Abstract: A method and apparatus are disclosed for drilling a wellbore using a concentric dual drill string. Multiple individually selectively isolable crossover ports intervaled may be provided along the length of the drill string thereby facilitating pumping a well control fluid within a wellbore annulus without the need to run-in or trip-out the drill string. Multiple one way check valves may be included at various points within an inner pipe of the dual drill string to minimize settling of particulate matter during long periods of non-circulation. In an offshore arrangement, the drill string may be used without a marine riser. A rotating control device is provided, and a hydraulic power unit is located at the seafloor for controlling and lubricating the rotating control device. A pump may be located at the seafloor for managing wellbore annulus pressure via the rotating control device.

Abstract: A riserless subsea drilling system includes a tubular drilling string including a drilling bit; a rotating control device including a seal sealed to the drilling string; and a drilling fluid circuit that circulates drilling fluid from a supply line, through an annulus exterior the drilling string and below the rotating control device, through the drilling bit at a downhole end of the drilling string, and through the drilling string toward an uphole end of the drilling string.

Abstract: A method and apparatus are disclosed for drilling a wellbore using a concentric dual drill string. Multiple individually selectively isolable crossover ports intervaled may be provided along the length of the drill string thereby facilitating pumping a well control fluid within a wellbore annulus without the need to run-in or trip-out the drill string. Multiple one way check valves may be included at various points within an inner pipe of the dual drill string to minimize settling of particulate matter during long periods of non-circulation. In an offshore arrangement, the drill string may be used without a marine riser. A rotating control device is provided, and a hydraulic power unit is located at the seafloor for controlling and lubricating the rotating control device. A pump may be located at the seafloor for managing wellbore annulus pressure via the rotating control device.