The use of hollow glass microspheres 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. We are currently studying the use of an hollow glass microspheres 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 hollow glass microspheres 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 hollow glass microspheres 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.