Annular barrier with expansion unit

1. An annular barrier to be expanded in an annulus between a well tubular structure and a wall of a borehole downhole for providing zone isolation between a first zone having a first pressure and a second zone, the annular barrier comprising:

a tubular metal part for mounting as part of the well tubular structure, the tubular metal part having a first expansion opening, an axial extension and an outer face,

an expandable sleeve surrounding the tubular metal part and having an inner face facing the tubular metal part and an outer face facing the wall of the borehole, each end of the expandable sleeve being connected with the tubular metal part, and

an annular space between the inner face of the expandable sleeve and the tubular metal part, the annular space having a space pressure,

wherein fluid inside the tubular metal part has a tubular pressure, and

wherein the annular barrier comprises an expansion unit having a first inlet in fluid communication with the first expansion opening, a second inlet in fluid communication with the first zone and an outlet in fluid communication with the annular space, and the expansion unit comprising an element movable at least between a first position and a second position, in the first position the first expansion opening being in bilateral fluid communication with the outlet to equalize pressure in the tubular metal part with the space pressure when the tubular pressure is higher than the first pressure, and in the second position the outlet being in bilateral fluid communication with the first zone via the second inlet to equalize the first pressure in the first zone with the space pressure when the first pressure is higher than the tubular pressure, wherein the tubular metal part comprises at least one second expansion opening being fluidly connected with the first inlet, and wherein the space pressure is equalized with the greater momentary pressure of the first pressure and the tubular pressure at a first time, even if the space pressure at a second time later than the first time is less than the greater momentary pressure.

2. The annular barrier according to claim 1 , wherein the expansion unit comprises a collection part fluidly connected to the first expansion opening and the second expansion opening.

3. The annular barrier according to claim 2 , wherein the collection part comprises a collection sleeve arranged outside the tubular metal part and connected to the tubular metal part, forming an annular chamber between the tubular metal part and the collection sleeve.

4. The annular barrier according to claim 3 , wherein the first expansion opening and the second expansion opening are fluidly connected to the annular chamber, and the first inlet is fluidly connected to the annular chamber.

5. The annular barrier according to claim 4 , wherein one or more groove(s) are arranged in the collection sleeve and/or the tubular metal part facing the annular chamber.

6. The annular barrier according to claim 4 , wherein the collection sleeve has an outer sleeve face in which one or more circumferential groove(s) is/are arranged.

7. The annular barrier according to claim 6 , wherein the outer sleeve face has one or more longitudinal groove(s) along the axial extension.

8. The annular barrier according to claim 7 , wherein the one or more longitudinal groove(s) is/are in fluid communication with the second inlet.

9. The annular barrier according to claim 4 , wherein a filtering element, is arranged between the tubular metal part and the collection sleeve and configured to filtrate the fluid from inside the tubular metal part.

10. The annular barrier according to claim 1 , wherein the expansion unit comprises a shuttle valve and the element of the expansion unit is comprised in the shuttle valve.

11. The annular barrier according to claim 10 , wherein the element of the expansion unit moves in the axial extension or radially perpendicular to the axial extension.

12. The annular barrier according to claim 1 , wherein the element is a ball movable between a first seat when the element is in the first position and a second seat when the element is in the second position.

13. A downhole system comprising:

a well tubular structure, and

a first annular barrier according to claim 1 .

14. The downhole system according to claim 13 , further comprising a second annular barrier which, when expanded, isolates a production zone together with the first annular barrier, the expansion units of the first annular barrier and the second annular barrier being arranged in a zone other than the production zone.