Downhole Drilling Tools Research Articles

Development status and application prospect of semi-active vibration reduction technology for down-hole drilling tools

Domestic and foreign oil companies have been constantly increasing the research and development investment in underground shock absorber, to reduce the vibration and shock of drilling tool under hard rock drilling environments, enhance the rate of penetration and decrease drilling cost under the premise of ensuring the normal life of drill string components and stable bit weight. Based on this, this paper has focused on the working principal of magneto-rheological fluid (MRF) semi-active damper, the composition of MRF and its internal parameters’ impact on the damping characteristics, combining with the status quo at home and abroad of down-hole vibration technology. Meanwhile, the test analysis of semi-active damping technology was conducted. And the results showed that semi-active vibration technology had greatly weakened the vibration level while improved the rate of penetration, guaranteed the service life of bit and other drill-string components, reduced additional tripping times and effectively solved the problems of bit weight instability and low penetration rate etc., caused by drill vibration. Therefore, in the current situation of worldwide oil price downturn, it has become increasingly prominent to reduce cost and increase efficiency, and it’s particularly necessary to research on the shock absorbers of down-hole drilling tools in China.

Dynamic Research and Experimental Analysis of a New Downhole Drilling Tool

With the increasing of drilling depth, the working conditions of the drilling engineering are becoming more complicated. When drilling in the complex well structure, there are many new problems or challenges such as low rate of penetration (ROP), serious stick–slip phenomenon, or high risk of downhole tools failure. The most critical factor in solving these new challenges is improving rock breaking efficiency. Considering this, this paper proposed a new oscillator based on the positive displacement motor. Combining with new complex drilling conditions, the new structure was designed. The mathematical models were presented, including the working mechanism of the new design with its structure parameters. Furthermore, the theoretical models of dynamics under new conditions were analyzed, including the new bottom hole assembly. Based on this, we can get the vibration displacement, velocity, and the system vibration spectrum at different drill string positions. Compared with the results of a numerical example, the lab test was carried out. The two important parameters of vibration frequency and impact forces were compared with the theoretical results, which verified the correctness of the theoretical model and the accuracy of the solution method. Moreover, field experiments were also tested to verify the results, and the field experimental data showed that the new design could increase ROP obviously. The method and conclusions of the research can provide a new reference for the new downhole technology of enhancing the ROP or improving the rock breaking efficiency in complex well structure.

Modeling and analyzing the motion state of bottom hole assembly in highly deviated wells

Motion state of bottom hole assembly (BHA) has a great effect on the performance of downhole drilling tools. In this article, we developed a finite element model for characterizing the lateral motion of BHA in highly deviated wells taking discontinuous interaction between drill strings and wellbore into consideration. Numerical simulations were conducted by solving the motion equation through Newmark method. To verify the established model, an indoor experimental apparatus was built based on the similarity criterion. Numerical and experimental simulation results were compared and analyzed under different rotary speed, weight on bit (WOB) and well inclination condition. Both of the results showed that BHA locates in and swings along the lower right part of borehole in highly deviated wells without forming into backward whirl motion. Rotary speed has an obvious effect on BHA lateral motion state where the vibration amplitude and frequency get improved with the increase of rotary speed. Compared with rotary speed, WOB and well inclination angle has a much smaller effect on the BHA lateral motion in highly deviated wells. Based on the analyses, relevant recommendations were given for the engineering practical use. This study can help understand the dynamic characteristics of BHA in highly deviated wells and select operation parameters for better drilling.

A critical review of the tribocorrosion of cemented and thermal sprayed tungsten carbide

Abstract Cemented and thermal sprayed tungsten carbide are extensively used in a wide range of applications, ranging from downhole drilling tools and oil and gas valves to gas turbine engines. These WC based systems offer improved wear resistance as a result of hard ceramic phases surrounded by a metallic binder matrix. However, the presence of hard and soft phases within these materials also leads to differing wear mechanisms and the formation of micro-galvanic couplings in aqueous environments often result in a reduction in combined wear-corrosion resistance. This paper examines the wear-corrosion performance of these WC based systems in a range of wear, electrochemical and wear-corrosion tests to develop models and establish relationships between wear mechanisms and environmental factors such as pH.

Mathematical model and optimum design approach of sinusoidal pressure wave generator for downhole drilling tool

• A model is proposed for the structure of sinusoidal pressure wave generator. • An optimum design for the generator is proposed based on CFD analysis. • Optimum generator design can reduce the risks of clogging and generate sinusoidal wave. • Simulation and experimental results validate the effectiveness of the method. Mud pulse generators have been widely used for the real-time transmission of valuable directional and formation data from downholes with depths of thousands of meters. There have been numerous studies on the design of mud pulse generators in which the pressure waves were typically nonsinusoidal. Sinusoidal waves provide improved long-distance data transmission and signal noise suppression compared with nonsinusoidal waves. Although sinusoidal pressure wave generators have been studied in the published literature, the influence of the risks of clogging on the design of the generator for producing sinusoidal pressure waves has rarely been considered. To generate sinusoidal pressure waves and to reduce the risks of clogging, a mathematical model for the design of a sinusoidal pressure wave generator is developed in this paper. The effects of the axial and radial clearances between the rotor and stator on the design of the generator are considered in the model. An optimum design method for the generator is provided by combining the developed model and a computational fluid dynamics analysis. Finally, an experimental platform was built and experiments at frequencies 2 Hz and 10 Hz were conducted to validate the design result. The simulation and experimental results show that the optimized pressure waves closely approximate sine waves. Therefore, the developed mathematical model and optimization approach can be used to design a sinusoidal pressure wave generator.

Drill Bit Contact Dynamics Including Side Cutting: Simulation and Validation

Simulation techniques are increasingly becoming popular in recent years as a way of simulating oil drilling processes. Among them, directional drilling is a specific method that benefits enormously from such numerical techniques, inasmuch as the estimation of the wellbore curvature is crucial and cannot be properly estimated through approximate geometry methods. We present here some of the latest advances in bit contact dynamics, wellbore update algorithms, and experimental validation of side cutting, in the context of a finite element (FE) and finite segment simulation framework. The framework is based on the high-fidelity dynamic simulation of the mechanical system, including detailed geometry, large displacements, and accurate contact forces. The theoretical aspects, along with the experimental results, are thoroughly presented. Overall, this paper constitutes a step toward a more deterministic way of calculating build rates and designing downhole drilling tools.

Failure analysis of drillstring in petroleum industry: A review

Abstract Understanding the failure analysis of drillstring and its components i.e., drill collar and drilling bit is one of the essential issues in the oil and gas industry for the high cost of oil well drilling. Different ways such as air drilling, percussion drilling and downhole hydraulic ultra-high pressure (UHP) jet assisted drilling have been often used to improve the rate of penetration (ROP), minimize the cost of drilling per foot and diminish well deviation. Nevertheless, these drilling ways aggravate the working conditions of the downhole drilling tools materials and hence their properties cannot meet the demands of these conditions and consequently causing a risk drillstring failure. The unfavorable geological conditions and the repeated impact for breaking the rock may also cause severe bit bouncing and violent vibration. Tooth loss, tooth fracture, tooth wear and microcracks in addition to drill pipe fatigue from bending stress caused by buckling load are realistic examples of failure modes which occurred in the drilling tools. This study comprehensively describes the reasons causing these failure modes in order to manage risks and achieve high performance of wells and borehole sections. The role of working parameters i.e., bottom hole temperature and solid content on the drilling tools' life time, and the role of predrill predictions of pore pressure or wellbore stability on the drilling process are presented.

Technology Focus: Drilling Management and Automation (September 2015)

Technology Focus Drilling automation is the use of computer-assisted or -controlled devices in drilling a wellbore. It involves a considerable amount of technology, including mechanized and robotized surface equipment and semiautonomous downhole drilling tools; entire drilling systems composed of linked downhole tools, surface control systems, and remote monitoring; and data analytics. It includes both conventional overbalanced drilling and managed-pressure drilling. The economic drivers for automation are increasing complexity, data overload, efficient drilling, and safety, to name a few. Automated systems and equipment for drilling are under development by many, including equipment providers, service companies, and operators. Interested members of these companies have formed a consortium, the SPE Drilling Systems Automation Technical Section, which is promoting open data standards and protocols to exchange quality data in a safe and predictable manner. The group also looks outside the oil industry to learn from the route to automation taken by other industries. It has become clear that, while the technology and infrastructure for drilling automation exist, there are obstacles to commercial implementation. The primary hurdle is transitioning all the technology to the business environment. The many silos of our drilling industry make this technology-transfer problem quite challenging. The tension between technology and business is not new to the oil field or to any industry. You can have the most breathtaking technology, but, if there is no attempt to communicate the need for it, it will simply stagnate and never see the light of day. However, if the business side of the equation can envision the commercial benefits of a technology, the economic pull-through can revolutionize an industry. A means of communicating that vision is to develop a technology roadmap showing the developmental pathway the technology is following. A means of ensuring that all can take advantage of new technology and profit from innovation is to develop open systems using agreed-upon standards. A means of rewarding both developers and users is to implement systems- automation products by use of performance-based business models. One of the interesting developments in the last few years is an emerging understanding of the need to develop the communication infrastructure for a drilling operation. This infrastructure links all facets and players in a drilling operation: downhole, surface, remote, and enterprise. It forms the framework supporting open standards and enables the implementation of modern data analytics, real-time modeling, and control systems. The papers presented here represent a good overview of technology road-mapping of drilling automation, of modeling and simulation critical to automation, of drilling-management processes that make use of easily automated repetitive work flows, and of the value of quality data. The topics are innovative and thought provoking. Enjoy! JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 172151 Achieving Drilling Excellence Through Next-Generation Work Flows Enabled by Integrating Historical Drilling Data and Real-Time Data by Richard Mohan David, Abu Dhabi Company for Onshore Oil Operations, et al. SPE/IADC 173121 For Better or Worse: Applications of the Transfer-Matrix Approach for Analyzing Axial and Torsional Vibration by Roman J. Shor, The University of Texas at Austin, et al. SPE 173858 Possibilities, Limitations, and Pitfalls in Using Real-Time Well-Flow Models During Drilling Operations by Knut Steinar Bjørkevoll, Sintef Petroleum Research, et al.

Failure analysis and finite element simulation of key components of PDM

As one of the most commonly used downhole drilling tools, PDM (Positive Displacement Motor) is widely used in drilling and workover. Drilling practice shows that PDM is frequently scraped for the failure of key components. The coupled thermo-mechanical finite element model of rubber linings, finite element models of thrust bearing and universal shaft petals were established respectively, and the failure reasons were discussed by simulation. It was found that there are oval holes caused by thermal failure in general rubber lining, while no oval holes in the uniform wall thickness rubber lining. Rubber layer peeling and broken appear on the surfaces of rubber linings under the load of drilling fluid and rotor. Thrust bearings experienced serious wear, corrosion and rupture in the terrible downhole environment. The universal shaft petals appear fracture in the root, and wear on contact surfaces under torque and axial load. The results obtained in the paper show that the analyzing model and evaluation methods are quite reasonable and can be generally applied, which have great significance on the enhancement of structural design and repair for PDM in the future industry.

Torsional Dynamics and Point-the-Bit Rotary-Steerable Systems

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163428, ’Torsional Resonance: An Understanding Based on Field and Laboratory Tests With Latest-Generation Point-the-Bit Rotary Steerable Systems,’ L.A. Lines, SPE, D.R.H. Stroud, SPE, and V.A. Coveney, Weatherford, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed. Torsional dynamics can be extremely damaging to downhole drilling tools and can significantly affect drilling efficiency. The effort to prevent this phenomenon has led to the development of various downhole mitigation tools, improved bit technologies and bottomhole-assembly (BHA) designs, and better management of drilling parameters. This paper outlines two lesser-known types of torsional dynamics observed while drilling interbedded carbonate formations in the Middle East with the latest generation in point-the-bit rotary-steerable systems (RSSs). Introduction Aspects of dynamic behavior considered to be particularly undesirable include the following: Large fluctuations of bit-rotation rate (Ω) and the often-associated amplitude modulation of higher-frequency vibrations. [These features are usually ascribed to stick/slip behavior, wherein Ω is periodically zero, then much larger than the rotation rate at surface (Ω). Potentially, stick/slip could also occur at positions in the drillstring other than the bit.] Backward whirl, where the bit rolls around the (enlarged) borehole in a sense opposite to Ω. Resonances of the drill string may-drive or be driven by Items 1 and 2; enlarged or irregularly shaped boreholes are likely to be involved. Background A major mainland oil and gas field in the Middle East is notorious for difficult and hazardous drilling conditions; high levels of stick/slip are the norm. The RSS has a number of onboard dynamics sensors. The two discussed in this paper are RSS whirl-average indicator. This consists of accelerometers, which are mounted radially (to the drillstring centerline) and measure changes in centripetal accelerations. These are used to infer the severity of off-hole centerline rotation (i.e., whirl). This measurement has an effective sample rate of 40 Hz at 100 rev/min. A whirl-severity indication is then transmitted in real time to the surface. RSS stick/slip average. This sensor monitors changes in the RSS rev/min measurement over a given sample period. The RSS measures rev/min at an equivalent sample rate of 1 Hz. It is therefore suit-able only for detecting torsional dynamics (rev/min changes) that occur at up to 1 Hz. The conventional representation of stick/slip can be seen in Fig. 1. This is typical of the rev/min traces experienced elsewhere in the world and is of sufficiently low frequency that it can be detected easily by existing measurements. This low-frequency stick/slip is not particularly damaging to drillstring components. Although reported stick/slip levels in this particular field are usually severe, the amount of drillstring/drilling-tool damage experienced is disproportionately high compared with that experienced in other fields with similar levels of reported stick/slip. The literature suggests that harmonic/sinusoidal torsional dynamics can occur at significantly higher frequencies than the 1 Hz that existing onboard sensors are capable of detecting. It was apparent that the severity of the drilling environment in this field was not reflected accurately in RSS-sensor data.

Mechanical Extrusion Offers Advantages Over Ball Activation for Downhole Tools

Technology Update One of the most innovative recent advances in downhole drilling tool activation has been the introduction of mechanical extrusion technology, incorporating the use of rigid metal darts to improve the cycling and control of a variety of processes and devices. Increasingly, operators are recognizing mechanical extrusion by means of dart activation as a time-, cost-, and labor-saving alternative to traditional ball activation methods. For example, conventional cycling of drilling bypass valves has used a polymer extrusion process that relies on balls as the activation device. However, Churchill Drilling Tools has developed an effective and accurate mechanical extrusion method that uses a dart-based valve. The system can perform activations up to five times faster than polymer methods. The company’s MX (mechanical extrusion) system allows the use of rigid Smart Darts for multicycle control and exploits their robustness and resilience at high pressures and temperatures (up to 660°F) to deliver greater operating speed, reliability, and performance. The system’s unique feature is its two configurable shearing modes, which solves reliability and power delivery problems. It requires a radius as small as 0.0075 in. for power transmission, thereby making implementation extremely compact. With the ability to control and power three or more tools independently, users eliminate the conventional inner diameter (ID) and obstruction conflicts between different tools in a string. This has implications for mono-cycling ball and shear systems, which commonly obstruct the bore after use. These can be turned into multicycling, nonobstructive, and multi-tool systems. The system can also enhance multicycling ball-activated tools that are based on polymer extrusion by improving performance and delivering greater multitool compatibility and interoperability. The system allows the mechanical extrusion to be delivered in a range of settings to suit the specific cycle application. With a variety of latching, sealing, and flow path geometries, as well as the adjustable shear mode ratings, this element of the system provides a tangible change in string design and program implementation. For example, in bypass valve implementation, users can cover multiple flow path contingencies with a single valve in hole and choose from the range of darts to establish the optimal setting for the situation encountered. The system advances the capability of simple hydromechanical control and its power and reliability benefits into areas that previously needed more complex electronic systems. Being mechanical, it is not subject to the same high pressure and high temperature limits that affect electronics and electrical components. Smart Darts enable a multicycle circulating sub (circ sub) tool to deliver a reliable and versatile bypass on demand. Whatever the drilling application, whether planned or a contingency, the system enables a rapid and reliable switching to the optimal flow path configuration.

Technology Focus: Drilling Technology (February 2012)

Technology Focus Since the first downhole electric measurement was made in 1927 by the Schlumberger brothers (first electrical-resistivity well log), the oil/gas industry has been striving to develop and improve new tools and sensors for downhole measurements. Indeed, these sensors aim at measuring many parameters, such as physical properties of rocks and fluids (formation evaluation), wellbore position (inclination and azimuth), or downhole drilling-mechanics conditions. Over the last 12 months, I have been impressed by the number of papers and news articles dealing with drilling mechanics and with vibration-data measurement, transmission, processing, and interpretation. Dynamics and vibration events still are responsible for high nonproductive time (NPT) (e.g., tool failures in many cases) and suboptimal drilling performances. With advances in electronics components, tool reliability, battery technology, and sensors, many companies have begun to develop their own memory-based drilling-measurement tools and to offer the associated service (data processing and interpretation) to operators to maximize drilling efficiency and, thus, reduce NPT. These downhole drilling-mechanics-measurement tools, rated up to 150°C, generally integrate the following sensors: bending moment, vibration (three-axis accelerometers), weight on bit, torque on bit, annular pressure, temperature, and magnetometers (downhole rotational speed). Data are stored in a memory-based subassembly powered by a lithium-based battery (capacity up to 200 hours), or are transmitted to the surface (by use of mud-pulse, electromagnetic, or wired-pipe telemetry). The latest developments include ingenious sensors placed in the pin of the drill bit (avoiding an extra subassembly in the bottomhole assembly). Though measurements originally were captured close to the bit in the bottom portion of the drillstring, the industry has identified the need to have multiple sensors deployed all along the string (from the bit to the topdrive) to monitor continuously and anticipate any drilling event. This outbreak of downhole-sensor technology is good news for the industry because it will probably accelerate the understanding of what is happening downhole even more, thus improving the overall drilling efficiency. Downhole drilling measurements should not be limited to only high-cost environments, but should be used in the early stage of the field development to accelerate the learning curve and, thus, optimize the drilling process for the next wells. Even though some downhole drilling and dynamics tools were developed in the 1980s, the industry now has more-accurate sensors, better physical models, and more computational power to process and analyze this huge amount of drilling data. Recommended additional reading at OnePetro: www.onepetro.org. SPE 146561 Mitigation of Torsional Stick/Slip Vibrations in Oilwell Drilling Through PDC-Bit Design: Putting Theories to the Test by Jayesh R. Jain, SPE, Baker Hughes, et al. (See JPT, December 2011, page 79.) SPE 140347 Testing the Combination of High-Frequency Surface and Downhole Drilling-Mechanics and -Dynamics Data Under a Variety of Drilling Conditions by Bill Lesso, SPE, Schlumberger, et al. OTC 21506 Buildup Construction in Salt Formations by Renato Amaro, Petrobras, et al. SPE 140317 Extension of Gauge Length To Reduce Vibrations and Improve Drilling Performance by Gregory F. Smyth, SPE, Hibernia Management and Development, et al.

Evaluation on Chloride Cracking of S135 High-Strength Drill Pipe

During the process of deep drilling with high temperature and high pressure, downhole drilling tools might be exposed to various corrosive mediums, such as water/oil-based drilling fluid systems, dissolved oxygen, H2S/CO2, halogen elements (Cl- and Br-), etc. Halogen elements existing in the drilling fluid are ions promoting corrosion of metals. This effect is mainly manifested in the forms of uniform corrosion, pitting corrosion, stress corrosion cracking, etc. of carbon steel. Quality of the drill pipe is determined by the DP body, joint and welding area of the drill pipe. Reasonable friction welding process and proper post weld heat treatment can make the mechanical property of weld joint satisfy related standards. If process of friction welding or post weld heat treatment is improper, the weld joint will be easily damaged and accidents of pricking, breaking, etc will be likely aroused. This paper carries out an evaluation experiment of chloride cracking on the DP body, joints and weld joints of the high-strength drill pipe (S135) and discusses corrosion of the high-strength drill pipe caused by chloride ions.

Polycrystalline diamond thrust bearings for down-hole oil and gas drilling tools

Down-hole tools used for drilling oil and gas wells are subjected to harsh environments where abrasive fluids, high loads and speeds, and high temperatures can cause tool components, including thrust bearings, to quickly fail. This paper discusses the advantages that polycrystalline diamond can provide when used as a bearing material in down-hole tools. Laboratory test results are presented that can be used to help predict the performance of polycrystalline diamond bearings in these down-hole applications. Results from two types of tests are presented including tests that measure bearing capacity and those that evaluate diamond bearing wear rates. Bearing failures, generated during laboratory testing, are discussed. These failures are very similar to those observed in down-hole drilling tools and indicate that thermal damage to the polycrystalline diamond structure is the main cause of bearing failure. Bearing wear rates measured during laboratory testing show that polycrystalline diamond thrust bearings can provide a long-lasting bearing solution for down-hole drilling tools.

Load-Responsive Hydrodynamic Bearing for Downhole Drilling Tools

A load-responsive hydrodynamic thrust bearing has been developed that has capabilities to operate under higher load and speed combinations than the current bearing designs used in roller cone drill bits, downhole drilling motors, and other downhole drilling tools. The bearing dynamic surface, which is initially flat, deflects elastically under load to provide an efficient hydrodynamic geometry that generates a lubricant film, with a minimum film thickness that varies from 0.25 to 2.0μm. The bearing operates with friction coefficients typically in the range of 0.003 to 0.005, which are significantly lower than the conventional roller cone bit thrust bearing designs that operate in a boundary/mixed lubrication regime. Lower friction will allow bit seals to run cooler, and higher load/speed capabilities will increase drilling efficiency and extend component life in hard rock formations. Additionally, the new bearing is suitable for applications where tilting pad thrust bearings are used, offering the advantage of being simple, compact, and more economical.