The colloidal gas aphron (CGA) based drilling fluids are designed to minimize formation damage by blocking the pores of the rock with microbubbles, which can later be removed easily when the well is open for production. Aphrons behave like a flexible bridging material and form an internal seal in a pore-structure.

Size and concentrations of the bridging materials are very critical to the fluid's ability to seal the high permeability zones. Proper sizing of the microbubbles with respect to pore size distribution is essential for developing an aphron drilling fluid with effective sealing ability. The physico-chemical properties (i.e., viscosity, density, fluid loss, etc.) of the CGA base drilling fluids also need to be understood in order to drill with these fluids more effectively.

Aqueous CGA based drilling fluids systems have been fairly well characterized and successfully implemented in high-angle and horizontal wells drilled in low permeability as well as highly depleted reservoirs. Effectiveness of pore blocking by colloidal gas aphrons is expected to be improved even more, if we can replace water with non-aqueous base fluid such as mineral oil.

An experimental study has been conducted to determine the effect of base fluid composition (i.e., surfactant and polymer concentration) on the microbubble size and stability. The surfactant and polymer concentrations required for optimum formulation of mineral oil base CGA drilling fluids were determined.

The physico-chemical properties of non-aqueous CGA drilling fluids are also investigated. The results of rheology, filtration loss and density measurement tests are also presented.

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