bluuebunny/crossref_metadata_2025 huggingface dataset:
Controle Ressonante Aplicado na Redução da Capacitância de Barramento em um Conversor Duplo Buck-Boost Integrado para Acionamento de LEDs
Authors: Luz Paulo Cesar Vargas , Cassol Jhonatan Antônio , Righi Matheus Farencena , Vargas Gabriel da Silva , Prado Ricardo Nederson do , Kirsten André Luís
Published: February 2018

Este trabalho propõe uma técnica para a redução da capacitância de barramento em topologias de estágios de potência integrados aplicada ao acionamento de LEDs. Esta redução é possível através de um controlador Proporcional Integral Ressonante. Mesmo com a redução do capacitor de barramento, a ondulação da corrente nos LEDs é mantida constante e dentro dos limites recomendados pela IEEE Std 1789. É abordada a distorção da corrente de entrada devido à aplicação do controle, visando à concordância com a norma internacional IEC 61000-3-2 classe C para equipamentos de iluminação. São apresentados os resultados experimentais de um protótipo dedicado a acionar 32 LEDs com 700 mA, com o intuito de validar e avaliar a viabilidade da técnica proposta.
Conversor CC-CC Paralelo Ressonante Meia Ponte Assimétrico com Saída em Tensão
Authors: Pont Neilor C. Dal , Jr Delvanei G. Bandeira , Lazzarin Telles B. , Barbi Ivo
Published: February 2018

Este artigo propõe uma topologia de um conversor CC-CC meia ponte, paralelo ressonante, com modulação PWM e comandos assimétricos, controle da tensão de saída pela variação da razão cíclica e saída em tensão. Além disto, o conversor é estudado com estágio de saída com dobrador de tensão. A configuração possui número reduzido de interruptores, elimina circulação de corrente média nos elementos passivos tanto no primário quanto no secundário, e pode utilizar os parâmetros intrínsecos do transformador em seu projeto, o que a torna atrativa para aplicações como fontes de alta tensão de saída. Análise das etapas de operação, característica de saída, equacionamento orientado ao projeto e a implementação de comutação sob tensão nula são abordados neste artigo. O estudo do conversor é verificado através de um protótipo de 1 kW, 400 V de entrada e 400 V de saída. O conversor apresentou rendimento elevado, acima de 97%, e comutação suave numa faixa de carga acima de 60% do valor nominal.
El financiamiento educativo público en Costa Rica a largo plazo (1860-2016)
Authors: Molina Jiménez Iván
Published: February 2018

El presente artículo analiza el financiamiento de la educación estatal en Costa Rica a largo plazo. Con este propósito, se revisaron los aportes y limitaciones de los estudios previos sobre el financiamiento educativo. Posteriormente, se identificaron las principales tendencias de crecimiento o decrecimiento del financiamiento educativo, y su relación con procesos como crisis económicas, golpes de Estado, guerras y ciclos de expansión de las actividades de exportación y del mercado interno. Por último, se analizó el impacto que los aumentos o los descensos en el financiamiento educativo tuvieron en las coberturas de la enseñanza primaria, secundaria y universitaria. Al final se concluye que el Estado costarricense ha mantenido, desde el siglo XIX, un compromiso sostenido y creciente con el financiamiento de la enseñanza pública, con  algunos retrocesos por lo general de corta duración, excepto el correspondiente al período 1981-2007.
Common Enemies at the Frontier of the Spanish Empire: Military Alliance between Pirates, African Americans and Native Americans in the Darién and Chocó regions. XVI - XVIII centuries.
Authors: Garzón Moreno Daniel Antonio
Published: February 2018

The present article aims to explore military alliance between pirates and corsairs, African Americans andNative Americans from the middle of the XVI century to the end of the XVIII century, in a border zone of the Spanish Empire formed by the Panama or Darien Isthmus. For the development of this research, it was essential to understand the internal dynamics of American piracy, Native Indians of the Caribbean and Paciic regions, African American slaves and marroons, and the Spanish authorities that exerted control in the Isthmus of Darién; a region which for more than two centuries confronted emerging military alliancesbetween the aforementioned agents, in order to hold their defense system and colonial domain in this border area. The multiplicity of factors that made possible an encounter or alliance among pirates, natives and negros in the American continent, whether for comercial, military or survival purposes, allows us to understand sociocultural phenomena developed in the New World, which gives evidence of forms of social relation that generated instability in the colonial order, with administrative, economic and military implications for the Spanish Empire.
Prada Rodríguez, Julio. Marcharon con todo. La represión económica en Galicia durante el primer franquismo. Madrid: Biblioteca Nueva, 2016.
Authors: Álvarez Gómez María Concepción
Published: February 2018

El profesor Julio Prada Rodríguez es un reconocido especialista en el ámbito de la violencia política y la represión franquista, campo en el que ha publicado obras de referencia como De la agitación republicana a la represión franquista. Ourense (Ariel, 2006), La España masacrada (Alianza, 2010) o Franquismo y represión de género en Galicia (Los Libros de la Catarata, 2013). A diferencia de sus trabajos anteriores, centrados en la represión física, en esta investigación profundiza en uno de los aspectos menos conocidos de la misma: su dimensión económica.
La útil presencia del pasado: a propósito de los años de la «Revolución Libertadora» en una ciudad del interior de la Argentina (1955-1958)
Authors: Escudero Eduardo Alberto
Published: February 2018

Este artículo se dedica a documentar e interpretar los usos del pasado desplegados durante la dictadura instaurada desde 1955 en Argentina, con posterioridad a la caída del peronismo. La perspectiva analítica asumida propone observar el modo en que el pasado resultó ser un recurso clave para legitimar un nuevo orden político y para caracterizar a los enemigos en vistas de ofrecer nuevas interpretaciones de la historia y rescatar, a la vez que resignificar, a los próceres del pasado nacional. El trabajo se centra en una mirada específicamente  local, investigando acerca de los discursos, las prácticas y las representaciones del pasado desplegadas en la ciudad de Río Cuarto, Córdoba, Argentina, en oportunidad del proceso político que buscó «desperonizar» el espacio público y restaurar la matriz liberal de la cultura política e histórica del país. La metodología empleada se basa, fundamentalmente, la exegesis de fuentes primarias, de corte periodístico, recuperando cualitativamente la discursividad de época. Como resultante del ejercicio analítico de los usos del pasado examinados, es posible observar cómo distintos actores claves de la política, la cultura y la educación riocuartense pusieron en marcha una serie de recursos cognitivos, argumentativos y simbólicos del pasado, para sobrellevar la tarea de forjar memoria merced al nuevo orden político: procurando la reactualización de la memoria de la nación liberal para contraponer pedagógica e intensamente al peronismo.
Editorial: Para una historia de la guerra y de las milicias. Siglos XVI a XIX
Authors: Bonnett Vélez Diana Inés
Published: February 2018

En su dossier, el número 16 de la revista Historia Y MEMORIA explorará las formas que han caracterizado las guerras y la organización de las milicias en occidente, durante el mundo moderno. Tres grandes cuestiones interesan al dossier. La importancia de la guerra en la disciplina de la Historia, las categorías empleadas para nombrarla y el carácter cambiante de la guerra.
Etienne Bloch: bibliógrafo de Marc Bloch
Authors: Rojas Reinaldo
Published: February 2018

Étienne Bloch (1921-2009) dedicó los últimos años de su vida al rescate y difusión de la obra escrita por su padre, el gran historiador francés Marc Bloch (1886-1944). Desde 1997 hasta su muerte en 2009, impulsó el estudio crítico de la historiografía blochiana a través de la creación de la Asociación Marc Bloch, la edición crítica de sus obras y el impulso de estudios sobre la vida de su padre gracias a la apertura de sus archivos familiares. Es un hecho extraordinario, casi sin precedentes, que el hijo de un gran historiador, sin conocer inicialmente el oficio, se transforme en uno de los más importantes conocedores y críticos de la obra de uno de los historiadores más importantes del siglo XX, a escala universal. El propósito de este ensayo es acercar al lector a la minuciosa labor desplegada por Étienne Bloch como bibliógrafo de Marc Bloch.
t-Representability of maximal subgroups of symmetric groups
Authors: P Sini
Published: February 2018

A subgroup \(H\) of the group \(S(X)\) of all permutations of a set \(X\) is called \(t\)−representable on \(X\) if there exists a topology \(T\) on \(X\) such that the group of homeomorphisms of \((X, T ) = K\). In this paper we study the \(t\)-representability of maximal subgroups of the symmetric group.
Lattice of generalized closure operators
Authors: T. Kavitha
Published: February 2018

In this paper, we compare the lattice of generalized closure operators and the lattice of generalized Cech closure operators.
Infuences of Rice Husk Biochar (RHB) on Rice Growth Performance and Fertilizer Nitrogen Recovery up to Maximum Tillering Stage
Authors: Sang Deniel Anak , Bakar Rosenani Abu , Ahmad Siti Hajar , Rahim Khairudin Abdul
Published: February 2018

A pot study was carried out to investigate the effects of rice husk biochar addition on rice growth performance and fertilizer nitrogen recovery. The biochar effect was studied by using 15N labelled fertilizer urea (10 atom% 15N), as isotopic tracer, until maximum tillering stage (75 days after sowing). Rice husk biochar (RHB) was applied at rates of 0, 5, 10 and 20 Mg ha-1 and laid in randomized complete block design with four replications. The result showed that biochar application significantly improved soil chemical properties (pH, total C, total N, and available P) compared to control treatment. Biochar addition increased number of tiller and root dry matter weight up to 4% and 35%, respectively, compared to un-amended pot. Likewise, application of biochar significantly increased N, P and K uptake by 3%, 19% and 33%, respectively, as compared to the nutrient uptake from the control treatment. Biochar treatment had no significant impact on fertilizer nitrogen recovery in aboveground biomass, in the range of 41% and 42%, in comparison to the control. However, nitrogen fertilizer recovery in soil significantly increased by 47% over the control at application rate of 20 Mg ha-1 RHB.  Increased fertilizer N recovery in soil possibly reduced N losses to the environment from volatilization and denitrification processes. Total 15N fertilizer recovery also found increase at highest application of RHB biochar with an increment of 16%. In general, addition of biochar appeared to enhance crop growth performance but its effect on fertilizer N recovery in plant requires further study up to maturity of rice plant.
The Distribution of Lead Accumulation (Soil, Water and Mangrove Vegetation) to Conserve Segara Anakan Lagoon
Authors: Hilmi Endang , Siregar Asrul Sahri , Syakti Agung Dhamar
Published: February 2018

Segara Anakan Lagoon  is a  specific lagoon as dispose industry waste area, i.e. lead waste.  Distribution of lead accumulation in vegetation, soil and water can explain pollution status in Segara Anakan Lagoon.  This study aims to analysis lead accumulation distribution  (soil, water and vegetation),  bioaccumulation factor (BAF), translocation factor (TF), leaf morphometric (the lead effect for mangrove vegetation), and to develop pre-design a mangrove  zoning based on lead accumulation. The results showed that lead accumulation in Segara Anakan Lagoon (SAL) was 0.177 – 0.233 mg/l (water),  0.320 – 0.780 mg/kg (soil),  4.80–8.67 mg/kg (mangrove roots), for stem between 2.48–6.96 mg/kg (mangrove stem), and 1.48–4.76 mg/kg (mangrove leaf).  BAF of mangrove vegetation scored between 22.2–40.1 and TF between 0.9–1.3. The lead accumulation of soil depths were 8.89 mg/kg (0-50 cm) to 0.56 mg/kg (150-200 cm). The effect of  lead accumulation was observed as leaf damage between 2-60 % of surface leafs. And based on best lead accumulation of mangrove vegetation showed that the first mangrove zoning was Rhizophora apiculata, Bruguiera sexangula, Aegiceras corniculatum and  Sonneratia caseolarisKeyword: lead accumulation; mangrove capacity; bioaccumulation factor; translocation factor;  lead effect
A MORTE EM HILDA HILST
Authors: Novais Joseane Aguiar , Moreira Marcello
Published: February 2018

O presente artigo discorre acerca do livro Da morte. Odes mínimas, de Hilda Hilst, ressaltando especificamente o tratamento dado à morte em suas pequenas odes, estas que fazem parte de uma obra perturbadora em virtude do posicionamento singular da criatura que as escreveu, denominada pela crítica como voluptuosa. No referido livro, a autora trata da finitude da vida de maneira singular, pensando-a sem querer ultrapassá-la, ressaltando seu processo lento e contínuo, que coroa toda uma existência e que é algo íntimo, sereno e natural. Visão bastante distinta daquela pessimista apresentada durante toda uma tradição, onde a mesma era vista como sombria, dolorosa, algo que provoca temor.
Effect of Salinity and Water Ions on Electrokinetic Interactions in Carbonate Reservoir Cores at Elevated Temperatures
Authors: Ayirala Subhash C. , Saleh Salah H. , Enezi Sultan M. , Al-Yousef Ali A.
Published: February 2018

Smartwater flooding through tailoring of injection-water salinity and ionic composition is becoming an attractive proposition for improved oil recovery in carbonate reservoirs. Most recent studies suggest that surface-charge change induced by lower salinity and certain water ions on carbonate surfaces is the main mechanism responsible for favorable wettability alteration and, consequently, higher oil recovery in smartwater flooding. Unfortunately, these studies determined ζ-potentials using the technique of electrophoretic-mobility (EPM) measurement with powdered-crushed-core samples, which may not reflect the natural conditions existing in the subsurface reservoirs. In this study we used an experimental technique dependent on streaming-potential (SP) measurements to determine ζ-potentials in intact carbonate reservoir core samples saturated with different brine salinities and individual ion compositions at both ambient and elevated temperatures.

The results indicated a favorable effect of sulfate ions in carbonate reservoir cores to alter ζ-potentials toward more negative, and the reactivity of these ions increased significantly by nearly one order of magnitude at higher temperatures. Among the positive ions, calcium showed the highest reactivity to shift the ζ-potentials to slightly positive. Both magnesium and sodium ions showed almost similar behavior to change the ζ-potentials toward less negative. In addition, only minor to moderate changes in ζ-potentials were observed with the positive ions when the temperature is increased. In view of considering the reported negative ζ-potentials at the carbonate crude-oil/brine interfaces, such a change in ζ-potential to an extreme negative obtained in carbonate reservoir cores upon exposure to injection waters containing sulfates could have a favorable effect on wettability alteration because of the resulting same polarity at both the interfaces. The dynamic time-dependent effects on ζ-potentials measured during the displacement of seawater by smartwater (10-times-reduced ionic strength seawater) in reservoir cores showed an immediate shift in the ζ-potential value from positive to negative. This instantaneous change to negative values observed in the ζ-potentials confirms the beneficial effect of smartwater to activate favorable electrokinetic interactions in carbonate reservoir cores.
A Semianalytical Method for Modeling Two-Phase Flow in Coalbed-Methane Reservoirs With Complex Fracture Networks
Authors: Yang Ruiyue , Huang Zhongwei , Yu Wei , Lashgari Hamid R. , Sepehrnoori Kamy
Published: February 2018

Coalbed-methane (CBM) reservoirs are naturally fractured formations with cleats surrounding the coal matrix. Analyzing and predicting CBM-production performance is challenging, especially for early-time production, because of the complex fracture networks and gas/water two-phase flow.

In this study, we develop an efficient semianalytical model to predict gas and water production in CBM reservoirs with multiscale fracture networks. The activated large-scale or interconnected cleats and hydraulic fractures are modeled explicitly as discretized segments with connected nodes. The small-scale cleats and disconnected natural fractures are described implicitly as “enhanced matrix permeability.” We incorporate critical gas-flow mechanisms and stress sensitivity of the fracture network in the model. The two-phase-flow mechanism is considered by iteratively correcting the relative permeability to gas/water for each fracture segment and capillary pressure at each node with the reservoir depletion. We verified the model against a numerical reservoir simulator, field data, and an analytical solution. Subsequently, we apply the model to quantify the effects of fracture-network complexity/connectivity and stress sensitivity on gas/water-production behavior.

This work presents an accurate and fast semianalytical model to perform two-phase flow of gas and water in CBM wells with complex fracture networks. The approach is easier to set up and less data-intensive than using a numerical reservoir simulator, and more flexible in handling the complex-fracture networks than full analytical models. This method provides a promising technique for better understanding the effect of the cleats and fracture networks present in CBM reservoirs on gas and water production.
Using Simulator to Prepare for Total Loss Risk Scenarios Utilizing Controlled Mud Cap Drilling in the Barents-Sea
Authors: Oedegaard S. I. , Hollman L. , Smaaskjaer G. , Claudey E. , Mehus Ø. , Andreassen T. , Nabavi J.
Published: February 2018

The objective was to be prepared for a total and sudden loss scenario while drilling and coring a challenging well in the Barents sea. A dual-gradient Controlled Mud Level (CML) system with Controlled Mud Cap Drilling (CMCD) mode was installed on the rig to manage minor and/or total losses. Prior to spud of the section, an advanced dynamic simulator with the actual well configuration loaded was used to conduct offline training, and prepare the drilling team and involved service personnel for the operation.

Experience from previous wells in the area identified the risk of drilling into karstified carbonate zones with the potential of leading to total and sudden losses. An advanced dynamic simulator was used to reflect the details of the CML system to be used. The rig crew together with the CML operator and other involved service personnel were trained on how to manage a total loss scenario by switching from CML to CMCD mode. All relevant operational procedures were used as a basis for creating training scenarios and operational preparations for the exercises.

This paper will briefly present the simulator set-up, the operation/training procedures and results from the training. Feedback from the operation itself will also be described including lesson-learned from utilizing a full-scale dynamic simulator with the actual well loaded during preparation for operation.
A Practical Model for Wellbore Strengthening
Authors: Chellappah Kuhan , Majidi Reza , Aston Mark , Cook John
Published: February 2018

This paper presents a new model that integrates relevant aspects of geomechanics and drilling fluids to provide practical solutions for wellbore strengthening. This integrated approach accounts for the influence of stress state, rock properties, wellbore design parameters, and the impact of particle-laden fluids on the creation, growth, and arrest of an induced fracture. A dimensionless parameter called the Wellbore Strengthening Index (WSI) is introduced as a measure of desired strengthening normalised to the rock stiffness. WSI is used to estimate the concentration of wellbore strengthening material (WSM) required for a given application. A semi-empirical correlation then relates solids loading to the length of an induced fracture at time of sealing. A closed-form equation is proposed to estimate fracture width using this calculated fracture length. Once induced fracture dimensions are determined, appropriately sized WSM is selected for efficient sealing. The model is relatively straightforward to code into a practical and user-friendly design tool for wellbore strengthening. Two case studies are presented to show successful implementation of the new model.
Fuel Economy and Emission Characteristics of a High Horsepower Natural Gas/Diesel Dual-Fuel Engine in Oil & Gas Operations
Authors: Wijesinghe Asanga , LaFleur Carolyn , Meng Fanxu , Colvin John , Haut Richard
Published: February 2018

Oil & gas industry continuously seeks alternative ways to combine cleaner and lower cost gaseous fuel with diesel fuel as a diesel fuel supplement to reduce undesirable emissions and expensive fuel cost from these diesel engines. One substantially increasing technology is converting CI diesel engines to natural gas/diesel dual-fuel engines using a moderate engine modification. However, just how these modified engines perform in drilling operations is not well documented and require further assessment. Using advanced instrumentation designed for use at active drilling sites, fuel consumption, gaseous emissions, and soot in exhaust from a high-horsepower engine coupled to a generator were measured in both dual-fuel and diesel-only operation modes. Dual-fuel engines have the advantages of providing the same power as conventional diesel engines, producing lower amounts of emissions such as nitrogen oxides and soot, and cost saving through diesel displacement up to 50 %. In addition, the results show that the emissions from combustion of natural gas are very different from those of the diesel fuel it displaces. Co-combustion of the two fuels in a CI engine exhibits distinct emissions characteristics, with advantages in reduced oxides of nitrogen, carbon dioxide, and soot. Significant disadvantages were seen in emissions of non-combusted methane and formaldehyde. In some conditions, as much as 30% of the gas fuel was emitted unburned, significantly diminishing fuel efficiency and increasing greenhouse gas emission.
Recorded Well Data Enriches the Testing of Automation Systems by Using a Deep Neural Network Approach
Authors: Yu Yingwei , Chambon Sylvain , Liu Qiuhua , Belaskie James Philip
Published: February 2018

One technique useful in the testing and development of drilling automation system is to use synthetic data. A good drilling time series simulator can enrich a dataset for testing, and enable the inference of the states of drilling in real time. However, conventional simulators do not generate the "warts" of real data (noise, gaps, etc.). The proposed solution is a model that learns from real data, characterizes the different drilling responses and conditions the data with a deep neural network (DNN) approach, and generate realistic drilling time series dataset.

To simulate a drilling-time series dataset, a DNN can model physical properties of the formation, rig, and sensors, and generates data with realistic curve patterns when it is trained on actual measurements, e.g. block position, hook load, standpipe pressure, and surface torque. The neural network has multiple convolutional, recurrent, and fully-connected layers. The model, trained with wellsite recorded data, captures the spatio-temporal distributions among data channels, and then uses a windowed input to predict the next data points, which are then fed back into the network to generate the simulated data sequence recursively. An actual sensor drilling-time series dataset containing various channels are input into the DNN. The networks contain eight convolutional layers with three max-pooling layers, three recurrent layers, and four fully-connected layers. The time window used in the input contains 512 samples for each channel, while the output is 1 sample for each channel.

After training the network for 200 epochs, the network can successfully simulate time series data recursively. The simulated time series preserve the features of the original training data, while maintaining the data distribution of multiple channels. For example, the network shows a consistent "inslips" pattern in the hook load channel when the block position moves quickly from bottom to top. Currently the simulation is autonomous based on the training data, and does not take input as controls, which is our future steps.

The proposed DNN model is a low-cost, robust model that simulate drilling-time series datasets containing complex spatio-temporal patterns. Our proposed algorithm is the first known simulator of drilling time series datasets that models the nontrivial physics laws and properties, including formation, rig, and sensors, and generates data containing realistic curve patterns with a deep neural network approach. The simulator greatly helps the inference component of automation systems with the enrichment of datasets that are available for testing.
Wellbore Stability Solution Incorporating the Weak Bedding Planes Effect with Field Case Study
Authors: Mehrabian Amin , Pérez Arturo Díaz , Santana Claudia
Published: February 2018

Wellbore stability in shale is often hampered by the detrimental effect of existing weak bedding planes on the strength of the rock surrounding the wellbore against shear failure. This paper presents results from a formal closed-form analytical solution to the wellbore stress problem that incorporates rock failure along weak bedding planes. The solution is used for a case study of a highly inclined well section in a laminated layer of troublesome shale with a strike-slip faulting regime above the target formation in the Latin America region.
Real-Time Bit Wear Monitoring and Prediction Using Surface Mechanics Data Analytics: A Step Toward Digitization Through Agile Development
Authors: Liu Yu , Kibbey Justin , Bai Yanbin , Wu Xianping
Published: February 2018

Severe bit damage is a known issue in west Texas land drilling due to abrasive sand formation and interbedded hard stringers. Operational performance and rig cost are often impacted by penalty fee of bit DBR (damage beyond repairable), low ROP (rate of penetration) with worn bit, and inefficient decision-making on tripping. A real-time data analytics application is developed aiming to provide actionable information to operation to expedite decision making process.

A historical dataset of surface mechanics data and bit records is collected from 40 bit runs drilled in 2016 and early 2017. A hybrid data analytics procedure consisting of conventional physical modeling of drilling mechanics and supervised learning using machine learning technique is conducted to separate bit failure pattern from normal formation transition and drilling parameters adjustment. A metric based algorithm is constructed for real-time monitoring of bit drilling performance and early warning on bit cutter wear conditions.

A web-based real-time software is developed and field trialed on three wells with satisfactory results. Subsequent deployments in DART (Drilling Automation Remote Technology) center and field offices have been quickly rolled out for five rigs in west Texas. Positive feedback is generated from operation and engineers. Attributed to the success of agile development framework and adaptive software architecture, other advisory mode features such as motor life monitoring, smart-tripping evaluation, and sliding diagnosis etc. are under development.

The application discussed in this paper combines expert's domain knowledge with machine learning techniques and provides actionable information to support on-site operational decisions. The development and deployment of this application follows an agile mode innovation framework, through which operational need and technical solution are quickly bridged and tangible business value is able to be delivered in short term.
The Role of Big Data in Operational Excellence and Real Time Fleet Performance Management—The Key to Deepwater Thriving in a Low-Cost Oil Environment
Authors: Bolen Matt , Crkvenjakov Vladimir , Converset Julien
Published: February 2018

Over the past three years, the oil and gas industry has experienced its deepest downturn since the 1980s. Recovery has been slow, setting the deepwater industry at a strategic inflection point where step changes are necessary to remain competitive. Considering that deepwater upstream capital projects are some of the most expensive projects in the industry, capital costs on a per well basis must be reduced in order for deepwater to continue to attract capital. Achieving operational excellence by embracing the big data revolution will help answer the challenge in thriving in a low-cost oil environment.

Oil and gas operators as well as others suffer from data overload. A major challenge in the process of achieving operational excellence is to find a way harness big data and capitalize on its benefits. The paper outlines the solution that a major operator and service company developed that established a unique well construction optimization process, improved consistency and moved every operation closer to the technical limit.

The solution was developed for the major operator in Gulf of Mexico (GOM) deepwater fleet and was successful in reducing the well cycle times by: Applying a unique approach and workflow to transform big data into usable knowledge and enable critical thinking in the process of data analysis. This led to challenging current established operational procedures, making adjustments to actual well conditions and maximizing the efficiency of the rig.Enhancing a standard set of key performance indicators (KPIs) so that each operation is measured and the performance is understood.Establishing an effective in-house real-time data analysis center that fully supports the integrated drilling teams in order to drive data-driven decision making.Utilizing concise visualization of surface digital data so that clarity from the data can be gained and insights communicated to the rig teams.
Well Integrity: Coupling Data-Driven and Physics of Failure Methods
Authors: Das Bibek , Samuel Robello
Published: February 2018

A hybrid model based on Physics of failure and Data-driven algorithms is developed that can estimate remaining useful life of production casing (well barrier). The state of integrity of the well barrier is assessed by updating the reliability under operational loads.

The interactions between the casing and surrounding formation, and effects of tribocorrosion on the casing are considered. Tribocorrosion is the process of degradation of a material resulting from a sequential process of (i) mechanical wear (due to sliding, friction, or impact) followed by (ii) a corrosive action of the surrounding environment. The model includes simulating casing wear due to drilling, and enhanced degradation due to conditions in the well.

The main capability of the model is to help well integrity analyst with insight of future health states of a monitored well. This is achieved in two main steps; the first being the offline module comprised of degradation models. The second is the pattern recognition based on well log and features mapping, and estimation of remaining useful life of well barrier. The production casing grade P-110 undergo reduction in strength due to wear during drilling, induced stress and hydrogen induced cracking. The remaining useful life is calculated for the depths of interest and time.

A comparative analysis is carried out using the industry standard soft-string model versus a more comprehensive stiff-string model to estimate wear. The paper presents a unique approach to predict the remaining useful life of a well barrier and the dynamic state of the well's operational integrity. The prediction is not solely based on statistical modeling but also incorporates barrier engineering and physics of failure in the model.
Gas Kicks in Non-Aqueous Drilling Fluids: A Well Control Challenge
Authors: Ma Z. , Vajargah A. Karimi , Chen D. , van Oort E. , May R. , MacPherson J. D. , Becker G. , Curry D.
Published: February 2018

Non-aqueous drilling fluids (such as synthetic-based mud) are frequently used to drill one or more sections of an oil/gas well to reduce drilling problems such as shale sloughing, wellbore stability, and stuck pipe. However, solubility of formation gas in such fluids makes early gas detection and thereby the well control process very challenging. This is of particular concern in deep offshore wells, in which large amount of gas can be dissolved in non-aqueous drilling fluids under high pressure and temperature conditions. The gas remains in solution until the bubble point is reached. Thereafter, a sudden release of gas at shallow depth can compromise wellbore and riser integrity, particularly when the gas has passed the blow out preventer installed at the seafloor. An advanced planning tool to simulate the transient multi-phase phenomena associated with gas kicks in non-aqueous drilling fluids is therefore highly desirable.

This paper presents a novel and comprehensive hydraulic model with associated calculation routines and software to simulate a gas kick in non-aqueous drilling fluids. A transient drift-flux approach based on conservation of mass and momentum was applied in association with appropriate algebraic closure equations and sophisticated friction and choke models. Advanced numerical schemes, where applied previously, have been modified to handle the mass transfer between the liquid (mud) and gas phases. In addition, PVT models have been included to investigate and predict the effect of gas solubility in various types of drilling fluids.

The calculation routines contained in a new software tool predict crucial parameters during well construction such as pit gain, gas break out location and void fraction, annular pressure profile, kick tolerance, choke opening, flow-out, standpipe and casing pressures. Simulation results generated using the tool are presented here for both water-based and synthetic-based muds to illustrate the impact of gas solubility on kick behavior. The tool can handle several other complexities which occur during a well control incident such as multiple influxes from one or several formations, dynamic well control (suitable for managed pressure drilling), automated choke control, sudden pump startup/shutdown, non-Newtonian drilling fluids, arbitrary wellbore path, lost circulation, etc.

Applying advanced numerical schemes associated with relevant PVT models and several types of boundary conditions makes the tool comprehensive, unique, robust, and efficient for well control analysis for a variety of complex drilling scenarios, particularly deepwater wells. As such, it has the potential to enhance well control operations and well design, thereby enhancing rig safety and reducing non-productive time and cost associated with well control-related events.
Drilling Interbedded and Hard Formations with PDC Bits Considering Structural Integrity Limits
Authors: Pastusek Paul , Sanderson Derek , Minkevicius Andrius , Blakeman Zachary , Bailey Jeff
Published: February 2018

Although PDC bits dominate the footage drilled in the oilfield, transitions at interbedded formations and high lateral vibrations are still problematic for PDC bits and reamers.

This paper describes design features, operational parameters, and procedures found to substantially reduce cutter damage, often allowing the section to be drilled in one run, resulting in significant cost savings. It also covers data analysis needed to determine if interfacial severity is the key limiter in a given application.

Time and depth based drilling mechanics data are used to determine the sections of the hole that cause the observed cutter damage and optimize parameters.

Forensics analysis is used to determine the type of cutter damage seen when drilling these formation intervals. Structural integrity of the cutters is estimated from forensics analysis, lab tests, as well as stress analysis of cutters loaded to replicate the observed damage.

Review of the bit and BHA designs often show opportunities for design improvements and cutter selection. Drilling parameters are identified to keep the bit and cutters below the structural integrity limit.

Drilling interbedded formations causes the cutters near the nose of the profile to fracture from tangential overload, through the diamond table and carbide support. This is a significantly different failure mode than the cutter spalling fracture on the bit shoulder seen with bit whirl.

Review of drilling mechanics data showed significant reamer damage and reductions in ROP at the formation transitions when entering salt with a bit and reamer combination. Drilling parameter and BHA design changes improved drilling performance in these transitions.

Finite element studies were requested of bit vendors to estimate the structural integrity of cutters loaded in the tangential direction. Independently, forensic analysis was also used to estimate the range of loads and depth of cut that cause structural overload.

Drilling interbedded formations and transitions at a controlled depth of cut, as opposed to weight on bit control, avoids exceeding the structural limit of the cutters while only part of the cutting structure is drilling the harder formation and the rest of the profile is in softer formation. Depth of cut elements are engaged to keep the bit stable while control drilling. Other design changes are considered to eliminate cutter overload using existing designs as a starting point.

The structural integrity concept applies to hard, interbedded, conglomerate and/or vuggy formations, as well as formation transitions and shoe drill out and milling operations. Effective drilling of such interfaces can be achieved by knowing the depth of cut that can be sustained in the harder formation, while avoiding damage from vibrations. Cutters must be selected for fracture resistance in the tangential direction, and many bit vendors do not yet track this property.
Anti-Collision Best Practices Developed for Horizontal Drilling Across Pre-Existing Horizontal Wellbores
Authors: Britton E. , Grande R.
Published: February 2018

This paper focuses on anti-collision best practices developed and implemented by Liberty Resources for horizontal drilling across pre-existing horizontal wellbores within the same horizon in the Williston Basin. These multidisciplinary collaborative workflows have allowed Liberty Resources to successfully drill multiple complex horizontal wellbores traversing as close as 10 feet wellbore-to-wellbore to existing laterals.

As the horizontal infill development of unconventional reservoirs progresses, complex wellbore trajectories with heightened collision concerns will be required. To achieve this requires advancing the industry's anti-collision standard practices with new and more precise anti-collision methods, detailed planning, and near perfect execution. In the Williston Basin alone there are over 13,000 vertical wells, 15,000 horizontal wells, and over 1,000 re-entry and directional wells drilled to date, with the first horizontal wells introduced to the basin over 30 years ago. Historically, the horizontal wells were drilled using a vast array of well designs and orientations due to the limitations of technology, industry practices and standards, and the insufficient understanding of the reservoir. Advancements in drilling and completions technologies and a better understanding of the reservoir now allow leases to be reassessed for infill potential. This increased infill development has led to increasingly complex wellbore trajectories with collision concerns not only for existing vertical wellbores but now also for existing horizontal wellbores within the same or proximal horizons.

The anti-collision best practices include directional and geologic planning considerations, operational tolerances and requirements including zonal determination, communication protocols, and risk management practices. Creating a broad framework that allows for flexibility to adjust for distinct operational constraints.

These workflows and tolerances have been implemented in three horizontal wellbores traversing seven same-formation pre-existing horizontal wellbores. The anti-collision method was successfully applied in both the Middle Bakken and Three Forks formations, each with their own varied and unique geologic characteristics, demonstrating applicability for a wide range of reservoirs. The ability to execute complex wellbores opens new opportunities to access additional resources in previously considered "fully developed" acreage.

The methods presented in this paper have allowed the routine drilling of horizontal laterals as close as 10 feet to existing laterals. This technology can be applied to a variety of reservoirs opening new opportunities to access additional resources previously considered unrecoverable due to existing wellbores.
Modeling of Cuttings Lag Distribution in Directional Drilling to Evaluate Depth Resolution of Mud Logging
Authors: Naganawa Shigemi , Suzuki Manabu , Ikeda Kenji , Inada Norihito , Sato Ryosuke
Published: February 2018

Dispersion of cuttings transport velocity limits the depth resolution in mud logging. An attempt to model the cuttings lag depth distribution caused by the dispersion of cuttings transport velocity in directional drilling is presented. The depth resolution of mud logging in directional and horizontal wells is evaluated based on the cuttings lag experiments and lag depth simulations using the developed model. The approach of cuttings lag calculation is based on the previously developed complete physical model of transient cuttings transport behavior in directional drilling. The lag distribution is modeled using the lognormal distribution probability density function. The parameters of the distribution function are determined by lag time measurement experiments for various hole inclination angles using a large-scale cuttings transport flow loop apparatus. The implementation of lag depth calculation can be generally achieved by convolving the lag distribution functions determined for each hole section with different inclination angles. In this study, however, the linear combination of distribution functions is mathematically considered for simplicity.

Lag depth simulation studies are presented for a realistic model directional well based on a field data with consideration of variation in rate of penetration. The significant finding is that cuttings sampled at the surface can be contaminated by cuttings originated from other unintended depths to the extent being not negligible compared to the typical sampling interval of 30 ft or 10 m. This tendency of smearing in the formations and depths from which the sampled cuttings are originated would be significant if the high inclination or horizontal hole section exceeds a certain length depending on the rate of penetration. The presented approach has the ability to quantitatively evaluate the uncertainty in the depth resolution of mud logging that is crucial for improving the lateral quality of reservoir characterization which can be beneficial such as in shale oil and gas projects.
The Impact of Molecular Diffusion of Methane into Wells with Oil Based Mud
Authors: Petersen Johnny
Published: February 2018

A model of the diffusion of methane into a wellbore in overbalance with Oil Based Mud is described. In some situations, methane diffusion may cause unexpected gas in riser and well control problems. The situation when the OBM contaminated with diffused methane is circulated is simulated. The model has been used to analyze measurements of hydrocarbon obtained during drilling and circulation in an off-shore well in the North Sea, showing promising agreement with the model.

The tools used are: a) a finite difference diffusion program that simulates the diffusion process of methane molecules from the formation, through the mud invasion zone and into the base oil in the well bore, and b) a finite difference dynamic hydraulics model with modules dealing with the interaction of hydrocarbons entering the mud from the formation and the base oil in the mud.

The lighter hydrocarbons in OBM from the well were measured using FID gas chromatographs capable of accurately measuring the amount of C1 through C5 continuously. The measurements were analyzed using a PVT simulation program.

The diffusion was simulated in two positions in the well; the two days waiting for the 13 5/8" liner, 1850 m TVD; and the four days waiting for pipe at full depth, 4500 m TVD. The inputs to the diffusion model were based on measurements obtained while drilling in the two depths. The hydrocarbon measurements from circulations after the two and four days were compared with the amounts provided by the diffusion theory.

The distribution of the light hydrocarbon elements obtained during drilling through the formation and circulation after the delay periods, were compared. After the delay period, the relative amount of methane (compared with ethane, propane, etc.) was substantially greater. This is because methane has greater diffusion coefficient than the "larger" hydrocarbon elements.

The potential problems of having diffused gas in the base oil are shown using a hypothetical well where the OBM has been left overbalanced for days in a one kilometer long horizontal reservoir section. The contaminated OBM is circulated through the riser, and the low level of methane produces a domino-effect as it starts to boil out in the riser.

In-line gas-chromatograph measurements have provided information that shows the diffusion of methane into OBM while overbalanced.

This model used together with in-line gas-chromatograph measurements will provide additional insight in how light hydrocarbons end up in Oil Based Mud. The dynamic hydraulics model can be used to show the safety limit when leaving the well without circulation.