Apparatus for using natural gas pressure for pumping a well

An apparatus for periodically raising a quantity of liquid from a well to the earth's surface comprises a piston assembly above which the liquid collects in a tubing in which the piston assembly slides, the piston assembly including a piston member having an outside diameter slightly smaller than the inside diameter of the tubing to permit liquid to seep about the piston member and accumulate above the piston assembly near the lower end of the tubing. An outlet on the tubing is periodically opened via a timed valve to permit natural gas pressure in the well to drive the piston assembly to the surface. The piston assembly includes a mandrel which carries a slide valve disposed to be closed when the piston assembly is at rest and to be opened by deceleration of the mandrel. An arresting assembly at the top of the tubing is engaged by the upwardly moving mandrel to cause the slide valve to open and thereby relieve natural gas pressure below the piston assembly to return the piston assembly to the lower end of the tubing at the end of each operating cycle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to gas lift systems for raising 
liquids in a well to the earth's surface and, more particularly, but not 
by way of limitation, to gas lift systems for oil wells. 
2. Brief Description of the Prior Art 
The operation of a gas lift pumping system has been generally described in 
my U.S. Pat. No. 2,893,493, issued July 7, 1959. As described in that 
patent, a gas lift system comprises a tubing which extends into a well for 
receiving liquids in the well and delivering them to the surface. The 
tubing is enclosed in a casing so that pressurized gas can be introduced 
into the annulus between the tubing and casing to provide the motive force 
for driving the liquids to the earth's surface. In order to prevent the 
pressurized gas from escaping through the tubing, a piston, generally 
known as a "traveling rabbit," is mounted in the tubing so that the 
introduction of pressurized gas into the well causes the piston to rise in 
the tubing to deliver any liquids above the piston to an outlet conduit 
that is in fluid communication with the tubing. The piston is provided 
with a valve mechanism that opens when the piston is dropped down the 
tubing and closes when pressurized gas is introduced into the well. A 
plunger near the upper end of the tubing catches the piston so that liquid 
can be permitted to accumulate in the tubing between operations of the 
system. 
The operation of such a system begins with the actuation of the plunger to 
permit the piston to fall to a stop located near the lower end of the 
tubing so as to be immersed in the accumulated liquid. Since the valve 
mechanism is open during this fall, the piston will enter the accumulated 
liquid with such liquid passing inwardly through the piston during the 
passage of the piston through the liquid. When the pressurized gas is 
subsequently introduced into the well, the pressure exerted on the piston 
causes the valve mechanism therein to close and then forces the piston, 
and the liquid in the tubing above the piston, up the tubing to the outlet 
conduit from which the liquid is delivered from the well. 
While a gas lift system of this type has many advantages, it also has 
drawbacks, the major one of which is the need in the prior art systems for 
a human attendant to operate the system. That is, the attendant actuates 
the plunger and subsequently introduces the pressurized gas into the 
annulus between the casing and the tubing. Additionally, the use of 
pressurized gas as the motive force for raising the liquids requires that 
the well be provided with a compressor which is both expensive and costly 
to operate. The present invention provides an improved gas lift system 
that eliminates these and other disadvantages of the prior art systems. 
SUMMARY OF THE INVENTION 
Liquids that are to be pumped from a well are often produced from a 
formation that also produces significant quantities of natural gas which 
can, if the well is closed, build up to a pressure which is sufficient to 
raise the piston of a gas lift system and a quantity of liquid disposed 
thereabove to the earth's surface. Moreover, if this pressure is relieved, 
the time required for a subsequent build up of pressure sufficient to 
raise the piston is often uniform over long periods of time; that is, a 
well in which pressure is intermittently relieved will often exhibit a 
well defined pressure "fingerprint" that is characteristic of the well and 
can be measured. The present invention exploits these well characteristics 
to provide a gas lift system that utilizes natural gas pressure to 
periodically deliver a quantity of liquid from the bottom of a well to the 
earth's surface without the requirement of human intervention to 
accomplish such delivery. 
To this end, a piston member, that is disposed in the tubing of the present 
gas lift system and forms a part of a piston assembly, is constructed to 
have an outside diameter that is slightly smaller than the inside diameter 
of the tubing so that liquid will seep about the piston member at such 
times that the piston member is at rest at the lower end of the tubing. On 
the other hand, since the difference in these two diameters is small, the 
piston member can still provide an effective seal with the tubing under 
dynamic conditions in which natural gas pressure is permitted to drive the 
piston member upwardly in the tubing. Under such conditions, the liquid 
between the periphery of the piston member and the internal wall of the 
tubing effectively becomes a part of the piston member so that the piston 
member, and liquid above the piston member, can be driven upwardly by 
releasing pressure in portions of the tubing disposed above the piston 
member. Such release is accomplished in the present invention via a timed 
valve on an outlet conduit that is connected to the tubing to receive 
liquid delivered to the top of the tubing. 
The piston member is mounted on a mandrel which carries a slide valve 
disposed thereon to open a fluid path through the mandrel when the mandrel 
is arrested at the top of the tubing by a mandrel arresting assembly 
provided for that purpose. Thus, at the end of the delivery of fluid to 
the outlet, pressure below the piston member is released so that the 
piston member can return to a position near the lower end of the well. The 
slide valve then operates under the influence of gravity to close the 
fluid path. 
Following the discharge of liquid above the piston member from the tubing, 
the timed valve closes for a period sufficient for natural gas to 
accumulate in the well to a pressure which is again sufficient to drive 
the piston assembly, along with a quantity of liquid above the piston 
assembly, to the surface. During this time, pressure in the tubing will 
tend to equalize with the well pressure while liquid seeps about the 
piston member to again prepare the gas lift system for delivery of a 
subsequent quantity of liquid to the surface. Thereafter, the operation of 
the system is periodically and automatically repeated by periodic 
operation of the timed valve. 
An object of the present invention is to provide a gas lift pumping system 
that operates without human intervention. 
Another object of the present invention is to provide an oil well pumping 
system which utilizes natural gas pressure as the motive force for pumping 
the well, thereby eliminating a large portion of operating costs that 
might otherwise be entailed in the operation of a well pumping system. 
Other objects, advantages and features of the present invention will become 
clear from the following detailed description of the preferred embodiment 
of the invention when read in conjunction with the drawings and appended 
claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in general and to FIGS. 1A, 1B and 1C in 
particular, shown therein and designated by the general reference numeral 
10 is an apparatus constructed in accordance with the present invention to 
use natural gas pressure in a well to pump liquid from the well. As is 
particularly shown in FIGS. 1B and 1C, the apparatus 10 comprises a casing 
12 that has an upper end 14 adjacent the earth's surface 16, the casing 12 
extending downwardly from its upper end 14 into a well as indicated by the 
borehole 18. The casing 12 extends to a subterranean formation (not shown) 
that produces liquids to be recovered and a portion of the casing 12 
within the formation is provided with a plurality of perforations 20 (FIG. 
1C) to permit such liquids and natural gas produced by the formation to 
enter the casing 12. 
The apparatus 10 further comprises a tubing, generally indicated by the 
numeral 22 in FIGS. 1A, 1B and 1C, that passes through the upper end 14 of 
the casing 12 and extends downwardly within the casing 12 to a position 
near the perforations 20 as is particularly shown in FIG. 1C. The casing 
12 and tubing 22 define an annular spacing 24 that is closed at its upper 
end by a packing member 26 that forms a seal between the casing 12 and 
tubing 22. In one preferred embodiment of the apparatus 10, an aperture 28 
is formed through the packing member 26 and a pipe 30 is fixed in the 
aperture 28 and sealed to the packing member 26 to permit compressed gas 
to be introduced into the annular spacing 24 from a suitable source which 
has not been shown. A valve 32 is mounted in the pipe 30 to permit the 
upper end of the annular spacing 24 to be closed at such times that 
compressed gas is not used in the operation of the apparatus 10; that is, 
at such times that the apparatus 10 undergoes normal operation in which 
natural gas pressure is used to raise liquids which have accumulated in 
the casing 12 and the tubing 22 from the well. 
Referring specifically to FIG. 1A, the tubing 22 comprises an upper portion 
34 positioned above the casing 12 and a lower portion 36 which extends 
into the casing 12. As has been indicated in FIG. 1B, the lower portion 36 
of the tubing 22 being comprised of a plurality of sections of pipe as has 
also been indicated in FIGS. 1B and 1C. The upper portion 34 of the tubing 
22 is attached to the upper end 38 of the lower portion 36 via a hammer 
type coupler 40 and is provided with a cap 42 so that the tubing 22 has a 
closed upper end 44. Pressure within the tubing 22 can be released via a 
conventional valve 46 mounted on the cap 42 and communicating with the 
interior of the tubing 22 via a threaded bore 48 formed through the cap 42 
into which a portion of the valve 46 screws. 
The coupling 40 has a bore 50 formed therethrough to communicate the two 
portions of the tubing 22, and the upper portion 34 of the tubing 22 forms 
a housing for a mandrel arresting assembly 52 whose purpose will be 
discussed below. In the preferred embodiment of the invention, the mandrel 
arresting assembly 52 comprises a piston 54, having a conical concavity 56 
in the side thereof facing the well, and a compression spring 58 which 
extends between the piston 54 and the cap 42 to bias the piston 54 against 
an internal shoulder 60 formed in the coupling 40 about the bore 50 
therethrough. 
An aperture 62 is formed through the wall of the lower portion 36 of the 
tubing 22, a short distance below the coupler 40, and an outlet conduit 64 
is welded to the tubing 22 about the aperture 62 to deliver the effluent 
of the well from the tubing 22 to conventional separation and storage 
equipment (not shown) which need not be discussed for purposes of the 
present disclosure. A timer operated valve 66 is disposed in the outlet 
conduit 64 so that the outlet conduit 64 can be periodically opened and 
closed in accordance with a preselected schedule. Such valves are 
conventional and, accordingly, need not be further discussed herein. 
A second aperture 68 is formed through the wall of the tubing 22 below the 
aperture 62 to permit a plunger 70, forming a part of the catcher assembly 
72 to be extended into the tubing 22. As shown in FIG. 2, the catcher 
assembly comprises, in addition to the plunger 70, a bushing 74 which is 
welded to the outer periphery of the tubing 22 about the aperture 68. The 
bushing 74 has a threaded bore 76 into which a catcher assembly body 78 is 
screwed. A bore 80 is formed axially through the body 78 and portions of 
the bore 80 near the end thereof abutting the tubing 22 are formed on an 
enlarged diameter to form an internal shoulder 82 in the bore 80 facing 
the tubing 22. The plunger has a reduced diameter shank 84 so that a 
corresponding shoulder 86 is formed on the plunger to face the shoulder 
82. 
A compression spring 88 mounted on the shank 84 between the shoulders 82 
and 86 is used to urge the plunger 70 into the tubing 22. (An O-ring and 
washer can be interposed between the compression spring 88 and shoulder 82 
to seal the catcher assembly 72. For clarity of illustration, the O-ring 
and washer have not been shown in FIG. 2.) The shank 84 of the plunger 70 
is threaded over a substantial portion of its length to receive a nut 90 
and an operating handle comprised of a knob 92 and a pin 94 that passes 
through holes (not numerically designated in the drawings) formed 
laterally through the shank 84 of the plunger 70 and through the knob 92. 
The nut 90 can, as shown in FIG. 2, fit within a correspondingly shaped 
recess 95 in the outer end of the body 78 to position the inner end of the 
plunger 70 in the tubing 22. Alternately, the nut 90 can be withdrawn from 
the recess 95 and turned about 90.degree. by manipulation of the handle 
94, to engage the outer end of the body 78 and hold the inner end of the 
plunger 70 out of the tubing 22. Pressure relief within the body 78 is 
provided by a port 96 formed longitudinally through larger diameter 
portions of the plunger 70, the port 96 having a lateral extension to the 
surface of the shank 84. 
Returning now to the tubing 22 and referring particularly to FIG. 1A, the 
apparatus 10 further includes a valve 97 which is disposed in the tubing 
22 so that above ground portions of the tubing 22 can be isolated from 
portions of the tubing 22 disposed in the well. As will become clear 
below, it will at times become necessary to open the upper end of the 
tubing 22 and the valve 97 is used to close in the well at such times. In 
order that the valve 97 will not interfere with the operation of the 
apparatus 10 to be discussed below, the valve 97 is selected to be a full 
bore valve; that is, the valve 97 is selected to have a flow passage, when 
open, that has a diameter equal to the inside diameter of the tubing 22. 
Referring now to FIG. 1C, the lower portion 36 of the tubing 22 terminates 
in an open lower end 97 within the perforated portion of the casing 12. In 
one preferred embodiment of the invention, portions of the tubing 22 
adjacent the lower end 100 thereof are counterbored to provide the casing 
with an internal shoulder 100 that engages the upper end of a standing 
valve 102 that is mounted in the tubing 22 near the lower end 98 thereof. 
The valve 102, which is positioned to permit fluids to pss from the casing 
12 into the tubing 22, but to prevent the reverse flow of fluids, is 
conveniently held in place via a strainer 104 that screws into the lower 
end 98 of the tubing 22. 
As further shown in FIG. 1C, a downhole packer 106 is mounted on the tubing 
22 above the lower end 98 thereof and engages the inside wall of the 
casing 12 to divide the annulus 24 between the casing 12 and tubing 22 
into non-communicating upper and lower portions. As will be clear from 
FIGS. 1B and 1C, the lower portion of the annulus 24 thus receives fluids 
produced by the formation into which the apparatus 10 extends, while the 
upper portion of the annulus 24 forms a conduit which extends to the 
earth's surface and is in fluid communication with the pipe 30 that 
extends to a source of compressed gas. 
Above the downhole packer 106, apertures 108 are formed through the wall of 
the tubing 22 and the apertures 108 are threaded to receive bored plugs 
110 that form a portion of a standing valve assembly 112 partially shown 
in FIG. 1B and continued into FIG. 1B. The valve assembly 112, which is 
fluidly communicated with the annulus 24 via the apertures 108, coacts 
with the downhole packer 106 and valve 102 to permit compressed gas to be 
introduced into portions of the tubing 22 above the lower end 98 thereof, 
without affecting the flow of fluids into the casing 12, for a purpose to 
be discussed below. To this end, the valve assembly 112 further comprises 
a cylindrical vent body 114 which is mounted in the tubing 22 and has a 
lateral bore 116 that extends through the vent body to receive portions of 
the plugs 110. That is, the vent body 114 is mounted in the tubing 22 by 
aligning the bore 116 with the apertures 108 before screwing the plugs 110 
into the apertures 108. A second bore 118, lower portions of which are 
threaded, is formed through portions of the vent body to intersect the 
bore 116 and the lower end 120 of the vent body 114 so that a tube 122 can 
be screwed thereinto. As shown in FIG. 1C, the lower end of the tube 122 
is counterbored to receive a standing valve 124 that is positioned to pass 
fluids from the upper portion of the annulus 24, via the bores 116 and 118 
and the tube 122, into the tubing 22 while preventing the passage of fluid 
from the tubing 22 upwardly through the valve 124. An extension tube 126 
is connected to the lower end of the tube 124 via a suitable coupling 128. 
In order to prevent the vent body 114 from obstructing the flow of fluid 
through the tubing 22, a plurality of passages 130, two of which have been 
indicated by dashed lines in FIG. 1B, are formed through the vent body 114 
to intersect the upper end 132 and lower end 120 thereof. 
Above the valve assembly 112, two diametrically opposed apertures 134 are 
formed through the wall of the tubing 22 and a pin 136 is mounted in the 
apertures 134 to form a stop for a piston assembly 138 which slides in the 
tubing 22 to deliver liquid from the well to the outlet conduit 64 as will 
be described below. (In oder to more clearly bring out the structure of 
the piston assembly 138, such assembly has been drawn in a configuration 
different from the configuration the piston assembly will assume at such 
times that the piston assembly rests upon the pin 136.) 
The piston assembly 138 comprises a mandrel 140 which has a frusto-conical 
head 142 to mate with the conical concavity 56 in the piston 54 of the 
mandrel arresting assembly 52 at its upper end 144 and extends downwardly 
from the upper end 144 to a lower end 146. A bore 148 is formed through 
lower portions of the mandrel 140, the bore 148 intersecting the lower end 
146 of the mandrel 140 and extending into the mandrel 140 approximately 
half the length of the mandrel 140. A plurality of ports 150 are formed 
between the bore 148 and the outer periphery of the mandrel 140 to form a 
fluid path through the piston assembly 138 at such times that such ports 
150 are uncovered. A shoulder 152 is formed on the mandrel 140 above the 
ports 150 and a ring 154 is secured to the mandrel 140 below the ports 
150. The bore 148, ports 150, shoulder 152 and ring 154 form a portion of 
a sliding valve assembly which further comprises a slide 156 that has the 
form of a sleeve that is mounted on the mandrel 140 for sliding movement 
thereon between the shoulder 152 and the ring 154. The slide 156 has 
frusto-conical end portions 158 and three grooves 160, only one of which 
has been illustrated, are formed in the periphery of the slide 156 to 
extend substantially the length of the slide 156. The grooves 160 and 
frusto-conical portions 158 prevent natural gas from collecting under the 
slide 156, at such times that the piston assembly rests upon the pin 136, 
and thereby possibly raising the slide to the position shown in FIG. 1B 
such that the fluid path through the piston assembly 138 would be open 
with the piston assembly resting upon the pin 136. Rather, the weight of 
the slide 156 will cause the slide 156 to rest upon the ring 154 at such 
times that the piston assembly 138 is disposed near the lower end of the 
tubing 22 in the position illustrated in the drawings. As will be 
discussed below, the slide 156 overlays the ports 150 at such times that 
the piston assembly 138 is driven up the tubing 22 and is in the position 
shown in FIG. 1B when the piston assembly 138 falls within the tubing 22. 
To insure that the slide 156 will assume such positions when the piston 
assembly 138 is moving, the slide 156 is constructed to have an outside 
diameter only slightly smaller than the inside diameter of the tubing 22 
so that the slide 158 will tend to occasionally engage the tubing 22, such 
engagement urging the slide 156 in a direction opposite the direction of 
movement of the piston assembly 138. 
The piston assembly 138 further comprises a piston member 162 which is 
preferably made of nylon and is disposed below the ring 154. The piston 
member 162 is constructed to have a diameter slightly smaller than the 
inside diameter of the tubing 22 so that fluid can seep about the piston 
member 162 at such times that the piston assembly 138 is at rest on pin 
136. However, such difference in diameters is made small so that, under 
dynamic conditions in which a pressure differential across the piston 
assembly 138 drives the piston assembly 138 upwardly in the tubing 22, 
liquid between the outer periphery of the piston member 162 and the inside 
wall of the tubing 22 will form an effective seal therebetween, an effect 
that can be enhanced by a plurality of grooves 164 formed in the outer 
periphery of the piston member 162 to extend circumferentially thereabout. 
In one preferred embodiment, a suitable diameter for the piston member 162 
has been found to be one and seven-eights inches where the inside diameter 
of the tubing 22 is two inches. The piston member 162 has a central bore 
166 that mates with the periphery of the mandrel 140 and the piston member 
162 is mounted on the mandrel 140 by sliding the bore 166 of the piston 
member 162 over portions of the mandrel 140 between the lower end 146 
thereof and the ring 154 and subsequently securing the piston member 162 
on the mandrel 40 via a spacer 168 and a nut 170, the latter screwing onto 
the mandrel via threads formed on the mandrel at the lower end 146 
thereof. 
OPERATION OF THE PREFERRED EMBODIMENT 
During the operation of the apparatus 10, the tubing 22 is extended into 
the casing 12 a distance sufficient to immerse the lower end 98 of the 
tubing 22 in liquids that accumulate in the casing 12. Accordingly, as 
such liquids, and natural gas, enter the annulus 24 between the tubing 22 
and casing 12, the liquids and natural gas will be forced into the 
strainer 104 by the natural gas pressure to enter the lower end of the 
tubing 22, the valve 102 opening in response to the natural gas pressure 
and liquid to admit these fluids into the tubing 22. The fluids will 
travel up the tubing 22 and pass through the passages 130 to accumulate 
above the pin 136 a distance determined by the pressure exerted by the 
natural gas. Thus, by moving the piston assembly 138 between the pin 136 
and the mandrel arresting assembly 52, a quantity of well liquids can be 
raised to the outlet conduit 64. 
In order to use natural gas pressure to cause such movement of the piston 
assembly 138, the pressure "fingerprint" of the well is first determined 
by means of suitable pressure gauges that can be placed into fluid 
communication with the tubing 22, for example, via the valve 46. Once such 
"fingerprint" is known, the valve 66 is set to open periodically with the 
timed interval between successive openings of the valve 66 being set equal 
to the time required for natural gas pressure in the well to recover 
following the release of such pressure. 
Following the measurement of the "fingerprint" of the well, the well is 
closed in at the valve 97 and the upper portion 34 of the tubing 22 is 
removed, at the coupling 40, to permit the piston assembly 138 to be 
introduced into the tubing 22. During such introduction, the plunger 70 of 
the catcher assembly 72 is extended as shown in FIG. 2 so that the piston 
assembly 138 will be in a position near the upper end of the tubing 22. 
The upper portion 34 of the tubing 22 is then replaced and the valve 97 
opened. 
The mandrel 140 is constructed to be of a length such that the 
frusto-conical head 142 thereof will engage the piston 54 of the mandrel 
arresting assembly 52, to compress the spring 58, so that the piston 
assembly 138 can be accelerated down the tubing, following the opening of 
the valve 97, by withdrawing the plunger 70 from the casing 22. (If need 
be, the well can be bled via the valves 46 and 66 to insure that the 
piston assembly 138 is forcefully urged down the tubing 22.) Since the 
force of the mandrel arresting assembly 52 is applied to the mandrel 140, 
the resulting acceleration of the mandrel 140 will cause the slide 156 to 
rise on the mandrel 140 to abut the shoulder 152. Thus, the fluid path 
formed through the piston assembly 138 by the mandrel bore 148 and ports 
150 will become open to prevent any pressure buildup in lower portions of 
the tubing that might impede the fall of the piston assembly 138. 
Accordingly, the piston assembly will eventually come to rest on the pin 
136 so that the slide 156 will come to rest on the ring 154 closing the 
fluid path through the piston assembly 138. The timing of the valve 66 is 
then started so that operation of the apparatus will commence after a time 
period equal to the time required for the natural gas pressure to recover 
following release of such pressure. During this period, the fluid level 
and natural gas pressure in the tubing will stabilize at a level and a 
pressure which will be characteristic of the "fingerprint" of the well, 
the fluids in the well seeping about the piston member 162 to effect such 
stabilization. 
At the end of the selected time period, the timed valve 66 automatically 
opens to relieve any natural gas pressure above the piston assembly 138 
with the result that natural gas pressure in the well will force the 
piston assembly 138 and any liquid thereabove upwardly in the tubing 22. 
Such liquid will be delivered to the outlet conduit 64. Near the upper end 
of the tubing 22, the mandrel 140 will come into engagement with the 
piston 54 of the mandrel arresting assembly 52 so that the mandrel 
arresting assembly 52 will exert a force on the mandrel 140 to halt the 
upward movement of the piston assembly 138. That is, the mandrel arresting 
assembly 52 will cause a deceleration of the mandrel 140, directed 
oppositely the velocity thereof, near the upper end of the tubing 22. Such 
deceleration, toward the upper end of the tubing 22, will result in the 
slide 156 moving upwardly on the mandrel 140 to uncover the ports 150 and 
thereby open the fluid path through the piston assembly 138 formed by such 
port and the mandrel bore 148. Thus, natural gas pressure below the piston 
assembly 138 will be relieved to permit the piston assembly 138 to again 
return to the pin 136 near the lower end of the tubing 22. Following the 
discharge of well fluids via the outlet conduit 64, the valve 66 is timed 
to close so as to permit natural gas pressure to again build up in the 
casing 12 and force liquids into the tubing 22 via the open lower end 98 
thereof. (The time required for movement of the piston assembly 138 
upwardly in the casing can be measured and the valve 66 set to close 
during the fall of the piston assembly 138 to the pin 136). Such liquids 
will seep about the piston member 162 so that, at the end of the period 
during which the timed valve 66 is closed, the natural gas pressure in the 
well and the level of liquids above the piston assembly 138 will again 
have stabilized so that the above described operation of the apparatus to 
lift a quantity of liquid to the outlet conduit 64 can be repeated. 
Thereafter, such repetitions of the operation of the apparatus 10 occur at 
regular intervals determined by the setting of the timed valve 66. 
At times, it will be useful to bring the piston assembly 138 to the surface 
without regard to the state of natural gas pressure in the casing 12 and 
the provision of the apparatus 10 with the downhole packer 106, the pipe 
30 via which compressed gas can be introduced into the annulus 24, and the 
valve assembly 112 permits such movement of the piston assembly 138 at 
such times. For example, it might be desirable to cycle the piston 
assembly 138 upwardly and downwardly in the tubing 22 to remove paraffin 
deposits that have formed on the inside wall of the tubing 22 or it might 
be desirable to remove liquid from the tubing 22 when insufficient natural 
gas pressure is present. At these times, compressed gas is introduced into 
the annulus 24 via the valve 32 and such gas will pass down the annulus 24 
to the aperture 108, through the bored plugs 110, and into the bore 116 of 
the vent body 114. From the vent body 114, the gas will enter the tube 
122, open the valve 124, and traverse the extension tube 126 to be 
introduced into the lower portions of the tubing 22. The pressure exerted 
by the compressed gas will close the valve 102 so that the gas is directed 
upwardly through the passages 130 in the vent body 114 to exert a force on 
the piston member 162 and thereby raise the piston assembly 138 to the 
surface. 
It will be noted that the lifting of the piston assembly 138 using 
compressed gas will in no way interfere with the buildup of natural gas 
pressure in the well because the valve 102 will close to isolate the well 
from the tubing 22 when compressed gas is introduced into the tubing 22. 
Moreover, the provision of the apparatus 10 with this additional liquid 
lifting capacity will in no way interfere with the automatic operation of 
the apparatus 10 because of the positioning of the valve 124 to permit 
fluid passage only from the annulus 24 to the tubing 22. That is, natural 
gas that enters the lower end 98 of the tubing 22 will be prevented from 
entering the upper portion of the annulus 24 by the valve 124 so that such 
gas will be directed through the passages 130 in the vent body 114 to 
provide the motive force for driving the piston assembly 138 up the tubing 
22. 
It will also be desirable, at times, to remove the piston assembly 138 from 
the tubing 22; for example, for cleaning the piston assembly 138, and the 
catcher assembly 72 provides the apparatus 10 with such a piston assembly 
removal capability. In particular, at such times that it is desired to 
remove the piston assembly 138 from the tubing 22, the plunger 70 of the 
catcher assembly 72 is extended into the tubing 22 by turning the knob 92 
to project the nose of the plunger 70 through the aperture 68. When the 
piston assembly 138 is subsequently driven toward the upper end of the 
tubing 22, either by natural gas pressure or by the introduction of 
compressed gas in the apparatus 10 via the pipe 30, the frusto-conical 
head 142 of the mandrel 140 will engage the plunger 70 to momentarily 
force the plunger 70 into the catcher assembly body 78. The plunger 70 
will subsequently be urged inwardly by the spring 88 to engage the lower 
end of the piston assembly 138 thereby maintaining the piston assembly 138 
near the upper end 38 of the lower portion 36 of the tubing 22. 
Thereafter, the valve 97 is closed and any pressure in the tubing 22 above 
atmospheric pressure is relieved via the valve 46 to permit removal of the 
upper portion 34 of the tubing 22 at the coupler 40. The piston assembly 
138 is then withdrawn from the tubing 22 through the upper end 38 of the 
lower portion 36 of the tubing 22. 
It is clear that the present invention is well adapted to carry out the 
objects and attain the ends and advantages mentioned as well as those 
inherent therein. While a presently preferred embodiment of the invention 
has been described for purposes of this disclosure, numerous changes may 
be made which will readily suggest themselves to those skilled in the art 
and which are encompassed within the spirit of the invention disclosed and 
as defined in the appended claims.