Fluid Bypass Control for Producing Well Plunger Assembly

This invention relates to a free piston type of plunger assembly commonly utilized for fluid lift purposes in wells from which fluids are extracted including but not necessarily limited to oil and natural gas such as CO.sub.2, etc.

Generally, the foregoing type of fluid lift plunger assembly is provided with pads establishing wiping contact with the internal wall surface of an enclosing tube string during reciprocation of the plunger assembly. During descent of the plunger assembly, the pads are retracted by positive mechanical linkages from the tube string walls for bypass flow of fluids according to U.S. Pat. No. 3,273,504 to Lyles. Bypass flow is conducted through internal passages in the mandrel body of the plunger assembly under valve control according to U.S. Pat. Nos. 3,424,093, 4,239,458 and 4,030,818 to Moore, Yeats and Coles, respectively, so that the pads remain in wiping contact with the tube string at all times.

In the case of a plunger assembly having linkage retracted pads, sand, grains and other substances from a fractured formation within which the tube string is installed often become wedged and trapped between moving parts of the retracting linkage mechanism to adversely affect performance. Further, the provision of such retracting mechanism makes manufacture of the plunger assembly costly while repair, parts replacement and maintenance sometimes becomes economically prohibitive. In the case of plunger assemblies through which internal bypass flow passages are established by valve control, other problems arise because of pad contact during descent, including tube string wear, deterioration of pad sealing and valve malfunction.

It is therefore an important object of the present invention to provide a plunger assembly that is inherently less costly to fabricate, repair and maintain despite the reliance on pads retracted during descent in order to establish a bypass flow passage, thereby avoiding the problems associated with valve controlled internal bypass flow types of plunger assemblies.

An aditional object in accordance with the foregoing object is to provide a fluid lift type plunger assembly utilizing pads that are retracted during descent without use of any complex linkage mechanism.

In accordance with the present invention, the wall contacting pads of the plunger assembly are retracted under a continuous bias of pad collapsing springs. The bias of the collapsing springs is overcome only during descent of the plunger assembly by automatic impact responsive displacement of a control rod slidably mounted within the mandrel body of the plunger assembly carryiing the pads. Detents yieldably hold the control rod in two operative positions. The detents include ball elements aligned with grooves in the control rod of different axial dimension to thereby change the force of springs biasing the detent balls. The detent engaging springs also exert a continuous radially outward bias on the pads so that only in the operative position assumed by the control rod during upward travel of the plunger assembly will the bias of the pad collapsing springs be automatically overcome to disable the collapsing means and permit expansion of the pads by the detent springs into wiping contact with the tube string.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

FIG. 1 is a side elevation view of a fluid lift plunger assembly in accordance with the present invention within a vertical tube string partially shown in section to expose the plunger assembly during descent.

FIG. 2 is a transverse section view taken substantially through a plane indicated by section line 2--2 in FIG. 1.

FIG. 3 is an enlarged longitudinal section view taken substantially through a plane indicated by section line 3--3 in FIG. 2.

FIG. 4 is a transverse section view taken substantially though a plane indicated by section line 4--4 in FIG. 1.

FIG. 4a is a transverse section view similar to FIG. 4, but showing a modification.

FIG. 5 is an enlarged partial section view taken substantially through a plane indicated by section line 5--5 in FIG. 3.

FIG. 6 is a partial longitudinal section view similar to that of FIG. 3 showing the tube string and the plunger assembly at a bottom hole position within a well formation.

FIG. 7 is an enlarged partial section view taken substantially through a plane indicated by section line 7--7 in FIG. 6.

Referring now to the drawings in detail, FIGS. 1 and 3 illustrate a fluid lift plunger assembly generally referred to by reference numeral 10 shown during descent within a tube string 12. FIG. 6 shows the plunger assembly descended to a bottom hole position in a well formation 14 within which the tube string 12 is adapted to be installed. After reaching such bottom hole position, the plunger assembly is drawn upwardly within the tube string to lift fluid to the surface as the plunger assembly approaches an upper limit position (not shown). In accordance with the present invention, during descent the plunger assembly is in a dimensionally contracted condition to form an annular bypass flow space thereabout within the tube string in order to enable descent without frictional resistance from contact with the internal wall surface 18 of the tube string. During upward travel the plunger assembly is in a dimensionally expanded conditions as shown in FIG. 6 in order to establish wiping contact with the internal wall surface of the tube string for fluid lift purposes.

As more clearly seen in FIG. 3 the plunger assembly includes an elongated body frame or mandrel 20 having an outer diameter somewhat less than the internal diameter of the tube string. The mandrel has a lower tapered nose portion 22 and a fishing enlargement 24 at its upper end axially spaced by neck portion 26 from the diametrically enlarged portion of the mandrel. By way of example, the mandrel supports two pad assemblies 28 through which wiping contact with the tube string wall surface 18 is established as shown in FIGS. 6 and 7. Each pad assembly includes by way of example only four arcuate pad elements 30 mounted in surrounding relation to a small diameter core portion 32 of the mandrel as more clearly seen in FIG. 2. The core portion 32 of the mandrel interconnects the upper end and lower nose portions as shown in FIG. 3 and has a flange portion 34 extending radially outward therefrom to the outer diameter. The flange portion 34 is located longitudinally between the two pad assemblies intermediate the upper and lower ends of the mandrel as shown in FIGS. 1 and 3. Flange portions are also provided at the upper and lower ends of the mandrel at the outer diameter as shown.

The pad elements 30 are biased radially outward into wiping contact with the tube string by coil springs 36 seated within recesses 38 formed in each pad element as more clearly seen in FIG. 2. In accordance with the present invention, the coil springs 38 react against detent ball elements 40 caged within radial bores 42 formed in the core portion 32 of the mandrel. The detent elements 40 serve the dual function of (a) changing the magnitude of the radially outward force of the springs 36 on the pad elements 30 and (b) yieldably holding an elongated control rod 44 in one of two operative positions within the mandrel. The control rod 44 is slidably displaceable within a central bore 46 extending through the mandrel. In the illustrated embodiment, there are two sets of axially spaced detent balls and springs 36 associated with each pad element exerting equal radially outward force on the pad elements to maintain uniform wiping contact throughout. Each set of four detent ball elements 40 is adapted to be received in one of two, closely spaced detent grooves 48 and 50 formed in the control rod. The detent grooves 48 are smaller in axial dimension than the detent grooves 50 as shown in FIGS. 3 and 6. In one of the operative axial positions of the control rod, each detent ball 40 is seated in a groove 50 as shown in FIGS. 3 and 5 so as to predetermine a lower spring force for its associated spring 36. In the other operative position of the control rod 44 as shown in FIGS. 6 and 7, the detent balls 40 engage the control rod at the smaller grooves 48 so as to assume radial positions spaced outwardly somewhat from the positions occupied when seated in grooves 50. Accordingly, the springs 36 are compressed to a somewhat grater extent by the detent balls when aligned with grooves 48 to predetermine a higher radially outward spring force exerted on the pad elements. It will therefore be apparent that the control rod when displaced between its two operative positions will change the magnitude of the radially outward force exerted on the pad elements.

The control rod 44 is displaced between its two operative positions by means of actuating end portions 52 and 54 alternatively projecting from the lower and upper ends of the mandrel. Thus, when the control rod is in the lower operative position as shown in FIG. 3, the lower end portion 52 projects from the lower nose portion 22 of the mandrel during descent of the plunger assembly. As the plunger assembly approaches the bottom hole position as shown in FIG. 6, the actuating end portion 52 of the control rod impacts to upwardly displace the control rod to its upper operative position relative to the mandrel in which the detent elements 40 are aligned with the smaller grooves 48 to increase the radially outward forces exerted by springs 36 on the pad elements 30. The pad assemblies 28 are thereby maintained in expanded condition during subsequent upward travel of the plunger assembly with the actuating end portion 54 of the control rod projecting from the upper end. When the plunger assembly reaches the upper limit of travel (not shown), the end portion 54 is also actuated by impact to displace the control rod downwardly to the operative position in which the detent balls 40 are aligned with grooves 50 to maintain the pad assemblies 28 in contracted condition subsequent during descent of the plunger assembly.

The pad assemblies are contracted against the radially outward bias of springs 36 by pad collapsing means in the form of coil springs 56 engaging smaller diameter, axial end sections 58 of the pad elements 30 in axial alignment with radially spaced socket portions 60 and 62 of the lower nose portion 22 and upper end portion, respectively, of the mandrel 20, and with the flange 34. Accordingly, a set of four pad collapsing coil springs 56 at each axial end of the pad assemblies 28 are provided, as more clearly seen in FIG. 2. The coil springs 56 are designed to exert a continuous radially inward bias on the pad elements 30 of a magnitude greater than the outward bias of springs 36 in the operative position of control rod 44 shown in FIGS. 3 and 5, but less than the outward bias in the other operative position shown in FIGS. 6 and 7. Accordingly, the pad collapsing means will be disabled only during upward travel of the plunger assembly when the higher outward bias of springs 36 is established by the control rod in its upper operative position. It is the higher bias force exerted by springs 36 that resists and overcomes the radially inner bias force of the pad collapsing springs 56 which are therefore effective only during descent of the plunger assembly to maintain the pad assemblies in the contracted condition.

FIG. 4a illustrates another embodiment or modification wherein each set of four pad collapsing coil springs 56 as shown in FIG. 4, are replaced by a single annular leaf spring 56' having circumferentially spaced portions alternately contacting the mandrel and the pad elements. The springs 56' perform the same pad collapsing function as coil springs 56 in exerting a radially inward bias on the pad elments overcome or disabled by the radially outward bias of springs 36 only in the operative position of the control rod 44 maintained by detents 40 during upward travel of the plunger assembly.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.