Wellbore drilling using dual drill string

摘要

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.