US3799192A

US3799192A - Velocity sensitive safety valve

Info

Publication number: US3799192A
Application number: US00278319A
Authority: US
Inventors: D Young
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1972-08-07
Filing date: 1972-08-07
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26
Also published as: DE2339670A1; GB1434105A; FR2195765A1; FR2195765B1; CA984286A

Abstract

In accordance with an illustrative embodiment of the present invention, a downhole safety valve that closes automatically in response to excessive flow rate or velocity has an enlarged piston section on the upper end of the valve actuator to reduce the influence of seal friction and the like as an impediment to repetitive closing movements of the valve, and oppositely extending sleeves providing for fluid communication to the low pressure side of the piston section in such a manner as to provide a protection against damage to seal elements and surfaces by abrasive particles in the production fluids.

Description

[ Mar. 26, 1974 Primary ExaminerAlan Cohan Assistant ExaminerGerald A. Michalsky Attorney, Agent, or Firm-David L. Moseley; William R. Sherman; Stewart F. Moore 57 ABSTRACT -ln accordance with an illustrative embodiment of the present invention, a downhole safety valve that closes automatically in response to excessive flow rate or velocity has an enlarged piston section on the upper end of the valve actuator to reduce the influence of seal friction and the like as an impediment to repetitive closing movements of the valve, and oppositely extending sleeves providing for fluid communication to the low pressure side of the piston section in such a United States Patent 1 Young VELOCITY SENSITIVE SAFETY VALVE [75] Inventor: David E. Young, Friendswood, Tex.

[73] Assignee: Schlumberger Technology Corporation, New York, NY.

[22] Filed: Aug. 7, 1972 21 Appl. No.: 278,319

[52] US. 137/498, 137/460, 166/224 [51] Int. Fl6k 17/00 [58] Field of Search 137/460, 462, 498, 501;

[56] References Cited UNITED STATES PATENTS manner as to provide a protection against damage to seal elements and surfaces by abrasive particles in the production fluids.

9 Claims, 3 Drawing Figures XXXMX OA D M %@27 2 539 770 5 .W m 7 m3 3 .1 l

Pistole et al.

VELOCITY SENSITIVE SAFETY VALVE This invention relates generally to control valves used in well installations, and more particularly to a downhole safety valve that reliably 'closes with repetitive operations.

In order to provide maximum protection to the environment and to insure against loss of lives and damage to property in connection with the development of offshore oilfields, it is necessary to install a downhole safety valve that closed off the production string of a well in the event of actual or impending disaster at the surface. One typical device for serving this purpose is a so-called velocity valve that includes a spring loaded operator piston which is sealingly slidable within a housing and carries a flow restriction through which the total well flow passes. The pressure drop across the restriction acts on an area defined generally by the piston seal diameter and the bore diameter of the flow restriction to produce an upward force that is related to the flow rate or velocity. When the flow rate increases to a value sufficient to compress the spring by a predetermined amount, the valve closes to shut off the flow.

In prior devices, the valve operator piston has taken the form of a constant diameter tube whose outer periphery is sealed against the surrounding housing wall by an O-ring seal or the like. The rate of the coil spring which has been used to oppose closing movement has been relatively low since it is chosen depending upon well requirements in relation to the size of the differential pressure area whose outer boundary is defined by the seal surface for the O-ring. However it has been found that particularly under conditions calling for repetitive opening and closing movements for the valve, seal friction and other factors reduce the net amount of upward force available to cause the valve to close,

whereas it is desirable to have, if any changes are to occur, a quite substantial net upward force to ensure valve closure and to provide that extra margin that may mean the difference between successful valve operation and failure.

Accordingly, it is the principle object of this invention to provide a new and improved velocity sensitive safety valve with the valve operator piston arranged so as to minimize the influence of an increase in seal friction or the like, and thus ensure closure, particularly for conditions of repetitive valve operations.

This and other objects are attained in accordance with the concepts of the present invention through the provision of a safety valve structure comprising an inner member movable within an outer member between a lower position where a valve means actuated thereby is open and an upper position where the valve means is closed. Upward movement is caused by a force that is developed by a pressure drop across a flow restriction within the inner member, and is opposed by the reaction force of a coil spring. The magnitude of the upward force is made quite substantial in relation to prior devices of this nature by providing the upper end portion of the inner member with an outwardly directed piston section that is sealingly slidable within said outer member above a stepped diameter portion thereof with the upper face of the piston section being subject to the pressure of fluids within the inner member above the flow restriction and the lower face being subject to the pressure of the fluids below the flow restriction. Thus the area over which the pressure drop acts is made as large as is practically possible since its outer boundary is defined by the seal surface for the piston section. A relatively stronger spring is used to oppose closing movement, however, the influence is minimized that an increase in seal friction, or other factors such as galling of seal surfaces or valve clogging, would otherwise have for a given pressure drop. ln accordance with a secondary feature of the present invention, the piston section is arranged together with adjacent housing structure to substantially isolate the seal surface for the piston section from abrasives or other debris in the production fluids.

The present invention has other objects and advantages that will become more clearly apparent in connection with the following detailed description of a preferred embodiment, taken in conjunction with the appended drawings in which:

FIG. I is a schematic view of a safety valve installed downhole in an oil well; and

FIGS. 2A and 2B are longitudinal sectional views, with portions in side elevation, of a safety valve assembly in accordance with the present invention, FIG. 28 forming a lower continuation of FIG. 2A.

Referring initially to FIG. 1, a downhole safety valve installation is shown somewhat schematically. The well bore 10 is lined with casing 11 and traverses the earth formation being produced. A production string of tubing 12 extends from the surface downwardly through a typical production packer 13 having a packing element 14 that seals off the production interval from the well casing thereabove. Well fluids enter the casing 11 through perforations (not shown) and pass upwardly through the tubing string 12. At a suitable downhole location in the tubing string, usually above the packer l3,a safety valve 15 constructed in accordance with the principles of the present invention is shown attached to the lower end of a conventional wireline setting and retrieving mandrel 16 that is seated in a landing nipple 17. The mandrel 16 carries locking dogs 18 and locator keys 19 to either side of seal packing rings 20, and the upper end of the mandrel 16 is provided with a running and retrieving neck 21. The details of construction of the setting mandrel assembly, as well as the procedures for running and retrieving the assembly on wireline, are well known to those skilled in the art and form no part of the present invention.

Turning now to FIGS. 2A and 2B for a detailed illustration of the safety valve 15, and outer housing member 25 is generally tubular in form and has an upper sub 26 with internal threads 27 for connection with the lower end of the setting mandrel l6. Thesub 28 at the Iowe end of the housing member 25 is open to fluid flow at 29. The housing member 25 is formed with separate upper and

lower sections

30 and 31 that are joined by a coupling 32 having an inwardly thickened wall section. An elongated tubular inner member 35 is sealingly slidable within the housing member 25 between a lower position as shown, and an upper position, fluid leakage being prohibited by a seal ring 36 that is carried by an enlarged piston section 37 fixed to the upper end of the member 35, and a seal ring 38 on the coupling section 32. The seal ring 36 slides against the inner wall surface 39 of the upper housing section 30, and the seal ring 38 is sealed against the outer circumference 40 of the inner member 35. The annular space Y 41 below the piston section 37 and above the coupling section 32 is vented externally of the housing by one or more ports 42.

A lower portion of the inner member 35 has an outwardly directed shoulder 44 that is engaged by the lower end of a coil spring 45, the upper end thereof pressing against the lower end face 46 of the coupling section 32. The coil spring 45 functions to yieldably resist upward movement of the inner member 35 in a predetermined manner. A tubular valve element 47 is threaded into the lower end of the member 35 and has several lateral flow ports 48 located above a barrier 49 that closes the lower end of the bore 50 in the inner member 35. The upper end face 51 of the valve element 47 retains an annular flow restriction in the form of a bean or choke 52 against a transverse shoulder 53.

A valve seat ring 60 is retained above an inwardly directed shoulder 61 on the lower housing section 31 and is sealed with respect thereto by an O-ring 62. The seat ring 60 presents an inclined stop surface 63 located just above an inwardly facing seal surface 64. The lower end portion of the valve element 47 is stepped at 65 and is provided with threads 66 by which an end cap 67 is coupled thereto. The stepped configuration provides an annular recess 68 that receives a seal assembly indicated generally at 69. The seal assembly 9 is comprised of an elastomeric packing ring 70 located between a shoulder surface 71 on the upper end of the cap 67, and an opposed shoulder surface 72 defined by compression ring 73. The compression ring 73 has an inclined upper surface 74 aligned to engage the stop surface 63 on the seat ring 60, and upon engagement can be advanced downwardly toward the fixed shoulder 7] in order to compress and expand the packing ring 70 and thereby energize it in intimate sealing contact with the seal surface 64 on the seat ring 60.

At the upper portion of the safety valve 15, an elongated, thin walled sleeve 76 extends upwardly from the piston section 37, and another thin walled sleeve 77 depends from the upper sub 26 and preferably is in laterally spaced relation to the sleeve 76. This arrangement provides a substantial fluid dead space or gravity barrier to prevent sand grains or other abrasives in the production fluids from contacting sea] surface 39 or settling out on top of the piston seal ring 36. This particular arrangement has been found to provide a substantial protection against gelling and seal failure.

In operation, the safety valve is installed by typical procedures. When the well is put on production, the fluids under flowing pressure enter the lower end opening 29 of the housing member 25 and pass upwardly around the cap 67, whereupon they enter the bore 50 of the inner member 35 via the lateral ports 48. Since the inner member 35 is sealed with respect to the housing member 25 by the

seals

36 and 38 on the piston section 37 and the coupling 32, respectively, all of the flow is constrained to pass through the flow bean 52. A pressure drop is created by the restriction afforded by the flow bean 52, developing upward force on the inner member 35 that essentially is the product of the pressure drop and the area defined between the seal surface 39 and the inner diameter of the flow bean 52, inasmuch as the upper surfaces of the piston section 37 are subject to the lesser pressure downstream (above) the flow bean 52, while the lower face thereof is subject to the greater pressure upstream of the flow bean via the vent ports 42. The upward force moves the inner member 35 upwardly by an amount dependent on the rate of the coil spring 45, which is calibrated to prohibit closing until a predetermined pressure differential corresponding to a selected flow rate is present. The rate of the spring 45 and the through bore size of the flow bean 52 are variables that can be selected to tailor the closing response of the valve to a particular well as will be appreciated by those skilled in the art.

Since a separate piston section 37 is provided at the upper end of the inner member 35 and is sealingly slidable with respect to the inner wall surface 39 of the upper housing section 30, the transverse cross sectional area that is exposed to pressure drop is made as large as is practically possible in accordance with the concepts of this invention. This construction when compared to prior art devices yields substantial improvement when it is realized that seal friction increases linearly with sea] diameter, whereas the upward force due to pressure increases with the square of the transverse dimension. Thus it has been found that the effect of seal friction, particularly insofar as it adversely affects the ability of a safety valve to reliably close repetitively, is minimized for a given pressure drop by maximizing the piston area and using a stronger srping to oppose closing movement.

As the valve element 47 reaches the upper closed position, the compression ring 73 engages the stop surface 63. Upon engagement, and under the influence of the upward force developed across the entire cross-section area bounded by the seal surface 39, the ring 73 is advanced downwardly somewhat toward the fixed shoulder 71 to compress and expand the packing ring into sealing contact with the sea] surface 64, thereby effecting a tightly sealed closure against upward flow through the ports 48 and killing the well. After closure, a full pressure differential remains applied to the inner member 35 to energize the packing ring 70in tight sealing engagement. To reopen the valve, fluid pressure is applied to the tubing string 12 at the surface to equalize pressures, whereupon the coil spring 45 forces the inner member 35 downwardly to the open position.

Since certain changes or modifications may be made in the disclosed embodiment without departing from the inventive concepts involved, it is the aim of the appended claims to cover all such changes or modifications falling within the true spirit and scope of the present invention.

I claim:

1. A safety valve apparatus comprising: housing means adapted for connection in the production string of an oil well, said housing means being generally tubular in form and having a stepped internal wall configuration providing an enlarged diameter cylinder portion and a reduced diameter bore portion; a valve actuator sealingly slidable in said bore portion between a lower position with respect to said housing means and an upper position; valve means responsive to sliding movement of said valve actuator for closing off a fluid flow passage through said housing means in the upper position of said valve actuator; yieldable means for opposing upward movement of said valve actuator; means in said valve actuator for restricting the flow of fluid through said flow passage in such a manner as to create a pressure drop, and piston means fixed to the upper end portion of said valve actuator and having its outer periphery sealingly slidable within said cylinder portion of said housing means; the downwardly facing transverse surface of said piston means being subject to the pressure of fluids externally of said housing means and the upwardly facing transverse surface of said piston means being subject to the pressure of fluids above said restricting means, whereby said pressure drop acts on an area whose outer boundary is defined by the inner wall surface of said enlarged diameter cylinder portion of said housing means to develop a substantial upward force tending to move said valve actuator toward said upper position.

2. The safety valve apparatus of claim 1 wherein said housing meansis formed by separable tubular upper and lower sections joined together by a coupling means, said upper section providing said cylinder portion and said coupling means providing said reduced diameter bore portion.

3. The safey valve apparatus of claim 2 further including at least one open port through the wall of said upper section below said piston means for subjecting said downwardly facing transverse surface of said piston means to the pressure of fluids externally of said housing means.

4. The safety valve apparatus of claim 1 further including means on said piston means and said housing means for substantially isolating said inner wall surface of said cylinder portion from abrasive particles and the like in the'production fluids.

5. The safety valve apparatus of claim 4 wherein said isolating means comprises oppositely extending, elongated sleeve members disposed in laterally spaced relationship, one of said sleeve members being fixed to said housing means and the other of said sleeve members being fixed to said piston means.

6. The safety valve apparatus of claim 5 wherein the upper end of said other sleeve member extends above the lower end of said one sleeve member to provide an elongated, annular fluid passage space of greater volume than the displacement volume of said piston means.

7. The safety valve apparatus of claim 1 wherein said valve means comprises annular seal means carried by said valve actuator and coacting in said upper position with a valve seat in said housing member to prohibit fluid flow, said seal means being disposed between spaced apart opposed shoulder surfaces that are movable relatively toward one another, and means engageable in said upper position fo moving said shoulder surfaces relatively toward one another to compress said seal means and energize it in intimate sealing contact with said valve seat.

8. A safety valve apparatus comprising: an outer member adapted for connection within the production string of an oil well; an inner member sealingly slidable within said outer member, said member defining a fluid flow passage, said inner member having a flow restriction therein for developing a pressure drop effective to apply upwardly directed froce tending to move said inner member upwardly within said outer member; valve means actuated by a predetermined extent of movement of said inner member for closing off said flow passage; means for yieldably resisting upward movement of said inner member; and means on said inner member and said outer member for substantially isolating the sea] surface between said members from abrasive particles and thelike in the production fluids, said inner member including a piston section subject to said pressure drop, said isolating means including laterally spaced, elongated sleeve members, one of said sleeve members being fixed to said piston section and extending upwardly therefrom, the other of said sleeve members being fixed to said outer member and extending downwardly within said one member.

9. The safety valve apparatus of claim 8 wherein said other sleeve member extends downwardly to a location below the upper end of said one sleeve member by an amount to provide an annular space between said sleeve members having a volume greater than the displacement volume for said piston section.

Claims

1. A safety valve apparatus comprising: housing means adapted for connection in the production string of an oil well, said housing means being generally tubular in form and having a stepped internal wall configuration providing an enlarged diameter cylinder portion and a reduced diameter bore portion; a valve actuator sealingly slidable in said bore portion between a lower position with respect to said housing means and an upper position; valve means responsive to sliding movement of said valve actuator for closing off a fluid flow passage through said housing means in the upper position of said valve actuator; yieldable means for opposing upward movement of said valve actuator; means in said valve actuator for restricting the flow of fluid through said flow passage in such a manner as to create a pressure drop, and piston means fixed to the upper end portion of said valve actuator and having its outer periphery sealingly slidable within said cylinder portion of said housing means, the downwardly facing transverse surface of said piston means being subject to the pressure of fluids externally of said housing means and the upwardly facing transverse surface of said piston means being subject to the pressure of fluids above said restricting means, whereby said pressure drop acts on an area whose outer boundary is defined by the inner wall surface of said enlarged diameter cylinder portion of said housing means to develop a substantial upward force tending to move said valve actuator toward said upper position.

2. The safety valve apparatus of claim 1 wherein said housing means is formed by separable tubular upper and lower sections joined together by a coupling means, said upper section providing said cylinder portion and said coupling means providing said reduced diameter bOre portion.

4. The safety valve apparatus of claim 1 further including means on said piston means and said housing means for substantially isolating said inner wall surface of said cylinder portion from abrasive particles and the like in the production fluids.

8. A safety valve apparatus comprising: an outer member adapted for connection within the production string of an oil well; an inner member sealingly slidable within said outer member, said member defining a fluid flow passage, said inner member having a flow restriction therein for developing a pressure drop effective to apply upwardly directed froce tending to move said inner member upwardly within said outer member; valve means actuated by a predetermined extent of movement of said inner member for closing off said flow passage; means for yieldably resisting upward movement of said inner member; and means on said inner member and said outer member for substantially isolating the seal surface between said members from abrasive particles and the like in the production fluids, said inner member including a piston section subject to said pressure drop, said isolating means including laterally spaced, elongated sleeve members, one of said sleeve members being fixed to said piston section and extending upwardly therefrom, the other of said sleeve members being fixed to said outer member and extending downwardly within said one member.