Patent ID: 6328107
Filing Date: 2001-12-11
Classification: E21B

Abstract:
A method for installing a well casing through a drilling riser into a subsea well being drilled with a dual density drilling system, said drilling riser initially containing seawater and extending from above the surface of the body of seawater downwardly to a subsea wellhead, said method comprising the steps of:lowering said well casing through said drilling riser to said subsea wellhead and allowing displaced seawater to flow out of said drilling riser;lowering said well casing through said subsea wellhead into said well and allowing displaced drilling fluid to flow upwardly into said drilling riser;monitoring the riser base pressure as said well casing is lowered into said well; andevacuating the seawater from said drilling riser to compensate for increases in riser base pressure due to said displaced drilling fluid so as to maintain said riser base pressure approximately equal to seawater pressure at the base of said drilling riser.