Patent ID: 11454075

Abstract:
A lock plug (7A) is inserted into a plug installation position of an insertion hole (5a) of a tool stem (5) connected to a drill string (10), and when a fluid has flowed to the insertion hole (5a), a stopper (62) protrudes radially outward from a tool body (6) and is locked to a subsea wellhead (4) and an internal stopper (66) protrudes radially inward from the tool body (6) and is locked to the tool stem (5) in a lock state. An unlock plug is inserted into the plug installation position of the insertion hole (5a), and when the fluid has flowed into the insertion hole (5a), the stopper (62) is separated from the subsea wellhead (4) and the internal stopper (66) is separated from the tool stem (5) to release the lock state.