Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
1999-11-17
2002-11-05
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S022180, C134S16900A, C134S16800C, C134S184000, C166S171000
Reexamination Certificate
active
06474349
ABSTRACT:
This invention relates to the use of ultrasonics as a means of cleaning tubulars. The invention provides or an ultrasonic tool that finds one application in the cleaning of down-hole completions. Other applications include production pipelines, sewage pipes, power stations, process facilities, refineries etc.
Herein, references to scale should be construed broadly and other deposits, particles, debris or the like, including for example waxes, grease and ashphaltines, may be substituted as alternatives to this term.
The development of scale in down-hole completions is known to have detrimental implications for the economic prosperity and operating efficiency of a well. Specifically, the collection of scale on a well's production tubing, casing and perforations serves to impose a constriction on the circulation and production flow paths, thereby limiting production capability. The full extent of the problem may be further realised in light of the additional costs associated with the removal of the scale, together with the loss of production while so doing.
Typically, scale may comprise strontium sulphate (notably a radioactive substance), barium sulphate, calcium carbonate and so on and may result from precipitation of fluids in the well or pipeline. For example, the formation of scale may result from these substances coming out of solution of the production fluid as it undergoes a pressure drop when, such as in an oil well, it passes from the oil reservoir into the well bore via perforations in the production casing. Furthermore, this may be exacerbated as a result of water flooding a reservoir using seawater. Seawater eventually “breaks through” to the production perforations resulting in the formation of other scales, typically barium sulphate.
The scale, while known to form in the production flow paths, often collects in areas that are difficult to clean or access, such as side pockets, production devices and the perforations in production casing.
In the past a number of alternative methods of removing or mitigating the effect of the formation of scale have been contemplated. In one case, the use of chemicals has been employed; the chemicals being adapted to inhibit the adherence of the scale deposits on the reservoir rock and well tubing. However, a disadvantage associated with this solution is that the chemicals only have a finite life and lose their effectiveness over time, necessitating regular re-application.
Another proposed method involves the use of chemicals in a remedial manner, namely to remove scale that has formed on the tubing. The chemicals, of this type, incorporate dissolving agents to attack the scale deposits. Unfortunately, these chemicals tend to be relatively expensive and slow acting.
Additional, both of the above types of chemicals can be detrimental to the surrounding environment, and usually involve the production or wastage of by-products arising from their manufacture or use, which may be abrasive in the well bore or harmful to the environment upon their disposal. Some of these chemicals are also hazardous to handle and, in this way, further undesirable.
Other methods of attacking or minimising scale involve physical means, but again, operations such as milling or grinding are slow, expensive and not entirely effective. Other physical operations involve bead blasting and have the aforementioned drawbacks with the added difficulty of handling the beads, both before and after use.
It may be seen therefore that until now there has been a lack of an effective or satisfactory system for scale removal in down-hole oil field applications that removes all scale, including the scale formed in remote or difficult areas such as side pockets or perforations, and which does not damage the tubular/cement/formation bond or have a waste by product of its own.
Another desirable attribute of a suitable means or agent for scale removal or prevention is that the means or agent should be deployed using standard running or well equipment.
In the present invention it is understood that the use of ultrasonics may provide an effective method for removing the scale or other matter such as wax or asphaltines.
Ultrasound is highly versatile and can be used in a broad range of applications from medical treatments to chemical transformations.
The effects of ultrasound are achieved by the formation of cavities in the medium through which the ultrasound is used. The formation of the cavities is as a result of the rarefaction of the medium and as a consequence bubbles are formed. Cavitation bubbles are created at sites of rarefaction as the liquid fractures or tears because of the negative pressure of the sound wave in the liquid. As the wave fronts pass, the cavitation bubbles oselate under the influence of positive pressure, eventually growing to an unstable size. Finally, the violent collapse of the cavitation bubbles results in implosions, which cause shock waves to be radiated from the sites of the collapse. The collapse and implosion of meriede cavitation bubbles throughout an ultrasonically activated liquid result in the effect commonly associated with ultrasonics. It has been calculated that temperatures in excess of 10,000 degrees fahrenheit and pressures in excess of 10,000 psi are generated at the implosion sites of cavitation bubbles.
British Patent GB 2 165 330A provides an example of the use of ultrasound as a cleaning system. This system relies on the focussing of the ultrasonic energy using a parabolic curve or a flat array in combination with a focusing means. However, this system would not be suitable for general cleaning operations that require precise focussing of the ultrasonic energy.
It is an object of the present invention to provide an ultrasonic tool that may be used in the cleaning of down-hole completions.
A further object of the invention is to provide an ultrasonic tool that is equally suitable for cleaning well casing, well liner or the well riser, irrespective of varying diameters.
A yet additional and desirable objective would be to provide an ultrasonic tool that, while capable of providing a cleaning function in a oil or gas drilling well, also had the capability of stimulating production by a process of mircofracturing rock formation so as to create additional flow paths in the producing zone. It is intended that the present invention meets this objective.
According to a first aspect or the present invention there is provided apparatus for cleaning tubulars, the apparatus comprising mechanical vibration means for creating acoustic waves, a high frequency current electrical source and a polarisation current source, wherein electrical current generated by the said sources is used to excite or activate the mechanical vibration means.
Preferably the mechanical vibration means is a submersible magnetostriction vibrator.
The apparatus is most typically suitable for cleaning well bore tubulars, and may further comprise an electric conductive wireline cable on which the acoustic vibrator is adapted to be run into the well, wherein the high frequency and polarisation electrical sources are adapted to be positioned at surface, and physically connected to the wireline cable for the conducting of electrical current to the vibrator.
Also according to the first aspect of the present invention there is provided apparatus for cleaning well bore tubulars, the apparatus comprising an ultrasound source suspended on a work string adapted to be run in the well, wherein the ultrasound source provides sufficient ultrasonic energy to remove scale or other undesirable debris or particles from the well bore tubular.
The ultrasound source may be a sonic horn or node. An alternative or additional ultrasound source may also be employed.
The work string may be wireline cable, drill pipe or coil tubing.
The apparatus may further comprise an insulator for preventing the diffusion of sonic energy in a direction up the work string to which the acoustic vibrator may be attached, in use.
The apparatus may further be provided with means for directing the ultrasonic energy; f
Fleshner & Kim LLP
Hamdeen Limited
Stinson Frankie L.
LandOfFree
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