bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection guidelines for ionic dielectrics with gigantic dielectric response (GDR) based on polaronic phase transition criteria
Authors: Ligatchev Valeri , Yu Zhigen , Zheng Jianwei , Sullivan Michael B.
Published: April 2013

Dielectric materials with GDR (e.g. CaCu3Ti4O12 – CCTO and isostructural systems, co-doped NiO etc) attract major research interest due to their bright prospective in energy storage and memory devices. However, after years of intensive experimental and theoretical studies of GDR materials, physical nature of their extremely high complex dielectric permittivity (specifically, real part ∼ 104 - 106) is still not established convincingly. Another serious problem is excessively high imaginary part of the permittivity (which usually exceeds real one). Better understanding on physical mechanisms and limitations of GDR behavior in aforementioned dielectrics could be achieved based on polaronic phase transition criteria, proposed S. Fratini and P. Quémerais [Eur. Phys. Journ. B14, 99 (2000)]. In particular, ‘melting’ of Polaronic Wigner Crystal (PWC) either to ‘polaronic liquid’ or ‘electron liquid’ manifests two different scenarios of PWC phase transition at increment of concentrations of appropriate dopants. The former scenario is certainly preferable for ionic dielectrics with GDR behavior, while the latter one would yield in metal-like dielectric response with very high real permittivity, but unacceptable loss. Described approach provides physically transparent guidelines for selection of prospective host dielectrics with GDR behavior and quantitative estimations on critical dopant/polaron concentrations, corresponding to both aforementioned types of the phase transitions as well as temperature ranges suitable for GDR.
Surface Dynamics and Hydrophobicity of High-Voltage Insulator Polymers
Authors: Fritz Oliver , Shemella Philip T. , Laino Teodoro , Curioni Alessandro
Published: April 2013

Using large-scale, all-atom molecular dynamics simulations, we show that microscopic mechanisms found for molecules on the material surface of siloxane polymers can explain an important surface-hydrophobicity restoration process. In particular, a net orientation and polarization on the surface can be found which is the result of an augmented motion of certain molecules. Based on this result, surface hydrophobicity, its loss through oxidation, and its restoration through a unique interaction between cyclomethicone molecules, oxidized methyl groups, and counterions can be understood.
Nickel Foam as a Substrate for III-nitride Nanowire Growth
Authors: Mastro Michael A. , Nepal Neeraj , Kub Fritz , Hite Jennifer K. , Kim Jihyun , Eddy Charles R.
Published: April 2013

This article presents the use of flexible metal foam substrates for the growth of III-nitride nanowire light emitters to tackle the inherent limitations of thin-film light emitting diodes as well as fabrication and application issues of traditional substrates. A dense packing of gallium nitride nanowires were grown on a nickel foam substrate. The nanowires grew predominantly along the a-plane direction, normal to the local surface of the nickel foam. Strong luminescence was observed from undoped GaN and InGaN quantum well light emitting diode nanowires.
Melting Gel Films for Low Temperature Seals
Authors: Jitianu Mihaela , Jitianu Andrei , Stamper Michael , Aboagye Doreen , Klein Lisa C.
Published: April 2013

Melting gels are silica-based hybrid gels with the curious behavior that they are rigid at room temperature, but soften around 110°C. A typical melting gel is prepared by mixing methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES). MTES has one methyl group substituted for an ethoxy, and DMDES has two substitutions. The methyl groups do not hydrolyze, which limits the network-forming capability of the precursors. To gain insight into the molecular structure of the melting gels, differential scanning calorimetry and oscillatory rheometry studies were performed on melting gels before consolidation. According to oscillatory rheometry, at room temperature, the gels behave as viscous fluids, with a viscous modulus, G″(t,ω0) that is larger than the elastic modulus, G′(t,ω0). As the temperature is decreased, gels continue to behave as viscous fluids, with both moduli increasing with decreasing temperature. At some point, the moduli cross over, and this temperature is recorded as the glass transition temperature Tg. The Tg values obtained from both methods are in excellent agreement. The Tg decreases from -0.3oC to -56oC with an increase in the amount of di-substituted siloxane (DMDES) from 30 to 50 mole %. A decrease of the Tg follows an increase of the number of hydrolytically stable groups, meaning a decrease in the number of oxygen bridges between siloxane chains.
Growth and physical properties of vanadium oxide thin films with controllable phases
Authors: Ji Yanda , Zhang Yin , Gao Min , Yuan Zhen , Jin Changqing , Lin Yuan
Published: April 2013

Vanadium oxides thin films with variable oxidation states have attracted great attention due to their unique electrical, optical properties and many important applications in microelectronics, infrared optical devices, and energy harvest systems. However, to fabricate vanadium oxide thin films with controllable phases and desired transport properties is still a challenge by using a chemical solution deposition (CSD) technique. In this paper, we report that vanadium oxide thin films with well controlled phases such as rhombohedral V2O3 and monoclinic VO2 could be synthesized on Al2O3 (0001) substrates using a CSD technique ---- polymer assisted deposition (PAD). Both V2O3 and VO2 thin films can be well controlled with good epitaxial quality by optimizing the fabrication parameters. The electrical resistivity changes 3∼4 orders of magnitude at metal insulator transition for both epitaxial V2O3 and VO2 thin films. The correlation between the physical properties and the microstructures of the films will be discussed.
Ipswich motorway, Australia: delivering transport solutions for urban corridors
Authors: Royle Graham
Published: April 2013

The A$1·95 billion (£1·3 billion) Ipswich motorway upgrade near Brisbane was Australia's largest road infrastructure alliance. Origin Alliance – comprising the client, two designers and three contractors – was tasked with transforming an existing substandard four-lane motorway into a modern, intelligent six-lane highway with a future capacity for eight lanes using network-managed hard-shoulder running. Only 8·5 km long, the upgrade demanded an unprecedented level of temporary traffic management for up to 100 000 vehicles a day. This paper outlines the complexities in design and construction and the means by which works were planned to guarantee the utmost level of safety to the travelling public and on-site workforce.
Design and construction of the Inner West Busway, Sydney, Australia
Authors: Hyndman Peter , Shoebotham Austen , Hespe Iain
Published: April 2013

Completed in 2011, the Inner West Busway project reduced travel times for thousands of bus commuters along Victoria Road in Sydney, Australia, by up to 17 min. The A$175 million (£117 million) project involved installing a new 3·5 km city-bound bus lane, which required a new 400 m long, incrementally launched box girder bridge across Iron Cove. This paper examines the design, construction issues and innovation associated with the project, including the country's first bridge launch from in front of an abutment, its first use of the Quickchange movable barrier system and a world first in-pavement light system. Other works included over 12 km of new bicycle shoulder lanes and on-road bicycle routes, a new children's playground and rehabilitation of a park.
Engineering The Shard, London: tallest building in western Europe
Authors: Parker John
Published: April 2013

The Shard in central London is 310 m high, making it the tallest building in western Europe. Designed for client Sellar Property Group, it is a ‘vertical city’, containing shops, offices, restaurants, hotel, apartments and a public viewing gallery. This paper describes the design and construction of the building, which has a concrete core, steel-framed floors to level 40, concrete floors to level 69 and a steel ‘spire’ at the top. Various innovative construction techniques were used to save time and improve safety, including building the three-storey basement and core top-down, installing plunge columns to high levels of accuracy, and using modular construction for the spire.
Negative emissions technologies could become the world’s largest industry
Authors: Kruger Tim , Darton Richard
Published: April 2013

With greenhouse gas emissions continuing to rise and oil in plentiful supply, taking carbon dioxide out of the air might be a more pragmatic way of curbing climate change. Tim Kruger and Richard Darton of Oxford University say negative emissions technologies could be the next big thing.
The diameter of single, double and triple fluid jet grouting columns: prediction method and field trial results
Authors: FLORA A. , MODONI G. , LIRER S. , CROCE P.
Published: April 2013

In this paper, a simple expression to predict the average diameter of columns created with single, double and triple fluid jet grouting is proposed considering both the energy of the eroding jet and the resistance of the soil. The injection system (single, double or triple) and the composition of the injected fluids are taken into account on the basis of theoretical analysis of the turbulent diffusion of submerged jets. Instead of separately considering the energy of the air jet shrouding the eroding fluid, a simple parameter is introduced which represents the beneficial effect of air in reducing the energetic dissipation on the jet external surface. In this way, a new expression of the specific kinetic energy of the jet at any distance from the nozzle is proposed, which is a relevant step forward if compared with that at the nozzle or at the pump previously proposed, as it takes into account both the system characteristics and the composition of the eroding jet (either grout or water). In the expression proposed to predict the diameter of jet grouting columns, soil resistance is considered by way of the results of the standard penetration test and cone penetration test, in terms of NSPT and qc respectively. The expression has been calibrated on a number of experimental data, and in most cases proved its efficiency in predicting columns' diameter with a scatter of less than ±20%. The field trials results highlight that jet grouting is more effective in coarse-grained soils, as clearly shown by an efficiency parameter proposed by the authors. Design charts are drawn to quickly estimate the average diameter Da for different soils, injection systems and input energies.
Direct and indirect effects of light environment generate ecological trade‐offs in herbivore performance and parasitism
Authors: Stoepler Teresa M. , Lill John T.
Published: April 2013

A variety of ecological factors influence host use by parasitoids, including both abiotic and biotic factors. Light environment is one important abiotic parameter that differs among habitats and influences a suite of plant nutritional and resistance traits that in turn affect herbivore performance. However, the extent to which these bottom‐up effects “cascade up” to affect higher trophic levels and the relative importance of direct and indirect effects of sunlight on tritrophic interactions are unclear. The objective of this study was to test how light environment (light gap vs. shaded forest understory) and leaf type (sun vs. shade leaves) affect the performance and incidence of parasitism of two species of moth larvae, Euclea delphinii and Acharia stimulea (Limacodidae). We manipulated the leaf phenotype of potted white oak saplings by growing them in either full sun or full shade throughout leaf expansion to produce sun and shade leaves, respectively. These saplings were then placed in light gap and adjacent shaded understory habitats in the forest in a full‐factorial design, and stocked with sentinel larvae that were exposed to parasitism (“exposed” experiments). We reared additional larvae in sleeve cages (protected from parasitism) to isolate light environment and leaf phenotype treatment effects on larval performance in the absence of enemies (“bagged” experiments). In the exposed experiments, light environment strongly affected the likelihood of parasitism, while leaf phenotype did not. Euclea delphinii larvae were up to 6.6 times more likely to be parasitized in light gaps than in shaded understory habitats. This pattern was consistent for both tachinid fly and wasp parasitoids across two separate experiments. However, the larval performance of both species in the bagged experiments was maximized in the shade‐habitat/sun‐leaf treatment, a habitat/leaf‐type combination that occurs infrequently in nature. Taken together, our results suggest that the direct effects of light environment on the incidence of parasitism supersede any indirect effects resulting from altered leaf quality and reveal inherent ecological trade‐offs for herbivores confronted with choosing between sunny (high leaf quality, harsh environment, high parasitism) and shaded (reduced leaf quality less harsh environment, reduced parasitism) habitats.
Is There a Positive Effect of Smoking Cessation on Periodontal Health? A Systematic Review
Authors: Fiorini Tiago , Musskopf Marta Liliana , Oppermann Rui Vicente , Susin Cristiano
Published: April 2013

Background: Although the detrimental effects of tobacco on the periodontal tissues have been reported extensively, little is known about the potential beneficial effect of smoking cessation on periodontal health. The aim of this systematic review is to evaluate the effect of smoking cessation on periodontitis progression and response to periodontal therapy.

Methods: Two independent reviewers completed the review process through title (n = 118), abstract (n = 24), and whole‐paper selection (n = 5). Sources include Medline and EMBASE databases (up to December 2012) and a reference list of selected studies. Prospective studies comparing progression rates of periodontitis between smokers and quitters and clinical trials evaluating the effect of smoking‐cessation programs, alone or in combination with periodontal treatment, were included. At least 1 year of follow‐up was required for inclusion.

Results: Of 331 potentially relevant publications, five studies fulfilled the inclusion criteria. Because of heterogeneity of the studies, a meta‐analysis could not be performed. One study reported that the progression of clinical attachment loss (AL) ≥3 mm during a 6‐year period was approximately three times higher among smokers than quitters (P <0.001). Two studies (10 and 20 years of follow‐up) observed a decrease in radiographic bone loss of ≈30% among quitters when compared with smokers. Among individuals receiving non‐surgical periodontal treatment, quitters were more likely to have periodontal probing depth reductions (P <0.05) than non‐quitters/oscillators. No differences in AL were observed.

Conclusion: Based on the limited available evidence, smoking cessation seems to have a positive influence on periodontitis occurrence and periodontal healing.
Clinical Correlates of a Lateral‐Flow Immunoassay Oral Risk Indicator
Authors: Nwhator S.O. , Ayanbadejo P.O. , Umeizudike K.A. , Opeodu O.I. , Agbelusi G.A. , Olamijulo J.A. , Arowojolu M.O. , Sorsa T. , Babajide B.S. , Opedun D.O.
Published: April 2013

Background: The aim of the present study is to investigate the clinical correlates of a novel lateral‐flow immunoassay with bleeding on probing (BOP), oral hygiene, and periodontal probing depth. This report offers a simple, rapid, and highly sensitive tool that addresses two issues important to periodontists: 1) detecting active periodontitis, and 2) predicting chronic periodontitis.

Methods: Seventy‐six of 86 males requiring seminal fluid analysis as part of a separate study were serially recruited into the study. After basic dental and periodontal examination under natural light and with the use of the community periodontal index of treatment needs (CPITN) probe, debris and calculus indices were recorded per participant. Participants were subsequently grouped into “good,” “fair,” and “poor” oral hygiene categories based on a simplified oral hygiene index. BOP was assessed with the ball‐ended tip of the probe, and periodontitis was assessed with pocket probing as well as a lateral flow of neutrophil collagenase‐2 immunoassay, which measures levels of matrix metalloproteinase‐8.

Results: Neutrophil collagenase‐2 immunoassay was 96% sensitive for poor oral hygiene, 95% sensitive for chronic periodontitis (defined as at least two sites with periodontal pockets), and 82.6% sensitive for at least two sites with BOP.

Conclusion: Neutrophil collagenase‐2 immunoassay had a high sensitivity for at least two sites with BOP and two sites with periodontal pockets but a lower relationship for single‐site pockets and BOP.
Comparison of Fracture Valves vs. Plug-and-Perforation Completion in the Oil Segment of the Eagle Ford Shale: A Case Study
Authors: Stegent Neil A. , Ferguson Kip , Spencer Jon
Published: April 2013

Which completion strategy is better: plug-and-perforation or fracture-valve? The authors of this paper will evaluate multiple completion strategies in two offset horizontal wells drilled in the oil section of the Eagle Ford shale. The first well was completed using a combination of single entry point, ball-activated fracture valves (first two-thirds of the lateral) and plug-and-perforation (P-n-P) with multiple entry points (the remainder of the lateral). The second wellbore was completed using only P-n-P with multiple entry points. Both wells were completed using comparable completion designs (hybrid fracture design, number of fracture stages, and pounds of proppant) and were cemented for annular isolation.

To determine the completion and production efficiency, microseismic mapping and oil-soluble tracer technologies were used to evaluate the differences between the completion strategies. Fracture mapping was used to compare stage “complexity,” while a hydrophobic oil tracer, which generated a pseudoproduction log of each individual stage, was used to determine the completion efficiency.

The integration of these diagnostic engineering technologies allows for interesting conclusions with respect to the fracture complexity generation from the different completion strategies, as well as the resulting production from the comparative wells. This data can provide important information regarding the difference between the two completion methods.
A Method To Perform Multiple Diagnostic Fracture Injection Tests Simultaneously in a Single Wellbore
Authors: Martin Alvin R. , Cramer David D. , Roberts Neale , Nunez Oswaldo
Published: April 2013

This paper presents a unique process for deriving reservoir properties (i.e., minimum horizontal stress, kh/u, and reservoir pressure) in isolated reservoir layers intersected by the same vertical wellbore. It is based on simultaneously performing multiple diagnostic fracture-injection tests (DFIT) with extended multiday shut-in periods using downhole shut-in tools and bottomhole memory gauges.

A case study of 58 vertical wells completed in the Mesaverde and Dakota sandstones of the San Juan basin is used to describe and assess the above application. These intervals are gas productive, slightly to significantly subpressured, and possess a very low permeability pore network enhanced by natural fracture networks. As many as seven individual intervals per well were tested using the simultaneous process in an area spanning the entire San Juan basin. Large-scale, multistage hydraulic fracturing is necessary to establish commercial production from these intervals. The diagnostic tests were done before the large-scale fracture treatments, yet did not impede the subsequent implementation of the treatments. In the Dakota interval, the diagnostic testing results agreed well with the kh derived from post-fracture production analysis and led to a process of treatment design optimization. In the Mesaverde interval, less agreement was found between diagnostic-test and production-analysis results. Despite the lack of validation, fluid leakoff rates measured during the diagnostic testing provided insight into fracture half-length differences documented in a previous study of microseismic mapping. As part of the case study, procedural guidelines and best practices developed in the process of performing over 200 tests will be discussed.
Effect of Heterogeneity on Formation Damage in Long Horizontal Wells: An Experimental Study
Authors: Menouar Habib
Published: April 2013

This study is directed toward an experimental investigation of formation damage in a large heterogeneous reservoir from the Middle East. A number of experiments using real reservoir core samples at reservoir conditions of pressure and temperature have been performed. Various drilling fluid contact times with the formation and overbalance pressures have been used during these experiments. The analysis of the experimental data shows that the results have been predominantly marked by the heterogeneous nature of this reservoir. The heterogeneity of the cores affects to a great extent how the damage due to drilling fluids occurs. The results show as expected that the damage permeability increases with the contact time. As a consequence, extended drilling causes additional formation damage and higher skin. Also, without contradicting the detrimental effect of the overbalance pressure on formation damage, the experimental data show an unexpected result: Higher permeability zones of the reservoir are affected much more significantly by the drilling fluids’ damage than lower permeability zones. Similar results are obtained for invasion depth. The effect of the magnitude of the permeability on formation damage is so strong that it masks the effect of overbalance pressure on formation damage. A straight-forward conclusion is that stimulation jobs in such reservoirs should have as a primary objective to stimulate in priority the most permeable zones that have been damaged along the horizontal well instead of the low permeability zones since it pays more to regain a fraction of a very high permeability than the same or smaller fraction of a low permeability zone. Another conclusion of this study is that it is of paramount importance in formation damage to assess accurately the effect of the horizontal well effective length and its contribution to the productivity of the well compared to other parameters such as the damage permeability, the invasion depth, or the anisotropy ratio.
Simulation of Waterflooding with Coarse-Scale Dual-Porosity Representation of Highly Heterogeneous Reservoirs
Authors: Yadecuri Mohammad Evazi , Jessen Kristian
Published: April 2013

Upscaling of the geological model is an important component of any reservoir simulation work flow. This process introduces error due to averaging of sub-grid heterogeneity and introduces additional numerical diffusion. Upscaling errors are more severe when waterflooding is simulated in highly heterogeneous (channelized) porous media. When coarse grid blocks involve high and low permeability channels or layers, current upscaling techniques generally fail in representing the fine scale response accurately.

In this work, the effect of heterogeneity on displacement efficiency in coarse-scale modeling is studied. The pore space of the fine-scale model is ranked based on the contribution to flow. Two levels of porosity are considered and classical dual-porosity models are used for coarse-scale flow simulation. A streamline index (SI), defined as the ratio of the streamline density to the time-of-flight, is used for storage categorization: An active pore volume represents the high flow paths in the porous system while a passive pore volume is considered as source/sink that feed into the major flow pathways. Several types of cut-off values, including the span of SI and local/global cut-offs, are discussed to determine the fraction of active pore volume in each coarse grid cell.

The proposed technique is used to simulate waterflooding on two highly heterogeneous models. Displacement calculations are performed on the original fine grid and on a uniform coarse grid with global flow-based transmissibility upscaling. Simulation results from coarse single-porosity models (classical approach) and dual-porosity systems are then compared. Upscaling with dual-porosity flow modeling is demonstrated to provide for significant improvements in the accuracy of the coarse-scale simulation and arrives at a more accurate representation of the displacement performance.
Hydraulic Fracture Design Flaws- Proppant Selection
Authors: Yang Mei , Proppants Cadre , Liu Xicai , Jiao Di , Economides Michael J.
Published: April 2013

Proppant selection has been discussed in previous works (Yang et al, 2012), as one of the most important elements in both the physical success of a hydraulic fracture and its economic optimization. This paper continues this in-depth discussion. The study presents the statistical usage of fracture technology in major locations in Texas. The geographic analysis is consistent and valuable: similar reservoirs in the same basin call for similar treatments. The research will particularly focus on the analysis of proper proppant selection.

Texas completion and production data from the past several years, specifically on fracturing treatments in the Eagle Ford Shale and the Permian Basin, have been studied and summarized. The statistical analysis includes, but is not limited to: the fracture job size, proppant type, pay formations and the true vertical depth of the well. Important factors involved in fracture design are also represented: formation type, depth, reservoir permeability, closure stress, stress isotropy/anisotropy and post-treatment productivity.

Studies show that natural sands are the appropriate proppants for reservoirs currently under exploration in the specified plays. However, while Premium Brown Sand and Premium White Sand are the recommended proppants, this study proves that by utilizing the Unified Fracture Design model, the Net Present Values of the treatments using Premium Brown Sand are superior to those using Premium White Sand. This is established not only because of the shallower depths (and therefore less crushing) but also because Premium Brown Sand creates similar EUR at a substantially lower completion cost.

With the theory guidance of the Unified Fracture Design and extensive completion and production data analysis, this study can considerably help the oil and gas industry to effectively implement hydraulic fracturing designs.
Mechanisms Behind Low Salinity Water Flooding in Carbonate Reservoirs
Authors: Al-Shalabi Emad W. , Sepehrnoori Kamy , Delshad Mojdeh
Published: April 2013

The low salinity water injection method (LoSal) has become one of the important research topics in the oil industry because of its enormous possible advantages. The objective of this paper is to investigate the mechanism behind the LoSal effect on oil recovery through data matching. The UTCHEM simulator was used to match the cycles of the injected seawater and different dilutions of the latter for two recently published coreflooding experiments. The result from the history matching revealed that the wettability alteration mechanism is believed to be the main contributor to LoSal. Based on this finding, an analytical model for oil recovery predictions can be developed.
Uncertainty Assessment in Geologic Modeling and Sensitivity Analysis of Static and Dynamic Models in Umiat: A Frozen Shallow Oil Accumulation in National Petroleum Reserve of Alaska
Authors: Kohshour I. O. , Ahmadi M. , Hanks C.
Published: April 2013

Current high oil price and availability of new technologies allow re-evaluation of oil resources previously considered uneconomic. Umiat oil field is one such resource: a unique, shallow (275–1055 feet), low-pressure (200–400 psia) reservoir within the permafrost zone with no initial gas cap located north of the Arctic Circle, 80 miles west of Trans Alaska Pipeline System (TAPS) with an estimated 1.5 billion barrels of oil-in-place.

A static model was built based on reinterpretation of original log and core data and seismic information. A permeability anisotropy ratio of 0.45 was incorporated into the geologic model. A Monte Carlo simulation was conducted to estimate the different degrees of uncertainty in the original oil in place (OOIP) estimates. To cover the wide permeability range (0–500 md), three sand groups (rock types) were defined and assigned appropriate capillary pressure and relative permeability curves. These were included in the dynamic model along with measured PVT data and gas-oil relative permeabilities in the presence of ice to evaluate the performance of immiscible gas injection using a multilateral wagon wheel well pattern with horizontal well length of 1500 ft.

The simulation results show that with 50 years of gas injection, recovery factors for the base case (400 psia injection pressure) and a case with 600 psia injection pressure are 12% and 15%, respectively, keeping other parameters constant. Those recovery numbers reduce by 18% and 6% when producing GOR is restricted to 5,000 scf/STB and 10,000 scf/STB, respectively. The potential effect of natural fractures was modelled by considering the effect of permeability anisotropy (Kv/Kh).. Simulation results indicate that lower anisotropy ratios will reduce oil recovery, probably due to inhibition of downward gas movement.

The results obtained in this study contribute to the understanding of uncertainties in resource estimation and evaluating ranges of oil recovery in reservoir modeling. Despite limited data and lack of production history to tune the model, the results demonstrate that the proposed development plan bears a high degree of uncertainty and risk. These findings strongly encourage the operator to include in development plan strategies to reduce the risk by enhancing the quantity and quality of simulation input data.
An Efficient Reservoir Simulation Approach to Design and Optimize Unconventional Gas Production
Authors: Yu Wei , Sepehrnoori Kamy
Published: April 2013

Shale gas production has gained worldwide attention over the past several years. Production from shale gas reservoirs requires horizontal drilling with multiple hydraulic fracturing to obtain the most economical production. However, there are high cost and uncertainty due to many inestimable and uncertain parameters such as reservoir permeability, porosity, fracture spacing, fracture half-length, fracture conductivity, gas desorption, geomechanics and existing natural fracture. Therefore, the development of a method quantifying uncertainties and optimization of shale gas production in an efficient and practical way is clearly desirable.

In this paper, we present a user-friendly and efficient framework to obtain the optimal gas production scenario by optimizing the uncertain factors by integrating several commercial simulators, an economic model, Design of Experiment (DoE), and Response Surface Methodology (RSM) with a global optimization search engine. Specifically, we use factorial design to screen insignificant factors and find the most influential design and uncertain factors, and then employ RSM to design over those most influential factors to fit a response surface using net present value (NPV) as the objective function, and finally identify the most economical production scenario under conditions of uncertainty. Eight uncertain parameters, such as porosity, permeability, reservoir thickness, reservoir pressure, bottom hole pressure (BHP), fracture spacing, fracture half-length, and fracture conductivity with a reasonable range based on Barnett Shale information are investigated. Also, different gas prices are considered for the optimization process.

This framework is effective and efficient for hydraulic fracturing treatment design and production scheme optimization in unconventional gas reservoirs. It can contribute to providing guidance for engineers to modify the design of a hydraulic fracture treatment prior to the actual fracture treatment.
Impact of Staggered Fracture Placement on Field Development of Unconventional Gas Reservoirs: a Critical Evaluation of Overlapping SRV's
Authors: Sahai Vivek , Jackson Greg , Rai Rakesh , Lalehrokh Farshad
Published: April 2013

Making optimal well spacing decisions in unconventional plays is critical for commercial viability. Given the huge areal extent of these plays and low permeability, a large number of wells are needed to optimally extract the resource. The well spacing decision has to incorporate changes in geology/reservoir characteristics, completion methodology, presence of offset wells, and economic constraints. This work shows the impact of changes in reservoir properties such as permeability, completion properties as fracture spacing and completion footprint or the areal configuration of the stimulated reservoir volume (SRV) in determining optimal well spacing.

As additional development or infill wells are drilled in a section, the possibility of SRV overlap increases. When the stage/cluster placement is not staggered between the neighboring wells, the created fractures may intersect resulting in SRV destruction i.e. the fracture area accessible to the neighboring wells is less than the total fracture area created in absence of SRV overlap. With staggered placement of stages, the created fractures are at an offset and the SRV's overlap without the fractures intersecting. This results in accelerated depletion of the region between the wells by reducing the rock volume each hydraulic fracture has to drain. Thus, the neighboring wells rob some late life production potential by draining the reservoir within the study well drainage volume.

The impact of the percentage of fracture overlap, fracture spacing, and reservoir permeability on overall recovery and economic value is evaluated using synthetic models. For the scenario of SRV destruction, the NPV decreased with increasing SRV overlap. With staggered placement of fractures, there is a minor loss in NPV for less than 50% SRV overlap under the economic constraints considered. Higher than 50% overlaps may be detrimental depending on permeability and fracture spacing. Changes in cost/economic constraints also impact optimal well spacing. The presented results will assist operators in planning closer well spacing by optimizing capital expenditures and hydrocarbon recovery.
Discussion on Carbon Dioxide Minimum Miscibility Pressure Estimation: An Experimental Investigation
Authors: Menouar Habib
Published: April 2013

Among existing enhanced oil recovery (EOR) processes, carbon dioxide (CO2) flooding is the most widely used. The popularity of CO2 as a miscible agent is due to its characteristics, which result in excellent macroscopic and microscopic efficiencies when miscibility conditions are optimal. In most CO2 flooding studies, these conditions are related to the minimum miscibility pressure (MMP), which is the pressure above which miscibility develops and materializes in recoveries equal to or higher than 90% (Metcalfe and Yarborough,1979). Since the MMP is a quick and convenient tool for conducting screening studies for post-evaluation of miscible projects, many correlations used to estimate the MMP have been developed for various crude oils and are presented in the literature. The problem is that not all correlations reflect the necessary process parameters needed in a typical CO2 flooding project. Correlations that work for reservoirs in North America may not be suitable for reservoirs in the Middle East. This paper addresses the issues related to experimental estimation of the MMP in a large, low-permeability reservoir in the Middle East and the evaluation of correlations as a means of estimating the MMP for a given reservoir. These issues range from the experimental approach and the verification of slim tube results by core flooding experiments to the use of dead versus live oil to estimate the MMP (for instance) or the effect of impurities on the MMP of pure CO2. The use of dead oil instead of live oil to conduct both slim tube and core flooding experiments resulted in errors up to 9%. Also the effect of some gases like nitrogen, hydrogen sulfide, and methane on the MMP of pure CO2 is discussed. Among the correlations tested, only one was found to apply with a reasonable accuracy to CO2 flooding in the reservoir studied. The deviation between live and dead oil MMP slim tube experimental results is also discussed as well as the correction due to contamination of CO2 by other gases.
Injection Scheduling Design for Reduced Order Waterflood Modeling
Authors: Rezapour Amin , Tafti Tayeb Ayatollahi , Ortega Antonio , Ershaghi Iraj
Published: April 2013

In this paper we use the concept of experimental design from the System Identification literature and introduce a novel methodology for more accurate characterization and monitoring of waterfloods using linear models. To improve the predictability of the low order linear models they must be trained with sufficiently informative data. To achieve this goal, the input (here injection rate) must contain sufficient variations (without exceeding the technical and operational limits) so that all the relevant dynamics of the system are excited and can be seen in the output (here production rate). In sum, a successful injection scheduling design boils down to introducing predetermined variations on top of the existing injection rates. We will discuss how to design these variations, specifically their amplitude, sampling time, experiment length, frequency of variations and signal type, using priori knowledge of the reservoir dynamics and the production constraints. Our proposed methodology can be applied to currently available linear modeling techniques such as CRM, FIR, subspace models, etc. This study shows that the prediction error of a model that has been trained with a proper injection scheduling design, in a multi injector multi producer oil field, can be reduced significantly regardless of the modeling technique.
A Comprehensive Review of Alkaline-Surfactant-Polymer (ASP) Flooding
Authors: Sheng James J.
Published: April 2013

Alkaline-surfactant-polymer (ASP) flooding is a combination process in which alkali, surfactant and polymer are injected at the same slug. Because of the synergy of these three components, ASP is the current world-wide focus of research and field trial in chemical enhanced oil recovery.

This paper is to provide a comprehensive review of the ASP process. The reviewed topics include the following:

ASP synergy and its EOR mechanisms Screening criteria Laboratory work Numerical simulation work Summary of pilots and large-scale applications Project economics Chemicals used Water quality Salinity gradient Mobility control requirement Problems associated with ASP flooding

In addition to the comprehensive review, future developments are also discussed. Data and analyzed results presented in this review will help oil operators save research and pilot costs, and to build their confidence to execute and expedite their ASP projects.
Contribution of Methane Molecular Diffusion in Kerogen to Gas-in-Place and Production
Authors: Moghanloo Rouzbeh Ghanbarnezhad , Javadpour Farzam , Davudov Davud
Published: April 2013

This study provides simple analytic expressions to study diffusion in the kerogenic material of the shale gas matrix. Gas flow from the shale matrix into natural and induced fractures is an important production process. Kerogenic material in shales is the source of methane molecules. Gas is stored as compressed gas in nanopores, as desorbed gas on the surface of the nanopores, and as dissolved gas in the body of the kerogen. The contribution of gas flux is different in aforementioned processes. Detailed studies of the scanning electron microscope (SEM) images revealed the large exposed surface area in kerogenic material (Milliken et al. 2013 and Loucks et al. 2012). This new finding suggests that although gas diffusion coefficient is very low in kerogen, but the diffusive flux could be considerable because of the large exposed area. Gas diffusion from dissolved gas in kerogen into the pore network and, finally, into gas production stream would significantly impact gas-in-place and production-performance estimates in a shale reservoir.

We used three spatial models; linear, spherical, and cylindrical to study gas flux from the body of the kerogenic material into pore spaces. The rational of linear and radial geometry is based on the observed geometry of the pores in kerogen. Some pores are elongated and fit to a slit, some are rounded or multi-lateral that fit to a ring. Both cases of inward diffusion from kerogen body into intrapores and outward diffusion from kerogen external boundary into surrounding minerals are considered. We then evaluate time lag in diffusion for different geometry and compare it with the numerical solution to the second Fick's law. Furthermore, we derive the mass transfer coefficients and the corresponding Sherwood dimensionless group for the models studied here. We found that diffusion's contribution can be significant in shale plays and pore geometry has different impacts on diffusion flux in shales with different TOC.
Simulation of Gas Desorption and Geomechanics Effects for Unconventional Gas Reservoirs
Authors: Yu Wei , Sepehrnoori Kamy
Published: April 2013

Shale gas resource plays an increasingly important role in energy supply worldwide. Hydraulic fracturing of horizontal wells is crucial for economic production of shale gas. Gas in shale reservoirs is mainly composed of free gas within fractures and pores and adsorbed gas in shale matrix. With gas production, more gas may be released or desorbed because of substantial pressure depletion, especially during late time of gas production. However, hydraulic fractures may close to some degree based on proppant quality and shale hardness, resulting in decreasing gas production. Impacts of gas desorption and geomechanics in hydraulic fractures, i.e., stress-dependent propped fracture conductivity, on ultimate gas recovery are not clearly understood and systematically investigated. Additionally, most reservoir modeling work in the literature have usually ignored the gas desorption and geomechanics effects together. Therefore, it is absolutely critical to study and evaluate the impacts of gas desorption and geomechanics on gas recovery for different shale reservoirs.

In this paper, we perform history matching with two field gas production data from Barnett Shale and Marcellus Shale, and first analyze the positive contribution of gas desorption and the negative effect of geomechanics on gas production, respectively, and then compare these two effects on gas production with the purpose of identifying which effect is dominant in the whole process of gas production.

Furthermore, we numerically study the effect of gas desorption on gas recovery with available laboratory data of Langmuir isotherm from five different shale formations including Barnett Shale, New Albany Shale, Eagleford Shale, Marcellus Shale, and Haynesville Shale. The impact of different fracture spacing on gas desorption is considered. Also, we use the method of Design of Experiment (DoE) to perform sensitivity studies with six uncertain parameters such as reservoir permeability, bottom hole pressure (BHP), fracture conductivity, initial reservoir pressure, porosity, and fracture spacing to screen insignificant parameters and obtain critical parameters that control this process.

This paper enables operators to develop an early better understanding of the effects of gas desorption and geomechanics on shale gas well performance, and provides insights into history matching and optimization of hydraulic fracturing treatment design for shale gas production.
Photoperiod and Vernalization Effect on Anthesis Date in Winter‐Sown Spring Wheat Regions
Authors: Ottman Michael J. , Anthony Hunt L. , White Jeffrey W.
Published: April 2013

Accurate prediction of phenology is required to guide crop management decisions and to predict crop growth and yield. However, the relative importance of photoperiod and vernalization in predicting anthesis dates for spring bread and durum wheat (Triticum aestivum L. and T. durum Desf.) sown in the winter has not been reported. The purpose of this research is to determine the improvement in predicting anthesis dates of spring wheat sown in the winter when photoperiod and vernalization are considered. Observed dates of anthesis were obtained from University of Arizona wheat variety trials conducted at Maricopa, Wellton, and Yuma, AZ. The Cropping Systems Model CROPSIM‐CERES as released in DSSAT 4.5 was used to simulate days to anthesis based on temperature, daylength, and vernalization. For 12 bread and durum wheat cultivars, the model predicted days to anthesis with a root mean square error (RMSE) of 7.6 d if all cultivar differences were ignored, 6.4 d considering only differences in thermal time (TT), 6.1 d with differences in TT and daylength response, 6.4 d with TT and vernalization, and 6.2 d with TT, daylength, and vernalization. Consideration of cultivar differences in TT and photoperiod response improved the prediction of days to anthesis for winter‐sown spring wheat, but there was no benefit from considering effects of vernalization in CROPSIM‐CERES.
Changes in Nitrogen Use Traits Associated with Genetic Improvement for Grain Yield of Maize Hybrids Released in Different Decades
Authors: Haegele Jason W. , Cook Kevin A. , Nichols Devin M. , Below Frederick E.
Published: April 2013

Further enhancement of maize (Zea mays L.) N‐use efficiency (NUE) will benefit from a thorough understanding of how genetic improvement has shaped N use parameters. Since selection for grain yield has occurred at high N fertilizer rates, our hypothesis was that modern hybrids would have a greater response to supplemental N than hybrids from earlier eras. In 2009 and 2010, 21 single‐cross maize hybrids released between 1967 and 2006 were characterized for grain yield and N use traits. While the ability to acquire mineralized soil N did not change over era, the utilization increased with decade of introduction (0.24 kg kg–1 of plant N [kgplantN–1] yr–1; R2 = 0.37). Increases of grain yield at high N (86 kg ha–1 yr–1; R2 = 0.68) over era were accompanied by increases at low N of 56 kg ha–1 yr–1 (R2 = 0.69). Grain yield improvements at all levels of N were associated with decreased barrenness and increased kernel number expressed on a per‐plant and per‐area basis. Fertilizer N response, NUE, increased at a rate of 0.16 kg kg–1 of fertilizer N (kgN–1) yr–1 (R2 = 0.40). Increased NUE was positively correlated with improved N‐uptake efficiency (r = 0.76, P ≤ 0.001), due to the greater postflowering N uptake of more recent hybrids. The response of grain yield to fertilizer N in current hybrids is more dependent on uptake of fertilizer N than the efficiency of fertilizer N utilization, and approximately two‐thirds of genetic gain for grain yield at high N can be explained by improvements in grain yield at low N.