bluuebunny/crossref_metadata_2025 huggingface dataset:
Plant diversity affects behavior of generalist root herbivores, reduces crop damage, and enhances crop yield
Authors: Staudacher Karin , Schallhart Nikolaus , Thalinger Bettina , Wallinger Corinna , Juen Anita , Traugott Michael
Published: February 2013

Soil‐dwelling pests inflict considerable economic damage in agriculture but are hard to control. A promising strategy to reduce pest pressure on crops is to increase the plant diversity in agroecosystems. This approach, however, demands a sound understanding of species' interactions, which is widely lacking for subterranean herbivore–plant systems. Here, we examine the effects of plant diversification on wireworms, the soil‐dwelling larvae of click beetles that threaten crops worldwide. We conducted a field experiment employing plant diversification by adding either wheat or a mix of six associated plants (grasses, legumes, and forbs) between rows of maize to protect it from Agriotes wireworms. Wireworm feeding behavior, dispersal between crop and associated plants, as well as maize damage and yield were examined. The former was assessed combining molecular gut content and stable isotope analysis. The pests were strongly attracted by the associated plants in August, when the crop was most vulnerable, whereas in September, shortly before harvest, this effect occurred only in the plant mix. In maize monoculture, the larvae stayed in the principal crop throughout the season. Larval δ13C signatures revealed that maize feeding was reduced up to sevenfold in wireworms of the vegetationally diversified treatments compared to those of the maize monoculture. These findings were confirmed by molecular analysis, which additionally showed a dietary preference of wireworms for specific plants in the associated plant mix. Compared to the monoculture, maize damage was reduced by 38% and 55% in the wheat and plant mix treatment, which translated into a yield increase of 30% and 38%, respectively. The present findings demonstrate that increasing the plant diversity in agroecosystems provides an effective insurance against soil pests. The underlying mechanisms are the diversion of the pest from the principle crop and a changed feeding behavior. The deployment of diverse mixes of associated plants, tailored to the specific preferences of the soil herbivores, provides a promising strategy for managing subterranean pests while maintaining crop yield.
Case History: Production Results from Partial Monolayer Proppant Fracture Treatments in the Pictured Cliffs Formation Horizontal Wells of San Juan Basin
Authors: Ramurthy Muthukumarappan , Magill Douglas , Parker Mark , Sanchez Patricio W.
Published: February 2013

The Pictured Cliffs formation in the San Juan basin has been a target interval for operators for many years. This tight gas reservoir lies just below the prolific Fruitland coals and has been completed either separately or as additional pay in vertical wells. With the advent of horizontal well technology, operators have begun drilling laterals in the Pictured Cliffs and completing them with multistage stimulation treatments. Because of the relatively shallow depths and the low closure pressure associated with it, 20/40-mesh proppant has been the main proppant used when completing the Pictured Cliffs formation. In this project, a different approach was necessary to complete the laterals because of limited accessibility to the well locations and the small size of the locations where storage of large mass of proppants is not viable. After analyzing the reservoir properties, the first lateral in this project was completed with a new type of thermoplastic alloy lightweight partial monolayer proppant (TPA-LWP). Following its success, three more horizontal Pictured Cliffs formation wells were completed with the partial monolayer proppant.

Production results from all four wells are presented in this work, along with the selection criteria and the operational aspects associated with pumping these proppants. This paper also discusses the production analysis performed on these four wells and compares them with five other Pictured Cliffs laterals in the basin that were stimulated with 20/40-mesh proppant.
Evolution of Drilling and Completions in the Slave Point to Optimize Economics
Authors: Lerner Nolan , Schaab Brent , Garcia Juan , Bianco Dan , Thomas Scott , Thompson Jason , Hollan Jeremy
Published: February 2013

This paper will detail the technological evolution of drilling and completion practices utilized to optimize economic development of the Slave Point carbonate platform specifically in the Evi and Otter fields in northern Alberta. The Slave Point platform was initially targeted for conventional production via vertical wells in the early 1980s.

Success was marginal due to the unpredictability of localized porosity development. As a result, full scale commercial development of this resource was deemed uneconomic due to poor reservoir quality. More recently, however, horizontal drilling and multistage fracturing technology has allowed operators to open up lower porosity horizons to improve flow capacity, improve recoveries, and allow for commercial development from zones previously deemed as uneconomic.

The Slave Point has a greater thickness and is less permeable than other tight rock plays in Alberta such as the Cardium and Viking. It produces high-quality, light oil with low water and solution gas production rates. Despite high estimates of original oil in place of approximately 3 to 10 MMbbl per section, horizontal well rates are still challenged due to lower permeability through the pay section. In this regard, the continued deployment of innovation and technology has been critical in improving well production performance, compressing project costs, and ultimately optimizing project economics.

The focus of this paper is solely upon one of the major Slave Point operators who has drilled 49 horizontal wells accounting for 200,000 m (656,000 ft) drilled and 1,350 fracture stages in the Evi and Otter Slave Point fields since 2008. This operator has continually deployed advancing technologies to improve project economics. The information will be presented in terms of the influence of technology on well design, the optimization and deployment of the various technologies, and the demonstrated improvement on productivity and reserve recovery. The discussion will focus on three development phases outlined below, which highlight the progression from vertical to horizontal technology. Vertical AppraisalSingle Lateral DevelopmentDual Lateral Development

The case studies presented will clearly demonstrate the production impact upon the utilization and application of these technologies. The methods and lessons learned through the use of dual laterals, open hole junctures and open hole multistage systems can be applied to other unconventional formations.
Characterizing Hydraulic Fractures in Shale Gas Reservoirs Using Transient Pressure Tests
Authors: Wang Cong , Ding Didier , Wu Yu-Shu
Published: February 2013

Hydraulic fracturing combined with horizontal drilling has been the technology that makes it possible to economically produce natural gas from unconventional shale gas reservoirs. Hydraulic fracturing operations, in particular, multistage fracturing treatments along horizontal wells in unconventional formations create complex fracture geometries or networks, which are difficult to characterize. The traditional analysis using a single vertical or horizontal fracture concept is no longer applicable. Knowledge of these created fracture properties, such as their spatial distribution, extension and fracture areas, is essential information to evaluate stimulation results. However, there are currently few effective approaches available for quantifying hydraulic fractures in unconventional reservoirs.

This work presents an unconventional gas reservoir simulator and its application to quantify hydraulic fractures in shale gas reservoirs using transient pressure data. The numerical model incorporates most known physical processes for gas production from unconventional reservoris, including two-phase flow of liquid and gas, Klinkenberg effect, non-Darcy flow, and nonlinear adsorption. In addition, the model is able to handle various types and scales of fractures or heterogeneity using continuum, discrete or hybrid modeling approaches under different well production conditions of varying rate or pressure. Our modeling studies indicate that the most sensitive parameter of hydraulic fractures to early transient gas flow through extremely low permeability rock is actually the fracture-matrix contacting area, generated by fracturing stimulation. Based on this observation, it is possible to use transient pressure testing data to estimate the area of fractures generated from fracturing operations. We will conduct a series of modeling studies and present a methodology using typical transient pressure responses, simulated by the numerical model, to estimate fracture areas created or to quantity hydraulic fractures with traditional well testing technology. The type curves of pressure transients from this study can be used for quantify hydraulic fractures in field application.
A Comparison of Proppant Placement, Well Performance, and Estimated Ultimate Recovery Between Horizontal Wells Completed With Multi-Cluster Plug & Perf and Hydraulically Activated Frac Ports in a Tight Gas Reservoir
Authors: Castro Luis , Bass Cody , Pirogov Alexander , Maxwell Scott
Published: February 2013

The search for the optimum stimulation method for unconventional/tight reservoirs (UTR) in the US has been the object of study of many papers due to increased activity in these hydrocarbon plays and the potential rewards to finding the ideal method. Rock heterogeneity, water zone proximity, stimulation design, and completion methods have a significant influence on the final outcome and add complexity to the quest. This paper describes a novel alternative to conventional stimulation methods in UTR. The document compares a well fractured using the traditional plug-and-perforate (PnP) method and a well fractured down the coiled tubing-casing annulus using Coiled Tubing-enabled fracturing sleeves (CTFS) with an equivalent stimulation treatment, both in a cemented application. CTFS are pressure-balanced fracturing sleeves that are hydraulically activated through a pressure differential induced by setting a coiled tubing-conveyed isolation packer in the sleeves. The CTFS are novel as they do not rely on composite plugs, ball-drop systems or darts to operate and therefore leave a full-bore internal diameter after the treatment has been completed.

A complete approach to the technology application is described as similarities and differences in drilling practices, cementing techniques, completion methods, and – more importantly – production results are highlighted. As a challenging application in a well with a measured depth over 18,000 feet, pre-job preparation and diagnostics are discussed. Challenges encountered and lessons learned throughout the study are included.

The comparison shows how the use of targeted fracturing with CTFS yielded a significant production increase over an offset well that was conventionally treated. Similarly, the positive effects of these results over the estimated ultimate recovery (EUR) figures are discussed. Production tests and tracer data are used to support field data.

The results have practical and significant application in emerging and established unconventional reservoirs, as it provides a targeted alternative with increased production results to PnP’s traditional "blanket" fracturing approach of stimulating multiple clusters at a time. Over the mid-to-long term, these results can potentially lead to operator financial savings/efficiencies by modifying drilling programs to drill fewer wells while achieving similar returns on reserves – an advantage during slow times – or drilling the same number of wells for increased returns of reserves.
Fracture Propagation Direction and Its Application in Hydraulic Fracturing
Authors: Jin Xiaochun , Shah Subhash
Published: February 2013

In recent years, horizontal completions have become "fashionable" with the consequence that induced fractures are usually not planar due to the inclination angle between the borehole and the prevailing reservoir in-situ principal stresses. Hence, such stimulations imply mixed-mode (opening and sliding modes) fracture propagation. Opening mode contributes to fracture opening, and sliding mode contributes to fracture twisting.

A hydraulic fracturing model is developed to study how and why a fracture gets twisted near the wellbore under biaxial loading. Three different fracture criteria (maximum tangential stress criterion, maximum energy release rate, and minimum strain energy density) have been applied to study fracture initiation mechanisms in mixed modes. Semi-analytical solutions of fracture initiation angles at different consecutive inclination angles based on the three criteria are obtained with analytical and modified bisection methods. It is found that the three criteria yield results with similar trends but with different magnitudes. The fracture initiation angle does not increase with the increasing inclination angle monotonically. The plot of fracture initiation angle with respect to inclination angle (0 to 90°) is a bell-shaped curve. The influence of pore pressure, fracturing pressure, stress anisotropy, Biot’s coefficient, and Poisson’s ratio on initiation angle is studied thoroughly, which shows that the initiation angle will decrease with increasing pore pressure, fracturing pressure, and Biot’s coefficient, but will increase with increasing stress anisotropy; however, the inclination angle is not sensitive to Poisson’s ratio. The analysis of the influence of fracturing pressure and pore pressure helps engineers understand why fracture tortuosities are different for various stages.

The conclusions and analysis in this paper can be applied to study both the fracture geometry near-wellbore and the optimization of hydraulic fracturing design for vertical, deviated, and horizontal wells. Recommendations on controlling wellbore azimuth and adjusting perforation phasing are given for wells in formation with high stress anisotropy.
Utilizing Hybrid Surface - Downhole Seismic Networks to Monitor Hydraulic Fracture Stimulations
Authors: Baig Adam , Urbancic Ted , Viegas Gisela
Published: February 2013

Typically, seismic networks are deployed downhole to monitor injection-related activity and are designed to detect and analyze microseismic events at very short distances. During hydraulic fracture treatments, thousands of events can be generated with magnitudes in the range of -M4 to –M0. These networks record relatively high frequency signals (> 15Hz) and use time records with a short duration; however, they are limited in low-frequency response. This lack of bandwidth results in underestimated magnitudes for events with larger magnitudes (from about –M0 to +M4) that may occur during stimulations. To correct this issue, recording with high -sensitivity, near-surface sensors with low-frequency capabilities (>0.5Hz) extends the frequency range thereby allowing for the correct assessment of magnitude. In this paper, we investigate the spatial and temporal variations in seismicity associated with hydraulic fracture treatments of a shale play in North America using two different monitoring configurations, with multiple, fibre-optic based wireline arrays, each with twenty to forty-eight three-component levels of omni 15Hz geophones deployed vertically in close proximity to the treatment well and using a near-surface network of five stations consisting of three component Force Balance Accelerometers and 4.5Hz geophones. The near-surface monitoring network detected hundreds of events ranging in magnitude from M0 to M3, the largest of which were also recorded on a nearby national seismic network station. The downhole events did not see such large events, but recoreded thousands of events up to M0. Here, we compare parameters from the downhole data to the near-surface data to try to answer what role the larger events are playing in the reservoir and how they can be put into proper context with the smaller, downhole data. The failure mechanisms and scaling relationships for these large events suggest that they are the response of larger features in the reservoir, slipping in response to the stress perturbations induced by the treatment. Based on these observations, we suggest that a hybrid solution is appropriate for reservoirs with structural controls in order to appropriately assess the reservoir response to stimulations.
Cemented Multi-Stage Sleeve Completion Improves Efficiency of Fracture-Stimulation in an Eagle Ford Shale Well
Authors: Adcock Glenn , Wellhoefer Ben , Daher Said , Fruge Eric
Published: February 2013

To economically develop unconventional resource plays such as the Eagle Ford Shale in South Texas, multiple complex hydraulic fracturing stages must be executed in the horizontal section of the wellbore. Traditionally, a plug and perforate (P-n-P) process has been used. However, inherent difficulties in the process often limited completion cycle time and created barriers to economic delivery of the hydraulic fracturing treatment.

The Eagle Ford shale in Zavala County, Texas is similar to many high-carbonate-content oil-shale formations. As with other shale plays, the industry has preferred using cemented lateral sections as the primary means of fracture-stage isolation, coupled with the P -n-P horizontal completion technique. This paper explores an alternative completion method, cemented multi-stage sleeves (CMSS), that recently improved efficiency and reduced completion cycle time. This study discusses the process, procedures used, and lessons learned from applying this technology.

The subject well design was similar to most Eagle Ford shale wells. The completion included setting a deep surface casing string at 3030 feet, and then, drilling an 8.75-in. openhole section to MD. A 5.5-in. production casing was then set and cemented into place. The well was drilled to a measured depth of 11,965 feet with a lateral section of 5,913 feet. The well was completed using 15 stages of CMSS to fracture stimulate the entire lateral section. 3.80MM lbm of proppant with 2,901,000 gallons of fluid was used to fracture stimulate the wellbore, averaging 54 bbl/min. The 16 stage stimulation operation was completed in 24 hours with continuous pumping compared to an average of 3 days for P-n-P. The discussion also will show that production was comparable to that of offset wells, thus proving the technique viable for this type of oil-shale formation.
Proppant Placement Using Alternate-Slug Fracturing
Authors: Malhotra Sahil , Lehman Eric R. , Sharma Mukul M.
Published: February 2013

New fracturing techniques such as hybrid fracturing (Sharma et. al., 2004), reverse hybrid fracturing (Liu et. al., 2007) and channel (HiWAY) fracturing (Gillard et al. 2010) have been deployed over the past few years to effectively place proppants in fractures. The goal of these methods is to generate a network of open channels within the proppant pack, providing highly conductive paths for hydrocarbons to flow from the reservoir to the wellbore. This paper presents an experimental study on proppant placement using a new method of fracturing, referred to as Alternate-Slug fracturing, which involves alternate injection of low viscosity and high viscosity fluids into the fracture. Alternate-slug fracturing ensures deeper placement of proppants through two primary mechanisms: (a) proppant transport in viscous fingers formed by the low viscosity fluid and (b) an increase in drag force in the polymer slug leading to better entrainment and displacement of any proppant banks that may have formed. Both these effects lead to longer propped fracture length and better vertical placement of proppants in the fracture. In addition the method offers lower polymer costs, lower pumping horsepower, smaller fracture widths, better control of fluid leakoff and less gel damage compared to conventional gel fracs.

Experiments are conducted in simulated fractures (slot cells) to study the mixing of fluids over a wide range of viscosity ratios. Data is presented to show that the finger velocities and mixing zone velocities increase with viscosity ratio up to viscosity ratios of about 350 and the trend is consistent with Koval’s theory. However, at higher viscosity ratios the mixing zone velocity values plateau signifying no further effect of viscosity contrast on the growth of fingers and mixing zone. Fluid elasticity is observed to slow down the growth of fingers and leads to growth of multiple thin fingers as compared to a single thick dominant finger in less elastic fluids.

Experiments are conducted with fluids of different viscosity and elasticity, with proppants being carried by the low viscosity fluid. It is shown that the injection rate, slug size and viscosity ratio can be used to control the geometry of the fingers created and, therefore, the proppant distribution in the fracture. The non-uniform placement of proppant in the viscous fingers leads to the creation of high permeability paths in the proppant pack.
Asset Development Drivers in the Bakken and Three Forks
Authors: Cherian Bilu V. , Nichols Chris M. , Panjaitan Maraden L. , Krishnamurthy Jayanth K. , Sitchler Jason
Published: February 2013

Home to one of the largest North American deposits discovered in the last few decades, the Bakken, spanning 200,000 square miles along the borders of Saskatchewan, North Dakota and Montana is rivaling some of the largest proven reserves. As the use of long horizontal wells and multi-stage fracturing technology has significantly increased productivity and activity in the basin, the challenges associated with infill-completions, depletion and controlled fracture growth must be addressed to ensure efficient and effective practices, encouraging long-term planning without hindering investment.

In this paper, models are built to replicate well performance (fracturing and production-numerical & rate-transient) and to understand the impact of key technologies (multi-stage/completion type and multi-laterals) across the basin to demonstrate why completion strategies must be modified based on reservoir quality and stress state. Confusion between the success of sliding sleeves/plug and-perf and what drives the optimal number of stages is also addressed using fracture modeling and production modeling with emphasis on key parameters (fracture length, connectivity, number of fractures) influencing productivity. The recent focus on data acquisition and modeling in the Three Forks has presented a range of challenges and opportunities due to the laminations in this reservoir. Log up-scaling methods and simulator engines were crucial to modeling and thus evaluating propagation behavior. This paper also presents how the use of data gathering (log, routine and specialized core) and modeling has enabled us to understand how in-fill drilling can alter drainage patterns and influence production success.
Net Pressure Trends: Is it Permeability, Complexity or just Fluid Response?: A Workflow To Determine Stimulation Effectiveness in Naturally Fractured and Matrix-Based Permeability Reservoirs
Authors: Lehman Lyle V. , Al-Tailji Wadhah , Northington Neill
Published: February 2013

Hydraulic fracturing stimulation in unconventional reservoirs has taken on a new emphasis in the search for oil and liquids from these low permeability reservoirs. Today, we are attempting to achieve economic production from reservoirs that were passed over just five years ago. The fracture stimulation goal: to provide a conductive path between the reservoir and the wellbore.

However, these reservoirs are inherently difficult, at best, to evaluate and to fully understand the completion environment at a distance from the wellbore. Fortunately, there is a workflow that allows understanding of permeability sources as the fracture treatment is placed in real time and certainly in post-frac analysis. The toolbox uses a "planar" frac model to analyze data gathered from surface sources.

This paper will discuss a workflow to differentiate between pressure trends due to fluid and/or proppant effects on friction, and actual net-pressure change due to permeability exposure by the frac fluid in the reservoir. By understanding that fracture stimulation is a highly invasive process, the authors will examine the data that can be used as a benchmarking tool for reservoir response. We will discuss examples from the Eagle Ford formation for naturally fractured permeability reservoirs and the Wolfberry trend for matrix-based reservoirs. The workflow will aid in fracture spacing in horizontal wells and well spacing in multi-layered vertical wells.
Velocity Building for Microseismic Hydraulic Fracture Mapping in Isotropic and Anisotropic Media
Authors: Du Jing , Warpinski Norm R.
Published: February 2013

Microseismic hydraulic fracture mapping is a very valuable tool for monitoring hydraulic fracture growth and behavior in unconventional reservoirs. During the development of these unconventional reservoirs, there are many engineering decisions that need to be made based on the microseismic event locations. In addition to recording the microseismic data with adequate signal-to-noise ratio, measuring, calibrating, or otherwise building an accurate velocity structure through the formation layers is another key element necessary to obtain acccurate event locations for making sound engineering decisions. The velocity building process starts with an initial velocity model usually derived from a dipole sonic log. After the receivers have all been placed, source shots in known positions, such as perforations or string shots, then are used to calibrate the velocity model, which is used to solve a nonlinear and mostly underdetermined system of equations, depending on the acquisition geometry and the number of layers in the model. In this paper, a modified Newton-Raphson method coupled with singular value decomposition (SVD) is presented to optimize the velocities and anisotropic parameters for individual layers, and the effectiveness of this method is demonstrated with examples.
Fluid Selection for Energized Fracture Treatments
Authors: Ribeiro Lionel H. , Sharma Mukul M.
Published: February 2013

As the development of unconventional (e.g., tight gas, shales, coalbed methane) and under-pressured reservoirs has increased, so has the demand for innovative hydraulic fracture designs. The use of gases and foams has experienced a significant resurgence in popularity with the development of unconventional reservoirs and with the growing limitations on water supply in some areas. Until recently, the tools available for fracture design were not capable of modeling hydraulic fracturing with compressible fluids and non-isothermal treatments. Ribeiro and Sharma (2012b) presented a model that was capable of simulating hydraulic fracturing treatments with multi-phase, compressible fracturing fluids with changing temperature, phase behavior, and multi-phase leak-off during the treatment. The main objective of this paper is to show how such a model can be used for screening fracturing fluid candidates and for optimizing energized fracture treatments.

In conducting this study, we have combined this 3-D compositional fracturing model with a multi-phase well-productivity model for hydraulically fractured wells. This paper presents results for slick water, linear gel, gelled CO2, gelled LPG, N2 foams and CO2 foams in a low permeability reservoir. The simulations showed that good proppant placement and high fracture conductivities can be achieved with foams and gelled fluid formulations. LPG, CO2, and high-quality foams prevent water invasion so they do not impede gas recovery because of water blocking or gel induced damage. In addition, several reservoir parameters appear to control well productivity and therefore fluid selection: (1) relative permeability curves, (2) initial gas saturation, (3) reservoir pressure, and (4) sensitivity to water. The benefits and disadvantages that must be considered when selecting a fracturing fluid are highlighted in this paper and a methodology is proposed to quantify these pros and cons.
Optimum Fluid and Proppant Selection for Hydraulic Fracturing in Shale Gas Reservoirs: a Parametric Study Based on Fracturing-to-Production Simulations.
Authors: Cohen C. E. , Abad C. , Weng X. , England K. , Phatak A. , Kresse O. , Nevvonen O. , Lafitte V. , Abivin P.
Published: February 2013

Production from shale gas reservoirs depends greatly on the efficiency of hydraulic fracturing treatments. The cumulated experience in the industry has led to several best practices in treatment design which have improved productivity in these reservoirs. However, further advances in treatment design require a deeper understanding of the complex physics involved in both hydraulic fracturing and production, such as stress shadow, proppant placement and interaction with natural fractures.

This paper investigates the non-linear physics involved in the production of shale gas reservoirs by improving the understanding of the complex relation between gas production, the reservoir properties, and several treatment design parameters, with a focus on proppant and fluid selection. A fracturing-to-production simulation workflow integrating the Unconventional Fracture Model, with the Unconventional Production Model is presented. This workflow has shown qualitative consistency with real production data.

In this paper we applied the workflow on a realistic reservoir with characteristics from the Marcellus play, and then studied the relation between production and treatment design parameters such as proppant size, proppant concentration, the treatment volume of the treatment, fracturing fluid viscosity, pumping rate and proppant injection sequence.

Since this paper focuses on fluid and proppant selection, our methodology was to run 28 simulations to cover the 2D parametric space of proppant size and fluid viscosity for every parameter. More than four hundred simulations were run in this parametric study and the results provide guidelines for optimized treatment design.

The behaviors observed confirm several best practices in treatment design for shale. For example, combination of different sizes of proppant optimizes production by maximizing initial production and slowing down production decline. Simulations also confirm the best practice of injecting the smallest proppant first. Another key finding is that the optimum fluid viscosity increases with treatment volume, and decreases when pumping rate increases.
Propping Outside the Pay: a Process to Potentially Increase Fracture Flow Capacity, Post-Frac Production, and Net Revenue from Hydraulic Fracturing
Authors: Veatch Ralph W. , Cooke Claude E.
Published: February 2013

"Propping Outside the Pay" is a hydraulic fracturing procedure used or applied on or to a vertical well. For applicable wells, it has the potential to enhance/increase fracture flow capacity and the resulting: (a) producing flow rate (b) total recoverable reserves and (c) monetary returns. It introduces an added aspect to optimizing treatment, i.e., proppant pile height above the pay. Hence "Propping Outside the Pay" is a double optimization approach, i.e., fracture penetration (Xƒ) and piled proppant height above the pay (Hƒp).

The process creates more flow capacity from the pay to the wellbore through hydraulically created fractures that extend significantly outside the pay. It employs either one or both of the following: (a) injecting quantities of fracture propping material (proppant) that are greater than that normally used, and/or (b) creating more flow connections (e.g. perforations or open hole) from the wellbore to the propped fracture than are normally made.

Additional proppant piled above the pay, and in the fracture below the pay (where proppant can settle) increases the fracture total cross sectional area and flow capacity. If the entire propped fracture is connected to the wellbore, the added fracture flow capacity enhances production rates over and above that predicted by the commonly used methods that are normalized on pay.

At issue is economic viability, i.e., the additional proppant and perforating additional costs versus the monetary returns. Perforating costs are usually not significant as compared to first order proppant costs. Also, the applicable candidate wells require in-situ stress profiles such that the fracture will vertically propagate sufficiently above and/or below the pay to provide the opportunity to create additional fracture flow capacity. Experience indicates that a significant number of candidate wells exist.

Computational studies showed that net present value returns from using the process can be significantly increased. The degree of increase depends upon the relative vertical fracture height to pay ratio, rock mechanics and reservoir parameters, hydrocarbon prices, fracturing costs, well spacing, etc. Examples comparing "Typical" cases to "Propping Outside the Pay" cases are shown.
Regulatory ecotoxicology testing in Canada – activities and influence of the Inter-Governmental Ecotoxicological Testing Group
Authors: Taylor Lisa N. , Doe Kenneth G. , Scroggins Richard P. , Wells Peter G.
Published: February 2013

The Inter-Governmental Ecotoxicological Testing Group (IGETG) is an ad hoc group of government scientists, technologists, data users, and scientific advisors that has been active in the development and application of ecotoxicological testing in Canada. Membership includes representatives from government laboratories that conduct toxicity testing for research and development purposes, monitor effluent discharge for compliance with regulations, and/or perform exploratory monitoring of non-regulated sectors. The original focus of the group was to support the development and application of standardized toxicity test methods under the Fisheries Act but as the group matured it broadened its focus to five goals: (1) to promote the use of ecotoxicity testing; (2) to disseminate and harmonize new knowledge and understanding of issues related to ecotoxicity testing; (3) to provide scientific support to environmental programs; (4) to develop, validate and publish toxicological test methods; and (5) to establish and implement quality assurance practices in toxicology laboratories. Since 1990, IGETG has assisted Environment Canada in standardizing 22 toxicity test methods and in developing eight guidance documents. In this context, we briefly outline the history and future of applied ecotoxicological testing in Canada illustrated by specific examples wherein standard toxicity tests are useful. This paper commemorates IGETG's 35th anniversary.
A Death in the Family: Death as a Zen Concept
Authors: Black Helen K. , Rubinstein Robert L.
Published: February 2013

This study is based on original research that explored family reaction to the death of an elderly husband and father. We interviewed 34 families (a family included a widow and two adult biological children) approximately 6 to 10 months after the death. In one-on-one interviews, we discussed family members' initial reaction to the death, how the family is coping with the loss, and the changes that occurred in family relationships. In this article we focus on family solidarity after the loved one's death and discuss one extended case from the larger study. In reviewing our data, we find that a Zen perspective is useful in understanding the effect of the death on family relationships because this perspective incorporates a focus on the paradoxes of life and death. As death forces the family into the “present in its fullness,” the contradictions of intimacy and distance, past and future, and life and death, emerge. Members of the family explore existential questions about life, death, and intimacy, in order to find meaning in: 1) the life and death of the loved one; 2) their own lives; and 3) the family.
Impermeable layers in landfill design
Authors: Karanac Milica , Jovanovic Mica , Timmermans Eugène , Mulleneers Huib , Mihajlovic Marina , Jovanovic Jovan
Published: February 2013

Landfills are complex systems which could potentially contaminate the
environment. It should be prevented by providing impermeability during the
landfill design. In that aim related regulations should be followed and
adequate materials that provide impermeability should be used. The first part
of the paper presents review of the current regulations, interpretations, and
recommendations from U.S., EU and Republic of Serbia. Knowing that the
Serbian regulation should fully follow related European Directive, in
analyses some inadequate formulations and terms were observed related to the
Directive Annex I, 3.2. Request of the Regulation that deals with the bottom
of the landfill leakage is formulated differently than in Directive as well.
Mentioned problems enable some design solutions which are not among the best
available techniques. In the second part the paper presents comparative
analysis of possible alternatives in impermeable layer design, both for the
bottom and landfill cover. Some materials like clay, CCL, GCL might not be
able to satisfy prescribed requirements. The longest lifetime and the lowest
coefficient of permeability, as well as excellent mechanical, chemical and
thermal stability, show the mixture of sand, bentonite and polymers (PEBSM).
Minimum dropout voltage on a serial pnp transistor of a moderately loaded voltage regulator in a gamma radiation field
Authors: Vukic Vladimir
Published: February 2013

The main examined value in an experiment performed on moderately loaded
voltage regulators was the serial pnp transistor?s minimum dropout voltage,
followed by the data on the base current and forward emitter current gain.
Minimum dropout voltage decreased by up to 12%, while the measured values of
the forward emitter current gain decreased by 20-40% after the absorption of
a total ionizing dose of 500 Gy. The oxide trapped charge increased the
radiation tolerance of the serial lateral pnp transistor owing to the
suppression of interface trap formation above the base area. Current flow
through the serial transistor of the voltage regulator had an influence on
the decrease in the power pnp transistor?s forward emitter current gain. Due
to the operation with a moderate load of 100 mA, loss of emitter injection
efficiency was not as important as during the operation with high current
density, thus eliminating the negative influence of emitter crowding on the
radiation hardness of the voltage regulator. For a moderate load, gain in the
negative feedback reaction was enough to keep output voltage in the
anticipated range. Only information procured from tests of the minimum
dropout voltage on the moderately loaded voltage regulators were not
sufficient for unequivocal determination of the examined integrated circuit?s
radiation hardness.
Influence of the particle size reduction on magnetic properties of electron-doped Ca1-xYxMnO3
Authors: Alqat Aboalqasim , Gebrel Zohra , Spasojevic Vojislav , Kusigerski Vladan , Boskovic Snezana , Blanusa Jovan
Published: February 2013

The electron-doped magnetic nanoparticles of Ca1-xYxMnO3 (x = 0, 0.05, 0.10,
0.15, 0.20, and 0.30) manganite with an average particle size of 50 nm are
analyzed and discussed in relation to their bulk counterparts. Nanoparticle
samples show dominant anti-ferromagnetic ordering with a significant increase
of coercivity, with the maximum value of 0.9 T for x = 0. Particle size
reduction in Ca1-xYxMnO3 retains the bulk-like magnetic behavior of samples
having up to 15% of Y3+, with the small ferromagnetic contribution from
disordered surface spins. Suppression of charge ordering state and
enhancement of saturation magnetization were found in samples with higher Y3+
concentration (x = 0.2, 0.3), indicating high ferro-magnetic contribution in
these samples.
232Th, 226Ra, and 40K activities and associated radiological hazards in building materials of Islamabad capital territory, Pakistan
Authors: Rahman Saeed , Rafique Muhammad
Published: February 2013

Radioactivity levels in building materials, collected from the Islamabad
capital territory have been determined by using a gamma spectrometric
technique. Measured specific activities of 226Ra, 232Th, and 40K in material
samples ranged from 8 ? 1 to 116 ? 6 Bq/kg, 9 ? 1 to 152 ? ? 5 Bq/kg, and 29
? 6 to 974 ? 23 Bq/kg, respectively. The radium equivalent activity, absorbed
dose rate, annual effective dose, and gamma index were evaluated from the
measured amounts of radioactivity to assess the radiation hazard associated
with the studied building materials. The mean radium equivalent activity, the
absorbed dose rate and annual effective dose estimated ranged from 81 ? 6 to
221 ? 11 Bq/kg, 38 ? 3 to 104 ? 5 nGy/h, and 0.23 ? 0.02 to 0.64 ? 0.03 mSv,
respectively. The ranges of the calculated Raeq were found to be lower than
the values recommended for construction materials (370 Bq/kg). The mean
values of the internal and external hazard indices were found in the range of
0.30 ? 0.02 to 0.78 ? 0.05 and 0.22 ? 0.02 to 0.60 ? 0.03, respectively. The
results of the materials examined indicate no significant radiological
hazards arise from using such material in building construction.
Prototype of the particle fluence measurement device
Authors: Trajic Ivan , Belicev Petar , Petrovic Srdjan , Rajcevic Milan , Munitlak Dragan , Bojovic Bosko
Published: February 2013

A method of measuring particle fluence and ion beam current in experiments of
ion implantation is presented. The design and technical details of a realized
prototype device are discussed. Special care is devoted to the effect of
secondary electrons and its elimination. An electrostatic solution with two
electrodes for the suppression of secondary electrons has been realized. Our
approach provides redundancy and allows lower bias voltages to be used for
the suppression of electrons. The presented results illustrate the efficiency
of the proposed solution.
Mortality rate of lip, oral cavity and pharynx malignant tumors in Serbia within a period 1991-2009
Authors: Ilic Milena , Radevic Svetlana , Stefanovic Vladimir , Cirkovic Tatjana , Zurovac Tamara , Savic Borivoje , Kovacevic Vladan
Published: February 2013

Background/Aim. Lip, oral cavity and pharynx malignant tumors account for
3.7% of all cancer deaths worldwide, with significant geographic variations
in frequency and distribution. The aim of this descriptive epidemiologic
study was to analyze the mortality rate of lip, oral cavity and pharynx
malignant tumors in Serbia proper within a period 1991-2009. Methods.
Mortality rates standardized directly using the world population as the
standard were used in data analysis. Linear trend and regression analyses
were used to analyze rate trends in mortality. Results. The Serbian
population demonstrated an increase in the mortality of lip, oral cavity and
pharynx malignant tumors (y = 3.32 + 0.03?; p = 0.002; average annual percent
change = + 0.8). The male population showed a significant increase in
mortality trend (y = 5.90 + 0.03?; p = 0.020; % change = + 0.9), while the
female population did not show a significant increase in mortality. The
male/female cancer mortality ratio was 5.5:1. Mortality rates for lip, oral
cavity and pharynx cancer increased with age in both genders, with rates
being the highest in the population aged 85 and older. Increasing trends of
lip, oral cavity and pharynx cancer mortality were observed in males aged
50-54; the average annual percent change was + 7.4 % (95% CI, 6.2-9.0). The
population of both genders aged 55-59 demonstrated an increase in lip, oral
cavity and pharynx cancer mortality, the increase being + 1.8% (95% CI,
1.4-2.2) in men and + 34.3% (95% CI, 28.4-40.2) in women. Conclusion. The
increasing trend in lip, oral cavity and pharynx cancer mortality points to
the necessity to investigate etiology and improve primary and secondary
prevention measures.
Health-related quality of life assessment in Serbian schoolchildren hospitalized for malignant disease
Authors: Nedovic Goran , Marinkovic Dragan , Rapaic Dragan , Berat Svetlana , Kozomara Ruzica
Published: February 2013

Background/Aim. Although long-term survival of childhood cancer patients is
significantly improved, prolonged treatment and hospitalization might have
negative impacts on child development. The aim of this study was to verify
profile of health-related quality of life parameters in population of
schoolchildren during hospitalization and treatment for malignant disease.
Methods. The Serbian version of Pediatric Quality of Life Inventory Version
4.0 (PedsQLTM4.0) Generic Core Scales was applied. A total of 120
schoolchildren were analyzed: 60 patients hospitalized for prolonged
malignant disease treatment and 60 healthy schoolchildren from public
schools. The study was done at the Institute for Oncology and Radiology of
Serbia, as well as in four schools. Results. Generally, schoolchildren
hospitalized for cancer treatment demonstrated lower scores on physical,
emotional, social and school functioning when compared to healthy
schoolchildren from regular public schools. Significant differences were
observed for all the 8 items of the Physical Health Scale, in 2 out of 5
items of the Emotional Functioning Scale, in 4 out of 5 items of the Social
Functioning Scale, and 3 out of 5 items of the School Functioning Scale.
Conclusions. The Serbian version of PedsQLTM 4.0 Generic Core Scales could be
successfully used to evaluate physical, emotional, social and school
functioning of hospitalized children and adolescent. Schoolchildren
hospitalized for prolonged tumor treatment have poorer HRQOL scores compared
to general healthy population, however the level of remaining physical,
emotional and social parameters should provide solid foundation for their
potential rehabilitation, education and inclusion.
Diurnal Variation in Vascular and Metabolic Function in Diet-Induced Obesity
Authors: Prasai Madhu J. , Mughal Romana S. , Wheatcroft Stephen B. , Kearney Mark T. , Grant Peter J. , Scott Eleanor M.
Published: February 2013

Circadian rhythms are integral to the normal functioning of numerous physiological processes. Evidence from human and mouse studies suggests that loss of rhythm occurs in obesity and cardiovascular disease and may be a neglected contributor to pathophysiology. Obesity has been shown to impair the circadian clock mechanism in liver and adipose tissue but its effect on cardiovascular tissues is unknown. We investigated the effect of diet-induced obesity in C57BL6J mice upon rhythmic transcription of clock genes and diurnal variation in vascular and metabolic systems. In obesity, clock gene function and physiological rhythms were preserved in the vasculature but clock gene transcription in metabolic tissues and rhythms of glucose tolerance and insulin sensitivity were blunted. The most pronounced attenuation of clock rhythm occurred in adipose tissue, where there was also impairment of clock-controlled master metabolic genes and both AMPK mRNA and protein. Across tissues, clock gene disruption was associated with local inflammation but diverged from impairment of insulin signaling. We conclude that vascular tissues are less sensitive to pathological disruption of diurnal rhythms during obesity than metabolic tissues and suggest that cellular disruption of clock gene rhythmicity may occur by mechanisms shared with inflammation but distinct from those leading to insulin resistance.