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Publication numberUS3280914 A
Publication typeGrant
Publication dateOct 25, 1966
Filing dateSep 22, 1964
Priority dateJun 20, 1956
Publication numberUS 3280914 A, US 3280914A, US-A-3280914, US3280914 A, US3280914A
InventorsCherry Vonner R, Sizer Phillip S, Wilhoit Lowell M
Original AssigneeOtis Engineering Corp Of Delaw
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method for controlling flow within a well
US 3280914 A
Abstract  available in
Images(3)
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Claims  available in
Description  (OCR text may contain errors)

Oct. 25, 1966 P. s. slzl-:R ETAL METHOD FOR CONTROLLING FLOW WITHIN A WELL 5 Sheets-Sheet 1 Original Filed June 20, 1956 INVENTORS BY M7 M *MW ATTORNEYS Oct. 25, 1966 P. s. slzER ETAL.

METHOD FOR CONTROLLING FLOW WITHIN A WELL 5 Sheets-Sheet 2 Original Filed June 20, 1956 lllrllrllrfllilllllllnllllhJielvfv. l

/ d A l Il Von/7er Che/'ry INVENTORS ATTORNEYS oct. 25, 1966 METHOD FOR CONTROLLING FLOW WITHIN A WELL Original Filed June 2D, 1956 P. S. SIZER ETAL 3 Sheets-Sheet 3 /fj j r f5 ,/2/ /f l i f \f k /9 //6 v .1N/Z0 E i\ 6,7 x 75.

/3/7/////0 J. J/Zer Vo/7er Cher/"y INVENTORS TTOR/VEVJ United States Patent Olice 3,280,914 Patented Oct. 25, 1966 3,280,914 METHQD FUR CNTRGLLING FLGW WITHHN A WELL Phillip S. Sizer, Dallas, Tex., Vonner R. Cherry, Mountain Home, Arlt., and Lowell M. Wilhoit, Dallas, Tex., assignors to Otis Engineering Corporation of Delaware, Dallas, Tex., a corporation of Delaware Original application .lune 2t), 1956, Ser. No. 592,691, now Patent No. 3,157,233, dated Nov. 17, 1964. Divided and this application Sept. 22, 1964, Ser. No. 398,253 5 Claims. (Cl. 16d-44) This application is a division of our copending application, Serial No. 592,691, led June 20, 1956, which issued on November 17, 1964, as United States Letters Patent No. 3,157,233. Application Serial No. 592,691 was a continuation-impart of our then copending application, Serial No. 483,318, which was led on January 21, 1955, and which has become subsequently abandoned.

This invention relates broadly to the control of tlow Within a well, and more particularly with novel methods employed in the producti-on and reworking of a permanently completed well having a high rate of flow capacity.

An object of the present invention is to provide, in a well having a subsurface flow control, a method of isolating both said subsurface liow control and surface flow control mechanism at the wellhead from the high squeeze pressures to which the production zone is subjected; and, more particularly, to accomplish such isolation in a well having a high rate of ow.

Still another object is to provide, in the production and reworking of a well, a method of using the tubing-casing annulus for production as Well as Workover purposes so as to produce the well at a high rate of flow.

Yet a further object is t-o provide a method of the character described in the foregoing object which involves, in addition to prior practices, the mere addition or removal and sealing off of a tubing extending from the wellhead to a selected location within the tubing.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the written specification, the attached claims and the annexed drawings.

In the drawings, wherein like reference characters are used throughout to designate like parts:

FIGS. 1A and 1B are successive diagrammatic sectional views of part of a well capable of an extremely high rate of production dow and provided with the novel safety devices of the present invention for automatically shutting off such flow at a subsurface level in response to damage or destruction to the well equipment thereabove;

FIG. 2 is a diagrammatic sectional view of part of the well of FIGS. 1A and 1B with a cementing tube extended through the substantially full opening in the valve of the safety device and connected and sealed to the tubing to provide a means of circulating tiuid from the wellhead to the lower end of the tubing and back;

FIGS. 2A and 2B are sectional views of a continuation of the lower end of the well of FIG. 2 and illustrating, respectively, the flow of cement downwardly through the tubing for the performance of a Bradenhead type squeeze and the reversal of llow downwardly through the annulus and upwardly through the tubing;

FIGS. 2C and 2D are views similar to FIGS. 2A and 2B, except that they illustrate a packer type squeeze and reversal; and

FIG. 3 is a sectional view of the connection and seal of the cementing tube with the tubing, as shown in FIG. 2.

According to the present invention, there is provided apparatus which includes a valve for shutting olf tlow at a subsurface level within a well conduit and which is provided with a substantially full opening therethrough to accommodate well tools. The valve is adapted to be closed by a control mechanism at surface level, and more particularly by a mechanism which includes a source of fluid under pressure for actuating a pressure-responsive means connected to the valve. The flow connection between such source and the pressure-responsive means is preferably provided with a choke to ensure a uniform effect of pressure change on such means.

A well structure is employed in-this particular embodiment of the invention which will ow a single production zone at an extremely high rate, and at the same time permit control of such flow at a subsurface level by means of only a single valve as the one embodying a part of this invention. For this purpose, the valve is provided with a llow passage having maximum capacity in its open position. The valve is also preferably constructed with its sealing surfaces protected by disposal out of the direct flow path therethrough and, for this purpose, is provided with a plug to provide an imperforate barrier across the flow passage therethrough. However, in accordance with a previously mentioned aspect of lthis invention, the plug is made removable by wire line or the like such that a substantially full opening is provided through the flow passage to accommodate well tools.

The fluid control medium for closing the valve is in turn automatically responsive to a predetermined pressure condition within the Well above the subsurface level. Thus, upon damage -or destruction to the well above this level, the flow-control apparatus serves as a safety device for automatically shutting olf oW therein. For this purpose, and in harmony with the maximum flow passage and full opening through the Valve, the automatic pressure-responsive means for the control fluid is located at surface level and, in this embodiment of the invention, comprises a pilot valve having a Huid connection between the flow wing on the wellhead and the source of control iluid. Furthermore, such a source Aof control fluid separate from that being controlled enables the valve to be opened without pumping down through the well conduit in which it is disposed.

The valve especially well suited for use with t-he subsurface safety device includes a movable valve member having a pressure-responsive surface communicating with the flow connection from the source of control fluid for urging said member to open position. The valve member is urged to closed position by a resilient means adapted to be overcome by the pressure-responsive means for opening the valve. Inasmuch as the pressure-responsive means for `opening the valve is resisted by the aforementioned resilient means, the effect of a change in pressure areas on the valve member, as it is unseated, is minimized and impact upon opening thereby reduced. On the other hand, closing impact is lessened because the valve starts to close as soon as the resilient means begins to overcome the pressure-responsive means.

The flow connection with the pressure-responsive means is preferably carried by a landing nipple for the valve and such nipple is made removable from the well such that the tlow connection can be repaired or replaced.

In accordance with the invention, control over an extremely high rate of production llow is enabled by a Well structure which includes a well tubing packed olf within a casing beneath the subsurface level and having openings therethrough beneath said packing to provide a flow path for the producing formation in the tubing-casing annulus coextensive with that through the tubing. Above the joinder of such flow paths, the tubing is provided with means for landing and sealing with the landing nipple -for the valve.

In accordance with still further novel concepts of the present invention, there is provided a tubing which mayl be extended through the well tubing such that an irnperforate lengthv thereofV may be sealed off above surface ow control means at the wellhead and below the uppermost openings or ports in the well tubing so as to bypass the subsurface as well as the surface flow controls and said openings. In this manner, there may be provided for workover purposes two separate llow paths within the well between said poinder and the wellhead. Additionally, upon closing of the previously mentioned circulating ports to ow upwardly therethrough, this tubing seres to isolate Aboth flow controls as well as the tubing-casing annulus from the high pressures involved in a'packer type squeeze.

Referring now particularly to the above-described drawings, there is shown in FIGS. 1A and 1B a well which includes conventional wellhead equipment at -surface lever and a casing 11 extending downwardly into communication with a producing formation through perforations 12. Disposed at surface lev-el adjacent the wellhead 1i) is a control system, designated in its entirety by the numeral 13, which will be described more particularly by connection with the improved safety device, which device is designated in its entirety by the numeral 14 and shown in FIG. 1A in position within the well for controlling flow of production therethrough.

Disposed within the casing and packed off as at 15 toward its lower end is a section of tubing 16 through which production may be llowed. However, this tubing section is also packed off as at 17 at a point within the casing above the lower packing 15 and below the safety device 14. Between Ithe packings 15 and 17, the tubing section 16 is provided with a number of openings or ports 18 and 19 communicating the interior of the tubing section with the `tubing-casing annulus. The openings 18 may be provided by ports in a series of conventional gas lift mandrels as shown and described, for example, on page 3988 of the 1955-56 edition of the Composite Catalog of Oil Field and Pipe Line Equipment, which mandrels make up a considerable portion of the tubing section, while the openings 19 constitute ports within a hold-down and seal assembly portion 20 of the tubing section which carries packing 17, said latter ports comprising the uppermost openings through the tubing section. It is noted that a commercial type landing nipple 21 having a substantially full opening therethrough, such as the Otis Type S shown on page 3990 of the Composite Catalog, may be provided in the tubing section 4intermediate the gas lift mandrels for locating various tools in a manner and for a purpose well known in the industry.

From the foregoing, it is apparent from FIGS. 1A and 1B that an extremely high rate of production ow is possible through the above-described subsurface well equipment. That is, production from the formation through the perforations 12 may How for a considerable length of the well through not only the tubing Ibut also the tubing-casing annulus, as shown by the broken arrows of FIGS. lA and 1B. Also, it will be appreciated that the ow through 'both these paths is joined at the openings 19 such that it may be controlled by a single safety device as at 14. In a manner to be described more fully hereinafter, the hold-down and seal assembly 20 is landed and locked in place within an enlarged portion of the casing by a latching device indicated diagrammatically at 23, and to 'be described more fully hereinafter.

Referring to FIGS. 2A to 2D, it will be seen that in accordance with conventional workover practices, an extension hanger 23a, such as the Otis Type S illustrated on pages 3988-9 of the aforementioned Composite Catalog, may be landed and sealed off as at 23b within the nipple 21 next above circulating ports 18 next above packer 1S. Additionally, however, and in accordance with this invention, a section of the safety device 14 is removed, as shown in FIG. 2 and as in a manner to be described hereinafter, to permit a tube or tubing 24 to be extended through the well tubing 16 and sealed off within the wellhead 10 by a blowout preventer valve 27 or the like disposed above the conventional control mechanism at surface level connecting with flow wing 23. This tubing 24 is connected at its lower end to the well tubing at 25 (see FIGS. 1B and 3) and sealed with respect thereto at 26 by O-rings or the like beneath ports 19.

Thus, the imperforate length of tubing 24 intermediate the seals at 27 and 26 by-passes both the surface and subsurface flow controls as well as ports 19 and cooperates with extension hangers 23a to establish two separate and concentrically arranged ow paths within the conduit which connect the wellhead and lower end of the well tubing adjacent the ports 12 at the production zone.

Referring specifically to FIGS. 2 and 2A, it will be seen Ithat a Bradenhead type squeeze may be performed by pumping cement down through the tubing 24 `and extension hanger 23a, as shown by the downwardly directed solid arrows, from the lower end of which it is forced into openings 12, as well known in the art. In this type of cement squeeze, the pressure is not so great that the casing must 'be isolated therefrom so, as shown in FIG. 2A, the mandrel next above packer 15 is left empty to permit the passage of cement therethrough and into the annulus, as shown by the upwardly directed solid arrows. Subsequent to the squeeze, circulation of fluid is reversed through the separate flow paths, as will be understood from the solid arrows of FIG. 2B and for a purpose which is'not pertainent to the present invention.

In some instances the pressures encountered in packer type squeezes are such that the casing must be isolated therefrom. Thus, as illustrated by FIGS. 2C and 2D, a suitable check valve 23C may be landed within the mandrel just above packer 15 for preventing ow upwardly therethrough and out of port 18 while permitting flow downwardly therethrough. Thus, as illustrated by the solid arrows of FIG. 2C, cement pumped downwardly through the tubing 24 and hanger 23a and into the production zone ports 12 Amay be held and the tubing-casing annulus isolated therefrom. On the other hand, the check valve 23e permits the reversal of flow shown by the solid arrows of FIG. 2D.

In accordance with the present invention, the tubing 24 also serves to isolate both the surface Iand subsurface flow controls from the high squeeze pressure. That is, as can be seen from FIG. 2, the valves and other parts of both controls which might otherwise be damaged by such pressure are by-passed iby the tubing 24.

The safety device 14, as it is shown diagrammatically in FIGS. 1A, 1B and 2, includes -a tubular member comprising a landing nipple 29 which, as shown, is releasably locked at 30 within the hold-down and seal assembly 20 and sealed with respect thereto at 31. A valve, designated in its entirety by the numeral 32, includes a body or casing 33 releasably and seal-ably lockable within and removable from the landing nipple and a valve member 34 movable within said body between open and closed posltion.

As shown in FIG. 1A, the valve member 34 is provided with a tubular part movable longitudinally within the body 33 and having -a substantially full opening or passage 35 therethrough which is closed by a plug 36 disposed within the passage ybeneath ports 37 in the valve member and sealed thereto at 3S to provide an imperforate barrier to flow therepast. The lbody 33 is provided with a tapered annular se-at 39 with which a sealing surface 40 on the movable valve member 34 is adapted to cooperate in the closed position of the valve. As it is shown in FIG. 1A, the valve is open and flow therethrough is indicated by the 'broken arrows as passing through the ports 37 and upwardly through the ow passage 35 to the wellhead 10. However, it will be understood that with the valve closed, the surface 40 seats upon the valve seat 39 to prevent passage of fluid within the well conduit through the valve member with, of course, the plug 36 landed, as shown.

It will be understood that the valve member 32 is thus operable at the subsurface level to either shut off or permit production flow at the high rate indicated. More particularly, it `controls such flow through a well conduit composed of the tubing section 16, landing nipple 29, and valve body 33. With each of the foregoing made up concentrically and sealed with respect to one another, the well conduit serves as conventional production or well tubing.

The plug 36 is releasably lockable within and removable upwardly through the valve flow passage to provide a substantially full opening through the valve through which well tools may be passed into the well conduit beneath said valve. An example of such an installation is shown in FIG. 2, wherein the movable plug or head 36 has 'been removed and the cementing tube 24 passed therethrough.

Pressure-responsive surfaces on the movable valve member 34 and the xedly landed body 33 define a variable capacity pressure chamber therebetween. Although, for the purposes of clarity, this chamber is not shown on the diagrammatic views of FIGS. 1A and 2, there is shown a ow connection thereto in the form of a pipe 42 which is extended downwardly within the tubing-casing annulus from the fiuid control system 13 at surface level.

It is preferred that the connection 42 be filled at all times with a liquid rather than a gas, such as air or nitrogen, as a quicker hydraulic reaction may thus be obtained through the liquid column. Gas or air should be used only as a means of maintaining the desired pressure and offsetting any loss of fluid through leaks in the system.

At surface level, the pipe 42 connects with a surge or volume tank, designated in its entirety by the numeral 4S, which contains control iiuid under any desired pressure. In this manner, fluid under a suit-ably high pressure may be exerted upon the pressure-responsivev means of the valve member for moving said valve member to an open position. It will be understood from the diagrammatic views that when the'yalve is closed such iluid control means acts against the pressure beneath the valve member while with the valve open it acts against the -frictional force of the liuid flowing through the valve as well as the force of such flow acting against an opposite pressure-responsive surface of the valve member.

As shown on the yblow-up in FIG. 1A, as well as on FIG. 2, a flow bean 46 is interposed in the fiow connection 42 between the source of control fluid 45 and the pressure chamber 41. This restriction in the iiow line ensures an even and uniform `distribution of pressure between the source of control fluid and the pressure chember 41, whereby impact upon movement between open and closed position of the valve member is substantially reduced. As well, it can be seen that the flow connection 42 is carried by the removable landing nipple 29 and is extended upwardly through the lower flange 47 of the wellhead 10 such that, upon removal of the wellhead, the flow connection can lbe removed with the landing nipple for repair Iand replacement, as desired. In fact, this is one of the principal reasons for providing a removable landing nipple for the valve 32.

It will be understood from the foregoing that the above-described apparatus provides a means of controlling ow through a well conduit at a subsurface level therein by means of a control system disposed at surface level and a valve member within the conduit at said subsurface level, which flow control means is provided with a substantially full opening therethrough whereby well tools and the like may lbe run therethrough. It will be further appreciated that with this arrangement the valve member may be reopened by either of two methods. According to one method, fiuid under pressure may be pumped down through the well conduit to force the valve open by exerting pressure above the removable head 36. However, an alternative method of reopening the valve is provided by the apparatus of the present invention inasmuch as the pressure of the control fluid within source 45 may be increased sufficiently to force'the v-alve open by exerting sufiicient pressure upon the pressureresponsive means of the valve member 34. It is obvious that this latter means of opening the Valve obviates the lnecessity of forcing fluid down through the well conduit and could be used to great advantage.

The remainder of the surface equipment comprises the means for automatically shutting the valve member in response to a predetermined pressure condition within the well conduit above the Valve member. Such equipment comprises pipes 48 and 51, a pilot valve 49 provided with a low-pressure type pilot 50 and a flow bean 52. The details and functioning of such equipment is fully described in our previously mentioned Patent No. 3,157,233.

The upper portion of the casing 11 is formed from large-diameter pipe which is connected at its upper end to the lower fiange 47 of wellhead 10 in a conventional manner, and at its lower end to a hold-down and seal nipple 73 (FIG. 3). A string of smaller-diameter pipe 75 may be connected to and extended downwardly from nipple 73.

The tubing section 16 includes at its upper end a holddown .and seal assembly 20, which asse-mbly has at its lower end a tubular part threadedly connected to a packer and side port nipple (FIG. 3). The packer and side port nipple 85 carries the packing 17 and has side ports 19 therebelow. The packer and side port nipple 85 also have an internal sealing surface 88 beneath side ports 19 so that the O-rings 26 carried on tube 24 may seal the exterior of tube 24 to the `sealing surface 88 below the ports 19.

The details of construction of the means 30 for releasably locking the landing nipple 29 within the tubing section 16 and of the safety device 14 do not form a part of the present invention. Such constructional details are fully illustrated and described in our previously referred to Patent No. 3,157,233.

From the the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth` together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without 4departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim is:

1. In a method of producing a well having a casing extending downwardly from the well head to a production zone and a tubing in said casing extending downwardly to said production zone, said tubing being packed to said [casing by a packer at a subsurface level near the top of the well, the steps comprising:

establishing a first ow path from said production zone to the wellhead through said tubing,

establishing a second ow path from said production zone through the tubing-casing annulus and joining said second flow path with said first flow path below and adjacent to said packer, and

controlling the flow through said tubing at a level above the level of joinder of said first and second flow paths.

2. A method of reworking a well having a casing extending downwardly from a wellhead to a production zone and a tubing in said casing extending downwardly to said production zone, said tubing being packed to said casing by an upper packer at a subsurface level in the well and :by a lower packer above the the steps comprising:

establishing a liow path from said production zone to the wellhead through said tubing; communicating said tubing with the tubing-casing annulus above said lower packer, communicating said tubing with the tubing-casing annulus below and adjacent to said upper packer, controlling the flow through said tubing at a level above the upper level of communication of said tubing with said tubing-casing annulus, establishing a rst separate How path from said Wellhead and communicating said first separate flow path with said tubing at a level below the upper level of communication of said tubing with said tubing-casing annulus, blocking ow through said tubing between the upper level of communication of said tubing with said tubing casing annulus and the level of communication of said tubing with said first separate ow path, establishing a second separate ow path from said production zone and communicating said second separate flow path with said tubing at a level above the lower level of communication of said tubing with the tubing-casing annulus, blocking ow through said tubing between the lower level of communication of said tubing with the tubing-casing annulus and the level of `communication of said tubing withlsaid second separate flow path. 3. In a method as set forth in claim 2 and further including the st-ep of:

inhibiting flow from the tubing to the tubing-casing annu-lus through the lower level of communication therebetween. 4. In a method as set forth in claim 2 and further including the step of:

allowing ow from the tubing-casing annulus to said production zone,

tubing and inhibiting flow from the tubing to said tubing-casingannulus through the lower level of communication therebetween. 5. A method of conducting ow from a well having a casing extending downwardly from thev wellhead to a production zone and a tubing in said casing extending downwardly to said production zone, said tubing ybeing packed to said casing by a packer at a subsurface level near the top of the well, the steps Comprising:

establishing a rst liow path from said production zone to the wellhead through said tubing, establishing a second flow path from said productionl zone through the tubing-casing annulus Iand joining said second flow path with said rst flow path below and adjacent to said packer, and establishing a third ow path from said Wellhead and joining said third flow path with said first flow path above the level of joinder of said rst and second flow paths, and blocking said first ow path between the levels of joinder ofsaid rst ow path with said second and third flow paths.

References Cited by the Examiner UNITED STATES PATENTS 2,416,842 3/1947 OLeary 166`27 XR 2,665,759 1/1954 Childers 166-45 XR 2,760,578 8/1956 Tausch 166-45 2,786,535 3/1957 Boer et al. 166-187 3,008,522 11/1961 Fredd et al. 166-46 XR 3,156,300 11/1964 Page et al. 166-224 XR 3,157,233 11/1964 Sizer et al. 166-102 XR CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, D. H. BROWN, Examiners.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2416842 *Jul 1, 1941Mar 4, 1947Herbert C OtisWell cementing apparatus
US2665759 *Dec 27, 1948Jan 12, 1954Baker Oil Tools IncMethod and apparatus for completing multiple production zone well bores
US2760578 *Jan 27, 1955Aug 28, 1956Exxon Research Engineering CoMethod for completion in a plurality of hydrocarbon productive strata
US2786535 *Dec 21, 1954Mar 26, 1957Exxon Research Engineering CoSubsurface blowout preventer
US3008522 *Sep 7, 1954Nov 14, 1961Otis Eng CoSelective cross-over devices
US3156300 *Aug 14, 1963Nov 10, 1964Page John SMethod and apparatus for protecting wells
US3157233 *Jun 20, 1956Nov 17, 1964Otis Eng CoApparatus for controlling flow within a well
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3426845 *Nov 29, 1965Feb 11, 1969Otis Eng CorpWell head system and method of installing the same
US3481395 *Feb 12, 1968Dec 2, 1969Otis Eng CorpFlow control means in underwater well system
US3675720 *Jul 8, 1970Jul 11, 1972Otis Eng CorpWell flow control system and method
US4473122 *Dec 14, 1983Sep 25, 1984Otis Engineering CorporationDownhole safety system for use while servicing wells
US5971004 *Mar 9, 1998Oct 26, 1999Camco International Inc.Variable orifice gas lift valve assembly for high flow rates with detachable power source and method of using same
US6068015 *Feb 5, 1999May 30, 2000Camco International Inc.Sidepocket mandrel with orienting feature
US6070608 *Aug 15, 1997Jun 6, 2000Camco International Inc.Variable orifice gas lift valve for high flow rates with detachable power source and method of using
US6148843 *Jun 16, 1998Nov 21, 2000Camco International Inc.Variable orifice gas lift valve for high flow rates with detachable power source and method of using
US6206645Apr 7, 2000Mar 27, 2001Schlumberger Technology CorporationVariable orifice gas lift valve for high flow rates with detachable power source and method of using
US6227302Jun 3, 1999May 8, 2001Cameo International, Inc.Apparatus and method for controlling fluid flow in a wellbore
US6231312Apr 7, 2000May 15, 2001Camco International, Inc.Variable orifice gas lift valve for high flow rates with detachable power source and method of using
US6305402Apr 7, 2000Oct 23, 2001Camco International Inc.Variable orifice gas lift valve for high flow rates with detachable power source and method of using
Classifications
U.S. Classification166/312, 166/72, 166/322, 166/369
International ClassificationE21B34/00, E21B34/10
Cooperative ClassificationE21B34/10
European ClassificationE21B34/10