Abstract: A swivelsub comprising a sleeve member which is sealable and lockable by means of the annular preventer of a blowout preventer, with at least one end portion of the sleeve being lockable to the drill string, and with means providing sealing and enable relative rotational movement between said sleeve member and the drill string. The swivelsub forms a sealable and pressure controlling passage for a dril string in a drilling well and is particularly useful for cutting operation of casings in an abandoned well.