Wells – Processes – Freeing stuck object – grappling or fishing in well
Reexamination Certificate
2002-02-25
2003-04-22
Tsay, Frank S. (Department: 3672)
Wells
Processes
Freeing stuck object, grappling or fishing in well
C166S177200
Reexamination Certificate
active
06550536
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to the freeing of stuck or jammed tubulars or other objects downhole and more particularly, to a downhole coiled tubing recovery apparatus and method designed to utilize a resonant frequency oscillator in combination with a specially designed coiled tubing bail for directing coiled tubing directly from a tubing reel through an injector head and to and from the well responsive to raising and lowering of the oscillator and the tubing bail. Freeing of the tubulars or objects is accomplished by typically resonance vibration of the bail and coiled tubing by operation of the oscillator.
Oil field tubulars such as well liners, casing, tubing and drill pipe stuck in a well bore due to various downhole conditions have been one of the principal sources of problems for oil operators and have expanded the business activity of fishing service companies in this century. During this period of time, many new and innovative tools and procedures have been developed to improve the success and efficiency of fishing operations. Apparatus such as electric line free point tools, string shot assisted backoff, downhole jarring tools, hydraulic-actuated tools of various types and various other tools and equipment have been developed for the purpose of freeing stuck or jammed tubulars downhole in a well. Although use of this equipment has become more efficient with time, the escalation in cost of drilling and workover operations has resulted in a proliferation of stuck pipe, liners, casing, and the like downhole, frequently leading to well abandonment as the most expedient resolution of the problem.
The use of vibration and resonant vibration in particular, as a means of freeing stuck tubulars from a well bore has the potential to be immediately effective and thus greatly and drastically reduce the cost involved in tubular recovery operations. Resonance occurs in vibration when the frequency of the excitation force is equal to the natural frequency of the system. When this happens, the amplitude (or stroke) of vibration will increase without bound and is governed only by the degree of damping present in the system.
A resonant vibrating system will store a significant quantity of energy, much like a flywheel. The ratio of the energy stored to the energy dissipated per cycle is referred to as the systems “Q”. A high energy level allows the system to transfer energy to a given load at an increased rate, much like an increase in voltage will allow a flashlight to burn brighter with a given bulb. Only resonant systems will achieve this energy buildup and exhibit the corresponding efficient energy transmission characteristics which assure large energy delivery and corresponding force application to a stuck region of pipe.
At resonant conditions, a string of pipe will transmit power over its length to a load at the opposite end with the only loss being that necessary to overcome resistance in the form of damping or friction. In effect, power is transmitted in the same manner as the drilling process transmits rotary power to a bit, the difference being that the motion is axial translation instead of rotation. The load accepts the transmitted power as a large force acting through a small distance. Resonant vibration of pipe can deliver substantially higher sustained energy levels to a stuck tubular than any conventional method, including jarring. This achievement is due to the elimination of the need to accelerate or physically move the mass of the pipe string. Under resonant conditions, the power is applied to a vibrating string of pipe in phase with the natural movement of the pipe string.
When an elastic body is subjected to axial strain, as in the stretching of a length of pipe, the diameter of the body will contract. Similarly, when the length of pipe is compressed, its diameter will expand. Since a length of pipe undergoing vibration experiences alternate tensile and compressive forces as waves along the longitudinal axis (and therefore longitudinal strains), the pipe diameter will expand and contract in unison with the applied tensile and compressive waves. This means that for alternate moments during a vibration cycle the pipe may actually be physically free of its bond.
The term “fluidization” is used to describe the action of granular particles when excited by a vibrational source of proper frequency. Under this condition, granular material is transformed into a fluidic state that offers little resistance to movement of body through the media. In effect, it takes some of the characteristics and properties of a liquid. Accordingly, skin friction, that force that confines a stuck tubular, is reduced to a fraction of its normal value due to the effect of vibration because of alternate tensile and compressive forces applied to a pipe and to the fluidization of granular particles packed around the pipe.
Another factor in reducing stuck tubulars downhole is acceleration, wherein a suitable vibrational stroke may need to be only about an inch in order to produce good acceleration for friction reduction and fluidization. Accordingly, the vibrational energy received at the stuck area works to effect the release of a stuck member through the application of large percussive forces, fluidization of granular material, dilation and contraction of the pipe body and a reduction of well bore friction or hole drag.
Description of the Prior Art
Resonant vibration systems for use in oilfield tubular extraction applications consist of three basic components: a mechanical oscillator with a suspension device for isolating the rig or support structure, a work string for transmitting vibrational energy, and the stuck tubular or fish to be recovered. The oscillator generates an axial sinusoidal force that can be tuned to a given frequency within a specified operating range. The force generated by the oscillator acts on the work string to create axial vibration of the string. When tuned to a resonant frequency of the system, energy developed at the oscillator is efficiently transmitted to the stuck member with the only losses being those attributed to frictional resistance. The effect of the system reactance is completely eliminated because mass inductance is equal to spring capacitance at the resonant frequency. The total resonant system must be designed so that the components act in concert with one another, thus providing an efficient and effective extraction system.
In conventional coiled tubing operations one of the actions that is detrimental to the life of the coiled tubing is that of continually working the pipe to and from the tubing reel, back and forth over the well entry gooseneck. This action induces bending yield stress into the tubing, which results in accumulated fatigue damage and can eventually lead to fatigue failure of the tubing wall. Modern instrumentation allows monitoring of the tubing bending action and the coil service company will monitor and record that action so that the coil is not used beyond its useful life.
The principal of resonant axial vibration of pipe can be applied to coiled tubing without using the gooseneck equipment. Additionally, it has been found that the coiled tubing does not necessarily need to be cut when used with the downhole coiled tubing recovery apparatus of this invention, thus saving the cost of a reel of tubing, as well as maintaining and enabling good well control, along with the facility for circulating fluids into and from the well.
Various pipe recovery techniques are well known in the art. An early pipe recovery device is detailed in U.S. Pat. No. 2,340,959, dated Feb. 8, 1944, to P. E. Harth. The Harth device is characterized by a suitable electrical or mechanical vibrator which is inserted into the pipe to be removed, such that the vibrator may be activated to loosen the pipe downhole in the well and enable removal of the pipe. A well pipe vibrating apparatus is detailed in U.S. Pat. No. 2,641,927, dated Jun. 16, 1953, to D. B. Grabel, et al. The device includes a vibrating element and a motor
Harrison John M.
Tsay Frank S.
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