US2865305A - Gas lift apparatus - Google Patents

Description

1958 R. P. VINCENT GAS LIFT APPARATUS Filed May 10. 1954 O 2 4 3 6 5 4 4 I? I l; p 9 5 5 2 4%: .3 2 4 I 6 7/// a L L P 3 0 A, v I 4, 5 N 2 '2 H M F (I n 8 2 0 6 5 5 5 O6 758 s 5 w w 44 5 4 m RENIC P. VINCENT IN VEN TOR.

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ATTORNEY GAS LIFT APPARATUS Renic P. Vincent, Tulsa, Okla., assignor to Pan American Petroleum Corporation, a corporation of Delaware Application May 10, 1954, Serial No. 428,4il1

4 Claims. (Cl. 103-232) This invention is directed to a gas lift apparatus and particularly to an improvement in gas lift apparatus wherein production of a gas lift well can be easily initiated and maintained.

In the production of oil and water wells by air or gas lift, particularly those oil wells which have a reasonably high bottom hole pressure and, therefore, a high static fluid level but which have a low Working or producing fluid level, the initiation of production after gas lift apparatus is installed has been a problem. Well of this type are typically produced intermittently. That is, the fluid production is normally so low that continuous operation of the pumping equipment is not justified and the well liquids are permitted to accumulate in the well or in an accumulation chamber attached to the producing equipment for a substantial period of time between producing cycles. Lifting gas is then injected into the well to produce the accumulated liquids. Once the intermittent operation is commenced and the liquid level in the well is lowered to working level, such systems, as a general rule, function satisfactorily unless for some reason operation must be shut down for such a long period that the liquid head builds up substantially above the working level.

In the operation of such wells in the past, various means have been devised for unloading the well when the gas lift apparatus is installed. Often very expensive apparatus is installed with the gas lift equipment to unload the well, and then it is of no further use unless the well is shut in for a long period of time and the fluid level in the well is allowed to rise substantially above the working fluid level. For example, kick-off valves have been spaced along the tubing in intermittent gas lift apparatus for the purpose of unloading the well initially or after a long shut-down period. These flow valves are then inactive and of no value in the operation until for some reason the liquid head is allowed to build up so that with working gas pressure flow cannot be initiated, i. e., the well cannot be kicked off.

It is, therefore, an object of this invention to provide an improved gas lift system which permits the economical initiation of production after a long shut-down period. A further object of this invention is to provide means to limit the amount of liquids which can accumulate in a gas lift system between production cycles. A more specific object of this invention is to provide a pressurelimiting standing valve for a gas lift apparatus whereby the maximum amount of liquid permitted to accumulate in a well between gas lift cycles is limited to an amount which can be lifted by the regular producing apparatus. These and other objects will become apparent from the following description. In this description reference will be made to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a well showing an intermittent gas lift installation and including a pressure-sensitive standing valve; and

Figure 2 is a cross-sectional view in detail of the pressure-sensitive standing valve shown in Figure l.

nited States Patt This invention may be described in brief as an apparatus for gas lifting a well including particularly a pressure-responsive standing valve which limits the amount of liquid that can enter the system. By limiting the amount of liquid in a well and in a gas lift system, pro duction from a gas lift well can be initiated after along shut-down period without special kick-off apparatus. Referring now more specifically to Figure 1 for a detailed description of the invention, a well it) is shown with intermittent gas lift equipment installed. The well has a casing 11 and a tubing 12. The annular space 13 be tween the tubing and casing is closed at the surface by tubing head 14. The tubing head has a side outlet 15 through which gas is injected to produce the well. Inasmuch as this well is equipped for intermittent operation, a time cycle intermitter valve 16 is provided in the gas supply line 17 from a high pressure source such as a compressor. An accumulation chamber 18 is attached to the lower end of-the tubing 12. The annular space between the walls of the accumulation chamber and the casing llil may be and normally is sealed with a packer 19. The lower end of the tubing within the accumulation chamber and near the bottom head of the accumulation chamber has a number of perforations 21 which provide fluid communication between the accumulation chamber and the tubing. The upper head 22 of the accumulation chamber may be provided with a gas lift valve or perforations 23 by which gas from the annular space 13 is injected into the accumulation chamber to displace liquid therefrom through perforations 21 into the tubing and to the surface. A liquid head-limiting standing valve 24 is located in the tubing inlet at the bottom of the tubing. This standing valve is preferably balanced, i. e., unaffected by variations in the pressure of the well fluids, so that its operation will be entirely dependent upon the pressure within the tubing, preferably the pressure at the gas inlet to the tubing. Well fluids entering the tubing must flow through the tubing inlet port 25 and through this standing valve to enter the tubing and the accumulation chamber.

Referring now more specifically to Figure 2 for a detailed description of the standing valve 24, which is shown in position at the lower end of tubing 12, the tubing, as indicated above, extends through the lower head Zil of the accumulation chamber 18. The perforations 21 in the tubing are located above and the tubing inlet port 25 is located below the lower head. The tubing inlet port is in a special seating nipple: 26 which is attached to the lower end of the tubing. This seating nipple has a lower head 27 which closes the lower end. It also has a concentric axial bore 28 in which the insert type standing valve 24 seats. The bottom of this bore has a tapered stop 29 on which the standing valve rests. The stop has a lower opening 31 which provides fluid communication between the axial bore 23 and the lower end of the tubing via radial passage 33 and annular passage 34. The standing valve which is preferably of the insert type is placed in this seating nipple during producing or pumping operations to control the fluid flow through the tubing inlet and intothe gas lift system. The standing valve housing 35 has an inlet opening 33 which is opposite the tubing inlet port 25 when the housing is in operating position. Seals 39 and 46 in the standing valve housing seal the bore 28 and the space between the housing and the seating nipple below and above the tubing inlet port so that well fluid entering the tubing must follow a flow channel through the standing valve. A soft metal ring 41) may be placed on the lower end of the housing and compressed in place to hold the valve in position. Other hold-down devices may be substituted.

Flow of well fluids into the tubing and the accumulation chamber is controlled by the balanced valve 41 having a lower valve member 42 with an O-ring seal 43 which closes the fluid passage through the seat 44. The upper valve member 45 having an O-ring seal 46 closes the fluid passage upward through the seat 4-7. This balanced valve is connected by valve stem 48 to a piston 49. This piston, together with a bellows 50 and the upper housing head 51, provides an enclosed. variable volume pressure chamber 52 which is filled with a gas under pressure, typically with an inert gas such as nitrogen. The bellows is connected at the upper end to the housing head 51 and at the lower end to the piston 49. This provides a flexible seal for the pressure chamber 52. Obviously, other means could beused in some cases to provide a variable volume pressure chamber in the upper end of the housing. Movement of the piston 49 is adapted to operate the balanced valve whenever the fluid head on the standing valve is varied. Fluid pressure from the tubing is transmitted through the fluid port 53 into the housing and passes up around the valve stem through the passage 54 and applies a force to the bottom side of the piston. Thus, when the pressure chamber 52 is filled with a compressible fluid, the balanced valve is normally forced down so that the piston strikes the shoulder 55. In this position the valve members are unseated so that fluid can enter the tubing through the tubing inlet. As fluid enters the tubing, the liquids flow into the accumulation chamber and build up a hydrostatic head in the standing valve housing via fluid port 53 below the piston forcing the piston up against the pressure of the gas in the chamber. As the piston is raised, the balanced valve which is connected to the piston by the valve stem is raised closing the fluid passages into the tubing. Thus after a certain fluid head has been built up in the tubing, the head depending upon the pressure of the gas in chamber 52, the piston area, etc., no more fluid is admitted to the tubing.

In some cases, it is desirable in order to avoid wire drawing and cutting of the valves and seats and in order to permit more rapid filling of the accumulation chamber that the balanced valve be opened and closed with a snap action. A suitable snap action device is shown in the pressure chamber 52. It consists of two or more cantilever spring elements 56 which are attached to the piston 49 inside the bellows. Each of these springs has a roller 57 or other cam means which snaps into an upper detent 58 and a lower detent 59 on the inside bore of the upper housing head 51. When the balanced valve is in a closed position, i. e., when the hydrostatic head on the standing valve is high and the piston 48 is raised compressing the gas in the chamber 52, the rollers 57 snap into detent 53. Subsequently, as the well fluids are produced and as the hydrostatic head on the standing valve is decreased, the gas in chamber 52 tends to expand and open the differential valve 42. This movement is, however, restrained by the snap action mechanism so that the balanced valve is not opened until the hydrostatic head in the tubing is reduced substantially to its minimum. This pressure is reached when the accumulated liquid in the tubing above the standing valve is displaced out of the top of the tubing. The balanced valve then snaps open providing a substantially unrestricted fluid passage through the standing valve into the bottom of the tubing and avoiding wire drawing which might destroy the valve members and the valve seats.

The pressure of the gas in chamber 52 is adjusted such that when the lower end of the tubing is substantially at separator pressure, typically 25-50 pounds, the piston 48 is at its lowest position against shoulder 55. When the piston and balanced valve are in this bottom position, the rollers 57 fall into lower detent 59. As the well fluids then enter the tubing through the standing valve, the hydrostatic head on the piston 48 is increased. Eventually when the hydrostatic head is great enough to produce an upward force on the piston 49 equal to the downward force produced by the compressed gas in the chamber 52 plus the force required to displace rollers 57 from the lower detent 59, the balanced valve snaps to a closed position, as shown. The force required to close the balanced valve is dependent, among other things, upon the pressure of the gas in the chamber 52. This gas pressure is predetermined by experimentation or calculation and preset by injecting gas into the chamber through the valved chamber inlet 61 in the upper housing head 51. in determining the gas pressure required in the chamber, the pressure of the lifting gas available together with the standing valve constants such as piston area are taken into consideration. That is, the pressure in the chamber is adjusted such that the maximum hydrostatic head in pounds per square inch permitted in the tubing, after the liquid in the accumulation chamber has been displaced into the tubing, is less than the pressure in pounds per square inch available for lifting the liquids out of the Well. Typically, the standing valve is closed at a pressure above the bottom hole pressure of the well so that liquid within the tubing cannot be forced back out into the well. In practice, the standing valve is generally adjusted to close at a tubing pressure above the bottom hole pressure and from 10 to 100 pounds below the available lifting gas pressure.

In operation the accumulation chamber 18 and packer 19 are made up at the surface and lowered into the well as the tubing 12 is lowered. The standing valve 24 may be inserted in the seating nipple at the bottom of the tubing before the tubing is lowered into the well. When the tubing is in position, preferably with the accumulation chamber near the bottom of the well, the packer is set and the well head connections made. The standing valve 24 will permit a predetermined amount of liquid to accumulate in the tubing and in the accumulation chamber and then the standing valve closes. Assuming that the liquid level in the well is below perforations 23, no additional fluid can enter the tubing or the accumulation chamber. When the pump has been out of operation for a long time and the liquid level in the well is above operating level, it is sometimes desirable to inject gas into the annular space and displace the well fluids back into the formation before the packer is set. In any case, after the packer is set, lifting gas is injected through line 17 by operation of time cycle intermitter valve 16 into the annular space 13 and through perforations 23 displacing the liquid therein down through perforations 21 and up the tubing. In some cases, it is considered desirable and more economical to inject gas into the accumulation chamber 18 by use of an intermitter or operating valve located between the annular space 13 and the accumulation chamber. Valves of this type which are actuated by the gas pressure in the annular space 13 and by the liquid head in the tubing are well known in the art. After the liquid in the accumulation chamber has been displaced out of the tubing, the pressure in the tubing drops and injection of gas into the annular space and into the top of the accumulation chamber is stopped so that the pressure in the accumulation chamber decreases to a pressure substantially equal to the well head or gas separator pressure. At this low pressure, the standing valve opens permitting well fluids to enter the tubing and the accumulation chamber. After suflicient time has elapsed to permit accumulation of a predetermined. liquid head and closing of the balanced valve, the intermitter valve 16 is again opened and the accumulated liquids are gas lifted to the surface.

in an alternative and a preferred operation, the tubing is lowered into the well before the standing valve is seated. As in the above-described embodiment, the tubing is run with the accumulation chamber andpacker attached. The packer is then set to seal the annular space between the accumulation chamber and the well wall at a point below the perforations 23 or other gas inlet means and above the tubing inlet. After the packer is set, the

standing valve is attached by fishing neck 62 on the upper housing head 51 to a fishing tool, preferably with jars, heavy weights, or the like, lowered into the tubing and stopped at a position a short distance above the tubing inlet port 25. Gas pressure is then applied either through the tubing or through the annular space to displace at least part of the liquids out of the tubing and accumulation chamber back into the well and into the formations surrounding the well. Desirably sutficient gas pressure is applied by this means to displace practically all of the liquid in the tubing back into the formation leaving the liquid level in the accumulation chamber at or below the Working level. In some cases, it may be desirable if pressure is available to displace all of the liquids from both the tubing and the accumulation chamber. The standing valve is then lowered into position in the seating nipple with the housing opening 38 opposite the tubing inlet port 25. This standing valve then admits well fluids into the tubing and the accumulation chamber until the hydrostatic head is equal to the predetermined head at which the balanced valve closes. liquid permitted to enter the gas lift system is thus limited, it can be lifted on the first producing cycle by injecting gas into the annulus at ordinary working pressure. That is, no additional pressure or special unloading valves are required to raise an excess accumulation of liquid in the system and kick the well off so that it can be produced with normal operating gas pressure. It will be apparent that a fishing tool can be run and connected to the fishing neck and that the standing valve can be removed should any trouble he encountered in the operation of the standing valve. When the system is placed in operation again following any such extended shut-down period, the excess liquids in the well which may rise to the static liquid level of the well are displaced back through the accumulation chamber into the producing formations and then the standing valve is seated. The system may then be placed in operation in the same manner as above described for initiating operations after installation of the gas lifting apparatus.

From the foregoing description which has been given by way of example of the operation of the gas lift pumping system and the apparatus, it can be seen that this invention is not limited to the apparatus specifically described. For example, while the invention has been described by reference to one type of gas lift system, particularly an intermittent gas lift system, it can readily be applied to the operation of intermittent gas lift systems of the free piston type shown for example in United States Patent No. 2,688,928 and the cycling ball pump type shown in United States Patent No. 2,698,582. Ac cordingly, this invention should be construed to be limited only by the scope of the appended claims.

Inasmuch as the amount of t I claim:

1. A gas lift apparatus including a production tubing, a well fluid inlet at the lower end of said tubing, a lifting gas inlet to said tubing, and a standing valve in said well fluid inlet, said standing valve comprising opposed valve members balanced to compensate for pressure variations in said well, means forming a pressure chamber, a compressible fluid in said chamber, a movable wall in said chamber, means to transmit production tubing pressure to said movable wall, and means connecting said movable wall and said opposed valve members, whereby said valve members will shut off the flow of well fluids into said production tubing when the pressure on said movable wall reaches a predetermined amount.

2. A gas lift apparatus including a production tubing, a seating nipple at the lower end of said tubing, a well fluid inlet in said seating nipple, a lifting gas inlet to said tubing above said seating nipple, an insert type standing valve, means to seat said standing valve in said seating nipple, opposed valve members in said standing valve balanced to compensate for pressure variations in said well, means forming a pressure chamber, a compressible fluid in said chamber, a movable wall in said chamber, means to transmit tubing pressure to said movable wall, and means connecting said movable wall and said opposed valve members to close said standing valve and prevent well fluids from entering said tubing at a predetermined tubing pressure on said movable Wall.

3. A standing valve for a Well conduit comprising a housing, a fluid passage including a well fluid entry port and an exhaust port through said housing, means to seal said housing to the inlet of said conduit and to cause fluids entering said conduit to pass through said entry port, a balanced valve in said housing, a movable wall in said housing defining a pressure chamber, a compressible fluid in said chamber, means to transmit the pressure within said conduit to said movable wall, and means connecting said balanced valve to said movable walll, said balanced valve being closed when a predetermined pressure is transmitted to said movable wall, whereby the amount of liquid entering said conduit can be limited.

4. A standing valve according to claim 3 including snap action means between said housing and said movable wall whereby said balanced valve is opened and closed instantaneously.

References Cited in the file of this patent UNITED STATES PATENTS 2,006,909 Boynton July 2, 1935 2,597,198 Staggs et a1. May 20, 1952 2,599,713 Kegay et al June 10, 1952

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