bluuebunny/crossref_metadata_2025 huggingface dataset:
The Drilling Technique Of The Parallel Horizontal Well Of Steam-Assisted Gravity Draingage And Vertical Well Connectivity
Authors: Nie Minghu , Zhang Wenbo , Lu Zongyu , Wang Zhaofei , Liu Yingbiao
Published: July 2012

To address the unfavorable thermal recovery factor of abundant ultra-viscous oil resources using vertical and horizontal wells in Xinjiang's Fengcheng Oilfield, Steam-Assisted Gravity Drainage (SAGD) parallel horizontal wells were experimentally drilled in block A in 2008, which delivered on 100% encountering rate of oil formations and controlled the wellbore trajectories within the design. However, the production witnessed difficulties in setting oil well pumps and insufficient submergence depth. To tackle this issue, a drilling test to connect one of the SAGD parallel horizontal wells and the vertical well was performed. With several pioneering technologies in China, the test succeeded and created a new technological approach for the development of ultra-viscous oil in Xinjiang Oilfield.

This paper describes the principle, process, and equipment of the drilling technology in the test, analyzes the field results of the section milling of large size casing, under-reaming of the intersection interval, intersection between a horizontal well and a vertical well, and down-hole gravel packing, and presents comments on the field application and future development of the technology.
Development and Application of Adjustable Frequency Pulse Jet Generating Tool to Improve Rate of Penetration in Deep Wells
Authors: Cui Longlian , Zhang Fucheng , Wang Haige , Ge Yuhua , Zhuo Lubin , Hong Li
Published: July 2012

Improving the rate of penetration in deep well is long-term problems for drilling industry. Pulsed jet drilling which has been proved in field, is a cost-effective way to improve the rate of penetration. An Adjustable frequency pulsed jet generating tool was developed in this paper. The main parts of the adjustable frequency pulsed jet generating tool include turbine, valves, and a resonance pulse chamber. Rotary valve is driven by the turbine. Rotation of the rotary valve causes the state of drilling fluid flow from the continuous to the periodic. So, the periodic flow has frequency and amplitude. In order to obtain higher amplitude, a resonance pulse chamber was used to amplify the amplitude of the periodic drilling fluid flow. The pulsed jet is formed when the periodic drilling fluid flow is issued from the nozzles of the bits. The frequency of the pulsed jet can be easily adjusted by changing the parameters of the rotary valves.

In this paper the working principle of the adjustable frequency pulsed jet generating tool was analyzed. Theoretical calculations and experiments were carried out to reveal the characteristic of the pulsed jet. The effect of the flow rates on the frequency and amplitude of the pulsed jet were studied in detailed. The experiment results show that the pulsed jet with lower frequency and higher amplitude can significantly enhance the rate of penetration in deep wells. The adjustable frequency pulsed jet generating tools have been tested in several wells. The field test results show that the rates of penetration were improved by 15-45% and the tool can meet the operation requirements. Adjustable frequency pulsed jet generating tool as an effective approach to improve ROP, has great application potential in deep well drilling.
Drilling of an Ultra-Deep Exploratory Well - Problems and Solutions: A Case Study
Authors: Chen Peng , Cheng Cunzhi , Xin Junhe , Wang Xi , Ye Dongqing , Feng Guoliang
Published: July 2012

This paper presents a case history on drilling of an ultra-deep exploratory well with a lot of problems and final solution in a complicated K structure in Uzbekistan. Drilling troubles include serious stuckpipe resulted from drilling-in the unexpected high pressure brine formation, malfunction of the high density drilling fluid system, and subsequent failure of the fishing jobs, unsuccessful sidetracking, bad job of cementing, etc.

After the drilling fluid system was improved, the high pressure layers were isolated, and the proper drilling measures were carried out, the second sidetracking gained success and the well was completed. Afterwards, an adjacent ultra-deep well in the same structure was smoothly drilled and completed by means of optimization of the casing programs, drilling fluid system and technical measures.

Drilling practices of previous offset well indicated that the formation is pay zone and produced oil, while the same formation at the same depth in the well JD3# produces brine water, which resulted in overflow during twice sidetracking of the same formation. The high and low pressure layers existed in the same section after drilling-in brine formation would produce complex against drilling and subsequent operations, therefore a 7-inch liner was set to isolate the high pressure formation, so as to create a good condition for deeper drilling operation. High-density drilling fluid with good precipitation stability and lubricant anti-sloughing properties also contributed to the success in drilling of high pressure brine layer and salt gypsum formation.

Accurate determination of the must-be-blocked point is the key to the success. Drilling of the well with problems and its final solution could be used for a technical reference as drilling in deep or ultra-deep wells in similar geologically complicated oil and gas fields.
Application of Water-base Semipermeable Membrane Drilling Fluid Technology in Sebei Natural Gas Field
Authors: Wu Jinxing , Li Xiucun , Liu Youcheng , Fan Zuoqi , Dai Dengzhi , Li Xiaojun , Wei Xihai , Wang Fengming , Chen Hua , Zhang Xiaoguang , Zhang Haiyang , Tang Bao
Published: July 2012

This paper introduces the application of new technology on water-base semipermeable membrane drilling fluid in Sebei Natural Gas Field. Experiments relating to low rate of mud yielding, rate of recovery for drilling cuttings and antipollution, etc. have been evaluated the performances of this drilling fluid, indicating a high semipermeable membrane performance, strong inhibition of shale aquation, expansion and dispersancy, good resistance of pollution by cuttings and high-temperature rheological behavior. In Sebei Natural Gas Field, the application of the drilling fluid shows the good performances as above said as well as prevention of borehole collapse, low wellbore expansion rate and borehole is regular.
Simulating Experiments of Hydrajet Perforating Process
Authors: Hu Qiangfa , Zhu Feng , Lv Weiping
Published: July 2012

Experimental researches introduced in this paper combined the fracturing technology, which was needed in Chang-6 stratum of Changqing Oilfield, were carried out with full-size and holo-authentic. and used field jetting tools, parameters and equipments to simulate the process of hydrajet perforating and fracture initiation. All of these were different from the previous.

A real-hole shape and crack structure of the near-wellbore were obtained while dissection 9 experimental samples by special tools.

The experiment results shown that: The whole jetting hole is tear-drop shaped, including four parts: casing perforation, entrance sputtering section, cement necking section and main section. When fracture initiates, a slim channel with gladiate shape is extended in the end of the hole. Secondly, the sample will fracture when jetting velocity is high enough under test condition. It indicates that pressure in jetting hole increases obviously when jetting velocity increases. Thirdly, jetting flow erodes out a slim channel along crack propagate direction when fracture initiates, which increases the jetting hole length doubly and enhances the penetration efficiency. Finally, six individual channels are connected by crack when fracture initiates. It indicates that jetting channels can guide the crack initiation and extension near the well bore under the test condition.

The results of the simulating experiments could be used as the design reference when jetting and fracturing in the similar stratum.
The Drilling Fluid Technology for the Top Formation in South Los Tan Blocks of Turkmenistan
Authors: Baojun Li , Lihua Gao , Changning Wang , zhipeng Lin , xiaobin Yang , Zhao Xiangyang , Changgeng Zhang
Published: July 2012

Engineering incidents frequently happened at the top formation of natural gas exploration wells and development wells in south Los Tan blocks of Turkmenistan, one of the reasons is the difficulty of conditioning drilling fluid technology. By laboratory studies & evaluations and field applications, strong inhibitory polymer and polysulfide drilling fluid used at Well's section I and section II to overcome the problems, which are included poor diagnostic grade, clay stone, unconsolidated cements for sand and clay stone, high clay content (more than 50%), serious mud-making, bit balling, sloughing and shrinking of hole, etc completely meet the need to drill big hole(26" and 17-1/2") in long open hole, as well as to deal with the downhole complexities for a long time(the longest up to 4 months) in TD 3700m wells, and they ensured the downhole's safety, made the logging and running 13-3/8"casing in long open hole with one time successful.How to achieve the performance were discussed as conclusion, for instance, polymer glue for earlier stage, polysulfide for later stage, removing useless solids effectively while highlighting inhibition, reducing dispersing agent as low as possible, keep good rheological property and carrying cutting capability, etc. These are important to process the drilling fluid, and build a a technological package of drilling fluid for the top claystone formation of natural gas well with big holes and long open hole, in south Los Tan blocks of Turkmenistan. This drilling fluid system improved the exploration &development technology in South Los Tan blocks of Turkmenistan, which well guide and offer support to explore big hole and long open hole in clay stone formation.
Multistage Pulse Deep Penetrating Perforation Technology
Authors: Weishan Zhang , Zhaohui Wang , Fengchun Liu , Guo Yang , Shuhua Wang , Yang Jing
Published: July 2012

This paper describes the effect of this technology on perforation and production increase mainly in three aspects, namely, the principle, technical characteristics and application. Field application in over 200 wells has demonstrated that multistage pulse deep perforating penetration technology is a safe and reliable perforating technology, for its utilization in an oil production well can improve the capacity, and in an exploration well can reduce leakage in the oil layer. This technology is a new perforating technology in the 21th century, which has overcomed the shortcomings of combined perforating technology and the deep- penetration jet perforating technology respectively featured by a low gunpowder load and single increase of penetration depth. It is a rational combination of jet perforating and gunpowder fracturing, with which three processes including jet perforating and two gunpowder fracturing operations can be accomplished in one running. Thus the compaction zone in the perforation channel will be crushed, and several radial and vertical cracks will be formulated around the hole to communicate natural cracks in the formation. Then the target of deep penetration into the damaged zone in near wellbore formation and improved flow conductivity of near wellbore formation will be realized and eventually the oil well capacity will be promoted. This paper is to introduce a new perforating technology, namely, the multistage pulse deep perforating penetration technology.
The Effect of High Pressure and Temperature Variation to the Hydraulic of Dual Gradient Drilling Operation
Authors: Marbun Bonar Tua , Adi Kurnia Hafiz
Published: July 2012

The petroleum industry is demanding new drilling concepts that make exploitation of deepwater resources economically feasible. Dual gradient drilling concepts have been introduced to overcome the challenges associated with deep water drilling, by providing simpler, safer, more economic well designs and therefore increasing the ultimate development and utilization of deepwater resources14.

In dual gradient drilling, the wellbore is drilled with two different annulus fluid gradients in place. By having two distinct pressure gradients, a favorable pressure profile in deepwater wells is expected specifically a profile closer to what naturally exists in the subsurface formations. This causes the utilization of dual gradient drilling will reduce the number of casing strings required, reduce the non-productive time and also enhances well control7.

Even though dual gradient drilling provides a system that makes the pressure profile closer to what naturally exists in the formation, the pressure across the annulus is also affected by changes of pressure and temperature over depth, as both of changes will affect mud density and its rheology. The study of the effects of pressure and temperature variation is required to understand the distribution of mud density and rheology over the depth and to ensure that the dual gradient drilling operation is able to be conducted in a safe manner.

As dual gradient drilling introduces additional circulation and injection lines, the calculation of injection fluid flowrate-based on the minimum flowrate required to lift the cutting to the surface-, bit hydraulic optimization and the injection fluid density-based on required pressure profile across the wellbore-is very important, since failure in determination of those parameters will cause hole cleaning problems, inefficient drilling operation, or even kick and lost circulation problems.

This paper presents a detailed hydraulic analysis of a Dual Gradient Drilling operation, which uses a liquid and gas-lift system and provides the determination of cutting transport parameters, hydraulic optimization, required injection fluid density, required injection fluid flowrate, and the pressure profile due to different annulus fluid gradients in place. To achieve an accurate determination of hydraulic parameters, a software application has been created and developed. A previous deepwater model that has been proposed by Lopes is used as the input for this software.
Development of a Marine Riser Gas Management System
Authors: Kozicz John
Published: July 2012

Drilling offshore oil and gas wells has become increasingly challenging as water and well depths have increased. In these areas drilling hazards resulting from narrow margins between pore and fracture pressures, pore pressure uncertainty, pore pressure regression, high pressure and high temperature have resulted in significant additional cost due to the time required to rectify problems associated with these hazards. As a consequence, industry has focused its efforts on developing mitigations to these challenges. Typically these developments have tended to focus on down hole solutions such as Managed Pressure Drilling and Dual Gradient Drilling; developments in drilling fluid management technologies and wellbore strengthening etc.

One area which has not received as much focus recently is that of managing the drilling process and in particular the unique aspects relatedto working in deep water from Mobile Offshore Drilling Units. In particular theprobability of relatively small undetected hydrocarbon influxes abovethe subsea BOP.

Depending on the drilling fluid and influx composition, unconstrained expansion of the influx (gas) may exceed the surface equipment handling capability (i.e. diverter system, capability and performance). Additionally, depending on the bubble pointof the drilling fluid / influx composition unconstrained evolution of fluid fromthe riser can result in a significant reduction in riser fluid level and thereforereduction in hydrostatic pressure which may impact the riser BOP system as wellas increase the probability of additional influxes entering the wellbore.

This paper describes the design, development and construction of a riser gas managementsystem which addresses these concerns.
New PDC Bit Technology Significantly Improves Performance in Hard Abrasive Bashijiqike Formation Iin China
Authors: Botton Benoit , Sha Dennis , Yinglin Jia , Guoyu Jia , Jian Zhou , Baitao Peng
Published: July 2012

Drilling the 6-5/8" vertical sections in the Tarim oilfield, in China's western Xinjiang Uygur Autonomous Region is challenging. The sections are a very hard and abrasive formation, typically a 300m interval starting at a depth of 7000m. The Cretaceous Bashijiqike formation consists of layers of quartzitic fine sandstone (35% quartz) and silificatedclaystone with conglomeratic sandstone stringers both at the top and bottom of the Section. Low rate of penetration (ROP) and short bit runs are typical for drilling this formation. With bottom hole temperatures at 148°C and mud density around 1.9sg, the application of roller cone bits and downhole tools with moving parts is limited.

Historically the section has been drilled with a simple rotary BHA consisting of a bit, 468m of 5-inch spiral drilling collar, 2565m of 4-inch drill pipe and 5-inch drill pipe to the surface. Bits used have been a variety of locally sourced 6 bladed matrix PDC bits with cutters from 8mm to 16mm. the average interval per bit was 30m at 0.47m/hr.

The increase in PDC bit performance was very critical to the overall improvement of drilling efficiency and economics in this application. A target of 50m interval at 0.5m/hr was set for the development of new PDC drill bits.

The new 6 bladed bits, using 16mm and 13mm cutters respectively, exceeded the objectives. This success is a combination of in depth analysis of the application and past performance, use of new high abrasion and impact resistant cutters and optimized cutting structure design. In the first well the new bits drilled 206% further and 62.7% faster than competitor bits used at shallower depth in the same well. On the second well, the new bits outperformed competitors by 159% on interval drilled and 38% on ROP.
The Application of Horizontal Well Coiled Tubing Frac Technique in the Daqing Oilfield
Authors: Li Lin , Wang Fengshan , Liu Chongjiang , Xu Dekui , Ji Haibo , Ban Li
Published: July 2012

The dominant horizontal frac technique is the sectional frac technique with dual-retrievable packers in the Daqing Oilfield, which adopts the small diameter dual packers to stimulate the targeted formations one by one. For several intervals treatment can be done in one trip, reverse sand flushing and pulling the tubing upward fulfill the frac operation. The well-head equipments need to be assembled and disassembled repeatedly and pulling the tubing upward can lead to the low job efficiency, intense labors and high risk of well operation when fracturing multiple formations. The coiled tubings were introduced in the Daqing Oilfield, which were integrated with the sectional frac technique in the horizontal wells to take advantage of the coiled tubing and improve the frac efficiency. Five aspects were researched as follows: The redress kits of the coiled tubing were developed to match the dual-packers frac tools; Anti-blowing equipments on the well head were researched according to the whole length of the frac tools; The resistance of the coiled tubing and filmed proppants’ tests were researched to optimize the reasonable frac parameters; The assemble test between the coiled tubing and the conventional tubing widens the application of coiled tubing.

Up to now, the coiled tubing frac technique has been applied on 3 horizontal wells in the Daqing Oilfield, among which 5 intervals were fractured in Well A. The time of tubing pull upward saved more than 1 hour to improve the rig efficiency, reduce the worker’ s labor and lower the risk of well operation. The coiled tubing frac technique indicates a step up in the field of shallow horizontal well fracturing.
Refinements to Cutter Technology and PDC Bit Hydraulics Lead to Faster Drilling in Hard/Abrasive Formations, East Texas
Authors: Zhang Youhe , Douglas Charles , Mueller Levi , Shen Yuelin , Likki Srinivas , Bits Smith
Published: July 2012

Drilling the hard/abrasive Travis Peak/Hosston and Cotton Valley formations in East Texas/North Louisiana creates a distinctive challenge for polycrystalline diamond compact (PDC) bits. Conventional PDC cutters fail quickly due to abrasive wear/spalling and/or delamination of the diamond table. Most bits are typically pulled in poor dull condition graded 1-2-WT or worse. The situation has caused stagnation in PDC performance and limited additional gains in total footage and rate of penetration (ROP). Recent scientific studies have indicated that thermal fatigue of the diamond table is the main contributing factor leading to cutter failure and is restricting further advancement of PDC drilling in East Texas and other hard and abrasive applications. To improve cutter performance the industry must:

Manufacture a cutter to resist abrasive wear and retain a sharp edge for an extended amount of footage Reduce/maintain temperature at the cutter edge to minimize thermal fatigue

To accomplish the objectives, engineers refined and implemented several new processes to increase abrasion resistance and maintain temperature at the cutter tip. This technology platform includes:

Enhanced High Temperature/High Pressure (HTHP)sintering process Refined post-pressing process to improve thermal stability Optimized hydraulics to maximizing cutter cooling

In laboratory experiments, the next generation O2 cutter has demonstrated approximately 15% improvement in resistance to abrasive wear compared to the previous generation of premium cutters (O1). Laboratory tests also confirm that optimizing cutter cooling has enhanced the life of the new shearing element. In East Texas field tests, PDC bits equipped with the new cutter and optimized hydraulics have achieved an average ROP increase of approximately 25% while producing improved dull bit condition. These new technologies are expected to have a positive economic impact in the East Texas/North Louisiana Haynesville shale play and in other hard and abrasive applications worldwide.
An Innovative Method for Horizontal Well Completion in Tight Shale Gas Reservoirs
Authors: Bai Mao
Published: July 2012

Tight shale gas is considered to be an unconventional resource because it cannot be produced without using the reservoir stimulation method. A new completion method is proposed to maximize the internal-flow surface area created from the injection. To prevent the prohibitive costs of drilling multiple vertical wells from the surface to the targeted depth interval, the multiple vertical tracks are branched from the horizontal well drilled either from the overburden layer or from underburden layer, depending on the formation suitability. The examples presented in this paper reveal the significant increase of internal surface areas when the proposed method is used as compared to the existing methods, such as the multi-stage method.
Using Qualitative Techniques to Constrain Normal Compaction Trendlines: A Methodology for Real-Time Pore Pressure Prediction in Exploration Wells
Authors: Villacastin Paulino F.
Published: July 2012

Methods used in real-time pore pressure prediction can be subdivided into two general categories: quantitative and qualitative techniques. Quantitative pore pressure prediction techniques normally used at the rigsite work with resistivity, sonic, DXC and shale density datasets and involve the use of formulae like Eaton. Qualitative techniques work with ROP, flowline temperature, cavings, background and produced gas, and torque, drag and fill datasets. These qualitative datasets are sometimes combined to come up with new techniques. Confining the analysis to one category without the other severely reduces the chances of success at correctly predicting the pore pressure profile.

In quantitative pore pressure analysis a normal compaction trend line (NCT) has to be drawn to calculate the pore pressure. The problem with drawing normal compaction trend lines is that available literature neglects to inform the reader on how to draw the normal compaction trend lines, how many trend lines are to be drawn and at what angle are they to be drawn. Examples project the simplistic idea that in most instances only one trend line is all needs to be drawn. Experience and the preponderance of drilling events, like kicks and stuck pipe, esp. in areas where minimum data is available point to the fact that compaction history is not that simplistic at all and that there are other factors at play. This now begs the question: How do you know that the normal compaction trendline being drawn, hence the calculated pore pressure is correct?

Incorporating two case studies, this paper demonstrates that qualitative techniques could be used to constrain the normal compaction trendlines that will be drawn in the quantitative study of pore pressure and in the process increase the degree of success in determining the pore pressure regime in real time.
The Path from Vertical to Horizontal Shale Gas Wells
Authors: Stolte Chris , Wu Chris , Carroll Darryrl , Liang Jin , Wang Shiqian
Published: July 2012

Shell China, in partnership with PetroChina Southwest, began exploration of the Fushun Shale Gas Block, completing its first wells in 2011. A campaign was designed to acquire subsurface data in the exploration campaign to assess the Lower Longmaxi Hot Shale interval with an end goal of assessing the feasibility of a shale gas field development in the block. As part of the first phase of the exploration campaign, two vertical wells were drilled and completed followed by three horizontal wells.

Over the execution of the first two vertical wells significant performance improvement was achieved by the service contractors involved in the project, resulting in decreased Non Productive Time (NPT). Significant preparation was conducted in order to prepare both local and international contractors for the horizontal wells in the campaign. In order to deliver the horizontal completions in an efficient manner, the Fushun team implemented learnings gained through similar projects in North America. Preparation for the horizontal well campaign included arrangement of the source water with the local community, ordering new equipment capable of completing the work, cross-posting of service contractors to unconventional assets in the U.S., and movement of experienced site-supervisors to support the Fushun project. The fracture design was also improved on each well in the campaign delivering more proppant per stage, key towards optimizing hydraulic fracturing and maximizing production potential.

Through the initial phase of exploration activities, a shale gas play in the Fushun Block has been confirmed. Operational challenges and technical learnings that were experienced in the initial exploration wells will be carried into the next phase of appraisal.
Setting design inflows to hydrodynamic flood models using a dependence model
Authors: Faulkner Duncan , Keef Caroline , Martin John
Published: July 2012

In setting design inflows to hydrodynamic models of flood flow along rivers, there can be a conflict between site-specific hydrological estimates of flow for a given return period and what the river model calculates as it routes flood hydrographs. This paper describes research carried out as part of the Flood Studies Update programme in Ireland, aimed at developing guidance on how to divide up river models and set the magnitude and timing of their inflows so that conditions in the model reach correspond to the expected design flood return period. A model for the joint distribution of flood peaks at pairs of catchments has been developed. The relationship between flood return periods is linked to physical differences between catchments. The model thus allows estimation of the statistical distribution of the flood return period expected at one site during a flood of specified return period elsewhere. A separate regression model predicts the relative timings of flood peaks on pairs of rivers. A summary of the resulting practitioner guidance is given, along with an overview of the testing of the method. The paper concludes with a discussion of the potential for application of the spatial dependence model to other problems in hydrology.
Evidence for the onset and persistence with depth of preferential flow in unsaturated fractured porous media
Authors: Ireson A. M. , Butler A. B. , Wheater H. S.
Published: July 2012

Two distinct types of fracture flow can occur in unsaturated fractured porous media: non-preferential flow, whereby the fractures and matrix wet up in equilibrium, and preferential flow, whereby water in the fractures bypasses the matrix. This has important implications for how infiltration, recharge, groundwater flooding and contaminant transport are modelled. Taking the UK Chalk as a case study, we explore evidence for the occurrence of unsaturated preferential fracture flow, considering separately its initiation in the near surface, and persistence at 20–30 m depth. We postulate a link between the apparent hysteretic response of the Chalk soil moisture characteristic, which was observed and simulated, and the initiation of preferential recharge. Focusing on observed water table responses to an extreme rainfall event on 20th July 2007, we show by inverse modelling of recharge that preferential flow persisted to a depth of 20 m below ground level, but not to 30 m, resulting in markedly different water table responses at two boreholes. These findings both lend support to our conceptualisation. However, since the observations from which preferential flow can be inferred are few and are indirect, quantification of the controls on the onset and depth persistence of preferential flow remains a significant challenge.
Frequency analysis of extreme rainfall in Cumbria, 16–20 November 2009
Authors: Stewart E. J. , Morris D. G. , Jones D. A. , Gibson H. S.
Published: July 2012

Towards the end of November 2009, west Cumbria in northwest England experienced severe flooding which caused extensive damage and disruption throughout the region. The flooding was triggered by an exceptional rainstorm during which a record 316.4 mm of rainfall was recorded at Seathwaite Farm, Borrowdale over the 24-hour period up to 00:00 on 20th November. Drawing on the results of a recent project which has developed a new model of point rainfall depth-duration-frequency (DDF) for the UK, return periods are estimated for the highest point rainfall observations available for the Cumbrian event and compared with frequency estimates derived from the Flood Estimation Handbook rainfall model (Faulkner 1999). The spatial and temporal characteristics of the storm event are examined using data from the Environment Agency's raingauge network. For the two most affected rivers, the Derwent and the Leven, return periods of catchment rainfall are estimated for durations up to 96 hours.
Safety, Security, Hygiene and Privacy in Migrant Farmworker Housing
Authors: Arcury Thomas A. , Weir Maria M. , Summers Phillip , Chen Haiying , Bailey Melissa , Wiggins Melinda F. , Bischoff Werner E. , Quandt Sara A.
Published: July 2012

Safety, security, hygiene, and privacy in migrant farmworker housing have not previously been documented, yet these attributes are important for farmworker quality of life and dignity. This analysis describes the safety, security, hygiene, and privacy of migrant farmworker housing and delineates camp characteristics that are associated with these attributes, using data collected in 183 eastern North Carolina migrant farmworker camps in 2010. Migrant farmworker housing is deficient. For example, 73.8 percent of housing had structural damage and 52.7 percent had indoor temperatures that were not safe. Farmworkers in 83.5 percent of the housing reported that they did not feel they or their possessions were secure. Bathing or toileting privacy was absent in 46.2 percent of the housing. Camps with residents having H-2A visas or North Carolina Department of Labor certificates of inspection posted had better safety, security, and hygiene. Regulations addressing the quality of migrant farmworker housing are needed.
The influence of organizational culture on organizational preferences towards the choice of organizational change strategy
Authors: Janicijevic Nebojsa
Published: July 2012

Organizational culture, through its assumptions, values, norms and symbols,
determines the way in which the members of an organization perceive and
interpret the reality within and around their organization, as well as the
way they behave in that reality. For this reason we may assume that
organizational culture has an impact on the way in which an organization
changes, and that matching of organizational culture and change strategy will
improve the efficiency of the change process. In this paper specific
hypotheses about the causal relationship between certain types of
organizational culture and certain change strategies are formulated. Types of
organizational culture are differentiated according to Handy?s and
Trompenaars? classifications. Organizational change strategies have been
differentiated according to previous work of Chin & Benne but one more
strategy has been added. Classifications of both the organizational cultures
and of the organizational change strategies are based on the same criteria of
differentiation: distribution of power in an organization and orientation
toward relationships or tasks. For this reason it is possible to formulate
hypotheses about the causal relationship between certain types of
organizational cultures and certain types of organizational change
strategies. Thus, eight hypotheses are formulated in this paper, relating
particular change strategies with particular types of organizational culture.
Analysis of variations in the performance of audit firms in the Republic of Serbia
Authors: Jaksic Dejan , Mijic Kristina , Andric Mirko
Published: July 2012

The paper presents an analysis of the performance of audit firms in the
Republic of Serbia in the period 2008-2010. For this period the trend in the
number of audit firms in the Republic of Serbia, the size and number of
employees in audit firms, and the participation of individual audit firms in
total operating revenue, employment, and net income were observed. Further,
correlation analysis of variations in operating revenue, employment, and net
income of audit firms was carried out. The analysis showed the absence of the
expected correlation between operating revenue and net income, as well as
between the number of employees and net income. Additional analysis showed
that the newly established audit firms achieved lower than average results
and a higher level of variation in the level of profitability in relation to
the audit firms that have been in the audit service market longer.
Thermodynamic modeling of the Na-X (X = Si, Ag, Cu, Cr) systems
Authors: Hao D. , Bu M. , Wang Y. , Tang Y. , Gao Q. , Wang M. , Hu B. , Du Y.
Published: July 2012

The Na-X (X = Si, Ag, Cu, Cr) systems have been critically reviewed and
modeled by means of the CALPHAD approach. The two compounds, NaSi and Ag2Na,
are treated as stoichiometric ones. By means of first-principles
calculations, the enthalpies of formation at 0 K for the LT-NaSi (low
temperature form of NaSi) and Ag2Na have been computed to be -5210 and
-29821.8 Jmol-1, respectively, with the desire to assist thermodynamic
modeling. One set of self-consistent thermodynamic parameters is obtained for
each of these binary systems. Comparisons between calculated and measured
phase diagrams show that most of the experimental information can be
satisfactorily accounted for by the present thermodynamic descriptions.
The role of cognitive-developmental tests in differential diagnosis of borderline and schizophrenic patients
Authors: Vulevic Gordana , Opacic Goran
Published: July 2012

The aim of our research was to find out whether cognitive-developmental tests
such as Nominal Realism Test and Vygotsky Concept Formation Test could
contribute to the process of diagnosing borderline and schizophrenic
patients. The specific aim of this study was to assess the diagnostic power
of subtests (such as Vocabulary, Comprehension, Similarities and Picture
Arrangement Test) on Wechsler Adult Intelligence Scale (VITI) in the
differential diagnosis of the two groups of patients. The study included 90
subjects, 30 of whom were diagnosed with borderline personality disorder
(BPD), 30 had the diagnosis of schizophrenic psychosis (SCH), while 30, who
had no psychiatric diagnosis, represented the control group. The findings
indicate that the patients with BPD, and particularly those diagnosed with
SCH, had both quantitative and qualitative cognitive impairment. The findings
show that cognitive developmental tests represent valuable tools in the
differential diagnosis of borderline personality disorder and schizophrenia.
Evaluation of Buss-Perry aggression Questionnaire with item response theory (IRT)
Authors: Dinic Bojana , Janicic Bojan
Published: July 2012

The aim of this research was to examine the psychometric properties of the
Buss-Perry Aggression Questionnaire on Serbian sample, using the IRT model
for graded responses. AQ contains four subscales: Physical aggression, Verbal
aggression, Hostility and Anger. The sample included 1272 participants, both
gender and age ranged from 18 to 68 years, with average age of 31.39 (SD =
12.63) years. Results of IRT analysis suggested that the subscales had
greater information in the range of above-average scores, namely in
participants with higher level of aggressiveness. The exception was
Hostilisty subscale, because it was informative in the wider range of trait.
On the other hand, this subscale contains two items which violate assumption
of homogenity. Implications for measurement of aggressiveness are discussed.
Stark broadening parameter tables for neutral calcium spectral lines, II
Authors: Dimitrijevic M.S. , Sahal-Brechot S.
Published: July 2012

Electron-, proton-, and ionized helium-impact broadening parameter tables for neutral calcium spectral lines, have been presented as a function of the temperature and the perturber density. Calculations have been performed within the semiclassical perturbation approach.
Stark broadening parameter tables for In II
Authors: Dimitrijevic M.S. , Sahal-Brechot S.
Published: July 2012

Electron-, proton-, and ionized helium-impact broadening parameter tables for In II spectral lines, are presented as a function of the temperature and the perturber density. Calculations have been performed within the semiclassical perturbation approach.
On the maximal quantity of processed information in the physical eschatological context
Authors: Cirkovic M.M. , Radujkov M.
Published: July 2012

An estimate of the maximal computing power available to advanced extraterrestrial or future (post)human civilizations is presented. It is shown that the fundamental thermodynamical considerations may lead to a quantitative estimate of the largest quantity of information to be processed by conceivable computing devices. This issue is interesting from the point of view of physical eschatology, as well as general futurological topics, like the degree of confidence in long-term physical predictions or viability of the large-scale simulations of complex systems.
The analysis of total solar eclipse observations on August 11th, 1999 in Kikinda
Authors: Popovic G.M. , Olevic D. , Pavlovic R. , Jovanovic P.
Published: July 2012

Because of poor meteorological conditions, the obtained observational material has not an even distribution in time. Therefore a special method was devised for treating this material. Using this method the durations of total and partial phases of this eclipse were established.
The gravitational microlens influence on X-ray spectral line generated by an AGN accretion disc
Authors: Popovic L.C. , Mediavilla E.G. , Munoz J.A. , Dimitrijevic M.S. , Jovanovic P.
Published: July 2012

The influence of gravitational microlensing on the X-ray spectral line profiles originated from a relativistic accretion disc has been studied. Using a disc model, we show that microlensing can induce noticeable changes in the line shapes when the Einstein ring radius associated with the microlens is of a size comparable to that of the accretion disc. Taking into account the relatively small size of the X-ray accretion disc, we found that compact objects (of about a Solar mass) which belong to the bulge of the host galaxy can produce significant changes in the X-ray line profile of AGN.
Pollutant emission from a heat station supplied with agriculture biomass and wood pellet mixture
Authors: Juszczak Marek , Lossy Katarzyna
Published: July 2012

Pollutant emission from a heat station supplied with agriculture biomass and wood pellet mixture

Tests for combustion of hay and sunflower husk pellets mixed with wood pellets were performed in a horizontal-feed as well as under-feed (retort) wood pellet furnace installed in boilers with a nominal heat output of 15 and 20 kW, located in a heat station. During the combustion a slagging phenomenon was observed in the furnaces. In order to lower the temperature in the furnace, fuel feeding rate was reduced with unaltered air stream rate. The higher the proportion of wood pellets in the mixture the lower carbon monoxide concentration. The following results of carbon monoxide concentration (in mg/m3presented for 10% O2content in flue gas) for different furnaces and fuel mixtures (proportion in wt%) were obtained: horizontal-feed furnace supplied with hay/wood: 0/100 - 326; 30/70 - 157; 50/50 - 301; 100/0 - 3300; horizontal-feed furnace supplied with sunflower husk/wood: 50/50 - 1062; 67/33 - 1721; 100/0 - 3775; under-feed (retort) furnace supplied with hay/wood: 0/100 - 90; 15/85 - 157; 30/70 - 135; 50/50 - 5179; under-feed furnace supplied with sunflower husk/wood: 67/33 - 2498; 100/0 - 3128. Boiler heat output and heat efficiency was low: 7 to 13 kW and about 55%, respectively, for the boiler with horizontal-feed furnace and 9 to 14 kW and 64%, respectively, for the boiler with under-feed furnace.
The Dark Energy Properties of the Dirac–Born–Infeld Action
Authors: Zhang Xinyou , Zhang Qing , Huang Yongchang
Published: July 2012

Introducing a new potential, we deduce a general Lagrangian for Dirac–Born– Infeld (DBI) inflation, in which the determinant of the induced metric naturally includes the kinetic energy and the potential energy. In particular, the potential energy and kinetic energy can convert into each other at any same order, which is in agreement with the limit of classical physics. We also present a general sound speed in the evolutions of the universe, and the exact expressions of energy-momentum tensor, pressure and density. Furthermore, from the results we obtain the new equation of states. The analytic form of the action that is consistent with data turns out to be surprisingly simple and easy to categorize. Finally, we examine properties of the dark energy and introduce a novel mechanism for realizing either quintessence or phantom dark energy dominated phases within a string theoretical context.
Sliding Mode Control Strategy for Wind Turbine Power Maximization
Authors: Barambones Oscar
Published: July 2012

The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a sliding mode control for variable speed wind turbine that incorporates a doubly fed induction generator is described. The electrical system incorporates a wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid. In the presented design the so-called vector control theory is applied, in order to simplify the electrical equations. The proposed control scheme uses stator flux-oriented vector control for the rotor side converter bridge control and grid voltage vector control for the grid side converter bridge control. The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand, that the proposed controller provides high-performance dynamic characteristics, and on the other hand, that this scheme is robust with respect to the uncertainties that usually appear in the real systems.
Power System Stability of a Small Sized Isolated Network Supplied by a Combined Wind-Pumped Storage Generation System: A Case Study in the Canary Islands
Authors: Merino Julia , Veganzones Carlos , Sanchez Jose A. , Martinez Sergio , Platero Carlos A.
Published: July 2012

Massive integration of renewable energy sources in electrical power systems of remote islands is a subject of current interest. The increasing cost of fossil fuels, transport costs to isolated sites and environmental concerns constitute a serious drawback to the use of conventional fossil fuel plants. In a weak electrical grid, as it is typical on an island, if a large amount of conventional generation is substituted by renewable energy sources, power system safety and stability can be compromised, in the case of large grid disturbances. In this work, a model for transient stability analysis of an isolated electrical grid exclusively fed from a combination of renewable energy sources has been studied. This new generation model will be installed in El Hierro Island, in Spain. Additionally, an operation strategy to coordinate the generation units (wind, hydro) is also established. Attention is given to the assessment of inertial energy and reactive current to guarantee power system stability against large disturbances. The effectiveness of the proposed strategy is shown by means of simulation results.
Phylogenetic Relationships of the Mangalitsa Swine Breed Inferred from Mitochondrial DNA Variation
Authors: Georgescu Sergiu Emil , Manea Maria Adina , Dudu Andreea , Costache Marieta
Published: July 2012

The Mangalitsa pig, a swine breed belonging to the protected gene fund of original and primitive animal breeds of the FAO (Food and Agriculture Organization), has been known to inhabit Romanian territories since the 19th century. The aim of this study was to compare the Mangalitsa breed with several European and Asiatic swine breeds in order to emphasize its uniqueness and to elucidate its origin. For this purpose, we analyzed a 613 bp mitochondrial DNA D-loop fragment and 1140 bp of the cytochrome b gene in a population of Mangalitsa pigs and the polymorphic sites were compared with sequences from GenBank originating from other swine breeds. Taking into account the total of 24 breeds and 5 different Wild Boar populations analyzed, 86 polymorphic sites representing 32 haplotypes were observed, with an average percentage of polymorphic sites of 4.9%. Three Neighbor-Joining phylogenetic trees were constructed based on Kimura 2-parameter distances, using D-loop, cytochrome b and mitochondrial reunited sequences. For the analyzed Mangalitsa population, four distinct haplotypes were identified, including one that was common to other breeds. Our study suggests that the Mangalitsa swine originate from primitive breeds which might be directly derived from the Wild Boar.
Terpenes as Green Solvents for Extraction of Oil from Microalgae
Authors: Dejoye Tanzi Celine , Abert  Vian Maryline , Ginies Christian , Elmaataoui Mohamed , Chemat Farid
Published: July 2012

Herein is described a green and original alternative procedure for the extraction of oil from microalgae. Extractions were carried out using terpenes obtained from renewable feedstocks as alternative solvents instead of hazardous petroleum solvents such as n-hexane. The described method is achieved in two steps using Soxhlet extraction followed by the elimination of the solvent from the medium using Clevenger distillation in the second step. Oils extracted from microalgae were compared in terms of qualitative and quantitative determination. No significant difference was obtained between each extract, allowing us to conclude that the proposed method is green, clean and efficient.