Pressure management system for a well annulus

1. A pressure maintenance system for an annulus of a well, comprising:

a passive accumulator coupled to the annulus to accept fluid expanding in the annulus or to supply fluid to replace fluid contracting in the annulus;

a gas pressure system to maintain a gas in a headspace over the fluid in the passive accumulator;

a pressure controller to maintain pressure in the headspace within a set range

a production valve to block a flow of a production fluid from the well in response to fluid expanding in the annulus: and

a production valve controller to maintain the blocked flow of production from the well while the accepted fluid in the passive accumulator passively flows back into the annulus as the well cools.

2. The pressure maintenance system of claim 1 , wherein the passive accumulator comprises a group of interconnected vessels.

3. The pressure maintenance system of claim 1 , wherein the gas pressure system comprises a nitrogen plant.

4. The pressure maintenance system of claim 3 , where the nitrogen plant comprises a nitrogen membrane system.

5. The pressure maintenance system of claim 3 , wherein the nitrogen plant comprises a pressure swing adsorption system.

6. The pressure maintenance system of claim 1 , wherein the gas pressure system comprises gas storage tanks.

7. The pressure maintenance system of claim 1 , wherein the pressure controller comprises a gas feed valve coupled to a gas storage system.

8. The pressure maintenance system of claim 1 , wherein the pressure controller comprises a vent valve coupled to the headspace of the passive accumulator.

9. The pressure maintenance system of claim 1 , wherein the pressure controller comprises a pressure sensor to monitor the pressure in the headspace.

10. The pressure maintenance system of claim 1 , comprising a level indicator on the passive accumulator.

11. The pressure maintenance system of claim 1 , comprising a liquid addition system to add liquid to the passive accumulator.

12. A method for maintaining a pressure on an annulus of a well, comprising:

coupling a passive accumulator in a pressure maintenance system to the annulus of the well while the well is blocked in and cool;

adding a fluid to the passive accumulator to set a cold fluid level;

starting production from a production line in the well;

allowing expanding fluid from the annulus to flow into the passive accumulator as the well heats;

maintaining a pressure set point in the passive accumulator;

blocking in the production line:

allowing fluid from the passive accumulator to flow into the annulus as the well cools: and

maintaining the pressure set point in the passive accumulator.

13. The method of claim 12 , wherein maintaining the pressure set point in the passive accumulator comprises venting gas from the passive accumulator as the fluid level increases in the passive accumulator.

14. The method of claim 12 , wherein maintaining the pressure set point in the passive accumulator comprises adding gas to the passive accumulator as the fluid level decreases in the passive accumulator.

15. The method of claim 12 , comprising:

waiting until a fluid level in the passive accumulator stabilizes at a hot fluid level; and

replacing a portion of the fluid with a fresh fluid.

16. The method of claim 15 , comprising blocking in the well to allow the annulus to cool and the fresh fluid to flow into the annulus.

17. The method of claim 12 , comprising producing a gas for pressure maintenance at a well site.

18. The method of claim 17 , comprising operating a nitrogen plant to produce the gas for pressure maintenance.

19. A method for maintaining a pressure on an annulus of a well, comprising:

coupling a passive accumulator in a pressure maintenance system to the annulus of the well while the well is in production and hot;

adding a fluid to the passive accumulator to set a hot level;

stopping production from a production line in the well;

allowing fluid from the passive accumulator to flow into the annulus as the well cools; and

maintaining a pressure set point in the passive accumulator.

20. The method of claim 19 , comprising:

starting production from the well;

allowing fluid from the annulus to flow into the passive accumulator as the well heats; and

maintaining the pressure set point in the passive accumulator.

21. A method for replacing a fluid in an annulus of a well, comprising:

coupling a passive accumulator in a pressure maintenance system to the annulus while the well is cool;

adding fluid to the passive accumulator to set a cold fluid level;

starting well production;

allowing expanding fluid from the annulus to flow into the passive accumulator as the well heats;

allowing a fluid level to stabilize in the passive accumulator;

replacing a portion of the fluid in the passive accumulator;

stopping the well production and allowing the well to cool; and

allowing contracting fluid in the annulus to pull fluid from the passive accumulator as the well cools.

22. The method of claim 21 , comprising maintaining a pressure set point range on the passive accumulator as the fluid level changes.

23. The method of claim 21 , comprising:

cycling a temperature on the well by starting and stopping production;

replacing a portion of the fluid in the passive accumulator after the level stabilizes at each high point; and

maintaining the pressure set point range on the passive accumulator through a procedure.

24. The method of claim 21 , comprising incorporating additives into the fluid that is used to replace fluid in the passive accumulator.