Method of drilling a lossy formation

1. A method of drilling a bore hole in a lossy formation, comprising the steps of

deploying a drill pipe into the borehole, whereby an annular space is formed between the drill pipe and the borehole wall;

pumping a drilling fluid into the bore hole via an internal conduit of the drill pipe and a drill pipe fluid outlet present in the vicinity of a distal end of the drill pipe;

pressure sealing the annular space using a pressure seal;

pumping a well control fluid into the annular space in the lossy formation via a well control conduit that fluidly connects the annular space in a location between the pressure seal and the drill pipe fluid outlet, to a back pressure system; and

pressure-balancing the well control fluid against the pressure seal and the backpressure system.

2. The method of claim 1 , wherein the pressure-balancing is actively controlled.

3. The method of claim 2 , wherein actively controlling of the pressure-balancing includes allowing pumped well control fluid to discharge in the back pressure system over a variable flow restriction and controlling a pressure drop over the flow restriction.

4. The method of claim 3 , wherein actively controlling the pressure-balancing includes automatically controlling the pressure-balancing by means of automatic control means controlling the back pressure system.

5. The method of claim 4 , wherein automatically controlling the pressure-balancing includes calculating a predicted down hole pressure using a model, comparing the predicted down hole pressure to a desired down hole pressure, and utilizing the differential between the calculated and desired pressures to control the pressure-balancing, all by means of a programmable pressure monitoring and control system.

6. The method of claim 2 , wherein actively controlling the pressure-balancing includes automatically controlling the pressure-balancing by means of automatic control means controlling the back pressure system.

7. The method of claim 6 , wherein automatically controlling the pressure-balancing includes calculating a predicted down hole pressure using a model, comparing the predicted down hole pressure to a desired down hole pressure, and utilizing the differential between the calculated and desired pressures to control the pressure-balancing, all by means of a programmable pressure monitoring and control system.

8. The method of claim 1 , wherein the well control fluid is selected to be essentially identical to the drilling fluid.

9. The method of claim 8 , wherein the well control fluid and the drilling fluid are pumped into the bore hole using the same pump means for generating a pumped stream of a selected fluid and dividing the pumped stream of the selected fluid into a well control stream and a drilling fluid and feeding the drilling fluid to the internal conduit of the drill pipe and feeding the well control fluid to the well control conduit.

10. A method of producing hydrocarbons from a subsurface formation, comprising extracting hydrocarbons from the formation using a well drilled according to a method wherein a drill pipe is deployed into a borehole, whereby an annular space is formed between the drill pipe and the borehole wall; a drilling fluid is pumped into the bore hole via an internal conduit of the drill pipe and a drill pipe fluid outlet present in the vicinity of a distal end of the drill pipe; the annular space is pressure-sealed using a pressure seal; and

a well control fluid is pumped into the annular space in the lossy formation via a well control conduit that fluidly connects the annular space in a location between the pressure seal and the drill pipe fluid outlet, to a backpressure system, and pressured balanced against the pressure seal and backpressure system.

11. The method of claim 10 , wherein the pressure-balancing is actively controlled.

12. The method of claim 11 , wherein actively controlling of the pressure-balancing includes allowing pumped well control fluid to discharge in the back pressure system over a variable flow restriction and controlling a pressure drop over the flow restriction.

13. The method of claim 11 , wherein actively controlling the pressure-balancing includes automatically controlling the pressure-balancing by means of automatic control means controlling the back pressure system.

14. The method of claim 13 , wherein automatically controlling the pressure-balancing includes calculating a predicted down hole pressure using a model, comparing the predicted down hole pressure to a desired down hole pressure, and utilizing the differential between the calculated and desired pressures to control the pressure-balancing, all by means of a programmable pressure monitoring and control system.

15. The method of claim 10 , wherein the well control fluid is selected to be essentially identical to the drilling fluid.

16. The method of claim 15 , wherein the well control fluid and the drilling fluid are pumped into the bore hole using the same pump means for generating a pumped stream of a selected fluid and dividing the pumped stream of the selected fluid into a well control stream and a drilling fluid and feeding the drilling fluid to the internal conduit of the drill pipe and feeding the well control fluid to the well control conduit.

17. The method of claim 15 , wherein actively controlling the pressure-balancing includes automatically controlling the pressure-balancing by means of automatic control means controlling the back pressure system.

18. The method of claim 17 , wherein automatically controlling the pressure-balancing includes calculating a predicted down hole pressure using a model, comparing the predicted down hole pressure to a desired down hole pressure, and utilizing the differential between the calculated and desired pressures to control the pressure-balancing, all by means of a programmable pressure monitoring and control system.