U.S. patent application number 09/204103 was filed with the patent office on 2002-06-20 for downhole tool utilizing opposed pistons.
Invention is credited to MOORE, RANDAL.
Application Number | 20020074129 09/204103 |
Document ID | / |
Family ID | 22756633 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074129 |
Kind Code |
A1 |
MOORE, RANDAL |
June 20, 2002 |
DOWNHOLE TOOL UTILIZING OPPOSED PISTONS
Abstract
A subsurface safety valve has a tubular valve housing, a valve
closure member movable between an open and a closed position, an
axially movable opening flow tube for opening the valve closure
member. Hydraulic pressure from a control line is used to move a
first piston, which in turn moves the axially movable opening prong
through the closure member. A balance line can be used to provide a
hydrostatic pressure against a second piston. The first and second
pistons are coupled to a sliding member within the valve housing.
Thus, the opposed piston arrangement substantially offsets any
downward force on the first piston.
Inventors: |
MOORE, RANDAL; (CARROLLTON,
TX) |
Correspondence
Address: |
DAVID W CARSTENS ESQ.
CARSTENS YEE & CAHOON, L.L.P.
13760 NOEL ROAD
SUITE 900
DALLAS
TX
75380
US
|
Family ID: |
22756633 |
Appl. No.: |
09/204103 |
Filed: |
December 1, 1998 |
Current U.S.
Class: |
166/375 ;
166/321; 166/324; 166/386 |
Current CPC
Class: |
E21B 2200/05 20200501;
E21B 34/10 20130101 |
Class at
Publication: |
166/375 ;
166/386; 166/324; 166/321 |
International
Class: |
E21B 034/10 |
Claims
We claim:
1. A downhole tool having an element movable by a piston force
between a first and second position comprising: (a) a valve
housing; (b) a first piston movable within the housing; (c) a
second piston movable within the housing, wherein the first and
second pistons are coupled to each other.
2. The downhole tool of claim 1 further comprising: (d) a valve
closure member captured in the housing and movable between an open
and closed position; (e) an axially shiftable flow tube captured in
the housing for opening the valve closure member.
3. The downhole of claim 1 wherein the first piston is coupled to a
control line.
4. The downhole tool of claim 3 wherein the second piston is
coupled to a balance line.
5. The downhole tool of claim 2 further comprising: (f) a spring
within the housing and opposing the motion of the axially shiftable
flow tube.
6. The downhole tool of claim 1 wherein the first and second
pistons are coupled to a movable member.
7. The downhole tool of claim 1 further comprises first and second
control lines coupled to a surface pressure source.
8. The downhole tool of claim 4 wherein the valve housing comprises
a first and second piston chamber for capturing the first and
second pistons, and wherein the control line and balance line are
coupled to the valve housing to move the pistons in opposite
directions.
9. The downhole tool of claim 4 wherein the valve housing comprises
a first and second piston chamber for capturing the first and
second pistons, and wherein a hydrostatic pressure is applied by
the balance line to the second piston which is substantially equal
and offsetting to a hydrostatic pressure applied by the control
line to the first piston.
10. A method of operating a downhole tool placed in the flow path
of a well tubing string within a well, comprising the steps of: (a)
coupling a control line to a first piston chamber having a first
piston; (b) coupling a balance line to a second piston chamber
having a second piston; and (c) coupling both the first and second
pistons to a movable member.
11. The method of claim 10 further comprising: (d) supplying a
substantially equal hydrostatic pressure through both the control
line and the balance line.
12. The method of claim 10 further comprising: (d) supplying a
sufficient pressure through the control line to move the first
piston downward.
13. The method of claim 12 further comprising: (e) overcoming an
opposing spring force; and (f) forcing an opening prong through a
closure member.
14. A safety valve for use in a well comprising: (a) a valve
housing; (b) a first piston movable within the housing; (c) a
second piston movable within the housing; wherein the first and
second pistons are coupled to each other; (d) a valve closure
member captured in the housing and movable between an open and
closed position; (e) an axially shiftable flow tube captured in the
housing for opening the valve closure member.
15. The safety valve of claim 14 wherein the first piston is
coupled to a control line.
16. The safety valve of claim 14 wherein the second piston is
coupled to a balance line.
17. The safety valve of claim 14 wherein the valve housing
comprises a first and second piston chamber for capturing the first
and second pistons, and wherein the control line and balance line
are coupled to the valve housing to move the pistons in opposite
directions.
18. The safety valve of claim 14 wherein the valve housing
comprises a first and second piston chamber for capturing the first
and second pistons, and wherein a hydrostatic pressure is applied
by the balance line to the second piston which is substantially
equal and offsetting to a hydrostatic pressure applied by the
control line to the first piston.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates to a downhole tool such as a
subsurface safety valve and, more particularly, to a subsurface
safety valve having a tubular housing and an axially shiftable flow
tube used to manipulate a valve closure member.
[0003] 2. Description of Related Art
[0004] Subsurface safety valves (SSSVs) are used within well bores
to prevent the uncontrolled escape of well bore fluids, which if
not controlled could directly lead to a catastrophic well blowout.
Certain styles of safety valves are called flapper type valves
because the valve closure member is in the form of a circular disc
or in the form of a curved disc. These flappers can be opened by
the application of hydraulic pressure to a piston and cylinder
assembly to move an opening prong against the flapper. The opening
prong is biased by a helical spring in a direction to allow the
flapper to close in the event that hydraulic fluid pressure is
reduced or lost.
[0005] FIGS. 1a and 1b illustrate a standard safety valve
configuration wherein a safety valve 10 is interposed in a tubing
string 12. A control line 16 is used to open the valve. The valve
10 includes a tubular valve housing 14 with an axial passage 20.
When hydraulic pressure is applied through port 22, the pressure
forces a piston 24 to engage an axially shiftable control rod 26
which is coupled to an opening prong 30. As the pressure forces the
piston downward, the opening prong 30 engages the closure member 32
and pushes the member into an open position. A spring 28 opposes
the motion of the piston so that when the hydraulic pressure is
released, the piston and opening prong 30 are returned to a first
position. The weight of the hydraulic fluid produces a hydrostatic
"head" force against the piston, and thus is a factor in sizing the
spring 28. In general, the pressure required to close the valve 10
is given by:
Pressure.sub.closing=Force.sub.spring/Area.sub.piston
[0006] Setting subsurface safety valves deeper is typically just a
matter of ensuring sufficient closing pressure to offset the
hydrostatic pressure acting to cause the valve to stay open.
Increasing closing pressure is accomplished by increasing the
Force.sub.spring term or decreasing the Area.sub.piston term.
[0007] As the valve closing pressure increases, so does the valve
opening pressure. The surface capacity to provide operating
pressure is a combination of the pressure needed to open the valve
and the wellbore pressure:
Pressure.sub.surface=Pressure.sub.opening+Pressure.sub.well
[0008] However, the umbilical line used to deliver the hydraulic
pressure can limit the available surface operating pressure. Thus,
if the surface pressure is fixed and the well pressure increases
with depth, the opening pressure decreases with depth. To
compensate for changes in pressure, the valve requires changes in
the spring force or piston area in accordance with the above
formulas, thus requiring customization of the valve depending on
the depth at which it will be placed. Design considerations of the
well, string, and tools involved can also make such valve designs
impractical at lower well depths.
[0009] For these reasons, designs which operate independent of well
pressure are required. Two well-known designs are the dome charges
safety valves and balance lines safety valves. A balance line valve
40 having a piston 48 in a housing 42 is illustrated in FIG. 2. Two
hydraulic chambers are pressurized on opposite sides of the piston
48. A control line is coupled to a first port 44 while the balance
line is coupled to a second port 46. Each hydraulic line is filled
with the same type of fluid. Hydrostatic pressure above and below
the piston is equal. Thus, there is no downward force on the spring
as a result of the hydrostatic pressure. The valve is operated by
pressurizing the upper chamber. This increases the downward force,
displacing fluid from the lower chamber and compressing the spring
50 to open the valve. Well pressure only has access to the seal
diameters with cross sectional areas A and A'.
[0010] Well pressure acts upwards on A' and downwards on A. A and
A' are equal, therefore well pressure has no upward or downward
force on the piston as long as the seals at A and A' remain intact.
Control line pressure acts downward on B-A while balance line
pressure acts upward on B-A'. Thus, the hydrostatic pressures on
opposite sides of the piston 48 are equalized. If seal 52 fails,
well pressure enters the balance pressure chamber, acting on B-A,
and increasing F3. If the well pressure is great, it may be
impossible to supply sufficient surface pressure to the control
line to force the opening prong downward. Thus, the safety valve
fails to a closed position. If seal 54 fails, well pressure would
enter the control chamber and act on B-A', increasing F1. Without
applying control line pressure, F1 could be greater than F2+F3. If
F1 is greater than F2+F3, this imbalance causes the valve to fail
in an open position. The valve can be closed by pressuring up the
balance line so that F3+F2 is greater than the well assisted F1.
This is only possible if sufficient balance line pressure can be
applied. Another failure mode occurs when gas in the well fluid
migrates into the balance line, reducing the hydrostatic pressure
applied by the balance line, i.e. reducing F3.
[0011] Another style of balance line safety valve is illustrated in
FIG. 3. The valve 60 has a piston 64 captured within a housing 62
and three hydraulic chambers 68, 70, and 72, two above and one
below the valve piston 64. Two control lines are run to the
surface. Well pressure acts on seals 74, 80. Since the piston areas
A and A' are the same, well pressure has no influence on the
pressure required to displace the piston. Control line and balance
line hydrostatic pressures act on identical piston areas B-A' and
B-A", so there is no net upward or downward force. If seal 74
leaks, well pressure accesses the balance line system. This
pressure acts on area B-A", boosting force F3, which with F2 will
overcome F1, to close the valve. If seal 76 leaks, communication
between the control and balance lines will be established. F1 will
always equal F3. Thus, F2 will be the only active force causing the
valve to close. If seal 78 leaks, it has the same effect as seal 76
leaking. If seal 80 leaks, tubing pressure accesses the balance
line system. This pressure acts to increase F3, overcoming F1 and
closing the valve. Thus, if sufficient control line pressure is
available and tubing pressure is relatively low, it may be possible
to open the valve if seals 72 and/or 80 leak. Control line force F1
is greater than the tubing assisted balance force F3 with the
spring force F2. In all modes of failure for this valve, the valve
fails permanently to a closed position.
[0012] A dome charge safety valve uses a captured gas charge. The
gas charge provides a heavy spring force to achieve an increased
closing pressure. However, dome charge designs are complex and
require specialized manufacturing and personnel. This increases the
cost and decreases the reliability of the design because numerous
seals are required. Also, industry standards favor metal-to-metal
(MTM) sealing systems. Gas charges require the use of elastomeric
seals.
[0013] A need exists for a safety valve suitable for deep setting
depth applications and which is well pressure insensitive. Thus, it
should incorporate the benefits of a balance line SSSV. Such a
design should utilize a metal-to-metal sealing system for increased
reliability and also allow for the application of balance line
pressure to cycle the valve's flow tube, thus opening the valve.
Further, the design should minimize operational friction to reduce
the required spring force to close the valve.
SUMMARY OF THE INVENTION
[0014] The present invention relates to an improved method of
actuating a downhole safety valve that uses a pair of opposed
pistons connected to individual control lines that are run to the
surface. The hydrostatic pressure in the control line and balance
line affects both pistons equally, thereby canceling out any net
affect. The pistons are situated in the valve housing so that one
will tend to ascend in reaction to the hydrostatic pressure, while
the other piston will tend to descend. Both are coupled to a common
axially movable member within the valve.
[0015] To open the valve, the control line attached to the first
piston is pressurized. The increased pressure forces the piston
downward until it rests against a downstop. The distal end of the
piston is attached to an axially movable flow tube that pushes
through the closure member of the valve thereby opening the valve's
central passage. A compression spring opposes the motion of the
piston. Therefore, when the opening pressure subsides, the
compression spring will return the flow tube to its original
position, allowing the closure member to close.
[0016] This arrangement allows for the isolation of the valve from
effects of hydrostatic pressure and wellbore pressure. It also
provides a method of positively closing the valve in the event of a
failure. The present invention also uses MTM and non-elastomeric
sealing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself however,
as well as a preferred mode of use, further objects and advantages
thereof, will best be understood by reference to the following
detailed description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
[0018] FIGS. 1a and 1b illustrate a prior art safety valve having a
single control line; FIG. 2 illustrates a balance line safety valve
having a balance line; FIG. 3 illustrates an improved prior art
balance line safety valve; FIGS. 4a, 4b and 4c are sectional views
of an embodiment of the present invention with the closure member
in the closed position; and
[0019] FIGS. 5a, 5b, and 5c are sectional views of the present
invention with the closure member in an open position.
DETAILED DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 4a, 4b and 4c provide partial sectional views along
the length of a safety valve 100 that embodies the present
invention. The safety valve 100 has an outer tubular housing that
defines a central passage 122. The outer housing can be constructed
of several sections 102, 104, 106, and 108. Each section can be
coupled by threaded connection during the construction of the valve
100. The housing defines a number of inner structures, including
piston chambers 110 and 112. The piston chamber 110 is coupled to
control line 114, while piston chamber 112 is coupled to balance
line 116. Both the control line and the balance line can be coupled
to a surface pressure source. The weight of the hydraulic fluid in
the control line and the balance line produces a hydrostatic force
within the chambers 110, 112.
[0021] Pistons 118 and 120 are captured in chambers 110, 112
respectively. In a static situation, the hydraulic fluid in the
control line and the balance line should exert a substantially
equal and offsetting force on the pistons. To open the valve, only
control line 114 is pressurized. When sufficient pressure is
applied, piston 118 moves downward compressing spring 128. The
piston simultaneously acts on movable member 124 and opening prong
130. The pistons are both coupled to a movable member 124. Thus,
when piston 118 descends in chamber 110, piston 120 also descends
in chamber 112. Likewise, the distal end 130a of the opening prong
130 contacts the closure member 132 of the valve. The closure
member 132 is hinged at 134, allowing it to pivot to an open
position. The piston 118 can travel between upstop 140 and downstop
142.
[0022] FIGS. 5a, 5b, and 5c illustrate the closure member in the
open position. Note that the spring 128 is shown in a compressed
state. The closure member 132 is in an open position, allowing well
fluids to pass through the central passage of the valve. The distal
end 130a of the opening prong rests against a stop 136. In the
event that the safety valve becomes stuck in an open state,
pressure can be applied to the balance line 116, thus moving piston
120 upward in chamber 112. The movable member 124 and piston 118
also move upward in conjunction with the piston 120. The ability to
cycle the motion of the valve through the use of the balance line
is an improvement over prior art valves.
[0023] Although preferred embodiments of the present invention have
been described in the foregoing Detailed Description and
illustrated in the accompanying drawings, it will be understood
that the invention is not limited to the embodiments disclosed, but
is capable of numerous rearrangements, modifications, closure
member types and substitutions of steps without departing from the
spirit of the invention. Accordingly, the present invention is
intended to encompass such rearrangements, modifications, closure
member types and substitutions of steps as fall within the scope of
the appended claims. This embodiment is not limited to tubing
conveyed safety valves, but encompasses wireline-conveyed safety
valves, sliding side door devices, and other downhole tools that
are movable.
* * * * *