Method and cooling system for electric submersible pumps/motors for use in geothermal wells

1. A method comprising:

delivering liquid nitrogen from a location proximate ground surface to a submerged electrical pump motor operating in a subterranean well;

converting the liquid nitrogen to nitrogen gas in an expansion volume defined at least partially by a pressure-controlled motor housing, the pressure-controlled motor housing containing the submerged electrical pump motor in the expansion volume;

cooling the submerged electrical pump motor in the pressure-controlled motor housing using the nitrogen gas,

venting the nitrogen gas out of the pressure-controlled motor housing; and

controlling a pressure of the pressure-controlled motor housing, wherein the pressure is between a vapor pressure of the liquid nitrogen and a venting pressure of the nitrogen gas.

2. The method as recited in claim 1 , wherein the subterranean well has a temperature of at least 200 degrees Celsius.

3. The method as recited in claim 1 , wherein delivering the liquid nitrogen comprises flowing the liquid nitrogen downhole through a cooling conduit extending from the location proximate ground surface to the submerged electrical pump motor.

4. The method as recited in claim 3 , wherein the cooling conduit with which the liquid nitrogen is conveyed downhole is a coil tubing or a concentric coil tubing.

5. The method as recited in claim 3 , further comprising flowing the liquid nitrogen through a one way inlet check valve and into a pump by-pass conduit and expanding the liquid nitrogen via an expansion nozzle located within the pressure-controlled motor housing.

6. The method as recited in claim 3 , wherein venting the nitrogen gas out of the pressure-controlled motor housing comprises flowing the nitrogen gas through a one way outlet check valve when pressure across the one way outlet check valve reaches a predetermined limit and into an outlet conduit connected in fluid communication with the cooling conduit.

7. The method as recited in claim 1 , wherein venting the nitrogen gas out of the pressure-controlled motor housing comprises flowing the nitrogen gas through an outlet conduit and into a fluid column lifted by a pump driven by the submerged electrical pump motor, wherein the fluid column comprises a downhole fluid.

8. The method as recited in claim 7 , further comprising providing a one way outlet check valve between the outlet conduit and the fluid column for venting the nitrogen gas the one way outlet check valve when pressure across the one way outlet check valve reaches a predetermined limit.

9. The method as recited in claim 8 , further comprising providing a gas-lift assist affect to the fluid column within which the nitrogen gas becomes entrained.

10. The method as recited in claim 9 , further comprising:

lifting the fluid column to the surface; and

separating entrained nitrogen gas from the downhole fluid at the location proximate ground surface.

11. The method as recited in claim 10 , further comprising compressing the nitrogen gas with a compressor to form liquid nitrogen.

12. The method as recited in claim 4 , wherein an electrical cable for powering the submerged electrical pump motor is disposed within the cooling conduit and liquid nitrogen is conveyed downhole through an annulus of the cooling conduit.

13. The method as recited in claim 1 , wherein a location of a coolant outlet is positioned within a perimeter of the pump housing.

14. The method as recited in claim 1 , wherein a check valve is adapted to actuate for controlling nitrogen gas flow therethrough at a predetermined venting pressure.

15. The method as recited in claim 1 , wherein a pump driven by the submerged electrical pump motor is positioned above the submerged electrical pump motor in the downhole well.