A rotating flow head (RFH) has a housing having an internal bore with diameter substantially equal to that of a riser and at least one flow port proximate one longitudinal end thereof. First and second arrays of radially extensible and retractable locking elements are disposed circumferentially around the RFH housing. The RFH has a bearing assembly (BA) housing having an exterior diameter selected to fit within the internal bore of the RFH housing so as to provide an annular space therein. The BA housing engages one of the arrays of locking elements when extended. A mandrel is rotatably, sealingly supported within the BA housing. Another end of the BA housing and the other array of locking elements provide longitudinal force on the BA housing when the other array is extended. A seal element disposed in the annular space is energized by the longitudinal force applied to the BA housing.