The use of Hollow Glass Spheres (HGS) to create a low density fluid has been studied previously for application to under pressure drilling and dual gradient drilling (DGD). Recent interest in DGD has focused on using submersible pumps to return drilling fluid and cuttings to the surface. The use of a lighter fluid in the riser has not been pursued because of a perceived complexity in the system and inability to maintain stability. The author's company is currently studying the use of an HGS slurry as an alternative to airlift or submerged pumps for ocean mining. Analysis of the ocean mining application shows that the power requirements and costs of the HGS lift system are comparable to submerged pumps. The big advantage is the lack of any subsea mechanical or electrical equipment. The technical challenge is the separation and recovery of all of the HGS for reinjection. If there is any appreciable attrition the replacement costs could render this concept to be uneconomic. Current work is focused on the separation and recovery of the spheres. This paper will review briefly the previous work performed on the DGD application and current work on ocean mining and how it might bear on the DGD application as well. The paper will discuss recent developments in extra low density high strength glass spheres, specific gravities approaching 0.2, and how they might be applied in either the drilling or mining applications.

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