bluuebunny/crossref_metadata_2025 huggingface dataset:
Ensino Tradicional de Gramática ou Prática de Análise Linguística: uma questão de (con)tradição nas aulas de português
Authors: Silva Noadia Íris da
Published: March 2011

Na presente pesquisa investigamos como os professores de português do Ensino Fundamental II estão lidando com o embate entre a tradição escolar gramatical e as novas propostas de ensino que visam desbancá-la, ao desenvolverem aquilo que os Parâmetros Curriculares Nacionais de Língua Portuguesa chamam de Eixo da Reflexão e Análise Sobre a Língua. Do ponto de vista teórico, nos apoiamos nos pressupostos da Linguística Aplicada de base interacionista e, do ponto de vista metodológico, na abordagem qualitativa. Nossos resultados indicam a coexistência de diferentes perspectivas teórico-metodológicas na prática dos professores nesse eixo de ensino, perspectivas essas que se delineiam mais claramente em função dos conteúdos linguísticos selecionados e trabalhados em sala de aula.
Finite Element Analysis Animated Simulation of Velopharyngeal Closure
Authors: Srodon P.D. , Miquel M.E. , Birch M.J.
Published: March 2011

Objective

To use finite element analysis animated simulations to investigate factors affecting velopharyngeal closure.

Design

A coronal section multicomponent finite element analysis model of a human soft palate was created in Simulia Abaqus 6.5–1 from high resolution WIR I images of a single adult female subject, interpreted by reference to published anatomic dissections. Tissues were assigned hyperelastic property coefficients for neo-Hookean behavior, with gravity at 9.8 ms–2 in the y-axis. Vector forces based on estimations in previous publications were applied throughout levator veli palatini and palatopharyngeus muscles, using a nonlinear analysis algorithm, to produce animated simulations of velopharyngeal space closure. Variation of levator veli palatini angle from 60° to 49°, the contribution of palatopharyngeus muscle, and the effect of submucous cleft were investigated for their effects on velopharyngeal closure.

Results

The animated simulations showed anthropomorphic behavior and supported the previously suggested effects of the levator veli palatini angle, with reduced effectiveness of velopharyngeal closure as levator veli palatini angle decreases. Palatopharyngeus action reduced the efficiency of closure for a levator veli palatini angle of 60°, and a submucous cleft reduced this for both our normal subject and for a levator veli palatini angle of 60°, but both palatopharyngeus action and a submucous cleft enhanced closure for a levator veli palatini angle of 49°.

Conclusions

This study advances soft palate finite element analysis to a real-subject-based multicomponent hyperelastic model that demonstrates anthropomorphic behavior. Animated simulations using the model demonstrate the possible effects of levator veli palatini angle, a submucous cleft, and the contribution of the palatopharyngeus.
Size, Weight and Power Efficiency for High-power, Nonlinear, Geophysical-transmitter, Rod-core Antennas
Authors: Jordan Jared Williams , Sternberg Ben K. , Dvorak Steven L.
Published: March 2011

There is a significant body of work that addresses the use of rod-core antennas as receiver coils. However, research on the use of rod-core antennas as transmitters is limited since high-permeability core materials are nonlinear at high-drive levels. This paper analyzes weight, power and volume efficiencies of rod cores constructed from six different materials: two types of ferrite toroids; black-oxide, low-carbon-steel wire; two types of Metglas foil tapes; and Nanocrystalline material foil tape. Weight efficiency is defined as the ratio of the antenna’s magnetic moment to the sum of the antenna’s core, wire and battery weights. Likewise, power efficiency is defined as the ratio of the antenna’s magnetic moment and the antenna’s resistive power losses, and volume efficiency is defined as the ratio of the antenna’s magnetic moment and the antenna’s volume.

The magnetic moment, core-series-loss-resistance, and inductance were measured at various magnetic core flux densities. These data were then modified to simulate the effects of changing the wire gauge and number of turns to determine the optimum drive level and coil design for a specific rod core. Furthermore, we compare the results to an air-core loop whose length of one side is comparable to the length of the constructed rod antennas. It is shown that rod-core antennas possess significant advantages over air-core transmitters in weight, power and volume efficiency for the types of antennas investigated here. Specifically, at [Formula: see text], the maximum weight efficiency for a [Formula: see text] long rod antenna made from Metglas was found to be 310% larger than a [Formula: see text] air-core antenna. The power efficiencies associated with the maximum weight efficiencies for these two cases differ by 420%. The volume efficiency of the Metglas rod antenna was calculated as about 500% larger than the [Formula: see text] air-core antenna.
Imaging Dispersion of MASW Data—Full vs. Selective Offset Scheme
Authors: Park Choon B.
Published: March 2011

The dispersion imaging scheme for multichannel surface waves involves summation of a given frequency component over all traces in one record, always including wavefields in the full-offset range in the calculation. The scheme, therefore, does not have any way to take into account near- and far-field effects of surface waves, especially far-field effects, which can result in degraded imaging performance because of low amplitudes in the image space. Far-field effects are caused by noise wavefields dominating at far offsets where source-generated surface waves become relatively weak because of attenuation and geometrical spreading. The adverse influence of far-field effects can be minimized by considering an optimum far offset, which may not be the same as the farthest offset surveyed, but shorter depending on the wavelength being considered. Because the surface wave attenuation is proportional to distance in wavelength, the optimum far offset can be set to a specific number of wavelengths. On the other hand, the geometrical spreading affects all wavelengths equally and this alleviates the need for any other elaborate scheme. In this study, a selective-offset scheme is presented that limits the minimum and maximum offsets used for the imaging to 0.1–1.0 and 3–7 times, respectively, the wavelengths considered. It is shown that a selective-offset scheme can result in dispersion images with improved details, especially at those points dealing with relatively short wavelengths that are vulnerable to attenuation. The common full-offset scheme is explained in more intuitive ways than previously presented and, by extending it, the selective-offset scheme is explained.
Determining Lengths of Reinforcements in Bored In Situ Concrete Piles Using the Magnetic Method
Authors: Dong Ping , Sun Bin , Fan Jingliang , Wang Liangshu
Published: March 2011

This research applies the magnetic method to determine reinforcement length in bored in situ concrete piles by investigating the magnetic difference between the steel reinforcement and the concrete pile body. Preliminary tests indicate the [Formula: see text]-component curves from magnetic prospecting at the center, east and west boreholes show a deep gradient changing from local minima to local maxima, which corresponds to the depth of the lower end of the steel reinforcement. [Formula: see text]-component curves at the south and north boreholes also show the same pattern, but instead the local maxima corresponds to the lower end of steel reinforcement. When there is a change in the number of steel bars in the reinforcement along the depth, a characteristic “valley between two ridges” pattern appears in the curve, denoting the position of the change. This method also can be used to survey old steel piles or bridge and dam foundations where foundation configurations are not available.
Rigorous Identification of Unplanned and Invisible Lost Time for Value Added Propositions Aimed at Performance Enhancement
Authors: Spoerker Hermann , Thonhauser Gerhard , Maidla Eric
Published: March 2011

During the SPE ATW on Automation (April 13-14, 2010 in Galveston), it was identified that one of the major opportunities in the Drilling and Completions industry is the identification of non-planned events, including invisible lost time with the objective to improve performance by building a value added proposition that involves operators, service companies, contractors and equipment manufactures.

The key point was to share risk and reward by using an unbiased system that is able to accurately measure, in an automated form, most of the routine drilling and completions operations that will be compared against pre-agreed benchmarks to establish if the goals and objectives are being achieved.

The technology presented in this paper explains how automatic operations detection are carried out to address the proposed challenges and the necessary reporting and user interaction needed. The theory and one case history on this will be presented and will cover the start up phase of such initiative, and all of its push backs, and lead the readers through the implementation and final results that were successfully achieved.
Psychological Effect on HSE Behaviour-New Initiative from a Drilling Team
Authors: Al-Mehailani Mohannad , Al-Hindi Khaled , Gohain Ashis , Muqeem Saleh , Akhtar Safi , Al-Rakdan Abdulwahab
Published: March 2011

"Making sure people are not harmed is how we do things in our workplaces" are the slogans consistently being instilled into the minds of every personnel in our workplaces. In spite of consistent campaign for HSE compliances, crew is often caught in unsafe acts. To minimize such unsafe acts, Drilling &Workover Team had conceptualized a new approach and implemented for the first time in the company. The program is basically an approach for improving safety performance through psychology. Proper implementations of this safety program will soon surpass the effectiveness of some traditional safety programs.

The program involves a jacket, with a slogan on its back "Caught in Unsafe Act… our company needs you…" kept under the custody of company man of the Rig. In a nutshell, this safety program is like a game: any person caught in an unsafe act has to keep wearing that jacket, as a penalty for the violation, till another person is caught doing some unsafe act. It labels the person as a violator and represents the violator as a man needs to be watched, among the crewmembers. The way of representation of the violator tends to stir up more HSE awareness, develop better HSE attitude and culture, among other fellow workers to ward off such representation.

The program has been launched for the first time the company at one of the drilling rigs and, it has yielded amazing results. With the implementation of this program, number of near misses and incidents declined substantially. The program is ongoing and efforts are underway, to further strengthen its effectiveness. The results of that chosen rig established the program's inbuilt potential for raising safety at workplaces to much higher echelons.
A Historical Review of Drill Pipe Capabilities and the Triggers for Change
Authors: Redlinger Thomas M. , McCormick John
Published: March 2011

Until very recently, drill pipe capacity has rarely been the limitation that controlled the ultimate depth or design of a wel l. Over the last 50 years drill pipe tensile and torsional capacities have typically exceeded the needs in most drilling applications; consequently, the significant separation between the capacity of the drill pipe and the actual needs of the well designs has resulted in the drill pipe being considered "dumb iron." The recent trend to drill deeper and longer reach wells has begun to push the limits of the drill pipe capacities. Improvements in drill pipe and connection technology as well as performance reliability have significantly enhanced our ability to drill these wells. Without further improvements to materials, connections and fatigue life, the capabilities of the drill pipe could become the limiting factor in some of the exciting new projects on the horizon. It is essential that manufacturers and suppliers play a larger role in well planning in order to mitigate these limitations and make sure the technologies required are available to the industry in time to coincide with the development.

This paper will review the evolution of drill pipe capabilities and compare the historical expectations of the well designs. It will also review the triggers that created the need for adoption of new grades and connection standards. Lastly, it will discuss the pending new drill pipe technologies and their effect on capacity improvements.
New Technology, Which Enables Closed, Looped Drilling (MPD) from Mobil Offshore Drilling Units (MODU)
Authors: Andresen Jan Atle , Askeland Tom
Published: March 2011

Siem WIS has developed a new seal solution that will be installed inside a riser below the slip joint; this will enable Managed Pressure Drilling from MODU utilizing standard equipment (slip joint etc.)

The new technology will give the operator at all time status of the seals and gives time to evaluate before entering into a well control situation.

The sealing method also enables a quick replacement of the seal package and can also be developed with several seal packages in series.

The well pressure is distributed over several seals with gradient chambers between and is monitored at all time. The stationary seals are lubricated directly into the seal area which then keeps the friction and temperature low.
Wellbore Stability Modeling and Real-Time Surveillance for Deepwater Drilling to Weak Bedding Planes and Depleted Reservoirs
Authors: Lang James , Li Shuling , Zhang Jincai
Published: March 2011

Wellbore instability is the primary cause of losses in boreholes and represents a serious challenge in the drilling industry. Drilling along bedding planes and in depleted reservoirs is risky, and when a well is drilled at shallow angles to thinly bedded shales, it is often highly unstable. Rock failure can occur as a result of large anisotropy in rock strength caused by bedding-parallel weak planes. In these cases, an increased mud weight while drilling is required. However, when the reservoir immediately beneath the bedded shales is depleted, the increased mud weight can lead to lost circulation. This paper presents some of the cases we encountered in surveying offset wells in depleted reservoirs located in deepwater Gulf of Mexico for a new predrill study, where borehole instabilities resulted in a loss of a hole section and a casing shoe became massively fractured.

The key solutions are to not only improve wellbore stability modeling associated with bedding planes, rock anisotropy, and pressure depletion, but also to account for their impact on horizontal stresses. These factors are considered in the proposed model, thereby enabling calculations of wellbore failures along borehole trajectories with various drilling orientations versus bedding directions. The model has been verified by case studies. The minimum stress and fracture gradient calculations are also implemented to consider rock anisotropy and the depletion. Lab test data of rock strengths with different loading directions are analyzed. A new correlation is developed to allow for predicting anisotropic rock strength from sonic velocities.
Overcoming Challenges for Drilling High-Dogleg-Severity Curves
Authors: Janwadkar S. , Hummes O. , Peter A. , Freeman M. , Privott S. , Greene D. , Loesel C.
Published: March 2011

Shale-gas plays and other unconventional resources have gained significant prominence in the USA and several other parts of the world. Maximizing well productivity and improving drilling efficiency remains a major challenge. Well placement in the sweet spot and extended laterals help maximize productivity. Drilling a high-dogleg-severity (DLS) curve maximizes the length of lateral in the productive zone. Wells in US shale-gas plays and other unconventional resources require a DLS of 10° to 14°/100 ft. Achieving high DLS with steerable motors presents numerous drilling challenges. Rotating a steerable motor with high adjustable kickoff (AKO) sub settings could result in fatigue failure. Alternate drilling in slide-rotate modes reduces drilling efficiency, increases tortuosity, and limits well placement in the productive zone. In the past, drilling high-DLS curves with rotary steerable systems (RSS) was a challenge. These challenges led to the development and ultimately the successful testing of a new high-dogleg RSS. Using the new system enabled drilling all sections, including high-DLS curves, tangents and laterals with one bottom hole assembly (BHA). Using closed-loop control and a short steering sleeve that decouples steering functionality from drilling dynamics, the system can drill high-DLS curves and extended reach laterals with precise well placement and improved borehole quality. The authors will discuss the design, and field test results in different environments such as shale-gas plays and tight sands. The new system significantly improves drilling performance with excellent directional control. Drilling high-DLS curves increases the length of laterals by several hundred feet, enabling additional recovery of hydrocarbons. The ability to drill all sections with one system and elimination of slide drilling significantly reduces drilling time and eliminates trips to make changes to the BHA. By minimizing wellbore tortuosity, the new system enables setting casing easily and quickly, leading to early production. Minimized tortuosity in the lateral also enables faster drilling out of completion plugs with coil tubing. The innovative system can be used in similar areas of the world to drill complex wells with high DLS and straight laterals with precision and efficiency.
Lateral Buckling – The Key to Lockup
Authors: Mitchell Robert F. , Weltzin Tore
Published: March 2011

Conventional wisdom suggests that buckled pipe first forms a plane buckled configuration, then transitions to a helical shape as the axial load increases. The helical configuration has been extensively studied using analytic solutions that allow calculation and analysis. Lateral buckling has received much less attention because no analytic solution exists for smooth pipe. Most conclusions about lateral buckling are just guesses. Tool joints have received some analysis, and buckling calculations, both lateral and helical, have been made for pipe with connectors, but these calculations have received little attention from the industry.

Buckling tests (Weltzin et al. 2009) were performed in the Ulrigg U2, a 2,020-m research well, with a buildup and 60° tangent geometry. These tests represent a major advance in the understanding of drillstring buckling. Although there have been many laboratory-scale studies and a few full-scale tests of limited value, this study is the first full-scale study to acquire a large amount of high-quality buckling-displacement data for analysis.

This paper presents the calculated drillstring positions for two loading tests performed in build and inclined sections of the Ulrigg U2 test well. Both tests were loaded until drillstring lockup. In both cases, lateral buckling was the primary buckling mode, with only a short interval in the build section tests showing actual helical buckling.

The results from the Ulrigg U2 tests show that: 1) connectors appeared to have primary importance in the buckling behavior of drillpipe, and 2) lateral buckling was the primary mode of behavior. These results, which were not expected, will require considerable revision of the conventional buckling models, with much more focus on the impact of connectors and a deeper understanding of lateral buckling. In particular, the analysis of casing running in extended reach horizontal wells will be significantly impacted.
Casing Design with Flowing Fluids
Authors: Mitchell Robert F.
Published: March 2011

Tubing forces and displacements have long been calculated for design purposes. Formulations, such as the Lubinski's buckling model, have the underlying assumption that the fluids are static. Adding the effects of fluid dynamics to the pipe force equilibrium problem is not as straight forward as one might think.

The key point is the loads generated by the fluid on the tubing. What information can we obtain from a simple balance of momentum of the fluid in bulk? For example, for flow inside a pipe, we can determine exactly the load exerted on the pipe by the flowing fluid in terms of only the fluid density, pressure, and momentum.

What might be the effect of fluid dynamics? Most papers have dealt with static fluids, but how are these static effects modified for a flowing fluid? Do we need to add a pressure gradient to the pipe buoyancy? How is fluid friction included in the pipe loading? How does fluid momentum affect the pipe? For curved pipes, we might expect a centrifugal force term. The answers to these questions are often surprising, even counter-intuitive.

In this paper, the general equations for the balance of fluid momentum are then combined with the equilibrium equation for the pipe. The effective force then emerges as a natural combination of pipe force and fluid-force terms. Pipe displacement is usually formulated in terms of the actual axial force, but the necessary modifications to this formulation are presented for the effective force.
Mitigating Stick-Slip in Deep Drilling Based on Optimization of PDC Bit Design
Authors: Pelfrene G. , Sellami H. , Gerbaud L.
Published: March 2011

Deep-hole drillstring vibrations are an important cause of premature failure of drillstring components and drilling inefficiency. PDC bits are more susceptible to the stick-slip phenomenon characterized by intense RPM fluctuations of the drill bit. Based on full scale laboratory drilling tests and numerical simulations, this paper aims at understanding the dynamic behaviour of the bit/rock interaction and assessing how stick-slip depends on bit design (bit profile and diameter; cutters geometry and set up). It is generally assumed in the scientific and technical literature that forces acting on PDC cutters do not depend on cutter velocity. However, an extensive single cutter experimental program shows that these forces are rate-dependent for four tested carbonate rocks. This rate-effect is associated with the dynamic shearing of a layer of crushed rock carried away beneath the moving cutter. Based on these experiments, a semi-empirical rate-dependent cutter-rock interaction model is developed, implemented in a bit design software and used to predict the velocity signature of various PDC bit designs. These predictions fit well with numerous experimental results obtained using a full scale drilling bench. In particular, the model accounts for the negative damping effect, considered as the main source of stick-slip, and for important operational trends like an increasing risk of stick-slip in harder rocks, at higher weights-on-bit or for advanced cutter wear. The bit-rock interaction model is used as the boundary condition of a drillstring vibration software designed to perform a time-domain analysis of lumped systems. Simulations show that the bit design significantly impacts the risk of stick-slip. As a result, general optimization guidelines are suggested in order to improve PDC bit design.
Fluid Hammer Drives Down Well Costs
Authors: Staysko Robert , Francis Brenda , Cote Brad
Published: March 2011

An innovative proven new tool, the "Fluid Hammer", provides axial percussive force and effective weight transfer to the bit which increases the rate of penetration (ROP) from 30-50% with no impact to bit life.

BBJ Tool's patent pending Fluid Hammer together with Suncor Energy Inc. of Calgary, Alberta, Canada has applied the Fluid Hammer in several wellbores with excellent results. The tool is positioned between the bit and the mud motor with an antiback off connection. The relatively simple mechanical design delivers effective agitation to the bottomhole assembly (BHA) and reduces issues in deviated wellbores, such as hole drag and proper weight transfer to the bit. It has been successful in improving ROP in vertical/deviated and horizontal hole sections.

The Fluid Hammer has been successful on >80 bit runs in vertical/deviated/horizontal wellbores with water, oil base and nitrified drilling fluid systems. Direct comparisons of formations with and without the Fluid Hammer have been completed. The study compares geological formations, compressive rock strength, mud weight and BHA parameters such as weight on bit, rpm, hole drag and ROP. Resulting sliding ROP matches rotating ROP in horizontal wellbores with the downhole agitation at the bit. Tool design improvements will be further enhanced with the use of an Axial Dynamic Simulator.

The Fluid Hammer increases ROP, has no effect on telemetry tools, causes no restriction to pump rate and can be used with any mud system. This tool can be run in conjunction with conventional adjustable housings or rotary steerable tools. No special percussion bits are required and it has been run with a wide variety of conventional bit types and sizes. An additional feature of the Fluid Hammer has been in extended reach horizontal hole sections in which the BHA has been simplified with the removal of conventional agitation tools.
Automation of the Drilling Fluid Mixing Process, Field Experiences and Development from North Sea Operations
Authors: Kvame Ove , Blom-Jensen Bjarne , Bastesen Yngve , Sandvik Jan Erik
Published: March 2011

There has been substantial development over the past years with respect to automation of drilling equipment and operations on the drill floor, and this trend is projected to increase over the coming years. Automation in bulk transfer and in the drilling fluid mixing process has also been and is continuing to be developed, but may not have received worldwide recognition yet. Indications from operators show there is a rising interest in developing this area and focusing on total integration of auto- mated drilling systems.

This paper will summarize the initial development and field performance feedback from several years of operating at different automated levels of bulk transfer and the drilling fluid mixing process, respective of rigs operating in the Norwegian sector of the North Sea. It will address systems from semi-automated sack cutting units to fully automated drilling fluid process systems which are able to automatically mix drilling fluid according to a preset recipe from the mud engineer. Examples of existing applications on typical North Sea rigs are the automatic mud and bulk transfer systems and automatic mud density regulation systems.

Initial field findings are the automation of the drilling fluid mixing process achieves: Improvements to HSE issues including personnel, equipment, and operationIncreased efficiency (reduced mixing time, more efficient use of resources)Improved drilling fluid quality and repeatable processes

This paper also includes thoughts for future implementations with respect to taking the automation of the mixing of drilling fluids process further, for instance employing an automated viscosity regulation system or even allowing the mixing process to be automatically controlled by well conditions.
On Interaction Buckling in Platform Conductors
Authors: Adams A. J.
Published: March 2011

For over thirty years, the design of platform and jack-up conductors has been based on Stahl and Baurs' famous hypothesis that internal string loads do not contribute to buckling (Stahl and Baur 1980). It is a vital result, allowing significant weight and cost savings. However, no derivation was ever given, and the result has remained a folk theorem: widely used, but never proved. The industry has therefore been at risk should the result prove to be a severe approximation, or to have unduly restrictive assumptions and/or limitations. This paper provides a rigorous proof of the hypothesis. It shows that it is an approximation, albeit an acceptable one, and gives a thorough exposition of its meaning, assumptions and limitations. Finally, it derives the exact counterpart of Stahl and Baurs' result. The improved result gives further minor weight and cost savings.
Analytical and Experimental Backward Whirl Simulations for Rotary Steerable Bottom Hole Assemblies
Authors: Stroud D. R. , Lines L. A. , Minett-Smith D. J.
Published: March 2011

A unique analytical model has been developed to predict dynamic behaviour of the drilling assembly and gain a better understanding of the dominant factors that cause backward whirl. A full-scale test rig has been constructed that is capable of initiating and sustaining full rolling contact backward whirl, repeatably, reliably and safely. Excellent correlation between these near real time analytical simulations and full-scale experimental results has been achieved giving confidence in using the model for serious predictive analysis of system response in real down-hole drilling conditions. This uniquely verified analytical model can be used for rapid iterative analysis to help generate and evaluate potential design improvements and whirl mitigation strategies.

These simulations have been focused on a latest generation point-the-bit rotary steerable system (Figure 1 shows the general arrangement of the steering system), but the principles can likely be applied to other rotary drilling assemblies.

Figure 1 Schematic diagram of a point-the-bit rotary steerable system

In the process of validating the analytical model, some interesting observations were made. The first being the appearance of a ‘partial whirl’ or transition phase preceeding full backward whirl in most cases. The large impact loads predicted by the analytical model over the partial whirl phase correlated with those experienced in full-scale testing and could explain the large lateral vibrations experienced in the field during supposed episodes of backward whirl. The parameters affecting both the length of the partial whirl period and the magnitude of the impacts were found, leading the way for preventative measures. The second finding, and possibly the most instantly useful, was that full backwards whirl could not occur in close to gauge hole unless the friction coefficient between the borehole and the drilling assembly was increased dramatically. This would indicate that devices and procedures aimed at maintaining good hole quality could be effective measures to prevent backward whirl.

Improvements to the analytical model have been suggested but even in its current form it has proved an extremely versatile and reliable tool. Now that both the simulated motion and predictive capabilities of the analytical model have been proven, future technical papers will explore the effect of drilling parameters in more depth and will attempt to provide whirl mitigation strategies for field use.
"Understanding XLOTs"
Authors: Heger Alexander , Spoerker Hermann F.
Published: March 2011

Leak-off Tests (LOTs) are a common procedure during the drilling process and have been performed for decades. Still the pressure vs. volume curve seems to be not fully understood, and slightly different explanation theories exist. The paper discusses these theories together with the commonly applied leak-off testing procedure and attempts to explain the curve from a stress calculation standpoint. Theories are presented about fracture initiation at the wellbore wall, SH determination from extended leak-off tests (XLOTs) and the change of the pressure vs. volume curve by repeating pressure cycles.

Industry estimates put the contribution of wellbore stability to non-productive time at approximately 40%, costing the industry approximately $8 billion dollars per year1. In addition wells are becoming more and more difficult to drill as complex trajectories are required and smaller drilling margins are encountered to discover new oil and gas deposits.

The authors advocate that fundamental understanding of geomechanic principles by all the engineers involved is required to efficiently and successfully drill complex wells. Better understanding of and familiarity with these phenomena will minimize inappropriate decisions which might cause down time or even a loss of the well.
Challenges Of Drilling In The Chilean Altiplano
Authors: De Angelis Roberto , Holdeman Matthew , Pidcock Gary , Levy Warren , Figueroa Horacio , Lyon Raul
Published: March 2011

Recent interest in Chile to develop renewable energy sources has created a new market for drilling contractors with geothermal well experience. The geothermal fields in Chile are unique in that they combine the issues of remote area drilling with additional challenges such as desert conditions, cold weather, deep snow, and, most importantly, high elevations. Over 50% of the geothermal concessions in Chile are located in the northern regions at elevations from 3500 meters to 5000 meters. These altitudes are the normal environment of mountaineers, not drilling rigs, with oxygen levels reduced between 35% and 50% compared with sea level.

Effects of altitude, geography and climate must be taken into account in the overall planning of a drilling operation. The effects on personnel can vary and are somewhat unpredictable. There are specific tests that must be performed before working at high elevation that can detect potential problems and there are mitigation methods that can be applied on site that can help personnel increase their performance.

Equipment is also affected by the high elevation and the climate. The lack of oxygen at elevations over 4000 meters results in a loss of power for internal combustion engines of more than 40%. This is exacerbated by the limited experience operating large drilling equipment at high altitudes. The contractor must overcome these power limitations not only for the drilling rig but also for all associated services for the operation using engines.

Overcoming these challenges can only be achieved through careful planning at all stages of the operation and by selecting specific technologies to mitigate the effects of the environment in the operations. In this contractor's experience, the use of mechanized pipe handling equipment and the minimization of internal combustion engines brought the biggest value to the operation.
Maximizing Core Recovery in Lower Tertiary Through Drilling Optimization Service and Intelligent Core Bit Design
Authors: Guarisco Peter , Meyer James , Mathur Rohit , Thomson Ian , Robichaux Jeremy , Young Clifford , Luna Edgar
Published: March 2011

The deepwater Gulf of Mexico (GoM) Lower Tertiary Wilcox group is still considered an area with many geological uncertainties. In this geological environment, core samples are crucial for geologists, geoscientists, and reservoir engineers to better understand and characterize the reservoir.

This paper will focus on the longest 12 ¼-in. coring application in a deepwater Gulf of Mexico lower tertiary well. A total of 360 ft of lower tertiary Wilcox sand was cored and recovered in a single run. 12 ¼-in. core barrels were assembled for this application along with a fit-for-purpose 12 ¼-in. core bit equipped with abrasion-resistant polycrystalline diamond compact (PDC) cutters and an integral stabilization sleeve for better bit and bottomhole assembly (BHA) stabilization throughout the operation. Extensive preplanning was done in order to ensure flawless execution in this challenging environment.

In deepwater coring operations, maintaining weight on bit (WOB) is crucial for good results. Lack of rig compensation and heavy rig heave can be a disastrous combination. Bit bounce associated with high rig heave and core barrel jamming are some of the hazards of having insufficient weight reaching the core bit, which leads to increased nonproductive time (NPT). In order to have better control of the downhole drilling parameters, such as downhole weight on bit, torque and vibration, a comprehensive drilling mechanics and dynamics measurement tool was placed on top of the core barrel. The benefit of implementing this tool is the ability to optimize the coring parameters in real time in order to maximize core recovery.

Additionally, the section was drilled using a constant rheology drilling fluid, and hydraulics simulations were performed to guarantee equivalent circulating density (ECD) management, optimized hole cleaning and reduced operational risks. Geomechanical modeling included fracture characterization analysis to select the proper particle size distribution for bridging and wellbore strengthening formulations.

The planning and collaboration between the service company and the operator, in a multidisciplinary team, was the key for the accomplishment of this record run. The record run eliminated two extra coring runs (the standard coring application in the Gulf of Mexico is 120 ft), accounting for significant reduction in operational cost.
Cutting the Cost of HP/HT Cleanups: Novel High Density Cleanup Package Enables Brine Reclamation and Reduces Costs
Authors: Richmond Michael , Hutton Alistair , Davidson Marcus , Howard Siv , Frost Bob , Leon Stuart , Jaspars Marcel
Published: March 2011

With the passing of "easy oil," the need for high-pressure, high-temperature (HP/HT) drilling and completion fluids has increased. This has, in turn, increased the need for sufficiently robust cleanup methodology. This requirement for high density, solids free cleanup fluids drove the investigation into the use of cesium formate as the base brine. The use of cesium formate brings unique challenges to the cleanup, most notably, the cost implications. The high price of cesium formate brine means that any losses could severely impact upon the cost of the cleanup operation. Furthermore, any brine used in cleanup pills that could not be recovered for re-use would have to be considered as lost. It was, therefore, imperative to return the brine to its original condition, thereby avoiding the need to dispose of a very expensive commodity. This paper will look at the laboratory testing surrounding the development of a high density cleanup fluid (HDCUF) and the ability to remove the contamination from the brine to bring it back to an acceptable condition.

The cleanup spacers were made up with cesium formate brine and several approaches to remove the contamination were investigated. Contamination was from both the chemicals used to formulate the cleanup spacer and from the oil based drilling fluid that would be used to drill the wells. Nuclear Magnetic Resonance (NMR) Spectroscopy was used to measure the level of contamination in the brine.

The results of the study showed that, using the method selected, it was possible to remove the cleanup chemicals to an acceptable level where the cesium formate brine was able to be re-used. This would enable the operator to recover the brine and avoid the significant costs from losing the volume and disposing of the waste.
Surface Hole Casing While Drilling (CwD); A Review of 5 Years Experience in Gabon, West Africa
Authors: Askew B. , Phillips A. , Wingate J. H.
Published: March 2011

This paper will document the experiences (both positive and negative) of surface hole Casing while Drilling (CwD) in onshore Gabon, West Africa over a 5 year period. Modifications and improvements to the CwD shoe will also be discussed as well as the Health and Safety benefits of the system.

The CwD system is a simple non-retrievable premium Polycrystalline Diamond Compact (PDC) bit mounted on the end of a casing string. The string is rotated at surface by means of a rudimentary drive-sub (water bushing). This technique requires no modifications to a standard drilling rig. The CwD bit can be drilled-out with a standard rock bit or a specialized PDC bit. CwD technology also lends itself to mitigating drilling hazards associated with drilling surface hole in Gabon. The surface hole geology consists of unconsolidated sands overlying fractured hard carbonates. CwD allows this interval to be drilled and cased simultaneously and provides health and safety benefits associated with eliminating tripping of conventional drill strings.

Since 2005 a total of 50 wells in Gabon have been drilled using CwD technology. Some of the performance highlights include; a cumulative distance drilled of 8,410m (27,593 ft), average run length is 172m (564 ft) with an average penetration rate of 6.75 m/hr (22.1 ft/hr). The average time to drill one joint of casing is 56 minutes.

As performance targets increase drilling further and faster will mean improvements to the current bit designs. The recommended bit changes include; diamond volume management, changes to cutter size to improve point loading and change to cutter type to improve durability and impact resistance. Changes to the current well designs are required before the addition of sophisticated casing drive systems to speed up connection times and minimize off-bottom drilling time become economic.

The trend is for more surface hole to be drilled using CwD techniques in Gabon and other West African countries. This technology is also readily transferable to offshore shallow water applications.
Analysis of Tubular Failures in Riserless Environments
Authors: Samuel Robello , Adari Rishi , Gradishar John , Willie lyoho A.
Published: March 2011

Riserless drilling poses numerous operational challenges that manifests itself in a number of ways, that can adversely affecting the efficiency of the drilling process. The problems include increased torque and drag, increased vibration, poor hole cleaning, tubular failures by buckling above the mud line, poor cement jobs, and associated problems during tripping operations. Drilling in deepwater and ultra-deepwater as well as extending the reach to a greater along hole depth in the riserless environment requires both improved models and comprehensive analysis, especially when the larger diameter casing pipes are run and cemented. The present calculations without proper modeling will gravely underestimate the hook load values when the casing strings are run in deepwater situations. This paper proposes a modeling approach, which uses scenarios in which the drillstring/casing strings are in open water and in openhole reservoirs under different operating conditions to arrive at appropriate hook-load values in addition to torque and drag calculations.

Both combinations of soft and stiff string models are used for the tension-force estimation as well as the wellhead-side loading calculations. The research results also present the hook-load calculations for scenarios when casing and inner string are run with drilling mud inside the inner string, sea water in the outer string, and pad mud in the hole below the mud line. The study concludes that various parameters influence the results, such as wellhead offset from the rig center, wellbore inclination, curvature, wellbore torsion, angle of entry into the wellhead besides the complexity from wind, wave forces, and ocean currents. This paper documents the comparison between the predicted mathematical simulation results with the actual well data from different wells to explain the rigor of implementation.
Case Histories of Recent Field Results for Advancement in Milling of Cemented Tubulars
Authors: Haq Mohammed A. , Fisher Jerry , Bailey Tom
Published: March 2011

Milling success is dependent upon the level of technology, mill design and overall efficiency of the operation. Any milling job requires that the mill be the most appropriate for the given set of circumstances and that the operating parameters used provide maximum efficiency to minimize time and costs. There are many different kinds of milling jobs which may arise and in each case a particular milling tool is the most appropriate to get the desired results. However, in some cases the tools available do not necessarily fit the job requirements and a lengthy and costly job can ensue.

One such set of circumstances is a tubular cemented inside casing with cement both inside the tubular and in the annulus, this is particularly difficult because the tubing is likely to be eccentric to the casing. This condition leads to a phenomenon known as coring which results in premature cessation of progress requiring that the mill be replaced. In recognition of this situation a project was commenced to develop an improved milling system which would provide substantially greater Rate of Penetration (ROP) and overall mill life. This lead to the development of the 2-pod mill for cemented tubulars and refined milling procedures which double the ROP and increase the overall mill life by a factor of 4 when compared to standard mills.

In this paper, the problems associated with milling cemented tubulars are reviewed; and the development and laboratory testing of the new mill design is described. The paper goes on to present several field results case studies which confirm the improvements noted during laboratory testing.
A Comparison of Collision Avoidance Calculations
Authors: Okewunmi Shola , Brooks Andrew
Published: March 2011

This paper will describe procedures commonly used in the industry for avoiding unwanted wellbore collisions. Unwanted collisions may occur if the actual position of a wellbore differs from its presumed position. Such differences may arise from errors in positioning the wellhead, errors in directional survey measurements, or incorrect assumptions regarding the survey errors or the trajectory between survey stations.

Normal practice is to assign an error model to each survey. The presumed position of the well then consists of a wellpath centerline and an associated envelope of uncertainty which is derived from the error model. Collision avoidance practices may be based on specifying minimum clearance between the centerlines or between the envelopes of uncertainty, or they may be based on estimates of collision probability.

Exercises have been conducted to compare uncertainty envelopes and estimates of collision probability, calculated by different service companies using different software packages. The exercises showed substantial variation among the results obtained, given the same input data. These results highlight the need for detailed specification of the problem, oversight of the process by suitably qualified personnel, and for clear annotation of all results to indicate the methods employed and assumptions made.

In spite of the complicated error models which are now available, it must be remembered that the values and error distributions assigned to several critical input parameters are little more than educated guesses. Under these circumstances, there are limits to how far it is worth proceeding with refining the details of error modeling, and the use of ample safety factors should be encouraged.