bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Fracture-Fluid Cleanup in Tight-Gas Wells
Authors: Wang John Yilin* , Holditch Stephen A. , McVay Duane A.
Published: June 2010

On occasion, a hydraulically fractured tight-gas well does not perform up to its potential because of slow or incomplete fracture- fluid cleanup. A number of papers have been written to address individual factors related to fracture-fluid cleanup, but many questions as to which factors mostly affect gas production from such wells remain unanswered. Numerical reservoir simulation is one of the best methods to study the fracture-fluid-cleanup problem. Continuing from our previous publication (Wang et al. 2008) on the effect of gel damage on fracture cleanup, we used reservoir simulation to analyze systematically the factors that affect fracture- fluid cleanup and gas recovery from tight-gas wells.

We first developed a comprehensive data set for typical tight gas reservoirs and then ran single-phase-flow cases for each reservoir and fracture scenario to establish the idealized base-case gas recovery. We then systematically evaluated the following factors: multiphase gas and water flow, proppant crushing, polymer filter cake, and, finally, yield stress of concentrated gel in the fracture. The gel in the fracture is concentrated because of fluid leakoff during the fracture treatment. We evaluated these factors additively in the order listed. We found that the most important factor that reduces fracture-fluid cleanup and gas recovery is the gel strength of the fluid that remains in the fracture at the end of the treatment.

This paper illustrates the complexity of the fracture-fluid- cleanup problem and points out the need to use reservoir simulation and to include all the pertinent factors to model fracture-fluid cleanup rigorously. The procedures presented can provide a useful, systematic guide to engineers in conducting a numerical simulation study of fracture-fluid cleanup.
Guidelines for the Proper Application of Critical Velocity Calculations
Authors: P. Sutton Robert , A. Cox Stuart , F. Lea James , Rowlan O. Lynn
Published: June 2010

Critical velocity calculations in the form of charts or simple equations are frequently used by field personnel to evaluate a gas well's flowing conditions to determine if the well is experiencing liquid-loading problems. Literature detailing the critical velocity necessary to keep a gas well unloaded suggests using the conditions at the top of the well as an evaluation point. This is convenient for personnel conducting the evaluation because wellhead pressure and temperature data are readily available. A number of situations exist where the use of the wellhead as the evaluation point can lead to erroneous conclusions. The most obvious situation occurs with a change in geometry downhole when a tapered tubing string is run in a well or when the tubing is set above the perforations. In these instances a more robust evaluation results from using conditions at the bottom of the well and the downhole tubing geometry. Other conditions exist where the use of downhole conditions provides a better evaluation point. The assumptions used in the development of the standard, simplified form of the critical velocity equations and charts may not be appropriate for downhole application. In these cases, the fundamental equations must be used. The calculation of critical velocity requires knowledge of pressure, temperature, produced fluids, and pressure/volume/temperature (PVT) properties. The determination of critical rate requires the same properties with the addition of pipe diameter. The required PVT properties, including surface tension and density for both the gas and liquid phases, are reviewed. Correlations to calculate water-gas surface tension were found to have excessive error, so a new, more accurate method is presented. This paper provides recommendations for the use of a surface or a downhole evaluation point is more appropriate for the determination of the minimum critical gas velocity in a well.
Effects of Monoethylene Glycol on Carbonate Equilibrium and Calcite Solubility in Gas/Monoethylene Glycol/NaCl/Water Mixed Systems
Authors: Lu Haiping , Kan Amy T. , Tomson Mason B.
Published: June 2010

Monoethylene glycol (MEG), HOCH2CH2OH, is an important raw material with numerous industry applications, which include polyester synthesis, automobile antifreeze, coolant, and aircraft anti-icer. In the oil and gas industry, MEG is commonly used as a gas-hydrate inhibitor, which can prevent the formation of gas hydrate during natural-gas production. However, common gas-hydrate inhibitors have the adverse effects of lowering the solubility of mineral salts and causing a higher risk of scale formation. Despite the importance of scale problems with MEG in oil production, there have been few investigations on the solubility of mineral salt in MEG/brine solutions. In our research, experiments have been conducted on carbonate equilibrium and calcite solubility at 2–70°C, 0- to 6.5-m (m = molality) ionic strengths, and 0–99.67 wt% MEG.

A self-consistent activity model based on the Pitzer theory to calculate the effect of salt and a Born-type equation were used to model the effect of MEG. MEG activity coefficients with respect to dissolved carbon dioxide (CO2), sodium bicarbonate, sodium carbonate (NaHCO3), and calcium are determined as a function of temperature, ionic strength, and mole fraction of MEG in mixed solvent.
Comparison of Flowback Aids: Understanding Their Capillary Pressure and Wetting Properties
Authors: Howard Paul R. , Mukhopadhyay Sumitra , Moniaga Nita , Schafer Laura , Penny Glenn , Dismuke Keith
Published: June 2010

Flowback aids are usually surfactants or cosolvents added to stimulation treatments to reduce capillary pressure and water blocks. As the stimulated gas reservoirs become tighter, the perceived value of these additives has grown. This value must be balanced with the cost of the additives, which can be significant in slickwater fracturing treatments. There is a range of different flowback additives containing water-wetting nonionic to amphoteric, microemulsion (ME), and oil-wetting components. Determining the best additive for a specific reservoir is not a simple matter for the end user, and the existing literature is full of conflicting claims as to which one is most appropriate.

This paper compares four different flowback aids: ME, two waterwetting flowback additives, and an oil-wetting additive. Careful laboratory testing was conducted to evaluate surface tension and contact angle for each flowback aid, using the recommended concentrations. Imbibition and drainage tests were performed that allowed calculation of the capillary pressures for the three additives. Drainage tests were performed on 1- to 3-md and 0.1-md cores. Capillary-tube-rise testing was also conducted as a check of the coreflood testing capillary pressures. This provided several different methods to determine capillary forces for the flowback aids. In addition, fluid-loss testing was conducted to determine if the flowback additives could improve fluid loss.

All the flowback aids demonstrated low surface tension (approximately 30 mN/m), but each was different in terms of surface wettability and adsorption in the rock. In all cases, the flowback aids reduced capillary pressure to similar levels 70% lower than water alone. One of the water-wetting additives had much stronger adsorption in the core material than the other additives. The ME and the oil-wetting additive had improved fluid loss in a fully formulated fracturing fluid. In spite of the low capillary pressures, the additives had little effect on cleanup or return permeability on cores greater than 1 md.

There are several implications of these results for the operator. Different flowback additives have a tradeoff of properties, and depending on the reservoir, selecting one that leaves the formation with certain wettability may be advantageous. Our testing indicated that understanding the reservoir is important in selecting the appropriate flowback aid.
Fluid-Diversion Monitoring: The Key to Treatment Optimization
Authors: Glasbergen Gerard , Yeager Valerie , Reyes Robert , Everett Don
Published: June 2010

In stimulation and injection treatments for removing or preventing formation damage, placement of the injected fluids is essential. Throughout the years, several diversion and placement techniques have been applied to obtain a desired fluid placement. A recent development is the application of distributed temperature sensing (DTS) to monitor the temperature profiles along the wellbore in real time during these treatments. Recent case histories showed that fluid placement can be quantified. Quantification of fluid distribution enables one to determine the flow distribution both before and after a diverter stage so that the diversion effect can be quantified.

This paper discusses several case histories where DTS was applied to quantify the effectiveness of different diverters. The effects of chemical diverters, such as relative permeability modifiers (RPMs) and in-situ-crosslinked acids (ICAs), and more-traditional diverters, such as rock salt, are discussed. Because of the advanced monitoring used with the temperature profiles, both the immediate and the sustained effect of the diverters can be measured. The changes in the flow distribution are not limited to diverters. Reactive fluid or changes in flow rate can change the flow distribution as well. These effects were measured during the stimulation treatments.

The post-treatment analysis of the measured temperature profiles in combination with treatment pressures and flow-rate information resulted in accurate knowledge of the effectiveness of the different diverters and stimulation effects over time. This knowledge will be used in future treatments to help optimize volumes, rates, fluid systems, and the selection of the appropriate diverter.
Controlling Bacteria in Recycled Production Water for Completion and Workover Operations
Authors: Tischler A.. , Woodworth T.R.. R. , Burton S.D.. D. , Richards R.D.. D.
Published: June 2010

Reusing flowback water and produced water from active wells becomes more and more important in today's oil and gas operations to control surface water volumes in order to keep surface water-disposal costs (reinjection or trucking off the premises) to a minimum, especially in operations that do not require secondary-lift support. However, reusing untreated produced and flowback water in workover and completion operations can promote bacteria growth both above and below ground.

Water produced from oil and gas wells is a perfect environment for sulfate-reducing bacteria (SRB) and certain types of acid-forming bacteria (AFB) because of its anaerobic nature [less than 2 ppm (O2) content] and high nutrients content (e.g., organics, free iron). Reuse of water introduces enough oxygen through regular pumping operations to allow aerobic bacteria to grow mostly slime-forming bacteria (SFB) and other species of AFB. The oxygen content is high enough for aerobic bacteria to grow but is too low to kill anaerobic bacteria. The oxygen content will cause the anaerobic bacteria to stay in a biostatic state that does not kill them, but prevents them from multiplying.

As soon as the bacteria find an environment that is conducive to growth, they will become active again and start multiplying. The anaerobic environment in the formation is ideal for growth of bacteria such as SRB and certain types of AFB. The aerobic environment of the wellbore is conducive for SFB and certain types of AFB. The growth of SRB will not only lead to health and safety (H&S) concerns because of increased sour-gas or hydrogen sulfide (e.g., H2S) production, but also to a slow souring of the formation. This also increases operation expenses because of added corrosion (H2S pitting, stress cracking, microbiologically influenced corrosion) in surface and increases subsurface tubulars and related prevention expenses. Other challenges in production can be related to AFB (pitting) and SFBs (emulsion like materials may form).

Different methods can be applied to prevent bacteria growth and reduce operational expenses related to corrosion prevention, remediation of corrosion effects, and remediation of emulsified produced fluids. This paper will take a closer look at the methods of aeration, chlorine-based applications (sodium hypochlorite, calcium hypochlorite, and chlorine dioxide), and biocide application.

The different methods will be compared through laboratory tests, actual field application, and a rating system. The rating system incorporates environmental, health, and safety (EH&S) concerns, operational application/considerations, effectiveness of the method, and cost.

Each method will be discussed and the pros and cons presented. The pros and cons will be supported by laboratory and field data. The conclusion portion of the paper will discuss why and how the current method of application was chosen and discuss future improvements and testing.
Well Testing of Tight Gas Reservoirs
Authors: Jahabani A. , Aguilera R.
Published: June 2010

A tight gas reservoir is commonly defined as a reservoir having less than 0.1 milliDarcies permeability. Because of the very low permeability, hydraulic fracturing is usually carried out in efforts to establish commercial production. There are several basic concepts and field cases of different well tests in tight gas reservoirs in the literature. In this paper, we gather information and provide a guide to some of the most important tests.

Generally because of low permeability, a well will not flow initially at measurable rates and conventional well testing cannot be applied. We review procedures for design of pre- and postfracture tests in single and dual porosity reservoirs. The prefracture test permits estimating preliminary values of reservoir permeability and initial pressure. The post-fracture test provides data for estimating fracture half length and conductivity. We also review the application of convolution/deconvolution methods to analyze well tests with significant wellbore storage.

Because of economic and environmental reasons, short duration procedures are preferred. However, although effective in many instances, these methods also have their own limitations.

Introduction

Unconventional reservoirs (tight gas, coal bed methane, shales gas and gas hydrates) will be an important pat of the global energy mix for decades to come. Large reserves, long-term potential, costs and gas prices and some other factors account for the great influence of these resources on the future of energy.

There is no formal definition for "tight gas." A commonly used definition, describes tight gas reservoirs as those having permeabilities smaller than 0.1 milliDarcies.

Well testing is generally done as an aid to estimate gas in-place and recoverable volumes. Initial pressure (pi) is a critical parameter not only for estimating gas in-place, but also for determining how much field development is required and whether or not the field is overdeveloped. In addition to pi, well testing provides an estimate of permeability and skin.

A problem associated with well testing in tight gas sands is that usually long times are required to reach radial flow, due to their extremely low permeabilities. Therefore, conventional well tests cannot be applied to these reservoirs. Because of initial uneconomic rates, fracturing is usually required. Lee(2) has suggested procedures for pre- and post-fracture tests design. In order to have measurable gas rates for pre-frac testing, often a breakdown with acid, KCl water or N2 is necessary.
The Role of the Geologist in the Assessment of Continuous Gas Accumulations
Authors: Jenkins C.D. , Levine J.R.
Published: June 2010

Finding and developing continuous gas accumulations such as shales, coal seams and tight sands requires the simultaneous development of accurate geological models together with effective engineering technologies. This linkage is well-established in conventional gas reservoirs where several decades of experience have resulted in a clear and important role for geology in exploration and production. Continuous gas accumulations, however, are substantially different, in that they are regional in extent and lack obvious seals or traps. Geologic controls on gas-in-place and production rates are no less important in continuous reservoirs, but these controls operate on a different scale. Moreover, geologic factors are often misunderstood and can be difficult to quantify. This can lead to the erroneous belief that the geology is either too complex to be understood, or that it is of little importance, or that regional variability is effectively unpredictable, or that reservoir behaviour can be sufficiently approximated with simplistic models. In all such cases, the importance of geology is underestimated.

Many companies have relied largely upon engineering solutions in developing continuous gas resources, while excluding basic geological data and analysis from the project budget as a low-priority item. This makes little sense, however, particularly for marginally economic projects that cannot sustain a high proportion of sub-economic wells. In addition, this approach introduces a high level of guesswork, and reduces the optimization of drilling and completion strategies to trial-and-error. To alter this approach, and to contribute more effectively to the exploration and development of continuous gas accumulations, geologists must do a better job of defining their responsibilities, demonstrating why geological knowledge is important, and offering specific recommendations that will favourably impact the bottom line.

Introduction

As compared with conventional gas reservoirs, continuous gas accumulations typically extend over large stratigraphic thicknesses (tens to hundreds of metres) and lateral distances (tens to hundreds of kilometres). Owing to their size, continuous gas accumulations can encompass a variety of rock-types, having widely varying reservoir properties. The three principal types of continuous gas accumulations are:coal seam gas (CSG), also known as coalbed methane;shale gas; andtight sands.
Technical Advancements in SAGD Evaporative Produced Water Treatment
Authors: Heins W.F.
Published: June 2010

There has been a shift away from the use of warm lime softening (WLS) and weak acid cation (WAC) ion exchange for produced water treatment to the use of mechanical vapour compression (MVC) evaporation followed by high pressure drum-type boilers. Approximately 18 steam assisted gravity drainage (SAGD) produced water evaporators are operating or are in various stages of construction in Alberta and overseas. Since the commissioning of the first such evaporators in 2002, many technical advancements have occurred which have resulted in reduced operating costs, improved reliability, reduced scaling and fouling potential, improved distillate quality and improved boiler feed quality for steam generation.

This paper provides details of the technical advancements in evaporative produced water treatment based on full-scale operating data and lessons learned. It also presents improved evaporator configurations, discusses improvements in contaminant reduction and scale prevention systems, demonstrates how capital and operating costs can be drastically reduced as compared to earlier evaporator system designs, and provides recent advancements in modularization, evaporator disposal treatment, deoiling, membrane preconcentration, and zero discharge solids drying techniques.

Introduction

Over the past few years, there has been a rapid shift away from the use of traditional produced water treatment methods using WLS for silica reduction and WAC ion exchange for hardness removal, to the use of evaporative produced water treatment methods at SAGD facilities. With the use of evaporative produced water treatment, standard drum boilers are utilized for steam generation in lieu of once through steam generators (OTSG) and vapour liquid separators. This shift has occurred because of technical, economic and reliability factors, resulting in markedly improved life cycle costs for SAGD facilities. A simplified block flow diagram of the traditional approach to produced water treatment and steam generation is provided in Figure 1. A block flow diagram for the evaporative approach is provided in Figure 2.
Preliminary Considerations on Application of Steamflooding in a Toe-to-Heel Configuration
Authors: Turta A.T. , Singhal A.K. , Xia T.X. , Greaves M. , Goldman J. , Ivory J.
Published: June 2010

With the advent of horizontal wells, a distinct change is tacitly taking place in our approach to the improved recovery of heavy oil—from displacing mobilized oil in a flood pattern from injector to producers over long distances on the order of hundreds of metres to short-distance oil displacement (SDOD) processes (typically over a few tens of metres).

SDOD processes comprise Steam Assisted Gravity Drainage (SAGD), Cyclic Steam Stimulation (CSS) and Toe-to-Heel (TTH) Displacement Processes, which comprise Toe-to-Heel Air Injection (THAI), with its variant catalytic THAI (CAPRI), and Toe-to-Heel Waterflooding (TTHW). Presently SAGD is commercially used, while THAI has been under field testing for 3 years; testing of CAPRI is scheduled to start in 2010. TTHW has been under field testing both in the US and Canada for more than 4 years.

Steamflooding in a TTH configuration (TTH steamflooding) uses vertical wells as injectors and horizontal wells as producers, arranged in a staggered line drive, with producers having their toes close to the shoes of vertical injectors; the horizontal section of producers is located at the base of the pay. The vertical wells are used for initiating the steam front, which subsequently is anchored at the toe of the horizontal producer; it is then propagated towards the producer's heel. In TTH steamflooding, the existing deficiency of conventional steamflooding schemes in terms of low vertical sweep is overcome by the beneficial use of gravity.

To investigate the potential of TTH steamflooding, some laboratory tests were conducted. The objective was to assess the feasibility of TTH steam and thermo-solvent flooding (steam+propane co-injection) by carrying out 3D model experiments using heavy oil with a viscosity of 15,000 cP.

Laboratory results showed that the concepts of TTH steamflooding and TTH steamflooding with solvent are feasible. All in all, stability of TTH steamflooding was relatively good, while the stability of TTH steamflooding with the addition of nitrogen or propane was much better. Significant improvements in design and operation of these processes were needed in order to promote override during the early phase, and obtain a stable and efficient process. The improvements included a cold (gas fingering) and a hot (steam-based) communication phase; and controlling lateral spread of steam by using two additional vertical control wells (positioned laterally but close to the heel of the horizontal producer) for conducting a limited steamflood. Nitrogen was injected along with steam in the conventional steamflood; propane replaced nitrogen in TTH steamflooding with solvent.
Integrated Modeling of the Fractured Carbonate Midale Field and Sensitivity Analysis Through Experimental Design
Authors: Bogatkov Dmitry , Babadagli Tayfun
Published: June 2010

We used an integrated solution by combining "direct" and "inverse" approaches to fracture network characterization in a stochastic numerical model. Static geological data obtained from cores and well logs were used together with dynamic data such as well-test responses to build 3D discrete fracture-network (DFN) models. We used the data obtained from the fractured carbonate Midale field in Canada.

The fractured-reservoir model was constructed from static and dynamic (drawdown and pulse-interference tests) data. Matrix and several fracture parameters including fracture length, density/ spacing, aperture, connectivity, and orientation were evaluated in a quantitative sensitivity study to determine which characteristics have a higher influence on the accurate match to well-test response. We used experimental design to optimize the number of simulations needed for a sensitivity study and history match. The sensitivity analysis revealed a strong influence of matrix quality on the pressure response, suggesting that the history match can be specific to the simulated process and not necessarily unique. The results emphasize the contribution of matrix in the Midale reservoir and the need to simulate a broader range of processes for an accurate description of the fracture/matrix system dynamics. In a general sense, the approach used in this study proved to be useful in integrating fracture data from different sources and assessing its reliability and relative importance.
Advanced Wells: A Comprehensive Approach to the Selection Between Passive and Active Inflow-Control Completions
Authors: Al-Khelaiwi F.T.. T. , Birchenko V.M.. M. , Konopczynski M.R.. R. , Davies D.R.. R.
Published: June 2010

Well architecture advances from conventional wells to horizontal. Then multilateral wells, which have maximized reservoir contact, have been paralleled by advances in completion-equipment development. Passive inflow-control devices (ICDs) and active intervalcontrol valves (ICVs) provide a range of fluid-flow control options that can enhance the reservoir sweep efficiency and increase reserves. ICVs were used originally for controlled, commingled production from multiple reservoirs, while ICDs were developed to counteract the horizontal well's heel/toe effect. The variety of their applications has proliferated since these beginnings. Their application areas now overlap, resulting in it becoming a complex, time-consuming process to select between ICVs or ICDs for a particular well's completion.

This publication summarizes the results of a comprehensive, comparative study of the functionality and applicability of the two technologies. It maps out a workflow of the selection process on the basis of the thorough analysis of the ICD and ICV advantages in major reservoir, production, operation, and economic areas. It provides detailed analysis of Reservoir-engineering aspects, such as uncertainty management, formation heterogeneity, and the level of flexibility required by the developmentProduction and completion characteristics, such as tubing size, the number of separately controllable zones, the completion of multiple laterals, and the value of real-time informationOperational and economical aspects, such as proper modeling, gas-and oilfield applications, equipment costs and installation risks, long-term reliability, and technical performance.

The results of this work's systematic approach form the basis of a screening tool to identify the most appropriate control technology for a wide range of situations. This selection framework can be applied by both production technologists and reservoir engineers when choosing between passive or active flow control in advanced wells. The value of these guidelines is illustrated by their application to synthetic- and real-field case studies.
Equivalent Rate Constant for Numerical Simulation of Linear Convection-Diffusion-Reaction
Authors: Abedi Jalal , Hassanzadeh Hassan , Pooladi-Darvish Mehran
Published: June 2010

The accurate numerical modelling of reactive flow is essential for the interpretation of experimental measurements and the design of field-scale processes. Sharp reaction fronts are difficult to capture using traditional numerical schemes, unless fine grid numerical simulations are used; however, fine grid simulations are computationally expensive. On the other hand, using coarse grid block simulations leads to excessive front dissipation and inaccurate results. In most practical cases, it is not feasible to choose small grid blocks; therefore, one needs to account for the small-scale gradients that cannot be captured by coarse grid blocks when using traditional methods. As a first step toward the development of upscaling techniques for reaction kinetics, an equivalent reaction constant for a simple steady-state convection-diffusion-reaction (CDR) was determined. This shows how an effective reaction constant can be obtained as a function of the Peclet number, Thiele modulus and size of the reaction zone, such that the coarse grid simulation agrees with the fine grid simulation.
Hole Cleaning Performance of Light-Weight Drilling Fluids During Horizontal Underbalanced Drilling
Authors: Ozbayoglu M.E. , Sorgun M. , Saasen A. , Svanes K.
Published: June 2010

Hole cleaning is a major consideration at both the design and application stages of a drilling operation. If the fluid velocity is lower than a critical value at horizontal or high inclinations, a stationary bed develops which may cause various problems, such as high drag, higher probability of stuck pipe and higher hydraulic requirements, etc., if not removed properly. Therefore, this becomes important and essential to identifying critical velocity. This study aims to estimate the critical fluid-flow velocity for preventing the development of a stationary bed using empirical correlations that can be used easily at the field. Also, a rough estimation of bed thickness is introduced if the flow velocity is lower than the critical velocity. For this purpose, extensive cuttings transport experiments with water, called the Cuttings Transport Flow Loop, were conducted by the Petroleum and Natural Gas Engineering Department at Middle East Technical University (METU) in order to determine various inclinations, flow rates and rate of penetrations. The inner pipe is subject to a sagging, therefore more realistic annulus representation is achieved. Observations showed that a stationary bed can be developed even when the inclination of the wellbore is down to 50°. Results showed that the critical velocity could be estimated using the proposed correlations with reasonable accuracy when compared with the experimental results. Also, for flow velocities less than the critical values, the thickness of the stationary bed can be detected mostly within an error range of ±15%.
Integrating Geological Characterization and Historical Production Analysis to Optimize Field Management of Lower Miocene Reservoir in White Tiger Field, Vietnam
Authors: Nguyen Ngoc T.B , Dang Cuong T.Q. , Bae Wisup , Phung Thuoc H. , Chung Taemoon , Lee HeoungYeoun
Published: June 2010

Near-shore oil reservoirs have become significantly depleted, forcing oil companies to explore deep-sea reservoirs with huge investments and the latest technology. However, these projects are often risky. Thus, the optimal solution is to explore shallow sea oil fields before proceeding to deep, high-risk areas.

The Lower Miocene reservoir of the White Tiger field is a sedimentary reservoir with high heterogeneity and complex geological characteristics. This reservoir was discovered 22 years ago. There is an urgent need to study procedures for an increased and maximum oil recovery. A detailed geological understanding of the reservoir, along with a reservoir simulation, is needed to gain a detailed reservoir description and determine the optimal recovery method for this oil reservoir. These are essential to having a successful operation, as well as reducing uncertainties and improving the efficiency of oilfield management.

With a large database collected from initial production stages of over 50 wells, the authors developed an integrated static and dynamic workflow to forecast oil production under several production scenarios for this reservoir. These integrated results served as input data for simulation with IMEXTM, which will be useful for the economical and technical evaluation of this study. In addition, the authors introduced history matching and pointed out the main reasons for the significant errors between actual data and simulation results. Based on the reservoir modelling, the authors optimized the wells? network locations and obtained good results in oil recovery. The oil recovery factor increased from 24.21% - 37.26% for the Lower Miocene reservoir. Specifically, oil recovery for the Southern dome structure was increased from 14.83% - 33.76%.
Surfactant Enhanced Biodegradation of Petroleum Hydrocarbons in Oil Refinery Tank Bottom Sludge
Authors: Zhang Xiaoxi , Li Jianbing , Huang Yuefei , Thring Ronald
Published: June 2010

Bioremediation has been recognized as an effective method to treat petroleum hydrocarbon pollutants. However, the biodegradation of crude oil-contaminated sludge could be a time-consuming and low-efficiency process. Among the reasons is that some petroleum hydrocarbons in the sludge are unavailable for micro-organisms? utilization. Surfactants have the potential to increase the bioavailability of such pollutants because of their capability to reduce the surface and interfacial tension and increase the solubility of hydrocarbons in water. In this study, the addition of two different chemical surfactants (Igepal CO-630 and Cedephos FA-600) were tested using a laboratory respirometer, and the effects of such surfactants on the biodegradation of total petroleum hydrocarbon (TPH) in the oil refinery sludge were investigated. Both surfactants have been found to be effective on improving microbial growth at low-concentration additions, while the concentration of 400 mg/kg has been found most effective for improving TPH (C10-C50) reduction after 14 days of biodegradation.
Practical Application of a Probabilistic Approach to Estimate Reserves Using Production Decline Data
Authors: Cheng Y.. , Wang Y.. , McVay D.A.. A. , Lee W.J.. J.
Published: June 2010

Analysts have increasingly used probabilistic approaches to evaluate the uncertainty in reserves estimates based on decline-curve analysis (DCA). This is because the results represent statistical analysis of historical data that usually possess significant amounts of noise. Probabilistic approaches usually provide a distribution of reserves estimates with three confidence levels (P10, P50, and P90) and a corresponding 80% confidence interval (CI). The question arises: How reliable is this 80% CI? In other words, in a large set of analyses, is the true value of reserves contained within this interval 80% of the time? Our investigation indicates that it is common in practice for true values of reserves to lie outside 80% CIs much more than 20% of the time using traditional statistical analyses. This indicates that uncertainty is being underestimated, often significantly. Thus, the challenge in probabilistic reserves estimation using DCA is not only how to appropriately characterize probabilistic properties of complex production-data sets, but also how to determine and then improve the reliability of the uncertainty quantifications.

This paper presents an improved methodology for probabilistic quantification of reserves estimates using DCA and practical application of the methodology to actual individual-well decline curves. Application of our proposed new method to 100 oil and gas wells demonstrates that it provides much wider 80% CIs than methods previously presented, and these CIs contain the true values approximately 80% of the time. In addition, the method yields more-accurate P50 values than previously published methods do. Thus, the new methodology provides more-reliable probabilistic reserves estimation, which has important impacts on economic risk analysis and reservoir management.
Tuning of Computer Model Parameters in Managed-Pressure Drilling Applications Using an Unscented-Kalman-Filter Technique
Authors: Gravdal Jan Einar , Lorentzen Rolf J. , Fjelde Kjell K. , Vefring Erlend H.
Published: June 2010

To manage the annular pressure profile during managed-pressure drilling (MPD) operations, simulations performed with advanced computer models are needed. To obtain a high degree of accuracy in these simulations, it is crucial that all parameters describing the system are as correct as possible. A new methodology for real-time updating of key parameters in a well-flow model by taking into account real-time measurements, including measuring uncertainty, is presented. Key model parameters are tuned using a recently developed estimation technique based on the traditional Kalman filter.

The presented methodology leads to a more-accurate prediction of well-flow scenarios. Although the present study is motivated by applications in MPD, the idea of tuning model parameters should be of great importance in a wide area of applications.

The performance of the filter is studied, using both synthetic data and real measurements from a North Sea high-pressure/high-temperature (HP/HT) drilling operation. Benefits by this approach are seen in more-accurate downhole-pressure predictions, which are of major importance for safety and economic reasons during MPD operations.
HERBAVATE an Alternative Approach for the Management of Eczema?
Authors: Vyas Aniruddha P , Rastogi Pramod K , Jaiswal Vijaya , Dave Darshan
Published: June 2010

HERBAVATE is a topical preparation that contains the oil extracts of Calotropis gigantea, Curcuma longa, Pongamia glabra & Solanum xanthocarpum in a cream base. The present study is a pilot study evaluating the efficacy and safety of HERBAVATE in the management of eczema.37 out-patients with a clinical diagnosis of eczema were enrolled in an open label study carried out at 2 centers. Patients applied HERBAVATE cream over the lesion twice daily and were followed up weekly for 4 weeks. Patients were assessed weekly on a 4 point scale for the severity of symptoms associated with eczema, viz. erythema, scaling, lichenification and pruritis. Local tolerance was assessed on a 4 point scale.All analysis were carried out on 32 patients, there were 5 dropouts. At the end of the study there was a significant fall in the mean scores for erythema, scaling, lichenification and pruritis. HERBAVATE was well tolerated with only 2 patients reporting mild burning at site of application which improved with continued application.HERBAVTE appears to an attractive alternate option for the management of eczema. However, larger studies of longer duration are needed.
Preparation of a Micro-Porous Alginate Gel Using a Microfluidic Bubbling Device
Authors: Martynov Sergey , Wang Xiaoliang , Stride Eleanor P , Edirisinghe Mohan J
Published: June 2010

Demand for low-energy food products has greatly increased in recent years due to the growing concerns over obesity related health problems. The aim of the work described in this short communication was to use a microfluidic T-junction device to prepare microporous calcium alginate gels by incorporating monodisperse air bubbles (177 ?m in diameter) which would both increase the volume to energy content ratio of the product and improve sample homogeneity. Homogeneous, 5mm-thick gel samples were successfully obtained and found to have a density of 365 kg/m3. The high gas content was confirmed by ultrasound reflectivity measurements. The mean pore diameter, determined by optical and SEM measurements, was 131?m with a standard deviation of 57?m.
Characterization of the Immobilized Fructosyltranferase from Rhodotorula sp.
Authors: Aguiar-Oliveira Elizama , Maugeri Francisco
Published: June 2010

The fructosyltransferase from Rhodotorula sp. recovered from a fermented medium, by precipitation was immobilized by adsorption onto niobium ore. Considering the biocatalyst system, the activity/pH profile moved towards more alkaline values as compared to the free enzyme system, indicating that the support affected the charge distribution between the enzyme and the support. The immobilized enzyme showed high activity and good stability at pH values of 4.5 and 6.0. The biocatalyst half-lives at 48 °C and pH values of 4.5 and 6.0 were 32 and 72 days, respectively. The kinetics for the immobilized system corresponded to that of substrate inhibition. The synthesis of fructooligosaccharides from 50% sucrose solutions was carried out in batch stirred reactors and the conversion was about 58%, similar to that with the free enzyme. Based on the biocatalyst activity, stability and process yields, the system developed in this work can be considered suitable for application in large-scale bioreactors.
The Effects of Power Mechanisms in Education: Bringing Foucault and Bourdieu Together
Authors: Hannus Susanna , Simola Hannu
Published: June 2010

The aim of this article is to outline a theoretical framework for an empirical study focusing on the question of how schools from socio-culturally different areas face new governance and its power mechanisms. The authors' aim is to bring together Pierre Bourdieu's and Michel Foucault's approaches to power, capitalising at the same time on Risto Heiskala's recent synthesising theorisation of power. In terms of elaboration, the authors outline a four-dimensional framework in which episteme, ethos, theasis and techne constitute the four faces from the Foucauldian perspective. The respective Bourdieuan contributions constitute linguistic markets, institutional habitus, distinctions, and mechanisms of reproduction. In this treatment, it appears that the strength of the Foucauldian tools in the authors' intellectual box for their empirical research on the effects of new governance is on the level of the political, whereas Bourdieu also provides tools for the analysis of politics. The authors' conclusion is a heuristic device, a catalogue of possibilities, a springboard for field study.
Mapping the Movement of Invention: Collaboration as Rhizome in Teaching and Research the (1+1+1) Collective
Authors: Forrest Michelle , Cooley Miriam , Wheeldon Linda
Published: June 2010

The collaborative education research as art created by The (1+1+1) Collective is examined as heuretics, the movement of invention. Heuretics both enacts and documents the movement of the research process and therefore helps balance the biases, which are expressions of power, inherent in the means of expressing any inquiry. This methodology, which acts as a rhizome, offers a model for academic collaboration; it maps the movement of invention by enacting moves provoked by the heuristic of chance as in the example of process art, which can be understood philosophically in terms of Deleuzian ontology and Deleuze & Guattari's conceptualisation of philosophy as one of the three great forms of thought. Throughout the article, connections are made to teacher education and research, and it is suggested that understanding the value of heuretics can help the teacher and the researcher avoid methodological fundamentalism.
Trust and Leadership in Post-Compulsory Education: Some Snapshots of Displaced Dissent
Authors: Jameson Jill
Published: June 2010

While education cannot function without trust, its loss in institutions sometimes goes unspoken, officially unreported, only shared in ways invisible to measurement or control. This article considers issues of trust, power and displaced dissent, providing some snapshots of participant views about questions of trust and leadership recorded in a series of 28 interviews and 242 electronic survey responses from the post-compulsory education or ‘lifelong learning’ sector in 2004–09. This formed part of an externally funded research project which collected data in three timed data collection phases. Snapshots of displaced dissent from a minority of participants expressed disquiet regarding the level of trust operating in their educational institutions, in response to questions about ‘trust and leadership’. These snapshots are random examples of dissent emerging from those whose power to speak out in their own institutions was limited, for fear of reprisals. They are collected together to provide evidence of otherwise unspoken things that may lie beneath the silences operating in a minority of post-compulsory educational institutions regarding considerations of trust. A theoretical model of the operation of organisational trust is proposed that recommends open and consensual dialogic practices for the development of more trusting situations in post-compulsory education workplaces.
The Power of Authority: Challenging Educational Theory and Practice
Authors: Thompson Christiane
Published: June 2010

In the modern pedagogical tradition, ‘authority’ refers to the educator's duty to make decisions and take responsibility when the child cannot yet do so. In this article, the author argues that this notion of authority is difficult not only because of the precarious balance Kant noted between freedom and constraint within education, but also because authority implies social references and measures, and therefore power structures and domination. Focusing on a pedagogical scene from the French documentary Être et avoir, this article analyzes the logic of power with reference to the works of Foucault, Bourdieu, and Derrida. The article closes with reflections on the role of educational philosophy concerning the ‘power of authority’.
Studies on the Non-Protein Thiols of a Human Prostatic Cancer Cell Line: Glutathione Content
Authors: Gronow Michael
Published: June 2010

The low molecular weight thiol (-SH) content of a human prostate carcinoma cell line (LNCap), important to the cellular resistance to drugs and irradiation, was investigated using three forms of thiol assay each utilizing different chemistries. The composition of the mixture was examined by derivatization of the thiols with a three-fold excess of the Ellman reagent to give mixed aromatic disulfides. The components were isolated by chromatography on C18 reverse phase silica gel followed by DE52 anion exchange separation, and then analyzed by capillary electrophoresis against prepared standards. The glutathione adduct (GSSE) and an unknown disulfide (RSSE) were the major components isolated on DE52 together with two minor ones. However, from the absorbance at 325 nm, it was found that the GSSE isolated (1.5 ± 0.2 femtomoles/cell) could only account for 28.5 ± 4.3% of the total ASF thiols. It appeared that the bulk of the thiol material had not formed a stable mixed disulfide with Ellman’s reagent, and this was confirmed by 35S labeling of the cells. A large proportion of the 35S labeled components, obtained after reaction of the ASF thiols with the Ellman reagent, did not form mixed aromatic disulfides and could therefore not be identified by this labeling method.
Serum Tumor Markers in Pancreatic Cancer—Recent Discoveries
Authors: Rückert Felix , Pilarsky Christian , Grützmann Robert
Published: June 2010

The low prevalence of pancreatic cancer remains an obstacle to the development of effective screening tools in an asymptomatic population. However, development of effective serologic markers still offers the potential for improvement of diagnostic capabilities, especially for subpopulations of patients with high risk for pancreatic cancer. The accurate identification of patients with pancreatic cancer and the exclusion of disease in those with benign disorders remain important goals. While clinical experience largely dismissed many candidate markers as useful markers of pancreatic cancer, CA19-9 continues to show promise. The present review highlights the development and the properties of different tumor markers in pancreatic cancer and their impact on the diagnostic and treatment of this aggressive disease.
Illumination-Based Synchronization of High-Speed Vision Sensors
Authors: Hou Lei , Kagami Shingo , Hashimoto Koichi
Published: June 2010

To acquire images of dynamic scenes from multiple points of view simultaneously, the acquisition time of vision sensors should be synchronized. This paper describes an illumination-based synchronization method derived from the phase-locked loop (PLL) algorithm. Incident light to a vision sensor from an intensity-modulated illumination source serves as the reference signal for synchronization. Analog and digital computation within the vision sensor forms a PLL to regulate the output signal, which corresponds to the vision frame timing, to be synchronized with the reference. Simulated and experimental results show that a 1,000 Hz frame rate vision sensor was successfully synchronized with 32 μs jitters.