Open loop cooling system and method for downhole tools

1. A downhole tool comprising:

an elongate tool string;

a container disposed within the tool string, the container to house a pressurized refrigerant therein;

a tank in fluid communication with the container;

a heat exchanger associated with the tank, wherein the heat exchanger is to exchange heat between the refrigerant and a downhole payload; and

a venturi located proximate to the container to create a low pressure region adjacent the tank when fluid flows through the venturi.

2. The tool as recited in claim 1 , wherein the venturi has a drilling mud passage therethrough, the drilling mud passage having a first portion and a second portion, and a convergence between the first portion and the second portion, wherein the fluid comprising drilling mud flowing through the convergence creates the low pressure region.

3. The tool as recited in claim 1 , wherein the container is pre-pressurized.

4. The tool as recited in claim 1 , wherein the pressure within the container is to be maintained by downhole pressure.

5. The tool as recited in claim 1 , wherein the pressure within the container is to be maintained by drilling mud flow.

6. The tool as recited in claim 1 , wherein the refrigerant comprises water.

7. The tool as recited in claim 1 , further comprising a check valve associated with the container.

8. The tool as recited in claim 1 , further comprising an actuator associated with the output of the container.

9. The tool as recited in claim 1 , wherein the downhole tool forms part of a drill string.

10. The tool as recited in claim 1 , wherein the downhole tool is a wireline tool.

11. A method comprising:

pressurizing a container having refrigerant therein to provide a pressurized container;

disposing the pressurized container within a downhole tool string;

disposing the downhole tool string within a wellbore,

maintaining pressure of the pressurized container; and

cooling a payload of the downhole tool string to a temperature lower than downhole ambient temperature by exchanging heat between the payload and the refrigerant, and by flowing drilling mud at a reduced pressure proximate to the container to flash the refrigerant to a pressure that drops a temperature of the refrigerant below the downhole ambient temperature.

12. The method as recited in claim 11 , wherein pressurizing the container occurs prior to disposing the downhole tool string within the wellbore.

13. The method as recited in claim 11 , wherein pressure of the drilling mud is reduced at a convergence of a venturi, the convergence located near the container.

14. The method as recited in claim 11 , further comprising disposing water as the refrigerant in the container.

15. The method as recited in claim 11 , wherein maintaining pressure of the pressurized container includes maintaining pressure with downhole pressure.

16. The method as recited in claim 11 , wherein maintaining pressure of the pressurized container includes maintaining pressure with drilling mud flow.

17. The method as recited in claim 11 , wherein maintaining pressure of the pressurized container includes displacing at least one of a piston, a spring, or a bellows with downhole pressure.

18. The method as recited in claim 11 , further comprising operating a regulator when the temperature of the refrigerant is at or greater than the downhole ambient temperature.

19. The method as recited in claim 11 , further comprising releasing the refrigerant to an upper surface portion of the wellbore.

20. The method as recited in claim 11 , further comprising sensing a temperature of the payload, and releasing the refrigerant based on a temperature of devices in the payload.

21. The method as recited in claim 11 , further comprising controlling flow from the pressurized container including flowing the refrigerant through an orifice.