bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictive factors for preterm delivery under rural conditions in post-tsunami Banda Aceh
Authors: Schwab Fabienne D. , Zettler Eva K. , Moh Andala , Schötzau Andreas , Gross Uwe , Günthert Andreas R.
Published: May 2015

To assess the risk for preterm deliveries <37 week of gestation and associated prevalence of vaginal infection in a rural setting after the tsunami in Banda Aceh, Indonesia.

Wet mount microscopy, vaginal pH and vaginal swabs for microbiological culture were collected in pregnant women during the 2

One hundred and fifty-nine pregnant patients were screened. Sixty-two could be followed up until delivery. Thirty-nine (62.9%) delivered at term and 23 (37.1%) delivered prematurely. Significant risk factors for preterm delivery were a history of preterm delivery and group B streptococcus infection. Increased vaginal pH alone had no significant influence on preterm delivery, although there was a trend.

The rate of preterm delivery was high in this cohort. We suggest risk stratification for preterm delivery in rural conditions by performing a vaginal pH and wet mount microscopy. If either is suspect we suggest collecting a vaginal swab for microbiological culture for targeted treatment. Patients with a history of preterm delivery are at increased risk and should be monitored closely.
Referential Indeterminacy with an Ontic Source? – A Criticism of Williams’s Defense of Vague Objects
Authors: Akiba Ken
Published: May 2015

J. Robert G. Williams argues that referential indeterminacy may arise as a result of ontic indeterminacy, and that lambda-abstraction is not applicable to indeterminate identity statements, i.e., statements of the form, ‘it is indeterminate whether

a

$$a$$

is identical with

b

$$b$$

,’ if they involve such ontically induced referential indeterminacy; so Evans’s

r
e
d
u
c
t
i
o

$$reductio$$

argument against vague objects does not work. This paper finds fault with Williams’s defense of vague objects and shows that there is much reason to doubt that the idea of ontically induced referential indeterminacy plays any significant role in a proper defense of vague objects against Evans’s argument.
Die Entwicklung von Public Health in Westdeutschland seit dem 2. Weltkrieg
Authors: Michel Brigitte
Published: May 2015

Einleitung

Die Disziplin Public Health und ihre Vorläuferin, die Sozialhygiene, haben in Deutschland eine sehr lange und wechselvolle Geschichte, die bis ins 19. Jh. zurückgeht. Nach der Zäsur durch den Nationalsozialismus war es in den Nachkriegsjahren in Westdeutschland jedoch nicht gelungen, an diese alten sozialen Traditionen anzuknüpfen und es brauchte eine mehrere Jahrzehnte dauernde Entwicklung, bis Public Health sich als wissenschaftliche Disziplin nach internationalen Standards etablieren konnte.
Adipositas als Ausdruck sozialer Ungleichheit
Authors: von Lengerke Thomas
Published: May 2015

Einleitung

Niedriger Sozialstatus gilt als eine Ursache der Adipositas, und auch manche Adipositasfolgen, wie Einschränkungen in der gesundheitsbezogenen körperlichen Lebensqualität, sind sozial ungleich verteilt. Der Beitrag stellt diese Ungleichheiten dar und diskutiert ihre Implikationen für Public Health. Adipositasbezogene Forschung und Interventionen sollten noch stärker berücksichtigen, dass Verhalten eine Funktion des Erlebens und der Umwelt von Menschen ist – und deren Wechselwirkungen modellieren.
Herausforderungen und Empfehlungen an Deutschland aus der Sicht der WHO
Authors: Jakubowski Elke , Kluge Hans
Published: May 2015

Trotz der Zunahme der Krankheitslast von chronischen Erkrankungen, die vermeidbar sind beziehungsweise sich zeitlich herauszögern lassen, schöpft Deutschland das Potenzial für die Gesundheitsförderung und die Prävention von Erkrankungen nur unzureichend aus. Das deutsche Gesundheitswesen konzentriert sich aufgrund der bestehenden Anreize auf die Versorgung durch Ärzte, Spezialisten und auf die Behandlung von Erkrankungen. Weniger als fünf Prozent der Gesamtausgaben für Gesundheit fließen in die Gesundheitsförderung und die Prävention von Erkrankungen. Kurzfristig sollten mehr kosteneffektive Leistungen der Gesundheitsförderung und Prävention solidarisch finanziert, und der bezirklich organisierte öffentliche Gesundheitsdienst in Deutschland gestärkt werden. Da die Bevölkerung weiter altern wird, und die Prävalenz von chronischen Erkrankungen und körperlichen und mentalen Einschränkungen weiter ansteigen werden, braucht Deutschland langfristig eine stärker interdisziplinär angelegte Versorgungsstruktur, in der nicht-ärztliche Berufsgruppen wie Pflegekräfte, Psychologen und Sozialarbeiter vermehrt in die gemeindenahe Prävention und das Management von Erkrankungen eingebunden werden.
Consciousness, awareness of insight and neural mechanisms of schizophrenia
Authors: Touskova Tereza , Bob Petr
Published: May 2015

According to recent research, disturbances of self-awareness and conscious experience have a critical role in the pathophysiology of schizophrenia, and in this context, schizophrenia is currently understood as a disorder characterized by distortions of acts of awareness, self-consciousness, and self-monitoring. Together, these studies suggest that the processes of disrupted awareness and conscious disintegration in schizophrenia might be related and represented by similar disruptions on the brain level, which, in principle, could be explained by various levels of disturbed connectivity and information disintegration that may negatively affect usual patterns of synchronous activity constituting adaptive integrative functions of consciousness. On the other hand, mental integration based on self-awareness and insight may significantly increase information integration and directly influence neural mechanisms underlying basic pathophysiological processes in schizophrenia.
Micro-XCT-based finite element method for predicting the elastic modulus of needle carbon-fiber-reinforced ceramic matrix composites
Authors: Gao Xiguang , Luo Piaoyang , Fang Guangwu , Zhang Sheng , Song Yingdong
Published: May 2015

In this study, a finite element method was developed based on X-ray computer tomography to predict the elastic modulus of needle carbon-fiber-reinforced ceramic matrix composites with voids randomly existing in the material. In these pictures, every pixel point contains all of the information of the components that we need, including voids. Using this information, the mechanical properties of components can be obtained, then a finite element model with voids was built and the predicted results fit well with the experiments. In addition, a volume average method was developed to determine the proper representative volume element size to reduce the computing time without losing the accuracy.
The grinding surface characteristics and evaluation of particle-reinforced aluminum silicon carbide
Authors: Liang Guiqiang , Zhou Xiaoqin , Zhao Feifei
Published: May 2015

The changes in grinding parameters have direct influences on the characteristics of surface morphology of workpieces during grinding. On the basis of the application of particle-reinforced aluminum silicon carbide (SiCp/Al), this paper analyzes the surface morphology of SiCp/Al after being ground by an electroplated diamond-grinding wheel by integrating studies on grinding processes. The typical morphology of grinding surfaces of SiCp/Al is elaborated, and the general principles of evaluating the grinding surfaces of particle-reinforced SiCp/Al are summarized by considering the surface morphology and formation mechanism. Comparison is made on the surface morphology between ultrasonic vibration-assisted grinding and traditional grinding. It indicates that the surface morphology can be evaluated in terms of the root mean square deviation of three-dimensional profiles, crushing ratio, and fractal dimension. Studies show that the surface morphology of workpieces after ultrasonic-assisted vibration grinding is better than that of the traditional machining.
A comparative analysis of evolutionary algorithms in the design of laminated composite structures
Authors: Tabakov Pavel Y. , Moyo Sibusiso
Published: May 2015

The increased use of composite materials and structures in many engineering applications led to the need for a more accurate analysis and design optimization. While methods of stress-strain analysis developed faster, optimization techniques have been lagging behind. As a result, many designed structures do not fulfill their full potential. The present study demonstrates the major achievements in recent years in an application of evolutionary algorithms to the design optimization of fiber-reinforced laminated composite structures. Such structures are of much interest due to high structural design sensitivity to fiber orientations as well as complex multidimensional discrete optimization problems. Using an anisotropic multilayered cylindrical pressure vessel and an exact elasticity solution as an example, we show how the optimum, or near–optimum, solution can be found in a more efficient way.
Reliability Detection of Process-Induced Metallization Defects in GaAs Devices
Authors: Kilgore Steve H.
Published: May 2015

Process-induced defects in electroplated Au interconnect metallization on GaAs devices were detected during the course of reliability testing. Abnormally high lognormal sigma values (σ > 0.7) indicated the existence of a bi-modal failure mechanism. A distinct early lifetime failure mode was observed along with the intrinsic electromigration metallization wear-out failure mode. Physical characterization of the electroplated Au film revealed as-deposited nanoscale voids. Elimination of these voids through process improvement as well as suggested mechanisms for the early failures are discussed.
Molecular Disorder in Prestrained Nanocomposites: Effects of Processing on Durability of Thermally-Active Ethylene-Vinyl Acetate | PyChol | Multiwall Carbon Nanotubes
Authors: Winter Allen D. , Jaye Cherno , Fischer Daniel , Omastová Maria , Campo Eva M.
Published: May 2015

In situ temperature-resolved Near-edge X-ray Absorption Fine Structure (NEXAFS) measurements were performed on thermo-active ethylene-vinyl acetate (EVA) – multiwall carbon nanotube (MWCNT) composites 12 months following synthesis, and compared with spectra acquired shortly after synthesis to examine aging effects on non-covalent interactions. Room temperature spectra revealed no difference between unstrained and strained composites, suggesting relaxation. Further, energy shifts in π* C=C resonances indicated a change in π–π interactions between MWCNT walls and chemical dispersant, supported also by AFM phase imaging. Temperature-resolved NEXAFS analysis showed a lack of interaction between nanotubes and polymeric chains, suggesting the chemical dispersant unlatched from MWCNT walls. The extent of this effect is finally quantified through a comparative study of spectral trends.
Self-catalyzed InP Nanowires on Patterned Si Substrates
Authors: Kawaguchi Kenichi , Sudo Hisao , Matsuda Manabu , Takemoto Kazuya , Yamamoto Tsuyoshi , Arakawa Yasuhiko
Published: May 2015

Self-catalyzed growth of position-defined InP nanowires (NWs) was investigated on SiO2-mask-pattered Si substrates using metalorganic vapor-phase epitaxy. Using low growth temperatures and high group-III flow rates, pyramidal InP NWs were formed vertically on the mask openings. The diameter and tapering of the InP NWs were successfully controlled by the introduction of HCl and H2S gases during the NW growth. In addition, crystal growth of radial InP/InAsP/InP quantum wells on the sidewall of the InP NWs was performed on Si substrates.
Cationic Cellulose Nanocrystals: Synthesis, Characterization and Cytotoxicity Studies
Authors: Sunasee Rajesh , Hemraz Usha D. , Ckless Karina , Burdick James S. , Boluk Yaman
Published: May 2015

Cellulose nanocrystals (CNCs) have emerged as a new class of renewable material for various applications due to their remarkable properties and commercialization prospect. The relative low density, expected low cost, non-toxic character, uniform nanosize distribution, high aspect ratios, high surface area, thermal properties and high modulus of elasticity make CNCs attractive nanomaterials that recently prompted the industrial production of CNCs in North America. Surface functionalization of CNCs continues to be an exciting area of research for the design of novel CNC-based materials. In this work, we report the synthesis, characterization and cytotoxicity studies of novel cationic surface modified CNC derivatives. The negative surface of CNC was rendered positive after grafting with cationic polymers via surface-initiated living radical polymerization method. The modified CNCs were characterized by both spectroscopic and microscopic techniques. Their cytotoxicity effects were evaluated using MTT assay in two cell lines such as mouse macrophages (J774.A1) and human breast cancer (MCF7). Preliminary studies indicated that only one of the modified CNCs caused significant decrease in J774.A1 cell viability (50%), at the highest concentration tested (100 µg/mL). However this concentration is well above of what would be applicable for biomedical purposes. MCF7 cells were not affected by any of the cationic CNCs at any concentration. A detailed cytotoxicity study is currently underway to fully understand the interaction of these cationic CNCs with the biological systems for possible bio-inspired applications.
Study of Growth and Characterization of Fe-Catalyzed β-Ga2O3 Nanowires
Authors: Kumar Sudheer , Tessarek C. , Hähnel A. , Christiansen S. , Singh R.
Published: May 2015

In the present study, Fe as a catalyst was used to grow single crystalline monoclinic gallium oxide (β-Ga2O3) nanowires using chemical-vapor-deposition method. The morphology, structure and luminescence properties of the as-grown β-Ga2O3 nanowires were investigated using various characterization techniques. The diameter of the as-grown nanowires was in the range of 50 to 100 nm, and the lengths up to tens of micrometers. The structural investigation of the nanowires was carried out using X-ray diffraction that showed monoclinic phase of Ga2O3. Further, the transmission electron microscope (TEM) investigations along with selected area diffraction pattern revealing single crystalline nature of the nanowires. The as-grown β-Ga2O3 nanowires had preferred orientation along [1-1-1] direction. The high resolution TEM image showed regular arrangement of atoms and the lattice spacing between (1-1-1) planes was around 0.266 nm. The luminescence properties of the as-grown nanowires were measured using cathodoluminescence (CL) spectroscopy. The CL measurements of β-Ga2O3 nanowires revealed a strong broad UV-blue emission band and a weak red emission band.
Angle-Dependent Polarized Raman Spectroscopy of TIPS Pentacene Single-Crystalline Domains Deposited on Au-Striped Substrates
Authors: Onojima Norio , Nakamura Ayato , Saito Hiroki , Daicho Norihiro
Published: May 2015

6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was deposited on SiO2/Si substrates with Au stripes using electrostatic spray deposition (ESD). We observed that crystalline domains on the substrates were preferentially oriented. To elucidate this phenomenon, the correlation between the orientation direction and stripe direction was investigated by angle-dependent polarized Raman spectroscopy. Since the acene planes in TIPS pentacene take an edge-on orientation on the substrates, C-C ring stretch modes can be used to probe the in-plane orientation. We found that the long molecular axis of acene planes is inclined at about 50° or 110° from the stripe direction. This result suggests that the molecular orientation of the crystalline domains can be controlled by the stripes.
Synthesis of alloyed Bi2TexSe(3-x) nanoparticles and thermoelectric characterization of bulk nanostructured materials obtained by their assembly
Authors: Bude Romain , Divay Laurent , Bisaro Renato , Servet Bernard , Leveugle Elodie , Wyczisk Frédéric , Carisetti Dominique , Ziaei Afshin , Galindo Christophe
Published: May 2015

The optimization of the figure of merit of thermoelectric materials requires the simultaneous control of the material composition and microstructure. Assembly of nanoparticles obtained by a solution route is an attractive bulk fabrication method because size and shape of the nanoparticles can be tuned by variation of the synthesis conditions. Recently, new synthetic pathways were reported among which reducing agent assisted, surfactant free processes. We report here the evaluation of this method for the synthesis of Bi2TexSe3-x alloyed nanoparticles with varying selenium concentrations. X-ray diffraction studies conducted on powder and pellet samples show that two alloyed phases are present in the sample even at low selenium content. The careful study of the position of the diffraction peaks as function of the formulation shows that this behaviour could arise from the difference in reactivity of selenium and tellurium. Moreover, the electrical conductivity of the samples is shown to increase upon selenium addition while the Seebeck coefficient is reduced. Power factor shows an optimum value around 20% selenium content with a large tolerance in composition.
Insulated Polyacetylene Chains in an Inclusion Complex by Photopolymerization
Authors: Dincă Steluţa A. , Allis Damian G. , Lashua Amanda F. , Sponsler Michael B. , Hudson Bruce S.
Published: May 2015

The properties of a material often depend on the degree of order of their atomic, molecular, or crystalline domain components. This is expected to be especially true for the case of polyacetylene, whose properties are highly anisotropic. For many applications, it may be necessary to have macroscopic order but not necessarily crystalline order. Having polyacetyelene chains fully extended and aligned parallel to each other may be sufficient for these applications even without order of the chains around their long axis. We report here progress in the use of an inclusion crystal containing a photo-reactive precursor to prepare high molecular weight polyacetylene. Raman spectroscopy was performed to probe the resulting conjugated polyene chains. Ultraviolet irradiation of a 1,4-diiodo-1,3-butadiene/urea inclusion complex results in the appearance of new resonance-enhanced Raman modes at 1125 and 1509 cm-1. The Raman spectra of the resulting confined polyene chains are very similar to freestanding isolated trans-polyacetylene prepared by solution methods.
Biohybrid Fibro-Porous Vascular Scaffolds: Effect of Crosslinking on Properties
Authors: Thomas Vinoy , Nozik Danna , Patel Harsh , Singh Raj K. , Vohra Yogesh K.
Published: May 2015

Tubular grafts were fabricated from blends of polycaprolactone (PCL) and poly(glycolide-co-caprolactone) (PGC) polymers and coated with an extracellular matrix containing collagens, laminin, and proteoglycans, but not growth factors (HuBiogel™). Multifunctional scaffolds from polymer blends and membrane proteins provide the necessary biomechanics and biological functions for tissue regeneration. Two crosslinking agents, a natural crosslinker namely genipin (Gp) and a carbodiimide reagent namely 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), were used for further stabilizing the protein matrix and the effect of crosslinking was evaluated for structural, morphological, mechanical properties using SEM, DSC and DMA. SEM images and fiber diameter distribution showed fiber-size between 0.2 μm to 1 μm with the majority of fiber diameters being under 500 nm, indicating upper range of protein fiber-sizes (for example, collagen fibers in extracellular matrix are in 50 to 500 nm diameter range). HB coating did not affect the mechanical properties, but increased its hydrophilicity of the graft. Overall data showed that PCL/PGC blends with 3:1 mass ratio exhibited mechanical properties comparable to those of human native arteries (tensile strength of 1-2 MPa and Young’s modulus of <10 MPa). Additionally, the effect of crosslinking on coating stability was investigated to assure the retention of proteins on scaffold for effective cell-matrix interactions.
Self-care and Well-being in Mental Health Professionals: The Mediating Effects of Self-awareness and Mindfulness
Authors: Richards Kelly C. , Campenni C. Estelle , Muse-Burke Janet L.
Published: May 2015

Because mental health professionals are susceptible to impairment and burnout that may negatively affect clinical work, it is ethically imperative that they engage in self-care. Previous research has found direct effects of self-care on self-awareness and well-being (e.g., Coster & Schwebel, 1997). Likewise, mindfulness has been found to positively affect well-being (Brown & Ryan, 2003). However, no studies currently available demonstrate a link between self-awareness and well-being. Mindfulness may be the link needed to support this association. A survey of mental health professionals (N = 148) revealed that mindfulness is a significant mediator between self-care and well-being. Consequently, mental health professionals are encouraged to explore their involvement in and beliefs about self-care practices.
Adapting the Safety Planning Intervention for Use in a Veterans Psychiatric Inpatient Group Setting
Authors: Rings Jeffrey , Alexander Patricia , Silvers Valerie , Gutierrez Peter
Published: May 2015

The Department of Veterans Affairs (VA) recently has adopted the Safety Planning Intervention (SPI; Stanley & Brown, 2011), a brief collaborative intervention, for use with veterans who are at high risk of suicide. The SPI is a hierarchical list of strategies for veterans to use in coping with a suicidal crisis. Its developers recommended that it be used with individual psychiatric inpatients working toward discharge, but its utility in a group format has not previously been addressed. This article describes the facilitation of a safety planning group with psychiatric inpatients at a large urban VA medical center. It depicts each step in the safety plan and offers case examples, anecdotal support, and specific considerations for its use in groups. Directions for further research are also discussed.
Treatment Guidelines for Clients with Antisocial Personality Disorder
Authors: Hatchett Gregory
Published: May 2015

The purpose of this article is to present treatment guidelines for mental health counselors who work with clients diagnosed with Antisocial Personality Disorder (ASPD) or characterized as psychopathic. The guidelines use the criteria of both treatment efficacy and clinical utility as recommended by an APA taskforce on treatment guidelines (American Psychological Association, 2002). A review of the literature revealed that psychosocial interventions lack both treatment efficacy and clinical utility in remediating the core characteristics of antisociality or reducing criminal recidivism. However, a strong case can be made for a guideline in which substance abuse treatment is recommended for ASPD clients with comorbid substance use disorders. Not only have such interventions been shown to possess adequate treatment efficacy, but there is additional evidence that such interventions are cost-effective and feasible for real-world, clinical settings (= clinical utility).
Stimulating High-Temperature Dolomitic Limestone Reservoirs with Chelant Fluids
Authors: de Antuñano Yuri , Losada M. , Milne A.
Published: May 2015

Oil production in southern Mexico is mainly from deep (>16,000 ft) high-temperature (> 300°F), naturally fissured dolomitic limestone reservoirs with clays present. With increasing depth, the dolomitization increases and the porosity and permeability decrease. These reservoirs must be stimulated to produce, and treatments are traditionally repeated to maintain production.

Although there is a substantial body of published research on stimulating carbonate formations, there is little on treating dolomites specifically. In general, the smaller the volume of reactive fluid required to penetrate into the formation to create a wormhole—a function of reactive fluid used, injection rate, and temperature—the more efficient the treatment. Hydrochloric acid (HCl) has both a high dissolution rate and dissolution capacity which, at high temperature, results in dissolution of the face of the formation, as opposed to wormholing, and uncontrollable corrosion rates. Organic acids have lower corrosion rates and limited dissolution capacity, but have a relatively high rate of dissolution, which also results in face dissolution at high temperature. Although, clays present in the formation may slow the rate of dissolution.

Chelant-based fluids are less corrosive, have lower dissolution rates, and are capable of creating effective wormholes at temperatures up to 400”F in carbonates. Although dolomite retards the dissolution rate of both acids and chelants, the difference is less with chelants. The wormholing efficiency of chelants in dolomites is also less rate dependent than is that of inorganic acids.

Acidic hydroxyethylethylenediaminetriacetic acid (HEDTA) fluids were developed to stimulate high-temperature carbonates and dolomites. These fluids have been highly effective in stimulating both carbonate, and even sandstone, formations worldwide. However, the optimum pH and injection rate for wormholing is markedly different for carbonates and dolomites. In addition, a low pH may result in emulsions and corrosion downhole or at surface when flowing back the treatment. Recent studies show that the efficiency of diammonium EDTA (DEA) with the correct pH is similar whether stimulating a high-temperature limestone or a dolomite formation, at similar injection rates.

A direct comparison has been made by performing treatments in the same reservoirs using the two chelant systems. In every case, the initial post-treatment production with the DEA-based fluid has been significantly higher and the production decline slower. This is attributed to stimulating both the dolomite and limestone intervals and removing the potentially damaging clay and fines. The fluid also eliminates the possible issues with using a low-pH fluid.
Operator Uses Advanced Perforation Flow Laboratory to Support HMX Perforating by Coiled Tubing in HPHT Field
Authors: Haggerty D. , Christie S.
Published: May 2015

By using the advanced perforation flow laboratory (APFL), the depth of penetration performance of shaped charges can be measured at downhole conditions to confirm whether or not the formation penetration will exceed the depth of formation damage attributable to drilling. In tubing-conveyed perforating, HNS explosive shaped charges have historically been used in elevated temperature environments. The option of using deeper penetrating, but less heat-resistant, HMX explosive shaped charges is possible in the Hejre field wells in the North Sea because the depth to the reservoir interval to be perforated is within the reach of coiled tubing. This process requires less time for the perforating guns to tolerate elevated temperatures, and coiled tubing provides a means of circulating cooling fluid, further increasing the charge lifespan. Based on conservative run times for deploying guns on coiled tubing (estimated to be 4 to 6 hours from surface), there will be sufficient time to position the guns at depth before detonation, and sufficient time to retrieve the gun string from the wellbore in the event of a misfire.

All perforation flow lab tests in the APFL were run at Hejre pressures, with overburden stress at 17,500 psi and pore pressure at 14,600 psi; several tests were run at the reservoir temperature of 160°C (320°F). Aligned with American Petroleum Institute Recommended Practice 19B Section 4 (2006), the APFL tests were conducted to closely match the expected conditions in the Hejre field, requiring minimal scaling of the results.

Tests in the APFL comparing the different explosive powder charges showed a nearly 50% increase in formation-analog target penetration using the HMX charge vs. the HNS charge. This depth of penetration increase improves the prospect of penetrating the estimated drilling damage zone to vastly improve production and the effectiveness of further stimulation. This paper discusses the methodology, obstacles encountered and means of addressing them, and the test program results.

Before the construction and development of testing equipment to shoot a shaped charge at elevated temperatures and high pressures, extrapolations had to be used to predict perforator performance with a higher level of uncertainty.
Exploitation of Danish Sector North Sea Chalk Field: A Case Study of the Hess South Arne Field – Acid Stimulation Design, Optimization and Execution
Authors: Miller Rory , Jakobsen Erik , Kalfayan Leonard , Troelsen Benny
Published: May 2015

The South Arne Field, located in the Danish sector of the North Sea, has been producing oil and gas since 1999 with an active waterflood since 2000. Producers and injectors are primarily horizontal with sliding sleeve completions targeting both the Ekofisk and Tor chalk formations. South Arne is currently in exploitation modewith a new (Phase III) development program. Phase III includes two new platform installations, a two-kilometer umbilical bundle and an eleven-well drilling program targeting the northern extension of the field. This paper discusses the first five Phase III wells, focusing on stimulation design, lessons learned from the fluid testing, experiences, and the continuous improvement of the operational execution process.

New producer and injector stimulation designs are generally based on a pad-acid procedure in which a cross-linked gel pad is followed by an in-situ cross-linked hydrochloric (HCl) acid treatment, to create viscosity contrast for diversion and differential acid fracture etching for sustained conductivity. The acid fracture treatment is then followed by a closed fracture acidizing (CFA) step to enhance near-wellbore fracture conductivity. For wells completed in zones that have the potential of short-circuiting to neighboring wells, lower rate and smaller volume HCl matrix treatments are pumped. The Phase III stimulations to date have been conducted through ball drop sliding sleeves, with the number of zones ranging from 10 to 14.

Establishing Phase III success has required extensive QA/QC testing to optimize the stimulation fluid systems and, in particular, the acid corrosion inhibition program. Use of real-time bottom-hole temperature measurements during stimulation treatments has enabled optimization of corrosion inhibitor loadings, resulting in both an environmental benefit and financial savings. The stimulation treatments are performed simultaneously with drilling operations, therefore extensive work was required to ensure that stimulation and drilling activities are safely executed without interference. Both platforms were initially designed to optimize productive time during stimulation operations, however as the project evolved, thorough risk evaluations pointed to the need to modify operating plans. Rigorous marine and vessel audits were performed to ensure that stimulation vessels could operate safely and effectively from both a marine and stimulation job execution standpoint. The design, testing and advance preparation for the South Arne Phase III program has resulted in safe and effective treatment execution.
The Effect of Stress Sensitive Permeability Reduction on the Evaluation of Post-Fracture Welltests in Tight Gas and Unconventional Reservoirs
Authors: Shaoul J. R. , Ayush A. , Park J. , Pater C. J.
Published: May 2015

The interpretation of well performance in propped fractured tight gas reservoirs is a topic that has been studied for decades, but still presents a number of difficulties. These issues are becoming more important as unconventional reservoirs with even lower permeabilities are developed (micro and nano- Darcy).

One of the most troublesome issues in tight-gas fracturing is that post-frac welltests often show very short effective fracture lengths. This is often blamed on gel damage due to poor proppant pack cleanup in the fracture or loss of propped width due to embedment and filtercake in the fracture. It has also been attributed to formation damage, due to “phase trapping” of fracture fluid filtrate along the fracture face. Much work has already been done on these topics, which show that extreme damage to the proppant pack or the fracture face would be needed to explain the short effective fracture lengths that are often seen. Regained permeability testing, when available, in many cases does not indicate that this much damage is expected, either in the proppant pack or on the fracture face, under normal circumstances.

In this paper, a large number of high resolution 3D numerical simulations have been performed, based on realistic reservoir parameters for a typical tight-gas reservoir, using stress sensitive permeability data derived from core testing. By modeling both the propped fracture and the reservoir with fine grid refinement, it is possible to simulate drawdown and buildup pressures with and without the effect of stress sensitive permeability in the reservoir matrix. The simulations also include the effect of the effective stress on the proppant pack, which is generally not significant in tight gas, unless the proppant concentration is extremely low. These synthetic drawdown and buildup data sets with known parameters are then analyzed using a standard welltest analysis package, and the results are compared.

The results of this work show that for tight and ultra-tight reservoirs, conventional welltest analysis methods will always show a smaller fracture length and a larger permeability, compared to the “correct” values used to generate the test data sets. This behavior is partly due to the rectangular fracture geometry assumed in the welltest solutions. An additional reduction in length can be explained by stress sensitive permeability, without any need for damage to the proppant pack or the fracture face. The results from the incorrect welltest analysis are used for a long-term forecast simulation (with a short fracture length, higher permeability and ignoring stress sensitive permeability), which is compared to a forecast based on the model with the correct fracture length and stress sensitive permeability. This shows a significant overestimation of the ultimate recovery when using the welltest derived parameters.
Applying Method of Characteristics to Study Utilization of Nanoparticles to Reduce Fines Migration in Deepwater Reservoirs
Authors: Yuan Bin , Ghanbarnezhad Moghanloo Rouzbeh , Pattamasingh Purachet
Published: May 2015

This paper examines an application of method of characteristics (MOC) to evaluate utilization of nanoparticles to mitigate fines migration. Deepwater reservoirs are poorly consolidated, strongly heterogeneous and less consolidated with high pressure, temperature, porosity and permeability. All these features increase the possibility of troublesome sand production. It has been shown that nanoparticles can effectively reduce double layer repulsive forces between sand particles through changing the associated zeta potentials; the reduction of repulsive forces between loose particles would maintain integrity of the rock texture. However, our understanding on the effectiveness of nanoparticles to mitigate sand production has been limited to some experimental studies serving as proof of concept. In practice, this paper also provides an efficient and simple model to optimize fines migration treatment via injection of nanoparticles.

In this paper, we develop an analytical model to study the interplay between adsorption of nanoparticles and their geochemical effects on fines migration and the consequent sand production. There are two governing mechanisms: 1) adsorption of nanoparticles on the surfaces of fines particles; 2) the positive contribution of adsorbed nanoparticles on integrity of the rock texture. We define a fictitious attachment reaction for which we interpret the existing lab results as the rate of reaction.

We consider nanoparticle adsorption front as borders of distinct regions. At upstream of adsorption front, adsorbed nanoparticles improve coalescence of particles; whereas at the downstream, dynamic detachments of fine particles occur. Similarly, adsorption of nanoparticles on the grain surface occurs only at the upstream of adsorption front. The main contribution of this work is to evaluate the propagation of adsorption front, and fine particles and nanoparticle concentration profile along the sand pack. We use method of characteristics and present a graphical solution to determine optimal concentration of nanoparticles required to reduce maximum sand production. We define mitigation index (MI) to describe the contribution of nanoparticles to mitigate fines migration.

The analytic solution is verified by numerical simulation. This model provides a novel and efficient approach to describe the impact of nanoparticles to mitigate fines migration. In practice, this method can be used to design an effective treatment for sand control in deepwater reservoirs as well as other type of reservoirs that suffer from fines migration problems.
Perforating on Wireline: Maximizing Productivity and Minimizing Gunshock
Authors: Baumann Carlos , Gultom Denny , Salsman Alan , Smart Moises , Primasari Indah , Rahman Risal , Warsito Sandy
Published: May 2015

We present perforating on wireline with dynamic underbalance (DUB) to simultaneously maximize productivity and minimize gunshock. We focus on perforating on wireline with DUB because, when compared with other approaches, perforating with DUB is probably the best method to deliver lower tunnel plugging and lower formation rock damage, with lower risk of tool damage due to gunshock or guns blown uphole. Specifically, we present two important aspects of perforating on wireline using DUB: prediction of wellbore dynamics to assess perforation tunnel and formation cleanup and gunshock prediction to assess the risk of tool damage. We present the latest models used to evaluate perforating jobs for well productivity and for operational risks.

It is well known that the DUB produced when perforating with the right gun system can remove formation rock damage and tunnel plugging produced by shape charges. What is not so well known is how much DUB (amplitude and duration) is necessary, and how to predict how much DUB will be generated by a gun system. To achieve formation tunnel cleanup, we need a DUB of large amplitude but short duration to remove perforating rock damage and plugging while minimizing gunshock loads. In the pre-job design, we simulate/predict the transient fluid pressure waves in the wellbore and formation rock to predict formation rock damage cleanup and also the associated gunshock loads. DUB amplitude and duration depend on job parameters that can be adjusted, such as type and size of guns, loading of standard perforating charges and DUB charges, and placement of packers, if present. Important physics included in the model are: gun filling, wellbore pressure waves, transient reservoir fluid flow, and the dynamics of all relevant solid components (cable, shock absorbers, tools, and guns).

The reliability of the DUB prediction model is demonstrated by comparing downhole fast-gauge pressure data with the corresponding simulated values. When the reservoir properties are well known, the predicted DUB amplitude and duration are very close to the field data values, typically within 15% or less. The reliability of the gunshock loads is demonstrated with residual shock absorber deformation and cable tension logs. We also demonstrate how gunshock simulations have been useful to explain equipment failures due to gunshock loads.

Reliable predictions of wellbore dynamics, transient reservoir flow, and gunshock loads enable operators to select perforating equipment capable of removing perforating formation damage and reduce the risk of unexpected release of tools and guns due to dynamic loads, thereby minimizing the probability of nonproductive time and fishing operations.
Selection of Non-damaging Phosphonate-Based Scale Inhibitors for Field Application in a Reservoir Containing Reactive Iron Minerals
Authors: Tahir M. A. , Orme Mike , Kidd Samuel , Hoeth Laurien Wichers , Wright Rob , Graham Gordon
Published: May 2015

Core flood testing of phosphonate-based scale inhibitors in reservoir sandstone containing iron minerals revealed potential formation damage caused by unmodified acid phosphonates, which are reactive toward the iron minerals. The mechanism of formation damage was shown to be due to dissolution and re-precipitation of iron phosphonate species, together with fines mobilized (also thought to be due to dissolution effects) which propagated some distance through the core, leading to pore throat blockages. In an example case, complete blockage occurred as the front of the injection chemical reached the outlet of the core due to a combination of silica fines and iron phosphonate chemical.

To mitigate the potential issue, different chemical formulations were prepared based on the same phosphonate scale inhibitor, in order to mitigate / minimise the potential for in-situ dissolution of iron bearing minerals within the reservoir formation. This allowed a less aggressive formulation to be prepared by part-neutralisation of the acid phosphonate, so achieving compatibility with the core material. Thus, no formation damage was induced and retention of scale inhibitor by adsorption ensured the potential for long squeeze treatment lifetimes. The modified product has since been applied in the field and results from the laboratory qualification, chemical re-formulation and field treatments are presented in this paper. To date, 27 wells have been squeezed; the part-neutralized chemical targeted at susceptible wells and the acid chemical used elsewhere. Excellent are results in both formation damage and return lifetimes minimising the requirement for coil tubing scale removal treatments in this field.
Characterization and Development of Deep Carbonaceous Shales: A North Kuwait Case Study
Authors: Al-Arouj M. A. , Barasia A. , Fidan E. , Darous C. , Sharma S. S. , Al-Mutairi M. D.
Published: May 2015

Objectives/Scope

Unconventional organic-rich carbonaceous shale (OCS) in North Kuwait has unique characteristics due to its high total organic content (12–14%), its complex mineralogy (blend of carbonates and clastics) and Jurassic/post-Jurassic complex burial and tectonic history. The OCS is under/over-laid by tight carbonates, where the system permeability is in the range of nano to micro-Darcy. Conventional techniques to initiate flow from this complex reservoir have proven ineffective, which led the appraisal team to develop novel and extensive workflows to characterize the formation properties for successful hydraulic fracturing and to determine the commercial flow potential of hydrocarbons.

Methods, Procedures, Process

Three vertical wells were identified as the high potential candidates in the appraisal program, prior to the completion of horizontals in this complex formation. A comprehensive logging suite was acquired which included spectroscopy, sonic and image logs. Fracture pressure analysis was performed on an offset well followed by exhaustive diagnostic tests using both non-viscous and viscous fluids. Bottom hole gauges were hanged in the well during the diagnostic tests as well as temperature logging was performed after the diagnostic pumping to define fracture height growth/containment. Proppant fracturing in these wells are planned using nonradioactive tracer proppant.

Results, Observations, Conclusions

Maximum clay content in the OCS is estimated close to 40% in addition to the high organic content. Anisotropic mechanical earth model was built using sonic log response for fracture modelling in planar 3-D simulators. Some open fractures were observed from the image logs. Fracture pressure analysis on the offset well confirmed “fraccability” of the OCS within the allowable pressure limits. Analysis of the diagnostic tests confirmed significant impact of natural fracture on hydraulic fracture propagation. Nolte-Smith plot using actual bottom-hole pressure revealed very high net pressure slope during viscous fluid stages that raised significant concerns on possibility of placing proppant. Interventions after the diagnostic tests showed flowback of formation material in the form of “formation creep” into the wellbore and that lead to concerns on formation integrity and risks in proppant placement.

Novel/Additive Information

This paper discusses various methods used to understand the complex OCS formation and integrates extensive analysis achieved through different methods. Interpretation of this data-set and building a model which will be used for development of future horizontal wells will also be presented. It is believed that the inherent challenges presented by the OCS are unique without any true global analogues in the unconventional gas and oil programs.
How to Determine True Acid Diffusion Coefficient to Optimize Formation Damage Treatment?
Authors: Qiu Xiangdong , Khalid Muhammad Ali , Sultan Abullah
Published: May 2015

Diffusion Coefficient (De) is a very important parameter for the formation damage treatment job design. Commonly a Rotating Disk Apparatus (RDA) is used to obtain acid De and reaction rate. There are two major limitations of conventional lab practices (1) The De is obtained at 1000 psi (or below) system pressure, which is too low to represent realistic reservoir conditions. (2)The De obtained from lab experiments are based on a fresh acid, which has been ignoring the impact of reaction products, especially CO2. Hence the results of De cannot represent the real reaction kinetics between carbonate rock and injected HCl during the acid treatment.

In this paper, we investigate the effects of De of HCl acid as it reacts with both calcite and dolomite. A modified RDA is used to obtain the true spent acid reaction kinetics at reservoir conditions. In order to provide accurate reaction kinetics data that is more representative of the true reservoir conditions, a true spent acid concept is adopted here in this study. The true spent acid is formulated at reservoir condition in various spending stages. In addition, different mineralogy including calcite and dolomite are fully studied. The reaction products of CO2 and counter ions are taken into consideration at different acid spending stages.

The experimental results show that the De of the HCl acid is much lower at high pressure than low pressure at the same concentration due to the impact of CO2 produced by the HCl-carbonate reaction. For example, at 150 °F, the diffusion coefficient of 15% HCl at 3,000 psi reduced 50% of its original value when at 1,000 psi of 15% HCl. The diffusion coefficient of the fresh acid is much higher than the diffusion coefficient of the same acid strength of true spent acid due to the presented count ion and CO2 in the true spent acid. The De of HCl/calcite is two orders of magnitude higher than De of HCl/dolomite at the same conditions (acid concentration, temperature).

Conventional experimental results significantly overestimate the De, dissolution rate and reaction rate. When the De implemented in a job (formation damage treatment) design, those defective data could result in dramatic errors in determining the treatment fluid schedule, rate, and volume. In order to properly design the formation damage treatment jobs, the De of acid acquired from high-pressure and various spent conditions should be used.