bluuebunny/crossref_metadata_2025 huggingface dataset:
First Applications of Inflow Control Devices (ICD) in Open Hole Horizontal Wells in Block 15, Ecuador
Authors: Davila E. , Almeida R. , Vela I. , Pazos J. , Coello K. , Chinellato F. , Humbert O. , Porturas F.
Published: May 2009

Horizontal wells are superior in production and recovery to conventional wells, however they are subjected to early water coning towards the heel (water can breakthrough anywhere in the well not only at the heel, due to permeability (K) variation and proximity of water traps). Furthermore, conventional completions do not handle effectivley heterogeneity or permeability contrasts exposed along the sand face. The ICD controls and interrogates more optimally both rock and fluid properties in the reservoir, hence delaying early water breakthrough. This early water breakthrough causes reduction in potential hydrocarbon recovery; the operation of the ICD is minimizing reserves left behind. If water breaks through in a well without ICD, these hydrocarbons are lost and cannot be drained subsequently.

This paper covers the design and application of new open hole sand face completion architectures equipped with Inflow Control Device technology (first in Ecuador) in Block 15. The design and well preparation prior to completion operations and results are presented for two types of formations e.g. consolidated and non-consolidated.

Detailed simulation models were performed and discussed with the Client prior to the drilling operations. The models are run using nodal analysis software and include the reservoir simulation grid.

A-priori simulations explored several scenarios to address and compare different uncertainty issues, flow conditions, well rates and pressure drawdowns both in the pre-planning and final installation of the completion.

The final design incorporates a removable housing ICD hardware, this allows on-site nozzle changes to create relevant delta P, to enhance well performance just after the well has been drilled and uses the real time data from the final logging operations.

The real time logs were then evaluated while the well was drilled and used to refine the final simulation model prior to completion installation in the ground.

The ICD completion architecture was successfully installed in consolidated sandstone and non-consolidated formations, with permeability varying from 250 mD to about 1D. The hydrocarbons viscosities varied from 5 cP, 8 cP, to 12 cP (consolidated sandstone, Well 1) and between 19 cP to 21 cP (non-consolidated formation, Well 2).

Well 1 in the consolidated formation is flowing with equipment ESP and its initial production was about 4000 BOPD dry oil, currently the water cut raised slowly from 1.5% about 24%. Well 2 required well conditioning and performing as expected.

The key advantage of using ICD is that it balances the flow across the entire horizontal section; delays early water breakthrough and uniform areal drainage.

It is concluded that Inflow Control Device proven technology is beneficial and successful in Bloque 15, Ecuador and its application will be considered in other fields.
Case History: Hydrocarbon Production Optimization in Cerro Dragon Using Latest Formation Evaluation and Perforating Technologies
Authors: Espina C. , Baldassa D. , Avagnina D. , Bonapace J. , Lopez E. , Quintavalla C. , Sorenson F.
Published: May 2009

Successful hydrocarbon production in the San Jorge basin requires precise understanding of the great variability in reservoir and fluid properties to determine the reservoir production capacity and achieve the optimum wellbore – reservoir connectivity during perforating.

Efforts to increase hydrocarbon production in the Cerro Dragon area of the San Jorge Gulf basin have been fueled by a combination of the latest formation evaluation, such Nuclear Magnetic Resonance (NMR) and perforating technologies associated with the extensive experience acquired during several years of team work between the operator and the service company.

The operator's needs for a method to help optimize well productivity and, at the same time, be cost effective without compromising the results of the operation required an improvement over traditional tubing-conveyed perforation (TCP). A propellant-assisted perforating (PAP) method that could optimize well productivity while maintaining stringent health safety and environmental standards was proposed. The PAP method uses an oxidizer that creates carbon dioxide gas at extremely high peak pressures in the millisecond time regime to overcome in-situ stress and creates perforation breakdown and mild fracturing near the wellbore. Standard perforating components and procedures are used, which provides the same safety features as when conventional TCP operations are used.

This paper focuses on different applications for the PAP method. It also describes the benefits of its use in the San Jorge basin, including enhancing connectivity beyond a damaged zone for better production and near the water contact, where hydraulic fracturing is not feasible, as well as reducing the hydraulic horsepower required for perforation breakdown to obtain production from marginal wells and pre-frac stimulation.
Changing Shale Strengths With Invert Emulsion Drilling Fluids: Theory, Measurement, and Modeling
Authors: Hemphill T. , Duran W.
Published: May 2009

Problems with wellbore stability while drilling in shale have plagued the drilling industry for a long time. For good reason, the bulk of trouble-related problems while drilling have been in shales, and great expeditures in time and money are made each year dealing with the problem. However, shale interaction with drilling fluids in the drilling process remains a complex and often misunderstood area of study. By comparison, fewer wellbore stability problems occur while drilling with invert emulsion fluids (IEF) than when water-based drilling fluids are used. The theory of shale interaction with invert emulsions is briefly reviewed in this paper.

Actual measurements of changes in shale strength of two shales have been recently made using a new test device from the University of Oklahoma. Two very different shales were studied: one from a deepwater environment and the other a more-competent shale cored in a land-drilling operation. These shales were exposed to invert emulsions having different water phase salinities, and the stresses required to cause sample failure were measured under in-situ conditions. The results showed use of invert emulsions under some conditions weakened the shales, while under other conditions, the shales were strengthened. These results were then interpreted using current osmotic pressure and membrane efficiency theory of invert emulsions.

The results were compared to the elastic and porochemoelastic modeling using the rock mechanical properties determined in the laboratory testing. Using a set of drilling and wellbore in-situ stress conditions, traditional elastic wellbore stability modeling is used to predict the changes in tangential stress in the wellbore wall. Next, porochemoelastic modeling is used to predict changes in pore pressure as a function of time and of IEF water phase salinity (WPS). These results are then discussed in relation to the changes in shale strength seen in the laboratory.

Knowing that there are significant differences in rock strengths of shales exposed to invert emulsions having varying water phase activity levels, the drilling engineer can more effectively plan future wells, especially those having narrow safe drilling windows.
Wavelet Filtering of Permanent Downhole Gauge Data
Authors: Ortiz C. E. P. , Aguiar R. B. , Pires A. P.
Published: May 2009

Permanent downhole gauges (PDG) for pressure and temperature are very common in oil and gas wells. The data collected by PDG's are used for monitoring the well condition and reservoir performance and, additionally, may provide new and complementary information for reservoir characterization. PDG record data at high sample rates, usually as high as thousands per hour. The computational analysis of this large volume of data requires a previous processing for the removal of noise and outliers and for the reduction of the filtered data. The Discrete Wavelet Transform (DWT) and the Multiresolution analysis were used successfully for this purpose. In the Multiresolution analysis, the DWT is used to decompose a signal in approximation and detail coefficients through low pass and high pass filters, respectively. The coefficients are modified, according to a thresholding method, to remove the noise and outliers before the reconstruction of the original signal. The final result depends on the kind of wavelet and resolution level used for the decomposition process, the method used to estimate the noise level and the rules used to modify the coefficients. In this work, the performance of different wavelet decomposition, noise threshold estimators and thresholding methods was investigated. Several combinations were tested on synthetic and actual data to establish a procedure that efficiently removes the noise and preserves the sharp features, characteristic of changes in production or injection rates, with minimum user intervention.
Visualization Process Approach to Identify Scenarios to Improve Recovery in a Mature and Stratigraphically Complex Reservoir: El Cordon Field
Authors: Santisteban M. , Altamiranda E. , Rodriguez M. I. , De Pellacani M. B. , Alvarez R.
Published: May 2009

The El Cordon Field is located in the prolific San Jorge Basin in Argentina. The El Cordon Field has produced from multiple fluvial volcano-clastic sandstones of Cretaceous age for more than 50 years. Production is primarily from the Cañadon Seco and Caleta Olivia members of the Cañadon Seco formation, and to a lesser degree from the Mina El Carmen formation. The field is characterized by a complex sedimentary environment and mineralogy which affects the quality of the reservoir and makes reservoir characterization and development of exploitation strategies difficult. The field is considered to be in a mature stage of development with over 630 wells under primary production and water injection projects on-going in selected areas of the field.

A Visualization Process Approach was developed in 2007 to identify scenarios to improve recovery and add economic value to the field. After a quick-look reservoir characterization, five scenarios were evaluated for maximizing reserves recovery. Historical and statistical data was analyzed to evaluate various development scenarios and the associated reserves. The various cases evaluated included: 1) a base case; 2) reactivation of existing wells; 3) drilling of wells at normal spacing; 4) infill drilling; and 5) water injection. Application of all cases indicates a potential increase of the field recovery factor from 9.4% to 14.2%. A technical screening for polymer injection feasibility was also analyzed. A second "Conceptualization" phase would include a detailed reservoir characterization study to help reduce uncertainty and support the definition and implementation of the best scenario for further field exploitation.
Upper Completion Design Methodologies for Deepwater Subsea and Dry Tree Applications
Authors: Arrazola A. , McAnally Y.
Published: May 2009

Deepwater fields are one of the largest growth segments of the industry. The technologies that enable this growth economically are those that provide improvements in operational reliability, flexibility, and cost, and which mitigated risks. With offshore rig rates often hitting $500K US per day, special considerations must be taken into account when specifying or designing an upper deepwater completion at depths greater than 1,000 ft (305 m). When selecting a completion scenario, an accurate assessment of risk versus reward must be analyzed in order to design a cost-effective, yet flexible completion. In this paper, the authors outline the proper methodologies in selecting existing technology for each completion approach in subsea and dry tree applications.

Design methodologies for deepwater completions vary when compared to conventional type completions. The basis of design in a conventional type completion includes: 1) a production packer to isolate pressure and fluids from the producing zone and manage production tubing movement and loads; 2) a surface-controlled subsurface safety valve (SCSSV), whose objective is to isolate the tubing and well head from well fluids in an emergency or planned shutdown; and 3) flow control equipment, such as landing nipples, chemical injection nipples, and sliding sleeves. Deepwater subsea or dry tree completions have similar basic requirements as that of conventional completions. However, critical to deepwater are the completion design, planning, quality assurance and quality control, reliability, execution/deployment, and longevity of the completion.

Drivers for completion methodologies in subsea and dry tree applications will be discussed. Issues such as tubing space-out, packer-setting methods, SCSSV operating parameters, sub-mudline tubing and packoff hangers will be reviewed. Temporary well suspension methods will also be discussed where applicable and different completion options will be outlined for each case.
Unified PTA and PDA Approach Enhances Well and Reservoir Characterization
Authors: Ehlig-Economides C. A. , Martinez Barron H. , Okunola D.
Published: May 2009

As permanent downhole gauges have become more reliable, increasingly operators are installing them on injection/production wells. Each time the well is shut in, often solely for operational reasons, pressure transient analysis (PTA) can be performed on the resulting falloff/buildup transient lasting from a few hours to a few days. When the well is flowing, the permanent gauge provides a long term record of pressure behavior during injection/production. Usually the well rate is also determined on a continuous basis, daily or monthly, although often at a much lower data rate than the pressures recorded by the permanent gauge. Recorded pressure and flow rate data are typically used for production data analysis (PDA). Due to the difference in data collection between PTA and PDA, these analyses are performed independently, yielding multiple interpretations from a diverse group of people and software programs. At times the results may conflict, and creating one consistent well and reservoir characterization can be quite challenging and time consuming. A unified interpretation of both analyses would reduce analysis time and increase confidence in the results.

In this study, relatively short-duration PTA data and long-term PDA data are combined to provide a more complete analysis than either PTA or PDA alone can provide. The unified analysis is displayed on a combined plot of pressure change and its derivative from a single transient flow period (preferably a falloff/buildup), and rate normalized pressure (RNP) and its derivative based on injection/production data. Data processing techniques follow a stepwise procedure to construct the combined plot. The result is a virtual drawdown response that can be diagnosed like pressure and pressure derivative and matched with an appropriate model for the well and its drainage area. The method is most effective when flow remains single phase or at least segregated in the reservoir.

Apart from the unified PTA and PDA approach, this study also offers significant improvements in the RNP data processing that leads to a much more conclusive PDA. Synthetic examples illustrate the effectiveness of the technique for known models. Then two field examples show its practical application.
Reservoir Modeling in Support of Shale Gas Exploration
Authors: Schepers K. C. , Gonzalez R. J. , Koperna G. J. , Oudinot A. Y.
Published: May 2009

Shale gas and other unconventional gas plays have become an important factor in the United States energy market, and are often referred to as statistical plays due to their high heterogeneity. They present real engineering challenges for characterization and exploitation, and their productivity depends upon an inter-related set of reservoir, completion and production characteristics.

Shale gas plays are generally characterized by low geologic risk and a high commercial risk. Extensive and continuous deposits of tight, usually naturally-fractured shale provide the duality of a potentially-productive reservoir being the hydrocarbon source. Commercial production is a huge unknown in these plays, and reservoir modeling as well as production predictions involve considerable uncertainty. Because of the large number of unknowns, a merely deterministic approach is often incapable of capturing the complete impact of all interdependencies present in a shale gas resource play.

Consequently, one must take into account multiple scenarios to find better exploitation plans. Tools are therefore needed to identify the most important geologic and engineering factors, and to quantify the range of variability in uncertain variables. Reservoir simulation coupled with stochastic methods, i.e., Monte Carlo and geostatistical procedures, have provided excellent means to predict production profiles with a wide variety of reservoir character and producing conditions.

Defining and representing uncertainties with a quantitative understanding of their respective impacts on commercial achievability is crucial to subsequent decisions involving continued investment for commercial purposes.

This paper describes a systematic process employed in the evaluation of a new prospect area (a shale gas play) with very limited available data. In order to properly model the problem with uncertainty, geological and engineering issues were framed within conventional Monte-Carlo procedures and geostatistical characterization algorithms to identify key production parameters so that relevant data can be collected. This process also allows for the investigation of how the combination of a nested natural fracture system, appropriate wellbore design and stimulation are necessary to drive productivity, and provide project results in terms of ranges of outcomes and associated probabilities. Consequently, managers can be in a better position to make informed decisions regarding the uncertainty of such projects.
Effect of Some Physicalchemical Variables on the Formation and Stability of Foam in an Oil-Air System and Their Correlation With the Formation of Foamy Crude Oil
Authors: Marcano L. , Gutierrez X. , Perez B. , Martínez E.
Published: May 2009

There are crude oil reservoirs, in Venezuela, where the foam generation or production combined with the crude oil has become a problem. Consequently the net volume of produced crude oil decreases and the problem is more severe in some reservoirs than in others. So far any effective techniques or methods have not been created in order to solve this problem. Neither there has been any systematic study which may explain why the foamy crude oil is produced, or why some foamy crude oil are more stable than others. The purpose of this paper was to find out the mechanism of formation and stabilization of the foam in the crude oil. The initial investigation was related to study a engine oil (Diesel)-air system which simulated the crude oil-gas system and the formation and stabilization variables, which affect the foam production. Finally the results were correlated with the crude oil-gas system, through exposition of hypothesis. Afterward we will work with the crude oil-gas systems. The method used to create or produce foam consisted in bubbling air in the engine oil phase containing surfactant, alcohol and water different concentrations. The tests basically were carried out to different air flow in order to determine the static stability or the lifetime of the foam produced. The foamability and stability foam were plotted as a function of the air flow. The results indicated that the foam production in the oil is not affected by the increase in the surfactant concentration, but it is improved with the increase of the dispersed water content in the oil. However, the favorable effect of the dispersed water on the foamability is related to the alcohol concentration dissolved in the oil. The most important conclusion is that the presence of dispersed water in the oil is responsible of the foam formation.
Definition of Reservoir Compartmentalization Applying Compositional Gradients: Mugrosa B Formation in Middle Magdalena Valley Basin, Lisama Field, Colombia
Authors: Castro R. H. , Canas-Marin W. , Osorio R. , Soto C.
Published: May 2009

Lisama is an oil field operated by ECOPETROL S.A. located in the east side of Middle Magdalena Valley basin in Colombia. The reservoir is a stratigraphic-structural combined trap and the oil comes from the Tertiary, mainly from the formations Mugrosa and Colorado.

A methodology of Integrated Fluid Analysis is applied. The methodology includes fluid sampling analysis, PVT test quality control and reservoir fluids representativeness. Then, a cubic Equation of State is developed to match the best PVT data. Finally, compositional gradients are built so that they can describe properly the variation of PVT properties with depth.

There are 16 PVT studies in Lisama Field. However, after applying the procedure described above, only the results from four PVT reports are found to be both reliable and representative. Afterwards, Peng-Robinson Equation of State is fitted against PVT depletion data applying a non linear regression technique in order to change systematically internal parameters of the equation of state such as binary interaction coefficients, critical pressures, critical temperatures, volume shifts, and critical Z factors. Finally, isothermal compositional gradients based on reliable compositions are built and a gas-oil contact (GOC) analysis is developed.

The results obtained by applying this methodology indicate that fluids in Lisama field's northwest sector, known as the Corridor of Gas, have a different behavior in comparison with those of the remaining area, particularly in relation to the location of the respective gas – oil contacts. That is, the two GOC values predicted for the fluid system in the Corridor of Gas are located within the Mugrosa formation, while the GOC value for the fluids of the remaining area are predicted out of this formation. Therefore, this would mean that the corridor of Gas is isolated from the rest of the Lisama area.

This study is a fundamental support for the initialization of the reservoir simulation model and the prediction of new development strategies that would lead to optimize the recovery of fluids in the area.
Improving MEOR Performance by a Selection Methodology in Mature Oilfields
Authors: Segovia G. C. , Huerta V. A. , Guitierrez G. C.
Published: May 2009

Microbial Enhanced Oil Recovery (MEOR) is a technique that uses bacterias and by-products, either as an organic formation damage removing mechanism to increase oil production, or as an agent to reduce residual oil saturation, and eventually increase ultimate recovery factor, specially in mature oilfields.

Successful applications reported in Argentina, United States, China and Venezuela were the main driving force to Peruvian local companies, which decided to implement some MEOR Projects in Talara oilfields, with positive and negative results. Consequently, it has been prepared a rigorous analytical and pragmatic methodology by integrating: Well Performance Evaluation, Reservoir Engineering Analysis, Physicochemical Characterization, Rheological Analysis and Sensitivity to Biotreatability Tests.

A flowchart including general criteria, as well as, fluid and reservoir properties application ranges was prepared to optimize oil wells and reservoirs selection to MEOR. This flow chart allowed us to recommend two wells of the MEOR pilot project recently implemented in a marginal oilfield of Talara, Peru; preliminary results showed in both wells, improvements in fluid properties (less oil viscosity and higher API°) and initial increase of more than 30% in oil production.
Unconventional Abandonment of Gavilan 1W Well
Authors: Lopez Davila A. M. , Farfan Collazos L. E.
Published: May 2009

Gavilan 1W Well was drilled in 1970 by Texas Petroleum, in Colombia, near to border's Ecuador. Final depth 7.700 ft. – 41 API, 1% BSW, Q = 25 BFPD. Well was closed, without conventional abandonment. In 2001, We identified an illegally exploited well with a gas leak from the wellhead (THP= 1.000 psi). Ecopetrol S.A. installed a clamp and control gas leak without exit in well control, in this place there is a permanent presence of guerrilla and there isn't road to arrive the location, we did all operations by Helicopter

In 2008, after Colombia Army's Operations, We found a crater near to wellhead, the well was in illegally exploited and the environment contaminated; after many operations with brines (plus sealant material), mud and cement, was possible seal leak's tubing-casing, and closed the crater
Water-Gas Migration Control and Mechanical Properties Comparison With a Quick-Setting Slurry Design QSSD to Be Applied in a Production Cementing Job for Ecuador
Authors: Ramirez H. B. , Santra A. , Martinez C. , Ramos X.
Published: May 2009

A slurry design based on Sorel cement technology with a median particle size of 5 to 10 microns has been optimized without using Portland cement. This mechanically modified slurry with quick-setting technology is designed to withstand the operational changes that may play a crucial role in the performance of the cement sheath once the well is drilled, completed, and in production. Two additional mechanically modified slurries were designed using local Class "G" cement for comparison.

The control of gas migration can be enhanced by obtaining a transition time value of less than 30 minutes. Transition time is defined as the length of time it takes for the static gel strength (SGS) to change from 100 lb/100 ft2 to 500 lb/100 ft2. The SGS tests were performed under simulated downhole pressure and temperature conditions. A value of 10 minutes for transition time was obtained. SGS tests were carried out with a static gel strength measuring device (SGSMD). It is important to mention that the zero gel time (ZGT), is defined as the amount of time the slurry can remain static after placement time and still transfer almost full hydrostatic-pressure from fluids before reaching an SGS of 100 lb/100 ft2; it can also be adjusted in regards to the cementing job.

The mechanical properties of this quick-setting slurry design (QSSD) were comparable and in some aspects were improved. The results included a Young's modulus around 5E+05-psi, Poisson ratio of 0.23, and a tensile strength of 250-psi. The bottomhole circulating temperature (BHCT) was 172°F and bottomhole static temperature (BHST) at MD was 208°F. Cylindrical samples were cured at 208°F and 2,000-psi for seven days and were used for measurement of mechanical properties.

This slurry design was developed for Ecuador to solve three major problems on production liners: Water-gas migration throughout the annulusLong waiting-on-cement time (WOC) to develop compressive strengthImprovement of the mechanical properties to minimize the effect of failure mechanisms on the cement (cracking, debonding, shear failure) that can result in poor cement bond logs and remedial cementing jobs
IPI Method: A Subsurface Approach to Understand and Manage Unfavorable Mobility Waterfloods
Authors: Elphick J. J. , Marquez L. J. , Amaya M.
Published: May 2009

Oil viscosities of about 2 cP and above (under downhole conditions) are common and often exhibit poor end-point mobility ratios when displaced by water in fields under waterflood or with active aquifers. This causes a triple hit on the recovery factor: Poor displacement efficiencyPoor areal sweepPoor vertical sweep

This is made worse by reservoir heterogeneity.

The commonly used concepts of productivity index (PI) and injectivity index (II) are not particularly useful when the mobility ratio is high since they require the use of a nominal drainage radius, whereas a two-fluid system with a moving fluid is more appropriate.

The novel concept of the injectivity productivity index (IPI) has been developed to consider a pair of wells comprising an injector and producer, and replaces the use of II and PI. The IPI method helps to quantify waterflood issues in the presence of poor mobility.

This paper will cover three main areas: The simple background theory of IPI.The consequences of IPI for breakthrough, sweep, and even sanding.The implication of IPI for an example waterflood field, Casabe, which has these challenges and required a new understanding of the waterflood.
Ultra-Low Invasion Fluids: A Viable Technical Solution to Drill in Eastern Venezuela
Authors: Arbizu A. G. , Reid P. , Moreno J. G. , Avila A. A. , Urbaneja N.
Published: May 2009

One of key tasks of he drilling fluids industry for many years has been to develop a fluid with as low invasion characteristics as possible. These are often referred to as low invasion or ultra-low invasion fluids. If we could sop invasion by the drilling fluid completely, it would be possible to eliminate several forms of wellbore instability, lost circulation and differential pressure sticking. In addition, well productivity improvements will be expected as there will be little or no formation damage from the drilling fluid. This scenario of zero invasion is not achievable with a fluid used in an overbalanced condition, at least not in the near future. However, the industry is working to understand the benefits of he next best thing: Ultra-Low Invasion Fluids (ULIF).

This paper presents the application of this technology to drill a development well in the San Joaquín field of Eastern Venezuela.
Numerical and Experimental Modeling of Relative Permeability in Heavy Oil Reservoirs
Authors: Castillo A. F. , Perez E. R. , Rojas J. A. , Zapata J. F.
Published: May 2009

Understanding of high viscous fluid flow in porous media is very important in the accurate development plan for heavy oil reservoirs. Viscous fingering and effects of unstable flow are phenomenon that must be considered during displacements of heavy oil by water in reservoirs.

Experimental problems in rock tests with high viscous fluids (due to exaggerated increases in pressure differential, early breakthrough times, large differences in mobility ratios) are some of the technical difficulties showed during the acquisition of relative permeability curves by unsteady state in heavy oil reservoirs. At the same way, difficulties in conventional interpretation (JBN interpretation is supposing uniform displacement) are challenges that numerical interpretations must be try to solve for modeling accurately what is happening inside rock.

This paper presents a number of "best practices" for defining a reliable relative permeability curve in heavy oil reservoirs related to numerical modeling and experimental modeling. Description of phenomenon in a Colombian heavy oil reservoir field are shown for three petrophysical quality rocks (less than 500 mD, around 5000 mD and larger than 10000 mD). Capillary pressure effects are included in the modeling and its importance in the displacement is analyzed.

Finally, results of sensibilities to different mobility ratios in crudes with different viscosities (5, 25, 100 and 1000 cp) are presented in the same group of rocks mentioned previously. The results of this study help to understand the influence of viscosity and its impact in total recovery.
When are Two Algorithms the Same?
Authors: Blass Andreas , Dershowitz Nachum , Gurevich Yuri
Published: June 2009

People usually regard algorithms as more abstract than the programs that implement them. The natural way to formalize this idea is that algorithms are equivalence classes of programs with respect to a suitable equivalence relation. We argue that no such equivalence relation exists.
Borel Reductibility and Classification of von Neumann Algebras
Authors: Sasyk Román , Törnquist Asger
Published: June 2009

We announce some new results regarding the classification problem for separable von Neumann algebras. Our results are obtained by applying the notion of Borel reducibility and Hjorth's theory of turbulence to the isomorphism relation for separable von Neumann algebras.
Degrees of rigidity for Souslin trees
Authors: Fuchs Gunter , Hamkins Joel David
Published: June 2009

We investigate various strong notions of rigidity for Souslin trees, separating them under ⟡ into a hierarchy. Applying our methods to the automorphism tower problem in group theory, we show under ⟡ that there is a group whose automorphism tower is highly malleable by forcing.
On bounded arithmetic augmented by the ability to count certain sets of primes
Authors: Woods Alan R. , Cornaros Ch.
Published: June 2009

Over 25 years ago, the first author conjectured in [15] that the existence of arbitrarily large primes is provable from the axioms IΔ0(π) + def(π), where π(x) is the number of primes not exceeding x, IΔ0(π) denotes the theory of Δ0 induction for the language of arithmetic including the new function symbol π, and def(π) is an axiom expressing the usual recursive definition of π. We prove a modified version in which π is replaced by a more general function ξ that counts some of the primes below x (which primes depends on the values of parameters in ξ), and has the property that π is provably Δ0(ξ) definable.
Pure-injectivity and model theory for G-sets
Authors: Rajani Ravi , Prest Mike
Published: June 2009

In the model theory of modules the Ziegler spectrum, the space of indecomposable pure-injective modules, has played a key role. We investigate the possibility of defining a similar space in the context of G-sets where G is a group.
Low upper bounds of ideals
Authors: Kučera Antonín , Slaman Theodore A.
Published: June 2009

We show that there is a lowT-upper bound for the class ofK-trivial sets, namely those which are weak from the point of view of algorithmic randomness. This result is a special case of a more general characterization of ideals inT-degrees for which there is a lowT-upper bound.
Biphasic Insulin Aspart 30/70: Pharmacokinetics and Pharmacodynamics Compared With Once-Daily Biphasic Human Insulin and Basal-Bolus Therapy
Authors: Heise Tim , Heinemann Lutz , Hövelmann Ulrike , Brauns Bianca , Nosek Leszek , Haahr Hanne L. , Olsen Klaus J.
Published: June 2009

OBJECTIVE

Pharmacological profiles of biphasic insulin aspart 30/70 (BIAsp 30) once daily (OD), twice daily (b.i.d.), and three times daily (t.i.d.) were compared with other insulin regimens in two crossover glucose clamp studies of insulin-treated type 2 diabetic patients.

RESEARCH DESIGNS AND METHODS

Study 1 consisted of BIAsp 30 OD, b.i.d., and t.i.d. versus biphasic human insulin 30/70 (BHI 30), OD (n = 24). Study 2 examined BIAsp 30 t.i.d. versus basal-bolus therapy (insulin glargine OD plus insulin glulisine t.i.d.) (n = 24). Pharmacokinetics/pharmacodynamics (PK/PD) were investigated over 24 h.

RESULTS

Study 1: PK and PD were markedly different between BIAsp 30 OD and BHI 30 OD: the maximum insulin concentration and glucose infusion rate (GIR) were higher for BIAsp 30; time to maximum metabolism was 1.7 h sooner for BIAsp 30. Study 2: both regimens showed three distinct prandial-related GIR peaks. GIR 24-h area under the curve for BIAsp t.i.d. was higher than for basal-bolus therapy: 2,585.2 vs. 2,289.2 mg/kg.

CONCLUSIONS

BIAsp had pharmacological advantages over BHI. BIAsp t.i.d. had a similar PD profile to basal-bolus therapy.
Hypoglycemia Unawareness in Older Compared With Middle-Aged Patients With Type 2 Diabetes
Authors: Bremer Jan P. , Jauch-Chara Kamila , Hallschmid Manfred , Schmid Sebastian , Schultes Bernd
Published: June 2009

OBJECTIVE

Older patients with type 2 diabetes are at a particularly high risk for severe hypoglycemic episodes, and experimental studies in healthy subjects hint at a reduced awareness of hypoglycemia in aged humans. However, subjective responses to hypoglycemia have rarely been assessed in older type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

We tested hormonal, subjective, and cognitive responses (reaction time) to 30-min steady-state hypoglycemia at a level of 2.8 mmol/l in 13 older (≥65 years) and 13 middle-aged (39–64 years) type 2 diabetic patients.

RESULTS

Hormonal counterregulatory responses to hypoglycemia did not differ between older and middle-aged patients. In contrast, middle-aged patients showed a pronounced increase in autonomic and neuroglycopenic symptom scores at the end of the hypoglycemic plateau that was not observed in older patients (both P < 0.01). Also, seven middle-aged patients, but only one older participant, correctly estimated their blood glucose concentration to be <3.3 mmol/l during hypoglycemia (P = 0.011). A profound prolongation of reaction times induced by hypoglycemia in both groups persisted even after 30 min of subsequent euglycemia.

CONCLUSIONS

Our data indicate marked subjective unawareness of hypoglycemia in older type 2 diabetic patients that does not depend on altered neuroendocrine counterregulation and may contribute to the increased probability of severe hypoglycemia frequently reported in these patients. The joint occurrence of hypoglycemia unawareness and deteriorated cognitive function is a critical factor to be carefully considered in the treatment of older patients.
Adherence to the DASH Diet Is Inversely Associated With Incidence of Type 2 Diabetes: The Insulin Resistance Atherosclerosis Study
Authors: Liese Angela D. , Nichols Michele , Sun Xuezheng , D'Agostino Ralph B. , Haffner Steven M.
Published: June 2009

OBJECTIVE

The Dietary Approaches to Stop Hypertension (DASH) diet has been widely promoted; however, little is known about its impact on type 2 diabetes.

RESEARCH DESIGN AND METHODS

We evaluated the association of the DASH diet with incidence of type 2 diabetes among 862 participants of the Insulin Resistance Atherosclerosis Study (IRAS) who completed a 1-year food frequency questionnaire at baseline. Type 2 diabetes odds ratios (ORs) were estimated at tertiles of the DASH score.

RESULTS

An inverse association was observed in whites (tertile 2 vs. tertile 1, OR 0.66 [95% CI 0.29–1.48]) that became significant for the most extreme contrast (tertile 3 vs. tertile 1, 0.31 [0.13–0.75]), with adjustment for covariates. No association was observed in blacks or Hispanics (tertile 2 vs. tertile 1, 1.16 [0.61–2.18 ]; tertile 3 vs. tertile 1, 1.34 [0.70–2.58 ]).

CONCLUSIONS

Adherence to the DASH dietary pattern, which is rich in vegetables, fruit, and low-fat dairy products, may have the potential to prevent type 2 diabetes.
Changes in Basal Insulin Infusion Rates With Subcutaneous Insulin Infusion
Authors: Heinemann Lutz , Nosek Leszek , Kapitza Christoph , Schweitzer Matthias-Axel , Krinelke Lars
Published: June 2009

OBJECTIVE

Evaluation of the time required until a change in the basal insulin infusion rate with an insulin pump induces subsequent changes in the metabolic effect.

RESEARCH DESIGN AND METHODS

In this euglycemic glucose clamp study, 10 male subjects with type 1 diabetes received three different subcutaneous insulin infusion rates (0.5, 1.0, and 2.0 units/h; for 4 h each) of insulin lispro (IL) with insulin pumps.

RESULTS

An increase in insulinemia occurred within 15–30 min after changing the infusion rate. While the serum IL levels reached a steady state at the end of the infusion period, the glucose infusion rates did not always reach steady-state levels with the higher infusion rates. However, an increase in the glucose consumption occurred within 30–60 min after switching the infusion rate.

CONCLUSIONS

Several hours are required until a new steady state in the metabolic effect is achieved after a significant change in basal insulin infusion.
Xenotime-(Y) veins in a Neoproterozoic metamudstone (Małopolska Block, S Poland)
Authors: Stanisławska Maja , Michalik Marek
Published: May 2009

Xenotime-(Y) veins in a Neoproterozoic metamudstone (Małopolska Block, S Poland)

First occurrence of xenotime-(Y) veins in the Neoproterozoic metamudstone, NW margin of the Małopolska Block, is reported here. The veins are <5 μm thick, inhomogeneous and of varied morphology. Their textural characteristics, exhibiting very low U and Th contents (<1 wt%) and relatively high heavy rare earth elements (REE) contents (12-24 REE2O3 wt%), suggest hydrothermal genesis, though diagenetic precursors of the veins are not excluded. The veins provide good evidence of the mobility of Y, REE, U and Th in low-temperature conditions (anchimetamorphic to greenschist facies). The observed differences in the chemical composition of the veins may indicate multiple stages of formation, possibly during several hydrothermal events that affected the area.
Fossil fuels, ore and industrial minerals
Authors: Sawlowicz Zbigniew
Published: May 2009

Fossil fuels, ore and industrial minerals
A comparison of hinge craniotomy and decompressive craniectomy for the treatment of malignant intracranial hypertension: early clinical and radiographic analysis
Authors: Kenning Tyler J. , Gandhi Ravi H. , German John W.
Published: June 2009

Object

Hinge craniotomy (HC) has recently been described as an alternative to decompressive craniectomy (DC). Although HC may obviate the need for cranial reconstruction, an analysis comparing HC to DC has not yet been published.

Methods

A retrospective review was conducted of 50 patients who underwent cranial decompression (20 with HC, 30 with DC). Baseline demographics, neurological examination results, and underlying pathology were reviewed. Clinical outcome was assessed by length of ventilatory support, length of intensive care unit stay, and survival at discharge. Control of intracranial hypertension was assessed by average daily intracranial pressure (ICP) for the duration of ICP monitoring and an ICP therapeutic intensity index. Radiographic outcomes were assessed by comparing preoperative and postoperative CT scans for: 1) Rotterdam score; 2) postoperative volume of cerebral expansion; 3) presence of uncal herniation; 4) intracerebral hemorrhage; and 5) extraaxial hematoma. Postoperative CT scans were analyzed for the size of the craniotomy/craniectomy and magnitude of extracranial herniation.

Results

No significant differences were identified in baseline demographics, neurological examination results, or Rotterdam score between the HC and DC groups. Both HC and DC resulted in adequate control of ICP, as reflected in the average ICP for each group of patients (HC = 12.0 ± 5.6 mm Hg, DC = 12.7 ± 4.4 mm Hg; p > 0.05) at the same average therapeutic intensity index (HC = 1.2 ± 0.3, DC = 1.2 ± 0.4; p > 0.05). The need for reoperation (3 [15%] of 20 patients in the HC group, 3 [10%] of 30 patients in the DC group; p > 0.05), hospital survival (15 [75%] of 20 in the HC group, 21 [70%] of 30 in the DC group; p > 0.05), and mean duration of both mechanical ventilation (9.0 ± 7.2 days in the HC group, 11.7 ± 12.0 days in the DC group; p > 0.05) and intensive care unit stay (11.6 ± 7.7 days in the HC group, 15.6 ± 15.3 days in the DC group; p > 0.05) were similar. The difference in operative time for the two procedures was not statistically significant (130.4 ± 71.9 minutes in the HC group, 124.9 ± 63.3 minutes in the DC group; p > 0.05). The size of the cranial defect was comparable between the 2 groups. Postoperative imaging characteristics, including Rotterdam score, also did not differ significantly. Although a smaller volume of cerebral expansion was associated with HC (77.5 ± 54.1 ml) than DC (105.1 ± 65.1 ml), this difference was not statistically significant.

Conclusions

Hinge craniotomy appears to be at least as good as DC in providing postoperative ICP control and results in equivalent early clinical outcomes.
Crossed-screw fixation of the unstable thoracic and lumbar spine
Authors: Benzel Edward C. , Baldwin Nevan G.
Published: June 2009

✓ An ideal spinal construct should immobilize only the unstable spinal segments, and thus only the segments fused. Pedicle fixation techniques have provided operative stabilization with the instrumentation of a minimal number of spinal segments; however, some failures have been observed with pedicle instrumentation. These failures are primarily related to excessive preload forces and limitations caused by the size and orientation of the pedicles.

To circumvent these problems, a new technique, the crossed-screw fixation method, was developed and is described in this report. This technique facilitates short-segment spinal fixation and uses a lateral extracavitary approach, which provides generous exposure for spinal decompression and interbody fusion. The technique employs two large transverse vertebral body screws (6.5 to 8.5 mm in diameter) to bear axial loads, and two unilateral pedicle screws (placed on the side of the exposure) to restrict flexion and extension deformation around the transverse screws and to provide three-dimensional deformity correction. The horizontal vertebral body and the pedicle screws are connected to rods and then to each other via rigid crosslinking. The transverse vertebral body screws are unloaded during insertion by placing the construct in a compression mode after the interbody bone graft is placed, thus optimizing the advantage gained by the significant “toe-in” configuration provided and further decreasing the chance for instrumentation failure.

The initial results of this technique are reported in a series of 10 consecutively treated patients, in whom correction of the deformity was facilitated. Follow-up examination (average 10.1 months after surgery) demonstrated negligible angulation. Chronic pain was minimal. The crossed-screw fixation technique is biomechanically sound and offers a rapid and safe form of short-segment three-dimensional deformity correction and solid fixation when utilized in conjunction with the lateral extracavitary approach to the unstable thoracic and lumbar spine. This approach also facilitates the secure placement of an interbody bone graft.
Wound healing in trophic ulcers in spina bifida patients
Authors: Srivastava Vinod Kumar
Published: June 2009

✓ Eight cases of tethered conus medullaris with trophic ulcers in the foot in spina bifida patients are presented. The ulcers, which had remained unhealed for 1 to 8 years prior to surgery, healed in a few weeks after the tethered conus was released. The possibility of some neurotrophic factor in wound healing is suggested.
Timing of postoperative intracranial hematoma development and implications for the best use of neurosurgical intensive care
Authors: Taylor William A. S. , Thomas Nicholas W. M. , Wellings Julia A. , Bell B. Anthony
Published: June 2009

✓ This study records the incidence and timing of postoperative hematomas in neurosurgical patients and analyzes the best use of neurosurgical intensive care. In 2305 patients undergoing freehand or stereotactic biopsy, elective or emergency craniotomy, or posterior fossa surgery, 50 (2.2%) developed a hematoma. Clinical deterioration as a result of postoperative hematoma occurred within 6 hours of surgery in 44 patients and more than 24 hours after surgery in six patients. Although patients undergoing posterior fossa surgery or emergency craniotomy warrant longer periods of intensive-care observation, patients having elective supratentorial operations can safely be transferred to a neurosurgical ward for observation, provided they have regained their preoperative neurological status by 6 hours postsurgery.