Dopeless Pipe Connections Yield Benefits
The ability to connect premium pipe threads without applying doping compound has brought significant improvements in running casing and tubing into production wellbores, with further benefits in postcompletion operations.
Liquid-based lubricants known as pipe dopes have traditionally been applied manually to thread surfaces in the mill for storage and again in the field before connections are made. These thread compounds help to fight corrosion and prevent galling—the tendency of thread surfaces to stick to each other during makeup, while under contact pressure, and in motion.
In Dopeless connection technology developed by Tenaris, a dry coating is applied to thread surfaces in the pipe mill as part of manufacturing, preventing corrosion and providing proper lubrication for connection makeup. The process is integrated into production line operations under tight quality control to ensure that the exact amounts of coating treatments are applied and distributed evenly throughout the thread surface. Figs. 1a and 1b show doped and dope-free thread surfaces.
The technology was first used for connections run on a major platform offshore Norway about 10 years ago. Since then, considerable data collected from many producing fields have shown several advantages to its use. The principal areas of benefit have been in rig time efficiency; string installation reliability; well productivity; and health, safety, and environmental protection. Following are four case studies that quantify benefits gained in these areas.
Rig Efficiency in the Arctic
For many operators, the biggest benefit of using the technology is a quicker casing and tubing running process, which results in faster tubular installations and reduced rig time. There are two reasons for this: the elimination of a number of rig-side steps formerly needed to prepare, clean, and dope conventional connections immediately before makeup; and a safer, more stable makeup process. The increased stability shows the improved quality and the uniformity of the multipurpose coating over conventional lubricants. This leads to significantly reduced downtime related to inconsistencies in makeup.
At a major oil and gas field in eastern Siberia, extreme Arctic weather conditions were forcing the operator to invest considerable time and personnel to deal with frozen thread compounds while preparing casing connections on the rig floor. The problem was exacerbated by the large number of wells involved.
Following the introduction of Dopeless connection technology, the average running speeds of the doped connections were compared with those performed dope-free on the 7-in. production casing strings for 73 wells. The doped connections were made at an average running speed of 11 joints per hour vs. a speed of 14 joints per hour for the dope-free connections (Fig. 2).
The results were in line with historically observed rig time efficiency data for Dopeless technology, which shows an average 25% improvement in running speed. There were zero rejects over the 73 wells. Doped connections register an average reject rate of 1.5% to 3%.
String Reliability in the North Sea
Another benefit is the elimination of overdoping and underdoping problems that hinder connection performance. As a result, connections perform more reliably.
With dope-free coating applied in an industrially controlled environment at the mill, connections show greater consistency even when several make-and-breaks occur.
An operator working on the first well of a new oil field in the North Sea needed to rerun a large portion of the upper completion. The 5½-in. tubing was expected to be assembled with 284 joints made of 13% chromium grade steel and incorporating Dopeless connections. However, after running about 250 joints, the operator experienced downhole problems and had to pull the entire string out of the hole before rerunning the tubing.
An inspection of the pipes retrieved from the first run showed that the coating had protected every connection from damage by galling, resulting in zero rejects attributed to galling after two makeups and one breakout. Had field repairs been necessary, it would have cost approximately USD 2,000 for each pipe repaired. The total repair cost was estimated at USD 50,000, assuming a conservative 10% rejection rate for the connections.
Well Productivity in the Middle East
Overdoping during tubing string assembly can critically impair well productivity. When excess chemical in the wellbore invades and plugs a porous formation, it can block flow paths and reduce permeability.
A major operator in the Middle East encountered formation damage caused by dope contamination in an onshore gas carbonate reservoir. The problem affected every well in the field, and remedial measures were taken that included acid baths to remove contaminants from the formation.
The operator installed pipes assembled with Dopeless connections to replace the original work strings. This step prevented further dope-induced damage to the formation and saved an estimated USD 100,000 per well in additional remedial costs.
The application of excess thread compound can also cause other types of problems. It can clog sand screens. It can affect the interior walls of tubing and liners, resulting in lost wheel traction for tractor tools and other downhole operating complications. Furthermore, thread compound can contaminate drilling fluids. Thus, dope-free connections can help ensure smoother downhole operations.
Environmental Protection in the Amazon
One of the motivations in developing the technology was to meet the need of a Barents Sea operator to comply with the zero discharge regulations for an environmentally sensitive offshore project. Since then, environmental considerations have had a significant influence in expanding the use of dope-free connections. Research by Det Norske Veritas has confirmed that Dopeless connections are a zero discharge technology.
In the Amazon jungle of Peru, an operator used Dopeless technology on a well in the Ucayali-Madre de Dios Basin. The gas field under development was located near numerous indigenous communities in an area with a rich biodiversity of plants and animals. It was the first well in a jungle environment in the Americas to have all casing, liner, and tubing strings made with dope-free connections. Because of the operator’s decision, no pipe storage or running compounds were needed, no fresh water or solvents for cleaning the connections were required, and no chemical discharge related to the connections occurred.
The absence of storage and running compounds also eliminates the hazard of potential slippery work surfaces caused by spillage of thread compounds. Whenever a pipe is lifted, lowered, or moved sideways, it increases the risk of injury to workers in the vicinity. Because Dopeless technology is applied in the mill, it reduces rig-side steps in the field and lowers accident risk.
Long-term experience from the use of Dopeless connections has shown them to reduce running times by up to 25% and to yield a typical pipe-related cost savings of 10% in offshore operations, when applied in all casing and tubing connections.
The technology eliminates the use of thread compounds during the makeup process, thus reducing the potential for formation damage, sand screen clogging, and impediment to the use of tools such as downhole tractors. In addition, it is a zero discharge technology that reduces handling from the wellsite. Taken together, these benefits can improve well productivity and the health, safety, and environmental profile of well operations.