bluuebunny/crossref_metadata_2025 huggingface dataset:
Early Weight Gain Predicts Retinopathy in Preterm Infants: New, Simple, Efficient Approach to Screening
Authors: Hellström Ann , Hård Anna-Lena , Engström Eva , Niklasson Aimon , Andersson Eva , Smith Lois , Löfqvist Chatarina
Published: March 2009

BACKGROUND. The risk for sight-threatening retinopathy of prematurity is predicted by using gestational age and/or weight at birth. All infants below a threshold undergo serial ophthalmologic examinations for identification of those who would benefit from treatment (∼10%). We hypothesized that factoring in postnatal weight gain could identify children at risk for sight-threatening retinopathy of prematurity more specifically and earlier.

METHODS. Weekly weights from birth to postmenstrual week 36 were retrospectively entered into a surveillance system that gave an alarm when the rate of weight gain decreased to a certain level. For all children (N = 354) screened and/or treated for retinopathy of prematurity at Sahlgrenska University Hospital in 2004–2007, weekly weights were recorded. One child was excluded because of known nonphysiologic weight gain (hydrocephalus).

RESULTS. For 127 (36%) of 353 children, no alarm was given; for 40%, alarm at low risk was given after postmenstrual week 32. None of those children developed retinopathy of prematurity requiring treatment. Of the remaining 24% of children who received alarm at high or low risk before 32 postmenstrual weeks, 41% developed proliferative retinopathy of prematurity and 29% were treated because of sight-threatening disease. The median time from alarm to treatment was 9 weeks.

CONCLUSIONS. The weight, insulin-like growth factor, neonatal retinopathy of prematurity algorithm detected early 100% of infants who developed retinopathy of prematurity requiring treatment and correctly predicted the majority who did not require treatment. With this simple postnatal evaluation, costly stressful eye examinations can be markedly reduced (∼75% of infants). In addition, early identification of children at risk may lead to the initiation of interventions and possibly prevent sight-threatening retinopathy of prematurity.
Morphology and Electrochemistry of Hydrothermally Prepared LiMnPO4
Authors: Allen Jan L. , Jow T. Richard , Wolfenstine Jeff
Published: March 2009

In this study, we explored the synthesis of LiMnPO4 through hydrothermal methods using urea as the hydroxide ion source. The hydrothermally prepared LiMnPO4 was examined through x, ray diffraction, microscopy, surface area and electrochemical measurements. Small crystallites were formed and significant agglomeration of particles was observed. The effect of additives to control nucleation and growth of the LiMnPO4 is reported. None of the attempted additives led to the desired morphology. At a C/5 discharge rate, a capacity of about 53 mAh/g was observed for a carbon coated sample of hydrothermally prepared LiMnPO4.
Effect of Particle Size of Mo Solid Solution on Hardness of Mo5SiB2/Mo-Based Alloys
Authors: Yoshimi Kyosuke , Kondo Yusuke , Maruyama Kouichi
Published: March 2009

Three kinds of Mo-Si-B ternary alloys and a 1 at.% Al added Mo-Si-B alloy with the compositions near Mo-8.7 at.% Si-17.4 at.% B that is in the Mo5SiB2 and Mo two-phase compositional region were produced by Ar arc-melting followed by the heat treatment at 1800 °C for 24 h. These alloys have the characteristic fine microstructure composed of small Mo solid solution (Moss) particles in the Mo5SiB2 (T2) matrix with the primary phase (Moss or T2 depending on composition). The volume fraction of the Moss particles ranges from 25.5 to 30.5 % and its average size from 3.0 to 6.4 μm in the fine microstructure of the alloys. Micro cracks were introduced by Vickers hardness tests into the microstructures, and their propagation is disturbed by the small Moss particles. Thus, each hardness value seems to relate to the cracking behavior around each indent. On the other hand, Vickers hardness values do not show correlation with the volume fraction of the Moss particles, but clearly decrease with increasing the average particle size of Moss. Therefore, it should be concluded that the increase in the particle size of Moss could enhance the toughness of the Mo5SiB2/Mo-based alloys effectively by ductile phase toughening.
An ecosystemic approach to evaluating ecological, socioeconomic and group dynamics affecting the prevalence of Aedes aegypti in two Colombian towns
Authors: Quintero Juliana , Carrasquilla Gabriel , Suárez Roberto , González Catalina , Olano Victor A.
Published: March 2009

This article focuses on the epidemiological methods and results of a global Ecohealth study that explored the complexity of the relationship between ecological, biological, economical, social and political factors and vector presence. The study was carried out in two dengue endemic areas of Colombia. A transdisciplinary team gathered quantitative and qualitative data. A survey in randomly sampled households was applied and, simultaneously, direct observation of potential breeding sites was carried out. Logistic regressions and qualitative techniques were used. Qualitative and quantitative data were compared using triangulation. The presence of low water containers increases seven-fold the risk of finding immature forms ofAedes aegypti in the household (OR = 7.5; 95%CI: 1.7-32.2). An inverse association between socioeconomic stratum and presence of the vector was identified (Low stratum OR = 0.9; 95%CI: 0.6-1.4; High stratum OR =0.4; 95%CI: 0.07-1.7). Water management is a complex social dynamic associated with the presence of Ae. aegypti. Dengue control is a challenge for public health authorities and researchers as they should address promotion and prevention strategies that take into account cultural, behavioral, socioeconomic and health factors.
Utility of Hyperspectral Reflectance for Differentiating Soybean (Glycine max) and Six Weed Species
Authors: Gray Cody J. , Shaw David R. , Bruce Lori M.
Published: March 2009

Reflectance data were subjected to a variety of analysis methods to determine the utility of hyperspectral reflectance for differentiating soybean, soil, and six weed species commonly found in Mississippi agricultural fields. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Hyperspectral reflectance data were collected from mature plant leaves three times in 2002 and two times in 2003. Vegetation indices were calculated and subjected to principal component analysis (PCA) and linear discriminant analysis (LDA). The PCA, using vegetation indices, produced the poorest classification accuracies for the plant species studied, generally less than 50%, whereas LDA resulted in classification accuracies greater than those from PCA. Best spectral band combination (BSBC) provided the greatest classification accuracies, with all better than 80% for all data sets. The BSBC indicated three wavelength bands of interest for species discrimination in the short wavelength infrared portion of the electromagnetic spectrum, which are not commonly used in current vegetation indices for species differentiation. These areas of interest were located from 1,445 to 1,475 nm, 2,030 to 2,090 nm, and 2,115 to 2,135 nm. The top 10 wavelengths determined by BSBC were then added to the vegetation indices and reanalyzed using PCA and LDA. Classification accuracies increased for all species when these wavelengths were added rather than using vegetation indices alone, suggesting greater crop and weed species differentiation can be obtained when using sensors that include these wavelength regions of the short wavelength infrared portion of the electromagnetic spectrum.
Virginia Creeper (Parthenocissus quinquefolia) and Wild Grape (Vitisspp.) Control in Fraser Fir
Authors: Richardson Robert J. , Marshall Michael W. , Uhlig Robert E. , Zandstra Bernard H.
Published: March 2009

Virginia creeper and wild grape are troublesome perennial vines that often infest Christmas tree plantations. Field studies were conducted to evaluate Fraser fir injury and Virginia creeper and wild grape control with directed applications of triclopyr (1,680 g ai/ha) alone and in combination with 2,4-D (1,120 g ai/ha), clopyralid (280 g ai/ha), and halosulfuron (36 g ai/ha). Additional treatments included 2,4-D, clopyralid, glyphosate (1,120 g ai/ha), halosulfuron, hexazinone (560 g ai/ha), mesotrione (105 g ai/ha), and sulfometuron (71 g ai/ha) applied alone; and a mixture of hexazinone plus mesotrione. In the triclopyr-containing treatments, Fraser fir injury ranged from 6 to 13% at 1 mo after treatment (MAT) and was 4 to 8% at 11 MAT. Leader growth was not impacted by the herbicide treatments. At 11 MAT, all triclopyr-containing treatments controlled Virginia creeper 93 to 98% and wild grape 98 to 100%, which was greater than the control observed with glyphosate at 63 and 59%, respectively. Virginia creeper and wild grape control with 2,4-D was 88 to 90%. Clopyralid, halosulfuron, hexazinone, hexazinone plus mesotrione, mesotrione, and sulfometuron provided less than 66% control of both perennial vines. Directed applications of triclopyr-containing treatments or 2,4-D were effective management tools for selective removal of wild grape and Virginia creeper from Fraser fir Christmas tree plantations. Additional research is needed on the potential sensitivity of other commonly grown Christmas tree species to triclopyr-containing treatments.
Response of Corn to Simulated Glyphosate Drift Followed by In-Crop Herbicides
Authors: Brown Lynette R. , Robinson Darren E. , Young Bryan G. , Loux Mark M. , Johnson William G. , Nurse Robert E. , Swanton Clarence J. , Sikkema Peter H.
Published: March 2009

Thirteen field experiments were conducted in Illinois, Indiana, Ohio, and Ontario from 2005 to 2007 to determine the effects of simulated glyphosate drift followed by in-crop applications of nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr or foramsulfuron plus bromoxynil plus atrazine on nontransgenic corn injury, height, stand count, shoot dry weight, and yield. Simulated glyphosate drift at 100 and 200 g/ha, resulted in 11 to 61% visual crop injury and a 19 to 45% decrease in corn height. Simulated glyphosate drift at 200 g/ha caused a reduction in shoot dry weight by 46%, stand count by 28% and yield by 49 to 56%. Generally, simulated glyphosate drift followed by the in-crop herbicides resulted in an additive response with respect to visual crop injury, height, stand count, shoot dry weight, and yield.
Differential Response of Grain Sorghum Hybrids to Foliar-Applied Mesotrione
Authors: Abit M. Joy M. , Al-Khatib Kassim , Regehr David L. , Tuinstra Mitchell R. , Claassen Mark M. , Geier Patrick W. , Stahlman Phillip W. , Gordon Barney W. , Currie Randall S.
Published: March 2009

The selection of herbicide-resistant weeds in grain sorghum production has prompted researchers to explore alternative herbicides to prevent, delay, and manage herbicide-resistant weed biotypes. Greenhouse and field experiments were conducted to evaluate the differential response of sorghum hybrids to POST application of mesotrione. In a greenhouse experiment, 85 sorghum hybrids were treated with 0, 52, 105, 210, and 315 g ai/ha mesotrione when plants were at the three- to four-leaf collar stage. Sorghum response ranged from susceptible to tolerant sorghum hybrids. ‘Pioneer 84G62’, ‘Pioneer 85G01’, and ‘Triumph TR 438’ were the three most susceptible, whereas ‘Dekalb DKS35-70’, ‘Frontier F222E’, and ‘Asgrow Seneca’ were the three most tolerant hybrids. One week after treatment (WAT), the mesotrione rate causing 50% visible injury ranged from 121 to 184 and 64 to 91 g/ha in the most tolerant and susceptible hybrids, respectively. Mesotrione dose–response studies were conducted under field conditions on four sorghum hybrids. One WAT, injury symptoms were greater (up to 23%) in Pioneer 85G01 than in Asgrow Seneca (< 14%). However, all plants appeared normal by the end of the growing season. In addition, sorghum yields were not reduced by mesotrione treatments as verified by correlation coefficient analysis.
A water vapour flux tool for precipitation forecasting
Authors: Neiman P. J. , White A. B. , Ralph F. M. , Gottas D. J. , Gutman S. I.
Published: March 2009

The skill of quantitative precipitation forecasts is poor, especially for extreme events. This paper describes a new tool that combines wind observations aloft (from wind profiling radars) with vertically integrated water vapour (IWV) measurements derived from global positioning system (GPS) receivers to estimate the bulk transport of water vapour. This transport strongly influences precipitation enhancement by mountains. Based on earlier research, a controlling wind layer is defined, which has maximum correlation between the horizontal component of the wind directed upslope at the coast and the rainfall measured downwind in the mountains. The altitude of the maximum correlation (∼ 1 km above sea level) often corresponds to the altitude of the low-level jet that typically resides in the region of enhanced water vapour transport ahead of an approaching cyclone's cold front (i.e. in the atmospheric river portion of the storm). The wind at this level usually differs from the wind at the surface, pointing to the need for wind measurements aloft. The upslope wind in the controlling layer is then combined with the IWV measurement to calculate hourly, layer-mean, bulk water vapour transport. Case studies and four winters of data, including rain-gauge networks, demonstrate the close relationship between bulk water vapour transport and mountain precipitation. For example, heavy rainfall capable of generating flooding (i.e. ≥10 mm/h) occurs at the mountain site almost exclusively when coastal observations of IWV and upslope flow exceed 2 cm and 12·5 m/s, respectively (i.e. the bulk water vapour transport surpasses 25 m/s cm). These results are integrated into a prototype real-time diagnostic tool that has the potential to improve short-term quantitative precipitation forecasts in coastal mountains.
True Matching of Bit and Multidiameter String Tools Delivers Optimized Drilling Performance
Authors: Barton Steve , Clegg John
Published: March 2009

The increased use of hole opening tools remote from the drill bit has led to a critical need to understand the interaction between the drill bit and the hole opening tool itself. Problems that can result from improper matching include vibration, inability to open hole, mechanical damage to string tools or to the bit, and sub-optimal drilling performance.

This paper explores the theoretical relationship between bit and reamer and modeling the relative agressivity and stability of both tools, building on already established indices for predicting and comparing the performance of bits. It also considers stabilization of the hole opening tool using both concentric and eccentric devices. It describes theoretical modeling of the vibration behavior of the assembly. It then describes field validation of the above using a unique downhole data recording device, located at various key points in the BHA and drill string.

Finally, the paper will review a number of case studies and demonstrate a linkage between the theoretical analysis, the measured validation, and actual field results. These relate to a variety of directional applications including vertical rotary, directional motor and rotary steerable, and demonstrate reduced vibration, improved hole quality and hole opening performance, superior penetration rates, and overall significantly reduced drilling costs.
Under-Rig-Floor Open Hole Logging in the Gulf of Thailand: Operational Implementation of the Oil Industry's First Simultaneous Open Hole Wireline Logging and Drilling Operation
Authors: Upchurch Eric R. , Laoamornpanich Thaveesub
Published: March 2009

Chevron Thailand, on average, drills 12000' MD / 8200' TVD wells in about 4.5 days. The factor that most contributes to this level of performance is the "offlining" of as many drilling rig activities as possible. In our drilling operation, almost all pipe handling and cementing operations are performed offline (i.e., off the critical operations path and therefore simultaneous to other activities on the rig). We have now taken the next logical step in performing offline operations. In May 2007, Chevron Thailand introduced the world's first simultaneous open hole wireline logging and drilling operation on Seadrill RT-7 (a tender-assist drilling rig), and presently is deploying the same system on additional tender-assist and jack-up rigs.

This paper is the second in a series of two that describe the engineering design and operational implementation of the tools and techniques necessary to make offline open hole wireline logging a reality. The first paper1 in this series details the engineering design aspects, and the resultant benefits, of this paradigm-changing logging system. This second paper describes the processes that were used to implement the system, along with the inherent risks and benefits of each phase of the implementation. Implementing radically new processes such as this into pre-existing drilling systems significantly increases the risk for technical failure, well control incidents and personnel injury. This paper details the processes that were developed for avoiding all three. In the case of this new technology, our phased approach to implementation has resulted in smooth, incident-free introductions to the various rig sites. The benefits of this new system and our method for implementing it incident-free are paying significant dividends to Chevron Thailand.
Analysis of Hook Load Forces During Jarring
Authors: Newman Kenneth R. , Procter Ray
Published: March 2009

Twice in a year, on opposite sides of the world, drilling rigs collapsed after prolonged jarring operations. This paper documents the analysis performed to determine if the jars could generate enough force to overload the rig structure.

Data from the drilling logs was taken at time intervals of 10 seconds or greater. These large time intervals did not allow the peak shock loads to be recorded. The rig instrumentation or sampling rate tends to damp out these peak shock loads. Thus, during jarring operations the loading can be significantly different than that displayed by the rig instrumentation.

A dynamic finite element jarring analysis was done for both of these cases. This analysis calculates the loads along the drill string before and after the jar is released. The impact load travels up and down the string at the speed of sound in steel, causing spikes in the surface loads. To simulate these dynamic loads the model is run with a time interval of 100th of a second. This allowed the loading seen by the rig structure to be simulated. The input parameters and modeling results from one of these analyses are presented in the paper.
Pattern Recognition-Based Remaining Useful Life Estimation of Bottomhole Assembly Tools
Authors: Garvey D. R. , Baumann J. , Lehr J. , Hines J. W.
Published: March 2009

This paper describes a new pattern recognition based system for estimating the remaining useful life (RUL) of bottomhole assembly (BHA) tools.

Modern drilling equipment operates in increasingly severe environments, with downhole temperatures in excess of 200°C and high impact vibration events being common. Additionally, rig operators are asking tools to perform mission profiles that have previously been impossible, thereby increasing the stress on the downhole tools. All the while, clients are beginning to contractually demand high reliability to help them prevent costly downhole failures and ensure profitability.

Current periodic maintenance practices are proving to be insufficient or cost-intensive to meet these new challenges. Because of this, industry is shifting toward simple condition-based maintenance, which uses design guidelines and rough operational thresholds to assess individual tool health. While there is value in the latter approach, there is a large amount of tool performance and environmental data collected during operation that has yet to be effectively incorporated into the health assessment process. This paper addresses this shortcoming by using the available data to infer the RUL of individual tools.

Using "real world" data collected from a rotating steering system tool, the prognosis system is shown to be able to predict the RUL of individual tools with an accuracy ranging from 0.88 to 8.76 hours over three test sets.

The developed system will allow service providers to make more agile maintenance decisions and provide operators the means to incorporate reliability into the well planning and operations processes, enabling monetary savings for both parties.
Use of Liner Drilling Technology as a Solution to Hole Instability and Loss Intervals: A Case Study Offshore Indonesia
Authors: Jianhua Liao , Darmawan Andrias , Chao Zhao , Rosenberg Steve , Hillis Keith , Utama Budi
Published: March 2009

The Banuwati field offshore South East Sumatra, Indonesia presents major challenges to both drilling and liner running operations, because of the problematic Lower Baturaja limestone formation, which is a carbonate reef structure known for severe lost circulation conditions. The operator had previously experienced severe losses with wellbore stability issues while drilling this formation with the inability to set the 7-in. drilling liner at the planned depth in well A-3. The liner had to be pulled out of the hole leading to the eventual abandonment of the existing open hole section and resulted in the sidetracking of the well. Liner-while-drilling technology was identified as the most suitable solution for setting the planned 7-in. drilling liner through the loss interval because:

Documented lost circulation problems have been minimized or eliminated through the use of liner drilling technology possibly attributed to the "smear effect"1 phenomenon. The liner system selected provided for high torsional capability as well as the requirement for both a mechanical and a pressure event to release the setting tool, thus minimizing the chances of premature release. A drill shoe with a displaceable PDC cutting structure was used to drill the 8 1/2-in. hole section and subsequently displaced prior to cementing so as to allow drill out with a conventional drill bit and BHA.

This paper will discuss the implementation of liner drilling technology in the Banuwati field project. This technology was used to drill successfully through the known lost circulation zone with the 7-in. liner cemented in place allowing the operator to reach their completion objectives while realizing a savings of more than US$1 million.
Electrical Cranes and Winches for Improved Safety and Better Operational Performance for use in Extreme Weather Conditions
Authors: Austefjord Arne , Kverneland Hege
Published: March 2009

Until recently, most drilling and production rigs have been designed for operation in temperate climatic zones, and within a typical temperature range of -20°C to +50°C. Increasing demand for petroleum products has moved oil exploration into more hostile and challenging areas like the Barents Sea, onshore in northern Siberian territories, and also in hot desert areas like Sahara and the Saudi Arabian desert. As a result, the hoisting and drilling equipment must be designed to operate reliable and safely also in extreme temperatures. This may be a problem, especially for hydraulically powered equipment which is highly temperature dependant, compromising both the working availability of the equipment, and the safety and accuracy of the machine when in operation.

A new electrical winch by use of permanent magnet motor (PM-motor) technology has been developed and implemented for use on hoisting appliances ranging from small man rider winches to large offshore cranes. This new technology uses an "inside-out" PM-motor integrated in the winch drum was first introduced to the offshore market four years ago in a Manrider winch application. This technology is now adapted to larger horsepower winches, increasing safety and operational performance for the crane. This PM-motor winch satisfies both the American Petroleum Institute (API) and the European Norm (EN) regulations for crane applications.

This paper will focus on the benefits using electrically powered cranes. The paper will especially focus on PM-motor technology, and the possibilities to optimize the design with respect to shape, size and performance. Extensive tests of the PM-motor itself, the crane winch and its control system and of the crane have been performed and will be discussed. The enhanced safety aspect for emergency lowering operations in offshore cranes for a PM-motor compared with AC-induction motor will also be discussed.

Definitions

AC-motor= Induction, squirrel cage motor controlled by means of a variable speed frequency drive

PM-motor= Permanent Magnet motor controlled by means of a variable speed frequency drive
New Washpipe Technology: Why Operators Should Care
Authors: Borland Brett , McCoy Steve , Mason Rick , O'Dwyer John , Ogg Jeremy
Published: March 2009

This paper will outline the application of a breakthrough technology to address Top Drive washpipe durability in high temperature and high pressure (HPHT) wells. The introduction, application, and submission of a performance comparison to support the advancement/proliferation of this technology are presented from an operating company's perspective.

Problem

Since the introduction of Top Drive Systems in the late 1980's, a consistent limiting factor has been the durability of the washpipe seal mechanism, particularly in HPHT + high speed drilling applications. This durability issue has greatly affected the efficiency of the circulation system's integrity, and it has also decreased overall operating efficiencies. Washpipe failures occurring during critical operations, such as during well control situations, can increase risk to personnel and equipment.

Solution

National Oilwell Varco has introduced a technical solution that utilizes mechanical sealing technology developed outside the oil and gas industry. This technology has proven itself in joint-effort field trials by ConocoPhillips and Ensco in the North Sea. The challenge is to promote the use of the technology worldwide to solve the habitual washpipe durability problem.

Challenges to Implementation

Traditionally, new technology is difficult to implement in the oilfield. The intent of this paper is to help overcome typical barriers and help rush this solution out to positively impact the drilling fleet as quickly as possible.

Conclusions

A reliable sealing mechanism has been identified to address the washpipe durability issues, and field trials of this new product have yielded positive results. The typical barriers to product implementation were minimized by applying previous lessons-learned, with successes in operations, cost savings, and safety.
The Use of a Novel Rigid Setting Fluid for Well-Isolation and to Cure High-Rate Losses by Pumping Through the Bit in the Southern North Sea
Authors: Couper Chris , Robertson Bruce , MacArthur Donald , Scott Doogal
Published: March 2009

Several lost circulation materials (LCMs) are available to operators who wish to minimize downtime while combating lost circulation. In general, fine to medium-sized particulate-based materials mixed into the mud system are the first line of defense. When this fails, the common response is coarser LCM, which often cannot be pumped through downhole tools. Operators then might choose to pull out of hole (POOH) with the drilling bottomhole assembly (BHA) and run in with a cement stinger.

This paper discusses a practical, field-proven solution that eliminates time-consuming and potentially hazardous trips in and out of hole. This is done by using a right-angled set, temperature-activated fluid that, once set, exhibits similar characteristics to Portland cement. It can be confidently pumped through the BHA to combat all static or dynamic losses.

The cases discussed in this paper were located in the 43/19a Cavendish field in the southern North Sea, while drilling through Plattendolomit. Plattendolomit is a thin, complexly folded and rafted dolomite that is found within the Zechstein halites. This formation presents significant well-control challenges with the potential for high overpressures coupled with high-rate dynamic losses, particularly Quads 43 and 44. The novel fluid was used to cure dynamic losses of up to 400 bbl/hr. The fluid was also used to isolate the well to allow safe tripping to replace worn blowout preventer (BOP) components. As small changes in bottomhole pressure caused high-rate losses and gains, it was not possible to kill the well by conventional means. A plug was set inside the casing that isolated the kick/loss zones from the wellbore.

Because it was possible to drill out the isolation plug with a drilling shoe on the liner, considerable rig-time was saved.
Improving Wellbore Seal Integrity in CO2 Injection Wells
Authors: Benge Glen
Published: March 2009

The challenges associated with the construction of an injection well for carbon sequestration are cross disciplinary, but highly manageable. Site selection, reservoir identification and formation evaluation involve geological and reservoir specialists that perform detailed evaluations of the subterranean environment.[1-4]

Materials selection identifies components that are designed to withstand the unique chemical and physical environments of these wells. Sealant selection is key to providing long term integrity of any well, with Portland cement being the material of choice for most oil field applications.

Work on Carbon Sequestration in subterranean formations has renewed interest in investigating the long term effects of CO2 on Portland cements. Portland cement will react with the injected CO2, and while recent research indicates these conventional cements are not a concern, additional work is ongoing to improve the long term effectiveness of the wellbore sealant.

Efforts have focused on enhancing the properties of Portland cement by reducing the permeability of the set cement, lowering the concentration of materials in the cement that react with CO2, or replacing the conventional Portland with specialty cements. Complementing technologies that have been used to further promote long term seals include the use of in-situ swell packers, and self healing cements.

Additional work has been done in evaluation of the long term stress environment of the well. This work goes beyond the simple drilling and completion of the well to include input from long range reservoir and wellbore stress modeling through the full life cycle of the well. These stresses are evaluated to confirm the selected sealants can withstand the changing stress environment.

This paper discusses various identified solutions to the challenges of selecting a proper wellbore sealant for a CO2 injection well. Additionally, the paper reviews the available sealant technologies, their application, and includes a discussion of stress modeling for these wells.
Probabilistic Well Time Estimation Revisited
Authors: Adams A. J. , Gibson C. , Smith R.
Published: March 2009

Probabilistic estimation of well duration has been common practice for over a decade; many papers have been written on the subject, and commercial software is available for the purpose. Is the subject therefore mature? The authors suggest that this is not the case, and show that several essential aspects of both data characterisation and probabilistic analysis have been overlooked in previous contributions.

A database of 104 central North Sea wells was independently re-analysed for non-productive time (NPT) from the original daily drilling reports. Mechanical extreme NPT events (those over 2.5 days) were only 4% by number, but contributed 51% of NPT by duration. It is shown that mechanical parent NPT, mechanical extreme NPT, open water WOW, and riser connected WOW are all statistically distinct, with very different occurrence frequencies and probability density functions (PDFs). These data vary widely by well type, installation type, and time of year.

The paper gives tables of all required occurrence frequencies and PDF parameters, together with a full theoretical basis. Earlier workers did not publish this information, nor did they observe that the four NPT types above are statistically distinct. It is shown that trouble-free time plus mechanical parent NPT is log-normally distributed, whereas the other PDFs are Weibull. These PDF types are not currently available in commercial software, and the authors are working with a software provider to remedy this deficiency.

Example results (PDFs of predicted duration) are given by well type, installation, and time of year. They are in good agreement with the historical database.
Improving the Reliability of Slip Joint Packer Systems
Authors: Upton Tom L.
Published: March 2009

The loss of drilling mud past the primary sealing element of marine riser slip (telescoping) joints has been a recurring source of releases [or discharges] within industry. This paper discusses work processes and equipment arrangements the operator has implemented to improve the sealing reliability of slip joint packer systems.

Slip joint packer designs have not changed significantly since they were first introduced for use on floating drilling rigs in the early 1960's. With non-aqueous drilling fluids (NADF) being used extensively in today's offshore drilling operations, leakage of drilling fluid past the slip joint packer is undesirable. In many cases, the loss of drilling fluid has been the result of either a failure of the packer element or failure of the pressure system used to energize the packer. Slip joint packers were originally designed for use with water-based mud systems and typically a minor amount of fluid seepage was relied upon to lubricate the packer. In order to provide complete containment of NADF, it has become common practice to apply higher closing pressure to the sealing element which has reduced lubricity and led to premature wear of the sealing element and occasional catastrophic failure of packer elements.

In order to contain NADF in the event of failure of the primary packer system, the operator now employs an independent backup pressure supply system that automatically energizes the lower (secondary) packer in the event of loss of pressure in the primary system. The lower packer is automatically energized when a predetermined pressure drop is detected in the primary system as a result of either loss of supply pressure or primary element wear damage.

The operator has also established a routine inspection and surveillance program intended to detect slip joint problems before they result in accidental NADF discharges.
Identification and Qualification of Shale Annular Barriers Using Wireline Logs During Plug and Abandonment Operations
Authors: Williams Stephen , Carlsen Truls , Constable Kevin , Guldahl Arne
Published: March 2009

It has long been recognised that during and after drilling through certain formations, the rock moves inward and begins to close off the well. Normally this phenomenon is considered undesirable since it can cause problems for drilling and casing running. It can however be put to good use as the mechanism to create an annular barrier behind casing.

In order to extend the life of a number of North Sea brown fields many well slots on production platforms and sub-sea templates are being re-used. This process involves permanent plug and abandonment of the old well track prior to sidetrack drilling into a fresh area of the reservoir. Norwegian Continental Shelf (NCS) regulatory requirements dictate that compliant procedures for well abandonment require the establishment of double barriers to avoid leakage from the reservoir. With a shortage of sufficient traditional cement barriers these wells often need costly remedial work in order to meet abandonment requirements.

Traditional sonic and ultrasonic azimuthal bond logging provides information on the material immediately behind the casing. Many such bond logs show solid material behind the casing far above the theoretical cement top. Clear correlation of this bonding pattern to shales, known to cause problems during drilling, indicates that the shale has sealed off the annular region and that it is the presence of such formation material that results in a good bond log response

Logging and pressure testing sealed off zones in a number of wells allowed the bond log response to be qualified for a certain formation without further pressure testing. In this manner logs can provide a clear answer of whether shale successfully seals off certain zones and consequently provides a natural annular barrier. This technique has been employed successfully on over 40 wells, proving non-destructively that high quality natural annular barriers had formed, resulting in elimination of complex remedial work and substantial cost savings.
Analysis of Complex Wellhead Load Events for Conductor and Surface Casing Strings
Authors: McSpadden Albert R. , Glover Simon
Published: March 2009

The analysis of mechanical and thermal-induced wellhead growth and resultant loads can be critical for tubular stress design and failure analysis of offshore platform wells. Standard simulation tools are typically used for this analysis. However, some common complex wellhead loading events are not explicitly accounted for in currently available software. Analysis of wellhead growth and loads from first principles is used to investigate these complex load events. Particular attention is given to conductor and surface casings and some non-intuitive results are discussed. A case study is presented to illustrate a range of field applications.

The analysis and related methodology apply to complex load events including: tension from conductor tension units (CTU's) or top-tension riser (TTR) systems, order of CTU overpull and landing of subsequent strings, lift-off of strings without lock-down, lift-off at mud-line hanger (MLH) systems and loss of pre-existing casing strings due to structural failure.

It is commonly recognized that standard single-string casing design which ignores wellhead movement is conservative for most casing strings. Similarly, it is understood that this single-string analysis is non-conservative for the outermost string. However, the extent and nature of non-conservatism as well as identification of all strings for which the standard analysis is truly non-conservative is not always understood. Also, the effect of sequencing CTU overpull and landing subsequent strings is also not always recognized.

The analysis methodology and case studies discussed in this work provide an explicit and intuitive approach to multistring wellhead movement and loads which can be implemented in spreadsheet calculations to model each step in the loading sequence on the wellhead. The nature of wellhead loads on the outermost conductor or surface string compared to inner strings is explained. The effect of CTU loads and the sequence of application are also explained. Certain types of wellhead load events, which are not accommodated using available commercial software tools, are modeled and analyzed. Even when numerically based software simulation tools do accommodate the load conditions considered, a closed-form analytical model based on first principles is still useful for understanding the nature of loads and also for first-order verification of numerical results.
Combining Proven Anti-Sag Technologies for HPHT North Sea Applications: Clay-Free Oil-Based Fluid and Synthetic, Sub-Micron Weight Material
Authors: Carbajal David , Burress Charlotte , Shumway Bill , Zhang Ying
Published: March 2009

North Sea wells drilled in high-pressure, high-temperature (HPHT) areas are known for presenting barite sag challenges. Fluid densities in the 17.5–18.0 lbm/gal range require a high percentage of barite, and 400°F temperatures can adversely impact the rheological properties needed for reliable suspension. Further, horizontal and extended reach drilling (ERD) wells can require specific hydraulic parameters for hole cleaning that may entail comparatively high pump rates which can contribute to excessive equivalent circulating densities (ECD).

Drilling fluid companies initially responded to these challenges by utilizing modified barite and alternative weighting agents. Micronized barite has been used to help lower ECD values for years. However, a non-barite manganese tetraoxide weighting agent has proven to provide equivalent anti-sag at a lower cost. The sub-micron sized material has a specific gravity (sg) of 4.8, which is higher than barite. Per Stokes' law, small particles settle more slowly so that sag resistance improves which is important during extended static periods like during extensive coring operations. Manganese tetraoxide is also acid-soluble. These parameters provide more operational flexibility.

The manganese tetraoxide weight material has now been tested successfully in a clay-free and economical paraffin/mineral oil-based fluid (OBF) for use in North Sea HPHT applications. The low-solids, clay-free system has a long history of reducing ECD and minimizing downhole losses while drilling, running casing and cementing. The 17.9 lbm/gal fluid weighted with manganese tetraoxide material exhibits effective hole cleaning properties at lower viscosities than conventional OBFs and shows no detectable sag tendency. Clay-free fluids also demonstrate excellent return permeability values in a wide range of well types.

This paper details the design and testing of the clay-free ERD system, including extreme HPHT static aging and sag testing and modifications to the emulsifier package. The economics of implementing the commercial system are also discussed.
Electric Wireline Milling—New Solutions for New Challenges
Authors: Joyce Robert H.
Published: March 2009

The concept of milling obstructions in wellbores, utilizing electric wireline as a means to deploy the service, was introduced in 2005. Since that time, oil and gas operators around the globe have used this well intervention technique efficiently and cost effectively. These wireline-conveyed technologies have performed well in both completion and workover programs by providing the means to drill out stuck isolation or safety valves, remove non-retrievable plugs and re-establish production by removing scale.

The additional cost of lost or deferred production is always unwanted. The deployment of a traditional rig or coiled tubing unit to help restore production comes with considerable cost owing to the equipment and personnel requirements to operate these heavy equipment platforms. Consequently, operators continually look to new techniques to minimize this burden. Milling on electric wireline, where applicable, is one such technique since it can be offered within a rig-less environment.

Experience has shown that each and every new milling challenge requires careful study of the problem along with extensive planning, testing and verification of the technique. Every downhole scenario provides a different characteristic to consider. As a result, many man-hours and research dollars are required to provide solutions for advanced milling projects.

This paper presents new applications for electric-wireline milling. First, a summary of the milling experience to date will be presented followed by the examination of some complex milling challenges through several unique case studies and verification tests. Value statements are also presented for each case study.
Implementation of Middleweight Fluids, between Lightweight Air or Foam Fluids, and Heavyweight Conventional Fluids
Authors: Green Taylor C.
Published: March 2009

Drilling fluid systems resulting in formation pressures between the equivalent of water and the equivalent of air would be useful, but have been difficult to develop. Since the successful field trial in January 2008 (Green, Minnett, Cremer 2008), these "middleweight" drilling fluid systems have been further developed. The original system has been refined, and a second approach has been prepared for field trial. The original system is generally referred to as the low pressure system, since air is mixed with liquid and then flows into the drilling rig mud pump. The second newer system is generally referred to as the high pressure system, because air is mixed with liquid after the liquid has passed through the drilling rig mud pump, just before entering the standpipe.

The drilling fluid is similar for both the low and the high pressure systems. It contains a small amount of polymer, clay and shale inhibitors and an air dispersant. The combination forms a solids free fluid that cleans the hole, keeps the formations stable, lowers equivalent circulating densities compared to conventional fluids, and allows the injected air to readily break out on return to surface. The fluid is not intended to form a filter cake, since filter cakes may result in diminished rates of penetration, and certainly result in higher than necessary pump pressures and equivalent circulating densities.

The low pressure system mixes air in a solids free drilling fluid just before entering the drilling rig mud pump. The first field trial showed that adequate pressure can be easily maintained while mixing air and liquid so that the drilling rig mud pumps can perform efficiently. The first field trial also showed that very small amounts of air volume are required to reduce the equivalent density of the fluid.

The high pressure system injects air into the fluid after it has passed through the mud pump. Higher operating pressures are required, and higher volumes of air can be injected into the fluid. The high pressure system may allow lower equivalent densities than the low pressure system.
Revolutionising the Top Drive for Improved Efficiency and Uptime on a Major International Drilling Contractor's North Sea Rig
Authors: Fraser C. , White G. , DePeuter E.
Published: March 2009

One of the biggest breakthroughs in drilling technology was the top drive first commercialised in the 1970's. The advent of the top drive brought vast time savings: through drillers being able to drill with 90ft. stands; elimination of connections and their impact on circulation and the wellbore; being able to rotate and circulate when tripping out giving the ability to get through tight spots, and much more. Since then, apart from changing from DC motors to AC motors the basic functional design has remained the same, that is, one or two large motors connected to a gearbox, driving a main shaft. A new type of top drive has now been developed with possibilities for significant drilling cost savings due to the improvements in reliability and easier maintenance.

A major drilling contractor who had significant experience using top drives on their rig fleet conducted an analysis of where most of their rig downtime occurred. They found that 40% of all their top drive failures were related to gearbox issues (gears, bearings and seals). Another significant failure was with the motors, particularly on their smaller top drives in their land rig fleet. These types of failures had been expensive for the drilling contractor and the operator with significant frustration, lost drilling time and lost revenue. The problems were exacerbated by top drive manufacturers not having spare parts stocked and service technicians not being readily available. This lead to the drilling contractor taking the decision to help develop a revolutionary, new, direct drive top drive, with less parts, no gearbox and improved motor. These systems have now been field trialed extensively, for a number of years onshore and offshore with significant success by this drilling contractor and others in the USA, Middle East, Russia, North Africa and Australia. The drilling contractor is now half way through a program to replace all the top drives on it's complete fleet of existing and new build rigs (31 land rigs and 31 jack ups) and the first DNV certified 750 ton version has just recently been retrofitted on the Rowan Gorilla V jack up in the North Sea. The rig went on location and the top drive performed satisfactoriy with no downtime on the first well for Total and at the time this paper was being written the well was drilled to 11,368 ft.