Rotary-shouldered drillstring connections save time, money

The first commercial deployment of a third-generation double-shouldered, double-start, rotary-connection run on theDiscoverer Deep Seas drillship in the Gulf of Mexico Walker Ridge block 678 in 7,016 ft (2,139 m) of water provided valuable lessons about use of the hardware in deepwater operations. The 5 7/8-in. OD, 26.30 ppf, S-135, Range-2 drillstring drilled the 28,000-ft (8,534-m) vertical well.

The thread form is a double-start design that reduces the number of revolutions required to assemble the connection by 50%. It also provides a dual-radius thread root that improves fatigue resistance. The new connection increases mechanical and hydraulic performance compared with earlier high-performance connections while providing fatigue performance greater than standard API connections. Conservative estimates suggest that the new connections can save approximately 7 1/2 hours in cumulative trip time for a 20,000-ft (6,096-m) well.

Since first deployed, the third generation has been proven in the Gulf of Mexico, North Sea, off West Africa, and in Southeast Asia. One operator has documented approximately $287,000 in savings on four high-cost deepwater GoM wells. Following rig crew education and iron roughneck maintenance, an average of 7.3 seconds per connection makeup time savings was achieved and compared to similar wells using second-generation DSC. Repair rates and cost were reduced over 80%.

Running procedures

Proper running and handling procedures for third-generation DSC can be remembered by recalling the four “Cs”:

• Calibration – Properly adjust and calibrate torque and handling equipment
• Clean – All connections (drill pipe, subs, lift plugs, saver subs, etc.) and thread protectors should be clean, and the thread compound should be free of contamination
• Coverage – 100% of connection thread, seal, and shoulder surfaces should be covered uniformly with a light coat of thread compound
• Control – Drill pipe should be handled, stabbed, and made up under complete control.

Calibration

The correct make-up torque (MUT) of the connection should be obtained from the manufacturer. Three makeup torques are defined for the third-generation DSC for the specific tool joint box OD and pin ID:

• Minimum MUT – For the connection to function as designed, normally only considered when makeup equipment limitations prevent the recommended MUT from being reached
• Recommended MUT – For typical drilling applications
• Maximum MUT – For unusual or unexpected drilling conditions.

Applied operational or drilling torque should not exceed the connection MUT. Drilling torque that exceeds connection MUT may cause downhole makeup, connection damage, or connection failure.

Proper calibration of the top drive, iron roughneck, and/or other automated make-up equipment can be verified using rig backup tongs with a calibrated load cell in the snub line to measure the torque applied to the connection. Care should be taken to assure that the snub line is rigged at a 90º angle to the tong handle. If not, the proper correction factor should be applied.

If using a top drive, its bell stabbing guide bore should be adjusted to a maximum of ½ in. clearance with the box tool joint to assure the pin connection is guided into the center of the box without contacting its shoulder. The top drive counter balance system should be adjusted to minimize the weight applied to the connection during make-up.

The top drive manufacturer should be consulted for proper overall saver sub length requirements, which is subjected to the highest tensile and torsional loading of any connection in the drillstring and multiple connection make and breaks. Saver subs should not be manufactured from typical sub material (100-110 ksi) but should be manufactured from material with a minimum strength comparable to that of the drill string tool joints (130 ksi).

Top drive grippers or tong dies should be positioned at least 1 in. below the box’s primary shoulder when making up the third-generation DSC box to the saver sub pin connection. The driller should be able to see whether the external shoulder of the connection is between the pin and box tong dies to insure that the tongs are not simultaneously positioned on both the pin and box connection. Tong dies should be placed on the tool joint OD and not on the drill pipe tube body. For iron roughnecks and other automated make-up equipment, care should be given to avoid gripping tong dies over connection hardbanding. Tonging on the hardband may lead to premature cracking, flaking, or spalling of the hardband. Tong die pressure should be set to the minimum necessary to avoid die slippage when applying the proper MUT. Excessive pressure may damage tool joints or give a false MUT reading.

If using manual tongs, box tool joints should be set to a comfortable working height above the rig floor. Tongs should be set to minimize bending load on the pipe. Guidelines are provided by International Association of Drilling Contractors (IADC), American Petroleum Institute (API), and International Standards Organization (ISO).

Cleaning

Handling plugs and thread protectors should be cleaned and visually inspected prior to each use. When not in use or when being moved, handling plug connections should be protected by a light coat of thread or storage compound and a thread protector.

Pipe, tool joints, and connections should be cleaned and visually inspected for damage. Inspect the threads’ primary (external) shoulder and secondary (internal) shoulder of connections for damage or foreign material. Damaged threads or foreign material on the threads and shoulders can cause galling or prevent proper makeup, and should be repaired.

Third-generation DSC should be clean and dry before applying thread compound, which may not properly adhere to wet surfaces. Thread compound must be free of contaminants, including water.

Use of thread protectors is recommended when moving the drill pipe to reduce the risk of damage to the connection shoulder, bevel, and thread areas. For pipe racking systems that are configured expressly to eliminate contact damage to the connections, thread protectors may be removed after moving the pipe into the racking system.

Thread protectors always should be installed when moving pipe through the V-door, and pin thread protectors should be installed on pipe that is placed in the mouse hole. Normally it is not necessary to install thread protectors on drill pipe racked in the derrick, provided the rack back area is kept clean of debris (gravel, cuttings, etc.). Excessive debris may damage the pin internal shoulder and inhibit proper make-up.

Coverage

Prior to make-up, third-generation pin and box connections both should have thread compound applied to the primary (external) and secondary (internal) torque shoulders and all of the threads. Surfaces should be completely covered and thread compound should be spread for uniform application. The proper amount of thread compound allows the thread profile to remain visible. Thread compound should partially fill the thread roots to approximately one-third to one-half of the thread height.

Any good quality thread compound such as zinc-based, copper-based, Teflon-based, and other metal and metal-free, or environmental thread compounds designed for use with rotary-shouldered connections is acceptable with the third-generation DSC. Based on in-house testing and field experience, copper-based thread compounds provide excellent anti-galling, a more consistent friction factor, and a higher coefficient of friction than most other products.

It is not recommended to change the MUT values for third-generation DSC on the basis of thread compound published friction factors.

Control

When making up or breaking out third-generation DSC, the drill pipe should be in complete control at all times.

When using manual tongs, a stabbing guide is recommended strongly for third-generation DSC. Use of a stabbing guide aids proper pin to box alignment, prevents stabbing damage to the box seal face, and reduces opportunities for finger pinch points to improve safety when handling the drill pipe. Overall, stabbing guides can reduce rig time by reducing connection damage, misalignment, and cross-threading. They should not be used when breaking out third-generation DSC. For automated systems that do not accommodate a stabbing guide, the top drive bell stabbing guide and guide arms should be adjusted prior to initial makeup to ensure proper pin to box alignment.

Proper alignment, controlled stabbing, and reduced initial speed during engagement and spin-up of the starting threads is critical for third-generation DSC. After stab, ensure the threads are engaged. If the connection will not spin-up freely, if the threads do not appear engaged, or if the connection appears cross-threaded, rotate the pin counterclockwise until it drops into the box. Then rotate ½ to 1 revolution clockwise at slow speed (up to approximately 25 RPM) until proper thread engagement is verified. Higher speed (up to approximately 100 RPM) then may be used to spin-up the connection to shoulder engagement. Slips should not be used as back-up tongs. Simultaneously making up multiple connections in a stand to final MUT using the top drive only is not recommended. Each connection should be made up to the proper MUT individually prior to going in the hole.

When tripping out of the hole, it is good practice to alternate the connection breaks, rinse the drill pipe OD with fresh water, and use drill pipe wipers. After breakout, when the pin connection has disengaged from the box, and prior to full separation of pin and box, continued spinning of the pin in the box may result in connection damage. Thread compound should be applied to box and pin connections prior to racking back in the derrick. Standing the pipe in the derrick will wipe thread compound off of the pin internal shoulder so it should be reapplied before the connection is made up again. Pin and box thread protectors should be installed if pipe is laid down.

Breaking in new connections

Special considerations should be taken when making up the third-generation DSC for the first time. Proper break-in of a new connection before it is run downhole is important to the connection’s life. During the first make-up, the connection’s contact surfaces undergo work hardening resulting in smoothing and hardening of the threads and shoulders contact areas. Each subsequent make-up to the same maximum recommended MUT will result in additional work hardening and in a slight increase in the connection’s degrees of rotation from shoulder to final makeup. Although diminishing with each cycle, this can continue untill the sixth break cycle.

Proper break-in of a new connection is one of the most important things that can be done to improve the longevity of the drillstring. To break in the third-generation DSC, three make-and-break cycles to the maximum recommended MUT are:

1. Determine the correct maximum make-up torque for the connection

2. Make up connections slowly, preferably using chain tongs

3. Tong them up to the predetermined torque using a properly working calibrated torque gauge to measure the required line-pull

4. Breakout, clean, visually inspect, redope, and repeat 1-3. Always use the backup tongs to make and break connections

5. Verify the break-out torque (BOT) value to ensure it is less than or equal to the MUT value.

The expected BOT of third-generation DSC is 65-70% of the MUT. If BOT exceeds MUT, ensure all procedures are being followed and verify all equipment is in calibration. High BOT typically indicates improper alignment during makeup/breakout, debris trapped between mated connections (such as from the setback area on pin nose), contaminated thread compound, a damaged connection, or downhole makeup. Refaced or recut connections should be broken-in like new connections.

Editor’s note: The preceding is based on concepts first presented in paper 115221 from IADC/SPE Asia Pacific Conference in 2008. Comments also were derived from paper 128316 presented at IADC/SPE Drilling Conference and Exhibition 2010. It has been updated with the latest information by the authors.