bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Analysis of a New Stochastic Bubble Population Foam Model
Authors: Zitha P. L. J. , Du D. -X. , Uijttenhout M. G. H. , Nguyen Q. P. 
Published: December 2007

Abstract
Foam flow in porous media plays an important role in oil and gas recovery. Besides experimental studies, the prediction of foam behavior in the applications relies on macroscopic modeling. In this paper, we present a numerical analysis of foam flow in porous media using a new stochastic bubble population (SBP) model. We also present a sensitivity analysis to the main parameters. The idea that foam flow in porous media can be described as a stochastic process emerged from recent studies of foam flow through porous media using X-ray computed tomography (CT). The model is simple as it describes the bubble generation using mainly two parameters, the maximum bubble density and a foam generation constant. It is also robust because it grasps the essence of foam physics in homogeneous porous media. A good qualitatively agreement exists between the numerical predictions and the water saturation profiles obtained from the CT scan experiments.
Comparison of Secondary and Tertiary Recovery with Change in Injection Brine Composition for Crude Oil/Sandstone Combinations
Authors: Zhang Y. , Morrow N. R. 
Published: December 2007

Abstract
Numerous examples of dependency of waterflood efficiency on brine composition have been observed for sandstones. Improved oil recovery depends on complex crude oil/brine/rock (COBR) interactions. Elucidation of the circumstances and mechanisms of increased oil recovery still requires extensive laboratory testing. Special attention is being given in laboratory and pilot tests to increased recovery by injection of low salinity brine in both secondary and tertiary modes. Investigation of connate brine composition as a key variable has been extended to variation in initial water saturation (Swi). Mixed-wettability (MXW) cores were prepared by aging with crude oil at reservoir temperature for a range of initial water saturations.
Oil recovery as % original oil in place (OOIP) generally increased with initial water saturation for secondary recovery by injection of low salinity brine. CS crude oil/Berea sandstone combinations were essentially insensitive to displacement with low salinity brine in secondary mode even when the injection pressure was double that for oil recovery by injection of reservoir brine (RB). However, significant increase in tertiary mode (about 6% OOIP) was observed for the same COBR combination when low salinity brine was injected after establishing residual oil by injection of reservoir brine.
Low salinity brine floods with Minnelusa oil and 400 md Berea sandstone showed more than 13% OOIP increase in recovery over that given by flooding with reservoir brine. For the Minnelusa oil, however, very little additional oil was produced in tertiary mode. From available data, response to injection of low salinity brine in tertiary mode was clearly highest for reservoir rock and crude oil. Overall, rock properties are the most important factor in improved recovery by injection of low salinity brine.
Effect of Oil Viscosity on Heavy-Oil/Water Relative Permeability Curves
Authors: Wang J. , Dong M. , Asghari K. 
Published: December 2007

Abstract
For heavy oil reservoirs, the oil viscosity usually varies dramatically during production processes, such as thermal process or solvent injection. This paper presents an investigation of the effect of oil viscosity on relative permeability curves for heavy oil-water systems. Unsteady-state displacement tests were conducted in sandpacks under a typical injection flow rate in a heavy oil recovery process. A series of crude oils with a wide range of viscosities were used in the measurements. Large pore volumes of water were injected to minimize the errors caused by the extrapolation of the recovery data. History matching was used to obtain the relative permeability curves, in which capillary pressure was included. It was found that, for the same injection flow rate, heavy oil-water relative permeability curves systematically shifted with oil viscosity. With increasing oil viscosity, the residual oil saturation increased and the oil and water relative permeabilities decreased at the higher water saturation range. Irreducible water saturation tended to decrease with increasing oil viscosity. Micromodel experiments were conducted to visually investigate the difference in the flow behaviour between heavy oil-water and light oil-water systems. Interacting capillary bundle models were used to analyze the impact of oil viscosity on the residual oil saturation. This work aids in the laboratory measurement and determination of the representative relative permeability curves for heavy oil-water systems, as well as in the proper use of relative permeability curves in reservoir simulation for heavy oil development.
Reducing the Permeability of Sandstone Porous Media to Water and CO2: Application of Bovine Carbonic Anhydrase Enzyme
Authors: Asghari K. , Mirjafari P. , Mahinpey N. , Dong M. 
Published: December 2007

Abstract
This paper presents the results of an investigation on the application of the enzyme bovine carbonic anhydrase for reducing the permeability of a sandstone porous medium during CO2 flooding. This process provides a method for improving conformance of injected water and CO2 in an absolutely environmentally friendly manner. Carbonic anhydrase enzyme accelerates the hydration reaction of CO2 with water. Hence, in presence of carbon dioxide and divalent ions, such as calcium, this enzyme leads to rapid precipitation of calcium carbonate. The precipitation reaction causes reduction in the permeability of the flooded regions of the reservoir. Therefore, upon subsequent injection of CO2 and water, injected fluids would flow through the unswept parts of reservoir, improving the conformance of the injected CO2 and water.
Experiments were carried out to investigate the effect of various enzyme concentrations, temperature and pH on the precipitation reaction. Enzyme concentrations at 2, 4 and 8 micro mole per litter were tested. Also, effect of temperature was studied by performing experiments at room temperature, 30 °C and 55 °C. A mathematical model was developed to predict the extent of precipitation of calcium carbonate. Subsequently, coreflood experiments, using Berea sandstone cores, were conducted and the degree of reduction in the permeability of the cores was measured. Also, in order to investigate the effect of injection scheme on permeability reduction, two different methods of injection were tested. For all sets of flow experiments, the permeability of the core was reduced to less than half of its initial value.
Evaluation of Acid Precursor-Enzyme System for Filter-Cake Removal by a Single-Stage Treatment
Authors: Siddiqui M. A. , Al-Anazi H. A. , Al-Ansari A. A. , Bataweel M. A. , Hembling D. E. 
Published: December 2007

Abstract
Water based drill-in fluids usually contain starch and xanthan polymers and sized calcium carbonate particles, which help in developing an effective filter cake during drilling process to control fluid loss. Proper removal of the drill-in fluid filter cake from the pay zone is essential to maximize productivity. The latest technique for filter cake clean-up is the application of acid and enzymes in a single stage. The prime advantage of this technique is the uniform placement of acid through precursor in long horizontal wells. Other benefits include: cost and time saving by avoiding multistage treatment and reduced risk of tools corrosion, which is associated with mineral acids.
A detailed study was conducted to evaluate the efficiency of acid-precursor-enzyme system to be used in multi-lateral, maximum reservoir contact wells. The evaluation was performed by using samples of polymer based drill-in fluids and dry bulk of sized calcium carbonate in terms of return permeability determination, change in particle size distribution, and weight loss.
Results indicated that the generated acid mainly targeted fine particles of calcium carbonate present in drill-in fluids and dry bulk. This paper presents results of lab investigations and merits (or demerits) of single stage treatments.
Performance Prediction of a Rich Gas/Condensate Reservoir Through Material Balance and PVT Behavior: A Case Study
Authors: Zeidouni M. , Movazi G. H. , Pourghasem B. 
Published: December 2007

Abstract
With a 217 STB/MMSCF liquid-gas ratio (LGR) Sarvak reservoir of CARBONATE field in Iran is one of the richest gas condensate reservoirs in the world. Due to asphaltene precipitation during well shut-in, it is impossible to acquire static pressure data for the reservoir. Since the reservoir pressure is of the main reservoir parameters for performance prediction, material balance calculations was performed based on volumetric and PVT data to determine current reservoir pressure. Furthermore the retrograde condensate deposition (liquid drop-out) is also calculated with the introduction of new parameter of Liquid-Fluid ratio (LFR).
The curve of P/z (the ratio of pressure and gas deviation factor) versus cumulative gas production is conventionally utilized to predict the gas reservoir performance. This method is used for gas condensate reservoirs by replacing gas z-factor with two-phase z-factor (zT). Since reservoir pressure data are not available a direct usage of the above method for CARBONATE-Sarvak reservoir is impossible. As such the experimental data of Constant Volume Depletion (CVD) experiment have been used that simulate the gas condensate fluid behavior. The experimental data are simulated using the PVT simulator of Winprop and tuned to Peng-Robinson EOS to provide non-available parameters and to check the validity of the data. Gas deviation factor at the dew point (zd) was determined as 1.2433 based on which the two-phase z-factor was calculated for different pressures below the dew point pressure. Backward calculation was performed to correct the available experimental data of produced gas percentage to reservoir conditions. The percentage of gas produced to reach the dew point was determined as 3.3029 percent of the Gas Initially In Place (GIIP). Utilizing the GIIP of 620 MMMSCF concluded from volumetric calculations the reservoir will reach the dew point after 20.48MMMSCF of gas production. It is estimated that current reservoir pressure after cumulative gas production (Gp) of 60 MMMSCF would be 5819 Psia. Furthermore the retrograde liquid deposition of the reservoir is determined to be 35.31 MMSTB through the plot of liquid-Feed Ratio (LFR) versus Gp/G.
Determination of Capillary Pressure and Relative Permeability From Spontaneous- Imbibition Data in Gas/Liquid/Rock
Authors: Jia F. , Zhou K. , Li K. 
Published: December 2007

AbstractCapillary pressure and relative permeability are important parameters in reservoir engineering. Techniques frequently used to measure capillary pressure and relative permeability simultaneously are complicated and time-consuming. On the other hand, it is also difficult to measure the two parameters in low permeability rocks. It would be useful if capillary pressure and relative permeability could be inferred from spontaneous imbibition tests. This is because such tests are relatively simple, fast, and economical. In the present study, an analytical approach was developed to determine capillary pressure and relative permeability simultaneously by using experimental data of spontaneous water imbibition into gas- saturated rock. Spontaneous water imbibition tests in different rocks were conducted to test the proposed approach. Both capillary pressure and relative permeability were calculated using the proposed approach and the results were closely equal to those measured using different methods.
Analysis and Interpretation of Interwell Connectivity From Production and Injection Rate Fluctuations Using a Capacitance Model
Authors: Yousef A. A. , Lake L. W. , Jensen J. L. 
Published: December 2007

Abstract
This paper presents new applications of a capacitance model to characterize reservoirs based on temporal fluctuations in injection and production rates. In a previous report (SPE 95322), two coefficients are determined for each injector-producer pair; one parameter, λ, quantifies the connectivity and another, τ, quantifies the fluid storage in the interwell region. This report describes the development of this method into a diagnostic tool to enhance inference about preferential transmissibility trends and the presence of flow barriers.
Applying the capacitance model to results from numerical flow simulation, we found that complex geological conditions are often not easily identified using λ and τ values separately. However, combining them in certain representations enhances the inference about geological features. Two different representations are used: one representation is a log-log plot of the λ's versus the τ's for a producer and nearby injectors, and another representation is the flow capacity plot where the λ's and the τ's are combined as in Lorenz plots. These techniques were tested using a numerical simulator and then applied to data sets from the South Wasson Clearfork and the North Buck Draw fields.
The simulation results and field applications show that the relation between λ's and corresponding τ's are consistent with the known heterogeneity, the distance between wells, and their relative positions. The flow capacity plots and the log-log plots are capable of identifying whether the connectivity of an injector-producer well pair is through fractures, a high-permeability layer, multiple-layers or through partially completed wells. Finally, the approach, based on Lorenz plots, can make use of the extensive literature already available on the interpretation of such plots.
The Katrina Effect: Was There a Bright Side to the Evacuation of Greater New Orleans?
Authors: Vigdor Jacob L 
Published: December 2007

Abstract
This paper uses longitudinal data from Current Population Surveys conducted between 2004 and 2006 to estimate the net impact of Hurricane Katrina-related evacuation on various indicators of well-being. While evacuees who have returned to the affected region show evidence of returning to normalcy in terms of labor supply and earnings, those who persisted in other locations exhibit large and persistent gaps, even relative to the poor outcomes of individuals destined to become evacuees observed prior to Katrina. Evacuee outcomes are not demonstrably better in destination communities with lower initial unemployment or higher growth rates. The impact of evacuation on total income was blunted to some extent by government transfer payments and by self-employment activities. Overall, there is little evidence to support the notion that poor underemployed residents of the New Orleans area were disadvantaged by their location in a relatively depressed region.
Proposal for a standardised identification of the mono‐exponential terminal phase for orally administered drugs
Authors: Scheerans Christian , Derendorf Hartmut , Kloft Charlotte 
Published: December 2007

AbstractThe area under the plasma concentration‐time curve from time zero to infinity (AUC0–inf) is generally considered to be the most appropriate measure of total drug exposure for bioavailability/bioequivalence studies of orally administered drugs. However, the lack of a standardised method for identifying the mono‐exponential terminal phase of the concentration‐time curve causes variability for the estimated AUC0–inf. The present investigation introduces a simple method, called the two times tmax method (TTT method) to reliably identify the mono‐exponential terminal phase in the case of oral administration. The new method was tested by Monte Carlo simulation in Excel and compared with the adjusted r squared algorithm (ARS algorithm) frequently used in pharmacokinetic software programs. Statistical diagnostics of three different scenarios, each with 10 000 hypothetical patients showed that the new method provided unbiased average AUC0–inf estimates for orally administered drugs with a monophasic concentration‐time curve post maximum concentration. In addition, the TTT method generally provided more precise estimates for AUC0–inf compared with the ARS algorithm. It was concluded that the TTT method is a most reasonable tool to be used as a standardised method in pharmacokinetic analysis especially bioequivalence studies to reliably identify the mono‐exponential terminal phase for orally administered drugs showing a monophasic concentration‐time profile. Copyright © 2007 John Wiley & Sons, Ltd.
Molecular basis for skeletal variation: insights from developmental genetic studies in mice
Authors: Kappen C. , Neubüser A. , Balling R. , Finnell R. 
Published: December 2007

AbstractSkeletal variations are common in humans, and potentially are caused by genetic as well as environmental factors. We here review molecular principles in skeletal development to develop a knowledge base of possible alterations that could explain variations in skeletal element number, shape or size. Environmental agents that induce variations, such as teratogens, likely interact with the molecular pathways that regulate skeletal development.Birth Defects Res (Part B), 80:425–450, 2007. © 2007 Wiley‐Liss, Inc.
Materialgesetz‐Formulierung für Riss‐Kontaktelemente in FEM‐Berechnungen
Authors: Fischer Jürgen 
Published: December 2007

AbstractBei FEM‐Berechnungen von Stahlbetontragwerken mit diskretem Rissverlauf unter Verwendung von Kontaktelementen besteht bei Mixed‐Mode Beanspruchungen der Risse die Schwierigkeit, dass hierfür keine allgemein anerkannten Materialgesetzformulierungen existieren. Es wird daher ein Vorschlag unterbreitet, wie ein solches Materialgesetz für die Kontaktelemente aussehen könnte, welches eine Kopplung des Rissverhaltens senkrecht und parallel zum Riss berücksichtigt und auf bisher vorliegenden Forschungsergebnissen basiert. Am Beispiel von Dübelauszugsversuchen wird gezeigt, dass mit diesem Vorschlag sehr gute Ergebnisse erzielt werden können.
Low‐temperature synthesis of 2′‐deoxyadenosine using immobilized psychrotrophic microorganisms
Authors: Fernández‐Lucas J. , Condezo L.A. , Quezada M.A. , Sinisterra J.V. 
Published: December 2007

AbstractSelective biocatalyzed synthesis of 2′‐deoxyadenosine from 2′‐deoxypyrimidine nucleosides was carried out using free or immobilized whole cells. The reaction was performed at 57°C without secondary reactions. Two psychrotrophic microorganisms, Bacillus psychrosaccharolyticus and Psychrobacter immobilis, are described for the first time as active and specific strains for the synthesis of 2′‐deoxyadenosine. Adenosine deaminase activity was not detected. Whole cells were immobilized in different matrixes. Calcium alginate and calcium pectate gave the best biocatalysts. The synthesis of 2′‐deoxyadenosine follows an apparent first order kinetic expression. External mass transfer control was negligible as deduced from ks, NA, and Ω values. Internal mass transfer was the rate controlling step according to ηT and ϕ values. Biotechnol. Bioeng. 2008;100: 213–222. © 2007 Wiley Periodicals, Inc.
An efficient approach to automate the manual trial and error calibration of activated sludge models
Authors: Sin Gürkan , De Pauw Dirk J.W. , Weijers Stefan , Vanrolleghem Peter A. 
Published: December 2007

AbstractAn efficient approach is introduced to help automate the rather tedious manual trial and error way of model calibration currently used in activated sludge modeling practice. To this end, we have evaluated a Monte Carlo based calibration approach consisting of four steps: (i) parameter subset selection, (ii) defining parameter space, (iii) parameter sampling for Monte Carlo simulations and (iv) selecting the best Monte Carlo simulation thereby providing the calibrated parameter values. The approach was evaluated on a formerly calibrated full‐scale ASM2d model for a domestic plant (located in The Netherlands), using in total 3 months of dynamic oxygen, ammonia and nitrate sensor data. The Monte Carlo calibrated model was validated successfully using ammonia, oxygen and nitrate data collected at high measurement frequency. Statistical analysis of the residuals using mean absolute error (MAE), root mean square error (RMSE) and Janus coefficient showed that the calibrated model was able to provide statistically accurate and valid predictions for ammonium, oxygen and nitrate. This shows that this pragmatic approach can perform the task of model calibration and therefore be used in practice to save the valuable time of modelers spent on this step of activated sludge modeling. The high computational demand is a downside of this approach but this can be overcome by using distributed computing. Overall we expect that the use of such systems analysis tools in the application of activated sludge models will improve the quality of model predictions and their use in decision making. Biotechnol. Bioeng. 2008;100: 516–528. © 2007 Wiley Periodicals, Inc.
Efficiency assessment of the one‐step production of astaxanthin by the microalga Haematococcus pluvialis
Authors: Del Río Esperanza , Acién F. Gabriel , García‐Malea M. Carmen , Rivas Joaquín , Molina‐Grima Emilio , Guerrero Miguel G. 
Published: December 2007

AbstractContinuous cultivation of Haematococcus pluvialis under moderate nitrogen limitation represents a straightforward strategy, alternative to the classical two‐stage approach, for astaxanthin production by this microalga. Performance of the one‐step system has now been validated for more than 40 combinations of dilution rate, nitrate concentration in the feed medium, and incident irradiance, steady state conditions being achieved and maintained in all instances. Specific nitrate input and average irradiance were decisive parameters in determining astaxanthin content of the biomass, as well as productivity of the system. The growth rate of the continuous photoautotrophic cultures was a hyperbolic function of average irradiance. As long as specific nitrate input was above the threshold value of 2.7 mmol/g day, cells performed green and astaxanthin was present at basal levels only. Below the threshold value, under moderate nitrogen limitation conditions, astaxanthin accumulated to reach cellular levels of up to 1.1% of the dry biomass. Increasing irradiance resulted in enhancement of astaxanthin accumulation when nitrogen input was limiting, but never under nitrogen sufficiency. Mean daily productivity values of 20.8 ± 2.8 mg astaxanthin/L day (1.9 ± 0.3 g dry biomass/L day) were consistently achieved for a specific nitrate input of about 0.8 mmol/g day and an average irradiance range of 77–110 µE/m2 s. Models relating growth rate and astaxanthin accumulation with both average irradiance and specific nitrate input fitted accurately experimental data. Simulations provided support to the contention of achieving efficient production of the carotenoid through convenient adjustment of the determining parameters, and yielded productivity estimates for the one‐step system higher than 60 mg astaxanthin/L day. The demonstrated capabilities of this production system, as well as its product quality, made it a real alternative to the current two‐stage system for the production of astaxanthin‐rich biomass. Biotechnol. Bioeng. 2008;100: 397–402. © 2007 Wiley Periodicals, Inc.