bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and petrophysical modeling of Ferron Sandstone data
Authors: Szerbiak Robert B. , McMechan George A. , Forster Craig , Snelgrove Stephen H.
Published: September 2006

As part of the 3D characterization of a fluvial reservoir analog site in the Ferron Sandstone in east-central Utah, new lab measurements of porosity, permeability, water content, and complex dielectric permittivity are collected and analyzed. Petrographic analysis of thin sections extracted from the same samples produced data on bulk, macro- and microporosity, lithology, and cementation. Thus, we have an unusually comprehensive data base for analysis. Debye models of complex dielectric permittivities are fitted using three frequency-dependent Debye relaxation mechanisms. Most ambient and dry samples are dominated by low-frequency relaxation mechanisms. The average dielectric constant and electrical conductivity at the typical ground-penetrating radar (GPR) frequency of [Formula: see text] are directly related to volumetric water content and are 3.86 and [Formula: see text] for oven-dried samples, 4.50 and [Formula: see text] for ambient saturated sam-ples, and 15.42 and [Formula: see text] for fully saturated samples. Electrical conductivity is poorly estimated from the oven-dried samples (for all clay content) because ion mobility is significantly reduced; thus, the dry conductivity is less useful for estimating petrophysical variations.

Multivariate regressions with the petrophysical parameters estimate the electrical properties at [Formula: see text] and [Formula: see text] with average correlation coefficients of [Formula: see text] and [Formula: see text], respectively. Empirically derived predictions of dielectric constant as a function of water content will always provide better fits to the observed values than either generic models (such as the CRIM model) or fits to other data sets (such as the Topp formula, which was derived for soils). The Topp model consistently underestimates the dielectric constant, while the CRIM model generally overestimates it, at both 75 and [Formula: see text]. The overall regression procedures can be applied to data from other sites and potentially used as the basis of inversion of petrophysical properties from measurements of electric and dielectric properties.
Joint estimation of porosity and saturation using stochastic rock-physics modeling
Authors: Bachrach Ran
Published: September 2006

Sediment porosity and saturation affect bulk modulus, shear modulus, and density. Consequently, estimating hydrocarbon saturation and reservoir porosity from seismic data is a joint estimation problem: Uncertainty in porosity will lead to errors in saturation prediction, and vice versa. Porosity and saturation can be jointly estimated using stochastic rock-physics modeling and formal Bayesian estimation methodology. Knowledge of shear impedance reduces the uncertainty in porosity and thus also reduces uncertainty in saturation estimation. This study investigates joint estimation of porosity and saturation by using rock-physics, stochastic modeling, and Bayesian estimation theory to derive saturation and porosity maps of expected pay sands. In the field example, the uncertainty in porosity, quantified by the standard deviation (STD) associated with the posterior probability density function (pdf), derived from inversion of seismic data is much less than the uncertainty in the derived saturation. For a typical case, the STD associated with saturation is [Formula: see text] while porosity STD is about 1.34 porosity units given seismic-derived inversion attributes with reasonable accuracy. Comparison of these numbers with prior estimates showed that inversion of seismic data decreased the uncertainty in porosity to 15% of the prior uncertainty while saturation uncertainty was only reduced to 92% of the prior uncertainty. Although these results may vary from one location to another, the methodology is general and can be applied to other locations.
A 2D multistage median filter to reduce random seismic noise
Authors: Liu Cai , Liu Yang , Yang Baojun , Wang Dian , Sun Jianguo
Published: September 2006

Random noise lowers the S/N of seismic data and decreases the accuracy of dynamic and static corrections, thus degrading final data quality. A 2D multistage median filter (MLM) that effectively reduces the high-frequency random noise can be implemented by applying 1D median filters (MF) in several directions and choosing a value derived from them to output at the center of the 2D window. The choice of window size depends on the intensity of the random noise and the percentage of the input data samples within the window that contain noise. Synthetic data can be used to demonstrate how to choose the window size. The tendency of the method to damage the signal while reducing the noise can be minimized by optimizing window size and by applying two passes with modest-sized windows as opposed to a single pass with a larger window. Results of using the method on prestack and poststack data from the Songliao basin in China demonstrate that the method is effective at both stages.
Focal mechanisms produced by shear faulting in weakly transversely isotropic crustal rocks
Authors: Vavryčuk Václav
Published: September 2006

Shear faulting in anisotropic rocks produces non-double-couple (non-DC) mechanisms. The non-DC mechanisms can comprise the isotropic (ISO) and compensated linear vector dipole (CLVD) components. The formulas for percentages of the ISO and CLVD are simplified under the assumption of weak transverse isotropy and can be expressed advantageously in terms of Thomsen’s anisotropy parameters. Shear faulting in crustal rocks with anisotropy strength of 10% can produce an ISO of up to 10% and a CLVD of up to 30%. Such values are significant and detectable in carefully determined focal mechanisms.
A limited-memory quasi-Newton inversion for 1D magnetotellurics
Authors: Avdeeva Anna , Avdeev Dmitry
Published: September 2006

We apply a limited-memory quasi-Newton (QN) method to the 1D magnetotelluric (MT) inverse problem. Using this method we invert a realistic synthetic MT impedance data set calculated for a layered earth model. The calculation of gradients based on the adjoint method speeds up the inverse problem solution many times. In addition, regularization stabilizes the QN inversion result and a few correction pairs are sufficient to produce reasonable results. Comparison with the L-BFGS-B algorithm shows similar convergence rates. This study is a first step towards the solution of large-scale electromagnetic problems, with a full treatment of the 3D conductivity structure of the earth.
3D volumetric multispectral estimates of reflector curvature and rotation
Authors: Al-Dossary Saleh , Marfurt Kurt J.
Published: September 2006

One of the most accepted geologic models is the relation between reflector curvature and the presence of open and closed fractures. Such fractures, as well as other small discontinuities, are relatively small and below the imaging range of conventional seismic data. Depending on the tectonic regime, structural geologists link open fractures to either Gaussian curvature or to curvature in the dip or strike directions. Reflector curvature is fractal in nature, with different tectonic and lithologic effects being illuminated at the [Formula: see text] and [Formula: see text] scales. Until now, such curvature estimates have been limited to the analysis of picked horizons. We have developed what we feel to be the first volumetric spectral estimates of reflector curvature. We find that the most positive and negative curvatures are the most valuable in the conventional mapping of lineations — including faults, folds, and flexures. Curvature is mathematically independent of, and interpretatively complementary to, the well-established coherence geometric attribute. We find the long spectral wavelength curvature estimates to be of particular value in extracting subtle, broad features in the seismic data such as folds, flexures, collapse features, fault drags, and under- and overmigrated fault terminations. We illustrate the value of these spectral curvature estimates and compare them to other attributes through application to two land data sets — a salt dome from the onshore Louisiana Gulf Coast and a fractured/karsted data volume from Fort Worth basin of North Texas.
Adaptive multiple subtraction using independent component analysis
Authors: Lu Wenkai
Published: September 2006

Adaptive multiple subtraction is a critical and challenging procedure for the widely used surface-related multiple attenuation (SRMA) techniques. In this paper, I present an adaptive multiple subtraction algorithm based on independent component analysis (ICA). The method expresses the problem of adaptive multiple subtraction as a blind source separation (BSS) problem with two mixtures (the seismic data and the predicted multiple) of two or more sources (primaries and multiples). By taking advantage of the sparse property of the seismic data, the method adopts a geometric ICA method to recover the mixing matrix and a linear programming technique to recover the sources when more than two sources are included. The major advantage of the proposed method is that it does not require that the multiples and primaries in the data be orthogonal to each other; that is, the method can perform adaptive multiple subtraction when multiples and primaries have overlap. Furthermore, by expressing the problem of adaptive multiple subtraction as an underdetermined BSS model (more sources with less mixtures), the method can separate the primaries and the multiples when there is time delay and amplitude inconsistency between the true and the predicted multiples. The proposed method is demonstrated on several synthetic datasets generated by simple convolution and finite-difference modeling.
Amplitude preservation of Radon-based multiple-removal filters
Authors: Nowak Ethan J. , Imhof Matthias G.
Published: September 2006

This study examines the effect of filtering in the Radon transform domain on reflection amplitudes. Radon filters are often used for removal of multiple reflections from normal moveout-corrected seismic data. The unweighted solution to the Radon transform reduces reflection amplitudes at both near and far offsets due to a truncation effect. However, the weighted solutions to the transform produce localized events in the transform domain, which minimizes this truncation effect. Synthetic examples suggest that filters designed in the Radon domain based on a weighted solution to the linear, parabolic, or hyperbolic transforms preserve the near- and far-offset reflection amplitudes while removing the multiples; whereas the unweighted solutions diminish reflection amplitudes which may distort subsequent amplitude-versus-offset (AVO) analysis.
Finite-difference simulation of borehole EM measurements in 3D anisotropic media using coupled scalar-vector potentials
Authors: Hou Junsheng , Mallan Robert K. , Torres-Verdín Carlos
Published: September 2006

This paper describes the implementation and successful validation of a new staggered-grid, finite-difference algorithm for the numerical simulation of frequency-domain electromagnetic borehole measurements. The algorithm is based on a coupled scalar-vector potential formulation for arbitrary 3D inhomogeneous electrically anisotropic media. We approximate the second-order partial differential equations for the coupled scalar-vector potentials with central finite differences on both Yee’s staggered and standard grids. The discretization of the partial differential equations and the enforcement of the appropriate boundary conditions yields a complex linear system of equations that we solve iteratively using the biconjugate gradient method with preconditioning. The accuracy and efficiency of the algorithm is assessed with examples of multicomponent-borehole electromagnetic-induction measurements acquired in homogeneous, 1D anisotropic, 2D isotropic, and 3D anisotropic rock formations. The simulation examples consider vertical and deviated wells with and without borehole and mud-filtrate invasion regions. Simulation results obtained with the scalar-vector coupled potential formulation favorably compare in accuracy with results obtained with 1D, 2D, and 3D benchmarking codes in the dc to megahertz frequency range for large contrasts of electrical conductivity. Our numerical exercises indicate that the coupled scalar-vector potential equations provide a general and consistent algorithmic formulation to simulate borehole electromagnetic measurements from dc to megahertz in the presence of large conductivity contrasts, dipping wells, electrically anisotropic media, and geometrically complex models of electrical conductivity.
Decomposition of electromagnetic fields into upgoing and downgoing components
Authors: Amundsen Lasse , Løseth Lars , Mittet Rune , Ellingsrud Svein , Ursin Bjørn
Published: September 2006

This paper gives a unified treatment of electromagnetic (EM) field decomposition into upgoing and downgoing components for conductive and nonconductive media, where the electromagnetic data are measured on a plane in which the electric permittivity, magnetic permeability, and electrical conductivity are known constants with respect to space and time. Above and below the plane of measurement, the medium can be arbitrarily inhomogeneous and anisotropic.

In particular, the proposed decomposition theory applies to marine EM, low-frequency data acquired for hydrocarbon mapping where the upgoing components of the recorded field guided and refracted from the reservoir, that are of interest for the interpretation. The direct-source field, the refracted airwave induced by the source, the reflected field from the sea surface, and mostmagnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagnetic measurements.

The viability and validity of the decomposition method is demonstrated using modeled and real marine EM data, also termed seabed logging (SBL) data. The synthetic data are simulated in a model that is fairly representative of the geologic area where the real SBL were collected. The results from the synthetic data study therefore are used to assist in the interpretation of the real data from an area with [Formula: see text] water depth above a known gas province offshore Norway. The effect of the airwave is seen clearly in measured data. After field decomposition just below the seabed, the upgoing component of the recorded electric field has almost linear phase, indicating that most of the effect of the airwave component has been removed.
Bayesian lithology/fluid prediction and simulation on the basis of a Markov-chain prior model
Authors: Larsen Anne Louise , Ulvmoen Marit , Omre Henning , Buland Arild
Published: September 2006

A technique for lithology/fluid (LF) prediction and simulation from prestack seismic data is developed in a Bayesian framework. The objective is to determine the LF classes along 1D profiles through a reservoir target zone. A stationary Markov-chain prior model is used to model vertical continuity of LF classes along the profile. The likelihood relates the LF classes to the elastic properties and to the seismic data, and it introduces vertical correlation because the seismic data are band-limited. An approximation of the likelihood model provides an approximate posterior model that is a Markov chain. The approximate posterior can be assessed by an exact and efficient recursive algorithm. The LF inversion approach is evaluated on a synthetic 1D profile that is inspired by a North Sea sandstone reservoir. With a realistic wavelet-colored noise model and a S/N ratio of three in the seismic data, the results are reliable. The LF classes and the interfaces between zones are largely correct. The prediction uncertainty increases if the number of zones increases and zone thicknesses decreases. The study clearly demonstrates the impact of a vertically coupled prior Markov model for the LF classes.
Interactive 2D magnetic inversion: A tool for aiding forward modeling and testing geologic hypotheses
Authors: Barbosa Valeria C. , Silva João B.
Published: September 2006

We present a method for inverting magnetic data with interfering anomalies produced by multiple complex 2D magnetic sources having arbitrary shapes and known magnetization vectors. Our method is stable and can recover a complex 2D magnetization distribution, leading to a reliable delineation of sectionally homogeneous sources with complex shapes. Our method, although similar to interactive forward modeling, is unique in that it automatically fits the observations and only requires that the interpreter know the outlines of the sources expressed by simple geometric elements such as points and line segments. Each geometric element operates as a skeletal outline of a particular homogeneous section of the magnetic source to be reconstructed. Also, the interpreter can define the geometric elements interactively without worrying about data fitting because data are fit automatically. The examples with synthetic data illustrate the good performance of the method in mapping the complex geometry of magnetic sources. The solution sensitivity to uncertainties in the a priori information shows that to produce good results, the uncertainty on the magnetization intensity of each homogeneous extent of the source should be smaller than 40%. A wrong magnetization vector direction can be detected easily because it often leads to poor data fitting and to estimated sources with abrupt borders. The method is also applied to two sets of real data from the Northwest Ore Body at Iron Mountain Mine, Missouri, and the Hatton-Rockall Basin in the northeast Atlantic Ocean. The estimated magnetization distribution in all tests demonstrates a good correlation of estimated magnetic sources with corresponding known geologic features.
Quick and accurate Q parameterization in viscoelastic wave modeling
Authors: Hestholm Stig , Ketcham Stephen , Greenfield Roy , Moran Mark , McMechan George
Published: September 2006

We introduce a procedure for including the attenuation factor [Formula: see text] in a consistent manner in seismic modeling and show 3D examples. The [Formula: see text] fitting over a chosen frequency band involves two algorithms: The first creates starting values of relaxation times, and the second does nonlinear inversion using the results of the first as initial values. The resulting [Formula: see text] function gives a good approximation to a constant [Formula: see text] over the chosen frequency band. The algorithm is combined with a finite-difference (F-D) code that includes topographies in 3D seismic media. The velocity-stress formulation for viscoelastic wave modeling is used with an arbitrary number of relaxation mechanisms to model a desired [Formula: see text] behavior. These equations are discretized by high-order F-Ds in the interior of the medium, and we gradually reduce the F-D order to two at the stress-free surface, where we implement our free-surface boundary conditions. The seismic F-D algorithm is applied to a marine seismic experiment, with and without viscoelasticity, to emphasize the importance of including physical attenuation and dispersion in seismic modeling. Their inclusion, even for marine surveys, is clearly important for lossy ocean bottoms. Our procedure for more accurate modeling of physical dispersion and attenuation may increase future motivation to include viscoelasticity in seismic inversion.
Multicomponent wave separation using HOSVD/unimodal-ICA subspace method
Authors: Vrabie Valeriu D. , Le Bihan Nicolas , Mars Jérôme I.
Published: September 2006

Multicomponent sensor arrays now are commonly used in seismic acquisition to record polarized waves. In this article, we use a three-mode model (polarization mode, distance mode, and temporal mode) to take into account the specific structure of signals that are recorded with these arrays, providing a data-structure-preserving processing. With the suggested model, we propose a multilinear decomposition named higher-order singular value decomposition and unimodal independent component analysis (HOSVD/unimodal ICA) to split the recorded three-mode data into two orthogonal subspaces: the signal and noise subspaces. This decomposition allows the separation and identification of polarized waves with infinite apparent horizontal propagation velocity. The HOSVD leads to a definition of a subspace method that is the counterpart of the well-known subspace method for matrices that is driven by singular value decomposition (SVD), a classic tool in monocomponent array processing.

The proposed three-mode subspace decomposition provides a multicomponent wave-separation algorithm. To enhance the separation result, when the signal-to-noise ratio is low or when orthogonality constraints are not well adapted to the recorded waves, a unimodal-ICA step is included on the temporal mode. Doing this replaces the classic orthogonality constraints between estimated waves with independence constraints that might allow better recovery of recorded seismic waves. A simulation on realistic two-component (2C) geophysical data shows qualitative and quantitative improvements for the wavefield-separation results. The relative-mean-square errors between the original and estimated signal subspaces are, respectively, 52% for SVD applied on each component separately, 27.4% for HOSVD-based technique applied to the whole three-mode dataset, and 7.3% for HOSVD/unimodal-ICA technique. The efficiency of the three-mode subspace decompositions also is shown on real three-component (3C) geophysical data. These results emphasize the potential of the HOSVD/unimodal-ICA subspace method for multicomponent seismic-wave separation.
Characterization of layered anisotropic media from prestack PS-wave-reflection data
Authors: Gumble Jason E. , Gaiser James E.
Published: September 2006

Anisotropy and fracture characterization in individual layers is realized through iterative layer stripping corrections of four, converted-wave (PS-wave) synthetic reflection seismic data sets, generated from azimuthally anisotropic (HTI and TTI) models, and a four component (4-C) data set from the Teal South, Gulf of Mexico. The corrections were applied on a layer-by-layer basis to evaluate the efficacy of constant polarization rotation and time-shift operators. Equivalent isotropic models were compared to anisotropic models after layer-stripping corrections using rms amplitude and shear-wave-splitting time-difference maps to quantify and identify inherent errors in estimating seismic polarization parameters. For HTI media radial and transverse components of PS data that have had layer-stripping corrections applied, exhibit incorrect symmetry and orientations. This may adversely affect inversion and/or amplitude-variation with angle offset (AVO) and amplitude versus azimuth (AVA)analysis. Layer-stripping corrections applied to fast and slow ([Formula: see text] and [Formula: see text], respectively) components exhibit the correct symmetry and orientation. Time differences between PS1 and PS2 are computed using crosscorrelation. Previous studies have addressed some of the problems associated with layer-stripping corrections for the case of vertical fractures (HTI media) and poststack layer-stripping analyses. This study includes an equivalent model with dipping fractures (TTI media) and extends the scope to encompass the effects of anisotropy on prestack data. The results from an application of the same technique are also applied to a limited set of 4-C data from the Teal South project in the Gulf of Mexico. Results are consistent with those of previous studies involving solely poststack 4-C rotation analysis in terms of average, or zero offset, time differences and symmetry orientation. Offset and azimuth amplitude/traveltime variations, however, indicate that there is more information contained in prestack seismic data than 4-C rotation can comprehend.
Modeling the scalar wave equation with Nyström methods
Authors: Chen Jing-Bo
Published: September 2006

High-accuracy numerical schemes for modeling of the scalar wave equation based on Nyström methods are developed in this paper. Space is discretized by using the pseudospectral algorithm. For the time discretization, Nyström methods are used. A fourth-order symplectic Nyström method with pseudospectral spatial discretization is presented. This scheme is compared with a commonly used second-order scheme and a fourth-order nonsymplectic Nyström method. For a typical time-step size, the second-order scheme exhibits spatial dispersion errors for long-time simulations, while both fourth-order schemes do not suffer from these errors. Numerical comparisons show that the fourth-order symplectic algorithm is more accurate than the fourth-order nonsymplectic one. The capability of the symplectic Nyström method in approximately preserving the discrete energy for long-time simulations is also demonstrated.
Testing the use of aeromagnetic data for the determination of Curie depth in California
Authors: Ross Hannah E. , Blakely Richard J. , Zoback Mark D.
Published: September 2006

Using California as a test region, we have examined the feasibility of using Curie-isotherm depths, estimated from magnetic anomalies, as a proxy for lithospheric thermal structure. Our method follows previous studies by dividing a regional aeromagnetic database into overlapping subregions and analyzing the power-density spectrum of each subregion, but we have improved on previous studies in two important ways: We increase subregion dimensions in a stepwise manner until long-wavelength anomalies are appropriately sampled, and each subregion spectrum determined from the magnetic anomalies is manually fit with a theoretical expression that directly yields the depth to the bottom of the magnetic layer. Using this method, we have obtained Curie-isotherm depths for California that show a general inverse correlation with measured heat flow, as expected. The Coast Ranges of California are characterized by high heat flow [Formula: see text] and shallow Curie depths [Formula: see text], whereas the Great Valley has low heat flow (less than [Formula: see text] and deeper Curie depths [Formula: see text].
A survey of current trends in near-surface electrical and electromagnetic methods
Authors: Auken Esben , Pellerin Louise , Christensen Niels B. , Sørensen Kurt
Published: September 2006

Electrical and electromagnetic (E&EM) methods for near-surface investigations have undergone rapid improvements over the past few decades. Besides the traditional applications in groundwater investigations, natural-resource exploration, and geological mapping, a number of new applications have appeared. These include hazardous-waste characterization studies, precision-agriculture applications, archeological surveys, and geotechnical investigations. The inclu-sion of microprocessors in survey instruments, development of new interpretation algorithms, and easy access to powerful computers have supported innovation throughout the geophysical community and the E&EM community is no exception. Most notable are development of continuous-measurement systems that generate large, dense data sets efficiently. These have contributed significantly to the usefulness of E&EM methods by allowing measurements over wide areas without sacrificing lateral resolution. The availability of these luxuriant data sets in turn spurred development of interpretation algorithms, including: Laterally constrained 1D inversion as well as innovative 2D- and 3D-inversion methods. Taken together, these developments can be expected to improve the resolution and usefulness of E&EM methods and permit them to be applied economically. The trend is clearly toward dense surveying over larger areas, followed by highly automated, post-acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost-effective manner.
Volume-based curvature computations illuminate fracture orientations — Early to mid-Paleozoic, Central Basin Platform, west Texas
Authors: Blumentritt Charles H. , Marfurt Kurt J. , Sullivan E. Charlotte
Published: September 2006

Volumetric curvature analysis is a simple but computationally intensive procedure that provides insight into fracture orientation and regional stresses. Until recently, curvature analysis has been limited to computation along horizon surfaces that may be affected by unintentional bias and picking errors introduced during the interpretation process. Volumetric curvature is best estimated in a two-step process. In the first step, we use a moving-analysis subvolume to estimate volumetric reflector dip and azimuth for the best-fit tangent plane for each sample in the full volume. In the second step, we calculate curvature from adjacent measures of dip and azimuth. We use larger curvature analysis windows to estimate longer wavelength curvatures. Such a technique allows us to output full 3D volumes of curvature values for one or more scales of analysis. We apply these techniques to a data set from the Central Basin Platform of west Texas and find lineaments not observable with other seismic attributes. These lineaments indicate that, in the lower Paleozoic interval, a left-lateral shear couple oriented due east-west controls the local stress regime. Such a model predicts that extension faulting and fractures will be oriented northeast-southwest. The example demonstrates the potential of this new technology to determine stress regimes and predict azimuths of open fractures.
Regularizing seismic inverse problems by model reparameterization using plane-wave construction
Authors: Fomel Sergey , Guitton Antoine
Published: September 2006

We define plane-wave construction (PWC), an operator for generating data aligned along predefined locally variable slopes, as the inverse of plane-wave destruction, an operator used for measuring the slopes. PWC can be applied for efficient regularization of seismic estimation problems. Using simple examples, we demonstrate how PWC enhances the coherency of seismic images, improves velocity estimation methods, and separates primaries and multiples with a pattern-based approach.
Efficient 3D wave-equation migration using virtual planar sources
Authors: Duquet Bertrand , Lailly Patrick
Published: September 2006

Full-volume seismic imaging is essential for a sound interpretation of structurally complex geologies. Prestack depth imaging is the most appropriate tool for such imaging, but it requires a precise and often complex velocity model. In such situations, 3D Kirchhoff prestack depth migration can be quite expensive. On the other hand, a wavefield approach, although generally tremendously expensive, is not affected by the complexity of the velocity model. We propose an affordable 3-D wavefield prestack depth-migration technique. It is designed for marine surveys for which the source-receiver azimuth is approximately constant. The technique applies a plane-wave migration algorithm to time-shifted data — quite a surprising approach when we realize that marine surveys do not allow the synthesis of genuine plane-wave data. Additionally, the imaging principle has to be modified to give results consistent with shot-record migration. Our technique also produces image gathers that allow an update of the velocity model by means of migration velocity analysis. Results from synthetics and conventional marine data demonstrate the effectiveness of the method.
Petrophysical inversion of borehole array-induction logs: Part II — Field data examples
Authors: Torres-Verdín Carlos , Alpak Faruk O. , Habashy Tarek M.
Published: September 2006

We describe the application of Alpak et al.’s (2006) petrophysical inversion algorithm to the interpretation of borehole array induction logs acquired in an active North American gas field. Layer-by-layer values of porosity and permeability were estimated in two closely spaced vertical wells that penetrated the same horizontal rock formation. The wells were drilled with different muds and overbalance pressures, and the corresponding electromagnetic induction logs were acquired with different tools. Rock-core laboratory measurements available in one of the two wells were used to constrain the efficiency of gas displacement by water-based mud during the process of invasion. Estimated values of porosity and permeability agree well with measurements performed on rock-core samples. In addition to estimating porosity and permeability, the petrophysical inversion algorithm provided accurate spatial distributions of gas saturation in the invaded rock formations that were not possible to obtain with conventional procedures based solely on the use of density and resistivity logs.
Rock property- and seismic-attribute analysis of a chert reservoir in the Devonian Thirty-one Formation, west Texas, U.S.A.
Authors: Fu Dongjun (Taller) , Sullivan E. Charlotte , Marfurt Kurt J.
Published: September 2006

In west Texas, fractured-chert reservoirs of Devonian age have produced more than 700 million barrels of oil. About the same amount of mobile petroleum remains in place. These reservoirs are characterized by microporosity; they are heterogeneous and compartmented, which results in recovery of less than 30% of the oil in place. In this case study the objective was to use cores, petrophysical logs, rock physics, and seismic attributes to characterize porosity and field-scale fractures. The relations among porosity, velocity, and impedance were explored and also reactions among production, impedance, and lineaments observed in 3D attribute volumes. Laboratory core data show that Gassmann’s fluid-substitution equation works well for microporous tripolitic chert. Also, laboratry measurements show excellent linear correlation between P-wave impedance and porosity. Volumetric calculations of reflector curvature and seismic inversion of acoustic impedance were combined to infer distribution of lithofacies and fractures and to predict porosity. Statistical relations were established between P-wave velocity and porosity measured from cores, between P-wave impedance and producing zones, and between initial production rates and seismic “fracture lineaments.” The strong quantitative correlation between thick-bedded chert lithofacies and seismic impedance was used to map the reservoir. A qualitative inverse relation between the first [Formula: see text] of production and curvature lineaments was documented.
Type I Pleuropulmonary Blastoma: A Report From the International Pleuropulmonary Blastoma Registry
Authors: Priest John R. , Hill D. Ashley , Williams Gretchen M. , Moertel Christopher L. , Messinger Yoav , Finkelstein Marsha J. , Dehner Louis P.
Published: September 2006

Purpose

Type I pleuropulmonary blastoma (PPB) is a rare, cystic lung neoplasm in infants characterized by subtle malignant changes and a good prognosis. Recurrences after type I PPB are usually advanced type II or type III neoplasms with a poor prognosis. This article describes the first collection of type I PPB cases, analyzes outcome based on treatments of surgery or surgery plus chemotherapy, and presents type I PPB management recommendations.

Patients and Methods

Type I PPB cases from the International PPB Registry and literature were evaluated using standard statistical methods for outcomes based on age at diagnosis, sex, thoracic side, surgical extent, length of follow-up, constitutional/familial disease, pre-existing lung cysts, intrathoracic findings, and treatments (surgery or surgery and chemotherapy).

Results

Thirty-eight type I PPB cases were identified: Registry (n = 30) and literature (n = 8). Twenty children had surgery alone; eight (40%) experienced recurrence; and four died. Eighteen children had surgery and adjuvant chemotherapy; one experienced recurrence and died. All recurrences were type II or III PPB. Recurrence-free survival was higher in the surgery + chemotherapy group (P = .01); overall survival did not differ (P = .18). The improved recurrence-free survival was found only in males. Four of nine children with recurrence survived.

Conclusion

Adjuvant chemotherapy appears to benefit type I PPB patients. Benefit limited to males requires broader substantiation. Salvage after types II and III recurrence is poor (four of nine; 44%). A rigorous surveillance schedule after type I PPB diagnosis might detect early recurrence and be an acceptable alternative to adjuvant chemotherapy.
Patients' Decision-Making Process Regarding Participation in Phase I Oncology Research
Authors: Agrawal Manish , Grady Christine , Fairclough Diane L. , Meropol Neal J. , Maynard Kim , Emanuel Ezekiel J.
Published: September 2006

Purpose

This study assesses the decision-making process of patients enrolling in phase I oncology studies.

Patients and Methods

Participants were eligible if they had consented to participate in a phase I cancer study at one of five cancer centers, understood English, and were older than 18 years. Trained interviewers conducted structured in-person interviews.

Results

Of the 163 participants, 88% were white, 96% had health insurance, and 51% were college graduates or post graduates. Overall, 81% were aware of hospice, but only 6% had seriously considered hospice for themselves; 84% were aware of palliative care and 10% seriously considered it for themselves; and 7% considered getting no treatment at all. Overall, 75% reported moderate or a lot of pressure to participate in the phase I study because their cancer was growing, whereas 7% reported such pressure from the study investigators and 9% felt such pressure from their families. For 63% of patients, the most important information for decision making was that the phase I drug killed cancer cells; only 12% reported that the adverse effects of the drug(s) was the most useful information. More than 90% of patients said they would still participate in the study even if the experimental drug caused serious adverse effects, including a 10% chance of dying.

Conclusion

Patients are aware of many alternatives to phase I studies, but do not seriously consider them. Very few experience pressure from family or researchers to participate in research. Their main goal is to fight their cancer, and almost no adverse effect, including death, would dissuade them from enrolling.
Sentinel and Nonsentinel Node Status in Stage IB and II Melanoma Patients: Two-Step Prognostic Indicators of Survival
Authors: Cascinelli Natale , Bombardieri Emilio , Bufalino Rosaria , Camerini Tiziana , Carbone Antonino , Clemente Claudio , Lenisa Leonardo , Mascheroni Luigi , Maurichi Andrea , Pennacchioli Elisabetta , Patuzzo Roberto , Santinami Mario , Tragni Gabrina
Published: September 2006

Purpose

To evaluate the prognostic significance of sentinel node biopsy in the management of stage IB and II melanoma patients, and to evaluate the status of nonsentinel nodes as a “second step key factor” to assess the prognosis of these patients.

Patients and Methods

We conducted an analysis of data collected in a prospective database.

Results

From February 1994 to June 2005, 1,108 consecutive patients with stage IB and II melanoma were submitted to sentinel node biopsy; 176 patients (15.9%) had occult node metastases. The frequency of positive nodes increased with increasing Breslow's thickness. The largest diameter of metastatic foci and their localization within the lymph node were associated with the risk of nonsentinel node metastases only. The 5-year survival of patients with positive sentinel nodes was 81.4% in patients with one positive node and 39.6% in patients with two positive nodes (P = .056). Multivariate analysis indicated that status of sentinel nodes is a key factor and that sex and Breslow's thickness maintain statistically significant relevance. Ulceration, which was associated with survival when considered as single factor (P < .001) had no impact on survival in the multivariate analysis (P = .10). To evaluate the relevance of metastases to nonsentinel nodes, we identified four groups of patients.

Conclusion

Evaluation of the sentinel node is a useful procedure to identify patients to be submitted for complete lymph node dissection. The procedure makes it possible to assess the best prognosis of patients.
Randomized Phase III Study of Exatecan and Gemcitabine Compared With Gemcitabine Alone in Untreated Advanced Pancreatic Cancer
Authors: Abou-Alfa Ghassan K. , Letourneau Richard , Harker Graydon , Modiano Manuel , Hurwitz Herbert , Tchekmedyian Nerses Simon , Feit Kevie , Ackerman Judie , De Jager Robert L. , Eckhardt S. Gail , O'Reilly Eileen M.
Published: September 2006

Purpose

Exatecan mesylate is a hexacyclic, water-soluble, topoisomerase-1 inhibitor. Exatecan has single-agent and combination activity with gemcitabine in advanced pancreatic cancer. A multicenter, randomized, phase III trial comparing exatecan plus gemcitabine versus gemcitabine alone in advanced pancreatic cancer was conducted.

Patients and Methods

Eligibility criteria included Karnofsky performance status ≥ 60%, locally advanced or metastatic pancreatic adenocarcinoma, and no prior chemotherapy. Radiation alone for locally advanced disease was permitted. Patients were randomly assigned on a 1:1 basis. For the exatecan plus gemcitabine arm, exatecan 2.0 mg/m2 and gemcitabine 1,000 mg/m2 were administered on days 1 and 8, every 3 weeks. Gemcitabine alone was dosed at 1,000 mg/m2 up to 7 weeks in the first cycle, then once a week for the first 3 weeks of a 4-week cycle. Tumor assessment was performed every 6 weeks. The primary end point was overall survival. An intent-to-treat analysis was used.

Results

From August 2001 to January 2003, 349 patients were randomly assigned, 175 to exatecan plus gemcitabine and 174 to gemcitabine alone. Twenty-four patients (6.9%) were not treated. The median survival time was 6.7 months for exatecan plus gemcitabine and 6.2 months for gemcitabine alone (P = .52). One complete response (CR; < 1%) and 11 partial responses (PRs; 6.3%) were observed in the exatecan plus gemcitabine treatment group, and one CR (< 1%) and eight PRs (4.6%) were observed in the gemcitabine-alone group. Grade 3 and 4 toxicities were higher for the exatecan plus gemcitabine arm versus the gemcitabine alone arm; neutropenia (30% v 15%) and thrombocytopenia (15% v 4%).

Conclusion

Exatecan plus gemcitabine was not superior to gemcitabine alone with respect to overall survival in the first-line treatment of advanced pancreatic cancer.
Longitudinal Study of the Relationship Between Chemoradiation Therapy for Non–Small-Cell Lung Cancer and Patient Symptoms
Authors: Wang Xin Shelley , Fairclough Diane L. , Liao Zhongxing , Komaki Ritsuko , Chang Joe Y. , Mobley Gary M. , Cleeland Charles S.
Published: September 2006

Purpose

Cancer patients undergoing aggressive therapy suffer from multiple nonspecific treatment-related symptoms. The goal of this prospective study was to establish a profile of the development of different symptoms over the time of therapy and to examine symptom-related functional interference in patients with non–small-cell lung cancer (NSCLC) undergoing concurrent chemoradiation therapy (CXRT).

Patients and Methods

Patients with locally advanced unresectable (stage II-IIIB) NSCLC were recruited for the study (N = 64). The M.D. Anderson Symptom Inventory (MDASI) was used to measure multiple symptoms before and weekly for 12 weeks after the start of CXRT. Mixed-effect growth curve models were used to estimate symptom development during CXRT.

Results

Approximately 63% of patients suffered from moderate to severe levels of multiple symptoms by the end of CXRT. Symptom clusters with four development patterns appeared over the time of CXRT. With some variation between patients, all symptoms had a significant impact on the level of interference (all P < .001). Fatigue, distress, and sadness were the single strongest predictors of total symptom interference (each R2 ≥ 0.49). Physical symptoms had greater impact on interference with function when they were moderate to severe, whereas affective symptoms had the largest effect on interference when they were mild to moderate.

Conclusion

Longitudinal analysis identified symptom clusters that have different development patterns in NSCLC patients receiving CXRT, providing a base for more accurate symptom management and suggesting the need for further study to identify potential mechanisms that might lead to better symptom control or prevention.
Polymer electrolyte fuel cell transport mechanisms: a universal modelling framework from fundamental theory
Authors: Rama P , Chen R , Thring R
Published: September 2006

A mathematical multi-species modelling framework for polymer electrolyte fuel cells (PEFCs) is presented on the basis of fundamental molecular theory. Characteristically, the resulting general transport equation describes transport in concentrated solutions and also explicitly accommodates for multi-species electro-osmotic drag. The multi-species nature of the general transport equation allows for cross-interactions to be considered, rather than relying upon the superimposition of Fick's law to account for the transport of any secondary species in the membrane region such as hydrogen. The presented general transport equation is also used to derive the key transport equations used by the historically prominent PEFC models. Thus, this work bridges the gap that exists between the different modelling philosophies for membrane transport in the literature. The general transport equation is then used in the electrode and membrane regions of the PEFC with available membrane properties from the literature to compare simulated one-dimensional water content curves, which are compared with published data under isobaric and isothermal operating conditions. Previous work is used to determine the composition of the humidified air and fuel supply streams in the gas channels. Finally, the general transport equation is used to simulate the crossover of hydrogen across the membrane for different membrane thicknesses and current densities. The results show that at 353 K, 1 atm, and 1 A/cm2, the nominal membrane thickness for less than 5 mA/cm2equivalent crossover current density is 30 μm. At 3 atm and 353 K, the nominal membrane thickness for the same equivalent crossover current density is about 150 μm and increases further to 175 μm at 383 K with the same pressure. Thin membranes exhibit consistently higher crossover at all practical current densities compared with thicker membranes. At least a 50 per cent decrease in crossover is chieved at all practical current densities, when the membrane thickness is doubled from 50 to 100 μm.
Efficiency optimization of an irreversible closed intercooled regenerated gas-turbine cycle
Authors: Wang W , Chen L , Sun F , Wu C
Published: September 2006

Thermal efficiency is optimized for an irreversible closed intercooled regenerated gas-turbine cycle coupled to variable-temperature heat reservoirs in the viewpoint of the theory of thermodynamic optimization (or finite-time thermodynamics). It is first performed by searching the optimum intercooling pressure ratio and the optimum heat conductance distributions among the four heat exchangers (the hot- and cold-side heat exchangers, the intercooler, and the regenerator) for fixed total heat exchanger inventory. Secondly, the optimization is performed further with respect to the total pressure ratio of the cycle, the maximum efficiency is maximized twice and the double-maximum efficiency is obtained. Thirdly, the optimization is performed additionally with respect to the thermal capacitance rate matching between the working fluid and the heat reservoir, the double-maximum efficiency is maximized again and a thrice-maximum efficiency is obtained. In the optimization, the following effects are taken into account: the irreversibility of heat transfer in the four heat exchangers, the irreversible compression and expansion losses in the compressors and the turbine, the pressure drop loss in the piping, and the finite thermal capacity rates of the three heat reservoirs. The optimization method is applied to the conceptual design of a closed-cycle intercooled regenerated helium turbine power plant for high-speed warship propulsion. The numerical example shows that the method herein is valid and effective.