Dry surface coatings for connections of OCTG have been developed that eliminate the need for thread compound.
There are many good reasons to reduce or eliminate the use of pipe dope. Environmental regulators seek to do so because it often contains heavy metals, which are discharged to the environment. Some of the compound is also squeezed into the wellbore during pipe make-up and contaminates or clogs the wellbore and can interfere with mechanical devices. Pipe dope creates a messy, slippery, and potentially hazardous work environment on the drill floor and requires extra handling operations and storage.
Thread compounds extend the pressure integrity of tubular connections, provide lubrication, assist sealing, and work within a standard torque range (i.e., American Petroleum Institute, API specifications). Compounds used with drill pipe also need to allow break out with predictable torque.
Thread galling is the most common failure, a microwelding (cold welding) of the metal surface due to friction. If pipe threads are damaged by improper makeup or galling, the connections may leak, causing corrosion of the metal, or lose mechanical integrity and fall, all of which are costly to operations.
Design criteria
The design of threaded connections involves many criteria. Tribology is a science that deals with design, friction, wear, and lubrication of interacting surfaces.
Premium connections rely on metal-to-metal seals for seal integrity. Thread compounds are used on these connections for lubrication and to prevent galling.
The sealability of metal-to-metal threaded connections depends on the contact pressure and length of the metal-to-metal seal, load history, and the use of sealing compounds. Based on experimental data and full-scale tests of tubular connections and finite-element analyses, Murtagian and colleagues proposed a sealability parameter and critical value for pipe connections.1
Commonly used in the US, integral or integral-upset connections feature tapered tubing threads that seal by forming a long, helical leak path when screwed together. As more torque is applied, the threads deform and the spiral leak path thins. Pipe dope designed for these threads must provide lubrication and antigalling protection and also seal the spiral leak path against liquids and gases.
Thread compounds often contain a high percentage of lead, zinc, particles of Teflon (polytetrafluoroethylene), or molybdenum and graphite. When Teflon is heated to high temperatures, it produces odorless, invisible, and toxic polytetraflouethylene (PTFE). Some types of pipe dope designed for use at lower temperatures and pressures may have no discernible particles (nongritty), but will seal because of the low viscosity.
The Texas Railroad Commission notes that the API specified that pipe dope may contain about 30 wt % lead; that lead-free, biodegradable pipe dopes are now available and, “if feasible, should be substituted for API specified pipe dope.”2
In addition to reduced environmental contamination, using dope-free connections eliminates or decreases the need to handle and store pipe dope. This promotes personnel safety because it reduces the frequency of handling operations.
Old solutions
Various products are available to prevent galling and offer corrosion resistance, such as phosphatized zinc or manganese, or thin copper coatings. Microthin copper coatings are bound to the steel surface with high-temperature resins then burnished into the steel surface during work hardening of the threaded connection. The introduction of a dissimilar metal prevents steel-to-steel contact that could cause galling damage.
Nontoxic pipe compounds for tubulars have been developed, including mixtures of petroleum sulfonate, paraffinic mineral oil and “antiwear extreme pressure additive” (Mercasol 633 SR), but many are not stable at high temperatures and pressures.
New solutions
Research and development of dope-free connections have been under way at several companies. Statoil ASA initially began research in-house and published some results in its company magazine in 2001. According to TenarisConnections Managing Director Jim Aivalis, Phillips Norge ASA approached Tenaris SA about supplying dope-free connections for Ekofisk, leading to a renewed R&D effort.
Tenaris looked into dry solid lubricants and carbon suspensions in water. TenarisConnections project leader Tomás H. Castiñeiras told OGJ that the company screened the more likely solutions using ring-on-disk testing and statistical and probability analyses at the Tenaris facility in Siderca, Argentina. The best-performing compounds were tested with variations in layering and coating techniques following standard guidelines for pipe dope: a minimum of three (and threshold of five) successful make and breaks for casing, said Castiñeiras.
In 1997, Tenaris had negotiated a 9-year agreement with ConocoPhillips to supply OCTG for the company’s operations worldwide. This led to the first installation of all dope-free connections in an offshore well for Phillips Norge ASA, according to TenarisNews, February 2005.
Tenaris SA ran the first dope-free dry connections offshore at the ConocoPhillips’ Ekofisk X50 well in the Norwegian North Sea in July 2003. The production liner was 5½-in., 32.6 lb/ft, Q125 psi. The well at Ekofisk was drilled horizontally and included torque up to 25,000 ft-lb as the pipe was used as a rotating liner. Engineers closely monitored the joint analyzed makeup chart while the liner was being run, said Castiñeiras.
The second Ekofisk well, X41, was completed with dope-free dry connections a few months later.
The Ekofisk field test was overseen by Øystein Ekeli, Ekofisk drilling director, who pronounced the joints as very strong and easy to stab. Using the dope-free pipe reduced time for rig preparation, said Ekeli, but more importantly, “it eliminated the risk of having personnel on the drill floor to apply dope, which resulted in a safer operation,” according to a Tenaris press release in October 2003. Ekeli noted “Conoco- Phillips has a strategic objective to improve drilling operations with new technology, while ensuring safety and reducing the environmental impact.”
TenarisBlue Dopeless connections feature a new thread design and the dry layered coating eliminates the need for chemical thread-sealing compounds during connection makeup. The connections have been tested at facilities in Argentina, Italy, and Japan and are available, says the company, for carbon steel and corrosion-resistant alloys (13% and 25% chrome) pipe in a range of sizes from 2 3/8-in. to 13 3/8-in. All connections in the premium TenarisBlue line can be provided with dope-free coatings.
More than 220,000-ft of dope-free carbon steel casing and tubing had been supplied worldwide through fourth-quarter 2004, according to a February 2005 press release. Tenaris dopeless connections were run in land wells by TechPetrol (wholly owned by the Techint Group) in Argentina using a small rig in early 2003, by Total SA at the Jusepin field in Venezuela at the end of 2003, and for Pan American Energy, a subsidiary of BP PLC and Bridas Corp., in first-quarter 2005, according to Aivalis.
Hunting
After 5 years of research and testing, Hunting Oilfield Services UK Ltd. and MP (Eastern) Ltd. developed a dope-free connection system involving a surface coating and a separate lubricant. The surface coating is applied to the box end of connections in place of copper plating or phosphating.
Hunting and MP tested six unlubricated alloy systems against the traditional copper-plated connection with pipe dope. Three performed well enough for further testing and the best performer was a white bronze alloy.3 The coating selected for commercialization, named Piotec, was advertised in September 2003. It has been successfully tested with KSBEAR, NSCC, and VAM premium connections.
Hunting worked with RS Clare & Co. Ltd. to develop a complementary lubricant (Piolube), designed to be applied as a thin film on Piotec-treated surfaces to reduce friction or as a coating during long-term storage. Although the Piotec-Piolube system eliminates the use of pipe dope, using an alternate lubricant means that the connections are not run “dry.”
In a March 2004 press release, Hunting announced that it had run the first dope-free connection system in the northern sector of the UK North Sea. The company ran more than 11,000 ft (264 joints) of 17 lb/ft 5½-in. API 13Cr L-80 tubulars in CNR International UK Ltd.’s Ninian South S73 well. The tubing string was threaded with KSBEAR premium connections from Japan’s Kawasaki Steel Corp. and delivered with Hunting’s Piotec dopeless-connection system. The joints had been stored outside for 15 months before use. There were no rejected make-ups and actual running time was 22 hr, compared with 24 hr predicted time. The time savings was attributed to reduced handling time on the drill floor.3
CNR International is a subsidiary of independent Canadian Natural Resources Ltd.
Hunter Engineering Manager Alun Roberts told OGJ that the company has installed 12 strings of its dope-free system in the UK North Sea through first-quarter 2005, including 3 wells in the Ninian field, 5 wells in the Lundin Broom field, and 4 wells in ConocoPhillips UK Ltd.’s Callanish/Brodgar development.
Norwegian regulations
The OSPAR Convention is the basis for national laws governing discharge of offshore drilling wastes in the waters of OSPAR signatory states: Belgium, Denmark, Finland, France, Germany, Iceland, Ireland, the Netherlands, Norway, Portugal, Spain, Sweden, and the UK. Luxembourg, Switzerland, and the European Community are also signatories.4
Norway is a signatory to the 1992 Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention) and is generally considered to have the most stringent regulatory environment. The Norwegian coastal current flows northwards along the coast from Skagerrak at 62º N latitude, flushing the coastal waters into the Barents Sea.
At INTSOK, the US-Norway oil and gas summit in Houston on Mar. 2, 2005, Norway’s King Harald V said, “The harsh, unique environment of the Arctic and other regions makes technological innovations critical” (OGJ, Mar. 28, 2005, p. 27).
The Norwegian State Pollution Control Authority is a directorate under the Norwegian Ministry of the Environment responsible for regulating drilling discharge permits. According to the Authority, the oil and gas industry is the “largest source of acute pollution of the marine environment” on the Norwegian continental shelf. The finest particles released during drilling operations are widely dispersed with ocean currents. Traces of drilling fluids from the North Sea have been found as far away as the outer Oslofjord and zero-discharge operations are now mandated north of the 62nd Parallel.5
The authority characterizes environmentally hazardous chemicals as either black, red, yellow, or green, according to their properties. Pipe dope is a “black” chemical, requiring special permits for use.6
Norsk Sokkels (NORSOK) standards are developed by the Norwegian petroleum industry for offshore sector and are jointly issued by the Norwegian Oil Industry Association and the Federation of Norwegian Engineering Industries. The standards are administered by the Norwegian Technology Standards Institution. NORSOK Standards 6.2-6.4 for drillstring components require that drill pipe threads and drill collars be treated against galling.
Norway dope-free
Dope-free tubulars have been used in Norwegian waters since the Ekofisk installation in July 2003.
In December 2004, the world’s first 13% chrome tubing string using dope-free dry connections was installed in the Ekofisk field in the Norwegian sector of the North Sea for ConocoPhillips. Tenaris installed more than 330 joints of 5½-in., 17-lb, 13Cr L-80 TenarisBlue Dopeless tubing with no rejects, cross-threading, or galled connections, according to a company press release issued in February 2005.
The successful application of dope-free technology to chrome strings is significant because the corrosion-resistant chrome alloy is softer than carbon steel and more prone to galling.
Barents Sea
At the Russian-Norwegian Oil and Gas Conference in Stavanger, January 2005, John Doyle Ong, US ambassador to Norway, said that the US Geological Survey estimates that as much as one quarter of the world’s undiscovered energy resources lie in arctic areas. He encouraged cooperation in the development of the Barents Sea, particularly in the gray zone.
At the 3rd Barents Industrial Partnership Meeting in Oslo in March 2005, Murmansk-based ArcticMorNefteGazRazvedka (Arctic seas oil and gas prospecting), founded in 1979, was recognized as one of the three major parties involved in Barents Sea development, along with Statoil and Norsk Hydro ASA.
Beginning with the first well drilled in 1980 by Norsk Hydro, 64 wells have been drilled in the Barents Sea through May 2005. Statoil’s Snøhvit field, in the Hammerfest basin, is the only commercial development to date. The Snøhvit development includes three fields: Snøhvit, Albatross, and Askeladd (OGJ, Aug. 16, 2004, p. 44).
Snøhvit Drilling Manager Thor Bensvik said that pipe dope has “traditionally been needed when connecting casing and tubing to reduce friction and to prevent corrosion and cold welding.” Because the material contains petroleum compounds and heavy metals, he said “we’re trying to reduce its use.”7
Statoil is using dry premium connections for all casing, tubing, and liners used in wells drilled in the Snøhvit field, under an exclusive contract with Tenaris SA. In addition to 13Cr connections that had been tested elsewhere, Statoil qualified 25Cr superduplex production liner installed in a CO2 injector well. The makeup torque for the 14-in.-diameter liner was 59,000 ft-lb and 24,000 ft-lb for the 25Cr 7-in. liner.
The base pipe used at Snøhvit was manufactured at Sandvik, Sweeden and threaded by TenarisDalmine, Italy. The 25% chrome string was successfully run in January 2005 with no running rejects and a running speed of 10 joints/hr.8
Future drilling
Two more exploration wells will be drilled in the Norwegian Barents Sea later in the year: the Uranus wildcat for the Statoil, Norsk Hydro, and ENI Norge group, and a development well at Goliath for ENI Norge.
Norway launches its 19th licensing round in June 2005, with a focus on the Norwegian and Barents Seas. Licenses will be awarded in first-quarter 2006.
The Russian part of the Barents Sea is estimated to hold about 22 billion boe. Future commercial development will focus on the Shtokman gas-condensate field (Shtokmanovskoye). Potential production scenarios for Shtokman were studied by Finland’s Fortum Oil & Gas Oy and subsidiary Neste Engineering; ConocoPhillips; Norsk Hydro; and Total SA. ConocoPhillips now has an agreement with OAO Gazprom to jointly study development of the Shtokman field (OGJ Online, Dec. 22, 2004).
According to the Moscow Times, Mar. 14, 2005, OAO Gazprom will name partners for its $10 billion Shtokman project in the second half of 2005.
Russia’s Prirazlomnoye oil field is in the adjacent Pechora Sea, south of Novaya Zemla. The development license for Prirazlomnoye was awarded to Rossneft in 1993 and transferred to Sevmorneftegaz in 2002. The field development concept was designed by Vniigaz Institute and was originally to begin production in 2006.
Goals
Expanding the use of dope-free connections, wherever possible, will benefit the marine environment, with particular attention on Arctic development projects. Russia’s adoption of strict environmental standards for its oil and gas developments in the Barents, Kara, and Pechora Seas should be a strategic goal.
The new dope-free treated connections are presently limited to single makeup tubulars (casing, tubing, and liners). As the technology is refined, there is future potential for dope-free drill pipe connections, which can be made-up and broken repeatedly.
References
- Murtagian, G.R., Fanelli, V., et al., “Sealability of Stationary Metal-to-Metal Seals,” Journal of Tribology, July 2004, Vol. 126, Issue 3, pp. 591-596.
- www.rrc.state.tx.us/divisions/og/key-programs/ogkwopro.html.
- Roberts, A., and Leech, A., “Running of 13%Cr OCTG with dope-free premium threaded connections,” SPE paper No. 92739-Alternate, SPE/IADC Drilling Conference, Amsterdam, Feb. 23-25, 2005.
- Wills, J., “Muddied Waters: A survey of Offshore Oilfield Drilling Wastes and Disposal Techniques to Reduce the Ecological Impact of Sea Dumping,” May 25, 2000, 139 p.
- Norwegian Pollution Control Authority, “Water pollution: Oil and gas activities,” www.environment.no/templates/themepage____2129.aspx, updated May 2, 2005.
- Nilssen, I., and Øren, H.M., “Zero Discharges to Sea from Petroleum Activity on the Norwegian Continental Shelf,” Business Briefing: Exploration & Production: The Oil & Gas Review 2003, Vol. 2, pp. 51-58. http://bbriefings.com/pdf/30/exp032_p_07nilssen.pdf
- Robberstad, K.H., “New tube thread benefits environment,” Scandinavian Oil Gas Magazine, June 29, 2004. www.scandoil.com/moxie/news/product_service/new-tube-thread-benefits-.shtml
- Castiñeiras, T.H., Aivalis, J.G., and Eiane, D.J., “25 Cr Super Duplex Liner Fitted with a Dope-free Connection in Statoil -Snøhvit Field,” IADC World Drilling Conference, Rome, June 9-10, 2005.