The study of mass transfer between phases is a very important issue during drilling operations with organic based drilling fluids. The research in the area is necessary to understand the interaction between the formation fluid (oil and/or gas) and the synthetic drilling fluid filtrate inside the invaded zone and also during a kick situation. A comprehensive literature search was conducted in order to identify the state of the art in the subject and to choose the appropriate experimental procedure and physical/mathematical modeling technique. The present experimental work comprises the measurement and modeling of the diffusivity and interface mass transfer coefficients for those gas-liquid systems. The experimental data were obtained with accurate PVT measurements, under high pressure and high temperature conditions. The tests were carried out in the 70oC through 120oC temperature range for n- paraffin liquids with the following mole fraction of gas: i) 15% to 91% mol of CH4 and ii) 27% to 75% mol of CO2. The pressure decay method, which is based on the gas phase pressure decline with time as a consequence of the diffusion process, was applied to data modeling. A transient state diffusion model, with short and long term analytical solution, was applied to determine the mass transfer parameters for the two mixtures: CH4/n-paraffin and CO2/n-paraffin. The results of this ongoing research have two important contributions: i) to increase the safety during well control operations, mitigating the risk of blowouts, and ii) to understand the interaction of formation gas and organic based drilling fluids, especially in reservoir with high CO2 content, as those encountered in the recently found Brazilian sub-salt reservoirs.
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