US2876703A

US2876703A - Multiple gas lift production

Info

Publication number: US2876703A
Application number: US627498A
Authority: US
Inventors: Willis C Carlisle; John H Mccarvell; Theodore R Stalder
Original assignee: Macco Oil Tool Co Inc
Current assignee: Macco Oil Tool Co Inc
Priority date: 1956-12-10
Filing date: 1956-12-10
Publication date: 1959-03-10
Anticipated expiration: 1976-03-10

Description

March 10,1959 w. c. CARLISLE ETAL MULTIPLE GAS LIFT PRODUCTION 5 Sheets-Sheet l Filed Dec. 10, 1956 y m a W. gm w. Z f6 a iii, /////4// ///p// ///4 7 f d 0a A Z Mai-ch 10, 1959 v w. c. CARLISLE ETAL 2,876,703

MULTIPLE GAS LIFT PRODUCTION Filed Dec. 10, 1956 3 Sheets-Sheet 2 A 77'0/P/VE VJ w. c, CARLISLE ETAL 2,876,703

MULTIPLE GAS LIFT PRODUCTION March 10, 1959 Y 5 Sheets-Sheet 3 Filed Dec. 10, 1956 v INVENTORS MULTIPLE GAS LIFT PRODUCTION Willis C. Carlisle, John H. McCarvell, and Theodore R. Stalder, Houston, Tex., assignors to Macco Oil Tool "Company, Inc., Houston, Tex., a corporation Application December 10, 1956, Serial No. 627,498

Claims. (Cl. 103-4) This invention relates to multiple production of oil or other liquid with gas lift valves.

This application is a continuation-impart of United States patent application Serial No. 616,499 filed October 17, 1956. now abandoned.

An obiect of this invention is to provide a new and improved method and apparatus for producing oil or other liquid from a plurality of well formations by using a plurality of gas lift valves which are supplied with gas from a common reservoir.

Another obiect of this invention is to provide a new and improved method and apparatus for producing oil or other liquid from a plurality of well formations, wherein each formation is produced through a separate pipe string, and wherein the fluid level in each pipe string controls the admission of gas thereto for effecting the lifting of the oil or other liquid with the gas.

A further object of this invention is to provide a new and improved method and apparatus for producing oil or other liquid from multiple formations through concentric pipe strings positioned in a well casing wherein gas under pressure is provided in the casing annulus from the surface, a gas-producing well formation, or any other gas pressure source, and wherein the gas is directed to a fluid operated gas lift valve on each of said pipe strings for admitting the gas separately to each pipe string while avoiding intermingling of the oil or other liquid in the two strings.

Still another object of this invention is to provide a new and improved multiple production assembly in which one of a plurality of pipe strings has a gas lift valve positioned internally thereof and another of the pipe strings has a gas lift valve positioned externally thereof, and in which both of the valves are in communication with a common source of gas under pressure.

A still further object of this invention is to provide a new and improved multiple production assembly wherein concentric pipe strings are disposed in a well casing with means being provided for sealing an area between the inner and the outer pipe strings for directing gas flow to the inner pipe string from the casing annulus, and with other means being provided to by-pass the oil flow in the outer pipe string around the area sealed oif to thereby maintain the gas flow to the inner pipe string separate from the fluid conditions in the outer pipe string.

The construction designed to carry out the invention will be hereinafter described, together with other features thereof.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, Wherein an example of the invention is shown, and wherein:

Fig. 1 is a diagrammatic view illustrating the apparatus of this invention in use for carrying out the method of this invention.

Figs. 2A and 2B are views, partly in elevation and partly in section, which together illustrate the upper portion of the assembly shown in Fig. 1, and particularly that portion which includes the gas lift valve disposed within the inner pipe string.

Fig. 3 is a horizontal sectional view taken on line 3--3 of Fig. 2B.

Fig. 4 is a view, partly in section, illustrating the details of the gas lift valve mounted on the outer pipe string.

Fig. 5 is a diagrammatic view similar to Fig. 1, but illustrating the assembly in position for triple production.

Fig. 6 is a cross-sectional view taken on line 66 of Fig. 5.

Fig. 7 is a cross-sectional view taken on line 7-7 of Fig. 5.

In the drawings, the letter P designates the inner one of the pipe strings. For dual well production, a second pipe string P-1 surrounds the inner pipe string P, and both of such pipe strings P and P1 are positioned in a well bore or casing W. It is to be understood that the term well bore as used herein includes an open well bore or one having a Well casing therein. Well packers X and Y of conventional construction are positioned in the well bore or casing W to provide longitudinally spaced fluid seals in the annulus surrounding the pipe string P-l. Another well packer Z which is also of conventional construction is positioned in the annular space between the pipe string P and the pipe string P-l. The lower end of the pipe string P is provided with perforations or openings 10, and the lower end of the pipe string P-l is also open so that oil or other liquid from the well formation F passes upwardly into the interior of the pipe string P. Similarly, the pipe string P-l is provided with perforations or openings 12 above the packer Z and between the packers X and Y so that oil or other liquid from the well formation F-l can flow through the perforated casing or well bore W and into the annular space between the pipe strings P and P-l. The pipe string P has one or more gas lift valves V mounted therewith, and similarly, the pipe string P-i has one or more gas lift valves V1 mounted therewith so that gas under pressure may be supplied from the common reservoir of the well bore annulus to either of the pipe strings P or P-l separately as required to facilitate the lifting of the oil or other liquid therein, as will be explained in detail.

Considering the invention in detail, the pipe string P extends from the surface of the well, and as explained above, such pipe string P has one or more gas lift valves V mounted thereon. As shown in Figs. 2A and 28, a sealing element 15 formed of a plurality of rubber sealing rings 16, or any other annular sealing material, is provided on the external surface of the pipe string P above the location of one of the gas lift valves V. Another sealing element 18 formed of resilient annular seal rings 19 made of rubber or other sealing material is positioned on the external surface of the pipe string P below the valve V. An opening or inlet passage 22 is provided in the pipe string P between the upper sealing element 15 and the lower sealing element 18 for establishing communication with the interior of the gas lift valve V, the details of which will be explained hereinafter in connection with the gas lift valve V-l. Although various types of gas lift valves may be used in this invention, it is preferable to use gas lift valves of the general type disclosed in United States Patent No. 2,610,644 granted to W. C. Carlisle and J. H. McCarvell on September 16, 1952, wherein a gas lift valve is disclosed which has a check valve therewith, and which is operable to admit gas into the pipe string when a predetermined head or height of oil or other liquid develops in the pipe string. Thus, with the valve V, the gas is admitted into the interior of the pipe string P through the inlet opening or passage 22 for discharge into the oil or other liquid in the pipe string P through the openings 24 of the valve V.

The pipe string P-l is formed with a by-pass sleeve 25 which extends longitudinally within the pipe string P-l a distance suflicient to project above and. below the sealing elements and 18 so that the

sealing elements

15 and 18 may seal with the internal surface of such sleeve 25, as will be more evident hereinafter. The bypass sleeve is mounted in the pipe string P-l with circumferentially spaced lugs 26 at the upper end of the sleeve 25 and similarly spaced lugs 27 at the lower end of the sleeve 25. Preferably, the lugs 26 are welded or otherwise secured to the inside of the pipe string P-1 and the internal surfaces of the

lugs

26 and 27 are welded or otherwise secured to the external surface of the sleeve 25. With such construction, fluid in the pipe string P-l may flow between the sleeves 25 and the internal surface of the pipe string P4, and since the

lugs

26 and 27 are circtunferentially spaced (as best seen in Fig. 3), such lugs do not interfere with such flow of fluid. The upper end 25a of the sleeve 25 is tapered downwardly and inwardly, and each of the lugs 26 has a similarly tapered surface 26a forming a continuation of the tapered surface 25a so as to guide the inner pipe string P into the sleeve 25. The lower end 25b of the sleeve 25 and the surfaces 27a of the lugs 27 are tapered upwardly and inwardly to also facilitate the guiding of well tools which may be moved upwardly within the pipe string P4.

One of the valves V-l which is mounted on the pipe string P-l is illustrated in Fig. 4. Such valve V1 illustrated in Fig. 4 is typical of the type of valve which is used in the apparatus of this invention. The pipe string P-l is provided with an opening 30 adjacent the gas lift valve V-1 for the admission of the gas from the casing or well bore annulus into the annular space 31 between the pipe string P and the pipe string P-1. As previously stated, the valves V and V1 are preferably of the type disclosed in U. S. Patent 2,610,644. Thus, the valve V-1 illustrated in Fig. 4 includes a housing or cap 32 which is welded or otherwise secured to the external surface of the pipe string P-l. A coupling 33 is threaded or otherwise connected to the lower end of the housing or cap 32, and a valve seat 34 is threaded or otherwise connected to the coupling 33. The valve seat 34 is formed or connected at the lower end of a valve body 35 in which the valve member 36 is positioned for seating on the valve seat 34. The valve 36 is urged to its seated or closed position by a coil spring 37 which works in conjunction with fluid under pressure contained in a chamber 33 formed by a bellows 39. The body 35 has an opening 35a which is aligned with an opening 32a and the opening 30 for directing the flow of gas from the interior of the valve V-1 to the area or annular space 31 between the pipe strings P and P-l. The pressure in the pressure chamber 38 is supplied through an opening 38:: which is closed by a removable threaded cap 49 so that the valve 36 is maintained in its seated position on the valve seat 34 until a predetermined head or height of the liquid in the pipe string P-l is developed. Thus, when the height of the liquid in the annular space 31 of the pipe string P-1 reaches a predetermined level, it exerts a force or pressure upwardly on the valve 36 to move same upwardly and oil the seat 34 to open the passage 33a and to admit gas into the annular space 31 through the opening 30. When the height of the liquid in the annular space 31 falls below such predetermined level, the pressure in the chamber 38, along with the spring pressure 39 act to close the valve 36 so that gas is no longer admitted to the annular space 31.

A check valve body 41 is mounted below the coupling 33 and is threaded or otherwise connected thereto. The check valve 42 is disposed Within the body 41 and is adapted to seat on a valve seat 43. When the valve 42 isseated on the valve seat 43, fluid cannot pass therethrough, but when the valve 42 is unseated, gas mayflow inwardly from the lower end of the check valve through openings 42a, and longitudinal passages 42b for subsequent in its open position against the action of the spring 45 which tends to urge it to its seated position. Thus, the

gas is ordinarily admitted through the check valve 42 when the valve 36 is unseated. However, the check valve 42 closes in the event the pressure of the gas in the casing annulus drops below the pressure of the liquid or fluid in the annular space 31 of the pipe string P-l so that oil or other liquid in the pipe string P-1 is prevented from escaping into the annulus of the well bore or casing W.

The gas under pressure in the well bore or casing W may be supplied from a well formation above the formation F-l and also above the packer X. However, in the ordinary case the annulus is supplied with pressure from the surface and such pressurev is maintained at a selected or predetermined amount.

The 'valves V and V4 are both supplied with gas under pressure from the casing annulus or well bore. To direct the gas under pressure from the casing annulus to the gas lift valve V, a metal insert 50 having an opening 50a therein is welded or otherwise attached in the pipe string P4 to provide a passage therethrough. A metal ring 5i having an opening 51:: therein is positioned in the annular space between the pipe P-t and the sleeve 25, and is welded or otherwise secured to'both the sleeve 25 and the pipe P-l. The opening 51a is aligned with the opening 59a and also with an opening 250 in the by-pass sleeve 25 so that fluid is directed through such openings from the casing annulus to the longitudinal annular area confined by the sealing

elements

15 and 18 between the sleeve 25 and the pipe string P. The metal ring or seal 51 prevents any of the liquid or fluid which is in the pipe string P-i from intermingling with the gas flowing through the openings 56a, Sla andZ-Sc. In effect, then, by reason of the by-pass sleeve 25 and the sealing elements 15 and 13 in sealing contact therewith, a gas chamber is provided within the bore of the pipe string P-l without causing any loss of the gas in the liquid or fluid flowing in the pipe string P1. As previously stated, the valve V illustrated in Figs. 2A and 2B is substantially the same as the valve V-l illustrated in Fig. 4. Thus, the parts of the valve V which are identical with the parts of the valve V4; bear the same numerals except that they are followed by a prime mark. Thus, the valve V has a pressure chamber with a bellows (not shown) similar to the chamber 38 and the bellows 39 of the valve V-1 which are positioned in the body 35' and which, together with a spring similar to the spring 37 control the opening of the valve 36 for the inlet of gas to the pipe string P from the chamber externally thereof between the

packer sealing elements

15 and 18. Check valve 42' at the lower end of the assembly operates as described above in connection with check valve 42 of the valve V4. The valve V is not mounted within a housing or cap such as the housing or cap 32, but instead is mounted on the inside of the pipe string P with a support member or chamber 6%? which has an inner bore or opening 60a which is in iiuid communication with the inlet opening 22. A threaded nipple 61 is used to connect the lower end of the valve V to the chamber support 60.

In the use of the apparatus of this invention, and in carrying out the method of this invention, the well packers X and Y are initially set in the well bore or casing W above and below the well formation F-1, respectively, and thereafter the pipe string P-1 is lowered into the well here to position same in sealing contact with the packers X and Y for locating the perforations 12 opposite the perforations in the well bore or casing W which are in fluid communication with the well formation F-l. The well packer Z is then set within thepipe string P-l below the perforations or; openings 12, Subsequently, the. pipe string P is lowered within the pipe string P-1 to position the perforations or openings below the well packer Z so that the pipe string P is in fluid communication with the well formation F at its lower end. The well packer Z, together with the well packer Y, prevents any intermingling of the fluids in the well formations F and F-l.

Since the sealing elements and 18 are mounted with the pipe string P, they are lowered with the pipe string P as it is moved to its position in the well bore W, but it will be appreciated that the sealing

elements

15 and 18 could be provided within the pipe string P-l to form the seal with the external surface of thepipe string P, in which case,

such sealing elements

15 and 18 would be lowered separately or they could be lowered with the pipe string P4. In any event, the seal by the sealing

elements

15 and 18 is provided between the bypass sleeve 25 and the pipe string P so that the gas from the casing annulus is thereafter directed to the longitudinal area between

seals

15 and 18.

The gas under pressure is supplied to the valves V and V-l from a common source, namely, the well bore or annulus therein. As previously pointed out, the gas under pressure may be supplied from a well formation positioned above the well packer X, but ordinarily the gas under pressure is supplied from the surface of the well and is maintained at a substantially fixed amount. The gas from the annulus in the well bore or casing W is admitted to the pipe string P and to the annular space 31 between the pipe string P and pipe string P-l separately as required by each of the pipe strings. Thus, when the oil or other liquid in the pipe string P rises to a predetermined height above the gas lift valve V, it exerts sufficient pressure to overcome the amount of gas pressure in the bellows chamber 38 and the spring pressure 37 so that the valve V is opened and the gas is admitted through the check valve 42 and into the interior of the pipe string P. When the level of the oil or other liquid in the pipe string P is thereafter reduced for any reason a sufficient amount to make the head of the liquid less than the pressure being exerted to seat the valve 36, then the gas is no longer admitted through the valve V. The admission of the gas and the closing off of such flow of the gas to the pipe string P continues repeatedly in accordance with the amount of oil or liquid flowing from the well formation F into the pipe string P.

The valve V-l functions in the same manner with repect to the oil or other liquid in the pipe string P-1. Therefore, when the oil or liquid in the pipe string P-1 reaches a predetermined height above the valve V-l which is sufficient to exert a greater upward pressure on the valve 36 than the gas pressure in the bellows chamber 38 and the pressure of the spring 37, then the valve 36 is unseated and gas is admitted from the annulus of the casing or well bore W. Also, the valve V-1 is closed when the head or height of the oil or liquid in the annular space 31 drops below the predetermined amount necessary to open the valve 36. Thus, the gas under pressure for lifting the oil or other liquid in both of the pipe strings P and P-l is supplied from a common source, but the gas is introduced to each of the pipe strings P and P-1 separately in accordance with the flow of the liquid therein.

. Although this invention has been described for dual production, it will be evident that the invention is also applicable to the production from three or more well formations. Also, although only one of each of the valves V and V-l have been illustrated and described herein, it will be evident that a plurality of the valves V may be utilized in connection with the pipe string P and a plurality of the gas lift valves V-l may be utilized with the pipe string P-l.

- In Figs. 5, 6 and 7, the invention has been illustrated for triple production. The entire assembly which is used for the dual production is used in the triple production, and the same parts bear like numerals in all figures of the drawings. Thus, the structure for establishingthe fluid communication with the lower Well formations F and F-1 includes the inner pipe string P and the outer pipe string P 1 which have the gas lift valves V and 'V-l, respectively, and the other parts as indicated diagrammatically in Fig. 5 of the drawings. Preferably, the pipe strings P and P-1 are angled or inclined above the packer X so as to position the pipe strings P and P-l to one side of the well bore W for providing adequate space to receive the third pipe string P-2. Of course, it is possible to provide the pipe strings P and P-1 which are straight throughout their length, in which case the packers X and Y would be modified to receive the strings P and P-l to one side of the center of the well bore W.

The third pipe string P-Z is a conventional tubing string or pipe string which is lowered into the well separately for establishing fluid communication with a third well formation F-2. The formation F4 is sealed off with the well packers X and A. All of the packers used with the apparatus of this invention are conventional in construction. The packer A has two openings for receiving the pipe strings P and P-1 through one opening thereof and the pipe string P-2 through the other opening thereof as best seen in Fig. 5. In such manner, the area above the packer A is sealed off from the well formations therebelow so that the gas under pressure in the well bore W above the packer A does not intermingle with the oil or other fluid being produced therefrom. A gas lift valve V-Z is mounted in the third pipe string P-2 and is preferably identical with the gas lift valve V mounted in the pipe string P. The details of-the valve V have been described heretofore in connection with the dualproduction assembly. It will be understood that other types of gas lift valves may be used for the valve V-2 if desired.

It should be pointed out that the gas lift valve V-2, and all other gas lift valves which may be connected in the pipe string P-2, are also in fluid communication with the gas in the annulus or well bore W. Thus, all of the gas lift valves on the three pipe strings P, P1 and P-Z are supplied with fluid under pressure from a common source, but each preferably operates independently or separately from the other pipe strings because the liquid or fluid level of the oil or other liquid coming from the formations controls the injection of the gas through the gas lift valves, as previously explained in connection with the valves V and V-l.

It is believed evident that additional tubing strings may be added for increasing the number of well formations being simultaneously produced by gas lift, if so desired. For example, if four well formations are to be produced simultaneously, an additional tubing string such as string P-Z could be inserted into the well bore or casing W, or, if preferred, another dual production assembly including the tubing strings P and P-l could be substituted for the tubing string P-Z so that four well formations could thereby be produced.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, maybe made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

I. An apparatus adapted to be positioned in a well aid second. pipe stringbelow the. comm. nicationv means in said second pipe string and. above the communication means in said first pipe. string for preventing intermingling of the oil or other liquid from the two well formations, a first gas lift valve mounted on said first pipe string for admitting gas under pressure into said first pipe string to effect lifting of the oil or other liquid therein, said first pipe string having an open unobstructed bore from its lower end to the first gas lift valve, a second gas lift valve mounted on said second pipe string for admitting gas under pressure into said second pipe string to effect lifting of oil or other liquid therein, means for directing gas, under pressure in said well bore to each of the gas lift valves whereby each of the pipe strings is supplied with gas under pressure from a common source, said means for directing gas including a seal means for sealing off an area between said pipe strings to prevent an intermingling of the gas passing from the well bore to said first gas lift valve with the oil or other liquid. fiowing in said second pipe string, and an annular by-pass opening between said first pipe string and said second pipe string around said seal means for the passage of the oil or other liquid upwardly in said second pipe string without being obstructed by. said seal means.

2. The structure set forth in claim 1, wherein said first gas lift valve is positioned interiorly of said first pipe string, and said second gas lift valve is positioned exteriorly of said second pipe string, whereby neither of said gas lift valves is positioned in the annular opening between the pipe strings.

3. An apparatus adapted to be positioned in a well bore for the production of oil or other liquid from a plurality of well formations, comprising a first pipe string disposed in said well bore, a second pipe string also disposed in said well bore surrounding said first pipe string, means establishing fluid communication between a first well formation and the interior of said first pipe string, means establishing fluid communication between a second well formation and the annular space between the first and second pipe strings, means for sealing ofl? an annular longitudinal area in said annular space between the first and second pipe strings, an annular passage means for by-passing the fluid flowing in said annular space around said longitudinal area, a first gas lift valve on said first pipe string for admitting gas into said first pipe string from said longitudinal area, passage means sealed off from said annular space connecting said longitudinal area with the annulus of the well bore for the fiow of gas from said annulus to said first gas lift valve, and a second gas lift valve on said second pipe string for admitting gas from saidannulus of the well bore to the annular space between the pipe strings, whereby the oil or other liquid in each pipe string is' lifted by the gas from the well bore.

4. The structure set forth in claim 3, wherein said first gas lift valve is adapted to open to admit gas to said first pipe string when theoil or other liquid in said first pipe string reaches a predetermined height above said first gas lift valve, and wherein said second gas lift valve is adapted to open to admit gas to the annular space between the pipe strings when the oil or other liquid in said annular space reaches a predetermined height above said second gas lift valve, whereby the functioning of the gas lift valves is separately controlled in connection with each pipe string.

5. The structure set-forth in claim 3, wherein said first gas lift valve is adapted to open to admit gas to said first pipe string when the oil or other liquid in said first pipe string reaches a predetermined height above said first gas lift valve, and wherein said second gas-lift valve is adapted to open to admit gas to the annularspace between the pipe strings when the oil or other-liquid in said annular space reaches a predetermined height above said second gas lift valve, whereby the functioning of the gas lift valves is separately-controlled in connection with each pipeistrin'g, and. each of the gas lift valves having a. check valve. therewith to. prevent the intermingling of the oil or.

posed in said well bore surrounding said first pipe string,

with an annular space formed therebetween, means establishing fiuid communication between a first well formation and the interior of said first pipe string, means establishing fluid communication between a second well formation and the annular space between the first and second pipe strings, a by-pass sleeve positioned in said annular. space, means connecting said by-pass sleeve to said second pipe string to form a flow passage between said sleeve and said second pipe string, longitudinally spaced annular seal means disposed between said sleeve and said first pipe string for forming a sealed-oh annular longitudinal area therebetween, a first gas, lift valve on said first pipe string for establishing communication between said sealed-off area and the interior of said first pipe string, tubular means sealed off from said annular space connecting said sealed-off area with the annulus of the well bore for the flow of gas from said annulus to said first gas lift valve, and a second gas lift valve on said outer pipe string for admitting gas from said annulus of the well bore to the annular space between the pipe strings.

7. The structure set forth in claim 6, wherein the means connecting said -bypass sleeve to said second pipestring includes a plurality of circumferentially spaced lugs secured to the internal surface of said second pipe.

string and the external surface of said sleeve.

8. The structure set forth in claim 6, wherein said seal means are resilient annular sealing elements attached to the external surface of said first pipe string, whereby said seal means are adapted to be positioned in sealing contact with the internal surface of said by-pass sleeve upon the lowering of said first pipe string into position within said second pipe string for production.

9. An apparatus adapted to be positioned in a well bore for the production of oil or other liquid from a plurality of well formations, comprising a first pipe string having means therewith establishing communication with a well formation producing oil or other liquid, a second pipe string having means therewith establishing communication with a second well formation producing oil or 7 other liquid, said first pipe string being positioned concentrically within said second pipe string, a third pipe string having means therewith establishing communication with a third well formation producing oil or other liquid, said third pipe string being separately mounted in a well adjacent to said first and second pipe strings, packer means between said second pipe string and the well bore below the communication means in said second pipe string, additional packer means between said first pipe string and said second pipe string below the communication means in said second pipe string and above the communication means in said first pipe string, further packer means positioned in sealing contact with the well bore and between said third pipe string and said second pipe string below the communication means in said third pipe string and above the communication means in said second pipe string for preventing intcrmingling of the oil or other liquid from the three well formations, a first gas lift valve mounted on said first pipe string for admitting gas under pressure into said first pipe string to effect lifting of the oil or other liquid therein, said first pipe string having an open unobstructed bore below said first gas lift valve, a second gas lift valve mounted on said second'pipe string for admitting gas under'pressure into" said second pipe string to effect lifting of oil or other liquid therein, a third gas lift valve mounted on said third pipe string for admitting gas under pressure into said third pipe string to eifect lifting of oil or other liquid therein, and means for directing gas under pressure in said well bore to each of the gas lift valves whereby each of the pipe strings is supplied with gas under pressure from a common source.

10. The structure set forth in claim 3, including a third pipe string having a third gas lift valve therewith for admitting gas from said annulus of the well bore to the interior of said third pipestring, and means establishl0 ing fluid communication between a third well formation and the interior of the third pipe string, whereby the oil or other liquid from the third well formation is lifted with the gas utilized for lifting the oil or other liquid in 5 the first and second pipe strings.

Tappmeyer May 18, 1954 Davis June 8, 1954