bluuebunny/crossref_metadata_2025 huggingface dataset:
Elasticity of high‐porosity sandstones: Theory for two North Sea data sets
Authors: Dvorkin Jack , Nur Amos
Published: October 2002

We have analyzed two laboratory data sets obtained on high‐porosity rock samples from the North Sea. The velocities observed are unusual in that they seem to disagree with some simple models based on porosity. On the other hand, the rocks are unusually poorly‐cemented (for laboratory studies, at least), and we investigate the likelihood that this is the cause of the disagreement. One set of rocks, from the Oseberg Field, is made of slightly cemented quartz sands. We find that we can model their dry‐rock velocities using a cementation theory where the grains mechanically interact through cement at the grain boundaries. This model does not allow for pressure dependence. The other set of rocks, from the Troll Field, is almost completely uncemented. The grains are held together by the applied confining pressure. In this case, a lower bound for the velocities can be found by using the Hertz‐Mindlin contact theory (interaction of uncemented spheres) to predict velocities at a critical porosity, combined with the modified Hashin‐Strikman lower bound for other porosities. This model, which allows for pressure‐dependence, also predicts fairly large Poisson’s ratios for saturated rocks, such as those observed in the measurements. The usefulness of these theories may be in estimating the nature of cement in rocks from measurements such as sonic logs. The theories could help indicate sand strength in poorly consolidated formations and predict the likelihood of sand production. Both theoretical methods have analytical expressions and are ready for practical use.
Gravity inversion of basement relief constrained by the knowledge of depth at isolated points
Authors: Leão Jorge W. D. , Menezes Paulo T. L. , Beltrão Jacira F. , Silva João B. C.
Published: October 2002

We present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media. It consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media. The knowledge of the interface depth at isolated points is used to estimate the depth [Formula: see text] of the shallowest point of the interface, the density contrast Δρ between the two media, and the coefficients [Formula: see text] and [Formula: see text] of a first‐order polynomial representing a linear trend to be removed from data. The solutions are stabilized by introducing a damping parameter in the computation of the downward‐continued anomaly by the equivalent layer method. Different from other interface mapping methods using gravity data, the proposed method: (1) takes into account the presence of an undesirable linear trend in data; (2) requires just intervals for both Δρ (rather than the knowledge of its true value) and coefficients [Formula: see text] and [Formula: see text]; and (3) does not require the knowledge of the average interface depth [Formula: see text]. As a result of (3), the proposed method does not call for extensive knowledge of the interface depth to obtain a statistically significant estimate of [Formula: see text]; rather, it is able to use the knowledge of the interface depth at just a few isolated points to estimate [Formula: see text], Δρ, [Formula: see text], and [Formula: see text]. Tests using synthetic data confirm that the method produces good and stable estimates as far as the established premises (smooth interface separating two homogeneous media and, at most, the presence of an unremoved linear trend in data) are not violated. If the density contrast is not uniform, the method may still be applied using Litinsky’s concept of effective density. The method was applied to gravity data from Recôncavo Basin, Brazil, producing good correlations of estimated lows and terraces in the basement with corresponding known geological features.
Parameter nonuniqueness in velocity versus depth functions
Authors: Al‐Chalabi M.
Published: October 2002

Except for hypothetical cases that are never encountered in practice, the solution for the parameters of analytic velocity versus depth functions is inherently nonunique. This nonuniqueness means that there is no particular parameter combination that represents “the” solution. The average discrepancy between the observed velocity‐depth (or time‐depth) curve and the calculated function curve gives a measure of the degree of fit between the two curves. In the parameter space, within a given degree of fit that may be considered as the margin of tolerance for the particular problem in hand, every parameter combination provides a valid solution. The solution trough is defined as the region in the parameter space containing these solutions. The shape of the solution trough depends on the relationship between the parameters and, therefore, on the form of the function being used. If the parameters are related linearly or if the relation is linearized then the axis of the solution trough is a straight line. The slope of the axis corresponds to a point close to the average depth of the interval to which the observed data pertain. The intercept corresponds to a velocity value that is quite close to the average velocity over the interval. These properties are extremely useful for understanding the nature of the solution trough in parameter space. Hence, composite displays of solution troughs pertaining to a number of wells can be interpreted to provide information on whether the unit to which the function corresponds has undergone any lateral changes. Such displays also illustrate how current practices that assume the existence of a unique or “true” solution need to be critically revised.
Modeling near‐field GPR in three dimensions using the FDTD method
Authors: Roberts Roger L. , Daniels Jeffrey J.
Published: October 2002

Complexities associated with the theoretical solution of the near‐field interaction between the fields radiated from dipole antennas placed near a dielectric half‐space and electrical inhomogeneities within the dielectric can be overcome by using numerical techniques. The finite‐difference time‐domain (FDTD) technique implements finite‐difference approximations of Maxwell's equations in a discretized volume that permit accurate computation of the radiated field from a transmitting antenna, propagation through the air‐earth interface, scattering by subsurface targets and reception of the scattered fields by a receiving antenna. In this paper, we demonstrate the implementation of the FDTD technique for accurately modeling near‐field time‐domain ground‐penetrating radar (GPR). This is accomplished by incorporating many of the important GPR parameters directly into the FDTD model. These variables include: the shape of the GPR antenna, feed cables with a fixed characteristic impedance attached to the terminals of the antenna, the height of the antenna above the ground, the electrical properties of the ground, and the electrical properties and geometry of targets buried in the subsurface. FDTD data generated from a 3-D model are compared to experimental antenna impedance data, field pattern data, and measurements of scattering from buried pipes to verify the accuracy of the method.
The effect of a percolation threshold in the Kozeny‐Carman relation
Authors: Mavko Gary , Nur Amos
Published: October 2002

One of the most important properties of reservoir rocks, and perhaps the most difficult to predict, is permeability. Laboratory studies have shown that permeability depends on a long list of parameters: porosity, pore size and shape, clay content, stress, pore pressure, fluid type, saturation—a nearly overwhelming complexity. In spite of this, the essential behavior can often be expressed successfully using the remarkably simple Kozeny‐Carman (Kozeny, 1927; Carman, 1937, 1956; Bear, 1972; Scheidegger, 1974) relation [Formula: see text]where κ is the permeability, ϕ is the porosity, S is the specific surface area (pore surface area per volume of rock), and B is a geometric factor.
Microgravity investigations of foundation conditions
Authors: Yule Donald E. , Sharp Michael K. , Butler Dwain K.
Published: October 2002

A microgravity investigation was conducted in the upstream and downstream switchyards of the Wilson Dam powerplant, Florence, Alabama. The objective of the survey was the detection in the switchyard foundations of subsurface cavities or other anomalous conditions that could threaten the stability of the switchyard structures. The survey consisted of 288 gravity stations in the downstream switchyard and 347 stations in the upstream switchyard. Significant anomalous areas in the switchyards were selected on the basis of residual gravity anomaly maps. These results were prioritized and used to guide an exploratory drilling program to investigate the cause of the anomalies. Highest‐priority boring location recommendations were in negative gravity anomaly areas, since negative anomalies could be caused by actual cavities or low‐density zones that might represent incipient cavity formation. Remaining boring locations were in positive anomaly areas for verification purposes. The results of the borings confirm the presence of cavities and soft zones indicative of cavity formation.
A simple method of transient electromagnetic data analysis
Authors: Meju Maxwell A.
Published: October 2002

Time-domain or transient electromagnetic (TEM) methods are used routinely in environmental, hydrogeological, energy, and mineral resources investigations owing to their ease of use and ability to generate diagnostic data. In some typical field situations, the gross structure of the subsurface may be approximately 1-D, so 1-D interpretation schemes can be used to retrieve an interpretive model for the depth soundings.
Stratal slicing, Part I: Realistic 3-D seismic model
Authors: Zeng Hongliu , Backus Milo M. , Barrow Kenneth T. , Tyler Noel
Published: October 2002

Two‐dimensional, fenced 2-D, and 3-D isosurface displays of some realistic 3-D seismic models built in the lower Miocene Powderhorn Field, Calhoun County, Texas, demonstrate that a seismic event does not necessarily follow an impedance boundary defined by a geological time surface. Instead, the position of a filtered impedance boundary relative to the geological time surface may vary with seismic frequency because of inadequate resolution of seismic data and to the en echelon or ramp arrangement of impedance anomalies of sandstone. Except for some relatively time‐parallel seismic events, the correlation error of event picking is large enough to distort or even miss the majority of the target zone on stratal slices. In some cases, reflections from sandstone bodies in different depositional units interfere to form a single event and, in one instance, an event tying as many as six depositional units (interbedded sandy and shaly layers) over 50 m was observed. Frequency independence is a necessary condition for selecting time‐parallel reference events. Instead of event picking, phantom mapping between such reference events is a better technique for picking stratal slices, making it possible to map detailed depositional facies within reservoir sequences routinely and reliably from 3-D seismic data.
Stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations
Authors: Barbosa Valéria C. F. , Silva João B. C. , Medeiros Walter E.
Published: October 2002

We present a new, stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast. The subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated. Any vertical line must intersect the basement relief only once, and the mass deficiency must be concentrated near the earth’s surface, subject to the observed gravity anomaly being fitted within the experimental errors. In addition, upper and lower bounds on the density contrast of each prism are introduced a priori (one of the bounds being zero), and the method assigns to each elementary prism a density contrast which is close to either bound. The basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts, the latter occupying the upper part of the discretized region. The method is stabilized by introducing constraints favoring solutions having the attributes (shared by most sedimentary basins) of being an isolated compact source with lateral borders dipping either vertically or toward the basin center and having horizontal dimensions much greater than its largest vertical dimension. Arbitrary laws of spatial variations of the density contrast, if known a priori, may be incorporated into the problem by assigning suitable values to the nonnull bound of each prism. The proposed method differs from previous stable methods by using no smoothness constraint on the interface to be estimated. As a result, it may be applied not only to intracratonic sag basins where the basement relief is essentially smooth but also to rift basins whose basements present discontinuities caused by faults. The method’s utility in mapping such basements was demonstrated in tests using synthetic data produced by simulated rift basins. The method mapped with good precision a sequence of step faults which are close to each other and present small vertical slips, a feature particularly difficult to detect from gravity data only. The method was also able to map isolated discontinuities with large vertical throw. The method was applied to the gravity data from Reco⁁ncavo basin, Brazil. The results showed close agreement with known geological structures of the basin. It also demonstrated the method’s ability to map a sequence of alternating terraces and structural lows that could not be detected just by inspecting the gravity anomaly. To demostrate the method’s flexibility in incorporating any a priori knowledge about the density contrast variation, it was applied to the Bouguer anomaly over the San Jacinto Graben, California. Two different exponential laws for the decrease of density contrast with depth were used, leading to estimated maximum depths between 2.2 and 2.4 km.
3-D high‐resolution reflection seismic imaging of unconsolidated glacial and glaciolacustrine sediments: processing and interpretation
Authors: Büker Frank , Green Alan G. , Horstmeyer Heinrich
Published: October 2002

Shallow 3-D seismic reflection techniques have been used to map glacial deposits in a Swiss mountain valley. A dense distribution of source and receiver positions resulted in a small subsurface sampling of 1.5 m × 1.5 m and a high fold of >40. Common processing operations that included pseudotrue amplitude scaling, deconvolution, and band‐pass filtering successfully enhanced shallow reflections relative to source‐generated noise. Careful top muting helped avoid erroneous stacking of direct and guided waves. Azimuth‐dependent velocity analyses proved to be unnecessary. Three‐dimensional (3-D) migration of the stacked data yielded the final high‐resolution images of the shallow subsurface (15–170 m). Because most reflections and diffractions were migrated to their correct subsurface locations, confident interpretations of 3-D structures were possible. Time slices and cross‐sections along arbitrary directions proved to be powerful analysis tools. Even small‐scale features (<20 m wide), such as subglacial channels and troughs, could be mapped. Five major lithologic units separated by four principal reflecting boundaries were distinguished on the basis of their characteristic seismic facies. The principal reflecting boundaries were semiautomatically tracked through the 3-D data volume. Borehole information allowed the uppermost boundary at 15–27 m to be identified as the top of a 68–80-m-thick sequence of basal and reworked tills characterized by high‐amplitude discontinuous to quasi‐continuous reflections. Low reflectivity of seismic units above and below the till units was associated with finely layered or massive glaciolacustrine clay/silt deposited during and after two principal phases of glaciation (Würm at 28 000 to 10 000 and Riss at 200 000 to 100 000 years before the present). Top of Tertiary Molasse basement was delineated by prominent east‐dipping reflections at variable depths of 85–170 m.
Permeability evaluation in a glauconite‐rich formation in the Carnarvon Basin, Western Australia
Authors: Zhang Yujin , Salisch Henry A. , Arns Christoph
Published: October 2002

It is usually difficult for petroleum engineers and geoscientists to obtain reliable estimates of permeability from geophysical logs, especially in lithologically complex formations such as the Mardie Greensand Formation in the Carnarvon Basin, Australia, which consists of lower Cretaceous glauconite‐rich sandstones. This paper presents an alternative petrophysical evaluation of permeability in this formation through the integration of the geological and petrophysical analyses. Neural network techniques were used to establish permeability prediction models in cored wells or sections and to predict permeability from well logs in uncored wells or sections. The permeabilities obtained from minipermeameter measurements were taken as the basis and reference for the petrophysical evaluation. Four log‐derived parameters, which best reflect the permeability in the Mardie Formation, were defined and extracted from the available conventional logs. These parameters (not original log responses) were taken as the log inputs to evaluate permeability. Through the training, testing, and validation of the networks using the log and core data in the cored intervals, a permeability prediction model/network was established. Further, the permeabilities in 15 wildcat wells were determined from conventional well logs. The results indicate that the petrophysical evaluation of permeability is valid and applicable in the Mardie Formation.
Developments in a model to describe low‐frequency electrical polarization of rocks
Authors: Dias Carlos A.
Published: October 2002

The author reworks his total current conductivity function introduced in a previous paper, related to electrical polarization of rocks in the frequency range of 1 MHz to 10−3Hz. The original five parameters in this function are replaced by new ones, which from the beginning have clear petrophysical and electrochemical meanings and well‐defined ranges of variation. Some classical models are derived as particular cases of it. The main existing models proposed to describe induced polarization (IP) are analyzed, and most of them are grouped together under a common circuit analog representation and a respective generating function. A circuit analog is assigned to each model. The multi‐Cole‐Cole model circuit analog reveals intrinsic constraints involving the values of its circuit elements. Because of these constraint relations and the relaxation times ratio (τ1/τ2)—usually many orders of magnitude from unity—the model has no physical validation to represent single‐phase material systems (in the sense of the polarization). The performance and analysis of the various models to describe a few well‐selected experimental data show that only two of the models, the multi‐Cole‐Cole and Dias models, can provide a function structure capable of fitting these data. This fact, the associated petrophysical interpretation consistency, and the basic characteristics of these two models, such as the way they were derived (empirically, the former; phenomenologically, the latter) and the number of coefficients in the function (directly related to the degree of ambiguity of their determination), make the author’s model attractive and promising.
Wavelet filtering of magnetotelluric data
Authors: Trad Daniel O. , Travassos Jandyr M.
Published: October 2002

A method is described for filtering magnetotelluric (MT) data in the wavelet domain that requires a minimum of human intervention and leaves good data sections unchanged. Good data sections are preserved because data in the wavelet domain is analyzed through hierarchies, or scale levels, allowing separation of noise from signals. This is done without any assumption on the data distribution on the MT transfer function. Noisy portions of the data are discarded through thresholding wavelet coefficients. The procedure can recognize and filter out point defects that appear as a fraction of unusual observations of impulsive nature either in time domain or frequency domain. Two examples of real MT data are presented, with noise caused by both meteorological activity and power‐line contribution. In the examples given in this paper, noise is better seen in time and frequency domains, respectively. Point defects are filtered out to eliminate their deleterious influence on the MT transfer function estimates. After the filtering stage, data is processed in the frequency domain, using a robust algorithm to yield two sets of reliable MT transfer functions.
Use of multiattribute transforms to predict log properties from seismic data
Authors: Hampson Daniel P. , Schuelke James S. , Quirein John A.
Published: October 2002

We describe a new method for predicting well‐log properties from seismic data. The analysis data consist of a series of target logs from wells which tie a 3-D seismic volume. The target logs theoretically may be of any type; however, the greatest success to date has been in predicting porosity logs. From the 3-D seismic volume a series of sample‐based attributes is calculated. The objective is to derive a multiattribute transform, which is a linear or nonlinear transform between a subset of the attributes and the target log values. The selected subset is determined by a process of forward stepwise regression, which derives increasingly larger subsets of attributes. An extension of conventional crossplotting involves the use of a convolutional operator to resolve frequency differences between the target logs and the seismic data. In the linear mode, the transform consists of a series of weights derived by least‐squares minimization. In the nonlinear mode, a neural network is trained, using the selected attributes as inputs. Two types of neural networks have been evaluated: the multilayer feedforward network (MLFN) and the probabilistic neural network (PNN). Because of its mathematical simplicity, the PNN appears to be the network of choice. To estimate the reliability of the derived multiattribute transform, crossvalidation is used. In this process, each well is systematically removed from the training set, and the transform is rederived from the remaining wells. The prediction error for the hidden well is then calculated. The validation error, which is the average error for all hidden wells, is used as a measure of the likely prediction error when the transform is applied to the seismic volume. The method is applied to two real data sets. In each case, we see a continuous improvement in predictive power as we progress from single‐attribute regression to linear multiattribute prediction to neural network prediction. This improvement is evident not only on the training data but, more importantly, on the validation data. In addition, the neural network shows a significant improvement in resolution over that from linear regression.
Discrimination between pressure and fluid saturation changes from time‐lapse seismic data
Authors: Landrø Martin
Published: October 2002

Explicit expressions for computing saturation‐ and pressure‐related changes from time‐lapse seismic data have been derived and tested on a real time‐lapse seismic data set. Necessary input is near‐and far‐offset stacks for the baseline seismic survey and the repeat survey. The method has been tested successfully in a segment where pressure measurements in two wells verify a pore‐pressure increase of 5 to 6 MPa between the baseline survey and the monitor survey. Estimated pressure changes using the proposed relationships fit very well with observations. Between the baseline and monitor seismic surveys, 27% of the estimated recoverable hydrocarbon reserves were produced from this segment. The estimated saturation changes also agree well with observed changes, apart from some areas in the water zone that are mapped as being exposed to saturation changes (which is unlikely). Saturation changes in other segments close to the original oil‐water contact and the top reservoir interface are also estimated and confirmed by observations in various wells.
CORRELATION OF GRAVITY OBSERVATIONS WITH THE GEOLOGY OF THE SMOOTHINGIRON GRANITE MASS, LLANO COUNTY, TEXAS
Authors: Romberg Frederick , Barnes Virgil E.
Published: October 2002

Gravitational observations were made, and the geology mapped, on the Smoothingiron granite mass in Llano County, Texas. The observed gravitational anomaly was interpreted to give depth and a subsurface shape for the mass. Maps are provided showing the gravity contours and the geology, and geological and mathematical appendices are added.
THE TOTAL GAMMA RAY ACTIVITY OF SEDIMENTARY ROCKS AS INDICATED BY GEIGER COUNTER DETERMINATIONS
Authors: Russell W. L.
Published: October 2002

Geiger counter determinations of the gamma ray intensity of 510 rock samples have been made to determine the average radioactivity and frequency distribution of radioactivities of the various types of sedimentary rocks. The results, expressed in units of gamma ray intensity, show that limestones, sandstones and dolomites are of relatively low radioactivity, shales much higher, and black bituminous shales highest of all. The new data on the gamma radiation of the sediments may be used to improve the interpretation of radioactivity logs and to determine the value of surface radioactivity surveys.
Characterization of fluid transport properties of reservoirs using induced microseismicity
Authors: Shapiro Serge A. , Rothert Elmar , Rath Volker , Rindschwentner Jan
Published: October 2002

We systematically describe an approach to estimate the large‐scale permeability of reservoirs using seismic emission (microseismicity) induced by fluid injection. We call this approach seismicity‐based reservoir characterization (SBRC). A simple variant of the approach is based on the hypothesis that the triggering front of hydraulically‐induced microseismicity propagates like a diffusive process (pore pressure relaxation) in an effective homogeneous anisotropic poroelastic fluid‐saturated medium. The permeability tensor of this effective medium is the permeability tensor upscaled to the characteristic size of the seismically active heterogeneous rock volume. We show that in a homogeneous medium the surface of the seismicity triggering front has the same form as the group‐velocity surface of thelow‐frequency anisotropic, second‐type Biots wave describing kinematic aspects of triggering‐front propagation in a way similar to the eikonal equation for seismic wavefronts. In the case of isotropic heterogeneous media, the inversion for the hydraulic properties of rocks follows from a direct application of this equation. In the case of an anisotropic heterogeneous medium, only the magnitude of a global effective permeability tensor can be mapped in a 3‐D spatial domain. We demonstrate the method on several field examples and also test the eikonal equation‐based inversion.
Velocity dispersion between ultrasonic and seismic frequencies in brine‐saturated reservoir sandstones
Authors: King Michael S. , Marsden J. Robert
Published: October 2002

Ultrasonic P‐ and S‐wave velocities have been measured on 44 specimens from core samples of relatively clean sandstones recovered from hydrocarbon reservoirs. Ten specimens have porosities less than 10%, and 34 have porosities in the range 20–30%. Velocities were measured with the specimens in both their dry and brine‐saturated states, under hydrostatic effective stresses to 60 MPa for the low‐porosity specimens and to 40 MPa for those of the high‐porosity set. Gassmann's poroelastic theory is found to account for changes in velocity for the low‐porosity set at 60 MPa effective stress when the dry specimens are fully saturated with brine. The velocities used for “dry” specimens in Gassmann's theory must, however, be those measured after the dry specimens have first adsorbed a small quantity of moisture. For saturated specimens at effective stresses of 40 MPa or less, local flow phenomena due to the presence of open microcracks are assumed to be responsible for the measured velocities being appreciably higher than those predicted theoretically.
Reflection and transmission of waves at a fluid/porous‐medium interface
Authors: Denneman Arthur I. M. , Drijkoningen Guy G. , Smeulders David M. J. , Wapenaar Kees
Published: October 2002

We study the wave properties at a fluid/porous‐medium interface by using newly derived closed‐form expressions for the reflection and transmission coefficients. We illustrate the usefulness of these relatively simple expressions by applying them to a water/porous‐medium interface (with open‐pore or sealed‐pore boundary conditions), where the porous medium consists of (1) a water‐saturated clay/silt layer, (2) a water‐saturated sand layer, (3) an air‐filled clay/silt layer, or (4) an air‐filled sand layer. We observe in the frequency range 5 Hz–20 kHz that the fast P‐wave and S‐wave velocities in the four porous materials are indistinguishable from the corresponding frequency‐independent ones calculated using Gassmann relations. Consequently, for these frequencies we would expect the reflection and transmission coefficients for the four water/porous‐medium interfaces to be similar to the ones for corresponding interfaces between water and effective elastic media (described by Gassmann wave velocities). This expectation is not fulfilled in the case of an interface between water and an air‐filled porous layer with open pores. A close examination of the expressions for the reflection and transmission coefficients shows that this unexpected result is because of the large density difference between water and air.
Comments on “AFMAG‐airborne and ground” by S. H. Ward
Authors: Holzer Robert E.
Published: October 2002

Dr. S. H. Ward has kindly shown me the manuscript of the preceding paper and has invited me to comment on the origin of the natural audio‐frequency signals used by his AFMAG system. He lists five possible sources of signals. Of these, the only natural sources of practical importance in the frequency range under consideration are lightning strokes. Man‐made noise may be important in the vicinity of cities or industrial areas.
Comparison of linear regression and a probabilistic neural network to predict porosity from 3‐D seismic attributes in Lower Brushy Canyon channeled sandstones, southeast New Mexico
Authors: Leiphart Daniel J. , Hart Bruce S.
Published: October 2002

The Lower Brushy Canyon Formation of the Delaware Basin, New Mexico, consists of a series of overlying sand‐filled channels and associated fans separated by laterally extensive organic siltstone and carbonate interbeds. This laterally and vertically complex geology creates the need for precise interwell estimation of reservoir properties. In this paper we integrate wireline log and 3‐D seismic data to directly predict porosity in the area of an existing oil field in southeast New Mexico. The 3‐D seismic data were used to interpret the location of major stratigraphic markers between wells, and these seismic horizons were used to constrain a time window for a volume‐based attribute analysis. Stepwise regression and crossvalidation were used to combine seismic attributes to predict porosity in wells where the porosity was known from the well logs. The results of a linear regression porosity model showed good correlation [Formula: see text] between seven seismic attributes and the observed porosity logs at 11 wells in the study area, but the porosity volume created from the regression model did not display the known geologic features. A probabilistic neural network was then trained to look for a nonlinear relationship between the input data (the seven attributes) and the observed porosity at the 11 wells. The correlation was better [Formula: see text], but the biggest improvement over the linear regression model came in the more geologically realistic predicted porosity distribution.
Seismic migration problems and solutions
Authors: Gray Samuel H. , Etgen John , Dellinger Joe , Whitmore Dan
Published: October 2002

Historically, seismic migration has been the practice (science, technology, and craft) of collapsing diffraction events on unmigrated records to points, thereby moving (“migrating”) reflection events to their proper locations, creating a true image of structures within the earth. Over the years, the scope of migration has broadened. What began as a structural imaging tool is evolving into a tool for velocity estimation and attribute analysis, making detailed use of the amplitude and phase information in the migrated image. With its expanded scope, migration has moved from the final step of the seismic acquisition and processing flow to a more central one, with links to both the processes preceding and following it. In this paper, we describe the mechanics of migration (the algorithms) as well as some of the problems related to it, such as algorithmic accuracy and efficiency, and velocity estimation. We also describe its relationship with other processes, such as seismic modeling. Our approach is tutorial; we avoid presenting the finest details of either the migration algorithms themselves or the problems to which migration is applied. Rather, we focus on presenting the problems themselves, in the hope that most geophysicists will be able to gain an appreciation of where this imaging method fits in the larger problem of searching for hydrocarbons.
Nonlinear adaptive co-ordinated control of multimachine power systems
Authors: Wu Q. H. , Jiang L.
Published: October 2002

This paper presents a novel nonlinear adaptive controller (NAC) for the co-ordinated control of generators and thyristor-controlled series compensators (TCSCs) in multimachine power systems. Discussions begin with power system de-coupling which is achieved by Lie differentiation. For each subsystem, the nonlinear adaptive control strategy is, at first, investigated based on the input/output feedback linearizing control. In this strategy, a fictitious state is defined to represent the combined effect of system nonlinearities, uncertainties and external disturbances and an extended-order sliding mode observer is employed to estimate the states and the fictitious state of the subsystem, which allows the NAC to be designed without requiring the knowledge of system nonlinearities and parameters. The NAC is then implemented locally, involving the external dynamics of the subsystem, which is estimated by the observer, for the co-ordinated control of generators and TCSCs in the multimachine power system. Simulation studies are undertaken based on a three-machine power system to evaluate the effectiveness of the NAC. The simulation results show that the locally installed NACs can coordinate each other to improve the power system stability.
Invited editorial
Authors: Fisk David
Published: October 2002

Twentieth century governments have committed themselves to the principle of sustainable development. Efforts to full this goal offer an insight into changes in building services provision in the opening decades of the new century. Sustainable development indicators are used to identify possible trends. The analysis also forms the basis for some speculative conjectures as a basis for a research agenda for the twenty-first century.
Levels of inflammatory markers in the blood processed by autotransfusion devices during cardiac surgery associated with cardiopulmonary bypass circuit
Authors: Amand T , Pincemail J , Blaffart F , Larbuisson R , Limet R , Defraigne J O
Published: October 2002

Intraoperative blood salvage devices allowing a reinfusion of red blood cells (RBCs) after processing of shed blood and stagnant blood in the mediastinal cavity are more and more used to reduce homologous blood requirements in cardiac surgery with cardiopulmonary bypass (CPB). As the proinflammatory activity of the shed blood also contributes to morbidity during CPB, we conducted a prospective study in order to examine the quality of autologous blood before and after processing with five different devices [BRAT2, Sequestra, Compact Advanced, Cell Saver 5 (CS5), Continuous Autologous Transfusion System (CATS)]. All systems resulted in an excellent haemoconcentration, ranging from 53.7% (Compact) to 68.9% (CATS). The concentrations and elimination rates of several inflammatory markers [IL-1β, IL-2, IL-8, TNFα, myeloperoxidase (MPO), elastase] were examined. Except for the Sequestra, an important increase in concentration of IL-1β (between 30% and 220%) has been observed after processing with each device. In contrast, the attenuation rate of IL-6 and TNFα (95%) was optimal for all investigated blood salvages systems. Regarding IL-8, only the CATS and CS5 systems were able to attenuate this biological parameter with an excellent efficacy. The rate of attenuation in MPO and elastase, as markers of leukocyte activation, was higher than 80% for all devices. In conclusion, the different RBC washing systems tested in this study resulted in a significant attenuation of the inflammatory response. Increased levels of IL-1β after processing remained, however, unclear. According to the type of protocol, based on inlet haematocrit, fill and wash speeds, and wash volumes, small variations in reducing the inflammatory response have been observed from one device to another.
The relationship between mixed venous and regional venous oxygen saturation during cardiopulmonary bypass
Authors: Lindholm Lena , Hansdottir Vigdis , Lundqvist Magnus , Jeppsson Anders
Published: October 2002

The relationship between mixed venous and regional venous saturation during cardiopulmonary bypass (CPB), and whether this relationship is influenced by temperature, has been incompletely elucidated. Thirty patients undergoing valve and/or coronary surgery were included in a prospective, controlled and randomized study. The patients were allocated to two groups: a hypothermic group (28°C) and a tepid group (34°C). Blood gases were analysed in blood from the hepatic vein and the jugular vein and from mixed venous blood collected before surgery, during hypothermia, during rewarming, and 30 min after CPB was discontinued. Oxygen saturation in the hepatic vein was lower than in the mixed venous blood at all times of measurement (-24.0 ± 3.0% during hypothermia, -36.5 ± 2.9% during rewarming, and -30.5 ± 3.0% postoperatively, p < 0.001 at all time points). In 23% of the measurements, the hepatic saturation was < 25% in spite of normal (> 60%) mixed venous saturation. There was a statistical correlation between mixed venous and hepatic vein oxygen saturation (r = 0.76, p < 0.0001). Jugular vein oxygen saturation was lower than mixed venous saturation in all three measurements (-21.6 ± 1.9% during hypothermia, p < 0.001; -16.7 ± 1.9% during rewarming, p < 0.001; and -5.6 ± 2.2% postoperatively, p = 0.037). No significant correlation in oxygen saturation could be detected between mixed venous and jugular vein blood ( r = 0.06, p = 0.65). Systemic temperature did not influence the differences in oxygen saturation between mixed venous and regional venous blood at any time point. In conclusion, regional deoxyge-nation occurs during CPB, in spite of normal mixed venous saturation. Mixed venous oxygen saturation correlates with hepatic, but not with jugular, vein saturation. The level of hypothermia does not influence differences in oxygen saturation between mixed venous and regional venous blood.
In vitro performance characteristics of a high-flux hemodialyzer with a novel polyester-polymer-alloy (PEPA) membrane
Authors: Smith M D , Mahiout A
Published: October 2002

Despite improvements in hemodialyzers with respect to their clearance of middle and high molecular mass molecules, accumulation of specific solutes in the circulation of dialysis patients continues to be a medical problem. A new membrane material, polyester-polymer alloy (PEPA) which has been developed to have a filtration profile akin to that of the natural kidney, is now being used in hemodialyzers. This study evaluates the performance of a PEPA-based hemodialyzer alongside a selection of available competing high-flux dialyzers using official standardized methods. The new membrane material appears to be a viable alternative which offers performance at least as good as that of the competition. The promising results obtained with the PEPA membrane suggest that a detailed clinical performance study should be undertaken.
Leukocyte filtration in lung transplantation
Authors: Kurusz Mark , Roach John D , Vertrees Roger A , Girouard Mark K , Lick Scott D
Published: October 2002

Controlled reperfusion of the transplanted lung has been used in nine consecutive patients to decrease manifestations of lung reperfusion injury. An extracorporeal circuit containing a roller pump, heat exchanger and leukodepleting filter is primed with substrate-enhanced reperfusion solution mixed with approximately 2000 ml of the patient’s blood. This solution is slowly recirculated to remove leukocytes prior to reperfusion. When the pulmonary anastomoses are completed, the pulmonary artery is cannulated through the untied anastomosis using a catheter containing a pressure lumen for measurement of infusion pressure. An atrial clamp is left in place on the patient’s native atrial cuff to decrease the risk of systemic air embolism during the brief period of reperfusion from the extracorporeal reservoir. During reperfusion, the water bath to the heat exchanger is kept at 35°C and the flow rate for reperfusion solution is between 150 and 200 ml/min, keeping the pulmonary artery pressure < 14 mmHg. Eight of nine patients were ventilated on 40% inspired oxygen within a few hours of operation and 7/9 were extubated on or before postoperative day 1. Six of nine patients are long-term survivors.
Development and implementation of the Rehabilitation Activities Pro” le for children: impact on the rehabilitation team
Authors: Roelofsen Eline E , Anne-Mei B , Beckerman Heleen , Lankhorst Gustaaf J , Bouter Lex M
Published: October 2002

Objective: To describe the changes in functioning of the rehabilitation team induced by the Rehabilitation Activities Pro”le for children (Children’s RAP), an instrument designed to improve interdisciplinary communication in paediatric rehabilitation.

Design: Multiple case-study design.

Subjects: Seven paediatric rehabilitation teams.

Intervention: A two-year project to develop and implement the Children’s RAP.

Data collection: During the project, data were gathered from observations, documents and informal interviews. After the project, formal interviews were held with team members and parents, and a focus group meeting with representatives of the teams was organized.

Data analysis: Data were analysed by the method of analytic induction. The analysis was checked by an independent researcher. The preliminary results and conclusions were discussed in detail with participating teams.

Results: Development and implementation, as well as the changes induced by the project, varied between teams. Changes were observed for individual team members, for the team as a whole and for the children and their parents. However, changes for individual team members occurred relatively quickly, in comparison with the other changes. To achieve an optimal interdisciplinary team approach all changes are necessary. Therefore, we postulated four hierarchical steps in the development of an interdisciplinary team approach: (1) process-oriented approach, (2) result-oriented approach, (3) problem-oriented approach, and (4) interdisciplinary team approach.
Evaluation of a home-based exercise and training programme to improve sit-to-stand in patients with chronic stroke
Authors: Monger Claire , Carr Janet H , Fowler Virginia
Published: October 2002

Objective: To investigate the feasibility and efficacy of a task-specific homebased exercise protocol for improving sit-to-stand (STS), with additional exercises to strengthen lower limb extensor muscles in patients with chronic stroke.

Design: A pre-test, post-test design was used.

Subjects: Six subjects at least one year post stroke and discharged from all rehabilitation services for at least six months participated in the study.

Outcome measures: Functional performance of sit-to-stand was evaluated using the Standing Up item of the Motor Assessment Scale (MAS). Peak vertical ground reaction force, walking speed over 10 m and grip strength were also measured.

Results: Group MAS score was significantly higher at post-test than at pretest with two subjects reaching the highest point on the scale and three subjects reaching the second highest point. Time-to-peak vertical ground reaction force occurred significantly closer to thighs-off, the critical time when the body mass is propelled into standing. Walking speed increased significantly over 10 m from a mean of 0.86 m/s to 1.10 m/s. Grip strength, which was not trained, did not change.

Conclusions: This study demonstrates that a home-based task-specific exercise and training protocol for STS can induce improved performance of STS and increase walking speed more than one year after stroke.
Cancer patients' interpretations of verbal expressions when given information about ending cancer treatment
Authors: Friedrichsen Maria J , Strang Peter M , Carlsson Maria E
Published: October 2002

Background: Cancer patients’ interpretations of the meaning of words used when given bad news are not well studied in medical settings. The aim of this study was to ascertain what significance verbal expressions had for cancer patients when they were given information about ending active tumour treatment, and what message they felt they received.

Methods: Tape-recorded semi-structured interviews were performed and analysed using a qualitative phenomenographical approach.

Results: Thirty patients with incurable cancer admitted to hospital-based home care unit in Sweden participated. Three main categories about the significance of words emerged: 1) words could indicate indirect warnings as being forewarnings, evasive or ambiguous; 2) words could also be perceived as emotionally trying, as threats or abandoning; 3) other words were fortifying and strengthened the patient in this situation. The overall message given during the information could be interpreted differently: either focused on treatment, on quality of life, or on threat and death. Conclusion: The understanding of the significance of words to tailor the information to patients helps the physician to use forewarnings and fortifying words and to identify and avoid the use of threatening words.
Information needs and awareness of diagnosis in patients with cancer receiving chemotherapy: a report from Greece
Authors: Iconomou Gregoris , Viha Anna , Koutras Angelos , Vagenakis Apostolos G , Kalofonos Haralabos P
Published: October 2002

This study assessed the information needs of Greek cancer patients and examined whether awareness of diagnosis had any impact on patients. One hundred patients were interviewed about overall and specific information needs, satisfaction, emotional distress, and quality of life. Patients exhibited a great desire for information overall. The need to have more information was high especially regarding the aftermath of chemotherapy, prognosis, how chemotherapy worked, and diagnosis. Patients were more satisfied with care but less satisfied with the information received. Only 37% knew they had cancer, especially the younger, the better educated, and those with breast cancer. Awareness was not related to satisfaction, emotional distress, or quality of life. Our findings suggest that Greek cancer patients need more factual information about their condition and management. Greek oncologists may feel freer to inform their patients about the diagnosis and other issues following their judgement, rather than employing the policy of concealing the truth.