Information
-
Patent Grant
-
6427778
-
Patent Number
6,427,778
-
Date Filed
Thursday, May 18, 200024 years ago
-
Date Issued
Tuesday, August 6, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 166 321
- 166 324
- 166 374
- 166 386
- 137 488
- 137 4925
-
International Classifications
-
Abstract
The hydraulic control system for operating a flow tube in a subsurface safety valve is disclosed. An isolation piston is used in conjunction with an operating control line and an engagement control line. Both control lines run from the surface. The isolation piston is spring loaded to equalize pressure across a dynamic piston to allow the flow tube to be shifted by a power spring to allow in turn the subsurface safety valve to close. Application of pressure on the engagement control line directs pressure applied through the operating control line to the top of the dynamic piston thus shifting the flow tube downwardly to open the subsurface safety valve. In an alternative embodiment, a coaxial control line directs fluid to the top of the dynamic piston and additionally to a parallel path leading to the bottom of the dynamic piston where a control valve is mounted. The control valve can be actuated hydraulically, electronically or other ways such that when it is closed the pressure applied to the dynamic piston shifts the flow to open the subsurface safety valve. A loss of signal to the control valve equalizes the dynamic piston allowing the flow tube to shift.
Description
FIELD OF THE INVENTION
The field that this invention relates to control systems for downhole valves and more particularly subsurface safety valves.
BACKGROUND OF THE INVENTION
Subsurface safety valves principally are designed around the concept of a spring actuated flow tube which is hydraulically operated so that when the flow tube is shifted downwardly it displaces a flapper off of a seat by rotating it ninety degrees leaving the central passage in the flow tube open. Reversal of these movements allows the spring loaded flapper to rotate ninety degrees against the seat and seal off the flow path. Control systems to actuate the flow tube into a downward motion to open the subsurface safety valve have come in a variety of configurations in the past. One of the design parameters is obviously the ability to shift the flow tube to open the subsurface safety valve. Another design parameter is to allow the hydraulic control system to have a fail safe operation in the event there are malfunctions in the system. Yet another criteria is to make such a system small and uncomplicated to ensure its reliability over an extended period of time in which the subsurface safety valve may be in operation in a well.
One of the problems of control system designs particularly in applications where the subsurface safety valve is set deeply such as depths below ten thousand feet from the surface is that the power spring on the flow tube may be required to support the hydrostatic pressure in the control lines to the dynamic piston which moves the flow tube. Since the required stroke of the flow tube is quite long, springs that can resist hydrostatic at such depths become very cumbersome. Accordingly one of the objects of the present invention is to provide a system for hydraulic flow tube control where the power spring requirements are such that it is not mandatory to be able to support the control line hydrostatic pressure in the control system. Another objective of the present invention is to eliminate charged chambers usually filled with nitrogen that have been employed in some of the designs used in the past. Another objective of the present invention is to offer a simplified system which can be easily modified for a variety of depths and can provide reliable service over a long period of time while at the same time being simple to construct and simple in its operation.
Control systems typical of those previously used can be readily understood from a review of U.S. Pat. Nos. 5310004, 5906220, 5415237, 4341266, 4361188, 5127477, 4676307, 466646, 4161219, 4252197, 4373587, 4448254, 5564501 as well as U.K. Applications 2159193, 2183695, 2047304.
SUMMARY OF THE INVENTION
The hydraulic control system for operating a flow tube in a subsurface safety valve is disclosed. An isolation piston is used in conjunction with an operating control line and an engagement control line. Both control lines run from the surface. The isolation piston is spring loaded to equalize pressure across a dynamic piston to allow the flow tube to be shifted by a power spring to allow in turn the subsurface safety valve to close. Application of pressure on the engagement control line directs pressure applied through the operating control line to the top of the dynamic piston thus shifting the flow tube downwardly to open the subsurface safety valve. In an alternative embodiment, a coaxial control line directs fluid to the top of the dynamic piston and additionally to a parallel path leading to the bottom of the dynamic piston where a control valve is mounted. The control valve can be actuated hydraulically, electronically or other ways such that when it is closed the pressure applied to the dynamic piston shifts the flow to open the subsurface safety valve. A loss of signal to the control valve equalizes the dynamic piston allowing the flow tube to shift.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic view of the preferred embodiment of the present invention showing the subsurface safety valve in the closed position.
FIG. 2
is a schematic view of an alternative embodiment of the present invention showing the subsurface safety valve in the open position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1
illustrates a flow tube
10
having a circular flange
12
on its outer periphery on which the power spring
14
delivers an upward force. The subsurface safety valve is presumed to be known by those skilled in the art. It is not depicted in FIG.
1
. Those skilled in the art already know that the movement of the flow tube
10
in a downward position which compresses the power spring
14
opens the subsurface safety valve. The reverse movement closes the subsurface safety valve.
The flow tube
10
is actuated downwardly by a dynamic piston
16
which has an upper seal
18
and a lower seal
20
. The dynamic piston
16
has a tab
22
which bears on flange
12
such that when the dynamic piston
16
is powered down, it compresses power spring
14
while moving flow tube
10
downwardly.
Running from the source of hydraulic fluid pressure at the surface are operating control line
24
and engagement control line
26
. Both lines
24
and
26
run into a housing
28
in which there is disposed an isolation piston
30
which is spring loaded by spring
32
. A seal
34
seals off the engagement control line
26
so that pressure applied in line
26
will shift the isolation piston
30
downwardly compressing spring
32
. The operating control line
24
enters housing
28
at inlet
36
. The isolation piston
30
has an upper face seal
38
and a lower face seal
40
. In the position shown in
FIG. 1
the bias of spring
32
seats the upper face seal
38
against the housing
28
. The size of the seal areas for upper face seal
38
and seal
34
are nearly the same putting the isolation piston
30
in pressure balance from applied pressures at port
36
from operating control line
24
in the position shown in FIG.
1
. Housing
28
also has outlets
42
and
44
. Outlet
42
is in fluid communication with dynamic piston
16
above seal
18
while outlet
44
is in fluid communication with dynamic piston
16
below seal
20
. There is a conduit
46
which branches into conduits
48
and
50
. Conduit
48
leads to dynamic piston
16
below seal
20
. Conduit
50
extends conduit
46
toward a coil
52
. Coil
52
has a filter
54
and is otherwise open at an outlet
56
to the surrounding annulus (not shown). Filter
54
keeps particulate matter out of coil
52
and conduit
50
.
The significant components of the preferred embodiment now having been described, its operation will be reviewed in greater detail. In order to shift the flow tube
10
downwardly against the bias of power spring
14
pressure is first applied in engagement control line
26
which downwardly shifts the isolation piston
30
against the bias of spring
32
. This downward movement of isolation piston
30
brings the upper face seal
38
away from body
28
thus opening up a flow path from inlet
36
to outlet
42
. The downward movement of isolation piston
30
ceases when the lower face seal
40
contacts the housing
28
effectively shutting off outlet
44
. Thereafter, applied pressure in operating control line
24
communicates through outlet
42
to dynamic piston
16
above seal
18
pushing downwardly and along with it tab
22
. Tab
22
in turn bears on flange
12
which in turn pushes down flow tube
10
against the power spring
14
. The subsurface safety valve is now open. The downward movement of the dynamic piston
16
with the lower face seal
40
against housing
28
will also result in displacement of fluid in conduit
50
through coil
52
and out the filter
54
through outlet
56
to the annulus (not shown).
In order to close the subsurface safety valve, the pressure on the engagement control line
26
is removed. The spring
32
which is sufficiently strong to resist the hydrostatic pressure in engagement control line
26
lifts the isolation piston
30
upwardly so as to move the lower face seal
40
away from housing
28
which in turn allows outlet
42
and
44
to communicate through housing
28
which has the effect of equalizing pressure on the dynamic piston
16
above and below seals
18
and
20
respectively. When this occurs, the power spring
14
can then move the flow tube
10
upwardly to allow the subsurface safety valve to close.
Clearly, if pressure is lost due to leakage or other surface system failures in the engagement control line
26
the flow tube
10
will shift upwardly as pressure is equalized across the dynamic piston
16
due to spring
32
shifting the isolation piston
30
upwardly. A leakage around the lower face seal
40
will equalize pressure on the dynamic piston
16
which will allow the flow tube
10
to move upwardly. As previously stated, a leakage past seal
34
will prevent movement of isolation piston
30
against spring
32
and should result in a closure of the subsurface safety valve by movement upwardly of the flow tube
10
.
A leakage around seal
18
when the flow tube
10
is in the down position will most likely leak hydraulic fluid from outlet
42
into the tubular string which the subsurface safety valve was mounted. A leakage around seal
20
may allow the annulus to leak into the tubular through outlet
56
if the annulus pressure exceeds the tubular pressure. If it is the other way, and tubular pressure will leak past seal
20
and into the annulus through filter
54
. In the event of leakage around seal
18
, the hydraulic fluid in the system coming from operating control line
24
will leak into the tubular as previously stated. However, as long as pressure is maintained in the engagement control line
26
, the flow tube
10
may not rise under the force of spring
14
if spring
14
is too weak to overcome the hydrostatic pressure in operating control line
24
. Spring
14
does not need to be sized to counteract the expected hydrostatic pressure for the given depth in operating control line
24
in that upon equalization around the dynamic piston
16
the power spring
14
merely needs to overcome frictional forces and the weight of the flow tube
10
to be able to raise it up. In deep settings of the subsurface safety valve and in view of the long stroke required for the flow tube
10
having a power spring
14
sufficiently strong to able to withstand the hydrostatic in a control line such as operating control line
24
would be difficult to configure in a compact design. On the other hand, the stroke of the isolation piston
40
is very short and therefore, it is far easier to equip a spring
32
suitable for resisting hydrostatic in engagement control line
26
and keep the size of the spring
32
reasonable.
The design described in
FIG. 1
has the advantage of not needing a pressurized chamber, but in turn it has the disadvantage of displacement of hydraulic fluid into the annulus when the dynamic piston
16
is stroked downwardly to open the subsurface safety valve. Additionally, if certain types of leaks develop, the arrangement in
FIG. 1
will not necessarily fail safe unless pressure is removed from the engagement control line
26
. For example, leakage past seal
18
from outlet
42
will keep the flow tube in the down position until the leak becomes catastrophic in size or until the pressure is removed from engagement control line
26
.
Those skilled in art will appreciate that the size in the power spring
14
in the design of
FIG. 1
is independent of depth. On the other hand, the spring
32
must be substantially stiff to be able to withstand the hydrostatic in the engagement control line
26
.
The spring
32
is far smaller and can be easily changed to reconfigure a particular control system to a depth to which it will be installed.
FIG. 2
represents an alternative embodiment which schematically illustrates a coaxial control line
58
which can simultaneously convey fluid pressure into conduit
60
and carry a conductor which is optical electromagnetic or even hydraulic or electrical
62
. Conduit
60
branches into conduits
64
and
66
. Conduit
64
leads to cylinder
68
in which is a piston
70
with a peripheral seal
72
. Piston
70
is biased by a power spring
74
. Upward movement of piston
70
moves a flow tube (not shown) which in turn allows the subsurface safety valve to close. Downward movement of piston
70
compresses spring
74
and pushes the flow tube down which opens the subsurface safety valve in a known matter. Conduit
66
extends to a control valve
76
which basically functions in two positions, open and closed. The signal to open or close comes from the conduit
78
through a conductor
62
, if used, to the control valve
76
. Conduit
80
extends from control valve
76
to the cylinder
68
below piston
70
. Those skilled in art can readily appreciate that when the control valve
76
is closed and hydraulic pressure is brought to bear in conduit
64
, the piston
70
is driven down compressing the spring
74
, thus, opening the subsurface safety valve. In order to close the subsurface safety valve, the control valve
76
is opened from a signal through conduit
78
which as previously stated can be any one of a variety of different signals. With the control valve
76
in the open position the pressure equalizes between conduit
66
and
80
thus allowing the spring
74
to move the piston
70
upwardly to allow the subsurface safety valve to close. The alternative embodiment shown in
FIG. 2
is again another simplified process which uses known coaxial technology to allow a conduit for communication of a hydraulic signal to be run coaxially or contemporaneously with a signal line which can be optical, electromagnetic, electrical, hydraulic or some other type of signal for operating a bypass valve between an opened and closed position. Those skilled in art will appreciate that if the signal is lost to the valve
76
it reverts to an open position which will close the subsurface safety valve. Additionally, loss of pressure in conduit
58
will also close the valve in the normal operation.
Those skilled in art will appreciate that there are alternatives even in the preferred embodiment shown in
FIG. 1
to the isolation piston arrangement. While the isolation piston
30
has been shown to be hydraulically actuated, it can be actuated in a variety of different ways. The assembly of the housing
28
and isolation piston
30
can also be replaced by equivalent structures which allow for the normal operation of the flow tube
10
. Thus, other types of valving arrangements which selectively allow pressurization of the dynamic piston
16
and equalization around the dynamic piston
16
for normal and emergency operations are also within the preview of the invention.
The preceding description of the preferred and alternative embodiment is illustrative of the invention and is by no means a limitation of what can be claimed to be the invention which can only be seen from an examination of the claims which appear below.
Claims
- 1. A control system extending from a well surface for a subsurface valve actuated by a dynamic piston, comprising:a dynamic piston mounted in a housing having an upper and lower seal and operably connected to the subsurface valve for movement of the subsurface safety valve between an open and a closed position; an equalizing valve mounted in a second housing and movable in opposed directions; at least one control line extending exclusively from the surface to said second housing for operation of said equalizing valve in said second housing in at least one direction to move said dynamic piston in at least one direction for desired movement of said subsurface safety valve between said open and said closed positions.
- 2. The system of claim 1 wherein:said control line comprises a plurality of passages.
- 3. The system of claim 2, wherein:said passages are coaxial.
- 4. The system of claim 3, wherein:one of said passages is used to operate said equalizing valve and another passage is used to supply pressure to said dynamic piston above said upper seal in said housing.
- 5. The system of claim 1, wherein:said equalizing valve is operated optically, electromagnetically, electronically or hydraulically.
- 6. The system of claim 1, wherein:opening of said equalizing valve allows for equal pressure to exist in said housing above said upper seal and below said lower seal; said dynamic piston further comprises a return spring which is incapable of overcoming hydrostatic pressure in said housing above said upper seal.
- 7. A control system for a subsurface valve, comprising:a dynamic piston in a first housing having an upper and lower seal and a return spring acting thereon; an isolation piston in a second housing, said second housing having at least two inlets; said inlets to said second housing connected to a first and second control line, respectively; said isolation piston further comprising a closure spring which is capable of overcoming hydrostatic pressure in at least one of said control lines; whereupon movement of said isolation piston by said closure spring pressure in said housing above said upper seal is equalized with pressure below said lower seal to allow said return spring to shift said dynamic piston.
- 8. The system of claim 7, further comprising:a first and second outlets from said second housing, said outlets in fluid communication with said first housing above and below said upper and lower seals, respectively; said isolation piston further comprises opposed seals for selectively equalizing said first and second outlets and selectively isolating them from each other.
- 9. The system of claim 8, further comprising:a vent outlet to said second outlet such that hydraulic fluid is displaced past said vent outlet when said dynamic piston experiences a greater pressure above said upper seal than below said lower seal.
- 10. The system of claim 8, further comprising:an inlet seal on said isolation piston to allow pressure buildup in said second inlet to shift said isolation piston against the force of said closure spring.
- 11. The system of claim 10, wherein:said first inlet is disposed in said second housing between said inlet seal and said opposed seals on said isolation piston; said isolation piston in substantial pressure balance from applied pressure from said first inlet.
- 12. The system of claim 11, wherein:said opposed seals comprise an upper and lower face seals, said upper face seal engaged by a force applied by said closure spring, whereupon said lower face seal is disabled to equalize said first and second outlets.
- 13. The system of claim 12, wherein:said lower face seal is energized in said second housing by pressure in said second inlet which overcomes said closure spring, whereupon said first inlet is aligned to said first outlet and isolated from said second outlet.
- 14. The system of claim 7, wherein:said return spring is weaker than hydrostatic pressure in said first housing above said upper seal.
- 15. The system of claim 9, further comprising:a coil and filter connected to said vent outlet.
- 16. The system of claim 7, further comprising:two control lines connected respectively to said first and second inlets of said second housing.
- 17. The system of claim 7, further comprising:one control line having discrete passages for connection to said first and second inlets of said second housing.
- 18. The system of claim 17, wherein:said passages are coaxial.
- 19. A control system for a subsurface safety valve comprising:a dynamic piston in a first housing with a return spring acting thereon, said dynamic piston comprising an upper and a lower seal and said return spring being weaker than hydrostatic pressure on said dynamic piston acting above said upper seal; an isolation piston in a second housing having two control lines connected thereto said isolation piston acted on by a closure spring which overcomes hydrostatic pressure in one of said control lines; said second housing in fluid communication with said first housing; said isolation piston movable from a first position where the pressure in said first housing above said upper seal is equalized with the pressure below said lower seal, and a second position where applied pressure in one of said control lines can put an unbalanced force on said dynamic piston in said first housing and above said upper seal.
- 20. The system of claim 19, wherein:pressure must be applied in both control lines to first overcome said closure spring and second to direct pressure to said first housing above said upper seal as a result of shifting of said isolation piston.
US Referenced Citations (20)
Foreign Referenced Citations (5)
Number |
Date |
Country |
0038034 |
Oct 1981 |
EP |
2047304 |
Apr 1979 |
GB |
2159193 |
May 1984 |
GB |
2183695 |
Nov 1985 |
GB |
2309241 |
Jul 1997 |
GB |