Modelling pore-scale displacement processes at near-critical conditions

Abstract

The importance of critical phenomena in EOR is reviewed and the merits and limitations of conventional experiments briefly discussed. In order to develop an adequate description of the significant flow phenomena involved in field-scale displacement processes the pore-scale mechanisms underlying the macroscopic behaviour must be identified and understood. Therefore, an approach which complements conventional experiments and provides the necessary insights into the pore-scale phenomenology is required: details of a new physical modelling approach are presented. The effects of near-critical behaviour (i.e. low interfacial tension and small density contrasts) on displacement processes are modelled by the critical solution behaviour of partially miscible binary liquids. In particular, the interfacial tension can be varied precisely, and over a wide range, by controlling the temperature deviation from the critical solution temperature. Micromodels, transparent networks etched in glass, replace cores as realisations of porous media. They permit great flexibility and control over the pore-space morphoogy, allow fluid distributions to be observed, and provide the best means of assessing the influence of the pore-space geometry and topology on the processes of interest. The key role of interfacial phenomena in determining the flow characteristics is emphasised. Experimental observations are presented which illustrate pore-scale behaviour when the interfacial tension is very low. In particular, the importance of gravity is highlighted; effects are seen even on the pore scale where the influence of gravity is usually ignored. Finally, the implications of these observations for EOR are discussed and further topics for study suggested, including the development of this versatile modelling approach.