The steel drill string attached to a drilling bit during typical rotary
drilling operations used to drill oil and gas wells is used for a second
purpose as the casing that is cemented in place during typical oil and
gas well completions. Methods of operation are described that provide for
the efficient installation of a cemented steel cased well wherein the
drill string and the drill bit are cemented into place during one single
drilling pass down into the earth. Apparatus is described having a
portion of a drilling assembly that is selectively removable from the
wellbore without removing the casing. A one-way cement valve is installed
near the drill bit of the drill string that allows the cement to set up
efficiently under ambient hydrostatic conditions while the drill string
and drill bit are cemented into place during one single drilling pass
into the earth.