bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulating the ES-SAGD Process With Solvent Mixture in Athabasca Reservoirs
Authors: Deng X. , Huang H. , Zhao L. , Law D.H.-S. , Nasr T.N.
Published: March 2010

Abstract

The ES-SAGD process was developed to improve the energy and oil drainage efficiency of the SAGD process. The idea of the ES-SAGD process is to co-inject solvent with steam and the co-injected solvent mixes with the bitumen to further reduce the viscosity of the heated bitumen along the boundary of the steam chamber thus enhances the oil recovery. Practically, the co-injected solvent will be a solvent mixture (such as diluent /naphtha) because of its availability and reduced cost than a pure hydrocarbon. This paper reports the results of an ES-SAGD lab test conducted with steam and diluent co-injection using Athabasca bitumen. To simulate the ES-SAGD test, a pseudo-component scheme to represent the complex solvent mixture in the numerical model is derived, based on the diluent composition and measured PVT data. The behaviours and effects of the co-injected solvent in the ES-SAGD process are analyzed through detailed history matching of the ES-SAGD test. Numerical sensitivity analyses are also performed to investigate the effects of some key parameters in the numerical approach.

Introduction

The Steam Assisted Gravity Drainage (SAGD)(1) and the Vapour Extraction (VAPEX)(2), combined with the horizontal well technology, are being developed to recover the enormous heavy oil and bitumen resources in Western Canada. The SAGD process has been successfully field-tested and is in the early stage of commercial-scale application, while the VAPEX process is still at the piloting stage. Both processes have their advantages and disadvantages. The advantage of the SAGD process is its high oil production rate. However, the high production rate of the SAGD process is associated with intensive energy consumption and CO2 emissions from burning natural gas to generate steam, and costly post-production water treatment. The VAPEX process, on the other hand, has the advantage of lower energy consumption and water usage, and therefore less CO2 emission and water treatment cost. However, the major drawbacks of the VAPEX process are its relatively lower oil production rate and the additional cost of solvent.
Feasibility of Monitoring Gas-Hydrate Production With Time-Lapse Vertical Seismic Profiling
Authors: Kowalsky Michael B. , Nakagawa Seiji , Moridis George J.
Published: March 2010

Many studies involving the application of geophysical methods in the field of gas hydrates have focused on determining rock-physics relationships for hydrate-bearing sediments, with the goal being to delineate the boundaries of gas-hydrate accumulations and to estimate the quantities of gas hydrate that such accumulations contain using remote-sensing techniques. However, the potential for using time-lapse geophysical methods to monitor the evolution of hydrate accumulations during production and, thus, to manage production has not been investigated. In this work, we begin to examine the feasibility of using time-lapse seismic methods—specifically, the vertical-seismic-profiling (VSP) method—for monitoring changes in hydrate accumulations that are predicted to occur during production of natural gas. A feasibility study of this nature is made possible through the coupled simulation of large-scale production in hydrate accumulations and time-lapse geophysical (seismic) surveys. We consider a hydrate accumulation in the Gulf of Mexico that may represent a promising target for production. Although the current study focuses on one seismic method (VSP), this approach can be extended easily to other geophysical methods, including other seismic methods (e.g., surface seismic or crosshole measurements) and electromagnetic surveys. In addition to examining the sensitivity of seismic attributes and parameters to the changing conditions in hydrate accumulations, our long-term goals in this work are to determine optimal sampling strategies (e.g., source frequency, time interval for data acquisition) and measurement configurations (e.g., source and receiver spacing for VSP), while taking into account uncertainties in rock-physics relationships. The numerical-modeling strategy demonstrated in this study may be used in the future to help design cost-effective geophysical surveys to track the evolution of hydrate properties. Here, we describe the modeling procedure and present some preliminary results.
Numerical Modelling of Geomechanical Response of Sandy-Shale Formation in Oil Sands Reservoir During Steam Injection
Authors: Du J. , Wong R.C.K.
Published: March 2010

Abstract

In this study, we conducted numerical simulations of steam injection into a horizontal well. A sandy-shale layer with thickness of 1 metre is located 2 metre above a horizontal injection well. The numerical simulations intend to study the variations of the stress state and the permeability in the sandy-shale layer during steam injection, and to provide useful effective stress paths for laboratory experiments to follow when testing material properties of the sandy-shale. A self-developed coupled geomechanics and thermal multi-phase flow simulator was employed to conduct the simulation cases. A strain-induced permeability model was used to describe the anisotropic permeability change of the sandy-shale caused by steam injection. The simulation results demonstrate that the permeability of 5 and 50 md for the sandy-shale in two simulation cases is sufficient to allow pore pressure dissipation to occur, therefore, preventing tensile or shear failure of sandy-shale as a result of high thermal-induced pore pressure. The stress paths within the sandy-shale are approaching the failure envelope as steam injection goes on indicating simultaneous influence of the temperature and the pore pressure on the stress state change.

Introduction

Sandy-shale formations of several metres in thickness frequently exist in oil sands deposit. Their material properties, sedimentary characteristics and distribution in a steam-assisted gravity drainage (SAGD) reservoir are important factors that determine SAGD performance and strategies of positioning horizontal well-pairs. It has been confirmed that sandy-shale formations are usually very sandy and discontinuous; therefore, they are expected to be permeable to varying degrees during SAGD operations. This is completely different from the interbedded shales that have extremely low permeability and can be considered as impermeable.

Analysis of stress state change and anisotropic permeability variation in the sandy-shale requires conducting coupled simulation of geomechanics and thermal reservoir flow. Numerical modelling of the coupled processes is historically carried out in the areas of geomechanics modelling and the reservoir simulation. Gutierrez and Lewis(1) extend Biot's theory to multi-phase fluid flow in deformable porous media. Based on their formulation, they conclude that the coupling between the geomechanics and the multi-phase flow occurs simultaneously. Thus, fully coupled system equations of deformations, multi-phase flow and heat transfer should be solved simultaneously.
Development of an Optimized Tubular Material for Thermal Slotted Liner Completions
Authors: Dall'Acqua D. , Turconi G. Lopez , Monterrubio I. , Allen M.D.
Published: March 2010

Use of slotted liner as a sand control device is widespread in SAGD operations in Western Canada. Operating temperatures in such thermal EOR wells can be extreme, sometimes exceeding 270°C (518°F), and the associated compressive axial mechanical strain imposed by constrained thermal expansion can load the pipe material beyond its proportional limit. Selection of an appropriate slotted liner configuration is critical to ensure that structural stability (and hence sand control) is reliably maintained during operation. Mechanical properties of the tubular material at elevated temperature strongly influence the compressive stability of the liner structure, but lower-temperature properties also affect the ease of pipe slotting on a production scale, which is typically achieved by plunging thin saw blades through the pipe wall. Common slotting issues include breakage or unacceptably high blade wear rates.

This paper describes the developmental basis for a new tubular material formulation that is specifically optimized for thermal structural stability in SAGD applications without compromising slotting performance. Elevated-temperature mechanical properties are designed to prevent compressive buckling failures and to minimize strain localization potential. Results of analytical and experimental work (including stability analysis of the liner structure, thermo-mechanical material testing, and bench-scale slotting trials) are described.

Introduction

Ongoing rapid development of bitumen reserves in Western Canada has led to an increased focus on developing robust tubular design bases for extreme service conditions in in-situ recovery schemes such as SAGD. Specifically, cemented or frictionally-constrained tubulars are subjected to thermally-induced, deformation-controlled loading that leads to a unique set of design challenges and more stringent requirements for post-yield material response than those employed in traditional elastic design. Slotted liner is used as a sand control device in a majority of SAGD wells.

Slotted liners used in thermal applications must provide a stable structure under extreme thermally-induced compressive loading in order to maintain wellbore access and to prevent excessive sand from entering the wellbore. While the deformation resistance of slotted liners depends on geometric attributes such as pipe wall thickness, slotting configuration, and slot geometry, material properties have a considerable impact on structural stability and localization resistance.
Is a Paradigm Shift in Produced Water Treatment Technology Occurring at SAGD Facilities?
Authors: Heins W.F.
Published: March 2010

Abstract

Over the past few years, a paradigm shift has occurred in the treatment of produced water for steam-assisted gravity drainage (SAGD) heavy oil recovery facilities. The shift has been away from the use of warm lime softening (WLS), filtration and weak acid cation (WAC) ion exchange to pretreat de-oiled produced water to an approach using falling film, mechanical vapour compression (MVC) evaporation to produce steam generator feedwater. Today, approximately 16 such evaporators are operating, under construction or in various stages of delivery in Alberta and overseas.

Many new SAGD facilities are evaluating MVC evaporation as the "baseline?? approach with the "traditional?? WLS/WAC system being treated as a secondary alternative, along with other alternative approaches. This shift in methodology is because of a combination of technical and economic factors, increased reliability and availability associated with MVC evaporation and, perhaps most significantly, because of the potential to use standard drum boilers and alternative fuels for steam generation [as opposed to the use of once-through steam generators (OTSGs) required with the traditional approach]. Requirements for increased water recovery at SAGD facilities, which are made possible by MVC evaporation, also play a significant role in the shift towards produced water evaporation.

This paper presents a technical and economic evaluation of the shift towards produced water evaporation, increased water reuse and recovery, use of standard drum boilers and the use of alternate fuels at SAGD heavy oil recovery facilities.

Introduction

Over the past few years, water treatment and steam generation methods for heavy oil recovery processes have rapidly evolved. Traditionally, especially for cyclic steam operations, OTSGs, driven by natural gas, have been used to produce about 80% quality steam (80% vapour, 20% liquid) for injection into the well to fluidize the heavy oil. However, the relatively new heavy oil recovery method, referred to as SAGD, requires 100% quality steam for injection. To allow the continued use of OTSG for SAGD applications, a series of vapour/liquid separators is required to produce the required steam quality. For both SAGD and non-SAGD applications, pretreatment of the OTSG feedwater has consisted of silica reduction in a hot lime softener (HLS) or WLS, filtration and hardness removal by WAC ion exchange.
Experimental Investigation of Immiscible Gas Process Performance for Medium Oil
Authors: Zhang Y.P. , Sayegh S.G. , Luo P. , Huang S.
Published: March 2010

Abstract

Immiscible CO2 injection is a potentially viable method of enhanced oil recovery (EOR) for medium oil reservoirs in southwestern Saskatchewan. The relatively high reservoir pressures could result in a large extent of CO2 dissolution, significant oil viscosity reduction and oil swelling. Laboratory corefloods were used to compare the performance of different modes of CO2 injection into a medium-gravity oil system. The following methods were compared: injection of a single CO2 slug chased by water, simultaneous injection of water/CO2, and different water-alternating-gas (WAG) cycles.

The results indicate that both a single CO2 slug and the first WAG cycle in a series produced oil very efficiently, possibly owing to good gas/oil contact at the relatively high residual oil saturation at this stage. The simultaneous injection of water/CO2 was not as effective as a single CO2 slug, possibly because the co-injected water shielded the oil from being contacted by the gas. Among the four runs, a coreflood with four WAG cycles recovered the most incremental oil—20.58% initial oil in place (IOIP)—while the co-injection process produced the least (8.91% IOIP).

This experimental study suggests that the immiscible CO2 EOR process is viable for medium oil reservoirs with relatively high pressures, and that proper process application is important for maximizing additional oil production.

Introduction

Miscible/immiscible CO2 flooding is an increasingly popular EOR technique. So far, most of the CO2 miscible/immiscible processes have been applied in light oil reservoirs, and there has been little application in medium oil reservoirs. The in-place resources of medium oils, defined as 20 - 30°API, in Saskatchewan are estimated at up to 1,338 × 106 m3 (8.42 billion barrels)(1). Most of these reservoirs are characterized by thin pay (2 to 10 metres in thickness) and shaly sand, and they have been under production for over four to five decades. The estimated average recovery by conventional waterflood, as listed in Table 1, is only approximately 23% IOIP because this method has generally exhibited early water breakthrough and high water cuts owing to the unfavourably high water-to-oil mobility ratio. By adapting miscible/immiscible CO2 flooding technologies that have matured in light oil applications, the immiscible CO2 process is potentially viable for recovering additional oil from these medium oil reservoirs if we can improve its displacement and sweep efficiency(2).
Computed Tomography Study of VAPEX Process in Laboratory 3D Model
Authors: Wu G.Q. , Kantzas A. , Salama D.
Published: March 2010

Abstract

The vapour extraction (VAPEX) process has been an intense research topic in recent years as an alternative technology to thermal recovery methods for heavy oil and bitumen resources. Most previous 2D transparent models had simulated the vapour chamber evolution behaviour of a vertical slice of the reservoir; however, the longitudinal vapour chamber evolution characteristic in 3D geometry could not be detected.

This paper presents the results of 3D monitoring of the VAPEX process in a laboratory model, using computed tomography (CT) technology to investigate the vapour chamber expansion behaviour in both radial and longitudinal directions.

The results show that in 3D geometry, "V?? shape vapour chamber expansion was a localized phenomenon. The dominant characteristic was that solvent gas first broke through upward to the top, progressing through the high-permeability zone by gravity segregation, forming a vapour chamber at the top. It then expanded downward from the top as the experiment progressed. From the numerical analysis of the CT images, the in-situ porous medium's porosity, density and oil saturation profiles were obtained. The results further imply that contained gravity drainage may be the key for the success of the VAPEX process.

Introduction

For the more than 400 billion m3 heavy oil and bitumen deposits in Canada, only 10% is surface minable. The major part of the deposits has to be relied on in-situ recovery processes(1). However, because of their high viscosities and low-degree API gravities in native state(2), these reservoirs can only be recovered with low recovery efficiency by conventional methods. For example, primary recovery in the best of these heavy oil reservoirs is approximately 6% of the original oil in place (OOIP). Subsequent waterflooding can improve the recovery to an extent of 1% ~ 2% incremental of OOIP(3). In order to more effectively recover these reserves, enhanced oil recovery (EOR) or improved oil recovery (IOR) methods have to be directly applied(4). The main technology challenge is to reduce the heavy oil viscosity in-situ(5). As the oil viscosity is very sensitive to temperature, thermal recovery methods seem to be very effective and have been widely researched and piloted(6), including cyclic steam simulation (CSS), in-situ combustion (ISC), steam assisted gravity drainage (SAGD) and steamflooding(7). The SAGD process has been commercially used by several oil companies in Canada. However, the SAGD process is not always applicable for all heavy oil reservoirs; some economic constraints arise if the high cost of steam generation and excessive heat losses in some thin oil reservoirs are considered(8). As alternatives, non-thermal processes such as solvent-based processes are still a logical choice to recover such heavy oil/bitumen reservoirs(9).
Multiphase Flow in Fractures: Co-Current and Counter-Current Flow in a Fracture
Authors: Shad S. , Gates I.D.
Published: March 2010

Abstract

Multiphase flow through fractures is important not only for naturally fractured petroleum reservoirs but also for underground disposal of radioactive waste and geothermal hydrotransport, cap rock integrity, as well as underground water and aquifer flow. For instance, naturally fractured reservoirs located in Northern Alberta contain large quantities of heavy oil and bitumen. It still remains unclear how multiple phases flow in fractures and how to determine the relative permeability of each phase that can be used in reservoir simulators. In typical practice, simulation of fractured reservoirs uses, in general, very crude and unproven hypotheses such as linear relative permeability curves. However, by using inaccurate relative permeability curves, large errors of the predicted oil recovery can result. In this work, a relatively simple flow model is derived to determine analytic functions for the relative permeability curves versus phase saturation in a single fracture. The results show that relative permeability is not just a function of the fluid saturations but also of the fluid properties and flow pattern within the fracture itself. The analysis reveals that at certain viscosity ratios and flow pattern conditions, the relative permeability of one phase can exceed unity owing to lubrication effects. The available experimental data confirms the validity of the proposed model.

Introduction

Fracture-dominated flow is not only important for naturally fractured petroleum reservoirs but also for underground disposal of radioactive waste, geothermal hydrotransport, cap rock integrity, and underground water and aquifer flow. In naturally fractured reservoirs, fractures are highly conductive flow pathways that dominate fluid transport throughout the reservoir. To examine flow of multiphase flow in fractures, many different experimental(1-12), theoretical(13-18) and numerical studies(19-26) have been done. However, flow structure and momentum transfer between flowing phases in fractures are not yet well understood(4, 27, 28). Transport parameters such as relative flow rates of phases and the relationship between fracture geometry and flow remain unclear. The relative permeability concept can be used to describe behaviour of multiple phases flowing together through porous media, interfering and aiding each other to move under the action of a pressure gradient. Despite the importance of relative permeability in fracture flows, still there is no unique and consistent theory which provides an easy, yet computationally inexpensive, method to calculate relative permeability curves in fractures.
Numerical Simulation and Sensitivity Analysis of Gas-Oil Gravity Drainage Process of Enhanced Oil Recovery
Authors: Jadhawar P.S. , Sarma H.K.
Published: March 2010

Abstract

The oil recovery process is controlled by the rates of gas injection and oil production, relative permeabilities, reservoir heterogeneities and the balance among viscous, capillary and gravity forces. Crestal gas injection in horizontal, vertical or reef type oil reservoirs recovers significant volumes of the residual oil due to the gas-oil gravity drainage mechanism, indicating the significance of gravity forces. This study investigates the effects of the parameters that control the process (e.g., rate of the gas injection and oil production) and reservoir heterogeneities on the overall performance of immiscible gravity drainage enhanced oil recovery (EOR). Reservoir simulation studies are conducted to map effective combinations of these parameters with respect to the oil recovery performance.

Introduction

Gravity forces play an important role at nearly every stage of the producing life of the reservoir, whether it is primary depletion, secondary water or gas injection schemes or tertiary enhanced or improved oil recovery methods(1). They can be advantageously used to maximize oil recovery from the oil bearing zone under investigation through gravity drainage mechanism. Several cases reported in the literature suggest that it could deliver as high as 87 to 95% incremental oil recoveries in contrast to other gas injection EOR methods.

Gas-Oil Gravity Drainage Process

Gravity drainage is a process in which gravity acts as a main driving force and where gas replaces voidage volume(2). It is commonly implemented in either of the dipping or pinnacle reef type reservoirs.

CO2-assisted gravity drainage EOR process is a top-down process in which gas is injected in the gas cap through vertical wells at a rate lower than the critical rate (Figure 1). Critical rate is the rate at which injection gas fingers through oil zone (viscous instabilities) leading to its premature breakthrough at the production wells. Injected gas segregates and creates a gas-oil interface. Controlled oil production is started through horizontal wells placed at the bottom of the oil zone such that the voidage created by oil withdrawal (in addition to minor dissolved volumes) is replaced by the equivalent CO2 injection volume. When this happens, pressure differential across the gas cap and oil zone [that is gas-oil contact (GOC)] stay at or close to zero implying that the pressure in the gas zone behind the CO2 floodfront would be constant(3). This helps to maintain the reservoir pressure nearly constant.
Optimization of Production Performance in a CO2 Flooding Reservoir Under Uncertainty
Authors: Chen S. , Li H. , Yang D.
Published: March 2010

Abstract

CO2  flooding has gained momentum in the oil and gas industry and might be suitable for approximately 80% of oil reservoirs worldwide based on the oil recovery criteria alone. In addition to miscibility, production performance needs to be optimized to achieve higher sweep efficiency and oil recovery. Although many techniques have been made available for production optimization in the upstream oil and gas industry, it is still a challenging task to optimize production performance in the presence of physical and/or financial uncertainties. In this paper, a new technique is developed to optimize production performance in a CO2 flooding reservoir under uncertainty. More specifically, potential uncertainties influencing production performance are analyzed and assessed by using the geostatistical technique. This enables us to integrate the available information within a unified and consistent framework and to generate multiple geological realizations accounting for uncertainty and spatial variability. Subsequently, the net present value (NPV) is selected as the objective function to be optimized by using the genetic algorithm, while well rates of the injectors and the flowing bottomhole pressure for the producers are chosen as the controlling variables. In addition, corresponding modifications have been made to accelerate the convergence speed of the genetic algorithm. A field case is used to demonstrate the procedures of the newly developed technique and the optimized results show that the oil recovery and the NPV can be increased by 6.4% and 9.2%, respectively. It is also found that the genetic algorithm is a powerful and reliable search method to optimize production performance of reservoirs with complex structures.

Introduction

CO2 flooding is considered as a promising and practical enhanced oil recovery (EOR) process because it not only increases oil recovery, but also reduces greenhouse gas emissions by sequestrating CO2 in the depleted reservoirs. In practice, CO2 flooding performance can be greatly affected by the reservoir heterogeneity, which can severely reduce the sweep efficiency, result in early CO2 breakthrough at the producers, and thus, leave a large amount of bypassed oil in the reservoir(1). Therefore, it is of fundamental and practical importance to optimize production performance of a CO2 flooding reservoir.
Impact of Uncertainty of Heavy Oil Fluid Property Measurements
Authors: Zabel F. , Law D.H.-S. , Taylor S. , Zuo J.
Published: March 2010

Abstract

Heavy oil is particularly known for the difficulty it presents in obtaining accurate fluid property measurements. The uncertainty of heavy oil fluid property measurements affects the quality of fluid property data which in turn affecting the accuracy of production forecast. In our investigation, we included the impact from certain heavy oil fluid property uncertainties, including live oil viscosity and saturation pressure [or the initial gas-oil ratio (GOR)]. The reservoir simulations were performed for case studies with a 9°API reservoir fluid and geology similar to those typically found in the Faja region in Venezuela. Two base cases and the underlying process mechanisms were established, one assuming primary production process and one assuming steam-assisted gravity drainage process (SAGD). We then performed sensitivity studies of the different fluid property variations to determine the effect on the process performances. We found that the process mechanism dictated the magnitude of the sensitivity to different fluid properties. The uncertainties of the recovery prediction obtained from a reservoir simulator confirmed importance of selecting accurate fluid property data on the dynamic simulation prediction.

Introduction

In upfront reservoir engineering study, the reservoir and fluid properties are very important input data for the dynamic reservoir simulation as they dictate the accuracy of the simulation prediction. The uncertainties of the reservoir properties, such as the geologic and petrophysic data, are often given more attention than the uncertainties of the fluid properties, such as oil viscosity and initial GOR.

It is well known that there are uncertainties in fluid property data, especially for heavy oil, because accurate measurements of heavy oil properties are quite difficult to obtain. For example, it has been observed that a large variation exists in the heavy oil viscosity measured from different laboratories using different measuring techniques. In addition to the inconsistency from the measurements, fluid sampling is another main source contributing to the accuracy of fluid property data. Therefore, it is essential to study the effect of the variation in fluid properties, such as oil viscosity and oil saturated pressure (or initial GOR), to predict the heavy oil recovery performance by means of dynamic reservoir simulation.
Experimental and Numerical Study of Improving Heavy Oil Recovery by Alkaline Flooding in Sandpacks
Authors: Wang J. , Dong M. , Arhuoma M.
Published: March 2010

Abstract

Chemical flooding has great potential for enhancing heavy oil recovery, especially for reservoirs where thermal methods are not feasible. It has been shown that the formation of emulsions during chemical flooding can effectively improve sweep efficiency and, consequently, increase heavy oil recovery. The mechanism of flow of oil-in-water (O/W) emulsion in porous media has been extensively studied and simulated using the filtration theory. Few studies have been done for the modelling of water-in-oil (W/O) emulsion flow in heavy oil reservoirs. This study experimentally investigated the effective viscosity of W/O emulsion in porous media. Alkaline flooding tests were performed in channelled sandpacks to demonstrate the effectiveness of sweep efficiency improvement by the in-situ produced W/O emulsions. High tertiary oil recoveries were obtained for all these tests. The alkaline flooding process was simulated by including the observed flow behaviour of extra resistance to water phase flow caused by the formation of W/O emulsions, as well as the adsorption of chemicals, interfacial tension reduction, and in-situ generation of W/O emulsions. These laboratory results and the developed simulation technique are proposed as an improvement to the simulation and design of the field-scale projects of chemical flooding for heavy oil recovery.

Introduction

Many heavy oil reservoirs in Western Canada are not suitable for steam injection techniques due to thin pay thickness. Both field and laboratory results demonstrate that waterflooding of heavy oil reservoirs can only achieve a very low oil recovery. The main causes for the poor sweep efficiency of waterflooding for these heavy oil reservoirs are very adverse mobility ratio, natural area and vertical reservoir heterogeneity and heterogeneity induced by primary production(1,2). Therefore, improving mobility ratio and blocking water flow through channels are essential for improving heavy oil recovery. The in-situ formation of emulsions during alkaline flooding has been recognized as one of the efficient methods to improve sweep efficiency for heavy oil recovery(3,4,5).

The effectiveness of alkaline flooding for acidic crudes was recognized as early as in the 1920s(6). Jennings et al.(3) proposed the mechanism of emulsification and entrapment for alkaline flooding. They carried out caustic flooding tests using a heavy oil. Their results showed that the in-situ produced O/W emulsions tended to plug water fingering and channels, resulting in improved sweep efficiency. Johnson(7) summarized possible mechanisms of alkaline flooding to improve oil recovery: dispersion and entrainment, wettability reversal, and emulsification and entrapment. The formation of W/O emulsions was also observed as a mechanism of improving oil recovery(8,9).
Enhancement of the Catalytic Performances in the Case of a Consecutive-Parallel Reaction Scheme
Authors: Benguerba Yacine , Djellouli Brahim
Published: March 2010

The determination of the optimal distribution of the catalytic activity profile, which maximizes the catalytic effectiveness and the selectivity, in created unsteady state conditions, is analyzed and treated numerically for the case of a consecutive-parallel reaction scheme. The optimal active element distribution is always a Dirac-? function, i.e., all the catalyst is deposited at a specific distance from the center of the catalytic pellet. The main result is that the location of this optimal position varies with time and that the modulation, of the temperature and the reactants concentrations of the external bulk fluid, leads to a considerable increase of the catalytic effectiveness. On the other hand the selectivity was found to be not affected by the modulation except for higher values of ?2 (?2>0.3).
Modelling of the Drying Kinetics of Opuntia Ficus Indica Fruits and Cladodes
Authors: Touil Amira , Chemkhi Saber , Zagrouba Fethi
Published: March 2010

The effect of the drying rates of fruit and cladode of Opuntia Ficus Indica was examined at different temperatures. The experimental drying curves show only a falling drying rate period. The values of drying rate of prickly pear (fruit and cladode) almost doubled when the drying temperature was increased from 40 to 60°C. The experimental drying data were applied to various drying equation (Logarithmic; Wang and Singh, Henderson and Pabis, MMF model and Midilli equation). Midilli equation was optimal for characterizing drying behaviour of prickly pear for the whole range of temperature with a correlation coefficient of 99.99% for the fruit and the cladode and a standard error of 0.0015 for the fruit and 0.0017 for the cladode.
Migration as Trade Facilitation: Assessing the Links between International Trade and Migration
Authors: Hatzigeorgiou Andreas
Published: March 2010

The cost of international trade matters. As traditional barriers to trade continue to diminish in importance, additional ways to lower trade costs become increasingly important to promoting international trade. Migrants can help lower trade costs between their country of birth and their country of residence by providing an information channel that reduces friction and facilitates trade relations. This paper applies a gravity model to a large set of data about developed and developing countries to estimate the extent of the relationship between migrants and trade. The results suggest that both immigrants and emigrants are significantly related to higher trade volumes. Immigrants seem to be especially good at facilitating trade in differentiated goods, for which information costs are particularly important.
Effect of dielectric medium on angiotensin converting enzyme inhibitors binding to Zn2+
Authors: Šramko Martin , Šille Július , Ježko Pavol , Garaj Vladimír
Published: March 2010

The Becke3LYP density functional was used to study structural and thermodynamic parameters of bivalent zinc cation complexes with selected substrates and ACE inhibitors (H2O/OH−, neutral forms of captopril, zofenoprilat, omapatrilat, CH3CONHCH3, and N-terminal anions of captopril, zofenoprilat, omapatrilat, enalaprilat, perindoprilat, trandolaprilat, and fosinoprilat). The combination of DFT and the conductor-like polarizable continuum model (CPCM) were employed to compute the Gibbs interaction energies (ΔG) between Zn2+ and the selected ACE inhibitors for dielectric media with ɛ = 5 (to simulate the protein environment) and for water media (ɛ = 78.39) for comparison purposes. The results show that ΔG is sensitive to the dielectric constant of the environment and that lower dielectric medium favors the binding of inhibitors to the zinc cation.
Voltammetry of resazurin at a mercury electrode
Authors: Çakir Semiha , Arslan Emine
Published: March 2010

Electrochemical behavior of resazurin on HMDE in Britton-Robinson (B-R) buffers (pH 2.0–10.0) was studied using the square-wave voltammetry (SWV), square-wave adsorptive stripping voltammetry (SWAdSV), and cyclic voltammetry (CV) techniques. The voltammogram of resazurin in B-R buffer at pH < 4.0 exhibited two cathodic reduction peaks. The voltammetric peaks were obtained at −0.144 V (reversible) and −1.250 V (irreversible) at pH 3.2, and correspond to the reduction of resorufin to dihydroresorufin and to the catalytic hydrogen wave, respectively. At pH > 4.0, a new irreversible cathodic reduction peak, assigned to the protonation of N-oxide on the phenoxazin ring, was observed. Electrochemical parameters (I p/E p, I p/v, I p/pH, I p/t acc) of the compound were determined. From the voltammetric data, electrochemical reduction mechanisms for all peaks have been suggested. Maximum peak current for the reversible peak was obtained at pH 4.1. A linear relationship between the current and concentration was determined, and also the lowest detection limit was found as 3.25 × 10−8 mol L−1 and 1.98 × 10−10 mol L−1 for SWV and SWAdSV, respectively.
Model predictive control of a CSTR: A hybrid modeling approach
Authors: Kvasnica Michal , Herceg Martin , Čirka Ľuboš , Fikar Miroslav
Published: March 2010

This paper presents a case study of model predictive control (MPC) applied to a continuous stirred tank reactor (CSTR). It is proposed to approximate nonlinear behavior of a plant by several local linear models, enabling a piecewise affine (PWA) description of the model used to predict and optimize future evolution of the reactor behavior. Main advantage of the PWA model over traditional approaches based on single linearization is a significant increase of model accuracy which leads to a better control quality. It is also illustrated that, by adopting the PWA modeling framework, MPC strategy can be implemented using significantly less computational power compared to nonlinear MPC setups.
A simple turbidimetric flow injection system for saccharin determination in sweetener products
Authors: Mendes Camila , Laignier Emiliane , Brigagão Maisa , Luccas Pedro , Tarley César
Published: March 2010

A new method for saccharin determination in liquid sweetener products was developed. The method is based on the precipitation reaction of Ag(I) ions with saccharin in aqueous medium (pH 3.0), using a flow injection analysis system with merging zones, the suspension was stabilized with 5 g L−1 Triton X-100. All experimental parameters influencing the flow injection system were optimized by means of chemometric approaches. The linear analytical curve was built from 2.4 g L−1 up to 9.64 g L−1 (r = 0.9968) with a quantification limit of 2.40 g L−1. The precision assessed as relative standard deviation (n = 10) was found to be 1.75 % for the saccharin concentration of 7.20 g L−1. Based on interference studies performed with the substances commonly found in liquid sweeteners, such as sodium cyclamate, methylparaben, sodium aspartame, and benzoic and citric acids, at the analyte to interferent mole ratio of up to 1: 10, no interference with the saccharin determination was observed. The presence of chloride ions interferes with the method, but a preceding liquid-liquid saccharin extraction with ethyl acetate was successfully employed to overcome this drawback. Accuracy of the method in sweetener products was evaluated by a comparison with the HPLC method.
Synthesis, spectral and electrochemical study of coordination molecules Cu4OX6L4: 4-cyanopyridine Cu4OBrnCl(6−n)(4-CNpy)4 complexes
Authors: Ondrejovič Gregor , Kotočová Adela , Koman Marian , Segľa Peter
Published: March 2010

New 4-cyanopyridine halide and mixed-halide Cu4OBrnCl(6−n)(4-CNpy)4 complexes (4-CNpy = 4-cyanopyridine, n = 0–6) were synthesised, characterised, and studied by infrared spectra, electronic spectra, and cyclic voltammetry. Infrared spectra revealed donor-acceptor vibrational couplings of the Cu4O, Cu-Cl, and Cu-N stretching vibrations with the in-plane and out-of-plane pyridine ring vibrations. The infrared spectra, electronic spectra, and half-wave potentials correspond to a weak donor and a strong acceptor behaviour of the 4-cyanopyridine ligands and to π-back bonding, Cu(II)→pyridine rings. The results were compared with the related pyridine and 4-substituted pyridine complexes.
What Is Diversity?
Authors: Silverman Sarah K.
Published: March 2010

The term diversity seems to carry a wide array of definitions. These definitions can affect the ways teachers understand and employ the term as well as the ways in which they approach sociocultural differences in their classrooms. The current study included a survey of preservice teachers’ beliefs about various identities associated with terms such as diversity and multicultural in order to better understand what is meant by these terms. Each identity was explored within the context of the classroom, including efficacy for multicultural instruction, sense of responsibility for teaching about diverse people, and sense of advocacy for oppressed groups. The findings suggest preservice teachers hold a limited view of what constitutes diversity, which affects their senses of efficacy, responsibility, and advocacy as individuals and as teachers.
Analysis of diagnostic confidence: Application to data from a prospective randomized controlled trial of CT for acute abdominal pain
Authors: Ng Chaan S. , Palmer Christopher R.
Published: March 2010

Background: Changes in diagnostic confidence are used as a measure of a test's efficacy. There are several methods for analyzing such data, but it is unclear which are most robust.

Purpose: To compare analytical methods for assessing diagnostic confidence, applied to data from a prospective study of computed tomography (CT) for acute abdominal pain.

Material and Methods: Changes in diagnostic confidence in an illustrative case study were evaluated using five methods: “Basic,” “Retained diagnosis,” “Omary,” “Tsushima,” and “Score-based.” The case study was a randomized controlled trial of patients admitted to hospital for acute abdominal pain for whom immediate CT was not indicated, comparing “early” CT undertaken within 24 h of admission versus routine standard practice. Admitting surgeons recorded their diagnoses and confidences (5-point scale, 10–90%) both on admission and after 24 h. One- and two-sample t tests, and intention-to-treat and as-treated analyzes, were performed using all five analytic methods.

Results: In the case study, 118 patients were randomized to early CT ( n=55) or standard practice ( n=63). Mean (SD) diagnostic confidence increased between the two time points by 20.7 (25.2)% and 13.0 (24.9)%, respectively. Early CT showed increases in diagnostic confidence by all one-sample analyzes (all P<0.055). Compared with standard practice, early CT showed significant increases in diagnostic confidence on an a) as-treated basis when using Basic, Omary and Score-based analyzes ( P<0.045), but not by the other two analytic methods, and b) intention-to-treat, only by Omary analysis.

Conclusion: The method of analysis used to evaluate diagnostic confidence can influence conclusions about a test's efficacy. Methods incorporating the soundest analytical principles are recommended.
Differentiation between grade 3 and grade 4 articular cartilage defects of the knee: Fat-suppressed proton density-weighted versus fat-suppressed three-dimensional gradient-echo MRI
Authors: Lee So Yeon , Jee Won-Hee , Kim Sun Ki , Koh In-Jun , Kim Jung-Man
Published: March 2010

Background: Fat-suppressed (FS) proton density (PD)-weighted magnetic resonance imaging (MRI) and FS three-dimensional (3D) gradient-echo imaging such as spoiled gradient-recalled (SPGR) sequence have been established as accurate methods for detecting articular cartilage defects.

Purpose: To retrospectively compare the diagnostic efficacy between FS PD-weighted and FS 3D gradient-echo MRI for differentiating between grade 3 and grade 4 cartilage defects of the knee with arthroscopy as the standard of reference.

Material and Methods: Twenty-one patients who had grade 3 or 4 cartilage defects in medial femoral condyle at arthroscopy and knee MRI were included in this study: grade 3, >50% cartilage defects; grade 4, full thickness cartilage defects exposed to the bone. Sagittal FS PD-weighted MR images and FS 3D gradient-echo images with 1.5 T MR images were independently graded for the cartilage abnormalities of medial femoral condyle by two musculoskeletal radiologists. Statistical analysis was performed by Fisher's exact test. Inter-observer agreement in grading of cartilage was assessed using κ coefficients.

Results: Arthroscopy revealed grade 3 defects in 17 patients and grade 4 defects in 4 patients in medial femoral condyles. For FS 3D gradient-echo images grade 3 defects were graded as grade 3 ( n=15) and grade 4 ( n=2), and all grade 4 defects ( n=4) were correctly graded. However, for FS PD-weighted MR images all grade 3 defects were misinterpreted as grade 1 ( n=1) and grade 4 ( n=16), whereas all grade 4 defects ( n=4) were correctly graded. FS 3D gradient-echo MRI could differentiate grade 3 from grade 4 defects ( P=0.003), whereas FS PD-weighted imaging could not ( P=1.0). Inter-observer agreement was substantial (κ=0.70) for grading of cartilage using FS PD-weighted imaging, whereas it was moderate (κ=0.46) using FS 3D gradient-echo imaging.

Conclusion: FS 3D gradient-echo MRI is more helpful for differentiating between grade 3 and grade 4 cartilage defects than is FS PD-weighted imaging.
MRI of the cat brain in the study of vascular permeability after intraarterial carotid injection of triolein
Authors: Ryu Ji Hwa , Jeong Yeon Joo , Kim Hak Jin , Kim Dong Hyun , Kim Dong Chan , Kim Myong Joon , Kim Yong Woo , Choi Seon Hee , Cho Byung Mann , Moon Tae Yong
Published: March 2010

Background: Triolein emulsion embolization into the carotid artery depicts reversible increased vascular permeability that can promote the effect of chemotherapy or can reduce the amount of chemotherapeutic drugs for equivalent effectiveness.

Purpose: To establish the minimum dosage of 0.5% triolein for studying vascular permeability changes in a triolein emulsion model.

Material and Methods: Sixty-six cats were divided into six groups based on the amount of emulsified triolein (0.5%) infused into the carotid artery: group 1 ( n=12, 6 ml/kg), group 2 ( n=12, 4.5 ml/kg), group 3 ( n=12, 3 ml/kg), group 4 ( n=10, 1.5 ml/kg), group 5 ( n=10, 1 ml/kg), and group 6 ( n=10, 3 ml/kg of saline (control group)). T1-weighted, T2-weighted, and post-contrast T1-weighted MRI was performed 2 h after the infusion of the triolein emulsion. Contrast enhancement ratios (CERs) were obtained with pre- and post-contrast T1-weighted images in the ipsilateral and contralateral hemispheres. Signal intensity ratios (SIRs) of the ipsilateral and contralateral hemispheres were evaluated on T2-weighted images. After removal of the brain tissues, edema ratios in the ipsilateral and contralateral hemispheres were obtained from wet versus dry brain weights. Data were statistically evaluated by analysis of variance, followed by the Tukey honestly significant difference test to compare the difference in the mean CER of the ipsilateral and contralateral hemispheres, mean SIR on T2-weighted image, and mean edema ratio between each group when overall significance was attained.

Results: In the ipsilateral hemispheres, the difference in the CER between the control group and groups 1 ( P=0.004), 2 ( P=0.043), and 3 ( P=0.008) were statistically significant. The difference in the CERs between the triolein emulsion groups was not statistically significant ( P>0.05). The T2-weighted SIRs were significantly different between the control group and groups 1 ( P=0.027) and 2 ( P=0.004). However, the edema ratios of all doses in the triolein emulsion groups showed no significant differences compared with the control group.

Conclusion: The minimum dosage of 0.5% triolein emulsion to achieve increased vascular permeability in the hemisphere in cat brains appears to be 3 ml/kg. This minimum dosage of triolein emulsion can be useful for acquiring basic data in further studies of vascular permeability changes in a triolein emulsion model.