Wells – With jar means for releasing stuck part
Reexamination Certificate
2000-06-15
2001-12-04
Will, Thomas B. (Department: 3672)
Wells
With jar means for releasing stuck part
C166S163000, C166S243000, C175S320000
Reexamination Certificate
active
06325145
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of downhole equipment, often used in oil and gas well drilling and downhole equipment recovery, the operation of which is accompanied by repetitive pressure pulses in the drilling fluid, such as jarring devices. More specifically, it is a device that absorbs pressure pulses in the drilling fluid, generated by the rapid impacts which can be delivered by a tool such as a jarring tool, for the purpose of loosening a stuck object.
2. Background Art
In well operation, there is often a need for jarring, impact or vibration devices to move downhole stuck members. Jars are typically included in a pipe or work string to provide upward or downward impacts when activated. The impact is typically initiated when some type of valve or other triggering device in the tool triggers an action which applies stored energy in the form of an impact delivered to the stuck object.
This type of tool is usually supplied with a flow of drilling fluid delivered through the work string by a pump at the surface of a well site. The jarring tool often functions by momentarily interrupting the flow of drilling fluid, as these momentary interruptions of drilling fluid flow can be used to move valving members within the jarring tool. The frequent, repeated interruption of drilling fluid flow often results in the generation of pressure pulses in the drilling fluid, at the jarring tool. These pressure pulses travel back up the fluid column within the work string, to the surface at the well site.
At the surface, these pressure pulses are absorbed by equipment used in the delivery of drilling fluid downhole, such as the pump, standpipe, flex hose, swivel, and all the related fittings. In some such cases, the flex hose has been known to deflect sharply, and fittings have been known to fail. A pressure attenuating device on the pump would not likely adequately protect all the affected equipment.
It would be desirable, then, to have a means for attenuating these pressure pulses, to prevent damage to the well drilling or workover equipment. Further, it would be highly desirable to attenuate the pressure pulses at a downhole location close to the jarring tool, thereby protecting the majority of the work string from damage, as well as protecting the surface equipment.
BRIEF SUMMARY OF THE INVENTION
The present invention is an attenuator for use in reducing or eliminating back pressure pulses at a downhole location, preferably just above the pressure pulse generating device, such as a downhole jar. Terms such as “upper” and “lower”, “above” and “below”, are used herein to refer to the uphole and downhole directions, since the tools discussed herein may be used at a non-vertical well bore location. A hollow tubular housing has an upper sub for attachment to a work string, and a lower sub for attachment, either directly or indirectly, to a downhole pulse generating device. Preferably, the attenuator device is installed immediately above the pulse generating equipment. An inner tube is suspended within the hollow housing, by having its upper end threaded into the upper sub. The lower end of the inner tube is suspended within the hollow housing. As the work string is lowered into the well and fluid fills the work string, an air pocket at atmospheric pressure is trapped in the annular upper cavity between the inner tube and the hollow housing. The open lower cavity below the lower end of the inner tube fills with drilling fluid.
As pressure pulses travel back up the work string into the attenuator, they alternatingly compress and decompress the trapped air pocket, by driving fluid momentarily from the open lower cavity up into the annular upper cavity. The air pocket thusly absorbs the pressure pulses, or at least significantly reduces their magnitude. A longer inner tube can be used, with its lower end suspended near the lower end of the hollow housing, to more effectively absorb pressure pulses generated at a lower frequency. Conversely, a shorter inner tube can be used, with its lower end suspended near the longitudinal midpoint of the hollow housing or even higher, to more effectively absorb pressure pulses generated at a higher frequency. The most effective frequency response of the particular configuration is related to the relative lengths of the fluid column above the lower end of the inner tube and the trapped air pocket. Further, the effectiveness of the attenuator is enhanced by establishing the largest possible cross sectional area in the annular upper cavity.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which:
REFERENCES:
patent: 2712831 (1955-07-01), Day
patent: 3370544 (1968-02-01), Thorpe, Sr.
patent: 4514151 (1985-04-01), Anders et al.
patent: 4936383 (1990-06-01), Towner et al.
patent: 5088557 (1992-02-01), Ricles et al.
Baker Hughes Incorporated
Gay Jennifer H
Spinks Gerald W.
Will Thomas B.
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