Drilling system and method

摘要

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. The back pressure control means is arranged to receive the pressure signal and to regulate the back pressure means in dependence of at least the pressure signal.