The ability of American carnivorous pitcher plants (Sarracenia) to digest insect prey is facilitated by microbial associations. Knowledge of the details surrounding this interaction has been limited by our capability to characterize bacterial diversity in this system. To describe microbial diversity within and between pitchers of one species, Sarracenia alata, and to explore how these communities change over time as pitchers accumulate and digest insect prey, we collected and analyzed environmental sequence tag (454 pyrosequencing) and genomic fingerprint (automated ribosomal intergenic spacer analysis and terminal restriction fragment length polymorphism) data. Microbial richness associated with pitcher plant fluid is high; more than 1,000 unique phylogroups were identified across at least seven phyla and 50 families. We documented an increase in bacterial diversity and abundance with time and observed repeated changes in bacterial community composition. Pitchers from different plants harbored significantly more similar bacterial communities at a given time point than communities coming from the same genetic host over time. The microbial communities in pitcher plant fluid also differ significantly from those present in the surrounding soil. These findings indicate that the bacteria associated with pitcher plant leaves are far from random assemblages and represent an important step toward understanding this unique plant-microbe interaction.

Traditional polycrystalline diamond cutter (PDC) technology has made tremendous gains over the past decade with corresponding footage and rate of penetration (ROP) improvements in drilling performance. The remaining challenge is managing interbedded formations with competent stringers while maintaining drilling efficiency and the highest ROP potential, such as those present in the 6 to 6⅛-in. Pinedale Anticline production hole and the 12¼-in. Cana intermediate section. By modifying the standard planar PDC cutter face geometry with novel shallow recessed features, a demonstrated improvement in drilling efficiency was observed in these applications and an increase in attained footage. Extensive analysis in Pinedale runs indicated this cutter design benefits a lower mechanical specific energy (MSE) in the shale and sand, shorter day curves, and higher average ROP per unit of motor horsepower. Initial runs in the Tonkawa sands of the Cana intermediate have started to show similar trends. The successful field runs have been supported by in-depth analysis and study of cutting efficiency including, single-point cutter testing in a pressurized vessel, atmospheric vertical turret lathe testing, and full-scale PDC bit laboratory testing in a state-of-the-art downhole drilling simulator. The results of this work improved the understanding of the thermo-mechanical behavior of cuttings formed by the drilling action of a PDC cutter in these applications. This study is part of an innovative approach to manage rock cuttings, cutting efficiency, and thermal loads as it applies to PDC durability in state-of-the-art drill bit designs. The design changes have improved cutting efficiency and aggressivity, which has improved the ROP of bits in abrasive sand and in the shale sections. This paper provides documentation and visual demonstrations of the features and benefits seen in the single-point test apparatus, the downhole simulator in the laboratory and in the field with case studies compared to offsets of standard bits with planar PDC cutters.

Stick/slip vibrations are known to cause damage to drill bits and other drilling system components. Recent investigations reported by the authors determined that the design of polycrystalline diamond compact (PDC) bits has a significant influence on stick/slip behaviour of the drilling systems. Among various bit design methodologies, a depth-of-cut (DOC) control technique has emerged as an effective way of mitigating bit-induced stick/slip. The research reported in this paper aims at enhancing this technique to accurately identify the optimal application of DOC control for maximum reliability and performance. A comprehensive testing program on a full-scale research rig was undertaken to characterize the optimal type, positioning, and extent of DOC control required for mitigating stick/slip. Several PDC bits incorporating strategically configured DOC control elements were designed and tested. The stick/slip tendencies of bits were determined based on diagnostics from downhole drilling dynamics monitoring devices while the surface operating parameters were varied in a controlled manner. Test results indicated that certain DOC control characteristics were the most effective in mitigating stick/slip. While under-application of DOC control did not mitigate stick/slip, over-application reduced performance without mitigating stick/slip. Formation type played a major role in instigating stick/slip, and was a significant factor in designing DOC control. The paper presents analysis details and proposes design guidelines based on testing in multiple formations within three research wells. These design guidelines are also supported by field evidence from the North Sea, where statistics on many bit runs indicate superior performance with properly tuned DOC control.

Stick-slip vibrations of drillstrings have been studied by researchers for several decades. The subject is gaining renewed interest as operating parameters for PDC bits have shifted to the stick-slip regime of higher bit weight and lower rotary speed for enhanced drilling performance. In Ledgerwood et al. (2010), stick-slip was identified as a primary cause of bit damage. The main objective of the current investigation is to answer the longstanding question: Do bit designs influence stick-slip behavior of the drilling system? Five prevailing industry perceptions reported in the literature are that anti-whirl bits, reduced exposure bits, and bits with bit-rock interaction number "β" > 1 are less prone to stick-slip, while highly aggressive bits and worn bits are more prone to stick-slip. Although the phenomenological basis of these theories has been provided, validation in most cases is based on anecdotal evidence from the field. Data with diagnosis based on downhole measurements in a controlled environment are scarce. Consequently, conflicting opinions continue to exist about whether any of these theories work in reality. To assess their validity, the five leading theories were reviewed and pairs of PDC bits were designed and manufactured. Each pair consisted of a bit with a standard design and a bit that embodied one of the theories. The bits were first tested in the laboratory to characterize their response. Full-scale wells were then drilled under controlled conditions using a research drill rig in Oklahoma. In these wells, only the operating parameters were varied while BHA, formation, and other variables were unchanged for a given bit pair. The downhole vibrations were measured with a new in-bit device and an industry-proven MWD vibration monitoring service. The most important conclusion emerging from this study is that PDC bit design has a significant effect on stick-slip vibrations. While some of the theories held true, evidence from this study did not support others. The details of test results are provided and various aspects of bit design are discussed in an attempt to enhance the understanding of stick-slip mitigation.

Suppressed oil prices amid a call for increased returns from shareholders has created opportunities for operators and service companies to work closely in developing and deploying new technology in well construction efforts. Under extreme pressure, operators are seeking innovations to reduce drilling time and shorten the time to production. An operator in Oman has tripled output over the last ten years using enhanced oil recovery (EOR) methods, making it the largest independent oil producer in the Sultanate. The development of polycrystalline diamond compacts (PDC) is one of the fastest-evolving technologies for fixed cutter drill bits. The application of PDC bits continues to expand performance by increasing rates of penetration (ROP) to lower drilling costs. The most recent developments in synthetic diamond cutters have been in 25mm-diameter cutters. Although 25mm-PDCs were developed in the mid-1990s, they lacked the necessary durability for demanding drilling applications. Only recently has the technology become available to meet these needs in this size. Several recent tests in Oman have shown the new 25mm-cutter technology drastically improved performance with shoe-to-shoe runs at increased ROP. With the new cutters came the need for paired frame improvements with special considerations for aggressiveness and mechanical limitations for torque, both for the drilling rigs and use with positive displacement motors. During vertical drilling through carbonates and shales in the Diba field, the technology established a new field record ROP of 217 feet per hour—an 80% improvement over the field average ROP. In the Jalal field, 275 feet per hour was achieved—29% higher than the previous best record. The technology was also introduced on a steerable motor in a directional well, delivering improved penetration rates and excellent stability in slide mode. An additional lesson learned was the smooth torque generated by the large cutters. The smooth drilling torque enabled improved directional tool face control. This operator has implemented an aggressive drilling and development program to drill faster and reduce cost per foot in heavy oil sands and fractured carbonates. The authors will present case studies to demonstrate how the latest technology 25mm-cutters and new frame technology helped lowered drilling costs for this operator's drilling program in Oman.