Injecting a fluid into a borehole ahead of the bit

1. A method for introducing a fluid into a borehole formed in an underground earth formation, in which borehole there is arranged a tubular drill string including a drill bit at its lower end, wherein the drill bit is provided with a passageway between the interior of the drill string above the drill bit and the borehole exterior of the drill bit, and with a removable closure element for selectively closing the passageway in a closing position, and wherein there is further provided a fluid injection tool comprising a tool inlet, and a tool outlet in fluid communication with the tool inlet, which method comprises the steps of:

passing the fluid injection tool from a position interior of the drill string to the closure element, and using the fluid injection tool to remove the closure element from the closing position;

passing the fluid injection tool to a landing position where the tool outlet has passed through the passageway and where the tool inlet resides inside the drill string in fluid communication with the interior of the drill string; and

introducing the fluid from the interior of the drill string into the borehole, wherein the fluid is received by the tool inlet and introduced into the borehole through the tool outlet.

2. The method according to claim 1 , wherein the fluid injection tool is provided with connection means for selectively connecting to the closure element, and wherein the step of removing the closure element from the closing position comprises connecting the fluid injection tool to the closure element.

3. The method according to claim 1 , wherein the fluid is cement.

4. The method according to claim 3 , wherein the method further comprises the steps of:

stopping the pumping of cement into the borehole;

waiting for the cement to harden;

retrieving of the fluid injection tool through the passageway so that the fluid injection tool is fully contained in the drill string;

moving the closure element into the closing position; and

drilling, using the drill bit.

5. The method according to claim 1 , wherein the fluid is a first cement-forming component, and wherein the method further comprises passing a second cement-forming component down along the annulus between the drill string and the borehole, so as to form cement after the first and second cement-forming components have come into contact with each other in the borehole.

6. The method according to claim 1 , wherein the fluid is lost circulation material.

7. The method according to claim 1 , wherein the fluid is a cleaning fluid.

8. The method according to claim 1 , wherein the method further comprises the steps of:

stopping the injection of fluid into the borehole;

retrieving the fluid injection tool through the passageway so that the fluid injection tool is fully contained in the drill string;

moving the closure element into the closing position; and

drilling, using the drill bit.

9. A system for drilling and for introducing a fluid into a borehole in an underground earth formation, the system comprising:

a tubular drill string having a drill bit at its lower end, wherein the drill bit is provided with a passageway between the interior of the drill string above the drill bit and the borehole exterior of the drill bit, and with a removable closure element for selectively closing the passageway in a closing position; and

a fluid injection tool comprising a tool inlet and a tool outlet in fluid communication with the tool inlet, which fluid injection tool is arranged so that it can pass from a position interior of the drill string to a landing position where the tool outlet has passed through the passageway and where the tool inlet resides inside the drill string in fluid communication with the interior of the drill string, and wherein the fluid injection tool is provided with means for removing the closure element from the closing position.

10. The system according to claim 9 , wherein the means for removing the closure element from the closing position comprises a connection means for selectively connecting the fluid injection tool from inside the drill string to the closure element in the closing position.

11. The system according to claim 9 , wherein the drill bit further comprises a bit nozzle, and wherein the fluid injection tool comprises a landing member, which is arranged so as to close off fluid passage through the bit nozzle when the fluid injection tool is in the landing position.

12. The system according to claim 9 , wherein the fluid injection tool comprises a cementing stinger.

13. The system according to claim 12 , wherein the cementing stinger comprises means for treating the cement before introducing it into the borehole, so as to influence the cement hardening process.

14. The system according to claim 9 , wherein the fluid injection tool comprises a jet cleaning tool.

15. The system according to claim 9 , wherein the fluid injection tool comprises a telescopic conduit between tool inlet and tool outlet.

16. The system according to claim 9 , wherein the passageway has a minimum cross-sectional area of at least 5 cm 2 .

17. The system according claim 9 , wherein the closure element is provided with cutting elements that form a joint bit face with other cutting elements on the bit face when the closure element is in the closing position.

18. The system according to claim 9 , wherein the drill bit with the closure element in the closing position has substantially the shape of a conventional PDC drill bit or of a conventional roller cone drill bit.

19. The system according to claim 9 , wherein the connection means of the fluid injection tool is arranged such that it can be disconnected from the closure element when the closure element has resumed the closing position after retracting the fluid injection tool from the borehole into the drill string.