Wells – Processes – Placing or shifting well part
Reexamination Certificate
2000-09-29
2002-10-01
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S077200, C242S421700
Reexamination Certificate
active
06457534
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for use in coiled tubing operations wherein fatigue of the coiled tubing owing to short trips is reduced.
BACKGROUND OF THE INVENTION
Coiled tubing is increasing in popularity as a method of drilling wells or conducting operations in an oil or gas wellbore. Coiled tubing is used as a continuous strand and is therefore easier and faster than conventional pipe in many applications involving well drilling or well bore operations, such as drilling wells, deploying reeled completions, logging high angle boreholes, and deploying treatment fluids. Coiled tubing is particularly useful in horizontal or multi-lateral wells.
Conventional coiled tubing operation equipment typically includes coiled tubing spooled on a reel, an injector to run coiled tubing into and out of a well, a gooseneck affixed to the injector to guide the coiled tubing between the injector and the reel, a control cab with the necessary controls and gauges, and a power supply. Additional or auxiliary equipment also may be included.
Typically, the coiled tubing is shipped, stored, and used on the same coiled tubing reel. Coiled tubing reels are deployed from trucks or trailers for land-based wells and from ships or platforms for offshore wells. When spooling or unspooling coiled tubing on a reel, the tubing is subjected to bending forces that can damage it. These bending forces cause tubing fatigue, and this fatigue is a major factor in determining the useful life of a coiled tubing work string.
Various injectors are known to handle various diameters of coiled tubing. A typical gooseneck injector comprises a curved guide member, with the curve extending in an arc of approximately ninety degrees (90°) or more and an injection head comprising a drive motor, drive chain(s), chain tensioners, and a weight indicator. These gooseneck injectors typically include a plurality of rollers for supporting and constraining the tubing while it is being guided along the curved guide member into the injector. The chain tensioners maintain effective traction between the chain and coiled tubing and permit movement of the coiled tubing into and out of the wellbore as controlled by the injector.
Coiled tubing reels typically rely on hydraulic power to operate the reel drive, brake, and spooling guide systems. Most coiled tubing reels can be powered in “in-hole”[i.e. running-in-hole (RIH)] and “out-hole”[i.e. pulling-out-of-hole (POH)] directions. The reel drive and its associated motor provide the reel back-tension, that is the tension in the coiled tubing between the reel and the injector that is used to spool and unspool the tubing on the reel and prevent tubing sagging between the reel and the injector while running coiled tubing into or out of the wellbore. The coiled tubing back-tension can be generated by either the reel or the injector or both. Typically, reel brake systems are self-actuated by an internal spring that requires air or hydraulic pressure to operate the brake release. In conventional operations, the reel brake generally is applied whenever the tubing is stationary. Applying the reel brake prevents the coiled tubing reel from rotating but it does not prevent the coiled tubing on the reel from unwinding owing energy that is stored in the coiled tubing while it is spooled on the reel. Even if the reel brake is applied and the reel is stationary, the coiled tubing can move or unwind if the coiled tubing back-tension is released.
The spooling guide system, commonly known as a levelwind assembly, guides the coiled tubing onto the reel by sensing the motion of the reel and moving the upper free end of the guide arm. Often, some vertical adjustment of levelwind assembly is necessary to achieve the desired angle of the coiled tubing to the reel. The levelwind system has the ability to move left and right (in the general horizontal direction) and up and down (in the general vertical direction). Typically, the vertical movement is controlled manually and the horizontal movement is controlled automatically, with a manual override for small horizontal alignment corrections. It is known to pivot the entire levelwind assembly on the reel support frame to allow the levelwind head to suit the angle at which the tubing leaves the reel.
It is necessary that coiled tubing have sufficient strength to conduct operations downhole without failure or buckling while being flexible enough to be spooled onto a coiled tubing reel. The high section modulus of coiled tubing is advantageous as to its strength and buckling characteristics but is disadvantageous as to its ability to be spooled on a reel. That is, properties that make coiled tubing perform well downhole work to a disadvantage when attempting to spool coiled tubing on the surface of the ground. One such disadvantage of the high section modulus is that high level of energy is stored in the coiled tubing while it is spooled on the reel.
Coiled tubing is subject to strains owing to bending and straightening movements in each coiled tubing operation. The bending and straightening movements lead to fatigue and the coiled tubing must be replaced after a certain number of runs or trips down a well. Furthermore, the strains in coiled tubing may cause residual bends in the tubing which may prevent it from straightening properly in the borehole or rolling properly on the reel.
Coiled tubing passing downward (generally running-in-hole) undergoes at least three straining events: 1) as the coiled tubing is straightened upon leaving the reel and on approach to the gooseneck; 2) as the coiled tubing is curved over the gooseneck; and 3) as the coiled tubing is straightened on its way from the gooseneck to the injector head. Similarly, coiled tubing passing upward (generally pulling-out-of-hole) undergoes at least three straining events: 1) as the coiled tubing is extracted from the wellbore and curved over the gooseneck; 2) as the coiled tubing is straightened upon leaving the gooseneck and on approach to the reel; and 3) as the coiled tubing is being curved onto the reel. These numerous bending and straightening movements strain the coiled tubing and lead to fatigue.
The cost of coiled tubing represents a large expense in coiled tubing drilling and conventional coiled tubing operations. Fatigue is a major factor in determining the useful working life of a coiled tubing work string. Fatigue is a cumulative phenomenon that is not directly measurable and therefore must be predicted in determining useful working life of coiled tubing. Some factors that effect fatigue include number of feet run, bending cycles, bending radii, internal pressure, and material characteristics.
Studies have shown that notable damage to coiled tubing is caused by the fatigue strains that result from the repeated bending and straightening of coiled tubing at the reel, gooseneck, and injector head. Studies of the behavior and fatigue of coiled tubing have shown that the useful life of coiled tubing string is largely determined by fatiguing events outside the wellbore, that is, the coiled tubing handling methods at the surface. In particular, damage is caused by the repeated bending and straightening of the coiled tubing at the gooseneck and reel. What is needed is a system that reduces the fatigue in coiled tubing by reducing the number of bending and straightening events that coiled tubing undergoes to accomplish a particular wellbore objective.
PRIOR ART
WO 98/14686 discloses a tubing reel and a tubing reel injection system that can be tilted about an axis to maintain a desired arch of the tubing between the reel injector and the main surface injector. A forty-five feet (45′) arch radius is considered desirable. The arch is maintained throughout the coiled tubing operation, and the tubing is spooled and unspooled from the reel when the tubing is moved in the well.
In the Transocean unit described in U.S. Pat. No. 6,092,756 entitled “Support of a combined feed-outfeed-in device for a coilable tubing”, the reel is mounted directly above the inject
Rolovic Radovan
Stein David
Bagnell David
Dougherty Jennifer
Kanak Wayne I.
Nava Robin C.
Schlumberger Technology Corporation
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