Methods and devices for retaining conveyed heat up a wellbore

1 . A system to retain heat in a production fluid being extracted via a wellbore, the system comprising:

a casing extending in the wellbore, the casing having an internal space;

a tubing string extending within the internal space, the tubing string configured to transport the production fluid;

an annular space located between the tubing string and the casing;

a gas having a thermal conductivity below 0.67 W/m·K filling the annular space; and

a first packer located between the casing and the tubing string, wherein the first packer is a boundary of the annular space, and wherein the first packer is configured to isolate the gas from a reservoir fluid.

2 . The system of claim 1 , wherein the gas is nitrogen.

3 . The system of claim 1 , wherein the gas comprises at least 95% nitrogen.

4 . The system of claim 1 , wherein the gas comprises at least 50 percent carbon dioxide.

5 . The system of claim 1 , further comprising a second packer located between the casing and the tubing string, wherein the second packer is a boundary of the annular space.

6 . The system of claim 1 , further comprising a sensor configured to identify one or more gases in the annular space.

7 . The system of claim 6 , further comprising an annular space controller configured to identify a leak in the annular space in response to the identifying.

8 . The system of claim 1 , further comprising a sensor configured to sense a concentration of the gas having a thermal conductivity below 0.67 W/m·K in the annular space.

9 . The system of claim 8 , further comprising an annular space controller configured to add the gas having a thermal conductivity below 0.67 W/m·K to the annular space in response to the sensing.

10 . The system of claim 1 , further comprising a sensor configured to measure gas pressure in the annular space.

11 . The system of claim 10 , further comprising an annular space controller configured to add the gas having a thermal conductivity below 0.67 W/m K to the annular space in response to the measuring.

12 . The system of claim 1 , further comprising an electricity generating device coupled to the tubing string, the electricity generating device configured to extract heat from the production fluid and generate electricity using the heat.

13 . A method of operating a wellbore, the method comprising:

providing a casing extending in the wellbore, the casing having an internal space;

providing a tubing string extending within the internal space, the tubing string configured to transport a production fluid;

locating a packer between the tubing string and the casing, the packer providing a boundary of an annular space between the tubing string and the casing; and

filling the annular space with a gas having a thermal conductivity below 0.67 W/m·K.

14 . The method of claim 13 , further comprising:

sensing a concentration of the gas having a thermal conductivity below 0.67 W/m·K in the annular space; and

adding the gas having a thermal conductivity below 0.67 W/m·K to the annular space in response to the sensing.

15 . The method of claim 13 , further comprising:

sensing a pressure of gas in the annular space; and

adding the gas having a thermal conductivity below 0.67 W/m K to the annular space in response to the sensing.

16 . The method of claim 13 , further comprising:

extracting heat from the production fluid; and

using the extracted heat to generate electricity.

17 . The method of claim 13 , wherein filling the annular space with the gas comprises filling the annular space with nitrogen.

18 . The method of claim 13 , wherein filling the annular space with the gas comprises filling the annular space with a gas having at least 95 percent nitrogen.

19 . A system to generate electricity using heat extracted from a production fluid flowing from a wellbore, the system comprising:

a casing extending in the wellbore, the casing having an internal space;

a tubing string extending within the internal space, the tubing string configured to transport the production fluid;

an annular space located between the tubing string and the casing;

a gas having a thermal conductivity below 0.67 W/m·K filling the annular space;

an annular space controller configured to monitor and regulate a concentration and pressure of the gas having a thermal conductivity below 0.67 W/m·K filling the annular space;

a packer located between the casing and the tubing string, wherein the packer is a boundary of the annular space, and wherein the packer is configured to isolate the gas from a reservoir fluid; and

an electricity generating device coupled to the tubing string and configured to extract heat from the production fluid and generate electricity using the extracted heat.