Punch and inject tool for downhole casing and method for use thereof

1. A downhole tool for punching a hole in a casing wall and injecting a sealant through said hole, comprising:

a tool housing having a longitudinal axis;

a sting comprising a fluid channel to establish fluid communication from within the tool housing to an exterior of the tool housing through the fluid channel;

a press device acting on the sting to force the sting in a radially outward direction from the tool housing, transversely to the longitudinal axis; and

a check valve arranged in said fluid channel which allows fluid communication in a direction from within the tool housing to the exterior of the tool housing and which blocks fluid flow in an opposite direction,

wherein the sting comprises a release section to sever a distal end of the sting from the tool housing, whereby said check valve is arranged in said distal end of the sting.

2. The downhole tool of claim 1 , wherein the check valve is in an internal cavity within the sting.

3. The downhole tool of claim 1 , wherein said release section is outside of the tool housing when the sting has been forced in said radially outward direction from the tool housing.

4. The downhole tool of claim 1 , wherein said release section comprises a frangible zone.

5. The downhole tool of claim 4 , wherein said frangible zone comprises a frangible tube section reinforced by a plurality of reinforcement rings around the frangible tube section in mutual abutment with neighboring reinforcement rings.

6. The downhole tool of claim 1 , further comprising a stop body on the sting which moves with the sting in said radially outward direction until the stop body engages with an inside of a casing wall when the downhole tool is activated within a casing.

7. The downhole tool of claim 1 , wherein said fluid channel, inside of said tool housing, is connectable to a source of fluid sealant.

8. A method of injecting a sealant in an annulus around a casing in a borehole, said method comprising:

traversing a punch and inject tool having a tool housing with a longitudinal axis axially through a bore of a casing which is prearranged in a borehole;

forcing a sting in a radially outward direction from the tool housing, transversely to the longitudinal axis, whereby perforating a casing wall with said sting;

injecting a sealant from within the tool housing to an exterior of the tool housing and into an annular space around the casing, through a fluid channel defined by the sting and through a check valve arranged in said fluid channel, thereby allowing fluid communication a direction from within the tool housing to the exterior of the tool housing and blocking fluid flow in an opposite direction; and

sever a distal end of the sting from the tool housing, whereby said check valve is arranged in said distal end of said sting.

9. The method of claim 8 , wherein the check valve is shielded from external mechanical loading during perforating of the casing wall.

10. The method of claim 8 , wherein said distal end remains stuck in the casing wall upon severing said distal end from the tool housing.

11. The method of claim 8 , further comprising retracting the tool housing through the bore of the casing while leaving the distal end behind.

12. The method of claim 11 , wherein the tool housing is retracted before the sealant in the annular space around the casing has hardened.