U.S. patent application number 11/833378 was filed with the patent office on 2009-02-05 for shape memory alloy closure spring for subsurface safety valves triggered by well fluids.
Invention is credited to David Z. Anderson, Darren E. Bane, Steve Rosenblatt.
Application Number | 20090032237 11/833378 |
Document ID | / |
Family ID | 40337044 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090032237 |
Kind Code |
A1 |
Bane; Darren E. ; et
al. |
February 5, 2009 |
Shape Memory Alloy Closure Spring for Subsurface Safety Valves
Triggered by Well Fluids
Abstract
A shape memory material is used for a power spring in a
subsurface safety valve. The spring is sized for the force it will
deliver when it goes past its transition temperature and reverts to
an original shape. The force released by having the spring pass its
transition temperature holds the valve closed against hydrostatic
pressure. Since the force exerted by the spring does not increase
as the valve opens less force is required to hold the valve in the
open position, thus lowering opening pressure. The trigger to cross
the transition temperature comes from the expected temperature of
well fluids at the mounting position of the subsurface safety
valve. Other downhole applications are anticipated.
Inventors: |
Bane; Darren E.; (Broken
Arrow, OK) ; Anderson; David Z.; (Glenpool, OK)
; Rosenblatt; Steve; (Houston, TX) |
Correspondence
Address: |
DUANE MORRIS LLP - Houston
3200 SOUTHWEST FREEWAY, SUITE 3150
HOUSTON
TX
77027
US
|
Family ID: |
40337044 |
Appl. No.: |
11/833378 |
Filed: |
August 3, 2007 |
Current U.S.
Class: |
166/53 |
Current CPC
Class: |
E21B 2200/05 20200501;
E21B 34/10 20130101 |
Class at
Publication: |
166/53 |
International
Class: |
E21B 43/12 20060101
E21B043/12 |
Claims
1. A downhole tool, comprising: a body; a movable member in said
body biased in at least one direction with a biasing member whose
output of force is increased beyond an initial value upon assembly
into said body by exposure to well fluids.
2. The tool of claim 1, wherein: said exposure is to the
temperature of well fluids.
3. The tool of claim 2, wherein: said biasing member comprises at
least one spring.
4. The tool of claim 3, wherein: said at least one spring is made
from a shape memory alloy.
5. The tool of claim 4, wherein: said movable member comprises a
flow tube in a subsurface safety valve.
6. The tool of claim 4, wherein: said movable member comprises a
torsion spring on a pivot of a flapper in a subsurface safety
valve.
7. The tool of claim 4, wherein: said movable member comprises an
equalizer valve in a flapper in a subsurface safety valve.
8. The tool of claim 5, wherein: said movable member comprises a
torsion spring on a pivot of a flapper in a subsurface safety
valve.
9. The tool of claim 8, wherein: said movable member comprises an
equalizer valve in a flapper in a subsurface safety valve.
10. The tool of claim 4, wherein: said shape memory material is
raised above its transition temperature only by the normal
temperature of well fluid.
11. The tool of claim 4, wherein: said at least one spring
comprises a plurality of springs with at least one spring not being
made from a shape memory alloy.
12. The tool of claim 4, wherein: said spring provides a near
linear force along the movement range of said movable member.
13. The tool of claim 12, wherein: said movable member comprises a
flow tube in a subsurface safety valve.
Description
FIELD OF THE INVENTION
[0001] The field of this invention is subsurface safety valves for
downhole use and more particularly operating systems for the
flapper that employ one or more closure springs made of a shape
memory alloy.
BACKGROUND OF THE INVENTION
[0002] Subsurface safety valves are emergency devices that shut in
a well. They are typically an integrated portion of a production
string and are actuated through one or more control lines that run
parallel to the production conduit in the surrounding annular
space. Typically, these valves require pressure in the control line
to hold the valve open and the valve closes on loss of or removal
of control line pressure. These valves have a hinged valve member
called a flapper that can pivot from being on a seat to define the
valve closed position to being rotated off the seat to define the
valve open position. Typically the control lines lead to an
operating piston in the valve housing and that operating piston is
linked to a flow tube that is biased by a closure spring. Applied
control line pressure pushes the operating piston and takes the
flow tube with it against the force of the closure spring. When the
flow tube is forced down, it contacts the flapper that is then on
the seat and rotates the flapper 90 degrees as it moves in front of
the flapper so that flow can occur through the bore in the flow
tube. The hinge for the flapper is biased by a torsion spring. When
control line pressure is removed or lost, the closure spring
releases its stored energy and pushes up the flow tube allowing the
torsion spring to rotate the flow tube back to its seat for the
valve closed position.
[0003] Springs to operate valves downhole that were made from shape
memory alloys (SMA) have been suggested in U.S. Pat. Nos.
4,619,320; 5,199,497 and 6,433,991. In each instance a source of
heat was provided to bring the SMA beyond the critical temperature
to get it to change dimension and move a valve actuating member.
These auxiliary heat sources were wire heaters, an exothermic
chemical reaction or infrared or microwave energy. In each
instance, the dimension change from the heating was used to have
the SMA revert to a previous dimension that is usually longer to
push another member.
[0004] What was not provided by the prior art and is addressed by
the present invention is using a SMA for a closure spring where the
material selected is such that the expected temperature of the well
fluids keeps the SMA spring above its critical temperature and lets
it operate in its normal fashion.
[0005] Prior to raising the SMA spring above its critical
temperature, it does not operate as a conventional spring. It has
no memory and produces zero spring force. Once the critical
temperature is exceeded, the SMA material changes state and gains
memory, producing a spring force; at which time a finite
temperature range exists in which the spring force remains near
constant along a finite stroke of the spring. For example, as the
spring is compressed the force produced by the spring remains near
constant.
[0006] This can be advantageous for the following reason: downhole
tools are often designed to have a predetermined amount of spring
force in its more uncompressed position. When moving parts force
the spring into a more compressed position the force increases
according to the spring constant. The biasing force that works
against the spring to force the tool into the desired position must
overcome this increased spring force. Since an SMA spring whose
critical temperature has been exceeded produces a similar force at
different compression lengths the force required to hold the
downhole tool in a position in which the spring is further
compressed relative to its initial length does not increase as the
spring is compressed. This results in less force being required to
hold a tool in a position in which a spring is compressed when
using an SMA spring in comparison to a conventional spring,
resulting in a lower opening/shifting pressure/force.
[0007] The SMA spring can be used by itself or in multiple
quantities or mixed with traditional spring designs such as those
made of steel. An individual spring can have a mix of materials
such as SMA and steel. Auxiliary energy inputs to get above the
critical temperature are not used. The well fluid temperature is
high enough with the properly selected SMA to come to an
equilibrium temperature above the critical SMA temperature. These
and other features of the present invention will be more readily
understood by those skilled in the art from a review of the
description of the preferred embodiment and the associated drawing
while recognizing that the claims are the full measure of the
invention.
SUMMARY OF THE INVENTION
[0008] A shape memory material is used for a power spring in a
downhole tool an example of which is a subsurface safety valve. The
spring is sized for the force it will deliver when it goes past its
transition temperature and reverts to an original shape. Opening
pressures are lower because the spring force in the compressed
position is lower for an SMA spring than a non-SMA spring. The
trigger to cross the transition temperature comes from the expected
temperature of well fluids at the mounting position of the downhole
tool.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a section view of a subsurface safety valve
showing the power spring made of a shape memory material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0010] FIG. 1 shows a subsurface safety valve S that has an upper
sub 10 connected to a lower sub 12 by a body 14. A seat 18
surrounds a passage 16 with a flapper 20 rotatably mounted onto
pivot assembly 22 which can also include a torsion spring to bias
the flapper 20 into contact with seat 18. A flow tube 24 is moved
against the flapper 20 to rotate the flapper about pivot assembly
22 as the flow tube continues to move down in front of the flapper
20 to define the valve S open position. This downward movement of
the flow tube 24 occurs against the force of a power spring 26. A
control line from the surface (not shown) is connected at
connection 28 to selectively power a piston 30 that is operably
connected to the flow tube 24. The power spring 26 is strong enough
to push the flow tube 24 up with piston 30 against hydrostatic
pressure in the control line to allow the flapper 20 to be rotated
about pivot assembly 22. In normal operation of the valve S
pressure is applied to connection 28 to move the piston 30 and with
it the flow tube 24 down against the power spring 26 so as to
contact the flapper 20 and rotate it away from seat 18 to open up
passage 16. To close the valve S, the pressure applied in the
control line is removed to allow the power spring to overcome the
hydrostatic pressure in the control line and reverse the movements
just described to allow the flapper 20 to be rotated toward seat 18
by the pivot assembly 22. Variations on this design are possible
such as by using a pressurized chamber in the valve S to counteract
control line hydrostatic pressure or by running a second control
line from the opposite end of the piston 30 back to the surface to
neutralize the effect of hydrostatic pressure in the control line.
With these variations, the power spring 26 can be sized smaller as
it no longer has to overcome the force of control line hydrostatic
pressure but the tradeoff is the valve gets more complicated and
expensive to build or to run into the well due to the additional
control line.
[0011] The preferred material for the power spring 26 is a shape
memory alloy whose transition temperature will be exceeded by the
expected well fluid temperature. The power spring 26 is reformed
from its original shape before being mounted in position against
the flow tube 24. When the valve S is lowered into position in the
wellbore, the well fluids raise the temperature of the spring 26
above its transition temperature. That causes it to seek its
original dimension and shape. At this time the SMA spring gains
spring force which translates against the flow tube 24 to resist
control line hydrostatic. As the valve opens the spring force
remains near constant due to the properties of the SMA material.
Opening pressures are lower because the spring force in the open
position is lower for an SMA spring than a non-SMA spring. Since
the temperature of well fluids at the expected depth is generally
known within a narrow range ahead of the placement of the valve S,
an appropriate material such as a shape memory alloy can be
selected so that the expected well temperatures will elevate its
temperature to above its transition temperature before the valve S
is placed in service. In this manner, there doesn't need to be any
artificial stimulus built into the tool that can malfunction. The
temperature of well fluids is a heat source that is ever present
and needs no equipment to enable using it. In this manner the cost
of a downhole tool can be reduced and its reliability enhanced. The
spring or other force storing component can be made smaller for the
same ultimate output force as a steel counterpart.
[0012] While the preferred embodiment is a subsurface safety valve,
other types of downhole tools are envisioned that use a force
storing member to create movement in a downhole tool. Even in the
context of a subsurface safety valve, the torsion spring that is
part of the pivot assembly 22 can be made of a shape memory alloy
that will cross its transition temperature when exposed to well
fluids at its installed location. Some subsurface safety valves
employ flapper equalizer valves that are spring loaded valve
members in the flapper designed to be contacted by a flow tube
before a flapper is pushed out of contact with its seat so as to
equalize pressure across the closed flapper before an attempt is
made to open it. The spring in a flapper equalizer valve can be
made from a shape memory alloy and take advantage of the
temperature of well fluid to release additional force so that it
can be designed to be even smaller than if it were made with
traditional materials such as steel. Other downhole tool
applications are contemplated. Other materials that respond to
thermal energy of well fluid for a boost in output force are also
contemplated.
[0013] Other applications are envisioned particularly those that
allow flow to reach the spring during normal operation so as to
gain a greater certainty of expected well temperatures being at or
above the critical temperature. Closing off flow can change well
temperatures as can surface initiated operations such as injection
operations. Applications such as sliding sleeves would leave a
spring exposed to flowing well fluids despite the position of the
valve, for example. Alternatively, a backup source of energy can be
provided either independently of the SMA spring or integral to its
design to ensure the availability of enough force for expected
operations even if well temperatures take an excursion below the
critical temperature. One example can be an auxiliary heater that
can be automatically actuated on sensing of a low well fluid
temperature.
[0014] The above description is illustrative of the preferred
embodiment and many modifications may be made by those skilled in
the art without departing from the invention whose scope is to be
determined from the literal and equivalent scope of the claims
below.
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