bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy-Oil Recovery in Naturally Fractured Reservoirs with Varying Wettability by Steam Solvent Co-Injection
Authors: Al Bahlani A. , Babadagli T.
Published: October 2008

In heavy-oil recovery, although steam injection has no alternative in many circumstances, it may not be an efficient process under certain reservoir conditions. These conditions include deep reservoirs, where steam injection may turn out to be ineffective hot-water flooding due to excessive heat loss, and oil-wet fractured carbonates, where steam channels through fractures without effectively sweeping the matrix oil.

Solutions for heavy oil recovery in consolidated/unconsolidated sandstones have been proposed and some of them are currently in the commercial phase, including steamflooding and its different versions. A more challenging case is heavy-oil fractured carbonates where the recovery is usually limited only to matrix oil drainage gravity due to unfavourable wettability or thermal expansion if heat is introduced during the process. Wettability alteration is usually thought to occur at elevated temperatures which are difficult to achieve in deep reservoirs. Thus, improvement of matrix oil recovery requires different methodologies. We propose a new approach to improve steam/hot-water injection effectiveness and efficiency for this type of reservoir.

Static imbibition experiments were run on Berea sandstone and carbonate cores with different wettabilities and for different oil viscosities ranging between 200 cp and 14,000 cP. For wettability alteration, cores were either aged or treated by a wettability altering agent. The experiments were conducted initially in imbibition cells in a 90 °C oven to mimic the matrix-fracture interaction in steam condensation zones. Due to its high boiling point, heptane was selected as the solvent and the core samples were exposed alternately to high temperature imbibition and solvent diffusion. The main ideas behind this process were to enhance capillary and gravity interaction by reducing viscosity (heat and solvent effect) and altering wettability (solvent effect). The results showed that further reduction in oil saturation due to s solvent diffusion process preceded by hot water is remarkably fast and the ultimate recovery is high. The magnitude of recovery depends on wettability and the amount of water existing in the core. It was also observed that solvent retrieval is a very fast process and may increase to 85-90% depending on core type, wettability, and saturation history.
Design and Optimization of Hybrid Ex Situ / In Situ Steam Generation Recovery Processes for Heavy Oil and Bitumen
Authors: Yang Xiaomeng , Larter Stephen Richard , Gates Ian Donald
Published: October 2008

Given the enormous capital costs, operating expenses, flue gas emissions, water consumption and handling conducted in thermal in situ bitumen recovery processes, improving overall efficiency by lowering energy requirements and environmental impact of these production techniques is a priority. Steam Assisted Gravity Drainage (SAGD) is a common thermal technique used in Athabasca reservoirs. Although SAGD is effective at producing bitumen, its energy efficiency can be poor due to enormous heat losses on the surface and in the wellbore. Given current attention to carbon dioxide emissions and water handling, there is a need to design and implement Reduced Emissions to Atmosphere Recovery (REAR) processes for heavy oil and bitumen extraction. One alternative is to generate steam in situ by in situ combustion (ISC) by injecting air or oxygen into the formation thus reducing or even avoiding transfer heat losses. In ISC, an energy generating oxidation zone propagates within the formation and generates heat which enables in situ steam generation from formation and injected water within the reservoir. In this research, design and optimization of hybrid in situ steam generation recovery processes are examined by using advanced three-dimensional reactive thermal reservoir simulation. Hybrid techniques combine the advantages of both ex situ steam and in situ steam generation processes in that it raises overall energy efficiency, lowers natural gas consumption as fuel, reduces overall gas emissions as well as water usage to generate steam, all on a per unit oil basis. The research here identifies steam-air based hybrid processes that use roughly 70% of the energy of conventional SAGD to recover the same amount of oil with substantial reduction of flue gas emissions and water use as viable REAR processes worthy of scaled physical model and potentially field testing.

Introduction

Two requirements of in situ heavy oil recovery processes must be met for successful performance: first, make the heavy oil or bitumen mobile, and second, move the mobilized oil to a production well. Since virgin viscosities of Athabasca bitumen generally exceed several million cP, especially near the base of the oil leg (Larter et al., 2006; Gates et al., 2008), the key to success is first measured by the process' ability to mobilize the heavy oil or bitumen. There are four main methods to accomplish this: heat, solvent dilution, solvent deasphalting, and in situ upgrading. An efficient source of heat is in situ combustion (ISC) which also provides combustion gases that could potentially aid movement of mobilized bitumen in the reservoir.
NCG Behavior in SAGD - A Numerical Simulation Analysis
Authors: Heron Caroline , Thimm Harald , Sullivan Laura , Atkinson Ian
Published: October 2008

The injection of non-condensable gases (NCG's) with steam in SAGD is a concept that has been much discussed in the literature, and tested via laboratory studies, and in a small number of field pilots, the most comprehensive being the UTF Phase B. There has been considerable discussion, both positive and negative, regarding the behaviour of these gases in the steam chamber, and their impact on ultimate bitumen recovery. Benefits to SAGD productivity have been suggested by some, while other authors have projected impacts on bitumen recovery.

The authors have reviewed the results of methane injection in several projects, and used thermodynamic theory to develop a method to effectively model this behavior via simulation. While conventional simulators use the Peng-Robinson Equation of State, the effectiveness of EOS's become challenging at high temperature. In addition, the effects of recent developments in high temperature solution thermodynamics become significant with increasing temperature in SAGD.

AOSC has developed a method of modeling the effects of NCG in a steam zone, via the development of a new set of equilibrium values for methane exchange between the oil/gas phase, water/gas phase and oil/water phases. This paper will present the results of these simulations and predicted impact of methane injection on SAGD performance, as well as implications for other NCG's.
Experimental and Numerical Modeling of Heavy-Oil Recovery by Electrical Heating
Authors: Hascakir B. , Babadagli T. , Akin S.
Published: October 2008

Electrical heating for heavy-oil recovery is not a new idea but commercialization and wider application of this technique require detailed analyses for determination of optimal application conditions. In this study, applicability of electrical heating for heavy-oil recovery from two heavy-oil fields in Turkey (Bati Raman and Camurlu) was tested experimentally and numerically. The physical and chemical properties of the oil samples for the two fields were compiled and measured. Then, core samples were exposed to electrical heating and oil recovery performances by the retort technique were determined for different conditions. Experiments with and without using iron powder were analyzed and in-situ viscosity reduction during the heating process was determined through a history matching process using the simulation of the laboratory experiments. Experimentally obtained oil recovery and temperature distributions were used in this history matching exercise. Iron powder addition to oil samples causes a decrease in the polar components of oil and the viscosity of oil can strongly be influenced by the magnetic fields created by iron powders. Therefore, three different iron powder types at three different doses were tested to observe their impact on oil recovery. Experimental observations showed that viscosity reductions were accomplished as 88% and 63% for Bati Raman and Camurlu crude oils, respectively, after 0.5% Fe addition, which was determined as the optimum type and dose for both crude oil samples. Different parameters (thermal diffusion coefficients, oil viscosity, and relative permeabilities) that are needed in numerical modeling as data were determined through experimentally validated numerical modeling study. Furthermore, field scale recovery was tested numerically using the parameters obtained from laboratory scale experimental and numerical modeling results. The power of the system, operation period and the number of heaters were optimized. Economic evaluation done using the field scale numerical modeling study showed that the production of one barrel petroleum costs about 5 USD and at the end of 70 days, 320 barrels petroleum can be produced. When 0.5% Fe is added, oil production increased to 440 barrels for the same operational time period.
Simulation of a SAGD Well Blowout Using a Reservoir/Wellbore Coupled Simulator
Authors: Vanegas P. J. Walter , Cunha Luciane B. , Worth Darren J. , Crepin Stephan
Published: October 2008

Under the expected operating conditions of a Steam Assisted Gravity Drainage (SAGD) pilot project, it is anticipated that both the injection and the production wells will be able to flow unassisted to surface should a loss of well control incident occur. Industry practice regarding the design of such flowing wells dictates that the well completion include double barriers in the production tubing string and the production casing annulus. Unfortunately, downhole equipment suitable for such a high temperature application does not currently exist. To help evaluate the comparative risk between a double and single barrier completion, a reservoir modeling study was conducted to investigate the flowing potential (flow rates, durations and composition of the fluids) of the SAGD pilot wells under various blowout scenarios.

This paper presents the results of this reservoir modeling study in terms of the coupled wellbore/reservoir behavior during the blowout condition. A commercial coupled wellbore/reservoir simulator was used along with a "custom" code developed to include a critical choke velocity constraint into the reservoir simulation considerations.

The various blowout scenarios investigated include flow through both the injection and the production wells, at three different points during the production life of the well pair (beginning of the steam injection phase, middle of the steam chamber development and end of the steam injection phase) and through three possible flow paths (through the tubing, through the tubing-casing annulus and through both the tubing and the annulus).

The reservoir modeling confirmed that both the injection and the production wells in this SAGD application have the potential for a blowout lasting for significant periods of times should a loss of well control occur, and with liquid rates that can be over 50 times the normal production liquid rates.
Geomechanics for Interpreting SAGD Monitoring Using Micro-Seismicity and Surface Tiltmeters
Authors: de Pater Hans , de Koning Johan , Maxwell Shawn , Walters Dale
Published: October 2008

We have modeled the warm-up phase of a SAGD project using a coupled reservoir simulator and stress model. We matched the injection pressure by adjusting the reservoir permeability. A fair match between data and model was obtained. Micro-seismic monitoring indicated localized injection at the toe, which was used in the model. Also, the seismic signature indicated strike slip and possibly overthrust fault slippage or casing failure as cause of the seismicity. This confirms the reservoir and stress model used in the interpretation. While most of the steam was injected at the toe, the uplift was largest at the heel of the well. This can be best explained by reservoir heterogeneity, which implies that surface heave measured with tiltmeters can best be interpreted using a geomechanical model. The matched coupled model can be used for optimizing the completion and injection process.
In-situ Water Vaporization Improves Bitumen Production During Electrothermal Processes
Authors: Wang Jie , McGee Bruce , Kantzas Apostolos
Published: October 2008

Thermal methods for heavy oil and bitumen recovery include the injection of steam as in the SAGD (Steam Assisted Gravity Drainage), CSS (Cyclic Steam Stimulation), and steam flooding processes. Thermal energy increases the temperature of the oil, reducing its viscosity and thereby allowing it to flow efficiently towards a production well. The electro-thermal process is an alternative (possibly a compliment) to steam injection processes. With ever-increasing natural gas prices, or corresponding reduction of natural gas supply, electro-thermal processes can be economically competitive compared to other thermal methods. An optimized electrothermal process can bring over 75% of heavy oil or bitumen to the surface as demonstrated by a recent field pilot in the Athabasca oil sands.

This study aims at optimizing electrothermal processes by vaporizing water in-situ. The Computer Modeling Group (CMG) reservoir simulation software is used to perform a series of preliminary simulation studies of electro-thermal heating in the Athabasca oil sands. First of all, the incremental oil recovery by vaporization is estimated based on a three block conceptual model. Secondly, a field scale model is set up to evaluate the effect of electrode spacing, water injection rate and electrical heating rate on the ultimate bitumen recovery. A statistic tool is used to analyze the simulation results in order to spot the optimum condition for maximizing bitumen production with water vaporization in-situ.

Simulation results showed that the incremental recovery brought by the water vaporization could be as high as 25% OOIP for Athabasca oil sands reservoirs based on the conceptual model. A sensitivity study on the field scale model, showed that the combination of medium electrical heating rate, low water injection rate, and small electrode spacing can maximize bitumen production economically with mild water vaporization in-situ.

The study demonstrated a promising technique for the future heavy oil / bitumen production. It also showed that electro-thermal processes could be operated independently and produce considerable amount of bitumen economically.
Preconditioning Methods to Improve SAGD Performance in Heavy Oil and Bitumen Reservoirs with Variable Oil Phase Viscosity
Authors: Gates I. D. , Larter S. R. , Adams J. J. , Snowdon L. , Jiang C.
Published: October 2008

The majority of the world's petroleum resources are contained in heavy oil and oil sand reservoirs. Average recoveries from heavy oil and oil sand reservoirs are typically low ranging from 5 to 15 percent for cold heavy oil production and from 30 to 85 percent for steam-based in situ processes. There are two reasons for this: first, geological heterogeneity in the form of variable porosity and permeability properties and secondly, fluid heterogeneities in the form of variable saturations, fluid compositions and thus viscosity. Geological heterogeneities refer to spatial variations of porosity, permeability, relative-permeability curves, shale and mud layers, etc. Fluid heterogeneities refer to spatial variations of the fluid composition and properties such as viscosity and density. Given that the permeability often varies by less than an order of magnitude whereas the oil viscosity varies by up to two orders of magnitude in a bitumen reservoir, the controlling variable on recovery of these resources is often fluid compositional variations. Due to the large viscosity contrast between oil and water at native reservoir conditions water is often the most mobile phase within a bitumen reservoir. This research identifies preconditioning techniques that can be used to alter reservoir or fluid (oil or water) properties prior to thermal recovery reducing adverse reservoir factors and improving recovery, environmental impact and process economics. We describe here a simulation study of one application related to modifying the variation of oil viscosity in the reservoir prior to steam injection. The methods make use of mobile water within the reservoir, to distribute viscosity-reducing agents before steam injection, and represent another means of geotailoring recovery processes to the features of the reservoir. The main benefit is that recovery process performance, both in terms of oil production rate and thermal efficiency, is improved.
Accurate Numerical Simulation of Reaction-Diffusion Processes for Heavy Oil Recovery
Authors: Govind Pradeep Ananth , Srinivasan Sanjay
Published: October 2008

Many examples of reaction-diffusion processes are encountered in enhanced heavy oil recovery applications. A typical instance of such a process is when a chemical diffuses through a fluid column and then undergoes reaction with another chemical species. The reaction products further diffuse through the porous media. The challenges involved in modeling these processes are accurate representation of the propagation of the reaction front which is very localized and accurate depiction of diffusion which is one of the main transport mechanisms. We evaluate a simulation model for the displacement of carbon dioxide in a simultaneous injection of carbon dioxide and elemental sodium in a heavy oil reservoir. The main objective of using sodium in this process is the highly exothermic reaction of sodium with the in-situ water that results in the liberation of heat that in turn reduces the oil viscosity. Another important advantage of this process is the formation of sodium hydroxide that reduces the interfacial tension at the bitumen interface.

The modeling of the mechanism of transport of sodium to the reaction interface through diffusion and the subsequent displacement of the reaction zone was attempted using the commercial software STARS™. When sodium suspended in liquid carbon dioxide is injected into the reservoir, it has to diffuse through the carrier phase and then interact with water. This mechanism has to be adequately captured at the scale of the simulation grid blocks. A random walk diffusion algorithm with reactive dissipation is implemented to more accurately represent reaction/diffusion processes and to study their scaling characteristics.
Potential Use of Produced Oil Sample Analysis to Monitor SAGD Performance
Authors: Li Z. , Wollen C. , Yang P. , Fustic M.
Published: October 2008

Bitumen is too viscous to be produced by conventional recovery methods and significant amounts are too deep to be recovered by mining, necessitating enhanced in-situ oil recovery techniques. The majority of operating and planned in-situ bitumen projects employ thermal techniques to lower the bitumen's viscosity, allowing it to be produced. The viscosity characteristics of the bitumen consequently have a significant effect on production rates and recovery. Bitumen viscosity and chemical composition variation with depth within a single reservoir column has been reported for many heavy oil and oil sand reservoirs in the Western Canadian Sedimentary Basin and elsewhere in the world.

This study investigates, through reservoir simulation, the effects of viscosity variation with depth on the SAGD process and the resulting produced oil characteristics. Oil characteristics, including chemical component and viscosity profiles were built into a variety of reservoir simulation models. The simulation results indicate that the produced oil viscosity and component concentration vary as the steam chamber develops. The trend of the produced oil characteristics is related to the original in-situ profiles of and the reservoir flow barriers. In conjunction with oil rate, surface heave, or other available data, the produced oil characteristics may be used to suggest steam chamber development and the presence of barriers or baffles. The presented approach has potential to become a useful technique for SAGD steam chamber growth monitoring and production optimization.
Applicability of CO2-Based Vapex Process to Recover Athabasca Bitumen
Authors: Badamchi-Zadeh A. , Maini B. B. , Yarranton H. W.
Published: October 2008

Employing CO2 as the non-condensable gas in the Vapex process is an attractive option that could provide environmental benefits of CO2 sequestration along with improved Vapex performance. Mixtures of CO2 and a hydrocarbon such as propane allow the solvent to be tailored to different reservoir conditions. To test potential solvent mixtures, the phase behavior and physical properties and physical model experiments are required. We have previously reported on the phase behavior, viscosity and density of the CO2-propane-Athabasca Bitumen systems (Badamchizadeh et al., 2008a,b). These results confirmed the ability of carbon dioxide and propane mixtures to sufficiently reduce Athabasca bitumen viscosity and were used to design the solvent compositions utilized in the physical model tests reported here.

The experimental approach used in these tests was to use a fixed composition of the CO2 and propane mixture as the Vapex solvent. The objective of this work was to evaluate the performance of this solvent in recovering the Athabasca bitumen. The experiments were carried out at room temperature in a physical model. In-line measurements of the density and viscosity of the produced oil were used to gain further insight into the mechanisms involved in the process.
Bridging HSE Risk with Cost Analysis: A Model for Optimising Completion Fluid Choice
Authors: Gilbert Ylva , Kumpulainen Anna
Published: October 2008

The hazard profile of a well construction fluid (WCF) impacts on environmental consent conditions, waste management choices and health, safety and environment (HSE) risk levels. All of these impacts can have a significant influence on the cost of the well construction operation. HSE hazards and hazard related costs should therefore be considered as an integral part of the process of choosing the most cost-effective WCF.

The quantification and absolute costing of the HSE risk posed by a WCF is laborious and there is no standard or universally acceptable method for absolute calculations. In order to overcome these constraints, a transparent, systematic and operation-specific model for assessing the overall cost consequences related to the HSE hazard profile was developed. The model has first and foremost been developed as a management tool, which allows fluid HSE aspects to be taken into account on par with other variables that impinge of project economics.

The model is based on relating inherent fluid HSE properties, such as ecotoxicology and occupational health hazards, to legal and corporate requirements for HSE and waste management. These requirements directly influence operational variables and consequent costs. The primary objective of the development work was to create a user friendly tool for comparing the overall effect on operational costs that different fluids may have. It includes costs related to normal operations as well as predicted cost of risk. The model also allows the costing of HSE risks associated with using a particular WCF to be related to corporate HSE policy targets.

The developed model was implemented in Excel. It provides the framework for comparing the WCF options based on operation-specific data input. This paper presents the model structure and the organisation of the supporting tool, using two high-density completion fluids (cesium formate and zinc bromide brines) as example fluids. The assessment gives a clear overview of the comparative HSE risk levels and the associated financial implications of choosing one or the other of the assessed fluids. The model allows operators the possibility to reflect their individual corporate HSE values in the costing exercise through application of weighting factors By bridging the gap between cost analysis and HSE assessments, the method provides a powerful yet practical means for incorporating HSE aspects into the process of defining and selecting the most cost-effective WCF.
Operational Risk Management Tools
Authors: Melhem Georges A. , Prophet Neil
Published: October 2008

Risk management in the petrochemical industry includes a wide variety of activities, one of which is quantitative risk assessment. The quality of a quantitative risk assessment study is highly dependent on the effectiveness of the hazard identification stage - it is essential that all applicable hazards and potential hazard scenarios are considered. When analyzing large refineries, the number of hazard scenarios can run into thousands; so it is important that these hazard scenarios have a relevant risk impact on the study results, while excluding those scenarios with negligible risk contribution. Two general types of scenarios leading to loss of containment are typically considered: "generic" and "non-generic".

This paper outlines and describes a tool to enhance operational risk management – it describes an effective methodology for streamlining hazard scenario identification and development for large, site wide, refinery quantitative risk assessments. The paper also provides practical guidance for the estimation of both "generic" and "non-generic" scenario failure rate data. Safeguards such as basic process controls and safety instrumented systems that can be used to mitigate undesirable events and to reduce risks are considered in the scenario identification and development methodology.
Managing Risks During the Transition of Dolphin Energy Project from Construction to Full Operations
Authors: Behie Stewart , Fryer Robert , Ashby Mike , Al Emadi Hassan , Al Rahbi Ali , Laczko Larry
Published: October 2008

Dolphin Energy Limited (DEL) is a Gas processing and distribution organization that produces and exports over 2.1 billion scfd of sales quality natural gas to the UAE and Oman from the State of Qatar. From inception to completion and full operation, the project took seven years to complete.

Once construction began, the DEL project consumed some 125 million man-hours (onshore and offshore) over a period of 5 years to complete at a cost of around $US 5 billion. The facilities involved two offshore platforms each with 12 wells, two 80 km 36 inch underwater wet gas pipelines from the platforms to the onshore plant, a four train onshore sour gas processing plant, a 364km 48 inch subsea, export gas pipeline from Ras Laffan, Qatar to Taweelah UAE, a gas receiving facility and a DEL managed distribution network which supplies gas to the UAE and Oman.

The two offshore platforms were the first facilities to be constructed to allow for drilling of production wells so that wet gas supply would be available to the staged processing trains onshore as they became available. The commissioning and start-up of the onshore plant and handover of processing units was executed in phases to maximise unit readiness and minimise exposure impact on the construction workforce.

This lengthy Simultaneous Operations (SIMOPS) period offered a number of major challenges from an overall risk management perspective. A number of risk control measures were successfully implemented to manage the work resulting in a controlled start-up and absence of any serious incidents and very good overall HSE performance.
Fitness to Work
Authors: Dipple John , Marcial Lilian
Published: October 2008

Personnel involved in incident response can be put under significant amounts of physical, thermal and emotional stress and it is unrealistic to expect them to perform either individually or as a team without proper pre assessment on real time monitoring during the incident. In this paper we will look at a well tested programme for a commercial and multi national HAZMAT incident response team that has responded to over 30 Incidents in the region over the last 12 months and how it works in practice for the permanent members of the team and also how it can be modified to be used with third party contractors to ensure that their health and safety is not compromised. The paper will cover Medical AssessmentBenchmarkingSurveillance monitoringIn field practicesFitness testing and programmes

Field results will be presented and used to demonstrate the difference that having an effective programme can make

Please note that the authors are operational personnel with a total of over 30 years of experience in this field and the paper is targeted at operational and HSE personnel rather than medical practitioners.
Risk Reduction for H2S Operations Offshore - A Mindset Change
Authors: Nevil Adkins , Refah Unsal
Published: October 2008

The Front End Engineering Design (FEED) for the Pearl GTL Offshore Platforms was based on a successful central North Sea sweet gas analogue with a few additions intended to address the problems of working with a highly sour process gas. As the detailed design progressed it became clear that although many of the features introduced by the FEED team were effective, certain aspects of the platform’s design could not be considered to have As Low As Reasonably Practicable (ALARP) residual risks since the initial assumptions could not be sustained. The Risk Reduction Philosophy harmonized the various engineering and operations philosophies that had been issued on the project and provided an overview of how the major hazards would be managed to ALARP. Of particular note is the drive to design a facility with maximum inherent safety, minimum personnel exposure and ensure that Operators can access and escape the facility with minimal risk.

Inherent Safety

A facility that is inherently safe is one that is impossible to have an incident with – a facility with a design pressure of 301bar connected to a well with a maximum closed-in tubing head pressure of 275bar cannot be over-pressured. If it cannot be over-pressured there is no need for a relief valve, so the number of flanges (leak paths) is reduced therefore reducing the probability of a leak. Additionally the maintainable equipment count is reduced, thereby reducing the personnel exposure hours – a double knock in reducing individual risk per annum.

Safe access, safe escape

The demands on the Pearl platforms are very tough; very high (~98%) availability production with a minimum intervention concept targeting maintenance only every 90days with the intent of using only the safest form of transport; boat access. Metocean forecasts have shown that with a conventional boat landing the expected waiting-on-weather time for a twelve hour bunkering operation could exceed a week in winter and the probability of getting a week long period to carry out routine maintenance was around 15%. Shell’s experience in the southern North Sea in using a heave-compensated gangway, deployed from a dynamically-positioned support vessel, provided the solution and due to having an operational window of up to 2.5m significant wave height the percentage of time in which the platform is inaccessible by sea drops from 30% to 3% during the winter months. Ready access also means a ready escape in case there is a gas release on the platform thereby increasing safety.
Hydrogen Sulfide Detection in Offshore Platforms
Authors: Edward Naranjo , Kornbech Mads
Published: October 2008

Hydrogen sulfide (H2S) is a toxic gas and one of the most common byproducts in the production of crude oil and natural gas. In offshore operations, hydrogen sulfide can be found in drilling fluids, recovered core samples or core barrels, and on downhole equipment. In most instances, the initial sources of hydrogen sulfide are small in volume, but can easily reach dangerous quantities; hence the need to protect personnel from the dangers of sour gas.

A variety of gas detection instruments are available for the detection of hydrogen sulfide. Solid state and electrochemical sensors are two widely used types in offshore installations. These instruments provide coverage at short ranges, around 1 – 5 meters, and are capable of establishing the presence of the gas at concentrations well below the Threshold Limit Value (TLV) of the gas. Equally important, the solid state and electrochemical devices offer quick response and stability. Such combination makes them suitable for use in harsh environments.

Recently ultrasonic gas leak detectors have also been employed as a last protective layer in the detection of hydrogen sulfide. Unlike point conventional detectors, the ultrasonic gas leak monitors supervise wide areas for high pressure sources of the gas. They do so by measuring the airborne ultrasound produced by a leak above a pre-defined threshold, providing a measure of the leak rate. These non-concentration based detectors do not require transport of the gas to the sensor, and in low noise environments, are capable of detecting leaks as low as 0.01 kg/s.

This paper examines the use of various detection techniques for improving the performance of hydrogen sulfide detection systems. An example of an oil and gas development project in central Asia is shown. Such case illustrates that a combination of different sensor technologies can enhance overall plant safety; and consequently, reduce the risk associated with the extraction of hydrogen sulfide in offshore facilities.
Securing Oil & Gas Assets
Authors: Mehdizadeh Yahya
Published: October 2008

This paper discusses the physical threat vectors that are impacting oil and gas assets. It identifies factors making these installations vulnerable, attack scenarios, and provides mitigation strategies based on physical security solutions. The concept of defense in depth is used to present technologies that can reduce and manage risk levels, while the integrated approach focuses on command and control (C2) technologies that give a holistic view to the security posture of an energy asset. This paper does not endorse or recommend specific types of deterrent technology, but options are presented to aid in fully understanding potential security solutions.
A dose estimation for persons occupationally exposed to ionizing radiation in Montenegro
Authors: Milatovic Aleksandra , Ivanovic Sonja , Spasic-Jokic Vesna , Jovanovic Slobodan
Published: October 2008

Background: Persons occupationally exposed to ionizing radiation are subject to radiation protection due to potential harmful effects of radiation. Dose monitoring of professionally exposed workers is an essential regulatory measure in radiation protec?tion. In Montenegro, which is a small "non-nuclear" country with population of 670.000, the use of radiation sources is limited to common medical applications and a few industrial ones, with estimated 500-600 occupationally exposed individuals. Methods: Centre for Eco-toxicological Research in Podgorica, acting as a technical support organization to regulatory authorities, is the first and only institution in the country performing personal dosimetry service (since 2007). Initial results, obtained using a Harshaw 4500 TLD reader, and as the results of personal electronic dosimeters DOSICARD readings were summarized in present paper. Results: Average equivalent doses per month are found to be 70.3 ?Sv for physicians and 82.7 ?Sv for technicians. The highest dose recorded in one month was 1100 ?Sv for a RTG technician in Niksic Hospital. Conclusion: Results for all subjects monitored up to now (medical staff) are below internationally recommended dose limits.
Radiotherapy of endometrial carcinoma: Who needs to be irradiated?
Authors: Erak Marko , Novakovic Petar , Erak Dragica , Mandic Aljosa , Tesanovic Dusanka , Djuran Branislav
Published: October 2008

Due to gynecological oncology general strategy and everyday aspiration for individual approach to malignant tumors, guidelines in treatment approach are not finally established, and they are controversial in some demands with age of the patients. If we look general treatment strategy approach to invasive endometrial cancer it is proved that operative treatment is priority and base line of treating endometrial carcinoma I and II clinical stage (FIGO) if there is general conditions for surgery, allowing complicated treatment in this age. Previous experience are showing that decision about application of therapy procedures in treatment of endometrial carcinoma every case have to has individual approach, regarding all known prognostic criteria: clinical stage, histological type, myometrial infiltration, lymph-vascular space involvement, size of the tumor and its localiza?tion, depth of myometrial infiltration, invading of serosa, cervix and adnexa, present of hormonal tissue receptors, information about lymph node: number, size and size of the biggest metastases, data about both extra nodular expansion of tumor and peritoneal cytology. The use of postoperative radiotherapy should be limited to group of patients with highly enough risk of locoregional recurrence (15% and more) as risk warranty of morbidity connected to radiological treatment. Therefore, the goal of postoperative radiotherapy appliance is to achieve maximum locoregional disease control and survival without relapse. New Radiotherapy (RT) techniques, Conformal Radiotherapy (CFRT) and Intensity Modulated radiotherapy (IMRT), reduce the risk of complications, especially for patients with multimodal treatment.
Rituximab for primary cutaneous large B-cell non-Hodgkin's lymphoma of the scalp
Authors: Colovic Natasa , Jurisic Vladimir , Colovic Milica
Published: October 2008

A 46-year-old man with a primary cutaneous large B-cell non-Hodgkin's lymphomas is reported. His mother died of gastric lymphoma and his sib brother is 20 years in a remission of T-cell lymphoma. He noticed the appearance of localized baldness and rash of the scalp 16 years before a hematological diagnosis was made. Diagnostic procedures performed in 2006 dem?onstrated progressive disease with crusted skin nodules (7x7.2cm) which exuded serous fluid. Histopathologcal and immuno?histochemical results suggested the diagnosis of a primary cutaneous large B-cell non-Hodgkin's lymphoma. The patient was treated with rituximab and chemotherapy (protocol R-CHOP) and achieved a complete remission. A rather protracted indolent phase of disease, the familial history of lymphoma, and an excellent response to immunochemotherapy contributed to an unusual presentation of this patient's disease.
A typology of rural areas in Serbia
Authors: Bogdanov Natalija , Meredith David , Efstratoglou Sophia
Published: October 2008

The goal of this paper is to present a method to establish the typology of rural areas in Serbia. Initially the OECD rurality criterion was applied to define the rural areas in Serbia. Subsequently, relevant indicators were selected (demographic, geographic, economic, employment-related, human capital, agricultural, tourism and infrastructure) and used to define and distinguish relatively homogeneous rural regions, based on correlation analysis, factor analysis (VARIMAX method) and cluster analysis. Cluster analysis revealed six regions of different sizes and characteristics. Practical considerations reduced this to four types, resulting in a robust scheme which accurately reflects the heterogeneous nature of rural Serbia.
Corporate strategic branding: How country and corporate brands come together
Authors: Djordjevic Bojan
Published: October 2008

The concept of countries as brands has been increasingly recognized in the post-modern global world. A strong country brand can provide corporate brands with a unique set of values, which supports their positioning on the international market. Simultaneously, once corporate brands achieve worldwide success, they contribute actively to developing new features of the country brand. Consumers pay more and more attention to products' country of origin. When the name of a country is mentioned, they can have positive associations (high quality, modern design, product innovation), which means that the country itself has a powerful brand. However, there are opposite cases where we talk about the weak branding of a particular country. It is necessary to mobilize all the available forces of politicians, business people, artists, sportsmen and scientists to create a strategy for enhancing the image and reputation of a country on the international markets, i.e. for creating the national branding strategy.
A question of strategy: To be a pioneer or a follower?
Authors: Kalicanin Djordje
Published: October 2008

One of the most important questions faced by business leaders in the strategic management process is a choice of timing to launch new product/technologies and enter new markets. There are two options: to be a pioneer or to be a follower. Both have advantages and risks. Pioneers often have higher profitability, greater market share, and a longer business life, but the relative success of each strategy depends on several factors, both internal and external (pace of evolution of technology and markets).
The market chain of fruit production in Serbia: A case study of raspberry and sour cherry cultivation
Authors: Radosavljevic Katica
Published: October 2008

The trade in fresh and frozen fruit is complex and fragmentary. Currently producers are forced to use a variety of marketing channels - farmers' markets, processing industries, trade companies and brokers. To increase quality, production, profitability and exports, it is essential to maximize cooperation between producers, processors, wholesalers and retailers. Vertically and laterally integrated fruit marketing channels demand the smallest number of intermediaries and direct relations with consumers. In past decades, fruit production in Serbia was characterized by irrational resource allocation. Neglect of the agribusiness marketing concept led to supply shortages. As a result, prices increased while quality decreased. Only integrated marketing concepts can boost quality, yields, profitability and competitiveness.
Increase of the energy efficiency in paper industry
Authors: Krgovic Milorad , Valent Vladimir , Krsikapa Marina , Milojevic Miodrag , Raseta Branko , Osap Danijela
Published: October 2008

In this work, phenomena of heat and mass transfer in process of paper drying are given, certain technology units are analyzed, while possibility for decrease of specific heat and electric energy consumption by modernization of technology is examined. Some of the solutions applied on paper machines worldwide in order to improve energy efficiency are shown. Theoretic and practical discoveries in this area are applied in Board factory UMKA, and these results are shown in the work as well.
Qualitative analysis of am and fm screening in multicolor offset printing
Authors: Pasic Roberto , Angelovska Silvana , Dimitrieska Cvete
Published: October 2008

This work is based on analysis and experimental verification with the aim to determine difference in several printing attributes, on AM and FM screenings at multicolor offset print.
Benzylation of N-phenyl-2-phenylacetamide under microwave irradiation
Authors: Mijin Dusan , Prascevic Masa , Petrovic Slobodan
Published: October 2008

N-Phenyl-2-phenylacetamide was alkylated with benzyl chloride in the presence of powdered potassium hydroxide under microwave irradiation in a solvent-free system. The reactions were also performed in the presence of phase-transfer catalysts. The formation of N-, O- and C-products of alkylation was followed by gas chromatography. The N-product was found to be the main product under microwave irradiation. The O-product was obtained in higher yields when an excess of base and benzyl chloride was used.
The impact of atrazine on several biochemical properties of chernozem soil
Authors: Radivojevic Lj. , Gasic Slavica , Santric Lj. , Stankovic-Kalezic R.
Published: October 2008

The impact of the pesticide atrazine on biochemical processes in soil was investigated. Atrazine loadings of 8.0, 40.0 and 80.0 mg/kg soil were laboratory tested in an experiment set up on a clay loam soil. Dehydrogenase activity, change in biomass carbon, soil respiration and metabolic coefficient were examined. The samples were collected for analysis 1, 7, 14, 21, 30 and 60 days after atrazine application. The acquired data indicated that the effect of atrazine on the biochemical activity of the soil depended on its application rate and duration of activity, and the effect was either stimulating or inhibiting. However, the detected changes were found to be transient, indicating that there is no real risk of the compound disrupting the balance of biochemical processes in soil.
Antifungal activity of Nepeta rtanjensis essential oil
Authors: Grbic-Ljaljevic Milica , Stupar Milos , Vukojevic Jelena , Sokovic Marina , Misic Danijela , Grubisic Dragoljub , Ristic Mihailo
Published: October 2008

The chemical composition and antifungal activity of the essential oil of an endemic Serbian plant Nepeta rtanjensis Diklic & Milojevic was studied. The essential oil was isolated from cultivated plants. Inhibition of mycelia growth of five micromycetes, two Alternaria species originally isolated from N. rtanjensis, Cladosporium cladosporoides, Trichoderma viride and Bipolaris spicifera, were tested using the agar dilution method. The essential oil of N. rtanjensis, the main component of which was 4aa,7a,7ab-nepetalactone, showed strong antifungal activity against all the tested micromycetes. The minimum inhibitory concentration of N. rtanjensis essential oil ranged from 0.6 to 1.4 ?g mL-1. The fungi most sensitive to the tested oil were Alternaria species, while Trichoderma viride was the most resistant.
Synthesis of lithium ferrites from polymetallic carboxylates
Authors: Gingasu Dana , Mindru Ioana , Patron Luminita , Stoleriu Stefania
Published: October 2008

Lithium ferrite was prepared by the thermal decomposition of three polynuclear complex compounds containing as ligands the anions of malic, tartaric and gluconic acid: (NH4)2[Fe2.5Li0.5(C4H4O5)3(OH)4(H2O)2]?4H2O (I), (NH4)6[Fe2.5Li0.5(C4H4O6)3(OH)8]?2H2O (II) and (NH4)2[Fe2.5Li0.5(C6H11O7)3(OH)7] (III). The polynuclear complex precursors were characterized by chemical analysis, IR and UV-Vis spectra, magnetic measurements and thermal analysis. The obtained lithium ferrites were characterized by XRD, scanning electron microscopy, IR spectra and magnetic measurements. The single a-Li0.5Fe2.5O4 phase was obtained by thermal decomposition of the tartarate complex annealed at 700?C for 1 h. The magnetization value ? 50 emu g-1 is lower than that obtained for the bulk lithium ferrite due to the nanostructural character of the ferrite. The particle size was smaller than 100 nm.
The Hall rule in fluoranthene-type benzenoid hydrocarbons
Authors: Djurdjevic Jelena , Radenkovic Slavko , Gutman Ivan
Published: October 2008

The applicability of the Hall rule (linear relation between the total ?-electron energy and the number of Kekul? structures) was investigated in the case of fluoranthene-type benzenoid hydrocarbons. It was found that the originnal Hall rule is not obeyed, but holds for sets of isomers with a fixed number of bay regions. For such groups of isomers, two apparently contradictory Hall-type rules were conceived, and it was found that both give almost identical numerical results.
Characterization of various zinc oxide catalysts and their activity in the dehydration-dehydrogenation of isobutanol
Authors: Saad Lamia , Riad Mary
Published: October 2008

Mono and bifunctional zinc oxide catalysts were prepared to study their activity in the catalytic conversion of isobutanol. The prepared catalysts were characterized by X-ray diffraction analysis and nitrogen adsorption measurements. The conversion of isobutanol was taken as a model reaction to measure the catalytic activity of the prepared oxide catalysts. The overall conversion yield of competitive dehydration-dehydrogenation reactions of isobutanol was found to be higher over the binary oxide catalysts than over the single oxide one at all reaction temperature within the range 250-400?C. The binary oxide catalysts were more selective for isobutene, as the predominant dehydrated product. The single oxide catalyst exhibited higher selectivity towards isobutyraldehyde as the dehydrogenated product, and the selectivity increased with increasing reaction temperature.