bluuebunny/crossref_metadata_2025 huggingface dataset:
Preterm birth does not affect bone mineral density in young adults
Authors: Breukhoven Petra E , Leunissen Ralph W J , de Kort Sandra W K , Willemsen Ruben H , Hokken-Koelega Anita C S
Published: October 2010

Objective

Previous studies showed conflicting data on the effect of prematurity on bone mineral density (BMD) in infants and children. Only a few studies investigated the long-term effects of prematurity on BMD in early adulthood. The objective of our study was to assess the long-term effects of preterm birth on BMD of the total body (BMDTB), lumbar spine (BMDLS) and bone mineral apparent density of the LS (BMADLS).

Design

Cross-sectional study.

Methods

It consists of two hundred and seventy-six healthy subjects without serious postnatal complications, aged 18–24 years. The contribution of gestational age to the variance in BMD in young adulthood and the differences in BMD between 151 subjects born preterm (median gestational age 32.2 weeks (interquartile range (IQR) 30.3–34.0)) and 125 subjects born at term (median gestational age 40.0 weeks (IQR 39.0–40.0)) were investigated. BMD was determined by dual-energy X-ray absorptiometry.

Results

There were no significant linear correlations between gestational age and BMDTB(r=0.063,P=0.30), BMDLS(r=0.062,P=0.31) and BMADLS(r=0.069,P=0.26). Also after adjustment for possible confounders, gestational age was no significant contributor to the variance in BMDTB(P=0.27), BMDLS(P=0.91) and BMADLS(P=0.87). No significant differences were found between preterm and term subjects with regard to BMDTB, BMDLSand BMADLS.

Conclusion

In our cohort of 276 young adults, aged 18–24 years, gestational age was not a significant determinant in the variance of BMD. Preterm birth without serious postnatal complications is not associated with a lower BMD in young adulthood.
Sobre as origens das definições dos produtos escalar e vetorial
Authors: Menon M.J.
Published: October 2010

Nos livros-texto de física e de matemática utilizados em cursos básicos universitários, as operações de multiplicação de dois vetores (produtos escalar e vetorial) são introduzidas apenas como definições, sem nenhuma referência ou discussão a respeito das razões formais e/ou motivações que levaram ao estabelecimento de tais estruturas. Neste trabalho, apresentamos uma breve revisão didática sobre as origens dessas definições, discutindo os resultados pertinentes, formais, estabelecidos por Hamilton no contexto da álgebra de quatérnions e certas "adaptações" feitas por Gibbs e Heaviside, as quais deram origem ao ramo da matemática que hoje é popularmente conhecido como "álgebra vetorial". Comentamos algumas desvantagens decorrentes dessas "adaptações", fazendo referência a outros sistemas algébricos práticos e formalmente bem fundamentados (álgebras de Grassmann e Clifford). Indicamos e comentamos alguns artigos e trabalhos, básicos e também recentes, nos quais o assunto pode ser aprofundado.
Classical charge oscillations in nanoscopic systems
Authors: De Luca R. , Ganci S.
Published: October 2010

A single charge confined on the axis of a nanocylinder, carrying a charge of opposite sign, and two equal free classical charges on a conducting thin nanoring are two systems which can oscillate with frequencies in the THz domain. The potential energy obtained for the latter case can be generalized to n equal charges (n > 2). It can be shown that the n charges occupy positions on the ring corresponding to the n roots of unity at equilibrium.
Induction Chemotherapy for Head and Neck Cancer: Recent Data
Authors: Vokes Everett E.
Published: October 2010

The addition of chemotherapy to radiotherapy in the treatment of locally advanced squamous cell carcinoma of the head and neck (SCCHN) patients improves survival. Meta-analyses of randomized trials have indicated that the benefit of this approach is associated with the timing of chemotherapy administration. It has been demonstrated that the greatest survival benefit over locoregional treatment alone is seen with the concurrent administration of chemotherapy and radiotherapy. However, sequential chemotherapy administration, in the form of induction chemotherapy followed by radiotherapy or concurrent chemoradiotherapy, has been successful as a strategy for organ function preservation in patients with potentially resectable SCCHN. In addition, a meta-analysis of trials using platinum and 5-fluorouracil (PF)-containing induction regimens demonstrated a significant survival benefit for this approach over locoregional treatment alone in locally advanced disease. In recent years, the introduction of the taxanes into induction chemotherapy has provided physicians with more active regimens. The triplet combination induction regimen of docetaxel, cisplatin, and 5-fluorouracil has been shown to be more effective in prolonging survival than the doublet PF. Current trials are testing whether the addition of induction chemotherapy to standard concomitant chemoradiotherapy is superior to concomitant chemoradiotherapy alone.
Induction Chemotherapy Before Chemoradiotherapy in Locally Advanced Head and Neck Cancer: The Future?
Authors: Paccagnella Adriano , Mastromauro Cataldo , D'Amanzo Paola , Ghi Maria Grazia
Published: October 2010

There is increasing interest in the use of induction chemotherapy before concurrent chemotherapy and radiotherapy in the treatment of locally advanced head and neck cancer. A modest but significant improvement in survival has been observed with cisplatin and 5-fluorouracil (PF) induction before radiotherapy over that seen with radiotherapy alone. The addition of docetaxel to the PF regimen (TPF) appears to provide further survival benefits. The phase II part of a phase II/III trial compared three cycles of TPF induction chemotherapy before concomitant PF chemoradiotherapy with PF chemoradiotherapy alone in 101 patients with locally advanced stage III–IV head and neck cancer. The incidences of hematologic and nonhematologic toxicities during concurrent chemoradiotherapy were not higher in the TPF plus chemoradiotherapy group, and the feasibility of chemoradiotherapy was not compromised. Radiologically evaluated complete response rates at 6–8 weeks from the end of chemoradiotherapy (the primary endpoint) were 21% (95% confidence interval [CI], 11%–36%) with chemoradiotherapy alone and 50% (95% CI, 35%–65%; p = .004) with TPF plus chemoradiotherapy. A median overall survival time of 33.3 months and a 1-year survival rate of 78% were observed with chemoradiotherapy alone, whereas the median survival time was 39.6 months in the TPF plus chemoradiotherapy group, with a 1-year survival rate of 86%. To conclude, increasing evidence suggests that TPF induction chemotherapy improves clinical response and does not compromise subsequent chemoradiotherapy. The results of the ongoing phase III part of the phase II/III study should provide further information about the efficacy and safety of this approach for patients with locally advanced head and neck cancer.
TPF: A Rational Choice for Larynx Preservation?
Authors: Calais Gilles
Published: October 2010

For many years, the standard approach for the treatment of resectable squamous cell carcinoma of the head and neck was surgery, with or without subsequent radiotherapy. However, the morbidity associated with this approach, particularly for patients requiring total laryngectomy, can severely impair a patient's quality of life. The finding that patients whose tumors responded to chemotherapy showed a good response to subsequent radiotherapy opened up the possibility of a new organ-preserving management strategy for patients with resectable disease. Randomized studies demonstrated that induction chemotherapy with a cisplatin–5-fluorouracil (5-FU) doublet (PF) prior to radiotherapy enabled larynx preservation in a substantial proportion of patients, compared with surgery plus radiotherapy, without compromising survival. The benefit in terms of larynx preservation when using platinum-based doublet induction chemotherapy followed by radiotherapy, compared with concurrent chemotherapy and radiotherapy, is less clear, although the sequential approach appears to be better tolerated. Adding the taxane docetaxel to PF, to create the TPF triplet regimen, led to significantly higher larynx preservation and laryngectomy-free survival rates than with the PF doublet. TPF is now the accepted standard induction chemotherapy regimen for future clinical trials in resectable disease. Methods for improving postinduction treatment strategies are being explored.
Candidates for Larynx Preservation: The Next Step?
Authors: Lefebvre Jean-Louis
Published: October 2010

Nonsurgical treatment approaches to enable larynx preservation in patients who would otherwise undergo laryngectomy have evolved over recent years. Randomized trials have demonstrated that concurrent chemotherapy and radiotherapy is more effective than doublet cisplatin and 5-fluorouracil (5-FU) (PF)-based induction chemotherapy and radiotherapy in enabling larynx preservation. However, concurrent chemotherapy and radiotherapy is also associated with more toxicities than induction PF followed by radiotherapy. The triplet induction regimen of docetaxel, cisplatin, and 5-FU (TPF) is more effective than PF and is now considered to be the standard induction chemotherapy regimen for future larynx preservation trials. Manipulating the postinduction treatment regimen may help to improve larynx preservation rates, and possibly survival, and the use of concurrent chemoradiotherapy and radiotherapy plus the epidermal growth factor receptor inhibitor cetuximab has been investigated in this setting. Determining the most effective treatment approach for larynx preservation will involve conducting a trial comparing concurrent chemotherapy and radiotherapy with sequential TPF induction chemotherapy followed by either radiotherapy or cetuximab plus radiotherapy. Collaboration among international groups is required to assess which approach would be most beneficial in terms of larynx function preservation, disease control, and survival.
Increased primary production shifts the structure and composition of a terrestrial arthropod community
Authors: Wimp Gina M. , Murphy Shannon M. , Finke Deborah L. , Huberty Andrea F. , Denno Robert F.
Published: October 2010

Numerous studies have examined relationships between primary production and biodiversity at higher trophic levels. However, altered production in plant communities is often tightly linked with concomitant shifts in diversity and composition, and most studies have not disentangled the direct effects of production on consumers. Furthermore, when studies do examine the effects of plant production on animals in terrestrial systems, they are primarily confined to a subset of taxonomic or functional groups instead of investigating the responses of the entire community. Using natural monocultures of the salt marsh cordgrass Spartina alterniflora, we were able to examine the impacts of increased plant production, independent of changes in plant composition and/or diversity, on the trophic structure, composition, and diversity of the entire arthropod community. If arthropod species richness increased with greater plant production, we predicted that it would be driven by: (1) an increase in the number of rare species, and/or (2) an increase in arthropod abundance. Our results largely supported our predictions: species richness of herbivores, detritivores, predators, and parasitoids increased monotonically with increasing levels of plant production, and the diversity of rare species also increased with plant production. However, rare species that accounted for this difference were predators, parasitoids, and detritivores, not herbivores. Herbivore species richness could be simply explained by the relationship between abundance and diversity. Using nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM), we also found significant changes in arthropod species composition with increasing levels of production. Our findings have important implications in the intertidal salt marsh, where human activities have increased nitrogen runoff into the marsh, and demonstrate that such nitrogen inputs cascade to affect community structure, diversity, and abundance in higher trophic levels.
Palatability mapping: a koala's eye view of spatial variation in habitat quality
Authors: Moore Ben D. , Lawler Ivan R. , Wallis Ian R. , Beale Colin M. , Foley William J.
Published: October 2010

Ecologists trying to understand the value of habitat to animals must first describe the value of resources contained in the habitat to animals and, second, they must describe spatial variation in resource quality at a resolution relevant to individual animal foraging. We addressed these issues in a study of koalas (Phascolarctos cinereus) in a Eucalyptus woodland. We measured beneficial and deterrent chemical characteristics as well as the palatability of trees using a near‐infrared spectroscopic model based on direct feeding experiments. Tree use by koalas was influenced by tree size and foliar quality but was also context‐dependent: trees were more likely to be visited if they were surrounded by small, unpalatable trees or by large, palatable trees. Spatial autocorrelation analysis and several mapping approaches demonstrated that foliar quality is spatially structured in the woodland at a scale relevant to foraging decisions by koalas and that the spatial structure is an important component of habitat quality.
Nuclear-Magnetic-Resonance Petrophysics in Thin Sand/Shale Laminations
Authors: Minh Chanh Cao , Sundararaman Padmanabhan
Published: October 2010

We discuss the use of nuclear-magnetic-resonance (NMR) logging in the petrophysical evaluation of thin sand/shale laminations. NMR helps detect thin beds, determine fluid type, establish the hydrocarbon type and volume if hydrocarbon is present, and, finally, determine the permeability of the sand layers (as opposed to that of the sand/shale system).

Experiments were conducted on samples of 100% sand, 100% clay, and sand/clay layers with an NMR-logging tool at surface to verify the characteristic T2 bimodal relaxation distribution often observed in NMR logs that are acquired in thin beds. From the bimodal distribution, it is often possible to determine a cutoff to separate the productive sand layers from the shale layers and, with it, the porosity fraction of each component. Subsequently, the sand fraction, or net/gross ratio, can be estimated assuming that the 100%-sand porosity is known. Because gas, oil, and water have different NMR properties, fluid-typing techniques such as 2D NMR offer useful insights into the fluid type and properties in thin-layer sands. Because the laminations thickness is often less than the antenna aperture, the estimated permeability of the sand/ shale system will undercall the true permeability of the sand layers only. In this case, their permeability can be estimated quickly from Darcy's fluid-flow model.

We show examples of thin sand/shale laminations that are oil-bearing and gas-bearing. In each case, the NMR detection was verified against borehole-imaging logs, and the fluid type in the sands was determined from multidimensional NMR analysis. The derived hydrocarbon volume was then compared with the results estimated from a triaxial induction tool. Permeability of the sand layers was also computed and compared to that of nearby thick sands. Core data in one well was used to validate NMR detection, porosity, permeability, and net sand thickness.
Quantitative Analysis of Mud Losses in Naturally Fractured Reservoirs: The Effect of Rheology
Authors: Majidi R.. , Miska S.Z.. Z. , Yu M.. , Thompson L.G.. G. , Zhang J..
Published: October 2010

Significant fluid loss while drilling through fractured formations is a major problem for drilling operations. From field experience, we know that the type and rheological parameters of the drilling fluid have a strong impact upon the rate and volume of losses.

A mathematical model for Herschel-Bulkley [yield-power-law (YPL)] drilling-fluid losses in naturally fractured formations is presented. As a result, the effect of rheological properties of drilling fluid such as yield stress and shear-thinning/-thickening effect (flow-behavior index) on mud losses in fractured formations is investigated. We found that the yield stress can control the ultimate volume of losses while the shear-thinning effect can tremendously decrease the rate of losses. Therefore, mud losses in fractures can be minimized by optimizing the rheology of the drilling fluid properly.

The model also allows for quantitative analysis of losses that take into account fluid rheology to characterize the fractures. Hydraulic aperture of conductive fractures can be obtained by continuously monitoring mud losses and fitting field records of mud losses to the model. The proposed model is very useful not only for drilling applications but also for well-completion design and fractured-reservoir-characterization purposes. To examine the validity of the model, a practical application of the proposed technique is demonstrated through a field example of mud-loss measurements in a fractured well in the Gulf of Mexico.
Equation-of-State-Based Downhole Fluid Characterization
Authors: Zuo Julian Y. , Zhang Dan , Dubost Francois , Dong Chengli , Mullins Oliver C. , O’Keefe Michael , Betancourt Soraya S.
Published: October 2010

Downhole fluid analysis (DFA), together with focused-sampling techniques and wireline-formation-tester (WFT) tools, provides real-time measurements of reservoir-fluid properties such as the compositions of four or five hydrocarbon components/groups and gas/oil ratio (GOR). With the introduction of a new generation of DFA tools that analyze fluids at downhole conditions, the accuracy and reliability of the DFA measurements are improved significantly. Furthermore, downhole measurements of live-fluid densities are integrated into the new tools. Direct pressure and temperature measurements of the flowline ensure capture of accurate fluid conditions. To enhance these advanced features further, a new method of downhole fluid characterization based on the equation-of-state (EOS) approach is proposed in this work.

The motivation for this work is to develop a new approach to maximize the value of DFA data, perform quality assurance or quality control of DFA data, and establish a fluid model for DFA log predictions along with DFA fluid profiling. The basic inputs from DFA measurements are weight percentages of CO2, C1, C2, C3–C5 and C6+, along with live-fluid density and viscosity. A new method was developed in this work to delump and characterize the DFA measurements of C3–C5 (or C2–C5) and C6+ into full-length compositional data. The full-length compositional data predicted by the new method were compared with the laboratory-measured gas chromatograph data up to C30+ for more than 1,000 fluids, including heavy oil, conventional black oil, volatile oil, rich gas condensate, lean gas condensate, and wet gas. These fluids have a GOR range of 8–140,000 scf/STB and a gravity range from 9 to 50°API. A good agreement was achieved between the delumped and gas-chromatograph compositions.

In addition, on the basis of the delumped and characterized full-length compositional data, EOS models were established that can be applied to predict fluid-phase behavior and physical properties by virtue of DFA data as inputs. The EOS predictions were validated and compared with the laboratory-measured pressure/volume/temperature (PVT) properties for more than 1,000 fluids. The GOR, formation-volume factor, density, and viscosity predictions were in good agreement with the laboratory measurements. The established EOS model then was able to predict other PVT properties, and the results were compared with the laboratory measurements in good agreement.

Consequently, the established EOS models have laid a solid foundation for DFA log predictions in DFA fluid profiling, which has been integrated successfully with DFA measurements in real time to delineate compositional and asphaltene gradients in oil columns and to determine reservoir connectivity. The latter results are beyond the scope of this work and have been given in separate technical papers.
Stress Amplification and Arch Dimensions in Proppant Beds Deposited by Waterfracs
Authors: Warpinski N.R.. R.
Published: October 2010

Equations and a procedure have been developed to calculate the excess stress induced on a proppant dune that is deposited by a waterfrac with poor proppant-transport characteristics. This method also calculates the dimensions of an arch region that forms above the bed. Stresses on the proppant at the top of such a dune are much greater than usually considered because of the need to support a wide proppant bed and the arch, suggesting that crushing and embedment are likely. The arch region itself is an extremely-high-conductivity pathway that may provide overall benefit in terms of cleanup and production, but may also aid sand production.
Cementing Casing Strings Across Salt Zones: An Overview of Global Best Practices
Authors: Hunter Bill , Tahmourpour Farzad , Faul Ronnie
Published: October 2010

The global oil and gas industry is being challenged to increase production to meet the rising world energy demand. One of the key areas now being explored and developed to meet this demand are reserves below massive salt formations.

To reach these reserves, it is necessary to drill through and case off the salt. Casing and cementing operations in such salt zones can pose particular challenges, ranging from the effect of salt dissolution on cement-slurry properties to the potential dangers presented by salt creep to the integrity of the well and the need to plan for contingencies for potential zones of overpressure or lost circulation. This paper examines and explores the challenges inherent with cementing across salt zones in the global arena.

The current best practices for cementing casing strings across salt zones in some of the major subsalt basins of the world, including the North Sea and the Gulf of Mexico, are detailed and discussed.

This work should assist those tasked with the construction of wells that have to penetrate significant salt formations to achieve their objectives safely and reliably.
A Conceptual Study of Finger-Type Slug Catcher for Heavy-Oil Fields
Authors: Márquez J.. , Manzanilla C.. , Trujillo J..
Published: October 2010

The gas/liquid-separation processes in heavy- and extra-heavy-oil fields are performed mainly with gravity conventional separators. However, the separation efficiency of this equipment depends on the operating conditions, an appropriate design, and the properties of the fluids. Therefore, the separation efficiency is affected mainly by the high liquid viscosity, low pressures, and the low gas-flow rate that are present in heavy- and extra-heavy-oil fields. Additionally, these conditions increase the probability of slug-flow formation through pipelines, which causes operational problems, mainly in the separation process.

This situation raises the need to design a gas/liquid separator able to handle viscous liquid, reduce the effects of slug flow, and perform an efficient separation. There are different technologies that can help improve gas/liquid separation, among them the finger-type slug catcher. This technology is usually used in gas fields or light- and medium-oil fields as a flow conditioner and slug-flow mitigator. However, this paper has changed that focus toward considering a heavy-oil design.

This paper presents an improvement in the methodology of Sarica et al. (1990), predicting the dimensions of a finger-type slug catcher for heavy-oil fields. It is derived from the effect from the transition of stratified flow to nonstratified flow when the liquid phase is viscous and only considers slug-flow characteristics under normal flow; on the basis of the improvement, the required diameter and length of the finger are determined.

This improvement is used to design a finger-type slug catcher for heavy-oil fields in the Orinoco belt. An economic comparison against conventional separators is presented, demonstrating the finger-type slug catcher to be more economical than the conventional separator.
Upscaling of Miscible Floods in Heterogeneous Reservoirs Considering Reservoir Mixing
Authors: Garmeh Gholamreza , Johns Russell T.
Published: October 2010

Inaccurate modeling of reservoir mixing by using large gridblocks in compositional simulation can affect recoveries significantly in miscible gasfloods and lead to inaccurate predictions of recovery performance. Reservoir mixing or dispersion is caused by diffusion of particles across streamlines; mixing can be enhanced significantly if the surface area of contact between the reservoir and injected fluid is increased as fluids propagate through the reservoir. A common way to convert geological models into simulation models is to upscale permeabilities on the basis of reservoir heterogeneity. Upscaling affects the degree of mixing that is modeled, but the importance of reservoir mixing in upscaling is largely ignored. This paper shows how to estimate the level of mixing in a reservoir and how to incorporate mixing into the upscaling procedure.

We derive the key scaling groups for first-contact miscible (FCM) flow and show how they have an impact on reservoir mixing. Heterogeneities are assumed to dominate the flow regime so that gravity effects are negligible. We examine only local mixing, not apparent mixing caused by variations in streamline path lengths (convective spreading). Local mixing is important because it affects the strength of the injected fluid and can cause an otherwise multicontact miscible (MCM) flood to become immiscible. More than 1,000 2D numerical simulations are carried out using experimental design to estimate dispersivity as a function of the derived scaling groups.

We show that reservoir mixing is enhanced owing to fluid propagation through heterogeneous media. Because mixing is dependent on heterogeneities, upscaling is an iterative process in which the level of mixing in both the longitudinal and transverse directions must be matched from the fine to the coarse scale. The most important groups that affect mixing are the mobility ratio, dispersion number, correlation lengths, and the Dykstra-Parson coefficient. Large dispersion numbers yield greater dispersivities away from the injection well. We show through simulations of both FCM and MCM floods that gridblock size can be increased significantly when reservoir mixing is large. Heterogeneous reservoirs with large longitudinal correlation lengths can be upscaled to larger gridblocks than reservoirs with random permeability fields. This paper shows how to determine a priori the maximum gridblock size allowed in both the x- and z-directions to predict the oil recovery from miscible gasfloods accurately.
Application of After-Closure Analysis to a Dual-Porosity Formation, to CBM, and to a Fractured Horizontal Well
Authors: Soliman M.Y.. Y. , Miranda Carlos , Wang Hong Max
Published: October 2010

Published techniques for after-closure analysis of fracturing data usually assume the presence of a vertical fracture intersecting a vertical well. In addition, these published techniques usually assume that the formation is homogeneous. When the formation is naturally fractured or the well is horizontally intersecting a transverse vertical fracture, those assumptions are obviously violated and the published analysis techniques might not be applicable. Through the use of analytical and numerical solutions and application to actual field data, this paper investigates the analysis of after-closure data for heterogeneous formations, a naturally fractured formation, a CBM, and a fractured horizontal well.

This paper briefly reviews the various available techniques for after-closure analysis, pointing out the strengths and weaknesses of each. An analytical solution for an injection-falloff test for a naturally fractured formation has been developed and is presented. This solution might be used to analyze data for a minifrac test in a naturally fractured formation where the fracture has healed. Numerical simulation validated the developed solution for a fracture that has healed. The same numerical simulator was used to expand the solution to a situation where the fracture maintains residual conductivity.

The solution for a minifrac test in the case of a transverse fracture is also presented and discussed. Using a numerical simulator, minifrac tests are simulated and analyzed for both heterogeneous formations and fractured horizontal wells. Guidelines for the analysis of such data have been developed and presented.

Field data are also presented. One case presents a minifrac test for a heterogeneous formation. A case for a transverse fracture intersecting a horizontal well is also presented and analyzed. A third case for CBM is discussed.
MEOR Success in Southern Saskatchewan
Authors: Town K.. , Sheehy A.J.. J. , Govreau B.R.. R.
Published: October 2010

A microbial enhanced-oil-recovery (MEOR) process was successfully applied in a mature waterflooded reservoir in Saskatchewan, Canada. A nutrient solution, which was designed specifically for this reservoir to stimulate indigenous microbes to grow, multiply, and help to release oil, was tested and piloted. A significant decrease in water cut and increase in oil production have been realized through the selective stimulation of bacteria using nutrient injection.

The field is a mature waterflood averaging more than 95% water cut. To combat the increasing water-cut issue, an in-situ microbial response analysis (ISMRA) was performed on a typical high-water-cut producer in the area. The test well was treated with a nutrient solution and then was shut in for a number of days to allow indigenous microbes to grow and multiply. Upon return to production, the well produced at an average of 200% more oil with a 10% decrease in water cut for a year. Pretreatment rates averaged 1.2 m3/d of oil (8 BOPD) and post-ISMRA treatment daily production peaked at 4.1 m3/d of oil (26 BOPD). The ISMRA provides a direct support of laboratory studies and frequently increases oil production.

As a result of the successful ISMRA, a pilot project was initiated and the nutrients were applied in three batch treatments on an injector with three offset production wells. Three weeks after the first batch treatment, a water-cut decrease was seen at one of the offset producers. This well's oil production gradually increased from 1.4 to more than 8 m3/d (9 to 50 B/D). Oil production in another producer doubled from 1.5 to more than 3.0 m3/d (9 to 19 B/D). Subsequent treatments were tried on marginally economic wells and on a reactivated idle producer. The average decrease in water cut in these wells was more than 10%. On the idle well, oil production increased from 0.5 m3/d (3 B/D) pretreatment to an average of 3.0 m3/d (19 B/D) post-treatment.

Throughout the world, there remains a huge target for enhanced-oil-recovery (EOR) processes to target (Bryant 1991). This successful MEOR application will have a tremendous impact on ultimate recovery in many of these reservoirs not only through an increase in production, but a decrease in operating costs through associated reduction in lifting costs with less water production.
Comprehensive Model for Flow Behavior of High-Performance-Fracture Completions
Authors: Zhang Y.. , Marongiu-Porcu M.. , Ehlig-Economides C.A.. A. , Tosic S.. , Economides M.J.. J.
Published: October 2010

Experience shows that high-performance fractures (HPFs) may retain near-unit-flow efficiency (equivalent to zero skin in a vertical well) and rarely fail, even in highly deviated wells. This may be partly because overly simplistic models of the well flow behavior lead operators to maintain wells at lower production rates than could have been achieved for the same amount of injected proppant with a vertical-well-completion design. Rigorous models that account for widely accepted rock-mechanics fundamentals indicate that the fracture-to-well connection is compromised in deviated wells and lead to questions concerning whether the bulk of the flow to the well actually passes through the fracture.

Distributed volumetric sources are used in this model to rigorously model a wide variety of possible fracture geometries such as an expanded wellbore because of halo effect, flow strictly through the fracture, and combined flow through a single fracture and to remaining flowing perforations not connected to the fracture. The model also includes turbulent-flow effects that may occur for radial-flow conditions in the fracture plane or in the reservoir opposite wellbore sections not connected to the fracture, along with high-velocity flow through the perforation tunnels. It also computes the effective flow area at the resulting face between the reservoir and the completion to check whether flow velocity exceeds conditions that would risk production of reservoir fines, and it estimates the screen-flow velocity on the basis of the number of flowing perforations.

This comprehensive view of the HPF completion enables a thorough analysis of the risks of flowing the well at high rate. Field examples show that the new model depicts real field conditions in calculating the total skin, flow fractions, and the flux for HPF completions in high-rate gas and oil wells.

Complete inflow-performance behavior for likely flow patterns for HPF wells in oil and gas reservoirs is provided.
A Practical Method for Minimum-Miscibility-Pressure Estimation of Contaminated CO2 Mixtures
Authors: Johns R.T.. T. , Ahmadi Kaveh , Zhou D.. , Yan M..
Published: October 2010

Minimum miscibility pressure (MMP) is a key parameter in the design of gasfloods. Injection-gas compositions often vary during the life of a gasflood owing to reinjection and mixing of fluids in situ. Understanding the impact of the gas compositional changes on the MMP is essential to optimal design of fieldwide pressure management and carbon dioxide (CO2) use. Determining the MMP by slimtube or other methods for each possible variation in the gas-mixture composition is impractical. This paper gives an easy and accurate way to determine impure CO2 MMPs for variable field solvent compositions on the basis of just a few MMPs. Alternatively, the approach could be used to estimate the enrichment level required to lower the MMP to a desired pressure.

The MMP-estimation method relies on determining the MMP for pure CO2 injection, and also for a few impure binary MMPs at small CO2-contaminant levels. The number of MMPs needed for the method is equal to the number of components in the injection gas. We use the method of characteristics (MOC) and our newly developed mixing-cell method to estimate the required MMPs, although any reliable MMP analytical or experimental method can be used. We demonstrate how to calculate MMPs for several multicomponent oils displaced by CO2 contaminated by mixtures of N2, CH4, C2, C3, and H2S. The results show that the predicted MMPs for a west Texas crude displaced by contaminated-CO2 injection streams are nearly linear over the range from pure-CO2 injection to any mole fraction combination of the five contaminants. The accuracy of the predicted MMPs is within ±15 psia of that from calculations using mixing-cell simulations, slimtube simulations, and slimtube experiments where available. For another example oil displacement by impure CO2, however, the linear trend in MMPs with contamination mole fractions is accurate only for total contamination levels less than approximately 20% mole fraction, but this is still within a useful range for CO2-gasflood design and optimization. We also examine the sensitivity of local displacement efficiency to dispersion for binary gas mixtures using 1D simulation.
A Crosslinkable Synthetic-Polymer System for High-Temperature Hydraulic-Fracturing Applications
Authors: Holtsclaw Jeremy , Funkhouser Gary P.
Published: October 2010

A new hydraulic-fracturing fluid has been developed that is capable of reaching fluid service temperatures up to 232°C. This fracturing fluid technology uses a synthetic polymer that is crosslinkable with metal ions to generate high viscosity. The synthetic-polymeric fracturing gel overcomes the thermal limitations of traditional guar and derivatized guar-based fracturing fluids. Several advancements have been made in the development of this technology to maximize the efficiency of crosslinking and to give an effective breaking profile, resulting in good laboratory gel cleanup in the proppant pack. Research efforts have yielded a fracturing fluid with good fluid stability at high temperatures to create better proppant transport and placement in these most-demanding environments.

An integral part of this fluid is a crosslinking system that can be "tuned" for crosslinking onset from 38 to 138°C, allowing for optimization for particular well conditions. The crosslinking system allows the treatment schedule to be tailored to the targeted well to help minimize frictional pressure loss. An efficient and effective oxidative-breaker package has been developed to give a controlled rheological break for the synthetic fluid and provide good regained conductivity data. The new, high-temperature fracturing technology provides a new tool to stimulate hotter, deeper hydrocarbon resources to help maximize hydrocarbon recovery. This fracturing-fluid system has been applied successfully in south Texas at temperatures approaching 232°C.

Laboratory rheological data that demonstrate fluid stability, crosslinking performance, and controlled fluid breaks are presented. Dynamic fluid-loss and regained-conductivity data are also presented to illustrate fluid cleanup in proppant packs.
Gas-Reserves Estimation in Resource Plays
Authors: Lee John , Sidle Rod
Published: October 2010

The petroleum industry's lack of understanding of physical properties and the physics controlling production from many important resource plays limits its ability to model and forecast with confidence production and reserves from these resources in many cases. While measurement technology and modeling accuracy is improving, the industry is often forced to resort to empirical methods that lack the usual validation required for high confidence in results. This paper analyzes some of the procedures in common use for forecasting and identifies some limitations in the techniques. Advances in the industry's ability to forecast future production (and thus estimate reserves) more accurately in resource plays will impact financial forecasts, perceived asset values, and accuracy of reserves disclosed to the public.
New Developments in the Analysis of Scale Inhibitors
Authors: Boak L.S.. S. , Sorbie K.S.. S.
Published: October 2010

Scale inhibitors (SIs) are used to control oilfield scale formation, and the ability to analyze these species is very important such that SI concentrations as low as 0.5-ppm active need to be measured accurately. If phosphorus is present in the SI molecule, then inductively-coupled-plasma (ICP) -based methods may be used for analysis. However, the oil industry's increasing requirement to be environmentally friendly means that polymeric "green" SIs are now being used more, which raises issues concerning detection techniques (i.e., ICP vs. wet-chemical techniques). ICP detection for SIs is generally easier, but if it cannot be used, then at least time-saving improvements to wet-chemical techniques are extremely beneficial.

In this paper, analytical approaches are described that have been used recently to improve chemical SI assay, especially at low near-threshold levels (a few ppm active of SI). Progress is reported in five areas of SI analysis: Assay of sulfonated copolymer (VS-Co) was not possible by straightforward analysis without extensive dialysis and sample preparation. However, calibrations and repeats of accuracy similar to that of the C18 were found for VS-Co using amino-propyl (NH2) cartridges and the Hyamine method.The Oasis® 2×4 method has been applied to SI analysis, and this is able to assay all types of polymeric SIs in principle. This method has been used to detect a VS-Co SI in a wide variety of different brine salinities from distilled water (DW) to high-salinity formation waters (FW) (e.g., a Heron-type FW). Although achievable under these different conditions, there was a significant decrease in the absorbance signals recorded with increasing salinity that was not significantly improved by a higher-capacity sorbent cartridge.Various elements have been assayed in the oil phase using the ICP method. Calibrations and accurate repeats within 5 to 10% error were achieved. After solving compatibility issues, the concentration of an oil-tolerant SI was determined successfully using calibrations and accurate repeats over a range of 0 to 10 ppm and 0 to 2,500 ppm active SI.A matrix-matching Hyamine technique has been developed that allows any chloride-ion effects on the chelating process between the Hyamine and SI to be negated, allowing accurate analysis of low-polymeric SI concentrations.ICP and wet-chemical techniques have been able to accurately detect a P-tagged (phosphorus-tagged) copolymer-type SI. The ability to apply two independent analytical methods to a given species offers some important advantages when more than one SI is deployed in a field system. In this work, excellent correlation is observed between the wet-chemical and ICP assay methods for this P-tagged SI.

This study updates and adds to the set of analytical methods and procedures reported for SI analysis almost 20 years ago (Graham et al. 1993, 1995a, 1995b, 1996; Sorbie et al. 1992) and are described in our Flow Assurance and Scale Team (FAST) laboratory procedures manual (Sorbie and Boak 2006).
A Dynamic Simulation Study of Water Hammer for Offshore Injection Wells To Provide Operation Guidelines
Authors: Tang Yula , Ouyang Liang-Biao
Published: October 2010

In water injectors, rapid shut-in creates a water hammer. Water-hammer effects resulting from the shutting in of water-injection wells have a considerable impact on injection-well performance and longevity. Over time, injectors that undergo repeated rapid shut-ins often have significantly reduced injectivity and show evidence of sanding and even failure of the downhole completion. This study seeks to provide an operational reference for the well-injection operation and valve installation to mitigate backflow and maintain the downhole- sand-control-device integrity and thus good water injectivity.

Two different shut-in scenarios for an offshore injection system have been investigated. One of the scenarios is that two wells are shut in and the third well is kept open. The other scenario is that the topside pump is stopped while the injection wells are still kept open. Water-hammer sensitivity on different parameters, such as valve-installation position, stroke time, water-backflow conditions, and the hydraulic characteristics, has been performed.

For Scenario I, the pressure change because of the wellhead shut-in is approximately 200 psi at bottomhole, which is much lower than the amplitude seen at the wellhead (3,400 psi). The third well, which stays open for injection, experiences an even larger pressure surge (approximately 450 psi at bottomhole). Backflow for the opening well could be close to 10,000 STB/D. With increasing skin because of cumulative injectivity damage by water-particle plugging and thermal-induced fracture closure at shut-in, the water-hammer-pressure fluctuation can be as high as 1,200 psi. For Scenario II, pressure fluctuation because of topside shut-in is 300 psi. With the surface-controlled subsurface safety valve (SCSSV) closing when backflow is felt, the water-hammer fluctuation can be reduced to 200 psi.

Unlike the classic water hammer in pipelines, water hammer in injection wells is much less in surge amplitude because the high-injectivity reservoir behaves like a cushion to absorb the water-hammer impact on the downhole completion and sandcontrol infrastructure. Water hammer in the wells and pipeline system experiences (1) after-flow with reduced bottomhole pressure (BHP) and flow rate into formation, (2) backflow when BHP becomes less than reservoir pressure, and (3) resumption of water flow into reservoir when BHP starts to increase. This cyclic process continues with reduced amplitude in each cycle because of friction. A check valve set at the bottomhole could stop the backflow in less than 1 second. This study provides useful reference and operation guidelines on offshore water-injection and completion design consideration.
An Evaluation of Microseismic Monitoring of Lenticular Tight-Sandstone Stimulations
Authors: Warpinski N.R.. R. , Waltman C.K.. K. , Weijers L..
Published: October 2010

Microseismic monitoring in lenticular tight gas formations has a number of challenging issues associated with both analysis and interpretation. The heterogeneous nature of the reservoir and the typically small microseismic-event amplitudes make it essential to understand the limits of interpretation that should be applied in these reservoirs. With proper care, fracture lengths and azimuth, along with zonal coverage, are readily obtainable. However, fracture-height growth in these complex reservoirs needs to be assessed carefully. Microseismic data provide a level of self-quality-control potential through the use of a magnitude/distance assessment to guide interpretation and design. Hydraulic fractures observed in these reservoirs tend to be long, penetrating fractures that wander through the distributed/sand lenses, with modest height growth in most projects.
Permeability of Laboratory-Formed Methane-Hydrate-Bearing Sand: Measurements and Observations Using X-Ray Computed Tomography
Authors: Kneafsey Timothy J. , Seol Yongkoo , Gupta Arvind , Tomutsa Liviu
Published: October 2010

Methane hydrate was formed in two moist sands and a sand/silt mixture under a confining stress in an X-ray-transparent pressure vessel. Three initial water saturations were used to form three different methane-hydrate saturations in each medium. X-ray computed tomography (CT) was used to observe location-specific density changes caused by hydrate formation and flowing water. Gas-permeability measurements in each test for the dry, moist, frozen, and hydrate-bearing states are presented. As expected, the effective permeabilities (intrinsic permeability of the medium multiplied by the relative permeability) of the moist sands decreased with increasing moisture content. In a series of tests on a single sample, the effective permeability typically decreased as the pore space became more filled in the order of dry, moist, frozen, and hydrate-bearing. In each test, water was flowed through the hydrate-bearing medium and we observed the location-specific changes in water saturation using CT scanning. We compared our data to a number of models, and our relative permeability data compare most favorably with models in which hydrate occupies the pore bodies rather than the pore throats. Inverse modeling (using the data collected from the tests) will be performed to extend the relative permeability measurements.
Characterizing Natural-Fracture Permeability From Mud-Loss Data
Authors: Huang Jinsong , Griffiths D. V. , Wong Sau-Wai
Published: October 2010

Liétard et al. (1999, 2002) have provided important insight into the mechanism and prediction of transient-state radial mud invasion in the near-wellbore region. They provided type curves describing mud-loss volume vs. time that allow the hydraulic width of natural fractures to be estimated through a curve-matching technique. This paper describes a simpler and more direct method for estimating the hydraulic width by the solution of a cubic equation, with input parameters given by the well radius rw, the overpressure ratio Δp/τy, and the maximum mud loss volume (Vm)max.