The Coiled Tubing Revolution Continues
In recent years, there have been significant advances in coiled tubing (CT) materials and manufacturing. Virtually flaw-free steel with increasingly higher yield strengths, corrosion-resistant alloys and tube-milling improvements, such as longer sections of flat stock, diagonal bias welds and larger pipe sizes, have been instrumental in expanding coiled tubing utilization. However, even during normal operations, coiled tubing is subjected to cyclic bending and stresses that exceed the steel yield strength at least six times on each trip into and out of a well. Pioneering work by Schlumberger and Dr. Steve Tipton at the University of Tulsa, Oklahoma, USA, in 1989 and 1990 investigated the unique properties of and mechanical demands on coiled tubing in greater detail than ever before.
This full-scale work and a subsequent Joint Industry Project (JIP) on bending fatigue initiated in 1994 improved our understanding of coiled tubing failures. Dr. Tipton found surprising mechanical responses to ultralow-cycle fatigue, including permanent diameter growth and elonga- tion, under pressures and axial loads considered harmless to conventional jointed tubing.
The importance of this research in advancing widespread use of coiled tubing during the past 15 years cannot be overstated. It was instrumental in the coiled tubing revolu- tion of the 1990s and led to the design software and systems for monitoring coiled tubing integrity that we use today. Development is continuing on many fronts, most geared to improving the safety, reliability and efficiency of coiled tubing operations. Many training facilities now include full- scale CT unit simulators. Computer programs automatically shut down CT operations in the field when parameters exceed safe working limits. New equipment designs reduce mobilization hazards and save time by significantly decreasing the number of required rig-up steps (see “ Coiled Tubing: The Next Generation,” page 38).
Efforts to develop standards for CT manufacturing, testing and operations continue within the American Petroleum Institute (API). Along with other API workgroups address- ing coiled tubing issues, a Well Intervention Well Control Task Group headed by Alex Sas-Jaworsky is preparing an API Recommended Practice (RP) on “ Coiled Tubing Well- Control Equipment Systems” to supplement the current RP on “ Coiled Tubing Operations.” The long-running University of Tulsa JIP was extended to include the influence of surface flaws and techniques to determine what real-time inspection signals mean in an operational environment. Schlumberger, for example, recently introduced the CT InSpec* real-time system, a new ultrasonic device that measures coiled tubing wall thickness. Work is also under way to combine this new inspection
technology with existing magnetic-flux leakage measure- ments to detect flaws in coiled tubing. In another research effort, Dr. Subhash Shah at The Uni- versity of Oklahoma in Norman is advancing our under- standing of real-world operations through full-scale testing and models to predict pressure drop when a significant length of coiled tubing is on the reel while the rest extends into a wellbore. Because coiled tubing-conveyed hydraulic fracturing is one of the fastest growing through-tubing applications, understanding the related physics is critical in predicting problems before they occur. This study has expanded to include forces and effects inside spooled coiled tubing when pumping proppant-laden fluids. Even with better design software and real-time monitor- ing, CT failures still occur; and problems with early CT strings and equipment have not been completely forgotten. Early users tell of wielding ball-peen hammers to seal pin- holes in continuous tubing strings made from end-to-end, or butt-welded, lengths of pipe. However, through better communication, more oilfield personnel are now comfortable having a CT unit on their wells.
Despite previous failures, technical innovations continue, as does the need to communicate new developments. The International Coiled Tubing Association (ICoTA), formed in 1994, addresses key issues related to CT and disseminates technical information at conferences sponsored jointly by the Society of Petroleum Engineers (SPE) in the USA and Europe.
Armed with new knowledge, engineers have expanded application of coiled tubing into areas that formerly were the exclusive domain of conventional workover and drilling rigs. Considering the large number of coiled tubing units in operation today, with more on the way, the revolution that started in the 1990s is still going strong.
Curtis G. Blount Well Supervisor, Downhole Tool Specialist ConocoPhillips Alaska, Inc. Anchorage, Alaska, USA
Curtis G. Blount is a well supervisor specializing in remedial well interventions and a worldwide coiled tubing technology advisor for ConocoPhillips. Previously, he worked as an ARCO well supervisor and as a completion engineer for Dresser Atlas. He has been active in coiled tubing research and applications for more than 18 years. His contributions include many tool developments and the initial implementation of coiled tubing drilling in Alaska. Curtis has coauthored more than 25 technical papers and 20 patents. He is active in SPE, ICoTA and API, and is currently serving on an API committee addressing blowout prevention equipment for remedial well work. Curtis was also an SPE distinguished lec- turer on coiled tubing drilling in 2002 and 2003.
An asterisk (*) is used to denote a mark of Schlumberger. 1
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76