US2674951A - Gas lift plunger - Google Patents

Description

April 13, 1954 J. zABA GAS LIFT PLUNGER Filed March 22, 1950 INVEN TOR.

Joseph Zobo Fig. 3

V ATTORNEY Patented Apr. 13, 1954 GAS LIFT PLUNGER Joseph Zaba, Tulsa, Okla., assigner to Stanolind Oil and Gas Company, Tulsa, Okla., a corporationof Delaware Application March 22, 1950, Serial No. 151,139

(Cl. S-52) 6 Claims.

This invention pertains to an apparatus for artificially producing wells. More particularly, this invention pertains-to an improved plunger for use in gas lifting oil Wells.

In gas lifting liquid from a Well, the common practice has been torinj ect gas by any of a number of means into anl eduction tube below the level of the fluid, thereby raising the liquid level to the surface either by-aeration of the column of liquid in the eduction tubing or by mere displacement of slugs of liquid with thegas. As is well known, by either method the gas-oil ratio is generally very high; and, therefore, the efficiency of the process is too low to justify gas lift operations in many wells-particularly stripper or marginal wells.

It has been proposed to improve this eiciency of gas lift by inserting a divider means, suchas a plunger, between the liquid column and the gas column which is used to lift the liquid column to the surface. By this means 'cy-passing of liquid with the gas is avoided, and the gas-oil ratio is substantially reduced. A plunger of `this typeand method of operation areshown in U. S. 1,833,778, Fletcher. Although variousmodincations and improvements have been madein` that system of gas lifting wells, it has not been widely used clue to the high installation cost. I have found that in that system the clearance between the plunger and the tubing must be very low to prevent the gas from by-passing the plunger and that, in order to maintain this clearancein the proper range, a specially bored or selected tubing string is required. The cost of special boring is often prohibitive, in the iirst place; and, second, thepossibility of injury, such as denting of the tubing string during handling, is rather high. Wells requiring articial lift generally will not justify such expense and suchl risk. While it would be possible occasionally to select tubing joints having a substantially uniform diameter, for a special string, obviously, no oil producer could afford to buy tubing, select joints therefrom, and sell or salvage the remainder of the joints. Even with selected joints, however, the eniciency of a plunger gas lift system using a fixed diameter plunger is reduced by even minor variations in the inside diameter ofv the tubing. Such variation cannot be avoided inv a long tubing string. Since the fixed diameter plunger must be small enough to pass the smallest diameter in the complete tubing string, it invaria'bly` allowsgas by-passing at the larger points in the string. These-diflicultieshavesubstantially limited the use of the plunger gas lift system.

It.isthereforeanlobject of this invention to provide an. improved apparatus for gas lifting-wells.

It is a further object of this invention to provide an improved gas lift plunger. A still further obj'ect of this invention is to provide a gas lift plunger which will prevent by-passing of fluid in tubing having random variations in diameter. These and other objects of this invention will becomeapparent from the following description o certain embodiments of my invention which are presented for the purpose of illustration. In this description, reference will be made to the accompanying drawings in which:

Figure 1 is a View partially in cross-section of a diagrammatic representation of one type of improved gas lift plunger, showing the sealing rings in an expanded or power stroke position;

Figure 2 is a View partially in cross-section of the gas lift plunger shown in Figure l, showingthe sealing rings in contracted or return stroke position;

Figure 3 is a cross-sectional view of an alternative means for contracting and expanding the sealing ring, the sealing ring being shown in exfpanded position; and

Figure 4 is a cross-sectional view of the apparatus shown in Figure 3, the sealing ring being shown in contracted position.

This invention, in brief, comprises a gas lift, plunger which is adapted to being reciprocated throughout substantially the whole length of a random-diameter well tubing string. As the plunger ascends with a load of liquid, ilexible seal.- ing rings mounted on a body are expanded resiliently against the inner walls of the tubing. When the plunger arrives at the surface with its load of liquid, the sealing rings are contracted and the plunger is allowed to fall relatively freely through the tubing string to a bottom stop (not shown) which is located substantially below the working fluid level of the well'. At substantially the position of the lower stop in the tubing, the sealing rings are again expanded; and, as gas pressure is applied below the plunger, the plunger is again driven to the surface.

Turning now to a detailed description of the drawings, an embodiment of my gas lift plunger is shown in a section of tubing lil. The plunger consists essentially of a tubular framework or body l l having a fishing neck l2 at the top thereof, a multiplicity of sealing rings i3 disposed along the body, and a central tripping rod i4. The sealing rings are, preferably, metallic-for example, hardened steel-and will operate for substantial periods of time in the tubing without appreciable wear. The diameter of these rings may-be variedV substantially due to the step out i5, asshown in Figures 1 and 2, without permitting the uid to by-pass the rings. It is desirable, for example, that in operation the diameter of the ring may Vary as much as one-half inch in the 2- or 21/2- inch tubing size ring without permitting fluid to by-pass the sealing ring. In larger tubing sizes the variation is proportionately larger. Furthermore, the ring is preferably highly flexible, so that it may be readily mounted in the recess or groove it of the body. A number of tapered ribs il may be attached to the inside of the sealing rings so that when the resilient frustro-conical expanders it, which are attached to central tripping rod i4, are moved up and down, the sealing ring will be resiliently expanded and contracted.

The body may be a grooved, tubular member substantially in one piece, as indicated in Figure 1, or it may be made up of a number of sections 2G, as indicated in Figure 2, each section containing a groove for the sealing ring and means to conneet to the sections above and below. This type of construction is preferred in seme cases, since it facilitates assembly of the sealing rings on the body of the gas lift plunger.

These frustro-conical cams or expanders It may be constructed of any resilient material, such as rubber, preferably synthetic, leaf springs longitudinally mounted on the rod, or the like. As indicated, they have the small-diameter end at the top and the large-diameter end at the bottom and are mounted along the tripping rod at distances corresponding to the spacing of the sealing rings on body Il. The tripping rod extends out of both ends of the body for a distance sufficient to provide the necessary axial movement of the expanders and lateral movement to the sealing ring when the rod is moved. That is, with reference specically to Figure l, during the power stroke, the tripping rod extends out of the upper end of the body a suflicient distance so that when the upper end of the tripping body strikes the upper stop (not shown) in the tubing, the tripping rod, including the expanders, will be moved downward in the body, and the sealing ringdiameter will be decreased from about one-eighth to about one-half inch, or more. Similarly, when the plunger is on the down stroke, the tripping rod. extends out of the bottom of the body a sufficient distance to return the rod and sealing rings to the expanded position when the rod strikes the lower stop (not shown) in the tubing.

In operation the plunger is placed in the tubing in the position shown in Figure Z-the contracted position. Being substantially smaller than the tubing, it falls relatively freely until the lower end of the tripping rod strikes the bottom stop in the tubing. When the tripping rod strikes the bottom stop, due to the inertia of the body, tapered ribs Il are forced down over expanders I8, and the sealing rings i4 are forced out against the inner wall of the tubing. Liquid-for example oilmay then be allowed to .dow into the tubing above the plunger; or, in some cases, the frequency of oscillations of the plunger in the tubing may be adjusted so that by the time the plunger reaches the bottom position sufficient oil has accumulated in the bottom of the tubing to start another cycle. In any case, when sufhcient oil has accumulated on top of the plunger, gas is injected into the tubing below the plunger at a pressure sufficient to overcome the friction Vof the sealing rings and the iiuid head. I have found, for example, that in 21/2-inch tubing a pressure of about 70 p. s. i. is required to overcome the static force due to 1 barrel of oil in the tubing and that the force required to overcome the friction between the sealing rings and the inner tubing wall varies substantially. Even though the frictional forces do vary substantially, I have found that a gas pressure of about 200 p. s. i. is adequate in practically all cases when about l barrel of oil is lifted per plunger trip in 21/2-inch tubing.

When sumcient pressure is applied to overcome the static force due to the head of oil and the friction between the sealing ring and tubing, the plunger moves upward in the tubing until the upper end of the tripping rod strikes the upper stop in the tubing. This stop is preferably above therow line connection to the tubing, so that al1 of the oil carried up by the plunger is discharged into the flow line from the well before the tripping rod strikes the upper stop. Obviously, various resilient means may be provided at the upper stop, as Well as at the lower stop, to decelerate the plunger and prevent injury thereto. When the upper end of the tripping rod strikes the upper stop, the inertia of the plunger body carries the sealing rings and tapered ribs upward relative to the expanders, contracting or decreasing the diameter of the sealing rings. When this diameter is decreased, the fluid will not support the plunger, so it falls relatively freely through the tubing. As it falls through the tubing, the sealing rings, the tripping rod, and expanders are in the position shown in Figure 2.

In the embodiment of my invention shown in Figures 1 and 2 and described above, the sealing ring is installed on the body in a contracted position; i. e., the ring without the application of an external force is normally smaller than the tubing in which it is to operate. It is expanded by the frustro-conical expander as indicated. In some cases I have found it desirable to construct the sealing ring so that in its normal position the diameter is equal to or greater than the maximum internal diameter of the tubing in which it is to operate. This alternative design is illustrated in Figures 3 and 4. In the expanded position, as shown in Figure 3, the condition during ascent of the plunger, no external force is applied to the sealing ring; instead, a cage 2l, consisting cf a number of tapered levers 22, is attached to tripping rod ld. These tapered members are vadapted to contract the diameter ofthe sealing ring when the tripping rod is moved downward relative to the sealing ring. That is, the tapered members, by moving downward relative to the links 2-3 attached to the inner surface of the sealing rings, contract the sealing rings, as shown in Figure 4.

The operation of this embodiment is substantially identical toi the operation of the embodiment previously described. As in that embodiment, the tripping rod is adapted to extend beyond the ends of the body il and contact the upper and lower stops to reverse the plunger. When the tripping rod is in the raised position relative to the body, as indicated in Figure 3, the cams or tapered levers 22 are out'of contact with links 23, and the sealing ring is free to expand or contract within the tubing. When the plunger reaches the surface and the tripping rod strikes the upper stop (not shown), the tripping rod is driven downward relative to the body, forcing the tapered levers 22 down into links 23 and compressing sealing ring I3 so that the pressure drop across the plunger is decreased, and the plunger falls relatively freely through the liquids and/or gases in the tubing. When the plunger reaches the bottom of the tubing, the tripping rod strikes the lower stop, forcing the tripping rod up rela- I tive to the body and withdrawing the tapered levers 22 from links 23, thereby allowing the sealing ring to again expand.

The plunger may be driven to the surface with formation gas or gas injected into the tubing below the plunger via the annulus between the tubing and casing. Various means have been proposed fo-r timing the injection of gas. For example, the gas may be injected in time cycles controlled by a clock mechanism at the surface; it may be injected by use of an intermitter valve actuated by liquid head in the tube; it may be injected by a bottom-hole valve actuated from the surface, or the like. This invention is therefore not limited by the method or apparatus used to inject gas, to shut off gas, or the like. Furthermore, various modifications of auxiliary apparatus proposed in this art, such as tubing packers, formation packers, gas-lift valves, and the like, can be applied to my improved gas lift plunger without departing from the spirit of my invention. The invention should, therefore, not be construed to be limited by the above description, which is presented merely for the purpose of illustration, but should be construed in light of the appended claims.

I claim:

1. A plunger having a plurality of hollow cylindrical members each having a vertically disposed annular sidewall and an opening extending along the vertical axis thereof, said cylindrical members being vertically spaced to provide an annular space between adjacent cylindrical members and having the axial openings therein in alignment, a exible metallic split ring member mounted in each annular space between adjacent cylindrical members and adapted for lateral movement inwardly and outwardly with respect to the vertical annular sidewalls of adjacent cylindrical members, a tripping rod mounted in said cylindrical members and extending through the axially aligned openings therein, said rod being vertically movable with respect to said cylindrical members, a plurality of cam means rigidly mounted on said tripping rod. one of said cam means being positioned in each annular space between adjacent cylindrical members, and a laterally extending member mounted in each annular space and engaging each of said split rings and adapted to be engaged by said cam means, said tripping rod and said cam means mounted thereon being movable along the vertical axis of said cylindrical members for causing engagement and, in turn, lateral movement of said laterally extending members and said split ring member with respect to the vertical annular sidewalls of adjacent cylindrical members.

2. A plunger as set forth in claim 1 having a pair of vertically spaced cylindrical members providing an annular space between said pair of cylindrical members, a iiexible metallic split ring member mounted in said annular space and a cam means rigidly mounted on said tripping rod and positioned in the annular space between said pair of cylindrical members.

3. A plunger as set forth in claim 2 in which said cam means is a frustroconical member and the outside diameter of said flexible metallic split ring member is normally substantially equal to the diameter of said cylindrical members and wherein said split ring member is expanded beyond said annular sidewalls of adjacent cylindrical members when said tripping rod and said cam means are displaced upwardly relative to said cylindrical members.

4. A plunger for raising liquids on the power stroke from wells with gas under pressure co-mprising a cylindrical body having a circumferential groove on the outer surface, a ilexible metallic sealing ring disposed in said groove and adapted for expansion beyond the periphery of said cylindrical body, and a longitudinal trip rod including cam means coupled to said sealing ring to maintain said sealing ring in a contracted position on the return stroke of said plunger.

5. A plunger for raising liquids through tubing having variable diameter comprising a 'body having circumferential grooves spaced along the outer surface, flexible metallic sealing rings disposed in said grooves and adapted for expansion beyond the periphery of said body, a tripping rod disposed within and movable longitudinally relative to said body and cages containing a multiplicity of cams secured to and spaced along said tripping rod corresponding to the spacing of said circumferential grooves on said body, said cams being operatively connected to said sealing rings and said cages and said cams being moved by said tripping rod to contract said sealing rings when said cages are displaced downward relative to said body, whereby said sealing rings in the expanded position will conform to variations in the diameter of said tubing, and said sealing rings may be contracted.

`8. A plunger for raising liquids on lthe power stroke from wells through tubing having variable diameter comprising a cylindrical bodyl having at least one cylindrical groove in the outer surface. a flexible metallic sealing ring disposed in said groove and adapted to expand beyond the periphery of said cylindrical body and to contract as the diameter of said tubing contracts, and cams extending longitudinally of said body and coupled to said sealing ring to contract said sealing ring when said cams are moved downward relative to said ring and to maintain said sealing ring in a contracted position on the return stroke of said plunger.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,002,173 Naegelen Aug. 29, 1911 1,776,889 Claytor Sept. 30, 1930 1,819,994 Claytor Aug. 18, 1931 2,001,012 Burgher May 14, 1935 2,018,205 Evans Oct. 22, 1935 2,237,408 Burgher Apr. 8, 1941 FOREIGN PATENTS Number Country Date 645,974 France July 9, 1928

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