An Overview of Top-Drive Drilling System Applications and Experiences

Abstract

Summary Top-drive drilling has become one of the new technologies of the 1980's. Application of this seemingly old concept is now widespread in most offshore areas of the world. Top-drive drilling may be one of the biggest changes made to the rotary-drilling method since the development of the rotary table. This paper analyzes why the concept of drilling with top drive, similar to the very old concept of a power swivel, has suddenly become so successful. Applications and locations are presented to show the system's worldwide use. Results of more than 50 systems currently in operation are analyzed to present benefits and trends. The results show surprising benefits for almost any type of well, and overall time savings generally exceed 20%. Benefits from the extended-reach potential associated with top drives are enormous. These results explain the primary motivation for most applications of the system. Introduction A top-drive drilling system is most often regarded as nothing more than a power swivel that works. Most drilling experts rightly point out that power swivels have always been around and are not examples of new technology. What then explains the sudden resurgence of a very old concept? Technically, the answer is not that "it works" or "it is reliable," although these two factors are necessary ingredients of any concept that is rapidly adopted. The technical explanation for the success of modern-day power swivels or top-drive drilling systems lies in new developments that relate to pipe-handling techniques associated with these systems, not in rotating the drillstem. Turning the pipe to the right with either a rotary table or a power swivel has never been a problem. provided that sufficient power could be applied. An unfortunate ' conception that developed with the first power swivels was that they had insufficient torque with which to drill. That problem could have been solved long ago had it been the only obstacle to overcome; in fact, hydraulic and electrical solutions were implemented in the early 1970's. The real obstacle to acceptance was efficient pipe handling with a power swivel. A more in-depth analysis of the pipe-handling methods associated with drilling is required to understand the significance of the recent break-through. Recent Top-Drive Developments Drilling with a rotary table requires a host of auxiliary equipment not normally identified with the drilling process, as well as those items obvious to the method. Those components normally associated with rotary-table drilling are the kelly, the kelly bushing, the swivel, and the rotary table. Components that are not frequently thought to be significant make the difference between operational efficiency and difficult, if not impossible, alternatives. These components are the mousehole, the rathole, and the hook. All the items associated with efficient drilling and tripping are diagrammed in Fig. A mousehole allows the driller and his crew to make a rapid connection, often accomplishing the task in less than 5 minutes. Without a mousehole and a long kelly that can be easily swung over to the mousehole, it would be hard to imagine making a connection in 5 minutes. The solution would have been an attempt to position the next joint between the kelly and the drillstring while the latter hangs 30 ft [9 m] above. Early attempts to introduce a 30,000-lbm [13 610-kg] power swivel into the derrick were faced with precisely this situation. Those who still tried to use the mousehole eliminated the advantage of the swivel's ability to drill with 90-ft [27-m] stands. Deepening the mousehole did not help, because one could not get the stand into the mousehole. Consequently, the solution was not easy. Next, consider the rathole. This seemingly innocent part of the drilling rig, together with the hook, permits another often-overlooked part of the process, the relatively rapid conversion from drilling to tripping. Tripping, a most efficient operation, is accomplished at the rate of roughly one stand every 1 to 2 minutes. It could not be done that rapidly if a very small but vital part of the hoisting system-the elevator-were not used. The elevator allows the derrickman and the floor hands to grip or release the end of the drillstring or the disconnected stands quickly. A large power swivel placed in the derrick is not easy to "rathole" rapidly so that the tripping process can be started. If the swivel could be ratholed, then how would it be used to accomplish its most attractive benefit-rotation during tripping? Finally, suppose that one could overcome all these obstacles-and it should now be evident that previous power swivels did not. One would be faced with an even more difficult challenge. SPEDE P. 435^