1. Field of the Invention
The present invention generally relates to a gas lift plunger assembly for use in a gas-producing well and, more particularly, is concerned with pad plunger assembly with one-piece locking end members.
2. Description of the Prior Art
Gas-producing wells typically employ a plunger disposed within tubing of the well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner well-known to one of ordinary skill in the art. The plunger is freely movable vertically in the well tubing and is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug of liquid has been delivered to the surface and the gas pressure in the well tubing has decreased due to the transmission of gas from the well tubing to a suitable storage location.
One prior art plunger assembly, called a pad plunger, includes an elongated rigid non-flexible central rod or mandrel and a pair of end members attached to the opposite ends of the mandrel. The end members of the plunger have larger diameters than the mandrel and are internally threaded to permit their removable attachment to the externally threaded opposite ends of the mandrel.
From the foregoing description, it is readily apparent that the pad plunger is made up of an assembly of various parts. It is very important to lock the end members on the plunger so that the pad plunger does not come apart while in the well. The cost of retrieving the plunger parts from the well can range from $1000 to $5000 not including lost production.
Drawbacks exist, however, with the above-described prior art plunger in the manner used to lock the end member on the mandrel. Locking subassemblies 10, such as the one shown in FIG. 1, that have been used are very labor intensive and have required numerous parts, namely, a locking ball 12 and one or more, usually three, locking rings 14 per plunger. The plunger mandrel 16 and end member 18 have to be drilled to provide a hole 20 extending through the side of the end member 18 and into the mandrel 16 so that the locking ball 12, such as xe2x85x9c inch in diameter, can be dropped in the hole 20 and then the locking ring 14 applied about an annular recess 22 in the end member 18 so as to overlie the hole 20 and retain the ball 12 in the hole. The presence of the ball 12 in the hole 20 prevents the end member 18 from turning and unthreading from the threaded end of the mandrel 16. However, corrosion problems typically occur behind the rings. Over a short period of time the rings become loose causing premature plunger wear. Therefore, the locking rings are being welded in addition to being crimped, adding more time for labor.
Consequently, a need still exists for an innovation which will provide a solution to the aforementioned problems in the prior art without introducing any new problems in place thereof.
The present invention provides a pad plunger assembly with one-piece locking end members designed to satisfy the aforementioned need. The solution of the present invention to the aforementioned problems is to provide one-piece locking end members with features which require less labor usage and eliminate multiple parts.
Accordingly, the present invention is directed to a pad plunger assembly which comprises: (a) an elongated central mandrel having a pair of opposite ends with fastening elements thereon; (b) a pair of annular collars each attached to and extending about the mandrel inwardly adjacent to one of the opposite ends thereof, each of the collars having formed therein a plurality of recesses circumferentially spaced from one another about the collar; (c) a pair of end members each having an inner end with an interior bore and fastening elements therein and being removably fastened to one of the opposite ends of the mandrel; and (d) a pair of inner annular flanges each attached to and extending axially from the inner end of one of the end members and adapted to be received over one of the collars such that, for locking the end members onto the mandrel, the end members are fastened onto the opposite ends of the mandrel and then the annular flanges are crimped so as to force circumferentially displaced portions thereof into the recesses of the collars thereby locking the end members in place on the opposite ends of the mandrel such that the end members cannot then be unfastened from the mandrel nor become loosened over time.
More particularly, the mandrel is an elongated rigid non-flexible solid rod. The collars are integrally connected to the mandrel. Each of the inner annular flanges is integrally attached to the inner end of one of the end members. The fastening elements on the ends of the mandrel are external threads. The fastening elements in the interior bores of the end members are internal threads which threadably receive the external threads on the ends of the mandrel when the end members are fastened thereon. The mandrel, collars, end members and flanges are made of a metal.
Also, the assembly includes at least one subassembly of spring-loaded interlocking pad sections disposed about the mandrel and extending over the mandrel between the collars.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.