A Study of the Rheology, Stability and Pore Blocking Ability of Aqueous Colloidal Gas Aphron Drilling Fluids

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.;The physical properties of CGA based drilling fluids are investigated. The results of rheology, API filtration loss and density measurement tests using various CGA based drilling fluid formulations are presented. The effects of time, pressure and temperature on the size and the stability of CGA based drilling fluids are investigated.;The pore blocking ability of the CGA fluid is investigated visually through micromodel experiments. Pore blocking is investigated further with sandpack experiments. The effect 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) is investigated. An increasing resistance to flow of CGA drilling fluids through porous media is observed as more CGA fluid is injected.;Finally, results for the prediction of the CGA diameter through the investigation of two models, the drainage model and the bubble break-up model, are presented. A new prediction method for determining CGA diameter with pressure and temperature is developed. As well, a PVT cell was used to find the effect of pressure and temperature on the bulk fluid and an equation of state is developed to predict bulk density. This prediction method can be used in the field for a specific reservoir.;Sizing CGA in accordance with the rock pore size distribution is essential for effective sealing of the pores during drilling. The effect of time, temperature, and pressure on the stability and size of the CGA needs to be better understood in order to design a fluid that will sufficiently block the pores of the formation for extended periods. The physical properties of the CGA based drilling fluids need to be known for more effective drilling. Most importantly, the mechanism behind the blocking ability is not fully understood for the CGA drilling fluid.