Wells – Processes – Cleaning or unloading well
Reexamination Certificate
2000-03-15
2001-10-02
Bagnell, David (Department: 3672)
Wells
Processes
Cleaning or unloading well
C166S063000, C166S299000, C166S319000, C166S373000
Reexamination Certificate
active
06296058
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a system for stimulation of oil and gas production from an oil or gas well which traverses earth formation and has been completed with shaped change perforations. More particularly, the system of the invention is used to develop a sudden differential of pressure shock effect in perforations in a well bore to flow or flush debris and compacted materials from the perforations with a relatively low shock effect in the tool.
BACKGROUND OF THE INVENTION
Prior Art
U.S. Pat. No. 4,142,583 issued Mar. 6, 1979 describes a shock tool for producing a differential pressure across perforations. The tool is lowered through a tubing string on a wire line and, at a selected level, the wire line connection to the tool is released so that a pressure differential sets a pack off means to close off the cross-section of the tubing string. The fluid in the bore of the tubing string is removed thereby creating a pressure differential across the tool. Next, a sinker bar is dropped from the surface through the tubing to operate a shear pin release whereby the pack off means is released and the perforations are subject to the differential pressure across the tool which provides a back flow on the perforations. Release of the pack off means permits the tool to irretrievably drop to the bottom of the well bore.
Some of the disadvantages of the above system are readily apparent. The tool becomes junk in the well and is not reusable. Also, the exact differential pressure acting on the perforation is imprecise because it depends upon the fluid removal above the tool and is not easily measured or calculated.
U.S. Pat. No. 4,285,402 issued Aug. 25, 1981 also discloses a system for cleaning perforations by differential pressures. In this system, a tool is lowered through a tubing string on a pipe. A manifold at the surface controls this pressure in the pipe and in the tubing string. A packer on the tool is sealed and locked in the tubing. The tool has a bypass passageway normally closed off by a piston which is held in place by a shear pin.
FIG. 3
shows a packer variation for seating in a seating nipple.
FIG. 4
shows a packer variation and a latching piston mechanism.
FIG. 5
shows a landing groove in a tubing string and locking keys for a latching mechanism. In all of the various configurations, a piston is shear pinned in place and when a predetermined differential reaches a force sufficient to shear the shear pin, the piston is released to open a bypass and apply a sudden pressure differential across the perforations. Subsequently, the tool is released by straight up retrieval (
FIG. 3
) or by pressure control (
FIG. 4
) or by a retrieving tool (
FIG. 6
) while the above system is retrievable, its useful life is quite limited because the impact of the suddenly released piston in the tool damages the tool requiring expensive reworking. Also, while the shear pin release can be reasonably calculated it is imprecise as to when the release will occur.
SUMMARY OF THE PRESENT INVENTION
In the present invention, the various embodiments embody the concept of shifting a valve sleeve in a well tool by use of an actuator which is responsive to a predetermined differential pressure between the pressure of fluid in the tubing string and shut in pressure of fluids in a well bore.
By controlling the predetermined differential pressure (by selecting an appropriate piston area relationship) the shut-in pressure relationship to the tubing pressure is related and a valve in the well tool can be opened at a predetermined pressure in the tubing string. When the valve is opened, the shut-in pressure is effectively released suddenly without severe damage to the well tool so that the life of the tool and re-dressing time are improved.
In a first embodiment, a large piston area in a well tool has fluid access to the pressure in a tubing string while a small piston area has fluid access to the pressure in the well bore. When the pressure in the tubing string is reduced to a predetermined amount as determined by the area relationship of the pistons and the shut in pressure, the pistons move a valve sleeve and open valve access ports so that an implosion effect occurs in the perforations in the well bore.
The relationship of the piston areas can be changed by use of a replaceable sleeve with a different piston area.
In a second embodiment, the large piston is provided with upwardly extending latching fingers normally located midway of a valve sleeve. When the pressure in the tubing string is reduced, the pistons move upwardly to latch the fingers to the upper end of the valve sleeve. When the tubing pressure is then increased, the valve sleeve is moved to open the valve access ports so that the implosion effect occurs.
In a third embodiment the small piston is provided with downwardly extending latching fingers normally located in the small piston cylinder bore. The valve sleeve is connected to the large piston and has multiple O-ring seals. When the tubing pressure is decreased (as in the first embodiment) the valve access ports are opened and the lower O-ring is blown out of its sealing groove. The latching fingers latch into a latching groove. When the tubing pressure is increased to overcome the force of the latching fingers and the piston area relationships, the valve is closed. Thereafter the operation can be repeated and stripping an O-ring on each operation.
In a fourth embodiment, a brass ring shock absorber is located above the valve sleeve. The valve sleeve is normally latched in a closed position by collet fingers. By reducing the pressure in the tubing string the collet fingers and the valve sleeve move upwardly to a position where the collet fingers unlock the valve sleeve so that the valve sleeve opens the access ports and the brass ring absorbs the shock impact of the valve sleeve in the tool.
REFERENCES:
patent: 3712378 (1973-01-01), Olivier
patent: 3743021 (1973-07-01), McCauley et al.
patent: 4185690 (1980-01-01), Kinney
patent: 4285402 (1981-08-01), Brieger
patent: 4529038 (1985-07-01), Brieger
Bagnell David
Dougherty Jennifer
Marnock Marvin J.
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