bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential requirements for myogenic regulatory factors distinguish medial and lateral somitic, cranial and fin muscle fibre populations
Authors: Hinits Yaniv , Osborn Daniel P. S. , Hughes Simon M.
Published: January 2009

Myogenic regulatory factors of the Myod family (MRFs) are transcription factors essential for mammalian skeletal myogenesis. However,the roles of each gene in myogenesis remain unclear, owing partly to genetic linkage at the Myf5/Mrf4 locus and to rapid morphogenetic movements in the amniote somite. In mice, Myf5 is essential for the earliest epaxial myogenesis, whereas Myod is required for timely differentiation of hypaxially derived muscle. A second major subdivision of the somite is between primaxial muscle of the somite proper and abaxial somite-derived migratory muscle precursors. Here, we use a combination of mutant and morphant analysis to ablate the function of each of the four conserved MRF genes in zebrafish, an organism that has retained a more ancestral bodyplan. We show that a fundamental distinction in somite myogenesis is into medial versus lateral compartments, which correspond to neither epaxial/hypaxial nor primaxial/abaxial subdivisions. In the medial compartment, Myf5 and/or Myod drive adaxial slow fibre and medial fast fibre differentiation. Myod-driven Myogenin activity alone is sufficient for lateral fast somitic and pectoral fin fibre formation from the lateral compartment, as well as for cranial myogenesis. Myogenin activity is a significant contributor to fast fibre differentiation. Mrf4 does not contribute to early myogenesis in zebrafish. We suggest that the differential use of duplicated MRF paralogues in this novel two-component myogenic system facilitated the diversification of vertebrates.
Survey of Liquid Coumarin Dyes and Their Fluorescence Properties
Authors: Park So-Yeon , Kubota Yasuhiro , Funabiki Kazumasa , Matsui Masaki
Published: January 2009

Novel liquid 7-dioctylamino-, 7-(didecylamino)-, 7-(1-butylpentyloxy)-, and 7-(1-octylnonyloxy)-4-methylcoumarins were found. They showed melting points in the range of −55.1 to −42.8 °C as a metastable liquid phase followed by rearrangement in the range of 1.7 to 20.0 °C to form stable liquid phase. The 7-dialkylamino and 7-alkoxy derivatives showed fluorescence maxima at around 440 and 400 nm with fluorescence quantum yields ca. 0.16 and 0.06 in neat form, respectively.
Experimental Investigation of Carbon Oxidization
Authors: Yao Shuiliang , Mine Chieko , Kodama Satoshi , Yamamoto Shin , Fujioka Yuichi
Published: January 2009

The oxidation of carbon samples: C60, C60(OH)n, C60(O)n, C60(H)n, C70, diesel particulate matter (PM), activated carbon, and graphite was carried out using a thermogravimetry equipped with a mass spectrometer. It was found that incorporation of O, OH, and H onto C60 surfaces promotes oxidation at a temperature lower than that without incorporation. This finding is helpful to understand the mechanism of PM removal in plasma discharges. A simple oxidation mechanism of C60 and its derivatives is given.
Intraperitoneal anaesthesia with propofol, medetomidine and fentanyl in mice
Authors: Alves H C , Valentim A M , Olsson I A S , Antunes L M
Published: January 2009

Fast recoveries are essential when looking for a safe anaesthetic protocol to use on mice. Propofol is a short-acting anaesthetic agent, which provides a smooth, fast recovery. A recent study carried out in our laboratory showed that the intraperitoneal (i.p.) administration of propofol combined with a fast-acting opioid does not provide a sufficiently stable anaesthesia. In this experiment, we hypothesized that the additional application of medetomidine would increase muscle relaxation and analgesia. Fifty-four male CD1 mice, divided into six groups of five and three groups of eight, were used to test nine different combinations of propofol, medetomidine and fentanyl administered i.p. and reversed with atipamezole 30 min after induction. These combinations were composed in the following manner: propofol 75 mg/kg, medetomidine 1 and 2 mg/kg and fentanyl 0.1, 0.15 and 0.2 mg/kg. The depth of anaesthesia, loss of righting reflex, loss of pedal withdrawal reflex, pulse rate and respiratory rate were recorded along with the duration and quality of the recovery. The combination of propofol and medetomidine provided a predictable induction, hypnosis and muscle relaxation, but surgical anaesthesia (loss of pedal withdrawal reflex) was not achieved. The addition of fentanyl increased analgesia leading to surgical anaesthesia. We concluded that a combination of 75/1/0.2 mg/kg of propofol, medetomidine and fentanyl, respectively, is a safe, easy and reversible technique for i.p. anaesthesia in mice, providing a surgical window of 15 min and restraint for 30 min with a fast recovery.
Beneficiários do trabalho voluntário: uma leitura a partir da bioética
Authors: Selli Lucilda , Garrafa Volnei , Junges José Roque
Published: January 2009

OBJETIVO: Descrever a percepção dos voluntários sobre os beneficiários do trabalho voluntário no setor de saúde hospitalar e a influência que o tema dos benefícios exerce sobre as motivações. MÉTODOS: Estudo exploratório com abordagem qualitativa. Participaram 110 voluntários em serviços de saúde referências no tratamento de câncer no Rio de Janeiro (RJ), com coleta de dados de outubro a dezembro de 2001. Os dados foram obtidos por dois instrumentos: um questionário com perfil socioeconômico e sobre motivações para atividade voluntária; e entrevista semi-estruturada para obtenção de dados complementares. RESULTADOS: A visão dos voluntários sobre os beneficiários da atividade voluntária esteve centrada mais freqüentemente no paciente (50,5%), no voluntário (41,9%) e na instituição e sociedade (7,6%). Paciente e voluntário foram considerados simultaneamente beneficiários, sendo o voluntário o que mais recebe benefícios. Foi relatada também uma compreensão do benefício social dessa atividade. CONCLUSÕES: Constatou-se que existe, entre os voluntários, uma noção da importância social do seu trabalho voluntário, faltando uma articulação maior entre motivações individuais e trabalho voluntário como espaço de enfrentamento de problemas sociais.
Managing quality, safety and environment as one
Authors: Griffith Alan , Bhutto Khalid
Published: January 2009

Integrated management of quality, safety and environmental issues is one the construction industry’s holy grails. Alan Griffith of Sheffield Hallam University and Khalid Bhutto of consultancy Safescope report on the latest thinking and progress.
Electronic notification of street works: a utility perspective
Authors: Solanki Anita
Published: January 2009

Electronic notification and permitting systems required by the UK Traffic Management Act 2004 are major IT challenges for anyone who needs to dig up British roads. Anita Solanki of Severn Trent Water says utilities are more than up to the task, but the pace of change may prove unduly expensive.
Climate change, risk and infrastructure policy-making
Authors: Venables Jean
Published: January 2009

This is the inaugural address of Jean Venables, who became 144th president of the Institution of Civil Engineers on 4 November 2008.
Decommissioning nuclear plants: experiences in Germany
Authors: Versemann R.
Published: January 2009

The complexity of components from nuclear installations requiring dismantling or decontamination is enormous, as is the number of approved and available techniques. To choose the ideal dismantling technique, a number of complex parameters have to be considered. The most important criteria are costs, the amount and kind of radioactivity involved, aspects of radiation protection, the kind of material to be treated, geometries and spatial accessibility. Based on these criteria, appropriate decontamination or dismantling processes are selected. Starting with a description of decommissioning projects in Germany, this paper then describes various decommissioning concepts and gives an overview of the management of materials and waste. A selection of techniques is presented and new developments and applications are described. The conclusion considers future developments in the area of nuclear power plant decommissioning in general.
Frictional properties of asphalt concrete mixes
Authors: Ongel A. , Lu Q. , Harvey J.
Published: January 2009

Skid resistance is an important factor in pavement performance because it is related to safety. It is controlled by the micro- and macrotexture of the pavement surface. The purpose of the study described herein was to identify variables related to the friction performance of surface asphalt mixes in order to optimise material selection and to provide information for the development of improved mix designs. This study evaluated the friction values of 72 asphaltic surfaces including open-, gap- and dense-graded mixes at different ages. Microtexture was measured using a British Pendulum Tester and macrotexture was measured by a high-speed laser profiler. Statistical models were developed for micro- and macrotexture using climate, traffic and pavement mix variables. Results indicated that microtexture is affected by temperature, age, and traffic whereas macrotexture is affected by rainfall, freeze–thaw cycles and pavement mix variables.
Rationality of a non-lane-based car-following theory
Authors: Gunay B.
Published: January 2009

Earlier work by the author developed a two-dimensional car-following model by taking into account the lateral discomfort experienced between the neighbouring vehicles moving in the same direction. This incorporation of lateral friction in car-following theory may offer a potential breakthrough in the field of microscopic simulation. However, that model was based on a small-scale scrutiny in which the interactions between only two or three vehicles were analysed in isolation. The treatment of the problem with many vehicles in a stream of traffic, say, on a link, was not made. The present paper, therefore, develops a simulation model with various types of vehicular interactions, including lane changing, and performs certain verification checks. The results show that the simulation behaves rationally giving credibility to the approach introduced. Although a number of comparisons with empirical observations are made in the paper, complete validation and experimentation are left for further work. Furthermore, the paper draws research attention to the area so that various existing car-following models can be modified in a similar way to mimic non-lane-based car following in multilane traffic flow. Potential practical implication of the work for traffic engineers is mainly capacity assessments especially in places where the discipline of lane-based-driving is weak.
Alternative decision-aid tool for pavement management
Authors: Ferreira A. J. L. , Meneses S. C. N. , Vicente F. A. A.
Published: January 2009

This paper presents the development and implementation of a new decision-aid tool to be used in the pavement management system of Oliveira do Hospital in Portugal. This system includes the following components: a road network database; a quality evaluation tool; a costs model; a pavement performance model; and a decision-aid tool. The current decision-aid tool uses a deterministic section-linked optimisation model with the objective of minimising the total expected discounted costs over the planning time-span while keeping the road pavements within given quality standards. The new decision-aid tool uses a deterministic section-linked optimisation model with the goal of maximising quality, performance or user benefits over the planning time-span for given annual budget levels. This new approach is suitable for road administrations that strictly adhere to known annual budgets for maintenance and rehabilitation. The current pavement quality and the constraints defined by the annual budgets determine the future quality and level of performance of the road pavements. The new decision-aid tool also uses the deterministic pavement performance model used in the flexible pavement design method of the American Association of State Highway and Transportation Officials, which allows the gap between project and network management to be resolved.
Paying for parking: improving stated-preference surveys
Authors: Dell'Olio L. , Ibeas A. , Moura J. L.
Published: January 2009

This article describes an experiment which introduced random ranges into the variables used for the design of a stated preference survey and its effects on willingness to pay for parking. User behaviour at the time of parking was modelled to determine their willingness to pay in order to get to their final destination more quickly. Calculating willingness to pay is fundamental during the social and economic assessment of projects. It is important to correctly model how car parks and their users interact in order to get values which represent reality as closely as possible. Willingness to pay is calculated using a stated preference survey and by calibrating multinomial logit models, taking variable tastes into account. It is shown that a value with a low variability can be obtained for willingness to pay by correctly establishing the context of the choice and randomly changing the variables around an average value.
A laboratory study on cold-mix, cold-lay emulsion mixtures
Authors: Thanaya I. N. A. , Zoorob S. E. , Forth J. P.
Published: January 2009

This paper describes laboratory experiments and presents results for the performances of cold-mix, cold-lay emulsion mixtures. The main objective of the experiments was to evaluate and improve the properties of the cold mixtures. The mixture properties evaluated were: volumetric properties, indirect tensile stiffness modulus (ITSM), repeated load axial creep and fatigue. These properties were compared with conventional hot asphalt mixtures not containing any waste/recycled materials. To optimise the performances of the mixtures, a target of ITSM value of 2000 MPa was selected. At full curing conditions, the stiffness of the cold mixes was found to be very similar to that of hot mixtures of the same penetration grade base bitumen (100 pen). Test results also show that the addition of 1–2% cement significantly improved the mechanical performance of the mixes and significantly accelerated their strength gain. The fatigue behaviour of the cold mixes that incorporated cement was comparable with that of the hot mixtures.
Point-Source Fracturing: Extension of the LMN Analytical Model to Turbulent Flow
Authors: Liétard Olivier
Published: January 2009

A new analytical model of hydraulic fracturing under point-source conditions (LMN) has recently been proposed1 and later on corrected from a series of non critical mistakes.2 Its results for viscous fluids do agree with field evidences of an almost constant, however slightly increasing net pressure all along pad stages.

One severe limitation of the LMN model is its assumption of laminar flow, which had initially been made to ease up the mathematical treatment of the basic differential equation of the model, hence to rapidly come up with results directly applicable to the most common hydraulic fracturing jobs in highly deviated wells, i.e. those making use of crosslinked gels as proppant carriers.

The cases of Step Rate Tests pumped with water (or thin linear gels) and of the so-called riverfracs were deliberately disregarded during this first phase of the development of the LMN model. The present paper now addresses these cases by extending the latter to turbulent flow.

It is found that the resulting equation of the net pressure indicates an even weaker, however still positive, slope of the diagnostic (Nolte-Smith) plot than under laminar flow. In other words, the fracture width at the wellbore is about constant all along a fracturing treatment pumping a thin fluid at constant rate.
Improved Friction Reducer for Hydraulic Fracturing
Authors: Aften C. W. , Watson W. P.
Published: January 2009

An improved polyacrylamide friction reducer delivered in an inverse emulsion form has been developed for use in fresh water up to 2% KCl. The main benefits realized were an increased level of friction reduction along with an enhanced rate of inversion. These benefits were obtained without compromising the emulsion storage stability. These improvements were gained primarily by optimizing the breaker surfactant package used to release the polymer from its delivered form into the aqueous based treatment fluid.

Friction reducers are often a significant portion of the aqueous based chemical stimulation package used in either the stimulation and/or completion of oil/gas wells. Common friction reducers used for fresh water operations typically have a decline in performance when exposed to aqueous based fluids of increased salt content. The performance decline is not solely due to the nature of the polymer, but rather the mechanism of polymer release from its inverse emulsion state. The presence of salt not only affects the polymer configuration but also the ability of the inverse emulsion to release the polymer from its water internal phase into the water continuous stimulation fluid.

The new friction reducer was developed by examination of various surfactants by way of simple additions to ternary mixture designed experiments. A variety of bench top performance tests were used to narrow the selection yielding a final surfactant package. The final candidates were then screened using an in-house friction loop. The improved friction reducer dosed at 0.5gpt had a 29% increase in ultimate friction reduction in fresh water and a 119% increased performance in 2% KCl when compared to a standard friction reducer of similar charge and molecular weight. Ultimate performance enhancement was gained within reasonable raw material costs and stability limits.

With the increased ultimate friction reduction and superior inversion rate, this new product will reduce the energy required to deliver a specific volume at a set rate or increase the rate of the delivered volume at the same power for water based systems containing up to 2% KCl for stimulations and/or completions.
Irrational Fracturing — How Heuristics and Biases Affect Judgments in Fracpacking
Authors: Ammachathram V. M.
Published: January 2009

Fracpacking has evolved as the single, most preferred sand control completion technique in the world today. This dramatic increase in the number of fracpacks is reflected in increasing number of technology vessels, skid pumping equipment, remote data transmission capabilities and increasing numbers of personnel. The technical jargon of fracturing has become more and more common place as operating and service companies constantly try to break new barriers in the scope of fracturing and fracpacking.

Most operators and service companies have dedicated fracturing personnel, who have tremendous levels of expertise and experience in fracpacking. Unfortunately, when an application is embraced globally at such a fast paced level, personnel tend to rely subconsciously on what is called "heuristics?? or "rules of thumb?? that enable them to make key decisions on how to execute a fracturing treatment. The use of heuristics leads to systematic errors called "biases?? that can affect the decision process as a whole; thereby affecting the entire treatment.

This paper examines the key heuristics that fracturing engineers employ. The goal of this paper is to minimize the probability of errors in judgment that are commonly made by exposing the underlying biases. For example, Anchoring and Adjustment is a common bias encountered in re-designing fracpack treatments everyday. If a group of engineers are involved in the re-design process, the first engineer that comes up with a pad volume has anchored his base volume in all the other participant's minds. The adjustments are then made based on the initial anchor and a desire to conform to the group's opinion (consensus bias). The net effect is that other possible values or solutions are either neglected or ignored. The Availability heuristic bases judgment on what is available in most recent or vivid memory. Engineers remember recently executed and problem jobs, and base their judgments on what they can instantly recall from these experiences. This paper combines the psychological impact in fracturing treatments and ways to harness these biases in a positive manner for a successful treatment.
Modified API/ISO Crush Tests With a Liquid-Saturated Proppant Under Pressure Incorporating Temperature, Time, and Cyclic Loading: What Does It Tell Us?
Authors: Freeman E. R. , Anschutz D. A. , Rickards A. R. , Callanan M. J.
Published: January 2009

The American Petroleum Institute (API) crush tests for proppants found in recommended practices (e.g. RP 56, 58, & 60) are typically used to compare the crush resistance of recognized API proppant sizes at a predetermined stress under dry and ambient conditions (API, 1995). This procedure has remained the same through several API committees since the early 1980s without change. More recently, the International Organization for Standardization, ISO 13503-2, reviewed the procedure and made only slight changes, most notably in the time for which the stress is to be applied (ISO, 2006). The "new" procedure from ISO gives no indication of how the stress changes the overall mesh distribution. It also sheds no light on how key factors such as moisture, temperature, time, or cyclic loading change performance characteristics. This work addresses these issues.

The down-hole environment where the proppants are placed is wet, hot, and pressurized. Incorporating these variables into a modified API test procedure for crush resistance better represents actual down-hole conditions to which a proppant is subjected. This information is critical in establishing required propped fracture conductivity, and thus, proppant selection.

In this study a standard API crush cell was modified for pressurized fluid flow at temperature and used to quantify the effects of the parameters described as compared to standard API crush tests. Tests were performed on the following proppants: light weight ceramic (LWC), intermediate density ceramic (IDC), and high strength bauxite (HSB).

Modified testing exposes critical proppant failures under conditions that more closely simulate those experienced downhole; these failures are not be revealed by current standard API/ISO test procedures. The modified procedure results in an improved method for better understanding downhole proppant pack performance.
Multiple Transverse Fracturing in Horizontal Open Hole Allows Development of a Low-Permeability Reservoir in the Foukanda Field, Offshore Congo
Authors: Casero Alberto , Tealdi Loris , Ceccarelli Roberto Luis , Ciuca Antonio , Pace Giamberardino , Malone Brad , Athans James
Published: January 2009

During the past decade, multiple transverse fracturing in horizontal wells has been applied so successfully in onshore low-permeability reservoirs that it is becoming the standard completion practice in many areas.

The reasons for the success of this technique vary, but the two main reasons are related to the undisputed effectiveness of hydraulic fracturing as a production enhancement technique and the relatively low cost of pumping services in onshore areas. Success and industry eagerness for process/cost optimization have contributed to many technological improvements in the multistage completion process allowing sequentially executing several fracturing treatments in a single pumping operation.

Nevertheless, the high direct and indirect costs and the risks associated with offshore operations have traditionally been limiting factors in spreading this technology to offshore applications. Sometimes, the misplaced perception of hydraulic fracturing as risky and costly operation prevented, rather than encouraged, its application in marginal offshore oilfields. Recent increases in oil prices and the success in onshore applications have encouraged the use of hydraulic fracturing in offshore applications.

This study documents the successful effort of taking these techniques to the offshore environment. Transverse fracturing with multistage completion concept— with properly engineered design of well trajectory—can make the difference between the economic success or failure in the field development of low-permeability reservoirs. This study used multidisciplinary and integrated approach to design and execute the treatments, involving reservoir, production optimization, and fracturing engineers from the early stages of well planning to construction.

The multilayer Foukanda field, located 52km offshore from Pointe Noire, Congo, has a low permeability and virgin target that was considered noncommercial after discouraging results of two wells. Based on the production results of three cased-hole wells in an analogous field where multiple propped fracturing was applied, the operator decided to drill an open-hole horizontal well that was to be multi-fractured. The initial 90 days average production of this Foukanda well was more than 2500bbl/day. This production rate was double the simulated rate of a vertical well and opened a wide range of further developments both in Foukanda and in other analogue fields in the offshore Congo.
A Simple and Accurate Model for Well Productivity for Hydraulically Fractured Wells
Authors: Friehauf Kyle E. , Suri Ajay , Sharma Mukul M.
Published: January 2009

A new model is developed that calculates the productivity of a hydraulically fractured well, including the effect of damage of the fracture face from fluid leak-off. Results of the new model are compared with three previous models (McGuire, Prats and Raymond). The existing models assume either elliptical or radial flow around the well with permeability varying azimuthally. Significant differences in the calculated well productivity indicate that earlier assumptions made about the flow geometry can lead to significant overestimates of well PI. Agreement with Prats analytical solution is achieved for finite conductivity fractures and no fracture damage. It is shown that the use of either McGuire and Sikora's or Raymond's model to estimate improvement in well PI in fractured wells can lead to a significant over-estimation of the well PI. The new model provides a useful tool to quickly calculate the productivity of wells that have both a finite-conductivity fracture and damage in the invaded zone. The simple and discrete nature of the model makes it ideal for implementation in spreadsheets and to connect to fracture performance models.

Clean-up of the damage in the invaded zone depends on the capillary properties of the formation and the drawdown pressure applied across the damaged zone during production. If capillary forces are small, and drawdown pressure is high, the water will be recovered, resulting in negligible damage. It is found that the invaded zone will cause significant damage when the permeability of the damaged zone is reduced by over 90%. For low permeability, depleted formations, where water recovery is poor, the fracturing fluid should be energized with a gas component so that the relative permeability damage to gas inflow can be minimized.
Application of a New Compositional Model for Hydraulic Fracturing With Energized Fluids: A South Texas Case Study
Authors: Friehauf Kyle E. , Sharma Mukul M. , Sullivan Richard B.
Published: January 2009

A gas component (CO2) is added to fracturing fluids in tight gas wells of South Texas in order to energize, or stimulate the invaded zone for improved flowback. It was observed that traditional fracturing fluids were being trapped because of the lack of drawdown pressure caused by depletion of the reservoir. This study uses a recently developed energized fracture model to predict fracture behavior. It is shown that this model can be used instead of costly trial and error methods in the field to help improve upon the design of the treatments. This study investigates the effects of drawdown pressure, inlet gas composition (or quality), inlet temperature, flowrate, base viscosity, and reservoir pressure on three previous fracture designs. The effect of energizing only specific stages of the fracture treatment is also demonstrated.

Our results show that if the drawdown pressure is much larger than the capillary forces holding water in the invaded zone, energizing the fluid may not be necessary. In wells with low drawdown pressure, adding CO2 to energize the fracturing fluid may be able to completely remove damage by increasing the gas saturation in the invaded zone. Specifically for the wells that were modeled, we determined that 30 quality CO2 would be sufficient to stimulate the invaded zone. When the reservoir pressure was as low as 800 psi, even less CO2 was necessary because of additional expansion of the gas during production. Pumping of a gas with high quality (> 52%) will result in foaming of the fluid that will increase the fracture fluid viscosity. This may be undesirable in tight formations where fracture length is favored over conductivity. Pumping volumes should be corrected in order to account for the expansion of gas when there is a large difference between inlet and reservoir temperature. Changing the inlet temperature of the fluid does not greatly affect the performance of the fractured wells in this area. No compositional or phase behavior issues arose when altering the flowrate or the base fluid viscosity. Finally, it is recommended that every stage of the treatment be energized. However, in some instances it may be possible to stimulate the invaded zone by energizing only certain stages of the treatment.
Hydraulic Fracture Offsetting in Naturally Fractures Reservoirs: Quantifying a Long-Recognized Process
Authors: Jeffrey R. G. , Zhang X. , Thiercelin M.
Published: January 2009

Offsets along the hydraulic fracture path have been observed in mapping of mined fractures and attempts have been made to reproduce their effects on fracture growth using numerical hydraulic fracture models. Such offsets have long been recognized as sites of restricted width in the fracture channel, potentially leading both to significant pressure drops and to proppant bridging as fluid and slurry move through the restrictions. New modeling results are presented that quantify these and other effects of offsets by using a coupled 2D hydraulic fracture model. Offsets are geometrically characterized by their angle with respect to the main fracture direction and by their length. Quantitative comparisons on fracture length, width and injection pressure are made for several offset angles and lengths. Large increases in net pressure and associated increases in overall fracture volume are shown, which can result in increased treatment costs, slower fracture growth, and shorter overall fracture length development compared with a straight fracture.
Analysis of Reserve Recovery Potential from Hydraulic Fracture Reorientation in Tight Gas Lenticular Reservoirs
Authors: Benedict D. S. , Miskimins J. L.
Published: January 2009

The basic concept of hydraulic fracture reorientation involves inducing a second artificial fracture into the producing zone, with this secondary fracture propagating in a different direction from the original. For reorientation to occur, the near wellbore stress has to have altered in orientation from the time the original fracture was created. To investigate the effects of this action on reserve recoveries in tight gas lenticular reservoirs, a series of simulations were run in a reservoir modeling program where orientation was assumed to occur at various given angles. The reservoir and fracture properties that were manipulated in order to run the model under different scenarios included the following: fracture orientation, fracture half-length, fracture conductivity, reservoir area, permeability anisotropy, and geologic aspect ratios. For each scenario, production of the field was then simulated over a period of time to study sensitivities of the parameters.

The research presented in this paper led to the following main conclusions: 1) refracture reorientation can be effectively studied using a reservoir simulator through manipulation of the fracture and reservoir parameters over time; 2) incremental gains in production and pressure responses were observed with the variance of these various reservoir and fracture properties that were consistent with the possibility of hydraulic fracture reorientation; and 3) results indicate that even assuming refracture reorientation is possible, it would not be economical under typical conditions in most tight gas lenticular reservoirs due to their limited volumes.
Hydraulic Fracturing Using Heavy Brine and Microseismic Monitoring in Yufutsu Oil and Gas Field
Authors: Kamitsuji R. , Nagai K. , Matsuno Y. , Ohsaki Y. , Tamagawa T. , Tezuka K.
Published: January 2009

Hydraulic fracturing using heavy brine was conducted to stimulate the deeper part of the completion interval in the naturally fractured reservoir, Yufutsu Japan. The microseismic monitoring and the temperature surveys showed that the deeper part was stimulated effectively as expected.

The Yufutsu oil and gas reservoir is seated at around 4 km depth in the Southern Ishikari Plain, central Hokkaido, in northern Japan is known as a basement fractured reservoir. The water frac inducing shear dilation is one of the effective stimulation methods for the fractured reservoir. However it is difficult to stimulate the bottom part of the vertically long completion interval with seawater or slick water because the gradient of the fracture closure stress (that is typically 0.6-0.7 psi/ft, equivalent mud weight 1.4-1.6 sg) is commonly larger than that of the injection fluid. The heavy brine (CaCl2/CaBr2 brine 1.8 sg) realizes a pressure gradient larger than the fracture closure stress gradient that can stimulate deeper zone effectively. The numerical prediction using "SHIFT" simulator shows consistent results with the above-mentioned considerations. SHIFT simulates shearing of fractures and related permeability changes in a dynamic process by coupling analyses of the fluid flow and the shear dilation along fractures.

The target well has a long completed interval of 700 m. The deeper part of this well showed poor productivity due to a damage of lost circulation materials. The fracturing operation using the 1.8 sg CaCl2/CaBr2 brine was conducted with the objective to stimulate the damaged zones. About 200kL of heavy brine was injected. The microseismic array sensor was installed in the adjacent well to monitor the stimulation during the injection.

Approximately a thousand microseismic events were observed during the injection. The location of the microseismic events showed that the deeper part was stimulated effectively. A temperature survey conducted after the stimulation revealed the new production zones appeared on the temperature profiles as anomalies which had not been seen before. The AOFC of the well increased by a factor of 1.5.
Assigning value to stimulation in the Barnett Shale: a simultaneous analysis of 7000 plus production hystories and well completion records
Authors: Valkó Peter P.
Published: January 2009

Analysis of publicly available monthly production history and well completion records can shed light onto such long-standing questions as 1) what is the value of a stimulation (re-stimulation) treatment in the Barnett Shale, 2) how does the ultimate recovery depend on treatment type and size, 3) what factors determine the performance of a fractured well. This study starts with the month-by-moth analysis of production history for all gas wells in the Barnett Shale. Using a specialized decline-curve analysis methodology developed for shale gas wells, significant production behavior changes are automatically detected and jumps in estimated ultimate recoveries are calculated for individual wells as well, as for groups of wells. The study then continues with the textual analysis of publicly available well completion records consisting of more than 16 Gigabyte data. The obtained database is submitted to analysis relating ultimate recovery to well inclination, to location, to treatment parameters, etc.
Comprehensive Coupled Modeling Analysis of Stimulations and Post-Frac Productivity—Case Study of a Tight Gas Field in Wyoming
Authors: Settari A. (Tony) , Sullivan R. B. , Rother R. J. , Skinner T. K.
Published: January 2009

This paper presents a new methodology of coupled hydraulic fracturing, geomechanical and reservoir modeling, and an example of integrated analysis of a tight gas well. The new modeling technology and its advantages in field application are demonstrated on a case study of a "science well?? in a tight gas Wyoming field. A detailed model of the well included its entire fracturing and production history, and was constrained by a large amount of field measurements. The model was successfully history matched to all of this data using a common reservoir description. This novel approach thus results in much higher level of confidence compared to using uncoupled models with different assumptions.

The history matching process provided insight in the mechanics of fracturing and flow in this field, and the importance of geomechanical effects. Some of the most important findings are that the formation permeability is highly stress sensitive and increases dramatically during frac injection, fracture length and conductivity is highly variable during flowbacks, and geomechanical effects on conductivity are still evident after several months of production. The calibrated model was then used to assess the gains in productivity possible from improved technology of fracturing, resulting in larger conductivity and length of fractures.
Frac Fluid Recycling and Water Conservation: A Case History
Authors: Gupta D. V. S. , Hlidek B. T.
Published: January 2009

Shallow gas fracturing is very prevalent in Western Canada. Several thousand wells are typically drilled and completed in the shallow gas fields every year. All these wells are typically hydraulically fractured. Prior to 1999, after testing for micro-toxicity, the flowback fluid was allowed to be land farmed in Southeastern Alberta. In that year, the Alberta Energy and Utilities Board began more stringent enforcement of Guide 58, which required that flowback fluid be disposed in a disposal well. More recently, several years of drought conditions in the shallow gas areas of Southeastern Alberta have caused water shortages.

Prior to 1999, the flowback from a particular surfactant-based fracturing fluid could be successfully land farmed. One operator typically had a project of 300 to 400 wells with an average of 5 fracs per day during spring/summer. When the fluid could no longer be land farmed, attempts were made to recycle the flowback fluid. The chemistry of the surfactant gel fluid was insensitive to the water quality, which made the recycling concept successful. Several cost advantages were achieved, which will be detailed in the paper. These included fresh water costs, disposal costs and chemical costs. An additional advantage that was realized involved a 50% reduction in the fresh water requirements for a project.

The paper will detail the chemistry of the fracturing gel, its field application, the optimized recycling operation and the details on cost advantages achieved as well as future direction for further reduction in fresh water usage on a project basis.
Determining Propped Fracture Width from a New Tracer Technology
Authors: McDaniel R. R. , Holmes D. V. , Borges J. F. , Bajoie B. J. , Peeples C. R. , Gardner R. P.
Published: January 2009

An accurate determination of propped fracture geometry will help optimize the benefits derived from a hydraulic fracturing treatment. While advancements in determining propped fracture height have been made recently, there has been no new technology introduced addressing the other aspects of propped fracture geometry.

A new tracer technology has been recently introduced and field tested. This technology incorporates a non-radioactive tag into the coating of a resin coated proppant. The tagged proppant is non-hazardous and environmentally safe. The tagged proppant is activated (after it has been placed in the fracture) by a logging tool that contains a neutron source. The activated tag emits gamma rays at a characteristic energy level that can be detected by the logging tool. Analysis of the data (from the logging run) not only identifies the location of the tagged proppant, but can also be used to develop other valuable information including propped fracture width in the near wellbore region.

The resin coated proppant containing the tag is manufactured in such a manner as to assure that the concentration of the tag in the coating is held at a constant throughout the coating process. Since the level of gamma ray emission is a function of the amount of tag irradiated by the logging tool, the count rate detected by the tool is proportional to both the concentration of the tag and the concentration of the tagged proppant that has been irradiated. Based on these factors, analysis of the logging data not only yields the location of the tagged proppant, but leads to a more accurate calculation of the propped fracture width as compared to previous methods.

This paper will detail the test procedures and resulting data that contributed to the development of this new method to calculate propped fracture width. This method of propped fracture width calculation will then be applied to a variety of actual field applications of the tag technology. The calculated propped fracture width results from the field tests will be presented and discussed in detail.
Are You Buying Too Much Friction Reducer Because of Your Biocide?
Authors: Rimassa Shawn M. , Howard Paul R. , Arnold Michael O.
Published: January 2009

Slickwater fracturing is a large portion of current stimulation treatments in tight gas reservoirs. The fluids typically contain only friction reducer and biocide. They are considered incredibly simple, with little attention paid to their composition beyond the effects of water quality. In many cases, the biocides are sold and added to the fluid stream by production chemical companies while the friction reducers are added by the service company performing the fracture treatment. The paper reviews the chemical interactions between the typical anionic friction reducers and the cationic biocides such as quaternary ammonium compounds. The impact of these biocide-friction reducer interactions is that both materials are consumed and therefore prevented from performing their desired functions. During a treatment this is not obvious, but additional friction reducer eventually must be added to control pumping pressure. Further, the biocide is expected to be unavailable to control bacteria. The goal of any stimulation fluid should be that all components are compatible. As expected, some biocides complex with the oppositely charged friction reducers. This results in the formation of flocks of insoluble polymers in the fluid. Laboratory testing and a field example indicate that the quaternary ammonium biocides reduce the drag reduction seen with the common friction reducer. In comparison, nonionic biocides such as gluteraldehyde do not interact with the friction reducer. The paper also reviews studies with compatible scale inhibitors.
Operators Evaluate Various Stimulation Methods for Multizone Stimulation of Horizontals in Northeast British Columbia
Authors: Thompson Dave , Rispler Keith , Stadnyk Shawn , Hoch Ottmar , McDaniel B. W.
Published: January 2009

Effective reservoir exploitation in tight-gas wells can be achieved by fracture-stimulating horizontal wells. A primary key to economic success when fracture stimulating horizontal wells is achieving the placement of propped fractures uniformly along the entire lateral section. This well completion strategy is becoming a more common method and is currently being used to effectively develop tight-gas reservoirs in northeast British Columbia, Canada.

This paper reviews different well completion and stimulation methods currently being applied in horizontal well stimulation in Northeast British Columbia, Canada. Specifically, the paper reviews horizontal well stimulation of the Montney formation that extends from northwestern Alberta into Northeastern British Columbia. Well construction and well completion strategy should be based on reservoir understanding and optimum stimulation design. This paper discusses a number of options for well construction and stimulation methods, including: packer isolation and frac sleeves, pump down bridge plugs and perforating guns, coiled tubing deployed bridge plugs and tubing conveyed perforating, and hydrajet perforating on CT with sand plug isolation. Evaluation and comparison of these different techniques include well construction, well completion including post-stimulation cleanouts, and post stimulation production analysis, including consideration of logistics, method reliability, and comparison of results.
Acid Fracturing: The Effect of Formation Strength on Fracture Conductivity
Authors: Gomaa A. M. , Nasr-El-Din H. A.
Published: January 2009

A few studies considered the role of rock strength on fracture conductivity retained at elevated closure strengths. Based on experimental results and field data, many correlations were derived with a consideration of both the surface roughness and rock mechanical properties. These studies found that acid fracture conductivity is sometimes lower with longer acid contact times than with shorter ones. This is apparently the result of the weakening of the rock structure along the face of the fracture with increased acid exposure, such that the conductivity decreases more rapidly with increasing the closure stress.

Based on extensive literature survey of three types of carbonate rocks, it was found that chalk has the lowest rock embedment strength and the fractures closed at much lower stresses compared with limestone or dolomite. Dolomite has the highest rock embedment strength and best conductivity results compared with other rocks tested.

A sensitivity analysis was performed to determine the effect of rock embedment strength, and dissolved rock equivalent conductivity on the fracture conductivity. The results of this analysis showed that dissolved rock equivalent conductivity determines the maximum conductivity at a closure stress equal to zero, while the value of rock embedment strength determines the decline in conductivity with increasing the closure stress. This analysis shows that the value of dissolved rock embedment conductivity doesn't affect the difference that exists in some of the developed correlations, while the value of rock equivalent strength has a significant impact on this difference. Finally, the rock embedment strength is a key parameter that affects the fracture conductivity. This paper discusses current correlations to predict fracture conductivity, and addresses the influences of several key parameters on the fracture conductivity.