Wells – With below and above ground modification – Eduction pump or plunger in well
Reexamination Certificate
2002-02-15
2004-04-27
Walker, Zakiya (Department: 3672)
Wells
With below and above ground modification
Eduction pump or plunger in well
C166S101000, C166S106000, C166S110000
Reexamination Certificate
active
06725916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in plungers used in a gas/fluid lift system in wells producing both fluids and gases, such as petroleum and natural gas, under variable pressure to facilitate the lifting of fluids from a subterranean reservoir to the surface through a well conduit or tubulars. Plungers of this type are designed to minimize the downward flow of fluids as well as the upward flow of gases beneath the plunger as the plunger travels upwardly to the surface. Tubulars include, but are not limited to, a variety of tubes and tubular members, such as cement casings, conduits, tubing and tubing strings which are placed in the well conduit, and may also be referred to as the production string. More specifically, the gas plunger invention concerns improvements in the internal and external sealing of the apparatus. The external sealing means or apparatus is typically comprised of a plurality of segments, which collectively forms a jacket assembly that sealingly and slidingly engages the well tubulars. A turbulent inner seal is accomplished by sealing means such as circumferential grooves on the inner core and/or fingers which project inwardly from the segments toward the inner core which may or may not be grooved. Alternatively, the inner surface of the segments may have furrows and there may be raised bands on the core which also effects a turbulent inner seal. The circumferential grooves and/or fingers, or the bands and/or furrows, provide a tortuous path of flow that deflects escaping gas streams and/or fluids, promotes turbulence in the manner of a labyrinth seal, and has gas sealing capabilities.
Another further and alternative improvement concerns a simplified sucker rod and valve-like assembly used to regulate and restrict the flow of fluids and gases through the internal passage of the plunger which allows such plungers to descend to the well bottom more rapidly than plungers without internal passages so that flow occurs only during the downward cycle or descent of the gas plunger.
2. Description of the Prior Art
Differential gas pressure operated pistons, also known as plungers, have been used in producing subterranean wells where the natural well pressure is insufficient to produce a free flow of gas, and especially fluids, to the well surface. A plunger lift system typically includes tubulars placed inside the well conduit, which extend from the reservoir(s) of the well to the surface. The tubulars have a well valve and lubricator at the top and a tubing stop and often a bumper spring or other type of spring assembly at the bottom. The cylindrical plunger typically travels between the bottom well stop and the top of the tubulars. The well is shut in for a selected time period which allows pressures to build up, then the well is opened for a selected period of time. When the well valve is opened, the plunger is able to move up the tubulars, pushing a liquid slug to the well surface. When the well valve is later closed, the plunger, aided by gravity, falls downwardly to the bottom of the tubulars. Typically, the open and closed times for the well valve are managed by a programmable electronic controller.
When the plunger is functioning properly, fluids accumulate and stay above the plunger and pressurized gases and/or fluids below the plunger are blocked from flowing up, around, and through the plunger. As a result, the plunger and accumulated fluids are pushed upwardly. The prior art devices use a variety of external, and sometimes internal, sealing elements which allow the plungers to block the upward flow of gases and slidingly and sealably engage the tubulars, which accomplishes the lifting of fluids to the surface depending upon the variable well pressures. Examples of prior art gas operated plungers include those disclosed in U.S. Pat. Nos. 5,427,504 and 6,045,335 (hereinafter the '504 and '335 patents). The prior art plunger of the '504 patent features mechanical sealing which is accomplished by segments that are biased outwardly against the tubulars by springs. The build up of internal pressure is accomplished by a flexible, elastomeric seal placed beneath the segments. The outer sealing assembly is comprised of a plurality of segments or pads. However because such resilient compounds like rubber do not last for extended periods of time in the harsh well environment, problems with inner sealing develop and the plunger must be taken out of service for time-consuming seal replacements. Further, if the inner spring member which assists in biasing of the segments becomes detached or lost, sealing problems could result.
In contrast, the prior art plunger of the '335 patent has upper and lower sets of segments whose sides are juxtaposed with respect to each other and collectively work together. The segments are biased outwardly against the tubulars by springs and the build up of internal pressure. The sealing element therein consists of a rigid inner ring member surrounding the intermediate portion of the piston body, which is positioned between the piston body and between the inner surfaces of each set of cylindrical segments, which cooperate to slidingly engage the rigid ring member and create an inner seal. However, the segments of this design can be prone to leakage.
Other prior art plungers which have externally grooved surfaces and which lack outer sealing elements or segments are, for example, disclosed in U.S. Pat. Nos. 4,410,300 and 6,200,103. These external grooves deflect the escaping gas streams and promote turbulence in the manner of a labyrinth seal and have gas sealing capability. However, the grooves are prone to structural failure due to external wear and erosion due to contact with the tubulars, and these plungers can also become jammed within the tubulars because these types of plungers do not have the capability of contracting radially inward, as do the plungers with cooperating mechanical sealing segments. The improved plunger design incorporates the concept of a labyrinth seal in its internal sealing elements.
Other examples of prior art gas operated plungers include those with internal bores or passages to speed the descent of the plungers. These plungers have a variety of valve closure members which seal the internal bore, and the prior art valve closure members are often spring loaded and work in conjunction with long rods which typically extend downwardly through the bore to unseat the valve closure member, as disclosed in the '504 and '335 patents. The design of the piston disclosed in the U.S. Pat. No. 6,045,335 includes a complicated valve mechanism which requires a unit to capture the piston at the surface and requires a long rod which moves downwardly through the plunger bore to disengage and unseat the valve closure member, and to open the internal valve. However, this rod used to reopen the valve assembly is prone to damage and bending if the rod and plunger bore become even partially unaligned, requiring expensive and time-consuming repair or replacement. Additionally, this type of plunger also requires expensive and customized installation of equipment at the well surface such as spring loaded stops to accomplish disengagement of the valve closure member. In contrast, the plunger of the '504 patent has a bypass valve with a ball-shaped closure member and a spring loaded rod activator, or shock spring, which pushes the ball up into the valve seat to seal off the flow path. The spring loaded rod activator opens the valve after the plunger reaches the lubricator at the top of the well and the pressures above and below the plunger are equalized.
In contrast, the improved stopper assembly which is housed in a chamber is typically located in a modified end cap and seals off the inner passage in a simplified manner. The stopper stem and stopper head is pushed up into the chamber when the plunger bottom contacts the well stop means, and the stopper is held up against the opening of the inner passage by the fluid and/or gas pressure bel
Gray William R.
Holt James H.
Gray William R.
The Matthews Firm
Walker Zakiya
LandOfFree
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