4Pettingill H S, Weimer P. World-wide deepwater exploration and production: past, present and future [C]//Houston, Texas : 21 st Annual Research Confer- ence,2001.
5Smith K L,Gauh A D,Witt D E,et al. Subsea mudlift drilling joint industry projeet: delivering dual gradient drilling technology to industry[G]. SPE 71357,2001.
6Schumacher J P, Dowell J D, Ribbeck L R, et al. Subsea MudLift Drilling(SMD) : planning and preparation for the first subsea field test of a full. scale dual gradient drilling system at green canyon 136, Gulf of Mexico EG2. SPE 71358,2001.
7Eggemeyer J C,Akins M E,Brainard P E,et al . SubSea mudllft drilling: design and implementation of a dual gra Bent drilling system[G]. SPE 71359,2001.
8Maurer W C,Medley G H,McDonald W J. Multigra-dient drilling method and system= United States, 006530437[P]. 2003 03-11.
