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.

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.