Wells – Processes – Freeing stuck object – grappling or fishing in well
Reexamination Certificate
2000-12-20
2002-07-02
Dang, Hoang (Department: 3672)
Wells
Processes
Freeing stuck object, grappling or fishing in well
C166S077300, C166S077400, C166S104000, C166S177600, C166S379000, C166S383000, C166S384000
Reexamination Certificate
active
06412560
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the running and freeing of stuck or jammed tubulars downhole without the use of overhead tubular and oscillator support structure, using eccentric weight mechanical oscillators. More particularly, the invention includes a snubbing-type jack and an oscillator apparatus having a central tubular stem for accommodating tubulars and designed to utilize resonant frequency vibration in combination with the snubbing-type for freeing tubulars such as drill pipe, casing and other jointed tubulars, as well as continuous or coiled tubing in the well. Freeing of the coiled tubing or other tubulars in the well by typically resonance vibration is effected when the coiled tubing or alternative tubular has been clamped to the oscillator and isolated from the jack. In a first embodiment the oscillator/snubbing jack combination operates to run jointed tubulars in a well and free stuck downhole members by selectively transferring the tubular load from the snubbing jack to the oscillator and operating the oscillator to vibrate and free the tubular load in the well. In a second embodiment the apparatus is modified to run coiled tubing from a reel by adding a “gooseneck” coiled tubing guide and a coiled tubing injector and for guiding the coiled tubing through a central stem of the oscillator and through the injector, into and from the well.
Oil field tubulars such as well liners, casing, tubing and drill pipe which become 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 like tubulars 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 in 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 and 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 in 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 or tubing.
Under resonant conditions, a string of pipe or tubing 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 or tubing 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 or tubing string. Under resonant conditions, the power is applied to a vibrating string of pipe or tubing in phase with the natural movement of the pipe or tubing 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 or tubing is compressed, its diameter will expand. Since a length of pipe or tubing undergoing vibration experiences alternate tensile and compressive forces as waves along the longitudinal axis (and therefore longitudinal strains), the pipe or tubing 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 or tubing 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, the force that confines a stuck tubular, is reduced to a small fraction of its normal value due to any unconsolidated media that may surround the tubular, tending to become fluid at the interface with the vibrating pipe. Accordingly, the vibrational energy received at the stuck area works to effect the release of a stuck tubular member through the application of large percussive forces, fluidization of granular material, dilation and contraction of the pipe or tubing body and a reduction of well bore friction or hole drag.
Snubbing units, coiled tubing units, jacks or casing jacks are typically used in well construction, completion and remedial or workover situations where there is no overhead tubular support structure, and where objects such as various tubulars may be stuck in the well bore and must be removed in order to complete the work. Additionally, the pipe work string or tubing itself may become stuck in the well bore and must be freed and recovered so that the work can continue. In either event, pipe or tubing vibration from the surface may be used as a method of recovering the stuck tubular members or the work string itself and for reducing tubular insertion and removal friction, as well as other useful purposes.
A typically resonant vibration system used in connection with snubbing-type jacks and units in oilfield tubular running and extraction applications according to this invention, consists of a mechanical oscillator mounted by means of vibration insulators, isolators or reflectors on a snubbing-type unit or jack. Under circumstances where the tubular in the well is coiled tubing, a coiled tubing injector and a “gooseneck” coiled tubing guide are added to this combination. The oscillator generates an axial sinusoidal force that can be tuned to a given frequency within a specified operating range when the tubular is clamped or otherwise secured to the oscillator and is thus isolated from the snubbing-type jack when the tubular is released by the jack or tubing injector and suspended by the operator. The axial force generated by the oscillator acts on the tubular extending through the snubbing unit or coiled tubing injector and secured to the oscillator, to create axial vibration of the tubular. 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 eliminated because mass inductance is equal to spring capacitance at the reson
Dang Hoang
Harrison John M.
LandOfFree
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