Abstract: A method of drilling a bore hole in a fractured formation. A drill pipe is deployed into the borehole, whereby an annular space is formed between the drill pipe and the borehole wall. A drilling fluid is pumped, by means of primary pumps, into the borehole 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 such as a rotating head on a BOP. A well control fluid is pumped into the annular space 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. The well control fluid is pressure-balanced against the pressure seal and the backpressure system.

Abstract: Drilling system and method for drilling a bore hole into an earth formation, the bore hole having an inside wall. A drill string reaches into the bore hole and leaves a drilling fluid return passage between the drill string and the bore hole inside wall. A drilling fluid discharge conduit is in fluid communication with the drilling fluid return passage, and pump means are provided for pumping a drilling fluid through the drill string into the bore hole and to the drilling fluid discharge conduit via the drilling fluid return passage. The drilling fluid back pressure is controlled utilizing back pressure control means for controlling back pressure means. The system further provides fluid injection means comprising an injection fluid supply passage fluidly connecting an injection fluid supply with the drilling fluid return passage and further comprising an injection fluid pressure sensor arranged to provide a pressure signal in accordance with an injection fluid pressure in the injection fluid supply passage.

Abstract: A drilling system for drilling a bore hole into an earth formation, the bore hole having an inside wall. A drill string reaches into the bore hole from a surface, leaving a drilling fluid return passage between the drill string and the bore hole inside wall. A bottom hole assembly is supported by the drill string, and a drilling fluid discharge conduit is provided in fluid communication with the drilling fluid return passage. A drilling fluid is pumped through the drill string into the bore hole and to the drilling fluid discharge conduit via the drilling fluid return passage. Means are provided for obtaining information on the existing down hole pressure of the drilling fluid in the vicinity of the bottom hole assembly and back pressure means for controlling the drilling fluid back pressure.