Apparatus and methods for drilling with casing

The invention provides an apparatus and methods to reduce ECD, equivalent arcutation density, and pressure associate therewith while drilling with casing. In one aspect, the invention provides an energy transfer assembly locatable at a predetermined location in a casing string. The assembly includes an impeller portion 135 in the interior of the casing to be acted upon by the downward moving fluid in the casing and a pump portion 140 disposed outwardly of the impeller portion and arranged in fluid communication with the upward moving fluid in the annulus between the casing and the borehole, adding energy thereto and reducing pressure in the annulus therebelow. The energy transfer assembly is retrievable to the surface of the wellbore prior to cementing during which fluid ports between the interior and exterior of the casing are remotely sealable prior to cementing by movement of a sleeve 200. Other pump arrangements may be used and the pump may be electrically driven. An alternative arrangement uses a jet arrangement.