New top drive casing running and drilling system removes personnel and equipment from the rig floor, gets through trouble zones and cuts time off casing jobs.

Conventional casing jobs run up against two time-consuming issues: First, the hole must be cleaned (reamed and wiped) in order to obtain a good cement job. This costs rig time and exposes the well bore to damage. Second, lost circulation may cause the casing to become differentially stuck. In a survey of incidents in the Gulf of Mexico, these two problems accounted for 24% of all days lost.

Weatherford's OverDrive top drive casing running and drilling system addresses both these problems by approaching casing running in a new way. Rather than simply lowering the casing into the hole, this top-drive system allows the casing to be circulated, rotated and even reciprocated during run-in. By putting a drill shoe on the casing, the operation can drill with casing or conventional methods and then clean the hole while running the casing. In essence, the junk can be removed from the hole while running in. This new technology replaces power tongs, elevator, fill-up and circulation tool and weight compensator, and it requires only a driller, a tool operator and one or two rig hands, all of which makes it a safer way to run casing.

Typical makeup cycle

The TorkDrive unit is lowered and the bales tilted out so that the single-lift elevator can be latched to the next joint of casing in the V-door. Once the joint has been latched in, the unit raises up until the joint is vertical, at which point the unit is lowered and stabbed into the joint.

When the joint is fully inserted, grapples within the gripping element grip the pipe. These grapples (Figure 3) differ from conventional slips in that each grapple has its own slot and load-bearing surface within the grapple holder. This distributes gripping force evenly over the surface and prevents crushing or scarring the casing. The grapples work on a "Chinese finger-lock" principle that grips more tightly as weight is applied. Most conventional slip systems result in concentrating the load at the bottom of a stack of slips, which can damage the pipe. It is vital to protect the pipe because the operation may require rotation up to 100 rpm.

After the gripping element has engaged, the built-in weight compensator automatically accommodates the additional weight of the joint, and the driller makes up the connection using the top drive instead of a power tong. During makeup, the compensator neutralizes about 90% of the joint's weight; during breakout, it exerts a slight upward pull. In both cases, the compensator helps prevent thread damage and speeds makeup or breakout (the compensator can switch from makeup to breakout by flipping a lever on the control unit).

Action of the compensator is visible to the driller during makeup; its cylinders stroke out of the actuator part of the unit as the threads engage. Once the joint has been made up and torqued, the driller raises the top drive to transfer the weight of the entire string to the top drive unit. The heavy-duty version of system can handle 7-in. to 14-in. diameter casing in strings weighing up to 750 tons, and with torques up to 80,000 ft-lbs. Other (modular) units will handle casing as small as 41¼2 in. and as large as 20 in.

Throughout the gripping and makeup process, the system monitors various factors to prevent the spider from being opened before the joint is fully made up: 1) the unit must be properly clamped on the casing joint with the required clamping pressure; 2) the weight compensator cylinders must be fully extended, indicating that the unit is taking the string's full weight; 3) the system operator must move the control lever to the "Spider Open" position; and 4) the driller must push the "Accept" button.

In conventional casing running, the crew fills each joint of casing with drilling fluid as it is being lowered into the spider. This tends to trap air inside the casing, and when the fill-up tool is removed from the casing, the pressurized air can spew fluid over the rig floor and create an environmental and safety risk. The system addresses the problem within the actuator module with a unique fill-up and circulating valve that vents air through a sliding sleeve mechanism while the casing is being filled. Once the joint is full, the system operator closes the back pump and switches to circulating mode. There is no tool to remove, and the driller can immediately start full-pressure circulation and fluid recovery.

When the casing has been lowered to the point where the single-joint elevator is within reach, the driller stops lowering and releases the elevator. The system operator extends the bales to move them out of the way and into position to retrieve the next joint, and the newly made-up joint is lowered into the spider. The operator then closes the spider. When the weight has been transferred to the spider from the TorkDrive, the operator receives an interlock signal that allows the unit to open, ready for the next joint of casing.

Built-in torque measurement

One of the most interesting features of the new system is a load cell built into the actuator module and designed to measure the exact torque as each joint of casing is made up. Power is transferred to this rotating sub from the stationary frame of the unit using transformer technology to bridge the gap between the rotating and stationary components. This electrical power is then used to monitor strain gages for torque and weight, and these measurements are transmitted back to the control system using radio waves.

The torque measuring system is wireless and there are no moving parts. The system operator can reliably monitor weight and torque for every joint of casing, critical when running casing with premium threads. The weight indicator reports when the unit is in control of the joint, which gives the system operator control over the casing both during makeup and in the hole.



Field application

The system is scheduled to complete its first run for a major operator near Corpus Christi, Texas, by early August, with the second field trial for a project in the Wytch Farm field coming up shortly thereafter.

Overall, the system offers the possibility of shortening the whole drilling program. With this system, operators can drill the last section - or even the entire well - with casing. This eliminates separate reaming and wiping operations. The risk of lost circulation and differential sticking is greatly reduced because of rotating the casing during run-in, which polishes the well bore and shores it up - this is the "smearing effect." This means operators need less mud to seal off a formation, and they get a better cement job and better logs. When total depth is reached, the well is ready to cement. The whole process can save days of rig time, and it is a lot safer because there is less equipment and fewer people on the rig floor.