Review of deepwater dual gradient drilling technology

To overcome problems associated with deepwater drilling,a new technology known as gradient drilling(DGD) has been introduced.Several new approaches to the deepwater dual gradient drilling were developed,including subsea mudlift drilling,riserless drilling,and dual density drilling.The research and application of some joint industry projects were reviewed,such as Conoco/Hydril subsea mudlift drilling system,Shell subsea pumping system,Baker/Transocean DeepVision pump system,MTI hollow sphere dual gradient drilling system,AGR Subsea riserless mud recovery system,as well as LSU riser gaslift and riser dilution,etc.Compared to conventional drilling techniques for deepwater drilling,the dual gradient drilling technology has the following advantages: lower cost,shorter well construction time,more operation safety,and increased production.It has a large potential market in the future exploitation of deepwater oil and gas in China.