bluuebunny/crossref_metadata_2025 huggingface dataset:
Meningitis in adult patients with a negative direct cerebrospinal fluid examination: value of cytochemical markers for differential diagnosis
Authors: Viallon Alain , Desseigne Nicolas , Marjollet Olivier , Birynczyk Albert , Belin Mathieu , Guyomarch Stephane , Borg Jacques , Pozetto Bruno , Bertrand Jean Claude , Zeni Fabrice
Published: June 2011

Introduction

The objective of this study was to determine the ability of various parameters commonly used for the diagnosis of acute meningitis to differentiate between bacterial and viral meningitis, in adult patients with a negative direct cerebrospinal fluid (CSF) examination.

Methods

This was a prospective study, started in 1997, including all patients admitted to the emergency unit with acute meningitis and a negative direct CSF examination. Serum and CSF samples were taken immediately on admission. The patients were divided into two groups according to the type of meningitis: bacterial (BM; group I) or viral (VM; group II). The CSF parameters investigated were cytology, protein, glucose, and lactate; the serum parameters evaluated were C-reactive protein and procalcitonin. CSF/serum glucose and lactate ratios were also assessed.

Results

Of the 254 patients with meningitis with a negative direct CSF examination, 35 had BM and 181, VM. The most highly discriminative parameters for the differential diagnosis of BM proved to be CSF lactate, with a sensitivity of 94%, a specificity of 92%, a negative predictive value of 99%, a positive predictive value of 82% at a diagnostic cut-off level of 3.8 mmol/L (area under the curve (AUC), 0.96; 95% confidence interval (CI), 0.95 to 1), and serum procalcitonin, with a sensitivity of 95%, a specificity of 100%, a negative predictive value of 100%, and a positive predictive value of 97% at a diagnostic cut-off level of 0.28 ng/ml (AUC, 0.99; 95% CI, 0.99 to 1).

Conclusions

Serum procalcitonin and CSF lactate concentrations appear to be the most highly discriminative parameters for the differential diagnosis of BM and VM.
Potential fields and their partial derivatives produced by a 2D homogeneous polygonal source: A summary with some revisions
Authors: Jia Zhen , Wu Shiguo
Published: June 2011

We summarized and revised the present forward modeling methods for calculating the gravity- and magnetic-field components and their partial derivatives of a 2D homogeneous source with a polygonal cross section. The responses of interest include the gravity-field components and their first- and second-order partial derivatives and the magnetic-field components and their first-order partial derivatives. The revised formulas consist of several basic quantities that are common in all the formulations. A singularity appears when the observation point coincides with a polygon vertex. This singularity is removable for the gravity formulas but not for the others. The compact forms of the revised formulas make them easy to implement. We compare the gravity- and magnetic-field components and their partial derivatives produced by a 2D prism whose polygonal cross section approximates a cylinder with the corresponding analytical fields and partial derivatives of the cylinder. The perfect fittings presented by both data sets confirm the reliability of the updated formulas.
LMO4 functions as a co-activator of neurogenin 2 in the developing cortex
Authors: Asprer Joanna S. T. , Lee Bora , Wu Chia-Shan , Vadakkan Tegy , Dickinson Mary E. , Lu Hui-Chen , Lee Soo-Kyung
Published: June 2011

The proneural protein neurogenin 2 (NGN2) is a key transcription factor in regulating both neurogenesis and neuronal radial migration in the embryonic cerebral cortex. However, the co-factors that support the action of NGN2 in the cortex remain unclear. Here, we show that the LIM-only protein LMO4 functions as a novel co-factor of NGN2 in the developing cortex. LMO4 and its binding partner nuclear LIM interactor (NLI/LDB1/CLIM2) interact with NGN2 simultaneously, forming a multi-protein transcription complex. This complex is recruited to the E-box containing enhancers of NGN2-target genes, which regulate various aspects of cortical development, and activates NGN2-mediated transcription. Correspondingly, analysis of Lmo4-null embryos shows that the loss of LMO4 leads to impairments of neuronal differentiation in the cortex. In addition, expression of LMO4 facilitates NGN2-mediated radial migration of cortical neurons in the embryonic cortex. Our results indicate that LMO4 promotes the acquisition of cortical neuronal identities by forming a complex with NGN2 and subsequently activating NGN2-dependent gene expression.
Polarity mediates asymmetric trafficking of the Gβ heterotrimeric G-protein subunit GPB-1 inC. elegansembryos
Authors: Thyagarajan Kalyani , Afshar Katayoun , Gönczy Pierre
Published: June 2011

Asymmetric cell division is an evolutionarily conserved process that gives rise to daughter cells with different fates. In one-cell stage C. elegans embryos, this process is accompanied by asymmetric spindle positioning, which is regulated by anterior-posterior (A-P) polarity cues and driven by force generators located at the cell membrane. These force generators comprise two Gα proteins, the coiled-coil protein LIN-5 and the GoLoco protein GPR-1/2. The distribution of GPR-1/2 at the cell membrane is asymmetric during mitosis, with more protein present on the posterior side, an asymmetry that is thought to be crucial for asymmetric spindle positioning. The mechanisms by which the distribution of components such as GPR-1/2 is regulated in time and space are incompletely understood. Here, we report that the distribution of the Gβ subunit GPB-1, a negative regulator of force generators, varies across the cell cycle, with levels at the cell membrane being lowest during mitosis. Furthermore, we uncover that GPB-1 trafficks through the endosomal network in a dynamin- and RAB-5-dependent manner, which is most apparent during mitosis. We find that GPB-1 trafficking is more pronounced on the anterior side and that this asymmetry is regulated by A-P polarity cues. In addition, we demonstrate that GPB-1 depletion results in the loss of GPR-1/2 asymmetry during mitosis. Overall, our results lead us to propose that modulation of Gβ trafficking plays a crucial role during the asymmetric division of one-cell stage C. elegans embryos.
Direct targets of theD. melanogasterDSXF protein and the evolution of sexual development
Authors: Luo Shengzhan D. , Shi Guang W. , Baker Bruce S.
Published: June 2011

Uncovering the direct regulatory targets of doublesex (dsx) and fruitless (fru) is crucial for an understanding of how they regulate sexual development, morphogenesis, differentiation and adult functions (including behavior) in Drosophila melanogaster. Using a modified DamID approach, we identified 650 DSX-binding regions in the genome from which we then extracted an optimal palindromic 13 bp DSX-binding sequence. This sequence is functional in vivo, and the base identity at each position is important for DSX binding in vitro. In addition, this sequence is enriched in the genomes of D. melanogaster (58 copies versus approximately the three expected from random) and in the 11 other sequenced Drosophila species, as well as in some other Dipterans. Twenty-three genes are associated with both an in vivo peak in DSX binding and an optimal DSX-binding sequence, and thus are almost certainly direct DSX targets. The association of these 23 genes with optimum DSX binding sites was used to examine the evolutionary changes occurring in DSX and its targets in insects.
A review on thromboangiitis obliterans pathophysiology: thrombosis and angiitis, which is to blame?
Authors: Fazeli Bahare , Rezaee Seyed Abdolrahim
Published: June 2011

A century has passed since thromboangiitis obliterans (TAO), or Buerger's disease, was first described, but the etiology remains unclear. It is still uncertain as to whether thrombosis or vascular inflammation is the first event. TAO is an episodic inflammatory and thrombotic-occlusive vascular disease of unknown origin. The involvement of the distal vessels and nerves within the neuro-vascular bundles occurs almost always in legs and occasionally in arms. The cumulative data demonstrate that at the cellular and molecular levels, at least four main components of inflammatory reactions, including endothelial cells, platelets, leukocytes and sensory neurons, might be involved in TAO pathogenesis. The interactions among these cells in an altered microenvironment of small- and medium-sized vessels may also orchestrate the onset of TAO events. In this review, the factors that may promote thrombosis and angiitis are reconsidered at three levels: (1) host characteristics such as male gender and genetic background; (2) probable triggers including cigarette smoking and infectious agents; and (3) environmental factors such as chronic anxiety and mental stress as a consequence of low socioeconomic status. At each level, the interactions among vascular endothelium, platelets, leukocytes and sensory neurons are discussed.
New Perspectives on Customer “Death” Using a Generalization of the Pareto/NBD Model
Authors: Jerath Kinshuk , Fader Peter S. , Hardie Bruce G. S.
Published: June 2011

Several researchers have proposed models of buyer behavior in noncontractual settings that assume that customers are “alive” for some period of time and then become permanently inactive. The best-known such model is the Pareto/NBD, which assumes that customer attrition (dropout or “death”) can occur at any point in calendar time. A recent alternative model, the BG/NBD, assumes that customer attrition follows a Bernoulli “coin-flipping” process that occurs in “transaction time” (i.e., after every purchase occasion). Although the modification results in a model that is much easier to implement, it means that heavy buyers have more opportunities to “die.”

In this paper, we develop a model with a discrete-time dropout process tied to calendar time. Specifically, we assume that every customer periodically “flips a coin” to determine whether she “drops out” or continues as a customer. For the component of purchasing while alive, we maintain the assumptions of the Pareto/NBD and BG/NBD models. This periodic death opportunity (PDO) model allows us to take a closer look at how assumptions about customer death influence model fit and various metrics typically used by managers to characterize a cohort of customers. When the time period after which each customer makes her dropout decision (which we call period length) is very small, we show analytically that the PDO model reduces to the Pareto/NBD. When the period length is longer than the calibration period, the dropout process is “shut off,” and the PDO model collapses to the negative binomial distribution (NBD) model. By systematically varying the period length between these limits, we can explore the full spectrum of models between the “continuous-time-death” Pareto/NBD and the naïve “no-death” NBD.

In covering this spectrum, the PDO model performs at least as well as either of these models; our empirical analysis demonstrates the superior performance of the PDO model on two data sets. We also show that the different models provide significantly different estimates of both purchasing-related and death-related metrics for both data sets, and these differences can be quite dramatic for the death-related metrics. As more researchers and managers make managerial judgments that directly relate to the death process, we assert that the model employed to generate these metrics should be chosen carefully.
Point of controversy: perioperative care of patients undergoing pheochromocytoma removal–time for a reappraisal?
Authors: Lentschener Claude , Gaujoux Sebastien , Tesniere Antoine , Dousset Bertrand
Published: June 2011

Adrenalectomy for pheochromocytoma is reported with a mortality close to zero in recent studies. The dogma of preoperative fluid and hypotensive drug administrations is widely applied in patients scheduled for pheochromocytoma removal and is assumed to have a beneficial effect on operative outcomes. This paradigm is only based on historical studies of non-standardized practices and criteria for efficacy, with no control group. Pre- and intraoperative hypovolemia have never been demonstrated in patients scheduled for pheochromocytoma removal. Recent improvements in outcome of patients undergoing adrenalectomy for pheochromocytoma could also be the result of improvement in surgical techniques and refinement in anesthetic practices. Whether better knowledge of the disease, efficiency of available intravenous short-acting vasoactive drugs, and careful intraoperative handling of the tumor make it possible to omit preoperative preparation in most patients scheduled for pheochromocytoma removal is presently questionable. We reviewed available literature in this respect.
Liver iron overload is associated with elevated SHBG concentration and moderate hypogonadotrophic hypogonadism in dysmetabolic men without genetic haemochromatosis
Authors: Gautier Alain , Lainé Fabrice , Massart Catherine , Sandret Laure , Piguel Xavier , Brissot Pierre , Balkau Beverley , Deugnier Yves , Bonnet Fabrice
Published: June 2011

Aims

To assess the relation between moderate iron overload on sex hormone binding globulin (SHBG) levels and gonadotroph function in men with dysmetabolic iron overload syndrome and the effects of phlebotomy.

Methods

The relationship between magnetic resonance imaging assessed liver iron concentration (LIC) and plasma ferritin levels with total testosterone, bioavailable testosterone (BT), SHBG and LH levels, were studied in 50 men with moderate dysmetabolic iron excess, in the absence of genetic haemochromatosis, who were randomised to phlebotomy therapy or to normal care.

Results

Four patients (8%) had low total testosterone (<10.4 nmol/l) and 13 patients (26%) had low BT (<2.5 nmol/l). In the entire population, those with LIC above the median (90 μmol/l) had a higher mean SHBG (P=0.028), lower LH (P=0.039) than those with LIC below the median. In multivariable analysis (adjusted for age, and fasting insulin) LIC was significantly associated with SHBG (positively) and LH (negatively). Patients in the highest quartile of SHBG had higher LIC (P=0.010) and higher ferritinaemia (P=0.012) than those in the three other quartiles. Iron depletion by venesection did not significantly improve any hormonal levels.

Conclusions

Hypogonadism is not infrequent in men with dysmetabolic iron overload syndrome. Liver iron excess is associated with increased plasma SHBG and moderate hypogonadotrophic hypogonadism. Phlebotomy therapy needs further investigation in symptomatic hypogonadal men with dysmetabolic iron excess.
Assessment of primary cancers in GH-treated adult hypopituitary patients: an analysis from the Hypopituitary Control and Complications Study
Authors: Child Christopher J , Zimmermann Alan G , Woodmansee Whitney W , Green Daniel M , Li Jian J , Jung Heike , Erfurth Eva Marie , Robison Leslie L
Published: June 2011

Objective

GH and IGFs have mitogenic properties, causing speculation that GH treatment could increase risk of malignancy. While studies in GH-treated childhood cancer survivors have suggested a slight increase in second neoplasms, studies in GH-treated adults have been equivocal.

Design

Incidence of de novo and second cancers was evaluated in 6840 GH-treated and 940 non GH-treated adult patients in the Hypopituitary Control and Complications Study pharmacoepidemiological database.

Methods

Evident cancer cases were evaluated in the main analysis, with sensitivity analyses including probable and possible cancers. Standardized incidence ratios (SIRs) for cancers were calculated using Surveillance, Epidemiology and End Results for the USA and GLOBOCAN for all other countries.

Results

During the mean follow-up of 3.7 years/GH-treated patient, 142 evident cancer cases were identified, giving an overall SIR of 0.88 (95% confidence interval (CI) 0.74–1.04); 95% CIs included the value of 1.0 for each country examined. The SIR for GH-treated patients from the USA (71 cases) was 0.94 (95% CI 0.73–1.18), and for non GH-treated patients from the USA (27 cases) was 1.16 (95% CI 0.76–1.69). For GH-treated patients from the USA aged <35 years, the SIR (six cases) was 3.79 (1.39–8.26), with SIR not elevated for all other age categories; SIR for patients from the USA with childhood onset (CO) GH deficiency (GHD) was 2.74 (95% CI 1.18–5.41). The SIR for colorectal cancer in GH-treated patients (11 cases) was 0.60 (95% CI 0.30–1.08).

Conclusions

With relatively short follow-up, the overall primary cancer risk in 6840 patients receiving GH as adults was not increased. Elevated SIRs were found for subgroups in the USA cohort defined by age <35 years or CO GHD.
Unacylated ghrelin is associated with changes in body composition and body fat distribution during long-term exercise intervention
Authors: Cederberg Henna , Rajala Ulla , Koivisto Vesa-Matti , Jokelainen Jari , Surcel Heljä-Marja , Keinänen-Kiukaanniemi Sirkka , Laakso Markku
Published: June 2011

Objective

Ghrelin, a gut–brain peptide involved in energy homeostasis, circulates predominantly (>90%) in unacylated form. Previous studies, however, have focused on total and acylated ghrelin, and the role of unacylated ghrelin (UAG) is not well understood. Particularly, the association of UAG with weight loss and changes in body composition in adults remains unclear. We hypothesized that exercise-associated increase in UAG level is associated with weight loss, favorable changes in body composition, and body fat distribution.

Design and methods

A prospective study of 552 young men (mean age 19.3 and range 19–28 years) undergoing military service with structured 6-month exercise training program. Exercise performance, body composition, and biochemical measurements were obtained at baseline and follow-up. Association between changes in UAG levels and body composition and body fat distribution were evaluated.

Results

An increase in UAG level during the exercise intervention was associated with reduced weight, fat mass (FM), fat percentage (fat %), and waist circumference, but not with fat-free mass. Inverse associations of changes in UAG level with changes in waist circumference and fat % were independent of weight at baseline, and changes in weight and exercise performance. Associations of changes in UAG level with waist circumference were significantly stronger than with fat % after the adjustment for confounding variables.

Conclusion

UAG is associated with changes in body weight and body composition during an intensive long-term exercise intervention in young men. The association of UAG levels with changes in central obesity was stronger than with total FM.
Behavior Outbursts, Orofacial Dyskinesias, and CSF Pleocytosis in a Healthy Child
Authors: Tamma Pranita D. , Agwu Allison L. , Hartman Adam L.
Published: June 2011

Anti–N-methyl-d-aspartate (NMDA) receptor encephalitis represents a new category of immune-mediated neurologic disorders. Viral encephalitis is often the presumptive diagnosis because of the acute neurologic changes, cerebrospinal fluid lymphocytic pleocytosis, and occasional hyperthermia. We report here the case of a previously healthy 7-year-old boy with new-onset aggressive behavior, seizure activity, and orofacial dyskinesias with cerebrospinal fluid and serum that tested positive for anti-NMDA receptors.
Prevalência de escoliose idiopática e variáveis associadas em escolares do ensino fundamental de escolas municipais de Cuiabá, MT, 2002
Authors: Espírito Santo Alcebíades do , Guimarães Lenir Vaz , Galera Marcial Francis
Published: June 2011

OBJETIVO: Estimar a prevalência de escoliose idiopática e variáveis associadas em escolares do ensino público fundamental. MÉTODOS: Estudo de corte transversal em duas fases, sendo a primeira nas salas de aula, com teste de Adams. Os que apresentaram Adams positivo foram convidados para a segunda fase, que constou de entrevista para fatores associados e exames para escoliose. Aqueles com teste confirmado nessa fase foram radiografados para escoliose e outras alterações. Para cálculo de prevalência utilizou-se, como ponto de corte, curvas > 5 e > 10 graus Cobb. RESULTADOS: Na primeira fase contaram-se 382 escolares com teste Adams positivo; destes, 210 compareceram para a segunda fase, sendo 142 com o teste confirmado. Comparando-se as variáveis idade, sexo e cor da pele, pelo teste de Qui-quadrado, do grupo das perdas (n = 172) com aqueles que atenderam ao convite (n = 210), não observamos diferenças com significância estatística, permitindo a validade para a amostra estudada (n = 3.105). A prevalência estimada de escoliose foi de 5,3% para curvas > 5 graus Cobb, e de 2,2% para curvas > 10 graus Cobb. Curva torácica foi observada em 44,8%, Risser grau 1 em 97,4% e 13,2% de rotação vertebral grau I. Observou-se significância estatística (p < 0,05) na associação de escoliose com atividade física. CONCLUSÃO: A prevalência estimada da escoliose, em nosso estudo, é comparável com aquelas descritas na literatura, e o seu diagnóstico e acompanhamento são importantes na promoção da saúde e prevenção de distúrbios mais graves.
Evaluation of Damage Mechanisms and Skin Factor in Tight Gas Reservoirs
Authors: Bahrami Hassan , Rezaee Reza , Ostojic Jakov , Nazhat Delair , Clennell Ben
Published: June 2011

Tight gas reservoirs normally have production problems due to very low matrix permeability and significant damage during well drilling, completion, stimulation and production. Therefore, they may not flow gas at optimum rates without advanced production improvement techniques.

The main damage mechanisms and the factors that have significant influence on total skin factor in tight gas reservoirs include mechanical damage to formation rock, plugging of natural fractures by mud solid particles invasion, relative permeability reduction around wellbore as a result of filtrate invasion, liquid leak-off into the formation during fracturing operations, water blocking, skin due to wellbore breakouts, and the damage associated with perforation. Drilling and fracturing fluids invasion mostly occurs through natural fractures and may also lead to serious permeability reduction in the rock matrix that surrounds the natural or hydraulic fractures.

This study represents evaluation of different damage mechanisms in tight gas formations, and examines the factors that can have significant influence on total skin factor and well productivity. Reservoir simulation was carried out based on a typical West Australian tight gas reservoir in order to understand how well productivity is affected by each of the damage mechanisms such as natural fractures plugging, mud filtrate invasion, water blocking and perforation.
Prediction and Localisation of Erosion Prone Areas along Non-Compliant Sand Control Completions
Authors: Tovar J. , Zheng Y. , McDonald L.
Published: June 2011

Sandface completions such as standalone screen completions have suffered from erosion problems for many years. A significant amount of catastrophic screen failures are considered to be the result of high velocities of solid's laden hydrocarbons creating hot spot areas in the interface between the sandface and the completion. Previous researchers investigated the change in permeability of failed rock into annular gaps generated in non-compliant sand control completions and identified that packed material in this space can result in severe distortion to flow patterns and restrictions. This paper describes the development and testing process for a new methodology that allows identification of the erosion prone areas in the annular space between the sandface and the screen. Detailed investigation, supported by laboratory testing, reviewed oil and gas well conditions at the startup, during a cleanout and after hydrocarbon's production have been stabilised. Radial flow, mode of sand collapse, compaction, voidage, sand quality and formation petro-physical properties were tested and analysed using high and low pressure flow cells in order to quantify the changes in pressure drops through the collapsed rock material. The results indicated that flow rate, viscosity, voidage, grain shape and volume are the main contributors to the variations in pressure drops across failed sand material in the annular space. On the basis of these tests, a continuous (foot-by-foot) analytical model was developed that allows identification of the specific location and variation in pressure drops across the annular packed material for oil and gas wells. The model is composed of five (5) main elements; a reservoir inflow module, a fluid drag module, a grain size and volume module, a pressure drop module and an erosion prediction module. The model was tested using data from a North Sea field and the results, algorithms and field samples will be discussed and presented in detail.
The Application of Sand Jet Perforation in Multistage Hydraulic Fracturing Treatments in Volcanic Reservoir India
Authors: Aora Gaurav , Stolyorov Sergey , Gupta Anish , Purusharthy Naresh , Mathur Mohit , Singh Ratan
Published: June 2011

The Raageshwari gas field is a relatively deep (3000m) unconventional volcanic reservoir with a gas column in excess of 800 m. Gas from the Raageshwari field is used to generate energy for production of waxy, high-pour-point crude in the nearby Mangala, Bhagyam and Aishwariya fields (which were discovered in January 2004) in Barmer basin, Western Rajasthan, India (Figures 1, 2). The gas reservoir has inherently low permeability, and hydro-fracturing treatment is essential for optimum production from the field. A series of hydro-fracturing operations have been carried out on the field and treatments optimized over a period of time. A recent fracturing campaign implemented a shift in perforation methodology from conventional e-line perforation to peroration using sand jetting through coiled tubing. This paper discusses the challenges that had been associated with hydro-fracturing work in the field and benefits achieved with sand-jet perforation technology.
Effect of Initial HCl Concentration on the Performance of New VES Acid System
Authors: Wang Guanqun , Gomaa Ahmed M. , Nasr-El-Din Hisham A.
Published: June 2011

Viscoelastic surfactant (VES) based self-diverting acid system has been developed for better matrix treatment of carbonate formations. Literature survey indicates that the highly viscous fluid acts as a temporary barrier to reduce further fluid loss into the wormholes and allows complete stimulation of all treating zones. After acid treatment, the viscous fluid is broken by either formation hydrocarbons or pre-flush fluids. However, recent lab work confirmed that a significant amount of surfactant was retained inside the core even when mutual solvent was used. The present study was conducted to better understand these acid systems and determine factors that impact their viscosity build-up and performance inside the carbonate formations.

A series of coreflood tests were conducted using carbonate cores at different injection rates. Propagation of the acid, surfactant, and reaction products inside the cores was examined in detail. Samples of the core effluent were collected and the concentrations of calcium, surfactant, and acid were measured. Permeability enhancement and location of any precipitation was detected using CT scanner to the core before and after the acid injection. Material balance was conducted to determine the amount of surfactant that retained in the core.

Experimental results show that VES acid was not able to buildup pressure drop across the core when it was injected inside 70 md permeability cores at various acid concentrations and injection rates when only one fourth pore volumes was injected. At high concentration of HCl, Calcium and the surfactant propagated with the same velocity. When low concentration of HCl was employed, Calcium propagated faster. Surfactant retention is higher when the acid concentration and the injection rate were lower. This number could be up to 100%. CT scan confirmed only small and short wormhole branches at the area near the inlet and one wormhole dominated till the end with a decreasing diameter. Reaction rate and extension of wormhole decreased when lower concentration HCl was used and injected at a higher rate.
Three-Dimensional Shear Data to Design Effective Completions in Unconventional Reservoirs
Authors: Bray Jim , Menendez Eliud , Smith Charles H.
Published: June 2011

Unconventional reservoirs require an effective system of completion. A major difference between unconventional and conventional reservoirs is the plastic nature of the rock itself. Within a very short period of time, certain portions of the reservoir will flow, sealing off the productive mechanism and capacity of the formation. Complicating matters even more is the near universality of horizontal drilling in these reservoirs.

Dipole sonic logs have been used for many years to establish rock mechanical properties for conventional formations. The use of Young's Modulus and Poisson's ratio in frac design is well established. This same relationship exists in the unconventional world, but the complication of plasticity in the formation makes the relationship more difficult to understand. Traditional twodimensional models have not been able to adequately identify intervals of the horizontal reservoir that could maintain the fracture treatment.

The calculation of three-dimensional rock mechanical properties has been advanced as a way to overcome this difficulty. This paper presents the application of this advancement in unconventional reservoirs. This paper will also discuss the differences in two-dimensional and three-dimensional data and the effects of ignoring this information.
A Novel Stimulation Approach for Scale Control in Marrat Carbonate Reservoir - Case Studies from Joint Operations, PZ Kuwait
Authors: Al-Ghamdi Saleh , Al-Najim Abdulaziz , Bouyabes Ahmed , Al-Hadyani Fahad S , Nugraha Ikhsan , Hamid Saad
Published: June 2011

Carbonate scaling is one of the common problems that occur in wells producing high amount of water. The tendency of scaling escalates in mature fields. This problem becomes critical in sub-hydrostatic wells with Electrical Submersible Pumps (ESP). In such cases, the scale not only reduces the flow of fluids into the wellbore, but also causes frequent failures in downhole equipment, eventually stopping production leading to well workover. Frequent ESP failures can increase the operating costs to unacceptable levels which may eventually lead to field abandonment.

Joint Operations (Chevron and KGOC) in Partitioned Zone (PZ) faced severe scaling problems in Humma field producing from Marrat Carbonate reservoir. A thick layer of calcium carbonate scale was observed in the completion string during the workover. As a result of this scale, ESP repair and replacement frequencies increased abnormally. Also, the ESP amperage charts showed erratic behavior due to solids interference inside the pump resulting in pump failures.

A combined scale control and stimulation treatment was applied in three wells in Humma field in Joint Operations to slow down scaling tendency in the formation and tubular. These wells are producing up to 1523 BWPD averaging 28% water cut. The treatment provided effective placement of scale inhibitor in the formation while controlling any increase in water production because of stimulation. As a result, the workover frequency due to pump failures was reduced. Not only did the production improve, the amount of deferred oil was also significantly reduced resulting in direct oil gain and significant savings in operating costs.

This paper describes the lab analyses, treatment design and execution procedure, adopted for the implementation of this technique as well as the recommendations and lessons learned from the field experience.
Formation Damage and Fluid Loss Reduction due to Plastering Effect of Casing Drilling
Authors: Karimi Moji , Ghalambor Ali , Montgomery Monty , Moellendick Eric
Published: June 2011

The objective of this work is to investigate the influence of cuttings size in Casing Drilling to plug pores for fluid loss control, and thereby reducing formation damage. Historically, the emphasis of drilling operations has been to drill wells cheaply and quickly without much consideration for the resulting impact on well productivity. Formation damage occurs frequently and rapidly during drilling operations with potentially severe consequences. The Plastering Effect of Casing Drilling reduces solids and filtrate invasion, resulting in less skin damage and improved productivity. It also reduces formation damage due to cement filtrate by creating a gauged wellbore and proper casing/wellbore standoff.

The Casing Drilling process grinds drill cuttings as they travel up the annulus and creates a larger particle size distribution (PSD) profile than conventional drilling operations. These finer cuttings are subsequently smeared into the wellbore face by the mechanical contact of the large diameter casing with the borehole wall. The result is a very high quality, tight, thin, almost impermeable mud cake that isolates the formation from the wellbore. Evidence shows that cement binds very well to this type of mud cake.

The PSD analysis determined that the smaller size and wide range of Casing Drilling cuttings make it possible for these particles to readily adhere to the wellbore; this helps seal the pore spaces of the formation and prevent further solids and filtrate invasion. Pore throats can most effectively be plugged when the cuttings are in the proper micron size range as any possible gap between the mud and cuttings PSD can be covered by adding minimal amounts of properly sized lost circulation materials.

Casing Drilling has proven to be a unique approach in mitigating formation damage due to the drilling process. One case study confirms that reservoir sections drilled with casing show enhanced productivity as much as twice the wells drilled conventionally. The Plastering Effect, as an inherent benefit of Casing Drilling, keeps the producing formation as intact as possible and reduces formation damage.
Temporary Zonal Isolation Minimizes Reservoir Damage During Workover Operations in Ecuador
Authors: Del Rio C. , Boucher A. , Salazar F. , Milne A. , Robles M.
Published: June 2011

In Ecuador, the principal reservoirs are subhydrostatic, with permeability ranging from 100 to 2,000 mD and significant clay content. The crude oils are prone to form emulsions in contact with completion fluids. After workover operations—pulling electric submersible pumps (ESP) or recompleting a well—it is common to lose more than 1,000 bbls of completion fluid, resulting in a 20% to 50% reduction in production.

Fluid loss control pills containing sized particulate, such as calcium carbonate or sized salt, are frequently used to control the fluid loss; however, a further treatment is required to remove the solids. Using this technique, 25 wells producing a total of 8,000 BPD were worked over, after which the production decreased to 5,000 BPD.

The main challenges in developing a solids-free fluid loss control pill to control losses of completion fluid during a well intervention are: a) the low, subhydrostatic (0.16 to 0.36 psi/ft.) reservoir pressure, b) high matrix permeability, and c) cleanup when well is put on production. To overcome this, a highly viscous, polymer crosslinked fluid with an internal breaker was developed to temporarily isolate the reservoirs. Using this fluid, it is possible to work over a well without losing fluid into the reservoirs and having the associated loss of production.

In 15 wells worked over using the fluid loss control fluid combined with modified workover procedures, fluid losses were controlled and production was maintained after the workovers. This technique also made it possible to selectively stimulate certain intervals, increasing production. The total production prior to the interventions was 7,300 bpd. Afterward, it increased 27% to 9,250 bpd.

The fluid-loss control fluid, together with the new workover procedures, has now been adopted as a standard. It has proved an effective means to protect the subhydrostatic reservoirs in mature fields during workover interventions.
Increasing Oil Production without Increasing Water Cut in Wells in Ecuador
Authors: Boucher A. , Del Rio C. , Salazar F. , Milne A. , Robles M.
Published: June 2011

An operator in Ecuador produces from the Napo "U" sandstone formation with permeability ranging from 90 to 2,000 mD. A lateral aquifer supports the oil production coming from this zone. Water breakthrough in this formation is common in intervals with high permeability streaks causing the water cut to increase substantially, thus affecting the oil producing zones. Besides the onset of water, additional oil decline results from high pressure drawdown and high clay content (including kaolinite) in the formation. The primary damage mechanism is identified as fines migration, a common problem in wells in Ecuador.

The main challenge is to increase oil production through stimulation in wells with high water cut and a strong aquifer, without increasing the water cut. A treatment was proposed that would remove the damage in the intervals producing oil and "good" water without stimulating the interval where water had already broken through. It consisted of combining a modified organic clay acid (OCA) and a viscous disproportionate permeability modifier (VDPM) to maximize zonal coverage and minimize water production.

The first stimulation treatment using the modified OCA and the VDPM enabled the treatment to be diverted to the intervals where water had not broken through. Post-treatment results showed production had doubled and water cut remained the same as it was pre-treatment. Production then remained stable after more than 3 months. A nodal analysis model predicted that the well had a skin of approximately 10 prior to the treatment, and this skin was reduced to nearly zero following the treatment.

A subsequent stimulation treatment performed in a horizontal openhole completion using coiled tubing increased oil production by more than ten times the initial production. It was not known where in the openhole the water breakthrough had occurred in this well, but through the use of the VDPM, the water cut was reduced.

An additional 13 wells with similar damage have been treated successfully using the same fluids resulting in an additional 2,100 BOPD of production. The combination of effective diversion, conformance control and modified OCA is an effective means of selectively increasing oil production in mature fields without increasing the water cut.
In-Depth Water Diversion Using Sodium Silicate on Snorre - Factors Controlling In-Depth Placement
Authors: Stavland A. , Jonsbråten H. C. , Vikane O. , Skrettingland K. , Fischer H.
Published: June 2011

The waterflood sweep efficiency can be increased considerably by in-depth placement of a blocking agent. Sodium silicate is one of the few PLONOR chemicals applicable for water control. This paper highlights key results obtained from a research program on qualifying sodium silicate for offshore applications. The main findings of this work can be summarized as follows: Sodium silicate is an alkaline liquid containing nano-size particles with water-like viscosity and good buffer capacity.Sodium silicate should be diluted in brines with a low divalent ion concentration addressing the need of a sufficiently large preflush.Upon reaction, triggered by an activator, sodium silicate forms silicate aggregates and gel which reduce rock permeability.The reaction rate is controlled by the formation temperature and sodium silicate concentrations.The flow behaviour of reacted silicate aggregates is understood by the classical theory on fine particle transport through porous medium, which includes a velocity-dependent deposition rate.Coreflood experiments at high flow rates demonstrated both a good injectivity of non-reacted sodium silicate and dynamic reaction rates similar to bulk reaction rates. At low injection rates, the plugging time decreased and was explained by fines particle transport which increased the deposistion rate of silicate.Interpretations of coreflood experiments unfold the effect of cation exchange.

It is concluded that large volumes of sodium silicate can be injected into offshore oil reservoirs. Prior to the injection, a preflush is needed and the silicate is to be diluted in desalinated water. The permeability reduction can be obtained either during dynamic injection or shut-in period. The design parameters involve temperature, velocity and concentration gradients.
Fingerprint of Mud Losses into Natural or Induced Fractures
Authors: Majidi R. , Miska S. Z. , Zhang Jianguo
Published: June 2011

Lost circulation in fractured formations is one of the drilling's biggest expenses in terms of non-productive time (NPT), unit mud cost and safety issues. The severity and persistence of losses are to a large extent determined by the type of formation into which the fluid is being lost. It is imperative to identify whether the losses are to natural or induced fractures as losses into naturally fractured rocks require different treatments than those into drilling induced fractures. One way of identifying the type of the fracture is by image logs which are very local and limited to conductive muds, so still in their infancy and have yet to gain wide acceptance. An alternative way is possible by looking into flow behavior of mud losses (flow in/out) and associated downhole pressure response (PWD data).

This work presents an analytical formulation describing mud losses in drilling induced fractures based on which the volume and rate of losses in an induced fracture are quantified in terms of fluid properties, fracture parameters and operational conditions. Comparison between the predicted mud losses into induced and natural fractures indicates that much higher pressure sensitivity is anticipated during mud losses into induced fractures. Hence, the pressure sensitivity analysis can be used as a means to distinguish between the losses into natural and induced fractures. Once the fracture type is identified, the fracture parameters (hydraulic width or compliance) can be estimated by analyzing mud loss data. As the outcome of this study, guidelines are provided for the best practices to be used for prevention and control of lost circulation.
Gravel Packing Depleted Reservoirs
Authors: El-Dabi Fady , Bulgachev Roman
Published: June 2011

Gravel packing, being one of the most reliable and robust downhole sand control techniques, is often the preferred method for establishing sand control. In reservoirs where the pressure has fallen below the water gradient, gravel placement using water based fluid will produce a high overbalance leading to excessive losses of fluid that might deeply invade the formation, cause premature bridging, and fracture the formation. The main focus of this paper is to identify fluids and techniques for gravel packing a depleted reservoir and evaluate the best technique and a fluids package for a candidate well.

A well candidate in the Mediterranean is planned to be completed with cased hole gravel pack and it is a twin of a cased and perforated gas well that started producing formation sand after 4 years of production. Continued production from the reservoir is expected to drive down the pressure to 7.5ppg by the time, when candidate well is completed.

Several techniques for gravel packing a depleted reservoir have been considered which included diesel, alcohol-, oil-, gas- and water-based fluids. However after extensive lab testing the most suitable fluids package for the well was found to be conventional water packing. Contrary to expectation, formation damage tests indicated that water based gravel packing caused less damage than non-viscous oil based fluids for this particular candidate well. Solids-free high-temperature perforation kill pill and breaker package were also designed for the well to be stable for up to 4 days, which pushed the limits of solids free kill pills currently available in the industry.

The paper will discuss in detail the gravel packing fluid package selection methodology, and completion fluid, gravel pack fluid, kill pill and breaker fluids package design and evaluation for the candidate well.
Perforation Cleanup via Dynamic Underbalance: New Understandings
Authors: Grove B. , Harvey J. , Zhan L.
Published: June 2011

Dynamic Underbalance perforating is a completion technique which uses a perforating system engineered to create a rapid underbalance immediately upon formation perforation. This technique – properly applied – improves well deliverability by effectively cleaning the newly-created perforation tunnels, regardless of initial static pressure conditions (overbalanced, underbalanced, or balanced).

Over the past 3 years, we have conducted dozens of perforate-and-flow laboratory experiments, carefully controlling and measuring wellbore transients, and measuring post-shot productivities. Our results indicate that the cleanup mechanisms are more involved than conventionally understood. We observed that a dominant mechanism of dynamic perforation cleanup is the increase in effective perforation length. We also confirmed previous findings that DUB perforating increases tunnel diameter, while reducing the thickness of the "crushed zone" of impaired permeability, which surrounds each tunnel. Although these processes have been mentioned in general terms previously, conventional models typically simplify things by reducing perforation cleanup to the enhancement of crushed zone permeability. Though this simplification has offered a convenient means of interpreting lab data, it can yield misleading results when applied downhole.

While increasing crushed zone permeability does indeed improve the productivity of real wells, the additional processes of enlarging tunnel diameter and reducing crushed zone thickness improve productivity further. Increasing the effective tunnel length provides yet another means of productivity gain, and under most circumstances is the dominant beneficial effect. We present productivity predictions of various downhole scenarios to quantify these newly-recognized effects.

These findings suggest the performance differential (between DUB and non-DUB techniques) at downhole conditions can be far greater than previously recognized.