bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrating Mini-DST-Derived Permeability With Other Sources: A Case Study
Authors: Harmawan I.. , Kabir C.S.. S. , Habib S.. , Kennedy J.. , Henson J.. , Minhas H.. 
Published: November 2012

SummaryPermeability is the cornerstone of any reservoir-flow modeling that leads to field development and production management. Typical sources of permeability include cores, logs, wireline formation tests [or minidrillstem tests (mini-DSTs)], and conventional DSTs. However, integrating various sources of permeability at different scales is problematic. Anchored in mini-DST-derived permeability, this study endeavors to integrate various sources of permeability, leading to reservoir description in a turbidite sandstone reservoir in the Sabah basin, Malaysia.Ordinarily, pressure-transient-test data recorded during a mini-DST operation differ significantly from data gathered during a conventional DST. Even though test quality was excellent, interpretation challenges were numerous in this well. Consequently, multidisciplinary information was brought to bear for integration of data derived from mini-DSTs. Other sources of information included sidewall cores, spot pressure measurements, nuclear magnetic resonance (NMR), and microelectrical imaging logs. This case study demonstrates that, in this particular setting, the use of mini-DSTs was cost-effective and yielded the subsurface information required to plan field-development options.
A Comparison of Stochastic Data-Integration Algorithms for the Joint History Matching of Production and Time-Lapse-Seismic Data
Authors: Jin L.. , Alpak F.O.. O. , van den Hoek P.. , Pirmez C.. , Fehintola T.. , Tendo F.. , Olaniyan E.. 
Published: November 2012

Summary
Quantitative integration of spatial and temporal information provided by time-lapse (4D) -seismic surveys to dynamic reservoir models calls for efficient and effective data-integration algorithms. We carry out a comprehensive comparison of stochastic optimization methods using both a synthetic and a field case.
Our first case is a challenging synthetic test problem known as the Imperial College Fault Model (ICFM). The methods of very-fast simulated annealing (VFSA), particle-swarm optimization (PSO), and the neighborhood algorithm (NA) are compared in terms of convergence characteristics, data-match quality, and posterior model-parameter distributions. On the basis of the knowledge developed from the ICFM problem, we isolate VFSA and PSO and evaluate their performance further on a field case involving a deepwater reservoir undergoing waterflooding. The field case has a reasonably long production history and good-quality 3D- and 4D-seismic data, allowing the construction of a geologically consistent model by means of dynamic calibration. As such, it constitutes a relevant field test for joint seismic/production history matching. We assess the data-match characteristics and the quality of dynamic forecasts delivered by VFSA and PSO in the field case.
Practical guidelines are developed over the course of these studies for selecting a "fit-for-purpose" optimal method for joint history-matching workflows. Our results show that PSO, a population-based method, incurs relatively more computational expense at a given iteration but exhibits good convergence characteristics and provides multiple history-matched models. The PSO method has emerged as more effective compared with the NA and VFSA methods in the ICFM problem. It was also quite effective on the field application. On the other hand, the VFSA method requires comparatively more iterations to converge because of its sequential nature, but it has advantageous features when moderate computing resources are available.
Multiscale Gas Transport in Shales With Local Kerogen Heterogeneities
Authors: Yucel Akkutlu I.. , Fathi Ebrahim 
Published: November 2012

SummaryOn the basis of micro- and mesoscale investigations, a new mathematical formulation is introduced in detail to investigate multiscale gas-transport phenomena in organic-rich-shale core samples. The formulation includes dual-porosity continua, where shale permeability is associated with inorganic matrix with relatively large irregularly shaped pores and fractures, whereas molecular phenomena (diffusive transport and nonlinear sorption) are associated with the kerogen pores. Kerogen is considered a nanoporous organic material finely dispersed within the inorganic matrix. The formulation is used to model and history match gas-permeation measurements in the laboratory using shale core plugs under confining stress. The results indicate significance of molecular transport and strong transient effects caused by gas/solid interactions within the kerogen. In the second part of the paper, we present a novel multiscale perturbation approach to quantify the overall impact of local porosity fluctuations associated with a spatially nonuniform kerogen distribution on the adsorption and transport in shale gas reservoirs. Adopting weak-noise and mean-field approximation, the approach applies a stochastic upscaling technique to the mathematical formulation developed in the first part for the laboratory. It allows us to investigate local kerogen-heterogeneity effects in spectral (Fourier-Laplace) domain and to obtain an upscaled "macroscopic" model, which consists of the local heterogeneity effects in the real time—space domain. The new upscaled formulation is compared numerically with the previous homogeneous case using finite-difference approximations to initial/boundary value problems simulating the matrix gas release. We show that macrotransport and macrokinetics effects of kerogen heterogeneity are nontrivial and affect cumulative gas recovery. The work is important and timely for development of new-generation shale-gas reservoir-flow simulators, and it can be used in the laboratory for organic-rich gas-shale characterization.
Lattice Boltzmann Method for Simulation of Shale Gas Transport in Kerogen
Authors: Fathi Ebrahim , Akkutlu I. Yucel 
Published: November 2012

SummaryFluid mechanics of natural gas in organic-rich shale involves nanoscale phenomena that could lead to potential non-Darcy effects during gas production. In general, these are low-Reynolds-number and noncontinuum effects and, more importantly, pore-wall-dominated multiscale effects. In this study, we introduce a new lattice Boltzmann method (LBM) to investigate these effects numerically in simple pore geometries. The standard method was developed in the 1980s to overcome the weaknesses of lattice gas cellular automata and has emerged recently as a powerful tool to solve fluid dynamics problems, in particular in the areas of micro- and nanofluidics. The new approach takes into account molecular-level interactions by use of adsorptive/cohesive forces among the fluid particles and defining a Langmuir-slip boundary condition at the organic pore walls. The model allows us to partition mass transport by the walls into two components: slippage of free gas molecules and hopping (or surface transport) of the adsorbed gas molecules. By use of the standard 2D D2Q9 lattice, low-Reynolds-number gas dynamics is simulated in a 100-nm model organic capillary and later in a bundle of smaller-sized organic nanotubes. The results point to the existence of a critical Knudsen-number value for the onset of laminar gas flow under typical shale-gas-reservoir pressure conditions. Beyond this number, the predicted velocity profile shows that the mechanisms of slippage and surface transport could lead to molecular streaming by the pore walls, which enhances the gas transport in the organic nanopores. The work is important for development of new-generation shale-gas-reservoir flow simulators, and it can be used in the laboratory for organic-rich-shale characterization.
Early Symptom Detection on the Basis of Real-Time Evaluation of Downhole Conditions: Principles and Results From Several North Sea Drilling Operations
Authors: Cayeux Eric , Daireaux Benoît , Wolden Dvergsnes Erik , Sælevik Gunnstein 
Published: November 2012

Summary
During drilling operations, downhole conditions may deteriorate and lead to unexpected situations that can result in significant delays. In most cases, warning signs of the deterioration can be observed in advance, and by taking proactive actions, drillers can avoid serious incidents such as packoffs or stuck pipes. A new analysis methodology, relying on an automatic real-time computer system, has been developed to detect those early indicator conditions.
The methodology involves constantly computing the various physical forces acting inside the well (mechanical, hydraulic, and thermodynamic). These physical forces are coupled by an automatic model calibration, which then gives a reliable picture of the expected well behavior. Through analysis of the deviations between modeled and measured values, an estimation of the current state of the well is derived in real time. Changes in the well condition are an early warning of deteriorating well conditions. This paper precisely describes the real-time analysis and the results during some drilling operations.
The software has been used for monitoring 15 unique wells located in five different North Sea fields. All major situations were signaled in advance at different event time scales: Rapidly changing downhole conditions (such as pulling a drillstring into a cuttings bed) were typically detected 30 minutes ahead of the actual event, medium-duration deteriorations were detected up to 6 hours before the incident, and slow-changing downhole conditions were signaled up to 1 day in advance. Several examples that illustrate the detected incidents over distinct time periods are described.
The availability of good-quality real-time data streams makes it possible to implement such analysis tools in an integrated operation setup. Early symptom detection can be used to make decisions in a timely fashion, on the basis of quantitative performance indicators rather than subjective feelings and personal experience.
Block Model for Growth of Steam-Heated Zone in Oil-Bearing Naturally Fractured Carbonate Reservoirs
Authors: Closmann Philip J. 
Published: November 2012

Summary
A model for steam injection into naturally fractured carbonate reservoirs provides a method of calculating the volume of heated formation for a given amount of steam, provided that the assumptions of the model are satisfied. The model represents the fractured reservoir by a system of blocks, dependent on fracture spacing and dimensions. The amount of oil mobilized can be estimated from prior measurements of oil saturation and laboratory tests of oil-displacement efficiency. Results comparable to observations are obtained. In addition, the temperature distribution along the direction of propagation in the reservoir may also be estimated, providing a guide to variation in the local oil mobility. These results can assist in evaluating the effectiveness of steam injection in the recovery of oil from naturally fractured formations.
History Matching Time-Lapse Surface-Gravity and Well-Pressure Data With Ensemble Smoother for Estimating Gas Field Aquifer Support—A 3D Numerical Study
Authors: Glegola M.. , Ditmar P.. , Hanea R.G.. G. , Eiken O.. , Vossepoel F.C.. C. , Arts R.. , Klees R.. 
Published: November 2012

Summary
Water influx is an important factor influencing production of gas reservoirs with an active aquifer. However, aquifer properties such as size, porosity, and permeability are typically uncertain and make predictions of field performance challenging. The observed pressure decline is inherently nonunique with respect to water influx, and large uncertainties in the actual reservoir state are common. Time-lapse (4D) gravimetry, which is a direct measure of a subsurface mass redistribution, has the potential to provide valuable information in this context.
Recent improvements in instrumentation and data-acquisition and -processing procedures have made time-lapse gravimetry a mature monitoring technique, both for land and offshore applications. However, despite an increasing number of gas fields in which gravimetric monitoring has been applied, little has been published on the added value of gravity data in a broader context of modern reservoir management on the basis of the closed-loop concept. The way in which gravity data can contribute to improved reservoir characterization, production-forecast accuracy, and hydrocarbon-reserves estimation is still to be addressed in many respects.
In this paper, we investigate the added value of gravimetric observations for gas-field-production monitoring and aquifer-support estimation. We perform a numerical study with a realistic 3D gas field model that contains a large and complex aquifer system. The aquifer support and other reservoir parameters (i.e., porosity, permeability, reservoir top and bottom horizons) are estimated simultaneously using the ensemble smoother (ES). We consider three cases in which gravity only is assimilated, pressure only is assimilated, and gravity and pressure data are assimilated jointly. We show that a combined estimation of the aquifer support with the permeability field, porosity field, and reservoir structure is a very challenging and nonunique history-matching problem, in which gravity certainly has an added value. Pressure data alone may not discriminate between different reservoir scenarios. Combining pressure and gravity data may help to reduce the nonuniqueness problem and provide not only an improved gas- and water-production forecast and gas-in-place evaluation, but also a more-accurate reservoir-state description.
New Type Curves for Modeling Productivity of Horizontal Well With Negative Skin Factors
Authors: Nie R.-S.. -S. , Jia Y.-L.. -L. , Meng Y.-F.. -F. , Wang Y.-H.. -H. , Yuan J.-M.. -M. , Xu W.-F.. -F. 
Published: November 2012

Summary
This paper first establishes a comprehensive semianalytical model for a horizontal well in a homogeneous, dual- or triple-porosity reservoir. By taking a negative-skin approach, including Laplace transform, separation of variables, and inverse Laplace transform, we obtain the solutions in a unified formula for both constant-rate production and constant-wellbore-pressure production. In the model, we consider a set of rich boundary conditions, including infinite reservoir and closed or constant-pressure boundary conditions for the top, bottom, and side of the bounded reservoir. Consequently, we plot a series of new standard log-log type curves and make a clear observation of different flow periods (e.g., early radial flow, hemiradial flow, linear flow, and late pseudoradial flow) from negative-skin type curves. We make a comparison between the solutions using the negative-skin approach and conventional solutions, which shows that there are some small differences between the two methods. We also analyze the type-curve characteristics for horizontal-well production in dual- and triple-porosity reservoirs, which shows that the derivative curves are V-shaped for dual media and W-shaped for triple media. Finally, we perform well-test interpretations for a horizontal well with positive skin and a horizontal well with negative skin and bottomwater, which shows that our new model performs well against the real field data.
Intelligent Prediction of Differential Pipe Sticking by Support Vector Machine Compared With Conventional Artificial Neural Networks: An Example of Iranian Offshore Oil Fields
Authors: Jahanbakhshi Reza , Keshavarzi Reza , Aliyari Shoorehdeli Mahdi , Emamzadeh Abolqasem 
Published: November 2012

Summary
Differential pipe sticking (DPS) is one of the most conventional and serious problems in drilling operations that imposes some extra costs to companies. This phenomenon originates mainly from improper mud properties, bottomhole assembly (BHA) (contacting area), still pipe time, and differential pressure between the formation and the drilling mud. Investigation on various conditions that lead to DPS makes it possible to develop some preventive treatments to avoid this problem's occurrence. In the past, statistical methods were applied in this area, but recently artificial neural network (ANN) approaches are frequently being used. ANNs have some priorities over conventional statistical methods such as the model-free form of predictions, tolerance to data errors, data-driven nature, and fast computation. On the other hand, the designed ANNs have some shortcomings and restrictions as they are developed to predict problems. In this paper, to solve most of the existing disadvantages of ANNs, a novel support-vector machine (SVM) approach has been developed to predict a DPS occurrence in horizontal and sidetracked wells in Iranian offshore oil fields. The results from the analysis have shown the potential of the SVM and ANNs to predict DPS, with the SVM results being more promising.
Effectiveness of computer-assisted orthodontic treatment technology to achieve predicted outcomes
Authors: Larson Brent E. , Vaubel Christopher J. , Grünheid Thorsten 
Published: November 2012

ABSTRACT

Objective:
To evaluate the effectiveness of computer-assisted orthodontic treatment technology to produce the tooth position prescribed by the virtual treatment plan.

Materials and Methods:
Posttreatment models of 23 patients treated with SureSmile were digitally superimposed on their corresponding virtual treatment plan models utilizing best-fit surface-based registration. Individual tooth-position discrepancies between virtual treatment plan and actual outcome were computed. Discrepancies less than 0.5 mm in mesial-distal, facial-lingual, and vertical dimensions, and less than 2° for crown torque, tip, and rotation were considered clinically ideal. One-sided test of equivalence was performed on each discrepancy measurement, with P &lt; .05 considered statistically significant.

Results:
Mesial-distal tooth position was clinically ideal for all teeth with the exception of maxillary lateral incisors and second molars. Facial-lingual tooth position was clinically ideal for all teeth except maxillary central incisors, premolars, and molars, and mandibular incisors and second molars. Vertical tooth position was clinically ideal for all teeth except mandibular second molars. For crown torque, tip, and rotation, discrepancy exceeded the limits considered clinically ideal for all teeth except for crown torque on mandibular second premolars and crown tip on mandibular second premolars and first molars.

Conclusions:
The effectiveness of computer-assisted orthodontic treatment technology to achieve predicted tooth position varies with tooth type and dimension of movement.
On the structure of perfect sets in various topologies associated with tree forcings
Authors: Nowik Andrzej , Reardon Patrick 
Published: November 2012

AbstractWe prove that the Ellentuck, Hechler and dual Ellentuck topologies are perfect isomorphic to one another. This shows that the structure of perfect sets in all these spaces is the same. We prove this by finding homeomorphic embeddings of one space into a perfect subset of another. We prove also that the space corresponding to eventually different forcing cannot contain a perfect subset homeomorphic to any of the spaces above.
Critical configurations of planar robot arms
Authors: Khimshiashvili Giorgi , Panina Gaiane , Siersma Dirk , Zhukova Alena 
Published: November 2012

AbstractIt is known that a closed polygon P is a critical point of the oriented area function if and only if P is a cyclic polygon, that is, P can be inscribed in a circle. Moreover, there is a short formula for the Morse index. Going further in this direction, we extend these results to the case of open polygonal chains, or robot arms. We introduce the notion of the oriented area for an open polygonal chain, prove that critical points are exactly the cyclic configurations with antipodal endpoints and derive a formula for the Morse index of a critical configuration.
Solution to the equations of the moment expansions
Authors: Amore Paolo , Fernández Francisco 
Published: November 2012

Abstract
We develop a formula for matching a Taylor series about the origin and an asymptotic exponential expansion for large values of the coordinate. We test it on the expansion of the generating functions for the moments and connected moments of the Hamiltonian operator. In the former case the formula produces the energies and overlaps for the Rayleigh-Ritz method in the Krylov space. We choose the harmonic oscillator and a strongly anharmonic oscillator as illustrative examples for numerical test. Our results reveal some features of the connected-moments expansion that were overlooked in earlier studies and applications of the approach.
Atazanavir Pharmacokinetics, Efficacy and Safety in Pregnancy: A Systematic Review
Authors: Eley Timothy , Bertz Richard , Hardy Hélène , Burger David 
Published: November 2012

Background For some antiretroviral therapies, drug concentrations are reduced during pregnancy, potentially compromising effective virological suppression. Methods Data on atazanavir boosted with ritonavir in pregnancy are reviewed. Results With standard atazanavir/ritonavir 300/100 mg once-daily dosing: atazanavir area-under-the-concentration–time curves were reduced during pregnancy in most studies, but overall interpretation differed according to the data used for comparison; atazanavir concentration 24 h post-dose was maintained >150 ng/ml in 97.6% of women; no instance of mother-to-child transmission occurred in treatment-adherent mothers; and infant hyperbilirubinaemia was not elevated beyond levels expected in the neonatal period. Conclusions With concurrent medications that reduce atazanavir drug concentrations, optimal therapy during pregnancy may require once-daily atazanavir/ritonavir 400/100 mg; however, using this dose during the third trimester doubled maternal grade 3–4 hyperbilirubi-naemia rates.
La performance comme marqueur d'une transformation des modes de subjectivation
Authors: Alix Jean-Sébastien 
Published: November 2012

Résumé Cet article tend à saisir la portée des réformes sur les pratiques des travailleurs sociaux. Si de tout temps les professionnels ont eu le souci de rendre compte de leur travail, cette obligation est aujourd’hui systématisée et codifiée selon des protocoles déterminés. Nous verrons que la compréhension de la « performance » nécessite de dépasser l’idée que c’est un « terme à la mode ». Cet engouement généralisé répond à un principe plus structurel d’une transformation des modes de subjectivation des travailleurs sociaux, c’est-à-dire qu’il s’inscrit plus profondément dans une nouvelle manière de penser l’action.