Vibrations have been identified as one of the most frequent and persistent performance limiters by limiting weight-on-bit, rate of penetration, or borehole quality even when they may be low enough not to cause damage to downhole tools and equipment.A general purpose drillstring mechanics model has been developed to analyze axial and torsional vibrations in the frequency domain and provide vibration indices indicative of dysfunction in these modes. The model utilizes transfer matrices to solve for harmonic perturbations around a baseline solution obtained from a torque-and-drag type analysis, and accounts for effects of well path, tool joints, viscous damping due to the drilling fluid, surface boundary conditions, bit characteristics, and special vibration mitigation tools. The model supports workflows for real-time vibration surveillance as well as post-drill root cause analysis and well redesign. For example, real-time stick/slip severity monitoring is enabled using 1-second surface measurements. As a well redesign tool, a large number of design alternatives can be quickly evaluated to mitigate vibrations.Case studies utilizing high-frequency surface/downhole drilling mechanics data validated the model and identified three types of torsional dysfunctions with distinct signatures and mitigators: Unstable Stick/Slip, an instability associated mostly with the lowest-frequency torsional resonance of the drillstring; Bit/Bottomhole Assembly (BHA) Stall, intermittent, sudden mechanical jamming at the bottom of the drillstring; and Synchronous Torsional Oscillation, the amplification of periodic excitations at torsional resonances of the drillstring. In one case study, the stick/slip surveillance tool was superior to realtime downhole measurements in lag time, bandwidth, and accuracy. In another case, the root cause of prevalent Unstable Stick/Slip was identified as velocity-weakening aggressiveness of the bit. Among redesign options using a topdrive controller tuned to damp out the lowest-frequency torsional resonance was deemed most effective. One such controller was evaluated in the field and was very effective at mitigating stick/slip in subsequent wells. IntroductionThe operator's drilling performance-management process (Dupriest et al. 2005a;Dupriest et al. 2005b;Remmert et al. 2007) has identified vibrations as one of the most frequent and persistent performance limiters. The issue is not restricted to potential damage to downhole tools and equipment or non-productive time caused by severe vibrations. Even low levels of vibration may impact performance by limiting weight-on-bit, rate of penetration, or borehole quality. A recently deployed lateral vibration modeling tool, which was developed to enable drilling engineers to design vibration resistant BHAs, has been providing substantial performance gains in worldwide drilling operations (Bailey et al. 2008;Bailey et al. 2010a;Bailey et al. 2010b). In order to complement this capability for other vibrational modes, a general purpose model has been developed to ana...

A modeling tool has been developed that enables drilling engineers to design vibration resistant bottom hole assemblies (BHA's), given tool placement constraints and desired directional objectives. This model can be applied to configurations with the majority of common components, including rotary steerables, bi-center bits, roller-reamers, hole openers, and eccentric mass stabilizers. Modeling results have been validated in large, intermediate, and small hole sizes. In these applications, predicted behavior and field observations have compared well. Redesign has resulted in improved drilling results, including increased on-bottom drilling time, longer tool life, higher Rate of Penetration (ROP), reduced non-productive time associated with tripping, and even better hole quality. As use of the operator's ROP management process has spread through the company (Dupriest, 2005), downhole vibrations have been identified as one of the most significant factors limiting further ROP and footage improvements. Rig site personnel use vibrations data from downhole sensors and Mechanical Specific Energy (MSE) diagnostics to achieve the minimum vibrational levels possible with the existing assembly. The nature of the remaining vibrations is identified, and the BHA is then redesigned in a way that addresses the specific form of vibration that is limiting performance. The field assessment of the vibrational limiter and the redesign process are repeated from well to well. Vibrations mitigation is posed more as a design problem than an analytical one. The model characterizes the lateral vibration, or whirl, tendencies of BHA's, enabling quick and easy comparison of potential BHA design candidates. A BHA can be designed to minimize vibrational tendencies for a given set of operating parameters, or the optimal operating parameters can be predicted for a given BHA configuration. The model has unique displays to support both pre-drill vibrations forecasting and post-drill hind casting. Several case studies are provided to illustrate the value of this technology. Introduction Vibration of drillstrings and bottom hole assemblies has contributed to operational problems since rotary drilling was first invented in 1930. Failure of drillstring components, such as Rotary Steerable (RSS) or Logging While Drilling (LWD) tools, may result in non-productive time while tripping to replace the failed equipment. Downhole components may eventually part so that fishing or sidetracking operations are required. In some situations, equipment failure may also result in well abandonment. In addition to these unplanned events, whirl or lateral vibration causes the cutting action of the bit to be inefficient and ROP may decline significantly. The operator drills approximately four million feet of hole each year, and MSE analysis suggests the performance in over 40% of this footage is adversely affected by whirl. At various times in the past, investigators have focused on certain elements of the drillstring dynamics problem and made some progress, to be succeeded by new theories using generally more complicated models. Critical rotary speed guidelines were included in early editions of the API RP7G drillstring standard (e.g., 1984). One critical speed formula depended on the length of a drillstring, thus identifying a vibrational depth-dependency, but this section was deleted from later versions because it was considered to be insufficiently precise. Dareing (1984) found that the length of drill collars in particular is a key element in the bottom hole assembly (BHA) vibration problem. Mitchell (1987) identified harmonic resonance of the BHA as a major factor in several case studies of BHA failures. Spanos and Payne (1992) used a frequency domain eigenmode analysis to investigate the problem, primarily focusing on the identification of critical modes and corresponding rotary speeds. Critical mode analysis is still of interest in present models (e.g. Chen, 2007).

Rac GTPases regulate a wide variety of cellular processes including actin cytoskeleton organization, gene expression, cell-cycle progression, and apoptosis. Here we report that the TRQQKRP motif of Rac2 located near the C-terminus, a region of sequence disparity among Rac proteins, is essential for complementation of Rac2 function in Rac2-deficient cells. Deletion of this sequence can also intragenically suppress the dominant-negative Rac2D57Nmutation in a variety of functional assays. In Rac2-deficient cells, expression of TRQQKRP-deleted Rac2 protein is unable to completely rescue migration and nicotinamide adenine dinucleotide phosphate oxidase deficiencies previously described in these cells. In fibroblasts, the Rac2D57N mutant phenotypes of abnormal proliferation, cell morphology, and membrane ruffling are suppressed by the TRQQKRP motif deletion. In myeloid hematopoietic cells, the deletion of the TRQQKRP motif eliminates a Rac2D57N-induced block in in vitro differentiation of neutrophils not previously described with this mutant. Mechanistically, deletion of the TRQQKRP motif results in diminished geranylgeranylation and delocalization of intracellular Rac2 protein. Taken together, these results indicate that the TRQQKRP motif in Rac2 protein is required for efficient prenylation and correct intracellular localization of Rac2 protein and is essential for Rac2 to mediate a variety of its biologic functions. These data suggest that precise localization of Rac2 protein in intracellular compartments and/or with other proteins/lipids is a prerequisite for its diverse functions.

Stick-slip and whirl are vibrational problems that commonly limit drilling performance in hard formations and extended reach wells. The introduction of roller reamers has resulted in significant performance improvement in a number of the operator's drill teams with chronic stick-slip or whirl-induced borehole features. Whirl is a dysfunction characterized by lateral vibration that may occur both at the bit and in the bottomhole assembly (BHA). When whirl becomes severe, lateral vibrations cause significant side forces in stabilizers. Frictional drag resulting from these side forces causes high levels of torque to be generated at stabilizers and can result in stick-slip (a condition characterized by fluctuations in the rotational speed of the BHA). The operator refers to this as "coupled stick-slip" because the condition is caused by whirl in stabilizers. When these conditions exist, the replacement of stabilizers with roller reamers significantly reduces the potential for torque-generation at the contact points. Consequently, more torque becomes available to the bit and the driller may raise weight on bit (WOB). This results in reduced levels of bit whirl and improved rate of penetration (ROP). The reduction of bit whirl and elimination of stick-slip prevent damage to bit and BHA components. Roller reamers are also seen to serve the historical purpose of conditioning the borehole. The operator's field experience indicates that the need for conditioning is often due to whirl-induced features in the borehole. These features include spiraling and ledges. The use of roller reamers greatly reduces the prevalence and impact of whirl features. This paper details the conditions where roller reamers provide benefits allowing improved performance. A conceptual model for coupled stick-slip is provided as well as a summary of whirl-induced borehole features which may be mitigated with roller reamers. Representative examples are provided that show drilling performance improvements using roller reamers to mitigate these conditions. Introduction When lateral and torsional vibrations in the BHA become coupled, a torque or torsional vibration limit of the drilling system often prevents the driller from running sufficient WOB to prevent bit whirl. Bit whirl can be detrimental to drilling operations in many ways. These detrimental effects include the development of ledges (Brett et al. 1990), borehole oscillations (Pastusek and Brackin 2003, Boualleg et al. 2006), hole spiraling (Gaynor et al. 2001), and premature failure of downhole tools (Bailey et al. 2008, Mitchell and Allen 1987). Dupriest et al. (2005) demonstrated that the presence of whirl in the bit itself may be observed by evaluating the impact of changes in drilling parameters in real time on mechanical specific energy (MSE). MSE measures the amount of energy consumed in drilling a unit volume of rock. Real-time surveillance of MSE across global operations suggests that over 40% of footage is affected by a detectable level of whirl. When the driller is not constrained by a limit of the rig or drillstring, parameters may be adjusted to reduce the level of bit whirl. Typically, weight on bit (WOB) is increased resulting in a reduction in MSE. This indicates that the amount of energy lost to side-cutting and heat generation from whirl vibrations was reduced. For example, Boualleg et al. (2006) documented a reduction in the amplitude of whirl-induced borehole oscillations that resulted from drilling the interface between two samples of rock with a contrast in compressive strength as WOB was increased. Field evidence confirms the presence of these whirl-induced oscillations in field conditions at the interface of laminated rocks. The operator has noted a couple of recent instances where the BHA became mechanically stuck as a result of whirl-induced borehole patterns after drilling a transition between rocks of varying strength.

Summary Significant performance improvement has been achieved by successfully managing drilling vibrations through bottomhole-assembly (BHA) redesign. This effort has resulted in increased footage per day and reduced tool damage. Prior literature has described improvements in operating practices to manage vibrations (Dupriest et al. 2005; Remmert et al. 2007) as a key component of this rate-of-penetration management process. In a parallel work activity, BHA redesign efforts have provided additional performance improvements of approximately 36% in one drilling application. Dynamic modeling of the BHA has identified the key design changes leading to these improvements. The redesigned BHA has lower calculated vibration indices than the standard BHA. The BHA design evaluation process uses a frequency-domain lateral dynamic model in both predrill forecast and post-drill hindcast modes. BHA lateral vibrations are characterized such that alternative BHA configurations may be developed and compared directly with a proposed baseline assembly. In the hindcast mode, the BHA model can be operated at the recorded weight on bit (WOB) and revolutions per minute (RPM) to generate corresponding model results in time or depth, and these values can be compared with the measured performance data. In one case study, the redesign of a BHA with downhole motor and roller reamer is described, with corresponding field data for four original BHAs and four redesigned assemblies. In a second application, model and field drilling results for two rotary-steerable assemblies are compared to evaluate the predictive ability of the model in smaller hole size and with different BHA types. Finally, the utility of the model to identify preferred rotary-speed "sweet spots" is demonstrated in a motor BHA operating in larger hole.