations within hydraulic units
Authors: Prasad Manika
Published: March 2003

Relationships between seismic velocity and permeability have been difficult to establish. I show that by grouping and sorting rocks into hydraulic units, we can establish relationships between velocity and permeability. The hydraulic units are calculated from measured porosity and permeability values. Correlation between velocity and permeability is significant within each hydraulic unit (the correlation coefficient, R2, lies in the range 0.65–0.87). This correlation is an extension of the match between porosity and permeability within a hydraulic unit. I show how the compaction and cementation history of a sediment can have effects on its physical properties such as porosity and permeability and on its seismic properties. The measured velocity data are further approximated with the Biot model. The velocity‐permeability relation and modeling results are demonstrated for a large data set of laboratory measurements. The good match between calculated and measured data demonstrates that this relation can be used to predict permeability from velocity in well logs by zoning the data from training wells into hydraulic units. One possible application is shown where, by using site‐specific data, the velocity‐permeability relation is vastly improved with a correlation coefficient R2of 0.9.
Determining formation shear‐wave transverse isotropy from borehole Stoneley‐wave measurements
Authors: Tang Xiaoming
Published: March 2003

Many rocks exhibit transversely isotropic (TI) characteristics. For determining the TI property using acoustic logging, Stoneley waves are the only borehole wave mode that has a significant sensitivity to TI effects, especially when the formation is acoustically slow compared to the borehole fluid. This study describes a method for deriving the formation shear‐wave TI parameter from the Stoneley wave data acquired by a logging tool. It is shown that the presence of the tool in the borehole can substantially affect the Stoneley wave propagation. Fortunately, for low‐frequency Stoneley waves, the tool effect can be satisfactorily modeled using an effective modulus, regardless of the actual structure of the tool. The modulus can be determined from a calibration procedure. In the inversion processing of the Stoneley wave data, the Stoneley wave slowness is related to the weighted average of the wave's dispersion curve over the frequency range occupied by the wave spectrum. This provides a fast method for the inversion. As a processing example, this method has been applied to estimate the shear‐wave TI parameter profile for the Lewis shale formation in Braggs, Wyoming. The resulting profile delineates the shear‐wave anisotropy magnitude and variation for this shale formation.
3D interpretation of electromagnetic data using a modified extended Born approximation
Authors: Tseng Hung‐Wen , Lee Ki Ha , Becker Alex
Published: March 2003

We present a new method, dubbed the modified extended Born approximation (MEBA), for efficient three‐dimensional (3D) simulation and inversion of geophysical frequency‐domain electromagnetic (EM) data for a targeted object lodged in a layered half‐space. Based on the integral equation method and modified from an extended Born approximation technique, the MEBA method calculates the total electric field in an electrical conductivity inhomogeneity without any need for solving a huge matrix equation. This is done by multiplying the background electric field by a depolarization tensor. The Fourier transform and the convolution theorem are used to dramatically increase the computational efficiency. Comparisons of MEBA‐generated numerical data for tabular targets with data generated by other means are used to verify the scheme and check its range of validity. The results indicate that the MEBA technique yields better accuracy when current channeling in the conductivity anomaly dominates over the induction process. The MEBA algorithm has been incorporated into a least‐squares inversion scheme which is used to interpret borehole‐to‐surface EM tomography field data. The survey served to monitor the subsurface conductivity change associated with the extraction of a volume of saltwater previously injected into a known aquifer.
Inherent nonuniqueness in magnetotelluric inversion for 1D anisotropic models
Authors: Yin Changchun
Published: March 2003

This paper investigates the inherent nonuniqueness in the inversion of magnetotelluric (MT) measurements over an earth with a layered anisotropic resistivity distribution. This kind of nonuniqueness arises from the fact that even accurate and complete data contain insufficient information to uniquely resolve the earth parameters.

For a very simple anisotropic case, where all layers in the earth have at least one horizontal principal axis in common coinciding with the x‐ or y‐axis of the Cartesian coordinate system, the resolvable parameters or parameter combinations from MT surface observations are identified by analyzing the structure of the conductivity tensor of the earth and the differential equations the electromagnetic (EM) fields satify. It is found that for a layered anisotropic earth model, several parameters can be uniquely resolved from the MT inversion while others are nonresolvable. However, particular combinations of the nonresolvable parameters can be uniquely resolved.

These theoretical findings on the parameter resolvability of MT anisotropic inversion are further verified by a number of numerical experiments using synthetic data and a nonlinear parameter estimation technique. For this purpose, I parameterize the resistivity tensor assigned to each layer of the earth with three principal resistivities and three Euler angles, and then use the three Euler angles, the logarithms of three principal resistivities, and the logarithmic thickness as inverse parameters. This guarantees that the layer thickness is positive and the resistivity tensor is positive‐definite, while at the same time the inverse parameters may span the whole real axis. Numerical inversion results for different anisotropic models also reveal the fact that the resolvable parameters and parameter combinations are invariant with respect to the starting model. This means that for different starting models, the inversion results for some earth parameters might be individually quite different; however, particular combinations of these parameters remain unchanged.
Near‐surface seismic reflection profiling of the Matanuska Glacier, Alaska
Authors: Baker Gregory S. , Strasser Jeffrey C. , Evenson Edward B. , Lawson Daniel E. , Pyke Kendra , Bigl Robert A.
Published: March 2003

Several common‐midpoint seismic reflection profiles collected on the Matanuska Glacier, Alaska, clearly demonstrate the feasibility of collecting high‐quality, high‐resolution near‐surface reflection data on a temperate glacier. The results indicate that high‐resolution seismic reflection can be used to accurately determine the thickness and horizontal distribution of debris‐rich ice at the base of the glacier. The basal ice thickens about 30% over a 300‐m distance as the glacier flows out of an overdeepening. The reflection events ranged from 80‐ to 140‐m depth along the longitudinal axis of the glacier. The dominant reflection is from the contact between clean, englacial ice and the underlying debris‐rich basal ice, but a strong characteristic reflection is also observed from the base of the debris‐rich ice (bottom of the glacier). The P‐wave propagation velocity at the surface and throughout the englacial ice is 3600 m/s, and the frequency content of the reflections is in excess of 800 Hz. Supporting drilling data indicate that depth estimates are correct to within ± 1 m.
Gravimagnetic anomaly formulas for polyhedra of spatially linear media
Authors: Holstein Horst
Published: March 2003

Formulas for the gravity potential, field, and field gradient tensor are derived for a polyhedral target body of a spatially linear density medium. The formulas also define the magnetic potential and field in the case of a medium of spatially linear magnetization. This work generalizes existing solutions for the gravity field of a polyhedral target of linearly varying density.

The formulas are analyzed for singularities and for numerical error growth. Error growth with increasing target distance is found to be higher than in the corresponding uniform polyhedral case. Examination of the error sources reveals that some error reduction is possible. On this basis, new algorithms of improved error control over existing algorithms are proposed for the linear medium. Computational results confirm the expected improvement.
Application of artificial intelligence for Euler solutions clustering
Authors: Mikhailov Valentine , Galdeano Armand , Diament Michel , Gvishiani Alexei , Agayan Sergei , Bogoutdinov Shamil′ , Graeva Elena , Sailhac Pascal
Published: March 2003

Results of Euler deconvolution strongly depend on the selection of viable solutions. Synthetic calculations using multiple causative sources show that Euler solutions cluster in the vicinity of causative bodies even when they do not group densely about the perimeter of the bodies. We have developed a clustering technique to serve as a tool for selecting appropriate solutions.

The clustering technique uses a methodology based on artificial intelligence, and it was originally designed to classify large data sets. It is based on a geometrical approach to study object concentration in a finite metric space of any dimension. The method uses a formal definition of cluster and includes free parameters that search for clusters of given properties.

Tests on synthetic and real data showed that the clustering technique successfully outlines causative bodies more accurately than other methods used to discriminate Euler solutions. In complex field cases, such as the magnetic field in the Gulf of Saint Malo region (Brittany, France), the method provides dense clusters, which more clearly outline possible causative sources. In particular, it allows one to trace offshore the main inland tectonic structures and to study their interrelationships in the Gulf of Saint Malo.

The clusters provide solutions associated with particular bodies, or parts of bodies, allowing the analysis of different clusters of Euler solutions separately. This may allow computation of average parameters for individual causative bodies. Those measurements of the anomalous field that yield clusters also form dense clusters themselves. Application of this clustering technique thus outlines areas where the influence of different causative sources is more prominent. This allows one to focus on these areas for more detailed study, using different window sizes, structural indices, etc.
Bayesian linearized AVO inversion
Authors: Buland Arild , Omre Henning
Published: March 2003

A new linearized AVO inversion technique is developed in a Bayesian framework. The objective is to obtain posterior distributions for P‐wave velocity, S‐wave velocity, and density. Distributions for other elastic parameters can also be assessed—for example, acoustic impedance, shear impedance, and P‐wave to S‐wave velocity ratio. The inversion algorithm is based on the convolutional model and a linearized weak contrast approximation of the Zoeppritz equation. The solution is represented by a Gaussian posterior distribution with explicit expressions for the posterior expectation and covariance; hence, exact prediction intervals for the inverted parameters can be computed under the specified model. The explicit analytical form of the posterior distribution provides a computationally fast inversion method. Tests on synthetic data show that all inverted parameters were almost perfectly retrieved when the noise approached zero. With realistic noise levels, acoustic impedance was the best determined parameter, while the inversion provided practically no information about the density. The inversion algorithm has also been tested on a real 3‐D data set from the Sleipner field. The results show good agreement with well logs, but the uncertainty is high.
Multiresolution parameterization for geophysical inverse problems
Authors: Chiao Ling‐Yun , Liang Wen‐Tzong
Published: March 2003

A model parameterization based on a multiresolution wavelet representation is proposed for geophysical inverse problems in this study. The matrix equation for the wavelet representation of the model is constructed by dual wavelet transforms of a readily built matrix based on the pixel parameterization. We demonstrate the merits of the proposed parameterization using the simple examples of geophysical data gridding and 3D seismic tomography, and comparing the results with those obtained by the conventional pixel parameterization. It is shown that for the conventional damped least‐squares solutions of pixel‐parameterized models, regularization by norm damping deteriorates the underlying model correlation due to sparse and heterogeneous sampling, whereas roughness damping schemes impose a priori arbitrary correlation length irrespective of the heterogeneous sampling. The scale hierarchy embedded in the proposed multiresolution parameterization facilitates the compromise between the dual spatial and scale resolution. Depending on the local richness of the data constraints across different scales at a site, model variation of various scale spectra can be robustly resolved through the scale hierarchy. There is thus no need to invoke additional smoothness regularization.
Traveltime and conversion‐point computations and parameter estimation in layered, anisotropic media by τ‐ptransform
Authors: van der Baan Mirko , Kendall J.‐Michael
Published: March 2003

Anisotropy influences many aspects of seismic wave propagation and, therefore, has implications for conventional processing schemes. It also holds information about the nature of the medium. To estimate anisotropy, we need both forward modeling and inversion tools. Forward modeling in anisotropic media is generally done by ray tracing. We present a new and fast method using the τ‐p transform to calculate exact reflection‐moveout curves in stratified, laterally homogeneous, anisotropic media for all pure‐mode and converted phases which requires no conventional ray tracing. Moreover, we obtain the common conversion points for both P‐SV and P‐SH converted waves. Results are exact for arbitrary strength of anisotropy in both HTI and VTI media (transverse isotropy with a horizontal or vertical symmetry axis, respectively).

Since inversion for anisotropic parameters is a highly nonunique problem, we also develop expressions describing the phase velocities that require only a reduced number of parameters for both types of anisotropy. Nevertheless, resulting predictions for traveltimes and conversion points are generally more accurate than those obtained using the conventional Taylor‐series expansions. In addition, the reduced‐parameter expressions are also able to handle kinks or cusps in the SV traveltime curves for either VTI or HTI symmetry.
Physical Wavelet Frame Denoising
Authors: Zhang Rongfeng , Ulrych Tadeusz J.
Published: March 2003

This paper deals with the design and implementation of a new wavelet frame for noise suppression based on the character of seismic data. In general, wavelet denoising methods widely used in image and acoustic processing use well‐known conventional wavelets which, although versatile, are often not optimal for seismic data. The new approach, physical wavelet frame denoising uses a wavelet frame that takes into account the characteristics of seismic data both in time and space. Synthetic and real data tests show that the approach is effective even for seismic signals contaminated by strong noise which may be random or coherent, such as ground roll or air waves.
Focusing in dip and AVA compensation on scattering‐angle/azimuth common image gathers
Authors: Brandsberg‐Dahl Sverre , de Hoop Maarten V. , Ursin Bjorn
Published: March 2003

Common image gathers (CIGs) in the offset and surface azimuth domain are used extensively in migration velocity analysis and amplitude variation with offset (AVO) studies. If the geology is complex and the ray field becomes multipathed, the quality of the CIGs deteriorates. To overcome these problems, the CIGs are generated as a function of scattering angle and azimuth at the image point. The CIGs are generated using an algorithm based on the inverse generalized Radon transform (GRT), stacking only over migration dip angles. Including only dips in the vicinity of the geological dip, or focusing in dip, suppresses artifacts in and results in improved signal‐to‐noise ratio on the CIGs.

Migration velocity analysis can be based upon the differential semblance criterion. The analysis~is~then carried out by minimizing a functional of the derivative of the CIGs with respect to horizontal coordinates (offset/azimuth or scattering‐angle/azimuth), but AVO/amplitude variation with angle (AVA) effects will degrade the performance of the velocity analysis. We overcome this problem by computing an inverse GRT modified to compensate for AVA effects. The resulting CIGs can be used for velocity analysis based upon differential semblance, while they can be stacked to produce improved images.

The algorithms are developed for inhomogeneous anisotropic elastic media, but they have so far only been tested on imaging‐inversion of PP and PS reflected waves in an isotropic elastic medium. This was done on two synthetic datasets generated by finite‐difference modeling and ocean‐bottom seismic (OBS) data from the Valhall field. We show that by performing the imaging of the real OBS data in the angle domain, it is possible to construct a well‐focused PP image of the Valhall reservoir directly beneath the “gas cloud” in the overburden.
Traveltime formulas of near‐zero‐offset primary reflections for a curved 2D measurement surface
Authors: Chira Pedro , Hubral Peter
Published: March 2003

Analytic moveout formulas for primary near‐zero‐offset reflections in various types of gathers (e.g., common midpoint, common shot, zero offset) play a significant role in the seismic reflection method. They are required in stacking methods like the common midpoint (CMP) or the common‐reflection‐surface (CRS) stack. They also play a very important role in Dix‐type traveltime inversions and are of prime interest for seismic imaging. They are particularly attractive if they can be given a physical interpretation, involving for instance the wavefront curvatures of specific waves. The new formulas presented here have such a form. They give particular attention to the influence that a smooth curved measurement surface has on the computation of the traveltime and the moveout in various gathers as well as on the normal‐moveout (NMO) velocity in the CMP gather. This influence should be accounted for in the CMP or CRS stack as well as in the Dix‐type inversion. In the computation of interval velocities and the recovery of the depth of reflectors, the new NMO velocity formula is therefore more suited than the root‐mean‐square or NMO velocity for a planar measurement surface. It can be extended to a rugged free surface (mountainous terrain), but this extension requires a different derivation and different considerations. The influence of the surface curvature on the NMO velocity can be estimated with the new formula given here.
Least‐squares wave‐equation migration for AVP/AVA inversion
Authors: Kühl Henning , Sacchi Mauricio D.
Published: March 2003

We present an acoustic migration/inversion algorithm that uses extended double‐square‐root wave‐equation migration and modeling operators to minimize a constrained least‐squares data misfit function (least‐squares migration). We employ an imaging principle that allows for the extraction of ray‐parameter‐domain common image gathers (CIGs) from the propagated seismic wavefield. The CIGs exhibit amplitude variations as a function of half‐offset ray parameter (AVP) closely related to the amplitude variation with reflection angle (AVA). Our least‐squares wave‐equation migration/inversion is constrained by a smoothing regularization along the ray parameter. This approach is based on the idea that rapid amplitude changes or discontinuities along the ray parameter axis result from noise, incomplete wavefield sampling, and numerical operator artifacts. These discontinuities should therefore be penalized in the inversion.

The performance of the proposed algorithm is examined with two synthetic examples. In the first case, we generated acoustic finite difference data for a horizontally layered model. The AVP functions based on the migrated/inverted ray parameter CIGs were converted to AVA plots. The AVA plots were then compared to the true acoustic AVA of the reflectors. The constrained least‐squares inversion compares favorably with the conventional migration, especially when incompleteness compromises the data. In the second example, we use the Marmousi data set to test the algorithm in complex media. The result shows that least‐squares migration can mitigate kinematic artifacts in the ray‐parameter domain CIGs effectively.
Crooked‐line 2D seismic reflection imaging in crystalline terrains: Part 1, data processing
Authors: Nedimović Mladen R. , West Gordon F.
Published: March 2003

For cost and access reasons, most of the seismic reflection data collected in crystalline terrains have been acquired by 2D crooked‐line profiling. When the survey geometry is significantly irregular and the geologic structures have cross‐profile dip, several standard 2D imaging procedures severely underperform. As a result, reflection signal is poorly aligned across individual common midpoint (CMP) gathers, and much is lost during the CMP stack. To improve imaging, either the methods used to align signal before stack need to be modified or more tolerant methods of combining trace signals than the standard CMP stack need to be applied.

Because a high‐fold 2D crooked‐line profile is really a 3D survey of a swath of terrain around the processing line, better signal alignment before CMP stacking may be achieved by revisiting the traveltime equation and including the cross‐dip terms into the moveout calculations. Therefore, in addition to the correction of NMO and in‐line dip moveout (DMO), we also locally compute and subsequently remove cross‐dip moveout (CDMO). This requires a procedure for estimating the amount of cross‐dip associated with each local reflection event. Stacking after the successful removal of the CDMO yields what we call an optimum cross‐dip stack—a seismic section that is significantly more complete and informative than the standard stack. Alternatively, amplitude stacking appears to be more robust to residual time anomalies. When little or no cross‐dip information can be extracted from the 2D crooked‐line data, we use it as a last resort to obtain a section that contains more structural information than the standard stack.
Crooked‐line 2D seismic reflection imaging in crystalline terrains: Part 2, migration
Authors: Nedimović Mladen R. , West Gordon F.
Published: March 2003

Seismic reflection surveys are frequently conducted over very complicated geological structure, but surveying often must be confined to existing crooked roads or tracks. Typically, data from such 2D crooked‐line surveys are processed using standard common midpoint (CMP) stacking techniques to obtain a 2D time section which is then 2D migrated. In Part I, we show that a reflector dip component across the processing line can cause serious problems for standard CMP stacking. We also propose a supplementary processing step in which cross‐dip is determined locally and cross‐dip moveout (CDMO) is removed from data to form an optimum cross‐dip stack. However, a crooked‐line survey is really a swath 3D survey, and ideally we would like to obtain a 3D image of reflectivity surrounding the profile.

Here we investigate the potential of 3D prestack Kirchhoff migration to directly image all observed reflections; i.e., we attempt to construct a 3D image volume of all reflectors viewed by the survey. Because reflectors that face away from the acquisition line cannot return much wave energy from available sources to available receivers, they cannot be imaged even if they lie directly beneath the survey profile. Tests show that the cross‐profile spread of trace midpoints usually is sufficient to provide a useful degree of cross‐line positioning of reflection points. A very helpful image volume is thus obtained.

Kirchhoff 3D prestack migration is computationally laborious. A much quicker but less complete method is to create the 3D migrated image volume from the 2D optimum cross‐dip stack and the associated set of cross‐dips. Robustness of migration methods to time errors in the prestack data traces such as poorly corrected statics is also an issue. Tests show that in difficult cases, particularly where only 2D processing is warranted, migration of trace absolute amplitude rather than standard phase data may lead to a superior result.
Autocorrelogram Migration: IVSPWD test
Authors: Yu Jianhua , Katz Lewis J. , Followill Fred , Sun Hongchuan , Schuster Gerard T.
Published: March 2003

We present the results of applying autocorrelogram migration to inverse vertical seismic‐while‐drilling (IVSPWD) profile data collected in the Austin Chalk formation. The seismic reflections were excited by a drill bit moving along a horizontal well at a depth of 2800 m. The data were recorded by a receiver array on the surface. There were 609 twenty‐second traces recorded at each of 10 three‐component stations. After preprocessing, the traces were autocorrelated and migrated. Two imaging conditions were examined. The ghost‐reflection imaging condition produced a reflectivity section that agreed with a nearby common‐depth‐point section. The migration section obtained with a primary‐reflection imaging condition produced a reflectivity section inferior in quality to that of the ghost image. A possible explanation is that the drill‐bit location was not precisely known, which can be shown to induce weak errors in the ghost‐imaging condition but stronger errors in the primary‐reflection imaging condition. Ghost migration images reflections not only below the drill bit, but also above the drill bit. This investigation is one of the first examples of successfully imaging the earth's reflectivity section from horizontal drill‐bit data, and it offers a potentially useful method for seismic imaging from drill‐bit data.
Single‐cycle terahertz electromagnetic pulses: A new test bed for physical seismic modeling
Authors: Dorney Timothy D. , Rossow Molly J. , Symes William W. , Mittleman Daniel M.
Published: March 2003

We describe a new technique for physical modeling, based on the use of short pulses of electromagnetic radiation. We employ radiation at a frequency near 1 THz (1012Hz), corresponding to a wavelength of ∼0.3 mm. Very recent advances in optoelectronic techniques have enabled the generation and detection of broadband terahertz pulses using compact room‐ temperature transducers. These pulses can be used to form images in a variety of modes, including a multistatic reflection configuration which mimics that of many seismic surveys. We illustrate the capabilities of the modeling technique with a simple experiment which demonstrates accurate surface reconstruction using migration techniques. With respect to conventional modeling techniques using piezoelectric transducers and microphones, the use of terahertz pulses has both benefits and limitations. To our knowledge, this work represents the first use of electromagnetic radiation for modeling acoustic imaging problems.
Elastic wave modeling with free surfaces: Stability of long simulations
Authors: Hestholm Stig
Published: March 2003

Three‐dimensional (3D) elastic wave propagation modeling in the velocity‐stress formulation using finite differences (FDs) have been investigated for a homogeneous medium covered by a representative, relatively steep surface topography consisting of a 1D square root function. This scenario using various numerical implementations is explored. The behavior with regard to stability of long simulations is expected to be indicative of each numerical implementation's robustness for other types of topographies/media. Employing various combinations of the FD order was found only to change the time of the first incidence of instability. On the other hand, nonequidistant grids in the horizontal and vertical directions are found to be extremely useful for long‐term stability of 3D wave propagation modeling with our free‐surface boundary condition for single‐valued topographies. In particular dz ≥ (3/2) dx is found completely stable for all tested vP/vSratios. Such relationships of using dz > dx are also favorable for more accurate Rayleigh‐wave modeling. Setting the density equal to 1/10 of its interior value at one layer only at the surface is another simple means of achieving stability.
Scale dependence of reflection and transmission coefficients
Authors: Imhof Matthias G.
Published: March 2003

Well logs show that heterogeneities occur at many different depth scales. This study examines the effects of these heterogeneities on the propagation of seismic waves, and specifically the dependence of reflection and transmission on the spatial scale content of the medium. Wavelet transformations are used to filter certain spatial scales from an acoustic sonic log. The scale‐filtered logs are used to construct layerstack models for which reflection and transmission seismograms are computed. The modified logs are also used to calculate frequency dependent reflection and transmission coefficients as functions of scale content. It is observed that features shorter than one‐fourth of the dominant wavelength have little effect on the reflection and transmission of seismic waves. Features larger than the dominant wavelength affect arrival times of individual packets within the wavetrain, but often these features hardly alter the overall appearance of individual wave packets. Reflection and transmission coda are primarily governed by heterogeneity at spatial scales similar to half the propagating wavelength. These scales appear to control the presence and shape of the events within the coda. The study also shows that the arrival times of packets at 1 kHz approach the theoretically expected value obtained from the harmonic velocity average, and the arrival times of packets below 1 Hz approach the theoretical value expected for the Backus average of the velocities.
Quantifying the effectiveness of stabilized inverseQfiltering
Authors: Wang Yanghua
Published: March 2003

Applying inverse Q filtering to surface seismic data may minimize the effect of dispersion and attenuation and hence improve the seismic resolution. In this case study, a stabilized inverse Q filter is applied to a land seismic data set, for which the prerequisite reliable earth Q function is estimated from the vertical seismic profile (VSP) downgoing wavefield. The paper focuses on the robust estimate of Q values from VSP data and on the quantitative evaluation of the effectiveness of the stabilized inverse Q filtering approach. The quantitative evaluation shows that inverse Q filtering may flatten the amplitude spectrum, strengthen the time‐variant amplitude, increase the spectral bandwidth, and improve the signal‐to‐noise (S/N) ratio. A parameter measuring the resolution enhancement is defined as a function of the changes in the bandwidth and the S/N ratio. The stabilized inverse Q filtering algorithm, which may provide a stable solution for compensating the high‐frequency wave components lost through attenuation, has positive changes in both the bandwidth and the S/N ratio, and thereby enhances the resolution of the final processed seismic data.
Multiple subtraction using an expanded multichannel matching filter
Authors: Wang Yanghua
Published: March 2003

An expanded multichannel matching (EMCM) filter is proposed for the adaptive subtraction in seismic multiple attenuation. For a normal multichannel matching filter where an original seismic trace is matched by a group of multiple‐model traces, the lateral coherency of adjacent traces is likely to be exploited to discriminate the overlapped multiple and primary reflections. In the proposed EMCM filter, a seismic trace is matched by not only a group of the ordinary multiple‐model traces but also their adjoints generated mathematically. The adjoints of a multiple‐model trace include its first derivative, its Hilbert transform, and the derivative of the Hilbert transform. The convolutional coefficients associated with the normal multichannel filter can be represented as a 2D operator in the time‐space domain. This 2D operator is expanded with an additional spatial dimension in the EMCM filter to improve the robustness of the adaptive subtraction. The multiple‐model traces are generated using moveout equations to afford efficiency in the multiple attenuation application.
Seismic trace interpolation in the Fourier transform domain
Authors: Gülünay Necati
Published: March 2003

A data adaptive interpolation method is designed and applied in the Fourier transform domain (f‐k or f‐kx‐kyfor spatially aliased data. The method makes use of fast Fourier transforms and their cyclic properties, thereby offering a significant cost advantage over other techniques that interpolate aliased data.

The algorithm designs and applies interpolation operators in the f‐k (or f‐kx‐kydomain to fill zero traces inserted in the data in the t‐x (or t‐x‐y) domain at locations where interpolated traces are needed. The interpolation operator is designed by manipulating the lower frequency components of the stretched transforms of the original data. This operator is derived assuming that it is the same operator that fills periodically zeroed traces of the original data but at the lower frequencies, and corresponds to the f‐k (or f‐kx‐kydomain version of the well‐known f‐x (or f‐x‐y) domain trace interpolators.

The method is applicable to 2D and 3D data recorded sparsely in a horizontal plane. The most common prestack applications of the algorithm are common‐mid‐point domain shot interpolation, source‐receiver domain shot interpolation, and cable interpolation.
Frequency estimates of seismic traces
Authors: Hardy H. H. , Beier Richard A. , Gaston Jonathan D.
Published: March 2003

Local estimates of amplitude, frequency, and phase have been used in the past to characterize seismic data. In particular, these attributes have sometimes been successfully related to well attributes at the reservoir scale (net pay thickness, sand fraction, etc.). This paper introduces a method called SINFIT for computing local amplitude, frequency, and phase estimates of seismic traces over short‐time windows. The SINFIT method uses a sine‐curve fitting approach. The method is shown to give more accurate and robust frequency estimates than four other common methods on a set of test traces where the true frequency components are known. The four methods compared with SINFIT are instantaneous frequency, zero‐crossings, short‐time Fourier analysis, and a more recent time‐frequency method called AOK. In a field case with fluvial sands, an average frequency over a 30‐ms time window of seismic data correlates with estimated shale volume from well logs. The SINFIT method gives an average frequency attribute that more strongly correlates with shale volume than corresponding attributes from any of the other four methods.