The proper segregation of chromosomes during meiosis or mitosis requires the assembly of well organized spindles. In many organisms, meiotic spindles lack centrosomes. The formation of such acentrosomal spindles seems to involve first assembly or capture of microtubules (MTs) in a random pattern around the meiotic chromosomes and then parallel bundling and bipolar organization by the action of MT motors and other proteins. Here, we describe the structure, distribution, and function of KLP-18, a Caenorhabditis elegans Klp2 kinesin. Previous reports of Klp2 kinesins agree that it concentrates in spindles, but do not provide a clear view of its function. During prometaphase, metaphase, and anaphase, KLP-18 concentrates toward the poles in both meiotic and mitotic spindles. Depletion of KLP-18 by RNAmediated interference prevents parallel bundling/bipolar organization of the MTs that accumulate around female meiotic chromosomes. Hence, meiotic chromosome segregation fails, leading to haploid or aneuploid embryos. Subsequent assembly and function of centrosomal mitotic spindles is normal except when aberrant maternal chromatin is present. This suggests that although KLP-18 is critical for organizing chromosome-derived MTs into a parallel bipolar spindle, the order inherent in centrosome-derived astral MT arrays greatly reduces or eliminates the need for KLP-18 organizing activity in mitotic spindles. INTRODUCTIONIn eukaryotes meiosis allows the exchange of genetic material between parental chromosomes and leads to the formation of haploid gametes. Reliable segregation of meiotic chromosomes depends on the correct assembly of microtubules (MTs) into a bipolar spindle. In most animal systems, female meiotic spindles lack centrosomes and their MT nucleating activity (Sawada and Schatten, 1988;Gard, 1992;Theurkauf and Hawley, 1992;Albertson and Thomson, 1993). Interestingly, vertebrate cultured cells in which centrosomes have been destroyed can use a centrosome-independent pathway to build a functional bipolar spindle (Khodjakov et al., 2000). These and other results suggest that although the diastral mode of spindle assembly dominates when centrosomes are present, chromatin-based spindle assembly can be used when centrosomes are absent. The question of how meiotic MTs become organized into a bipolar structure remains largely unanswered.Studies in Xenopus egg extracts have provided some important insights into acentrosomal spindle assembly. The observation that bipolar spindles can form around DNAcoated beads confirmed that chromatin itself can provide a platform for the nucleation, stabilization, and/or capture of MTs (Heald et al., 1996). Analysis of the effects of inactivating or depleting specific MT motor proteins from Xenopus extracts along with analysis of mutations that affect assembly of acentrosomal meiotic spindles in Drosophila (Merdes and Cleveland, 1997;Walczak et al., 1998;Walczak, 2000) have led to the following model for chromatin-based assembly of bipolar spindles. Chromatin-associated kinesins, e.g., X...

Well known in the oil and gas industry is the importance of understanding drilling system vibrations and bit-reamer weight transfer when drilling with hole openers. A field testing program was carried out on a full-scale experimental test rig in the state of Oklahoma, USA, with known lithological formations, in order to evaluate underreaming system designs. In this context, the underreaming system comprised the bit, the drive system, and the underreaming element. To fully understand how the system interacts with the formation and reacts to inputs from the surface, drilling mechanics measurements were taken above and below the reamer element. Drilling dynamics measurements were also taken at three places in the BHA, with two drilling dynamics packages spaced out below the reamer and one positioned directly above it. That way, dynamics on the bit and reamer could be studied separately to understand how bit and reamer performance affect each other and the overall system dynamics. The first well was directionally drilled with a rotary steerable system, concentric reamer, and vibration monitoring equipment set up in an industry-standard arrangement. This paper will describe how the findings and learning from the initial field test led to bit redesign and operational techniques implemented to enhance the drilling system stability. Another borehole was then drilled through identical formations with this improved system, offering a unique detailed comparison between the two field tests. The new bit design allowed the bit to control the drilling rate with better weight distribution between bit and reamer, significantly reducing vibration, and in this study, without impacting penetration rate. A concentric reaming tool new to the drilling industry was used in both wells as a part of this study and will also be described. This tool demonstrated good steerability with a rotary steerable tool system and operated properly, drilling closed, activating, reaming, and finally, closing for retrieval from the hole. Introduction The purpose of this paper is to describe testing done under downhole-controlled conditions in identical, side-by-side wellbores with heavily instrumented BHAs. The testing compared the results of drilling with a conventional bit/reamer system compared to a specially designed pilot bit synchronized to the reamer. In both cases, the BHA was designed with dynamics modeling software with the objective of minimizing vibration. The test results proved a methodology that matched the reamer and pilot bit to substantially reduce vibration.

This paper evaluates the effect of cutter density, back rake angle, size, and speed on the steady state wear rate and performance of Polycrystalline Diamond Compact (PDC) cutters. The analysis is based on laboratory and controlled field testing results at Amoco's Catoosa Test Facility. P. 131

This paper discusses the development, testing and optimization of a rotary steerable system (RSS) developed specifically to address the challenges around drilling wells in unconventional reservoirs in North America. As with offshore areas, rotary steerable drilling technology has rapidly gained acceptance for onshore use because of its clear advantages in directional control, wellbore placement and lateral reach, while matching or exceeding the drilling performance of conventional systems. The further growth of RSS into the drilling of unconventional reservoirs has been limited by the build-rate (BUR) capabilities of established RSS that prevent operators from successfully drilling curve and lateral sections in one run. In recent years, service companies have worked to improve the capabilities of rotary steerable drilling systems to meet the specific needs of drilling horizontal wells in unconventional oil and gas reservoirs. Due to lease spacing and limited vertical depths to achieve horizontal orientation, greater buildup rates (BUR) are required to maximize the lateral lengths in the reservoir. In addition to developing higher doglegs in the curve, the system should also enable lateral control to minimize tortuosity, facilitate easy casing running and optimize successful multistage fracturing. The authors outline how specific challenges, such as reduction in drilling time, improved wellbore placement, and more efficient completion and fracturing operations are addressed by the introduction of the new system. Included in this paper is a description of how the bottomhole assembly (BHA) and drill-bit properties are matched and optimized to deliver best directional control and drilling performance, according to formation characteristics in the Granite Wash play in the central USA. Explanations detail how the new system capabilities expand the possibilities to develop reservoirs using pad drilling, the use of more complex well profiles and real-time reservoir navigation, leading to increased hydrocarbon production.