Recent field data have shown significant economic benefits are achievable when utilizing electronic autodrilling technology in conjunction with surface sensors, wellsite computers and data acquisition systems. An electronic autodrilling system was developed to provide steady-state weight at the drill bit and/or differential pressure across the motors to produce a higher quality wellbore and faster rate of penetration (ROP). Recent field applications demonstrated conclusively that the electronic autodriller not only improved control of drilling parameters such as weight on bit (WOB) and ROP, but also provided other favorable drilling attributes like controlled reaming. Longer bit runs and shorter rotating times were also observed. This study outlines the results of an advanced electronic autodriller's field application, reviews the history of various autodrilling systems, and compares and contrasts each design with respect to practical application and economic benefit. While brake technology improvements historically have led advances in autodrilling development, recent progress in computers and programmable logic controllers (PLCs) have significantly increased the capability of automated drilling machines, culminating in multiparameter control algorithms that maximize drilling efficiency. More recently, signal processing capabilities and variable frequency drive (VFD) electronic control have been extended to allow modern digital control technologies to be combined with older band-brake type braking systems, enabling conventional drilling rigs to be equipped with a sophisticated level of control without brake replacement and the associated capital investment. The new electronic automatic drilling system, when combined with computing and data acquisition technology, optimized drilling by controlling the existing non-linear rig braking system while simultaneously examining multiple drilling parameters: WOB, ROP, differential pressure (also called delta P) and torque. Multiparameter control was proven demonstrably better than single parameter or manual control. Introduction Automatic drillers, or autodrillers, have been used since the early 1970s, although it was not until relatively recently that they could out perform an experienced driller on conventional rigs. The development of the modern autodriller has been supported with the rise of more sophisticated mechanical braking and electronic control systems, which has resulted in systems with substantial capability. However, a considerable capital investment was required to incorporate both components. Recently though, improvements in signal processing and electronic control have allowed the modern digital control to be implemented with early generation braking systems, making a sophisticated level of control available for conventional drilling rigs. Computerized autodrillers can monitor up to four drilling parameters simultaneously and continuously, adjusting line payout to optimize overall drilling performance. However, it is important to choose hardware and software that are both appropriate and compatible to provide smooth and accurate brake control. Such a system has been developed and deployed with considerable success on land rigs drilling throughout the USA. This paper outlines the history of automated drilling technology development, its operational capabilities and its economic benefits demonstrated in the field.
Automatic Drillers have been used for decades. Most of these systems did a poor job of controlling weight on bit, which resulted in equally poor performance. Thus prompting two questions: "What is required to achieve a much better level of control of drilling parameters like weight on bit?" and "What field performance results do we see from improved control?" This paper will address these questions by examining the development and field performance of an advanced automatic drilling system. It will show how the entire system, not just the mechanics or the software, needs to be designed from a control system point of view. It will present the results of field usage of the system, and demonstrating the performance benefits resulting from improved control. Finally, it will suggest future developments for this type of advanced product. Introduction Attempts to develop Automatic Drilling controls for earth boring rigs started before the turn of the century. They were generally described as Drilling Feed Controls. Over the years many different designs were tried with limited success and the driller-operated "brake handle" feed system continued to be the preferred method. The efficiency of an automatic feed control was never denied. However, implementation proved to be illusive. With the recent advent of microprocessors and the development of proportional brake controls, the limitations experienced in the past no longer seemed insurmountable. In 1997 Helmerich and Payne approached Varco International with the challenge of developing an "electronic" feed control system. The first effort, installed on six H&P land rigs, referred to as the "six pac rigs" proved very successful. Significant improvements in drilling efficiency were recorded. Although the initial results exceeded expectations, further development of the control algorithms have greatly reduced the original design's dependency on operator's expertise. At the same time, development of improved control components resulted in another step improvement to drilling efficiency. Today's systems are highly automatic, adapting themselves to different methods of control including weight on bit (WOB), fixed rates of penetration (ROP), constant pressure (?P), and constant torque. This paper describes the evolution of this modern day design, referred to as an "Electronic Driller" and the field performance of various design irritations. History Of Feed Control Brantly in his book on History of Oil Well Drilling1, devoted a whole chapter to Drilling Feed Controls. A French mining engineer, Rololphe Leschot, developed the first "automatic" means employed for controlling bit feed-off into the formation in the early 1860's. The application was a diamond core drill used to drill blast holes for a tunneling project. Leschot used a simple hydraulic cylinder feed with a constant pressure to produce constant force on the bit. Over the subsequent years, numerous methods were tried, many of them quite novel in approach. Examples include so-called torque-based machines built by National Supply Company and Oil Well Supply Company. In the 1930's hydraulic feed rotary tables of various designs were applied. These hydraulic feed machines used cylinders that operated similar to Leschot's original design. By the 1940's most feed control machines became band brake control machines as brake performance improved. Most of these devices were pneumatically actuated and used inputs from the rig's standard weight indicating instruments. They were connected to the manual brake handle and controlled the feed by keeping the string weight constant.
It is well accepted that torque and drag calculations are essential for well construction applications. To the authors' knowledge, the calculations are performed based on the concepts of the soft string model. This approach enables the wellbore designer to determine torque and other forces in the drillstring. While several modifications of the soft string model have been proposed and implemented in commercial software, the model mainly used in the oil and gas drilling industry is the static soft string model. As such, not only the string bending stiffness is neglected, but also it is assumed that the string is motionless and the direction of motion changes by merely changing the sign of friction coefficient. Clearly, there is a strong need for including acceleration effects in the soft string model to permit analysis of tripping operations and more accurate evaluation of the drillstring loading and consequently, the rig equipment (hoisting system, etc.).In this paper, an improved dynamic soft string model is proposed that accounts for drillstring motion in 2D and 3D wellbores. This mathematical model explains how to compute forces along a moving drillstring or casing. The aims of this model are: 1) to analyze dynamic drillstring behavior, 2) to estimate local contact forces, and 3) to predict the effect of different tripping velocity profiles on axial and lateral contact forces. A system of equations for drillstring translational motion is solved using numerical methods. A computer code has been developed for practical design calculations.The improved dynamic soft string model can be used to determine surface load and contact force as functions of time and measured depth. This model is also applied to predict surface load and contact forces in tripping operations. In particular, the model is implemented for drillpipe in two different 2D wellbores: horizontal and S-shaped, and a 3D wellbore while tripping in and out of the hole. As expected, the surface load vs. time plot shows a similar trend of tripping accelerations. Depending on the well path shape, drillstring properties, tripping acceleration, and velocity profile, the maximum dynamic loads can be in the range of 4-40% higher compared to the conventional soft string model. In addition, results for two different tripping velocity profiles (trapezoidal and parabolic) are compared. The maximum surface load is up to 4% higher with trapezoidal velocity profile which is not significant, because both velocity profiles provide 90 ft displacement. It is noted that the governing parameter for the maximum load needed is the maximum tripping acceleration, not the maximum velocity.Improved dynamic soft string model will have significant impact on well path shape, drillstring design, drillpipe failure analysis, tripping operations optimization, and automatic control of the drawworks.
Automation of drilling rig functions can improve efficiency by reducing personnel and operating costs while providing an additional benefit of increased safety. Methods which use existing drilling equipment provide the most economic means to implement this automation. One function which can be implemented in this way is automatic positioning of the traveling block. This paper examines general design requirements for achieving automatic positioning of the traveling block. It also presents details of a control system developed to provide controlled braking of the traveling block using previously installed eddy current brake systems. The system provides closed-loop braking control while monitoring the traveling block position, velocity and acceleration through its entire range of travel. Various parameters are constantly monitored to assure that the eddy current brake capacity limits are not exceeded at any time. The system smoothly stops the traveling block at positions selected by the operator, even with wide variations in load. Sensors may be added to prevent moving the traveling block to collide with pipe handling equipment. The advantages of closed-loop control utilizing eddy current brakes over kinetic energy monitoring and friction brake application will be detailed. The technical requirements for future extension of this system into a full automatic positioning controller are discussed. Field performance data will be presented to illustrate the benefits obtained from closed-loop control of the eddy current brake to position the traveling block.
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