Patent ID: 6209663
Filing Date: 2001-04-03
Classification: E21B

Abstract:
A method for underbalanced drilling a well bore through a well bore formation, a first tubular string being cemented in said wellbore, said first tubular string having a bottom end, a second tubular string for said well bore, a drilling string being moveable through the second tubular string, said method comprising:providing said second tubular string for placement within said well bore, said second tubular string being an outermost tubular string at well depths below said bottom end of said first tubular string;mounting a deployment valve within said second tubular string such that at least a portion of said deployment valve is positioned at a well depth above said bottom end of said first tubular string;cementing said second tubular string at least below said bottom end of said first tubular string within said well bore; andcontrolling a fluid pressure for opening and closing said deployment valve.