Drilling activity has increased rapidly in Iraq over the last few years. With the lack of reliable downhole data to develop a solid strategy to optimize drilling operations, the drilling performance has been inconsistent with frequent failures of drill stem components. Without the aid of quality downhole data it is very difficult to identify the root cause of these failures, and more importantly, provide a means to identify a solution to improve performance. This paper showcases a project in South Iraq where modeling of the drilling BHA's using a unique Finite Element Analysis software package identified critical natural frequencies of the drillstring. The integration of high frequency downhole vibration data collected in multiple positions of the string provided the evidence to validate the vibration road map delivered by the BHA analysis.The objective of the project was to identify the primary vibration mode, evaluate the vibrations severity, cause and source in the 12 !" vertical section and provide recommendations to achieve performance improvement through controlled step changes in bit & BHA design, drilling parameters and operational procedures. The pre-well BHA model analysis identified that the premature bit failure was a direct result of lateral vibrations induced by operating in a critical lateral harmonic zone. This was validated with the downhole vibration data.A well-established optimization process including expert detailed analysis of the high frequency downhole vibration data provided a clear understanding of the relationship between the pre-well BHA model, the drilling parameters planed and the associated downhole drilling dynamics.The impact on performance was clear. Implementation of the new recommended drilling parameters derived from the BHA analysis applied to the same bit and BHA used in Well #1 resulted on a 26% increase in drilling performance in well 2. 2-IntroductionThere are multiple drillstring dynamics modeling software packages available in the industry that enable any drilling team to do a pre-well analysis of each BHA design and model the downhole behavior of the system. Most these packages provide the similar approach of using Finite Element Analysis of the entire string to calculate the combination of drilling parameters based on a proven, scientific approach that will most likely initiate downhole vibration and high impact loading that leads to premature bit and/or downhole tool failures.It should be a requirement to run such modeling analysis for every BHA for two main reasons. First it allows the drilling engineer to twick the BHA design to minimize the impact of the natural resonant frequencies on the system performance. And second, and in case the BHA design remains the same, it ensures that the drilling parameter combination selected (weight and surface RPM) will not initiate disruptive harmonics generated from the natural frequencies of the system itself.

Drill string twist-offs are an expensive problem to the oil and gas drilling industry. With ever increasing rig and operating costs, there is an increased focus to avoid twist-off related expenses, such as: costs associated with time required to trip out of hole and replace the failed components, the cost of repair or replacement of failed equipment, fishing operations and possibly the cost of side-tracking. Oil and gas operators attempt to prevent drill string failures by optimizing the drill string and trajectory designs. Drill string manufacturers aim to engineer drill pipe and tools with ever increasing strength properties and maximum fatigue resistance. In addition to this, drilling contractors and service companies have extensive inspection programs to avoid failure. Despite these efforts, twist-offs remain an important problem for a large number of drilling applications. Recent research and analyses suggest that the majority of drill string failures are caused by fatigue. Since the root cause of a fatigue failure cannot always be identified from surface drilling parameters or laboratory analysis, the evaluation of drilling dynamics data is essential for understanding the cause of a twist-off. This paper will present several case studies from the North Africa region to illustrate the important contribution of drill string vibration on fatigue-related failures. In all cases, high resolution dynamics recorders were incorporated into the BHA, or drill string, close to the location of the twist-off. Analysis of the dynamics data revealed that the drill string was exposed to severe lateral vibration prior to the twist-off events. Furthermore, the observed vibration was the major contributor to the sustained fatigue due to the resulting severe shock loading and increased bending stresses generated during vibration. The paper will also present mitigation practices or changes that were implemented based on the drilling dynamic analyses as well as potential solutions for the remaining case studies. Generally, these solutions are significantly more cost effective than the traditional approaches of reducing twist-offs such as: increased frequency of inspection programs or enhanced mechanical properties on connections and drill strings.

The San Juan basin is a prolific natural gas play in northwestern New Mexico and southwestern Colorado. For more than four years, all attempts to find a poly crystalline diamond compact (PDC) solution for the northern part of the basin have been unsuccessful or uneconomic; in addition, the performance of insert bits had also reached a plateau of roughly 60 ft/hr. In order to achieve the next step change in drilling performance, it was decided that a drilling optimization process that was integrated with high speed downhole drilling dynamics was required. The optimization process required the cooperation of the client, the directional drilling company, and the optimization company. The team was challenged to find a fixed cutter solution that could drill from surface to total depth (TD) in one run and at over 100 ft/hr; these challenges thus became the project's two primary objectives. This paper discusses how an optimization process was integrated with high speed, multiple placement, downhole drilling dynamics analysis in order to discover what was limiting the performance of fixed cutter bits. The process involved four phases -analysis, planning, execution, and evaluation -utilizing a four well project. The lessons learned from each well were then applied to the next well in the sequence. From the lessons learned, small changes were made to the drilling assembly after each well in the sequence. These changes were then analyzed on the subsequent well. On each section, the downhole drilling dynamics data was merged with surface data.The analysis of this data demonstrated that the main limiters to drilling performance were poor weight transfer and vibration. On the fourth well in the sequence, a specially designed, six bladed fixed cutter PDC bit drilled the entire 2,858ft of the 7 7/8" section, in one run. The overall rate of penetration (ROP) including connection time, was 102 ft/hr, surpassing the goal of 100 ft/hr.

The geometry of a stabilizer, when it is used as a near-bit pivot within specific point-the-bit rotary-steerable bottomhole assemblies (BHAs), is critical to both stability and deflection to provide optimal directional response. This paper describes the testing of a rotary-steerable system (RSS) and unique ring gauge pivot stabilizer at a purpose-built, full-size drilling test facility. The extensive, systematic testing of a point-the-bit RSS with both full ring gauge and conventional pivot stabilizer has enabled a direct comparison of the directional response, hole quality, and drillstring vibration to be made for the various combinations tested. Aside from comparison of the ring gauge stabilizer against conventional pivot, the testing also evaluated the interaction between the gauge design of the bit and the pivot stabilizer. Test monitoring required use of a proprietary downhole dynamic data recorder (DDDR) in a specially modified housing. The DDDR was used to assess both lateral and torsional stability of the stabilizer geometries and their relationship with bit gauge style and length. Further to the laboratory testing, trial applications have been sought where severe vibration issues are problematic to efficient operation of the RSS. Use of full ring stabilization geometry with an RSS in these applications will advance the industry's understanding of downhole dynamics. Enhanced understanding, in turn, will enable more efficient drilling of better-quality directional wellbores, significantly reducing cost per foot. Introduction The introduction of RSS has given the industry the ability to successfully drill complex and challenging well profiles such as extended-reach and infill designer re-entry wells. In addition, the use of polycrystalline diamond compact (PDC) bits, combined with RSS, has drastically changed the economics of directional drilling by significantly decreasing the time taken to drill hole sections and improve the quality of wellbores drilled, thus increasing the chances of trouble-free wireline logging and running of completions. The improve-ment in economics is particularly relevant in this era of high rig rates. It is recognized that the selection of correct design of bit is crucial to the successful directional performance of an RSS. The stability and steerability of the bit are key features in matching a bit to the specific RSS, while matching the durability and aggressivity to the formation is of importance in achieving the optimal rate of penetration (ROP) and bit run life. Point-the-bit RSS can take advantage of longer passive gauge lengths to reduce hole spiraling and improve borehole quality because they rely less on side-cutting action from the gauge than do push-the-bit systems.1,2 Key focus is maintained on providing very stable bit cutting structures that resist lateral instability and provide low variance in reactive torque. Furthermore the interaction between the bit, the RSS, and the BHA elements is extremely important to the successful directional performance of the system. Maintaining wellbore quality, and in particular hole gauge, is crucial to the steering performance of point-the-bit RSS.3 One aspect of wellbore quality is the stability of the active BHA, as vibration will contribute to wellbore enlargement. BHA instability can have a significant detrimental effect on the directional performance of the RSS. Prior testing has focused only on optimization of the cutting structure and gauge geometry to maximize stability of the drill bit.4,5 This paper details the introduction and systematic testing of stabilizer geometries to further enhance stability, and thus steering efficiency, of RSS.

TX 75083-3836 U.S.A., fax 1.972.952.9435. AbstractThe oil industry is increasingly interested in drilling dynamics as a primary cause of drilling inefficiency. It has become ever more important to be able to both accurately predict and detect downhole vibration/instability throughout the entire drill string. The drill bit is often assigned as the cause, and frequently bears the scars of dynamic drilling problems. Historically bit manufacturers have used a combination of dull grades and surface data to speculate on cause and effect of downhole events with insufficient attention to what may be occurring in between.A small vibration logging tool has been employed in hundreds of applications worldwide. This paper discusses the implementation of this device and its flexibility for placement of multiple tools in various locations, such as specific built subs and/or existing tools, within the drillstring. The versatility of this tool design offers the possibility to be run with any type of bit, fixed cutter or roller cone, regardless of manufacturer thus making it transparent to drilling operations throughout the entire drilling assembly.Specific field cases will be presented including; validation of pre-run dynamics modeling software, rotary steerable tools, concentric and eccentric hole opening tools, and response of different BHA configurations. This type of data is important to further the understanding of drill bit, drillstring component, and overall drillstring dynamic performance.