A joint research effort between Bentec and its sister company KCA Deutag recently observed causes and conditions surrounding NPT in land drilling operations. Looking at approximately 100 rigs, Bentec estimated NPT accounts for less than 3% of overall drilling time. Of this number, more than 40% of rig downtimes was attributed to top drive failures.

Downtime related to top drive failures was split 50/50 between electrical problems (motors, sensors, and electrical connections) and mechanical problems (gear box, moving parts, and structural parts). On the basis of hours, motor and gear box failures accounted for 1,400 of the overall 3,400 hours – nearly 35% of all top drive-related downtime.

“Increasing reliability was the number one driver” in designing the top drive, said Andreas Rentzsch, area sales manager, Europe, at Bentec.

After 18 months in development, the company first commercialized its TD-500-HT top drive in mid-2010. With more than 10 top drives now being finalized for delivery in Europe and Russia, including two in Russia’s Sakahlin field where multiple extended reach records have been set in recent years, the company has seen a massive increase in manufacturing.

Same box, more capacity

One of the more interesting features of Bentec’s new top drive is its increased torque capacity. The Bentec TD 500 HT top drive is an AC-motor-powered top drive developed for use as a portable or permanently installed unit on either land and offshore applications. The compact size allows for many mast designs.

The system is driven by a variable frequency drive control system for a wide range of torque and speed performance. Main components include an integrated swivel, a special high-safety link tilt system, remote and manual IBOP valves, a backup clamp for making and breaking connections, a guide beam for drill torque reaction, and an electrical service loop. A compact integrated hydraulic power unit mounted on the top drive eliminates the need for hydraulic service loops.

In offshore applications, most facilities use 650- to 750-ton top drives. Onshore usually requires only a 500-ton lift capacity. However, for longer horizontal wells, achieving optimal drilling conditions often requires more torque capacity. As a result of this demand, Bentec redesigned the internal structure of the 500-HT top drive to accommodate higher torque capacity, like a 650-ton top drive.

“With the torque limit set 25% higher, drilling operations can be carried out smoothly with fewer opportunities for failures,” Rentzsch said. “Our main goal was to improve reliability and effectively reduce nonproductive time.”

The internal structure of the TD 500-HT is redesigned to accommodate higher torque capacity like a 650-ton top drive. (Photo courtesy of Bentec)

Currently, the TD 500-HT provides the highest torque capacity on the market. “All the power is in the same housing,” Rentzsch said. At 16 tons, the tool is a bit heavier than comparable top drives that range from 12 to 14 tons. Although the top drive remains interchangeable with other top drives, internally the TD 500-HT gear box is a more robust offering, extending torque capacity and power without compromising the size of the box.

On-demand features, easier maintenance

By incorporating “on-demand” features to many top drive functions, Bentec has increased reliability by providing the driller with the option to motor only when necessary. “If it’s not running, it can’t be broken,” Renztsch said.

With standard top drives, drilling 1,000 hours also means that pumps have been running 1,000 hours. By eliminating the continuous operation on pumps and motors, the TD 500-HT eliminates exposures to failures in specific areas of the drilling process. It also reduces service time and maintenance.

The top drive’s encoder is enhanced as well. “We designed this top drive with a demand for increasing reliability of sensors,” Rentzsch said. In comparable models, an encoder failure can take up to three hours to repair due to the internal placement of sensors. The Bentec encoder is designed on top of the motor for easy replacement. “Educated personnel can change out the encoder on TD 500-HT in around 20 minutes,” Rentzsch said.

“It’s not that we are cleverer than our competitors, but we know the weaknesses of other top drives,” Rentzsch said.

Bentec applied its 15 years of service experience to develop a robust, service-friendly top drive capable of delivering continuous reliability. “This alone can reduce nonproductive time by one-third,” Rentzsch said. To date, the TD 500-HT has achieved a zero rating for downtime events.

Weathering harsh environments

The top drive system is designed for rough conditions and complies with the strictest approvals for the drilling industry. Its design also conforms to the most recent European CE design standards and international API standards.

Comparable top drives range in working conditions from -20°C (-4F) to 50°C (122°F). The TD 500-HT is designed to work in both arctic and desert conditions in a range of -40°C (-40°F) to 55°C (131°F). Logistically, no rig would be deployed such that it would contend with this entire range. However, for certain areas like Eastern Europe, arctic reliability can help overcome specific limitations.

For example, in Poland, winter temperatures can often reach -30°C (-22°F). Typical equipment is permitted to work in the region to the -20°C limit. Should the temperature drop below this mark, additional equipment would be required, or at a minimum the company would need to pay the cost of winterizing its current top drive. Operating outside the permitted range increases liability should a failure take place. With Bentec’s expanded operating ranges, the equipment is well suited for year-round development.

Looking ahead

Bentec has 15 top drives under construction with approximately 25 more on order. It is actively pursuing markets in North and South America and in the Middle East. “Our primary goal is to reduce NPT through a reliable system that requires very little maintenance,” Rentzsche said.