The colloidal gas aphron (CGA) drilling fluids are designed to minimize formation damage by blocking pores of the rock with microbubbles and reducing the filtration loss.

In order to gain a better understanding of the factors controlling the pore blocking mechanisms of microbubbles, a set of core flooding experiments were conducted by using various CGA drilling fluid formulations. The differential pressure drop along the sand-pack was measured.

Effects of CGA fluid composition, flow rates, type of reservoir saturating fluids, permeability and wettability on the resistance to CGA drilling fluid flow through porous media (i.e., pressure drop due to CGA fluid flow) have been investigated.

An increasing resistance to flow of CGA drilling fluids through porous media was observed as more CGA fluid was injected. Results confirmed that CGA microbubble build-up across the pore structure could establish an effective seal for controlling filtration loss.

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