bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Exact and Efficient Algorithm for the Constrained Dynamic Operator Staffing Problem for Call Centers
Authors: Bhandari Atul , Scheller-Wolf Alan , Harchol-Balter Mor 
Published: February 2008

Call center managers are facing increasing pressure to reduce costs while maintaining acceptable service quality. Consequently, they often face constrained stochastic optimization problems, minimizing cost subject to service-level constraints. Complicating this problem is the fact that customer-arrival rates to call centers are often time varying. Thus, to satisfy their service goals in a cost-effective manner, call centers may employ permanent operators who always provide service, and temporary operators who provide service only when the call center is busy, i.e., when the number of customers in system increases beyond a threshold level. This provides flexibility to dynamically adjust the number of operators providing service in response to the time-varying arrival rate. The constrained dynamic operator staffing (CDOS) problem involves determining the number of permanent and temporary operators, and the threshold value(s) that minimize time-average hiring and opportunity costs subject to service-level constraints. We model the CDOS problem as a constrained Markov decision process (MDP) and seek the optimal nonrandomized policy. The only exact method in the literature to obtain the optimal nonrandomized policy for a constrained MDP is enumeration, which is often computationally prohibitive. We provide a novel exact and efficient solution method, the modified balance equations disjunctive constraints (MBEDC) algorithm, yielding a mixed-integer program formulation; the computation times of this algorithm for sample problems are lower than enumeration by up to a factor of 200, and by a factor of 10 on average. Using our algorithm, we quickly solve diverse instances of the CDOS problem, generating managerial insights into the effects of temporary operators and service-level constraints.
Analysis of the Impact of Team-Based Organizations in Call Center Management
Authors: Jouini Oualid , Dallery Yves , Nait-Abdallah Rabie 
Published: February 2008

We investigate the benefits of migrating from a call center, where all agents are pooled and customers are treated indifferently by any agent, toward a call center where customers are grouped into clusters with dedicated teams of agents. Each cluster is referred to as a portfolio. Customers of the same portfolio are always served by an agent of the corresponding team. There is no specialization involved in this organization in the sense that all customer portfolios as well as all agent teams have (statistically) identical behaviors. The reason for moving to this organization is that dealing with teams of limited size allows a much better workforce management than the situation usually encountered in large call centers. The purpose of this paper is to examine how the benefits of moving to this new organization can outweigh the drawbacks. The drawbacks come from the fact that there is less of a pooling effect in the new organization than in the original one. The benefits come from the better human resource management that results in a higher efficiency of the agents, both in terms of speed and quality of the answers they provide to customers. Our analysis is supported by the use of some simple queueing models and provides some interesting insights. In particular, it appears that for some reasonable ranges of parameters, the new organization can outperform the original organization. We then extend the analysis to the case where, in addition to the identified customer portfolios, there is an additional flow of calls called out-portfolio flow. It is shown that this feature makes the new organization even more efficient.
Predicting the Likelihood of Remission in Children With Graves’ Disease: A Prospective, Multicenter Study
Authors: Glaser Nicole S. , Styne Dennis M. ,   for the Organization of Pediatric Endocrinologists of Northern California Collaborative Graves’ Disease Study Group
Published: February 2008

OBJECTIVE. The optimal treatment for Graves’ disease in children is controversial. Antithyroid medications are often used initially, but many children eventually require alternative therapies. We evaluated predictors of remission after 2 years of antithyroid medication use.
METHODS. We prospectively studied children who had Graves’ disease and were treated with antithyroid medications. We compared children who achieved remission after 2 years with those who had persistent disease to determine which variables were associated with remission; multiple logistic regression and binary recursive partitioning analyses were used to evaluate interactions among predictive variables.
RESULTS. Of 51 children who completed the study, 15 (29%) achieved remission. Children who achieved remission had lower thyroid hormone concentrations at presentation than those with persistent disease (free thyroxine: 6.17 ± 3.10 vs 9.86 ± 7.54 ng/dL; total triiodothyronine: 431 ± 175 vs 561 ± 225 ng/dL). Children who achieved remission were also more likely to be euthyroid within 3 months of initiating propylthiouracil (82% vs 29%). Binary recursive partitioning analysis identified rapid achievement of euthyroid status after initiation of propylthiouracil, lower initial triiodothyronine, and older age as significant predictors of remission.
CONCLUSIONS. Thyroid hormone concentrations at diagnosis, age, and initial response to propylthiouracil can be used to stratify patients according to the likelihood of remission after 2 years of antithyroid medication use. These data provide a useful guide for clinical decision-making regarding Graves’ disease in children.
Economic and Physical Optimization of Hydraulic Fracturing
Authors: Marongiu-Porcu M. , Economides M. J. , Holditch S. A. 
Published: February 2008

Abstract
Optimization has taken several different hues in all areas of engineering. Hydraulic fracturing, as applied to petroleum wells, has had its share. In the past, and before the maturing of high-permeability fracturing and the tip screen out techniques, this well stimulation procedure was limited to low-permeability reservoirs and unrestricted fracturing. In such cases, the fracture length would be an appropriate design optimization variable against an economic criterion, e.g., the Net Present Value (NPV). This involved the balancing of incremental future revenue against the cost of execution. Also interesting are parametric studies, allowing the variation of execution variables and the detection of differences in their respective design NPV. Such differences would be useful in decisions to measure a variable or stay within reasonable assumptions. The emergence of higher-permeability fracturing and the Unified Fracture Design (UFD) concept allowed two important notions. First, there is no difference between low and high-permeability reservoirs in terms of benefiting for fracturing. Just execution issues need to be resolved. Second, and more important, for any mass of proppant to be injected in any well, there exists only one fracture geometry that would maximize production. This geometry, consisting of length and propped width (with height as a parasitic variable) can be readily determined and, if placed, it will provide the maximum productivity index. All other configurations would result in lower productivity values. This is physical optimization.
In this paper we combine the two: the economic and physical. For each proppant mass we first optimize the fracture physically and then we apply the NPV criterion. We perform a series of parametric studies for a range of reservoirs and we use economic variables that differ in various parts of the world. We show how to determine the optimum fracture size. We then show how fracture treatments may be attractive in certain reservoirs in mature areas but not attractive elsewhere. We also show that for a diversified company, given the choice, few successful fractures in high-permeability reservoirs are far preferable to fracturing large numbers of wells in lower permeability fields, although the latter can be made economically attractive only through hydraulic fracturing.
A Novel Technique for Determining Screen Failure in Offshore Wells: A GOM Case History
Authors: Navaira G. , Hupp M. , Palisch T. , Renkes J. 
Published: February 2008

Abstract
Offshore completions in the Gulf of Mexico must typically address sand control. Our industry has made significant progress with respect to sand control equipment and implementation. However, even properly designed and executed completions are subject to mechanical failure, with the first indications often being production of solids into a common separation facility. In many offshore completions, particularly sub-sea or multi-zone completions, it is often difficult and expensive to determine which well or specific completion interval has failed, most times requiring production to be shut in for diagnosis. Not until that point can a remedy be evaluated.
One GOM producer engaged the services of a proppant supplier to determine whether a suite of proppants/gravel could be developed that could be uniquely identified and placed in each completion interval. In the event of proppant production to surface (mechanical failure), the surface samples would be analyzed to directly determine which interval had failed. The proppant needed to be non-radioactive yet identifiable with standard laboratory techniques.
The supplier subsequently developed a methodology whereby the proppant could be "tagged" with over 20 unique markers. This paper will discuss how the tagging agents are incorporated to become a permanent component of the pellet. The results of laboratory testing will be provided, verifying that the taggant does not materially affect the performance of the proppant.
In addition, the authors will review case histories where this new product was successfully placed in multi-zone frac pack completions in several deepwater GOM completions. The paper will also describe basic laboratory techniques used to successfully identify the source of proppant found in a surface choke subsequent to the frac. The economic savings provided by this novel approach will be presented, as well as other potential applications for this new product.
Reasons for Oil-Based Hydraulic Fracturing in Western Siberia
Authors: Elgassier M. M , Stolyarov S. M. 
Published: February 2008

Abstract
Both water- and oil-base fracturing have been used in West Siberian wells. However, the vast majority of these wells are hydraulically fracture stimulated using water-base fracturing fluids because for the same job size, the base fluid for water-base jobs is much cheaper than that of oil-base jobs. However, in some situations oil-base fracturing fluid may be the only option to improve well production performance.
This paper reviews oil-base hydraulic fracturing case histories in Western Siberia. Such treatments were used in Jurassic formations because of formation water sensitivity and in Cretaceous formations to control fracture height. Oil-base fracture stimulation treatments were specifically designed with base fluid that had lower than usual viscosity while maintaining its ability to carry proppant and withstand the high asphaltene and water content of Siberian crude and reduce the risk of fracture extension into water zones.
In many cases post-treatment incremental production of oil-base jobs was better than that of water-base jobs. Switching to oil-base fracturing fluids led to control of fracture geometry and eliminated the problem of formation sensitivity to the fracturing fluid. Much lower water cuts were also achieved post oil-base treatments because of fracture height containment. Excluding the cost of base fluid, oil-base treatments saved the operator, on average, 35% of the job cost. This is mainly due to reducing job size and lowering water cut.
Designing Well Fluids for the Ormen Lange Gas Project, Right on the Edge
Authors: Vickers Stephen , Hutton Alistair , Lund Arne , McKay Ian , Van Kranenburg Aart , Twycross Jean 
Published: February 2008

Abstract
The challenges in developing the Ormen Lange field were the harsh weather conditions, deep-water depth, subsea topography and sub-zero seabed temperatures. Due to environmental constraints and the selected sand face completion type, a water-based fluid system was required. This paper discusses the design of the fluids to give full hydrate inhibition, maximize breaker effectiveness, provide low overbalance, and reduce corrosion risk. An extensive research and development program was initiated that spanned over two years. The study included bridging and chemical component selection, brine evaluation, hydrate suppression measurement, elastomers compatibility, extensive breaker treatment studies, formation damage measurements using actual reservoir core and long term corrosion testing. An in-situ generating acid/enzyme breaker treatment deployed in the gravel pack carrier fluid was developed to optimise filtercake cleanup whilst providing a non-corrosive environment for the selected gravel pack screens and lower completion metallurgy. The basis of design and knowledge gained in the laboratory testing phase was transferred to the field and the first three wells of the initial development phase have been drilled and completed trouble-free. The resulting production rates have met expected targets proving low formation damage and an efficient cleanup was achieved.
Acoustic Surveillance of Production Impairment With Real-Time Completion Monitoring
Authors: Bakulin Andrey , Sidorov Alexander , Kashtan Boris , Jaaskelainen Mikko 
Published: February 2008

Abstract
Deepwater production is challenged by well underperformance problems that are hard to diagnose early on and expensive to deal with later. Problems are amplified by reliance on few complex wells with sophisticated sand control media. New downhole data is required for better understanding and prevention of completion and formation damage. We introduce Real-Time Completion Monitoring (RTCM), a new non-intrusive surveillance method for identifying impairment in sand-screened completions that utilizes acoustic signals sent via the fluid column. These signals are carried by tube waves that move borehole fluid back and forth radially across the completion layers. Such tube waves are capable of "instant" testing of the presence or absence of fluid communication across the completion and are sensitive to changes occurring in sand screens, gravel sand, perforations, and possibly reservoir. The part of the completion that has different impairment from its neighbors will carry tube waves with modified signatures (velocity, attenuation) and also would produce a reflection from the boundary where impairment changes. The method relies on permanent acoustic sensors performing acoustic soundings at the start of production and then repeating these measurements during the life of the well. Thus, it could be thought of as "miniaturized" 4D seismic and "permanent log" in an individual wellbore. In the meantime repeated conventional wireline measurements can be performed to assess the completion permeability.
Protecting Sand Control Screens Against Solids Plugging During Installation
Authors: McElfresh Paul , Welch John 
Published: February 2008

Abstract
In the completion of many offshore wells, the installation of sand control screens is a necessary and vital step to ensure optimum production rates. Current procedures usually involve displacing the solids laden drilling fluid from the well with a clear or weighted completion brines in order to minimize any solids that could potentially plug the filtration media of the screens. Other methods entail special sizing of the drilling fluid solids such that they will pass through the screens. This paper describes a new method to protect against solids plugging while installing sand screens in muds containing solids of any size distribution.
The protection takes the form of a film which is wrapped or coated on the outside of the woven mesh filtration medium of the screen. The film is protected from mechanical deterioration by the outside shroud of the screen itself. During the installation of the screen, the film prohibits invasion of solids into the filtration area by providing a physical barrier. Once the screens are in place, the film is removed through decomposition by the well bore fluids. The decomposition step is initiated by a material in the film which has a minimum solubility threshold near the temperature of the fluids at the bottom of the hole.
The treatment is engineered for wells requiring sand control up to about 200° F (93° C) using either water-or oil-based muds. The treatment also offers a method to maintain the maximum filtration efficiency by protecting from solids invasion during installation.
New Alternatives of Water Shutoff Treatments: Application of Water Sensitive Metastable Systems
Authors: Lakatos István , Lakatos-Szabó Julianna , Bódi Tibor , Vágó Árpád 
Published: February 2008

Abstract
The primary aim of the research project was to develop such chemical systems, which triggered by mixing with water will form the blocking phase. As a novelty, water sensitive homogeneous solutions and water external microemulsions were developed, which are stable until they are diluted with water forming thus stable macroemulsions. Transformation of different metastable systems to stable ones in reservoir space having high water saturation may radically restrict the water flow through their high viscosity and entrapment of the dispersed particles by the pores. As dispersed phases organic silicon compounds, tensides and natural crude oil fractions were tested. The transformation and structure of phases and size of particles were analyzed by photon correlation spectrometry, rheometry, while the flow properties were studied in natural sandstone systems.
The core studies confirmed that all metastable systems reduce the flow of water by 80-90% in water-saturated sandstone. Using chemical-free postflush the flow resistance remains substantial against water in case of silicones; meanwhile the permeability deterioration against oil or gas is negligible. The metastable systems are effective and single step disproportional permeability modifying fluids.
The metastable systems may offer an excellent opportunity for water shutoff in matured oil and gas fields and gas storage facilities. The unique properties of the techniques are that flow resistance may occur only in water saturated reservoir space and in case of technical failure; the flow barrier can be eliminated by oil and gas injection.
Novel Acid-Diversion Technique Increases Production in the Cantarell Field, Offshore Mexico
Authors: Garcia Benjamin , Soriano Eduardo , Chacon Wendy , Eoff Larry 
Published: February 2008

AbstractCantarell, which is an offshore complex of fields in the Bay of Campeche, is the most important complex in Mexico and is the second-largest producing field in the world. It is comprised of five fields, with the main pay zones consisting of highly fractured, vuggy carbonate formations from Jurassic, Cretaceous and Lower Paleocene geological ages. Matrix acidizing has always been the main stimulation process used to improve production from these carbonate reservoirs and this is especially the case now that this mature complex has reached its production peak.As with all acidizing programs, a critical factor for success of the treatments is distribution of the acid between all productive zones. Since most producing wells are not homogeneous and contain layers of varying permeability, even distribution of the acid is a difficult task. In addition, the water saturation of the various zones has a major effect on the acid distribution. Since acid is an aqueous fluid, it will tend to predominantly enter the zones with the highest water saturation, in many cases resulting in increased water production. This brings with it the multitude of problems associated with high water production.This paper will present the results of approximately 55 high permeability wells ranging from 1,000 to 6,000 md, which have been acidized using a novel acid diverter based on associative polymer technology (APT). This polymer inherently reduces the formation permeability to water with little or no effect on the permeability to hydrocarbon. Data from production logs from several of the treated wells will be presented, which show excellent oil production distribution along the perforated intervals. In addition, production logs will also be shown for wells acidized with other diverters, such as foams and in-situ crosslinked acid, which showed poorer results.
An Effective Technique to Reduce Bottomhole Friction Pressure During Hydraulic Fracturing Treatments
Authors: Smith Caleb G. , Khiat Smail , Albadraoui Dhafir 
Published: February 2008

Abstract
During a hydraulic fracturing treatment, it is imperative that adequate perforation channels link the wellbore to the formation. Bottomhole friction is a critical issue that can worsen as the result of poor perforation channels. Excessive bottomhole friction begets high treating pressures, which in turn can lead to premature screenouts when a well is hydraulically fractured.
The traditional method of perforating using through-tubing explosives has inherent disadvantages. These disadvantages can contribute to bottomhole friction in a multitude of ways. Drawbacks include the damage done to the near-wellbore area by the compaction force of the explosives and the debris left behind in the perforation channel. The small entry-hole diameter (EHD) made by through-tubing guns contributes to bottomhole friction by creating a large pressure drop across the perforations.
Hydraulically jetting with proppant (HJP) to create perforations entails pumping a combination of fluid and either proppant or sand down a string of jointed tubing or coiled tubing to create perforations. The slurry exits the jetting nozzle at a high velocity and creates a channel through the casing and cement and into the formation, in turn connecting the wellbore to the formation. The perforation depth is determined by the time the slurry is allowed to act in one area. Details such as perforation diameter, shot density, and phasing are determined by the specifications of the jetting tool.
This technical paper presents field data from a hydraulic fracturing treatment in which HJP was used to reduce bottomhole friction by 70%. This procedure creates superior connectivity between the wellbore and formation and leaves less near-wellbore damage. This benefit is significant in that it reduces the risk of premature screenouts when fracturing, as can often happen when perforating using through-tubing explosives.