Downhole system for unloading liquid

1. A downhole system for unloading a liquid of a well having an annulus between an intermediate casing and a production tubular metal structure, comprising:

the intermediate casing,

a pump at a top of the well, configured to pressurise the annulus to displace the liquid in the annulus,

the production tubular metal structure having a first inner diameter, arranged partly in the intermediate casing, thereby defining the annulus,

a production packer arranged between the intermediate casing and the production tubular metal structure, and

a first liquid unloading assembly and a second liquid unloading assembly, each comprising:

a tubular part having a wall having a second inner diameter, an outer face and an aperture, the tubular part being configured to be mounted as part of the production tubular metal structure, and

a check valve connected with the outer face, the check valve having an inlet in fluid communication with the annulus and an outlet in fluid communication with the aperture,

wherein the downhole system further comprises a sliding sleeve positioned radially inward relative to each said check valve so that the sliding sleeve and the check valve are positioned on radially opposite sides of the wall, each sliding sleeve being arranged to slide along an inner face of the tubular part between an open position and a closed position to open or close the respective aperture, each said sliding sleeve including a groove on its inner surface and adapted to be engaged by a downhole tool that slides the sliding sleeve between the open and closed positions.

2. A downhole system according to claim 1 , wherein each liquid unloading assembly comprises a plurality of check valves.

3. A downhole system according to claim 1 , wherein the second inner diameter is larger than the first inner diameter, which forms a recess in which the sliding sleeve slides.

4. A downhole system according to claim 1 , wherein a sliding sleeve is arranged opposite each of the first and second liquid unloading assemblies for opening or closing fluid communication to the first and second liquid unloading assemblies.

5. A downhole system according to claim 1 , further comprising the downhole tool.

6. A downhole system according to claim 1 , wherein each liquid unloading assembly has an outer diameter which is larger than but less than 20% larger than the outer diameter of the production tubular metal structure.

7. A downhole system according to claim 2 , wherein each liquid unloading assembly comprises a plurality of assembly inlets, each assembly inlet being fluidly connected with the inlet of one of the check valves.

8. A downhole system according to claim 1 , wherein the first inner diameter of the production tubular metal structure is equal to the second inner diameter of the tubular part of the liquid unloading assembly.

9. A downhole system according to claim 1 , wherein the sliding sleeve is arranged in a recess of the tubular part.

10. A downhole system according to claim 1 , wherein the sliding sleeve has a third inner diameter which is equal to the first inner diameter of the production tubular metal structure.

11. A downhole system according to claim 1 , further comprising a liner hanger casing and a second production packer, the liner hanger casing being arranged between the first production packer and the second production packer, and the second production packer being arranged between the liner hanger casing and the production tubular metal structure.

12. A downhole system according to claim 11 , wherein at least some of the check valve assemblies are arranged below the first production packer.

13. A downhole system according to claim 1 , further comprising a tool with a detection unit configured to detect the presence of gas in the production tubular metal structure.

14. A liquid unloading method for unloading liquid of a well in an annulus between an intermediate casing and a production tubular metal structure, comprising:

pressurising the annulus with gas to displace the liquid from the top of the well in through the check valves in the downhole system according to claim 1 ,

letting gas through the first check valve into the production tubular metal structure,

detecting gas in the production tubular metal structure,

closing the first check valve by means of the tool,

displacing the liquid by letting the liquid in through the second check valve,

letting gas through the second check valve into the production tubular metal structure, and

detecting a gas in the production tubular metal structure.

15. A liquid unloading method according to claim 14 , wherein detecting a gas is performed at the top of the well or by means of the tool.

16. A liquid unloading method according to claim 14 , further comprising closing the second check valve.

17. A liquid unloading method according to claim 14 , further comprising producing hydrocarbon-containing fluid.