Top Drives

April 2, 2013
Lance Lee

Top Drives

The Top Drive Drilling System is recognized as one of the most significant advancements in drilling technology since the introduction of the rotary table. When comparing them to regular drilling rigs, Top Drive Systems consistently drill faster and safer, with less chance of drill pipes being stuck. Top Drives also allow operators to reach areas and types of formations that would not be accessible with conventional rotary drilling. Horizontal drilling and extended reach have brought about drastic increases in production rates, and these wells can only be drilled with Top Drives. Along with improved well control and better hole conditioning, these benefits contribute to the unquestionable financial justification for the Top Drive.
In 1981, Duke Zinkgraf of Sedco (now Transocean) sought out a way to drill from the top down from the drillstring and adding complete strand of pipe, which would end the need for the kelly drilling process. He searched for a company that was willing to embrace and develop his new concept. Duke found a partner with Varco (now National Oilwell Varco). George Boyadjieff, Varco?s president, assembled a team of engineers and dedicated it solely to this project. Their initial prototypes were first installed in the Middle East, they then made their way to the U.S. At first, the road to acceptance was bumpy. Many companies did not want the hassle of integrating the top drive drilling systems into the existing drilling processes. Once alterations were made to the top drives to make them easier to incorporate and more reliable, companies took notice. Once the industry began to realize the practical drilling capabilities of the top drive methods, new and radical well programs were being designed around them. More and more advances in top drive equipment and operation are rapidly changing the way drilling is done. More than 60 percent of all drilling rigs are now incorporating top drives. The main reasons are increased safety and efficiency.
A Top Drive is a motor that is suspended from the derrick, or mast, of the rig. This motor can be either electrical or hydraulic. These motors produce at least 1,000 horsepower. It is connected to a short section of pipe called the quill. From there, the quill is either screwed into a saver sub or the drillstring itself. Because the Top Drive is suspended, it is free to move up and down the derrick. Top Drives average around 15 feet in length and about 4 feet in width, which make it convenient to transfer due to its slender build. The average weight is somewhere around 10,000 lbs.
A Top Drive has many advantages. It is capable of drilling with three joints stands, instead of just one pipe at a time. Top Drives typically decrease the frequency of stuck pipe, which contributes to cost savings. They also allow for quicker pump engagement and disengagement or the rotary while removing or restringing the pipe. Top Drives are also preferable for challenging extended reach and directional wells. A major advantage is safety related. Top Drives reduce risks and increase safety during the drilling process because they remove much of the manual labor that was previously required to drill wells. They are often completely automated, offering rotational control and maximum torque, as well as control over the weight on the bit.
Top Drives have only a few disadvantages. The initial cost of installation and purchase are high. This initial cost would eventually be offset by increase production though. Also, the weight of the Top Drive is top heavy and the rig will have to be adjusted to counteract it. While initial costs and installation are high, the advantages greatly outweigh the disadvantages. To utilize Top Drives, the Top Drive must be appropriately sized to fit into the rigs which do this work. Their load rating and torque capacities must fit the characteristics of the wells to be drilled. Either the rig must have the additional power available for the Top Drive or a separate power unit must be supplied. Finally the contractual terms necessary to obtain the top drive must match the business needs of the end user
Top Drives can be used in all environments and on all types of rigs, from truck-mounted units to the largest offshore rig. Although top drives can be used on both offshore and onshore rigs, there are differences between the two. For example, an offshore rig top drive travels