Downhole valve

Abstract

A tool that is usable with a well includes a valve element, a mechanical operator, a pressure chamber and a regulator. The valve element has a first state and a second state. The mechanical operator responds to a predetermined signature in an annulus pressure relative to a baseline level of the annulus pressure to transition the valve element from the first state to the second state. The pressure chamber exerts a chamber pressure to bias the mechanical operator to transition from the second state to the first state. The baseline level is capable of varying over time, and the regulator regulates the chamber pressure based on the baseline level.

1 . A tool usable with a well, comprising:
 a valve element having a first state and a second state;   a mechanical operator to respond to a predetermined signature in an annulus pressure relative to a baseline level of the annulus pressure to transition the valve element from the first state to the second state, the baseline level capable of varying over time;   a pressure chamber to exert a chamber pressure to bias the mechanical operator to transition from the second state to the first state; and   a regulator to regulate the second pressure based on the baseline level.   
     
     
         2 . The tool of  claim 1 , wherein the predetermined signature comprises a momentary increase in the annulus pressure above the baseline level. 
     
     
         3 . The tool of  claim 1 , wherein the tool comprises:
 a first gas chamber to store a gas; and   a compensator to isolate the gas from fluid in the annulus and communicate the predetermined signature to the first gas chamber.   
     
     
         4 . The tool of  claim 3 , further comprising:
 a second gas chamber,   wherein the mechanical operator comprises a piston to travel between an upper position and a lower position in response to a differential between a pressure exerted by the gas stored in the first gas chamber and a pressure in the second gas chamber.   
     
     
         5 . The tool of  claim 4 , wherein the mechanical operator further comprises:
 a pressure equalizer to bleed gas between the first and second gas chambers to equalize the pressure in the first and second gas chambers in response to the pressure differential.   
     
     
         6 . The tool of  claim 5 , wherein the pressure equalizer is adapted to accelerate equalization of the pressures in the first and second chambers in response to the second piston nearing the first position or the second piston nearing the second position. 
     
     
         7 . The tool of  claim 1 , further comprising:
 an indexer to establish a predetermined travel pattern from the mechanical operator before the valve element transitions from the first state to the second state.   
     
     
         8 . A method usable with a well, comprising:
 responding to a predetermined signature in an annulus pressure relative to a baseline level of the annulus pressure transition a valve element from a first state to a second state, the baseline level capable of varying over time;   exerting a chamber pressure to bias the valve element to transition from the second state to the first; and   regulating the chamber pressure based on the baseline level.   
     
     
         9 . The method of  claim 8 , wherein the predetermined signature comprises a momentary increase in the annulus pressure above the baseline level. 
     
     
         10 . The method of  claim 8 , wherein the act of regulating comprises regulating the chamber pressure to track the baseline level. 
     
     
         11 . The method of  claim 8 , further comprising:
 bleeding gas between the first and second chambers to equalize the pressure in the first and second chambers in response to a pressure differential between the first and second chambers.   
     
     
         12 . The method of  claim 8 , further comprising:
 using an indexer to establish a predetermined pressurization schedule for the annulus for the valve element to transition from the first state to the second state.   
     
     
         13 . A tool usable with a well, comprising:
 a valve element having a first state and a second state;   a spring;   a pressure chamber;   a mechanical operator to:
 respond to forces exerted in concert by the spring and the pressure chamber to bias transitioning of the valve element from the first state to the second state; and 
 respond to annulus pressure to transition the valve element from the second state to the first state. 
   
     
     
         14 . The tool of  claim 13 , wherein the spring comprises a Belleville spring. 
     
     
         15 . The tool of  claim 13 , further comprising:
 a collet to selectively restrict operation of the mechanical operator to establish a predetermined force for transitioning the mechanical operator.   
     
     
         16 . The tool of  claim 13 , wherein the pressure chamber is filled with an inert gas. 
     
     
         17 . The tool of  claim 13 , further comprising:
 an indexer to selectively restrict travel of the mechanical operator until a predetermined number of pressurization cycles occur in the well.   
     
     
         18 . A method comprising:
 biasing a valve element to transition from a first state to a second state, comprising responding to forces exerted in concert by a spring and a pressure chamber; and   responding to annulus pressure to transition the valve element from the second state to the first state.   
     
     
         19 . The method of  claim 18 , wherein the act of responding to the annulus pressure comprises transitioning a circulating valve from the second state to the first state. 
     
     
         20 . The method of  claim 18 , further comprising:
 restricting transitioning of the valve element with a collet until the forces exerted in concert by the spring and the pressure chamber exceed a predetermined threshold.   
     
     
         21 . The method of  claim 18 , further comprising:
 regulating the transition of the valve element using an indexer.   
     
     
         22 . A tool usable with a well, comprising:
 a valve element having a first state and a second state;   a first mechanical operator;   a pilot valve to control communication of an annulus pressure to the first mechanical operator; and   a second mechanical operator to respond to annulus pressure to control operation of the pilot valve,   wherein the second mechanical operator is adapted to cause pilot valve to communicate the annulus pressure to the first mechanical operator to cause the first mechanical operator to transition the valve element from the first state to the second state in response to the annulus pressure exhibiting a predetermined signature and otherwise block the communication of the annulus pressure to the first mechanical operator to cause the first mechanical operator to transition the valve element from the second state to the first state.   
     
     
         23 . The tool of  claim 22 , further comprising:
 a dump chamber to receive fluid from the first mechanical operator in response to the transition of the second mechanical operator from the second state to the first state.   
     
     
         24 . The tool of  claim 22 , further comprising:
 a compensator to transfer pressure from the annulus and isolate the annulus fluid from the second mechanical operator.   
     
     
         25 . The tool of  claim 22 , wherein the valve element comprises a circulation valve element. 
     
     
         26 . A method comprising:
 operating a pilot valve to communicate annulus pressure to a first mechanical operator to cause the first mechanical operator to transition a valve element from a first state to a second state in response to the annulus pressure exhibiting a first predetermined signature; and   using the pilot valve to block the communication of the annulus pressure to the first mechanical operator to cause the first mechanical operator to transition the valve element from the second state to the first state in response to the annulus pressure exhibiting a second predetermined signature.   
     
     
         27 . The method of  claim 26 , further comprising:
 receiving fluid from the first mechanical operator in a dump chamber in response to the transition of the second mechanical operator from the second state to the first state.   
     
     
         28 . The method of  claim 26 , further comprising:
 transferring pressure from the annulus and isolating the annulus fluid from the second mechanical operator.   
     
     
         29 . The method of  claim 26 , wherein the valve element comprises a circulation valve element.