To meet the world's increasing demand for energy, petroleum-producing companies must search for oil and gas in increasingly hostile environments. One area showing great promise is in the deepwater areas of the US Gulf of Mexico. This is evidenced by increased lease sales and drilling activity that have occurred there within the recent years. As drilling moves into deeper waters, new technologies must be developed for safe and successful operations.
Around 1996, four projects were initiated to develop dual-gradient drilling (DGD) technology for use in water depths greater than 5,000 ft. The four projects are Shell Oil Co.'s project (Gonzalez 2000), the SubSea MudLift Drilling Joint Industry Project (Smith 2000) (SMD), the Deep Vision project (Sjoberg 2000), and Maurer Technology's Hollow Glass Spheres project (Maurer 2000). Several publications have discussed the advantages that DGD technology has over conventional deepwater drilling in ultradeepwaters (Gault 1996; Schubert 1999; Smith et al. 1999).
Although the advantages of the dual-gradient projects are well documented, there has been little published on one of the major concerns expressed by all four projects. That is, how does well control differ for Dual-Gradient Drilling as compared to conventional riser drilling (Schubert 1999; Juvkam-Wold and Schubert 2000; Weddle and Schubert 2000)? This paper reports on a comparison of the well-control aspects of DGD to those of conventional riser drilling. It is based on the work that the authors performed as part of the SMD project.