bluuebunny/crossref_metadata_2025 huggingface dataset:
FBG-Sensor-Interrogator mit Time-of-Flight- und Peak-Tracking-Algorithmen
Authors: Plattner Markus , Koch Alexander W. , Zeh Thomas , Reutlinger Arnd
Published: June 2010

Um die Struktur und den Temperaturhaushalt von Ariane-Trägerraketen zu überwachen, wird ein neuartiges Messgerät zum Auslesen faseroptischer Sensoren entwickelt. Dieses System basiert auf einem MG-Y-Diodenlaser, mit dem es möglich ist, jede verfügbare Ausgangswellenlänge innerhalb weniger Nanosekunden auszugeben. Dadurch wird ein sehr vielseitig verwendbares Messgerät realisiert, bei dem verschiedene faserbasierte Sensortypen in beliebiger Reihenfolge ausgelesen werden können. Eine Anpassung der Messrate an jeden einzelnen Sensor ist dadurch genauso einfach zu realisieren wie eine dynamische Auswahl der Sensoren, welche ausgelesen werden sollen. In diesem Artikel stellen wir die Zusammenhänge zwischen der zeitlichen Pulsfolge und der spektralen Abtastung der Sensorantworten dar. Mit einer Methode, welche “Time-of-Flight”- und “Peak-Tracking”-Algorithmen kombiniert, wird die gesamte Messdauer, im Vergleich zu herkömmlichen scannenden Verfahren deutlich reduziert.
3D-Terahertz-Bildgebung für die zerstörungsfreie Materialprüfung
Authors: Löffler Torsten , Quast Holger
Published: June 2010

Terahertz- und Millimeterwellen sind gesundheitlich unbedenkliche elektro-magnetische Wellen im Bereich von 100–10.000 Gigahertz. Bei diesen Frequenzen sind die meisten nicht-leitfähigen Materialien transparent, sodass eine kontaktlose, zerstörungsfreie Prüfung der inneren Struktur moderner (Kunststoff-Komposite-) Werkstücke mit einer Orts- und Tiefenauflösung im Submillimeterbereich möglich ist. Die hier vorgestellte vollelektronische Technologie ermöglicht hochqualitative Bilder in einer extrem kurzen Messzeit.
Bone density and metabolism in subjects with microdeletion of chromosome 22q11 (del22q11)
Authors: Stagi Stefano , Lapi Elisabetta , Gambineri Eleonora , Manoni Cristina , Genuardi Maurizio , Colarusso Gloria , Conti Camilla , Chiarelli Francesco , de Martino Maurizio , Azzari Chiara
Published: June 2010

Introduction

Although hypoparathyroidism with hypocalcaemia is one of the most frequent clinical features of monoallelic microdeletion of chromosome 22q11 (22q11DS), bone mass and metabolism have not yet been assessed in these patients.

Design

This study aimed to evaluate bone mass and metabolism in a cohort of patients, both children and adults, with 22q11DS.

Methods

In twenty-eight patients with 22q11DS (median age 12.5, range 6.1–42.8 years), serum levels of ionised and total calcium, phosphate, parathyroid hormone (PTH), 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, osteocalcin and bone-specific alkaline phosphatase (BSAP), and urinary deoxypyridinoline concentrations were evaluated. In these patients, bone mineral density (BMD) was evaluated by dual-energy X-ray absorptiometry (DXA) examination, and volumetric BMD (bone mineral apparent density (BMAD)) was calculated.

The data obtained from paediatric and adult patients were compared with two age-, sex- and body size-matched healthy subject control groups.

Results

Patients with 22q11DS showed a reduced BMAD Z-score compared with controls (P<0.001). These patients also had significantly lower ionised (P<0.001) and total calcium (P<0.05) levels as well as lower PTH levels (P<0.05), compared with the controls. In particular, children and young patients with 22q11DS had significantly lower serum osteocalcin levels (P<0.001), BSAP levels (P<0.001) and urinary deoxypyridinoline concentrations (P<0.001) than controls. These results were not confirmed in adults.

Finally, patients with hypoparathyroidism and/or hypocalcaemia at the time of the study showed significantly lower ionised (P<0.001) and total calcium levels (P<0.001), PTH levels (P<0.05), BSAP levels (P<0.001), osteocalcin levels (P<0.001) and urinary deoxypyridinoline concentrations (P<0.001), compared with patients without hypoparathyroidism and/or hypocalcaemia. Nonetheless, the BMAD Z-score did not show substantial differences between these two groups.

Conclusions

Subjects with 22q11DS have a significant reduction in bone mass that appears to be more severe in adults who have already attained peak bone mass than in children who are still growing. Therefore, we suggest a close monitoring of bone mass and metabolism in 22q11DS patients.
Multiple endocrine neoplasia type 2 syndromes (MEN 2): results from the ItaMEN network analysis on the prevalence of different genotypes and phenotypes
Authors: Romei Cristina , Mariotti Stefano , Fugazzola Laura , Taccaliti Augusto , Pacini Furio , Opocher Giuseppe , Mian Caterina , Castellano Maurizio , degli Uberti Ettore , Ceccherini Isabella , Cremonini Nadia , Seregni Ettore , Orlandi Fabio , Ferolla Piero , Puxeddu Efisio , Giorgino Francesco , Colao Annamaria , Loli Paola , Bondi Fabio , Cosci Barbara , Bottici Valeria , Cappai Antonello , Pinna Giovanni , Persani Luca , Uberta Verga , Boscaro Marco , Castagna Maria Grazia , Cappelli Carlo , Zatelli Maria Chiara , Faggiano Antongiulio , Francia Giuseppe , Brandi Maria Luisa , Falchetti Alberto , Pinchera Aldo , Elisei Rossella , _ _
Published: June 2010

Objective

Multiple endocrine neoplasia type 2 (MEN 2) is a genetic disease characterized by medullary thyroid carcinoma (MTC) associated (MEN 2A and 2B) or not familial MTC (FMTC) with other endocrine neoplasia due to germline RET gene mutations. The prevalence of these rare genetic diseases and their corresponding RET mutations are unknown due to the small size of the study population.

Methods

We collected data on germline RET mutations of 250 families with hereditary MTC followed in 20 different Italian centres.

Results and conclusions

The most frequent RET amino acid substitution was Val804Met (19.6%) followed by Cys634Arg (13.6%). A total of 40 different germline RET mutations were present. Six families (2.4%) were negative for germline RET mutations. The comparison of the prevalence of RET germline mutations in the present study with those published by other European studies showed a higher prevalence of Val804Met and Ser891Ala mutations and a lower prevalence of Leu790Phe and Tyr791Phe (P<0.0001). A statistically significant higher prevalence of mutations affecting non-cysteine codons was also found (P<0.0001).

Furthermore, the phenotype data collection showed an unexpected higher prevalence of FMTC (57.6%) with respect to other MEN 2 syndromes (34% MEN 2A and 6.8% of MEN 2B). In conclusion, we observed a statistically significant different pattern of RET mutations in Italian MEN 2 families with respect to other European studies and a higher prevalence of FMTC phenotype. The different ethnic origins of the patients and the particular attention given to analysing apparently sporadic MTC for RET germline mutations may explain these findings.
Association of variants in gastric inhibitory polypeptide receptor gene with impaired glucose homeostasis in obese children and adolescents from Berlin
Authors: Sauber Jeannine , Grothe Jessica , Behm Maria , Scherag André , Grallert Harald , Illig Thomas , Hinney Anke , Hebebrand Johannes , Wiegand Susanna , Grüters Annette , Krude Heiko , Biebermann Heike
Published: June 2010

Objective

In the past 20 years, obesity has become a major health problem due to associated diseases like type 2 diabetes mellitus. The gastric inhibitory polypeptide receptor (GIPR) modulates body weight and glucose homeostasis and, therefore, represents an interesting candidate gene for obesity and the comorbidity impaired glucose homeostasis. Recently, a GIPR variation was found to be associated with impaired insulin response in humans.

In this study, we screened the GIPR gene for mutations and examined the association between three single-nucleotide polymorphisms (SNPs; rs8111428, rs2302382, rs1800437) and childhood obesity, as well as impaired glucose homeostasis.

Methods

The coding region of the GIPR was screened for mutations by direct sequencing. We genotyped three known SNPs in 2280 healthy normal weight (1696) and obese (584) children and adolescents. Genotyping was performed using the SNaPshot protocol, the iplex, and matrix-assisted laser desorption ionization time-of-flight spectrometry technique. Obesity was defined by a body mass index SDS above 2; homeostatic model assessment was calculated.

Results

No evidence for an association was found between the SNPs and the obesity phenotype. Significant association was found between the minor allele C of the SNP rs1800437 and elevated homeostasis model of insulin resistance values (P=0.001). No further sequence variations in the GIPR were found to be associated with childhood obesity.

Conclusion

Variations of the GIPR sequence are not associated with childhood obesity. This study points to a potential role for rs1800437 in glucose homeostasis. Further studies are necessary to confirm these results.
Language Shift: A Case Study of Ghana
Authors: Agyekum Kofi
Published: June 2010

This paper discusses language shift in Ghana from two perspectives. The first will be language shift from a Ghanaian language to English which is the official language. The second category will be the shift from one or two Ghanaian languages to a third Ghanaian language that has become a lingua franca of an area. The paper will define language shift, and discuss the factors that bring about language shift in general and Ghana in particular. We will look at language shift that are societal and based on governmental and institutional policies and others that are individual and based on people’s negative or positive attitudes to certain languages and also for practical reasons on communication.
The paper further discusses the characteristics and major features of languages that are being shifted. It will look at major areas where language shift is predominant and focus on politics, parliament and the judiciary, the electronic media, education, commerce, advertising, migratory and settlement patterns. The paper will look at the problems with language shift and resistance to language shift and provide suggestions that can be employed to reduce or curb language shift.
Mining and Risk of Tuberculosis in Sub-Saharan Africa
Authors: Stuckler David , Basu Sanjay , McKee Martin , Lurie Mark
Published: June 2010

Objectives. We estimated the relationship between mining and tuberculosis (TB) among countries in sub-Saharan Africa.

Methods. We used multivariate regression to estimate the contribution of mining activity to TB incidence, prevalence, and mortality, as well as rates of TB among people living with HIV, with control for economic, health system, and population confounders.

Results. Mining production was associated with higher population TB incidence rates (adjusted b = 0.093; 95% confidence interval [CI] = 0.067, 0.120; with an increase of mining production of 1 SD corresponding to about 33% higher TB incidence or 760 000 more incident cases), after adjustment for economic and population controls. Similar results were observed for TB prevalence and mortality, as well as with alternative measures of mining activity. Independent of HIV, there were significant associations between mining production and TB incidence in countries with high HIV prevalence (≥ 4% antenatal HIV prevalence; HIV-adjusted B = 0.066; 95% CI = 0.050, 0.082) and between log gold mining production and TB incidence in all studied countries (HIV-adjusted B = 0.053; 95% CI = 0.032, 0.073).

Conclusions. Mining is a significant determinant of countrywide variation in TB among sub-Saharan African nations. Comprehensive TB control strategies should explicitly address the role of mining activity and environments in the epidemic.
Investigation of the Effect of Rock Mechanical Properties and In-Situ Stresses on Seismic Velocity Through a Coupled Geomechanical Reservoir Model
Authors: Vidal-Gilbert S..
Published: June 2010

The dynamic poroelastic model identifies how dynamic elastic properties (P-wave and S-wave velocities and density) change during reservoir production. This forms the basis of time-lapse seismic feasibility studies. To provide accurate and meaningful predictions, the model requires appropriate input from reservoir engineering (pore-pressure and saturation variations) and geomechanics (stress and strain variations). In stress-sensitive reservoirs, a geomechanical simulation, coupled with the conventional reservoir simulation, updates vertical deformation and provides the mean-effective-stress field in and around the reservoir. The key objective of this work is to identify how combined reservoir and geomechanical effects will influence predictions of the dynamic poroelastic model.

A method integrating reservoir engineering, geomechanics, and rock physics is applied to a 3D synthetic case. The first task of this study is to model deformation and stresses induced by exploitation within the reservoir and surrounding formations. For this, the pore pressure extracted from the reservoir simulation is introduced into the geomechanical model. Then, a sensitivity analysis with different mechanical parameters (Young's modulus, Poisson's ratio) and with different conditions (initial effective-stress ratio, plasticity behavior) is performed on a 3D model that includes the reservoir and its surroundings. The results of this geomechanical modeling are analyzed by considering the compression effect, the stress arching effect, and the mean effective-stress value in and above the reservoir. Then, the mean effective stress resulting from each geomechanical simulation enables us to update seismic velocities and the time shifts associated with seismic horizons, using Hertz-Mindlin's model. Last, this approach, considering the geomechanical aspect, is improved by the contribution of the fluid substitution on the dynamic poroelastic model, taking the saturation effects into account. The geomechanical approach is compared with some classical nongeomechanical approaches commonly used. This work demonstrates that the geomechanical approach influences the results in and around the reservoir. The time-shift values of the seismic horizons produced using this approach would be detectable on 4D-seismic data, and in this case study, the effect is much stronger than the saturation effect alone.
Detection and Spatial Delineation of Thin-Sand Sedimentary Sequences With Joint Stochastic Inversion of Well Logs and 3D Prestack Seismic Amplitude Data
Authors: Merletti Germán D. , Torres-Verdín Carlos
Published: June 2010

We describe the successful application of a new prestack stochastic inversion algorithm to the spatial delineation of thin reservoir units otherwise poorly defined with deterministic inversion procedures. The inversion algorithm effectively combines the high vertical resolution of wireline logs with the relatively dense horizontal coverage of 3D prestack seismic amplitude data. Multiple partial-angle stacks of seismic amplitude data provide the degrees of freedom necessary to estimate spatial distributions of lithotype and compressional-wave (P-wave) and shear-wave (S-wave) velocities in a high-resolution stratigraphic/sedimentary grid. In turn, the estimated volumes of P- and S-wave velocity permit the statistical cosimulation of lithotype-dependent spatial distributions of porosity and permeability.

The new stochastic inversion algorithm maximizes a Bayesian selection criterion to populate values of lithotype and P- and S-wave velocities in the 3D simulation grid between wells. Property values are accepted by the Bayesian selection criterion only when they increase the statistical correlation between the simulated and recorded seismic amplitudes of all partial-angle stacks. Furthermore, inversion results are conditioned by the predefined measures of spatial correlation (variograms) of the unknown properties, their statistical cross correlation, and the assumed global lithotype proportions.

Using field data acquired in a fluvial-deltaic sedimentary-rock sequence, we show that deterministic prestack seismic-inversion techniques fail to delineate thin reservoir units (10-15 m) penetrated by wells because of insufficient vertical resolution and low contrast of elastic properties. By comparison, the new stochastic inversion yields spatial distributions of lithotype and elastic properties with a vertical resolution between 10-15 m that accurately describe spatial trends of clinoform sedimentary sequences and their associated reservoir units.

Blind-well tests and cross validation of inversion results confirm the reliability of the estimated distributions of lithotype and P- and S-wave velocities. Inversion results provide new insight to the spatial and petrophysical character of existing flow units and enable the efficient planning of primary and secondary hydrocarbon recovery operations.
A Semianalytical Approach To Model Pressure Transients in Heterogeneous Reservoirs
Authors: Medeiros F.. , Ozkan E.. , Kazemi H..
Published: June 2010

Pressure-transient responses of wells in a heterogeneous reservoir are usually computed with numerical models by using fine gridding and very short timesteps. An exceptions to this practice has been the use of analytical, semianalytical, and boundary-element methods for relatively simpler forms of heterogeneity, such as layering or the existence of natural fractures. This paper presents a semianalytical approach to compute pressure transients for more-complex forms of heterogeneity including composite, layered, and compartmentalized reservoirs. In this approach, the reservoir is divided into blocks corresponding to locally homogeneous substructures, and analytical pressure-transient solutions for adjacent blocks are coupled at the boundaries. This approach is consistent with the averaging effect of pressure transients and provides an alternative to full numerical modeling of pressure-transient responses in heterogeneous formations. The validation of the approach is demonstrated in comparison to the analytical solution for horizontal wells in a homogeneous reservoir. Application examples highlight the physical consistency of the approach and demonstrate its capability to model different types of reservoir heterogeneity.
An Efficient Algebraic Multigrid Solver Strategy for Adaptive Implicit Methods in Oil-Reservoir Simulation
Authors: Clees T.. , Ganzer L..
Published: June 2010

We propose a new, efficient, adaptive algebraic multigrid (AMG) solver strategy for the discrete systems of partial-differential equations (PDEs) arising from structured or unstructured grid models in reservoir simulation. The proposed strategy has been particularly tailored to linear systems of equations arising in adaptive implicit methods (AIMs). The coarsening process of the AMG method designed automatically employs information on the physical structure of the models; as a smoother, an adaptive incomplete LU factorization with thresholding (ILUT) method is employed, taking care of an efficient solution of the hyperbolic parts while providing adequately smooth errors for the elliptic parts. To achieve a good compromise of high efficiency and robustness for a variety of problem classes—ranging from simple, small black-oil to challenging, large compositional models—an automatic, adaptive ILUT parameter and AMG solver switching strategy, α-SAMG. has been developed. Its efficiency is demonstrated for eight industrial benchmark cases by comparison against standard one-level and AMG solvers, including constraint pressure residual (CPR), as well as the pure one-level variant of the proposed new strategy. In addition, very promising results of first parallel runs are shown.
Simulation of Dynamic Filtrate Loss During the Drilling of a Horizontal Well With High-Permeability Contrasts and Its Impact on Well Performance
Authors: Wu Z. , Vaidya R. N. , Suryanarayana P. V.
Published: June 2010

In this paper, we present a new approach for modeling filtrate invasion during the drilling of a horizontal well through regions with high-permeability contrasts, such as those caused by fractures and high-permeability streaks, and the impact that the cleanup of this approach has on well performance. The approach incorporates the drilling schedule and experiment-based dynamic filtrate-loss data into a fine-grid multiphase reservoir simulator. Unlike the traditional leakoff model, which assumes piston-like displacement in the filtrate-invaded zone, fluid flow in the invaded and the reservoir zones is described by the use of more-realistic two-phase water/ gas flow equations. The equations are solved under the dynamic boundary conditions of the leakoff model and time-varying reservoir exposure from drilling, tripping, completions, and work-overs. Because the impact of fractures on both invasion and flowback is more pronounced in low-permeability (tight) formations, the focus of this paper is on such formations.

In overbalanced drilling, the initial dynamic mudcake formation is critical in controlling filtrate loss. A dynamic fluid-loss model, which reflects the spurt loss and non-Darcy and non-Newtonian characteristics of filtrate flow through the mudcake is coupled with the reservoir simulator. Mud properties and different events during drilling influence compression, dynamic deposition, and erosion of the mudcake. The application of the dynamic filtrate-loss model avoids the complexity in building a multiparameter mathematical mudcake model without loss of generality. As in previous work, parameters in the dynamic filtrate-loss model are based on special core tests.

In existing experiments, leakoff coefficients are measured only for the matrix. The extrapolation of the dynamic leakoff coefficients for simulation of fluid loss into intersecting fractures is discussed. Driven by Buckley-Leverett equations, theoretical analysis is presented to emphasize the quantitatively spatial correlation between the invaded-filtrate saturation and the spatial permeability reduction in the invaded zone. The influence of water blocking, relative permeability alteration, and damaged permeability variation on well performance is simulated. A horizontal-well example is used to illustrate the flexibility of this approach, and the results are discussed in the context of well performance.
Control-Relevant Upscaling
Authors: Vakili-Ghahani S.A.. A. , Jansen J.D.. D.
Published: June 2010

The conventional reason for upscaling in reservoir simulation is the computational limit of the simulator. However, we argue that, from a system-theoretical point of view, a more fundamental reason is that there is only a limited amount of information (output) that can be observed from production data, while there is also a limited amount of control (input) that can be exercised by adjusting the well parameters; in other words, the input/output behavior is usually of much lower dynamical order than the number of grid-blocks in the model. Therefore, we propose an upscaling approach to find a coarse model that optimally describes the input/output behavior of a reservoir system. In this control-relevant method, the coarse-scale-model parameters are calculated as the solution of an optimization problem that minimizes the distance between the input/output behaviors of the fine- and coarse-scale models. This distance is measured with the aid of the Hankel or energy norms, in which we use Hankel singular values as a measure of the combined controllability and observability and Markov parameters as a measure of the response of the system, respectively. The method is particularly attractive to scale up simulation models in flooding-optimization or history-matching studies for a given configuration of wells. An advantage of our upscaling method is that it relies most heavily on those parameter values that directly influence the input/output behavior. It is a global method in the sense that it relies on the system properties of the entire reservoir. It does not, however, require any forward simulation, either of the full or of the upscaled model. It also does not depend on a particular control strategy but instead uses the dynamical system equations directly. Its dependency on well locations, however, implies that it should be (partially) repeated when those locations are changed. We tested the method on several examples and, for nearly all cases, obtained coarse-scale models with a superior input/output behavior compared to common upscaling algorithms.
Dynamic Buckling and Snaking Motion of Rotating Drilling Pipe in a Horizontal Well
Authors: Gao Guohua , Miska Stefan
Published: June 2010

This paper is a focused theoretical and experimental study on the dynamic buckling and snaking motions of rotating pipe in a horizontal well. First, a comprehensive dynamic buckling model is presented. As part of this model, a group of fourth-order nonlinear partial-differential equations is derived and discussed. Then, a perturbation solution of the model is obtained that represents the snaking motion of the rotating pipe. On the basis of the perturbation solution, critical dynamic buckling load and dynamic behavior of rotating pipe are analyzed. It has been found that there are two different kinds of snaking motion. In one type, the pipe moves up and down around its static buckling configuration. In the other type, the pipe moves from one side of the wellbore to the other side.

The authors also conducted an experimental study with a small- scale experimental facility. Depending on axial compressive load and rotating speed, different motion patterns of drilling pipe are observed. Measurements of axial load at both ends and axial displacement at the loaded end are recorded. These observations and measurements provide us with very important information about the dynamic behavior of rotating pipe in a horizontal well. Observations also show that the pipe may take two different patterns of snaking motions. Both critical static buckling load and dynamic buckling load were measured with this facility. Both theoretical and experimental results show that pipe rotation does not affect the critical load of dynamic buckling. Experiments also show that there exist two different kinds of snaking motions, which support the analytical solution of the dynamic model presented in this paper. The results are useful for practical design applications related to calculation of buckling loads and selection of bottomhole-assembly (BHA) elements and pipe rotational speeds.
Case Study: Production Data and Pressure Transient Analysis of Horseshoe Canyon CBM Wells
Authors: Clarkson C.R.
Published: June 2010

The Horseshoe Canyon (HSC) CBM play of the Western Canadian Sedimentary Basin is unique to low-rank coal reservoirs because of lack of water production; the production characteristics are qualitatively similar to conventional low-pressure dry gas reservoirs. However, the complex geological history of the coals and non-coal interbeds has imparted strong vertical and lateral heterogeneities that make the play difficult to characterize using conventional methods.

Recently, advances in production data analysis (PDA) methodologies have been made for CBM wells; techniques developed for conventional oil and gas reservoirs have been adapted by incorporating some CBM reservoir properties. For example, the popular flowing material balance (FMB) technique, as well as production type-curve and pressure transient analysis (PTA) have been modified to include relatively simple CBM reservoir behaviour (ex. equilibrium desorption). These methods, however, are primarily restricted to the analysis of single-layer reservoirs; significant errors in estimates of original-gas-in-place (OGIP) and other reservoir properties may occur if strong contrasts exist from layer-to-layer. In this work, multi-layer analysis tools are discussed, including analytical simulators that are used to history-match layer-allocated rates and pressures, and layer-specific FMB, which is used as a PDA method for individual layers.

The applicability of advanced PDA methods to the quantitative assessment of HSC reserves was investigated. Single-layer and multi-layer analysis tools were first tested against simulated data. Next, single-layer-equivalent analysis was performed on >40 real wells using type-curve, FMB, and analytical simulation. Finally, a more rigorous multi-layer analysis was performed on a subset of wells where spinner surveys and individual-seam pressure buildup data were available. Analysis of these wells included PTA of the individual seams, individual seam material balance, and multi-layer analytical model history-matching of total commingled flow rates, individual coal zone rates estimated from spinner surveys and shut-in pressures. The single-layer- equivalent analysis appears to yield conservative estimates of OGIP compared to the more rigorous multi-layer analysis in the cases analyzed.

Future work will include continued comparisons of multi-layer vs. single-layer PDA, investigation of additional constraints on input reservoir properties used in multi-layer history-matching process, and time-lapse PTA work to quantify changes in layer permeability and skin during depletion.
Polymer-Flood Modeling Using Streamlines
Authors: Thiele M.R.. R. , Batycky R.P.. P. , Pöllitzer S.. , Clemens T..
Published: June 2010

The successful design of a polymer flood relies on the ability to properly model the in-situ distribution of polymer concentration while accounting for its effects on fluid properties such as increasing water viscosity as a function of polymer concentration and loss of polymer caused by adsorption. Despite advances in numerical techniques and computer hardware, the numerical modeling of polymer floods using Eulerian-based approaches such as finite difference (FD) remains a challenge: Coarse grids tend to excessively smear concentration fronts, masking the true impact of polymers; yet introducing finer grids inevitably leads to excessive run times, making the use of modern reservoir-engineering workflows unrealistic. This problem was already outlined by Lake et al. (1981). We revisit the same problem 30 years later in the context of modern streamline (SL) simulation techniques.

We present the extension of modern SL simulation to field-scale polymer flooding, which represents a step change from the hybrid, 2D steady-state models used in the 1970s. We apply well-established physical models for polymer flooding to capture the displacement efficiency in 1D, and couple it with a 3D SL simulator to capture the interpattern sweep efficiency caused by well rates, reservoir architecture, and reservoir heterogeneity. Because modern 3D SL simulators account for changing well rates, nonuniform initial conditions, and gravity, adding polymer functionality means that real-field polymer floods can be modeled efficiently using SLs so as to be useful in modern reservoir-engineering workflows that center on assessing uncertainty and risk associated with design parameters and geological scenarios.

In this paper, we proceed to outline the basic architecture of a SL simulator with a polymer option. The physics of polymer flooding is the same as that being used in established FD codes. We discuss advantages and disadvantages of the formulation and present numerical experiments in 1D, 2D, and 3D to illustrate our results.
Debottlenecking and Computational-Fluid-Dynamics Studies of High-and Low-Pressure Production Separators
Authors: Lee Joseph M. , Khan Rafiqul I. , Phelps Daniel W.
Published: June 2010

Efficient and effective oil/water/gas separation is required for success of many production operations. A major oil producer was experiencing difficulties with the oil/water/gas separation equipment on an offshore platform and improvements were required to meet both present and future production rates. Both high-pressure (HP) and low-pressure (LP) separators on a major oil production platform were studied to determine the design limitations for foamy service and basic sediment and water (BS&W) levels. Computational-fluid-dynamics (CFD) studies were completed to show the volumetric utilization and flow-pattern improvements made with the design changes.

Both HP and LP separators showed substantial foam and poor efficiency because of poor inlet-device design, plugging, and other general vessel-design limitations. Debottlenecking efforts determined that, while the inlet device was somewhat ineffective, major improvements could be made from changes to perforated plate baffles, fluid-level adjustments, and weir placement and operations.

CFD calculations performed on both vessels indicated similar problems. The perforated plate baffles with improper design lead to countercurrent flow through the baffles, making them less effective in flow control and distribution. Fluid-level settings for the weir height affected the velocity differences between fluid layers and contributed to promotion of recirculation within the vessel, which lead to low volumetric utilization.

With adjustments to vessel internal equipment and changes to fluid-phase levels, CFD calculations showed that overall vessel volumetric utilization was improved by 22% for the HP vessel and by 38% for the LP vessel. CFD results also showed the changes to the flow patterns accompanying these improvements.

Vessels with the proposed changes were operating effectively with substantially higher throughputs and meeting the expected BS&W levels for operations of the downstream oil-processing equipment. Details about the vessel internals, flow properties, and other changes required to accomplish these improvements will be discussed.
Characterization of Reservoir Heterogeneity Through Fluid Movement Monitoring With Deep Electromagnetic and Pressure Measurements
Authors: Zhan Lang , Kuchuk Fikri , Al-Shahri Ali M. , Ma S. Mark , Ramakrishnan T.S.. S. , Altundas Y.B.. B. , Zeybek Murat , Manin Yves , Tartaras Efthimios , Loubens Romain de , Chugunov Nikita
Published: June 2010

This paper presents a novel technique to characterize detailed formation heterogeneity for a carbonate reservoir using measurements from electrode resistivity array (ERA), a wireline formation tester, and a permanent downhole pressure sensor. The ERA was installed on tubing in a barefoot well rather than permanently cemented outside the casing as in previous applications. This notable difference provided flexibility for device installation and operation but also introduced particular issues in the ERA data acquisition and interpretation. Furthermore, the ERA measurements were carried out in conjunction with low-salinity water injection and oil and water production in the same well. The primary finding presented in this paper is that the time-lapse ERA voltages near a source electrode showed unique characteristics that represented local formation heterogeneity. This localized sensitivity of ERA data allows detailed characterization of the formation heterogeneity within the length of the ERA string in the vertical direction and about 100 ft laterally around the wellbore. The scale size of the investigated formation heterogeneity is comparable to typical grid sizes used in current reservoir simulations. Models were developed to identify stratified permeability heterogeneities from the time-lapse ERA voltages. The stratified heterogeneity estimated from the ERA measurements was compared to and verified by openhole logs and core analyses data. The final heterogeneous reservoir model from the ERA was subsequently applied to a numerical simulation that integrated the dynamic fluid flow, salt transport, and electrode array responses for monitoring water-front movement and estimating multiphase formation properties. The history matching of the time-lapse ERA data confirmed the first pass estimates of the identified heterogeneities.
Comparative Proof of Concept Results for Electrothermal Dynamic Stripping Process: Integrating Environmentalism With Bitumen Production
Authors: McGee Bruce C. W. , McDonald Craig W. , Little Les
Published: June 2010

The electrothermal dynamic stripping process (ET-DSP™) was commercialized as an environmental remediation technology to remove volatile soil contaminants. After nearly 10 years of use, it has been adapted for the thermal stimulation and recovery of bitumen from oil sand reservoirs. A proof of concept field pilot (McGee 2008) in the McMurray formation was conducted in 2007 and was deemed to be successful. Using a tight well spacing, the pilot demonstrated the effective recovery of approximately 75% of the original bitumen in place. Sand production was minimal, and the produced bitumen was emulsion-free. An expanded field test is currently under way to establish commercial viability of the ET-DSP process as an in-situ recovery process. Validation and calibration of the computer simulation model from the initial pilot test is presented along with details of the expanded field test.

The Athabasca oil sands are well known to the public as open-pit mining or steam-assisted gravity drainage (SAGD) in-situ projects. Approximately two-thirds of the Athabasca oil sands resource base occurs at depths that are defined as either too deep to surface mine or too shallow for currently available in-situ techniques. Furthermore, concerns regarding environmental issues that arise from these methods have the potential to slow their development. The ET-DSP process represents an alternative in-situ recovery technology that delivers significant environmental advantages in addition to its ability to access bitumen reserves that otherwise would not be recoverable. With growing public expectations for reduced greenhouse gas emissions, reduced fresh water usage, and improved management of waste water, as well as the accelerated reclamation of disturbed land and boreal forest, there are many drivers to support the commercial development of the ET-DSP technology.
Compositional and PVT Analysis for Determining Liquid Dropout in Pipelines
Authors: Esmaiel T. E. H. , Al Qallaf A. A. A.
Published: June 2010

A lot of equipment is not designed to handle liquids in the operations of a gathering center or gas booster station. In the study area, some compressors were having vibration problems because of amounts of liquid condensate in the flowline caused by sudden changes in pressure and temperature.

The primary objectives of this study are to determine under what pressure and temperature conditions liquids occur and to determine the proper operating conditions. The process involves collecting samples in the field, laboratory analysis, computer equation of state (EOS) modeling of the fluids, and analysis of the phase regions.

Samples were collected at two different locations in the gas line. The samples were sent to the laboratory for compositional and PVT analysis where physical properties were measured. Compositional analysis was performed on the gas and the condensate samples, and liquid dropout tests were performed on the samples.

An EOS simulator was used to characterize the samples and was tuned to match the pressure, volume, and temperature (PVT) data. The tuned simulator was used to perform flash calculations to calculate vapor liquid equilibrium (VLE) for the samples. The simulator was used to develop phase envelopes and physical properties of the gas to determine the amount of liquid dropout at the current operating conditions. These phase envelopes were used to determine new operating conditions to avoid liquid dropout. As anticipated, the primary solution was an increase in the pressure in the line to avoid the two-phase region.
Lagrangian Decomposition of Oil-Production Optimization Applied to the Troll West Oil Rim
Authors: Foss Bjarne , Gunnerud Vidar , Díez Marta Dueñas
Published: June 2010

This paper proposes a method based on Lagrangian decomposition for real-time production optimization. It argues the method is well suited for the well-allocation and routing problem in the upstream industries. A semirealistic field case assuming steady-state conditions is used to compare the merits of the method with current industrial practice. The method compares favorably and is therefore an interesting option in real-time production optimization. There are several reasons for this. An error bound on the solution of the production optimization problem can be computed, which is clearly information of interest to any user. Furthermore, the algorithm is efficient and can be parallized for an even higher efficiency. Finally, the Lagrangian decomposition method provides a tool for understanding how a limited resource, such as gas capacity, is used in production optimization.
Kinetics of the Reaction of Citric Acid With Calcite
Authors: Alkhaldi M.H.. H. , Nasr-El-Din H.A.. A. , Sarma H..
Published: June 2010

Previous studies of citric acid/calcite have been limited to coreflood tests and bench-scale experiments. However, the kinetics of a citric acid reaction with calcite has not been measured. This paper gives, for the first time, the kinetics of citric-acid/calcite reaction, which will provide a better way to model the performance of citric acid as a standalone stimulation fluid.

In this paper, the rotating disk apparatus was used to study citric-acid/calcite reaction at a pressure of 1,000 psi, temperatures from 25 to 50°C, citric acid concentrations from 1 to 7.5 wt%, and disk rotational speeds from 100 to 1,000 rev/min. The reaction rate of citric acid with calcite was found to be dependent on the initial citric acid concentration, disk rotational speed, and temperature. For example, at 50°C, the reaction was reaction-rate-limited at rotational speeds greater than 500 rev/min, using high initial citric acid concentrations (3, 5, and 7.5 wt%), while at low acid concentrations (1 and 2 wt%), the reaction was mass-transfer-limited even at high rotational speeds (1,000 rev/min). During the reaction of citric acid with calcite, calcium citrate precipitation occurred at different acid concentrations and rotational speeds. The amount of this precipitation was found to be a function of both the initial citric acid concentration and disk rotational speed. More calcium citrate precipitated at high initial citric acid concentrations, especially at high rotational speeds.

Calcium citrate precipitation occurred at the calcite surface, even at low initial citric acid concentrations. Because of this precipitation, the equilibrium of the citric-acid/calcite reaction was disturbed and the reaction shifted toward the forward reaction (toward the products). Therefore, the overall reaction rate was governed mainly by the rate of the forward reaction, and, hence, it was modeled by a new simplified reaction-rate equation; rate = kf{Ka1·CB}n/2 The average value of the reaction order (n) was found to be 0.833. In addition, the value of the reaction-rate constant (kf)was determined at various temperatures. The effect of temperature on the reaction-rate constant was found to follow the Arrhenius law, where the activation energy was found to be 63.1 kJ/mol.
History Matching With Parameterization Based on the Singular Value Decomposition of a Dimensionless Sensitivity Matrix
Authors: Tavakoli Reza , Reynolds Albert C.
Published: June 2010

In gradient-based automatic history matching, calculation of the derivatives (sensitivities) of all production data with respect to gridblock rock properties and other model parameters is not feasible for large-scale problems. Thus, the Gauss-Newton (GN) method and Levenberg-Marquardt (LM) algorithm, which require calculation of all sensitivities to form the Hessian, are seldom viable. For such problems, the quasi-Newton and nonlinear conjugate gradient algorithms present reasonable alternatives because these two methods do not require explicit calculation of the complete sensitivity matrix or the Hessian. Another possibility, the one explored here, is to define a new parameterization to radically reduce the number of model parameters.

We provide a theoretical argument that indicates that reparameterization based on the principal right singular vectors of the dimensionless sensitivity matrix provides an optimal basis for reparameterization of the vector of model parameters. We develop and illustrate algorithms based on this parameterization. Like limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS), these algorithms avoid explicit computation of individual sensitivity coefficients. Explicit computation of the sensitivities is avoided by using a partial singular value decomposition (SVD) based on a form of the Lanczos algorithm. At least for all synthetic problems that we have considered, the reliability, computational efficiency, and robustness of the methods presented here are as good as those obtained with quasi-Newton methods.
A Multiscale Mixed Finite-Element Method for Vuggy and Naturally Fractured Reservoirs
Authors: Gulbransen Astrid Fossum , Hauge Vera Louise , Lie Knut-Andreas
Published: June 2010

Vugs, caves, and fractures can alter the effective permeability of carbonate reservoirs significantly and should be accounted for accurately in a geomodel. Accurate modeling of the interaction between free-flow and porous regions is essential for flow simulations and detailed production-engineering calculations. However, flow simulation of such reservoirs is very challenging because of the coexistence of porous and free-flow regions on multiple scales that need to be coupled.

Multiscale methods are conceptually well-suited for this type of modeling because they allow varying resolution and provide a systematic procedure for coarsening and refinement. However, to date there are hardly any multiscale methods developed for problems with both free-flow and porous regions. Herein, we develop a multiscale mixed finite-element (MsMFE) method for detailed modeling of vuggy and naturally fractured reservoirs as a first step toward a uniform multiscale, multiphysics framework. The MsMFE method uses a standard Darcy model to approximate pressure and fluxes on a coarse grid, whereas fine-scale effects are captured through basis functions computed numerically by solving local Stokes-Brinkman flow problems on the underlying fine-scale geocellular grid. The Stokes-Brinkman equations give a unified approach to simulating free-flow and porous regions using a single system of equations, they avoid explicit interface modeling, and they reduce to Darcy or Stokes flow in certain parameter limits.

In this paper, the MsMFE solutions are compared with finescale Stokes-Brinkman solutions for test cases including both short- and long-range fractures. The results demonstrate how fine-scale flow in fracture networks can be represented within a coarse-scale Darcy-flow model by using multiscale elements computed solving the Stokes-Brinkman equations. The results indicate that the MsMFE method is a promising path toward direct simulation of highly detailed geocellular models of vuggy and naturally fractured reservoirs.