Top-Drive Casing-Running Tool Solves Tough ERD Problems

Over the past 15 to 20 years, top-drive technology has brought substantial improvements in efficiency and safety to drilling operations. However, casing-running methods have evolved more slowly and have not taken advantage of all the potential offered by top-drive drilling. Weatherford International has designed its new Overdrive system for running casing and drilling with casing to make full use of the weight and power of top drives (Fig. 1). The system won a Spotlight on New Technology Award at the 2007 Offshore Technology Conference.

Fig. 1—The Weatherford Overdrive system, which performs top-drive casing running and casing drilling.

This top-drive casing-running system was used recently by Shell to land casing on bottom at more than 18,200 ft depth on a troublesome North Sea extended-reach-drilling (ERD) well with hole restrictions caused by inability to clean the hole completely.

Torque-Drive Tool

The centerpiece of the technology is the torque-drive tool that combines several conventional casing-running tools into one—power tongs, main hoisting elevators, bails and single-joint elevators, a fill-up/circulation tool, and a weight compensator. All system operations are remote so that no personnel are required in the derrick or on the rig floor, resulting in a significantly lower safety risk (Fig. 2). The removal of equipment and scaffolding from the rig floor also creates a safer work environment.

Fig. 2—The system can be run remotely with the operator a safe distance from the rotary table and out of the way of moving equipment.

The torque-drive tool is connected below the rig’s top drive and can be run with any topdrive system. To run casing, the tool’s integral bails and single-joint elevators are used to retrieve each joint or stand of casing, lift it into the derrick, and lower it into position for makeup. The torque-drive tool is then hydraulically clamped onto the casing, and the connection is made up using the rotational power of the top drive to transfer the torque through the torque-drive tool and casing connections.

A key component used in conjunction with the torque-drive tool is an integral electronic-load cell called the torque sub, mounted at the top of the torque-drive tool and used to measure the makeup torque of the casing connections. The sub is independent of the top drive and measures true torque, as opposed to conventional techniques that calibrate torque from the voltage that supplies rotational power to the top drive. This new level of accuracy is especially important when making up premium connections, which require torque-turn monitoring and a very low margin of torque-measurement error.

Once the connection is made up, the driller can instantly perform a number of operations as needed, including fill-up of the casing string while lowering, and simultaneous circulation, rotation, and reciprocation of the entire casing string. This combination enables the driller to overcome virtually any unexpected hole problems, such as ledges, lost-circulation zones, shallow-water flows, and swelling formations. This greatly enhances the ability to run the casing string to bottom in a predrilled well.

A further dimension of the new top-drive casing-running system is the ability to push down the casing string safely and efficiently while circulating and rotating. This ability is especially applicable for highly deviated and ERD wells where “negative” casing-string weights can be encountered. The external “grapple” hydraulic gripping system on the torque-drive tool creates up to 60 tonnes of constant gripping force. This allows the weight of the top drive and the torque-drive tool to be applied to the casing string to push down at any time if necessary, increasing ERD well capabilities. The gripping forces in the torque-drive tool are evenly distributed throughout the tool through eight grapple assemblies with a total of 80 grapple plates each individually supported by its own “load shoulder,” preventing pipe crushing or scarring.

By comparison, the gripping force of conventional casing-running elevators is created by the casing string itself, as the weight of the string pulls the elevator slips down into gripping position. Pushing down on the casing is not possible, as the casing string will move upward back through the elevator, and the elevator will lose its grip on the pipe, creating an unsafe environment.

In addition to the torque-drive tool’s ability to push down the casing string, rotation speeds of up to 100 rev/min are possible. Special reamer or drill shoes with built-in cutting structures can be added to the bottom of the casing string, enabling operators to ream through trouble zones, perform hole cleaning, or drill the entire hole section with the casing string.

The combination of reduced wellbore exposure, less flat time, the ability to move casing across trouble zones, and enhanced safety through remote equipment operation can reduce well-construction costs and maintain wellbore integrity.

Case Study: Shell ERD Well in UK North Sea

On an ERD well in the North Sea, Shell had drilled an extended horizontal section to 18,420 ft in a 12 1/4-in. hole with 81° tangent inclination. Despite numerous circulations, the hole still showed signs of cuttings and some cave-ins. The rig struggled for 3 weeks to get the drillstring out of the hole because of multiple packoffs and hampered circulations. Thus, the chances of improving the wellbore condition with a wiper trip were rated as low.

It was decided to equip the 9 5/8-in. casing string with a reamer shoe and run casing with the top-drive-mounted casing-running and -drilling system described above, enabling string rotation, pushdown, and circulation that can help work the casing string through problems.

The top-drive casing-running system was also viewed as a step change in safety for casing operations because it eliminated the need for a casing tong, a stabber, a fill-up line, and numerous rig-floor hoses, and it reduced manual handling by as much as 80%. Prior to going through the shoe, a decision was made to circulate 100 bbl of oil-based mud. Casing running proceeded. At 11,494 ft, the casing hung up. After unsuccessful attempts to wash and work down, three joints were pulled and rerun, working past the restriction.

Casing running continued, with the casing worked up and down when drag was encountered at 13,094 ft. Two joints were retrieved and then rerun, again holding up at 13,074 ft (20 ft higher than the original restricted depth). The string was worked and circulated in an attempt to clear the obstruction. Eventually, +/-90 ft of movement was achieved after setting weight down on the string, and the obstruction was passed. The casing was run to near total depth with only a few more tight spots experienced, each of them worked past quickly by setting weight down. At 18,053 ft, another restriction was encountered, and the string then was worked a further two joints down. Due to conditions worsening, the hanger was picked up, the casing string was worked and washed down, and the string was finally landed at 18,209 ft, leaving a 211-ft rathole.

The use of the top-drive casing-running system was viewed by the operator as having contributed greatly to the achievement of safely running casing to 18,209 ft in these difficult hole conditions in a long tangent section of a formation that had been open for about 5 weeks. The string was worked to bottom over an extended period through several ledges and restrictions, with the top-drive-mounted casing-running system considered the key to landing the hanger successfully.

Information provided by Tracy Cummins, Global Product Champion—Overdrive Systems,Weatherford International.