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Abstract Prudhoe Bay Alaska is a mature oilfield where coiled tubing (CT) drilled sidetracks are the preferred method for gaining access to small reserves. For the CT drilling provider, and ultimately the client, the cost of the CT is a significant component of the overall operational cost and increasing the life of the working CT directly impacts operational economics. A primary contributor to CT fatigue is plastic deformation. This occurs when the CT is spooled on and off the reel and also when it passes through the injector head. Both these events subject the CT to bending stress and any attempt to reduce the number of such cycles will increase the CT life. Particular operations such as window milling, stuck coil, drilling in open hole require the CT to be moved short distances in and out of the well which increase the number of CT fatigue cycles. The Short-Trip Module (STM) has been developed to minimize fatigue peaks during these short movements. The system allows small (maximum 20 ft) CT movements in and out of the well without the need to turn the CT reel. This is done by keeping the CT reel stationary and letting the CT, between the reel and injector head, form a natural parabolic arch. Depending on the circulating pressure and CT movement schedule the fatigue can be reduced over 50% in CT fatigue life prediction model. This paper will detail the theory and design of the STM as well as the issues of its integration onto a CT drilling unit. Introduction A significant variable cost when operating a CT drilling unit is the cost of the CT itself. Any attempt to expand its life expectancy directly impacts the operational economics. A typical CT drilling unit operating in Prudhoe Bay used a total of nine strings of CT in the year 2000! The following is a list of CT drilling constraints that must be considered when endeavoring to change any component part of the system:Large diameter, thick walled CT is expensive Large diameter CT has a lower fatigue life Gooseneck and reel radii are at the maximum limits and can not be increased because of logistical limitations CT drilling requires continuous pumping while moving CT in or out of the hole. CT drilling operations require a large number of short trips when performing window milling and open hole drilling operations Transportation, crane use and labor are costly The distribution of fatigue over the length of a CT string shows that it is localized to certain areas over the CT length. Areas exhibiting high fatigue are typically experienced at the CT reel and injector head during specific repetitive operations. Multiple short-trips during window milling and the drilling of hard formations translate to fatigue being caused by cycling the CT in and out of the well at or around a specific depth. This fatigue though is taking place at the CT reel and injector head area where the CT is being repeatedly subject to plastic deformation. In order to reduce these fatigue peak points and extend the usage life of whole pipe, an innovative system, the STM, has been developed and is in the process of being installed on a CT drilling unit in Prudhoe Bay.
The CT injector is the equipment component used to grip the continuous-length tubing and provide the forces needed for deployment and retrieval of the tube into and out of the wellbore. Figure 1.5--CT injector and typical well-control stack rig-up (courtesy of SAS Industries Inc.). The tubing guide arch assembly may incorporate a series of rollers along the arch to support the tubing or may be equipped with a fluoropolymer-type slide pad run along the length of the arch. The tubing guide arch should also include a series of secondary rollers mounted above the CT to center the tubing as it travels over the guide arch. The number, size, material, and spacing of the rollers can vary significantly with different tubing guide arch designs. For CT used repeatedly in well intervention and drilling applications, the radius of the tubing guide arch should be at least 30 times the specified OD of the CT in service. This factor may be less for CT that will be bend-cycled only a few times, such ...
ABSTRACT ABSTRACT Coiled pipe or conduit has been considered for well operations for over 30 years, and some trial units have been built for drilling and workover service in recent years. Humble Oil & Refining Company and Brown oil Tools have jointly built a workover and service rig which utilizes thin-walled 3/4-in OD continuous steel tubing as the work string The rig is unitized for unloading with offshore production-platform cranes. Initial field usage has shown the rig capable of most concentric rig operations currently conducted with jointed pipe The continuous string makes some operations more versatile than current concentric operations with jointed pipe, and time savings are indicated with the coiled-tubing techniques Other advantages include smaller crews, improved safety, ability to work on live wells, and the clearance advantages of pipe without couplings More utility and an expansion of application appears possible with additional testing and development. INTRODUCTION The idea of uncoiling pipe or a flexible conduit into an oil well for drilling, workover, or servicing operations has intrigued the oil industry for over 30 years Several ingenious ideas have been formulated that have waited for materials, techniques, or sufficient demand to make the ideas economically attractive in the last 10 years, several units have been built that use the spooled-conduit principle for drilling operations on a limited depth basis In addition, completions have been made with smaller and smaller casing as Ideas have evolved into workable tools Multiple completions and tubingless completions led to big advancements in through-tubing techniques for workover and well servicing The appeal of a continuous coiled-tubing system for these operations is apparent in the additional new ideas generated and the construction of one unit to perform concentric string operations Incentive for Successful Development A decrease in the time spent on pipe trips is one of the key advantages attributed to a coiled-tubing system This advantage is realized through the elimination of numerous connections, but the side advantages of a continuous string may outweigh the direct economy of reduced trip time Each connection made in pipe is a potential leak, and the care and expense of connections is a large part of the cost of conventional concentric systems The size of a workover-unit crew or a drilling-rig crew is determined by the number of men required to trip the pipe. If pipe is continuous and on a reel, it is possible to economically automate the tripping operations and reduce crew size from 4 or 5 men to as few as 2 men Well and personnel safety is inherently better with a continuous tube because the inside of the pipe string is not left open to the atmosphere at each connection The pipe can always be connected to the circulating system, which is ready to circulate the well at any time The well can be continuously circulated while tripping pipe, if desired, and "wet strings" are eliminated. The continuous tubing makes it possible to work on live wells without the time and expense of a snubbing operation.
Torres, Carlos (Schlumberger Coiled Tubing Services) | Ottolina, Renny (Schlumberger Coiled Tubing Services) | Rudnik, Alexander (Schlumberger Coiled Tubing Services) | Creppel, Carl (Shell) | Bergeron, Ernest (Shell) | Broussard, Mike (Shell)
Abstract Since the Bureau of Safety and Environmental Enforcement (BSEE) released and implemented the updated version of the Code of Federal Regulations (CFR) in recent years, Operators now have the need to reenter wells that had been deemed as abandoned in the 1980’s, and perform operations to comply with the updated regulations. All of these wells have surface plugs (either cement plugs or cast iron bridge plugs) that require milling in order to access the wellbores to be abandoned. The use of a pulling unit is generally the method used for these abandonment operations. However, the risks of having pressure trapped below those surface plugs, and the ability to maintain well control during milling operations with the pulling and jacking units (PJU) poses a great concern to the Operators. Upon evaluation, Shell decided to use large outside diameter (OD) coiled tubing (CT) to mill the surface cement plugs and the cast iron bridge plugs. The use of CT enabled several operational advantages, such as the ability to handle potentially live well situations safely and efficiently, faster operations to mobilize (mob) from well to well, the use of larger bottom hole assemblies (BHA) with mills manufactured to drift the different casings 7", 9 5/8" and 10 ¾" inner diameter (ID), ensure optimal downhole motor (DHM) performance and to provide efficient removal of solids from the wellbore back to surface. This paper describes the CT operations performed on two shallow waters platforms projects in the GoM for Shell, where a total of 9 wells were intervened using 2 3/8" and 2 7/8" OD CT. The challenges encountered together with the developed solutions, equipment used, lessons learned are also discussed. Full compliance with BSSE regulations for well abandonment was the final result.