bluuebunny/crossref_metadata_2025 huggingface dataset:
Optional screening strategies for cervical cancer using standalone tests and their combinations among low- and medium-income populations in Latin America and Eastern Europe
Authors: Sarian Luis Otavio , Derchain Sophie , Shabalova Irena , Tatti Silvio , Naud Paulo , Longatto-Filho Adhemar , Syrjänen Stina , Syrjänen Kari
Published: January 2011

Background

The performance of cervical cancer (CC) screening can be improved by combining Pap smear with human papillomavirus (HPV) testing or visual methods, addressing local demographic, clinical and economic characteristics.

Objectives

To examine the performance of standalone and combined screening tools in populations with variable prevalence of cervical intraepithelial neoplasia (CIN) and CC.

Methods

Merged data-sets from the Latin American Screening Study and New Independent States cohorts provided results for 15,000 women, screened using Pap smear, HPV testing and visual inspection with acetic acid, in Brazil, Argentina, Russia, Belarus and Latvia. Bayesian correction for verification bias was used.

Results

At CIN2+ cut-off, HPV detection alone was the most sensitive technique. There was an improvement (88.5% to 92.7%) in Hybrid Capture 2 (HC2) sensitivity among women ≥35 years old. Using HPV detection alone was the least specific screening tool, regardless of the age group (69.9% [95% CI 66.5–72.8%] and 86.4% [95% CI 84.6–88.2%], in < or ≥35 years, respectively). Of the test combinations, Pap smear (LSIL threshold) with HC2 had the highest specificity (98.7%; 95% CI 98.3–99.0%). However, in women ≥35 years, the sensitivity of Pap alone was superior to that of the combination.

Conclusions

The Pap test is a highly specific screening option in populations with medium-range CC prevalence. Combined testing for HPV in this scenario may yield slightly better positive predictive values in women ≥35 years of age with LSIL, but at a high incremental cost.
Is human papillomavirus screening preferable to current policies in vaccinated and unvaccinated women? A cost-effectiveness analysis
Authors: Accetta Gabriele , Biggeri Annibale , Carreras Giulia , Lippi Giuseppe , Carozzi Francesca Maria , Confortini Massimo , Zappa Marco , Paci Eugenio
Published: January 2011

Objectives

Italy was the first European nation to offer free vaccination against human papillomavirus (HPV) types 16 and 18. The vaccination is actively encouraged and is available free of charge to 11-year-old girls. The introduction of new technologies such as HPV DNA testing and HPV vaccination requires cost-effectiveness analysis of cervical cancer strategies in Italy for both vaccinated and unvaccinated women.

Methods

A calibrated Markov model was developed to describe the natural history of HPV infection and cervical carcinogenesis. We performed a microsimulation generating the life histories of 10 million women. Changes in these life histories occur as consequences of prevention strategies. We estimated costs of screening activities using an activity-based costing analysis. We assessed lifetime risk due to cervical cancer, lifetime costs and quality-adjusted life-expectancy (QALE) for 18 scenarios. Strategies varied by screening interval (three and five years), primary and triage test (Pap test and HPV DNA test), and HPV 16 and 18 vaccination.

Results

The current screening policy (Pap test every three years) is more costly and less effective than HPV DNA test and Pap test triage every five years. For unvaccinated women an HPV DNA test every five years with a Pap test triage was cost-effective (ICER €5753/QALE). Vaccination followed by the same screening strategy was cost-effective (ICER €23,951/QALE) for women who are eligible to be vaccinated.

Conclusions

Our findings strongly support changing the Pap screening policy to the use of HPV DNA as a primary test with Pap test triage for both vaccinated and unvaccinated women.
Implementing the national invasive cervical cancer audit: correlation between local and regional classification
Authors: Moss E L , Askew S , Jones P W , Redman C W E , Pearmain P
Published: January 2011

Objective

To determine the accuracy of information recorded regionally and locally on the screening classification of cervical cancer cases using the national invasive cervical cancer audit categories.

Methods

Comparison of the audit categorization of all cervical cancer cases diagnosed at the University Hospital of North Staffordshire (UHNS) between January 2003 and December 2006 with the classification assigned by the West Midlands Cervical Screening Quality Assurance Reference Centre (WMQARC).

Results

Eighty-seven cases of cervical cancer were diagnosed during the three-year study period. There was agreement between the UHNS and WMQARC classification of cases in 52 cases (59.7%), moderate agreement κ = 0.51 (95% CI 0.39–0.63). The greatest disparity was seen in the classification of lapsed attenders, with nine of the 26 cases categorized as ‘lapsed’ by the UHNS being assigned to the ‘lost to follow-up’ category by WMQARC. Three cases were deemed unclassifiable by WMQARC using the national classification since the women were over the age of 70 years but had previously been enrolled in the screening programme, and currently there is no national category for these women.

Conclusions

Accurate and consistent classification of invasive cervical cancer cases is essential in order to obtain useful information on the efficiency of the national screening programme at a local, regional and national level. The use of a national algorithm would provide reassurance that all data used in the national evaluation of the NHS Cervical Screening Programme are consistent, meaning that robust conclusions could then be drawn from the data.
Women's preferences for the delivery of the National Health Service Breast Screening Programme: a cross-sectional survey
Authors: Linsell Louise , Forbes Lindsay J L , Patnick Julietta , Wardle Jane , Austoker Joan , Ramirez Amanda J
Published: January 2011

Objective

To elicit women's preferences for delivery of the National Health Service (NHS) Breast Screening Programme.

Design

Interview survey.

Setting

Private households in the UK.

Population

Five hundred and ninety-seven women aged 45–75 interviewed as part of the National Statistics Omnibus Survey, December 2008 and January 2009.

Outcomes

Preferred setting (hospital or community) and preferred type of screening unit (mobile or permanent). Rated importance of distance, time, convenience and cost of travelling to a screening unit.

Results

Forty per cent of women did not mind whether the screening unit was based in a community or hospital setting, and 52% did not mind whether the unit was permanent or mobile. Among those who expressed a preference, 59% preferred a hospital to a community setting, and 62% preferred a permanent to a mobile unit. Many women (63%) said distance to a breast screening unit was an important factor, as was time to travel (58%). Among those with access to a car, 80% regarded the availability of parking as important, but only 40% regarded the cost of car travel as important. Among women with no access to a car, there was a similar pattern for ease of public transport (76%) and cost of public transport (48%).

Conclusions

Many women were unconcerned about the type and setting of breast screening units. Among those who were concerned, most preferred hospital over community settings and permanent over mobile units, but nonetheless most women said time and distance were important. Well-situated units with advanced publicity about public transport links and parking facilities may encourage greater uptake.
Experience with a wipe guaiac-based faecal occult blood test as an alternative test in a bowel screening programme
Authors: Fraser C G , McDonald P J , Colford L , Irvine A , Kenicer M , Morton C , Birrell J , Steele R J C
Published: January 2011

The format of the traditional guaiac faecal occult blood test (gFOBT), particularly the collection technique, might cause difficulties for some. A multistage evaluation of alternative tests was performed. Firstly, four tests with different faecal collection approaches were assessed: a focus group recommended further investigation of a wipe gFOBT. Secondly, 100 faecal samples were analysed using two wipe tests and the routine gFOBT: no differences were found. Thirdly, a wipe gFOBT was introduced. Over 21 months, 400 requests were made and 311 wipe kit sets were submitted for analysis: 153 (49.2%) were negative, 21 (6.8%) positive (all 3 kits positive), 96 (30.9%) weak positive (1 or 2 positive) and 41 (13.2%) un-testable. Forty-three participants were referred for colonoscopy. Outcome data were provided on 39 participants: nine declined colonoscopy, two were judged unsuitable, two did not attend, two were already in follow-up, 13 had normal colonoscopy and two normal barium enema, two had diverticular disease, two had a metaplastic polyp, four had a low-risk adenoma and one had a high-risk adenoma. No participant had cancer. Detection of significant neoplasia was small. The use of the wipe gFOBT was ceased: it cannot be recommended as a screening test for bowel cancer.
A randomized double-blind crossover trial to investigate the efficacy of screening for adult hypothyroidism
Authors: Abu-Helalah M , Law M R , Bestwick J P , Monson J P , Wald N J
Published: January 2011

Objective

To assess the value of population screening for adult hypothyroidism.

Setting

Healthy people attending for a general health assessment.

Methods

A thyroid-stimulating hormone (TSH) measurement was performed on people attending for a general health assessment (women aged 50–79 [35–49 with a family history of thyroid disease] and men aged 65–79). Those with TSH levels above 4.0 mU/L were invited to join a randomized double-blind crossover trial of thyroxine and placebo, each given in random order for four months. On entry a second blood sample was collected for a TSH measurement after the end of the trial to determine whether this would help select individuals for thyroxine treatment. The daily thyroxine dose started at 50 µg and if necessary was increased to achieve a TSH level of 0.6–2.0 mU/L.

Results

There were 341 (8%) people with a TSH level above 4.0 mU/L, 110 met eligibility criteria (64 agreed to participate), and 56 (49 women, 7 men) completed the trial. Among the 15 individuals with a repeat TSH measurement above 4.5 mU/L, 11 reported feeling better on thyroxine than placebo and none reported feeling better on placebo ( P = 0.001; four felt no different), indicating that in this group 73% benefitted (i.e. 11/15; 95% CI 45–92%). The main symptoms relieved were tiredness and loss of memory. There was no indication of harm. In the 41 individuals with a repeat serum TSH of 4.5 mU/L or less: 10 reported feeling better on thyroxine than placebo and 16 better on placebo ( P = 0.42, 15 felt no different). Thus about 8% of men and women in the specified age groups had a TSH above 4.0 mU/L, and of these about a quarter had a repeat TSH above 4.5 mU/L, of whom about half would benefit from thyroxine treatment.

Conclusion

The results indicate that screening for hypothyroidism would be worthwhile. Approximately 1% of people screened would have a better quality of life. Pilot screening programmes for adult hypothyroidism are justified.
Playing Squash Against Ralph Keeney: Should Weaker Players Always Prefer Shorter Games?
Authors: Mumpower Jeryl L.
Published: January 2011

In games such as squash, it is generally assumed that weaker players maximize their chances of winning when they play as few points as possible against superior opponents. The failure of squash players to recognize this and to prefer shorter games against stronger opponents has been cited multiple times in the literature as evidence of the foibles of lay decision makers. This error has been categorized as an error of application, attributed to the representativeness bias, and ascribed to sudden death aversion. Decision analyses presented here demonstrate, however, that under certain conditions the maxim for weaker players to minimize the number of points played against better players does not lead to optimal decisions. This holds true for choices about how many points to play in tiebreakers and the choice between playing games to 9 or to 15 points. The analyses illustrate the danger in overgeneralizing about lay tendencies to make irrational or suboptimal choices without careful examination of the task environment. The analyses also illustrate that optimization will not necessarily involve a corner solution that minimizes or maximizes total number of points played even for such a straightforward game as squash or in analogous circumstances off the court.
Hybrid Advertising Auctions
Authors: Zhu Yi , Wilbur Kenneth C.
Published: January 2011

Facebook and Google offer hybrid advertising auctions that allow advertisers to bid on a per-impression or a per-click basis for the same advertising space. This paper studies the properties of equilibrium and considers how to increase efficiency in this new auction format. Rational expectations require the publisher to consider past bid types to prevent revenue losses to strategic advertiser behavior. The equilibrium results contradict publisher statements and suggest that, conditional on setting rational expectations, publishers should consider offering multiple bid types to advertisers. For a special case of the model, we provide a payment scheme that achieves the socially optimal allocation of advertisers to slots and maximizes publisher revenues within the class of socially optimal payment schemes. When this special case does not hold, no payment scheme will always achieve the social optimum.
Laboratory Tests of Window-Wall Interface Details to Evaluate the Risk of Condensation on Windows
Authors: Maref Wahid , Van De Bossche Nathan , Armstrong Marianne , Lacasse Michael A. , Elmahdy Hakim , Glazer Rock
Published: January 2011

The development of alternative details to manage water intrusion at the window-wall interface has produced a number of novel approaches to detailing the interface between the window and the adjacent wall assembly. Many of these approaches advocate the need to provide drainage at the rough opening of the window subsill, given that the window components themselves are susceptible to water entry over their expected life. Depending on the types of windows used and the cladding into which the windows are installed, there arise different methods to provide drainage that may also affect air leakage through the assembly. This in turn may give rise to the formation of condensation along the window, at the sill, or along the window sash and glazing panels. Hence, there is a need to determine if, under cold weather conditions, specific interface details that incorporate sill pans provide a potential for condensation on the window components in which air leakage paths may be prominent at the sill or elsewhere on the window assembly. The paper reports on a laboratory evaluation of conditions suitable for the formation of condensation at the window frame perimeter of the interface assembly as a function of both temperature deferential and air leakage rate across the test assembly. A summary of the laboratory test protocol is provided, which includes a description of the test setup and apparatus, fabrication details of the specimen, information on instrumentation and calibration, and experimental results for one type of window (flange window). In parallel, preliminary simulation results were presented and compared to those obtained from the experiment using the commercially available thermal software BISCO.
Spatial Distribution of the Compressive Stress-Strain of Recycled Polymeric Piling
Authors: Iskander Magued G. , Bozorg-Haddad Amir H.
Published: January 2011

Fiber reinforced polymer (FRP) composites represent an alternative construction material without many of the performance disadvantages of traditional construction materials. The use of FRP as a pile material can eliminate deterioration problems of conventional piling materials in water front environments and aggressive soils. Most of the available polymeric piling for light load applications is made of foamed recycled High Density Polyethylene (HDPE). A comprehensive understanding of the mechanical properties of foamed recycled polymers is essential for widespread use of polymeric piling. This paper presents the results of 178 compression tests conducted to assess the in-plane spatial distribution of the compressive strength of piling made of foamed recycled HDPE. Several methods were attempted to predict the stress-strain of the cross section from the compressive strength of small coupons extracted from within the cross section. Comparing the predicted behavior from coupon specimens to the measured behavior obtained by loading the whole cross section illustrates that the approach is promising.
The Enlightened Image of Nature in the Dutch East Indies: Consequences of Postmodernist Doctrine for Broad Structures and Intimate Life
Authors: Pyenson Lewis
Published: January 2011

Eighteenth-century natural-history illustration in the Dutch East Indies reveals verisimilitude as a goal shared between colonial artists and their counterparts in Europe. Natural-history images more generally exhibit common styles in the world settled and dominated by Europeans. Apparently dramatic differences in the local settings of the artists produced only trivial variations in representing nature pictorially, in just the way that astronomy and physics in the European colonies and spheres of influence departed hardly at all from European practice. The overwhelming strength of disciplinary norms, in science and in art, is the standard explanation for this circumstance. An alternative explanation from social history is proposed. It centers on the hypothesis of a homology between households in colonial settings and in Europe. The alternative explanation implies that both the observatory and the artist's workshop were insensitive to superstructural variation in costume and architecture, as well as variation in climate and cuisine. The hypothesis behind the alternative explanation, designated by the term complementarity, derives directly from the postmodernist dictum that ideas are extrusions of social interactions. Nevertheless, just as the strength of disciplinary norms is unresolved in postmodernist doctrine, so complementarity directly challenges the postmodernist predilection for affirming the distinctiveness of colonial cultures.
Visualizing "Race" in the Eighteenth Century
Authors: Gissis Snait B.
Published: January 2011

This paper looks at the conditions of the emergence of "race" as a new scientific category during the eighteenth century, arguing that two modes of discourse and visualization played a significant role: that on society, civility, and civilization—as found principally in the travel literature—and that on nature, as found in natural history writings, especially in botanical classifications. The European colonizing enterprise had resulted in an extensive flow of new objects at every level. Visual representations of these new objects circulated in the European cultural world and were transferred and transformed within travelogue and natural history writings. The nature, boundaries, and potentialities of humankind were discussed in this exchange within the conceptual grid of classifications and their visual representations. Over the course of the century the discourse on society, civility, and civilization collapsed into the discourse on nature. Humans became classified and visually represented along the same lines as flora, according to similar assumptions about visible features. Concurrently, these visible features were related necessarily to bundles of social, civilized, and cognitive characteristics taken from the discourse on society, civility, civilization, as found in the contemporaneous travelogue.
A költő, az atléta és az isten tekintete Pindarosnál
Authors: Adorjáni Zsolt
Published: January 2011

Dolgozatomban a tekintet motívumának három különböző, ám egymással szorosan összefüggő megjelenését elemzem. A látási vonatkozás mindháromnál metaforikus, Pindaros értékrendszerének és hitvallásának szemléletes kifejezője. A költő tekintete különbözik aszerint, hogy a dalnok a dicsőítést vagy a rágalmazást választja életcéljául. Az atléta és az isten tekintete hasonlóan zárt képi-gondolati szerkezetbe illeszkedik. A tanulmány több hely és vers értelmezését új fénybe állítja, így például a 4. nemeai és 8. pythói óda egy-egy rendkívül vitatott részletét.
A Római Birodalom igazságosságának elmélete Polybiosnál
Authors: Mohay Gergely
Published: January 2011

A Kr. e. II. században megszületik egy olyan ideológia, mely a Római Birodalom létjogosultságát igazolta a meghódítottak előtt. Lényege a következőkben összegezhető: akkor igazságos egy állam uralma más államok felett, hogyha ez a viszony az alávetett állam érdekét is szolgálja, ez pedig akkor lehetséges, hogyha az uralkodó állam kiválóbb, és az alávetetteket jobbá teszi, jobb irányba vezeti, mintha ők önmagukat irányítanák. A tanulmány első részében amellett érvelek, hogy ezt az elméletet Panaitiosnak, a sztoikus filozófia középső korszakában alkotó filozófusnak kell tulajdonítanunk. Ezután azt bizonyítom, hogy a Róma világbirodalommá válását megíró megalopolisi Polybios – aki baráti viszonyban volt Panaitiosszal, és vele gyakran cserélt eszmét államelméleti, politikai kérdésekről – az elméletet ismerte, és a Római Birodalom, valamint a meghódított államok viszonyára alkalmazta is.
A görög irodalom újraéledése az első humanista fordításokban
Authors: Marton József
Published: January 2011

A reneszánsz-humanizmus egyik sajátos, a többi reneszánsz mozgalomtól megkülönböztető jegye a görög kultúra újjászületése. Ebben döntő szerepet játszottak a görög klasszikusok új latin nyelvű fordításai, melyek jellegét az egész korszakra előre meghatározta Leonardo Bruni programadó tevékenysége. Jelen tanulmány ezen újraélesztésnek elemzi mind a metódusát („hogyan?”), mind a motivációját („miért és mit?”). A dolgozat először a Bruni által kidolgozott modern fordítói módszert értelmezi, mely a szöveg lényegét a benne megnyilvánuló értelemben látta, aztán a korabeli szellemi irányzatok tükrében mutatja be a módszer történeti-filológiai hátterét, illetve összetett nyelvi szempontrendszerét; majd föltárja azokat az irodalmi és aktuális jellegű indítékokat, netán személyes momentumokat, melyek alapján az egyes görög szerzőket és műveket fordításra kiválasztották és célzatos rendbe állították.
712 jelentősége a 25. dinasztia kronológiájában és az egyiptomi-kusita történelemben
Authors: Erdős Gábor
Published: January 2011

Dahn’el Kahn 2001-ben új kronológiát javasolt a 25. (kusita) dinasztia történelmére vonatkozóan, amelyet II. Sarrukín 1999-ben publikált Tang-i Var-i feliratában olvasható új adatokra alapozott. Bár az általa felállított új kronológia számos ponton értelmezte át a korszak egyiptomi és kusita történelmének eseményeit, az ő felvetései sem mentesek félreértelmezésektől és hiányosságoktól. Jelen tanulmány szerzője a már ismert források pontosabb értelmezésével, és a probléma kontextusában még nem vizsgált néhány újabb forrás együttes vizsgálatával próbálja bizonyítani, hogy miért nem elfogadható minden kétséget kizáróan Dahn’el Kahn elmélete.
A Nondamaging Friction Reducer for Slickwater Frac Applications
Authors: Sun Hong , Wood Benjamin , Stevens Dick , Cutler Jennifer , Qu Qi , Lu Meng
Published: January 2011

Friction reducers used in slickwater fracturing can cause damage to the formation and, especially, to natural fractures because of their chemical nature as high molecular weight polyacrylamides and because of the large volumes injected during a typical treatment. Such concerns can be addressed with two approaches: 1. developing more effective friction reducers with a) more efficient polymers and/or b) faster hydration to shorten the dormant period before friction reducers are fully hydrated, considering the fact that fluids typically travel from surface to perforation within only 3 minutes; 2. developing breakable friction reducers, which are effective during pumping but degrade under downhole conditions, leaving little residue.

A new friction reducer was developed, encompassing all of these desired features. Improved hydration and more effective chemistry make it possible to achieve significant reduction of polymer loading in the field, and effective breaking downhole minimizes residue. The new friction reducer is delivered in liquid form to simplify logistics and field operations. It is very effective as a friction reducer, compatible with common chemical additives (scale inhibitors, biocides, clay stabilizers, surfactants, brines, etc) and stable under mechanical shearing. More than 30 multi-stage slickwater frac completions have been performed using this new friction reducer in tight sandstone and shale formations. The effectiveness of the friction reducer was compared with conventional ones during the field trials and will be described in the paper. The field results were corroborated by laboratory tests of the new friction reducer in water and various brines. This paper will also present chemical compatibility, breaking profiles and formation damage studies on tight sandstone and shale formation core in comparison with conventional products. Production history of field-trial wells for 30, 60, 90 days will be presented and compared to those of the offsets.
Multiple-Fractures Propagation, Orientation and Complexities in Drilling Waste Injection
Authors: Shokanov T. , Gumarov S. , Ronderos J. , Fragachán F. E.
Published: January 2011

The subsurface injection of drilling waste has become an increasingly popular and well-accepted technology over the last several decades. The popularity of this technology is primary spurred by its economic advantages in meeting more stringent drilling waste management requirements, especially in remote and environmentally sensitive areas. Furthermore, its use has become more attractive with the dramatic development and improvement in the processes associated with surface and sub-surface engineering, fracture modeling, risks identification and mitigation options, injection monitoring and in-depth pressure analysis. Together, these advancements have improved considerably the assurance and efficiency of waste injection operations worldwide.

Nevertheless, despite the tremendous advancements in the fracture modeling attained from subsurface feasibility studies, a major uncertainty exists with the propagation of multiple-fractures that apparently accompanies the intermittent batch injection process, essential to the drilling waste injection operation. The propagation of multiple-fractures, along with their orientation and complexities, strongly influence the fracture design, ultimate disposal capacity and injection pressure behavior. Consequently, this uncertainty is a critical issue, both in drilling waste injection and re-fracturing in conventional stimulation treatments.

This paper describes the evolution of understanding of multiple-fracture mechanics in drilling waste injection, starting from the conventional "wagon-wheel" uniform disposal-domain concept to the branching multiple-fractures approach that becomes practical through mathematical computations of near-wellbore changes in the stresses resulting from prior fracture creation and solids accumulation. Moreover, the authors present four potential scenarios of subsequent fracture initiation and propagation during intermittent injections, and provide revised re-assessment of data from the joint industry Mounds Drill Cuttings Injection Field Experiment.
Rheology Measurements of Concentrated Broken Gel for Filtercake Modeling
Authors: Gdanski Rick , Bryant Jason
Published: January 2011

A common explanation for disappointing production results from fracturing treatments in tight-gas sand reservoirs is gel filtercake damage. Gel filtercake rheology is poorly understood, which makes modeling efforts difficult. The current method of describing gel filtercake movement is by measuring the "pressure drop to initiate flow" in special laboratory tests conducted at room temperature and atmospheric pressure. Typical filtercake concentrations are considered to be 0.6 to 0.8 lbm/gal, but can become much higher on fracture closure in low sand-concentration proppant packs. Laboratory experiments have been completed that measured the rheology of concentrated depolymerized (broken) hydroxypropyl guar (HPG) across a molecular weight (MW) range of 26 to 580 Kg/mole, a temperature range of 60 to 280°F, a concentration range of 0.25 to 3 lbm/gal, and shear rates of 0.001 to 1000 1/sec. Results from these experiments have been applied to calculate apparent pressure drops to initiate flow of decrosslinked filtercakes across a broad range of conditions.

The rheology of the noncrosslinked fluids was found to have Carreau type behavior. The Flory-Huggins equation was used to match the behavior of the infinite and zero shear rate viscosities at a reference temperature of 62°F. The remaining Carreau parameters were determined as a function of temperature and MW. The complete rheology model is presented. The rheology model was combined with flow-through porous media equations to successfully determine apparent pressure drops to initiate flow according to the currently accepted experimental criteria. This work significantly advances the understanding of the rheology of decrosslinked filtercakes, demonstrates that the Carreau behavior can still exhibit an apparent pressure drop to initiate flow in porous media, and provides a useful rheology model for further fracture-cleanup modeling.
New Thermo Thickening Associative Polymer System Pushes Limits of Surfactant Gels
Authors: Shaefer M. , Carman P. S. , Ngoma V.
Published: January 2011

When viscoelastic fluids systems first appeared, they provided a very good non-damaging no polymer option for many tight gas applications. These fluids were operationally simplistic with only a few additives, usually less than five. However, they are temperature limited to about 140°F as a single fluid. For temperatures to about 220°F you have to foam with gas (carbon dioxide (CO2) or nitrogen (N2), usually 65 to 75 quality (Q) in order to achieve stability with adequate viscosity. In addition the typical VES systems do not have very good friction reduction because at high shear they tend to behave more like water.

The new thermo thickening system raises the temperature limit for traditional VES fluids. Rheology testing exhibits good structure along with viscosity. The time necessary to gel with temperature can be accelerated and delayed chemically. Although it does contain a polymer, regain conductivity tests show very high numbers usually associated with VES fluids. The system also exhibits unique traits of clay control, surfactant properties and fluid loss. The system also has the potential to extend further as a foamed fluid. This project will show laboratory testing results and a field test case history of this new and unique fluid system.
Surface Area vs Conductivity Type Fracture Treatments in Shale Reservoirs
Authors: Ramurthy Muthukumarappan , Barree Robert D. , Kundert Donald P. , Petre Erik , Mullen Mike
Published: January 2011

Hydraulic fracturing continues to be the primary mechanism to produce hydrocarbons out of the tight shale reservoirs. Ever since the success of Barnett shale program, operators are inclined to pump similar large volume water fracture treatments with little or no proppants in their respective shale plays. This assumes that all shale plays are the same and react accordingly to large volume treatments. The basic objective behind such treatments is to contact large surface area, which has been very successful in the Barnett shale play. Such large volume treatments in other shale plays may not be an optimized solution for the specific shale attributes and the response may lead to uneconomical production results. Some shales based on their reservoir characteristics might require a conductivity type fracture treatment. So, it is important to understand the characteristics of these shales before deciding the stimulation treatments. In addition to core and log analysis of these shales, fluid sensitivity tests, Brinell hardness tests, unpropped fracture conductivity tests and more importantly a Diagnostic Fracture Injection Test (DFIT) can help define the guidelines for choosing between a surface area and a conductivity type fracture treatment.

Integrating the various data sources is important in arriving at these guidelines. The main objective of this paper is to provide these guidelines along with examples such that the costly trial and error approach for stimulating shales can avoided. Examples from both oil and gas shales namely, the Gothic, Haynesville, Eagle Ford and Barnett shale plays in the USA are included in this work.
Integrating Microseismic Mapping and Complex Fracture Modeling to Characterize Fracture Complexity
Authors: Cipolla C. , Weng X. , Mack M. , Ganguly U. , Gu H. , Kresse O. , Cohen C.
Published: January 2011

Microseismic mapping (MSM) has shown that the occurrence of complex fracture growth is much more common than initially anticipated and is becoming more prevalent with the increased development of unconventional reservoirs (shale-gas). The nature and degree of fracture complexity must be clearly understood to select the best stimulation design and completion strategy. Although MSM has provided significant insights into hydraulic fracture complexity, in many cases the interpretation of fracture growth has been limited due to the absence of evaluative and predictive hydraulic fracture models.

Recent developments in the area of complex hydraulic fracture propagation models now provide a means to better characterize fracture complexity. This paper illustrates the application of two complex fracture modeling techniques in conjunction with microseismic mapping to characterize fracture complexity and evaluate completion performance. The first complex fracture modeling technique is a simple, yet powerful, semi-analytical model that allows very efficient estimates of fracture complexity and distance between orthogonal fractures. The second technique is a gridded numerical model that allows complex geologic descriptions and more rigorous evaluation of complex fracture propagation.

With recent advances in complex fracture modeling, we can now evaluate how fracture complexity is impacted by changes in fracture treatment design in each geologic environment. However, quantifying the impact of changes in fracture design using complex fracture models alone is difficult due to the inherent uncertainties in both the Earth Model and "real" fracture growth. The integration of MS mapping and complex fracture modeling enhances the interpretation of the MS measurements, while also calibrating the complex fracture model. Examples are presented that show that the degree of fracture complexity can vary significantly depending on geologic conditions.
Fracture Stimulation Treatment Best Practices in the Bakken Oil Shale
Authors: Hlidek Barry T. , Rieb Brad
Published: January 2011

This paper summarizes fracture stimulation treatment best practices determined by a three-year study of production results of several thousand fracture treatments in more than 460 wells in the Bakken Shale formation in Saskatchewan, Canada. Treatment variables include: proppant type, proppant concentration, fracturing fluid formulation, treatment size, well-bore azimuth, and lateral frac density. Treatment effectiveness is based on four month cumulative production comparisons that include: oil, water, and total fluid.

The Bakken is a low-permeability oil and water-producing formation at a depth of about 1500 m (4900 ft). The study area covers about 390,000 hectares (1500 mile2) in the northern region of the Williston Basin. Wells in this region require propped fracture stimulations for economic production. All wells in this study are drilled horizontally, normally completed open-hole in the Middle Bakken. Most completions consist of isolated multistage treatments. One of the significant challenges encountered during fracture treatment design is the presence of an overlaying water aquifer, known as the Lodgepole. Fracture treatments that breach the Lodgepole aquifer are considered less than optimum because of excess water production.

This paper will also review design and operational considerations for the area, including treatment volumes, pump rates and fluid chemistry. Wells in the study were primarily completed with two types of water based fluids. Treatment size and treatment rates are important considerations. The requirement to limit fracture growth conflicts with the theoretical need for a large, conductive propped fracture. However, the study shows that proppant concentration and the resulting fracture conductivity impact fluid production. Lateral length, number of frac stages, and distance between stages are also addressed in the paper.

Results of this study will be presented as best practices that may be used to refine completion techniques to maximize hydrocarbon production without excessive water production in this important oil-producing basin.
Modeling of Hydraulic Fracture Network Propagation in a Naturally Fractured Formation
Authors: Weng X. , Kresse O. , Cohen C. , Wu R. , Gu H.
Published: January 2011

Hydraulic fracturing in shale gas reservoirs has often resulted in complex fracture network growth, as evidenced by microseismic monitoring. The nature and degree of fracture complexity must be clearly understood to optimize stimulation design and completion strategy. Unfortunately, the existing single planar fracture models used in the industry today are not able to simulate complex fracture networks.

A new hydraulic fracture model is developed to simulate complex fracture network propagation in a formation with preexisting natural fractures. The model solves a system of equations governing fracture deformation, height growth, fluid flow, and proppant transport in a complex fracture network with multiple propagating fracture tips. The interaction between a hydraulic fracture and pre-existing natural fractures is taken into account by using an analytical crossing model and is validated against experimental data. The model is able to predict whether a hydraulic fracture front crosses or is arrested by a natural fracture it encounters, which leads to complexity. It also considers the mechanical interaction among the adjacent fractures (i.e., the "stress shadow" effect). An efficient numerical scheme is used in the model so it can simulate the complex problem in a relatively short computation time to allow for day-to-day engineering design use.

Simulation results from the new complex fracture model show that stress anisotropy, natural fractures, and interfacial friction play critical roles in creating fracture network complexity. Decreasing stress anisotropy or interfacial friction can change the induced fracture geometry from a bi-wing fracture to a complex fracture network for the same initial natural fractures. The results presented illustrate the importance of rock fabrics and stresses on fracture complexity in unconventional reservoirs. They have major implications on matching microseismic observations and improving fracture stimulation design.
Characterization of Small Scale Heterogeneity to Predict Acid Fracture Performance
Authors: Oeth C. V. , Hill A. D. , Zhu D. , Sullivan R. B.
Published: January 2011

Recently developed models of the acid fracturing process have shown that the differential etching necessary to create lasting fracture conductivity is caused by the heterogeneous distributions of permeability and mineralogy along the fracture faces. To predict the conductivity that can be created by acid in a particular formation, the models require information about these formation properties and their spatial variation. This research aims to quantify the small scale heterogeneity by using a geostatistical description to ascertain the distribution of permeability in a carbonate formation. Parameters that quantify the directional correlation and variance of the data are developed. The correlation length and variance parameters are a first step in being able to couple acid transport and rock dissolution models at reservoir scale with a model of fracture conductivity based on channels and roughness features caused by small scale heterogeneity. These geostatistical parameters are developed for a well in the Hugoton Field. Data leading to their derivation are obtained from a combination of well logs and cores. The resulting geostatistical parameters and acid etched width are used to predict acid fracture performance. Application of new model conductivity correlations results in a unique prediction for the acid fracture case study that differs from the industry standard.
Application of Multivariate Statistical Analysis to Slickwater Fracturing Parameters in Unconventional Reservoir Systems
Authors: Kazakov Nikita Y. , Miskimins Jennifer L.
Published: January 2011

Hydraulic fracturing is essential for economic production in tight gas and shale gas reservoirs due to their low permeability nature. Slickwater fracturing has been successfully performed in shales and tight gas reservoirs using low viscosity fluid, usually water, with friction reducers. Slickwater fracturing has the advantage of reducing formation damage and generally being less expensive than conventional gel. Predicting which slickwater parameters are important to successful production and which are less important has been an important but unanswered question. This research uses multivariate statistical methods to discover whether production from the Jonah Field, Wyoming, and the Barnett Shale, Texas, can be predicted using slickwater parameters and whether these parameters can provide insight into the design and analysis parameters of the slickwater treatments.

Factor, cluster, and multiple regression analysis show that production data from the sampled Barnett Shale and Jonah Field databases group separately from the slickwater parameters. Multiple regression, used to predict the EUR and the cumulative produced water from the slickwater parameters in the Barnett Shale, yielded best adjusted-R²’s of 34.7% and 25.3%, respectively. Multiple regression was also used to predict the EUR from the slickwater parameters in Jonah Field resulting in the best R² of 22.9%. Multiple regression analysis established a relationship with an adjusted R² of 93.0% between the fluid pumped and the fluid recovered from the Barnett Shale treatments. Multiple regression analysis also established that the amount of proppant used for Jonah Field hydraulic fracturing operations was calculated from the total fluid pumped and the net pay.

This research provides a methodology to use multivariate statistics to analyze stimulation treatments. Additionally, it opens opportunities for the analysis of different fields with more data using multivariate statistics and can aid in improving designs in an operator's current field or in understanding previous designs in a newly acquired field. Finally, it also demonstrates how "no information" can be valuable in cutting costs on commodities purchased to stimulate a well when no benefit is seen from those additional purchases.
Fluid Injection Experiments in Two-dimensional Porous Media
Authors: Huang H. , Zhang F. , Callahan P. , Ayoub J.
Published: January 2011

A series of injection experiments were conducted in a Hele-Shaw cell-like radial flow device filled with fine sands to better understand the fundamental failure/flow mechanisms when dense granular media is invaded and displaced by a fluid. Both aqueous glycerin solutions and polyacrylamide solutionswere used as the invading fluids. The experimental findings suggest that there is a transition from the solid-like (fracturing) to fluid-like (fingering) behavior in the injection process. Based on the gain displacements and fluid flow patterns, four distinct failure/flow regimes can be identified fromthe experiments, namely, 1) the simple radial flow regime, 2) the leakoff-dominated regime, 3) the grain displacement-dominated regime, and 4) the viscosity fingering-dominated regime. These failure/flow patterns emerge as a result of competition among various forms of energy dissipation, i.e., viscousdissipation through flow in porous media, dissipation through mechanical deformation, and viscous dissipation through flow in thin channels.
Hydraulic Fracturing, Microseismic Magnitudes, and Stress Evolution in the Barnett Shale, Texas, USA
Authors: Vermylen John P. , Zoback Mark D.
Published: January 2011

We present new techniques to analyze the effectiveness of hydraulic fracturing for stimulating production in shale gas reservoirs. The case study we have analyzed involves five parallel horizontal wells in the Barnett shale with 51 frac stages. To investigate the numbers, sizes and types of microearthquakes initiated during each frac stage, we created Gutenberg-Richter-type magnitude distribution plots to see if the size of events follows the characteristic scaling relationship found in natural earthquakes. We found that slickwater fracturing does generate a log-linear distribution of microearthquakes, but that it creates proportionally more small events than natural earthquake sources. Finding considerable variability in the generation of microearthquakes, we have used the magnitude analysis as a proxy for the "robustness" of the stimulation of a given stage. We have found that the conventionally fractured well and the two alternately fractured wells ("zipperfracs") were more effective than the simultaneously fractured wells ("simulfracs") in generating microearthquakes.

We also found that the later stages of fracturing a given well were more successful in generating microearthquakes than the early stages. This increase in microearthquake activity in the latter frac stages corresponded with an increase in the instantaneous shut-in pressure (ISIP). The net ISIP increase was most pronounced in the simulfrac wells and least pronounced in the zipperfrac wells. We have attempted to model this increase as a cumulative "stress shadow" using an elastic crack-opening model. However, even the maximum reasonable propped fracture aperture causes a stress increase that is less than what was measured in the wells. Since the fracturing of the simulfrac wells took only half the time of the fracturing of the zipperfrac wells, we believe that poroelastic effects associated with time-dependent leak-off is controlling the rate of ISIP escalation and the increase in microseismic creation. We are incorporating poroelasticity in the model to fully integrate stress evolution and permeable volume creation.